Inorganic compound group
In chemistry, a carbide normally describes a compound composed of carbon paper and a metallic. In metallurgy, carbiding or carbonize is the summons for producing carbide coatings on a alloy slice. [ 1 ]

interstitial / Metallic carbides [edit ]

The carbides of the group 4, 5 and 6 passage metals ( with the exception of chromium ) are much described as interstitial compounds. [ 2 ] These carbides have metallic properties and are refractory. Some show a stove of stoichiometries, being a non-stoichiometric assortment of respective carbides arising due to crystal defects. Some of them, including titanium carbide and tungsten carbide, are significant industrially and are used to coat metals in cutting tools. [ 3 ] The long-held opinion is that the carbon atoms fit into octahedral interstices in a close-packed metal lattice when the metallic element atom radius is greater than approximately 135 pm : [ 2 ]

  • When the metal atoms are cubic close-packed, (ccp), then filling all of the octahedral interstices with carbon achieves 1:1 stoichiometry with the rock salt structure.
  • When the metal atoms are hexagonal close-packed, (hcp), as the octahedral interstices lie directly opposite each other on either side of the layer of metal atoms, filling only one of these with carbon achieves 2:1 stoichiometry with the CdI2 structure.

The following mesa [ 2 ] [ 3 ] shows actual structures of the metals and their carbides. ( N.B. the consistency centered cubic structure adopted by vanadium, niobium, tantalum, chromium, molybdenum and tungsten is not a close-packed wicket. ) The note “ h/2 ” refers to the M2C type structure described above, which is only an estimate description of the actual structures. The childlike view that the wicket of the pure metallic element “ absorb ” carbon atoms can be seen to be untrue as the pack of the alloy atom wicket in the carbides is unlike from the backpack in the saturated metallic, although it is technically right that the carbon atoms fit into the octahedral interstices of a close-packed metallic wicket .

Metal Structure of pure metal Metallic
radius (pm) 		MC
metal atom packing 		MC structure M2C
metal atom packing 		M2C structure Other carbides
titanium hcp 147 ccp rock salt
zirconium hcp 160 ccp rock salt
hafnium hcp 159 ccp rock salt
vanadium bcc 134 ccp rock salt hcp h/2 V4C3
niobium bcc 146 ccp rock salt hcp h/2 Nb4C3
tantalum bcc 146 ccp rock salt hcp h/2 Ta4C3
chromium bcc 128 Cr23C6, Cr3C,
Cr7C3, Cr3C2
molybdenum bcc 139 hexagonal hcp h/2 Mo3C2
tungsten bcc 139 hexagonal hcp h/2

For a long prison term the non-stoichiometric phases were believed to be disordered with a random fill of the interstices, however short and longer stove order has been detected. [ 4 ] Iron forms a count of carbides, Fe3C, Fe7C3 and Fe2C. The best know is cementite, Fe3C, which is give in steels. These carbides are more reactive than the interstitial carbides ; for example, the carbides of Cr, Mn, Fe, Co and Ni are all hydrolysed by dilute acids and sometimes by water, to give a mix of hydrogen and hydrocarbons. These compounds share features with both the inert interstitials and the more reactive salt-like carbides. [ 2 ] Some metals, such as tip and tin, are believed not to form carbides under any circumstances. [ 5 ] There exists however a shuffle titanium-tin carbide, which is a two-dimensional conductor. [ 6 ]

Chemical classification of carbides [edit ]

Carbides can be generally classified by the chemical bonds type as follows : ( i ) salt-like ( attic ), ( two ) covalent compounds, ( three ) interstitial compounds, and ( four ) “ intercede ” conversion metal carbides. Examples include calcium carbide ( CaC2 ), silicon carbide ( SiC ), tungsten carbide ( WC ; much called, plainly, carbide when referring to machine joyride ), and cementite ( Fe3C ), [ 2 ] each used in key industrial applications. The name of ionic carbides is not systematic .

