WorldWideScience

Sample records for metal atom heat

  1. Atomic spectrometry based on metallic tube atomizers heated by flame: Innovative strategies from fundamentals to analysis

    Arruda, Marco Aurelio Zezzi; Figueiredo, Eduardo Costa

    2009-01-01

    This review describes recent developments in atomic absorption spectrometry using metallic tube atomizers heated by flames. Sample introduction in spray or gaseous form is emphasized, describing some proposed systems for this task and the fundamentals involved in each context. The latest challenges and future possibilities for use of metallic tubes in atomic/mass spectrometry are also considered.

  2. Mechanism of yttrium atom formation in electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

    Wahab, H.S.; Chakrabarti, C.L.

    1981-01-01

    Mechanism of Y atom formation from pyrocoated graphite, tantalum and tungsten metal surfaces of a graphite tube atomizer has been studied and a mechanism for the formation for Y atoms is proposed for the first time. (author)

  3. Metal atom oxidation laser

    Jensen, R.J.; Rice, W.W.; Beattie, W.H.

    1975-01-01

    A chemical laser which operates by formation of metal or carbon atoms and reaction of such atoms with a gaseous oxidizer in an optical resonant cavity is described. The lasing species are diatomic or polyatomic in nature and are readily produced by exchange or other abstraction reactions between the metal or carbon atoms and the oxidizer. The lasing molecules may be metal or carbon monohalides or monoxides

  4. Heat capacity measurements of atoms and molecules adsorbed on evaporated metal films

    Kenny, T.W.

    1989-05-01

    Investigations of the properties of absorbed monolayers have received great experimental and theoretical attention recently, both because of the importance of surface processes in practical applications such as catalysis, and the importance of such systems to the understanding of the fundamentals of thermodynamics in two dimensions. We have adapted the composite bolometer technology to the construction of microcalorimeters. For these calorimeters, the adsorption substrate is an evaporated film deposited on one surface of an optically polished sapphire wafer. This approach has allowed us to make the first measurements of the heat capacity of submonolayer films of 4 He adsorbed on metallic films. In contrast to measurements of 4 He adsorbed on all other insulating substrates, we have shown that 4 He on silver films occupies a two-dimensional gas phase over a broad range of coverages and temperatures. Our apparatus has been used to study the heat capacity of Indium flakes. CO multilayers, 4 He adsorbed on sapphire and on Ag films and H 2 adsorbed on Ag films. The results are compared with appropriate theories. 68 refs., 19 figs

  5. Atomic absorption spectrometry using tungsten and molybdenum tubes as metal atomizer

    Kaneco, Satoshi; Katsumata, Hideyuki; Ohta, Kiyohisa; Suzuki, Tohru

    2007-01-01

    We have developed a metal tube atomizer for the electrothermal atomization atomic absorption spectrometry (ETA-AAS). Tungsten, molybdenum, platinum tube atomizers were used as the metal atomizer for ETA-AAS. The atomization characteristics of various metals using these metal tube atomizers were investigated. The effects of heating rate of atomizer, atomization temperature, pyrolysis temperature, argon purge gas flow rate and hydrogen addition on the atomic absorption signal were investigated for the evaluation of atomization characteristics. Moreover, ETA-AAS with metal tube atomizer has been combined with the slurry-sampling techniques. Ultrasonic slurry-sampling ETA-AAS with metal tube atomizer were effective for the determination of trace metal elements in biological materials, calcium drug samples, herbal medicine samples, vegetable samples and fish samples. Furthermore, a preconcentration method of trace metals involving adsorption on a metal wire has been applied to ETA-AAS with metal tube atomizer. (author)

  6. Chain formation of metal atoms

    Bahn, Sune Rastad; Jacobsen, Karsten Wedel

    2001-01-01

    The possibility of formation of single-atomic chains by manipulation of nanocontacts is studied for a selection of metals (Ni, Pd, Pt, Cu, Ag, Au). Molecular dynamics simulations show that the tendency for chain formation is strongest for Au and Pt. Density functional theory calculations indicate...... that the metals which form chains exhibit pronounced many-atom interactions with strong bonding in low coordinated systems....

  7. Atomic bonding between metal and graphene

    Wang, Hongtao

    2013-03-07

    To understand structural and chemical properties of metal-graphene composites, it is crucial to unveil the chemical bonding along the interface. We provide direct experimental evidence of atomic bonding between typical metal nano structures and graphene, agreeing well with density functional theory studies. Single Cr atoms are located in the valleys of a zigzag edge, and few-atom ensembles preferentially form atomic chains by self-assembly. Low migration barriers lead to rich dynamics of metal atoms and clusters under electron irradiation. We demonstrate no electron-instigated interaction between Cr clusters and pristine graphene, though Cr has been reported to be highly reactive to graphene. The metal-mediated etching is a dynamic effect between metal clusters and pre-existing defects. The resolved atomic configurations of typical nano metal structures on graphene offer insight into modeling and simulations on properties of metal-decorated graphene for both catalysis and future carbon-based electronics. © 2013 American Chemical Society.

  8. Shocked plate metal atom oxidation laser

    De Koker, J.G.; Rice, W.W. Jr.; Jensen, R.J.

    1975-01-01

    A method and apparatus for producing metal atom oxidation lasing wherein an explosively shocked grooved metal plate produces metal vapor jets directed through an appropriate gaseous oxidizer are described. Reaction of the metal vapor with the oxidizer produces molecular species having a population inversion therein. (U.S.)

  9. Calculated Atomic Volumes of the Actinide Metals

    Skriver, H.; Andersen, O. K.; Johansson, B.

    1979-01-01

    The equilibrium atomic volume is calculated for the actinide metals. It is possible to account for the localization of the 5f electrons taking place in americium.......The equilibrium atomic volume is calculated for the actinide metals. It is possible to account for the localization of the 5f electrons taking place in americium....

  10. Atomic bonding between metal and graphene

    Wang, Hongtao; Feng, Qiong; Cheng, Yingchun; Yao, Yingbang; Wang, Qingxiao; Li, Kun; Schwingenschlö gl, Udo; Zhang, Xixiang; Yang, Wei

    2013-01-01

    and graphene, agreeing well with density functional theory studies. Single Cr atoms are located in the valleys of a zigzag edge, and few-atom ensembles preferentially form atomic chains by self-assembly. Low migration barriers lead to rich dynamics of metal

  11. Highly Dense Isolated Metal Atom Catalytic Sites

    Chen, Yaxin; Kasama, Takeshi; Huang, Zhiwei

    2015-01-01

    -ray diffraction. A combination of electron microscopy images with X-ray absorption spectra demonstrated that the silver atoms were anchored on five-fold oxygen-terminated cavities on the surface of the support to form highly dense isolated metal active sites, leading to excellent reactivity in catalytic oxidation......Atomically dispersed noble-metal catalysts with highly dense active sites are promising materials with which to maximise metal efficiency and to enhance catalytic performance; however, their fabrication remains challenging because metal atoms are prone to sintering, especially at a high metal...... loading. A dynamic process of formation of isolated metal atom catalytic sites on the surface of the support, which was achieved starting from silver nanoparticles by using a thermal surface-mediated diffusion method, was observed directly by using in situ electron microscopy and in situ synchrotron X...

  12. Atomization process for metal powder

    Lagutkin, Stanislav; Achelis, Lydia; Sheikhaliev, Sheikhali; Uhlenwinkel, Volker; Srivastava, Vikas

    2004-01-01

    A new atomization process has been developed, which combines pressure and gas atomization. The melt leaves the pressure nozzle as a hollow thin film cone. After the pre-filming step, the melt is atomized by a gas stream delivered by a ring nozzle. The objectives of this investigation are to achieve a narrow size distribution and low specific gas consumption compared to conventional gas atomization techniques. Both lead to a higher efficiency and low costs. Tin and some alloys have been atomized successfully with this technique. The mass median diameters from different experiments are between 20 and 100 μm. Sieving analysis of the tin powder shows close particle size distributions

  13. Liquid metal heat transfer issues

    Hoffman, H.W.; Yoder, G.L.

    1984-01-01

    An alkali liquid metal cooled nuclear reactor coupled with an alkali metal Rankine cycle provides a practicable option for space systems/missions requiring power in the 1 to 100 MW(e) range. Thermal issues relative to the use of alkali liquid metals for this purpose are identified as these result from the nature of the alkali metal fluid itself, from uncertainties in the available heat transfer correlations, and from design and performance requirements for system components operating in the earth orbital microgravity environment. It is noted that, while these issues require further attention to achieve optimum system performance, none are of such magnitude as to invalidate this particular space power concept

  14. Ultrahigh stability of atomically thin metallic glasses

    Cao, C. R.; Huang, K. Q.; Zhao, N. J.; Sun, Y. T.; Bai, H. Y.; Gu, L., E-mail: l.gu@iphy.ac.cn, E-mail: dzheng@iphy.ac.cn, E-mail: whw@iphy.ac.cn; Zheng, D. N., E-mail: l.gu@iphy.ac.cn, E-mail: dzheng@iphy.ac.cn, E-mail: whw@iphy.ac.cn; Wang, W. H., E-mail: l.gu@iphy.ac.cn, E-mail: dzheng@iphy.ac.cn, E-mail: whw@iphy.ac.cn [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2014-07-07

    We report the fabrication and study of thermal stability of atomically thin ZrCu-based metallic glass films. The ultrathin films exhibit striking dynamic properties, ultrahigh thermal stability, and unique crystallization behavior with discrete crystalline nanoparticles sizes. The mechanisms for the remarkable high stability and crystallization behaviors are attributed to the dewetting process of the ultrathin film. We demonstrated a promising avenue for understanding some fundamental issues such as glassy structure, crystallization, deformation, and glass formation through atomic resolution imaging of the two dimensional like metallic glasses.

  15. Living Colloidal Metal Particles from Solvated Metal Atoms. Clustering of Metal Atoms in Organic Media 15.

    1986-09-23

    attributed to these solutions, especially toward heart disease. And in 1618 Antoni published Panacea Aurea : Auro Potabile 4 which centered on the...probably a slow process (discussed next under the electrophoresis section ). Electrophoresis: Electrophoresis, the movement of charged particles in...electrical properties. Experimental Section Preparation of a Typical Au-Acetone Colloid The metal atom reactor has been described previo sly. 3 9 ’ 5 9 ’ 6 0

  16. Atomic defects and diffusion in metals

    Siegel, R.W.

    1981-11-01

    The tracer self-diffusion data for fcc and refractory bcc metals are briefly reviewed with respect to (i) the available monovacancy formation and migration properties and (ii) the high-temperature diffusion enhancement above that expected for mass transport via atomic exchange with monovacancies. While the atomic-defect mechanism for low-temperature self-diffusion can be reliably attributed to monovacancies, the mechanisms responsible for high-temperature mass transport are not so easily defined at this time; both divacancies and interstitials must be seriously considered. Possibilities for improving our understanding in this area are discussed. 68 references, 7 figures

  17. Nonstationary Heat Conduction in Atomic Systems

    Singh, Amit K.

    Understanding heat at the atomistic level is an interesting exercises. It is fascinating to note how the vibration of atoms result into thermodynamic concept of heat. This thesis aims to bring insights into different constitutive laws of heat conduction. We also develop a framework in which the interaction of thermostats to the system can be studied and a well known Kapitza effect can be reduced. The thesis also explores stochastic and continuum methods to model the latent heat release in the first order transition of ideal silicon surfaces into dimers. We divide the thesis into three works which are connected to each other: 1. Fourier's law leads to a diffusive model of heat transfer in which a thermal signal propagates infinitely fast and the only material parameter is the thermal conductivity. In micro- and nano-scale systems, non-Fourier effects involving coupled diffusion and wavelike propagation of heat can become important. An extension of Fourier's law to account for such effects leads to a Jeffreys-type model for heat transfer with two relaxation times. In this thesis, we first propose a new Thermal Parameter Identification (TPI) method for obtaining the Jeffreys-type thermal parameters from molecular dynamics simulations. The TPI method makes use of a nonlinear regression-based approach for obtaining the coefficients in analytical expressions for cosine and sine-weighted averages of temperature and heat flux over the length of the system. The method is applied to argon nanobeams over a range of temperature and system sizes. The results for thermal conductivity are found to be in good agreement with standard Green-Kubo and direct method calculations. The TPI method is more efficient for systems with high diffusivity and has the advantage, that unlike the direct method, it is free from the influence of thermostats. In addition, the method provides the thermal relaxation times for argon. Using the determined parameters, the Jeffreys-type model is able to

  18. Self-interstitial atoms in metals

    Schilling, W.

    1978-01-01

    The present state of knowledge and understanding of the properties of self-interstitial atoms (SIAs) in metals is reviewed. Special emphasis is given to a discussion of the structure of SIAs and those properties which relate to structure such as relaxation volumes, elastic polarizabilities, defect vibrations, geometry of jump processes, and elastic interactions. The present experimental status with respect to these properties is summarized, and the basic theoretical concepts for their understanding are presented as simply as possible. (Auth.)

  19. The atomic structure of transition metal clusters

    Riley, S.J.

    1995-01-01

    Chemical reactions are used to probe the atomic (geometrical) structure of isolated clusters of transition metal atoms. The number of adsorbate molecules that saturate a cluster, and/or the binding energy of molecules to cluster surfaces, are determined as a function of cluster size. Systematics in these properties often make it possible to propose geometrical structures consistent with the experimental observations. We will describe how studies of the reactions of cobalt and nickel clusters with ammonia, water, and nitrogen provide important and otherwise unavailable structural information. Specifically, small (less than 20 atoms) clusters of cobalt and nickel atoms adopt entirely different structures, the former having packing characteristic of the bulk and the latter having pentagonal symmetry. These observations provide important input for model potentials that attempt to describe the local properties of transition metals. In particular, they point out the importance of a proper treatment of d-orbital binding in these systems, since cobalt and nickel differ so little in their d-orbital occupancy

  20. Modeling of microwave heating of metallic powders

    Buchelnikov, V.D.; Louzguine-Luzgin, D.V.; Anzulevich, A.P.; Bychkov, I.V.; Yoshikawa, N.; Sato, M.; Inoue, A.

    2008-01-01

    As it is known from the experiment that bulk metallic samples reflect microwaves while powdered samples can absorb such a radiation and be heated efficiently. In the present paper we investigate theoretically the mechanisms of penetration of a layer of metallic powder by microwave radiation and microwave heating of such a system

  1. Atomically Precise Metal Nanoclusters for Catalytic Application

    Jin, Rongchao [Carnegie Mellon Univ., Pittsburgh, PA (United States)

    2016-11-18

    The central goal of this project is to explore the catalytic application of atomically precise gold nanoclusters. By solving the total structures of ligand-protected nanoclusters, we aim to correlate the catalytic properties of metal nanoclusters with their atomic/electronic structures. Such correlation unravel some fundamental aspects of nanocatalysis, such as the nature of particle size effect, origin of catalytic selectivity, particle-support interactions, the identification of catalytically active centers, etc. The well-defined nanocluster catalysts mediate the knowledge gap between single crystal model catalysts and real-world conventional nanocatalysts. These nanoclusters also hold great promise in catalyzing certain types of reactions with extraordinarily high selectivity. These aims are in line with the overall goals of the catalytic science and technology of DOE and advance the BES mission “to support fundamental research to understand, predict, and ultimately control matter and energy at the level of electrons, atoms, and molecules”. Our group has successfully prepared different sized, robust gold nanoclusters protected by thiolates, such as Au25(SR)18, Au28(SR)20, Au38(SR)24, Au99(SR)42, Au144(SR)60, etc. Some of these nanoclusters have been crystallographically characterized through X-ray crystallography. These ultrasmall nanoclusters (< 2 nm diameter) exhibit discrete electronic structures due to quantum size effect, as opposed to quasicontinuous band structure of conventional metal nanoparticles or bulk metals. The available atomic structures (metal core plus surface ligands) of nanoclusters serve as the basis for structure-property correlations. We have investigated the unique catalytic properties of nanoclusters (i.e. not observed in conventional nanogold catalysts) and revealed the structure-selectivity relationships. Highlights of our

  2. A library of atomically thin metal chalcogenides.

    Zhou, Jiadong; Lin, Junhao; Huang, Xiangwei; Zhou, Yao; Chen, Yu; Xia, Juan; Wang, Hong; Xie, Yu; Yu, Huimei; Lei, Jincheng; Wu, Di; Liu, Fucai; Fu, Qundong; Zeng, Qingsheng; Hsu, Chuang-Han; Yang, Changli; Lu, Li; Yu, Ting; Shen, Zexiang; Lin, Hsin; Yakobson, Boris I; Liu, Qian; Suenaga, Kazu; Liu, Guangtong; Liu, Zheng

    2018-04-01

    Investigations of two-dimensional transition-metal chalcogenides (TMCs) have recently revealed interesting physical phenomena, including the quantum spin Hall effect 1,2 , valley polarization 3,4 and two-dimensional superconductivity 5 , suggesting potential applications for functional devices 6-10 . However, of the numerous compounds available, only a handful, such as Mo- and W-based TMCs, have been synthesized, typically via sulfurization 11-15 , selenization 16,17 and tellurization 18 of metals and metal compounds. Many TMCs are difficult to produce because of the high melting points of their metal and metal oxide precursors. Molten-salt-assisted methods have been used to produce ceramic powders at relatively low temperature 19 and this approach 20 was recently employed to facilitate the growth of monolayer WS 2 and WSe 2 . Here we demonstrate that molten-salt-assisted chemical vapour deposition can be broadly applied for the synthesis of a wide variety of two-dimensional (atomically thin) TMCs. We synthesized 47 compounds, including 32 binary compounds (based on the transition metals Ti, Zr, Hf, V, Nb, Ta, Mo, W, Re, Pt, Pd and Fe), 13 alloys (including 11 ternary, one quaternary and one quinary), and two heterostructured compounds. We elaborate how the salt decreases the melting point of the reactants and facilitates the formation of intermediate products, increasing the overall reaction rate. Most of the synthesized materials in our library are useful, as supported by evidence of superconductivity in our monolayer NbSe 2 and MoTe 2 samples 21,22 and of high mobilities in MoS 2 and ReS 2 . Although the quality of some of the materials still requires development, our work opens up opportunities for studying the properties and potential application of a wide variety of two-dimensional TMCs.

  3. Alkali Metal Heat Pipe Life Issues

    Reid, Robert S.

    2004-01-01

    One approach to fission power system design uses alkali metal heat pipes for the core primary heat-transfer system. Heat pipes may also be used as radiator elements or auxiliary thermal control elements. This synopsis characterizes long-life core heat pipes. References are included where information that is more detailed can be found. Specifics shown here are for demonstration purposes and do not necessarily reflect current Nasa Project Prometheus point designs. (author)

  4. Heat Transfer in Metal Foam Heat Exchangers at High Temperature

    Hafeez, Pakeeza

    Heat transfer though open-cell metal foam is experimentally studied for heat exchanger and heat shield applications at high temperatures (˜750°C). Nickel foam sheets with pore densities of 10 and 40 pores per linear inch (PPI), have been used to make the heat exchangers and heat shields by using thermal spray coating to deposit an Inconel skin on a foam core. Heat transfer measurements were performed on a test rig capable of generating hot gas up to 1000°C. The heat exchangers were tested by exposing their outer surface to combustion gases at a temperature of 550°C and 750°C while being cooled by air flowing through them at room temperature at velocities up to 5 m/s. The temperature rise of the air, the surface temperature of the heat exchangers and the air temperature inside the heat exchanger were measured. The volumetric heat transfer coefficient and Nusselt number were calculated for different velocities. The heat transfer performance of the 40PPI sample brazed with the foil is found to be the most efficient. Pressure drop measurements were also performed for 10 and 40PPI metal foam. Thermographic measurements were done on 40PPI foam heat exchangers using a high temperature infrared camera. A high power electric heater was used to produce hot air at 300°C that passed over the foam heat exchanger while the cooling air was blown through it. Heat shields were made by depositing porous skins on metal foam and it was observed that a small amount of coolant leaking through the pores notably reduces the heat transfer from the hot gases. An analytical model was developed based assuming local thermal non-equilibrium that accounts for the temperature difference between solid and fluid phase. The experimental results are found to be in good agreement with the predicted values of the model.

  5. Photoionization microscopy of hydrogen atom near a metal surface

    Yang Hai-Feng; Wang Lei; Liu Xiao-Jun; Liu Hong-Ping

    2011-01-01

    We have studied the ionization of Rydberg hydrogen atom near a metal surface with a semiclassical analysis of photoionization microscopy. Interference patterns of the electron radial distribution are calculated at different scaled energies above the classical saddle point and at various atom—surface distances. We find that different types of trajectories contribute predominantly to different manifolds in a certain interference pattern. As the scaled energy increases, the structure of the interference pattern evolves smoothly and more types of trajectories emerge. As the atom approaches the metal surface closer, there are more types of trajectories contributing to the interference pattern as well. When the Rydberg atom comes very close to the metal surface or the scaled energy approaches the zero field ionization energy, the potential induced by the metal surface will make atomic system chaotic. The results also show that atoms near a metal surface exhibit similar properties like the atoms in the parallel electric and magnetic fields. (atomic and molecular physics)

  6. Self-excitation of Rydberg atoms at a metal surface

    Bordo, Vladimir

    2017-01-01

    The novel effect of self-excitation of an atomic beam propagating above a metal surface is predicted and a theory is developed. Its underlying mechanism is positive feedback provided by the reflective surface for the atomic polarization. Under certain conditions the atomic beam flying in the near...... field of the metal surface acts as an active device that supports sustained atomic dipole oscillations, which generate, in their turn, an electromagnetic field. This phenomenon does not exploit stimulated emission and therefore does not require population inversion in atoms. An experiment with Rydberg...... atoms in which this effect should be most pronounced is proposed and the necessary estimates are given....

  7. Heating effects in a liquid metal ion source

    Mair, G.L.R.; Aitken, K.L.

    1984-01-01

    A reassessment is made of the heating occurring at the anode of a liquid metal ion source, in the light of new microscopic observations. The apex region of the cones is in the form of a cusp, or jet, even at very low currents. The calculation for ohmic heating is conclusive for low currents; no heating occurs at the anode; for high currents (approx. 50-100 μA), substantial heating is conceivable, if a long, very thin, cylindrical jet exists at the apex of the anode. The answer to the problem of external heating, in the form of electrons bombarding the anode, is not quite conclusive; this is because of the impossibility of correctly assessing the electron flux entering the anode. However, it would appear to be a definite conclusion that for reasons of self-consistency field-ionisation of thermally released atoms cannot be a significant ion emission mechanism. (author)

  8. Supplementary plasma heating studies in the Atomic Energy Commission France

    Consoli, T.

    1976-01-01

    The research on supplementary heating of toroidal plasma made in France at the Atomic Energy Commission and in the European Community are described (with special reference to the J.E.T. project) in the frame of the national programs. A non exhaustive description of the world effort in this topic is also presented: (neutral injection heating, TTMP (transit time magnetic pumping) heating, electron and ion cyclotron resonance, and lower hybrid resonance heating)

  9. The effect of atoms excited by electron beam on metal evaporation

    Xie Guo Feng; Ying Chun Tong

    2002-01-01

    In atomic vapor laser isotope separation (AVLIS), the metal is heated to melt by electron beams. The vapor atoms may be excited by electrons when flying through the electron beam. The excited atoms may be deexcited by inelastic collision during expansion. The electronic energy transfers translational energy. In order to analyse the effect of reaction between atoms and electron beams on vapor physical parameters, such as density, velocity and temperature, direct-simulation Monte Carlo method (DSMC) is used to simulate the 2-D gadolinium evaporation from long and narrow crucible. The simulation results show that the velocity and temperature of vapor increase, and the density decreases

  10. Relaxation processes during amorphous metal alloys heating

    Malinochka, E.Ya.; Durachenko, A.M.; Borisov, V.T.

    1982-01-01

    Behaviour of Te+15 at.%Ge and Fe+13 at.%P+7 at.%C amorphous metal alloys during heating has been studied using the method of differential scanning calorimetry (DSC) as the most convenient one for determination of the value of heat effects, activation energies, temperature ranges of relaxation processes. Thermal effects corresponding to high-temperature relaxation processes taking place during amorphous metal alloys (AMA) heating are detected. The change of ratio of relaxation peaks values on DSC curves as a result of AMA heat treatment can be explained by the presence of a number of levels of inner energy in amorphous system, separated with potential barriers, the heights of which correspond to certain activation energies of relaxation processes

  11. Metal powder production by gas atomization

    Ting, E. Y.; Grant, N. J.

    1986-01-01

    The confined liquid, gas-atomization process was investigated. Results from a two-dimensional water model showed the importance of atomization pressure, as well as delivery tube and atomizer design. The atomization process at the tip of the delivery tube was photographed. Results from the atomization of a modified 7075 aluminum alloy yielded up to 60 wt pct. powders that were finer than 45 microns in diameter. Two different atomizer designs were evaluated. The amount of fine powders produced was correlated to a calculated gas-power term. An optimal gas-power value existed for maximized fine powder production. Atomization at gas-power greater than or less than this optimal value produced coarser powders.

  12. Long-range interactions among three alkali-metal atoms

    Marinescu, M.; Starace, A.F.

    1996-01-01

    The long-range asymptotic form of the interaction potential surface for three neutral alkali-metal atoms in their ground states may be expressed as an expansion in inverse powers of inter-nuclear distances. The first leading powers are proportional to the dispersion coefficients for pairwise atomic interactions. They are followed by a term responsible for a three body dipole interaction. The authors results consist in evaluation of the three body dipole interaction coefficient between three alkali-metal atoms. The generalization to long-range n atom interaction terms will be discussed qualitatively

  13. Controlled Fabrication of Metallic Electrodes with Atomic Separation

    Morpurgo, A.; Robinson, D.; M. Marcus, C.

    1998-01-01

    We report a new technique for fabricating metallic electrodes on insulating substrates with separations on the 1 nm scale. The fabrication technique, which combines lithographic and electrochemical methods, provides atomic resolution without requiring sophisticated instrumentation. The process is...

  14. Momentum densities and Compton profiles of alkali-metal atoms

    Abstract. It is assumed that the dynamics of valence electrons of alkali-metal atoms can be well accounted for by a quantum-defect theoretic model while the core electrons may be supposed to move in a self-consistent field. This model is used to study the momentum properties of atoms from. 3Li to 37Rb. The numerical ...

  15. Electromigration of single metal atoms observed by scanning tunneling microscopy

    Braun, K.-F.; Soe, W.H.; Flipse, C.F.J.

    2007-01-01

    The authors show in this letter that single metal atoms on a Ni(111) surface can be pushed by electromigration forces from a scanning tunneling microscope tip. This repulsive interaction is obsd. over a length scale of 6 nm. While for voltages above -300 mV the atoms are pulled by the microscope

  16. METAL CHIP HEATING PROCESS INVESTIGATION (Part I

    O. M. Dyakonov

    2007-01-01

    Full Text Available The main calculation methods for heat- and mass transfer in porous heterogeneous medium have been considered. The paper gives an evaluation of the possibility to apply them for calculation of metal chip heating process. It has been shown that a description of transfer processes in a chip has its own specific character that is attributed to difference between thermal and physical properties of chip material and lubricant-coolant components on chip surfaces. It has been determined that the known expressions for effective heat transfer coefficients can be used as basic ones while approaching mutually penetrating continuums. A mathematical description of heat- and mass transfer in chip medium can be considered as a basis of mathematical modeling, numerical solution and parameter optimization of the mentioned processes.

  17. A heated vapor cell unit for DAVLL in atomic rubidium

    McCarron, Daniel J.; Hughes, Ifan G.; Tierney, Patrick; Cornish, Simon L.

    2007-01-01

    The design and performance of a compact heated vapor cell unit for realizing a dichroic atomic vapor laser lock (DAVLL) for the D2 transitions in atomic rubidium is described. A 5 cm-long vapor cell is placed in a double-solenoid arrangement to produce the required magnetic field; the heat from the solenoid is used to increase the vapor pressure and correspondingly the DAVLL signal. We have characterized experimentally the dependence of important features of the DAVLL signal on magnetic field...

  18. Compact device to heat up a liquid metal

    Blanc, R.; Pelloux, L.

    1981-01-01

    Device for heating a liquid metal, sodium for instance, this device being in one piece and capable of being introduced in one go into the tank containing the liquid metal and comprising heating rods and an electromagnetic pump [fr

  19. Formation and properties of metal-oxygen atomic chains

    Thijssen, W.H.A.; Strange, Mikkel; de Brugh, J.M.J.A.

    2008-01-01

    of longer atomic chains. The mechanical and electrical properties of these diatomic chains have been investigated by determining local vibration modes of the chain and by measuring the dependence of the average chain-conductance on the length of the chain. Additionally, we have performed calculations......Suspended chains consisting of single noble metal and oxygen atoms have been formed. We provide evidence that oxygen can react with and be incorporated into metallic one-dimensional atomic chains. Oxygen incorporation reinforces the linear bonds in the chain, which facilitates the creation...

  20. Removal of foreign atoms from a metal surface bombarded with fast atomic particles

    Dolotov, S.K.; Evstigneev, S.A.; Luk' yanov, S.Yu.; Martynenko, Yu.V.; Chicherov, V.M.

    1976-07-01

    A metal surface coated with foreign atoms was irradiated with periodically repeating ion current pulses. The energy of the ions bombarding the target was 20 to 30 keV, and inert gas ions were used. A study of the time dependences of the current of the dislodged foreign atoms showed that the rate of their removal from the target surface is determined by the sputtering coefficient of the substrate metal.

  1. Removal of foreign atoms from a metal surface bombarded with fast atomic particles

    Dolotov, S.K.; Evstigneev, S.A.; Luk'yanov, S.Yu.; Martynenko, Yu.V.; Chicherov, V.M.

    A metal surface coated with foreign atoms was irradiated with periodically repeating ion current pulses. The energy of the ions bombarding the target was 20 to 30 keV, and inert gas ions were used. A study of the time dependences of the current of the dislodged foreign atoms showed that the rate of their removal from the target surface is determined by the sputtering coefficient of the substrate metal

  2. Laser Pulse Heating of Spherical Metal Particles

    Michael I. Tribelsky

    2011-12-01

    Full Text Available We consider the general problem of laser pulse heating of spherical metal particles with the sizes ranging from nanometers to millimeters. We employ the exact Mie solution of the diffraction problem and solve the heat-transfer equation to determine the maximum temperature rise at the particle surface as a function of optical and thermometric parameters of the problem. Primary attention is paid to the case when the thermal diffusivity of the particle is much larger than that of the environment, as it is in the case of metal particles in fluids. We show that, in this case, for any given duration of the laser pulse, the maximum temperature rise as a function of the particle size reaches a maximum at a certain finite size of the particle. We suggest simple approximate analytical expressions for this dependence, which cover the entire parameter range of the problem and agree well with direct numerical simulations.

  3. Metal-halide lamp design: atomic and molecular data needed

    Lapatovich, Walter P

    2009-01-01

    Metal-halide lamps are a subset of high intensity discharge (HID) lamps so named because of their high radiance. These lamps are low temperature (∼0.5 eV), weakly ionized plasmas sustained in refractory but light transmissive envelopes by the passage of electric current through atomic and molecular vapors. For commercial applications, the conversion of electric power to light must occur with good efficiency and with sufficient spectral content throughout the visible (380-780 nm) to permit the light so generated to render colors comparable to natural sunlight. This is achieved by adding multiple metals to a basic mercury discharge. Because the vapor pressure of most metals is very much lower than mercury itself, metal-halide salts of the desired metals, having higher vapor pressures, are used to introduce the material into the basic discharge. The metal compounds are usually polyatomic iodides, which vaporize and subsequently dissociate as they diffuse into the bulk plasma. Metals with multiple visible transitions are necessary to achieve high photometric efficiency (efficacy) and good color. Compounds of Sc, Dy, Ho, Tm, Ce, Pr, Yb and Nd are commonly used. The electrons, atoms and radicals are in local thermodynamic equilibrium (LTE), but not with the radiation field. Strong thermal (10 6 K m -1 ) and density gradients are sustained in the discharge. Atomic radiation produced in the high-temperature core transits through colder gas regions where it interacts with cold atoms and un-dissociated molecules before exiting the lamp. Power balance and spectral output of the lamp are directly affected by the strength of atomic transitions. Attempts to simulate the radiative output of functional metal-halide lamps have been successful only in very simple cases. More data (e.g. the atomic transition probabilities of Ce i) are necessary to improve lamp performance, to select appropriate radiators and in scaling the lamp geometry to various wattages for specific applications.

  4. Direct electrical heating of irradiated metal fuel

    Fenske, G.R.; Emerson, J.E.; Savoie, F.E.; Johanson, E.W.

    1985-01-01

    The Integral Fast Reactor (IFR) concept proposed by Argonne National Laboratory utilizes a metal fuel core. Reactor safety analysis requires information on the potential for fuel axial expansion during severe thermal transients. In addition to a comparatively large thermal expansion coefficient, metallic fuel has a unique potential for enhanced pre-failure expansion driven by retained fission gas and ingested bond sodium. In this paper, the authors present preliminary results from three direct electrical heating (DEH) experiments performed on irradiated metal fuel to investigate axial expansion behavior. The test samples were from Experimental Breeder Reactor II (EBR-II) driver fuel ML-11 irradiated to 8 at.% burnup. Preliminary analysis of the results suggest that enhanced expansion driven by trapped fission gas can occur

  5. A heated vapor cell unit for dichroic atomic vapor laser lock in atomic rubidium.

    McCarron, Daniel J; Hughes, Ifan G; Tierney, Patrick; Cornish, Simon L

    2007-09-01

    The design and performance of a compact heated vapor cell unit for realizing a dichroic atomic vapor laser lock (DAVLL) for the D(2) transitions in atomic rubidium is described. A 5 cm long vapor cell is placed in a double-solenoid arrangement to produce the required magnetic field; the heat from the solenoid is used to increase the vapor pressure and correspondingly the DAVLL signal. We have characterized experimentally the dependence of important features of the DAVLL signal on magnetic field and cell temperature. For the weaker transitions both the amplitude and gradient of the signal are increased by an order of magnitude.

  6. A heated vapor cell unit for dichroic atomic vapor laser lock in atomic rubidium

    McCarron, Daniel J.; Hughes, Ifan G.; Tierney, Patrick; Cornish, Simon L.

    2007-01-01

    The design and performance of a compact heated vapor cell unit for realizing a dichroic atomic vapor laser lock (DAVLL) for the D 2 transitions in atomic rubidium is described. A 5 cm long vapor cell is placed in a double-solenoid arrangement to produce the required magnetic field; the heat from the solenoid is used to increase the vapor pressure and correspondingly the DAVLL signal. We have characterized experimentally the dependence of important features of the DAVLL signal on magnetic field and cell temperature. For the weaker transitions both the amplitude and gradient of the signal are increased by an order of magnitude

  7. Polarizabilities and hyperpolarizabilities of the alkali metal atoms

    Fuentealba, P. (Chile Univ., Santiago (Chile). Departamento de Fisica and Centro de Mecanica Cuantica Aplicada (CMCA)); Reyes, O. (Chile Univ., Santiago (Chile). Dept. de Fisica)

    1993-08-14

    The electric static dipole polarizability [alpha], quadrupole polarizability C, dipole-quadrupole polarizability B, and the second dipole hyperpolarizability [gamma] have been calculated for the alkali metal atoms in the ground state. The results are based on a pseudopotential which is able to incorporate the very important core-valence correlation effect through a core polarization potential, and, in an empirical way, the main relativistic effects. The calculated properties compare very well with more elaborated calculations for the Li atom, excepting the second hyperpolarizability [gamma]. For the other atoms, there is neither theoretical nor experimental information about most of the higher polarizabilities. Hence, the results of this paper should be seen as a first attempt to give a complete account of the series expansion of the interaction energy of an alkali metal atom and a static electric field. (author).

  8. Polarizabilities and hyperpolarizabilities of the alkali metal atoms

    Fuentealba, P.; Reyes, O.

    1993-01-01

    The electric static dipole polarizability α, quadrupole polarizability C, dipole-quadrupole polarizability B, and the second dipole hyperpolarizability γ have been calculated for the alkali metal atoms in the ground state. The results are based on a pseudopotential which is able to incorporate the very important core-valence correlation effect through a core polarization potential, and, in an empirical way, the main relativistic effects. The calculated properties compare very well with more elaborated calculations for the Li atom, excepting the second hyperpolarizability γ. For the other atoms, there is neither theoretical nor experimental information about most of the higher polarizabilities. Hence, the results of this paper should be seen as a first attempt to give a complete account of the series expansion of the interaction energy of an alkali metal atom and a static electric field. (author)

  9. Momentum densities and Compton profiles of alkali-metal atoms

    It is assumed that the dynamics of valence electrons of alkali-metal atoms can be well accounted for by a quantum-defect theoretic model while the core electrons may be supposed to move in a self-consistent field. This model is used to study the momentum properties of atoms from 3Li to 37Rb. The numerical results ...

