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Sample records for fcc f-shell metals

  1. Thermodynamic Properties of 4f- and 5f-SHELL Metals at Finite Temperatures:

    NASA Astrophysics Data System (ADS)

    Bhatt, N. K.; Vyas, P. R.; Jani, A. R.; Gohel, V. B.

    The thermodynamic properties of 4f- and 5f-shell metals have been studied at high temperatures using mean-field potential approach. The MFP seen by the lattice ion is constructed in terms of the total energy-volume relation using local pseudopotentials due to Pandya et al. [Physica B 307, 138 (2001)]. We have calculated static compression, shock-wave compression, volume thermal expansion, isothermal and adiabatic bulk moduli (BT and BS), specific heats (CV and CP), thermodynamic Grüneisen parameter (γth), anharmonic contribution to the specific heat and temperature along shock Hugoniot for 4f (γ-Ce)- and 5f (fcc-Th)-shell metals. The results are well compared with the other theoretical and experimental findings, which ensure the use of pseudopotentials for studying thermodynamic properties at higher temperatures in case of lanthanides and actinides.

  2. Core and shallow-core d- to f-shell excitations in rare-earth metals

    NASA Astrophysics Data System (ADS)

    Bradley, J. A.; Moore, K. T.; van der Laan, G.; Bradley, J. P.; Gordon, R. A.

    2011-11-01

    We report on the results of probing the light lanthanide metals Ce, Pr, and Nd with inelastic x-ray and electron scattering. Aberration-corrected transmission electron microscope-based electron spectroscopy and nonresonant inelastic x-ray scattering are shown to be in a high degree of accord and here serve as complementary probes of electronic structure. The high resolution and high signal-to-noise electron technique allows for the measurement of the complex and subtle excitation spectra in the lanthanide metals, validating the applicability of the screened trivalent atomic model used for these materials. In addition, the momentum transfer dependence of the x-ray scattering is extracted and compared against atomic calculations for the most tightly bound excitonic resonances, which provides a direct test of the predicted atomic radial wave functions.

  3. Structural and elastic properties of fcc/fcc metallic multilayers: A molecular-dynamics study

    NASA Astrophysics Data System (ADS)

    Tȩcza, Grzegorz W.

    1992-12-01

    Interplanar and intraplanar spacings as well as the elastic constants of fcc/fcc metallic multilayers stacked along [001] were determined via variable-cell molecular-dynamics simulation in (HtN) and (EhN) ensembles at room temperature. Qualitative differences in the structural and elastic properties of the multilayers, simulated using various 12-6 Lennard-Jones potentials, were observed. The anomalous behavior of the elastic constants and the biaxial modulus was linked to the modulation wavelength dependence of various structural parameters. The importance of the fluctuation contributions for the calculation of the full elastic constants is demonstrated.

  4. Interaction of hydrogen with transition metal fcc(111) surfaces

    NASA Astrophysics Data System (ADS)

    Löautber, R.; Hennig, D.

    1997-02-01

    The interaction of atomic hydrogen with the fcc(111) surfaces of Pd and Rh was investigated theoretically with an ab initio method, to find out the differences and similiarities between these neighboring metals. At the Rh surface the hcp site of the threefold-coordinated adsorption sites is preferred, while at Pd almost no difference between the hcp and fcc sites was found. For Pd, the occupation of subsurface positions was calculated to be more stable than bulklike positions. The energy gain caused by hydrogen absorption in subsurface positions is only about 100 meV lower than for hydrogen adsorption at the surface. In contrast, for Rh, significant differences between adsorption and absorption were calculated. The diffusion barrier for hydrogen diffusion from surface to subsurface positions was calculated and compared to the diffusion barrier in bulk. The hydrogen-induced work-function changes for the considered 4d transition-metal surfaces were positive for coverage θ=1.

  5. Deformation twinning mechanisms in FCC and HCP metals

    SciTech Connect

    Wang, Jian; Tome, Carlos N; Beyerlein, Irene J; Misra, Amit; Mara, N

    2011-01-31

    We report the recent work on twinning and detwinning in fcc and hcp metals based on the in situ and ex situ TEM observations and molecular dynamics simulations. Three aspects are discussed in this paper. (1) Detwinning in single-phase Cu with respect to growth twins, (2) deformation twinning in Ag-Cu composites, and (3) deformation twinning mechanisms in hcp metals. The main conclusion is that atomic structures of interfaces (twin boundaries, two-phases interface, and grain boundaries) play a crucial role in nucleating and propagating of deformation twins.

  6. Folding in FCC metal single crystals under compression

    NASA Astrophysics Data System (ADS)

    Lychagin, D. V.; Alfyorova, E. A.

    2015-10-01

    Results of the analysis of folding during compression deformation of metals with fcc lattice are presented. Single crystals with orientations at angles of the standard stereographic triangle and different crystallographic orientations of lateral faces have been studied. It has been found that the major factor affecting the folding intensity is the slip plane shear with respect to lateral faces. Such a shear results in face bending and the formation of fold systems in maximum curvature regions. It has been shown that, among all considered orientations, the maximum susceptibility to the formation of different folds is inherent in single crystals with bar 1 compression axis orientation. For this orientation, the development of shear and rotational components during folding is traced by interference microscopy and electron backscatter diffraction methods. It has been found that an excess dislocation density is accumulated when shear is activated in the folding region, which results in an increase in fold misorientation. The activation of this process in fcc metals is promoted by an increase in the homologous deformation temperature and stacking fault energy.

  7. Defect structures in deformed F.C.C. metals

    SciTech Connect

    Dai, Y.; Victoria, M.

    1997-08-01

    A high density of small defect clusters, similar to those observed in irradiated or quenched metals, has been observed in the deformed f.c.c. metals Cu, Au and Ni. The preliminary results show that the defect clusters are predominantly stacking fault tetrahedral (SFT). The SFT number density, rather than the size distribution, is deformation dependent. The defect cluster density is greater in the vicinities of dislocation tangles and grain boundaries. Their size distribution is wider than that produced by irradiation with an important number of larger clusters being formed. It is argued that these deformation-produced clusters may play a role in determining the flow stress and work hardening at low deformations.

  8. Dislocation Interactions with Voids and Helium Bubbles in FCC Metals

    SciTech Connect

    Robertson, I; Robach, J; Wirth, B; Young, J

    2003-11-18

    The formation of a high number density of helium bubbles in FCC metals irradiated within the fusion energy environment is well established. Yet, the role of helium bubbles in radiation hardening and mechanical property degradation of these steels remains an outstanding issue. In this paper, we present the results of a combined molecular dynamics simulation and in-situ straining transmission electron microscopy study, which investigates the interaction mechanisms between glissile dislocations and nanometer-sized helium bubbles. The molecular dynamics simulations, which directly account for dislocation core effects through semi-empirical interatomic potentials, provide fundamental insight into the effect of helium bubble size and internal gas pressure on the dislocation/bubble interaction and bypass mechanisms. The combination of simulation and in-situ straining experiments provides a powerful approach to determine the atomic to microscopic mechanisms of dislocation-helium bubble interactions, which govern the mechanical response of metals irradiated within the fusion environment.

  9. Formation of fivefold axes in the FCC-metal nanoclusters

    NASA Astrophysics Data System (ADS)

    Myasnichenko, Vladimir S.; Starostenkov, Mikhail D.

    2012-11-01

    Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu-Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000 K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu-Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

  10. Attrition resistant catalysts and sorbents based on heavy metal poisoned FCC catalysts

    DOEpatents

    Gangwal, S.; Jothimurugesan, K.

    1999-07-27

    A heavy metal poisoned, spent FCC catalyst is treated by chemically impregnating the poisoned catalyst with a new catalytic metal or metal salt to provide an attrition resistant catalyst or sorbent for a different catalytic or absorption process, such as catalysts for Fischer-Tropsh Synthesis, and sorbents for removal of sulfur gases from fuel gases and flue-gases. The heavy metal contaminated FCC catalyst is directly used as a support for preparing catalysts having new catalytic properties and sorbents having new sorbent properties, without removing or passivating the heavy metals on the spent FCC catalyst as an intermediate step.

  11. Attrition resistant catalysts and sorbents based on heavy metal poisoned FCC catalysts

    DOEpatents

    Gangwal, Santosh; Jothimurugesan, Kandaswamy

    1999-01-01

    A heavy metal poisoned, spent FCC catalyst is treated by chemically impregnating the poisoned catalyst with a new catalytic metal or metal salt to provide an attrition resistant catalyst or sorbent for a different catalytic or absorption processes, such as catalysts for Fischer-Tropsh Synthesis, and sorbents for removal of sulfur gasses from fuel gases and flue-gases. The heavy metal contaminated FCC catalyst is directly used as a support for preparing catalysts having new catalytic properties and sorbents having new sorbent properties, without removing or "passivating" the heavy metals on the spent FCC catalyst as an intermediate step.

  12. Scaling Laws and Critical Properties for fcc and hcp Metals.

    PubMed

    Desgranges, Caroline; Widhalm, Leanna; Delhommelle, Jerome

    2016-06-16

    The determination of the critical parameters of metals has remained particularly challenging both experimentally, because of the very large temperatures involved, and theoretically, because of the many-body interactions that take place in metals. Moreover, experiments have shown that these systems exhibit an unusually strong asymmetry of their binodal. Recent theoretical work has led to new similarity laws, based on the calculation of the Zeno line and of the underlying Boyle parameters, which provided results for the critical properties of atomic and molecular systems in excellent agreement with experiments. Using the recently developed expanded Wang-Landau (EWL) simulation method, we evaluate the grand-canonical partition function, over a wide range of conditions, for 11 fcc and hcp metals (Ag, Al, Au, Be, Cu, Ir, Ni, Pb, Pd, Pt, and Rh), modeled with a many-body interaction potential. This allows us to calculate the binodal, Zeno line, and Boyle parameters and, in turn, obtain the critical properties for these systems. We also propose two scaling laws for the enthalpy and entropy of vaporization, and identify critical exponents of 0.4 and 1.22 for these two laws, respectively. PMID:27228416

  13. Continuum modeling of plastic flow localization in irradiated fcc metals

    NASA Astrophysics Data System (ADS)

    Po, Giacomo; Ghoniem, Nasr

    2013-11-01

    Under mechanical loading, neutron or ion irradiated metals may develop a mechanical instability characterized by the localization of plastic flow in narrow channels that are cleared of irradiation-induced defects. The resulting highly heterogeneous deformation can play a significant role in crack nucleation, fracture propagation, and premature failure of structural components used in nuclear applications. In this work, we develop a two-dimensional continuum model of plastic flow localization based on the continuum theory of dislocations. This framework allows a mechanism-based description of deformation in which plastic distortion is directly calculated from the evolution of dislocation density tensor fields on each slip system. The dislocation densities mutually interact through the self-consistent stress field derived from the deformation gradient and through back and flow stress corrections. The interaction between dislocation fields and irradiation-induced defects (mainly stacking fault tetrahedra (SFTs) in fcc metals) is twofold. First, the flow stress depends locally on the SFT density. Second, and based on existing molecular dynamics (MD) simulation results, dislocation fluxes are included as sink terms in the evolution equation of the SFT density. The model is implemented numerically using the finite element method (FEM) and simulation results for simple shear loading are presented. It is demonstrated here that small spatial fluctuations in the density of SFTs, coupled with their destruction by dislocation interaction, leads to plastic flow localization.

  14. Properties of Helium Defects in BCC and FCC Metals Investigated with Density Functional Theory

    SciTech Connect

    Zu, Xiaotao T.; Yang, Li; Gao, Fei; Peng, SM; Heinisch, Howard L.; Long, XG; Kurtz, Richard J.

    2009-08-03

    The relative stability of single He defects in bcc and fcc metals is investigated using ab initio calculations based on density functional theory (DFT). The results indicate that the tetrahedral position is energetically more favorable for a He interstitial than the octahedral site in bcc metals, but the relative stability of He defects in fcc metals varies, depending on local environments. The He formation energies in bcc Fe and fcc Ni at the tetrahedral and octahedral positions with and without spin polarization are investigated. It is of interest to find that the magnetism of host atoms does not directly affect the relative stabilities of He in interstitial sites in bcc Fe and fcc Ni.

  15. Dislocation dissociation in some f.c.c. metals

    NASA Technical Reports Server (NTRS)

    Esterling, D. M.

    1980-01-01

    The dissociation of a perfect screw dislocation into a stacking fault in an f.c.c. lattice is modeled by the modified lattice statics. The interatomic potentials are obtained from the work of Esterling and Swaroop and differ substantially from those empirical potentials usually employed in defect simulations. The calculated stacking fault widths for aluminum, copper, and silver are in good agreement with weak beam microscopy results.

  16. Multilayer Relaxation and Surface Energies of FCC and BCC Metals Using Equivalent Crystal Theory

    NASA Technical Reports Server (NTRS)

    Rodriguez, Agustin M.; Bozzolo, Guillermo; Ferrante, John

    1993-01-01

    The multilayer relaxation of fcc and bcc metal surfaces is calculated using equivalent crystal theory. The results for changes in interplanar spacings of planes close to the surface and the ensuing surface energies are discussed in reference to other theoretical results and compared to available experimental data. The calculation includes high-index surfaces for which no other theoretical results are known.

  17. Melting and solidification point of fcc-metal nanoparticles with respect to particle size: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Shibuta, Yasushi; Suzuki, Toshio

    2010-10-01

    The phase transition between liquid droplets and solid nanoparticles of face-centered cubic (fcc) metals is investigated by the molecular dynamics simulation. Depression of both the melting and solidification points is negatively correlated with the inverse of particle radius. Polycrystalline nanoparticles are obtained by cooling and the polycrystalline structure causes a fluctuation in the trend of the melting point with respect to particle size. It was found that the Gibbs-Thomson coefficient is proportional to the melting point among various body-centered cubic (bcc) and fcc metals in the same matter, even though different interatomic potentials are employed between bcc and fcc metals.

  18. Pressure Induced Metal-Nonmetal and FCC-BCC Transitions in Calcium*

    NASA Astrophysics Data System (ADS)

    Wang, G. M.; Blaisten-Barojas, E.; Papaconstantopoulos, D. A.

    2001-04-01

    The band structure of fcc and bcc calcium at different densities is obtained with the Augmented Plane Wave (APW) method using a soft-core approximation and Gaspar-Kohn-Sham potential. A tight-binding(TB) model is then built successfully to reproduce the first principles band structure and density of states. Properties examined within TB include bulk modulus, elastic constants, metal-nonmetal transition and fcc to bcc structural transition under pressure. Results are in an excellent agreement with experimental observations. Several dynamical properties of calcium under pressure are further explored with TB molecular dynamics at finite temperature. *Work supported in part by the Office of Naval Research grant N00014-98-1-0832

  19. Phonon instabilities in uniaxially compressed fcc metals as seen in molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Kimminau, Giles; Erhart, Paul; Bringa, Eduardo M.; Remington, Bruce; Wark, Justin S.

    2010-03-01

    We show that the generation of stacking faults in perfect face-centered-cubic (fcc) crystals, uniaxially compressed along [001], is due to transverse-acoustic phonon instabilities. The position in reciprocal space where the instability first manifests itself is not a point of high symmetry in the Brillouin zone. This model provides a useful explanation for the magnitude of the elastic limit, in addition to the affects of box size, temperature, and compression on the time scale for the generation of stacking faults. We observe this phenomenon in both simulations that use the Lennard-Jones potential and embedded atom potentials. Not only does this work provide fundamental insight into the microscopic response of the material but it also describes certain behavior seen in previous molecular dynamics simulations of single-crystal fcc metals shock compressed along the principal axis.

  20. Thermal and mechanical stability of nanograined FCC metals

    NASA Astrophysics Data System (ADS)

    Hattar, Khalid Mikhiel

    The mechanisms governing and factors controlling the thermal and mechanical stability of nanograined free-standing face-centered cubic thin films were investigated through in situ transmission electron microscopy annealing and straining experiments. A variety of sample preparation techniques were developed to investigate the active mechanisms. The results obtained from the select face-centered cubic metals studied were used to develop a general understanding of face-centered cubic metals with microstructure limited to the nanometer scale. The films were analyzed, both prior to and following the in situ transmission electron microscopy experiments, via a range of analytical techniques in order to characterize chemical and microstructural details. The mechanisms observed were compared to the pertinent theories and models. In situ transmission electron microscopy heating and annealing experiments were performed on free-standing pulsed-laser deposited Au, Cu, and Ni thin films. The grain growth of pulsed-laser deposited Ni films was studied and the growth rate was found to be a function of time, temperature, film thickness, and surface abnormalities. The grain growth was classified as abnormal in nature resulting in a bimodal grain size distribution. Abnormal grain growth was found to increase with an increase in film thickness. This increase was attributed to the presence of a higher density of preferred nanograins for abnormal grain growth in thicker films, although the mechanisms that induce the rapid growth were not determined. A higher percentage of abnormal large grains were found along ridges templated from the substrate, and in regions with extensive electron beam exposure. Post-annealing analysis of pulsed-laser deposited Ni films revealed an unexpected myriad of microstructural defects including dislocations, twins, stacking faults, dislocation loops, and stacking-fault tetrahedra, as well as a metastable hexagonal closed-packed phase. The production of these

  1. Dislocation creation and void nucleation in FCC ductile metals under tensile loading: A general microscopic picture

    PubMed Central

    Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

    2014-01-01

    Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies. PMID:25382029

  2. A simple model for large-scale simulations of fcc metals with explicit treatment of electrons

    NASA Astrophysics Data System (ADS)

    Mason, D. R.; Foulkes, W. M. C.; Sutton, A. P.

    2010-01-01

    The continuing advance in computational power is beginning to make accurate electronic structure calculations routine. Yet, where physics emerges through the dynamics of tens of thousands of atoms in metals, simplifications must be made to the electronic Hamiltonian. We present the simplest extension to a single s-band model [A.P. Sutton, T.N. Todorov, M.J. Cawkwell and J. Hoekstra, Phil. Mag. A 81 (2001) p.1833.] of metallic bonding, namely, the addition of a second s-band. We show that this addition yields a reasonable description of the density of states at the Fermi level, the cohesive energy, formation energies of point defects and elastic constants of some face-centred cubic (fcc) metals.

  3. Effect of vacancy defects on generalized stacking fault energy of fcc metals.

    PubMed

    Asadi, Ebrahim; Zaeem, Mohsen Asle; Moitra, Amitava; Tschopp, Mark A

    2014-03-19

    Molecular dynamics (MD) and density functional theory (DFT) studies were performed to investigate the influence of vacancy defects on generalized stacking fault (GSF) energy of fcc metals. MEAM and EAM potentials were used for MD simulations, and DFT calculations were performed to test the accuracy of different common parameter sets for MEAM and EAM potentials in predicting GSF with different fractions of vacancy defects. Vacancy defects were placed at the stacking fault plane or at nearby atomic layers. The effect of vacancy defects at the stacking fault plane and the plane directly underneath of it was dominant compared to the effect of vacancies at other adjacent planes. The effects of vacancy fraction, the distance between vacancies, and lateral relaxation of atoms on the GSF curves with vacancy defects were investigated. A very similar variation of normalized SFEs with respect to vacancy fractions were observed for Ni and Cu. MEAM potentials qualitatively captured the effect of vacancies on GSF. PMID:24589571

  4. Defect clusters formed from large collision cascades in fcc metals irradiated with spallation neutrons

    NASA Astrophysics Data System (ADS)

    Satoh, Y.; Matsuda, Y.; Yoshiie, T.; Kawai, M.; Matsumura, H.; Iwase, H.; Abe, H.; Kim, S. W.; Matsunaga, T.

    2013-11-01

    Fcc pure metals were irradiated with spallation neutrons (energies up to 500 MeV) at room temperature to a neutron fluence of 1 × 1018 n m-2 at KENS, High Energy Accelerator Research Organization (KEK). Defect clusters induced by large collision cascades were examined using transmission electron microscopy (TEM). In Au, large groups of defects included more than 10 clusters, and the damage zone extended over 50 nm, which was larger than that induced by fusion neutron irradiation (<20 nm). Although small stacking fault tetrahedra (SFT) are formed in subcascades by fission and fusion neutron irradiation, dislocation loops were also observed in the present experiments. Large dislocation loops (>10 nm) were identified as vacancy type by the conventional inside-outside contrast method. Because of the low neutron fluence, spatial overlapping of collision cascades was ignored. Large vacancy loops are formed through cooperative reactions among subcascades in a single collision cascade with large recoil energy.

  5. On the interaction between perfect interstitial clusters and a vacancy in BCC, FCC and HCP metals

    SciTech Connect

    Puigvi, Mary Angels; Serra, Anna; de Diego, Nieves; Osetskiy, Yury N; Bacon, David J

    2004-01-01

    Point defects and defect clusters have been observed in metals irradiated by high-energy particles. Interactions of these defects between themselves and with existing microstructure features cause microstructure evolution and lead to changes in mechanical and physical properties of the irradiated materials. Models for prediction of radiation-induced changes should include details of reactions involving defects, and so in this paper we present the results of atomic-scale computer modelling of interactions between a cluster of self-interstitial atoms (SIAs) and a single vacancy in models of bcc, fcc and hcp metals. The vacancy is taken to lie on or within the glide prism of the cluster. This type of reaction is considered to be one of the most frequent because formation of SIA clusters, particularly glissile clusters, is commonly observed in high-energy displacement cascades in all metals. The interaction depends strongly on the dislocation nature of the cluster and therefore these interactions are different in the three crystal structures. Vacancy-SIA recombination, in particular, is inhibited by dissociation of the SIA loop on its glide prism.

  6. Effect of the FCC to HCP Phase Transition on Trace Element Partitioning Between Metal and Sulfide Melt

    NASA Astrophysics Data System (ADS)

    Campbell, A. J.; Thomas, R. B.; Fei, Y.

    2006-12-01

    Most of what we understand about the chemical behavior of iron alloys, even at high pressure, pertains to the fcc phase. However, it is widely thought that the relevant structure in the Earth's core is hcp, not fcc. In this study we aim to understand the effect of the fcc-hcp transition on siderophile element partitioning between metal and coexisting sulfide melt. This is important, for example, in evaluating models in which Re-Os-Pt isotope fractionations are attributed to partitioning between the Earth's inner and outer core. Experiments were doped with trace elements Ni, Re, Os, Ir, and Pt, which partitioned between Fe-Ru alloys and sulfide melt. Most experiments were performed at 1 bar in sealed silica tubes in a tube furnace, and some experiments were performed at 6 GPa in a multi-anvil press. The fcc-hcp transition was investigated by varying the Ru content of the experiments; the metal is fcc at Ru-poor compositions but hcp at higher Ru contents. The sulfur content of the melt varied with temperature and with bulk composition. The run products were characterized by electron microprobe, and abundances of the trace elements in both metal and melt were determined by laser ablation ICP-MS. The effect on partitioning of the phase transition can be distinguished from compositional effects because a range of Ru contents was studied. Our Ru-free dataare in good agreement with previously published data in the Fe-S system at 1 bar. However, our highest-Ru compositions show significant differences in their D values, attributable to the phase transition in the metal.

  7. 3D dislocation dynamics: stress-strain behavior and hardening mechanisms in FCC and BCC metals

    SciTech Connect

    Hirth, J P; Rhee, M; Zhib, H M; de la Rubia, T D

    1999-02-19

    A dislocation dynamics (DD) model for plastic deformation, connecting the macroscopic mechanical properties to basic physical laws governing dislocation mobility and related interaction mechanisms, has been under development. In this model there is a set of critical reactions that determine the overall results of the simulations, such as the stress-strain curve. These reactions are, annihilation, formation of jogs, junctions, and dipoles, and cross-slip. In this paper we discuss these reactions and the manner in which they influence the simulated stress- strain behavior in fcc and bcc metals. In particular, we examine the formation (zipping) and strength of dipoles and junctions, and effect of jogs, using the dislocation dynamics model. We show that the strengths (unzipping) of these reactions for various configurations can be determined by direct evaluation of the elastic interactions. Next, we investigate the phenomenon of hardening in metals subjected to cascade damage dislocations. The microstructure investigated consists of small dislocation loops decorating the mobile dislocations. Preliminary results reveal that these loops act as hardening agents, trapping the dislocations and resulting in increased hardening.

  8. Grain Size Dependence of Uniform Elongation in Single-Phase FCC/BCC Metals

    NASA Astrophysics Data System (ADS)

    Liu, Haiting; Shen, Yao; Ma, Jiawei; Zheng, Pengfei; Zhang, Lei

    2016-07-01

    We studied the dependence of uniform elongation on grain size in the range of submicron to millimeter for single-phase FCC/BCC metals by reviewing recent experimental results and applying crystal plasticity finite element method simulation. In the order of increasing grain size, uniform elongation can be divided into three stages, namely low elongation stage, nearly constant elongation stage, and decreased elongation with large scatters stage. Low elongation stage features a dramatic increase near the critical grain size at the end of the stage, which is primarily attributed to the emergence of dislocation cell size transition from ultrafine to mid-size grain. Other factors can be neglected due to their negligible influence on overall variation trend. In nearly constant elongation stage, uniform elongation remains unchanged at a high level in general. As grain size keeps growing, uniform elongation starts decreasing and becomes scattered upon a certain grain size, indicating the initiation of decreased elongation with large scatters stage. It is shown that the increase is not linear or smooth but rather sharp at the end of low elongation stage, leading to a wider range in nearly constant elongation stage. The grain size dependence of uniform elongation can serve as a guiding principle for designing small uniaxial tensile specimens for mechanical testing, where size effect matters in most cases.

  9. Twin boundary spacing effects on shock response and spall behaviors of hierarchically nanotwinned fcc metals

    NASA Astrophysics Data System (ADS)

    Yuan, Fuping; Chen, Liu; Jiang, Ping; Wu, Xiaolei

    2014-02-01

    Atomistic deformation mechanisms of hierarchically nano-twinned (NT) Ag under shock conditions have been investigated using a series of large-scale molecular dynamics simulations. For the same grain size d and the same spacing of primary twins λ1, the average flow stress behind the shock front in hierarchically NT Ag first increases with decreasing spacing of secondary twins λ2, achieving a maximum at a critical λ2, and then drops as λ2 decreases further. Above the critical λ2, the deformation mechanisms are dominated by three type strengthening mechanisms: (a) partial dislocations emitted from grain boundaries (GBs) travel across other boundaries; (b) partial dislocations emitted from twin boundaries (TBs) travel across other TBs; (c) formation of tertiary twins. Below the critical λ2, the deformation mechanism are dominated by two softening mechanisms: (a) detwinning of secondary twins; (b) formation of new grains by cross slip of partial dislocations. Moreover, the twin-free nanocrystalline (NC) Ag is found to have lower average flow stress behind the shock front than those of all hierarchically NT Ag samples except the one with the smallest λ2 of 0.71 nm. No apparent correlation between the spall strength and λ2 is observed in hierarchically NT Ag, since voids always nucleate at both GBs and boundaries of the primary twins. However, twin-free NC Ag is found to have higher spall strength than hierarchically NT Ag. Voids can only nucleate from GBs for twin-free NC Ag, therefore, twin-free NC Ag has less nucleation sources along the shock direction when compared to hierarchically NT Ag, which requiring higher tensile stress to create spallation. These findings should contribute to the understandings of deformation mechanisms of hierarchically NT fcc metals under extreme deformation conditions.

  10. Twin boundary spacing effects on shock response and spall behaviors of hierarchically nanotwinned fcc metals

    SciTech Connect

    Yuan, Fuping Chen, Liu Jiang, Ping Wu, Xiaolei

    2014-02-14

    Atomistic deformation mechanisms of hierarchically nano-twinned (NT) Ag under shock conditions have been investigated using a series of large-scale molecular dynamics simulations. For the same grain size d and the same spacing of primary twins λ{sub 1}, the average flow stress behind the shock front in hierarchically NT Ag first increases with decreasing spacing of secondary twins λ{sub 2}, achieving a maximum at a critical λ{sub 2}, and then drops as λ{sub 2} decreases further. Above the critical λ{sub 2}, the deformation mechanisms are dominated by three type strengthening mechanisms: (a) partial dislocations emitted from grain boundaries (GBs) travel across other boundaries; (b) partial dislocations emitted from twin boundaries (TBs) travel across other TBs; (c) formation of tertiary twins. Below the critical λ{sub 2}, the deformation mechanism are dominated by two softening mechanisms: (a) detwinning of secondary twins; (b) formation of new grains by cross slip of partial dislocations. Moreover, the twin-free nanocrystalline (NC) Ag is found to have lower average flow stress behind the shock front than those of all hierarchically NT Ag samples except the one with the smallest λ{sub 2} of 0.71 nm. No apparent correlation between the spall strength and λ{sub 2} is observed in hierarchically NT Ag, since voids always nucleate at both GBs and boundaries of the primary twins. However, twin-free NC Ag is found to have higher spall strength than hierarchically NT Ag. Voids can only nucleate from GBs for twin-free NC Ag, therefore, twin-free NC Ag has less nucleation sources along the shock direction when compared to hierarchically NT Ag, which requiring higher tensile stress to create spallation. These findings should contribute to the understandings of deformation mechanisms of hierarchically NT fcc metals under extreme deformation conditions.

  11. Thermal stability and hcp-fcc allotropic transformation in supported Co metal catalysts probed near operando by ferromagnetic NMR.

    PubMed

    Andreev, Andrey S; d'Espinose de Lacaillerie, Jean-Baptiste; Lapina, Olga B; Gerashenko, Alexander

    2015-06-14

    Despite the fact that cobalt based catalysts are used at the industrial scale for Fischer-Tropsch synthesis, it is not yet clear which cobalt metallic phase is actually at work under operando conditions and what is its state of dispersion. As it turns out, the different phases of metallic cobalt, fcc and hcp, give rise to distinct ferromagnetic nuclear magnetic resonance. Furthermore, within one Co metal particle, the occurrence of several ferromagnetic domains of limited sizes can be evidenced by the specific resonance of Co in multi-domain particles. Consequently, by ferromagnetic NMR, one can follow quantitatively the sintering and phase transitions of dispersed Co metal particles in supported catalysts under near operando conditions. The minimal size probed by ferromagnetic Co NMR is not precisely known but is considered to be in the order of 10 nm for supported Co particles at room temperature and increases to about 35 nm at 850 K. Here, in Co metal Fischer-Tropsch synthesis catalysts supported on β-SiC, the resonances of the fcc multi-domain, fcc single-domain and hcp Co were clearly distinguished. A careful rationalization of their frequency and width dependence on temperature allowed a quantitative analysis of the spectra in the temperature range of interest, thus reflecting the state of the catalysts under near operando conditions that is without the uncertainty associated with prior quenching. The allotropic transition temperature was found to start at 600-650 K, which is about 50 K below the bulk transition temperature. The phase transition was fully reversible and a significant part of the hcp phase was found to be stable up to 850 K. This anomalous behavior that was observed without quenching might prove to be crucial to understand and model active species not only in catalysts but also in battery materials. PMID:25970204

  12. Tight-binding study of stacking fault energies and the Rice criterion of ductility in the fcc metals

    NASA Astrophysics Data System (ADS)

    Mehl, Michael J.; Papaconstantopoulos, Dimitrios A.; Kioussis, Nicholas; Herbranson, M.

    2000-02-01

    We have used the Naval Research Laboratory (NRL) tight-binding (TB) method to calculate the generalized stacking fault energy and the Rice ductility criterion in the fcc metals Al, Cu, Rh, Pd, Ag, Ir, Pt, Au, and Pb. The method works well for all classes of metals, i.e., simple metals, noble metals, and transition metals. We compared our results with full potential linear-muffin-tin orbital and embedded atom method (EAM) calculations, as well as experiment, and found good agreement. This is impressive, since the NRL-TB approach only fits to first-principles full-potential linearized augmented plane-wave equations of state and band structures for cubic systems. Comparable accuracy with EAM potentials can be achieved only by fitting to the stacking fault energy.

  13. Linear-in-temperature resistivity close to a topological metal insulator transition in ultra-multi valley fcc-ytterbium

    NASA Astrophysics Data System (ADS)

    Enderlein, Carsten; Fontes, Magda; Baggio-Saitovich, Elisa; Continentino, Mucio A.

    2016-01-01

    The semimetal-to-semiconductor transition in fcc-Yb under modest pressure can be considered a picture book example of a metal-insulator transition of the Lifshitz type. We have performed transport measurements at low temperatures in the closest vicinity of the transition and related DFT calculations of the Fermi surface. Our resistivity measurements show a linear temperature dependence with an unusually low dρ / dT at low temperatures approaching the MIT. The calculations suggest fcc-ytterbium being an ultra-multi valley system with 24 electron and 6 hole pockets in the Brillouin zone. Such Fermi surface topology naturally supports the appearance of strongly correlated phases. An estimation of the quasiparticle-enhanced effective mass shows that the scattering rate is by at least two orders of magnitude lower than in other materials which exhibit linear-in-T behavior at a quantum critical point. However, we cannot exclude an excessive effective mass enhancement, when the van Hove singularity touches the Fermi level.

  14. Deformation and erosion of f.c.c. metals and alloys under cavitation attack

    NASA Technical Reports Server (NTRS)

    Rao, B. C. S.; Buckley, D. H.

    1984-01-01

    Experimental investigations have been conducted to determine the early stages of cavitation attack on 6061-T6 aluminum alloy, electrolytic tough pitch copper, brass, and bronze, all having polycrystalline fcc matrices. The surface profiles and scanning electron micrographs show that the pits are initially formed at the grain boundaries, while the grain surfaces are progressively roughened by multiple slip and twinning. The initial erosion is noted to have occurred from the material in the grain boundaries, as well as by fragmentation of part of the grains. Further erosion occurred by shearing and necking of the surface undulations caused by plastic deformation. The mean penetration depth, computed on the basis of mass loss, was lowest on the bronze and greatest on the copper. Attention is given to the relation of cavitation attack to grain size, glide stress and stacking fault energy.

  15. Effect of stacking fault energy on mechanism of plastic deformation in nanotwinned FCC metals

    SciTech Connect

    Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.; LeSar, Richard

    2015-05-15

    Starting from a semi-empirical potential designed for Cu, we have developed a series of potentials that provide essentially constant values of all significant (calculated) materials properties except for the intrinsic stacking fault energy, which varies over a range that encompasses the lowest and highest values observed in nature. In addition, these potentials were employed in molecular dynamics (MD) simulations to investigate how stacking fault energy affects the mechanical behavior of nanotwinned face-centered cubic (FCC) materials. The results indicate that properties such as yield strength and microstructural stability do not vary systematically with stacking fault energy, but rather fall into two distinct regimes corresponding to 'low' and 'high' stacking fault energies.

  16. Effect of stacking fault energy on mechanism of plastic deformation in nanotwinned FCC metals

    DOE PAGESBeta

    Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.; LeSar, Richard

    2015-05-15

    Starting from a semi-empirical potential designed for Cu, we have developed a series of potentials that provide essentially constant values of all significant (calculated) materials properties except for the intrinsic stacking fault energy, which varies over a range that encompasses the lowest and highest values observed in nature. In addition, these potentials were employed in molecular dynamics (MD) simulations to investigate how stacking fault energy affects the mechanical behavior of nanotwinned face-centered cubic (FCC) materials. The results indicate that properties such as yield strength and microstructural stability do not vary systematically with stacking fault energy, but rather fall into twomore » distinct regimes corresponding to 'low' and 'high' stacking fault energies.« less

  17. Kinetics of segregation formation in the vicinity of edge dislocation in fcc metals

    NASA Astrophysics Data System (ADS)

    Nazarov, A. V.; Mikheev, A. A.; Ershova, I. V.; Zaluzhnyi, A. G.

    2016-04-01

    We use new equations for the interstitial impurity diffusion fluxes under strain to study impurity atom redistribution in the vicinity of dislocations taking into account the strain generated by mentioned defects. Two levels of simulation are applied. First one is evaluation of coefficients that determine the influence of strain tensor components on interstitial diffusion fluxes in fcc structures for different kinds of atom jumps. For this purpose we have developed a model into the framework of molecular static method taking into account an atom environment as near the interstitial site as for the saddle-point configuration. The second level is modeling of interstitial segregation formation based on nonlinear diffusion equations taking strains generated by defects. The results show, that the distributions of the interstitials near the dislocations have quite complicated characters and the vacancy distribution has qualitatively different character as compared with carbon distribution.

  18. Recrystallization as a controlling process in the wear of some f.c.c. metals

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Wisander, D.

    1977-01-01

    Detailed examination of copper specimens after sliding against 440 C steel in liquid methane at speeds up to 25 m/s and loads of up to 2 kg showed the metal comprising the wear surface to possess a fine cell recrystallized structure. Wear proceeded by the plastic shearing of metal in this near surface region without the occurrence of visible metal transfer. A dynamic balance between the intense shear process at the surface and the nucleation of recrystallized grains was proposed to account for the behavior of the metal at the wear surface. Sliding wear experiments were also conducted on Ag, Cu-10% Al, Cu-10% Sn, Ni and Al. It was found that low wear and the absence of heavy metal transfer were associated with those metals observed to undergo recrystallization nucleation without prior recovery.

  19. Ab initio continuum model for the influence of local stress on cross-slip of screw dislocations in fcc metals

    NASA Astrophysics Data System (ADS)

    Ramírez, Benjamín R.; Ghoniem, Nasr; Po, Giacomo

    2012-09-01

    We develop a model of cross-slip in face-centered cubic (fcc) metals based on an extension of the Peierls-Nabarro representation of the dislocation core. The dissociated core is described by a group of parametric fractional Volterra dislocations, subject to their mutual elastic interaction and a lattice-restoring force. The elastic interaction between them is computed from a nonsingular expression, while the lattice force is derived from the γ surface obtained directly from ab initio calculations. Using a network-based formulation of dislocation dynamics, the dislocation core structure is not restricted to be planar, and the activation energy is determined for a path where the core has three-dimensional equilibrium configurations. We show that the activation energy for cross-slip in Cu is 1.9eV when the core is represented by only two Shockley partials, while this value converges to 1.43eV when the core is distributed over a bundle of 20 Volterra partial fractional dislocations. The results of the model compare favorably with the experimental value of 1.15±0.37eV [J. Bonneville and B. Escaig, Acta Metall.AMETAR0001-616010.1016/0001-6160(79)90170-6 27, 1477 (1979)]. We also show that the cross-slip activation energy decreases significantly when the core is in a particular local stress field. Results are given for a representative uniform “Escaig” stress and for the nonuniform stress field at the head of a dislocation pileup. A local homogeneous stress field is found to result in a significant reduction of the cross-slip energy. Additionally, for a nonhomogeneous stress field at the head of a five-dislocation pileup compressed against a Lomer-Cottrell junction, the cross-slip energy is found to decrease to 0.62eV. The relatively low values of the activation energy in local stress fields predicted by the proposed model suggest that cross-slip events are energetically more favorable in strained fcc crystals.

  20. High Pressure Phase Transformations in Heavy Rare Earth Metals and Connections to Actinide Crystal Structures

    SciTech Connect

    Vohra, Yogesh K.; Sangala, Bagvanth Reddy; Stemshorn, Andrew K.; Hope, Kevin M.

    2008-07-01

    High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp {yields} Sm-type {yields} dhcp {yields} distorted fcc (hR-24) {yields} monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures. (authors)

  1. Chemomechanical Origin of Hydrogen Trapping at Grain Boundaries in fcc Metals.

    PubMed

    Zhou, Xiao; Marchand, Daniel; McDowell, David L; Zhu, Ting; Song, Jun

    2016-02-19

    Hydrogen embrittlement of metals is widely observed, but its atomistic origins remain little understood and much debated. Combining a unique identification of interstitial sites through polyhedral tessellation and first-principles calculations, we study hydrogen adsorption at grain boundaries in a variety of face-centered cubic metals of Ni, Cu, γ-Fe, and Pd. We discover the chemomechanical origin of the variation of adsorption energetics for interstitial hydrogen at grain boundaries. A general chemomechanical formula is established to provide accurate assessments of hydrogen trapping and segregation energetics at grain boundaries, and it also offers direct explanations for certain experimental observations. The present study deepens our mechanistic understanding of the role of grain boundaries in hydrogen embrittlement and points to a viable path towards predictive microstructure engineering against hydrogen embrittlement in structural metals. PMID:26943544

  2. Chemomechanical Origin of Hydrogen Trapping at Grain Boundaries in fcc Metals

    NASA Astrophysics Data System (ADS)

    Zhou, Xiao; Marchand, Daniel; McDowell, David L.; Zhu, Ting; Song, Jun

    2016-02-01

    Hydrogen embrittlement of metals is widely observed, but its atomistic origins remain little understood and much debated. Combining a unique identification of interstitial sites through polyhedral tessellation and first-principles calculations, we study hydrogen adsorption at grain boundaries in a variety of face-centered cubic metals of Ni, Cu, γ -Fe , and Pd. We discover the chemomechanical origin of the variation of adsorption energetics for interstitial hydrogen at grain boundaries. A general chemomechanical formula is established to provide accurate assessments of hydrogen trapping and segregation energetics at grain boundaries, and it also offers direct explanations for certain experimental observations. The present study deepens our mechanistic understanding of the role of grain boundaries in hydrogen embrittlement and points to a viable path towards predictive microstructure engineering against hydrogen embrittlement in structural metals.

  3. A theoretical prediction of the paradoxical surface free energy for FCC metallic nanosolids

    NASA Astrophysics Data System (ADS)

    Abdul-Hafidh, Esam H.; Aïssa, Brahim

    2016-08-01

    We report on the development of an efficient and simple method to calculate the surface free energy (surface tension) of a general-shaped metallic nanosolid. Both nanoparticles and nanostructures that account for the crystal structure and size were considered. The surface free energy of a face-centered cubic structure of a metallic nanoparticles was found to decrease as the size decreases, for a shape factor equal to 1.0 (i.e., spherical). However, when the shape factor exceeds this value, which includes disk-like, regular tetrahedral, regular hexahedral, regular octahedral, nanorod, and regular quadrangular structures, the behavior of the surface free energy was found to reverse, especially for small nanoparticles and then increases as the size decreases. Moreover, this behavior was systematically recorded for large nanoparticles when the mechanical distortion was appreciable. As a matter of fact, this model was also applied to the noble transition metals, including gold and silver nanoparticles. This work is a clear step forward establishing a systematic mechanism for controlling the mechanical properties of nanoscale particles by controlling the shape, size and structure.

  4. Molecular Dynamics Study of Void Growth and Dislocations in Dynamic Fracture of FCC and BCC Metals

    SciTech Connect

    Seppala, E T; Belak, J; Rudd, R E

    2003-06-17

    Void growth with concomitant dislocation formation has been studied in single crystal face-centered-cubic and body-centered-cubic metals using molecular dynamics method with Embedded-Atom and Finnis-Sinclair potentials for copper and tantalum, respectively. We have concentrated on the quantitative analysis of the void shape evolution, on the structure of dislocations, which emerge from the void, and on the continuum measures such as plastic strain. The effects of strain-rate, differences between lattice structures, and loading conditions as uniaxial, biaxial, and triaxial expansion on the shape of the void and on the dislocations have been investigated.

  5. Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals.

    PubMed

    Zhang, Jiayong; Zhang, Hongwu; Ye, Hongfei; Zheng, Yonggang

    2016-01-01

    Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship. PMID:26961273

  6. Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals

    PubMed Central

    Zhang, Jiayong; Zhang, Hongwu; Ye, Hongfei; Zheng, Yonggang

    2016-01-01

    Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship. PMID:26961273

  7. Twin Boundaries merely as Intrinsically Kinematic Barriers for Screw Dislocation Motion in FCC Metals

    NASA Astrophysics Data System (ADS)

    Zhang, Jiayong; Zhang, Hongwu; Ye, Hongfei; Zheng, Yonggang

    2016-03-01

    Metals with nanoscale twins have shown ultrahigh strength and excellent ductility, attributed to the role of twin boundaries (TBs) as strong barriers for the motion of lattice dislocations. Though observed in both experiments and simulations, the barrier effect of TBs is rarely studied quantitatively. Here, with atomistic simulations and continuum based anisotropic bicrystal models, we find that the long-range interaction force between coherent TBs and screw dislocations is negligible. Further simulations of the pileup behavior of screw dislocations in front of TBs suggest that screw dislocations can be blocked kinematically by TBs due to the change of slip plane, leading to the pileup of subsequent dislocations with the elastic repulsion actually from the pinned dislocation in front of the TB. Our results well explain the experimental observations that the variation of yield strength with twin thickness for ultrafine-grained copper follows the Hall-Petch relationship.

  8. Transition metal solute interactions with point defects in fcc iron from first principles

    NASA Astrophysics Data System (ADS)

    Hepburn, D. J.; MacLeod, E.; Ackland, G. J.

    2015-07-01

    We present a comprehensive set of first-principles electronic structure calculations of the properties of substitutional transition metal solutes and point defects in austenite (face-centered cubic, paramagnetic Fe). Clear trends were observed in these quantities across the transition metal series, with solute-defect interactions strongly related to atomic size, and only weakly related to more subtle details of magnetic or electronic structure. Oversized solutes act as strong traps for both vacancy and self-interstitial defects and as nucleation sites for the development of protovoids and small self-interstitial loops. The consequent reduction in defect mobility and net defect concentrations in the matrix explains the observation of reduced swelling and radiation-induced segregation. Our analysis of vacancy-mediated solute diffusion demonstrates that below about 400 K Ni and Co will be dragged by vacancies and their concentrations should be enhanced at defect sinks. Cr and Cu show opposite behavior and are depleted at defect sinks. The stable configuration of some oversized solutes is neither interstitial nor substitutional; rather they occupy two adjacent lattice sites. The diffusion of these solutes proceeds by a novel mechanism, which has important implications for the nucleation and growth of complex oxide nanoparticles contained in oxide dispersion strengthened steels. Interstitial-mediated solute diffusion is negligible for all except the magnetic solutes (Cr, Mn, Co, and Ni). Our results are consistent across several antiferromagnetic states and surprising qualitative similarities with ferromagnetic (body-centered cubic) Fe were observed; this implies that our conclusions will be valid for paramagnetic iron.

  9. Microstructural Characterization of Dislocation Networks During Harper-Dorn Creep of fcc, bcc, and hcp Metals and Alloys

    SciTech Connect

    Przystupa, Marek A.

    2007-12-13

    Harper-Dorn (H-D) creep is observed in metals and geological materials exposed to very low stresses at temperatures close to the melting point. It is one of several types of creep processes wherein the steady-state strain rate is proportional to the applied stress, Nabarro-Herring creep and Coble creep being two other important processes. H-D creep can be somewhat insidious because the creep rates are much larger than those expected for Nabarro-Herring or Coble creep. Since the working conditions of structural components of power plants and propulsion systems, as well as the motion of the earth’s mantle all involve very low stresses, an understanding of the factors controlling H-D creep is critical in preventing failures associated with those higher-than-expected creep rates. The purpose of this investigation was to obtain missing microstructural information on the evolution of the dislocation structures during static annealing of materials with fcc, bcc and hcp structure and use obtained results to test predictive capabilities of the dislocation network theory of H-D creep. In our view the evolutionary processes during static annealing and during Harper-Dorn creep are intimately related. The materials used in this study were fcc aluminum, hcp zinc and bcc tin. All characterizations of dislocation structures, densities and dislocation link length distributions were carried out using the etch pit method. To obtain quantitative information on the evolution of the dislocation networks during annealing the pure fcc aluminum samples were pre-deformed by creep at 913 and 620 K and then annealed. The higher deformation temperature was selected to generate starting dislocation networks similar to those forming during Harper-Dorn creep and the lower, to obtain higher dislocation densities suitable for reliable estimates of the parameters of the network growth law. The measured experimental link length distribution were, after scaling, (1) the same for all annealing

  10. The influence of the dislocation distribution heterogeneity degree on the formation of a non-misoriented dislocation cell substructures in f.c.c. metals

    NASA Astrophysics Data System (ADS)

    Cherepanov, D. N.; Selivanikova, O. V.; Matveev, M. V.

    2016-06-01

    Dislocation loops emitted by Frank-Reed source during crossing dislocations of the non-coplanar slip systems are accumulates jogs on the own dislocation line, resulting in the deceleration of the segments of dislocation loops with high jog density. As a result, bending around of the slowed segments the formation of dynamic dipoles in the shear zone occurs. In the present paper we consider formation mechanism of non-misoriented dislocation cell substructure during plastic deformation of f.c.c. metals and conclude that the increase in the degree heterogeneity of dislocation distribution leads to an increase in the jog density and reduce the mean value of arm dynamic dipoles.

  11. Dependence of Initial Grain Orientation on the Evolution of Anisotropy in FCC and BCC Metals Using Crystal Plasticity and Texture Analysis

    NASA Astrophysics Data System (ADS)

    Raja, Daniel Selvakumar

    Abundant experimental analyses and theoretical computational analyses that had been performed on metals to understand anisotropy and its evolution and its dependence on initial orientation of grains have failed to provide theories that can be used in macro-scale plasticity. Ductile metals fracture after going through a large amount of plastic deformation, during which the anisotropy of the material changes significantly. Processed metal sheets or slabs possess anisotropy due to textures produced by metal forming processes (such as drawing, bending and press braking). Metals that were initially isotropic possess anisotropy after undergoing forming processes, i.e., through texture formation due to large amount of plastic deformation before fracture. It is therefore essential to consider the effect of anisotropy to predict the characteristics of fracture and plastic flow performances in the simulation of ductile fracture and plastic flow of materials. Crystal plasticity simulations carried out on grains at the meso-scale level with different initial orientations (ensembles) help to derive the evolution of anisotropy at the macro-scale level and its dependence on initial orientation of grains. This paper investigates the evolution of anisotropy in BCC and FCC metals and its dependence on grain orientation using crystal plasticity simulations and texture analysis to reveal the mechanics behind the evolution of anisotropy. A comparison of anisotropy evolution between BCC and FCC metals is made through the simulation, which can be used to propose the theory of anisotropy evolution in macro-scale plasticity. Keywords: ensembles; grains; initial orientation; anisotropy; evolution of anisotropy; crystal plasticity; textures; homogeneity; isotropy; inelastic; equivalent strain.

  12. FCC main fractionator revamps

    SciTech Connect

    Golden, S.W.; Martin, G.R.; Sloley, A.W. )

    1993-03-01

    Structured packing use in fluid catalytic cracker (FCC) main fractionators significantly impacts unit pressure profile. Unit pressure balance links the FCC main fractionator, reactor, regenerator, air compressor and wet gas compressor. Unit pressure balance should be viewed as a design variable when evaluating FCC unit revamps. Depending upon limitations of the particular FCC unit, capacity increases of 12.5% to 22.5% have been achieved without modifications to major rotating equipment, by revamping FCC main fractionators with structured packing. An examination of three FCC main fractionator revamps show improvements to pressure profiles and unit capacity. The three revamps described included a wet gas compressor volume limit; an air blower limitation; and a wet gas compressor motor limitation.

  13. Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary

    PubMed Central

    Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y.; Prassides, Kosmas; Rosseinsky, Matthew J.; Arčon, Denis

    2014-01-01

    The alkali fullerides, A3C60 (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs3C60 polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/kBTc = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/kBTc decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached. PMID:24584087

  14. Retention of Hydrogen in FCC Metals Irradiated at Temperatures Leading to High Densities of Bubbles or Voids

    SciTech Connect

    Garner, Francis A.; Simonen, Edward P.; Oliver, Brian M.; Greenwood, Lawrence R.; Grossbeck, M L.; Wolfer, W. G.; Scott, P M.

    2006-09-15

    Large amounts of hydrogen and helium are generated in structural metals in accelerator-driven systems. It is shown that under certain conditions, hydrogen can be stored in irradiated nickel and stainless steels at levels strongly in excess of that predicted by Sieverts Law. These conditions are first, the availability of hydrogen from various radiolytic and environmental sources and second, the formation of radiation-induced cavities to store hydrogen. These cavities can be highly pressurized bubbles or under-pressurized voids, with concurrent helium in the cavities at either low or very high levels. Transmutant sources of hydrogen are often insufficient to pressurize these cavities, and therefore environmental sources are required. The stored hydrogen appears to be stable for many years at room temperature. A conceptual model to describe such behavior requires the continuous generation of hydrogen from (n, p) reactions and possibly other radiolytic sources which can create a supersaturation of hydrogen in the metal, leading to the pressurization of voids and helium bubbles. Once captured in a bubble, the hydrogen is assumed to be in molecular form. Dissolution back into the metal requires chemisorption and dissociation on the bubble surface. Both of these processes have large activation barriers, particularly when oxygen, carbohydrates, and other impurities poison the bubble surface. However, these chemisorbed poisons may reduce but not entirely restrict the ingress or egress of atomic hydrogen.

  15. Does the 4f-shell contribute to bonding in tetravalent lanthanide halides?

    SciTech Connect

    Ji, Wen-Xin; Xu, Wei; Xiao, Yi; Wang, Shu-Guang

    2014-12-28

    Lanthanide tetrahalide molecules LnX{sub 4} (Ln = Ce, Pr, Tb; X = F, Cl, Br, I) have been investigated by density functional theory at the levels of the relativistic Zero Order Regular Approximation and the relativistic energy-consistent pseudopotentials, using frozen small- and medium-cores. The calculated bond lengths and vibrational frequencies are close to the experimental data. Our calculations indicate 4f shell contributions to bonding in LnX{sub 4}, in particular for the early lanthanides, which show significant overlap between the Ln 4f-shell and the halogen np-shells. The 4f shells contribute to Ln-X bonding in LnX{sub 4} about one third more than in LnX{sub 3}.

  16. Comments on the thermoelectric power of intermetallic rare-earth compounds with well localized 4f shells

    NASA Astrophysics Data System (ADS)

    Szukiel, A. E.

    2016-05-01

    The anomalous temperature variation of the thermoelectric power in the metallic rare-earth compounds with well-localized 4f shells is sometimes interpreted as resulting from the conduction electrons scattering in the Born approximation on the acoustic phonons and on the localized spins in the s-f exchange interaction. Such an interpretation relies on the results of some theoretical works where the sign reversal and the maxima of the thermoelectric power were obtained within these simple models. In the present paper we prove that neither the electron-phonon scattering nor the magnetic s-f scattering in the Born approximation (nor both of them) do lead to the effects mentioned above.

  17. The FCC and Broadcasting.

    ERIC Educational Resources Information Center

    Federal Communications Commission, Washington, DC.

    This report outlines the Federal Communications Commission's (FCC) regulatory authority over the licensing and operation of commercial, educational, and public broadcasting in the United States. Also described are rules and regulations governing the program content and advertising, in relation to the fairness doctrine, free speech, and public…

  18. Electrical impedance of FCC

    NASA Technical Reports Server (NTRS)

    Liu, Y. S.

    1972-01-01

    The electrical characteristics of FCC are investigated in the context of multiple transmission lines theory. Analytical expressions for the coefficients of capacitance of conductors in a single cable are obtained. Numerical values calculated with these expressions are in good agreement with experimental data. Crosstalk, attenuation constants and phase angles of the current and voltage in flat conductor cable are also calculated.

