Uranium thermodynamic properties

In the sohd state, uranium metal exists in three aHotropic modifications. The transformation temperatures and the enthalpies of transformation are given in Table 5. The thermodynamic properties of uranium metal have been deterrnined with great accuracy and have been discussed (50). 

Americium. The low solubilities and high sorption affinity of thorium and americium severely limit their mobility under environmental conditions. However, because each exists in a single oxidation state—Th(IV) and Am(III)— under environmentally relevant conditions, they are relatively easy to study. In addition, their chemical behaviors provide valuable information about the thermodynamic properties of trivalent and tetravalent species of uranium, neptunium, and plutonium. 

Chiotti, P. Mason, J. T., Phase Diagram and Thermodynamic Properties of the Uranium-Zinc System, J. Less Common Metals, 1975, Uo, 39. 

Eh are usually less than 10 M because of the extremely low solubilities of these solids. In the U(V) oxidation state, uranium occurs as the UOJ ion which forms relatively weak complexes (Grenthe et al. 1992). This species is only found at intermediate oxidation potentials and low pH s and is unstable relative to U(IV) and U(VI). In oxidized surface- and groundwater-uranium is transported as highly soluble uranyl ion (UOf ) and its complexes, the most important of which are the carbonate complexes. The thermodynamic properties of these minerals and aqueous species must be known if we are to understand the reactions that may control U concentrations in natural waters. 

Hemingway, B. S. 1982. Thermodynamic properties of selected uranium compounds and aqueous species at 298.15 K and 1 bar at higher temperatures—Preliminary models for the origin of coffinite deposits. Open File Report 82-619, U.S. Geol. Survey. 

TAK/WES] Takahashi, Y., Westrum, Jr., E. F., Uranium monoselenide. Heat capacity and thermodynamic properties from 5 to 350 K, J. Phys. Chem., 69, (1965), 3618-3621. Cited on page 385. 

II. International Atomic Energy Agency The Plutonium-Oxygen and Uranium-Plutonium-Oxygen Systems A Thermochemical Assessment, Report of a Panel on Thermodynamic Properties of Plutonium Oxides, Vienna, Oct. 1966, Tech. Rept. Series No. 79, Vieima, 1967. 

Uranium Halides. The principal halides are listed in Table 28-9 they have been studied in great detail and chemical, structural and thermodynamic properties are well-known. 

Rand, M. H., and O. Kubaschewski, The Thermodynamic Properties of Uranium Compounds, Wiley, New York, 1963. 

Cater, E. D., Thom, R. J., Walters, R. R., Thermodynamic properties of uranium and thorium monosulfide, IMD Special Report Series, Report 10, (1964). Cited on pages 271, 481. 

Willis, B.T.M., 1965, Thermodynamic Properties of Uranium Dioxide and Related Phases, in Technical Reports Series No. 39 (International Atomic Energy Agency, Vienna) ch. 

Tagawa, H., Phase Relations and Thermodynamic Properties of the Uranium Ntride System, Journal of Nuclear Materials, pp. 78-79, Vol. 51, 1974. 

D6. Wagman, D.D. W.H. Evans V.B. Parker R.H. Schumm B.L. Nuttall Selected Values of Chemical Thermodynamic Properties Corapounda of Uranium, Protactinium, Thorium. Actinium, and the Alkali Metals. NBS Tech Note 270-8 (1981)... 

Langmuir D. and Applin K. Refinement of the thermodynamic properties of uranium minerals and dissolved species, with application to the chemistry of groundwaters in sandstone-type uranium deposits. Circ. U.S. geol. Surv. 753, 1977, 57-60. 

The thermodynamic data, Gibbs energies, enthalpies and entropies of formation of intermetallic compounds have been obtained from a literature search. We have also consulted the handbook Selected values of thermodynamic properties of binary alloys by Hultgren et al. (1973a) and a compilation of thermodynamic data on transition metal based alloys done by de Boer et al. in 1988. For the actinide-based alloys a literature search and a critical analysis of the data was done by Rand and Kubaschewski (1963) for uranium compounds, by Rand et al. (1966) for plutonium alloys, by Rand et al. (1975) for thorium alloys, and more recently by Chiotti et al. (1981) for binary actinide alloys. We have included in our review the data obtained from the original publications and also the assessed data of Chiotti et al. (1981) when they were different. 

