A simple model for the study of magnetism in transition-based alloys with actinide impurities

A simple model taking into account a 6d and a 5f virtual bound state and describing spin-orbit effects for the 5f electrons is developed here in order to explain the magnetic properties of actinide impurities in transition metals and especially the occurrence of magnetism for neptunium and plutonium. The model can account for the decrease of the superconducting temperature of lanthanum-based alloys with actinide impurities from thorium to americium.Part of Doctorat d'Etat thesis to be submitted by R. Jullien to the Faculté des Sciences d'Orsay.Supported by Consiglio Nazionale delle Richerche, Roma.Laboratoire associé au C.N.R.S.     

Single crystal growth of actinide compounds

During recent years, the importance of solid state actinide research has been increasingly recognized. Further progress in actinide solid state physics depends on the availability of pure and perfect single crystals. Actinide compounds have large magnetic anisotropy with anisotropy fields of 8 × 10⁷ A·m^?1 or higher. Investigation of the mechanism responsible for such unique behaviour requires large single crystals of high purity for magnetization, neutron diffraction, angular and energy dependent photoemission measurements. Materials of interest for actinide solid state research are the metals and compounds with simple crystal structures like dioxides (CaF₂ structure), monopnictides and monochalcogenides (NaCl structure), and intermetallic compounds (Laves phases).This article gives an overview of actinide single crystal growth facilities in Karlsruhe and Geel. The actinide compounds are prepared by direct synthesis from the purest elements available using non-contaminating techniques. The reaction occurs in vacuum sealed quartz tubes where the actinide metal reacts with the vapour of the other element, or by levitation melting in a Hukin crucible. Different techniques have been developed to grow single crystals of actinide metals and compounds. High temperature solution growth from molten salts is used to prepare actinide dioxide single crystals. Oxides, pnictides and chalcogenides are grown by chemical vapour transport. Large single crystals of the monopnictides and monochalcogenides are obtained with the recrystallization (or mineralization) technique in sealed tungsten crucibles. Single crystals of congruently melting intermetallic compounds are pulled from levitated or semilevitated melts by the Czochralski method. Selected single crystals are characterized, orientated and encapsulated for safe handling during measurements.     

Multilayer Co/Pd films with nanocrystalline and amorphous Co layers: Coercive force, random anisotropy, and exchange coupling of grains

The values of saturation magnetization M _s, exchange coupling constant A, local magnetic anisotropy field H _a, random anisotropy correlation radius R _c, and coercive force H _c were independently measured for multilayer Co/Pd films with nanocrystalline and amorphous Co layers. It is shown that variation of the coercive force H _c(t _Co) as a function of the cobalt layer thickness t _Co is related to changes in characteristics of the magnetic microstructure. The main factor determining changes in the ferromagnetic correlation radius R _f and the average anisotropy 〈K〉 of a magnetic block in multilayer Co/Pd films is variation of exchange coupling constant A(t ^Co).     

Anhydrous Lanthanide and Actinide(III) and (IV) Orthophosphates Me<Subscript>m</Subscript>(PO<Subscript>4</Subscript>)<Subscript>n</Subscript>. Synthesis,Crystallization, Structure,and Properties

Anhydrous orthophosphates Me_m(PO₄)_n, where Me is an element in the oxidation state +1 (A), +2 (B), +3 (R), +4 (M), or +5 (C), containing f elements(III) and (IV), are systematized. Their crystallographic characteristics are described, and the common and specific features of structure formation are discussed. The main structural (mineral) types realized in lanthanide and actinide phosphates are revealed: eulytite, zircon, monazite, NaZr₂(PO₄)₃ (NZP), NaTh₂(PO₄)₃ (NThP), rhabdophane, Sb_0.5Bi_1.5(PO₄)₃ (SbBi), whitlockite, arcanite, glaserite, langbeinite, scheelite, Sc₂(WO₄)₃ (ScW). The crystal-chemical factors determining the stability of structures, polymorphism of cations, morphotropy in the series, and possibility of formation of solid solutions on the basis of iso- and heterovalent isomorphism and isodimorphism are analyzed. The possibility of predicting new compounds of f elements of the expected structure is demonstrated.__________Translated from Radiokhimiya, Vol. 47, No. 1, 2005, pp. 15–30.Original Russian Text Copyright © 2005 by Orlova, Kitaev.     

