Abstract: Sub-micron alumina ceramics were fabricated by spark plasma sintering technique (SPS), using commercial α-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℃ for 5min under 60MPa, doped with 0.05wt%MgO. The relative density and the average grain size are 99.8%TD and 0.68μm, respectively. Moreover, the Vickers hardness can reach 20.75GPa (HV5), and the in-line transmission (1mm thickness) in the 3-5μm mid-infrared range is measured beyond 83%. However, second phase MgAl₂O₄ is found in the samples doped with more than 0.1wt%MgO, resulting in a lower transmittance because of light scattering.

Key words: α-Al₂O₃, MgO, spark plasma sintering, sub-micron grain