Silicon Carbide Used For Refractory Materials

Silicon carbide has unique physical and chemical properties. In terms of physical properties, it has a relatively high density of 3.21 g/cm³. It is insoluble in water but soluble in molten alkali and iron water. SiC shows an interesting electrical property - for high-purity SiC, as the temperature increases, its resistivity decreases, which is contrary to the resistance-temperature characteristics of metals. The hardness of SiC is very high, but it varies with different crystal axis directions. The hardness decreases with increasing temperature. In terms of chemical properties, SiC has good chemical stability. Although thermodynamically it is prone to oxidation, at a certain temperature, the generated silica film can slow down the oxidation process. It has strong acid resistance but poor alkali resistance. For example, above 1000 °C, it can react with molten alkali and alkali metal sulfates.

There are multiple ways to prepare silicon carbide. The carbon reduction of silica is a common industrial method. By controlling the reaction temperature, different crystal forms of SiC can be obtained. The gas-phase deposition method is mainly used to prepare high-purity SiC. For example, a mixture of silicon-containing gas, carbon-containing gas, and hydrogen gas is introduced into a reaction chamber. Under high-temperature conditions, chemical reactions occur on the substrate surface, and SiC is deposited layer by layer. Another method is the reaction-bonded method. First, a mixture of SiC powder, carbon powder, and a plasticizer is formed into the desired shape, then the plasticizer is burned off, and finally, gaseous or molten silicon is introduced. The silicon reacts with the remaining carbon to form more SiC, enhancing the performance of the product.

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