High pressure compaction and sintering of nano-size gamma-Al2O3 powder

The effects of pressure on the compaction and subsequent sintering of nanosize gamma-Al2O3 powder were studied. Pressures up to 5 GPa were used to compact the powder in a WC piston/cylinder type die and also in a diamond anvil cell. The green body compacts obtained from both methods of compaction were pressureless sintered at temperatures between 1000 degrees C to 1600 degrees C. Results demonstrated that green body density was enhanced with increased compaction pressure. For compaction pressures less than 3 GPa, microstructures containing significant porosity developed at all sintering temperatures studied and is due to the development of a highly porous or vermicular structure during the gamma to alpha phase transformation, occurring at temperatures between 1000 degrees C and 1150 degrees C. At compaction pressures greater than 3 GPa, however, the formation of the vermicular structure did not occur and near theoretical densities with grain size approximate to 150 nm were obtained.