The problem of incorporating high levels of sodium nitrate into silica gels without segregation

Na2O-SiO2 sols were prepared using silicon alkoxide and colloidal silica precursors with sodium nitrate as the salt. The experimental procedure carried out was changed depending on the precursors used. Several tests with dialysis membranes were performed in order to study the possibility of incorporating Na+-ions into the sols. These ions were introduced into silica sols contained in membranes from an exterior solution. In addition, washing tests were carried out with Na2O-SiO2 sols contained inside the membranes and with several exterior washing solutions. Resistivity of the washing solutions was measured against time. The washing solutions were changed periodically. After drying and heat-treatment, Na2O content in the gels was determined using flame photometry. The crystalline phases formed were detected by X-ray diffraction. The results show a small incorporation of alkaline ions in Na2O-SiO2 gels, even in those samples prepared through the dialysis membranes tests.