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GMR in intermetallics

Description: Typical examples of giant magnetoresistance (GMR) effects observed in intermetallic compounds at various conditions are reviewed and some comparisons with the GMR magnetic multilayer systems are shown. Possibilities of tuning material parameters desired for applications are discussed in context of present understanding of the mechanisms responsible for GMR in this class of materials. 18 refs.
Date: April 1, 1996
Creator: Sechowsky, V.; Havela, L.; Nakotte, H. & Brueck, E.
Partner: UNT Libraries Government Documents Department

TEM investigation on the low temperature phase of HfV{sub 2}

Description: HfV2, a particularly attractive C15 Laves phase structural material, undergoes a structural transformation at 115K. A tentative reciprocal lattice for low-temperature HfV2 based on a combination of selected area diffraction patterns is illustrated. The results reveal structural characteristics inconsistent with earlier claims by other investigators. Further and detailed studies are under way, using a combination of CBED and synchrotron diffraction to determine the low-temperature structure`s crystal symmetry, lattice parameters, and atomic positions.
Date: April 1, 1995
Creator: Chu, Fuming & Mitchell, T.E.
Partner: UNT Libraries Government Documents Department

Tritium Separation Using Metal Hydrides

Description: This paper discusses some of the metal hydride and intermetallic compounds which readily absorb the hydrogen gas by a simple contact to form metal hydrides. Metal hydrides have several important properties for the hydrogen isotope separation.
Date: March 9, 2001
Creator: Lee, M.W.
Partner: UNT Libraries Government Documents Department

Synthesis and design of silicide intermetallic materials

Description: The overall objective of this program is to develop structural silicide-based materials with optimum combinations of elevated temperature strength/creep resistance, low temperature fracture toughness, and high temperature oxidation and corrosion resistance for applications of importance to the U.S. processing industry. A further objective is to develop silicide-based prototype industrial components. The ultimate aim of the program is to work with industry to transfer the structural silicide materials technology to the private sector in order to promote international competitiveness in the area of advanced high temperature materials and important applications in major energy-intensive U.S. processing industries.
Date: November 1, 1998
Creator: Petrovic, J.J.; Castro, R.G.; Butt, D.P.; Park, Y.; Hollis, K.J. & Kung, H.H.
Partner: UNT Libraries Government Documents Department

Lattice disorder and magnetism in f-electron intermetallics

Description: Real materials can have real differences compared to ideal systems. For instance, non-Fermi liquid (NFL) behavior was initially thought to be due to chemical disorder, since the first such materials were all substituted. Although several nominally well-ordered NFL's have been discovered and extensively studied, the effect of disorder on the magnetic properties of f-electron intermetallic systems remains poorly understood. Disorder in NFL systems is reviewed from an experimental, local structure point of view, including a discussion of results on the nominally ordered U{sub 3}Ni{sub 3}Sn{sub 4} and CeCoIn{sub 5} systems, and the chemically disordered UCu{sub 4}Pd and CeRhRuSi{sub 2} systems.
Date: July 29, 2004
Creator: Booth, C.H.; Han, S.-W.; Skanthakumar, S. & Sarrao, J.L.
Partner: UNT Libraries Government Documents Department

