Synthesis and Processing of Nano-alpha-Al_2O_3 Powders

摘要

Nano-corundum powders have been synthesised for use as raw materials in advanced ceramic technologies or as CMP polishing agent. The approach avoids the formation of platelet-shaped boehmite. Instead, a quasi-aniorphous precursor obtained from different (inorganic or organic) sources gives equiaxed alumina particles and exhibits a reduced activation energy for the final transformation to corundum. Seeding with alpha-Al_2O_3 or diaspore reduces die transformation temperature to 800-900 deg C. Depending on seeds, the size of the obtained individual re-dispersed nano-corundum particles is 25-100 run. The sintering behaviour of these nano-powders is significantly affected by processing, it depends on the purity of raw materials and processes (e.g. impurities from wear on ball milling), on the particle size and the amount of seeds. High-purity processing enables low-temperature sintering (< 1300 deg C) of high-density corundum ceramics with sub-urn grain sizes and an exceptionally high hardness. After HIP, a fully dense alumina with a high in-line transparency was obtained. By introducing a ZrO_2 dopant, on the other hand, mesoporous corundum membranes were prepared with average pore sizes of 16-60 nm and a high open porosity of 40-50 percent.