Effect of Isomorphous Substitutions in Calcium Triphosphate, Ca₃(PO₄)₂, on the Microstructural and Chemical Properties of Phosphate Cements Prepared from It

Abstract—

This paper reports on the preparation and properties of phosphate materials for medical applications: brushite (CaHPO₄·2H₂O) or monetite (CaHPO₄) based cements prepared from β- and α-Ca₃(PO₄)₂ (TCP) via isomorphous substitutions of Na⁺ or K⁺ for Ca²⁺ and of ${\text{SiO}}_{4}^{{4 - }}$ or ${\text{SO}}_{4}^{{2 - }}$ for ${\text{PO}}_{4}^{{2 - }}$. The mixing liquid used to prepare phosphate cements from substituted TCP was orthophosphoric acid or H₂O, and TCP was mixed with dry Ca(H₂PO₄)₂·H₂O. Isomorphous substitutions of Na⁺ and K⁺ for Ca²⁺ ions and ${\text{SiO}}_{4}^{{4 - }}$ and ${\text{SO}}_{4}^{{2 - }}$ for ${\text{PO}}_{4}^{{2 - }}$ were confirmed by scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. It has been shown that, as a result of hardening of cement pastes with the use of different mixing liquids, one can obtain materials differing in microstructure, in which brushite or monetite prevails, depending on the TCP phase used in the preparation of the cement. In addition, we have studied interaction of the cements with water for a long time (16 days). The pH of the aqueous medium has been shown to vary from 5 to 7.5. This pH range is favorable for medical applications of the phosphate materials studied.