The effect of sodium hydroxide concentration as stabiliser on the properties of aqueous silicon dioxide sols and their xerogels

The effect of sodium hydroxide concentration as a stabiliser on the properties of aqueous silicon dioxide sols and their xerogels, prepared in the “polymeric silicic acid – water – sodium hydroxide” system, was studied. The sol of polymeric silicic acid, prepared from a solution of sodium silicate using an acidic ion exchanger, was stabilised by addition of a sodium hydroxide solution so that the weight ratios of silicon dioxide to sodium oxide were 80:1, 100:1, 150:1, 200:1 and 250:1. Xerogels were prepared by drying of sols at 80 °C. Dynamic light scattering method was used for determination of the particle size of sols. The xerogels were characterised by scanning electron microscopy, atomic force microscopy, nitrogen adsorption and infrared spectroscopy. Several months stable monodisperse sols with diameter of particles around 2.0 nm were prepared. The xerogel surfaces are formed by spherical particles or their aggregates with the average size of approximately 50 nm. A reduction in the concentration of the sodium hydroxide stabiliser has effect on an increase in the specific surface area and porosity of the xerogels.