The Influence of the Concentration of Liquid Glass Solution on the Formation of Hollow SiO2 Particles with Plasma-Electrolyte Spraying

The aim of the work is to evaluate the influence of the concentration of a liquid glass solution (Na2O·nSiO2) on the parameters of plasma-electrolyte spraying and the morphology of hollow SiO2 microspheres. Solutions with SiO2 concentration of 0.1, 0.5, 1.0, and 1.5 mol/L were used simultaneously as an electrolyte and a source of silica. The synthesis was carried out at atmospheric pressure in a tip-ring cell at a constant voltage of 400 V for 10 min, followed by washing and drying of the precipitate. The morphology was analyzed using scanning electron microscopy; size statistics were determined for at least 200 particles for each mode, and wall thickness was determined for 30–50 shell fractures. It has been shown that increasing the concentration leads to an increase in the average particle diameter from 4.5 ± 1.8 to 7.0 ± 2.0 μm and a thickening of the shell from 50 ± 10 to 180 ± 30 nm. The proportion of destroyed shells has a minimum in the range of 0.5–1.0 mol/L (15 ± 4 and 10 ± 3%, respectively) and increases both at insufficient and at excessively high concentrations. The optimal range of liquid glass concentrations for obtaining predominantly solid hollow particles is 0.5–1.0 mol/L SiO2.