UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Analysis of corrosion products in stress corrosion cracks 1976

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1976_A7 N54.pdf
UBC_1976_A7 N54.pdf [ 11.83MB ]
UBC_1976_A7 N54.pdf
Metadata
JSON: 1.0078790.json
JSON-LD: 1.0078790+ld.json
RDF/XML (Pretty): 1.0078790.xml
RDF/JSON: 1.0078790+rdf.json
Turtle: 1.0078790+rdf-turtle.txt
N-Triples: 1.0078790+rdf-ntriples.txt
Citation
1.0078790.ris

Full Text

ANALYSIS OF CORROSION PRODUCTS IN STRESS CORROSION CRACKS by THOMAS PHILIP NIKIFORUK B.A.-Sc. U n i v e r s i t y o f B r i t i s h Columbia, 1973 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF We a c c e p t t h i s t h e s i s as co n f o r m i n g t o the r e q u i r e d s t a n d a r d MASTER OF APPLIED SCIENCE i n the Department o f METALLURGY THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1976 Thomas P h i l i p Nikiforuk, 1976 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . o D e p a r t m e n t o f M e t a l l u r g y The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a D a t e J u l y 9 t h , 1 9 7 6 - i - ABSTRACT C i r c u m f e r e n t i a l l y n o t ched rods o f t h r e e t y p e s o f a u s t e n i t i c s t a i n l e s s s t e e l were s t r e s s c o r r o d e d under f r e e l y c o r r o d i n g c o n d i t i o n s a t t h e i r y i e l d s t r e s s i n b o i l i n g 154 0C MgCl2, and b o i l i n g M g C l 2 w i t h a d d i t i o n s o f H C l , C o C l 2 , and F e C l 3 . A l l o y t y p e s 30"4, 316, and 310 were chosen because o f t h e i r known d i f f e r e n t s t r e s s c o r r o s i o n s u s c e p t i b i l i t y . The c o r r o s i o n p r o d u c t s formed on the s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e were a n a l y z e d by e l e c t r o n d i f f r a c t i o n and energy d i s p e r s i v e x - r a y a n a l y s i s . E l e c t r o n d i f f r a c t i o n o f c o r r o s i o n p r o d u c t s , b o t h i n s i t u and s t r i p p e d from the f r a c t u r e s u r f a c e , showed t h e c o r r o s i o n p r o d u c t was a s p i n e l o x i d e i n a l l c a s e s . Q u a l i t a t i v e x - r a y a n a l y s i s o f c o r r o s i o n p r o d u c t s , i n s i t u and s t r i p p e d from t h e f r a c t u r e s u r f a c e , i n d i c a t e d t h e c o r r o s i o n p r o d u c t formed on a l l a l l o y s was e n r i c h e d i n chromium and c o n t a i n e d l e s s e r amounts o f the elements i r o n , n i c k e l , s i l i c o n , molybdenum, magnesium, phosphorous and c h l o r i n e . O b s e r v a t i o n s l e d t o the c o n c l u s i o n t h a t t h e c o r r o s i o n p r o d u c t formed i n the c r a c k s o f the v a r i o u s a l l o y s was s i m i l a r , b e i n g p r e d o m i n a n t l y a • chromium e n r i c h e d o x i d e s p i n e l w i t h p o s s i b l e t r a c e s o f m e t a l c h l o r i d e s o r a corundum type o x i d e . The p r e s e n c e o f the s p i n e l o x i d e was c o n s i s t e n t w i t h a n t i c i p a t e d E-pH e q u i l i b r i u m w i t h i n t h e c r a c k . However, i t was f e l t t h e v a r i a t i o n i n s . c . c . b e h a v i o u r between the d i f f e r e n t a l l o y s c o u l d not be a d e q u a t e l y a c c o u n t e d f o r i n terms o f the c o m p o s i t i o n o f t h e o x i d e . ACKNOWLEDGMENT I would l i k e to thank Dr. D. Tromans f o r h i s a d v i c e , help and understanding. I would a l s o l i k e t o thank the f a c u l t y , s t a f f and f e l l o w students of the Department of Met a l l u r g y f o r making my many years a t U.B.C. a l l worthwhile. Thanks i s a l s o due t o Ms L. F r e d e r i c k f o r her help and encouragement. F i n a n c i a l a s s i s t a n c e f o r t h i s t h e s i s was provided by Mean In d u s t r i e s Ltd. and the Department of Metallurgy a t U.B.C. TABLE OF CONTENTS INTRODUCTION EXPERIMENTAL 2.1 G e n e r a l 2.2 M a t e r i a l s 2.2.1 S t e e l s 2.2.2 Environments 2.3 Specimen P r e p a r a t i o n 2.4 S t r e s s C o r r o s i o n T e s t s 2.5 C o r r o s i o n P r o d u c t S t r i p p i n g 2.6 E l e c t r o n D i f f r a c t i o n 2.7 X-ray S p e c t r o s c o p y 2.7.1 I n t r o d u c t i o n 2.7.2 X-ray S p e c t r o s c o p y o f T h i n F i l m s 2.7.3 Mounting o f T h i n F i l m s f o r S.E.M. X-ray S p e c t r o s c o p y 2.7.4 Procedure f o r X-ray S p e c t r o s c o p y RESULTS AND OBSERVATIONS 3.1 S t r e s s C o r r o s i o n T e s t s 3.2 S t r i p p i n g o f Oxides 3.2.1 Bromine-Methanol S t r i p p i n g 3.2.2 A c e t a t e S t r i p p i n g 3.3 E l e c t r o n D i f f r a c t i o n - i v - PAGE 3.4 X-ray Spectroscopy 1+2 3.4.1 X-ray Spectroscopy of St r i p p e d Oxides 42 3.4.2 In S i t u Spectroscopy 53 3.5 P a r t i a l Crack 55 4. DISCUSSION 60 4.1 D i f f r a c t i o n Studies 60 4.2 X-ray A n a l y s i s 62 4.3 P o t e n t i a l -pH E q u i l i b r i a Within the S.C.C. Crack 64 4.4 Growth of Oxide Films 68 4.5 Envisioned Events Within the Stress Corrosion Crack 70 4.6 E f f e c t of A l l o y Composition 71 5. CONCLUSIONS 74 BIBLIOGRAPHY 75 APPENDIX A 78 APPENDIX B 139 - V - LIST OF TABLES TABLES PAGE I Chemical A n a l y s i s o f C o r r o s i o n P r o d u c t I s o l a t e d from S t r e s s C o r r o s i o n Cracks i n Type 316 S t a i n l e s s S t e e l , from N i e l s e n . [14] 14 I I C omposition o f S t a i n l e s s S t e e l 12 I I I A n n e a l i n g Data f o r S t a i n l e s s S t e e l 12 I V S t r e s s C o r r o s i o n T e s t Performed 15 V S t r e s s C o r r o s i o n T e s t R e s u l t s 28 VI Summary o f E l e c t r o n D i f f r a c t i o n R e s u l t s 34 VII d-Spacings and R e l a t i v e I n t e n s i t i e s f o r the S p i n e l s o f I r o n , F e 3 0 i t , YFe203, F e C r 2 0 i +, from ASTM X-ray D i f f r a c t i o n Cards 35 V I I I D, and d-Spacings o f D i f f r a c t i o n P a t t e r n s Shown i n F i g . 7 37 IX D, d - S p a c i n g s , and R e l a t i v e V i s u a l I n t e n s i t i e s from D i f f r a c t i o n p a t t e r n s Taken from Bromine S t r i p and A c e t a t e S t r i p Oxides (see F i g . 8) 40 X a Q Values C a l c u l a t e d from P l o t s o f D vs ( h 2 + k 2 + l 2 ) ^ i n Appendix A, where Slope M = K / a Q , M Determined from L e a s t Squares A n a l y s i s . A l l Oxides S t r i p p e d i n 1% Bromine-Methanol S o l u t i o n E x c e p t Where Noted 43 XI Summary o f X-ray S p e c t r o s c o p y R e s u l t s , See Appendix B 44 XII X-ray I n t e n s i t i e s and d-Spacings f o r FesO^ and FeCl2 from ASTM Index Cards #11-614 and 1-1106 R e s p e c t i v e l y 52 A l 304 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22217 camera c o n s t a n t K = 1.88 ins'A° 79 A2 304 S.C.C. i n MgCl2, Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23299 camera c o n s t a n t K = 1.95 ins«A° 81 - v i - 304 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23389 camera c o n s t a n t K = 1.88 ins*A°. 304 S.C.C. i n M g C l 2 + C o C l 2 , Oxide S t r i p p e d i n 1% Bromine- Methanol S o l u t i o n p a t t e r n #23462 camera c o n s t a n t K = 1.84 ins'A°. 304 S.C.C. i n M g C l 2 + C o C l 2 , Oxide S t r i p p e d i n 1% Bromine- Methanol S o l u t i o n p a t t e r n #23459 camera c o n s t a n t K = 1.84 ins*A°. 304 S.C.C. i n M g C l 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine Methanol S o l u t i o n p a t t e r n #23464 camera c o n s t a n t K = 1.80 i n s ' A 0 . 304 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23452 camera c o n s t a n t K = 1.91 ins'A° • 304 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23434 camera c o n s t a n t K = 1.91 ins*A° • 304 S.C.C. i n MgC.l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23436 camera c o n s t a n t K = 1.91 i n s ' A 0 • 304 S.C.C. i n M g C l 2 + F e C l 3 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23580 camera c o n s t a n t K = 1.90 ins*A° • 304 S.C.C. i n M g C l 2 + F e C l 3 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23579 camera c o n s t a n t K = 1.90 i n s ' A 0 • 304 S.C.C. i n M g C l 2 + F e C l 3 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23581 camera c o n s t a n t K = 1.90 ins*A° • 316 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23333 camera c o n s t a n t K = 1.93 ins*A° • 316 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23329 camera c o n s t a n t K = 1.92 ins*A° • VI1 TABLES A19 PAGE A15 316 S.C.C. i n MgCJ 2, Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22222 camera c o n s t a n t K = 1.91 ins-A° 107 A16 316 S.C.C. i n MgCl 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23406 camera c o n s t a n t K = 1.91 i n s . A° 109 A17 316 S.C.C. i n MgCl 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23407 camera c o n s t a n t K = 1.91 ins-A° • • • • 111 A18 316 S.C.C. i n MgCl 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23404 camera c o n s t a n t K = 1.91 i n s . A° 113 316 S.C.C. i n MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23483 camera c o n s t a n t K = 1.80 i n s ' A 0 . . . . 115 A20 316 S.C.C. i n MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23472 camera c o n s t a n t K = 1.80 ins-A° 117 A21 316 S.C.C. . i n MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23474 camera c o n s t a n t K - 1.82 ins*A° 119 A22 310 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22205 camera c o n s t a n t K = 1.91 i n s - A° 121 A23 310 S.C.C. i n MgCls , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22200 camera c o n s t a n t K = 1.88 ins-A° 123 A24 310 S.C.C. i n MgCl2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22196 camera c o n s t a n t K = 1.88 ins*A° 125 A25 310 S.C.C. i n MgCfe , Oxide S t r i p p e d w i t h C e l l u l o s e A c e t a t e p a t t e r n #23146 camera c o n s t a n t K = 2.28 ins- A 0 127 A26 310 S.C.C. i n MgCJ2 , Oxide S t r i p p e d w i t h C e l l u l o s e A c e t a t e p a t t e r n #23124 camera c o n s t a n t K = 2.31 ins»A° 129 - v i i i - £ c j £ £ PAGE A27 310 S.C.C. i n M g C l 2 , O x i d e . S t r i p p e d w i t h C e l l u l o s e A c e t a t e p a t t e r n #23043 camera c o n s t a n t K = 2.28 i n s ' A 0 • • • • 131 A28 310 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23418 camera c o n s t a n t K = 1.91 ins*A° 133 A29 310 S.C.C. i n MgCl2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23417 camera c o n s t a n t K = 1.91 ins«A°---- 135 A30 310 S.C.C. i n MgCl 2 + C o C l 2 , 0 x i d e S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23488 camera c o n s t a n t K = 1.85 ins-A° 137 - i x - FIGURE LIST OF FIGURES PAGE 1 L a t t i c e parameter v a r i a t i o n w i t h c o m p o s i t i o n f o r N i , C r , Fe, s p i n e l s , from F r a n c i s [22] 8 2 S.C.C. C e l l w i t h 7 i n c h l o n g specimen i n p l a c e 16 3 Schematic r e p r e s e n t a t i o n o f i n s i t u d i f f r a c t i o n o f s u r f a c e o x i d e i n h i g h r e s o l u t i o n d i f f r a c t i o n s t a g e o f the T.E.M. The p r i m a r y e l e c t r o n beam s t r i k e s the s u r f a c e f i l m and i s d i f f r a c t e d 19 4 Schematic diagrams o f b a c k s c a t t e r e d e l e c t r o n e f f e c t from specimen h o l d e r d u r i n g x-ray a n a l y s i s o f t h i n f i l m s . a) from c o n v e n t i o n a l specimen h o l d e r b) from h o l l o w g r a p h i t e b l o c k 25 5 R e p r e s e n t a t i v e f r a c t o g r a p h s (40x m a g n i f i c a t i o n ) from s t a i n l e s s s t e e l s . a) 304, b) 316, c) 310 29 6 M i c r o g r a p h o f c o r r o s i o n p r o d u c t from f r a c t u r e s u r f a c e o f type 310 s t a i n l e s s s t e e l s t r e s s c o r r o d e d i n b o i l i n g MgCl^ s o l u t i o n . S t r i p p e d i n bromine-methanol s o l u t i o n ( m a g n i f i c a t i o n 1200x) 31 7 Sample d i f f r a c t i o n p a t t e r n s from s t r i p p e d s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o x i d e s . a) 304, b) 316, c) 310 36 8 D i f f r a c t i o n p a t t e r n s taken from s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o x i d e s o f type 310 s t r e s s c o r r o d e d i n MgCl2. a) bromine-methanol s t r i p b) c e l l u l o s e a c e t a t e s t r i p 39 9 D i f f r a c t i o n p a t t e r n s taken from exposed n o t c h a r e a s o f specimens a) type 304 i n MgCl 2 + F e C l 3 . M 30 4 ( s p i n e l ) p a t t e r n b) type 304 i n MgCl 2 + F e C l 3 . M 20 3 (rhombohedral) p a t t e r n c ) t y p e 304 i n MgCl 2 + F e C l 3 . M 30 4 ( s p i n e l ) p a t t e r n . . . 41 10 D i f f r a c t i o n p a t t e r n and x- r a y spectrum t a k e n from t h e same a r e a on a f r a c t u r e : s u r f a c e o x i d e s t r i p p e d from 316-type specimen s t r e s s c o r r o d e d i n MgCl 2 + C o C l 2 s o l u t i o n 46 11 X-ray spectrum taken from c h r o m i t e ore 47 12 X-ray s p e c t r a taken from t h e f r a c t u r e s u r f a c e o x i d e s t r i p p e d from a type 304 specimen s t r e s s c o r r o d e d i n MgCl 2 + F e C l 3 s o l u t i o n . The t h r e e d i f f e r e n t s p e c t r a r e p r e s e n t t h e v a r i a t i o n i n i n t e g r a t e d CrKa/FeKa r a t i o o b s e r v e d f o r t h i s o x i d e . a) CrKa/FeKa = 4.99/1 b) CrKa/FeKa = 1.01/1 c) CrKa/FeKa = 0.405/1 49 X-ray s p e c t r a taken from f r a c t u r e s u r f a c e o x i d e s t r i p p e d from a t y p e 310 specimen s t r e s s c o r r o d e d i n MgCl 2 s o l u t i o n . a) o x i d e s t r i p p e d w i t h bromine-methanol s o l u t i o n . b) o x i d e s t r i p p e d w i t h c e l l u l o s e a c e t a t e 51 Comparison o f i n s i t u x - r a y s p e c t r a from m e c h a n i c a l f r a c t u r e s u r f a c e s , w i t h f r a c t u r e s u r f a c e s from specimens s . c . c . i n M g C l 2 s o l u t i o n a) type 304 m e c h a n i c a l f r a c t u r e b) t y p e 316 m e c h a n i c a l f r a c t u r e a') type 304 s . c . c . b') type 316 s . c . c . c ) t y p e 310 m e c h a n i c a l f r a c t u r e c') type 310 s . c . c 54 In s i t u x - r a y s p e c t r a t a k e n from f r a c t u r e s u r f a c e o x i d e o f t y p e 304 specimen s . c . c . i n a M g Cl 2 + F e C l 3 s o l u t i o n . Shows v a r i a t i o n i n x - r a y spectrum w i t h beam p e n e t r a t i o n (as i n d i c a t e d by i n c r e a s i n g x-ray count r a t e ) a) CrKa/FeKa = .764/1 (100 c o u n t s / s e c ) b) CrKa/FeKa = 1.15/1 (300 c o u n t s / s e c ) c ) CrKa/FeKa = 1.40/1 (900 c o u n t s / s e c ) 56 S o l i d i f i e d c r a c k s o l u t i o n on f r a c t u r e s u r f a c e o f t y p e 304 specimen p a r t i a l l y s t r e s s c o r r o d e d i n b o i l i n g M g C l 2 s o l u t i o n and m e c h a n i c a l l y f r a c t u r e d a t room temperature (800x m a g n i f i c a t i o n ) 58 P o t e n t i a l -pH (E-pH) diagram f o r the Cr-H 20 system. C o n c e n t r a t i o n o f s o l u b l e s p e c i e s 10 6M. , from Brook [33] 65 P o t e n t i a l -pH (E-pH) diagram f o r the Ni-H20 system. C o n c e n t r a t i o n o f s o l u b l e s p e c i e s 10 6M., from Brook [33] 65 P o t e n t i a l -pH (E-pH) diagram f o r the Fe--H20 system a t 150°C. U n i t a c t i v i t y o f s o l u b l e s p e c i e s , from B i e r n a t and R o b i n s [ 3 1 ] . . . 66 C a l c u l a t e d a r e a s o f s t a b i l i t y o f Fe, FeCl2*4H20, and Fe30i+ i n the p r e s e n c e o f a s o l u t i o n e l e c t r o n e u t r a l i n F e C l 2 , ( s c h e m a t i c ) from P o u r b a i x [ 5 ] 66 Schematic Evans diagram showing p o s s i b l e e f f e c t s o f a l l o y i n g on e l e c t r o c h e m i c a l b e h a v i o u r . Base a l l o y has e l e c t r o c h e m i c a l p o l a r i - z a t i o n b e h a v i o u r d e p i c t e d by c u r v e s a and c. Upon a l l o y i n g w i t h n i c k e l , t h e a l l o y r e v e r s i b l e p o t e n t i a l i n c r e a s e s from E c t o E^, r e s u l t i n g i n a lower c o r r o s i o n c u r r e n t I t o I' . A l l o y i n g c o r r c o r r may a l s o lower t h e exchange c u r r e n t d e n s i t y f o r hydrogen r e d u c t i o n from I_ t o I', a g a i n , l o w e r i n g I t o I ' [39] 73 0 0 c o r r c o r r \, P l o t o f D vs ( h 2 + k 2 + l 2 ) 2 from T a b l e A l . D i f f r a c t i o n p a t t e r n #22217, 304 s . c . c . i n MgCl2, o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 80 P l o t o f D vs ( h 2 + k 2 + l 2 ) 2 from T a b l e A2. D i f f r a c t i o n p a t t e r n #23299, 304 s . c . c . i n MgCl2, o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 82 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A3. D i f f r a c t i o n p a t t e r n #23389, 304 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 84 - x i - FIGURE PAGE A4 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A4. D i f f r a c t i o n p a t t e r n #23462, 304's.c.c. i n M g C l 2 + "C6C12' o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 86 A5 P l o t o f D v s ( h 2 + k 2 + l ^ f r o m T a b l e A5. D i f f r a c t i o n p a t t e r n #23459, 304 s . c . c . i n M g C l 2 + C o C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 88 A6 P l o t o f D vs ( h 2 + k 2 + I 2)* 5 from T a b l e A6. D i f f r a c t i o n p a t t e r n #23464, 304 s . c . c . i n MgCl 2+ C o C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 90 A7 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A7. D i f f r a c t i o n p a t t e r n #23452, 304 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 92 A8 P l o t o f D vs ( h 2 + k 2 + l 2 ) * 5 from T a b l e A8. D i f f r a c t i o n p a t t e r n #23434, 304 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 94 A9 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A9. D i f f r a c t i o n p a t t e r n #23436, 304 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 96 A10 P l o t o f D v s . ( h 2 + k 2 + l 2 ) i 2 from T a b l e A10. D i f f r a c t i o n p a t t e r n #23580, 304 s . c . c . i n M g C l 2 + F e C l 3 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 98 A l l P l o t o f D vs ( h 2 + k 2 + l 2 ) * 5 from T a b l e A l l . D i f f r a c t i o n p a t t e r n #23579, 304 s . c . c . i n MgCl2 + F e C l 3 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . A12 P l o t o f D vs ( h 2 + k 2 + l ^ f r o m T a b l e A12. D i f f r a c t i o n p a t t e r n #23581, 304 s . c . c . i n M g C l 2 + F e C l 3 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . -^2 A13 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A13. D i f f r a c t i o n p a t t e r n #23333, 316 s . c . c . i n MgClo, o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n ± A14 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A14. D i f f r a c t i o n p a t t e r n #23329, 316 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h .1% bromine- methanol s o l u t i o n . - x i i - FIGURE PAGE A15 P l o t o f D vs C h 2 " + k 2 + l 2 ) ^ from T a b l e A15. D i f f r a c t i o n p a t t e r n #22222, 316 s . c . c . i n M g C l 2 s o x i d e s t r i p p e d w i t h .1% bromine- methanol s o l u t i o n 108 A16 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ f r om T a b l e A16 D i f f r a c t i o n p a t t e r n #23406, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h .1% bromine- methanol s o l u t i o n 110 A17 P l o t o f D vs ( h 2 + k 2 + l 2 ) " 2 " from T a b l e A17. D i f f r a c t i o n p a t t e r n #23407, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 112 A18 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ f r om T a b l e A18. D i f f r a c t i o n p a t t e r n #23404, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 114 A19 P l o t o f D v s . ( h 2 + k 2 + l 2 ) ' 1 from T a b l e A19. D i f f r a c t i o n p a t t e r n #23483, 316 s . c . c . i n M g C l 2 + C 0 C I 2 , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n '. 116 A20 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A20. D i f f r a c t i o n p a t t e r n #23472, 316 s . c . c . i n MgCl2 + C 0 C I 2, o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 118 A21 P l o t o f D vs ( h 2 + k 2 + l 2 ) ' 2 from T a b l e A21. D i f f r a c t i o n p a t t e r n #2347^, 316 s . c . c . i n MgCl2 + C 0 C I 2 , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 120 A22 P l o t o f D vs ( h 2 + k 2 + l2)^ from T a b l e A22. D i f f r a c t i o n p a t t e r n #22205, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 122 A23 P l o t o f D vs ( h 2 + k 2 + l2)^ from T a b l e A23. D i f f r a c t i o n p a t t e r n #22200, 310 s . c . c . i n M g C l 2 , oxide, s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 124 A24 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A24. D i f f r a c t i o n p a t t e r n #22146, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n 126 - x i i i - FIGURE PAGE A25 P l o t o f D vs ( h 2 + k 2 + I 2 ) ' 5 from T a b l e A25. D i f f r a c t i o n p a t t e r n #23146, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h c e l l u l o s e a c e t a t e 128 2 2 2 3" A26 P l o t o f D vs (h + k + 1 ) 2 from T a b l e A26. D i f f r a c t i o n p a t t e r n #23124, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h c e l l u l o s e a c e t a t e 130 2 2 2 !^ A27 P l o t o f D vs (h + k + 1 ) 2 from T a b l e A27. • D i f f r a c t i o n p a t t e r n #23043, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h c e l l u l o s e a c e t a t e 132 , 2 2 2 , h A28 P l o t o f D vs (h + k + 1 ) from T a b l e A28. D i f f r a c t i o n p a t t e r n #23418, 310 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 134 A29 P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ f r o m T a b l e A29. D i f f r a c t i o n p a t t e r n #23417, 310 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 136 2 2 2 !" A30 P l o t o f D vs (h + k + 1 ) 2 from T a b l e A30. D i f f r a c t i o n p a t t e r n #23488, 310 s . c . c . i n ' M g C l 2 + C o C l 2 , o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n 138 B l S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f type 304 s t r e s s c o r r o d e d i n MgC.l2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n . 