Preparation and Thermal Changes of Carbonate-Containing Apatite

Abstract

The hydrolysis of dicalcium phosphates (CaHPO₄·2H₂O ; DCPD and CaHPO₄ DCPA) to apatite in the presence of CaCO₃, which was convenient for the preparation of carbonate-containing apatite (CO₃AP), was studied on the reaction process and properties of reaction products.
CaCO₃ functioned as a pH compensator to realize pH conditions for the hydrolysis. CO₃Ap formed according to the succesive reaction DCPD→Ca₈H₂ (PO₄) ₆·H₂O→CO₃Ap or the simple reaction DCPA→CO₃Ap. DCPD tended to form nonstoichiometric CO₃Ap containing CO₃^2- locating at the both PO₄ and OH sites of the apatite structure, whereas DCPA nearly stoichiometric CO₃Ap containing CO₃^2- locating preferentially at the PO₄ site. CO₃Ap showed various characteristic thermal changes, e. g., additional formation of apatitic OH, formation and trap of CO₂ in the apatite structure, shift of CO₃^2- from the PO₄ site to the OH site, and finally the formation of hydroxyapatite containing no CO₃^2- and CO₂.