The Effect of Compression and of Hydrostatic Pressure on the Diffusion Anisotropy in Zinc

Abstract

Measurements have been made on the rate of self-diffusion in single crystals of zinc along the directions both parallel and perpendicular to the C axis. The effects of compression by an applied force and hydrostatic pressure up to 10 000 atmospheres on the rate of diffusion were studied. The self-diffusion coefficients of polycrystalline zinc were also measured under both atmospheric pressure and compression. The rate of self-diffusion in single crystals of zinc was found always to be larger in the direction parallel to the C axis, while the enthalpy of activation was found always to be smaller in this direction. Both compression and hydrostatic pressure tend to reduce the rate of self-diffusion, the greater effect being observed in the direction parallel to the C axis. Compression perpendicular to the direction of diffusion gave essentially the same effect as compression in the direction of diffusion. The enthalpy of activation was found to be increased 30 percent by the application of a pressure of 8000 atmospheres and to be decreased slightly by compression. The anisotropy in the rate of diffusion was found to decrease with increased hydrostatic pressure. The self-diffusion coefficients of polycrystalline zinc were found to be intermediate between the values observed in the two directions (parallel and perpendicular to the C axis) in single crystals and to be closer in magnitude to the values observed in the direction perpendicular to the C axis.