Composite Bioceramics Engineering Based on Analysis of Phase Equilibria in the Ca3(PO4)2–CaNaPO4–CaKPO4 System

Abstract

Based on analysis of phase equilibria in the Ca₃(PO₄)₂–CaNaPO₄–CaKPO₄ system at 500 and 1200°C, we have proposed compositions of composite bioceramics which lie in the single-phase field of a solid solution of phase A (Ca₅Na₂(PO₄)₄), the A + β-Ca₃(PO₄)₂ two-phase field, and the A + X (Са₈К₂(РО₄)₆) + β-Ca₃(PO₄)₂ three-phase field at the sintering temperature. Better strength properties—Vickers microhardness (H_V) and fracture toughness (K_Ic)—have been obtained in the case of ceramic samples whose compositions lie in the single-phase field of phase A (H_V = 265 MPa and K_Ic = 0.31 MPa m^1/2) and samples in the A + X + β-Ca₃(PO₄)₂ three-phase field (H_V ≤ 235 MPa and K_Ic = 0.22 MPa m^1/2). The proposed ceramic materials based on calcium sodium potassium phosphates have a relatively low and essentially constant dissolution (resorption) rate at pH = 5, at a level of 2 × 10^–4 min^–1.