Grain boundary grooving on the polished surfaces of polycrystalline samples was studied after annealing in air, vacuum, or Ar atmospheres at temperatures ranging from 1273 to 1736K (table 12). It was found that the groove angles, as measured using optical interferometry, exhibited no significant dependence upon the experimental conditions. They indicated a mean value of 138.57 and a ratio, of the grain-boundary energy to the surface energy, of 0.707. It was determined that surface diffusion was the predominant mechanism of mass transport, and that the surface diffusion coefficient:

D(cm2/s) = 0.48 exp[-256(kJ/mol)/RT]

was essentially independent of the furnace atmosphere. In the low-temperature region which was examined, it depended upon the structural damage in the near-surface region which occurred during mechanical polishing.

A.Tsoga, P.Nikolopoulos: Journal of the American Ceramic Society, 1994, 77[4], 954-60

Table 12

Surface Diffusivity on Polycrystalline Al2O3