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Sample records for fcc f-shell metals

  1. Twinning in nanocrystalline fcc and bcc metals

    NASA Astrophysics Data System (ADS)

    Boyko, Vladimir S.; Kezerashvili, Roman Ya.

    2013-03-01

    The deformation twinning in nanocrystalline (nc) face-centered cubic (fcc) metals, body-centered cubic (bcc) metals, and in nc Si is analyzed. The phenomenological approach is used to make a bridge between microscopical mechanisms of twin nucleation and macroscopical characteristics of twinning with different crystal structures and to calculate the grain size range of the twinning propensity, the requisite external stress for twinning propagation in nc polycrystals, and the grain size at which the slip begins to prevail over the twinning. The developed approach allows to derive analytical expressions and estimate lower and and upper limits of grain sizes at which a twinning propensity is occurred. Results of calculations for the nc fcc metals Al, Cu, Ni, Pd, Au, nc bcc metals Ta, Fe, Mo, W, Nb, and nc diamond-cubic Si are compared with the experimental data, otherwise predictions are made.

  2. Molecular Dynamics Simulation of FCC Metallic Nanowires: A Review

    NASA Astrophysics Data System (ADS)

    Lao, Jijun; Naghdi Tam, Mehdi; Pinisetty, Dinesh; Gupta, Nikhil

    2013-02-01

    Molecular dynamic simulation studies are reviewed to understand the influence of strain rate, temperature, and cross-section size on the mechanical properties of face-centered cubic (FCC) metallic nanowires (MNWs). The yield stress of FCC MNWs is found to be 100 times higher than that of the corresponding bulk metals. The yield strain and fracture stress of MNWs are also found to be significantly higher compared with those of the bulk metals. The influence of deformation mechanisms (slip and twinning) on the mechanical properties of FCC MNWs is discussed. FCC MNWs are found to exhibit novel structural reorientation, phase transformation, elastic recovery, pseudoelasticity, and shape memory effect. MNWs with body-centered cubic (BCC) and hexagonal closed-packed crystal structures are compared with the FCC MNWs. Pseudoelasticity was also observed in BCC MNWs similar to that of FCC MNWs. Dense nano-twin arrays were found in Mg nanowires despite the high twin boundary energy.

  3. 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.

  4. 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.

  5. Pre-melting Behaviour in fcc Metals

    NASA Astrophysics Data System (ADS)

    Pamato, M. G.; Wood, I. G.; Dobson, D. P.; Hunt, S.; Vocadlo, L.

    2016-12-01

    Although the Earth's core is accepted to be made of an iron-nickel alloy with a few percent of light elements, its exact structure and composition are still unknown. Seismological and mineralogical models in the Earth's inner core do not agree, with mineralogical models derived from ab initiocalculations predicting shear-wave velocities up to 30% greater than seismically observed values. Recent computer simulations revealed that such difference may be explained by a dramatic, non-linear, softening of the elastic constants of Fe prior to melting. Up to date, computer calculations are the only result on pre-melting of direct applicability to the Earth's core and it is essential to systematically investigate such phenomena at inner core pressures and temperatures. Measuring the pressure dependence of pre-melting effects at such conditions and to the required precision is however extremely challenging. Also, pre-melting effects have been observed or suggested to occur in other materials, particularly noble metals, which exhibit large departures from linearity (modulus defects) at elevated temperatures. The aim of this study is to investigate to what extent pre-melting behaviour occurs in the physical properties of other metals at more experimentally tractable conditions. In particular, we report measurements of density and thermal expansion coefficients of both pure and alloyed gold (Au) up to their melting points. Au is an ideal test material since it crystallises in a simple monatomic face-centred structure and has a relatively low melting temperature. Precise measurements of unit cell lattice parameters were performed using a PANalytical X'Pert Pro powder diffractometer, equipped with an incident beam monochromator (giving very high resolution diffraction patterns) and with environmental stages covering the range from 40 K to 1373 K, with a readily achievable temperature resolution of 1K. We will discuss the circumstances under which pre-melting occurs, its

  6. Structure and Magnetism in fcc Magnetic Metals on (001) Diamond

    NASA Astrophysics Data System (ADS)

    Wolf, J. A.; Krebs, J. J.; Idzerda, Y. U.; Prinz, G. A.; Kemner, K. M.

    1996-03-01

    We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co, Ni, Fe) on (001) diamonds, the thickness of the films varying from ~1nm to over 100nm. The crystalline quality and fourfold symmetry of these layers was monitored in-situ during film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex-situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout the entire film. The magnetic characterization of the Co-, Ni- and Fe-films was carried out with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops, yielding information on the cubic anisotropy constant K_1, the magnetic moment M and the magnetization reversal. The Co displays extremely high quality growth and magnetic characteristics up to thicknesses well in excess of 100nm, while the Ni is tetragonally distorted resulting in an out-of-plane anisotropy component. The fcc Fe is only stable up to ~2nm before the transition to the bcc crystal structure starts.

  7. Software for Mathematical Modeling of Plastic Deformation in FCC Metals

    NASA Astrophysics Data System (ADS)

    Petelin, A. E.; Eliseev, A. S.

    2017-08-01

    The question on the necessity of software implementation in the study of plastic deformation in FCC metals with the use of mathematical modeling methods is investigated. This article describes the implementation features and the possibility of using the software Dislocation Dynamics of Crystallographic Slip (DDCS). The software has an advanced user interface and is designed for users without an extensive experience in IT-technologies. Parameter values of the mathematical model, obtained from field experiments and accumulated in a special database, are used in DDCS to carry out computational experiments. Moreover, the software is capable of accumulating bibliographic information used in research.

  8. Alkali cation specific adsorption onto fcc(111) transition metal electrodes.

    PubMed

    Mills, J N; McCrum, I T; Janik, M J

    2014-07-21

    The presence of alkali cations in electrolyte solutions is known to impact the rate of electrocatalytic reactions, though the mechanism of such impact is not conclusively determined. We use density functional theory (DFT) to examine the specific adsorption of alkali cations to fcc(111) electrode surfaces, as specific adsorption may block catalyst sites or otherwise impact surface catalytic chemistry. Solvation of the cation-metal surface structure was investigated using explicit water models. Computed equilibrium potentials for alkali cation adsorption suggest that alkali and alkaline earth cations will specifically adsorb onto Pt(111) and Pd(111) surfaces in the potential range of hydrogen oxidation and hydrogen evolution catalysis in alkaline solutions.

  9. Synthesis of 4H/fcc-Au@Metal Sulfide Core-Shell Nanoribbons.

    PubMed

    Fan, Zhanxi; Zhang, Xiao; Yang, Jian; Wu, Xue-Jun; Liu, Zhengdong; Huang, Wei; Zhang, Hua

    2015-09-02

    Although great advances on the synthesis of Au-semiconductor heteronanostructures have been achieved, the crystal structure of Au components is limited to the common face-centered cubic (fcc) phase. Herein, we report the synthesis of 4H/fcc-Au@Ag2S core-shell nanoribbon (NRB) heterostructures from the 4H/fcc Au@Ag NRBs via the sulfurization of Ag. Remarkably, the obtained 4H/fcc-Au@Ag2S NRBs can be further converted to a novel class of 4H/fcc-Au@metal sulfide core-shell NRB heterostructures, referred to as 4H/fcc-Au@MS (M = Cd, Pb or Zn), through the cation exchange. We believe that these novel 4H/fcc-Au@metal sulfide NRB heteronanostructures may show some promising applications in catalysis, surface enhanced Raman scattering, solar cells, photothermal therapy, etc.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Multiscale modeling of radiation effects in fcc and bcc metals

    SciTech Connect

    Alonso, E; Caturla, M; Diaz de la Rubia, T; Felter, T; Fluss, M; Perlado, J; Wall, M; Wirth, B

    1999-07-15

    The prospect of using computer simulations to calculate radiation-induced defect production and its influence on microstructure evolution and mechanical property changes during prolonged irradiation of nuclear materials has been a beckoning, yet elusive goal for many years. However, the enormous progress achieved in computational physics for calculating reliable, yet tractable interatomic potentials, coupled with vast improvements in computational power have brought this hope to near reality. In order to develop modeling and simulation tools for predicting the irradiation response of nuclear structural materials, models must be implemented and tested across all relevant length and time scales. We discuss the development and implementation of a modeling methodology that consists of the linkage and hierarchical use of ab initio electronic structure calculations, molecular dynamics (MD) simulations, and kinetic Monte Carlo (KMC) simulations. This methodology can describe length and time scales from nanometers to hundreds of microns and from picoseconds to years, respectively. The ideas are demonstrated in two applications. First, we describe simulations that describe the irradiation and subsequent isochronal annealing of Pb, a low melting point fcc metal, and compare the results to experiments. Second, we show how these methods can be used to investigate damage production and freely migrating defect formation in irradiated V, the key component of candidate low activation alloys for fusion energy applications.

  15. Wulff polyhedra derived from morse potentials and crystal habits of bcc and fcc metal particles

    NASA Astrophysics Data System (ADS)

    Saito, Yahachi

    1981-05-01

    Using the broken-bond method and the pairwise potentials of Morse type, relative surface energies were calculated to derive the Wulff polyhedra for bcc and fcc metals. When only the first and the second nearest neighbour interactions are taken into account, the resulting Wulff polyhedron is a rhombic dodecahedron truncated by {100} faces and an octahedron truncated by {100} and {100} faces for bcc and fcc metals, respectively. The truncation degrees calculated are in good agreement with those measured from smoke particles grown in an atmosphere of rarefied inactive gas. The effect of the higher order terms of interactions is simply to make the edges and corners round.

  16. Response of FCC and BCC Metals to High-Amplitude Dynamic Compression

    NASA Astrophysics Data System (ADS)

    Meyers, Marc; Remington, Bruce; Maddox, Brian; Bringa, Eduardo; Park, Hye-Sook; Lu, Chia-Hui

    2013-06-01

    The experimentally observed response of FCC and BCC metals to high-amplitude compressive waves is compared with analytical predictions using constitutive models based on dislocations and twinning and with molecular dynamics simulations. In FCC metals (Cu and Ni), the predictions of dislocation densities from a homogeneous nucleation model are close to those of molecular dynamics simulations. Both are orders of magnitude higher than experimentally observed residual dislocation densities. MD calculations predict a drastic decrease in dislocation densities upon unloading, bringing the values in agreement with measurements. For BCC metals (Ta), on the residual densities are close to predictions of Orowan dislocation multiplication. Due to the much higher Peierls-Nabarro stress, the MD simulations predict much lower dislocation densities than in FCC metals subjected to similar pressures. At higher amplitudes, both FCC and BCC metals experience extensive twinning. The threshold pressure for twinning is successfully modeled by constitutive model based on a critical shear stress for twinning, at the imposed strain rate and temperature. Research funded by UCOP/UC Labs Program.

  17. 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.

  18. Adatom Ascending at Step Edges and Faceting on fcc Metal (110) Surfaces

    SciTech Connect

    Zhu, W.; de Mongeot, F. B.; Valbusa, U.; Wang, E. G.; Zhang, Zhenyu

    2004-01-01

    Using first-principles total-energy calculations, we show that an adatom can easily climb up at monatomic-layer-high steps on several representative fcc metal (110) surfaces via a place exchange mechanism. Inclusion of such novel adatom ascending processes in kinetic Monte Carlo simulations of Al(110) homoepitaxy as a prototypical model system can lead to the existence of an intriguing faceting instability, whose dynamical evolution and kinetic nature are explored in comparison with experimental observations.

  19. Comparison of void strengthening in fcc and bcc metals : large-scale atomic-level modelling.

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2005-01-01

    Strengthening due to voids can be a significant radiation effect in metals. Treatment of this by elasticity theory of dislocations is difficult when atomic structure of the obstacle and dislocation is influential. In this paper, we report results of large-scale atomic-level modelling of edge dislocation-void interaction in fcc (copper) and bcc (iron) metals. Voids of up to 5 nm diameter were studied over the temperature range from 0 to 600 K. We demonstrate that atomistic modelling is able to reveal important effects, which are beyond the continuum approach. Some arise from features of the dislocation core and crystal structure, others involve dislocation climb and temperature effects.

  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. Coupled Simulations of Texture Evolution during Deformation and Recrystallization of FCC and BCC Metals

    SciTech Connect

    Radhakrishnan, Balasubramaniam; Gorti, Sarma B

    2008-01-01

    Thermo-mechanical processing to produce optimum grain structure and texture is key to the successful utilization of commercial aluminum alloys and steels as sheet products. Several modeling techniques have been developed in the past with a reasonably good predictive capability for bulk deformation textures. However, prediction of texture evolution during recrystallization remains very challenging because of uncertainties involved in predicting the mechanisms that lead to nuclei formation and crystallographic orientations of the nuclei, and the uncertainties involved in predicting the grain boundary properties that determine the growth kinetics of the nuclei. We present some of our recent work in modeling the recrystallization textures following hot deformation in polycrystalline BCC and FCC metals.

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

    PubMed

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

    2014-11-10

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

  4. Strong screening by lattice confinement and resultant fusion reaction rates in fcc metals

    NASA Astrophysics Data System (ADS)

    Prados-Estévez, F. M.; Subashiev, A. V.; Nee, H. H.

    2017-09-01

    The effects of electronic screening on the cross sections and reactivities for the nuclear reactions between light nuclei in Pd and Ni is studied. We consider the applicability of the theory of thermonuclear burning in stars to the D-D nuclear reaction in metals. The screening model based on the mean field potential of the electron cloud in the metal plasma is used. We discuss the specifics of the screening for the H (D) atoms embedded in vacancies and divacancies. High concentration of hydrogen isotopes segregated to monovacancies and divacancies in face-centered cubic (fcc) metals such as Ni and Pd with densities of ∼ 6 ×1023atom /cm3 , makes the hydrogen cluster a favorable active site for the fusion reaction. Still the observation of a nuclear reaction requires an accumulation of energy in D nuclei of at least several eV, which is far above what can be achieved in the thermal heating experiments.

  5. 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.

  6. <110> symmetric tilt grain-boundary structures in fcc metals with low stacking-fault energies

    NASA Astrophysics Data System (ADS)

    Rittner, J. D.; Seidman, D. N.

    1996-09-01

    Twenty-one <110> symmetric tilt grain boundaries (GB's) are investigated with atomistic simulations, using an embedded-atom method (EAM) potential for a low stacking-fault energy fcc metal. Lattice statics simulations with a large number of initial configurations are used to identify both the equilibrium and metastable structures at 0 K. The level of difficulty in finding the equilibrium structures is quantitatively assessed. The stability of the structures at an elevated temperature is investigated by Monte Carlo annealing. A form of GB dissociation is identified in a number of the boundaries. These structures are used to develop a dislocation model of GB dissociation by stacking-fault emission. Also, an attempt is made to apply the structural unit model (SUM) to the simulated boundaries and problems that are encountered for GB structures in low stacking-fault energy metals are enumerated and discussed.

  7. Indium-defect interactions in FCC and BCC metals studied using the modified embedded atom method

    NASA Astrophysics Data System (ADS)

    Zacate, M. O.

    2016-12-01

    With the aim of developing a transferable potential set capable of predicting defect formation, defect association, and diffusion properties in a wide range of intermetallic compounds, the present study was undertaken to test parameterization strategies for determining empirical pair-wise interaction parameters in the modified embedded atom method (MEAM) developed by Baskes and coworkers. This report focuses on indium-solute and indium-vacancy interactions in FCC and BCC metals, for which a large set of experimental data obtained from perturbed angular correlation measurements is available for comparison. Simulation results were found to be in good agreement with experimental values after model parameters had been adjusted to reproduce as best as possible the following two sets of quantities: (1) lattice parameters, formation enthalpies, and bulk moduli of hypothetical equiatomic compounds with the NaCl crystal structure determined using density functional theory and (2) dilute solution enthalpies in metals as predicted by Miedema's semi-empirical model.

  8. Structure and magnetism in fcc magnetic transition metals on (001) diamond (abstract)

    NASA Astrophysics Data System (ADS)

    Wolf, J. A.; Krebs, J. J.; Idzerda, Y. U.; Prinz, G. A.; Kemner, K. M.

    1996-04-01

    We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co,Ni,Fe) on (001) diamonds, the thickness of the films varying between a few tenths of a nanometer to over 100 nm. The crystalline quality and fourfold symmetry of these layers was monitored in situ during the film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout each entire film. The magnetic characterization was performed with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops. The saturation magnetization of the Co films is only slightly lower than the literature values. The coercive fields are very small (˜25 Oe) and the magnetization reversal very sharp. The FMR yielded a fourfold anisotropy comparable to literature values. The observation of the first standing spinwaves underlines the good quality. The Ni films are tetragonally distorted due to the 1.2% mismatch. The FMR data indicate a significant perpendicular anisotropy slightly smaller than 4πM, the fourfold in-plane anisotropy being comparable to the bulk value. The saturation magnetization is reduced by 30% compared to bulk values, probably due to nickel-carbide which was observed in the XRD data from some samples. Neither the in-plane <110> nor the in-plane <100> axis show an easy axis behavior and both require fields in excess of 6000 Oe to saturate, the coercive fields being about 200 Oe. The RHEED patterns of the Fe films show single crystal growth with a lattice constant comparable to diamond, indicating an fcc structure. A similar structural and magnetic characterization of these films will also be presented.

  9. Assessment of the dislocation bias in fcc metals and extrapolation to austenitic steels

    NASA Astrophysics Data System (ADS)

    Chang, Zhongwen; Sandberg, Nils; Terentyev, Dmitry; Samuelsson, Karl; Bonny, Giovanni; Olsson, Pär

    2015-10-01

    A systematic study of dislocation bias has been performed using a method that combines atomistic and elastic dislocation-point defect interaction models with a numerical solution of the diffusion equation with a drift term. Copper, nickel and aluminium model lattices are used in this study, covering a wide range of shear moduli and stacking fault energies. It is found that the dominant parameter for the dislocation bias in fcc metals is the width of the stacking fault ribbon. The variation in elastic constants does not strongly impact the dislocation bias value. As a result of this analysis and its extrapolation, the dislocation bias of the widely applied austenitic stainless steels of 316 type is predicted to be about 0.1 at temperature close to the swelling peak (815 K) and typical dislocation density of 1014 m-2. This is in line with the bias calculated using the elastic interaction model, which implies that the prediction method can be used readily in other fcc systems even without EAM potentials. By comparing the bias values obtained using atomistic- and elastic interaction energies, about 20% discrepancy is found, therefore a more realistic bias value for the 316 type alloy is 0.08 in these conditions.

  10. The microstructure and associated tensile properties of irradiated fcc and bcc metals

    NASA Astrophysics Data System (ADS)

    Victoria, M.; Baluc, N.; Bailat, C.; Dai, Y.; Luppo, M. I.; Scha̋ublin, R.; Singh, B. N.

    2000-01-01

    The differences and similarities of behaviour between fcc and bcc metals after irradiation have been investigated. For this purpose, fcc Cu, Pd and 304 stainless steel and bcc Fe, Mo and Mo-5% Re were irradiated with either neutrons or 590 MeV protons at temperatures below recovery stage V. It is shown that a dense population of defect clusters (up to 10 22-10 24 m -3) develops, the type of cluster formed depending apparently on the stacking fault energy. In the case of stacking fault tetrahedra formed in Cu, their size is independent of dose, while interstitial loops in stainless steel grow at neutron doses higher than 1 dpa. The defect microstructure is found to be independent of the recoil energy spectra in this temperature region, but shows a very strong dependence on the type of crystalline structure. The results of tensile testing indicate the presence of radiation hardening, starting at very low doses as an upper yield point develops followed by a (serrated) yield region. The main deformation mode observed is dislocation channeling. The hardening is modelled in terms of the initial dislocation locking by the irradiation-induced defects followed by the dispersed hardening induced by the global distribution of clusters in the matrix.

  11. Temperature dependence of dynamic deformation in FCC metals, aluminum and invar

    NASA Astrophysics Data System (ADS)

    Chen, Laura; Swift, D. C.; Austin, R. A.; Florando, J. N.; Hawreliak, J.; Lazicki, A.; Saculla, M. D.; Eakins, D.; Bernier, J. V.; Kumar, M.

    2017-01-01

    Laser-driven shock experiments were performed on fcc metals, aluminum and invar, at a range of initial temperatures from approximately 120-800 K to explore the effect of initial temperature on dynamic strength properties at strain rates reaching up to 107 s-1. In aluminum, velocimetry data demonstrated an increase of peak stress of the elastic wave, σE, with initial temperature. Alternatively, for invar, σE exhibits little-to-no decrease over the same initial temperature range. Aluminum's unusual deformation behavior is found to primarily be due to anharmonic vibrational effects. Differences in the magnetic structure of aluminum and invar can account for discrepancies in high rate deformation behavior.

  12. Crystal plasticity finite element modelling of low cycle fatigue in fcc metals

    NASA Astrophysics Data System (ADS)

    Grilli, Nicolò; Janssens, Koenraad G. F.; Van Swygenhoven, Helena

    2015-11-01

    A new dislocation-based model for low cycle fatigue in fcc metals at a length scale smaller than the feature size of the dislocation structures is presented. It uses the crystal plasticity finite element method and dislocation densities as internal variables. Equations for the dipole distance distribution, for the double cross slip mechanism and a new dislocation multiplication law are introduced, which can predict the emergence of vein and channel structures starting from a randomly perturbed dislocation distribution. The characteristics of these structures in copper and aluminium, as well as the mechanical properties, are compared with experiments. Compared with existing density-based theories, the capability to reproduce dislocation patterning is a significant step forward.

  13. 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.

  14. Ab initio calculations of generalized-stacking-fault energy surfaces and surface energies for FCC metals

    NASA Astrophysics Data System (ADS)

    Wu, Xiao-Zhi; Wang, Rui; Wang, Shao-Feng; Wei, Qun-Yi

    2010-08-01

    The ab initio calculations have been used to study the generalized-stacking-fault energy (GSFE) surfaces and surface energies for the closed-packed (1 1 1) plane in FCC metals Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt, and Pb. The GSFE curves along <112> (1 1 1) direction and <110> (1 1 1) direction, and surface energies have been calculated from first principles. Based on the translational symmetry of the GSFE surfaces, the fitted expressions have been obtained from the Fourier series. Our results of the GSFEs and surface energies agree better with experimental results. The metals Al, Pd, and Pt have low γ/γI value, so full dislocation will be observed easily; while Cu, Ag, Au, and Ni have large γ/γI value, so it is preferred to create partial dislocation. From the calculations of surface energies, it is confirmed that the VIII column elements Ni, Rh, Ir, Pd, and Pt have higher surface energies than other metals.

  15. Dissolving, trapping and detrapping mechanisms of hydrogen in bcc and fcc transition metals

    NASA Astrophysics Data System (ADS)

    You, Yu-Wei; Kong, Xiang-Shan; Wu, Xue-Bang; Xu, Yi-Chun; Fang, Q. F.; Chen, J. L.; Luo, G.-N.; Liu, C. S.; Pan, B. C.; Wang, Zhiguang

    2013-01-01

    First-principles calculations are performed to investigate the dissolving, trapping and detrapping of H in six bcc (V, Nb, Ta, Cr, Mo, W) and six fcc (Ni, Pd, Pt, Cu, Ag, Au) metals. We find that the zero-point vibrations do not change the site-preference order of H at interstitial sites in these metals except Pt. One vacancy could trap a maximum of 4 H atoms in Au and Pt, 6 H atoms in V, Nb, Ta, Cr, Ni, Pd, Cu and Ag, and 12 H atoms in Mo and W. The zero-point vibrations never change the maximum number of H atoms trapped in a single vacancy in these metals. By calculating the formation energy of vacancy-H (Vac-Hn) complex, the superabundant vacancy in V, Nb, Ta, Pd and Ni is demonstrated to be much more easily formed than in the other metals, which has been found in many metals including Pd, Ni and Nb experimentally. Besides, we find that it is most energetically favorable to form Vac-H1 complex in Pt, Cu, Ag and Au, Vac-H4 in Cr, Mo and W, and Vac-H6 in V, Nb, Ta, Pd and Ni. At last, we examine the detrapping behaviors of H atoms in a single vacancy and find that with the heating rate of 10 K/min a vacancy could accommodate 4, 5 and 6 H atoms in Cr, Mo and W at room temperature, respectively. The detrapping temperatures of all H atoms in a single vacancy in V, Nb, Ta, Ni, Pd, Cu and Ag are below room temperature.

  16. Reduce FCC corrosion

    SciTech Connect

    Walker, H.B.

    1984-01-01

    Efficiency of fluid catalytic cracking (FCC) vapor recovery units can be significantly reduced by corrosion and fouling. The fundamentals of FCC light ends corrosion, including diagnoses, control and monitoring of hydrogen blistering, general metal loss, pitting, erosion and under-deposit attack are discussed, relating actual unit problems to effective treatment program solutions.

  17. 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.

  18. Molecular dynamics simulation on generalized stacking fault energies of FCC metals under preloading stress

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Cheng, Lü; Kiet, Tieu; Zhao, Xing; Pei, Lin-Qing; Guillaume, Michal

    2015-08-01

    Molecular dynamics (MD) simulations are performed to investigate the effects of stress on generalized stacking fault (GSF) energy of three fcc metals (Cu, Al, and Ni). The simulation model is deformed by uniaxial tension or compression in each of [111], [11-2], and [1-10] directions, respectively, before shifting the lattice to calculate the GSF curve. Simulation results show that the values of unstable stacking fault energy (γusf), stable stacking fault energy (γsf), and unstable twin fault energy (γutf) of the three elements can change with the preloaded tensile or compressive stress in different directions. The ratio of γsf/γusf, which is related to the energy barrier for full dislocation nucleation, and the ratio of γutf/γusf, which is related to the energy barrier for twinning formation are plotted each as a function of the preloading stress. The results of this study reveal that the stress state can change the energy barrier of defect nucleation in the crystal lattice, and thereby can play an important role in the deformation mechanism of nanocrystalline material. Project supported by Australia Research Council Discovery Projects (Grant No. DP130103973). L. Zhang, X. Zhao and L. Q. Pei were financially supported by the China Scholarship Council (CSC).

  19. 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

    2016-09-01

    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.

  20. Atomic-Scale Mechanisms of Void Hardening in BCC and FCC Metals

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2010-01-01

    Strengthening due to voids can be a significant effect of radiation damage in metals, but treatment of this by elasticity theory of dislocations is difficult when the mechanisms controlling the obstacle strength are atomic in nature. Results are reported of atomic-scale modelling to compare edge dislocation-void interaction in fcc copper and bcc iron. Voids of up to 6 nm diameter in iron and 8 nm diameter in copper were studied over the temperature range 0 to 600 K at different applied strain rates. Voids in iron are strong obstacles, for the dislocation has to adopt a dipole-like configuration at the void before breaking away. The dipole unzips at the critical stress when the dislocation is able to climb by absorbing vacancies and leave the void surface. Dislocation dissociation into Shockley partials in copper prevents dislocation climb and affects the strength of small and large voids differently. Small voids are much weaker obstacles than those in iron because the partials break from a void individually. Large voids are at least as strong as those in iron, but the controlling mechanism depends on temperature.

  1. A self-consistent plasticity theory for modeling the thermo-mechanical properties of irradiated FCC metallic polycrystals

    NASA Astrophysics Data System (ADS)

    Xiao, Xiazi; Song, Dingkun; Xue, Jianming; Chu, Haijian; Duan, Huiling

    2015-05-01

    A self-consistent theoretical framework is developed to model the thermo-mechanical behaviors of irradiated face-centered cubic (FCC) polycrystalline metals at low to intermediate homologous temperatures. In this model, both irradiation and temperature effects are considered at the grain level with the assist of a tensorial plasticity crystal model, and the elastic-visocoplastic self-consistent method is applied for the scale transition from individual grains to macroscopic polycrystals. The proposed theory is applied to analyze the mechanical behaviors of irradiated FCC copper. It is found that: (1) the numerical results match well with experimental data, which includes the comparison of results for single crystals under the load in different directions, and for polycrystals with the influences of irradiation and temperature. Therefore, the feasibility and accuracy of the present model are well demonstrated. (2) The main irradiation effects including irradiation hardening, post-yield softening, strain-hardening coefficient (SHC) dropping and the non-zero stress offset are all captured by the proposed model. (3) The increase of temperature results in the decrease of yield strength and SHC. The former is attributed to the weakened dislocation-defect interaction, while the latter is due to the temperature-strengthened dynamic recovery of dislocations through the thermally activated mechanism. The present model may provide a theoretical guide to predict the thermo-mechanical behaviors of irradiated FCC metals for the selection of structural materials in nuclear equipment.

  2. Structural Studies of Clean and Adsorbate-Covered Fcc Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Statiris, Panayiotis Athanasiou

    We have used medium energy ion scattering (MEIS) to study the structural and vibrational properties of the clean metal surfaces of Ni(110) and Ag(111), the structural changes induced by the presence of small amounts ( {~}1 atomic layer) of heteroatoms on the Ni(001) and Ni(110) surfaces (Cs, K, K and CO on Ni(110) and Au on Ni(001)) as well as the arrangement of the heteroatoms on the surface. The thesis consists of five chapters two of which serve as an introduction and provide general information about metal surfaces and medium energy ion scattering (chapters 1 and 2) and three chapters (3, 4, 5) in which the experimental results are being presented, and structural models are proposed for the surfaces studied. The purpose of the material contained in chapter one is to familiarize the reader with the general concepts, and provide an overview of the progress (experimental and theoretical) in the field of clean and adsorbate covered metal surfaces. The second chapter contains an extensive discussion about the principles and applications of medium energy ion scattering. A study of the structure of the clean Ni(001) surface and the K/Ni(110) and K/CO/Ni(110) surfaces is presented in chapter 3. Both the K/Ni(110) and K/CO/Ni(110) exhibit the missing row reconstruction. The change in the surface unit cell observed upon adsorption of CO atoms on the K/Ni(110) surface observed with low energy electron diffraction is due to the ordering of the CO molecules. The growth and structure of thin Au films (0.35 -3 layers) deposited on the Ni(001) surface is the subject of chapter 4. Au forms an almost incommensurate overlayer with a c(2 times 8) unit cell whose structure resembles that of fcc Au(111). The Au atoms exhibit unusually high vibrational amplitudes, indicating the presence of a soft phonon mode as predicted by theoretical work. The growth mode resembles the Stranski-Krastanov mode without exactly following it. The temperature dependence of the vibrational amplitudes

  3. 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.

  4. 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.

  5. 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.

  6. On the limitation of density functional theory (DFT) for the treatment of the anharmonicity in FCC metals

    NASA Astrophysics Data System (ADS)

    Seifitokaldani, Ali; Gheribi, Aïmen E.; Dollé, Mickael

    2016-12-01

    It has been already shown that the density functional theory (DFT) combined with the quasi-harmonic approximation (QHA) overestimates the specific heat capacity (and in general the thermal properties) of fcc metals. DFT + QHA seemingly shows a large anharmonic contribution to the heat capacity. However, in this article we show that this anharmonicity has no physical origin and it is a consequence of the deviation of the QHA from the Maxwell relations. We show that one can simply avoid this overestimation by enforcing the QHA method to obey the Maxwell relations throughout the thermodynamically self-consistent (TSC) method, instead of considering non-real local anharmonic effects.

  7. Configurational correlations in the coverage dependent adsorption energies of oxygen atoms on late transition metal fcc(111) surfaces

    NASA Astrophysics Data System (ADS)

    Miller, Spencer D.; İnoğlu, Nilay; Kitchin, John R.

    2011-03-01

    The coverage dependence of oxygen adsorption energies on the fcc(111) surfaces of seven different transition metals (Rh, Ir, Pd, Pt, Cu, Au, and Ag) is demonstrated through density functional theory calculations on 20 configurations ranging from one to five adsorption sites and coverages up to 1 ML. Atom projected densities of states are used to demonstrate that the d-band mediated adsorption mechanism is responsible for the coverage dependence of the adsorption energies. This common bonding mechanism results in a linear correlation that relates the adsorption energies of each adsorbate configuration across different metal surfaces to each other. The slope of this correlation is shown to be related to the characteristics of the valence d-orbitals and band structure of the surface metal atoms. Additionally, it is shown that geometric similarity of the configurations is essential to observe the configurational correlations.

  8. Why FCC

    NASA Technical Reports Server (NTRS)

    Angele, W.

    1972-01-01

    Summaries are given of design characteristics and various advantages of FCC use. The information is presented in tables that include the following headings: (1) mechanical design, (2) electrical design, (3) manufacturing advantages, (4) inspection and reliability, and (5) cost savings. In addition, the results are summarized of a Saturn 4B FCC-RWC comparison study.

  9. Bcc and Fcc transition metals and alloys: a central role for the Jahn-Teller effect in explaining their ideal and distorted structures.

    PubMed

    Lee, Stephen; Hoffmann, Roald

    2002-05-01

    Transition metal elements, alloys, and intermetallic compounds often adopt the body centered cubic (bcc) and face centered cubic (fcc) structures. By comparing quantitative density functional with qualitative tight-binding calculations, we analyze the electronic factors which make the bcc and fcc structures energetically favorable. To do so, we develop a tight-binding function, DeltaE(star), a function that measures the energetic effects of transferring electrons within wave vector stars. This function allows one to connect distortions in solids to the Jahn-Teller effect in molecules and to provide an orbital perspective on structure determining deformations in alloys. We illustrate its use by considering first a two-dimensional square net. We then turn to three-dimensional fcc and bcc structures, and distortions of these. Using DeltaE(star), we rationalize the differences in energy of these structures. We are able to deduce which orbitals are responsible for instabilities in seven to nine valence electron per atom (e(-)/a) bcc systems and five and six e(-)/a fcc structures. Finally we demonstrate that these results account for the bcc and fcc type structures found in both the elements and binary intermetallic compounds of group 4 through 9 transition metal atoms. The outline of a theory of metal structure deformations based on loss of point group operation rather than translational symmetry is presented.

