Study on morphology and chemical states of surface active layer of Ce-W cathode.

Abstract In this paper, commercial Ce-W cathode was selected as research object. The cathode working environment was simulated by heating in an ultra-high vacuum (UHV) chamber. Scanning electron microscopy (SEM), Nano-scanning Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to study the surface morphology and chemical states from 900 °C to 1200 °C. The results showed that W6+ disappeared and the surface of the cathode was composed entirely of W0 in heating process. The content of Ce4+ gradually decreased by heating and cerium oxide had a tendency to reduce. The adsorbed oxygen disappeared and the lattice oxygen was present in CeO 2 and Ce 2 O 3. Moreover, when raising heating temperature, the rare earth oxide diffused from the aggregation areas to the tungsten matrix surface to form an active layer. The surface cerium oxide was highest at 1100 °C. Then the thickness of active layer was about 6 nm. At 1200 °C, the evaporation rate of cerium oxide on the surface was greater than the rate of migration from the body to the surface. And the loss of the surface active layer was severe at 1200 °C. Graphical abstract Unlabelled Image Highlights • The content of cerium was highest at 1100 °C. • The thickness of the active layer was about 6 nm at 1100 °C. • At 1200 °C, the loss of the surface active layer was severe. • The content of Ce4+ gradually decreased by heating and cerium oxide had a tendency to reduce. [ABSTRACT FROM AUTHOR]