Fabrication of sub-micron alumina by spark plasma sintering

Sub-micron alumina ceramics were fabricated by spark plasma sintering technique (SPS), using commercial alpha-Al2O3 powders as starting material and MgO as sintering-aid. The effects of sintering temperature and sintering-aid content on densification and grain growth of sub-micron alumina were systemically studied. The results show that the optimal sub-micron alumina is obtained by sintering at 1250 degrees C for 5min under 60MPa, doped with 0.05wt%MgO. The relative density and the average grain size are 99.8%TD and 0.68 mu m, respectively. Moreover, the Vickers hardness can reach 20.75GPa (HV5), and the in-line transmission (1mm thickness) in the 3-5 mu m mid-infrared range is measured beyond 83%. lHowever, second phase MgAl2O4 is found in the samples doped with more than 0.1wt%MgO, resulting in a lower transmittance because of light scattering.