Influence of reactivity of the colloidal silica on the properties of conjugate phases

Abstract

The properties of hydrosols (brand Ludox) are studied by dynamic light scattering (photon correlation spectroscopy, PCS) and colorimetric analysis (formation of a colored β-silicomolybdate complex, KMK). Experimental sol samples for silicate modulus M = 50.0 and М = 3.0 M (M = [SiO₂]/[Me₂O], mol/mol) are obtained by introducing an alkali metal hydroxide (Me). According to the PCS data, the hydrodynamic radius of the sol particles (\({C_{Si{O_2}}}\)= 41.0 g/L) is r = 8.0 nm and increases with the dilution of the sol. These particles’ radii r_∞ (at \({C_{Si{O_2}}}\) → 0) for the initial sol are r_∞ = 13.8 nm and r_∞ = 16.8 nm in sols with alkali metal hydroxides (M = 50). The conjugated phase properties (silica particles and aqueous solution) were considered in the light of polycondensation and depolymerization kinetic reactions involving reactive silicate anions (HO)₃SiO^– and Si(OH)₄) on the surface of the particles and in the composition of soluble fractions. The result is the formation of surface layers of a gel-like structure. With the introduction of alkali metal hydroxides, the initial dissolution rate increases in the range from LiOH to KOH. The existence of peaks in the kinetic dependences of the active silica fractions in highly alkaline environments (M = 50 and M = 3.0) characterizes the secondary polycondensation of silicic acid in the aqueous phase, resulting in the formation of the oligo- and polymeric molecules of a linear structure.