Preparation and structural analysis of CaO-SiO₂ gel by sol-gel method

It has been proposed that the CaO-SiO₂ binary system can be good basic composition of bioactive glasses and glass-ceramics. In the present study, various kinds of CaO-SiO₂ gels were prepared by sol-gel method in order to control the microstructure which are related to their dissolution rate, induction period of apatite formation in body environment. Characterization of the gels were done by wet chemical analysis, SEM observation, FT-IR spectroscopy and XRD. The gelation time decreased with CaO content. However, the volume of all the dried gel decreased to 50% of the wet gels irrespective of increasement of CaO content. All the CaO-SiO₂ gels were amorphous and contained a large amount of silanol groups on their surfaces after heat treatment up to 800°C. The interconnected structure of the gel changed to agglomerated spherical powders when Ca content exceed to 20 mol%. Most of the CaO-SiO₂ gel showed amorphous when heat-treated up to 900°C. However, quartz and cristobalite was produced when heat-treated at 1000°C and resultant microstructure of the gel contained microporous structure.