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CHROMIUM
Natural Abundance, Stable Isobars Cr50, 4.31%, Ti50 Cr52, 83.76%, aV50 Cr53, 9.55%, Fe54 Cr54, 2.38% Potassium dichromate, chromium sesquioxide, chromium oxychloride, and chromic chloride have been used as charge material in the separation of chromium isotopes. Chromic chloride is the preferred material, and a charge usually consists of 150 g CrCl3 in a style C-16 graphite charge bottle. A two step procedure is used to prepare CrCl3 in the laboratory. Ammonium dichromate is thermally decomposed to produce low density chromium sesquioxide which is reacted with carbon tetrachloride to produce the charge material. Ammonium dichromate is dropped into a heated stainless steel beaker with a cover. Only a few grams are used at a time since the decomposition is violent. The resulting sesquioxide, which is of very low density, is placed in a quartz boat and this vessel is inserted into a Vycor reactor tube 10 cm in diameter by 80 cm in length. One end of the reactor is reduced to a diameter of 1.5 cm and connected to the side arm of a 500 ml flask containing carbon tetrachloride. The exhaust end of the reactor is plugged with glass wool to develop a slight back pressure of carbon tetrachloride vapor, thus increasing the efficiency of the chlorination process. The Vycor reactor tube is heated by an electric tube furnace to 725 deg. C and the carbon tetrachloride flask is warmed by an electric mantle. Carbon tetrachloride vapor is conducted through the side arm of the flask into the tube, where it reacts on contact with the hot chromium oxide to form CrCl3 . The reaction is terminated after six hours. The unreacted green chromium sesquioxide is localized at each end of the boat and can be separated easily from the purple CrCl3 . The bulk density of CrCl3 produced in this manner is low, and it is necessary to press it into a dense cake in order to get the desired amount into the charge bottle. Metallic chromium is not considered toxic; however, all of its compounds are acute toxicants. Most chromium salts have a corrosive action on the skin and mucous membranes producing deep lesions or ulcers which heal slowly. Ingestion, inhalation, and skin contact must be prevented by the use of a fume hood with good exhaust ventilation, respirators, and rubber gloves. aV50, natural abundance 0.25%, is radioactive with a half-life of 4.8 x 1014 years. |
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