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Activity of ZnO in the ternary system ZnO-CaO-SiO2 1967

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THE ACTIVITY OF ZnO IN THE TERNARY SYSTEM ZnO-CaO-SiO, by MICHAEL JOHN FAIRWEATHER A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER. OF APPLIED 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 THE UNIVERSITY OF BRITISH COLUMBIA February, I967. In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study . I f u r t h e r agree that permiss ion fo r ex - tens i ve copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be gran by the Heacl of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n - c i a l gain s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of M e t a l l u r g y The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date F e b r u a r y 7, 1967 - i - ABSTRACT The a c t i v i t y of ZnO i n ternary Zno-CaO-SiO^ slags has; been measured at 1300 C b y e q u i l i b r a t i o n with copper r i c h brass and low oxygen p o t e n t i a l gas u t i l i z i n g the following r e v e r s i b l e galvaniccce.il: Pt I H 2,H 2 0 || 0 . 8 5 Z r 0 2 - O . I 5 C a O || 0 2 ( A i r ) | P t Thermodynamic data on the component b i n a r i e s was employed to cal c u l a t e the excess free energy of the ternary system and the i s o a c t i v i t y patterns of the three components at 1600 C with respect to the metastable pure l i q u i d standard states. An estimate of 6 E.U. was made f o r the entropy of - f u s i o n iofu ZnO. The measured a c t i v i t i e s are i n good agreement with the cal c u l a t e d values. The proposed excess free energy contours tnoth&i'ZnOcCaQoSiOg ternary are s i m i l a r i n shape to those calculated i n a s i m i l a r manner f o r the FeO~CaO~SiO„ system. Also the calculated zinc oxide i s o a c t i v i t y f i g u r e resembles 'c. the ferrous oxide i s o a c t i v i t y diagram. This zinc oxide i s o a c t i v i t y pattern projects to- weerds the lime o r t h o s i l i c a t e composition. ThlS:. shape i s c h a r a c t e r i s t i c of FeO, 'but i n the case of ZnO the pro j e c t i o n i s less pronounced. Both these observations are i n keeping with the s l i g h t l y more basic behaviour of zinc oxide. i i ACKNOWLEDGEMENT The author would like to extend his sincere thanks to his research director, Dr. C S. Samis for his continued encouragement and guidance throughout this work. The explanations and contributions by Dr. G. W. Toop and Dr. W. G. Davenport are greatly appreciated. The help and interest shown by various members of the faculty, staff and especially fellow graduate students is warmly acknowledged. Appreciation i s expressed to the Defence Research Board and the National Research Council of Canada whose financial support made this work possible. i i i TABLE OF CONTENTS Page I. INTRODUCTION 1. A . General 1 B. Previous Work 1 C. Scope of Present Investigation 2 D. Experimental Method 3 II. THERMODYNAMIC . MEASUREMENT BY OXYGEN HALF-CELLS 3 A. Theory of Oxygen Solid Electrolytes 3 1. Defect Structure 3 2. Conduction Mechanism ^ B. Cr i t e r i a for Reversibility 6 III. THERMODYNAMIC CALCULATIONS " 9 A. Binary Oxide Systems 9 1. CaO-Si0 2 9 2. ZnO-CaO ' 9 3. ZnO-Si0 2 11 B. ZnO-CaO-Si02 Ternary 11 IV. EXPERIMENTAL 18 A. Equipment 18 1. Oxygen C e l l Design 18 2. Furnace 18 3. Temperature Control . 18 k. Emf Measurement 18 5. Purification Train 23 6. Air Pump 23 iv TABLE OF CONTENTS (continued) Page B. Materials 23 1. Reagents 23 2. Crucibles 23 3. Oxygen Cells 23 k. Electrodes 23 C. Procedure 2k 1. Oxygen Potential 2k a. Oxygen Potential Range Available 2k b. Oxygen Potential Control 2k c. Purification Train . . 25 d. Duration of Run 25 2. Zinc Activity 25 a. Alloy Preparation . . . : 25 b. Sampling 25 c. Analysis 26 3. Slags 26 a. Preparation 26 b. Sampling ' . 28 c. Analysis 28 k. Time for Equilibria 28, 5. Reversibility of the Oxygen Half C e l l . . . . 28 V. RESULTS 31 A. Zinc Oxide Activity 31 B. Solid Zinc Oxide Saturation Line 3̂ C. Slag Analysis 3̂ TABLE OF CONTENTS (continued) Page VI. INTERPRETATION OF RESULTS 36 A. Calculation of a ZnO (Liquid Standard State) in ZnO-CaO-Si02 Slags 36 B. Comparison between Experimental G^^nO  an<^ Calculated ZnO Isoactivity Lines in the ZnO-CaO-Si02 System 37 C. Comparison with Davenport's Calculated (X <£nQ Data for the ZnO-CaO-Si02 Ternary 37 6 D. Comparison with Work by Azuma, Goto and Ogawa . . 40 E. Comparison Between Zn0-Ca0-Si02 and Fe0-Ca0-Si02 Ternaries hO 1. Zn0-Si0 2 and Fe0-Si0 2 Binaries kO 2. Fe0-Ca0-Si02 Ternary k-2 VII. SUGGESTIONS FOR FURTHER WORK k2 VIII. CONCLUSIONS k6 IX. REFERENCES 7̂ X. APPENDICES I. Calculation: of Infinitely Dilute Properties of Zinc in the Copper-Zinc System 9̂ II. The System ZnO-Si02 53 III. Toop's Ternary Integration Technique 65 IV. Oxygen Potential Limits 69 V. Free Energy of Formation of Zn SiO, 70 v i LIST OF FIGURES F i g . No- Page l a . Pure Zirconium Dioxide 5 l b . Zirconium Dioxide with Calcium Oxide Addition 5 2. Oxide Conductivity as a Function of Oxygen P a r t i a l Pressure-1-^ 7 3- Conductivity Reactions at Cathode and Anode i n an Oxygen . E l e c t r o l y t e with a Large Concentration of Oxygen Ion Vacancies 8 k. Excess Free Energy of the CaO-SiOg Binary at l600°C Based on the Metastable Pure L i q u i d Standard States? 10 5. Phase Diagram, ZnO-SiOg System 1 12 6. Calculated Excess Free Energy i n the Zn0-Si02 Binary at l600°C 13 7- C a l c u l a t e d . A F X S of the Zn0-Ca0-Si0 2 Ternary at l600°C . . . Ik 8. Calculated I s o a c t i v i t y Lines f o r ZnO at l600°C 15 9. Calculated I s o a c t i v i t y Lines f o r S i 0 2 at l600°C - 16 10. Calculated I s o a c t i v i t y Lines f o r CaO at l600°C 17 11. The Experimental Layout 19 12. Schematic Diagram of the Experimental Apparatus 20 13. Oxygen C e l l 21 . I k . Temperature P r o f i l e of Super Kanthal Furnace at 1300°C . . . 22 - 15. Standardization Curves f o r the SP-90 Atomic Absorption Unit as a Function of the Zn to Cu Ratio i n the Standards . . . . 27 16. Experimental V a r i a t i o n i n A c t i v i t y of ZnO as a Function of Time 29 17. Conductivity of O.85 Z r 0 2 - 0.15 CaO S o l i d E l e c t r o l y t e as a Function of Oxygen P o t e n t i a l at 1300°C 30 18. Data from Runs I and K (ZnO Saturated) Together with Calculated T h e o r e t i c a l Line f o r Zinc Oxide Saturation. . . . 35 19- Measured ZnO A c t i v i t y Values Compared with the Calculated ZnO I s o a c t i v i t y Lines i n the Zn0-Ca0-Si02 Ternary 38 20. Comparison Between the I s o a c t i v i t y Lines f o r ZnO at l600°C Calculated by Davenport-5 and i n the Present Study 39 v i i LIST OF FIGURES (continued) Fig. No- Page 21- Comparison Between the Excess QFree Energies of the Binaries FeO-Si0 2 and Zn0-Si0 2 at 1600 C 1̂ 22. Calculated A F X S of the FeO-CaO-Si02 Ternary at l600°C. . . . 4 3 23. Calculated Isoactivity Lines for FeO at l600°C kk 2k- D a t a of Everett, Jacobs and Kitchener-^1 51 25- Thermodynamic Data on the Infinitely Dilute Free Energy of Zinc i n Copper 52 26. ZnO-Rich Side of Zn0-Si02 Binary 1 5k 27. Estimate of Enthalpy of Fusion for ZnO from the Liquidus Line 55 28- Graphical Integration of the Liquidus Curve of Zn 2SiO^. . . . 59 29. CX Plots for Zn0-Si0 2 Binary 62 30. Comparison Between the Free Energy of the Zn0-Si0 2 Binary at l600°C as Given by Richardson and as derived i n the Present Study 6̂ 31. Definition and Location of Terms Used in Appendix I I I 1 ^ . . . . 66 32. CX Plots for the Fe0-Si0 2 Binary 67 33. 