Phase stability aspects of various apatite-aluminium oxide composites

For aluminium oxide-hydroxyapatite composites sintered in air, decompositio n of hydroxyapatite to tricalcium phosphate was initiated at temperatures b elow 1000 degreesC and completed at 1200 degreesC. Composites of aluminium oxide and various apatites (hydroxyapatite, fluorapatite and chlorapatite) as well as the pure materials were hot isostatically pressed at 1200 degree sC for 1 h at a pressure of 160 MPa. Due to the closed system used, the the rmal stability was improved and no phase changes were detected in the hot i sostatically pressed aluminium oxide-apatite composites. These materials we re crushed and thereafter heat-treated in air at several temperatures in or der to study the phase stability. In the fluorapatite and chlorapatite base d composites, the apatite reacted with the moisture in the air and partly c onverted to oxyhydroxyapatite and decomposition of the latter phase was ini tiated. The phase composition in the materials was evaluated by X-ray powde r diffraction and the microstructure of the hot isostatically pressed sampl es was studied in a scanning electron microscope.