Activities of titanium in molten copper at dilute concentrations measured by solid- state electrochemical cells at 1373
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= - 8 6 , 1 0 0 _ 8900 at 1373 K
INTRODUCTION
DURINGthe course of experimental studies directed toward the determinations of the activities of Ti203 in molten fluxes used as mold lubricant of the continuous casting machine for copper-titanium alloys, it became necessary to measure the activities of titanium in molten copper at relatively dilute concentration, i.e., less than 0.01 mole fraction. In the present study, liquid copper containing titanium was brought into equilibrium with molten {CaC12 § Ti203} slag saturated with Ti203 (s) at 1373 K and the equilibrium oxygen partial pressures were measured by means of a solid-oxide galvanic cell of the type M o / M o + MoO2/ZrO2(MgO)/(Cu + Ti)~oy + Ti203 (s) § {CaCI 2 + TiEOa}slag/Mo
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EXPERIMENTAL ASPECTS
The experimental apparatus is shown schematically in Figure 1. About 300 g of high-purity oxygen-free copper was molten in a dense high-purity alumina crucible of 40-ram OD, 50-mm ID, and 100-ram length, together with 35 g of Ti203 + CaC12 mixture, under a stream of purified argon inside a SiC resistance furnace which was equipped with a mullite reaction tube of 70-mm OD, 60-mm ID, and 1000-ram length. The electrochemical half cell, M o / M o + MOO2/ ZrO2(MgO), shown in Figure 1, consisted of a zirconia tube and a two-phase mixture of Mo + MOO2. The details of the zirconia cell have been reported elsewhere, t~
H. HOSHINO, Graduate Student, and M. IWASE, Associate Professor, are with the Department of Metallurgy, Kyoto University, Sakyo-Ku, Kyoto 606, Japan. T. SHIMADA, Research Associate, Research Department, and M. YAMAMOTO, Manager, Production Department, are with Nippon Mining Co. Ltd., Samu-kawa, Kurami, Kohza-gun, Kanagawa, Japan. Manuscript submitted April 22, 1991. METALLURGICALTRANSACTIONSB
Zirconia tubes, closed at one end and stabilized by 9 mol pet of MgO, were supplied by Nippon Kagaku Togyo Co. Ltd., Osaka, Japan. These tubes had an ID of 4 mm, an OD of 6 ram, and a length of 50 mm. A molybdenum rod of 3 mm in diameter and 800 to 1000 mm in length was used as an electrical lead to the reference electrode which consisted of four parts Mo and one part M o O 2 by weight. The molybdenum rod was fixed at the top of the zirconia tube by means of zirconia cement (SUMICERAM S-301, Sumitomo Chemical Industry Co. Ltd., Osaka, Japan). The electrical contact to the outer electrode of the zirconia probe was also made by a molybdenum rod of 3-mm diameter. Dissolution of molybdenum in liquid copper was negligibly small; Hansen and Anderko t21 stated that copper and molybdenum form a miscibility gap in the liquid state ranging from 0 to 100 pct Mo. The furnace was assembled with the alumina crucible containing the oxygen-free copper, the thermocouple sheath, and the molybdenum rod; initially, the nonmetallic phases were not charged inside the crucible. The furnace was first evacuated in order to obtain a rigidly moisture-free atmosphere inside the reaction tube. The furnace temperature was then gradually raised to 1373 K in a stream of {Ar + 3 pct HE} gas mixtu
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