Sol–gel preparation and crystallisation of 2.5CaO·2SiO2 glassy powders

Abstract 2.5CaO·2SiO 2 gel was synthesised by hydrolytic polycondensation of tetramethyl orthosilicate (TMOS) with calcium nitrate in alcoholic medium. Thermal treatments were carried out to convert the gel into the glass. However, a completely amorphous sample was not obtained. The gel-derived material structure was examined by FTIR spectroscopy. The IR spectra suggested that the gel-derived material has a different structure than the corresponding melt-quenched glass, for having a more uniform distribution of non-bridging oxygens among the SiO 4 tetrahedra. Crystallisation of the gel-derived material, examined by differential thermal analysis is reported and discussed. The activation energy for crystal growth, E c =782 kJ/mol, and the Avrami parameter, n =1, which indicates a surface nucleation mechanism, were evaluated by non-isothermal methods. The results were compared with those obtained for a conventionally prepared glass of the same composition.