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Deformation of compacts of magnesium hydroxide during dehydroxylation Sunderland, Philip William 1970

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DEFORMATION O F C O M P A C T S O F MAGNESIUM HYDROXIDE DURING DEHYDROXYLATION  PHILIP WILLIAM SUNDERLAND, P. E N G . B. A. Sc. , UNIVERSITY O F BRITISH COLUMBIA 1965  A THESIS S U B M I T T E D IN P A R T I A L F U L F I L M E N T O F T H E REQUIREMENTS O F T H E D E G R E E O F M A S T E R O F A P P L I E D SCIENCE  in the Department of METALLURGY  We accept this thesis as conforming to the standard required from candidates for the degree of Master of Applied Science  Members of the Department of Metallurgy T H E UNIVERSITY O F BRITISH COLUMBIA August, 1970  In  presenting  this  an a d v a n c e d d e g r e e the L i b r a r y I  further  for  of  at  the U n i v e r s i t y  agree  written  thesis  freely  that permission  for  It  financial  Date  SclPT  Zl j  H7P..  of  Columbia,  British  by  for  gain shall  Columbia  the  requirements  reference copying  of  I agree and this  that  not  copying  or  for  that  study. thesis  t h e Head o f my D e p a r t m e n t  is understood  tM£THU.Urt 6-V  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  of  for extensive  permission.  Department o f  fulfilment  available  p u r p o s e s may be g r a n t e d  representatives.  this  in p a r t i a l  s h a l l make i t  scholarly  by h i s  thesis  or  publication  be a l l o w e d w i t h o u t  my  ABSTRACT  T h e d e f o r m a t i o n b e h a v i o u r of p o l y c r y s t a l l i n e c o m p a c t s of Mg(OH)2 d u r i n g d e h y d r o x y l a t i o n has b e e n s t u d i e d i n an attempt to e v a l u a t e the n a t u r e of s t r a i n that c a n be i n t r o d u c e d i n t o the c o m p a c t d u r i n g the r e a c t i o n .  A s t u d y of n e c k - g r o w t h b e t w e e n t i p s of s i n g l e  c r y s t a l s of Ca(OH)-, a n d b e t w e e n two h e m i s p h e r i c a l t i p s of Mg(OH),, c o m p a c t s s h o w e d b o t h d e f o r m a t i o n a n d i n t e r a c t i o n at the c o n t a c t p o i n t d u r i n g the d e h y d r o x y l a t i o n r e a c t i o n .  L o a d - d e p e n d e n t d e f o r m a t i o n of  the c o m p a c t s gave a t o t a l s t r a i n p r o p o r t i o n a l t o the o n e - t h i r d p o w e r of the a p p l i e d s t r e s s .  T h e c r e e p d e f o r m a t i o n of M g ( O H ) 2  compacts  d u r i n g d e h y d r o x y l a t i o n was a l s o studied under i s o t h e r m a l conditions. T h e o v e r a l l c r e e p b e h a v i o u r c a n be d i v i d e d i n t o t h r e e s t a g e s . i n i t i a l s t a g e i s i n i t i a t e d b y the d e h y d r o x y l a t i o n r e a c t i o n .  The  D u r i n g the  s e c o n d o r s t e a d y state c r e e p s t a g e the h i g h e s t c r e e p r a t e w a s o b t a i n e d . T h e s t e a d y state c r e e p r a t e w a s d e t e r m i n e d  a s a f u n c t i o n of t e m p e r -  a t u r e . p r e s s u r e , a n d r e l a t i v e d e n s i t y of the g r e e n c o m p a c t .  The  results are represented by: A e_  °  +  cr  ?  e  x  P  ( \  -17500 R T  J \  t  P a r t i c l e s l i d i n g w a s c o n s i d e r e d t o be the m o s t p r o b a b l e f o r c r e e p d u r i n g the s e c o n d stage.  - 1  mechanism  ii  ACKNOWLEDGEMENTS  The author  w i s h e s t o a c k n o w l e d g e the a s s i s t a n c e a n d  encouragement generously  g i v e n b y D r . A . C. D. C h a k l a d e r a n d  others throughout this work.  T h a n k s a r e a l s o extended to the  f a c u l t y a n d s t a f f of the D e p a r t m e n t of M e t a l l u r g y f o r t h e i r a d v i c e . Financial assistance provided by Clayburn-Harbison the f o r m of a F e l l o w s h i p i s g r a t e f u l l y a c k n o w l e d g e d .  Co. L t d . i n  iii TABLE OF CONTENTS Page Introduction  I 1. 1  1 Reactive Hot P r e s s i n g  1  1. 1. 1  Hypotheses for Reactive Hot P r e s s i n g  2  1. 1. 2  T h e o r i e s of H o t P r e s s i n g  4  1. 2  O b j e c t i v e s of t h i s I n v e s t i g a t i o n  6  1. 3  C h o i c e of E x p e r i m e n t a l S y s t e m  8  1. 4  Properties  9  1. 4. 1  P h y s i c a l and C h e m i c a l P r o p e r t i e s  1. 4. 2  S t r u c t u r a l A s p e c t s of the  1. 4. 3 II  of the E x p e r i m e n t a l S y s t e m  Decomposition  11  K i n e t i c s of D e c o m p o s i t i o n  18  Experimental 2. 1  9  20  Apparatus  20  2. 1. 1  F u r n a c e and L o a d F r a m e  20  2. 1. 2  Vacuum System  23  2. 1. 3  Photography  23  2. 1. 4  L o a d i n g and D i s p l a c e m e n t Measurement Furnace Temperature Control  24  and P o w e r Supply  25  E x p e r i m e n t a l Technique  26  G r o w t h of C a ( O H ) z Single C r y s t a l s  26  2. 1. 5  2. 2 2. 2. 1  (Portlandite)  Page 2. 2. 2  2. 2. 3  2. 2. 4  E x p e r i m e n t s on T i p t o T i p Contact  28  A.  28  Ca(OH)2 C r y s t a l s  P r e p a r a t i o n of Mg(OH);? C o m p a c t s  30  B.  30  Mg(OH)2 Compacts  D e f o r m a t i o n of M g ( O H ) Cylindrical Compacts  2. 2. 5  Temperature  2  33  Distribution  in Specimens III  37  Results  40  3. 1  C a l c i u m Hydroxide Single C r y s t a l s  40  3. 2  T i p to T i p C o n t a c t of M a g n e s i u m Hydroxide Compacts  40  3. 3  D e f o r m a t i o n of M a g n e s i u m  3. 3. 1 3. 3. 2  Hydroxide Compacts  42  U n i f o r m Heating Rate  42  11  Isothermal" D e f o r m a t i o n (Creep) (a) (b)  E f f e c t s of T e m p e r a t u r e on D e f o r m a t i o n E f f e c t of S t r e s s at  IV  51  Constant  and T e m p e r a t u r e (c)  47  E f f e c t of G r e e n D e n s i t y  51 51  Discussion 4.1  Shrinkage V e r s u s Creep  57  4. 2  Weight L o s s V e r s u s C r e e p  59  iv  V  Page 4. 3  S t a g e s of C r e e p  59  4. 4  C r e e p Rate  66  4. 4. 1  E f f e c t of T e m p e r a t u r e  66  4. 4. 2  Stress Dependence  69  4. 4. 3  Density Dependence  69  Total Creep Strain  75  4. 5. 1  E f f e c t of T e m p e r a t u r e  75  4. 5. Z  E f f e c t of S t r e s s  77  4. 5, 3  E f f e c t of D e n s i t y  77  4. 5. 4  Phenomenological Behaviour  82  Postulated  83  4. 5  4. 6 4. 6, 1  4. 6. Z  4. 6. 3  4 6. 4  Physical  Mechanisms  Changes  of C r e e p  Accompanying  Dehydroxylation  83  Activation Energies Concurrent Processes  84  Viscous F l o w and G r a i n Boundary Sliding  85  Possible  M e c h a n i s m s of  Deformation  86  4. 6. 4. 1  Slip M e c h a n i s m s  87  4.6.4,2  Stacking Rearrangement  88  V  S u m m a r y and Conclusions  90  VI  Suggestions  93  for Future  Work  Page VII  Appendices I  Temperature Distribution Within the C y l i n d r i c a l  VIII  Specimen  94  II  C r e e p Data - I s o t h e r m a l Conditions  97  III  A c c u r a c y of the T h e r m a l E x p a n s i o n Correction  115  Bibliography  118  Publications: 1)  P . W. Sunderland and A . C . D . C h a k l a d e r , M a t . R e s . B u l l . , 2, 1111-1118 (1967).  2)  P . W. Sunderland and A . C . D . C h a k l a d e r , C e r a m . S o c , 52_ , 410-414 (1969).  J. A m .  vii LIST O F  FIGURES  NO. 1  PAGE C o m p a c t i o n of M g ( O H ) 2 a s f u n c t i o n of temperature. (After C h a k l a d e r and C o o k ^ and M o r g a n and Sc a l a ( )  7  2  2  a)  b)  S t r u c t u r e of M g ( O H ) 2 - S c h e m a t i c rep re sentation S t r u c t u r e of M g O  - Schematic  12  r e p r e s e n t a t i o n ... 12  (13) 3  Goodman's  ' p r o p o s e d m e c h a n i s m f o r the de-  v  hydroxylation, 0- p l a n e s 4  showing  c o l l a p s e n o r m a l to the  i n the f o r m a t i o n  B a l l and T a y l o r ' s  of p e r i c l a s e  proposed inhomogeneous  m e c h a n i s m f o r the d e h y d r o x y l a t i o n , donor and acceptor of M g 5  +  +  15  regions,  showing  a n d the d i f f u s i o n  a n d H+  17  S c h e m a t i c r e p r e s e n t a t i o n of the  experimental  apparatus  21  6  The  loading frame,  7  The  a p p a r a t u s u s e d f o r g r o w i n g C a ( O H ) 2 c r y s t a l s . . . 27  8  Time-temperature  s h o w i n g the t h e r m o c o u p l e s  p r o f i l e u s e d f o r the d e c o m p o -  s i t i o n of C a ( O H ) 2 t i p s a n d f o r u n i f o r m  heating  rate e x p e r i m e n t s  29  9  E l e c t r o n m i c r o g r a p h of M g ( O H )  10  R e l a t i v e density obtained i n g r e e n compacts of M g ( O H ) 2 >  11  versus  2  powder  pressure. .  S p e c i m e n s u r f a c e t e m p e r a t u r e as a f u n c t i o n of t i m e f o r the " i s o t h e r m a l "  t e s t s at f o u r 36  S p e c i m e n surface and centre t e m p e r a t u r e s f o r two d i f f e r e n t " i s o t h e r m a l "  13  . . . 31  34  different temperatures . 12  22  conditions . . .  .39  G r o w t h of c o n t a c t a r e a d u r i n g d e c o m p o s i t i o n of C a ( O H ) 2 t i p s u n d e r l o a d  :.  41  viii LIST. O F F I G U R E S  - continued  NO. 14  PAGE G r o w t h of c o n t a c t a r e a d u r i n g d e c o m p o s i t i o n of M g ( O H ) 2 c o m p a c t t i p s u n d e r l o a d  15  43  E v i d e n c e of b o n d f o r m a t i o n d u r i n g t h e t i p - t o - t i p c o n t a c t s h o w n i n F i g u r e 14 a)  c r a t e r i n one t i p  b) m a t e r i a l r e m o v e d f r o m t h e c r a t e r a d h e r e i n g to the 16  other tip  44  F a m i l y of D e f o r m a t i o n - t i m e c u r v e s f o r experiments heating rate,  u n d e r v a r i o u s l o a d s at a u n i f o r m s h o w i n g the m e t h o d of m e a s u r i n g  the t o t a l d e f o r m a t i o n (e  )  T  17  18  T o t a l : d e f o r m a t i o n a s a f u n c t i o n of l o a d ( u n i f o r m h e a t i n g rate) . . Log-Log  T e m p e r a t u r e , deformation and s y s t e m p r e s s u r e s versus time f o r a typical isothermal" run 11  20  49  50  D e f o r m a t i o n v e r s u s t i m e f o r s p e c i m e n s of 0. 50 r e l a t i o n d e n s i t y , at " i s o t h e r m a l " t e m p e r a t u r e s as shown.  21  48  p l o t of t o t a l d e f o r m a t i o n a s a f u n c t i o n  of l o a d ( u n i f o r m h e a t i n g r a t e ) . 19  45  S t r e s s 6. 0 k g / c m ^  52  D e f o r m a t i o n v e r s u s t i m e f o r s p e c i m e n s of 0. 50 r e l a t i v e d e n s i t y , at " i s o t h e r m a l " t e m p e r a t u r e s a s shown.  S t r e s s 13. 6 k g / c m ^  53  22  D e f o r m a t i o n v e r s u s t i m e f o r s p e c i m e n s of 0. 50 r e l a t i v e d e n s i t y , at 3 6 0 ° C , f o r s t r e s s e s a s s h o w n . . . 54  23  D e f o r m a t i o n v e r s u s t i m e f o r s p e c i m e n s of v a r i o u s r e l a t i v e d e n s i t i e s a s shown, at 9. 25 kg/ cm^  56  24  Creep,  60  25  S t a g e s of C r e e p  weight l o s s and shrinkage v e r s u s t i m e  61  LIST O F FIGURES  - continued  NO. 26  PAGE Deformation  and S y s t e m p r e s s u r e .  versus time 27  Deformation  ,  63  and S y s t e m p r e s s u r e  versus time 28  Arrhenius  64  - t y p e p l o t of c r e e p  rate  versus temperature  67  29  S t r e s s d e p e n d e n c e of m a x i m u m c r e e p r a t e  70  30  D e n s i t y d e p e n d e n c e of m a x i m u m c r e e p r a t e  73  31  Total strain versus temperature  76  32  Total strain versus stress  78  33  L o g - L o g p l o t of t o t a l s t r a i n v e r s u s  34  T o t a l s t r a i n v e r s u s d e n s i t y . ...  80  35  Total strain versus  81  36  Theoretical temperature  stress  l/c» d i s t r i b u t i o n i n the  s p e c i m e n s for i s o t h e r m a l creep tests 37  79  C o m p a r a t i v e v a l u e s of the  96  deformation  m e a s u r e d b y the n o r m a l a p p a r a t u s a n d a travelling microscope  117  x LIST O F  TABLES  NO. I II  III IV V VI  PAGE P r o p e r t i e s of M g ( O H )  2  and MgO  10  S u m m a r y of M e c h a n i s m s a n d K i n e t i c s of M g ( O H ) 2 Dehydroxylation  13  D e f o r m a t i o n D a t a f o r U n i f o r m H e a t i n g Rate.  46  Temperature  68  D e p e n d e n c e of I s o t h e r m a l C r e e p  S t r e s s D e p e n d e n c e of I s o t h e r m a l C r e e p  71  D e n s i t y D e p e n d e n c e of I s o t h e r m a l C r e e p  74  -1CHAPTERI 1.  Introduction  1. 1  R e a c t i v e Hot  Pressing  Several workers i n g of the d e c o m p o s i b l e the d e c o m p o s i t i o n process  utilizes  _  c o m p o u n d s s u c h as Mg(OH)2>  etc. d u r i n g  r e a c t i o n results i n high density products.  a transient  c a l d e c o m p o s i t i o n (^ ~4) to o b t a i n d e n s e ,  h a v e r e c e n t l y ( 1 4 ) s h o w n t h a t the hot p r e s s -  11  reactivity" resulting f r o m either  or a p o l y m o r p h i c  high strength  c e r a m i c b o d i e s at c o m p a r a t i v e l y l o w  T h e p r o c e s s h a s a l l the a d v a n t a g e s  and  10,000 p s i .  of c o n v e n t i o n a l hot p r e s s i n g : l o w  p o r o s i t y a n d h e n c e h i g h s t r e n g t h i n the p r o d u c t , f i n e g r a i n r e c r y s t a l l i z a t i o n and g r a i n growth  w e l l as r e q u i r i n g  chemi-  phase t r a n s f o r m a t i o n  t e m p e r a t u r e s and p r e s s u r e s , u s u a l l y b e i o w 1 0 0 0 ° C  t i v e l y low t e m p e r a t u r e s ,  The  are minimized  size since  by the c o m p a r a -  a n d a c c u r a t e d i m e n s i o n s of the p r o d u c t , as  l o w e r t e m p e r a t u r e s a n d h o l d i n g t i m e s t h a n the  c o n v e n t i o n a l hot p r e s s i n g p r o c e s s . T h e p r o c e s s h a s b e e n a p p l i e d to m a n y c e r a m i c C h a k l a d e r and  systems.  McKenzie (4) p r e s s e d s e v e r a l n a t u r a l c l a y s as w e l l as  s y n t h e t i c h y d r o x i d e s of a l u m i n u m z i r c o n i a was  and m a g n e s i u m .  Unstabilized  d e n s i f i e d ^ ^ b y c y c l i n g i t t h r o u g h the m o n o c l i n i c  i ^ = = = = * » t e t r a g o n a l p h a s e t r a n s f o r m a t i o n , a n d up to 99. 8 % of t h e o 860°C r e t i c a l d e n s i t y was  obtained.  p r o d u c t i o n of c e r m e t s low t e m p e r a t u r e  A n o t h e r a p p l i c a t i o n ^ ) was  of a l u m i n a  with iron,  to the  copper and c h r o m i u m .  r e q u i r e d f o r the d e c o m p o s i t i o n of b o e h e m i t e  The  (600°C)  -2r e s u i t e d i n a m i n i m a l f o r m a t i o n of i n t e r f a c i a l p h a s e s w h i c h c o u l d r e d u c e the s t r e n g t h of the  product.  M o r g a n and S c h a e f f e r  have r e p o r t e d  f a b r i c a t i o n of m a g n e s i a b y a p r o c e s s  w o r k on the  they c a l l " p r e s s u r e  calcintering" ,  w h i c h i s e s s e n t i a l l y i d e n t i c a l to r e a c t i v e hot p r e s s i n g ; T h e y c o n d u c t e d a s e r i e s of i n v e s t i g a t i o n of the p r o c e s s , nature content  ( c h e m i c a l h i s t o r y ) of the p r e c u r s o r  a n d the e f f e c t of i m p u r i t y  on d e n s i f i c a t i o n . Chaklader  and  Cook  c h a r a c t e r i s t i c s of the M g ( O H ) 2 a n d two  a n a l y s i n g s u c h e f f e c t s a s the  h a v e a l s o s t u d i e d the hot p r e s s i n g *** M g O  s y s t e m , as w e l l as b o e h m i t e  clays.  1. 1. 1  H y p o t h e s e s f o r R e a c t i v e Hot  Pressing  (8) I n the e a r l i e r p a p e r s t h e y s u g g e s t e d that the f o r m a t i o n s t r o n g , d e n s e c o m p a c t s b y r e a c t i v e hot p r e s s i n g m i g h t be with an "enhanced  associated  r e a c t i v i t y " d u r i n g o r just after a p h a s e change,  w h i c h i s k n o w n a s the " H e d v a l l E f f e c t " . ^ )  The  p r e c i s e nature  r e a c t i v i t y has not b e e n e s t a b l i s h e d , a l t h o u g h C h a k l a d e r following  of  s t a t e m e n t s r e g a r d i n g the m e c h a n i s m s  of t h i s  h a s m a d e the  of r e a c t i v e hot  p r e s s i n g : ^ 4 )• "The  i d e a of u s i n g the h i g h r e a c t i v i t y of a s o l i d d u r i n g a  d e c o m p o s i t i o n r e a c t i o n o r a p o l y m o r p h i c p h a s e c h a n g e (the H e d v a l l Effect) for densification observations:  s t e m s f r o m the f o l l o w i n g h y p o t h e s e s  and  -3(a)  B r o k e n bonds and u n s a t i s f i e d v a l e n c e l i n k s e x i s t  b o t h o n the s u r f a c e a n d  i n the b u l k of p a r t i c l e s u n d e r g o i n g  sition r e a c t i o n ; these b r o k e n bonds and  links may  a decompo-  be a v a i l a b l e f o r i n t e r -  f a c e r e a c t i o n l e a d i n g to i n t e r p a r t i c l e b o n d i n g . (b)  V e r y t r a n s i e n t i n s t a b i l i t y of the a t o m i c p o s i t i o n d u r i n g  a r e a c t i o n c a n p r o d u c e a t r a n s i e n t p l a s t i c state w h i c h m a y  be  utilized  for densification". The  f i r s t proposition is easily accepted.  It i s w e l l k n o w n  that b o n d s of s t r e n g t h c o m p a r a b l e t o the b u l k t e n s i l e s t r e n g t h of material  are. f o r m e d b y  clean metal surfaces in frictional  high v a c u u m where surface are obtained f r o m  contamination i s prevented.  electrical  the  contact  in  Contact areas  resistance measurements.  W h i l e the  n a t u r e of c h e m i c a l b o n d i n g i n c e r a m i c s i s quite u n l i k e the m e t a l l i c b o n d , i t i s e a s y to u n d e r s t a n d the p o s s i b i l i t y of b o n d f o r m a t i o n clean oxide s u r f a c e s are brought together scale.  It i s the n e c e s s i t y of p r o d u c i n g  the p r o d u c t i o n  i n t i m a t e l y on a n  i s r e q u i r e d to b r i n g f i n i t e a r e a s i n t o c o n t a c t , conditions  s u f f i c i e n t f l o w i s not p o s s i b l e .  the f o r m a t i o n  of i n t e r p a r t i c l e b o n d s  atomic  s u i t a b l e c o n t a c t that  of f r i c t i o n a l b o n d i n g i n c e r a m i c s y s t e m s .  