  19. FCC catalyst selection

    SciTech Connect

    Carter, G.D.L. ); McElhiney, G. )

    1989-09-01

    This paper discusses a commonly used technique for comparing FCC catalytic selectivities based on the ASTM microactivity test (MAT) procedure, ASTM D-3907-80. In its original form the ASTM test provides only very limited information on selectivity. However, extension of the ASTM MAT procedure by using additional product analyses gives a microselectivity test capable of providing detailed yield structure information. This modified MAT procedure thus provides a cost-effective and rapid means of comparing many catalysts.

  20. In-situ transmission electron microscopy study of ion-irradiated copper : comparison of the temperature dependence of cascade collapse in FCC- and BCC- metals.

    SciTech Connect

    Daulton, T. L.

    1998-10-23

    The kinetics which drive cascade formation and subsequent collapse into point-defect clusters is investigated by analyzing the microstructure produced in situ by low fluence 100 keV Kr ion irradiations of fcc-Cu over a wide temperature range (18-873 K). The yield of collapsed point-defect clusters is demonstrated unequivocally to be temperature dependent, remaining approximately constant up to lattice temperatures of 573 K and then abruptly decreasing with increasing temperature. This drop in yield is not caused by defect loss during or following ion irradiation. This temperature dependence can be explained by a thermal spike effect. These in-situ yield measurements are compared to previous ex-situ yield measurements in fcc-Ni and bcc-Mo.

  1. Regeneration of Hydrotreating and FCC Catalysts

    SciTech Connect

    CM Wai; JG Frye; JL Fulton; LE Bowman; LJ Silva; MA Gerber

    1999-09-30

    Hydrotreating, hydrocracking, and fluid catalytic cracking (FCC) catalysts are important components of petroleum refining processes. Hydrotreating and hydrocracking catalysts are used to improve the yield of high-quality light oil fractions from heavier crude oil and petroleum feedstocks containing high levels of impurities. FCC catalysts improve the yield of higher octane gasoline from crude oil. Residuum hydrotreating and cracking catalysts are susceptible to irreversible deactivation caused by adsorption of sulfur and by metals impurities, such as vanadium and nickel. The gradual buildup of these impurities in a hydrotreating catalyst eventually plugs the pores and deactivates it. Nickel and vanadium adversely affect the behavior of cracking catalysts, reducing product yield and quality. Replacing deactivated catalysts represents a significant cost in petroleum refining. Equally important are the costs and potential liabilities associated with treating and disposing spent catalysts. For example, recent US Environmental Protection Agency rulings have listed spent hydrotreating and hydrorefining catalysts as hazardous wastes. FCC catalysts, though more easily disposed of as road-base or as filler in asphalt and cement, are still an economic concern mainly because of the large volumes of spent catalysts generated. New processes are being considered to increase the useful life of catalysts or for meeting more stringent disposal requirements for spent catalysts containing metals. This report discusses a collaborative effort between Pacific Northwest National Laboratory (PNNL) and Phillips Petroleum, Inc., to identify promising chemical processes for removing metals adhered to spent hydrodesulfurization (HDS, a type of hydrotreating catalyst) and FCC catalysts. This study, conducted by PNNL, was funded by the US Department of Energy's Bartlesville Project Office. Fresh and spent catalysts were provided by Phillips Petroleum. The FCC catalyst was a rare-earth exchanged

  2. Commercial FCC License Study Guide.

    ERIC Educational Resources Information Center

    Swearer, Harvey F.

    Jobs in radio arts, from serviceman to station engineer, are easier to get if one has a recommendation of the U.S. Government in the form of a license from the Federal Communications Commission (FCC). This study guide for FCC radiotelephone licenses is designed to thoroughly prepare the applicant for any radiotelephone exam and to serve as a…

  3. Increasing FCC regenerator catalyst level

    SciTech Connect

    Wong, R.F. )

    1993-11-01

    A Peruvian FCC unit's operations were improved by increasing the regenerator's catalyst level. This increase resulted in lower stack losses, an improved temperature profile, increased catalyst activity and a lower catalyst consumption rate. A more stable operation saved this Peruvian refiner over $131,000 per year in catalyst alone. These concepts and data may be suitable for your FCC unit as well.

  4. Matrix elements of scalar three-electron operators for the atomic f shell

    SciTech Connect

    Hansen, J.E.; Judd, B.R.; Crosswhite H.

    1996-01-01

    Tables are provided for the matrix elements of an orthogonal set of Hermitian three-electron operators t{sub i} for the states of the f shell. The t{sub i} are scalar with respect to the total spin S and total orbital angular momentum L, and they are among the effective operators needed to be included in an f-electron Hamiltonian in order to represent the coupling of the ground configuration f{sup N} to excited configurations via the interelectronic Coulomb interaction. 15 refs., 2 tabs.

  5. Effective three-particle interactions in atoms with partly filled f-shell

    NASA Astrophysics Data System (ADS)

    Kozlov, Mikhail; Konovalova, Elena; Viatkina, Anna; Safronova, Marianna

    2016-05-01

    Three particle forces are known to be very important in nuclear physics. In atoms such forces appear between valence electrons in the second order of many-body perturbation theory due to the exchange interaction with the core. Usually their contribution to the valence energy is very small, of the order of few inverse centimeters. However, for atoms and ions with partly filled d and f shells the overlap between valence and core electrons may be large. This leads to significant enhancement of the effective three particle interactions. In Ti II (ground configuration (GC) 3 d2 4s) these interactions change binding energy by few hundred inverse centimeters. In Ce I (GC 4f5d 6 s2) these interactions contribute few thousand inverse centimeters. Three particle forces are also important for highly charged ions with low-lying f shell, such as Pr9 + , 10 +, Nd10 + , 11 +, and Sm13+. These ions may have narrow optical transitions and are now considered for the new generation of optical clocks. This work was supported in part by RFBR Grant No. 14-02-00241.

  6. Status and availability of FCC hardware

    NASA Technical Reports Server (NTRS)

    Romriell, G. K.

    1973-01-01

    The source availability of FCC and/or FCC connectors was surveyed. The results for the following areas are presented: (1) cost of FCC versus standard round cable, (2) qualification status, (3) size of wire available in FCC, (4) availability of hermetic connectors for FCC, (5) conversion from flat cable to round cable and visa versa, (6) availability of shielded flat cable for RF usage, (7) termination techniques, and (8) repair techniques.

  7. Atomic structure of [110] tilt grain boundaries in FCC materials

    SciTech Connect

    Merkle, K.L.; Thompson, L.J.

    1997-04-01

    High-resolution electron microscopy (HREM) has been used to study the atomic-scale structure and localized relaxations at grain boundaries (GBs) in Au, Al, and MgO. The [110] tilt GBs play an important role in polycrystalline fcc metals since among all of the possible GB geometries this series of misorientations as a whole contains the lowest energies, including among others the two lowest energy GBs, the (111) and (113) twins. Therefore, studies of the atomic-scale structure of [110] tilt GBs in fcc metals and systematic investigations of their dependence on misorientation and GB plane is of considerable importance to materials science. [110] tilt GBs in ceramic oxides of the fcc structure are also of considerable interest, since in this misorientation range polar GBs exist, i.e. GBs in which crystallographic planes that are made up of complete layers of cations or anions can join to form a GB.

  8. Consider topped crude for FCC

    SciTech Connect

    Louder, K.E.; Juno, E.J.; Kulapaditharom, L.

    1985-09-01

    A case study is presented that illustrates the mechanics for evaluating use of topped crude to load the FCC for more profit. Declining product demands combined with high crude costs has shut down many refineries and left others operting well below design capacity. The study illustrates the step-by-step requirements to debottleneck an existing Kellogg Orthoflow Model B FCC to process topped crude mixed with gas oils. This study was limited to the catalytic converter defined as the reactor, regenerator, air blower, and wet gas compressor. The scope was to examine the ability to process topped crude and to consider modernizing the FCC to employ riser cracking and complete CO combustion regeneration.

  9. Use desalting for FCC feedstocks

    SciTech Connect

    Harris, J.R.

    1996-08-01

    The heart of profitability in a modern refinery is the fluid catalytic cracking unit (FCCU). As a major process unit, the FCCU generates substantial profits from small improvements. One such improvement, desalting FCC feedstocks, increases refinery profits by over $25,000 per day after a two-month payout period. Desalting improves FCC feedstocks in three distinct ways: (1) reducing feed sodium content, (2) eliminating entrained water or slugs of water, and (3) reducing particulates and contaminants in both the water and hydrocarbon. Each of these improvements reduces or eliminates several problems in the typical FCCU. The paper discusses each of these mechanisms, the cost of desalting, and a typical case.

  10. FCC-ee: Energy Calibration

    SciTech Connect

    Koratzinos, M.; Blondel, A.; Gianfelice-Wendt, E.; Zimmermann, F.

    2015-06-02

    The FCC-ee aims to improve on electroweak precision measurements, with goals of 100 ke V on the Z mass and width, and a fraction of MeV on the W mass. Compared to LEP, this implies a much improved knowledge of the center-of-mass energy when operating at the Z peak and WW threshold. This can be achieved by making systematic use of resonant depolarization. A number of issues have been identified, due in particular to the long polarization times. However the smaller emittance and energy spread of FCC-ee with respect to LEP should help achieve a much improved performance.

  11. FCC, CATV, ETV, and ITFS.

    ERIC Educational Resources Information Center

    Schwartz, Louis; Woods, Robert A.

    Actions taken in 1970 by the Federal Communications Commission (FCC) are reviewed and discussed in this paper. These actions include amendment of educational broadcast rules for the first time in 17 years, decisions in the area of educational programing, a decision regarding the ultra high frequency (UHF)-land mobile dilemma, and a promise to…

  12. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS information...) FCC World Wide Web homepage: http://www.fcc.gov/wtb/prs. (c) In writing, to the FCC, Attention:...

  13. Three dimensional simulation of flow and heat transfer in an F shell heat exchanger

    SciTech Connect

    Prithiviraj, M.; Andrews, M.J.

    1998-12-31

    Shell-and-tube heat exchangers are the most commonly used design in process and petrochemical industries. Over the last four years, a three-dimensional numerical model has been developed at Texas A and M University to model flow and heat transfer within shell-and-tube heat exchangers. This model is based on the distributed resistance concept of Patankar and Spalding (1974). Sub-models used for pressure drop, heat transfer and turbulence generation are briefly described. Leakage flow through the baffle-tube and baffle-shell clearances are modeled using a Bernoulli type approach. The discretized governing equations are solved using a SIMPLE type finite volume method on a colocated grid. The numerical model was previously used to perform E shell simulations. Here the 3D model is used to analyze flow through an F shell heat exchanger. Velocity vector plots for the shellside fluid and temperature contours for the shellside and tubeside fluids are used to study the flow structure. The performance of the 3D model is compared with the Bell Method (1981) for the prediction of overall pressure drop. Good agreement is obtained between the computed overall pressure drop and the pressure drop predicted by the Bell method.

  14. Neutron Skins and Halo Orbits in the s d and p f Shells

    NASA Astrophysics Data System (ADS)

    Bonnard, J.; Lenzi, S. M.; Zuker, A. P.

    2016-05-01

    The strong dependence of Coulomb energies on nuclear radii makes it possible to extract the latter from calculations of the former. The resulting estimates of neutron skins indicate that two mechanisms are involved. The first one—isovector monopole polarizability—amounts to noting that when a particle is added to a system it drives the radii of neutrons and protons in different directions, tending to equalize the radii of both fluids independently of the neutron excess. This mechanism is well understood and the Duflo-Zuker (small) neutron skin values derived 14 years ago are consistent with recent measures and estimates. The alternative mechanism involves halo orbits whose huge sizes tend to make the neutron skins larger and have a subtle influence on the radial behavior of s d and p f shell nuclei. In particular, they account for the sudden rise in the isotope shifts of nuclei beyond N =28 and the near constancy of radii in the A =40 - 56 region. This mechanism, detected here for the first time, is not well understood and may well go beyond the Efimov physics usually associated with halo orbits.

  15. Advances in FCC reactor technology

    SciTech Connect

    Schnaith, M.W.; Gilbert, A.T.; Lomas, D.A.; Myers, D.N.

    1995-09-01

    The riser termination device and the feed distribution system are the key elements that enable FCC reactor technology to achieve the high performance demanded in the 1990s and beyond. UOP`s development efforts have combined cold flow modeling and commercial optimization testing to produce new technology in both areas. A key differentiation of the UOP feed-catalyst contacting system is the use of a catalyst acceleration zone to moderate density and achieve plug flow before feed injection. Commercial data confirm the benefit and importance of elevated feed injection and proper catalyst environment in this three-phase system. A new high-performance Optimix feed nozzle has been developed and cold-flow tested and is currently undergoing commercial demonstration. New riser disengagement technology with prestripping has been extended to internal riser FCC units. The new disengager design will achieve at least 98% hydrocarbon containment. Cold-flow modeling has confirmed catalyst separation efficiency, and the design has been accepted for two FCC reactor revamps scheduled for mid-1995 and for 1996.

  16. Shear responses of [\\bar{1}\\,1\\,0] -tilt {1 1 5}/{1 1 1} asymmetric tilt grain boundaries in fcc metals by atomistic simulations

    NASA Astrophysics Data System (ADS)

    Wan, Liang; Li, Ju

    2013-07-01

    The shear response of the \\Sigma3 \\ [\\bar{1}\\,1\\,0] -tilt (\\bar{1}\\,\\bar{1}\\,5)/(1\\,1\\,1) and \\Sigma9 \\ [\\bar{1}\\,1\\,0] -tilt (1 1 5)/(1 1 1) asymmetric tilt grain boundaries (GBs) in fcc metals Cu and Al has been studied by atomistic simulation methods with the embedded atom method interatomic potentials and with a bicrystal model. It is found that the structure of the GBs studied can be well described by the coincidence site lattice (CSL) theory. Shear of these GBs at room temperature along eight different directions within the GB plane shows that these two types of GBs can transform between each other by the formation of a coherent twin boundary. The structure transformation of the GBs can also take the form of GB sliding, GB sliding-migration coupled motion, GB faceting, GB 9R structure formation, etc, depending on the shear directions adopted and the material involved (Cu or Al). The detailed structure transformation mechanisms have been analyzed with the aid of the CSL-DSC (displacement shift complete) theory. Several structure transformation paths adherent to these two types of GBs have been identified for the activation of the GB sliding-migration coupled motion. It is concluded that, although CSL-DSC theory can be applied to describe the sliding-migration coupled motion of the GBs studied, some other effects such as the shear direction within the GB plane and the bonding characteristics of the materials should also play a significant role in the shear response of these GBs.

  17. Atomistically-informed Dislocation Dynamics in fcc Crystals

    SciTech Connect

    Martinez, E; Marian, J; Arsenlis, T; Victoria, M; Perlado, J M

    2006-09-06

    We develop a nodal dislocation dynamics (DD) model to simulate plastic processes in fcc crystals. The model explicitly accounts for all slip systems and Burgers vectors observed in fcc systems, including stacking faults and partial dislocations. We derive simple conservation rules that describe all partial dislocation interactions rigorously and allow us to model and quantify cross-slip processes, the structure and strength of dislocation junctions and the formation of fcc-specific structures such as stacking fault tetrahedra. The DD framework is built upon isotropic non-singular linear elasticity, and supports itself on information transmitted from the atomistic scale. In this fashion, connection between the meso and micro scales is attained self-consistently with core parameters fitted to atomistic data. We perform a series of targeted simulations to demonstrate the capabilities of the model, including dislocation reactions and dissociations and dislocation junction strength. Additionally we map the four-dimensional stress space relevant for cross-slip and relate our findings to the plastic behavior of monocrystalline fcc metals.

  18. The FCC and the Electric Church.

    ERIC Educational Resources Information Center

    Abrams, Michael F.

    This newsletter focuses on the relationship between the Federal Communications Commission (FCC) and religious broadcasters. It traces the history of that relationship and discusses some of the pressures put on both. It includes a discussion of a recent avalanche of mail at the FCC supporting the church on the airways. It also summarizes some of…

  19. New FCC Goal in Ownership Regulation.

    ERIC Educational Resources Information Center

    Rappaport, Josh

    By first describing the historical stance of the Federal Communications Commission (FCC) toward ownership of broadcast facilities and then describing the FCC's most recent policy statements, this report compares the differing viewpoints and recognizes that the new value or goal that seems to have been established conflicts with the past emphasis…

  20. Attrition Resistant Fischer-Tropsch Catalysts Based on FCC Supports

    SciTech Connect

    Adeyiga, Adeyinka

    2010-02-05

    Commercial spent fluid catalytic cracking (FCC) catalysts provided by Engelhard and Albemarle were used as supports for Fe-based catalysts with the goal of improving the attrition resistance of typical F-T catalysts. Catalysts with the Ruhrchemie composition (100 Fe/5 Cu/4.2 K/25 spent FCC on mass basis) were prepared by wet impregnation. XRD and XANES analysis showed the presence of Fe{sub 2}O{sub 3} in calcined catalysts. FeC{sub x} and Fe{sub 3}O{sub 4} were present in the activated catalysts. The metal composition of the catalysts was analyzed by ICP-MS. F-T activity of the catalysts activated in situ in CO at the same conditions as used prior to the attrition tests was measured using a fixed bed reactor at T = 573 K, P = 1.38 MPa and H{sub 2}:CO ratio of 0.67. Cu and K promoted Fe supported over Engelhard provided spent FCC catalyst shows relatively good attrition resistance (8.2 wt% fines lost), high CO conversion (81%) and C{sub 5}+ hydrocarbons selectivity (18.3%).

  1. 47 CFR 2.926 - FCC identifier.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... electronically via the Internet at http://www.fcc.gov/eas. The code may be obtained at any time prior to... marketing. Labelling of such equipment may include model or type numbers, but shall not include a...

  2. 47 CFR 2.926 - FCC identifier.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... electronically via the Internet at http://www.fcc.gov/eas. The code may be obtained at any time prior to... marketing. Labelling of such equipment may include model or type numbers, but shall not include a...

  3. 47 CFR 2.926 - FCC identifier.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... electronically via the Internet at http://www.fcc.gov/eas. The code may be obtained at any time prior to... marketing. Labelling of such equipment may include model or type numbers, but shall not include a...

  4. 47 CFR 2.926 - FCC identifier.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... representative may receive a grantee code electronically via the Internet at https://gullfoss2.fcc.gov/prod/oet... which has not been granted equipment authorization where such grant is required prior to...

  5. 47 CFR 2.926 - FCC identifier.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... representative may receive a grantee code electronically via the Internet at https://gullfoss2.fcc.gov/prod/oet... which has not been granted equipment authorization where such grant is required prior to...

  6. Ferromagnetic properties of fcc Gd thin films

    SciTech Connect

    Bertelli, T. P. Passamani, E. C.; Larica, C.; Nascimento, V. P.; Takeuchi, A. Y.

    2015-05-28

    Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature T{sub S} and film thickness x. Gd fcc samples were obtained when T{sub S} = 763 K and x = 10 nm, while the hcp structure was stabilized for lower T{sub S} (300 K) and thicker film (20 nm). The fcc structure is formed on the Ta buffer layer, while the hcp phase grows on the fcc Gd layer as a consequence of the lattice relaxation process. Spin reorientation phenomenon, commonly found in bulk Gd species, was also observed in the hcp Gd thin film. This phenomenon is assumed to cause the magnetization anomalous increase observed below 50 K in stressed Gd films. Magnetic properties of fcc Gd thin films are: Curie temperature above 300 K, saturation magnetization value of about 175 emu/cm{sup 3}, and coercive field of about 100 Oe at 300 K; features that allow us to classify Gd thin films, with fcc structure, as a soft ferromagnetic material.

  7. Economically recover olefins from FCC offgases

    SciTech Connect

    Netzer, D.

    1997-04-01

    The concept of ethylene and propylene recovery from fluid catalytic cracking (FCC) offgases is not new; however, its application has been infrequent. For typical catalytic cracking of atmospheric and vacuum gas oils, ethylene yields range from 2.0 to 3.5 lb/bbl of FCC feed. The ethylene typically amounts to 8 to 18 vol% of FCC offgas and is normally routed to the fuel gas system. Variations in ethylene concentrations are affected by the FCC feed composition and cracking severity. This ethylene yield is anywhere from 0.7% to 1.1% of the FCC feed, as opposed to 26% to 36% for naphtha or gas oil cracking in conventional olefin plants. Due to high FCC unit feedrates (typically 25,000 to 85,000 bpsd for most North American refineries) even with a low ethylene yield, the olefins production can be significant. Here, two approaches to olefins recovery are addressed. In the first, ethylene is recovered as a dilute gas at a concentration of about 15 vol% and serves as raw material for ethylbenzene and, subsequently, styrene. In the second approach, ethylene is recovered as a pure polymer-grade liquid. Propylene recovery is identical for both approaches. The concept for producing polymer-grade liquid ethylene is described in detail in terms of process technology, cost estimates and economic parameters.

  8. Catalytic reforming of heart cut fcc naphthas

    SciTech Connect

    Gerritsen, L.A.

    1985-03-01

    The anticipated lead phasedown in the USA and the growing demand for unleaded gasoline will require a higher gasoline pool octane number. One of the possibilities to achieve this increase of pool octane will be catalytic reforming of FCC naphtha. In this paper we evaluate the effects of FCC naphtha reforming on the reformer operation and gasoline pool volume for various lead phasedown scenarios. High-stability reforming catalysts, like TPR-8/CK-522 TRILOBE catalyst, will be required to maintain acceptable cycle lengths at the more severe reformer operating conditions. The properties and octane distribution of FCC naphtha are discussed, as well as its hydrotreating with high-active NiMo catalysts.

  9. Deeply etherify FCC light cracked Naphtha (LCN)

    SciTech Connect

    Trotta, R.

    1996-03-01

    Drastic changes in refinery operations and economics resulting from implementation of environmentally driven U.S. legislation such as the Complex Model in 1998, as well as possible changes beyond that will necessitate several changes. An effective method of adjusting to these process challenges is by deep etherification of the entire FCC light cracked naphtha (LCN) stream, which is the FCC product fraction containing C{sub 5}, C{sub 6} and C{sub 7} hydrocarbons having a typical 1 atm boiling range of 95{degrees}F to 212{degrees}F. Deep etherification technology (DET) can solve five or six problems at once. All U.S. refineries which have an FCC unit have an LCN stream (or possibly a separate LCN stream). Snaprogetti`s LCN DET technology is essentially an upgrade of an otherwise already finished product-which in today`s processing and operations environment, would be sent directly to the gasoline pool. The technology is simply an add-on and does not substantially change refinery operations. As the LCN DET does not require changes in the FCC and catalytic reformer, DET does not cause disturbances to the refinery`s operation.

  10. Inside the FCC: A Guide for Information Seekers.

    ERIC Educational Resources Information Center

    Le Duc, Don R., Ed.; Krasnow, Erwin G., Ed.

    1975-01-01

    To aid the public in obtaining information and documents from the files of the Federal Communications Commission (FCC) this guide, written with assistance from the FCC staff, explains which office to approach and in what form to make the request. Ways to obtain informaion by visiting the FCC are explained along with methods for obtaining…

  11. 78 FR 69415 - Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-19

    ..., in FR Doc. 2013-26482, on page 66358 make the following corrections: 1. On page 66358, in the... COMMISSION Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions. AGENCY: Federal... quarterly Telecommunications Reporting Worksheet, FCC Form 499-Q (Form 499-Q) and accompanying...

  12. Computational study of dislocation based mechanisms in FCC materials

    NASA Astrophysics Data System (ADS)

    Yellakara, Ranga Nikhil

    Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechanical behavior of metallic alloys, particularly focusing on face centered cubic (FCC) structured metals through a unique computational methodology called three-dimensional dislocation dynamics (3D-DD). In these simulations, the equations of motion for dislocations are mathematically solved to determine the evolution and interaction of dislocations. Microstructure details and stress-strain curves are a direct observation in the simulation and can be used to validate experimental results. The effect of initial dislocation microstructure on the yield strength has been studied. It has been shown that dislocation density based crystal plasticity formulations only work when dislocation densities/numbers are sufficiently large so that a statistically accurate description of the microstructure can be obtainable. The evolution of the flow stress for grain sizes ranging from 0.5 to 10 mum under uniaxial tension was simulated using an improvised model by integrating dislocation pile-up mechanism at grain boundaries has been performed. This study showed that for a same initial dislocation density, the Hall--Petch relationship holds well at small grain sizes (0.5--2 mum), beyond which the yield strength remains constant as the grain size increases. Various dislocation-particle interaction mechanisms have been introduced and investigations were made on their effect on the uniaxial tensile properties. These studies suggested that increase in particle volume fraction and decrease in particle

  13. FCC process options for reformulated gasoline

    SciTech Connect

    Chapin, L.E.; Letzsch, W.S.; Martin, T.W.

    1995-12-31

    In addition to certain process modifications, the main focus for RFG in the United States has been the addition of oxygenates, primarily MTBE, and to a lesser extent TAME and ETBE. As FCC-derived isobutylene is the primary feedstock source for MTBE, much interest has been shown in increasing its yield. At the same time, increasing the C3-C5 olefin yield is highly desirable as these olefins can be further processed into alkylate and/or oxygenates for gasoline blending. The incremental volumetric yield associated with these products will help offset the RFG pool volumetric loss due to distillation, benzene, aromatics and sulfur specifications. The paper discusses catalyst and process choices for the future. Three catalytic cracking technologies are described which can be applied to existing FCC units. These are DCC (deep catalytic cracking), MGG (more gasoline and gas), and MIO (maximum iso olefin).

  14. Computer simulation of FCC riser reactors.

    SciTech Connect

    Chang, S. L.; Golchert, B.; Lottes, S. A.; Petrick, M.; Zhou, C. Q.

    1999-04-20

    A three-dimensional computational fluid dynamics (CFD) code, ICRKFLO, was developed to simulate the multiphase reacting flow system in a fluid catalytic cracking (FCC) riser reactor. The code solve flow properties based on fundamental conservation laws of mass, momentum, and energy for gas, liquid, and solid phases. Useful phenomenological models were developed to represent the controlling FCC processes, including droplet dispersion and evaporation, particle-solid interactions, and interfacial heat transfer between gas, droplets, and particles. Techniques were also developed to facilitate numerical calculations. These techniques include a hybrid flow-kinetic treatment to include detailed kinetic calculations, a time-integral approach to overcome numerical stiffness problems of chemical reactions, and a sectional coupling and blocked-cell technique for handling complex geometry. The copyrighted ICRKFLO software has been validated with experimental data from pilot- and commercial-scale FCC units. The code can be used to evaluate the impacts of design and operating conditions on the production of gasoline and other oil products.

  15. Prediction of elastic and vibrational stability for Sc, Ti, Y, Zr, Tc, Ru, Hf, Re, and Os in the fcc structure

    NASA Astrophysics Data System (ADS)

    de Coss, Romeo; Cifuentes-Quintal, Eduardo; Aguayo, Aaron; Murrieta, Gabriel

    2014-03-01

    The discovery of a metastable phase for a given material is interesting because corresponds to a new bonding and new properties are expected. The calculation of the total-energy along the Bain path is frequently used as a method to find tetragonal metastable states. However, a local minimum in the tetragonal distortion is not a definitive proof of a metastable state, and the elastic and vibrational stability needs to be evaluated. In a previous work, using the elastic stability criteria for a cubic structure, we have shown that the transition metals with hcp ground state; Ti, Zr, and Hf have a fcc metastable phase. That result is interesting since the fcc crystal structure does not appear in the current pressure-temperature phase diagram of these metals, and support the experimental observations of fcc Ti and Zr in thin films. In the present work, we extend the stability study of the fcc structure to the non-magnetic transition metals with hcp ground state; Sc, Ti, Y, Zr, Tc, Ru, Hf, Re, and Os. We find that all the metals involved in this study have a metastable fcc structure, since the phonon band structure shows only positive frequencies. Finally, substrates on which the fcc structure of these metals could be growth epitaxially are predicted.

  16. Ground state searches in fcc intermetallics

    SciTech Connect

    Wolverton, C.; de Fontaine, D. ); Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)

    1991-12-01

    A cluster expansion is used to predict the fcc ground states, i.e., the stable phases at zero Kelvin as a function of composition, for alloy systems. The intermetallic structures are not assumed, but derived regorously by minimizing the configurational energy subject to linear constraints. This ground state search includes pair and multiplet interactions which spatially extend to fourth nearest neighbor. A large number of these concentration-independent interactions are computed by the method of direct configurational averaging using a linearized-muffin-tin orbital Hamiltonian cast into tight binding form (TB-LMTO). The interactions, derived without the use of any adjustable or experimentally obtained parameters, are compared to those calculated via the generalized perturbation method extention of the coherent potential approximation within the context of a KKR Hamiltonian (KKR-CPA-GPM). Agreement with the KKR-CPA-GPM results is quite excellent, as is the comparison of the ground state results with the fcc-based portions of the experimentally-determined phase diagrams under consideration.

  17. The impact of quadrupole moment of 4f shell on the hyperfine interactions anisotropy in RAl2 (R=Sm, Tb) intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Delyagin, N. N.; Erzinkyan, A. L.

    2016-03-01

    The magnetic hyperfine interactions for 119Sn impurity atoms in SmAl2 and TbAl2 ferromagnetic compounds have been investigated by Mössbauer spectroscopy technique. These compounds have the same structure but differ in the sign of the quadrupole moment of the R3+ ion. In both cases, the spectrum contains two magnetic subspectra with the ratio of the intensities 1:3, which correspond to a and b Al sites with significantly different hyperfine parameters. The phenomenon change the order the component of inversion component of the Mössbauer spectra was found. This phenomenon is explained by the influence of the quadrupole moment 4f-shell of R3+ ions on the electron density distribution in the valence band. The degree of overlap of electron wave functions being on hybrid orbitals greatly depends on the sign of the 4f-shell quadrupole moment, which gives rise to huge anisotropy in the hyperfine magnetic field and the electric field gradient. Quadrupole deformation induced by the 4f quadrupole moment and the electric field gradient, greatly affects the d-like and p-like components of the electron wave functions, but little effect on the its s-components.

  18. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Where to contact the FCC. 95.117 Section 95.117 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES General Mobile Radio Service (GMRS) § 95.117 Where to contact the FCC. Additional GMRS information may be obtained from any...

  19. 47 CFR 76.1714 - FCC rules and regulations.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 4 2012-10-01 2012-10-01 false FCC rules and regulations. 76.1714 Section 76.1714 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES MULTICHANNEL VIDEO AND CABLE TELEVISION SERVICE Documents to be Maintained for Inspection § 76.1714 FCC rules and regulations. (a) The operator of a...

  20. 47 CFR 76.1714 - FCC rules and regulations.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 4 2013-10-01 2013-10-01 false FCC rules and regulations. 76.1714 Section 76.1714 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES MULTICHANNEL VIDEO AND CABLE TELEVISION SERVICE Documents to be Maintained for Inspection § 76.1714 FCC rules and regulations. (a) The operator of a...

  1. 47 CFR 76.1714 - FCC rules and regulations.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 4 2011-10-01 2011-10-01 false FCC rules and regulations. 76.1714 Section 76.1714 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES MULTICHANNEL VIDEO AND CABLE TELEVISION SERVICE Documents to be Maintained for Inspection § 76.1714 FCC rules and regulations. (a) The operator of a...

  2. 47 CFR 76.1714 - FCC rules and regulations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false FCC rules and regulations. 76.1714 Section 76.1714 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES MULTICHANNEL VIDEO AND CABLE TELEVISION SERVICE Documents to be Maintained for Inspection § 76.1714 FCC rules and regulations. (a) The operator of a...

  3. 47 CFR 76.1714 - FCC rules and regulations.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 4 2014-10-01 2014-10-01 false FCC rules and regulations. 76.1714 Section 76.1714 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES MULTICHANNEL VIDEO AND CABLE TELEVISION SERVICE Documents to be Maintained for Inspection § 76.1714 FCC rules and regulations. (a) The operator of a...

  4. Guide to Understanding Broadcast License Applications and Other FCC Forms.

    ERIC Educational Resources Information Center

    Jennings, Ralph M.

    In order to encourage more citizen action and public awareness in broadcasting, this guide enumerates the step-by-step procedures that citizens must take to deal with the Federal Communications Commission (FCC). The guide exhaustively reviews the policy areas where current FCC television and radio licenses are vulnerable to public scrutiny. It…

  5. Modulating fcc and hcp Ruthenium on the Surface of Palladium-Copper Alloy through Tunable Lattice Mismatch.

    PubMed

    Yao, Yancai; He, Dong Sheng; Lin, Yue; Feng, Xiaoqian; Wang, Xin; Yin, Peiqun; Hong, Xun; Zhou, Gang; Wu, Yuen; Li, Yadong

    2016-04-25

    Herein, we report an epitaxial-growth-mediated method to grow face-centered cubic (fcc) Ru, which is thermodynamically unfavorable in the bulk form, on the surface of Pd-Cu alloy. Induced by the galvanic replacement between Ru and Pd-Cu alloy, a shape transformation from a Pd-Cu@Ru core-shell to a yolk-shell structure was observed during the epitaxial growth. The successful coating of the unconventional crystallographic structure is critically dependent on the moderate lattice mismatch between the fcc Ru overlayer and PdCu3 alloy substrate. Further, both fcc and hexagonal close packed (hcp) Ru can be selectively grown through varying the lattice spacing of the Pd-Cu substrate. The presented findings provide a new synthetic pathway to control the crystallographic structure of metal nanomaterials. PMID:27010243

  6. The electronic structure and bonding of hydrogen near a fcc Fe stacking fault

    NASA Astrophysics Data System (ADS)

    Moro, L.; Ferullo, R.; Brizuela, G.; Juan, A.

    2000-02-01

    The atom superposition and electron delocalization molecular orbital (ASED-MO) semiempirical method is used to analyse the atomic hydrogen-Fe interaction. The face centred cubic (fcc) Fe model contains a stacking fault and as a comparison the H-fcc Fe (normal) system is also studied. The solid is represented by a cluster of 180 metallic atoms distributed in five layers. The interstitial atoms localized in different geometric positions found an energetic minimum in a zone close to octahedral interstitial holes in the stacking fault. The electronic structure shows that the H-Fe bond involves mainly the Fe 4s and 4p orbitals and the 1s H orbital. The Fe-Fe bond near H is destabilized, to approximately 27% of its original value.

  7. 77 FR 74010 - Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-12

    ... 2013 to report 2012 revenues, and the quarterly Telecommunications Reporting Worksheet, FCC Form 499-Q (Form 499-Q) and accompanying instructions (Form 499-Q Instructions) to be used in 2013 to report... 2013 to report 2012 revenues, and (2) the quarterly Telecommunications Reporting Worksheet, FCC...

  8. 78 FR 66357 - Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-11-05

    ...In this document the Federal Communications Commission's Wireline Competition Bureau (Bureau) seeks comment on proposed revisions to the annual Telecommunications Reporting Worksheet, FCC Form 499-A (Form 499-A) and accompanying instructions (Form 499-A Instructions) to be used in 2014 to report 2013 revenues, and the quarterly Telecommunications Reporting Worksheet, FCC Form 499-Q (Form......

  9. Crack Tip Dislocation Nucleation in FCC Solids

    NASA Astrophysics Data System (ADS)

    Knap, J.; Sieradzki, K.

    1999-02-01

    We present results of molecular dynamic simulations aimed at examining crack tip dislocation emission in fcc solids. The results are analyzed in terms of recent continuum formulations of this problem. In mode II, Au, Pd, and Pt displayed a new unanticipated mechanism of crack tip dislocation emission involving the creation of a pair of Shockley partials on a slip plane one plane below the crack plane. In mode I, for all the materials examined, Rice's continuum formulation [J. Mech. Phys. Solids 40, 239 (1992)] underestimated the stress intensity for dislocation emission by almost a factor of 2. Surface stress corrections to the emission criterion brought the agreement between continuum predictions and simulations to within 20%.

  10. Factorization of the matrix elements of three-electron operators used in configuration-interactions studies of the atomic f shell

    SciTech Connect

    Judd, B.R.; Lo, E.

    1996-01-01

    Single-electron excitations of the atomic f shell are usually taken into account in analyses of lanthanide and actinide spectra by including six three-electron scalar operators t{sub i} in the Hamiltonian. Their matrix elements have been factorized for all f{sup N} by using the Wigner-Eckart theorem applied to Racah`s groups SO(7) and G{sub 2}. The two component parts, namely a reduced matrix element in G{sub 2} and an isoscalar factor, are tabulated. This provides a compact representation of the values of the matrix elements and also enables unusual selection rules and proportionalities to be exposed. 16 refs., 2 tabs.

  11. Epitaxial growth of fcc Cr on Au(100)

    SciTech Connect

    Durbin, S.M.; Berman, L.E.; Batterman, B.W.; Brodsky, M.B.; Hamaker, H.C.

    1988-04-15

    Synchrotron x-ray diffraction and anomalous dispersion measurements of 25A Cr layers epitaxially grown on (100) Au surfaces indicate the presence of fcc Cr domains, while extended x-ray absorption fine-structure spectra are consistent with the usual bcc phase of Cr. Together these data suggest that the fcc phase is a major fraction of the larger epitaxial Cr domains, but that most Cr atoms are in a bcc environment with much smaller domain sizes. This unusual, epitaxially stabilized fcc Cr structure may be related to previously reported low-temperature resistance anomalies.

  12. Finite-temperature elasticity of fcc Al: Atomistic simulations and ultrasonic measurements

    NASA Astrophysics Data System (ADS)

    Pham, Hieu H.; Williams, Michael E.; Mahaffey, Patrick; Radovic, Miladin; Arroyave, Raymundo; Cagin, Tahir

    2011-08-01

    Though not very often, there are some cases in the literature where discrepancies exist in the temperature dependence of elastic constants of materials. A particular example of this case is the behavior of C12 coefficient of a simple metal, aluminum. In this paper we attempt to provide insight into various contributions to temperature dependence in elastic properties by investigating the thermoelastic properties of fcc aluminum as a function of temperature through the use of two computational techniques and experiments. First, ab initio calculations based on density functional theory (DFT) are used in combination with quasiharmonic theory to calculate the elastic constants at finite temperatures through a strain-free energy approach. Molecular dynamics (MD) calculations using tight-binding potentials are then used to extract the elastic constants through a fluctuation-based formalism. Through this dynamic approach, the different contributions (Born, kinetic, and stress fluctuations) to the elastic constants are isolated and the underlying physical basis for the observed thermally induced softening is elucidated. The two approaches are then used to shed light on the relatively large discrepancies in the reported temperature dependence of the elastic constants of fcc aluminum. Finally, the polycrystalline elastic constants (and their temperature dependence) of fcc aluminum are determined using resonant ultrasound spectroscopy (RUS) and compared to previously published data as well as the atomistic calculations performed in this work.

  13. FCC046: A CANDIDATE GASEOUS POLAR RING DWARF ELLIPTICAL GALAXY IN THE FORNAX CLUSTER

    SciTech Connect

    De Rijcke, S.; Buyle, P.; Koleva, M.

    2013-06-20

    FCC046 is a Fornax Cluster dwarf elliptical galaxy. Optical observations have shown that this galaxy, besides an old and metal-poor stellar population, also contains a very young centrally concentrated population and is actively forming stars, albeit at a very low level. Here, we report on 21 cm observations of FCC046 with the Australia Telescope Compact Array which we conducted in the course of a small survey of Fornax Cluster early-type dwarf galaxies. We have discovered a {approx}10{sup 7} M{sub Sun} H I cloud surrounding FCC046. We show that the presence of this significant gas reservoir offers a concise explanation for this galaxy's optical morphological and kinematical properties. Surprisingly, the H I gas, as evidenced by its morphology and its rotational motion around the galaxy's optical major axis, is kinematically decoupled from the galaxy's stellar body. This is the first time such a ring of gaseous material in minor-axis rotation is discovered around a dwarf galaxy.

  14. Reformulated gasoline will change FCC operations and catalysts

    SciTech Connect

    Stokes, G.M.; Wear, C.C.; Suarez, W.; Young, G.W. )

    1990-07-02

    Operation of fluid catalytic cracking units (FCCUs) will be significantly affected by new regulations that will in all probability require gasoline to be produced with lower aromatics and olefins contents, lower vapor pressure, and a minimum oxygen content. This paper reports on a study conducted to better define the basic relationship between operating variables, including catalyst and naphtha quality, in the context of reformulated gasoline. The study helped to define specific operating strategies, potential problem areas, and opportunities for improved FCC unit and catalyst technologies. FCC feedstock quality can have a significant influence on the composition of FCC naphtha. However, even extremely paraffinic or aromatic feeds can yield substantial levels of both olefins and aromatics in FCC naphtha, particularly when compared to the levels proposed in a reformulated gasoline pool.

  15. Cluster expansion of fcc Pd-V intermetallics

    SciTech Connect

    de Fontaine, D.; Wolverton, C.; Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)

    1991-06-01

    A cluster expansion is used to compute fcc ground states from first principles for the Pd-V system. Intermetallic structures are not assumed but derived rigorously by minimizing the configurational energy subject to linear constraints. A large number of concentration-independent interactions are calculated by the method of direct configurational averaging. Agreement with the fcc-based portion of the experimentally-determined Pd-V phase diagram is quite satisfactory. 25 refs., 2 figs.

  16. Dislocation core fields and forces in FCC metals

    SciTech Connect

    Henager, Charles H.; Hoagland, Richard G.

    2004-04-01

    Atomistic models were used to obtain dislocation core fields for edge, screw, and mixed dislocations in Al and Cu using EAM. Core fields are analyzed using a line force dipole representation, with dilatant and dipole terms. The core field contribution to the force between dislocations is shown to be significant for interactions within 50b.

  17. Strain hardening of fcc metal surfaces induced by microploughing

    SciTech Connect

    Day, R.D.; Dickerson, R.M.; Russell, P.E.

    1998-12-01

    Microploughing experiments were used as a method for better understanding the ploughing mechanism in gold and iridium single crystals. The plough depths ranged from 20 nm in iridium to 1,600 nm in gold. Yield stress profiles and TEM analyses indicate that both materials strain harden even when very small volumes of material are involved. Strain hardening theory, as applied to bulk material, is useful in analyzing the results.

  18. Selection of the Space Station Freedom (SSF) Flat Collector Circuit (FCC) insulation material

    NASA Technical Reports Server (NTRS)

    Emerson, Dawn

    1994-01-01

    The topics are presented in viewgraph form and include the following: function of the Space Station Freedom (SSF) Flat Collector Circuit (FCC); requirements of the FCC which affect the selection of the insulation material; data to support the selection of the FCC insulation material; development history; modified design; coverlay testing; effects on modified design on FCC; arc tracking tests performed on FCC; and arc tracking test results.

  19. Complex band structure with ultrasoft pseudopotentials: fcc Ni and Ni nanowire

    NASA Astrophysics Data System (ADS)

    Smogunov, Alexander; Dal Corso, Andrea; Tosatti, Erio

    2003-06-01

    We generalize to magnetic transition metals the approach proposed by Choi and Ihm for calculating the complex band structure of periodic systems, a key ingredient for future calculations of conductivity of an open quantum system within the Landauer-Buttiker theory. The method is implemented with ultrasoft pseudopotentials and plane wave basis set in a DFT-LSDA ab initio scheme. As a first example, we present the complex band structure of bulk fcc Ni (which constitutes the tips of a Ni nanocontact) and monatomic Ni wire (the junction between two tips). Based on our results, we anticipate some features of the spin-dependent conductance in a Ni nanocontact.

  20. Understanding Anharmonicity in fcc Materials: From its Origin to ab initio Strategies beyond the Quasiharmonic Approximation

    NASA Astrophysics Data System (ADS)

    Glensk, A.; Grabowski, B.; Hickel, T.; Neugebauer, J.

    2015-05-01

    We derive the Gibbs energy including the anharmonic contribution due to phonon-phonon interactions for an extensive set of unary fcc metals (Al, Ag, Au, Cu, Ir, Ni, Pb, Pd, Pt, Rh) by combining density-functional-theory (DFT) calculations with efficient statistical sampling approaches. We show that the anharmonicity of the macroscopic system can be traced back to the anharmonicity in local pairwise interactions. Using this insight, we derive and benchmark a highly efficient approach which allows the computation of anharmonic contributions using a few T =0 K DFT calculations only.

  1. Magnetic Properties of Diluted Fcc System Nickel

    NASA Astrophysics Data System (ADS)

    Feng, Zhen

    Starting from Ni and Mg nitrates, about 20 samples of Ni_{rm p}Mg _{rm 1-p}O (0.06 <=q p <=q 0.86) were prepared and X-ray diffraction studies showed the samples to have the NaCl structure with the lattice constant fitting the equation a(p) = 4.2115 - 0.0340p A. Temperature dependent dc magnetic susceptibility (chi ) studies of the samples were carried out between 1.8K and 600K using a SQUID magnetometer and the Neel temperature T_{rm N} were determined from the peak in partial(chiT)/ partialT. The variation of t = T _{rm N}(p)/T _{rm N}(1) versus p is compared with that in Co_{rm p}Mg _{rm 1-p}O. For both systems, the variations for p > 0.31 are found to fit the predicted values for a simple cubic Heisenberg antiferromagnet and a theoretical basis for this anomalous results is advanced. The experimental percolation threshold p_{rm c} = 0.15 +/- 0.01. For p_ {rm c} <=q p <=q 0.33, chi below T_{rm N} shows irreversible behavior for the zero-field-cooled and field -cooled cases, suggestive of spin-glass-like behavior, also observed in other diluted fcc antiferromagnets such as Co_{rm p}Mg _{rm 1-p}O and Eu _{rm p}Sr_ {rm 1-p}Te. It is suggested that the differences in the t vs p variations for p < 0.33 in Ni_{rm p} Mg_{rm 1-p}O, Co_{rm p}Mg _{rm 1-p}O and Eu _{rm p}Sr_ {rm 1-p}Te may be related to the differences in the ratio of the next-nearest-neighbor to nearest-neighbor exchange constants in these systems. A higher order correction to Curie-Weiss law was applied for sample with 0.19 <=q p <=q 0.59 which explains why 1/ chi curve versus T bends downward with decreasing temperatures. For the sample Ni_{0.33} Mg_{0.67}O, the magnetization M versus magnetic field H (0 to 0.2T) are measured with temperature ranging from 5.2K to 13.4K at intervals of 0.2K. The magnitude of the non-linear susceptibility, a_3, is determined from the M versus H data at different temperatures. The divergence of a _3 around 9.4 +/- 0.6K indicates spin-glass behavior in this system.

  2. Ultra-high strain rate behavior of FCC nanostructures

    NASA Astrophysics Data System (ADS)

    Crum, Ryan Scott

    This work addresses the influence of ultra-high strain rates loading observed in our world today via ballistics, explosions and astrophysical collisions on well-defined metal structures. There is a plentiful amount of research examining metals at a macroscopic level that are subjected to ballistics and explosions but observing the microstructure is difficult as those procedures are fairly destructive testing mechanisms. Therefore, to understand the true mechanisms that occur in these loading situations a more novel technique is necessary. Modifications were made to the Laser Spallation Technique in order to load structures under a single transient wave pulse. This study characterized FCC nanostructures shock loaded at extreme pressures, strain rates and temperatures. By utilizing nanostructures, extremely large values of stain could be produced within the structure. It was first observed that at lower laser fluence levels and subsequently low stress states that there was a chemical activation of the surface of Cu nanopillars. This occurred due to nanofacet formation on the surface of the nanopillars which left pristine Cu surfaces to recombine with the environment. Dislocation motion was also observed and clearly identified in Cu nanopillars, Cu nanobenches and Al nanopillars. Further studies analyzed Cu nanopillars subjected to higher laser fluence generated stress waves, which led to bending and axial shortening deformation. These deformations were observed at laser fluence values of 144 kJ/m2 for bending and 300 kJ/m 2 for bulging similar to that of Taylor Impact experiments. To explore an even more extreme loading environment, a specialized test setup was employed to cryogenically cool the copper nanopillars to a temperature of 83K in an attempt to elucidate brittle behavior. Under these loading conditions the nanopillars continued to deform in a ductile manner but with delayed onset of both bending deformation and bulging deformation compared to the room

  3. Nucleation of fcc Ta when heating thin films

    SciTech Connect

    Janish, Matthew T.; Mook, William M.; Carter, C. Barry

    2014-10-25

    Thin tantalum films have been studied during in-situ heating in a transmission electron microscope. Diffraction patterns from the as-deposited films were typical of amorphous materials. Crystalline grains were observed to form when the specimen was annealed in-situ at 450°C. Particular attention was addressed to the formation and growth of grains with the face-centered cubic (fcc) crystal structure. As a result, these observations are discussed in relation to prior work on the formation of fcc Ta by deformation and during thin film deposition.

  4. Impact of magnetic fluctuations on lattice excitations in fcc nickel

    NASA Astrophysics Data System (ADS)

    Körmann, Fritz; Ma, Pui-Wai; Dudarev, Sergei L.; Neugebauer, Jörg

    2016-02-01

    The spin-space averaging formalism is applied to compute atomic forces and phonon spectra for magnetically excited states of fcc nickel. Transverse and longitudinal magnetic fluctuations are taken into account by a combination of magnetic special quasi random structures and constrained spin-density-functional theory. It turns out that for fcc Ni interatomic force constants and phonon spectra are almost unaffected by both kinds of spin fluctuations. Given the computational expense to simulate coupled magnetic and atomic fluctuations, this insight facilitates computational modeling of magnetic alloys such as Ni-based superalloys.

  5. A formulation for the characteristic lengths of fcc materials in first strain gradient elasticity via the Sutton-Chen potential

    NASA Astrophysics Data System (ADS)

    Shodja, H. M.; Tehranchi, A.

    2010-05-01

    The usual continuum theories are inadequate in predicting the mechanical behavior of solids in the presence of small defects and stress concentrators; it is well known that such continuum methods are unable to detect the change of the size of the inhomogeneities and defects. For these reasons various augmented continuum theories and strain gradient theories have been proposed in the literature. The major difficulty in implication of these theories lies in the lack of information about the additional material constants which appear in such theories. For fcc metals, for the calculation of the associated characteristic lengths which arise in first strain gradient theory, an atomistic approach based on the Sutton-Chen interatomic potential function is proposed. For the validity of the computed characteristic lengths, the phenomenon of the size effect pertinent to a nano-sized circular void within an fcc (111) plane is examined via both first strain gradient theory and lattice statics. Comparison of the results explains the physical ramifications of the characteristic lengths in improving the usual continuum results. Moreover, by reconsideration of the Kelvin problem it is shown that a commonly employed variant of the first strain gradient theory is only valid for a few fcc metals.

  6. Ab initio study of He point defects in fcc Au-Ag alloys

    SciTech Connect

    Zhu, Zi Qiang; Yang, Li; Nie, JL; Peng, SM; Long, XG; Zhou, X. S.; Zu, Xiaotao; Gao, Fei

    2013-04-25

    The relative stabilities of He defects in two fcc Au-Ag alloys (Au3Ag2 and AuAg) are investigated using ab initio method based on density functional theory. The results show that the stabilities of He defects in the two alloys mainly depend on the atomic arrangements of the nearest neighboring host metals. A He interstitial prefers to stay at a site with more Ag neighboring atoms, while the favorable substitutional site has more Au neighboring atoms in Au-Ag alloys. Moreover, the substitutional He defects are the most stable configurations in both the alloys, and the octahedral He interstitials are energetically more favorable than the tetrahedral interstitials. It is of interest to note that the properties of He defects slightly depend on the mass-density of Au-Ag alloys. The results also demonstrate that the relative stabilities of He defects are primarily attributed to the hybridization between metals d states and He p states.

  7. A Guide to Federal Regulation; Understanding the FCC Rules.

    ERIC Educational Resources Information Center

    Cable Television Information Center, Washington, DC.

    While it is apparent that the Federal Communications Commission (FCC) has given a great deal of thought to the regulation of cable systems, the basic success or failure of cable as a communications service will depend on local development. Relatively little guidance has been provided to local franchising authorities for selecting among applicants,…

  8. Statement on CATV from the FCC to the Senate Committee.

    ERIC Educational Resources Information Center

    Federal Communications Commission, Washington, DC.

    In this statement to the Senate, the Federal Communications Commission (FCC) describes in detail their specific policies relevant to cable television (CATV) regulation under four general areas. The rules for the first of these, television broadcast signal carriage, are outlined in terms of three classifications which would divide all signals:…

  9. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 4 2011-10-01 2011-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  10. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  11. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 4 2012-10-01 2012-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  12. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 4 2014-10-01 2014-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  13. 47 CFR 73.1226 - Availability to FCC of station logs and records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 4 2013-10-01 2013-10-01 false Availability to FCC of station logs and records... Availability to FCC of station logs and records. The following shall be made available to any authorized representative of the FCC upon request: (a) Station records and logs shall be made available for inspection...

  14. Strategies for catalytic octane enhancement in an FCC unit

    SciTech Connect

    Creighton, J.E.; Edwards, G.C.; Rajagopalan, K.; Peters, A.W.; Young, G.W. )

    1987-08-01

    Gasoline quality is largely determined by motor and research octane numbers. There is good correlation between octane number and the structure of the C{sub 5} to C{sub 12} hydrocarbons typically present in gasoline. For paraffins, octane number decreases as molecular weight increases with degree of branching. The same is true of olefins. Catalytic strategies for making high octane gasolines include decreasing the amount of higher molecular weight, less branched paraffins, isomerizing paraffins to a more highly branched product, and producing more olefins or aromatics. A number of catalytic processes in current use make use of these strategies, including reforming, isomerization, dimerization, alkylation and fluid catalytic cracking (FCC). The subject of this paper is to discuss the catalytic strategies available to produce octane number in the FCC unit.

  15. Maximizing the FCC`s potential for RFG production

    SciTech Connect

    Chapin, L.E.

    1996-12-31

    The Fluidized Catalytic Cracking (FCC) unit has traditionally been the dominant conversion process in U.S. refineries. It has served as a major source of high octane naphtha for blending into the gasoline pool. With the passage of the Clean Air Act, U.S. refiners are reformulating their gasoline blends utilizing increasing volumes of {open_quotes}clean burning{close_quotes} alkylate and ethers. Both of these premium products use light olefins including propylene as feedstocks. Environmental trends in other major world markets will force much of the world FCC operating capacity to follow the same path. The intent of this paper is to quantify the impact of deep catalytic cracking on the gasoline pool and overall profitability of a refinery dedicated to producing reformulated gasoline.

  16. Magneto-optic constants of hcp and fcc Co films

    SciTech Connect

    Osgood, R.M. III,; Riggs, K.T.; Johnson, A.E.; Mattson, J.E.; Sowers, C.H.; Bader, S.D.

