Electrical Resistivity of Charge Materials in the Si Process and Its Effect on Energy and CO2 Emissions

The resistivity of mixtures of charge materials in the Si furnace was investigated from 25 to 1600 °C. Char was measured first, followed by char + quartz, and finally char + quartz + woodchips in a 1:1.8:0.5 weight ratio. The results show that the resistivity of char + quartz is roughly four times higher than with char alone and that the resistivity rises rapidly after 1500 °C. Char + quartz + woodchips had a similar resistivity to char + quartz after the woodchips had transformed to charcoal. The transformation of the woodchips to charcoal led to a large volume change and high variability at lower temperatures. Both char + quartz and char + quartz + woodchips were nonconductive at lower temperatures. Charcoal made from the woodchips during the resistivity measurements had a slightly higher resistivity than industrial-made charcoal, but it was conductive over the whole temperature range. The resistivity of the charge mix has the ability to affect the quality of the furnace operations through power consumption and Si recovery, and therefore CO2 emissions.