Phase transition of γ-Al 2O 3 under hot isostatic pressure

Abstract

Phase transition of γ-Al 2O 3 was studied under hot isostatic pressure (HIP), using a SUS304 capsule. The transition of γ- to α-phase was accelerated by the pressure. In order to complete the transition, it is necessary to heat γ-Al 2O 3 at high temperature of 1300 °C for a long time. However, applying 200 MPa, γ-Al 2O 3 transformed into α-Al 2O 3 even at 500 °C. The transition temperature increased with the decrease of HIPing pressure. Typical “S” curves were obtained in the kinetic relation between the conversion and time. Avrami plots of the conversion and time revealed that the phase transition proceeded by nucleation process. Hence, the nucleation seems to be induced by the stress at the contact points of powder particles, which is applied by the HIPing pressure through the capsule. On the other hand, particle size was largely increased by the transition. A small amount of water contained in the γ-Al 2O 3 was also considered to play a role of hydrothermal medium for the transition. Therefore, it is deduced that the HIPing pressure induces the nucleation and that a small amount of water in γ-Al 2O 3 accelerates the transport at low temperature.