“Tantalum carbide”的意思、由来-开放百科全书

Tantalum carbides form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaC_x, where x usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metallic electrical conductivity. They appear as brown-gray powders, which are usually processed by sintering. Being important cermet materials, tantalum carbides are commercially used in tool bits for cutting applications and are sometimes added to tungsten carbide alloys.^[4] The melting points of tantalum carbides peak at about 3880 °C depending on the purity and measurement conditions; this value is among the highest for binary compounds.^[5]^[6] Only tantalum hafnium carbide may have a slightly higher melting point of about 3942 °C,^[7] whereas the melting point of hafnium carbide is comparable to that of TaC.

Preparation

TaC_x powders of desired composition are prepared by heating a mixture of tantalum and graphite powders in vacuum or inert-gas atmosphere (argon). The heating is performed at temperature of about 2000 °C using a furnace or an arc-melting setup.^[13]^[14] An alternative technique is reduction of tantalum pentoxide by carbon in vacuum or hydrogen atmosphere at a temperature of 1500–1700 °C. This method was used to obtain tantalum carbide in 1876,^[8] but it lacks control over the stoichiometry of the product.^[6] Production of TaC directly from the elements has been reported through self-propagating high-temperature synthesis.^[9]

Crystal structure

TaC_x compounds have a cubic (rock-salt) crystal structure for x = 0.7–1.0;^[10] the lattice parameter increases with x.^[19] TaC_0.5 has two major crystalline forms. The more stable one has an anti-cadmium iodide-type trigonal structure, which transforms upon heating to about 2000 °C into a hexagonal lattice with no long-range order for the carbon atoms.^[11]

Here Z is the number of formula units per unit cell, ρ is the density calculated from lattice parameters.

Properties

The bonding between tantalum and carbon atoms in tantalum carbides is a complex mixture of ionic, metallic and covalent contributions, and because of the strong covalent component, these carbides are very hard and brittle materials. For example, TaC has a microhardness of 1600–2000 kg/mm²^[16] (~9 Mohs) and an elastic modulus of 285 GPa, whereas the corresponding values for tantalum are 110 kg/mm² and 186 GPa. The hardness, yield stress and shear stress increase with the carbon content in TaC_x.^[17] Tantalum carbides have metallic electrical conductivity, both in terms of its magnitude and temperature dependence. TaC is a superconductor with a relatively high transition temperature of T_C = 10.35 K.^[12]

The magnetic properties of TaC_x change from diamagnetic for x ≤ 0.9 to paramagnetic at larger x. An inverse behavior (para-diamagnetic transition with increasing x) is observed for HfC_x, despite that it has the same crystal structure as TaC_x.^[18]

Natural occurrence

Tantalcarbide is a natural form of tantalum carbide. It is cubic, extremely rare mineral.^[19]

