A method of obtaining a carbon-containing coatings

 

(57) Abstract:

The method can be used to obtain the composite materials used for tooling in producing highly pure elements and substances. The source components are cleaned and fed into the reactor, the gas-vapor mixture of compounds of carbon and hydrogen. Decompose the mixture on the heated surface. Remove the formed degradation products and unreacted substances. Spend their separation by fractional condensation and recirculation of the initial components. While the coatings are produced by the sequential alternation of deposition of layers of pyrocarbon and silicon carbide. The deposition is carried out on the surface of the items in the same apparatus at the same temperature of the deposition surface. Products obtained by this method have high technical performance and quality of coverage, including high density and purity. 4 C.p. f-crystals, 3 tables.

The invention relates to the technology of wear-resistant, high-temperature carbon composite materials by deposition from the gas phase, is used as the tooling in producing highly pure elements and s by thermal decomposition of carbon-containing chemical compounds on heated surfaces, for example in the manufacture of heaters and components of thermal units in the plant production of silicon single crystals and other equipment requiring low background level of impurities in the manufacture of heating elements, graphite based General purpose, able to work in inert and oxidative atmosphere at temperatures up to 1600oWith; in the manufacture of container elements for transportation, storage and isolation of various substances, including nuclear waste production.

The use of products with carbon coatings as tooling in obtaining monocrystalline silicon opens up new possibilities for the creation of modern element base of micro - and power electronics and new energy systems based on it.

A method of obtaining layers of pyrocarbon deposition from the gas phase on a heated surface [see U.S. Pat. 2149215, With 23 16/26, the Russian Federation, 2000], in which a deposition process is conducted at atmospheric pressure and a temperature of 950-1350oWith gas mixture of carbon tetrachloride and hydrogen at a molar ratio of carbon tetrachloride to hydrogen is 1:(5-50). The method allows to obtain a dense waytodeal.com deposition process, high energy consumption and pollution by the products of reaction.

Known method of applying a coating on the carbon fiber, including heating and extract them for 5-180 with in the melt with carbidopa element at a temperature of 1000o[See U.S. Pat. 685720, WITH 23 16/26, USSR, 1979] . For hardening of the fibres the method involves a preliminary deposition on them pyrocarbon layer thickness of 0.4 μm.

The disadvantages of the method of deposition of silicon carbide from the melt are low yield, due to the necessity of removal from the surface of the products obtained unreacted carbidopa metal and metal-solvent; strict limitations on the shape and size of the products obtained, i.e. the method can be applied only to fibrous materials; the ability to obtain extremely thin layers of pyrocarbon and silicon carbide, as well as the low productivity of the deposition process from the melt, high energy consumption and pollution by the products of reaction.

Closest to the claimed invention is a method of obtaining a layer of silicon carbide deposition from the gas phase using recircula is eltriclirelm and hydrogen in the reactor, its decomposition on the heated substrate with the formation of silicon carbide and decomposition products, while the gas-vapor mixture is served with a density of 3-4 g/cm2h with a molar ratio of methyltrichlorosilane and hydrogen equal to 1: (1-3), heated to 1200-1250oWith the substrate, the decomposition products away from the reactor, separated into gas and liquid phase condensation, the liquid phase by gravity send rectification, separate methyltrichlorosilane and return to the reactor, the condensation of the liquid phase is carried out at a temperature of -70 - -75oWith or at a temperature of from 0oC to -120oWith, sequentially selecting from the liquid phase of methyltrichlorosilane, other organochlorosilane after rectification unite with methyltrichlorosilane and return in the process, the gas phase obtained after condensation, containing hydrogen chloride, methane, hydrogen, cooled to a temperature of -185 - -196oWith the separation of hydrogen chloride and methane in the form of a solid residue and the hydrogen komprimiert and return in the process.

The disadvantage of this method is the high sensitivity of the deposited silicon carbide to the quality of the carbon substrate materials. Mechanical incompatibility characteristics of the materials deposited sdit to the appearance of stresses in the resulting products, what affects the quality of the coatings (lower temperature limit of operation, reduced resistance to oxidation, the increase in gas permeability). Get a high-quality layer of silicon carbide is only possible when using as a substrate of graphite materials with a high degree of perfection of the crystal structure. The high cost of these materials framework limits the applicability of the method, making inappropriate usage of it by getting products General purpose.

The technical result of the claimed invention is the possibility of obtaining products with high technical performance, while maintaining high productivity, reduce energy consumption, environmental cleanliness and waste products of the process. An additional advantage of obtaining products on the basis of a composite material pyrocarbon - silicon carbide is the possibility of crystallization of silicon carbide using a wide range of materials and surface deposition.

In addition, the obtained composite carbon coating of pyrocarbon and silicon carbide layers of the nature of the (impurity content of not more than 10-3-10-4wt. %), high degree of ordering of the crystal structure (pyrocarbon), the stoichiometric composition and inclusions of the second phase (silicon carbide).

