Densification begins earlier and is more pronounced in the presence of glass phase and alumina nanoparticles in the composition (FIGURE and TABLE ). Indeed, samples without glass phase and alumina nanoparticles (AP samples) shows a lower relative density (between 92% and 95%) as compared to AP ng samples (between 96% and 97%). In contrast, for the AP-Zt-HP sample, sintered at a pressure of 80 MPa, the density is close to that of samples with glass phase and nanoparticles. This seems to show that the glass phase and the alumina nanoparticles act as an aid to densification.