Study of Metallic Carbides by Electron Diffraction Part I. Formation and Decomposition of Nickel Carbide

抄録

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 a_h=2.628 Å and c_h=4.306 Å, but showed super-lattice reflections due to a hexagonal lattice of a=\sqrt3a_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⁄⁄[10\bar1]_Ni (Ni₃C: 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.