    1997-08-01

    We tabulate the wavelength dependence of the complex magneto-optic constants for epitaxial fcc (001) and hcp (1{bar 1}00) Co films with the magnetization along two different in-plane crystallographic directions. The magneto-optic constants of epitaxial hcp Co films are strongly dependent on crystallographic direction for the same sample, while those of epitaxial fcc Co films are not, as anticipated from the trends in the magnetic anisotropy due to the spin-orbit interaction. Our results for (i) the anisotropic magneto-optic constants, (ii) the magnetic anisotropy, and (iii) the indices of refraction, are compared to other studies of Co. {copyright} {ital 1997} {ital The American Physical Society}

  17. Emerging technology for the reduction of sulfur in FCC fuels

    SciTech Connect

    Wormsbecher, R.F.; Weatherbee, G.D.; Kim, G.; Dougan, T.J. )

    1993-01-01

    Passage of the Clean Air Act of 1990 and new regulations issued in California will set new limits on the sulfur content of gasoline. Because most of the sulfur in the gasoline pool comes from FCC naphtha, there is a strong incentive to reduce the sulfur content of this stream in the most cost efficient manner. This work introduces emerging catalytic technology for the direct reduction of the sulfur content of FCC gasolines, called the GSR[trademark] (Gasoline Sulfur Reduction) technology. Studies of this new technology were carried out using the Davison Circulating Riser pilot unit. The GSR technology is shown to reduce the sulfur in FCC naphtha by 15%, with two feedstocks. It is shown that this technology is selective to sulfur species in the middle of the gasoline boiling range, and converts these species to H[sub 2]S, while preserving most of the base catalyst selectivities. Various other catalytic scenarios for minimizing the gasoline sulfur content are also given.

  18. (Al, B)-ZSM-11 FCC additive performance

    SciTech Connect

    Hsing, L.H.; O`Young, C.L.

    1996-10-01

    ZSM-5 additive has been used extensively in the petroleum refining industry to enhance the light olefins production from the FCCU operation. In this paper, an FCC additive, (Al, B)-ZSM-11 was evaluated for its performance on a circulated FCC pilot unit. This additive was prepared by partially replacing the frame-work aluminum with boron, which in turn, will alternate its acid characteristics and performance as an FCC additive in promoting light olefin production. The (Al, B)-ZSM-11 additive increased C3=, C4=, and C5= yields, but was less effective in increasing C3=, C4= yields, particularly I-C4= than ZSM-5 additive. The (Al, B)-ZSM-11 additive increased branched C5= and decreased linear C5= yields resulting from skeletal isomerization. C5= and FC naphtha yields with (Al, B)-ZSM-11 additive are higher than those obtained with ZSM-5 additive indicating lower cracking of FC naphtha and C%= to lower olefins with (Al, B)-ZSM-11 additive than ZSM-5. The product selectivity difference between ZSM-5 and (Al, B)-ZSM-11 additives can be correlated with their respective acidity.

  19. Formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters.

    PubMed

    Li, Guojian; Wang, Qiang; Sui, Xudong; Wang, Kai; Wu, Chun; He, Jicheng

    2015-09-01

    The formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters has been studied by molecular dynamics simulation using an embedded atom method. Structural evolution of the clusters, coalesced under varying temperature, Ni content and substrate conditions, was explored by interatomic energy, snapshots, pair distribution functions and bond order parameters. The results show that the formation of bcc and fcc is strongly related to Ni content, substrate and coalescence temperature. Free clusters coalesced at 1200 K form bcc at lower Ni contents with fcc forming at higher Ni concentrations and no observable coexistence of bcc and fcc. Differences in coalescence at 1000 K result from the coexistence of bcc and fcc within the Ni range of 50-70%. Free clusters supported on disordered Ni substrates were shown to transform from spherical morphology to islands of supported clusters with preferred epitaxial orientation. The Ni content required to form bcc and fcc coexistence on supported clusters at 1000 K decreased to 30-50% Ni. Free clusters possessing bcc and fcc generally stacked along the bcc (110) and fcc (111) facets, whereas supported clusters stacked along the (111) bcc and (100) fcc planes. Structural transformation was induced by clusters containing greater numbers of atoms. Spread over the substrate enhanced interatomic energy, order substrates affect the epitaxial growth direction and increase the melting points of the supported clusters. This study can be used to predict the nature of fcc and bcc formation in Fe-Ni films. PMID:26234423

  20. Atomistic simulation of the fcc-hcp transition in single-crystal Al under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Li, L.; Shao, J. L.; Duan, S. Q.; Liang, J. Q.

    2010-03-01

    The dynamic behavior of the single-crystal Al under [001] uniaxial strain is simulated by classic molecular dynamics. The fcc-hcp structural transition is successfully observed when the loading pressure reaches about 90 GPa, and the reverse transition is also found with hysteresis. The mechanism and morphology evolution of both the forward and backward transitions are analyzed in detail. It is found in the process of the structural transition that the (010)fcc or (100)fcc planes transit into (0001)hcp planes, and the twins of the hcp phase along the (112)-plane appear, whose boundaries finally become along the (110)-plane. Besides, we find the twinning (along the (110)fcc planes) in the hcp phase prior to the back transition (hcp-fcc). Our simulations show the coexistence of fcc and hcp phases over a wide range of pressures, and finally, the phase transition is evaluated by using the radial distribution functions.

  1. A general kinetic-flow coupling model for FCC riser flow simulation.

    SciTech Connect

    Chang, S. L.

    1998-05-18

    A computational fluid dynamic (CFD) code has been developed for fluid catalytic cracking (FCC) riser flow simulation. Depending on the application of interest, a specific kinetic model is needed for the FCC flow simulation. This paper describes a method to determine a kinetic model based on limited pilot-scale test data. The kinetic model can then be used with the CFD code as a tool to investigate optimum operating condition ranges for a specific FCC unit.

  2. Polarization Issues in the $e\\pm$ FCC

    SciTech Connect

    Gianfelice-Wendt, E.

    2015-08-10

    After the Higgs boson discovery at LHC, the international physics community is considering the next energy frontier circular collider (FCC). A pp collider of 100 km with a center of mass energy of about 100 TeV is believed to have the necessary discovery potential. The same tunnel could host first a e+e- collider with beam energy ranging between 45 and 175 GeV. In this paper preliminary considerations on the possibility of self-polarization for the e± beams are presented.

  3. Moessbauer spectroscopy evidence of a spinodal mechanism for the thermal decomposition of fcc FeCu

    SciTech Connect

    Crespo, P. |; Barro, M.J.; Hernando, A.; Escorial, A.G.; Menendez, N.; Tornero, J.D.; Barandiaran, J.M.

    1998-07-24

    Moessbauer spectroscopy shows the existence of compositional fluctuations, where different Fe environments coexist, during decomposition upon heat treatment of metastable f.c.c. FeCu solid solution. The presence of isolated Fe atoms in the Cu matrix, f.c.c. Fe{sub rich}Cu, f.c.c. FeCu{sub rich} and b.c.c. Fe has been detected in early decomposition stages. At later decomposition stages, low temperature Moessbauer spectroscopy indicates the presence of a broad distribution of Curie temperatures, coexisting with isolated Fe atoms in the Cu matrix, f.c.c. Fe and b.c.c. Fe.

  4. The effect of feedstock additives on FCC catalyst deactivation

    SciTech Connect

    Hughes, R.; Koon, C.L.; McGhee, B.

    1995-12-31

    Fluid catalytic cracking is a major petroleum refining process and because of this the deactivation of FCC catalysts by coke deposition has been the subject of considerable investigation during the past 50 years. Nevertheless, a lack of understanding of the fundamental understanding of processes leading to coke formation still exists. Basic studies using Zeolites have usually involved excessively high levels of coke deposits compared to normal FCC operation. The present study addresses coke formation at realistic levels of 0.5 to 1.0% w/w using a standard MAT reactor in which concentrations of 1% and 10% of various additives were added to the n-hexadecane feedstock. These additives included, quinoline, phenanthrene, benzofuran, thianaphthene and indene. The coke formed was characterised by mass spectrometry and was significantly aliphatic in nature, the amount formed increasing in the order quinoline, phenanthrene, thianaphthene, benzofuran, indene. Quinoline acts primarily as a poison, whereas the other additives tend to promote coke formation in n-hexadecane cracking.

  5. Electronic Structure of Crystalline Buckyballs: fcc-C60

    NASA Astrophysics Data System (ADS)

    Jalali-Asadabadi, Saeid; Ghasemikhah, E.; Ouahrani, T.; Nourozi, B.; Bayat-Bayatani, M.; Javanbakht, S.; Aliabad, H. A. Rahnamaye; Ahmad, Iftikhar; Nematollahi, J.; Yazdani-Kachoei, M.

    2016-01-01

    The electronic properties of pristine fcc-C60 are calculated by utilizing a variety of density functional theory (DFT) approaches including the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), PBE-GGA+DFT-D3(vdW), Engel and Vosko GGA (EV-GGA), GGA plus Hubbard U parameter (GGA+U), hybrids Becke-Perdew-Wang hybrid functional (B3PW91), Becke-Lee-Yang-Parr hybrid functional (B3LYP), the PBE exchange-correlation functional (PBE0), and Tran and Blaha regular and non-regular modified Becke and Johnson (TB-mBJ) potential within a DFT frame work using augmented plane waves plus local orbital method. The comparison of the calculated results with the experimental values shows that the non-regular TB-mBJ method reproduces a correct experimental direct band gap of 2.12 eV at X symmetry for this compound. The effectiveness of this theoretical approach in the reproduction of the experimental band gap is due to the proper treatment of the electrons in the interstitial region of the crystal. Our results show that the C60 clusters are weakly interacting with each other in the fcc crystal. This study also reveals that the five-fold degeneracies of the isolated C60 molecule due to its icosahedral symmetry are completely lifted at an X symmetry point by the crystal field.

  6. The Impact of Public Affairs Programming Regulation: A Study of the FCC's Effectiveness.

    ERIC Educational Resources Information Center

    Chamberlin, Bill F.

    1979-01-01

    Explores the effectiveness of the Federal Communications Commission (FCC) public affairs program regulation through analysis of annual reports for 75 television stations, examining amount of time for public issues programing, amount of local affairs programing, total prime time programing, and whether FCC standards are met. (CWM)

  7. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station...

  8. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station...

  9. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station...

  10. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station...

  11. 47 CFR 97.27 - FCC modification of station license grant.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false FCC modification of station license grant. 97.27 Section 97.27 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE General Provisions § 97.27 FCC modification of station...

  12. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  13. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  14. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  15. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  16. 47 CFR Appendix A to Subpart A of... - Locations Where GMRS Is Regulated by the FCC

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Locations Where GMRS Is Regulated by the FCC A Appendix A to Subpart A of Part 95 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY.... A, App. A Appendix A to Subpart A of Part 95—Locations Where GMRS Is Regulated by the FCC In...

  17. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false State and Local Area plans and FCC Mapbook. 11.21 Section 11.21 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL EMERGENCY ALERT SYSTEM (EAS) General § 11.21 State and Local Area plans and FCC Mapbook. EAS plans contain guidelines...

  18. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false State and Local Area plans and FCC Mapbook. 11.21 Section 11.21 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL EMERGENCY ALERT SYSTEM (EAS) General § 11.21 State and Local Area plans and FCC Mapbook. EAS plans contain guidelines...

  19. 47 CFR 0.409 - Commission policy on private printing of FCC forms.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false Commission policy on private printing of FCC forms. 0.409 Section 0.409 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL COMMISSION ORGANIZATION General Information General § 0.409 Commission policy on private printing of FCC forms. The Commission has established a policy regarding...

  20. On Campus Web-Monitoring Rules, Colleges and the FCC Have a Bad Connection

    ERIC Educational Resources Information Center

    Hartle, Terry W.

    2006-01-01

    A regulation issued by the US Federal Communications Commission (FCC) requires facilities-based Internet services providers who operate their own equipment, including colleges, to make their Internet systems compliant with a statute known as the Communications Assistance for Law Enforcement Act (Calea) by April 2007. However, the FCC does not…

  1. Diversity of Voice? The FCC's Bright-Line "Anti-Monopoly" Rule.

    ERIC Educational Resources Information Center

    Haddock, David D.; Polsby, Daniel D.

    The Federal Communications Commission (FCC) has long had rules that prohibit anyone from owning more than one television station in any given location. Two of the stated purposes behind the FCC's anti-monopoly rules are to foster diversity of programming for the sake of First Amendment interests, and to promote programming among media outlets in…

  2. 47 CFR 0.409 - Commission policy on private printing of FCC forms.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false Commission policy on private printing of FCC forms. 0.409 Section 0.409 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL COMMISSION ORGANIZATION General Information General § 0.409 Commission policy on private printing of FCC forms. The Commission has established a policy regarding...

  3. Investigation of Three-Dimensional Stress Fields and Slip Systems for FCC Single Crystal Superalloy Notched Specimens

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Magnan, Shannon; Ebrahimi, Fereshteh; Ferroro, Luis

    2004-01-01

    Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.

  4. Germanium FCC structure from a colloidal crystal template

    SciTech Connect

    Miguez, H.; Meseguer, F.; Lopez, C.; Holgado, M.; Andreasen, G.; Mifsud, A.; Fornes, V.

    2000-05-16

    Here, the authors show a method to fabricate a macroporous structure in which the pores, essentially identical, arrange regularly in a face-centered cubic (FCC) lattice. The result is a network of air spheres in a germanium medium. This structure presents the highest dielectric contrast ({epsilon}{sub Ge}/{epsilon}{sub air} = 16) ever achieved in the optical regime in such periodic structures, which could result in important applications in photonics. The authors employ solid silica colloidal crystals (opals) as templates within which a cyclic germanium growth process is carried out. Thus, the three-dimensional periodicity of the host is inherited by the guest. Afterward, the silica is removed and a germanium opal replica is obtained.

  5. Mechanism of aromatic hydrocarbon formation in FCC naphtha

    SciTech Connect

    Mota, C.J.A.; Rawet, R.

    1995-12-01

    A microactivity test study of the FCC naphtha composition at increasing conversions was carried out. At low conversions (ca. 10--20%), the naphtha is rich in olefinic and aromatic hydrocarbons. As the conversion increases, the composition changes dramatically. The olefins initially increase and then decrease sharply. The paraffins increase continually, and the aromatics initially decrease and then increase slightly. The naphthenics remain constant in the conversion range studied. These results indicate that, at low conversions, the aromatics in the gasoline are mainly formed by dealkylation of heavy aromatic molecules present in the feed. At higher conversions, however, the aromatics in the naphtha are mainly formed by cyclization followed by hydrogen transfer of the olefins formed during cracking. This reaction also increases the relative concentration of paraffinic hydrocarbons. The distribution of C9 aromatics showed that, as the conversion increases, there occurs an isomerization of the alkyl chain, to increase the branching of the ring.

  6. Interactions of multiphase hydrodynamics, droplet evaporation, and chemical kinetics in FCC riser reactors.

    SciTech Connect

    Chang, S. L.

    1998-02-17

    A computational fluid dynamics (CFD) computer code, ICRKFLO, has been developed for flow simulation of fluid catalytic cracking (FCC) riser reactors, which convert crude oil into gasoline and other valuable products. The FCC flow, especially in the entry region, is a three-phase reacting flow including hot catalyst particles, inert lift gas, and feed oil droplets. The impact of the hydrodynamics processes of heat transfer, droplet evaporation, and mixing on the chemical kinetics or riser performance can be significant. ICRKFLO was used to evaluate the impact of these processes on the performance of an advanced FCC unit. The code solves for major flow properties of all three phases in an FCC riser, with models governing the transport of catalyst particles and feed oil droplet, the vaporization of the feed oil droplets, the cracking of the oil vapor, and the formation and deposition of coke on particles. First, the code was validated against available test data of a pilot-scale FCC unit. Then, flow calculations for the FCC unit were performed. Computational results indicate that the heat transfer and droplet vaporization processes have a significant impact on the performance of a pilot-scale FCC unit. The impact is expected to be even greater on commercial scale units.

  7. Controlled FCC/on-top binding of H/Pt(111) using surface stress

    NASA Astrophysics Data System (ADS)

    Shuttleworth, I. G.

    2016-08-01

    The preferred binding site of H/Pt(111) has been shown to be change from the on-top to FCC as the Pt(111) surface goes approximately from a state of compressive to tensile strain. A chemical analysis of the system has shown that for both FCC and on-top bound cases the H ssbnd Pt s and H ssbnd Pt d interactions have a similar importance in determining the preferred binding position. It has been seen that FCC-bound H forms a distinct state below the Pt d-band, whereas the on-top bound H does not.

  8. Specific features of defect and mass transport in concentrated fcc alloys

    DOE PAGESBeta

    Osetsky, Yuri N.; Béland, Laurent K.; Stoller, Roger E.

    2016-06-15

    We report that diffusion and mass transport are basic properties that control materials performance, such as phase stability, solute decomposition and radiation tolerance. While understanding diffusion in dilute alloys is a mature field, concentrated alloys are much less studied. Here, atomic-scale diffusion and mass transport via vacancies and interstitial atoms are compared in fcc Ni, Fe and equiatomic Ni-Fe alloy. High temperature properties were determined using conventional molecular dynamics on the microsecond timescale, whereas the kinetic activation-relaxation (k-ART) approach was applied at low temperatures. The k-ART was also used to calculate transition states in the alloy and defect transport coefficients.more » The calculations reveal several specific features. For example, vacancy and interstitial defects migrate via different alloy components, diffusion is more sluggish in the alloy and, notably, mass transport in the concentrated alloy cannot be predicted on the basis of diffusion in its pure metal counterparts. Lastly, the percolation threshold for the defect diffusion in the alloy is discussed and it is suggested that this phenomenon depends on the properties and diffusion mechanisms of specific defects.« less

  9. [In situ FTIR and XPS study on selective hydrodesulfurization catalyst of FCC gasoline].

    PubMed

    Qiherima; Yuan, Hui; Zhang, Yun-hong; Li, Hui-feng; Xu, Guang-tong

    2011-07-01

    Improvement of the selectivity of hydrodesulfurization (HDS) for hydrogenation (HYD) of olefins is crucial to produce sulfur-free (S < 0.001%) gasoline from fluid catalytic-cracked (FCC) gasoline. A series of sulfided CoMo/Al2O3 catalysts with different metal loading were prepared by pore-filling impregnation. MoS2 and COMoS active phases on the surface of sulfided COMo/Al2O3 catalyst were identified and analyzed quantitatively by XPS and in-situ FTIR of adsorbed CO. The results reveal that the increase in COMoS phase on the catalyst surface improves the HDS activity and selectivity. And the HDS selectivity correlates linearly with the ratio of active site number of CoMoS and MoS2, the higher the ratio of active site number of CoMoS and MoS2, the better the HDS selectivity. In situ variable temperature FTIR analysis shows that CoMoS phase has stronger electron accepting ability than MoS2. The strong electron deficient property of CoMoS active sites is the main reason for its excellent HDS activity and selectivity. PMID:21942017

  10. Specific features of defect and mass transport in concentrated fcc alloys

    SciTech Connect

    Osetskiy, Yury N; Stoller, Roger E

    2016-01-01

    Diffusion and mass transport are basic properties that control materials performance, such as phase stability, solute decomposition and radiation tolerance. While understanding diffusion in dilute alloys is a mature field, concentrated alloys are much less studied. Here, atomic-scale diffusion and mass transport via vacancies and interstitial atoms are compared in fcc Ni, Fe and equiatomic Ni-Fe alloy. High temperature properties were determined using conventional molecular dynamics on the microsecond timescale, whereas the kinetic activation-relaxation (k-ART) approach was applied at low temperatures. The k-ART was also used to calculate transition states in the alloy and defect transport coefficients. The calculations reveal several specific features. For example, vacancy and interstitial defects migrate via different alloy components, diffusion is more sluggish in the alloy and, notably, mass transport in the concentrated alloy cannot be predicted on the basis of diffusion in its pure metal counterparts. The percolation threshold for the defect diffusion in the alloy is discussed and it is suggested that this phenomenon depends on the properties and diffusion mechanisms of specific defects.

  11. Highly anisotropic exchange interactions of jeff=1/2 iridium moments on the fcc lattice in La2B IrO6 (B =Mg ,Zn )

    NASA Astrophysics Data System (ADS)

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; Calder, S.; Christianson, A. D.; Cao, G.-X.; Mandrus, D.; Kim, Yong-Baek; Paramekanti, A.

    2016-06-01

    We have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO6 and La2MgIrO6 , which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated jeff=1/2 Mott insulators provide clear evidence for gapped spin-wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in jeff=1/2 Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly directional Kitaev interaction is a type of exchange anisotropy which is symmetry allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order by disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry lowering due to lattice distortions can pin the order and enhance the magnon gap. Our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly directional exchange interactions rooted in strong spin-orbit coupling.

  12. Highly anisotropic exchange interactions of jeff=12 iridium moments on the fcc lattice in La2BIrO6 (B=Mg,Zn)

    DOE PAGESBeta

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; Calder, S.; Christianson, A. D.; Cao, G. -X.; Mandrus, D.; Kim, Yong-Baek; Paramekanti, A.

    2016-06-20

    Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $_2$ZnIrO$_6$ and La$_2$MgIrO$_6$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

  13. Improvements in FCC catalyst technology for light hydrocarbon production

    SciTech Connect

    Ritter, R.E.; Habib, E.T.; Peters, A.W.; Rheaume, L.; Thiel, P.G.; Wallace, D.N.; Wormsbecher, R.F.

    1985-03-01

    As the refining industry continues to undergo dramatic changes due to crude pricing, environmental demands, and product demand, cracking catalyst manufacturers continue to make significant strides in the understanding of the processes and products to meet the refiners' needs. This paper builds on information reported to the industry in previous articles, with the aim of keeping the industry informed of the many dramatic changes taking place in cracking catalyst technology. From our vantage point, the key refining industry concerns today are gasoline octane quality due to the lead phase-down, atmospheric emissions due to increasingly strict EPA and local limits on SOx emissions, and catalytic upgrading of resid feeds due to an expected long term price differential between high and low quality crudes. Hence, we focus here on the significant changes in cracking catalyst technology which will help the refiner handle these issues. In particular, we discuss the catalytic enhancement of gasoline octane with Davison's Octacat and GXO catalyst families, the reduction of FCC SOx emissions with Davison's Additive R SOx catalyst, and the passivation of vanadium with Davison's DVT, so that catalyst deactivation is minimized.

  14. Chevron process reduces FCC/coker corrosion and saves energy

    SciTech Connect

    Knowlton, H.E.; Coombs, J.W.; Allen, E.R.

    1980-01-01

    The Chevron Polysulfide process for controlling cyanide-induced corrosion was installed in seven fluid catalytic cracking (FCC) and coker fractionation systems at six Chevron refineries. Besides reducing corrosion, the process conserves energy that would otherwise be required for foul water stripping, and provides environmental benefits that include a reduction in effluent volume due to less-stripped foul water, less ammonia in effluent, low cyanide in the stripped foul-water, additional foul-water stripper capacity, and reduced foul-water stripper corrosion. In all units, the process was economically justified by the energy and additive savings associated with its use (no credits were taken for corrosion benefits). The mechanism by which cyanide induces corrosion and hydrogen blistering, i.e., removal of the protective iron sulfide film, in vapor lines, knockout drums, compressors, heat exchangers, and fractionation columns, and their elimination by the Chevron Polysulfide process, which involves the reaction of purchased ammonium polysulfide with cyanide to form thiocyanate, are discussed based on the above case histories.

  15. Orbitide Composition of the Flax Core Collection (FCC).

    PubMed

    Burnett, Peta-Gaye Gillian; Olivia, Clara Marisa; Okinyo-Owiti, Denis Paskal; Reaney, Martin John Tarsisius

    2016-06-29

    The flax (Linum usitatissimum L.) core collection (FCC) was regenerated in Saskatoon, Saskatchewan and Morden, Manitoba in 2009. Seed orbitide content and composition from successfully propagated plants of 391 accessions were analyzed using high-throughput analyses employing high-performance liquid chromatography (HPLC) with reverse-phase monolithic HPLC columns and diode array detection (HPLC-DAD). Seed from plants regenerated in Morden had comparatively higher orbitide content than those grown in Saskatoon. Concentrations of orbitides encoded by contig AFSQ01016651.1 (1, 3, and 8) were higher than those encoded by AFSQ01025165.1 (6, 13, and 17) for most accessions in both locations. The cultivar 'Primus' from Poland and an unnamed accession (CN 101580 of unknown origin) exhibited the highest ratio of sum of [1,3,8] to a sum of [6,13,17]. Conversely, the lowest orbitide concentrations and ratio of [1,3,8] to [6,13,17] were observed in cultivars 'Hollandia' and 'Z 11637', both from The Netherlands. Orbitide expression did not correlate with flax morphological and other chemical traits. PMID:27256931

  16. Role of distortion in the hcp vs fcc competition in rare-gas solids

    NASA Astrophysics Data System (ADS)

    Krainyukova, N. V.

    2011-05-01

    As a prototype of an initial or intermediate structure between hcp and fcc lattices we consider a distorted bcc crystal. We calculate the temperature and pressure dependences of the lattice parameters for the heavier rare gas solids Ar, Kr, Xe in a quasiharmonic approximation with Aziz potentials, and confirm earlier predictions that the hcp structure predominates over fcc in the bulk within wide ranges of P and T. The situation is different for confined clusters with up to 105 atoms, where, owing to the specific surface energetics and terminations, structures with five-fold symmetry made up of fcc fragments are dominant. As a next step we consider the free relaxation of differently distorted bcc clusters, and show that two types (monoclinic and orthorhombic) of initial distortion are a driving force for the final hcp vs fcc configurations. Possible energy relationships between the initial and final structures are obtained and analyzed.

  17. Cesium under pressure: First-principles calculation of the bcc-to-fcc phase transition

    NASA Astrophysics Data System (ADS)

    Carlesi, S.; Franchini, A.; Bortolani, V.; Martinelli, S.

    1999-05-01

    In this paper we present the ab initio calculation of the structural properties of cesium under pressure. The calculation of the total energy is done in the local-density approximation of density-functional theory, using a nonlocal pseudopotential including the nonlinear core corrections proposed by Louie et al. The calculation of the pressure-volume diagram for both bcc and fcc structures allows us to prove that the transition from bcc to fcc structure is a first-order transition.

  18. Bond-Energy and Surface-Energy Calculations in Metals

    ERIC Educational Resources Information Center

    Eberhart, James G.; Horner, Steve

    2010-01-01

    A simple technique appropriate for introductory materials science courses is outlined for the calculation of bond energies in metals from lattice energies. The approach is applied to body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal-closest-packed (hcp) metals. The strength of these bonds is tabulated for a variety metals and is…

  19. Synthesis and microstructure of electrodeposited and sputtered nanotwinned face-centered-cubic metals

    DOE PAGESBeta

    Bufford, Daniel C.; Wang, Morris; Liu, Yue; Lu, Lei

    2016-04-01

    The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. When we understand the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, we realize how key it is to understanding and utilizing these materials. Furthermore, our article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, whilemore » engineered approaches are necessary for fcc metals with higher stacking-fault energies. Finally, growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.« less

  20. High-pressure behavior of fcc phase FeHx

    NASA Astrophysics Data System (ADS)

    Thompson, E. C.; Chidester, B.; Fischer, R. A.; Prakapenka, V.; Bi, W.; Alp, E. E.; Campbell, A. J.

    2015-12-01

    Earth's core is composed of iron with the inclusion of light elements to compensate for the difference between seismically obtained densities and the density of pure Fe at relevant pressure and temperature conditions. As the most abundant and lightest element in the solar system, hydrogen is a plausible contributor to this core density deficit. Nearly stoichiometric iron hydride (FeHx) has been shown to result from the reaction of Fe and hydrous silicates, and is stable up to at least 80 GPa [1]. Iron hydride formation at Earth's surface is unlikely because the equilibrium hydrogen solubility in iron at atmospheric conditions is prohibitively low, yet as hydrogen solubility increases with pressure, so does the likelihood of FeHx formation within the Earth's interior [2]. Recent experimental and ab initio attempts disagree on the equation of state parameters needed to describe the compressional behavior of FeHx [3-5]. The work presented here combines synchrotron x-ray diffraction of laser-heated diamond anvil cell compressed samples with high-pressure, ambient temperature nuclear resonant inelastic scattering (NRIXS) and synchrotron Mössbauer spectroscopy (SMS) to better constrain the behavior of the fcc phase of FeHx at elevated pressures and temperatures. By pairing P-V-T data for iron hydride with the sound velocity information available through high-pressure NRIXS studies, we can better understand the degree to which hydrogen may contribute to the density deficit of Earth's iron core. [1] Antonov et al. (1998) J. Alloys Compd. 264, 214-222 [2] Fukai and Akimoto (1983) Proc. Japan Acad. 59, 158-162 [3] Pépin et al. (2014) Phys. Rev. Lett. 265504, 1-5 [4] Hirao (2004) Geophys. Res. Lett. 31, L06616 [5] Badding et al. (1991) Science. 253, 421-424

  1. CFD code development for performance evaluation of a pilot-scale FCC riser reactor

    SciTech Connect

    Chang, S.L.; Lottes, S.A.; Zhou, C.Q.; Golchert, B.; Petrick, M.

    1997-09-01

    Fluid Catalytic Cracking (FCC) is an important conversion process for the refining industry. The improvement of FCC technology could have a great impact on the public in general by lowering the cost of transportation fuel. A recent review of the FCC technology development by Bienstock et al. of Exxon indicated that the use of computational fluid dynamics (CFD) simulation can be very effective in the advancement of the technology. Theologos and Markatos used a commercial CFD code to model an FCC riser reactor. National Laboratories of the U.S. Department of Energy (DOE) have accumulated immense CFD expertise over the years for various engineering applications. A recent DOE survey showed that National Laboratories are using their CFD expertise to help the refinery industry improve the FCC technology under DOE`s Cooperative Research and Development Agreement (CRADA). Among them are Los Alamos National Laboratory with Exxon and Amoco and Argonne National Laboratory (ANL) with Chevron and UOP. This abstract briefly describes the current status of ANL`s work. The objectives of the ANL CRADA work are (1) to use a CFD code to simulate FCC riser reactor flow and (2) to evaluate the impacts of operating conditions and design parameters on the product yields. The CFD code used in this work was originally developed for spray combustion simulation in early 1980 at Argonne. It has been successfully applied to diagnosing a number of multi-phase reacting flow problems in a magneto-hydrodynamic power train. A new version of the CFD code developed for the simulation of the FCC riser flow is called Integral CRacKing FLOw (ICRKFLO). The CFD code solves conservation equations of general flow properties for three phases: gaseous species, liquid droplets, and solid particles. General conservation laws are used in conjunction with rate equations governing the mass, momentum, enthalpy, and species for a multi-phase flow with gas species, liquid droplets, and solid particles.

  2. Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

    NASA Astrophysics Data System (ADS)

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-04-01

    Magnetic ordering temperatures in heavy rare earth metal dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to a pressure of 69 GPa and a temperature of 10 K. Previous studies using magnetic susceptibility measurements at high pressures were able to track magnetic ordering temperature only till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This is followed by a rapid increase in the magnetic ordering temperatures in the double hcp phase and finally leveling off in the distorted face centered cubic phase of Dy. Our studies reaffirm that 4f-shell remains localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.

  3. Dynamic damage evolution in aluminum as a model system for understanding FCC materials in extreme conditions

    NASA Astrophysics Data System (ADS)

    Sanchez, Nathaniel Jonathon

    Materials play a key role in many emerging technologies. Future technologies in the energy and defense sectors will place huge demands on material performance with respect to stress, strain, temperature, and pressure. These applications require that the response of materials on dynamic (microsecond) time scales be predictable and controllable. Hence, the goal of this research project was to study the extreme environment of shock loaded damage evolution in aluminum as a model system for understanding dynamic response of FCC metals in these environments. Phase one utilized plate impact experiments to study the influence of spatial effects (in the form of microstructural defect distributions) on the dynamic damage evolution process. Samples were soft recovered for shot analysis and comparison to real time laser velocimetry. Results revealed that the length scale of defects controls the failure mechanisms of the microstructure; suggesting defect density and the spatial distribution of defects are critical factors in the deformation process in extreme environments. Phase two studied the influence of kinetic effects (in the form of dynamic tensile loading rate) to reveal time dependence on the dynamic deformation process. Results concluded damage nucleation and growth rates are highly time dependent and can be overdriven as higher tensile loading rates result in extremely short time durations. It was shown that laser velocimetry provides an adequate means for understanding the dynamic damage evolution process when soft recovery of the sample is unavailable. This was shown by comparing laser velocimetry results with data obtained from optical analysis on recovered specimens. The methodology here provides a means to systematically study materials of interest in extreme conditions and provides a pathway for obtaining the relevant physics needed for model development leading to a predictive capability.

  4. Bulk Nanostructured FCC Steels With Enhanced Radiation Tolerance

    SciTech Connect

    Zhang, Xinghang; Hartwig, K. Ted; Allen, Todd; Yang, Yong

    2012-10-27

    The objective of this project is to increase radiation tolerance in austenitic steels through optimization of grain size and grain boundary (GB) characteristics. The focus will be on nanocrystalline austenitic Fe-Cr-Ni alloys with an fcc crystal structure. The long-term goal is to design and develop bulk nanostructured austenitic steels with enhanced void swelling resistance and substantial ductility, and to enhance their creep resistance at elevated temperatures via GB engineering. The combination of grain refinement and grain boundary engineering approaches allows us to tailor the material strength, ductility, and resistance to swelling by 1) changing the sink strength for point defects, 2) by increasing the nucleation barriers for bubble formation at GBs, and 3) by changing the precipitate distributions at boundaries. Compared to ferritic/martensitic steels, austenitic stainless steels (SS) possess good creep and fatigue resistance at elevated temperatures, and better toughness at low temperature. However, a major disadvantage of austenitic SS is that they are vulnerable to significant void swelling in nuclear reactors, especially at the temperatures and doses anticipated in the Advanced Burner Reactor. The lack of resistance to void swelling in austenitic alloys led to the switch to ferritic/martensitic steels as the preferred material for the fast reactor cladding application. Recently a type of austenitic stainless steel, HT-UPS, was developed at ORNL, and is expected to show enhanced void swelling resistance through the trapping of point defects at nanometersized carbides. Reducing the grain size and increasing the fraction of low energy grain boundaries should reduce the available radiation-produced point defects (due to the increased sink area of the grain boundaries), should make bubble nucleation at the boundaries less likely (by reducing the fraction of high-energy boundaries), and improve the strength and ductility under radiation by producing a higher

  5. Molecular dynamics simulations of the mechanisms controlling the propagation of bcc/fcc semi-coherent interfaces in iron

    NASA Astrophysics Data System (ADS)

    Ou, X.; Sietsma, J.; Santofimia, M. J.

    2016-06-01

    Molecular dynamics simulations have been used to study the effects of different orientation relationships between fcc and bcc phases on the bcc/fcc interfacial propagation in pure iron systems at 300 K. Three semi-coherent bcc/fcc interfaces have been investigated. In all the cases, results show that growth of the bcc phase starts in the areas of low potential energy and progresses into the areas of high potential energy at the original bcc/fcc interfaces. The phase transformation in areas of low potential energy is of a martensitic nature while that in the high potential energy areas involves occasional diffusional jumps of atoms.

  6. Phase stability, ordering, and magnetism of single-phase fcc Fe-Au alloys

    NASA Astrophysics Data System (ADS)

    An, Joonhee M.; Barabash, Sergey V.; Belashchenko, Kirill D.

    2013-03-01

    Motivated by experimental evidence of L10 ordering in single-phase fcc Fe-Au nanoparticles, we study the structural thermodynamics of Fe-Au alloys. First, separate cluster expansions for fcc and bcc lattices are constructed for fully optimized ferromagnetic structures using density functional theory calculations. The optimized structures were assigned to fcc or bcc lattice by a structural filter. Although the lowest formation enthalpy at 50% Au is reached in the bcc lattice, the fcc lattice is preferred for the random alloy. Dynamical stability of specific orderings strongly depends on the magnetic configuration. To analyze the ordering tendencies of the fcc alloy, we restrict uniform lattice relaxations and separate the contributions of chemical interaction and local relaxations. By using the effective tetrahedron model (Ruban et al., Phys. Rev. B 67, 214302 (2003)) and explicit calculations for ordered and special quasi-random structures, we find that the local relaxation energies depend weakly on the magnetization. Although the L10 ordering is the ground state at 50% Au on the ideal lattice, local relaxations make it unfavorable compared to the random alloy. Moderate compression due to the size effect tends to slightly stabilize the L10 ordering.

  7. Topology of the spin-polarized charge density in bcc and fcc iron.

    PubMed

    Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P

    2008-01-11

    We report the first investigation of the topology of spin-polarized charge density, specifically in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical. In these cases, the two spin densities are correlated: the spin-minority electrons have directional bond paths and deep minima, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of distinct spin topologies allows us to show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter involves a topological catastrophe. PMID:18232817

  8. Topology of the Spin-Polarized Charge Density in bcc and fcc Iron

    NASA Astrophysics Data System (ADS)

    Jones, Travis E.; Eberhart, Mark E.; Clougherty, Dennis P.

    2008-01-01

    We report the first investigation of the topology of spin-polarized charge density, specifically in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical. In these cases, the two spin densities are correlated: the spin-minority electrons have directional bond paths and deep minima, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of distinct spin topologies allows us to show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter involves a topological catastrophe.

  9. Kinetics of disorder-to-fcc phase transition via an intermediate bcc state

    SciTech Connect

    Liu Yongsheng; Nie Huifen; Bansil, Rama; Steinhart, Milos; Bang, Joona; Lodge, Timothy P.

    2006-06-15

    Time-resolved small-angle x-ray scattering measurements reveal that a long-lived intermediate bcc state forms when a poly(styrene-b-isoprene) diblock copolymer solution in an isoprene selective solvent is rapidly cooled from the disordered micellar fluid at high temperature to an equilibrium fcc state. The kinetics of the epitaxial growth of the [111] fcc peak from the [110] bcc peak was obtained by fitting the scattering data to a simple model of the transformation. The growth of the [111] fcc peak agrees with the Avrami model of nucleation and growth kinetics with an exponent n=1.4, as does the initial decay of the [110] bcc peak, with an exponent n=1.3. The data were also found to be in good agreement with the Cahn model of grain boundary nucleation and growth.

  10. Crystallographic dependence of CO activation on cobalt catalysts: HCP versus FCC.

    PubMed

    Liu, Jin-Xun; Su, Hai-Yan; Sun, Da-Peng; Zhang, Bing-Yan; Li, Wei-Xue

    2013-11-01

    Identifying the structure sensitivity of catalysts in reactions, such as Fischer-Tropsch synthesis from CO and H2 over cobalt catalysts, is an important yet challenging issue in heterogeneous catalysis. Based on a first-principles kinetic study, we find for the first time that CO activation on hexagonal close-packed (HCP) Co not only has much higher intrinsic activity than that of face centered-cubic (FCC) Co but also prefers a different reaction route, i.e., direct dissociation with HCP Co but H-assisted dissociation on the FCC Co. The origin is identified from the formation of various denser yet favorable active sites on HCP Co not available for FCC Co, due to their distinct crystallographic structure and morphology. The great dependence of the activity on the crystallographic structure and morphology of the catalysts revealed here may open a new avenue for better, stable catalysts with maximum mass-specific reactivity. PMID:24147726

  11. Prediction of a metastable cubic phase for the transition metals with hcp ground state.

    NASA Astrophysics Data System (ADS)

    de Coss, Romeo; Aguayo, Aaron; Murrieta, Gabriel

    2007-03-01

    The discovery of a metastable phase for a given material is interesting because corresponds to a new bonding and new properties are expected. The calculation of the total-energy along the Bain path is frequently used as a method to find tetragonal metastable states. However, a local minimum in the tetragonal distortion is not a definitive proof of a metastable state, and the elastic stability needs to be evaluated. In a previous work, using the elastic stability criteria for a cubic structure, we have shown that the transition metals with hcp ground state; Ti, Zr, and Hf have a fcc metastable phase [Aguayo, G. Murrieta, and R. de Coss, Phys. Rev. B 65, 092106 (2002)]. That result is interesting since the fcc crystal structure does not appear in the current pressure-temperature phase diagram of these metals, and support the experimental observations of fcc Ti and Zr in thin films. In the present work, we extend the elastic stability study of the fcc structure to the non-magnetic transition metals with hcp ground state; Sc, Ti, Y, Zr, Tc, Ru, Hf, Re, and Os. We find that all the metals involved in this study have a metastable fcc structure. From these results, substrates on which the fcc structure of these metals could be growth epitaxially are predicted.

  12. Orthogonalized operators for the f shell

    SciTech Connect

    Judd, B.R.; Crosswhite, H.

    1984-04-01

    Orthogonalized operators are introduced in the atomic configurations f/sup N/ in order to yield parameters that are more precisely defined and more stable than the conventional ones. Of the four Racah operators e/sub 0/, e/sub 1/, e/sub 2/, only e/sub 1/ needs adjusting. The set of two-electron scalars is made complete by the generalized Trees operators e/sub ..cap alpha../', e/sub ..beta../', and e/sub ..gamma../'. Of the three-electron scalars t/sub i/, only t/sub 2/ requires alteration. The theory is illustrated for f/sup 3/ by adding the orthogonalized operators in successive steps and comparing the fits with those obtained if the conventional operators are used.

  13. Spent fluid catalytic cracking catalyst (FCC) applications in the preparation of hydraulic binders: Pozzolanic properties study

    NASA Astrophysics Data System (ADS)

    Velazquez Rodriguez, Sergio

    At the present work the replacement of Portland cement in pastes and mortars by spent fluid catalytic cracking catalyst (FCC) is studied. The study has been focused in four physicochemical characterization, hydrated lime/catalyst and cement/catalyst pastes and mortars studies, and environmental impact aspects. The FCC characterization establishes that it is a silicoaluminate, having a mainly amorphous structure, with a great specific surface, and that is necessary its mechanical activation (grinding) to obtain a pozzolanic behaviour material. The reactivity was studied by: thermogravimetry, X ray diffractometry, aqueous media electrical conductivity measurements, Fourier transform infrared spectroscopy, scanning electron microscopy, mechanical strength development evaluation and cementing effectiveness k-factor evaluation. The very high pozzolanic activity of the material has been demonstrated, besides that this reactivity has been superior to others similar products such as the metakaolin. The products formed in the hydration, pozzolanic and hydration catalysis of cement reactions have been studied, comparing the reactivity characteristics with others better known pozzolans. The nature of the reaction products between FCC and hydrated lime is similar to the ones formed by the metakaolin, being fundamentally calcium silicate hydrates and hydrated gehlenite, and their formation allow to obtain microstructures with higher mechanical strength. The possibility of preparation materials containing cement/FCC with improved mechanical strength and drying shrinkage has been demonstrated, compared to homologous materials without ground FCC. The optimal FCC dosage for the lime fixation maximization has been determined, showing a pozzolanic behaviour similar to metakaolin, nevertheless very superior to others studied pozzolans, behaviour that is improved with the aid of certain chemical activators, and with the increasing of the curing temperature. Measurements of electrical

  14. 76 FR 12733 - Shenzhen Tangreat Technology Co., Ltd., Grantee of Equipment Authorization FCC ID No. XRLTG-VIPJAMM

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-08

    ... COMMISSION Shenzhen Tangreat Technology Co., Ltd., Grantee of Equipment Authorization FCC ID No. XRLTG... hearing proceeding by directing Shenzhen Tangreat Technology Co., Ltd. (``Shenzhen''), Grantee of... Technology Co., Ltd. (``Shenzhen'') to show cause why the equipment authorization it holds under FCC ID...

  15. Two-mode Ginzburg-Landau theory of crystalline anisotropy for fcc-liquid interfaces

    NASA Astrophysics Data System (ADS)

    Wu, Kuo-An; Lin, Shang-Chun; Karma, Alain

    2016-02-01

    We develop a Ginzburg-Landau (GL) theory for fcc crystal-melt systems at equilibrium by employing two sets of order parameters that correspond to amplitudes of density waves of principal reciprocal lattice vectors and amplitudes of density waves of a second set of reciprocal lattice vectors. The choice of the second set of reciprocal lattice vectors is constrained by the condition that this set must form closed triangles with the principal reciprocal lattice vectors in reciprocal space to make the fcc-liquid transition first order. The capillary anisotropy of fcc-liquid interfaces is investigated by GL theory with amplitudes of <111 > and <200 > density waves. Furthermore, we explore the dependence of the anisotropy of the excess free energy of the solid-liquid interface on density waves of higher-order reciprocal lattice vectors such as <311 > by extending the two-mode GL theory with an additional mode. The anisotropy calculated using GL theory with input parameters from molecular dynamics (MD) simulations for fcc Ni is compared to that measured in MD simulations.

  16. 75 FR 34450 - FCC to Hold Open Commission Meeting Thursday, June 17, 2010

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-17

    ... COMMISSION FCC to Hold Open Commission Meeting Thursday, June 17, 2010 DATES: June 10, 2010. The Federal Communications Commission will hold an Open Meeting on the subject listed below on Thursday, June 17, 2010, which... consideration at the open meeting on June 17. BUREAU SUBJECT OFFICE OF THE TITLE: Framework GENERAL COUNSEL....

  17. Nitrogen Chemistry and Coke Transformation of FCC Coked Catalyst during the Regeneration Process.

    PubMed

    Shi, Junjun; Guan, Jianyu; Guo, Dawei; Zhang, Jiushun; France, Liam John; Wang, Lefu; Li, Xuehui

    2016-01-01

    Regeneration of the coked catalyst is an important process of fluid catalytic cracking (FCC) in petroleum refining, however, this process will emit environmentally harmful gases such as nitrogen and carbon oxides. Transformation of N and C containing compounds in industrial FCC coke under thermal decomposition was investigated via TPD and TPO to examine the evolved gaseous species and TGA, NMR and XPS to analyse the residual coke fraction. Two distinct regions of gas evolution are observed during TPD for the first time, and they arise from decomposition of aliphatic carbons and aromatic carbons. Three types of N species, pyrrolic N, pyridinic N and quaternary N are identified in the FCC coke, the former one is unstable and tends to be decomposed into pyridinic and quaternary N. Mechanisms of NO, CO and CO2 evolution during TPD are proposed and lattice oxygen is suggested to be an important oxygen resource. Regeneration process indicates that coke-C tends to preferentially oxidise compared with coke-N. Hence, new technology for promoting nitrogen-containing compounds conversion will benefit the in-situ reduction of NO by CO during FCC regeneration. PMID:27270486

  18. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (CB Rule 28) How do I contact the FCC? 95.428 Section 95.428 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know §...

  19. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (CB Rule 28) How do I contact the FCC? 95.428 Section 95.428 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know §...

  20. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (R/C Rule 25) How do I contact the FCC? 95.225 Section 95.225 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other Things You Need to Know §...

  1. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other...

  2. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other...

  3. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other...

  4. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other...

  5. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (R/C Rule 25) How do I contact the FCC? 95.225 Section 95.225 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other Things You Need to Know §...

  6. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (R/C Rule 25) How do I contact the FCC? 95.225 Section 95.225 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other Things You Need to Know §...

  7. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (CB Rule 28) How do I contact the FCC? 95.428 Section 95.428 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know §...

  8. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (R/C Rule 25) How do I contact the FCC? 95.225 Section 95.225 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other Things You Need to Know §...

  9. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (CB Rule 28) How do I contact the FCC? 95.428 Section 95.428 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know §...

  10. 47 CFR 95.422 - (CB Rule 22) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (CB Rule 22) How do I answer correspondence from the FCC? 95.422 Section 95.422 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other...

  11. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (R/C Rule 25) How do I contact the FCC? 95.225 Section 95.225 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other Things You Need to Know §...

  12. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (CB Rule 28) How do I contact the FCC? 95.428 Section 95.428 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know §...

  13. Exchange coupled L10-FePt/fcc-FePt nanomagnets: Synthesis, characterization and magnetic properties

    NASA Astrophysics Data System (ADS)

    Srivastava, Sachchidanand; Gajbhiye, Namdeo S.

    2016-03-01

    We report synthesis, characterization and magnetic properties of exchange-coupled L10-FePt/fcc-FePt nanomagnets. Structural and morphological characterization of exchange-coupled L10-FePt/fcc-FePt was carried out by powder X-ray diffraction, Mössbauer spectroscopy and transmission electron microscopy. Rietveld refinement of powder X-ray diffraction pattern has been used to quantify L10-FePt and fcc-FePt phases present in samples. Room temperature Mössbauer spectroscopy showed sextets of both L10-FePt and fcc-FePt phases with their respective hyperfine interaction parameters. Transmission electron microscopic (TEM and HRTEM) images confirmed nanocrystalline nature of exchange-coupled nanomagnets with particle size ranges from 15 nm to 50 nm after annealing for different time at 700 °C. Room temperature magnetic studies showed ferromagnetic nature of nanomagnets and maximum energy product (BH)max~10.92 MGOe was obtained for sample containing 89.0% volume fraction of L10-FePt phase.

  14. Nitrogen Chemistry and Coke Transformation of FCC Coked Catalyst during the Regeneration Process

    NASA Astrophysics Data System (ADS)

    Shi, Junjun; Guan, Jianyu; Guo, Dawei; Zhang, Jiushun; France, Liam John; Wang, Lefu; Li, Xuehui

    2016-06-01

    Regeneration of the coked catalyst is an important process of fluid catalytic cracking (FCC) in petroleum refining, however, this process will emit environmentally harmful gases such as nitrogen and carbon oxides. Transformation of N and C containing compounds in industrial FCC coke under thermal decomposition was investigated via TPD and TPO to examine the evolved gaseous species and TGA, NMR and XPS to analyse the residual coke fraction. Two distinct regions of gas evolution are observed during TPD for the first time, and they arise from decomposition of aliphatic carbons and aromatic carbons. Three types of N species, pyrrolic N, pyridinic N and quaternary N are identified in the FCC coke, the former one is unstable and tends to be decomposed into pyridinic and quaternary N. Mechanisms of NO, CO and CO2 evolution during TPD are proposed and lattice oxygen is suggested to be an important oxygen resource. Regeneration process indicates that coke-C tends to preferentially oxidise compared with coke-N. Hence, new technology for promoting nitrogen-containing compounds conversion will benefit the in-situ reduction of NO by CO during FCC regeneration.

  15. 76 FR 69738 - Revised 2011 Annual Telecommunications Reporting Worksheet (FCC Form 499-A) and Accompanying...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-09

    ...-interconnected VoIP filers subject to TRS contribution obligations must submit the FCC Form 499-A to register... Relay Services Fund (TRS Fund). The revisions to the Form and accompanying instructions include the... for non-interconnected VoIP service providers with interstate end-user revenues subject to TRS...

  16. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false State and Local Area plans and FCC Mapbook. 11.21 Section 11.21 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL EMERGENCY ALERT SYSTEM... emergency alert system is capable of initiating EAS messages formatted in the Common Alerting Protocol...

  17. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false State and Local Area plans and FCC Mapbook. 11.21 Section 11.21 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL EMERGENCY ALERT SYSTEM... emergency alert system is capable of initiating EAS messages formatted in the Common Alerting Protocol...

  18. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false State and Local Area plans and FCC Mapbook. 11.21 Section 11.21 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL EMERGENCY ALERT SYSTEM... emergency alert system is capable of initiating EAS messages formatted in the Common Alerting Protocol...

  19. Phonons transmission by thin films sandwiched between two similar fcc structures

    NASA Astrophysics Data System (ADS)

    Belkacemi, Ghania; Bourahla, Boualem

    2015-09-01

    An analytical and numerical formalism are developed to study the influence of the sandwiched atomic films on the vibration properties and phonon transmission modes in fcc waveguides. The model system consists of two identical semi-infinite fcc leads joined by ultrathin atomic films in between. The matching technique is applied to calculate the local Green's functions for the irreducible set of sites that constitute the inhomogeneous domain. Numerical results are presented for the reflection/transmission, total phonon transmittance and localized vibration states in considered fcc lattices. The results show that vibrational properties of the sandwich materials are strongly dependent on the scattering frequency, the thickness of the insured films, incidence angles and elastic boundary conditions. We note that some of the fluctuations, observed in the vibration spectra, are related to Fano resonances, they are due to the coherent coupling between travelling phonons and the localized vibration modes in the neighborhood of the nanojunction domains. The number of localized modes which interact with the propagating modes of the continuum is proportional to the number of the sandwiched Slabs in the interfacial zone. The results give also the effect of the sandwiched ultrathin films on elastic waves propagation by atomic interfaces in fcc lattices.

  20. Government Ownership Restrictions and Efficiency: The Case of the FCC's Dupoply Rule.

    ERIC Educational Resources Information Center

    Anderson, Keith B.; Woodbury, John R.

    Recently the Federal Communications Commission (FCC) has been considering modifications to its regulations governing local and national media ownership and has indicated more interest in the efficiency consequences of the regulations, including those that might arise from common ownership of multiple radio stations. This paper seeks to determine…

  1. The FCC's AM Stereo Experiment: Seven Years in the Uncharted Broadcast Marketplace.

    ERIC Educational Resources Information Center

    Huff, W. A. Kelly

    To examine the success of the Federal Communications Commission's (FCC) 1982 decision not to select a standard transmission system for AM stereophonic broadcasting (instead leaving it to the marketplace), this paper documents and analyzes the first 7 years of the AM stereo marketplace. Following an explanatory introduction, the paper's first…

  2. Letter of Complaint to the FCC Against the Columbia Broadcasting System.

    ERIC Educational Resources Information Center

    Council on Children, Media, and Merchandising, Washington, DC.

    The Council on Children, Media, and Merchandising, in a letter to the Federal Communication Commission (FCC), issued a formal complaint against the Columbia Broadcasting System (CBS). The Council charges that CBS has failed to meet its public interest obligations, as well as its obligations under the fairness doctrine, with respect to advertising…

  3. The Ignominious Death of FCC Docket 19142: Ending the Crusade for Children's Television.

    ERIC Educational Resources Information Center

    McGregor, Michael A.

    On December 22, 1983, the Federal Communications Commission formally ended its consideration of rule making for children's television programing. Opponents of government regulation view the FCC's decision as a victory for the First Amendment freedoms of speech and the press; proponents of mandatory children's programing guidelines feel that the…

  4. Nitrogen Chemistry and Coke Transformation of FCC Coked Catalyst during the Regeneration Process

    PubMed Central

    Shi, Junjun; Guan, Jianyu; Guo, Dawei; Zhang, Jiushun; France, Liam John; Wang, Lefu; Li, Xuehui

    2016-01-01

    Regeneration of the coked catalyst is an important process of fluid catalytic cracking (FCC) in petroleum refining, however, this process will emit environmentally harmful gases such as nitrogen and carbon oxides. Transformation of N and C containing compounds in industrial FCC coke under thermal decomposition was investigated via TPD and TPO to examine the evolved gaseous species and TGA, NMR and XPS to analyse the residual coke fraction. Two distinct regions of gas evolution are observed during TPD for the first time, and they arise from decomposition of aliphatic carbons and aromatic carbons. Three types of N species, pyrrolic N, pyridinic N and quaternary N are identified in the FCC coke, the former one is unstable and tends to be decomposed into pyridinic and quaternary N. Mechanisms of NO, CO and CO2 evolution during TPD are proposed and lattice oxygen is suggested to be an important oxygen resource. Regeneration process indicates that coke-C tends to preferentially oxidise compared with coke-N. Hence, new technology for promoting nitrogen-containing compounds conversion will benefit the in-situ reduction of NO by CO during FCC regeneration. PMID:27270486

  5. The influence of defects on magnetic properties of fcc-Pu

    SciTech Connect

    Shorikov, A. O.; Anisimov, V. I.; Korotin, M. A.; Dremov, V. V. Sapozhnikov, Ph. A.

