Influence of colloid synthesis techniques on barium silicates formation using silica hydrogel derived from serpentine minerals

Abstract

In the paper the interaction between silica SiO2 hydrogel recovered from serpentines (Mg(Fe))6[Si4O10](OH)8, sodium hydroxide NaOH and barium chloride BaCl2 in aqueous medium has been investigated by thermal and X-ray diffraction analyses. The experimental results have shown that depending on colloid synthesis conditions, the reactions occurring in the SiO2–NaOH–BaCl2–H2O system can develop in different directions. The stirring of the boiling aqueous suspension prepared in different ways from the mentioned reagents in air at ambient pressure can either lead to the precipitation of hydrated barium silicate species like BaSiO3·H2O or BaH2SiO4. On heating BaSiO3·H2O begins to crystallize into barium metasilicate BaSiO3 nano-sized particles after crystalline water removal at the temperature of 400 °C and reaches final crystallization at 800 °C. Unlike BaSiO3·H2O, the heat-treatment of BaH2SiO4 is accompanied by the formation of two barium silicate species: BaSiO3 and barium orthosilicate Ba2SiO4. The data derived from the experiments have allowed to better understand the mechanism of interactions occurring in the solution and to reveal the main factor governing the precipitates formation.