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Modeling of the phase evolution in Mg1-xAlxB2 (0<x<0.5) and its experimental signatures

Description: Despite the chemical and structural simplicity of MgB{sub 2}, at 39 K this compound has the highest known {Tc} of any binary compound. Electron doping by substituting Al for Mg leads to decreasing Tc and the observed concentration dependent rate of decrease has been proposed to arise from the non-ideal character of MgB{sub 2}-AIB{sub 2} solid solutions, which derives from the existence of an ordered Mg{sub 0.5}Al{sub 0.5}B{sub 2} compound. Heterogeneous nano-scale structure patterns in solid solutions have emerged as an important concept for complex materials, ranging from actinide alloys and oxides to high-temperature cuprate superconductors and mallganite-based materials exhibiting colossal magnetoresistivity. In this work we investigate the formation of structural heterogeneities in Mg{sub 1-x}AI{sub x}B{sub 2}, which take the form of nano-scale AI-AI and AI-Mg domains of different geometry and size, using molecular statics/dynamics simulations and in particular we study the corresponding signatures in diffraction experiments. In order to undertake this task we first derive appropriate Mg-AI-B semi-empirical potentials within the Modified Embedded Atom Method formalism. These potentials are also applied to explore the equilibrium Mg{sub 1-x}AI{sub x}B{sub 2} phase diagram for 0 &lt; x &lt; 0.5. Additionally, density functional theory calculations were utilized to study the influence of heterogeneities on the electronic structure and charge distribution in Mg{sub 1-x}AI{sub x}B{sub 2}.
Date: January 1, 2009
Creator: Andersson, Anders David; Casillas, Luis; Lezama Pacheco, Juan & Conradson, Steven D
Partner: UNT Libraries Government Documents Department

Characterization of Tank 48H Samples for Alpha Activity and Actinide Isotopics

Description: This document reports the total alpha activity and actinide isotopic results for samples taken from Tank 48H prior to the addition of sodium tetraphenylborate and MST in Batch {number_sign}1 of the ITP process. This information used to determine the quantity of MST for Batch {number_sign}1 of the ITP process and the total actinide content in the tank for dose calculations.
Date: December 4, 1995
Creator: Hobbs, D.T.; Coleman, C.J. & Hay, M.S.
Partner: UNT Libraries Government Documents Department

Structural and magnetic characterization of actinide materials

Description: 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{sub 2.4} and PuO{sub 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 PuO{sub 2} indicating that the recombination reaction is faster than radiolytic decomposition of adsorbed water but a chemical reaction produces H{sub 2}; (4) PVT studies of the reaction between PuO{sub 2} and water demonstrate that PuO{sub 2+x} and H{sub 2} form and that PuO{sub 2} 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.
Date: December 31, 1998
Creator: Cort, B.; Allen, T.H. & Lawson, A.C.
Partner: UNT Libraries Government Documents Department

Thermal simulation of quenching uranium-0. 75% titanium alloy in water

Description: A computer model, The Quench Simulator, has been developed to simulate and predict in detail the behavior of U-0.75 Ti alloy when quenched at high temperature (about 850/sup 0/C) in cold water. The code allows one to determine the time- and space-dependent distributions of temperature, residual stress, distortion, and microstructure that evolve during the quenching process. The nonlinear temperature- and microstructure-dependent properties, as well as the cooling rate-dependent heats of transformation, are incorporated into the model. The complex boiling heat transfer with its various regimes and other thermal boundary conditions are simulated. Experiments have been performed and incorporated into the model. Both sudden submersion and gradual controlled immersion can be applied. A parametric and sensitivity study has been performed demonstrating the importance of the thermal boundary conditions applied for achieving certain product characteristics. The thermal aspects of the model and its applications are discussed and demonstrated.
Date: January 1, 1985
Creator: Siman-Tov, M.; Llewellyn, G.H.; Childs, K.W.; Ludtka, G.M. & Aramayo, G.A.
Partner: UNT Libraries Government Documents Department

Potentiometric determination of percent porosity in nickel electroplates on uranium metal

