|Molar mass||103.235 g/mol|
|Appearance||gray refractory solid|
|Solubility in water||insoluble|
|Solubility||soluble in concentrated H2SO4, HF, HNO3|
|Crystal structure||Cubic, cF8|
|Space group||Fm3m, No. 225|
|Std enthalpy of
|−207 kJ/mol (extrapolated to stoichiometric composition)|
|EU classification||not listed|
|Related refractory ceramic materials||zirconium nitride, tantalum carbide, niobium carbide|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Zirconium carbide (ZrC) is an extremely hard refractory ceramic material, commercially used in tool bits for cutting tools. It is usually processed by sintering. It has the appearance of a gray metallic powder with cubic crystal structure. It is highly corrosion resistant. This Group IV interstitial transition-metal carbide is also a member of ultra high temperature ceramics or (UHTC). Due to the presence of metallic bonding ZrC has thermal conductivity of 20.5 W/m·K and electrical conductivity (resistivity ~43 μΩ·cm) similar to zirconium metal. Strong covalent Zr-C bond gives this material very high melting point (~3530 °C), high modulus (~440 GPa) and hardness (25 GPa). ZrC has lower density (6.73 g/cm3) compared to other carbides like WC (15.8 g/cm3), TaC (14.5 g/cm3) or HfC (12.67 g/cm3). Potentially this material is ideally suitable for re-entry vehicle, rocket/SCRAM jet engine or supersonic vehicle where lower density and high temperature load bearing capability is most important requirement.
Like most carbides of refractory metals, zirconium carbide is sub-stoichiometric, i.e., it contains carbon vacancies. At carbon contents higher than approximately ZrC0.98 the material contains free carbon. Stability range of ZrC is carbon to metal ratio ranging from 0.65 to 0.98.
Hafnium-free zirconium carbide and niobium carbide can be used as refractory coatings in nuclear reactors. Because of low neutron absorption cross-section and weak damage sensitivity under irradiation it has potential application as coating of uranium dioxide and thorium dioxide particles of nuclear fuel. The coating is usually deposited by thermal chemical vapor deposition in a fluidized bed reactor. It also has high emissivity and high current capacity at elevated temperatures rendering it as a promising material for use in thermo-photovoltaic radiators and field emitter tips and arrays.
Zirconium carbide is made by carbo-thermal reduction of zirconia by graphite. Densified ZrC is made by sintering powder of ZrC at upwards of 2000 °C. Hot pressing of ZrC can bring down the sintering temperature consequently helps in producing fine grained fully densified ZrC. Spark plasma sintering also has been used to produce fully densified ZrC.
Poor oxidation resistance over 800 °C limits the applications of ZrC. One way to improve the oxidation resistance of ZrC is to make composites. Important composites proposed are ZrC-ZrB2 and ZrC-ZrB2-SiC composite. These composites can work up to 1800 °C.
|This article needs additional citations for verification. (May 2009)|
- Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 4–96, ISBN 0-8493-0594-2
- Baker, Floyd B.; Storms, Edmund K.; Holley Jr., Charles E. (1969), "Enthalpy of formation of zirconium carbide", J. Chem. Eng. Data 14: 244–246, doi:10.1021/je60041a034
- Measurement and theory of the hardness of transition- metal carbides , especially tantalum carbide. Schwab, G. M.; Krebs, A. Phys.-Chem. Inst., Univ. Muenchen, Munich, Fed. Rep. Ger. Planseeberichte fuer Pulvermetallurgie (1971), 19(2), 91-110