r e g i o n s were a n a l y z e d u s i n g a l i n e a r r e g r e s s i o n method and the r e s u R i n g plots a r e shown in F i g . 3. F r o m this it can be s e e n that over the r a n g e of h y d r o gen contents e x a m i n e d , the chill r e g i o n of the ingot is c o n s i s t e n t l y less p o r o u s than the nonchilled, upper r e g i o n s of the ingot. T h i s is in good a g r e e m e n t with the work of J o r d a n , D e n y e r and T u r n e r 4 who e x a m i n e d the effect of s e c t i o n s i z e in s e m i c o n t i n u o u s l y cast A t - C u - M g alloys, and found that the s m a l l e r the c r o s s s e c t i o n of the ingot, the l o w e r the p o r o s i t y , F i n a l l y it m u s t be e m p h a s i z e d that the r e s u l t s p r e s e n t e d h e r e apply only to p o r e s f o r m e d d u r i n g the s o l i d ification p r o c e s s itself. U n d e r c e r t a i n c o n d i t i o n s s e c o n d a r y hydrogen p o r o s i t y s u c h as that d i s c u s s e d by T a l b o t and G r a n g e r 7 can f o r m in the solid s t a t e by p r e c i p i t a t i o n of h y d r o g e n f r o m s u p e r s a t u r a t e d s o l i d s o l u tLon at hydrogen l e v e l s below the t h r e s h o l d v a l u e s for s o l i d i f i c a t i o n induced p o r o s i t y . On the b a s i s of the p r e s e n t work t h e r e a r e s e v e r a l c o n c l u s i o n s that can be drawn: i) T h e r e is a l i n e a r r e l a t i o n s h i p between the hydrogen content and l e v e l of p o r o s i t y for the A1-8 pct Si alloy e x a m i n e d s i m i l a r to

Thermodynamic Measurements in Liquid Copper-Tin Alloys A. K. SENGUPTA, K. P. JAGANNATHAN, AND A. GHOSH T h e r e v e r s i b l e galvanic cell, Sn(/), S n O 2 ( S ) / C a l c i a - s t a b i l i z e d / C u - S n ( l ) , Zirconia

SnO2(S)

[I]

was employed to d e t e r m i n e activity and p a r t i a l f r e e e n e r g y of mixing of tin in m o l t e n c o p p e r - t i n alloys at 800~ (1073 K) in the c o m p o s i t i o n r a n g e , 0.2 -< XSn <- 0.9 where XSn d e n o t e s atom f r a c t i o n of t i n in the alloy. The emf (E) of such a cell is r e l a t e d to the p a r t i a l f r e e e n e r g y of m i x i n g (GsMn)and a c t i v i t y of tin (aSh) as follows I

that o b s e r v e d for o t h e r a l u m i n u m a l l o y s , ii) A p r a c t i cal t h r e s h o l d hydrogen v a l u e of a p p r o x i m a t e l y 0.08 m l H2 (STP)/100 g A1 can be defined below which p o r o s i t y should not o c c u r d u r i n g s o l i d i f i c a t i o n , iii) The exact level of p o r o s i t y is dependent on the local cooling conditions, the lowest p o r o s i t y b e i n g found in the r e g i o n s of highest cooling r a t e . T h i s work was supported by the National R e s e a r c h Council of Canada and the G o v e r n m e n t of Quebec (FCAC). The hydrogen a n a l y s e s and the A1-8 pct Si alloy w e r e kindly supplied by the A l u m i n u m Company of Canada Ltd. The a u t h o r s a r e indebted to M r . Z e n o n Lewycky who p e r f o r m e d the d e n s i t y m e a s u r e m e n t s . 1. C. E. Ransley and H. Neufeld: J. Inst. Metals, 1948, vol. 74, pp. 599-620. 2. C. E. Ransley and D. E. J. Talbot: Z. Metallk., 1955, vol. 46, pp. 328-37, 3. G. J. Metcalfe: J. Inst. Metals, I945, vol. 71, pp. 618-19. 4. M. F. Jordan, G. D. I)enyer, and A. N. Turne[: J. Inst. Metals, 1962-63, vol. 91, pp. 48-53. 5. C. E. Ransley and D. E. J. Talbot: J. Inst. Metals, 1955-56, vol. 84, pp. 445-52. 6. R. A. Entwistle: The Formation of Microporosity in Castings; M.Eng. Thesis, McGill University, Montreal, 1976. 7. D. E. J. Talbot and D. A. Granger: J. Inst. Metals, 1963-64, vol. 92, pp. 290-97.

