Niobium carbide

Niobium carbide
Identifiers
CAS Number	12069-94-2 ;
ECHA InfoCard	100.031.913
CompTox Dashboard (EPA)	DTXSID00893838 ;
Properties
Chemical formula	NbC
Molar mass	104.917 g/mol
Density	7.820 g/cm3
Melting point	3,608 °C (6,526 °F; 3,881 K)
Structure
Crystal structure	Cubic, cF8
Related compounds
Related Refractory ceramic materials	zirconium nitride, tantalum carbide, zirconium carbide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Niobium carbide (Nb C and Nb₂C) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering and is a frequent additive as grain growth inhibitor in cemented carbides. It has the appearance of a brown-gray metallic powder with purple lustre. It is highly corrosion resistant.

Niobium carbide is a frequent intentional product in microalloyed steels due to its extremely low solubility product in austenite, the lowest of all the refractory metal carbides. This means that micrometre-sized precipitates of NbC are virtually insoluble in steels at all processing temperatures and their location at grain boundaries helps prevent excessive grain growth in these steels. This is of enormous benefit, and the cornerstone of microalloyed steels, because it is their uniform, very fine grain size that ensures both toughness and strength. The only commonly occurring compound with a lower solubility and hence, greater potential for restricting the grain growth of steels is titanium nitride.

Depending on grain size, niobium carbide may burn at 200-800 °C in air. A layer of niobium carbide can be created by chemical vapor deposition. Zirconium carbide and niobium carbide can be used as refractory coatings in nuclear reactors.

Synthesis

Niobium carbide can be produced by the heating of Niobium oxide in a vacuum at 1800 °C and adding coke.

Physical properties

Niobium carbide has an Young's modulus of approximately 452GPa, and a shear modulus of 182GPa.^[1] It has a Poisson's ratio of 0.227.^[1]

Natural occurrence

Niobocarbide - the naturally occurring form of niobium carbide - shall be regarded as an extremely rare mineral.^[2]

References

^ ^a ^b Brenton, R.; et al. (1969). "Elastic properties and thermal expansion of niobium mono-carbide to high temperatures". Journal of the Less Common Metals. 19 (3): 273–278. doi:10.1016/0022-5088(69)90103-9. Abstract at Sciencedirect
^ Mindat, http://www.mindat.org/min-7196.html

[LCM-1] Brenton, R.; et al. (1969). "Elastic properties and thermal expansion of niobium mono-carbide to high temperatures". Journal of the Less Common Metals. 19 (3): 273–278. doi:10.1016/0022-5088(69)90103-9. Abstract at Sciencedirect

[2] Mindat, http://www.mindat.org/min-7196.html

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