SU1546421A1 - Method of obtaining alloyed silicon carbide - Google Patents

Abstract

The invention relates to a technology of carbides, namely, a method for producing polycrystalline silicon carbide of cubic modification doped with nitrogen, used for electrical resistivity for various purposes, for example, to create enhanced reliability of low-thrust engines used in spacecraft control and orientation systems. The aim of the invention is to obtain silicon carbide with an electrical resistance of 0.1-0.20 ohms. ^. cm, stable at high temperatures. This is ensured by the fact that in the process of producing silicon carbide by thermal decomposition of methyltrichlorosilane at 1300-1600 ° C in an atmosphere of hydrogen, the synthesis of silicon carbide is carried out simultaneously with its doping with nitrogen introduced in the form of propionitrile vapor, whose concentration in the gaseous medium is within 0.04-0.135 mg / l, and the molar ratio of it to methyltrichlorosilane is 1: 3000-10000. The resulting polycrystalline silicon carbide doped with nitrogen, has an electrical resistance of 0.1-0.2 ohms ^. cm with stability when heated to 900-1200 ° C in the range of up to 5%. 4 tab.

Description

The invention relates to a technology of carbides, namely, a method for producing polycrystalline silicon carbide of cubic modification doped with nitrogen, used for electrical resistivity for various purposes, for example, to create enhanced reliability of a small thrust engine used in spacecraft control and orientation systems.

The purpose of the invention is to obtain silicon carbide with a specific resistance of 0.1-0.2 OM CM, stable when heated to high temperatures.

Example 1. Pour 50 ml of pure methyltrn-chlorosilane into the first evaporator and set the temperature to 30 ° C. In the second evaporator, pour 10 ml of propionitrile and cool it to -60 ° C. Pure hydrogen is passed over the surface of methyltrichlorosilane at a rate of 12 l / h; and above the surface of propionitrile 1 l / h. The resulting vapor-gas mixture, in which the concentration of propionitrile is 0.04 mg / l, and the molar ratio of propionitrile to methyltrichlorosilane is 1: 10,000, enters the reactor.

The decomposition of the mixture occurs on the surface of a graphite rod of 6 mm and a length of 120 mm, heated to T 1430 i 10 ° C. The process continues until the formation of a layer of silicon carbide with a thickness of 1.25-1.30 mm. The resistivity of nitrogen-doped silicon carbide is 0.20 ohm-cm and retains this value at 1000 ° C.

Example 2, 50 ml of liquid methyl trichlorosilane are poured into the first evaporator and the temperature is set to 32 ° C. In the second evaporator pour 10 ml of propionitrile and cool it to a temperature of -55 ° C.

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up to T 1430 + 10 ° С; The process lasts 3 hours until a nitrogen-doped layer of silicon carbide with a thickness of 1.25-1.30 mm is formed. Its resistivity is 0.10 ohm-cm and it is at 1000 ° C.

PRI me R 4 (comparative). 50 ml of pure methyltrichlorosilane are poured into the first evaporator and the temperature in it is set at 30 ° C. In the second evaporator pour 10 ml of propionitrile and cool to -40 ° C. Pure hydrogen is passed over the surface of methyltrichlorosilane at a rate of 12 l / h, above the surface of propionitrile 2 l / h.

The vapor-gas mixture, in which the concentration of propionitrile, 0.4 mg / liter, and the molar ratio of propionitrile to methyltrichlorosilane is 1: 1000, goes to the reactor. The decomposition of the mixture occurs on the surface of a graphite rod with a diameter

Pure hydrogen is passed over a surface of 25 ° and a length of 120 mm heated by methyl trichlorosilane at a rate of 8 l / h; above the surface of propionitrile 1 l / h. The resulting vapor-gas mixture, in which the concentration of propionitrile is 0.089 mg / l and the molar ratio of 1: 4500 to methyltrichlorosilane, flows into the reactor. The decomposition of the mixture occurs on the surface of a graphite rod, with a diameter of 6 mm and a length of 120 mm at a temperature T of 1430 + 10 ° C.

The process lasts 3 hours before the formation of a layer of silicon carbide with a thickness of 1.25-1.30 mm. The resistivity of the product is 0.13 ohm-cm and the same at 1000 ° C.