s e e n that  depends upon some  o r d i f f u s i o n . It i s to be  e x p e c t e d that the l a r g e e v o l u t i o n of w a t e r v a p o u r ( o r s o m e o t h e r would have a p u r g i n g  effect, reducing  flow  temperature  i t c a n be  of f i n i t e s t r e n g t h  m a s s t r a n s f e r m e c h a n i s m , s u c h as p l a s t i c f l o w  precludes  Plastic  and under low  Therefore  where  possible surface  gas)  contaminants  to  s u c h a l o w l e v e l that b o n d i n g c a n t a k e p l a c e f r e e l y b e t w e e n c o n t a c t i n g  -4asperities. The  second propostion,  concerning  mation p l a s t i c i t y * , is m o r e important. f l o w e n t e r s the d e n s i f i c a t i o n p r o c e s s  a transient transfor-  To  see e x a c t l y how  i t i s u s e f u l to c o n s i d e r  p o s s i b l e m e a n s of d e n s i f i c a t i o n of a p o w d e r pressure 1. 1. 2  plastic the  c o m p a c t s u b j e c t e d to  at a n e l e v a t e d t e m p e r a t u r e (hot p r e s s i n g ) . Theories The  of H o t  behaviour  Pressing of a c o m p a c t t h r o u g h a h i s t o r y of d i e f i l l i n g  in a gravitational field, v i b r a t o r y compaction, applied pressure, d e n s i f i c a t i o n up to the p o i n t of c l o s e d p o r e f o r m a t i o n , mechanisms  of p o r e e l i m i n a t i o n c a n be f o l l o w e d .  and  The  finally  factors which  c o n t r o l the c o m p a c t i o n of a p o w d e r to a d e n s e b o d y a r e  manifold:  p a r t i c l e s i z e , p a r t i c l e s i z e d i s t r i b u t i o n , p a r t i c l e s h a p e , the m e c h anical properties or flow,  of the m a t e r i a l  or its w o r k hardening  - i . e.  i t s s u s c e p t i b i l i t y to f r a c t u r e  rate if plastic flow occurs,  the a n i s o -  t r o p y of m e c h a n i c a l p r o p e r t i e s , the m e l t i n g p o i n t , s u r f a c e e n e r g y and f i n a l l y the r a t e s of s e l f d i f f u s i o n a n d these p r o p e r t i e s a r e obviously  * propensity  Transformation  of g r a i n g r o w t h .  S o m e of  interrelated.  p l a s t i c i t y i s t a k e n to d e n o t e  f o r p l a s t i c flow, m a n i f e s t e d  anomalous  by low flow s t r e s s and  usually by l a r g e " ductility ', a c c o m p a n y i n g 1  t r a n s f o r m a t i o n or d e c o m p o s i t i o n  an  reaction.  a solid-solid  phase  -5W h e n a p o w d e r i s p l a c e d i n s o m e c o n t a i n e r ( s a y a die) the d e n s i t y o b t a i n e d w i l l be quite l o w may  form  b r i d g e s , o r p o w d e r w i t h a r a n g e of p a r t i c l e  segregate , giving thoroughly mixed. sequent  sizes  may  r i s e t o l e s s e f f i c i e n t p a c k i n g t h a n i f the s i z e s w e r e ( T h i s s e g r e g a t i o n w i l l not be a l t e r e d by  sub-  o p e r a t i o n s a n d t h e r e f o r e w i l l not be c o n s i d e r e d f u r t h e r ) .  If s u b j e c t e d to e i t h e r v i b r a t i o n will occur, filling large voids. ing  since i r r e g u l a r l y shaped particles  density characteristic  or p r e s s u r e , p a r t i c l e  rearrangement  V i b r a t i o n will quickly produce a pack-  of the p a r t i c l e s h a p e a n d s i z e d i s t r i b u t i o n .  A p p l i c a t i o n of p r e s s u r e w i l l c a u s e d e n s i f i c a t i o n b y f r a c t u r e of the p a r t i c l e s , d e p e n d i n g particles.  and f l o w  on the s t r e n g t h a n d d u c t i l i t y of the  O n l y a v e r y soft m a t e r i a l c a n d e n s i f y c o m p l e t e l y  f l o w m e c h a n i s m , a n d no u s e f u l c e r a m i c  b y the  m a t e r i a l c a n by f a b r i c a t e d to  h i g h d e n s i t y b y f l o w a l o n e on a c o m m e r c i a l b a s i s .  The  constraint  offered by surrounding p a r t i c l e s probably prevents  densification  b e y o n d the p o i n t at w h i c h a l i n e c o n t a c t b e t w e e n t h r e e o r m o r e  particles  is f o r m e d .  surface  F r o m this point m a s s t r a n s p o r t by bulk diffusion,  (i. e. g r a i n b o u n d a r y ) d i f f u s i o n , probably a m o r e important cases N a b a r r o - H e r r i n g this m e c h a n i s m  - condensation  f a c t o r than p l a s t i c behaviour,  is  i n most  (diffusional) c r e e p m a y b e operative, although  i s not c o n s i d e r e d a l i k e l y o n e ( ^ ' .  of t r a p p e d gas f r o m p o r e s m a y eventually  or by e v a p o r a t i o n  be a p r o b l e m  The  elimination  s i n c e the p r e s s u r e w i l l  c o u n t e r a c t the a v a i l a b l e d r i v i n g f o r c e ( r e d u c t i o n of s u r f a c e  -6energy  p l u s a p p l i e d p r e s s u r e ) u n l e s s the gas i s s o l u b l e a n d t h e r e -  f o r e c a n d i f f u s e t h r o u g h the s t r u c t u r e .  The  d e n s i f i c a t i o n of  MgO  b y p r e s s u r e c a l c i n t e r i n g of M g ( O H ) 2 has b e e n s h o w n t o o c c u r stages. A p p r o x i m a t e l y  h a l f the o b s e r v e d  densification occurs  s i m u l t a n e o u s l y w i t h the d e h y d r o x y l a t i o n of the b r u c i t e . of the d e n s i f i c a t i o n t a k e s p l a c e f r o m about 5 5 0 ° C density is reached,  M o r g a n and S c h a e f f e r ^  and C o o k ^ .  remainder  Similar  be-  T h i s is shown  h a v e s u g g e s t e d that the f i r s t  stage of d e n s i f i c a t i o n i s a r e s u l t of a s l i p  mechanism  o b s e r v a t i o n of the f o r m a t i o n of a (111) t e x t u r e i n f r o m the f i r s t s t a g e .  The  u n t i l the f i n a l  u s u a l l y at a b o u t 8 5 0 ° to 9 0 0 ° C .  h a v i o u r has b e e n o b s e r v e d by C h a k l a d e r i n F i g u r e 1.  i n two  based  on t h e i r  magnesia  resulting  T h i s d e p a r t s f r o m the t h e o r y e a r l i e r p r o p o u n d e d (2)  by M o r g a n and S c a l a  who  s u g g e s t e d that c r u m b l i n g  b r u c i t e f l a k e s i n t o t i n y p e r i c l a s e (MgO) the i n i t i a l  c u b e l e t s was  second  stage i s p r o b a b l y due to d i f f u s i o n a l t r a n s p o r t o r  grain growth processes.  This is confirmed  b y the f a c t that no  additional t e x t u r a l d e v e l o p m e n t has b e e n o b s e r v e d previously determined  are s u m m a r i z e d i n section 1. 2  responsible for  densification.  The  The  of the p r e c u r s o r  d u r i n g stage II.  p r o p e r t i e s of the e x p e r i m e n t a l  system  1. 4.  O b j e c t i v e s of t h i s I n v e s t i g a t i o n The  p u r p o s e of t h i s i n v e s t i g a t i o n i s to s t u d y the f l o w  characteristics  of p o w d e r c o m p a c t s of M g ( O H ) 2 d u r i n g the d e h y d r o x y -  l a t i o n r e a c t i o n a n d thus to p r o v i d e e v i d e n c e  of t r a n s f o r m a t i o n  -7 -  F I G U R E I Compaction  of M g ( O H )  2  as a function of temperature.  (After C h a k l a d e r and Cook, Q  (8) a n d M o r g a n a n d S c a l a , /\ (2))-  -8plasticity.  If a f l o w p r o c e s s i s o p e r a t i n g d u r i n g the d e h y d r o x y l a t i o n ,  its p r e s e n c e observed  s h o u l d a i d i n u n d e r s t a n d i n g the e n h a n c e d d e n s i f i c a t i o n  d u r i n g the r e a c t i v e hot p r e s s i n g of a  decomposible  compound. A n a t t e m p t h a s a l s o b e e n m a d e to e x p l o r e the p o s s i b i l i t y of b o n d f o r m a t i o n a c r o s s the i n t e r f a c e b e t w e e n two  single  crystals  f i r s t b e i n g c o n s i d e r e d i t was  f e l t that  s o m e m a t e r i a l a v a i l a b l e as n a t u r a l o r e a s i l y g r o w n s i n g l e  crystals  while d e c o m p o s i n g under load. 1. 3  C h o i c e of E x p e r i m e n t a l S y s t e m W h e n this s t u d y was  would make a suitable p r e c u r s o r .  Calcite  i s an obvious  c h o i c e , as  v e r y l a r g e a n d quite p u r e s i n g l e c r y s t a l s a r e c o m m e r c i a l l y a v a i l a b l e . U n f o r t u n a t e l y , h o w e v e r , the d e c o m p o s i t i o n of c a l c i t e d o e s not g i v e a coherent CaO  layer  on the c a l c i t e  s u r f a c e , as has b e e n d e m o n -  s t r a t e d b y s e v e r a l w o r k e r s ^ ^ T h u s , as e x p e c t e d , e a r l y  experiments  with this m a t e r i a l were u n s u c c e s s f u l . The - CaO,  second  c h o i c e was  the s y s t e m C a ( O H ) 2 ( P o r t l a n d i t e )  as s m a l l c r y s t a l s of C a ( O H ) 2 a r e quite e a s i l y g r o w n  T h i s s y s t e m has the d i s a d v a n t a g e that b o t h the p r o d u c t a n d p r e c u r s o r t r a n s f o r m r e a d i l y to c a l c i u m c a r b o n a t e c o n t a i n i n g CO2, difficult  upon exposure  to m o i s t a i r  i . e . the l a b o r a t o r y a t m o s p h e r e , m a k i n g h a n d l i n g  i f c o n t a m i n a t i o n i s t o be a v o i d e d . T h e r e f o r e , i n o r d e r to s t u d y q u a n t i t a t i v e l y the n a t u r e of  transformation plasticity  c o l d c o m p a c t s of s y n t h e t i c  magnesium  -9hydroxide  powder were produced.  to c o m p r e s s i v e  These  compacts were subjected  c r e e p d e f o r m a t i o n (at l o w s t r e s s e s ) d u r i n g the  dehydroxylation reaction, under v a r y i n g conditions. hydroxide advantages  was  chosen  f o r these e x p e r i m e n t s as it has  over other possible choices:  a r e s i m p l e , a n d the r e a c t i o n k i n e t i c s  quite w e l l u n d e r s t o o d . handle  several  the s t r u c t u r a l r e l a t i o n s h i p  b e t w e e n p r e c u r s o r a n d p r o d u c t i s s i m p l e , the c r y s t a l themselves  Magnesium  structures  and m o r p h o l o g y a r e  T h e m a t e r i a l s a r e a l s o r e l a t i v e l y e a s y to  (although m a g n e s i a with high s u r f a c e a r e a r e h y d r a t e s  in m o i s t a i r ) and f i n a l l y m a g n e s i a i s a u s e f u l r e f r a c t o r y .  The  relevant  p r o p e r t i e s of t h i s s y s t e m a r e c o n s i d e r e d i n the next s e c t i o n . 1. 4  P r o p e r t i e s of the E x p e r i m e n t a l S y s t e m T h e b e h a v i o u r of the M g ( O H ) 2 - M g O  s y s t e m h a s b e e n the  s u b j e c t of c o n s i d e r a b l e i n v e s t i g a t i o n , m a i n l y b e c a u s e of the c o n d i t i o n s of d e c o m p o s i t i o n sintering behaviour  o n the s u b s e q u e n t  of the p r o d u c t p h a s e .  of the i n f l u e n c e hot p r e s s i n g o r  "Active" MgO  is produced  b y the c a l c i n a t i o n of M g ( O H ) 2 at l o w t e m p e r a t u r e s , w h i c h  produces  h i g h s p e c i f i c s u r f a c e a r e a s , a s w i l l be s e e n l a t e r . 1. 4. 1  P h y s i c a l and C h e m i c a l  Properties  T a b l e I s u m m a r i z e s s o m e i m p o r t a n t p r o p e r t i e s of the p r e cursor-product pair.  The  decomposition M g ( O H )  o c c u r s at t e m p e r a t u r e s i n e x c e s s of 3 0 0 ° C ,  2  ^-MgO  and i s e s s e n t i a l l y  ( e x c e p t f o r the r e m o v a l of a b s o r b e d w a t e r ) at about 4 0 0 ° C.  +  H2O  complete  - 10 -  TABLE I  PROPERTIES  of M g ( O H ) ? a n d  Brucite Mg(OH)  Formula  Weight  Ratio  Periclase MgO  2  58. 34  40. 32  1  0. 691  1. 449 Specific Gravity  MgO  1  2. 385 3.58< > 20  Structure  Hexagonal Cubic  Type  Cdl  2  NaCl Lattice  Bond  Parameters  Lengths  a  c  Q  = 3.147A  0  = 4. 769A  a  0 - 0  0 - 0 3. 13, 2. 9 8 A M g - 6 0 2. 16A  + 19 K c a l / m o l at 6 0 0 °  = 4. 2 1 3 A ( ) 2 1  Q  Mg  K  -  2. 98A<22)  6 0 2. 10A  -11Decomposition morphous from  of s i n g l e c r y s t a l s h a s  p r o d u c t i s obtained, with only a few p e r c e n t  the o r i g i n a l  percent  MgO,  (about 100  The  to the  shrinkage  p r o d u c t c r y s t a l i s o n l y 47  volume  of v e r y s m a l l  (1^)) c r y s t a l l i t e s h a v i n g a d e f i n i t e  crystallographic  brucite.  S t r u c t u r a l A s p e c t s of the Brucite  xyl  dimensions.  a n d i s c o m p o s e d of a n a g g r e g a t e  A,  relationship 1. 4. 2  s h o w n (13-15) that a p s e u d o -  Decomposition  (Mg(OH)2) has a C d l  ions a r r a n g e d in hexagonal  sequence.  The  p a i r of O H  layers.  F i g u r e 2.  T h i s s t a c k i n g of O H  2  t y p e s t r u c t u r e , w i t h the  hydro-  ( c l o s e p a c k e d l a y e r s ) i n hep s t a c k i n g  Mg"*~^ i o n s a r e i n o c t a h e d r a l s i t e s b e t w e e n e v e r y The  arrangement layers  second  is shown s c h e m a t i c a l l y in results i n a pronounced  c l e a v a g e a n d i n the c h a r a c t e r i s t i c I'platy" s h a p e  of the  basal  hydroxide  (Figure 9 ) . Periclase (Figure the  (MgO)  has a N a C l  type (cubic) s t r u c t u r e ,  2), c o n s i s t i n g of o x y g e n i o n s i n c l o s e p a c k e d l a y e r s ,  (111)  planes, with Mg  forming  i n a l l the o c t a h e d r a l s i t e s .  A n u m b e r of i n v e s t i g a t o r s (1^-15) h a v e c o n s i d e r e d the structural The  relationships  i n v o l v e d i n the d e h y d r o x y l a t i o n r e a c t i o n .  m o s t r e c e n t and a u t h o r i t a t i v e  w o r k i s that of G o r d o n a n d  (15), w h i c h c o n s i s t s of e l e c t r o n a n d o p t i c a l m i c r o s c o p y , study.  The  m e c h a n i s m s p r o p o s e d by v a r i o u s authors  are  i n T a b l e II, w h i c h i n c l u d e s b o t h m o r p h o l o g i c a l a n d k i n e t i c  Kingery  and a k i n e t i c summarized aspects.  -  -e— o - . o  12  -  o  Q  Brucite  e—e^o  Q o  a)  (edge view of ( 0 0 0 1 ) planes,  -e—e—e—e--e-aion g  <n2o>  direction )  e  e e e  e Periclase  b  )  A  '-Mg FIGURE  O-O  9-0H  2 a) S t r u c t u r e of M g ( O H ) b) S t r u c t u r e o f M g O  2  " Schematic  - Schematic  representation  representation  TABLE  II  Authors  SUMMARY  OF  M E C H A N I S M S AND  M e c h a n i s m or  KINETICS OF  Model  Mg(OH)  2  DEHYDROXYLATION  T y p e of K i n e t i c s  Activation Energy,  Kingery Gordon  and (  l 5 )  1) N u c l e a t i o n  and  growth process,  coherentnucleation,  with  F i r s t order  resultant large  small  for  particles,  s t r a i n s and f i s s u r i n g .  thick single c r y s  2) A  tals m o r e  s m a l l a m o u n t of d e c o m p o s i t i o n c a u s e s  kcal/mol  -  complex,  l a r g e c h a n g e s i n the p h y s i c a l state of the crystal, having a considerable  effect on  s u b s e q u e n t p r o c e s s and p r o d u c t . T h e  the  model  e x p l a i n s : a) the s t r u c t u r a l r e l a t i o n s h i p . b)the product c r y s t a l l i t e size, process, A n d e r s o n and Horlock ( ) l4  An  and  c) the  d) the d" s p a c i n g  38 ~ 43  cracking range.  i n t e r f a c e r e a c t i o n , d e s c r i b e d i n t e r m s of  a c o n t r a c t i n g d i s c a l o n g the b a s a l  19-27  w  i  plane.  G r e g g and  Described  Razouk  t e r m s of the c o n t r a c t i n g s p h e r e m o d e l .  weight l o s s data s a t i s f a c t o r i l y i n  Z h a b r o v a and Gordeeva^'  S h o w e d that t h e i r d a t a c o u l d be  described  e q u a l l y w e l l b y the c o n t r a c t i n g s p h e r e o r unimolecular  decay  law.  12 -  27  -14The  l i s t i s not e x h a u s t i v e , but i n c l u d e s the m o s t r e c e n t a n d  significant  w o r k i n this field. V a r i o u s decomposition studies performed microscope  h a v e s h o w n the c r y s t a l l o g r a p h i c r e l a t i o n s h i p  b e t w e e n the p e r i c l a s e the  (111.) p l a n e s  brucite.  i n the e l e c t r o n  a n d the p a r e n t b r u c i t e (13-15)_  of the p e r i c l a s e a r e n o r m a l  In addition, the^HO)  developed  One  set of  to the c - a x i s of the  d i r e c t i o n of the p e r i c l a s e i s  p a r a l l e l to the ( l i o ) d i r e c t i o n of the p a r e n t b r u c i t e . G o r d o n and K i n g e r y concluded  t h a t the d e c o m p o s i t i o n of  b r u c i t e i s m o s t l i k e l y a n u c l e a t i o n and growth c o h e r e n t n u c l e a t i o n of M g O  process i n which  results i n large coherency  strains  and  c r a c k i n g , i n the v e r y e a r l y s t a g e s of w e i g h t l o s s as s h o w n i n Figure  3  .  T h i s c r a c k i n g i s a m a j o r c h a n g e i n the p h y s i c a l  the c r y s t a l , a n d has a p r o n o u n c e d e f f e c t on the s u b s e q u e n t and p r o d u c t s .  s t a t e of  process  T h i s m o d e l e x p l a i n s : a) the o b s e r v e d s t r u c t u r a l r e -  l a t i o n s h i p , b) the s m a l l c r y s t a l l i t e s i z e of the p r o d u c t , c) the  observed  c r a c k i n g p r o c e s s , a n d d) the o b s e r v a t i o n of a r a n g e of d - s p a c i n g s d u r i n g the d e c o m p o s i t i o n p r o c e s s . A n d e r s o n a n d H o r l o c k ^ f o u n d t h a t the r e a c t i o n  proceeded  f r o m the e d g e s of the b r u c i t e p l a t e l e t s ( f o r l a r g e s i n g l e c r y s t a l s approximately  1 by 3 mm),  producing a "polycrystallization"  q u e n t l y a t t r i b u t e d t o the c o h e r e n c y  subse-  s t r a i n by G o r d o n and K i n g e r y .  T h e f o r m e r a u t h o r s f o u n d t h a t the m a j o r p a r t of the d e c o m p o s i t i o n  Brucite OH  Mg  Mg-  Periclase 0  OH  0 + H 0 2  Mg 0  OH  Mg  Mg  Mg 0  OH  0 •  H 0 2  Mg 0  OH  Mg  Mg OH FIGURE 3  Goodman's  (13)  p r o p o s e d m e c h a n i s m f o r the d e h y d r o x y l a t i o n ,  n o r m a l to the c l o s e d ~ p a c k e d  showing collapse  o x y g e n p l a n e s i n the f o r m a t i o n of p e r i c l a s e .  - 1 6 -  o r i g i n a t e d at the " e d g e " of the p l a t e l e t s , a n o b s e r v a t i o n  contradicted  by G o r d o n and K i n g e r y . Goodman microscope  w  a  s  the f i r s t w o r k e r t o u s e a n  t o s t u d y t h i s d e c o m p o s i t i o n , b u t he d i d not o b s e r v e the  i n i t i a l c r a c k i n g r e p o r t e d b y the o t h e r s . that the 0 ~ l a y e r s decomposition;  remained  3.  