Silicon Carbide Engineering Ceramics
Silicon carbide (SiC) is an extremely hard engineering ceramic. It behaves similarly to diamond making an excellent wear resistant solution for highly abrasive environments. With a host of other attractive properties including low density, excellent thermal shock resistance and excellent resistance to acids and alkalis, it is finding new areas of application all the time.
SiC also retains many of its mechanical properties up to high temperatures, allowing it to outperform other materials such as refractory metals.
With origins as an abrasive material, key mechanical and thermal properties have seen it evolve into a widely accepted and utilised technical ceramic material. Properties that have contributed to its success include:
- High hardness
- High strength
- Low density
- Good high temperature strength
- High thermal conductivity
- Low co-efficient of thermal expansion
- Excellent thermal shock resistance
- High elastic modulus
- Excellent chemical resistance
Types of Silicon Carbide
There are three types of silicon carbide used for engineering purposes:
- Reaction Bonded Silicon Carbide – Also referred to as self bonded SiC, mixtures of SiC and silicon metal or carbon powder are formed into green shapes. They are then fired under controlled atmosphere, carburising (with silicon powder) or infiltrated with molten silicon metal. Under these hot conditions the silicon and carbon react to form SiC that bonds the original silicon carbide grains together.
- Sintered Silicon Carbide – Fine SiC powder can be sintered with the addition of sintering aids like Boron Carbide (B4C). This process results in high strength provided exaggerated grain growth and any other strength limiting process can be avoided.
- Bonded Silicon Carbide – SiC can be bonded using secondary phases e.g. resin, glass, silicon nitride, clay or metal. Often the bonding phase requires a suitable treatment (e.g. firing) such that it will bond the SiC particles together. This type of SiC is most commonly used in refractory applications.
Some application of SiC include:
- Wear plates and tiles
- Kiln furniture
- Turbine components
- Valves e.g. ball valves
- Hot gas flow liners
- Heat exchangers