Increasing the Longevity of Tungsten Filaments in a Zone Refiner

Zone refining is used for its ability to purify material and grow single crystals. To produce these single crystals, a suspended molten zone, generated by electron bombardment, passes along the polycrystalline stock. During a zone refining run, the filaments that produce the electron bombardment can fail. In this project, the longevity of tungsten filaments in a zone refiner was investigated. A new bombardment geometry was constructed to attempt to increase the longevity of the filaments. The new geometry had a shield machined into it to prevent line-of-sight impurities originating in the molten zone from striking the filaments. It was found that the new geometry did not significantly increase the lifespan of the filaments. The longevity of the tungsten filaments was longer in a zone refiner that had a pillbox with larger dimensions. It is thought that the increased pillbox size allows for a reduction in the density of impurities, thus limiting the amount striking the filament