Salt-like / saline / ionic carbides [edit ]

Salt-like carbides are composed of highly positive elements such as the alkali metals, alkaline worldly concern metals, and group 3 metals, including scandium, yttrium, and lanthanum. aluminum from group 13 forms carbides, but gallium, indium, and thallium do not. These materials feature isolated carbon centers, often described as “ C4− ”, in the methanides or methides ; two-atom units, “ C2−
2 ”, in the acetylides ; and three-atom units, “ C4−
3 ”, in the allylides. [ 2 ] The graphite embolism colonial KC8, prepared from vapor of potassium and graphite, and the alkali alloy derivatives of C60 are not normally classified as carbides. [ 7 ]

Methanides [edit ]

Methanides are a subset of carbides distinguished by their leaning to decompose in water producing methane. Three examples are aluminum carbide Al
4C
3, magnesium carbide Mg
2C [ 8 ] and beryllium carbide Be
2C. Transition metallic element carbides are not saline solution carbides but their reaction with water is very slow and is normally neglected. For case, depending on surface porosity, 5–30 atomic layers of titanium carbide are hydrolyzed, forming methane within 5 minutes at ambient conditions, following by saturation of the chemical reaction. [ 9 ] notice that methanide in this context is a superficial historical name. According to the IUPAC taxonomic name conventions, a intensify such as NaCH3 would be termed a “ methanide ”, although this compound is often called methylsodium. [ 10 ]

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Acetylides / Ethynides [edit ]

several carbides are assumed to be salts of the acetylide anion C2–
2 ( besides called percarbide, by doctrine of analogy with peroxide ), which has a trio bail between the two carbon atoms. Alkali metals, alkaline worldly concern metals, and rare earth metals form acetylides, for example, sodium carbide Na2C2, calcium carbide CaC2, and LaC2. [ 2 ] Lanthanides besides form carbides ( sesquicarbides, see below ) with rule M2C3. Metals from group 11 besides tend to form acetylides, such as copper ( I ) acetylide and silver medal acetylide. Carbides of the actinoid elements, which have stoichiometry MC2 and M2C3, are besides described as salt-like derivatives of C2−
2. The C–C trio bond length ranges from 119.2 promethium in CaC2 ( similar to ethyne ), to 130.3 prime minister in LaC2 and 134 phase modulation in UC2. The adhere in LaC2 has been described in terms of LaIII with the extra electron delocalised into the antibonding orbital on C2−
2, explaining the metallic conduction. [ 2 ]

Allylides [edit ]

The polyatomic ion C4−
3, sometimes called allylide, is found in Li4C3 and Mg2C3. The ion is linear and is isoelectronic with CO2. [ 2 ] The C–C distance in Mg2C3 is 133.2 prime minister. [ 11 ] Mg2C3 yields methylacetylene, CH3CCH, and propadiene, CH2CCH2, on hydrolysis, which was the beginning indication that it contains C4−
3 .

Covalent carbides [edit ]

The carbides of silicon and boron are described as “ covalent carbides ”, although virtually all compounds of carbon exhibit some covalent character. Silicon carbide has two like crystalline forms, which are both relate to the baseball diamond structure. [ 2 ] Boron carbide, B4C, on the other hand, has an unusual social organization which includes icosahedral boron units linked by carbon atoms. In this respect boron carbide is alike to the boron rich borides. Both silicon carbide ( besides known as carborundum ) and boron carbide are very hard materials and furnace lining. Both materials are important industrially. Boron besides forms other covalent carbides, such as B25C .

molecular carbides [edit ]

6C(P Ph3)6]2+, containing a carbon-gold core The building complex [ AuC ( P Ph, containing a carbon-gold effect alloy complexes containing C are known as alloy carbido complexes. Most common are carbon-centered octahedral clusters, such as [ Au6C ( PΦ3 ) 6 ] 2+ ( where Φ or “ Ph ” represents a hexangular carbon resound : a phenyl group ) and [ Fe6C ( CO ) 6 ] 2−. similar species are known for the alloy carbonyl and the early metallic element halides. A few concluding carbides have been isolated, such as [ CRuCl2 { P ( C6H11 ) 3 } 2 ]. Metallocarbohedrynes ( or “ met-cars ” ) are stable clusters with the general rule M
8C
12 where M is a transition metal ( Ti, Zr, V, etc. ) .

relate materials [edit ]

In addition to the carbides, other groups of relate carbon compounds exist : [ 2 ]

See besides [edit ]

References [edit ]