1. Basic concepts and classification
Precipitated silica: Also known as hydrated silica, activated 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 powdered X-ray amorphous silicic acid and silicate products. It mainly refers to precipitated silica, fumed silica, ultrafine silica gel and aerogel, and also includes powder. Synthesis of aluminum silicate and calcium silicate. Silica is a porous substance whose composition can be represented by SiO2*nH2O, wherein nH2O is present in the form of a surface hydroxyl group. Soluble in caustic and hydrofluoric acid, insoluble in water, solvents and acids (except hydrofluoric acid). High temperature resistance, non-combustible, odorless, odorless, and has good electrical insulation.
The white carbon black is roughly classified into a precipitated white carbon black and a fumed white carbon black according to a production method.
The fumed silica is normally white amorphous flocculent translucent solid colloidal nanoparticles (particle size less than 100 nm), non-toxic, and has a large specific surface area (100-400 m2/g) (using F-Sorb 2400 specific surface area) Instrument BET test). The fumed silica is all nano-silica, the purity of the product is up to 99%, the particle size can reach 10-20 nm, but the preparation process is complicated and expensive.
The precipitated white carbon black is further divided into a conventional precipitation method white carbon black and a special precipitation method white carbon black. The former refers to white carbon black produced by using sulfuric acid, hydrochloric acid, CO2 and water glass as the basic raw materials, and the latter refers to the use of supergravity technology, sol-gel method, chemical crystal method, secondary crystallization method or reverse micelle micro Silica produced by special methods such as emulsion method.
Precipitated silica is mainly used as a reinforcing agent for natural rubber and synthetic rubber, a toothpaste friction agent, and the like.

2, the main physical and chemical properties
White carbon black, also known as light silica, has a scientific name for the precipitation of hydrated silica. It is a high-tech inorganic fine chemical product with the main component SiO2. The performance is similar to that of carbon black, and the appearance is white, highly dispersed amorphous powder or flocculent powder, and also processed into pellets as a commodity. Light weight, the original particle size is 0.3μm or less, the relative density is 2.319～2.653, the melting point is 1750°C, it is insoluble in water and most of the acid, it has water absorption, and it will become aggregated fine particles after absorbing water in the air. Soluble in caustic soda and hydrofluoric acid. It is stable to other chemicals, does not decompose under high temperature, and does not burn. It is chemically inert to the matrix and active ingredients and additives, and has good compatibility with many active ingredients commonly used in vitamins, hormones, fluorides, antibiotics, enzyme preparations and cosmetics. Has a high electrical insulation. Due to its porosity and large specific surface area, it has a large dispersing power in the raw rubber, and exhibits high reinforcing property in the rubber. The surface-modified hydrophobic white carbon black is easily soluble in oil, and is used as a reinforcing filler for rubber and plastics, and the mechanical strength and tear resistance of the product are significantly improved. Due to different manufacturing methods, the physicochemical properties and microstructure of silica are different, so its application fields and application effects are also different.

3. Physical and chemical properties of precipitated silica
Precipitated hydrated silica
Molecular formula SiO2 * nH2O
Main component SiO2
Original particle size below 0.3μm
Relative density 2.319～2.653
Melting point 1750 ° C
Appearance White amorphous powder
Solubility insoluble in water and acid; soluble in caustic soda and hydrofluoric acid

4, the main application areas
Silica is a highly dispersed amorphous powder or flocculent powder which is light in weight and has high electrical insulation, porosity and water absorption. Its original particle size is less than 3um, so it has a large surface area, good reinforcement and viscosity enhancement, and good dispersion, suspension and vibration liquefaction properties. It has been widely used in plastics, rubber, paper, paint, dyes and inks. In several areas, especially in the rubber industry, silica has been ranked first for its superior reinforcement and transparency.
Depending on the quality, there are different applications. Precipitation method white carbon black is mainly used in automotive rubber tires, pesticide feed, paint, toothpaste and other additives.
Precipitated silica is widely used in rubber and plastic fillers, ink thickeners, paint coating additives, synthetic greases and silicone grease thickeners, tanners, pesticide dispersants, paper fillers, synthetic Resins (polyester resin, elastic polyurethane) additives, electrical and electronic insulation insulation fillers and daily chemical raw materials and other industries. It is also used as an opening agent for polypropylene, non-toxic polyvinyl chloride plastic film, and an anti-caking agent and carrier for food and pesticide medicine.
In the resin-based composite material, the white carbon black particles can be sufficiently and uniformly dispersed into the resin material, so that the strength, toughness and ductility of the epoxy resin material are greatly improved, the wear resistance is improved, and the surface smoothness of the material is improved and improved. Anti-aging properties. Thereby achieving the purpose of comprehensively improving the performance of the resin-based material.
In the plastics industry, the use of white carbon black for light transmission and small particle size can make plastics more dense. It not only improves its transparency, strength and toughness, but also improves water resistance, aging resistance, hardness and finish. For example: Using nano-silica to modify ordinary plastic polypropylene, the main technical indicators (water absorption, insulation resistance, compression residual deformation, flexural strength, etc.) have reached or exceeded the performance index of engineering plastic nylon 6, and realized The use of polypropylene railway fittings instead of nylon 6 has greatly reduced the cost of the products, and its economic and social benefits are remarkable.
In the rubber industry, carbon black is usually added to the rubber to improve strength, abrasion resistance and aging resistance, but the products are black due to the addition of carbon black. If a small amount of nano-silica is added to ordinary rubber, the strength, wear resistance and aging resistance of the product can reach or exceed the high-grade rubber products, and the color can be kept unchanged for a long time. Tires are usually also black, but the tires produced using nano-materials are not only brightly colored, but also greatly improved in performance. The folding performance of the side rubber of the tire is increased from 100,000 times to 500,000 times.
In home appliances such as color TVs, because the material needs to be added with carbon black for electrostatic shielding, the home appliances are generally black and are called black appliances. With nano-silica, it is possible to develop an electrostatically shielded coating that further controls the color of the coating, and the black appliance will become a color appliance.
In the coating industry, the nano-silica modified coating has changed the shortage of the previous products, and greatly improved such as poor suspension stability, poor thixotropy, poor weather resistance, and poor scrub resistance.
In the pigment and dye industry, it can overcome the shortcomings of organic pigments (dye) which have bright color and strong coloring power, but generally have poor light resistance, heat resistance, solvent resistance and migration resistance. The surface modification of the organic pigment (dye) by adding nano-silica black not only greatly improves the anti-aging performance of the pigment (dye), but also increases the brightness, hue and saturation. The earth has broadened the grade and application range of organic pigments.
The white carbon black has strong ability to reflect ultraviolet rays and has good stability. It does not decompose or discolor after being irradiated by ultraviolet rays, and does not react with other components in the formulation. Therefore, it can be applied to advanced cosmetics, UV-resistant new plexiglass, and the like.