Fabrication of transparent gamma -Al sub 2 O sub 3 from nanosize particles

Compaction and heat-treatment behavior of gamma -Al sub 2 O sub 3 powder (avg diam. of 20 nm) were studied. A diamond anvil high-pressure cell was used to compact the powder at pressures to 3 GPa, both in air at RT and under liquid N sub 2 , followed by pressureless heat treatment at 800 degrees C. Fabricated compacts were optically transparent. For ambient and cryogenic compaction, sample hardness increased with pressure, and heat treatment increased hardness approximately 50%, independent of initial green-state value. Samples compacted in LN sub 2 were up to 9.6 GPa harder than those compacted in air. TEM revealed a random-dense-packed particle structure and interconnected porosity; interstitial void dimensions, however, were always less than the avg particle diam. (20 nm).