PREPARATION OF THE ACTINIDE METALS
1982; Elsevier BV; Linguagem: Inglês
10.1016/b978-0-08-029193-2.50021-3
Autores Tópico(s)Fusion materials and technologies
ResumoThe actinide elements are a unique series of elements with properties changing from those of the transition elements to those typical of the localised partially filled shell. In the first part of the series (from Pa to Pu) the 5f electrons are similar to the d electrons in the transition metals, in particular they hybridize with the 6d and 7s electrons and participate in the chemical bond. The lanthanide behaviour appears at americium with well localised 5f electrons. This situation complicates the work of the metallurgist who has to diversify his efforts into different preparation, refining, and crystal growth techniques, mastering those typical of transition elements as well as those typical of the lanthanides to produce a sufficiently large spectrum of samples of the different elements. Thorium and protactinium metals are obtained by a van Arkel process starting from the carbides. The van Arkel process allows an excellent refining of the metal and small single crystals are produced. Uranium, neptunium and plutonium are prepared by the calciothermie reduction of the fluorides and refined by electrolysis in molten salts. Starting with americium, the typical lanthanide metal preparation processes are used (metallothermic reduction of the oxide by lanthanum (Am, Cf) or thorium (Pu, Cm) or of the carbide by tantalum (Pu, Cm) followed by the evaporation of the metal in vacuum). The metals are refined by evaporation in high vacuum and large single crystals are obtained by physical vapour transport. The purest actinide metal (with the exception of thorium) never reaches a 99.9% purity level. The lack of characterization methods which was limiting progress in the refining of the actinide metals is now corrected and complete characterization of the purest actinide metal single crystal is possible down to the ppma level.
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