Electron-beam zone melting

Magnesium chloride and excess magnesium are removed by distillation at reduced pressure. Pure zirconium may be prepared by several methods that include iodide decomposition process, zone refining, and electron beam melting. Also, Zr metal may be electrorefined in a molten salt bath of potassium zirconium fluoride, K2ZrFe... 

Microstructure. The microstructure of a tungsten sample, which influences the mechanical properties within a wide range, depends on the type of preparation (powder metallurgy, arc cast, electron beam melted, zone refined, chemical vapor deposition) and the subsequent working (deformation, annealing, recrystallization). 

If further purification is desired, rods are produced by compacting and sintering and are subjected to electron beam floating zone melting. This procedure does not further reduce the concentrations of uranium and thorium, but does reduce the concentrations of many other elements as shown in Table 5.15. Moreover, residual impurity elements are distributed homogeneously. 

Figures 1 and 2 shows the principles of thermal and electron beam evaporation. Materials with a low melting point (many metals) are evaporated from graphite boats by resistive heating. For materials with a higher melting point (e.g., metal oxides), electron beam evaporation is commonly used. Evaporation is a fast process with deposition rates of 500-5,000 nm/s for metals and 100-1,000 nm/s for oxides. Film quality and adhesion to the substrate may suffer from the low energy of evaporated particles (0.2-0.5 eV). Modem evaporatiOTi processes therefore make use of an additional plasma. The evaporated particles crossing the plasma zone are activated and ionized and consequently can form a much denser film.

Crucible-less techniques require no physical containment and rely on the surface tension of a free floating molten zone in contact with the corresponding solid. This method of crystal growth is concerned primarily with vertical float zone melting with RF, electron beam or infra-red heating and will be discussed in section 4.3.4. 

In the very pure electron beam melted and zone-refined quality, the hardness of niobium is 0.04-0.05 N/mm, that of tantalum 0.07-0.09 N/mm. ... 

Fig. 104. Selected-aiea electron difOaction patterns of the icosahedial Zn55Mg Yj alley prepared by melt spinning. Incident beam along (a) fivefold axis, (b) threefold axis, (c) twofold axis, and (d) mirror-zone axes.

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