Description: A potentiometric procedure has been developed to determine the percent porosity of nickel electroplates on uranium metal. In this case, percent porosity is defined as the ratio of the exposed uranium surface to the nickel electroplate surface times 100. Basically, this procedure exploits the high chemical reactivity between uranium metal and chloride ions in aqueous solution. It involves the potentiometric measurement of the corrosion potentials of coupled uranium/nickel metal electrodes in 0.01 molar potassium chloride solution versus a double-junctioned calomel electrode. A mathematical treatment of observed potentiometric measurements from a two-point calibration technique permits a best-fit calibration for a particular porosity determination on the same nickel-plated sample.
Date: January 1, 1982
Creator: Dietrich, W.C. & Johnson, E.E.
Partner: UNT Libraries Government Documents Department

Evaluation of two styles of slotted, flat-head screws. [U--6% Nb alloys]

Description: A series of torque tests were performed to evaluate the relative merits of two different flat-head screws fabricated from a uranium--6% niobium alloy. The screws tested were machined with both normal, straight-through slots in the head and with slots having radiused bottoms. Test results indicate that both designs easily surpass the required 20-inch-pound-proof torque.
Date: April 30, 1979
Creator: Reeves, C.A. Jr. & Johnson, W.B.
Partner: UNT Libraries Government Documents Department

X-ray diffraction study of reversible deformation mechanisms in the aged uranium-6. 5 niobium alloy

Description: The x-ray diffraction (XRD) data from 200/sup 0/C/2h-aged uranium-6.5 wt % niobium (U-6.5Nb) alloys, taken under stress as a function of strain, revealed a gamma-zero (..gamma../sup 0/)..-->.. alpha prime-prime (..cap alpha..'') thermoelastic martensitic phase transformation. It was concluded that the primary reversible deformation modes consisted of the movement of ..gamma../sup 0//..cap alpha..'' interphase interfaces and ..cap alpha..'' intervariant interfaces. Specimen elasticity at low strains was associated with the retreat of interphase interfaces. At higher strains, interphase interfaces did not recover significantly on unloading, and elasticity was due primarily to the retreat of ..cap alpha..'' intervariant interfaces.
Date: June 21, 1985
Creator: Carpenter, D.A.
Partner: UNT Libraries Government Documents Department

Magnetic properties and electronic structure of the actinide systems UAl/sub 2/, NpAl/sub 2/, and PuAl/sub 2/

Description: The electronic ground states of UAl/sub 2/, NpAl/sub 2/ and PuAl/sub 2/ have been determined by band theory techniques. These calculations indicate that both actinide d-f hybridization and spin-orbit coupling are important in these systems. Using a new scheme for obtaining the paramagnon parameters for UAl/sub 2/ it is shown that calculated and experimentally derived 5f band width are consistent. The fact that orbital angular momentum may not be quenched in these systems is suggested as a possible mechanism for damping spin-fluctuations in NpAl/sub 2/ and PuAl/sub 2/.
Date: January 1, 1985
Creator: Albers, R.C.; Boring, A.M. & Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Band description of materials with localizing orbitals

Description: Density functional theory is a form of many-body theory which maps the problem onto an equivalent single particle-like system by limiting to the ground state (or some limited ensemble). So it should be surprising that this ground state theory could have any relevance whatsoever to the excitation properties of a material - and yet it does when used carefully. However, the most interesting materials involve active orbitals which are at least partially localized in space and this has profound effects both on the ground state and the excitation spectrum. My long term interest is in Ce and actinide compounds such that the popular concerns are mixed valence, heavy fermions, and the various forms of magnetic transitions. Band structure calculations can give a great deal of information concerning the mechanisms and degree of the localization as shown by examples using the Ce and U Ll/sub 2/ structured materials and the Ce cubic Laves phase materials. There are some difficulties due to an incomplete knowledge of the functionals involved which causes an underestimate of the local character. This is illustrated and discussed.
Date: March 1, 1986
Creator: Koelling, D.D.
Partner: UNT Libraries Government Documents Department

