INFILTRATION OF GLASS MELTS INTO FULLY DENSE AL2O3 AND MGO CERAMICS

The infiltration of glass melts into fully dense Al2O3 and MgO ceramic s has been studied with emphasis on elucidating the penetration mechan ism and the change in shape and size of the solid grains that accompan y the penetration process. For Al2O3, penetrated by a Ca-Al-Si-O glass melt, the grains developed a prismatic shape consistent with interfac e-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 dens e polycrystalline alumina specimen, it resulted in a homogeneous distr ibution of liquid phase and a uniform grain size throughout the whole specimen, In contrast, when glass penetrated the magnesia specimen, th e volume fraction of liquid phase at the surface region (which was in direct contact with the melt) was higher than that in the center regio n, Furthermore, the average grain size was larger in the center, where the volume fraction of glass was lower, This microstructural inhomoge neity stayed uncorrected even after prolonged annealing treatments, Re asons for this behavior are discussed.