Study of metallic carbides by electron diffraction Part I. formation and decomposition of nickel carbide

Article abstract of DOI:10.1143/JPSJ.12.482

Thin nickel films formed by evaporation were carburized in CO gas stream at temperatures from 250°C to 500°C and were studied by electron diffraction. Only Ni₃C was found to be formed. This has c.p.h. arrangement of nickel atoms with lattice constants αh=2.628 A and Ch=4.306 A, but showed super-lattice reflections due to a hexagonal lattice of α= √3α_h and C=3C_h, which is considered to be caused by a regular arrangement of carbon atoms. The carbide was formed below 450°C in CO gas with slow rate and decomposed rapidly above 430°C in vacuum. The rate of the carbide formation was highest at about 350°C, although it depended very much on the texture of nickel films. Hydrogen atmosphere did not alter essentially the stability of the carbide. It was found -that nickel carbide is formed from metallic nickel with an epitaxial relation (00.1)Ni3C//(111)Ni and [10.0]Ni3C//[101]Ni (Ni ₃C: c.p.h. indices) at the nucleation stage. A mechanism of the lattice transformation from metallic nickel to the carbide was suggested. This mechanism explains the epitaxy and its destruction in the growth stage of the carbide crystal.