  10. Temperature-pressure-induced solid-solid <100> to <110> reorientation in FCC metallic nanowire: a molecular dynamic study.

    PubMed

    Sutrakar, Vijay Kumar; Roy Mahapatra, D; Pillai, A C R

    2012-01-11

    Atomistic simulation of initial <100> oriented FCC Cu nanowires shows a novel coupled temperature-pressure dependent reorientation from <100> to <110> phase. A temperature-pressure-induced solid-solid <100> to <110> reorientation diagram is generated for Cu nanowire with varying cross-sectional sizes. A critical pressure is reported for Cu nanowires with varying cross-sectional sizes, above which an initial <100> oriented nanowire shows temperature independent reorientation into the <110> phase. The effect of surface stresses on the <100> to <110> reorientation is also studied. The results indicate that above a critical cross-sectional size for a given temperature-pressure, <100> to <110> reorientation is not possible. It is also reported here that for a given applied pressure, an increase in temperature is required for the <100> to <110> reorientation with increasing cross-sectional size of the nanowire. The temperature-pressure-induced solid-solid <100> to <110> reorientation diagram reported in the present paper could further be used as guidelines for controlling the reorientations/shape memory in nano-scale applications of FCC metallic nanowires.

  11. 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.

  12. Mechanism of decrease in the strength of submicron-sized specimens of FCC metals with a nanocrystalline structure

    NASA Astrophysics Data System (ADS)

    Malygin, G. A.

    2017-02-01

    The effect of decrease in the strength of submicron-sized specimens of face-centered cubic (fcc) metals with a nanocrystalline structure and a cross-sectional size D < 5 d, as compared to the strength of the specimens with D ≫ 5 d (where d is the grain size), has been considered theoretically on the basis of the dislocation-kinetic equations and relationships. Previously, it has been found that this decrease is caused by the escape of a part of the dislocations through the surface of the specimen under the action of single-pole dislocation sources in grains adjacent to the surface. In this study, it has been shown that the absorption of lattice dislocations by grain boundaries and its accompanying grain boundary sliding lead to a further decrease in the flow stress of specimens, which is equally related to both thin ( D < 5 d) and thick ( D ≫ 5 d) specimens.

  13. 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.

  14. 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.

  15. Topological Dirac nodal lines and surface charges in fcc alkaline earth metals

    NASA Astrophysics Data System (ADS)

    Hirayama, Motoaki; Okugawa, Ryo; Miyake, Takashi; Murakami, Shuichi

    2017-01-01

    In nodal-line semimetals, the gaps close along loops in k space, which are not at high-symmetry points. Typical mechanisms for the emergence of nodal lines involve mirror symmetry and the π Berry phase. Here we show via ab initio calculations that fcc calcium (Ca), strontium (Sr) and ytterbium (Yb) have topological nodal lines with the π Berry phase near the Fermi level, when spin-orbit interaction is neglected. In particular, Ca becomes a nodal-line semimetal at high pressure. Owing to nodal lines, the Zak phase becomes either π or 0, depending on the wavevector k, and the π Zak phase leads to surface polarization charge. Carriers eventually screen it, leaving behind large surface dipoles. In materials with nodal lines, both the large surface polarization charge and the emergent drumhead surface states enhance Rashba splitting when heavy adatoms are present, as we have shown to occur in Bi/Sr(111) and in Bi/Ag(111).

  16. Analysis of reversed torsion of FCC metals using polycrystal plasticity models

    SciTech Connect

    Guo, Xiao Qian; Wang, Huamiao; Wu, Pei Dong; Mao, Xian Biao

    2015-06-19

    Large strain behavior of FCC polycrystals during reversed torsion are investigated through the special purpose finite element based on the classical Taylor model and the elastic-viscoplastic self-consistent (EVPSC) model with various Self-Consistent Schemes (SCSs). It is found that the response of both the fixed-end and free-end torsion is very sensitive to the constitutive models. The models are assessed through comparing their predictions to the corresponding experiments in terms of the stress and strain curves, the Swift effect and texture evolution. It is demonstrated that none of the models examined can precisely predict all the experimental results. However, more careful observation reveals that, among the models considered, the tangent model gives the worst overall performance. As a result, it is also demonstrated that the intensity of residual texture during reverse twisting is dependent on the amounts of pre-shear strain during forward twisting and the model used.

  17. 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.

  18. 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.

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

    DOE PAGES

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

    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

  20. Topological Dirac nodal lines and surface charges in fcc alkaline earth metals.

    PubMed

    Hirayama, Motoaki; Okugawa, Ryo; Miyake, Takashi; Murakami, Shuichi

    2017-01-11

    In nodal-line semimetals, the gaps close along loops in k space, which are not at high-symmetry points. Typical mechanisms for the emergence of nodal lines involve mirror symmetry and the π Berry phase. Here we show via ab initio calculations that fcc calcium (Ca), strontium (Sr) and ytterbium (Yb) have topological nodal lines with the π Berry phase near the Fermi level, when spin-orbit interaction is neglected. In particular, Ca becomes a nodal-line semimetal at high pressure. Owing to nodal lines, the Zak phase becomes either π or 0, depending on the wavevector k, and the π Zak phase leads to surface polarization charge. Carriers eventually screen it, leaving behind large surface dipoles. In materials with nodal lines, both the large surface polarization charge and the emergent drumhead surface states enhance Rashba splitting when heavy adatoms are present, as we have shown to occur in Bi/Sr(111) and in Bi/Ag(111).

  1. Atomic-level interaction of an edge dislocation and localized obstacles in fcc and bcc metals.

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2004-01-01

    Interaction between a moving dislocation and localized obstacles determines microstructure-induced hardening. The mechanisms and parameters of such interactions are necessary inputs to large scale dislocation dynamics modelling. We have developed a model to investigate these characteristics at the atomic level for dislocation-obstacle interactions under both static (T=0K) and dynamic (T>0K) conditions. We present results on hardening due to pinning of edge dislocations at obstacles such as voids, coherent precipitates and stacking fault tetrahedra in bcc-iron and fcc-copper at temperatures from 0 to 600K. It is demonstrated that atomic-scale simulation is required to determine the effects of stress, strain rate and temperature and that such effects cannot always be rationalized within continuum theory.

  2. Metal-organic pathways for anisotropic growth of a highly symmetrical crystal structure: example of the fcc Ni.

    PubMed

    Mourdikoudis, Stefanos; Collière, Vincent; Amiens, Catherine; Fau, Pierre; Kahn, Myrtil L

    2013-11-05

    The control of the metallic nanocrystal shape is of prime importance for a wide variety of applications. We report a detailed research work on metal-organic chemical routes for the synthesis of a highly symmetrical crystal structure. In particular, this study shows the key parameters ensuring the anisotropic growth of nickel nanostructures (fcc crystal). Numerous reaction conditions are investigated (precursors, solvents, temperature, reducing agents, reaction time, and types and ratios of surfactants, such as alkyl amines, carboxylic acids, and phosphine oxides), and their effects on the size and shape of the final product are reported. The role of the growth modifiers and the structuring of the reaction media on the anisotropic growth are demonstrated. This metal-organic approach generates several novel anisotropic nanostructures in a wide size range depending on the reaction conditions. In this way, nanomaterials with reproducible size, shape, and composition are obtained with good yield. Transmission electron microscopy techniques (TEM and HRTEM) are the principal methods for monitoring the morphology.

  3. 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)

  4. Analysis of reversed torsion of FCC metals using polycrystal plasticity models

    DOE PAGES

    Guo, Xiao Qian; Wang, Huamiao; Wu, Pei Dong; ...

    2015-06-19

    Large strain behavior of FCC polycrystals during reversed torsion are investigated through the special purpose finite element based on the classical Taylor model and the elastic-viscoplastic self-consistent (EVPSC) model with various Self-Consistent Schemes (SCSs). It is found that the response of both the fixed-end and free-end torsion is very sensitive to the constitutive models. The models are assessed through comparing their predictions to the corresponding experiments in terms of the stress and strain curves, the Swift effect and texture evolution. It is demonstrated that none of the models examined can precisely predict all the experimental results. However, more careful observationmore » reveals that, among the models considered, the tangent model gives the worst overall performance. As a result, it is also demonstrated that the intensity of residual texture during reverse twisting is dependent on the amounts of pre-shear strain during forward twisting and the model used.« less

  5. Topological Dirac nodal lines and surface charges in fcc alkaline earth metals

    PubMed Central

    Hirayama, Motoaki; Okugawa, Ryo; Miyake, Takashi; Murakami, Shuichi

    2017-01-01

    In nodal-line semimetals, the gaps close along loops in k space, which are not at high-symmetry points. Typical mechanisms for the emergence of nodal lines involve mirror symmetry and the π Berry phase. Here we show via ab initio calculations that fcc calcium (Ca), strontium (Sr) and ytterbium (Yb) have topological nodal lines with the π Berry phase near the Fermi level, when spin–orbit interaction is neglected. In particular, Ca becomes a nodal-line semimetal at high pressure. Owing to nodal lines, the Zak phase becomes either π or 0, depending on the wavevector k, and the π Zak phase leads to surface polarization charge. Carriers eventually screen it, leaving behind large surface dipoles. In materials with nodal lines, both the large surface polarization charge and the emergent drumhead surface states enhance Rashba splitting when heavy adatoms are present, as we have shown to occur in Bi/Sr(111) and in Bi/Ag(111). PMID:28074835

  6. Channel formation and multiplication in irradiated FCC metals: a 3D dislocation dynamics investigation

    NASA Astrophysics Data System (ADS)

    Gururaj, K.; Robertson, C.; Fivel, M.

    2015-04-01

    Our goal in this work is to investigate post-irradiation tensile deformation of FCC grains using 3D dislocation dynamics (DD) simulations. We focus on irradiation dose conditions where plastic strain is expected to localize into defect-depleted channels. Two DD simulation types are used for treating distinct space and time scale effects. Type-I simulations describe the formation of single dislocation channels at a high resolution (nm). Here, the irradiation-induced defects are described explicitly, in the form of prismatic dislocation loops. Type-II simulations are used to describe the channel multiplication process itself, i.e. at the grain scale (μm). This time, the irradiation-induced defects are treated in a simplified way, taking advantage of Type-I simulation results. Simulated channel spacing is found to depend on three main input parameters: the dose-dependent stress level, grain size and critical cross-slip stress. The results are rationalized in terms of a micro-model based on simple, finite-sized dislocation arrangements. The model is further validated by comparison with available experimental evidence.

  7. 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.

  8. 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.

  9. Analysis of the heat capacity of nanoclusters of FCC metals on the example of Al, Ni, Cu, Pd, and Au

    NASA Astrophysics Data System (ADS)

    Gafner, Yu. Ya.; Gafner, S. L.; Zamulin, I. S.; Redel, L. V.; Baidyshev, V. S.

    2015-06-01

    The heat capacity of ideal nickel, copper, gold, aluminum, and palladium fcc clusters with diameter of up to 6 nm has been studied in the temperature range of 150-800 K in terms of the molecular-dynamics theory using a tight-binding potential. The heat capacity of individual metallic nanoclusters has been found to exceed that characteristic of the bulk state, but by no more than 16-20%, even in the case of very small clusters. To explain the discrepancy between the simulated data and the experimental results on the compacted metals, aluminum and palladium samples with 80% theoretical density have also been investigated. Based on the simulation results and analysis of the experimental data, it has been established that the increased heat capacity of the compacted nanomaterials does not depend on the enhanced heat capacity of the individual clusters but rather, can be due to either the disordered state of the nanomaterial or a significant content of impurities (mainly, hydrogen).

  10. Origin of tension-compression asymmetry in ultrafine-grained fcc metals

    NASA Astrophysics Data System (ADS)

    Tsuru, T.

    2017-08-01

    A mechanism of anomalous tension-compression (T-C) asymmetry in ultrafine-grained (UFG) metals is proposed using large-scale atomistic simulations and dislocation theory. Unlike coarse-grained metals, UFG Al exhibits remarkable T-C asymmetry of the yield stress. The atomistic simulations reveal that the yield event is not related to intragranular dislocations but caused by dislocation nucleation from the grain boundaries (GBs). The dislocation core structure associated with the stacking fault energy in Al is strongly affected by the external stress compared with Cu; specifically, high tensile stress stabilizes the dissociation into partial dislocations. These dislocations are more likely to be nucleated from GBs and form deformation twins from an energetic viewpoint. The mechanism, which is different from well-known mechanisms for nanocrystalline and amorphous metals, is unique to high-strength UFG metals and can explain the difference in T-C asymmetry between UFG Cu and Al.

  11. 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.

  12. Long-range empirical potential model: Application to fcc transition metals and alloys

    NASA Astrophysics Data System (ADS)

    Dai, X. D.; Kong, Y.; Li, J. H.

    2007-03-01

    Under the framework of the second moment approximation of tight-binding theory, a long-range empirical potential (LREP) is developed for transition metals in the present study and successfully applied to Cu, Ag, Au, Ni, Pd, Pt, and their alloys. It is found that the LREP model has successfully overcome the structural stability problem of traditional short-range potentials and resolved the energy and force jumps taking place in previous long-range potentials at cutoff radius without any truncated function. Importantly, the equations of state derived by the LREP model for the metals and alloys are in excellent agreement with those obtained from the Rose equation and experiments, indicating that the present model can relevantly predict the properties of metals and alloys at nonequilibrium state. Furthermore, the other calculated properties, such as the lattice constant, cohesive energy, elastic constants, and phonon spectra, also match well with those obtained by experiments or ab initio calculations.

  13. Genetic algorithm approach to global optimization of the full-dimensional potential energy surface for hydrogen atom at fcc-metal surfaces

    NASA Astrophysics Data System (ADS)

    Kammler, Marvin; Janke, Svenja M.; Kandratsenka, Alexander; Wodtke, Alec M.

    2017-09-01

    We have developed a genetic algorithm approach for the parametrization of a multi-dimensional potential energy surface based on the analytical expression for energy derived from Effective Medium Theory by fitting it to DFT data. This approach yields consistent results for the H-atom interaction energy with a number of fcc-metal surfaces (Al, Ag, Au, Cu, Ni, Pd, Pt and Rh) and provides reasonable energy values for virtually any system geometry including various facets.

  14. EAM potentials for BCC, FCC and HCP metals with farther neighbor atoms

    NASA Astrophysics Data System (ADS)

    Jin, Hak-Son; An, Jong-Do; Jong, Yon-Song

    2015-07-01

    The modified analytic embedded atom method (EAM) theory considering farther neighbor atoms is improved. We not only adopt an end processing function and an enhanced smooth continuous condition of the pair potential, but also adjust model parameters of multi-body potential by fitting cohesion energies, mono-vacancy formation energies, Rose equation curves, energy differences between several structures, elastic parameters and the equilibrium conditions of crystals. The calculation results of structure energy differences misfit the experiment data for several metallic materials in the unimproved EAM, because its model parameters have not considered these differences. After the modification, the coincidence degree of the structure energy—the reduced distance r/r 1 from the present model with that from the Rose equation is greatly improved for Cr. The calculated results of structure stabilities are in good agreement with experiment data and other calculated results for all considered metals, significantly better than the unimproved model with farther neighbor atoms.

  15. Magnetic states, correlation effects and metal-insulator transition in FCC lattice

    NASA Astrophysics Data System (ADS)

    Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

    2016-12-01

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  16. Magnetic states, correlation effects and metal-insulator transition in FCC lattice.

    PubMed

    Timirgazin, M A; Igoshev, P A; Arzhnikov, A K; Yu Irkhin, V

    2016-12-21

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals [Formula: see text]. In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most [Formula: see text]. The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on [Formula: see text]. The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  17. 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.

  18. 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

  19. 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.

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

    PubMed

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

    2016-03-10

    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.

  1. Three-Dimensional Characterization and Modeling of Microstructural Weak Links for Spall Damage in FCC Metals

    DOE PAGES

    Krishnan, Kapil; Brown, Andrew; Wayne, Leda; ...

    2014-11-25

    Local microstructural weak links for spall damage were investigated using three-dimensional (3-D) characterization in multicrystalline copper samples (grain size ≈ 450 µm) shocked with laser-driven plates at low pressures (2 to 4 GPa). The thickness of samples and flyer plates, approximately 1000 and 500 µm respectively, led to short pressure pulses that allowed isolating microstructure effects on local damage characteristics. Electron Backscattering Diffraction and optical microscopy were used to relate the presence, size, and shape of porosity to local microstructure. The experiments were complemented with 3-D finite element simulations of individual grain boundaries (GBs) that resulted in large damage volumesmore » using crystal plasticity coupled with a void nucleation and growth model. Results from analysis of these damage sites show that the presence of a GB-affected zone, where strain concentration occurs next to a GB, correlates strongly with damage localization at these sites, most likely due to the inability of maintaining strain compatibility across these interfaces, with additional effects due to the inclination of the GB with respect to the shock. Results indicate that strain compatibility plays an important role on intergranular spall damage in metallic materials.« less

  2. Three-Dimensional Characterization and Modeling of Microstructural Weak Links for Spall Damage in FCC Metals

    SciTech Connect

    Krishnan, Kapil; Brown, Andrew; Wayne, Leda; Vo, Johnathan; Opie, Saul; Lim, Harn; Peralta, Pedro; Luo, Sheng-Nian; Byler, Darrin; McClellan, Kenneth J.; Koskelo, Aaron; Dickerson, Robert

    2014-11-25

    Local microstructural weak links for spall damage were investigated using three-dimensional (3-D) characterization in multicrystalline copper samples (grain size ≈ 450 µm) shocked with laser-driven plates at low pressures (2 to 4 GPa). The thickness of samples and flyer plates, approximately 1000 and 500 µm respectively, led to short pressure pulses that allowed isolating microstructure effects on local damage characteristics. Electron Backscattering Diffraction and optical microscopy were used to relate the presence, size, and shape of porosity to local microstructure. The experiments were complemented with 3-D finite element simulations of individual grain boundaries (GBs) that resulted in large damage volumes using crystal plasticity coupled with a void nucleation and growth model. Results from analysis of these damage sites show that the presence of a GB-affected zone, where strain concentration occurs next to a GB, correlates strongly with damage localization at these sites, most likely due to the inability of maintaining strain compatibility across these interfaces, with additional effects due to the inclination of the GB with respect to the shock. Results indicate that strain compatibility plays an important role on intergranular spall damage in metallic materials.

  3. Insulating fcc YH

    SciTech Connect

    Molen, S. J. van der; Nagengast, D. G.; Gogh, A. T. M. van; Kalkman, J.; Kooij, E. S.; Rector, J. H.; Griessen, R.

    2001-06-15

    We study the structural, optical, and electrical properties of Mg{sub z}Y{sub 1{minus}z} switchable mirrors upon hydrogenation. It is found that the alloys disproportionate into essentially pure YH{sub 3{minus}{delta}} and MgH{sub 2} with the crystal structure of YH{sub 3{minus}{delta}} dependent on the Mg concentration z. For 0{lt}z{lt}0.1, both hcp and fcc YH{sub 3{minus}{delta}} are observed, whereas for z{ge}0.1 only cubic YH{sub 3{minus}{delta}} is present. Interestingly, cubic YH{sub 3{minus}{delta}} is expanded compared to YH{sub 2}, in disagreement with theoretical predictions. From optical and electrical measurements we conclude that cubic YH{sub 3{minus}{delta}} is a transparent insulator with properties similar to hexagonal YH{sub 3{minus}{delta}}. Our results are inconsistent with calculations predicting fcc YH{sub 3{minus}{delta}} to be metallic, but they are in good agreement with recent GW calculations on both hcp and fcc YH{sub 3}. Finally, we find an increase in the effective band gap of the hydrided Mg{sub z}Y{sub 1{minus}z} alloys with increasing z. Possibly this is due to quantum confinement effects in the small YH{sub 3} clusters.

  4. 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

  5. An examination of the indentation size effect in FCC metals and alloys from a kinetics based perspective using nanoindentation

    NASA Astrophysics Data System (ADS)

    Stegall, David Earl

    The indentation size effect (ISE) in metals is described as the rise in hardness with decreasing depth of indentation and contradicts conventional plasticity behavior. The goal of this dissertation is to further examine the fundamental dislocation mechanisms that may be contributing to the so-called indentation size effect. In this work, we examined several metals and alloys including 99.999% Aluminum, 99.95% Nickel, 99.95% Silver, and three alloys, alpha brass 70/30, 70/30 nickel copper, and 7075 AlZn to study the effect of stacking fault energy on the ISE. The current work sought to address several objectives including; 1) Verify the existence of an ISE and the bilinear behavior of various FCC metals using single indentation test platform and the same tip for various stress decades: 2) Examine the thermally activated mechanisms that could contribute to the ISE via the kinetics of plastic deformation based on indentation experiments for constant load creep and load relaxation as well as classical uniaxial testing to study the coupled relationship between strain rate, dislocation density, and dislocation velocity: 3) Examine the possible contribution of stacking fault energy (SFE) on the ISE by comparing pure metals over a wide SFE range as well as the effect of alloying. We demonstrate that all the metals tested exhibit a clear ISE using a new approach that included the use of a single machine and using a single tip capable of reaching depths of 30 microm. This eliminated any uncertainty in measurements when comparing data for any metal across the nano to micro-range (from 0.07 mN to 10 N). It was found that the pure metals should be examine separately from the alloys when examining any dependency on SFE. Activation volume analysis, based on indentation creep experiments, was used to examine the stress dependency of the activation volume for each metal. We verified through various experiments across a wide stress range that the ISE has a kinetic signature similar

  6. 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.

  7. 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.

  8. Minor element partitioning between fcc Fe metal and Fe-S liquid at high pressure: The role of crystal lattice strain

    NASA Astrophysics Data System (ADS)

    Stewart, Andrew J.; van Westrenen, Wim; Schmidt, Max W.; Günther, D.

    2009-07-01

    We present a new approach to model element distribution between solid and liquid metal phases, based on experimentally determined data for the partitioning of P, S, selected transition metals, and chalcophile elements between face-centred cubic (fcc) Fe and Fe-S liquid at pressures of 9, 15 and 23 GPa and temperatures between 1523 and 1773 K. Solid/liquid partition coefficients ( D) for the transition metals V, Cr, Mn, Fe, Co, and Ni range from a minimum D of 0.16-0.64 for V to a maximum D of 1.1-1.2 for Co, indicating modest but significant fractionation. D for the chalcophile elements Cu, Zn, Ga, Sn, and Pb varies from 0.029-0.051 for DPb up to 1.6-2.4 for DGa and for non-metals from 0.02-0.04 for S to 0.23-0.66 for P. A modified lattice strain model (as in common use for silicate mineral-melt partitioning) describes the variations in D values for the first row transition metals through the deviance in metal radius from the ideal site radius of Fe in solid metal, indicating that these metals all substitute into the iron site of the solid phase. Variations in D values for the chalcophile elements can also be rationalized using a lattice strain model, but chalcophiles occupy a different site in the solid metal, probably related to the presence of sulphur defects. We show that the lattice strain model can be applied to previously published low pressure experimental data, as well as to third-row transition metals as to first-row transition metals and chalcophiles. The fact that solid-liquid metal D values are amenable to interpretation using lattice strain models paves the way for the development of a new class of element partitioning models applicable to metallic core crystallization processes.

  9. {l_angle}110{r_angle} symmetric tilt grain-boundary structures in fcc metals with low stacking-fault energies

    SciTech Connect

    Rittner, J.D.; Seidman, D.N.

    1996-09-01

    Twenty-one {l_angle}110{r_angle} symmetric tilt grain boundaries (GB{close_quote}s) are investigated with atomistic simulations, using an embedded-atom method (EAM) potential for a low stacking-fault energy fcc metal. Lattice statics simulations with a large number of initial configurations are used to identify both the equilibrium and metastable structures at 0 K. The level of difficulty in finding the equilibrium structures is quantitatively assessed. The stability of the structures at an elevated temperature is investigated by Monte Carlo annealing. A form of GB dissociation is identified in a number of the boundaries. These structures are used to develop a dislocation model of GB dissociation by stacking-fault emission. Also, an attempt is made to apply the structural unit model (SUM) to the simulated boundaries and problems that are encountered for GB structures in low stacking-fault energy metals are enumerated and discussed. {copyright} {ital 1996 The American Physical Society.}

  10. Approximate Dependence of Diffusion Barriers on Nearest-Neighbor Configurations on fcc(100) Metals, and Some Consequences

    NASA Astrophysics Data System (ADS)

    Einstein, T. L.; Jacobsen, J.; Schiff, C.

    1997-03-01

    To simulate epitaxial growth, one needs an a priori understanding of how atomic diffusion barriers depend on the occupation of near-neighbor sites of the initial and final positions. From a histogram of such barriers computed for Cu/Cu(100) using the embedded atom method (EAM), Karimi et al.(M. Karimi, T. Tomkowski, G. Vidali, and O. Biham, Phys. Rev. B 52), 5364 (1995); O. Biham et al., preprint found that these energies fell into four groups. They proposed a simple approximation for the local-configuration dependence of the energy barriers. From a reexamination of these energies, using effective medium theory, we propose an approximation which also depends solely on near-neighbor occupations but accounts better for the energy barriers. The scheme is comparably accurate for Ag/Ag(100), but requires some modification for Ni/Ni(100). We also describe some noteworthy effects of fcc geometry in this approximation, particularly a mechanism which, like the Ehrlich-Schwoebel barrier, enhances roughness with increasing temperature. In the next talk we describe and compare simulations using both approximations.

  11. 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}.

  12. A unified relation for the solid-liquid interface free energy of pure FCC, BCC, and HCP metals.

    PubMed

    Wilson, S R; Mendelev, M I

    2016-04-14

    We study correlations between the solid-liquid interface (SLI) free energy and bulk material properties (melting temperature, latent heat, and liquid structure) through the determination of SLI free energies for bcc and hcp metals from molecular dynamics (MD) simulation. Values obtained for the bcc metals in this study were compared to values predicted by the Turnbull, Laird, and Ewing relations on the basis of previously published MD simulation data. We found that of these three empirical relations, the Ewing relation better describes the MD simulation data. Moreover, whereas the original Ewing relation contains two constants for a particular crystal structure, we found that the first coefficient in the Ewing relation does not depend on crystal structure, taking a common value for all three phases, at least for the class of the systems described by embedded-atom method potentials (which are considered to provide a reasonable approximation for metals).

  13. A unified relation for the solid-liquid interface free energy of pure FCC, BCC, and HCP metals

    NASA Astrophysics Data System (ADS)

    Wilson, S. R.; Mendelev, M. I.

    2016-04-01

    We study correlations between the solid-liquid interface (SLI) free energy and bulk material properties (melting temperature, latent heat, and liquid structure) through the determination of SLI free energies for bcc and hcp metals from molecular dynamics (MD) simulation. Values obtained for the bcc metals in this study were compared to values predicted by the Turnbull, Laird, and Ewing relations on the basis of previously published MD simulation data. We found that of these three empirical relations, the Ewing relation better describes the MD simulation data. Moreover, whereas the original Ewing relation contains two constants for a particular crystal structure, we found that the first coefficient in the Ewing relation does not depend on crystal structure, taking a common value for all three phases, at least for the class of the systems described by embedded-atom method potentials (which are considered to provide a reasonable approximation for metals).

  14. On the electron density localization in elemental cubic ceramic and FCC transition metals by means of a localized electrons detector

    NASA Astrophysics Data System (ADS)

    Aray, Yosslen; Paredes, Ricardo; Álvarez, Luis Javier; Martiz, Alejandro

    2017-06-01

    The electron density localization in insulator and semiconductor elemental cubic materials with diamond structure, carbon, silicon, germanium, and tin, and good metallic conductors with face centered cubic structure such as α-Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au, was studied using a localized electrons detector defined in the local moment representation. Our results clearly show an opposite pattern of the electron density localization for the cubic ceramic and transition metal materials. It was found that, for the elemental ceramic materials, the zone of low electron localization is very small and is mainly localized on the atomic basin edges. On the contrary, for the transition metals, there are low-valued localized electrons detector isocontours defining a zone of highly delocalized electrons that extends throughout the material. We have found that the best conductors are those in which the electron density at this low-value zone is the lowest.

  15. Retention of hydrogen in fcc metals irradiated at temperatures leading to high densities of bubbles or voids

    NASA Astrophysics Data System (ADS)

    Garner, F. A.; Simonen, E. P.; Oliver, B. M.; Greenwood, L. R.; Grossbeck, M. L.; Wolfer, W. G.; Scott, P. M.

    2006-09-01

    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, carbon, and other impurities poison the bubble surface. However, these chemisorbed poisons may reduce but not entirely restrict the ingress or egress of atomic hydrogen.

  16. Interactions between edge lattice dislocations and Σ11 symmetrical tilt grain boundary: comparisons among several FCC metals and interatomic potentials

    NASA Astrophysics Data System (ADS)

    Yu, Wenshan; Wang, Zhiqiang

    2014-07-01

    Interactions between edge dislocations and a ? symmetrical tilt grain boundary (GB) in face-centred cubic metals of Ni and Al are studied via a quasicontinuum method (QCM). A variety of embedding atom method potentials are used, and the results are compared to previous studies of Cu [W.S. Yu, Z.Q. Wang, Acta Mater., 60 (2012) 5010]. Different potentials do not significantly affect the edge dislocation-GB interactions in these metals. Edge dislocations can easily transmit across grain boundaries in Ni and Cu, even for a single incoming dislocation. However, slip-transmission in Al occurs only after the GB absorbs many incoming dislocations. Stable nucleation of grain boundary dislocations (GBD) in Cu and Ni plays an important role in the slip-transmissions. The slip transmission in Al is found to be difficult due to the metastable nucleation of GBD. The incoming leading and trailing partials in Al are absorbed together by the GB because of the larger values of ? (?, ? and ? are the shear modulus, magnitude of Burgers vector of a partial dislocation and the stable stacking fault (SF) energy, respectively). The parameter ? (? as the unstable SF energy) [Z.H. Jin et al., Acta. Mater. 56 (2008) 1126] incorporates ? and ?, and can be used to measure the slip transmission ability of an edge dislocation in these metals. It is also shown that certain loading conditions can help enhance the nucleation of GBDs and GBD dipoles in Al, such that the incoming, leading and trailing partial dislocations can be absorbed separately.

  17. 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.

  18. Shear deformation, ideal strength, and stacking fault formation of fcc metals: A density-functional study of Al and Cu

    NASA Astrophysics Data System (ADS)

    Jahnátek, Michal; Hafner, Jürgen; Krajčí, Marián

    2009-06-01

    Ab initio density-functional calculations have been used to study the response of two face-centered-cubic metals (Al and Cu) to shearing parallel to the close-packed (111) planes along two different directions, [112¯] and [1¯10] . Two different types of deformations—affine and alias—have been investigated. Under an affine shear deformation, all atoms are shifted parallel to the shearing direction by a distance proportional to their distance from the fixed basal plane. In the alias regime, only the top layer is displaced in the shearing direction. In both regimes, calculations have been performed with (pure shear) and without (simple shear) relaxation. For a pure alias shear, due to the interaction between the atoms, the displacement propagates through the sample; this is certainly the most realistic description of the shearing processes. In the pure alias regime, shear deformation, theoretical shear strength, and stacking fault formations may be described on a common footing. For small strains (in the elastic region), affine and alias shears lead to very similar results. Beyond the elastic limit, relaxation has a strong influence of the response on an applied shear strain. The elastic shear moduli are significantly larger for Cu than for Al, but a much higher shear strength is calculated for Al, although the shear strength is limited by the occurrence of a stacking fault instability before the stress maximum is reached. Under ⟨1¯10⟩ {111} shear the analysis of the atomistic deformation mechanism shows that in this case the formation of a stacking fault leads to a splitting of the (1)/(2)[1¯10] dislocation into two partial Shockley dislocations. Due to the repulsive interaction between the atoms in adjacent close-packed planes, the atoms in the top A layer move along (1)/(6)[2¯11] to a position directly above the B layer such that the stable intrinsic stacking fault configuration is the same for both slip systems. The analysis of the variation in the

  19. 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.

  20. 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…

  1. Temperature rise of installed FCC

    NASA Technical Reports Server (NTRS)

    Hankins, J. D.

    1976-01-01

    Report discusses temperature profiles of installed FCC for wood and tile surfaces. Three-conductor FCC was tested at twice nominal current-carrying capacity over bare floor and under carpet, with result indicating that temperature rise is not a linear function of current with FCC at this level.

  2. The FCC in Fiscal 1971.

    ERIC Educational Resources Information Center

    Federal Communications Commission, Washington, DC.

    Fiscal 1971 saw major actions by the Federal Communications Commission (FCC) in all areas of its jurisdiction. In broadcasting, the FCC proposed new renewal rules and policies and issued a number of significant rulings on Fairness Doctrine matters. A policy statement outlining FCC cable television plans was submitted to the Congress. In the common…

  3. High pressure phase transitions in the rare earth metal erbium to 151 GPa.

    PubMed

    Samudrala, Gopi K; Thomas, Sarah A; Montgomery, Jeffrey M; Vohra, Yogesh K

    2011-08-10

    High pressure x-ray diffraction studies have been performed on the heavy rare earth metal erbium (Er) in a diamond anvil cell at room temperature to a pressure of 151 GPa and Er has been compressed to 40% of its initial volume. The rare earth crystal structure sequence hcp → Sm type → dhcp → distorted fcc (hcp: hexagonal close packed; fcc: face centered cubic; dhcp: double hcp) is observed in Er below 58 GPa. We have carried out Rietveld refinement of crystal structures in the pressure range between 58 GPa and 151 GPa. We have examined various crystal structures that have been proposed for the distorted fcc (dfcc) phase and the post-dfcc phase in rare earth metals. We find that the hexagonal hR 24 structure is the best fit between 58 and 118 GPa. Above 118 GPa, a structural transformation from hR 24 phase to a monoclinic C 2/m phase is observed with a volume change of - 1.9%. We have also established a clear trend for the pressure at which a post-dfcc phase is formed in rare earth metals and show that there is a monotonic increase in this pressure with the filling of 4f shell.