Low-Temperature Synthesis Routes to Intermetallic Superconductors

Description: Over the past few years, our group has gained expertise at developing low-temperature solution-based synthetic pathways to complex nanoscale solids, with particular emphasis on nanocrystalline intermetallic compounds. Our synthetic capabilities are providing tools to reproducibly generate intermetallic nanostructures with simultaneous control over crystal structure, composition, and morphology. This DOE-funded project aims to expand these capabilities to intermetallic superconductors. This could represent an important addition to the tools that are available for the synthesis and processing of intermetallic superconductors, which traditionally utilize high-temperature, high-pressure, thin film, or gas-phase vacuum deposition methods. Our current knowledge of intermetallic superconductors suggests that significant enhancements could result from the inherent benefits of low-temperature solution synthesis, e.g. metastable phase formation, control over nanoscale morphology to facilitate size-dependent property studies, robust and inexpensive processability, low-temperature annealing and consolidation, and impurity incorporation (for doping, stoichiometry control, flux pinning, and improving the critical fields). Our focus is on understanding the superconducting properties as a function of synthetic route, crystal structure, crystallite size, and morphology, and developing the synthetic tools necessary to accomplish this. This research program can currently be divided into two classes of superconducting materials: intermetallics (transition metal/post transition metal) and metal carbides/borides. Both involve the development and exploitation of low-temperature synthesis routes followed by detailed characterization of structures and properties, with the goal of understanding how the synthetic pathways influence key superconducting properties of selected target materials. Because of the low-temperature methods used to synthesize them and the nanocrystalline morphologies of many of the products, the superconductors and their nanocrystalline precursors are potentially amenable to inexpensive and large-scale solution-based processing into wires, coatings, films, and templated or patterned structures with nanoscale and microscale features. Also, because of the new synthetic variables that play a key role in the low-temperature formation of intermetallics, the possibility exists to discover ...
Date: January 8, 2008
Creator: Schaak, Raymond E.
Partner: UNT Libraries Government Documents Department

Wall pressure exerted by hydrogenation of sodium aluminum hydride.

Description: Wall pressure exerted by the bulk expansion of a sodium aluminum hydride bed was measured as a function of hydrogen content. A custom apparatus was designed and loaded with sodium alanates at densities of 1.0, 1.1, and 1.16 g/cc. Four complete cycles were performed to identify variations in measured pressure. Results indicated poor correlation between exerted pressure and hydrogen capacity of the sodium alanate beds. Mechanical pressure due to the hydrogenation of sodium alanates does not influence full-scale system designs as it falls within common design factors of safety. Gas pressure gradients within the porous solid were identified and may limit reaction rates, especially for high aspect ratio beds.
Date: June 1, 2009
Creator: Perras, Yon E.; Dedrick, Daniel E. & Zimmerman, Mark D.
Partner: UNT Libraries Government Documents Department

The role of ALCHEMI in understanding the properties of ordered intermetallic alloys

Description: After one and one-half decades of development, ALCHEMI is approaching the status of an established analytical technique. Many of the problems that have plagued ALCHEMI, especially for the analysis of ordered intermetallic alloys, are now well understood, and accurate site-distributions can be extracted from a variety of intermetallic alloys. This paper begins with an overview of the factors that can lead to large systematic errors or gross misinterpretations of ALCHEMI data, with illustrations from a variety of ordered intermetallic alloys. The paper concludes with a discussion of ALCHEMI in the broader context of understanding the properties of ordered intermetallic alloys. The results of systematic studies are used to illustrate the role of ALCHEMI in determining the competing effects of thermodynamic and kinetic factors during alloy processing and the correlation of alloy properties with the atomic site distributions on which the properties ultimately depend.
Date: November 1, 1998
Creator: Anderson, I.M.
Partner: UNT Libraries Government Documents Department

Reduction in Defect Content of ODS Alloys

Description: The work detailed within this report is a continuation of earlier work carried out under contract number 1DX-SY382V. The earlier work comprises a literature review of the sources and types of defects found principally in Fe-based ODS alloys as well as experimental work designed to identify defects in the prototype ODS-Fe{sub 3}Al alloy, deduce their origins and to recommend methods of defect reduction. The present work is an extension of the experimental work already reported and concentrates on means of reduction of defects already identified rather than the search for new defect types. This report also includes results gathered during powder separation trials, conducted by the University of Groningen, Netherlands and coordinated by the University of Liverpool, involving the separation of different metallic powders in terms of their differing densities. The scope and objectives of the present work were laid out in the technical proposal ''Reduction in Defect Content in ODS Alloys-III''. All the work proposed in the ''Statement of Work'' section of the technical proposal has been carried out and all work extra to the ''Statement of Work'' falls within the context of an ODS-Fe{sub 3}Al alloy of improved overall quality and potential creep performance in the consolidated form. The outturn of the experimental work performed is reported in the following sections.
Date: May 15, 2001
Creator: Ritherdon, J.
Partner: UNT Libraries Government Documents Department

