SIMULATION OF COMPOSITE MATERIALS COMPOSITION PROCESSES WITH SILICON PYROCARBIDE

Abstract

The paper examines the peculiarities of obtaining and using materials of the C/SiC class in the form of carbon-silicon carbide structures in various fields of technology. The work is aimed at developing a mathematical model of the deposition of pyrolytic silicon carbide on the porous surface of carbon-carbon composite materials from a mixture of gases based on methane CH4 and SiCl4. Pyrolytic silicon carbide is formed as a result of thermal dissociation of organosilicon compounds of silicon tetrachloride (SiCl4) or methyltrichlorosilane (CH3SiH3). When compacting reinforced composite materials with pyrolytic silicon carbide, organosilicon compounds enter the reaction zone together with hydrogen or methane, which are both a reducing gas and a carrier gas. The deposition process of pure silicon carbide competes with the deposition of carbon and mixtures of silicon carbide with carbon. Therefore, one of the tasks of the work is to ensure such conditions for the flow of homogeneous-heterogeneous processes, which would realize the deposition of pure SiC. During the pyrolysis of methyltrichlorosilane in the temperature range of 800-1000 °C, highdensity SiC with a purple hue is formed. As the pyrolysis temperature of methyltrichlorosilane increases, the color of the coating changes to gray. The size of the crystals is about 22 nm. The yield of SiC is in the range of 25-35%. The maximum yield of silicon carbide is observed in the temperature range of 1250 – 1500 °C. Increasing the temperature to 1600 °C does not significantly affect the yield of SiC. During the research, it was established that the most relevant is chemical-thermal deposition from a gaseous mixture of methane and silicon tetrachloride, during which stoichiometric deposition of SiC is achieved without damage to carbon fibers in carbonized carbon plastics with a carbidized matrix. The paper defines the theoretical equilibrium constants of representations of thermochemical reactions. Formulas for evaluating the productivity of a thermochemical reactor under the conditions of a quasi-equilibrium regime of silicon carbide deposition have been determined.