Impurity precipitation along grain boundaries in sintered alumina

Impurity precipitation along grain boundaries in sintered alumina obtained in an industrial process and sintered alumina used as a crucible for annealing PbTiO3 was characterized with a scanning electron microscope and a transmission electron microscope and by energy-dispersed X-ray analysis. Spherical and cylindrical impurity precipitates were present at grain boundaries in sintered alumina reheated at 1000 degrees C. On the other hand, the intergranular amorphous phase was present at grain boundaries in sintered alumina quenched to room temperature from 1700 degrees C. The elements of the impurity precipitates in the sintered alumina were Na, Ca, Al, and Si. The swelling of a sintered alumina used for annealing PbTiO3 was related to low-viscosity glass formation by the reaction of the impurity precipitates with PbTiO3.