The Polymerization of Silicic Acid

Abstract

This paper describes a light scattering study of the formation of polysilicic acid in basic media prepared by mixing very clean solutions of ammonium acetate and sodium metasilicate. The growth of the colloidal silica sols was observed by t,wbidity, dissymmetry and depolarization measurements. The rate of polymerization of silicic acid was followed in equivolume mixtures of 3% ammonium acetate and sodium metasilicate solutions whose concentrations varied from 0.1 to 10%. It was found that the rate increased with silicate concentration up to 1%.Similarly, equivolume mixtures of 1% sodium silicate and 1, 3, 6 and 10% solutions of ammonium acetate showed an increase in rate with ammonium acetate concentration. Measurements of the pH of the solutions show that the reaction does not proceed above the pH of 11 and increases in rate as the pH is lowered to 8.6. Depolarization and dissymmetry measurements indicate that the particles are large isotropic spheres.Above this concentration the rates were lower.Mechanisms of polymerization and aggregation are discussed.

The effect of Al on Si isotope fractionation investigated by silica precipitation experiments

“…Disilicic acid reacts further with monosilicic acid to form trisilicic acid and tetrasilicic acid (Iler, 1979). With ongoing oligomerization cyclic tetramers form and higher orders of polymerized silicic acid, silica colloids, gel and particles form (Greenberg and Sinclair, 1955;Iler, 1979;Tarutani, 1989). In the zero-Al experimental series (a) and the low-Al experimental series (b) the removal of Si from solution is only induced by polymerization of monosilicic acid, which leads to the formation of the solid.…”

Co-precipitation of silica and alkaline-earth carbonates using TEOS as silica source

“…2À [17]: Fig. 1 shows the change of the pH with time during TEOS hydrolysis at two different EtOH concentrations.…”

High‐Zirconium‐Content Nano‐Sized Bimodal Mesoporous Silicas

“…In this way, the already studied role played by TEAH 3 in order to orchestrate the hydrolytic reactions of the Si and Zr precursor species [36] is preserved in the current synthesis of the Zr-UVM-7 solids. Finally, once the hydrolytic reactions have been completed, the total concentration of soluble silica can be accounted for by Si(OH) 4 and (HO) 3 -SiO -species in an approximate ratio of 10:1.6, [57,58] while the majority Zr species should be the Zr(OH) 5 -mono-mer. [59] The subsequent condensation processes will proceed from these monomeric entities.…”