Time resolved alkali silicate decondensation by sodium hydroxide solution

Abstract

Abstract Silica is by far the chemical compound the most widespread and used around the world: as a raw product in the buildings and roads industry, as concrete, or as a processed product in the manufacture of glass, ceramics or zeolites. In alkali silicate solutions—often used to synthesize those materials—a complex interplay of decondensation and condensation processes leads to the restructuring of silicate clusters at the atomic scale on a short time-scale. We were able to deconvolute these effects by combining time resolved small angle x-ray scattering, nuclear magnetic resonance, and parallel tempering simulations. We investigated the impact of a dilution by pure water or by a sodium hydroxide solution on the speciation and size of the dissolved silicates in solution. Herein, we show that the silicate clusters are not affected by dilution, suggesting that sodium cations protect the silicate clusters from hydrolysis. Decondensation is triggered by hydroxide ions that weaken and break Si–O bonds. Alongside the decondensation, the evolution of the computed protonation state of the silica species indicates a change in the interaction potential. Our results pave the way towards the investigation at the atomic scale of more complex systems implying alkali silicate solutions in condensation process by the addition of calcium or aluminum to synthesize aluminosilicate binders, hydrogels or zeolites.