Structure factor measurement in TiAl and silicon

Description: It proved impossible to obtain results with sufficient precision for TiAl reproducibly (<0.1%) from samples of different thicknesses. In order to ascertain the origin of this inconsistency, this study concentrates on the development of the experimental and theoretical tools required for such refinement and measurements for Si have been performed.
Date: March 1, 1996
Creator: Swaminathan, S.; Wiezorek, J.M.; Jones, I.P.; Zaluzec, N.J.; Fraser & Maher, D.M.
Partner: UNT Libraries Government Documents Department

Test data for the calculation of powder paterns for intermetallic phases

Description: Powder diffraction patterns are often calculated from structural parameters to assist in the identification of materials. To ensure that powder pattern calculations are correct, it is useful to have data to test the computer program doing the calculations. this paper contains test data for each of the crystallographic point groups and 63 of the 230 space groups. An important feature of the data is that many tests involve two high-symmetry structures (sodium and magnesium) that are set in successively lower-symmetry space groups. Thus, the calculated powder intensities for sodium, for example, are identical whatever the setting is. Though the data were chosen to be especially useful for the calculation of the powder patterns of metals and intermetallic compounds, the data have wider utility.
Date: September 1, 1996
Creator: Calvert, L.D.; Mueller, M.H.; Wallace, P.L.; Huang, J.A.; Kaduk, J.A.; Dann, J.N. et al.
Partner: UNT Libraries Government Documents Department

Reaction synthesis of intermetallics

Description: Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.
Date: December 1994
Creator: Deevi, S. C. & Sikka, V. K.
Partner: UNT Libraries Government Documents Department

A model for the yield strength anomaly in FeAl

Description: A phenomenological model is used to explain the yield strength anomaly in FeAl. The model incorporates hardening by thermal vacancies at intermediate temperatures, and dislocation creep at elevated temperatures. Since the vacancy concentration increases exponentially with temperature, the model predicts an exponential increase in strength with temperature. This increase is terminated by onset of dislocation creep. The model captures the experimentally observed strain rate dependency of the yield stress at high temperatures and yields an activation enthalpy for vacancy formation which is in excellent agreement with a previously measured value.
Date: December 31, 1996
Creator: Baker, I. & George, E.P.
Partner: UNT Libraries Government Documents Department

The mechanical properties of FeAl

Description: Only in the last few years has progress been made in obtaining reproducible mechanical properties data for FeAl. Two sets of observations are the foundation of this progress. The first is that the large vacancy concentrations that exist in FeAl at high temperature are easily retained at low temperature and that these strongly affect the low-temperature mechanical properties. The second is that RT ductility is adversely affected by water vapor. Purpose of this paper is not to present a comprehensive overview of the mechanical properties of FeAl but rather to highlight our understanding of key phenomena and to show how an understanding of the factors which control the yield strength and fracture behavior has followed the discovery of the above two effects. 87 refs, 9 figs.
Date: December 31, 1996
Creator: Baker, I. & George, E.P.
Partner: UNT Libraries Government Documents Department

Modeling non-isothermal intermetallic layer growth in the 63Sn-37Pb/Cu system

Description: A model describing diffusion-controlled growth of multiple intermetallic layers and the displacement of the interfaces between layers was developed and implemented in a 1-D computer code based on method-of-lines. The code was applied to analysis of intermetallic layer growth in isothermal solder aging experiments performed with 100 Sn/Cu and 63Sn-37Pb/Cu solder-substrate systems. Analyses indicated that intermetallic layer growth was consistent with a bulk diffusion mechanism involving Cu and/or Sn. In this work, nonisothermal solder-aging experiments were done with the 63Sn- 37Pb/Cu system using two temperature histories (4 cycles/day between 223-443 K, and 72 cycles/day between 223-443 K). Isothermal experiments were also done at 443 K. Thickness of Cu{sub 3}Sn and Cu{sub 6}Sn{sub 5} intermetallic layers were determined vs time for each temperature history. An updated version of the model and code were used to predict the intermetallic layer growth. Arrhenius expressions for diffusion coefficients in both Cu3Sn and Cu6Sn5 layers were determined. Agreement between prediction and experiment was generally good. In some cases, predicted layer growth was less than experiment, but within error. This paper describes the nonisothermal experiments and a comparison of predicted and observed layer growth vs time.
Date: December 31, 1996
Creator: Vianco, P.T.; Hopkins, P.L.; Erickson, K.L.; Frear, D.R. & Davidson, R.
Partner: UNT Libraries Government Documents Department

