Surface composition and morphology of a carbon matrix/Mo2C composite material

Resumo

The surface composition and morphology of a carbon matrix/Mo₂C composite have been studied by scanning electron microscopy and X-ray photoelectron spectroscopy. The results demonstrate that the carbon matrix has the form of entangled filaments of carbon nanotubes. The surface layer of the composite contains 57 carbon atoms per molybdenum atom. Molybdenum is present here in the form of the Mo₂C carbide (39 at %) and the Mo₂O₅ (50 at %) and MoO₂ (11 at %) oxides, with E_b(Mo 3d_5/2) = 228.2, 229.6, and 231.9 eV, respectively. The presence of the Mo⁴⁺ and Mo⁵⁺ oxides in the surface layer is due to active reaction of the Mo₂C in the composite with atmospheric oxygen and moisture during the sample preparation process and can be accounted for by the small particle size of the material. Based on analysis of the structure of the C 2s and C 2p valence electron spectra, we assume that the carbon nanotubes of the composite are graphitelike carbon structures. The composite studied here does not become charged when exposed to an X-ray beam, which suggests that it is a weak dielectric.