ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Formation of carbonated apatite in equilibrium system CaO–P₂O₅–H₂CO₃–H₂O at 298 K in air

Marina V. Chaikina, Natalia V. Bulina, Igor Yu. Prosanov, Konstantin B. Gerasimov, and Svetlana V. Makarova

Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of Russian Academy of Science, Novosibirsk, Russian Federation

E-mail: bulina@solid.nsc.ru

Received: 21 March 2023  Accepted: 26 May 2023

Abstract:

Equilibrium in the quaternary CaO–P₂O₅–H₂CO₃–H₂O system at 298 K in air was studied in a region of low concentrations of liquid-phase components. We revealed a dependence of the composition of resultant equilibrium solid phases on the Ca/P ratio of the initial components and on pH of the equilibrium liquid phase. It was found that the entire region of the system having low concentrations of liquid-phase components is occupied by variable-composition compounds with apatite structure. Two types of carbonate-containing apatite compounds were detected. The first type of apatite forms at 5.4 ≤ pH ≤ 7.0, contains HPO₄²⁻ groups in the lattice, and has an invariant point with brushite \({\text{CaHPO}}_{{4}} \cdot {\text{2H}}_{{2}} {\text{O}}\) at pH ≈ 5.4. The second type arises at pH > 7.0, does not contain an acidic group, and has an invariant point with CaCO₃ at pH ≥ 8.

Keywords: Calcium phosphate system; Equilibrium; Hydroxyapatite; Formation

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-023-02895-0

Chemical Papers 77 (10) 5763–5771 (2023)