Intermediate Transition Metal Carbides
In these carbides, 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 are all hydrolysed by dilute acids and sometimes by water, to give a mixture of hydrogen and hydrocarbons. These compounds share features with both the inert interstitials and the more reactive salt-like carbides.
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