Sintering and Grain Growth of Alumina

Abstract

The sintering and grain growth of alumina as a function of the type of impurity (oxide) added was studied. One weight per cent of the impurity was added to a commercial Be‐grained alumina or was coprecipitated with iilcl3 to form hydroxides. Fired shrinkage, bulk density, and apparent porosity measurements were used to correlate sintering with grain growth as observed by the petrographic and electron microscope. Some additives which increased grain growth were believed to enter into solid solution with alumina and to strain the lattice sufficiently to increase material transport greatly. Other additives were believed to produce a glassy phase which would greatly increase surface difusion and resulting grain growth. Some additives decreased grain growth because of the relatively large vapor phase produced by the impurity upon heating which may have been sorbed on the alumina; other additives may have Wed anion vacancies to reduce material transport or may have produced complex anions whose flow or diffusion may have been impeded.