Transparent alumina with submicrometer grains by float packing and sintering

Commercially available alpha-alumina powder with high-purity, submicrometer particle size and narrow particle-size distribution is used as starting material to prepare dense ceramic parts with transparent properties. The powder is dispersed and stabilized 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 1275degreesC to transparency, while the mean grain size remains at 0.4 mum. 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.