140 B2 S.E.M. x- r a y spectrum from f r a c t u r e s u r f a c e o x i d e o f t y p e 304 s t r e s s c o r r o d e d i n MgCl2 + HCl s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 141 B3 S.E.M. x- r a y spectrum from f r a c t u r e s u r f a c e o x i d e o f t y p e 304 s t r e s s c o r r o d e d i n M g C l 2 + C 0 C I 2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 142 B4 S.E.M. x- r a y spectrum from f r a c t u r e s u r f a c e o x i d e o f type 316 s t r e s s c o r r o d e d i n M g C l 2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n . 143 - x i v - FIGURE PAGE B5 S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f typ e 3 1 6 . s t r e s s c o r r o d e d i n MgCl2 + HCl s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 144 B6 S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o f o x i d e o f type 316 s t r e s s c o r r o d e d i n MgCl2 + C0CI2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 14 5 B7 S.E.M. x- r a y spectrum from f r a c t u r e s u r f a c e o x i d e o f type 310 s t r e s s c o r r o d e d i n MgCl2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 146 B8 S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f ty p e 310 s t r e s s c o r r o d e d i n M g C l 2 + H C l s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 147 B9 S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f type 310 s t r e s s c o r r o d e d In MgCl2 + C0CI2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n 148 - 1 - 1. INTRODUCTION A u s t e n i t i c s t a i n l e s s s t e e l s a r e n o t o r i o u s l y s u s c e p t i b l e t o s t r e s s c o r r o s i o n c r a c k i n g ( s . c . c . ) i n the p r e s e n c e o f h o t aqueous c h l o r i d e s o l u t i o n s . Such environments f r e q u e n t l y , o c c u r i n t h e c h e m i c a l i n d u s t r y where c h l o r i d e r e s i d u a l s o r contaminants a r e u s u a l l y p r e s e n t , and the problem has been e x t e n s i v e l y s t u d i e d i n the l a b o r a t o r y by u t i l i s i n g b o i l i n g aqueous s o l u t i o n s o f M g C l 2 . The f r e q u e n t t e s t i n g o f s t e e l s i n M g C l 2 s o l u t i o n s has been j u s t i f i e d because o f t h e g e n e r a l l y good c o r r e l a t i o n w i t h i n d u s t r i a l performance. However, d e s p i t e the. many p u b l i s h e d papers on t h e s u b j e c t , few s t u d i e s have been conducted on the n a t u r e o f c o r r o s i o n p r o d u c t s on s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e s and t h e i r r e l a t i o n t o aqueous s . c . c . In many s i t u a t i o n s some ty p e o f r e a c t i o n f i l m i s c o n s i d e r e d n e c e s s a r y f o r s . c . c . [ 1 ] , [ 2 ] p r o c e s s because o f i t s i n f l u e n c e on c r a c k geometry and/or l o c a l i z e d d i s s o l u t i o n . The c o r r o s i o n f i l m s may r e s t r i c t l a t e r a l d i s s o l u t i o n and p r e v e n t c r a c k b l u n t i n g , by e i t h e r f o r m i n g a p a s s i v e type f i l m , o r by means o f noble m e t a l enrichment o f t h e c r a c k w a l l s . The c o r r o s i o n f i l m may a c t as a l o c a l cathode t o a c r a c k t i p u n d e r g o i n g a n o d i c d i s s o l u t i o n , depending on the environment and c r a c k geometry [ 3 ] . The m e c h a n i c a l and e l e c t r o c h e m i c a l p r o p e r t i e s o f the c o r r o s i o n p r o d u c t a t the c r a c k t i p may be t h e c o n t r o l l i n g f a c t o r i n s . c . c , as i s p r o p o s e d by f i l m r u p t u r e / s l i p s t e p d i s s o l u t i o n models [ 4 ] . P o u r b a i x [ 5 ] has s t u d i e d t h e e l e c t r o c h e m i c a l a s p e c t s o f c o r r o s i o n i n aqueous c h l o r i d e environments w i t h r e s t r i c t e d geometry; p i t s , c r e v i c e s , and c r a c k s . He c o n c l u d e s t h a t i n s i d e t h e s e o c c l u d e d c e l l s the c o r r o s i o n o f i r o n s h o u l d o c c u r w i t h the e v o l u t i o n o f hydrogen i n an a c i d i f i e d s o l u t i o n s a t u r a t e d i n b o t h F e C l 2 ' 4 H 2 0 and FesO^. L a t a n i s i o n and S t a e h l e - 2 - [ 4 ] p r o p o s e d a mechanism where the s i d e s o f t h e c r a c k become e n r i c h e d i n t h e n o b l e element o f th e a l l o y , ( n i c k e l i n t h e case o f s t a i n l e s s s t e e l ) t h u s becoming i n a c t i v e w i t h r e s p e c t t o t h e c r a c k t i p . E v i d e n c e o f t h i s o c c u r r i n g has been found f o r f e r r i t i c s t a i n l e s s s t e e l s [ 6 ] and 304L a u s t e n i t i c s t a i n l e s s s t e e l [ 3 ] . S l i p d i s s o l u t i o n models [ 7 ] , where c r a c k i n g o c c u r s by t h e c o n t i n u o u s r u p t u r e and r e f o r m a t i o n o f p a s s i v e f i l m s , depend on the m e c h a n i c a l and e l e c t r o c h e m i c a l p r o p e r t i e s o f t h e c o r r o s i o n p r o d u c t . F o r example, d e f o r m a t i o n s t u d i e s on m a g n e t i t e f i l m s [ 8 ] i n d i c a t e they w i l l c r a c k i n t e n s i o n a t s t r a i n s o f 0.05 - 0.08%, and the r a t e o f r e p a s s i v a t i o n may t h e n be a major f a c t o r i n s . c . c . o f s t e e l s . Hydrogen c r a c k i n g models f o r s . c . c . i n d i r e c t l y depend on the c o r r o s i o n p r o d u c t s . C o r r o d i n g s t e e l may h y d r o l y s e a c c o r d i n g t o ; C3, 9-11] 3 F e + 2 + 4 H 2 0 ^ F e 3 0 4 + 8 H + + 2e~ ( l ) Thus, i n aqueous M g C l 2 hydrogen i o n s a r e p r o d u c e d which a r e c a t h o d i c a l l y r e d u c e d a c c o r d i n g t o H + + e H , and d i f f u s e i n t o t h e m e t a l . The to ad hydrogen i n the m e t a l l a t t i c e may p r e c i p i t a t e i n v o i d s o r i n d u c e deform- a t i o n m a r t e n s i t e [12] ahead o f t h e c r a c k ; p r o p a g a t i o n o f t h e c r a c k c o u l d then o c c u r by e i t h e r c l e a v a g e o r p r e f e r e n t i a l d i s s o l u t i o n a l o n g m a r t e n s i t e a u s t e n i t e i n t e r f a c e s . S t r e s s s o r p t i o n models f o r s . c . c . r e q u i r e t h e a d s o r p t i o n o f c h l o r i d e i o n s onto d e f e c t s i t e s a t t h e p l a s t i c a l l y d e f o r m i n g c r a c k t i p , l o w e r i n g t h e s u r f a c e energy o f th e l a t t i c e and r e s u l t i n g i n a p h y s i c a l p a r t i n g o f t h e s u r f a c e [ 1 3 ] . A c o r r o s i o n r e a c t i o n which r e s u l t s i n n i c k e l enrichment o f t h e s u r f a c e w i l l s t r o n g l y a f f e c t t h e a d s o r p t i o n o f c h l o r i d e i o n s . N i e l s e n [14] s t u d i e d t h e r o l e o f c o r r o s i o n p r o d u c t s i n s . c . c . c r a c k - 3 - p r o p a g a t i o n o f a u s t e n i t i c s t a i n l e s s s t e e l s i n b o i l i n g M g C l 2 s o l u t i o n s and c o n c l u d e d t h e i r p r i m a r y e f f e c t was t o e x e r t a wedging a c t i o n , which, t o g e t h e r w i t h r e s i d u a l and a p p l i e d s t r e s s was enough t o t r i g g e r s . c . c . He i s o l a t e d the p r o d u c t from t h e s t r e s s c o r r o s i o n c r a c k by d i s s o l v i n g t h e s u r r o u n d i n g m e t a l m a t r i x i n a s o l u t i o n c o n t a i n i n g 5% by volume o f bromine i n methanol. T h i s l e f t " f a n shaped" c o r r o s i o n p r o d u c t s a few hundred angstroms t h i c k . E l e c t r o n d i f f r a c t i o n p a t t e r n s o f the f a n s i n d i c a t e d a p r i m a r i l y s p i n e l M 30 t t s t r u c t u r e w i t h t r a c e s o f a rhombohedral o x i d e M2O3. He a l s o n o t e d t h a t the c o r r o s i o n p r o d u c t underwent a t r a n s f o r m a t i o n i n the e l e c t r o n beam; an i n i t i a l l y "amorphous" a r e a would c o n v e r t t o a m i c r o p o r o u s a r e a g i v i n g a d i s t i n c t c r y s t a l l i n e p a t t e r n . T h i s was i n t e r p r e t e d as a l o s s o f water due t o h e a t i n g e f f e c t s , w i t h subsequent r e c r y s t a l l i z a t i o n . C h e m i c a l a n a l y s i s , see. T a b l e 1, o f t h e c o r r o s i o n p r o d u c t , t o g e t h e r w i t h t h e e l e c t r o n d i f f r a c t i o n s t u d i e s l e d N i e l s e n t o c o n c l u d e t h a t t h e c o r r o s i o n p r o d u c t was a h y d r a t e d o x i d e e n r i c h e d i n chromium and d e f i c i e n t i n n i c k e l . . The s e r i e s o f e v e n t s e n v i s i o n e d by N i e l s e n was as f o l l o w s : The c o r r o s i o n p r o d u c t s a r e d e p o s i t e d a f i n i t e d i s t a n c e b e h i n d t h e a d v a n c i n g c r a c k t i p and the subsequent wedging a c t i o n o f the p r e c i p i t a t e d m a t e r i a l b u i l d s up s t r e s s w i t h i n the c r a c k t o such a l e v e l t h a t c r a c k p r o p a g a t i o n o c c u r s . The c h l o r i d e environment i s drawn i n t o t h e e n l a r g e d c r a c k and f u r t h e r c o r r o s i o n o f l o c a l anodes o c c u r . The s o l u b l e m e t a l i o n s m i g r a t e under the e l e c t r i c a l f i e l d away from t h e c r a c k t i p towards the c a t h o d i c r e g i o n s , r e a c t i n g w i t h h y d r o x i d e i o n s t o p r e c i p i t a t e m e t a l h y d r o x i d e s . In the h o t s o l u t i o n , t h e h y d r o x i d e would t r a n s f o r m t o h y d r a t e d m e t a l o x i d e s and t h e p r o c e s s i s r e p e a t e d . In t h e l i g h t o f r e c e n t work by Smith e t a l . [ 9 ] , Baker e t a l . [ 1 5 ] , - 4 - T a b l e I. C h e m i c a l A n a l y s i s o f C o r r o s i o n P r o d u c t I s o l a t e d from S t r e s s C o r r o s i o n Cracks i n Type 316 S t a i n l e s s S t e e l , from N i e l s e n [14] Element wt % Oxide wt % 1 i j C r 21.12 C r 2 0 3 30.9 Fe 13.23 F e 2 0 3 18.9 N i 1.85 NiO 2.36 | Mo i 1.95 Mo 203 1.49 Mg - • MgO - S i - S i 0 2 - 5 - Brown [ 1 1 ] , and Marek and Hochman [16] which i n d i c a t e the h o t c h l o r i d e s o l u t i o n a t the c r a c k t i p t o be a c i d i c w i t h a pH 1-3, i t i s f e l t t h a t h y d r o x i d e s c o u l d not e x i s t . F u r t h e r more, a l t h o u g h t h e o b s e r v a t i o n o f a s p i n e l f i l m on i r o n has been o b s e r v e d by o t h e r s , i t i s f e l t t h a t t h e wedging a c t i o n o f t h e c o r r o s i o n p r o d u c t s , w h i l e b e i n g s i g n i f i c a n t , i s not n e c e s s a r y f o r s . c . c . p r o p a g a t i o n . D i r e c t work by B i r l e y [ 1 7 ] , i n d i r e c t s t u d i e s by Baker e t a l . [ l 5 ] and work by S t a e h l e [ 7 ] i n d i c a t e t h e p r e s e n c e o f a chromium and i r o n s p i n e l s . c . c . c o r r o s i o n p r o d u c t . S t a e h l e and h i s co-workers have shown f o r F e - C r - N i a l l o y s , t h a t n i c k e l w i l l p r e f e r e n t i a l l y go i n t o s o l u t i o n w h i l e chromium and i r o n w i l l form an o x i d e f i l m . T h i s f i l m w i l l p a s s i v a t e t h e s t r e s s c o r r o s i o n c r a c k t i p , which i n t u r n w i l l be r u p t u r e d by s l i p s t e p emergence a t the c r a c k t i p thus r e p e a t i n g t h e c y c l e . Baker e t a l . [ 1 5 ] , w orking w i t h 304 s t a i n l e s s s t e e l i n a s o l u t i o n o f 67 wt % MgCl 2-6H2 0 , 8 wt % F e C l 3 - 6 H 2 0 and 25 v t % d i s t i l l e d water m a i n t a i n e d a t a b o i l i n g p o i n t o f 125°C, found t h a t a p r o t e c t i v e c o r r o s i o n f i l m formed on the e x t e r i o r o f the sample when the pH was between 1.2 and 2.5, whereas, below pH 1-2 a n o n - p r o t e c t i v e f i l m formed. However c r a c k i n g o c c u r r e d i n b o t h c a s e s . I t was found t h a t the pH o f the a d v a n c i n g c r a c k was independent o f t h e b u l k s o l u t i o n pH and was always i n th e range o f 1.2 - 2.5. The t h i n c o r r o s i o n f i l m f o u n d i n t h e s t r e s s c o r r o s i o n c r a c k s was assumed t o be t h e same as the f i l m s t h a t formed on the e x t e r i o r s u r f a c e s i n s o l u t i o n s o f the same p'H. T h i s f i l m was a poor e l e c t r i c a l c o n d u c t i n g chromium e n r i c h e d s p i n e l . To determine t h e r o l e o f f i l m d e p o s i t i o n i n c r a c k f o r m a t i o n , o r g a n i c compounds were added i n o r d e r t o complex the i r o n and chromium i o n s thus p r e v e n t i n g f i l m f o r m a t i o n . - 6 - G e n e r a l c o r r o s i o n was o b s e r v e d but no p r e c i p i t a t e o r p r o t e c t i v e f i l m d e v e l o p e d on the specimen s u r f a c e and no c r a c k s were o b s e r v e d . Baker e t a l . c o n c l u d e d t h a t a c r i t i c a l pH and a p r o t e c t i v e p o o r e l e c t r i c a l c o n d u c t i n g f i l m were n e c e s s a r y f o r s . c . c . The pH i s m a i n t a i n e d by h y d r o l y s i s and the o x i d e f i l m produced c o n f i n e s t h e e l e c t r o c h e m i c a l c e l l r e a c t i o n t o t h e c r a c k t i p . B i r l e y [17] i n d i f f r a c t i o n and c h e m i c a l a n a l y s i s s t u d i e s on 304L and 310 a u s t e n i t i c s t a i n l e s s s t e e l s i n 45 wt % MgCl2 and MgCl2 + F e C l 3 aqueous s o l u t i o n s , found the c o r r o s i o n p r o d u c t i n the s . c . c . c r a c k t o be p r i m a r i l y a s p i n e l . C h e m i c a l a n a l y s i s o f o x i d e s formed i n b o i l i n g 45 wt % M g C l 2 s o l u t i o n s was not p o s s i b l e due t o the t h i n n e s s o f th e o x i d e . Oxides formed i n the F e C l 3 + M g C l 2 s o l u t i o n s ( t h e same as Baker e t al.'[15]) however, were t h i c k enough t o p e r f o r m c h e m i c a l a n a l y s i s ; t h e o x i d e s were p r i m a r i l y i r o n , chromium, magnesium, and n i c k e l . He c o n c l u d e d the o x i d e formed i n M g C l 2 + F e C l 3 s o l u t i o n s was an i r o n e n r i c h e d s p i n e l w i t h t r a c e s o f magnesium o x y c h l o r i d e s . Marek and Hochman [18] have o b s e r v e d by i n s i t u energy d i s p e r s i v e x-ray a n a l y s i s , a chromium e n r i c h e d , i r o n and n i c k e l d e f i c i e n t , c o r r o s i o n p r o d u c t on the s . c . c . f r a c t u r e s u r f a c e o f s i n g l e c r y s t a l s o f 316 a u s t e n i t i c s t a i n l e s s s t e e l i n b o i l i n g 45 wt % M g C l 2 s o l u t i o n s . Davis and Wilde [19] have shown t h a t a p a s s i v e f i l m does e x i s t on t h e s u r f a c e o f s t a i n l e s s s t e e l s exposed t o b o i l i n g MgCl2 s o l u t i o n s . Wilde [20] has conducted c o n t r o l l e d p o t e n t i a l , c o r r o s i o n and p o l a r i z a t i o n s t u d i e s on 304 a u s t e n i t i c s t a i n l e s s s t e e l s i n b o i l i n g MgCl2 and L i C l 2 s o l u t i o n s which showed a chromium e n r i c h e d f i l m i s formed on the s t e e l s u r f a c e . D e s p i t e the work o f p r e v i o u s a u t h o r s which s u p p o r t the p r e s e n c e o f - 7 - an i r o n and chromium c o n t a i n i n g s p i n e l i n t h e s t r e s s c o r r o s i o n c r a c k , no s t u d y has been performed on the e f f e c t o f a l l o y elements i n s t a i n l e s s s t e e l on t h e s t r u c t u r e and c o m p o s i t i o n o f t h e s t r e s s c o r r o s i o n p r o d u c t . The a u s t e n i t i c s t a i n l e s s s t e e l s , 304, 316 and 310 have v a r y i n g f a i l u r e times i n h o t c h l o r i d e s o l u t i o n s a t c o n s t a n t temperature and a t c o n s t a n t i n i t i a l s t r e s s l e v e l . The n i c k e l , chromium, and molybdenum c o n t e n t v a r y i n a l l t h r e e , but i t s n o t known i f the c o m p o s i t i o n o r s t r u c t u r e o f t h e s . c . c . c o r r o s i o n p r o d u c t v a r i e s l i k e w i s e . Francombe[21] and F r a n c i s [22] have s t u d i e d t h e l a t t i c e changes i n i r o n s p i n e l s r e s u l t i n g from a d d i t i o n s o f chromium and n i c k e l . The normal s p i n e l ( M + 2 ) ( M + 3 ) 2 0 4 has t h e 0~2 i o n s a r r a n g e d i n a f a c e c e n t r e d c u b i c s t r u c t u r e , w i t h t h e M + 2 i o n s i n t h e t e t r a h e d r a l s i t e s and t h e M + 3 i o n s ' i n t h e o c t a h e d r a l s i t e s . The u n i t c e l l has 56 atoms; 32 oxygen, 8 M + 2 and 16 M + 3. In i r o n s p i n e l s , the M +2 i o n s p r e f e r t o s i t u a t e i n the o c t a h e d r a l s i t e s , thus the s t r u c t u r e i s an i n v e r s e s p i n e l , F e + 3 ( F e + 2 F e + 3 ) 0 1 + . A d d i t i o n s o f chromium i o n s w i l l r e p l a c e f e r r o u s F e + 2 i o n s i n the o c t a h e d r a l s i t e s w i t h C r + 3 and move F e + 2 t o t h e t e t r a h e d r a l s i t e s . Large a d d i t i o n s o f chromium w i l l c o n v e r t t h e i n v e r s e s p i n e l t o a normal s p i n e l , t h e t r a n s i t i o n o c c u r r i n g a t a p p r o x i m a t e l y Fe-^gCr-]^ 2 0 ^ F u r t h e r a d d i t i o n s o f C r + 3 w i l l l e a d t o a s t o i c h i o m e t r i c o x i d e , F e + 2 ( C r + 3 ) 0^ , known as c h r o m i t e . The change from i n v e r s e t o normal s p i n e l i s accompanied by a change i n l a t t i c e parameter (see F i g . 1) and c o n d u c t i v i t y . M a g n e t i t e has a h i g h e r c o n d u c t i v i t y than c h r o m i t e due t o t h e p r e s e n c e o f b o t h f e r r i c and f e r r o u s i o n s i n the o c t a h e d r a l s i t e s [ 3 7 ] . N i c k e l and manganese can a l s o form s p i n e l s w i t h i r o n and chromium; N i C r 2 0 i + , NiFe20i t, MnFe 20i t. A s o l i d s o l u t i o n o f mixed s p i n e l phases may - 8 - ! 3 ° ' P'CrzO! NiCrzOi NiF;,O t Fe,Oi F i g . 1. L a t t i c e parameter v a r i a t i o n w i t h c o m p o s i t i o n f o r N i , C r , Fe s p i n e l s , f rom F r a n c i s [ 2 2 ] . - 9 - o c c u r s i n c e a l l t y p e s o f i r o n - c o n t a i n i n g s p i n e l s a r e c o m p l e t e l y m i s c i b l e [ 2 2 ] . Any m i x t u r e o f s p i n e l s w i l l r e s u l t i n a v a r i a t i o n o f l a t t i c e parameter o f t h e e n t i r e o x i d e , thus s p i n e l phases cannot be i d e n t i f i e d s o l e l y by e l e c t r o n o r x-ray d i f f r a c t i o n . T h e r e f o r e , i t i s n e c e s s a r y f o r a c h e m i c a l a n a l y s i s t o be performed t o i d e n t i f y t h e s p i n e l phase o r phases p r e s e n t . E l e c t r o n and x-ray d i f f r a c t i o n s t u d i e s o f o x i d e f i l m s , b o t h i n s i t u and s t r i p p e d from t h e s u b s t r a t e , have been p e r f o r m e d by s e v e r a l a u t h o r s [14,15,17,23]. T r a n s m i s s i o n e l e c t r o n d i f f r a c t i o n i s easy and c o n v e n i e n t and i s a p p l i c a b l e t o t h i n and t h i c k o x i d e s . C h e m i c a l a n a l y s i s o f o x i d e s can be a c c o m p l i s h e d i n a v a r i e t y o f ways. In t h e p r e s e n t work, the most c o n v e n i e n t and q u i c k e s t was by means o f an energy d i s p e r s i v e x - r a y a n a l y z e r attachment mounted on a s c a n n i n g e l e c t r o n m i croscope (S.E.M.) and a t r a n s m i s s i o n e l e c t r o n m i croscope (T.E.M.). T h i s a l l o w s a q u i c k q u a l i t a t i v e a n a l y s i s f o r a l l elements above sodium, atomic number 11. With S.E.M. c a p a b i l i t i e s i t i s a l s o p o s s i b l e t o a n a l y z e s e l e c t e d a r e a s up t o a p p r o x i m a t e l y 60,000x m a g n i f i c a t i o n , making i t p o s s i b l e t o determine i f t h e r e a r e any major c o m p o s i t i o n v a r i a t i o n s i n the o x i d e . F o r t h e p r e s e n t s t u d y c i r c u m f e r e n t i a l l y n o t c h e d r o d s o f t h r e e a u s t e n i t i c s t a i n l e s s s t e e l s , 304, 316, and 310 were s t r e s s c o r r o d e d under f r e e l y c o r r o d i n g c o n d i t i o n s a t t h e i r y i e l d s t r e s s i n a b o i l i n g aqueous s o l u t i o n c o n t a i n i n g 45 wt % o f M g C l z (b.p. 1 5 4 ° C ) . The s t r u c t u r e and c o m p o s i t i o n o f the r e s u l t i n g c o r r o s i o n p r o d u c t on t h e f r a c t u r e s u r f a c e was then determined. A d d i t i o n s o f H C l , FeCl3 and C o C l 2 were made t o the b a s i c M g C l 2 s o l u t i o n t o determine t h e i r e f f e c t on the o x i d e . Specimens were a l s o p a r t i a l l y c r a c k e d i n an attempt t o examine the s o l u t i o n i n s i d e - 10 - the stress corrosion crack. In order to understand the mechanism of s.c.c, maximum information is required regarding the phases present at the crack t i p . This study- was an attempt to provide further information on the crack tip chemistry. - 11 - 2. EXPERIMENTAL 2.1 G e n e r a l Three a u s t e n i t i c s t a i n l e s s s t e e l s , 304, 316, and 310, were s e l e c t e d f o r l o a d r e l a x a t i o n s t r e s s c o r r o s i o n t e s t s i n b o i l i n g c h l o r i d e s o l u t i o n s . C i r c u m f e r e n t i a l l y n o t c h e d s t e e l r o ds were p l a c e d i n t h e t e s t environment, a l l o w e d t o r e a c h e q u i l i b r i u m t e m p e r a t u r e , t h e n l o a d e d u n t i l y i e l d i n g o c c u r r e d . F o l l o w i n g s t r e s s c o r r o s i o n , the. f r a c t u r e s u r f a c e was washed i n hot tap water, d r i e d w i t h e t h a n o l and s t o r e d i n a d e s i c c a t o r . E l e c t r o n d i f f r a c t i o n and x - r a y s p e c t r o s c o p y o f t h e f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t was performed i n s i t u on the m e t a l s u b s t r a t e and on the c o r r o s i o n p r o d u c t s t r i p p e d from the m e t a l . The t e c h n i q u e o f B i r l e y and Tromans [12] was employed f o r d i f f r a c t i o n s t u d i e s o f c o r r o s i o n p r o d u c t s i n s i t u , whereby a t r a n s m i s s i o n e l e c t r o n m i c r o s c o p e i s used as a sim p l e e l e c t r o n d i f f r a c t i o n camera. X-ray s p e c t r o s c o p y was conducted w i t h an energy d i s p e r s i v e s p e c t r o m e t e r a t t a c h e d t o t h e d i f f r a c t i o n chamber o f t h e t r a n s m i s s i o n e l e c t r o n m i c roscope (T.E.M.) and t o the specimen chamber o f a s c a n n i n g e l e c t r o n m i c roscope (S.E.M.) C o n v e n t i o n a l t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y and d i f f r a c t i o n s t u d i e s were conducted on t h e s t r i p p e d o x i d e f i l m s . 