hibits n e g l i g i b l e n o n s t o i c h i o m e t r y . 4) The solubility of oxygen in m o l t e n tin and Cu-Sn alloys is expected to be l e s s than 0.1 at. pct. 2'3 The a p p a r a t u s and e x p e r i m e n t a l p r o c e d u r e were the s a m e as r e p o r t e d by Das and Ghosh. z T i n and copper of 99.99 pct p u r i t y were obtained f r o m S e m i - E l e m e n t s Inc., U.S.A., and F i s h e r Scientific Co., U.S.A. r e s p e c tively. SnOz of 99.9 pct p u r i t y was obtained f r o m E. M e r c k , G e r m a n y , The emf v a l u e s were c o n s i d e r e d steady if the v a r i a t i o n was within 0.1 mV over a period of 10 to 15 h. P o l a r i z a t i o n t e s t s showed excellent r e v e r s i b i l i t y . R e p r o d u c i b i l i t y of the values was checked by t e m p e r a t u r e cycling and r e p e a t i n g some of the exp e r i m e n t s . T e m p e r a t u r e was m a i n t a i n e d c o n s t a n t at 1073 :e 2 K u s i n g a L~eds and N o r t h r u p E l e c t r o m a x S i g n a l l i n g C o n t r o l l e r , A t t e m p t s to d e t e r m i n e the activity v a l u e s for t e m p e r a t u r e s higher than 1125 K Xcu

(~sMn = R T In asn = - 4 F E

where E is in volts. R = 1.987 c a l f K mole, T is in K and F = 23,0B0 caL/volt g . e q u i v . In o r d e r to obtain r e l i a b l e m e a s u r e m e n t s by this technique, a set of c r i t e r i a m u s t be s a t i s f i e d . Roychowdhury and Ghosh ~ who i n v e s t i g a t e d liquid S n - A g a l l o y s by this method have p r e s e n t e d d e t a i l e d d i s c u s s i o n s on this a s p e c t . The Cu-Sn s y s t e m s a t i s f i e s these c r i t e r i a b e c a u s e , 1) Cu20 is c o n s i d e r a b l y l e s s stable c o m p a r e d to Sn02. 2) SnO~ is the only oxide that c o e x i s t s w i t h Sn in the condensed state. 3) SnO2 exA. K. SENGUPTAis Scientist, Radiometallurgy Section, Bhabha Atomic Research Centre, Bombay-400085, India, K. P. JAGANNATHAN is Research Engineer, Research and Development, Hindustan Steels, Ltd., Ranchi-2, India, and A. GHOSH is Professor, Department of Metallurgical Engineering,Indian Institute of Technology, Kanpur208016, India. Manuscript submitted April 11, 1977. METALLURGICALTRANSACTIONS B

0.8

1-0

[1]

t

0-4

0-6 i

i

0.2 i

0

0,8

0.6

~

0.2

_.~*"

j

[

[

J

0.2

0.4

0-6

0.8

1.0

Xsn~

Fig. 1--Activity vs composition curves in molten Cu-Sn system at 1073 K. o-o-othis study; . . . . selected values; ~ 9 values r e ported by Vreaet anct ~cnatLner.S

ISSN 0360-214117810310-0141500.7510 9 1978AMERICANSOCIETY FOR METALSAND THE METALLURGICALSOCIETYOF AIME

VOLUME 9B, MARCH 1978-141

were not s u c c e s s f u l . T h i s is s i m i l a r to the findings in Sn-Ag s y s t e m . 1 Since the t e m p e r a t u r e r a n g e a v a i l a b l e for r e l i a b l e emf m e a s u r e m e n t s was r a t h e r s m a l l (~100~ it was felt that d e t e r m i n a t i o n of r e l i a b l e heat and e n t r o p y v a l u e s was not p o s s i b l e . T h e r e f o r e the study was r e s t r i c t e d to one t e m p e r a t u r e only, viz 1073 K. As noted e a r l i e r the composition r a n g e of this study was 0.2 <- XSn -< 0.9 and, in this r a n g e , the alloy comp o s i t i o n s w e r e above the liquidus. F i g u r e 1 shows the v a r i a t i o n of a c t i v i t y with c o m p o s i t i o n . Dotted lines denote the e x t r a p o l a t e d b e h a v i o r of the s u p e r c o o l e d molten alloys for c o m p o s i t i o n s below the liquidus. The p a r t i a l f r e e e n e r g y of m i x i n g (GMu) and a c t i v i t y (acu) of copper w e r e c a l c u l a t e d as follows e m p l o y i n g the G i b b s - D u h e m equations with pure liquid copper as the standard state. log aca = l o g X c u _ X c u X s n a s n

