Activities of oxygen in liquid Cu-Sb and Cu-Ge alloys
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INTRODUCTION
DURING the past two decades, a considerable number of investigations have been devoted to determining the effect of dilute alloying elements on the activity coefficients of oxygen, Yta,in liquid metals. The data are indeed important from a technological point of view. However, for a better understanding of the thermodynamic behavior of oxygen dissolved in liquid alloys, it is highly desirable to measure 1'0 over the whole composition range of various binary alloys and evaluate the shape of the In 7~ vs alloy composition curves. With this in mind, several groups have performed research programs. Negative deviations of In 7o from the additivity equation: NalnTo(a) + NB In Yo(B), have been reported over the entire composition range of many binary alloys, 1-7 where NA and NB are the atom fraction of the alloying elements A and B, and Yfl(a)and Yo(8)are the activity coefficients of the infinitely dilute solution of oxygen in pure A and pure B, respectively. Positive deviations from additivity, limited to a narrow composition range of alloys, implying an inflection point in the curve, have been observed for several binary systems, e.g., Cu-Sn, s'9 In, 1~Ga, 11 Ge.12 Further, it has been reported 6'1~ that a quasichemical equation proposed by Jacob and Alcock6 is capable of describing curves having an inflection point. Recently, it was observed that positive deviations of lnyta from the additivity equation occurred over the whole composition range of Bi-T1 alloys. 13The measured values of 7~ in liquid Bi-T1 alloys, however, were found to differ significantly from those predicted by Jacob and Alcock's quasichemical equation. Thus, attention has been directed again to the systems including copper. Positive deviations from additivity, as observed for Bi-T1 alloys, have been predicted over the entire composition range for Cu-Sb alloys by quasichemical equation. Cu-Ge-O system is also a system of great interest because the published data have exhibited a pronounced point of inflection.12 It was therefore decided to measure y0 in liquid Cu-Sb and Cu-Ge alloys at 1373 K by a modified coulometric titration method described previously. 14,15.16The present results are discussed and compared with published values and with values predicted by several solution models. SHINYA OTSUKA is Research Associate, Department of Metallurgical Engineering, Faculty of Engineering, Osaka University, Osaka, Japan. YOSHIHIRO MATSUMURA, formerly a Graduate Student, Osaka University, is now with Sumitomo Metal Industries, Ltd., Wakayama, Japan. ZENSAKU KOZUKA is Professor, Department of Metallurgical Engineering, Faculty of Engineering, Osaka University, Osaka, Japan. Manuscript submitted December 29, 1980. METALLURGICALTRANSACTIONS B
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EXPERIMENTAL
Details for the theoretical basis for the coulometric technique have been presented in earlier publications. 14.15The apparatus and experimental procedure used in this study are similar to those in a previous study for pure copper and silver,16 so that a brief account will suffice
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