  10. Inner-shell excitation of alkali-metal atoms

    Tiwary, S.N.

    1987-06-01

    Inner-shell excitation of alkali-metal atoms, which leads to auto-ionization, is reviewed. The validity of quantum mechanical approximation is analyzed and the importance of exchange and correlation is demonstrated. Basic difficulties in making accurate calculations for inner-shell excitation process are discussed. Suggestions are made for further study of inner-shell process in atoms and ions. (author). 26 refs, 4 figs, 1 tab

  11. Thermoplasmonics heating metal nanoparticles using light

    Baffou, Guillaume

    2017-01-01

    Plasmonics is an important branch of optics concerned with the interaction of metals with light. Under appropriate illumination, metal nanoparticles can exhibit enhanced light absorption, becoming nanosources of heat that can be precisely controlled. This book provides an overview of the exciting new field of thermoplasmonics and a detailed discussion of its theoretical underpinning in nanophotonics. This topic has developed rapidly in the last decade, and is now a highly-active area of research due to countless applications in nanoengineering and nanomedicine. These important applications include photothermal cancer therapy, drug and gene delivery, nanochemistry and photothermal imaging. This timely and self-contained text is suited to all researchers and graduate students working in plasmonics, nano-optics and thermal-induced processes at the nanoscale.

  12. Heat dissipating nuclear reactor with metal liner

    Gluekler, E.L.; Hunsbedt, A.; Lazarus, J.D.

    1985-11-21

    A nuclear reactor containment including a reactor vessel disposed within a cavity with capability for complete inherent decay heat removal in the earth and surrounded by a cast steel containment member which surrounds the vessel is described in this disclosure. The member has a thick basemat in contact with metal pilings. The basemat rests on a bed of porous particulate material, into which water is fed to produce steam which is vented to the atmosphere. There is a gap between the reactor vessel and the steel containment member. The containment member holds any sodium or core debris escaping from the reactor vessel if the core melts and breaches the vessel.

  13. Tritiated hydrogen conversion on heated metallic surfaces

    Ionita, G.; Mihaila, V.; Purghel, L.; Rebigan, F.

    1995-01-01

    This work reports investigations on tritiated hydrogen conversion to tritiated water on heated metallic surfaces. The HT conversion process has been revealed for copper, aluminium and stainless steel W4541 surfaces in the temperature range 150 to 300 o C, in case of the static regime and in the range 250 to 400 o C for the dynamic case. The most significant catalytic activity was shown by the copper sample. Studies on this subject are used as input information for different nuclear accident scenarios implying tritium leakage

  14. Microstructure, Properties and Atomic Level Strain in Severely Deformed Rare Metal Niobium

    Lembit KOMMEL

    2012-12-01

    Full Text Available The mechanical and physical properties relationship from atomic level strain/stress causes dislocation density and electrical conductivity relationship, as well as crystallites deformation and hkl-parameter change in the severely deformed pure refractory rare metal Nb at ambient temperature and during short processing times. The above mentioned issues are discussed in this study. For ultrafine-grained and nanocrystalline microstructure forming in metal the equal-channel angular pressing and hard cyclic viscoplastic deformation were used. The flat deformation and heat treatment at different parameters were conducted as follows. The focused ion beam method was used for micrometric measures samples manufacturied under nanocrystalline microstructure study by transmission electron microscope. The microstructure features of metal were studied under different orientations by X-ray diffraction scattering method, and according to the atomic level strains, dislocation density, hkl-parameters and crystallite sizes were calculated by different computation methods. According to results the evolutions of atomic level strains/stresses, induced by processing features have great influence on the microstructure and advanced properties forming in pure Nb. Due to cumulative strain increase the tensile stress and hardness were increased significantly. In this case the dislocation density of Nb varies from 5.0E+10 cm–2 to 2.0E+11 cm–2. The samples from Nb at maximal atomic level strain in the (110 and (211 directions have the maximal values of hkl-parameters, highest tensile strength and hardness but minimal electrical conductivity. The crystallite size was minimal and relative atomic level strain maximal in (211 orientation of crystal. Next, flat deformation and heat treatment increase the atomic level parameters of severely deformed metal.DOI: http://dx.doi.org/10.5755/j01.ms.18.4.3091

  15. Metal nanoparticles via the atom-economy green approach.

    Kalidindi, Suresh Babu; Sanyal, Udishnu; Jagirdar, Balaji R

    2010-05-03

    Metal nanoparticles (NPs) of Cu (air-stable), Ag, and Au have been prepared using an atom-economy green approach. Simple mechanical stirring of solid mixtures (no solvent) of a metal salt and ammonia borane at 60 degrees C resulted in the formation of metal NPs. In this reaction, ammonia borane is transformed into a BNH(x) polymer, which protects the NPs formed and halts their growth. This results in the formation of the BNH(x) polymer protected monodisperse NPs. Thus, ammonia borane used in these reactions plays a dual role (reducing agent and precursor for the stabilizing agent).

  16. Atomic structure of non-stoichiometric transition metal carbides

    Moisy-Maurice, Virginie.

    1981-10-01

    Different kinds of experimental studies of the atomic arrangement in non-stoichiometric transition metal carbides are proposed: the ordering of carbon vacancies and the atomic static displacements are the main subjects studied. Powder neutron diffraction on TiCsub(1-x) allowed us to determine the order-disorder transition critical temperature -Tsub(c) approximately 770 0 C- in the TiCsub(0.52-0.67) range, and to analyze at 300 K the crystal structure of long-range ordered samples. A neutron diffuse scattering quantitative study at 300 K of short-range order in TiCsub(0.76), TiCsub(0.79) and NbCsub(0.73) single crystals is presented: as in Ti 2 Csub(1+x) and Nb 6 C 5 superstructures, vacancies avoid to be on each side of a metal atom. Besides, the mean-square carbon atom displacements from their sites are small, whereas metal atoms move radially about 0.03 A away from vacancies. These results are in qualitative agreement with EXAFS measurements at titanium-K edge of TiCsub(1-x). An interpretation of ordering in term of short-range interaction pair potentials between vacancies is proposed [fr

  17. Single-Atom Catalysts of Precious Metals for Electrochemical Reactions.

    Kim, Jiwhan; Kim, Hee-Eun; Lee, Hyunjoo

    2018-01-10

    Single-atom catalysts (SACs), in which metal atoms are dispersed on the support without forming nanoparticles, have been used for various heterogeneous reactions and most recently for electrochemical reactions. In this Minireview, recent examples of single-atom electrocatalysts used for the oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), hydrogen evolution reaction (HER), formic acid oxidation reaction (FAOR), and methanol oxidation reaction (MOR) are introduced. Many density functional theory (DFT) simulations have predicted that SACs may be effective for CO 2 reduction to methane or methanol production while suppressing H 2 evolution, and those cases are introduced here as well. Single atoms, mainly Pt single atoms, have been deposited on TiN or TiC nanoparticles, defective graphene nanosheets, N-doped covalent triazine frameworks, graphitic carbon nitride, S-doped zeolite-templated carbon, and Sb-doped SnO 2 surfaces. Scanning transmission electron microscopy, extended X-ray absorption fine structure measurement, and in situ infrared spectroscopy have been used to detect the single-atom structure and confirm the absence of nanoparticles. SACs have shown high mass activity, minimizing the use of precious metal, and unique selectivity distinct from nanoparticle catalysts owing to the absence of ensemble sites. Additional features that SACs should possess for effective electrochemical applications were also suggested. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Experimental and theoretical studies of metal vapor atoms

    Whitfield, S.B.; Wehlitz, Ralf; Martins, Michael

    2004-01-01

    Employing electron spectrometry in conjunction with tuneable synchrotron radiation, we will present a detailed examination of the photoionization dynamics of selected metal vapor atoms. In particular, this paper will focus on the relative partial cross sections of the atomic Li K-shell main and satellite (ionization with excitation) photoelectron lines in the region of the strong 1snln'l' autoionizing transitions, the atomic Sc 3d, 4s main and satellite photoelectron lines in the region of the 3p→3d giant resonance, and also the atomic Fe 3d, 4s main and satellite photoelectron lines in the same resonance region. Our experimental data for Sc and Fe will be compared to our state-of-the-art calculations based on the superposition of configuration method developed by Cowan (The Theory of Atomic Structure and Spectra. University of California Berkeley Press, Berkeley and Los Angeles, 1981). Our partial cross section measurements for Li and Sc will be complemented with measurements of the angular distribution parameter, β. In addition, our Li data will also be compared with recent R-matrix calculations (Phys. Rev. 57 (1998) 1045). In the case of Fe, we will also address the term dependent behavior of the partial cross sections on resonance. These results will highlight what can be achieved with today's technology and point the way towards future endeavors in the study of the photoionization dynamics of open-shell metal vapor atoms

  19. Shuttling single metal atom into and out of a metal nanoparticle.

    Wang, Shuxin; Abroshan, Hadi; Liu, Chong; Luo, Tian-Yi; Zhu, Manzhou; Kim, Hyung J; Rosi, Nathaniel L; Jin, Rongchao

    2017-10-10

    It has long been a challenge to dope metal nanoparticles with a specific number of heterometal atoms at specific positions. This becomes even more challenging if the heterometal belongs to the same group as the host metal because of the high tendency of forming a distribution of alloy nanoparticles with different numbers of dopants due to the similarities of metals in outmost electron configuration. Herein we report a new strategy for shuttling a single Ag or Cu atom into a centrally hollow, rod-shaped Au 24 nanoparticle, forming AgAu 24 and CuAu 24 nanoparticles in a highly controllable manner. Through a combined approach of experiment and theory, we explain the shuttling pathways of single dopants into and out of the nanoparticles. This study shows that the single dopant is shuttled into the hollow Au 24 nanoparticle either through the apex or side entry, while shuttling a metal atom out of the Au 25 to form the Au 24 nanoparticle occurs mainly through the side entry.Doping a metal nanocluster with heteroatoms dramatically changes its properties, but it remains difficult to dope with single-atom control. Here, the authors devise a strategy to dope single atoms of Ag or Cu into hollow Au nanoclusters, creating precise alloy nanoparticles atom-by-atom.

  20. Functionalised metal-organic frameworks : A novel approach to stabilising single metal atoms

    Szilagyi, P.A.; Rogers, D. M.; Zaiser, I.; Callini, E; Turner, Stuart; Borgschulte, A; Züttel, A.; Geerlings, J.J.C.; Hirscher, M; Dam, B.

    2017-01-01

    We have investigated the potential of metal-organic frameworks for immobilising single atoms of transition metals using a model system of Pd supported on NH2-MIL-101(Cr). Our transmission electron microscopy and in situ Raman spectroscopy results give evidence for the first time that

  1. A new atomization cell for trace metal determinations by tungsten coil atomic spectrometry

    Donati, G.L., E-mail: georgedonati@yahoo.com.br [Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109 (United States); Wildman, R.B.; Jones, B.T. [Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109 (United States)

    2011-02-28

    A new metallic atomization cell is used for trace metal determinations by tungsten coil atomic absorption spectrometry and tungsten coil atomic emission spectrometry. Different protecting gas mixtures are evaluated to improve atomic emission signals. Ar, N{sub 2}, CO{sub 2} and He are used as solvents, and H{sub 2} and C{sub 2}H{sub 2} as solutes. A H{sub 2}/Ar mixture provided the best results. Parameters such as protecting gas flow rate and atomization current are also optimized. The optimal conditions are used to determine the figures of merit for both methods and the results are compared with values found in the literature. The new cell provides a better control of the radiation reaching the detector and a small, more isothermal environment around the atomizer. A more concentrated atomic cloud and a smaller background signal result in lower limits of detection using both methods. Cu (324.7 nm), Cd (228.8 nm) and Sn (286.3 nm) determined by tungsten coil atomic absorption spectrometry presented limits of detection as low as 0.6, 0.1, and 2.2 {mu}g L{sup -1}, respectively. For Cr (425.4 nm), Eu (459.4 nm) and Sr (460.7 nm) determined by tungsten coil atomic emission spectrometry, limits of detection of 4.5, 2.5, and 0.1 {mu}g L{sup -1} were calculated. The method is used to determine Cu, Cd, Cr and Sr in a water standard reference material. Results for Cu, Cd and Cr presented no significant difference from reported values in a 95% confidence level. For Sr, a 113% recovery was obtained.

  2. Gas-solid heat exchange in a fibrous metallic material measured by a heat regenerator technique

    Golombok, M.; Jariwala, H.; Shirvill, C.

    1990-01-01

    The convective heat transfer properties of a porous metallic fibre material used in gas surface combustion burners are studied. The important parameter governing the heat transfer between hot gas and metal fibre—the heat transfer coefficient—is measured using a non-steady-state method based on

  3. Clustered field evaporation of metallic glasses in atom probe tomography

    Zemp, J.; Gerstl, S.S.A.; Löffler, J.F.; Schönfeld, B.

    2016-01-01

    Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3 nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different – as yet unknown – physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses. - Highlights: • Field evaporation of metallic glasses is heterogeneous on a scale of up to 3 nm. • Amount of clustered evaporation depends on ion species and temperature. • Length scales of clustered evaporation and correlative evaporation are similar.

  4. Electronic specific heat of transition metal carbides

    Conte, R.

    1964-07-01

    The experimental results that make it possible to define the band structure of transition metal carbides having an NaCI structure are still very few. We have measured the electronic specific heat of some of these carbides of varying electronic concentration (TiC, either stoichiometric or non-stoichiometric, TaC and mixed (Ti, Ta) - C). We give the main characteristics (metallography, resistivity, X-rays) of our samples and we describe the low temperature specific heat apparatus which has been built. In one of these we use helium as the exchange gas. The other is set up with a mechanical contact. The two use a germanium probe for thermometer. The measurement of the temperature using this probe is described, as well as the various measurement devices. The results are presented in the form of a rigid band model and show that the density of the states at the Fermi level has a minimum in the neighbourhood of the group IV carbides. (author) [fr

  5. Plasma heating with multi-MeV neutral atom beams

    Grisham, L.R.; Post, D.E.; Mikkelsen, D.R.; Eubank, H.P.

    1981-10-01

    We explore the utility and feasibility of neutral beams of greater than or equal to 6 AMU formed from negative ions, and also of D 0 formed from D - . The negative ions would be accelerated to approx. 1 to 2 MeV/AMU and neutralized, whereupon the neutral atoms would be used to heat and, perhaps, to drive current in magnetically confined plasmas. Such beams appear feasible and offer the promise of significant advantages relative to conventional neutral beams based on positive deuterium ions at approx. 150 keV

  6. Determination of metals in atmospheric particulates using atomic absorption spectrometry

    Alduan, F.A.; Capdevila, C.

    1979-01-01

    Nineteen trace metals in atmospheric samples have been determined by atomic absorption spectrometry, using a graphite furnace for most elements. Paper filters have been used to collect air samples. The sample preparation procedure involves the removal of organic matter and the conversion of the metals to soluble salts by ashing the filters in an oxygen plasma at 125 deg C for 6 h. and by subsequent dissolution in HN0 3 HCl solution. The sensitivities achieved are in the range of 2,5.10 -5 and 6,3.10 -3 μg/m 3 , for an air volume of 2000 m 3 . (author)

  7. Issues involved in the atomic layer deposition of metals

    Grubbs, Robert Kimes

    Auger Electron Spectroscopy (AES) was used to study the nucleation and growth of tungsten on aluminum oxide surfaces. Tungsten metal was deposited using Atomic Layer Deposition (ALD) techniques. ALD uses sequential surface reactions to deposit material with atomic layer control. W ALD is performed using sequential exposures of WF6 and Si2H6. The step-wise nature of W ALD allows nucleation studies to be performed by analyzing the W surface concentration after each ALD reaction. Nucleation and growth regions can be identified by quantifying the AES signal intensities from both the W surface and the Al2O3 substrate. W nucleation occurred in 3 ALD reaction cycles. The AES results yielded a nucleation rate of 1.0 A/ALD cycle and a growth rate of ≈3 A/ALD cycle. AES studies also explored the nucleation and growth of Al2O3 on W. Al2O3 nucleated in 1 ALD cycle giving a nucleation rate of 3.5 A/ALD cycle and a subsequent growth rate of 1.0 A/ALD cycle. Mass spectrometry was then used to study the ALD reaction chemistry of tungsten deposition. Because of the step-wise nature of the W ALD chemistry, each W ALD reaction could be studied independently. The gaseous mass products were identified from both the WF6 and Si2H6 reactions. H2, HF and SiF4 mass products were observed for the WF6 reaction. The Si2H6 reaction displayed a room temperature reaction and a 200°C reaction. Products from the room temperature Si2H6 reaction were H2 and SiF3H. The reaction at 200°C yielded only H2 as a reaction product. H2 desorption from the surface contributes to the 200°C Si2H6 reaction. AES was used to confirm that the gas phase reaction products are correlated with a change in the surface species. Atomic hydrogen reduction of metal halides and oganometallic compounds provides another method for depositing metals with atomic layer control. The quantity of atomic hydrogen necessary to perform this chemistry is critical to the metal ALD process. A thermocouple probe was constructed to

  8. Spectra of matrix isolated metal atoms and clusters

    Meyer, B.

    1977-01-01

    The matrix isolation spectra of all of the 40 presently known atomic metal species show strong matrix effects. The transition energies are increased, and the bands are broad and exhibit splitting of sublevels which are degenerate in the gas phase. Several models have been proposed for splitting of levels, but basic effects are not yet understood, and spectra cannot be predicted, yet it is possible to correlate gas phase and matrix in many of the systems. Selective production of diatomics and clusters via thermal and optical annealing of atomic species can be monitored by optical spectra, but yields spectroscopically complex systems which, however, especially in the case of transition metals, can be used as precursors in novel chemical reactions. A combination of absorption, emission, ir, Raman, ESR, and other methods is now quickly yielding data which will help correlate the increasing wealth of existing data. 55 references, 6 figures

  9. Van der Waals interaction between metal and atom

    Rao, P.R.; Mukhopadhyay, G.

    1984-07-01

    A dielectric response approach to the Van der Waals interaction between an atom and a planar metal surface is presented. An exact formula in terms of a form factor is derived within the point dipole approximation and non-retarded limit valid for shorter separation. The interaction potential is studied via SCIB model, and a substantial modification over its classical form is found at shorter distances. (author)

  10. Measurement of trace metals in vitiligo by atomic absorption spectroscopy

    Abdel-Hamid, Abdel-Aziz M.; Amin, N.E.; Mohy El-Din, Safaa M.

    1985-01-01

    Zn, Cu, Fe, Pb, Mn, Co, Ag, Ca, and Mg were estimated in hair, fingernails and epidermis of vitiligo patients by atomic absorption spectroscopy. There has been a significant reduction in the concentration of trace metals in the studied sites. It seems that any speculation on the role of trace elements in vitiligo would have to take into account the structural defect which underlies the absence of melanin

  11. Beating Homogeneous Nucleation and Tuning Atomic Ordering in Glass-Forming Metals by Nanocalorimetry.

    Zhao, Bingge; Yang, Bin; Abyzov, Alexander S; Schmelzer, Jürn W P; Rodríguez-Viejo, Javier; Zhai, Qijie; Schick, Christoph; Gao, Yulai

    2017-12-13

    In this paper, the amorphous Ce 68 Al 10 Cu 20 Co 2 (atom %) alloy was in situ prepared by nanocalorimetry. The high cooling and heating rates accessible with this technique facilitate the suppression of crystallization on cooling and the identification of homogeneous nucleation. Different from the generally accepted notion that metallic glasses form just by avoiding crystallization, the role of nucleation and growth in the crystallization behavior of amorphous alloys is specified, allowing an access to the ideal metallic glass free of nuclei. Local atomic configurations are fundamentally significant to unravel the glass forming ability (GFA) and phase transitions in metallic glasses. For this reason, isothermal annealing near T g from 0.001 s to 25,000 s following quenching becomes the strategy to tune local atomic configurations and facilitate an amorphous alloy, a mixed glassy-nanocrystalline state, and a crystalline sample successively. On the basis of the evolution of crystallization enthalpy and overall latent heat on reheating, we quantify the underlying mechanism for the isothermal nucleation and crystallization of amorphous alloys. With Johnson-Mehl-Avrami method, it is demonstrated that the coexistence of homogeneous and heterogeneous nucleation contributes to the isothermal crystallization of glass. Heterogeneous rather than homogeneous nucleation dominates the isothermal crystallization of the undercooled liquid. For the mixed glassy-nanocrystalline structure, an extraordinary kinetic stability of the residual glass is validated, which is ascribed to the denser packed interface between amorphous phase and ordered nanocrystals. Tailoring the amorphous structure by nanocalorimetry permits new insights into unraveling GFA and the mechanism that correlates local atomic configurations and phase transitions in metallic glasses.

  12. Direct atomic absorption determination of silicon in metallic niobium

    Blinova, Eh.S.; Guzeev, I.D.; Nedler, V.V.; Khokhrin, V.M.

    1984-01-01

    Consideration is being given to realization of the basic advantage of non-flame atomizer-analysis of directly solid samples-for silicon determination in niobium for the content of the first one of less than 1x10 -3 mass %. Analysis technique is described. Diagrams of the dependences of atomic silicon absorption in graphite cells of usual type as well as lined by tungsten carbide and atomic silicon absorption on the value of niobium weighed amount are presented. It is shown that Si determination in metallic niobium according to aqueous reference solutions results in understatement of results 2.4 times. The optimal conditions for Si determination in niobium are the following: 2400 deg C temperature, absence of carbon and oxygen. Different niobium specimens with the known silicon content were used as reference samples

  13. Metal screen retention for thoron daughter free atoms and atoms attached to condensation nuclei

    Cash, W.; Webb, J.; Fitts, D.; Skrable, K.W.; Chabot, G.E.

    1978-01-01

    Metal support screens available in a 47 mm commercial filter holder (model F3052-4, available from Scientific Products, Bedford, MA) assembly were tested for retention of thoron daughter atoms and atoms attached to condensation nuclei as a function of the flow rate of the carrier air stream. Sources of Pb-212 were generated on the surface of a metal disk by exposing the disk to thoron emanation generated from a special preparation of Th-228. This source of Pb-212, in transient equilibrium with its daughters, was placed in a flow through chamber connected in series to two of the metal screens backed by a glass fiber filter. Most of the recoil product radioactivity emitted from the Pb-212 source and collected on the screens was due to single atoms of Tl-208, which is born by alpha decay of Bi-212 with a recoil energy of 116 keV. Some free atoms of Bi-212 were also observed. Alpha autoradiographs of Filter samples placed on the downstream side of the two metal screens gave proof of the existence of Pb-212 aggregates through their alpha star images. These aggregate recoil particles were found to have a much higher penetration through the screens than free atoms of Tl-208 and Bi-212. Penetration of Tl-208 atoms and ions decreased exponentially as the inverse of the carrier air flow rate. Penetration varied from 0.047 at 0.088 cfm to 0.661 at 2.47 cfm. Atoms of Pb-212 attached to condensation nuclei were obtained by passing thoron into a reaction chamber containing naturally occurring condensation nuclei from the laboratory. The retention for these attached species varied both as a function of the flow rate and the age of the aerosol. The maximum retention varied from 0.525% at 6.38 cfm to 3.5% at 0.636 cfm for respective delay times of 120 and 30 minutes post the introduction of the thoron into the reaction chamber. A system consisting of a single screen backed by a glass fiber filter may be used to obtain the numbers of radon or thoron daughter free atoms and attached

  14. Spatial Distributions of Metal Atoms During Carbon SWNTs Formation: Measurements and Modelling

    Cau, M.; Dorval, N.; Attal-Tretout, B.; Cochon, J. L.; Loiseau, A.; Farhat, S.; Hinkov, I.; Scott, C. D.

    2004-01-01

    Experiments and modelling have been undertaken to clarify the role of metal catalysts during single-wall carbon nanotube formation. For instance, we wonder whether the metal catalyst is active as an atom, a cluster, a liquid or solid nanoparticle [1]. A reactor has been developed for synthesis by continuous CO2-laser vaporisation of a carbon-nickel-cobalt target in laminar helium flow. The laser induced fluorescence technique [2] is applied for local probing of gaseous Ni, Co and CZ species throughout the hot carbon flow of the target heated up to 3500 K. A rapid depletion of C2 in contrast to the spatial extent of metal atoms is observed in the plume (Fig. 1). This asserts that C2 condenses earlier than Ni and Co atoms.[3, 4]. The depletion is even faster when catalysts are present. It may indicate that an interaction between metal atoms and carbon dimers takes place in the gas as soon as they are expelled from the target surface. Two methods of modelling are used: a spatially I-D calculation developed originally for the arc process [5], and a zero-D time dependent calculation, solving the chemical kinetics along the streamlines [6]. The latter includes Ni cluster formation. The peak of C2 density is calculated close to the target surface where the temperature is the highest. In the hot region, C; is dominant. As the carbon products move away from the target and mix with the ambient helium, they recombine into larger clusters, as demonstrated by the peak of C5 density around 1 mm. The profile of Ni-atom density compares fairly well with the measured one (Fig. 2). The early increase is due to the drop of temperature, and the final decrease beyond 6 mm results from Ni cluster formation at the eutectic temperature (approx.1600 K).

  15. Molar Heat Increment under Impact of Transverse Contraction in Metals

    Pekárek, Viktor

    2007-01-01

    Roč. 52, č. 3 (2007), s. 261-268 ISSN 0001-7043 Institutional research plan: CEZ:AV0Z20570509 Keywords : atomic structure * thermal agitation * heat expansion Subject RIV: BM - Solid Matter Physics ; Magnetism

  16. Metal-Insulator-Metal Single Electron Transistors with Tunnel Barriers Prepared by Atomic Layer Deposition

    Golnaz Karbasian

    2017-03-01

    Full Text Available Single electron transistors are nanoscale electron devices that require thin, high-quality tunnel barriers to operate and have potential applications in sensing, metrology and beyond-CMOS computing schemes. Given that atomic layer deposition is used to form CMOS gate stacks with low trap densities and excellent thickness control, it is well-suited as a technique to form a variety of tunnel barriers. This work is a review of our recent research on atomic layer deposition and post-fabrication treatments to fabricate metallic single electron transistors with a variety of metals and dielectrics.

  17. Review of liquid metal heat pipe work at Los Alamos

    Reid, R.S.; Merrigan, M.A.; Sena, J.T.

    1990-01-01

    A survey of space-power related liquid metal heat pipe work at Los Alamos National Laboratory is presented. Heat pipe development at Los Alamos has been on-going since 1963. Heat pipes were initially developed for thermionic nuclear-electrical power production in space. Since then Los Alamos has developed liquid metal heat pipes for numerous applications related to high temperature systems in both the space and terrestrial environments. Some of these applications include thermionic electrical generators, thermoelectric energy conversion (both in-core and direct radiation), thermal energy storage, hypersonic vehicle leading edge cooling, and heat pipe vapor laser cells. Some of the work performed at Los Alamos has been documented in internal reports that are often little-known. A representative description and summary of progress in space-related liquid metal heat pipe technology is provided followed by a reference section citing sources where these works may be found. 53 refs

  18. Understanding Solar Coronal Heating through Atomic and Plasma Physics Experiments

    Savin, Daniel Wolf; Arthanayaka, Thusitha; Bose, Sayak; Hahn, Michael; Beiersdorfer, Peter; Brown, Gregory V.; Gekelman, Walter; Vincena, Steve

    2017-08-01

    Recent solar observations suggest that the Sun's corona is heated by Alfven waves that dissipate at unexpectedly low heights in the corona. These observations raise a number of questions. Among them are the problems of accurately quantifying the energy flux of the waves and that of describing the physical mechanism that leads to the wave damping. We are performing laboratory experiments to address both of these issues.The energy flux depends on the electron density, which can be measured spectroscopically. However, spectroscopic density diagnostics have large uncertainties, because they depend sensitively on atomic collisional excitation, de-excitation, and radiative transition rates for multiple atomic levels. Essentially all of these data come from theory and have not been experimentally validated. We are conducting laboratory experiments using the electron beam ion trap (EBIT) at Lawrence Livermore National Laboratory that will provide accurate empirical calibrations for spectroscopic density diagnostics and which will also help to guide theoretical calculations.The observed rapid wave dissipation is likely due to inhomogeneities in the plasma that drive flows and currents at small length scales where energy can be more efficiently dissipated. This may take place through gradients in the Alfvén speed along the magnetic field, which causes wave reflection and generates turbulence. Alternatively, gradients in the Alfvén speed across the field can lead to dissipation through phase-mixing. Using the Large Plasma Device (LAPD) at the University of California Los Angeles, we are studying both of these dissipation mechanisms in the laboratory in order to understand their potential roles in coronal heating.

  19. Device for removing alkali metal residues from heat exchanger

    Matal, O.

    1987-01-01

    The main parts of the facility consists of a condensing vessel and a vacuum pump unit interconnected via a vacuum pipe. The heat exchanger is heated to a temperature at which the alkali metal residues evaporate. Metal vapors are collected in the condensing vessel where they condense. The removal of the alkali metal residues from the heat exchanger pipes allows thorough inspection of the pipe inside during scheduled nuclear power plant shutdowns. The facility can be used especially with reverse steam generators. (E.S.). 1 fig

  20. Heat transfer characteristics of alkali metals flowing across tube banks

    Sugiyama, K.; Ishiguro, R.; Kojima, Y.; Kanaoka, H.

    2004-01-01

    For the purpose of getting heat transfer coefficients of alkali metals flowing across tube banks at an acceptable level, we propose to use an inviscid-irrotational flow model, which is based on our flow visualization experiment. We show that the heat transfer coefficients obtained for the condition where only the test rod is heated in tube banks considerably differ from those obtained for the condition where all the rods are heated, because of interference between thick thermal boundary layers of alkali metals. We also confirm that the analytical values obtained by this flow model are in a reasonable agreement with experimental values. (author)

  1. Angular distribution of atoms ejected by laser ablation of different metals

    Konomi, I.; Motohiro, T.; Asaoka, T.

    2009-01-01

    Angular distributions of 13 different metals ejected by laser ablation using fourth harmonics (wavelength=266 nm) of neodymium doped yttrium aluminum garnet laser and a fluence close to near-threshold value (2.3 J/cm 2 ) have been investigated with a high angular resolution. The angular distribution which is characterized by the exponent n of cos n θ distribution showed very broad range of values between 3 and 24 for different metals. A simple relation that the exponent n is proportional to the square root of particle atomic weight as reported previously has not been observed. Instead, a general trend has been found that the metals with higher sublimation energy such as Ta and Zr show narrower angular distribution than those with lower sublimation energy such as Sn and In. While the sublimation energy of metals has a great influence on the angular distribution of ejected atoms, a simple consideration suggests that their thermal conductivity and specific heat have little effect on it.

  2. Natural convection heat transfer in the molten metal pool

    Park, R.J.; Kim, S.B.; Kim, H.D.; Choi, S.M.

    1997-01-01

    Analytical studies using the FLOW-3D computer program have been performed on natural convection heat transfer of a high density molten metal pool, in order to evaluate the coolability of the corium pool. The FLOW-3D results on the temperature distribution and the heat transfer rate in the molten metal pool region have been compared and evaluated with the experimental data. The FLOW-3D results have shown that the developed natural convection flow contributes to the solidified crust formation of the high density molten metal pool. The present FLOW-3D results, on the relationship between the Nusselt number and the Rayleigh number in the molten metal pool region, are more similar to the calculated results of Globe and Dropkin's correlation than any others. The natural convection heat transfer in the low aspect ratio case is more substantial than that in the high aspect ratio case. The FLOW-3D results, on the temperature profile and on the heat transfer rate in the molten metal pool region, are very similar to the experimental data. The heat transfer rate of the internal heat generation case is higher than that of the bottom heating case at the same heat supply condition. (author)

  3. Study of the embedded atom method of atomistic calculations for metals and alloys

    Johnson, R.A.

    1990-10-01

    Two projects were completed in the past year. The stability of a series of binary alloys was calculated using the embedded-atom method (EAM) with an analytic form for two-body potentials derived previously. Both disordered alloys and intermetallic compounds with the L1 0 and L1 2 structures were studied. The calculated heats of solution of alloys of Cu, Ag, Au, Ni, and Pt were satisfactory, while results for alloys containing Pd were too high. Atomistic calculations using the EAM were also carried out for point defects in hcp metals. By comparison with results in the literature, it was found that many body effects from the EAM significantly alter predicted physical properties of hcp metals. For example, the EAM calculations yield anisotropic vacancy diffusion with greater vacancy mobility in the basal plane, and imply that diffusion will start at a lower fraction of the melting temperature

  4. A quasi-stationary numerical model of atomized metal droplets, II: Prediction and assessment

    Pryds, Nini H.; Hattel, Jesper Henri; Thorborg, Jesper

    1999-01-01

    been illustrated.A comparison between the numerical model and the experimental results shows an excellent agreement and demonstrates the validity of the present model, e.g. the calculated gas temperature which has an important influence on the droplet solidification behaviour as well as the calculated......A new model which extends previous studies and includes the interaction between enveloping gas and an array of droplets has been developed and presented in a previous paper. The model incorporates the probability density function of atomized metallic droplets into the heat transfer equations....... The main thrust of the model is that the gas temperature was not predetermined and calculated empirically but calculated numerically based on heat balance consideration. In this paper, the accuracy of the numerical model and the applicability of the model as a predictive tool have been investigated...

  5. Potential of Transition Metal Atoms Embedded in Buckled Monolayer g-C3N4 as Single-Atom Catalysts

    Li, Shu-Long

    2017-10-27

    We use first-principles calculations to systematically explore the potential of transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) embedded in buckled monolayer g-C3N4 as single-atom catalysts. We show that clustering of Sc and Ti on g-C3N4 is thermodynamically impeded and that V, Cr, Mn, and Cu are much less susceptible to clustering than the other TM atoms under investigation. Strong bonding of the transition metal atoms in the cavities of g-C3N4 and high diffusion barriers together are responsible for single-atom fixation. Analysis of the CO oxidation process indicates that embedding of Cr and Mn in g-C3N4 gives rise to promising single-atom catalysts at low temperature.

  6. Potential of Transition Metal Atoms Embedded in Buckled Monolayer g-C3N4 as Single-Atom Catalysts

    Li, Shu-Long; Kan, Xiang; Yin, Hui; Gan, Li-Yong; Schwingenschlö gl, Udo; Zhao, Yong

    2017-01-01

    We use first-principles calculations to systematically explore the potential of transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) embedded in buckled monolayer g-C3N4 as single-atom catalysts. We show that clustering of Sc and Ti on g-C3N4 is thermodynamically impeded and that V, Cr, Mn, and Cu are much less susceptible to clustering than the other TM atoms under investigation. Strong bonding of the transition metal atoms in the cavities of g-C3N4 and high diffusion barriers together are responsible for single-atom fixation. Analysis of the CO oxidation process indicates that embedding of Cr and Mn in g-C3N4 gives rise to promising single-atom catalysts at low temperature.

  7. Photo-induced-heat localization on nanostructured metallic glasses

    Uzun, Ceren; Kahler, Niloofar; Grave de Peralta, Luis; Kumar, Golden; Bernussi, Ayrton A.

    2017-09-01

    Materials with large photo-thermal energy conversion efficiency are essential for renewable energy applications. Photo-excitation is an effective approach to generate controlled and localized heat at relatively low excitation optical powers. However, lateral heat diffusion to the surrounding illuminated areas accompanied by low photo-thermal energy conversion efficiency remains a challenge for metallic surfaces. Surface nanoengineering has proven to be a successful approach to further absorption and heat generation. Here, we show that pronounced spatial heat localization and high temperatures can be achieved with arrays of amorphous metallic glass nanorods under infrared optical illumination. Thermography measurements revealed marked temperature contrast between illuminated and non-illuminated areas even under low optical power excitation conditions. This attribute allowed for generating legible photo-induced thermal patterns on textured metallic glass surfaces.

  8. Development of indigenous laboratory scale gas atomizer for producing metal powders

    Khan, K.K.; Qasim, A.M.; Ahmed, P.

    2011-01-01

    Gas atomization is one of the methods for production of clean metal powders at relatively moderate cost. A laboratory scale gas atomizer was designed and fabricated indigenously to produce metal powders with a batch capacity of 500 g of copper (Cu). The design includes several features regarding fabrication and operation to provide optimum conditions for atomization. The inner diameter of atomizing chamber is 440 mm and its height is 1200 mm. The atomizing nozzle is of annular confined convergent type with an angle of 25 degree. Argon gas at desired pressure has been used for atomizing the metals to produce relatively clean powders. A provision has also been made to view the atomization process. The indigenous laboratory scale gas atomizer was used to produce tin (Sn) and copper (Cu) powders with different atomizing gas pressures ranging from 2 to 10 bar. The particle size of different powders produced ranges from 40 to 400 im. (author)

  9. Synthesis and Doping of Ligand-Protected Atomically-Precise Metal Nanoclusters

    Aljuhani, Maha A.