The technical result is achieved in that in a method of producing carbon coatings by deposition from the gas phase on a heated surface, including the treatment of the source components, the feed gas mixture of compounds of carbon and hydrogen in the reactor, the decomposition of the mixture on the heated surface, removing the formed degradation products and unreacted substances, their separation by fractional condensation and recirculation of the components according to the invention the coatings are produced by the sequential alternation of deposition of layers of pyrocarbon and silicon carbide, the deposition is carried out on the surface of the items in the same apparatus at the same temperature of the deposition surface, and the deposition is carried out at a temperature of 900-1350oWith the first layer on a substrate precipitated pyrocarbon, the total number of alternating layers is not less than 3 and the substrate using the graphite materials with a degree of perfection of the crystal structure from 10 to 100%, quartz, Santi - carbon tetrachloride (CCl4), methyltrichlorosilane (MTHS) and hydrogen is subjected to fine purification. CCl4and MTHS purified by rectification with selection medium fractions, a light fraction and a bottom residue is removed from the process. The hydrogen is purified by means of sorption and palladium on the filter. In the first stage, the original gas-vapor mixture of carbon tetrachloride with hydrogen produced by passing a carrier gas (hydrogen) through the evaporator. The molar ratio of carbon tetrachloride to hydrogen fed to the reactor gas mixture support equal to 1:(5-50), the temperature of the substrate 950-1350oC. Preliminary deep cleansing component gas mixture required to obtain pyrocarbon high quality - thick porous precipitation, high performance process and rate of deposition of pyrocarbon to 0.2 mm/h and more. In the second stage purified MTHS and hydrogen are mixed in the evaporator-barbaterom in a molar ratio MTHS: N2=1: (1-3) and a couple of the mixture fed into the reactor. The temperature of the substrate is the same as in the first stage, 950-1350oC. These operations provide in addition to the high quality of the obtained silicon carbide and high productivity of the process, the speed of Asadi. Composite coating of a combination of layers of pyrocarbon and silicon carbide obtained in a single technological cycle, contributes to the quality of coverage by obtaining benporath layers, provides an improvement of the conditions of crystallization as pyrocarbon and silicon carbide and the possibility of compensation of the influence of the mismatch of thermal expansion coefficients of the substrate and deposited layers as a whole. The possibility of combining technological processes of deposition of carbonaceous coating of pyrocarbon and silicon carbide from the gas phase in a single technological cycle due to their similarity with the physico-chemical point of view and from the point of view of instrumentation. The same temperature deposition of pyrocarbon and silicon carbide is a new feature, since it makes the process in a single technological cycle without changing thermal characteristics of the processes of deposition of two different chemical composition and properties of the layers of pyrocarbon and silicon carbide, and a new set of techniques improves the characteristics of the composite coating in comparison with the known. The claimed method has a high environmental clean the IDA silicon is directed to condensation, followed by distillation and recycling of all components of the CBC. Return components ASG increases the technical and economic performance of the process.

Substantiation of the parameters.

During the process of deposition of pyrocarbon and silicon carbide at a temperature below 950oWith the formation of pyrocarbon is not observed, the residue has a carbon structure, in addition, there has been a violation of the stoichiometry of the precipitate of silicon carbide and the formation of second phases. Heating the substrate to temperatures in excess of 1350oC is also undesirable due to the decrease of the degree of ordering of the structure of pyrocarbon sediment and its density, as well as the emergence of "friends" on the surface of the sediment silicon carbide, and decrease the rate of deposition and pyrocarbon and silicon carbide, and increase the intensity of the process.

The method is illustrated by an example.

Example. To obtain carbon coatings using a vertical flow reactor. As the substrate using a porous graphite (HMP) or carbon fiber and fabric. Hydrogen is subjected to pre-treatment by means of sorption and palladium on the filter. Carbon tetrachloride and MTHS, purified by distillation, is placed in the evaporator. Using system timing formicoidea ratio of components of the SGS. The obtained gas mixture fed into the reactor, where the process of thermal decomposition on the heated substrate with a serial receiving layers of pyrocarbon and silicon carbide, respectively, and gaseous decomposition products. The deposition is carried out in four stages. The parameters of the process are presented in tables.

Composite layer obtained by alternating layers of pyrocarbon and silicon carbide, can reduce the surface porosity of the graphite substrate, and to reduce the magnitude of thermal stresses in the sample caused by the difference of coefficients of thermal expansion of the substrate and deposited layers. Conducted thermosphere showed that the obtained coating according to the invention, in 2-2,5 times longer than the life of the samples in inert and oxidative atmosphere compared to coatings only pyrocarbon and silicon carbide. The amount of cycles for samples with carbon composite coating was 400%, whereas for samples coated only pyrocarbon and silicon carbide standard cycles - 250 units

1. The method of obtaining carbon coatings by deposition from the gas phase on negritude in the reactor, the decomposition of the mixture on the heated surface, removing the formed degradation products and unreacted substances, their separation by fractional condensation and recirculation of the initial components, characterized in that the coatings are produced by the sequential alternation of deposition of layers of pyrocarbon and silicon carbide, the deposition is carried out on the surface of the items in the same apparatus at the same temperature of the deposition surface.

2. The method according to p. 1, characterized in that the deposition of layers of pyrocarbon and silicon carbide is carried out at 900-1350oC.

3. The method according to p. 1 or 2, characterized in that the first layer on a substrate precipitated pyrocarbon.

4. The method according to any of paragraphs.1-3, characterized in that the total number of alternating layers is not less than 3.

5. The method according to any of paragraphs.1-4, characterized in that the substrate using a graphite material with a degree of perfection of the crystal structure from 10 to 100%: quartz, sapphire, refractory metals.

 

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