Post-sintering of apatite ceramics from fine powders synthesized under hydrothermal conditions

Hydroxyapatite fine powders prepared from (NH₄)₂HPO₄ and Ca(NO₃)₂ by a wet method were treated under hydrothermal conditions at 200°C under 2MPa for 10h. The obtained single-crystal fine powders of 90nm × 25nm were sintered in air at a temperature from 1000°C to 1100°C for 3h. The obtained ceramics with relative densities of 73±2% (1000°C) - 92±2% (1100°C) were HIP'ed at 1000°C under 200MPa of Ar for 1h without any capsules. The post-sintering brought about densification up to 99% for the samples of more than 90% dense having closed pores, but it barely increased the density of samples with lower densities. Transparent apatite ceramics were obtained by HIP.