Towards the Development of a New Iron Age

Steel in its various forms is the most widely utilized metallic alloy and comprises over 80 % by weight of all metallic alloys in industrial use.^[1] The development of steel microstructures is based on manipulation of a very specific solid/solid state transformation called an eutectoid transformation (i.e. γ_austenite → α_ferrite+ Fe₃C_cementite). The control of this transformation is the primary factor resulting in wide variety of microstructures and resulting properties found in commercial steel alloys. However, the full benefit of its main constituent, iron has never been realized. Based on the metallic bonding in iron, the theoretical tensile strength has been calculated to be 13.2 GPa but ultra high strength steels, even today, only achieve maximum tensile strength levels from 1 to 1.5 GPa. Thus, our modern technological society has been established utilizing approximately only ～ 10 % strength level of iron. Here we demonstrate that a high level of strength (6.2 GPa) and strength to weight ratio of 8.3 × 10⁴/m³ may be obtained in iron‐based alloys by their solidification into metallic glasses, as well as, by employing another solid state transformation called glass devitrification.     

New Arsenide Yb2Cu4As3: Crystal Structure and Electronic State of Ytterbium

A new arsenide of composition Yb₂Cu₄As₃ was prepared by elemental synthesis, and its structure was determined by x-ray diffraction (Rietveld powder-diffraction analysis, 118 independent reflections, R _I = 0.064, R _p = 0.097): Hf₂Co₄P₃ type, sp. gr. P 2m, a = 1.33072(3) nm, c = 0.40091(1) nm. Magnetic susceptibility measurements and EXAFS data indicate that Yb₂Cu₄As₃ contains roughly equal amounts of Yb²⁺ (4f ¹⁴ configuration) and Yb³⁺ (4f ¹³).     

Preparation of targets for the gas-filled recoil separator TASCA by electrochemical deposition and design of the TASCA target wheel assembly

The Transactinide Separator and Chemistry Apparatus (TASCA) is a recoil separator with maximized transmission designed for performing advanced chemical studies as well as nuclear reaction and structure investigations of the transactinide elements (Z>103) on a one-atom-at-a-time basis. TASCA will provide a very clean transactinide fraction with negligible contamination of lighter elements from nuclear side reactions in the target.For TASCA a new target chamber was designed and built at GSI including the rotating target wheel assembly ARTESIA for beam intensities up to 2 μA (particle). For the production of longer-lived isotopes of neutron-rich heavier actinide and transactinide elements, hot fusion reactions with actinide targets are required. Here, possible target materials range from thorium up to curium or even heavier elements.For the deposition of lanthanide and actinide elements on thin aluminum and titanium backings by means of Molecular Plating (MP), a new deposition cell has been constructed that allows precise temperature control of the organic solvent and stirring of the solution. The electrode geometry ensures homogeneity of the electric field inside the cell. With the new set-up, holmium and gadolinium layers (500 μg/cm²) on 2–5 μm thin titanium backings have been produced with deposition yields of the order of 90%. Systematic investigations are under way to further optimize the deposition conditions for other lanthanide and actinide elements including uranium and plutonium on different backing materials.     

The effect of pressure on the growth rate of trans-1,4-polyisoprene crystals at pressures of 1 bar to 3.5 kbar

The growth rates of both low-melting form and high-melting form trans-1, 4-polyisoprene crystals have been measured in thin films by transmission electron microscopy over a range of pressures up to 3.5 kbar. The effect of pressure is to shift the growth rate versus temperature curves to higher temperatures and to cause a continuous decrease in the maximum with increasing pressure. The variation of the crystal growth rate with temperature can be represented, at all pressures, by an equation derived from secondary nucleation theory. The variation of the crystal growth rate with increasing pressure can be largely accounted for by the measured increase in the equilibrium melting temperature of 15 K kbar^–1 and the calculated increase in the glass transition temperature of 20 K kbar^–1. The decrease in the maximum growth rate with increasing pressure results from the continuous decrease in (T _m ⁰ -T _g). It is suggested that crystals of the same form, grow by the same basic mechanism as at atmospheric pressure and that the major effect of pressure is on the melt rather than on the crystals.     

