What exactly is silicone?

Classification of silicone

Silica gel, chemical formula mSiO2·nH2O. Transparent or milky white granular solid, with open porous structure, strong adsorption, can adsorb a variety of substances, these are our basic understanding of it. It can also be seen from the chemical formula that the main component of silica gel is SiO2, but in fact it has completely different properties from SiO2.
In daily life, the silica gel we often talk about does not all refer to this silica hydrate. If we want to classify silica gel products, it can be divided into two categories: inorganic silica gel and organic silica gel: mSiO2·nH2O belongs to inorganic silica gel. Silica gel, and those compounds that have at least one organic group directly connected to silicon atoms, or those compounds that connect organic functional groups to silicon atoms through oxygen, sulfur, nitrogen, etc. are called organosilicon compounds. Also directly called organic silica gel or silica gel. Let us interpret the relationship between inorganic silica gel, organic silica gel and silica by tracing the process flow of silica gel manufacturing.

The history of inorganic silicon

The synthetic route of silica gel (mSiO2·nH2O) was discovered and patented in 1918 by Walter A. Patrick, a professor of chemistry at Johns Hopkins University in the United States. It was first used in the First World War as a gas mask. absorbent. It is because of the advent of chemical weapons that silica gel has been prepared on a small scale. In 1920, the American Davidson Company carried out semi-industrial production of silica gel on this basis. Since then, the industrial line of silica gel has been on the right track. With the rapid rise of modern industry after World War II, the application field of silica gel has been further developed, and the search for a simpler, economical and environmentally friendly silica gel production route has naturally become an important part of industrial practice.
The production methods of various silica gels have also gradually developed, including the gas phase method using silane halides as raw materials; the chemical precipitation method using sodium silicate and inorganic acid as raw materials; and sols using silicates as raw materials— Gel method and microemulsion method. Since 1970, the sol-gel method has received extensive attention and has been widely used in the production of ultrafine powders, oxide coatings, fibers, and especially complex oxide materials that are difficult to prepare by traditional methods. The raw materials for preparing silica gel by sol-gel method are sodium silicate and sulfuric acid. Sodium silicate generates orthosilicic acid under acidic conditions. Because orthosilicic acid is unstable, it will condense intermolecularly into SiO2 particles with a three-dimensional network structure. , and the particle size and stacking method directly determine the pore structure of silica gel. The silica gel needs to be washed and dried to obtain silica gel. Therefore, the production process of silica gel generally goes through the three steps of gelation, washing and drying.

The relationship between inorganic silica gel and SiO2

The gelation process of silica gel is to make sodium silicate react with H2SO4 to generate SiO2 sol, and then emulsify it with a hydrophobic solvent to make it gel, and finally form a gel. The raw material sodium silicate used for gel is what we commonly call Paohua alkali, water glass, and the formation of this silicate is inseparable from SiO2. The synthesis of sodium silicate can be generated by the reaction of SiO2 (quartz sand) existing in nature with hot concentrated alkali solution or molten alkali. The difference between silica and silica can be seen through the synthesis route of silica gel. SiO2 can be regarded as the most source material for generating silica gel. The difference between SiO2 and silica gel can also be regarded as the difference between crystalline and amorphous substances. SiO2 is a crystalline substance and is the main material for making glass, quartz glass and water glass. Due to its crystal anisotropy, it has also become a light guide. Important raw materials for fibers and optical instruments. Silica gel can be regarded as an amorphous form of silica, so its application field is also very different from SiO2.

Application of Inorganic Silica Gel

In chemical applications, due to the high chemical stability, thermal stability and mechanical strength of silica gel, and its pore structure and specific surface area can be changed through different processes, so that it has excellent adsorption performance, so carbon dioxide in the pressure swing adsorption process. It has a very mature application in adsorption and denitrification of oil products. The surface of silica gel is covered with a large number of silyl hydroxyl groups, which is weak in acidity and has a certain adsorption selectivity. It has a certain catalytic effect on some organic synthesis reactions. Therefore, it has been widely used as a catalyst carrier. The transformation of catalysts from homogeneous to heterogeneous provides more possibilities for catalytic control in industrial production. In addition, the field of chromatographic analysis is also an important part of the application of silica gel. Silica gel as a chromatographic filler has excellent performance under different pressures and analysis systems of different specifications, such as gravity chromatography running on its own weight, medium and low pressure Flash, As well as high-performance liquid chromatography columns under high pressure conditions, and thin-layer chromatography for spot analysis, etc...
In addition to a large part of the application in the chemical industry, silica gel also has a place in the food industry. In 1961, Dr. Karl of Steinbek, Germany first discovered that silica gel can be used in beer brewing. Silica gel has a particularly strong adsorption capacity for sensitive proteins in beer, and can be used as a beer stabilizer without losing beer foam and taste. Under long-term storage, it acts as a stabilizer to improve the shelf life of beer. Other applications include agriculture, as soil moisturizing and animal feed additives. And in printing technology, with its good ink fixation, silica gel forms a specific microporous network to firmly fix the ink droplets, which can ensure the image quality and shorten the drying time. It is considered to be the most suitable for color inkjet paper. good paint.

Organic Silicone

After talking about inorganic silica gel, let's talk about organic silica gel. Silicone products mainly include silicone rubber, silicone resin and silicone oil. Silicone oil usually refers to a linear polysiloxane product that remains liquid at room temperature, and is often used in the electromechanical industry. Silicone rubber and silicone resin both refer to a polymer whose main chain is alternately composed of silicon and oxygen atoms. The silicon atom usually has two organic groups connected to it. Compared with silicone resin, silicone rubber has a greater degree of cross-linking. products, applications are also more than silicone. All kinds of silicone products we see every day: silicone bracelets, silicone coasters, cosmetic prostheses made of silicone, etc. are all made of silicone rubber. Because of their different molding processes (molding, extrusion, etc.) Rubber takes on different shapes. We are accustomed to referring to these silicone rubber products as silicone for short, so the main components of silicone referred to by different industries are also different.
In the development of organosilicon compounds, there are also many pioneers who have invested their efforts. The history of organic silicon compounds can be traced back to the 18th century. The compound tetraethylsilane (SiEt4), after that, many scholars have synthesized some organosilicon compounds by sealing tube or Grignard reaction, sodium condensation method, etc. Chemist Frederick Stanley Kipping of the University of Nottingham used the classical Grignard reaction to synthesize organochlorosilanes. The realization of the synthesis of these organosilicon compounds also provides more possibilities for the development of raw materials and technological processes for the manufacture of organosilica. In the 1930s, J.F.Hyde of Corning Glass Company in the United States explored the preparation of a heat-resistant glass fiber binder for electrical insulation. Finally, according to the research published by Kipping, he synthesized a high-heat-resistant composite material by using the format reaction. Silicone. This also brings the various properties of organosilicon polymers into people's field of vision, opening a new chapter for organosilicon compounds.
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