Isothermal transformation kinetics and coarsening rates were studied in unseeded and α-Al2O3-seeded γ-Al2O3 powders heated in dry air and water vapor. Unseeded samples heated in dry air transformed to α-Al2O3 with an activation energy of 567 kJ/mol. Seeding with α-Al2O3 increased the transformation rates and reduced incubation times by providing low-energy sites for nucleation/growth of the α-Al2O3 transformation. The activation energy for the transformation was reduced to 350 kJ/mol in seeded samples heated in dry air. Seeded samples completely transformed to α-Al2O3 after 1 h at 1050 °C when heated in dry air compared to 1 h at 925 °C when heated in saturated water vapor. The combined effects of a lower nucleation barrier due to seeding and the increased diffusion due to water vapor reduced the activation energy for the transformation by 390 kJ/mol and the transformation temperature by approximately 225 °C compared to the unseeded samples heated in dry air. The accelerated kinetics is believed to be due to increased surface diffusion.
|Number of pages
|Journal of the American Ceramic Society
|Published - 1999
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Materials Chemistry