0( Plots for the Ca0-Si0 2 Binary 68 v i i i LIST OF TABLES Table No- Page 1. Experimental Zinc Oxide Activities 32 2. Activity of ZnO with respect to Metastable Pure Liquid ZnO at l600°C 36 3. Calculation of A s f ZnO % k. Activity of Si0 2 from N S 1 0 = 1-0 to = 0.235 58 5. Activity of ZnO from N Z n Q = 1.0 to WZn0 = 0-5 60 6. Si02-ZnO Binary Integration 6l 7- Excess Free Energy of Zh0-Si0 2 at l600°C 63 THE ACTIVITY OF ZnO IN THE TERNARY SYSTEM Z n 0 - C a 0 - S i O 2 INTRODUCTION A . G e n e r a l Z i n c o x i d e b e a r i n g s l a g s have i n d u s t r i a l i m p o r t a n c e . In s e v e r a l m e t a l - l u r g i c a l p r o c e s s e s t h e z i n c o x i d e i n t h e s e s l a g s i s s e l e c t i v e l y r e d u c e d i n f a m i n g f u r n a c e s t o r e c o v e r t h e z i n c v a l u e s . As t h e f u m i n g r a t e s o f z i n c o x i d e a r e d i r e c t l y r e l a t e d t o i t s a c t i v i t y i n a s l a g , s t u d i e s o f t h e a c t i v i t y o f z i n c o x i d e i n v a r i o u s s l a g s have a n economic j u s t i f i c a t i o n . B . P r e v i o u s Work B e l l , - T u r n e r and Pe te rs - ^ c a l c u l a t e d t h e a c t i v i t i e s o f z i n c o x i d e f r o m o p e r a t i n g p l a n t d a t a i n s e v e r a l s l a g s f r o m a n o p e r a t i n g l e a d b l a s t f u r n a c e . In t h i s p a r t i c u l a r p r o c e s s t h e f u r n a c e s o p e r a t e a t a p p r o x i m a t e l y 1 2 0 0 ° C and u t i l i z e s l a g s c o n t a i n i n g a maximum o f 25 p e r c e n t ZnO. These c a l c u l a t i o n s were done w i t h r e s p e c t t o s o l i d z i n c o x i d e and f o r s l a g s o f c o n s t a n t CaO t o S i 0 2 + A l 2 0 2 r a t i o . R i c h a r d s and Thorne^" e q u i l i b r a t e d F e 0 - C a 0 - S i 0 2 and F e 0 - S i 0 2 m e l t s c o n - t a i n i n g one t o two p e r c e n t ZnO i n i r o n b o a t s w i t h a C 0 - C 0 2 gas c o n t a i n i n g z i n c v a p o u r . They f o u n d t h a t t h e t e r n a r y sys tem Z n 0 - F e 0 - S i 0 2 c o u l d be r e p r e s e n t e d b y a r e g u l a r s o l u t i o n a p p r o x i m a t i o n i n w h i c h t h e i n t e r a c t i o n e n e r g y be tween z i n c o x i d e and f e r r o u s o x i d e was assumed t o be z e r o . - 2 - 6 The most r e c e n t work , b y Azuma e t . a l . , r e p o r t s a c t i v i t i e s o f z i n c o x i d e i n s l a g s c o n t a i n i n g i r o n o x i d e , s a t u r a t e d and u n s a t u r a t e d w i t h s i l i c a , as a f u n c t i o n o f l i m e c o n t e n t . They s t a t e t h a t f o r s i l i c a s a t u r a t e d s l a g s , $£n0 r e m a i n s c o n s t a n t a t about 1 w i t h i n c r e a s i n g C a O , w h i l e f o r s l a g s n o t s a t - u r a t e d i n s i l i c a , ^ n O i n c r e a s e s f r o m 1.8 t o 3 . 1 w i t h an i n c r e a s e i n t h e CaO c o n t e n t f r o m z e r o t o 1 6 . 5 w e i g h t p e r c e n t . U n f o r t u n a t e l y i n f o r m a t i o n on t h e z i n c o x i d e c o n t e n t s , t h e e x p e r i m e n t a l t e m p e r a t u r e s and t h e e n t r o p y o f f u s i o n u s e d f o r z i n c o x i d e i s u n a v a i l a b l e a t t h e p r e s e n t t i m e . 5 The most e x t e n s i v e i n v e s t i g a t i o n a v a i l a b l e i s b y D a v e n p o r t ^ who d e t e r - mined a c t i v i t i e s i n t h e Z n O - F e O - S i 0 2 t e r n a r y and Z n O - F e O - S i 0 2 - C a O q u a t e r n a r y . ' 7 He a l s o c a l c u l a t e d a c t i v i t i e s i n t h e Z n O - C a O - S i 0 2 t e r n a r y u s i n g E l l i o t t s i n f o r m a t i o n on t h e F e 0 - C a 0 - S i 0 2 s y s t e m . In o r d e r t o d e t e r m i n e t h e a c t i v i t y o f z i n c i n t h e s y s t e m he u s e d a n i r o n s a t u r a t e d b r a s s h e l d i n a n i r o n c u r c i b l e . The r e s u l t i n g F e - F e O e q u i l i b r i a d e t e r m i n e d t h e oxygen p o t e n t i a l and hence t h e range o f z i n c o x i d e a c t i v i t y a v a i l a b l e was l i m i t e d . I t was f e l t t h a t t h i s work might be e x t e n d e d i f a means c o u l d be f o u n d t o remove t h i s l i m i t a t i o n . C . Scope o f P r e s e n t I n v e s t i g a t i o n The t e r n a r y Z n O - C a O - S i 0 2 i s t h e s i m p l e s t s l a g s y s t e m c o n t a i n i n g z i n c o x i d e w i t h a wide range o f a c i d - b a s e b e h a v i o u r . Based on t h e s i m i l a r i t y b e - tween t h e f r e e e n e r g i e s , w i t h r e s p e c t t o t h e s o l i d s t a n d a r d s t a t e , o f t h e two 8 o x i d e s FeO and ZnO w i t h s i l i c a , t h i s s y s t e m s h o u l d r e s e m b l e t h e F e 0 - C a 0 - S i 0 2 t e r n a r y . The Z n 0 - C a 0 - S i 0 2 t e r n a r y has a somewhat l i m i t e d a r e a w i t h a m e l t i n g 2 p o i n t u n d e r 1300°C . I t i s p r o p o s e d t o use t h e s imple - e q u i l i b r i u m Z n ( 1 ) + l / 2 0 2 ( g ) ^ * r Z n O ( s ) . . . ( l a . ) f o r w h i c h -7 (9) K 1 5 7 3 ° K = 7-3x10 K 7 > . . . ( l b . ) - 3 - to determine zinc oxide activities in slags from this ternary, primarily along the line of s i l i c a saturation at 1300°C. D. Experimental Method In order to thermodynamically f i x the activity of zinc oxide in a slag i t is necessary to measure the oxygen potential and the zinc activity. In appendix I a discussion is given of the available information on the copper- zinc binary. For low concentration of zinc the following approximate expression is derived. A.F Z£ "= -8200 + 2.58 T . .. (2) Hence the activity coefficient for zinc w i l l be less than unity. It is also possible to directly measure the oxygen potential of a gas phase using an oxygen solid electrolyte of the type to be described in section II. The activity of zinc oxide in a slag may .be measured by the zinc content of a copper rich brass and the oxygen potential of gas when both are in equilibrium with a ZnO bearing slag. THERMODYNAMIC MEASUREMENT BY OXYGEN HALF-CELLS A . Theory of Oxygen Solid Electrolytes 1) Defect Structure 10 Hund f i r s t showed that oxide mixtures containing a predominance of valence IV metallic ion with a small percentage of valence II or III metallic ion snould be capable of acting as solid oxygen electrolytes. Due to tne oxygen ion mobility in tne oxygen ion deficient lattice structure, under certain conditions - k - (temperature and oxygen partial pressure) oxygen ion transport is the major 11 conduction mechanism. Kuikkola and Wagner made several of tnese oxide mixtures at varying composition and showed that at certain conditions, many of these structures do conduct almost entirely by oxygen ion transport. Zirconium dioxide forms an anion vacancy type of l a t t i c e . This is known from measurements of conductivity and oxidation rate as a function of oxygen par t i a l pressure. In the pure zirconia ionic lattice (Figure la) as oxygen ions are removed, free electrons are formed. In the pure material the con- centration of these defects is relatively small. The addition of a lower valence impurity oxide such as lime or y t t r i a to this structure w i l l cause a proportional increase in the number of anion defects to keep the cation to anion charge balance within tne original structure. For every calcium ion that enters the lattice on a zirconium ion site there w i l l be an oxygen vacancy formed without increasing the number of free electrons. (Figure lb). 2. Conduction Mechanism In a pure oxide of tnis type (anion deficient) at low oxygen partial pressure the conduction reaction w i l l be: 1/2 0-2 + 0 n + + k e~ 0 ••• (3) As the oxygen partial pressure is increased the oxide tends to approach stoichiometry. At high oxygen partial pressure oxygen ion i n t e r s t i t i a l s together with electron holes w i l l be formed. 