Fumed silica is currently the main method for the industrialized production of nano-scale silica in developed countries. Fumed silica is an amorphous powder formed by the high temperature hydrolysis of silicon chloride silicon tetrachloride or trichloro-methylsilane in a mixed gas flow of hydrogen and oxygen. It is often spherical particles with hydroxyl groups and adsorbed water on the surface. , the particle size is between 7 and 40nm, the specific surface area is large, the chemical purity is high, and SiO2>99.8%. Fumed silica can be divided into hydrophilic type and hydrophobic type according to whether the surface treatment has been carried out, and can be divided into different types according to the size of the specific surface.

The process is as follows: the homogeneous gas composed of gasified silicon tetrachloride, hydrogen and oxygen is mixed and burned in a hydrolysis furnace to carry out high-temperature hydrolysis reaction. Deacidification is carried out in a deacidification furnace to obtain ultrafine silica. The HCl gas generated by the reaction is washed with water in the washing tower and becomes low-concentration hydrochloric acid.

The reaction formula is:

SiCl4+(n+2)H2+(n/2+1)O2——SiO2·nH2O +4HC1

The product obtained by this method has high purity, good dispersion, fine and spherical particles, and few surface hydroxyl groups. It is obtained by hydrolyzing silicon tetrachloride gas at high temperature in hydrogen-oxygen gas flow. Has excellent reinforcing properties. However, the equipment requirements are relatively high, the raw materials are scarce and extremely expensive, the technical control is complicated, and the investment scale is large.