The Production of Ultrafine Silica Powders from Silicon Tetrachloride: Control of the Primary Particle Size

Ultra fine silica powders were prepared by hydrolysis of SiCl₄ using aqueous ammonia solution followed by supercritical drying. Using different methods of combining the SiCl₄ and ammonia solution, to vary the initial and final pH of the solution, large silica powders surface areas (271–905 m²/g), fine average particle diameters (3.5–17) nm and low tapping densities (0.02–0.05 g/cm²) could be prepared. Powders with characteristics similar to pyrogenic silica, and with similar thermal stability at temperatures up to 1000°C, could be produced.