Theoretical and experimental investigation of the nature of crystallization processes in systems Ca(NO3)2-(NH4)2HPO4-Na2SiO3-H2O

The theoretical investigation of phase formation processes in systems Ca( NO3)(2-)(NH4)(2)HPO4-Na2SiO3-H2O was carried out at the varied concentration of phosphate ions, Si/P molar ratio, and pH taking into account the absorption of CO2 from air. The formation of hydroxyapatite is most probable in aqueous solutions as it was established by the results of calculation of the change in the Gibbs energy of crystallization. The supersaturation of the systems with respect to calcium silicate and calcite and thermodynamic probability of their precipitation together with basic calcium phosphate increase with an increase in the alkalinity of the reaction medium. The formation of mixtures of poorly crystallized nonstoichiometric calcium phosphate and calcium silicate was experimentally detected in the studied media. The method of precipitation from aqueous solutions can be used to produce composites based on these salts for biomedical purposes.