Formation of octacalcium phosphate in the interaction of calcium carbonate and monocalcium phosphate monohydrate under galvanostatic conditions

Abstract

The calcium phosphate composite octacalcium phosphate / calcite was obtained at pH 5–7 from the CaCO3/Ca(H2PO4)2 aqueous suspension in a galvanostatic mode at a current density of 20 mA/cm2 for 20 min. Drying at 80 °C without the precipitate maturation stage led to a powder formation consisting of brushite, calcite and a small amount of octacalcium phosphate. Prolonged maturation in air for 2 months led to the hydrolytic transformation of brushite into octacalcium phosphate stabilized by calcite. The use of electric current made it possible to increase the amount of octacalcium phosphate in the composite powder with the morphology of lamellar rosettes. Calcination at 800 °C of the composite powders led to the formation of α/β-tricalcium phosphate, β-calcium pyrophosphate, hydroxyapatite, and calcium oxide.