J. M. Haschke

Equilibria and thermodynamic properties of the plutonium-hydrogen system

Abstract Equilibrium, kinetic and X-ray diffraction data show the existence of two stability regimes in the PuH system. A metastable solid solution between CaF2-type PuH1.9 and AlFe3-type PuH3.0 forms at low temperatures and behaves as an ideal solid solution. Equilibrium and calorimetric results show that the enthalpy of formation varies linearly from −38 to −50 kcal mol−1 between the lower phase boundary and the trihydride. The stable regime established at high temperature is similar to those of the MF2-MF3 (M  lanthanide) systems. A series of CaF2-related phases apparently forms between PuH1.9 and PuH2.5; a non-stoichiometric hexagonal (LaF3-type) hydride exists in the range PuH2.9–PuH3.0. A procedure for preparing pure hexagonal PuH3.00 is described and the hysteresis behavior of the PuH system is discussed.

Equilibrium and structural properties of the PuH system

Abstract The findings of recent work on PuH are described and employed in resolving several inconsistencies in the reported properties of plutonium hydride. Results of pressure measurements establish the nature of a large hysteresis effect and suggest revisions in the phase diagram. The existence of five hydride phases between the dihydride and trihydride compositions is indicated. Recently reported properties and neutron diffraction data are employed in formulating conceptual models for bonding and hydrogen accommodation in the fluorite-related hydride solid solution. Evidence for the existence of vacancy clusters in the cubic hydride is presented, and the influence of cation and anion ordering on various hydride properties is discussed.

Equilibria and thermodynamic properties of the ThZr2H system

Abstract The ThZr2-H(D) system has been characterized by equilibrium pressure measurements and X-ray diffraction analysis. At temperatures above 1180 K, the b.c.c. ThZr2 alloy is saturated at [H] : [M] = 0.2 ([M] = [Th] + [Zr]). A two-phase region observed for 0.2 1.3 can be cooled without transition, but the formation of a two-phase mixture of Fd3m hydrides on cooling products with [H]: [M] ratios between 0.6 and 1.3 indicates the presence of a miscibility gap at low temperature in this composition range. Lattice parameters and integral thermodynamic properties are presented for several Laves-type hydride compositions. The enthalpy and entropy of hydriding ThZr2 to form ThZr2H6 at 1250 K are -413 ± 25 kJ mol−1 and -334 ± 20 J K−1 mol−1 respectively. The phase equilibria are discussed and compared with those of TiCr2H and PaH.

Hydrothermal equilibria and crystal chemistry of phases in the oxide-hydroxide-sulfate systems of La, Pr, and Nd

Abstract Equilibria of the aqueous Ln + O + SO 4 ( Ln = La, Pr, Nd) system have been investigated at water pressures of 120 ± 20 MPa and temperatures of 450 ± 50°C. At low sulfate contents, the UCl 3 -type trihydroxides coexist with the orthorhombic dioxide monosulfates. A second two-phase region, Ln 2 O 2 SO 4 + Ln (OH)SO 4 , appearing at higher sulfate concentrations is followed by a third two-phase region, Ln (OH)SO 4 + Ln 2 (SO 4 ) 3 · n H 2 O. Whereas the monohydroxide monosulfates all have the same monoclinic structure, several new hydrate compositions and structures form in hydrothermal media. X-ray diffraction data indicate that the n = 7 hydrates of La and Pr and the monohydrate of La have closely related orthorhombic structures similar to that of the anhydrous La 2 (SO 4 ) 3 phase obtained by decomposition of the hydrates at low temperature. The n = 5 sulfate hydrates of Pr and Nd have also been characterized, and a metastable La 2 (OH) 4 SO 4 phase has been identified. Lattice parameters and diffraction data obtained by powder and single crystal methods are reported, and the thermal decomposition reactions of the products are described.

Handling, Storage, and Disposition of Plutonium and Uranium

The need to address topics of handling, storage, and disposal of plutonium and uranium is driven by concern about hazards posed by the element and by the worldwide quantity of civilian and military materials. The projected inventory of separated civilian plutonium for use in fabricating mixed-oxide (MOX) reactor fuel during initial decades of this century is constant at about 120 metric tons and a comparable amount of excess military plutonium is anticipated from reductions in nuclear weapon stockpiles (IAEA Report, 1998). Although inventories of civilian material are in oxide form, Pu from weapons programs exists primarily as metal. Plutonium is a radiological toxin (Voelz, 2000); its management in a safe and secure manner is essential for protecting workers, the public, and the environment.