1/2 0 2 -« 0 = + 2 © . . . (k) Conductivity is due to three charge carriers in any combination: oxygen ions, free electrons and positive electron holes ^ 1/n -l/m ( 1 2 ) = ^:'ion + K i P ° 2 + K 2P0 2 . . . (5) where K a, K2, n and m are constants. +k +k Zr., e - 0 0 Zr +k = 0 Zr 0 0 0 l—l Zr g - 0 +k = +h Zr 0 0 Zr Figure l a . Pure Zirconium Dioxide. Zr o" o" Zr o" +k 0 0 +2 Ca 0 Zr 0" +U = 0 Zr 0 +k Zr +h Figure l b . Zirconium Dioxide with .'. Calcium Oxide Addition With increasing oxygen partial pressure conductivity owing to positive hole conduction,will increase and conductivity due to electron conduction w i l l decrease (Figure 2). , Witn oxide mixtures of the zirconia-yttria,zirconia-lime types, there are large numbers-of vacant oxygen sites, which are uncharged. Conductivity reactions then occur as in figure 3. If the^ contribution of charge carried by the electrons ..in, .  the; oxide is negligible with respect to that carried by oxygen ions then the transport number for oxygen ions may be taken as unity. Steele and • 13 Alcock indicate that both lime and yt t r i a stabilized zirconia would be useful for the range of oxygen potential to be used in the present study. \ B. Cri t e r i a for Reversibility The determination of chemical potential by emf .methods is based on: the Nernst equation. -nFE = AF This applies to a chemical reaction having a Gibbs free energy AF when carried out reversibly in an electrochemical c e l l . E is the ^electromotive force generated, n is the number of electrons transported by the reaction and F is the Faraday constant. The emf of the c e l l Ft, 02 (/%) | 0.85Zn02-0.15CaO | 0 2 (yU2), Pt is given exactly by E = _1 ̂  ... (7) V 2 D / * Here t Q 2 is the transport number of oxygen ions in the electrolyte. In the simple case where t n ~ 2 = 1 equation 7 reduces to E = - i (M2 - / ^ l ) ••• ( 8 a ) kF E = RT In a 0 " 2 II ... (8b) 5F I  - 8 - High 0 2 PP 2 0 2 + . 0 Q + 2 e 0 Oxygen E l e c t r o l y t e 0„ External C i r c u i t Electrons. 0" Low Oo PP 2°2 + °D + 2 E " Figure 3- Conductivity Reactions at Cathode and Anode i n an Oxygen E l e c t r o l y t e with a Large Concentration of Oxygen Ion Vacancies. This means that the c e l l functions as a simple concentration c e l l for oxygen potential. THERMODYNAMIC CALCULATIONS Toop has shown that a simple proportional combination of the excess properties in the component binaries may adequately describe the excess properties in the ternary system. He has successfully applied this technique in the Fe0-Ca0-Si02 ternary to calculate the excess free energy at 1600 C based on the pure liquid metastable standard states. It is shown (Appendix III) that from the CX plots (RTln o* i/( 1-Ni ) 2 versus Ni) for each component in i t s binaries, the act i v i t i e s and excess free energies may be calculated. A. Binary Oxide Systems 1. ) CaO-SiOg 7 E l l i o t t gives the excess free energy curve for the CaO-Si02 binary based on the metastable pure liquids (Figure k). Tangent intercepts were taken from this curve to determine the CX plots for the two components. 2. ) . ZnO-CaO No information is available on the ZnO-CaO binary. As an approximation i t i s assumed that the curve for FeO-CaO may be used for the ZnO-CaO binary. C V = RTln ZnO = RTln j) CaO = -8580 cals mol" 3 U-Nzno) 2 (i-Ncao) 8 This assumption gives the simplest shape for the excess free energy, a simple parabola.  - 11 - 3.) ZnO-SlOg In order to derive suitable & plots for the ZnO-Si0 2 binary i t is necessary to know acti v i t i e s of the two components relative to the metastable pure liquids 1 at l600°C. Bunting has shown the phase diagram consists of a congruent melting compound, zinc orthosilicate, together with two simple eutectics (76-5 a n d 50 mol fo ZnO ) and a two phase liquid region at the s i l i c a rich side of the binary (Figure 5). Activities may then be calculated from this phase diagram using Chipman's melting point depression method and Hauffe and Wagner s congruent melting 19 compound technique The following thermodynamic information was used: 17 1. ) Entropy of fusion of s i l i c a (Cristobalite) estimated at 1.8 E.U. 20 2. ) Kitchener and Ignatowitz s estimated heat of fusion for zinc orthosilicate of 18.7 Kcals/mol 1 " 3. ) An entropy of fusion for zinc oxide of 6 E.U. estimated from E l l i o t t ' s 1 ,26 activity diagram for the Zn0-Si0 2 binary. This calculation and the derivation /N/ 21 of mutually compatible OC curves based on the Duhem Margules equation is given in appendix II. The excess free energy curve for the Zn0-Si0 2 binary is shown in figure 6. B. Zn0-Ca0-Si0 2 Ternary A Fortran computer program was written for processing the binary data according to the equations developed in appendix III on the University IBM 70̂ 0 computer. The excess free energy of the Zn0-Ca0-Si0 2 ternary is given in figure 7 and the calculated isoactivity lines for the three components ZnO, S i 0 2 and CaO are presented in figures 8, 9 a n d 10 respectively. - 12 - 10 20 30 40 50 60 70 8o 90 loo Mol io ZnO Figure 5- Phase Diagram, ZnO-Si0 2 System? Figure j£. Calculated Excess Free Energy i n the ZnO-SiOp Binary at l600°C   Figure 9. C a l c u l a t e d I s o a c t i v i t y Lines f o r S i 0 2 at l600°C. Figure 10. Calculated I s o a c t i v i t y Lines ffor CaO at l600°C. - 18 - EXPERIMENTAL A Equipment The experimental lay-out and apparatus are shown in figures 11 and 12 . 1. ) Oxygen C e l l Design 22 A c e l l design similar to that of Fischer and Ackermann employing a i r as the reference oxygen half c e l l was used (Figure 13). Such a design avoided any loading of the ceramic electrolyte and permitted i t s placement in the best position relative to the temperature gradient of the furnace. (Figure Ik). 2 . ) Furnace A vertical Super Kanthal furnace was used. It was capable of attaining 1600°C on a 1 3A" diameter cross section about three inches in length. The power input at the experimental temperature (1300°C) was 1.9 kilowatts. 3. )" Temperature Control Furnace temperature was measured with a Pt-Pt-10# Rh thermocouple. Maximum sensitivity of control was achieved by setting the voltage at a known level for the temperature desired and having continuous power into the furnace. In this way i t is estimated that furnace temperature and control were accurate + to within - 10°C. A Honeywell Brown Electronik controlling potentiometer was available and acted as a maximum temperature cut-off device. k.) Emf Measurement The oxygen c e l l emf was measured with a Pye portable potentiometer. It was found that this was as sensitive as a high impedance, vacuum tube voltmeter. At 1300°C the emf could be measured to within - 1 mv. I - 19 - Figure 11. The E x p e r i m e n t a l L a y o u t . Legend 1. Brass End Cap-Water Cooled 2. 0-Ring Seal 3. 0.85Zr02-0.15Ca0 Impervious Tube (Solid Oxygen Electrolyte) Pt-Pt lOfoRh Thermocouple 5- Inner Platinum Electrode • 6. Outer Platinum Electrode 7- Crucible Containing melt 8. Mullite Furnace Tube 9. Fireclay Pedestal 10. V i t r e o s i l Pedestal Rod 11. 0-Ring Seal 12. Brass End Cap-Water Cooled 13. Anhydrite 14. Hot Copper Turnings 15. S i l i c a Gel 16. Ascarite 17- Deoxp Catalyst 18. Silicone Oil. Bubbler 19- Nitrogen Flow Meter 20. Needle Valve 21. Nitrogen,. Supply 22. Hydrogen Supply 23. Pye Potentiometer 24. Controller and Variac. 25- Air Supply Figure 12. Schematic Diag Figure 13• Oxygen C e l l Ik 13 I 12 11 (U -p a3 in a; EH 10 9 8 7 6 5 X Refers to the Position of the Thermocouple and Oxygen Cell. RXXXH Refers to the Position of the Crucible. _L _L 7 8 9 10 11 12 Inches From Top of the Furnace 13 Ik 15 Figure lk.' Temperature Profile of Super Kanthal Furnace at 1300°C. 16 17 ro ro X Refers to the Position of the Thermocouple and Oxygen Cell . Refers to the Position of the Crucible. l i s 1 1 1 I ! I I 1 J— h 5 6 7 8 9 10 l l 12 13 Ik 15 Inches From Top of the Furnace Figure lUv Temperature Profile of Super Kanthal Furnace at 1300°C. - 23 - 5. ) Purification Train The gas purification train w i l l be discussed under oxygen potential control in the section on procedure. 