Molybdenum Carbides

The carbide, Mo₂C, may be obtained by heating molybdenum dioxide with carbon or with calcium carbide in an electric furnace. The product shows a brilliant, white, crystalline fracture, cleaves readily, and has a density of 8-9. If a mixture of fused molybdenum, carbon, and excess of aluminium is heated in the electric furnace, the carbide, MoC, is obtained as a grey crystalline powder, of density 8.40 at 20° C., and of hardness 7 to 8. It burns readily in fluorine, forming carbon tetrafluoride and molybdenum fluoride, and is attacked by chlorine, bromine, and iodine, but not by hydrogen, at higher temperatures. It is oxidised by heating in air or oxygen, or by the action of cold nitric acid, but is only slowly attacked by other mineral acids, and remains unaltered in solutions of alkali hydroxides.

Carbides of molybdenum have been prepared by heating the finely powdered metal, or the trioxide, in a current of carbon monoxide or in a mixture of methane and hydrogen, and it was found from experiments at different temperatures that the limiting amount of carbon taken up corresponded with simple stoicheiometric proportions. When molybdenum was heated with carbon monoxide, the product had the composition Mo₂C at 600° C. and 1000° C., while at 800° C. the composition varied between MoC and Mo₂C₃.