  4. 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.

  5. 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.

  6. Thermoreversible, epitaxial fcc<-->bcc transitions in block copolymer solutions.

    PubMed

    Bang, Joona; Lodge, Timothy P; Wang, Xiaohui; Brinker, Kristin L; Burghardt, Wesley R

    2002-11-18

    Uncharged block copolymer micelles display thermoreversible transitions between close-packed and bcc lattices for a range of concentration, solvent selectivity, and copolymer composition. Using small-angle x-ray scattering on shear-oriented solutions, highly aligned fcc crystals are seen to transform epitaxially to bcc crystals, with fcc/bcc orientational relationships that are well established in martensitic transformations in metals. The transition is driven by decreasing solvent selectivity with increasing temperature, inducing solvent penetration of the micellar core.

  7. 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

  8. The FCC: A Research Tool.

    ERIC Educational Resources Information Center

    Wilson, Paul

    The numerous forms filed with the Federal Communications Commission (FCC) provide information about a variety of topics. Basic licensing information that is available concerns engineering, ownership, and equal employment opportunity. The FCC's broadcast bureau collects information about programing, the ascertainment of community needs, public…

  9. 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…

  10. Absolute rate coefficients for the recombination of open f-shell tungsten ions

    NASA Astrophysics Data System (ADS)

    Krantz, C.; Spruck, K.; Badnell, N. R.; Becker, A.; Bernhardt, D.; Grieser, M.; Hahn, M.; Novotný, O.; Repnow, R.; Savin, D. W.; Wolf, A.; Müller, A.; Schippers, S.

    2014-04-01

    We have carried out direct measurements of the absolute recombination rate coefficients of four charge states of tungsten in the range from W18+ to W21+ in a heavy ion storage ring. We find that the rich atomic fine structure of the open f-shell leads to very high resonant enhancement of the recombination rate at energies below ~50 eV. Even in the higher energy domain relevant to fusion plasma this leads to a recombination rate coefficient that is more than four times higher than predicted by the commonly used ADAS database of recombination rates. In addition to the experimental measurements we have carried out theoretical calculations using Autostructure. For W20+ these predict a plasma recombination rate coefficient that agrees much better with the measurement than the ADAS model but still fail to reproduce the experimental data in detail.

  11. Atomic force imaging of the surface of a FCC after thermal and hydrothermal treatments

    SciTech Connect

    Occelli, M.L.; Gould, S.A.G.; Baldiraghi, F.; Leoncini, S.

    1996-10-01

    An atomic force microscope (AFM) operating in a contact mode was used to observe surface variations in FCC resulting from aging. AFM images of a commercial FCC sample before and after steam-aging have been compared with those of the same FCC after use in a major refinery. Large scale (5 {mu}m x 5 {mu}m) images reveal that the FCC surface is formed by platelets and platelet aggregates and that the catalyst microporosity result mainly from elongated and narrow spacings between these plates. Steam-aging does not seem to greatly change the FCC surface architecture. However, in the corresponding equilibrium catalyst (containing several metals impurities) the FCC surface roughness decreases. Atomic scale images were obtained for all the samples examined. The hexagonal symmetry observed in these images is consistent with the structure of the silicate layer in Kaolin, a major component of these types of catalysts.

  12. 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.

  13. 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.

  14. 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.

  15. Calculation of thermodynamic potentials with the inclusion of fractional occupation numbers and investigation of FCC-BCC structural phase transitions in alkaline-earth metals

    NASA Astrophysics Data System (ADS)

    Pozhivatenko, V. V.

    2013-10-01

    The smearing near the Fermi level has been taken into account in the calculations of the thermodynamic characteristics of metals in order to improve the convergence of the performed calculations and to increase the quality of the obtained results. The choice of the smearing parameter usually has not been explained, although the results of the calculations differ significantly for different values of this parameter. Possible schemes for calculating the thermodynamic potentials with the inclusion of the smearing parameter and additional parameters of the volume and energy shifts have been considered. The influence of these parameters on the calculations of the thermodynamic properties of alkaline-earth metals under pressure and on the description of the structural phase transition has been analyzed.

  16. FCC and the Sunshine Act.

    ERIC Educational Resources Information Center

    Weiss, Kenneth

    The Sunshine Act, designed to encourage open meetings to increase public understanding of the governmental decision-making process, went into effect in March 1977. A total of 50 agencies, including the Federal Communications Commission (FCC), are subject to the provisions of the Sunshine Act. The act lists 10 exemptions, any of which can result in…

  17. 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…

  18. Sequential slip transfer of mixed-character dislocations across Σ3 coherent twin boundary in FCC metals: a concurrent atomistic-continuum study

    NASA Astrophysics Data System (ADS)

    Xu, Shuozhi; Xiong, Liming; Chen, Youping; McDowell, David L.

    2016-01-01

    Sequential slip transfer across grain boundaries (GB) has an important role in size-dependent propagation of plastic deformation in polycrystalline metals. For example, the Hall-Petch effect, which states that a smaller average grain size results in a higher yield stress, can be rationalised in terms of dislocation pile-ups against GBs. In spite of extensive studies in modelling individual phases and grains using atomistic simulations, well-accepted criteria of slip transfer across GBs are still lacking, as well as models of predicting irreversible GB structure evolution. Slip transfer is inherently multiscale since both the atomic structure of the boundary and the long-range fields of the dislocation pile-up come into play. In this work, concurrent atomistic-continuum simulations are performed to study sequential slip transfer of a series of curved dislocations from a given pile-up on Σ3 coherent twin boundary (CTB) in Cu and Al, with dominant leading screw character at the site of interaction. A Frank-Read source is employed to nucleate dislocations continuously. It is found that subject to a shear stress of 1.2 GPa, screw dislocations transfer into the twinned grain in Cu, but glide on the twin boundary plane in Al. Moreover, four dislocation/CTB interaction modes are identified in Al, which are affected by (1) applied shear stress, (2) dislocation line length, and (3) dislocation line curvature. Our results elucidate the discrepancies between atomistic simulations and experimental observations of dislocation-GB reactions and highlight the importance of directly modeling sequential dislocation slip transfer reactions using fully 3D models.

  19. 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.

  20. Detection of helium bubble formation at fcc-bcc interfaces using neutron reflectometry

    NASA Astrophysics Data System (ADS)

    Kashinath, A.; Wang, P.; Majewski, J.; Baldwin, J. K.; Wang, Y. Q.; Demkowicz, M. J.

    2013-07-01

    We use neutron reflectometry to find the critical helium (He) fluence required to form He bubbles at interfaces between fcc and bcc metals. Our findings are in agreement with previous experimental as well as modeling results and provide evidence for the presence of stable He platelets at fcc-bcc interfaces prior to bubble formation. The stable storage of He in interfacial platelets may provide the basis for the design of materials with increased resistance to He-induced degradation.

  1. 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…

  2. 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…

  3. 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…

  4. 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%).

  5. 47 CFR 80.417 - FCC Rules and Regulations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false FCC Rules and Regulations. 80.417 Section 80... STATIONS IN THE MARITIME SERVICES Station Documents § 80.417 FCC Rules and Regulations. The Commission's... available on the Commission's web site at www.fcc.gov or ftp.fcc.gov....

  6. Low voltage FCC for home and business

    NASA Technical Reports Server (NTRS)

    Wolf, L.

    1972-01-01

    A thin pressure-sensitive FCC for low voltage usage is described. It is recommended for installing in speakers, intercoms, doorbells, burglar alarms, and clocks, without running wires between walls. The specifications are given.

  7. Military and aerospace applications of FCC

    NASA Technical Reports Server (NTRS)

    Swanson, C.

    1972-01-01

    Military and NASA programs are discussed in which FCC were used. Included are Saturn 4, Pegasus satellites solar, array for Skylab orbital workshop, Poseidon missiles, MK 48 torpedo fire control, and Lunar Surveyor.

  8. Low voltage FCC for home and business

    NASA Technical Reports Server (NTRS)

    Wolf, L.

    1972-01-01

    A thin pressure-sensitive FCC for low voltage usage is described. It is recommended for installing in speakers, intercoms, doorbells, burglar alarms, and clocks, without running wires between walls. The specifications are given.

  9. 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

    ... COMMISSION Proposed Changes to FCC Form 499-A, FCC Form 499-Q, and Accompanying Instructions. AGENCY: Federal... to (1) the annual Telecommunications Reporting Worksheet, FCC Form 499-A (Form 499-A) and... quarterly Telecommunications Reporting Worksheet, FCC Form 499-Q (Form 499-Q) and accompanying...

  10. 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.

  11. Electronic spectra of GdF reanalyzed by decomposing state functions according to f-shell angular momentum

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shigeyoshi; Tatewaki, Hiroshi

    2011-04-01

    The electronic structure of the GdF molecule was studied by means of four-component relativistic configuration interaction (CI) calculations [S. Yamamoto, H. Tatewaki, and T. Saue, J. Chem. Phys. 129, 244505 (2008), 10.1063/1.3039794]. To analyze the electronic spectra more accurately, the CI wave function is decomposed according to the angular momentum (Ωf) generated from the (4f)7 electrons. The weight of a specified Ωf is referred to as the "f-shell Omega component weight." This Ωf plays a crucial role in classifying the strong electronic transitions from the upper states (0.7 eV-3.0 eV) to the lower states (˜0.55 eV). For these transitions, the upper and lower states have almost identical Ωf weights. This appears to be a necessary condition for a transition to be strong. The same condition is expected to hold for other lanthanide linear molecules. A point charge model is also studied, acting as a simplified model of GdF; it successfully reproduces the spectra of GdF, justifying studies based on ligand field theory.

  12. Ru nanoframes with an fcc structure and enhanced catalytic properties

    SciTech Connect

    Ye, Haihang; Wang, Qingxiao; Catalano, Massimo; Lu, Ning; Vermeylen, Joseph; Kim, Moon J.; Liu, Yuzi; Sun, Yugang; Xia, Xiaohu

    2016-03-21

    Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd–Ru core–frame octahedra could be easily converted to Ru octahedral nanoframes of ~2 nm in thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. Furthermore, the fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.

  13. Ru nanoframes with an fcc structure and enhanced catalytic properties

    DOE PAGES

    Ye, Haihang; Wang, Qingxiao; Catalano, Massimo; ...

    2016-03-21

    Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd–Ru core–frame octahedra could be easily converted to Ru octahedral nanoframes of ~2 nm inmore » thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. Furthermore, the fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.« less

  14. Ru Nanoframes with an fcc Structure and Enhanced Catalytic Properties.

    PubMed

    Ye, Haihang; Wang, Qingxiao; Catalano, Massimo; Lu, Ning; Vermeylen, Joseph; Kim, Moon J; Liu, Yuzi; Sun, Yugang; Xia, Xiaohu

    2016-04-13

    Noble-metal nanoframes are of great interest to many applications due to their unique open structures. Among various noble metals, Ru has never been made into nanoframes. In this study, we report for the first time an effective method based on seeded growth and chemical etching for the facile synthesis of Ru nanoframes with high purity. The essence of this approach is to induce the preferential growth of Ru on the corners and edges of Pd truncated octahedra as the seeds by kinetic control. The resultant Pd-Ru core-frame octahedra could be easily converted to Ru octahedral nanoframes of ∼2 nm in thickness by selectively removing the Pd cores through chemical etching. Most importantly, in this approach the face-centered cubic (fcc) crystal structure of Pd seeds was faithfully replicated by Ru that usually takes an hcp structure. The fcc Ru nanoframes showed higher catalytic activities toward the reduction of p-nitrophenol by NaBH4 and the dehydrogenation of ammonia borane compared with hcp Ru nanowires with roughly the same thickness.

  15. 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.

  16. Unique Bonding Properties of the Au36(SR)24 Nanocluster with FCC-Like Core.

    PubMed

    Chevrier, Daniel M; Chatt, Amares; Zhang, Peng; Zeng, Chenjie; Jin, Rongchao

    2013-10-03

    The recent discovery on the total structure of Au36(SR)24, which was converted from biicosahedral Au38(SR)24, represents a surprising finding of a face-centered cubic (FCC)-like core structure in small gold-thiolate nanoclusters. Prior to this finding, the FCC feature was only expected for larger (nano)crystalline gold. Herein, we report results on the unique bonding properties of Au36(SR)24 that are associated with its FCC-like core structure. Temperature-dependent X-ray absorption spectroscopy (XAS) measurements at the Au L3-edge, in association with ab initio calculations, show that the local structure and electronic behavior of Au36(SR)24 are of more molecule-like nature, whereas its icosahedral counterparts such as Au38(SR)24 and Au25(SR)18 are more metal-like. Moreover, site-specific S K-edge XAS studies indicate that the bridging motif for Au36(SR)24 has different bonding behavior from the staple motif from Au38(SR)24. Our findings highlight the important role of "pseudo"-Au4 units within the FCC-like Au28 core in interpreting the bonding properties of Au36(SR)24 and suggest that FCC-like structure in gold thiolate nanoclusters should be treated differently from its bulk counterpart.

  17. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  18. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  19. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  20. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  1. 47 CFR 2.936 - FCC inspection.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false FCC inspection. 2.936 Section 2.936 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Conditions Attendant to An...

  2. Current Policy Problems at the FCC.

    ERIC Educational Resources Information Center

    Wiley, Richard E.

    In the past year the Federal Communications Commission (FCC) has instituted new programs and initiatives designed to improve the exchange of information between the Commission and the research and academic community. An Office of Plans and Policy has been formed. As a result of the Future Planning Conference held last year, a research project is…

  3. 47 CFR 74.3 - FCC inspections of stations.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false FCC inspections of stations. 74.3 Section 74.3... Services in Part 74 § 74.3 FCC inspections of stations. (a) The licensee of a station authorized under this part must make the station available for inspection by representatives of the FCC during the...

  4. 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…

  5. 47 CFR 73.1225 - Station inspections by FCC.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Station inspections by FCC. 73.1225 Section 73... BROADCAST SERVICES Rules Applicable to All Broadcast Stations § 73.1225 Station inspections by FCC. (a) The... FCC during the station's business hours, or at any time it is in operation. (b) In the course of...

  6. Recycled plastics in FCC feedstocks: Specific contributions

    SciTech Connect

    Puente, G. de la; Sedran, U.A.; Arandes, J.M.

    1997-11-01

    Following a tertiary recycling option for plastics focused on the FCC process, styrene-based polymers were dissolved in benzene and injected over fresh and equilibrium samples of a commercial FCC catalyst. Reaction times were up to 12 s in a discontinuous fluidized bed reactor at 550 C. The major reaction products were ethylbenzene, benzene, toluene, and styrene, and the production of coke was very significant. A reaction mechanism which includes polymer thermal cracking, surface oligomerization of styrene molecules, and further cracking, in parallel to hydrogen-transfer reactions, was delineated based on the comparison of the catalytic behaviors of the different samples. Increases in the yields of ethylbenzene, styrene, and coke are predictable for the industrial conditions.

  7. Manufacturing and quality control of FCC harnesses

    NASA Technical Reports Server (NTRS)

    Malohm, W. L.; Vandergriff, J.

    1972-01-01

    The Saturn 5 program contractors encountered many technological challenges and problems relative to inter-connecting wiring and cabling during the development stages of the Saturn program. The knowledge gained from solving these problems, plus recently developed state-of-the-art techniques, materials, and processes were documented in a report prepared for NASA/MSFC. The portions of that report which deal with FCC harnesses are presented.

  8. 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.

  9. 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.

  10. A novel potential: the interlayer potential for the fcc (111) plane family.

    PubMed

    Tian, Fu-Yang; Chen, Nan-Xian; Shen, Jiang; Vitos, Levente

    2012-02-01

    We propose a novel interlayer potential, which is different from usual interatomic potentials. The interlayer potential represents the interaction between atomic layers in a layered material. Based on the Chen-Möbius inversion method in combination with ab initio calculations, the interlayer interactions are obtained for the face centered cubic (fcc) (111) planes. In order to check the validity of our interlayer potential, we calculate the intrinsic stacking fault energy (γ(sf)) and the surface energy (γ(s)) of five metals: Al, Ni, Cu, Ag and Au. The predicted γ(sf) and γ(s) values are compared with the theoretical results obtained from direct calculations and also with the available experimental data. Using the interlayer potentials, we also investigate the phonon dispersion and phonon density of state in the fcc (111) plane family of the considered metals.

  11. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (CB Rule 28) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: CB, 1270 Fairfield Road...

  12. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (R/C Rule 25) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: R/C, 1270 Fairfield Road...

  13. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (R/C Rule 25) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: R/C, 1270 Fairfield Road...

  14. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... (CB Rule 28) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: CB, 1270 Fairfield Road...

  15. 47 CFR 95.225 - (R/C Rule 25) How do I contact the FCC?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... (R/C Rule 25) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: R/C, 1270 Fairfield Road...

  16. 47 CFR 95.428 - (CB Rule 28) How do I contact the FCC?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (CB Rule 28) How do I contact the FCC? (a) FCC National Call Center at 1-888-225-5322. (b) FCC World Wide Web homepage: http://www.fcc.gov. (c) In writing, to FCC, Attention: CB, 1270 Fairfield Road...

  17. A novel approach to octane enhancement via FCC catalysis

    SciTech Connect

    Yanik, S.J.; Campagna, R.J.; Demmel, E.J.; Humphries, A.P.

    1985-03-01

    The development of FCC catalysts containing the shape selective zeolite, ZSM-5, has been successfully completed. Both experimental and commercial results have demonstrated that significant octane enhancement can be achieved using these FCC catalysts. The Z catalysts reduce FCC gasoline yield, but total C/sub 3//sup +/ liquid yields increase. Total prime products yields also increase if sufficient alkylation capacity is available. Significant economic benefits are achieved. Because of Filtrol's flexible catalyst production process, ZSM-5 can be included in all grades of Filtrol's FCC catalysts. These new materials are now commercially available.

  18. High resolution electron microscopy of interfaces in fcc materials

    SciTech Connect

    Merkle, K.L.

    1990-08-01

    Modern high-resolution electron microscopy (HREM) instruments, which are capable of a point-to-point resolution of better than 0.2 nm, have allowed atomic-scale observations of a variety of internal interfaces. The application of the HREM technique to fcc model systems for the purpose of addressing a number of interface issues will be examined in this paper. Atomic structure observations for heterophase interfaces of metal/metal and metal/metal-oxide systems as well as HREM studies of grain boundaries in NiO and Au will be discussed with emphasis on generic structural features and the role of the interface plane. Comparisons between observed interface structures and atomistic computer modeling results have shown agreements for some interfaces, as well as certain differences in others. A number of structural features are common to both metal and oxide grain boundaries, as well as certain heterophase boundaries. Of particular importance in close-packed solids appears to be the tendency to preserve, as much as possible, local atomic coordination, giving rise to atomically well-matched regions that alternate along the interface with regions of misfit. It is commonly observed that heterophase interfaces are being preferentially formed on dense-packed planes. Low-index planes are also frequently observed in asymmetric grain boundaries. In addition to the observation of misfit dislocations in heterophase boundaries, misfit-dislocation-like defects have also been found in asymmetric, incommensurate grain boundaries. The tendency for maintaining coherence between dense-packed planes across the interface has resulted in the formation of novel three-dimensional GB structures. HREM observations have brought new insights into the correlations between macroscopic geometry, interfacial energy, and microscopic atomic relaxations.

  19. 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.

  20. Ground state searches in fcc intermetallics

    SciTech Connect

    Wolverton, C.; de Fontaine, D.; Ceder, G.; Dreysse, H.

    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.

  1. 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.

  2. Microcalorimetry of oxygen adsorption on fcc Co{110}.

    PubMed

    Liao, Kristine; Fiorin, Vittorio; Jenkins, Stephen J; King, David A

    2012-05-28

    The coverage dependent heats of adsorption and sticking probabilities for oxygen on fcc Co{110} have been measured at 300 K using single crystal adsorption calorimetry (SCAC). Initial adsorption is consistent with dissociative chemisorption at low coverage followed by oxide formation above 0.6 ML coverage. The initial heat of adsorption of 633 kJ mol(-1) is similar to heat values calorimetrically measured on other ferromagnetic metal surfaces, such as nickel and iron. As the coverage increases, the heat of adsorption and sticking probability drop very rapidly up to the onset of oxidation. As already observed for other oxygen-metal surface systems, strong lateral adatom repulsions are responsible for the transition from the chemisorption regime to oxide film formation at higher coverage. The heat of oxide formation at the onset is 475 kJ mol(-1), which is consistent with the formation of CoO crystallites. The oxide film formation is discussed in terms of nucleation and island growth, and the Mott-Cabrera mechanisms, the latter being evidenced by the relatively constant heat of adsorption and sticking probability in contrast to the nickel and iron oxidation cases.

  3. Simulation for F.C.C. deformation texture by modified pencil glide theory[Face Centered Cubic

    SciTech Connect

    Masui, H.

    1999-11-26

    Inspired by the pencil glide theory for b.c.c. metal, modified pencil glide theory for f.c.c. metal was proposed, dividing the 12 glide systems of f.c.c. metal into three groups individually composed of eight {l{underscore}brace}111{r{underscore}brace}{l{underscore}angle}110{r{underscore}angle} glide systems around the principal axes X[100], Y[010] and Z[001]. These assumptions yielded two mathematical solutions {Omega}(3) and {Omega}(1). In {Omega}(3), from the three groups with four complete conjugated glide systems composed of, respectively, two glide systems of common {l{underscore}angle}110{r{underscore}angle} direction, only one group with the maximum plastic work may operate if the requirements are satisfied, otherwise glide systems in {Omega}(1) where one of the four conjugated glide systems is zero are activated. The model considering the 12 glide systems of f.c.c. as a whole explained many experimentally stable orientations in axisymmetric and rolling deformation. The differences between the two pencil glide theories for b.c.c. and f.c.c. are also discussed with data.

  4. 76 FR 10827 - Modernizing the FCC Form 477 Data Program

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-28

    ... submitting comments. Federal Communications Commission's Web Site: http://fjallfoss.fcc.gov/ecfs2/ . Follow... available on the Commission's Web site at http://www.fcc.gov . Pursuant to Sec. Sec. 1.415 and 1.419 of the... . Filers should follow the instructions provided on the Web site for submitting comments. For ECFS...

  5. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 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...

  6. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 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...

  7. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 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...

  8. 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...

  9. 47 CFR 95.117 - Where to contact the FCC.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 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...

  10. 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...

  11. 47 CFR 73.4000 - Listing of FCC policies.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 4 2010-10-01 2010-10-01 false Listing of FCC policies. 73.4000 Section 73... BROADCAST SERVICES Rules Applicable to All Broadcast Stations § 73.4000 Listing of FCC policies. The following sections list, solely for the purpose of reference and convenience, certain Policies of the...

  12. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  13. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  14. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  15. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  16. 47 CFR 73.878 - Station inspections by FCC; availability to FCC of station logs and records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... of station logs and records. 73.878 Section 73.878 Telecommunication FEDERAL COMMUNICATIONS... (LPFM) § 73.878 Station inspections by FCC; availability to FCC of station logs and records. (a) The...) Station records and logs shall be made available for inspection or duplication at the request of the...

  17. Surface energy and work function of fcc and bcc crystals: Density functional study

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Wang, Shao-Qing

    2014-12-01

    The surface energies and work functions for six close-packed surfaces of 19 common fcc and bcc metals in the periodic table have been systematically calculated by means of the density functional theory (DFT) method. The accuracy of the results is established in comparison with the experimental and other theoretical values. The variations of work functions with the surface crystallographic orientation display a good regularity. For alkali metals, the work functions follow the sequence Φ(110) > Φ(133) > Φ(311) > Φ(120) > Φ(100) > Φ(111). But for the same crystal structure of bcc transition metals (Nb, Mo, Ta, W), the order is Φ(110) > Φ(133) > Φ(120) > Φ(111) > Φ(311) > Φ(100). The work functions for 3d, 4d and 5d transition fcc metals also display an obvious regularity and ordered as Φ(111) > Φ(100) > Φ(211) > Φ(123) > Φ(310) > Φ(110). Particular attention is paid to the surface energies anisotropy with the same crystal structure metals and the variations present a good regularity, too. Especially, a roughly inverse proportional relationship between the surface energy and work function is found.

  18. 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%.

  19. Universal relationships for the phonon spectra in BCC, FCC, and HCP crystals with a short-range interatomic interaction

    SciTech Connect

    Vaks, V. G. Zhuravlev, I. A.; Zabolotskii, A. D.

    2012-03-15

    The frequencies of the phonon branches that correspond to the vibrations of the close-packed atomic planes in bcc, fcc, and hcp crystals with short-range interatomic interaction are shown to be described by a universal relationship, which only contains two parameters for each branch, for any polarization {lambda}. These phonon branches correspond to the ({xi}, {xi}, 0) direction in bcc crystals, the ({xi}, {xi}, {xi}) direction in fcc crystals, and the (0, 0, {xi}) direction in hcp crystals. This universal relationship can only be violated by long-range interactions, namely, the interactions outside the sixth coordination shell in a bcc crystal, the fifth coordination shell in an fcc crystal, and the eleventh or tenth coordination shell in an hcp crystal. The effect of these long-range interactions for each phonon branch can be quantitatively characterized by certain parameters {Delta}{sub n{lambda}}, which are simply expressed in terms of the frequencies of three phonons of the branch. The values of these parameters are presented for all bcc, fcc, and hcp metals whose phonon spectra are measured. In most cases, the proposed relationships for the frequencies are found to be fulfilled accurate to several percent. In the cases where the {Delta}{sub n{lambda}} parameters are not small, they can give substantial information on the type and scale of long-range interaction effects in various metals.

  20. The elastic properties and stability of fcc-Fe and fcc-FeNi alloys at inner-core conditions

    NASA Astrophysics Data System (ADS)

    Martorell, Benjamí; Brodholt, John; Wood, Ian G.; Vočadlo, Lidunka

    2015-07-01

    The agreement between shear wave velocities for the Earth's inner core observed from seismology with those derived from mineral physics is considerably worse than for any other region of the Earth. Furthermore, there is still debate as to the phase of iron present in the inner core, particularly when alloying with nickel and light elements is taken into account. To investigate the extent to which the mismatch between seismology and mineral physics is a function of either crystal structure and/or the amount of nickel present, we have used ab initio molecular dynamics simulations to calculate the elastic constants and seismic velocities (Vp and Vs) of face centred cubic (fcc) iron at Earth's inner core pressures (360 GPa) and at temperatures up to ˜7000 K. We find that Vp for fcc iron (fcc-Fe) is very similar to that for hexagonal close packed (hcp) iron at all temperatures. In contrast, Vs for fcc-Fe is significantly higher than in hcp-Fe, with the difference increasing with increasing temperature; the difference between Vs for the core (from seismology) and Vs for fcc-Fe exceeds 40 per cent. These results are consistent with previous work at lower temperatures. We have also investigated the effect of 6.5 and 13 atm% Ni in fcc-Fe. We find that Ni only slightly reduces Vp and Vs (e.g. by 2 per cent in Vs for 13 atm% Ni at 5500 K), and cannot account for the difference between the velocities observed in the core and those of pure fcc-Fe. We also tried to examine pre-melting behaviour in fcc-Fe, as reported in hcp-Fe by extending the study to very high temperatures (at which superheating may occur). However, we find that fcc-Fe spontaneously transforms to other hcp-like structures before melting; two hcp-like structures were found, both of hexagonal symmetry, which may most easily be regarded as being derived from an hcp crystal with stacking faults. That the structure did not transform to a true hcp phase is likely as a consequence of the limited size of the

  1. Simulation of mechanical performance of nanoporous FCC copper under compression with pores mimicking several crystalline arrays

    NASA Astrophysics Data System (ADS)

    Cui, Yi; Chen, Zengtao

    2017-08-01

    The mechanical performance of porous metal with assembly of pores mimicking typical crystalline structures is studied via atomistic simulation and finite element method. The pore lattices are made with the same orientation as the face-centered cubic (FCC) copper lattice. The compression is applied in the [0 0 1] direction. Under the same initial porosity and identical pore size, pores assembled in diamond array result in a superior stress response under compression. The sample with pores assembled in body-centered cubic array, whose surface-to-volume ratio is close to that of either FCC or hexagonally close-packed (HCP) array, has a yet much higher yield stress. However, the FCC- and HCP-structured nanoporous samples exhibit a greater hardening effect. The Lubarda model for critical stress to trigger dislocation emission is extended to the nanoporous geometry numerically. The magnitude and distribution of shear stress on the slip plane are found crucial to dislocation activities. No strong correlation between dislocation formation and early densification of nanoporous geometry is found. Through comparing the yielding and hardening behavior among differently structured nanoporous samples, new understanding could be established on their mechanical performance. Enhanced structural integrity could better support their diverse applications by design.

  2. Stability of the fcc structure in block copolymer systems.

    PubMed

    Nonomura, Makiko

    2008-11-19

    The stability of the face-centered cubic (fcc) structure in microphase separated copolymers is investigated by a coarse-grained approach. Direct simulations of the equation for the microphase separation in three dimensions indicate that there is a narrow area above a certain degree of segregation in the phase diagram, where the fcc structure is the most stable structure. By employing the mode expansion, we have confirmed that the fcc structure can form as a metastable structure even in the weak segregation regime.

  3. Non-empirical Prediction of the Photophysical and Magnetic Properties of Systems with Open d- and f-Shells Based on Combined Ligand Field and Density Functional Theory (LFDFT).

    PubMed

    Daul, Claude

    2014-09-01

    Despite the important growth of ab initio and computational techniques, ligand field theory in molecular science or crystal field theory in condensed matter offers the most intuitive way to calculate multiplet energy levels arising from systems with open shells d and/or f electrons. Over the past decade we have developed a ligand field treatment of inorganic molecular modelling taking advantage of the dominant localization of the frontier orbitals within the metal-sphere. This feature, which is observed in any inorganic coordination compound, especially if treated by Density Functional Theory calculation, allows the determination of the electronic structure and properties with a surprising good accuracy. In ligand field theory, the theoretical concepts consider only a single atom center; and treat its interaction with the chemical environment essentially as a perturbation. Therefore success in the simple ligand field theory is no longer questionable, while the more accurate molecular orbital theory does in general over-estimate the metal-ligand covalence, thus yields wave functions that are too delocalized. Although LF theory has always been popular as a semi-empirical method when dealing with molecules of high symmetry e.g. cubic symmetry where the number of parameters needed is reasonably small (3 or 5), this is no more the case for molecules without symmetry and involving both an open d- and f-shell (# parameters ∼90). However, the combination of LF theory and Density Functional (DF) theory that we introduced twenty years ago can easily deal with complex molecules of any symmetry with two and more open shells. The accuracy of these predictions from 1(st) principles achieves quite a high accuracy (<5%) in terms of states energies. Hence, this approach is well suited to predict the magnetic and photo-physical properties arbitrary molecules and materials prior to their synthesis, which is the ultimate goal of each computational chemist. We will illustrate the

  4. 47 CFR 1.8001 - FCC Registration Number (FRN).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... unique identifying number that is assigned to entities doing business with the Commission. (b) The FRN is obtained through the Commission Registration System (CORES) over the Internet at the CORES link at www.fcc...

  5. 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.

  6. Magnetic properties of the 2D Fen core Xm (X = C, N, O, Cl, S and F) shell clusters embedded in graphene

    NASA Astrophysics Data System (ADS)

    Zhao, Ming-Yu; Zhao, Ru-Meng; Li, Wei; Ma, Ya-Qiang; Wang, Tian-Xing; Dai, Xian-Qi

    2017-01-01

    Utilizing first-principle calculations, the structural, electronic and magnetic properties of monolayer graphene embedded with Fen/Xm (X = C, N, O, Cl, S and F) core/shell clusters are investigated, where n = 1, 2, 3 and m = 4, 6, respectively. We find that the graphene embedding with the Fen/Xm core/shell clusters are magnetic except the Fe/S4, Fe2/C4 and Fe3/Cl6 core/shell clusters. The graphene embedding with the Fe3/F6 core/shell cluster has the largest magnetic moment in these systems. Magnetism for Fen/Xm core/shell clusters embedded in monolayer graphene can be ascribed to the ferromagnetic coupling between the Fe atoms. Our calculations demonstrate that Fe atoms are successfully isolated at various C, N, O, Cl, S and F shells in graphene to preserve the high-spin state. On the other hand, the high-spin state is also effectively controlled by the amount of Fe atoms. The electron spin can be stored in magnetic thin film, lithographically prepared quantum dots, and electromagnetic traps. The Fen/Xm core/shell clusters embedded in graphene can be considered to have potential applications in nanoelectronics, spintronics and magnetic storage devices.

  7. 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.

  8. Dislocation-defect interactions in irradiated and quenched FCC metals

    NASA Astrophysics Data System (ADS)

    Robach, Joshua Shane

    An in situ transmission electron microscope straining technique has been used to investigate the dynamics of dislocation-defect interactions in Kr ion irradiated copper. He ion irradiated copper, rapidly quenched copper, and rapidly quenched gold. The formation of defect-free channels in copper was observed in real-time for the first time in these experiments. Pre-existing dislocations were not responsible for creating the defect-free channels and had a limited contribution to the total plasticity. Defect-free channels originated from grain boundaries or regions of high stress concentration such as a crack tip. Based on these observations, dislocation propagation is the rate-limiting step in the onset of plasticity. The critical shear stress required for a dislocation to move past a Frank loop, measured from observed bowing angles and defect spacing, was found to vary from 10.3 to 157.5 MPa. In He ion irradiated copper, dislocations were observed interacting with He bubbles during in situ TEM deformation. The defect pinning strengths of the bubbles were measured from observed bowing angles and defect spacing and exhibited values ranging from 38.6 to 283.5 MPa. Rapidly quenched copper and gold were strained in situ in the TEM in order to observe dislocations interacting with stacking-fault tetrahedra and vacancy loops similar to those found in irradiated materials. The conversion of a sessile quenching defect in copper into a glissile defect by a moving straight dislocation was observed. This interaction is in qualitative agreement with molecular dynamics simulations. In gold, a moving dislocation sheared a stacking-fault tetrahedron, leaving a step on two of the faces and was observed to collapse. This shearing is also seen in molecular dynamics simulations. The experimental results are combined with atomistic simulations of the interaction of partial dislocations with defects in copper to form the basis for a new dispersed-barrier hardening crystal plasticity model that predicts the important features of the mechanical response of irradiated materials.

