Actinide metals purity

These early studies were carried out on metals of typically 90-99% purity, which sufficed to determine at least their gross properties. During the 1960s, interest diminished somewhat in actinide metallurgy due in part to the increasing use of ceramic rather than metallic fuel elements in nuclear reactors. The bulk of actinide metal research was for secret military purposes and only a fraction of the fundamental research was published. 

The actual situation with regard to the purity of most of the actinide metals is far from ideal. Only thorixun (99), uranium 11,17), neptunium 20), and plutonium 60) have been produced at a purity > 99.9 at %. Due to the many grams required for preparation and for accurate analysis, it is probable that these abundant and relatively inexpensive elements (Table I) are the only ones whose metals can be prepared and refined to give such high purities, and whose purity can be verified by accurate analysis. The purity levels achieved for some of the actinide metals are listed in Table II. For actinium (Ac), berkelium (Bk), californium (Cf),... 

The yield and rate of the tantalothermic reduction of plutonium carbide at 1975 K are given in Fig. 3. Producing actinide metals by metallothermic reduction of their carbides has some interesting advantages. The process is applicable in principle to all of the actinide metals, without exception, and at an acceptable purity level, even if quite impure starting material (waste) is used. High decontamination factors result from the selectivities achieved at the different steps of the process. Volatile oxides and metals are eliminated hy vaporization during the carboreduction. Lanthanides, Y, Ti, Zr, Hf, V, Nb, Ta, Mo, and W form stable carbides, whereas Rh, Os, Ir, Pt, and Pd remain as nonvolatile metals in the actinide carbides. Thus, these latter elements... 

The Preparation of High Purity Actinide Metals and Compounds... 

High purity actinide metals are subject to sophisticated investigations of bonding related properties they are starting materials for the synthesis of compounds. 

The preparation of larger quantities of high purity actinide metals is being based increasingly on separation or purification via evaporation of the actinide metal In these methods, actinide compounds (oxides or carbides) are reduced by metals forming nonvolatile oxides or carbides under conditions where the actinide metals can be volatilized ... 

The vapour pressure ratio of actinides to noble metals is also the basis of the actinide metal preparation by thermal dissociation of intermetallic compounds. Such intermetallic compounds of An and noble metals can be prepared by hydrogen reduction of a mixture of an An oxide and a finely divided noble metal (Pt, Ir.. in the absence of noble metals, hydrogen reduction of An oxides is impossible. Am and Cm metals have been obtained by thermal dissociation of their intermetallic compounds with Pt and Ir High purity Th and Pa, the least volatile actinide metals, can be prepared by thermal dissociation of their iodides, which form readily by reaction of iodine vapour with car-... 

As many physical properties of the actinide metals depend significantly on the sample purity, refining of the metals is mandatory. The choice of the refining methods is determined by the chemical reactivity of the actinide metal in the presence of the constituents of air, by high temperature reactions with crucible materials, by the specific radioactivity and the availability of the actinide elements. 

Muller, W., Spirlet, J.-C. The Preparation of High Purity Actinide Metals and Compounds. 

Preparation Methods. Actinide metal preparation is based on methods known or developed to yield high purity material by metallothermic reduction or thermal dissociation of prepurified compounds. Electrolytic reduction is possible from molten salts, but not from aqueous solutions. Further purification of the metals can be achieved by electrorefining, selective evaporation or chemical vapour transport. 

Due to its drawbacks (difficult preparation of water-free starting material, neutron emission from ( a,n) reactions, presence of non-volatile impurities in the product), methods involving vaporisation of the actinide metal after reduction of a compound (oxide, carbide) are preferred. If the vapour pressure of the reductant and that of the actinide compound are markedly lower than that of the metal formed, the latter can be removed from the reaction mixture via the vapour phase and condensed in high purity ... 

Characterization. Actinide metal samples for the determination of properties related to bonding have to be characterized for chemical purity and phase homogeneity. Purity is checked by chemical or physical analysis, crystal structure is determined by X-ray or neutron diffraction techniques phase heterogeneities can be observed by metallography. 

Purity. The use of evaporation methods for the preparation of actinide metals reduces the number and quantities of impurities. Nevertheless, possible chemical contaminations from reactions with reducing agents, container vessel or crucible material or with constituents of the atmosphere as well as the accumulation of products of radioactive decay have to be taken into account. 

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