Formation of β-Mo2C below 600 °C using MoO2 nanoparticles as precursor

Abstract

In this work MoO2 nanoparticles were prepared using ethylene glycol as a reducing agent and their transformation into the desired phase β-Mo2C (hexagonal) was followed by in-situ X-ray diffraction with synchrotron radiation. CH4/H2 was employed as carburizing mixture and two different concentrations were tested, 10 and 20% v/v. TEM images obtained indicated that the particle size of the oxide precursor was about 4nm while the XRD patterns showed that an amorphous phase precipitated along with the crystalline phase. This amorphous phase seemed to decrease the onset temperature of carburization and its transformation started before the crystalline MoO2. On the other hand, an effect from the orientation of the (011), (−211) and (022) faces of the MoO2 precursor toward a less energy demanding transformation might be occurring as well. The carburization process of the amorphous phase/MoO2 nanoparticles started at about 560°C, while in contrast for a commercial MoO2 such process began at the temperature commonly reported in the literature (∼670°C). The hexagonal, thermodynamically stable phase of the Mo2C was the main carburization product and no other intermediate phases were detected by XRD. The gas stream of the reaction was analyzed by mass spectrometry indicating the formation of CO and H2O as by-products of the formation of the carbide.