Concentration- and pH-dependence of highly alkaline sodium silicate solutions

In this study two routes for the gelation of water glass have been investigated; the destabilization by a change in pH and by an increase in concentration through evaporation. Both methods produce optically transparent, highly viscous, homogeneous solutions. The structure and dynamics of the solutions along the two routes have been investigated with dynamic light scattering, 29Si-Nuclear Magnetic Resonance spectroscopy, viscosity measurements and infrared spectroscopy. We find that the two routes are fundamentally different. Increasing the concentration of the sodium silicate system leaves the silica speciation apparently unchanged. Lowering the pH leads to condensation reactions, thus a change in the silica speciation.

Gel-like materials have been prepared from commercial sodium silicate solutions, by two different routes. The resulting microstructures are found to be very different in the two cases giving the opportunity to tailor the microstructure of gels prepared from sodium silicate solutions by combining the two routes.Figure optionsDownload high-quality image (82 K)Download as PowerPoint slideResearch highlights
► The structure and speciation of water glass can be controlled by concentration and pH.
► With increasing concentrations the equilibrium particle size shifts to smaller sizes.
► With decreasing pH condensation of the low molecular weight species occurs.