6. ) Air Pump It was found necessary to maintain a flow of ai r against the bottom of the ce l l to avoid the formation of an oxygen gradient from the top to the bottom of the c e l l . A small vibrator pump supplied sufficient a i r pressure to accomplish this. B. Materials 1. ) Reagents Baker and Adamson analysed granulated zinc, shot copper, powdered zinc oxide and powdered calcium carbonate were used. S i l i c a was standard commercial grade. 2. ) Crucibles S i l i c a saturated slags were held in 2f0 ml. V i t r e o s i l 97$ s i l i c a crucibles. Non-silica saturated slags were contained in y t t r i a stablized zirconia crucibles supplied by the Zircoa Corporation^ 1 l/k" o.d.. x 3" long. 3. ) Oxygen Cells The oxygen cells used were 0.85Zr02 - O.PpCaO impervious tubes l/k" od fifteen inches long, closed one end, supplied by Zircoa Corporation. k.) Electrodes The inner electrode was simply the platinum lead from the thermocouple held in el e c t r i c a l contact against the solid electrolyte by the thermocouple insulator. The outer electrode was a piece of platinum wire wrapped around the base of the c e l l immediately above the melt. - 2k - C. Procedure A crucible containing about ten grams of alloy together with fifteen grams of slag was loaded into the bottom of the furnace, at a temperature such that the brass would remain solid. The system was purged with low oxygen potential gas. When a suitable emf was reached the pedestal was raised to bring the crucible just below the c e l l and the variacset to give the desired experimental temperature. The metal phase was sampled at various oxygen part i a l pressures allowing time for equilibrium to be established at each potential. When a l l the alloy was removed the furnace was cooled and the crucible withdrawn. 1.) Oxygen Potential a. ) Oxygen Potential Range Available At any given temperature and zinc oxide activity two considerations f i x the range of oxygen potential available. The lower side is determined principly by the boiling point of zinc in the alloy. At 1300°C with unit activity of zinc oxide this gives a lower oxygen potential limit of 2.0 x 10 atm. (Appendix IV). The highest oxygen part i a l pressure i s fixed by the limit of detectability of zinc in the brass and by the necessity of keeping copper from oxidizing into the slag. Assuming that the oxidation of copper is the determining factor at 1300 C, the highest oxygen potential would be 1.1 x 10 atm. (Appendix IV). b. ) Oxygen Potential Control The oxygen potential was controlled by the water equilibrium constant in a flow of commercial grade nitrogen into which a small amount of hydrogen was bled through a silicone o i l bubbler. The oxygen potential was varied by adjusting the needle valve on the nitrogen flow meter to change the relative flow rates of the two gases. A total flow rate of about 100 cc's a minute was - 25 - s u f f i c i e n t t o m a i n t a i n e q u i l i b r i u m c o n d i t i o n s i n t h e f u r n a c e . c . ) P u r i f i c a t i o n T r a i n The gas t r a i n c o n s i s t e d m a i n l y o f d e v i c e s t o h e l p r e d u c e t h e oxygen p o t e n t i a l o f t h e c o m m e r c i a l g rade n i t r o g e n wh ich p r o b a b l y c o n t a i n e d about two p e r c e n t oxygen . The deoxo c a t a l y s t s e r v e d t o combine most o f t h e oxygen w i t h h y d r o g e n t o f o r m w a t e r . The h o t c o p p e r t u r n i n g s " s e r v e d as a f u r t h e r c o n t r o l as t h e oxygen p o t e n t i a l o f t h e gas s h o u l d be d e t e r m i n e d b y t h e e q u i l i b r i u m oxygen p o t e n t i a l w i t h s o l i d c o p p e r a t t n e t e m p e r a t u r e o f the t u r n i n g s . . A s c a r i t e was u s e d t o remove any CO2 p r e s e n t a n d s i l i c a g e l and a n h y d r i t e were u s e d t o r e d u c e t h e wate r c o n t e n t o f t n e g a s . d . ) D u r a t i o n o f Run The method o f c o n t r o l l i n g oxygen p o t e n t i a l was a l a r g e f a c t o r i n t h e l e n g t h o f t i m e a r u n was k e p t i n t h e f u r n a c e . I n o r d e r t o keep t h e oxygen p o t e n t i a l c o n s t a n t a t any l e v e l i t was n e c e s s a r y t o c o n t i n u o u s l y m o n i t o r the f l o w o f t h e two g a s e s . The l o n g e s t r u n was e i g h t h o u r s . 2.) Z i n c A c t i v i t y a . ) A l l o y P r e p a r a t i o n To r e d u c e z i n c l o s s i t was f e l t i n a d v i s a b l e t o s i m p l y l o a d p r e m i x e d m e t a l powder i n t o t h e f u r n a c e . C o p p e r - r i c h b r a s s ( N ^ ' f i * . 0.01) was p r e p a r e d a t the b e g i n n i n g o f t h e e x p e r i m e n t a s none was r e a d i l y a v a i l a b l e . We ighed amounts o f t h e two m e t a l s were s e a l e d i n e v a c u a t e d q u a r t z and m e l t e d i n t h e Super K a n t h a l f u r n a c e . The c o m p o s i t i o n g r a d i e n t " o f t h e a l l o y was s l i g h t and was no s e r i o u s l i m i t a t i o n . b . ) S a m p l i n g The m e t a l phase was sampled by i n s e r t i n g a 2 mm i . d . q u a r t z q u i l l i n t o t h e m e l t and w i t h d r a w i n g a p e n c i l o f a l l o y w i t h an a t t a c h e d a s p i r a t o r b u l b . .-26- It was found that the introduction of the tube only momentarily, lowered the oxygen potential and i t returned to i t s original value within a minute of withdrawal. ' c.) Analysis ' Metal specimens were dissolved in diluted 1:1 n i t r i c acid and the solution analyzed for zinc using a Unicam SP-90 atomic adsorption spectrophotometer. For ! pure zinc the effective sensitivity limit of this instrument was found to be about 0.05 /Uo/ml of solution. For a 0.1 gram sample dissolved in the minimum amount of n i t r i c acid and made up to 10 ml.', the minimum deiectable zinc i s about 0.'005 mol percent. Pure copper has some'absorption at the 2139A0 line used for zinc analysis. One gram of copper in f i f t y £ubic cen- timeters of solution gives an absorption equivalent to one microgram per m i l l i - l i t e of zinc. This coincides with the sensitivity of the instrument for pure zinc. Hence the effective sensitivity of the instrument for detecting zinc in a copper rich brass is 0.01 mol percent*. In a l l the specimens the experimental ratio was in the order of one hundred parts of copper to one part of zinc. In this range the exact proportion interfered, l i t t l e (Figure 18). A brass standard containing one hundred parts of copper to one part of zinc was used + , in a l l the analysis. Accuracy was estimated at - yp. 3.) Slags . * a.) Preparation On i n i t i a l runs i t was found that there was considerable d i f f i c u l t y in melting the oxide powders to form a slag during a run at temperatures only slightly higher than the estimated melting point of the slag". Segnit and 23 Wolfe's technique for quenching prefused slags in a platinum crucible was adapted for use in the Super Kanthal furnace. The furnace design was not very suitable for this work since a crucible had to be lowered on the pedestal and the pedestal removed before the crucible could f a l l into a bucket of cold water under furnace. Thus higher melting po nt slags cou d no  be readily made. Mainly  - 28 - for.this reason i t was decided to work principly along the 1J000C s i l i c a saturation line. In addition the job of chipping only partially glassy slags from the platinum crucible was somewhat laborious. b. ) Sampling Slags were sampled by a cold steel rod with a notch cut into the lower end. c. ) Analysis Slag samples of about .0.5 gram were ground to minus 100 mesh and treated with a mixture of equal parts of concentrated hydrofluoric and perchloric acids in a platinum crucible. The baked constant weight residue was weighed as metal chlorides. The difference was assumed to be s i l i c a . The residue was treated with boiling water to bring the chlorides into solution. The solution was then analyzed for zinc and' copper using the absorption spectrophotometer. The difference was again used to check the original CaO to Si0 2 ratio of the oxide powders. ) Time for Equilibria The length of time required for equilibrium to be established was a r b i t r a r i l y set at one half hour to minimize the length of time during which the gas flows would require continuous monitoring. In figure 16 a plot is given from one run of the actual over the average ZnO activity as a function of time. It is seen that although there is considerable scatter, the length of time between readings had l i t t l e effect between one half hour and four hours. It was assumed that equilibrium was attained within one half hour at each different level of oxygen, potential. 