Silicon carbide (SiC) has become an important abrasive because of its great hardness, but its application scope exceeds that of ordinary abrasives. For example, its high temperature resistance and thermal conductivity make it one of the first choice kiln furniture materials for tunnel kiln or shuttle kiln, and its electrical conductivity makes it an important electric heating element. To prepare SiC products, firstly, SiC frits [or SiC granular materials] should be prepared. Because it contains C and is super hard, SiC granular material was once called emery. However, it should be noted that its composition is different from that of natural emery (also called garnet). In industrial production, the silicon carbide smelting block is usually made of timely, petroleum coke and other raw materials, supplemented by recycled materials and waste materials. After grinding and other processes, it is prepared into a charge with reasonable proportion and appropriate particle size (in order to adjust the air permeability of the charge, a proper amount of sawdust should be added, and a proper amount of salt should be added when preparing green silicon carbide), and it is prepared at high temperature. The thermal equipment for preparing SiC frits at high temperature is a special silicon carbide electric furnace, and its structure consists of a furnace bottom, an end wall with electrodes embedded in the inner surface, a detachable side wall and a furnace core (full name: charged heater in the center of the electric furnace, which is generally installed in the center of the furnace charge with graphite powder or petroleum coke according to a certain shape and size, and is generally round or rectangular. Both ends of which are connected with electrodes). The sintering method used in this electric furnace is commonly known as: buried powder sintering. As soon as the electricity was turned on, the heating began. The furnace core temperature is around 2500℃, or even higher (2600 ~ 2700℃). When the charge reaches 1450℃, SiC is synthesized (but SiC is mainly formed at ≥ 1800℃) and co is released. However, when the temperature is ≥2600℃, siC will decompose, but the decomposed Si will react with C in the charge to generate SiC. Each group of electric furnaces is equipped with a transformer, but only a single electric furnace supplies power during production, so that the voltage can be adjusted according to the characteristics of electric load and the constant power can be basically maintained. The high-power electric furnace needs to be heated for about 24 h, and the reaction of forming SiC basically ends after power failure. After a period of cooling, the side wall can be removed, and then the baggage can be gradually taken out.
The charge after high-temperature calcination is, from the outside to the inside, unreacted material (which plays the role of heat preservation in the furnace) and silicon carbide oxide (semi-reactive material, mainly composed of C and SiO). ), adhesive layer (a tightly bonded material layer, the main components of which are C, SiO _ 2, 40% ~ 60% SiC and carbonate of Fe, al, Ca and Mg), amorphous layer (the main components are 70% ~ 90% SiC, which is cubic SiC, that is, β-sic, and the rest are C, SiO _ 2, Fe and A/C.