RU2240979C2 - Silicon carbide production process - Google Patents

Abstract

FIELD: abrasive materials.

SUBSTANCE: process comprises high-temperature heating of silicon and carbon-containing raw material, heating being carried out under nitrogen atmosphere at pressure 0.049-0.13 MPa or in nitrogen flow at velocity 0.5-3.3 L/h.

EFFECT: increased purity and yield of product.

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Description

The invention relates to the production of abrasive materials and can be used to obtain silicon carbide.

A known method of producing silicon carbide by carbothermic reduction in accordance with the equation SiO ₂ + 3C = SiC + 2CO (-1120 cal). The process of silicon carbide formation consists in the interaction of silicon oxide and carbon at a temperature of 2200-2300 ° С (I.S. Kainarsky, E.V. Degtereva "Carborundum refractories", Metallurgizdat, 1963, pp. 9-14).

The disadvantages of this method are the low purity and low yield of the final product, which are the result of the following processes: firstly, silicon monoxide SiO formed as an intermediate product in the process of carbothermic reduction does not have time to completely react and is carried away in significant amounts with furnace gases, causing silicon losses and polluting the environment; secondly, in the temperature range 1800–2000 ° С, silicon carbide decomposes into silicon and carbon, which also increases the loss of silicon carbide. Thus, technical silicon carbide is obtained, contaminated with impurities of carbon, silicon oxide (quartz, crystallite, etc.) with a yield of 15-20%.

A known method of producing silicon carbide by electric heating of natural rock - shungite containing silicon oxide and carbon, at 1600-1800 ° C in a vacuum furnace with a residual pressure in its working space of 0.25-1.3 kPa (RF Patent No. 2163563, IPC C 01 B 31/36, 2001).

The disadvantage of this method is the low yield of the final product (about 30%), which is due to the fact that during the heating of schungite while continuously removing the released carbon monoxide from the furnace working space, silicon monoxide is also removed with it, which inevitably leads to silicon losses.

Thus, the authors were faced with the task of developing a method for producing silicon carbide, which would ensure a high yield of the final product along with its high purity.

The problem is solved in the proposed method for producing silicon carbide, including high-temperature heating of silicon and carbon-containing raw materials, in which heating is carried out in a nitrogen atmosphere at a pressure of 0.049-0.13 M Pa or a stream of nitrogen at a speed of 0.5-3.3 l / h.

Currently, from the patent and scientific literature there is no known method for producing silicon carbide, in which high-temperature heating is carried out in an atmosphere or a stream of nitrogen in the claimed pressure or speed limits, respectively.

In the proposed method, either a mixture of silicon-containing raw materials and carbon, for example, a mixture of quartz rock and soot, or industrial waste, such as a mixture of ash and carbon (soot, etc.), or silicon-carbon-containing raw materials, for example shungite, can be used as feedstock. The process in the atmosphere or in a stream of nitrogen almost completely eliminates the loss of silicon due to the formation of silicon monoxide, since the formation of nitrogen-containing silicon compounds such as silicon oxynitrides (Si ₂ ON ₂ ), which are non-volatile intermediate products of the interaction of silicon oxide and carbon in a nitrogen environment, which can significantly reduce the loss of silicon. At the same time, heating at a pressure lower than 0.049 MPa or a nitrogen feed rate of less than 0.5 l / h leads to the appearance of intermediate silicon compounds, which further pollute the final product. At the same time, heating at a pressure higher than 0.13 MPa or a nitrogen feed rate of more than 3.3 l / h leads to unjustified overspending of nitrogen and electricity without improving the performance of the final product.

The proposed method can be implemented as follows. The feedstock is a mixture of silicon-containing raw materials and carbon, such as a mixture of quartz rock and soot, or silicon-carbon-containing raw materials, such as shungite, are thoroughly mixed and loaded into a heating apparatus, such as a TVB-4 furnace or a continuous electric furnace through which nitrogen gas is supplied in an amount necessary to create a pressure in the working space of the furnace equal to 0.049-0.13 MPa, or if the furnace is continuous, at a speed of 0.5-3.3 l / h. The initial mixture is used in bulk or tabletted and heated at a temperature of 1600-1900 ° C for 3-8 hours. Then the resulting product is cooled and analyzed by chemical and x-ray phase analysis methods.

The proposed method is illustrated by the following examples.

Example 1. Take a mixture of the following composition (wt.%): SiO ₂ - 62.5; C (soot) - 37.5. The mixture is thoroughly mixed and the resulting powder mixture is placed in a graphite-tube furnace, into the working space of which nitrogen is supplied to create a pressure of 0.049 MPa. The mixture is heated at a temperature of 1600 ° C for 8 hours. The resulting product is cooled. According to the data of chemical and x-ray phase analyzes, a single-phase product is obtained: pure silicon carbide SiC with lattice parameters α = 0.4355 Nm. There are no impurities.

Example 2. Take a mixture of the following composition (wt.%): SiO ₂ - 62.5; C (soot) - 37.5. The mixture is thoroughly mixed and the resulting powder mixture is placed in a graphite tube furnace, into the working space of which nitrogen is supplied to create a pressure of 0.13 MPa. The mixture is heated at a temperature of 1900 ° C for 3 hours. The resulting product is cooled. According to chemical and x-ray phase analysis, a single-phase product is obtained: pure silicon carbide SiC with lattice parameters α = 0.4354 Nm. There are no impurities.

Example 3. Take a mixture of the following composition (wt.%): SiO ₂ - 62.5; C (soot) - 37.5. The mixture is thoroughly mixed and the resulting powder mixture is placed in a continuous furnace, the working space of which is purged with nitrogen at a rate of 0.5 l / h. The mixture is heated at a temperature of 1600 ° C for 8 hours. The resulting product is cooled. According to chemical and x-ray phase analysis, a single-phase product is obtained: pure silicon carbide SiC with lattice parameters α = 0.4353 Nm. There are no impurities.

Example 4. Take a mixture of the following composition (wt.%): SiO ₂ - 62.5; C (soot) - 37.5. The mixture is thoroughly mixed and the resulting powder mixture is placed in a continuous furnace, the working space of which is purged with nitrogen at a rate of 3.3 l / h. The mixture is heated at a temperature of 1900 ° C for 3 hours. The resulting product is cooled. According to chemical and x-ray phase analysis, a single-phase product is obtained: pure silicon carbide SiC with lattice parameters α = 0.4354 Nm. There are no impurities.

The proposed method allows to increase the yield of silicon carbide. So when heating the starting mixture at a temperature of 1600 ° C in a nitrogen atmosphere in accordance with the proposed method, the weight percent of silicon compounds is 39.75%, and when heating the starting mixture at a temperature of 1600 ° C in vacuum in accordance with the known method, the weight percent of silicon compounds is 20.83%. When the initial mixture is heated at a temperature of 1700 ° C in a nitrogen atmosphere in accordance with the proposed method or vacuum in accordance with the known method, the weight percent of silicon compounds is 63.35 or 23.01, respectively.

Thus, the proposed method for producing silicon carbide can improve the purity and yield of the final product.

Claims (1)

A method of producing silicon carbide, including high-temperature heating of silicon and carbon-containing raw materials, characterized in that the heating is carried out in a nitrogen atmosphere at a pressure of 0.049 ÷ 0.13 MPa or in a stream of nitrogen at a rate of 0.5 ÷ 3.3 l / h.