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

    PubMed

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

    2015-05-15

    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.

  10. C-language package for standalone embedded atom method molecular dynamics simulations of fcc structures

    NASA Astrophysics Data System (ADS)

    Ocaya, R. O.; Terblans, J. J.

    Ab-initio molecular dynamics (MD) employs Newtonian mechanics to model and simulate the time evolution of particle trajectories in material science ensembles using a differentiable potential function. Although commercial and free packages exist for MD, their heuristic nature prevents dissection. This open-source C-language package arose out of the interest to study effects of embedded atoms in metallic face-centered cubic structures (fcc) on a standalone computer. The algorithms use velocity-time integration to output instantaneous particle parameters for up to several thousands of particles in the NVT ensemble. The functions are coded in a reusable and redistributable standalone header library file.

  11. 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.

  12. Phase-field-crystal model for fcc ordering.

    PubMed

    Wu, Kuo-An; Adland, Ari; Karma, Alain

    2010-06-01

    We develop and analyze a two-mode phase-field-crystal model to describe fcc ordering. The model is formulated by coupling two different sets of crystal density waves corresponding to <111> and <200> reciprocal lattice vectors, which are chosen to form triads so as to produce a simple free-energy landscape with coexistence of crystal and liquid phases. The feasibility of the approach is demonstrated with numerical examples of polycrystalline and (111) twin growth. We use a two-mode amplitude expansion to characterize analytically the free-energy landscape of the model, identifying parameter ranges where fcc is stable or metastable with respect to bcc. In addition, we derive analytical expressions for the elastic constants for both fcc and bcc. Those expressions show that a nonvanishing amplitude of [200] density waves is essential to obtain mechanically stable fcc crystals with a nonvanishing tetragonal shear modulus (C11-C12)/2. We determine the model parameters for specific materials by fitting the peak liquid structure factor properties and solid-density wave amplitudes following the approach developed for bcc [K.-A. Wu and A. Karma, Phys. Rev. B 76, 184107 (2007)]. This procedure yields reasonable predictions of elastic constants for both bcc Fe and fcc Ni using input parameters from molecular dynamics simulations. The application of the model to two-dimensional square lattices is also briefly examined.

  13. Color octet electron search potential of FCC based e–p colliders

    NASA Astrophysics Data System (ADS)

    Acar, Y. C.; Kaya, U.; Oner, B. B.; Sultansoy, S.

    2017-04-01

    Resonant production of color octet electrons, e 8, at the FCC based e–p colliders is analyzed. It is shown that e-FCC will cover much a wider region of e 8 masses compared to the LHC. Moreover, with the highest electron beam energy, the e 8 search potential of the e-FCC exceeds that of the FCC p–p collider. If e 8 is discovered earlier by the FCC p–p collider, e-FCC will give an opportunity to handle very important additional information. For example, the compositeness scale can be probed up to the hundreds of TeV region.

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

    PubMed

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

    2016-02-24

    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.

  15. Nucleation of fcc Ta when heating thin films

    DOE PAGES

    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.

  16. 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.

  17. Heavy oil extraction ups FCC feed out first-stage grass roots ROSE unit, in Kansas

    SciTech Connect

    Newcomer, R.M.; Soltau, R.C.

    1982-07-12

    This paper describes operation of a residuum oil supercritical extraction unit which produces oils, resins, and high asphaltene pitch from feedstocks ranging from partially topped crude to vacuum-reduced and brown asphalts. Deasphalted oil products (DAO) are substantially lower in metals, carbon residue, and other impurities than the feedstock. Vacuum bottoms are charged to a fixed element in-line mixer where the vacuum bottoms are contacted with several volumes of solvent at elevated temperature and pressure. Carryover of product droplets from flash drums and strippers into solvent condensers and coolers resulted in frequent plugging of fin-fan tubes with subsequent shutdown for physical cleanout. Installation of a small superheater on the stripping steam solved the problem. DAO is mixed with atmospheric and vacuum gas oils and fed to an FCC unit. Overall metals content of this mixed gas oil stream has increased with DAO.

  18. Fcc-bcc transition for Yukawa interactions determined by applied strain deformation.

    PubMed

    Hoy, Robert S; Robbins, Mark O

    2004-05-01

    Calculations of the work required to transform between bcc and fcc phases yield a high-precision bcc-fcc transition line for monodisperse point Yukawa (screened-Coulomb) systems. Our results agree qualitatively but not quantitatively with recently published simulations and phenomenological criteria for the bcc-fcc transition. In particular, the bcc-fcc-fluid triple point lies at a higher inverse screening length than previously reported.

  19. Folding tool for preparing FCC molded-plug terminations

    NASA Technical Reports Server (NTRS)

    Campbell, E. C.; Chambers, C. M.

    1971-01-01

    Assemblies consist of window piece, conductor spacer, insulator, outer seal, and molded portion that integrates all components. Preparation of FCC for molded plug termination requires that terminated ends of conductors in each cable be accurately folded simultaneously into spacer end and groove.

  20. Fixture for multiple-FCC chemical stripping and plating

    NASA Technical Reports Server (NTRS)

    Angele, W.; Norton, W. E.

    1971-01-01

    For chemical stripping, lead tape applied near ends to be stripped protects insulation. Taped ends are submerged half way in stripping solution. For electroplating, both ends of FCC are stripped - top ends for electric contact, others for submersion in electroplating solution.

  1. Congress, the FCC and Children's Television Regulation: A Shift in the Balance of Power.

    ERIC Educational Resources Information Center

    Markin, Karen

    The Federal Communications Commission (FCC) of the late 1980s appeared to pursue its own agenda of broadcast deregulation, notwithstanding congressional pressures. The apparent power shift is evident in a case study of the interactions between Congress and the FCC on the subject of children's television. In the early 1970s, the FCC tended to…

  2. 76 FR 12308 - Modernizing the FCC Form 477 Data Program; Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-07

    ... COMMISSION 47 CFR Parts 1, 20, and 43 Modernizing the FCC Form 477 Data Program; Correction AGENCY: Federal... FCC Form 477. Inadvertently the Comment Filing Procedures section of the February 28, 2011 publication... February 28, 2011 (76 FR 10827) relating to the modernization of the FCC Form 477. The document (FR...

  3. 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...

  4. 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...

  5. 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...

  6. 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...

  7. 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...

  8. Ab initio random structure search for 13-atom clusters of fcc elements.

    PubMed

    Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M

    2013-03-27

    The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd13 and Au13, we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au13, which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons.

  9. Low-cycle fatigue-cracking mechanisms in fcc crystalline materials

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Qu, S.; Duan, Q. Q.; Wu, S. D.; Li, S. X.; Wang, Z. G.; Zhang, Z. F.

    2011-01-01

    The low-cycle fatigue (LCF) cracking behavior in various face-centered-cubic (fcc) crystalline materials, including Cu single crystals, bicrystals and polycrystals, Cu-Al and Cu-Zn alloys, ultrafine-grained (UFG) Al-Cu and Cu-Zn alloys, was systematically investigated and reviewed. In Cu single crystals, fatigue cracking always nucleates along slip bands and deformation bands. The large-angle grain boundary (GB) becomes the preferential site in bicrystals and polycrystals. In addition, fatigue cracking can also nucleate along slip bands and twin boundaries (TBs) in polycrystalline materials. However, shear bands and coarse deformation bands are observed to the preferential sites for fatigue cracking in UFG materials with a large number of GBs. Based on numerous observations on fatigue-cracking behavior, the fatigue-cracking mechanisms along slip bands, GBs, TBs, shear bands and deformation bands were systematically compared and classified into two types, i.e. shear crack and impingement crack. Finally, these fatigue-cracking behaviors are discussed in depth for a better understanding of their physical nature and the transition from intergranular to transgranular cracking in various fcc crystalline materials. These comprehensive results for fatigue damage mechanisms should significantly aid in obtaining the optimum design to further strengthen and toughen metallic materials in practice.

  10. Ginzburg-Landau-type multiphase field model for competing fcc and bcc nucleation.

    PubMed

    Tóth, G I; Morris, J R; Gránásy, L

    2011-01-28

    We address crystal nucleation and fcc-bcc phase selection in alloys using a multiphase field model that relies on Ginzburg-Landau free energies of the liquid-fcc, liquid-bcc, and fcc-bcc subsystems, and determine the properties of the nuclei as a function of composition, temperature, and structure. With a realistic choice for the free energy of the fcc-bcc interface, the model predicts well the fcc-bcc phase-selection boundary in the Fe-Ni system.

  11. Post-riser quench improves FCC yields, profitability

    SciTech Connect

    Quinn, G.P.; Silverman, M.A.

    1996-01-15

    Performance tests of a post-riser quench system have shown increases in gasoline yield; reductions in fuel gas, butadienes, and pentadienes; and improved oxidation stability of FCC gasoline. Following commercial trials in six of Amoco Petroleum Products` refineries for some 10 years, the system is now being installed by other refiners. Elimination of post-riser thermal cracking is essential to achieving the most desirable product slate. Most of Amoco`s FCC units (FCCUs) have rough-cut cyclone systems in which there is significant vapor residence time in the disengaging vessel. To overcome this problem Amoco chose to reduce the temperature in the dilute phase. This technology involves quenching the dilute phase, thereby reducing the thermal cracking rates. The approach is very effective and virtually eliminates post-riser cracking. This paper reviews this design.

  12. Magnetism in bcc and fcc Fe with carbon and manganese.

    PubMed

    Medvedeva, N I; Van Aken, D; Medvedeva, J E

    2010-08-11

    Density functional theory calculations were performed to study the structure and magnetic properties of bcc (α) and fcc (γ) Fe with 3 at.% carbon and manganese impurities. We find that all bcc-based Fe, Fe-C and Fe-Mn-C phases exhibit a ferromagnetic (FM) ground state, while the antiferromagnetic double-layer (AFMD) state is lowest in energy within the collinear spin approach in fcc Fe, Fe-C and Fe-Mn-C phases. However, the carbon and manganese impurities affect the local magnetic interactions significantly. The states with opposite manganese magnetic moments are quasi-degenerate in bcc Fe-Mn alloy, whereas octa-site carbon stabilizes ferromagnetic coupling of the nearest manganese atom with the Fe host. We demonstrate that the antiferromagnetic (AFM) fcc Fe-C and Fe-Mn-C alloys are intrinsically inhomogeneous magnetic systems. Carbon frustrates the local magnetic order by reorientation of magnetic moments of the nearest Mn and Fe atoms, and favors their ferromagnetic coupling. The competition between ferromagnetic and antiferromagnetic Fe-Fe and Fe-Mn interactions and the local magnetovolume instability near carbon may give rise to the spin-glass-like regions observed in austenitic Fe-Mn-C alloys.

  13. The most stable mono-layers of (111)-Pt (fcc) on Graphene: A first-principles GGA study

    NASA Astrophysics Data System (ADS)

    Otalora-Acevedo, J.; Rodríguez Martínez, J. A.; Moreno-Armenta, G.; Vera, E.; Takeuchi Tan, N.

    2016-08-01

    We investigate monolayers of planes (111) of Pt in the FCC structure located on graphene. The energy of formation showed that the most stable structure is √3×√3 — Pt on 2 × 2 — graphene. This system has a mismatch in the lattice constant of 0.45. The layers are completely flat, and its band structure shows that the new structure is metallic and the Dirac's cones are displaced 0.6eV above of the Fermi level. In this work we present the dependence of the enthalpy of formation of these structures and we calculated all structural parameters of their relaxation.

  14. 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

    2015-09-07

    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.

  15. 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.

  16. Magnetism and structure of ultrathin fcc FexCo1 - x films on Cu(001) (abstract)

    NASA Astrophysics Data System (ADS)

    Dittschar, A.; Zharnikov, M.; Kuch, W.; Schneider, C. M.; Kirschner, J.

    1996-04-01

    Ultrathin films of 3d-transition metal alloys, and in particular FeCo alloys, currently receive considerable interest because of their potential technological application and the possibility to adjust magnetic properties via the variation of composition and structure. To study magnetic and structural properties of the otherwise unstable fcc phase of FeCo, this structural phase was stabilized by epitaxial growth on Cu(001). Ultrathin FexCo1-x films were deposited at room temperature by coevaporation from two separate Knudsen cells, operated under stabilized conditions. The film thickness was varied between 2 and 9 monolayers (ML) and the Fe concentration between x=0.2 and x=0.95. The growth process was monitored by medium energy electron diffraction (MEED). Auger electron spectroscopy and low energy electron diffraction (LEED) were employed to analyze the composition and structure of the films. A nearly perfect layer-by-layer growth up to at least 9 ML, as seen by MEED, is encountered for x≤0.7. For higher Fe concentrations and thicknesses greater than 4 ML, deviations from the layer-by-layer growth are observed, indicating a structural rearrangement. LEED-I(V) curves reveal the coexistence of two structural phases with different interlayer spacings, the relative amount of which depends on the composition. Magnetic properties were characterized by the magneto-optical Kerr effect (MOKE). The remanent magnetization was found to lie within the film plane over the whole range of thicknesses and concentrations investigated. A linear increase of the Kerr signal at saturation magnetization with increasing thickness indicates that practically the whole film is magnetic. As a function of composition, the saturation Kerr signal develops continuously with increasing Fe content. This suggests that in fcc FeCo alloys the contribution of Fe and Co to the total magnetic moment is nearly constant over the whole compositional range.

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

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... must be followed by EAS Participants' personnel, emergency officials, and National Weather Service (NWS... are consistent with national plans, FCC regulations, and EAS operation. (a) The State EAS...

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

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... must be followed by EAS Participants' personnel, emergency officials, and National Weather Service (NWS... are consistent with national plans, FCC regulations, and EAS operation. (a) The State EAS...

  19. 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.

  20. Virus-mediated FCC iron nanoparticle induced synthesis of uranium dioxide nanocrystals.

    PubMed

    Ling, Tao; Yu, Huimin; Shen, Zhongyao; Wang, Hui; Zhu, Jing

    2008-03-19

    A reducing system involving M13 virus-mediated FCC Fe nanoparticles was employed to achieve uranium reduction and synthesize uranium dioxide nanocrystals. Here we show that metastable face-centered cubic (FCC) Fe nanoparticles were fabricated around the surface of the M13 virus during the specific adsorption of the virus towards Fe ions under a reduced environment. The FCC phase of these Fe nanoparticles was confirmed by careful TEM characterization. Moreover, this virus-mediated FCC Fe nanoparticle system successfully reduced contaminable U(VI) into UO(2) crystals with diameters of 2-5 nm by a green and convenient route.

  1. Structural transformation between bcc and fcc in Fe-Ni nanoparticle during heating process

    NASA Astrophysics Data System (ADS)

    Li, Guojian; Sui, Xudong; Qin, Xuesi; Ma, Yonghui; Wang, Kai; Wang, Qiang

    2016-10-01

    Phase transformation between bcc and fcc in Fe-Ni nanoparticle has been studied by using molecular dynamics simulation with an embedded atom method. The transformation has been explored by designing the nanoparticles with different initial structures, sizes and elemental distributions at various Ni concentrations. The results show that the structural transformation is strongly related to the Ni content and elemental distribution. Initial fcc structure transforms to bcc for a lower Ni content and bcc transforms to fcc for a higher Ni content. The transformation is accompanied with a sharp reduction in energy even for the nanoparticle with a large size. Furthermore, lattice distortion first occurs before the transformation. The transformation from fcc to bcc is occurred by elongating fcc (100) to bcc (110) and that from bcc to fcc by compressing bcc (110) to fcc (100). The reason is that the nanoparticle has a low energy state for bcc structure with a lower Ni content and also for fcc structure with a higher Ni content. The coexistence of bcc and fcc phases appears with the change of elemental distribution.

  2. Preliminary design of FCC-ee pre-injector complex

    NASA Astrophysics Data System (ADS)

    Ogur, S.; Barnyakov, A.; Furukawa, K.; Iida, N.; Levichev, A.; Miyahara, F.; Nikiforov, D.; Oide, K.; Papaphilippou, Y.; Zimmermann, F.

    2017-07-01

    The design of a 100 km circular e + e - collider with extremely high luminosity is an important component of the global Future Circular Collider (FCC) study hosted by CERN. FCC-ee is being designed to serve as Z, W, H and top factory, covering beam energies from 45.6 to 175 GeV. For the injectors, the Z-operation is the most challenging mode, due to the high total charge and low equilibrium emittance in the collider at this energy. Thus, fulfilling the Z-mode will also meet the demands for all other modes of FCC-ee. This goal can be achieved by using a 6 GeV NC linac with an S-band RF frequency of 2.856 GHz and a repetition rate of 100 Hz. This linac will accelerate two bunches per RF pulse, each with a charge of 6.5 nC. Positrons will be generated by sending 4.46 GeV e - onto a hybrid target so that the e + created can still be accelerated to 1.54 GeV in the remaining part of the same linac. The emittance of the e + beam will then shrink to the nm level in a 1.54 GeV damping ring. After damping, the e + will be reinjected into the linac and accelerated to 6 GeV. The e - and e + will then be accelerated alternately to 45.6 GeV in the booster, before they are injected into the collider.

  3. 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.

  4. Synchrotron radiation backgrounds for the FCC-hh experiments

    NASA Astrophysics Data System (ADS)

    Collamati, F.; Boscolo, M.; Burkhardt, H.; Kersevan, R.

    2017-07-01

    In this paper we present a detailed analysis of the Synchrotron Radiation emitted by the 50 TeV protons of the FCC-hh in the last bending and quadrupole magnets upstream of the interaction region. We discuss the characteristics of this radiation in terms of power, flux, photon spectrum and fans with and without crossing angle for comparison. We mainly focus our study on the fraction of photons that may hit the detector, with a full tracking in GEANT4 that simulates the interaction within the central beam pipe.

  5. Collisional viscosity of FCC particles in a CFB

    SciTech Connect

    Gidaspow, D.; Lu Huilin

    1996-09-01

    Particle velocity distributions were measured for a flow of 75-{micro}m FCC (fluidized catalytic cracking) particles in a CFB (circulating fluidized bed) using a new video-digital camera technique. From the spread of particle histograms, a random oscillating particle velocity was determined. This random velocity was used to compute the powder viscosity with the help of dense-phase kinetic theory of granular flow. There was excellent agreement between this kinetic-theory measurement and previous macroscopic viscosity measurements. The dimensionless group kinematic viscosity divided by the oscillating velocity and particle diameter correlated all available data as a function of particle volume fraction.

  6. 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.

  7. Key elements in optimizing catalyst selections for resid FCC units

    SciTech Connect

    Yanik, S.J.; O`Connor, P.

    1995-09-01

    Achieving the optimum activity and yield structure from a commercial Resid FCC Unit (RFCC) is essential to maximizing profitability in today`s modern refinery. Proper catalyst selection is a key element in this optimization. This paper is written to provide FCC Process Engineers with an understanding of some basic elements of RFCC operation. The necessity of using realistic evaluation methods to assure proper RFCC catalyst selection is explained. The differences between Activity limited and Delta Coke limited RFCC operations are elucidated and the related catalyst performance requirements are discussed. The effect of the catalyst to oil ratio on conversion and on catalyst site utilization and poisoning plays a key role in the transition of an RFCC unit from Catalyst Activity limited regime to a Cat-to-Oil limited regime. For the Activity limited operation the catalyst resistance to poisons with the appropriate feedstock will be the most important selection criteria. For the Delta Coke limited operation, a reduction of the commercial delta coke of the catalyst will be crucial. The types of commercial delta coke are discussed and methods for their evaluation are suggested. In both cases the use of realistic catalyst evaluation methods and feedstock will be essential in order to arrive at the correct catalyst selection. Finally, commercial data comparisons illustrate the improvements in product value that can be achieved when the proper catalyst is chosen.

  8. 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.

  9. Growth of fcc(111) Dy multi-height islands on 6H-SiC(0001) graphene.

    PubMed

    Hershberger, M T; Hupalo, M; Thiel, P A; Tringides, M C

    2013-06-05

    Graphene based spintronic devices require an understanding of the growth of magnetic metals. Rare earth metals have large bulk magnetic moments so they are good candidates for such applications, and it is important to identify their growth mode. Dysprosium was deposited on epitaxial graphene, prepared by thermally annealing 6H-SiC(0001). The majority of the grown islands have triangular instead of hexagonal shapes. This is observed both for single layer islands nucleating at the top of incomplete islands and for fully completed multi-height islands. We analyze the island shape distribution and stacking sequence of successively grown islands to deduce that the Dy islands have fcc(111) structure, and that the triangular shapes result from asymmetric barriers to corner crossing.

  10. 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.

  11. 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.

  12. Crystal Chemistry of Ceramic/Metal Systems.

    DTIC Science & Technology

    2007-11-02

    temperature thermal expansion of alkali halides, rare earth oxides, group IV elements, fcc metals, bcc metals, SiC , III-V and II-VI compounds. Analytical...to high pressure thermal expansion of MgO , NaCl, Group IV elements, and W. The bulk modulus and self-diffusion for W and Ta have been predicted to their melting points.

  13. 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…

  14. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false FCC inspection and submission of equipment for... ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Declaration of Conformity § 2.1076 FCC inspection and submission of equipment for testing. (a)...

  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

    ... COMMISSION Revised 2011 Annual Telecommunications Reporting Worksheet (FCC Form 499-A) and Accompanying... Competition Bureau released the revised Telecommunications Reporting Worksheet (FCC Form 499-A) and... Competition Bureau, Telecommunications Access Policy Division, at (202) 418-7400 or via the Internet...

  16. 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... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  17. 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... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  18. 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... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  19. 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... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  20. 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... You Need to Know § 95.422 (CB Rule 22) How do I answer correspondence from the FCC? (a) If it...

  1. 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 license...

  2. 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 license...

  3. 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 license...

  4. 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 license...

  5. 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 license...

  6. 47 CFR 64.1110 - State notification of election to administer FCC rules.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false State notification of election to administer FCC rules. 64.1110 Section 64.1110 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED... Telecommunications Service Providers § 64.1110 State notification of election to administer FCC rules. (a)...

  7. 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…

  8. Inequities in Mass Communication Law: The FCC's Application of the Duopoly Rule to Public Broadcasting.

    ERIC Educational Resources Information Center

    Avery, Robert K.

    A three-part petition was filed in December 1974 with the Federal Communications Commission (FCC) which presented the first serious threat to public broadcasters' exemption from the FCC's multiple-ownership rules. The petition requested a revision of the rules that permit multiple ownership of noncommercial educational stations within a single…

  9. 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)

  10. 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 ITU...

  11. The FCC, The Coverage Principle of the Fairness Doctrine and the First Amendment.

    ERIC Educational Resources Information Center

    Chamberlin, Bill F.

    This review of the history of the coverage principle developed by the Federal Communications Commission (FCC) concludes that government regulation of mass media program content can be dangerous and that the coverage principle needs to be abolished. The first section of the report discusses the FCC's interpretation of the 1934 Communications Act…

  12. 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...

  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, 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...

  15. 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...

  16. In situ TEM observation of FCC Ti formation at elevated temperatures

    DOE PAGES

    Yu, Qian; Kacher, Josh; Gammer, Christoph; ...

    2017-07-04

    Pure Ti traditionally exhibits the hexagonal closed packed (HCP) crystallographic structure under ambient conditions and the body centered cubic (BCC) structure at elevated temperatures. In addition to these typical structures for Ti alloys, the presence of a face centered cubic (FCC) phase associated with thin films, interfaces, or high levels of plastic deformation has occasionally been reported. Here in this paper we show that small FCC precipitates form in freestanding thin foils during in situ transmission electron microscope (TEM) heating and we discuss the potential origins of the FCC phase in light of the in situ observations. This FCC phasemore » was found to be stable upon cooling and under ambient conditions, which allowed us to explore its mechanical properties and stability via nanomechanical in situ TEM testing. It was found that FCC platelets within the HCP matrix phase were stable under mechanical deformation and exhibited similar mechanical deformation behavior as the parent HCP phase.« less

  17. Solution based synthesis of simple fcc Si nano-crystals under ambient conditions.

    PubMed

    Balcı, Mustafa H; Sæterli, Ragnhild; Maria, Jerome; Lindgren, Mikael; Holmestad, Randi; Grande, Tor; Einarsrud, Mari-Ann

    2013-02-28

    We demonstrate for the first time that simple face-centered cubic (fcc) silicon nano-crystals can be produced by a solution based bottom-up synthesis route under ambient conditions. Simple fcc Si nano-crystals (2-7 nm) were prepared at room temperature by using sodium cyclopentadienide as a reducing agent for silicon tetrachloride. Photoluminescence emission at 550 nm was observed for the fcc silicon nano-crystals upon excitation at 340 nm, indicating that fcc Si nano-crystals were exhibiting direct bandgap like semiconductor properties with very fast radiative recombination rates. The new synthesis route makes possible the production and study of simple fcc polymorphs of Si nano-crystals with an easy alteration of surface termination groups.

  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. 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…

  20. Diffusion and segregation of niobium in fcc-nickel.

    PubMed

    Connétable, Damien; Ter-Ovanessian, Benoît; Andrieu, Éric

    2012-03-07

    Niobium is one of the major alloying elements, among the refractory elements, contributing to the strengthening of superalloys. Consequently, data about its behavior and its migration mechanism in fcc-Ni are essential knowledge to understand and control the strengthening in such alloys. We present in this work Nb interactions, solubility and diffusion in Ni performed by using the GGA approximation of the density functional theory. The substituted site is found to be the most favorable configuration in comparison to the tetrahedral and octahedral sites. The effect of temperature on solubility is discussed taking into account the thermal expansion of the lattice parameter and the vibrational contribution. Its diffusion mechanism is also discussed and compared to the literature. We finally discuss the segregation of Nb atoms on a Σ(5)-(012) symmetric tilt grain boundary.

  1. 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.

  2. Developing of a test procedure to evaluate FCC catalyst regenerability

    SciTech Connect

    Murthy, V.L.N.; Debnath, S.; Bao, M.R.

    1995-12-31

    FCC catalyst comprises various active ingredients e.g. Y Zeolites, ZSM-5 and other medium pore Zeolites, active, matrix etc. with wide variation in Zeolite/matrix ratio and pore size distribution. The effect of pore size distribution on the accessibility of the active sites is a subject for intensive research at present. The accessibility of these active sites has a major effect on the overall reaction and regeneration kinetics. Catalyst regenerability is a very important factor particularly for moderate and low temperature regenerators, since it directly effects the CRC (Coke on-Regenerated Catalyst) value. The regenerability of catalyst is critical to minimize the overall catalyst inventory. Unfortunately, till date, there is no suitable laboratory equipment available to test catalyst regenerability.

  3. Shear strength of metals under uniaxial deformation and pure shear

    NASA Astrophysics Data System (ADS)

    Latypov, F. T.; Mayer, A. E.

    2015-11-01

    In this paper, we investigate the dynamic shear strength of perfect monocrystalline metals using the molecular dynamics simulation. Three types of deformation (single shear, uniaxial compression and tension) are investigated for five metals of different crystallographic systems (fcc, bcc and hcp). A strong dependence of the calculated shear strength on the deformation type is observed. In the case of bcc (iron) and hcp (titanium) metals, the maximal shear strength is achieved at the uniaxial compression, while the minimal shear strength is observed at the uniaxial tension. In the case of fcc metals (aluminum, copper, nickel) the largest strength is achieved at the pure shear, the lowest strength is obtained at the uniaxial compression.

  4. Ab initio lattice stability of fcc and hcp Fe-Mn random alloys.

    PubMed

    Gebhardt, T; Music, D; Hallstedt, B; Ekholm, M; Abrikosov, I A; Vitos, L; Schneider, J M

    2010-07-28

    We have studied the lattice stability of face centred cubic (fcc) versus hexagonal close packed (hcp) Fe-Mn random alloys using ab initio calculations. In the calculations we considered the antiferromagnetic order of local moments, which for fcc alloys models the magnetic configuration of this phase at room temperature (below its Néel temperature) as well as their complete disorder, corresponding to paramagnetic fcc and hcp alloys. For both cases, the results are consistent with our thermodynamic calculations, obtained within the Calphad approach. For the room temperature magnetic configuration, the cross-over of the total energies of the hcp phase and the fcc phase of Fe-Mn alloys is at the expected Mn content, whereas for the magnetic configuration above the fcc Néel temperature, the hcp lattice is more stable within the whole composition range studied. The increase of the total energy difference between hcp and antiferromagnetic fcc due to additions of Mn as well as the stabilizing effect of antiferromagnetic ordering on the fcc phase are well displayed. These results are of relevance for understanding the deformation mechanisms of these random alloys.

  5. 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.

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

    SciTech Connect

    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, while 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.

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

    DOE PAGES

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

    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

  8. Ligand π-radical interaction with f-shell unpaired electrons in phthalocyaninato-lanthanoid single-molecule magnets: a solution NMR spectroscopic and DFT study.

    PubMed

    Damjanović, Marko; Morita, Takaumi; Katoh, Keiichi; Yamashita, Masahiro; Enders, Markus

    2015-10-05

    The phthalocyaninato double-decker complexes [M(obPc)2 ](0) (M= Y(III) , Tb(III) , Dy(III) ; obPc=2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato), along with their reduced ([M(obPc)2 ](-) [P(Ph)4 ](+) ; M=Tb(III) , Dy(III) ) and oxidized ([M(obPc)2 ](+) [SbCl6 ](-) (M=Y(III) , Tb(III) ) counterparts were studied with (1) H, (13) C and 2D NMR. From the NMR data of the neutral (i.e., with one unpaired electron in the ligands) and anionic Tb(III) complexes, along with the use of dispersion corrected DFT methods, it was possible to separate the metal-centered and ligand-centered contributions to the hyperfine NMR shift. These contributions to the (1) H and (13) C hyperfine NMR shifts were further analyzed in terms of pseudocontact and Fermi contact shifts. Furthermore, from a combination of NMR data and DFT calculations, we have determined the spin multiplicity of the neutral complexes [M(obPc)2 ](0) (M=Tb(III) and Dy(III) ) at room temperature. From the NMR data of the cationic Tb(III) complex, for which actually no experimental structure determination is available, we have analyzed the structural changes induced by oxidation from its neutral/anionic species and shown that the interligand distance decreases upon oxidation. The fast electron exchange process between the neutral and anionic Tb(III) double-decker complexes was also studied. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. A first-principles study of the phase stability of fcc-based Ti-Al alloys

    SciTech Connect

    Asta, M. . Dept. of Materials Science and Mineral Engineering); de Fontaine, D. . Dept. of Materials Science and Mineral Engineering Lawrence Berkeley Lab., CA ); van Schilfgaarde, M. ); Sluiter, M. (Lawrence Livermore National Lab., CA (Un

    1992-04-01

    In this paper we present results of a first-principles phase stability study of fcc-based Ti-Al alloys. In particular the full-potential linear muffin tin orbital method has been used to determine heats of format on and other zero-temperature properties of 9 fcc ordered superstructures as well as fcc and hcp Ti, and fcc Al. From these results a set of effective cluster interactions are determined which are used in a cluster variation method calculation of the thermodynamic properties and the composition-temperature phase diagram of fcc-based alloys.

  10. Single-crystal adsorption calorimetry and density functional theory of CO chemisorption on fcc Co{110}.

    PubMed

    Liao, Kristine; Fiorin, Vittorio; Gunn, David S D; Jenkins, Stephen J; King, David A

    2013-03-21

    Using single-crystal adsorption calorimetry (SCAC) and density functional theory (DFT), the interaction of carbon monoxide on fcc Co{110} is reported for the first time. The results indicate that adsorption is consistent with molecular chemisorption at all coverages. The initial heat of adsorption of 140 kJ mol(-1) is found in the range of heat values calorimetrically measured on other ferromagnetic metal surfaces, such as nickel and iron. DFT adsorption energies are in good agreement with the experimental results, and comparison between SCAC and DFT for CO on other ferromagnetic surfaces is made. The calculated dissociation barrier of 2.03 eV implies that dissociation at 300 K is unlikely even at the lowest coverage. At high coverages during the adsorption-desorption steady state regime, a pre-exponential factor for CO desorption of 1.2 × 10(17) s(-1) is found, implying a localised molecular adsorbed state prior to desorption in contrast to what we found with Ni surfaces. This result highlights the importance of the choice of the pre-exponential factor in evaluating the activation energy for desorption.

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

    DOE PAGES

    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

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

    SciTech Connect

    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. 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.

  13. Modifications in the grain boundary character distribution in FCC materials through thermomechanical processing

    SciTech Connect

    King, W E; Kumar, M; Schwartz, A J

    1999-03-01

    Recently, a body of work has emerged that indicates the potential to improve certain materials' properties through thermomechanical processing (TMP) solely by controlling grain misorientations. The grain boundary character distribution (GBCD) is defined as a microstructural property that describes the proportions of ''special'' and ''random'' boundaries with reference to the coincident site lattice model. Most of the ''optimization'' treatments reported in the literature have been performed on f.c.c. metals and alloys with medium to low stacking fault energies and have resulted in microstructures with high fractions of {Sigma}3, {Sigma}9, and {Sigma}27 boundaries, or {Sigma}3{sup n} type boundaries. It could be interpreted that only an increased incidence of annealing twinning is required to improve the GBCD. However, it also appears imperative that the formation of annealing twins disrupt the connectivity of the random boundary network, thus implying that {Sigma}3{sup n} reactions and resultant triple junctions are critical. Experiments to modify the GBCD in model materials like oxygen-free electronic Cu and Inconel 600 are presented and the efficacy of the processing routes is assessed in terms of the random boundary network and evolution of texture in the processed microstructures.