Vaporization and thermodynamic properties of samarium dicarbide and sub-stoichiometric disamarium tricarbide

The complex reaction for SmC, occurs because the composition of the carbon-rich boundary 01 the phase decreases as temperature increases. For reaction (i), the equilibrium pressure is describedbylog,,{(p/p”)(Sm,g,1548K i T< 2049K)l = (3.60+0.01)-(14309+21)(T/K) I, The non-linear pressure equation for reaction (ii) is log,,{ (p/p‘)(Sm, g, 1.42 < r < 1.44, 1372 K < 7’ < 1636 K)) = {12.009 28449(T/K)-’ + 70185OO(T/K)-*+0.0381. Thermodynamic values for the vaporization and formation reactions of SmC,(s) and SmC,(s) at 298.15 K have been calculated: AH,“(SmC2. s, 298.15 K) = (96.2 + 7.5) kJ.mol-’ and

Preparation, phase equilibria, and crystal chemistry of La, Pr, and Nd hydroxide bromides and hydroxide lodides☆

Abstract Hydrothermal phase equilibria in the pseudoternary hydroxide bromide and hydroxide iodide systems of lanthanum, praseodymium, and neodymium have been investigated. The condensed products obtained by composition variation along isothermal (550–600°C) and isobaric (1330 atm) sections have been characterized by X-ray diffraction and thermogravimetry. The hexagonal UCl3-type trihydroxides are stable in all cases. In the hydroxide bromide systems, the hexagonal Ln7(OH)18Br3 and monoclinic Ln(OH)2Br (Ln = La, Pr, Nd) phases are found. A single hydroxide iodide, Ln7(OH)18I3, is observed for La and Pr; hydroxide iodides are not found for Nd. Lattice parameters are reported for both the Y(OH)2Cl- and La7(OH)18I3-type phases. Quaternary Ln7O7(OH)4 X phases (X = Br−, I−) are formed during thermal decomposition of the Ln7(OH)18X3 phases. The phase equilibria and structural features of the hydroxide halides and hydroxide nitrates are discussed.

Phase equilibria of the oxide hydroxide halide systems of Sm, Eu, and Gd. The crystal structure of Gd3O(OH)5Br2

An investigation of hydrothermal phase equilibria in the halide-containing (Cl, Br, I) systems of Sm, Eu, and Gd has shown that diversities in behavior occur across the lanthanide (Ln) series and within the halide group. In the chloride systems, the trihydroxide, two phases at a ClLn ratio of 0.4, and Ln(OH)2Cl phases are found. Equilibria in the bromide systems are more complex; Ln(OH)3, Ln7(OH)18Br3, a high-temperature phase at BrLn = 0.45, Ln3O(OH)5Br2, and Ln(OH)2Br are observed. A single iodide-containing phase, Ln(OH)2.67I0.33, is found. X-Ray diffraction data are reported for all the previously unreported phases and the thermal decomposition behaviors of representative phases are described. The results of a single-crystal X-ray structure determination of orthorhombic (Pmmn) Gd2O(OH)5Br2 are reported and discussed.

The heat capacity (8 to 350 K) of PuH1.9, heat capacity (340 to 600 K) of PuH2.0, and recommended thermodynamic properties of PuH2 to 600 K

Abstract The low-temperature heat capacity of PuH1.9, where the major plutonium isotope was 242Pu, has been determined from 8 to 350 K. The results of this investigation at 298.15 K have been adjusted to correspond to stoichiometric plutonium dihydride: PuH2. Standard molar thermodynamic quantities were obtained for PuH2 at T = 298.15 K: Cpmo(T) = (43.50±0.44) J·K−1·mol−1; Smo(T) = (72.84±0.73) J·K−1·mol−1; {Hmo(T)−Hmo(0)} = (85.93±86) J·mol−1; and − {G m o (T)−H m o (0)}/ T = (44.02±0.44) J·K −1 ·mol −1 . These have been combined with experimental high-temperature heat capacities (340 to 600 K) of a sample of PuH2.0, where the major plutonium isotope as 239Pu, to give the thermodynamic functions of PuH2 over the temperature range from 298.15 to 600 K.

Chapter 32 Halides

Publisher Summary This chapter provides an overview of halides. The historical development of the chemistry of the rare earth halides is similar to that of most elements in that the halides were some of the first compounds to be prepared. Several areas of halide chemistry have recently been active or have been significantly altered by recent results. The area of preparative methods has been surprisingly active and has expanded to include crystal growth procedures. Substantial progress has been made in the definition and refinement of structural properties and in the expansion of thermodynamic data. Other important areas of progress include the identification and characterization of both novel reduced halides and interesting gas phase species. Interest in the halides has also been enhanced by a variety of recently developed uses and potential uses for the halides.