    2013-10-15

    The influence of vacancies and interstitial atoms on magnetism in Pu is considered in the framework of the density functional theory. The crystal structure relaxation arising due to various types of defects is calculated using the molecular dynamics method with a modified embedded atom model. The local density approximation with explicit inclusion of Coulomb and spin-orbit interactions is applied in matrix invariant form to describe correlation effects in Pu with these types of defects. The calculations show that both vacancies and interstitials give rise to local moments in the f-shell of Pu in good agreement with experimental data for aged Pu. Magnetism appears due to the destruction of a delicate balance between spin-orbit and exchange interactions.

  6. Plastic flow in FCC metals induced by single-ion impacts.

    SciTech Connect

    Birtcher, R. C.; Donnelly, S. E.

    1997-10-30

    Irradiation of Au and Pb foils with Xe ions at temperatures between 30 and 450 K has been monitored using in-situ transmission electron microscopy. Single ion impacts give rise to surface craters on the irradiated surface with sizes as large as 12 nm. Approximately 2--5% of impinging ions produce craters on Au while only about 0.6% produce craters on Pb. Larger craters on Au frequently have expelled material associated with them. Temporal details of crater formation and annihilation has been recorded on video with a time-resolution of 33 milliseconds. Craters annihilate in discrete steps due to subsequent ion impacts or anneal in a continuous manner due to surface diffusion. Craters production (those persisting for one or more video-frames) as a function of temperature indicates that the surface diffusion process responsible for thermal annealing of craters has an activation energy of 0.76 eV in Au. Crater creation results from plastic flow associated with near surface cascades. Crater annihilation in discrete steps results from plastic flow induced by subsequent ion impacts, including those that do not themselves produce a crater.

  7. Plastic flow in fcc metals induced by single-ion impacts

    SciTech Connect

    Birtcher, R.C.; Donnelly, S.E.

    1997-09-01

    Irradiation of Au and Pb foils with Xe ions at temperatures between 30 and 450 K has been monitored using in-situ transmission electron microscopy. Single ion impacts give rise to surface craters on the irradiated surface with sizes as large as 12 nm. Approximately 2--5% of impinging ions produce craters on Au while only about 0.6% produce craters on Pb. Larger craters on Au frequently have expelled material associated with them. Temporal details of crater formation and annihilation has been recorded on video with a time resolution of 33 milliseconds. Craters annihilate in discrete steps due to subsequent ion impacts or anneal in a continuous manner due to surface diffusion. Craters production (those persisting for one or more video frames) as a function of temperature indicates that the surface diffusion process responsible for thermal annealing of craters has an activation energy of 0.76 eV in Au. Crater creation results from plastic flow associated with near surface cascades. Crater annihilation in discrete steps results from plastic flow induced by subsequent ion impacts, including those that do not themselves produce a crater.

  8. A calculation of the diffusion energies for adatoms on surfaces of F.C.C. metals

    NASA Technical Reports Server (NTRS)

    Halicioglu, T.; Pound, G. M.

    1979-01-01

    The activation energies for diffusion were determined for gold, platinum and iridium adatoms on plane and plane PT surfaces and were found to be in good agreement with the measurements reported by Bassett and Webber. The Lennard-Jones pair potentials were used to model the interatomic forces, and relaxation of the substrate atoms in near proximity to the adatom was considered in detail. The present calculations clarify the mechanism of the observed two-dimensional diffusion of platinum and iridium atoms on a plane PT surface. The results are compared with those obtained using Morse potential functions and different relaxation techniques.

  9. Ultra short-time dynamics of radiation damage in fcc metals

    SciTech Connect

    Hayoun, Marc; Coddens, Gerrit; Petite, Guillaume

    2009-11-01

    We have performed molecular-dynamics simulations of displacement cascades in copper in order to investigate the nonequilibrium ultra-short-time damage and to evaluate the possibility of observing it experimentally in situ (e.g., in a pump/probe laser experiment). The atomic trajectories have been analyzed by calculating their x-ray diffraction patterns as a function of time. The results show that an integrated x-ray intensity can indeed be used to evidence the irradiation effects. Even though the number of Frenkel defects is large, the main effect of the irradiation showing up in the x-ray intensities at ultrashort times is an important alteration of the lattice vibrations. On the basis of these results, a pump/probe setup is proposed.

  10. Unusual cluster shapes and directional bonding of an fcc metal: Pt/Pt(111).

    PubMed

    Schmid, Michael; Garhofer, Andreas; Redinger, Josef; Wimmer, Florian; Scheiber, Philipp; Varga, Peter

    2011-07-01

    Small clusters of Pt adatoms grown on Pt(111) exhibit a preference for the formation of linear chains, which cannot be explained by simple diffusion-limited aggregation. Density functional theory calculations show that short chains are energetically favorable to more compact configurations due to strong directional bonding by d(z)(2)-like orbitals, explaining the stability of the chains. The formation of the chains is governed by substrate distortions, leading to funneling towards the chain ends. PMID:21797553

  11. The Hexagonal Close-Packed (HCP) ⇆ Face-Centered Cubic (FCC) Transition in Co-Re-Based Experimental Alloys Investigated by Neutron Scattering

    NASA Astrophysics Data System (ADS)

    Mukherji, Debashis; Strunz, Pavel; Piegert, Sebastian; Gilles, Ralph; Hofmann, Michael; Hölzel, Markus; Rösler, Joachim

    2012-06-01

    Co-Re-based alloys have been developed to supplement the Ni-base superalloys used in gas turbine applications at high temperatures (1473 K [1200 °C] bare metal temperature). Unlike other commercial Co-based alloys, the Co matrix in the Co-Re alloys has a stable hexagonal close-packed (hcp) structure at room temperature. In situ neutron diffraction measurements on experimental Co-Re alloys hardened by carbide precipitates showed that the matrix undergoes an hcp ⇆ face-centered cubic (fcc) allotropic transformation after heating to high temperatures. Furthermore, it was found that this transformation has a large hysteresis (~100 K). Thermodynamic calculations were undertaken to study the high-temperature phase stability and transformations in the complex multicomponent, multiphase Co-Re-Cr-C system with or without the addition of Ta. The results show that the minor phases (Cr23C6-type carbides and the Cr2Re3-type σ phase) play an important role in the hcp ⇆ fcc hysteresis by influencing the partitioning of Cr and Re between the matrix and the other phases.

  12. In Situ Determination of BCC-, FCC- and HPC-Iron Textures at Simultaneous High- Pressure and -Temperature by Means of the Resistive Heated Radial Diffraction Diamond Anvil Cell (RH-RD-DAC): Implications for the iron core.

    NASA Astrophysics Data System (ADS)

    Liermann, H.; Merkel, S.; Miyagi, L.; Wenk, H.; Shen, G.; Cynn, H.; Evans, W. J.

    2008-12-01

    Radial diffraction in the diamond anvil cell (DAC) has long been used to determine the stress state of materials under non-hydrostatic compression. This technique is also a major tool to investigate textures and infer deformation mechanisms in the earth mantle and core. However, most of these experiments have been conducted at ambient temperatures and therefore the results of these measurements may be difficult to extrapolate to the deep Earth. Here, we present texture data collected at HPCAT sector 16 BMD of the Advanced Photon Source during the plastic deformation of BCC-, FCC- and HPC-iron at simultaneous high-pressure and temperature in the new Resistive Heated Radial Diffraction Diamond Anvil Cell (RH-RD-DAC). Initial results from Rietveld refinements in MAUD indicate that BCC- iron develops a mixed {100} and {111} texture that remains active during heating. Latter is compatible with previous observations on BCC-iron and interpreted as slip along {110}<111>. Texture obtained after formation of FCC-iron at simultaneous high- pressure and temperatures show a pronounced maximum at {110} with minima at {100} and {111}. This texture is typical for FCC metals in compression with slip on {111}<110>. Processing of the HCP-iron textures at high-pressure and -temperature are under way. We will discuss the implications that the experimental results have for the deformation mechanisms of iron at pressure temperature conditions of the inner core.

  13. 3D crack tip fields for FCC single crystals

    SciTech Connect

    Cuitino, A.M.; Ortiz, M.

    1995-12-31

    Cracks in single crystals are of concern in a number of structural and non-structural applications, ranging form single-crystal turbine blades and rotors to metal interconnect lines in microcircuits. In this paper we present 3D numerical simulations of the crack-tip fields of a Cu single crystal, including stress, strain and slip activity patterns. The orientation of the crack tip is along the crystallographic orientation (101), while the crack plane is (010). A material model based on dislocation mechanics is used in these simulations. This model correctly predicts the observed behavior of Cu, including the basic hardening characteristics of single crystals, orientation dependence and stage I-II-III structure of the stress-strain curves, the observed levels of latent hardening and their variation with orientation and deformation in the primary system and slip activities and dislocation densities. We use the FEM within the context of finite deformation plasticity. In the figure below, we show the finite element mesh composed by 12-noded tetrahedrons with 6-noded triangular faces. The model simulates half of a beam, which is subjected to a concentrated load at 1/8 of total length from the support. Detailed results of the stress, deformation and slip activity are presented at different radii from crack tip and at different depths from the surface. In general, the results show a strong difference in the slip activity pattern form the interior to the exterior, while smaller differences are encountered in the stress and strain fields.

  14. Size dependence and phase transition during melting of fcc-Fe nanoparticles: A molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Shen, Tong; Meng, Wenjian; Wu, Yongquan; Lu, Xionggang

    2013-07-01

    Continuous melting and cooling of isolated fcc-Fe nanoparticles with 59-9577 atoms are studied by Molecular Dynamics (MD) simulation with Sutton-Chen potential. An energy minimization process was employed to obtain the stable solid structure for simulation of melting. The energy-minimized nanoparticles show lower potential energy and radius compared with the counterparts without energy minimizing. The size dependence of melting point shows perfect linear variation with N-1/3 for particles above a limit of 113 atoms. The bulk melting temperature of 1833.3 K, which is close to the experimental data (1811 K for bcc and 1800.8 K for fcc), has been predicted by a linear relationship. Two different inner structures, including five-fold twinning and lamellar structures, have been found to be the initial stable configurations prior to melting, and both surface premelting and internal defects were verified as the origins for melting behavior.

  15. Atomic Mobilities and Interdiffusivities for fcc Ni-Cr-Nb Alloys

    NASA Astrophysics Data System (ADS)

    Xu, Gaochi; Liu, Yajun; Kang, Zhitao

    2016-06-01

    The atomic mobilities and diffusion characteristics for fcc Ni-Cr-Nb alloys are explored by diffusion couples annealed at 1273 K (1000 °C) for 200 hours. The interdiffusion coefficients are extracted from intersection points of two diffusion paths, after which the atomic mobilities of Ni, Cr, and Nb in fcc Ni-Cr-Nb alloys are inversely obtained within the CALPHAD framework with the aid of related thermodynamic descriptions. In order to verify the quality of obtained kinetic parameters so that an accurate Ni-based atomic mobility database can be established, the composition profiles in diffusion couples and the diffusion paths superimposed upon Gibbs triangle are explored, where the experimentally measured and calculated values show good agreement.

  16. FCC reactor product-catalyst separation: Ten years of commercial experience with closed cyclones

    SciTech Connect

    Miller, R.B.; Johnson, T.E.; Santner, C.R.; Avidan, A.A.; Johnson, D.L.

    1995-09-01

    FCC reactor closed cyclones were first commercialized ten years ago and have now been installed in over 22 FCC units worldwide. Cumulative commercial experience has shown significant yield benefits, in some cases higher than first estimated, and excellent reliability. By nearly eliminating post-riser cracking, they reduce dry gas make and produce higher yields of desirable liquid products. Trouble-free operation with closed cyclones is attributed to proper design, instrumentation, and operating procedures. The Mobil-Kellogg Closed Cyclone technology is the only design offered for license which uses the positive-pressure riser cyclone system which has proven to be least sensitive to upsets. This paper traces the development and commercialization of closed cyclones, discusses differences between competing closed cyclone designs, and documents the benefits which have been observed for Mobil-Kellogg Closed Cyclones.

  17. The impact of the Family Communication Coordinator (FCC) Protocol on the role stress of hospital chaplains.

    PubMed

    Dodd-McCue, Diane; Tartaglia, Alexander

    2005-01-01

    The Family Communication Coordinator (FCC) Protocol was implemented to provide early family intervention and to facilitate effective communications during potential organ donation cases. Previous studies found the Protocol associated with improved donor outcome measures and with reduced role stress for ICU nurses caring for potential donors. The present study examines the impact of the Protocol on the perceived role stress of hospital chaplains serving as FCCs. All hospital chaplains serving as FCCs at an academic teaching hospital were surveyed. Their perceptions of job dimensions, role stress, job satisfaction, and commitment were measured; interviews and secondary data supplemented the surveys. The findings demonstrate that the FCC Protocol is associated with improved role stress, specifically role ambiguity and role conflict, among hospital chaplains serving as FCCs. Additionally, the findings suggest that satisfaction with the Protocol may be associated with experience with the Protocol. PMID:16392645

  18. Effect of uniaxial tensile stress on the isomer shift of 57Fe in fcc stainless steels

    NASA Astrophysics Data System (ADS)

    Ratner, E.; Ron, M.

    1982-05-01

    The electron wave-function response to uniaxial tensile stress in fcc steels (SS310 and SS316) was investigated through the isomer shift of the Mössbauer effect. Stresses up to 12 kbar (the ultimate tensile stress is approximately 14 kbar) were applied at room temperature. The isomer shift changes linearly in these circumstances. It is concluded that, as in the case of hydrostatic pressure, the paramount factor here is the volume strain of the wave functions of 4S electrons.

  19. Solidification and fcc- to metastable hcp- phase transition in krypton under modulating dynamic pressures

    NASA Astrophysics Data System (ADS)

    Chen, Jing-Yin; Yoo, Choong-Shik; Kim, Minseob; Liermann, Hanns-Peter; Cynn, Hyunchae; Jenei, Zsolt; Evans, William

    2014-03-01

    We describe high-pressure kinetic studies of the solidification, melting and fcc-hcp transitions of Krypton under dynamic loading conditions, using a dynamic-diamond anvil cell (d-DAC) coupled with time-resolved x-ray diffraction. The time-resolved diffraction patterns and dynamic pressure responses show compression-rate dependencies associated with both the decay and growth time constants of the liquid-solid and solid-liquid transitions. According to the Avrami equation, both the solidified and melting processes are spontaneous nucleation and a rod-like (1-D) growth. Furthermore, under dynamic loading conditions, Kr-hcp forms from fcc close to the melting line. The nucleation time of fcc and hcp are very fast, with little dependence of compression rates or shorter than the time resolutions. The threshold pressure for the formation of Kr-hcp is ~ 0.8 GPa at the dynamic loadings of 0.004-13 GPa/s. This work was carried out at DESY. This work was performed under the auspices of DOE by LLNL under contracts(W-7405-Eng-48 and DE-AC52-07NA27344) and funded by the LDRD(11-ERD-046). The work at WSU was funded by NSF-DMR(1203834), DTRA(HDTRA1-12-01-0020).

  20. fcc-hcp phase transformation in Co nanoparticles induced by swift heavy-ion irradiation

    NASA Astrophysics Data System (ADS)

    Sprouster, D. J.; Giulian, R.; Schnohr, C. S.; Araujo, L. L.; Kluth, P.; Byrne, A. P.; Foran, G. J.; Johannessen, B.; Ridgway, M. C.

    2009-09-01

    We demonstrate a face-centered cubic (fcc) to hexagonally close-packed (hcp) phase transformation in spherical Co nanoparticles achieved via swift heavy-ion irradiation. Co nanoparticles of mean diameter 13.2 nm and fcc phase were first formed in amorphous SiO2 by ion implantation and thermal annealing and then irradiated at room temperature with 9-185 MeV Au ions. The crystallographic phase was identified with x-ray absorption spectroscopy and electron diffraction and quantified, as functions of the irradiation energy and fluence, with the former. The transformation was complete at low fluence prior to any change in nanoparticle shape or size and was governed by electronic stopping. A direct-impact mechanism was identified with the transformation interaction cross-section correlated with that of a molten ion track in amorphous SiO2 . We suggest the shear stress resulting from the rapid thermal expansion about an ion track in amorphous SiO2 was sufficient to initiate the fcc-to-hcp phase transformation in the Co nanoparticles.

  1. Meteorites and thermodynamic equilibrium in f.c.c. iron-nickel alloys /25-50% Ni/

    NASA Astrophysics Data System (ADS)

    Albertsen, J. F.; Knudsen, J. M.; Roy-Poulsen, N. O.; Vistisen, L.

    Mossbauer spectroscopy and X-ray investigations show that taenite (fcc iron-nickel alloy) in meteorites generally has decomposed into an ordered phase FeNi with the L10 structure and a disordered fcc iron-nickel alloy containing less than 25% Ni. The two phases have the same bravais lattice, i.e., they form a pseudo monocrystal. The decomposition is discussed in terms of Fe-Ni phase diagram.

  2. Mixed valent metals.

    PubMed

    Riseborough, P S; Lawrence, J M

    2016-08-01

    We review the theory of mixed-valent metals and make comparison with experiments. A single-impurity description of the mixed-valent state is discussed alongside the description of the nearly-integer valent or Kondo limit. The degeneracy N of the f-shell plays an important role in the description of the low-temperature Fermi-liquid state. In particular, for large N, there is a rapid cross-over between the mixed-valent and the Kondo limit when the number of f electrons is changed. We discuss the limitations on the application of the single-impurity description to concentrated compounds such as those caused by the saturation of the Kondo effect and those due to the presence of magnetic interactions between the impurities. This discussion is followed by a description of a periodic lattice of mixed-valent ions, including the role of the degeneracy N. The article concludes with a comparison of theory and experiment. Topics covered include the single-impurity Anderson model, Luttinger's theorem, the Friedel sum rule, the Schrieffer-Wolff transformation, the single-impurity Kondo model, Kondo screening, the Wilson ratio, local Fermi-liquids, Fermi-liquid sum rules, the Noziéres exhaustion principle, Doniach's diagram, the Anderson lattice model, the Slave-Boson method, etc. PMID:27376888

  3. Mixed valent metals

    NASA Astrophysics Data System (ADS)

    Riseborough, P. S.; Lawrence, J. M.

    2016-08-01

    We review the theory of mixed-valent metals and make comparison with experiments. A single-impurity description of the mixed-valent state is discussed alongside the description of the nearly-integer valent or Kondo limit. The degeneracy N of the f-shell plays an important role in the description of the low-temperature Fermi-liquid state. In particular, for large N, there is a rapid cross-over between the mixed-valent and the Kondo limit when the number of f electrons is changed. We discuss the limitations on the application of the single-impurity description to concentrated compounds such as those caused by the saturation of the Kondo effect and those due to the presence of magnetic interactions between the impurities. This discussion is followed by a description of a periodic lattice of mixed-valent ions, including the role of the degeneracy N. The article concludes with a comparison of theory and experiment. Topics covered include the single-impurity Anderson model, Luttinger’s theorem, the Friedel sum rule, the Schrieffer–Wolff transformation, the single-impurity Kondo model, Kondo screening, the Wilson ratio, local Fermi-liquids, Fermi-liquid sum rules, the Noziéres exhaustion principle, Doniach’s diagram, the Anderson lattice model, the Slave-Boson method, etc.

  4. Atom-atom interactions in continuous metallic nanofilms

    NASA Astrophysics Data System (ADS)

    Shirinyan, A. S.; Bilogorodskyy, Yu. S.

    2012-09-01

    Physical reasons of the existence of the nanosystem-size dependence of the potential energy of the neighboring atoms are considered, and a thermodynamic validation of this dependence is given. Solid nanofilms of monoatomic metallic systems having an fcc structure are simulated by the molecular-statics method with the Morse and Sutton-Chen potentials.

  5. The t-matrix resistivity of liquid rare earth metals using pseudopotential

    SciTech Connect

    Bhatia, Kamaldeep G.; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.

    2015-06-24

    Present theoretical study of liquid metal resistivity of some trivalent (La,Ce,Gd) and divalent (Eu,Yb) rare earth metals using pseudopotential has been carried out employing Ziman’s weak scattering and transition matrix (t-matrix) approaches. Our computed results of liquid metal resistivity using t-matrix approach are better than resistivity computed using Ziman’s approach and are also in excellent agreement with experimental results and other theoretical findings. The present study confirms that for f-shell metals pseudopotential must be determined uniquely and t-matrix approach is more physical in comparison with Ziman’s nearly free electron approach. The present pseudopotential accounts s-p-d hybridization properly. Such success encourages us to study remaining liquid state properties of these metals.

  6. FCC – An automated rule-based processing tool for life science data

    PubMed Central

    2013-01-01

    Background Data processing in the bioinformatics field often involves the handling of diverse software programs in one workflow. The field is lacking a set of standards for file formats so that files have to be processed in different ways in order to make them compatible to different analysis programs. The problem is that mass spectrometry vendors at most provide only closed-source Windows libraries to programmatically access their proprietary binary formats. This prohibits the creation of an efficient and unified tool that fits all processing needs of the users. Therefore, researchers are spending a significant amount of time using GUI-based conversion and processing programs. Besides the time needed for manual usage, such programs also can show long running times for processing, because most of them make use of only a single CPU. In particular, algorithms to enhance data quality, e.g. peak picking or deconvolution of spectra, add waiting time for the users. Results To automate these processing tasks and let them run continuously without user interaction, we developed the FGCZ Converter Control (FCC) at the Functional Genomics Center Zurich (FGCZ) core facility. The FCC is a rule-based system for automated file processing that reduces the operation of diverse programs to a single configuration task. Using filtering rules for raw data files, the parameters for all tasks can be custom-tailored to the needs of every single researcher and processing can run automatically and efficiently on any number of servers in parallel using all available CPU resources. Conclusions FCC has been used intensively at FGCZ for processing more than hundred thousand mass spectrometry raw files so far. Since we know that many other research facilities have similar problems, we would like to report on our tool and the accompanying ideas for an efficient set-up for potential reuse. PMID:23311610

  7. Proceedings, High-Precision $\\alpha_s$ Measurements from LHC to FCC-ee

    SciTech Connect

    d'Enterria, David; Skands, Peter Z.

    2015-01-01

    This document provides a writeup of all contributions to the workshop on "High precision measurements of $\\alpha_s$: From LHC to FCC-ee" held at CERN, Oct. 12--13, 2015. The workshop explored in depth the latest developments on the determination of the QCD coupling $\\alpha_s$ from 15 methods where high precision measurements are (or will be) available. Those include low-energy observables: (i) lattice QCD, (ii) pion decay factor, (iii) quarkonia and (iv) $\\tau$ decays, (v) soft parton-to-hadron fragmentation functions, as well as high-energy observables: (vi) global fits of parton distribution functions, (vii) hard parton-to-hadron fragmentation functions, (viii) jets in $e^\\pm$p DIS and $\\gamma$-p photoproduction, (ix) photon structure function in $\\gamma$-$\\gamma$, (x) event shapes and (xi) jet cross sections in $e^+e^-$ collisions, (xii) W boson and (xiii) Z boson decays, and (xiv) jets and (xv) top-quark cross sections in proton-(anti)proton collisions. The current status of the theoretical and experimental uncertainties associated to each extraction method, the improvements expected from LHC data in the coming years, and future perspectives achievable in $e^+e^-$ collisions at the Future Circular Collider (FCC-ee) with $\\cal{O}$(1--100 ab$^{-1}$) integrated luminosities yielding 10$^{12}$ Z bosons and jets, and 10$^{8}$ W bosons and $\\tau$ leptons, are thoroughly reviewed. The current uncertainty of the (preliminary) 2015 strong coupling world-average value, $\\alpha_s(m_Z)$ = 0.1177 $\\pm$ 0.0013, is about 1\\%. Some participants believed this may be reduced by a factor of three in the near future by including novel high-precision observables, although this opinion was not universally shared. At the FCC-ee facility, a factor of ten reduction in the $\\alpha_s$ uncertainty should be possible, mostly thanks to the huge Z and W data samples available.

  8. Elastic compliances and stiffnesses of the fcc Lennard-Jones solid

    NASA Astrophysics Data System (ADS)

    Quesnel, D. J.; Rimai, D. S.; Demejo, L. P.

    1993-09-01

    The isothermal elastic compliances, stiffnesses, and bulk moduli of a Lennard-Jones solid organized into an fcc crystal structure (256 atoms in 43 unit cells) have been calculated as a function of testing temperature (expressed as the mean kinetic energy per atom). Tests conducted in pure shear were used to determine S44 and C44=G100, where 100 refers to crystallographic directions. Tests imposing axial elongation with fixed lateral dimensions established C11 and C12. Axial deformation with zero lateral pressure (a tension test) was used to determine S11, S12, E100 and ν100. This provided an independent set of results for comparison with the dilatational stiffnesses C11 and C12. The bulk modulus K was obtained by independent triaxial tension testing. The stiffnesses, compliances, and moduli were determined by regression analysis and digital filtering applied to combinations of the stress-tensor and strain-tensor data stored at each iteration during the constant-rate deformation experiments. While the cubic fcc Lennard-Jones solid expectedly obeys the Cauchy relations for central-force potentials, it is not isotropic, allowing ν to take on values other than 1/4 as originally proposed by Poisson. The present calculations show ν100=0.347 for the fcc Lennard-Jones solid with a Young's modulus of E100=61.1ɛ/σ3, an initial (as indicated by superscript 0) shear modulus of G0100=57.2ɛ/σ3, and an initial bulk modulus of K0=71.2ɛ/σ3 at zero temperature. The moduli all decreased with increasing temperature. Reuss, Voigt, and Hashin and Shtrikman [J. Mech. Phys. Solids 10, 335 (1962)] bounds on the isotropic elastic properties of polycrystalline aggregates of Lennard-Jones material were also determined. Computed values of the moduli are in reasonable agreement with experimental results for solid argon and crystalline polyethylene.

  9. Microstructure and mechanical properties of bulk highly faulted fcc/hcp nanostructured cobalt microstructures

    SciTech Connect

    Barry, Aliou Hamady; Dirras, Guy; Schoenstein, Frederic; Tétard, Florent; Jouini, Noureddine

    2014-05-01

    Nanostructured cobalt powders with an average particle size of 50 nm were synthesized using a polyol method and subsequently consolidated by spark plasma sintering (SPS). SPS experiments performed at 650 °C with sintering times ranging from 5 to 45 min under a pressure of 100 MPa, yielded to dense bulk nanostructured cobalt (relative density greater than 97%). X-ray diffraction patterns of the as-prepared powders showed only a face centered cubic (fcc) crystalline phase, whereas the consolidated samples exhibited a mixture of both fcc and hexagonal close packed (hcp) phases. Transmission electron microscopy observations revealed a lamellar substructure with a high density of nanotwins and stacking faults in every grain of the sintered samples. Room temperature compression tests, carried out at a strain rate of 10{sup −3} s{sup −1}, yielded to highest strain to fracture values of up to 5% for sample of holding time of 15 min, which exhibited a yield strength of 1440 MPa, an ultimate strength as high as 1740 MPa and a Young's modulus of 205 GPa. The modulus of elasticity obtained from the nanoindentation tests, ranges from 181 to 218 GPa. The lowest modulus value of 181 GPa was obtained for the sample with the highest sintering time (45 min), which could be related to mass density loss as a consequence of trapped gases releasing. - Highlights: • Co nanopowder (50 nm) was prepared by reduction in polyol medium. • SPS was used to process bulk nanostructured Co specimens. • Microstructures were made of intricate fcc/hcp, along with nanotwins and SFs. • High strengths and moderate compressive ductility were obtained. • Deformation mechanisms related to complex interplay of different length scales.

  10. Simulation of atomic diffusion in the Fcc NiAl system: A kinetic Monte Carlo study

    SciTech Connect

    Alfonso, Dominic R.; Tafen, De Nyago

    2015-04-28

    The atomic diffusion in fcc NiAl binary alloys was studied by kinetic Monte Carlo simulation. The environment dependent hopping barriers were computed using a pair interaction model whose parameters were fitted to relevant data derived from electronic structure calculations. Long time diffusivities were calculated and the effect of composition change on the tracer diffusion coefficients was analyzed. These results indicate that this variation has noticeable impact on the atomic diffusivities. A reduction in the mobility of both Ni and Al is demonstrated with increasing Al content. As a result, examination of the pair interaction between atoms was carried out for the purpose of understanding the predicted trends.

  11. Synthesis of 4H/fcc-Au@M (M = Ir, Os, IrOs) Core-Shell Nanoribbons For Electrocatalytic Oxygen Evolution Reaction.

    PubMed

    Fan, Zhanxi; Luo, Zhimin; Chen, Ye; Wang, Jie; Li, Bing; Zong, Yun; Zhang, Hua

    2016-08-01

    The high-yield synthesis of 4H/face-centered cubic (fcc)-Au@Ir core-shell nanoribbons (NRBs) is achieved via the direct growth of Ir on 4H Au NRBs under ambient conditions. Importantly, this method can be used to synthesize 4H/fcc-Au@Os and 4H/fcc-Au@IrOs core-shell NRBs. Significantly, the obtained 4H/fcc-Au@Ir core-shell NRBs demonstrate an exceptional electrocatalytic activity toward the oxygen evolution reaction under acidic condition, which is much higher than that of the commercial Ir/C catalyst. PMID:27345872

  12. α-uranium phase in compressed neodymium metal

    NASA Astrophysics Data System (ADS)

    Chesnut, Gary N.; Vohra, Yogesh K.

    2000-02-01

    The light rare-earth metal, neodymium, has been studied up to 155 GPa in a diamond-anvil cell using energy dispersive x-ray diffraction with a synchrotron source. The pressures were calibrated using copper as an internal x-ray pressure standard. A phase transformation from a monoclinic phase (C2/m, 4 atoms/cell) to an orthorhombic α-U phase (Cmcm, 4 atoms/cell) was observed at 113+/-6 GPa without any observable volume collapse. The observation of α-U phase in Nd and, previously, in cerium and praseodymium clearly establishes this phase in light rare-earth metals. Our equation of state measurements suggest that delocalization of the f shell in Nd occurs without any volume collapse unlike Ce and Pr.

  13. On the shock response of cubic metals

    NASA Astrophysics Data System (ADS)

    Bourne, N. K.; Gray, G. T.; Millett, J. C. F.

    2009-11-01

    The response of four cubic metals to shock loading is reviewed in order to understand the effects of microstructure on continuum response. Experiments are described that link defect generation and storage mechanisms at the mesoscale to observations in the bulk. Four materials were reviewed; these were fcc nickel, the ordered fcc intermetallic Ni3Al, the bcc metal tantalum, and two alloys based on the intermetallic phase TiAl; Ti-46.5Al-2Cr-2Nb and Ti-48Al-2Cr-2Nb-1B. The experiments described are in two groups: first, equation of state and shear strength measurements using Manganin stress gauges and, second, postshock microstructural examinations and measurement of changes in mechanical properties. The behaviors described are linked through the description of time dependent plasticity mechanisms to the final states achieved. Recovered targets displayed dislocation microstructures illustrating processes active during the shock-loading process. Reloading of previously shock-prestrained samples illustrated shock strengthening for the fcc metals Ni and Ni3Al while showing no such effect for bcc Ta and for the intermetallic TiAl. This difference in effective shock hardening has been related, on the one hand, to the fact that bcc metals have fewer available slip systems that can operate than fcc crystals and to the observation that the lower symmetry materials (Ta and TiAl) both possess high Peierls stress and thus have higher resistances to defect motion in the lattice under shock-loading conditions. These behaviors, compared between these four materials, illustrate the role of defect generation, transport, storage, and interaction in determining the response of materials to shock prestraining.

  14. Electronic structure and vibrational entropies of fcc Au-Fe alloys

    SciTech Connect

    Munoz, Jorge A.; Lucas, Matthew; Mauger, L; Halevy, I; Horwath, J; Semiatin, S L; Xiao, Yuming; Stone, Matthew B; Abernathy, Douglas L; Fultz, B.

    2013-01-01

    Phonon density of states (DOS) curves were measured on alloys of face-centered-cubic (fcc) Au-Fe using nuclear resonant inelastic x-ray scattering (NRIXS) and inelastic neutron scattering (INS). The NRIXS and INS results were combined to obtain the total phonon DOS and the partial phonon DOS curves of Au and Fe atoms. The 57Fe partial phonon DOS of the dilute alloy Au0.97 57Fe0.03 shows a localized mode centered 4.3% above the cutoff energy of the phonons in pure Au. The Mannheim model for impurity modes accurately reproduced this partial phonon DOS using the fcc Au phonon DOS with a ratio of host-host to impurity-host force constants of 1.55. First-principles calculations validated the assumption of first-nearest-neighbor forces in the Mannheim model and gave a similar ratio of force constants. The high energy local mode broadens with increasing Fe composition, but this has a small effect on the composition dependence of the vibrational entropy. The main effect on the vibrational entropy of alloying comes from a stiffening of the Au partial phonon DOS with Fe concentration. This stiffening is attributed to two main effects: 1) an increase in electron density in the free-electron-like states, and 2) stronger sd-hybridization. These two effects are comparable in magnitude.

  15. Flow-induced alignment of (100) fcc thin film colloidal crystals.

    PubMed

    Joy, Midhun; Muangnapoh, Tanyakorn; Snyder, Mark A; Gilchrist, James F

    2015-09-28

    The realization of structural diversity in colloidal crystals obtained by self-assembly techniques remains constrained by thermodynamic considerations and current limits on our ability to alter structure over large scales using imposed fields and confinement. In this work, a convective-based procedure to fabricate multi-layer colloidal crystal films with extensive square-like symmetry is enabled by periodic substrate motion imposed during the continuous assembly. The formation of film-spanning domains of (100) fcc symmetry as a result of added vibration is robust across a range of micron-scale monosized spherical colloidal suspensions (e.g., polystyrene, silica) as well as substrate surface chemistries (e.g., hydrophobic, hydrophilic). The generation of extensive single crystalline (100) fcc domains as large as 15 mm(2) and covering nearly 40% of the colloidal crystalline film is possible by simply tuning coating conditions and multi-layer film thickness. Preferential orientation of the square-packed domains with respect to the direction of deposition is attributed to domain generation based upon a shear-related mechanism. Visualization during assembly gives clues toward the mechanism of this flow-driven self-assembly method. PMID:26238223

  16. Impact of local magnetism on stacking fault energies: A first-principles investigation for fcc iron

    NASA Astrophysics Data System (ADS)

    Bleskov, I.; Hickel, T.; Neugebauer, J.; Ruban, A.

    2016-06-01

    A systematic ab initio study of the influence of local magnetism on the generalized stacking fault energy (GSFE) surface in pure fcc iron at 0 K has been performed. In the calculations we considered ferro- and antiferro- (single- and double-layer) magnetic order of local moments as well as their complete disorder, corresponding to paramagnetic (PM) state. We have shown that local magnetism is one of the most important factors stabilizing austenitic structure in iron (with respect to more stable at 0 K hcp) and that the perturbation of magnetic structure by the formation of stacking fault is a short-range effect. Local magnetism also strongly influences the GSFE surface topology and, therefore, the material's plasticity by reducing the energetic barriers that need to be overcome to form the intrinsic stacking fault (ISF) or return from the ISF structure to fcc. The influence of atomic relaxations on such barriers is moderate and does not exceed 15%. In addition, a methodology to evaluate the PM ISF energy using a superposition of the ISF energies obtained for ordered magnetic structures is proposed to overcome computational impediments arising when dealing with disorder in the PM state. The complications of the proposed methodology together with the ways to overcome them are also discussed.

  17. FURTHER DISCUSSION OF ORIENTATION RELATIONSHIPS, SURFACE RELIEFS AND FCC-BCC TRANSFORMATIONS IN STEELS

    SciTech Connect

    Dahmen, U.

    1980-11-01

    In a recent communication, Bhadeshia gives an explanation of the tent-shaped surface relief effects observed in association with Widmanstatten ferrite and lower bainite. Based on his proposed explanation he concludes that the diffusional fcc{yields}bcc transformation tn steel takes place by a displacive mechanism. This conclusion is disputed by Aaronson in a letter following that of Bhadeshia by showing that the experimentally observed orientation relationships are different from the one ( Nishyama-Wassermann ( N-W) , necessary for Bhadeshia' s mechanism. He therefore holds that the transformation is purely diffusional and that "any attempts to understand diffusional phase transformations in terms of a shear mechanism are counterproductive." The purpose of the present note is (l) to show that Bhadeshia's mechanism seems to be based on a misinterpretation of the lattice symmetries resulting from the fcc {yields} bcc transformation and cannot explain a tent-shaped surface relief even if the N-W orientation relationship is followed, and (2) to suggest that attempts to formally understand diffusional phase transformations in terms of shear may not always be counterproductive.

  18. Adsorbate modification of the structural, electronic, and magnetic properties of ferromagnetic fcc {110} surfaces

    NASA Astrophysics Data System (ADS)

    Gunn, D. S. D.; Jenkins, Stephen J.

    2011-03-01

    We identify trends in structural, electronic, and magnetic modifications that occur on ferromagnetic {110} surfaces upon varying either the substrate material or the adsorbate species. First, we have modeled the adsorption of several first-row p-block elements on the surface of fcc Co{110} at two coverages [0.5 and 1.0 monolayer (ML)]. All adsorbates were found to expand the distance between the first and second substrate layers and to contract the distance between the second and third layers. The energetic location of a characteristic trough in the density-of-d-states difference plot correlates with the direction of the adsorbate magnetic coupling to the surface, and a trend of antiferromagnetic to ferromagnetic coupling to the surface was observed across the elements from boron to fluorine. A high fluorine adatom coverage (1.0 ML) was found to enhance the surface spin magnetic moment by 11%. Second, we also calculate and contrast adsorption of 0.5 and 1.0 ML of carbon, nitrogen, and oxygen adatoms on fcc iron, cobalt, and nickel {110} surfaces and compare the structural, electronic, and magnetic properties of these systems. Carbon and nitrogen are found to couple antiferromagnetically, and oxygen ferromagnetically, to all surfaces. It was found that antiferromagnetically coupled adsorbates retained their largest spin moment values on iron, whereas ferromagnetically coupled adsorbates possessed their lowest moments on this surface. The strongly localized influence of these adsorbates is clearly illustrated in partial density-of-states plots for the surface atoms.

  19. Molecular dynamics prediction of phonon-mediated thermal conductivity of f.c.c. Cu

    NASA Astrophysics Data System (ADS)

    Evteev, Alexander V.; Momenzadeh, Leila; Levchenko, Elena V.; Belova, Irina V.; Murch, Graeme E.

    2014-03-01

    The phonon-mediated thermal conductivity of f.c.c. Cu is investigated in detail in the temperature range 40-1300 K. The calculations are performed in the framework of equilibrium molecular dynamics making use of the Green-Kubo formalism and one of the most reliable embedded-atom method potentials for Cu. It is found that the temporal decay of the heat current autocorrelation function (HCACF) of the Cu model at low and intermediate temperatures demonstrate a more complex behaviour than the two-stage decay observed previously for the f.c.c. Ar model. After the first stage of decay, it demonstrates a peak in the temperature range 40-800 K. A decomposition model of the HCACF is introduced. In the framework of that model we demonstrate that a classical description of the phonon thermal transport in the Cu model can be used down to around one quarter of the Debye temperature (about 90 K). Also, we find that above 300 K the thermal conductivity of the Cu model varies with temperature more rapidly than ?, following an exponent close to -1.4 in agreement with previous calculations on the Ar model. Phonon thermal conductivity of Cu is found to be about one order of magnitude higher than Ar. The phonon contribution to the total thermal conductivity of Cu can be estimated to be about 0.5% at 1300 K and about 10% at 90 K.

  20. Equilibrium phase boundary between hcp-cobalt and fcc-cobalt

    NASA Astrophysics Data System (ADS)

    Cynn, Hyunchae; Lipp, Magnus J.; Evans, William J.; Baer, Bruce J.

    In 2000 (Yoo et al., PRL), fcc-cobalt was reported as a new high pressure phase transforming from ambient hcp-cobalt starting at around 105 GPa and 300 K. Both cobalts coexist up to 150 GPa and thereafter only fcc-cobalt was found to be the only stable phase to 200 GPa. Our recent synchrotron x-ray diffraction data on cobalt are at odds with the previous interpretation. We will present our new finding and elaborate on our understanding in terms of the equilibrium phase boundary of cobalt. We will also compare our previous work on xenon (Cynn et al., 2001, PRL) with our new results on cobalt. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Portions of this work were performed at HPCAT (Sector 16), APS, Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DENA0001974 and DOE-BES under Award No. DE-FG02-99ER45775. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

  1. Magnetic instabilities in fcc FexNi1-x thin films

    NASA Astrophysics Data System (ADS)

    Foy, E.; Andrieu, S.; Finazzi, M.; Poinsot, R.; Teodorescu, C. M.; Chevrier, F.; Krill, G.

    2003-09-01

    We present the results obtained on FexNi1-x alloy films epitaxially grown on Cu(100). They are characterized by a fcc structure pseudomorphic to the substrate over a wide range of concentration and thickness. In particular, the martensitic transition which in bulk alloys occurs around the “Invar” concentration (x≈0.65) is suppressed. We report the concentration dependence at low temperature of the total magnetic moment and of its Fe-3d and Ni-3d projected components in such thin fcc FexNi1-x alloy films. Magnetic instabilities that might be associated with noncollinear spin alignments of Fe atoms are clearly observed for x>0.73, where the magnetic moment decreases with increasing Fe concentration. In this Fe-rich concentration range the layers are still ferromagnetic and a magnetic moment is still observed, even on Ni atoms and at room temperature, up to x=0.86. We also show how the variation of the magnetization in this region is correlated with a very small variation of the atomic volume (˜1%).

  2. The Evaluation of a Public Document: The Case of FCC's Marine Radio Rules for Recreational Boaters. Document Design Project, Technical Report No. 11.

    ERIC Educational Resources Information Center

    Felker, Daniel B.; Rose, Andrew M.

    In a collaborative effort, the Federal Communications Commission (FCC) and the Document Design Project conducted an evaluation of marine radio rules for recreational boaters that had been rewritten in plain English by FCC personnel. The revised rules were evaluated by 53 experienced boaters and 52 inexperienced boaters, who were given either the…

  3. Microstructural evolution of Fe grown on a (001) Cu film and its implication to the elastic anomaly in metallic superlattices

    SciTech Connect

    Koike, J.; Nastasi, M.

    1990-01-01

    A large softening of the shear modulus has been reported in metallic superlattices composed of insoluble bcc/fcc metals. In an attempt to understand this elastic anomaly, we have studied the microstructure of Fe/Cu bilayers as a function of the Fe thickness with transmission electron microscopy (TEM). Analysis of the moire fringes observed in plan-view TEM images revealed that the fcc Fe structure epitaxially grows on the (001) Cu up to a thickness of 2.0 nm. At 2.3 nm. At 2.3 nm, the bcc Fe structure nucleates, accompanying lattice rotation around the growth direction with respect to the underlying fcc structure. As the Fe thickness further increases, the submicron polycrystalline grains formed. Based on these results, the microstructure of the metallic superlattices and its relation to the softening of the shear modulus will be discussed. 22 refs., 2 figs

  4. Accurate Monte Carlo simulations on FCC and HCP Lennard-Jones solids at very low temperatures and high reduced densities up to 1.30

    NASA Astrophysics Data System (ADS)

    Adidharma, Hertanto; Tan, Sugata P.

    2016-07-01

    Canonical Monte Carlo simulations on face-centered cubic (FCC) and hexagonal closed packed (HCP) Lennard-Jones (LJ) solids are conducted at very low temperatures (0.10 ≤ T∗ ≤ 1.20) and high densities (0.96 ≤ ρ∗ ≤ 1.30). A simple and robust method is introduced to determine whether or not the cutoff distance used in the simulation is large enough to provide accurate thermodynamic properties, which enables us to distinguish the properties of FCC from that of HCP LJ solids with confidence, despite their close similarities. Free-energy expressions derived from the simulation results are also proposed, not only to describe the properties of those individual structures but also the FCC-liquid, FCC-vapor, and FCC-HCP solid phase equilibria.

  5. When Magnetic Catalyst Meets Magnetic Reactor: Etherification of FCC Light Gasoline as an Example

    NASA Astrophysics Data System (ADS)

    Cheng, Meng; Xie, Wenhua; Zong, Baoning; Sun, Bo; Qiao, Minghua

    2013-06-01

    The application of elaborately designed magnetic catalysts has long been limited to ease their separation from the products only. In this paper, we for the first time employed a magnetic sulphonated poly(styrene-divinylbenzene) resin catalyst on a magnetically stabilized-bed (MSB) reactor to enhance the etherification of fluidized catalytic cracking (FCC) light gasoline, one of the most important reactions in petroleum refining industry. We demonstrated that the catalytic performance of the magnetic acid resin catalyst on the magnetic reactor is substantially enhanced as compared to its performance on a conventional fixed-bed reactor under otherwise identical operation conditions. The magnetic catalyst has the potential to be loaded and unloaded continuously on the magnetic reactor, which will greatly simplify the current complex industrial etherification processes.

  6. When Magnetic Catalyst Meets Magnetic Reactor: Etherification of FCC Light Gasoline as an Example

    PubMed Central

    Cheng, Meng; Xie, Wenhua; Zong, Baoning; Sun, Bo; Qiao, Minghua

    2013-01-01

    The application of elaborately designed magnetic catalysts has long been limited to ease their separation from the products only. In this paper, we for the first time employed a magnetic sulphonated poly(styrene-divinylbenzene) resin catalyst on a magnetically stabilized-bed (MSB) reactor to enhance the etherification of fluidized catalytic cracking (FCC) light gasoline, one of the most important reactions in petroleum refining industry. We demonstrated that the catalytic performance of the magnetic acid resin catalyst on the magnetic reactor is substantially enhanced as compared to its performance on a conventional fixed-bed reactor under otherwise identical operation conditions. The magnetic catalyst has the potential to be loaded and unloaded continuously on the magnetic reactor, which will greatly simplify the current complex industrial etherification processes. PMID:23756855

  7. Simulation of atomic diffusion in the Fcc NiAl system: A kinetic Monte Carlo study

    DOE PAGESBeta

    Alfonso, Dominic R.; Tafen, De Nyago

    2015-04-28

    The atomic diffusion in fcc NiAl binary alloys was studied by kinetic Monte Carlo simulation. The environment dependent hopping barriers were computed using a pair interaction model whose parameters were fitted to relevant data derived from electronic structure calculations. Long time diffusivities were calculated and the effect of composition change on the tracer diffusion coefficients was analyzed. These results indicate that this variation has noticeable impact on the atomic diffusivities. A reduction in the mobility of both Ni and Al is demonstrated with increasing Al content. As a result, examination of the pair interaction between atoms was carried out formore » the purpose of understanding the predicted trends.« less

  8. Quantum calculation of disordered length in fcc single crystals using channelling techniques

    NASA Astrophysics Data System (ADS)

    Abu-Assy, M. K.

    2006-04-01

    Lattices of face-centred cubic crystals (fcc), due to irradiation processes, may become disordered in stable configurations like the dumb-bell configuration (DBC) or body-centred interstitial (BCI). In this work, a quantum mechanical treatment for the calculation of transmission coefficients of channelled positrons from their bound states in the normal lattice regions into the allowed bound states in the disordered regions is given as a function of the length of the disordered regions. In order to obtain more reliable results, higher anharmonic terms in the planar channelling potential are considered in the calculations by using first-order perturbation theory where new bound states have been found. The calculations were executed in the energy range 10 200 MeV of the incident positron on a copper single crystal in the planar direction (100).

  9. A dislocation dynamics model of the plastic flow of fcc polycrystals

    NASA Astrophysics Data System (ADS)

    Hunter, Abigail

    2015-06-01

    Describing material strength at very high strain rates is a key component for investigating and predicting material deformation and failure under shock loading. However, accurately describing deformation physics in this strain rate regime remains a challenge due to the break down of fundamental assumptions that apply to material strength at low strain rates. We present a dislocation dynamics model of the plastic flow of fcc polycrystals from quasi-static to very high strain rates (106 s-1 and above), pressures from ambient to 1000 GPa, and temperatures from zero to melt. The model is comprised of three coupled ordinary differential equations: a kinetic equation, which relates the strain rate to the stress, mobile and immobile dislocation densities, mass density, and temperature using a mean first passage time (MFPT) framework, and two equations describing the evolution of the mobile and immobile (network, forest) dislocation densities.

  10. Vacancy-mediated fcc/bcc phase separation in Fe1 -xNix ultrathin films

    NASA Astrophysics Data System (ADS)

    Menteş, T. O.; Stojić, N.; Vescovo, E.; Ablett, J. M.; Niño, M. A.; Locatelli, A.

    2016-08-01

    The phase separation occurring in Fe-Ni thin films near the Invar composition is studied by using high-resolution spectromicroscopy techniques and density functional theory calculations. Annealed at temperatures around 300 ∘C ,Fe0.70Ni0.30 films on W(110) break into micron-sized bcc and fcc domains with compositions in agreement with the bulk Fe-Ni phase diagram. Ni is found to be the diffusing species in forming the chemical heterogeneity. The experimentally determined energy barrier of 1.59 ±0.09 eV is identified as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separation process is attributed to vacancy creation without interstitials.

  11. Twinning in fcc lattice creates low-coordinated catalytically active sites in porous gold.

    PubMed

    Krajčí, Marian; Kameoka, Satoshi; Tsai, An-Pang

    2016-08-28

    We describe a new mechanism for creation of catalytically active sites in porous gold. Samples of porous gold prepared by de-alloying Al2Au exhibit a clear correlation between the catalytic reactivity towards CO oxidation and structural defects in the fcc lattice of Au. We have found that on the stepped {211} surfaces quite common twin boundary defects in the bulk structure of porous gold can form long close-packed rows of atoms with the coordination number CN = 6. DFT calculations confirm that on these low-coordinated Au sites dioxygen chemisorbs and CO oxidation can proceed via the Langmuir-Hinshelwood mechanism with the activation energy of 37 kJ/mol or via the CO-OO intermediate with the energy barrier of 19 kJ/mol. The existence of the twins in porous gold is stabilized by the surface energy. PMID:27586937

  12. Conversion of pine sawdust bio-oil (raw and thermally processed) over equilibrium FCC catalysts.

    PubMed

    Bertero, Melisa; Sedran, Ulises

    2013-05-01

    A raw bio-oil from pine sawdust, the liquid product from its thermal conditioning and a synthetic bio-oil composed by eight model compounds representing the main chemical groups in bio-oils, were converted thermally and over a commercial equilibrium FCC catalyst. The experiments were performed in a fixed bed reactor at 500 °C. The highest hydrocarbon yield (53.5 wt.%) was obtained with the conditioned liquid. The coke yields were significant in all the cases, from 9 to 14 wt.%. The synthetic bio-oil produced lesser hydrocarbons and more oxygenated compounds and coke than the authentic feedstocks from biomass. The previous thermal treatment of the raw bio-oil had the positive effects of increasing 25% the yield of hydrocarbons, decreasing 55% the yield of oxygenated compounds and decreasing 20% the yield of coke, particularly the more condensed coke. PMID:23375765

  13. Imaging phonons in a fcc Pu-Ga alloy by thermal diffuse x-ray scattering

    NASA Astrophysics Data System (ADS)

    Wong, Joe; Wall, M.; Schwartz, A. J.; Xu, R.; Holt, M.; Hong, Hawoong; Zschack, P.; Chiang, T.-C.

    2004-05-01

    X-ray thermal diffuse scattering intensity patterns from phonons in a fcc δ-Pu-Ga alloy have been recorded using an 18 keV undulator x-ray beam with a beam diameter of 25 μm. The results are consistent with patterns calculated using the Born-von Karman force constant model of lattice dynamics, and support the pronounced softening of the transverse acoustic branch along the [111] direction observed from inelastic x-ray scattering measurements. This work demonstrates the feasibility of using a "large-grain, small beam" approach to study lattice properties, such as phonon dispersion curves, of materials not readily available in the form of large single crystals.

  14. Chemical conversion of VRDS-FCC process for Gudao vacuum residue

    SciTech Connect

    Honghong Shan; Jianfang Zhang; Guohe Que

    1995-12-31

    The physical-chemical properties and catalytic cracking behaviors of Gudao VR and Gudao VRDS VR were studied. The properties are structural parameters show that the C/H, Mw, R{sub A}, f{sub A} values and nitrogen, sulfur, nickel, resin contents of the Gudao VRDS VR are obviously lower than those of Gudao VR, and that the content of saturates of Gudao VRDS VR are considerably higher than that of Gudao VR. The catalytic cracking experiments of Gudao VRDS VR in laboratory scale show that VRDS VR has good cracking behaviour. The research and industry scale results indicate that the VRDS process using Gudao VR as feedstock is a kind of high efficiency hydrotreating process, and that VRDS-FCC complex technology can realize the deep processing of the crude, increase the light oil yields and enhance the economical profit of the enterprise.

  15. Influence of the slip conditions on the stress corrosion cracking microprocesses in fcc materials

    SciTech Connect

    Chambreuil-Paret, A.; Chateau, J.P.; Magnin, T.

    1997-11-01

    The aim of the present paper is to carefully analyze the stress corrosion cracking (SCC) microprocesses of f.c.c. single crystals, not only for the influence of the tensile axis orientation but also for the influence of the cracking direction (imposed or not). 316L (in MgCl{sub 2}) and copper (in nitrites) single crystals of well defined tensile axis will be strained using the slow strain rate technique. The authors focus on the influence of the relative orientations of the cracking direction and the slip planes on the crystallography of fracture. The effect of slip conditions on the corrosion-deformation interactions leading to fracture are then emphasized, which gives major information relevant to the micromodelling of SCC.

  16. Transition saddle points and associated defects for a triaxially stretched FCC crystal

    NASA Astrophysics Data System (ADS)

    Delph, T. J.; Zimmerman, J. A.

    2016-05-01

    We demonstrate the use of a single-ended method for locating saddle points on the potential energy surface for a triaxially stretched FCC crystal governed by a Lennard-Jones potential. Single-ended methods require no prior knowledge of the defected state and are shown to have powerful advantages in this application, principally because the nature of the associated defects can be quite complicated and hence extremely difficult to predict ab initio. We find that while classical spherical cavitation occurs for high stretch values, for lower values the defect mode transitions to a non-spherical pattern without any apparent symmetries. This non-spherical mode plays the primary role in harmonic transition state theory predictions that are used to examine how instabilities vary with applied loading rate. Such a defect mode would be difficult to determine using double-ended methods for finding saddle points.

  17. Federal Communications Commission (FCC) Transponder Loading Data Conversion Software. User's guide and software maintenance manual, version 1.2

    NASA Technical Reports Server (NTRS)

    Mallasch, Paul G.