5.) Reversibility of the Oxygen Half C e l l The most important condition for oxygen c e l l reversibility is that the transference number for oxygen ions be unity. As a further check that the c e l l - 29 - o id o d 0.5 0 100 200 300 Time i n Minutes A f t e r F i r s t Sample 1+00 Figure 16. Experimental V a r i a t i o n i n A c t i v i t y of ZnO as a Function of Time. -4.0 -3-5 o H o -3.0 -2-5 -7 Figure 17• Log 1 0 P 0 2 Conductity of O.85 Zr02-0.15 CaO Solid Electrolyte as a Function of Oxygen Potential at 1300°C. - 31 - was measuring the true oxygen potential of the system two brief experiments were carried out. Using a Bye potentiometer as a voltage source i t was found that after imposing a one volt emf across the c e l l in either direction, the resting potential of the operating c e l l was unchanged. Thus i t was concluded that the c e l l was not polarized. A simple ohmmeter was used as a conductivity meter at several different values of oxygen partial pressure. It is seen (Figure 17) that the variations in conductivity is slight over a relatively wide range of oxygen partial pressure. This indicates that oxygen ions are the major charge carriers» RESULTS A. Zinc Oxide Activity The experimental results are presented in table 1. The ac t i v i t i e s of zinc oxide with respect to the solid standard state are measured at the particular experimental temperature using the free energy expression given by Wicks and Block^. Reproducibility is well within the calculated standard deviations which are admittedly quite large. Considering that this work required a three phase equilibrium at high temperature i t is not unreasonable to find such large standard deviations. -32 - T a b l e I E x p e r i m e n t a l Z i n c Ox ide A c t i v i t i e s KEY TEMP °C a Z n EMF mv PPOg x l O ° aZnppo22 x l O 7 a Z n O a Z n O ZnO SLAG CaO S i 0 2 D l 1240 .00155 490 4.2 3.17 1 . 4 8 D3 1240 .00083 524 1.18 .897 .44 .94 26.5 23 50.5 . 4 8 D4 1235 .00072 483 4.4 1.51 • 75 E l 1310 .OOI89 490 8.37 5.45 • 733 E2 1300 .OOO96 507 4.71 2 . 1 .283 E3 1305 .00086 472 13.3 3 -14 .4221 .45 24 21 55 .38 E4 1305 .OOO57 455 22 2.67 .36' F I 1305 .0015 536 1.88 2.05 .275 F2 1305 .00129 494 6.96 3.4 • 457 F3 1320 .00154 499 7.5̂  4.19 • 538 •519 24 21 55 .23 F4A 1320 .ooi4i 494 8.37 4.07 .523 F4B 1320 .00189 494 8.37 5.45 •70 F 6 1315 .00373 55̂  1.68 4.82 .620 G1A GIB 1340 1340 .00523 .00555 708 708 .021 .021 • 755 .802 • 364 G2 1335 .00501 653 .094 1.54 • 759 .503 24 21 55 • 36 G 3 1320 .00328 573 • 835 3 -0 .39 -33 - KEY TEMP °C <*Zn EMF mv PPOg x l O 8 X l O : ^ZnO Q Z n 0 SLAG ZnO CaO S i 0 2 11 1365 .0019 409 149. 2 3 . 1 1 . 2 1 12 1365 .0022 383 348. 41 . ' 2.15 1 . 1 1 42 22 36 13 1365 .0017 475 2 2 . • 79 .42 l 4 1365 .0030 475 2 2 . 1 . 4 • 735 J l 1330 .00345 501 8.36 9-93 .827 J2A 1325 .00238 480 1 . 3 8 8.85 • 737 J2B 1325 .00225 480 1 . 3 8 9.25 .772 1 . 0 0 42 22 36 . 2 8 J 3 1330 .0028 460 2 . 6 5 14.4 1 . 2 J4 1330 .0039 463 2 . 2 18.3 1 . 52 J 6 1345 .003 484 1 . 4 9 1 1 . 6 •97 K l 1335 .0032 600 1 . 0 1 3-2 .263 K2 1365 .00305 477 24. 1 . 4 8 .78 .405 14 27.5 5 8 . 5 • 13 K3 1345 .0033 ^29 80. 2 . 9 5 .209 K4 1345 .0012 4 8 0 I 8 . 7 5 - 2 • 37 -34 - B. Solid Zinc Oxide Saturation Line ( aZnO = !) In figure 18 the results of two separate runs are plotted using a slag saturated in both zinc oxide and zinc orthosilicate (,22~CuO, .42 ZnO, -36 SiOg)-. It is seen that the line calculated, from the assumption that 1/2 zinc oxide activity is unity (i.e. u^n x PP02 = Ke(^ w.r.t. solid ZnO) f i t s these points reasonably well. Hence i t is concluded that at 1300°C the transport number for oxygen ions in the solid electrolyte O.85 Zr.02 - 0.15 CaO over an oxygen potential range of 2.3 x 10 ̂  to Q 8.4 x 10 is unity. C. Slag Analysis Extensive slag analysis was done on one of the early runs and showed that the variation in composition of the slag over a.six hour period was within five percent of the original fraction of oxide powders. This was negligible in comparison with the variation in measured ZnO activity and hence i t was assumed for the other runs that the slag composition present was that given by the original oxide mixture. The presence of large amounts of cuprous oxide in the slag was evident from those runs in which the controlled atmosphere was lost and copper was allowed to oxidize. These slags were very dark brown in colour and textured rather than glassy. In the analyzed slag samples which were clear or slightly green in colour the maximum cuprous oxide content was less than one mole percent. As long as the slag remained clear i t was assumed that the amount of cuprous oxide present was negligible. Figure 18. Data f o r Runs I and_J. (ZnO Saturated) Together with Calculated T h e o r e t i c a l Line f o r Zinc Oxide Saturation. - 36 - •INTERPRETATION OF RESULTS A. Calculation of a ZnO (Liquid Standard State) in ZnO-CaQ-SiOg Slags In order to compare the experimental results with those calculated hy 16 Toop's method at l600°C i t is necessary to recalculate these a c t i v i t i e s using the pure metastable liquid as the standard state. The entropy of fusion for zinc oxide (6 E.U.) established from thermodynamic data (Appendix II) was used together with the regular solutions theory temperature adjustment. These results are given in table 2. Table II Activity of ZnO with respect to Metastable pure liquid ZnO at l600°C Run a ( s ) a (1)T °l600°C 1̂) i6oo°c D .21 • 792 -.233 .828 .22 E M .124 .515 -.662 •571 .14 F • 534 •15 .623 -.472 .669 .16 G • 503 •15 .623 -.472 .669 .16 I l . l l •35 .833 -.182 .853 • 36 J 1.00 .29 .691 -.368 .729 • 31 K .405 .12 • 857 -.154 .875 .12 " 3 7 - B. Comparison between Experimental and Calculated ZnO Isoactivity Lines in the ZnO-CaO-Si02 System The act i v i t i e s from Table 2 are plotted in Figure 19 together with the zinc oxide isoactivity lines at l600°C from section III. The two points along the s i l i c a saturation line at 1300°C check the upper shape of the line Q_ZNQ = 0.1. The slag in equilibrium with solid ZnO and Zn 2Si0 4 at 1300°C gives an activity very close to the calculated activity at that point. Insufficient work was done to validate this theoretical treatment but the slags studied produced several ac t i v i t i e s remarkably close to those calculated 16 from binary data by Toop's method . It should be remarked that these ZnO acti v i t i e s were actually measured with reference to solid zinc oxide at 1300°C. It is assumed that the regular solution theory temperature adjustment is valid and that the entropy of fusion of ZnO is 6 E.U. in the calculations comparing these act i v i t i e s with the calculated isoactivity lines in Figure 12. C. Comparison with Davenport's Calculated CL Data for the Zn0-Ca0-Si02 Ternary It is d i f f i c u l t to make comparisons between this work and work done previous to Davenport. A l l these studies measured ZnO act i v i t i e s in slags containing a large percentage of FeO in contact with Fe. The presence of this FeO tends to complicate the effect of the increasing CaO to Si0 2 ratio on the activity of ZnO. The agreement between this work and Davenport's calculated data is rather poor (Figure 20). Several reasons may be given by way of explanation. The entropy of fusion for zinc oxide used in the present study was 6 E.U. Davenport estimated a value of 2.85 E.U.5 , The excess free energy of the Zn-Cu system was found to have the following temperature dependence A C = - 8 2 0 0 + 2 . 