Obtaining octacalium phosphate in aqueous medium during the interaction of calcite with monocalcium phosphate monohydrate

Calcium phosphate composite powders consisting of brushite and calcite were obtained in an aqueous medium from a CaCO3/Ca(H2PO4)2 suspension at Ca/P ratios of 1,33, 1,50, 1,67, pH 5–7, and maturation time of 21-50 days. Prolonged maturation (up to 68 days) of composite calcium phosphate powders led to a hydrolytic transition of brushite to octacalcium phosphate, the amount of which increased with increasing duration of the maturation stage. Drying calcium phosphate powders at 37°C for 24 h contributed to the partially transition of the metastable phase of octacalcium phosphate to apatite represented by amorphous calcium phosphate. The presence of vibrations of О–Н at 633 cm-1 as the shoulder on the IR spectra indicates the presence of apatite in calcium phosphate powders. The use of an electric current (20 mA/cm2, 3–20 min) for a local increase of the pH value made it possible to increase the amount of octacalcium phosphate in the composition of the composite powder, which has a characteristic rosette morphology of thin lamellar crystallites.