    1993-01-01

    This volume contains the complete software system documentation for the Federal Communications Commission (FCC) Transponder Loading Data Conversion Software (FIX-FCC). This software was written to facilitate the formatting and conversion of FCC Transponder Occupancy (Loading) Data before it is loaded into the NASA Geosynchronous Satellite Orbital Statistics Database System (GSOSTATS). The information that FCC supplies NASA is in report form and must be converted into a form readable by the database management software used in the GSOSTATS application. Both the User's Guide and Software Maintenance Manual are contained in this document. This volume of documentation passed an independent quality assurance review and certification by the Product Assurance and Security Office of the Planning Research Corporation (PRC). The manuals were reviewed for format, content, and readability. The Software Management and Assurance Program (SMAP) life cycle and documentation standards were used in the development of this document. Accordingly, these standards were used in the review. Refer to the System/Software Test/Product Assurance Report for the Geosynchronous Satellite Orbital Statistics Database System (GSOSTATS) for additional information.

  18. 47 CFR Appendix 1 to Part 97 - Places Where the Amateur Service is Regulated by the FCC

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Places Where the Amateur Service is Regulated...) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE Pt. 97, App. 1 Appendix 1 to Part 97—Places Where the Amateur Service is Regulated by the FCC In ITU Region 2, the amateur service is regulated by...

  19. 47 CFR Appendix 1 to Part 97 - Places Where the Amateur Service is Regulated by the FCC

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Places Where the Amateur Service is Regulated...) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE Pt. 97, App. 1 Appendix 1 to Part 97—Places Where the Amateur Service is Regulated by the FCC In ITU Region 2, the amateur service is regulated by...

  20. 47 CFR Appendix 1 to Part 97 - Places Where the Amateur Service is Regulated by the FCC

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Places Where the Amateur Service is Regulated...) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE Pt. 97, App. 1 Appendix 1 to Part 97—Places Where the Amateur Service is Regulated by the FCC In ITU Region 2, the amateur service is regulated by...

  1. 47 CFR Appendix 1 to Part 97 - Places Where the Amateur Service is Regulated by the FCC

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Places Where the Amateur Service is Regulated...) SAFETY AND SPECIAL RADIO SERVICES AMATEUR RADIO SERVICE Pt. 97, App. 1 Appendix 1 to Part 97—Places Where the Amateur Service is Regulated by the FCC In ITU Region 2, the amateur service is regulated by...

  2. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other...

  3. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other...

  4. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other...

  5. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other...

  6. 47 CFR 95.219 - (R/C Rule 19) How do I answer correspondence from the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (R/C Rule 19) How do I answer correspondence from the FCC? 95.219 Section 95.219 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control (R/C) Radio Service Other...

  7. Magnetic and structural properties of fcc/hcp bi-crystalline multilayer Co nanowire arrays prepared by controlled electroplating

    NASA Astrophysics Data System (ADS)

    Pirota, K. R.; Béron, F.; Zanchet, D.; Rocha, T. C. R.; Navas, D.; Torrejón, J.; Vazquez, M.; Knobel, M.

    2011-04-01

    We report on the structural and magnetic properties of crystalline bi-phase Co nanowires, electrodeposited into the pores of anodized alumina membranes, as a function of their length. Co nanowires present two different coexistent crystalline structures (fcc and hcp) that can be controlled by the time of pulsed electrodeposition. The fcc crystalline phase grows at the early stage and is present at the bottom of all the nanowires, strongly influencing their magnetic behavior. Both structural and magnetic characterizations indicate that the length of the fcc phase is constant at around 260-270 nm. X-ray diffraction measurements revealed a strong preferential orientation (texture) in the (1 0-1 0) direction for the hcp phase, which increases the nanowire length as well as crystalline grain size, degree of orientation, and volume fraction of oriented material. The first-order reversal curve (FORC) method was used to infer both qualitatively and quantitatively the complex magnetization reversal of the nanowires. Under the application of a magnetic field parallel to the wires, the magnetization reversal of each region is clearly distinguishable; the fcc phase creates a high coercive contribution without an interaction field, while the hcp phase presents a smaller coercivity and undergoes a strong antiparallel interaction field from neighboring wires.

  8. 75 FR 42376 - Proposed Information Collection; Comment Request; NTIA/FCC Web-based Frequency Coordination System

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-21

    ...; NTIA/FCC Web- based Frequency Coordination System AGENCY: National Telecommunications and Information... Telecommunications and Information Administration (NTIA) hosts a Web-based system that collects specific...-primary basis by federal and non-federal users. The Web-based system provides a means for...

  9. Pharmacological evaluation of the histamine H1 and 5-HT blocking properties of 2-N-(carboxamidinonormianserin) (FCC5): in-vitro studies.

    PubMed

    Leitch, I M; Boura, A L; King, R G

    1992-04-01

    Some in-vitro pharmacological effects of a novel analogue of mianserin, 2-carboxamidino-1,2,3,4,10,14b-hexahydrodibenzo (c,f) pyrazino (1,2-alpha) azepine hydrochloride (FCC5) have been studied. FCC5 was a non-competitive antagonist of both histamine-induced contractions of the guinea-pig ileum and 5-HT-induced contractions of rat fundal strips with pD'2 values of 6.13 and 5.57, respectively. The insurmountable antihistaminic effect of FCC5, 100 nM, in the guinea-pig isolated ileum was not removed by washing. FCC5, 10-100 nM, had no effect on responses to acetylcholine or barium chloride of the guinea-pig isolated ileum. In guinea-pig isolated right atria, FCC5, 1-30 microM, had no effect on H2-receptor-mediated chronotropic responses to histamine. FCC5, 10-1000 nM, had no alpha 2-adrenoceptor antagonist activity, as assessed by lack of effect on the inhibitory responses to B-HT 920 in the electrically stimulated rat isolated vas deferens. FCC5 resembles mianserin by being a potent, non-competitive antagonist at histamine H1 and 5-HT receptors, but differs from mianserin in a number of respects including having much less effect at alpha 2-adrenoceptors. PMID:1355543

  10. Ideal compressive strength of fcc Co, Ni, and Ni-rich alloys along the <001 > direction: A first-principles study

    NASA Astrophysics Data System (ADS)

    Breidi, A.; Fries, S. G.; Ruban, A. V.

    2016-04-01

    We perform density functional theory based first-principles calculations to identify promising alloying elements (X ) capable of enhancing the compressive uniaxial theoretical (ideal) strength of the fcc Ni-matrix along the <001 > direction. The alloying element belongs to a wide range of 3 d ,4 d , and 5 d series with nominal composition of 6.25 at. %. Additionally, a full elastic study is carried to investigate the ideal strength of fcc Ni and fcc Co. Our results indicate that the most desirable alloying elements are those with half d -band filling, namely, Os, Ir, Re, and Ru.

  11. Transferable force-constant modeling of vibrational thermodynamic properties in fcc-based Al-TM ( TM=Ti , Zr, Hf) alloys

    NASA Astrophysics Data System (ADS)

    Liu, Jefferson Z.; Ghosh, G.; van de Walle, A.; Asta, M.

    2007-03-01

    The vibrational thermodynamic properties of ordered and disordered fcc-based alloys in three aluminum transition-metal (TM) systems, Al-TM ( TM=Ti , Zr, and Hf), are computed by first principles methods employing supercell calculations and the transferable-force-constant (TFC) approach. In order to obtain accurate values for the high-temperature limit of the vibrational mixing entropies in these systems, it is necessary to parametrize the dependence of the force constants on both the equilibrium bond length and the TM concentration in the TFC method. Provided this concentration dependence is accounted for, the TFC approach is shown to lead to predictions for the vibrational mixing entropy accurate to within approximately 20%. The utility of the TFC method is demonstrated by its application to the calculation of vibrational entropies of mixing for approximately 30 structures in each of the three Al-TM systems, facilitating the construction of well converged vibrational-entropy cluster expansions. The calculations yield large and negative values for the vibrational mixing entropies of both ordered and disordered alloys, with an overall magnitude of up to 1.0kB /atom, and ordering entropies (i.e., the difference between the vibrational entropy of ordered and disordered phases at the same composition) in the range of 0.2-0.3kB /atom for concentrated alloys. Calculated results are shown to be in good agreement with experimental data available for the Al-Ti system.

  12. Temperature Dependence of the Mechanical Properties of Equiatomic Solid Solution Alloys with FCC Crystal Structures

    SciTech Connect

    Wu, Zhenggang; Bei, Hongbin; Pharr, George M.; George, Easo P.

    2014-10-03

    We found that compared to decades-old theories of strengthening in dilute solid solutions, the mechanical behavior of concentrated solid solutions is relatively poorly understood. A special subset of these materials includes alloys in which the constituent elements are present in equal atomic proportions, including the high-entropy alloys of recent interest. A unique characteristic of equiatomic alloys is the absence of “solvent” and “solute” atoms, resulting in a breakdown of the textbook picture of dislocations moving through a solvent lattice and encountering discrete solute obstacles. Likewise, to clarify the mechanical behavior of this interesting new class of materials, we investigate here a family of equiatomic binary, ternary and quaternary alloys based on the elements Fe, Ni, Co, Cr and Mn that were previously shown to be single-phase face-centered cubic (fcc) solid solutions. The alloys were arc-melted, drop-cast, homogenized, cold-rolled and recrystallized to produce equiaxed microstructures with comparable grain sizes. Tensile tests were performed at an engineering strain rate of 10-3 s-1 at temperatures in the range 77–673 K. Unalloyed fcc Ni was processed similarly and tested for comparison. The flow stresses depend to varying degrees on temperature, with some (e.g. NiCoCr, NiCoCrMn and FeNiCoCr) exhibiting yield and ultimate strengths that increase strongly with decreasing temperature, while others (e.g. NiCo and Ni) exhibit very weak temperature dependencies. Moreover, to better understand this behavior, the temperature dependencies of the yield strength and strain hardening were analyzed separately. Lattice friction appears to be the predominant component of the temperature-dependent yield stress, possibly because the Peierls barrier height decreases with increasing temperature due to a thermally induced increase of dislocation width. In the early stages of plastic flow (5–13% strain, depending on material), the

  13. Temperature Dependence of the Mechanical Properties of Equiatomic Solid Solution Alloys with FCC Crystal Structures

    DOE PAGESBeta

    Wu, Zhenggang; Bei, Hongbin; Pharr, George M.; George, Easo P.

    2014-10-03

    We found that compared to decades-old theories of strengthening in dilute solid solutions, the mechanical behavior of concentrated solid solutions is relatively poorly understood. A special subset of these materials includes alloys in which the constituent elements are present in equal atomic proportions, including the high-entropy alloys of recent interest. A unique characteristic of equiatomic alloys is the absence of “solvent” and “solute” atoms, resulting in a breakdown of the textbook picture of dislocations moving through a solvent lattice and encountering discrete solute obstacles. Likewise, to clarify the mechanical behavior of this interesting new class of materials, we investigate heremore » a family of equiatomic binary, ternary and quaternary alloys based on the elements Fe, Ni, Co, Cr and Mn that were previously shown to be single-phase face-centered cubic (fcc) solid solutions. The alloys were arc-melted, drop-cast, homogenized, cold-rolled and recrystallized to produce equiaxed microstructures with comparable grain sizes. Tensile tests were performed at an engineering strain rate of 10-3 s-1 at temperatures in the range 77–673 K. Unalloyed fcc Ni was processed similarly and tested for comparison. The flow stresses depend to varying degrees on temperature, with some (e.g. NiCoCr, NiCoCrMn and FeNiCoCr) exhibiting yield and ultimate strengths that increase strongly with decreasing temperature, while others (e.g. NiCo and Ni) exhibit very weak temperature dependencies. Moreover, to better understand this behavior, the temperature dependencies of the yield strength and strain hardening were analyzed separately. Lattice friction appears to be the predominant component of the temperature-dependent yield stress, possibly because the Peierls barrier height decreases with increasing temperature due to a thermally induced increase of dislocation width. In the early stages of plastic flow (5–13% strain, depending on material), the temperature

  14. Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

    SciTech Connect

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-04-03

    Magnetic ordering temperatures in heavy rare earth metal Dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to extreme conditions of pressure to 69 GPa and temperature to 10 K. Previous studies using magnetic susceptibility measurements at high pressures were only able to track magnetic ordering temperature till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This is followed by a rapid increase in the magnetic ordering temperatures in the double hexagonal close packed phase and finally leveling off in the distorted face centered cubic phase of Dy. Lastly, our studies reaffirm that 4f-shell remain localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.

  15. Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

    DOE PAGESBeta

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-04-03

    Magnetic ordering temperatures in heavy rare earth metal Dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to extreme conditions of pressure to 69 GPa and temperature to 10 K. Previous studies using magnetic susceptibility measurements at high pressures were only able to track magnetic ordering temperature till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This ismore » followed by a rapid increase in the magnetic ordering temperatures in the double hexagonal close packed phase and finally leveling off in the distorted face centered cubic phase of Dy. Lastly, our studies reaffirm that 4f-shell remain localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.« less

  16. A comparative study of Burakovsky's and Jacobs's volume dependence Grüneisen parameter for fcc aluminum

    NASA Astrophysics Data System (ADS)

    Nie, Chuanhui; Zong, Baochun; Wang, Junping

    2015-07-01

    We compare two expressions for the volume dependence of the Grüneisen parameter γ for fcc Al presented by Burakovsky and Preston (2004) [3] and Jacobs and Schmid-Fetzer (2010) [4], respectively. It's found that both calculated results of the melting temperature Tm are in good agreement with experimental data. But the higher order Grüneisen parameters are different. We obtain the values of the third order Grüneisen parameter λ∞ and the pressure derivative of bulk modulus K‧∞ at extreme pressure, and the parameter f in the generalized free volume formula for the two models. The results show that the Jacobs's expression of Grüneisen parameter is more suitable for fcc Al.

  17. Spin dynamics and two-dimensional correlations in the fcc antiferromagnetic Sr2YRuO6

    NASA Astrophysics Data System (ADS)

    Disseler, S. M.; Lynn, J. W.; Jardim, R. F.; Torikachvili, M. S.; Granado, E.

    2016-04-01

    The face-centered-cubic (fcc) lattice of Ru5 + spins in the double perovskite Sr2YRuO6 shows a delicate, three-dimensional antiferromagnetic (AFM) ground state composed of stacked square AFM layers. Inelastic neutron scattering data taken on this state reveal a gapped low-energy excitation band emerging from [001] with spin excitations extending to 8 meV. These magnetic excitations are modeled by a simple J1-J2 interaction scheme allowing quantitative comparisons with similar materials. At higher temperatures, the low-energy excitation spectrum is dominated by a quasielastic component associated with size fluctuations of two-dimensional AFM clusters that exhibit asymmetric correlations even at low temperatures. Thus, the fcc lattice in general and the double-perovskite structure in particular emerge as hosts of both two-dimensional and three-dimensional dynamics resulting from frustration.

  18. The Microstructure of Near-Equiatomic B2/f.c.c. FeNiMnAl Alloys

    SciTech Connect

    Baker, Ian; Wu, H; Wu, Xiaolan; Miller, Michael K; Munroe, P R

    2011-01-01

    A microstructural analysis of two FeNiMnAl alloys, Fe{sub 30}Ni{sub 20}Mn{sub 30}Al{sub 20} and Fe{sub 25}Ni{sub 25}Mn{sub 30}Al{sub 20}, was performed by a combination of atom probe tomography and transmission electron microscopy techniques. Although the microstructures of both alloys, which consist of alternating platelets aligned along <100> of the B2-ordered phase, are similar to B2/b.c.c. two-phase alloys previously observed in the FeNiMnAl system, the two phases present in the current alloys are B2-ordered and f.c.c., with the latter phase being heavily twinned. Very fine ({approx} 5 nm) precipitates, whose chemistry was similar to that of the f.c.c. (Fe, Mn)-rich phase, were found within the B2 (Ni, Al)-rich phase in both alloys.

  19. Experimental investigations and DICTRA simulations on formation of diffusion-controlled fcc-rich surface layers on cemented carbides

    NASA Astrophysics Data System (ADS)

    Garcia, José; Prat, Orlando

    2011-08-01

    Wear resistant fcc-rich surface layers were produced on cemented carbides by nitridation of W-Ti-Ta-Nb-Co-C compositions at 1400 °C in nitrogen atmosphere. A 15 ± 3 μm thick (Ti,Ta,Nb,W)(C,N) top-layer formed on the surface of the cemented carbides. The driving force for formation of the fcc-rich layers was the difference in nitrogen activity between the sintering atmosphere and the cemented carbide bulk, which promoted in-diffusion of nitrogen and out-diffusion of Ti, Ta and Nb. The diffusion-controlled process was modeled by DICTRA considering that all diffusion occurred in the liquid binder phase of a dispersed system model with a labyrinth factor of λ( f) = f. Good agreement between experimental and simulations regarding layer thickness, phase fraction distribution and element profiles was obtained for the presented model.

  20. Correlation effects in fcc-FexNi1-x alloys investigated by means of the KKR-CPA

    NASA Astrophysics Data System (ADS)

    Minár, J.; Mankovsky, S.; Šipr, O.; Benea, D.; Ebert, H.

    2014-07-01

    The electronic structure and magnetic properties of the disordered alloy system fcc-FexNi1-x (fcc: face centered cubic) have been investigated by means of the KKR-CPA (Korringa-Kohn-Rostoker coherent potential approximation) band structure method. To investigate the impact of correlation effects, the calculations have been performed on the basis of the LSDA (local spin density approximation), the LSDA + U as well as the LSDA + DMFT (dynamical mean field theory). It turned out that the inclusion of correlation effects hardly changed the spin magnetic moments and the related hyperfine fields. The spin-orbit induced orbital magnetic moments and hyperfine fields, on the other hand, show a pronounced and element-specific enhancement. These findings are in full accordance with the results of a recent experimental study. This work is dedicated to the memory of Balazs Gyorffy.

  1. Core-level shifts in fcc random alloys: A first-principles approach

    NASA Astrophysics Data System (ADS)

    Olovsson, W.; Göransson, C.; Pourovskii, L. V.; Johansson, B.; Abrikosov, I. A.

    2005-08-01

    First-principles theoretical calculations of the core-level binding-energy shift (CLS) for eight binary face-centered-cubic (fcc) disordered alloys, CuPd, AgPd, CuNi, NiPd, CuAu, PdAu, CuPt, and NiPt, are carried out within density-functional theory (DFT) using the coherent potential approximation. The shifts of the Cu and Ni 2p3/2 , Ag and Pd 3d5/2 , and Pt and Au 4f7/2 core levels are calculated according to the complete screening picture, which includes both initial-state (core-electron energy eigenvalue) and final-state (core-hole screening) effects in the same scheme. The results are compared with available experimental data, and the agreement is shown to be good. The CLSs are analyzed in terms of initial- and final-state effects. We also compare the complete screening picture with the CLS obtained by the transition-state method, and find very good agreement between these two alternative approaches for the calculations within the DFT. In addition the sensitivity of the CLS to relativistic and magnetic effects is studied.

  2. The invariant line and precipitate morphology in fcc-bcc systems

    SciTech Connect

    Weatherly, G.C.; Zhang, W.Z. . Dept. of Materials Science and Engineering)

    1994-09-01

    Second-phase precipitates in many face-centered cubic-body-centered cubic (fcc-bcc) systems (e.g., Ni-Cr, Cu-Cr, Fe-Cu, and [alpha]-[gamma] stainless steels) have a lath-shaped morphology, the long axis of the lath being an invariant line of the transformation. The invariant line direction and major (habit) facet plane of the product phase can be predicted by O-lattice (O-line) models. For N-W-, and K-S-oriented precipitates, the habit plane is shown to be an unrotated plane of the transformation. This contains a single set of dislocations lying parallel to the invariant line, with their Burgers vector in the habit plane. Structural ledge models for the habit-plane interface also are considered. For the range of lattice parameter ratios of interest in this study, structural ledge and O-line models can make almost identical predictions as to the optimum habit plane. A variety of elasticity calculations for the energy of fully constrained or fully relaxed precipitates is presented. These models are shown to have limited predictive capabilities. It is suggested that better atomic matching along or near to the invariant line direction might explain the preference for K-S-related precipitates in many systems.

  3. Characterisation of coke from FCC catalysts by solid state {sup 13}C NMR and mass spectrometry

    SciTech Connect

    Andresen, J.M.; McGhee, B.; Snape, C.E.

    1995-12-31

    Coke has been concentrated by demineralisation from deactivated FCC catalysts from both refinery operations with actual feeds and MAT tests using n-hexadecane to facilitate detailed characterisation by solid state {sup 13}C NMR and mass spectrometry. All the catalysts investigated contained about 1% w/w carbon. As for solid fuels, the use of a low-field spectrometer for solid state {sup 13}C NMR in conjunction with the single pulse excitation (SPE or Bloch decay) technique has enabled quantitative carbon skeletal parameters to be obtained for the cokes. Internal standard measurements demonstrated that most of the carbon was observed by SPE and, therefore, NMR-invisible graphitic layers are not thought to be major structural features of the cokes. Differences in feedstock composition were reflected in the structure of the refinery cokes with the aromatic nuclei from a residue feed (5% Conradson carbon) corresponding to 15-20 peri-condensed aromatic rings and being more highly condensed than those from a hydrotreated vacuum gas oil. Mass spectrometry (EI, CI and FIMS) has confirmed that the refinery cokes are highly condensed, but those obtained from n-hexadecane in the MAT tests displayed significant aliphatic character.

  4. Atomic-scale properties of Ni-based FCC ternary, and quaternary alloys

    SciTech Connect

    Tamm, Artur; Aabloo, Alvo; Klintenberg, Mattias; Stocks, Malcolm; Caro, Alfredo

    2015-08-26

    The aim of our study is to characterize some atomic-scale properties of Ni-based FCC multicomponent alloys. For this purpose, we use Monte Carlo method combined with density functional theory calculations to study short-range order (SRO), atomic displacements, electronic density of states, and magnetic moments in equimolar ternary NiCrCo, and quaternary NiCrCoFe alloys. The salient features for the ternary alloy are a negative SRO parameter between Ni Cr and a positive between Cr Cr pairs as well as a weakly magnetic state. For the quaternary alloy we predict negative SRO parameter for Ni Cr and Ni Fe pairs and positive for Cr Cr and Fe Fe pairs. Atomic displacements for both ternary and quaternary alloys are negligible. In contrast to the ternary, the quaternary alloy shows a complex magnetic structure. The electronic structure of the ternary and quaternary alloys shows differences near the Fermi energy between a random solid solution and the predicted structure with SRO. Despite that, the calculated EXAFS spectra does not show enough contrast to discriminate between random and ordered structures. Finally, the predicted SRO has an impact on point-defect energetics, electron phonon coupling and thermodynamic functions and thus, SRO should not be neglected when studying properties of these two alloys.

  5. Crystal Dynamics of (delta) fcc Pu-Ga by High Resolution Inelastic X-Ray Scattering

    SciTech Connect

    Wong, J; Krisch, M; Farber, D; Occelli, F; Xu, R; Chiang, T C; Clatterbuck, D; Schwartz, A J; Wall, M; Boro, C

    2004-09-28

    We have used a microbeam on large grain sample concept to carry out an inelastic x-ray scattering experiment to map the full phonon dispersion curves of an fcc {delta}-phase Pu-Ga alloy. This approach obviates experimental difficulties with conventional inelastic neutron scattering due to the high absorption cross section of the common {sup 239}Pu isotope and the non-availability of large (mm size) single crystal materials for Pu and its alloys. A classical Born von-Karman force constant model was used to model the experimental results, and no less than 4th nearest neighbor interactions had to be included to account for the observation. Several unusual features including, a large elastic anisotropy, a small shear elastic modulus, (C{sub 11}-C{sub 12})/2, a Kohn-like anomaly in the T{sub 1}[011] branch, and a pronounced softening of the T[111] branch towards the L point in the Brillouin are found. These features can be related to the phase transitions of plutonium and to strong coupling between the crystal structure and the 5f valence instabilities. Our results represent the first full phonon dispersions ever obtained for any Pu-bearing material, thus ending a 40-year quest for this fundamental data. The phonon data also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory (DMFT) calculations for {delta}-plutonium.

  6. First-principles study of atomic ordering in fcc Ni-Cr alloys

    NASA Astrophysics Data System (ADS)

    Rahaman, Moshiour; Johansson, B.; Ruban, A. V.

    2014-02-01

    We investigate atomic ordering in fcc Ni-rich Ni-Cr alloys using first-principles techniques and statistical mechanics simulations based on the Ising Hamiltonian with effective cluster interactions computed by the screened generalized perturbation method (SGPM) and projector augmented wave (PAW) method. We demonstrate that effective chemical interactions in this system are quite sensitive to alloy composition and in fact to the specific configurational state. The chemical interactions for the high-temperature random state produce the atomic short-range order (SRO) with intensity maximum close to the (2/32/30) point of the reciprocal space in agreement with the previous first-principles investigation. A consistent with diffuse neutron scattering data maximum at the (11/20) position is obtained only when we take into consideration relatively small strain-induced interactions, which solves a long-standing inconsistency between theory and experiment in this system. The calculated transition temperature of order-disorder transition of Ni2Cr alloy, 880 K, is in good agreement with the experimental value of 863 K.

  7. Benchmark of a modified iterated perturbation theory approach on the fcc lattice at strong coupling

    NASA Astrophysics Data System (ADS)

    Arsenault, Louis-François; Sémon, Patrick; Tremblay, A.-M. S.

    2012-08-01

    The dynamical mean-field theory approach to the Hubbard model requires a method to solve the problem of a quantum impurity in a bath of noninteracting electrons. Iterated perturbation theory (IPT) has proven its effectiveness as a solver in many cases of interest. Based on general principles and on comparisons with an essentially exact continuous-time quantum Monte Carlo (CTQMC) solver, here we show that the standard implementation of IPT fails away from half-filling when the interaction strength is much larger than the bandwidth. We propose a slight modification to the IPT algorithm that replaces one of the equations by the requirement that double occupancy calculated with IPT gives the correct value. We call this method IPT-D. We recover the Fermi liquid ground state away from half-filling. The Fermi liquid parameters, density of states, chemical potential, energy, and specific heat on the fcc lattice are calculated with both IPT-D and CTQMC as benchmark examples. We also calculated the resistivity and the optical conductivity within IPT-D. Particle-hole asymmetry persists even at coupling twice the bandwidth. A generalization to the multiorbital case is suggested. Several algorithms that speed up the calculations are described in appendixes.

  8. Atomic-scale properties of Ni-based FCC ternary, and quaternary alloys

    DOE PAGESBeta

    Tamm, Artur; Aabloo, Alvo; Klintenberg, Mattias; Stocks, Malcolm; Caro, Alfredo

    2015-08-26

    The aim of our study is to characterize some atomic-scale properties of Ni-based FCC multicomponent alloys. For this purpose, we use Monte Carlo method combined with density functional theory calculations to study short-range order (SRO), atomic displacements, electronic density of states, and magnetic moments in equimolar ternary NiCrCo, and quaternary NiCrCoFe alloys. The salient features for the ternary alloy are a negative SRO parameter between Ni Cr and a positive between Cr Cr pairs as well as a weakly magnetic state. For the quaternary alloy we predict negative SRO parameter for Ni Cr and Ni Fe pairs and positive formore » Cr Cr and Fe Fe pairs. Atomic displacements for both ternary and quaternary alloys are negligible. In contrast to the ternary, the quaternary alloy shows a complex magnetic structure. The electronic structure of the ternary and quaternary alloys shows differences near the Fermi energy between a random solid solution and the predicted structure with SRO. Despite that, the calculated EXAFS spectra does not show enough contrast to discriminate between random and ordered structures. Finally, the predicted SRO has an impact on point-defect energetics, electron phonon coupling and thermodynamic functions and thus, SRO should not be neglected when studying properties of these two alloys.« less

  9. The microstructure of near-equiatomic B2/f.c.c. FeNiMnAl alloys

    SciTech Connect

    Baker, I.; Wu, H.; Wu, X.; Miller, M.K.; Munroe, P.R.

    2011-10-15

    A microstructural analysis of two FeNiMnAl alloys, Fe{sub 30}Ni{sub 20}Mn{sub 30}Al{sub 20} and Fe{sub 25}Ni{sub 25}Mn{sub 30}Al{sub 20}, was performed by a combination of atom probe tomography and transmission electron microscopy techniques. Although the microstructures of both alloys, which consist of alternating platelets aligned along < 100> of the B2-ordered phase, are similar to B2/b.c.c. two-phase alloys previously observed in the FeNiMnAl system, the two phases present in the current alloys are B2-ordered and f.c.c., with the latter phase being heavily twinned. Very fine ({approx} 5 nm) precipitates, whose chemistry was similar to that of the f.c.c. (Fe, Mn)-rich phase, were found within the B2 (Ni, Al)-rich phase in both alloys. - Highlights: {yields} The microstructures of the novel alloys Fe{sub 30}Ni{sub 20}Mn{sub 30}Al{sub 20} and Fe{sub 25}Ni{sub 25}Mn{sub 30}Al{sub 20} were characterized. {yields} Atom probe tomography and transmission electron microscopy were used in the study. {yields} A < 100>-aligned B2-ordered phase and heavily-twinned f.c.c. phase were present. {yields} Very fine (Fe, Mn)-rich precipitates were found within the B2 (Ni, Al)-rich phase.

  10. Metal Preferences and Metallation*

    PubMed Central

    Foster, Andrew W.; Osman, Deenah; Robinson, Nigel J.

    2014-01-01

    The metal binding preferences of most metalloproteins do not match their metal requirements. Thus, metallation of an estimated 30% of metalloenzymes is aided by metal delivery systems, with ∼25% acquiring preassembled metal cofactors. The remaining ∼70% are presumed to compete for metals from buffered metal pools. Metallation is further aided by maintaining the relative concentrations of these pools as an inverse function of the stabilities of the respective metal complexes. For example, magnesium enzymes always prefer to bind zinc, and these metals dominate the metalloenzymes without metal delivery systems. Therefore, the buffered concentration of zinc is held at least a million-fold below magnesium inside most cells. PMID:25160626

  11. A local view of bonding and diffusion at metal surfaces

    SciTech Connect

    Feibelman, P.J.

    1996-09-01

    First-principles density functional calculations and corresponding experimental results underline the importance of basic chemical concepts, such as coordination, valence saturation and promotion-hybridization energetics, in understanding bonding and diffusion of atoms at and on metal surfaces. Several examples are reviewed, including outer-layer relaxations of clean hcp(0001) surfaces, liquid-metal-embrittlement energetics, separation energies of metal-adatom dimers, concerted substitutional self-diffusion on fcc(001) surfaces, and adsorption and diffusion barrier sites for adatoms near steps.

  12. Pair vs many-body potentials: Influence on elastic and plastic behavior in nanoindentation of fcc metals

    NASA Astrophysics Data System (ADS)

    Ziegenhain, Gerolf; Hartmaier, Alexander; Urbassek, Herbert M.

    2009-09-01

    Molecular-dynamics simulation can give atomistic information on the processes occurring in nanoindentation experiments. In particular, the nucleation of dislocation loops, their growth, interaction and motion can be studied. We investigate how realistic the interatomic potentials underlying the simulations have to be in order to describe these complex processes. Specifically we investigate nanoindentation into a Cu single crystal. We compare simulations based on a realistic many-body interaction potential of the embedded-atom-method type with two simple pair potentials, a Lennard-Jones and a Morse potential. We find that qualitatively many aspects of nanoindentation are fairly well reproduced by the simple pair potentials: elastic regime, critical stress and indentation depth for yielding, dependence on the crystal orientation, and even the level of the hardness. The quantitative deficits of the pair potential predictions can be traced back: (i) to the fact that the pair potentials are unable in principle to model the elastic anisotropy of cubic crystals and (ii) as the major drawback of pair potentials we identify the gross underestimation of the stable stacking fault energy. As a consequence these potentials predict the formation of too large dislocation loops, the too rapid expansion of partials, too little cross slip and in consequence a severe overestimation of work hardening.

  13. Nanoindentation of hcp metals: a comparative simulation study of the evolution of dislocation networks.

    PubMed

    Alhafez, Iyad Alabd; Ruestes, Carlos J; Gao, Yu; Urbassek, Herbert M

    2016-01-29

    Using molecular dynamics simulation, we study the nanoindentation of three hcp metals: Mg, Ti, and Zr. Both the basal and two prismatic surface planes are considered. We focus on the characterization of the plasticity generated in the crystal. The similarities to, and the differences from, the behavior of the more commonly investigated fcc and bcc metals are highlighted. We find that hcp metals show a larger variety than the fcc and bcc metals studied up until now. The prolific emission of prismatic loops can lead to extended plastic zones. The size of the plastic zone is quantified by the ratio f of the plastic zone radius to the radius of the contact area. We find values of between 1.6 (an almost collapsed zone) and >5; in the latter case, complex dislocation networks build up which are extended in the direction of easy glide. PMID:26655887

  14. Nanoindentation of hcp metals: a comparative simulation study of the evolution of dislocation networks

    NASA Astrophysics Data System (ADS)

    Alabd Alhafez, Iyad; Ruestes, Carlos J.; Gao, Yu; Urbassek, Herbert M.

    2016-01-01

    Using molecular dynamics simulation, we study the nanoindentation of three hcp metals: Mg, Ti, and Zr. Both the basal and two prismatic surface planes are considered. We focus on the characterization of the plasticity generated in the crystal. The similarities to, and the differences from, the behavior of the more commonly investigated fcc and bcc metals are highlighted. We find that hcp metals show a larger variety than the fcc and bcc metals studied up until now. The prolific emission of prismatic loops can lead to extended plastic zones. The size of the plastic zone is quantified by the ratio f of the plastic zone radius to the radius of the contact area. We find values of between 1.6 (an almost collapsed zone) and >5 in the latter case, complex dislocation networks build up which are extended in the direction of easy glide.

  15. Size dependence of structural parameters in fcc and hcp Ru nanoparticles, revealed by Rietveld refinement analysis of high-energy X-ray diffraction data

    NASA Astrophysics Data System (ADS)

    Song, Chulho; Sakata, Osami; Kumara, Loku Singgappulige Rosantha; Kohara, Shinji; Yang, Anli; Kusada, Kohei; Kobayashi, Hirokazu; Kitagawa, Hiroshi

    2016-08-01

    To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data. For hexagonal close-packed (hcp) Ru NPs, the CO oxidation activity decreased with decreasing domain surface area. However, for face-centered cubic (fcc) Ru NPs, the CO oxidation activity became stronger with decreasing domain surface area. In comparing fcc Ru NPs with hcp Ru NPs, we found that the hcp Ru NPs of approximately 2 nm, which had a smaller domain surface area and smaller atomic displacement, showed a higher catalytic activity than that of fcc Ru NPs of the same size. In contrast, fcc Ru NPs larger than 3.5 nm, which had a larger domain surface area, lattice distortion, and larger atomic displacement, exhibited higher catalytic activity than that of hcp Ru NPs of the same size. In addition, the fcc Ru NPs had larger atomic displacements than hcp Ru NPs for diameters ranging from 2.2 to 5.4 nm. Enhancement of the CO oxidation activity in fcc Ru NPs may be caused by an increase in imperfections due to lattice distortions of close-packed planes and static atomic displacements.

  16. Size dependence of structural parameters in fcc and hcp Ru nanoparticles, revealed by Rietveld refinement analysis of high-energy X-ray diffraction data

    PubMed Central

    Song, Chulho; Sakata, Osami; Kumara, Loku Singgappulige Rosantha; Kohara, Shinji; Yang, Anli; Kusada, Kohei; Kobayashi, Hirokazu; Kitagawa, Hiroshi

    2016-01-01

    To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data. For hexagonal close-packed (hcp) Ru NPs, the CO oxidation activity decreased with decreasing domain surface area. However, for face-centered cubic (fcc) Ru NPs, the CO oxidation activity became stronger with decreasing domain surface area. In comparing fcc Ru NPs with hcp Ru NPs, we found that the hcp Ru NPs of approximately 2 nm, which had a smaller domain surface area and smaller atomic displacement, showed a higher catalytic activity than that of fcc Ru NPs of the same size. In contrast, fcc Ru NPs larger than 3.5 nm, which had a larger domain surface area, lattice distortion, and larger atomic displacement, exhibited higher catalytic activity than that of hcp Ru NPs of the same size. In addition, the fcc Ru NPs had larger atomic displacements than hcp Ru NPs for diameters ranging from 2.2 to 5.4 nm. Enhancement of the CO oxidation activity in fcc Ru NPs may be caused by an increase in imperfections due to lattice distortions of close-packed planes and static atomic displacements. PMID:27506187

  17. Modelling of Surfaces. Part 1: Monatomic Metallic Surfaces Using Equivalent Crystal Theory

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Ferrante, John; Rodriguez, Agustin M.

    1994-01-01

    We present a detailed description of equivalent crystal theory focusing on its application to the study of surface structure. While the emphasis is in the structure of the algorithm and its computational aspects, we also present a comprehensive discussion on the calculation of surface energies of metallic systems with equivalent crystal theory and other approaches. Our results are compared to experiment and other semiempirical as well as first-principles calculations for a variety of fcc and bcc metals.

  18. First-principles study of He point-defects in HCP rare-earth metals

    SciTech Connect

    Li, Yang; Chen, Ru; Peng, SM; Long, XG; Wu, Z.; Gao, Fei; Zu, Xiaotao

    2011-05-01

    He defect properties in Sc, Y, Gd, Tb, Dy, Ho, Er and Lu were studied using first-principles calculations based on density functional theory. The results indicate that the formation energy of an interstitial He atom is smaller than that of a substitutional He atom in all hcp rare-earth metals considered. Furthermore, the tetrahedral interstitial position is more favorable than an octahedral position for He defects. The results are compared with those from bcc and fcc metals.

  19. Defusing Complexity in Intermetallics: How Covalently Shared Electron Pairs Stabilize the FCC Variant Mo2Cu(x)Ga(6-x) (x ≈ 0.9).

    PubMed

    Kilduff, Brandon J; Yannello, Vincent J; Fredrickson, Daniel C

    2015-08-17

    Simple sphere packings of metallic atoms are generally assumed to exhibit highly delocalized bonding, often visualized in terms of a lattice of metal cations immersed in an electron gas. In this Article, we present a compound that demonstrates how covalently shared electron pairs can, in fact, play a key role in the stability of such structures: Mo2Cu(x)Ga(6-x) (x ≈ 0.9). Mo2Cu(x)Ga(6-x) adopts a variant of the common TiAl3 structure type, which itself is a binary coloring of the fcc lattice. Electronic structure calculations trace the formation of this compound to a magic electron count of 14 electrons/T atom (T = transition metal) for the TiAl3 type, for which the Fermi energy coincides with an electronic pseudogap. This count is one electron/T atom lower than the electron concentration for a hypothetical MoGa3 phase, making this structure less competitive relative to more complex alternatives. The favorable 14 electron count can be reached, however, through the partial substitution of Ga with Cu. Using DFT-calibrated Hückel calculations and the reversed approximation Molecular Orbital (raMO) method, we show that the favorability of the 14 electron count has a simple structural origin in terms of the 18 - n rule of T-E intermetallics (E = main group element): the T atoms of the TiAl3 type are arranged into square nets whose edges are bridged by E atoms. The presence of shared electron pairs along these T-T contacts allows for 18 electron configurations to be achieved on the T atoms despite possessing only 18 - 4 = 14 electrons/T atom. This bonding scheme provides a rationale for the observed stability range of TiAl3 type TE3 phases of ca. 13-14 electrons/T atom, and demonstrates how the concept of the covalent bond can extend even to the most metallic of structure types. PMID:26214504

  20. Using PM(2.5) lanthanoid elements and nonparametric wind regression to track petroleum refinery FCC emissions.

    PubMed

    Du, Li; Turner, Jay

    2015-10-01

    A long term air quality study is being conducted in Roxana, Illinois, USA, at the fenceline of a petroleum refinery. Measurements include 1-in-6 day 24-hour integrated ambient fine particulate matter (PM2.5) speciation following the Chemical Speciation Network (CSN) sampling and analysis protocols. Lanthanoid elements, some of which are tracers of fluidized-bed catalytic cracker (FCC) emissions, are also measured by inductively coupled plasma-mass spectrometry (ICP-MS) after extraction from PM2.5 using hot block-assisted acid digestion. Lanthanoid recoveries of 80-90% were obtained for two ambient particulate matter standard reference materials (NIST SRM 1648a and 2783). Ambient PM2.5 La patterns could be explained by a two-source model representing resuspended soil and FCC emissions with enhanced La/Ce ratios when impacted by the refinery. Nonparametric wind regression demonstrates that when the monitoring station was upwind of the refinery the mean La/Ce ratio is consistent with soil and when the monitoring station is downwind of the refinery the mean ratio is more than four times higher for bearings that corresponds to maximum impacts. Source apportionment modeling using EPA UNMIX and EPA PMF could not reliably apportion PM2.5 mass to the FCC emissions. However, the weight of evidence is that such contributions are small with no large episodes observed for the 164 samples analyzed. This study demonstrates the applicability of a hot block-assisted digestion protocol for the extraction of lanthanoid elements as well as insights obtained from long-term monitoring data including wind direction-based analyses. PMID:26005750

  1. Selective hydrodesulfurization of FCC naphtha with supported MoS{sub 2} catalysts : the role of cobalt.

    SciTech Connect

    Marshall, C. L.; Kropf, A. J.; Miler, J. T.; Reagan, W. J.; Kaduk, J. A.; Chemical Engineering; BP Amoco Research Center

    2000-07-01

    The catalytic activity and selectivity for hydrodesulfurization (HDS) and olefin hydrogenation of FCC naphtha have been determined for MoS2 (no Co) catalysts on different supports and for a commercial CoMo/alumina HDS catalyst both with and without the addition of alkali. For MoS2 catalysts, the specific HDS activity is higher on silica than alumina, while addition of Cs resulted in no change in the activity. The differences in activity, however, are relatively small, a factor of less than two. EXAFS and XRD structural analysis indicate that small MoS2 particles are present on all catalysts. The differences in rate are not due to differences in particle size, dispersion, or support physical properties, but are likely due to the modification of catalytic properties by an interaction with the support. While there is a small influence on the rate, the composition of the support, or modification by Cs, has no effect on the HDSlolefin hydrogenation selectivity. The olefin hydrogenation conversion increases linearly with HDS conversion, and at high HDS conversion, few olefins remain in the FCC naphtha. Similar to the effect for Cs promotion of MoS2 on alumina, the addition of K to sulfided CoMo/alumina had little affect on the activity or selectivity for HDS and olefin hydrogenation. Unlike MoS2 catalysts, however, with sulfided CoMo at less than about 85% HDS conversion, the rate of olefin hydrogenation is low, but it increases rapidly as the sulfur in the naphtha drops below about 300 ppm. Selective HDS of FCC naphtha appears to correlate primarily to the formation of the CoMoS phase, rather than to the basic nature of the support. It is proposed that the enhanced olefin hydrogenation selectivity of CoMo catalysts is due to the competitive adsorption of sulfur compounds, which inhibit adsorption and saturation of olefins in the naphtha.

  2. Stage IV work hardening in cubic metals

    SciTech Connect

    Rollett, A.D.; Kocks, U.F.; Doherty, R.D.

    1986-01-01

    The work hardening of fcc metals at large strains is discussed with reference to the linear stress-strain behavior often observed at large strains and known as Stage IV. The experimental evidence shows that Stage IV is a work hardening phenomenon that is found quite generally, even in pure fcc metals subjected to homogeneous deformation. A simple model for Stage IV in pure metals is presented, based on the accumulation of dislocation debris. Experiments are described for large strain torsion tests on four aluminum alloys. The level and extent of Stage IV scaled with the saturation stress that would represent the end of Stage III in the absence of a Stage IV. Reversing the torsion after large prestrains produced transient reductions in the work hardening. The strain rate sensitivity was also measured before and during the transient and found not to vary significantly. The microstructure observed at large strains in an Mg alloy suggest that Stage IV can occur in the absence of microband formation. Previous proposals for the cause of Stage IV are reviewed and found to be not supported by recent experimental data.

  3. Computer simulation of the motion of a straight dislocation line in concentrated solid solutions. II. [in fcc alloys

    NASA Technical Reports Server (NTRS)

    Kuo, C. T. K.; Arsenault, R. J.

    1977-01-01

    An investigation was undertaken to determine if the size and modulus interaction of a solute atom with a screw dislocation and the modulus interaction with an edge dislocation contributed to strengthening, in addition to the size interaction with an edge dislocation. The results indicate that the size interaction between solute atom and an edge dislocation accounts for most of the solid solution strengthening in f.c.c. alloys. The contribution to the yield stress from the modulus interaction with an edge dislocation is less than 15%. The interaction between a solute atom and a screw dislocation is much less than that between a solute atom and an edge dislocation.

  4. Numerical study of spray injection effects on the heat transfer and product yields of FCC riser reactors.

    SciTech Connect

    Chang, S. L.; Lottes, S. A.; Zhou, C. Q.; Bowman, B. J.; Petrick, M.; Energy Systems; Purdue Univ. at Calumet

    2001-06-01

    A three-phase reacting flow computational fluid dynamics (CFD) computer code was used to study the major effects of spray injection parameters on mixing, heat transfer, vaporization, and reaction product yields in fluidized catalytic cracking (FCC) riser reactors. The CFD code was validated using experimental or field data. A number of computations were performed with varied injection parameters, including injection velocity, injection angle, and droplet size. Local optimum operating windows for spray injection parameters were identified, and the sensitivity of local optima to variation in spray parameters was also investigated.

  5. Pressure-induced superconductivity in europium metal

    SciTech Connect

    Debessai, M.; Matsuoka, T.; Hamlin, J.J.; Bi, W.; Meng, Y.; Shimizu, K.; Schilling, J.S.

    2010-05-24

    Of the 52 known elemental superconductors among the 92 naturally occurring elements in the periodic table, fully 22 only become superconducting under sufficiently high pressure. In the rare-earth metals, the strong local magnetic moments originating from the 4f shell suppress superconductivity. For Eu, however, Johansson and Rosengren have suggested that sufficiently high pressures should promote one of its 4f electrons into the conduction band, changing Eu from a strongly magnetic (J=7/2) 4f{sup 7}-state into a weak Van Vleck paramagnetic (J=0) 4f{sup 6}-state, thus opening the door for superconductivity, as in Am (5f{sup 6}). We report that Eu becomes superconducting above 1.8 K for pressures exceeding 80 GPa, T{sub c} increasing linearly with pressure to 142 GPa at the rate +15 mK/GPa. Eu thus becomes the 53rd elemental superconductor in the periodic table. Synchrotron x-ray diffraction studies to 92 GPa at ambient temperature reveal four structural phase transitions.

  6. Physical vapour deposition growth and transmission electron microscopy characterization of epitaxial thin metal films on single-crystal Si and Ge substrates

    NASA Astrophysics Data System (ADS)

    Westmacott, K. H.; Hinderberger, S.; Dahmen, U.

    2001-06-01

    Epitaxial fcc, bcc and hcp metal and alloy films were grown in high vacuum by physical vapour deposition at high rate ('flash' deposition) on the (111), (110) and (100) surfaces of Si and Ge at different deposition temperatures. The resulting epitaxial relationships and morphological features of these films were characterized by transmission electron microscopy and diffraction. Simple epitaxial relationships were found mainly for the fcc metals that form binary eutectic systems with Si and G e. Of these, Ag exhibited exceptional behaviour by forming in a single crystal cube-cube relationship on all six semiconductor surfaces. Al and Au both formed bicrystal films on (100) substrates but differed in their behaviours on (111) substrates. Silicide formers such as the fcc metals Cu and Ni, as well as all bcc and hcp metals investigated, did not adopt epitaxial relationships on most semiconductor substrates. However, epitaxial single-crystal, bicrystal and tricrystal films of several metals and alloys could be grown by using a Ag buffer layer. The factors controlling the epitaxial growth of metal films are discussed in the light of the observations and compared with the predictions of established models for epitaxial relationships. It is concluded that epitaxial films can be grown easily if the film forms a simple eutectic or monotectic system with the substrate. The epitaxial relationships of those films depend on crystallographic factors for metal-metal epitaxy and on the substrate surface structure for metal-semiconductor epitaxy.

  7. Refractory metal particles in refractory inclusions in the Allende meteorite

    NASA Technical Reports Server (NTRS)

    Fuchs, L. H.; Blander, M.

    1980-01-01

    SEM and X-ray analysis were used to study refractory metal particles in five calcium-aluminum-rich inclusions in the Allende meteorite, and a complex variety of compositions and large departures from equilibrium were found. It is suggested that these particles could have been primordial condensates which were isolated from the nebula and from each other at different times by cocondensing oxides. Selective diffusion and/or oxidation of the more oxidizable metals (Mo, W, Fe, and Ni), phase segregations into different alloy phases (fcc, bcc, hcp, and, possibly, ordered phases), and the formation of metastable condensates could have been involved in the genesis of these materials

  8. Evaluation of Kapton pyrolysis, arc tracking, and arc propagation on the Space Station Freedom (SSF) solar array flexible current carrier (FCC)

    NASA Technical Reports Server (NTRS)

    Stueber, Thomas J.

    1991-01-01

    Recent studies involving the use of polyimide Kapton coated wires indicate that if a momentary electrical short circuit occurs between two wires, sufficient heating of the Kapton can occur to themally chlar (pyrolyze) the Kapton. Such charred Kapton has sufficient electricxl conductivity to create an arc which tracks down the wires and possibly propagates to adjoining wires. These studies prompted an invetigation to ascertain the likelihood of Kapton pyrolysis, arc tracking and propagation phenomena, and the magnitude of destruction conceivably inflicted on Space Station Freedom's (SSF's) Flexible Current Carrier (FCC) for the photovoltaic array. The geometric layout of the FCC, having a planar-type orientation as opposed to bundles, may reduce the probability of sustaining an arc. An experimental investigation was conducted to simulate conditions under which an arc can occur on the FCC of the SSF, and the consequences of arc initiation.

  9. Evaluation of Kapton pyrolysis, arc tracking, and arc propagation on the Space Station Freedom (SSF) solar array Flexible Current Carrier (FCC)

    NASA Technical Reports Server (NTRS)

    Stueber, Thomas J.

    1991-01-01

    Recent studies involving the use of polyimide Kapton coated wires indicate that if a momentary electrical short circuit occurs between two wires, sufficient heating of the Kapton can occur to thermally char (pyrolyze) the Kapton. Such charred Kapton has sufficient electrical conductivity to create an arc which tracks down the wires and possibly propagates to adjoining wires. These studies prompted an investigation to ascertain the likelihood of the Kapton pyrolysis, arc tracking and propagation phenomena, and the magnitude of destruction conceivably inflicted on Space Station Freedom's (SSF) Flexible Current Carrier (FCC) for the photovoltaic array. The geometric layout of the FCC, having a planar-type orientation as opposed to bundles, may reduce the probability of sustaining an arc. An experimental investigation was conducted to simulate conditions under which an arc can occur on the FCC of SSF, and the consequences of arc initiation.

  10. Neon helium mixtures as a refrigerant for the FCC beam screen cooling: comparison of cycle design options

    NASA Astrophysics Data System (ADS)

    Kloeppel, S.; Quack, H.; Haberstroh, C.; Holdener, F.

    2015-12-01

    In the course of the studies for the next generation particle accelerators, in this case the Future Circular Collider for hadron-hadron interaction (FCC-hh), different aspects are being investigated. One of these is the heat load on the beam screen, which results mainly from the synchrotron radiation. In case of the FCC-hh, a heat load of 6 MW is expected. The heat has to be absorbed at 40 to 60 K due to vacuum restrictions. In this range, refrigeration is possible with both helium and neon. Our investigations are focused on a mixed refrigerant of these two components, which combines the advantages of both. Especially promising is the possible substitution of the oil flooded screw compressors by more efficient turbo compressors. This paper investigates different flow schemes and mixture compositions with respect to complexity and efficiency. Furthermore, thermodynamic aspects, e.g. whether to use cold or warm secondary cycle compressors are discussed. Additionally, parameters of the main compressor are established.

  11. Studies of charge neutral FCC Lattice Gas with Yukawa Interaction and Accelerated Cartesian Expansion method

    NASA Astrophysics Data System (ADS)

    Huang, He

    In this thesis, I present the results of studies of the structural properties and phase transition of a charge neutral FCC Lattice Gas with Yukawa Interaction and discuss a novel fast calculation algorithm---Accelerated Cartesian Expansion (ACE) method. In the first part of my thesis, I discuss the results of Monte Carlo simulations carried out to understand the finite temperature (phase transition) properties and the ground state structure of a Yukawa Lattice Gas (YLG) model. In this model the ions interact via the potential q iqjexp(-kappar> ij)/rij where qi,j are the charges of the ions located at the lattice sites i and j with position vectors R i and Rj; rij = Ri-Rj, kappa is a measure of the range of the interaction and is called the screening parameter. This model approximates an interesting quaternary system of great current thermoelectric interest called LAST-m, AgSbPbmTem+2. I have also developed rapid calculation methods for the potential energy calculation in a lattice gas system with periodic boundary condition bases on the Ewald summation method and coded the algorithm to compute the energies in MC simulation. Some of the interesting results of the MC simulations are: (i) how the nature and strength of the phase transition depend on the range of interaction (Yukawa screening parameter kappa) (ii) what is the degeneracy of the ground state for different values of the concentration of charges, and (iii) what is the nature of two-stage disordering transition seen for certain values of x. In addition, based on the analysis of the surface energy of different nano-clusters formed near the transition temperature, the solidification process and the rate of production of these nano-clusters have been studied. In the second part of my thesis, we have developed two methods for rapidly computing potentials of the form R-nu. Both these methods are founded on addition theorems based on Taylor expansions. Taylor's series has a couple of inherent advantages: (i) it

  12. Characterization of erosion of metallic materials under cavitation attack in a mineral oil

    NASA Technical Reports Server (NTRS)

    Rao, B. C. S.; Buckley, D. H.

    1984-01-01

    Cavitation erosion and erosion rates of eight metallic materials representing three crystal structures were studied using a 20-kHz ultrasonic magnetostrictive oscillator in viscous mineral oil. The erosion rates of the metals with an fcc matrix were 10 to 100 times higher than that of an hcp-matrix titanium alloy. The erosion rates of iron and molybdenum, with bcc matrices, were higher than that of the titanium alloy but lower than those of the fcc metals. Scanning electron microscopy indicates that the cavitation pits are initially formed at the grain boundaries and precipitates and that the pits that formed at the triple points grew faster than the others. Transcrystalline craters formed by cavitation attack over the surface of grains and roughened the surfaces by multiple slip and twinning. Surface roughness measurements show that the pits that formed over the grain boundaries deepended faster than other pits. Computer analysis revealed that a geometric expression describes the nondimensional erosion curves during the time period 0.5 t(0) t 2.5 t(0), where t(0) is the incubation period. The fcc metals had very short incubation periods; the titanium alloy had the longest incubation period.

