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TELLURIUM
Natural Abundance, Stable Isobars Te120, 0.089%, Sn120 Te122, 2.46%, Sn122 aTe123, 0.87%, Sn124 Te124, 4.61%, Sb123 Te125, 6.99%, Xe124 Te126, 18.71%, Xe126 Te128, 31.79%, Xe128 Te130, 34.49%, Xe130 Ba130 Tellurium tetrabromide, tellurium tetrachloride, tellurium dioxide, and tellurium metal have been used as charge material in the separation of tellurium isotopes. The oxide is preferred over the bromide or the chloride since it has a lower vapor pressure. The usual charge consists of 450 g TeO2 in a style C-16 graphite charge bottle. Tellurium dioxide is prepared by dissolving the metal in hot nitric acid and pouring the resulting solution into a beaker of cool water, causing hydrolysis and precipitation of tellurous acid. Warming to 50ºC converts tellurous acid to TeO2 which is removed by filtration, washed, transferred to an evaporating dish, and heated at 400ºC for two hours under vacuum. After cooling, the material is stored in sealed containers. Tellurium dioxide does not sublime at atmospheric pressure but melts to a dark yellow liquid at 452ºC. Tellurium tetrabromide can be prepared by gradually adding the metal to an excess of liquid bromine. The reaction vessel should be immersed in an ice bath since the reaction is highly exothermic and may be difficult to control. Excess bromine is removed by heating and leaves the desired compound, tellurium tetrabromide. Tellurium tetrachloride can be formed by the direct combination of the elements at 350ºC. The rate of reaction is controlled by the flow rate of chlorine gas. Tellurium and its compounds are quite toxic. Every precaution must be taken to eliminate the possibility of ingestion, inhalation, or skin absorption. The use of a fume hood with good exhaust ventilation and the wearing of respirator, rubber gloves, and safety goggles are strongly recommended when handling tellurium and its compounds. aTe123 is radioactive with a half- life of > 1014 years. |
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