THE PREPARATION OF PROTACTINIUM METAL ON THE GRAM SCALE
Protactinium occupies a particularly interesting position in the actinide series as it is the first element in which a 5f electron is expected to participate in the chemical bond. Owing to the scarcity of this element only a few measurements have been made on well characterized material. Progress in actinide solid state research largely depends on the availability of sufficiently large samples, of the order of grams, of pure metal for physical property measurement and as starting materials for the preparation of compounds by direct synthesis between the constituent elements. The production of protactinium metal by the reduction of the fluoride with barium, with lithium, with calcium, and with Mg - Zn alloys is described in the literature. The van Arkel process (iodide process) is successfully applied to refine the crude metals. The metal is transported as volatile iodide via the gas phase to a hot zone in which the iodide decomposes into its components. The iodine diffuses by a chemical transport process. The van Arkel process can be used to prepare the metal from compounds which react with the transporting agent at a temperature compatible with the experimental conditions. This is the case with thorium and protactinium carbide which can easily be produced by the carbothermic reduction of the oxides and reacted with iodine at temperatures above 300 degrees C to give volatile iodides. When protactinium iodide is thermally dissociated on tungsten wire or strips, filament breaking, low deposition rates (10 mg h**-1) and difficulties associated with the recovery of the metal deposit limit the yield and the purity. An improved van Arkel system in which the volatile iodide is thermally dissociated on an r.f.- heated tungsten or protactinium sphere allows the preparation of protactinium metal in gram amounts.
Bibliographic Reference: JOURNAL OF THE LESS-COMMON METALS, VOL. 92 (1983), PP. L27-L32
Record Number: 1989122021900 / Last updated on: 1987-01-01
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