Thermal stability of hydroxylapatite-titanium and hydroxylapatite-titania composites

The aim of the current study is to investigate the reaction of hydroxylapatite with both metallic titanium and titanium oxide, and to examine the effect of atmosphere on these reactions. For this purpose, hydroxylapatite composites with both metallic titanium powder and titanium oxide were prepared and sintered at 1100 °C for 2 h under 2 different conditions: in air and in evacuated glass tubes with hot isostatic pressing at 120MPa. The reaction was monitored with XRD and thermal analysis. No significant reaction was identified between hydroxylapatite and metallic titanium in the vacuum environment. However, a reaction occurred between hydroxylapatite and titanium oxide, which formed CaTiO₃ with a perovskite structure, Ca₃(PO₄)₂ (whitlockite) and water. The presence of air in the sintering environment promoted this reaction.