+ fXSn

ot sndXsn

O

[2]

OcMu = 2.303 R T log a c u where log 7Sn ash t~Sn = ( 1 - XSn) 2 and 7Sn = XSn 9 Evaluation of the i n t e g r a l in Eq. [2] r e q u i r e s the value of aSn up to XSn = 0. Since copper is solid at this t e m p e r a t u r e and the fact that in the c o m p o s i t i o n r a n g e , 0 -< XSn -< 0.15, no e x p e r i m e n t a l data a r e a v a i l a b l e , ex-

-1,6

\

-1,4 _ \ \ -1.2

-1.0

\

t r a p o l a t i o n of. ~Sn was done for hypothetical and s u p e r cooled m o l t e n a l l o y s . F i g u r e 2 shows t~Sn v s XSn curve and r e v e a l s the difficulty of e x t r a p o l a t i o n in the r a n g e 0 < XSn < 0.2 due to the s t e e p slope in the c u r v e . T h e r e f o r e , in o r d e r to choose the most r e l i a b l e e x t r a p o l a t e d c u r v e , the following p r o c e d u r e was adopted. The a c t i v i t y of copper was e s t i m a t e d f r o m the phase d i a g r a m of the c o p p e r - t i n s y s t e m at one c o m p o s i t i o n (Xsn = 0.05). T h e v a l u e s of a c u w e r e a l s o evaluated at this c o m p o s i tion by the G i b b s - D u h e m i n t e g r a t i o n of ash v s Xsn c u r v e s e x t r a p o l a t e d in a n u m b e r of ways in the r a n g e 0 < XSn < 0.2. The e x t r a p o l a t i o n that yielded the value of a c u in a g r e e m e n t with that e s t i m a t e d f r o m the phase d i a g r a m was accepted and is shown in F i g . 2. At v a l u e s of XSn > 0.7, the smooth e x t r a p o l a t e d curve f r o m the r e g i o n XSn < 0.7 was a c c e p t e d for c a l c u l a t i o n b a s e d on d i s c u s s i o n by D a r k e n . 5 T h e technique of e s t i m a t i o n of a Cu f r o m the phase d i a g r a m may be b r i e f l y explained a s follows. P h a s e d i a g r a m c a l c u l a t i o n n e c e s s i t a t e s the a s s u m p t i o n that both the solid as well as liquid solution at the c o p p e r r i c h end obey some s o l u t i o n model. Since at 1073 K, the s o l i d u s contains a p p r e c i a b l e c o n c e n t r a t i o n of tin, it could not be a s s u m e d that a c u would m e r g e with the R a o u l t ' s Law line. T h e r e f o r e c a l c u l a t i o n s w e r e done at a t e m p e r a t u r e higher than 1073 K where the s o l u b i l i t y of tin was lower. T h e m o l t e n alloy was a s s u m e d to behave r e g u l a r l y . T h e n u s i n g the s t a n d a r d p r o c e d u r e a c u in the m o l t e n alloy at the liquidus was c a l c u l a t e d and e x t r a p o l a t e d to 1073 K at constant c o m p o s i t i o n

(Xsn

= o.o5).

A g a i n at Xsn > 0.7 v a l u e s of ~Sn taken for G i b b s D u h e m i n t e g r a t i o n w e r e those e x t r a p o l a t e d following the b e h a v i o r of aSn vs XSn c u r v e at Xsn < 0.7. T h i s follows a s u g g e s t i o n made by D a r k e n . s All r e l e v a n t data a r e p r e s e n t e d in T a b l e I along with an u n c e r t a i n t y a n a l y s i s at XSn = 0.5. T h e e x p e r i m e n t a l v a l u e s of asn y i e l d a s m o o t h c u r v e when plotted as function of XSn (Fig. 1). F u r t h e r m o r e

I I I I

i -0.2 ]