  13. An effective evolutionary algorithm for protein folding on 3D FCC HP model by lattice rotation and generalized move sets

    PubMed Central

    2013-01-01

    Background Proteins are essential biological molecules which play vital roles in nearly all biological processes. It is the tertiary structure of a protein that determines its functions. Therefore the prediction of a protein's tertiary structure based on its primary amino acid sequence has long been the most important and challenging subject in biochemistry, molecular biology and biophysics. In the past, the HP lattice model was one of the ab initio methods that many researchers used to forecast the protein structure. Although these kinds of simplified methods could not achieve high resolution, they provided a macrocosm-optimized protein structure. The model has been employed to investigate general principles of protein folding, and plays an important role in the prediction of protein structures. Methods In this paper, we present an improved evolutionary algorithm for the protein folding problem. We study the problem on the 3D FCC lattice HP model which has been widely used in previous research. Our focus is to develop evolutionary algorithms (EA) which are robust, easy to implement and can handle various energy functions. We propose to combine three different local search methods, including lattice rotation for crossover, K-site move for mutation, and generalized pull move; these form our key components to improve previous EA-based approaches. Results We have carried out experiments over several data sets which were used in previous research. The results of the experiments show that our approach is able to find optimal conformations which were not found by previous EA-based approaches. Conclusions We have investigated the geometric properties of the 3D FCC lattice and developed several local search techniques to improve traditional EA-based approaches to the protein folding problem. It is known that EA-based approaches are robust and can handle arbitrary energy functions. Our results further show that by extensive development of local searches, EA can also be very

  14. Structure analyses of Cu nanoclusters in the soft magnetic Fe85.2Si1B9P4Cu0.8 alloy by XAFS and fcc cluster model

    NASA Astrophysics Data System (ADS)

    Matsuura, M.; Nishijima, M.; Konno, K.; Ofuchi, H.; Takenaka, K.; Makino, A.

    2016-05-01

    Size of the clusters and structure details of fcc Cu clusters in nanocrystalline soft magnetic alloy of Fe85-86Si1-2B8P4Cu1 (NANOMET) are investigated. A linear combination fitting of XAFS data indicates that about 30% of Cu atoms are partitioned in the fcc clusters and the rest in the amorphous matrix. EXAFS of the fcc Cu nanocluster embedded in amorphous matrix is calculated on the basis of a simple fcc structure model using FEFF9. Surface effect of the nanoclusters is considered by counting a fraction of the nearest neighbour atoms in amorphous matrix. Good agreement with the experimental result is obtained for the fcc nanocluster with 9 coordination shells which consists of total 177 atoms within 1.5 nm in a diameter.

  15. On the interaction between a vacancy and interstitial loops in metals

    SciTech Connect

    Puigvi, Mary Angels; de Diego, Nieves; Serra, Anna; Osetskiy, Yury N; Bacon, David J

    2007-01-01

    Atomic-scale computer simulation is used to study interaction between a vacancy and clusters of self-interstitial atoms in metals with hcp, fcc and bcc crystal structure: -zirconium, copper and -iron. Effects of cluster size, atomic structure, dislocation nature of the cluster side and temperature are investigated. A vacancy can recombine with any interstitial in small clusters and this does not affect cluster mobility. In large clusters interaction depends on whether the cluster sides dissociate into partial dislocations. A vacancy recombines only on undissociated sides and corners created with undissociated segments. Vacancies inside the cluster perimeter do not recombine but restrict cluster mobility. Temperature enhances recombination by either increasing the number of recombination sites or assisting vacancy diffusion towards such sites. The results are relevant to differences in bcc, fcc and hcp metals microstructure evolution under irradiation observed experimentally and studied by theoretical or higher level modelling techniques.

  16. Fabrication of FCC-SiO2 colloidal crystals using the vertical convective self-assemble method

    NASA Astrophysics Data System (ADS)

    Castañeda-Uribe, O. A.; Salcedo-Reyes, J. C.; Méndez-Pinzón, H. A.; Pedroza-Rodríguez, A. M.

    2014-05-01

    In order to determine the optimal conditions for the growth of high-quality 250 nm-SiO2 colloidal crystals by the vertical convective self-assemble method, the Design of Experiments (DoE) methodology is applied. The influence of the evaporation temperature, the volume fraction, and the pH of the colloidal suspension is studied by means of an analysis of variance (ANOVA) in a 33 factorial design. Characteristics of the stacking lattice of the resulting colloidal crystals are determined by scanning electron microscopy and angle-resolved transmittance spectroscopy. Quantitative results from the statistical test show that the temperature is the most critical factor influencing the quality of the colloidal crystal, obtaining highly ordered structures with FCC stacking lattice at a growth temperature of 40°C.

  17. Estimation of interaction energies Me-(C, N) in fcc iron-based alloys using Thermo-Calc thermodynamic database

    SciTech Connect

    Sozinov, A.L.; Gavriljuk, V.G.

    1999-08-20

    At present, there is a number of thermodynamic data for Fe base liquid and solid systems containing substitutional and interstitial solute elements. A variety of properties of carbon and nitrogen austenitic steels is essentially determined by the distribution of interstitials in solid solutions, which, in turn, depends on the interaction between solute atoms. The aim of this study is to estimate the values of interaction energy Me-i in f.c.c. Fe-Me-i systems, where Me represents various substitutional alloying elements and i is an interstitial (C or N), using the Fe-base database of the Thermo-Calc program created by the Swedish Royal Institute of Technology.

  18. Spin Dynamics and Two-Dimensional Correlations in the FCC Antiferromagnetic Sr2 YRuO6

    NASA Astrophysics Data System (ADS)

    Disseler, Steven; Lynn, J. W.; Jardim, R. F.; Torikachvili, M. S.; Gr, E.

    The face-centered cubic lattice lattice of Ru5+ spins in the double perovskite Sr2YRuO6 shows a delicate three dimensional antiferromagnetic (AFM) ground state composed of stacked square AFM layers. We present new inelastic neutron scattering data taken on this state revealing a gapped low-energy excitation band that may be modeled by a simple J1 -J2 interaction scheme allowing quantitative comparison of similar materials. At higher temperatures, the low-energy excitation spectrum is dominated by a quasi-elastic component associated with size fluctuations of two-dimensional AFM clusters that exhibit asymmetric correlations even at low temperatures. Thus, the FCC lattice in general and the double perovskite structure in particular emerge as hosts of both two-dimensional and three-dimensional dynamics resulting from frustration.

  19. Magnetic Excitations from the Exotic Ground State of the Quantum FCC Antiferromagnet Ba2YMoO6

    SciTech Connect

    Carlo, Jeremy P; Clancy, James P; Aharen, T.; Yamani, Zahra; Ruff, Jacob; Wagman, J.; Van Gastel, G. J.; Noad, H. M.; Granroth, Garrett E; Greedan, John E; Dabkowska, H. A.; Gaulin, Bruce D.

    2011-01-01

    The geometrically frustrated double perovskite Ba{sub 2}YMoO{sub 6} is characterized by quantum s = 1/2 spins at the Mo{sup 5+} sites of an undistorted fcc lattice. Previous low-temperature characterization revealed an absence of static long-range magnetic order and suggested a nonmagnetic spin-singlet ground state. We report unique time-of-flight and triple-axis neutron spectroscopy of Ba{sub 2}YMoO{sub 6} that shows a 28 meV spin excitation with a bandwidth of {approx}4 meV, which vanishes above {approx}125 K. We identify this as the singlet-triplet excitation that arises out of a singlet ground state, and further identify a weaker continuum of magnetic states within the gap, reminiscent of spin-polaron states arising due to weak disorder.

  20. Fabrication of FCC-SiO{sub 2} colloidal crystals using the vertical convective self-assemble method

    SciTech Connect

    Castañeda-Uribe, O. A.; Salcedo-Reyes, J. C.; Méndez-Pinzón, H. A.; Pedroza-Rodríguez, A. M.

    2014-05-15

    In order to determine the optimal conditions for the growth of high-quality 250 nm-SiO{sub 2} colloidal crystals by the vertical convective self-assemble method, the Design of Experiments (DoE) methodology is applied. The influence of the evaporation temperature, the volume fraction, and the pH of the colloidal suspension is studied by means of an analysis of variance (ANOVA) in a 3{sup 3} factorial design. Characteristics of the stacking lattice of the resulting colloidal crystals are determined by scanning electron microscopy and angle-resolved transmittance spectroscopy. Quantitative results from the statistical test show that the temperature is the most critical factor influencing the quality of the colloidal crystal, obtaining highly ordered structures with FCC stacking lattice at a growth temperature of 40°C.

  1. 47 CFR 95.220 - (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference? 95.220 Section 95.220 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control...

  2. 47 CFR 95.423 - (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference? 95.423 Section 95.423 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band...

  3. 47 CFR 95.220 - (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference? 95.220 Section 95.220 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control...

  4. 47 CFR 95.423 - (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference? 95.423 Section 95.423 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band...

  5. 47 CFR 95.423 - (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference? 95.423 Section 95.423 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band...

  6. 47 CFR 95.220 - (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference?

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference? 95.220 Section 95.220 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control...

  7. 47 CFR 95.220 - (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference? 95.220 Section 95.220 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control...

  8. 47 CFR 95.423 - (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference? 95.423 Section 95.423 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band...

  9. 47 CFR 95.220 - (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false (R/C Rules 20) What must I do if the FCC tells me that my R/C station is causing interference? 95.220 Section 95.220 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Radio Control...

  10. 47 CFR 95.423 - (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false (CB Rule 23) What must I do if the FCC tells me that my CB station is causing interference? 95.423 Section 95.423 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band...

  11. Regulation of Fumonisin B1 Biosynthesis and Conidiation in Fusarium verticillioides by a Cyclin-Like (C-Type) Gene, FCC1†

    PubMed Central

    Shim, Won-Bo; Woloshuk, Charles P.

    2001-01-01

    Fumonisins are a group of mycotoxins produced in corn kernels by the plant-pathogenic fungus Fusarium verticillioides. A mutant of the fungus, FT536, carrying a disrupted gene named FCC1 (for Fusarium cyclin C1) resulting in altered fumonisin B1 biosynthesis was generated. FCC1 contains an open reading frame of 1,018 bp, with one intron, and encodes a putative 319-amino-acid polypeptide. This protein is similar to UME3 (also called SRB11 or SSN8), a cyclin C of Saccharomyces cerevisiae, and contains three conserved motifs: a cyclin box, a PEST-rich region, and a destruction box. Also similar to the case for C-type cyclins, FCC1 was constitutively expressed during growth. When strain FT536 was grown on corn kernels or on defined minimal medium at pH 6, conidiation was reduced and FUM5, the polyketide synthase gene involved in fumonisin B1 biosynthesis, was not expressed. However, when the mutant was grown on a defined minimal medium at pH 3, conidiation was restored, and the blocks in expression of FUM5 and fumonisin B1 production were suppressed. Our data suggest that FCC1 plays an important role in signal transduction regulating secondary metabolism (fumonisin biosynthesis) and fungal development (conidiation) in F. verticillioides. PMID:11282612

  12. 47 CFR 3.53 - FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s). 3.53 Section 3.53 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL AUTHORIZATION AND ADMINISTRATION OF ACCOUNTING AUTHORITIES IN MARITIME AND MARITIME...

  13. 47 CFR 3.53 - FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s). 3.53 Section 3.53 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL AUTHORIZATION AND ADMINISTRATION OF ACCOUNTING AUTHORITIES IN MARITIME AND MARITIME...

  14. 47 CFR 3.53 - FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s). 3.53 Section 3.53 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL AUTHORIZATION AND ADMINISTRATION OF ACCOUNTING AUTHORITIES IN MARITIME AND MARITIME...

  15. 47 CFR 3.53 - FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s). 3.53 Section 3.53 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL AUTHORIZATION AND ADMINISTRATION OF ACCOUNTING AUTHORITIES IN MARITIME AND MARITIME...

  16. 47 CFR 3.53 - FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false FCC notification of refusal to provide telecommunications service to U.S. registered vessel(s). 3.53 Section 3.53 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL AUTHORIZATION AND ADMINISTRATION OF ACCOUNTING AUTHORITIES IN MARITIME AND MARITIME MOBILE-SATELLITE RADIO...

  17. Critical Rural Considerations Regarding Joint Board Recommendations to the FCC Concerning Section 254 of the Telecommunications Act of 1996, P97-4.

    ERIC Educational Resources Information Center

    Missouri Univ., Columbia. Rural Policy Research Inst.

    The Rural Policy Research Institute's Rural Telecommunications Task Force assessed the rural impacts and unintended or adverse rural consequences of the Federal-State Joint Board's recommendations to the FCC regarding Section 254 of the Telecommunications Act of 1996. Ten critical rural components of the Joint Board recommendations are listed: (1)…

  18. First-principles study of point defects in an fcc Fe-10Ni-20Cr model alloy

    NASA Astrophysics Data System (ADS)

    Piochaud, J. B.; Klaver, T. P. C.; Adjanor, G.; Olsson, P.; Domain, C.; Becquart, C. S.

    2014-01-01

    The influence of the local environment on vacancy and self-interstitial formation energies has been investigated in a face-centered-cubic (fcc) Fe-10Ni-20Cr model alloy by analyzing an extensive set of first-principle calculations based on density functional theory. Chemical disorder has been considered by designing special quasirandom structures and four different collinear magnetic structures have been investigated in order to determine a relevant reference state to perform point defect calculations at 0 K. Two different convergence methods have also been used to characterize the importance of the method on the results. Although our fcc Fe-10Ni-20Cr would be better represented in terms of applications by the paramagnetic state, we found that the antiferromagnetic single-layer magnetic structure was the most stable at 0 K and we chose it as a reference state to determine the point defect properties. Point defects have been introduced in this reference state, i.e., vacancies and Fe-Fe, Fe-Ni, Fe-Cr, Cr-Cr, Ni-Ni, and Ni-Cr dumbbell interstitials oriented either parallel or perpendicular to the single layer antiferromagnetic planes. Each point defect studied was introduced at different lattice sites to consider a sufficient variety of local environments and analyze its influence on the formation energy values. We have estimated the point defect formation energies with linear regressions using variables which describe the local environment surrounding the point defects. The number and the position of Ni and Cr first nearest neighbors to the point defects were found to drive the evolution of the formation energies. In particular, Ni is found to decrease and Cr to increase the vacancy formation energy of the model alloy, while the opposite trends are found for the dumbbell interstitials. This study suggested that, to a first approximation, the first nearest atoms to point defects can provide reliable estimates of point defect formation energies.

  19. The frustrated fcc antiferromagnet Ba2 YOsO6: Structural characterization, magnetic properties and neutron scattering studies

    DOE PAGESBeta

    Kermarrec, E.; Marjerrison, Casey A.; Thompson, C. M.; Maharaj, Dalini D.; Levin, K.; Kroeker, S.; Granroth, Garrett E.; Flacau, Roxana; Yamani, Zahra; Greedan, John E.; et al

    2015-02-26

    Here we report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2 YOsO6. The Fmmore » $$\\bar{3}$$m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) Å and 8.3435(4) Å, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ~₋700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN~69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ~3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2 YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. We find time-of-flight inelastic neutron results reveal a large spin gap Δ~17 meV, unexpected for an orbitally quenched, d3 electronic configuration. In conclusion, we discuss this in the context of the ~5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ~3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.« less

  20. The structure of small metal clusters

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Pettersson, L. G. M.

    1986-01-01

    One metal atom surrounded by its 12 nearest neighbors is considered for both D(3d) (face-centered cubic-like) and D(3h) (hexagonal close-packed-like) geometries. For Al and Be, the neutral cluster and the positive and negative ions are considered for idealized (all bonds equal) and distorted geometries. The D(3d) geometry is found to be the lowest for Be13, while the D(3h) geometry is lower for Al13. This is the reverse of what is expected based upon the bulk metal structures, Be(hcp) and Al(fcc). Al13 is found to have only small distortions, while Be13 shows large distortions for both the D(3d) and D(3h) geometries. The ions have geometries which are similar to those found for the neutral systems. Both all-electron and effective core potential calculations were carried out on the X13 clusters; the agreement is very good.

  1. Characterization of erosion of metallic materials under cavitation attack in a mineral oil

    NASA Technical Reports Server (NTRS)

    Rao, B. C. S.; Buckley, D. H.

    1985-01-01

    Cavitation erosion and erosion rates of eight metallic materials representing three crystal structures were studied. The erosion experiments were conducted with a 20-kHz ultrasonic magnetostrictive oscillator in a viscous mineral oil. The erosion rates of the metals with an fcc matrix were 10 to 100 times higher than that of an hop-matrix titanium alloy. The erosion rates of iron and molybdenum, with bcc matrices, were higher than that of the titanium alloy but lower than those of those of the fcc materials. Studies with scanning electron microscopy indicated that the cavitation pits were initially formed at the grain boundaries and precipitates and that the pits formed at the junction of grain boundaries grew faster than the others. Transcrystalline craters formed by cavitation attack over the surface of grains and roughened the surfaces by multiple slip and twinning. Surface roughness measurements showed that the pits that formed over the grain boundaries deepened faster than pits. Computer analysis revealed that a geometric expression describes the nondimensional erosion curves during the time period 0.5 t (sub 0) t 2.5 t (sub 0), where t (sub 0) is the incubation period. The fcc metals had very short incubation periods; the titanium alloy had the longest incubation period.

  2. Growth of coronene on (100)- and (111)-surfaces of fcc-crystals

    NASA Astrophysics Data System (ADS)

    Huempfner, Tobias; Sojka, Falko; Forker, Roman; Fritz, Torsten

    2015-09-01

    The growth of coronene thin films is studied via low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) comparing metal substrates with different lattice constants, different surface symmetry, and also with surface passivation, namely Cu(111), Ag(111), Ag(100), and (100)-terminated KCl/Ag(100). In particular, we investigate the evolution of the coronene lattice parameters upon coverage- and temperature-variation. On the pristine metal surfaces we observe disordered phases at low coverage. Further deposition leads to hexagonal arrangement of the molecules. With increasing coverage the lattice constant decreases continuously, whereas on Cu(111) the molecular unit cell additionally rotates w.r.t. the substrate lattice. We also discuss the interaction mechanisms that are responsible for this behavior. Due to the continuous change in the lattice dimensions we observe many incommensurate structures that were stable during our measurements, however the close-packed structures we found were always commensurate. The use of a passivation layer leads to the formation of a bulk-like structure consisting of molecules adsorbed in an upright standing manner which is stable at low temperatures only.

  3. Quantum Conductance in Metal Nanowires

    NASA Astrophysics Data System (ADS)

    Ugarte, Daniel

    2004-03-01

    Quantum Conductance in Metal Nanowires D. Ugarte Brazilian National Synchrotron Light Laboratory C.P. 6192, 13084-971 Campinas SP, Brazil. Electrical transport properties of metallic nanowires (NWs) have received great attention due to their quantum conductance behavior. Atomic scale wires can be generated by stretching metal contacts; during the elongation and just before rupture, the NW conductance shows flat plateaus and abrupt jumps of approximately a conductance quantum. In this experiments, both the NW atomic arrangement and conductance change simultaneously, making difficult to discriminate electronic and structural effects. In this work, the atomic structure of NWs was studied by time-resolved in situ experiments in a high resolution transmission electron microscope, while their electrical properties using an UHV mechanically controllable break junction (MCBJ). From the analysis of numerous HRTEM images and videos, we have deduced that metal (Au, Ag, Pt, etc.) junctions generated by tensile deformation are crystalline and free of defects. The neck structure is strongly dependent on the surface properties of the analyzed metal, this was verified by comparing different metal NWs (Au, Ag, Cu), which have similar atomic structure (FCC), but show very different faceting patterns. The correlation between the observed structural and transport properties of NW points out that the quantum conductance behavior is defined by preferred atomic arrangement at the narrowest constriction. In the case of magnetic (ex. Fe,Co,Ni) or quasi-magnetic (ex. Pd) wires, we have observed that one-atom-thick structures show a conductance of half the quantum as expected for a fully spin polarized current. This phenomenon seems to occur spontaneously for magnetic suspended atom-chains in zero magnetic field and at room temperature. These results open new opportunities for spin control in nanostructures. Funded by FAPESP, LNLS and CNPq.

  4. Deformation in metals after low temperature irradiation: Part II - Irradiation hardening, strain hardening, and stress ratios

    SciTech Connect

    Byun, Thak Sang; Li, Meimei

    2008-03-01

    Effects of irradiation at temperatures 200oC on tensile stress parameters are analyzed for dozens of bcc, fcc, and hcp pure metals and alloys, focusing on irradiation hardening, strain hardening, and relationships between the true stress parameters. Similar irradiation-hardening rates are observed for all the metals irrespective of crystal type; typically, the irradiation-hardening rates are large, in the range 100 - 1000 GPa/dpa, at the lowest dose of <0.0001 dpa and decrease with dose to a few tens of MPa/dpa or less at about 10 dpa. However, average irradiation-hardening rates over the dose range of 0 dpa − (the dose to plastic instability at yield) are considerably lower for stainless steels due to their high uniform ductility. It is shown that whereas low temperature irradiation increases the yield stress, it does not significantly change the strain-hardening rate of metallic materials; it decreases the fracture stress only when non-ductile failure occurs. Such dose independence in strain hardening behavior results in strong linear relationships between the true stress parameters. Average ratios of plastic instability stress to unirradiated yield stress are about 1.4, 3.9, and 1.3 for bcc metals (and precipitation hardened IN718 alloy), annealed fcc metals (and pure Zr), and Zr-4 alloy, respectively. Ratios of fracture stress to plastic instability stress are calculated to be 2.2, 1.7, and 2.1, respectively. Comparison of these values confirms that the annealed fcc metals and other soft metals have larger uniform ductility but smaller necking ductility when compared to other materials.

  5. A new high pressure and temperature equation of state of fcc cobalt

    SciTech Connect

    Armentrout, Matthew M.; Kavner, Abby

    2015-11-21

    The high pressure and temperature equation of state of cobalt metal in the face-centered cubic phase was measured up to 57 GPa and 2400 K using the laser heated diamond anvil cell in conjunction with synchrotron X-ray diffraction. The measured region is bisected by a ferromagnetic to paramagnetic transition across the Curie temperature necessitating use of an equation of state that incorporates a 2nd order phase transition within its formalism. A third order Birch-Murnaghan equation of state with a Mie-Grüneisen-Debye thermal correction and a Hillert-Jarl magnetic correction is employed to describe the data above and below the Curie temperature. We find best fit parameters of V{sub 0} = 6.753 (fixed) cm{sup 3}/mol, K{sub 0} = 196 (3) GPa, K′ = 4.7 (2), γ{sub 0} = 2.00 (11), q = 1.3 (5), and θ{sub 0} = 385 K (fixed)

  6. New FCC Mg-Zr and Mg-Zr-ti deuterides obtained by reactive milling

    NASA Astrophysics Data System (ADS)

    Guzik, Matylda N.; Deledda, Stefano; Sørby, Magnus H.; Yartys, Volodymyr A.; Hauback, Bjørn C.

    2015-03-01

    Results for binary Mg-Zr and ternary Mg-Zr-Ti mixtures ball milled at room temperature under reactive deuterium atmosphere (5.6-6.7 MPa) are reported. X-ray and neutron powder diffraction combined with Rietveld refinements show that two new cubic phases were formed during milling. Mg0.40Zr0.60D1.78 and Mg0.40Zr0.26Ti0.34D1.98 crystallize with disordered face centered cubic metal atom arrangements. Results of differential scanning calorimetry and termogravimetric measurements demonstrate that both deuterides desorb deuterium at lower temperatures than MgD2, ZrD2 or TiD2; 528 and 575 K in the Mg-Zr-D and Mg-Zr-Ti-D system, respectively. Interestingly, Mg0.40Zr0.26Ti0.34D1.98 stores deuterium reversibly at 673 K and 10 MPa of D2.

  7. X-ray Fluorescence Tomography of Aged Fluid-Catalytic-Cracking Catalyst Particles Reveals Insight into Metal Deposition Processes

    PubMed Central

    Kalirai, Sam; Boesenberg, Ulrike; Falkenberg, Gerald; Meirer, Florian; Weckhuysen, Bert M

    2015-01-01

    Microprobe X-ray fluorescence tomography was used to investigate metal poison deposition in individual, intact and industrially deactivated fluid catalytic cracking (FCC) particles at two differing catalytic life-stages. 3 D multi-element imaging, at submicron resolution was achieved by using a large-array Maia fluorescence detector. Our results show that Fe, Ni and Ca have significant concentration at the exterior of the FCC catalyst particle and are highly co-localized. As concentrations increase as a function of catalytic life-stage, the deposition profiles of Fe, Ni, and Ca do not change significantly. V has been shown to penetrate deeper into the particle with increasing catalytic age. Although it has been previously suggested that V is responsible for damaging the zeolite components of FCC particles, no spatial correlation was found for V and La, which was used as a marker for the embedded zeolite domains. This suggests that although V is known to be detrimental to zeolites in FCC particles, a preferential interaction does not exist between the two. PMID:26613011

  8. Selective Growth of Noble Gases at Metal/Oxide Interface.

    PubMed

    Takahashi, Keisuke; Oka, Hiroshi; Ohnuki, Somei

    2016-02-17

    The locations and roles of noble gases at an oxide/metal interface in oxide dispersed metal are theoretically and experimentally investigated. Oxide dispersed metal consisting of FCC Fe and Y2Hf2O7 (Y2Ti2O7) is synthesized by mechanical alloying under a saturated Ar gas environment. Transmission electron microscopy and density functional theory observes the strain field at the interface of FCC Fe {111} and Y2Hf2O7 {111} whose physical origin emerges from surface reconstruction due to charge transfer. Noble gases are experimentally observed at the oxide (Y2Ti2O7) site and calculations reveal that the noble gases segregate the interface and grow toward the oxide site. In general, the interface is defined as the trapping site for noble gases; however, transmission electron microscopy and density functional theory found evidence which shows that noble gases grow toward the oxide, contrary to the generally held idea that the interface is the final trapping site for noble gases. Furthermore, calculations show that the inclusion of He/Ar hardens the oxide, suggesting that material fractures could begin from the noble gas bubble within the oxides. Thus, experimental and theoretical results demonstrate that noble gases grow from the interface toward the oxide and that oxides behave as a trapping site for noble gases. PMID:26840881

  9. Exotic magnetism on the quasi-FCC lattices of the d3 double perovskites La2NaB'O6 (B' = Ru, Os)

    SciTech Connect

    Aczel, Adam A; Baker, Peter J.; Bugaris, Dan; Yeon, Jeongho; Zur Loye, Hans-Conrad; Guidi, T.; Adroja, D. T.

    2014-01-01

    We find evidence for long-range and short-range ($\\zeta$~$=$~70~\\AA~at 4~K) incommensurate magnetic order on the quasi-face-centered-cubic (FCC) lattices of the monoclinic double perovskites La$_2$NaRuO$_6$ and La$_2$NaOsO$_6$ respectively. Incommensurate magnetic order on the FCC lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbour and next nearest neighbour exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap $\\Delta$~$\\sim$~2.75~meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally-coordinated $3d^3$ systems, so the large gap observed for La$_2$NaRuO$_6$ may result from the significantly enhanced value of spin-orbit coupling in this $4d^3$ material.

  10. Exotic Magnetism on the Quasi-fcc Lattices of the d3 Double Perovskites La2NaB'O6 (B'=Ru, Os)

    NASA Astrophysics Data System (ADS)

    Aczel, A. A.; Baker, P. J.; Bugaris, D. E.; Yeon, J.; zur Loye, H.-C.; Guidi, T.; Adroja, D. T.

    2014-03-01

    We find evidence for long-range and short-range (ζ =70 Å at 4 K) incommensurate magnetic order on the quasi-face-centered-cubic (fcc) lattices of the monoclinic double perovskites La2NaRuO6 and La2NaOsO6, respectively. Incommensurate magnetic order on the fcc lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbor and next nearest neighbor exchange interactions. In the Ru system with long-range order, inelastic neutron scattering also reveals a spin gap Δ ˜2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally coordinated 3d3 systems, so the large gap observed for La2NaRuO6 may result from the significantly enhanced value of spin-orbit coupling in this 4d3 material.

  11. Analytic formulations for one-dimensional decay of rectangular homoepitaxial islands during coarsening on anisotropic fcc (110) surfaces

    SciTech Connect

    Wang, Chi-Jen; Han, Yong; Walen, Holly; Russell, Selena M.; Thiel, Patricia A.; Evans, James W.

    2013-10-01

    Submonolayer homoepitaxial fcc (110) systems display behavior reflecting strong anisotropy at lower temperatures, including one-dimensional decay during Ostwald ripening of rectangular islands maintaining constant width in the (001) direction. To appropriately describe this behavior, we first develop a refined continuum Burton-Cabrera-Frank formalism, which accounts for a lack of equilibration of island shape and importantly also for inhibited incorporation of adatoms at almost-faceted (1¯10) island edges through effective kinetic coefficients. This formalism is shown to describe accurately the adatom diffusion fluxes between islands and thus island evolution for a complex experimental island configuration, as confirmed by matching results from realistic atomistic simulations for this configuration. This approach also elucidates basic dependencies of flux on island geometry and temperature. Second, a further refinement is presented incorporating separate terrace and edge adatom density fields either in a continuum setting or alternatively in a spatially discrete diffusion equation setting. The second approach allows more flexibility and accuracy in accounting for edge-diffusion kinetics including corner rounding, a lack of equilibration of the edge adatom density at (1¯10) island edges, and the effect of rare kinks on (1¯10) island edges. Finally and significantly, it suggests facile two-way corner rounding at the island periphery during island decay, contrasting the previous picture.

  12. Effect of Bi Substitution on the FCC to L10 Phase Transformation in CoPt(Bi) Nanoparticles

    NASA Astrophysics Data System (ADS)

    Abel, Frank; Tzitzios, Vasilis; Sellmyer, David; Hadjipanayis, George

    The transformation from the fcc to fct structure L10 in CoPt requires annealing at temperatures over 6000 C, as compared to FePt which can occur at 5500 C. In the past, similar attempts to lower the transformation temperature in CoPt have been unsuccessful. In this work, we report for the first time a decrease in the phase transformation temperature of chemically synthesized CoPt nanoparticles by the addition of a small amount of bismuth. Our studies have shown that the phase transformation occurs in as-made CoPt(Bi) nanoparticles at refluxing temperatures as low as 330 0C, which is significantly lower than previously reported values in CoPt nanoparticles and thin films. The as-made CoPt nanoparticles with 5% atomic weight Bi show partial L10 ordering with an average size of 11.7 nm, as shown by TEM imaging, and have a coercivity of 1 kOe and saturation magnetization of 32 emu/g. Annealing of the CoPt(Bi) nanoparticles produced maximum coercivities of 12.4 kOe when annealed at 700 0C for 1 hour. The effect of amount of Bi addition on the formation and ordering of L10 structure will be discussed.

  13. Formation of Superlattices of Gold Nanoparticles Using Ostwald Ripening in Emulsions: Transition from fcc to bcc Structure.

    PubMed

    Schmitt, Julien; Hajiw, Stéphanie; Lecchi, Amélie; Degrouard, Jéril; Salonen, Anniina; Impéror-Clerc, Marianne; Pansu, Brigitte

    2016-06-30

    An efficient method to form 3D superlattices of gold nanoparticles inside oil emulsion droplets is presented. We demonstrate that this method relies on Ostwald ripening, a well-known phenomenon occurring during the aging of emulsions. The key point is that the nanoparticle concentration inside the smaller droplets is increasing very slowly with time, thus inducing the crystallization of the nanoparticles into superlattices. Using oil-in-water emulsions doped with hydrophobic gold nanoparticles, we demonstrate that this method is efficient for different types of oils (toluene, cyclohexane, dodecane, and hexadecane). 3D superlattices of the nanoparticles are obtained, with dimensions reaching a hundred nanometers. The kinetics of the crystallization depends on the solubility of the oil in water but also on the initial concentration of the gold nanoparticles in oil. This method also provides an innovative way to obtain the complete phase diagram of nanoparticle suspensions with concentration. Indeed, during this slow crystallization process, a transition from a disordered suspension to a fcc structure is observed, followed by a transition toward a bcc structure. This evolution with time provides key results to understand the role played by the ligands located at the surface of the nanoparticles in order to control the type of superlattices which are formed. PMID:27267312

  14. A Study of Microstructural Length Scale Effects on the Behaviour of FCC Polycrystals Using Strain Gradient Concepts

    SciTech Connect

    Cheong, K S; Busso, E P; Arsenlis, A

    2004-05-07

    Grain size is a critically important aspect of polycrystalline materials and experimental observations on Cu and Al polycrystals have shown that a Hall-Petchtype phenomenon does exist at the onset of plastic deformation. In this work, a parametric study is conducted to investigate the effect of microstructural and deformation-related length scales on the behavior of such FCC polycrystals. It relies on a recently proposed non-local dislocation-mechanics based crystallographic theory to describe the evolution of dislocation mean spacings within each grain, and on finite element techniques to incorporate explicitly grain interaction effects. Polycrystals are modeled as representative volume elements (RVEs) containing up to 64 randomly oriented grains. Predictions obtained from RVEs of Cu polycrystals with different grain sizes are shown to be consistent with experimental data. Furthermore, mesh sensitivity studies revealed that, when there is a predominance of geometrically necessary dislocations (GNDs) relative to statistically-stored dislocations (SSDs), the polycrystal response becomes increasingly mesh sensitive. This was found to occur specially during the early stages of deformation in polycrystals with small grains.

  15. Crystal dynamics of δ fcc Pu-Ga alloy by high-resolution inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Wong, Joe; Krisch, M.; Farber, D. L.; Occelli, F.; Xu, R.; Chiang, T.-C.; Clatterbuck, D.; Schwartz, A. J.; Wall, M.; Boro, C.

    2005-08-01

    We have used a microbeam on large grain sample concept to carry out inelastic x-ray scattering experiments to measure the phonon dispersion curves of a fcc δ -phase Pu-Ga alloy along the main symmetry directions of the cubic lattice. This approach obviates experimental difficulties with conventional inelastic neutron scattering due to the high absorption cross section of the common Pu239 isotope and the nonavailability of large (millimeter size) single crystal materials for Pu and its alloys. A classical Born-von Kármán force constant model was used to model the experimental results, and up to fourth nearest neighbor interactions had to be included to obtain sufficient agreement. Several unusual features including, a large elastic anisotropy, a small shear elastic modulus (C11-C12)/2 , a positive kink in the T1[0ξξ] branch, and a pronounced bending (toward lower energy) of the T[ξξξ] branch near the L point in the Brillouin zone are found. These features are discussed in light of the various phase transformations of δ plutonium. The phonon dispersion data also provide a critical test and benchmark for theoretical treatments of highly correlated 5f electron systems.

  16. Self-consistent linearized augmented-plane-wave study of the electronic structure and superconductivity of fcc lanthanum under pressure

    NASA Astrophysics Data System (ADS)

    Pickett, Warren E.; Freeman, A. J.; Koelling, D. D.

    1980-09-01

    We report the results of a linearized augmented-plane-wave calculation of the electronic structure of fcc La at three lattice constants corresponding to ambient pressure, 50, and 120 kbars. The Kohn-Sham-Gáspar approximation for exchange and correlation is used and the potential is allowed a fully non-muffin-tin form. The f bands lie ~2-2.5 eV above the Fermi level and are ~1 eV wide, resulting in a very small (0.05 electrons) localized f occupation. Under pressure the f bands rise and broaden appreciably, resulting in only a slight increase in f occupation. The rigid-muffin-tin approximation for the electron-phonon interaction λ overestimates the superconducting transition temperature Tc by 40%, but we find that the drastic increase in Tc under pressure can be attributed primarily to changes in the electronic stiffness η. Structural transitions which occur at 25 and 53 kbars may be related to changes in Fermi-surface topology which we find to occur approximately at these pressures.

  17. Diffusion of a self-interstitial atom in an ultrathin fcc film bonded to a rigid substrate

    NASA Astrophysics Data System (ADS)

    Shodja, Hossein M.; Tabatabaei, Maryam; Pahlevani, Ladan; Ostadhossein, Alireza

    2013-04-01

    The determination of the interstitial sites and saddle points corresponding to the diffusion of an interstitial atom in ultrathin face-centered cubic (fcc) film is of particular interest. The outcome is strongly influenced not only by the orientation of the free surface but also by the location of the defect with respect to the free surface and film-rigid substrate interface. In this article, an atomic-scale simulation is conducted to analyze the effects of depth on the out-of-plane interstitial mechanism of diffusion. To ensure reasonable accuracy and numerical convergence, the atomic interaction up to the second-nearest neighbor is considered. The ab initio examination of the above-mentioned problem associated with thin films requires a large supercell and is computationally time consuming. However, for the sake of demonstration, the values of the barrier height energy pertinent to a diffusing self-interstitial atom in the bulk material are computed using both the first principles density functional theory (DFT) and the developed technique, indicating reasonable correspondence.

  18. Fractal-like behaviour of the BCC/FCC phase separation in the iron-gold alloys.

    PubMed

    Błachowski, A; Ruebenbauer, K; Rakowska, A; Kac, S

    2010-03-01

    Iron-gold alloys with compositions Fe(70)Au(30) and Fe(50)Au(50) were prepared by arc melting. The alloys were investigated by means of the high-resolution scanning electron microscopy (SEM-FEG) in the as-cast state and upon annealing in two steps, i.e. at 250 degrees C for 24 h and subsequently at 500 degrees C for 48 h. The alloys were composed of two phases, i.e. a BCC phase rich in iron and a FCC phase rich in gold. The single-phase regions have equivalent diameter of about 50 nm. SEM images show self-similar structure for the spatial distribution of the above phases on scales ranging from about 1 mm till about 100 nm. The roughness of the images has been used to estimate a fractal dimension of the phase mixture. For larger scales of the as-cast samples one finds fractal dimension of about 1.7 for Fe(70)Au(30) composition, i.e. very close to the dimension of typical diffusion limited aggregation (DLA) fractals. For annealed samples, dimension 1.1 was found. PMID:20500404

  19. Temperature-driven phase transitions from first principles including all relevant excitations: The fcc-to-bcc transition in Ca

    NASA Astrophysics Data System (ADS)

    Grabowski, B.; Söderlind, P.; Hickel, T.; Neugebauer, J.

    2011-12-01

    The temperature-driven fcc-to-bcc phase transition in calcium is examined by a fully ab initio-based integrated technique including all relevant finite-temperature excitation mechanisms. The approach is based on density-functional-theory calculations with a controlled numerical stability of below 0.5 meV/atom for the electronic, quasiharmonic, and structural excitations and better than 1 meV/atom for the explicitly anharmonic contribution. The latter is achieved by successfully utilizing the recently developed hierarchical upsampled thermodynamic integration using Langevin dynamics method. This approach gives direct access to a numerically highly precise volume- and temperature-dependent free-energy surface and derived properties. It enables us to assign the remaining deviations from experiment to inherent errors of the presently available exchange-correlation functionals. Performing the full analysis with both of the conventional functionals, local density approximation and generalized gradient approximation, we demonstrate that—when considered on an absolute scale—thermodynamic properties are dictated by a strikingly similar free energy vs volume curve. Further, we show that, despite an error in the T=0 K energy difference between the two phases (≈6 meV in the present case), an excellent agreement of the temperature dependence of the Gibbs energy difference with experimentally derived data is feasible. This makes it possible, for instance, to unveil unreliable and possibly erroneous experimental input used in popular thermodynamic databases as we explicitly demonstrate for the isobaric heat capacity of calcium.

  20. Modified Iterated perturbation theory in the strong coupling regime and its application to the 3d FCC lattice

    NASA Astrophysics Data System (ADS)

    Arsenault, Louis-François; Sémon, Patrick; Shastry, B. Sriram; Tremblay, A.-M. S.

    2012-02-01

    The Dynamical Mean-Field theory(DMFT) approach to the Hubbard model requires a method to solve the problem of a quantum impurity in a bath of non-interacting electrons. Iterated Perturbation Theory(IPT)[1] has proven its effectiveness as a solver in many cases of interest. Based on general principles and on comparisons with an essentially exact Continuous-Time Quantum Monte Carlo (CTQMC)[2], here we show that the standard implementation of IPT fails when the interaction is much larger than the bandwidth. We propose a slight modification to the IPT algorithm by requiring that double occupancy calculated with IPT gives the correct value. We call this method IPT-D. We show how this approximate impurity solver compares with respect to CTQMC. We consider a face centered cubic lattice(FCC) in 3d for different physical properties. We also use IPT-D to study the thermopower using two recently proposed approximations[3]S^* and SKelvin that do not require analytical continuation and show how thermopower is essentially the entropy per particle in the incoherent regime but not in the coherent one.[1]H.Kajueter et al. Phys. Rev. Lett. 77, 131(1996)[2]P. Werner, et al. Phys. Rev. Lett. 97, 076405(2006)[3]B.S. Sriram Shastry Rep. Prog. Phys. 72 016501(2009)

  1. Effects of particle size and synthesis temperature on the structural properties of the Ni nanoparticles: Insights about the formation of the fcc-Ni structure

    NASA Astrophysics Data System (ADS)

    de Souza, Edvaldo Alves; Winnischofer, Hebert; Haddad, Paula; Costa, Tulio C. R.; Zanchet, Daniela

    2009-01-01

    Nickel nanoparticles (NPs) have been studied due to their superparamagnetic features and potential applications in magnetic devices. Nickel NPs are also interesting because they can be synthesized in three different structures, amorphous, hcp-Ni and fcc-Ni. This work presents the structural studies of Nickel NPs. The results are based on the analysis of the oxidation state and the structural local order around Ni atoms of NPs synthesized at different particle sizes and synthesis temperatures.

  2. Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches.

    PubMed

    Li, Ruihuan; Lu, Song; Kim, Dongyoo; Schönecker, Stephan; Zhao, Jijun; Kwon, Se Kyun; Vitos, Levente

    2016-10-01

    The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the 'pseudo-interfacial energy' that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches. PMID:27484794

  3. Self-nanoemulsifying performance of two grades of Lauroglycol (Lauroglycol-90 and Lauroglycol-FCC) in the presence of mixed nonionic surfactants.

    PubMed

    Shakeel, Faiyaz; Haq, Nazrul; Alanazi, Fars K; Alsarra, Ibrahim A

    2014-11-01

    The present study was undertaken to evaluate the impact of various combinations of nonionic surfactants on self-nanoemulsifying performance of two grades of Lauroglycol (Lauroglycol-90 and Lauroglycol-FCC) in glibenclamide (GBN) nanoemulsion. Formulations (L1-L30) were prepared by spontaneous emulsification method. Prepared formulations were subjected to thermodynamic stability and self-nanoemulsification test. Results of thermodynamic stability and self-nanoemulsification tests were confirmed by further characterization of these formulations in terms of droplet size, viscosity, refractive index and % transmittance. Formulations prepared with Labrasol, HCO-60 and Gelucire-44/14 were found to be suitable for self-emulsifying drug delivery system only whereas those prepared with Tween-80 and Cremophor-EL were found to be suitable for self-nanoemulsifying or self-microemulsifying drug delivery system of GBN with respect to Lauroglycol-90 or Lauroglycol-FCC. Formulation L24 (Lauroglycol-FCC/Tween-80/ethanol/water) was optimized as best formulation for self-nanoemulsifying drug delivery system of GBN. These results indicated that Tween-80 could be the best surfactant in terms of self-nanoemulsification. PMID:23964928

  4. Structural and magnetic studies of fcc Fe films with self-organized lateral modulation on striped Cu(110)-O(2x1) substrates.

    SciTech Connect

    Li, D.

    1998-09-21

    Fcc Fe wedges of 0-12 monolayer (ML) were grown by means of molecular beam epitaxy onto a novel substrate: flat Cu(110) with an oxygen-induced, long-range ordered striped phase, and studied in-situ with medium energy electron diffraction (MEED) and the surface magneto-optical Kerr effect (SMOKE). In contrast to Fe growth on either clean or oxygen-saturated Cu(110), the films on the striped substrates retain a layer-by-layer growth mode up to 6-7 ML and are fcc at least up to 12 ML. In addition, satellite peaks were observed on both sides of the MEED (0,0) streak, indicating a long-range-ordered lateral modulation of the Fe surface. We postulate that the Fe films grow conformally onto the original striped substrate. SMOKE studies show that these fcc Fe wedges are ferromagnetic with an easy axis along the original stripes for Fe thickness > 4ML and a remnant magnetization that increases linearly with thickness beyond 4 ML.

  5. Exotic magnetism on the quasi-FCC lattices of the d3 double perovskites La2NaB'O6 (B' = Ru, Os)

    NASA Astrophysics Data System (ADS)

    Aczel, Adam

    2015-03-01

    B-site ordered double perovskites with quantum spins S = 1/2 (d1) and S = 1 (d2) on the B' site have attracted a great deal of recent interest, due to the possibility of studying 4d and 5d magnetism combined with magnetic frustration on the face-centered-cubic (FCC) lattice. There has been less focus on d3 systems, as they are generally expected to behave more classically and yield simple, commensurate magnetic ground states. In contrast, we find evidence for long-range and short-range (ξ = 70 Å at 4 K) incommensurate magnetic order on the quasi-FCC lattices of the monoclinic double perovskites La2NaRuO6andLa2NaOsO6 respectively. Incommensurate magnetic order on the FCC lattice has not been predicted by mean field theory, but may arise via a delicate balance of inequivalent nearest neighbor and next nearest neighbor exchange interactions. Furthermore, in the Ru system with long-range order, inelastic neutron scattering reveals a spin gap Δ = 2.75 meV. Magnetic anisotropy is generally minimized in the more familiar octahedrally-coordinated 3d3 systems, so the large gap observed for La2NaRuO6 may result from the significantly enhanced value of spin-orbit coupling in this 4d3 material.

  6. Brillouin scattering from metal superlattices

    SciTech Connect

    Bell, J.A.

    1987-01-01

    Acoustic modes guided by thin-film metal superlattices were investigated using Brillouin spectroscopy. Samples were grown on both single-crystal sapphire and fused-silica substrates by alternately sputtering two different metals to yield a total thickness in the range of 0.3-0.5 ..mu..m. Structural and chemical characterization of the polycrystalline films were performed using x-ray diffraction, Rutherford backscattering, and optical interferometry. The dependence of bilayer wavelength on the elastic properties of both Cu/Nb and Mo/Ta superlattices over the range of roughly 10 to 200 A was determined. It is shown that the elastic stiffness coefficient with the largest variation is c/sub 44/. The stiffness variations determined for the Mo/Ta samples are much smaller than for Cu/Nb. It is suggested that this is due to either structural differences (Cu/Nb is fcc-bcc and Mo/Ta is bcc-bcc) or the smaller interfacial lattice mismatch for Mo/Ta. Interfacial strain is found to be strongly correlated with the stiffness variations of the Mo/Ta samples. This dissertation also reports the first observations of Love waves and Stoneley waves by Brillouin scattering. The purely transverse Love waves guided by Cu/Nb films were detected by elasto-optic scattering from the evanescent acoustic strain in the sapphire substrate.

  7. Influences of the third and fourth nearest neighbouring interactions on the surface anisotropy of face-centred-cubic metals

    NASA Astrophysics Data System (ADS)

    Luo, Yongkun; Qin, Rongshan

    2014-06-01

    The structure and the anisotropic properties of the surfaces of face-centred-cubic (FCC) metals have been studied using the broken-bond model while considering the third and fourth nearest neighbouring (3rd and 4th NN) interactions. The pair potential expressions are obtained using the Rose-Vinet universal potential equation. The model is suitable for calculation of the property of a surface with arbitrary crystallographic orientations and can provide absolute unrelaxed surface energy values using three input parameters, namely the lattice constant, bulk modulus and cohesive energy. These parameters are available for the majority of FCC metals. The numerical results for 7 FCC metals have been obtained and compared with these obtained from ab initio calculations and experimental measurements. Good agreement is observed between the two. Taking into account up to the 4th NN interactions, the overall surface energy anisotropy for FCC metals was found to be between 12% to 16%, and the ratio between the surface energies at (100) and (111) planes was found to be 1.05. These values are less than those reported by conventional calculations but more similar to experimental measurements. It is found that the strength of 3rd and 4th NN interactions differs from one element to another, the Ni and Cu interactions being the most significant while the Au, Pt and Pb interactions are the least significant. This suggests that the polar diagrams of the surface energy of Ni and Cu are different from those of Au, Pt and Pb by showing cusps of the unconventional {110} and high-index {210}, {311} and possibly {135} poles. This provides explanations to the recent experimental observations of the {110}, {210}, {311} and {135} facets in equilibrated Ni and Cu crystallines.

  8. Phase transformations and thermodynamics of aluminum-based metallic glasses

    NASA Astrophysics Data System (ADS)

    Gao, Changhua (Michael)

    This thesis examines the thermodynamics and associated kinetics and phase transformations of the glass forming Al-Ni-Gd and Al-Fe-Gd systems. In order to fully understand the unique glass forming ability (GFA) of Al-based metallic glasses, the ternary Al-Fe-Gd and Al-Ni-Gd systems in their Al-rich corners were examined experimentally to assist in a thermodynamic assessment. The solid-state phase equilibria are determined using XRD and TEM-EDS techniques. While this work basically confirms the solid-state equilibria in Al-Fe-Gd reported previously, the ternary phase in Al-Ni-Gd system has been identified to be Al15Ni3Gd2 rather than Al16Ni 3Gd reported in the literature. DTA analysis of 24 alloys in the Al-Fe-Gd system and 42 alloys in the Al-Ni-Gd system have yielded critical temperatures pertaining to the solid-liquid transition. Based on these data and information from the literature, a self-consistent thermodynamic database for these systems has been developed using the CALPHAD technique. Parameters describing the Gibbs free energy for various phases of the Al-Gd, Al-Fe-Gd and Al-Ni-Gd systems are manually optimized in this study. Once constructed, the database is used to calculate driving forces for nucleation of crystalline phases which can qualitatively explain the phase formation sequence during crystallization at low temperatures. It was also confirmed that alloy compositions with the lowest Gibbs free energy difference between the equilibrium state and undercooled liquid state exhibit better GFA than other chemistries. Based on 250°C isothermal devitrification phase transformations of 17 Al-Ni-Gd alloys, a phase formation sequence map is constructed. Fcc-Al nanocrystals are formed first in most of the alloys studied, but eutectic crystallization of a metastable phase and fcc-Al is also observed. Addition of Al or Ni promotes fcc-Al phase formation, while increasing Gd suppresses it. The continuous heating DSC scans revealed that crystallization in Al

  9. New FCC Mg–Zr and Mg–Zr–ti deuterides obtained by reactive milling

    SciTech Connect

    Guzik, Matylda N. Deledda, Stefano; Sørby, Magnus H.; Yartys, Volodymyr A.; Hauback, Bjørn C.

    2015-03-15

    Results for binary Mg–Zr and ternary Mg–Zr–Ti mixtures ball milled at room temperature under reactive deuterium atmosphere (5.6–6.7 MPa) are reported. X-ray and neutron powder diffraction combined with Rietveld refinements show that two new cubic phases were formed during milling. Mg{sub 0.40}Zr{sub 0.60}D{sub 1.78} and Mg{sub 0.40}Zr{sub 0.26}Ti{sub 0.34}D{sub 1.98} crystallize with disordered face centered cubic metal atom arrangements. Results of differential scanning calorimetry and termogravimetric measurements demonstrate that both deuterides desorb deuterium at lower temperatures than MgD{sub 2}, ZrD{sub 2} or TiD{sub 2}; 528 and 575 K in the Mg–Zr–D and Mg–Zr–Ti–D system, respectively. Interestingly, Mg{sub 0.40}Zr{sub 0.26}Ti{sub 0.34}D{sub 1.98} stores deuterium reversibly at 673 K and 10 MPa of D{sub 2}. - Graphical abstract: High resolution SR-PXD patterns obtained for Mg{sub 0.40}Zr{sub 0.60}D{sub 1.78} and first time reported Mg{sub 0.40}Zr{sub 0.26}Ti{sub 0.34}D{sub 1.98}. - Highlights: • Synthesis and characterization of Mg{sub 0.40}Zr{sub 0.60}D{sub 1.78} and Mg{sub 0.40}Zr{sub 0.26}Ti{sub 0.34}D{sub 1.98}. • New deuterides obtained by milling under H{sub 2} gas pressure in the order of a few MPa. • Phases desorb deuterium at temperature lower than corresponding binary deuterides. • Mg{sub 0.40}Zr{sub 0.26}Ti{sub 0.34}D{sub 1.98} stores hydrogen reversibly at 673 K and 10 MPa of D{sub 2}.

  10. Mapping Metals Incorporation of a Whole Single Catalyst Particle Using Element Specific X-ray Nanotomography

    PubMed Central

    2015-01-01

    Full-field transmission X-ray microscopy has been used to determine the 3D structure of a whole individual fluid catalytic cracking (FCC) particle at high spatial resolution and in a fast, noninvasive manner, maintaining the full integrity of the particle. Using X-ray absorption mosaic imaging to combine multiple fields of view, computed tomography was performed to visualize the macropore structure of the catalyst and its availability for mass transport. We mapped the relative spatial distributions of Ni and Fe using multiple-energy tomography at the respective X-ray absorption K-edges and correlated these distributions with porosity and permeability of an equilibrated catalyst (E-cat) particle. Both metals were found to accumulate in outer layers of the particle, effectively decreasing porosity by clogging of pores and eventually restricting access into the FCC particle. PMID:25555190

  11. Systematic DFT-GGA study of hydrogen adsorption on transition metals

    NASA Astrophysics Data System (ADS)

    Vasić, D.; Ristanović, Z.; Pašti, I.; Mentus, S.

    2011-12-01

    Computational study of hydrogen adsorption on (111) surface of transition metals with face centered cubic (fcc) lattice is reported and the results are compared with available experimental and theoretical data. In addition, dissociative adsorption of hydrogen on Pt(111), Pt(100) and Pt(110) is studied in the range of coverage from 0.25 to 1 monolayer. In the case of Pt(111) preferential adsorption site was found to be three-coordinated fcc-hollow site, while on Pt(100) and Pt(110) surface hydrogen settles on two-coordinated bridge and short bridge site, respectively. Hydrogen adsorption energy was found to decrease with the increasing coverage. Structural changes of studied Pt surfaces upon hydrogen adsorption have been compared with the experimental data existing in the literature and good qualitative agreement has been obtained.

  12. Mapping Metals Incorporation of a Whole Single Catalyst Particle Using Element Specific X-ray Nanotomography

    SciTech Connect

    Meirer, Florian; Morris, Darius T.; Kalirai, Sam; Liu, Yijin; Andrews, Joy C.; Weckhuysen, Bert M.

    2015-01-02

    Full-field transmission X-ray microscopy has been used to determine the 3D structure of a whole individual fluid catalytic cracking (FCC) particle at high spatial resolution and in a fast, noninvasive manner, maintaining the full integrity of the particle. Using X-ray absorption mosaic imaging to combine multiple fields of view, computed tomography was performed to visualize the macropore structure of the catalyst and its availability for mass transport. We mapped the relative spatial distributions of Ni and Fe using multiple-energy tomography at the respective X-ray absorption K-edges and correlated these distributions with porosity and permeability of an equilibrated catalyst (E-cat) particle. Both metals were found to accumulate in outer layers of the particle, effectively decreasing porosity by clogging of pores and eventually restricting access into the FCC particle.

