Grain Growth and Sintering of Translucent Polycrystalline Alumina

Abstract

Sintering of translucent polycrystalline alumina has improved through optimization of dopants and sintering atmosphere. The role of the magnesia dopant and mechanisms of the densification process in alumina have been active topics for numerous studies in the literature. It is widely recognized that the mass transport required for densification involves grain-boundary diffusion, and oxygen vacancies play an important role. The retardation of grain growth has been ascribed to drags due to solute and/or spinel second phase particles. Some researchers have conceived the notion that magnesia solubility in alumina is dependent on grain size. In this paper, we will report that the solid solubility of magnesia in alumina is indeed a strong function of grain size in the range of submicron to one micron. The grain-boundary enrichment factor and width appear to be a function of grain size. Grain growth occurs in small-grained MgO-doped alumina at temperatures as low as 1150°C. During the initial stage of grain growth and sintering of compacts of magnesia-doped, submicron alumina powders, the grain size, enriched dopant level at grain boundaries, boundary width, and equilibrium dopant content in the lattice, undergo dynamic evolution, in a background of boundary motion, precipitation of spinel second phase, and diffusional flux of the dopant.