Activities of oxygen in liquid Bi-Pb and Bi-Sb alloys
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I.
INTRODUCTION
T H E R E has been growing theoretical and technological interest in clarifying the thermodynamic behavior o f oxygen dissolved in liquid alloys. Several theories and models have been proposed to describe the compositional variation o fthe activity coefficient o f oxygen, Yo, in liquid binary alloys. 1-9 Alcock and Richardson~,2 used the quasi-chemical theory for randomly distributed atoms in solution as the basis of their calculations. In their initial paper, the coordination number for all three types o f atoms was assumed to be the same. The resulting equation for Yo does not have an unknown parameter. Later, using a similar approach, Jacob and Alcock3 formulated a more generalized quasi-chemical equation. This expression also does not contain an unknown parameter, provided one uses a single set o f values for the unknown factors, n and a . Wagner4 derived a different expression for 3'o using a statistical approach for solvent atoms which exhibit ideal solution behavior. This expression has two unknown factors, Z and h. Blander and co-workers,5 using a statistical mechanical approach, modified Wagner's expression to incorporate nonideal behavior o f the solvent atoms. The equation obtained has three unknown factors, Z, t , and h. However, the calculations of In 3% are fairly weakly dependent on Z and t in the range o f physically reasonable values o f these parameters. Thus, one can reduce the number o f unknown parameters to only one, h, in the models o f Wagner and o f Blander et a l . by using constant values of Z and t . An equation for Yo with no or one adjustable parameter is preferable f o r obtaining primary information for systems where the data are not available. Recently, the present authors have pointed outl°.H that all the published data on Yo over the entire composition range of the solvent, used to support these solution models, have been limited to systems satisfying the conditions o f (Vb/Va) 2 < 7 1 or ~. 1, and AG°(A) > AG°(B), where Va, Vb, AG°(A)and AG°(B) denote the metallic valences and the standard Gibbs energies of solution o f oxygen for solvent A and B, respectively. The data on Yo for In-Sb-O system,I° satisfying the conditions o f (Vb/Va)2 >> 1 and A G ° ( A ) > AG°(B), cannot be described, even qualitatively, by the SHINYA OTSUKA, Instructor, and ZENSAKU KOZUKA, Professor, are with the Department of Metallurgical Engineering, Faculty of Engineering, Osaka University, Osaka, 5 6 5 , Japan. YOSHIKAZU KUROSE, formerly a Graduate Student, Osaka University, Osaka, 565, Japan, is now with Kawasaki Steel Corporation, Kurashiki, 715, Japan. Manuscript submittedFebruary 2 2 , 1983. METALLURGICAL
TRANSACTIONS B
quasi-chemical equation o fJacob and Alcock.3The metallic valences, or the ratio o f valences is likely to be one of the factors governing the compositional dependence o f Yo. In order to test this hypothesis, the present experiments were performed at 1073 K for the Bi-Pb-O system satisfying the same conditions as for the In-Sb-O system. Recently, Taskinen~2 calcula
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