    2016-01-01

    by controlling their size, shape, and composition. Among the most thriving areas of research about nanoparticle is the synthesis and doping of the ligand-protected atomically-precise metal nanoclusters. In this thesis, we developed three different novel metal

  10. Deformation in Metallic Glass: Connecting Atoms to Continua

    Hinkle, Adam R.; Falk, Michael L.; Rycroft, Chris H.; Shields, Michael D.

    Metallic glasses like other amorphous solids experience strain localization as the primary mode of failure. However, the development of continuum constitutive laws which provide a quantitative description of disorder and mechanical deformation remains an open challenge. Recent progress has shown the necessity of accurately capturing fluctuations in material structure, in particular the statistical changes in potential energy of the atomic constituents during the non-equilibrium process of applied shear. Here we directly cross-compare molecular dynamics shear simulations of a ZrCu glass with continuum shear transformation zone (STZ) theory representations. We present preliminary results for a methodology to coarse-grain detailed molecular dynamics data with the goal of initializing a continuum representation in the STZ theory. NSF Grants Awards 1107838, 1408685, and 0801471.

  11. Quantized conductance in atom-sized wires between two metals

    Brandbyge, Mads; Schiøtz, Jakob; Sørensen, Mads Reinholdt

    1995-01-01

    We present experimental and theoretical results for the conductance and mechanical properties of atom-sized wires between two metals. The experimental part is based on measurements with a scanning tunneling microscope (STM) where a point contact is created by indenting the tip into a gold surface...... is the origin of the scatter in the experimental data, and what is the origin of the scaling of the scattering with the number of conductance quanta? The theoretical discussion is based on a free-electron-like model where scattering from the boundary of the nanowire is included. The configurations...... of the nanowires are deduced from molecular dynamics simulations, which also give information about the mechanical properties of the system. We show that such a model can account semiquantitatively for several of the observed effects. One of the main conclusions of the theoretical analysis is that,; due...

  12. Superradiance of several atoms near a metal nanosphere

    Protsenko, I E; Uskov, A V

    2015-01-01

    Assuming that the number of emitters (atoms) near a spherical metal nanoparticle is large (more than a few hundred), so that their interaction with each other is strong and sufficient for the emergence of their collective states (Dicke states), it is shown that the nanoparticle accelerates the superradiance of the emitters in a similar way as it accelerates the spontaneous emission of a single emitter. In this case, part of the energy stored by the emitters is absorbed by a nanoparticle, and the rest of the energy is radiated as a superradiance pulse. For the parameters selected in this paper, the energy absorbed by the nanoparticle is approximately equal to the emitted energy. We have found the collective states of the emitters and nanoparticle and have derived expressions for the time dependence of the superradiance pulse power, pulse duration and time delay with respect to the moment of excitation of the emitters. (superradiance)

  13. Design of a liquid metals heat exchanger

    Roffiel C, L.

    1976-01-01

    The method that has been used in this design is that of the summation of the partial resistances to the heat transference, permitting to obtain the value of the total coefficient of heat transfer which will be equal to the reciprocal of the summation of all the resistances. The obtained exchanger is of tubes and rod type shield with the primary sodium flowing through the tubes and the secondary sodium flowing in counter-current through the shield. The shield has a nominal diameter of 6 inches and the bundle of tubes is formed by 31 tubes with a nominal diameter of 1/2 inch. The shield as well as the tubes are of stainless steel. The total heat transfer area is of 7.299 square meters, and the effective length of heat transfer is of 3.519 meters. After sizing the interchanger it was proceeded to simulate its functioning through a computer program in which the effective length of heat transfer was divided in 150 points in such a way that according to the integration of the distinct parameters along these points a comparison can finally be made between the design values and those of the simulation, which show a concordance. (author)

  14. Chemically assisted release of transition metals in graphite vaporizers for atomic spectrometry

    Katskov, Dmitri; Darangwa, Nicholas; Grotti, Marco

    2006-01-01

    The processes associated with the vaporization of microgram samples and modifiers in a graphite tube ET AAS were investigated by the example of transition metals. The vapor absorption spectra and vaporization behavior of μg-amounts Cd, Zn, Cu, Ag, Au, Ni, Co, Fe, Mn and Cr were studied using the UV spectrometer with CCD detector, coupled with a continuum radiation source. The pyrocoated, Ta or W lined tubes, with Ar or He as internal gases, and filter furnace were employed in the comparative experiments. It was found that the kinetics of atomic vapor release changed depending on the specific metal-substrate-gas combination; fast vaporization at the beginning was followed by slower 'tailing.' The absorption continuum, overlapped by black body radiation at longer wavelengths, accompanied the fast vaporization mode for all metals, except Cd and Zn. The highest intensity of the continuum was observed in the pyrocoated tube with Ar. For Cu and Ag the molecular bands overlapped the absorption continuum; the continuum and bands were suppressed in the filter furnace. It is concluded that the exothermal interaction of sample vapor with the material of the tube causes the energy evolution in the gas phase. The emitted heat is dispersed near the tube wall in the protective gas and partially transferred back to the surface of the sample, thus facilitating the vaporization. The increased vapor flow causes over-saturation and gas-phase condensation in the absorption volume at some distance from the wall, where the gas temperature is not affected by the reaction. The condensation is accompanied by the release of phase transition energy via black body radiation and atomic emission. The particles of condensate and molecular clusters cause the scattering of light and molecular absorption; slow decomposition of the products of the sample vapor-substrate reaction produces the 'tailing' of atomic absorption signal. The interaction of graphite with metal vapor or oxygen, formed in the

  15. Colloquium: Excitons in atomically thin transition metal dichalcogenides

    Wang, Gang; Chernikov, Alexey; Glazov, Mikhail M.; Heinz, Tony F.; Marie, Xavier; Amand, Thierry; Urbaszek, Bernhard

    2018-04-01

    Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here recent progress in understanding of the excitonic properties in monolayer TMDs is reviewed and future challenges are laid out. Discussed are the consequences of the strong direct and exchange Coulomb interaction, exciton light-matter coupling, and influence of finite carrier and electron-hole pair densities on the exciton properties in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.

  16. Effect of charging on silicene with alkali metal atom adsorption

    Li, Manman; Li, Zhongyao; Gong, Shi-Jing

    2018-02-01

    Based on first-principles calculations, we studied the effects of charging on the structure, binding energy and electronic properties of silicene with alkali metal (AM) atom (Li, Na or K) adsorption. In AMSi2, electron doping enlarges the lattice constant of silicene, while the influence of hole doping is non-monotonic. In AMSi8, the lattice constant increases/decreases almost linearly with the increase in electron/hole doping. In addition, the AM-Si vertical distance can be greatly enlarged by excessive hole doping in both AMSi2 and AMSi8 systems. When the hole doping is as large as  +e per unit cell, both AMSi2 and AMSi8 can be transformed from metal to semiconductor. However, the binding energy would be negative in the AM+ Si2 semiconductor. It suggests AM+ Si2 is unstable in this case. In addition, the electron doping and the AM-Si vertical distance would greatly influence the band gap of silicene in LiSi8 and NaSi8, while the band gap in KSi8 is relatively stable. Therefore, KSi8 may be a more practicable material in nanotechnology.

  17. Metal cluster compounds - chemistry and importance; clusters containing isolated main group element atoms, large metal cluster compounds, cluster fluxionality

    Walther, B.

    1988-01-01

    This part of the review on metal cluster compounds deals with clusters containing isolated main group element atoms, with high nuclearity clusters and metal cluster fluxionality. It will be obvious that main group element atoms strongly influence the geometry, stability and reactivity of the clusters. High nuclearity clusters are of interest in there own due to the diversity of the structures adopted, but their intermediate position between molecules and the metallic state makes them a fascinating research object too. These both sites of the metal cluster chemistry as well as the frequently observed ligand and core fluxionality are related to the cluster metal and surface analogy. (author)

  18. Liquid metal heat transfer in heat exchangers under low flow rate conditions

    Mochizuki, Hiroyasu

    2015-01-01

    The present paper describes the liquid metal heat transfer in heat exchangers under low flow rate conditions. Measured data from some experiments indicate that heat transfer coefficients of liquid metals at very low Péclet number are much lower than what are predicted by the well-known empirical relations. The cause of this phenomenon was not fully understood for many years. In the present study, one countercurrent-type heat exchanger is analyzed using three, separated countercurrent heat exchanger models: one is a heat exchanger model in the tube bank region, while the upper and lower plena are modeled as two heat exchangers with a single heat transfer tube. In all three heat exchangers, the same empirical correlation is used in the heat transfer calculation on the tube and the shell sides. The Nusselt number, as a function of the Péclet number, calculated from measured temperature and flow rate data in a 50 MW experimental facility was correctly reproduced by the calculation result, when the calculated result is processed in the same way as the experiment. Finally, it is clarified that the deviation is a superficial phenomenon which is caused by the heat transfer in the plena of the heat exchanger. (author)

  19. First-principles calculations of heat capacities of ultrafast laser-excited electrons in metals

    Bévillon, E.; Colombier, J.P.; Recoules, V.; Stoian, R.

    2015-01-01

    Ultrafast laser excitation can induce fast increases of the electronic subsystem temperature. The subsequent electronic evolutions in terms of band structure and energy distribution can determine the change of several thermodynamic properties, including one essential for energy deposition; the electronic heat capacity. Using density functional calculations performed at finite electronic temperatures, the electronic heat capacities dependent on electronic temperatures are obtained for a series of metals, including free electron like, transition and noble metals. The effect of exchange and correlation functionals and the presence of semicore electrons on electronic heat capacities are first evaluated and found to be negligible in most cases. Then, we tested the validity of the free electron approaches, varying the number of free electrons per atom. This shows that only simple metals can be correctly fitted with these approaches. For transition metals, the presence of localized d electrons produces a strong deviation toward high energies of the electronic heat capacities, implying that more energy is needed to thermally excite them, compared to free sp electrons. This is attributed to collective excitation effects strengthened by a change of the electronic screening at high temperature

  20. Electrocatalysis of the oxidations of some organic compounds on noble-metal electrodes by foreign-metal ad-atoms

    Tsang, R.W.

    1981-10-01

    Electrochemical oxidation of formic acid was studied on Pt electrodes in acid, and that of dextrose was studied on Pt and Au in alkali. Poisoning was observed on Pt but not on Au. Several heavy-metal ad-atoms (Pb, Bi, Tl) enhance greatly the anodic currents on Pt, while transition metals (Cu, Zn) inhibit the oxidation on Pt. The enhancement effect of the metal ad-atoms is correlated with electron structure. All metal ad-atoms showed an inhibitory effect on Au. Amperometry showed that Pt electrodes are completely deactivated within 10 s during dextrose oxidation without ad-atoms, while Au retains much of its activity even after 10 min. Ad-atoms maintains the Pt activity over much more than 10 s. 50 figures, 38 tables

  1. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd, E-mail: gerd.meyer@uni-koeln.de

    2014-11-15

    Comproportionation reactions of rare-earth metal trihalides (RX{sub 3}) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ((T{sub 3}R{sub 11})X{sub 15}-type, P6{sub 3}/m), tetramers ((T{sub 4}R{sub 16})X{sub 28}(R{sub 4}) (P-43m), (T{sub 4}R{sub 16})X{sub 20} (P4{sub 2}/nnm), (T{sub 4}R{sub 16})X{sub 24}(RX{sub 3}){sub 4} (I4{sub 1}/a) and (T{sub 4}R{sub 16})X{sub 23} (C2/m) types of structure) and pentamers ((Ru{sub 5}La{sub 14}){sub 2}Br{sub 39}, Cc) of (TR{sub r}){sub n} (n=2–5) clusters. These oligomers are further enveloped by inner (X{sup i}) as well as outer (X{sup a}) halido ligands, which possess diverse functionalities and interconnect like oligomers through i–i, i–a and/or a–i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of (TR{sub 6}) octahedra via common edges are more frequent than trimers and pentamers, in which the (TR{sub r}) clusters share common faces. - Graphical abstract: Rare earth-metal cluster complexes with endohedral transition metal atoms (TR{sub 6}) may connect via common edges or faces to form dimers, trimers, tetramers and pentamers of which the tetramers are the most prolific. Packing effects and electron counts play an important role. - Highlights: • Rare-earth metal cluster complexes encapsulate transition metal atoms. • Oligomers are built via connection of octahedral clusters via common edges or faces. • Dimers through pentamers with closed structures are known. • Tetramers including a tetrahedron of endohedral atoms are the most prolific.

  2. Heat exchanger selection and design analyses for metal hydride heat pump systems

    Mazzucco, Andrea; Voskuilen, Tyler G.; Waters, Essene L.

    2016-01-01

    This study presents a design analysis for the development of highly efficient heat exchangers within stationary metal hydride heat pumps. The design constraints and selected performance criteria are applied to three representative heat exchangers. The proposed thermal model can be applied to select...... the most efficient heat exchanger design and provides outcomes generally valid in a pre-design stage. Heat transfer effectiveness is the principal performance parameter guiding the selection analysis, the results of which appear to be mildly (up to 13%) affected by the specific Nusselt correlation used....... The thermo-physical properties of the heat transfer medium and geometrical parameters are varied in the sensitivity analysis, suggesting that the length of independent tubes is the physical parameter that influences the performance of the heat exchangers the most. The practical operative regions for each...

  3. Molecular dynamics for near melting temperatures simulations of metals using modified embedded-atom method

    Etesami, S. Alireza; Asadi, Ebrahim

    2018-01-01

    Availability of a reliable interatomic potential is one of the major challenges in utilizing molecular dynamics (MD) for simulations of metals at near the melting temperatures and melting point (MP). Here, we propose a novel approach to address this challenge in the concept of modified-embedded-atom (MEAM) interatomic potential; also, we apply the approach on iron, nickel, copper, and aluminum as case studies. We propose adding experimentally available high temperature elastic constants and MP of the element to the list of typical low temperature properties used for the development of MD interatomic potential parameters. We show that the proposed approach results in a reasonable agreement between the MD calculations of melting properties such as latent heat, expansion in melting, liquid structure factor, and solid-liquid interface stiffness and their experimental/computational counterparts. Then, we present the physical properties of mentioned elements near melting temperatures using the new MEAM parameters. We observe that the behavior of elastic constants, heat capacity and thermal linear expansion coefficient at room temperature compared to MP follows an empirical linear relation (α±β × MP) for transition metals. Furthermore, a linear relation between the tetragonal shear modulus and the enthalpy change from room temperature to MP is observed for face-centered cubic materials.

  4. Liquid Metals as Plasma-facing Materials for Fusion Energy Systems: From Atoms to Tokamaks

    Stone, Howard A. [Princeton Univ., NJ (United States); Koel, Bruce E. [Princeton Univ., NJ (United States); Bernasek, Steven L. [Princeton Univ., NJ (United States); Carter, Emily A. [Princeton Univ., NJ (United States); Debenedetti, Pablo G. [Princeton Univ., NJ (United States); Panagiotopoulos, Athanassios Z. [Princeton Univ., NJ (United States)

    2017-06-23

    The objective of our studies was to advance our fundamental understanding of liquid metals as plasma-facing materials for fusion energy systems, with a broad scope: from atoms to tokamaks. The flow of liquid metals offers solutions to significant problems of the plasma-facing materials for fusion energy systems. Candidate metals include lithium, tin, gallium, and their eutectic combinations. However, such liquid metal solutions can only be designed efficiently if a range of scientific and engineering issues are resolved that require advances in fundamental fluid dynamics, materials science and surface science. In our research we investigated a range of significant and timely problems relevant to current and proposed engineering designs for fusion reactors, including high-heat flux configurations that are being considered by leading fusion energy groups world-wide. Using experimental and theoretical tools spanning atomistic to continuum descriptions of liquid metals, and bridging surface chemistry, wetting/dewetting and flow, our research has advanced the science and engineering of fusion energy materials and systems. Specifically, we developed a combined experimental and theoretical program to investigate flows of liquid metals in fusion-relevant geometries, including equilibrium and stability of thin-film flows, e.g. wetting and dewetting, effects of electromagnetic and thermocapillary fields on liquid metal thin-film flows, and how chemical interactions and the properties of the surface are influenced by impurities and in turn affect the surface wetting characteristics, the surface tension, and its gradients. Because high-heat flux configurations produce evaporation and sputtering, which forces rearrangement of the liquid, and any dewetting exposes the substrate to damage from the plasma, our studies addressed such evaporatively driven liquid flows and measured and simulated properties of the different bulk phases and material interfaces. The range of our studies

  5. Fast switching of alkali atom dispensers using laser-induced heating

    Griffin, P.F.; Weatherill, K.J.; Adams, C.S.

    2005-01-01

    We show that by using an intense laser source to locally heat an alkali atom dispenser, one can generate a high flux of atoms followed by fast recovery (<100 ms) of the background pressure when the laser is extinguished. For repeated heating pulses a switch-on time for the atomic flux of 200 ms is readily attainable. This technique is suited to ultracold atom experiments using simple ultrahigh vacuum (UHV) chambers. Laser-induced heating provides a fast repetition of the experimental cycle, which, combined with low atom loss due to background gas collisions, is particularly useful for experiments involving far-off resonance optical traps, where sufficient laser power (0.5-4 W) is readily available

  6. Numerical simulation of heat transfer in metal foams

    Gangapatnam, Priyatham; Kurian, Renju; Venkateshan, S. P.

    2018-02-01

    This paper reports a numerical study of forced convection heat transfer in high porosity aluminum foams. Numerical modeling is done considering both local thermal equilibrium and non local thermal equilibrium conditions in ANSYS-Fluent. The results of the numerical model were validated with experimental results, where air was forced through aluminum foams in a vertical duct at different heat fluxes and velocities. It is observed that while the LTE model highly under predicts the heat transfer in these foams, LTNE model predicts the Nusselt number accurately. The novelty of this study is that once hydrodynamic experiments are conducted the permeability and porosity values obtained experimentally can be used to numerically simulate heat transfer in metal foams. The simulation of heat transfer in foams is further extended to find the effect of foam thickness on heat transfer in metal foams. The numerical results indicate that though larger foam thicknesses resulted in higher heat transfer coefficient, this effect weakens with thickness and is negligible in thick foams.

  7. First-principles studies on 3d transition metal atom adsorbed twin graphene

    Li, Lele; Zhang, Hong; Cheng, Xinlu; Miyamoto, Yoshiyuki

    2018-05-01

    Twin graphene is a new two-dimensional semiconducting carbon allotrope which is proposed recently. The structural, magnetic and electronic properties are investigated for 3d transition metal (TM) atom adsorbed twin graphene by means of GGA+U calculations. The results show most of single 3d transition metal atom except Zn can make twin graphene magnetization. The adsorption of single TM atom can also make the twin graphene systems turn to half metal (V adsorption), half-semiconductor (Fe adsorption) or metal (Sc, Cr, Mn, Co and Cu adsorption). The semiconducting nature still exists for Ti, Ni and Zn adsorption. All the 3d TM adatoms belong to n-type doping for transferring charge to the neighboring C atoms and have strong covalent bond with these C atoms. The influence of Hubbard U value on half-metallic V adsorbed system is also considered. As the U increases, the system can gradually transform from metal to half metal and metal. The effect of the coverage is investigated for two TM atoms (Sc-Fe) adsorption, too. We can know TM atoms adsorbed twin graphene have potentials to be spintronic device and nanomagnets from the results.

  8. Trace Metal Levels in Raw and Heat Processed Nigerian Staple ...

    The levels of some trace metals (Fe, Zn, Cu, Ni, Cd) were quantitatively determined in raw and heat processed staple food cultivars (yam, cassava, cocoyam and maize) from oil producing areas of part of the Niger Delta and compared with a non-oil producing area of Ebonyi State as control. The survey was conducted to ...

  9. Numerical Simulations of Particle Deposition in Metal Foam Heat Exchangers

    Sauret, Emilie; Saha, Suvash C.; Gu, Yuantong

    2013-01-01

    Australia is a high-potential country for geothermal power with reserves currently estimated in the tens of millions of petajoules, enough to power the nation for at least 1000 years at current usage. However, these resources are mainly located in isolated arid regions where water is scarce. Therefore, wet cooling systems for geothermal plants in Australia are the least attractive solution and thus air-cooled heat exchangers are preferred. In order to increase the efficiency of such heat exchangers, metal foams have been used. One issue raised by this solution is the fouling caused by dust deposition. In this case, the heat transfer characteristics of the metal foam heat exchanger can dramatically deteriorate. Exploring the particle deposition property in the metal foam exchanger becomes crucial. This paper is a numerical investigation aimed to address this issue. Two-dimensional (2D) numerical simulations of a standard one-row tube bundle wrapped with metal foam in cross-flow are performed and highlight preferential particle deposition areas.

  10. Enhancement of the atomic absorbance of Cr, Zn, Cd, and Pb in metal furnace atomic absorption spectrometry using absorption tubes

    Yuya Koike

    2017-03-01

    Full Text Available Trace amounts of Cr, Zn, Cd, and Pb were determined by metal furnace atomic absorption spectrometry using absorption tubes. Various absorption tubes were designed as roof- and tube-types, and fixed above the metal furnace in order to extend the light path length. Aqueous standards and samples were injected in the metal furnace and atomized in a metal atomizer with an absorption tube (6 cm length, 15.5 mm diameter. The used of an absorption tube resulted in an enhancement of the atomic absorbance. The ratios of absorbance values with and without the roof- and tube-type absorption tubes were 1.33 and 1.11 for Cr; 1.42 and 1.99 for Zn; 1.66 and 1.98 for Cd; and 1.31 and 1.16 for Pb, respectively. The use of an absorption tube was effective for Zn and Cd analysis, as the absorbance values for these low boiling point metals doubled. The proposed method was successfully applied in the determination of Zn in tap water.

  11. Heat conduction in double-walled carbon nanotubes with intertube additional carbon atoms.

    Cui, Liu; Feng, Yanhui; Tan, Peng; Zhang, Xinxin

    2015-07-07

    Heat conduction of double-walled carbon nanotubes (DWCNTs) with intertube additional carbon atoms was investigated for the first time using a molecular dynamics method. By analyzing the phonon vibrational density of states (VDOS), we revealed that the intertube additional atoms weak the heat conduction along the tube axis. Moreover, the phonon participation ratio (PR) demonstrates that the heat transfer in DWCNTs is dominated by low frequency modes. The added atoms cause the mode weight factor (MWF) of the outer tube to decrease and that of the inner tube to increase, which implies a lower thermal conductivity. The effects of temperature, tube length, and the number and distribution of added atoms were studied. Furthermore, an orthogonal array testing strategy was designed to identify the most important structural factor. It is indicated that the tendencies of thermal conductivity of DWCNTs with added atoms change with temperature and length are similar to bare ones. In addition, thermal conductivity decreases with the increasing number of added atoms, more evidently for atom addition concentrated at some cross-sections rather than uniform addition along the tube length. Simultaneously, the number of added atoms at each cross-section has a considerably more remarkable impact, compared to the tube length and the density of chosen cross-sections to add atoms.

  12. Elements including metals in the atomizer and aerosol of disposable electronic cigarettes and electronic hookahs.

    Monique Williams

    Full Text Available Our purpose was to quantify 36 inorganic chemical elements in aerosols from disposable electronic cigarettes (ECs and electronic hookahs (EHs, examine the effect of puffing topography on elements in aerosols, and identify the source of the elements.Thirty-six inorganic chemical elements and their concentrations in EC/EH aerosols were determined using inductively coupled plasma optical emission spectroscopy, and their source was identified by analyzing disassembled atomizers using scanning electron microscopy and energy dispersive X-ray spectroscopy.Of 36 elements screened, 35 were detected in EC/EH aerosols, while only 15 were detected in conventional tobacco smoke. Some elements/metals were present in significantly higher concentrations in EC/EH aerosol than in cigarette smoke. Concentrations of particular elements/metals within EC/EH brands were sometimes variable. Aerosols generated at low and high air-flow rates produced the same pattern of elements, although the total element concentration decreased at the higher air flow rate. The relative amount of elements in the first and last 60 puffs was generally different. Silicon was the dominant element in aerosols from all EC/EH brands and in cigarette smoke. The elements appeared to come from the filament (nickel, chromium, thick wire (copper coated with silver, brass clamp (copper, zinc, solder joints (tin, lead, and wick and sheath (silicon, oxygen, calcium, magnesium, aluminum. Lead was identified in the solder and aerosol of two brands of EHs (up to 0.165 μg/10 puffs.These data show that EC/EH aerosols contain a mixture of elements, including heavy metals, with concentrations often significantly higher than in conventional cigarette smoke. While the health effects of inhaling mixtures of heated metals is currently not known, these data will be valuable in future risk assessments involving EC/EH elements/metals.

  13. Electronic specific heats in metal--hydrogen systems

    Flotow, H.E.

    1979-01-01

    The electronic specific heats of metals and metal--hydrogen systems can in many cases be evaluated from the measured specific heats at constant pressure, C/sub p/, in the temperature range 1 to 10 K. For the simplest case, C/sub p/ = γT + βT 3 , where γT represents the specific heat contribution associated with the conduction electrons, and βT 3 represents lattice specific heat contribution. The electronic specific heat coefficient, γ, is important because it is proportional to electron density of states at the Fermi surface. A short description of a low temperature calorimetric cryostat employing a 3 He/ 4 He dilution refrigeration is given. Various considerations and complications encountered in the evaluation of γ from specific heat data are discussed. Finally, the experimental values of γ for the V--Cr--H system and for the Lu--H system are summarized and the variations of γ as function of alloy composition are discussed

  14. Ab initio theory of noble gas atoms in bcc transition metals.

    Jiang, Chao; Zhang, Yongfeng; Gao, Yipeng; Gan, Jian

    2018-06-18

    Systematic ab initio calculations based on density functional theory have been performed to gain fundamental understanding of the interactions between noble gas atoms (He, Ne, Ar and Kr) and bcc transition metals in groups 5B (V, Nb and Ta), 6B (Cr, Mo and W) and 8B (Fe). Our charge density analysis indicates that the strong polarization of nearest-neighbor metal atoms by noble gas interstitials is the electronic origin of their high formation energies. Such polarization becomes more significant with an increasing gas atom size and interstitial charge density in the host bcc metal, which explains the similar trend followed by the unrelaxed formation energies of noble gas interstitials. Upon allowing for local relaxation, nearby metal atoms move farther away from gas interstitials in order to decrease polarization, albeit at the expense of increasing the elastic strain energy. Such atomic relaxation is found to play an important role in governing both the energetics and site preference of noble gas atoms in bcc metals. Our most notable finding is that the fully relaxed formation energies of noble gas interstitials are strongly correlated with the elastic shear modulus of the bcc metal, and the physical origin of this unexpected correlation has been elucidated by our theoretical analysis based on the effective-medium theory. The kinetic behavior of noble gas atoms and their interaction with pre-existing vacancies in bcc transition metals have also been discussed in this work.

  15. Radiant heating tests of several liquid metal heat-pipe sandwich panels

    Camarda, C.J.; Basiulis, A.

    1983-08-01

    Integral heat pipe sandwich panels, which synergistically combine the thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich construction, were conceived as a means of alleviating thermal stress problems in the Langley Scramjet Engine. Test panels which utilized two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and a liquid metal working fluid (either sodium or potassium) were tested by radiant heating at various heat load levels. The heat pipe panels reduced maximum temperature differences by 31 percent with sodium working fluid and 45 percent with potassium working fluid. Results indicate that a heat pipe sandwich panel is a potential, simple solution to the engine thermal stress problem. Other interesting applications of the concept include: cold plates for electronic component and circuit card cooling, radiators for large space platforms, low distortion large area structures (e.g., space antennas) and laser mirrors

  16. Liquid metal heat exchanger for efficient heating of soils and geologic formations

    DeVault, Robert C [Knoxville, TN; Wesolowski, David J [Kingston, TN

    2010-02-23

    Apparatus for efficient heating of subterranean earth includes a well-casing that has an inner wall and an outer wall. A heater is disposed within the inner wall and is operable within a preselected operating temperature range. A heat transfer metal is disposed within the outer wall and without the inner wall, and is characterized by a melting point temperature lower than the preselected operating temperature range and a boiling point temperature higher than the preselected operating temperature range.

  17. Inelastic scattering and local heating in atomic gold wires

    Frederiksen, Thomas; Brandbyge, Mads; Lorente, N.

    2004-01-01

    We present a method for including inelastic scattering in a first-principles density-functional computational scheme for molecular electronics. As an application, we study two geometries of four-atom gold wires corresponding to two different values of strain and present results for nonlinear...

  18. Long Spin-Relaxation Times in a Transition-Metal Atom in Direct Contact to a Metal Substrate.

    Hermenau, Jan; Ternes, Markus; Steinbrecher, Manuel; Wiesendanger, Roland; Wiebe, Jens

    2018-03-14

    Long spin-relaxation times are a prerequisite for the use of spins in data storage or nanospintronics technologies. An atomic-scale solid-state realization of such a system is the spin of a transition-metal atom adsorbed on a suitable substrate. For the case of a metallic substrate, which enables the direct addressing of the spin by conduction electrons, the experimentally measured lifetimes reported to date are on the order of only hundreds of femtoseconds. Here, we show that the spin states of iron atoms adsorbed directly on a conductive platinum substrate have a surprisingly long spin-relaxation time in the nanosecond regime, which is comparable to that of a transition metal atom decoupled from the substrate electrons by a thin decoupling layer. The combination of long spin-relaxation times and strong coupling to conduction electrons implies the possibility to use flexible coupling schemes to process the spin information.

  19. Review of the critical heat flux correlations for liquid metals

    Lee, Yong Bum; Han, H. D.; Chang, W. P.; Kwon, Y. M.

    1999-09-01

    The CHF phenomenon in the two-phase convective flows has been an important issue in the fields of design and safety analysis of light water reactor (LWR) as well as sodium cooled liquid metal reactor (LMR). Especially in the LWR application, many physical aspects of the CHF phenomenon are understood and reliable correlations and mechanistic models to predict the CHF condition have been proposed over the past three decades. Most of the existing CHF correlations have been developed for light water reactor core applications. Compared with water, liquid metals show a divergent picture of boiling pattern. This can be attributed to the consequence that special CHF conditions obtained from investigations with water cannot be applied to liquid metals. Numerous liquid metal boiling heat transfer and two-phase flow studies have put emphasis on development of models and understanding of the mechanism for improving the CHF predictions. Thus far, no overall analytical solution method has been obtained and the reliable prediction method has remained empirical. The principal objectives of the present report are to review the state of the art in connection with liquid metal critical heat flux under low pressure and low flow conditions and to discuss the basic mechanisms. (author)

  20. Methodology for Life Testing of Refractory Metal / Sodium Heat Pipes

    Martin, James J.; Reid, Robert S.

    2006-01-01

    This work establishes an approach to generate carefully controlled data to find heat pipe operating life with material-fluid combinations capable of extended operation. To accomplish this goal acceleration is required to compress 10 years of operational life into 3 years of laboratory testing through a combination of increased temperature and mass fluence. Specific test series have been identified, based on American Society for Testing and Materials (ASTM) specifications, to investigate long-term corrosion rates. The refractory metal selected for demonstration purposes is a molybdenum-44.5% rhenium alloy formed by powder metallurgy. The heat pipes each have an annular crescent wick formed by hot isostatic pressing of molybdenum-rhenium wire mesh. The heat pipes are filled by vacuum distillation with purity sampling of the completed assembly. Round-the-clock heat pipe tests with 6-month destructive and non-destructive inspection intervals are conducted to identify the onset and level of corrosion. Non-contact techniques are employed to provide power to the evaporator (radio frequency induction heating at 1 to 5 kW per heat pipe) and calorimetry at the condenser (static gas gap coupled water cooled calorimeter). The planned operating temperature range extends from 1123 to 1323 K. Accomplishments before project cancellation included successful development of the heat pipe wick fabrication technique, establishment of all engineering designs, baseline operational test requirements, and procurement/assembly of supporting test hardware systems. (authors)

  1. Ceramic-glass-metal seal by microwave heating

    Meek, Thomas T.; Blake, Rodger D.

    1985-01-01

    A method for producing a ceramic-glass-metal seal by microwaving mixes a slurry of glass sealing material and coupling agent and applies same to ceramic and metal workpieces. The slurry and workpieces are then insulated and microwaved at a power, time and frequency sufficient to cause a liquid phase reaction in the slurry. The reaction of the glass sealing material forms a chemically different seal than that which would be formed by conventional heating because it is formed by diffusion rather than by wetting of the reactants.

  2. Theoretical study of the magnetic heat capacity of praseodymium metal

    Glenn, R.L.

    1976-01-01

    The heat capacity of praseodymium metal at low temperatures is calculated using a valence change model. The effect of the presence of a small temperature-dependent and field-dependent percentage of 4+ ions is computed using crystalfield techniques. Good agreement with the experimentally determined values is obtained for polycrystalline and single-crystal praseodymium in zero field and various other fields up to 30 koe. In addition, the effects of selected exchange models on the heat capacity and susceptibility are computed. The model is shown to be compatible with both the parallel and perpendicular susceptibilities

  3. Scattering cross section of metal catalyst atoms in silicon nanowires

    Markussen, Troels; Rurali, R.; Cartoixa, X.

    2010-01-01

    A common technique to fabricate silicon nanowires is to use metal particles (e.g., Au, Ag, Cu, Al) to catalyze the growth reaction. As a consequence, the fabricated nanowires contain small concentrations of these metals as impurities. In this work we investigate the effect of the metallic impurit...

  4. Modeling hydrogen storage in boron-substituted graphene decorated with potassium metal atoms

    Tokarev, A

    2015-03-01

    Full Text Available Boron-substituted graphene decorated with potassium metal atoms was considered as a novel material for hydrogen storage. Density functional theory calculations were used to model key properties of the material, such as geometry, hydrogen packing...

  5. Metallic nanoparticles in a standing wave: Optical force and heating

    Šiler, Martin; Chvátal, Lukáš; Zemánek, Pavel

    2013-01-01

    Roč. 126, September (2013), s. 84-90 ISSN 0022-4073 R&D Projects: GA ČR GPP205/12/P868; GA MŠk LH12018; GA MŠk ED0017/01/01 Institutional support: RVO:68081731 Keywords : Metallic nanoparticles * Optical trapping * Heating * Generalized Lorenz-Mie theory Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.288, year: 2013

  6. Interaction mechanisms between ceramic particles and atomized metallic droplets

    Wu, Yue; Lavernia, Enrique J.

    1992-10-01

    The present study was undertaken to provide insight into the dynamic interactions that occur when ceramic particles are placed in intimate contact with a metallic matrix undergoing a phase change. To that effect, Al-4 wt pct Si/SiCp composite droplets were synthesized using a spray atomization and coinjection approach, and their solidification microstructures were studied both qualitatively and quantitatively. The present results show that SiC particles (SiCp) were incor- porated into the matrix and that the extent of incorporation depends on the solidification con- dition of the droplets at the moment of SiC particle injection. Two factors were found to affect the distribution and volume fraction of SiC particles in droplets: the penetration of particles into droplets and the entrapment and/or rejection of particles by the solidification front. First, during coinjection, particles collide with the atomized droplets with three possible results: they may penetrate the droplets, adhere to the droplet surface, or bounce back after impact. The extent of penetration of SiC particles into droplets was noted to depend on the kinetic energy of the particles and the magnitude of the surface energy change in the droplets that occurs upon impact. In liquid droplets, the extent of penetration of SiC particles was shown to depend on the changes in surface energy, ΔEs, experienced by the droplets. Accordingly, large SiC particles encoun- tered more resistance to penetration relative to small ones. In solid droplets, the penetration of SiC particles was correlated with the dynamic pressure exerted by the SiC particles on the droplets during impact and the depth of the ensuing crater. The results showed that no pene- tration was possible in such droplets. Second, once SiC particles have penetrated droplets, their final location in the microstructure is governed by their interactions with the solidification front. As a result of these interactions, both entrapment and rejection of

  7. Phase-coherent electron transport through metallic atomic-sized contacts and organic molecules

    Pauly, F.

    2007-02-02

    This work is concerned with the theoretical description of systems at the nanoscale, in particular the electric current through atomic-sized metallic contacts and organic molecules. In the first part, the characteristic peak structure in conductance histograms of different metals is analyzed within a tight-binding model. In the second part, an ab-initio method for quantum transport is developed and applied to single-atom and single-molecule contacts. (orig.)

  8. Long-range interactions between excited helium and alkali-metal atoms

    Zhang, J.-Y.; Schwingenschlö gl, Udo; Shi, T.-Y.; Tang, L.-Y.; Yan, Z.-C.

