Iron dicarbide, FeC₂

Iron dicarbide, FeC₂, has been prepared by allowing melts of iron, containing from 6 to 10 per cent, of carbon, to cool. Crystallisation begins at 2380° to 2000° C., a pale yellow carbide separating out, with a silvery reflex. It is slowly attacked by nitric acid, and, when immersed in dilute copper sulphate solution, becomes coated with a film of metallic copper.

When ammonium ferrocyanide, or its double compound with ammonium chloride, is heated, a black magnetic powder is obtained. This, upon ignition in air, is completely transformed into ferric oxide without any change in weight, and is believed to be the dicarbide, FeC₂.

Several other carbides have been described, namely, the mono-carbide, FeC; tetraferro carbide, Fe₄C₂ (which decomposes into γ iron and graphite at temperatures below 1130° C.); FeC₄, Fe₃C₂, Fe₅C, and Fe₁₂C. The two last-named are obtained by the prolonged action of carbon monoxide on iron at red heat. Fe₁₂C is more readily soluble in sulphuric acid than Fe₅C, which enables the latter to be separated: -

Fe₁₂C + 12H₂SO₄ = 12FeSO₄ + CH₄ + 10H₂.