Effect of the reactive gas on the solid-state transformation of molybdenum trioxide to carbides and nitrides

Abstract

A temperature-programmed reaction method was employed to investigate the solid-state transformation of molybdenum oxides to carbides or nitrides by reaction with various reacting gases such as H-2 and NH3 and the mixtures of CH4 and H-2 (CH4/H-2 1/4), CO and H-2 (CO/H-2 1/4), and N-2 and H-2 (N-2/H-2 1/3 and 3/1). The solid-state transformation of MoO3 to nitride by reaction with NH3 was topotactic. In contrast, MoO3 took a nontopotactic route by reaction with the other gases or their mixtures, leading to products that were thermodynamically stable under the investigated conditions. For the synthesis to take a topotactic route it required that the carburization or nitridation occurs in the initial stage of reduction to form intermediate phases containing carbon or nitrogen at low temperatures.