Anomalous vomume expansion of plutonium alloys

Description: A simple heuristic model for the valence of Pu in its various phases is used to explain the large positive deviations from Vegard's Law in ..cap alpha..-Pu(Al), ..cap alpha..-Pu(Ti), and delta-Pu(Sc).
Date: January 1, 1981
Creator: Fisk, Z.; Elliott, R.O.; Tate, R.E. & Roof, R.B.
Partner: UNT Libraries Government Documents Department

Fabrication and characterization of uranium-6--niobium alloy plate with improved homogeneity

Description: Chemical inhomogeneities produced during arc melting of uranium--6 weight percent niobium alloy normally persist during fabrication of the ingot to a finished product. An investigation was directed toward producing a more homogeneous product (approx. 13.0-mm plate) by a combination of mechanical working and homogenization. Ingots were cast, forged to various reductions, homogenized under different conditions, and finally rolled to 13.0-mm-thick plate. It was concluded that increased forging reductions prior to homogenization resulted in a more homogeneous plate. Comparison of calculated and experimentally measured niobium concentration profiles indicated that the activation energy for the diffusion of niobium in uranium--niobium alloys may be lower than previously observed.
Date: October 31, 1978
Creator: Snyder, W.B.
Partner: UNT Libraries Government Documents Department

Electrical resistivity of U/sub 1/minus/x/M/sub x/Be/sub 13/ under pressure

Description: Measurements of the electrical resistivity of U/sub 1/minus/x/ Th/sub x/ Be/sub 13/ compounds as a function of pressure provide a possible explanation for the unusual behavior of these materials. 10 refs., 2 figs.
Date: January 1, 1988
Creator: Borges, H.A.; Thompson, J.D.; Aronson, M.C.; Fisk, Z. & Smith, J.L.
Partner: UNT Libraries Government Documents Department

Corrosion testing of the General Electric-MANTECH II GAU 8/A penetrator

Description: A series of 8-inch artillery projectiles featuring mass properties variation were fired to determine the effect on crossrange deflection (drift). The results of this experimental program are presented. The drift of a spinning projectile away from the vertical plane of the firing azimuth is primarily caused by the yaw of repose. Analytic expressions for the repose angle and the crossrange deflection or drift have been developed by several authors. Previous analytical work showed that the drift of a spinning projectile is dependent upon the projectile roll moment of inertia and center-of-gravity position, but is independent of the pitch moment of inertia. The present work provides an experimental verification of the previous analyses. This program was conducted in support of the ballistic match effort in which slightly dissimilar projectiles are to have impact points within a specified dispersion, i.e., though the mass properties of two nearly similar projectiles cannot be exactly matched, they can be tailored to provide for similar trajectories. A more accurate analytic expression for the crossrange deflection of a spinning projectile is also developed.
Date: May 1, 1978
Creator: Johnson, H.R. & Weirick, L.J.
Partner: UNT Libraries Government Documents Department

High-strength uranium-0. 8 weight percent titanium alloy penetrators

Description: Long-rod kinetic-energy penetrators, produced from a uranium-0.8 titanium (U-0.8 Ti) alloy, are normally water quenched from the gamma phase (approximately 800/sup 0/C) and aged to the desired hardness and strength levels. High cooling rates from 800/sup 0/C in U-0.8 Ti alloy cylindrical bodies larger than about 13 mm in diameter cause internal voids, while slower rates of cooling can produce material that is unresponsive to aging. For the present study, elimination of quenching voids was of paramount importance; therefore, a process including the quenching of plate was explored. Vacuum-induction-cast ingots were forged and rolled into plate and cut into blanks from which the penetrators were obtained. Quenched U-0.8 Ti alloy blanks were aged at 350 to 500/sup 0/C to determine the treatment that would provide maximum tensile and impact strengths. Both tensile and impact strengths were maximized by aging in vacuum for six hours at 450/sup 0/C.
Date: September 1978
Creator: Northcutt, W. G.
Partner: UNT Libraries Government Documents Department

