Bulk Resistivity of Materials in the Si/FeSi Furnace

Abstract

The formation of silicon carbide (SiC) and the energy distribution in the furnace are two important parameters in evaluating furnace operations. The energy distribution is determined by the resistivity of the materials in the furnace. This work aims to investigate the bulk resistivity of materials in the silicon (Si) furnace using both partially transformed carbon materials and raw charge mixes. In this study, the impact of temperature, SiC and Si content, and the addition of insulating charge materials are investigated up to 1600 °C using carbon materials as a base. The materials were treated under similar conditions to the industrial furnace. The resistivity of the carbon materials was between 7 and 17 mΩm at 1600 °C, where the char and coal were generally more conductive than the charcoal. The resistivity of partially transformed materials increased with conversion to SiC, and coal with a higher SiC content than 60% had an average resistivity at 1600 °C of around 30 mΩm. The resistivity then began to decrease as elemental Si formed in the pores. Up to 36%, the amount of Si did not affect the measured resistivity, but its presence likely causes a slight decrease. Computed tomography (CT) scans show that the SiC material is not visibly changing or transforming in the crucible during measurement. Comparing the SiC materials to carbon materials and SiC crust from the literature shows that partially transformed SiC will be as conductive or less conductive than carbon at high temperatures. At 1400 °C, the resistivity of the charge mixes that included char, quartz, woodchips, and silica–iron ore showed that the resistivity is directly proportional to the amount of the main conductive material, in this case, char. Temperature, transformation to SiC, and volume of conductive materials appear to influence the resistivity most heavily in this work. At higher temperatures, the effect of SiC content and heat treatment temperature is lessened as the range becomes smaller for these materials.