SURFACE SPECIES AND THE STABILITY OF GAMMA-MO2N

The surface species of passivated and nonpassivated Mo2N end their sta bility at elevated temperature in various environments have been inves tigated by thermal programmed desorption with mass spectrometry (TPD-M S), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) . The results demonstrate that two types of NHx and H species remain o n fresh Mo2N, and a small amount of weakly adsorbed NHx species is pre sent on passivated Mo2N. During heating at 1000 degrees C in He, fresh Mo2N transforms first from gamma-Mo2N to beta-Mo2N and then decompose s to metallic Mo. No obvious change of the crystalline phase occurs fo r passivated Mo2N before its decomposition or reduction. The XRD spect ra showed a high stability of the Mo2N bulk structure against sulphida tion. XPS data indicated that some changes of the surface composition occurred in sulphided Mo2N. Oxygen incorporated during passivation rea cted with sulphur and formed a thin layer molybdenum of sulphide cover ing the nitride surface.