-0-8 t-

"6

t

-0.q

-0.1

t~

o

-0.6

-0.8

-0.: O

-1.0

0.2

I 0.2

t

-1.2

I

0.6

1.0

Xsn Fig. 2--Alpha function for tin at 1073 K in molten copper-tin system; dotted portions are extrapolated. 142-VOLUME 9B, MARCH 1978

o

o12

0.6 o.8 1.0 ( 1 Xsn) 2 - - - - . Fig. 3--log ~Sn vs (1 - XSn)2 in molten Cu-Sn system at 1073 K. 9 value arrived at on the basis of extrapolated c~-function. -

METALLURGICALTRANSACTIONS B

Table I. Data on Molten Cu-Sn System at 1073 K

XSn

emf, mV

asn

acu*

(J/g mole)t

ash (Calculated from Selected Values6)

asn (Ref. 8)

0.1 0.2 0.3

66.90 35.65

0.007 0.055 0.214

0.858 0.600 0.386

-5,602 -8,755 -10,011

0.004 0.058 0.202

0.137

0.4 0.5

24.04 17.25

0.296 0.240

-9,467 -9,190

0.367 0.503

0.6 0.7 0.8 0.9

12.80 8.80 5.00 2.35

0.353 0.474 (-+0.007) 0.575 0.683 0.805 0.903

0.182 0.133 0.086 0.040

-8,491 -7,373 -5,669 -3,479

0.613 0.705 0.799 0.897

AG M

(at Xsn = 0.35) 0.501 0.839 0.949

*Reportedvaluesof acu are with respect to pure liquidcopper as the standard state. The valuesshould be multipliedby 1.34 if pure solidcopper is taken as the standard state. "{'AGMis integralmolalfreeenergy of mixingwith pure liquidsas standard state.

the c u r v e m e r g e s with the R a o u l t ' s Law line at XSn > 0.8. T h e s e e s t a b l i s h the g e n e r a l r e l i a b i l i t y of the data. T h e s y s t e m e x h i b i t s a s t r o n g n e g a t i v e d e v i a t i o n f r o m the R a o u l t ' s L a w line indicating s t r o n g i n t e r a c t i o n b e t w e e n c o p p e r and tin a t o m s . V a l u e s of asn of this study w e r e c o m p a r e d with t h o s e c a l c u l a t e d f r o m the s e l e c t e d v a l u e s of H Sn M and SMn.6 T h e s e a r e p r e s e n t e d in T a b l e I. It is s e e n that the d i s a g r e e m e n t is l e s s than 5 pct. F i g u r e 3 shows the plot of log 7Sn v s (1 - X S n ) 2. F r o m this f i g u r e it a p p e a r s that the solution b e h a v e s in a s i m p l e m a n n e r in the two e x t r e m e s but b e h a v e s in a c o m p l i c a t e d m a n n e r in the m i d d l e c o m p o s i t i o n r a n g e and this is in a c c o r d a n c e with D a r k e n ' s f o r m a l i s m . 7 In p a s s i n g yet a n o t h e r a s p e c t of this study is w o r t h m e n t io n i n g . T h e a c t i v i t y v a l u e s of this study when c o m p a r e d with t h o s e of P r e d e l and S c h a l l n e r 8 d e m o n s t r a t e that the l a t t e r v a l ue s e x c e p t f o r XSn = 0.5 did not match. T h i s can be

Solubility of Water in at 1600~ C

CaO-AI203Melts

KLAUS S C H W E R D T F E G E R AND HANS GEORG S C H U B E R T In the p r e s e n t study we have m e a s u r e d the w a t e r s o l u b i l i t y in CaO-A1203 s l a g s at 1600~ This work was c a r r i e d out in c o n j u n c t io n with o t h e r r e s e a r c h p r o j e c t s a i m e d at i m p r o v i n g o u r knowledge of the c h e m i s t r y of e l e c t r o s l a g r e m e l t i n g of s t e e l . It is w e l l known that h y d r o g e n p i c k up of the s t e e l is a s e v e r e p r o b l e m in the ESR p r o c e s s . Slags u s e d in e l e c t r o s l a g r e m e l t i n g u s u a l l y c o n s i s t of C a F 2 - C a O A1203 m i x t u r e s . No r e l i a b l e s o l u b i l i t y data a r e a v a i l able fo r such s l a g s which is due to the e x p e r i m e n t a l d i f f i c u l t i e s involved with m e a s u r e m e n t s of w a t e r s o l u b i l i t i e s in f l u o r i d e c o n t a i n i n g s l a g s . S o m e e s t i KLAUS SCHWERDTFEGERand HANS GEORG SCHUBERT are with the Max-Planck-Institut f~ir Eisenforschung, Max-Planck-Strasse 1 4000 Dt~sseldorf, Germany. Manuscript submitted August 31, ! 977. METALLURGICAL TRANSACTIONS B

