Infiltration of Glass Melts into Fully Dense Al2O3 and MgO Ceramics

Abstract

The infiltration of glass melts into fully dense Al2O3 and MgO ceramics has been studied with emphasis on elucidating the penetration mechanism and the change in shape and size of the solid grains that accompany the penetration process. For Al2O3, penetrated by a Ca—Al—Si—O glass melt, the grains developed a prismatic shape consistent with interface‐reaction‐controlled grain growth. For MgO, penetrated by a Ca—Mg—Si—O glass melt, the grains maintained a spherical shape consistent with diffusion‐controlled grain growth. When glass penetrated into the dense polycrystalline alumina specimen, it resulted in a homogeneous distribution of liquid phase and a uniform grain size throughout the whole specimen. In contrast, when glass penetrated the magnesia specimen, the volume fraction of liquid phase at the surface region (which was in direct contact with the melt) was higher than that in the center region. Furthermore, the average grain size was larger in the center, where the volume fraction of glass was lower. This microstructural inhomogeneity stayed uncorrected even after prolonged annealing treatments. Reasons for this behavior are discussed.