substantially undisturbed  l a y e r s , as s c h e m a t i c a l l y  -  was u n i f o r m l y  d u r i n g the  of w a t e r ( o r i t s i o n i c  Goodman proposed an atomistic m e c h a n i s m  essentially homogeneous. H^O  H e w a s the f i r s t t o r e c o g n i z e  This required diffusion  c o m p o n e n t s ) b e t w e e n the O Figure  electron  represented i n that w a s  I n t h i s m e c h a n i s m , he c o n s i d e r e d  removed  f r o m a l l p a r t s of the d e c o m p o s i n g  (though not n e c e s s a r i l y at the s a m e t i m e ) b y a two stage Water  that  would f i r s t be f o r m e d by r e a c t i o n between h y d r o x y l  process. ions,  c a u s i n g the f i r s t o b s e r v e d s h i f t i n l a t t i c e p a r a m e t e r , a n d t h e n tually escape  b e t w e e n the o x y g e n l a y e r s  crystal  even-  of the p a r t i a l l y d e c o m p o s e d  c r y s t a l , a s s h o w n i n the F i g u r e . A l t h o u g h G o r d o n a n d K i n g e r y did not m a k e s p e c i f i c on the m a s s t r a n s p o r t (1^) p o i n t  n e c e s s a r y f o r decomposition, B a l l and T a y l o r  out that the m o v e m e n t  of the p r o d u c t w a t e r w o u l d be  e x t r e m e l y l i k e l y t o c a u s e d i s r u p t i o n of the m a t e r i a l . the o b s e r v e d b e h a v i o u r  comment  was d e s c r i b e d  T h e y f e l t that  better by the concept  of a n  i n h o m o g e n o u s s o l i d state r e a c t i o n , o p e r a t i n g a s f o l l o w s : The regions  decomposing c r y s t a l would develop  ( F i g u r e 4) b e t w e e n w h i c h d i f f u s i o n  of M g  donor and acceptor +  +  ( ionic  FIGURE 4  B a l l and T a y l o r ' s p r o p o s e d inhomogenous m e c h a n i s m f o r the dehydroxylation, s h o w i n g d o n o r a n d a c c e p t o r r e g i o n s , a n d the d i f f u s i o n of Mg++ a n d  H+.  -18radius  = 0. 78A,  c o m p a r e d to about  o c c u r as shown.  The  1. 75  f o r water) and H  +  would  donor r e g i o n s ( p r o b a b l y a d j a c e n t to f r e e  f a c e s o r c r a c k s ) w o u l d e v e n t u a l l y be c o m p l e t e l y d e s t r o y e d . close packed O H p a c k e d O" 1. 4. 3  -  layers  of the a c c e p t o r  The  The  regions would become close  l a y e r s , w i t h the a d d i t i o n of s u f f i c i e n t M g  K i n e t i c s of  sur-  +  +  to f o r m  MgO.  Decomposition  decomposition  k i n e t i c s have b e e n e x t e n s i v e l y investigated  but no g e n e r a l a g r e e m e n t as to a n e x a c t m e c h a n i s m  has been made.  F a i l u r e to o b t a i n a g r e e m e n t h a s b e e n a t t r i b u t e d to v a r i a t i o n s i n the m a t e r i a l , e x p e r i m e n t a l c o n d i t i o n s , a n d i n the s i z e of the  sample  u s e d (15). G r e g g and R a z o u k contracting sphere  v  ' i n t e r p r e t e d t h e i r d a t a b y m e a n s of a  model: (1 - *  1/3  ^  = 1 R  o b t a i n i n g a c t i v a t i o n e n e r g i e s of 12 to 27 k c a l / m o l e p o w d e r s , a n d 27. 6 k c a l / m o l e A n d e r s o n and H o r l o c k  for M g ( O H )  2  for brucite. ' used a contracting disc model:  v  1/2 (1 - <A ) * U  and obtained a c t i v a t i o n e n e r g i e s  = 1 -•  R  ^  of 27.6 k c a l / m o l e  a n d 23. 6 k c a l / m o l e f o r two t y p e s of b r u c i t e .  for powder,  -19Z h a b r o v a and G o r d e e v a single model  (*^ had e a r l i e r  c o u l d u n e q u i v o c a b l y be u s e d :  t h a t no  T h e y fitted t h e i r data  s u c c e s s f u l l y to a c o n t r a c t i n g s p h e r e r e l a t i o n s h i p molecular  shown  a n d to a u n i -  ( f i r s t o r d e r ) d e c a y l a w of the f o r m  In ( l - « ) = k i t + constant  in which k j is a nucleation  r a t e c o n s t a n t a n d o*> i s the  fractional  weight l o s s . G o r d o n and K i n g e r y ( ^ )  c o n c l u d e d that t h e i r data c o u l d b e s t  be i n t e r p r e t e d u s i n g the u n i m o l e c u l a r m o d e l , b e c a u s e of the  complete  d i s r u p t i o n of the s t a r t i n g m a t e r i a l e a r l y i n the d e c o m p o s i t i o n . c r y s t a l s p r o b a b l y s h o w m i x e d c o n t r o l as the f r a g m e n t a t i o n be i n c o m p l e t e , mechanism vapour  m a k i n g b o t h c o n t r a c t i n g d i s c a n d the f i r s t  operative.  order  causing discernable  of r a t e w i t h s a m p l e s i z e , a n d f r o m w o r k e r to w o r k e r  o n the d e c o m p o s i t i o n ,  is much higher  variation  with various  H o r l o c k , M o r g a n a n d A n d e r s o n (19) s t u d i e d the  of w a t e r v a p o u r ioss  may  T h e y a l s o c o n c l u d e d t h a t the e f f e c t of w a t e r  back p r e s s u r e was considerable  conditions.  Large  effect  s h o w i n g that the r a t e of w e i g h t  i n v a c u u m than i n w a t e r vap our  atmosphere.  -20C H A P T E R II 2.  Expe rimental  2. 1  Apparatus The apparatus, shown in a schematic view in Figure 5, was  constructed to permit the decomposition of various systems in a controlled atmosphere, since it was felt that gaseous atmospheres .could produce considerable effects during and following decomposition.  The  design was intended to have fairly general applicability in the area of neck growth, sintering model studies, and for that reason incorporated some features not absolutely essential to the work forming the present study. 2.1. 1  Furnace and Load Frame The specimens themselves were mounted in a loading frame  (Figure 6) which was removeable from the furnace for specimen mounting.  The load frame was fabricated from Inconel X-750.  The pushrod  slid in boron nitride bushings, gave fairly low values of coefficient of static friction (about 0. 0 5 when clean), permitting the use of small loads for studies with single crystals.  The various "grips" slid onto the  pushrod and anvil, permitting ready change from one type of specimen to another. When in position in the furnace the load frame was enclosed by a resistant element consisting of 10 turns of No. 6 A. W. G. Chromel wire, operating at 10 volts.  The furnace had a power rating of one  FIGURE 5  Schematic  r e p r e s e n t a t i o n of the e x p e r i m e n t a l a p p a r a t u s .  r  f X  i  6 1  1  r-  FIGURED  T h e loading f r a m e , - showing the t h e r m o c o u p l e s .  k i l o w a t t w i t h t h i s w i n d i n g . T h e h e a t e r w a s i n s u l a t e d f r o m the w a t e r jacketted v a c u u m c h a m b e r by c o n c e n t r i c s i l i c a tubes separated corrugated  stainless steel radiation shields, which provided  efficient insulation  by  reasonably  with m i n i m u m surface area, p e r m i t t i n g easy pump-  down to high v a c u u m s . Z. 1. Z  Vacuum  System  The furnace  c h a m b e r w a s f i t t e d w i t h two Z i n c h d i a m e t e r  P y r e x windows, p e r m i t t i n g viewing the f u r n a c e .  of the s p e c i m e n w h e n i n p o s i t i o n i n  T h e s i g h t p a t h was t h r o u g h 3/4 i n c h h o l e s i n the f u r n a c e  i n s u l a t i o n a n d b e t w e e n t u r n s of the h e a t i n g  coil.  T h e p u m p i n g s y s t e m c o n s i s t e d of a Z i n c h E d w a r d s  EOZ  oil d i f f u s i o n pump with l i q u i d n i t r o g e n t r a p and b u t t e r f l y i s o l a t i o n valve, b a c k e d b y a B a l z e r s D u o 5 m e c h a n i c a l pump. valves permitted admission  C o a r s e and fine bleed  of a n y d e s i r e d gas o r v a p o u r i n t o the c h a m b e  and b y b a l a n c i n g b l e e d rate a g a i n s t p u m p i n g rate any d e s i r e d  pressure  _5 between 1 atmosphere and 1 x Vacuum  10  T o r r c o u l d be o b t a i n e d f a i r l y e a s i l y .  g a u g i n g w a s b y m e a n s of a n E d w a r d s P i r a n n i -  P e n n i n g gauge unit. Z. 1. 3  Photography S p e c i m e n s i n the f u r n a c e w e r e p h o t o g r a p h e d w i t h one of two  d i f f e r e n t l e n s s y s t e m s , d e p e n d i n g on the m a g n i f i c a t i o n r e q u i r e d . conventional  135 m m  Telephoto  lens with e x t e n s i o n tubes  A  permitted  m a g n i f i c a t i o n s l i g h t l y i n e x c e s s of 1:1, a n d h i g h e r m a g n i f i c a t i o n s  were  p r o v i d e d b y L e i t z O p t i c s , h a v i n g a m a g n i f i c a t i o n of about 4 x  The  .  -24s p e c i m e n s w e r e photographed i n sihouette, being backlighted by a microscope illuminator. 2. 1. 4  single lens reflex.  Loading and D i s p l a c e m e n t M e a s u r e m e n t The  loading device. 10 g r a m s system  T h e c a m e r a w a s a 35 m m  p u s h r o d of the l o a d i n g f r a m e w a s c o n t a c t e d b y a s p r i n g S u b s t i t u t i o n of d i f f e r e n t s p r i n g s p e r m i t t e d l o a d s  t o about 3 k i l o g r a m s  f o r the p r e s e n t e x p e r i m e n t s .  had an inherent load v a r i a t i o n with displacement  small displacements significant.  from  This  but f o r the  i n v o l v e d i t w a s not f e l t that the v a r i a t i o n w o u l d be  T h e s p r i n g s w e r e s e l e c t e d to m i n i m i z e t h i s e f f e c t .  A  p i e c e of h a r d e n e d 0. 030 d i a m e t e r d r i l l r o d p a s s i n g t h r o u g h a s l i g h t l y u n d e r s i z e d hole i n a p i e c e  of 1/8 i n c h t h i c k n e o p r e n e r u b b e r  provided  a m e a n s of t r a n s m i t t i n g the m o t i o n o u t s i d e the v a c u u m s y s t e m .  The  r o d was s m e a r e d w i t h v a c u u m g r e a s e and p r o v i d e d a v e r y low f r i c t i o n f o r c e w h i c h was a l m o s t e x a c t l y b a l a n c e d  b y the r a m f o r c e of the d i a l  i n d i c a t o r , about 20 g r a m s , a n d w a s o n l y u s e d f o r l o a d s i n e x c e s s of 100 g r a m s a n d s o d i d not p r o v i d e a l a r g e s o u r c e The displacement and H e a t h k i t indicator ducer.  displacement  transducer  w a s m e a s u r e d i n two w a y s ; b y a n i n d u c t i v e  c o n n e c t e d t o a P h i l l i p s s t r a i n gauge b r i d g e  strip chart recorder,  or directly by a Starret dial  (0. 0001 i n c h p e r d i v i s i o n ) ,  U s e of the t r a n s d u c e r -  after experience  of e r r o r i n the l o a d .  c o n n e c t e d i n t a n d e m w i t h the t r a n s -  recorder  c o m b i n a t i o n was  terminated  s h o w e d that c o r r e c t i o n f o r the d r i f t of the r e c o r d e r  i n v o l v e d m o r e d i f f i c u l t y t h a n m a n u a l r e c o r d i n g of the d i a l i n d i c a t o r readings.  - 25 -  2. 1. 5  Furnace Temperature Temperature  thermocouples.  C o n t r o l and P o w e r Supply  m e a s u r e m e n t was  b y m e a n s of  Chromel-Alumel  T h e s e w e r e either connected d i r e c t l y to a compensated  potentiometer controller (Honeywell Servotronik or Versatronik) or c o n n e c t e d to a P y e P o t e n t i o m e t e r o r Heathkit r e c o r d e r w i t h an i c e w a t e r (0°C) c o l d j u n c t i o n . h y d r o x i d e was A. W. G.  M o s t of the e x p e r i m e n t a l w o r k w i t h m a g n e s i u m  done u s i n g t h r e e t h e r m o c o u p l e s ( F i g u r e 6) of No.  wire.  32  F o r the e x p e r i m e n t s two of t h e t h e r m o c o u p l e s w e r e i n  c o n t a c t w i t h the s p e c i m e n a n d g r i p ( N o s . 1 & 2) w h i l e the t h i r d w a s to m e a s u r e r a d i a n t t e m p e r a t u r e w i t h i n the f u r n a c e .  free  Thermocouples  1 and 2 w e r e g e n e r a l l y i n a g r e e m e n t w i t h i n 5 d e g r e e s C e n t i g r a d e , w h i l e the t h i r d w a s  a s m u c h a s 20 a n d 30 d e g r e e s d i f f e r e n t , d e p e n d i n g o n the  p a r t i c u l a r t h e r m a l conditions. For  s o m e of the e a r l y e x p e r i m e n t s t e m p e r a t u r e  m e a s u r e d b y m e a n s of a 1/8 i n c h O. D. p l a c e d i n s i d e the f i x e d g r i p .  was  Inconel sheathed thermocouple,  T h i s o b v i o u s l y was  not r e p r e s e n t a t i v e of  the s p e c i m e n t e m p e r a t u r e e x c e p t u n d e r i s o t h e r m a l ( s t e a d y state) c o n d i t i o n s , but i t w a s  used for temperature control during linearly i n -  c r e a s i n g temperature runs. T h e p o w e r t o the f u r n a c e w i n d i n g s w a s P o w e r s t a t . w h i c h was  supplied by 2  KVA  u s e d i n c o n j u n c t i o n w i t h the c o n t r o l l e r s t o p r o v i d e  o p t i m u m c o n t r o l at a p a r t i c u l a r t e m p e r a t u r e  setting.  -262. 2  E x p e r i m e n t a l Technique  2. 2. 1  G r o w t h of C a ( O H ) z The  (Portlandite) Single  Crystals  C a ( O H ) 2 s i n g l e c r y s t a l s u s e d w e r e g r o w n b y the i n t e r -  d i f f u s i o n of s o l u t i o n s of p o t a s s i u m h y d r o x i d e a n d c a l c i u m b y a t e c h n i q u e due to D a v e a n d C h o p r a ( 1 ^ )  >  chloride  m o d i f i e d s l i g h t l y as  follows: A F i g u r e 7,  100 m l b e a k e r w a s  p l a c e d i n s i d e a 600 m l  beaker,  a n d the two w e r e f i l l e d w i t h C O 2 - f r e e d i s t i l l e d  water  ( p r e p a r e d b y b u b b l i n g n i t r o g e n t h r o u g h d i s t i l l e d w a t e r ) j u s t a b o v e the top  of the 100 m l b e a k e r .  I n t h i s w o r k the s o l u t i o n s w e r e i n t r o d u c e d t h r o u g h  two s t o p p e d f u n n e l s t h r o u g h f i n e g l a s s t u b i n g e x t e n s i o n s r a t h e r t h a n b y p i p e t t e as s u g g e s t e d i n the r e f e r e n c e i n o r d e r t o p r e v e n t t u r b u l e n c e and p r e m a t u r e  m i x i n g of the s o l u t i o n s .  W h e n the d i s t i l l e d w a t e r h a d b e e n a d d e d a n d the f u n n e l s f i l l e d w i t h s a t u r a t e d s o l u t i o n s of K O H was  and C a C l 2  molten paraffin  wax  p o u r e d onto the d i s t i l l e d w a t e r to a d e p t h of about 1/4 i n c h to p r e v e n t  c o n t a m i n a t i o n by a t m o s p h e r i c gases. 40 m l of C a C l 2 was  50 m l of the K O H  a d m i t t e d to the b e a k e r s .  In two  solution and  or three  days  c r y s t a l s s t a r t e d t o a p p e a r on the o u t s i d e of the s m a l l b e a k e r a n d the i n s i d e of the l a r g e r one. a n d the w a x  was  In f o u r d a y s g r o w t h was  essentially  complete  l i f t e d out a n d the c r y s t a l s c a r e f u l l y r e m o v e d f r o m the  w a l l s of the b e a k e r b y s c r a p i n g t h e m off w i t h a s t i r r i n g r o d e q u i p p e d w i t h a rubber  scraper.  The  c r y s t a l s were r i n s e d with distilled water  then s t o r e d i n tightly capped jars. small crystals.  E a c h r u n p r o d u c e d about  500  O n l y a s m a l l n u m b e r of t h e m w e r e s u i t a b l e f o r  and  -28experiments  as m a n y w e r e e i t h e r v e r y s m a l l ,  f r a g m e n t s of l a r g e r c r y s t a l s . morphology and fractured  i n t o the c r y s t a l s The  or broken  The c r y s t a l s had obvious hexagonal  v e r y e a s i l y o n the b a s a l p l a n e s .  d e f e c t s w e r e p o c k e t s of t r a p p e d s o l u t i o n , distance  quite i m p e r f e c t  Typical  o r "pipe" extending some  f r o m the r o o t end.  c r y s t a l s w e r e not a n a l y s e d a s p u r i t y w a s not f e l t t o b e  of g r e a t i m p o r t a n c e at t h i s s t a g e of the i n v e s t i g a t i o n , b u t D a v e a n d C h o p r a < ) quote 99- 6 5 % C a ( O H ) 12  2  a n d 99. 6 %  of the t h e o r e t i c a l  calcium  in their crystals. 2. 2. 2  E x p e r i m e n t s on T i p to T i p  Contact  A.  Ca(OH)?, C r y s t a l s  For  t h e s e e x p e r i m e n t s the c a m e r a s e t - u p w i t h 4 X  mag-  n i f i c a t i o n w a s u s e d t o v i e w a n d r e c o r d the b e h a v i o u r of t h e c r y s t a l s . D u r i n g t h e s e e a r l y e x p e r i m e n t s the l i n e a r t e m p e r a t u r e was  not a v a i l a b l e  s o the h e a t i n g r a t e w a s u n c o n t r o l l e d ,  erature - time profile The  similar  t o that s h o w n i n F i g u r e  programmer giving 8.  p r o c e d u r e of s e l e c t i o n a n d m o u n t i n g w a s t e d i o u s  useful c r y s t a l s w e r e t y p i c a l l y v e r y small; l e s s than 1 m m and  2 to 3 m m  a temp-  long.  Crystals  in diameter  of g o o d s i z e a n d s h a p e w e r e  f r o m their storage jar, examined  under a m i c r o s c o p e  as the  selected  (50X)  to e n s u r e  _4 suitable tip shape, then l i g h t l y e t c h e d followed  i n 10  N Hydrochloric acid  by r i n s i n g i n d i s t i l l e d water to give a f r e s h surface,  mounted, loaded and evacuated t r a n s f o r m a t i o n to C a C 0 3 «  as quickly as possible  solution;  then  to m i n i m i z e  surface  Time, minutes FIGURE 8  T i m e - t e m p e r a t u r e p r o f i l e used for the d e c o m p o s i t i o n o f C a { O H ) u n i f o r m beating rate experiments.  2  tips a n d f o r  -30M o u n t i n g the c r y s t a l s i n the l o a d f r a m e was commercial  furnace cement " S a i r s e t "  i n g f o r the c r y s t a l s i n a s m u c h a s i t was  done w i t h a  as this p r o v i d e d a s u i t a b l e m o u n t quick setting,  s t r o n g and yet  e a s i l y r e m o v e d f r o m the g r i p s a f t e r a r u n . A f t e r the s y s t e m  h a d b e e n e v a c u a t e d to a v a c u u m of about  0. 02 T o r i ; the f u r n a c e p o w e r was Photographs  s w i t c h e d on a n d the r u n  w e r e t a k e n b e f o r e , d u r i n g a n d a f t e r the  commenced.  decomposition,  w h i c h c o u l d be f o l l o w e d e a s i l y , a s the p r e s s u r e i n the f u r n a c e was s o m e e x t e n t p r o p o r t i o n e d to the d e c o m p o s i t i o n 2. 2. 3  P r e p a r a t i o n of M g ( O H ) ? B. To  Mg(OH)2  rate.  Compacts  Compacts  study qualitatively both flow and bond f o r m a t i o n , p a i r s  of h e m i s p h e r i c a l t i p p e d p e l l e t s w e r e p l a c e d i n the l o a d f r a m e a n d composed under v a r i o u s loads. g i v e n i n the f o l l o w i n g  section.  