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

    SciTech Connect

    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. 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.

  15. 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.

  16. Martensitic fcc-to-hcp transformation observed in xenon at high pressure.

    PubMed

    Cynn, H; Yoo, C S; Baer, B; Iota-Herbei, V; McMahan, A K; Nicol, M; Carlson, S

    2001-05-14

    Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr.

  17. First-principles calculations of free energies of unstable phases: the case of fcc W.

    PubMed

    Ozolins, V

    2009-02-13

    Ab initio molecular dynamics simulations are used to solve the long-standing problem of calculating the free energies of unstable phases, such as fcc W. We find that fcc W is mechanically unstable with respect to long-wavelength shear at all temperatures considered (T>2500 K), while the short-wavelength phonon modes are anharmonically stabilized. The calculated fcc-bcc enthalpy and entropy differences at T=3500 K (308 meV and 0.74k_{B} per atom, respectively) agree well with the recent values derived from analysis of experimental data.

  18. Antiferromagnetic resonance in the Mott insulator fcc-Cs3C60.

    PubMed

    Suzuki, Yuta; Shibasaki, Seiji; Kubozono, Yoshihiro; Kambe, Takashi

    2013-09-11

    The magnetic ground state of the fcc phase of the Mott insulator Cs3C60 was studied using a low-temperature electron spin resonance technique, and antiferromagnetic resonance (AFMR) below 1.57 K was directly observed at ambient pressure. The AFMR modes for the fcc phase of Cs3C60 were investigated using a conventional two-sublattice model with uniaxial anisotropy, and the spin-flop field was determined to be 4.7 kOe at 1.57 K. The static magnetic exchange interactions and anisotropy field for fcc-Cs3C60 were also estimated.

  19. Observation of continuous and reversible bcc-fcc phase transformation in Ag/V multilayers

    SciTech Connect

    Wei, Q. M.; Liu, X.-Y.; Misra, A.

    2011-03-14

    A continuous and reversible bcc-fcc phase transformation via a rotation of bcc(110) or fcc(111) planes is observed in the Bain orientation relationship in a sputter deposited V/Ag multilayers using high resolution transmission electron microscopy and analyzed using molecular dynamics simulations. As a result of the continuous phase transformation, an intermediate bct phase connecting the bcc and fcc phases coexists, giving rise to the Bain path. The periodic displacement of atoms occurs in every two adjacent Ag and V layers. The alternating shear stress created by misfit strain is responsible for generating such transformation.

  20. Ferromagnetic Fe on Cu(001) throughout the fcc-like phase: arguing from the viewpoint of the electronic structure.

    PubMed

    Donath, M; Pickel, M; Schmidt, A B; Weinelt, M

    2009-04-01

    The scientific enthusiasm for ultrathin Fe films on Cu(001) has now lasted for more than 20 years. Is there ferromagnetic iron with a face-centred cubic (fcc) structure? Does ferromagnetism in Fe hinge on the body-centred cubic (bcc) structure? In this contribution, we try to establish that the electron system gives evidence of ferromagnetic behaviour with fcc-like electronic bands. We examine a crystal-induced surface state, which is characteristic of fcc surface order. Furthermore, we compare electronic signatures of fcc and bcc: the d-band exchange splitting, image-potential-state energies and the work function. We conclude that, from the viewpoint of the electronic structure, Fe on Cu(001) is found to be ferromagnetic throughout the fcc-like phase. This result raises a new question: how much deviation from the relaxed fcc order is acceptable without losing the electronic signature of fcc?

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

    DOE PAGES

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; ...

    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

  2. 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.

  3. Spin frustration and magnetic ordering in the Mott insulating fcc-Cs3C60

    NASA Astrophysics Data System (ADS)

    Kasahara, Yuichi; Takeuchi, Yuki; Itou, Tatsuaki; Iwasa, Yoshihiro; Arcon, Denis; Rosseinsky, Matthew; Prassides, Kosmas

    2014-03-01

    The low-temperature magnetic state at ambient pressure has been investigated by specific heat and nuclear magnetic resonance (NMR) measurements in face-centered-cubic (fcc-) Cs3C60, which is characterized by a Mott insulating state with S = 1 / 2 spins in C603- anions and a geometrical spin frustration inherent in the fcc lattice. Specific heat exhibited no sharp anomaly down to 0.4 K, but both magnetic specific heat and NMR relaxation rate revealed a broad peak around 2.5 K, indicating that the reported antiferromagnetic ordering is accompanied by a gradual freezing of electronic spins with distributed transition temperatures. These results are unexpected in the conventional fcc antiferromagnets. Interplay of geometrical frustration, orientational disorder of C60 molecules, and weak Mottness gives rise to the unique magnetic ground state in fcc-Cs3C60.

  4. 76 FR 20976 - Wireline Competition Bureau Releases 2011 Annual Telecommunications Reporting Worksheet (FCC Form...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-14

    ... COMMISSION Wireline Competition Bureau Releases 2011 Annual Telecommunications Reporting Worksheet (FCC Form.... SUMMARY: In this document, the Wireline Competition Bureau released the revised annual Telecommunications... (describing a filer's principal telecommunications activities) into Appendix B. (5) Noting that...

  5. Lattice parameters of fcc binary alloys using a new semiempirical method

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Ferrante, John

    1992-01-01

    A new method is presented for the calculation of heats of formation, lattice parameters and cohesive energies of binary alloys. The method is applied to some fcc alloys and compared with experimental data, as well as other semiempirical results.

  6. 47 CFR 0.409 - Commission policy on private printing of FCC forms.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... ORGANIZATION General Information General § 0.409 Commission policy on private printing of FCC forms. The... in quality to the original document, without change to the page size, image size, configuration...

  7. First Principles Theory of the hcp-fcc Phase Transition in Cobalt.

    PubMed

    Lizárraga, Raquel; Pan, Fan; Bergqvist, Lars; Holmström, Erik; Gercsi, Zsolt; Vitos, Levente

    2017-06-19

    Identifying the forces that drive a phase transition is always challenging. The hcp-fcc phase transition that occurs in cobalt at ~700 K has not yet been fully understood, although early theoretical studies have suggested that magnetism plays a main role in the stabilization of the fcc phase at high temperatures. Here, we perform a first principles study of the free energies of these two phases, which we break into contributions arising from the vibration of the lattice, electronic and magnetic systems and volume expansion. Our analysis of the energy of the phases shows that magnetic effects alone cannot drive the fcc-hcp transition in Co and that the largest contribution to the stabilization of the fcc phase comes from the vibration of the ionic lattice. By including all the contributions to the free energy considered here we obtain a theoretical transition temperature of 825 K.

  8. 78 FR 44121 - FCC Extends Reply Comment Dates for Indecency Cases Policy

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-23

    ... From the Federal Register Online via the Government Publishing Office FEDERAL COMMUNICATIONS COMMISSION FCC Extends Reply Comment Dates for Indecency Cases Policy AGENCY: Federal Communications Commission. ACTION: Notice. SUMMARY: In this document, the Federal Communications Commission Enforcement...

  9. 78 FR 34099 - FCC Extends Pleading Cycle for Indecency Cases Policy

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-06

    ... From the Federal Register Online via the Government Publishing Office FEDERAL COMMUNICATIONS COMMISSION FCC Extends Pleading Cycle for Indecency Cases Policy AGENCY: Federal Communications Commission. ACTION: Notice. SUMMARY: In this document, the Federal Communications Commission Enforcement Bureau and...

  10. Growth and micromagnetism of self-assembled epitaxial fcc(111) cobalt dots.

    PubMed

    Fruchart, O; Masseboeuf, A; Toussaint, J C; Bayle-Guillemaud, P

    2013-12-11

    We develop the self-assembly of epitaxial submicrometer-sized face-centered-cubic (fcc) Co(111) dots using pulsed laser deposition. The dots display atomically flat facets, from which the ratios of surface and interface energies for fcc Co are deduced. Zero-field magnetic structures are investigated with magnetic force and Lorentz microscopies, revealing vortex-based flux-closure patterns. A good agreement is found with micromagnetic simulations.

  11. 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.

  12. Vacancy behavior in a compressed fcc Lennard-Jones crystal

    SciTech Connect

    Beeler, J.R. Jr.

    1981-12-01

    This computer experiment study concerns the determination of the stable vacancy configuration in a compressed fcc Lennard-Jones crystal and the migration of this defect in a compressed crystal. Isotropic and uniaxial compression stress conditions were studied. The isotropic and uniaxial compression magnitudes employed were 0.94 less than or equal to eta less than or equal to 1.5, and 1.0 less than or equal to eta less than or equal to 1.5, respectively. The site-centered vacancy (SCV) was the stable vacancy configuration whenever cubic symmetry was present. This includes all of the isotropic compression cases and the particular uniaxial compression case (eta = ..sqrt..2) that give a bcc structure. In addition, the SCV was the stable configuration for uniaxial compression eta < 1.29. The out-of-plane split vacancy (SV-OP) was the stable vacancy configuration for uniaxial compression 1.29 < eta less than or equal to 1.5 and was the saddle-point configuration for SCV migration when the SCV was the stable form. For eta > 1.20, the SV-OP is an extended defect and, therefore, a saddle point for SV-OP migration could not be determined. The mechanism for the transformation from the SCV to the SV-OP as the stable form at eta = 1.29 appears to be an alternating sign (101) and/or (011) shear process.

  13. Local elastic constants in thin films of an fcc crystal.

    PubMed

    van Workum, Kevin; de Pablo, Juan J

    2003-03-01

    In this work we present a formalism for the calculation of the local elastic constants in inhomogeneous systems based on a method of planes. Unlike previous work, this formalism does not require the partitioning of the system into a set of finite volumes over which average elastic constants are calculated. Results for the calculation of the local elastic constants of a nearest-neighbor Lennard-Jones fcc crystal in the bulk and in a thin film are presented. The local constants are calculated at exact planes of the (001) face of the crystal. The average elastic constants of the bulk system are also computed and are consistent with the local constants. Additionally we present the local stress profiles in the thin film when a small uniaxial strain is applied. The resulting stress profile compares favorably with the stress profile predicted via the local elastic constants. The surface melting of a model for argon for which experimental and simulation data are available is also studied within the framework of this formalism.

  14. Elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys studied by the combinatorial thin film approach and ab initio calculations.

    PubMed

    Reeh, S; Kasprzak, M; Klusmann, C D; Stalf, F; Music, D; Ekholm, M; Abrikosov, I A; Schneider, J M

    2013-06-19

    The elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys with additions of up to 8 at.% X were studied by combinatorial thin film growth and characterization and by ab initio calculations using the disordered local moments (DLM) approach. The lattice parameter and Young's modulus values change only marginally with X. The calculations and experiments are in good agreement. We demonstrate that the elastic properties of transition metal alloyed Fe-Mn can be predicted by the DLM model.

  15. Synthesis of 4H/fcc Noble Multimetallic Nanoribbons for Electrocatalytic Hydrogen Evolution Reaction.

    PubMed

    Fan, Zhanxi; Luo, Zhimin; Huang, Xiao; Li, Bing; Chen, Ye; Wang, Jie; Hu, Yanling; Zhang, Hua

    2016-02-03

    Noble multimetallic nanomaterials, if only consisting of Au, Ag, Pt, and Pd, typically adopt the high-symmetry face-centered cubic (fcc) structure. Here for the first time, by using the 4H/fcc Au@Ag nanoribbons (NRBs) as seeds, we report the synthesis of 4H/fcc trimetallic Au@PdAg core-shell NRBs via the galvanic reaction method under ambient conditions. Moreover, this strategy can also be used to synthesize 4H/fcc trimetallic Au@PtAg and quatermetallic Au@PtPdAg core-shell NRBs. Impressively, for the first time, these alloy shells, i.e., PdAg, PtAg, and PtPdAg, epitaxially grown on the 4H/fcc Au core with novel 4H hexagonal phase were successfully synthesized. Remarkably, the obtained 4H/fcc Au@PdAg NRBs exhibit excellent electrocatalytic activity toward the hydrogen evolution reaction, which is even quite close to that of the commercial Pt black. We believe that our findings here may provide a novel strategy for the crystal-structure-controlled synthesis of advanced functional noble multimetallic nanomaterials with various promising applications.

  16. Role of five-fold twin boundary on the enhanced mechanical properties of fcc Fe nanowires.

    PubMed

    Wu, J Y; Nagao, S; He, J Y; Zhang, Z L

    2011-12-14

    The role of 5-fold twin boundary on the structural and mechanical properties of fcc Fe nanowire under tension is explored by classical molecular dynamics. Twin-stabilized fcc nanowire with various diameters (6-24 nm) are examined by tension tests at several temperatures ranging from 0.01 to 1100 K. Significant increase in the Young's modulus of the smaller nanowires is revealed to originate from the central area of quinquefoliolate-like stress-distribution over the 5-fold twin, rather than from the surface tension that is often considered as the main source of such size-effects found in nanostructures. Because of the excess compressive stress caused by crossing twin-boundaries, the atoms in the center behave stiffer than those in bulk and even expand laterally under axial tension, providing locally negative Poisson's ratio. The yield strength of nanowire is also enhanced by the twin boundary that suppresses dislocation nucleation within a fcc twin-domain; therefore, the plasticity of nanowire is initiated by strain-induced fcc→bcc phase transformation that destroys the twin structure. After the yield, the nucleated bcc phase immediately spreads to the entire area, and forms a multigrain structure to realize ductile deformation followed by necking. As temperature elevated close to the critical temperature between bcc and fcc phases, the increased stability of fcc phase competes with the phase transformation under tension, and hence dislocation nucleations in fcc phase are observed exclusively at the highest temperature in our study.

  17. Aluminum exchanged sepiolite as components of FCC catalysts

    SciTech Connect

    Corma, A.; Fornes, V.; Mifsud, A.; Perez-Pariente, J. )

    1990-08-01

    Sepiolite is a fibrous magnesium silicate, which is formed of talc-like ribbons arranged in such a way that the tetrahedral sheet is continuous but inverts apical directions in adjacent ribbons. In this way, channels of 10.8 {times} 4.0 {angstrom} in a cross-section perpendicular to the length of the fiber (C axis) are generated. The average fiber length of the mineral varies between 0.5 and 1.0 {mu}m, and reagent molecules have only access to a small portion of the interior of the channels. Natural or acid leached sepiolite have been found useful for vanadium passivation in FCC catalysts. The authors have modified the sepiolite in order to improve the textural characteristics, while removing the Mg{sup 2+} ions of the border and introducing other cations which can give acid properties to this material. Conclusions are as follows: (1) It is possible to prepare, by a conventional treatment, sepiolites in which the magnesium at the borders of the channels has been substituted by Al{sup 3+}. (2) These samples show a much higher acidity and hydrothermal stability than natural sepiolites, being most of the acidity in the range of mild strengths. (3) Aluminic sepiolites, while being good for vanadium passivation, do not present the inconvenience due to Mg migrations to the zeolite (if in the same particle) shown by natural sepiolite. (4) They present a good gasoil cracking activity and selectivity, specially useful for bottoms conversion. All these characteristics make aluminum sepiolites materials worth testing in a larger scale for catalytic cracking of residues.

  18. 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

  19. Monte Carlo Studies of the Fcc Ising Model.

    NASA Astrophysics Data System (ADS)

    Polgreen, Thomas Lee

    Monte Carlo simulations are performed on the antiferromagnetic fcc Ising model which is relevant to the binary alloy CuAu. The model exhibits a first-order ordering transition as a function of temperature. The lattice free energy of the model is determined for all temperatures. By matching free energies of the ordered and disordered phases, the transition temperature is determined to be T(,t) = 1.736 J where J is the coupling constant of the model. The free energy as determined by series expansion and the Kikuchi cluster variation method is compared with the Monte Carlo results. These methods work well for the ordered phase, but not for the disordered phase. A determination of the pair correlation in the disordered phase along the {100} direction indicates a correlation length of (DBLTURN) 2.5a at the phase transition. The correlation length exhibits mean-field-like temperature dependence. The Cowley-Warren short range order parameters are determined as a function of temperature for the first twelve nearest-neighbor shells of this model. The Monte Carlo results are used to determine the free parameter in a mean-field-like class of theories described by Clapp and Moss. The ability of these theories to predict ratios between pair potentials is tested with these results. In addition, evidence of a region of heterophase fluctuations is presented in agreement with x-ray diffuse scattering measurements on Cu(,3)Au. The growth of order following a rapid quench from disorder is studied by means of a dynamic Monte Carlo simulation. The results compare favorably with the Landau theory proposed by Chan for temperatures near the first-order phase transition. For lower temperatures, the results are in agreement with the theories of Lifshitz and Allen and Chan. In the intermediate temperature range, our extension of Chan's theory is able to explain our simulation results and recent experimental results.

  20. 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.

  1. Structure Fluctuation Model of Melting and Polymorphic Transformations in Metals

    NASA Astrophysics Data System (ADS)

    Filippov, E. S.

    2017-09-01

    Relationships of volumes during thermal expansion of metals are analyzed. It is demonstrated that metals with BCC structure undergo two-step structural change at the melting point: at the beginning the BCC structure is transformed into FCC structure and then clusters are formed with K = 12 and statistical packing of atoms of the liquid phase. Before melting, hexagonal layer-by-layer (6 + 6) packed Cd and Zn change their structure from K = 6 to K = 8. Metals with FCC structure do not change the number of neighbors before melting, forming clusters with K = 12. It is shown that conditions of pre-melting and polymorphic FCC (HDP) → BCC transformations are reached for the critical volume of thermal expansion caused by leveling of fluctuations of atom and electron densities.

  2. Nucleation of hcp and fcc phases in bcc iron under uniform compression: classical molecular dynamics simulations.

    PubMed

    Wang, B T; Shao, J L; Zhang, G C; Li, W D; Zhang, P

    2010-11-03

    By classical molecular dynamics simulations employing an embedded atom method potential, we have simulated the bcc to hcp/fcc structural transition in single-crystal iron under uniform compression. Results showed that the transition pressure is different from uniaxial compression and shock loading. The transformation occurs on a picosecond timescale and the transition time decreases along with the increase of pressure. The nucleation and growth of the hcp and fcc phases under constant pressure and temperature are analyzed in detail. The nucleation planes, all belonging to the {110}(bcc) family and parallel to the three compression directions [100], [010], and [001], have been observed. About 20% bcc atoms have transformed to fcc phase under pressure just over the critical point, and under higher pressure the fraction of the fcc phase increases steadily to exceed that of the hcp phase. We have investigated the transition mechanism of iron from initial bcc to hcp/fcc and found that the transition mainly consists of compression, rotation, and shuffle.

  3. The hcp to fcc transformation path of scandium trihydride under high pressure.

    PubMed

    Pakornchote, T; Pinsook, U; Bovornratanaraks, T

    2014-01-15

    We used density functional theory to calculate the phase stability of the hcp (hexagonal close packed) and the fcc (face centered cubic) structures of ScH3. The hcp form is stable up to 22 GPa according to the generalized gradient approximation calculation. Then the fcc form becomes energetically more stable. In order to provide insight into the phase transition mechanism, we modeled the hcp to fcc transition by sliding the hcp basal planes, i.e. (001)h planes, in such a way that the ABABAB sequence of the hcp form is altered into the ABCABC sequence of the fcc form. This sliding was suggested by the experiment. The configurations of these sliding steps are our proposed intermediate configurations, whose symmetry group is the Cm group. By using the Cm crystallography, we can match the d-spacings from the lattice planes of the hcp and fcc forms and the intermediate planes measured from the experiment. We also calculated the enthalpy per step, from which the energy barrier between the two phases at various pressures was derived. The barrier at 35 GPa is 0.370 eV per formula or 0.093 eV/atom. The movements of the hydrogen atoms during the hcp to intermediate phase transition are consistent with the result from the Raman spectra.

  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. Random hcp and fcc structures in thermoresponsive microgel crystals.

    PubMed

    Brijitta, J; Tata, B V R; Joshi, R G; Kaliyappan, T

    2009-08-21

    Monodisperse thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles having a diameter of 520 nm were synthesized by free-radical precipitation polymerization and centrifuged to obtain a concentrated suspension. The centrifuged mother suspension was made to self-order into a crystalline state by repeated annealing beyond the volume phase transition (VPT) of the particles. We report here the three-dimensional (3D) real space structure, determined using a confocal laser scanning microscope, of PNIPAM microgel crystal samples prepared by two different recrystallized routes: (1) solidifying a shear melted colloidal liquid (referred as as-prepared sample) and (2) slow cooling of a colloidal liquid (referred as recrystallized sample). We have recorded images of several regions of the crystal with each region containing 15 horizontal crystal planes for determining the in-plane [two-dimensional (2D)] and 3D pair-correlation functions. The 2D pair-correlation function g(r) revealed hexagonal long-range order of particles in the layers with a lattice constant of 620 nm. The analysis of stacking sequence of layers recorded on as-prepared sample has revealed the existence of stacking disorder with an average stacking probability alpha approximately 0.42. This value of alpha together with the analysis of 3D pair-correlation function determined from particle positions revealed the structure of microgel crystals in the as-prepared sample to be random hexagonal close packing. We report the first observation of a split second peak in the 3D g(r) of the microgel crystals obtained from a shear melted liquid. Upon melting the sample above VPT and recrystallizing it the split second peak disappeared and the crystals are found to have a face centered cubic (fcc) structure with alpha approximately 0.95. From simulations, the split second peak is shown to arise from the displacement of some of the B-planes from the ideal hcp positions. The present results are discussed in

  6. Appropriate deposition parameters for formation of fcc Co-Ni alloy nanowires during electrochemical deposition process

    NASA Astrophysics Data System (ADS)

    Mukhtar, Aiman; Shahzad Khan, Babar; Mehmood, Tahir

    2016-12-01

    The effect of deposition potential on the crystal structure and composition of Co-Ni alloy nanowires is studied by XRD, FE-SEM and EDX. The alloy nanowires deposited at -3.2 V are metastable fcc phase Co-Ni. The alloy nanowires deposited at -1.8 V are hcp phase Co-Ni. The formation of the metastable fcc alloy nanowires can be attributed to smaller critical clusters formed at the high potential as the smaller critical clusters favor fcc structure because of the significant surface energy effect. The content of Co inside nanowires increases with increasing potential. This can be understood by the polarization curves of depositing Co and Ni nanowires, which show that the current density ratio of Ni to Co at low potential has larger value than that at high potential.

  7. 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

    2013-11-06

    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.

  8. Preparation and characterization of Co single-crystal thin films with hcp, fcc and bcc structures

    SciTech Connect

    Ohtake, Mitsuru; Yabuhara, Osamu; Higuchi, Jumpei; Futamoto, Masaaki

    2011-04-01

    Co crystals with three different structures are realized in the form of single-crystal thin films hetero-epitaxially grown on single-crystal substrates by ultrahigh vacuum rf magnetron sputtering. hcp-, fcc-, and bcc-Co single-crystal films are formed on Cr(211){sub bcc}, Cu(100){sub fcc}, and GaAs(110){sub B3}, respectively. The film growth process is studied by RHEED, and the lattice constants of these Co films are determined by x-ray diffraction. The magnetization properties of these thin films are reflecting the magnetocrystalline anisotropies of Co crystals with the easy magnetization axes along hcp<0001>, fcc<111>, and bcc<100> directions.

  9. Interdiffusion and Diffusion Mobility for fcc Ni-Co-Al Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zhu, Naqiong; Wang, Hao; Lu, Xiao-Gang

    2016-12-01

    Ternary fcc Ni-Co-Al diffusion couples annealed at 1173 K (900 °C), 1373 K (1100 °C), and 1573 K (1300 °C) have been studied by using electron probe microanalysis. The interdiffusion coefficients were extracted using the Sauer-Freise and Whittle-Green methods from the measured concentration profiles of binary and ternary diffusion couples, respectively. Based on the diffusion coefficients reported in the literature and those determined in the present work, the diffusion mobilities for fcc Ni-Co-Al alloys were assessed. In general, reasonable agreements were reached and the resulted mobility database can be used to study the diffusion behavior of the ternary fcc Ni-Co-Al alloys in a wide composition range.

  10. Hydrodynamics and catalytic reactions in the riser of a FCC plant

    SciTech Connect

    Derouin, C.; van Landeghem, F.; Turlier, P.; Bernard, J.R.

    1996-12-31

    The hydrodynamic characteristics of the riser of a FCC plants are investigated in a cold pilot plant. The results are checked and completed with measurements made in real operating FCC units. In both cases, tracing of the gas, velocity probes and {gamma}-tomography were used. The gas and solid velocity profiles are described by using a plug flow model with radial dispersion. The gas velocity profile is formally represented by an Ostwald - de Waele type equation; the radial and axial solid concentration profile is fitted to data obtained in the real plant. The kinetics of the reactions occurring during catalytic cracking are investigated in a MAT equipment and are represented by a 19 lumps model including deactivation by coking of the catalyst. A combination of this reaction model with the hydrodynamic model is able to predict with a satisfactory precision the yields of the different product families obtained in an industrial FCC unit. 12 refs., 3 tabs.

  11. Reducing the formation of FIB-induced FCC layers on Cu-Zn-Al austenite.

    PubMed

    Zelaya, Eugenia; Schryvers, Dominique

    2011-01-01

    The irradiation effects of thinning a sample of a Cu-Zn-Al shape memory alloy to electron transparency by a Ga(+) focused ion beam were investigated. This thinning method was compared with conventional electropolishing and Ar(+) ion milling. No implanted Ga was detected but surface FCC precipitation was found as a result of the focused ion beam sample preparation. Decreasing the irradiation dose by lowering the energy and current of the Ga(+) ions did not lead to a complete disappearance of the FCC structure. The latter could only be removed after gentle Ar(+) ion milling of the sample. It was further concluded that the precipitation of the FCC is independent of the crystallographic orientation of the surface.

  12. Kinetics study of crystallization with the disorder-bcc-fcc phase transition of charged colloidal dispersions.

    PubMed

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Du, Xuan; Liu, Lixia

    2011-06-21

    Structure transformation (disorder-bcc-fcc) in charged colloidal dispersions, as a manifestation of the Ostwald's step rule, was confirmed by means of reflection spectrum (RS) measurements in our previous study. By taking advantage of a reflection spectrum containing plenty of information about the crystallization behaviors, time-dependent changes of parameters associated with the crystal structure and composition during the disorder-bcc-fcc transition are reported by treating the data from RS in this article. In addition, Avrami's model is adopted to analyze the transition process and investigate the transition rate. On the basis of the above investigations, associated kinetic features of crystallization with the disorder-bcc-fcc transition are described.

  13. Interdiffusion and Diffusion Mobility for fcc Ni-Co-Al Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zhu, Naqiong; Wang, Hao; Lu, Xiao-Gang

    2017-03-01

    Ternary fcc Ni-Co-Al diffusion couples annealed at 1173 K (900 °C), 1373 K (1100 °C), and 1573 K (1300 °C) have been studied by using electron probe microanalysis. The interdiffusion coefficients were extracted using the Sauer-Freise and Whittle-Green methods from the measured concentration profiles of binary and ternary diffusion couples, respectively. Based on the diffusion coefficients reported in the literature and those determined in the present work, the diffusion mobilities for fcc Ni-Co-Al alloys were assessed. In general, reasonable agreements were reached and the resulted mobility database can be used to study the diffusion behavior of the ternary fcc Ni-Co-Al alloys in a wide composition range.

  14. Correlation-induced anomalies and extreme sensitivity in fcc-Pu

    SciTech Connect

    Chen, Shao-ping

    2008-01-01

    We have used GGA + U density functional theory to study the effects of correlation on the properties of fcc Pu. We found that the structural and elastic properties of fcc-Pu are highly sensitive to the Hubbard U parameter. Within an interval of 0.05 eV of the U parameter, the equilibrium lattice constants of fcc-Pu can change from 0.42 to 0.47 nm. While the bulk modulus can drop by a factor of 5 to 10. The pressure derivative, dB/dp, of the bulk modulus can rise dramatically from 5 to 15 and then drop to the negative values before recovering to the more normal values. These observations are partially supported by existing experiments and the prediction of a negative dB/dp need to be tested in future experiments.

  15. Progress towards next generation hadron colliders: FCC-hh, HE-LHC, and SPPC

    NASA Astrophysics Data System (ADS)

    Zimmermann, Frank; EuCARD-2 Extreme Beams Collaboration; Future Circular Collider (FCC) Study Collaboration

    2017-01-01

    A higher-energy circular proton collider is generally considered to be the only path available in this century for exploring energy scales well beyond the reach of the Large Hadron Collider (LHC) presently in operation at CERN. In response to the 2013 Update of the European Strategy for Particle Physics and aligned with the 2014 US ``P5'' recommendations, the international Future Circular Collider (FCC) study, hosted by CERN, is designing such future frontier hadron collider. This so-called FCC-hh will provide proton-proton collisions at a centre-of-mass energy of 100 TeV, with unprecedented luminosity. The FCC-hh energy goal is reached by combining higher-field, 16 T magnets, based on Nb3Sn superconductor, and a new 100 km tunnel connected to the LHC complex. In addition to the FCC-hh proper, the FCC study is also exploring the possibility of a High-Energy LHC (HE-LHC), with a centre-of-mass energy of 25-27 TeV, as could be achieved in the existing 27 km LHC tunnel using the FCC-hh magnet technology. A separate design effort centred at IHEP Beijing aims at developing and constructing a similar collider in China, with a smaller circumference of about 54 km, called SPPC. Assuming even higher-field 20 T magnets, by relying on high-temperature superconductor, the SPPC could reach a c.m. energy of about 70 TeV. This presentation will report the motivation and the present status of the R&D for future hadron colliders, a comparison of the three designs under consideration, the major challenges, R&D topics, the international technology programs, and the emerging global collaboration. Work supported by the European Commission under Capacities 7th Framework Programme project EuCARD-2, Grant Agreement 312453, and the HORIZON 2020 project EuroCirCol, Grant Agreement 654305.

  16. Effects of Co doping on the metamagnetic states of the ferromagnetic fcc Fe-Co alloy.

    PubMed

    Ortiz-Chi, Filiberto; Aguayo, Aarón; de Coss, Romeo

    2013-01-16

    The evolution of the metamagnetic states in the ferromagnetic face centered cubic (fcc) Fe(1-x)Co(x) alloy as a function of Co concentration has been studied by means of first-principles calculations. The ground state properties were obtained using the full-potential linear augmented plane wave method and the generalized gradient approximation for the exchange-correlation functional. The alloying was modeled using the virtual crystal approximation and the magnetic states were obtained from the calculations of the total energy as a function of the spin moment, using the fixed spin moment method. For ferromagnetic fcc Fe, the binding-energy curve shows metamagnetic behavior, with two minima corresponding to a small-volume, low-spin (LS) state and a large-volume, high-spin (HS) state, which are separated by a small energy (E(LS) ≲ E(HS)). The evolution of the magnetic moment, the exchange integral (J), and the binding-energy curve is analyzed in the whole range of Co concentrations (x). The magnetic moment corresponding to the HS state decreases monotonically from 2.6 μ(B)/atom in fcc Fe to 1.7 μ(B)/atom in fcc Co. In contrast, the exchange integral for the HS state shows a maximum at around x = 0.45. The thermal dependence of the lattice parameter is evaluated with a method based on statistical mechanics using the binding-energy curve as an effective potential. It is observed that the behavior of the lattice parameter with temperature is tuned by Co doping, from negative thermal expansion in fcc Fe to positive thermal expansion in fcc Co, through the modification of the energetics of the metamagnetic states.

  17. Observation of the fcc-to-hcp transition in ensembles of argon nanoclusters.

    PubMed

    Krainyukova, N V; Boltnev, R E; Bernard, E P; Khmelenko, V V; Lee, D M; Kiryukhin, V

    2012-12-14

    Macroscopic ensembles of weakly interacting argon nanoclusters are studied using x-ray diffraction in low vacuum. As the clusters grow by fusion with increasing temperature, their structure transforms from essentially face-centered cubic (fcc) to hexagonal close packed as the cluster size approaches ~10(5) atoms. The transformation involves intermediate orthorhombic phases. These data confirm extant theoretical predictions. They also indicate that growth kinetics and spatial constraints might play an important role in the formation of the fcc structure of bulk rare-gas solids, which still remains puzzling.

  18. Magnetic phases of fcc Fe films in the 5{endash}11 monolayer thickness range

    SciTech Connect

    Escorcia-Aparicio, E.J.; Choi, H.J.; Kawakami, R.K.; Qiu, Z.Q.

    1998-07-01

    Using the methods of artificial roughening and interfacial doping, we investigated the effects of film roughness and interdiffusion on the formation of the magnetic phase of the fcc Fe film in the Fe/Co/Cu(100) system. We found that it is the degree of film roughness that determines the magnetic phase of the fcc Fe film in the 5{endash}11 monolayer thickness range, and that the interdiffusion plays no appreciable role in the formation of the magnetic phase. {copyright} {ital 1998} {ital The American Physical Society}

  19. Dislocation Multiplication by Single Cross Slip for FCC at Submicron Scales

    NASA Astrophysics Data System (ADS)

    Cui, Yi-Nan; Liu, Zhan-Li; Zhuang, Zhuo

    2013-04-01

    The operation mechanism of single cross slip multiplication (SCSM) is investigated by studying the response of one dislocation loop expanding in face-centered-cubic (FCC) single crystal using three-dimensional discrete dislocation dynamic (3D-DDD) simulation. The results show that SCSM can trigger highly correlated dislocation generation in a short time, which may shed some light on understanding the large strain burst observed experimentally. Furthermore, we find that there is a critical stress and material size for the operation of SCSM, which agrees with that required to trigger large strain burst in the compression tests of FCC micropillars.

