An overview of reaction bonded silicon carbide

The constant pursuit of engines with excellent energy efficiency has led to a series of innovations. Reaction bonded silicon carbide is a direct result of that relentless pursuit.

Here is an overview of reaction bonded silicon carbide (RBSC) that will reveal its massive significance for a great number of industries. So far, reaction bonded silicon carbide (RBSC) was mainly used in refractories, abrasives, and metallurgy. However, from the look of things, that’s about to change and the use of RBSC will expand in many other industries.

The following overview should give you a clue or a few about the future use of RBSC in new industries.

The processing
Reaction bonded silicon is created by adding liquid silicon into mixtures made of carbon and silicon. That produces a reaction between the carbon and the silicon. What comes out of that are silicon carbide particles. The carbon to silicon ration can vary and it depends on the desired properties we want to achieve.

Almost by default, reaction bonded silicon carbide comes from a formulation that includes carbide particles, carbon, and organic plasticizer.

Key Properties of Reaction Bonded Silicon Carbide (RBSC)
A fully dense reaction bonded silicon carbide (RBSC) has an excellent bend strength at room temperature. It can maintain that until silicon starts to melt. That’s around 1410 ºC at which point it will start decreasing to about 250 MPa.

Thanks to its thermal and oxidation resistance, as well as it’s very high-temperature strength, reaction bonded silicon carbide is a top choice for low mass kiln supports. Kiln products such as posts, rolls, burner nozzles, and setters. Their biggest downside is not a technical thing, but cost-related. Typically, these products cost twice or three times more than the ones that feature cordierite.

Thanks to its excellent strength, wear, and high-temperature resistance, reaction bonded silicon carbide is top material for components such as impellers, plates, and screws. Furthermore, RBSC is often used for thrust bearings which are used in heavily contaminated environments that are under constant heavy loads. Thanks to the properties of RBSC, we can have bearings that can operate in temperatures ranging from -200°C to 400°C.

Vanes and mechanical seals made from our factory has shown to be a success. The parts that included free graphite as a seal nose were particularly durable in hostile operating environments.

Our factory has shown as a top choice for precision components such as optical benches, wafer handling devices, and laser mirror blanks. These are components that are both quite stiff and lightweight and feature great thermal integrity.

In Conclusion
Properties such as good weight ratios, endurance during high temperatures, and excellent stiffness are important for all sorts of applications. The only real question is how fast and to what extent RBSC will be used in the many new emerging technologies. There are certain predictions that the demand for RBSC will be exponential in the years that come. But, that is about to be seen and materialized.

The reaction bonded silicon carbide is a handicraft which is pressed into a green body by fine particles α-SiC and an additive, and is in contact with liquid silicon at a high temperature, and the carbon in the body reacts with the infiltrated Si to form β-SiC, and α – SiC is combined, and free silicon is filled with pores to obtain a highly dense ceramic material. It can be used in medium concentration acid or base media.

The reaction bonded silicon carbide is also referred to as a self-bonding silicon carbide ceramic. Typical articles are commercially available materials REFEL and KT, and silicon impregnated sintered silicon carbide. The plastic blank is generally formed by mixing silicon carbide powder (~5 μm), carbon or graphite, and a plasticizer, and is also obtained by mixing silicon carbide powder with a plastic sintering agent. The blank is made into a green body by pressing, extruding, grouting or other forming methods.

The plasticizer is burned or pyrolyzed into a porous carbon, and the liquid or gaseous silicon reacts with amorphous carbon or graphite to form SiC. The SiC polycrystal formed by the reaction is integrated with the SiC powder, and excess silicon [~10% (vol)] is filled with micropores to obtain a non-porous product. 25 degree bending strength up to 400-600MPa, melting point (1410 degrees) strength 250MPa, elastic modulus about 115MPa.

Silicon carbide for process equipment applications is manufactured by the sintering process. First the silicon carbide parts are shaped by extrusion (tubes) or cold isostatic pressing (plates and blocks). The silicon carbide manufacturing process includes numerous steps namely, powder preparation, mixing with the binder, shape forming, machining, sintering, and eventually lapping or grinding.