2.2 M a t e r i a l s 2.2.1 S t e e l s The s t a i n l e s s s t e e l s were r e c e i v e d as 3/8 i n c h d i a m e t e r r o d s . The a n a l y s e s i n weight p e r c e n t are shown i n T a b l e I I . - 12. - TABLE I I : Com p o s i t i o n o f S t a i n l e s s S t e e l Element 304 wt % r — ! 316 i wt % ! 1 | 310 j i wt % Fe 69 .89 i I 65 .84 49 .82 | Cr 18 .67 17 .92 1 25 .74 j | N i 8 .91 11 .61 21 .57 \ l c 0 .05 0 .045 0 f • 09 j Co 0 .1 0 .1 0 i I l i Cu 0 .2 0 2 0 2 \ i Mn 1. -2. 1.--2. 1.--2. 1 i Mo 0 .2 2 0 0 1 2 j S i • 0.5 -1.0 0.5-•1.0 0.5-•1.0 J V 0 .03 0. 03 0 03 s 0 .006 0. 013 0. 006 j TABLE I I I : A n n e a l i n g Data f o r S t a i n l e s s S t e e l S t e e l Temp. °C Time ( h r ) Room Temp. Notch y i e l d s t r e s s , ( p s i ) 304 1150 1 65,000 316 1150 1 63,500 310 1150 1 69,000 - 13 - 2.2.2 Environments Four d i f f e r e n t environments were used i n t h i s s t u d y ; 1) MgCl 2 + water 2) MgCl^ + HCl + water 3) MgCl 2 + F e C l 3 + water 4) MgCl 2 + C o C l 2 + water A l l were made w i t h r e a g e n t grade c h e m i c a l s and d i s t i l l e d water. T e s t s were conducted a t t h e b o i l i n g p o i n t o f the s o l u t i o n s , t e m p e r a t u r e s u s u a l l y f l u c t u a t i n g ± 2°C. The b a s i c environment was 45 wt % MgCl 2 and water ( b o i l i n g p o i n t 1 5 4 ° C ) . For t e s t s i n an a c i d i f i e d s o l u t i o n , l c c o f c o n c e n t r a t e d 37.5% HCl s o l u t i o n was added t o 40 cc o f the b a s i c MgCl 2 s o l u t i o n t o g i v e an approximate c o n c e n t r a t i o n o f 0.3 M/l HCl. The MgCl 2 + F e C l 3 s o l u t i o n was the same as B i r l e y ' s [17] and Baker's [ 1 5 ] ; 8 wt % F e C l ^ . 6H 20, 67 wt % M g C l 2"6H 20, and s u f f i c i e n t d i s t i l l e d water t o a d j u s t the b o i l i n g p o i n t t o 125°C. S i n c e F e C l 3 w i l l d e c r e a s e the time t o f a i l u r e , T^, o f a u s t e n i t i c s t a i n l e s s s t e e l s i n b o i l i n g c h l o r i d e s o l u t i o n s , and C o + 2 has a h i g h e r r e d u c t i o n p o t e n t i a l a t 25°C than F e + 3 [ 2 4 ] , t h e n C o C l 2 might a l s o d e c r e a s e T f . T h e r e f o r e , C0CI2 was added t o MgCl2 t o make a s o l u t i o n h a v i n g the same mole r a t i o Mg /Co as the mole r a t i o Mg Z / F e 0 i n the F e C l 3 s o l u t i o n . The c o m p o s i t i o n was -17 gr C o C l 2 * H 2 0 , 203 g r M g C l 2 « 6 H 2 0 , b o i l i n g p o i n t 160°C. 2.3 Specimen P r e p a r a t i o n S t r e s s c o r r o s i o n specimens were 7 i n c h s e c t i o n s o f 3/8 d i a m e t e r r o d , t h r e a d e d a t e i t h e r end w i t h a c e n t r a l l y l o c a t e d 60° c i r c u m f e r e n t i a l - 14 - n o t c h , machined t o a 0.2 i n c h d i a m e t e r t o l o c a l i z e the s . c . c . The specimens were a n n e a l e d a c c o r d i n g t o T a b l e I I I . A f t e r a n n e a l i n g , t h e notched r e g i o n o f each specimen was e l e c t r o p o l i s h e d a t 25-30 v o l t s d.c. i n a c h r o m i c - a c e t i c a c i d s o l u t i o n ; 25 gr chromic o x i d e , 133 cc a c e t i c a c i d , 7 cc water, then s t o r e d i n a d e s i c c a t o r u n t i l t e s t e d . 2.4 S t r e s s C o r r o s i o n T e s t s The s t r e s s c o r r o s i o n t e s t s p erformed a r e l i s t e d i n T a b l e I V . A f l o o r model I n s t r o n was used f o r s t r e s s c o r r o s i o n t e s t s . The specimen and environment were c o n t a i n e d i n a Pyrex c e l l w i t h an a t t a c h e d r e f l u x condenser and thermometer, see F i g . 2. Heat was s u p p l i e d by an e l e c t r i c a l h e a t i n g t a p e . The p r o c e d u r e was as f o l l o w s : The specimen, w i t h t h e s u r f a c e o u t s i d e t h e n o t c h a r e a c o v e r e d w i t h T e f l o n t a p e , was p l a c e d i n the Pyrex c e l l and the ends s e a l e d w i t h T e f l o n bungs, the lower b e i n g f i x e d t i g h t and t h e upper one b e i n g a l o o s e f i t . The c e l l was wrapped w i t h the h e a t i n g t a p e , s e t i n t h e I n s t r o n and c o n n e c t e d t o t h e r e f l u x condenser. T u r n i n g on the h e a t i n g tape p r i o r t o i n t r o d u c i n g the environment p r e v e n t e d t h e s o l u t i o n , from f r e e z i n g on the w a l l s o f the c e l l . The environment was added a t i t s b o i l i n g p o i n t and t h e c e l l a l l o w e d t o r e a c h t h e r m a l e q u i l i b r i u m . T h i s g e n e r a l l y took a t l e a s t . 30 minutes. D u r i n g t h i s time a s l i g h t l o a d was a p p l i e d t o c o u n t e r a c t the e x p a n s i o n o f the specimen due t o h e a t i n g and t o m o n i t o r when the specimen was i n t h e r m a l e q u i l i b r i u m w i t h the s o l u t i o n . Upon r e a c h i n g e q u i l i b r i u m a t e n s i l e l o a d was a p p l i e d t o i n i t i a t e y i e l d i n g w i t h i n the n o t c h (see Table, I I I f o r y i e l d s t r e s s ) and t h e c r o s s h e a d o f the TABLE -IV: S t r e s s C o r r o s i o n T e s t Performed A l l o y Environment Temp. °C Type o f T e s t 304 M g C l 2 ( b o i l i n g ) 154 s . c . c . f u l l and p a r t i a l f a i l u r e 304 M g C l 2 + HCl ( b o i l i n g ) 154 . s . c . c . f u l l f a i l u r e 304 M g C l 2 + F e C l 3 ( b o i l i n g ) 125 s . c . c . f u l l f a i l u r e 304 M g C l 2 + C o C l 2 ( b o i l i n g ) 160 s . c . c . f u l l f a i l u r e 316 M g C l 2 ( b o i l i n g ) 154 s . c . c . f u l l f a i l u r e ! 316 M g C l 2 + HCl ( b o i l i n g ) 154 s . c . c . f u l l f a i l u r e 316 M g C l 2 + C o C l 2 ( b o i l i n g ) 160 s . c . c . f u l l f a i l u r e 310 M g C l 2 ( b o i l i n g ) 154 s . c . c . f u l l f a i l u r e 310 M g C l 2 + HCl ( b o i l i n g ) 154 s . c . c . f u l l f a i l u r e 310 M g C l 2 + C o C l 2 ( b o i l i n g ) 160 s . c . c . f u l l f a i l u r e Fig. 2 . S.C.C. c e l l w i t h 7 i n c h l o n g specimen i n p l a c e . - 17 - I n s t r o n t h e n l o c k e d . A c i r c u m f e r e n t i a l s t r e s s c o r r o s i o n c r a c k o r i g i n a t e d at the r o o t o f the not c h and p r o p a g a t e d t o the c e n t r e o f the specimen, r e l a x i n g the l o a d t o z e r o , and p r o d u c i n g a w h o l l y s . c . c . f r a c t u r e s u r f a c e d e v o i d o f o v e r l o a d f a i l u r e . The specimen was removed from t h e environment and the two f r a c t u r e s u r f a c e s washed i n hot t a p water t o remove the s o l u t i o n , then d r i e d w i t h e t h a n o l p r i o r t o s t o r i n g i n a d e s i c c a t o r . P a r t i a l l y c r a c k e d specimens were removed from t h e environment when th e l o a d had dropped t o o n e - h a l f t h e i n i t i a l v a l u e . These specimens were not washed, b u t p l a c e d immediately i n a d e s i c c a t o r and l a t e r m e c h a n i c a l l y f r a c t u r e d i n a H o u n s f i e l d Tensometer a t 25°C, a t which temperature the c r a c k s o l u t i o n i s a s o l i d h y d r a t e d p r o d u c t and may be examined i n the S.E.M. 2.5 C o r r o s i o n P r o d u c t S t r i p p i n g The f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t was s t r i p p e d by two d i f f e r e n t methods; 1) d i s s o l u t i o n o f the m e t a l s u b s t r a t e i n a bromine-methanol s o l u t i o n and 2) m e c h a n i c a l l y s t r i p p i n g t h e c o r r o s i o n p r o d u c t w i t h c e l l u l o s e a c e t a t e . One o f the two f r a c t u r e s u r f a c e s was immersed i n a s o l u t i o n o f 1 v o l % bromine, 99 v o l % anhydrous methanol. N i e l s o n [14] used a 5% bromine s o l u t i o n but t h i s i s a v e r y a g g r e s s i v e s o l u t i o n and t h e r e was some co n c e r n t h a t i t might damage the o x i d e . The 1% bromine s o l u t i o n was used and was .quite s a t i s f a c t o r y . A f t e r a few hours i n the s o l u t i o n t h e c o r r o s i o n p r o d u c t f l o a t e d f r e e o f t h e m e t a l s u b s t r a t e and was washed i n s u c c e s s i v e s o l u t i o n s o f methanol. C e l l u l o s e a c e t a t e s h e e t , s o f t e n e d i n ace t o n e , was p r e s s e d onto the o t h e r f r a c t u r e s u r f a c e and s t r i p p e d o f f when i t had hardened. The r e s u l t i n g a c e t a t e r e p l i c a was - 18 - c o a t e d w i t h carbon, t h e n d i s s o l v e d i n acetone and washed i n . m e t h a n o l l e a v i n g a carbon r e p l i c a w i t h t h e s t r i p p e d c o r r o s i o n p r o d u c t a t t a c h e d . The two s t r i p p i n g methods, p e r f o r m e d on s e p a r a t e f r a c t u r e s u r f a c e o f the same specimen, p r o v i d e d a means o f t e s t i n g t h e v a l i d i t y o f u s i n th e bromine-methanol method t o s t r i p c o r r o s i o n p r o d u c t s f o r c h e m i c a l a n a l y s i s . 2.6 E l e c t r o n D i f f r a c t i o n E l e c t r o n d i f f r a c t i o n s t u d i e s o f t h e f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t , b o t h i n s i t u and s t r i p p e d , were performed on a 100 kv H i t a c h i t r a n s m i s s i o n e l e c t r o n m i c roscope (T.E.M.). B i r l e y and Tromans [12,17] d e s c r i b e d t h e t e c h n i q u e f o r e l e c t r o n d i f f r a c t i o n o f c o r r o s i o n p r o d u c t s i n s i t u . The s t r e s s c o r r o s i o n f r a c t u r e d specimen was p l a c e d i n t h e h i g h r e s o l u t i o n d i f f r a c t i o n s t a g e o f t h e T.E.M. w i t h the ma c r o s c o p i c s . c . c . f r a c t u r e p l a n e p a r a l l e l t o t h e e l e c t r o n beam. D i f f r a c t i o n p a t t e r n s were o b t a i n e d when p r o t u b e r a n c e s on t h e f r a c t u r e s u r f a c e i n t e r s e c t e d t h e e l e c t r o n beam, see F i g . 3. The advantages o f t h i s t e c h n i q u e were; 1) i t p e r m i t s e x a m i n a t i o n o f t h e c o r r o s i o n f i l m w i t h o u t any p r i o r t r e a t m e n t . 2) t h e r e i s l e s s l i k e l i h o o d t h a t h e a t i n g e f f e c t s from t h e e l e c t r o n beam w i l l damage t h e c o r r o s i o n p r o d u c t because o f t h e l a r g e heat s i n k p r o v i d e d by t h e m e t a l s u b s t r a t e . 3) t h e r e l a t i v e i n t e n s i t i e s o f t h e d i f f r a c t i o n r i n g s a r e s i m i l a r t o t h o s e f o r randomly o r i e n t e d powders. S t r i p p e d c o r r o s i o n f i l m s were mounted on specimen mounting g r i d s - 19 - E L E CTRON B E A M S.C.C. F R A C T U R E S U R F A C E X-RAYS DIFFRACTED BEAM F i S - 3. Schematic r e p r e s e n t a t i o n of i n s i t u d i f f r a c t i o n of surface oxide i n high r e s o l u t i o n d i f f r a c t i o n stage of the T.E.M. The primary e l e c t r o n beam s t r i k e s the surface f i l m and i s d i f f r a c t e d . - 20 - f o r the T.E.M., the n p l a c e d i n t h e specimen s t a g e o f the m i c r o s c o p e and d i f f r a c t i o n p a t t e r n s o b t a i n e d from s e l e c t e d a r e a s . The chemically- s t r i p p e d f i l m s from the 304- and 316 s t a i n l e s s s t e e l f r a c t u r e s u r f a c e s were t o o t h i n t o be d e t e c t e d i n the bromine-methanol s o l u t i o n u n l e s s t h e s . c . c . f r a c t u r e s u r f a c e was carbon c o a t e d p r i o r t o s t r i p p i n g . Upon s t r i p p i n g the carbon f l o a t e d f r e e w i t h t h e c o r r o s i o n p r o d u c t a t t a c h e d . 2.7 X-ray S p e c t r o s c o p y 2.7.1 I n t r o d u c t i o n X-ray s p e c t r o s c o p y was conducted i n t h e T.E.M. and S.E.M. u s i n g an O r t e c energy d i s p e r s i v e x - r a y s p e c t r o m e t e r (E.D.S.). The S.E.M. equipped w i t h an E.D.S. i s s i m i l a r t o an e l e c t r o n probe. The p r i m a r y f u n c t i o n o f the S.E.M. i s t o produce a h i g h r e s o l u t i o n image o f the specimen s u r f a c e . The p r i m a r y e l e c t r o n beam has a low c u r r e n t and s m a l l d i a m e t e r , a p p r o x i m a t e l y 150-200A 0. The image i s produced by low energy secondary e l e c t r o n s , c r e a t e d when p r i m a r y e l e c t r o n s knock an o r b i t a l e l e c t r o n f r e e from t h e s u r f a c e atoms. The x-ray i n t e n s i t y r e s u l t i n g from the e x c i t a t i o n by t h e e l e c t r o n beam o f t h e S.E.M. i s lower than the x - r a y i n t e n s i t y produced by an e l e c t r o n probe which has a r e l a t i v e l y h i g h beam c u r r e n t (10 i 0 Amps v s . 10 7 Amps). The d e t e c t i o n and i d e n t i f i c a t i o n o f the x - r a y s i s t h e f u n c t i o n o f the x-ray s p e c t r o m e t e r o f which t h e r e are two t y p e s , wavelength d i s p e r s i v e and energy d i s p e r s i v e . The wavelength d i s p e r s i v e s p e c t r o m e t e r (W.D.S.) i s b a s e d on the Bragg law; ^ = 2d Sin© , where d i s the i n t e r p l a n a r s p a c i n g , 0 i s t h e h k l a n g l e o f d i f f r a c t i o n and A i s t h e wavelength o f t h e r a d i a t i o n . - 21 - X-rays o r i g i n a t i n g from the specimen a r e d i f f r a c t e d by an a n a l y z i n g c r y s t a l o f s p e c i f i c i n t e r p l a n a r s p a c i n g d ^ ^ and m o n i t o r e d by a c o u n t i n g d e v i c e . S i n c e each element has a s e t o f c h a r a c t e r i s t i c x - r a y s , wavelength A, e l e m e n t a l a n a l y s i s can be pe r f o r m e d on an unknown specimen by s c a n n i n g the s p e c t r o m e t e r through a range o f a n g l e s . A l l elements above b e r y l l i u m , a t o m i c number 4, can be d e t e c t e d w i t h the use o f v a r i o u s d i f f r a c t i n g c r y s t a l s . Only a s m a l l f r a c t i o n o f t h e x - r a y s p r o d u c e d w i l l s a t i s f y t h e Bragg law and be p i c k e d up by the c o l l i m a t e d c o u n t e r . T h e r e f o r e , t o a c h i e v e a good count r a t e , a l a r g e volume o f x-r a y s must be g e n e r a t e d . F o r t h i s r e a s o n , the p r i m a r y beam must have a h i g h beam c u r r e n t which n o r m a l l y r e q u i r e s a l a r g e r d i a m e t e r and makes the W.D.S. u n s u i t a b l e f o r i n s t r u m e n t s l i k e the S.E.M. The r e s o l u t i o n o f the wavelength s p e c t r o m e t e r i s good, eg. c h a r a c t e r i s t i c x - r a y s 10 eV a p a r t can be s e p a r a t e d w i t h h i g h peak t o background r a t i o s . The major drawbacks t o the W.D.S. a r e t h a t t h e complete c h e m i c a l a n a l y s i s o f an unknown specimen i s time consuming and t h a t the specimen s u r f a c e must be normal t o t h e pr i m a r y e l e c t r o n beam t o ensure h i g h count r a t e s . Energy d i s p e r s i v e s p e c t r o m e t e r s s e p a r a t e c h a r a c t e r i s t i c r a d i a t i o n a c c o r d i n g t o i t s energy. T h i s can be a c h i e v e d w i t h f l o w p r o p o r t i o n a l c o u n t e r s , o r a s o l i d s t a t e c r y s t a l d e t e c t o r . F o r t h e O r t e c E.D.S., the d e t e c t o r i s a l i t h i u m d r i f t e d s i l i c o n c r y s t a l S i ( L i ) , ( O r t e c s e r i e s 7000T). When an x-ray from t h e specimen h i t s the S i ( L i ) c r y s t a l , e l e c t r o n s from t h e s i l i c o n atoms a r e e x c i t e d . Each e x c i t e d e l e c t r o n absorbs 3.8 eV o f energy. Thus, a s i n g l e x - r a y photon e x c i t e s many e l e c t r o n s , which - 22 - a r e c o l l e c t e d , r e s u l t i n g i n a c u r r e n t t h a t i s p r o p o r t i o n a l t o t h e energy o f t h e x - r a y photon. T h i s c u r r e n t charge i s a m p l i f i e d and s t o r e d i n a m u l t i c h a n n e l a n a l y z e r (M.C.A.) which s i m u l t a n e o u s l y s t o r e s t h e c u r r e n t f o r e v e r y o t h e r x-ray s t r i k i n g t h e S i ( L i ) c r y s t a l . The output o f the a n a l y z e r i s a c o n t i n u o u s spectrum o f f r e q u e n c y v s . energy f o r a l l x - r a y s s t r i k i n g t h e c r y s t a l . In t h e p r e s e n t s t u d i e s an Or t e c model 6200 M.C.A. was employed. The advantages o f the E.D.S. a r e ; 1) the e n t i r e x-ray spectrum g e n e r a t e d may be a n a l y z e d and d i s p l a y e d s i m u l t a n e o u s l y , thus t o t a l e l e m e n t a l a n a l y s i s may be done i n a few minutes. 2) because no c o l l i m a t i o n i s n e c e s s a r y , a h i g h p e r c e n t a g e o f x-r a y s produced are a n a l y z e d . T h i s a l l o w s t h e E.D.S. t o be o p e r a t e d w i t h t h e low beam c u r r e n t s a s s o c i a t e d w i t h s c a n n i n g e l e c t r o n m i c r o s c o p e s . 3) specimen p o s i t i o n and topography a r e n ot as c r i t i c a l as f o r wavelength d i s p e r s i v e s p e c t r o m e t e r s . The d i s a d v a n t a g e s a r e ; 1) o n l y elements above sodium, atomic number 11, can be a n a l y z e d . 2) r e s o l u t i o n i s i n f e r i o r t o t h e W.D.S.; g e n e r a l l y o n l y peaks s e p a r a t e d by 160 eV o r more may be r e s o l v e d . 3) peak t o background r a t i o s a r e i n f e r i o r t o t h e W.D.S. I t s h o u l d be not e d t h a t x-ray energy a n a l y s i s o n l y d e t e c t s the. presence o f elements, and conveys no i n f o r m a t i o n about t h e i r i o n i c o r c o v a l e n t s t a t e . F o r example c h l o r i n e may be p r e s e n t i n a c o r r o s i o n p r o d u c t and one may have t o assume i t i s p r e s e n t as a c h l o r i d e . - 23 - 2.7.2 X-ray S p e c t r o s c o p y o f T h i n F i l m s The u s u a l i n t e n s i t y vs c o n c e n t r a t i o n c o r r e c t i o n s a s s o c i a t e d w i t h x-ray s p e c t r o s c o p y , do n o t h o l d f o r v e r y t h i n f i l m s . The m a t h e m a t i c a l models t h a t r e l a t e i n t e n s i t i e s t o c o n c e n t r a t i o n s a r e b a s e d on t h e assumption t h a t f o r v e r y t h i n specimens t h e x - r a y s g e n e r a t e d by th e beam can pass t o t h e s u r f a c e w i t h n e g l i g i b l e a b s o r p t i o n and f l u o r e s c e n c e . The v a l i d i t y o f t h i s has been v e r i f i e d f o r t h i n f o i l s used i n 40-100 kv t r a n s m i s s i o n e l e c t r o n m i s c r o s c o p y [ 2 5 ] . In g e n e r a l , i f t h e specimen i s t r a n s p a r e n t i n a 100 kv t r a n s m i s s i o n e l e c t r o n b e a m , a b s o r p t i o n and f l u o r e s c e n c e e f f e c t s can be i g n o r e d . The use o f t h e lower e l e c t r o n v o l t a g e s i n t h e S.E.M. (20-30kv) s h o u l d i n c r e a s e e l e c t r o n s c a t t e r i n g b u t not a f f e c t the a b s o r p t i o n o f x - r a y s produced. In c o n v e n t i o n a l x-ray s p e c t r o s c o p y o f t h i c k m a t e r i a l s t h e r e i s no t r a n s m i t t e d e l e c t r o n beam and c o n s i d e r a b l e x - r a y a b s o r p t i o n and f l u o r e s c e n c e Q u a n t i t a t i v e e l e m e n t a l a n a l y s i s can be p erformed by comparing specimen e l e m e n t a l i n t e n s i t i e s t o e l e m e n t a l i n t e n s i t i e s o f s t a n d a r d s , and a p p l y i n g c o r r e c t i o n f a c t o r s , p r o v i d i n g b o t h specimen and s t a n d a r d s a r e e x c i t e d under s i m i l a r c o n d i t i o n s . F o r t h i n n e r specimens where t h e r e a r e some t r a n s - m i t t e d e l e c t r o n s the c o r r e c t i o n f a c t o r s may s t i l l be a p p l i e d but t h e s t a n d a r d must be the same t h i c k n e s s as the specimen. For v e r y t h i n f i l m s , w h i l e c o r r e c t i o n f a c t o r s a r e n e g l i g i b l e , s t a n d a r d s must a l s o be t h e same t h i c k n e s s as t h e specimen. For c o r r o s i o n p r o d u c t f i l m s from t h e f r a c t u r e s u r f a c e i t i s n o t p o s s i b l e t o get an a c c u r a t e measurement o f t h e f i l m t h i c k n e s s , n o r i s i t p o s s i b l e t o o b t a i n a s t a n d a r d which would d u p l i c a t e the s u r f a c e topography o f the o x i d e . S i n c e x-ray i n t e n s i t y w i l l v a r y w i t h t h i c k n e s s - 24 - and r o u g h n e s s , as w e l l as c o m p o s i t i o n , q u a n t i t a t i v e a n a l y s i s o f t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t by x - r a y s p e c t r o s c o p y i s n o t p o s s i b l e . Even though q u a n t i t a t i v e s p e c t r o s c o p y i s not p o s s i b l e , semi- q u a n t i t a t i v e a n a l y s i s o f t h i n s e c t i o n s can be done. S i n c e x-rays produced i n t h e t h i n s e c t i o n s are not s u b j e c t t o a b s o r p t i o n a f f e c t s , t h e i n t e n s i t y r a t i o s o f d i f f e r e n t elements w i l l be p r o p o r t i o n a l t o t h e i r c o n c e n t r a t i o n r a t i o s assuming s i m i l a r e x c i t a t i o n e f f i c i e n c y ( e x c i t a t i o n e f f i c i e n c y i s s i m i l a r f o r elements w i t h s i m i l a r atomic numbers). These r a t i o s , t o g e t h e r w i t h d i f f r a c t i o n p a t t e r n s from t h e c o r r o s i o n p r o d u c t , p r o v i d e an adequate means o f c o r r o s i o n ' p r o d u c t i d e n t i f i c a t i o n . 