Example 3. In the first evaporator, 50 ml of pure methyl t 1430 + 10 C are poured. The process lasts 3 hours until a layer of silicon carbide, 1.25-130 mm thick, is doped with nitrogen. Its resistivity is 0.04 ohm-cm and retains this value at 1000 C.

PRI me R 5 (comparative). 50 ml of methyltrichlorosilane is poured into the first evaporator, the temperature is set at 30 ° С. 10 ml of propionitrile is poured into the second evaporator and cooled to -78. Pure hydrogen is passed over the methyl trichlorosilane level at a rate of 12 l / h and above the surface pionitrile -1 l / h The resulting vapor-gas mixture, in which the concentration of propionitrile is 0.006 mg / l, and the molar ratio of prionitrile to methyltrichlorosilane is 1: 66000, enters the reactor. The mixture decomposes on the surface of the rod f 6 mm and length

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trichlorosilane and set the temperature in it, equal to 32 ° C. In the second evaporator pour 10 ml of propionitrile and cool it to a temperature of -50 ° C. Begin to pass pure hydrogen over the surface of methyltrichlorosilane at a rate of 8 l / h, above the surface of propionitrile 1 l / h. The resulting vapor-gas mixture, in which the concentration of propionitrile is 0.135 mg / l and the molar ratio of propionitrile to methyltrichlorosilane is 1: 3000, goes to the reactor. The decomposition of the mixture occurs on the surface of a graphite rod $ 6 mm and a length of 120 mm, heated

5 ° and 120 mm long, heated 0

up to T 1430 + 10 ° C. The process lasts 3 hours until the formation of a layer of silicon carbide doped with nitrogen, with a thickness of 1.25-130 mm. Its resistivity is 0.04 ohm-cm and retains this value at 1000 C.

PRI me R 5 (comparative). In the first evaporator pour 50 ml of pure methyltrichlorosilane, set the temperature in it, equal to 30 ° C. In the second evaporator pour 10 ml of propionitrile and cool it to. (Pure hydrogen is passed over the surface of methyltrichlorosilane at a rate of 12 l / h and above the surface of propionitrile -1 l / h. The vapor-gas mixture formed in which the concentration of propionitrile is 0.006 mg / l and the molar ratio of propionitrile to methyltrichlorosilane is 1: 66000 enters the reactor. The decomposition of the mixture occurs on the surface of the rod f 6 mm and length

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120 mm heated to 1430410 C. The process is continued for three hours until the formation of nitrogen-doped silicon carbide, 1.25-1.30 mm thick. The resistivity of the product is 0.45 ohm-cm and is maintained when the sample is heated to 1000 ° C.

The results are presented in table 1. The data in Table 1 show that the invention provides

silicon carbide with an electrical resistivity of 0.1-0.2 ohm-cm.

As follows from Table 2, the resistance value is essentially maintained when the sample is heated in the range of 860-1200 ° C.

The results of experiments on the reproducibility of p at 1000 ° С of ft-SiC samples grown at different periods of time are presented in Table 3.

Table A presents the data on the value of polycrystalline $ -SiC samples measured at room temperature (p2o) and in the temperature range of 900-1200 ° C in units of ohm "cm.

The invention thus makes it possible to obtain ft -SiC with a resistivity of 0.1-0.2 ohms "cm. The value of samples jb-SiC at high temperatures is stable.

Note. In all experiments, the temperature in the evaporator with methyl trichlorosilane

30 ° C or.

The value of sample З / S-SiC in the range of 860-1200 ° C.

1546421

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Claims (1)

Invention Formula The method of obtaining doped silicon carbide, including thermal decomposition of methyltrichlorosilane vapor in hydrogen atmosphere at 1300-1600 ° C and the deposition of polycrystalline silicon carbide on the surface in the presence of vapors of an organic nitrogen-containing compound, characterized in that in order to obtain silicon carbide with electrical resistance 0.1-0.2 Ω cm, stable at high temperatures, thermal decomposition and precipitation is carried out in the presence of propionitrile vapors at a concentration of hydrogen 0.04-0.135 mg / l molar ratio of methyl trichlorosilane equal to 1: 3000-10000. Table} Table 2 Table3 15464218 Table 11,10,500,450,36 20,460,210,20-0-0,20 30,300,130,13 - - - 0,13 40,200,110,100,10- - 0.10 - 0.10 50.050.040.04-0.04 - 0.04