Study of Metallic Carbides by Electron Diffraction Part IV. Cobalt Carbides

抄録

Thin cobalt films formed by evaporation were carburized in town gas at temperatures below 550°C for several hours. Electron diffraction studies of these films confirmed the existence of two kinds of carbide, Co₂C and Co₃C. Co₂C is an orthorhombic crystal with lattice constants a=2.910, b=4.469 and c=4.426 Å, and has a distorted c.p.h. structure. The lattice relation between Co₂C and Co is (001)_Co2C\varparallel(00.1)_α-Co\varparallel(111)_β-Co and [100]_Co2C\varparallel[10.0]_α-Co\varparallel[10\bar1]_β-Co. Co₂C is formed at temperatures in a range 450°∼500°C, and decomposes gradually to α-Co containing stacking faults and graphitic carbon at temperatures in a range 450°∼470°C. Co₃C is an orthorhombic crystal with lattice constants a=4.483, b=5.033 and c=6.731 Å and is isomorphous with cementite (Fe₃C). The lattice relation is (1\bar21)_Co3C\varparallel(10.1)_α-Co\varparallel(100)_β-Co, and [111]_Co3C\varparallel[0\bar1.0]_α-Co\varparallel[001]_β-Co. Co₃C is formed at temperatures in a range 450°∼500°C and decomposes gradually to α-Co containing stacking faults and to graphitic carbon at temperatures in a range 480°∼490°C. The mechanisms of Co₂C and Co₃C formation and decomposition are discussed.