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[en] We present our preliminary results of the investigation of the modification of the structure of the CoFe₂O₄ colloids due to the variation of the temperature by means of small angle neutron scattering. The modification of the radius of gyration of the system obtained in the Guinier's approximation, consequently of the hydrodynamic radius, with the variation of the temperature is explained by two phenomena: the Van der Waals attraction between the long tails of the oleic acid molecules adsorbed at the surface of the same particle, determining the surfactant layer to become thinner, and the interpretation of the surfactant shells due to the increasing of the dipole-dipole interaction between the particles with the lowering of the temperature

[en] In the work ultra-dispersive powders of Al₂ O₃-Zr O₂ system with minor Y₂ O₃, Ca O additions are studied. These powders were received by method of plasma chemical technology with following concentration. The powders of the oxides have been subjected for additional processing (grinding, vibration treatment, annealing at 1173 K) too. Peculiarities of ultra dispersive condition were considered. It was defined that a micro stresses are considerable in particles of very small sizes. The micro stresses are cause of essential distortion of crystal lattice and have influence on activation energy of most of processes

[en] A multiply-faulted dipole in the C15 Laves phase of composition Nb₁₅Cr₆₈Ti₁₇ has been characterized. The dislocations all lie along [011] and show no residual contrast when imaged edge-on at B = [0 bar 1 bar 1] indicating that they are edge in character. Given this, the Burgers vectors for the Shockley partials are ± 1/6[2 bar 11] and those of the stair-rods are ± 1/6[0 bar 11]. This is consistent with a g · b analysis which was performed. The stacking fault energy was determined to be 35 mJ/m² which is higher than the experimental value of 25 mJ/m² from NbCr₂. Simulations are currently underway to understand, given the site occupancies and observed trend in stacking fault energy, whether Ti would be expected to raise the stacking fault energy of the C15 Laves phase

[en] In an effort to minimize costs and to obtain optimum designs, computer simulation of shape casting processes is more and more used as a development tool. Accurate predictions are possible by means of three dimensional fluid flow and solidification modelling. The bases of the model are the transient laminar Navier-Stokes-equations for a Newtonian fluid including the tracking of the free surface. They are describing the melt flow pattern during the mold filling sequence. Simultaneously, the temperature development in the alloy and mold is calculated using Fourier's heat transfer equation. At OEGI, a commercial software package (MAGMAsoft) with a finite difference equation solver is used for improvement of casting processes. Different examples of industrial applications will be shown. (author)

[en] In Taiwan, many groups engage in the development of TiNi SMAs. The two-stage martensitic transformations of B2<=>R-phase<=>B19' and B2<=>B19<=>B19' have been clarified for both TiNi binary and ternary alloys. The deformation behaviours have been investigated by cold-rolling, hot-rolling and wire drawing. Both shape memory effect and pseudoelasticity can be improved by some thermo-mechanical treatments. The damping characteristics of TiNi and TiNiX SMAs have also been systematically studied. Both B19'/B19 martensite (M) and R-phase (R) have high damping capacities due to stress induced movement of twin boundaries. Meanwhile, the addition of third elements, Fe and Cu, can largely increase the damping capacity. Recently, some high temperature shape memory alloys of TiNiPd and TiNiAu SMAs and thin films of TiNi and TiNiX alloys have also been intensively studied in Taiwan. All these potential investigations on the TiNi SMAs in Taiwan have attracted much attention and their important characteristics will be applied widely in the near future. (author)

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[en] This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The authors have successfully used neutron scattering techniques to investigate physicochemical properties of elements, compounds, and alloys of the light actinides. The focus of this work is to extend the fundamental research capability and to address questions of practical importance to stockpile integrity and long-term storage of nuclear material. Specific subject areas are developing neutron diffraction techniques for smaller actinide samples; modeling of inelastic scattering data for actinide metal hydrides; characterizing actinide oxide structures; and investigating aging effects in actinides. These studies utilize neutron scattering supported by equilibrium studies, kinetics, and x-ray diffraction. Major accomplishments include (1) development of encapsulation techniques for small actinide samples and neutron diffraction studies of AmD_2.4 and PuO_2.3; (2) refinement of lattice dynamics model to elucidate hydrogen-hydrogen and hydrogen-metal interactions in rare-earth and actinide hydrides; (3) kinetic studies with PuO₂ indicating that the recombination reaction is faster than radiolytic decomposition of adsorbed water but a chemical reaction produces H₂; (4) PVT studies of the reaction between PuO₂ and water demonstrate that PuO_2+x and H₂ form and that PuO₂ is not the thermodynamically stable form of the oxide in air; and (5) model calculations of helium in growth in aged plutonium predicting bubble formation only at grain boundaries at room temperature. The work performed in this project has application to fundamental properties of actinides, aging, and long-term storage of plutonium

[en] Uranium is the only element know so far to exhibit a charge-density wave instability. The structure below the transition (T₀∼43 K) is complex consisting of small displacements of the atoms away from their α-phase equilibrium structure position. It is usually assumed that this transition involves a soft-phonon condensing at (or near) the charge density wave position in the Brillouin zone. New high-resolution neutron scattering experiments at low temperature show that the principal softening occurs exactly at the charge-density wave positions, as expected for a pure Fermi-surface instability. This result is in disagreement with a model of Yamada (1993), but in agreement with a recent theory which suggests that the charge-density wave vector components are related to the Fermi-surface nesting topology. (authors)