Silicon carbide (SiC) is an important abrasive due to its high hardness, but its applications extend beyond those of ordinary abrasives. For example, its high-temperature resistance and thermal conductivity make it a preferred material for kiln furniture in tunnel kilns or shuttle kilns, and its electrical conductivity makes it an important electric heating element. The preparation of SiC products begins with the preparation of SiC smelting blocks (or SiC granules; due to their carbon content and extreme hardness, SiC granules were once called "carborundum"-but it's important to note that their composition differs from natural carborundum (garnet). In industrial production, SiC smelting blocks are typically made from raw materials such as quartz and petroleum coke, supplemented by recycled materials and waste materials. These materials are ground and blended to create a furnace charge with a suitable proportion and particle size (a suitable amount of sawdust is added to adjust the charge's permeability; a suitable amount of salt is also added when preparing green silicon carbide). The resulting product is then processed at high temperatures.
The thermal equipment for high-temperature SiC smelting blocks is a dedicated silicon carbide electric furnace. Its structure consists of a furnace bottom, end walls with electrodes embedded in their inner surfaces, removable side walls, and a furnace core (the central energized heating element of the furnace, typically made of graphite powder or petroleum coke installed in a specific shape and size at the center of the charge, usually circular or rectangular, with both ends connected to the electrodes). The firing method used in this furnace is commonly known as "buried powder firing." Heating begins as soon as electricity is applied, with the furnace core temperature reaching approximately 2500℃, or even higher (2600–2700℃). SiC synthesis begins when the charge reaches 1450℃ (but SiC mainly forms at ≥1800℃), releasing CO. However, at ≥2600℃, SiC decomposes, but the decomposed Si reacts with C in the charge to form more SiC. Each electric furnace is equipped with a transformer, but only a single furnace is powered during production. This allows the voltage to be adjusted according to the electrical load characteristics to maintain a relatively constant power. A high-power electric furnace needs to be heated for about 24 hours. After the power is cut off, the reaction that produces SiC is basically over. After a period of cooling, the side walls can be removed, and then the furnace charge can be gradually taken out.
