Tungsten thoriated

Also increasingly common, as CVD precursors, are many halogen-acetylacetonate complexes, such as trifluoro-acetylacetonate thorium, Th(C5H4F302)4, used in the deposition of thoriated tungsten for thermionic emitters, the trifluoro-acetylacetonates of hafnium and zirconium and the hexafluoro-acetylacetonates of calcium, copper, magnesium, palladium, strontium, and yttrium. 

Thoriated tungsten, whose surface has been carburized at high temperatures, have lower work functions than pure tungsten and emit equivalent electron beam currents at lower temperatures thereby extending the life and stability when compared to regular tungsten sources. These sources require a stable, high vacuum (10 to 10 torr) and are more difficult to fabricate. 

Apparatus. Plasma Jet. A section of the plasma arc gun is shown in Figure 1. A direct current arc was struck between the thoriated tungsten rod, which acted as the cathode, and the copper tube anode. Both electrodes were... 

Use Ceramics (high temperature), gas mantles, nuclear fuel, flame spraying, crucibles, medicine, nonsilica optical glass, catalyst, thoriated tungsten filaments. 

Use Reagent for determination of fluorine, thoriated tungsten filaments. 

FIGURE 1.21. Variation of emission current density with tungsten for pure and thoriated tungsten electrodes [1.93] according to Ref. 1.92. 

In most of diese applications, either thoriated tungsten is used (service temperature 1700-1800 °C), or impregnated cathodes, based on Ba0/Al203/Ca0 additions (so-called dispenser cathodes service temperature 900-1250 °C). However, because of its radioactive nature, thoriated tungsten is currently being more and more replaced by timgsten with rare earth (RE) oxide additions or W-Zr02 (see also Section 6.2.2). 

Thorium is a radioactive element and a natural a-emitter (specific activity 4250 Bq/g and half-life 1.4 x lO a). Health and environmental considerations (evaporation and inhalation of thorium during welding disposal of grinding dust) have therefore in the past led to a partial replacement of thoriated tungsten for welding operations and in the lighting industry by thoria-free ODS tungsten alloys [6.24]. 

FIGURE 7.5. Thoriated tungsten cathode (left) and thoriated tungsten anode (right) for xenon short-arc lamps used for wide-angle cinema projection. By courtesy of Plansee AG, Austria. 

Typical examples, which will be discussed in more detail below, are the zinc process, or the Coldstream process for reclamation of cemented carbide scrap, and the oxidation and subsequent reduction of tungsten heavy metal turnings or thoriated tungsten (see Table 11.3). 

Thoriated tungsten powder Thoriated tungsten pieces, turnings, powder... 

For information about hazardous substances in the production of tungsten alloys, such as thoriated tungsten, cobalt, or nickel-containing cemented carbides, see Chapter 14. 

Electrodes of 2%-thoriated tungsten are the most frequently used water-cooled nonconsumable electrodes. Water-cooled copper anodes have been widely used in experimental work. Figure 1 shows a typical plasma jet assembly. A reactor chamber may be of any configuration desired to accommodate different feeding and quenching devices. 

The reaction occurring in thoriated tungsten filaments was also discussed. [1963ALL/MCD]... 

Electron sources used in EBL exposure tools are similar to those used in conventional electron microscopes. They can be divided into two main groups— thermionic or field emission—depending on the way in which they emit electrons. The sources that rely on the emission of electrons from a material that is heated to a temperature at which electrons are emitted from the surface are referred to as thermionic sources. These sources are fabricated from materials such as tungsten, thoriated tungsten, or lanthanum hexaboride (LaBe). ... 

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