GROOVE ANGLES AND SURFACE MASS-TRANSPORT IN POLYCRYSTALLINE ALUMINA

Grain-boundary grooving was studied on polished surfaces of polycrysta lline alumina, after annealing, in air, under vacuum, and in argon atm ospheres in the temperature range 1273 to 1736 K. The groove angles, m easured by optical interferometry, showed no significant change with e xperimental 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 surfa ce diffusion coefficient, D(s)(cm2/s) = 0.48 exp(-256(kJ/mol)/RT), was practically independent,of the furnace atmosphere, and, in the low-te mperature region examined, depended on the structural damage in the ne ar-surface region which occurred during mechanical polishing.