Forsberg, H.C., 1960, Thermodynamic Properties of Uranium Mercurides, Rep. ORNL-2885 (Oak Ridge National Laboratory, Oak Ridge, TN). 

The last chapter (134) in this volume is an extensive review by Colinet and Pasturel of the thermodynamic properties of landianide and actinide metallic systems. In addition to compiling useful theiTnodynamic data, such as enthalpies, entropies, and free eneigies of formation and of mixing, the authors have made an extensive comparative analysis of the thermodynamic behavior of the rare earths and actinides when alloyed with metallic elements. They note that when alloyed with non-transition metals, the enthalpies of formation of uranium alloys are less negative than those of the rare earths while those of thorium and plutonium are about the same as the latter. For transition metal alloys the formation enthalpies of thorium and uranium are more negative than diose of the rare earths and plutonium (the latter two are about the same). The anomalous behaviors of cerium, europium and ytterbium in various compounds and alloys are also discussed along with the effect of valence state changes found in uranium and plutonium alloys. 

In the assessment of the refining performance of uranium, systematic data has been reported for the chemical properties of uranium complex in various alkali chlorides such as LiCl-RbCl and LiCl-CsCl mixtures [3-5], Information on the coordination circumstance of solute ions is also important since it should be correlated with stability. The polarizing power of electrolyte cations controls the local structure around neodymium trivalent Nd " " as an example of f-elements and the degree of its distortion from octahedral symmetry is correlated with thermodynamic properties of NdClg " complex in molten alkali chlorides [6]. On the other hand, when F coexists with Cr in melts, it is well-known that the coordination circumstances of solute ions are drastically changed because of the formation of fluoro-complexes [7-9]. A small amount of F stabilizes the higher oxidation states of titanium and induces a negative shift in the standard potentials of the Ti(IV)ITi(ni) and Ti(III)ITi(II) couples [7, 8], The shift in redox potentials sometimes causes specific electrochemical behavior, for example, the addition of F to the LiCl-KCl eutectic leads to the disproportionation of americium Am into Am " and Am metal [9],... 

Critical efforts to compile and to assess actinide thermodynamic properties have improved in more recent years. Krestov [10] prepared an extensive compilation of rare-earth and actinide thermochemical properties. Rand [11] comprehensively and critically reviewed thorium thermodynamics, and the thermodynamics group of the US National Bureau of Standards [12] published the final volume of the Technical Note 270 series, which included the elements actinium through uranium. At nearly the same time the parallel compendium of Glushko et al. [13] was published in the USSR. The most contemporary and thoroughly annotated compilation is the fourteen-part series issued under the auspices of the International Atomic Energy Agency, 7%e Chemical Thermodynamics of Actinide Elements and Compounds, of which nine volumes [14-21, 354] have been published as of the time of writing. 

Although a number of binary uranium oxides with 0/U > 2.00 are known, along with many of their thermodynamic properties, there are no comparable properties of heavier actinide oxides with which to compare them. (The only transuranium binary oxide with O/An > 2.00 is NpjOs and none of its thermodynamic properties have been measured.) To compare thermodynamic properties of actinide oxides in high oxidation states, scientists have studied complex oxides. 

Table 17.14 represents a listing of all actinide compounds and other species for which measured or estimated thermodynamic properties are available. The sequence of species is by actinide element, with subordinate elements following the US National Bureau of Standards standard order of arrangement. Original literature references have been cited, unless there is an authoritative review or assessment. Error limits are given wherever possible. This tabulation attempts to be self-consistent with the CODATA [128] thermodynamic compilations, and in general accepts IAEA assessments [14-21], which are consistent with CODATA-IUPAC selected data. In many cases for thorium and uranium compounds the NBS [12] tabulations were accepted it should be pointed out that the NBS compilation is self-consistent but not always contemporary and not in exact agreement with CODATA key values. Estimated values of thermodynamic properties are shown in parentheses. 

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