5 8 T  CaO Mol f> ZnO -~ ^ i Figure 20. Comparison Between the Isoactivity Lines for ZnO at l600°C Calculated by Davenport 5 and in the Present Study. . . . - 4 0 - at low zinc composition. Davenport assumed complete regularity with an interaction energy of 755^ cals mol 1 } 5 . Different methods of combining tne auxiliary data were used in tne two investigations. The present study used Toop's ternary integration technique based on the regular solution theory; Davenport used Schumann's ternary integration 2^ and tangent intercept techniques'^ Both are based..on the Gibbs Duhem relationship and hence should be compatible. It is quite obvious that tne two studies measured activities in slags of widely different composition and i t may well be tnat a slightly different theoretical treatment might bring both closer into agreement. 6 D. Comparison with Work by Azuma, Goto and Ogawa In keeping with their results i t i s seen that an increase in lime content to move the slag composition away from the line of s i l i c a saturation increases the activity coefficient of zinc oxide in the slag, i E. Comparison Between Zn0-Ca0-Si02 and Fe0-Ca0-Si02 Ternaries 1.) ZnO-SiOg and Fe0-Si0 2 Binaries In figure 21 tne excess free energy of the Zn0-Si0 2 binary i s replotted ' ' • , 1 together with E l l i o t t s curve for the excess free energy of Fe0-Si0 2 . The seemingly large difference between the two curves is attributed to the fact that the Fe0-Si0 2 binary has slignt positive deviation from ideality whereas the Zn0-Si0 2 binary has slightly greater negative deviation. The difference between them, is never much greater tnan two kilocalories. When based on tne solid 8 standard states both curves are relatively close to ideal . - kl - 2500 2000 1500 1000 500 f- 03 o . f a -500 1000 -1500 -2000 -2500 \ Fe0-Si0 2 7 Zn0-S10 2 Difference _ J . 1 Figure 21. .6 .7 'Mo Comparison Between the Excess Free Energies of the Binaries Fe0-Si0 2 and ZnO-SiOg a t l600°C. - k2 - 2.) FeO-CaO-S102 Ternary The excess free energy contours and the isoactivity lines for FeO are shown In figures 22 and 23 respectively. Figure 22 shows a somewhat larger area with a positive excess free energy than does the corresponding figure for zinc oxide (Figure 7), but otherwise tne shape of the contours is quite similar over most of the diagram. The isoactivity lines for FeO have a characteristic projection extending further towards the lime orthosilicate composition than does tne characteristic projection for the zinc oxide isoactivity lines (Figure 8). This is in keeping with the sligntly more basic behaviour of ferrous oxide. SUGGESTIONS FOR FURTHER WORK The most important limitation was the effective restriction on slag melting point because of the technique used for slag preparation. If an induction furnace had been available, slags could have been prefused in a i r using a platinum crucible as a susceptor. The crucible could tnen have been immediately quenched in water on removal from the coils. At 1600 °C, for unit activity of zinc oxide: [Zn](P0 2)2 = 8.7 x 10"5 ( 9 ) ...(9) At this temperature the zinc-copper alloy boils at a zinc activity of approximately 0.01 (Appendix IV). From the thermodynamics of tne copper- oxygen equilibrium, this w i l l result in an activity of about 0.2 for cuprous oxide in the slag, wnich is no longer negligible. Further work might be done using a modification of the technique used by Richards and Thorne^ . Using a horizontal bed furnace, i t would  io 20 30 4o 50 60 70 80 90 Mol <fo .FeO >- Figure 23. Calculated Isoactivity Lines for FeO at l600°C. - 4 5 - be relatively simple to use a zinc source to establish a zinc partial pressure in the incoming low oxygen potential gas. Slag zinc loss would be completely avoided. Slags could be equilibrated with this gas in a platinum boat, circumventing the problem of containment for a slag- metal equilibrum melt. Zinc activity could then be determined by measuring the zinc partial pressure of the equilibrium gas. The oxygen potential could be measured using an oxygen h a l f - c e l l as in the present study. The slag could be sampled once equilibrium conditions were established. CONCLUSIONS Activities of ZnO.in ZnO-CaO-Si02 slags have been measured at 1300°C by a slag-metal-gas equilibrium technique. The experimental zinc oxide activities agree closely with the isoactivity lines calculated on tne basis of Toop s ternary integration technique and an estimated entropy of fusion for zinc oxide of 6 E.U. The calculated excess free energy contours for the ZnO-CaO-Si02 ternary are similar in shape to those calculated" in a similar manner 7 for the FeO-CaO-Si02 system using E l l i o t t ' s data on the component binaries . Also the calculated zinc oxide isoactivity figure is similar to the ferrous oxide isoactivity diagram. The zinc oxide isoactivity pattern shows a projection towards the lime orthosilicate composition. This shape is characteristic of FeO^but in the case of ZnO the projection i s not so pronounced. Both these observations are in keeping with the slightly more basic behaviour of zinc oxide. It is f e l t that the estimated entropy of fusion for zinc oxide is reasonable based on the close agreement between the calculated isoactivity lines and the measured activities and on the similarity between the two ternaries, ZnO-CaO-Si02 and FeO-CaO-Si02. In addition, the calculated free energy curve for the ZnO-Si02 binary agrees quite closely with the 8 free energy curve given by Richardson for this binary based on solid standard states for the two components. It was found that the solid oxygen electrolyte O.85 Zr0 2 - 0.15 CaO -6 behaves reversibly at 1300°C over an oxygen potential range of 2.3 x 10 -8 to 8.4 x 10 atmospheres. - 47 - REFERENCES 1. E. N. Bunting, J. Am. Ceram. Soc; 13, 1 8 (1930). 2. E. R. Segnit, J. Am. Ceram. Soc; 37, 6 274 (1954). 3- R. C B e l l , G. H. Turner and E. Peters, J. Metals; 6, 472 (1955). 4. A. W. Richards and D. J. Thorne, "Physical Chemistry of Process Metallurgy - Part 1", Interscience, New York, (1961) p. 277. 5. W. G. Davenport, "The Activity of Zinc Oxide in Multi-component Slags", M.A.Sc. Thesis, University of British Columbia, i960. 6. K. Azuma, S. Goto, 0. Ogawa, Nippon Kogyo Kaishi; 8l, l8 (1965). 7- J. F. E l l i o t t , J. Metals; 6, 485 (1955). 8. F. D. Richardson, "Physical Chemistry of Melts", Inst. Min. Met., London, (1953) P- 86. 9. C. E. Wicks and F. E. Block, U. S. Bureau of Mines Bulletin 605 (1963). 10. F. Hund, Z. physik. Chem.; 199, 142 (1952). 11. K. Kiukkola and C. Wagner, J. Electrochem. Soc; 104, 379 (1957). 12. S. P. Mittoff, J. Chem. Phys.; 36, I383 (1962). 13. B. C. H. Steele and C B. Alcock, Trans. A.I.M.E.; 233, 1359 (1965)• 14. R. Littlewood, Can. Met. Quarterly; 5, 8 (1966). 15. N. J. Olson and G. W. Toop, Trans. A.I.M.E.; 236, 590 (1966). 16. G. W. Toop, Trans. A.I.M.E.; £33, 850 (1965). 