Zone-refining has been used to optimize the ductility of copper, making it possible to cold-draw the fine-gauge threads needed for interconnects in very large-scale integrated circuits.Ī lamellar composite of soft, ductile ferrite Crystal defects are also eliminated: Pfann reduced the dislocation density in metallic and semi-metallic crystals from about 3.5 to almost zero. Repeated traversing of the bar with a set of coils can reduce the impurity content well below the limit of detection (e.g.
A net movement of impurity atoms to one end of the bar takes place. The first solid to freeze is purer than the average composition by a factor of k, while that which freezes last, at the trailing interface, is correspondingly enriched in solute. If a bar of impure metal is threaded through a heating coil and the coil is slowly moved, a narrow zone of melt can be made to progress along the bar. Considering the portion of Figure 3.12 where addition of solute lowers the liquidus temperature, the concentration of solute in the liquid,, will always be greater than its concentration in the solid phase that is, the distribution coefficient k = / is less than unity. The method takes advantage of non-equilibrium effects associated with the ‘pasty’ zone separating the liquidus and solidus of impure metal. Pfann, its development being ‘driven’ by the demands of the newly invented transistor for homogeneous and ultrapure metals (e.g. Make sure that you know the following words and word combinations:Įxtreme purification - экстремальная очисткаĬorrosion resistance - устойчивость к коррозииĮxtreme purification of a metal can radically improve properties such as ductility, strength and corrosion resistance. Read text B and choose the best title for it:
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