Determination of site-occupancies in aluminide intermetallics by ALCHEMI

Description: The site-distributions of Fe in four B2-ordered NiAl-based alloys with Fe concentrations of 10%, 2%, and 0.5% have been determined by ALCHEMI (atom-location by channeling-enhanced microanalysis). Site-distributions have been extracted with standard errors between {approximately} 1.5% (10% Fe concentration) and {approximately} 6% (0.5% Fe concentration). The results show that Fe has no strong site-preference in NiAl and tends to reside on the site of the stoichiometrically deficient host element. An improved ALCHEMI analysis procedure is outlined. The analysis explicitly addresses the phenomenon of ionization delocalization, which previously complicated the determination of site-distributions in aluminide intermetallics, leading to inaccurate and oftentimes nonphysical results. The improved ALCHEMI analysis also addresses the presence of anti-site defects. The data acquisition conditions have been optimized to minimize the sources of statistical and systematic error. This optimized procedure should be suitable for all analyses of B2-ordered alloys. Several analyses at different channeling orientations show that the extracted site-occupancies are robust as long as the data are acquired at orientations that are remote from any major pole of the crystal.
Date: April 1, 1995
Creator: Anderson, I. M.; Bentley, J. & Duncan, A. J.
Partner: UNT Libraries Government Documents Department

Magnetic designs and field quality of Nb{sub 3}Sn accelerator magnets

Description: This paper presents a new approach to accelerator magnet design, based on simple and robust single-layer coils with minimum number of turns arranged horizontally or vertically in a common iron yoke. Cos-theta and block type coil geometries as well as cold and warm iron yoke designs were studied. Coils and yokes were optimized for the maximum field, minimum field harmonics, and minimum sizes.
Date: January 14, 2002
Creator: Kashikhin, Vadim V. & Zlobin, Alexander V.
Partner: UNT Libraries Government Documents Department

Reduction in Defect Content in ODS Alloys

Description: The work detailed within this report is a continuation of earlier work that was carried out under contract number IDX-SY382V. The earlier work comprised a literature review of the sources and types of defects found principally in Fe-based ODS alloys together with a series of experiments designed to identify defects in ODS Fe{sub 3}Al material and recommend methods of defect reduction. Defects found in the Mechanically Alloyed (MA) ODS Fe{sub 3}Al included regions of incomplete MA, porosity, intrusions and fine-grained stringers. Some defects tended to be found in association with one another e.g. intrusions and fine-grained stringers. Preliminary powder separation experiments were also performed. The scope and objectives of the present work were laid out in the technical proposal ``Reduction in Defect Content in ODS Alloys--II'' which formed the basis of amendment 3 of the current contract. The current studies were devised in the context of the preceding work with a view to extending and concluding certain experiments while exploring new avenues of investigation of defect control and reduction where appropriate. All work proposed was within the context of achieving an ODS Fe{sub 3}Al alloy of improved overall quality and potential creep performance (particularly) in the consolidated, release condition. The interim outturn of the experimental work performed is also reported.
Date: February 1, 2000
Creator: Ritherdon, J. & Jones, A.R.
Partner: UNT Libraries Government Documents Department

Development of cos-theta Nb{sub 3}Sn dipole magnets for VLHC

Description: This paper describes the double aperture dipole magnets developed for a VLHC based on Nb{sub 3}Sn superconductor, a cos-theta coil, cold and warm iron yokes, and the wind-and-react fabrication technique. Status of the model R and D program, strand and cable and other major component development are also discussed.
Date: July 20, 2001
Creator: al., Alexander Zlobin et
Partner: UNT Libraries Government Documents Department