Formation of SiC from silicon and CO gas

This thesis investigates the formation of silicon carbide (SiC) in liquid silicon and ferrosilicon (FeSi75) through reaction with carbon monoxide (CO) gas at temperatures relevant to industrial processes. The work builds on the author’s previous project work of Si/FeSi-CO interactions and aims to provide a more detailed understanding of the reaction mechanism and kinetics. Particular emphasis is placed on the amount of SiC produced, the SiC formation rate, the thickness and morphology of the SiC layer, and the characterization of b-SiC. The main reaction investigated was: Si(l) + 2CO(g) = SiC(s) + CO₂(g) Laboratory-scale experiments were conducted in a sessile drop furnace at temperatures relevant for industrial processes. Initial experiments with pure silicon were performed at 1389 °C and 1439 °C in argon and CO atmospheres to study the onset temperature of the reaction. Further experiments with pure Si and FeSi75 were conducted at temperatures between 1500 °C and 1750 °C, where the samples were first heated in argon and subsequently exposed to CO for selected holding times. SiO2 substrates were used to avoid direct carbon contact from the substrate. The samples were characterized using SEM and EDS, supported by EPMA and XRD phase identification. SiC formed under all investigated conditions, confirming that CO can react with liquid silicon and FeSi75 to produce SiC. The extent of formation increased with temperature and holding time, particularly up to 1650 °C, where thicker and more continuous layers were observed. In the pure Si samples, further growth at higher temperatures appeared to be limited by availability of free silicon within the samples. The observed morphology suggests that liquid Si was transported outward and reacted with CO at the outer SiC surface. Pure Si generally showed higher formation rates and larger relative SiC volumes than FeSi75, likely due to the higher Si activity and availability compared to the Fe-Si alloy.