Polysilicate equilibria in concentrated sodium silicate solutions have been studied using potentiometric (glass electrode) and 29 Si n.m.r. methods. Experimental data cover the ranges: 11.36 ≤ pH ≤ 14.09, 2.4 ≤ [Na + ] tot /mol dm -3 ≤ 9.6, 2.1 ≤ [Si] tot /mol dm -3 ≤ 9.3 with a variation of SiO 2 /Na 2 O between 3.3 and 1.0. From available pH and n.m.r. data an equilibrium model is derived describing polymerization and protonation of silicate species in these water-glass solutions. With SiO 2 /Na 2 O = 1.0, i.e. in the most alkaline solutions (pH ≳ 13), dimeric as well as cyclic forms of tri- and tetra-meric silicate species predominate. At higher SiO 2 /Na 2 O, polymerization leads to the formation of polysilicate species containing branching groups with nuclearities 6-8 dominating. With SiO 2 /Na 2 O ≳ 3.3, i.e. close to the precipitation boundary of amorphous silica, cage-like polysilicate species dominate. The average charge per Si atom for the different polysilicate species varied between -2 in the most alkaline solutions down to -0.5 close to the precipitation boundary. The buffering capacity of the different water-glass solutions was found to decrease with increasing SiO 2 /Na 2 O. The change in the different formation constants (log β pq) due to variation in total Si and SiO 2 /Na 2 O, was found to be linear with respect to the Na + concentration, i.e. log β pq = log β° pq + k[Na + ]. Distribution diagrams describing speciation and equilibria in water-glass solutions of different SiO 2 /Na 2 O and total Si concentrations are derived using the computer program SOLGASWATER.
CITATION STYLE
Svensson, I. L., Sjöberg, S., & Öhman, L. O. (1986). Polysilicate equilibria in concentrated sodium silicate solutions. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 82(12), 3635–3646. https://doi.org/10.1039/F19868203635
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