Hydrated silica (SiO ₂ · nH ₂ O), also known as white carbon black or lightweight silica, is a white amorphous powder with high specific surface area, porous structure, and surface hydroxyl properties. Its core component, silica, binds water molecules in the form of surface hydroxyl groups, endowing it with excellent moisture absorption, chemical stability, and electrical insulation properties. In terms of physical properties, hydrated silica has a melting point of 1610 ℃ and a boiling point exceeding 1000 ℃. It is insoluble in water and most acids (except hydrofluoric acid), but soluble in alkaline solutions. In terms of chemical properties, its surface hydroxyl groups (including isolated hydroxyl groups, adjacent hydroxyl groups, and silicon oxide groups) give it high reactivity. At room temperature, it can react with alkali to form silicates and with hydrofluoric acid to form fluorosilicic acid.


The industrial preparation is mainly based on precipitation method, which generates silica precipitation through the acid-base neutralization reaction of sodium silicate and sulfuric acid, and forms micrometer sized particles (with a purity of about 93%) through dehydration condensation. The gas-phase method produces nanoscale particles (purity ≥ 99%) through high-temperature hydrolysis of silicon tetrachloride, but the cost is relatively high. The application areas cover rubber reinforcement, paint extinction, toothpaste friction agents, and paper reinforcement. For example, in the rubber industry, gas-phase white carbon black can increase the tensile strength of silicone rubber by 40 times; In coatings, its diffuse reflection characteristics can achieve a matte effect; In toothpaste, its adsorption capacity can effectively clean tooth enamel.