A study of chemical behavior of lanthanum in La2O3–Mo thermionic cathode materials

The chemical reaction of La2O3 and Mo2C in La2O3–Mo cathode materials has been studied by thermal analysis, X-ray diffraction, scanning electron microscopy and in-situ X-ray photoelectron spectroscopy (XPS). The thermal analysis and X-ray diffraction results show that molybdenum is one of the reaction products of lanthanum oxide and molybdenum carbide. In-situ XPS results show that chemical state of lanthanum changes during heating. We proved, for the first time, that reacted metallic lanthanum appears at the surface of this kind of cathode material at high temperature.