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SELENIUM
Natural Abundance, Stable Isobars Se74, 0.87%, Ge74 Se76, 9.02%, Ge76 Se77, 7.58%, Kr78 Se78, 23.52%, Kr80 Se80, 49.82%, Kr82 Se82, 9.19% Selenium tetrachloride, selenium dioxide, and selenium metal have been used as charge material in the separation of selenium isotopes. The oxide is preferred. The usual charge consists of 500 g SeO2 a style X-5 stainless steel charge bottle. Selenium dioxide may be easily prepared in the laboratory. Selenium metal pellets are dissolved in hot concentrated nitric acid forming selenious acid. The solution is evaporated to dryness and the solid selenious acid is heated until the yellow color disappears, leaving the white product SeO2 . The SeO2 is outgassed by heating to 300ºC, or just below its sublimation temperature of 317ºC, for two hours. Selenium tetrachloride may be prepared by reacting the metal with chlorine gas under a protective blanket of liquid carbon tetrachloride. Selenium metal pellets are placed in a flask and covered with carbon tetrachloride. Chlorine gas is then passed through the carbon tetrachloride. The chlorine gas flow must be carefully controlled since the reaction is exothermic and temperatures above 65ºC tend to produce selenium monochloride. After conversion to the yellow solid selenium tetrachloride is complete, the product is transferred from the flask to a suitable storage container, care being taken to maintain a layer of carbon tetrachloride over it. Selenium tetrachloride is hygroscopic and the layer of carbon tetrachloride protects it from atmospheric moisture. Selenium and its compounds are toxic. Every precaution should be taken to eliminate the possibility of ingestion, inhalation, or skin absorption. It is recommended that a fume hood with good exhaust ventilation be used, and respirator, rubber gloves, and safety goggles be worn when working with selenium and its compounds. |
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