Mg(OH)2 compacts were p r e p a r e d f r o m A l c a n magnesium (Alcan Ltd. , Montreal, Chemical Products Division). contained impurities  The microscope  de-  D e t a i l s of s p e c i m e n p r e p a r a t i o n a r e  F o r deformation studies under c o m p r e s s i v e  CaO+Si02~2. 5 % ,  to  as follows:  MgO-96%-Al2G"3+Fe2  loading, hydroxide  This material O 3 - 1. 5 % ,  (after ignition). p a r t i c l e s i z e a n d s h a p e was  d e t e r m i n e d i n an  electron  b y s u s p e n d i n g a s m a l l a m o u n t of the p o w d e r i n a d i l u t e  s o l u t i o n , t h e n p l a c i n g a d r o p of t h i s s u s p e n s i o n on a g r i d w i t h a s u p p o r t f i l m a n d a l l o w i n g the w a t e r to e v a p o r a t e .  The  HC1  carbon  powder is shown  31 -  a) B e f o r e  dehydroxylation  b) A f t e r d e h y d r o x y l a t i o n at 4 5 0 ° C  FIGURE  9  E l e c t r o n m i c r o g r a p h s of t h e M g ( O H )  2  powder.  -32i n F i g u r e 9-  The  m e a n p a r t i c l e d i m e n s i o n i n the b a s a l p l a n e  e s t i m a t e d t o be 150oA a n d the a v e r a g e a r e a was  approximately The  diameter rod. R.^60  t h i c k n e s s was  was  a b o u t 250  A.  Surface  15m^/gm.  p o w d e r was  p r e s s e d i n t o c o m p a c t s i n a 0. 190 i n c h  die m a d e f r o m A t l a s K e e w a t i n  s t e e l , w i t h p l u n g e r s of d r i l l  B o t h d i e a n d p l u n g e r s w e r e h a r d e n e d a n d t e m p e r e d , the d i e to a n d the p l u n g e r s t o R 5 5 . t  The  100,000 p s i w i t h M g ( O H ) 2 , a l t h o u g h p r e s s u r e s with MgO  die was  used  s u c c e s s f u l l y to  g a l l i n g o c c u r e d at m u c h  i n a s i m i l a r die.  The  lower  b o r e had a v e r y slight t a p e r  i  (about It w a s  0.0005 i n c h e s /  inch),  felt that e x p e r i m e n t s  w h i c h f a c i l i t a t e d r e m o v a l of the  compacts.  w i t h the t i p t o t i p c o n t a c t of d e c o m p o s i n g  bodies might d e m o n s t r a t e both flow and bond f o r m a t i o n with this m a t e r i a l a n d to t h i s e n d a n u m b e r of c o m p a c t s w e r e p r e s s e d f r o m M g ( O H ) 2 u s i n g a ram Figure  s h a p e d t o g i v e a h e m i s p h e r i c a l e n d on the p e l l e t , ( s h o w n l a t e r i n 13). The  compacts were produced  M a c h i n e w h i c h was per square inch.  using a floor model Instron  c a l i b r a t e d s o that the c h a r t r e a d d i r e c t l y i n p o u n d s By  u s i n g the l o a d c y c l e c o n t r o l i t was  p o s s i b l e to  obtain v e r y r e p r o d u c i b l e s p e c i m e n density. The  pressing procedure  was  as f o l l o w s :  1)  The  d i e was  l o a d e d (with p r e - w e i g h e d charge).  2)  The  die was  p l a c e d i n the m a c h i n e  a n d p r e l o a d e d to a b o u t  100 p s i b y m e a n s of the m a n u a l c r o s s h e a d t r a v e r s e .  -333)  The  specimen  was  p r e s s e d under a constant c r o s s h e a d  s p e e d of 0. 0 5 i n c h e s / m i n . 4)  The  c r o s s h e a d m o t i o n was  5)  The  l o a d was  s t o p p e d at a p r e d e t e r m i n e d l o a d .  a l l o w e d to r e l a x w i t h constant c r o s s h e a d p o s i -  tion f o r 5 minutes. 6)  The  l o a d was  specimen The  r e l e a s e d at 0. 05 i n c h e s / m i n u t e , a n d the  p r e s s e d out at 5 i n c h e s / m i n u t e .  specimens  w e r e then weighed, m e a s u r e d f o r length  and d i a m e t e r and s t o r e d i n s t o p p e r e d v i a l s until needed f o r e x p e r i m e n t s . P r a c t i c a l c o n s i d e r a t i o n s l i m i t e d the d e n s i t i e s a v a i l a b l e f o r study.  It was  f o u n d that b e l o w a r e l a t i v e  were too f r a g i l e  t o be h a n d l e d  density  of 0. 40 the  specimens  e a s i l y , w h i l e a b o v e 0. 70 t h e y t e n d e d to  d e v e l o p c i r c u m f e r e n t i a l c r a c k s u p o n r e m o v a l f r o m the d i e . The (4. 839  completed specimens  to 4. 851 mm)  l o n g . F i g u r e 10  d i a m e t e r , a n d a p p r o x i m a t e l y 0. 32 i n c h e s (8. 13  mm)  s h o w s the r e l a t i o n s h i p b e t w e e n f r a c t i o n a l d e n s i t y a n d the  pressure used in compacting was  w e r e 0. 190 5 to 0. 191 i n c h e s  the s p e c i m e n s .  The  c o n s i s t e n c y of d e n s i t y  e x c e l l e n t ; the' r a n g e of d e n s i t i e s o b s e r v e d was  about + 0. 4 %  at  5.0% r e l a t i v e d e n s i t y . 2. 2. 4  D e f o r m a t i o n of M g ( O H ) p C y l i n d r i c a l Several different approaches  characterizing  w e r e t a k e n to the p r o b l e m of  the c r e e p b e h a v i o u r of the m a g n e s i u m  In a l l c a s e s the s p e c i m e n s anvils  Compacts  hydroxide  compacts.  w e r e p l a c e d b e t w e e n the f l a t s u r f a c e s of the  o r g r i p s a n d the f u l l l o a d a p p l i e d at r o o m  temperature.  -35T h e t y p e s of e x p e r i m e n t s i)  undertaken were as follows:  Q u a s i - u n i f o r m Heating Rate T h e f i r s t s e r i e s of r u n s w e r e m a d e t o e x p l o r e the r e p r o d u c e -  a b i l i t y of the e x p e r i m e n t s , a n d t o d e t e r m i n e the e f f e c t of l o a d o n t h e creep behaviour under these conditions.  T h e heating rate was obtained  b y u s i n g a f i x e d s e t t i n g of the p o w e r s t a t , g i v i n g the h e a t i n g r a t e  shown  i n F i g u r e 8. ii)  "Isothermal  1 1 ,  Runs  In o r d e r t o f a c i l i t a t e the d e t e r m i n a t i o n of a n a c t i v a t i o n e n e r g y f o r the d e f o r m a t i o n , m o s t of the e x p e r i m e n t s r e p o r t e d h e r e w e r e done u n d e r available  i s o t h e r m a l conditions.  w a s u s e d t o b r i n g the s p e c i m e n  T h e m a x i m u m heating rate a n d l o a d f r a m e to the t e s t  t e m p e r a t u r e , a n d t h i s w a s done w i t h i n 10 t o 12 m i n u t e s heating.  T h e average heating rate was 40°C/minute,  l i n e a r r a t e of 2 6 ° C / m i n u t e  f r o m 3 2 0 ° C to 4 0 5 ° C  of the s t a r t of  with an almost  (the m a x i m u m  temper-  ature used i n these e x p e r i m e n t s ) , as shown i n a t i m e - t e m p e r a t u r e profile,  Figure  11.  Temperature  all experimental runs.  was r e c o r d e d continuously during  P e r i o d i c c h e c k s of the r e c o r d e r  calibration  w a s m a d e d u r i n g the r u n s . T h e r m a l e x p a n s i o n c o r r e c t i o n w a s n e c e s s i t a t e d b y the r a t h e r r a p i d r i s e i n t e m p e r a t u r e , w h i c h c a u s e d u n e v e n t h e r m a l s t r a i n s i n the d i f f e r e n t p a r t s of the l o a d i n g f r a m e . performed  for each r u n or pair  T w o t h e r m a l expansion runs were  of i d e n t i c a l  runs f o r given temperature  and load conditions, u s i n g a d u m m y quartz s p e c i m e n .  The expansion  -  o o  o  o  84 S9 101 86  -  -  o o co  -  o o  1 f  CM  m  i  0  5  10  15  20  Time, minutes F I G U R E 11  i  i  25  30  a 35  S p e c i m e n s u r f a c e t e m p e r a t u r e a s a f u n c t i o n of t i m e f o r the " i s o t h e r m a l " t e s t s at f o u r d i f f e r e n t t e m p e r a t u r e s .  -37d a t a w e r e s u b s e q u e n t l y u s e d f o r c o r r e c t i n g the d e f o r m a t i o n data. The  t h e r m a l e x p a n s i o n c o r r e c t i o n was a l s o v e r i f i e d  microscope  using a travelling  ( A p p e n d i x III). T h e v a r i a b l e s c o n s i d e r e d i n t h i s s e r i e s of e x p e r i m e n t s  were temperature, load (compressive stress) density.  and specimen  bulk  O t h e r f a c t o r s w h i c h c o u l d c o n c e i v a b l y be e x p e r i m e n t a l  variables,  s u c h as p a r t i c l e s i z e ,  constant.  The specimens  shape and c h e m i c a l p u r i t y w e r e h e l d  w e r e l o a d e d i n t o the l o a d f r a m e ,  then into  the f u r n a c e , a n d the s y s t e m w a y s e a l e d a n d p u m p e d d o w n to about 10 was  Torr.  T h e r u n was u s u a l l y c o m m e n c e d  a s s o o n as p u m p d o w n  c o m p l e t e , but e x t e n d e d h o l d i n g p e r i o d s at l o w p r e s s u r e s (as l o n g  a s 46 h o u r s ) h a d no d i s c e r n a b l e e f f e c t on the c r e e p c u r v e . Temperature  m e a s u r e m e n t s d u r i n g t h i s g r o u p of r u n s w e r e  m a d e u s i n g the t h e r m o c o u p l e s d e s c r i b e d e a r l i e r , but s e v e r a l a d d i t i o n a l r u n s w e r e m a d e w i t h a t h e r m o c o u p l e i n s e r t e d a l o n g the s p e c i m e n  axis  to m e a s u r e t e m p e r a t u r e at the c e n t r e of the s p e c i m e r i j as d e s c r i b e d i n the f o l l o w i n g 2. 2. 5  section. Temperature The  Distribution i n Specimens  c r e e p tests were p e r f o r m e d " i s o t h e r m a l l y " .  However,  s i n c e the s p e c i m e n w a s t a k e n to the t e m p e r a t u r e f o r c r e e p s t u d y as f a s t as p r a c t i c a l l y p o s s i b l e , t h e r e w a s a p e r i o d at the b e g i n n i n g of e a c h experiment  during which large t h e r m a l gradients existed.  There are  two w a y s of d e t e r m i n i n g the t e m p e r a t u r e d i s t r i b u t i o n i n the s p e c i m e n t  -38d u r i n g the e x p e r i m e n t s :  b y t h e o r e t i c a l c o n s i d e r a t i o n of t h e r m a l  d i f f u s i v i t y , o r b y e x p e r i m e n t a l d e t e r m i n a t i o n of the t e m p e r a t u r e of the c e n t e r a n d on the s u r f a c e of the  specimen.  A p r e c i s e t h e o r e t i c a l a n a l y s i s was  not p o s s i b l e  of the l a c k of d a t a n e c e s s a r y f o r s u c h c a l c u l a t i o n s . l i m i n a r y o r d e r of m a g n i t u d e c a l c u l a t i o n , was  because  However, a p r e -  m a d e u s i n g the m e t h o d  of C a r s l a w a n d J a e g e r (22). T h i s , c a l c u l a t i o n , w h i c h i n d i c a t e s that an i n t e r i o r t e m p e r a t u r e  of a p p r o x i m a t e l y 0. 97 of the s u r f a c e  tempera-  t u r e w i l l be r e a c h e d i n 8 to 10 m i n u t e s i s p r e s e n t e d i n A p p e n d i x I. T h e t e m p e r a t u r e d i s t r i b u t i o n d u r i n g the c r e e p s t u d y also determined experimentally.  A thermocouple  (No.  3) w a s  was  inserted  at the c e n t e r of the s p e c i m e n f r o m one end, a s s h o w n b y the d o t t e d l i n e i n F i g u r e 5.  T h e t e m p e r a t u r e was  (using t h e r m o c o u p l e s  m e a s u r e d c o n t i n u o u s l y on the s u r f a c e  1 a n d 2) a n d at the c e n t r e .  Experimentally  d e t e r m i n e d t e m p e r a t u r e p r o f i l e s f o r two  surface temperatures,  3 4 5 ° a n d 4 0 8 ° C a r e s h o w n i n F i g u r e 12.  After a very large  temperature  g r a d i e n t i n the i n i t i a l s t a g e s , a s t e a d y s t a t e , h a v i n g a d i f f e r e n t i a l of from  10° to 12°C  b e t w e e n the s u r f a c e a n d the c e n t r e t e m p e r a t u r e  r e a c h e d , w i t h i n 10 to 12 m i n u t e s k i n e t i c a n a l y s i s , i t was  of the s t a r t of h e a t i n g .  was  Thus, for  p o s s i b l e t o a s s u m e the s p e c i m e n to be at s o m e  ''steady s t a t e " t e m p e r a t u r e c h a r a c t e r i s e d by'the m e a n t e m p e r a t u r e .  8  TIME (MIN.) 10 12  I ' I ' I  4 F I G U R E 12  14  6 TIME  1  16  18  ' I ' l  20  8 (MIN.)  S p e c i m e n s u r f a c e a n d c e n t r e t e m p e r a t u r e s f o r two d i f f e r e n t conditions.  "isothermal'  -40III  CHAPTER 3  Results  3. 1  Calcium As  Hydroxide Single C r y s t a l s  d i s c u s s e d e a r l i e r only a v e r y few  s p e c i m e n s of  i  single c r y s t a l c a l c i u m hydroxide for deformation  s t u d y i n t i p to t i p c o n t a c t .  with single c r y s t a l s  3 to 4 m m  hexagonal c r o s s section.  Experiments were performed  long, about 1 m m  The  of 10 g r a m s a n d d e c o m p o s e d . pressure  were obtained with suitable p r o p e r t i e s  s p e c i m e n p a i r was  in diameter,  and  of  p l a c e d under a load  This load corresponds  to a c o n t a c t  of a b o u t 0. 5 k g / m m , b a s e d on the f i n a l c o n t a c t a r e a . 2  Figure p a i r of c r y s t a l s  13 s h o w s a s e r i e s of p h o t o g r a p h s of a p a r t i c u l a r  b e f o r e , during, and after d e c o m p o s i t i o n .  Due  to the  i r r e g u l a r g e o m e t r y of the c o n t a c t a n d the v i r t u a l i m p o s s i b i l i t y of duplicating  the c u r v a t u r e of the t i p s , no a t t e m p t was  the n e c k g r o w t h d a t a q u a n t i t a t i v e l y . growth during decomposition photographs.  ma.de to a n a l y s e  H o w e v e r , the p h e n o m e n o n of n e c k  i s c l e a r l y d e m o n s t r a t e d i n t h i s s e r i e s of  M i c r o s c o p i c examination  of the c o n t a c t f a c e s of the  crystal  a f t e r the n e c k g r o w t h e x p e r i m e n t s i n d i c a t e d f u s i o n h a d t a k e n p l a c e . T h i s was  the f i r s t i n d i c a t i o n that d e f o r m a t i o n  c o u l d take p l a c e i n the  p r e s e n c e of a p p l i e d s t r e s s d u r i n g the d e c o m p o s i t i o n 3. 2  of h y d r o x i d e .  T i p to T i p C o n t a c t of M a g n e s i u m H y d r o x i d e Following a similar procedure,  Mg(OH)  2  Compacts  compacts  with  h e m i s p h e r i c a l tips w e r e d e c o m p o s e d while l o a d e d into contact ( F i g u r e D e f o r m a t i o n of the c o n t a c t a r e a r e s u l t e d , as c a n be s e e n .  14)  Considerably  - 41 -  After  decomposition  F I G U R E 13  G r o w t h of c o n t a c t a r e a d u r i n g the d e c o m p o s i t i o n of C a ( O H ) tips under load. ?  m o r e i n t e r e s t i n g w a s the e x p l i c i t e v i d e n c e of b o n d f o r m a t i o n w h i c h i s p r o v i d e d i n the f o r m of a s m a l l p i e c e of one t i p l e f t on the o t h e r , w h e n the t i p s w e r e b r o k e n a p a r t f o l l o w i n g the d e c o m p o s i t i o n ( F i g u r e  15).  This  s h o w e d that the a d h e s i o n b e t w e e n the t w o t i p s w a s at l e a s t a s g r e a t a s the cohesion within them. 3. 3  D e f o r m a t i o n of M a g n e s i u m H y d r o x i d e A f t e r the i n i t i a l e x p e r i m e n t  Compacts  just d e s c r i b e d , attempts  were  m a d e to s t u d y q u a n t i t a t i v e l y the d e f o r m a t i o n b e h a v i o u r of m a g n e s i u m h y d r o x i d e c o m p a c t s d u r i n g d e h y d r o x y l a t i o n , b o t h at a u n i f o r m h e a t i n g rate and under i s o t h e r m a l conditions.  The experiments  at u n i f o r m  h e a t i n g r a t e u n d e r d i f f e r e n t l o a d s w e r e c a r r i e d oat to d e t e r m i n e the e x t e n t of d e f o r m a t i o n o b t a i n e d , a n d to e s t a b l i s h l i m i t o n l o a d s , a n d d e n s i t y w h i c h c o u l d be u s e d i n s u b s e q u e n t  studies.  These  temperature, experiments  a l s o s h o w e d the r e l a t i v e a m o u n t of s h r i n k a g e a n d l o a d - d e p e n d e n t  de-  f o r m a t i o n which were produced under these conditions. 3. 3. 1  U n i f o r m Heating The  relative  Rate  s p e c i m e n s u s e d i n t h i s s e r i e s of t e s t s a l l h a d a n o m i n a l  b u l k d e n s i t y of 0. 50 ( T a b l e III):.  A s e t of t e m p e r a t u r e - d e -  f o r m a t i o n c u r v e s f o r t h i s s e r i e s of r u n s i s s h o w n i n F i g u r e 16.  The  c u r v e s s h o w a t e n d e n c y to i n c r e a s i n g m a x i m u m s l o p e a n d i n c r e a s i n g total d e f o r m a t i o n with i n c r e a s i n g load. The  total deformation obtained during decomposition  was  m e a s u r e d f r o m the i n i t i a l a n d f i n a l l e n g t h at the e n d of the d e c o m p o s i t i o n ,  - 43 -  a) Before decomposition  A£ti€i~ decomposition  FlGfa'BE? M  Gr^wtfa. &£ miii&ei area, during decomposition of M g ( © H ) | Go^Mpa^et tips" under lead.-  - 44 -  b)  F I G U R E 15  M a t e r i a l r e m o v e d f r o m the c r a t e r ad h e r i n g to the o t h e r t i p .  E v i d e n c e of b o n d f o r m a t i o n d u r i n g the d e c o m p o s i t i o n of Mg(OH)2 compact tips under load.  - St -  -46 T A B L E III DEFORMATION D A T A FOR UNIFORM H E A T I N G R A T E  io/ \  _gm '°'  SPECIMEN  LOAD, kg  kg/err/  49 50  0.10 0.10  0.54 0.54  2.62 2.69  1.19 1-20  38 39  0.35 0.35  1.9 1.9  3.56 4.08  1.19 1.19  45 46  0.66 0.66  3.58 3.56  4.78 4.69  1.19 1.20  42 43  0.88 0.88  4.78 4.78  5.15 5.20  1.18 1.19  40 41  1.2 1.2  6.53 6.53  5.65 5.96  1.19 1.18  47 48  1.63 1.63  8.76 8.76  6.22 6.47  1.19 1.19  33 34  2.06 2.06  11.2 11.2  6.72 6.90  1.20 1.20  52 53 54  2.5 2.5 2.5  13.6 13.6 13.6  7.26 6.85 7.10  1.21 1.20 1.20  c  L  p  c  0  m  -47as s h o w n i n F i g u r e 16.  T h i s t o t a l d e f o r m a t i o n was  t h e n c o n v e r t e d to  p e r c e n t t o t a l s t r a i n a n d i s p l o t t e d a g a i n s t l o a d i n F i g u r e 17.  A  log-log  p l o t of t h i s d a t a ( F i g i x r e 18) s u g g e s t s a r e l a t i o n s h i p of the f o r m  e~ T  where  n  eo + K < T  i s a p p r o x i m a t e l y 1/3,  u n d e r z e r o l o a d was 3. 3. 2  n  T  a n d the e x t r a p o l a t e d c h a n g e of l e n g t h  c a l c u l a t e d to be 0. 3%.  "Isothermal" Deformation  (Creep)  A s p r e v i o u s l y d i s c u s s e d , the o p t i m u m r e l a t i v e d e n s i t y that c o u l d be e a s i l y a c h i e v e d b y c o l d p r e s s i n g w a s m a g n e s i u m hydroxide.  0. 50  of the d e n s i t y of  F o r t h i s r e a s o n m o s t of the e x p e r i m e n t s  under  i s o t h e r m a l c o n d i t i o n s w e r e c a r r i e d out u s i n g c o m p a c t s of 0. 