Dissolution of solid antimony in molten bismuth under static conditions
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ALTHOUGHconsiderable attention has been paid to the dissolution of a solid metal in a molten metal/-5 comparatively little is known of the effect of natural convection on the dissolution, 6-8 and nothing is known of the distribution of the dissolving species in a melt. In preceding papers, 9-~3the authors studied the dissolution of solid copper in molten pure tin and tin-lead alloys under static and dynamic conditions using reaction couple and immersion methods, in connection with a soldering process. And it was shown that a hydrodynamic flow is usually present even in a melt which is not artificially stirred, and vortices occur in a melt which is stirred by a rotating cylinder. In the static dissolution process using immersion method, concentration of solute in the melt have generally been taken to be maintained uniform. However, the distribution of dissolving species in the melt under static dissolution was not observed in the liquid metal systems. The purpose of the present paper is to demonstrate the distribution of the dissolving antimony in molten bismuth which is stirred by natural convection, and determine the dissolution rate of solid antimony in molten bismuth under natural convection. The bismuth-antimony system was used because of homogeneous solid solution. And moreover the diffusion coefficient of antimony in bismuth in molten state was obtained by diffusion couple method in order to discuss the result. I. E X P E R I M E N T A L 1. Measurement of Diffusion Rates of Antimony in Molten Bismuth Antimony of 99.9 pct purity was cast into cylindrical specimens, 8 mm in diam and about 5 mm in height. Before each experiment, the specimens were annealed for 10.8 ks at 773 K in a vacuum of 1.3 • 10 -2 Pa or YOSHIFUSA SHOJI is Graduate Student, SOSUKE UCHIDA is Professor, Department of Metallurgical Engineering, Faculty of Engineering, Tokai University, Shibuya, Tokyo 151, Japan. Manuscript submitted December 30, 1980.
less, and degreased in acetone using a supersonic wave device. Each antimony specimen was measured to be +_ 0.01 mm in height. Bismuth of 99.9 pct weighing 10.00 g was degreased in acetone. Figure 1 shows the apparatus for determining the diffusion rates using reaction couple method. The solid-liquid assembly, which placed the antimony specimen in top position and the bismuth one in bottom position, was made in order to prevent natural convection resulting from a density difference in the melt during the dissolution. The antimony specimen was fixed to the specimen holder made of graphite to limit the dissolution to the bottom face of antimony. The stainless steel rod could be pulled in order to allow the solid specimen to be lowered. The graphite crucible, which was 20 mm OD, 10 mm ID, and 50 mm in height, was charged with bismuth, and the antimony specimen was inserted in the specimen holder. After the electric resistance furnace was heated and stabilized at a desired temperature, a run was started by pulling the stainless steel rod. In the present resistance furnace, induced current which might
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