TRANSPARENT ALUMINA WITH SUBMICROMETRE GRAINS BY FLOAT PACKING AND SINTERING

Commercially available alpha-alumina powder with high-purity, submicron particle size and a narrow particle-size distribution is used as starting material to prepare dense ceramic parts with transparent properties. The powder is dispersed and stabilised in a water-based suspension. Controlled consolidation and drying by float packing leads to homogeneous green compacts, which can be densified without additives by sintering in air at 1275 C to transparency, while the mean grain size remains at 0.4 micron. The in-line transmittance for wavelengths of 300-450 nm is comparable to commercial polycrystalline alumina tubes for lighting technologies, whose grain sizes are larger by a factor of 40. 36 refs.