50 r e l a t i v e density.  A l l c r e e p c u r v e s p r e s e n t e d have been c o r r e c t e d f o r t h e r m a l  e x p a n s i o n of the l o a d i n g f r a m e a s o u t l i n e d i n S e c t i o n 2. 2. 4, (ii). compressive  l o a d was  t h r o u g h o u t the t e s t .  a p p l i e d to the c o l d s p e c i m e n ,  maintained  A typical time deformation curve is shown i n F i g u r e  19, a l o n g w i t h the s p e c i m e n vacuum chamber.  and  The  The  surface temperature  a n d p r e s s u r e i n the  a p p a r e n t r e l a t i o n s h i p b e t w e e n the p r e s s u r e of  the w a t e r v a p o u r p r o d u c e d b y the d e c o m p o s i t i o n (as n o t e d f r o m the v a c u u m gauge  on the s y s t e m ) a n d the d e f o r m a t i o n i s n o t a b l e ; the p e a k  of the p r e s s u r e c u r v e c o i n c i d e s i n t i m e w i t h the ( m a x i m u m c r e e p r a t e ) of the d e f o r m a t i o n c u r v e . r e s u l t w i l l be d i s c u s s e d i n m o r e d e t a i l l a t e r .  r e g i o n of m a x i m u m s l o p e The  s i g n i f i c a n c e of t h i s  F I G U R E 17  Total deformation  as a f u n c t i o n of l o a d ( u n i f o r m h e a t i n g r a t e ) .  F I G U R E 18  L o g - L o g p l o t of t o t a l d e f o r m a t i o n  a s a f u n c t i o n of l o a d ( u n i f o r m h e a t i n g r a t e ) .  -51(a)  E f f e c t s of T e m p e r a t u r e  on D e f o r m a t i o n  T h e f i r s t s e r i e s of r u n s w e r e p e r f o r m e d u s i n g a l o a d 2. 50 k g (13. 6 k g / c m ) at d i f f e r e n t t e m p e r a t u r e s  i n the r a n g e of 3 4 0 °  2  to 4 0 5 ° C.  A t l e a s t two r u n s w e r e m a d e f o r a g i v e n s e t of e x p e r i m e n t a l  conditions , to test r e p r o d u c i b i l i t y .  F o u r p a i r s of r e p r e s e n t a t i v e t i m e -  d e f o r m a t i o n c u r v e s a r e s h o w n i n F i g u r e 20, a n d t i m e - t e m p e r a t u r e formation  de-  d a t a a r e t a b u l a t e d i n A p p e n d i x II (a). The  s e c o n d s e r i e s of r u n s w e r e p e r f o r m e d w i t h a l o a d of  1. 1 kg, (6. 0 k g / c m ^ ) , a n d the s a m e t e m p e r a t u r e previous series.  was  u s e d i n the  F o u r p a i r s of c u r v e s f o r t h i s s e r i e s a r e s h o w n i n  F i g u r e 21, a n d d a t a a r e p r e s e n t e d i n A p p e n d i x II (b). (b)  E f f e c t of S t r e s s at C o n s t a n t  Temperature  F o l l o w i n g the s a m e p r o c e d u r e o u t l i n e d a b o v e ,  isothermal  c r e e p t e s t s w e r e p e r f o r m e d to d e t e r m i n e the e f f e c t of l o a d on d e f o r m a t i o n , using specimens  of 0. 50 r e l a t i v e d e n s i t y .  A t e m p e r a t u r e of 3 6 0 ° C  was  c h o s e n f o r t h i s s t u d y a s i t a l l o w e d a m a x i m u m r a n g e of l o a d s to be u s e d w i t h o u t f r a c t u r e of the c o m p a c t .  F i v e s t r e s s e s b e t w e e n 0. 55 a n d  kg/cm^ were used f o r these experiments.  The  13. 6  results are plotted in  F i g u r e 22 a n d r e c o r d e d i n t a b u l a r f o r m i n A p p e n d i x II (c). (c)  E f f e c t of G r e e n D e n s i t y P r e v i o u s c r e e p s t u d i e s of p o r o u s  c e r a m i c b o d i e s have  s h o w n that the c r e e p r a t e v a r i e s w i t h the r e l a t i v e d e n s i t y of the c o m p a c t ' ^ ).  In o r d e r to d e t e r m i n e the e f f e c t of the g r e e n d e n s i t y of  CN  h  340 °C  to 405°C^7 7 7  3 8 5  ocT ^^ 3  360 °C  CO  0 F I G U R E 20  10  20  Time, min.  30  40  50  D e f o r m a t i o n v e r s u s t i m e f o r s p e c i m e n s o f 0. 50 r e l a t i v e d e n s i t y , at " i s o t h e r m a l " tempe r a t u r e s a s shown. S t r e s s 6. 0 k g / c m .  Ul  F I G U R E 21 D e f o r m a t i o n v e r s u s t i m e f o r s p e c i m e n s o f 0. 50 r e l a t i v e d e n s i t y , at " i s o t h e r m a l " t e m p e r a t u r e s a s shown. S t r e s s 6 . 0 k g / c m ^ .  - 55 -  the c o m p a c t on the d e f o r m a t i o n b e h a v i o u r , a s e r i e s of e x p e r i m e n t s w e r e c a r r i e d out u n d e r i s o t h e r m a l c o n d i t i o n s .  F o r this s e r i e s a tern  2 p e r a t u r e of 3 6 0 ° C a n d a l o a d of 9. 2 5 k g / c m w a s  used.  A s the s p e c i m e n s  c o u l d be p r o d u c e d w i t h r e l a t i v e d e n s i t i e s i n the r a n g e 0. 4 t o 0. 7, compacts having densities i n this range were used.  As  expected,  the v a r i a t i o n i n g r e e n d e n s i t y s i g n i f i g a n t l y a f f e c t e d the c r e e p b e h a v i o u r as c a n be s e e n i n F i g u r e 23.  The  t a b u l a r f o r m i n A p p e n d i x II (d).  c r e e p data a r e a l s o p r e s e n t e d i n  -57CHAPTER 4  IV  Discussion  4. 1  Shrinkage V e r s u s The  Creep  first consideration requiring clarification  n a t u r e of the d e f o r m a t i o n o b s e r v e d .  i s that of the  It m u s t f i r s t be e s t a b l i s h e d that  the d e f o r m a t i o n p r o d u c e d d u r i n g the d e c o m p o s i t i o n of m a g n e s i u m droxide  compacts under load, either with a u n i f o r m heating rate  under i s o t h e r m a l  c o n d i t i o n s , i s not due  w i t h the d e c o m p o s i t i o n .  The  2  s i m p l y to m a s s l o s s a s s o c i a t e d  MgO  +  H 0 2  and t h i s r e s u l t s i n a t h e o r e t i c a l w e i g h t l o s s of 30. 9% It c a n e a s i l y be  would if fully t r a n s f o r m e d volume.  of the  initial  s h o w n that a f u l l y d e n s e s p e c i m e n to p e r i c l a s e o c c u p y o n l y 4 7 %  T h u s , t h e r e i s a net v o l u m e r e d u c t i o n of 5 3 %  this d e c o m p o s i t i o n .  or  reaction involved in decomposition is -  Mg(OH) -  specimen.  hy-  of b r u c i t e  of i t s o r i g i n a l associated  H o w e v e r , it i s w e l l e s t a b l i s h e d ( ^  ) that the  with de-  c o m p o s i t i o n of b r u c i t e p r o d u c e s p s e u d o m o r p h o u s r e l i c s w i t h o n l y s l i g h t d i m e n s i o n a l change. It was  t h e r e f o r e n e c e s s a r y to e x p e r i m e n t a l l y  d e t e r m i n e the  extent of s h r i n k a g e d i r e c t l y a s s o c i a t e d w i t h m a s s l o s s so that t h i s be d i f f e r e n t i a t e d f r o m the c r e e p d e f o r m a t i o n r e s u l t i n g f r o m the nally applied s t r e s s (during dehydroxylation). a p p a r a t u s u s e d , a f i n i t e l o a d on the s p e c i m e n  could  exter-  H o w e v e r , w i t h the was  r e q u i r e d to e n s u r e  -58the f u n c t i o n of the m e a s u r i n g s y s t e m , so d i r e c t m e a s u r e m e n t of s h r i n k age w i t h o u t l o a d i n the e x p e r i m e n t a l s e t u p was  not p o s s i b l e .  Therefore,  s e v e r a l s p e c i m e n s w e r e d e c o m p o s e d u n d e r the s a m e c o n d i t i o n s of t e m p e r a t u r e a n d v a c u u m i n the f u r n a c e of the c r e e p a p p a r a t u s . s p e c i m e n s w e r e s e t v e r t i c a l l y on a f o i l p a n t o e n s u r e shrinkage  could occur during decomposition.  of the s p e c i m e n s , h e a t e d at t e m p e r a t u r e s were determined  shrinkage measurement that the s h r i n k a g e  was  was  that u n r e s t r i c t e d  dimensional  (sensitivity  after decomposition,  difficult.  cylindrical  changes  i n the r a n g e of 3 0 0 ° t o 5 0 0 ° C,  with a conventional m i c r o m e t e r  A s the s p e c i m e n s w e r e quite f r a g i l e  The  The  The  0. 0001  i n . ).  precise  H o w e v e r , the r e s u l t s i n d i c a t e d  l e s s t h e n 0. 4%.  r e s u l t s p r e s e n t e d i n S e c t i o n 3. 3. 1, f o r the  of m a g n e s i u m h y d r o x i d e  deformation  c o m p a c t s s u b j e c t e d to v a r y i n g l o a d s a n d  de-  c o m p o s e d u n d e r a u n i f o r m h e a t i n g r a t e a l s o s u p p o r t t h i s e s t i m a t e of the s h r i n k a g e .  The  e x t r a p o l a t e d v a l u e of t o t a l s t r a i n at z e r o l o a d  c a l c u l a t e d to be 0. 3 % compares  on the b a s i s of the e x p e r i m e n t a l data.  f a v o u r a b l y w i t h that o b t a i n e d b y d i r e c t s h r i n k a g e  was  T h i s value measure-  me nt s. T h u s t h i s s h r i n k a g e , due to the m a s s l o s s o n l y , c a n be c o n s i d e r e d i n s i g n i f i c a n t i n c o m p a r i s o n w i t h the 6 to 8% l i n e a r sional change o b s e r v e d  d u r i n g the c r e e p study.  No  attempt  has  dimenbeen  m a d e to c o r r e c t the c r e e p c u r v e s f o r the s h r i n k a g e , w h i c h i s s m a l l e r t h a n o t h e r p o t e n t i a l e x p e r i m e n t a l s o u r c e s of e r r o r . T h i s o b s e r v a t i o n f i r m l y e s t a b l i s h e s f o r the f i r s t t i m e _ t h a t the m a t e r i a l c a n be d e f o r m e d p l a s t i cally during a decomposition  reaction.  . 4. 2  -59-  Weight L o s s V e r s u s The  Creep  s h a p e of the c r e e p c u r v e (as o p p o s e d to the s h r i n k a g e  c u r v e ) i s s i m i l a r to that of the w e i g h t l o s s c u r v e d e t e r m i n e d graphically. T h i s i s shown  thermo-  c l e a r l y i n F i g u r e 24, w h e r e a c r e e p  curve  and a weight l o s s c u r v e p r e p a r e d u n d e r i d e n t i c a l h e a t i n g c o n d i t i o n s are compared.  A l o a d of 6. Q k g / c m ^ a n d a l i n e a r h e a t i n g r a t e of  2 5 ° C / m i n were used, (0. 50).  on c o m p a c t s h a v i n g the s a m e r e l a t i v e d e n s i t y  A s h r i n k a g e c u r v e i s a l s o i n c l u d e d for c o m p a r i s o n  served deformation.  T h e c o n d i t i o n s of d e c o m p o s i t i o n d i f f e r e d  i n that the t h e r m o g r a v i m e t r i c atmosphere.  w i t h the o b -  This may  slightly  a n a l y s i s w a s c a r r i e d out i n a n i t r o g e n  e x p l a i n the n o n - c o i n c i d e n c e  of the c r e e p a n d  w e i g h t l o s s c u r v e s i n F i g u r e 24. 4. 3  S t a g e s of C r e e p The  c r e e p c u r v e i s of s i g m o i d a l f o r m  F i g u r e s 20 - 23), w i t h t h r e e a p p a r e n t s t a g e s .  ( F i g u r e 25 a n d  T h e s e c a n be t e r m e d :  Stage I The  i n i t i a t i o n p e r i o d , w h e r e a r a p i d i n c r e a s e of c r e e p r a t e  occurs. Stage II A p e r i o d of rapid, c r e e p , w h i c h i n s e v e r a l c a s e s to a p p r o a c h  appears  linearity. Stage III A d e c a y r e g i o n , d u r i n g w h i c h the r a t e d e c r e a s e s  and a p p e a r s to a p p r o a c h  zero asymptotically.  rapidly  F I G U R E 24  C r eep,  w e i g h t l o s s and  shrinkage versus  time.  - 6 1 -  F I G U R E 25  S t a g e s of C r e e p  -62The reaction.  f i r s t s t a g e a p p e a r s t o be i n i t i a t e d b y the d e h y d r o x y l a t i o n  T h i s i s s h o w n i n F i g u r e 19, w h e r e the b e g i n n i n g of Stage I  c o i n c i d e s w i t h the r i s e of p r e s s u r e i n the v a c u u m s y s t e m . a p p e a r s to l a s t f o r the f i r s t  10 t o 2 0 %  s t a g e , the c r e e p r a t e i s h i g h e s t .  of the t o t a l c r e e p .  D u r i n g t h i s s t a g e the  of the s u r f a c e a n d the i n s i d e of the s p e c i m e n  In the  second  temperature  r e a c h e d a s t e a d y state  t h e r m a l c o n d i t i o n , w i t h a d i f f e r e n t i a l of 10° to 12°C decomposition,  T h i s stage  throughout  the  as d i s c u s s e d i n S e c t i o n 2. 2. 5, a n d s h o w n i n F i g u r e  12.  T h i s s t a g e of the d e f o r m a t i o n c o i n c i d e s w i t h the m o s t r a p i d e v o l u t i o n of w a t e r v a p o u r f r o m , pressures.  The  tendency  as s h o w n i n F i g u r e 19, (specimen  the s p e c i m e n , a n d h e n c e the h i g h e s t  of the s y s t e m p r e s s u r e to f o r m a s h a r p p e a k ,  d e p e n d s u p o n the t e m p e r a t u r e  surface temperature).  pronounced; temperatures  of  At  385° a n d 405°C  340° a n d 360° p r o d u c e d  f l a t t e r p r e s s u r e c u r v e , as i s e x p e c t e d , to the d e c o m p o s i t i o n . lationships  of the r u n , the p e a k i s quite a broader  i f the c r e e p i s d i r e c t l y  and related  Several more time-deformation-pressure  are shown i n F i g u r e s  26  a n d 27  •  These  re-  demonstrate  c l e a r l y the r e l a t i o n s h i p b e t w e e n the s y s t e m p r e s s u r e a n d The  system  deformation.  r e l a t i o n s h i p b e t w e e n the s y s t e m p r e s s u r e a n d the  r a t e of m a s s l o s s a c c o m p a n y i n g d e h y d r o x y l a t i o n i s i n p r i n c i p l e a s i m p l e one.  The  p u m p i n g r a t e i s p r o b a b l y a f u n c t i o n of the a b s o l u t e  s y s t e m p r e s s u r e , a n d i f the e x a c t p u m p i n g r a t e i s k n o w n i t s h o u l d be p o s s i b l e to d e t e r m i n e  r e a s o n a b l y a c c u r a t e l y the r a t e of m a s s l o s s d u r i n g  F I G U R E 26  D e f o r m a t i o n and s y s t e m p r e s s u r e v e r s u s t i m e .  F I G U R E 27  D e f o r m a t i o n and s y s t e m p r e s s u r e v e r s u s t i m e  -65the d e h y d r o x y l a t i o n . F r o m t h i s , t h e m a s s l o s s v e r s u s t i m e c u r v e c o u l d be o b t a i n e d b y i n t e g r a t i o n . T h i s a p p r o a c h i s c o m p l i c a t e d , u n f o r t u n a t e l y , by the v a r i a t i o n of s u c h p a r a m e t e r s a s t h e p u m p i n g r a t e , w h i c h d e p e n d s t o s o m e e x t e n t o n t h e m e c h a n i c a l c o n d i t i o n of t h e b a c k i n g p u m p » t h e t y p e of gas p r e v i o u s l y pumped, the s y s t e m t e m p e r a t u r e , and other f a c t o r s .  These  f a c t o r s a r e p r o b a b l y c o n t r o l l a b l e , h o w e v e r , a n d t h e m e a s u r e m e n t of system p r e s s u r e represents a potentially useful technique f o r correlating mass loss with m e c h a n i c a l deformation during dehydroxylation i n this t y p e of e x p e r i m e n t . In o r d e r to c h a r a c t e r i z e the o b s e r v e d c r e e p q u a n t i t a t i v e l y , d i f f e r e n t a s p e c t s of t h e t i m e - d e f o r m a t i o n c u r v e s h o u l d be c o n s i d e r e d . T h e b e g i n n i n g of S t a g e I s e e m s t o be r e l a t e d d i r e c t l y t o t h e o n s e t of d e h y d r o x y l a t i o n , a n d t h e e x t e n t of t h i s s t a g e v a r i e s w i t h t h e t e m p e r a t u r e , l o a d a n d d e n s i t y of t h e s p e c i m e n a s c a n be s e e n i n F i g u r e s 20 - 23. L o w e r t e m p e r a t u r e s , a n d c o n s e q u e n t l y l o w e r r a t e s of d e h y d r o x y l a t i o n produce a more prolonged initiation period. The applied load.  d u r a t i o n of S t a g e I I v a r i e s w i t h t h e t e m p e r a t u r e a n d  A t h i g h e r t e m p e r a t u r e s and loads, and l o w e r densities,  a l o n g e r a n d n e a r l y l i n e a r S t a g e II i s o b s e r v e d .  A t lower temperatures,  h i g h e r d e n s i t i e s a n d l o w e r s t r e s s e s , the Stage III d e c a y r e g i o n s e e m s to f o r m a l a r g e r p o r t i o n of t h e c u r v e .  I n a l l c a s e s , h o w e v e r , the s l o p e  of t h e c u r v e ( m a x i m u m c r e e p r a t e ) i s s t r o n g l y i n f l u e n c e d b y v a r i a t i o n s  i  -66in stress, density and temperature The phenomenon  parameters  .  s e l e c t e d t o c h a r a c t e r i z e the c r e e p  a r e , t h e r e f o r e , the t o t a l c r e e p s t r a i n d e v e l o p e d  i s o t h e r m a l c o n d i t i o n s a n d the m a x i m u m r a t e of c r e e p . d e f o r m a t i o n w a s m e a s u r e d f o l l o w i n g the p r o c e d u r e  under  The total  s h o w n i n F i g u r e . 16,  a n d the m a x i m u m c r e e p r a t e w a s d e t e r m i n e d f r o m the s l o p e of a l i n e d r a w n tangent  t o t h e s t e e p e s t p a r t of the c r e e p c u r v e .  is e x p r e s s e d as i n c h e s / i n c h / m i n u t e T h e s e two p a r a m e t e r s  T h e c r e e p rate  ( o r m i n u t e " •*•)•  a r e somewhat a r b i t r a r i l y defined,  but a s i s s h o w n i n the f o l l o w i n g s e c t i o n s , t h e y p r o v i d e a b a s i s f o r analyzing  q u a n t i t a t i v e l y the c r e e p  behaviour.  In the f o l l o w i n g s e c t i o n s , the e f f e c t s of t e m p e r a t u r e , a n d r e l a t i v e d e n s i t y o n the m a x i m u m c r e e p r a t e a n d the t o t a l  stress  observed  strain are considered. 4. 4  Creep  Rate  4. 4. 1  E f f e c t of T e m p e r a t u r e To determine  the a c t i v a t i o n e n e r g y f o r the c r e e p p r o c e s s ,  the m a x i m u m c r e e p r a t e s have b e e n p l o t t e d a g a i n s t r e c i p r o c a l a b s o l u t e temperature  i n F i g u r e 28.  T h e A r r h e n i u s p l o t of b o t h s e t s of c r e e p  r a t e s , d e t e r m i n e d u s i n g s p e c i m e n s of r e l a t i v e b u l k d e n s i t y 0. 50 a n d s t r e s s e s of 6. 0 a n d 13. 6 k g / c m 17. 5 k c a l / m o l .  2  produced  a n a c t i v a t i o n e n e r g y of  The specimen properties, temperatures,  c r e e p rate a r e s u m m a r i z e d i n T a b l e IV.  stresses and  2  -I  145  1™  _ L _ _  1-50 1-55 1000/T °K"'  I  1-60  1-65  F I G U R E ZH A r r h e n i u s - t y p e p l o t o f c r e e p r a t e v e r s u temperature.  - 68 T A B L E IV  TEMPERATURE  DEPENDENCE  OF ISOTHERMAL  N o m i n a l R e l a t i v e B u l k D e n s i t y = 0. 50  C-  13. 6 k g / c m  e SPECIMEN 81  T°C 340  min  _ 1  X10  CREEP  e  2  T  %  4  24. 6  7. 55  340  22. 9  7. 48  1. 206  360 360  43 4  7. 25 7. 25  83 76 75 82  360  79 80  385  77 78  405  1. 206  42. 9 39. 0 66. 6  6. 86  1. 208 1. 203 1. 196  6. 95  1. 202  385  70. 6  6. 94  1. 