17. F. D. Richardson, "The Physical Chemistry of Melts", Inst. Min. Met., London, (1953) P- 93- 18. J. Chipman, Discussion Faraday Soc; 4, 23 (1948). 19. Hauffe and Wagner, Z. Elektrochem.; 46, 160 (1940). 20. J. A. Kitchener and S. Ignatowitz, Trans Faraday Soc; 4j_, 1278 (1951). 21. L. S. Darken and R. W. Gurry, "Physical Chemistry of Metals", McGraw-Hill, New York, (1953) P- 264. 22. W. A. Fischer and W. Ackermann, Archiv. f. d. Eisenhutt.; 9_, 643 (1965). - 48 - 23- E. R. Segnit and J. D. Wolfe, Chem. Eng. Mining Rev.; 45, 215 (1953)- 24. R. Schuhmann, Jr., Acta Met.; 3, 223 (1955)- 25- R• Schuhmann, Jr., Acta Met.; 3, 220 (1955). 26. J. F. E l l i o t t , M. Gle iser and V. Ramakrishna, "Thermochemistry for Steelmaking, Volume II", Addison-Wesley, Reading, Massachusetts, (1963) p. 578. 27- R- Hargreaves, Journal Institute of Metals; 6k, 115 (1939). .28. W. Leitgebel, Z. anorg. Chem.; 202, 305 (1931). 29. A. Schneider and H. Schmid, Z. Elektrochem.; 48, 627 (1942). 30. A. W. Herbenar, C. A. Siebert and 0. S. Duffendack, J. of Metals; 2, 323 (1950). 31. L. H. Everett, P. W. M. Jacobs and J. A. Kitchener, Acta Met; 5, 28l (1957). 32. 0. Kubaschewski and E. LL. Evans, "Metallurgical Thermochemistry", Pereamon, London, (1965) p. 177- 33- J- Lumsden, "Thermodynamics of Alloys", Institute of Metals, Clowes and Sons, London, (1952) p. 272. 34. 0. Kubaschewski and J. A. Catterall, "Thermochemical Data of Alloys", Pergamon, London, (1956) P- 69. 35- Kleppa and King, "Metallic Solid Solutions", W. A. Benjamin Inc., Mew York, (1965). 36. L. Guttman, Trans. A.I.M.E.; 175, 178 (1948). 37- K. K. Kelly, U. S. Bureau of Mines Bulletin 393'(1936). 38. A. Glassner, A.N.L. - 5750, (1959)- 39- M. J. N. Pourbaix and C. M. Rorive-Boute, Discussion Faraday Soc; 4, 140 (1948). - 4 9 - APPENDIX I Calculation of Infinitely Dilute Properties of Zinc in the Copper-Zinc System A. Hargeaves Datsfr? , NZn ^Zn G(Zn .052 .0045 - 5 3 0 0 . 0 9 4 .0086 -5720 .144 .OI85 -5520 • 195 .OJOl - 5 6 8 O . .255 . O 5 4 5 - 5 4 3 0 • 373 .134 -5150 .453 . 2 0 0 -5410 .481 . 2 4 6 - 4 9 2 0 .504 .291 -4410 B, LeitgebeJ 2 8 T°K AF Zn <*Zn 1*188 -200 0.883 +7930 1198 -440 0.828 + 338: 1246 - 1 5 7 0 O.7O7 - 8 2 8 0 1 2 8 3 -2440 O.577 - 5 8 1 0 - 1337 - 3 7 1 0 0.441 - 4 9 0 0 1373 -4540 O . 3 8 I -5000 1438 - 6 O 5 O 0 . 2 7 3 -4440 1518 - 7 9 2 0 0.191 -4480 1773 - 1 3 7 9 0 0.063 -4630 C . Schneider and Schmid 29 T°K NZn a zn « Z n 9 7 3 O . 7 9 8 0 . 8 0 0 9 7 3 0.714 0.57 - 5 3 7 0 , 9 7 3 0.664 0.48 - 5 5 7 0 9 7 3 0 . 5 8 0 0.35 - 5 5 7 0 9 7 3 0.428 0.14 - 6 6 0 0 1 1 2 3 O . 7 9 8 0.795 -2440 7 1 2 3 0 . 7 1 4 0 . 6 1 2 -4150 1 1 2 3 0.664 0 . 5 3 1 - 4 3 4 0 1 1 2 3 O . 5 8 0 0 . 3 9 8 - 4 7 8 0 1 1 2 3 0.428 0.184 - 5 7 5 0 - 50 - D. Herbenar et. a l 30 Temp. 1073°K ll48°K 1198°K N 0 u O^Zn ^ Z n .9^65 -5920 -5100 -it-780 .8895 -56OO -5230 -5030 .8382 -5570 '' -514 0 ' -^750 . 8001 -5700 -5230 -4840 • -7^97 -585O -5270 .7105 -5530 -1+880 E. EveYett, Jacobs and Kitchener31 The data of'Everett, Jacobs and .Kitchener-^1 i s presented in.figure 24. On this figure are drawn the regular solution line used by Davenport and a.sloping line which f i t s the data somewhat better. F. Kubaschewski and Evans^ Their book gives a curve for the integral heats of formation of Cu-Zn alloys based on several techniques. Taking the slope of this line at Zn=0 gives A H . From this must be subtracted the heat of fusion of zinc, I76O cals/gm atom. This gives: , -1 ^ \-\ = -916O cals atom G. Excess Free Energy Expression Results from a l l available sources i s given in figure 24. The equation of the line drawn for the excess free energy i s : " A F z n = -8200 +2.58 T. -8500 -8000 -7500 -7000 -6500 -6000 -5500 -5000 -4500 -4000 " A A ~ A A A A A Improved F i t Line Original F i t Line N, Zn .6 Figure 2k. Data of Everett, Jacobs and Kitchener 31 A A A - 52 - Figure 2\ 1000 1200 Temperature °K thermodynamic Data on the Infinitely Dilute Free Energy of Zinc i n Copper. - 53 - APPENDIX II The System ZnO-SiOp A. Previous Work 1. ) K.K. Kelly 37 From Bunting's data 1, Kelly plotted RlnN^nO a s a function of reciprocal temperature and derived a value for AH-p from the slope of this line of 4480 cals mol - 1 3̂7) _ F r o m figure 26 i t is seen that Bunting's measured compositions do not l i e exactly on a line joining the eutectic at "76.5 mol $ ZnO with pure ZnO. In fugure 27 values from the linear plot and Bunting's actual values are plotted. Kelly's value l i e s i n between. The error probably l i e s in the fact that the range of temperature covered is only 22 percent of the temperature difference between the melting point of, pure ZnO and the eutectic. Kelly's value gives an entropy of fusion for ZnO of 1-99 E.U. 37 \ 4 2. ) Richards and Thorne Richards and Thorne used an entropy of fusion of 5 E.U.'̂  There was no reference' given as to the source of this value. 3-) G-lassner 3 8 Glassner gives a difference i n enthalpy between solid and liquid zinc oxide at 2248°K of 8600 cals'38. This value is presumably calculated from heat capacity considerations. This enthalpy gives an entropy of fusion for ZnO of 3-8 E.U. k.) Davenport 5 Based on a somewhat arbitrary closure of his Otplot for SiOg in the Zn0-Si02 binary 5 } Davenport derived a value for the entropy of fusion for ZnO of 2.85 E.U.5 He used much the same technique as was used in the present study.  - 55 - Figure 27- Estimate of Enthalpy of Fusion for ZnO from the Liquidus Line. - 5 6 - B. Estimation of A s f ZnO E l l i o t t 2 ^ has plotted activities calculated from Richardson's free energy- curve 8 for the ZnO-SiC>2 binary. These act i v i t i e s from Nznn = O . 765 (the eutectic between Z^SiOlj. and ZnO) to saturation at l 6 0 0°C may be used together with Bunting's phase diagram^ to satisfy the formula used in Chipman's melting point depression expression to derive am average value for the entropy of fusion for ZnO. This i s shown in table 3- The f i r s t composition (N^nO = O . 8 0 7 ) is not very useful as the liquidus i s not well established at this point. The average of the other two points i s taken as 6 E.U. Table III Calculation of ASf ZnO Chipman1s Liquidus Curve Expression : 1 8 A s f = • -RTlnaZnO T-TmznO NZnO AT 4l6oo°C* ° 1 6 0 0 O C a T lnOlT A F A S f .807 18 .96 1.188 I.I89 •96 -.0407 -151 8-3 .783 55 •91 1.16 I.I65 .912 -.O918 -331 6 .02 •772 75 .85 1 . 1 0 l.lkk .883 -.124 -442 5-9 C. Calculation of Activity for S i l i c a to Ns-jnp = 0-235 S i l i c a activity may be calculated from the phase diagram using the techniques developed by Chipman1 8 and Hauffe and Wagner-*-9(Table 4). *From E l l i o t t ' - 57 " Table IV A c t i v i t y of S i0 2 from N S i 0 2 = 1.0 to Nsio 2 = 0.235 1. Congruent melting Compound Method 1^ Symbols: Hf = Heat of f u s i o n of Z^ S i O ^ = 18.7 kcals mol" 1 0 = Melting Point of Z ^ S i O ^ = 1784°K x Z n 0 = 0.666 M q 1 f r a c t i o n s i n Z n S i Q xSiO? = 0 - 3 3 3 T = Liquidus temperature NZnO> NSi02 = C o m P ° s i t i o n II I RTlnCLsi0 2 = R T l n a S i 0 2 AHj e NZnO(Q-T) + x Z n 0 [ (Q-T) Nsi02"XSi02 I I^0(F dNsiOc Si02 1 1 r l Nsi02 T°K •(Q-T) (N-X) (9-T)/(N-X) 2 XznOjC J d N s i 0 2 [Parti] A H , e L J • 50 1705 80 .166 2900 A 293 241 5600 •45 1751 34 .116 2520 204 161 3830 .4o 1775 10 .066 2290 124 90 2240 •38 1780 5 .046 2360 93 67 1680 •36 1783 2 .026 2940 58 49 1120 •32 1784.5 • 5 -.013 2960 -29 -26 -580 •30 1783.5 1-5 -.033 l46o -59 -32 -950 .28 1782.5 2-5 -.053 890 -74 -3^ -1120 .26 1781.5 3-5 -.073 650 -85 -36 -1270 •235 1780 5 -.098 520 -95 -39 -1400 The graphical i n t e g r a t i o n of (Q-T)/(Ef-X) 2 against N, fig u r e 28. Si0 2 i s ^ v e n i n - 58 " -i Q 2. Liquidus Curve Method InCL = T-TraASf T R A s f = Entropy of Fusion of Si0 2 = 1.8 E.U. 1 7 NSi02 T°K T-Tm/T In a a CVsi02 •975 