Radioscopic visualization of isothermal solidification of eutectic Ga-ln alloy
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R. DEREBAIL and J.N. KOSTER The phase diagram for a gallium-indium alloy shows that the eutectic is formed at a temperature of 15.3 ~ and has a eutectic composition of 14.2 at. pct In (21.4 wt pct In).tq A eutectic melt is expected to solidify completely when the eutectic temperature is reached. This requires that no gravitational segregation occurs in the melt. A survey of the available literature on eutectic Ga-In revealed no prior experiments on the in situ visualization of solidification. The goal of this experimental work was to observe the isothermal solidification of a vertical layer of molten eutectic GaIn in real-time using X-ray radioscopy. Figure 1 is a schematic of the PLEXIGLAS* test cell *PLEXIGLAS is a trademark of Rohm & Haas Company, Philadelphia, PA.
used in the present eutectic Ga-In experiment. The PLEXIGLAS walls on the front, back, top, and bottom walls of the central cavity provide insulating thermal boundary conditions while being transparent to X-rays. Molybdenum cladded copper thermodes were inserted into the two outer cavities of the test cell. These high conductivity thermodes apply defined thermal boundary conditions at the vertical sidewalls of the melt layer. Heating and cooling are achieved by flowing a mixture of water and ethylene glycol from a constant temperature bath through the flow channels of the thermodes. The thermostats have a stability of better than _ 0.1 ~ The best experimentally possible isothermal end-wall temperature conditions could be achieved with the thermodes. An adjustable lid made of PLEXIGLAS was inserted into the cavity to fix the aspect ratio and to provide a rigid upper surface on the fluid. The dimensions of the test volume in the present experiments were 50 • 35 • 2 mm (length • height • width). An overflow volume is provided above the lid to accommodate volume expansion. The noninvasive, real-time, in situ X-ray radioscopy technique was used to visualize the melting and solidification of the eutectic Ga-In melt. X-ray radioscopy is an absorptive technique, and the transmitted radiation intensity provides a real-time visualization of the combined density and concentration variations from that of an isothermal GaIn melt. The X-ray radioscopy technique is discussed in detail elsewhere, t2-5] The test cell is framed by lead sheets (6.35-mm thick), except for the central cavity containing the eutectic Ga-In
R. DEREBAIL, formerly Research Associate, Department of Aerospace Engineering Sciences, University of Colorado, is Manufacturing Development Engineer with Hewlett Packard Company, San Jose, CA 95131. J.N. KOSTER, Associate Professor, is Manufacturing Development Engineer with the Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO 80309-0429. Manuscript submitted January 23, 1996. 686--VOLUME 27B, AUGUST 1996
Ple~gl~ test cell Fig. l--Schematic of experimental test cell.
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