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

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 (HV) and fracture toughness (KIc)—have been obtained in the case of ceramic samples whose compositions lie in the single-phase field of phase A (HV = 265 MPa and KIc = 0.31 MPa m1/2) and samples in the A + X + β-Ca3(PO4)2 three-phase field (HV ≤ 235 MPa and KIc = 0.22 MPa m1/2). 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.