2.7.3 Mounting o f T h i n F i l m s f o r S.E.M. X-ray S p e c t r o s c o p y When d e a l i n g w i t h t h i n f i l m s i t must be remembered t h a t a good p o r t i o n o f t h e p r i m a r y beam w i l l pass through t h e f i l m and s t r i k e t h e specimen h o l d e r the f i l m i s mounted on. 'Back-scattered e l e c t r o n s w i l l be r e f l e c t e d from t h e . specimen h o l d e r back towards the specimen s u p p o r t g r i d , where they w i l l produce f u r t h e r e x c i t a t i o n and g e n e r a t i o n o f c h a r a c t e r i s t i c x - r a y s . Thus, x - r a y s w i l l be d e t e c t e d from both the sup p o r t g r i d and a r e a s remote from t h e p r i m a r y ' e l e c t r o n beam, (see F i g . 4 ) , r e s u l t i n g i n m i s l e a d i n g a n a l y s e s . C h a r a c t e r i s t i c x - r a y s g e n e r a t e d from t h e specimen h o l d e r may be e l i m i n a t e d by c o a t i n g w i t h c a r b o n . - Attempts t o a v o i d t h i s p roblem i n v o l v e d mounting t h e s t r i p p e d c o r r o s i o n f i l m on a s u p p o r t g r i d , o v e r a h o l e i n a h o l l o w a n a l y t i c a l g r a p h i t e c y l i n d e r . T r a n s m i t t e d e l e c t r o n s s t r i k i n g the bottom o f t h e h o l l o w c y l i n d e r w i l l g e n e r a t e .back-scattered e l e c t r o n s which w i l l be abs o r b e d i n the h o l l o w c y l i n d e r i n s t e a d o f h i t t i n g the c o r r o s i o n f i l m (see F i g . 4 ) . ELECTRON BEAM BACKSCATTERED ELECTRONS SPECIMEN COPPER GRID GRAPHITE BLOCK ELECTRONS X-RAYS Schematic diagrams o f b a c k s c a t t e r e d e l e c t r o n e f f e c t from specimen h o l d e r d u r i n g x - r a y a n a l y s i s o f t h i n f i l m s a) from c o n v e n t i o n a l specimen h o l d e r b) from h o l l o w g r a p h i t e b l o c k - 26 - T h i s d i d not t o t a l l y e l i m i n a t e t h e '. b a c k s c a t t e r e d e l e c t r o n and x - r a y ' e f f e c t b u t d i d improve the s i t u a t i o n . 2.7.1 P r o c e d u r e f o r X-ray S p e c t r o s c o p y X-ray s p e c t r o s c o p y o f t h e c o r r o s i o n p r o d u c t i n s i t u was per f o r m e d by p l a c i n g t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e i n the h i g h r e s o l u t i o n d i f f r a c t i o n s t a g e o f t h e T.E.M. f i t t e d w i t h t h e O r t e c x - r a y a n a l y z e r . The advantage o f t h i s s e t u p was t h a t d i f f r a c t i o n p a t t e r n s and c h e m i c a l a n a l y s i s were o b t a i n e d from t h e sample i n t h e same p i e c e o f equipment. However the s u r f a c e a r e a c o v e r e d by t h e beam i n t h e T.E.M. was l a r g e r t h a n t h e s u r f a c e a r e a c o v e r e d by t h e beam i n t h e S.E.M., t h u s i t was n o t p o s s i b l e t o i s o l a t e n e i g h b o u r i n g phases o f d i f f e r e n t c o m p o s i t i o n i n the c o r r o s i o n , f i l m . X-ray a n a l y s i s o f the s t r i p p e d c o r r o s i o n p r o d u c t was more i n v o l v e d . The s t r i p p e d p r o d u c t , mounted on specimen g r i d s , was examined by c o n v e n t i o n a l t e c h n i q u e s i n t h e T.E.M., where d i f f r a c t i o n p a t t e r n s and s u r f a c e f e a t u r e s were s t u d i e d , t h e n p l a c e d on t h e h o l l o w g r a p h i t e c y l i n d e r f o r e x a m i n a t i o n i n t h e S.E.M. With t h e m a g n i f i c a t i o n c a p a b i l i t i e s o f the S.E.M., i t was p o s s i b l e t o p e r f o r m x - r a y s p e c t r o s c o p y on p r e - s e l e c t e d T.E.M. a r e a s t h a t gave good d i f f r a c t i o n p a t t e r n s , thus o b t a i n i n g e l e c t r o n d i f f r a c t i o n p a t t e r n s and e l e m e n t a l a n a l y s i s o f t h e same a r e a . A l l x-ray a n a l y s i s , i n T.E.M. and S.E.M., was performed w i t h the e l e c t r o n beam v o l t a g e s e t a t 20 kv. Q u a l i t a t i v e comparison o f element i n t e n s i t i e s was performed by i n t e g r a t i n g the x-ray peaks o v e r .5 c h a n n e l s (40 eV/channel) and s u b t r a c t i n g t h e background i n t e n s i t y . A l l quoted Cr/Fe and C r / N i r a t i o s were d e t e r m i n e d i n t h i s manner. - 27 - 3. RESULTS AND OBSERVATIONS 3.1 S t r e s s C o r r o s i o n T e s t s The r e s u l t s o f t h e s t r e s s c o r r o s i o n t e s t s a r e summarized i n T a b l e V. G e n e r a l s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e micrographs a r e shown i n F i g . 5. On a m a c r o s c o p i c s c a l e , the type 310 f r a c t u r e s u r f a c e s were r e l a t i v e l y f l a t , the type 304 f r a c t u r e s u r f a c e s were v e r y i r r e g u l a r , and the type 316 f r a c t u r e s u r f a c e s were s i m i l a r t o t y p e 304. The s t r e s s c o r r o s i o n c r a c k p a t h v a r i e d ; t r a n s g r a n u l a r f o r 310 s t a i n l e s s s t e e l s , p r e d o m i n a n t l y t r a n s g r a n u l a r w i t h some i n t e r g r a n u l a r f o r 316, and a mixed mode f a i l u r e f o r 304. The'type 3 1 0 ' s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e s had a t h i c k b l u e - green c o r r o s i o n d e p o s i t . The 304 and 316 f r a c t u r e s u r f a c e s had a s h i n y straw l u s t r e and d i d n o t appear t o have a t h i c k c o r r o s i o n f i l m . These o b s e r v a t i o n s were t h e same f o r a l l t h e specimens t e s t e d i n t h e v a r i o u s s o l u t i o n s , e x c e p t 304 s t r e s s c o r r o d e d i n the M g C l 2 + F e C l 3 s o l u t i o n where ~ t h i c k r e d brown c o r r o s i o n p r o d u c t c o v e r e d the f r a c t u r e s u r f a c e . S t r e s s c o r r o d e d specimens o f 304 a l l o w e d t o remain i n the MgCl2 s o l u t i o n f o r 40 hours d i d not form a n o t i c e a b l y t h i c k e r c o r r o s i o n f i l m than specimens removed immediately upon f r a c t u r e . The exposed e l e c t r o p o l i s h e d a r e a s on t h e s u r f a c e s o f t h e specimens were not n o t i c e a b l y a f f e c t e d by t h e v a r i o u s s o l u t i o n s , e x c e p t the a c i d i f i e d M g C l 2 s o l u t i o n and the MgCl2 + F e C l 3 s o l u t i o n . On immersion i n the a c i d i f i e d M g C l 2 s o l u t i o n t h e e l e c t r o p o l i s h e d a r e a s r e a c t e d , f o r m i n g a smooth g r e y - b l a c k c o r r o s i o n f i l m and p r o d u c i n g a s t e a d y stream o f b u b b l e s , b e l i e v e d t o be H 2 gas. No p i t t i n g was o b s e r v e d . T h i s r e a c t i o n slowed and s t o p p e d w i t h i n a p p r o x i m a t e l y one hour. The exposed s u r f a c e TABLE V: S t r e s s C o r r o s i o n T e s t R e s u l t s S t e e l # o f Spec. Load ( p s i ) Environment Temp. °C. Time t o F a i l u r e (min) 304 3 61400/63200/65700 M g C l 2 154 74/99/89 304 1 59000 M g C l 2 +.HC1 154 76 304 1 61000 M g C l 2 + F e C l 3 125 150 304 1 72000 M g C l 2 + C o C l 2 160- : 210 316 3 66000/63500/65800 M g C l 2 154 200/160/240 316 1 54800 M g C l 2 + HCl 154 230 316 1 63400 M g C l 2 + C o C l 2 160 250 310 3 85800/82600/82500 M g C l 2 154 2130/2436/2172 310 1 71900 M g C l 2 + HCl. 154 2012 310 1 68900 M g C l 2 + C o C l 2 160 • 1910 - 29 - F i g . 5. Representative fractographs (40x m a g n i f i c a t i o n ) from s t a i n l e s s S t e e l s , a) 304, b) 316, C) 310 - 30 - a r e a s on t h e 304 specimen i n t h e MgC]2 + FeCl3 s o l u t i o n were h e a v i l y p i t t e d and c o v e r e d w i t h a rough r e d brown f i l m s p o t t e d w i t h a few s m a l l p a t c h e s o f a b l u e - g r e e n c o l o u r . 3.2 S t r i p p i n g o f Oxides 3.2.1 Bromine-Methanol S t r i p p i n g The bromine-methanol s o l u t i o n removed t h e c o r r o s i o n p r o d u c t from t h e m e t a l s u b s t r a t e w i t h i n a few h o u r s . The c o r r o s i o n p r o d u c t s on t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e s o f 304 and 316 specimens were so t h i n t h a t the f r a c t u r e s u r f a c e s had t o be c o a t e d w i t h an e v a p o r a t e d carbon f i l m ; t h e c o r r o s i o n p r o d u c t came o f f the m e t a l s u b s t r a t e a t t a c h e d t o t h e carbon s u p p o r t f i l m . The c o r r o s i o n p r o d u c t removed from t h e s u r f a c e o f 310 specimens was a t h i c k sponge, r e t a i n i n g the shape o f the f r a c t u r e s u r f a c e a f t e r the m e t a l s u b s t r a t e had d i s s o l v e d . The c o r r o s i o n p r o d u c t morphology from the 310 s u r f a c e was s i m i l a r t o t h e o x i d e o b s e r v e d by N i e l s e n [14] showing c o r r o s i o n p r o d u c t f a n s as w e l l as c o r r o s i o n s p i k e s (see F i g . 6 ) . The c o r r o s i o n f i l m s formed on th e c r a c k s u r f a c e s o f 304 and 316 i n a l l e nvironments, e x c e p t MgCl + F e C l , were v e r y t h i n . The straw c o l o u r e d i n t e r f e r e n c e c o l o u r on t h e f r a c t u r e s u r f a c e s s u g g e s t e d t h e f i l m was about 400-500A 0 t h i c k [ 2 6 ] . Carbon c o a t i n g t h e f r a c t u r e s u r f a c e p r i o r t o s t r i p p i n g was n o t t o o s u c c e s s f u l as t h e r e were o n l y a few a r e a s o f c o r r o s i o n p r o d u c t on the carbon f i l m s . The p r o d u c t t h a t was p i c k e d up was t o o t h i n t o be v i s u a l l y d i s t i n g u i s h e d on t h e carbon f i l m s , and c o u l d o n l y be d e t e c t e d by, e l e c t r o n d i f f r a c t i o n and x - r a y s p e c t r o s c o p y . The - 31 - F i g . 6. M i c r o g r a p h o f c o r r o s i o n p r o d u c t from f r a c t u r e s u r f a c e o f t y p e 310 s t a i n l e s s s t e e l s t r e s s c o r r o d e d i n b o i l i n g M g C l 2 s o l u t i o n . S t r i p p e d i n bromine-methanol s o l u t i o n , ( m a g n i f i c a t i o n 1200x) - 32 - carbon c o a t e d f i l m was p l a c e d i n t h e S.E.M. and an x - r a y s t u d y made o f the s u r f a c e . Those r e g i o n s which produced an x-ray spectrum were r e l o c a t e d i n the T.E.M. and d i f f r a c t i o n p a t t e r n s t a k e n . T h i s a n a l y t i c a l p r o c e d u r e f o r 304 and 316 c o r r o s i o n p r o d u c t s p r o v e d t o be v e r y t e d i o u s . The c o r r o s i o n p r o d u c t on t h e f r a c t u r e s u r f a c e s o f t h e 310 s t a i n l e s s s t e e l was much t h i c k e r than t h a t on 304 and 316, b e i n g e a s i l y s t r i p p e d i n t a c t from the f r a c t u r e s u r f a c e . The s t r i p p e d p r o d u c t was b r i t t l e and c o u l d e a s i l y be r e d u c e d t o powder. E l e c t r o n d i f f r a c t i o n was d i f f i c u l t as h e a t i n g and c h a r g i n g caused the c o r r o s i o n p r o d u c t t o bre a k a p a r t i n the e l e c t r o n beam. X-ray s p e c t r o s c o p y o f t h e s t r i p p e d c o r r o s i o n f i l m i n the S.E.M. r e q u i r e d i t t o be h e l d on t h e specimen g r i d w i t h a carbon s u s p e n s i o n p a s t e ( c a r b o n dag). H e a t i n g and c h a r g i n g d i d n o t o c c u r i n the S.E.M. as the beam c u r r e n t was much lower than i n the T.E.M. 3.2.2 A c e t a t e S t r i p p i n g The a c e t a t e s t r i p p i n g t e c h n i q u e was s u c c e s s f u l i n removing the c o r r o s i o n p r o d u c t from t h e s u r f a c e o f 310 specimens, b u t n o t t o o s u c c e s s f u l i n the case o f 304 and 316 specimens. The s t r i p p e d a c e t a t e p i c k e d up some c o r r o s i o n p r o d u c t b u t a l s o r i p p e d out s m a l l segments o f s t e e l from t h e f r a c t u r e s u r f a c e . D i r e c t x-ray a n a l y s i s o f t h e carbon c o a t e d a c e t a t e s t r i p was not p o s s i b l e because o f t h e d i f f i c u l t y i n f i n d i n g t h e p r o d u c t among t h e s t e e l segments on t h e s u r f a c e . In o r d e r f o r the s t r i p p e d f i l m t o be a n a l y z e d , the carbon c o a t e d a c e t a t e f i l m was d i s s o l v e d i n ac e t o n e . The carbon f i l m w i t h the c o r r o s i o n p r o d u c t a t t a c h e d f l o a t e d f r e e and was examined i n the T.E.M. and S.E.M. The a c e t a t e s t r i p f o r the 304 and 316 f r a c t u r e - 33 - s u r f a c e s had o n l y s m a l l amounts o f a t t a c h e d p r o d u c t . Thus, a c e t a t e s t r i p p i n g was not a s u c c e s s f u l t e c h n i q u e f o r removing c o r r o s i o n f i l m s from t h e s e s u r f a c e s . The a c e t a t e s t r i p from the 310 f r a c t u r e s u r f a c e had more p a t c h e s o f c o r r o s i o n f i l m which were e a s i l y a n a l y z e d i n t h e T.E.M. and S.E.M. 3.3 E l e c t r o n D i f f r a c t i o n The e l e c t r o n d i f f r a c t i o n r e s u l t s a r e summarized i n T a b l e V I. E l e c t r o n d i f f r a c t i o n p a t t e r n s o b t a i n e d from t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t i n s i t u and s t r i p p e d , were s i m i l a r i n a l l cases and c o u l d be f i t t e d t o a s p i n e l o x i d e s t r u c t u r e , MgO^. The i n t e r p l a n a r s p a c i n g s (d) and x-ray i n t e n s i t i e s f o r Fe^O^, FeCr 20j, and Y Fe203 [23] a r e shown i n T a b l e V I I . Sample p a t t e r n s t a k e n from f r a c t u r e s u r f a c e o x i d e s a r e shown i n F i g . 7, w i t h c o r r e s p o n d i n g d - s p a c i n g s i n T a b l e V I I I . P a t t e r n s o f t h i s q u a l i t y were n o t t h e g e n e r a l r u l e , the u s u a l p a t t e r n b e i n g more d i f f u s e ( i n d i c a t i n g s m a l l g r a i n s i z e ) . S t r i p p e d c o r r o s i o n p r o d u c t s produced p a t t e r n s which were c l e a r e r and c o n t a i n e d more l i n e s than p a t t e r n s o b t a i n e d from c o r r o s i o n p r o d u c t s i n s i t u . In some c a s e s , not a l l the d i f f r a c t i o n p a t t e r n l i n e s c o u l d be f i t t e d t o the s p i n e l . These l i n e s were g e n e r a l l y v e r y f a i n t and c o u l d f i t a rombohedral (corundum) type M2O3 o x i d e p a t t e r n , o r a m e t a l . c h l o r i d e p a t t e r n . D i f f r a c t i o n p a t t e r n s t a k e n from t h e o x i d e i n s i t u on 304 and 316 f r a c t u r e s u r f a c e s sometimes c o n t a i n e d e x t r a l i n e s p r o d u c e d by d i f f r a c t i o n o f the u n d e r l y i n g a u s t e n i t e due t o t h e t h i n n e s s o f the o x i d e on t h e s e s u r f a c e s . E x a m i n a t i o n o f t h e s t r i p p e d o x i d e f i l m s i n t r a n s m i s s i o n showed b o t h d i f f u s e r i n g p a t t e r n s and sharp r i n g p a t t e r n s from b o t h t h i c k a r e a s and t h i n TABLE VI: Summary o f E l e c t r o n D i f f r a c t i o n R e s u l t s A l l o y Environment Oxide S t r u c t u r e 304 M g C l 2 s.c.c.. f r a c t u r e s u r f a c e W30k 304 MgCl 2+HCl s . c . c . f r a c t u r e s u r f a c e M3O4 304 MgCl 2+HCl e x t e r i o r specimen s u r f a c e M30h 304 M g C l 2 + C o C l 2 s . c . c . f r a c t u r e s u r f a c e M3O4 304 M g C l 2 + F e C l 3 s . c . c . f r a c t u r e s u r f a c e M3O4 304 M g C l 2 - f F e C l 3 e x t e r i o r specimen s u r f a c e K203/M30h 316 M g C l 2 s . c . c . f r a c t u r e s u r f a c e M3O4 316 MgCl 2+HCl s . c . c . f r a c t u r e s u r f a c e M3O4 316 MgCl 2+HCl e x t e r i o r speciment s u r f a c e M3O4 316 MgCl 2-K;oCl 2 s . c . c . f r a c t u r e s u r f a c e M3O4 310 M g C l 2 . s . c . c . f r a c t u r e s u r f a c e M 304 310 MgCl2-t-HCl s . c . c . f r a c t u r e s u r f a c e M30h 310 MgCl 2+HCl e x t e r i o r specimen s u r f a c e M3O4 310 Mg C l 2 - f C o C l 2 s . c . c . f r a c t u r e s u r f a c e M3O4 T a b l e V I I . d-Spacings and R e l a t i v e I n t e n s i t i e s f o r t h e S p i n e l s o f I r o n , FeaOit, Y F e 2 0 3 , F e C r 2 0 i t , from ASTM X-ray D i f f r a c t i o n Cards F e 3 0 ^ Y - F e 2 0 3 F e C r 2 04 d A° I / I l h k l d A° I / I l - h k l d A° I / I l h k l 4.85 40 111 5.90 2 110 4.83 50 111 2.966 70 220 4.82 5 111 2.95 50 220 2.53 100 311 4.18 1 200 2.51 100 311 2.49 10 222 3.73 5 210 2.08 50 400 2.096 70 400 3.41 2 211 1.91 75 331 1.712 60 422 2.95 34 220 1.71 25 422 1.614 85 333/511 2.78 19 221 1.61 75 511/333 1.483 . 85 440 2.64 - 310 1.49 75 440 1.327 20 620 2.52 100 311 1.33 10 620 1.279 30 533 2.41 1 222 1.28 50 533 1.264 10 622 2.32 6 320 1.21 25 444 1.211 20 444 2.23 .5 321 1.17 10 • 711/551 1.1214 30 642 2.08 24 400 1.12 10 642 1.0922 60 553/731 1.87 .5 420 1.08 50 731 1.0489 40 800 1.70 12 422 1.05 25 800 0.989 10 660/822 1.61 33 511/333 0.965 50 751/555 0.962 40 555/751 1.55 .5 432/520 0.933 25 840 1.53 . 1 521 1.48 53 440 • 1.43 1 433/530 1.32 7 620 1.27 11 533 1.26 3 622 1.21 5 444 1.12 7 642 1.09 19 553/731 1.07 1 650' F i g - 7. Sample d i f f r a c t i o n p a t t e r n s from s t r i p p e d s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o x i d e s , a) 304, b) 316, C) 310 T a b l e V I I I . D, and d-Spacings o f D i f f r a c t i o n P a t t e r n s Shown i n F i g . 7 304 p a t t e r n #23462 316 p a t t e r n #23404 310 p a t t e r n #23418 D i n . dA° D i n . dA° I/Io D i n . dA° I/Io 0.38 4.74 M 0.385 4.96 M 0.40 4.78 S 0.61 2.95 W-M 0.45 4.24* WW 0.53 3.60* Dots 0.72 2.50 S 0.64 2.98 M 0.65 2.94 M 0.75 2.40 W 0.745 2.56 S 0.77 2.48 VS 0.81 2.22* WW 0.785 2.43 W 0.92 2.08 S 0.85 2. .2 M 0.90 2.12 M 1.00 1.91 . W 0.94 1.92 W 0.985 1.94 WW 1.06 1.80* Dots 1.06 1.70 W 1.02 1.88* WW 1.14 1.68 W 1.13 1.60 W-M 1.1 1.74 M-W 1.2 1.60 M 1.23 1.46 W-M 1.17 1.63 M 1.31 1.46 S 1.29 1.40 W 1.28 1.49 M 1.37 1.39 W 1.36 1.32 WW 1.335 1.43 VW 1;46 1.30 VW 1.42 1.27 W 1.425 1.34 VW 1.51 1.26 W 1.49 1.21 W 1.48 1.29 W 1.6 1.2 M 1.54 1.17 VW 1.56 1.22 W 1.65 1.16 W S- s t r o n g D= d i a m e t e r o f d i f f r a c t i o n r i n g on d i f f r a c t i o n p a t t e r n M- medium d= i n t e r p l a n a r s p a c i n g W- weak VW- v e r y weak WW- v e r y , v e r y weak *- denotes a l i n e which does not f i t i n the s p i n e l (M3O4) p a t t e r n - 38 - a r e a s . T r a n s f o r m a t i o n o f a d i f f u s e r i n g p a t t e r n t o a s h a r p r i n g p a t t e r n under t h e i n f l u e n c e o f t h e beam, as o b s e r v e d by N i e l s e n [ 1 4 ] , was n o t o b s e r v e d i n t h i s s t u d y . A comparison between the d i f f r a c t i o n p a t t e r n from a c h e m i c a l l y (bromine-methanol) s t r i p p e d o x i d e and the d i f f r a c t i o n p a t t e r n from a m e c h a n i c a l l y ( a c e t a t e ) s t r i p p e d o x i d e i s shown i n F i g . 8, w i t h c o r r e s p o n d i n g d - s p a c i n g s i n T a b l e IX. These p a t t e r n s were s i m i l a r . C h e m i c a l s t r i p p i n g d i d not a l t e r the c r y s t a l s t r u c t u r e o f the c o r r o s i o n p r o d u c t . D i f f r a c t i o n p a t t e r n s taken from o x i d e s s t r i p p e d from the exposed n o t c h s u r f a c e r e g i o n s o f specimens exposed t o a c i d i f i e d MgCl2 and M g C l 2 + F e C l 3 s o l u t i o n s a r e shown i n F i g . 9. Two d i s t i n c t p a t t e r n s were ob s e r v e d on the o x i d e s formed i n M g C l 2 + F e C l 3 . One p a t t e r n b e l o n g s t o a s p i n e l s t r u c t u r e , the o t h e r f i t s a corundum M^O^ s t r u c t u r e . T h i s d u p l e x s t r u c t u r e was not o b s e r v e d on the f r a c t u r e s u r f a c e o x i d e formed i n the same s o l u t i o n . The p a t t e r n s t a k e n from t h e e x t e r i o r s u r f a c e o x i d e s formed i n M g C l 2 + HCl s o l u t i o n were s i m i l a r t o p a t t e r n s t a k e n from the s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o x i d e s . The l a t t i c e parameters o f t h e o x i d e s were d e t e r m i n e d t o see i f t h e r e was a v a r i a t i o n between o x i d e s . F r a n c i s [22] and Francombe[21] determined t h a t t h e l a t t i c e parameter v a r i e d w i t h c o m p o s i t i o n f o r chromium, i r o n and n i c k e l s p i n e l s . The d e t e r m i n a t i o n o f l a t t i c e parameters o f c u b i c c r y s t a l s can be made from a p l o t o f D vs ( h 2 + k 2 + l 2 ) 2 where D i s t h e d i a m e t e r o f t h e r i n g on t h e e l e c t r o n d i f f r a c t i o n p a t t e r n which c o r r e s p o n d s t o the l a t t i c e p l a n e £hkl^ . T h i s i s d e r i v e d from the camera c o n s t a n t r e l a t i o n f o r a n a l y z i n g d i f f r a c t i o n p a t t e r n s t a k e n i n a T.E.M., Dd = c o n s t a n t ( K ) , where d = a Q / ( h 2 + k 2 + l 2 ) , 2 a Q i s t h e l a t t i c e ' 39 " F i g . 