    2012-01-01

    –5% in the coefficient C6, and 1–10% in the coefficients C8 and C10. The dispersion coefficients Cn for the interaction of He(2 1,3S) and He(2 1,3P) with the ground-state alkali-metal atoms and for the interaction of He(2 1,3S) with the alkali-metal atoms in their first

  9. Electronic and atomic structure at metal-oxide heterointerfaces

    Schlueter, Christoph Friedrich

    2013-07-01

    The results of a series of investigations on modern oxide materials using hard X-ray photoelectron spectroscopy (HAXPES) combined with the X-ray standing wave (XSW) method are described in this thesis. The combination of hard X-ray photoelectron spectroscopy and X-ray standing waves enables the electronic structure to be measured with a spatial resolution in the picometer range. Under suitable preparation conditions, a quasi two-dimensional electron gas (2DEG) is formed at the heterointerfaces of strontium titanate (SrTiO{sub 3}) with polar oxides, such as lanthanum aluminate (LaAlO{sub 3}) or lanthanum gallate (LaGaO{sub 3}). Samples were grown at the ESRF and in Naples and surface X-ray diffraction confirmed the excellent epitaxial quality of the films. The XSW-method was used to reconstruct images of the structure of LaAlO{sub 3} layers in real space. These images give evidence of distortions in the LaAlO{sub 3} structure which facilitate the compensation of the potential differences. Furthermore, XSW/HAXPES measurements permit the Ti and Sr,O contributions to the 2DEG close to the Fermi level to be identified unambiguously. The analysis shows that the 3d band crosses the Fermi level and that some density of states is associated with oxygen vacancies. Superlattices of SrTiO{sub 3} with polar calcium cuprate (CaCuO{sub 2}) were investigated by HAXPES. Similar to the case of SrTiO{sub 3}/LaAlO{sub 3}, the polarity of CaCuO{sub 2} should lead to a diverging surface potential. The core level spectra from Ca, Sr, and Ti show that there is a redistribution mechanism for oxygen which compensates the potential differences. When the oxygen concentration is enhanced these superstructures become superconducting (T{sub C} = 40 K). The increased oxidation of the superconducting material is revealed by the additional components in the core level spectra of the metal atoms and in the appearance of a new screening channel in Cu 2p core level spectra, which signals the hole

  10. Electronic and atomic structure at metal-oxide heterointerfaces

    Schlueter, Christoph Friedrich

    2013-01-01

    The results of a series of investigations on modern oxide materials using hard X-ray photoelectron spectroscopy (HAXPES) combined with the X-ray standing wave (XSW) method are described in this thesis. The combination of hard X-ray photoelectron spectroscopy and X-ray standing waves enables the electronic structure to be measured with a spatial resolution in the picometer range. Under suitable preparation conditions, a quasi two-dimensional electron gas (2DEG) is formed at the heterointerfaces of strontium titanate (SrTiO 3 ) with polar oxides, such as lanthanum aluminate (LaAlO 3 ) or lanthanum gallate (LaGaO 3 ). Samples were grown at the ESRF and in Naples and surface X-ray diffraction confirmed the excellent epitaxial quality of the films. The XSW-method was used to reconstruct images of the structure of LaAlO 3 layers in real space. These images give evidence of distortions in the LaAlO 3 structure which facilitate the compensation of the potential differences. Furthermore, XSW/HAXPES measurements permit the Ti and Sr,O contributions to the 2DEG close to the Fermi level to be identified unambiguously. The analysis shows that the 3d band crosses the Fermi level and that some density of states is associated with oxygen vacancies. Superlattices of SrTiO 3 with polar calcium cuprate (CaCuO 2 ) were investigated by HAXPES. Similar to the case of SrTiO 3 /LaAlO 3 , the polarity of CaCuO 2 should lead to a diverging surface potential. The core level spectra from Ca, Sr, and Ti show that there is a redistribution mechanism for oxygen which compensates the potential differences. When the oxygen concentration is enhanced these superstructures become superconducting (T C = 40 K). The increased oxidation of the superconducting material is revealed by the additional components in the core level spectra of the metal atoms and in the appearance of a new screening channel in Cu 2p core level spectra, which signals the hole doping of the CaCuO 2 blocks. Magnetoresistive

  11. Collisional effects on metastable atom population in vapour generated by electron beam heating

    Dikshit, B; Majumder, A; Bhatia, M S; Mago, V K

    2008-01-01

    The metastable atom population distribution in a free expanding uranium vapour generated by electron beam (e-beam) heating is expected to depart from its original value near the source due to atom-atom collisions and interaction with electrons of the e-beam generated plasma co-expanding with the vapour. To investigate the dynamics of the electron-atom and atom-atom interactions at different e-beam powers (or source temperatures), probing of the atomic population in ground (0 cm -1 ) and 620 cm -1 metastable states of uranium was carried out by the absorption technique using a hollow cathode discharge lamp. The excitation temperature of vapour at a distance ∼30 cm from the source was calculated on the basis of the measured ratio of populations in 620 to 0 cm -1 states and it was found to be much lower than both the source temperature and estimated translational temperature of the vapour that is cooled by adiabatic free expansion. This indicated relaxation of the metastable atoms by collisions with low energy plasma electrons was so significant that it brings the excitation temperature below the translational temperature of the vapour. So, with increase in e-beam power and hence atom density, frequent atom-atom collisions are expected to establish equilibrium between the excitation and translational temperatures, resulting in an increase in the excitation temperature (i.e. heating of vapour). This has been confirmed by analysing the experimentally observed growth pattern of the curve for excitation temperature with e-beam power. From the observed excitation temperature at low e-beam power when atom-atom collisions can be neglected, the total de-excitation cross section for relaxation of the 620 cm -1 state by interaction with low energy electrons was estimated and was found to be ∼10 -14 cm 2 . Finally using this value of cross section, the extent of excitational cooling and heating by electron-atom and atom-atom collisions are described at higher e-beam powers

  12. Graphene as a flexible template for controlling magnetic interactions between metal atoms.

    Lee, Sungwoo; Kim, Dongwook; Robertson, Alex W; Yoon, Euijoon; Hong, Suklyun; Ihm, Jisoon; Yu, Jaejun; Warner, Jamie H; Lee, Gun-Do

    2017-03-01

    Metal-doped graphene produces magnetic moments that have potential application in spintronics. Here we use density function theory computational methods to show how the magnetic interaction between metal atoms doped in graphene can be controlled by the degree of flexure in a graphene membrane. Bending graphene by flexing causes the distance between two substitutional Fe atoms covalently bonded in graphene to gradually increase and these results in the magnetic moment disappearing at a critical strain value. At the critical strain, a carbon atom can enter between the two Fe atoms and blocks the interaction between relevant orbitals of Fe atoms to quench the magnetic moment. The control of interactions between doped atoms by exploiting the mechanical flexibility of graphene is a unique approach to manipulating the magnetic properties and opens up new opportunities for mechanical-magnetic 2D device systems.

  13. Liquid-metal-gas heat exchanger for HTGR type reactors

    Werth, G.

    1980-01-01

    The aim of this study is to investigate the heat transfer characteristics of a liquid metal heat exchanger (HE) for a helium-cooled high temperature reactor. A tube-type heat exchanger is considered as well as two direct exchangers: a bubble-type heat exchanger and a heat exchanger according to the spray principle. Experiments are made in order to determine the gas content of bubble-type heat exchangers, the dependence of the droplet diameter on the nozzle diameter, the falling speed of the droplets, the velocity of the liquid jet, and the temperature variation of liquid jets. The computer codes developed for HE calculation are structured so that they may be used for gas/liquid HE, too. Each type of HE that is dealt with is designed by accousting for a technical and an economic assessment. The liquid-lead jet spray is preferred to all other types because of its small space occupied and its simple design. It shall be used in near future in the HTR by the name of lead/helium HE. (GL) [de

  14. Adsorption of alkali and alkaline-earth metal atoms on stanene: A first-principles study

    Kadioglu, Yelda; Ersan, Fatih [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Gökoğlu, Gökhan [Department of Physics, Karabük University, 78050 Karabük (Turkey); Aktürk, Olcay Üzengi [Department of Electrical & Electronics Engineering, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey); Aktürk, Ethem, E-mail: ethem.akturk@adu.edu.tr [Department of Physics, Adnan Menderes University, 09100 Aydın (Turkey); Nanotechnology Application and Research Center, Adnan Menderes University, 09100 Aydın (Turkey)

    2016-09-01

    This paper presents a study on the adsorption of alkali and alkaline-earth metal atoms on single-layer stanene with different levels of coverage using first-principles plane wave calculations within spin-polarized density functional theory. The most favorable adsorption site for alkali atoms (Li, Na, K) were found to be the hollow site similar to other group IV single-layers, but the case of alkaline-earths on stanene is different from silicene and germanene. Whereas Mg and Ca are bound to stanene at hollow site, the bridge site is found to be energetically favorable for Be adatom. All adsorbed atoms are positively charged due to the charge transfer from adatom to stanene single-layer. The semimetallic bare stanene become metallic except for Be adsorption. The Beryllium adsorption give rise to non-magnetic semiconducting ground state. Our results illustrate that stanene has a reactive and functionalizable surface similar to graphene or silicene. - Highlights: • Alkali and alkaline-earth metal atoms form stronger bonds with stanene compared to other group IV monolayers. • Semi-metallic stanene becomes nonmagnetic metal for Li, Na, K, Mg, and Ca atoms adsorption. • Semi-metallic stanene becomes nonmagnetic semiconductor with 94 meV band gap for Be atom adsorption.

  15. A laboratory manual for the determination of metals in water and wastewater by atomic absorption spectrophotometry

    Smith, R.

    1983-01-01

    This guide presents, in addition to a brief discussion of the basic principles and practical aspects of atomic absorption spectrophotometry, a scheme of analysis for the determination of 19 metals in water and wastewater, 16 by flame atomic absorption and 3 by vapour generation techniques. Simplicity, speed and accuracy were the main criteria considered in the selection of the various methods

  16. Effect of temperature on atom-atom collision chain length in metals

    Makarov, A.A.; Demkin, N.A.; Lyashchenko, B.G.

    1981-01-01

    Focused atom-atom collision chain lengths are calculated for fcc-crystals with account of thermal oscillations. The model of solid spheres with the Born-Merier potential has been used in the calculations. The dependence of chain lengths on the temperature, energy and movement direction of the first chain atom for Cu, Au, Ag, Pb, Ni is considered. The plot presented shows that the chain lengths strongly decrease with temperature growth, for example, for the gold at T=100 K the chain length equals up to 37 interatomic spacings, whereas at T=1000 K their length decreases down to 5 interatomic distances. The dependence of the energy loss by the chain atoms on the atom number in the chain is obtained in a wide range of crystal temperature and the primary chain atom energy [ru

  17. High-speed cinematography of gas-metal atomization

    Ting, Jason [ALCOA Specialty Metals Division, 100 Technical Drive, Alcoa Center, PA 15069 (United States)]. E-mail: jason.ting@alcoa.com; Connor, Jeffery [Material Science Engineering Department, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Ridder, Stephen [Metallurgical Processing Group, NIST, 100 Bureau Dr. Stop 8556, Gaithersburg, MD 20899 (United States)

    2005-01-15

    A high-speed cinematographic footage of a 304L stainless steel gas atomization, recorded at the National Institute of Standard and Technology (NIST), was analyzed using a discrete Fourier transform (DFT) algorithm. The analysis showed the gas atomization process possesses two prominent frequency ranges of melt oscillation (pulsation). A low-frequency oscillation in the melt flow occurring between 5.41 and 123 Hz, with a dominant frequency at 9.93 Hz, was seen in the recirculation zone adjacent to the melt orifice. A high-frequency melt oscillation range was observed above 123 Hz, and was more prominent one melt-tip-diameter downstream in the melt atomization image than upstream near the melt tip. This high-frequency range may reflect the melt atomization frequency used to produce finely atomized powder. This range also included a prominent high frequency at 1273 Hz, which dominated in the image further away downstream from the melt tip. This discrete high-frequency oscillation is most probably caused by the aeroacoustic ''screech'' phenomenon, intrasound (<20 kHz), a result of the atomizing gas jets undergoing flow resonance. It is hypothesized that this discrete intrinsic aeroacoustic tone may enhance melt breakup in the atomization process with evidence of this fact in the melt images.

  18. High-speed cinematography of gas-metal atomization

    Ting, Jason; Connor, Jeffery; Ridder, Stephen

    2005-01-01

    A high-speed cinematographic footage of a 304L stainless steel gas atomization, recorded at the National Institute of Standard and Technology (NIST), was analyzed using a discrete Fourier transform (DFT) algorithm. The analysis showed the gas atomization process possesses two prominent frequency ranges of melt oscillation (pulsation). A low-frequency oscillation in the melt flow occurring between 5.41 and 123 Hz, with a dominant frequency at 9.93 Hz, was seen in the recirculation zone adjacent to the melt orifice. A high-frequency melt oscillation range was observed above 123 Hz, and was more prominent one melt-tip-diameter downstream in the melt atomization image than upstream near the melt tip. This high-frequency range may reflect the melt atomization frequency used to produce finely atomized powder. This range also included a prominent high frequency at 1273 Hz, which dominated in the image further away downstream from the melt tip. This discrete high-frequency oscillation is most probably caused by the aeroacoustic ''screech'' phenomenon, intrasound (<20 kHz), a result of the atomizing gas jets undergoing flow resonance. It is hypothesized that this discrete intrinsic aeroacoustic tone may enhance melt breakup in the atomization process with evidence of this fact in the melt images

  19. Role of Self-Interstitial Atoms on the High Temperature Properties of Metals

    Nordlund, K.; Averback, R.S.

    1998-01-01

    Equilibrium concentrations of self-interstitial atoms and divacancies have been determined in Cu by molecular dynamics computer simulations using embedded atom potentials. Near the melting temperature these concentrations are both ∼10 -6 . Owing to the higher mobility of the interstitial atoms, however, they contribute more to diffusion. In perfect, or pulse-heated crystals, spontaneous Frenkel pair production results in even higher interstitial concentrations. copyright 1998 The American Physical Society

  20. Study of absorption spectra for alkali and alkaline earth metal salts in flameless atomic absorption spectrometry using a carbon tube atomizer

    Yasuda, Seiji; Kakiyama, Hitoo

    1975-01-01

    Absorption spectra of various salts such as alkali metal salts, alkaline earth dichlorides, and ammonium halides were investigated and absorptions of some molecular species produced in the carbon tube were identified. The aqueous solution (20 μl) containing 1.0 mg/ml of each salt was placed in the carbon tube atomizer and heated in a similar manner to usual flameless atomic absorption method. D 2 -lamp was used as a continuous light source and argon gas was employed as an inert sheath gas. The spectra were obtained over the range of wavelength 200 to 350 nm. When alkali halides were feeded, the absorption spectra agreed with those of alkali halide vapors. Therefore, in such cases vapors of the alkali halides were probably produced by the sublimation or vaporization in the atomizer. The spectra of alkali perchlorates were considered to be those of alkali chlorides produced by the pyrolysis of the perchlorates in the atomizer. The absorptions of alkaline earth chlorides below 250 nm were probably due to their gaseous states. Sulfur dioxide was found to be produced by the pyrolysis of alkali sulfates, bisulfates and sulfites in the atomizer, Alkali phosphates and pyrophosphates gave almost identical spectra below 300 nm. Gamma band spectrum of nitrogen monoxide was observed from 200 to 240 nm during ashing at bout 330 0 C for alkali nitrates and nitrites. Ammonia vapor was produced from ammonium halides during drying at about 170 0 C. Although the absorptions of alkali carbonates and hydroxides were almost undetectable, the same spectra as those of alkali halides were observed by the addition of ammonium halides to the solutions of alkali compounds. This shows that alkali halides are produced in the atomizer by the addition of halide ions. (auth.)

  1. He atom surface spectroscopy: Surface lattice dynamics of insulators, metals and metal overlayers

    1990-01-01

    During the first three years of this grant (1985--1988) the effort was devoted to the construction of a state-of-the-art He atom scattering (HAS) instrument which would be capable of determining the structure and dynamics of metallic, semiconductor or insulator crystal surfaces. The second three year grant period (1988--1991) has been dedicated to measurements. The construction of the instrument went better than proposed; it was within budget, finished in the proposed time and of better sensitivity and resolution than originally planned. The same success has been carried over to the measurement phase where the concentration has been on studies of insulator surfaces, as discussed in this paper. The experiments of the past three years have focused primarily on the alkali halides with a more recent shift to metal oxide crystal surfaces. Both elastic and inelastic scattering experiments were carried out on LiF, NaI, NaCl, RbCl, KBr, RbBr, RbI, CsF, CsI and with some preliminary work on NiO and MgO

  2. Behaviour of TEM metal grids during in-situ heating experiments.

    Zhang, Zaoli; Su, Dangsheng

    2009-05-01

    The stability of Ni, Cu, Mo and Au transmission electron microscope (TEM) grids coated with ultra-thin amorphous carbon (alpha-C) or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500-850 degrees C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to the metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nano-materials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once the heating temperature reaches 600 degrees C. In the case of Ni grid covered with alpha-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches 600 degrees C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with alpha-C film exhibit good stability at elevated temperature, for instance, up to 680 and 850 degrees C for Mo and Au, respectively, and any other metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 degrees C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.

  3. Spin-rotation interaction of alkali-metal endash He-atom pairs

    Walker, T.G.; Thywissen, J.H.; Happer, W.

    1997-01-01

    A treatment of the spin-rotation coupling between alkali-metal atoms and He atoms is presented. Rotational distortions are accounted for in the wave function using a Coriolis interaction in the rotating frame. The expectation value of the spin-orbit interaction gives values of the spin-rotation coupling that explain previous experimental results. For spin-exchange optical pumping, the results suggest that lighter alkali-metal atoms would be preferred spin-exchange partners, other factors being equal. copyright 1997 The American Physical Society

  4. Atomic-scale simulations of the mechanical deformation of nanocrystalline metals

    Schiøtz, Jakob; Vegge, Tejs; Di Tolla, Francesco

    1999-01-01

    that the main deformation mode is sliding in the grain boundaries through a large number of uncorrelated events, where a few atoms (or a few tens of atoms) slide with respect to each other. Little dislocation activity is seen in the grain interiors. The localization of the deformation to the grain boundaries......Nanocrystalline metals, i.e., metals in which the grain size is in the nanometer range, have a range of technologically interesting properties including increased hardness and yield strength. We present atomic-scale simulations of the plastic behavior of nanocrystalline copper. The simulations show...

  5. Reagent-Free Electrophoretic Synthesis of Few-Atom-Thick Metal Oxide Nanosheets

    Hou, Chengyi; Zhang, Minwei; Zhang, Lili

    2017-01-01

    Engineering traditional materials into the new form of atomic and free-standing two-dimensional structures is of both fundamental interest and practical significance, but it is in general facing challenges especially for metal oxide semiconductors. We herein report an ultragreen method for the cost......-effective and fast preparation of atomic metal oxide nanosheets that can be further transformed into nanofilms. The method combines top-down building block synthesis and bottom-up electrophoretic assembly in water under ambient conditions, using only bulk metal and Milli-Q water without involving any additional...

  6. Utilization of an arc-heated jet for production of supersonic seeded beams of atomic nitrogen

    Bickes, R.W. Jr.; Newton, K.R.; Herrmann, J.M.; Bernstein, R.B.

    1976-01-01

    Intense supersonic beams of atomic nitrogen (>10 17 atoms sr -1 sec -1 ) have been produced from the dissociation of N 2 in an Ar arc (at temperatures in excess of 6000 K) using the arc-heated nozzle beam source of Young, Rodgers, and Knuth. Experiments characterizing the N 2 dissociation and the translational energies of the N, N 2 , and Ar components in the beams are described. Evidence is presented for the formation of atomic C as well as C 2 and CH from the pyrolysis of CH 4 and C 2 H 4 in the Ar arc

  7. Emission Channeling Studies of the Lattice Site of Oversized Alkali Atoms Implanted in Metals

    2002-01-01

    % IS340 \\\\ \\\\ As alkali atoms have the largest atomic radius of all elements, the determination of their lattice configuration following implantation into metals forms a critical test for the various models predicting the lattice site of implanted impurity atoms. The site determination of these large atoms will especially be a crucial check for the most recent model that relates the substitutional fraction of oversized elements to their solution enthalpy. Recent exploratory $^{213}$Fr and $^{221}$Fr $\\alpha$-emission channeling experiments at ISOLDE-CERN and hyperfine interaction measurements on Fr implanted in Fe gave an indication for anomalously large substitutional fractions. To investigate further the behaviour of Fr and other alkali atoms like Cs and Rb thoroughly, more on-line emission channeling experiments are needed. We propose a number of shifts for each element, where the temperature of the implanted metals will be varied between 50$^\\circ$ and 700$^\\circ$~K. Temperature dependent measurements wi...

  8. Trends in preconcentration procedures for metal determination using atomic spectrometry techniques

    Godoi Pereira, M. de; Arruda, M.A.Z.

    2003-01-01

    Methods for metal preconcentration are often described in the literature. However, purposes are often different, depending on whether the methods are applied in environmental, clinical or technological fields. The respective method needs to be efficient, give high sensitivity, and ideally also is selective which is useful when used in combination with atomic spectroscopy. This review presents the actual tendencies in metal preconcentration using techniques such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), hydride generation atomic absorption spectrometry (HGAAS), inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS). Procedures based on related to electrochemical, coprecipitation/precipitation, liquid-liquid and solid-liquid extraction and atom trapping mechanisms are presented. (author)

  9. Inhomogeneous thermal expansion of metallic glasses in atomic-scale studied by in-situ synchrotron X-ray diffraction

    Taghvaei, Amir Hossein, E-mail: amirtaghvaei@gmail.com [Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz (Iran, Islamic Republic of); Shakur Shahabi, Hamed [IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, 01069 Dresden (Germany); Bednarčik, Jozef [Photon Science DESY, Notkestraße 85, 22603 Hamburg (Germany); Eckert, Jürgen [IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, 01069 Dresden (Germany); TU Dresden, Institute of Materials Science, 01062 Dresden (Germany)

    2015-01-28

    Numerous investigations have demonstrated that the elastic strain in metallic glasses subjected to mechanical loading could be inhomogeneous in the atomic-scale and it increases with distance from an average atom and eventually reaches the macroscopic strain at larger inter-atomic distances. We have observed a similar behavior for the thermal strain imposed by heating of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} glassy particles below the glass transition temperature by analysis of the scattering data obtained by in-situ high-energy synchrotron X-ray diffraction (XRD). The results imply that the volumetric thermal strains calculated from the shift in position of the principal diffraction maximum and reduced pair correlation function (PDF) peaks are in good agreement for the length scales beyond 0.6 nm, corresponding to the atoms located over the third near-neighbor shell. However, smaller and even negative volumetric thermal strains have been calculated based on the shifts in the positions of the second and first PDF peaks, respectively. The structural changes of Co{sub 40}Fe{sub 22}Ta{sub 8}B{sub 30} glassy particles are accompanied by decreasing the average coordination number of the first near-neighbor shell, which manifests the occurrence of local changes in the short-range order upon heating. It is believed that the detected length-scale dependence of the volumetric thermal strain is correlated with the local atomic rearrangements taking place in the topologically unstable regions of the glass governed by variations in the atomic-level stresses.

  10. Atomic-level structures and physical properties of magnetic CoSiB metallic glasses

    Shan, Guangcun; Liang Zhang, Ji; Li, Jiong; Zhang, Shuo; Jiang, Zheng; Huang, Yuying; Shek, Chan-Hung

    2014-01-01

    Two CoSiB metallic glasses of low Co contents, which consist of different clusters, have recently been developed by addition of solute atoms. In this work, the atomic structure and the magnetic properties of the two CoBSi metallic glasses were elucidated by state-of-the-art extended X-ray absorption fine structure spectroscopy (EXAFS) combining with ab initio molecular-dynamics (AIMD) computational techniques. Besides, the origin of these magnetic behaviors was discussed in view of the EXAFS results and atomic structures of the metallic glasses. - Graphical abstract: The atomic structure and the origins of the magnetic properties of two ternary CoBSi metallic glasses were elucidated by state-of-the-art extended X-ray absorption fine structure spectroscopy (EXAFS) combining with ab initio molecular-dynamics (AIMD) techniques. - Highlights: • The atomic structure and the origins of the magnetic properties of two ternary CoBSi metallic glasses were revealed. • The atomic structures were elucidated by state-of-the-art extended X-ray absorption fine structure spectroscopy (EXAFS) combining with ab initio molecular-dynamics (AIMD) techniques. • The experimental spectra were in good agreement with the predictions of ab initio full multiple scattering theory using the FEFF8.4 code. • The origin of these magnetic behaviors was discussed in view of the EXAFS results and atomic structures of the metallic glasses. • These two metallic glasses consist of different clusters, and hence different magnetic properties, which are dominated by short-range orders (SROs)

  11. s-wave elastic scattering of antihydrogen off atomic alkali-metal targets

    Sinha, Prabal K.; Ghosh, A. S.

    2006-01-01

    We have investigated the s-wave elastic scattering of antihydrogen atoms off atomic alkali-metal targets (Li, Na, K, and Rb) at thermal energies (10 -16 -10 -4 a.u.) using an atomic orbital expansion technique. The elastic cross sections of these systems at thermal energies are found to be very high compared to H-H and H-He systems. The theoretical models employed in this study are so chosen to consider long-range forces dynamically in the calculation. The mechanism of cooling suggests that Li may be considered to be a good candidate as a buffer gas for enhanced cooling of antihydrogen atoms to ultracold temperature

  12. Design and construction of a heat stage for investigations of samples by atomic force microscopy above ambient temperatures

    Bækmark, Thomas Rosleff; Bjørnholm, Thomas; Mouritsen, Ole G.

    1997-01-01

    The construction from simple and cheap commercially available parts of a miniature heat stage for the direct heating of samples studied with a commercially available optical-lever-detection atomic force microscope is reported. We demonstrate that by using this heat stage, atomic resolution can...... be obtained on highly oriented pyrolytic graphite at 52 °C. The heat stage is of potential use for the investigation of biological material at physiological temperatures. ©1997 American Institute of Physics....

  13. Lorentz force actuation of a heated atomic force microscope cantilever.

    Lee, Byeonghee; Prater, Craig B; King, William P

    2012-02-10

    We report Lorentz force-induced actuation of a silicon microcantilever having an integrated resistive heater. Oscillating current through the cantilever interacts with the magnetic field around a NdFeB permanent magnet and induces a Lorentz force that deflects the cantilever. The same current induces cantilever heating. With AC currents as low as 0.2 mA, the cantilever can be oscillated as much as 80 nm at resonance with a DC temperature rise of less than 5 °C. By comparison, the AC temperature variation leads to a thermomechanical oscillation that is about 1000 times smaller than the Lorentz deflection at the cantilever resonance. The cantilever position in the nonuniform magnetic field affects the Lorentz force-induced deflection, with the magnetic field parallel to the cantilever having the largest effect on cantilever actuation. We demonstrate how the cantilever actuation can be used for imaging, and for measuring the local material softening temperature by sensing the contact resonance shift.

  14. Distinct atomic structures of the Ni-Nb metallic glasses formed by ion beam mixing

    Tai, K. P.; Wang, L. T.; Liu, B. X.

    2007-01-01

    Four Ni-Nb metallic glasses are obtained by ion beam mixing and their compositions are measured to be Ni 77 Nb 23 , Ni 55 Nb 45 , Ni 31 Nb 69 , and Ni 15 Nb 85 , respectively, suggesting that a composition range of 23-85 at. % of Nb is favored for metallic glass formation in the Ni-Nb system. Interestingly, diffraction analyses show that the structure of the Nb-based Ni 31 Nb 69 metallic glass is distinctly different from the structure of the Nb-based Ni 15 Nb 85 metallic glass, as the respective amorphous halos are located at 2θ≅38 and 39 deg. To explore an atomic scale description of the Ni-Nb metallic glasses, an n-body Ni-Nb potential is first constructed with an aid of the ab initio calculations and then applied to perform the molecular dynamics simulation. Simulation results determine not only the intrinsic glass forming range of the Ni-Nb system to be within 20-85 at. % of Nb, but also the exact atomic positions in the Ni-Nb metallic glasses. Through a statistical analysis of the determined atomic positions, a new dominant local packing unit is found in the Ni 15 Nb 85 metallic glass, i.e., an icositetrahedron with a coordination number to be around 14, while in Ni 31 Nb 69 metallic glasses, the dominant local packing unit is an icosahedron with a coordination number to be around 12, which has been reported for the other metallic glasses. In fact, with increasing the irradiation dose, the Ni 31 Nb 69 metallic glasses are formed through an intermediate state of face-centered-cubic-solid solution, whereas the Ni 15 Nb 85 metallic glass is through an intermediate state of body-centered-cubic-solid solution, suggesting that the structures of the constituent metals play an important role in governing the structural characteristics of the resultant metallic glasses

  15. Photothermal heating in metal-embedded microtools for material transport

    Villangca, Mark Jayson; Palima, Darwin; Banas, Andrew Rafael

    2016-01-01

    Material transport is an important mechanism in microfluidics and drug delivery. The methods and solutions found in literature involve passively diffusing structures, microneedles and chemically fueled structures. In this work, we make use of optically actuated microtools with embedded metal layer...... as heating element for controlled loading and release. The new microtools take advantage of the photothermal-induced convection current to load and unload cargo. We also discuss some challenges encountered in realizing a self-contained polymerized microtool. Microfluidic mixing, fluid flow control...... and convection currents have been demonstrated both experimentally and numerically for static metal thin films or passively floating nanoparticles. Here we show an integration of aforementioned functionalities in an opticallyfabricated and actuated microtool. As proof of concept, we demonstrate loading...

  16. Occupational heat strain in a hot underground metal mine.

    Lutz, Eric A; Reed, Rustin J; Turner, Dylan; Littau, Sally R

    2014-04-01

    In a hot underground metal mine, this study evaluated the relationship between job task, physical body type, work shift, and heat strain. Thirty-one miners were evaluated during 98 shifts while performing deep shaft-sinking tasks. Continuous core body temperature, heart rate, pre- and postshift urine specific gravity (USG), and body mass index were measured. Cutting and welding tasks were associated with significantly (P < 0.05) increased core body temperature, maximum heart rate, and increased postshift urine specific gravity. Miners in the obese level II and III body mass index categories, as well as those working night shift, had lower core body temperatures (P < 0.05). This study confirms that job task, body type, and shift are risk factors for heat strain.

  17. Heated Hydro-Mechanical Deep Drawing of Magnesium Sheet Metal

    Kurz, Gerrit

    In order to reduce fuel consumption efforts have been made to decrease the weight of automobile constructions by increasing the use of lightweight materials. In this field of application magnesium alloys are important because of their low density. A promising alternative to large surfaced and thin die casting parts has been found in construction parts that are manufactured by sheet metal forming of magnesium. Magnesium alloys show a limited formability at room temperature. A considerable improvement of formability can be achieved by heating the material. Formability increases above a temperature of approximately T = 225 °C.

  18. Selective heating and separation of isotopes in a metallic plasma

    Moffa, P.; Cheshire, D.; Flanders, B.; Myer, R.; Robinette, W.; Thompson, J.; Young, S.

    1983-01-01

    Several types of metallic plasmas have been produced at the Plasma Separation Process facility of TRW. Selective heating and separation of specific isotopes in these plasmas have been achieved. In this presentation the authors concentrate on the modeling of the selective heating and separation of the isotope Ni 58 . Two models are currently used to describe the excitation process. In both, the electromagnetic fields in the plasma produced by the ICRH antenna are calculated self-consistently using a kinetic description of the warm plasma dielectric. In the Process Model Code, both the production of the plasma and the heating are calculated using a Monte Carlo approach. Only the excitation process is treated in the second simplified model. Test particles that sample an initial parallel velocity distribution are launched into the heating region and the equations of motion including collisional damping are calculated. For both models, the perpendicular energy for a number of particles with different initial conditions and representing the different isotopes is calculated. This information is then input into a code that models the performance of our isotope separation collector. The motion of the ions of each isotope through the electrically biased collector is followed. An accounting of where each particle is deposited is kept and hence the isotope separation performance of the collector is predicted

  19. Quality assurance: recommended guidelines for safe heating by capacitive-type heating technique to treat patients with metallic implants.

    Kato, Hirokazu; Kondo, Motoharu; Imada, Hajime; Kuroda, Masahiro; Kamimura, Yoshitsugu; Saito, Kazuyuki; Kuroda, Kagayaki; Ito, Koichi; Takahashi, Hideaki; Matsuki, Hidetoshi

    2013-05-01

    This article is a redissemination of the previous Japanese Quality Assurance Guide guidelines. Specific absorption rate and temperature distribution were investigated with respect to various aspects including metallic implant size and shape, insertion site, insertion direction, blood flow and heating power, and simulated results were compared with adverse reactions of patients treated by radio frequency capacitive-type heating. Recommended guidelines for safe heating methods for patients with metallic implants are presented based on our findings.

  20. Adsorption and migration of single metal atoms on the calcite (10.4) surface

    Pinto, H; Haapasilta, V; Lokhandwala, M; Foster, Adam S; Öberg, S

    2017-01-01

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3 d (Ti, Cr, Fe, Ni, Cu), 4 d (Zr, Nb, Mo, Pd, Ag) and 5 d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface. (paper)

  1. Measuring the temperature history of isochorically heated warm dense metals

    McGuffey, Chris; Kim, J.; Park, J.; Moody, J.; Emig, J.; Heeter, B.; Dozieres, M.; Beg, Fn; McLean, Hs

    2017-10-01

    A pump-probe platform has been designed for soft X-ray absorption spectroscopy near edge structure measurements in isochorically heated Al or Cu samples with temperature of 10s to 100s of eV. The method is compatible with dual picosecond-class laser systems and may be used to measure the temperature of the sample heated directly by the pump laser or by a laser-driven proton beam Knowledge of the temperature history of warm dense samples will aid equation of state measurements. First, various low- to mid-Z targets were evaluated for their suitability as continuum X-ray backlighters over the range 200-1800 eV using a 10 J picosecond-class laser with relativistic peak intensity Alloys were found to be more suitable than single-element backlighters. Second, the heated sample package was designed with consideration of target thickness and tamp layers using atomic physics codes. The results of the first demonstration attempts will be presented. This work was supported by the U.S. DOE under Contract No. DE-SC0014600.

  2. Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

    Liu, Lichen; Corma, Avelino

    2018-05-23

    Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

  3. Relaxation volumes of self-interstitial-atoms and vacancies in metals

    Ehrhart, P.

    1983-01-01

    Experimental results for the relaxation volumes of self-interstitial-atoms and vacancies as obtained after low temperature irradiation of different metals are reviewed. For fcc metals the relaxation volumes of the SIA's are very similar: ΔVsup(rel) = 1.6 +- 0.3 atomic volumes. This value is valid as well for the pure fcc metals (Al, Cu, Ni) as for different alloys. Vacancy relaxation volumes are small and vary between: ΔVsup(rel) = -0.05 and -0.25 atomic volumes. For bcc metals (Fe, Mo) the relaxation volume of the SIA is significantly smaller: ΔVsup(rel) = 1.1 +- 0.2 atomic volumes. In spite of the obvious similarity of the close-packed fcc and hcp structures, the SIA parameters for hcp metals are much different: ΔVsup(rel) = 3.5 for Zn, ΔVsup(rel) = 1.5 for Co and ΔVsup(rel) = 0.6 at. vol. for Zr. Vacancy relaxation volumes seem to be small as in cubic metals. The influence of lattice nonharmonicity on the validity of an extrapolation of the values determined at 6 K to higher temperatures is discussed. (author)

  4. Atomic-level Electron Microscopy of Metal and Alloy Electrocatalysts

    Deiana, Davide

    , the elemental distribution of the PtxY, before and after the electrochemical tests, has been determined. A core-shell structure is formed after the ORR chemical treatment, with an alloyed core embedded by a ~1 nm Pt-rich shell, due to the segregation of the Y from the first few atomic layers of the particle...... was the only matching structure. In the case of Pd−Hg, a core-shell structure has been found, with a pure Pd core and a Pd-Hg shell. Through atomic resolution STEM, the structure of the alloy in the shell of different particles has been revealed, showing the formation of an ordered alloy structure....... flat surfaces and exposed to different sintering conditions. Ex situ STEM imaging has been used to monitor the variation of the particle dimensions through the analysis of particle area distributions. Clusters with a monomodal size distribution exhibited intrinsic sintering resistance on different...

  5. Flotation atomic absorption determination of bismuth in nonferrous metal alloys

    Ososkov, V.K.; Plintus, A.M.; Kornelli, M.Eh.; Zakhariya, A.N.; Lozanova, E.V.