Crystal structure of the Np(IV) compound [Np(DMSO)7(NO3)](ClO4)3 (DMSO = dimethyl sulfoxide)

The Np(IV) complex [Np(DMSO)₇(NO₃)](ClO₄)₃ was synthesized and studied by single crystal X-ray structural analysis. The crystal structure contains three crystallographically independent formula units. The complex cations [Np(DMSO)₇(NO₃)]³⁺ contain bidentate chelate nitrate ions and DMSO molecules coordinated to the Np atom via O atom. The coordination polyhedra (CPs) of the two crystallographically independent Np atoms can be described as base-monocapped tetragonal antiprisms, whereas the CP of the third crystallographically independent Np atom should be described as a trigonal prism tricapped at lateral faces. In contrast to many other structures of dimethyl sulfoxide complexes of actinide and lanthanide perchlorates, the DMSO molecules and perchlorate ions in the structure under consideration show no disordering.     

Changes in the self-diffusion coefficient during the crystal-melt phase transition

It is shown that the self-diffusion coefficients (D _f) of metals and semiconductors acquire a universal value of D _f(S−L) × 10⁻⁵ cm²/s during the solid-liquid (crystal-melt) phase transition (PT). Attaining this value can be considered a necessary condition for the onset of PT, while D _f < 2.5 × 10⁻⁷ cm²/s and D _f > 10⁻⁴ cm²/s are the sufficient conditions for the termination of a PT to the solid and liquid state, respectively. These values are applicable both to substances that exhibit normal melting and to those melting with a decrease in the specific volume upon the liquid phase formation. It is pointed out that the melting is cased by a sharp delocalization of a certain fraction of atoms in a crystal.     

Concentration dependence of the anomalous thermoelectric power of dilute magnetic alloys

It has been pointed out recently by one of us (M.S.R.C.) that the variation of the Kondo slopesd (of the /c vs. lnT curves) of dilute magnetic alloys containing a finite solute concentrationc bears a close resemblance to the variation of the functionf (=cos⁶ cos2) with the phase shift for ordinary spin-independent scattering. Sinced is itself primarily determined byf the inference is that is a function ofc when the criterion of infinite dilution is violated. For infinite dilutions theory expects the anomalous thermoelectric power in such alloys to be independent ofc as well as ofT. Taking the experimentally observed extremum in the TEP (S _m) as an approximation to such a TEP, we report, for finite solute concentrations, the variation ofS _m withc, to correspond with the variation off(=cos ⁶ sin2) with . This substantiates the above inference. In fact, one can predict the sign and the variation (withc) ofd, knowing that ofS _m, and vice versa, for a given dilute magnetic alloy system.     

Effect of stoichiometry on the thermal expansion coefficients of lithium niobate single crystals

The chemical analysis of LiNbO₃ single crystals, with different melt compositions (Li/Nb) _m =0·945, 1·0, 1·1 and 1·2, grown by slow cooling technique, reveals a remarkable difference in solid and melt compositions. The thermal expansion coefficients alonga andc axes, determined by using Newton’s ring experiment, are found to increase anisotropically with increase in (Li/Nb) _m ratio. The variation in thermal expansion coefficient with increase in the (Li/Nb) _m ratio is discussed in the light of defect chemistry i.e. the partial replacement of Li⁺ by excess Nb⁵⁺ creates additional cation vacancies to attain the electro-neutrality in the crystal.     

