In order to explore the mechanism of grain growth, gas-phase synthesized Al2O3 nanopowders were heated under ambient conditions at high temperatures. Transmission electron microscopy and X-ray line-broadening studies were performed in order to determine microstructural parameters such as crystallite size and root-mean-square strain. An increase in crystallite size, with a decrease in dislocation density, was observed upon annealing the powder at higher temperatures. From a detailed analysis of the dislocation interactions, it was shown that polygonization-like interactions of dislocations were the main cause of such growth. A model for this growth was proposed. From the measured values of the root-mean-square strain and crystallite size at various temperatures, the ratio of the bulk to the shear modulus was determined. This ratio was found, to within experimental uncertainty, to be close to the bulk value.

Grain Boundary Dislocation Interactions in Nanocrystalline Al2O3. S.Dhabal: Journal of Materials Research, 2007, 22[4], 900-7