  20. Effects of Dynamic Impact Loading on Microstructure of FCC (TWIP) Steel

    DTIC Science & Technology

    2014-08-01

    Gazder, 2011, Texture evolution of cold rolled and annealed Fe-24 Mn-3 Al-2Si-1Ni-0.06C TWIP steel , Mater Sci. Eng. A, 528, 4537-4549. 13. J.K. Kim, L...representatively in the current investigation. Figure 9(a) shows the typical rolling texture components in FCC alloys [12] as reference, consisting of ideal...Figure 9: (1 1 1) pole figures of the (a) ideal rolling texture components in FCC materials, and (b) original, (c) Specimen 1, (d) Specimen 2, (e

  1. Beam-beam and electron cloud effects in CEPC/FCC-ee

    NASA Astrophysics Data System (ADS)

    Ohmi, Kazuhito

    2016-11-01

    We discuss beam dynamics issues in CEPC/FCC-ee, especially focusing on the beam-beam and electron cloud effects. Beamstrahlung is strong in extreme high energy collision such as Higgs and top factory. Beam-beam simulations considering beamstrahlung are now ready. Several points of beam-beam effects for FCC-ee are presented. Electron cloud effects are serious for high current positron machine, especially in Z factory that many bunches are stored. Analytical estimate for threshold of electron density and electron build-up for CEPC are presented.

  2. Fcc r arrow bct phase transition in Th at extreme compressions: Theory

    SciTech Connect

    Eriksson, O. ); Soederlind, P. ); Wills, J.M. )

    1992-06-01

    The experimentally observed fcc{r arrow}bct crystallographic phase transition in Th, at {similar to}1 Mbar, is reproduced by means of full-potential, linear-muffin-tin-orbitals calculations. Both the calculated volume and pressure for which the transition occurs, agrees with the experimental data. The calculated pressure dependence of the {ital c}/{ital a} ratio of the bct structure is also in good agreement wtih experimental data. Calculations for La predict the fcc phase to be stable over the bct phase up to {similar to}7 Mbar.

  3. Micromagnetic simulations of interacting dipoles on an fcc lattice: application to nanoparticle assemblies.

    PubMed

    Plumer, M L; van Lierop, J; Southern, B W; Whitehead, J P

    2010-07-28

    Micromagnetic simulations are used to examine the effects of cubic and axial anisotropy, magnetostatic interactions and temperature on M-H loops for a collection of magnetic dipoles on fcc and sc lattices. We employ a simple model of interacting dipoles that represent single-domain particles in an attempt to explain recent experimental data on ordered arrays of magnetoferritin nanoparticles that demonstrate the crucial role of interactions between particles in an fcc lattice. Significant agreement between the simulation and experimental results is achieved, and the impact of intra-particle degrees of freedom and surface effects on thermal fluctuations is investigated.

  4. Molecular dynamics study of melting and fcc-bcc transitions in Xe.

    PubMed

    Belonoshko, A B; Ahuja, R; Johansson, B

    2001-10-15

    We have investigated the phase diagram of Xe over a wide pressure-temperature range by molecular dynamics. The calculated melting curve is in good agreement with earlier experimental data. At a pressure of around 25 GPa and a temperature of about 2700 K we find a triple fcc-bcc liquid point. The calculated fcc-bcc boundary is in nice agreement with the experimental points, which, however, were interpreted as melting. This finding suggests that the transition from close-packed to bcc structure might be more common at high pressure and high temperature than was previously anticipated.

  5. 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... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  6. 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... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  7. 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... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  8. 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... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  9. 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... You Need to Know § 95.219 (R/C Rule 19) How do I answer correspondence from the FCC? (a) If it...

  10. 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.

  11. Relative stability of the FCC and HCP polymorphs with interacting polymers.

    PubMed

    Mahynski, Nathan A; Kumar, Sanat K; Panagiotopoulos, Athanassios Z

    2015-01-14

    Recent work [Mahynski et al., Nat. Commun., 2014, 5, 4472] has demonstrated that the addition of long linear homopolymers thermodynamically biases crystallizing hard-sphere colloids to produce the hexagonal close-packed (HCP) polymorph over the closely related face-centered cubic (FCC) structure when the polymers and colloids are purely repulsive. In this report, we investigate the effects of thermal interactions on each crystal polymorph to explore the possibility of stabilizing the FCC crystal structure over the HCP. We find that the HCP polymorph remains at least as stable as its FCC counterpart across the entire range of interactions we explored, where interactions were quantified by the reduced second virial coefficient, -1.50 < B < 1.01. This metric conveniently characterizes the crossover from entropically to energetically dominated systems at B ≈ 0. While the HCP relies on its octahedral void arrangement for enhanced stability when B > 0, its tetrahedral voids produce a similar effect when B < 0 (i.e. when energetics dominate). Starting from this, we derive a mean-field expression for the free energy of an infinitely-dilute polymer adsorbed in the crystal phase for nonzero B. Our results reveal that co-solute biasing of a single polymorph can still be observed in experimentally realizable scenarios when the colloids and polymers have attractive interactions, and provide a possible explanation for the experimental finding that pure FCC crystals are elusive in these binary mixtures.

  12. Interface effect of magnetic properties in Ni nanoparticles with a hcp core and fcc shell structure.

    PubMed

    Choo, Seongmin; Lee, Kyujoon; Jo, Younghun; Yoon, Seon-Mi; Choi, Jae-Young; Kim, Jea-Young; Park, Jea-Hoon; Lee, Kyung-Jin; Lee, Jong-Heun; Jung, Myung-Hwa

    2011-07-01

    We have fabricated hexagonal close-packed (hcp) Ni nanoparticles covered by a face-centered cubic (fcc) Ni surface layer by polyol method. The magnetic properties have been investigated as a function of temperature and applied magnetic field. The magnetic behavior reveals that the system should be divided magnetically into three distinct phases with different origins. The fcc Ni phase on the shell contributes to the superparamagnetism through a wide temperature range up to 360 K. The hcp Ni phase at the core is associated with antiferromagnetic nature below 12 K. These observations are in good agreement with the X-ray absorption spectroscopy and magnetic circular dichroism measurements. In our particular case, the unique hcp core and fcc shell structure gives rise to an additional anomaly at 20 K in the zero-field-cooled magnetization curve. Its position is barely affected by the magnetic field but its structure disappears above 30 kOe, showing a metamagnetic transition in the magnetization versus magnetic field curve. This new phase originates from the magnetic exchange at the interface between the hcp and fcc Ni sublattices.

  13. 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

  14. 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.

  15. Special Report: FCC Program Offers Schools and Libraries Steep Telecommunications Discounts.

    ERIC Educational Resources Information Center

    Crowe, Thomas K.

    1998-01-01

    In the Telecommunications Act of 1996, Congress directed the Federal Communications Commission (FCC) to establish the Universal Service program to provide financial support for communications services for all K-12 schools/libraries. A Washington telecommunications attorney discusses eligible services and the application process, and offers tips…

  16. 47 CFR 2.956 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false FCC inspection and submission of equipment for testing. 2.956 Section 2.956 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  17. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false FCC inspection and submission of equipment for testing. 2.1076 Section 2.1076 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  18. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false FCC inspection and submission of equipment for testing. 2.1076 Section 2.1076 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  19. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false FCC inspection and submission of equipment for testing. 2.1076 Section 2.1076 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  20. 47 CFR 2.956 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false FCC inspection and submission of equipment for testing. 2.956 Section 2.956 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  1. 47 CFR 2.956 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false FCC inspection and submission of equipment for testing. 2.956 Section 2.956 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  2. 47 CFR 2.956 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false FCC inspection and submission of equipment for testing. 2.956 Section 2.956 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  3. 47 CFR 2.1076 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false FCC inspection and submission of equipment for testing. 2.1076 Section 2.1076 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  4. 47 CFR 2.956 - FCC inspection and submission of equipment for testing.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false FCC inspection and submission of equipment for testing. 2.956 Section 2.956 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization...

  5. 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…

  6. 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.

  7. Broadcast Access and Reply Rights for Politicians and PACs: A Continuing Headache for the FCC.

    ERIC Educational Resources Information Center

    Gentry, Richard H.

    The major policy issues raised by Federal Communications Commission (FCC) regulations with regard to the year-round nature of political media campaigns and the emergence of political action committees (PACs) are explored in this paper. The first part of the paper introduces the major policy issues, specifically who should have an affirmative right…

  8. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... must be followed by EAS Participants' personnel, emergency officials, and National Weather Service (NWS... are consistent with national plans, FCC regulations, and EAS operation. (a) The State plan contains... transmitted to all EAS Participants who provide services in the state, and must include specific and...

  9. 47 CFR 11.21 - State and Local Area plans and FCC Mapbook.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... must be followed by EAS Participants' personnel, emergency officials, and National Weather Service (NWS... are consistent with national plans, FCC regulations, and EAS operation. (a) The State plan contains... transmitted to all EAS Participants who provide services in the state, and must include specific and...

  10. 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 §...

  11. 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 §...

  12. 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 §...

  13. 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 §...

  14. 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

    2016-06-08

    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. FCC catalysts containing shape-selective zeolites boost gasoline octaine number and yield

    SciTech Connect

    Yanik, S.J.; Campagna, R.J.; Demmel, E.J.; Humphries, A.P.

    1985-05-13

    This article reviews the results of laboratory and commercial testing by Filtrol of a shape-selective, zeolite-containing catalyst that can increase the octane of fluid catalytic cracker (FCC) gasoline by 1 to 6 numbers with increased yield of gasoline and alkylate.

  16. Carbon flow analysis and Carbon emission reduction of FCC in Chinese oil refineries

    NASA Astrophysics Data System (ADS)

    Jia, Fengrui; Wei, Na; Ma, Danzhu; Liu, Guangxin; Wu, Ming; Yue, Qiang

    2017-08-01

    The major problem of the energy production in oil refineries is the high emission of CO2 in China. The fluid catalytic cracking unit (FCC) is the key source of carbon emission in the oil refineries. According to the statistical data, the carbon emission of FCC unit accounts for more than 31% for the typical oil refineries. The carbon flow of FCC in the typical Chinese oil refineries were evaluated and analysed, which aimed at the solution of CO2 emission reduction. The method of substances flow analysis (SFA) and the mathematical programming were used to evaluate the carbon metabolism and optimize the carbon emission. The results indicated that the combustion emission of the reaction-regeneration subsystem (RRS) was the major source of FCC. The quantity of CO2 emission of RSS was more than 90%. The combustion efficiency and the amount of residual oil affected the carbon emission of RRS most according to the optimized analysis of carbon emission reduction. Moreover, the fractionation subsystem (TFS) had the highest environmental efficiency and the absorption-stabilization subsystem (ASS) had the highest resource efficiency (approximately to 1) of carbon.

  17. 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.

  18. Double Higgs production at FCC-he and prospects for measurements of self-coupling

    NASA Astrophysics Data System (ADS)

    Kumar, Mukesh; Ruan, Xifeng; Cornell, Alan S.; Islam, Rashidul; Mellado, Bruce

    2015-06-01

    The measurement of the triple Higgs boson coupling is one of the most important goals of the Higgs physics program in present and future collider experiments. This would provide the first direct information on the Higgs potential, which is responsible for electroweak symmetry breaking mechanism. We present a double Higgs production scenario at the Large Hadron-Electron Collider (LHeC) and Future Circular Hadron-Electron Collider (FCC- he) through e-p collisions, which will provide information about trilinear coupling and the possibility of probing new physics, if there is any. The LHeC will provide e- beams to collide head-on with proton beams of 7 TeV from the Large Hadron Collider (LHC). The prospect of replacing the LHC with the high energy FCC, with proton beams of 50 TeV, is used for FCC-he studies. Energy of the e- is taken to be 60 GeV for both LHeC and FCC-he. Effects of non-standard CP-even and CP-odd couplings for hhh, hWW and hhWW have been studied and constrained at a 95% C.L.

  19. 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…

  20. Workhardening correlations based on state variables in some FCC metals in monotonic loading

    NASA Astrophysics Data System (ADS)

    Korhonen, M. A.; Hannula, S.-P.; Li, Che-Yu

    1985-03-01

    This paper reports an investigation of the workhardening properties of 316 stainless steel, commercial purity aluminum, and OFHC copper at room temperature by using a state-variable approach. Based on the results of experiments, it is proposed that a generalized workhardening correlation can be formulated by using two state variables only, the structural state parameter and the inelastic strain rate. Particularly, an absolute workhardening coefficient is proposed to be a product of two parts. The athermal part, which is structure dependent only, will be approached at low homologous temperatures and/or high strain rates, while the strain rate sensitive part describes a dynamic recovery contribution at high homologous temperatures and/or low strain rates. Correspondingly, based on this approach a new way of separating thermal and athermal contributions to workhardening rate are suggested. Moreover, it is shown that a single master curve can be constructed to display the dependence of workhardening coefficient on structure and strain rate.

  1. The effect of size on the strength of FCC metals at elevated temperatures: annealed copper.

    PubMed

    Wheeler, Jeffrey M; Kirchlechner, Christoph; Micha, Jean-Sébastien; Michler, Johann; Kiener, Daniel

    2016-12-01

    As the length scale of sample dimensions is reduced to the micron and sub-micron scales, the strength of various materials has been observed to increase with decreasing size, a fact commonly referred to as the 'sample size effect'. In this work, the influence of temperature on the sample size effect in copper is investigated using in situ microcompression testing at 25, 200 and 400 °C in the SEM on vacuum-annealed copper structures, and the resulting deformed structures were analysed using X-ray μLaue diffraction and scanning electron microscopy. For pillars with sizes between 0.4 and 4 μm, the size effect was measured to be constant with temperature, within the measurement precision, up to half of the melting point of copper. It is expected that the size effect will remain constant with temperature until diffusion-controlled dislocation motion becomes significant at higher temperatures and/or lower strain rates. Furthermore, the annealing treatment of the copper micropillars produced structures which yielded at stresses three times greater than their un-annealed, FIB-machined counterparts.

  2. The effect of size on the strength of FCC metals at elevated temperatures: annealed copper

    PubMed Central

    Wheeler, Jeffrey M.; Kirchlechner, Christoph; Micha, Jean-Sébastien; Michler, Johann; Kiener, Daniel

    2016-01-01

    Abstract As the length scale of sample dimensions is reduced to the micron and sub-micron scales, the strength of various materials has been observed to increase with decreasing size, a fact commonly referred to as the ‘sample size effect’. In this work, the influence of temperature on the sample size effect in copper is investigated using in situ microcompression testing at 25, 200 and 400 °C in the SEM on vacuum-annealed copper structures, and the resulting deformed structures were analysed using X-ray μLaue diffraction and scanning electron microscopy. For pillars with sizes between 0.4 and 4 μm, the size effect was measured to be constant with temperature, within the measurement precision, up to half of the melting point of copper. It is expected that the size effect will remain constant with temperature until diffusion-controlled dislocation motion becomes significant at higher temperatures and/or lower strain rates. Furthermore, the annealing treatment of the copper micropillars produced structures which yielded at stresses three times greater than their un-annealed, FIB-machined counterparts. PMID:28003795

  3. 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.

  4. An analysis of key characteristics of the Frank-Read source process in FCC metals

    NASA Astrophysics Data System (ADS)

    Xu, Shuozhi; Xiong, Liming; Chen, Youping; McDowell, David L.

    2016-11-01

    A well-known intragranular dislocation source, the Frank-Read (FR) source plays an important role in size-dependent dislocation multiplication in crystalline materials. Despite a number of studies in this topic, a systematic investigation of multiple aspects of the FR source in different materials is lacking. In this paper, we employ large scale quasistatic concurrent atomistic-continuum (CAC) simulations to model an edge dislocation bowing out from an FR source in Cu, Ni, and Al. First, a number of quantities that are important for the FR source process are quantified in the coarse-grained domain. Then, two key characteristics of the FR source, including the critical shear stress and critical dislocation configuration, are investigated. In all crystalline materials, the critical stresses and the aspect ratio of the dislocation half-loop height to the FR source length scale well with respect to the FR source length. In Al, the critical stress calculated by CAC simulations for a given FR source length agrees reasonably well with a continuum model that explicitly includes the dislocation core energy. Nevertheless, the predictions of the isotropic elastic theory do not accurately capture the FR source responses in Cu and Ni, which have a relatively large stacking fault width and elastic anisotropy. Our results highlight the significance of directly simulating the FR source activities using fully 3D models and shed light on developing more accurate continuum models.

  5. 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.

  6. Surface Vibrations and (2x1) Superstructures on FCC(110) Metal Surfaces.

    DTIC Science & Technology

    1986-06-01

    1 /2 a -. twhere a and a, are the phonon creation and annihilation operators which A obey the com..utation relations [a,,a ,] = and M (L , k ) is...dynamical matrix given by D(Q,, ;L , k ;L’, k ’) = Y e(C, K ; ’, k ’),z [ M (Lzk) M (L k ’ )] 1 /2 exp-i, .(( , k )-9(i’, k ) 5(5) where is the force constant matrix.25 With...normalized effective charge field V*(Lzk) as, S( ) to t( 1 + n(w)) g(j, fv*(Lz, k )V), (6)

  7. High Temperature Properties of the Fcc Metallic Crystals in the Anharmonic Approximation

    DTIC Science & Technology

    2001-01-01

    interactions were approximated by the Morse and Lennard - Jones pair potential functions. Unfortunately, the parameters of these potentials were...Au) we take as a model of interatomic interactions the (alpha,m) Buckingham, (n,m) Lennard - Jones and (alpha,beta) Morse pair potentials with the

  8. 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.

  9. FCC-HCP coexistence in dense thermo-responsive microgel crystals

    NASA Astrophysics Data System (ADS)

    Karthickeyan, D.; Joshi, R. G.; Tata, B. V. R.

    2017-06-01

    Analogous to hard-sphere suspensions, monodisperse thermo-responsive poly (N-isopropyl acrylamide) (PNIPAM) microgel particles beyond a volume fraction (ϕ) of 0.5 freeze into face centered cubic (FCC)-hexagonal close packed (HCP) coexistence under as prepared conditions and into an FCC structure upon annealing. We report here FCC-HCP coexistence to be stable in dense PNIPAM microgel crystals (ϕ > 0.74) with particles in their deswollen state (referred to as osmotically compressed microgel crystals) and the FCC structure with particles in their swollen state by performing annealing studies with different cooling rates. The structure of PNIPAM microgel crystals is characterized using static light scattering technique and UV-Visible spectroscopy and dynamics by dynamic light scattering (DLS). DLS studies reveal that the particle motion is diffusive at short times in crystals with ϕ < 0.74 and sub-diffusive at short times in PNIPAM crystals with ϕ > 0.74. The observed sub-diffusive behavior at short times is due to the overlap (interpenetration) of the dangling polymer chains between the shells of neighbouring PNIPAM microgel particles. Overlap is found to disappear upon heating the crystals well above their melting temperature, Tm due to reduction in the particle size. Annealing studies confirm that the overlap of dangling polymer chains between the shells of neighbouring PNIPAM spheres is responsible for the stability of FCC-HCP coexistence observed in osmotically compressed PNIPAM microgel crystals. Results are discussed in the light of recent reports of stabilizing the HCP structure in hard sphere crystals by adding interacting polymer chains.

  10. 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.

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  14. Multiscale calculations of dislocation bias in fcc Ni and bcc Fe model lattices

    NASA Astrophysics Data System (ADS)

    Chang, Z.; Olsson, P.; Terentyev, D.; Sandberg, N.

    2015-06-01

    In order to gain more insights on void swelling, dislocation bias is studied in this work. Molecular static simulations with empirical potentials are applied to map the dislocation-point defects interaction energies in both fcc Ni and bcc Fe model lattices. The interaction energies are then used to numerically solve the diffusion equation and obtain the dislocation bias. The importance of the dislocation core region is studied under a the temperature range 573-1173 K and the dislocation densities 1012-1015m-2 . The results show that larger dislocation bias is found in the fcc Ni than in the bcc Fe under different temperatures and dislocation densities. The anisotropic interaction energy model is used to obtain the dislocation bias and the result is compared to that obtained using the atomistic interaction model, the contribution from the core structure is then shown in both the Ni lattice and the Fe lattice.

  15. Spin waves in the fcc lattice antiferromagnet: competing interactions, frustration, and instabilities in the Hubbard model

    NASA Astrophysics Data System (ADS)

    Singh, Avinash; Mohapatra, Shubhajyoti; Ziman, Timothy; Chatterji, Tapan

    2017-02-01

    Spin waves in the type-III ordered antiferromagnetic state of the frustrated t- t ' Hubbard model on the face-centred-cubic (fcc) lattice are calculated to investigate finite-U-induced competing interaction and frustration effects on magnetic excitations and instabilities. Particularly strong competing interactions generated due to the interplay of fcc lattice geometry and magnetic order result in significant spin wave softening. The calculated spin wave dispersion is found to be in qualitative agreement with the measured spin wave dispersion in the pyrite mineral MnS2 obtained from inelastic neutron scattering experiments. Instabilities to other magnetic orders (type I, type II, spiral, non-collinear), as signalled by spin wave energies turning negative, are also discussed.

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

    NASA Astrophysics Data System (ADS)

    Xu, Gaochi; Liu, Yajun; Kang, Zhitao

    2016-10-01

    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.

  17. 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.

  18. Stacking fault energy in FCC plutonium with multiple reference states in the modified embedded atom method

    NASA Astrophysics Data System (ADS)

    Valone, S. M.; Baskes, M. I.; Rudin, S. P.

    2012-03-01

    Basic concepts from the multi-reference state formalism for determining the functions for the modified embedded atom method (MEAM) are adopted to modeling elemental plutonium (Pu). In the case of elemental Pu, the focus is on the background electron density. Here we utilize a portion of the formalism that determines the structure of the background density necessary to capture correct phase ordering between fcc and ideal hcp crystal structures. The critical information comes from cold curves, that is the energy/volume relationships, for these phases. Practically speaking, the energy difference between these two phases determines the stacking fault energy of the material. At the same time, the simple monoclinic phase of elemental Pu also becomes higher in energy at the equilibrium volume of the fcc phase. The new model is based on first-principles electronic structure calculations and captures the basic phase ordering of those calculations.

  19. Realizing high magnetic moments in fcc Fe nanoparticles through atomic structure stretch.

    PubMed

    Baker, S H; Roy, M; Thornton, S C; Binns, C

    2012-05-02

    We describe the realization of a high moment state in fcc Fe nanoparticles through a controlled change in their atomic structure. Embedding Fe nanoparticles in a Cu(1-x)Au(x) matrix causes their atomic structure to switch from bcc to fcc. Extended x-ray absorption fine structure (EXAFS) measurements show that the structure in both the matrix and the Fe nanoparticles expands as the amount of Au in the matrix is increased, with the data indicating a tetragonal stretch in the Fe nanoparticles. The samples were prepared directly from the gas phase by co-deposition, using a gas aggregation source and MBE-type sources respectively for the nanoparticle and matrix materials. The structure change in the Fe nanoparticles is accompanied by a sharp increase in atomic magnetic moment, ultimately to values of ~2.5 ± 0.3 μ(B)/atom .

  20. First-principles study of the thermodynamics of hydrogen-vacancy interaction in fcc iron

    SciTech Connect

    Nazarov, R.; Hickel, T.; Neugebauer, J.

    2010-12-01

    The interaction of vacancies and hydrogen in an fcc iron bulk crystal was studied combining thermodynamic concepts with ab initio calculations and considering various magnetic structures. We show that up to six H atoms can be trapped by a monovacancy. All of the studied point defects (single vacancy, H in interstitial positions, and H-vacancy complexes) cause an anisotropic elastic field in antiferromagnetic fcc iron and significantly change the local and total magnetization of the system. The proposed thermodynamical model allows the determination of the equilibrium vacancy concentration and the concentration of dissolved hydrogen for a given temperature and H chemical potential in the reservoir. For H-rich conditions a dramatic increase in the vacancy concentration in the crystal is found.

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

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... areas , and Johnston Island (Islets East, Johnston, North and Sand) and Midway Island (Islets Eastern and Sand) in the Pacific Insular areas. In ITU Region 3, the amateur service is regulated by the FCC...

  2. Electronic and geometric structure of transition-metal nanoclusters

    SciTech Connect

    Jennison, D.R.; Schultz, P.A.; Sears, M.P.; Klitsner, T.

    1996-08-01

    A massively-parallel ab initio computer code, which uses Gaussian bases, pseudopotentials, and the local density approximation, permits the study of transition-metal systems with literally hundreds of atoms. We present total energies and relaxed geometries for Ru, Pd, and Ag clusters with N = 55, 135, and 140 atoms; we also used the DMOL code to study 13-atom Pd and Cu clusters, with and without hydrogen. The N = 55 and 135 clusters were chosen because of simultaneous cubo-octahedral (fcc) and icosahedral (icos) sub-shell closings, and we find icos geometries are preferred. Remarkably large compressions of the central atoms are observed for the icos structures (up to 6% compared with bulk interatomic spacings), while small core compressions ({approx} 1 %) are found for the fcc geometry. In contrast, large surface compressive relaxations are found for the fcc clusters ({approx} 2-3% in average nearest neighbor spacing), while the icos surface displays small compressions ({approx} 1%). Energy differences between icos and fcc are smallest for Pd, and for all systems the single-particle densities of states closely resembles bulk results. Calculations with N = 134 suggest slow changes in relative energy with N. Noting that the 135-atom fcc has a much more open surface than the icos, we also compare N = 140 icos and fcc, the latter forming an octahedron with close packed facets. These icos and fcc clusters have identical average coordinations and the octahedron is found to be preferred for Ru and Pd but not for Ag. Finally, we compare Harris functional and LDA energy differences on the N = 140 clusters, and find fair agreement only for Ag.

  3. Origin of the thermoreversible fcc-bcc transition in block copolymer solutions.

    PubMed

    Lodge, Timothy P; Bang, Joona; Park, Moon Jeong; Char, Kookheon

    2004-04-09

    The thermoreversible fcc-bcc transition in concentrated block copolymer micellar solutions is shown to be driven by decreases in the aggregation number as the solvent penetrates the core, leading to a softer intermicelle potential. Small-angle neutron scattering measurements in a dilute solution are used to quantify the temperature-dependent micellar characteristics. The observed phase boundary is in excellent agreement with recent simulations of highly branched star polymers.

  4. Strength of Dislocation Junctions in FCC-monocrystals with a [\\overline{1}11] Deformation Axis

    NASA Astrophysics Data System (ADS)

    Kurinnaya, R. I.; Zgolich, M. V.; Starenchenko, V. A.

    2017-07-01

    The paper examines all dislocation reactions implemented in FCC-monocrystals with axis deformation oriented in the [\\overline{1}11] direction. It identifies the fracture stresses of dislocation junctions depending on intersection geometry of the reacting dislocation loop segments. Estimates are produced for the full spectrum of reacting forest dislocations. The paper presents the statistical data of the research performed and identifies the share of long strong dislocation junctions capable of limiting the zone of dislocation shift.

  5. Ferromagnetism in fcc twinned 2.4 nm size Pd nanoparticles.

    PubMed

    Sampedro, B; Crespo, P; Hernando, A; Litrán, R; Sánchez López, J C; López Cartes, C; Fernandez, A; Ramírez, J; González Calbet, J; Vallet, M

    2003-12-05

    The onset of ferromagnetism has been experimentally observed in small Pd particles of average diameter 2.4 nm. High-resolution studies reveal that a high percentage of the fcc particle exhibits single and multiple twinning boundaries. The spontaneous magnetization close to 0.02 emu/g seems to indicate that only a small fraction of atoms holds a permanent magnetic moment and contributes to ferromagnetism. The possible origin of ferromagnetism is briefly discussed according to different models recently reported.

  6. Development of OCDMA system based on Flexible Cross Correlation (FCC) code with OFDM modulation

    NASA Astrophysics Data System (ADS)

    Aldhaibani, A. O.; Aljunid, S. A.; Anuar, M. S.; Arief, A. R.; Rashidi, C. B. M.

    2015-03-01

    The performance of the OCDMA systems is governed by numerous quantitative parameters such as the data rate, simultaneous number of users, the powers of transmitter and receiver, and the type of codes. This paper analyzes the performance of the OCDMA system using OFDM technique to enhance the channel data rate, to save power and increase the number of user of OSCDMA systems compared with previous hybrid subcarrier multiplexing/optical spectrum code division multiplexing (SCM/OSCDM) system. The average received signal to noise ratio (SNR) with the nonlinearity of subcarriers is derived. The theoretical results have been evaluated based on BER and number of users as well as amount of power saved. The proposed system gave better performance and save around -6 dBm of the power as well as increase the number of users twice compare to SCM/OCDMA system. In addition it is robust against interference and much more spectrally efficient than SCM/OCDMA system. The system was designed based on Flexible Cross Correlation (FCC) code which is easier construction, less complexity of encoder/decoder design and flexible in-phase cross-correlation for uncomplicated to implement using Fiber Bragg Gratings (FBGs) for the OCDMA systems for any number of users and weights. The OCDMA-FCC_OFDM improves the number of users (cardinality) 108% compare to SCM/ODCMA-FCC system.

  7. Comparing the structural stability of PbS nanocrystals assembled in fcc and bcc superlattice allotropes.

    PubMed

    Bian, Kaifu; Wang, Zhongwu; Hanrath, Tobias

    2012-07-04

    We investigated the structural stability of colloidal PbS nanocrystals (NCs) self-assembled into superlattice (SL) allotropes of either face-centered cubic (fcc) or body-centered cubic (bcc) symmetry. Small-angle X-ray scattering analysis showed that the NC packing density is higher in the bcc than in the fcc SL; this is a manifestation of the cuboctahedral shape of the NC building block. Using the high-pressure rock-salt/orthorhombic phase transition as a stability indicator, we discovered that the transition pressure for NCs in a bcc SL occurs at 8.5 GPa, which is 1.5 GPa higher than the transition pressure (7.0 GPa) observed for a fcc SL. The higher structural stability in the bcc SL is attributed primarily to the effective absorption of loading force in specific SL symmetry and to a lesser extent to the surface energy of the NCs. The experimental results provide new insights into the fundamental relationship between the symmetry of the self-assembled SL and the structural stability of the constituent NCs.

  8. Effect of Stacking Sequence on Surface Magnetism: Strained hcp Gd(0001) vs fcc Gd(111) Surface

    NASA Astrophysics Data System (ADS)

    Hong, S. C.; Freeman, A. J.

    1997-03-01

    Very recently, the distortion of the bulk bands of Gd was observed with angle resolved photoemission spectrocopy for Gd(0001) films grown on the corrugated Mo(112) surface(C. Waldfried, D.N. McIlroy, C.W. Hutchings, P.A. Dowben, private communication). To clarify the origin of this band distortion, first principles calculations have been done on hcp Gd(0001) and fcc Gd(111) with 2D lattice constants expanded by 20% using the highly precise full-potential linearized augmented plane wave (FLAPW) method(E. Wimmer, H. Krakauer, M. Weinert, and A.J. Freeman Phys. Rev. B24), 864 (1981).. The interlayer spacings were fully relaxed with atomic force and total energy calculations. We found that the strain does not distort the bulk bands significantly; for hcp Gd(0001), the spin magnetic moment(0.61 μ_B) of conduction electrons at the surface layer is enhanced by 13% compared to that (0.54 μ_B) of the bulk-like layer, but for the fcc Gd(111) the moment (0.65 μ_B) at the surface is reduced by 11% compared to that (0.72 μ_B) of the bulk-like layer. This unusal reduction of the magnetic moment at the fcc Gd(111) surface will be discused.

  9. A numerical investigation of the scale-up effects on flow, heat transfer, and kinetics processes of FCC units.

    SciTech Connect

    Chang, S. L.

    1998-08-25

    Fluid Catalytic Cracking (FCC) technology is the most important process used by the refinery industry to convert crude oil to valuable lighter products such as gasoline. Process development is generally very time consuming especially when a small pilot unit is being scaled-up to a large commercial unit because of the lack of information to aide in the design of scaled-up units. Such information can now be obtained by analysis based on the pilot scale measurements and computer simulation that includes controlling physics of the FCC system. A Computational fluid dynamic (CFD) code, ICRKFLO, has been developed at Argonne National Laboratory (ANL) and has been successfully applied to the simulation of catalytic petroleum cracking risers. It employs hybrid hydrodynamic-chemical kinetic coupling techniques, enabling the analysis of an FCC unit with complex chemical reaction sets containing tens or hundreds of subspecies. The code has been continuously validated based on pilot-scale experimental data. It is now being used to investigate the effects of scaled-up FCC units. Among FCC operating conditions, the feed injection conditions are found to have a strong impact on the product yields of scaled-up FCC units. The feed injection conditions appear to affect flow and heat transfer patterns and the interaction of hydrodynamics and cracking kinetics causes the product yields to change accordingly.

  10. Quantum and isotope effects in lithium metal

    NASA Astrophysics Data System (ADS)

    Ackland, Graeme J.; Dunuwille, Mihindra; Martinez-Canales, Miguel; Loa, Ingo; Zhang, Rong; Sinogeikin, Stanislav; Cai, Weizhao; Deemyad, Shanti

    2017-06-01

    The crystal structure of elements at zero pressure and temperature is the most fundamental information in condensed matter physics. For decades it has been believed that lithium, the simplest metallic element, has a complicated ground-state crystal structure. Using synchrotron x-ray diffraction in diamond anvil cells and multiscale simulations with density functional theory and molecular dynamics, we show that the previously accepted martensitic ground state is metastable. The actual ground state is face-centered cubic (fcc). We find that isotopes of lithium, under similar thermal paths, exhibit a considerable difference in martensitic transition temperature. Lithium exhibits nuclear quantum mechanical effects, serving as a metallic intermediate between helium, with its quantum effect-dominated structures, and the higher-mass elements. By disentangling the quantum kinetic complexities, we prove that fcc lithium is the ground state, and we synthesize it by decompression.