    1986-01-01

    Technique of flotation concentration and atomic absorption determination of bismuth microquantities in alloys on the basis of copper and zinc has been developed. Fine-dispersed EhDEh-10P anionite was used as a carrier in flotation concentration. State standard samples (SSS) of brasses and German silver were used as analysed objects. Effect of macrocomponents on the results of bismuth content determination has been studied. Satisfactory coincidence of the results obtained and SSS certificates is shown

  6. Intelligent Sensors for Atomization Processing of Molten Metals and Alloys

    1988-06-01

    20ff. 12. Hirleman, Dan E. Particle Sizing by Optical , Nonimaging Techniques. Liquid Particle Size Measurement Techniques, ASTM, 1984, pp. 35ff. 13...sensors are based on electric, electromagnetic or optical principles, the latter being most developed in fields obviously related to atomization. Optical ...beams to observe various interference, diffraction, and heterodyning effects, and to observe, with high signal-to-noise ratio, even weak optical

  7. Stripping scattering of fast atoms on surfaces of metal-oxide crystals and ultrathin films

    Blauth, David

    2010-01-01

    In the framework of the present dissertation the interactions of fast atoms with surfaces of bulk oxides, metals and thin films on metals were studied. The experiments were performed in the regime of grazing incidence of atoms with energies of some keV. The advantage of this scattering geometry is the high surface sensibility and thus the possibility to determine the crystallographic and electronic characteristics of the topmost surface layer. In addition to these experiments, the energy loss and the electron emission induced by scattered projectiles was investigated. The energy for electron emission and exciton excitation on Alumina/NiAl(110) and SiO 2 /Mo(112) are determined. By detection of the number of projectile induced emitted electrons as function of azimuthal angle for the rotation of the target surface, the geometrical structure of atoms forming the topmost layer of different adsorbate films on metal surfaces where determined via ion beam triangulation. (orig.)

  8. The importance of atomic and molecular correlation on the bonding in transition metal compounds

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Walch, Stephen P.

    1986-01-01

    The determination of accurate spectroscopic parameters for molecular systems containing transition metal atoms is shown to require extensive data sets and a high level correlation treatment, and techniques and their limitations are considered. Extensive results reported on the transition metal atoms, hydrides, oxides, and dimers makes possible the design of a calculation to correctly describe the mixing of different atomic asymptotes, and to give a correct balance between molecular bonding and exchange interactions. Examples considered include the dipole moment of the 2Delta state of NiH, which can help determine the mixture of 3d(8)4s(2) and 3d(9)4s(1) in the NiH wavefunction, and the bonding in CrO, where an equivalent description of the relative energies associated with the Cr 3d-3d atomic exchange and the Cr-O bond is important.

  9. Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

    Fang, Xinzuo; Shang, Qichao; Wang, Yu; Jiao, Long; Yao, Tao; Li, Yafei; Zhang, Qun; Luo, Yi; Jiang, Hai-Long

    2018-02-01

    It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h -1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H 2 production activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Convective heat transfer the molten metal pool heated from below and cooled by two-phase flow

    Cho, J. S.; Suh, K. Y.; Chung, C. H.; Park, R. J.; Kim, S. B.

    1998-01-01

    During a hypothetical servere accident in the nuclear power plant, a molten core material may form stratified fluid layers. These layers may be composed of high temperature molten debris pool and water coolant in the lower plenum of the reactor vessel or in the reactor cavity. This study is concerned with the experimental test and numerical analysis on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. This work examines the crust formation and the heat transfer characteristics of the molten metal pool immersed in the boiling coolant. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. The simulant molten pool material is tin (Sn) with the melting temperature of 232 .deg. C. Demineralized water is used as the working coolant. Tests were performed under the condition of the bottom surface heating in the test section and the forced convection of the coolant being injected onto the molten metal pool. The constant temperature and constant heat flux conditions are adopted for the bottom heating. The test parameters included the heated bottom surface temperature of the molten metal pool, the input power to the heated bottom surface of the test section, and the coolant injection rate. Numerical analyses were simultaneously performed in a two-dimensional rectangular domain of the molten metal pool to check on the measured data. The numerical program has been developed using the enthalpy method, the finite volume method and the SIMPLER algorithm. The experimental results of the heat transfer show general agreement with the calculated values. In this study, the relationship between the Nusselt number and Rayleigh number in the molten metal pool region was estimated and compared with the dry experiment without coolant nor solidification of the molten metal pool, and with the crust formation experiment with subcooled coolant, and against other correlations. In the experiments, the

  11. A heat transfer study for vertical straight-tube steam generators heated by liquid metal

    Valette, M.

    1984-04-01

    A single-tube mockup of a vertical straight-tube steam generator heated by sodium-potassium alloy NaK was submitted to thermal and hydraulic testing in conditions representative of fast breeder reactor operation. The mockup consisted of a 10mm I.D. ferritic steel heat exchange tube centered inside a cylindrical stainless steel shell. The complete assembly was 20.9 meters long. Water flowed upward inside the exchange tube, and NaK flowed downward in the annular gap between the tube and the shell. The steam outlet pressure ranged from 90 to 195 bars, while the liquid metal temperature at the mockup inlet was between 480 and 580 0 C. The water flowrate in the tube ranged from 153 to 2460 kg.m -2 .s -1 . During the tests the fluid inlet and outlet temperatures, flowrate and pressures were measured, as was the NaK temperature profile over the full length of the device. The test results were subsequently compared with heat exchange and pressure drop values calculated using the standard formulas for straight-tube heat exchangers. The heat exchange coefficients predicted by these correlations in the boiling zone were found to be largely overestimated, while the calculated pressure drop values proved satisfactory. A set of modified correlations is proposed to account for the observed phenomena, and for use in designing commercial units, provided the sodium flow in the tube bundle is adequately distributed

  12. Generation of dense, pulsed beams of refractory metal atoms using two-stage laser ablation

    Kadar-Kallen, M.A.; Bonin, K.D.

    1994-01-01

    We report a technique for generating a dense, pulsed beam of refractory metal atoms using two-stage laser ablation. An atomic beam of uranium was produced with a peak, ground-state number density of 1x10 12 cm -3 at a distance of z=27 cm from the source. This density can be scaled as 1/z 3 to estimate the density at other distances which are also far from the source

  13. Dynamical interaction of He atoms with metal surfaces: Charge transfer processes

    Flores, F.; Garcia Vidal, F.J.; Monreal, R.

    1993-01-01

    A self-consistent Kohn-Sham LCAO method is presented to calculate the charge transfer processes between a He * -atom and metal surfaces. Intra-atomic correlation effects are taken into account by considering independently each single He-orbital and by combining the different charge transfer processes into a set of dynamical rate equations for the different ion charge fractions. Our discussion reproduces qualitatively the experimental evidence and gives strong support to the method presented here. (author). 24 refs, 4 figs

  14. Transfer matrix treatment of atomic chemisorption on transition metal surface

    Mariz, A.M.; Koiller, B.

    1980-05-01

    The atomic adsorption of hydrogen on paramagnetic nickel 100 surface is studied, using the Green's function formalism and the transfer matrix technique, which allows the treatment of the geometry of the system in a simple manner. Electronic correlation at the adatom orbital in a self consistent Hartree-Fock approach is incorporated. The adsorption energy, local density of states and charge transfer between the solid and the adatom are calculated for different crystal structures (sc and fcc) and adatom positions at the surface. The results are discussed in comparison with other theories and with available experimental data, with satisfactory agreement. (Author) [pt

  15. Long-range interactions between excited helium and alkali-metal atoms

    Zhang, J.-Y.

    2012-12-03

    The dispersion coefficients for the long-range interaction of the first four excited states of He, i.e., He(2 1,3S) and He(2 1,3P), with the low-lying states of the alkali-metal atoms Li, Na, K, and Rb are calculated by summing over the reduced matrix elements of the multipole transition operators. For the interaction between He and Li the uncertainty of the calculations is 0.1–0.5%. For interactions with other alkali-metal atoms the uncertainty is 1–3% in the coefficient C5, 1–5% in the coefficient C6, and 1–10% in the coefficients C8 and C10. The dispersion coefficients Cn for the interaction of He(2 1,3S) and He(2 1,3P) with the ground-state alkali-metal atoms and for the interaction of He(2 1,3S) with the alkali-metal atoms in their first 2P states are presented in this Brief Report. The coefficients for other pairs of atomic states are listed in the Supplemental Material.

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

    Osetsky, Yu.N.; Bacon, D.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

  17. Heat-resistant organic molecular layer as a joint interface for metal reduction on plastics surfaces

    Sang, Jing; Aisawa, Sumio; Hirahara, Hidetoshi; Kudo, Takahiro; Mori, Kunio

    2016-01-01

    Graphical abstract: - Highlights: • In situ adsorption behaviors of TES on PA6 surface were clarified by QCM. • Highest adsorption of TES on PA6 was obtained in pH 3 and 0.1 M solution. • Molecular layers of TES with uniform structures were prepared on PA6 surface. • TES layer improved PA6 local heat resistance from 150 °C to 230 °C. • TES molecular layer successfully reduced Ag ion to Ag"0. - Abstract: Heat-resistant organic molecular layers have been fabricated by triazine-based silane coupling agent for metal reduction on plastic surfaces using adsorption method. These molecular layers were used as an interfacial layer between polyamide (PA6) and metal solution to reduce Ag"+ ion to Ag"0. The interfacial behaviors of triazine molecular layer at the interfaces between PA6 and Ag solution were investigated using quartz crystal microbalance (QCM). The kinetics of molecular adsorption on PA6 was investigated by using triazine-based silane coupling agent solutions at different pH and concentration. X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and local nano thermal analysis were employed to characterize the surfaces and interfaces. The nano thermal analysis results show that molecular layers of triazine-based silane coupling agent greatly improved heat resistance of PA6 resin from 170 °C up to 230 °C. This research developed an in-depth insight for molecular behaviors of triazine-based silane coupling agent at the PA6 and Ag solution interfaces and should be of significant value for interfacial research between plastics and metal solution in plating industry.

  18. Heat-resistant organic molecular layer as a joint interface for metal reduction on plastics surfaces

    Sang, Jing [Department of Frontier Materials and Function Engineering, Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan); Aisawa, Sumio, E-mail: aisawa@iwate-u.ac.jp [Department of Frontier Materials and Function Engineering, Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan); Hirahara, Hidetoshi [Department of Frontier Materials and Function Engineering, Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan); Kudo, Takahiro [Sulfur Chemical Institute, 210, Collabo MIU, 4-3-5, Ueda, Morioka 020-0066 (Japan); Mori, Kunio [Department of Frontier Materials and Function Engineering, Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551 (Japan); Sulfur Chemical Institute, 210, Collabo MIU, 4-3-5, Ueda, Morioka 020-0066 (Japan)

    2016-04-15

    Graphical abstract: - Highlights: • In situ adsorption behaviors of TES on PA6 surface were clarified by QCM. • Highest adsorption of TES on PA6 was obtained in pH 3 and 0.1 M solution. • Molecular layers of TES with uniform structures were prepared on PA6 surface. • TES layer improved PA6 local heat resistance from 150 °C to 230 °C. • TES molecular layer successfully reduced Ag ion to Ag{sup 0}. - Abstract: Heat-resistant organic molecular layers have been fabricated by triazine-based silane coupling agent for metal reduction on plastic surfaces using adsorption method. These molecular layers were used as an interfacial layer between polyamide (PA6) and metal solution to reduce Ag{sup +} ion to Ag{sup 0}. The interfacial behaviors of triazine molecular layer at the interfaces between PA6 and Ag solution were investigated using quartz crystal microbalance (QCM). The kinetics of molecular adsorption on PA6 was investigated by using triazine-based silane coupling agent solutions at different pH and concentration. X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and local nano thermal analysis were employed to characterize the surfaces and interfaces. The nano thermal analysis results show that molecular layers of triazine-based silane coupling agent greatly improved heat resistance of PA6 resin from 170 °C up to 230 °C. This research developed an in-depth insight for molecular behaviors of triazine-based silane coupling agent at the PA6 and Ag solution interfaces and should be of significant value for interfacial research between plastics and metal solution in plating industry.

  19. Turbulent heavy liquid metal heat transfer along a heated rod in an annular cavity

    Lefhalm, C.-H.; Tak, N.-I.; Piecha, H.; Stieglitz, R.

    2004-01-01

    Heavy liquid metals (HLM) are considered as coolant and spallation material in accelerator driven systems (ADS), because of their good molecular heat conductivity. This property leads to a separation of the spatial extension of thermal and viscous boundary layers. Commercially available computational fluid dynamic codes (CFD) assume an analogy of momentum and energy transfer, which is problematic for liquid metals flow. Therefore, benchmark experiments are required, in order to validate codes or modify existing models used therein. Within this article an experimental and numerical study of a thermally developing turbulent lead bismuth (PbBi) flow along a uniformly heated rod in a circular tube is presented. Local temperatures and velocity distributions are measured using thermocouples and Pitot tubes. The data are compared to simulation results computed with the CFX code package. The measured velocity profiles coincide nearly perfect with the simulation results. However, discrepancies up to 7% between the measured and computed temperatures appear. A minor part of the deviations can be explained by the imperfect experimental set-up. But, the measured shape of the thermal boundary is different to the calculated one, indicating the inadequateness of the presently used models describing the turbulent heat transport within the thermal boundary layer

  20. Metals on graphene and carbon nanotube surfaces: From mobile atoms to atomtronics to bulk metals to clusters and catalysts

    Sarkar, Santanu C.

    2014-01-14

    In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal-graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight some of the latest advances in understanding the nature of interactions between metals and graphene surfaces from the standpoint of metal overlayers deposited on graphene and SWNT thin films. Finally, we comment on the major challenges facing the field and the opportunities for technological applications. © 2013 American Chemical Society.

  1. Synthesis and Doping of Ligand-Protected Atomically-Precise Metal Nanoclusters

    Aljuhani, Maha A.

    2016-05-01

    Rapidly expanding research in nanotechnology has led to exciting progress in a versatile array of applications from medical diagnostics to catalysis. This success resulted from the manipulation of the desired properties of nanomaterials by controlling their size, shape, and composition. Among the most thriving areas of research about nanoparticle is the synthesis and doping of the ligand-protected atomically-precise metal nanoclusters. In this thesis, we developed three different novel metal nanoclusters, such as doped Ag29 with five gold (Au) atoms leading to enhance its quantum yield with remarkable stability. We also developed half-doped (alloyed) cluster of Ni6 nanocluster with molybdenum (Mo). This enabled enhanced stability and better catalytic activity. The third metal nanocluster that we synthesized was Au28 nanocluster by using di-thiolate as the ligand stabilizer instead of mono-thiolate. The new metal clusters obtained have been characterized by spectroscopic, electrochemical and crystallographic methods.

  2. Atomic polar tensors and acid-base properties of metal-oxide building blocks

    Ferris, K.F.

    1993-02-01

    The sensitivity of the atomic polar tensor to compositional substituents is reported for the alkali silicate series. Rotational invariants, effective atomic charge (GAPT) and charge normalized anisotropy and dipole (α n and γ n ) are used to characterize the charge distribution and chemical environment of the atomic sites. Comparison of α n and γ n with a series of known Bronsted and Lewis acids and bases suggests that these rotational invariants may act as indicators for metal-oxide site acidities. Basis set and electron correlation particularly affect the determined effective charge, but show minimal effect on α and γ quantities

  3. A slow atomic diffusion process in high-entropy glass-forming metallic melts

    Chen, Changjiu; Wong, Kaikin; Krishnan, Rithin P.; Embs, Jan P.; Chathoth, Suresh M.

    2018-04-01

    Quasi-elastic neutron scattering has been used to study atomic relaxation processes in high-entropy glass-forming metallic melts with different glass-forming ability (GFA). The momentum transfer dependence of mean relaxation time shows a highly collective atomic transport process in the alloy melts with the highest and lowest GFA. However, a jump diffusion process is the long-range atomic transport process in the intermediate GFA alloy melt. Nevertheless, atomic mobility close to the melting temperature of these alloy melts is quite similar, and the temperature dependence of the diffusion coefficient exhibits a non-Arrhenius behavior. The atomic mobility in these high-entropy melts is much slower than that of the best glass-forming melts at their respective melting temperatures.

  4. Nonlocal Response of Metallic Nanospheres Probed by Light, Electrons, and Atoms

    Christensen, Thomas; Yan, Wei; Raza, Søren

    2014-01-01

    Inspired by recent measurements on individual metallic nanospheres that cannot be explained with traditional classical electrodynamics, we theoretically investigate the effects of nonlocal response by metallic nanospheres in three distinct settings: atomic spontaneous emission, electron energy loss...... blueshifted surface plasmon but also an infinite series of bulk plasmons that have no counterpart in a local-response approximation. We show that these increasingly blueshifted multipole plasmons become spectrally more prominent at shorter probe-to-surface separations and for decreasing nanosphere radii...

  5. Studying nearest neighbor correlations by atom probe tomography (APT) in metallic glasses as exemplified for Fe40Ni40B20 glassy ribbons

    Shariq, Ahmed

    2012-01-01

    A next nearest neighbor evaluation procedure of atom probe tomography data provides distributions of the distances between atoms. The width of these distributions for metallic glasses studied so far is a few Angstrom reflecting the spatial resolution of the analytical technique. However, fitting Gaussian distributions to the distribution of atomic distances yields average distances with statistical uncertainties of 2 to 3 hundredth of an Angstrom. Fe 40Ni40B20 metallic glass ribbons are characterized this way in the as quenched state and for a state heat treated at 350 °C for 1 h revealing a change in the structure on the sub-nanometer scale. By applying the statistical tool of the χ2 test a slight deviation from a random distribution of B-atoms in the as quenched sample is perceived, whereas a pronounced elemental inhomogeneity of boron is detected for the annealed state. In addition, the distance distribution of the first fifteen atomic neighbors is determined by using this algorithm for both annealed and as quenched states. The next neighbor evaluation algorithm evinces a steric periodicity of the atoms when the next neighbor distances are normalized by the first next neighbor distance. A comparison of the nearest neighbor atomic distribution for as quenched and annealed state shows accumulation of Ni and B. Moreover, it also reveals the tendency of Fe and B to move slightly away from each other, an incipient step to Ni rich boride formation. © 2011 Elsevier B.V.

  6. Density dependent atomic motion in a liquid alkali metal

    Pilgrim, W.-C.; Hosokawa, S.; Morkel, C.

    2001-01-01

    Inelastic X-ray and neutron scattering results obtained from liquid sodium and rubidium are presented. They cover the entire liquid range between melting and liquid vapour critical point. At high densities the dynamics of the liquid metal is characterized by collective excitations. The corresponding dispersion relations indicate the existence of surprisingly stable next neighbouring shells leading to an increase of the propagation speed for the collective modes. Below 2ρ crit. the dynamics changes from collective to localized indicating the existence of molecular aggregates. This interpretation is in accord with a simple model where the properties of a Rb- and a Rb 2 - lattice are calculated using density functional theory. (orig.)

  7. Controlling Magnetism of a Complex Metallic System Using Atomic Individualism

    Mudryk, Y.; Paudyal, D.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Misra, S.; Miller, G. J.

    2010-08-01

    When the complexity of a metallic compound reaches a certain level, a specific location in the structure may be critically responsible for a given fundamental property of a material while other locations may not play as much of a role in determining such a property. The first-principles theory has pinpointed a critical location in the framework of a complex intermetallic compound—Gd5Ge4—that resulted in a controlled alteration of the magnetism of this compound using precise chemical tools.

  8. [Applications of atomic emission spectrum from liquid electrode discharge to metal ion detection].

    Mao, Xiu-Ling; Wu, Jian; Ying, Yi-Bin

    2010-02-01

    The fast and precise detection of metal ion is an important research project concerning studies in diverse academic fields and different kinds of detecting technologies. In the present paper, the authors review the research on atomic emission spectrum based on liquid electrode discharge and its applications in the detection of metal ion. In the first part of this paper the principles and characteristics of the methods based on electrochemistry and spectroscopy were introduced. The methods of ion-selective electrode (ISE), anodic stripping voltammetry, atomic emission spectrum and atomic absorption spectrum were included in this part and discussed comparatively. Then the principles and characteristics of liquid electrode spectra for metal ion detection were introduced. The mechanism of the plasma production and the characteristics of the plasma spectrum as well as its advantages compared with other methods were discussed. Secondly, the authors divided the discharge system into two types and named them single liquid-electrode discharge and double-liquid electrode respectively, according to the number of the liquid electrode and the configuration of the discharge system, and the development as well as the present research status of each type was illustrated. Then the characteristics and configurations of the discharge systems including ECGD, SCGD, LS-APGD and capillary discharge were discussed in detail as examples of the two types. By taking advantage of the technology of atomic emission spectrum based on liquid electrode discharge, the detecting limit of heavy metals such as copper, mercury and argent as well as active metal ions including sodium, potass and magnesium can achieve microg x L(-1). Finally, the advantages and problems of the liquid-electrode discharge applied in detection of metal ion were discussed. And the applications of the atomic emission spectrum based on liquid electrode discharge were prospected.

  9. Flexibility analysis of main primary heat transport system : Narora Atomic Power Project

    Rastogi, S.K.

    1975-01-01

    The paper presents flexibility analysis problem of main primary heat transport system and the approximate analysis that has been made to estimate the loads coming on major equipments. The primary heat transport system for Narora Atomic Power Project is adopting vertical steam generators and pumps equally divided on either side of the reactor with inter-connecting pipes and feeders. Since the system is mainly spring supported with movement of a few points in certain direction defined but no anchorage, it represents a good problem for flexibility analysis which can only be solved in one step by developing a good computer programme. (author)

  10. A normal metal tunnel-junction heat diode

    Fornieri, Antonio, E-mail: antonio.fornieri@sns.it; Martínez-Pérez, María José; Giazotto, Francesco, E-mail: giazotto@sns.it [NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy)

    2014-05-05

    We propose a low-temperature thermal rectifier consisting of a chain of three tunnel-coupled normal metal electrodes. We show that a large heat rectification is achievable if the thermal symmetry of the structure is broken and the central island can release energy to the phonon bath. The performance of the device is theoretically analyzed and, under the appropriate conditions, temperature differences up to ∼200 mK between the forward and reverse thermal bias configurations are obtained below 1 K, corresponding to a rectification ratio R∼2000. The simplicity intrinsic to its design joined with the insensitivity to magnetic fields make our device potentially attractive as a fundamental building block in solid-state thermal nanocircuits and in general-purpose cryogenic electronic applications requiring energy management.

  11. Application of metal foam heat exchangers for a high-performance liquefied natural gas regasification system

    Kim, Dae Yeon; Sung, Tae Hong; Kim, Kyung Chun

    2016-01-01

    The intermediate fluid vaporizer has wide applications in the regasification of LNG (liquefied natural gas). The heat exchanger performance is one of the main contributors to the thermodynamic and cost effectiveness of the entire LNG regasification system. Within the paper, the authors discuss a new concept for a compact heat exchanger with a micro-cellular structure medium to minimize volume and mass and to increase thermal efficiency. Numerical calculations have been conducted to design a metal-foam filled plate heat exchanger and a shell-and-tube heat exchanger using published experimental correlations. The geometry of both heat exchangers was optimized using the conditions of thermolators in LNG regasification systems. The heat transfer and pressure drop performance was predicted to compare the heat exchangers. The results show that the metal-foam plate heat exchanger has the best performance at different channel heights and mass flow rates of fluid. In the optimized configurations, the metal-foam plate heat exchanger has a higher heat transfer rate and lower pressure drop than the shell-and-tube heat exchanger as the mass flow rate of natural gas is increased. - Highlights: • A metal foam heat exchanger is proposed for LNG regasification system. • Comparison was made with a shell and tube heat exchanger. • Heat transfer and pressure drop characteristics were estimated. • The geometry of both heat exchangers is optimized for thermolators. • It can be used as a compact and high performance thermolators.

  12. The properties of helium atoms and positrons as impurities in metals

    Pendry, J.B.

    1980-01-01

    Topics covered include: (A) atoms in simple metals: (1) the highly repulsive e - /He interaction and its consequences for binding energies in simple metals; (2) binding energy calculations for jellium and their implications for validity of pair-potential He/M interactions; and (3) the need for experimental data on high negative binding energy systems: (B) low energy positrons in simple metals: (1) behaviour of the positron especially its range (< 100A); (2) consequences for experiments on voids; and (3) possibility for non-destructive depth profiling of defect concentration. (author)

  13. Tuning the electronic structure of graphene through alkali metal and halogen atom intercalation

    Ahmad, Sohail; Miró, Pere; Audiffred, Martha; Heine, Thomas

    2018-04-01

    The deposition, intercalation and co-intercalation of heavy alkali metals and light halogens atoms in graphene mono- and bilayers have been studied using first principles density-functional calculations. Both the deposition and the intercalation of alkali metals gives rise to n-type doping due to the formation of M+-C- pairs. The co-intercalation of a 1:1 ratio of alkali metals and halogens derives into the formation of ionic pairs among the intercalated species, unaltering the electronic structure of the layered material.

  14. Dynamics of a Rydberg hydrogen atom near a metal surface in the electron-extraction scheme

    Iñarrea, Manuel [Área de Física Aplicada, Universidad de La Rioja, Logroño (Spain); Lanchares, Víctor [Departamento de Matemáticas y Computación, Universidad de La Rioja, Logroño, La Rioja (Spain); Palacián, Jesús [Departamento de Ingeniería Matemática e Informática, Universidad Pública de Navarra, Pamplona (Spain); Pascual, Ana I. [Departamento de Matemáticas y Computación, Universidad de La Rioja, Logroño, La Rioja (Spain); Salas, J. Pablo, E-mail: josepablo.salas@unirioja.es [Área de Física Aplicada, Universidad de La Rioja, Logroño (Spain); Yanguas, Patricia [Departamento de Ingeniería Matemática e Informática, Universidad Pública de Navarra, Pamplona (Spain)

    2015-01-23

    We study the classical dynamics of a Rydberg hydrogen atom near a metal surface in the presence of a constant electric field in the electron-extraction situation [1], e.g., when the field attracts the electron to the vacuum. From a dynamical point of view, this field configuration provides a dynamics richer than in the usual ion-extraction scheme, because, depending on the values of field and the atom–surface distance, the atom can be ionized only towards the metal surface, only to the vacuum or to the both sides. The evolution of the phase space structure as a function of the atom–surface distance is explored in the bound regime of the atom. In the high energy regime, the ionization mechanism is also investigated. We find that the classical results of this work are in good agreement with the results obtained in the wave-packet propagation study carried out by So et al. [1]. - Highlights: • We study a classical hydrogen atom near a metal surface plus a electric field. • We explore the phase space structure as a function of the field strength. • We find most of the electronic orbits are oriented along the field direction. • We study the ionization of the atom for several atom–surface distances. • This classical study is in good agreement with the quantum results.

  15. Determination of heavy metals in polar snow and ice by laser-excited atomic fluorescence spectrometry

    Bolshov, M.A.; Boutron, C.F.

    1994-01-01

    The new laser-excited atomic fluorescence spectrometry technique offers unrivalled sensitivity for the determination of trace metals in a wide variety of samples. This has allowed the direct determination of Pb, Cd and Bi in Antarctic and Greenland snow and ice down to the sub pg/g level. (authors). 11 refs., 2 figs

  16. Laser-induced fluorescence of metal-atom impurities in a neutral beam

    Burrell, C.F.; Pyle, R.V.; Sabetimani, Z.; Schlachter, A.S.

    1984-10-01

    The need to limit impurities in fusion devices to low levels is well known. We have investigated, by the technique of laser-induced fluorescence, the concentration of heavy-metal atoms in a neutral beam caused by their evaporation from the hot filaments in a conventional high-current multifilament hydrogen-ion source

  17. Charge transfer between hydrogen(deuterium) ions and atoms in metal vapors

    Alvarez T, I.; Cisneros G, C.

    1981-01-01

    The current state of the experiments on charge transfer between hydrogen (deuterium) ions and atoms in metal vapors are given. Emphasis is given to describing different experimental techniques. The results of calculations if available, are compared with existing experimental data. (author)

  18. [Novel Hyphenated Techniques of Atomic Spectrometry for Metal Species Interaction with Biomolecules].

    Li, Yan; Yan, Xiu-ping

    2015-09-01

    Trace metals may be adopted by biological systems to assist in the syntheses and metabolic functions of genes (DNA and RNA) and proteins in the environment. These metals may be beneficial or may pose a risk to humans and other life forms. Novel hybrid techniques are required for studies on the interaction between different metal species and biomolecules, which is significant for biology, biochemistry, nutrition, agriculture, medicine, pharmacy, and environmental science. In recent years, our group dwells on new hyphenated techniques based on capillary electrophoresis (CE), electrothermal atomic absorption spectrometry (ETAAS), and inductively coupled plasma mass spectroscopy (ICP-MS), and their application for different metal species interaction with biomolecules such as DNA, HSA, and GSH. The CE-ETAAS assay and CE-ICP-MS assay allow sensitively probing the level of biomolecules such as DNA damage by different metal species and extracting the kinetic and thermodynamic information on the interactions of different metal species with biomolecules, provides direct evidences for the formation of different metal species--biomolecule adducts. In addition, the consequent structural information were extracted from circular dichroism (CD) and X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The present works represent the most complete and extensive study to date on the interactions between different metal species with biomolecules, and also provide new evidences for and insights into the interactions of different metal species with biomolecules for further understanding of the toxicological effects of metal species.

  19. Modulating the electronic and magnetic properties of bilayer borophene via transition metal atoms intercalation: from metal to half metal and semiconductor.

    Zhang, Xiuyun; Sun, Yi; Ma, Liang; Zhao, Xinli; Yao, Xiaojing

    2018-07-27

    Borophene, a two-dimensional monolayer made of boron atoms, has attracted wide attention due to its appealing properties. Great efforts have been devoted to fine tuning its electronic and magnetic properties for desired applications. Herein, we theoretically investigate the versatile electronic and magnetic properties of bilayer borophene (BLB) intercalated by 3d transition metal (TM) atoms, TM@BLBs (TM = Ti-Fe), using ab initio calculations. Four allotropes of AA-stacking (α 1 -, β-, β 12 - and χ 3 -) BLBs with different intercalation concentrations of TM atoms are considered. Our results show that the TM atoms are strongly bonded to the borophene layers with fairly large binding energies, around 6.31 ∼ 15.44 eV per TM atom. The BLBs with Cr and Mn intercalation have robust ferromagnetism, while for the systems decorated with Fe atoms, fruitful magnetic properties, such as nonmagnetic, ferromagnetic or antiferromagnetic, are identified. In particular, the α 1 - and β-BLBs intercalated by Mn or Fe atom can be transformed into a semiconductor, half metal or graphene-like semimetal. Moreover, some heavily doped TM@BLBs expose high Curie temperatures above room temperature. The attractive properties of TM@BLBs entail an efficient way to modulate the electronic and magnetic properties of borophene sheets for advanced applications.

  20. Characteristics of plasma in uranium atomic beam produced by electron-beam heating

    Ohba, Hironori; Shibata, Takemasa

    2000-08-01

    The electron temperature of plasma and the ion flux ratio in the uranium atomic beam produced by electron-beam heating were characterized with Langmuir probes. The electron temperature was 0.13 eV, which was lower than the evaporation surface temperature. The ion flux ratio to atomic beam flux was more than 3% at higher evaporation rates. The ion flux ratio has increased with decreasing acceleration energy of the electron-beam under constant electron-beam power. This is because of an increase of electron-beam current and a large ionization cross-section of uranium by electron-impact. It was confined that the plasma is produced by electron-impact ionization of the evaporated atoms at the evaporation source. (author)

  1. Semiempirical calculation of van der Waals coefficients for alkali-metal and alkaline-earth-metal atoms

    Mitroy, J.; Bromley, M.W.J.

    2003-01-01

    The van der Waals coefficients, C 6 , C 8 , and C 10 for the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are estimated by a combination of ab initio and semiempirical methods. Polarizabilities and atom-wall coefficients are given as a diagnostic check, and the lowest order nonadiabatic dispersion coefficient, D 8 and the three-body coefficient, C 9 are also presented. The dispersion coefficients are in agreement with the available relativistic many-body perturbation theory calculations. The contribution from the core was included by using constrained sum rules involving the core polarizability and Hartree-Fock expectation values to estimate the f-value distribution

  2. Effects of Al addition on atomic structure of Cu-Zr metallic glass

    Li, Feng; Zhang, Huajian; Liu, Xiongjun; Dong, Yuecheng; Yu, Chunyan; Lu, Zhaoping

    2018-02-01

    The atomic structures of Cu52Zr48 and Cu45Zr48Al7 metallic glasses (MGs) have been studied by molecular dynamic simulations. The results reveal that the molar volume of the Cu45Zr48Al7 MG is smaller than that of the Cu52Zr48 MG, although the size of the Al atom is larger than that of the Cu atom, implying an enhanced atomic packing density achieved by introducing Al into the ternary MG. Bond shortening in unlike atomic pairs Zr-Al and Cu-Al is observed in the Cu45Zr48Al7 MG, which is attributed to strong interactions between Al and (Zr, Cu) atoms. Meanwhile, the atomic packing efficiency is enhanced by the minor addition of Al. Compared with the Cu52Zr48 binary MG, the potential energy of the ternary MG decreases and the glass transition temperature increases. Structural analyses indicate that more Cu- and Al-centered full icosahedral clusters emerge in the Cu45Zr48Al7 MG as some Cu atoms are substituted by Al. Furthermore, the addition of Al leads to more icosahedral medium-range orders in the ternary MG. The increase of full icosahedral clusters and the enhancement of the packing density are responsible for the improved glass-forming ability of Cu45Zr48Al7.

  3. First row transition metal atoms embedded in multivacancies in a rippled graphene system

    Mombrú, Dominique; Faccio, Ricardo; Mombrú, Alvaro W.

    2018-03-01

    Ab-initio calculations based on density functional theory (DFT) have been performed to study systems where a first row transition metal atom is embedded in a rippled graphene due to the existence of an 8-order multivacancy. In addition to these cases, also the inclusion of a zinc atom, with a 3d10 electron configuration, was also studied. Structural distortions and magnetic response for each system were studied. A correlation was found for the magnitude of the rippling and the distortion in the vacancy. Variation in the trends was found for Cu and Zn cases, which were explained on the basis of the filling of the 3dx2-y2 orbital. All the systems exhibit lower magnetic moment in comparison to the metal-less system. The quenching of the magnetic moment due to the carbon atoms in the vacancy is observed for Sc and Cu.

  4. Atomic Resolution Imaging of Nanoscale Structural Ordering in a Complex Metal Oxide Catalyst

    Zhu, Yihan

    2012-08-28

    The determination of the atomic structure of a functional material is crucial to understanding its "structure-to-property" relationship (e.g., the active sites in a catalyst), which is however challenging if the structure possesses complex inhomogeneities. Here, we report an atomic structure study of an important MoVTeO complex metal oxide catalyst that is potentially useful for the industrially relevant propane-based BP/SOHIO process. We combined aberration-corrected scanning transmission electron microscopy with synchrotron powder X-ray crystallography to explore the structure at both nanoscopic and macroscopic scales. At the nanoscopic scale, this material exhibits structural and compositional order within nanosized "domains", while the domains show disordered distribution at the macroscopic scale. We proposed that the intradomain compositional ordering and the interdomain electric dipolar interaction synergistically induce the displacement of Te atoms in the Mo-V-O channels, which determines the geometry of the multifunctional metal oxo-active sites.

  5. Anomalous conductance oscillations and half-metallicity in atomic Ag-O chains

    Strange, Mikkel; Thygesen, Kristian Sommer; Sethna, James P

    2008-01-01

    . The conductances of the chains exhibit weak even-odd oscillations around an anomalously low value of 0.1G(0) (G(0) = 2e(2)/h) which coincide with the averaged experimental conductance in the long chain limit. The unusual conductance properties are explained in terms of a resonating-chain model, which takes...... the reflection probability and phase shift of a single bulk-chain interface as the only input. The model also explains the conductance oscillations for other metallic chains.......Using spin density functional theory, we study the electronic and magnetic properties of atomically thin, suspended chains containing silver and oxygen atoms in an alternating sequence. Chains longer than 4 atoms develop a half-metallic ground state implying fully spin-polarized charge carriers...

  6. Metal hydride heat pump engineering demonstration and evaluation model

    Lynch, Franklin E.

    1993-01-01

    Future generations of portable life support systems (PLSS's) for space suites (extravehicular mobility units or EMU's) may require regenerable nonventing thermal sinks (RNTS's). For purposes of mobility, a PLSS must be as light and compact as possible. Previous venting PLSS's have employed water sublimators to reject metabolic and equipment heat from EMU's. It is desirable for long-duration future space missions to minimize the use of water and other consumables that need to be periodically resupplied. The emission of water vapor also interferes with some types of instrumentation that might be used in future space exploration. The test article is a type of RNTS based on a metal hydride heat pump (MHHP). The task of reservicing EMU's after use must be made less demanding in terms of time, procedures, and equipment. The capability for quick turnaround post-EVA servicing (30 minutes) is a challenging requirement for many of the RNTS options. The MHHP is a very simple option that can be regenerated in the airlock within the 30 minute limit by the application of a heating source and a cooling sink. In addition, advanced PLSS's must provide a greater degree of automatic control, relieving astronauts of the need to manually adjust temperatures in their liquid cooled ventilation garments (LCVG's). The MHHP includes automatic coolant controls with the ability to follow thermal load swings from minimum to maximum in seconds. The MHHP includes a coolant loop subsystem with pump and controls, regeneration equipment for post-EVA servicing, and a PC-based data acquisition and control system (DACS).

