Study On The Processing Technology Of Ternary Rare-Earth Oxides Tungsten Electrodes

The widely used thorium-tungsten electrodes have radioactive activity. Its preparation and usage pollute environment and harm people's health. To replace it, the ternary rare earth tungsten electrode has been developed. In recent years, small rods (Ф10mm) of ternary rare earth tungsten electrodes have already been produced industrially. Basing on it, we focused on its industry preparation technology of large rods (Ф16mm) in order to improve producing efficiency, save resources and enrich its production kinds.The preparation process of large rods electrodes with diameter of 16mm was investigated. The starting materials was blue tungsten doped with rare earth nitrate, It was reduced in hydrogen in two stages. The relationship of oxide content, particle size and reducing temperature was studied. Nitrogen gas was used in order to prevent tungsten powder oxidation. rods with a diameter of 19mm was prepared by isopressing. Then different sintering processes were performed to determine the optimized process that can obtain homogeneous structure and high density rods.Many modern analysis techniques such as SEM, XRD were applied to characterize the property of reduced powder. AES was used to study the oxide film coating on tungsten powder. SEM, OM were used to investigate edge and center morphology of the rods prepared in different processes. EPMA was applied to analyze rare earth distribution on the fracture of rods. .ICP-AES was used to measure rare earth contents in different area on the rods. The rare earth tungstates migration behavior during sintering process was discussed.Results showed: The best reduction process of first stage was 670℃with hydrogen flow of 1m3/h, boat loading of 300g/boat and 30min/boat pushing speed. The best reduction process of second stage was 990℃with hydrogen flow of 1.5m3/h, boat loading of 400g/boat and 40min/boat pushing speed. By using nitrogen in mixing process can protect the tungsten powder oxidation. With keeping time of 10-15 minutes in lower temperature and sintered at 2550℃for 20 min, can prepare rods with density of 17.80g/cm3 and homogenous rare earth distribution.