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TUNGSTEN
Natural Abundance, Stable Isobars aW180, 0.135%, Hf180 W182, 26.4%, bTa180 W183, 14.4%, Os184 W184, 30.6%, Os186 W186, 28.4% Tungsten hexafluoride, tungsten hexachloride, tungsten hexabromide, tungsten dibromide, tungsten dioxide, tungsten dioxydichloride, and tungsten trioxide have been used as charge material in the separation of tungsten isotopes. Tungsten hexachloride is the preferred charge compound from an operational standpoint, The usual charge consists of 400 g WCl6 in a style X-5 stainless steel charge bottle. Tungsten hexachloride is prepared in the laboratory by direct combination of the elements at an elevated temperature. It has been found that powdered tungsten metal will chlorinate at a much faster rate when platinized asbestos is used as a catalyst in the chlorination process. Chlorination of tungsten is performed in a Pyrex tube 10 cm in diameter by 120 cm in length, which has one end open and the other constricted to a diameter of approximately 1.5 cm. A gas-scrubbing bottle containing concentrated sulfuric acid is connected with rubber tubing to the constricted end of the chlorination reactor. Approximately 500 g tungsten powder is placed on top of 15 g of 5% platinized asbestos spread over the bottom of a Pyrex boat, and the boat is then inserted into the reactor. The chlorination reactor tube is placed in an electric tube furnace in such a manner that the tungsten is in the heated zone and near the constricted end. Nitrogen gas is passed through the reactor while it is being heated to a temperature of 550ºC. Any moisture condensing in the cool end of the reactor is driven out by carefully flaming the outside of the tube. A constricting plug of glass wool is inserted into the open exhaust end of the reactor to prevent entry of atmospheric moisture. This porous plug also creates a slight back pressure which increases the efficiency of chlorination. At this point the flow of nitrogen is replaced by chlorine and the reaction allowed to continue overnight. As the tungsten hexachloride forms, it sublimes from the heated zone and collects near the cool exhaust end of the reactor. The heat is turned off the following morning and the reactor allowed to cool with a flow of nitrogen passing through it. The WCl6 product is removed from the reactor and stored in sealed containers. Spectrographic analysis of the product indicates contamination by platinum is < 0.04%. Tungsten and its compounds are not considered to be industrial hazards; however, respirators should be worn when dusting occurs. aW180 is radioactive with a half-life of ~ 3 × 1014 years. bTa180, natural abundance 0.012%, is radioactive with a half-life of >107 years. |
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