Vacuum Hot‐Pressing of Magnesium Aluminate Spinel

The densification kinetics of magnesium aluminate spinel during vacuum hot‐pressing were studied between 1175° and 1460° C and from 500 to 5100 psi. A phenomenologi‐cal rate equation, which suggests a logarithmic relation between strain rate and porosity, excellently described the observed densification. Treating porosity as an independent variable was shown to be reasonable; it does not functionally restrict porosity as a modifier of the applied stress. The strain rate dependence on porosity decreased at a porosity of approximately 0.15. Below 1350° C the densification characteristics were similar to those reported for other oxide systems. At 1450°C an increase in the stress dependence of the densification rate and an interaction between stress and porosity suggested that plastic flow by dislocation motion was an operative mechanism during densification.