a s c r i b e d to the u n c e r t a i n t i e s of t h e i r b i n a r y v a l u e s when e x t r a p o l a t e d f r o m t e r n a r y e x p e r i m e n t a l data. The a u t h o r s wish to g r a t e f u l l y acknowledge the fin a n c i a l s u p p o r t g i v en to one of the a u t h o r s (A.K.S.) by the D e p a r t m e n t of A t o m i c E n e r g y , India d u r i n g the c o u r s e of this i n v e s t i g a t i o n .

1. P. J. Roychowdhury and A. Ghosh: Met. Trans., 1971, vol. 2, p. 2171. 2. T. N. Belford and C. B. Alcock: Trans. FaradaySoe., 1965, vol. 61, p. 443. 3. R. J. Fruehan and F. D. Richardson: Trans. TMS-AIME, 1969, vol. 245, p. 1721. 4. S. K. Das and A. Ghosh: Met. Trans., 1972, vol. 3, p. 803. 5. L. S. Darken: J. Amer. Chem. Soc., 1950, vol. 72, p. 2909. 6. R. Hultgren and P. D. Desai: Selected Thermodynamic Valuesand Phase Diagrams for Copper and Some of Its Binary Alloys, p. 160, INCRA series on metallurgy of copper, Monograph I, ] 97 I. 7. L. S. Darken: Trans. TMS-AIME, 1967, vol. 239, p. 80. 8. B. Predel and U. Schallner: Z. Metallk., 1972, p. 122.

m a t e s of w a t e r s o l u b i l i t y in CaFz-CaO-A1203 s l a g s would be p o s s i b l e , h o w e v e r , if c o r r e s p o n d i n g data f or the CaF2 f r e e bounding s y s t e m CaO-A1203 w e r e known. S e v e r a l l a b o r a t o r y i n v e s t i g a t i o n s d e a l with the s o l u bility of w a t e r in s i l i c a t e m e l t s . l - l ~ Although t h e r e is s o m e d i s a g r e e m e n t b e t w e e n the v a r i o u s i n v e s t i g a t o r s on the a b s o l u t e q u a n t i t i e s of w a t e r d i s s o l v e d , the r e s u l t s of al l t h ese s t u d i e s a g r e e that the w a t e r content i n c r e a s e s p r o p o r t i o n a l l y to the s q u a r e r o o t of w a t e r v a p o r p r e s s u r e . Some s t r u c t u r a l m o d e l s have b e e n s u g g e s t e d . At high b a s i c i t y the w a t e r is a s s u m e d to be p r e s e n t in the s i l i c a t e s as f r e e h y d r o x y l ions OHw h e r e a s in acid s l a g s the w a t e r m a y be bound to s i l i con f o r m i n g - S i - O H g r o u p s . W h e r e a s in the p r e v i o u s i n v e s t i g a t i o n s the w a t e r contents of the s a m p l e s w e r e d e t e r m i n e d by c h e m i c a l a n a l y s i s of quenched s a m p l e s , we m e a s u r e d the s o l u b i l i t i e s applying the t h e r m o g r a v i m e t r t c method. T h i s has the a d v a n t a g e that the d i f f i c u l t i e s a s s o c i a t e d with the a n a l y s e s a r e avoided. A p l a t i n u m c r u c i b l e containing 6 g of CaO-A1203 s l a g was s u s p e n d e d on a s e n s i t i v e s c a l e ( C a h n / V e n t r o n R100) in the hot zone of a m o l y b d e n u m wound tube f u r n a c e . The f u r n a c e a t m o s p h e r e c o n s i s t e d of A r - H 2 0

ISSN 0360-2141/7810310-0143500.7510 9 1978 A M E R I C A N SOCIETY F O R M E T A L S A N D

V O L U M E 9B, M A R C H 1 9 7 8 - 1 4 3