Seasonal variation of microstructure and sintered strength of dry-pressed alumina

An origin was investigated for the variation of the density and the fracture strength of sintered alumina with the manufacturing season. Direct observation using immersion microscopy was utilized to examine the microstructures of granules, green bodies, and sintered samples for two specific cases: samples made in summer and others made in winter, This method revealed a seasonal difference in the pore structure of both green and sintered bodies. The variation of the density and the fracture strength with the manufacturing season was ascribed to the different concentrations of large pore defects in sintered bodies, which were developed from the green body structures. Formation of large pore defects resulted from void spaces at the center and at the boundary of granules in the green bodies. High temperature and humidity contributed to an increase in the deformability of granules, reducing defect sizes in summer and thus improving fracture strength.