High-Temperature and Pressure Preparation and Properties of Iron Carbides Fe sub 7 C sub 3 and Fe sub 3 C

The formation regions of Fe sub 7 C sub 3 and Fe sub 3 C were determined at high temp. and high pressure in the Fe--graphite system. Fe sub 7 C sub 3 formed at relatively higher pressures and Fe sub 3 C at lower pressures. Both Fe sub 7 C sub 3 and Fe sub 3 C were isolated from coexisting excess carbon powders by a magnetic method. Fe sub 7 C sub 3 had a Curie point of 250 deg C and a saturation magnetization of 120 emu g exp --1 at room temp. and Fe sub 3 C had those of 210 deg C and 125 emu g exp --1 . Fe sub 7 C sub 3 decomposed to Fe sub 3 C and C at 600 deg C, but to alpha -Fe and C at 700 deg C at atmospheric pressure, and Fe sub 3 C to alpha -Fe and C at 700 deg C. The substitution of other metals (Cr, Mo and tungsten) for Fe in these carbides leads to changes in the thermal stabilities and magnetic properties. 12 ref.--AA