  13. Mapping Metals Incorporation of a Whole Single Catalyst Particle Using Element Specific X-ray Nanotomography

    DOE PAGESBeta

    Meirer, Florian; Morris, Darius T.; Kalirai, Sam; Liu, Yijin; Andrews, Joy C.; Weckhuysen, Bert M.

    2015-01-02

    Full-field transmission X-ray microscopy has been used to determine the 3D structure of a whole individual fluid catalytic cracking (FCC) particle at high spatial resolution and in a fast, noninvasive manner, maintaining the full integrity of the particle. Using X-ray absorption mosaic imaging to combine multiple fields of view, computed tomography was performed to visualize the macropore structure of the catalyst and its availability for mass transport. We mapped the relative spatial distributions of Ni and Fe using multiple-energy tomography at the respective X-ray absorption K-edges and correlated these distributions with porosity and permeability of an equilibrated catalyst (E-cat) particle.more » Both metals were found to accumulate in outer layers of the particle, effectively decreasing porosity by clogging of pores and eventually restricting access into the FCC particle.« less

  14. Electronic structure, conductivity and superconductivity of metal doped C60

    SciTech Connect

    Haddon, R.C.

    1993-12-31

    The curvature and topology required for fullerene formation strongly enhances the electronegativity of the carbon clusters and as a result C60 readily accepts electrons. Solid C60 undergoes doping with a variety of metals to produce intercalation compounds which are conductors. In the case of the alkali metals the predominant phases present are: C60, A3C60, and A6C60. The A3C60 compounds are formed from C60 by occupancy of the interstitial sites of the fcc lattice. These phases constitute the first 3-dimensional organic conductors and for A=K, Rb the A3C60 compounds are superconductors with transition temperatures of Tc=19 and 28K, respectively. There is evidence to suggest that the superconductivity in these systems is driven by the intramolecular vibrations of the reduced C60 molecule. Recent experiments on a variety of metal doped C60 thin films will be presented.

  15. Charging dynamics of metal clusters in intense laser fields

    NASA Astrophysics Data System (ADS)

    Döppner, T.; Teuber, S.; Schumacher, M.; Tiggesbäumker, J.; Meiwes-Broer, K. H.

    2000-09-01

    Clusters of heavy metal atoms in strong femtosecond laser-light fields undergo multi-ionization with the loss of hundreds of electrons. The cross section largely exceeds that of corresponding isolated atoms, which leads in the case of PbN to a complete ionization of the 4f shell with a light intensity of 1.2×1015 W/cm2. Experimental investigations on Pb and Pt clusters with variable pulse widths and, for the first time, with the pump&probe technique give insight into the dynamics of the coupling of electromagnetic radiation into the clusters. Both approaches support the picture according to which, after an initial charging, the clusters expand due to Coulomb forces. This expansion is accompanied by a reduction of the electron density and at the same time by an increase of the optical sensitivity. Once the plasmon energy of the diluted nanoplasma approaches the photon energy, the charging efficiency increases significantly. The experimental observations are confirmed by random-phase approximation (RPA) calculations of the optical response, including molecular-dynamics simulations of the expanding systems.

  16. Radiation damage of transition metal carbides

    SciTech Connect

    Dixon, G.

    1991-01-01

    In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC[sub 0.88] in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V[sub 8]C[sub 7] superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

  17. Microstructures and mechanical properties of compositionally complex Co-free FeNiMnCr18 FCC solid solution alloy

    DOE PAGESBeta

    Wu, Z.; Bei, H.

    2015-07-01

    Recently, a structurally-simple but compositionally-complex FeNiCoMnCr high entropy alloy was found to have excellent mechanical properties (e.g., high strength and ductility). To understand the potential of using high entropy alloys as structural materials for advanced nuclear reactor and power plants, it is necessary to have a thorough understanding of their structural stability and mechanical properties degradation under neutron irradiation. Furthermore, this requires us to develop a similar model alloy without Co because material with Co will make post-neutron-irradiation testing difficult due to the production of the 60Co radioisotope. In order to achieve this goal, a FCC-structured single-phase alloy with amore » composition of FeNiMnCr18 was successfully developed. This near-equiatomic FeNiMnCr18 alloy has good malleability and its microstructure can be controlled by thermomechanical processing. By rolling and annealing, the as-cast elongated-grained-microstructure is replaced by homogeneous equiaxed grains. The mechanical properties (e.g., strength and ductility) of the FeNiMnCr18 alloy are comparable to those of the equiatomic FeNiCoMnCr high entropy alloy. Both strength and ductility increase with decreasing deformation temperature, with the largest difference occurring between 293 and 77 K. Extensive twin-bands which are bundles of numerous individual twins are observed when it is tensile-fractured at 77 K. No twin bands are detected by EBSD for materials deformed at 293 K and higher. Ultimately the unusual temperature-dependencies of UTS and uniform elongation could be caused by the development of the dense twin substructure, twin-dislocation interactions and the interactions between primary and secondary twinning systems which result in a microstructure refinement and hence cause enhanced strain hardening and postponed necking.« less

  18. Phase diagram and magnetic properties of the diluted fcc system NipMg1-pO

    NASA Astrophysics Data System (ADS)

    Feng, Zhen; Seehra, Mohindar S.

    1992-02-01

    Starting from Ni and Mg nitrates, about 20 samples of NipMg1-pO samples (with 0.06<=p<=0.86) were prepared and x-ray-diffraction studies showed the samples to have the NaCl structure with the lattice constant fitting the expression a(p)=4.2115-0.0340p Å. Temperature-dependent magnetic-susceptibility (χ) studies of the samples were carried out between 1.8 and 600 K using a superconducting-quantum-interference-device magnetometer and Néel temperatures TN's were determined from the peak in ∂(χT)/∂T. The variation of t=TN(p)/TN(1) vs p is compared with that of CopMg1-pO. For both systems, the variations for p>0.31 are found to fit the predicted values for a simple-cubic Heisenberg antiferromagnet and a theoretical basis for this anomalous result is advanced. The experimental percolation threshold pc=0.15+/-0.01 and for pcfcc antiferromagnets, such as CopMg1-pO and EupSr1-pTe. It is suggested that the differences in the t-vs-p variations for p<0.31 in NipMg1-pO, CopMg1-pO, and EupSr1-pTe may be related to the differences in the ratio of the next-nearest-neighbor to nearest-neighbor exchange constants in these systems.

  19. Atomistically determined phase-field modeling of dislocation dissociation, stacking fault formation, dislocation slip, and reactions in fcc systems

    NASA Astrophysics Data System (ADS)

    Rezaei Mianroodi, Jaber; Svendsen, Bob

    2015-04-01

    The purpose of the current work is the development of a phase field model for dislocation dissociation, slip and stacking fault formation in single crystals amenable to determination via atomistic or ab initio methods in the spirit of computational material design. The current approach is based in particular on periodic microelasticity (Wang and Jin, 2001; Bulatov and Cai, 2006; Wang and Li, 2010) to model the strongly non-local elastic interaction of dislocation lines via their (residual) strain fields. These strain fields depend in turn on phase fields which are used to parameterize the energy stored in dislocation lines and stacking faults. This energy storage is modeled here with the help of the "interface" energy concept and model of Cahn and Hilliard (1958) (see also Allen and Cahn, 1979; Wang and Li, 2010). In particular, the "homogeneous" part of this energy is related to the "rigid" (i.e., purely translational) part of the displacement of atoms across the slip plane, while the "gradient" part accounts for energy storage in those regions near the slip plane where atomic displacements deviate from being rigid, e.g., in the dislocation core. Via the attendant global energy scaling, the interface energy model facilitates an atomistic determination of the entire phase field energy as an optimal approximation of the (exact) atomistic energy; no adjustable parameters remain. For simplicity, an interatomic potential and molecular statics are employed for this purpose here; alternatively, ab initio (i.e., DFT-based) methods can be used. To illustrate the current approach, it is applied to determine the phase field free energy for fcc aluminum and copper. The identified models are then applied to modeling of dislocation dissociation, stacking fault formation, glide and dislocation reactions in these materials. As well, the tensile loading of a dislocation loop is considered. In the process, the current thermodynamic picture is compared with the classical mechanical

  20. Convergence of the Møller-Plesset perturbation series for the fcc lattices of neon and argon

    NASA Astrophysics Data System (ADS)

    Schwerdtfeger, Peter; Assadollahzadeh, Behnam; Hermann, Andreas

    2010-11-01

    Complete basis set limit calculations are carried out for the fcc lattices of solid neon and argon, using second- to fourth-order Møller-Plesset theory, MP2-MP4, and coupled-cluster calculations, CCSD(T), to describe electron correlation within a many-body expansion of the interaction potential up to third order. A correct description of the three-body Axilrod-Teller-Muto term for the solid state is only obtained from third order on in the many-body expansion of the correlation energy, correcting the severe underestimation of long-range three-body effects at the MP2 level of theory. MP4 shows good agreement with the CCSD(T) results, and the latter are in good agreement with experimental lattice constants, cohesive energies, and bulk moduli. However, with increasing pressures the convergence of the Møller-Plesset series deteriorates as the electronic band gap decreases, resulting in rather large deviations for the equation of state (pressure-volume dependence). For neon, however, the errors in the MP2 two- and three-body terms almost cancel, i.e., at a volume of V=3cm3/mol the MP2 pressure is underestimated by only 1 GPa compared to the pressure of P=251GPa calculated at the CCSD(T) level of theory. In contrast, for argon this is not the case, and at V=5.5cm3/mol the calculated MP2 pressure of 228 GPa deviates substantially from the CCSD(T) result of 252 GPa.

  1. Metal aminoboranes

    DOEpatents

    Burrell, Anthony K.; Davis, Benjamin J.; Thorn, David L.; Gordon, John C.; Baker, R. Thomas; Semelsberger, Troy Allen; Tumas, William; Diyabalanage, Himashinie Vichalya Kaviraj; Shrestha, Roshan P.

    2010-05-11

    Metal aminoboranes of the formula M(NH.sub.2BH.sub.3).sub.n have been synthesized. Metal aminoboranes are hydrogen storage materials. Metal aminoboranes are also precursors for synthesizing other metal aminoboranes. Metal aminoboranes can be dehydrogenated to form hydrogen and a reaction product. The reaction product can react with hydrogen to form a hydrogen storage material. Metal aminoboranes can be included in a kit.

  2. Analysis of the twin spacing and grain size effects on mechanical properties in hierarchically nanotwinned face-centered cubic metals based on a mechanism-based plasticity model

    NASA Astrophysics Data System (ADS)

    Zhu, Linli; Qu, Shaoxing; Guo, Xiang; Lu, Jian

    2015-03-01

    Hierarchical twin lamellae in polycrystalline face-centered cubic (fcc) metals possess a possibility to achieve higher strength with keeping an acceptable elongation. The present work is concerned with the analysis of twin spacing and grain size-dependent plastic performance in hierarchically nanotwinned fcc metals using a generalized strain-gradient plasticity model. The dislocation density-based physical model for constitutive description of nanotwinned fcc metals is expanded for the hierarchical structures of nanotwins. The strengthening mechanism and the failure behavior in these hierarchical nanostructures are studied to evaluate the strength and ductility. Moreover, the transition twin spacing between the strengthening and softening is obtained in different order of twin lamellae. A dislocation-based model on nucleating deformation twins is presented to predict the critical twin spacing in the lowest twin lamellae for generating the subordinate twin lamellae. Our simulation results demonstrate that the existence of the hierarchical nanotwins gives rise to a significant enhancement in the strength, and the resulting global flow stresses are sensitive to the twin spacings of the hierarchical twin lamellae and the grain size. Two softening stages are observed with variation of twin spacing, and the relevant transition twin spacing depends on the microstructural size in hierarchically nanotwinned metals. We further find that the predicted failure strain decreases with decreasing the twin spacing, which is quite different from the case of the individually nanotwinned fcc metals. The critical twin spacing for generating subordinate twins also depends on the twin spacing of superordinate twin lamellae and the grain size. These findings suggest that the high yield strength and good ductility can be achieved by optimizing the grain size and the twin spacings in the hierarchical twins.

  3. Basic criteria for formation of growth twins in high stacking fault energy metals

    SciTech Connect

    Yu, K. Y.; Zhang, X.; Bufford, D.; Chen, Y.; Liu, Y.; Wang, H.

    2013-10-28

    Nanotwinned metals received significant interest lately as twin boundaries may enable simultaneous enhancement of strength, ductility, thermal stability, and radiation tolerance. However, nanotwins have been the privilege of metals with low-to-intermediate stacking fault energy (SFE). Recent scattered studies show that nanotwins could be introduced into high SFE metals, such as Al. In this paper, we examine several sputter-deposited, (111) textured Ag/Al, Cu/Ni, and Cu/Fe multilayers, wherein growth twins were observed in Al, Ni, and face-centered cubic (fcc) Fe. The comparisons lead to two important design criteria that dictate the introduction of growth twins in high SFE metals. The validity of these criteria was then examined in Ag/Ni multilayers. Furthermore, another twin formation mechanism in high SFE metals was discovered in Ag/Ni system.

  4. Phase transition from fcc to bcc structure of the Cu-clusters during nanocrystallization of Fe85.2Si1B9P4Cu0.8 soft magnetic alloy

    NASA Astrophysics Data System (ADS)

    Nishijima, Masahiko; Matsuura, Makoto; Takenaka, Kana; Takeuchi, Akira; Ofuchi, Hironori; Makino, Akihiro

    2014-05-01

    A role of Cu on the nanocrystallization of an Fe85.2Si1B9P4Cu0.8 alloy was investigated by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM). The Cu K-edge XAFS results show that local structure around Cu is disordered for the as-quenched sample whereas it changes to fcc-like structure at 613 K. The fcc Cu-clusters are, however, thermodynamically unstable and begin to transform into bcc structure at 638 K. An explicit bcc structure is observed for the sample annealed at 693 K for 600 s in which TEM observation shows that precipitated bcc-Fe crystallites with ˜12 nm are homogeneously distributed. The bcc structure of the Cu-clusters transforms into the fcc-type again at 973 K, which can be explained by the TEM observations; Cu segregates at grain boundaries between bcc-Fe crystallites and Fe3(B,P) compounds. Combining the XAFS results with the TEM observations, the structure transition of the Cu-clusters from fcc to bcc is highly correlated with the preliminary precipitation of the bcc-Fe which takes place prior to the onset of the first crystallization temperature, Tx1 = 707 K. Thermodynamic analysis suggests that an interfacial energy density γ between an fcc-Cu cluster and bcc-Fe matrix dominates at a certain case over the structural energy between fcc and bcc Cu, ΔGfcc - bcc, which causes phase transition of the Cu clusters from fcc to bcc structure.

  5. Mechanics/heat-transfer relation for particulate materials. [Measure of particle pressure generated in a bed of FCC catalyst that is undergoing particulate fluidization

    SciTech Connect

    Campbell, C.S.

    1991-07-01

    The major emphasis this quarter has been in two areas. The first is to continue working the bugs out of the new particle pressure transducer. The second was to try and measure the particle pressures generated in a bed of FCC catalyst that is undergoing particulate fluidization. The results indicate that the stabilization of fluidized beds in that regime cannot be explained in terms of particle pressure generation. Instead, consistent with other recent observations,the observations can be explained by a material is that not completely fluidized but, instead, retains much of the properties of a solid and, in particular, can transmit particle pressure like a solid. 2 figs.

  6. The effect of the cube texture component on the earing behavior of rolled f. c. c. metals

    SciTech Connect

    Rollett, A.D.; Canova, G.R.; Kocks, U.F.

    1986-01-01

    An application of texture simulation to the formability of rolled f.c.c. sheet is described. Control of the earing behavior of such sheet is crucial to the efficient utilization of material. Cold-rolled f.c.c. metals characteristically give ears at 45/sup 0/ to the rolling direction but it is known that if a large cube component is present before the material is rolled, the severity of the earing is reduced. The cube component, (010)(001), by itself is known to give ears at 90/sup 0/ to the rolling direction and could thus balance a 45/sup 0/ earing tendency. The cube component is unstable to rolling deformation, however, and is generally not observed in heavily cold-rolled f.c.c. metals. Therefore, the challenge is to explain how a large cube component, present prior to rolling, can affect the earing behavior at large rolling reductions. Texture simulation shows that orientations near cube tend to rotate primarily about the rolling direction towards the Goss orientation, (110)(001). It has been established both experimentally and theoretically that all orientations between the cube and the Goss positions give 90/sup 0/ ears. Therefore, the effect of a prior cube component is due to the special behavior of orientations near cube under rolling deformation.

  7. The local orientational orders and structures of liquid and amorphous metals Au and Ni during rapid solidification

    NASA Astrophysics Data System (ADS)

    Luhong, Wang; Haozhe, Liu; Kuiying, Chen; Zhuangqi, Hu

    1997-02-01

    Based on the empirical embedded-atom method, the molecular dynamics studies of the local orientational orders and structures of liquid and amorphous solid of FCC-type metals Au and Ni are performed. During the rapid solidification, the amorphous structures can be obtained and their amorphous transition temperatures are determined. The icosahedral ordering and the short-range ordering are enhanced, and FCC-type as well as HCP-type ordering changes slightly during the quench of Au and Ni. In the mean time, the BCC-type ordering of Au is Ni enhanced, but that of Ni is weakened. The results of the simulation also indicate that the diffusion coefficients in Au and Ni decrease rapidly with decreasing temperature above their glass transition temperatures.

  8. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Reliable Lateral Manipulation of Single Adatom on Metal fcc(111) Surfaces with a Single-Atom Tip

    NASA Astrophysics Data System (ADS)

    Xie, Yi-Qun; Liu, Qing-Wei; Zhang, Peng; Gan, Fu-Xi; Zhuang, Jun

    2008-05-01

    Using molecular statistics simulations based on the embedded atom method potential, we investigate the reliability of the lateral manipulation of single Pt adatom on Pt(111) surface with a single-atom tip for different tip heights (tip-surface distance) and tip orientations. In the higher tip-height range, tip orientation has little influence on the reliability of the manipulation, and there is an optimal manipulation reliability in this range. In the lower tip-height range the reliability is sensitive to the tip orientation, suggesting that we can obtain a better manipulation reliability with a proper tip orientation. These results can also be extended to the lateral manipulation of Pd adatom on Pd(111) surface.

  9. Heat-Resistant Co-W Catalytic Metals for Multilayer Graphene Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Ueno, Kazuyoshi; Karasawa, Yusuke; Kuwahara, Satoru; Baba, Shotaro; Hanai, Hitoshi; Yamazaki, Yuichi; Sakuma, Naoshi; Kajita, Akihiro; Sakai, Tadashi

    2013-04-01

    Multilayer graphene (MLG) is expected to be a low-resistance and high-reliability interconnect material replacing copper (Cu) in nanoscale interconnects. Chemical vapor deposition (CVD) on catalytic metals is expected as a practical method for MLG deposition. To obtain high-quality MLG films without catalyst agglomeration by CVD, heat-resistant Co-W catalytic metals were investigated. The agglomeration of the Co-W catalytic metals was suppressed by increasing the W composition; however, MLG deposition was suppressed at the same time. The effects of W addition on the MLG growth were discussed from the viewpoints of the crystallographic change of the Co-W catalysts and chemical reactions. It was found that the Co grain size was reduced and the fcc Co formation was suppressed by W addition. In addition, graphite formation was supposed to be suppressed by W addition owing to the formation of phases other than fcc Co according to the Co-W-C phase diagram. With the optimum W concentration, MLG crystallinity was improved by high-temperature CVD using the heat-resistant Co-W catalytic metals (0.7 at. %) without agglomeration, compared with that in the case of using pure-Co catalysts.

  10. Metal inks

    DOEpatents

    Ginley, David S; Curtis, Calvin J; Miedaner, Alex; van Hest, Marinus Franciscus Antonius Maria; Kaydanova, Tatiana

    2014-02-04

    Self-reducing metal inks and systems and methods for producing and using the same are disclosed. In an exemplary embodiment, a method may comprise selecting metal-organic (MO) precursor, selecting a reducing agent, and dissolving the MO precursor and the reducing agent in an organic solvent to produce a metal ink that remains in a liquid phase at room temperature. Metal inks, including self-reducing and fire-through metal inks, are also disclosed, as are various applications of the metal inks.

  11. Complete basis set limit second-order Møller-Plesset calculations for the fcc lattices of neon, argon, krypton, and xenon.

    PubMed

    Hermann, Andreas; Schwerdtfeger, Peter

    2009-12-28

    Complete basis set (CBS) limit calculations using second-order Møller-Plesset (MP2) theory for electron correlation within a many-body expansion of the interaction potential up to third order are carried out for the fcc lattices of Ne, Ar, Kr, and Xe. Lattice constants and cohesive energies from recent localized MP2 solid-state calculations by Halo et al. [Chem. Phys. Lett. 467, 294 (2009)] are in reasonable agreement with our CBS limit results. A detailed analysis reveals that MP2 severely underestimates long-range three-body effects, thus the Axilrod-Teller term is incorrectly described causing bond contractions for all rare gas solids considered. Further, any deviations in the MP2 lattice constant, cohesive energy, and bulk modulus can be traced back to inaccuracies in the binding energy and equilibrium distance of the rare gas dimer. Without inclusion of phonon dispersion, MP2 prefers the hcp over the fcc crystal structure for all rare gas solids considered. PMID:20059080

  12. Epitaxial growth of fcc-Co{sub x}Ni{sub 100-x} thin films on MgO(110) single-crystal substrates

    SciTech Connect

    Ohtake, Mitsuru; Nukaga, Yuri; Sato, Yoichi; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-12-15

    Co{sub x}Ni{sub 100-x} (x=100, 80, 20, 0 at. %) epitaxial thin films were prepared on MgO(110) single-crystal substrates heated at 300 deg. C by ultrahigh vacuum molecular beam epitaxy. The growth mechanism is discussed based on lattice strain and crystallographic defects. CoNi(110) single-crystal films with a fcc structure are obtained for all compositions. Co{sub x}Ni{sub 100-x} film growth follows the Volmer-Weber mode. X-ray diffraction analysis indicates that the out-of-plane and the in-plane lattice spacings of the Co{sub x}Ni{sub 100-x} films are in agreement within +-0.5% with the values of the respective bulk Co{sub x}Ni{sub 100-x} crystals, suggesting that the strain in the film is very small. High-resolution cross-sectional transmission microscopy shows that an atomically sharp boundary is formed between a Co(110){sub fcc} film and a MgO(110) substrate, where periodical misfit dislocations are preferentially introduced in the film at the Co/MgO interface. The presence of such periodical misfit dislocations relieves the strain caused by the lattice mismatch between the film and the substrate.

  13. Metallization failures

    NASA Technical Reports Server (NTRS)

    Beatty, R.

    1971-01-01

    Metallization-related failure mechanisms were shown to be a major cause of integrated circuit failures under accelerated stress conditions, as well as in actual use under field operation. The integrated circuit industry is aware of the problem and is attempting to solve it in one of two ways: (1) better understanding of the aluminum system, which is the most widely used metallization material for silicon integrated circuits both as a single level and multilevel metallization, or (2) evaluating alternative metal systems. Aluminum metallization offers many advantages, but also has limitations particularly at elevated temperatures and high current densities. As an alternative, multilayer systems of the general form, silicon device-metal-inorganic insulator-metal, are being considered to produce large scale integrated arrays. The merits and restrictions of metallization systems in current usage and systems under development are defined.

  14. METAL PHTHALOCYANINES

    DOEpatents

    Frigerio, N.A.

    1962-03-27

    A process is given for preparing heavy metal phthalocyanines, sulfonated or not. The process comprises mixing an inorganic metal salt with dimethyl formamide or methyl sulfoxide; separating the metal complex formed from the solution; mixing the complex with an equimolar amount of sodium, potassium, lithium, magnesium, or beryllium sulfonated or unsulfonated phthalocyanine whereby heavy-metal phthalocyanine crystals are formed; and separating the crystals from the solution. Uranyl, thorium, lead, hafnium, and lanthanide rare earth phthalocyanines can be produced by the process. (AEC)

  15. Silicone metalization

    DOEpatents

    Maghribi, Mariam N.; Krulevitch, Peter; Hamilton, Julie

    2006-12-05

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  16. Silicone metalization

    DOEpatents

    Maghribi, Mariam N.; Krulevitch, Peter; Hamilton, Julie

    2008-12-09

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  17. Controlled polarity of sputter-deposited aluminum nitride on metals observed by aberration corrected scanning transmission electron microscopy

    SciTech Connect

    Harumoto, T.; Sannomiya, T.; Matsukawa, Y.; Muraishi, S.; Shi, J.; Nakamura, Y.; Sawada, H.; Tanaka, T.; Tanishiro, Y.; Takayanagi, K.

    2013-02-28

    The polarity determination process of sputter-deposited aluminum nitride (AlN) on metals has been analyzed using aberration corrected atomic resolution scanning transmission electron microscope. Direct growth of c-axis orientated AlN on face centered cubic metals (fcc) (111) with the local epitaxy has been observed, and the polarity was determined at the AlN/metal interface. We found that the AlN polarity can be controlled by the base metal layer: N-polarity AlN grows on Pt(111) while Al-polarity AlN forms on Al(111). Based on these results, the growth mechanism of AlN on metals is discussed.

  18. Formation and atomic configuration of binary metallic glasses studied by ion beam mixing and molecular dynamics simulation

    SciTech Connect

    Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Liu, B. X.

    2007-06-15

    Metallic glasses are obtained in an immiscible Ag-Nb system with overall composition ranging from 25 to 90 at. % of Nb by ion beam mixing. Interestingly, the diffraction analysis shows that the formed Nb-rich metallic glass features are two distinct atomic configurations. In atomistic modeling, an n-body Ag-Nb potential is derived, under the assistance of ab initio calculation, and then applied in molecular dynamics simulations. An atomic configuration is discovered, i.e., an icositetrahedral ordering, and as well as an icosahedral ordering observed in the Ag-Nb metallic glasses and in some previously reported systems. Simulations confirm that the two dominate local atomic packing units are formed through a structural phase transition from the Nb-based bcc and fcc solid solutions, respectively, suggesting a concept of structural heredity that the crystalline structure of the constituent metals play a decisive role in determining the atomic structure of the resultant metallic glasses.

  19. Theory of ordering transformations in metals and minerals

    SciTech Connect

    Lindsey, T.F. . Dept. of Materials Science and Mineral Engineering Lawrence Berkeley Lab., CA )

    1991-07-01

    This dissertation presents an investigation of ordering in FCC based systems using the pair potential approximation in the ground state and mean field limits. The theoretical approach is used to explain the occurrence of observed equilibrium phases and characteristics of thermodynamic instabilities, in particular, spinodal ordering and decomposition. It is shown that the stability of non-integer domain sizes in long period superstructures such as Al{sub 3}Ti and Ag{sub 3}Mg may result from the tendency of a system to reduce the number of non-dominant ordering waves, thus producing domain sizes that have rational fraction form n/m. This conclusion is used to explain the domain size stability with respect to variations in temperature and electron concentration. The cation ordering in the precipitate phases in calcite and dolomite is analyzed by analogy with ordering in FCC based metals. The ordered phases in calcite and dolomite are shown to be consistent with pair potential minima at {l brace}100{r brace} and {l brace}1/2, 1/2, 1/2{r brace} positions in reciprocal space respectively. 32 refs., 6 figs.

  20. The influence of composition gradients on tensile properties of weld metal

    SciTech Connect

    Choi, I.D.; Matlock, D.K.; Olson, D.L.

    1988-09-01

    In this study, the effects of weld metal microsegregation, as altered by post-weld heat treatments, on both low and high temperature tensile properties were investigated on an alloy system which exhibits significant segregation of the major alloying elements without complex transformations or precipitation. Monel alloy 400, which consists primarily of nickel and copper, was chosen as a model system. This system is a single phase FCC solid solution at all temperatures, and has a low distribution coefficient, k. On solidification, significant microsegregation occurs with copper segregating to the interdendritic boundaries.

  1. Nature and evolution of the fusion boundary in ferritic-austenitic dissimilar weld metals. Part 1 -- Nucleation and growth

    SciTech Connect

    Nelson, T.W.; Lippold, J.C.; Mills, M.J.

    1999-10-01

    A fundamental investigation of fusion boundary microstructure evolution in dissimilar-metal welds (DMWs) between ferritic base metals and a face-centered-cubic (FCC) filler metal was conducted. The objective of the work presented here was to characterize the nature and character of the elevated-temperature fusion boundary to determine the nucleation and growth characteristics of DMWs. Type 409 ferritic stainless steel and 1080 pearlitic steel were utilized as base metal substrates, and Monel (70Ni-30Cu) was used as the filler metal. The Type 409 base metal provided a fully ferritic or body-centered-cubic (BCC) substrate at elevated temperatures and exhibited no on-cooling phase transformations to mask or disguise the original character of the fusion boundary. The 1080 pearlitic steel was selected because it is austenitic at the solidus temperature, providing an austenite substrate at the fusion boundary. The weld microstructure generated with each of the base metals in combination with Monel was fully austenitic. In the Type 409/Monel system, there was no evidence of epitaxial nucleation and growth as normally observed in homogeneous weld metal combinations. The fusion boundary in this system exhibited random grain boundary misorientations between the heat-affected zone (HAZ) and weld metal grains. In the 1080/Monel system, evidence of normal epitaxial growth was observed at the fusion boundary, where solidification and HAZ grain boundaries converged. The fusion boundary morphologies are a result of the crystal structure present along the fusion boundary during the initial stages of solidification. Based on the results of this investigation, a model for heterogeneous nucleation along the fusion boundary is proposed when the base and weld metals exhibit ferritic (BCC) and FCC crystal structures, respectively.

  2. Chromium removal by zeolite-rich materials obtained from an exhausted FCC catalyst: Influence of chromium incorporation on the sorbent structure.

    PubMed

    Gonzalez, Maximiliano R; Pereyra, Andrea M; Torres Sánchez, Rosa M; Basaldella, Elena I

    2013-10-15

    A spent FCC catalyst was converted into a zeolitic mixture, and the product obtained was afterward used as trapping material for Cr(III) species frequently found in aqueous solutions. Eventual changes in the sorbent structure produced by Cr incorporation were studied by different characterization techniques such as point of zero charge determinations (PZC), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and infrared absorption (FTIR). The XRD and FTIR analyses indicated that chromium incorporation produces an amorphization of the material, and PZC measurements show no surface adsorption of charged chromium species. SEM and EDX analyses clearly show that after chromium sorption, the initial microspheroidal catalyst morphology was maintained, and the presence of chromium species was mainly detected in the outer microsphere surface, where the zeolite crystals were hydrothermally grown. PMID:23910499

  3. International Satellite Issues: The Roles of the Executive Branch and FCC. Hearing before the Subcommittee on Telecommunications, Consumer Protection, and Finance of the Committee on Energy and Commerce. House of Representatives, Ninety-Ninth Congress, First Session.

    ERIC Educational Resources Information Center

    Congress of the U.S., Washington, DC. House Committee on Energy and Commerce.

    This hearing addressed the general topic of the role of the Federal Communications Commission (FCC) in establishing U.S. policy toward new international communications satellite systems. Statements presented by the following people are included: (1) Mark S. Fowler, Chairman, Federal Communications Commission; (2) David J. Markey, Assistant…

  4. Tunable magnetocaloric effect in transition metal alloys.

    PubMed

    Belyea, Dustin D; Lucas, M S; Michel, E; Horwath, J; Miller, Casey W

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based "high entropy alloys" in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  5. Tunable magnetocaloric effect in transition metal alloys

    PubMed Central

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-01-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants. PMID:26507636

  6. Fatigue crack nucleation in metallic materials

    SciTech Connect

    Peralta, P.; Laird, C.; Ramamurty, U.; Suresh, S.; Campbell, G.H.; King, W.E.; Mitchell, T.E.

    1999-04-01

    The process of fatigue crack nucleation in metallic materials is reviewed placing emphasis in results derived for pure FCC metals with wavy slip behavior. The relationship between Persistent Slip Bands (PSB`s) and crack initiation will be examined for both single crystals and polycrystals, including the conditions for inter- and transgranular crack nucleation and their connection to type of loading, crystallography and slip geometry. The latter has been found to be an important parameter in the nucleation of intergranular cracks in polycrystals subjected to high strain fatigue, whereby primary slip bands with long slip lengths impinging on a grain boundary produce intergranular crack nucleation under the right conditions. Recent results related to intergranular crack nucleation in copper bicrystals and crack nucleation in Cu/Sapphire interfaces indicate that this mechanism controls crack nucleation in those simpler systems as well. Furthermore, it is found that under multiple slip conditions the crack nucleation location is controlled by the presence of local single slip conditions and long slip lengths for a particular Burgers vector that does not have to be in the primary slip system.

  7. Migration of helium-pair in metals

    NASA Astrophysics Data System (ADS)

    Cao, J. L.; Geng, W. T.

    2016-09-01

    We have carried out a first-principles density functional theory investigation into the migration of both a single interstitial He and an interstitial He-pair in Fe, Mo, W, Cu, Pd, and Pt. We find the migration trajectories and barriers are determined predominantly by low-energy He-pair configurations which depend mainly on the energy state of a single He in different interstices. The migration barrier for a He-pair in bcc metals is always slightly higher than for a single He. Configurations of a He-pair in fcc metals are very complicated, due to the existence of interstitial sites with nearly identical energy for a single He. The migration barrier for a He-pair is slightly lower than (in Cu), or similar to (in Pd and Pt) a single He. The collective migrations of a He-pair are ensured by strong Hesbnd He interactions with strength-versus-distance forms resembling chemical bonds and can be described with Morse potentials.

  8. Tunable magnetocaloric effect in transition metal alloys

    NASA Astrophysics Data System (ADS)

    Belyea, Dustin D.; Lucas, M. S.; Michel, E.; Horwath, J.; Miller, Casey W.

    2015-10-01

    The unpredictability of geopolitical tensions and resulting supply chain and pricing instabilities make it imperative to explore rare earth free magnetic materials. As such, we have investigated fully transition metal based “high entropy alloys” in the context of the magnetocaloric effect. We find the NiFeCoCrPdx family exhibits a second order magnetic phase transition whose critical temperature is tunable from 100 K to well above room temperature. The system notably displays changes in the functionality of the magnetic entropy change depending on x, which leads to nearly 40% enhancement of the refrigerant capacity. A detailed statistical analysis of the universal scaling behavior provides direct evidence that heat treatment and Pd additions reduce the distribution of exchange energies in the system, leading to a more magnetically homogeneous alloy. The general implications of this work are that the parent NiFeCoCr compound can be tuned dramatically with FCC metal additives. Together with their relatively lower cost, their superior mechanical properties that aid manufacturability and their relative chemical inertness that aids product longevity, NiFeCoCr-based materials could ultimately lead to commercially viable magnetic refrigerants.

  9. In situ purification, alloying and casting methodology for metallic plutonium

    NASA Astrophysics Data System (ADS)

    Lashley, Jason C.; Blau, Michael S.; Staudhammer, Karl P.; Pereyra, Ramiro A.

    Plutonium metal that has been double ER (electrorefined/electrorefining) was further purified via zone refining, using a floating molten zone to minimize the introduction of impurities. The temperature of the molten zone was 750°C, and the atmosphere was 10 -5 Pa. A total of ten zone refining passes were made at a travel rate of 1.5 cm/h. There were 19 elements reduced to quantities below the minimum detectable limits (MDL) by zone refining, while P, K, and W were significantly reduced. The zone-refined metal was then used in an in situ distillation, alloying, and casting step to prepare tapered specimens for single-crystal growth experiments. Specifically, 241Am was distilled from Pu metal by levitating Pu metal with 1 wt% Ga in the melt in a Crystallox vertical electromagnetic levitation crucible at 10 -5 Pa. The Pu is alloyed with Ga to stabilize the δ phase (fcc symmetry) upon solidification. The Pu was chill-cast directly from the electromagnetic levitation field into 1- cm tapered specimens. A water-cooled ceramic mold was used, and the Pu metal was cooled at a rate of 100°C/min. A microstructure examination of the specimen showed 10 × 25 μm acicular grains with a density of 15.938 g/cm 3 (±0.002 g/cm 3).

  10. Electronic Properties of Pseudomorphic Metallic Films: Photoemission and Inverse Photoemission Measurements

    NASA Astrophysics Data System (ADS)

    Mankey, Gary Jay

    Recent developments in experimental physics have made possible the production and characterization of ultrathin metallic films of atomic dimension. The methods used to grow pseudomorphic fcc films of Ni, Co, and Fe on Cu(001) are described. High-quality epitaxial films are produced by vapor deposition in an ultra-high vacuum environment on suitably prepared substrates. The morphology of these films is characterized using a variety of experimental techniques: Auger electron spectroscopy, low-energy electron diffraction, reflection high-energy electron diffraction, and thermal desorption spectroscopy of adsorbed hydrogen. The magnetic properties of the films are measured with a surface magneto-optic Kerr effect magnetometer. The occupied and unoccupied electronic band dispersions and critical point energies are determined with photoemission and inverse photoemission measurements. These measurements are used as eigenvalues for an empirical combined interpolation scheme bandstructure calculation of the energy bands along the fcc(001) surface normal. Results are presented for Cu(001), Ni(001), Co(001), and paramagnetic Fe(001). Changes in the unoccupied electronic states in the ultrathin film limit are determined for Co and Fe films on Cu(111). The Co films exhibit a bulk-like electronic structure similar to hcp Co(0001) down to films one atomic layer thick. The low-spin ferromagnetic phase of fcc Fe is produced on Cu(111) for films below 5 atomic layers thick. Above this thickness, the Fe films revert to a bulk-like bcc(110) phase. The development of the electronic structure is measured for ultrathin Cu films grown on a specially prepared fcc Co(001) substrate. The Cu 3d band is significantly narrowed for films 1 atomic layer thick and bulk-like for films 3 atomic layers thick (one fcc unit cell). The s, p band exhibits quantum-well states due to the discretization of reciprocal space in the direction perpendicular to the film surface. These quantum-well states are

  11. Computer simulation of boundary effects on bubble growth in metals due to He.

    SciTech Connect

    Zimmerman, Jonathan A.

    2003-03-01

    Atomistic simulation methods were used to investigate and identify the relevant physical mechanisms necessary to describe the growth of helium gas bubbles within a metal lattice. Specifically, molecular dynamics simulations were performed to examine the material defects that originate from growing spherical He bubbles in a palladium crystal. These simulations consist of a model system containing bubbles within a metal and near a free surface. The simulation code employed was ParaDyn using the Embedded Atom Method to model the constitutive properties of Pd atoms in a FCC lattice. The results of these simulations are compared with previously run calculations of He bubbles in a bulk lattice [l]. These simulations show the influence of the free surface on defect creation and evolution. Features compared include the formation of inter-bubble dislocations, bubble pressure and swelling as functions of He to metal (He/M) concentration.

  12. Metal Detectors.

    ERIC Educational Resources Information Center

    Harrington-Lueker, Donna

    1992-01-01

    Schools that count on metal detectors to stem the flow of weapons into the schools create a false sense of security. Recommendations include investing in personnel rather than hardware, cultivating the confidence of law-abiding students, and enforcing discipline. Metal detectors can be quite effective at afterschool events. (MLF)

  13. Application of Smooth-Particle Hydrodynamics in Metal Machining

    NASA Astrophysics Data System (ADS)

    Zahedi, Abolfazl; Li, Simin; Roy, Anish; Babitsky, Vladimir; Silberschmidt, Vadim V.

    2012-08-01

    The finite element (FE) method has been extensively used to model complex cutting processes. However, due to large strains in a process zone, leading to increased element distortions, such simulations are confronted with numerical difficulties. Smooth-particle hydrodynamics (SPH) is a mesh-free computational method, which has been used to simulate multi-body problems. In this paper we present a 3D hybrid modelling approach for orthogonal micro-machining of a copper single crystal with the use of SPH and continuum FE. The model is implemented in a commercial FE software ABAQUS/Explicit. The study is used to gain insight into the effects of crystallographic anisotropy on the machining response of f.c.c. cubic metals.

  14. Metal oxide films on metal

    DOEpatents

    Wu, Xin D.; Tiwari, Prabhat

    1995-01-01

    A structure including a thin film of a conductive alkaline earth metal oxide selected from the group consisting of strontium ruthenium trioxide, calcium ruthenium trioxide, barium ruthenium trioxide, lanthanum-strontium cobalt oxide or mixed alkaline earth ruthenium trioxides thereof upon a thin film of a noble metal such as platinum is provided.

  15. Mechanism-based crystal plasticity modeling of twin boundary migration in nanotwinned face-centered-cubic metals

    NASA Astrophysics Data System (ADS)

    Mirkhani, Hamidreza; Joshi, Shailendra P.

    2014-08-01

    Nanotwinned (nt) metals are an important subset of nanostructured materials because they exhibit impressive strength and ductility. Several recent investigations on nt face-centered-cubic (FCC) metals indicate that their macroscopic responses emerge from complex microscopic mechanisms that are dominated by dislocation-TB interactions. Under applied stimulus, nt microstructures evolve through migration of twin boundaries (TBs) that may have implications on the material strength and stability. This work focuses on modeling TB migration within finite element framework in an explicit manner and studying its effects on the micromechanics of twinned FCC metals under quasi-static loading conditions. The theoretical setting is developed using three-dimensional single crystal plasticity as a basis wherein the plastic slip on the {111}<1bar10> slip systems in an FCC crystal structure is modeled as visco-plastic behavior. Owing to their governing role, twins are modeled as discrete lamellas with full crystallographic anisotropy. To model TB migration, an additional visco-plastic slip-law for twinning partial systems ({111}<112bar>) based on the nucleation and motion of twin partial dislocations is introduced. This size-dependent constitutive law is presumed to prevail in the vicinity of the TB and naturally facilitates TB migration when combined with a twinning condition that is based on the accrual of the necessary shear strain. The constitutive development is implemented within a finite element framework through a User Material (UMAT) facility within ABAQUS/STANDARD®. Detailed micromechanics simulations on model microstructures involving single-grained and polycrystalline topologies are presented.

  16. Metal Coatings

    NASA Technical Reports Server (NTRS)

    1994-01-01

    During the Apollo Program, General Magnaplate Corporation developed process techniques for bonding dry lubricant coatings to space metals. The coatings were not susceptible to outgassing and offered enhanced surface hardness and superior resistance to corrosion and wear. This development was necessary because conventional lubrication processes were inadequate for lightweight materials used in Apollo components. General Magnaplate built on the original technology and became a leader in development of high performance metallurgical surface enhancement coatings - "synergistic" coatings, - which are used in applications from pizza making to laser manufacture. Each of the coatings is designed to protect a specific metal or group of metals to solve problems encountered under operating conditions.

  17. First-principles study of liquid and amorphous metals

    NASA Astrophysics Data System (ADS)

    Ganesh, Panchapakesan

    Computer simulations using state of the art First-Principles ab-initio methods enable us to probe the structural features of novel materials like liquid metals and metallic glass forming alloys, both in their supercooled liquid state as well as in their quenched amorphous forms where available. The ab-initio nature of the calculations enable us to capture the chemical identity realistically at the atomistic level without any free parameters. The results show that even though elemental liquid metals like face-centered cubic (FCC) Cu and body-centered cubic (BCC) Fe (and W) have similar atomic structure at high temperature, which is also similar to jammed packing of hard-spheres, they differ quite appreciably even with slight supercooling. This difference enables us to further supercool Fe and W to a much greater degree than Cu. The origin of this difference between elemental metals with different crystalline ground states can be understood based on concepts of geometric frustration. Further, the role played by atoms of different sizes in controlling the geometric frustration in glass forming alloys has been investigated. Studies of Silicon in its supercooled regime have been made to investigate the existence of a possible structural transition. Attempts to clarify if the structural transition could be a thermodynamic phase transition have been made and changes in electronic properties accompanying this structural change have been studied.

  18. Strains and photovoltaic response in Ta-sputtered Si metal-insulator-semiconductor solar cells

    NASA Astrophysics Data System (ADS)

    Lalevic, B.; Murty, K.; Ito, T.; Kalman, Z. H.; Weissmann, S.

    1981-07-01

    Deformation by bending of Si or Si-SiO2 wafers is achieved by sputter deposition of tantalum films. Strains induced at Si-SiO2 interface and in Ta films are investigated using a combination of X-ray diffraction, electron diffraction, and transmission electron microscopy. Thin Ta film deposits are found to have predominantly a fcc structure, while thicker films have the normal bcc structure with certain admixture of fcc. Film strains generated by the coexistence of the polymorph structure are accommodated by formation of misfit dislocations at the film-Si substrate interface. The effect of the induced stress on the electronic parameters characterizing the Si-SiO2 interface is studied in the metal-oxide-semiconductor structure, and for the effect on photovoltaic response a metal-insulator-semiconductor solar cell configuration is used. Large changes with increasing stress are observed in the values of recombination time, capture cross section, and diffusion length and in sharply decreased conversion efficiency, fill factor, open-circuit voltage, and short-circuit current.

  19. Metals 2000

    SciTech Connect

    Allison, S.W.; Rogers, L.C.; Slaughter, G.; Boensch, F.D.; Claus, R.O.; de Vries, M.

    1993-05-01

    This strategic planning exercise identified and characterized new and emerging advanced metallic technologies in the context of the drastic changes in global politics and decreasing fiscal resources. In consideration of a hierarchy of technology thrusts stated by various Department of Defense (DOD) spokesmen, and the need to find new and creative ways to acquire and organize programs within an evolving Wright Laboratory, five major candidate programs identified are: C-17 Flap, Transport Fuselage, Mach 5 Aircraft, 4.Fighter Structures, and 5. Missile Structures. These results were formed by extensive discussion with selected major contractors and other experts, and a survey of advanced metallic structure materials. Candidate structural applications with detailed metal structure descriptions bracket a wide variety of uses which warrant consideration for the suggested programs. An analysis on implementing smart skins and structures concepts is given from a metal structures perspective.

  20. Variation in electromagnetic radiation during plastic deformation under tension and compression of metals

    NASA Astrophysics Data System (ADS)

    Singh, Ranjana; Lal, S. P.; Misra, Ashok

    2014-06-01

    This paper presents some significant variations in the intermittent electromagnetic radiation (EMR) during plastic deformation under tension and compression of some metals with selected crystal structure, viz. zinc, hexagonal closed packed (hcp), copper, face-centred cubic (fcc: stacking fault energy 0.08 J/m2), aluminium (fcc: stacking fault energy 0.2 J/m2) and 0.18 % carbon steel, body-centred cubic (bcc). The intermittent EMR signals starting near yielding are either oscillatory or exponential under both modes of deformation except a very few intermediate signals, random in nature, in zinc under compression. The number and amplitude of EMR signals exhibit marked variations under tension and compression. The smooth correlation between elastic strain energy release rate and average EMR energy release rate suggests a novel technique to determine the fracture toughness of metals. The first EMR emission amplitude and EMR energy release rate occurring near the yield increase, but maximum EMR energy burst frequency decreases almost linearly with increase in Debye temperature of the metals under tension while all EMR parameters decrease nonlinearly under compression. These results can be developed into a new technique to evaluate dislocation velocity. The EMR amplitude and energy release rate of the first EMR emission vary parabolically showing a maxima with increase in electronic heat constant of the metals under tension while they first sharply decrease and then become asymptotic during compression. However, the variation in EMR maximum energy burst frequency is apparently similar under both modes of deformation. These results strongly suggest that the mechanism of EMR emission during plastic deformation of metals involves not only the interaction of conduction electrons with the lattice periodic potential as presented in the previous theoretical models but also the interaction of conduction electrons with phonons. However, during crack propagation and fracture

  1. The frustrated fcc antiferromagnet Ba2 YOsO6: Structural characterization, magnetic properties and neutron scattering studies

    SciTech Connect

    Kermarrec, E.; Marjerrison, Casey A.; Thompson, C. M.; Maharaj, Dalini D.; Levin, K.; Kroeker, S.; Granroth, Garrett E.; Flacau, Roxana; Yamani, Zahra; Greedan, John E.; Gaulin, Bruce D.

    2015-02-26

    Here we report the crystal structure, magnetization, and neutron scattering measurements on the double perovskite Ba2 YOsO6. The Fm$\\bar{3}$m space group is found both at 290 K and 3.5 K with cell constants a0=8.3541(4) Å and 8.3435(4) Å, respectively. Os5+ (5d3) ions occupy a nondistorted, geometrically frustrated face-centered-cubic (fcc) lattice. A Curie-Weiss temperature θ ~₋700 K suggests the presence of a large antiferromagnetic interaction and a high degree of magnetic frustration. A magnetic transition to long-range antiferromagnetic order, consistent with a type-I fcc state below TN~69 K, is revealed by magnetization, Fisher heat capacity, and elastic neutron scattering, with an ordered moment of 1.65(6) μB on Os5+. The ordered moment is much reduced from either the expected spin-only value of ~3 μB or the value appropriate to 4d3 Ru5+ in isostructural Ba2 YRuO6 of 2.2(1) μB, suggesting a role for spin-orbit coupling (SOC). Triple-axis neutron scattering measurements of the order parameter suggest an additional first-order transition at T=67.45 K, and the existence of a second-ordered state. We find time-of-flight inelastic neutron results reveal a large spin gap Δ~17 meV, unexpected for an orbitally quenched, d3 electronic configuration. In conclusion, we discuss this in the context of the ~5 meV spin gap observed in the related Ru5+,4d3 cubic double perovskite Ba2YRuO6, and attribute the ~3 times larger gap to stronger SOC present in this heavier, 5d, osmate system.

  2. Closed and open-ended stacking fault tetrahedra formation along the interfaces of Cu-Al nanolayered metals

    NASA Astrophysics Data System (ADS)

    Li, Ruizhi; Beng Chew, Huck

    2015-09-01

    Stacking fault tetrahedra (SFTs) are volume defects that typically form by the clustering of vacancies in face-centred cubic (FCC) metals. Here, we report a dislocation-based mechanism of SFT formation initiated from the semi-coherent interfaces of Cu-Al nanoscale multilayered metals subjected to out-of-plane tension. Our molecular dynamics simulations show that Shockley partials are first emitted into the Cu interlayers from the dissociated misfit dislocations along the Cu-Al interface and interact to form SFTs above the triangular intrinsic stacking faults along the interface. Under further deformation, Shockley partials are also emitted into the Al interlayers and interact to form SFTs above the triangular FCC planes along the interface. The resulting dislocation structure comprises closed SFTs within the Cu interlayers which are tied across the Cu-Al interfaces to open-ended SFTs within the Al interlayers. This unique plastic deformation mechanism results in considerable strain hardening of the Cu-Al nanolayered metal, which achieves its highest tensile strength at a critical interlayer thickness of ~4 nm corresponding to the highest possible density of complete SFTs within the nanolayer structure.

  3. Metallic Hydrogen

    NASA Astrophysics Data System (ADS)

    Silvera, Isaac; Zaghoo, Mohamed; Salamat, Ashkan

    2015-03-01

    Hydrogen is the simplest and most abundant element in the Universe. At high pressure it is predicted to transform to a metal with remarkable properties: room temperature superconductivity, a metastable metal at ambient conditions, and a revolutionary rocket propellant. Both theory and experiment have been challenged for almost 80 years to determine its condensed matter phase diagram, in particular the insulator-metal transition. Hydrogen is predicted to dissociate to a liquid atomic metal at multi-megabar pressures and T =0 K, or at megabar pressures and very high temperatures. Thus, its predicted phase diagram has a broad field of liquid metallic hydrogen at high pressure, with temperatures ranging from thousands of degrees to zero Kelvin. In a bench top experiment using static compression in a diamond anvil cell and pulsed laser heating, we have conducted measurements on dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K. We observe a first-order phase transition in the liquid phase, as well as sharp changes in optical transmission and reflectivity when this phase is entered. The optical signature is that of a metal. The mapping of the phase line of this transition is in excellent agreement with recent theoretical predictions for the long-sought plasma phase transition to metallic hydrogen. Research supported by the NSF, Grant DMR-1308641, the DOE Stockpile Stewardship Academic Alliance Program, Grant DE-FG52-10NA29656, and NASA Earth and Space Science Fellowship Program, Award NNX14AP17H.

  4. Weak crystallization theory of metallic alloys

    NASA Astrophysics Data System (ADS)

    Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.

    2016-06-01

    Crystallization is one of the most familiar, but hardest to analyze, phase transitions. The principal reason is that crystallization typically occurs via a strongly first-order phase transition, and thus rigorous treatment would require comparing energies of an infinite number of possible crystalline states with the energy of liquid. A great simplification occurs when crystallization transition happens to be weakly first order. In this case, weak crystallization theory, based on unbiased Ginzburg-Landau expansion, can be applied. Even beyond its strict range of validity, it has been a useful qualitative tool for understanding crystallization. In its standard form, however, weak crystallization theory cannot explain the existence of a majority of observed crystalline and quasicrystalline states. Here we extend the weak crystallization theory to the case of metallic alloys. We identify a singular effect of itinerant electrons on the form of weak crystallization free energy. It is geometric in nature, generating strong dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of fcc, rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. As an application, we find the condition for stability of iQC that is consistent with the Hume-Rothery rules known empirically for the majority of stable iQC; namely, the length of the primary Bragg-peak wave vector is approximately equal to the diameter of the Fermi sphere.

  5. Trends in the electron-phonon coupling parameter in some metallic hydrides

    SciTech Connect

    Gupta, M.; Burger, J.P.

    1981-12-15

    We present an evaluation of the electron-phonon coupling parameter lambda, using the McMillan formalism, for several classes of stoichiometric mono- and dihydrides with a metallic underlying fcc structure. We calculate the electronic term eta and use experimental estimates for the phonon energies when available. We derive systematic trends concerning both contributions to eta stemming, respectively, from the metallic site M and the hydrogen site H. We show that eta/sub H/ is generally small, but it may become large if the Fermi energy is in the metal s-p band as in the filled d-band transition-metal (TM) hydrides such as PdH; eta/sub H/ may also be large when a metal-hydrogen antibonding band crosses the Fermi level, a case which happens in AlH and may happen for some unstable dihydrides. The metallic contribution eta/sub M/ is calculated to be small for all stable mono- and dihydrides like PdH, NiH, ZrH/sub 2/, NbH/sub 2/, etc., but nothing in principle prevents this contribution from becoming as large as in some pure TM, if one sweeps the Fermi level through the whole metallic d band. Good agreement with the available experimental data is obtained concerning the occurrence of superconductivity in the compounds considered.

  6. Magnetic anisotropy of vicinal (001) fcc Co films: Role of crystal splitting and structure relaxation in the step-decoration effect

    NASA Astrophysics Data System (ADS)

    Cinal, M.; Umerski, A.