Crystallographic considerations of the delta in equilibrium. cap alpha. displacive transformation in plutonium alloys

Description: Determination of invariant-plane strain crystallographic solutions for martensitic transformation between the FCC delta and monoclinic ..cap alpha.. phases in plutonium alloys, using three possible lattice correspondences and 53 possible lattice-invariant shear systems, identifies the most probable delta-..cap alpha.. lattice correspondence. The operative lattice-invariant shear systems are predicted by comparison of both shape strain magnitudes and computed interfacial energies. For delta ..-->.. ..cap alpha.. transformation twinning on (001) (100)/sub ..cap alpha../ is favored, giving a (.817, .538, .208)/sub delta/ habit and a (.947, .269, .174)/sub delta/ shape strain of magnitude m/sub 1/ = .324. The ..cap alpha.. ..-->.. delta transformation favors slip on (111) (101)/sub delta/, giving a (.255, .844, .471)/sub ..cap alpha../ habit and (.822, .466, .355)/sub ..cap alpha../ shape strain of magnitude m/sub 1/ = .417.
Date: June 10, 1986
Creator: Adler, P.H. & Olson, G.B.
Partner: UNT Libraries Government Documents Department

Preparation, heat treatment, and mechanical properties of the uranium-5 weight percent chromium eutectic alloy

Description: The eutectic alloy of uranium-5 wt % chromium (U-5Cr) was prepared from high-purity materials and cast into 1-in.-thick ingots. This material was given several simple heat treatments, the mechanical properties of these heat-treated samples were determined; and the microstructure was examined. Some data on the melting point and transformation temperatures were obtained.
Date: October 1, 1980
Creator: Townsend, A. B.
Partner: UNT Libraries Government Documents Department

Interaction between computational modelling and experiments for vacuum consumable arc remelting

Description: A combined computational-experimental modelling effort is currently underway to characterize the vacuum consumable arc remelt process. This effort involves the coupling of experimental results with a magnetohydrodynamic flow model which is capable of time accurate solutions of the interdependent fluid flow-solidification process in the ingot. Models such as this are driven by boundary conditions. Considerable data have been compiled from direct observation of the electrode tip and molten pool surface by means of high speed photography in order to gain an understanding of the processes at the pool surface and the appropriate corresponding boundary conditions. The crucible wall/molten metal miniscus conditions are less well understood. Pool volumes are computed at different melting currents and show reasonable agreement with experimentally determined values. Current flow through the ingot is evaluated numerically and the results indicate that a significant portion of the melt current does not reach the interior of the ingot. U-6 wt. % Nb alloy was used.
Date: January 1, 1980
Creator: Bertram, L. A. & Zanner, F. J.
Partner: UNT Libraries Government Documents Department

X-ray diffraction studies of binary plutonium. Uranium alloys: an interim report

Description: This report describes x-ray diffraction studies of Pu-U alloys carried on at LLNL in 1972. These studies were part of a larger project to understand the 2-phase, banded microstructures observed in Pu-15 wt% U alloys by Riefenberg and Ellinger. This work has produced relatively high-quality diffraction patterns for both components of the banded structures, but computer indexing of these patterns did not produce acceptable solutions for either the zeta-phase or the second component of the banded structures. The effect of uranium on ..cap alpha..-Pu's lattice parameters is determined, and the data for the effect of uranium on ..beta..-Pu's lattice parameters are extended.
Date: December 15, 1980
Creator: Wallace, P.L. & Harvey, M.R.
Partner: UNT Libraries Government Documents Department

Literature study of metallic ternary and quanternary hydrides

Description: Metallic hydrides are being considered as an attractive solution to storage problems involved in using hydrogen as an alternative fuel. In this application, the unclassified literature was surveyed to find metallic ternary hydride systems of the type MM'H/sub x/; M is a transition element, a member of the rare earth element series, or a member of the actinide element series, and M' is a transition element. Reported quaternary hydrides of the same metallic element series were also reviewed. The hydride-forming systems found and some of their most interesting properties are summarized. Recent advances in the understanding of the absorption characteristics and the stability of these hydride materials are reviewed. (auth)
Date: September 19, 1975
Creator: Newkirk, H.W.
Partner: UNT Libraries Government Documents Department