Recent advances in the numerical analysis of heat pipes

Numerical simulation of heat pipes has progressed significantly in recent years. The state-of-the-art has been advanced in steady state, continuum transient, and frozen startup simulation for high, moderate, and low temperature heat pipes of conventional cylindrical and nonconventional geometries such as wing leading edges and spacecraft nosecaps. This review summarizes these advancements and discusses the important results.List of symbols A cross-sectional area of the vapor channel, m² - c specific heat, J/(kg-K) - C _p specific heat at constant pressure, J/(kg-K) - C _v specific heat at constant volume, J/(kg-K) - D vapor space diameter, m - D _v coefficient of self-diffusion, m²/s - G vapor mass flux, kg/(m²-s) - h convective heat transfer coefficient, W/(m²-K) - h _fg latent heat of evaporation, J/kg - H latent heat due to melting or freezing, J/kg - k thermal conductivity, W/(m-K) - Kn Knudsen number, /D - L total length of the heat pipe, m - L _a length of the adiabatic section, m - L _c length of the condenser, m - M molecular weight, kg/kmol - Ma Mach number, - m _i mass flux at the liquid-vapor interface, kg/(m²-s) - P pressure, N/m² - q heat flux, W/m² - Q heat input at the active evaporator, W - Q _o heat output at the condenser, W - r radial coordinate, m - R gas constant, J/(kg-K) - R _o outer pipe wall radius, m - R _u universal gas constant, J/(kmol-K) - R _v vapor space radius, m - t time, s - T temperature, K - T _i,c interfacial temperature on the continuum vapor flow side, K - T _i,r interfacial temperature on the rarefied vapor flow side, K - T _rf reference (saturation) temperature, K - T _tr transition vapor temperature, K - v radial velocity, m/s Funding for this work was provided by a joint effort of the NASA Lewis Research Center and the Thermal Technology Center of Wright Laboratory under contract No. F33615-88-C-2820     

Complex moduli of aligned discontinuous fibre-reinforced polymer composites

This paper describes recent analytical and experimental efforts to determine the effects of fibre aspect ratio, fibre spacing, and the viscoelastic properties of constituent materials on the damping and stiffness of aligned discontinuous fibre-reinforced polymer matrix composites. This includes the analysis of trade-offs between damping and stiffness as the above parameters are varied. Two different analytical models show that there is an optimum fibre aspect ratio for maximum damping, and that the predicted optimum aspect ratios lie in the range of actual aspect ratios for whiskers and microfibres when the fibre damping is small. When the fibre damping is great enough, however, the optimum fibre aspect ratio corresponds to continuous fibre reinforcement. Experimental data for E-glass/epoxy specimens are presented for comparison with predictions.Nomenclature A _c,A_f,A_m Cross-sectional area of composite, fibre, and matrix, respectively - d Fibre diameter - E _c ^* ,E _f ^* ,E _m ^* Complex extensional modulus of composite, fibre, and matrix, respectively. - E_c,E_f,E_m Extensional storage modulus of composite, fibre, and matrix, respectively - E_c,E_f,E_m Extensional loss modulus of composite, fibre, and matrix, respectively - G_m Complex shear modulus of matrix - G_m Shear storage modulus of matrix - i –1^1/2 - K Defined in Equation A9 - K ₁ Defined in Equation A5 - l Fibre length - r Radial distance from centre of fibre - r ₀ Fibre radius - R Radius of representative volume element, or one-half of centre-to-centre fibre spacing - v _f,v _m Volume fraction of fibre and matrix, respectively - W _c Total strain energy stored in a unit volume of composite - W _f Strain energy stored in volumev _f of fibre - W _m Strain energy stored in a volumev _m of matrix - W _m Shear strain energy stored in a volumev _m of matrix - W _m Extensional strain energy stored in a volumev _m of matrix - w _rm Shear strain energy stored in the matrix inr ₀rR - w _f Extensional strain energy stored in a single fibre - x Distance along fibre from end of fibre - Defined in Equation 12 - Defined in Equation 2 - ^* Defined in Equation A2 - Extensional (longitudinal) strain - _c, _f, _m Extensional loss factor of composite, fibre, and matrix, respectively - _Gm Shear loss factor of matrix - Polar angle measured in a plane perpendicular to fibre axis - ¯gs _c,¯gs _f,¯gs _m Average longitudinal stress in composite, fibre, and matrix, respectively - _f Longitudinal stress in fibre - Shear stress in matrix - Defined in Equation 27     

Chemically resistant alloys for immobilization of radioactive wastes

The possibility of using intermetallic compounds or alloys of actinides with nickel for preparing matrices incorporating radioactive wastes was examined. Such intermetallic compounds or alloys are prepared by electrolytic deposition of a lanthanide or actinide from a melt of its salt in eutectic mixtures of alkali metal chlorides. The process is performed under the conditions when an actinide being reduced reacts with the cathode material to form a layer of an intermetallic compound. Based on the results of the physicochemical studies performed, an electrochemical process was developed for compacting highly radioactive toxic nuclides of Am, Pu, and REE in environmentally safe forms with high chemical, thermal, and radiation resistance: (a) in the form of alloys or intermetallic compounds containing up to 90 wt % radionuclide, with the leaching rate in water of 10^?5–10^?6 g cm^?2 day^?1; (b) in the form of layers of alloys or intermetallic compounds of the radionuclides on metal supports, with the radionuclide content of up to 80 wt % and leaching rate in water of ～10^?6–10^?7 g cm^?2 day^?1.     

