Under normal circumstances, fumed silica is white amorphous flocculent translucent solid colloidal nanoparticles (particle size less than 100nm), which is non-toxic and has a huge specific surface area (100 ~ 400 m2/g) (measured by the BET method of F-Sorb 2400 specific surface area instrument). The fumed silica is nano-silica, the purity of the product can reach 99%, and the particle size can reach 10~20nm, but the preparation process is complex and expensive.
1942 degussa applied for a patent for the preparation of ultrafine particle oxides by high-temperature hydrolysis, which formed a large-scale production process in the 1950s. After being registered as the trademark of AEROSIL, the silicon dioxide produced by this method has been spread all over the world.
Chemical vapor deposition (CAV) method, also known as pyrolysis, dry method or combustion method. Its raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which react at high temperature. The reaction formula is:
Sicl4+2h2+O2-> silica+hydrochloric acid
Air and hydrogen are respectively pressurized, separated, cooled, dehydrated, dried by silica gel, dedusted and filtered, and then sent to a synthetic hydrolysis furnace. The raw material silicon tetrachloride is sent to a rectification tower for rectification, then heated and evaporated in an evaporator, and then sent to a synthetic hydrolysis furnace with dried and filtered air as a carrier. Silicon tetrachloride is gasified at a high temperature (flame temperature 1000~ 1800℃), and then hydrolyzed with a certain amount of hydrogen and oxygen (or air) at a high temperature of 1800℃. At this time, the generated fumed silica particles are extremely fine, and form aerosol with gas, which is difficult to capture. Therefore, they are first aggregated into larger particles in the concentrator, then collected by the cyclone separator, and then sent to the deacidification furnace, and the gas-phase silica is purged with nitrogen-containing air until the PH value is 4 ~ 6, which is the finished product.
Evonik Degussa in Germany and cabot in the United States are in the leading position in gas phase production technology. Their production facilities are large in scale, highly automated, with low product cost, many brands (especially functional special products used in special fields) and good quality, such as uniform surface area distribution and low water content. China's Shenyang Chemical Co., Ltd. and Shanghai Chlor-Alkali Chemical Co., Ltd. also use gas phase production, but they are far behind foreign big companies in terms of production scale, production technology, automation degree and product brand. Guangzhou Jibisheng Technology Industry Co., Ltd. is the supplier of fumed silica with the largest output, the most complete brand and the most advanced technology in China, and is the drafting unit of the national standard GB20020-2005 for fumed silica.
Fumed silica (scientific name: fumed silica) is mainly composed of silica with molecular formula: SiO2. White fluffy powder, porous, non-toxic, tasteless and pollution-free, high temperature resistant. At the same time, its chemical inertness and special thixotropy obviously improve the tensile strength, tear resistance and wear resistance of rubber products, and the improved rubber strength is improved by dozens of times. Rheological and thixotropic control of liquid systems, adhesives, polymers, etc. , used as anti-settling, thickening and anti-sag additives, reinforced HCR and RTV-2K silicone rubber, used to adjust free flow and used as anti-caking agent to improve powder properties.
Fumed silica (scientific name: fumed silica) is one of the most important high-tech ultrafine inorganic new materials. Because of its small particle size, it has special properties such as large specific surface area, strong surface adsorption, high surface energy, high chemical purity, good dispersibility, heat resistance and resistance. It has excellent stability, reinforcement, thickening and thixotropy, has unique characteristics in many disciplines and fields, and plays an irreplaceable role. Nano-silica, commonly known as "ultrafine silica", is widely used in various industries as additives, catalyst carriers, petrochemicals, decolorants, matting agents, rubber reinforcing agents, plastic fillers, ink thickeners, metal soft polishes, insulating fillers, high-grade daily cosmetics fillers and spraying materials, medicine, environmental protection and other fields. It also provides a new material foundation and technical guarantee for the development of related industries.
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