On the metastability of an Au-Sn phase prepared by splat cooling
- PDF / 256,277 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 12 Downloads / 167 Views
(X~m /XAuSn ) = (V AuSn/V ~m ) [I ~m (htkllO/I AuSn (hakz/a)]
[1] where
X~m = atom f r a c t i o n of ~m in the s p l a t cooled alloy
[3]
The a t o m i c v o l u m e s V; and VAuSn a r e 17.98 and 22.35A s, r e s p e c t i v e l y . t , ~n In this m a n n e r , atom f r a c tions of the t h r e e p h a s e s w e r e d e t e r m i n e d f r o m one X - r a y i n t e n s i t y r a t i o , Eq. [1]. The heat effects on addition of s a m p l e s of s p l a t cooled a l l o y s at 78 K to a liquid t i n - r i c h bath at 623 K were m e a s u r e d . For c a l i b r a t i o n , s a m p l e s of p u r e tin were added f r o m 273 K. The e x p e r i m e n t a l p r o c e d u r e has b e e n d e s c r i b e d p r e v i o u s l y in d e t a i l . 3,s The heat effects due to additions of s e v e r a l s a m p l e s of a given s p l a t - c o o l e d s p e c i m e n of the a l l o y w e r e plotted a g a i n s t the gold c o n t e n t of the solvent bath and the heat effect at Infinite dilution was obtained by l i n e a r e x t r a p o l a t i o n ; such an e x t r a p o l a t i o n is j u s t i f i e d b e c a u s e the solute content of the s o l v e n t bath did not exceed 0.2 at. pct Au and the c o m p o s i t i o n dependence of the heat of s o l u t i o n of gold in t i n is known to be v e r y s m a l l . The c o r r e s p o n d ing heat effect at infinite d i l u t i o n of a m i x t u r e of t i n and gold was c a l c u l a t e d f r o m the d i f f e r e n c e in the heat cont e n t s at 623 and 78 I r and the heat of s o l u t i o n of gold i n tin at 623 K. 7 The d i f f e r e n c e b e t w e e n the heat effect of the s p l a t - c o o l e d alloy and the heat effect of the c o r r e sponding A u - S n m i x t u r e is the heat of f o r m a t i o n of the s p l a t - c o o l e d alloy AHsp at 78 K. The heat of f o r m a t i o n of the s p l a t - c o o l e d alloy is given by [4]
In o r d e r to c a l c u l a t e AH~ f r o m AHS# by Eq. [4], the v a l u e s of x obtained f r o m X - r a y a n a l y s i s and the following v a l u e s of AHAuSn and AH~ w e r e used. A value
phase and XAuSn, VAuSn, and IAuSn(hzkzla)are the c o r r e s p o n d ing q u a n t i t i e s for AuSn. Further,
Table I. Phase Composition and Calorimetric Data for Splat-Cooled 71.0 At. Pct Au-29.0 At. Pct Sn Alloy
[2]
A. K. JENA is Assistant Professor, Department of MetallurgicalEngineering, Indian Institute of Technology, Kanpur, India. B. C. GIESSEN is Associate Professor, Department of Chemistry, Northeastern University, Boston, Mass. M. B. BEVER is Professor of Metallurgy, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology, Cambridge, Mass. 02139. Manuscript submitted April 30, 1971. METALLURGICALTRANSACTIONS
XAuSn = 8.5//[29.5 - 0.5 (Xgrn/XAuSn)]
&I-Is# =xTAH v + X ~m AHem + XAuSn&/-/AuSn
VCm = a t o m i c v o l u m e of ~rn l~rn (htk~ll) = i n t e g r a t e d i n t e n s i t y of a peak due to the (hlk~l,) r e f l e c t i o n of the ~m
XCm + XT + XAuSn = 1
and f r o m a m a t e r i a l b a l
Data Loading...