See also

References

1. ^¹²³{{CRC90}}
2. ^¹²{{cite patent|5196273}}
3. ^{{nist|name=Tantalum carbide|id=C12070063|accessdate=2014-07-02|mask=FFFF|units=SI}}
4. ^{{cite book|author=John Emsley|title=Nature's building blocks: an A-Z guide to the elements|url=https://books.google.com/books?id=j-Xu07p3cKwC&pg=PA421|accessdate=2 May 2011|date=11 August 2003|publisher=Oxford University Press|isbn=978-0-19-850340-8|pages=421–}}
5. ^The claim of melting point of 4000 °C in TaC_0.89 is based not on actual measurement but on an extrapolation of the phase diagram, using an analogy with NbC, see Emeléus
6. ^¹{{cite book|author=Harry Julius Emeléus|title=Advances in Inorganic Chemistry and Radiochemistry|url=https://books.google.com/books?id=-SnCsg5jM_kC&pg=PA169|accessdate=3 May 2011|year=1968|publisher=Academic Press|isbn=978-0-12-023611-4|pages=174–176}}
7. ^{{cite journal|title=Researches on Systems with Carbides at High Melting Point and Contributions to the Problem of Carbon Fusion|issn=0373-0093|journal=Zeitschrift für technische Physik|last1=Agte|first1= C.|last2= Alterthum|first2= H.| volume= 11|year= 1930|pages=182–191}}
8. ^{{cite journal|author=Joly, A.|title=Sur les azotures et carbures de niobium et de tantale |year=1876 |page=1195 |journal=Compt. Rend. |volume=82|language=fr|url=http://gallica.bnf.fr/ark:/12148/bpt6k30396/f1190.item}}
9. ^{{cite journal|last1=Shuck|first1=Christopher E.|last2=Manukyan|first2=Khachatur V.|last3=Rouvimov|first3=Sergei|last4=Rogachev|first4=Alexander S.|last5=Mukasyan|first5=Alexander S.|title=Solid-flame: Experimental validation|journal=Combustion and Flame|date=January 2016|volume=163|pages=487–493|doi=10.1016/j.combustflame.2015.10.025}}
10. ^{{cite journal|title=Electronic structure of cubic HfxTa1–xCy carbides from X-ray spectroscopy studies and cluster self-consistent calculations|doi=10.1016/j.jallcom.2007.08.018|year=2008|last1=Lavrentyev|first1=A|last2=Gabrelian|first2=B|last3=Vorzhev|first3=V|last4=Nikiforov|first4=I|last5=Khyzhun|first5=O|last6=Rehr|first6=J|journal=Journal of Alloys and Compounds|volume=462|pages=4–10 }}
11. ^¹{{cite journal|doi=10.1016/0022-5088(86)90648-X |title=A neutron powder diffraction study of Ta2C and W2C|year=1986|last1=Lonnberg|first1=B|last2=Lundstrom|first2=T|last3=Tellgren|first3=R|journal=Journal of the Less Common Metals|volume=120|issue=2|pages=239–245 }}
12. ^¹²{{cite journal|doi=10.1002/pssa.2210640114|title=X-ray diffraction study of Debye temperature and charge distribution in tantalum monocarbide|year=1981|last1=Valvoda|first1=V.|journal=Physica Status Solidi A|volume=64|pages=133–142}}
13. ^{{cite journal|doi=10.1107/S0567740870002091 |title=On the crystal chemistry of the close-packed transition-metal carbides. I. The crystal structure of the [zeta]-V, Nb and Ta carbides|year=1970|last1=Yvon|first1=K.|last2=Parthé|first2=E.|journal=Acta Crystallographica Section B|volume=26|issue=2|pages=149–153}}
14. ^{{cite journal|doi=10.1107/S0365110X65002670|title=The crystal structures of V2C and Ta2C|year=1965|last1=Bowman|first1=A. L.|last2=Wallace|first2=T. C.|last3=Yarnell|first3=J. L.|last4=Wenzel|first4=R. G.|last5=Storms|first5=E. K.|journal=Acta Crystallographica|volume=19|pages=6–9}}
15. ^¹{{cite journal|title=Constitution of Ternary Ta-Mo-C Alloys|doi=10.1111/j.1151-2916.1968.tb13850.x|year=1968|last1=Rudy|first1=Erwin|last2=Brukl|first2=C. E.|last3=Windisch|first3=Stephan|journal=Journal of the American Ceramic Society|volume=51|issue=5|pages=239–250}}
16. ^Kurt H. Stern (1996). Metallurgical and Ceramic Protective Coatings. Chapman & Hall.
17. ^{{cite book|author=Oyama, S. Ted|title=The chemistry of transition metal carbides and nitrides|url=https://books.google.com/books?id=0N-3d-LfiWEC&pg=PA29|accessdate=3 May 2011|year=1996|publisher=Springer|isbn=978-0-7514-0365-7|pages=29–30}}
18. ^{{cite book|author1=Aleksandr Ivanovich Gusev|author2=Andreĭ Andreevich Rempel|author3=Andreas J. Magerl|title=Disorder and order in strongly nonstoichiometric compounds: transition metal carbides, nitrides, and oxides|url=https://books.google.com/books?id=jc2D7TGZcyUC&pg=PA513|accessdate=3 May 2011|year=2001|publisher=Springer|isbn=978-3-540-41817-7|pages=513–516}}
19. ^Mindat, http://www.mindat.org/min-7327.html