Synthesis of metastable Fe_3C,Co_3C and Ni_3C by mechanical alloying

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Metastable Fe_3C,Co_3C and Ni_3C could be obtained by mechanical alloying of metal Fe, Co and Ni powders with carbon powders at room temperature. Their crystal structures, thermal stabilities and magnetic properties were evaluated by X-ray diffraction (XRD), defferential scanning calorimetory (DSC) and vibration sample magnetometer (VSM).These metastable metal carbides have not been obtaioned by conventional methods, so their presence are not discribed in equilibrium phase diagrams. Mechanical alloying method enabled us the preparation of metastable phases, because this is a method to synthesize any power samples at room temperature.By XRD analysis, it is concluded that Fe_3C is orthothombic, Co_3C transition type from orthorhomibic to hcp, Ni_3C hcp structure, which suggested that the structure of these carbides were governed by the state of 3d electrons of these metal elements{(3d)^6for fe, (3d)^7for Co and (3d)^8for Ni}. The decomposition temperatures were 1227ﾟC,468ﾟC respectively. Saturation magnetizations were 218emu/g, 1.98emu/g and 0.45emu/g. The latter two were not ferromagnetic for M-T mesurements, which it were not fitted by Curie Weiss rule.