Ripening of Na-silicate gels in basic media: Identification of involved chemical species.

Decreasing the pH value of a concentrated sodium silicate solution while maintaining its basic environment, largely affects solution stability. The charge modification induces by the presence of acidic species is expected to destabilize initial equilibrium, thus affecting original structure. Acidification along with dilution of a concentrated sodium silicate solution ([Si] = 7 mol/L, Si/Na = 1.71, pH = 11.56) was realized by slightly adding a 0.5–2 mol/L hydrochloric acid solution under stirring. Through small angle X-ray scattering (SAXS), Fourier Transform Infrared (FTIR) spectroscopy, specific surface area and elementary chemical analysis, chemical species involved in the gelation and maturation of a concentrated sodium silicate solution were characterized. Results show that the initial mother solution which is a high pH-sensitive solution, is composed of both neutral and charged species such as Si 7 O 18 H 4 Na 4 , Si 7 O 18 H 5 Na 3 , (Si 7 O 18 H 3 Na 4)− and (Si 7 O 18 H 4 Na 3)−. These complex species are likely to dissociate, aggregate and/or condense as a function of both pH and silicon concentration. Accordingly, it is possible to master these solutions for appropriate usage. • Characterization of species involved in Na silicate gelation and maturation • Si 7 -type colloids responsible for stabilization of high concentrated Na silicate • Low pH variation of Na silicate solution induces great behavior changes • Reversible gels controlled by physical interactions such as Van der Waals • Stable silica compound obtained by dissolution/precipitation reactions [ABSTRACT FROM AUTHOR]