Derivation of the thermal resistance of the contact between systems with corrugated surfaces

Contact thermal resistance is considered for joints with corrugated surfaces. Formulas are derived that are confirmed by experiment.Notation R_c total thermal resistance of contact, m₂ · deg/W - R_M, R_cl thermal resistance of real contact and of contactless region, m₂· deg/W - coefficient of contraction of heat flux lines to spots of real contact - S_m, S_c S_o real, contour and nominal areas of contact surfaces, m² - a mean radius of contact spot, m - ¯_M reduced thermal conductivity of contact (1 and 2) materials, W/m · deg - _c thermal conductivity of contact medium, W/m · deg - n number of contact spots of microroughnesses at nominal contact surface - area ratio - b, parameters of support curve of surface - r radius of roughness, m - q_c contour pressure, N/m₂ - N normal load, N - coefficient depending on deformation mechanism - B coefficient characterizing properties - K coefficient depending on and - h_max h_av maximum and mean height of microroughness protrusions, m - P specific normal load to contact surface, N/m² - E Young's modulus, N/m² - R_w wave radius, m - n_w numbers of wave contact spots at nominal surface - L_el, L_p longitudinal and transverse wave pitch, m - _eq equivalent thickness of intercontact laminar, m - H_av mean height of waves, m - relative approach of surfaces under load - c approach of surfaces under load - HB Brinell hardness, N/m₂ - Poisson's ratio - ₂ relative contact surfaces Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 5, pp. 846–852, May, 1971.     

Magneto-optical activity of f–f transitions in elpasolite Rb2NaDyF6

Absorption and magnetic circular dichroism (MCD) spectra of f–f transitions ⁶H_15/2 → ⁶F_3/2, ⁶F_5/2, ⁶(F_7/2 + H_5/2) have been measured in cubic crystal Rb₂NaDyF₆ with Dy³⁺ ions in centrosymmetrical O_h positions. Magneto-optical activities (MOA) of the transitions (the ratio of zero moments of the MCD and absorption bands) have been obtained from the corresponding spectra. Origins of the transitions MOA have been analyzed and theoretical estimations of the MOA values have been made. It turned out, that MOA of the transitions in the centrosymmetrical crystal Rb₂NaDyF₆ (being allowed by odd vibrations) are noticeably larger than those in non-centrosymmetrical compounds, where f–f transitions are allowed by static odd components of crystal field.     

Thermophysical Properties of Rare-Earth-Stabilized Zirconia and Zirconate Pyrochlores as Surrogates for Actinide-Doped Zirconia

Thermophysical properties of rare-earth-stabilized zirconia and zirconate pyrochlores, A₂Zr₂O₇ (A = La, Nd, Sm, Gd, Dy, Y), were evaluated by X-ray diffractometry, Raman spectroscopy, and the ultrasound pulse-echo method. Crystallographic analyses elucidated that La₂Zr₂O₇, Nd₂Zr₂O₇, Sm₂Zr₂O₇, and Gd₂Zr₂O₇ had the pyrochlore structure, whereas Dy₂Zr₂O₇ and Y₂Zr₂O₇ had the defect fluorite structure. For lanthanide pyrochlores, the thermal expansion became smaller with increasing ionic radius of A and increasing crystal binding energy. The elastic moduli and Debye temperature evaluated using longitudinal and transverse sound velocities also depend on the ionic radius and binding energy, and hence these values related to mechanical properties increase with the ionic radius of A. On the other hand, Poisson’s ratio was almost comparable among these pyrochlores. In addition, thermophysical properties of actinide pyrochlore are discussed in this study.