206  405  90. 3  7. 26  1 204  100. 8  7. 52  1. 199  <T=  6. 0 k g / c m ^  85  340  16 35  5. 97  1. 204  86 96 97  340 340 340  17. 9 20. 8 20. 0  5. 40 5. 43  1. 203 1.217  5. 08  1. 216  101  360 360 385  27. 6 30. 0 41. 3  5. 39 5. 38 5. 40  1. 208 1. 214 1. 217  84  385 405  40. 2 70. 0  5. 36 5. 68  1. 209 1. 210  98  405  60. 2  5. 42  1. 219  102 99 100  -694. 4. 2  Stress The  Dependence  o b s e r v e d m a x i m u m c r e e p rate is plotted as a function  of s t r e s s i n F i g u r e 29.  T h e stress dependence is e s s e n t i a l l y l i n e a r ,  showing p s e u d o - N e w t o n i a n b e h a v i o u r , with a n a p p a r e n t i n t e r c e p t on the r a t e a x i s , i . e. f i n i t e r a t e a t z e r o s t r e s s . between c r e e p rate and s t r e s s is generally  A direct proportionality  attributed to v i s c o u s flow,  grain boundary sliding or N a b a r r o - H e r r i n g creep. m e c h a n i s m s of c r e e p d u r i n g d e h y d r o x y l a t i o n The  D e t a i l s of p o s s i b l e  w i l l be d i s c u s s e d l a t e r .  data i s s u m m a r i z e d i n T a b l e V.  4. 4. 3  Density Dependence The  of the  m a x i m u m c r e e p r a t e v a r i e d s t r o n g l y w i t h the g r e e n  specimen.  A s i m i l a r density dependence  density  was a l s o o b s e r v e d by  (24 ) Coble  f o r t h e c r e e p of a l u m i n a at e l e v a t e d To  temperatures.  e x p l a i n the d e n s i t y d e p e n d e n c e of c r e e p r a t e , the e f f e c t i v e  s t r e s s a c t i n g w i t h i n the  s p e c i m e n m u s t be c o n s i d e r e d .  In a p a r t i c u l a t e  compact, the e f f e c t i v e s t r e s s a c t i n g on contact a r e a A, (on a  cross  s e c t i o n of the c o m p a c t ) , a n d the s t r e s s a r e r e l a t e d b y -  . CT e f f =  CTapplied A  Any  increase  i n the  relative density increases  the c o n t a c t  a r e a ( a s s u m i n g c o n s t a n t p a c k i n g g e o m e t r y ) a n d t h u s r e d u c e s the effective stress,  T h e c o n t a c t a r e a i n a p o w d e r c o m p a c t of s p h e r e s a f t e r  d e f o r m a t i o n a n d the  relative density  of the  compact a r e related by  v  ( 25 ) '  o  LO  F I G U R E 29  S t r e s s d e p e n d e n c e of m a x i m u m c r e e p r a t e  - 71 TABLE STRESS D E P E N D E N C E  Isothermal T  =  Creep  V  OF ISOTHERMAL  CREEP  Stress Dependence  360°C  N o m i n a l relative bulk density  =  0.  SPECIMEN  STRESS kg/cm  103  0, 54  20. 9  3. 16  1. 214  104  0. 54  19. 9  3. 48  1. 214  105  0. 54  17. 7  2. 53  1. 212  101  6. 0  27. 6  6. 0  30. 0  39 38  1. 208  102  1. 212  2  min  _ 1  X10  4  %  1. 214  108  9. 25  30. 6  109  9. 25  31.2  6. 58 6. 27  1. 220  106 107  3. 53 3. 53  24. 9 24. 7  5. 02 4. 70  1. 205 1 212  75  13. 6  42. 9  7. 25  1. 203  76  13. 6  43. 4  7. 25  1. 208  82  13. 6  39. 0  6. 86  1 196  •72-  2  w h e r e ^> a and  and  a =0,  p  o  a r e the r e l a t i v e d e n s i t i e s at a n y f a c e of r a d i u s  r e s p e c t i v e l y , and R  T h i s m e a n s that <j> ct, density.  i s the r a d i u s of the d e f o r m e d  a " or c o n t a c t a r e a ,  f o r a constant  sphere.  initial packing  Hence,  T h i s r e l a t i o n may  a l s o be o b t a i n e d by  c o n s i d e r i n g the s o l i d a r e a f r a c t i o n  i n a p l a n e cut t h r o u g h the s p e c i m e n , the s t r e s s e f f e c t i v e on t h i s and the r e l a t i v e d e n s i t y of the s p e c i m e n . o-xov, m.«.w^ ^.y a.  ,v..  ^.  Finally,  A  s i m i l a r conclusion  area, was  s i n c e the s t r a i n r a t e i s p r o p o r t i o n a l  to the s t r e s s ,  The  e x p e r i m e n t a l v a l i d i t y of the r e l a t i o n i s s h o w n i n F i g u r e  the c r e e p r a t e i s p l o t t e d a s a f u n c t i o n of Kingery  1/^  .  The  b o t h s e t s of data.  It c a n be  where  d a t a of C o b l e  ^ f o r the c r e e p b e h a v i o u r of A I 2 O 3 of v a r y i n g  densities are also plotted.  30,  and  relative  s e e n that t h i s r e l a t i o n s a t i s f i e s  T h i s r e s u l t i m p l i e s that the d e n s i t y d e p e n d e n c e of  the c r e e p r a t e a r i s e s f r o m the s t r e s s c o n c e n t r a t i o n  on the g r a i n b o u n d a -  r i e s o r the c o n t a c t a r e a b e t w e e n the p a r t i c l e s b e c a u s e of the p o r o s i t y i n the  specimen.  Up I G U R E 30  D e n s i t y d e p e n d e n c e of m a x i m u m c r e e p  rate.  - 74 TABLE DENSITY DEPENDENCE  Stress  9. 25  Temperature  kg/cm  VI  OF ISOTHERMAL  CREEP  2  360°C. NOMINAL  e  e  T  RELATIVE ° Vo  DENSITY  129  0. 963  0. 40  44. 9  collapsed  130  0.972  0.40  51.3  collapsed  0.45  41.2  SPECIMEN  m i nn ~ *XX1100 ' _ 1  4  %%  124  1.072  125  1. 073  0. 45  40. 7  7. 05  108  1. 212  0. 50  30. 6  6. 58  109  1.220  0.50  31.2  6.27  120  1. 313  0. 55  31.4  5. 96  121  1. 317  0. 55  29. 2  6. 04  116 117  1. 425 1. 430  0. 60 0. 60  25. 5 24. 3  5. 42  132  1. 537  0. 65  21.3  5. 02  133  1. 535  0. 65  20. 2  4. 87  136  1. 702 1. 700  0. 70  19. 1 20. 1  4. 28  137  0. 70  7.62  5. 59  4. 21  -75It s h o u l d b e p o i n t e d out t h a t t h e a c t u a l d e n s i t y of the  compact  at the i n s t a n t of m a x i m u m c r e e p r a t e i s n o t the s a m e a s t h e g r e e n d e n s i t y , s i n c e a c e r t a i n a m o u n t of d e c o m p o s i t i o n (and h e n c e m a s s l o s s ) has t a k e n p l a c e at t h e t i m e t h e m a x i m u m c r e e p r a t e i s m e a s u r e d . The  f a c t t h a t the d e n s i t y d e p e n d e n c e m a y be d e s c r i b e d b y a s s i m p l e  a r e l a t i o n s h i p as e ^  _L_  shows that:  1) e i s i n d e p e n d e n t of w e i g h t  ?~ l o s s d u r i n g S t a g e I l ^ o r 2) t h e m a x i m u m r a t e o c c u r s at a c e r t a i n f r a c t i o n of the t o t a l w e i g h t l o s s i n a l l c a s e s . The constant,  c r e e p r a t e d u r i n g S t a g e II a p p e a r s t o b e r e l a t i v e l y  e v e n t h o u g h the s y s t e m p r e s s u r e  v a r i a t i o n shows that the  reaction reaches m a x i m u m rate and diminishes v e r y rapidly, indicating t h a t the d e h y d r o x y l a t i o n  rate has the s a m e behaviour.  This  suggests  s t r o n g l y t h a t the c r e e p r a t e m a y b e i n d e p e n d e n t of the e x t e n t of d e h y d r o x y l a t i o n as long as the r e a c t i o n i s a c t u a l l y i n p r o g r e s s . 4. 5  Total Creep Strain The  total percent strain is s u m m a r i z e d for a p a r t i c u l a r set  of c o n d i t i o n s i n e a c h of the t a b l e s m e n t i o n e d i n the p r e c e d i n g (Tables I V - VI).  T h e e f f e c t s of t e m p e r a t u r e , s t r e s s a n d g r e e n d e n s i t y  u p o n the t o t a l s t r a i n w i l l n o w be 4. 5. 1  section.  considered.  E f f e c t of T e m p e r a t u r e The  t o t a l s t r a i n i n p l o t t e d i n F i g u r e 31, f o r two d i f f e r e n t  s t r e s s e s (6. 0 a n d 13. 6 k g / c m ) a n d a r a n g e of t e m p e r a t u r e s . 2  A  least  s q u a r e s f i t p e r f o r m e d o n the d a t a gave l i n e s t h r o u g h b o t h s e t s of p o i n t s having a zero slope.  T h a t i s , the t o t a l s t r a i n d e v e l o p e d i s independent  -76-  340  o  13.6 kg/cm  *  6.0  360  kg/cm  2  2  380  T,°C  FIGURE  31 T o t a l S t r a i n V e r s u s T e m p e r a t u r e  400  -77of t e m p e r a t u r e . 4. . 2 5  E f f e c t of The  Stress  total percentage s t r a i n under i s o t h e r m a l  is a l s o p l o t t e d as a f u n c t i o n of s t r e s s i n F i g u r e 32.  conditions  In o r d e r to f i n d  the s t r e s s d e p e n d e n c e of the t o t a l s t r a i n , a l o g - l o g p l o t of the is m a d e ( F i g u r e  33).  d a t a i s f o u n d to be  e  The  T  n i s a p p r o x i m a t e l y one determined  data  equation which adequately r e p r e s e n t s  =  e  third.  f r o m this plot.  +k  o T  e  o T  the  w h e r e the v a l u e of the is very small,  and  power  so c a n not  be  T h i s b e h a v i o u r i s s t r i k i n g l y s i m i l a r to  that o b s e r v e d e a r l i e r ( S e c t i o n 3. 3. 1) f o r t o t a l , s t r a i n at a u n i f o r m heating rate. 4. 5. 3  E f f e c t of D e n s i t y The  v a l u e s of t o t a l s t r a i n o b s e r v e d f o l l o w i n g  c r e e p at 3 6 0 ° C , f o r a c o n s t a n t s t r e s s of 9. 2 k g / c m d e n s i t y i n F i g u r e 34.  The  isothermal  , are plotted  against  d a t a h a v e a l s o b e e n t e s t e d on a l o g - l o g p l o t ,  on w h i c h a l i n e d r a w n t h r o u g h the p o i n t g i v e s a s l o p e of a p p r o x i m a t e l y -1,  suggesting a r e c i p r o c a l relationship.  against  '  a  s  s h o w n i n F i g u r e 35.  The  The  data are t h e r e f o r e  experimental scatter in  t h e s e d a t a m a k e s i t i m p o s s i b l e to d e t e r m i n e w i t h c e r t a i n t y the f o r m the  plotted  of  relationship. H o w e v e r , as the s t r a i n r a t e was  proportional  to the d e n s i t y ,  probable.  inversely  it i s l i k e l y that the d e n s i t y d e p e n d e n c e of  the t o t a l s t r a i n u n d e r i s o t h e r m a l c o n d i t i o n s s t r e s s a c t i n g on the  s h o w n to be  a l s o a r i s e s f r o m the e f f e c t i v e  c o m p a c t , m a k i n g the r e c i p r o c a l r e l a t i o n s h i p m o r e  F I G U R E 32  Total strain versus stress  -824.5.4  Phenomenological Behaviour The relationship o b s e r v e d between total s t r a i n and  s t r e s s , i . e.  e  y  (T  '  n  w  r  i  e  r  e  n  1/3  i s s i m i l a r to the d e p e n d e n c e of the c o l d c o m p a c t e d d e n s i t y material,  of the  w h i c h gave  fo  j '=^  0  p  -  w i t h  n  a  l  s  °  »  i /  T h e s i m i l a r i t y of the s t r e s s d e p e n d e n c e s u g g e s t s s o m e mechanistic relationship,  d e p e n d e n c e of d e n s i t y  Smith  possible  p e r h a p s p a r t i c l e s l i d i n g , but no t h e o r e t i c a l  a r g u m e n t c a n be a d v a n c e d f o r t h i s p o w e r law. law  3  A s i m i l a r power  on s t r e s s h a s a l s o b e e n r e p o r t e d b y  a l s o on the b a s i s  of e x p e r i m e n t a l data.  -83-  4. 6  P o s t u l a t e d M e c h a n i s m s of C r e e p  4. 6, 1  P h y s i c a l Changes Accompanying Dehydroxylation In o r d e r to p o s t u l a t e a m e c h a n i s m f o r the o b s e r v e d  creep  it i s n e c e s s a r y t o c o n s i d e r the c h a n g e s w h i c h a c c o m p a n y the d e composition.  As  d i s c u s s e d i n the I n t r o d u c t i o n , the d e h y d r o x y l a t i o n  j  of M g ( O H ) 2 f o r m s p a r t i c l e s of M g O ,  a p p r o x i m a t e l y 100 A  C a l c i n a t i o n of the M g ( O H ) 2 u s e d f o r t h i s s t u d y I 5 m ^ / g m ) i n the t e m p e r a t u r e s u r f a c e a r e a s of up t o 2 5 0 m to f r e e c u b e s of a v e r a g e  (specific surface area  r a n g e 3 5 0 ° to 4 0 0 ° C h a s /gm  on the p r o d u c t MgO.  66 A to a s i d e .  diameter.  produced This corresponds  T h i s c a l c u l a t e d size i s i n good  a g r e e m e n t w i t h X - r a y l i n e b r o a d e n i n g e x p e r i m e n t s ^ on the s a m e m a t e r i a l , calcined  between 4 0 0 ° and 500°C, w h i c h p r o d u c e d a p a r t i c l e  r a n g e of 60 to 75 ?S  2  size  \  7  S a m p l e s of the M g ( O H ) 2 h a v e b e e n e x a m i n e d b e f o r e a f t e r d e h y d r o x y l a t i o n i n the e l e c t r o n m i c r o s c o p e . h y d r o x i d e p o w d e r was  The  and  magnesium  p l a c e d on c a r b o n s u p p o r t f i l m s on c o p p e r  grids,  t h e n c a l c i n e d i n a v a c u u m f u r n a c e ( 1 0 ~ ^ T o r r ) at t e m p e r a t u r e s 3 5 0 ° to 5 0 0 ° C .  The  s a m p l e s w e r e t h e n e x a m i n e d to d e t e r m i n e  extent of v i s i b l e c h a n g e at v a r i o u s t e m p e r a t u r e s .  A t the  from the  temperatures  u s e d f o r t h i s s t u d y ( b e l o w 4 5 0 ° C ) the h e x a g o n a l b r u c i t e p l a t e l e t s  retained  t h e i r c h a r a c t e r i s t i c shape, although c o m p l e t e l y t r a n s f o r m e d  MgO.  These experiments of t h i s m a t e r i a l was ( S e c t i o n 1. 4) on  to  s e r v e d to c o n f i r m that the b e h a v i o u r  q u a l i t a t i v e l y s i m i l a r to that o b s e r v e d b y o t h e r s  materials f r o m different sources.  -84-  4. 6. Z  A c t i v a t i o n E n e r g i e s of C o n c u r r e n t  Processes  It i s i n t e r e s t i n g to c o m p a r e the a c t i v a t i o n e n e r g y  obtained  h e r e f o r the c r e e p p r o c e s s w i t h the a c t i v a t i o n e n e r g i e s of o t h e r p r o c e s s e s which may  occur concurrently during dehydroxylation.  approach may  Although this  not r e v e a l the e x a c t m e c h a n i s m s i n v o l v e d i n the  de-  f o r m a t i o n p r o c e s s , i t i s a b a s i s f o r c o m p a r i n g quite d i f f e r e n t p h e n o mena.  Such comparison  may  l e a d to a h y p o t h e t i c a l m e c h a n i s m f o r the  d e f o r m a t i o n o b s e r v e d i n this investigation. The  d e h y d r o x y l a t i o n i t s e l f i s the m o s t i m p o r t a n t  process  a s s o c i a t e d w i t h the c r e e p , a s the c r e e p p r o c e s s o b s e r v e d i s a c t i v a t e d by the d e c o m p o s i t i o n r e a c t i o n .  The  m o s t a u t h o r i t a t i v e w o r k on the  de-  {15} h y d r o x y l a t i o n k i n e t i c s i s that of G o r d o n a n d K i n g e r y s h o w n that the a c t i v a t i o n e n e r g y  v  who  have  of the p r o c e s s v a r i e s w i t h the  specimen  g e o m e t r y , p r i m a r i l y due to the b a c k p r e s s u r e of the w a t e r v a p o r b y the d e h y d r o x y l a t i o n .  The  a c t i v a t i o n e n e r g y f o r the d e h y d r o x y l a t i o n ,  w h e n c o r r e c t e d f o r the s p e c i m e n g e o m e t r y a p p e a r s to be i n the of 38 to 40 k c a l / m o l . determined  range  T h i s a c t i v a t i o n e n e r g y i s m o r e than double  that  f o r the c r e e p p r o c e s s , w h i c h i n d i c a t e s that a l t h o u g h the  decomposition  reaction  i n i t i a t e s the d e f o r m a t i o n , the r a t e c o n t r o l l i n g  m e c h a n i s m f o r the c r e e p i s p r o b a b l y d i f f e r e n t f r o m that of the hydroxylation. second  created  The  observation  stage i s i n d e p e n d e n t  de-  that the c r e e p r a t e d u r i n g the  of the r a t e of d e h y d r o x y l a t i o n l e n d s s u p p o r t  to t h i s a r g u m e n t . ( S e c t i o n 4. 4. 3).  - 85 -  S t u d i e s of the r e h y d r a t i o n of M g O  p r e p a r e d b y the c a l c i n a t i o n  of M g C 0 3 at 1 0 0 0 ° C w e r e c a r r i e d out b y L a y d e n a n d B r i n d l e y T h e s e s t u d i e s i n d i c a t e d that the t e m p e r a t u r e  d e p e n d e n c e of the  r e a c t i o n r a t e c o n s t a n t m a y be d e s c r i b e d b y a n A r r h e n i u s - t y p e r e l a t i o n s h i p w i t h a n a c t i v a t i o n e n e r g y of about m e c h a n i s m w a s not d e t e r m i n e d , o v e r a l l rate was  b u t i t w a s f e l t m o s t l i k e l y that the  g o v e r n e d b y the r a t e of a n i n t e r f a c i a l r e a c t i o n .  could p r e s u m a b l y A  16 k c a l / m o l . T h e e x a c t  This  i t s e l f be d i f f u s i o n c o n t r o l l e d .  g r a i n g r o w t h s t u d y of M g O  p r e p a r e d b y the c a l c i n a t i o n  of M g f O H ) ^ h a s b e e n p e r f o r m e d b y K o t e r a , S a i t o a n d T e r a d a ^ W o r k i n g i n a i r i n the t e m p e r a t u r e  range  5 0 0 ° to 9 0 0 ° C t h e y f o u n d a n  a c t i v a t i o n e n e r g y of 1 7 k c a l / m o l f o r the g r a i n g r o w t h , u s i n g p r e p a r e d f r o m p r e c i p i t a t e d Mg(OH)2-  .  material  O n the b a s i s of the l o w a c t i v a t i o n  e n e r g y of the p r o c e s s a n d the t i m e e x p o n e n t of g r a i n g r o w t h  (t  n  , n = 1/6),  K o t e r a et a l s u g g e s t e d that the r a t e m a y be c o n t r o l l e d b y s u r f a c e  dif-  fusion. The  g o o d a g r e e m e n t b e t w e e n the a c t i v a t i o n e n e r g y of the  g r a i n g r o w t h p r o c e s s a s d e t e r m i n e d b y K o t e r a e t a l , a n d that of the c r e e p p r o c e s s i n v e s t i g a t e d h e r e s u g g e s t s that the r a t e c o n t r o l l i n g m e c h a n i s m s f o r t h e s e t w o p r o c e s s e s m a y be the s a m e . 4. 6. 3  Viscous F l o w and Grain Boundary Sliding The  s t r e s s d e p e n d e n c e of the m a x i m u m c r e e p r a t e i s  l i n e a r , s u g g e s t i n g that the m e c h a n i s m of the d e f o r m a t i o n m a y be either viscous flow or grain boundary sliding (interparticle  sliding).  - 86 G r a i n b o u n d a r i e s i n the p r o p e r s e n s e do not e x i s t i n a p a r t i c u l a t e c o m p a c t of the t y p e u s e d , s o p a r t i c l e ( e q u i v a l e n t t o g r a i n s ) s l i d i n g i s c o n s i d e r e d t o be s y n o n y m o u s h e r e . G r a i n b o u n d a r y c r e e p i s g e n e r a l l y i m p o r t a n t o n l y at t e m p e r a t u r e s a b o v e 0. 5 T  m  . T h i s suggests that some  f o r m of i n c r e a s e d a t o m i c m o b i l i t y m u s t be p r e s e n t f o r t h i s m e c h a n i s m t o be o p e r a b l e at the t e m p e r a t u r e s u s e d i n t h i s s t u d y . 4. 6. 4  P o s s i b l e M e c h a n i s m s of D e f o r m a t i o n F r o m the f o r e g o i n g i t a p p e a r s t h a t the c r e e p d e f o r m a t i o n  o b s e r v e d d u r i n g the d e c o m p o s i t i o n of M g ( O H )  2  may  be d i f f u s i o n c o n -  t r o l l e d , as the a c t i v a t i o n e n e r g y of the c r e e p p r o c e s s i s s i m i l a r t o t h o s e of g r a i n g r o w t h a n d r e h y d r a t i o n .  