Silicon carbide thermal conductivity

TITANIUM CARBIDE AND SILICON CARBIDE THERMAL CONDUCTIVITY UNDER HEAVY IONS IRRADIATION... 

Titanium Carbide and Silicon Carbide Thermal Conductivity Under Heavy Ions Irradiation... 

Titanium carbide exhibits the same behaviour than silicon carbide. Thermal conductivity decreases down to 7 W/m.K reached for a fluence of lO ions/cm. However, in contrast to SiC, TiC is not totally amorphous for a such fluence. Only small damaged domains are observed. Even if thermal conductivity of irradiated silicon carbide remains higher than titanium carbide, thermal conductivity measurement and microstructural analyses reveal that titanium carbide is less sensitive to irradiation than silicon carbide. 

Silicon Carbide. Sihcon carbide is made by the electrofusion of siUca sand and carbon. SiUcon carbide is hard, abrasion resistant, and has a high thermal conductivity. It is relatively stable but has a tendency to oxidize above 1400°C. The siUca thus formed affords some protection against further oxidation (see Carbides). 

Silicon carbide has very high thermal conductivity and can withstand thermal shock cycling without damage. It also is an electrical conductor and is used for electrical heating elements. Other carbides have relatively poor oxidation resistance. Under neutral or reducing conditions, several carbides have potential usehilness as technical ceramics in aerospace appHcation, eg, the carbides (qv) of B, Nb, Hf, Ta, Zr, Ti, V, Mo, and Cr. Ba, Be, Ca, and Sr carbides are hydrolyzed by water vapor. 

Bricks of silicon carbide, either recrystaUized or clay-bonded, have a high thermal conductivity and find use in muffle walls and as a slag-resisting material. 

There are, of course, many more ceramics available than those listed here alumina is available in many densities, silicon carbide in many qualities. As before, the structure-insensitive properties (density, modulus and melting point) depend little on quality -they do not vary by more than 10%. But the structure-sensitive properties (fracture toughness, modulus of rupture and some thermal properties including expansion) are much more variable. For these, it is essential to consult manufacturers data sheets or conduct your own tests. 

G. A. Slack. Thermal Conductivity of Prue + Impru e Silicon, Silicon Carbide + Diamond , Journal of Applied Physics 35 (1964), 3460-3466. 

Because of high thermal conductivity and low thermal expansion, silicon carbide is very resistant to thermal shock as compared to other refractory materials. 

Semiconducting Properties. Silicon carbide is a semiconductor it has a conductivity between that of metals and insulators or dielectrics (4,13,46,47). Because of the thermal stability of its electronic structure, silicon carbide has been studied for uses at high (>500° C) temperature. The Hall mobility in silicon carbide is a function of polytype (48,49), temperature (41,42,45—50), impurity, and concentration (49). In n-type crystals, activation energy for ionization of nitrogen impurity varies with polytype (50,51). 

High Temperature. The low coefficient of thermal expansion and high thermal conductivity of silicon carbide bestow it with excellent thermal shock resistance. Combined with its outstanding corrosion resistance, it is used in heat-transfer components such as recuperator tubes, and furnace components such as thermocouple protection tubes, cmcibles, and burner components. Silicon carbide is being used for prototype automotive gas turbine engine components such as transition ducts, combustor baffles, and pilot combustor support (145). It is also being used in the fabrication of rotors, vanes, vortex, and combustor. 

Refractories. Its low coefficient of expansion, high thermal conductivity, and general chemical and physical stability make silicon carbide a valuable material for refractory use. Suitable applications for silicon carbide refractory shapes include boiler furnace walls, checker bricks, mufflers, kiln furniture, furnace skid rails, trays for zinc purification plants, etc (see REFRACTORIES). 

Other solid-state applications of silicon carbide include its use as an electroluminescent diode for use in sound recording equipment and photomultipliers and controllers. It has been studied as a reflective surface for lasers. By combining its excellent thermal conductivity and high electrical resistance, silicon carbide has also found application as an insulating material for integrated circuit substrates. 

Russell, L.M., Donaldson, K.Y., Hasselman, D.P.H., Corbin, N.D. Petrovic, J.J. and Rhodes, J.F. Effect of vapor-liquid-solid and vapor-solid silicon carbide whiskers on the effective thermal diffusivity/conductivity of silicon nitride matrix composites , J. Am. Ceram. Soc., 74[4] (1991) 874-877. 

Collin, K.M., Rowcliffe, D.J. (2001), Influence of thermal conductivity and fracture toughness on the thermal shork resistance of alumina-silicon-carbide-whisker compositer Journal of the American Ceramic Society, 84(6), 1334—1340. 

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