Description: This project enhanced our theoretical capabilities geared towards establishing the basic science of a high-throughput protocol for the development of advanced nuclear fuel that should couple modern computational materials modeling and simulation tools, fabrication and characterization capabilities, and targeted high throughput performance testing experiments. The successful conclusion of this ER project allowed us to upgrade state-of-the-art modeling codes, and apply these modeling tools to ab initio energetics and thermodynamic assessments of phase diagrams of various mixtures of actinide alloys, propose a tool for optimizing composition of complex alloys for specific properties, predict diffusion behavior in diffusion couples made of actinide and transition metals, include one new equation in the LLNL phase-field AMPE code, and predict microstructure evolution during alloy coring. In FY11, despite limited funding, the team also initiated an experimental activity, with collaboration from Texas A&amp;M University by preparing samples of nuclear fuels in bulk forms and for diffusion couple studies and metallic matrices, and performing preliminary characterization.
Date: November 28, 2011
Creator: Turchi, P
Partner: UNT Libraries Government Documents Department


Description: In this report we investigate order, stability, and phase transformations for a series of actinide-based alloys. The statics and kinetics of precipitation and ordering in this class of alloys are modeled with a scheme that couples fundamental information on the alloy energetics obtained from experimental and assessed thermo-chemical data to the CALPHAD approach commonly used in industry for designing alloys with engineering specificity with the help of the Thermo-Calc software application. The CALPHAD approach is applied to the study of the equilibrium thermodynamic properties of Pu-based alloys, Pu-X, where X=Al, Fe, Ga. The assessment of the equilibrium phase diagrams in the whole range of alloy composition has been performed with the PARROT module of the Thermo-Calc application software. Predictions are made on the low temperature and Pu-rich side of the phase diagrams of Pu-Ga and Pu-Al for which controversy has been noted in the past. The validity of the assessed thermo-chemical database will be discussed by comparing predicted heats of transformation for pure Pu with measured values from differential scanning calorimetry analysis. An overall picture for the stability properties of Pu-Ga and Pu-Al that reconciles the results of past studies carried out on these alloys is proposed. Results on phase stability in the ternary Fe-Ga-Pu and Al-Fe-Pu alloys are discussed. The information collected in this study is then used to model metastability, long-term stability and aging for this class of alloys by coupling Thermo-Calc with DICTRA, a series of modules that allow the analysis of DIffusion Controlled TRAnsformations. Kinetics information is then summarized in so-called TTT (temperature-time-transformations) diagrams for the most relevant phases of actinide alloys. Specifically, results are presented on kinetics of phase transformations associated with the eutectoid-phase decomposition reaction occurring at low temperature, and with the martensitic transformation that takes place at low Ga content in Pu-Ga alloys. ...
Date: August 18, 2004
Creator: Turchi, P A; Kaufman, L; Liu, Z & Zhou, S
Partner: UNT Libraries Government Documents Department

Homogenization of arc-melted uranium-6 weight percent niobium alloy ingots

Description: Microsegregation and macrosegregation in uranium-6 niobium arc-melted ingots were characterized by electron microprobe analysis. Homogenization studies determined that microsegregation can be eliminated by heat treating the alloy for six hours at 1100/sup 0/C. Extensive homogenization did not eliminate macrosegregation (banding) from the as-cast alloy, but a mathematical model describing banding and coring indicated that banding could possibly be eliminated by working prior to homogenization.
Date: January 31, 1978
Creator: Snyder, W. B., Jr.
Partner: UNT Libraries Government Documents Department

Gallium in the alpha and delta plutonium lattice

Description: Some general ideas are offered to further an understanding of the nature of the delta-phase plutonium--gallium alloys and their stability. Attention is given to a hypothesis relating to the role of gallium atom positions in the plutonium lattice. (GHT)
Date: January 1, 1976
Creator: Fischer, R. B.
Partner: UNT Libraries Government Documents Department