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| Metallurgy - Special Methods of Refining Metals |
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| This method is used for obtaining ultra pure metals like germanium, silicon and gallium. |
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| Principle |
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| A molten metal when gradually cooled, crystallizes into ultra pure metal. The impurities continue to be in the molten state and flow away from the crystallized metal. |
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| Zone Refining |
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| Method |
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 A circular heater is fit around one end of a rod of impure germanium |
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The heater heats a zone or band of the impure rod, it is in contact with |
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The heated zone of germanium melts along with its impurities |
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When the heater gradually shifts to the next zone pure germanium cools and crystallizes out |
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The molten impurities shift to the next zone along with the heater |
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As the heater shifts from one end of the rod to the other, impurities also shift to the extreme end from where it is discarded |
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| Thus, after repeating the process a few times, ultra pure germanium is obtained. |
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| This method is used for obtaining ultra pure titanium. |
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| Principle |
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| Thermal decomposition of titanium tetraiodide. |
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| Method |
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Impure titanium is heated to 250oC with iodine. When titanium reacts to form volatile titanium tetraiodide |
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| Impurities present in titanium do not react with iodine. Therefore, the vapors titanium tetraiodide formed is ultra pure. |
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Vapors of titanium tetraiodide are passed through a bulb containing a tungsten filament heated to 14000c. |
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| Titanium formed is
ultra pure. The iodine vapor formed is recycled. |
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