RU2339574C1 - Method of obtaining highly- dispersible silicon carbide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: highly- dispersible silicon carbide is obtained by precipitation from gas phase by thermal destruction of carbosylane at temperature 600-800°C. As carbosylane saturated perclorcarbosylane selected from line Si₄CCl₁₂, Si₆C₂Cl₁₆, Si₈C₃Cl₂₀, C₄Si₁₀Cl₂₄, Si₁₂C₅Cl₂₈ is used. Claimed method allows obtaining silicon carbide with crystallite size not more than 5 nm.

EFFECT: high degree of initial compounds conversion without formation of corrosion and highly explosive compounds.

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Description

The invention relates to inorganic chemistry, specifically to the production of amorphous and polycrystalline silicon carbide by thermal degradation of compounds containing only carbon, silicon and chlorine, and can be used to obtain powders, coatings and bulk matrices.

A known method of producing coatings of silicon carbide, which consists in passing a mixture of silane (SiH ₄ ) and various hydrocarbons, for example With ₃ H ₈ in a reducing atmosphere of hydrogen over a substrate heated to temperatures above 1500 ° C [US patent 3520740, 1970]. The thermal interaction of silane and carbon-containing components leads to the deposition of silicon carbide from the gas phase in the form of a polycrystalline coating. The main disadvantages of this method are the high synthesis temperature and the low degree of conversion of the initial volatile components. In addition, all three starting products are explosive, and the toxicity of volatile silane makes the technology very difficult for industrial applications.

A known method of producing silicon carbide coatings for microelectronics by deposition from the gas phase containing methyltrichlorosilane and hydrogen (patent FR 2403296, 1979). The substrate of polycrystalline silicon carbide at a temperature of 1000-1700 ° C is blown with a mixture of H ₂ and CH ₃ SiCl ₃ . As a result of thermal decomposition of methyltrichlorosilane, β-SiC particles of ~ 600 nm in size are deposited on the substrate. The disadvantages of this method are: high specific energy consumption; the formation of chemically active and corrosive products (HCl, Cl ₂ , SiH _x Cl _y , etc.); low specific surface area of the resulting particles (3.3 m ² / g).

The closest analogue of the claimed invention is a method for producing a composite material, including the deposition of silicon carbide from the gas phase by thermal destruction of carbosilane, namely methylsilane (CH ₃ SiH ₃ ), in an inert gas atmosphere (patent RU 2130509, 1999). The process is conducted at a temperature of 600-800 ° C, resulting in the formation of crystalline β-SiC. Since the main by-product of the synthesis is hydrogen, the process is carried out at low concentrations of methylsilane in an inert carrier gas, which significantly increases the synthesis time. In addition, chemical stability and high volatility of methylsilane lead to a low degree of conversion (maximum 60% at 750 ° C) and, as a consequence, to the complexity of the process.

The invention is directed to the development of a method of producing silicon carbide with a crystallite size of not more than 5 nm, with a high degree of conversion and yield of the target product at temperatures of 600-800 ° C, without the formation of corrosive and explosive compounds, which allows the use of silicon carbide in the form of powders, coatings and volumetric matrices of composite materials.

The technical result is achieved by the fact that the proposed method of producing highly dispersed silicon carbide at a temperature of 600-800 ° C, including the deposition of silicon carbide from the gas phase by thermal destruction of carbosilane, according to the invention, saturated perchlorocarbosilane selected from the series Si ₄ CCl ₁₂ , Si is used as carbosilane ₆ C ₂ Cl ₁₆ , Si ₈ C ₃ Cl ₂₀ , C ₄ Si ₁₀ Cl ₂₄ , Si ₁₂ C ₅ Cl ₂₈ .

The claimed method is characterized in that said perchlorocarbosilanes at temperatures of 600-800 ° C are volatile, easily decomposable compounds and undergo complete destruction with the formation of highly dispersed silicon carbide in the condensed phase and chemically stable over a wide temperature range of silicon tetrachloride (SiCl ₄ ) in the gas phase.

The table below shows the dependence of the molar ratio of thermal degradation products on the stoichiometric composition of the starting perchlorocarbosilanes.