O n the o t h e r h a n d , i t i s p o s -  s i b l e t h a t the d e f o r m a t i o n o c c u r s b y s o m e o t h e r m e a n s . F o r e x a m p l e ,  (33) it h a s b e e n d e m o n s t r a t e d  recently  that a l o o s e p a r t i c u l a t e c o m p a c t  of a m i x t u r e of t u n g s t e n a n d o x a l i c a c i d c a n be d e n s i f i e d d u r i n g the d e c o m p o s i t i o n of t h e o x a l i c a c i d , a p p a r e n t l y w i t h o u t a n y r e a c t i o n b e t w e e n the two m a t e r i a l s . f i c a t i o n of the t u n g s t e n p o w d e r w a s  chemical  I n t h i s c a s e the e n h a n c e d d e n s i a t t r i b u t e d t o the e f f e c t of gas  phase lubrication. A t p r e s e n t i t i s difficult to choose between these  two  mechanisms: a) D e f o r m a t i o n c o n t r o l l e d b y d i f f u s i o n ,  and  b) D e f o r m a t i o n c o n t r o l l e d b y gas p h a s e l u b r i c a t i o n . T h i s s y s t e m i s f u r t h e r c o m p l i c a t e d b y the f a c t t h a t the  Mg(OH)  2  d i s i n t e g r a t e s i n t o v e r y f i n e c r y s t a l l i t e s of M g O  thus c r e a t i n g a l a r g e n u m b e r of new  ( about 70 A ),  i n t e r p a r t i c l e contact  s l i d i n g . In a d d i t i o n , the p o s s i b l e c o n t r i b u t i o n of s l i p to the  areas for observed  d e f o r m a t i o n m u s t be c o n s i d e r e d . 4. 6. 4. 1  Slip As  Mechanisms n e a r t h e o r e t i c a l l y dense bodies have been  j u s t a b o v e the d e c o m p o s i t i o n t e m p e r a t u r e ,  produced  the d e f o r m a t i o n of i n d i -  v i d u a l c r y s t a l l i t e s m u s t o c c u r d u r i n g the hot p r e s s i n g p r o c e s s at h i g h e r s t r e s s e s , i n d i c a t i n g that the f r e s h l y f o r m e d This plasticity may  MgO  is plastic.  be m a n i f e s t e d e v e n at l o w  stresses,  g i v i n g r i s e t o s o m e o r a l l of the c r e e p d e f o r m a t i o n o b s e r v e d i n t h i s (31) study.  H u l s e , C o p l e y and P a s k  talline MgO  showed that f u l l y dense p o l y c r y s -  ( of a c e r t a i n a n d g r a i n s i z e ) c a n y i e l d p l a s t i c a l l y  at as l o w as 4 0 0 ° C . (at 35, 000 p s i ). T h e y a l s o s h o w e d that the y i e l d s t r e s s on the J l O O j ^ l l O ^ s l i p s y s t e m of s i n g l e c r y s t a l M g O is approxi m a t e l y 10, 000 p s i at 4 0 0 ° C .  I n the p r e s e n t i n v e s t i g a t i o n the p a r t i c l e s  a r e not c o n s t r a i n e d i n the s a m e m a n n e r a s g r a i n s i n a s o l i d b o d y , a n d the i n d i v i d u a l c o n t a c t a r e a s m a y  be v e r y s m a l l ,  g i v i n g r i s e to  v e r y h i g h s t r e s s c o n c e n t r a t i o n s . A l s o , the f r e s h l y f o r m e d particles may rearrangement  MgO  be h i g h l y d e f e c t i v e as a r e s u l t of the t y p e of s t r u c t u r a l i n v o l v e d i n the d e c o m p o s i t i o n .  these effects may  A  c o m b i n a t i o n of a l l  c o n t r i b u t e t o the c r e e p d e f o r m a t i o n  observed.  - 88 -  4, 6. 4. 2  Stacking  Rearrangement  A n o t h e r p o s s i b l e s t r e s s d e p e n d e n t m e c h a n i s m of formation  of the p a r t i c l e s m a y  de-  s t e m f r o m the e f f e c t of s t r e s s on  the r e a r r a n g e m e n t of the s t a c k i n g s e q u e n c e n e c e s s a r y f o r the t r a n s f o r m a t i o n f r o m the h e x a g o n a l to the c u b i c l a t t i c e c o n f i g u r a t i o n . In c o n s i d e r i n g the t r a n s f o r m a t i o n previous  i n v e s t i g a t o r s have  of s t a c k i n g s e q u e n c e . T w o  of M g C O H ) ^ to M g O  , none of the  s t u d i e d i n d e t a i l the r e q u i r e d c h a n g e  b a s i c m o d e l s have, however, b e e n  p r o p o s e d f o r the r e m o v a l of w a t e r v a p o r f r o m the m a t e r i a l  during  the r e a c t i o n . The  m o d e l suggested by Goodman^  ^ f o r the t r a n s f o r -  m a t i o n , as s h o w n i n F i g u r e 3, n e c e s s i t a t e s a s t r u c t u r a l c o l l a p s e n o r m a l to the b a s a l o x y g e n p l a n e s due l a y e r s of o x y g e n ( h y d r o x y l )  ions.  to the r e m o v a l of w h o l e  B e c a u s e of e x p e r i m e n t a l  dif-  f i c u l t i e s none of the i n v e s t i g a t o r s , h a v e b e e n a b l e to d e t e r m i n e the extent of the d i m e n s i o n a l ever,  c h a n g e n o r m a l to the b a s a l p l a n e s .  if s u c h a c o l l a p s e o c c u r s ,  an e x t e r n a l s t r e s s h a v i n g  i t i s p o s s i b l e that the p r e s e n c e of  a c o m p o n e n t p a r a l l e l to the o x y g e n  c a n c a u s e d e f o r m a t i o n d u r i n g the  How-  planes  dehydroxylation.  A l t e r n a t i v e l y , i f the d e c o m p o s i t i o n p r o c e e d s b y the i n h o m o g e n e o u s m e c h a n i s m of B a l l a n d  Taylor  t  F i g u r e 4,  a stackin  -89sequence r e a r r a n g e m e n t reaction.  i s n e c e s s a r y at s o m e t i m e d u r i n g the  It c a n be s h o w n that the n e c e s s a r y r e a r r a n g e m e n t  o c c u r b y the p a s s a g e of a p a r t i a l d i s l o c a t i o n of the f o r m between e v e r y second oxygen layer. stacking rearrangement the s u c c e s s i o n of 1/6  <,12l)  1/6 | ^ 2 1 l J  T o p r o v i d e the n e c e s s a r y  w i t h o u t g r o s s s h a p e c h a n g e of the c r y s t a l l i t e  s h i f t s w o u l d be i n the s e q u e n c e 1/6  ("b") a n d 1/6  ^211^  < 112) ("c") on s u c c e s s i v e p l a n e s .  A n a r b i t r a r i l y c h o s e n plane r e q u i r i n g shift f r o m to A B C A c o u l d m a k e the r e q u i r e d c h a n g e w i t h a, b o r c. presence  can  ABAB  In the  of a n a p p l i e d s t r e s s the s h i f t w o u l d be i n the d i r e c t i o n of  that s t r e s s . O n e p r o p e r t y of the d e f o r m a t i o n c o u l d be r e l a t e d t o t h i s rearrangement.  T h e o b s e r v e d d e p e n d e n c e of s t r a i n r a t e on s t r e s s ;  e  where  e  0  =  e  i s the i n t e r c e p t  +  0  AO"  w i t h the r a t e a x i s , a n d A i s a c o n s t a n t ,  c o u l d r e s u l t f r o m the f a c t that a s m a l l e x t e r n a l s t r e s s c o u l d c a u s e the s e q u e n c e of p a r t i a l d i s l o c a t i o n s t o c h a n g e f r o m a b c e t c . to a n o t h e r sequence causing gross  strain.  T h i s h y p o t h e s i s has not b e e n d e v e l o p e d i n d e t a i l , as t h e r e i s no d i r e c t i n d i c a t i o n particles themselves  i n t h i s s t u d y that d e f o r m a t i o n of the  isactually occurring.  - 90 -  V.  S u m m a r y and  5. 1  C o n t a c t d e f o r m a t i o n and bond f o r m a t i o n have been de-  monstrated  in experiments  and c o l d - c o m p a c t e d  Conclusions  i n w h i c h t i p s of s i n g l e c r y s t a l Ca(OH>2  Mg(OH)2 powder were decomposed while loaded  in contact. 5. 2  C o m p a c t s of M g ( O H ) 2 , of 0. 50 r e l a t i v e d e n s i t y h a v e sheen  decomposed under varying compressive  loads.  n y i n g d e h y d r o x y l a t i o n i n the a b s e n c e of l o a d w a s load-dependent  The  shrinkage  l e s s t h a n 0. 4%.  d e f o r m a t i o n of up to 7 % at 13. 6 k g / c m  s t r e s s used) has b e e n o b s e r v e d .  The  accompa-  2  A  (the m a x i m u m  d e p e n d e n c e of t o t a l s t r a i n on  stress,  at u n i f o r m h e a t i n g r a t e t a k e s the f o r m : e where  e  O T  .  T  =  e  # T  +  i s l e s s t h a n 0. 4 %  k <T  n  and n i s a p p r o x i m a t e l y  1/3.  T h e s e o b s e r v a t i o n s f i r m l y e s t a b l i s h f o r the f i r s t t i m e that t h i s m a t e r i a l c a n be d e f o r m e d p l a s t i c a l l y d u r i n g a  decomposition  reaction. 5. 3  The  c r e e p b e h a v i o u r of the c o m p a c t s was  different i s o t h e r m a l temperatures, The  compressive  explored, for  s t r e s s e s and relative densities.  c r e e p c u r v e i s of s i g m o i d a l f o r m ,  t h e r m o g r a v i m e t r i c c u r v e f o r the s a m e m a t e r i a l .  s i m i l a r to the  The  creep  curve  has t h r e e s t a g e s ; Stage I  -  an initiation period, with rapid i n c r e a s e of c r e e p  rate.  - 91  Stage II  -  -  a p e r i o d of n e a r l y l i n e a r  rapid  creep. Stage III  -  a decay region, with rapidly decreasing rate, a p p a r e n t l y approaching  zero  asymptotically. 5. 4  The  m a x i m u m c r e e p r a t e ( s l o p e of the c r e e p  has b e e n m e a s u r e d , a n d i t s d e p e n d e n c e on t e m p e r a t u r e , density  curve)  stress  and  determined. The  Arrhenius form,  c r e e p rate shows a t e m p e r a t u r e  d e p e n d e n c e of the  w i t h a n a c t i v a t i o n e n e r g y of 17. 5kcal/mo.l.  This is  a p p r o x i m a t e l y o n e - h a l f the b e e t p u b l i s h e d v a l u e f o r the a c t i v a t i o n e n e r g y of d e h y d r o x y l a t i o n , s o the m e c h a n i s m s of the two a r e thought to be  processes  different.  C o m p a r i s o n of the a c t i v a t i o n e n e r g y w i t h t h o s e of g r a i n g r o w t h a n d r e h y d r a t i o n (17 a n d that the c r e e p p r o c e s s m a y The stress  lb. 1 kcal/mol,  respectively) suggest  be d i f f u s i o n c o n t r o l l e d .  c r e e p r a t e has a l i n e a r r e l a t i o n s h i p w i t h a p p l i e d  , i n the s t r e s s r a n g e e x a m i n e d ( . 54 to 13. 6 k g / c m  ), a n d  an  a p p a r e n t f i n i t e c r e e p r a t e at z;ero s t r e s s : e  =  e  0  +  ACT  A f u l l e x p l a n a t i o n of t h i s b e h a v i o u r has -not b e e n but i t m a y  r e l a t e to s t a c k i n g sequence r e a r r a n g e m e n t  hydroxylation.  developed,  d u r i n g de-  - 92  The  creep  -  r a t e h a s b e e n s h o w n to be of the  e  *  form  1/j  T h i s h a s b e e n e x p l a i n e d i n t e r m s of a n e f f e c t i v e a c t i n g on i n t e r p a r t i c l e c o n t a c t s . T h e  interparticle  p r o p o r t i o n a l to d e n s i t y , g i v i n g the a b o v e The  0  + A f f  contact a r e a i s  result.  f i n a l f o r m of the c r e e p r a t e e  stress  j-  exp  equation i s :  ILi.00)  t  -1  RT  5. 5  The  total creep strain developed under i s o t h e r m a l  c o n d i t i o n s has a l s o b e e n d e t e r m i n e d . to be i n d e p e n d e n t  of t e m p e r a t u r e .  The  total s t r a i n has been found  Its v a r i a t i o n v e r s u s s t r e s s i s of the  form n e_  =  e__ +  where n is again approximately  1/3  e  and e  d e n s i t y d e p e n d e n c e a p p e a r s to be of the e  5. 6  The  T  *  cr o T  l e s s t h a n 0. 5%.  The  form  1/<J  c r e e p m e c h a n i s m i s p o s t u l a t e d t o be  interparticle  s l i d i n g , p r o b a b l y s i m i l a r to g r a i n b o u n d a r y s l i d i n g i n s o l i d m a t e r i a l s . H o w e v e r , i t i s p o s s i b l e that d e f o r m a t i o n of the p a r t i c l e s b a b l y by a m e c h a n i s m a s s o c i a t e d w i t h s t a c k i n g s e q u e n c e  occurs, prorearrangement,  a l t h o u g h t h i s w o r k d o e s not p e r m i t t h e - f o r m u l a t i o n of a r i g o r o u s h y p o thesis.  It has,  h o w e v e r , s h o w n that l o a d - d e p e n d e n t d e f o r m a t i o n  o c c u r d u r i n g d e h y d r o x y l a t i o n of M g f O H ) ^ .  can  - 93 -  VI  Suggestions for Future  6. 1  In o r d e r to e s t a b l i s h m o r e d e f i n i t i v e l y the  between weight l o s s and c r e e p ,  Work  experiments  relationship  s h o u l d be d e v i s e d t o  m e a s u r e s i m u l t a n e o u s l y , a n d a c c u r a t e l y , the w e i g h t l o s s a n d d i m e n sional 6. 2  change. T h e e f f e c t of s p e c i m e n s i z e h a s n o t b e e n s t u d i e d ,  and  e x p e r i m e n t s w i t h v a r y i n g d i a m e t e r s m i g h t p e r m i t e x t r a p o l a t i o n to i  zero diameter,  a n d h e n c e e l i m i n a t i o n of a n y b a c k w a t e r v a p o u r  pres-  s u r e e f f e c t due t o the c o m p a c t s i z e . 6. 3  A s the M g ( O H ) 2 p a r t i c l e s i n the c o m p a c t s  show a strong texture,  undoubtedly  due t o t h e i r p l a t y s h a p e a n d the u n i a x i a l  pres-  s i n g , i t w o u l d be i n t e r e s t i n g to e x p l o r e the e f f e c t of t e x t u r a l o r i e n t a t i o n on the d e f o r m a t i o n . pressed 6. 4  T h e e f f e c t of w a t e r v a p o u r p r e s s u r e on the  deformation  T h i s m i g h t s e r v e to c l a r i f y the m e c h a n i s m .  T h e r a n g e of s t r e s s e s u s e d c o u l d be e x p a n d e d ,  l a r l y to l o w e r s t r e s s e s ,  s o t h a t the t r u e f o r m of the s t r e s s  at v e r y s m a l l s t r e s s e s c o u l d be d e t e r m i n e d . require optical measurement 6. 6  specimens  sideways.  c o u l d a l s o be s t u d i e d . 6. 5  T h i s c o u l d be done b y u s i n g  particudependence  This would probably  of d i m e n s i o n a l c h a n g e s .  T h e a c t i v a t i o n e n e r g y f o r the c r e e p p r o c e s s  s h o u l d be  c o m p a r e d w i t h one a c c u r a t e l y d e t e r m i n e d f o r the d e h y d r o x y l a t i o n of the  same material.  APPENDICES  r 94 APPENDIX  I  i TEMPERATURE  DISTRIBUTION WITHIN THE  CYLINDRICAL  SPECIMEN  In o r d e r t o a s s e s s the p o s s i b l e t i m e l a g b e t w e e n the specimen's s u r f a c e and its centre, an approximate formed  c a l c u l a t i o n was  per-  u s i n g a m e t h o d due to C a r s l a w a n d J a e g e r ( 23)_ V a l u e s f o r the t h e r m a l c o n d u c t i b i t y a n d s p e c i f i c h e a t w e r e  f i r s t e s t i m a t e d , as e x p e r i m e n t a l v a l u e s f o r M g ( O H ) 2 w e r e not a v a i l a b l e i n the l i t e r a t u r e . One  The  s p e c i f i c heat m a y  e s t i m a t e , b a s e d on c o m p a r i s o n  and M g O  i s 0. 30 c a l / g m ° C .  be o b t a i n e d i n s e v e r a l w a y s .  w i t h v a l u e s ( 20) f  o  r  CaO,  Ca(OH)2,  V a l u e s f o r the s p e c i f i c h e a t of M g O  from  (32) Wicks  i n d i c a t e a v a l u e b e t w e e n 0. 30  0. 265 c a l / g m ° C f o r MgO.  t o 0. 40  f o r Mg(OH)2> b a s e d  A v a l u e of 0. 35 c a l / g m ° C w a s  on  selected for  the c a l c u l a t i o n s . The  t h e r m a l c o n d u c t i v i t y was  the p u b l i s h e d v a l u e s f o r MgO, (cal/sec/cm The  /  C/cm)for  e s t i m a t e d on the b a s i s of  w h i c h r a n g e f r o m about 0. 08  p u r e , dense MgO,  to 1 0 f  o  r  r e l a t i v e b u l k d e n s i t i e s u s e d i n the e x p e r i m e n t s w e r e  g r e a t e r t h a n e x p e c t e d f o r l o o s e p o w d e r s , but i t w a s pressure (10~  2  powdered  MgO.  somewhat  f e l t that the  T o r r ) w o u l d c o m p e n s a t e , a n d a v a l u e of K = 1 0 " ^  reduced was  selected. The  m e t h o d u s e d p e r m i t s the c a l c u l a t i o n of t e m p e r a t u r e  as a f u n c t i o n of t i m e , the t h e r m a l d i f f u s i v i t y (K/^>) a n d a r e d u c e d r a d i u s f o r a n i n f i n i t e c y l i n d e r s u b j e c t e d to a s t e p i n c r e a s e i n i t s s u r f a c e temperature.  The  s t e p i n c r e a s e i s i n d i c a t e d by V on F i g u r e 36  •  - 95 a n d the l o c a l t e m p e r a t u r e at a n y t i m e t b y v.  A t y p i c a l s t e a d y state  t e m p e r a t u r e of 4 0 0 ° i s p l o t t e d on the l e f t h a n d m a r g i n . It c a n be s e e n that a t e m p e r a t u r e i n e x c e s s of 3 9 0 ° F i s r e a c h e d at the s p e c i m e n  c e n t r e ( v / R = 0 ) i n 8 to 10 m i n u t e s .  This  was  f e l t to j u s t i f y c o n d u c t i n g the e x p e r i m e n t a n d o b t a i n i n g e x p e r i m e n t a l v e r i f i c a t i o n of the s p e c i m e n t e m p e r a t u r e d u r i n g the t e s t s . It s h o u l d be n o t e d that the heat of r e a c t i o n ( e n d o t h e r m i c ) has not b e e n t a k e n i n t o a c c o u n t i n t h i s c a l c u l a t i o n .  S i n c e i t was  found  i n the e a r l y t e s t s that the m a x i m u m r e a c t i o n r a t e d i d not d e v e l o p u n t i l approximately 5  m i n u t e s a f t e r test t e m p e r a t u r e (405°C) h a d b e e n r e a c h e d  (about 12 m i n u t e s f r o m the s t a r t of the r u n ) , i t was  f e l t that the  major  e n d o t h e r m i c r e a c t i o n t o o k p l a c e a f t e r the q u a s i - u n i f o r m t e m p e r a t u r e d i s t r i b u t i o n has b e e n a c h i e v e d .  Temperature  m e a s u r e m e n t s i n the  c e n t r e of the s p e c i m e n d u r i n g the t e s t e v e n t u a l l y c o n f i r m e d the p r e dicted temperature  distribution.  TIME, FIGURE  36  Minutes  Theoretical temperature distribution in the specimens for the isothermal creep tests.  »• 97 A P P E N D I X II CREEP DATA  - "ISOTHERMAL"  The  CONDITIONS  data i s p r e s e n t e d i n t a b u l a r ( c o l u m n a r ) f o r m as t i m e  f r o m the s t a r t of the r u n ( m i n u t e s ) , s p e c i m e n s u r f a c e  temperature  ( T ° C ) , a n d s h r i n k a g e f r o m the i n i t i a l l e n g t h i n i n c h e s  X10~5  (hundred thousandths). for comparison. presented.  The  D u p l i c a t e r u n s a r e p r e s e n t e d i n the s a m e t a b l e s p e c i m e n p a r t i c u l a r s and r u n load a r e also  Initial length i s given i n inches and s p e c i m e n density i n  gm/cm . The  s p e c i m e n n u m b e r s a r e i n c l u d e d on the F i g u r e s i n  S e c t i o n 3, s o that d i r e c t c o m p a r i s o n s  may  be m a d e .  A l l the d a t a  p r e s e n t e d h a v e b e e n c o r r e c t e d f o r t h e r m a l e x p a n s i o n b y the m e t h o d s h o w n in Appendix  III.  