Fabrication of Sub-micron Alumina by Spark Plasma Sintering

Sub-micron alumina ceramics were fabricated by spark plasma sintering technique(SPS), using commercialα-Al_2O_3 powders as starting material and MgO as sintering-aid.The effects of sinter- ing 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 MgAl_2O_4 is found in the samples doped with more than 0.1wt%MgO,resulting in a lower transmittance because of light scattering.