Fumed silica model
Fumed silica model
Silica is roughly divided into precipitated silica and fumed silica according to the production method. Fumed silica is a white amorphous flocculent translucent solid colloidal nanoparticle (particle size less than 100nm) under normal conditions, which is non-toxic and has a huge specific surface area. The fumed silica is all nano-silica, the product purity can reach 99%, and the particle size can reach 10~20nm, but the preparation process is complicated and expensive; the precipitation silica is divided into traditional precipitation silica and Special precipitation method white carbon black, the former refers to silica produced with sulfuric acid, hydrochloric acid, CO2 and water glass as the basic raw materials, the latter refers to the use of hypergravity technology, sol-gel method, chemical crystallization method, secondary crystallization Silica produced by special methods such as the reverse micellar microemulsion method or the reverse micellar microemulsion method. Precipitated silica is mainly used as reinforcing agent for natural rubber and synthetic rubber, toothpaste friction agent, etc. Fumed silica is mainly used as a reinforcing agent for silicone rubber, coatings and unsaturated resin thickeners, and ultra-fine silica gel and aerogel are mainly used as coating matting agents, thickening agents, plastic film opening agents, etc.
gas phase method
Mainly chemical vapor deposition (CAV) method, also known as pyrolysis method, dry method or combustion method. The raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which are reacted at high temperature. The reaction formula is:
SiCl4＋ 2H2＋ O2—>SiO2＋4HCl
Air and hydrogen are respectively pressurized, separated, cooled and dehydrated, dried on silica gel, filtered by dust removal, and sent to the synthesis hydrolysis furnace. After the silicon tetrachloride raw material is sent to the rectification tower for rectification, it is heated and evaporated in the evaporator, and is sent to the synthesis hydrolysis furnace with the dried and filtered air as the carrier. After silicon tetrachloride is gasified at high temperature (flame temperature 1000~1800°C), gas phase hydrolysis is carried out with a certain amount of hydrogen and oxygen (or air) at a high temperature of about 1800°C; the fumed silica particles generated at this time It is extremely fine and forms aerosol with gas, which is not easy to be captured, so it is first aggregated into larger particles in the agglomerator, then collected by the cyclone separator, and then sent to the deacidification furnace, and the fumed silica is purged with nitrogen-containing air When the pH value is 4 to 6, it is the finished product.