Table. Gross formula Connection Name The molar volume of thermolysis products target product SiC by-product of SiCl ₄ CSi ₄ Cl ₁₂ Tetrakis (trichlorosilyl) methane one one C ₂ Si ₆ Cl ₁₆ 1,1,3,3-tetrachloro-2,2,4,4-tetrakis (trichlorosilyl) -1,3-disilacyclobutane 2 four C ₃ Si ₈ Cl ₂₀ 1,1,3,3,5,5,7,7-octachloro-2,2,6,6-tetrakis (trichlorosilyl) -1,3,5,7-tetrasilaspiro (3.3) heptane 3 5 C ₄ Si ₁₀ Cl ₂₄ 1,1,3,3,5,5,7,7,9,9,9,10,10-dodecachloro-2,2,8,8-tetrakis (trichlorosilyl) -1,3,5,7,9,10 hexasiladispiro [3,13,1] dean four 6 C ₅ Si ₁₂ Cl ₂₈ 1,3,5,7,9,11,12,13-octasilatraspiro [3.1.1.3.1.1] tridecane 5 7

Thermal destruction of perchlorocarbosilanes at a temperature of 600-700 ° C leads to the formation of amorphous silicon carbide, which was established by x-ray phase analysis. At temperatures of 700-800 ° C, silicon carbide precipitates in polycrystalline form. According to X-ray diffraction data, the crystal structure corresponds to cubic modification (β-SiC) with an average crystallite size of about 3 nm, which corresponds to a specific surface area of the polycrystalline coating of at least 400 m ² / g.

The achievement of the claimed technical result is confirmed by the following examples.

Example 1

All claimed perchlorocarbosilanes obtained according to the method of [Rich. Muller und H. Beyer, Chem. Ber. v.92, p.1018, 1959] by passing vapor of carbon tetrachloride over a powder of silicon and copper at a temperature of 300-400 ° C, cleaned of low boiling fractions (SiCl ₄ , CCl ₄ , Si ₂ Cl ₆ , C ₂ Cl ₄ , SiCl ₃ CCl ₃ ). Then, any of these compounds is sublimated in an argon atmosphere and subjected to thermal degradation at atmospheric pressure and a temperature of 650 ° C in a tubular quartz reactor. The condensed products are deposited on the inner surface of the quartz reactor in two thermal zones: amorphous light gray silicon carbide is deposited directly in the reaction zone, and amorphous carbon is deposited in the cold part. The decomposition of perchlorocarbosilanes at this temperature proceeds completely with a degree of conversion of 100% with the formation of only SiCl ₄ in the gas phase, which was established by chemical analysis of solid condensate on the walls of the reactor. The resulting material according to x-ray diffraction data is a crystallite with an average size of less than 1 nm.

Example 2

Thermal destruction of any of these perchlorocarbosilanes is carried out in a tubular quartz reactor at a temperature of 750 ° C in an argon atmosphere, ceteris paribus in Example 1. Precipitation of condensed products also occurs in two thermal zones of the reactor: gray silicon carbide precipitates in the reaction zone, in the cold part - amorphous carbon. X-ray diffraction revealed that the obtained silicon carbide of cubic modification with an average crystallite size of ~ 3 nm. The decomposition of perchlorocarbosilanes at a given temperature also proceeds completely with the formation of only SiCl ₄ in the gas phase, which was established by chemical analysis.

The claimed method has the following advantages:

- the use of perchlorocarbosilanes allows to achieve complete conversion of the starting compounds to obtain highly dispersed silicon carbide by chemical vapor deposition at a sufficiently low synthesis temperature;

- in the synthesis process does not form chemically active, explosive and corrosive products from the series: HCl, Cl ₂ , SiH _x Cl _x , H ₂ , SEC, etc .;

- the size and structure of the deposited crystallites of silicon carbide varies in temperature from a size of less than 1 nm (amorphous form) to ~ 3 nm (polycrystalline form of β-SiC).

Claims (1)

A method of producing highly dispersed silicon carbide at a temperature of 600-800 ° C, including the deposition of silicon carbide from the gas phase by thermal degradation of carbosilane, characterized in that saturated perchlorocarbosilane selected from the range of Si ₄ CCl ₁₂ , Si ₆ C ₂ Cl _{16 is} used as carbosilane , Si ₈ C ₃ Cl ₂₀ , C ₄ Si ₁₀ Cl ₂₄ , Si ₁₂ C ₅ Cl ₂₈ .