The  r u n s a r e g r o u p e d i n the m a n n e r i n w h i c h t h e y  w e r e p r e s e n t e d i n S e c t i o n 3. i n c l u d e d (Nos.  85,  p r e s s u r e of f r o m (temperature).  86,96,  One  97).  10 to 5 0 y n H g ,  s e t of f o u r d u p l i c a t e r u n s has b e e n  A l l runs were started with a  system  d e p e n d i n g o n the r a t e of r e a c t i o n  - 98 APPENDIX  II (a)  Specimen  Temperature 340°C  81  83  0. 3174  0. 321  1. 206  1. 206  S t r e s s 13.6 k g / c m  N o m i n a l relative density 11  T°C  me  0. 50  S p e c i m e n No. T i m e  T°C  Specimen  No.  Min.  Min.  0 1  40 .  4  0  ' 55 125 194 240 280 308 336 340 340  :  3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  2  :  340  340  340  340  81  83  0  0 0 -2 -74 -1 18 32 44 70 98 127 155 174 199 224 265 312 376 433 497 558 629 703 785 863 934 1003 1069 1144 1211 1292  L  0 29 44 64 70 85 106 125 152 179 207 242 282 334 385 458 526 608 686 763 840 918 999 1070 1148 1220 1297 1371 1438  81 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56  <  340  340  340  340  340  340  1504 1564 1620 1674 1727 1783 1835 1884 1932 1976 2017 2058 2092 2125 2160 2189 2216 2239 2264 2296 2315 2348 2364 2386 2393  83 1438 1506 1565 1626 1691 1749 1809 1860 1909 1951 1996 2036 2072 2105 2136 2165 2188 2211 2243 2248 2259 2279 2283 2294  - 99 APPENDIX  II (a)  Specimen  1o  75  76  0. 318 1. 208  0. 3178 1. 203  T e m p e r a t u r e 360°C S t r e s s 13.6 k g / c m N o m i n a l r e l a t i v e density 0. 50 Time Min.  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  T°C  40 4P  75 145 200 244 283 312 344 362 360 360 360 360 360 360  Specimen No. Time Min.  75  76  0 0 -7 13 28 31 27 14 16 70 113 190 302 416 539  0 0 7 0 -12 -13 -12 -2 -2  816  360  360  360  1050 1163 1270 1374 1493 1590 1669 1755 1845 1913 1986 2067 2116  -130 192 275 361 459 580 708 850 998 1099 1246 1459 1546 1631 1726 1793 1880 1968 2032  31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50  T°C  360  360  360  360  360  2  Specimen No.  75  76  2164 2204 2243 2264 2284 2296 2310 2316 2346 2364 2378 2385 2392 2399  2095 2152 2210  2423 2435 2439  2278 2291 2305 2321 2339 2355 2369 2376 2386 2397 2410 2419 2423 2426  -100 A P P E N D I X  II  (a)  Specimen  79 l  0  Temperature Nominal Time  T  o  C  78 0. 3195  0. 3165  0. 317  0. 3166  1.206  1.204  C,  <^ Stress  AneOr* 405°C  density  Specimen  1.199  i o L !__./ 2 13. 6 k g / c m  0. 50 No. Time  Min.  0 1 2 3 4 5. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  77  1.202 385  relative  80  T  o  C  Specimen  No.  M i n .  40 -40 60 125 205 255 292 320 350 369 382 386 385 385 385 385  385  385  385  79  80  0 4 3 7 5 2 -3 -16 -21 0 50 155 299 460 640 831 1011 1199 1265 1517 1643 1767 1858 19 50 2073 2104 2156 2187 2214 2234 2262  0 0 -1 -3 20 32 25 33 39 58 118 229 390 566 758 956 1120 1296 1448 1588 1717 1845 1946 203 6 2100 2152 2181 2200 2224 2244 2272  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24  40 45 102 191 255 300 334 360 3 84 400 407 405 405 405 405 405  405  77  78  0 0 0 23 45 58 60  0 0 0 -5 17 22 32 37 47 62 94 174 347 620 928 1223  74 117 187 301 404 770 1045 1310 1573 1798 1991 2128 2202 2258 2282 2400  1723 1911 2077 2204 2277 2306 2333 2360  - 101 * APPENDIX  Specimen  1  Q  Temperature  II (b)  85  86  96  0.3182 1.204  0.3150 1.211  0.3135 0.3148 1.217 1.216  340°C  Stress  Nominal relative density Time  T°C  40 40 . 84 165 228 285 320 340 340 340 340  340  340  2 1  22 23 24 25 26 27 28 29 30  2  Specimen  No. T i m e  T  o  C  Specimen  No.  Min.  1 6  17 18 19 20  kg/cm  0. 50  Min.  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15  6. 0  97  340  340  85  86  0 3 -3 -3 -5 -4 -4 -1 18 32 61 88 114 155 200 149 292 342 402 452 509 556 605 654 704 756 819 858 921 974 1030  0 0 -2 -16 -14 -17 -32 -42 -41 -25 -7 25 32 45 55 81 1 1 6  152 191 234 283 333 384 441 499 549 605 659 720 773 829  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  40 40 84 165 228 285 320 340 340 340 340  340  96  97  0 -2 1 -1 -11 - 18 -15 -4 31 58 78 96 111 120 132 157 179  0 1 -2 -19 -42 -52 -62 -68 -61 -35 -14 11 29 66 78 104 136  2 1 6  340  340  340  256 300 349 387 437 494 550 608 659 . 715 774 840 904  1 9 6  237 296 352 413 483 547 611 678 741 799 857 907 976  - 102 -  APPENDIX  Specimen  Time Min.  T°C  II (b) cont.  85  340  33  96  S p e c i m e n No. T i m e Min. 85  31 32  86  T°C  86  97  Specimen  No.  96  97  1080  883  31  970  1040  1119  929 974  32  1030  33  1087  1091 1140  1 144  1182  1192  340  1168 1216  1024  34  1266  1073  35  1117  36  1243  1220 1257  1304  1295  38  1334  39 40  1459 1497  1160 1200 1235  37  38  1317 1360 1415  1379 1422 1456 1493  1328 1363  1277  39 40  34 35  340  36 37  340  41 42  1531 1564  1317 1361  41 42  43  1594  44 45  1636 1680  1395 1431  43 44  1461  45 46  340  46  1699 1728  47  1492  48  17 53  1525 1542  49 50  1776 1821  1565 1592  340  340  340  340  1453  1528  1474  1558 1589 1610  1507  47  1636  48 49 50  1659 1680 1703  340  1398 1423  1494 1518 1537 1545 1560  - 103 -  APPENDIX  II (b)  Specimen I o ° Temperature  84  98  99  100  0.3169  0.3140  0.3145  0.316  I. 210  I. 219  I. 217  I. 209  385°C  Stress  N o m i n a l relative density  6. 0 k g / c m  0. 50  ° Time  T  n C  S p e c i m e n No. T i m e  Min.  T  C  Specimen  No.  Min. 84  98  99  100  0  40;  0  0  0  40  0  0  1 2  40  1  0  1  40  0  1  (5  1  0  2  0  153  10  -11  -24  4  217  28  -12  3 4  62 144  -5  3  714  5  270  44  -12  5  263  -29 -31  -9 -3  6  300  55  -14  297  -40  -6  7  3 31  -27  -4  355 375  -19  8  -49  -9 23 86  9 10  329 354 371  -48  8  59 64  6 7  11 37  9 10  390  11 12  405 405  13 14  405 405  15  405  80 105 164  197  11 12  667 877  348 543 733  13 14 15  16  1087  921  17  1305  18  1430 1553  1091 1250  16 17  19 20 21  40 5  1653 1717 1747 1773 1803  22 23 24 25  291 462  19 20  1655 1675  25  1697  1837  26 27 28 40 5  1499 1545 1599 1625  385 385 385  -39 - 11 30  82 142  85  225  169 283 411 521  321  664  43 7 563 687 814 931  18  21 22 23 24  1821 1825  29 30  405  1389  388 385 385  -3  385  895 1011  1045  1115  1259 1348 1423  1206 1304 1380  1490  1441  1546  26 .  1490  1708  27  1531  1599 1624  1852 1867  1729 1741  28  1573 1592  1651 1671  1877  1747  1617  1702  29 30  385  1152  385  - 104 APPENDIX  II (c)  Specimen  I  p  Temperature  103  104  0.316 1.214  0.316 1.214  360°C  Stress  N o m i n a l relative density Time  T  o  C  0.3167 1.212 0. 54  kg/cm  2  0. 50  Specimen  No. T i m e  Min.  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  105  T  o  C  Specimen  Min.  40 40 78 148 214 267 302 322 354 360 360  360  360  360  360  103  104  0 0 -5 -9 -5 -23 -37 -52 -57 -50 -47 -40 -25 -9 4 26 44 91 135 191 245 306 3 74 440 502 570 636 705 768 818 862  0 0 -5 -11 -18 -19" -43 -63 -63 -58 -50 -43 -25 12 47 96 143 196 256 305 365 428 493 558 617 676 740 800 856 918 964  105 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  40 40 78 148 214 267 302 322 354 360 360  360  360  360  360  0 0 -5 -17 -14 -30 -48 -65 -65 -61 -60 -60 -59 -47 -34 -17 -4 32 74 119 164 211 272 341 384 443 500 562 608 659 698  No.  - 105 APPENDIX  II (c) cont.  103  Specimen  Time Min.  31 32 33 34 35  T C U  105  104  S p e c i m e n No. T i m e  T  C  Specimen  Min.  360  360  103  104  407 940 966 984 1004  1006 1042 1076 1099 1119  105 31 32 33 34 35  360  360  732 759 786 804 824  No.  - 106 APPENDIX  Specimen l  Q  Temperature  II (c)  101  102  106  107.  0.3176  0.316  0.3194  0.3165  1.208  1.214  1.205  1.212  360°C  S t r e s s 6.0, 3. 5 k g / c m  Nominal relative density Time Min.  0  T°C  0. 50  S p e c i m e n No. T i m e Min. 101  102  0  0  0 -3  1  40 40  2 3  95 172  4  218  -28 -24  5  267  -41  •6 7  ' 307 335  8 9 10  No.  106  107  0  0  7  1  40  0  0  1 -20  2 3  75 145  -4  -4  4  200  -29 -51  -29  -33 -46  5  ' -57 -84  -79 -110  6 7  244 283  360  -99  8  360  -91 -86  -129 -138 -134  360  13 14  -4  -43  -129 -105  50  -74 -33  107 195  16 94  263 345 33 525  152 231 316 414  21  617  22  703  508 602  23 24  783  360  16 17 18  25  Specimen  40  -70  19 20  T°C  0  11 12  15  2  360  360  869 953  312 344  -70 -88 -102  -49 -72 -87 -94  9 10  362  -80 -75  360  -67  11  360  -50  -66  12 13  360 360  -24  -39 -5  14  360  15  360  49 98  16 17  159 220 294 371  18 19 20 21  360  23 24 •  884  25  460 543  22  696 795  6  360  -100 -85  -88  46 102 168 242 319 397 479 553  614 686 766  627  835  853 916  699 782  26  1028  975  26  898'  27  1098  1055  27  954  28  1176 1247  1145  28  1036  978 1047  1224  1096  1104  1308  1294  29 30  1143  1152  29 30  360  360  -  APPENDIX  Specimen  Time Min.  31 32 33 34 35 36 37 38 39 40  T°C  107  -  II (c) cont.  101  102  S p e c i m e n No.  106 Time  T°C  107 Specimen  No.  Min.  360  360  360  101  102  1359 1410 1458 1500 1538 1568 1598 1644 1771 1793  1359 1419 1473 1523 1564 1592 1616 1636  31 32 33 34 35 36 37 38 39 40  360  360  360  106  107  1194 1248 1290 1327 1359 1405 1434 1463 1481 1498  1199 1248 1283 1329 1349 1391 1411 1430 1447 1464  - 108 APPENDIX  II (d)  Specimen lo  So Temperature  136  137  0. 3045 1. 702  0. 3035 1. 700  360°C  Stress  N o m i n a l relative density Time Min .  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  T°C  40 40 62 132 192 240 277 307 336 360 360  360  360  360 :  360  9. 2  kg/cm/  0. 70  S p e c i m e n No. T i m e Min.  136  137  0 2 -6 -22 -33 -43 -56 -82 -111 -134 -152 -163 -164 -165 -159 -148 -135 -122 -107 -84 -64 -39 -13 19 56 93 139 194 248 303 361  0 1 -7 -29 -51 -71 -94 -129 -162 -194 -122 -232 -235 -232 -226 -213 -197 -176 -152 -119 -87 -50 .-7 45 98 146 207 271 331 392 458  31 32 33 34 35 36 37 38 39 40 41 • 42 43 44 45 46 47 48 49 50  T°C  360  360  360  360  360  Specimen  No.  136  137  417 477 533 590 643 717 765 821 871 924 976 1020 1061 1097 1133 1166 1198 1223 1244 1263  523 582 638 698 755 820 873 928 966 1014 1055 1090 1124 1157 1185 1211 123 7 1256 1274 1287  - 109 APPENDIX  II (d)  Specimen 1  o  132  133  0. 309 1. 537  0. 3108 1. 535  T e m p e r a t u r e 360°C Stress N o m i n a l relative density 0. 65 Time Min.  0  T°C  9- 2 k g / c m ^  S p e c i m e n No. T i m e  T  C  Specimen  40 42  1 2  . '86  3  156  4  218  5  262  6 7  298 335  8  360  9 10 11  360 360  132  133  0  360  132  133  736  727  797  0 3  31  0 -7  -5  33  854  791 850  -25  -17  34  920  908  -39 -54  -24  35  -31  -74 -97 -120 -135 -150 -154  -57 -87 -110  36 37  32  38  -155  39 40 41 . 42  -132 -144  360  360  978  964  1048 1103 1150 1200  1031  1248  1221 1264 1301  1291 1326  12  -152  -155  43  1364  13 14  -146 -138  -153 -145  44 45  1391 1418  -122  -132  16 17  -105  -107 -75  46 47  18  -65  15  19 20  360  -80  360  21  0 42  . -34 15 63  93  117  145 209 270 331  175 235 294 351  26  398  411  27  468  477  28  536  29 30  601  539 596  670  662  22 23 24 25  No.  Min.  360  360  360  49 50  360  1336 1363  1467  1389 1418 1446  1481 1495  1475 1484  1506  1501  1442  48  1080 1127 1177  -  APPENDIX  110 -  II (d)  Specimen 1 $o Q  120  121  0. 3189 1. 313  0. 3148 I. 317  Temperature 360°C Stress N o m i n a l relative density 0. 55 Time  T°C  S p e c i m e n No. T i m e  Min.  0 1  120  121  40 40  0  0  31  0  0  32  80  -8 -26 -37  -6 -10 -17  33  -59 -76 -95  -26 -46  155  4  210  5  • 246  6 7  276 300  8  326  11 12 13 14 15 16 17  3 54  -177 -125  ;363  -114  360  -99 -67  360 360 360 360  -22 40 111 200 290  -109 -114 -108 -91 -63 -19 36  793 890 995 1068  618 712 801 883  1161  964  27  1252  1047  28  1322  1121  1404  1191 .1258  360  1472  1445  1676 1712  1499 1550  36  1758  1608  37  1648  34 35  360  1824 1843  23 24 360  1329 1390  1589 1632  38  518  26  1536  39 40  692  360  360  121  -98  21 22  29 30  No.  120  -72  391 495 597  18  25  Specimen  1784 1802  97 166 258 336 434  19 20  T°C  2  Min.  2 3  9 10  9. 2 k g / c m  360  1691 1713 1740  - Ill A P P E N D I X  II  (d)  Specimen  1o Temperature Nominal  T°C  129  130  108  109  0.3142 0. 963  0. 3104 0. 972  0. 3165 1. 212  0. 3132 1. 220  360°C  relative  Time  -  Stress  density  Specimen  0. 40,  9. 2  No. T i m e  Min.  k g / c m  2  0. 51 T  C  Specimen  No.  Min.  0 40 40 1 2 , 86 160 3 215 4 5 254 6 292 7 320 348 8 9 ' 360 10 360 360 11 12 360 360 13 14 360 15 360 16 17 18 19 • 360 20 21 22 23 24 . 2 5 . 360 26 ' :  129  130  0 0 -8 6 14 6 -2 -12 5 45 101 185 290 414 545 682 822 967 1110 1251 1381 1510 1639 1763 1872 1976 2067  0 0 -8 -7 -3 -1 -8 -13 10 38 79 171 246 394 541 697 865 1019 1174 1325 1464 1594 1718 1832 1967 2120  0 40 40 1 2 80 3 157 4 219 5 262 300 6 7 334 360 8 360 9 10 ; 360 11 12 13 14 15' 360 16 17 18 19 20 360 21 22 23 24 25 360 26 27 28 29 30 360  108  109  0 0 -11 -13 -7 3 -17 -25 -33 -15 -1 33 87 160 237 315 443 498 603 704 802 908 1008 1110 1199 1280 1362 1445 1524 1593 1660  0 0 -10 -11 -13 -18 -24 -36 -39 -36 -21 4 47 102 171 262 350 451 555 659 751 848 945 1039 1122 1200 1275 1352 1419 1479 1535  -  APPENDIX  112  -  II (d) cont.  Specimen  108  Time Min.  31  T°C  360  109  Specimen  No.  108  109  1725  1590  1783  1643  33  1833  1688  34  1881  1732  1915  1766  32  35  360  36  1948  1798  37  1980  1826  38  2005  1852  39  2030  1874  2050  1889  40  360  - 113 APPENDIX  II (d)  Specimen  1  0  o  0  Temperature  360°C  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  T°C  40 40 86 160 214 254 293 320 347 360 360  360  360  360  360  125  0. 3275 1.072  0.3120 .073  Stress  Nominal relative density Time Min.  124  9.2 k g / c m  2  0. 45  S p e c i m e n No. T i m e Min.  124  125  0 0 -8 0 4 -2 -9 -19 -8 10 52 117 216 320 446 587 718 854 986 1103 1213 1325 1439 1548 1642 1734 1810 1892 1950 2021 2088  0 1 -6 -1 5 7 -2 -8 -7 8 20 52 111 180 271 369 600 601 728 861 985 1105 1218 1332 1438 1532 1631 1725 1799 1858 1924  T°C  Specimen  124 31 32 33 34 35 36 37 38 39  360  360  No.  125  2137 1989 2186 2031 2223 2068 2260 2099 2292 2120 2334 2357 2374 2395  - 114 APPENDIX  II (d)  Specimen  1  o  Temperature  360 C P  T°C  117  0. 3142 1. 425  0. 3130 1. 430  Stress  N o m i n a l relative density Time  116  Specimen  No. T i m e  Min.  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 . 27 28 29 30  9-2  kg/cm^  0. 60 T°C  Specimen  No.  Min.  40 40 78 150 208 256 294 326 350 362 360 360 360 360 360 360  360  360  360  116  117  0 0 -8 -19 -33 -32 -42 -75 -98  0 0 -8 -15 -14 -16 -29 -51 -67 -69 -73 -66 -53 -40 -24 -3 28 65 111 164 216 279 346 416 491 558 637 713 786 853 926  121 122 114 101 -77 -46 -2 65 106 173 241 313 389 472 552 624 705 787 863 935 1005  31 32 33 34 35 36 37 38 39 40 41 42 43 44 45  360  360  360  360  116  117  1074 1136 1195 1249 1302 1380 1413 1456 1501 1540 1579 1600 1725 1641 1657  1002 1062 1119 1178 1235 1304 1360 1410 1464 1512 1557 1590 1623 1647 1674  - 115 -  A P P E N D I X III A c c u r a c y of the T h e r m a l E x p a n s i o n The  Correction  d a t a f r o m the e x p e r i m e n t a l r u n s w e r e c o r r e c t e d f o r  the t h e r m a l e x p a n s i o n of the l o a d i n g f r a m e b y the s u b t r a c t i o n of a c o r r e c t i o n obtained f r o m runs made using a dummy quartz to o b t a i n the e x p a n s i o n c u r v e f o r the f r a m e a l o n e .  The  specimen  corrections  w e r e a v e r a g e d a n d s u b t r a c t e d f r o m the i n d i c a t e d c r e e p d e f o r m a t i o n values, i.e. : L (t) where  =  L' (t) - c (t)  L (t) = the a c t u a l l e n g t h at t i m e t, L ' (t) = the i n d i c a t e d  length and  c (t) = the a v e r a g e c h a n g e i n l e n g t h d e v e l o p e d d u r i n g the  t h e r m a l expansion runs. The  c o r r e c t i o n h a s b e e n v e r i f i e d b y two 1)  Comparison  methods:  of the t o t a l s t r a i n , ( w i t h a  M i c r o m e t e r ) as d e t e r m i n e d by d i r e c t m e a s u r e m e n t s of the s p e c i m e n s  before  and after dehydroxylation. 2)  D i r e c t m e a s u r e m e n t i n the f u r n a c e using a travelling  microscope.  (Cathetometer). T h e f i r s t m e t h o d gave a n a p p a r e n t a c c u r a c y of about 0. 001 i n c h e s  f o r d e f o r m a t i o n s of f r o m 0. 010 t o 0. 020 i n c h e s , i n d i c -  a t i n g that the m e a s u r e m e n t s a r e c o r r e c t t o one p a r t i n t e n o r twenty.  - 116 -  F i g u r e 3 7 c o m p a r e s the d e f o r m a t i o n c u r v e , a s c o r r e c t e d b y the n o r m a l p r o c e d u r e w i t h l e n g t h s m e a s u r e d w i t h the t r a v e l l i n g scope.  micro-  T h e two a r e i n a g r e e m e n t t o w i t h i n 10%, w h i c h i s f e l t t o be  satisfactory.  - 118 BIBLIOGRAPHY  A . C. D.  Chaklader, Nature,  2 0 6 , 392 (1965)  P. E . D. M o r g a n a n d E . S c a l a , " H i g h DensityO x i d e s b y D e c o m p o s i t i o n P r e s s u r e S i n t e r i n g of H y d r o x i d e s " , p r e s e n t e d at the S i x t y - S e v e n t h Annual Meeting,  The A m e r i c a n  Philadelphia, Pa. , May  Ceramic  Society,  3 r d , 1965.  T. G. C a r r u t h e r s a n d T. A. W h e a t , B r i t i s h C e r a m i c Society,  Proc.  3_, 259 (1965).  a) A. C. D. C h a k l a d e r a n d L . G. McKenzie, J. Am. C e r a m . S o c , 4 9 , 4 7 ( 1 9 6 6 ) . b) A.  C. D.  Am.  C h a k l a d e r a n d L. G.  Ceram.  Soc. B u l l . ,  McKenzie,  43, 892 (1964).  A. C. D. C h a k l a d e r a n d V. T. B a k e r , C e r a m . S o c . , 44, 258 (1965). A . C. D.  C h a k l a d e r a n d M.  Soc. A. I. M.  Bull.  Am.  N. S h e t t y , T r a n s .  Met.  E . , 233, 1441 (1965).  P. E . D. M o r g a n a n d N. C. S c h a e f f e r , T e c h . A F M L - T R - 6 6 - 3 5 6 , N o v . 1966.  A . ' C. D. C h a k l a d e r a n d R. Soc. 47, 712 (1968).  Rep.  C. 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B l o c k , " T h e r m o d y n a m i c P r o p e r t i e s of 65 E l e m e n t s - T h e i r O x i d e s , H a l i d e s , C a r b i d e s a n d N i t r i d e s , B u l l . 605, U S B u r e a u of M i n e s , W a s h i n g t o n (1963)." A.  C D .  Soc,  C h a k l a d e r a n d G.  Oct.  1970,  ( T o be  B e y n o n , J . Am.  published).  Ceram.  

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