Gravitational influences on the liquid-state homogenization and solidification of aluminum antimonide

Bulk Crystal Growth Under Microgravity Conditions

“…Some experiments concerned several samples and sometimes two or more flights were necessary: Ang andLacy, 1979 ASTP, 1975 AlSb 10 Better homogeneity obtained in space (on ground: sedimentation is suspected). Averyanov et al, 1999Salyut-6, 1979 HgCdTe 8 0.19…”

Diffusion kinetics and some aspects of solidification under microgravity environment

“…In a binary melt in which an interplay of gravity-dependent concentration driven convection and sedimentation exists, it is difficult to estimate (from diffusion theory) the time required for complete homogenisation of the liquid after a compositional fluctuation (Ang and Lacy 1979). For example, in the case of a sinusoidal ttuctuation in the concentration C of one of the components with distance x, a solution of Fick's second law is…”

“…where C is the maximum initial variation in C, L is the effective diffusion distance between the two phases, D is the temperature-dependent diffusion coefficient and t is the homogenisation time (Carruthers, 1977). Application of the equation to At-Sh melts (Ang and Lacy 1979), which represent the class of liquids under consideration, shows that even when the compositional fluctua.tion yields a pure phase, a soaking period of 15 rain should homogenise the melt at temperatures where D =I x 10-Sere z sec-L In practice, however, even holding for as long as 4 hr is insufficient to bring about uniformity in composition. Ang and Lacy (1979) have developed an elegant analysis in which a parameter H defined by…”

Materials processing under microgravity conditions using drop tubes

“…It is the latter situation which can benefit from microgravity processing. Ang and Lacy's (1979)work on A1Sb is probably the best example, Although AlSb stoichiometric compound is an attractive material for solar energy conversion, it is not possible to produce stoichiometric segregation-free A1Sb crystal due to the unfavourabte value of H. The microgravity processing with a g level of four orders of magnitude less will make H << 1 and could improve the situation significantly. The actual experiment in ASTP mission showed a five-fold increase in the homogeneity of A1Sb specimens over that of ground-based samples:…”