Kinetic Analysis of Solution‐Precipitation During Liquid‐Phase Sintering of Alumina

Densification controlled by solution‐precipitation during liquid‐phase sintering was analyzed for the aluminamagnesium aluminosilicate glass system. As a model system for liquid‐phase sintering, narrowly sized alumina powders and up to 20 vol% magnesium aluminosilicate glass samples were isothermally sintered at 1550° to 1650°C. Densification rate increases with increasing liquid content and sintering temperature but decreases with increasing density. For samples with >15% grain growth, the densification rate during the solution‐precipitation stage of sintering was proportional to (particle size) −2 and thus interface reaction‐controlled. Activation energies ranged from 270 to 500 kJ/mol over the relative density range of 66% to 96%, respectively. The low activation energy is attributed to densification by particle rearrangement, whereas the higher activation energy is due to densification controlled by interface‐reaction‐controlled solution‐precipitation. Intermediate activation energies are attributed to simultaneous densification by the two mechanisms.