White soot is a hydrated silica obtained by precipitation from a sodium silicate solution. The latter is liquid glass. The reaction process uses an acid, and the next step is filtration, washing and further drying.
The described substance is the basis for obtaining fillers for polymer composite materials. The latter are products of the modification of white carbon with organic modifiers. Sometimes the described material is also called boron nitride, which is obtained by burning pentaborane in nitrogen.
Description
The material formula is as follows: SiO. Depending on the quality indicators and purpose, soot can be represented by four grades:
- BS-30.
- BS-50.
- BS-100.
- BS-120.
Its characteristics meet the requirements of GOST 18307-78. Each brand has its own particle size. For the first of those mentioned above, this parameter reaches 108 nm, while the fraction is 77 if the material is determined by the BS-50 brand. The particle size is reduced to 34 and 27 forcarbon black grades BS-100 and BS-120.
A certain amount of bound water can be used in the process of obtaining and processing. In this case, the form of the bond with SiO2 changes. It can be weakly adsorptive or coordinating.
Obtaining is carried out by the liquid-phase or gas-phase method. The first is the precipitation of amorphous silicic acid. The solutions used are sodium silicates. Acid reagents, for example, carbon dioxide or hydrochloric acid, act as one of the participants in the chemical process. The reaction takes place at a temperature of 70 to 90 °C.
The resulting product goes through three stages before drying. Depending on which precipitation conditions are used, alkaline, neutral, or acidic carbon blacks are obtained. The dry product is then ground. The degree of porosity and dispersion of particles depends on the nature of the decomposition agent, which is a substance that decomposes the silicate. During filtration and drying, the particles can aggregate during the condensation of polysilicic acids. In this regard, the conditions of these stages are strictly regulated.
Description of the gas-phase method
White soot can be obtained in the process of gas-phase technology. It consists in the hydrolysis of silicon tetrachloride or tetrafluoride silicon with an explosive mixture. The temperature can reach up to 1,100 °C. As a result, it is possible to obtain a pure low-hydrated product, which is characterized by high dispersion. However, its porosity is quite low. But this method is accompanied by large expenditures of energy, raw materials, high cost andthe formation of a by-product in the form of HC1, which should be used rationally.
White soot can be obtained by another technique, which is a variation of the technology described above. We are talking about the hydrolysis of silicon tetrachloride at low temperatures. This method is also called airgel. In addition to the methods described above, the technology of silicate and silicate-oil rubbers has been developed. The process uses cold deposition of silicon dioxide. The reaction involves the coagulation of rubber.
Some flaws
White soot is silicon dioxide, which has some disadvantages. They significantly limit the scope of the product in the rubber industry. The disadvantage is the density, which is much greater than that of carbon black. Wetting by rubbers is the worst. To improve this characteristic, the material is subjected to carbofilization, which is also called hydrophobization and involves treatment with active substances adsorbed on the silica surface by polar groups. Used as surfactants:
- alcohols;
- aliphatic or cycloaliphatic amines.
They contain over 6 carbons and silicone oil-like compounds.
Scope of application
The use of white carbon is quite common. It improves the mechanical characteristics of rubber made on the basis of silicone rubbers. These materials have increasedfire resistance and heat resistance. Carbon black is comparable in reinforcing properties to carbon black and surpasses it in its effect on heat and oil resistance.
With the help of a substance, impressive slip resistance can be given. It is being introduced together with carbon black into the tread rubber of tires that are operated in difficult conditions. The use in small quantities reduces the wear resistance of the tread and increases the resistance of the elements of the pattern to chipping. Materials are recommended as an additive in carcass rubber to increase the strength of the connection with the cord.
Some physical and chemical indicators
When considering the composition of white carbon, you should understand that this material is composed of sodium silicate and acid. The latter may be chamois. To date, several grades of this material are known, each of them has its own physical and chemical properties. For example, white carbon black BS-100 has 86% silicon dioxide, like the brand BS-120. Whereas BS-50 contains silicon dioxide in the amount of 70%.
Mass fraction of moisture for BS-100 is 6.5%. Weight loss on ignition can vary from 5 to 7%. In terms of iron oxide, the mass fraction can be 0.15%, as is the case with the mass fraction of aluminum when converted to aluminum oxide. The mass fraction of chlorides does not exceed 1%. The mass fraction of calcium and magnesium is 0.8% when converted to calcium oxide. The mass fraction of alkalinity is not standardized.
In conclusion
The material is packed in laminated four-layer bags with onea layer of polyethylene. The maximum volume can be 20 kg. The substance is also sold in specialized disposable containers. Their weight reaches 400 kg. Material is transported by any means of transport. Guaranteed shelf life does not exceed 6 months from the date of manufacture.
The material consists of solid colorless crystals, the melting point of which is very high. The substance does not dissolve in water, and when heated, it begins to interact with alkalis and oxides. Silicon dioxide is used as a component in the manufacture of ceramics, as well as in the production of concrete glass products.