  11. Ultrahigh hardness on a face-centered cubic metal

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenyu; Huang, Siling; Chen, Leilei; Wang, Bo; Wen, Bin; Zhang, Bi; Guo, Dongming

    2017-09-01

    Nanotwinned (NT) surfaces are developed on a face-centered cubic (fcc) metal with ultrahigh hardness under cyclic loading using plastic deformation at room temperature. The hardness on NT surfaces remains constant at 7.9 and 8.5 GPa indented at 1 and 7 N under 0-100 cycles respectively, which are about three times that of their pristine surfaces. This is different from the NT metals and nonmetallic materials, on which the hardness is about two times that of their pristine counterparts. Moreover, NT metals usually consist of randomly oriented twin and grain boundaries, making it difficult to control the uniform mechanical property. Here, novel nt structure is proposed on an fcc metal, in which all the twin boundaries are along (-1-11) orientation, forming bundles of nanotwins to several micrometers in length.

  12. 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.

  13. Size effects on plasticity and fatigue microstructure evolution in FCC single crystals

    NASA Astrophysics Data System (ADS)

    El-Awady, Jaafar Abbas

    In aircraft structures and engines, fatigue damage is manifest in the progressive emergence of distributed surface cracks near locations of high stress concentrations. At the present time, reliable methods for prediction of fatigue crack initiation are not available, because the phenomenon starts at the atomic scale. Initiation of fatigue cracks is associated with the formation of Persistent slip bands (PSBs), which start at certain critical conditions inside metals with specific microstructure dimensions. The main objective of this research is to develop predictive computational capabilities for plasticity and fatigue damage evolution in finite volumes. In that attempt, a dislocation dynamics model that incorporates the influence of free and internal interfaces on dislocation motion is presented. The model is based on a self-consistent formulation of 3-D Parametric Dislocation Dynamics (PDD) with the Boundary Element method (BEM) to describe dislocation motion, and hence microscopic plastic flow in finite volumes. The developed computer models are bench-marked by detailed comparisons with the experimental data, developed at the Wright-Patterson Air Force Lab (WP-AFRL), by three dimensional large scale simulations of compression loading on micro-scale samples of FCC single crystals. These simulation results provide an understanding of plastic deformation of micron-size single crystals. The plastic flow characteristics as well as the stress-strain behavior of simulated micropillars are shown to be in general agreement with experimental observations. New size scaling aspects of plastic flow and work-hardening are identified through the use of these simulations. The flow strength versus the diameter of the micropillar follows a power law with an exponent equal to -0.69. A stronger correlation is observed between the flow strength and the average length of activated dislocation sources. This relationship is again a power law, with an exponent -0.85. Simulation results

  14. Many-Body Electronic Structure of Curium metal

    NASA Astrophysics Data System (ADS)

    Toropova, Antonina; Haule, Kristjan; Kotliar, Gabriel

    2006-03-01

    We report computer-based simulations for the many-body electronic structure of Curium metal. Cm belongs to the actinide series and has a half-filled shell with seven 5f electrons. As a function of pressure, curium exhibits five different crystallographic phases. At low temperatures all phases demonstrate either antiferromagnetic or ferrimagnetic ordering. In this study we perform LDA+DMFT calculations for the antiferromagnetic state of high-pressure fcc modification of Curium metal.

  15. Phase stability of ternary fcc and bcc Fe-Cr-Ni alloys

    NASA Astrophysics Data System (ADS)

    Wróbel, Jan S.; Nguyen-Manh, Duc; Lavrentiev, Mikhail Yu.; Muzyk, Marek; Dudarev, Sergei L.

    2015-01-01

    The phase stability of fcc and bcc magnetic binary Fe-Cr, Fe-Ni, and Cr-Ni alloys, and ternary Fe-Cr-Ni alloys is investigated using a combination of density functional theory (DFT), cluster expansion (CE), and magnetic cluster expansion (MCE) approaches. Energies, magnetic moments, and volumes of more than 500 alloy structures have been evaluated using DFT, and the predicted most stable configurations are compared with experimental observations. Deviations from the Vegard law in fcc Fe-Cr-Ni alloys, resulting from the nonlinear variation of atomic magnetic moments as functions of alloy composition, are observed. The accuracy of the CE model is assessed against the DFT data, where for ternary Fe-Cr-Ni alloys the cross-validation error is found to be less than 12 meV/atom. A set of cluster interaction parameters is defined for each alloy, where it is used for predicting new ordered alloy structures. The fcc Fe2CrNi phase with Cu2NiZn -like crystal structure is predicted to be the global ground state of ternary Fe-Cr-Ni alloys, with the lowest chemical ordering temperature of 650 K. DFT-based Monte Carlo (MC) simulations are applied to the investigation of order-disorder transitions in Fe-Cr-Ni alloys. The enthalpies of formation of ternary alloys predicted by MC simulations at 1600 K, combined with magnetic correction derived from MCE, are in excellent agreement with experimental values measured at 1565 K. The relative stability of fcc and bcc phases is assessed by comparing the free energies of alloy formation. The evaluation of the free energies involved the application of a dedicated algorithm for computing the configurational entropies of the alloys. Chemical order is analyzed, as a function of temperature and composition, in terms of the Warren-Cowley short-range order (SRO) parameters and effective chemical pairwise interactions. In addition to compositions close to binary intermetallic phases CrNi2, FeNi, FeNi3, and FeNi8, pronounced chemical order is found

  16. 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.

  17. 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.

  18. 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.

  19. A new Bcc-Fcc orientation relationship observed between ferrite and austenite in solidification structures of steels

    NASA Astrophysics Data System (ADS)

    Headley, T. J.; Brooks, J. A.

    2002-01-01

    A new crystallographic orientation relationship (OR) between delta-ferrite and austenite has been observed in solidification microstructures of 304L and 309S austenitic stainless steels and a ternary Fe-Cr-Ni alloy. Evidence for the new OR was obtained from electron diffraction patterns in transmission electron microscopy (TEM). This relationship, (111)fcc//(110)bcc and [bar 110]_{fcc} //[bar 110]_{bcc} , has not been previously reported for bcc-fcc systems. The <110>fcc//#x2329;110>bcc alignment is distinctive among known bcc-fcc ORs. The new OR is related to the Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W) ORs by relative rotations of 35.26 and 30 deg, respectively, about the normal to the parallel close-packed planes. In 304L fabricated by laser-engineered net shaping (LENS), delta-ferrite with the new OR was found to coexist in the microstructure with both K-S and N-W oriented ferrite, but in separate austenite grains and with less frequent occurrence. In gas-tungsten arc (GTA) welds of 309S and the Fe-Cr-Ni alloy, the new OR was the only one observed within a few grains, whereas ferrite within other grains did not establish an apparent OR with the austenite matrix.

  20. 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.

  1. Unusual finite size effects on critical temperature in fcc Ising antiferromagnets

    NASA Astrophysics Data System (ADS)

    Pommier, J.; Diep, H. T.; Ghazali, A.; Lallemand, P.

    1988-04-01

    A new multispin coding technique is presented for Monte Carlo simulation of antiferromagnetic Ising spin systems on an fcc lattice. The nearest- and next-nearest-neighbor interactions J1 and J2 are included. This technique allows a considerable gain in CPU time and computer memory. As a first application, we have studied samples of 4L3 spins with L up to 48. An unusual behavior of the critical temperature with increasing L is found in the case of nearest-neighbor interaction in zero field. Finite size effects on the locations of tricrical points in the (T,J2/J1) plane are discussed.

  2. Dynamic stability of fcc crystals under isotropic loading from first principles.

    PubMed

    Rehák, Petr; Cerný, Miroslav; Pokluda, Jaroslav

    2012-05-30

    Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.

  3. Study Of Boosted W-Jets And Higgs-Jets With the SiFCC Detector

    SciTech Connect

    Yu, Shin-Shan; Chekanov, Sergei; Gray, Lindsey; Kotwal, Ashutosh; Sen, Sourav; Tran, Nhan Viet

    2016-11-04

    We study the detector performance in the reconstruction of hadronically-decaying W bosons and Higgs bosons at very high energy proton colliders using a full GEANT4 simulation of the SiFCC detector. The W and Higgs bosons carry transverse momentum in the multi-TeV range, which results in collimated decay products that are reconstructed as a single jet. We present a measurement of the energy response and resolution of boosted W-jets and Higgs-jets and show the separation of two sub-jets within the boosted boson jet.

  4. Transient localizations in metals using microstructure-based yield surfaces

    NASA Astrophysics Data System (ADS)

    Voyiadjis, G. Z.; Abed, F. H.

    2007-01-01

    Classical constitutive models of phenomenological plasticity/viscoplasticity rely heavily on yield functions to distinguish plastic flow from reversible elastic deformation. Physically based yield functions are utilized here for body-centred cubic (bcc) and face-centred cubic (fcc) types of metal structures in investigating necking and dynamic shear localizations over a wide range of temperatures and strain rates. The consistency model is employed in determining the increment of the viscoplastic multiplier and consequently a proper definition for the continuum elasto-viscoplastic tangent modulus is derived. Mesh-independent results are obtained using the finite element analysis in investigating the localization behaviour for tantalum, vanadium and niobium for bcc metals and OFHC copper for fcc metals.

  5. Spin-disorder resistivity of heavy rare-earth metals from Gd to Tm: An ab-initio study

    NASA Astrophysics Data System (ADS)

    Glasbrenner, James; Belashchenko, Kirill

    2010-03-01

    Electrical resistivity of heavy rare-earth metals has a dominant contribution from thermal spin disorder scattering. In the paramagnetic state, this spin-disorder resistivity (SDR) decreases through the Gd-Tm series. Models based on the assumption of fully localized 4f states treated as S or J multiplets predict that SDR is proportional to S^2 (S is the 4f shell spin) times a quantum correction (S+1)/S or (J+1)/J. The interpretation of this correction using experimental results is ambiguous. Since the 4f bandwidth is not small compared to the multiplet splitting, it is not clear whether the 4f shells in rare-earth metals behave as if they were fully localized and have a good quantum number S or J. To address this issue, in this work we calculate the paramagnetic SDR of the rare-earth metal Gd-Tm series using a non-collinear implementation of the tight-binding linear muffin-tin orbital method. The conductance is found using the Landauer-B"uttiker approach applied to the active region of a varying size, averaging the conductance over random spin-disorder configurations and fitting its size dependence to Ohm's law. The results are compared with experiment and discussed. The sensitivity to basis set and the treatment of the 4f electrons, as well as the role of exchange enhancement in the conduction band is considered. The issue of the quantum correction is examined in light of the new results.

  6. Molecular dynamics simulations of hcp/fcc nucleation and growth in bcc iron driven by uniaxial compression.

    PubMed

    Wang, B T; Shao, J L; Zhang, G C; Li, W D; Zhang, P

    2009-12-02

    Molecular dynamics simulations have been performed to study the structural transition in bcc iron under uniaxial strain loading. We found that the transition pressures are less dependent on the crystal orientations, ∼14 GPa for [001], [011], and [111] loadings. However, the pressure interval of a mixed phase for [011] loading is much shorter than loading along other orientations. In addition, the temperature increased amplitude for [001] loading is evidently lower than other orientations. The nucleation and growth of the hcp/fcc phases, and their crystal orientation dependence, were analyzed in detail, where the atom structure was presented by the topological medium-range-order analysis. For [001] compression, the hcp structure occurs first and grows into a laminar morphology in the (011)(bcc) plane with some fcc atoms as an intermediate structure. For loading along [011] and [111] directions, both hcp and fcc structure nucleation and growth along the {110}(bcc) planes are observed; their morphology is also discussed.

  7. LatticeLibrary and BccFccRaycaster: Software for processing and viewing 3D data on optimal sampling lattices

    NASA Astrophysics Data System (ADS)

    Linnér, Elisabeth Schold; Morén, Max; Smed, Karl-Oskar; Nysjö, Johan; Strand, Robin

    In this paper, we present LatticeLibrary, a C++ library for general processing of 2D and 3D images sampled on arbitrary lattices. The current implementation supports the Cartesian Cubic (CC), Body-Centered Cubic (BCC) and Face-Centered Cubic (FCC) lattices, and is designed to facilitate addition of other sampling lattices. We also introduce BccFccRaycaster, a plugin for the existing volume renderer Voreen, making it possible to view CC, BCC and FCC data, using different interpolation methods, with the same application. The plugin supports nearest neighbor and trilinear interpolation at interactive frame rates. These tools will enable further studies of the possible advantages of non-Cartesian lattices in a wide range of research areas.

  8. Electronic structure and magnetism of strained bcc phases across the fcc to bcc transition in ultrathin Fe films

    NASA Astrophysics Data System (ADS)

    Calloni, Alberto; Berti, Giulia; Bussetti, Gianlorenzo; Fratesi, Guido; Finazzi, Marco; Ciccacci, Franco; Duò, Lamberto

    2016-11-01

    We investigated the electronic structure of the bcc metastable phases involved in the fcc to bcc transition of Fe. Ultrathin Fe films were grown on a 2-monolayer (ML) Ni/W(110) substrate, where a fcc lattice is stabilized at low Fe coverages and the transition proceeds through the formation of bcc nuclei showing a specific "Kurdjumov-Sachs" orientation with the substrate. A comprehensive description of the electronic structure evolution is achieved by combining spin-resolved UV photoemission spectroscopy and ab initio calculations. According to our results, an exchange-split band structure is observed starting from 2 ML of Fe, concomitant with the formation of ferromagnetic bcc nuclei. Continuous modifications are observed in the spin-resolved photoemission spectra for increasing Fe coverage, especially for what concerns the minority states, possibly indicative of the progressive relaxation of the strained bcc phase starting from the bcc/fcc interface.

  9. Interaction between Ni and HZSM-5 in aromatization-enhanced reactive adsorption desulfurization catalysts for FCC gasoline upgrading.

    PubMed

    Zhao, Jinchong; Zhang, Lulu; She, Nannan; Liu, Yunqi; Chai, Yongming; Liu, Chenguang

    A compound catalyst (RA) consisted of Ni, ZnO and HZSM-5 with functions of reactive adsorption desulfurization (RADS) and olefin aromatization for fluid catalytic cracking (FCC) gasoline upgrading was prepared. X-ray powder diffraction (XRD), temperature-programmed reduction and low-temperature N2 adsorption were used to characterize the properties of the catalysts. Performance evaluation by FCC gasoline was carried out, and the result showed that the catalyst RA performed well in desulfurization and aromatization. For comparison, RADS catalyst (represented by DS) consisted of Ni and ZnO and aromatization catalyst (represented by Ar) consisted of HZSM-5 were prepared, respectively. They were combined in different ways to help investigating interaction between Ni and HZSM-5. Performance evaluated by FCC gasoline showed that catalyst RA performed best in desulfurization with a slight octane number loss. Interaction between Ni and HZSM-5 is a significant factor which influences the performance of the catalyst.

  10. Saddle-point equilibrium lines between fcc and bcc phases in Al and Ca from first principles

    NASA Astrophysics Data System (ADS)

    Qiu, S. L.; Marcus, P. M.

    2013-10-01

    Phase equilibrium lines (denoted ph-eq lines) of face-centered-cubic (fcc) and body-centered-cubic (bcc) phases, as well as saddle-point equilibrium lines (denoted sp-eq lines) in Al and Ca are studied by first-principles total-energy calculations. For a non-vibrating crystal of Al we determine the transition pressure p t = 2.62 Mbar from fcc to bcc phase. The sp-eq line lies between the two ph-eq lines, merges with the bcc-eq line at V = 61 au3/atom ( p = 1.64 Mbar) and with the fcc-eq line at V = 42.4 au3/atom ( p = 5.50 Mbar), gives the Gibbs free energy barrier ΔG = 0.64 mRy/atom at p t . The bcc phase is unstable below 1.64 Mbar, while the fcc phase is unstable above 5.50 Mbar. In a non-vibrating crystal of Ca two sp-eq lines (denoted sp1-eq line and sp2-eq line, respectively) are found corresponding to two phase transitions: one is from fcc to bcc at p t1 = 89.6 kbar, the other is from bcc to fcc at p t2 = 787 kbar. The sp1-eq line merges with the bcc-eq line at V = 231 au3/atom ( p = 50 kbar) and with the fcc-eq line at V = 183 au3/atom ( p = 174 kbar), gives a barrier of Δ G 1 = 0.62 mRy/atom at p t1. The sp2-eq line merges with the bcc-eq line at V = 90 au3/atom ( p = 981 kbar) and with the fcc-eq line at V = 110 au3/atom ( p = 624 kbar), gives a barrier of Δ G 2 = 1.1 mRy/atom at p t2. The bcc phase is stable in the range from 50 kbar to 981 kbar but unstable outside this range, while the fcc phase is unstable in the range from 174 to 624 kbar but stable outside this range. This work confirms all the features of the sp-eq line described in our recent work [S.L. Qiu, P.M. Marcus, J. Phys.: Condens. Matter 24, 225501 (2012)] and finds two additional features: (1) there are two sp-eq lines corresponding to the two phase transitions between fcc and bcc phases in Ca; (2) fcc phase of Ca is unstable between the two merge points on the fcc-eq line but stable beyond them, while bcc phase of Ca is stable between the two merge points on the bcc-eq line but

  11. Identifying self-interstitials of bcc and fcc crystals in molecular dynamics

    NASA Astrophysics Data System (ADS)

    Bukkuru, S.; Bhardwaj, U.; Warrier, M.; Rao, A. D. P.; Valsakumar, M. C.

    2017-02-01

    Identification of self-interstitials in molecular dynamics (MD) simulations is of critical importance. There exist several criteria for identifying the self-interstitial. Most of the existing methods use an assumed cut-off value for the displacement of an atom from its lattice position to identify the self-interstitial. The results obtained are affected by the chosen cut-off value. Moreover, these chosen cut-off values are independent of temperature. We have developed a novel unsupervised learning algorithm called Max-Space Clustering (MSC) to identify an appropriate cut-off value and its dependence on temperature. This method is compared with some widely used methods such as effective sphere (ES) method and nearest neighbor sphere (NNS) method. The cut-off radius obtained using our method shows a linear variation with temperature. The value of cut-off radius and its temperature dependence is derived for five bcc (Cr, Fe, Mo, Nb, W) and six fcc (Ag, Au, Cu, Ni, Pd, Pt) crystals. It is seen that the ratio of the cut-off values "r" to the lattice constant "a" lies between 0.23 and 0.3 at 300 K and this ratio is on an average smaller for the fcc crystals. Collision cascade simulations are carried out for Primary knock-on Atom (PKA) energies of 5 keV in Fe (at 300 K and 1000 K) and W (at 300 K and 2500 K) and the results are compared using the various methods.

  12. Design of an Inductive Adder for the FCC injection kicker pulse generator

    NASA Astrophysics Data System (ADS)

    Woog, D.; Barnes, M. J.; Ducimetière, L.; Holma, J.; Kramer, T.

    2017-07-01

    The injection system for a 100 TeV centre-of-mass collider is an important part of the Future Circular Collider (FCC) study. Due to issues with conventional kicker systems, such as self-triggering and long term availability of thyratrons and limitations of HV-cables, innovative design changes are planned for the FCC injection kicker pulse generator. An inductive adder (IA) based on semiconductor (SC) switches is a promising technology for kicker systems. Its modular design, and the possibility of an active ripple suppression are significant advantages. Since the IA is a complex device, with multiple components whose characteristics are important, a detailed design study and construction of a prototype is necessary. This paper summarizes the system requirements and constraints, and describes the main components and design challenges of the prototype IA. It outlines the results from simulations and measurements on different magnetic core materials as well as on SC switches. The paper concludes on the design choices and progress for the prototype to be built at CERN.

  13. Properties of non-fcc hard-sphere solids predicted by density functional theory.

    PubMed

    Lutsko, James F

    2006-08-01

    The free energies of the fcc, bcc, hcp, and simple cubic phases for hard spheres are calculated as a function of density using the fundamental measure theory models of Rosenfeld [Phys. Rev. E 55, 4245 (1997)], Tarazona [Phys. Rev. Lett. 84, 694 (2001)], and Roth [J. Phys.: Condens. Matter 14, 12063 (2002)] in the Gaussian approximation. For the fcc phase, the present work confirms the vanishing of the Lindemann parameter (i.e., vanishing of the width of the Gaussians) near close packing for all three models and the results for the hcp phase are nearly identical. For the bcc phase and for packing fractions above eta approximately 0.56 , all three theories show multiple solid structures differing in the widths of the Gaussians. In all three cases, one of these structures shows the expected vanishing of the Lindemann parameter at close packing, but this physical structure is only thermodynamically favored over the unphysical structures in the Tarazona theory and even then, some unphysical behavior persists at lower densities. The simple cubic phase is stabilized in the model of Rosenfeld for a range of densities and in the Tarazona model only very near close packing.

  14. 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.

  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.

  16. 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.

  17. 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…

  18. 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... telecommunications service to U.S. registered vessel(s). An accounting authority must inform the FCC...

  19. 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... telecommunications service to U.S. registered vessel(s). An accounting authority must inform the FCC...

  20. 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... telecommunications service to U.S. registered vessel(s). An accounting authority must inform the FCC...

  1. 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... telecommunications service to U.S. registered vessel(s). An accounting authority must inform the FCC...

  2. 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... telecommunications service to U.S. registered vessel(s). An accounting authority must inform the FCC...

  3. 5 CFR 3902.102 - Employees required to submit FCC Form A54A, “Confidential Supplemental Statement of Employment...

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 5 Administrative Personnel 3 2010-01-01 2010-01-01 false Employees required to submit FCC Form... 3902.102 Administrative Personnel FEDERAL COMMUNICATIONS COMMISSION SUPPLEMENTAL FINANCIAL DISCLOSURE REQUIREMENTS FOR EMPLOYEES OF THE FEDERAL COMMUNICATIONS COMMISSION § 3902.102 Employees required to submit FCC...

  4. Access is Fairness: A Petition for Reconsideration of the Federal Communications Commission's Fairness Report, F.C.C. Docket No. 19260. Summary.

    ERIC Educational Resources Information Center

    Jacklin, Phil; And Others

    This petition, submitted to the Federal Communications Commission (FCC), proposes an "adequate access policy" that would enable broadcasters to comply with the FCC's Fairness Doctrine. Following this policy, broadcasters would provide individuals with free public access time in the form of "free-speech messages"--one-minute,…

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

    PubMed

    Adidharma, Hertanto; Tan, Sugata P

    2016-07-07

    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.

  6. 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.

  7. Theoretical Investigations of Phonon Anomalies in Fcc Lanthanum and TUNGSTEN(001)

    NASA Astrophysics Data System (ADS)

    Wang, Xuewen

    1987-09-01

    Studies of the electron-phonon interaction were carried out for fcc La by the efficient tight-binding method. This scheme was then extended and generalized to surface studies. Application of this extended scheme to the W(001) surface provided detailed information about the driving mechanism for surface reconstruction. Together with the further studies on the Mo(001) surface, our investigation showed very promising potential applications of this scheme to various surface phonon and surface phase transition studies. For the fcc La, first-principles pseudopotential band-structure calculations were performed and revealed a small but sharp nesting feature of the Fermi surface. Then the non-orthogonal tight binding parameters were derived from the first-principles results and lattice dynamics calculations were carried out with the tight-binding scheme. The calculated phonon dispersion curves showed very good agreement with neutron scattering data. Our detailed analysis revealed the crucial role played by d-electron, the speculated role of the f-levels contribution was clarified, and the phonon spectrum under high pressure (>50 Kbar) was predicted. The unique properties of fcc La, for example, the negative thermal expansion coefficient and relatively high superconducting temperature, were explained in terms of the anomalously strong electron-phonon coupling. Also, the possible connection with the interesting phase transformation observed at high pressure was explored. The calculations for W(001) p(1x1) surface phonons successfully demonstrated the electronic origin of the c(2x2) surface reconstruction. The reason for the stable M_1 and soft M_5 surface phonon modes was found to be the dramatic differences in their electron-phonon coupling matrix elements. The subtle interplay between the Fermi surface nesting and real-space d-orbital interaction was found to cause the surface reconstruction. Subsequent studies on the Mo(001) surface further established the relationship

  8. Geometry explains the large difference in the elastic properties of fcc and hcp crystals of hard spheres.

    PubMed

    Sushko, Nazar; van der Schoot, Paul

    2005-12-01

    As is well known, hard-sphere crystals of the fcc and hcp type differ very little in their thermodynamic properties. Nonetheless, recent computer simulations by Pronk and Frenkel indicate that the elastic response to mechanical deformation of these two types of crystal are quite different [S. Pronk and D. Frenkel, Phys. Rev. Lett. 90, 255501 (2003)]. By invoking a geometrical argument put forward by Martin some time ago [R. M. Martin, Phys. Rev. B 6, 4546 (1972)], we suggest that this is largely due to the different symmetries of the fcc and hcp crystal structures. Indeed, we find that elastic constants of the fcc hard-sphere crystal can be mapped onto the equivalent ones of the hcp crystal to very high accuracy, as a comparison with the computer simulation data of Pronk and Frenkel shows. The same procedure applied to density functional theoretical predictions for the elastic properties of the fcc hard-sphere crystal also produces remarkably accurate predictions for those of the hcp hard-sphere crystal.

  9. 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.

  10. Theory and practice of “shape spectroscopy” of local FCC structures in computer simulations of nucleation and crystallization

    NASA Astrophysics Data System (ADS)

    Mitus, A. C.; Smolej, F.; Hahn, H.; Patashinski, A. Z.

    1996-02-01

    Starting from the previously developed probabilistic method for recognition of structures of small clusters of atoms undergoing thermal fluctuations, we derive simple algorithms for the very detailed study of local face-centered-cubic (FCC) arrangements of the atoms, directly in a configuration of atoms when it is being simulated. This includes (i) an algorithm for a local identification of FCC-like clusters, with the discussion of its reliability, and (ii) an algorithm for the calculation of the relative orientational correlations between the clusters. As an illustration, the method is used for studying nucleation and growth of an FCC phase in a rapidly quenched melt of 4000 Lennard-Jones atoms. On the basis of this analysis, we propose two trial hypotheses about (i) the existence of “slow” and “quick” regimes during the nucleation and growth and (ii) that in the intermediate stages of nucleation and crystallization the FCC-like local order appears rather in two-, than in three-dimensional aggregates.

  11. 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 non-federal...

  12. 78 FR 49480 - Proposed Information Collection; Comment Request; NTIA/FCC Web-based Frequency Coordination System

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-14

    ...; 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... basis by federal and non-federal users. The web-based system provides a means for non-federal applicants...

  13. 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

    ... FCC's Enforcement Bureau (``Bureau'') launched an investigation. The Division staff observed that the... intentionally generates and emits radio frequency energy by radiation or induction.'' 47 CFR 15.3(o). \\30\\ See... based on the field tests conducted by Bureau staff, the TxTStopper TM --the device apparently being...

  14. Elemental vacancy diffusion database from high-throughput first-principles calculations for fcc and hcp structures

    NASA Astrophysics Data System (ADS)

    Angsten, Thomas; Mayeshiba, Tam; Wu, Henry; Morgan, Dane

    2014-01-01

    This work demonstrates how databases of diffusion-related properties can be developed from high-throughput ab initio calculations. The formation and migration energies for vacancies of all adequately stable pure elements in both the face-centered cubic (fcc) and hexagonal close packing (hcp) crystal structures were determined using ab initio calculations. For hcp migration, both the basal plane and z-direction nearest-neighbor vacancy hops were considered. Energy barriers were successfully calculated for 49 elements in the fcc structure and 44 elements in the hcp structure. These data were plotted against various elemental properties in order to discover significant correlations. The calculated data show smooth and continuous trends when plotted against Mendeleev numbers. The vacancy formation energies were plotted against cohesive energies to produce linear trends with regressed slopes of 0.317 and 0.323 for the fcc and hcp structures respectively. This result shows the expected increase in vacancy formation energy with stronger bonding. The slope of approximately 0.3, being well below that predicted by a simple fixed bond strength model, is consistent with a reduction in the vacancy formation energy due to many-body effects and relaxation. Vacancy migration barriers are found to increase nearly linearly with increasing stiffness, consistent with the local expansion required to migrate an atom. A simple semi-empirical expression is created to predict the vacancy migration energy from the lattice constant and bulk modulus for fcc systems, yielding estimates with errors of approximately 30%.

  15. Non-linear modelling of the effects of strain on transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Shuttleworth, I. G.

    2016-12-01

    A sequence of polynomial expressions have been shown to describe the strained surface energy of low-index hexagonal and square transition metal surfaces. Distinguishable functions describe the hexagonal FCC (1 1 1) and HCP (0 0 0 1) surfaces, but a single function describes the FCC (1 0 0) and BCC (1 0 0) surfaces. A far weaker dependence exists between the strained surface energy and the electronic state of the surface, and the competition between geometric and electronic states across is discussed.

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

    DOE PAGES

    Mentes, T. O.; Stojic, N.; Vescovo, E.; ...

    2016-08-01

    The phase separation occurring in Fe-Ni thin lms 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 lms 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 di using species in forming the chemical heterogeneity. The experimentally-determined energy barrier of 1.59 0.09 eV is identi ed as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separation process ismore » attributed to vacancy creation without interstitials.« less

  17. A synthetic route to size-controlled fcc and fct FePt nanoparticles.

    PubMed

    Howard, Luciano E M; Nguyen, H Loc; Giblin, Sean R; Tanner, Brian K; Terry, Ian; Hughes, Andrew K; Evans, John S O

    2005-07-27

    We report here a new synthetic route to FePt nanoparticles using a stoichiometric mixture of Na2Fe(CO)4 and Pt(acac)2. The structure of FePt nanoparticles, their size, chemical composition, and magnetic property can be controlled by various synthetic parameters, such as the solvent type, nature, and molar ratio of surfactants and stabilizers, synthesis temperature, and purification process. Partially ordered fct (L10) nanoparticles with room temperature magnetic coercivity can be synthesized directly in tetracosane solution at 389 degrees C. The fcc FePt synthesized in nonadecane can be transformed into the magnetically important fct phase at 430 degrees C without significant particle sintering.

  18. Prediction of FCC gasoline octane numbers using FT-MIR and PLS.

    PubMed

    Andrade, J M; Prada, D; Muniategui, S; Lopez, P

    1996-06-01

    A method for predicting "octane numbers" (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm(-1) at 4 cm(-1) intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP(RON)=0.38; SEP(MON)=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).

  19. Ab initio simulation of dissolution energy and carbon activity in fcc Fe

    NASA Astrophysics Data System (ADS)

    Ridnyi, Ya. M.; Mirzoev, A. A.; Mirzaev, D. A.

    2017-07-01

    The equilibrium structure and properties of fcc iron with a carbon impurity were simulated ab initio using the WIEN2k software package. A procedure is proposed that enables the simulation of the magnetically disordered state of a system within the density functional theory. In the framework of this procedure, the value of the dissolution energy of carbon was calculated, which was 0.25 eV. Interaction energies between carbon atoms in the first, second, and third coordination spheres of each other were also determined, which were E 1 = 0.06 eV, E 2 = 0.1 eV, and E 3 = 0.005 eV. To verify the reliability of the obtained energy values, the activity of carbon was calculated by the Monte Carlo method. A good qualitative agreement of the calculated activity with the experimental data indicates the reliability of the obtained energy parameters.

  20. Structural variants of fcc Ti[sub 2]Ni phase by shock synthesis

    SciTech Connect

    Zhu, Y.L.; Ma, X.L.; Li, T.C.; Yang, D.Z. . Dept. of Materials Engineering)

    1994-11-01

    NiTi alloys have excellent properties such as superelasticity, shape memory effect, high damping (HD) etc. they are one of the most attractive functional materials, therefore, much attention has been paid to NiTi alloys for years. Using the explosive consolidation technique to produce NiTi alloys not only reduces the cost due to multiple melting and complicated machining processes, but also makes the products have net shapes. In the previous paper, the authors reported that in some NiTi compounds, B2 phase, Ti[sub 2]Ni, R-phase and martensite, were directly formed by shock synthesis. In this paper, they report two new structures of FCC Ti[sub 2]Ni variants, which were also formed directly by explosion.

  1. 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.

  2. 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

  3. 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.

  4. Martensitic fcc-to-hcp transformations in solid xenon under pressure: a first-principles study.

    PubMed

    Kim, Eunja; Nicol, Malcolm; Cynn, Hyunchae; Yoo, Choong-Shik

    2006-01-27

    First-principles calculations reveal that the fcc-to-hcp pressure-induced transformation in solid xenon proceeds through two mechanisms between 5 and 70 GPa. The dynamics of the phase transition involves a sluggish stacking-disorder growth at lower pressures (path I) that changes to a path involving an orthorhombic distortion at higher pressures (path II). The switchover is governed by a delicate interplay of energetics (enthalpy of the system for the structural stability) and kinetics (energy barrier for the transition). The two types of martensitic transformations involved in this pressure-induced structural transformation are a twinned martensitic transition at lower pressures and a slipped martensitic transition at higher pressures.

  5. When magnetic catalyst meets magnetic reactor: etherification of FCC light gasoline as an example.

    PubMed

    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.

  6. 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.

  7. Spin-driven symmetry breaking in the frustrated fcc pyrite MnS2.

    PubMed

    Kimber, Simon A J; Chatterji, Tapan

    2015-06-10

    We report the characterisation of natural samples of the cubic pyrite mineral MnS2 using very high resolution synchrotron x-ray diffraction techniques. At low temperatures we find a new low temperature polymorph, which results from coupling between magnetic and lattice degrees of freedom. Below the magnetic ordering temperature T(N) = 48 K, we detect a pseudo-tetragonal distortion with a tiny c/a ratio of 1.0006. The structure can be refined in the space group Pbca The symmetry lowering reduces magnetic frustration in the fcc Mn(2+) lattice and is likely responsible for the previously reported lock-in of the magnetic propagation vector. This behaviour is similar to the spin-Peierls phase transitions reported in other three-dimensional Heisenberg magnets like the chromate spinels.

  8. 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.