1968 . -.00913 -.OO83 .992 1.018 111000 • 95 " " " 1.044 67200 .90 " " 1.102 37800 .85 " " " 1.166 26600 .80 " " " 1.241 21100 •75 " " 1.321 17400 • 70 " " " " 1.418 15100 .657 " " " 1.51 13600 •65 1951 -•0179 -.0163 .984 1.51 12900 .60 1853 -.0718 -.0652 .937 I.56 10200 • 55 1773 -.1200 -.1093 .896 I.63 8480 • 50 1705 -.165 -.150 .86 1.72 7330 .45 1751 -•705 .493 1.095 1040 .40 1775 -1.172 .309 •773 -2510 • 36 1783 -1.492 .223 .62 -4080 • 30 1783.5 -2.065 .126 .420 -6230 .26 1781.5 -2.17 •113 .435 -5330 .235 1780 -2.207 .109 .464 -4590 D. Calculation of Activity for ZnO to N r ^ y = O.50 The same techniques may be used to calculate activities for ZnO from the phase diagram u t i l i z i n g the estimated entropy of fusion of 6 E.U. - 59 - - 6o - Table V A c t i v i t y o f ZnO f r o m N^nO = 1.0 t o N Z n 0 =0.5 1 . C o n g r u e n t M e l t i n g Compound. M e t h o d 1 9 K Z n 0 T ° K (Q-T) ( N - X ) (Q - T ) / ( N - X ) 2 NT x S i 0 2 ^ C J d N Z n 0 [ P a r t I] AH f Q r n • 765 •74 •72 • 70 .68 .64 .62 .60 •55 • 50 1780 1781.5 1782.5 1783.5 1784.5 1783.5 1780 1775 1751 1705 5 3-5 2 - 5 1 - 5 •5 2 5 10 3k 80 .098 •073 •053 •033 .013 -.026 -.046 -.066 -.116 -.166 520 654 890 1460 2960 2940 2360 2290 2520 2900 47 42 37 30 15 -29 -kl -62 -102 - 1 4 7 12 12 14 14 12 -28 -41 -60 •132 •24l 618 566 524 46l 283 -597 -922 -1280 -2450 -4070 2 .. L i q u i d u s Curve Method NznO T ° K T -Tm/T i n a a CX ZnO • 95 .90 • 85 .80 • 765 .Ik .70 ,6k .60 • 55 • 50 2148 2048 1948 1848 I78O 1781.5 1783.5 1783.5 1Y75 1751 1705 -.0465 -.0977 -.1540 -.2170 - . 2 6 3 0 - . . . 1 4 1 - .296 - .467 - .657 - .797 - .812 - .842 - 1 . 1 4 1 -1.336 -I.678 -2.176 .868 .743 .626 .517 .45 .458 • 43 • • 351 . 2 6 1 .I85 .112 .913 .825 • Y37 .647 .588 .62 .615 • 55 • 435 • 337 .224 -IbOOOO -78OOO -52200 -39700 -33600 -24700 -19000 -16100 -18200 -18500 -17400 E\ Gibbs Duhem Integration The Duhem-Margules Equation^! may be written as: or ZnO rtdN&io2 - ^sPiXsio2 % i 0 2 Table VI SiOo-ZnO Binary Integration % i 0 2 ^Si02 Part I Part II °^Zn0 °<Zn0* NznO .02 -24400 -1400000 -1195000 -205000 -205000' .98 •05 -15800 -460000 -300000 -160000 -160000 •95 ' .10 -11000 -178000 -99000 -78400 -78000 .90 •15 -8000 -99200 -45200 -54000 -52000 • 85 .20 -6000 -64500 -24,000 -40500 -40000 .80 •25 -6000 -46ooo -18000 -28OOO . -28000 • 75 •30 "-6000 -35400 -14000 -21400 ••: -20000 •70 •35 -5000 -27800 - 9250 -I855O -17000 •65 - .40 -3000 -22700 - 4500 -18200 -18000 .60 •45 1000 -18200 1100 -19300 -18000 •55 • 50 • .4000 -14000 4000 -18300 -18000 •50 .60 10000 -7850 6670 -14500 .40 • 70 14000 -3310 6000 -9300 •30 .80 21000 195 5250 -5050 .20 • 90 38000 3550 4230 -680 .10 •95 67OOO 6100 3530 2570 •05 *From Table V. The resulting C^plots are given i n figure .29- - 62 - - 63 - F. . Excess Free Energy Curve Table VII Excess Free Energy of Zn0-Si02 at l600°C NZnO A F X S •05 227 .10 280 •15 155 .20 -37 • 25 -265 •30 -555 •35 -892 AO -1260 •45 -1593 • 50 -1750 •55 -1927 .60 -2064 •65 -2064 •70 -2048 •75 -2257 .80 -2166 •85 -1781 •90 -1584 •95 -408 Based on the metastable l i q u i d standard states and calculated from the (X curves by the method shown i n Appendix I I I . G. Comparison with Richardson's Free Energy Curve 0 Richardson's free energy curve f o r the binary Zn0-Si02 with respect to the s o l i d standard states of the two components 8 i s shown i n fi g u r e 30- In the same figu r e the standard states are changed to the two pure l i q u i d s and the r e s u l t i n g curve compared to that calculated i n the previous section. The agreement i s quite good.  - 65 - APPENDIX III Toop's Ternary Integration Technique The l o c a t i o n and d e f i n i t i o n of terms used i n t h i s d e r i v a t i o n are shown i n f i g u r e 3 1 . Toop gives the following expression f o r the excess free energy within the t e r n a r y : 1 ^ The excess free energy i n a binary system i s given by: AFX S = RT(Nj_ln #2.(2) + N 2 l n ^ 2 ( l ) ) = ^ ( 1 - ^ ) ^ X 1 ( 2 ) + N 2 ( l - N 2 ) 2 t f 2 ( l ) = % N 2 ( N 2 C X i ( 2 ) + N i t f 2 ( i ) ) Thus by using the values of a l l three ordinates of any one point, the excess free energy at that point may be calculated by using the binary CX p l o t s . The l o g of Jthe " a c t i v i t y c o e f f i c i e n t of a component within a ternary i s given by the following expression L o g ^ 2 ( t e r n ) = L o g * 2 ( l ) + ^ L o g » 2 ( 3 ) ] " [ A F 1 - J ^ 3 L°S* 2(tern) 'M [ * i U - N 2 ) « 2 ( l ) + N 3(l-N 2 ) C X 2 ( 3 ) ] ^ RT \^ + ( 1-N 2) 2 ^ 3 ( ^ 0 ( 3 ( 1 ) + NgOf!^) )] Ni/N^) • a / x - w „ « L o s ^ 2 ( t e r n ) u , 2 ( t e r n ) = N 2 e v ' The CX plots of the binary systems CaO-SiOg and FeO-Si0 2 are included (Figures 32 and 33 r e s p e c t i v e l y ) . - 6 5 - APPENDIX I I I loop's Ternary Integration Technique The l o c a t i o n and d e f i n i t i o n of terms used i n t h i s d e r i v a t i o n are shown i n f i g u r e 31* Toop gives the following expression f o r the excess free energy within the ternary: 1-' a » 5 » - u V C^-J * t 1 - " ! ) 2 N 2 / N 3 + < * - % > 2 [^h] w The excess free energy i n a binary system i s given by: A F X S - R T ( N 1 l n ? 1 ( 2 ) + N 2 l n ^ 2 ( l ) ) = N i ( l - N 1 ) ^ X i ( 2 ) + N 2 ( l - N 2 ) 2 t f 2 ( l ) = N ^ N a Q f i ^ ) + N i C V 2 ( l ) ) Thus by using the values of a l l three ordinates of any one point, the excess free energy at that point may be calculated by using the binary Of p l o t s . The l o g of.,:the " a c t i v i t y c o e f f i c i e n t of a component within a ternary i s given by the following expression: 1^ Lo« ^ 2 ( tern) = L o 6 * 2(1) + Log8 2 ( 3 ) 1 - ( l - N 2 ) 2 [ A F j f J v L l - N 2 I-N2 J N g L ^ r ' i J N i / N 3 L ° S ^ 2 ( t e r n ) 1-N 2)C< 2( 1) + N 3(l-N 2 )a 2 ( 3 )] ^ + ( 1-N 2) 2 ^ 3 ( ^ 0 ( 3 ( 1 ) + N 30fK3) )] N l/N^> • CL/*. \ - M o e L o s ^ 2 ( t e ^ ) ^ 2 ( t e r n ) - N 2 e v ' The CX plots of the binary systems CaO-Si0 2 and Fe0-Si0 2 are included (Figures 32 and 33 r e s p e c t i v e l y ) . - 66 - Figure 31. Definition and Location of Terms Used in Appendix I I I . ^ - 67 - Figure 32.. CX Plots f o r the FeO-Si0 2 Binary. - 68 - 69 APPENDIX IV Oxygen P o t e n t i a l Limits A. 1300oC 1.) Lover L i m i t Z n ( l ) — Z n ( g ) 0 = -6275 + 5-33 - Log P Z n 3 9 T flzn(g) a Z n ( l ) = 22 0 1 Zn(l)i0-0^55 G ^ z J (p02)^ = 7.3= x 1 0 •7 (9) -10 P Q 2 £2,6 x 10 2.) Upper Limit 2Cu + -gQ2 Cu 20 A F Q ^ ^ ^OK = -14200 c a l s . For u n i t a c t i v i t y of Cu20 at 1300°C PP 02 = 1.1 x 10"̂ B. l600°C ^Zn (g) TK = 78 Qzn(l) P0 2 2- U.5 x 10-5 C9) kCu + 02—*-2Cu20 Ki873°K = 1 ,3 8 x 1 0 - 3 Cu 20> 0.18 70 APPENDIX V Free Energy of Formation of Zn 2 S i 0 k The slag used i n runs I and J was saturated i n both ZnO and Zn 2SiO^. This i n d i c a t e s that t h i s slag may be used to determine the free energy of formation of Zn 2Si0ij. at 1300 C. The calculated value f o r the s i l i c a a c t i v i t y at t h i s point i s approximately Q-giQ^ = 0.2. The standard state may be changed from l i q u i d to s o l i d by the following expression based on an entropy of fusibar, f o r S i 0 2 of 1.8 E.U.: .gzao(i) = 1560 - 0.91 dZnO(s) T hence a s i 0 2 ( s ) 1600 C = .22 a n d Q S i 0 2 ( s ) 1300 C = .2:0 using the regular s o l u t i o n theory temperature adjustment. For the free energy of formation of Zn^SiO^ = 0.2 K = [ZnO] 2 f SiO g] [zn 2SiO^] A F 1300 C = (1.98)(1573) In (-20) = -5000 c a l s . 20 Kitchener and Ignatowicz give the f o l l o w i n g expression f o r the free energy of formation of ZngSiO^. A F = -7129 + 0.23 T AF1300 C = -6800 c a l s . In view of the rather large estimate-, of e r r o r i n A H ° and A S ° quoted i n Kitchener and Ignatowicz's paper, the agreement i s quite good.

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