Monitoring the structure of water soluble silicates

Commercial 3.22 ratio sodium silicate glasses were dissolved in water at around 150 degrees C and 4.6 atm pressure and the process was followed by in situ and ex situ Raman spectroscopy. Both methods proved to be suitable for measuring the concentration of dissolved silicate as a function of time, but marked differences were observed in the spectra obtained in the two different ways. The in situ measured Raman spectra proved to be identical with those of the commercial silicate solutions mostly composed of ring structured nanoparticles. The rapid sample quenching generates terminal Si-O(H) bonds and hydrated monomer crystallites mostly by consuming the three member rings. In contrast to the common belief mostly polymer pieces seem to detach from the solid sodium silicate and only a negligible fraction is leached out in monomer form. Dilution of a 3 mol/L silicate solution to 0.2 mol/L at ambient conditions reduces the average particle size from about 10.5 [SiO4]/mol to 1 [SiO4]mol which is reflected in the Raman spectra of these liquids. (c) 2006 Elsevier B.V. All rights reserved.