Desulfurization and deoxidation of Cu-S-O alloy in induction melting and solidification under argon and their rates of e
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INTRODUCTION
C R U D E copper produced in a converter contains many impurities other than oxygen, such as lead, sulfur, antimony, arsenic, and bismuth. In order to produce electrolytic copper of high purity, it is necessary to remove these impurities as much as possible. The refining of crude copper by vacuum melting has been investigated, and it was confirmed that lead, bismuth, and sulfur can be easily removed. In view of the equilibrium pressure of sulfur dioxide, sulfur can be removed in the presence of oxygen as this compound by vacuum melting. A few studies were made of the elimination of sulfur and oxygen from crude copper by vacuum melting. Kameda and Yazawa tlJ discussed their elimination from a thermodynamic standpoint and observed that the rate of their elimination was great. It is particularly noteworthy that most of the sulfur and/or oxygen in crude copper is removed when it is melted down under vacuum, and that in crude copper containing 0.051 wt pct S and 0.28 wt pct O, sulfur is considerably removed even under argon at 0.1 and 0.01 MPa. Kametani and Yamauchi t2'31 studied the elimination of oxygen and sulfur from molten crude copper by vacuum lift refining. In 0.6 kg of a synthetic crude copper containing 0.130 wt pct O and 0.107 wt pct S, 78 pct of the oxygen and 94 pct of the
REIICHI OHNO, Associate Professor, is with the Institute for Materials Research, Tohoku University, Katahira, Sendai 980, Japan. Manuscript submitted March 5, 1990. METALLURGICAL TRANSACTIONS B
sulfur were eliminated after four vacuum lifts at an average pressure of about 266 Pa. The rates of their elimination followed the first-order kinetics, t21 In 6 kg of a crude copper containing 0.089 wt pct O and 0.102 wt pct S, 80 pct of each element could be eliminated after 15 vacuum lifts at the minimum pressure of about 133 Pa. t3] Considerable desulfurization and deoxidation of Cu-S-O alloy occurred when the solid alloy was melted or the molten alloy was solidified and subsequently remelted under argon at 0.101 MPa (1 atm). The present study was undertaken to investigate the extent and mechanism of desulfurization and deoxidation in these processes and the rates of desulfurization and deoxidation in vacuum induction melting of Cu-S-O alloy. For this purpose, examination was made of the effects of argon pressure on the desulfurization and deoxidation of Cu-S-O alloy in these processes and of the rates of removal of sulfur and oxygen from molten Cu-S-O alloy kept at 1373, 1473, and 1573 K under vacuum. In the melting of solid Cu-S-O alloy, desulfurization of 64 to 80 pct and deoxidation of 75 to 82 pct occurred, and in solidification and remelting, desulfurization of 49 to 90 pct and deoxidation of 63 to 81 pct occurred. The extent does not depend on the pressure of argon. These desulfurizations and deoxidations are probably due to the high pressure of sulfur dioxide in equilibrium with solid copper and melt. The rates of desulfurization and deoxidation of molten Cu-S-O alloy under vacuum followed first-order kinetics, and d
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