8. D i f f r a c t i o n p a t t e r n s t a k e n from s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o x i d e s o f t y p e 310 s t r e s s c o r r o d e d i n M g C l 2 a) bromine-methanol s t r i p b) c e l l u l o s e a c e t a t e s t r i p - 40 - T a b l e IX. D, d - S p a c i n g s , and R e l a t i v e V i s u a l I n t e n s i t i e s from D i f f r a c t i o n P a t t e r n s Taken from Bromine S t r i p and A c e t a t e S t r i p Oxides (see F i g u r e 8) 310 M g C l 2 - Bromine s t r i p 310 M g C l 2 - A c e t a t e S t r i p D i n . dA° I n t e n s i t y D i n . dA° I n t e n s i t y 0.395 4.76 M 0.475 4.86 M 0.52 3.62''= VW 0.545 4.24* Dots 0.64 2.94 W 0.63 3.67* Dots 0.72 2.61- WW 0.78 2.96 M 0.75 2.51 s 0.905 S.55 S 0.86 2.19* WW 1.1 2.10 M 0.915 2.06 S 1.26 1.83* Dots 0.98 1.92 WW 1.34 1.72 W 1.04 1.81* WW 1.43 1.62 M 1.11 1.69 VW 1.56 1.48 M 1.18 1.59 w 1.62 1.43 Dots 1.275 1.47 M 1.74 1.33 Dots 1.325 1.42 VW 1.8 1.28 W 1.47 1.28 VW 1.57 1.20 VW *- denotes a l i n e t h a t does not f i t i n the s p i n e l M301+ patterns - 41 _ a) b ) c ) 9 . D i f f r a c t i o n p a t t e r n s t a k e n from exposed n o t c h a r e a s o f specimens a) t y p e 304 i n M g C l 2 + F e C l 3 . M30h(spinel) p a t t e r n . b) t y p e 304 i n M g C l 2 + F e C l 3 . M 2 0 3 ( r h o m b o h e d r a l ) p a t t e r n c ) t y p e 304 i n M g C l 2 + HCl. M30k(spinel) p a t t e r n - J+2 - parameter, and d i s t h e i n t e r p l a r t a r s p a c i n g . The c o n s t a n t K i s o b t a i n e d by r e c o r d i n g t h e d i f f r a c t i o n p a t t e r n from a m a t e r i a l o f known d and \h~klf, ( u s u a l l y g o l d ) a t t h e same i n s t r u m e n t s e t t i n g s as t h e d i f f r a c t i o n p a t t e r n o f the unknown specimen. Thus, the r e l a t i o n ; D = K/a D ( h 2 + k 2 + l 2 ) ^ (2) G r a p h i c a l p l o t s o f D vs ( h 2 + k 2 + l 2 ) " % o r the d i f f e r e n t o x i d e s a r e shown i n Appendix A. The e x c e l l e n t l i n e a r i t y o f t h e p l o t s p r o v i d e s overwhelming e v i d e n c e f o r t h e p r e s e n c e o f a s p i n e l c r y s t a l s t r u c t u r e . The l a t t i c e parameters determined from t h e s e p l o t s a r e . t a b u l a t e d i n T a b l e X. They v a r y i n c o n s i s t e n t l y and a r e g e n e r a l l y h i g h e r th an t h e l a t t i c e parameters determined by F r a n c i s [22] and Francombe[21]. T h i s i s p r o b a b l y due t o t h e p r e s e n c e o f i m p u r i t i e s and t h e i n a c c u r a c y o f u s i n g e l e c t r o n d i f f r a c t i o n p a t t e r n s t o determine a Q v a l u e s . 3.4 X-ray S p e c t r o s c o p y The x-ray s p e c t r o s c o p y r e s u l t s a r e summarized i n T a b l e XI. 3.4.1 X-ray S p e c t r o s c o p y o f S t r i p p e d Oxides X-ray s p e c t r o s c o p y o f s t r i p p e d o x i d e f i l m s , showed the e l e m e n t a l c o m p o s i t i o n t o be p r e d o m i n a n t l y chromium and i r o n w i t h l e s s e r amounts o f n i c k e l , s i l i c o n , molybdenum, magnesium, phosphorous, and c h l o r i n e . The c h a r a c t e r i s t i c energy peaks o f c h l o r i n e , phosphorous, molybdenum, s i l i c o n and magnesium were i n c o n s i s t e n t . They showed no c o r r e l a t i o n between time t o f a i l u r e , a l l o y c o m p o s i t i o n , environment, o r between samples from t h e same specimen. In some i n s t a n c e s , a spectrum from a sample o f f r a c t u r e s u r f a c e o x i d e would have a l a r g e S i Ka peak. However, a spectrum from a n o t h e r p a r t o f t h e same o x i d e would have a r e l a t i v e l y - 43 - T a b l e X. a Q V a l u e s C a l c u l a t e d from P l o t s o f D vs ( h 2 + k 2 + l 2 ) ^ i n Appendix A, where Sl o p e M = K / a Q , M Determined from L e a s t Squares A n a l y s i s . A l l Oxides S t r i p p e d i n 1% Bromine-Methanol S o l u t i o n Except Where Noted A l l o y a 0 ( A ° ) f o r o x i d e s i n v a r i o u s environments MgCl 2 M g C l 2 + H C l M g C l 2 + Co.Cl 2 M g C l 2 + F e C l 3 304 8.36 8.41 8.52 8.52 8.41 8.45 8.52 8.44 8.39 8.45 8.33 8.44 316 8.36 8.45 8.49 8.35 8.38 8.45 8.30 8.45 8.58 310 8.36 8.27 8.45 8.36 8.23 8.41 310 *8.38 *8.40 *8.44 - Oxide s t r i p p e d w i t h c e l l u l o s e a c e t a t e T A B L E X I 304 304 304 304 304 304 316 316 316 310 310 310 M g C l 2 M g C l 2 + HCl M g C l 2 + H C l ' M g C l 2 + C o C l 2 M g C l 2 + F e C l 3 M g C l 2 + F e C l 3 M g C l 2 M g C l 2 + HCl M g C l 2 + C o C l 2 M g C l 2 M g C l 2 + HCl M g C l 2 + C o C l 2 f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e e x t e r i o r n o t c h s u r f a c e f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e e x t e r i o r n o t c h s u r f a c e f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e f r a c t u r e s u r f a c e C r ,Fe,Ni ,C1,Mo ,P,Si,Mg Cr ,Fe ,Ni ,C1,Mo ,P,Si,Mg Cr ,Fe,Ni,C1,Mo,P,Si,Mg Cr ,Fe ,Ni,C1,Mo,P ,Si,Mg Cr ,Fe ,Ni ,C1 ,Mo ,P, S i ,Mg Cr,Fe,Ni,C1,Mo,P,Si,Mg Cr ,Fe,Ni ,C1,Mo,Si,P,Mg Cr,Fe,Ni,C1,Mo,P,Si,Mg Cr,Fe sNi,Cl,Mo,P,Si,Mg Cr,Fe,Ni,C1,Mo,P,Si,Mg Cr,Fe,Ni,C1,Mo,P,Si,Mg Cr,Fe,Ni,Cl,Mo,P,Si,Mg CrKa/FeKa >1 >1 >1 >1 v a r i a b l e v a r i a b l e >1 >1 >1 >1 >1 >1 - 45 - minor S i K a p e a k . The i n t e n s i t y o f t h e s e lower energy peaks was f e l t t o be dependent upon the s u c c e s s w i t h which samples were washed t o remove t r a c e s o f MgCl2, and upon the random p r e s e n c e o f magnesium o x y c h l o r i d e s [ 1 7 ] , as w e l l as a l l o y i n c l u s i o n s (eg. s u l p h i d e s and s i l i c a t e s ) i n t h e o x i d e . C o n s e q u e n t l y , major d e d u c t i o n s were o b t a i n e d by c o n f i n i n g a t t e n t i o n t o the more c o n s i s t e n t Fe, C r , N i peaks. R e p r e s e n t a t i v e s p e c t r a t a k e n from the s t r i p p e d o x i d e f i l m s formed i n the v a r i o u s s o l u t i o n s a r e shown i n Appendix B. These s p e c t r a , as w e l l as o t h e r s a p p e a r i n g i n the t e x t a r e n o r m a l i z e d w i t h r e s p e c t t o t h e chromium Ka peak. In g e n e r a l , t h e same elements were p r e s e n t i n the s p e c t r a t a k e n from the d i f f e r e n t a l l o y s and environments a l t h o u g h t h e peak h e i g h t s v a r y . T h i s v a r i a t i o n c o u l d be due t o d i f f e r e n c e s i n c o m p o s i t i o n , o r i t c o u l d r e s u l t from f l u o r e s c e n c e and a b s o r p t i o n o c c u r r i n g i n the o x i d e . I t i s a l s o p o s s i b l e t h a t s c a t t e r i n g e f f e c t s caused by the rough n a t u r e o f t h e f r a c t u r e s u r f a c e o x i d e caused the peak v a r i a t i o n s . Chromium K°< was t h e s t r o n g e s t peak, u s u a l l y . f o l l o w e d by the i r o n Kot. The s p e c t r a t a k e n from the o x i d e formed on 304 and 316 specimens i n the v a r i o u s environments had i n t e g r a t e d CrKa/FeKa r a t i o s ranging' from 1.5/1 t o 6/1. Some o f the s p e c t r a t a k e n from t h e s e o x i d e s c o u l d be r e l a t e d t o d i f f r a c t i o n p a t t e r n s , see F i g . 10, thus c o n f i r m i n g t h e assumption o f t h i n c o r r o s i o n f i l m s , and n e g l i g i b l e a b s o r p t i o n and f l u o r e s c e n c e e f f e c t s . The s p e c t r a from t h e f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t s o f t h e 310 specimens had v e r y h i g h i n t e g r a t e d CrKa/FeKa r a t i o s , as h i g h as 10/1 i n some c a s e s . T h i s was thought t o be i n c o n s i s t e n t w i t h a s p i n e l s t r u c t u r e . However, x-ray s p e c t r o s c o p y o f c h r o m i t e o r e , F e C r 2 d + , (see F i g . 1 1 ) , gave s i m i l a r r e s u l t s . Thus, the h i g h i n t e g r a t e d - 46 - F i g - 10. D i f f r a c t i o n p a t t e r n and x - r a y spectrum taken from the same area on a f r a c t u r e surface oxide s t r i p p e d from 316-type specimen s t r e s s corroded i n MgCl 2 + C o C l 2 s o l u t i o n . F i g . 11. X-ray spectrum t a k e n from c h r o m i t e o r e . - 48 - CrKa/FeKa r a t i o was due t o a b s o r p t i o n and f l u o r e s c e n c e e f f e c t s i n t h e o x i d e ; the t h i n f i l m assumption b e i n g i n v a l i d f o r the t h i c k c o r r o s i o n p r o d u c t on the 310 specimens. X-ray s p e c t r o s c o p y o f t h e c o r r o s i o n p r o d u c t on t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o f 304 c r a c k e d i n t h e M g C l 2 + FeCl3 s o l u t i o n showed t h e o x i d e had a v a r i a b l e c o m p o s i t i o n . S p e c t r a i n F i g . 12 show t h e i n t e g r a t e d CrKa/FeKa r a t i o changes from <1 t o >1. V a r i a t i o n s l i k e t h i s were not o b s e r v e d i n any o f the o t h e r o x i d e s . O p t i c a l e x a m i n a t i o n o f t h e o x i d e showed t h a t i t had two d i s t i n c t c o l o u r e d l a y e r s ; a s i l v e r g r a y c o l o u r on the m e t a l / o x i d e i n t e r f a c e , and a r e d brown c o l o u r on the o x i d e / s o l u t i o n i n t e r f a c e . A n a l y s i s o f t h e r e d brown o x i d e always showed t h e i n t e g r a t e d CrKa/FeKa r a t i o « 1 w h i l e a n a l y s i s o f t h e s i l v e r gray s i d e always showed r a t i o s >1. E l e c t r o n d i f f r a c t i o n o f t h i s composite o x i d e produced a s p i n e l p a t t e r n . T h i s c o u l d i n d i c a t e t h e composite o x i d e formed on the s . c . c . s u r f a c e i n the M g C l 2 + F e C l 3 s o l u t i o n i s a s p i n e l , chromium e n r i c h e d a t t h e m e t a l i n t e r f a c e and i r o n e n r i c h e d a t t h e s o l u t i o n i n t e r f a c e . I r o n and chromium s p i n e l s are m i s c i b l e [ 2 2 ] , th u s t h e r e was. p r o b a b l y no d i s t i n c t boundary w i t h i n the o x i d e . The o x i d e s t r u c t u r e c o u l d remain t h e same w h i l e t h e c o m p o s i t i o n v a r i e d from chromium e n r i c h e d t o i r o n e n r i c h e d a t the ox i d e s o l u t i o n i n t e r f a c e . The o x i d e t h a t formed o u t s i d e t h e c r a c k on t h e specimen s u r f a c e i n the MgCl 2 + F e C l 3 s o l u t i o n had a s i m i l a r x-ray spectrum as t h e o x i d e t h a t formed i n t h e c r a c k . X-ray s p e c t r o s c o p y showed t h e o x i d e c o n t a i n e d r e g i o n s o f v a r y i n g i n t e g r a t e d CrKa/FeKa r a t i o s . Chromium r i c h r e g i o n s e x i s t e d as nodules o f o x i d e w h i l e the i r o n e n r i c h e d r e g i o n s formed a l a y e r . The two d i s t i n c t c o l o u r l a y e r s o b s e r v e d on t h e s t r e s s c o r r o s i o n c r a c k - 49 - ENERGY KeV F i g . 12. X-ray s p e c t r a t a k e n from t h e f r a c t u r e s u r f a c e o x i d e s t r i p p e d from a type 304 specimen s t r e s s c o r r o d e d i n MgCl2 + FeCl^ s o l u t i o n . The t h r e e d i f f e r e n t s p e c t r a r e p r e s e n t the v a r i a t i o n i n i n t e g r a t e d CrKa/FeKa r a t i o o b s e r v e d f o r t h i s o x i d e . a) CrKa/ FeKa = 4.99/1 b) CrKa/ FeKa = 1.01/1 c ) CrKa/ FeKa = 0.405/1 - 50 - s u r f a c e o x i d e were not o b s e r v e d on the o x i d e formed on the e x t e r i o r s u r f a c e o f the specimen. X-ray s p e c t r a o f the o x i d e s t r i p p e d from the o u t e r n o t c h s u r f a c e o f specimens exposed t o a c i d i f i e d MgCl 2 s o l u t i o n s were s i m i l a r t o the s p e c t r a o f the o x i d e formed on t h e s . c . c . f r a c t u r e s u r f a c e s . No v a r i a t i o n i n peak r a t i o s were o b s e r v e d and no s u r f a c e i r r e g u l a r i t i e s were o b s e r v e d . S p e c t r a o b t a i n e d from the m e c h a n i c a l l y and c h e m i c a l l y s t r i p p e d o x i d e formed on the 310 f r a c t u r e s u r f a c e a r e shown i n F i g . 13. A c h a r a c t e r i s t i c peak a t 1.48 eV i n t h e c h e m i c a l l y s t r i p p e d spectrum was i d e n t i f i e d as a bromine L a peak. Thus d u r i n g t h e s t r i p p i n g p r o c e s s bromine had become i n c o r p o r a t e d i n t o t h e o x i d e . However, t h e major peaks were s i m i l a r , w i t h t h e e x c e p t i o n o f t h e r e l a t i v e h e i g h t s (which c o u l d be due t o f l u o r e s c e n c e and a b s o r p t i o n e f f e c t s ) . Thus bromine-methanol s t r i p p i n g d i d not s t r o n g l y a l t e r the e l e m e n t a l c o m p o s i t i o n o f m e t a l i n the c o r r o s i o n p r o d u c t . The p r e s e n c e o f c h l o r i n e peaks i n a l l t h e x-ray s p e c t r a , a f t e r t h e o x i d e had been washed e x t e n s i v e l y , s u g g e s t e d t h a t c h l o r i d e i o n s c o u l d be p a r t o f t h e c o r r o s i o n p r o d u c t and not a p o r t i o n o f s o l i d i f i e d s . c . c . s o l u t i o n t h a t had n o t been washed from the f r a c t u r e s u r f a c e . O x y c h l o r i d e s may be p r e s e n t , however, P o u r b a i x [ 5 ] s u g g e s t e d t h a t F e C l 2 , 4 H 2 0 c o u l d be p a r t o f the c o r r o s i o n p r o d u c t formed i n s . c . c . c r a c k s . X-ray d i f f r a c t i o n c h a r t s f o r F e C l 2 show t h a t i t s p a t t e r n would be masked to a c e r t a i n e x t e n t by t h e s p i n e l p a t t e r n s , see T a b l e X I I . Thus, t h e d e t e c t i o n o f s m a l l q u a n t i t i e s o f m e t a l c h l o r i d e s by . e l e c t r o n d i f f r a c t i o n o f t h e o x i d e would be d i f f i c u l t i n t h i s c a s e . Hence i t i s p o s s i b l e t h a t m e t a l c h l o r i d e s c o u l d be p r e s e n t i n t h e c o r r o s i o n p r o d u c t . - 51 - ENERGY KeV F i g . 13. X-ray spe c t r a taken from f r a c t u r e surface oxide s t r i p p e d from a type 310 specimen s t r e s s corroded i n MgCl2 s o l u t i o n . a) oxide s t r i p p e d with bromine-methanol s o l u t i o n b) oxide s t r i p p e d w i t h c e l l u l o s e acetate - 52 - TABLE XII: Xray I n t e n s i t i e s and d-Spacings f o r TezOi) and F e C l 2 from ASTM Index Cards #11-614 and 1-1106 R e s p e c t i v e l y . F e 3 0 4 F e C l 2 dA° I / I l h k l dA° I / I l h k l 4.85 40 111 5.9 63 003 2.966 70 220 3.07 30 101 2.5 30 100 311 2.54 100 104 2.419 10 222 2.32 7 015 2.096 70 400 2.09 7 N.I. 1.712 60 422 1.953 13 009 1.614 85 333/511 1.80 63 018 1.483 85 440 1.721 13 112 1.327 20 620 1.632 2 N.I. 1.279 30 533 1.552 4 021 1.264 10 622 1.467 20 0012/024 1.211 20 444 1.421 5 0111/205 1.1214 ' 30 642 1.272 3 208 1.0922 60 553/731 1.173 2 0015/211 1.0489 40 800 1.138 18 1112/214 - 53 - 3.4. 2 In S i t u S p e c t r o s c o p y • I t was found t h a t m e a n i n g f u l i n s i t u x - r a y s p e c t r o s c o p y o f c o r r o s i o n p r o d u c t s was not p o s s i b l e u n l e s s t h e o x i d e was s u f f i c i e n t l y t h i c k t h a t t h e volume o f x - r a y e x c i t a t i o n was w i t h i n t h e o x i d e and not t h e m e t a l s u b s t r a t e . I f the s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e was p a r a l l e l t o t h e e l e c t r o n beam (as i n t h e h i g h r e s o l u t i o n d i f f r a c t i o n s t a g e o f t h e T.E.M.), work by Bo l o n and L i f s h i n on s c a t t e r i n g i n t h i n f i l m s [ 28] i n d i c a t e s t h a t the o x i d e s h o u l d be about one micron' t h i c k f o r a s i g n i f i c a n t amount o f x-rays t o be produced i n t h e o x i d e . X-ray s p e c t r a were taken In the h i g h r e s o l u t i o n d i f f r a c t i o n s t a g e o f the T.E.M., from t y p e 304, 316, and 310 s t a i n l e s s s t e e l s m e c h a n i c a l f r a c t u r e s u r f a c e s , and compared t o x - r a y s p e c t r a t a k e n from t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e s o f ty p e 304, 316, and 310 s t a i n l e s s s t e e l s (see F i g . 14). The s p e c t r a o b t a i n e d from t h e s . c . c . s u r f a c e s o f 304 and 316 were s i m i l a r t o t h e s p e c t r a o b t a i n e d from t h e m e c h a n i c a l f r a c t u r e s u r f a c e s . The c o r r o s i o n p r o d u c t f i l m s on the 304 and 316 s . c . c . f r a c t u r e s u r f a c e s were so t h i n t h a t most o f t h e x-rays, came from t h e m e t a l s u b s t r a t e . The c o r r o s i o n p r o d u c t s formed on t h e f r a c t u r e s u r f a c e s o f a l l type 310 specimens and ty p e 304 i n MgCl 2 + FeCl3 s o l u t i o n s were s u f f i c i e n t l y t h i c k t h a t most o f t h e x-rays came from the o x i d e . S p e c t r a t a k e n from t h e s e f r a c t u r e s u r f a c e s i n d i c a t e d the o x i d e was e n r i c h e d i n chromium and i r o n w i t h n i c k e l , s i l i c o n , molybdenum, and c h l o r i n e i m p u r i t i e s , s i m i l a r t o the r e s u l t s from s t r i p p e d o x i d e a n a l y s i s . In o r d e r t o minimize the e x c i t a t i o n o f the m e t a l s u b s t r a t e , s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e s o f 310 i n MgCl 2 and 304 i n MgCl 2 + FeCl3 s o l u t i o n s were l e f t i n t h e bromine s o l u t i o n f o r 24 h o u r s , d i s s o l v i n g the 5 6 7 ENERGY KeV F i g . 14. Comparison o f i n s i t u x - r a y s p e c t r a from m e c h a n i c a l f r a c t u r e s u r f a c e s , w i t h f r a c t u r e s u r f a c e s from specimens s . c . c . i n MgCl2 s o l u t i o n . a) t y p e 304 m e c h a n i c a l f r a c t u r e b) type 316 m e c h a n i c a l f r a c t u r e a') t y p e 304 s . c . c . b') type 316 s . c . c . 0.5 1.0 0.5 0.0 8 c n c ) t y p e 310 m e c h a n i c a l f r a c t u r e c") "tyP e 310 s . c . c . - 55 - s t e e l and l e a v i n g t h e s u r f a c e o x i d e as a sponge on the s u r f a c e . The i n s i t u s p e c t r a t a k e n from t h e s . c . c . s u r f a c e s o f t h e 304 specimen i n MgCl2 + FeCLj s o l u t i o n s showed a v a r i a t i o n i n t h e i n t e g r a t e d CrKa/FeKa r a t i o s from <1 t o >1 as the o x i d e sponge was moved f u r t h e r i n t o t h e beam (see F i g . 15). T h i s c o u l d i n d i c a t e an o x i d e e n r i c h e d i n i r o n a t the s u r f a c e , o r t h e I n c r e a s i n g chromium i n t e n s i t y c o u l d be due t o a b s o r p t i o n and f l u o r e s c e n c e e f f e c t s o c c u r i n g as t h e volume o f o x i d e exposed t o the beam i n c r e a s e s . However, x-ray s p e c t r a t a k e n from the c o r r o s i o n p r o d u c t sponge on t h e 310 s . c . c . s u r f a c e d i d not show t h i s v a r i a t i o n i n the CrKa/FeKa r a t i o as t h e o x i d e was moved i n t o th e beam. The i n t e g r a t e d CrKa/FeKa r a t i o was c o n s i s t e n t l y g r e a t e r t h a n one. Thus, the v a r i a t i o n i n t h e i n t e g r a t e d CrKa/FeKa r a t i o i n t h e 304 specimen c o u l d be due t o a c o n c e n t r a t i o n g r a d i e n t i n t h e oxide,, as o b s e r v e d i n x-ray s p e c t r o s c o p y o f t h i s o x i d e s t r i p p e d from t h e f r a c t u r e s u r f a c e . 3.5 P a r t i a l Crack C o o l i n g a p a r t i a l l y c r a c k e d specimen t o room temperature caused t h e whole s o l u t i o n which was t r a p p e d w i t h i n t h e c r a c k t o form a h y d r a t e d s o l i d . T h i s h y d r a t e ( p r e d o m i n a n t l y h y d r a t e d MgCl2 p l u s t r a c e s o f m e t a l i o n s from the s t e e l ) w i l l be r e f e r r e d t o as t h e s o l i d i f i e d c r a c k s o l u t i o n . S t r i p p i n g t h i s s o l i d i f i e d s o l u t i o n from the c r a c k was u n s u c c e s s f u l . There was v e r y l i t t l e s o l i d i f i e d s o l u t i o n on the specimen s u r f a c e and, a l s o , i t absorbed m o i s t u r e from the a i r and f l o w e d from the s u r f a c e . O b s e r v a t i o n o f t h e p a r t i a l c r a c k s u r f a c e i n t h e S.E.M. showed the s o l i d i f i e d c r a c k s o l u t i o n had c o l l e c t e d i n the bottom o f f i s s u r e s a 0 3 . a * <3. a <j> o U- C D W W 6 7 8 5 ENERGY KeV 8 F i g . 15. In s i t u x - r a y s p e c t r a t aken from f r a c t u r e s u r f a c e o x i d e o f typ e 304 specimen s . c . c . i n a MgCl2 + FeCl3 s o l u t i o n . Shows v a r i a t i o n i n x - r a y spectrum w i t h beam p e n e t r a t i o n (as i n d i c a t e d by i n c r e a s i n g x - r a y count r a t e ) a) CrKa/FeKa = .764/1 (100 c o u n t s / s e c ) b) CrKa/FeKa = 1.15/1 (300 c o u n t s / s e c ) c) CrKa/FeKa = 1.40/1 (900 c o u n t s / s e c ) - 57 - on the surface (see F i g . 16). D i r e c t x-ray spectroscopy o f t h i s s o l i d i f i e d s o l u t i o n showed l a r g e magnesium and c h l o r i n e peaks, together w i t h s m a l l peaks o f chromium, i r o n and n i c k e l i n the same r a t i o as the u n d e r l y i n g metal. This was i n c o n c l u s i v e as i t was p o s s i b l e t h a t the i r o n , chromium and n i c k e l peaks were caused by the und e r l y i n g metal, and not from the presence o f these elements i n the crack s o l u t i o n . Using the techniques.of q u a l i t a t i v e aqueous i n o r g a n i c chemical a n a l y s i s , i t was p o s s i b l e t o detect the presence of fer r o u s ions as opposed t o f e r r i c ions i n the s o l i d i f i e d crack s o l u t i o n [29]. P a r t i a l l y cracked specimens were taken from the s t r e s s corroding environment and immediately mechanically f r a c t u r e d . A drop of potassium f e r r i c y a n i d e s o l u t i o n was placed on one f r a c t u r e surface and ammonium thiocyanate s o l u t i o n on the other. Potassium f e r r i c y a n i d e turned the hydrate on the f r a c t u r e s urface deep blue forming a p r e c i p i t a t e , i n d i c a t i n g the presence o f f e r r o u s ions i n the s o l i d i f i e d crack s o l u t i o n . Ammonium thiocyanate should t u r n the s o l i d i f i e d crack s o l u t i o n deep red i n the presence of f e r r i c ions but the only r e a c t i o n was a f a i n t pink c o l o r i n d i c a t i n g that the ferrous io n was the predominant i o n w i t h i n the crack environment. During bromine-methanol s t r i p p i n g experiments on washed surfaces o f p a r t i a l l y cracked specimens of 310, i t was observed that the oxide removed from the f r a c t u r e surface was t h i n n e r than the oxide s t r i p p e d from the f r a c t u r e surface of f u l l y cracked specimens. Further evidence t h a t the oxide was t h i n n e r could be seen by comparing i n s i t u x-ray s p e c t r a - 58 - F i g . 