  9. Void growth and coalescence in triaxial stress fields in irradiated FCC single crystals

    NASA Astrophysics Data System (ADS)

    Ling, Chao; Tanguy, Benoît; Besson, Jacques; Forest, Samuel; Latourte, Felix

    2017-08-01

    Void growth and coalescence, known as main mechanisms of ductile fracture, are investigated for irradiated FCC single crystals. Finite element simulations of voided unit cells are performed with a single crystal plasticity model accounting for strain hardening and softening associated with irradiation-induced defects. The simulations predict a rather brittle overall behavior for the voided irradiated single crystal at high stress triaxiality, with a large amount of local plastic deformation, which is consistent with experimental observations reported in the literature for stainless steels irradiated in fast reactors. Compared with unirradiated single crystals, irradiated crystals exhibit a higher void growth rate leading to an earlier void coalescence, which is caused by a stronger plastic slip localization in the region near the voids.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

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

    DOE PAGES

    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

  12. 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).

  13. Magnetisation reversal by uniform rotation (Stoner-Wohlfarth model) in FCC cobalt nanoparticles

    NASA Astrophysics Data System (ADS)

    Wernsdorfer, W.; Thirion, C.; Demoncy, N.; Pascard, H.; Mailly, D.

    2002-04-01

    The combination of high sensitive superconducting quantum interference device (SQUID) with high quality nanoparticles allowed to check the simplest classical model describing the magnetisation reversal by uniform rotation which were proposed more than 50 yr ago by Néel, Stoner and Wohlfarth. The micrometer sized SQUIDs were elaborated by electron beam lithography and the nanoparticles were synthesised by arc-discharge. The measured angular dependence of switching fields of nearly all FCC. Co nanoparticles revealed a dominating uniaxial magnetic anisotropy. This result suggests that twin boundaries and stacking faults strongly alter the cubic magnetocrystalline anisotropy leading to dominating uniaxial anisotropy. However, few particles were sufficiently "perfect" in order to show a more complex switching field surface and a field path dependence of the switching field which is the important signature of the cubic magnetocrystalline anisotropy.

  14. Superferromagnetism in mechanically alloyed fcc Fe23Cu77 with bimodal cluster size distribution

    NASA Astrophysics Data System (ADS)

    Silva, N. J. O.; Amaral, J. S.; Amaral, V. S.; Costa, B. F. O.; LeCaër, G.

    2009-01-01

    Magnetic measurements, x-ray diffraction and Mössbauer spectroscopy were used to characterize a nanostructured fcc Fe23Cu77 at.% alloy prepared by high-energy ball-milling, addressing in particular the effect of clustering on the nature of the interacting magnetic entities. The interpretation of magnetization measurements leads to the conclusion that grains, whose mean size is ~16 nm, contain two populations of magnetic Fe-rich nanoclusters with a bimodal size distribution. These two sets of clusters contain about 14 and 400 Fe atoms and have magnetic moments of 30 µB and 860 µB, respectively. The inter-cluster ferromagnetic interactions that lead to superferromagnetism with a Curie temperature TC~220 K can be described by a mean field determined by the smaller clusters only, which account for 90% of the magnetization.

  15. 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

  16. 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.

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

    DOE PAGES

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

    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

  18. From Kepler's conjecture and fcc lattice to modelling of crowding in living matter.

    PubMed

    Del Monte, Ugo; Caiani, Enrico G

    2013-01-01

    Up to now, sphere packing has been investigated without any reference to living matter. This study focuses on the void space (VS) of sphere packing to mimic the extracellular spaces of living tissues. It was inspired by the importance of the extracellular matrix, the vehicle of micro and macromolecules involved in cell metabolism, intercellular communication and drug delivery. The analysis of sphere packing evidenced that in uniform random packing VS is about 1.9 times greater than in the face centered cubic (fcc) lattice (thus being very close to the 1.9 volume ratio of the cube to the sphere). This datum is a good reference for cell packing in vivo. The disproportionate increase of VS per sphere in loose packing in vitro is analyzed having in mind the variability in volume and composition of the interstitial spaces in vivo and cell trafficking. Arrangements of lymphocytes mimicking a two-dimensional hexagonal pattern and dense packing of disks generated by numerical procedures, are described in 7 micro m-thick haematoxylin and eosin-stained histological slices from a human lymph node. In narrow tubes simulating roundish cells arranged in limited compartments of the interstice, sphere packing is characterized by noticeable increases of VS. The VS of this packing in vitro is compatible with variability in volume and composition of the interstitial spaces and with cell trafficking in vivo. This paper stresses that in mammalian tissues and organs cells can be packed quite more densely than spheres in the fcc lattice. As to pathology, attention is focused: (i) on overcrowding of cell organelles in some diseases, (ii) on shrinking or swelling of high amplitude, whose opposite effects are to concentrate or dilute intracellular structures and crowding of macromolecules, and (iii) on neoplastic tissues.

  19. Face-centered-cubic B80 metal: Density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Yan, Qing-Bo; Zheng, Qing-Rong; Su, Gang

    2008-06-01

    By means of ab initio calculations within the density functional theory, we have found that B80 fullerenes can condense to form stable face-centered-cubic (fcc) solids. It is shown that when forming a crystal, B80 cages are geometrically distorted, the Ih symmetry is lowered to Th , and four boron-boron chemical bonds are formed between every two nearest neighbor B80 cages. The cohesive energy of B80 fcc solid is 0.23 eV/atom with respect to the isolated B80 fullerene. The calculated electronic structure reveals that the fcc B80 solid is a metal. The predicted solid phase would constitute a form of pure boron and might have diverse implications. In addition, a simple electron counting rule is proposed, which could explain the stability of B80 fullerene and the recently predicted stable boron sheet.

  20. 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.

  1. FCC Fe2NiSi prepared by mechanical alloying and stabilization effect of L21B disorder on BCC Heusler structure

    NASA Astrophysics Data System (ADS)

    Luo, Hongzhi; Xin, Yuepeng; Ma, Yuexing; Liu, Bohua; Meng, Fanbin; Liu, Heyan; Liu, Enke; Wu, Guangheng

    2016-12-01

    Fe2NiSi FCC phase has been prepared by ball-milling successfully, which is different from the BCC Heusler phase prepared by arc-melting in previous literatures. The FCC Fe2NiSi is a ferromagnet with a lattice constant of 3.58 Å. The phase stability of the FCC and BCC Fe2NiSi has been compared by first-principles calculations. It has been found that the FCC structure has a lower total energy compared with the highly-ordered Heusler structures XA and L21, that is the reason why the FCC phase can be prepared by ball-milling. However, the Fe (A)-Ni (C) disorder in the BCC XA structure can lower its total energy further and make it smaller than the FCC phase. So the most stable structure in Fe2NiSi is L21B, as has been observed in the arc-melting sample. This can be explained from their DOS structures. The calculated total moments for the FCC and BCC phases agree with their Ms at 5 K quite well.

  2. Periplasmic Electron Transfer via the c-Type Cytochromes MtrA and FccA of Shewanella oneidensis MR-1 ▿

    PubMed Central

    Schuetz, Bjoern; Schicklberger, Marcus; Kuermann, Johannes; Spormann, Alfred M.; Gescher, Johannes

    2009-01-01

    Dissimilatory microbial reduction of insoluble Fe(III) oxides is a geochemically and ecologically important process which involves the transfer of cellular, respiratory electrons from the cytoplasmic membrane to insoluble, extracellular, mineral-phase electron acceptors. In this paper evidence is provided for the function of the periplasmic fumarate reductase FccA and the decaheme c-type cytochrome MtrA in periplasmic electron transfer reactions in the gammaproteobacterium Shewanella oneidensis. Both proteins are abundant in the periplasm of ferric citrate-reducing S. oneidensis cells. In vitro fumarate reductase FccA and c-type cytochrome MtrA were reduced by the cytoplasmic membrane-bound protein CymA. Electron transfer between CymA and MtrA was 1.4-fold faster than the CymA-catalyzed reduction of FccA. Further experiments showing a bidirectional electron transfer between FccA and MtrA provided evidence for an electron transfer network in the periplasmic space of S. oneidensis. Hence, FccA could function in both the electron transport to fumarate and via MtrA to mineral-phase Fe(III). Growth experiments with a ΔfccA deletion mutant suggest a role of FccA as a transient electron storage protein. PMID:19837833

  3. 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.

  4. 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.

  5. Electron Irradiation Induced Phase Transition of an Amorphous Phase and Face-Centered Cubic Solid Solutions in Zr66.7Pd33.3 Metallic Glass

    NASA Astrophysics Data System (ADS)

    Nagase, Takeshi; Hosokawa, Takashi; Umakoshi, Yukichi

    2007-02-01

    Both amorphization and crystallization were observed in Zr66.7Pd33.3 metallic glass under electron irradiation. The melt-spun amorphous phase was not stable under 2.0 MV electron irradiation and two kinds of fcc-solid solution were precipitated through electron irradiation induced crystallization at 103 and 298 K. The fcc-solid solution obtained by electron irradiation induced crystallization at 298 K transformed to an amorphous phase during irradiation at 103 K. Electron irradiation induced phase transformation behavior in Zr66.7Pd33.3 metallic glass can be explained by phase stability of an amorphous phase and crystalline phases against electron irradiation.

  6. 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.

  7. 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.

  8. 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.

  9. An ab initio study of the fcc and hcp structures of helium.

    PubMed

    Røeggen, I

    2006-05-14

    The hexagonal close packed (hcp) and face centered cubic (fcc) structures of helium are studied by using a new ab initio computational model for large complexes comprising small subsystems. The new model is formulated within the framework of the energy incremental scheme. In the calculation of intra- and intersystem energies, model systems are introduced. To each subsystem associated is a set of partner subsystems defined by a vicinity criterion. In the independent calculations of intra- and intersystem energies, the calculations are performed on model subsystems defined by the subsystems considered and their partner subsystems. A small and a large basis set are associated with each subsystem. For partner subsystems in a model system, the small basis set is adopted. By introducing a particular decomposition scheme, the intermolecular potential is written as a sum of effective one-body potentials. The binding energy per atom in an infinite crystal of atoms is the negative value of this one-body potential. The one-body potentials for hcp and fcc structures are calculated for the following nearest neighbor distances (d0): 4.6, 5.1, 5.4, 5.435, 5.5, 5.61, and 6.1 a.u. The equilibrium distance is 5.44 a.u. for both structures. The equilibrium dimer distance is 5.61 a.u. For the larger distances, i.e., d0 > 5.4 a.u., the difference of the effective one-body potentials for the two structures is less than 0.2 microE(h). However, the hcp structure has the lowest effective one-body potential for all the distances considered. For the smallest distance the difference in the effective one-body potential is 3.9 microE(h). Hence, for solid helium, i.e., helium under high pressure, the hcp structure is the preferred one. The error in the calculated effective one-body potential for the distance d0 = 5.61 a.u. is of the order of 1 microE(h) (approximately 0.5%).

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

    DOE PAGES

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

    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

  11. 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

  12. Correlation effects in fcc-Fe(x)Ni(1-x) alloys investigated by means of the KKR-CPA.

    PubMed

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

    2014-07-09

    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.

  13. The fcc-bcc Bain path in In-Sn and related alloys at ambient and high pressure.

    PubMed

    Degtyareva, Valentina F

    2009-03-04

    Experimental high-pressure structural studies on an In-Sn alloy containing 8 at.% Sn reveal an isostructural transition of a face-centered tetragonal phase at pressures above 15 GPa with a switch of the axial ratio from c/a>1 to c/a<1. Such tetragonal phases in binary alloys based on In and Sn are analyzed in relation to the Bain path, i.e. a transformation between a face-centered cubic (fcc) and a body-centered cubic (bcc) structure. Variation of the axial ratio c/a in these phases correlates with the average number of valence electrons per atom in an alloy. A common Bain path from fcc to bcc is discussed within a nearly-free-electron model of Brillouin-zone-Fermi-sphere interactions.

  14. A systematic study on the interfacial energy of O-line interfaces in fcc/bcc systems

    NASA Astrophysics Data System (ADS)

    Dai, Fuzhi; Zhang, Wenzheng

    2013-10-01

    Habit planes between face-centered cubic (fcc)/body-centered cubic (bcc) phases usually exhibit irrational orientations, which often agree with the O-line criterion. Previously, energy calculation was made to test whether the habit planes were energetically favorable, but the values of the energy were found very sensitive to the initial atomic configuration in an irrationally orientated interface. In this paper, under the O-line condition, simple selection criteria are proposed to define and remove interfacial interstitials and vacancies in the initial atomic configuration. The criteria are proved to be effective in obtaining robust energy results. Interfacial energies of two types of O-line interfaces in fcc/bcc systems are calculated following the criteria. The observed transformation crystallography of precipitates in Ni-Cr and Cu-Cr systems can be explained consistently as the irrational habit plane in each system is associated with the lowest energy O-line interface.

  15. Pressure-induced fcc to hcp phase transition in Ni-based high entropy solid solution alloys

    NASA Astrophysics Data System (ADS)

    Zhang, F. X.; Zhao, Shijun; Jin, Ke; Bei, H.; Popov, D.; Park, Changyong; Neuefeind, J. C.; Weber, W. J.; Zhang, Yanwen

    2017-01-01

    A pressure-induced phase transition from the fcc to a hexagonal close-packed (hcp) structure was found in NiCoCrFe solid solution alloy starting at 13.5 GPa. The phase transition is very sluggish and the transition did not complete at ˜40 GPa. The hcp structure is quenchable to ambient pressure. Only a very small amount (<5%) of hcp phase was found in the isostructural NiCoCr ternary alloy up to the pressure of 45 GPa and no obvious hcp phase was found in NiCoCrFePd system till to 74 GPa. Ab initio Gibbs free energy calculations indicated the energy differences between the fcc and the hcp phases for the three alloys are very small, but they are sensitive to temperature. The critical transition pressure in NiCoCrFe varies from ˜1 GPa at room temperature to ˜6 GPa at 500 K.

  16. Cation Ordering in [(Tl,M)O] Layers of ``1201''-Based Cuprates: Similarity to Ordering in fcc-Based Alloys

    NASA Astrophysics Data System (ADS)

    Van Tendeloo, G.; De Meulenaere, P.; Letouzé, F.; Martin, C.; Hervieu, M.; Raveau, B.

    1997-08-01

    "1201" Tl-based substituted cuprates of the type (Tl1-xMx)Sr2CuO5have been synthesized forM=Nb, Ta, or W. These materials do not superconduct due to a statistical distribution of some of theMfor Cu. The remarkable feature of these materials is the ordering observed between Tl andMin the (Tl1-xMx-ε)O plane. The type of ordering depends on the composition and shows remarkable similarities with the ordering in Ni-Mo or other so-called 1 1/2 0 type fcc-based alloys or with the ordering in rocksalt oxides TiOx. The short-range order, forM=W, can be readily interpreted in terms of a mixing of nano-clusters with two different compositions. These observations of two-dimensional ordering confirm recent ideas about ordering in three-dimensional fcc-based alloys.

  17. 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.

  18. The influence of additions of Al and Si on the lattice stability of fcc and hcp Fe-Mn random alloys.

    PubMed

    Gebhardt, T; Music, D; Ekholm, M; Abrikosov, I A; Vitos, L; Dick, A; Hickel, T; Neugebauer, J; Schneider, J M

    2011-06-22

    We have studied the influence of additions of Al and Si on the lattice stability of face-centred-cubic (fcc) versus hexagonal-closed-packed (hcp) Fe-Mn random alloys, considering the influence of magnetism below and above the fcc Néel temperature. Employing two different ab initio approaches with respect to basis sets and treatment of magnetic and chemical disorder, we are able to quantify the predictive power of the ab initio methods. We find that the addition of Al strongly stabilizes the fcc lattice independent of the regarded magnetic states. For Si a much stronger dependence on magnetism is observed. Compared to Al, almost no volume change is observed as Si is added to Fe-Mn, indicating that the electronic contributions are responsible for stabilization/destabilization of the fcc phase.

  19. 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

    ... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know § 95.423 (CB Rule 23) What must I do if the FCC tells...

  20. 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

    ... COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Citizens Band (CB) Radio Service Other Things You Need to Know § 95.423 (CB Rule 23) What must I do if the FCC tells...

  1. Graphene oxide-templated synthesis of ultrathin or tadpole-shaped au nanowires with alternating hcp and fcc domains.

    PubMed

    Huang, Xiao; Li, Shaozhou; Wu, Shixin; Huang, Yizhong; Boey, Freddy; Gan, Chee Lip; Zhang, Hua

    2012-02-14

    Ultrathin Au nanowires (AuNWs) and tadpole-shaped nanowires are synthesized on graphene oxide (GO) sheet templates. For the first time, 1.6 nm-diameter AuNWs are shown to contain hexagonal close-packed (hcp) crystal domains, and the tadpole-shaped nanowires exhibit alternating sets of hcp and face-centered cubic (fcc) structures, associated with variation in wire thickness.

  2. Orientation dependence of the plastic slip near notches in ductile FCC single crystals

    NASA Astrophysics Data System (ADS)

    Crone, W. C.; Shield, T. W.; Creuziger, A.; Henneman, B.

    2004-01-01

    Results from experiments conducted on copper FCC single crystals are reported. Two symmetric crystallographic orientations and four nonsymmetric crystallographic orientations were tested. The slip line fields that form near a pre-existing notch in these specimens were observed. The changes in these patterns as the orientation of the notch in the crystal is rotated in an {101} plane are discussed. Sectors of similar slip line patterns are identified and the type of boundaries between these sectors are discussed. A type of sector boundary called mixed kink is identified. Specimen orientations that differ by 90° are found to have different slip line patterns, contrary to the predictions of perfectly plastic slip line theory. The locations of the first slip lines to form are compared to the predictions obtained using anisotropic linear elastic stress field solutions and the initial plane-strain yield surfaces. It is found that comparison of these surface slip line fields to plane strain crack tip solutions in the annular region between 350 and 750 μm is justified. The differences in anisotropic elastic solutions for orientations that are 90° apart explain the lack of agreement with perfectly plastic slip line theory.

  3. 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.

  4. Crystal-momentum dispersion of ultrafast spin change in fcc Co

    PubMed Central

    Si, M. S.; Li, J. Y.; Yang, D. Z.; Xue, D. S.; Zhang, G. P.

    2014-01-01

    Nearly twenty years ago, Beaurepaire and coworkers showed that when an ultrafast laser impinges on a ferromagnet, its spin moment undergoes a dramatic change, but how it works remains a mystery. While the current experiment is still unable to resolve the minute details of the spin change, crystal momentum-resolved techniques have long been used to analyze the charge dynamics in superconductors and strongly correlated materials. Here we extend it to probe spin moment change in the entire three-dimensional Brillouin zone for fcc Co. Our results indeed show a strong spin activity along the Δ line, supporting a prior experimental finding. The spin active pockets coalesce into a series of spin surfaces that follow the Fermi surfaces. We predict two largest spin change pockets which have been elusive to experiments: one pocket is slightly below the Δ line and the other is along the Λ line and close to the L point. Our theory presents an opportunity for the time-, spin- and momentum-resolve photoemission technique. PMID:24852331

  5. Ab initio prediction of vacancy properties in concentrated alloys: The case of fcc Cu-Ni

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Sluiter, Marcel H. F.

    2015-05-01

    Vacancy properties in concentrated alloys continue to be of great interest because nowadays ab initio supercell simulations reach a scale where even defect properties in disordered alloys appear to be within reach. We show that vacancy properties cannot generally be extracted from supercell total energies in a consistent manner without a statistical model. Essential features of such a model are knowledge of the chemical potential and imposition of invariants. In the present work, we derive the simplest model that satisfies these requirements and we compare it with models in the literature. As illustration we compute ab initio vacancy properties of fcc Cu-Ni alloys as a function of composition and temperature. Ab initio density functional calculations were performed for SQS supercells at various compositions with and without vacancies. Various methods of extracting alloy vacancy properties were examined. A ternary cluster expansion yielded effective cluster interactions (ECIs) for the Cu-Ni-Vac system. Composition and temperature dependent alloy vacancy concentrations were obtained using statistical thermodynamic models with the ab initio ECIs. An Arrhenius analysis showed that the heat of vacancy formation was well represented by a linear function of temperature. The positive slope of the temperature dependence implies a negative configurational entropy contribution to the vacancy formation free energy in the alloy. These findings can be understood by considering local coordination effects.

  6. 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.

  7. Thermodynamic behavior of the carbon schwarzite fcc (C36)2

    NASA Astrophysics Data System (ADS)

    Rosato, Vittorio; Celino, Massimo; Benedek, Giorgio; Gaito, Sabrina

    1999-12-01

    The thermodynamic behavior of the carbon schwarzite fcc (C36)2 has been studied by tight-binding molecular-dynamics simulations at constant temperature and pressure. The system is totally sp2 bonded and it can be represented as a folded graphite sheet made by hexagonal and heptagonal rings. The structure has a density ρ as low as ρ=1.05 gr/cm3 at T=300 K and a bulk modulus B, evaluated by measuring the volume variation upon application of an external hydrostatic load, as large as B=0.70 Mbar. At T~4000 K, the structure unfolds via a topological transformation, which brings the value of the topological connectivity of the structure kc from kc=19 (for a cell including four molecules) to kc=3 (which is the value of a graphite sheet). The behavior of the structural, dynamical, and electronic-structure properties has been evaluated in the whole temperature range, below and above the temperature of the topological transition.

  8. Crystal-momentum dispersion of ultrafast spin change in fcc Co.

    PubMed

    Si, M S; Li, J Y; Yang, D Z; Xue, D S; Zhang, G P

    2014-05-23

    Nearly twenty years ago, Beaurepaire and coworkers showed that when an ultrafast laser impinges on a ferromagnet, its spin moment undergoes a dramatic change, but how it works remains a mystery. While the current experiment is still unable to resolve the minute details of the spin change, crystal momentum-resolved techniques have long been used to analyze the charge dynamics in superconductors and strongly correlated materials. Here we extend it to probe spin moment change in the entire three-dimensional Brillouin zone for fcc Co. Our results indeed show a strong spin activity along the Δ line, supporting a prior experimental finding. The spin active pockets coalesce into a series of spin surfaces that follow the Fermi surfaces. We predict two largest spin change pockets which have been elusive to experiments: one pocket is slightly below the Δ line and the other is along the Λ line and close to the L point. Our theory presents an opportunity for the time-, spin- and momentum-resolve photoemission technique.

  9. Pressure induced manifold enhancement of Li-kinetics in FCC fullerene.

    PubMed

    Das, Deya; Han, Sang Soo; Lee, Kwang-Ryeol; Singh, Abhishek K

    2014-10-21

    The reduction of the diffusion energy barrier for Li in electrodes is one of the required criteria to achieve better performances in Li ion batteries. Using density functional theory based calculations, we report a pressure induced manifold enhancement of Li-kinetics in bulk FCC fullerene. Scanning of the potential energy surface reveals a diffusion path with a low energy barrier of 0.62 eV, which reduces further under the application of hydrostatic pressure. The pressure induced reduction in the diffusion barrier continues till a uniform volume strain of 17.7% is reached. Further enhancement of strain increases the barrier due to the repulsion caused by C-C bond formation between two neighbouring fullerenes. The decrease in the barrier is attributed to the combined effect of charge transfer triggered by the enhanced interaction of Li with the fullerene as well as the change in profile of the local potential, which becomes more attractive for Li. The lowering of the barrier leads to an enhancement of two orders of magnitude in Li diffusivity at room temperature making pressurized bulk fullerene a promising artificial solid electrolyte interface (SEI) for a faster rechargeable battery.

  10. Mechanism of the fcc-to-hcp phase transformation in solid Ar

    NASA Astrophysics Data System (ADS)

    Li, Bingxi; Qian, Guangrui; Oganov, Artem R.; Boulfelfel, Salah Eddine; Faller, Roland

    2017-06-01

    We present an atomistic description of the fcc-to-hcp transformation mechanism in solid argon (Ar) obtained from transition path sampling molecular dynamics simulation. The phase transition pathways collected during the sampling for an 8000-particle system reveal three transition types according to the lattice deformation and relaxation details. In all three transition types, we see a critical accumulation of defects and uniform growth of a less ordered transition state, followed by a homogeneous growth of an ordered phase. Stacking disorder is discussed to describe the transition process and the cooperative motions of atoms in {111 } planes. We investigate nucleation with a larger system: in a system of 18 000 particles, the collective movements of atoms required for this transition are facilitated by the formation and growth of stacking faults. However, the enthalpy barrier is still far beyond the thermal fluctuation. The high barrier explains previous experimental observations of the inaccessibility of the bulk transition at low pressure and its sluggishness even at extremely high pressure. The transition mechanism in bulk Ar is different from Ar nanoclusters as the orthorhombic intermediate structure proposed for the latter is not observed in any of our simulations.

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

    DOE PAGES

    Tamm, Artur; Aabloo, Alvo; Klintenberg, Mattias; ...

    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

  12. Understanding the catalytic activity of nanoporous gold: Role of twinning in fcc lattice

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

    Nanoporous gold (NPG) prepared by de-alloying Al2Au exhibits correlation between the high catalytic reactivity towards CO oxidation and the density of twinning defects in the fcc lattice of NPG. It was also discovered that on the internal surface of NPG, quite common twinning defects can create close-packed rows of six-coordinated catalytically active Au atoms denoted as W-chains. In this work, using density functional theory methods, we investigate energy conditions for formation, thermal stability, and chemical reactivity of these active sites. The possibility of dioxygen chemisorption on various surface sites is studied in detail. A contribution from the dispersion interactions is also considered. The calculated surface density of the active six-coordinated atoms in NPG comparable with that of supported gold nanoparticle catalysts, exothermic chemisorption of dioxygen, and the energy profiles of reaction pathways for CO oxidation indicate that the six-coordinated sites created by twinning can significantly contribute to the catalytic activity of NPG.

  13. Conceptual design of a pre-booster ring for FCC e+e- injector

    NASA Astrophysics Data System (ADS)

    Etisken, O.; Papaphilippou, Y.; Ciftci, A. K.

    2017-07-01

    The FCC-e+e- injector complex needs to produce and to transport a high-intensity e+/e- beam at a fast repetition rate of about 0.1 Hz for topping up the collider at its collision energy. A basic parameter set exists for all the collider energies, assuming a 10 GeV linac operating with a large number of bunches being accumulated in the existing SPS, which serves as pre-accelerator and damping ring before the bunches are transferred to the high-energy booster. The purpose of this study is to provide the conceptual design of an alternative accelerator ring, replacing the SPS in the present scheme. This ring will have injection energy of 6 GeV and extraction energy of 20 GeV. In this study, the basic parameters of the ring are established, including the optics design and layout. Preliminary consideration for non-linear dynamics optimization and the impact of intra beam scattering are also presented.

  14. 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.

  15. First-principles study of fcc-Ag/bcc-Fe interfaces

    NASA Astrophysics Data System (ADS)

    Lu, Song; Hu, Qing-Miao; Punkkinen, Marko P. J.; Johansson, Börje; Vitos, Levente

    2013-06-01

    Ab initio calculations are employed to determine the lower and upper bounds of the interfacial energy and work of separation of a fcc-Ag/bcc-Fe interface. The strain-free interfacial energy of the coherent interface is taken as the lower bound and the interfacial energy of the commensurate incoherent interface as the upper bound of the interfacial energy of a realistic semicoherent interface. The latter is estimated by applying an averaging scheme based on the interfacial energies obtained for the coherent interfaces. Similar calculations are performed for determining the bounds of the work of separation. We justify the use of the averaging scheme by carrying out large supercell calculations for a semicoherent interface. For a Fe(110)/Ag(111) semicoherent interface, we show that taking either Fe or Ag as the underlying lattice, our averaging scheme can yield a reasonable estimation of the work of separation of the semicoherent interface. However, when taking Ag as the underlying lattice, the averaged interfacial energy of the semicoherent interface is significantly underestimated due to the magnetism. The structure and magnetism at the coherent and semicoherent interfaces are discussed.

  16. Tunneling anisotropic magnetoresistance in Co/AlOx/Al tunnel junctions with fcc Co (111) electrodes

    NASA Astrophysics Data System (ADS)

    Wang, K.; Tran, T. L. A.; Brinks, P.; Sanderink, J. G. M.; Bolhuis, T.; van der Wiel, W. G.; de Jong, M. P.

    2013-08-01

    Tunneling anisotropic magnetoresistance (TAMR) has been characterized in junctions comprised of face-centered cubic (fcc) Co (111) ferromagnetic electrodes grown epitaxially on sapphire substrates, amorphous AlOx tunnel barriers, and nonmagnetic Al counterelectrodes. Large TAMR ratios have been found, up to ˜7.5% and ˜11% (at 5 K), for the in-plane and out-of-plane magnetization geometry, respectively. Such large TAMR values were not expected a priori, given the weak anisotropy of the (bulk) Co bands due to spin-orbit interaction, and the absence of Co (111) surface states that cross the Fermi energy. Both the in-plane and out-of-plane TAMR effects exhibit a predominantly twofold symmetry, and a strong bias dependence. The in-plane TAMR shows a maximum along the (twofold) magnetic hard axis, suggesting a relation between magnetic anisotropy and TAMR. We propose that uniaxial strain in combination with Bychkov-Rashba spin-orbit interaction, producing an interfacial tunneling DOS that depends on the magnetization direction, is responsible for the TAMR effect. The importance of the interfacial Co/AlOx (electronic) structure for the TAMR effect is underlined by measurements on junctions with overoxidized AlOx barriers, which show markedly different bias and angle dependence.

  17. Experimental Evaluation of the Taylor-Type Polycrystal Model for the Finite Deformation of an FCC Metal (OFHC Copper)

    DTIC Science & Technology

    1991-05-01

    McClintock , Massachusetts Institute of Technology, Department of Mechanical Engineering, Cambridge, MA 02139 1 R. M. McMeeking, University of California...at Santa Barbara , Department of Material Science, Santa Barbara , CA 93111 1 Prof. Alan Miller, Stanford Univerrsity, Department of Materials Science

  18. Structure and magnetic properties of hcp and fcc nanocrystalline thin Ni films and nanoparticles produced by radio frequency magnetron sputtering.

    PubMed

    Kapaklis, Vassilios; Pappas, Spiridon D; Poulopoulos, Panagiotis; Trachylis, Dimitrios; Schweiss, Peter; Politis, Constantin

    2010-09-01

    We report on the growth of thin Ni films by radio frequency magnetron sputtering in Ar-plasma. The growth temperature was about 350 K and the films were deposited on various substrates such as glass, silicon, sapphire and alumina. The thickness of the thinnest films was estimated by the appearance of Kiessig fringes up to about 2theta = 8 degrees in the small-angle X-ray diffraction pattern, as expected for high-quality atomically-flat thin films. With the help of this, a quartz balance system was calibrated and used for measuring the thickness of thicker samples with an accuracy of better than 5%. Structural characterization via X-ray diffraction and high resolution transmission electron microscopy revealed an Ar-gas pressure window, where single phase hcp Ni films may be grown. The magnetic response of the Ni films was checked at room temperature via a newly established and fully automatic polar magneto-optic Kerr effect magnetometer. The hcp films show no magnetic response. Interestingly, the magnetic saturation field of fcc films deposited at low Ar pressure is comparable to the one of bulk Ni, while the one of fcc films deposited at high Ar pressures is decreased, revealing the presence of residual strain in the films. Finally, it is shown that it is possible to form films which contain magnetic Ni fcc nanoparticles in a non-magnetic hcp matrix, i.e., a system interesting for technological applications demanding a single Ni target for its production.

  19. Reuse of spent FCC catalyst, waste serpentine and kiln rollers waste for synthesis of cordierite and cordierite-mullite ceramics.

    PubMed

    Ramezani, A; Emami, S M; Nemat, S

    2017-09-15

    Spent fluid catalytic cracking (FCC) was gathered from several petrochemical plants and calcined in a rotary furnace between 1000 and 1100°C in order to remove sulphur and hydrocarbon based impurities. Calcining process on FCC led to formation of AlVO4 ceramic phase, so converted the hazardous waste to non-hazardous applicable raw material. In this study, two ceramic bodies as cordierite and cordierite-mullite were synthesized with calcined spent FCC, waste serpentine, kiln rollers waste and high grade kaolin as raw materials. The XRD results showed that the cordierite and cordierite-mullite were synthesized successfully so that 96.4% of F1 (cordierite) sample fired at 1400°C was cordierite phase and F2 (cordierite-mullite) sample fired at 1450°C was completely cordierite and mullite phases. The synthesized cordierite and cordierite-mullite samples had lower porosity values and coefficient of thermal expansion (CTE) than similar industrial products. The negative CTE value that obtained from the cordierite sample up to 800°C is favorable for some applications. The considerable results of the synthesized cordierite and cordierite-mullite from this work present cost reduction of the two ceramic bodies production and may help to solve the environmental problems with the use of three waste sources in large scales. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. Microemulsion-mediated synthesis of cobalt (pure fcc and hexagonal phases) and cobalt-nickel alloy nanoparticles.

    PubMed

    Ahmed, Jahangeer; Sharma, Shudhanshu; Ramanujachary, Kandalam V; Lofland, Samuel E; Ganguli, Ashok K

    2009-08-15

    By choosing appropriate microemulsion systems, hexagonal cobalt (Co) and cobalt-nickel (1:1) alloy nanoparticles have been obtained with cetyltrimethylammonium bromide as a cationic surfactant at 500 degrees C. This method thus stabilizes the hcp cobalt even at sizes (<10 nm) at which normally fcc cobalt is predicted to be stable. On annealing the hcp cobalt nanoparticles in H(2) at 700 degrees C we could transform them to fcc cobalt nanoparticles. Microscopy studies show the formation of spherical nanoparticles of hexagonal and cubic forms of cobalt and Co-Ni (1:1) alloy nanoparticles with the average size of 4, 8 and 20 nm, respectively. Electrochemical studies show that the catalytic property towards oxygen evolution is dependent on the applied voltage. At low voltage (less than 0.65 V) the Co (hexagonal) nanoparticles are superior to the alloy (Co-Ni) nanoparticles while above this voltage the alloy nanoparticles are more efficient catalysts. The nanoparticles of cobalt (hcp and fcc) and alloy (Co-Ni) nanoparticles show ferromagnetism. The saturation magnetization of Co-Ni nanoparticles is reduced compared to the bulk possibly due to surface oxidation.