Determination of Nitrogen in Powdered Niobium by High Temperature Vacuum Extraction with the Graphite Addition Procedure

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  • Ishikawa Makoto
    Department of Industrial and Engineering Chemistry, Faculty of Science and Technology, Science University of Tokyo
  • Ogahara Iichi
    Department of Industrial and Engineering Chemistry, Faculty of Science and Technology, Science University of Tokyo

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A graphite addition procedure proposed by the authors has been successfully applied to the determination down to the ppm range of nitrogen in powdered niobium. The optimum experimental conditions were established as follows: a 1:1 atomic ratio mixture of powdered niobium to powdered graphite was made into a pellet in cold press; the pellet was extracted in a graphite crucible at 2200–2250°C by the vacuum extraction method; and the time required for the complete extraction of a pellet weighing 0.5–1.2 g was within 30–60 min at the given temperatures. The results obtained by this method agreed well with those obtained by the Kjeldahl method. The precision of the variation coefficient was less than 5% for −60 to −325 mesh niobiums containing 0.01–0.04 wt% of nitrogen.<BR>Results of the studies of the effect of graphite and kinetics of the release of nitrogen by the present graphite addition procedure showed that the extraction of niobium pellets with graphite at high temperature promoted the formation of highly extractive NbC, and that the rate of release of nitrogen proceeded according to the first-order rate equation, making complete extraction possible in a relatively short time at high temperature. It was found that the extraction of nitrogen was closely related to the composition of the extracted products. It was supposed that the extraction from a niobium rod in a graphite crucible was difficult owing to Nb2C phase formation even at high temperatures.<BR>Incorporating the use of a molybdenum crucible free from the formation of carbides allowed the nitrogen extraction at high temperature from a niobium rod, with an extended collection time for nitrogen.

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