Why Can A Small Amount Of Silicon Carbide Be Used in Smelting Ferrosilicon

The "silicon carbide" referred to here is not a specific raw material, but the insulation waste of the graphitization furnace in the production of graphite electrodes. It contains a large amount of silicon carbide, which is why this waste is commonly referred to as "silicon carbide". Its composition is as follows:

SiC25~40%; SiO220%; C25%; The rest is Al2O3, CaO, etc.

In ferrosilicon smelting, the reduction of silica is a reaction that absorbs a lot of heat energy. Therefore, for this reaction to take place intensively, it is necessary to maintain a very high temperature (about 1800~1900°C), so a lot of electricity is consumed. When a portion of the silicon carbide is added to the charge, it reacts with the steel scraps in the charge in the furnace as follows:

SiC+Fe=FeSi+C

This reaction is endothermic. The heat absorbed by it and the reaction temperature are lower than the heat and temperature required for the reduction of silicon dioxide. Therefore, adding a part of the silicon carbide to the charge allows you to reduce energy consumption.

In the smelting of 45 ferrosilicon, the charge contains more steel scraps, and the silicon carbide fracture reaction is mainly SiC+Fe=FeSi+C. Therefore, the utilization rate of silicon carbide is higher at this time.

When smelting 75 ferrosilicon in the charge, there are fewer steel scraps and more silica, and the silicon carbide destruction reaction will proceed mainly according to the following formula:

2SiO2+SiC= 3SiO+CO↑

SiO+SiC=2Si+CO↑

Both reactions take place at a high temperature of about 1800°C, and therefore gaseous SiO participates in them. However, because SiO gas is more volatile, the silicon carbide-destroying reaction is not easy to carry out safely. It can be seen that when smelting 75 ferrosilicon, the silicon carbide utilization rate is low.