Carbon sic is an advanced ceramic material with exceptional damage tolerance, strength, thermal stability and wear resistance properties.
Materials produced through reaction bonding and sintering processes. Forming method is crucial as microstructure determines material properties; using the LSI process efficiently provides near net shape parts.
Electrical Conductivity
Electrical conductivity is one of the key attributes of carbon sic, as it allows it to efficiently transfer heat between its ends, making it ideal for applications requiring high temperature resistance and thermal management.
Electrical conductivity of porous SiC is determined by many variables, such as its porosity, SiC polytype (a or b), physical state (crystalline or amorphous) and amount and type of second phase additives such as oxides, elements, nitrides and carbides – as well as the sintering atmosphere.
Second-phase additives can increase or decrease the electrical resistivity of porous SiC by creating energy levels near its bandgap. Oxide additives typically create energy levels on the left side, while metal nitrides and carbides activate acceptor-donor compensation mechanisms instead.
Electrical conductivity can be enhanced through changes to additive composition, sintering atmosphere and processing technique. For example, adding graphite to spark plasma-sintered SiC can increase its conductivity up to eight orders of magnitude in both directions parallel and perpendicular to its grafting area [11]. Furthermore, increasing sintering time reduces electrical resistance, possibly due to nitrogen doping of silicon during sintering process [12-13].
Thermal Conductivity
Thermal conductivity of carbon sic is defined as the amount of heat transferred per unit time across a temperature gradient, expressed as an ansotropic second-rank tensor in an anisotropic material. While its value may depend on which testing methods were employed to measure it, its true worth may also vary based on water content in samples being studied.
Thermal conductivity can be determined using steady-state testing methods by dividing heat flux (Q) passing through a cross section of a material by its temperature difference (DT). When conducting transient-state tests, samples are exposed to sudden temperature changes which result in temperature responses over time which are then measured over time to calculate thermal diffusivity [69].
Figure 13 displays that optimised natural-stabilised CEBs were capable of attaining excellent thermal properties, both in terms of bulk density and thermal conductivity, as shown. This remarkable success demonstrates how natural components can serve as powerful tools in optimising composite materials’ thermal behavior.
Contrasting with conventional binders, the combination of low-density wood powder and carbon fibre cloth enabled significant increases in thermal conductivity of CEBs in both directions, thanks to mass transfer channels between natural materials and resin resin.
High Strength
Silicon carbide demonstrates superior mechanical strength, combined with impressive durability. Its fracture toughness rating of 6.8 MPa m0.5 indicates resistance to crack propagation while its Young’s modulus of 440 GPa showcases stiffness of this material. Flexural strength stands out at 490 MPa which offers great bending stress resistance.
Silicon carbide’s high hardness makes it an excellent material choice for applications that demand resistance to wear and impact damage, such as coatings and cutting tools. Furthermore, its low thermal expansion coefficient prevents expansion/contraction when exposed to extreme temperatures; both features make silicon carbide an ideal material choice for mirror material in astronomical telescopes such as Herschel Space Telescope and Gaia space observatory.
Carbon fiber reinforced silicon carbide (Cf/SiC) ceramic matrix composites feature superior flexural, tensile, creep rupture strength as well as excellent corrosion, oxidation and thermal shock resistance properties.
Carbon SiC’s impressive strength can be attributed to its distinct microstructure formed during processing that includes carbon fibers, pyrolyzed carbon matrix and residual silicon. Testing using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy confirmed their presence and distribution within the composite. Furthermore, Weibull weakest link analysis did not hold true under flexural load for carbon/SiC; rather its strength varied depending on specimen size.
High Temperature Resistance
SiC retains elastic resistance at temperatures that surpass those for silicon nitride and zirconia ceramic, yet remain below those necessary to break metallic superalloys or carbon fiber reinforced plastic (CFRP). As it offers exceptional thermal shock resistance, SiC makes an excellent material choice for aerospace applications.
SiC is known for its outstanding resistance to corrosion in harsh environmental conditions and boasts an excellent oxidation resistance, offering long-term service under demanding environmental conditions. It features low abrasion coefficient and resists hydrofluoric acid corrosion as well as other chemicals. Unfortunately, one drawback of using SiC for large parts is brittleness; thus increasing carbon content should help increase resistance.
Carbon-doped SiC composites provide an alternative material solution for harsh environments. Produced through liquid silicon infiltration process, which offers near net shape formation. Furthermore, this technique is cost effective and capable of creating larger parts than traditional carbon fiber reinforcements.
Establishments engaged in producing carbon, graphite and metal-graphite brushes and stock; carbon or graphite electrodes for thermal and electrolytic use; carbon graphite fibers, and other carbon graphite and metal-graphite products fall under US SIC Code 3624 – Carbon and Graphite Products. This industry includes all businesses who supply these materials to aerospace, energy, automotive, chemical industries for use in aircraft engines, turbines and spacecraft components that must remain durable against harsh environments.
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