Crystallization behavior of silica-calcium phosphate biocomposites: XRD and FTIR studies

Silica and calcium phosphates (CaP) are the most important ingredients in bioactive materials that bond to bone and enhance bone tissue formation. In this study, silica-calcium phosphate (SiO2-CaP) composites were developed by powder metallurgy method, using silica (SiO2) and anhydrous dicalcium phosphate (CaHPO4) powders (CaP) in the ratios (wt%): 20/80, 40/60, 60/40 and 80/20. The effects of temperature and chemical composition on crystallization and phase transformation of the SiO2-CaP composites were evaluated by XRD and FTIR. Thermal treatment of the starting material suggested that CaHPO4 transforms into: y-Ca2P2O7 at 800°C; p-Ca2P2O7 at 1000°C and a-Ca2P2O7 at 1200°C. On the other hand, P-quartz was the only detected phase after thermal treatment of silica in the temperature range 800-1200 °C. For all SiO2-CaP composites, SiO2 and CaP did not modify the crystallization behavior of each other when sintered in the temperature range 800-1000°C. However, at 1200°C, CaP promoted the transformation of p-quartz into a-cristobalite. Moreover, SiO2 stabilized p-Ca2P2O7. The modifications in the crystallization behavior were related to ion substitution and formation of solid solutions.