Silicon carbide (SiC) is one of the hardest known to mankind. Found naturally as moissanite mineral and mass produced since 1893 for use as an abrasive, SiC is available in different polytypes that differ based on their crystal lattice structures.
Sintered alpha-SiC is affected by many factors, including large voids and shrinkage cracks present in its starting powder. Recent advances in processing techniques have been proven to effectively mitigate such defects and enhance strength of alpha-SiC.
Hardness
Alpha SiC stands out with its hardness; boasting a Mohs hardness of 13, it stands as an invaluable property. Only slightly less resistant than diamond and boron carbide, alpha SiC’s Mohs hardness 13 makes it nearly indestructible; making it perfect for high precision grinding, cutting and polishing applications such as blade grinding. Furthermore, alpha SiC is used in manufacturing applications including nozzles, ceramic seal faces military equipment as well as high stress industrial manufacturing applications.
Sintered silicon carbide’s hardness depends on its sintering temperature. At very high temperatures, cubic polytype phase of a-SiC changes into hexagonal b-SiC during sintering which reduces hardness significantly.
As part of the sintering process, it’s crucial to ensure all grains are uniform. This helps increase hardness while improving wear resistance. Flexural strength and fracture toughness were also evaluated; high amounts of nano b-SiC in the matrix led to decreased fracture toughness and flexural strength values while reduced amounts increased these values.
Density
Alpha sic density depends on several factors including processing (forming and firing), material purity, grain size/morphology/pore orientation etc. It typically ranges between 41 Wm-1K-1; variations due to measurement techniques.
Beta silicon carbide, on the other hand, can be made to have a greater density than alpha sic and thus make for superior sealing applications due to its dense microcrystalline structure compared to alpha’s more spherical shape.
Densification of material can also be affected by temperature. Flash sintering, for instance, may lead to non-uniform temperature distribution and thus an eventual reduction of sample resistance; this issue can be avoided through thermal insulation and improving electrode geometries used during sintering processes.
Abrasion Resistance
Abrasion resistance is a crucial property of materials used for industrial applications. Conventional steel equipment is susceptible to gradual mechanical abrasion over time, which reduces its efficacy of operations and increases maintenance downtime for repair or replacement. By contrast, Hexoloy SiC can withstand wear from high-speed rotation forces as well as particles penetrating into it more easily than steel counterparts can.
Alpha silicon carbide (a-SiC) features an attractive sphalerite crystal structure which affords it excellent chemical and thermal properties, including extreme hardness suitable for abrasives. Furthermore, its resistance to heat makes a-SiC an ideal material choice for slurry pumps, bearings, nozzles, pump trim components and paper and textile components.
Sintered alpha silicon carbide boasts a final density of more than 98% theoretical. A special sintering process creates an ultra-pure single phase material capable of withstanding abrasion and erosion. Furthermore, its low porosity and engineered microstructure make hexoloy sa sintered alpha silicon carbide an ideal replacement to traditional industrial materials which deteriorate over time in corrosive environments.
Thermal Conductivity
Thermal conductivity (k) of materials measures how efficiently they conduct heat, making it an essential characteristic for many applications that must maintain high temperatures or endure prolonged exposure to extreme heat conditions.
Silicon carbide polymorphs include alpha sic as one of their more frequently encountered forms, boasting a hexagonal crystal structure similar to that found in wurtzite and formed at temperatures over 1700 degC. Due to its superior hardness and stability in harsh environments, alpha silicon carbide has proven itself an invaluable choice for industrial use.
Hexoloy SP SiC, sintered alpha sic, was designed for optimal performance in sliding contact applications like mechanical seal faces and product lubricated bearings. This sintered alpha sic contains spherical pores which act as reservoirs to retain fluid film on components surfaces for self-lubricating action – significantly outperforming conventional reaction-bonded and sintered silicon carbide materials across an extensive variety of conditions.
Wear Resistance
Alpha sic’s denseness, hardness and self-sharpenness make it the ideal material for applications requiring high abrasion resistance, including cutting tools. While its primary use may be in abrasives or cutting tools, other applications include mechanical armors, spray and blast nozzles, sintered wear parts and ceramics.
Sinter-pure alpha silicon carbide offers outstanding wear resistance, particularly against abrasion and impact damage. Furthermore, it can withstand very high temperatures without succumbing to corrosion or erosion damage and offers great corrosion and erosion resistance.
Hexoloy SP SiC is a sintered alpha silicon carbide material specifically engineered for sliding contact applications like mechanical seal faces and product lubricated bearings, with its unique spherical pores acting as fluid or lubricant reservoirs, outperforming conventional reaction bonded and sintered alpha silicon carbides under various operating conditions.
Borrero-Lopez and colleagues explored the effect of intergranular phase chemistry on the sliding wear behavior of LPS a-SiC ceramics produced under an atmosphere rich in nitrogen (N2) for sintering. Sintering under this atmosphere resulted in incorporation of nitrogen in crystalline y3Al5O12 intergranular phases which then solid-solution hardened, leading to improved sliding-wear resistance of these ceramics.
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