The basic concept and classification of precipitated silica Precipitated silica: also known as hydrated silica, active silica, precipitated silica and precipitated hydrated silica.
English name: Silica
CAS RN: 14464-46-1
Molecular formula: SiO2 * nH2O.
Silica is a general term for white powdery X-ray amorphous silicic acid and silicate products, mainly referring to precipitated silica, fumed silica, ultrafine silica gel and aerogel, also including powdered silica Synthetic aluminum silicate and calcium silicate, etc. Silica is a porous material whose composition can be represented by SiO2 * nH2O, where nH2O exists in the form of surface hydroxyl groups. Soluble in caustic alkali and hydrofluoric acid, insoluble in water, solvents and acids (except hydrofluoric acid). High temperature resistance, non-flammable, odorless, odorless, with good electrical insulation.
Silica is roughly divided into precipitated silica and fumed silica according to the production method.
Fumed silica is white amorphous flocculent translucent solid colloidal nanoparticles (particle size less than 100nm) under normal conditions, non-toxic, and has a huge specific surface area (100-400m2/g) (using F-Sorb 2400 specific surface area) instrument BET method test). The fumed silica is all nano-silica, the product purity can reach 99%, and the particle size can reach 10-20 nm, but the preparation process is complicated and expensive.
Precipitated silica is divided into traditional precipitation silica and special precipitation silica. The former refers to white carbon black produced with sulfuric acid, hydrochloric acid, CO2 and water glass as the basic raw materials, and the latter refers to the use of hypergravity technology, sol-gel method, chemical crystallization method, secondary crystallization method or reversed-phase micellar microarray. Silica produced by special methods such as emulsion method.
Precipitated silica is mainly used as reinforcing agent for natural rubber and synthetic rubber, toothpaste friction agent, etc.
1.2 The main physical and chemical properties of precipitated silica
Silica, also known as light silica, scientific name precipitated hydrated silica. It is a high-tech inorganic fine chemical product, the main component is SiO2. The properties are similar to carbon black, and the appearance is white, highly dispersed amorphous powder or flocculent powder, and some are processed into granules as commercial products. Light weight, the original particle size is below 0.3μm, the relative density is 2.319～2.653, the melting point is 1750℃, insoluble in water and most acids, and has water absorption. After absorbing moisture in the air, it will become agglomerated fine particles. Soluble in caustic soda and hydrofluoric acid. It is stable to other chemicals, resistant to high temperature, does not decompose, and does not burn. It exhibits chemical inertness to substrates and active ingredients and additives, and has good compatibility with vitamins, hormones, fluorides, antibiotics, enzyme preparations and many active ingredients commonly used in cosmetics. Has high electrical insulation. Due to its porosity and large specific surface area, it has a large dispersing force in raw rubber, and shows high reinforcement when filled in rubber. The surface-modified hydrophobic silica is easily soluble in oil, and is used as a reinforcing filler in rubber and plastics, which will significantly improve the mechanical strength and tear resistance of the product. Due to different manufacturing methods, the physicochemical properties and microstructure of silica will be different to a certain extent, so its application fields and application effects are also different.