Decomposition mechanisms in aluminum oxide-apatite systems

Aluminum oxide was mixed with solid solutions of hydroxyapatite and fluorap atite, prepared by solid-state reactions, for a study of the relation betwe en composites of apatite and of their phase stability in the presence of al uminum oxide. The amount of water released from the apatite was quantified from thermogravimetric measurements, and the fraction of vacancies present at the onset temperature of its decomposition in the presence of aluminum o xide was estimated. The results show that the decomposition takes place whe n a certain fraction of vacancies has been formed. By incorporation of F- i n the structure, the fraction of vacancies was reduced and the thermal stab ility of apatite was improved. Based on these findings, a modified mechanis m describing the thermal decomposition of hydroxyapatite in the aluminum ox ide-hydroxyapatite system is formulated.