High-pressure spark plasma sintering (SPS) of transparent polycrystalline magnesium aluminate spinel (PMAS)

A high pressure SPS (spark plasma sintering) process was applied for consolidation of un-doped polycrystalline magnesium aluminate spinel. This approach allows fabricating a fully dense transparent ceramic with submicron grain size and high hardness values at a relatively low temperature (1200 °C). The light transmittance of the specimens increases with increasing applied pressure, while the hardness gradually decreases. The optimal combination of properties was achieved after sintering at 1200 °C at a heating rate of 5°/min, a holding time of 15 min and an applied pressure of 350–400 MPa. The specimens display the level of transmittance in the visible wavelengths and hardness values comparable with the best results reported in the literature for the two-stage fabrication process (pressureless sintering and hot isostatic pressing).