Influence of P₂O₅ on thermal behavior and bioactivity of sol-gel glasses

Two bioactive glasses in the system CaO-P₂O₅-SiO₂ were prepared by sol-gel process, from tetraethylorthosilicate (TEOS), triethylphosphate (TEP) and hydrated calcium nitrate (one with P₂O₅ and the other P₂O₅ free). Thermal behavior and reaction mechanism of xerogels were analyzed by TG-DTA methods. The in vitro bioactivity of both glasses was assessed by soaking them in simulated body fluid. The results reveal that the presence of P₂O₅ in the glass composition gives rise to the change of thermal behavior: the organic groups of triethyl phosphate are decomposed in the temperature range 300-420°C and the residual OH groups are removed at 570°C or so. The crystal of hydroxyl carbonate apatite formed on the surface of the glass containing P₂O₅ is larger and, relatively, the bioactivity is improved.