Investigation of evolved layer structure of Ba-containing emission materials

The emission material in High Intensity Discharge (HID) lamps plays a significant role in lowering the electrode work function and thus the lamps´ operating temperature. Ba-containing rare earth- and alkali earth tungstate materials are commonly used as cathode thermionic emission materials because of the production of high intensity discharge. The goal of this present work is to model a cathode tip surface evolved during sintering and to compare the physical and chemical properties of emission materials currently used in the industry. In order to achieve this goal, we investigated and compared the layer structure of Ba-Ca- and Ba-Y-containing emission materials evolved on polycrystalline tungsten foils. Simultaneously, the tendency of the work function was also monitored as a function of Ba/BaO layer thickness. The Ba coverage of cathode is one of the most important factors during the lifetime of HID lamps. The initial Ba diffusion was also examined. We also proposed a layer model, valuable for the structures occurring during the operation of lamps. The chemical composition of the flat samples was analysed by X-ray Photoelectron Spectroscopy (XPS) and the electron emission properties by Work Function Spectroscopy (WFS)

X-ray photoelectron spectroscopic and atomic force microscopic studies of pyrolytically coated graphite and highly oriented pyrolytic graphite used for electrothermal vaporization

The interaction between solid or liquid samples on the one hand and pyrolytically coated graphite or highly oriented pyrolytic graphite (HOPG) sample holders on the other hand during electrothermal vaporization was studied, For the characterisation of the micrometer scale topographical changes occurring on these graphite surfaces as a result of solid sample evaporation, atomic force microscopy (AFM) was used. The migration of Cd(NO3)(2) and Na2HAsO4 deposited as solutions on the surface of the HOPG was studied by depth resolved X-ray photoelectron spectroscopy(XPS) using argon ion sputter etching, It was found that the investigated compounds migrate into the graphite to a depth of at least 1-1.5 mu m. XPS data suggest that the migration involves either the hydrated metal ions or the molecules