  7. Computer simulation of void formation in residual gas atom free metals by dual beam irradiation experiments

    Shimomura, Y.; Nishiguchi, R.; La Rubia, T.D. de; Guinan, M.W.

    1992-01-01

    In our recent experiments (1), we found that voids nucleate at vacancy clusters which trap gas atoms such as hydrogen and helium in ion- and neutron-irradiated copper. A molecular dynamics computer simulation, which implements an empirical embedded atom method to calculate forces that act on atoms in metals, suggests that a void nucleation occurs in pure copper at six and seven vacancy clusters. The structure of six and seven vacancy clusters in copper fluctuates between a stacking fault tetrahedron and a void. When a hydrogen is trapped at voids of six and seven vacancy, a void can keep their structure for appreciably long time; that is, the void do not relax to a stacking fault tetrahedron and grows to a large void. In order to explore the detailed atomics of void formation, it is emphasized that dual-beam irradiation experiments that utilize beams of gas atoms and self-ions should be carried out with residual gas atom free metal specimens. (author)

  8. Developments in the application of atomic spectroscopy to trace metal analysis

    Fuavao, V.A.

    1983-01-01

    A method is described for the determination of selenium in horse blood by generation, atomization and analysis of the selenium hydride. A pooled horse blood sample which contained 8.8 μg 1 -1 of selenium exhibited a precision of analysis of 4.32% for ten replicate analyses. A study of the sensitivity of nonresonance and resonance lines of ytterbium utilizing microboat and platform atomization was investigated. Increases of at least twofold for all nonresonance lines were observed. Microboat sensitivity fell between that of the wall and the platform. Alternative surfaces of electrothermal atomization atomic absorption spectrophotometry (ETAAS) and the thermodynamic process for atom formation in ETAAS were investigated. Sensitivities for carbide-formation elements such as ytterbium and molybdenum and other noncarbide formation elements were determined by precoating graphite tubes and inserting collars. An improvement in analytical sensitivity and reduction in memory effect compared to commercially available pyrolytic graphite tubes were observed for all except the molybdenum analyte where a depression in analytical sensitivity resulted. The useful lifetime (analysis cycles) of all surfaces (except metal collars) were recorded at 250 to 400 cycles with acceptable and comparable precisions. A method is described for proposing the thermodynamic process in IL655 ETAAS. Appearance temperatures of analytes and free energy were studied and two major pathways were found operative: 1) thermal dissociation of the analyte oxide; 2) carbon reduction of the oxide followed by atomization of the free metal

  9. THE STUDY OF HEAVY METAL FROM ENVIRONMENTAL SAMPLES BY ATOMIC TECHNIQUES

    Ion V. POPESCU

    2011-05-01

    Full Text Available Using the Atomic Absorption Spectrometry (AAS and Energy Dispersive X-ray spectrometry (EDXRF techniques we analyzed the contents of heavy metals ( Cd, Cr, Ni, Pb, Ti, Sr, Co, Bi from eight wild mushrooms and soil substrate samples (48 samples of eight fungal species and 32 underlying soil samples, collected from ten forest sites of Dambovița County Romania. It was determined that the elements, especially heavy metals, in soil were characteristic of the acidic soils of the Romanian forest lands and are influenced by industrial pollution. Analytical possibilities of AAS and EDXRF analytical techniques have been compared and the heavy metal transfer from substrate to mushrooms has been studied. The coefficient of accumulation of essential and heavy metals has been calculated as well. Heavy metal contents of all analyzed mushrooms were generally higher than previously reported in literature.

  10. First-principles simulations on the new hybrid phases of germanene with alkali metal atoms coverage

    Yuan, Jianmei [Hunan Key Laboratory for Computation and Simulation in Science and Engineering, School of Mathematics and Computational Science, Xiangtan University, Hunan 411105 (China); Tang, Chan; Zhong, Jianxin [Hunan Key Laboratory for Micro-Nano Energy Materials and Devices, School of Physics and Optoelectronic Engineering, Xiangtan University, Hunan 411105 (China); Mao, Yuliang, E-mail: ylmao@xtu.edu.cn [Hunan Key Laboratory for Micro-Nano Energy Materials and Devices, School of Physics and Optoelectronic Engineering, Xiangtan University, Hunan 411105 (China)

    2016-01-01

    Graphical abstract: - Highlights: • The predicted new phase of complete lithiated germanene is more favorable to form than germanane. • Besides ionic interactions, covalent component in some extent leads the complete lithiated germanene into a semiconductor. • 2D phases of Ge{sub 2}X{sub 1} (X = Li, Na, K) are metallic with weak polarization. • Half-lithiated germanene exhibits local magnetic moments on the Ge atoms neighbored with Li adatoms. - Abstract: We present first-principles calculations of a new type hybrid phases composed by buckled germanene with saturated or half-saturated alkali metal atoms adsorption. Our energetics and electronic structure analysis suggests that adsorbed alkali metal atoms (Li, Na, K) can be used as covered adatoms to synthesize germanene-based new phases in two dimensional. The predicted new phases of Ge{sub 2}X{sub 2} and Ge{sub 2}X{sub 1} (X = Li, Na, K) relative to the single germanene sheet could exist at room temperature. The formation energy of Ge{sub 2}Li{sub 2} configuration obtained from complete lithiation is even more favorable than that of germanane. Charge transfer is significant between the alkali metal atoms and Ge, indicating the ionic interactions between them. Furthermore, our charge density analysis indicates that covalent component in some extent exists in Ge{sub 2}X{sub 2} and Ge{sub 2}X{sub 1} (X = Li, Na, K) 2D phases, which even leads the complete lithiated germanene into a semiconductor with an energy gap of 0.14 eV. We report that 2D phases of Ge{sub 2}X{sub 1} (X = Li, Na, K) are metallic with weak polarization on the Fermi level and in unoccupied states. It is found that half-lithiated germanene exhibits local magnetic moments of 0.48 μ{sub B} on the Ge atoms neighbored with Li adatoms.

  11. Incorporation of defects into the central atoms model of a metallic glass

    Lass, Eric A.; Zhu Aiwu; Shiflet, G.J.; Joseph Poon, S.

    2011-01-01

    The central atoms model (CAM) of a metallic glass is extended to incorporate thermodynamically stable defects, similar to vacancies in a crystalline solid, within the amorphous structure. A bond deficiency (BD), which is the proposed defect present in all metallic glasses, is introduced into the CAM equations. Like vacancies in a crystalline solid, BDs are thermodynamically stable entities because of the increase in entropy associated with their creation, and there is an equilibrium concentration present in the glassy phase. When applied to Cu-Zr and Ni-Zr binary metallic glasses, the concentration of thermally induced BDs surrounding Zr atoms reaches a relatively constant value at the glass transition temperature, regardless of composition within a given glass system. Using this 'critical' defect concentration, the predicted temperatures at which the glass transition is expected to occur are in good agreement with the experimentally determined glass transition temperatures for both alloy systems.

  12. Phase transformations, heat evolution, and atomic diffusion during slow heating of Al-rich Al/Zr multilayered foils

    Fisher, Kaitlynn; Barron, S. C.; Knepper, R.; Weihs, T. P., E-mail: weihs@jhu.edu [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218-2689 (United States); Bonds, M. A.; Browning, N. D. [Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616 (United States); Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Livi, K. J. T. [High-Resolution Analytical Electron Microbeam Facility, Integrated Imaging Center, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Campbell, G. H. [Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

    2013-12-28

    We describe the energy and sequence of phase transformations in multilayered Al/Zr foils with atomic ratios of 3 Al:1 Zr during low temperature (<350 °C) heat treatments in a differential scanning calorimeter. The initial phase formed is an Al-rich amorphous phase that appears to grow by Zr diffusion through the amorphous phase. The subsequent nucleation and growth of tetragonal Al{sub 3}Zr along the Al/amorphous layer interface is mediated by Al diffusion through the crystalline intermetallic phase. Diffusion coefficients associated with these processes are higher than expected from reports of diffusivities measured at higher temperatures. The inferred heat of formation of the tetragonal Al{sub 3}Zr phase is 1240 ± 40 J/g (53 ± 2 kJ/mol atom). No anomalous variation in the energy or sequence of phase transformations is found with bilayer thickness for samples with bilayer thickness in the range of 17 nm to 90 nm despite anomalies in the bilayer dependence of self-propagating reaction velocities in the same foils.

  13. Atoms

    Fuchs, Alain; Villani, Cedric; Guthleben, Denis; Leduc, Michele; Brenner, Anastasios; Pouthas, Joel; Perrin, Jean

    2014-01-01

    Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)

  14. Optical emission spectroscopy of metal-halide lamps: Radially resolved atomic state distribution functions of Dy and Hg

    Nimalasuriya, T.; Flikweert, A.J.; Stoffels, W.W.; Haverlag, M.; Mullen, van der J.J.A.M.; Pupat, N.B.M.

    2006-01-01

    Absolute line intensity measurements are performed on a metal-halide lamp. Several transitions of atomic and ionic Dy and atomic Hg are measured at different radial positions from which we obtain absolute atomic and ionic Dy intensity profiles. From these profiles we construct the radially resolved

  15. Giant metal sputtering yields induced by 20-5000 keV/atom gold clusters

    Andersen, H.H.; Brunelle, A.; Della-Negra, S.; Depauw, J.; Jacquet, D.; Le Beyec, Y.

    1997-01-01

    Very large non-linear effects have been found in cluster-induced metal sputtering over a broad projectile energy interval for the first time. Recently available cluster beams from tandem accelerators have allowed sputtering yield measurements to be made with Au 1 to Au 5 from 20 keV/atom to 5 MeV/atom. The cluster-sputtering yield maxima were found at the same total energy but not at the same energy/atom as expected. For Au 5 a yield as high as 3000 was reached at 150 keV/atom while the Au 1 yield was only 55 at the same velocity. The Sigmund-Claussen thermal spike theory, which fits published data at low energy, cannot reproduce our extended new data set. (author)

  16. Tunable meta-atom using liquid metal embedded in stretchable polymer

    Liu, Peng; Yang, Siming; Wang, Qiugu; Jiang, Huawei; Song, Jiming; Dong, Liang, E-mail: ldong@iastate.edu [Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa 50011 (United States); Jain, Aditya [Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa 50011 (United States); Ames Laboratory, U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States); Koschny, Thomas; Soukoulis, Costas M. [Ames Laboratory, U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)

    2015-07-07

    Reconfigurable metamaterials have great potential to alleviate complications involved in using passive metamaterials to realize emerging electromagnetic functions, such as dynamical filtering, sensing, and cloaking. This paper presents a new type of tunable meta-atoms in the X-band frequency range (8–12 GHz) toward reconfigurable metamaterials. The meta-atom is made of all flexible materials compliant to the surface of an interaction object. It uses a liquid metal-based split-ring resonator as its core constituent embedded in a highly flexible elastomer. We demonstrate that simple mechanical stretching of the meta-atom can lead to the great flexibility in reconfiguring its resonance frequency continuously over more than 70% of the X-band frequency range. The presented meta-atom technique provides a simple approach to dynamically tune response characteristics of metamaterials over a broad frequency range.

  17. Tunable meta-atom using liquid metal embedded in stretchable polymer

    Liu, Peng; Yang, Siming; Wang, Qiugu; Jiang, Huawei; Song, Jiming; Dong, Liang; Jain, Aditya; Koschny, Thomas; Soukoulis, Costas M.

    2015-01-01

    Reconfigurable metamaterials have great potential to alleviate complications involved in using passive metamaterials to realize emerging electromagnetic functions, such as dynamical filtering, sensing, and cloaking. This paper presents a new type of tunable meta-atoms in the X-band frequency range (8–12 GHz) toward reconfigurable metamaterials. The meta-atom is made of all flexible materials compliant to the surface of an interaction object. It uses a liquid metal-based split-ring resonator as its core constituent embedded in a highly flexible elastomer. We demonstrate that simple mechanical stretching of the meta-atom can lead to the great flexibility in reconfiguring its resonance frequency continuously over more than 70% of the X-band frequency range. The presented meta-atom technique provides a simple approach to dynamically tune response characteristics of metamaterials over a broad frequency range

  18. A numerical study of spin-dependent organization of alkali-metal atomic clusters using density-functional method

    Liu Xuan; Ito, Haruhiko; Torikai, Eiko

    2012-01-01

    We calculate the different geometric isomers of spin clusters composed of a small number of alkali-metal atoms using the UB3LYP density-functional method. The electron density distribution of clusters changes according to the value of total spin. Steric structures as well as planar structures arise when the number of atoms increases. The lowest spin state is the most stable and Li n , Na n , K n , Rb n , and Cs n with n = 2–8 can be formed in higher spin states. In the highest spin state, the preparation of clusters depends on the kind and the number of constituent atoms. The interaction energy between alkali-metal atoms and rare-gas atoms is smaller than the binding energy of spin clusters. Consequently, it is possible to self-organize the alkali-metal-atom clusters on a non-wetting substrate coated with rare-gas atoms.

  19. Atomic structure of Mg-based metallic glass investigated with neutron diffraction, reverse Monte Carlo modeling and electron microscopy

    Rafał Babilas

    2017-05-01

    Full Text Available The structure of a multicomponent metallic glass, Mg65Cu20Y10Ni5, was investigated by the combined methods of neutron diffraction (ND, reverse Monte Carlo modeling (RMC and high-resolution transmission electron microscopy (HRTEM. The RMC method, based on the results of ND measurements, was used to develop a realistic structure model of a quaternary alloy in a glassy state. The calculated model consists of a random packing structure of atoms in which some ordered regions can be indicated. The amorphous structure was also described by peak values of partial pair correlation functions and coordination numbers, which illustrated some types of cluster packing. The N = 9 clusters correspond to the tri-capped trigonal prisms, which are one of Bernal’s canonical clusters, and atomic clusters with N = 6 and N = 12 are suitable for octahedral and icosahedral atomic configurations. The nanocrystalline character of the alloy after annealing was also studied by HRTEM. The selected HRTEM images of the nanocrystalline regions were also processed by inverse Fourier transform analysis. The high-angle annular dark-field (HAADF technique was used to determine phase separation in the studied glass after heat treatment. The HAADF mode allows for the observation of randomly distributed, dark contrast regions of about 4–6 nm. The interplanar spacing identified for the orthorhombic Mg2Cu crystalline phase is similar to the value of the first coordination shell radius from the short-range order.

  20. Direct high-temperature ohmic heating of metals as liquid pipes.

    Grosse, A V; Cahill, J A; Liddell, W L; Murphy, W J; Stokes, C S

    1968-05-03

    When a sufficiently high electric current is passed through a liquid metal, the electromagnetic pressure pinches off the liquid metal and interrupts the flow of current. For the first time the pinch effect has been overcome by use of centrifugal acceleration. By rotation of a pipe of liquid metal, tin or bismuth or their alloys, at sufficiently high speed, it can be heated electrically without intermission of the electric current. One may now heat liquid metallic substances, by resistive (ohmic) heating, to 5000 degrees K and perhaps higher temperatures.

  1. Numerical simulation of the alloying process during impulse induction heating of the metal substrate

    Popov, V. N.

    2017-10-01

    2D numerical modeling of the processes during the alloying of the substrate surface metal layer is carried out. Heating, phase transition, heat and mass transfer in the molten metal, solidification of the melt are considered with the aid the proposed mathematical model. Under study is the applicability of the high-frequency electromagnetic field impulse for metal heating and melting. The distribution of the electromagnetic energy in the metal is described by empirical formulas. According to the results of numerical experiments, the flow structure in the melt and distribution of the alloying substances is evaluated.

  2. Clustered atom-replaced structure in single-crystal-like metal oxide

    Araki, Takeshi; Hayashi, Mariko; Ishii, Hirotaka; Yokoe, Daisaku; Yoshida, Ryuji; Kato, Takeharu; Nishijima, Gen; Matsumoto, Akiyoshi

    2018-06-01

    By means of metal organic deposition using trifluoroacetates (TFA-MOD), we replaced and localized two or more atoms in a single-crystalline structure having almost perfect orientation. Thus, we created a new functional structure, namely, clustered atom-replaced structure (CARS), having single-crystal-like metal oxide. We replaced metals in the oxide with Sm and Lu and localized them. Energy dispersive x-ray spectroscopy results, where the Sm signal increases with the Lu signal in the single-crystalline structure, confirm evidence of CARS. We also form other CARS with three additional metals, including Pr. The valence number of Pr might change from 3+ to approximately 4+, thereby reducing the Pr–Ba distance. We directly observed the structure by a high-angle annular dark-field image, which provided further evidence of CARS. The key to establishing CARS is an equilibrium chemical reaction and a combination of additional larger and smaller unit cells to matrix cells. We made a new functional metal oxide with CARS and expect to realize CARS in other metal oxide structures in the future by using the above-mentioned process.

  3. Nanosheet Supported Single-Metal Atom Bifunctional Catalyst for Overall Water Splitting.

    Ling, Chongyi; Shi, Li; Ouyang, Yixin; Zeng, Xiao Cheng; Wang, Jinlan

    2017-08-09

    Nanosheet supported single-atom catalysts (SACs) can make full use of metal atoms and yet entail high selectivity and activity, and bifunctional catalysts can enable higher performance while lowering the cost than two separate unifunctional catalysts. Supported single-atom bifunctional catalysts are therefore of great economic interest and scientific importance. Here, on the basis of first-principles computations, we report a design of the first single-atom bifunctional eletrocatalyst, namely, isolated nickel atom supported on β 12 boron monolayer (Ni 1 /β 12 -BM), to achieve overall water splitting. This nanosheet supported SAC exhibits remarkable electrocatalytic performance with the computed overpotential for oxygen/hydrogen evolution reaction being just 0.40/0.06 V. The ab initio molecular dynamics simulation shows that the SAC can survive up to 800 K elevated temperature, while enacting a high energy barrier of 1.68 eV to prevent isolated Ni atoms from clustering. A viable experimental route for the synthesis of Ni 1 /β 12 -BM SAC is demonstrated from computer simulation. The desired nanosheet supported single-atom bifunctional catalysts not only show great potential for achieving overall water splitting but also offer cost-effective opportunities for advancing clean energy technology.

  4. Metal-atom fluorescence from the quenching of metastable rare gases by metal carbonyls

    Hollingsworth, W.E.

    1982-11-01

    A flowing afterglow apparatus was used to study the metal fluorescence resulting from the quenching of metastable rare-gas states by metal carbonyls. The data from the quenching or argon, neon, and helium by iron and nickel carbonyl agreed well with a restricted degree of freedom model indicating a concerted bond-breaking dissociation

  5. First-principles study of the alkali earth metal atoms adsorption on graphene

    Sun, Minglei [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Tang, Wencheng, E-mail: 101000185@seu.edu.cn [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Ren, Qingqiang [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, Hunan (China); Wang, Sake [Department of Physics, Southeast University, Nanjing 210096, Jiangsu (China); JinYu [School of Materials Science and Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189, Jiangsu (China); Du, Yanhui [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Zhang, Yajun [Department of Engineering Mechanics, School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, Zhejiang (China)

    2015-11-30

    Graphical abstract: - Highlights: • The adsorption of Be and Mg adatoms on graphene is physisorption. • Ca, Sr, and Ba adatoms bond ionically to graphene and the most stable adsorption site for them is hollow site. • The zero band gap semiconductor graphene becomes metallic and magnetic after the adsorption of Ca, Sr, and Ba adatoms. - Abstract: Geometries, electronic structures, and magnetic properties for alkali earth metal atoms absorbed graphene have been studied by first-principle calculations. For Be and Mg atoms, the interactions between the adatom and graphene are weak van der Waals interactions. In comparison, Ca, Sr and Ba atoms adsorption on graphene exhibits strong ionic bonding with graphene. We found that these atoms bond to graphene at the hollow site with a significant binding energy and large electron transfer. It is intriguing that these adatoms may induce important changes in both the electronic and magnetic properties of graphene. Semimetal graphene becomes metallic and magnetic due to n-type doping. Detailed analysis shows that the s orbitals of these adatoms should be responsible for the arising of the magnetic moment. We believe that our results are suitable for experimental exploration and useful for graphene-based nanoelectronic and data storage.

  6. First-principles study of the alkali earth metal atoms adsorption on graphene

    Sun, Minglei; Tang, Wencheng; Ren, Qingqiang; Wang, Sake; JinYu; Du, Yanhui; Zhang, Yajun

    2015-01-01

    Graphical abstract: - Highlights: • The adsorption of Be and Mg adatoms on graphene is physisorption. • Ca, Sr, and Ba adatoms bond ionically to graphene and the most stable adsorption site for them is hollow site. • The zero band gap semiconductor graphene becomes metallic and magnetic after the adsorption of Ca, Sr, and Ba adatoms. - Abstract: Geometries, electronic structures, and magnetic properties for alkali earth metal atoms absorbed graphene have been studied by first-principle calculations. For Be and Mg atoms, the interactions between the adatom and graphene are weak van der Waals interactions. In comparison, Ca, Sr and Ba atoms adsorption on graphene exhibits strong ionic bonding with graphene. We found that these atoms bond to graphene at the hollow site with a significant binding energy and large electron transfer. It is intriguing that these adatoms may induce important changes in both the electronic and magnetic properties of graphene. Semimetal graphene becomes metallic and magnetic due to n-type doping. Detailed analysis shows that the s orbitals of these adatoms should be responsible for the arising of the magnetic moment. We believe that our results are suitable for experimental exploration and useful for graphene-based nanoelectronic and data storage.

  7. Application of wire electrodes in electric discharge machining of metal samples of reactor blocks of the operative atomic power station

    Gozhenko, S.V.

    2007-01-01

    Features of application of electroerosive methods are considered during the process of direct definition of properties of metal of the equipment of power units of the atomic power station. Results of development of a complex of the equipment for wire electric discharge machining of metal templet and its use are presented at the control of the basic metal of the main circulating pipelines over blocks of the atomic power station of Ukraine over long terms of operation

  8. Tensorial analysis of the long-range interaction between metastable alkaline-earth-metal atoms

    Santra, Robin; Greene, Chris H.

    2003-01-01

    Alkaline-earth-metal atoms in their lowest (nsnp) 3 P 2 state are exceptionally long lived and can be trapped magnetically. The nonspherical atomic structure leads to anisotropic long-range interactions between two metastable alkaline-earth-metal atoms. The anisotropy affects the rotational motion of the diatomic system and couples states of different rotational quantum numbers. This paper develops a tensorial decomposition of the most important long-range interaction operators, and a systematic inclusion of molecular rotations, in the presence of an external magnetic field. This analysis illuminates the nature of the coupling between the various degrees of freedom. The consequences are illustrated by application to a system of practical interest: metastable 88 Sr. Using atomic parameters determined in a nearly ab initio calculation, we compute adiabatic potential-energy curves. The anisotropic interatomic interaction, in combination with the applied magnetic field, is demonstrated to induce the formation of a long-range molecular potential well. This curve correlates to two fully polarized, low-field seeking atoms in a rotational s-wave state. The coupling among molecular rotational states controls the existence of the potential well, and its properties vary as a function of magnetic-field strength, thus allowing the scattering length in this state to be tuned. The scattering length of metastable 88 Sr displays a resonance at a field of 339 G

  9. Effect of component substitution on the atomic dynamics in glass-forming binary metallic melts

    Nowak, B.; Holland-Moritz, D.; Yang, F.; Voigtmann, Th.; Evenson, Z.; Hansen, T. C.; Meyer, A.

    2017-08-01

    We investigate the substitution of early transition metals (Zr, Hf, and Nb) in Ni-based binary glass-forming metallic melts and the impact on structural and dynamical properties by using a combination of neutron scattering, electrostatic levitation (ESL), and isotopic substitution. The self-diffusion coefficients measured by quasielastic neutron scattering (QENS) identify a sluggish diffusion as well as an increased activation energy by almost a factor of 2 for Hf35Ni65 compared to Zr36Ni64 . This finding can be explained by the locally higher packing density of Hf atoms in Hf35Ni65 compared to Zr atoms in Zr36Ni64 , which has been derived from interatomic distances by analyzing the measured partial structure factors. Furthermore, QENS measurements of liquid Hf35Ni65 prepared with 60Ni , which has a vanishing incoherent scattering cross section, have demonstrated that self-diffusion of Hf is slowed down compared to the concentration weighted self-diffusion of Hf and Ni. This implies a dynamical decoupling between larger Hf and smaller Ni atoms, which can be related to a saturation effect of unequal atomic nearest-neighbor pairs, that was observed recently for Ni-rich compositions in Zr-Ni metallic melts. In order to establish a structure-dynamics relation, measured partial structure factors have been used as an input for mode-coupling theory (MCT) of the glass transition to calculate self-diffusion coefficients for the different atomic components. Remarkably, MCT can reproduce the increased activation energy for Hf35Ni65 as well as the dynamical decoupling between Hf and Ni atoms.

  10. ANALYSIS OF NONMAGNETIC METAL INDUCTION HEATING PROCESSES BY FLAT-TYPE CIRCULAR SOLENOIDAL FIELD

    Yu. Batygin

    2016-12-01

    Full Text Available The article analyzes the electromagnetic processes in the system of induction heating with estimating the main characteristics of heating the non-magnetic sheet metal. The analytical expressions for numerical estimates of the induced current in terms of the phase of the excitation signal are presented. The dependence for the heating temperature of the considered circular sheet metal area for the time corresponding to the interval phase has been determined.

  11. Containerless Heating Process of a Deeply Undercooled Metal Droplet by Electrostatic Levitation

    Wang Fei-Long; Dai Bin; Liu Xue-Feng; Sun Yi-Ning; Sun Zhi-Bin; Yu Qiang; Zhai Guang-Jie

    2015-01-01

    We present the containerless heating process of a deeply undercooled metal droplet by electrostatic levitation. The problem of surface charge loss in the heating process is discussed and specific formulas are given to describe the basic process of charge supplement by the photoelectric and thermoelectric effects. The pure metal zirconium is used to be melted and solidified to analyze the heating process. The temperature-time curve clearly shows the features including melting, undercooling, recalescence and solid-state phase transformation. (paper)

  12. Atomic layer deposition to prevent metal transfer from implants: An X-ray fluorescence study

    Bilo, Fabjola [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy); Borgese, Laura, E-mail: laura.borgese@unibs.itl [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy); Prost, Josef; Rauwolf, Mirjam; Turyanskaya, Anna; Wobrauschek, Peter; Kregsamer, Peter; Streli, Christina [Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna (Austria); Pazzaglia, Ugo [Dipartimento Specialità Medico Chirurgiche Sc. Radiol. e Sanità Pubblica, University of Brescia, v.le Europa, 11, 25121 Brescia (Italy); Depero, Laura E. [INSTM and Chemistry for Technologies Laboratory, University of Brescia, via Branze, 38, 25123 Brescia (Italy)

    2015-12-30

    Highlights: • Co and Cr migrate from bare alloy implant to the surrounding tissue showing a cluster distribution. • Co and Cr migrate from the TiO{sub 2} coated implant to the surrounding tissue showing a decreasing gradient distribution from the alloy surface. • TiO{sub 2} coating layers obtained by ALD on Co–Cr alloy show a barrier effect for the migration of metals. • The thicker the TiO{sub 2} layer deposited by ALD, the lower the metal migration. • The migration of metals from bare alloy toward the surrounding tissue increases with time. This effect is not detected in the coated samples. - Abstract: We show that Atomic Layer Deposition is a suitable coating technique to prevent metal diffusion from medical implants. The metal distribution in animal bone tissue with inserted bare and coated Co–Cr alloys was evaluated by means of micro X-ray fluorescence mapping. In the uncoated implant, the migration of Co and Cr particles from the bare alloy in the biological tissues is observed just after one month and the number of particles significantly increases after two months. In contrast, no metal diffusion was detected in the implant coated with TiO{sub 2}. Instead, a gradient distribution of the metals was found, from the alloy surface going into the tissue. No significant change was detected after two months of aging. As expected, the thicker is the TiO{sub 2} layer, the lower is the metal migration.

  13. Heat of solution and site energies of hydrogen in disordered transition-metal alloys

    Brouwer, R.C.; Griessen, R.

    1989-01-01

    Site energies, long-range effective hydrogen-hydrogen interactions, and the enthalpy of solution in transition-metal alloys are calculated by means of an embedded-cluster model. The energy of a hydrogen atom is assumed to be predominantly determined by the first shell of neighboring metal atoms. The semiempirical local band-structure model is used to calculate the energy of the hydrogen atoms in the cluster, taking into account local deviations from the average lattice constant. The increase in the solubility limit and the weak dependence of the enthalpy of solution on hydrogen concentration in disordered alloys are discussed. Calculated site energies and enthalpies of solution in the alloys are compared with experimental data, and good agreement is found. Due to the strong interactions with the nearest-neighbor metal atoms, hydrogen atoms can be used to determine local lattice separations and the extent of short-range order in ''disordered'' alloys

  14. Probing the atomic structure of metallic nanoclusters with the tip of a scanning tunneling microscope.

    Schouteden, Koen; Lauwaet, Koen; Janssens, Ewald; Barcaro, Giovanni; Fortunelli, Alessandro; Van Haesendonck, Chris; Lievens, Peter

    2014-02-21

    Preformed Co clusters with an average diameter of 2.5 nm are produced in the gas phase and are deposited under controlled ultra-high vacuum conditions onto a thin insulating NaCl film on Au(111). Relying on a combined experimental and theoretical investigation, we demonstrate visualization of the three-dimensional atomic structure of the Co clusters by high-resolution scanning tunneling microscopy (STM) using a Cl functionalized STM tip that can be obtained on the NaCl surface. More generally, use of a functionalized STM tip may allow for systematic atomic structure determination with STM of nanoparticles that are deposited on metal surfaces.

  15. Subthermal linewidths in photoassociation spectra of cold alkaline-earth-metal atoms

    Machholm, Mette; Julienne, Paul S.; Suominen, Kalle-Antti

    2002-01-01

    Narrow s-wave features with subthermal widths are predicted for the 1 Π g photoassociation spectra of cold alkaline-earth-metal atoms. The phenomenon is explained by numerical and analytical calculations. These show that only a small subthermal range of collision energies near threshold contributes to the s-wave features that are excited when the atoms are very far apart. The resonances survive thermal averaging, and may be detectable for Ca cooled near the Doppler cooling temperature of the 4 1 P 1 S laser-cooling transition

  16. Two-photon Doppler cooling of alkaline-earth-metal and ytterbium atoms

    Magno, Wictor C.; Cavasso Filho, Reinaldo L.; Cruz, Flavio C.

    2003-01-01

    The possibility of laser cooling of alkaline-earth-metal atoms and ytterbium atoms using a two-photon transition is analyzed. We consider a 1 S 0 - 1 S 0 transition with excitation in near resonance with the 1 P 1 level. This greatly increases the two-photon transition rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that for calcium, for example, two-photon cooling can be used to achieve a Doppler limit of 123 μK. The efficiency of this cooling scheme and the main loss mechanisms are analyzed

  17. Exploiting flow Injection and sequential injection schemes for trace metal determinations by electrothermal atomic absorption spectrometry

    Hansen, Elo Harald

    Determination of low or trace-level amounts of metals by electrothermal atomic absorption spectrometry (ETAAS) often requires the use of suitable preconcentration and/or separation procedures in order to attain the necessary sensitivity and selectivity. Such schemes are advantageously executed...... by superior performance and versatility. In fact, two approaches are conceivable: The analyte-loaded ion-exchange beads might either be transported directly into the graphite tube where they are pyrolized and the measurand is atomized and quantified; or the loaded beads can be eluted and the eluate forwarded...

  18. Screened Coulomb interactions in metallic alloys. I. Universal screening in the atomic-sphere approximation

    Ruban, Andrei; Skriver, Hans Lomholt

    2002-01-01

    We have used the locally self-consistent Green's-function (LSGF) method in supercell calculations to establish the distribution of the net charges assigned to the atomic spheres of the alloy components in metallic alloys with different compositions and degrees of order. This allows us to determine......-site local interaction zone. We demonstrate that the basic mechanism that governs the charge distribution is the screening of the net charges of the alloy components that makes the direct Coulomb interactions short ranged. In the atomic-sphere approximation, this screening appears to be almost independent...

  19. Reversal of atomic contrast in scanning probe microscopy on (111) metal surfaces

    Ondráček, Martin; González, C.; Jelínek, Pavel

    2012-01-01

    Roč. 24, 08 (2012), 084003/1-084003/7 ISSN 0953-8984 R&D Projects: GA ČR(CZ) GPP204/11/P578; GA ČR GAP204/10/0952; GA ČR GA202/09/0545; GA MŠk(CZ) ME10076 Grant - others:AVČR(CZ) M100100904 Institutional research plan: CEZ:AV0Z10100521 Keywords : atomic force microscopy * metallic surfaces * atomic contrast * scanning tunneling microscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.355, year: 2012 http://iopscience.iop.org/0953-8984/24/8/084003

  20. Copper metal foam as an essential construction element of innovative heat exchanger

    R. Rybár

    2016-07-01

    Full Text Available Paper deals with creation of the innovative heat exchanger - manifold header for the heat pipe evacuated tube solar collector, which essential functional element is heat exchange chamber made of the copper metal foam. Design of the heat exchanger is based on effective utilization of the unique properties of the metal foam which makes it possible to design highly effective and space saving devices. Inner volume of heat exchanger was reducing from 0,00045 m3 to 0,000135 m3 and heat exchange surface was increase from 0,0104 m2 to 0,1403 m2 at proposed prototype, what drastically increase heat exchange efficiency. The proposal itself is based on the unique physical properties of the metal foam, which was described by computational analysis.

  1. High-efficiency heat pump technology using metal hydrides (eco-energy city project)

    Morita, Y.; Harada, T.; Niikura, J.; Yamamoto, Y.; Suzuki, J. [Human Environmental Systems Development Center, Matsushita Electric Industrial Co., Ltd., Moriguchi, Osaka (Japan); Gamo, T. [Corporate Environmental Affairs Div., Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka (Japan)

    1999-07-01

    Metal hybrides are effective materials for utilizing hydrogen as a clean energy medium. That is, when the metal hydrides absorb or desorb the hydrogen, a large heat output of reaction occurs. So, the metal hydrides can be applied to a heat pump. We have researched on a high efficiency heat pump technology using their metal hydrides. In this report, a double effect type metal hydride heat pump configuration is described in which the waste heat of 160 C is recovered in a factory cite and transported to areas far distant from the industrial district. In the heat recovery unit, a low pressure hydrogen is converted into highly effective high pressure hydrogen by applying the metal hydrides. Other metal hydrides perform the parts of heating by absorbing the hydrogen and cooling by desorbing the hydrogen in the heat supply unit. One unit scale of the system is 3 kW class as the sum of heating and cooling. This system using the hydrogen absorbing alloy also has good energy storage characteristics and ambient hydrogen pressure self-safety control ability. Furthermore, this heating and cooling heat supply system is not harmful to the natural environment because it is a chlorofluorocarbon-free, and low noise type system. We have developed in the following element technologies to attain the above purposes, that is development of hydrogen absorbing alloys with high heat outputs and technologies to construct the heat pump system. This study is proceeded at present as one of the programs in New Sunshine Project, which aims for development of ingenious energy utilization technology to achieve reduction of primary energy consumption with keeping cultural and wealthy life and preventing deterioration of global environment. (orig.)

  2. Numerical study of metal foam heat sinks under uniform impinging flow

    Andreozzi, A; Bianco, N; Iasiello, M; Naso, V

    2017-01-01

    The ever-increasing demand for performance improvement and miniaturization of electronics has led to a significant generation of waste heat that must be dissipated to ensure a reliable device operation. The miniaturization of the components complicates this task. In fact, reducing the heat transfer area, at the same required heat rate, it is necessary to increase the heat flux, so that the materials operate in a temperature range suitable to its proper functioning. Traditional heat sinks are no longer capable of dissipating the generated heat and innovative approaches are needed to address the emerging thermal management challenges. Recently, heat transfer in open-cell metal foams under an impinging jet has received attention due to the considerable heat transfer potential of combining two cooling technologies: impinging jet and porous medium. This paper presents a numerical study on Finned Metal Foam (FMF) and Metal Foam (MF) heat sinks under impinging air jet cooling. The analysis is carried out by means of the commercial software COMSOL Multiphysics®. The purpose is to analyze the thermal performance of the metal foam heat sink, finned or not, varying its geometric parameters. Results are presented in terms of predicted dissipated heat rate, convective heat transfer coefficient and pressure losses. (paper)

  3. Calculation of thermal stress condition in long metal cylinder under heating by continuous laser radiation

    Uglov, A.A.; Uglov, S.A.; Kulik, A.N.

    1997-01-01

    The method of determination of temperature field and unduced thermal stresses in long metallic cylinder under its heating by cw-laser normally distributed heat flux is offered. The graphically presented results of calculation show the stress maximum is placed behind of center of laser heat sport along its movement line on the cylinder surface

  4. Semi-empirical model for heat transfer coefficient in liquid metal turbulent flow

    Fernandez y Fernandez, E.; Carajilescov, P.

