Zirconium carbide

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Zirconium carbide
Zirconium carbide in the unit cell
Powder of zirconium carbide
Identifiers
CAS number 12070-14-3 YesY
UN number 3178
Properties
Molecular formula CZr
Molar mass 103.23 g mol−1
Appearance Gray refractory solid
Odor Odorless
Density 6.73 g/cm3 (24 °C)[1]
Melting point 3,532–3,540 °C (6,390–6,404 °F; 3,805–3,813 K)[1][2]
Boiling point 5,100 °C (9,210 °F; 5,370 K)[2]
Solubility in water Insoluble
Solubility Soluble in concentrated H2SO4, HF,[1] HNO3
Structure
Crystal structure Cubic, cF8[3]
Space group Fm3m, No. 225[3]
Lattice constant a = 4.6976(4) Å[3]
Lattice constant α = 90°, β = 90°, γ = 90°
Coordination
geometry
Octahedral[3]
Thermochemistry
Specific
heat capacity
C
37.442 J/mol·K[4]
Std molar
entropy
So298
33.14 J/mol·K[4]
Std enthalpy of
formation
ΔfHo298
−207 kJ/mol (extrapolated to stoichiometric composition)[5]
−196.65 kJ/mol[4]
Hazards
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[6]
GHS signal word Danger
GHS hazard statements H228, H302, H312, H332[6]
GHS precautionary statements P210, P280[6]
EU classification Highly Flammable F Harmful Xn
R-phrases R11, R20/21/22
S-phrases S16, S27, S33, S36/37/39
Main hazards Pyrophoric
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Other anions Zirconium nitride
Zirconium oxide
Other cations Titanium carbide
Hafnium carbide
Vanadium carbide
Niobium carbide
Tantalum carbide
Chromium carbide
Molybdenum carbide
Tungsten carbide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Zirconium carbide (ZrC) is an extremely hard refractory ceramic material,[7] commercially used in tool bits for cutting tools. It is usually processed by sintering.

Properties[edit]

Thermal expansion
coefficients of ZrC
[2]
T αV
100 °C 0.141
200 °C 0.326
400 °C 0.711
800 °C 1.509
1200 °C 2.344

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 a thermal conductivity of 20.5 W/m·K and an electrical conductivity (resistivity ~43 μΩ·cm), both of which are similar to that for zirconium metal. The strong covalent Zr-C bond gives this material a very high melting point (~3530 °C), high modulus (~440 GPa) and hardness (25 GPa). ZrC has a 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). ZrC seems suitable for use in re-entry vehicles, rocket/SCRAM jet engines or supersonic vehicles in which low densities and high temperatures load-bearing capabilities are crucial requirements.[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 ZrC0.98 the material contains free carbon.[5] ZrC is stable for a 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]

Uses[edit]

Hafnium-free zirconium carbide and niobium carbide can be used as refractory coatings in nuclear reactors. Because of a low neutron absorption cross-section and weak damage sensitivity under irradiation, it finds use as the 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]

Production[edit]

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[edit]

  1. ^ a b c Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0. 
  2. ^ a b c Perry, Dale L. (2011). Handbook of Inorganic Compounds (2nd ed.). CRC Press. p. 472. ISBN 978-1-4398-1461-1. 
  3. ^ a b c d Kempter, C. P.; Fries, R. J. (1960). "Crystallographic Data. 189. Zirconium Carbide". Analytical Chemistry 32 (4): 570. doi:10.1021/ac60160a042.  edit
  4. ^ a b c Zirconium carbide in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 2014-06-30)
  5. ^ a b Baker, F. B.; Storms, E. K.; Holley, C. E. (1969). "Enthalpy of formation of zirconium carbide". Journal of Chemical & Engineering Data 14 (2): 244. doi:10.1021/je60041a034.  edit
  6. ^ a b c Sigma-Aldrich Co., Zirconium(IV) carbide. Retrieved on 2014-06-30.
  7. ^ 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