Effect of the Two-Step Sintering in the Microstructure of Ultrafine Alumina

Sintering in two-steps has been applied with success for densification of nanometric and submicrometer ceramic powders without grain growth. In this work the applicability of two-step sintering as a means of suppressing the grain growth of submicrometer alumina is verified. Experiments, in which the grain growth and densification were characterized after conventional sintering and two-step sintering, were conducted. Conventional sintering is used as a choice of the steps for two-step sintering. In the first two-step sintering studied, one hypothesis that the maximization of final density with minimum grain growth can be achieved by improving the narrowing of grain size distribution at a pre-densification sintering stage was assumed. And the other two-step sintering is based on works of Chen and Wang, in which the samples are first heated to a higher temperature to achieve an intermediate density, and then cooled down and held at a lower temperature until they are dense. The results showed that the choice of steps does not permit to suppress grain growth, but, the two-step sintering influenced in the development of the final microstructure, taking to microstructures which were finer grained than in alumina sintered conventionally.