Liquid Diffusion Measurement of Pb1- xSnxTe Using TR-IA-4 Sounding Rocket

Abstract

In order to obtain the -true- diffusion coefficient of liquid Pb1- xSnxTe, a microgravity ex­periment was conducted using a TR-IA-4 rocket launched on August 25, 1995. A diffusion couple composed of Pb0.8Sn0.2Te and Pb0.7Sn0.3Te cylinders with 2 mm in diameter s kept at )277 K for 231 seconds and quenched by injecting helium gas. All processes were realized under microgravity. Cooling was controlled so as to avoid axial directional solidification, which might spoil the diffusion experiments due to a large degree of segregation. The diffu­ sion during the heating and cooling periods was included in the analysis, based on an analyti­cal solution of Fick's second law with an assumption of D=A(T/ Tm)n (A and n are constants and Tm is the melting point). A diffusion coefficient of 7.9 x 10- 9 m2s- 1 at 1277 K was obtained from the microgravity experiment. Convection in the liquid diffusion couple spoiled the diffusion experiment in the 1 g reference experiment, however.