The Unexpectedly Slow Approach to Thermodynamic Equilibrium of the Silicate Anions in Aqueous Tetramethylammonium Silicate Solutions

Contrary to the widely accepted picture of the dynamics of alkaline silicate solutions, tetramethylammonium silicate solutions require many days to re-establish thermodynamic equilibrium following a perturbation, as monitored by 29Si n. m. r. spectroscopy. Aqueous alkaline silicate solutions are now known to contain a variety of low molecular weight silicate anions in dynamic equilibrium.lJ In early studies it was widely believed that concentrated solutions required many days for their constitu-ents to reach thermodynamic equilibrium following a pertur-bation, such as dilution or a change of pH.3 Lagerstrom4 in 1959 demonstrated that this notion is only correct for solutions that were in, or had passed through, an 'instability range,' characterised by an alkali to silica ratio low enough to allow colloidal silica to exist. Equilibrium is attained 'very rapidly' for solutions whose composition places them outside this range. His findings have since been confirmed by severa