Structural study of the effect of SiO2/K2O molar ratio on the stability and transparency of potassium silicate gel

Abstract

The silica sol and potassium hydroxide solution are mixed under certain conditions to form a precursor solution, which is poured into a closed cavity and gelled at 75 °C for 24 h to form potassium silicate gel. The structural evolution, stability, and transmittance of potassium silicate gels with different SiO₂/K₂O molar ratios were investigated. Raman spectroscopy is applied to analyze the SiO₄ tetrahedral network of potassium silicate gel and the polymerization index I_p (A500/A1000) increases linearly with the increase of the molar ratio. The relative fractional area of different species Qⁿ as a function of the molar ratio is described in detail through the deconvolution of band 700–1200 cm⁻¹. A(Q² + Q³)/A(Q² + Q³ + Q⁴) is first employed to characterize the polymerization degree of the SiO₄ tetrahedral network, which is proven to be reliable. In addition, the stability of potassium silicate gel is measured indirectly by its deformation over time. The higher the molar ratio, the smaller the deformation and the better the stability. When the molar ratio is >6, excessive silica not only acts as a forming agent to increase the polymerization degree of the SiO₄ tetrahedral network, but also acts as a filler added into the potassium silicate gel, causing a rapid decrease in transmittance and a sharp increase in haze.

Highlights

• The polymerization index I_p increases linearly with the increase of the SiO₂/K₂O molar ratio.

• A(Q² + Q³)/A(Q² + Q³ + Q⁴) employed to characterize the polymerization degree is proven to be reliable.

• The higher the SiO₂/K₂O molar ratio, the better the stability of the potassium silicate gel.

• The excess silica causes a rapid decrease in transmittance and a sharp increase in haze.