Growth of aluminum antimonide in solid aluminum-liquid antimony diffusion couples
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IN a previous
paper,I we reported that aluminum antimonide (AISb) grows in a highly anisotropic way after being nucleated at the interface of a solid aluminum vs solid antimony diffusion couple. In some of the diffusion couples, the morphology of the AISb crystals was very similar to that characterizing gallium antimonide (GaSh) and indium arsenide (InAs) platelets grown at slow growth rates from metallic solutions in whichthe extent of supersaturation is low.2,3 It occurred to us that we might gain additional insight into the anisotropic growth phenomenon by comparing the growth of AISb in solid aluminum vs liquid antimony diffusion couples with its growth in the solid aluminum vs solid antimony couples. By substituting liquid antimony for solid antimony in the diffusion couples, we expected to gain added flexibility in controlling diffusional mass transport of aluminum in the antimony terminal phase. Assuming that the diffusion coefficient in liquid antimony is of the order of 5 x 10-5 sq cm per sec,4 we estimated that this would correspond to an increase of 105 or so over that insolid antimony. Consequently, we would be able to vary diffusional mass transport in the liquid antimony over a relatively large interval by using two sets of diffusion couples. In one set, we could maximize diffusional mass transport by using liquid antimony initially unalloyed with aluminum; in the second set, we could minimize diffusionaimass transport by using liquid antimony which would be slightly supersaturated initially with aluminum at the diffusion anneal temperature. We anticipated that changes in diffusional mass transport resulting from the substitution of solid aluminum vs liquid antimony diffusion couples for solid aluminum vs solid antimony couples would alter the kinetics but not the processes themselves. The results we obtained were unexpected, and we discuss them below.
N. GRADO, formerly Graduate Student, Department of Physical and EngineeringMetallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N.Y., is now serving in the U. S. Peace Corps. L. S. CASTLEMAN is Professor, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn. Manuscript submitted December 2 1 , 1 9 7 0 . METALLURGICAL TRANSACTIONS
I) EXPERIMENTAL
PROCEDURE
The aluminum used in this investigation was 99.999 pct pure and was obtained in the form of 0.5 in. diam rods. The antimony was received as an ingot and was at least 99.999 pct pure; it was remelted and cast in the form of 0.5 in. diam rods. Also, a 0.5 in. diam rod of an antimony-rich alloy containing 2 at. pct A1 was prepared from the starting materials by melting and casting techniques. The rods were cut into 0.375 in. discs, and the faces were rough polished through No. 600 emery paper and degreased. The diffusion couples were prepared by simply placing a pair of pure antimony and aluminum discs or a pair of antimony-rich alloy and aluminum discs in a high purity graphite cylinder having a central hole 0.5 in. in diameter and I in. deep. The polished surfaces
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