Graphite (siliconized) is a kind of composite material which is made of silicon carbide coating on the surface of graphite material. The hardness of silicon carbide is the hardness of SiC, it is only after diamond, boron nitride, boron carbide, the hardness is higher than that of tungsten carbide, three aluminum oxide, two. Silicified graphite used as phosphoric acid, hydrofluoric acid and amine and phosphorus bearing pump. In addition, the semiconductor industry, as silicon epitaxial growth of the heating sheet matrix and fixture and manufacture of artificial joint, artificial heart valve, artificial root and so on
There are three methods to make the production of siliconized graphite : chemical vapor deposition (CVD), Chemical vapor reaction method (CVR), and liquid silicon infiltration reaction.
Chemical vapor deposition (CVD) method
The gas containing silicon and carbon was decomposed by the high temperature graphite matrix, and the SiC was deposited on the surface of graphite matrix. Raw materials for the three (CH3SiC3), four hydrogen chloride, hydrogen, silicon vapor, etc.. The deposition temperature range is wide, from 1175 to 1775. The SiC layer generated by this method is very compact, uniform thickness, average thickness is about 0.1 ~ 0.3mm. But SiC and graphite matrix with pure mechanical binding, the binding force is weak, in temperature blast SiC layer prone to cracking and spalling.
Chemical vapor reaction method (CVR)
Raw material for coke powder and excessive amounts of quartz sand or no amorphous silica fume, when heated to 2000 degrees occurred chemical reaction to generate the SiO vapor. SiO vapor and carbon matrix reaction to generate SiC. SiC layer and the carbon matrix without obvious interface, are firmly combined, under high load and sudden changes in temperature will not fall off, but CVR method is SiO gas infiltration of carbon base body reaction, therefore, still retains the porous carbon matrix, when used as a sealing material, need resin dip stains or CVD pore filling.
liquid silicon infiltration reaction.
liquid silicon infiltration reaction.is also a kind of CVR. Under the vacuum condition, the carbon matrix is directly immersed into the molten silicon liquid by heating up to 1700-1900, and liquid silicon is gradually infiltrated into the carbon matrix, and the reaction is generated by SiC. Raw materials for 99.9999% of pure silicon. The thickness of SiC layer is 3.5mm. After the reaction, the carbon matrix contains about 17% of the free silicon in the matrix, so that the matrix becomes dense and opaque. However, the corrosion resistance and high temperature oxidation resistance of silicon carbide were decreased by the presence of free silicon.
