Silicon Carbide Manufacturing Process

Due to the low natural content, silicon carbide is mostly man-made. The common method is to mix quartz sand with coke, use silica and petroleum coke in it, add salt and sawdust, put it in an electric furnace, heat it to a high temperature of about 2000°C, and obtain silicon carbide micropowder after various chemical processes.

Silicon carbide (SiC) is an important abrasive because of its great hardness, but its application range exceeds that of ordinary abrasives. For example, its high temperature resistance and thermal conductivity make it one of the preferred kiln furniture materials for tunnel kilns or shuttle kilns, and its electrical conductivity makes it an important electric heating element. To prepare SiC products, the first step is to prepare SiC smelting blocks [or: SiC pellets, because they contain C and are super hard, so SiC pellets were once called: emery. But beware: it has a different composition than natural emery (garnet). In industrial production, SiC smelting blocks usually use quartz, petroleum coke, etc. as raw materials, auxiliary recovered materials and spent materials, and are prepared into a charge with a reasonable ratio and suitable particle size through grinding and other processes (in order to adjust the gas permeability of the charge, it is necessary to add an appropriate amount of The sawdust is prepared by adding appropriate amount of salt when preparing green silicon carbide) by high temperature. The thermal equipment for preparing SiC smelting blocks at high temperature is a special silicon carbide electric furnace, and its structure consists of the furnace bottom, the end wall with electrodes on the inner surface, the detachable side wall, and the furnace core body (full name: energized heating body in the center of the electric furnace, generally It is composed of graphite powder or petroleum coke installed in the center of the charge according to a certain shape and size, generally circular or rectangular. Its two ends are connected with electrodes) and so on. The firing method used by the electric furnace is commonly known as: buried powder firing. As soon as it is energized, the heating starts. The temperature of the furnace core body is about 2500°C, or even higher (2600-2700°C). When the charge reaches 1450°C, SiC begins to be synthesized (but SiC is mainly formed at ≥1800°C), and CO is released. However, SiC will decompose when ≥2600 °C, but the decomposed Si will form SiC with C in the charge. Each group of electric furnaces is equipped with a set of transformers, but only a single electric furnace is supplied with power during production, so as to adjust the voltage according to the electrical load characteristics to basically maintain constant power. The high-power electric furnace needs to be heated for about 24 hours. After a period of cooling, the side walls can be removed, and then the charge is gradually removed.

The charge after high temperature calcination is from outside to inside: unreacted material (in the furnace for heat preservation), silicon oxycarbide (semi-reacted material, the main components are C and SiO), adhesive layer (it is very tightly bonded). material layer, the main components are C, SiO2, 40%-60% SiC and carbonates of Fe, Al, Ca, Mg), amorphous layer (the main component is 70%-90% SiC, and it is cubic SiC That is, β-sic, the rest are carbonates of C, SiO2 and Fe, A1, Ca, Mg), second-grade SiC layer (the main component is 90% to 95% SiC, this layer has formed hexagonal SiC, but the crystal is relatively small. Small, very fragile, can not be used as abrasive), first-grade SiC ((SiC content<96%, and is hexagonal SiC, i.e., a coarse crystal of SiC), furnace core graphite. In the above-mentioned layers, usually untreated The reaction material and a part of the silicon oxycarbide layer material are collected as spent materials, and another part of the silicon oxycarbide layer is collected together with the amorphous material, secondary products, and part of the binder as the return material, while some are tightly bonded and lumpy. The binders with high degree and many impurities are discarded, while the first-grade products are classified, coarsely crushed, finely crushed, chemically treated, dried and sieved, and magnetically separated into black or green SiC particles of various particle sizes. To make silicon carbide micropowder, it has to go through the water selection process; to make silicon carbide products, it has to go through the process of forming and sintering.