Synthesis of metastable Fe_3C,Co_3C and Ni_3C by mechanical alloying

金属Fe、Co、Ni粉末与碳粉在室温下机械合金化可得到亚稳态的Fe3C、Co3C和Ni3C。用X射线衍射仪(XRD)、差示扫描量热仪(DSC)和振动样品磁强计(VSM)对它们的晶体结构、热稳定性和磁性能进行了表征。这些亚稳态金属碳化物是用常规方法没有得到的，因此在平衡相图中没有描述它们的存在。由于机械合金化是一种在室温下合成任何粉末样品的方法，因此我们能够制备出亚稳态相。X射线衍射分析表明，Fe3C是正交晶型，Co3C从正交晶系转变为HCP结构，Ni3CHCP结构，这表明这些碳化物的结构是由这些金属元素{(3D)^6(Fe)，(3D)^7(Co)和(3D)^8(Ni)的三维电子状态决定的。分解温度分别为1227ﾟC和468ﾟC。饱和磁化强度分别为218emu/g、1.98emu/g和0.45emu/g，后两种磁化强度对M-T测量不具有铁磁性，不符合居里-魏斯定律。

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.