Uranium sesquioxide

Ives et al. (79) tended to reject our hypothesis that brown colours of mixed oxides (and in particular less pure NdaOs) are due to traces of praseodymium. However, these authors noted the interesting effect that such dark colours (also of Pro,oaTho.9802) bleach in the reflection spectrum at higher T. It was noted that mantles of NdaOa alone rapidly hydrate to a pinkish powder (carbonate ) in humid air. It is weU-known that -type sesquioxides are far more reactive, and for instance dissolve almost instantaneously in aqueous acid, than cubic C-type samples. Ives et al. 19) also studied the broad continuous spectrum of the orange light emitted from Thi- 11 0 2+2/ where the oxidation state of uranium is rather uncertain. 

Isostructural compounds include some other lanthanide and actinide sesquioxides and oxide-chalcogenides such as La202X (X = S or Se) as well as Th2N2X (X = O, S, Se), Th2NOX (X = P, As) and analogous uranium compounds. In all cases the third anion is the one in octahedral coordination. (Antistructures include N2Li2Zr.)... 

The so-called sesquioxide (PuOi 5 i.75) is a typical mixed oxidation state oxide, similar to those formed by uranium, praseodymium, terbium, titanium, and many other metals. Its composition shows continuous variation with changes in temperature and pressure of oxygen above the oxide. 

The melting-point of tungsten is higher than that of any other known metal. The metals are stable in air at ordinary temperatures, but when heated they exhibit a remarkable difference in behaviour. Uranium burns briskly at 170° C., producing uranous oxide UO2 molybdenum at a red heat yields the trioxide M0O3 chromium only burns at 2000° C. and forms the sesquioxide CrjOg tungsten is not oxidised at any temperature, except in the vapour form. 

After complete conversion to U02(B02)2 is achieved, the uranyl salt is freed from B2O3 by dissolving the excess sesquioxide in absolute methanol. Reasonable care should be taken to minimize access of moisture to the metaborate during the purification step, but completely anhydrous conditions are not required. A sample of IJO2B2O4 prepared as described above gave the following analytical results uranium found 66.80%, theoretical 66.93%, and boron found 6.02%, theoretical 6.08%. 

Unlike the results found by Loyland et al (30) for uranium, we observed no repartitioning of either plutonium or americium amongst the various operational soil fractions after SFE. In all SFE experiments conducted in this work a net reduction of both plutonium and americium activity was observed across all soil fractions. Additionally, as the ligand system was changed from the less acidic beta-diketone TTA to the more acidic beta-diketone HFA the extraction efficiency of plutonium from the sesquioxide and residual fractions increased dramatically. Thus, it is likely that a more effective, and possibly complete, extraction could be performed if a reagent were added in small quantities to the extraction mixture to specifically attack the sesquioxide fraction. 

As Am is considered to be the first of the lanthanide-like actinides, it would be expected that its oxide system would bear some resemblance to the oxide systems of the lanthanides. For Am, a monoxide, sesquioxide,.a dioxide, and an oxide with an O/M ratio intermediate to that of the sesquioxide and dioxide have been reported. Although the quantity of Am has permitted extensive investigations of its oxide system, the number of studies is still small relative to the efforts that have been extended on the uranium and plutonium oxide systems. In part this is due to the more intense radioactive nature of Am but also to a decreased interest in its chemistry in contrast to those of U and Pu, whose applications in weapons and reactors promoted many detailed studies of those elements. However, the number of studies that have been carried out on the americium oxygen system is still large in comparison to the number of studies with higher actinides. 

Simple calculations confirm that the sesquioxides of uranium and neptunium are significantly unstable with respect to disproportionation into metal and dioxide, e.g. using enthalpies of formation from Tables 17.5 and 17.14 and estimated entropies,... 

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