Reaction with actinide oxides

An interesting, peculiar laboratory preparative reaction may finally be mentioned. This is based on the very high stability of the intermetallic compounds of actinides (and lanthanides) with the platinum family metals. The combined reduction capability of Pt with H2 (coupled reduction, see 6.7.2 fi) can be used to obtain, from its oxide, the platinide of the actinide metal. The An-Pt intermetallic compound can then be decomposed by heating in vacuum and the actinide can be obtained by distillation. 

Therefore, and to avoid possible reactions with the quartz wall, it was attempted to combine synthesis and crystal growth of actinide pnictides in a modified van Arkel process Actinide metal or carbide - the latter obtained by carboreduction of the oxide - are heated in the presence of the pnictogen and of the transporting agent at the... 

A single oxo bridge may subtend an angle between 140° and 180°, this angle being determined by steric or electronic factors (Table 3).95 103 Almost all these examples refer to the solid state, but there are also several homo- and hetero-nuclear M—O—M and M—O—M—O—M species known in solution. Often these are intermediates in, or products of, electron transfer reactions with oxide-bridging inner-sphere mechanisms. Examples include V—O—V in V(aq)2+ reduction of VO(aq)2+, and Act—O—Cr in Cr(aq)2+ reduction of UOj+ or PuOj+ a useful and extensive list of such species has been compiled. Tlie most recent examples are another V—O—V unit, this time from VO(aq)2+ and VOJ,105 and an all-actinide species containing neptunium(VI) and uranium-(VI).106 An example of a trinuclear anion of this type, with the metal in two oxidation states, is provided by (31).107... 

Th02—ternary oxides or oxide phases with tetravalent americium are stabilized. The solid-state reaction of Am02 with most group V elements yields compounds with trivalent americium which are isostructural with the analogous rare earth compounds. In the last types of reactions americium exhibits a typical actinide behavior. 

III and V elements. It was to be expected that americium would behave as a typical actinide element—i.e., that the majority of the ternary oxides to be expected contain Am (III). This assumption is based upon the analogous behavior of Ce02, PreOn, and Tb407 found in reactions with oxides of group V elements as well as upon the excellent thermal stability and the high lattice symmetry of compounds like and... 

The experimental observations on the actinide oxidation-reduction reactions are described, and the empirical results are tabulated. The rate laws have been interpreted in terms of net activation processes, and these have been tabulated togther with the associated activation parameters— aF, AH, and AS. An electrical analog is described which has been useful in interpreting complicated rate laws. Empirical correlations have been found between the formal entropies of the activated complexes and their charges, and for sets of similar reactions, between the hydrogen ion dependence and AF°, between AF and aF°, and between AH and AH°. The kinetic and physical evidence for binuclear species is discussed. 

Entropies of Activation vs. Heats of Activation. Kazakov, Pesh-chevitskii, and Erhenburg (36) plotted AS vs. AH for 34 actinide oxidation-reduction reactions and found a correlation which they expressed by AS = —50 -j- 3.44 X 10 AH this is equivalent to AF (at 208°K.) = 14,900 — 0.025 AH cal./mole, or that AF (298°K.) is essentially constant. The observed range is 12 to 21 kcal./mole so we believe that the "correlation" reported merely reflects the fact that for the reactions studied, the range of AF is small compared with those of AH or TaS. ... 

Because both zinc and magnesium are volatile, these acceptor alloy elements are separated from the actinides by vacuum distillation. The zinc-magnesium overhead product from vacuum distillation is recycled. After the volatile solvent metals are removed, the resultant distillation bottom products (U-Pu for core fuel and U for blanket fuel) are converted to suitable oxides by reaction with oxygen. The oxide products are available for refabrication into new fuel. The FP-3 elements that follow plutonium and the... 

Semiempirical calculations of free energies and enthalpies of hydration derived from an electrostatic model of ions with a noble gas structure have been applied to the ter-valent actinide ions. A primary hydration number for the actinides was determined by correlating the experimental enthalpy data for plutonium(iii) with the model. The thermodynamic data for actinide metals and their oxides from thorium to curium has been assessed. The thermodynamic data for the substoicheiometric dioxides at high temperatures has been used to consider the relative stabilities of valence states lower than four and subsequently examine the stability requirements for the sesquioxides and monoxides. Sequential thermodynamic trends in the gaseous metals, monoxides, and dioxides were examined and compared with those of the lanthanides. A study of the rates of actinide oxidation-reduction reactions showed that, contrary to previous reports, the Marcus equation ... 

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