Zirconium carbide

Zirconium carbide[1]
Other names zirconium(IV) carbide
Identifiers
CAS number	12070-14-3 Y
	Properties
Molecular formula	ZrC
Molar mass	103.235 g/mol
Appearance	gray refractory solid
Density	6.73 g/cm3
Melting point	3532 °C
Boiling point	5100 °C
Solubility in water	insoluble
Solubility	soluble in concentrated H2SO4, HF, HNO3
Structure
Crystal structure	Cubic, cF8
Space group	Fm3m, No. 225
Coordination geometry	Octahedral
Thermochemistry
Std enthalpy of formation ΔfHo298	−207 kJ/mol (extrapolated to stoichiometric composition)[2]
Hazards
EU classification	not listed
Main hazards	pyrophoric
Related compounds
Related refractory ceramic materials	zirconium nitride, tantalum carbide, niobium carbide
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Zirconium carbide (ZrC) is an extremely hard refractory ceramic material,^[3] 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.^{[citation needed]}

Like most carbides of refractory metals, zirconium carbide is sub-stoichiometric, i.e., it contains carbon vacancies. At carbon contents higher than approximately ZrC_0.98 the material contains free carbon.^[2] Stability range of ZrC is carbon to metal ratio ranging from 0.65 to 0.98.

ZrC reacts with water and acids and is pyrophoric.^{[citation needed]}

The mixture of zirconium carbide and tantalum carbide is an important cermet material.^{[citation needed]}

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.^{[citation needed]}

It is also used as an abrasive, in cladding, in cermets, incandescent filaments and cutting tools.^{[citation needed]}

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.^{[citation needed]}

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.^{[citation needed]}

References