    2006-05-01

    The uniaxial in-plane magnetic anisotropy (UIP-MA) constant is calculated for a single step on the (001) surface of fcc Co(N) films. The calculations are done for both an undecorated step and the step decorated with one or more, up to seven, Cu wires. Our objective is to explain the mechanisms by which the decoration decreases the UIP-MA constant, which is the effect observed experimentally for ultrathin Co films deposited on vicinal (001) Cu surfaces and can lead to reorientation of magnetization within the film plane. Theoretical calculations performed with a realistic tight-binding model show that the step decoration changes the UIP-MA constant significantly only if the splitting between the on-site energies of various d -orbitals is included for atoms located near the step edge. The local relaxation of atomic structure around the step is also shown to have a significant effect on the shift of the UIP-MA constant. The influence of these two relevant factors is analyzed further by examining individual contributions to the UIP-MA constant from atoms around the step. The magnitude of the obtained UIP-MA shift agrees well with experimental data. It is also found that an additional shift due to possible charge transfer between Cu and Co atoms is very small.

  7. Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

    SciTech Connect

    Morey, R M

    1998-12-08

    In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.

  8. Atomistic simulations of fcc Pt{sub 75}Ni{sub 25} and Pt{sub 75}Re{sub 25} cubo-octahedral nanoparticles

    SciTech Connect

    Wang, Guofeng; Van Hove, M.A.; Ross, P.N.; Baskes, M.I.

    2004-03-30

    We have developed interatomic potentials for Pt-Ni and Pt-Re alloys within the modified embedded atom method (MEAM). Furthermore, we applied these potentials to study the equilibrium structures of Pt75Ni25 and Pt75Re25 nanoparticles at T=600 K using the Monte Carlo method. In this work, the nanoparticles are assumed to have disordered fcc cubo-octahedral shapes (terminated by {l_brace}111{r_brace} and {l_brace}100{r_brace} facets) and contain from 586 to 4033 atoms (corresponding to a diameter from 2.5 to 5 nm). It was found that, due to surface segregation, (1) the Pt75Ni25 nanoparticles form a surface-sandwich structure: the Pt atoms are enriched in the outermost and third atomic shells, while the Ni atoms are enriched in the second atomic shell; (2) the equilibrium Pt75Re25 nanoparticles adopt a core-shell structure: a Pt-enriched shell surrounding a Pt-deficient core.

  9. Voidage and pressure profile characteristics of sand-iron ore-coal-FCC single-particle systems in the riser of a pilot plant circulating fluidized bed

    SciTech Connect

    Das, M.; Meikap, B.C.; Saha, R.K.

    2008-06-15

    Hydrodynamic behaviors of single system of particles were investigated in a circulating fluidized bed (CFB) unit. Particles belonging to Geldart groups A and B like sand of various sizes (90, 300, 417, 522, 599, and 622 mu m), FCC catalyst (120 mu m), iron ore (166 and 140 {mu} m), and coal (335 and 168 {mu} m) were used to study the hydrodynamic characteristics. Superficial air velocity used in the present study ranged between 2.01 and 4.681 m/s and corresponding mass fluxes were 12.5-50 kg/(m{sup 2} s). A CFB needs the creation of some special hydrodynamic conditions, namely a certain combination of superficial gas velocity, solids circulation rate, particle diameter, density of particle, etc. which can give rise to a state wherein the solid particles are subjected to an upward velocity greater than the terminal or free fall velocity of the majority of the individual particles. The hydrodynamics of the bed was investigated in depth and theoretical analysis is presented to support the findings. Based on gas-solid momentum balance in the riser, a distinction between apparent and real voidage has been made. The effects of acceleration and friction on the real voidage have been estimated. Results indicated a 0.995 voidage for higher superficial gas velocity of 4.681. m/s.

  10. Metal nanoshells.

    PubMed

    Hirsch, Leon R; Gobin, Andre M; Lowery, Amanda R; Tam, Felicia; Drezek, Rebekah A; Halas, Naomi J; West, Jennifer L

    2006-01-01

    Metal nanoshells are a new class of nanoparticles with highly tunable optical properties. Metal nanoshells consist of a dielectric core nanoparticle such as silica surrounded by an ultrathin metal shell, often composed of gold for biomedical applications. Depending on the size and composition of each layer of the nanoshell, particles can be designed to either absorb or scatter light over much of the visible and infrared regions of the electromagnetic spectrum, including the near infrared region where penetration of light through tissue is maximal. These particles are also effective substrates for surface-enhanced Raman scattering (SERS) and are easily conjugated to antibodies and other biomolecules. One can envision a myriad of potential applications of such tunable particles. Several potential biomedical applications are under development, including immunoassays, modulated drug delivery, photothermal cancer therapy, and imaging contrast agents. PMID:16528617

  11. Theoretical study of stimulated desorption of protons from transition metal surfaces

    SciTech Connect

    Melius, C.F.; Noell, J.O.; Stulen, R.H.

    1982-03-01

    The mechanism for near-threshold photon-stimulated desorption (PSD) and electron-stimulated desorption (ESD) is examined theoretically using finite cluster, quantum chemical techniques to model the interaction of a hydrogen atom with a metal surface. Configuration interaction calculations on clusters modeling both the <100> and <111> faces of an fcc crystal yield a consistent picture of the process. A band of strongly repulsive states which asymptotically dissociate to ions is found to lie approx.25 eV above the ground state. This excitation energy is consistent with the threshold observed in ESD and PSD experiments on the <100> surfaces of Ni and Pd. The states of this band all involve double excitations from the metal--hydrogen bonding orbitals.

  12. Transition metals and their carbides and nitrides: Trends in electronic and structural properties

    NASA Astrophysics Data System (ADS)

    Grossman, Jeffrey C.; Mizel, Ari; Côté, Michel; Cohen, Marvin L.; Louie, Steven G.

    1999-09-01

    A study of the structural and electronic properties of selected transition metals and their carbides and nitrides is presented. We focus on assessing trends of possible importance for understanding their hardness. Lattice constants, bulk moduli (Bo), and charge densities are calculated using the local density approximation with a pseudopotential plane wave approach. An fcc lattice is employed for the transition metal elements in order to make comparisons and study trends relateable to their carbides and nitrides. Our results show that both increasing the number of valence d electrons and the presence of f electrons in the core lead to larger (Bo). Charge density plots and histograms enable us to explain the nature of the charge distribution in the interstitial region for the different compounds considered. In addition, we include the heavier elements seaborgium, bohrium, and hasnium in order to test further trends. Surprisingly, the calculated Bo for Hs is comparable to that of diamond.

  13. Metallized Products

    NASA Technical Reports Server (NTRS)

    1980-01-01

    Since the early 1960's, virtually all NASA spacecraft have used metallized films for a variety of purposes, principally thermal radiation insulation. King Seeley manufactures a broad line of industrial and consumer oriented metallized film, fabric, paper and foam in single layer sheets and multi-layer laminates. A few examples, commercialized by MPI Outdoor Safety Products, are the three ounce Thermos Emergency Blanket which reflects and retains up to 80 percent of the user's body heat helping prevent post accident shock or keeping a person warm for hours under emergency cold weather conditions.

  14. The relaxation of shear stress in a metal alloys with a wide grain size distribution under shock loadings

    NASA Astrophysics Data System (ADS)

    Skripnyak, Evgeniya G.; Skripnyak, Vladimir V.; Skripnyak, Nataliya V.

    The influence of a grain size distribution on the relaxation of shear stress in the metal alloys under shock wave loading was investigated by numerical simulation. The model takes into account the influence of a grain size distribution and a precipitation concentration on the kinetics of shear stress relaxation. The relaxation rate of shear stress in shock waves depends on the specific volume of nano- and ultra-fine grains in the FCC and HCP metal alloys. A wide distribution of grain size reduces the relaxation rate of elastic precursor in HCP alloys. The relaxation of the elastic precursor depends on size and volume concentration of precipitates in metal alloys. Results of simulation show that the rate of plastic deformation in the shock wave exceeds significantly that of the elastic precursor at the same value of shear stresses. Linkoping University, Sweden.

  15. Phase transition from fcc to bcc structure of the Cu-clusters during nanocrystallization of Fe{sub 85.2}Si{sub 1}B{sub 9}P{sub 4}Cu{sub 0.8} soft magnetic alloy

    SciTech Connect

    Nishijima, Masahiko; Matsuura, Makoto; Takenaka, Kana; Takeuchi, Akira; Makino, Akihiro; Ofuchi, Hironori

    2014-05-15

    A role of Cu on the nanocrystallization of an Fe{sub 85.2}Si{sub 1}B{sub 9}P{sub 4}Cu{sub 0.8} alloy was investigated by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM). The Cu K-edge XAFS results show that local structure around Cu is disordered for the as-quenched sample whereas it changes to fcc-like structure at 613 K. The fcc Cu-clusters are, however, thermodynamically unstable and begin to transform into bcc structure at 638 K. An explicit bcc structure is observed for the sample annealed at 693 K for 600 s in which TEM observation shows that precipitated bcc-Fe crystallites with ∼12 nm are homogeneously distributed. The bcc structure of the Cu-clusters transforms into the fcc-type again at 973 K, which can be explained by the TEM observations; Cu segregates at grain boundaries between bcc-Fe crystallites and Fe{sub 3}(B,P) compounds. Combining the XAFS results with the TEM observations, the structure transition of the Cu-clusters from fcc to bcc is highly correlated with the preliminary precipitation of the bcc-Fe which takes place prior to the onset of the first crystallization temperature, T{sub x1} = 707 K. Thermodynamic analysis suggests that an interfacial energy density γ between an fcc-Cu cluster and bcc-Fe matrix dominates at a certain case over the structural energy between fcc and bcc Cu, ΔG{sub fcc} {sub −} {sub bcc}, which causes phase transition of the Cu clusters from fcc to bcc structure.

  16. The role of crystallography and nanostructures on metallic friction.

    SciTech Connect

    Michael, Joseph Richard; Prasad, Somuri V.; Battaile, Corbett Chandler; Majumdar, Bhaskar Sinha; Kotula, Paul Gabriel

    2010-06-01

    In ductile metals, sliding contact is often accompanied by severe plastic deformation localized to a small volume of material adjacent to the wear surface. During the initial run-in period, hardness, grain structure and crystallographic texture of the surfaces that come into sliding contact undergo significant changes, culminating in the evolution of subsurface layers with their own characteristic features. Here, a brief overview of our ongoing research on the fundamental phenomena governing the friction-induced recrystallization in single crystal metals, and how these recrystallized structures with nanometer-size grains would in turn influence metallic friction will be presented. We have employed a novel combination of experimental tools (FIB, EBSD and TEM) and an analysis of the critical resolved shear stress (RSS) on the twelve slip systems of the FCC lattice to understand the evolution of these friction-induced structures in single crystal nickel. The later part of the talk deals with the mechanisms of friction in nanocrystalline Ni films. Analyses of friction-induced subsurfaces seem to confirm that the formation of stable ultrafine nanocrystalline layers with 2-10 nm grains changes the deformation mechanism from the traditional dislocation mediated one to that is predominantly controlled by grain boundaries, resulting in significant reductions in the coefficient friction.

  17. METAL COMPOSITIONS

    DOEpatents

    Seybolt, A.U.

    1959-02-01

    Alloys of uranium which are strong, hard, and machinable are presented, These alloys of uranium contain bctween 0.1 to 5.0% by weight of at least one noble metal such as rhodium, palladium, and gold. The alloys may be heat treated to obtain a product with iniproved tensile and compression strengths,

  18. Heavy Metal.

    ERIC Educational Resources Information Center

    Shoemaker, W. Lee

    1998-01-01

    Discusses the advantages, both functional and economic, of using a standing-seam metal roof in both new roof installations and reroofing projects of educational facilities. Structural versus non-structural standing-seam roofs are described as are the types of insulation that can be added and roof finishes used. (GR)

  19. Transmission Electron Microscopy of Iron Metal in Almahata Sitta Ureilite

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; Yubuta, K.; Sugiyama, K.; Aoyagi, Y.; Yasuhara, A.; Mihira, T.; Zolensky, M. E.; Goodrich, C. A.

    2013-01-01

    Almahata Sitta (AS) is a polymict breccia mainly composed of variable ureilite lithologies with small amounts of chondritic lithologies [1]. Fe metal is a common accessory phase in ureilites, but our earlier study on Fe metals in one of AS fragments (#44) revealed a unique mineralogy never seen in other ureilites [2,3]. In this abstract we report detailed transmission electron microscopy (TEM) on these metal grains to better understand the thermal history of ureilites. We prepared FIB sections of AS#44 by JEOL JIB-4000 from the PTS that was well characterized by SEM-EBSD in our earlier study [2]. The sections were then observed by STEM (JEOL JEM- 2100F). One of the FIB sections shows a submicron-sized symplectic intergrown texture composed of Fe metal (kamacite), Fe carbide (cohenite), Fe phosphide (schreibersite), and Fe sulfide (troilite). Each phase has an identical SAED pattern in spite of its complex texture, suggesting co-crystallization of all phases. This is probably caused by shock re-melting of pre-existing metal + graphite to form a eutectic-looking texture. The other FIB section is mostly composed of homogeneous Fe metal (93 wt% Fe, 5 wt% Ni, and 2 wt% Si), but BF-STEM images exhibited the presence of elongated lathy grains (approx. 2 microns long) embedded in the interstitial matrix. The SAED patterns from these lath grains could be indexed by alpha-Fe (bcc) while interstitial areas are gamma-Fe (fcc). The elongated alpha-Fe grains show tweed-like structures suggesting martensite transformation. Such a texture can be formed by rapid cooling from high temperature where gamma-Fe was stable. Subsequently alpha-Fe crystallized, but gamma-Fe remained in the interstitial matrix due to quenching from high temperature. This scenario is consistent with very rapid cooling history of ureilites suggested by silicate mineralogy.

  20. Composite metal membrane

    DOEpatents

    Peachey, Nathaniel M.; Dye, Robert C.; Snow, Ronny C.; Birdsell, Stephan A.

    1998-01-01

    A composite metal membrane including a first metal layer of Group IVB met or Group VB metals, the first metal layer sandwiched between two layers of an oriented metal of palladium, platinum or alloys thereof is provided together with a process for the recovery of hydrogen from a gaseous mixture including contacting a hydrogen-containing gaseous mixture with a first side of a nonporous composite metal membrane including a first metal of Group IVB metals or Group VB metals, the first metal layer sandwiched between two layers of an oriented metal of palladium, platinum or alloys thereof, and, separating hydrogen from a second side of the nonporous composite metal membrane.

  1. Composite metal membrane

    DOEpatents

    Peachey, N.M.; Dye, R.C.; Snow, R.C.; Birdsell, S.A.

    1998-04-14

    A composite metal membrane including a first metal layer of Group IVB met or Group VB metals, the first metal layer sandwiched between two layers of an oriented metal of palladium, platinum or alloys thereof is provided together with a process for the recovery of hydrogen from a gaseous mixture including contacting a hydrogen-containing gaseous mixture with a first side of a nonporous composite metal membrane including a first metal of Group IVB metals or Group VB metals, the first metal layer sandwiched between two layers of an oriented metal of palladium, platinum or alloys thereof, and, separating hydrogen from a second side of the nonporous composite metal membrane.

  2. Microstructures and mechanical properties of compositionally complex Co-free FeNiMnCr18 FCC solid solution alloy

    SciTech Connect

    Wu, Z.; Bei, H.

    2015-07-01

    Recently, a structurally-simple but compositionally-complex FeNiCoMnCr high entropy alloy was found to have excellent mechanical properties (e.g., high strength and ductility). To understand the potential of using high entropy alloys as structural materials for advanced nuclear reactor and power plants, it is necessary to have a thorough understanding of their structural stability and mechanical properties degradation under neutron irradiation. Furthermore, this requires us to develop a similar model alloy without Co because material with Co will make post-neutron-irradiation testing difficult due to the production of the 60Co radioisotope. In order to achieve this goal, a FCC-structured single-phase alloy with a composition of FeNiMnCr18 was successfully developed. This near-equiatomic FeNiMnCr18 alloy has good malleability and its microstructure can be controlled by thermomechanical processing. By rolling and annealing, the as-cast elongated-grained-microstructure is replaced by homogeneous equiaxed grains. The mechanical properties (e.g., strength and ductility) of the FeNiMnCr18 alloy are comparable to those of the equiatomic FeNiCoMnCr high entropy alloy. Both strength and ductility increase with decreasing deformation temperature, with the largest difference occurring between 293 and 77 K. Extensive twin-bands which are bundles of numerous individual twins are observed when it is tensile-fractured at 77 K. No twin bands are detected by EBSD for materials deformed at 293 K and higher. Ultimately the unusual temperature-dependencies of UTS and uniform elongation could be caused by the development of the dense twin substructure, twin-dislocation interactions and the interactions between primary and secondary twinning systems which result in a microstructure refinement and hence cause enhanced strain hardening and postponed necking.

  3. Photonic band structures of periodic arrays of pores in a metallic host: tight-binding beyond the quasistatic approximation

    NASA Astrophysics Data System (ADS)

    Kim, Kwangmoo; Stroud, David

    2014-03-01

    We have calculated the photonic band structures of metallic inverse opals and of periodic linear chains of spherical pores in a metallic host, below a plasma frequency ωp. In both cases, we use a tight-binding approximation, assuming a Drude dielectric function for the metallic component, but without making the quasistatic approximation. The tight-binding modes are linear combinations of the single-cavity transverse magnetic (TM) modes. For the inverse-opal structures, the lowest modes are analogous to those constructed from the three degenerate atomic p-states in fcc crystals. For the linear chains, in the limit of small spheres compared to a wavelength, the results bear some qualitative resemblance to the dispersion relation for metal spheres in an insulating host, as calculated by Brongersma et al. [Phys. Rev. B 62, R16356 (2000)]. Because the electromagnetic fields of these modes decay exponentially in the metal, there are no radiative losses, in contrast to the case of arrays of metallic spheres in air. We suggest that this tight-binding approach to photonic band structures of such metallic inverse materials may be a useful approach for studying photonic crystals containing metallic components. This work was supported by KIAS, by NSF-MRSEC at OSU (DMR-0820414), and by DOE Grant No. DE-FG02-07ER46424. Computing resources were provided by OSC and by Abacus at KIAS.

  4. Photonic band structures of periodic arrays of pores in a metallic host: tight-binding beyond the quasistatic approximation.

    PubMed

    Kim, Kwangmoo; Stroud, D

    2013-08-26

    We have calculated the photonic band structures of metallic inverse opals and of periodic linear chains of spherical pores in a metallic host, below a plasma frequency ωp. In both cases, we use a tight-binding approximation, assuming a Drude dielectric function for the metallic component, but without making the quasistatic approximation. The tight-binding modes are linear combinations of the single-cavity transverse magnetic (TM) modes. For the inverse-opal structures, the lowest modes are analogous to those constructed from the three degenerate atomic p-states in fcc crystals. For the linear chains, in the limit of small spheres compared to a wavelength, the results bear some qualitative resemblance to the dispersion relation for metal spheres in an insulating host, as calculated by Brongersma et al. [Phys. Rev. B 62, R16356 (2000)]. Because the electromagnetic fields of these modes decay exponentially in the metal, there are no radiative losses, in contrast to the case of arrays of metallic spheres in air. We suggest that this tight-binding approach to photonic band structures of such metallic inverse materials may be a useful approach for studying photonic crystals containing metallic components, even beyond the quasistatic approximation. PMID:24105532

  5. Relative edge energy in the stability of transition metal nanoclusters of different motifs.

    PubMed

    Zhao, X J; Xue, X L; Guo, Z X; Li, S F

    2016-07-01

    When a structure is reduced to a nanometer scale, the proportion of the edge atoms increases significantly, which can play a crucial role in determining both their geometric and electronic properties, as demonstrated by the recently established generalized Wulff construction principle [S. F. Li, et al., Phys. Rev. Lett., 2013, 111, 115501]. Consequently, it is of great interest to clarify quantitatively the role of the edge atoms that dominate the motifs of these nanostructures. In principle, establishing an effective method valid for determining the absolute value of the surface energy and particularly the edge energy for a given nanostructure is expected to resolve such a problem. However, hitherto, it is difficult to obtain the absolute edge energy of transition metal clusters, particularly when their sizes approach the nanometer regime. In this paper, taking Ru nanoclusters as a prototypical example, our first-principles calculations introduce the concept of relative edge energy (REE), reflecting the net edge atom effect over the surface (facet) atom effect, which is fairly powerful to quasi-quantitatively estimate the critical size at which the crossover occurs between different configurations of a given motif, such as from an icosahedron to an fcc nanocrystal. By contrast, the bulk effect should be re-considered to rationalize the power of the REE in predicting the relative stability of larger nanostructures between different motifs, such as fcc-like and hcp-like nanocrystals. PMID:27296770

  6. Synthesis and mechanical behavior of highly nanotwinned metals

    NASA Astrophysics Data System (ADS)

    Furnish, Timothy Allen

    Metals containing high densities of nanoscale growth twins have shown potential as an alternative to nanocrystalline (nc) metals. Some reports on nanotwinned (NT) Cu, for example, have revealed that high strengths, comparable to nc metals, can be produced while improving other properties such as ductility, thermal stability, and mechanical stability. However, since the synthesis of highly NT metals is not yet fully understood, most studies have been limited to only NT-Cu; therefore, it is unclear if similar trends in the mechanical performance of NT-Cu can be extended to other NT systems. In addition, the majority of the work on determining the mechanical properties and deformation mechanisms of NT metals has been produced using nano-indentation; consequently, the larger-scale deformation mechanisms (i.e. those observed using mum to mm scale mechanical testing) of NT metals is still relatively unexplored. In this study, the synthesis of a variety of NT metals was investigated using magnetron sputtering, wherein the deposition conditions were systematically changed in order to produce highly columnar grained NT Cu, Ag, and Cu-6wt%Al (CuAl). The Cu and Ag served as representatives for moderate to low stacking fault energy (SFE) pure fcc metals, respectively, while the CuAl allowed for the study of NTs in low SFE alloyed fcc systems. It was observed that the relatively low SFE of these materials facilitated NT growth during sputtering. In addition, magnetron sputtering enabled the fabrication of relatively thick (26-170 mum) free-standing foils with low initial defects, internal stresses, and dislocation densities. The mechanical performance of the NT metals was evaluated using multiple testing techniques under various conditions, including tensile tests and micro-indentation. The NT microstructures and deformation behaviors were evaluated using advanced characterization methods, including focused ion beam (FIB) and high energy microdiffraction (HEMD). Tensile results

  7. Phase stability in metallic multilayers

    NASA Astrophysics Data System (ADS)

    Genc, Arda

    this problem has been solved by the correction of the spherical aberration of the microscope using a set of non-round lenses and consequently the information limit in an aberration corrected microscope (<0.1nm) has been pushed beyond an uncorrected microscope (˜0.13nm). In 2007, such a corrector system in the probe-forming lens of a Scanning TEM microscope was successfully installed at The Ohio State University. The preliminary results from this microscope were presented in the content of this work where we have studied the microscope and performed first hand experiments. Finally we have addressed the phase stability in Cu/Nb and Ti/Nb nanoscale metallic multilayers by extensive use of these advance characterization techniques and tools. At reduced layer thickness (<2nm) the change in fcc to bcc phase in Cu and hcp to bcc phase in Ti were experimentally confirmed using X-ray diffraction electron diffraction and electron imaging techniques along the plan-view and cross-section directions. These structural transformations were often referred to as being thermodynamic in nature and a classical thermodynamical model explains and predicts the formation of such pseudomorphic phases through the competition of volumetric and interfacial free energy variables. We have investigated both the structural and chemical changes in the Cu/Nb and Ti/Nb nanoscale metallic mutilayers as a function of length scale in order to understand and predict the phase stability. The important constituents: volumetric free energy and interfacial energy changes were experimentally derived considering the chemistry and structure of the multilayers and competition between these thermodynamic terms well explains the observed structural changes in nanoscale metallic multilayers.

  8. Mechanochemical processing for metals and metal alloys

    DOEpatents

    Froes, Francis H.; Eranezhuth, Baburaj G.; Prisbrey, Keith

    2001-01-01

    A set of processes for preparing metal powders, including metal alloy powders, by ambient temperature reduction of a reducible metal compound by a reactive metal or metal hydride through mechanochemical processing. The reduction process includes milling reactants to induce and complete the reduction reaction. The preferred reducing agents include magnesium and calcium hydride powders. A process of pre-milling magnesium as a reducing agent to increase the activity of the magnesium has been established as one part of the invention.

  9. Effect of electron excitation on radiation damage in fce metals

    NASA Astrophysics Data System (ADS)

    Iwase, A.; Iwata, T.

    1994-05-01

    Defect production, radiation annealing and defect recovery are studied in several fcc metals (Al, Cu, Ni, Ag and Pt) irradiated with low-energy (˜ 1 MeV) and high-energy (˜ 100 MeV) ions. Irradiation of the metals with strong electron-lattice interaction (Al, Ni and Pt) by ˜ 100 MeV ions causes an anomalous reduction, or even a complete disappearance of stage-I recovery. This experimental result shows that the energy transferred from excited electrons to lattice atoms through the electron-lattice interaction contributes to the annihilation of single interstitials. This effect is also observed in Ni as a large cross section for radiation annealing, and a decrease of the damage efficiency. On the other hand, in Cu and Ag thin foils, we find that lattice defects are produced not only through elastic interactions, but also through a process strongly associated with electron excitation. In the latter process, the defect production cross section is proportional to Se1.7 in Cu and Se1.5 in Ag. The nearly quadratic dependence of the cross section on Se suggests that the mutual Coulomb repulsion of ions positively charged by electron excitation causes the defect production.

  10. Quantum Chemistry for Surface Segregation in Metal Alloys

    SciTech Connect

    Sholl, David

    2006-08-31

    Metal alloys are vital materials for the fabrication of high-flux, high-selectivity hydrogen separation membranes. A phenomenon that occurs in alloys that does not arise in pure metals is surface segregation, where the composition of the surface differs from the bulk composition. Little is known about the strength of surface segregation in the alloys usually considered for hydrogen membranes. Despite this lack of knowledge, surface segregation may play a decisive role in the ability of appropriately chosen alloys to be resistant to chemical poisoning, since membrane poisoning is controlled by surface chemistry. The aim of this Phase I project is to develop quantum chemistry approaches to assess surface segregation in a prototypical hydrogen membrane alloy, fcc Pd{sub 75}Cu{sub 25}. This alloy is known experimentally to have favorable surface properties as a poison resistant H{sub 2} purification membrane (Kamakoti et al., Science 307 (2005) 569-573), but previous efforts at modeling surfaces of this alloy have ignored the possible role of surface segregation (Alfonso et al., Surf. Sci. 546 (2003) 12-26).

  11. Atomistic modeling to optimize composition and characterize structure of Ni-Zr-Mo metallic glasses.

    PubMed

    Yang, M H; Li, S N; Li, Y; Li, J H; Liu, B X

    2015-05-28

    An interatomic potential was constructed for the Ni-Zr-Mo ternary metal system with the newly proposed long-range empirical formulism, which has been verified to be applicable for fcc, hcp and bcc transition metals and their alloys. Applying the constructed potential, molecular dynamics simulations predict a hexagonal composition region within which metallic glass formation is energetically favored. Based on the simulation results, the driving force for amorphous phase formation is derived, and thus an optimized composition is pinpointed to Ni45Zr40Mo15, of which the metallic glass could be most stable or easiest to obtain. Further structural analysis indicates that the dominant interconnected clusters for Ni64Zr36-xMox MGs are 〈0, 0, 12, 0〉, 〈0, 1, 10, 2〉, 〈0, 2, 8, 2〉 and 〈0, 3, 6, 4〉. In addition, it is found that the appropriate addition of Mo content could not only make a more ordered structure with a higher atomic packing density and a lower energy state, but also improve the glass formation ability of Ni-Zr-Mo alloys. Moreover, inherent hierarchical atomic configurations for ternary Ni-Zr-Mo metallic glasses are clarified via the short-range, medium-range and further in the extended scale of the icosahedral network. PMID:25923843

  12. Use of naphtha as riser diluent in carbo-metallic oil conversion

    SciTech Connect

    Myers, G.D.

    1983-03-08

    A process is disclosed for the production of high octane gasoline and/or other valuable lower molecular weight products from carbo-metallic oils. Examples include crude oil, topped crude, reduced crude, residua, the extract from solvent deasphalting and other heavy hydrocarbon fractions. These carbometallic oils contain quantities of coke precursors and heavy metal catalyst poisons substantially in excess of what is normally considered acceptable for fluid catalytic cracking (fcc) and substantial amounts of sulfur, nitrogen and other troublesome components may also be present. Such carbo-metallic oils are converted to the desired products in a catalytic conversion process where the oil feed is mixed with naphtha and brought together with a high-metal content cracking catalyst. Named ''rcc'' (reduced crude conversion) after a particularly common or useful carbo-metallic feed, the present process is by no means restricted to reduced crude or to oils of petroleum origin, having utility in the processing of oils from coal, shale and other sources.

  13. The possibility to measure the magnetic moments of short-lived particles (charm and beauty baryons) at LHC and FCC energies using the phenomenon of spin rotation in crystals

    NASA Astrophysics Data System (ADS)

    Baryshevsky, V. G.

    2016-06-01

    The use of spin rotation effect in bent crystals for measuring the magnetic moment of short-lived particles in the range of LHC and FCC energies is considered. It is shown that the estimated number of produced baryons that are captured into a bent crystal grows as ∼γ 3 / 2 with increasing particle energy. Hence it may be concluded that the experimental measurement of magnetic moments of short-lived particles using the spin rotation effect is feasible at LHC and higher energies (for LHC energies, e.g., the running time required for measuring the magnetic moment of Λc+is 2 ÷ 16 hours).

  14. The possibility to measure the magnetic moments of short-lived particles (charm and beauty baryons) at LHC and FCC energies using the phenomenon of spin rotation in crystals

    NASA Astrophysics Data System (ADS)

    Baryshevsky, V. G.

    2016-06-01

    The use of spin rotation effect in bent crystals for measuring the magnetic moment of short-lived particles in the range of LHC and FCC energies is considered. It is shown that the estimated number of produced baryons that are captured into a bent crystal grows as ∼γ 3 / 2 with increasing particle energy. Hence it may be concluded that the experimental measurement of magnetic moments of short-lived particles using the spin rotation effect is feasible at LHC and higher energies (for LHC energies, e.g., the running time required for measuring the magnetic moment of Λc+ is 2 ÷ 16 hours).

  15. Metal filled porous carbon

    DOEpatents

    Gross, Adam F.; Vajo, John J.; Cumberland, Robert W.; Liu, Ping; Salguero, Tina T.

    2011-03-22

    A porous carbon scaffold with a surface and pores, the porous carbon scaffold containing a primary metal and a secondary metal, where the primary metal is a metal that does not wet the surface of the pores of the carbon scaffold but wets the surface of the secondary metal, and the secondary metal is interspersed between the surface of the pores of the carbon scaffold and the primary metal.

  16. First-principles study on stability of transition metal solutes in aluminum by analyzing the underlying forces

    SciTech Connect

    Liu, Wei; Xu, Yichun; Li, Xiangyan; Wu, Xuebang Liu, C. S.; Liang, Yunfeng; Wang, Zhiguang

    2015-05-07

    Although there have been some investigations on behaviors of solutes in metals under strain, the underlying mechanism of how strain changes the stability of a solute is still unknown. To gain such knowledge, first-principles calculations are performed on substitution energy of transition metal solutes in fcc Al host under rhombohedral strain (RS). Our results show that under RS, substitution energy decreases linearly with the increase of outermost d radius r{sub d} of the solute due to Pauli repulsion. The screened Coulomb interaction increases or decreases the substitution energy of a solute on condition that its Pauling electronegativity scale ϕ{sub P} is less or greater than that of Al under RS. This paper verifies a linear relation of substitution energy change versus r{sub d} and ϕ{sub P} under RS, which might be instructive for composition design of long life alloys serving in high stress condition.

  17. Extracting metals directly from metal oxides

    DOEpatents

    Wai, C.M.; Smart, N.G.; Phelps, C.

    1997-02-25

    A method of extracting metals directly from metal oxides by exposing the oxide to a supercritical fluid solvent containing a chelating agent is described. Preferably, the metal is an actinide or a lanthanide. More preferably, the metal is uranium, thorium or plutonium. The chelating agent forms chelates that are soluble in the supercritical fluid, thereby allowing direct removal of the metal from the metal oxide. In preferred embodiments, the extraction solvent is supercritical carbon dioxide and the chelating agent is selected from the group consisting of {beta}-diketones, halogenated {beta}-diketones, phosphinic acids, halogenated phosphinic acids, carboxylic acids, halogenated carboxylic acids, and mixtures thereof. In especially preferred embodiments, at least one of the chelating agents is fluorinated. The method provides an environmentally benign process for removing metals from metal oxides without using acids or biologically harmful solvents. The chelate and supercritical fluid can be regenerated, and the metal recovered, to provide an economic, efficient process. 4 figs.

  18. Extracting metals directly from metal oxides

    DOEpatents

    Wai, Chien M.; Smart, Neil G.; Phelps, Cindy

    1997-01-01

    A method of extracting metals directly from metal oxides by exposing the oxide to a supercritical fluid solvent containing a chelating agent is described. Preferably, the metal is an actinide or a lanthanide. More preferably, the metal is uranium, thorium or plutonium. The chelating agent forms chelates that are soluble in the supercritical fluid, thereby allowing direct removal of the metal from the metal oxide. In preferred embodiments, the extraction solvent is supercritical carbon dioxide and the chelating agent is selected from the group consisting of .beta.-diketones, halogenated .beta.-diketones, phosphinic acids, halogenated phosphinic acids, carboxylic acids, halogenated carboxylic acids, and mixtures thereof. In especially preferred embodiments, at least one of the chelating agents is fluorinated. The method provides an environmentally benign process for removing metals from metal oxides without using acids or biologically harmful solvents. The chelate and supercritical fluid can be regenerated, and the metal recovered, to provide an economic, efficient process.

  19. Metals production

    NASA Technical Reports Server (NTRS)

    Beck, Theodore S.

    1992-01-01

    Existing procedures for design of electrochemical plants can be used for design of lunar processes taking into consideration the differences in environmental conditions. These differences include: 1/6 Earth gravity, high vacuum, solar electrical and heat source, space radiation heat sink, long days and nights, and different availability and economics of materials, energy, and labor. Techniques have already been developed for operation of relatively small scale hydrogen-oxygen fuel cell systems used in the U.S. lunar landing program. Design and operation of lunar aqueous electrolytic process plants appears to be within the state-of-the-art. Finding or developing compatible materials for construction and designing of fused-magma metal winning cells will present a real engineering challenge.

  20. Direct imaging of local atomic ordering in a Pd-Ni-P bulk metallic glass using Cs-corrected transmission electron microscopy.

    PubMed

    Hirata, Akihiko; Hirotsu, Yoshihiko; Nieh, T G; Ohkubo, Tadakatsu; Tanaka, Nobuo

    2007-01-01

    In amorphous alloys, crystalline atomic clusters as small as 1-2 nm are frequently observed as local lattice fringe images by high-resolution electron microscopy (HREM). These clusters can be understood as local structures of amorphous alloys corresponding to "medium-range-order (MRO)". The MRO structure can be observed only under suitable defocusing conditions of the objective lens in HREM. A clear imaging of the MRO structure is difficult in conventional TEMs, mainly due to the delocalization of the image, caused mainly by the spherical aberration of the objective lens and eventually by the chosen defocus. In the present study, we have examined MRO in a Pd-based bulk metallic glass (Pd(40)Ni(40)P(20)) using a high-resolution TEM (acceleration voltage 200 kV) fitted with a spherical aberration constant corrector (Cs corrector) for aberration correction. We found that when Cs was close to zero and defocus values were near the Gaussian focus, MRO regions with an FCC-Pd structure could be clearly observed with a low image disturbance. Under these conditions, the phase-contrast transfer function was understood to act as an ideal filter function, which distinctly selects specific lattice periods of the FCC-Pd clusters. The obtained atomic images of the glass structure including the FCC-Pd clusters are in good agreement with those expected from image simulation according to our amorphous structure model. In this study, we have demonstrated that the Cs-corrected HREM is a powerful tool to directly image locally ordered structures in metallic glasses. PMID:16872747

  1. Neurotoxicity of metals.

    PubMed

    Caito, Samuel; Aschner, Michael

    2015-01-01

    Metals are frequently used in industry and represent a major source of toxin exposure for workers. For this reason governmental agencies regulate the amount of metal exposure permissible for worker safety. While essential metals serve physiologic roles, metals pose significant health risks upon acute and chronic exposure to high levels. The central nervous system is particularly vulnerable to metals. The brain readily accumulates metals, which under physiologic conditions are incorporated into essential metalloproteins required for neuronal health and energy homeostasis. Severe consequences can arise from circumstances of excess essential metals or exposure to toxic nonessential metal. Herein, we discuss sources of occupational metal exposure, metal homeostasis in the human body, susceptibility of the nervous system to metals, detoxification, detection of metals in biologic samples, and chelation therapeutic strategies. The neurologic pathology and physiology following aluminum, arsenic, lead, manganese, mercury, and trimethyltin exposures are highlighted as classic examples of metal-induced neurotoxicity. PMID:26563789

  2. Fundamental radiation effects parameters in metals and ceramics

    SciTech Connect

    Zinkle, S.J.

    1998-03-01

    Useful information on defect production and migration can be obtained from examination of the fluence-dependent defect densities in irradiated materials, particularly when a transition from linear to sublinear accumulation is observed. Further work is needed on several intriguing reported radiation effects in metals. The supralinear defect cluster accumulation regime in thin foil irradiated metals needs further experimental confirmation, and the physical mechanisms responsible for its presence need to be established. Radiation hardening and the associated reduction in strain hardening capacity in FCC metals is a serious concern for structural materials. In general, the loss of strain hardening capacity is associated with dislocation channeling, which occurs when a high density of small defect clusters are produced (stainless steel irradiated near room temperature is a notable exception). Detailed investigations of the effect of defect cluster density and other physical parameters such as stacking fault energy on dislocation channeling are needed. Although it is clearly established that radiation hardening depends on the grain size (radiation-modified Hall-Petch effect), further work is needed to identify the physical mechanisms. In addition, there is a need for improved hardening superposition models when a range of different obstacle strengths are present. Due to a lack of information on point defect diffusivities and the increased complexity of radiation effects in ceramics compared to metals, many fundamental radiation effects parameters in ceramics have yet to be determined. Optical spectroscopy data suggest that the oxygen monovacancy and freely migrating interstitial fraction in fission neutron irradiated MgO and Al{sub 2}O{sub 3} are {approximately}10% of the NRT displacement value. Ionization induced diffusion can strongly influence microstructural evolution in ceramics. Therefore, fundamental data on ceramics obtained from highly ionizing radiation sources

  3. Transition metal dimer on Au(111) surface: A first principle study

    NASA Astrophysics Data System (ADS)

    Sahoo, Suman Kalyan; Nigam, Sandeep; Sarkar, Pranab; Majumder, Chiranjib

    2012-06-01

    The adsorption behaviour of transition metal dimers M2 (M= Cu, Ag, Au) on the Au(111) surface have been studied using the density functional theory formalism. The projector augmented wave method under the spin polarized version of generalized gradient approximation scheme was employed to calculate the total energy. The results suggest that all dimers prefer to orient in parallel to the surface plane, where two M atoms are adsorbed on two nearby threefold fcc sites. We have investigated the chemical interaction between M atoms and Au surface through electronic density of state analysis. It is found that on deposition, the electronic density of states (EDOS) of M2 dimer becomes broader in comparison to their gas phase spectrum.

  4. Electronic and Structural Properties of Transition - and Transition-Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Chan, Che-Ting

    The electronic and structural properties of transition metals and transition metal surfaces are studied theoretically from first-principles, with emphasis on understanding their properties under different physical and chemical environments. A new general self-consistency procedure for calculating the electronic structure of crystalline solids is developed and applied to extend a first-principles pseudopotential linear combination of atomic orbitals (LCAO) method to full point-by-point self-consistency. This scheme is tested by applying to a study of the structural and electronic properties of Si and W, prototypical systems of very different bonding characters. The importance of self-consistency is investigated. The structural properties of Mo and W in the bcc, fcc and hcp structures are calculated with the new scheme. Equilibrium lattice constants, cohesive energies, bulk moduli, differences in structural energies and Mulliken population analyses are obtained. For both elements, the cohesive energies decrease in the order E(,coh)('bcc) > E(,coh)('fcc) (DBLTURN) E(,coh)('hcp). The results show that the relative stability of the bcc and fcc structures can be explained qualitatively but not quantitatively by the difference in the sum of the electronic eigenvalues. The structural properties of the W(001)(1 x 1) surface are also calculated with the same method. Surface energy, top layer relaxation, and relaxation energy are obtained with good agreement with available experimental data. The electronic structures of PdH and Pd(,4)H are calculated by a pseudopotential mixed basis approach with emphasis on the nature of the Pd-H bonding state and the effect of changing hydrogen concentration. The essential physical nature of the hydride system is summarized in a simple conceptual model. The mixed basis method is then applied to study the electronic structures of monolayer atomic hydrogen at surface and subsurface sites of the Pd(111) surface. Electronic properties and

  5. X-ray diffraction and Mössbauer spectroscopy study of fcc iron hydride FeH at high pressures and implications for the composition of the Earth;s core

    SciTech Connect

    Narygina, Olga; Dubrovinsky, Leonid S.; McCammon, Catherine A.; Kurnosov, Alexander; Kantor, Innokenty Yu.; Prakapenka, Vitali B.; Dubrovinskaia, Natalia A.

    2011-10-28

    The phase fcc FeH{sub x} (x {approx} 1) was synthesized at pressures over 30 GPa and temperatures over 1600(50) K. At room temperature this iron hydride is stable at pressures from 19(1) GPa up to at least 68(2) GPa (the highest pressure achieved in this study). A fit of the PV data collected for fcc FeH{sub x} at room temperature gives the following parameters for the equation of state: V{sub 0} = 53.8(3) {angstrom}{sup 3}, K{sub 0} = 99(5) GPa, K' = 11.7(5). Using this data the amount of H required to match the density of the Earth's core was estimated to be 0.5-1 wt.% hydrogen in the outer core and 0.08-0.16 wt.% hydrogen in the inner core. Our results also suggest that hydrogen and carbon do not occur together in the Earth's core.

  6. Metal-phosphate binders

    DOEpatents

    Howe, Beth Ann [Lewistown, IL; Chaps-Cabrera, Jesus Guadalupe [Coahuila, MX

    2009-05-12

    A metal-phosphate binder is provided. The binder may include an aqueous phosphoric acid solution, a metal-cation donor including a metal other than aluminum, an aluminum-cation donor, and a non-carbohydrate electron donor.

  7. Metal treatment

    SciTech Connect

    Carlson, R.; Johnson, P.M.; Pierce, J.R.

    1993-07-13

    A process is described for increasing the corrosion resistance of a metal object bearing a preexisting protective conversion coating, said process comprising steps of: (A) contacting the pre-existing coating with a composition having a pH from about 5 to about 12 and consisting essentially of: (1) water, (2) from 25-5,000 ppm of triazole molecules selected from the group consisting of aryl triazoles containing from 6 to about 10 carbon atoms and alkyl triazoles containing from 1 to about 6 carbon atoms, and, optionally, (3) at least partially substituted poly(vinylphenol) polymer or copolymer including substituents on at least some of the phenol rings: wherein each of R[sub 5] through R[sub 12] is selected from hydrogen, an alkyl, an aryl, an aryl, a hydroxy-alkyl, an amino-alkyl, a mercapto-alkyl, or a phospho-alkyl moiety, except that R[sub 12] can also be [minus]O[sup [minus]1] or [minus]OH and that at least one of R[sub 9] and R[sub 10] must include a polyhydroxy functionality resulting from the condensation of an amine or ammonia with a ketose, aldose, or other polyhydroxyl compound having from about 3 to about 8 carbon atoms, followed by reduction from imino to amino, and, optionally, (4) polar organic solvents; and (B) drying the object completion of step (A).

  8. Memory Metals

    NASA Technical Reports Server (NTRS)

    1995-01-01

    Under contract to NASA during preparations for the space station, Memry Technologies Inc. investigated shape memory effect (SME). SME is a characteristic of certain metal alloys that can change shape in response to temperature variations. In the late 1980s and early 1990s, Memry used its NASA-acquired expertise to produce a line of home and industrial safety products, and refined the technology in the mid-1990s. Among the new products they developed are three MemrySafe units which prevent scalding from faucets. Each system contains a small valve that reacts to temperature, not pressure. When the water reaches dangerous temperatures, the unit reduces the flow to a trickle; when the scalding temperature subsides, the unit restores normal flow. Other products are the FIRECHEK 2 and 4, heat-activated shutoff valves for industrial process lines, which sense excessive heat and cut off pneumatic pressure. The newest of these products is Memry's Demand Management Water Heater which shifts the electricity requirement from peak to off-peak demands, conserving energy and money.

  9. Computational studies of experimentally observed structures of sulfur on metal surfaces

    SciTech Connect

    Alfonso, Dominic

    2011-09-01

    First-principles electronic structure calculations were carried out to examine the experimentally observed structures of sulfur on close packed surfaces of a number of important metals - Ag(111), Cu(111), Ni(111), Pt(111), Rh(111), Re(0001) and Ru(0001). At low coverages ({le} 1/3 ML), the prediction is consistent with the typical pattern of preferred sulfur occupancy of threefold hollow sites, notably the fcc site on the (111) surfaces and the hcp site on the (0001) surfaces. Theoretical confirmation for the existence of pure sulfur overlayer phases on Pt(111), Rh(111), Re(0001) and Ru(0001) at higher coverages (> 1/3 ML) was provided. For the ({radical}7 x {radical}7) phase seen on Ag(111), the most preferred structure identified for adsorbed S trimer consists of an S atom on the top site bonded to two S atoms situated on the nearest neighbor off-bridge site positions. Among the different densely packed mixed sulfur-metal overlayer models suggested for the ({radical}7 x {radical}7) phase on Cu(111), the structure which consists of metal and S atoms in a hexagonal-like arrangement on the top substrate was found to be the most energetically favorable. For the (5{radical}3 x 2) phase on Ni(111), the calculations confirm the existence of clock-reconstructed top layer metal atoms onto which sulfur atoms are adsorbed.

  10. METAL PRODUCTION AND CASTING

    DOEpatents

    Magel, T.T.

    1958-03-01

    This patent covers a method and apparatus for collecting the molten metal produced by high temperature metal salt reduction. It consists essentially of subjecting the reaction vessel to centrifugal force in order to force the liberatcd molten metal into a coherent molten mass, and allowing it to solidify there. The apparatus is particularly suitable for use with small quantities of rare metals.

  11. Ceramic to metal seal

    DOEpatents

    Snow, Gary S.; Wilcox, Paul D.

    1976-01-01

    Providing a high strength, hermetic ceramic to metal seal by essentially heating a wire-like metal gasket and a ceramic member, which have been chemically cleaned, while simultaneously deforming from about 50 to 95 percent the metal gasket against the ceramic member at a temperature of about 30 to 75 percent of the melting temperature of the metal gasket.

  12. Fabrication of metal nanoshells

    NASA Technical Reports Server (NTRS)

    Kim, Jae-Woo (Inventor); Choi, Sang H. (Inventor); Lillehei, Peter T. (Inventor); Chu, Sang-Hyon (Inventor); Park, Yeonjoon (Inventor); King, Glen C. (Inventor); Elliott, Jr., James R. (Inventor)

    2012-01-01

    Metal nanoshells are fabricated by admixing an aqueous solution of metal ions with an aqueous solution of apoferritin protein molecules, followed by admixing an aqueous solution containing an excess of an oxidizing agent for the metal ions. The apoferritin molecules serve as bio-templates for the formation of metal nanoshells, which form on and are bonded to the inside walls of the hollow cores of the individual apoferritin molecules. Control of the number of metal atoms which enter the hollow core of each individual apoferritin molecule provides a hollow metal nonparticle, or nanoshell, instead of a solid spherical metal nanoparticle.

  13. Amorphous metal composites

    DOEpatents

    Byrne, Martin A.; Lupinski, John H.

    1984-01-01

    An improved amorphous metal composite and process of making the composite. The amorphous metal composite comprises amorphous metal (e.g. iron) and a low molecular weight thermosetting polymer binder. The process comprises placing an amorphous metal in particulate form and a thermosetting polymer binder powder into a container, mixing these materials, and applying heat and pressure to convert the mixture into an amorphous metal composite.

  14. Metal phthalocyanine polymers

    NASA Technical Reports Server (NTRS)

    Achar, B. N.; Fohlen, G. M.; Parker, J. A. (Inventor)

    1984-01-01

    Metal 4, 4', 4", 4"'=tetracarboxylic phthalocyanines (MPTC) are prepared by reaction of trimellitic anhydride, a salt or hydroxide of the desired metal (or the metal in powdered form), urea and a catalyst. A purer form of MPTC is prepared than heretofore. These tetracarboxylic acids are then polymerized by heat to sheet polymers which have superior heat and oxidation resistance. The metal is preferably a divalent metal having an atomic radius close to 1.35A.

  15. Platinum group metals base refractory superalloys

    SciTech Connect

    Yamabe-Mitarai, Y.; Koizumi, Y.; Murakami, H.; Harada, H.; Maruko, T.

    1997-12-31

    Ir- and Rh-base refractory superalloys wit h an fcc and L1{sub 2} two phase structure similar to Ni-base superalloys, yet with considerably higher melting temperatures have been proposed. Fcc and L1{sub 2} two phases were observed in these alloys by transmission electron microscopy and X-ray powder diffractometry. The compression tests of these alloys showed that the strengths of several alloys were about 200 MPa at 1,800 C and these alloys have potential to become ultra-high temperature materials for use in power engineering field.

  16. Predicting dietborne metal toxicity from metal influxes.

    PubMed

    Croteau, Marie-Noële; Luoma, Samuel N

    2009-07-01

    Dietborne metal uptake prevails for many species in nature. However, the links between dietary metal exposure and toxicity are not well understood. Sources of uncertainty include the lack of suitable tracers to quantify exposure for metals such as copper, the difficulty to assess dietary processes such as food ingestion rate, and the complexity to link metal bioaccumulation and effects. We characterized dietborne copper, nickel, and cadmium influxes in a freshwater gastropod exposed to diatoms labeled with enriched stable metal isotopes. Metal influxes in Lymnaea stagnalis correlated linearly with dietborne metal concentrations over a range encompassing most environmental exposures. Dietary Cd and Ni uptake rate constants (k(uf)) were, respectively, 3.3 and 2.3 times higher than thatfor Cu. Detoxification rate constants (k(detox)) were similar among metals and appeared 100 times higher than efflux rate constants (K(e)). Extremely high Cu concentrations reduced feeding rates, causing the relationship between exposure and influx to deviate from linearity, i.e., Cu uptake rates leveled off between 1500 and 1800 nmol g(-1) day(-1). L. stagnalis rapidly takes up Cu, Cd, and Ni from food but detoxifies the accumulated metals, instead of reducing uptake or intensifying excretion. Above a threshold uptake rate, however, the detoxification capabilities of L. stagnalis are overwhelmed. PMID:19673285

  17. Magnetostatic spin wave resonance in square-patterned Ni0.77Fe0.16Cu0.05Cr0.02 (Mu-metal) thinfilms

    NASA Astrophysics Data System (ADS)

    Deger, Caner; Ozdemir, Mustafa; Yildiz, Fikret

    2016-06-01

    Behavior of spin waves was investigated in patterned Mu-metal thin film both theoretically and experimentally. The Mu-metal(111) thinfilms with 7 nm thickness were grown by thermal evaporation technique in high vacuum condition. X-ray diffraction measurements showed that the film has a highly FCC crystalline structure. Saturation magnetization and coercive field values of sample obtained from vibrating sample magnetometer are around 500 emu/cm3 and 10 Oe respectively at room temperature. The patterns were square shaped and size of squares were changed between 40-80 μm. Theoretical model and computer program were developed for analyzing the FMR spectra. There is no magnetic anisotropy for in-plane and out-of-plane geometry by both theoretical and experimental investigations. Magnetostatic modes were observed for out-of-plane geometry and these modes were highly compatible with outputs of simulation model.

  18. Cold rolling induced alloying behaviors in metallic multilayers

    NASA Astrophysics Data System (ADS)

    Wang, Zhe

    Phase transformation and atomic scale intermixing induced by deformation are important and fundamental issues in the mechanical alloying processes. Repeated cold rolling and folding experiments were performed on the metallic multilayers in order to study the deformation driven behaviors. Various binary systems such as isomorphous, eutectic and thermodynamically immiscible systems were studied. Moreover, monometallic Pd, Pt and Fe were selected in order to study the deformation driven recrystallization behavior. In Cu/Ni multilayers, the composition of the solid solution is revealed by an oscillation in the composition profile across the multilayers, which is different from the smoothly varying profile due to thermally activated diffusion. During the reaction, Cu mixed into Ni preferentially compared to Ni mixing into Cu, which is also in contrast to the thermal diffusion behavior. During the cold rolling of multilayers of Ni and V, deformation induces phase transformation and an interfacial mixing with suppression of nucleation of intermetallic phases. The results also demonstrate that between pure Ni and V layers a metastable fcc solid solution phase forms in Ni70V30, a metastable bcc solid solution phase forms in Ni30V70 and metastable fcc and bcc solid solution phases form in Ni57V43. Compared to the stored energy due to dislocation and interfaces, the excess chemical free energy from the interfacial mixing is the largest portion of total stored energy from deformation, which represents a form of mechanochemical transduction. The difference in the intermixing behaviors between Cu/Ni and Ni/V systems is due to that the systems have different heat of mixing and interface characters. Deformation of Cu/Fe multilayers yields a smooth and monotonic variation in the composition profile. From the local composition consumption it is revealed that that Fe mixes into Cu preferentially than Cu mixing into Fe. The room temperature deformation driven recrystallization was

  19. Metal-Air Batteries

    SciTech Connect

    Zhang, Jiguang; Bruce, Peter G.; Zhang, Gregory

    2011-08-01

    Metal-air batteries have much higher specific energies than most currently available primary and rechargeable batteries. Recent advances in electrode materials and electrolytes, as well as new designs on metal-air batteries, have attracted intensive effort in recent years, especially in the development of lithium-air batteries. The general principle in metal-air batteries will be reviewed in this chapter. The materials, preparation methods, and performances of metal-air batteries will be discussed. Two main metal-air batteries, Zn-air and Li-air batteries will be discussed in detail. Other type of metal-air batteries will also be described.

  20. Alkali metal nitrate purification

    DOEpatents

    Fiorucci, Louis C.; Morgan, Michael J.

    1986-02-04

    A process is disclosed for removing contaminants from impure alkali metal nitrates containing them. The process comprises heating the impure alkali metal nitrates in solution form or molten form at a temperature and for a time sufficient to effect precipitation of solid impurities and separating the solid impurities from the resulting purified alkali metal nitrates. The resulting purified alkali metal nitrates in solution form may be heated to evaporate water therefrom to produce purified molten alkali metal nitrates suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of purified alkali metal nitrates.