16. S o l i d i f i e d crack s o l u t i o n on f r a c t u r e s urface o f type 304 specimen p a r t i a l l y s t r e s s corroded i n b o i l i n g M g C l 2 s o l u t i o n and mechanically f r a c t u r e d at room temperature (800x m a g n i f i c a t i o n ) - 59 - from f u l l y c r a c k e d type 310 specimens t o t h o s e taken from p a r t i a l l y c r a c k e d t y p e 310 specimens. I t was o b s e r v e d t h a t the h e i g h t o f t h e CrKa, FeKa, and NiKa peaks o b t a i n e d from t h e p a r t i a l l y c r a c k e d s u r f a c e were o f t h e same r a t i o as peaks o b t a i n e d from m e c h a n i c a l l y f r a c t u r e d specimens. Thus, the o x i d e was s u f f i c i e n t l y t h i n t h a t t h e m a j o r i t y o f the x - r a y s were coming from t h e m e t a l s u b s t r a t e . - 60 - 4. DISCUSSION 4.1 D i f f r a c t i o n S t u d i e s E l e c t r o n d i f f r a c t i o n p a t t e r n s from c o r r o s i o n p r o d u c t s , b o t h i n s i t u and s t r i p p e d , were c o n s i s t e n t w i t h a s p i n e l s t r u c t u r e . T h i s i s i n agreement w i t h t h e o b s e r v a t i o n s and p r e d i c t i o n s o f o t h e r s [5,17,14], On some d i f f r a c t i o n p a t t e r n s , f a i n t l i n e s not r e l a t e d t o t h e s p i n e l were ob s e r v e d and i d e n t i f i e d as p o s s i b l y b e l o n g i n g t o o x i d e s o f t h e type M 2 0 3 ( e i t h e r Cr203 o r F e 2 0 3 ) , o r p o s s i b l y t o m e t a l c h l o r i d e s . B i r l e y [17] o b s e r v e d e x t r a l i n e s i n s p i n e l p a t t e r n s t a k e n from c o r r o s i o n p r o d u c t s formed on t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e s o f 304 and 310 s t a i n l e s s s t e e l s i n b o i l i n g 154°C MgCl2 s o l u t i o n s and b o i l i n g 125°C MgCl2 + FeCl3 s o l u t i o n s . He i n t e r p r e t e d them as b e l o n g i n g t o magnesium o x y c h l o r i d e s . However, the l i n e s o b s e r v e d on B i r l e y ' s d i f f r a c t i o n p a t t e r n s c o u l d a l s o be a s s o c i a t e d w i t h C r 2 0 3 , o r Fe203. N i e l s e n [14] a l s o o b s e r v e d l i n e s not a s s o c i a t e d w i t h s p i n e l p a t t e r n s and c o n c l u d e d they b e l o n g e d t o a rhombohedral t y p e o x i d e , M203(eg. C r 2 0 3 , Fe203). D i f f r a c t i o n p a t t e r n s t a k e n from o x i d e s formed on t h e e x t e r i o r s u r f a c e o f t h e 304 specimen i n MgCl2 + ' F e C l 3 s o l u t i o n s were d i f f e r e n t from p a t t e r n s taken from t h e o x i d e on t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e . The o x i d e on the e x t e r i o r s u r f a c e produced two d i s t i n c t p a t t e r n s , one b e l o n g i n g t o a corundum type o x i d e M2O3, and t h e o t h e r b e l o n g i n g t o a s p i n e l . T h i s i s i n c o n t r a s t t o t h e o b s e r v a t i o n s o f Baker e t a l . [15] who o b s e r v e d o n l y a s p i n e l o x i d e p a t t e r n on the e x t e r i o r s u r f a c e . In c o n t r a s t , t h e s . c . c . f r a c t u r e s u r f a c e o x i d e i n t h i s s t u d y had a s p i n e l type s t r u c t u r e i n which no d i s t i n c t M2 0 3 type o x i d e p a t t e r n was o b s e r v e d . T h i s s u g g e s t s t h e r e was a d i f f e r e n c e - 61 - between t h e c r a c k environment and t h e b u l k s o l u t i o n environment, r e s u l t i n g i n two d i f f e r e n t o x i d e s . N i e l s e n [14] ob s e r v e d t r a n s f o r m a t i o n s i n c o r r o s i o n p r o d u c t s i s o l a t e d from s t r e s s c o r r o s i o n cracks, and s p e c u l a t e d t h e y were caused by h y d r a t e d o x i d e s l o s i n g water under t h e i n f l u e n c e o f t h e beam. T r a n s f o r m a t i o n o f i r o n h y d r o x i d e s i n t h e e l e c t r o n beam has been ob s e r v e d by o t h e r s , t h e end r e s u l t b e i n g a s p i n e l [30,31]. No t r a n s f o r m a t i o n s were o b s e r v e d i n t h e o x i d e s d u r i n g t h i s . s t u d y , but i t i s n ot p o s s i b l e t o say they d i d not o c c u r w h i l e the specimen was i n the e v a c u a t e d m i c r o s c o p e column. I t was f e l t , however, t h a t h y d r o x i d e s would n o t be s t a b l e i n s . c . c . environments o f such low pH as r e p o r t e d f o r b o i l i n g MgCl2 s o l u t i o n s . Sato e t a l . [32] s t u d i e d p a s s i v e f i l m s on i r o n i n s o l u t i o n s o f v a r i o u s pH and c o n c l u d e d t h a t i n a c i d environments o f pH *5 t h e o x i d e on t h e s u r f a c e was an anhydrous s p i n e l . Thus, t h e r e i s some doubt as t o whether a h y d r a t e d o x i d e e x i s t s i n t h e c r a c k environment. T r a n s f o r m a t i o n s were o b s e r v e d i n the p r e s e n t s t u d y d u r i n g d i f f r a c t i o n a n a l y s i s o f r e a g e n t grade F e C l 2 ' 4 H 2 0 . P o u r b a i x [ 5 ] sug g e s t e d t h a t m e t a l c h l o r i d e s c o u l d e x i s t as a s t a b l e phase i n t h e s t r e s s c o r r o s i o n c r a c k environment and t h i s was s u p p o r t e d by the p r e s e n c e o f c h l o r i n e peaks i n the x-ray s p e c t r a t a k e n from the s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e c o r r o s i o n p r o d u c t s . The d e h y d r a t i o n o f a h y d r a t e d m e t a l c h l o r i d e c o u l d be t h e t r a n s f o r m a t i o n o b s e r v e d by N i e l s e n [ 1 4 ] ; t h e FeCl2 p a t t e r n b e i n g s i m i l a r t o an Fe 3 C i t p a t t e r n ( T a b l e X I I ) . N i e l s e n i s o l a t e d c o r r o s i o n p r o d u c t s from s t r e s s c o r r o s i o n c r a c k s by d i s s o l v i n g the s u r r o u n d i n g metal' and washing t h e o x i d e i n methanol. In our s t u d y , t h e c o r r o s i o n p r o d u c t s were t a k e n from t h e f r a c t u r e s u r f a c e a f t e r i t - 62 - had been washed i n hot water. I t i s l i k e l y t h a t the c o r r o s i o n p r o d u c t s i s o l a t e d from c r a c k s would c o n t a i n more m e t a l c h l o r i d e s and t r a p p e d s o l i d i f i e d s o l u t i o n t h a n p r o d u c t s s t r i p p e d from washed f r a c t u r e s u r f a c e s . T h e r e f o r e , i t i s more p r o b a b l e t h a t a d e h y d r a t i o n o f a h y d r a t e d m e t a l c h l o r i d e would be o b s e r v e d i n N i e l s e n ' s [14] s t u d y t h a n i n the p r e s e n t study. S i n c e N i e l s e n conducted no a n a l y s i s f o r elements o t h e r th an n i c k e l , i r o n , chromium, and molybdenum, the p o s s i b i l i t y t h a t t h e c o r r o s i o n p r o d u c t i s o l a t e d from c r a c k s c o n t a i n e d some m e t a l c h l o r i d e s d i s p e r s e d i n t h e s p i n e l o x i d e cannot be r u l e d o u t . 4.2 X-ray A n a l y s i s X-ray s p e c t r o s c o p y , a l t h o u g h q u a l i t a t i v e , was c o n s i s t e n t . I t i n d i c a t e d a chromium e n r i c h e d Fe-Cr o x i d e onthe s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e i n a l l cases e x c e p t t h e MgCl^ + F e C l 3 s o l u t i o n . D i f f r a c t i o n and x-ray a n a l y s i s o f s i m i l a r a r e a s on s t r i p p e d c o r r o s i o n p r o d u c t s showed t h e o x i d e was p r i m a r i l y a c h r o m i t e s p i n e l ( F e C ^ C ^ ) w i t h i m p u r i t i e s o f n i c k e l , s i l i c o n , molybdenum, magnesium, phosphorous, and c h l o r i n e . The p r e s e n c e o f i m p u r i t i e s s u g g e s t s t h a t the o x i d e i s d e f e c t i v e and i s not a s t o i c h i o m e t r i c F e C r 2 0 l t s p i n e l . These r e s u l t s were i n g e n e r a l agreement w i t h N i e l s e n ' s [14] work on 316 s t a i n l e s s s t e e l i n MgCl 2 s o l u t i o n s and Marek and Hochman's [18] o b s e r v a t i o n s on t y p e 316 s i n g l e c r y s t a l s i n MgCl 2 s o l u t i o n s . The a d d i t i o n o f C o C l 2 and H C l t o t h e b a s i c M g Cl 2 s o l u t i o n had no e f f e c t on the s t r u c t u r e o r c o m p o s i t i o n o f t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o x i d e . Smith, e t a l . [ 9 ] i n s t u d i e s on 4340 s t e e l i n MgC'l2 s o l u t i o n s o b s e r v e d t h a t the pH i n s i d e t h e c r a c k d i d n o t v a r y , - 63 - b e i n g c o n s t a n t l y pH 3.5-3.9, w h i l e t h e b u l k s o l u t i o n was v a r i e d from pH 2-10. S i m i l a r l y Baker e t a l . [15] o b s e r v e d t h e c r a c k s o l u t i o n t o have a c o n s t a n t pH 1.2-2.5 i n 304 s t a i n l e s s s t e e l . These o b s e r v a t i o n s suggest t h a t t h e c r a c k pH i s c o n t r o l l e d by c o n d i t i o n s w i t h i n t h e c r a c k . Hence, a c i d a d d i t i o n s t o t h e b u l k s o l u t i o n would n o t be e x p e c t e d t o a f f e c t t h e c r a c k environment o r o x i d e . The absence o f any e f f e c t by C0CI2 i s n o t s u r p r i s i n g c o n s i d e r i n g t h e s e l e c t i v i t y o f s . c . c . environments. A l t h o u g h a t room temperature C o + 2 has a h i g h e r r e d u c t i o n p o t e n t i a l t h a n Fe 0 , t h e thermodynamics o f t h i s i o n c o u l d be q u i t e d i f f e r e n t i n a deoxygenated, h i g h c h l o r i d e c o n c e n t r a t i o n , low pH s o l u t i o n . A d d i t i o n o f F e C l 3 t o t h e b a s i c MgCl2 s o l u t i o n d e c r e a s e d t h e time t o f a i l u r e (see T a b l e V) and produced a l a y e r e d s p i n e l o x i d e w i t h a c o m p o s i t i o n g r a d i e n t . The n a t u r e o f t h e c o m p o s i t i o n g r a d i e n t s u g g e s t s a s p i n e l a p p r o a c h i n g an Fe3C\ c o m p o s i t i o n a t t h e s o l u t i o n i n t e r f a c e and a s p i n e l a p p r o a c h i n g an F e C r 2 0 l t c o m p o s i t i o n a t the m e t a l i n t e r f a c e . The c o m p o s i t i o n g r a d i e n t c o u l d be e x p l a i n e d by assuming t h a t the environment was t h e same a t the c r a c k t i p f o r b o t h M g C l 2 s o l u t i o n s and M g C l 2 + FeCl3 s o l u t i o n s . In both c a s e s , t h e o n l y i r o n i o n s e n t e r i n g s o l u t i o n d u r i n g e l e c t r o c h e m i c a l d i s s o l u t i o n a t t h e p r o p a g a t i n g c r a c k t i p a r e f e r r o u s i o n s F e + ^ , and t h e c o r r o s i o n p r o d u c t approached an F e C r ^ ^ s p i n e l . However, i n the s i t u a t i o n w i t h M g C l 2 + F e C l 3 s o l u t i o n s , f e r r i c i o n s m i g r a t i n g from t h e b u l k s o l u t i o n a r e a b l e t o p a r t i c i p a t e i n c a t h o d i c r e a c t i o n s o c c u r r i n g on t h e c r a c k w a l l s remote from t h e c r a c k t i p . The r e d u c t i o n o f f e r r i c i o n s t o f e r r o u s i o n s , w i l l , y i e l d a s o l u t i o n c o n t a i n i n g b o t h F e + 3 and F e + 2 . H y d r o l y s i s r e a c t i o n s i n - 64 - such s o l u t i o n s c o u l d y i e l d s p i n e l s a p p r o a c h i n g an Fe^C^ c o m p o s i t i o n which d e p o s i t on t h e p r e - e x i s t i n g F e C r 2 0 l t . eg; r e d u c t i o n F e + 3 + e~ !=* F e + 2 ^ h y d r o l y s i s 2 F e + 3 + F e + 2 + 4 ^ 0 5 = * FesOi+ + 8H + (1+) Furthermore, t h e r e d u c t i o n o f f e r r i c i o n s i n t h e M g C l 2 + FeCl3 s o l u t i o n s h o u l d y i e l d a h i g h e r c o r r o s i o n p o t e n t i a l and c o r r o s i o n c u r r e n t t h a n i n t h e M g C l 2 s o l u t i o n . The h i g h e r c o r r o s i o n c u r r e n t would l e a d t o i n c r e a s e d d i s s o l u t i o n r a t e s a t t h e c r a c k t i p , and a c o r r e s p o n d i n g r e d u c e d time t o f a i l u r e , as o b s e r v e d . 4.3 P o t e n t i a l -pH E q u i l i b r i a W i t h i n t h e S.C.C. Crack P o t e n t i a l -pH diagrams f o r the a u s t e n i t i c s t a i n l e s s s t e e l s i n b o i l i n g c h l o r i d e environments do n o t e x i s t . T h e r e f o r e , i t i s n o t p o s s i b l e t o p r e d i c t the s t a b l e phases i n t h e s e environments. However, E -pH diagrams f o r i r o n , chromium, and n i c k e l i n water a t 150°C a r e a v a i l a b l e [ 3 1 ,33], as a r e diagrams f o r chromium i n water + 0.1 M C l a t 25°C, and f o r Fe-FeCl2-H20 system a t 25°C [5,34] (see F i g . 17-20, where E i s measured w i t h r e f e r e n c e . t o t h e s t a n d a r d hydrogen e l e c t r o d e , S . H , E . ) . T h e s e diagrams a r e no s u b s t i t u t e f o r s t a i n l e s s s t e e l - M g C l 2 diagrams, b u t t h e y do p r o v i d e u s e f u l i n f o r m a t i o n . The pH i n s i d e c r a c k s has been r e p o r t e d t o v a r y between pH 1 a t t h e t i p and pH 4.5 i n t h e b u l k o f t h e c r a c k [16,15,9,36]. Newburg and U h l i g [35] measured c r i t i c a l a p p l i e d p o t e n t i a l s below which no s t r e s s c o r r o s i o n was o b s e r v e d f o r a u s t e n i t i c s t a i n l e s s s t e e l s i n b o i l i n g 154°C M g C l 2 s o l u t i o n s , -0.128V (S.H.E.) f o r 304 and -0.103V (S.H.E.) f o r 310 ( t h e s e a r e a p p l i e d p o t e n t i a l s , n o t c r a c k t i p p o t e n t i a l s ) . Comparing t h i s d a t a w i t h t h e E -pH diagrams shows t h a t t h e . c r a c k environment i s i n t h e a c t i v e a r e a f o r a l l t h r e e a l l o y s . Under t h e s e c o n d i t i o n s o n l y a - 65 - F i g - 1 7 - P o t e n t i a l -pH (E-pH) diagram f o r t h e Cr-H 20 system. C o n c e n t r a t i o n o f s o l u b l e s p e c i e s 10 6M., from Brook [ 3 3 ] . F i g . 18. P o t e n t i a l -pH (E-pH) diagram f o r t h e Ni-H 20 system. C o n c e n t r a t i o n o f s o l u b l e s p e c i e s 10 6M., from Brook [ 3 3 ] . - 66 - Fig. 2 0 . C a l c u l a t e d areas of s t a b i l i t y o f Fe, F e C l 2 * 4 H 2 0 , and F e 3 0 [ + i n the presence of a s o l u t i o n e l e c t r o n e u t r a l i n F e C l 2 , (schematic) from Pourbaix [ 5 ] . - 67 - chromium h y d r o x i d e ( o x i d e ) i s s t a b l e . C o n s e q u e n t l y , F e C r 2 0 l t would p r o b a b l y be s t a b l e i n t h i s environment. These E -pH diagrams i n d i c a t e t h e c r a c k s o l u t i o n w i l l c o n t a i n F e + 2 , N i + 2 , C r + 3 , and C r + 2 i o n s . F e r r o u s i o n s were d e t e c t e d i n t h e s o l i d i f i e d c r a c k s o l u t i o n t r a p p e d on t h e f r a c t u r e s u r f a c e o f p a r t i a l l y c r a c k e d specimens. No t e s t s f o r n i c k e l o r chromium i o n s were performed i n t h i s s t u d y , however, Wilde [20] has performed c o n t r o l l e d p o t e n t i a l c o r r o s i o n t e s t s o f 304 a u s t e n i t i c s t a i n l e s s s t e e l s i n b o i l i n g M g C l 2 s o l u t i o n s and dete r m i n e d t h e m e t a l i o n s i n s o l u t i o n . H i s work showed t h a t t h e s o l u t i o n e n r i c h e d i n i r o n compared t o t h e s t e e l c o m p o s i t i o n and was d e p l e t e d i n chromium, which he assumed made up t h e b u l k o f the c o r r o s i o n p r o d u c t o x i d e . The C r + 3 / C r + 2 r a t i o s a t -0.103V and -0.128V (S.H.E.) o b t a i n e d from F i g . 17 by u s i n g the Nernst e q u a t i o n [ E = E Q + RT 2.303 l o g ( a C r + 3 / a C r + 2 ) ] nF + o are.949 and .494, i n d i c a t i n g a s i g n i f i c a n t f r a c t i o n o f Cr ^ i o n s p r e s e n t . I t i s p o s s i b l e t h a t t h e s e chromous i o n s c o u l d r e a c t w i t h c h l o r i d e i o n s t o form C r C l 2 , as w e l l as F e C r 2 0 t j . The f a t e o f t h e n i c k e l appears t o be u n r e s o l v e d . S t a e h l e [ 7 ] r e p o r t s t h a t the n i c k e l i s p r e f e r e n t i a l l y d i s s o l v e d from the a l l o y s u r f a c e , b u t Wilde [20] r e p o r t e d t h a t n i c k e l d i s s o l v e d u n i f o r m l y , n e i t h e r e n r i c h i n g t h e a l l o y s u r f a c e nor d e p l e t i n g i t . The E -pH diagram o f F i g . 17 f o r pure n i c k e l i n water i n d i c a t e s t h a t t h e a c t i v i t y o f N i + 2 i o n s a t t h e a f o r e m e n t i o n e d p o t e n t i a l s s h o u l d be q u i t e low. However, t h e e f f e c t o f the p r e s e n c e o f o t h e r i o n s (eg. C r 2 , F e + 2 , C l ) a t h i g h c o n c e n t r a t i o n s on the i o n i c a c t i v i t y o f N i i s unknown. Wilde [20] and S t a e h l e ' s [ 7 ] work, on a u s t e n i t i c s t a i n l e s s s t e e l s - 68 - i n c h l o r i d e s o l u t i o n s has been performed, i n t h e b u l k s o l u t i o n s on t h e b u l k specimen s u r f a c e . S t u d i e s o f s u r f a c e p r o p e r t i e s i n b u l k s o l u t i o n s may be s i g n i f i c a n t f o r c r a c k i n i t i a t i o n , but c a r e must be used when a p p l y i n g t h e s e r e s u l t s t o c r a c k p r o p a g a t i o n . The c r a c k t i p s o l u t i o n i s v e r y d i f f e r e n t from t h e b u l k s o l u t i o n as i s e v i d e n c e d by pH s t u d i e s i n s t r e s s c o r r o s i o n c r a c k s , and t h e v a r i a t i o n i n o x i d e s formed on e x t e r i o r s u r f a c e s and f r a c t u r e s u r f a c e s i n MgCl^ + FeCl^ s o l u t i o n s . 4.4 Growth o f Oxide F i l m s I t was o b s e r v e d t h a t t h e o x i d e on t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o f type 310 specimens was u n i f o r m l y t h i c k e r t h a n t h e o x i d e on t h e s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e o f 304 and 316 specimens. However, f u l l y c r a c k e d specimens o f .304 l e f t In the b o i l i n g MgClg s o l u t i o n f o r 40 hours d i d not have a n o t i c e a b l y t h i c k e r f i l m t h a n specimens removed immediately upon f r a c t u r e . A l s o , specimens o f 304 and 310 m e c h a n i c a l l y f r a c t u r e d i n the p r e s e n c e o f b o i l i n g 154°C MgCL^ and l e f t f o r one hour i n the s o l u t i o n had a s i m i l a r f r a c t u r e s u r f a c e appearance. Thus 310 does not i n h e r e n t l y form a t h i c k e r o x i d e i n t h e b u l k s o l u t i o n . O b s e r v a t i o n s o f o x i d e s t r i p p e d from f r a c t u r e s u r f a c e s o f p a r t i a l l y c r a c k e d specimens o f 310 i n d i c a t e d t h a t t h e o x i d e t h i c k e n e d w i t h time i n t h e s t r e s s c o r r o s i o n c r a c k . S i m i l a r l y , o x i d e s i s o l a t e d by N i e l s e n [ 1 4 ] , and Marek and Hochman [ 1 8 ] , i n b o i l i n g MgCI^ s o l u t i o n s were t h i c k e r t h a n o x i d e s i n t h i s s t u d y . T h i s s u g g e s t s dynamic c o n d i t i o n s i n s i d e the c r a c k cause the 310 o x i d e t o t h i c k e n . The o x i d e c o u l d grow by g e n e r a l d i s s o l u t i o n o f t h e u n d e r l y i n g m e t a l through a porous o x i d e w i t h r e s u l t i n g o x i d e f o r m a t i o n . However, - 69 - i t i s not l i k e l y t h a t the o x i d e t h i c k e n e d by u n d e r l y i n g m e t a l d i s s o l u t i o n because t h e c r a c k e d sample o f 304 l e f t i n s o l u t i o n f o r 40 hours d i d not t h i c k e n . A l s o , a n o d i c d i s s o l u t i o n o f t h e c r a c k w a l l s would not be a n t i c i p a t e d as t h i s would l e a d t o c r a c k b l u n t i n g and absence o f s . c . c . Assume the c r a c k w a l l s a r e c a t h o d i c t o an a n o d i c c r a c k t i p , t h e n i t i s p o s s i b l e f o r hydrogen i o n s t o be r e d u c e d on t h e c r a c k w a l l s , p r o v i d i n g the o x i d e i s c o n d u c t i v e . Chromite i s not a good c o n d u c t o r . However, the f r a c t u r e s u r f a c e o x i d e was not t o t a l l y c h r o m i t e , b u t c o n t a i n e d o t h e r elements which may modify the c o n d u c t i v i t y . S i n c e f e r r o u s i o n s and v e r y l i m i t e d c o n c e n t r a t i o n s o f f e r r i c i o n s a r e p r e s e n t w i t h i n the c r a c k s o l u t i o n , i t i s p o s s i b l e f o r some Fe 3 0 ^ t o be p r e s e n t i n the o x i d e . The p r e s e n c e o f s m a l l amounts o f b o t h F e + 3 a n d F e + 2 w i l l r e s u l t i n a s i g n i f i c a n t i n c r e a s e i n c o n d u c t i v i t y [ 3 7 ] . F u r t h e r m o r e , i t i s p o s s i b l e f o r th e c r a c k o x i d e t o be porous. I f m e t a l c h l o r i d e s , form a t the c r a c k t i p [ 5 ] , and then d i s s o l v e a f t e r t h e c r a c k has p r o p a g a t e d , t h e o x i d e c o u l d c o n t a i n p o r e s , which a l l o w hydrogen i o n s t o be r e d u c e d on the metal i n t e r f a c e . The hydrogen i o n s c o u l d a r i s e . f r o m t h e h y d r o l y s i s o f m e t a l i o n s produced by d i s s o l u t i o n a t the c r a c k t i p ; eg. F e + 2 + 2 C r + 3 + 4H 20 Z=± F e C r ^ + 8H + (5) E q u a t i o n (5) i s c o n s i s t e n t w i t h b o t h t h e p r e s e n t o b s e r v a t i o n s o f chromium e n r i c h e d s p i n e l s and the o b s e r v a t i o n o f o t h e r s o f low pH w i t h i n t h e c r a c k . C o n s e q u e n t l y , r e d u c t i o n o f