White carbon black is hydrated silicon dioxide obtained by precipitation from a solution of sodium silicate. The latter is liquid glass. Acid is used in the reaction process, and the next step is filtration, washing and further drying.
The described substance is the basis for obtaining fillers of polymer composite materials. The latter are the products of carbon black modification with organic modifiers. Sometimes the described material is also called boron nitride, which is obtained by burning pentaborane in nitrogen.
Description
The formula of the material is as follows: SiO. Depending on the quality and purpose indicators, soot can be represented by four brands:
- BS-30.
- BS-50.
- BS-100.
- BS-120.
Its characteristics comply with the requirements of GOST 18307-78. Each brand has its own particle size. In the first of the above, this parameter reaches 108 nm, while the fraction is equal to 77, if the material is determined by the brand BS-50. The particle size is reduced to 34 and 27 for the soot grades BS-100 and BS-120.
In the process of obtaining and processing can be used a certain amount of bound water. In this case, the form of bonding with SiO2 changes. It can be weakly adsorption or coordination.
Obtaining is carried out by a liquid-phase or gas-phase method. The first is the deposition of amorphous silicic acid. The solutions used are sodium silicates. As one of the participants in the chemical process are acidic reagents, for example, carbon dioxide or hydrochloric acid. This reaction takes place at a temperature of 70 to 90 ° C.
The resulting product goes through three stages until drying. Depending on which deposition conditions are used, alkaline, neutral or acidic soot is obtained. Then the dry product is ground. The degree of porosity and dispersion of the particles depends on the nature of the decomposition agent, which is a substance that decomposes silicate. During filtration and drying, 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 carbon black can be obtained by gas phase technology. It consists in the hydrolysis of silicon tetrachloride or tetrafluoride silicon by an explosive mixture. The temperature can reach 1,100 ° C. As a result, it is possible to obtain a pure, low-hydrated product, which is characterized by high dispersion. Moreover, its porosity is quite low. But this method is accompanied by large expenditures of energy, raw materials, high cost and the formation of a by-product in the form of HC1, which should be used rationally.
White carbon black can be obtained by another technique, which is a variation of the above technology. We are talking about the hydrolysis of silicon tetrachloride at low temperatures. This method is also called airgel. In addition to the above methods, a 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 disadvantages
White soot is silicon dioxide, which has some disadvantages. They significantly limit the area of use of the product in the rubber industry. The disadvantage is the density, which is much higher than that of carbon black. Rubber wettability is the worst. To improve this characteristic, the material undergoes carbophilization, which is also called hydrophobization and involves treatment with active substances adsorbed on the surface of silica by polar groups. The following are used as surfactants:
- alcohols;
- aliphatic or cycloaliphatic amines.
They contain more than 6 carbon atoms and silicone oil type compounds.
Application area
The use of white soot is quite common. It allows you to improve the mechanical characteristics of rubber made on the basis of siloxane rubbers. These materials increase fire resistance and heat resistance. Soot in terms of reinforcing properties is compared with carbon black and surpasses it in its effect on heat and oil resistance.
With the help of a substance, impressive glide resistance can be imparted. It is being introduced together with carbon black into the tread rubber of tires that are used in harsh conditions. Use in small quantities can reduce the wear resistance of the tread and increase the resistance of the elements of the pattern to chipping. Materials are recommended as an additive in carcass rubber to increase bond strength with cord.
Some physical and chemical indicators
Considering the composition of soot, you should understand that this material consists of sodium silicate and acid. The latter may be sulfuric. To date, several brands of this material are known, each of them has its own physicochemical properties. For example, BS-100 white carbon black has 86% silicon dioxide, as does BS-120. Whereas BS-50 contains silicon dioxide in a volume of 70%.
The mass fraction of moisture for the BS-100 is 6.5%. Losses in mass during calcination can vary from 5 to 7%. In terms of the calculation for iron oxide, the mass fraction can be 0.15%, as in the case of the mass fraction of aluminum in the calculation of aluminum oxide. Mass fraction of chlorides does not exceed 1%. Mass fraction of calcium and magnesium is 0.8% when converted to calcium oxide. Mass fraction of alkalinity is not standardized.
Finally
Material is packed in laminated four-layer bags with one layer of polyethylene. The maximum volume can be 20 kg. The substance is also sold in specialized disposable containers. Their weight reaches 400 kg. They transport material 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, 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 products from glass.