Reaction bonded silicon carbide (RBSiC) is a high temperature ceramic used in a variety of applications. Its properties are comparable to the hard metal which is with a lower weight and higher thermal conductivity. It has a very low porosity and a hardness that rivals that of tungsten carbide. These properties make reaction bonded silicon carbide to be suitable for use in bearings and other applications where thermal shock is a factor. But making RBSiC can be tricky. Here are some tips:
First, the biggest secret to making reaction bonded silicon carbide is in the sintering process. Basically, it is filled with a liquid silicon melt. At the same time, a small amount of carbon is infiltrated. In a controlled environment, the carbon can react with the infiltrated silicon to form a b-SiC member. The resultant fired body has a large carbon content of 8% to 30% by weight. This is important because a higher carbon content can lead to cracking during the sintering process.
While the formation of b-SiC is not new thing, the fact is that the process is scalable to a large scale. A number of techniques are now available for producing this kind silicon carbide ceramic, including chemical vapor deposition and selective laser sintering. CVD SiC is much more expensive than sintered SiC, but the thermal conductivity of the former approaches 300 W/mK. Compared to the aforementioned methods, the selective laser sintering method produces a large-scale sized RBSiC member with excellent ceramic properties.
Reaction bonded silicon carbide is not the only type, but it is by far the cheapest. Another type of silicon carbide ceramic is the direct Sintered SiC. It is produced by sintering pure sic powder in an inert atmosphere. Unlike RBSiC, direct Sintered SiC is usually specified for high-temperature work. Interestingly, it is more difficult to machine after the sintering phase. Despite its disadvantages, it is still the material of choice for high-temperature seals and other applications.
Other methods include selective laser sintering, pyrolysis, and the traditional method of forming a RBSiC. All of them are effective in their own ways. With the right equipment, they can produce a bonded silicon carbide ceramic with a very high thermal conductivity and an impressive microstructural morphology. They also offer a wide range of application possibilities, including aerospace, automotive, medical, and petrochemical. As with any other manufacturing process, it is always a good idea to do a bit of research before investing in a new process.
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