hydrogen i o n s on t h e c r a c k w a l l s would d i s p l a c e e q u a t i o n (5) t o t h e r i g h t and cause f u r t h e r growth o f t h e s p i n e l f i l m . Specimens o f 310 take a p p r o x i m a t e l y 40 hours t o break i n b o i l i n g 154° C M g C l 2 s o l u t i o n s , w h i l e specimens o f 304 and 316 take a p p r o x i m a t e l y 2-4 ho u r s . I f a p r o c e s s s i m i l a r t o the above o c c u r s , i t su g g e s t s t h a t the c o r r o s i o n p r o d u c t s would be t h i c k e r i n the s . c . c . c r a c k s i n 310 specimens as ob s e r v e d . - 70 - 4.5 Envisioned Events w i t h i n the Stress Corrosion Crack The r e s u l t s of t h i s study were c o n s i s t e n t w i t h an e l e c t r o c h e m i c a l mechanism of s . c . c , whereby the crack advanced by anodic d i s s o l u t i o n of the crack t i p f o l l o w e d by p r e c i p i t a t i o n of the c o r r o s i o n products on the w a l l s of the crack. P r e c i p i t a t i o n o f the c o r r o s i o n products prevented l a t e r a l a t t a c k of the crack w a l l s and l o c a l i z e d d i s s o l u t i o n to the crack t i p . H y d r o l y s i s of a n o d i c a l l y d i s s o l v e d metal ions (see equation 5) gave r i s e t o the observed s p i n e l c o r r o s i o n product and increased the hydrogen i o n concentration w i t h i n the crack. Reduction of the hydrogen ions on the crack w a l l s provided the cathodic r e a c t i o n necessary f o r maintenance of anodic d i s s o l u t i o n . Thus there was an a u t o c a t a l y t i c r e a c t i o n w i t h i n the crack. [The r o l e o f s t r e s s could be c o n f i n e d t o the rupture of any c o r r o s i o n product ( f i l m ) which tends to block the crack t i p and prevent exposure to the environment]. The envisioned process r e q u i r e s the c o r r o s i o n product t o be e l e c t r i c a l l y conducting, as i t has t o f u n c t i o n as the cathode f o r the anodic crack t i p . I t could be conductive e i t h e r because i t i s a n o n - s t o i c h i o m e t r i c s p i n e l , or because p o r o s i t y i n the f i l m exposes the u n d e r l y i n g metal. P o r o s i t y could a r i s e from c o n j o i n t p r e c i p i t a t i o n of metal c h l o r i d e s and s p i n e l s , f o l l o w e d by d i s s o l u t i o n o f the metal c h l o r i d e s a f t e r the crack t i p had advanced. The p o s s i b i l i t y t h a t metal c h l o r i d e s are formed at the crack t i p has been proposed by Beck [38]. Working with t i t a n i u m a l l o y s , Beck proposed that an oxide could not form f a s t enough to e x p l a i n the current time behaviour he observed, whereas a metal c h l o r i d e could. The formation of a s p i n e l u n i t c e l l r e q u i r e s 56 atoms. Thus, a u n i t c e l l - 71 - o f F e C ^ O ^ w o u l d r e q u i r e 8 f e r r o u s and 16 chromic i o n s i n t h e i r s o l v a t i o n sheaths t o come t o g e t h e r , r e a c t and form the o x i d e . Meanwhile, the m e t a l i o n s a r e surrounded by a h i g h c o n c e n t r a t i o n o f c h l o r i d e i o n s . T h e r e f o r e , i t i s p o s s i b l e t h a t f o r m a t i o n o f m e t a l c h l o r i d e s and/or h y d r a t e d m e t a l c h l o r i d e s may have more f a v o u r a b l e r e a c t i o n k i n e t i c s than o x i d e f o r m a t i o n . 4.6 E f f e c t o f A l l o y C o m p o s i t i o n There was no e v i d e n c e t o s u p p o r t a c o n s i s t e n t v a r i a t i o n i n c o r r o s i o n p r o d u c t c o m p o s i t i o n w i t h v a r i a t i o n i n a l l o y c o m p o s i t i o n . C o n s e q u e n t l y , the c o r r o s i o n p r o d u c t f i l m was not t h e o n l y f a c t o r i n s t r e s s c o r r o s i o n c r a c k i n g . The e f f e c t s o f a l l o y c o m p o s i t i o n on e l e c t r o c h e m i c a l k i n e t i c s , c r a c k p a t h , d i s l o c a t i o n s t r u c t u r e , and s t a c k i n g f a u l t energy were e q u a l l y i m p o r t a n t , as i s e v i d e n t by t h e d i f f e r e n t f r a c t u r e p a t h s . C e r t a i n l y t h e e f f e c t o f n i c k e l on the s t r e s s c o r r o s i o n c r a c k i n g b e h a v i o u r has y e t t o be s a t i s f a c t o r i l y e x p l a i n e d . N i c k e l - f r e e , i r o n and chromium f e r r i t i c s t a i n l e s s s t e e l s a r e r e s i s t a n t t o s . c . c . i n hot aqueous c h l o r i d e environments. A d d i t i o n s o f a few p e r c e n t n i c k e l r e n d e r s a u s t e n i t i c s t a i n l e s s s t e e l s , v e r y s u s c e p t i b l e t o s . c . c . A d d i t i o n s o f n i c k e l g r e a t e r t h a n 20 wt % r e s u l t s i n r e s i s t a n c e t o s . c . c . a g a i n [ 4 ] . C r y s t a l s t r u c t u r e a l o n e cannot e x p l a i n t h e v a r i a t i o n , as f e r r i t i c s t a i n l e s s s t e e l s w i l l s t r e s s c o r r o d e [ 3 6 ] . S h i b a t a and Takeyama [40] and S t a e h l e [ 7 ] s t u d i e d the e f f e c t o f n i c k e l c o n t e n t on the d i s s o l u t i o n k i n e t i c s o f i r o n chromium a l l o y s i n b o i l i n g MgCl^ s o l u t i o n s . S h i b a t a and Takeyama,found t h e maximum d i s s o l u t i o n c u r r e n t d e n s i t y , I , o b s e r v e d d u r i n g s t r a i n i n g e l e c t r o d e e x p e r i m e n t s , max d e c r e a s e d w i t h i n c r e a s i n g n i c k e l c o n t e n t . S t a e h l e [ 7 ] o b s e r v e d t h a t t h e a c t i v a t i o n energy f o r d i s s o l u t i o n i n c r e a s e d as t h e n i c k e l c o n t e n t - 72 - i n c r e a s e d , l e a d i n g t o a decrease i n d i s s o l u t i o n c u r r e n t . Shibata and Takeyama a l s o found t h a t the current d e n s i t y decay dl/dT i s more r a p i d f o r 304 than 310. They i n t e r p r e t e d t h i s as meaning 304 had a higher f i l m formation ( r e p a s s i v a t i o n ) r a t e than 310. I f 304 does re p a s s i v a t e f a s t e r i t means there could be more general c o r r o s i o n at the crack t i p i n 310 a l l o y s , thereby b l u n t i n g the crack and lowering the s t r e s s i n t e n s i t y at the crack t i p . An a l t e r n a t i v e and important e f f e c t of the n i c k e l composition may be through i t s e f f e c t on the r e v e r s i b l e , e l e c t r o d e p o t e n t i a l , E Q , of the bare a l l o y s u r f ace. N i c k e l has been noted to r a i s e both the c r i t i c a l p o t e n t i a l f o r s.c.c. and the c o r r o s i o n p o t e n t i a l [13,35]. A higher c o r r o s i o n p o t e n t i a l , E , could l e a d t o a reduced c o r r o s i o n & c. c o r r c u r r e n t , I , and a reduced r a t e of metal d i s s o l u t i o n at the a n o d i c a l l y c o r r J propagating crack t i p . This i s most e a s i l y v i s u a l i z e d w i t h respect t o an Evans diagram [4 1 ] , as shown i n F i g . 21. - 7 3 - < I- Z Ul \— o OL X LU . o o Ul C U R R E N T— (log scale) F i g . 21« S c h e m a t i c E v a n s d i a g r a m s h o w i n g p o s s i b l e e f f e c t s o f a l l o y i n g on e l e c t r o c h e m i c a l b e h a v i o u r . Base a l l o y has e l e c t r o c h e m i c a l b e h a v i o u r d e p i c t e d by c u r v e s a a n d c . Upon a l l o y i n g w i t h n i c k e l , t h e a i l o y r e v e r s i b l e p o t e n t i a l i n c r e a s e s f r o m E Q t o E 0 ' , r e s u l t i n g i n a l o w e r c o r r o s i o n c u r r e n t I t o I' . A l l o y i n g c o r r c o r r may l o w e r t h e e x c h a n g e c u r r e n t d e n s i t y f o r h y d r o g e n r e d u c t i o n f r o m I n t o I ' , a g a i n , l o w e r i n g I t o I ' [ 3 9 ] . ° ° c o r r c o r r .5. CONCLUSIONS E l e c t r o n d i f f r a c t i o n and q u a l i t a t i v e x-ray a n a l y s i s of c o r r o s i o n products formed i n s t r e s s c o r r o s i o n c r a c k s of the a u s t e n i t i c s t a i n l e s s s t e e l s 304, 316, and 310 te s t e d i n b o i l i n g aqueous MgCl2 s o l u t i o n s l e d to the f o l l o w i n g c o n c l u s i o n s ; . 1) The c o r r o s i o n product on the s t r e s s c o r r o s i o n f r a c t u r e s u r f a c e of the d i f f e r e n t a l l o y s was s i m i l a r , being a chromium enriched s p i n e l oxide c o n t a i n i n g l e s s e r amounts of the elements i r o n , n i c k e l , molybdenum, s i l i c o n , phosphorous, magnesium, and c h l o r i n e . 2) There was a s i g n i f i c a n t d i f f e r e n c e between the oxide (and environment) on the e x t e r i o r specimen notch s u r f a c e , and the oxide (and environment) i n the s t r e s s c o r r o s i o n crack. 3) The presence of s p i n e l oxide was c o n s i s t e n t w i t h the observations of others on the pH and e l e c t r o c h e m i c a l p o t e n t i a l (E) of s t r e s s c o r r o s i o n cracks i n a u s t e n i t i c s t a i n l e s s s t e e l s . These r e s u l t s i n d i c a t e the crack environment was i n the low pH " a c t i v e t r i a n g l e " r e g i o n of the E-pH diagrams f o r the a l l o y s . 4) The v a r i a t i o n i n s.c.c. behaviour between the d i f f e r e n t a l l o y s could not be adequately accounted f o r i n terms of the composition of the oxide. - 75 - BIBLIOGRAPHY ENGELL, H.J. Theory o f S t r e s s C o r r o s i o n C r a c k i n g i n A l l o y s , P. 86, Nato S c i e n t i f i c A f f a i r s D i v i s i o n (1971).. STAEHLE, R.W. Fundamental A s p e c t s o f S t r e s s C o r r o s i o n C r a c k i n g , P. 3, P r o c e e d i n g s o f C o n f e r e n c e , p u b l i s h e d by N a t i o n a l A s s o c i a t i o n o f C o r r o s i o n E n g i n e e r s (1969). NIELSEN, N.A. C o r r o s i o n , V o l . 27, #5, P. 173 (1971). STAEHLE, R.W. Fundamental A s p e c t s o f S t r e s s C o r r o s i o n C r a c k i n g , P. 214, P r o c e e d i n g s o f C o n f e r e n c e , p u b l i s h e d by N a t i o n a l A s s o c i a t i o n o f C o r r o s i o n E n g i n e e r s (1969). POURBAIX, M. Theory o f S t r e s s C o r r o s i o n C r a c k i n g i n A l l o y s , P. 17, Nato S c i e n t i f i c A f f a i r s D i v i s i o n (1971). BOND, A.P. and DUNDAS, H.J. C o r r o s i o n , V o l . 24, #10, P. 344 (1968). STAEHLE, R.W. Theory o f S t r e s s C o r r o s i o n C r a c k i n g i n A l l o y s , P. 223, Nato S c i e n t i f i c A f f a i r s D i v i s i o n (1971). MCCARTHY, H.A. and HARRISON, P.L. C o r r o s i o n S c i e n c e , V o l . 14, P. 469 (1974). SMITH, J.A.; PETERSON, M.H. and BROWN, B.F. C o r r o s i o n , V o l . 26, #12, P. 539 (1970). RHODES, P.R. C o r r o s i o n , V o l . 25, #11, P. 462 (1969). BROWN, B.F.; F U J I I , C.T. and DAHLBERG, E.P. J . E l e c t r o c h e m . S o c , V o l . 116, #2, P. 218 (1969). BIRLEY, S . S . a n d TROMANS, D. C o r r o s i o n , V o l . 27, #2, P. 63 (1971). LEE, H.H. and UHLIG, H.H. J . E l e c t r o c h e m . S o c , V o l . 117, #1, P. 18 (1970). NIELSEN, N.A. P h y s i c a l M e t a l l u r g y o f S t r e s s C o r r o s i o n C r a c k i n g , M e t a l l u r g i c a l S o c i e t y C o n f e r e n c e s , V o l . 4, I n t e r s c i e n c e P u b l i s h e r s , New York, N.Y. (1959), - 76 - BAKER, H.R. ; BLOOM, M.C: BOLSTER, R.N. and SINGLETERRY, C.R. C o r r o s i o n , V o l . 26, #10, P. 420 (1970). MAREK, M. and HOCHMAN, R.F. C o r r o s i o n , V o l . 26, #1, P. 5 (1970). BIRLEY, S.S. Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, Canada (1972). MAREK, M. and HOCHMAN, R.F. C o r r o s i o n , V o l . 27, #9, P. 361 (1971) DAVIS, J.A. and WILDE, B.E. J . E l e c t r o c h e m . S o c , V o l . 117, #11 P. 1348 (1970). WILDE, B.E. J . E l e c t r o c h e m . S o c , V o l . 118, #11, P. 1717 (1971) FRANCOMBE, M.H. J . Phys. Chem. S o l i d s , V o l . 3, P. 37 (1957). FRANCIS, J.M. J . A p p l . Chem., V o l . 16, S e p t . , P. 264 (1966). NAKAYAMA, T. and 0SHIDA, Y. C o r r o s i o n , V o l . 24, #10, P. 336 (1966). LATIMER, W.M. The o x i d a t i o n s t a t e s o f the elements and t h e i r p o t e n t i a l s i n aqueous s o l u t i o n s , 2nd ed., P r e n t i c e H a l l , New York. (1952). JACOBS, M.H. and BABOROVSKA P r o c . F i f t h European Congress on E l e c t r o n M i c r o s c o p y (1972). KUBASCHEWSKI and HOPKINS O x i d a t i o n o f M e t a l s and A l l o y s , 2nd ed. , B u t t e r w o r t h and Co. L t d . (1962). ASTM STANDARDS, X-ray d i f f r a c t i o n c a r d s #11-614, 4-0755, 4-0759. B0L0N, R.B. and LIFSHIN, E. Scanning E l e c t r o n M i c r o s c o p y , P. 285, P r o c e e d i n g s o f the 6th a n n u a l Scanning E l e c t r o n M i c r o s c o p y Symposium, I I T Research I n s t i t u t e , C h i c a g o , I l l i n o i s (1973). VOGEL, A . J . Macro and Semicro Q u a l i t a t i v e I n o r g a n i c A n a l y s i s , f o u r t h e d i t i o n , Longmans, Green and Co. L t d . , London FEDORCHENKI, I.M. and TRUSHKO, P.V. Doklady Akademii Nauk S.S.S.R., V o l . 211, #4, P. 905 (1973). - 77 - 31. BIERNAT, R.J. and ROBINS, R.G. E l e c t r o c h i m i c a A c t a , V o l . 17, P. 1261 (1972). 32. SATO, N.; NODA, T. and KUDO, K. E l e c t r o c h i m i c a A c t a , V o l . 19, P. 471 (1974). 33. BROOK, P.A. C o r r o s i o n S c i e n c e , V o l . 12, P. 307 (1972). 34. POURBAIX, M. A t l a s o f E l e c t r o c h e m i c a l E q u i l i b r i a i n Aqueous S o l u t i o n s , Pergamon P r e s s (1966). 35. NEWBURG, R.T. and UHLIG, H.H. J . E l e c t r o c h e m . S o c , V o l . 120, #12, P. 1629 (1973). • 36. BROWN, B.F. Theory o f S t r e s s C o r r o s i o n C r a c k i n g i n A l l o y s , P. 186, Nato S c i e n t i f i c A f f a i r s D i f i s i o n (1971). 37. STANDLEY, K.J. Oxide Magnetic M a t e r i a l s , O x f o r d U n i v e r s i t y P r e s s (1962). 38. BECK, T.R. C o r r o s i o n , V o l . 30, #11, P. 408 (1974). 39. KRUGER, J . Fundamental A s p e c t s o f S t r e s s C o r r o s i o n C r a c k i n g , P. 296, P r o c e e d i n g s o f C o n f e r e n c e , P u b l i s h e d by N a t i o n a l A s s o c i a t i o n o f C o r r o s i o n E n g i n e e r s (1969). 40. SHIBATA, T. and TAKEYAMA, T. Boshoku G i j u t s u , 23, P. 379 (1974). 41. EVANS, V.R. The C o r r o s i o n and O x i d a t i o n o f M e t a l s : S c i e n t i f i c P r i n c i p l e s and P r a c t i c a l A p p l i c a t i o n s , Edward A r n o l d L t d . London (1960). - 78 - APPENDIX A T h i s appendix c o n t a i n s the d a t a summarized by T a b l e s VI and X. A n a l y s i s o f r e p r e s e n t a t i v e d i f f r a c t i o n p a t t e r n s from t h e v a r i o u s f r a c t u r e s u r f a c e o x i d e s a r e p r e s e n t e d as a r e g r a p h i c a l p l o t s o f D vs ( h 2 + k 2 + l 2 ) (from which the l a t t i c e parameters i n T a b l e X were d e t e r m i n e d ) . The d i f f r a c t i o n p a t t e r n s are a l l t a k e n from s t r i p p e d c o r r o s i o n p r o d u c t f i l m s by c o n v e n t i o n a l means i n the t r a n s m i s s i o n e l e c t r o n m i c r o s c o p e . The symbols used i n t h i s a p p e n c i x a r e as f o l l o w s ; h k l - M i l l e r i n d i c e s o f c r y s t a l l a t t i c e p l a n e s K - camera c o n s t a n t (see page 38) u n i t s o f i n s - A 0 D - d i a m e t e r o f t h e e l e c t r o n d i f f r a c t i o n r i n g on the d i f f r a c t i o n p a t t e r n , u n i t s o f i n c h e s d t h e i n t e r p l a n a r s p a c i n g c o r r e s p o n d i n g t o p l a n e £hklj which r i v e r i s e t o d i f f r a c t i o n r i n g D. u n i t s o f Angstroms I v r e l a t i v e v i s u a l i n t e n s i t y o f d i f f r a c t i o n r i n g M s l o p e o f D vs ( h 2 t k 2 + l 2 ) d e t e r m i n e d by l e a s t squares f i t a o l a t t i c e parameter o f c u b i t c r y s t a l as o b t a i n e d from p l o t s o f D vs ( h 2 + k 2 + l 2 ) " 5 where a = K/M o - 79 - T a b l e A l . 304 S.C.C. i n MgCl 2 , Oxide S t r i p p e d w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #22217 camera c o n s t a n t K = 1.88 ins-A° l i n e D i n . dA° I V FeCr20i + ( h k l ) Jhz + k 2 + l 2 1 0.39 4.82 W 111 1.73 2 0.63 2.98 W 220 2.83 3 0.74 2.54 S 311 3.32 4 0.77 2.44 WW 222 3.46 5 0.835 2.25 VW — _ 6 0.90 2.09 s 400 4.0 7 0.98 1.92 WW 331 4.36 8 1.05 1.79 WW - — 9 1.115 1.68 WW 422 4.9 10 1.16 1.62 M 333/511 5.2 11 1.275 1.47 S 440 5.66 12 1.33 1.41 WW 531 5.92 13 1.385 1.36 Dots 620 6.32 14 1.47 1.28 VW 533 6.56 15 1.555 1.21 W 444 6.93 16 . 1.59 1.18 Dots 551/711 7.14 Data p l o t t e d i n F i g . A l , D vs ( h 2 + k 2 + l 2 ) Slop e M = K = 0.225 i n a 0 = 1.88 A 0 0.225 L a t t i c e parameter a D = 8.36A° - 80 - (hr* k2* I*)? F i g . A l . P l o t of D vs ( h 2 + k 2 + .1 2)' 2 from Table A l . D i f f r a c t i o n p a t t e r n #22217, 304 s.c.c. i n MgCl 2, oxide s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n - 81 - Table A2. 304 S.C.C. i n MgCl 2 , Oxide Stripped w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #23299 camera constant K - 1.95 ins-A° l i n e D i n . dA° I \r F e C r 2 0 i + J h 2 + k 2 + l 2 V ( h k l ) 1 0.79 2.47 311 3.32 2 0.82 2 . 3 8 222 3.46 3 0.93 2.10 400 4.0 4 1.32 1.48 440 5.66 5 1.53 1.27 533 6.56 6 1.61 1,21 444 6.93 7 1.86 1,05 800 8.00 8 2.00 0.975 555/751 8.66 9 2.10 0.93 840 8.94 Data p l o t t e d i n F i g . A2, D vs ( h 2 + k 2 + 1 2 ) % Slope M = K = 0.232 i n a Q = 1.95 A° 0.232 L a t t i c e parameter a 0 = 8.41A° - 82 - F i g . A2. P l o t o f D vs ( h 2 + k 2 +.1 2) 2 from T a b l e A2. D i f f r a c t i o n p a t t e r n #23299, 304 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 83 - Table A3. 304- S.C.C. i n MgCl 2, Oxide Stripped w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #23389 camera constant K = 1.88 ins'A° l i n e D i n . dA° I V FeCr 20i + ( h k l ) Jh2 + k 2 + l 2 1 0.39 4.90 W 111 1.73 2 0.63 3,03 M 220 2.83 3 0.75 2.55 S 311 3.32 4 0.90 2.12 M 400 4.0 5 1.05 1,82 WW - - 6 1.1 1,71+ WW 422 4.9 7 1.17 1.63 W 511/333 5.2 8 1,28 , 1,49 M 440 5.66 9 1.47 1.30 W 533 6.56 10 1,55 1,23 W 444 6.93 11 1,72 1,11 W 553/731 7.68 12 1.80 1.06 W 800 8.0 Data p l o t t e d i n F i g . A3, D vs (h 2+ k 2 + l 2 ) * 5 Slope M = K = 0.224 i n a Q = 1.88 A 0 0.224 L a t t i c e parameter a D = 8.39 A°  - 85 - Table A4. 304 S.C.C. i n MgCl 2 + C o C l 2 , Oxide St r i p p e d i n 1% Bromine- Methanol S o l u t i o n p a t t e r n #23462 camera constant K = 1.84 ins*A° l i n e D i n . dA° I V FeCr20it (hkl) J h 2 + k 2 + l 2 1 0.375 4,-91 M 111 1.73 2 0.61 3.02 W 220 2.83 3 0.72 2.55 S 311 3.32 4 0.87 2.12 S 400 4 5 1.12 1.64 WM 511/333 5.2 6 1.22 1.51 M 440 5.66 7 1.29 1.43 VW - _ 8 1.42 1.30 VW 533 6.56 9 1.50 1.23 W 444 6.93 10 1.55 1.19 VW 711/551 7.14 11 1.66 1.11 VW 553/731 7.6 12 1.73 1.06 VW 800 8.0 Data p l o t t e d i n F i g . A4, D vs ( h 2 + k 2 + l 2 ) ^ Slope M = K = 0.216 a Q = 1.84 A° 0.216 L a t t i c e parameter a c = 8.52 A 0 - 86 - F i g - A4. P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A4. D i f f r a c t i o n p a t t e r n #23462, 304 s . c . c . i n M g C l 2 + C o C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 87 ~ • T a b l e A 5 - 3 0 4 S.C.C. i n MgCl 2 + C o C l 2 , Oxide.Stripped i n 1% Bromine- Methanol S o l u t i o n p a t t e r n #23459 camera constant K = 1.84 ins*A° l i n e D i n . dA° . I V FeCr 20it ( h k l ) Jh* + k^+ I1 1 0.38 4,-84 M 111 1.73 2 0.62 2.97 w 220 2.83 3 0.72 2,55 S 311 3.32 4 0.87 2.12 M 400 . 4 5 0.95 1.94 WW 331 4.36 6 1.08 1.70 VW 422 4.90 7 1.12 1.64 M 511/333 5.2 8 1.22 1,-51 W 400 5.66 9 1.29 1,43 VW _ 10 1,43 1,29 WW 533 6.56 11 1.50 1,23 WW 444 6.93 12 1.55 1.19 WW 711/551 7.14 Data p l o t t e d i n F i g . A5, D vs ( h 2 + k 2 + l 2 ) ^ Slope M = K = 0.216 i n a n ;•= 1.84 A 0 0.216 L a t t i c e parameter a Q = 8.52 A 0 - 88 F i g - A5, P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A5. D i f f r a c t i o n p a t t e r n #23459, 304 s . c . c . i n M g C l 2 + C 0 C I 2, o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . 89 - Ta b l e A6. 304 S.C.C. In MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Br Methanol S o l u t i o n p a t t e r n #23464 camera c o n s t a n t K = 1.80 ins«A° l i n e D i n . dA° I V F e C r 2 0 H ( h k i ) H JhZ + k 2 + I 2 1 0.38 4.74 M 111 1.73 2 0.61 2.95 W-M 220 2.83 3 0.72 2.50 S 311 3.32 4 0.75 2.40 w 222 3.46 5 0.81 2.22 WW - - 6 0.85 2.12 M 400 4 7 0.94 1.92 W 331 4.36 8 1.06 1.70 W 422 4.90 9 1.13 1.60 W-M 511/333 5.2 10 1.23 1.46 W-M 440 5.66 11 1.29 1.40 w 531 5.92 12 1.36 1,32 WW 620 6.32 13 1.42 1,27 W 533 6.56 14 1.49 1.21 W 444 6.93 15 1.54 1.17 VW 711 7.14 . Data p l o t t e d i n F i g . A6, D vs ( h 2 + k 2 + l 2 ) " Slope M = K = 0.216 i n a Q = -1.80 A 0 0.216 L a t t i c e parameter a G = 8.33 A 0 - . 90 - - 91 - T a b l e A7. 304- S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23452 camera c o n s t a n t K = 1.91 ins«A° l i n e D i n . dA° I V FeCr20 i+ ( h k l ) Jhz + k z + l 2 1 0.39 4.90 M 111 1.73 2 0.44 4.34 WW - - 3 0.64 2.98 M 220 2.83 4 0.75 2.55 S 311 3.32 5 0.90 2.12 M 400 4.0 6 1.00 1.9. WW 331 4,36 7 1.11 1.72 W 422 4.9 8 1.18 1.62 M 511/333 5.2 9 1.28 1.49 M 440 5.66 10 1.34 1.42 VW - - 11 1.44 1.33 VW 620 6.32 12 1.49 1.28 W 533 6.56 13 1.57 1,22 W 444 6.93 14 1.62 1.18 VW 711/551 7.1, Data p l o t t e d i n F i g . A7, D vs ( h 2 + k 2 + l * ) * 5 Slope M = K = 0.227 i n a 0 = 1.91 A 0 0.227 L a t t i c e parameter a Q = 8.41 A° - '92' - bromine-methanol s o l u t i o n - -93 - T a b l e A8. 