    1982-01-01

    The heat transfer by forced convection in a metal liquid turbulent flow for circular ducts is analyzed. An analogy between the momentum and heat in the wall surface, is determined, aiming to determine an expression for heat transfer coefficient in function of the friction coefficient. (E.G.) [pt

  5. Direct Measurements of Half-Cycle Reaction Heats during Atomic Layer Deposition by Calorimetry

    Lownsbury, James M. [Department; Gladden, James A. [Department; Campbell, Charles T. [Department; Department; Kim, In Soo [Materials; Martinson, Alex B. F. [Materials

    2017-10-05

    We introduce a new high-temperature adsorption calorimeter that approaches the ideal limit of a heat detector whereby the signal at any time is proportional to the heat power being delivered to the sample and prove its sensitivity for measuring pulse-to-pulse heats of half-reactions during atomic layer deposition (ALD) at 400 K. The heat dynamics of amorphous Al2O3 growth via sequential self-limiting surface reaction of trimethylaluminum (TMA) and H2O is clearly resolved. Calibration enables quantitation of the exothermic TMA and H2O half-reactions with high precision, -343 kJ/mol TMA and -251 kJ/mol H2O, respectively. A time resolution better than 1 ms is demonstrated, allowing for the deconvolution of at least two distinct surface reactions during TMA microdosing. It is further demonstrated that this method can provide the heat of reaction versus extent of reaction during each precursors half-reaction, thus providing even richer mechanistic information on the surface processes involved. The broad applicability of this novel calorimeter is demonstrated through excellent signal-to-noise ratios of less exothermic ALD half-reactions to produce TiO2 and MnO.

  6. Numerical Investigation of Turbulent Natural Convection Heat Transfer in an Internally-Heated Melt Pool and Metallic Layer

    Nourgaliev, R.R.; Dinh, A.T.; Dinh, T.N.; Sehgal, B.R.

    1999-01-01

    This paper presents results of numerical investigation of turbulent natural convection in an internally-heated oxidic pool, and in a metallic layer heated from below and cooled from top and sidewalls. Emphasis is placed upon applicability of the existing heat transfer correlations (obtained from simulant-material experiments) in assessments of a prototypic severe reactor accident. The objectives of this study are (i) to improve the current understanding of the physics of unstably stratified flows, and (ii) to reduce uncertainties associated with modeling and assessment of natural convection heat transfer in the above configuration. Prediction capabilities of different turbulence modeling approaches are first examined and discussed, based on extensive results of numerical investigations performed by present authors. Findings from numerical modeling of turbulent natural convection flow and heat transfer in melt pools and metallic layers are then described. (authors)

  7. Analysis of atomic mobility in a Cu38Zr46Ag8Al8 bulk metallic glass

    Qiao, J.C.; Pelletier, J.M.

    2013-01-01

    Highlights: ► Atomic mobility in Cu 38 Zr 46 Ag 8 Al 8 bulk metallic glass have been investigated by DMA. ► Loss factor is directly connected to the energy lost during application of the stress. ► Structural relaxation and crystallization induces a decrease of the atomic mobility. ► The concentration of quasi-point defects links to atomic mobility in metallic glasses. - Abstract: Atomic mobility in as-cast and annealed Cu 38 Zr 46 Ag 8 Al 8 bulk metallic glass samples is analyzed by performing dynamic mechanical analysis. The loss factor is directly connected to the energy lost during application of the stress. Structural relaxation process and crystallization lead to a decrease of the atomic mobility in the bulk metallic glass. A physical model, based on the concept of quasi point defects is introduced, to describe the atomic mobility. Movements in amorphous materials are correlated. The correlation factor χ reflects the atomic mobility in bulk metallic glasses: structural relaxation and crystallization lead to a decrease of χ, implying the reduction of atomic mobility. The evolution of elastic, visco-elastic and viscoplastic components after structural relaxation and partial crystallization state during the mechanical response has been obtained. Compared with as-cast state, structural relaxation induced an increase of elastic component and a decrease of visco-elastic component in the metallic glass.

  8. Copper Benzenetricarboxylate Metal-Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition.

    Lemaire, Paul C; Zhao, Junjie; Williams, Philip S; Walls, Howard J; Shepherd, Sarah D; Losego, Mark D; Peterson, Gregory W; Parsons, Gregory N

    2016-04-13

    Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

  9. Isolated Pt Atoms Stabilized by Amorphous Tungstenic Acid for Metal-Support Synergistic Oxygen Activation.

    Zhang, Qian; Qin, Xixi; Duanmu, Fanpeng; Ji, Huiming; Shen, Zhurui; Han, Xiaopeng; Hu, Wenbin

    2018-06-05

    Oxygen activation plays a crucial role in many important chemical reactions such as organics oxidation and oxygen reduction. For developing highly active materials for oxygen activation, herein, we report an atomically dispersed Pt on WO3 nanoplates stabilized by in-situ formed amorphous H2WO4 out-layer and the mechanism for activating molecular oxygen. Experimental and theoretical studies demonstrate that the isolated Pt atoms coordinated with oxygen atoms from [WO6] and water of H2WO4, consequently leading to optimized surface electronic configuration and strong metal support interaction (SMSI). In exemplified reactions of butanone oxidation sensing and oxygen reduction, the atomic Pt/WO3 hybrid exhibits superior activity than those of Pt nanoclusters/WO3 and bare WO3 as well as enhanced long-term durability. This work will provide insight on the origin of activity and stability for atomically dispersed materials, thus promoting the development of highly efficient and durable single atom-based catalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Direct observation of atomic-level nucleation and growth processes from an ultrathin metallic glass films

    Huang, K. Q.; Cao, C. R.; Sun, Y. T.; Li, J.; Bai, H. Y.; Zheng, D. N., E-mail: l.gu@iphy.ac.cn, E-mail: dzheng@iphy.ac.cn, E-mail: whw@iphy.ac.cn; Wang, W. H., E-mail: l.gu@iphy.ac.cn, E-mail: dzheng@iphy.ac.cn, E-mail: whw@iphy.ac.cn [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Gu, L., E-mail: l.gu@iphy.ac.cn, E-mail: dzheng@iphy.ac.cn, E-mail: whw@iphy.ac.cn [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100190 (China)

    2016-01-07

    Till date, there have been no direct atomic-level experimental observations of the earliest stages of the nucleation and growth processes of nanocrystals formed by thermally induced crystallization in ultrathin metallic glasses (MGs). Here, we present a study of the crystallization process in atomically thin and highly stable MG films using double spherical aberration-corrected scanning transmission electron microscopy (Cs-TEM). Taking advantage of the stability of MG films with a slow crystallization process and the atomic-level high resolution of Cs-TEM, we observe the formation of the nucleus precursor of nanocrystals formed by atom aggregation followed by concomitant coalescence and stepwise evolution of the shape of the nanocrystals with a monodispersed and separated bimodal size distribution. Molecular dynamics simulation of the atomic motion in the glass film on a rigid amorphous substrate confirms the stepwise evolution processes of atom aggregation, cluster formation, cluster movement on the substrate, and cluster coalescence into larger crystalline particles. Our results might provide a better fundamental understanding of the nucleation and growth processes of nanocrystals in thin MG films.

  11. Electronic relaxation dynamics of a metal atom deposited on argon cluster

    Awali, Slim

    2014-01-01

    This thesis is a study on the interaction between electronically excited atomic states and a non-reactive environment. We have theoretically and experimentally studied situations where a metal atom (Ba or K) is placed in a finite size environment (argon cluster). The presence of the medium affects the electronic levels of the atom. On the other side, the excitation of the atom induces a relaxation dynamics of the electronic energy through the deformation of the cluster. The experimental part of this work focuses on two aspects: the spectroscopy and the dynamics. In both cases a first laser electronically excites the metal atom and the second ionizes the excited system. The observable is the photoelectron spectrum recorded after photoionization and possibly information on the photoion which are also produced. This pump/probe technique, with also two lasers, provide the ultrafast dynamic when the lasers pulses used are of ultrashort (60 fs). The use of nanosecond lasers leads to resonance spectroscopic measurement, unresolved temporally, which give information on the position of the energy levels of the studied system. From a theoretical point-of-view, the excited states of M-Ar n were calculated at the ab initio level, using large core pseudo-potential to limit the active electrons of the metal to valence electrons. The study of alkali metals (potassium) is especially well adapted to this method since only one electron is active. The ab-initio calculation and a Monte-Carlo simulation where coupled to optimize the geometry of the KAr n (n = 1-10) cluster when K is in the ground state of the neutral and the ion, or excited in the 4p or 5s state. Calculations were also conducted in collaboration with B. Gervais (CIMAP, Caen) on KAr n clusters having several tens of argon atoms. Absorption spectra were also calculated. From an experimental point-of-view, we were able to characterize the excited states of potassium and barium perturbed by the clusters. In both cases a

  12. Experimental study of conjugate heat transfer from liquid metal layer cooled by overlying freon

    Cho, J.S.; Suh, K.Y.; Chung, C.H.; Park, R.J.; Kim, S.B.

    2001-01-01

    Steady-state and transient experiments were performed for the heat transfer from the liquid metal pool with overlying Freon (R113) coolant in the process of boiling. The simulant molten pool material is tin (Sn) with the melting temperature of 232 Celsius degrees. The metal pool is heated from the bottom surface and the coolant is injected onto the molten metal pool. Tests were conducted under the condition of the bottom surface heating in the test section and the forced convection of the R113 coolant being injected onto the molten metal pool. The bottom heating condition was varied from 8 kW to 14 kW. The temperature distributions of the metal layer and coolant were obtained in the steady-state experiment. The boiling mechanism of the R113 coolant was changed from the nucleate boiling to film boiling in the transient experiment. The critical heat flux (CHF) phenomenon was observed during the transition from the nucleate boiling to the film boiling. Also, the Nusselt (Nu) number and the Rayleigh (Ra) number in the molten metal pool region were obtained as functions of time. Analysis was done for the relationship between the heat flux and the temperature difference between the metal layer surface and the boiling coolant. In this experiment, the heat transfer is achieved with accompanying solidification in the molten metal pool by the boiling R113 coolant there above. The present test results of the natural convection heat transfer on the molten metal pool are higher than those of the liquid metal natural convection heat transfer without coolant boiling. It can be interpreted that the heat transfer rate is enhanced by the overlying boiling coolant having the high heat removal rate. Analysis of the relationship between the heat flux and the difference between the metal layer surface temperature and the coolant bulk boiling temperature revealed that the CHF occurs when the temperature difference reaches a neighborhood of 50 Celsius degrees. Also, if the temperature

  13. Heat-processing method and facility for helium-containing metal material

    Kato, Takahiko; Kodama, Hideyo; Matsumoto, Toshimi; Aono, Yasuhisa; Nagata, Tetsuya; Hattori, Shigeo; Kaneda, Jun-ya; Ono, Shigeki.

    1996-01-01

    Electric current is supplied to an objective portion of a He-containing metal material to be applied with heat processing without causing melting, to decrease the He content of the portion. Subsequently, the defect portion of the tissues of the He-containing metal is modified by heating the portion with melting. Since electric current can be supplied to the metal material in a state where the metal material is heated and the temperature thereof is elevated, an effect of further reducing the He content can be obtained. Further, if the current supply and/or the heating relative to the metal material is performed in a vacuum or inert gas atmosphere, an effect of reducing the degradation of the surface of the objective portion to be supplied with electric current can be obtained. (T.M.)

  14. Dimensional crossover and cold-atom realization of gapless and semi-metallic Mott insulating phases

    Orth, Peter P.; Scheurer, Mathias; Rachel, Stephan

    2014-03-01

    We propose a realistic cold-atom setup which allows for a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator phase by simply tuning the hopping between the layers. We further employ cluster slave-rotor mean-field theory to study the effect of additional Hubbard onsite interactions that give rise to various spin liquid-like phases such as gapless and semi-metallic Mott insulating states.

  15. Properties of the triplet metastable states of the alkaline-earth-metal atoms

    Mitroy, J.; Bromley, M.W.J.

    2004-01-01

    The static and dynamic properties of the alkaline-earth-metal atoms in their metastable state are computed in a configuration interaction approach with a semiempirical model potential for the core. Among the properties determined are the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths, and the dispersion coefficients of the van der Waals interaction. A simple method for including the effect of the core on the dispersion parameters is described

  16. Automated installation for atomic emission determination of gold, silver and platinum group metals

    Zayakina, S.B.; Anoshin, G.N.; Gerasimov, P.A.; Smirnov, A.V.

    1999-01-01

    An automated installation for the direct atomic emission determination of silver, gold and platinum-group metals (Ru) in geological and geochemical materials with software for automated data acquisition and handling is designed and developed. The installation consists of a DFS-458 diffraction spectrograph, a MAES-10 multichannel analyzer of emission spectra, and a dual-jet plasmatron. A library of spectral lines of almost all elements excited in the dual-jet plasmatron is complied [ru

  17. Nanometer-Scale Dissection of Chromosomes by Atomic Force Microscopy Combined with Heat-Denaturing Treatment

    Tsukamoto, Kazumi; Kuwazaki, Seigo; Yamamoto, Kimiko; Shichiri, Motoharu; Yoshino, Tomoyuki; Ohtani, Toshio; Sugiyama, Shigeru

    2006-03-01

    We have developed a method for dissecting chromosome fragments with a size of a few hundred nanometers by atomic force microscopy (AFM). By using this method, we demonstrated reproducible dissections of silkworm chromosomes in the pachytene phase. The dissected fragments were successfully recovered on the cantilever tips, as confirmed by fluorescent microscopy using fluorescent stained chromosomes. To recover dissected chromosome fragments from a larger chromosome, such as the human metaphase chromosome of a somatic cell, heat denaturation was found to be effective. Further improvements in this method may lead to a novel tool for isolating valuable genes and/or investigating local genome structures in the near future.

  18. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    Cho, Jae Seon; Suh, Kune Yull; Chung, Chang Hyun; Park, Rae Joon; Kim, Sang Baik

    1997-01-01

    This paper presents results of experimental studies on the heat transfer and solidifcation of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. As a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 .deg. C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleight number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer

  19. Computational analysis of the atomic size effect in bulk metallic glasses and their liquid precursors

    Kokotin, V.; Hermann, H.

    2008-01-01

    The atomic size effect and its consequences for the ability of multicomponent liquid alloys to form bulk metallic glasses are analyzed in terms of the generalized Bernal's model for liquids, following the hypothesis that maximum density in the liquid state improves the glass-forming ability. The maximum density that can be achieved in the liquid state is studied in the 2(N-1) dimensional parameter space of N-component systems. Computer simulations reveal that the size ratio of largest to smallest atoms are most relevant for achieving the maximum packing for N = 3-5, whereas the number of components plays a minor role. At small size ratio, the maximum packing density can be achieved by different atomic size distributions, whereas for medium size ratios the maximum density is always correlated to a concave size distribution. The relationship of the results to Miracle's efficient cluster packing model is also discussed

  20. Metal-Insulator Transition Revisited for Cold Atoms in Non-Abelian Gauge Potentials

    Satija, Indubala I.; Dakin, Daniel C.; Clark, Charles W.

    2006-01-01

    We discuss the possibility of realizing metal-insulator transitions with ultracold atoms in two-dimensional optical lattices in the presence of artificial gauge potentials. For Abelian gauges, such transitions occur when the magnetic flux penetrating the lattice plaquette is an irrational multiple of the magnetic flux quantum. Here we present the first study of these transitions for non-Abelian U(2) gauge fields. In contrast to the Abelian case, the spectrum and localization transition in the non-Abelian case is strongly influenced by atomic momenta. In addition to determining the localization boundary, the momentum fragments the spectrum. Other key characteristics of the non-Abelian case include the absence of localization for certain states and satellite fringes around the Bragg peaks in the momentum distribution and an interesting possibility that the transition can be tuned by the atomic momenta

  1. Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges.

    Duan, Xidong; Wang, Chen; Pan, Anlian; Yu, Ruqin; Duan, Xiangfeng

    2015-12-21

    The discovery of graphene has ignited intensive interest in two-dimensional layered materials (2DLMs). These 2DLMs represent a new class of nearly ideal 2D material systems for exploring fundamental chemistry and physics at the limit of single-atom thickness, and have the potential to open up totally new technological opportunities beyond the reach of existing materials. In general, there are a wide range of 2DLMs in which the atomic layers are weakly bonded together by van der Waals interactions and can be isolated into single or few-layer nanosheets. The van der Waals interactions between neighboring atomic layers could allow much more flexible integration of distinct materials to nearly arbitrarily combine and control different properties at the atomic scale. The transition metal dichalcogenides (TMDs) (e.g., MoS2, WSe2) represent a large family of layered materials, many of which exhibit tunable band gaps that can undergo a transition from an indirect band gap in bulk crystals to a direct band gap in monolayer nanosheets. These 2D-TMDs have thus emerged as an exciting class of atomically thin semiconductors for a new generation of electronic and optoelectronic devices. Recent studies have shown exciting potential of these atomically thin semiconductors, including the demonstration of atomically thin transistors, a new design of vertical transistors, as well as new types of optoelectronic devices such as tunable photovoltaic devices and light emitting devices. In parallel, there have also been considerable efforts in developing diverse synthetic approaches for the rational growth of various forms of 2D materials with precisely controlled chemical composition, physical dimension, and heterostructure interface. Here we review the recent efforts, progress, opportunities and challenges in exploring the layered TMDs as a new class of atomically thin semiconductors.

  2. Steam generation device with heat exchange between a liquid metal coolant and the feedwater

    Malaval, C.

    1983-01-01

    The invention is particularly applicable to a liquid metal fast breeder reactor plant, the liquid metal being sodium. The steam generation device is described in detail, it allows to get an upper liquid metal level without turbulence and an easier passage for the shock wave towards the steam generator up to the liquid metal level without being laterally reflected back to the intermediate heat exchangers [fr

  3. Anelastic relaxation of interstitial foreign atoms and their complexes with intrinsic defects in B.C.C. metals

    Weller, M.

    1985-01-01

    In body-centred cubic metals, heavy interstitial foreign atoms (IFA) O, N and C give rise to relaxations of Snoek type. For dilute alloys, relaxation parameters are summarized. In concentrated alloys (group Va metals containing O or N) Snoek relaxations are influenced by the interaction of IFA. The recent controversy is discussed as to whether this interaction is based on clustering or anticlustering. In irradiated metals complexes of IFA with intrinsic atomic defects (vacancies or self interstitial atoms) also give rise to relaxations

  4. Drop impacts onto cold and heated rigid surfaces: Morphological comparisons, disintegration limits and secondary atomization

    Moita, A.S.; Moreira, A.L.N.

    2007-01-01

    This paper addresses an experimental study aimed at characterizing the mechanisms of disintegration which occur when individual water and fuel droplets impact onto heated surfaces. The experiments consider the use of a simplified flow configuration and make use of high-speed visualization together with image processing techniques to characterize the morphology of the impact and to quantify the outcome of secondary atomization in terms of droplet size and number. The results evidence that surface topography, wettability and liquid properties combine in a complex way to alter the wetting behaviour of droplets at impact at different surface temperatures. The relative importance of the dynamic vapor pressure associated with the rate of vaporization and surface roughness increases with surface temperature and becomes dominant at the film boiling regime. The analysis is aimed at giving a phenomenological description of droplet disintegration within the various heat transfer regimes

  5. Determination of the neutral oxygen atom density in a plasma reactor loaded with metal samples

    Mozetic, Miran; Cvelbar, Uros

    2009-08-01

    The density of neutral oxygen atoms was determined during processing of metal samples in a plasma reactor. The reactor was a Pyrex tube with an inner diameter of 11 cm and a length of 30 cm. Plasma was created by an inductively coupled radiofrequency generator operating at a frequency of 27.12 MHz and output power up to 500 W. The O density was measured at the edge of the glass tube with a copper fiber optics catalytic probe. The O atom density in the empty tube depended on pressure and was between 4 and 7 × 1021 m-3. The maximum O density was at a pressure of about 150 Pa, while the dissociation fraction of O2 molecules was maximal at the lowest pressure and decreased with increasing pressure. At about 300 Pa it dropped below 10%. The measurements were repeated in the chamber loaded with different metallic samples. In these cases, the density of oxygen atoms was lower than that in the empty chamber. The results were explained by a drain of O atoms caused by heterogeneous recombination on the samples.

  6. Atomic contributions to the valence band photoelectron spectra of metal-free, iron and manganese phthalocyanines

    Bidermane, I., E-mail: ieva.bidermane@physics.uu.se [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Institut des Nanosciences de Paris, UPMC Univ. Paris 06, CNRS UMR 7588, F-75005 Paris (France); Brumboiu, I.E. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Totani, R. [Department of Physical and Chemical Sciences, University of L’Aquila, Via Vetoio, Coppito, I-67010 L’Aquila (Italy); Grazioli, C. [CNR-IOM, Laboratorio TASC, ss. 14 km. 163.5, Basovizza, 34149 Trieste (Italy); Departement of Chemical and Pharmaceutical Sciences, University of Trieste (Italy); Shariati-Nilsson, M.N.; Herper, H.C.; Eriksson, O.; Sanyal, B. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden); Ressel, B. [University of Nova Gorica, Vipavska Cesta 11c, 5270 Ajdovščina (Slovenia); Simone, M. de [CNR-IOM, Laboratorio TASC, ss. 14 km. 163.5, Basovizza, 34149 Trieste (Italy); Lozzi, L. [Department of Physical and Chemical Sciences, University of L’Aquila, Via Vetoio, Coppito, I-67010 L’Aquila (Italy); Brena, B.; Puglia, C. [Department of Physics and Astronomy, Uppsala University, Box-516, 75120 Uppsala (Sweden)

    2015-11-15

    Highlights: • In detail comparison between the valence band structure of H{sub 2}Pc, FePc and MnPc. • Comparison between the gas phase samples and thin evaporated films on Au (1 1 1). • Detailed analysis of the atomic orbital contributions to the valence band features. • DFT/HSE06 study of the valence band electronic structure of H{sub 2}Pc, FePc and MnPc. - Abstract: The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H{sub 2}Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H{sub 2}Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

  7. Dispersion coefficients for H and He interactions with alkali-metal and alkaline-earth-metal atoms

    Mitroy, J.; Bromley, M.W.J.

    2003-01-01

    The van der Waals coefficients C 6 , C 8 , and C 10 for H and He interactions with the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are determined from oscillator strength sum rules. The oscillator strengths were computed using a combination of ab initio and semiempirical methods. The dispersion parameters generally agree with close to exact variational calculations for Li-H and Li-He at the 0.1% level of accuracy. For larger systems, there is agreement with relativistic many-body perturbation theory estimates of C 6 at the 1% level. These validations for selected systems attest to the reliability of the present dispersion parameters. About half the present parameters lie within the recommended bounds of the Standard and Certain compilation [J. Chem. Phys. 83, 3002 (1985)

  8. Atom

    Auffray, J.P.

    1997-01-01

    The atom through centuries, has been imagined, described, explored, then accelerated, combined...But what happens truly inside the atom? And what are mechanisms who allow its stability? Physicist and historian of sciences, Jean-Paul Auffray explains that these questions are to the heart of the modern physics and it brings them a new lighting. (N.C.)

  9. Some metals determination in beers by atomic emission spectrometry of induced argon plasma

    Matsushige, I.

    1990-01-01

    It was made the identification and determination of metals in brazilian bottled and canned beer, using atomic emission spectrometry with d.c. are and argon coupled plasma excitation sources. The elements Co, Cr, Cu, Fe, Pb and Zn were determined in beer samples, after treatment with HNO sub(3) conc. /H sub(2) O sub(2) (30%). In the determination of Co, Cr, Cu, Pb and Zn and alternative method using HNO sub(3) conc. /O sub(3) was proved be useful. The results obtained for Co, Cr, Cu, Fe, Pb and Zn were below the limits established by brazilian legislation, showing the good quality of the beer concerning the metals. The results of this work were requested by the previous Ministerio do Meio Ambiente e Urbanismo in order to contribute to review the brazilian legislation in foods and beverages about metals contents. (author)

  10. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Deng, Fengjie, E-mail: fengjiedeng@aliyun.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Zhang, Xiaoyong, E-mail: xiaoyongzhang1980@gmail.com [Department of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031 (China); Wei, Yen, E-mail: weiyen@tsinghua.edu.cn [Department of Chemistry and the Tsinghua Center for Frontier Polymer Research, Tsinghua University, Beijing, 100084 (China)

    2016-12-30

    Highlights: • Surface modification of ND with water soluble and biocompatible polymers. • Functionalized ND through metal free surface initiated ATRP. • The metal free surface initiated ATRP is rather simple and effective. • The ND-poly(MPC) showed high dispersibility and desirable biocompatibility. - Abstract: Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by {sup 1}H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  11. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2016-01-01

    Highlights: • Surface modification of ND with water soluble and biocompatible polymers. • Functionalized ND through metal free surface initiated ATRP. • The metal free surface initiated ATRP is rather simple and effective. • The ND-poly(MPC) showed high dispersibility and desirable biocompatibility. - Abstract: Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by 1 H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  12. One dimensional metallic edges in atomically thin WSe2 induced by air exposure

    Addou, Rafik; Smyth, Christopher M.; Noh, Ji-Young; Lin, Yu-Chuan; Pan, Yi; Eichfeld, Sarah M.; Fölsch, Stefan; Robinson, Joshua A.; Cho, Kyeongjae; Feenstra, Randall M.; Wallace, Robert M.

    2018-04-01

    Transition metal dichalcogenides are a unique class of layered two-dimensional (2D) crystals with extensive promising applications. Tuning the electronic properties of low-dimensional materials is vital for engineering new functionalities. Surface oxidation is of particular interest because it is a relatively simple method of functionalization. By means of scanning probe microscopy and x-ray photoelectron spectroscopy, we report the observation of metallic edges in atomically thin WSe2 monolayers grown by chemical vapor deposition on epitaxial graphene. Scanning tunneling microscopy shows structural details of WSe2 edges and scanning tunneling spectroscopy reveals the metallic nature of the oxidized edges. Photoemission demonstrates that the formation of metallic sub-stoichiometric tungsten oxide (WO2.7) is responsible for the high conductivity measured along the edges. Ab initio calculations validate the susceptibility of WSe2 nanoribbon edges to oxidation. The zigzag terminated edge exhibits metallic behavior prior the air-exposure and remains metallic after oxidation. Comprehending and exploiting this property opens a new opportunity for application in advanced electronic devices.

  13. The role of atomic hydrogen in regulating the scatter of the mass-metallicity relation

    Brown, Toby; Cortese, Luca; Catinella, Barbara; Kilborn, Virginia

    2018-01-01

    In this paper, we stack neutral atomic hydrogen (H I) spectra for 9720 star-forming galaxies along the mass-metallicity relation. The sample is selected according to stellar mass (109 ≤ M⋆/M⊙ ≤ 1011) and redshift (0.02 ≤ z ≤ 0.05) from the overlap of the Sloan Digital Sky Survey and Arecibo Legacy Fast ALFA survey. We confirm and quantify the strong anticorrelation between H I mass and gas-phase metallicity at fixed stellar mass. Furthermore, we show for the first time that the relationship between gas content and metallicity is consistent between different metallicity estimators, contrary to the weaker trends found with star formation which are known to depend on the observational techniques used to derive oxygen abundances and star formation rates. When interpreted in the context of theoretical work, this result supports a scenario where galaxies exist in an evolving equilibrium between gas, metallicity and star formation. The fact that deviations from this equilibrium are most strongly correlated with gas mass suggests that the scatter in the mass-metallicity relation is primarily driven by fluctuations in gas accretion.

  14. Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

    Zhang Min; Shi Jun-Jie

    2014-01-01

    The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μ B among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  15. Atomic theory of viscoelastic response and memory effects in metallic glasses

    Cui, Bingyu; Yang, Jie; Qiao, Jichao; Jiang, Minqiang; Dai, Lanhong; Wang, Yun-Jiang; Zaccone, Alessio

    2017-09-01

    An atomic-scale theory of the viscoelastic response of metallic glasses is derived from first principles, using a Zwanzig-Caldeira-Leggett system-bath Hamiltonian as a starting point within the framework of nonaffine linear response to mechanical deformation. This approach provides a generalized Langevin equation (GLE) as the average equation of motion for an atom or ion in the material, from which non-Markovian nonaffine viscoelastic moduli are extracted. These can be evaluated using the vibrational density of states (DOS) as input, where the boson peak plays a prominent role in the mechanics. To compare with experimental data for binary ZrCu alloys, a numerical DOS was obtained from simulations of this system, which also take electronic degrees of freedom into account via the embedded-atom method for the interatomic potential. It is shown that the viscoelastic α -relaxation, including the α -wing asymmetry in the loss modulus, can be very well described by the theory if the memory kernel (the non-Markovian friction) in the GLE is taken to be a stretched-exponential decaying function of time. This finding directly implies strong memory effects in the atomic-scale dynamics and suggests that the α -relaxation time is related to the characteristic time scale over which atoms retain memory of their previous collision history. This memory time grows dramatically below the glass transition.

  16. Joining of parts via magnetic heating of metal aluminum powders

    Baker, Ian

    2013-05-21

    A method of joining at least two parts includes steps of dispersing a joining material comprising a multi-phase magnetic metal-aluminum powder at an interface between the at least two parts to be joined and applying an alternating magnetic field (AMF). The AMF has a magnetic field strength and frequency suitable for inducing magnetic hysteresis losses in the metal-aluminum powder and is applied for a period that raises temperature of the metal-aluminum powder to an exothermic transformation temperature. At the exothermic transformation temperature, the metal-aluminum powder melts and resolidifies as a metal aluminide solid having a non-magnetic configuration.

  17. Natural convection and boiling heat transfer of a liquid metal in a magnetic field

    Seki, Masahiro; Kawamura, Hiroshi

    1983-02-01

    A liquid metal is often assumed as a coolant and a breeding material of a Tokamak fusion reactor. However, many problems on the thermo-hydraulics of a liquid metal in a magnetic field are still remained to be studied. In the present report, natural convection and boiling of a liquid metal in a strong magnetic field are studied to examine a fundamental feasibility of a fusion reactor cooled by a liquid metal. In the experimental study of the natural convection, the circulation of a liquid metal was found to be surpressed even by a magnetic field parallel to the gravity. A numerical study has confirmed the conclusion drawn by the experiment. In the study of boiling heat transfer, stable boiling of a liquid metal has been found also in a strong magnetic field. The burnout heat flux hardly affected by the magnetic field. These indicate a fundamental feasibility of the liquid-metal cooling for a Tokamak fusion reactor. (author)

  18. Stripping scattering of fast atoms on surfaces of metal-oxide crystals and ultrathin films; Streifende Streuung schneller Atome an Oberflaechen von Metalloxid-Kristallen und ultraduennen Filmen

    Blauth, David

    2010-03-11

    In the framework of the present dissertation the interactions of fast atoms with surfaces of bulk oxides, metals and thin films on metals were studied. The experiments were performed in the regime of grazing incidence of atoms with energies of some keV. The advantage of this scattering geometry is the high surface sensibility and thus the possibility to determine the crystallographic and electronic characteristics of the topmost surface layer. In addition to these experiments, the energy loss and the electron emission induced by scattered projectiles was investigated. The energy for electron emission and exciton excitation on Alumina/NiAl(110) and SiO{sub 2}/Mo(112) are determined. By detection of the number of projectile induced emitted electrons as function of azimuthal angle for the rotation of the target surface, the geometrical structure of atoms forming the topmost layer of different adsorbate films on metal surfaces where determined via ion beam triangulation. (orig.)

  19. A pump/intermediate heat exchanger assembly for a liquid metal reactor

    Nathenson, R.D.; Alexion, C.C.; Sumpman, W.C.

    1987-01-01

    A heat exchanger and electromagnetic pump assembly is disclosed comprising a heat exchanger housing defining an annularly shaped cavity and supporting therein a plurality of heat transfer tubes. An electromagnetic pump disposed beneath the heat exchanger comprises a circular array of flow couplers. Each flow coupler comprises a pump duct receiving primary liquid metal and a generator duct receiving a pumped intermediate liquid metal. A first plenum chamber is in communication with the generator ducts of all the flow couplers and receives intermediate liquid metal from inlet duct. The generator ducts exit their flows of intermediate liquid metal to a second plenum chamber in communication with the heat exchanger annularly shaped cavity to permit the flow of the intermediate liquid metal therethrough. A third plenum chamber receives collectively the flows of the primary liquid metal from the tubes and directs the primary liquid metal to the pump ducts of the flow couplers. The annular magnetic field of the electromagnetic pump is produced by a circular array of electromagnets having hollow windings cooled by a flow of intermediate liquid metal via tubes and manifolds. The leads to the electromagnets pass through an annular space around the inlet duct. (author)

  20. The Laser ablation of a metal foam: The role of electron-phonon coupling and electronic heat diffusivity

    Rosandi, Yudi; Grossi, Joás; Bringa, Eduardo M.; Urbassek, Herbert M.

    2018-01-01

    The incidence of energetic laser pulses on a metal foam may lead to foam ablation. The processes occurring in the foam may differ strongly from those in a bulk metal: The absorption of laser light, energy transfer to the atomic system, heat conduction, and finally, the atomistic processes—such as melting or evaporation—may be different. In addition, novel phenomena take place, such as a reorganization of the ligament network in the foam. We study all these processes in an Au foam of average porosity 79% and an average ligament diameter of 2.5 nm, using molecular dynamics simulation. The coupling of the electronic system to the atomic system is modeled by using the electron-phonon coupling, g, and the electronic heat diffusivity, κe, as model parameters, since their actual values for foams are unknown. We show that the foam coarsens under laser irradiation. While κe governs the homogeneity of the processes, g mainly determines their time scale. The final porosity reached is independent of the value of g.

  1. Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals.

    Tang, Jau

    2008-04-28

    In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.

  2. A Dilute-Limit Heat of Solution of 3d Transition Metals in Iron Studied with 57Fe Moessbauer Spectroscopy

    Chojcan, Jan

    2004-01-01

    The room-temperature 57 Fe Moessbauer spectra for binary iron-based solid solutions Fe 1-x D x with D=V, Cr, Mn and Co, were analysed in terms of binding energy E b between two D atoms in the Fe-D system. The extrapolated values of E b for x=0 were used for computation of the dilute-limit heat of solution of D metals in iron. The results were compared with those derived from calorimetric data concerning the heat of formation of the systems mentioned as well as with those resulting from the Miedema's model of alloys. The comparison shows that our Moessbauer spectroscopy findings are in a qualitative agreement with the available calorimetric data and they are at variance with corresponding Miedema's values for Fe-Mn and Fe-Co systems.

  3. Alternatives for metal hydride storage bed heating and cooling

    Fisher, I.A.; Ramirez, F.B.; Koonce, J.E.; Ward, D.E.; Heung, L.K.; Weimer, M.; Berkebile, W.; French, S.T.

    1991-01-01

    The reaction of hydrogen isotopes with the storage bed hydride material is exothermic during absorption and endothermic during desorption. Therefore, storage bed operation requires a cooling system to remove heat during absorption, and a heating system to add the heat needed for desorption. Three storage bed designs and their associated methods of heating and cooling and accountability are presented within. The first design is the current RTF (Replacement Tritium Facility) nitrogen heating and cooling system. The second design uses natural convection cooling with ambient glove box nitrogen and electrical resistance for heating. This design is referred to as the Naturally Cooled/Electrically Heated (NCEH) design. The third design uses forced convection cooling with ambient glove box nitrogen and electrical resistance for heating. The design is referred to as the Forced Convection Cooled/Electrically Heated (FCCEH) design. In this report the operation, storage bed design, and equipment required for heating, cooling, and accountability of each design are described. The advantages and disadvantages of each design are listed and discussed. Based on the information presented within, it is recommended that the NCEH design be selected for further development

  4. A model for the latent heat of melting in free standing metal nanoparticles

    Shin, Jeong-Heon; Deinert, Mark R.

    2014-01-01

    Nanoparticles of many metals are known to exhibit scale dependent latent heats of melting. Analytical models for this phenomenon have so far failed to completely capture the observed phenomena. Here we present a thermodynamic analysis for the melting of metal nanoparticles in terms of their internal energy and a scale dependent surface tension proposed by Tolman. The resulting model predicts the scale dependence of the latent heat of melting and is confirmed using published data for tin and aluminum

  5. Effects of vacuum heat treatment on the photoelectric work function and surface morphology of multilayered silver–metal electrical contacts

    Akbi, Mohamed; Bouchou, Aïssa; Zouache, Noureddine

    2014-01-01

    Contact materials used for electrical breakers are often made with silver alloys. Mechanical and thermodynamical properties as well as electron emission of such complicated alloys present a lack of reliable and accurate experimental data. This paper deals mainly with electron work function (EWF) measurements about silver–metal (Ag–Me) electrical contacts (Ag–Ni (60/40) and Ag–W (50/50)), before and after surface heat treatments at 513 K–873 K, under UHV conditions (residual gas pressure of 1.4 × 10 −7 mbar). The electron work function (EWF) of silver alloyed contacts was measured photoelectrically, using both Fowler's method of isothermal curves and linearized Fowler plots. An interesting fact brought to light by this investigation is that after vacuum heat treatments, the diffusion and/or evaporation phenomena, affecting the atomic composition of the alloy surface, somehow confine the EWF of the silver–nickel alloy, Φ(Ag–Ni), determined at room temperature in interval]Φ(Ag), Φ(Ni) [=] 4.26 eV, 4.51 eV[. Surface analysis of two specimens before and after heating showed a significant increase of tungsten atomic proportion on the contact surface for Ag–W contacts after VH treatments. A multilayer model, taking into account the strong intergranular and volume segregation gives a good interpretation of the obtained results.

