Information AboutCarbide |
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In Chemistry , Carbide is a compound of Carbon with a less Electronegative element. Carbides are important industrially; for example Calcium Carbide is a feedstock for the chemical industry and iron carbide, Fe3C ( Cementite ), is formed in steels to improve their properties. Many carbides can be generally classified by chemical bonding type as follows:
In addition to the carbides there are other groups of binary carbon compounds i.e.
EXAMPLES
See for a bigger list. TYPES OF CARBIDES Ionic salts Salt like carbides are formed by the metals of
Most commonly they are salts of C22 Some compounds contain other anionic species:
The naming of ionic carbides is not consistent and can be quite confusing. Acetylides The Polyatomic Ion C22 Methanides The Monatomic Ion C4 C4 Examples of compounds that contain C4 Sesquicarbides The Polyatomic Ion C34 Covalent carbides Silicon and boron form covalent carbides. Silicon Carbide has two similar crystalline forms, which are both related to the diamond structure. Boron Carbide , B4C, on the other hand has an unusual structure which includes icosahedral boron units linked by carbon atoms. In this respect Boron Carbide is similar to the boron rich Boride s. Both Silicon Carbide , SiC, (carborundum) and Boron Carbide , B4C are very hard materials and Refractory . Both materials are important industrally. Boron also forms other covalent carbides, e.g. B25C. Interstitial carbides Properties The carbides of the group 4, 5 and 6 transition metals (with the exception of chromium) are often described as Interstitial Compound s. These carbides are chemically quite inert, have metallic properties and are Refractory . Some exhibit a range of stoichiometries, e.g. Titanium Carbide , TiC. Titanium Carbide and Tungsten Carbide are important industrially and are used to coat metals in cutting tools. Structure The longheld view is that the carbon atoms fit into octahedral interstices in the metal lattice when the metal atom radius is the greater than 135 pm. If the metal atoms are and niobium, NbC . For a long time the non stoichiometric phases were believed to be disordered with a random filling of the interstices, however short and longer range ordering has been detected ''Order and disorder in transition metal carbides and nitrides: experimental and theoretical aspects'' C.H. de Novion and J.P. Landesman Pure & Appl. Chem., 57, 10,(1985)1391. Intermediate transition metal carbides In these the transition metal ion is smaller than the critical 135 pm and the structures are not interstitial but are more complex. Multiple stoichiometries are common, for example iron forms a number of carbides, Fe3C, Fe7C3 and Fe2C. The best known is Cementite , Fe3C, which is present in steels. These carbides are more reactive than the interstitial carbides, for example the carbides of Cr, Mn, Fe, Co and Ni all are hydrolysed by dilute acids and sometimes by water, to give a mixture of hydrogen and hydrocarbons. These compounds share fetaures with both the inert interstitals and the more reactive salt-like carbides. REFERENCES
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