Monitoring the carburization of molybdenum bimetallic nitrides and oxynitrides with CH4/H2/Ar mixtures: identification of a new carbonitride

Abstract

A new carbonitride Ni₂Mo₃(C_xN_y) has been synthesized by temperature-programmed carburization of the Ni₂Mo₃N precursor with a CH₄/H₂/Ar gas mixture at 923 K. This compound has been characterized by X-ray diffraction, elemental analysis, Auger electron spectroscopy, laser Raman spectroscopy, thermogravimetric analysis and field-emission scanning electron microscopy. Ni₂Mo₃(C_xN_y) crystallizes in the cubic space groupP4₁32, with a lattice parameter of a = 6.64575(3) Å, corresponding to the unusual filled β-Mn structure. Its formation occurs by partial substitution of N by Cvia a topotactic and pseudomorphic reaction and its stability in air is higher that of Ni₂Mo₃N. A two-phase mixture with a cubic structure has always been obtained by the same synthetic method applied to the V₂Mo(O_xN_y) precursor. One of these would be of carbidic nature formed at 1153 K following a reaction similar to that proposed for Ni₂Mo₃(C_xN_y).