Composite Ceramics in the Na2O–CaO–SiO2–P2O5 System Obtained from Pastes including Hydroxyapatite and an Aqueous Solution of Sodium Silicate

Abstract

The new approach to obtaining ceramic materials in the Na2O–CaO–SiO2–P2O5 system based on the binder—an aqueous solution of sodium silicate and filler—hydroxyapatite was shown in current research. After heat treatment at 500 °C and 700 °C, the ceramic samples included non-reacted hydroxyapatite Ca10(PO4)6(OH)2, β-rhenanite β-NaCaPO4 and sodium calcium silicophosphate Na2Ca4(PO4)2SiO4. An increase in temperature to 900 °C and 1100 °C allowed to obtain ceramic materials with the following phases: devitrite Na2Ca3Si6O16, β-rhenanite β-NaCaPO4, β-wollastonite β-CaSiO3, and silicon dioxide SiO2. The strength of ceramic samples rose with increasing temperature from ≈7.0 MPa (bending) and ≈7.2 MPa (compression) at 500 °C to ≈9.5 MPa (bending) and ≈31.6 MPa (compression) at 1100 °C. At the same time, the apparent density decreased from 1.71 g/cm3 to 1.15 g/cm3. The top of the compressive strength equal to 31.6 MPa was observed when the apparent density was 1.15 g/cm3. Obtained ceramics consisted of biocompatible phases, widely studied in the literature; thus, it confirms the possibility of using an aqueous solution of sodium silicate in medical materials science.