Effect of phase transformations during synthesis on the chemical composition and structure of calcium-deficient hydroxyapatite

The chemical and phase changes during the precipitation of calcium-deficient hydroxyapatite from a solution of natural chalk in a mixture of phosphoric and nitric acids, with the use of aqueous ammonia as the precipitant, have been studied by potentiometric titration and physicochemical analysis. The initial solution concentration and precipitation time are shown to have a significant effect on the composition and structure of the precipitate. The processes in the solution and precipitate are interpreted in terms of thedegree of protonation of phosphate ions under various conditions.