KINETICS OF VACANCY MOTION IN HIGH-PURITY ALUMINUM

It is shown that in very high-purity aluminum, Al/sub II/, the rate of vacancy annealing depends on vacancy concentration and annealing temperature but is independent of the temperature T. of vacancy injection per se. The rate can be described as the sum of first and second order components. The first order component becomes most prominent at a monovacancy concentration estimated to be 10/sup -6/ atom fraction. It is shown that the results are consistent with the Koehler-SeitzBauerle dissociative mechanism. The activation energy for diffusion of monovacancies in Al/sub II/ is found to be 0.65 plus or minus 0.06 ev. This, combined with earlier results on the formation energy of vacancies, gives 1.44 plus or minus 0.11 ev for the activation energy for self-diffusion in aluminum by a monovacancy mechanism. In zone-refined aluminum, Al/sub I/, of lesser purity, the rate of vacancy annealing depends upon T/sub i/ per se and falls off more rapidly wiih decreasing vacancy concentration than in Al/sub II/. Two hypotheses for the impurity effects are considered, namely: (1) trapping of vacancies by impurity atoms and (2) inhibiiion of dislocation climb by adsorbed impurities. (auth)