304 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23434 camera c o n s t a n t K = 1.91 ins-A° l i n e D i n . dA° I V FeCraO^ ( h k l ) k2 + k2 3-1* 1 0.39 4.90 M 111 1.73 2 0.64 2.98 M 220 2.83 3 0.76 2.51 VS 311 3.32 4 0.91 2.10 s 400 4 .0 5 1.11 1.72 w 422 4.9 6 1.18 1.62 M 511/333 5.2 7 1.29 1.48 M 440 5.66 8 1.44 1,33 VW 620 6.32 9 1.48 1,29 W 533 6.56 10 1.57 1,22 W 444 6.93 11 1.61 1.19 VW 711/551 7.14 Data p l o t t e d i n F i g . A8, D vs ( h 2 + k 2 + l 2 ) " Slope M = K = 0.226 i n a o a D = 1.91 A° 0.226 L a t t i c e parameter a Q = 8.45 A° i - 94 - (h*-> k2* I2 )i I F i g . A8. P l o t o f D vs ( h 2 + k 2 + l 2 ) ' 5 from T a b l e Asj. D i f f r a c t i o n p a t t e r n #23434, 304 s . c . c . i n MgCl2 + H C l , ' o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 95 _ T a b l e A9. 304 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23436 camera c o n s t a n t K = 1.91 i n s - A 0 ' l i n e D i n . dA° I V FeCr 0i+ ( h k l ) Jhz + k 2 + l 2 1 0.39 4.90 M 111 1.73 2 0.51 3,75 WW - — 3 0.63 3.03 s 220 2.83 4 0.75 2.55 vs 311 3.32 5 0.90 2.12 s 400 4.0 6 1.10 1,74 M 422 4.9 7 1.18 1,62 s 511/333 5.2 8 1.28 1.49 s 440 5.66 9 1.34 1.42 w 531 5.92 10 . 1.43 1,34 VW 620 6.32 11 1.48 1,29 w 533 6.56 12 1.56 1,22 w 444 6.93 13 1.61 1.19 VW . 711/551 7.14 Data p l o t t e d i n F i g . A9, D vs ( h 2 + k 2 + l 2 ) " Slope M = K = 0.226 i n a o a 0 = 1.91 A 0 0.226 L a t t i c e parameter a Q = 8.45 A° ~ 9 6 _ F i g . A9. P l o t o f D vs ( h2 + k 2 + l 2 ) ^ from T a b l e A9. D i f f r a c t i o n p a t t e r n #23436, 304 s . c . c . i n MgCl2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 97 - .T a b l e A10. 304 S.C.C. i n MgCl 2'+•FeCl 3, Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23580 camera c o n s t a n t K •= 1.90 ins«A° . line D i n . dA° I V FeCr204 (hkl) c/hJt k 2 + l 2 1 0.385 4.94 M 111 1.73 2 0.445 4.28 WW - _ 3 0.63 3.02 M 220 2.83 4 0.75 2.5 3 S 311 3.32 5 0.90 2.11 M 400 4.0 6 0.99 1.92 WW 331 4.36 7 1.09 1.74 W 422 4.90 8 1.16 1.64 M 333/511 5.20 9 1.26 1.51 M 440 5.66 10 1.32 1.44 VW 531 5.92 11 1.41 1.35 VW 620 6.32 12 1.47 1.29 W 533 6.56 13 1.55 1.23 VW 444 6.93 14 1.60 1.19 VW 551/711 7.14 Data p l o t t e d i n F i g . A10, D vs (hz + k 2 + l 2 ) ^ S lope M = K = 0.223 i n a o a c = 1.90 A° 0.223 L a t t i c e parameter a Q = 8.52 A° 98 - - 99 - T a b l e A l l . 304 S.C.C. In M g C l 2 + F e C l 3 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23579 camera c o n s t a n t K = 1.90 ins«A° l i n e D i n . dA° I V FeCv20k ( h k l ) Jh2 + k 2 + l 2 1 0.39 4.87 M 111 1.73 2 0.44 4.32 WW - - 3 0.515 3.70 W - — 4 0.635 2.99 M 220 2.83 5 0.71 2.68 W - _ 6 0.75 2.53 S 311 3.32 7 0.86 2.21 W - - 8 0.90 2.11 M 400 4.0 9 1.03 1.85 WW - - 10 1.1 1.73 W 422 4.9 11 1.17 1.62 M 511/333 5.2 12 1.27 1.50 M 440 5.66 13 •1.33 1.43 VW 531 5.92 14 :1.43 1.33 VW 620 6.32 15 1.47 1.29 W 533 6.56 16 1.56 1,22 VW 444 6.93 17 1.61 1.18 VW 711/551 7.14 Data p l o t t e d i n F i g . A l l , D vs ( h 2 + k 2 + l 2 ) ^ Slope M:= K = 0.225 i n a o a Q = 1.90 A 0 0.225 L a t t i c e parameter a Q = 8.44 A° - 100 - F i g . A l l . P l o t o f D vs ( h 2 + k 2 + l 2 ) " 5 from T a b l e A l l . D i f f r a c t i o n - p a t t e r n #23579, 304 s . c . c . i n MgCl2 + F e C l 3 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . _ 101 _ T a b l e A12. 304 S.C.C. i n M g C l 2 + F e C l 3 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23581 camera c o n s t a n t K = 1.90 ins«A° l i n e D i n . dA° I V F e C r 2 0 H ( h k l ) fh2 + k 2 + l 2 1 0.39 4.87 W 111 1.73 2 0.63 3.02 M 220 2.83 3 0.75 2.53 S 311 3.32 4 0190 2.11 M 400 4.0 5 1.1 1.73 VW 422 4.9 6 1.17 1.62 M 333/511 5.2 7 1.27 1.50 M-S 440 5.66 8 1.46 1.30 VW 533 6.56 9 1.57 1.21 VW 444 6.93 Data p l o t t e d i n F i g . A12, D vs ( h z + k 2 + l 2 ) Slope M = K = 0.225 i n a 0 = 1.90 A° 0.225 L a t t i c e parameter a Q = 8.44 A° - 102 - F i g . A12. P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A12. D i f f r a c t i o n p a t t e r n #23581, 304 s . c . c . i n MgCl2 + F e C l 3 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 103 - T a b l e A13. 316 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #23333 camera c o n s t a n t K = 1.93 ins-A° line D in. dA° I V F e C r 2 0 H . (hkl) / h ^ V k r + I 2 . 1 0.39 4.95 W 111 1.73 2 0.65 2,97 M 220 ' 2.83 3 0.76 2.54 S 311 3.32 4 0.92 2.10 M 400 4.00 5 1.00 1.93 WW 331 4.36 6 1.12 1.72 W 422 4.90 7 1.2 1.61 M 511/333 5.20 8 1.3 1.48 M 440 5.66 9 1.36 1.42 WW 531 '5.92 10 1.46 1,32 WW 620 6.32 11 1,51 1,28 M 533 6.56 12 1.60 1,21 W 444 6.93 13 1.64 1.18 W 711/551 7.14 Data p l o t t e d i n F i g . A13, D vs (h2 + k2 + 1 2 ) ^ Slope M = K = 0.231 i n a o a 0 = 1.93 A 0 0.231 L a t t i c e parameter a 0 = 8.36 A° - 104 - F i g . A13. P l o t o f D vs ( h 2 + k 2 + l 2 ) 2 from T a b l e A13. D i f f r a c t i o n p a t t e r n #23333, 316 s . c . c . i n MgCl2, o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . _ 105 _ T a b l e A14. 316 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #23329 camera c o n s t a n t K = 1.92 ins*A° l i n e D i n dA° I V F e C r 2 0 H ( h k l ) Jh2 + k 2 + l 2 1 0.40 4.8 M 111 1.73 2 0.46 4.17 WW - - 3 0.65 2.95 M 220 2.83 4 0.76 2.53 VS 311 3.32 5 0.92 2.09 S 400 4.0 6 1.01 1,91 WW 331 4.36 7 1.125 1.71 W 422 4.90 8 1.2 1,60 M 333/511 5.20 9 1.31 1,47 M 440 5.66 10 1.36 1.41 M 531 5.92 11 1.46 1,32 VW 620 6.32 12 1.51 1,27 W 533 6.56 13 1.59 1.21 VW 444 6.93 14 1.64 1.17 VW 551/711 7.14 Data p l o t t e d i n F i g . A14, D vs (hz + k 2 + l 2 ) " Slope M = K = 0.230 i n a o a Q= 1.92 A° 0.230 L a t t i c e parameter a Q = 8.35 A° - 106 - F i g . A14. P l o t o f D vs ( h 2 + k 2 + l2)^ from T a b l e A14. D i f f r a c t i o n p a t t e r n #23329, 316 s . c . c . i n MgCl2, o x i d e s t r i p p e d w i t h 1% bromine- methanol s o l u t i o n . - 107 - T a b l e A15. 316 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #22222 camera c o n s t a n t K = 1.91 i n s - A 0 l i n e D i n . dA° I V FeCr 2 0 i + ( h k l ) Jh2 + k 2 •+ l 2 , 1 0.39 4.90 M 111 1.73 2 0.43 4,44 VW - -3 0.53 3.60 VW - 4 0.64 2,98 M 220 2.83 5 0.70 2.73 WW - - 6 0.76 2.51 S 311 3.32 7 0.865 2.21 WW - -8 0.905 2.11 W 400 4.0 9 1.04 1,83 WW - - 10 1.115 1.71 VW 422 4.90 11 1.18 1,52 w. 333/511 5.20 12 1.285 1,49 s 400 5.66 13 1.32 1,45 VW - - 14 1.48 1.29 WW 620 6.32 15 1.52 1.26 WW 533 6.56 16 1.57 1.21 VW 444 6.93 T a t a p l o t t e d i n F i g . A15, D vs ( h 2 + k 2 + l 2 ) ^ Slope M = K = 0.230 i n a o a 0 = 1.91 A° .230 L a t t i c e parameter a 0 = 8.30 A° 108 - 109 - Table.A16. 316 S.C.C. i n MgCl 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23406 camera c o n s t a n t K = 1.91 ins«A 0 l i n e D i n . *• dA° I V F e C r 2 0 L t ( h k l ) Jh2 + k 2 + I 2 1 0.395 4.84 M 111 1.73 2 0.46 4.15 WW - - 3 0.525 3.64 M - - 4 0.56 3.41 WW - - 5 0.64 2.98 M 220 2.83 6 0.705 2.71 M - - 7 0.76 2.51 S 311 3.32 8 0.875 2.18 M - - 9 0.91 2.10 M 400 4.0 10 1.01 1.89 WW 331 4.36 11 1.05 1.82 W - - 12 1.12 1.71 W 422 4.90 13 1.18 1,62 M 511/333 5.20 14 1.29 1.48 M 440 5.66 Data p l o t t e d i n F i g . A16, D vs ( h 2 + k 2 + l 2 )' Slope M = K = 0.226 i n a 0 = 1.91 A° 0.226 L a t t i c e parameter a 0 = 8.45 A° - n o - F i g . A16. P l o t o f D vs ( h z + k 2 + l 2 ) 5 2 from T a b l e A16. D i f f r a c t i o n p a t t e r n #23406, 316 s . c . c . i n MgCl 2+ H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - I l l - T a b l e A17. 316 S.C.C. i n MgCl 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23407 camera c o n s t a n t K = 1.91 ins-A° l i n e D i n . dA° I V F e C ^ O ^ (hkl) J h 2 + k 2 + l 2 1 0.39 4.90 M 111 1.73 2 0.64 2.98 M 220 2.83 3 0.76 2.51 S 311 3.32 4 0.91 2.10 M 400 4.0 5 1.11 1.72 W 422 4.90 6 1.18 1.61 M 511/333 5.2 7 1.28 1.49 M 440 5.66 8 1.35 1.42 VW 531 5.92 9 1.43 1.34 VW 621 6.32 10 1.50 1.27 W 533 6.56 11 1.58 1.21 W 444 6.93 12 1.62 . 1.18 VW 551/711 7.14 Data p l o t t e d i n F i g . A17, D vs ( h 2 + k 2 + l 2 ) ' Slope M = K = 0.228 i n . a 0 = 1.91 A° 0.228 L a t t i c e parameter a Q = 8.38 A° - 112 - F i g . A17. P l o t o f D vs ( h 2 + k 2 + l 2 f t from T a b l e A17. D i f f r a c t i o n p a t t e r n #23407, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d wi 1% bromine-methanol s o l u t i o n - 113 Ta b l e A18. 316 S.C.C. i n MgCl 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23404 camera c o n s t a n t K = 1.91 i n s . A 0 l i n e D i n . dA° I V F e C r 2 0 L t ( h k l ) </h2 + k 2 + I 2 1 0.385 4.96 M 111 1.73 2 0.45 4.24 WW - — 3 0.64 2.98 M 220 2.83 4 0.745 2.56 S 311 3.32 5 0.785 2.43 w 222 3.46 6 0.90 2.12 M 400 4.0 7 0.985 1,94 WW 331 4.36 8 1.02 1.88 WW - - 9 1.1 1.74 W 422 4.90 10 1.17 1,63 M 511/333 5.2 11 1.28 1,49 M 440 5.66 12 1.34 1.43 VW 531 5.92 13 1.42 1.34 VW 620 6.32 14 1.48 1.29 W 533 6.56 15 1.56 1.22 W 444 6.93 Data p l o t t e d i n F i g . A18, D vs ( h 2 + k 2 + l2)"' Slope M = K = 0.226 i n . a ° a 0 = 1.91 A° 0.226 L a t t i c e parameter a Q = 8.45 A° - 114 - F i g . A18. P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ f r o m T a b l e A18. D i f f r a c t i o n p a t t e r n #23404, 316 s . c . c . i n M g C l 2 + H C l , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 115 - T a b l e A19. 316 S.C.C. i n MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23483 camera c o n s t a n t K = 1.80 ins*A° l i n e - D i n . dA° I V FeCr^Q, ( h k l ) / h 2 + k2 + 12 j 1 0.365 4.93 M 111 1.73 2 0.60 3.0 ' M 220 2.83 3 0.70 2,57 S 311 3.32 4 0.80 2.25 VW - - 5 0.845 2.13 M 400 4.0 6 0.94 1.92 WW 331 4.36 7 1.04 1.73 W 422 4.90 8 1.1 1.64 M 511/333 5.2 9 1.15 1.57 WW - - 10 1.25 1,44 WW 531 5.92 11 1,25 1,44 WW 531 5.92 12 1.34 1.34 VW 620 6.32 • 13 ; 1.39 1.30 W 533 6.56 14 1.45 1.24 VW 4.44 6.93 15 1.52 1.18 VW 551/711 7.14 Data p l o t t e d i n F i g . A19, D vs ( h 2 + k 2 + 1*)' Slope M = K = 0.212 i n . a 0 = 1.80 A° 0.212 L a t t i c e parameter a Q = 8.49 A° - 116 - (h2* k2 • I2 )i F i g . A19. P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A19. D i f f r a c t i o n p a t t e r n #23483, 316 s . c . c . i n M g C l 2 + C o C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n - 117 - T a b l e A20. 316 S.C.C. i n MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n . • p a t t e r n -#23472 camera c o n s t a n t K = 1.80 ins«A° ' l i n e D i n . dA° I V FeCr20it (hkl) J h 2 + k 2 + I 2 1 0.365 4.93 M 111 1.73 2 0.60 3.0 M 220 2.83 3 0.71 2.54 S 311 3.32 4 0.86 2.09 M 400 4.0 5 1.04 1.73 W 422 4.9 6 1.09 1.65 W 511/333 5.2 7 1.20 1,50 M 440 5.66 8 1.40 1.29 W 533 6.56 9 1.47 1.22 W 444 6.93 10 1.64 1.10 w 553/731 7.68 11 1.71 1.05 w 800 8.0 Data p l o t t e d i n F i g . A20, D vs ( h 2 + k 2 + I 2 ) Slope M = K = 0.213 i n . a D = 1.80 A° 0.213 L a t t i c e parameter a D = 8.45 A° - 118 - F i g . A20. P l o t o f D vs ( h 2 + k 2 + l 2 ) * 5 from T a b l e A20. D i f f r a c t i o n p a t t e r n #23472, 316 s . c . c . i n M g C l 2 + C o C l 2 . o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n > - 119 - T a b l e A21. 316 S.C.C. i n MgCl 2 + C o C l 2 , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23474 camera c o n s t a n t K =1.82 ins*A° • l i n e D i n . dA° I V F e C r a O i ^ ( h k l ) Jh 2 + k 2 + l 2 1 0.365 4.99 M 111 . 1.73 2 0.60 3,03 M 220 2.83 . 3 0.70 2,6 S 311 3.32 4 0.74 2.46 W 222 3.46 5 0.85 2.14 M 400 4.0 6 0.92 1.98 VW 331 4.36 7 1.04 1,75 W 422 4.90 8 1.10 1.65 M 511/333 5.20 9 1.20 1,52 M 440 5.66 10 1.255 1.45 VW 531 5.92 11 1,34 1,36 VW 620 6.32 12 1.40 1,30 W 533 6.56 13 1,47 1.24 W 444 6.93 14 1.51 1.21 VW 711/551 7.14 Data p l o t t e d i n F i g . A21, D vs ( h 2 + k 2 + l 2 ) h Slope M = K_ = 0.212 i n . a o a D = 1.82 A° 0.212 L a t t i c e parameter a 0 = 8.58 A 0 - 12Q - (h** k2* I* )* F i g . A21. P l o t o f D vs ( h 2 + k 2 + l 2 ) ^ from T a b l e A21. D i f f r a c t i o n p a t t e r n #23474, 316 s . c . c . i n M g C l 2 + C o C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 121 - Ta b l e A22. 310 S.C.C. i n MgCl, , Oxide S t r i p p e d w i t h 1% Bromine-Methanol S o l u t i o n p a t t e r n #22205 camera c o n s t a n t K = 1.91 ins-A° • l i n e D i n . dA° I V FeCrgO^ ( h k l ) Jh2 + k 2 + l 2 1 0.39 4.9 M 111 1.73 2 0.52 3.68 VW - _ 3 0,64 2.98 W 220 2.83 4 0.72 2.66 VW - _ 5 0.75 2.55 S 311 3.32 6 0.86 2.22 VW - _ 7 0.91 2.10 M 400 4.0 8 1.04 1.84 VW - -9 1.13 1.69 VW 422 4.9 10 1.18 1,62 W 333/511 5.2 11 1.29 1,48 M 440 5.66 1 12 1.27 1.30 VW 533 6.56 Data p l o t t e d i n F i g . A22, D vs ( h 2 + k 2 + l 2 f2 Slope M = K » 0.227 i n . a D = 1.91 A° 0.227 L a t t i c e parameter a D = "8.41 A° - 122 - F i g . A22. P l o t o f D vs ( h 2 t k 2 + l 2 ) ' 5 from T a b l e A22. D i f f r a c t i o n p a t t e r n #22205, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 123 - T a b l e A2 3. 310 S.C.C. i n MgClg , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22200 camera c o n s t a n t K = 1.88 ins»A 0 l i n e D i n . dA° I V F e C r 2 Ck ( h k l ) Jh2 + k 2 + l 2 , 1 0.39 4.82 M 111 1.73 2 0.42 4.48 Dots - 0 3 0.54 3.48 Dot a - -4 0.635 2.96 S 220 2.83 5 0.74 2.54 S 311 3.32 6 0.79 2.38 Dots 222 3.46 7 0.89 2.11 VW 400 4.0 8 0.98 1.92 VW 331 4.36 9 1.11 1,70 WW 422 4.9 10 1.17 1.61 W 333/511 5.2 11 1.27 1.48 VW 440 5.66 12 1.335 1.41 VW 531 5.92 13 1.42 1.32 Dots 620 6.32 , 14 1.47 1,29 Dots 533 6.56 15 1.56 1.21 Dots 444 6.93 Data p l o t t e d i n F i g . A23, D vs ( h 2 + k 2 + l 2 f2 Slope M = K = 0.225 i n . a o a Q = 1.88 A° 0.225 L a t t i c e parameter a D = 8.36 A° _ 124 _ ( h 2 * k 2 * I2 )£ F i g . A23. P l o t o f D vs ( h 2 + k 2 + l 2 ) 2 from T a b l e A23. D i f f r a c t i o n p a t t e r n #22200, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 125 - T a b l e A24. 310 S.C.C. i n MgCl, , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #22196 camera c o n s t a n t K = 1.88 ins«A° l i n e D i n . dA° I V F e C r 2 0 l t ( h k l ) Jh2 + k 2 + l 2 1 0.395 4.76 M 111 1.73 2 0.52 3,62 VW - - 3 0.64 2.94 W 220 2.83 4 0.72 2,61 WW - - 5 0.75 2.51 S 311 3.32 6 0.86 2,19 WW - - 7 0.915 2,06 S 400 - 4.0 8 0.98 1.92 WW 331 4.36 9 1,04 1,81 WW - - 10 1.11 1.69 VW 422 4.90 11 1.18 1.59 w 511/333 5.2 12 1.275 1,47 M 440 5.66 13 1.325 1.42 VW 531 5.92 14 1.47 1.28 VW 533 6.56 15 1.57 1.20 VW 444 6.93 Data p l o t t e d i n F i g . A24, D vs ( h 2 + k 2 + l2)h Slope M = K = 0.225 i n . a o a G = 1.88 A° 0.225 L a t t i c e parameter a Q = 8.36 A° - 126 - F i g . A24. P l o t o f D vs ( h 2 + k 2 + l 2 ) ' 2 from T a b l e A24. D i f f r a c t i o n : p a t t e r n #2219.6, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 127 - T a b l e A25. 310 S.C.C. i n MgClg , Oxide S t r i p p e d w i t h C e l l u l o s e A c e t a t e p a t t e r n #23146 camera c o n s t a n t K = 2,28 ins-A° • l i n e D i n . dA° I V F e C r 2 0 4 ( h k l ) Jh2 + k2 + l2 1 0.465 4.90 M 111 1.73 2 0.64 3.56 WW - - 3 6.76 3,00 M 220 2.83 4 0.90 2.53 S 311 3.32 5 1.09 2.09 M 400 4.0 6 1.22 1,87 Dots 331 4.36 7 1.325 1,72 W 422 4.9 8 1,41 1,-62 M 511/333 5.2 9 1.54 1.48 M 440 5.66 10 1.61 1.42 W 531 5.92 11 1.72 1.33 WW 620 6.32 12 1.78 1,28 W 533 6.56 13 1.885 1.21 VW 444 6.93 14 1.95 1.17 VW 551/711 7.14 Data p l o t t e d i n F i g . A 25, D vs ( h 2 + k 2 + l 2 f' Slope M = K = 0.272 i n . a Q = 2.28 A° 0.272 L a t t i c e parameter a c = 8.38 A° - 12§ -- - 129 - T a b l e A26._ 310 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h C e l l u l o s e A c e t a t e p a t t e r n #23124 camera c o n s t a n t K = 2.31 ins-A° l i n e D i n . dA° I V F e C r 2 0 4 ( h k l ) Jh2 + k 2 + l 2 1 0.475 4.86 M 111 1.73 ' 2 0.545 4.24 Dots - - 3 0.63 3.67 Dots - -4 0.78 2.96 M 220 2.83 5 0.905 2.55 S 311 3.32 6 1.1 2.10 M 400 4.0 7 1.26 1.83 Dots - - 8 1.34 1.72 W 422 4.9 9 1.43 1.62 M 511/333 5.2 10 1.56 1.48 M 440 5.66 11 1.62 1.43 Dots 531 5.92 12 1.74 1,33 Dots 620 6.32 ' 13 1.80 1.28 W 533 6.56 Data p l o t t e d i n F i g . A26, D vs ( h 2 + k 2 + l 2 ) h Slope M = K = 0.275 i n . a 0 = 2.31 A° 0.275 L a t t i c e parameter a Q •= 8.40 A 0 - 130- - F i g . A26. P l o t o f D vs ( h 2 + k 2 + l 2 ) " 1 from T a b l e A26. D i f f r a c t i o n , p a t t e r n #23124, 310 s . c . c . i n M g C l 2 , o x i d e s t r i p p e d w i t h c e l l u l o s e a c e t a t e - 131 - T a b l e A27. 310 S.C.C. i n M g C l 2 , Oxide S t r i p p e d w i t h C e l l u l o s e A c e t a t e p a t t e r n #23403 camera c o n s t a n t K = 2.28 ins«A° l i n e D i n . dA° I V YeCr20k ( h k l ) Jh 2 + k 2 + l 2 1 0.465 4.90 M 111 1.73 2 0.53 4,-30 Dots - -3 0.76 3.00 M •220 2.83 4 0.89 2.56 S 311 3.32 5 0.935 2.44 W 222 3.46 6 1.08 2.11 M 400 4.0 7 1,17 1.-95 Dots 331 4.36 8 1.33 1,-71 W 422 '4.9 9 1.41 1.62 M 511/333 5.2 10 1.54 1.48 • M 440 5.66 11 1.59 1,43 WW 531 5.92 12 1,72 1,-33 WW 620 6.32 13 1.78 1.28 VW 533 6.56 14 1.84 1.24 WW 444 6.93 Data p l o t t e d i n F i g . A27, D vs ( h 2 + k 2 + l 2 )' Slope M = K = 0.270 i n . a o a 0 = 2.28 A° 0.270 L a t t i c e parameter a D = 8.44 A° - 132: - 133 - Ta b l e A28. 310 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23418 camera c o n s t a n t K = 1.91 ins'A° l i n e D i n . dA° I V FeCr^O^ ( h k l ) / h 2 + k 2 + l 2 1 0.40 4.78 S 111 1.73 2 0.53 3.60 Dots - - 3 0.65 2.94 M 220 2.83 4 0.77 2.48 VS 311 3.32 5 0.92 2.08 S 400 4.0 6 1.00 1.91 W 331 4.36 7 . 1,06 1,80 Dots - - 8 1,14 1.68 W 422 4.9 9 1.2 1,60 M 511/333 5.2 10 1,31 1,46 S 440 5.66 11 1,37 1,39 W 531 5.92 12 1.46 1.30 VW 620 6.32 ' 13 1.51 1,26 w 533 6.56 14 1.6 1.2 M 444 6.93 15 1.65 1.16 W 711/551 7.14 Data p l o t t e d i n F i g . A28, D vs ( h 2 + k 2 + l 2 X s Slope M = K = 0.231 i n . a 0 = 1.91 A 0 0.231 L a t t i c e parameter a Q = 8.27 A° - 134 A28. P l o t of D vs ( h 2 +. k 2 + l 2 ) " 2 from Table A28.' D i f f r a c t i o n p a t t e r n #23418, 310 s.c.c. i n MgCl 2 + HCl, oxide s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 135 - T a b l e A29. 310 S.C.C. i n M g C l 2 + H C l , Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23417 camera c o n s t a n t K = 1.91 i n s - A 0 l i n e D i n . dA° I V FeCrgC^ ( h k l ) t/h 2 + k 2 + 12 1 0.40 4.78 S 111 ' .1.73 2 0.66 2.90 M 220 2.83 3 0.77 2.48 VS 311 3.32 4 0.92 2.08 S 400 4.0 5 1.01 1.89 VW 331 4.36 6 1.15 1.66 VW 422 4.9 7 1.2 1.60 M 511/333 5.2 8 1.31 1,46 S 440 5.66 9 1.36 1.40 VW 531 5.92 10 1.52 1.26 W 533 6.56 11 1.61 1.19 W 444 6.93 12 1.66 1.15 W 711/551 7.14 Data p l o t t e d i n F i g . A29, D vs ( h 2 + k 2 + l 2 )' Slope M = K = 0.232 i n . a o a 0 = 1.91 A° 0.232 L a t t i c e parameter a D = 8.23 A 0 - 13.6 - - 137 - T a b l e A30. 310 S.C.C. i n M g C l 2 +CoCl 2,Oxide S t r i p p e d w i t h 1% Bromine- Methanol S o l u t i o n p a t t e r n #23488 camera c o n s t a n t K = 1.85 ins«A° • l i n e D i n . dA° 1 F e C r 2 0 1 + ( h k l ) / h 2 + k 2 + I 2 1 0.375 4.93 M H I 1.73 2 0.47 3.94 VW - - 3 0.61 3.03 VW 220 2.83 4 0.73 2.53 s 311 3.32 5 0.875 2.11 s 400 4.0 6 1.04 1.78 Dots - - 7 1.13 1.64 VW 511/333 5.2 8 1.23 1.50 M 440 5.66 9 1.42 1,30 WW 533 6.56 , 10 1.50 1,23 W 444 6.93 11 1.72 1.08 W 553/731 7.68 Data p l o t t e d i n F i g . A30, D vs ( h 2 + k 2 + l 2 )' Slope M = K = 0.219 i n . a o a Q = 1.85 A° 0.219 L a t t i c e parameter a Q = 8.45 A° - 138 _ F i g . A30. P l o t o f D vs ( h 2 + k 2 + l 2 ) 2 from T a b l e A30. D i f f r a c t i o n p a t t e r n #23488, 310 s . c . c . i n MgCl2 + C0CI2, o x i d e s t r i p p e d w i t h 1% bromine-methanol s o l u t i o n . - 139 - APPENDIX B Appendix B c o n t a i n s examples o f x - r a y spectrum t a k e n from f r a c t u r e s u r f a c e o x i d e s of. t h e d i f f e r e n t a l l o y s s t r e s s c o r r o d e d i n t h e v a r i o u s hot c h l o r i d e environments. The o x i d e s were s t r i p p e d w i t h a 1% bromine- methanol s o l u t i o n and examined i n t h e s c a n n i n g e l e c t r o n m i c r o s c o p e a t a gun v o l t a g e o f 20 kv. A l l spectrum n o r m a l i s e d t o t h e chromium Kct peak. - 140 - o 1.00,- 0.75 to I- z ZD o u Q 0.50 N - I < 0.25L 0.00 o 00. o o I ft 1 j . 5.0 5.5 6.0 E N E R G Y KeV 6.5 7.0 7.5 8.0 F i g - B l . S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f type 304 s t r e s s c o r r o d e d i n MgCl2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n . - 141 - F i g . B2. S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o,*ide o f t y p e 304 s t r e s s c o r r o d e d i n M g C l 2 + H C l s o l u t i o n s t r i p p e d w i t h bromine-methanol s o l u t i o n . - 142 - F i g . B3. S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e . o f type 304 s t r e s s c o r r o d e d i n MgCl2 + C0CI2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n . - 143 - F i g - B4. S.E.M. x-ray spectrum from f r a c t u r e surface oxide of type 316 s t r e s s corroded i n MgCl 2 s o l u t i o n . S t r i p p e d w i t h bromine- methanol s o l u t i o n . - 144 - 5.0 5.5 6.0 6.5 7.0 7.5 8.0 ENERGY KeV F i g . B5. S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f type 316 s t r e s s c o r r o d e d i n M g C l 2 + HCl s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n . - 145 - ENERGY KeV F i g - B6. S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f type 316 s t r e s s c o r r o d e d i n M g C l 2 + C o C l 2 s o l u t i o n . S t r i p p e d w i t h bromine- methanol s o l u t i o n . - 146 - * * * * 5,0 5.5 6.0 6.5 7.0 7.5 8.0 ENERGY K eV F i g . B 7 . S.E.M. x - r a y spectrum from f r a c t u r e s u r f a c e o x i d e o f t y p e 310 s t r e s s c o r r o d e d i n M g C l 2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n . - 147 - o 03. o 03. a 5.0 5.5 6.0 6.5 7.0 7.5 8.0 ENERGY KeV F i g - B8. S.E.M. x-ray spectrum from f r a c t u r e s u r f a c e o x i d e o f t y p e 310 s t r e s s c o r r o d e d i n M g C l 2 +.HC1 s o l u t i o n . S t r i p p e d w i t h bromine- methanol s o l u t i o n . - 1 4 8 - si ENERGY KeV F i g . B9. S . E . M . x-ray spectrum .from f r a c t u r e s u r f a c e o x i d e o f type 310 s t r e s s c o r r o d e d i n MgCl2 + C0CI2 s o l u t i o n . S t r i p p e d w i t h bromine-methanol s o l u t i o n .

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
United States 2 1
China 1 0
City Views Downloads
Ashburn 2 0
Beijing 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}

Share

Share to:

Comment

Related Items