Calcium Phosphate Apatites: Wet Formation, Thermal Transformations, Terminology, and Identification

Abstract—Apatite calcium phosphates have been synthesized at pH 9–11, Ca/P = 1.50–1.67 under variable isolation conditions. A complex procedure for identification of inclusion of amorphous calcium phosphate by precipitation of hydroxyapatite under non-equilibrium conditions, including XRD/FTIR/DTA methods. The maximal stabilization of amorphous phase inclusions in hydroxyapatite structure proceeds at precipitation pH 9, fast reaction of the chemicals without precipitate maturation stage under mother solution and careful dehydration by ethanol followed by heating at 400°C. Contradictions in reported physicochemical properties apatite calcium phosphates are related to formation of amorphous inclusions. A scheme of formation and thermal transformations of apatitic calcium phosphates under different equilibrium and formation conditions has been suggested for monophase stoichiometric hydroxyapatite, biphasic composites based on calcium-deficient hydroxyapatites, and amorphous calcium phosphate