Synthesis and characterization of silicate polymers

Abstract

In this work an inorganic polymer is developed based on Elkem microsilica and potassium hydroxide. Using experimental data and the partial charge model a model for the gelation is suggested based on the hydrolysis and condensation reactions occurring during synthesis. In addition the optimal composition of the binder system was determined using compressive strength test and solubility experiments. Based on partial charge calculations and experimental data for the hydroxide concentration and the viscosity obtained in this study it is suggested that the polymerization of the inorganic polymer is determined by the concentration of silica species. It was found that the alkalinity has a crucial effect on the condensation process. The optimal potassium hydroxide concentration used in the synthesis of the inorganic polymer was found to be around 3.5 M, which resulted in a compressive strength of the product in the region of 50 MPa.

ESI-MS investigation of the polymerization of inorganic polymers

“…The increase in the intensity can be explained by the dissolution of microsilica leading to a greater amount of silicate species in the solution. The pH evolution during the dissolution process reported in previous work [20] indicates that the dissolution process proceeds for approximately 10 h correlating with the observed increase in silicate species. The rapid drop in the intensity observed after 12 h in Fig.…”

“…From the figure it is seen that the particle size of the polymer increase rapidly between 8 and 12 h suggesting polymerization. In addition previous studies of the same system have shown that the viscosity changes during synthesis [20]. It was found that the viscosity of the solution started to increase approximately 10 h after mixing also suggesting polymerization.…”

“…Partial charge calculations for the polymerization of the inorganic polymer have shown that polymerization at the initial pH of the reaction solution (pH 14) may not be favored since the partial charges of the leaving group and nucleophilic group are similar [20]. In addition the high degree of ionisation of the silicate species at very high pH results in repulsive interaction between the reactants.…”

“…In addition the high degree of ionisation of the silicate species at very high pH results in repulsive interaction between the reactants. As the pH drop to below 12, condensations between the silicate species are more favored, since the difference between the partial charge of the leaving group and the nucleophile is greater [20]. Moreover, the overall charge of the silicate species decreases resulting in less repulsion between the reactants.…”

XPS and FT-IR investigation of silicate polymers

“…In previous work, inorganic polymers have been synthesized by a sol-gel process in which the silicate precursors were formed in situ by dissolution of amorphous silica particles (microsilica, Elkem 983 U) by an alkaline solution (0.75-4 M KOH) [3]. The dissolution of the amorphous silica in alkaline conditions can be expressed by the following reactions.…”