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BORON
Natural Abundance, Stable Isobars B10, 18.45%, None B11, 81.55% The two charge compounds which have been used for the separation of the isotopes of boron are boron trichloride and the calcium fluoride-boron trifluoride complex. The preferred charge material is BCl3. Normal BC13 is procured from commercial sources as a cylinder gas and used as received. Boron enriched to 96% B10 in one case and to 89% B11 in another, was available in the form of CaF2 · BF3 for calutron separations. A charge of 500 g of this complex was used in a style X-5 stainless steel charge bottle. Since recovery of the unresolved charge material is necessary in separations of enriched boron, a controlled experiment using normal boron in the form of CaF2 · BF3 was run to determine where within the calutron system and in what form the unresolved material would deposit. This experiment showed that approximately 5% of the unresolved boron charge was trapped in the vacuum pump oil, and that 95% passed into the vacuum exhaust system where it could be absorbed in a 10% sodium hydroxide scrubber system. Such an exhaust scrubber system was used in all separations of enriched boron, and following each series of runs the unresolved boron was recovered from the scrubber solution. In making this recovery a slight excess of calcium chloride solution is added to the scrubber solution to remove the fluoride ion by the precipitation of calcium fluoride, which is removed by filtration. The basic filtrate is evaporated to dryness, pulverized in a mortar, and transferred to a distillation flask containing methanol. Acetic acid is added to the flask until the mixture is slightly acidic. Heat is applied gently to the flask and methyl borate begins to distill at 65° C. A small flow of dry air is used to sweep the distillate into a flask fitted with a reflux condenser containing 8 N hydrochloric acid. The hydrochloric acid solution is heated under reflux conditions to completely hydrolyze the methyl borate. After completing the distillation and hydrolysis, the hydrochloric acid solution containing the boron is cooled, transferred to a beaker, and evaporated to dryness on a steam bath. The resulting boric acid is dissolved in hot water, decolorized with activated charcoal, filtered, and again evaporated to dryness. The purified product is stored as boric acid. Boron and its compounds are considered toxic. The use of a respirator during dusting or misting operations and the use of safety glasses and rubber gloves are recommended. |
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