Nickel Carbide, Ni₃C

Nickel Carbide, Ni₃C, is an endothermic compound, the molecular heat of formation of which is -394±10 cals. It results when metallic nickel and carbon are heated together, the optimum temperature of formation being approximately 2100° C., and the maximum carbon content 6.42 per cent. At lower temperatures dissociation takes place, which is fairly rapid at 1600° C., but much slower at 900° C. Hence in preparing the carbide it is essential to cool rapidly, although even the quenched product contains but little of the carbide. Furthermore the carbide cannot be separated from the dissociated graphite owing to the extreme toughness of the quenched product which refuses to be powdered.

The nickel-carbon system appears to be similar to that of iron and carbon, and an alloy containing 1 per cent, of carbon is so brittle that it can be broken by a hammer. Alloys containing larger quantities of carbon, on the other hand, are tough.