Formation Mechanism of SiC in the Diffusion Couple Interface during the MG-Si Production Process

SiC is an important intermediate product in the production process of metallurgical-grade silicon (MG-Si), and is of great significance for the improvement of the efficiency of MG-Si production. In this study, the formation mechanism of SiC is revealed via an experimental system of a silica-charcoal diffusion couple. The phase transition and microscopic characteristics of the contact interface of the diffusion couple indicate that SiC forms on the carbon side, while the silica side is eroded. The element distribution characteristics of the reaction cross-section reveal that SiC forms inside the carbon along the longitudinal direction. Via the combination of thermodynamic calculation and experimental analysis, the formation mechanisms of SiC on the surface and inside the carbon are confirmed; the SiC on the surface is formed by both one-step and two-step reactions, while the internal SiC is formed only by a two-step reaction. Moreover, increasing the temperature is found to be beneficial to the formation of SiC, and the thickness of the SiC layer increased from 130 to 135 μm with the increase of the temperature from 1673 K to 1773 K. SiO is found to be the key intermediate of the two-step reaction. The prevention of the escape of SiO has great significance for the reduction of the costs and the increase of the yield of MG-Si production.