SELF-DIFFUSION IN ALPHA-AL2O3 .1. ALUMINUM DIFFUSION IN SINGLE-CRYSTALS

Aluminum self-diffusion has been measured in single crystals of alpha-Al2O3 in the temperature range 1540-1697-degrees-C using Al-26 as a radioactive tracer. Two diffusion mechanisms are involved: a lattice diffusion mechanism and a subboundary mechanism. Lattice and subboundary diffusion coefficients obey equations D(Al)(cm2s-1) almost-equal-to 0.16 exp (- 510kJ mol-1/RT) and D''(Al)(cm2s-1) almost-equal-to 1.3 x 10(14) exp (- 850 kJ mol-1/RT). respectively. The results show that lattice diffusion coefficients of aluminium are much lower than those determined earlier. The comparison with oxygen diffusion determined by other workers for the same specimens shows that oxygen and aluminium diffusion coefficients are of the same order of magnitude in the lattice but that aluminium diffusion coefficients are greater than oxygen diffusion coefficients in subboundaries.