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What is Reaction Bonded Silicon Carbide (RBSiC)?

                                                                       ---Process and application

Process Overview:
A mixture of SiC particles (typically 1-10 μm) and carbon is formed into a green body, followed by a silicon infiltration reaction at high temperatures. Part of the silicon reacts with carbon to form SiC, which combines with the original SiC in the green body to achieve sintering. There are two methods of silicon infiltration: one involves reaching the melting temperature of silicon (1450-1470°C) to create a liquid phase, allowing silicon to enter the green body through capillary action and react with carbon to form SiC, achieving sintering. The other method involves temperatures above the melting point of silicon to generate silicon vapor, which infiltrates the green body to achieve sintering.

SiC Powder + C Powder + Binder → Forming → Drying → Atmosphere-Protected Degreasing → High-Temperature Si Infiltration → Post-Processing

It's worth noting that the operating temperature range of RBSiC is limited by the free silicon content, typically within 1400°C. Above this temperature, the strength of the material decreases rapidly due to the melting of free silicon. The first method typically leaves a higher residual free silicon content of 10% to 15%, sometimes exceeding 15%, which adversely affects the performance of the product. With vapor-phase silicon infiltration, the residual free silicon content can be reduced to below 10%, and with good process control, it can be further reduced to below 8%, significantly improving the overall performance of the product.

The process also illustrates that SiC ceramics prepared using this method contain varying amounts of residual Si (up to 15% or as low as approximately 8%). Therefore, the resulting ceramic is not a single-phase SiC ceramic and can be considered a "silicon + silicon carbide" composite material. As a result, RBSiC is also known as SiSiC (silicon carbide silicon composite).

Process Characteristics and Applications:
RBSiC offers advantages such as low sintering temperature, low production cost, and high material densification. The carbon and SiC skeleton can be pre-machined into any shape, and the shrinkage of the green body during sintering is within 3%, which facilitates product size control and significantly reduces the grinding required for finished products. This is particularly suitable for the preparation of large-sized components with complex shapes.

Due to its high production volume, RBSiC is primarily used in furnaces, crucibles, and saggers. With its low thermal expansion coefficient and high elastic modulus, RBSiC is also an ideal material for space reflectors. The internationally renowned manufacturer of RBSiC is Refel in the UK, which has extensively applied its high-temperature exchangers. Nippon Electric Glass (NEG) in Japan has also introduced this technology to produce heat exchanger tubes of 0.5-1m length and other products.

With the increase in wafer size and heat treatment temperature, higher requirements are placed on components during the process. The use of high-purity SiC powder and silicon can produce high-purity SiC components containing partial silicon phases, gradually replacing quartz glass components in support fixtures for electron tubes and semiconductor wafer manufacturing equipment.

Drawbacks: As mentioned earlier, the process inherently leaves residual free silicon in the sintered body, which can affect the application of the product. The strength and wear resistance of the sintered body are inferior to those of other processes. Most importantly, free silicon is not resistant to corrosion by strong acids such as alkalis and hydrofluoric acid, limiting its use. Additionally, high-temperature strength is also affected by free silicon, restricting its usage temperature to below 1350-1400°C.

Classic Application of RBSiC: Spiral nozzles (common applications include exhaust gas scrubbing, gas cooling, washing and rinsing processes)



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