Three preparation methods and processes of white carbon black Silica is hydrated silica, which is a fine powder or fine particle silica. The high-purity one has a SiO2 content of 99.8%, light weight, an original particle size of <0.0003mm, a specific gravity of 2.319 to 2.653, and a melting point of 1750°C. The classic manufacturing methods of silica are divided into 3 categories: gas phase method, precipitation method and dissociation method. Industrial preparation methods are all combinations or improvements of these three methods.

1. Gas phase method
(1) Production of fumed silica Fumed silica is an amorphous powder produced by high temperature hydrolysis of silicon chloride silicon tetrachloride or trichloromonomethylsilane in a mixed gas stream of air and hydrogen. , often spherical particles with hydroxyl groups and adsorbed water on the surface, particle size between 7 and 40nm, large specific surface area, high chemical purity, 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.

1.2 Application of fumed silica Fumed silica is widely used in silicone rubber, cable materials and unsaturated polyester resins, adhesives, paint coatings, inks and copier toners, food and cosmetics. Thickening, anti-caking, control system rheology and thixotropy.

2) Application in silicone rubber
Fueled silica is widely used in room temperature vulcanized silicone rubber and high temperature vulcanized silicone rubber. They are often dispersed in the matrix in the form of agglomerates to form a three-dimensional network structure, and the contact surface with the silicone rubber base material is large. There are many cross-linking points formed during the vulcanization process, which thickens and reinforces the silicone rubber. The three-dimensional network structure formed by fumed silica has relative stability and is in an "elastic" state. Under the action of external force, it will be temporarily destroyed, which will reduce the viscosity of the system and present good fluidity; After the shear force is removed, the three-dimensional network structure will quickly return to the state before the force, so that the system has good thixotropy. In addition, because the particle size of fumed silica is very small and the particles are spherical, it is dispersed in the base material to form a uniform system, which often has good optical properties and can be used to manufacture white and transparent silicone rubber products. The room temperature vulcanized acid silicone adhesive produced with fumed silica as filler has a wide range of consistency and effective vulcanization performance, and has excellent adhesion to various primed or unprimed substrates , has excellent storage stability at room temperature, and is widely used in the construction industry.

(3) Application in plastics and unsaturated polyester resins
Fumed silica is also commonly used in plastics and elastomers and unsaturated polyester resins. In addition to adding traditional fillers during plastic mixing, adding a small amount of fumed silica will have a significant reinforcing effect, greatly improving the hardness and mechanical properties of the material, thereby improving the processing technology and product performance. Adding a small amount of fumed silica to the unsaturated polyester resin can give the resin better transparency and excellent physical properties, all of which help improve the quality of downstream products. Fumed silica plays an important role in industrial development, but due to its high price, its wide application is often limited. For example, the rubber industry is still using a large amount of precipitated silica.

2. Precipitation method
The precipitation method is to react water glass with sulfuric acid or hydrochloric acid to generate silicic acid, which is then decomposed to obtain white carbon black. The content of SiO2 is about 90%, and the market demand is large, and it is mainly used as a rubber reinforcing filler. my country's white carbon black production plants mainly use this method to produce white carbon black. The production technology and equipment of precipitation silica are simple, the product activity is not high, the particles are not easy to control, the affinity is poor, the reinforcing performance is low, and the hydrophilic groups on the particle surface are seriously bonded, which weakens the bonding force of the product. The production of the finest silica by secondary crystallization is an improved technology of secondary seed treatment under the premise of the precipitation production technology. Using the new secondary crystallization process, the industrial production can be fully controlled. Its SiO2 content is above 94%, the specific surface area is 269-320m^2/g, the particle size is 1000 mesh, and the finer can reach nanometer. Precipitated silica is widely used as filling and reinforcing agent for rubber and plastic, additive for synthetic resin (polyester resin, elastic polyurethane), opening agent for polypropylene, non-toxic PVC plastic film, insulation in electrical and electronic industry Insulation filler, etc.

3. Dissociation method
(1) The raw materials used to prepare silica from non-metallic minerals are diatomite, opal, serpentine, bentonite, kaolin, wollastonite, quartz sand, sepiolite, attapulgite, Fly ash, zircon, coal gangue, yellow phosphorite, etc. It is technically feasible and economical to use non-metallic ores to produce white carbon black, which provides a new way for the deep processing and comprehensive utilization of non-metallic ores. Silica can also be prepared by calcination conversion of clay minerals. If water glass is first produced from non-metallic ores, and then the technology to produce silica from water glass is still the precipitation method.
(2) By-product recovery methods include: producing white carbon black from yellow phosphorus slag; producing white carbon black from sodium fluorosilicate; producing white carbon black from coal ash; one step from silicon tetrafluoride, a by-product of a phosphate fertilizer plant The hydrolysis method is used to prepare silica; the by-product SiO2 of NaF is used to prepare silica; the waste residue of water purifier is used to prepare silica; and the waste silica sol is used to prepare silica.