GROOVE ANGLES AND SURFACE MASS-TRANSPORT IN POLYCRYSTALLINE ALUMINA

Grain-boundary grooving was studied on polished surfaces of polycrystalline alumina, after annealing, in air, under vacuum, and in argon atmospheres in the temperature range 1273 to 1736 K. The groove angles, measured by optical interferometry, showed no significant change with experimental conditions, giving a mean value of 138.57-degrees +/- 0.08-degrees and a ratio of the grain-boundary energy to surface energy of 0.707 +/- 0.001. From the experiments it was determined that surface diffusion was the dominant mechanism for the mass transport. The surface diffusion coefficient, D(s)(cm2/s) = 0.48 exp(-256(kJ/mol)/RT), was practically independent,of the furnace atmosphere, and, in the low-temperature region examined, depended on the structural damage in the near-surface region which occurred during mechanical polishing.