Final Stage Densification in Vacuum Hot-Pressing of Alumina

The kinetics of the final stage of densification of fine-grained aluminum oxide were studied by vacuum hot-pressing between 1150° and 1350°C and from 2000 to 6000 psi. The kinetics are consistent with the Nabarro-Herring diffusional creep model. The activation energy for the final stage densification is 115 kcal/mole which agrees with the activation energy for diffusion of aluminum ions. Densification takes place by particle rearrangement and by diffusional creep. The extent of densification in the initial stage depends on the amount of sliding, fragmentation, and plastic flow. The final stage of densification takes place by diffusional creep and is controlled by aluminum ion diffusion in aluminum oxide. It is shown that gases entrapped within pores of the hot-pressed compact will produce end-point porosities. A technique is described for removing adsorbed water when it is the source of the Presented at the Fall Meeting of the Basic Science Division and the Seventeenth Pacific Coast Regional Meetings of the American Ceramic Society, San Francisco, California, October 30, 1964.