The thermodynamic modeling of the phases quantitative relations in the process of the carbothermic -SiC synthesis

The unique properties of silicon carbide in the form of ultrafine powders make it widely used as various fillers and alloys modifiers, ceramic and metal-ceramic materials, protective coatings for various purposes. Currently, almost all ultrafine silicon carbide powder is obtained from α-SiC modification, synthesized by Acheson multistage technology. The current trend in the development of SiC synthesis technologies is aimed to obtain the silicon carbide powders from 3C-SiC(β) modification, which has more attractive characteristics. This aspect determines the research relevance, focused on the development and testing of effective production technologies of ultrafine powders from 3C-SiC(β) silicon carbide modification. In this work, the thermodynamic modeling of phase equilibria are presented for Si-O-C system with C-SiO2 section in the temperature range 1400-1900 °C at different ratios of carbon and silicon oxide. For this calculations, the possible formation of gas phase and liquid silicon, carbon and silicon oxide in the system was taken into account. The ratios of main components, as well as the gases volume and composition formed during the synthesis are theoretically determined. In accordance to phase diagrams, the formation of gaseous interaction products is observed only at temperatures above 1514 °C. Carbon monoxide is determined as the main component of the gas mixture formed during the synthesis in the reaction zone. Other components of the gas mixture include silicon monoxide and carbon dioxide. The content of other components, among which silicon-containing ones prevail, is insignificant. With the ratio C/(SiO2+C) ≥ 0.37 in the gas phase, there is an abrupt decrease in the content of all impurity gases. The obtained data provide a theoretical basis for the selection of optimal conditions in order to form of a stable autonomous protective atmosphere during the carbothermal synthesis of 3C-SiC(β) silicon carbide modification. It provides a reliable theoretical basis of an energy-efficient carbothermal method for the synthesis of micro-dimensional SiC from pure natural quartz and graphite without the use of an external protective atmosphere.