Dissolution of solid copper cylinder in molten tin-lead alloys under dynamic conditions
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I.
INTRODUCTION
DISSOLUTION of a solid metal in a liquid metal is one of the fundamental problems bearing on many metallurgical processes, such as soldering, I brazing, 2 hot tinning, 3 galvanizing, 4 extractive metallurgy, 5 and liquid metal corrosion. 6 It has long been known that solid base metal dissolved into molten solder, and several investigations on the dissolution of base metal into molten solder have been reported in literature. ~.7However, very little is known about the influence of flow conditions on dissolution. Kim et a l 5 found that the mass transfer process is dominated by natural convection when a specimen is stationary and by forced convection when a specimen is rotated. In an earlier papers concerning the dissolution of copper into molten tin under static conditions using two kinds of vertical solid-liquid couple method, the authors concluded that the dissolution of copper under the copper placed in lower position is governed by diffusion, whereas the dissolution under the copper placed in upper position is governed by natural convection in the melt. The purpose of the present paper is to investigate the effect of flow on the dissolution of solid copper in molten tin-lead alloys for several rotational speeds of copper and also to establish a quantitative mass transfer correlation for the dissolution of copper in the melt.
II.
EXPERIMENTAL
The copper cylinders, machined from pure copper (99.9 pet), were 18 mm OD, 5 mm ID, and about 20 mm in height. Before each experiment, the specimens were annealed for 10.8 ks at 773 K in a vacuum of 1.3 x 10 -2 Pa or less. The specimens were degreased in acetone and cleaned in the chemical polishing bath containing 2 vol pet HCI, 18 vol pet H 2 5 0 4 , 37 vol pet HNO3, and 43 vol pct H20. Each copper specimen was weighed to ---0.001 g and its height was measured to +-0.01 mm. The composition of
YOSHIFUSA SHOJI, formerly Graduate Student, Tokai University, Tokyo, is now with Sumitomo Light Metal Industries, Ltd., Nagoya 455, Japan. SOSUKE UCHIDA, Professor, and TADASHI ARIGA, Associate Professor, are both with the Department of Metallurgical Engineering, Faculty of Engineering, Tokai University, Shibuya, Tokyo 151, Japan. Manuscript submitted July 29, 1981. METALLURGICALTRANSACTIONS B
the tin-lead alloys studied, which are JIS soft solders of A class, was 99.9 pct purity lead, Pb-25.9 at. pct Sn, Pb-53,8 at. pct Sn, Pb-74.8 at. pet Sn, Pb-87.6 at. pct Sn, and 99.9 pct purity tin. Each tin-lead alloy of 0.7 mol was weighed to +--0.01 g and degreased in acetone. Figure 1 shows the apparatus. It consisted of a resistance furnace, a specimen holding and stirring assembly, and a gas train. The stainless steel shaft was guided by ball bearings and rotated by a variable-speed motor. The drive assembly could be raised and lowered in order to allow the copper specimen to be quickly moved in and out of the melt. The copper specimen was covered on the top and bottom faces with a specimen holder of identical diameter, and connected to the shaft. In this way only the
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