Mechanism of reactions in the Si l + C f system and the self-propagating high-temperature synthesis of silicon carbide

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Using moderately and highly reactive carbon fibres and high-purity silicon powders, the kinetics and mechanism of reactions in the Si + C system have been investigated in order to explain the possibility of occurrence of the self-propagating high-temperature synthesis (SHS) in this system. After a review of conditions required for SHS in different C-containing systems, the experimentally found main parametrs of the Si + C reaction and the self-ignition temperature in the Si + C system are described and discussed. The high reaction enthalpy and the very high activation energy of the reaction found confirm that the requirements for SHS are satisfied in this system under certain experimental conditions. In order to explain the high reaction rate and the specific microstructure of the product in the first stages of the reaction, a mechanism of the reaction has been postulated in which repeating steps of solution of carbon in liquid silicon followed by precipitation of SiC from the liquid solution occur successively as the reaction front moves.