Activation Energies for Densification, Creep, and Grain‐Boundary Sliding in Nitrogen Ceramics

The activation energies for densification, creep, and grain‐boundary sliding in HP‐Si 3 N 4 are consistent and large, approaching the heat of sublimation of Si 3 N 4 . If solution‐precipitation through the intergranular glass (or fluid) is invoked as a common underlying mechanism, then it can be concluded that the high activation energy results from the high heat of solution of the crystal into the glass. This is consistent with the finding that it is difficult to retain Si 3 N 4 in a glassy state.