Building a Sintering Front through Fast Firing

High-density alumina was produced by fast firing (5 min, temperatures =1550 degrees C). Most of densification occurred under nonisothermal conditions. High densification rates observed are related to a change in the internal structure of the compact. The formation of a dense outer alumina layer controlled the heat flux to the interior of the compact, and increased the amount of energy available for sintering. Sintering in fast firing occurred as a densification front moving from the outer surface toward the sample center. As long as the rate of heat transfer is enough to sustain its advance, no differential densification occurs.