Characterization and study of Na2O-B2O3-SiO2 glasses prepared by the sol-gel method

The sol-gel procedure has been used to prepare vitreous materials whose compositions are situated in the liquid-liquid immiscibility area of the Na₂O-B₂O₃ SiO₂ phase equilibrium diagram. Gels were prepared from different precursors and under different experimental conditions. After determining optimum conditions for gelling and heat-treatment, the gels were characterized with the aid of thermal analysis, X-ray diffraction, density and specific surface area measurements, as well as infrared and near-infrared spectroscopy. The textures of the samples and their microstructures were studied by means of scanning electron microscopy and transmission electron microscopy, respectively. The phase separation in the gels was compared to the same phenomenon in one of the glasses of identical composition, but prepared by conventional melting.