Effect of the average particle size and the surface oxidation layer of silicon on the colloidal silica particle through direct oxidation

Colloidal silica was prepared using a direct oxidation process of silicon powders with different purities, average particle sizes, and surface oxidation layer thicknesses in a water solvent with the base catalysts. Purities of 97.00–99.96% and average particle sizes of 200 and 500 mesh of silicon starting materials were evaluated. The materials were thermally oxidized for 3, 16, and 30 h to observe the effect of the surface oxidation layer on the formation of colloidal silica. The longer the thermal oxidation time, the higher the oxide layer thickness on the silicon, and the larger the average size of silica particle observed in the product of colloidal silica when silicon particles had the oxide layer up to approximately 50 nm. When the oxide film was higher than 50 nm, the silica particle size did not increase with an increase in the oxide layer of silicon. The dependence of the average particle silica size on the oxide layer thickness of silicon was observed to be smaller in the colloidal silica from the 200 mesh size of silicon than from the 500 mesh size. The average particle size of silicon was found to affect the average particle size of silica in the direct oxidation, however the correlation between the purity of silicon and the average particle size of silica was not determined as it fell outside the range of this experiment.