Orthophosphates. Part V. Phase equilibria in the system calcium oxide–phosphorus pentoxide–calcium fluoride–water along the fluoroapatite–hydroxyapatite join under aqueous conditions

Abstract

Data from the F^–-induced transformation of CaHPO₄,2H₂O into Ca₅F(PO₄)₃, and from the hydrolysis of CaHPO₄,-2H₂O in H₂O were used to determine the variation with composition of ΔG_f° along the Ca₅F(PO₄)₃–Ca₅OH(PO₄)₃ join of the system CaO–CaF₂–P₂O₅–H₂O. The variation of ΔG_f° departs from linearity near the Ca₅OH(PO₄)₃ end of the system. The ΔG_f° values obtained were used to calculate the stability of fluorohydroxyapatite solid solutions under aqueous conditions relative to pH at constant dissolved [Ca²⁺], [phosphate], or [F^–].