  6. Joule heating of Fe-B metallic glasses

    Miglierini, M.; Sitek, J.; Lipka, J.

    1993-01-01

    Amorphous Fe 80 B 20 and Fe 83 B 17 ribbons were heated in air and in vacuum, respectively, by a dc electric current passing through the specimen. During the Joule heating, 57 Fe transmission Moessbauer spectra were recorded. Ribbons of the same geometrical dimensions, cut from a natural iron foil, were treated in the same way as a reference. The influence of the current-induced magnetic field in addition to the Joule heating is supposed to cause fluctuations in a short-range order observed. Changes in the hyperfine magnetic fields are compared with those obtained by a conventional heating in a vacuum furnace. (orig.)

  7. Atomic mechanism of shear localization during indentation of a nanostructured metal

    Sansoz, F.; Dupont, V.

    2007-01-01

    Shear localization is an important mode of deformation in nanocrystalline metals. However, it is very difficult to verify the existence of local shear planes in nanocrystalline metals experimentally. Sharp indentation techniques may provide novel opportunities to investigate the effect of shear localization at different length scales, but the relationship between indentation response and atomic-level shear band formation has not been fully addressed. This paper describes an effort to provide direct insight on the mechanism of shear localization during indentation of nanocrystalline metals from atomistic simulations. Molecular statics is performed with the quasi-continuum method to simulate the indentation of single crystal and nanocrystalline Al with a sharp cylindrical probe. In the nanocrystalline regime, two grain sizes are investigated, 5 nm and 10 nm. We find that the indentation of nanocrystalline metals is characterized by serrated plastic flow. This effect seems to be independent of the grain size. Serration in nanocrystalline metals is found to be associated with the formation of shear bands by sliding of aligned interfaces and intragranular slip, which results in deformation twinning

  8. Charge Transport in Metal-Molecule-Metal Junctions Probed by Conducting Atomic Force Microscopy

    Lee, Min Hyung; Song, Hyunwook

    2013-01-01

    We have demonstrated a proof of intrinsic charge transport properties in alkanedithiol molecular junctions using a multiprobe approach combining a variety of transport techniques. The temperature-independent I(V) behavior and the correct exponential decay of conductance with respect to molecular length shows that the dominant charge transport mechanism is off-resonant tunneling. Length-dependent TVS measurements for the saturated alkane-dithiol series indicate that we did indeed probe a molecular system with CAFM. These results can provide stringent criteria to establish a valid molecular transport junction via a probabilistic measurement technique. In this study, we report a study of charge transport in alkanedithiol SAMs formed in metal-molecule-metal junctions using CAFM in combination with a variety of molecular transport techniques including temperature-and length-variable transport measurements and transition voltage spectroscopy. The main goal of this study is to probe the intrinsic transport properties of component molecules using CAFM, but not parasitic or defect-related effects

  9. Metallic and highly conducting two-dimensional atomic arrays of sulfur enabled by molybdenum disulfide nanotemplate

    Zhu, Shuze; Geng, Xiumei; Han, Yang; Benamara, Mourad; Chen, Liao; Li, Jingxiao; Bilgin, Ismail; Zhu, Hongli

    2017-10-01

    Element sulfur in nature is an insulating solid. While it has been tested that one-dimensional sulfur chain is metallic and conducting, the investigation on two-dimensional sulfur remains elusive. We report that molybdenum disulfide layers are able to serve as the nanotemplate to facilitate the formation of two-dimensional sulfur. Density functional theory calculations suggest that confined in-between layers of molybdenum disulfide, sulfur atoms are able to form two-dimensional triangular arrays that are highly metallic. As a result, these arrays contribute to the high conductivity and metallic phase of the hybrid structures of molybdenum disulfide layers and two-dimensional sulfur arrays. The experimentally measured conductivity of such hybrid structures reaches up to 223 S/m. Multiple experimental results, including X-ray photoelectron spectroscopy (XPS), transition electron microscope (TEM), selected area electron diffraction (SAED), agree with the computational insights. Due to the excellent conductivity, the current density is linearly proportional to the scan rate until 30,000 mV s-1 without the attendance of conductive additives. Using such hybrid structures as electrode, the two-electrode supercapacitor cells yield a power density of 106 Wh kg-1 and energy density 47.5 Wh kg-1 in ionic liquid electrolytes. Our findings offer new insights into using two-dimensional materials and their Van der Waals heterostructures as nanotemplates to pattern foreign atoms for unprecedented material properties.

  10. Atomic structure and formation of CuZrAl bulk metallic glasses and composites

    Kaban, I.; Jóvári, P.; Escher, B.; Tran, D.T.; Svensson, G.; Webb, M.A.; Regier, T.Z.; Kokotin, V.; Beuneu, B.; Gemming, T.; Eckert, J.

    2015-01-01

    Graphical abstract: Partial radial distribution functions for Cu 47.5 Zr 47.5 Al 5 metallic glass and relevant crystal structures. - Abstract: Cu 47.5 Zr 47.5 Al 5 metallic glass is studied experimentally by high-energy X-ray diffraction, neutron diffraction with isotopic substitution, electron diffraction and X-ray absorption spectroscopy. The atomic structure of the glass is modeled by reverse Monte-Carlo and molecular dynamics simulations. RMC modeling of seven experimental datasets enabled reliable separation of all partial pair distribution functions for Cu 47.5 Zr 47.5 Al 5 metallic glass. A peculiar structural feature of the ternary alloy is formation of the strong Al–Zr bonds, which are supposed to determine its high viscosity and enhanced bulk glass formation. Analysis of the local atomic order in Cu 47.5 Zr 47.5 Al 5 glass and Cu 10 Zr 7 , CuZr 2 and CuZr B2 crystalline structures elucidates their similarities and differences explaining the phase formation sequence by devitrification of the glass.

  11. Comprehensive uranium thiophosphate chemistry: Framework compounds based on pseudotetrahedrally coordinated central metal atoms

    Neuhausen, Christine; Panthoefer, Martin; Tremel, Wolfgang; Hatscher, Stephan T.; Urland, Werner

    2013-01-01

    The new ternary compounds UP 2 S 6 , UP 2 S 7 , U(P 2 S 6 ) 2 , and U 3 (PS 4 ) 4 were prepared from uranium metal, phosphorus pentasulfide, and sulfur at 700 C. The crystal structures were determined by single-crystal X-ray diffraction methods. UP 2 S 6 (I) crystallizes in the ZrP 2 S 6 structure type [tetragonal, P4 2 /m, a = 6.8058(7) Aa, c = 9.7597(14) Aa, Z = 2], which consists of central uranium(IV) atoms coordinated by P 2 S 6 4- anions (staggered conformation). The anions are two-dimensional connectors for four uranium cations arranged in one plane. The structure of UP 2 S 7 (II) [orthorhombic, Fddd, a = 8.9966(15) Aa, b = 15.2869(2) Aa, c = 30.3195(5) Aa, Z = 16] is closely related to the monoclinic ZrP 2 S 7 structure type. It consists of U 4+ cations linked by P 2 S 7 4- ligands, the resulting 3D network contains large pores (diameter approx. 3.5 x 16.7 Aa). In the previously reported compound U(P 2 S 6 ) 2 (III) [I4 1 /a, a = 12.8776(9) Aa, c = 9.8367(10) Aa, Z = 2], the metal atoms are coordinated by four bidentate P 2 S 6 2- ligands. This arrangement can be considered as a pseudotetrahedral coordination of the uranium atoms by the linear ligands. Three of the resulting diamondoid frameworks are inseparably interwoven in order to optimize space filling. U 3 (PS 4 ) 4 (IV) [I4 1 /acd, a = 10.7440(9) Aa, c = 19.0969(2) Aa, Z = 2] crystallizes in a defect variant of the PrPS 4 structure type, with 50 % of the U2 sites statistically occupied with uranium atoms. The resulting stoichiometry is U 3 (PS 4 ) 4 with tetravalent uranium atoms. The structure of U 3 (PS 4 ) 4 consists of uranium atoms connected by PS 4 3- groups, each PS 4 group linking four central uranium atoms. Vibrational spectra, which were recorded for I-III, show good agreement between the obtained results and the expected values for the anionic units, while magnetic measurements confirm the presence of tetravalent uranium. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGa

  12. Recent advances in on-line coupling of capillary electrophoresis to atomic absorption and fluorescence spectrometry for speciation analysis and studies of metal-biomolecule interactions

    Li Yan; Yin Xuebo; Yan Xiuping

    2008-01-01

    Speciation information is vital for the understanding of the toxicity, mobility and bioavailability of elements in environmental or biological samples. Hyphenating high resolving power of separation techniques and element-selective detectors provides powerful tools for studying speciation of trace elements in environmental and biological systems. During the last five years several novel hybrid techniques based on capillary electrophoresis (CE) and atomic spectrometry have been developed for speciation analysis and metal-biomolecule interaction study in our laboratory. These techniques include CE on-line coupled with atomic fluorescence spectrometry (AFS), chip-CE on-line coupled with AFS, CE on-line coupled with flame heated quartz furnace atomic absorption spectrometry (FHF-AAS), and CE on-line coupled with electrothermal atomic absorption spectrometry (ETAAS). The necessity for the development of these techniques, their interface design, and applications in speciation analysis and metal-biomolecule interaction study are reviewed. The advantages and limitations of the developed hybrid techniques are critically discussed, and further development is also prospected

  13. Colonization by Cladosporium spp. of painted metal surfaces associated with heating and air conditioning systems

    Ahearn, D. G.; Simmons, R. B.; Switzer, K. F.; Ajello, L.; Pierson, D. L.

    1991-01-01

    Cladosporium cladosporioides and C. hebarum colonized painted metal surfaces of covering panels and register vents of heating, air conditioning and ventilation systems. Hyphae penetrated the paint film and developed characteristic conidiophores and conidia. The colonies were tightly appressed to the metal surface and conidia were not readily detectable via standard air sampling procedures.

  14. Heat transfer on liquid-liquid interface of molten-metal and water

    Tanaka, T.; Saito, Yasushi; Mishima, Kaichiro

    2001-01-01

    Molten-core pool had been formed in the lower-head of TMI-2 pressure vessel at the severe accident. The lower head, however, didn't receive any damage by reactor core cooling. Heat transfer at outside of the lower head and boiling heat transfer at liquid-liquid interface of molten-metal and water, however, are important for initial cooling process of the molten-core pool. The heat transfer experiments for the liquid-liquid interface of molten-metal and water are carried out over the range of natural convection to film boiling region. Phenomenon on the heat transfer experiments are visualized by using of high speed video camera. Wood's metal and U-alloy 78 are used as molten-metal. The test section of the experiments consists of a copper block with heater, wood's metal, and water. Three thermocouple probes are used for temperature measurement of water side and the molten-metal side. Stability of the liquid-liquid interface is depended on the wetness of container wall for molten metal and the temperature distribution of the interface. Entrainment phenomena of molten-metal occurs by a fluctuation of the interface after boiling on the container wall surface. The boiling curves obtained from the liquid-liquid interface experiments are agree with the nucleate boiling and the film boiling correlations of solid-liquid system. (Suetake, M.)

  15. Gas atomization of Cu-modified AB5 metal hydride alloys

    Young, K.; Ouchi, T.; Banik, A.; Koch, J.; Fetcenko, M.A.; Bendersky, L.A.; Wang, K.; Vaudin, M.

    2011-01-01

    Research highlights: → The gas atomization process together with a hydrogen annealing process was demonstrated on AB5 alloys. → The method was found to be effective in restoring the original cycle life sacrificed by the incorporation of copper in the alloy formula as a means of improving the low temperature performance of AB 5 alloys. → The new process also improves high rate, low temperature, and charge retention performances for both Cu-free and Cu-containing AB 5 alloys. - Abstract: Gas atomization together with a hydrogen annealing process has been proposed as a method to achieve improved low-temperature performance of AB 5 alloy electrodes in Ni/MH batteries and restore the original cycle life which was sacrificed by the incorporation of copper in the alloy formula. While the gas atomization process reduces the lattice constant aspect ratio c/a of the Cu-containing alloys, the addition of a hydrogen annealing step recovers this property, although it is still inferior to the conventionally prepared annealed Cu-free alloy. This observation correlates very well with the cycle life performance. In addition to extending the cycle life of the Cu-containing metal hydride electrode, processing by gas atomization with additional hydrogen annealing improves high-rate, low-temperature, and charge retention performances for both Cu-free and Cu-containing AB 5 alloys. The degradation mechanisms of alloys made by different processes through cycling are also discussed.

  16. Spin-dependent electronic transport properties of transition metal atoms doped α-armchair graphyne nanoribbons

    Fotoohi, Somayeh; Haji-Nasiri, Saeed

    2018-04-01

    Spin-dependent electronic transport properties of single 3d transition metal (TM) atoms doped α-armchair graphyne nanoribbons (α-AGyNR) are investigated by non-equilibrium Green's function (NEGF) method combined with density functional theory (DFT). It is found that all of the impurity atoms considered in this study (Fe, Co, Ni) prefer to occupy the sp-hybridized C atom site in α-AGyNR, and the obtained structures remain planar. The results show that highly localized impurity states are appeared around the Fermi level which correspond to the 3d orbitals of TM atoms, as can be derived from the projected density of states (PDOS). Moreover, Fe, Co, and Ni doped α-AGyNRs exhibit magnetic properties due to the strong spin splitting property of the energy levels. Also for each case, the calculated current-voltage characteristic per super-cell shows that the spin degeneracy in the system is obviously broken and the current becomes strongly spin dependent. Furthermore, a high spin-filtering effect around 90% is found under the certain bias voltages in Ni doped α-AGyNR. Additionally, the structure with Ni impurity reveals transfer characteristic that is suitable for designing a spin current switch. Our findings provide a high possibility to design the next generation spin nanodevices with novel functionalities.

  17. Determination of metallic impurities in raw materials for radioisotope production by atomic absorption spectroscopy

    Roca, M.; Alvarez, F.; Capdevila, C.

    1969-01-01

    Atomic absorption spectrometry has been used for the determination of traces of calcium in scandium oxide, copper in zinc, iron in cobalt oxide, manganese In ferric oxide, nickel in copper and zinc in gallium oxide. The influences on the sensitivities arising from the hollow cathode currents, the gas pressures and the acid concentrations have been considered. A study of the interferences from the metallic matrices has also been performed, the interference due to the absorption of the manganese radiation by the atoms of iron being the most outstanding . In order to remove the interfering elements and increase sensitivity, pre-concentration methods have been tested. The addition methods has also been used. (Author) 14 refs

  18. Coherent, atomically thin transition-metal dichalcogenide superlattices with engineered strain

    Xie, Saien; Tu, Lijie; Han, Yimo; Huang, Lujie; Kang, Kibum; Lao, Ka Un; Poddar, Preeti; Park, Chibeom; Muller, David A.; DiStasio, Robert A.; Park, Jiwoong

    2018-03-01

    Epitaxy forms the basis of modern electronics and optoelectronics. We report coherent atomically thin superlattices in which different transition metal dichalcogenide monolayers—despite large lattice mismatches—are repeated and laterally integrated without dislocations within the monolayer plane. Grown by an omnidirectional epitaxy, these superlattices display fully matched lattice constants across heterointerfaces while maintaining an isotropic lattice structure and triangular symmetry. This strong epitaxial strain is precisely engineered via the nanoscale supercell dimensions, thereby enabling broad tuning of the optical properties and producing photoluminescence peak shifts as large as 250 millielectron volts. We present theoretical models to explain this coherent growth and the energetic interplay governing the ripple formation in these strained monolayers. Such coherent superlattices provide building blocks with targeted functionalities at the atomically thin limit.

  19. Mechanical instability in non-uniform atomic structure: Application to amorphous metal

    Umeno, Yoshitaka; Kitamura, Takayuki; Tagawa, Motoki

    2007-01-01

    It is important to reveal the deformation of amorphous metal in the atomistic scale level as materials with non-crystal structure have been attracting attention with their prominent functions. In this paper atomistic simulations of tensile deformation of an amorphous model are conducted and local mechanical instability is analyzed to clarify the deformation mechanism of the amorphous structure. Instability causing sharp stress drop is associated with unstable motion of atoms within local region. The size of the region where the unstable atomic motion occurs corresponds to the magnitude of total stress decrease. At instability with large stress decrease the deformation at the onset of the instability propagates to surrounding region, which gives rise to a hysteresis loop in the stress-strain relation. This manifests the microscopic mechanism of the plasticity of amorphous structure

  20. Nuclear prehistory influence on transfer velocity of 54Mn impurity 'hot' atoms in irradiated metallic iron

    Alekseev, I.E.

    2007-01-01

    Influence of nuclear prehistory on transfer velocity of 54 Mn impurity 'hot'-atoms - got by different nuclear channels: 56 Fe(d, α), 54 Fe(n,p) in irradiated metallic iron - is studied. Irradiation of targets were carried out in U-120 accelerator (energy range 7.3/5.3 MeV, deuteron beam current makes up 5 μA). Mean density of thermal neutron (WWR-M reactor) makes up 8.6·10 13 neutron·cm -2 ·s -1 . It is shown, that transfer velocity of 54 Mn 'hot' atoms is defining by rate of radiation damage of targets in the irradiation process at that a key importance has a bombarding particles type applied for radioactive label getting

  1. Heat transport and electron cooling in ballistic normal-metal/spin-filter/superconductor junctions

    Kawabata, Shiro; Vasenko, Andrey S.; Ozaeta, Asier; Bergeret, Sebastian F.; Hekking, Frank W.J.

    2015-01-01

    We investigate electron cooling based on a clean normal-metal/spin-filter/superconductor junction. Due to the suppression of the Andreev reflection by the spin-filter effect, the cooling power of the system is found to be extremely higher than that for conventional normal-metal/nonmagnetic-insulator/superconductor coolers. Therefore we can extract large amount of heat from normal metals. Our results strongly indicate the practical usefulness of the spin-filter effect for cooling detectors, sensors, and quantum bits

  2. Heat transport and electron cooling in ballistic normal-metal/spin-filter/superconductor junctions

    Kawabata, Shiro, E-mail: s-kawabata@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Vasenko, Andrey S. [LPMMC, Université Joseph Fourier and CNRS, 25 Avenue des Martyrs, BP 166, 38042 Grenoble (France); Ozaeta, Asier [Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 5, E-20018 San Sebastián (Spain); Bergeret, Sebastian F. [Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 5, E-20018 San Sebastián (Spain); Donostia International Physics Center (DIPC), Manuel de Lardizabal 5, E-20018 San Sebastián (Spain); Hekking, Frank W.J. [LPMMC, Université Joseph Fourier and CNRS, 25 Avenue des Martyrs, BP 166, 38042 Grenoble (France)

    2015-06-01

    We investigate electron cooling based on a clean normal-metal/spin-filter/superconductor junction. Due to the suppression of the Andreev reflection by the spin-filter effect, the cooling power of the system is found to be extremely higher than that for conventional normal-metal/nonmagnetic-insulator/superconductor coolers. Therefore we can extract large amount of heat from normal metals. Our results strongly indicate the practical usefulness of the spin-filter effect for cooling detectors, sensors, and quantum bits.

  3. Relationship between the shear viscosity and heating rate in metallic glasses below the glass transition

    Khonik, Vitaly A.; Kobelev, N. P.

    2008-01-01

    It has been shown that first-order irreversible structural relaxation with distributed activation energies must lead to a linear decrease of the logarithm of Newtonian shear viscosity with the logarithm of heating rate upon linear heating of glass. Such a behavior is indeed observed in the experiments on metallic glasses. Structural relaxation-induced viscous flow leads to infra-low-frequency Maxwell viscoelastic internal friction, which is predicted to increase with the heating rate

  4. Local, atomic-level elastic strain measurements of metallic glass thin films by electron diffraction

    Ebner, C. [Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Sarkar, R. [Department of Materials Science and Engineering, School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287 (United States); Rajagopalan, J. [Department of Materials Science and Engineering, School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287 (United States); Department of Mechanical and Aerospace Engineering, School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287 (United States); Rentenberger, C., E-mail: christian.rentenberger@univie.ac.at [Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria)

    2016-06-15

    A novel technique is used to measure the atomic-level elastic strain tensor of amorphous materials by tracking geometric changes of the first diffuse ring of selected area electron diffraction patterns (SAD). An automatic procedure, which includes locating the centre and fitting an ellipse to the diffuse ring with sub-pixel precision is developed for extracting the 2-dimensional strain tensor from the SAD patterns. Using this technique, atomic-level principal strains from micrometre-sized regions of freestanding amorphous Ti{sub 0.45}Al{sub 0.55} thin films were measured during in-situ TEM tensile deformation. The thin films were deformed using MEMS based testing stages that allow simultaneous measurement of the macroscopic stress and strain. The calculated atomic-level principal strains show a linear dependence on the applied stress, and good correspondence with the measured macroscopic strains. The calculated Poisson’s ratio of 0.23 is reasonable for brittle metallic glasses. The technique yields a strain accuracy of about 1×10{sup −4} and shows the potential to obtain localized strain profiles/maps of amorphous thin film samples. - Highlights: • A TEM method to measure elastic strain in metallic glass films is proposed. • Method is based on tracking geometric changes in TEM diffraction patterns. • An automatic procedure is developed for extracting the local strain tensor. • Atomic-level strain in amorphous TiAl film was analysed during in-situ deformation. • Capability of the method to obtain micrometer scale strain profiles/maps is shown.

  5. Investigation of Some Transparent Metal Oxides as Damp Heat Protective Coating for CIGS Solar Cells: Preprint

    Pern, F. J.; Yan, F.; Zaaunbrecher, B.; To, B.; Perkins, J.; Noufi, R.

    2012-10-01

    We investigated the protective effectiveness of some transparent metal oxides (TMO) on CIGS solar cell coupons against damp heat (DH) exposure at 85oC and 85% relative humidity (RH). Sputter-deposited bilayer ZnO (BZO) with up to 0.5-um Al-doped ZnO (AZO) layer and 0.2-um bilayer InZnO were used as 'inherent' part of device structure on CdS/CIGS/Mo/SLG. Sputter-deposited 0.2-um ZnSnO and atomic layer deposited (ALD) 0.1-um Al2O3 were used as overcoat on typical BZO/CdS/CIGS/Mo/SLG solar cells. The results were all negative -- all TMO-coated CIGS cells exhibited substantial degradation in DH. Combining the optical photographs, PL and EL imaging, SEM surface micro-morphology, coupled with XRD, I-V and QE measurements, the causes of the device degradations are attributed to hydrolytic corrosion, flaking, micro-cracking, and delamination induced by the DH moisture. Mechanical stress and decrease in crystallinity (grain size effect) could be additional degrading factors for thicker AZO grown on CdS/CIGS.

  6. Thermophysical properties of 22 pure metals in the solid and liquid state - The pulse-heating data collection

    Hüpf, T.; Cagran, C.; Pottlacher, G.

    2011-05-01

    The workgroup of subsecond thermophysics in Graz has a long tradition in performing fast pulseheating experiments on metals and alloys. Thereby, wire-shaped specimens are rapidly heated (108 K/s) by a large current-pulse (104 A). This method provides thermophysical properties like volume-expansion, enthalpy and electrical resistivity up to the end of the liquid phase. Today, no more experiments on pure metals are to be expected, because almost all elements, which are suitable for pulse-heating so far, have been investigated. The requirements for pulse-heating are: a melting point which is high enough to enable pyrometric temperature measurements and the availability of wire-shaped specimens. These elements are: Co, Cu, Au, Hf, In, Ir, Fe, Pb, Mo, Ni, Nb, Pd, Pt, Re, Rh, Ag, Ta, Ti, W, V, Zn, and Zr. Hence, it is the correct time to present the results in a collected form. We provide data for the above mentioned quantities together with basic information on each material. The uniqueness of this compilation is the high temperature range covered and the homogeneity of the measurement conditions (the same method, the same laboratory, etc.). The latter makes it a good starting point for comparative analyses (e.g. a comparison of all 22 enthalpy traces is in first approximation conform with the rule of Dulong-Petit which states heat capacity - the slope of enthalpy traces - as a function of the number of atoms). The data is useful for input parameters in numerical simulations and it is a major purpose of our ongoing research to provide data for simulations of casting processes for the metal working industry. This work demonstrates some examples of how a data compilation like this can be utilized. Additionally, the latest completive measurement results on Ag, Ni, Ti, and Zr are described.

  7. Thermophysical properties of 22 pure metals in the solid and liquid state – The pulse-heating data collection

    Pottlacher G.

    2011-05-01

    Full Text Available The workgroup of subsecond thermophysics in Graz has a long tradition in performing fast pulseheating experiments on metals and alloys. Thereby, wire-shaped specimens are rapidly heated (108 K/s by a large current-pulse (104 A. This method provides thermophysical properties like volume-expansion, enthalpy and electrical resistivity up to the end of the liquid phase. Today, no more experiments on pure metals are to be expected, because almost all elements, which are suitable for pulse-heating so far, have been investigated. The requirements for pulse-heating are: a melting point which is high enough to enable pyrometric temperature measurements and the availability of wire-shaped specimens. These elements are: Co, Cu, Au, Hf, In, Ir, Fe, Pb, Mo, Ni, Nb, Pd, Pt, Re, Rh, Ag, Ta, Ti, W, V, Zn, and Zr. Hence, it is the correct time to present the results in a collected form. We provide data for the above mentioned quantities together with basic information on each material. The uniqueness of this compilation is the high temperature range covered and the homogeneity of the measurement conditions (the same method, the same laboratory, etc.. The latter makes it a good starting point for comparative analyses (e.g. a comparison of all 22 enthalpy traces is in first approximation conform with the rule of Dulong-Petit which states heat capacity – the slope of enthalpy traces – as a function of the number of atoms. The data is useful for input parameters in numerical simulations and it is a major purpose of our ongoing research to provide data for simulations of casting processes for the metal working industry. This work demonstrates some examples of how a data compilation like this can be utilized. Additionally, the latest completive measurement results on Ag, Ni, Ti, and Zr are described.

  8. Autoionic microscopy of damage regions of single atom displacement cascades in metals

    Suvorov, A.L.

    1981-01-01

    The defect region formation characterized by zones of depletion with atoms and interstitial halos arizing during displacement cascade development in an irradiated metal is considered. in experimental autoionmicroscopic analysis technique is used. The analysis procedure is briefly discussed: the experiment, the defect identification on autoionic image microphotos, computer data processing. The technique was applied for pure tungsten irradiated with 12 and 5.8 MeV deuterons and fission neutrons, and for tungsten-1.5% ThO 2 alloy irradiated with fast neutrons from fission fragments

  9. Mechanical deformation of atomic-scale metallic contacts: Structure and mechanisms

    Sørensen, Mads Reinholdt; Brandbyge, Mads; Jacobsen, Karsten Wedel

    1998-01-01

    We have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain using molecular dynamics and effective medium theory potentials. The evolution of the structure of the contacts and the underlying deformation mechanisms are described along with the calculated......, but vacancies can be permanently present. The transition states and energies for slip mechanisms have been determined using the nudged elastic band method, and we find a size-dependent crossover from a dislocation-mediated slip to a homogeneous slip when the contact diameter becomes less than a few nm. We show...

  10. Atomic absorption determination of metals in soils using ultrasonic sample preparation

    Chmilenko, F.A.; Smityuk, N.M.; Baklanov, A.N.

    2002-01-01

    It was shown that ultrasonic treatment accelerates sample preparation of soil extracts from chernozem into different solvents by a factor of 6 to 60. These extracts are used for the atomic absorption determination of soluble species of Cd, Co, Cr, Cu, Ni, Pb, and Zn. The optimum ultrasound parameters (frequency, intensity, and treatment time) were found for preparing soil extracts containing analytes in concentrations required in agrochemical procedures. Different extractants used to extract soluble heavy metals from soils of an ordinary chernozem type in agrochemical procedures using ultrasonic treatment were classified in accordance with the element nature [ru

  11. Optical nonlinearities of excitonic states in atomically thin 2D transition metal dichalcogenides

    Soh, Daniel Beom Soo [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Proliferation Signatures Discovery and Exploitation Department

    2017-08-01

    We calculated the optical nonlinearities of the atomically thin monolayer transition metal dichalcogenide material (particularly MoS2), particularly for those linear and nonlinear transition processes that utilize the bound exciton states. We adopted the bound and the unbound exciton states as the basis for the Hilbert space, and derived all the dynamical density matrices that provides the induced current density, from which the nonlinear susceptibilities can be drawn order-by-order via perturbative calculations. We provide the nonlinear susceptibilities for the linear, the second-harmonic, the third-harmonic, and the kerr-type two-photon processes.

  12. Hyperfine structure of 2Σ molecules containing alkaline-earth-metal atoms

    Aldegunde, Jesus; Hutson, Jeremy M.

    2018-04-01

    Ultracold molecules with both electron spin and an electric dipole moment offer new possibilities in quantum science. We use density-functional theory to calculate hyperfine coupling constants for a selection of molecules important in this area, including RbSr, LiYb, RbYb, CaF, and SrF. We find substantial hyperfine coupling constants for the fermionic isotopes of the alkaline-earth-metal and Yb atoms. We discuss the hyperfine level patterns and Zeeman splittings expected for these molecules. The results will be important both to experiments aimed at forming ultracold open-shell molecules and to their applications.

  13. Impurities determination of uranium metal flame spectrophotometry and atomic absorption spectrophotometry

    Rukihati.

    1978-01-01

    The atomic absorption flame spectrophotometry has been applied to the determination of chromium, copper, iron, lead, manganese and nickel in the metal of uranium. The first step to be done is to dissolve the uranium sample in nitric acid and then the uranium is extracted by a tributylphosphate-carbon tetrachloride solution. The aqueous phase which contains the chromium, copper, iron, lead, manganese and nickel is aspirated into an airacetylene flame. The results of this method are compared with the results of emission spectrographic method. It is found that this technique is competative to other methods in the sense that it is quite fast and accurate. (author)

  14. Activation barriers for series of exothermic homologous reactions. VI. Reactions of lanthanide and transition metal atoms.

    Blue, Alan S.; Fontijn, Arthur

    2001-09-01

    Semiempirical configuration interaction (SECI) theory to predict activation barriers, E, as given by k(T)=ATn exp(-E(RT), has been applied to homologous series of lanthanide (LN) and transition metal (TM) atom oxidation reactions. This was achieved by considering as homologous series reactions of elements differing only by the number of electrons in one subshell. Comparison between SECI and experimental results leads to an average deviation for the LN+N2O reactions of 0.66 kJ mol-1, and up to 5.5 kJ mol-1 for other series. Thirty-one activation barriers are reported.

  15. Atomic structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)

    Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou

    2005-01-01

    The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed

  16. The low-temperature water-water reactor for district heating atomic power plant (DHPP)

    Skvortsov, S.A.; Sokolov, I.N.; Krauze, L.V.; Nikiporetz, Yu.G.; Philimonov, Yu.V.

    1977-01-01

    The district heating atomic power plant in the article is distinguished by the increased reliability and safety of operation that was provided by the use of following main principles: relatively low parameters of the coolant; the intergral arrangement of equipment and accordingly the minimum branching of the reactor circuit; the natural circulation of coolant of the primary circuit in the steady-state, transient and emergency regimes of reactor operation; the considerable reserves of cold water of the primary circuit in the reactor vessel, providing the emergency cooling; the application of two shells each of which is designed for the total working pressure, the second shell is made of prestressed reinforced concrete that eliminates its brittle failure. (M.S.)

  17. Physics. Examples and problems. Mechanics, heat, electricity and magnetism, oscillations and waves, atomic and nuclear physics

    Stroppe, Heribert; Streitenberger, Peter; Specht, Eckard; Zeitler, Juergen; Langer, Heinz

    2017-01-01

    The present book is the unification of the proved problem collections for the basic physical training of studyings of especially engineering courses at technical colleges and universities. The book contains - didactically prepared and structured in the style of a textbook as well as with increasing difficulty - a total of 960 exemplary and additional tasks from the fields mechanics, heat, electricity and magnetism, oscillations and waves, as well as atomic and nuclear physics. For the exemplary problems the whole solution path and the complete calculation process with explanation of the relevant physical laws are extensively presented, for the additional problems for the self-control only the solutions and, if necessary, intermediate calculations are given. The examples and problems with mostly practice-oriented content are selected in such a way that they largely cover the matter treated in courses and exercises and make by their didactical preparation an effective repetition and optimal examination-preparation possible.

  18. Finite-field evaluation of the Lennard-Jones atom-wall interaction constant C3 for alkali-metal atoms

    Johnson, W.R.; Dzuba, V.A.; Safronova, U.I.; Safronova, M.S.

    2004-01-01

    A finite-field scaling method is applied to evaluate the Lennard-Jones interaction constant C 3 for alkali-metal atoms. The calculations are based on the relativistic single-double approximation in which single and double excitations of Dirac-Hartree-Fock wave functions are included to all orders in perturbation theory

  19. From Single Atoms to Nanoparticles : Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO2 Nanopowder

    Grillo, Fabio; Van Bui, Hao; La Zara, Damiano; Aarnink, Antonius A.I.; Kovalgin, Alexey Y.; Kooyman, Patricia; Kreutzer, Michiel T.; van Ommen, Jan Rudolf

    2018-01-01

    A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO2 nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O2 as the coreactant

  20. Decay heat removal for the liquid metal fast breeder reactor

    Zemanick, P.P.; Brown, N.W.

    1975-01-01

    The functional and reliability requirements of the decay heat removal systems are described. The reliability requirement and its rationale as adequate assurance that public health and safety are safeguarded are presented. The means by which the reliability of the decay heat removal systems are established to meet their requirement are identified. The heat removal systems and their operating characteristics are described. The discussion includes the overflow heat removal service and its role in decay heat removal if needed. The details of the systems are described to demonstrate the elements of redundancy and diversity in the systems design. The quantitative reliability assessment is presented, including the reliability model, the most important assumptions on which the analysis is based, sources of failure data, and the preliminary numerical results. Finally, the qualitative analyses and administrative controls will be discussed which ensure reliability attainment in design, fabrication, and operation, including minimization of common mode failures. A component test program is planned to provide reliability data on selected critical heat removal system equipment. This test plan is described including a definition of the test parameters of greatest interest and the motivation for the test article selection. A long range plan is also in place to collect plant operational data and the broad outlines of this plan are described. A statement of the high reliability of the Clinch River Breeder reactor Plant decay heat removal systems and a summary of the supporting arguments is presented. (U.S.)

  1. Decay Heat Removal for the Liquid Metal Fast Breeder Reactor

    Zemanick, P. P.; Brown, N. W.

    1975-10-15

    The functional and reliability requirements of the decay heat removal systems are described. The reliability requirement and its rationale as adequate assurance that public health and safety are safeguarded are presented. The means by which the reliability of the decay heat removal systems are established to meet their requirement are identified. The heat removal systems and their operating characteristics are described. The discussion includes the overflow heat removal service and its role in decay heat removal if needed. The details of the systems are described to demonstrate the elements of redundancy and diversity in the systems design. The quantitative reliability assessment is presented, including the reliability model, the most important assumptions on which the analysis is based, sources of failure data, and the preliminary numerical results. Finally, the qualitative analyses and administrative controls will be discussed which ensure reliability attainment in design, fabrication, and operation, including minimization of common mode failures. A component test program is planned to provide reliability data on selected critical heat removal system equipment. This test plan is described including a definition of the test parameters of greatest interest and the motivation for the test article selection. A long range plan is also in place to collect plant operational data and the broad outlines of this plan are described. The paper closes with a statement of the high reliability of the Clinch River Breeder Reactor Plant decay heat removal systems and a summary of the supporting arguments. (author)

  2. Relaxation and final-state structure in XPS of atoms, molecules, and metals

    Shirley, D.A.; Martin, R.L.; McFeely, F.R.; Kowalczyk, S.P.; Ley, L.

    1975-03-01

    Photoemission from a many-electron system is a many-electron process, even though the transition operator may affect only one electron directly. Relaxation and ''shake-up'' structure are related by a sum rule. When one is present, the other must be also. Shake-up structure is shown to be accurately predictable in atomic neon and molecular HF if the CI calculations are done carefully. In metals the sum rule also applies but final-state effects usually appear as relaxation energy, which is large even for valence electrons. Finally, in rare-earth metals discrete shake-up structure is observable in the 4p region. (7 figs, 30 refs) (auth)

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

    Zacate, M. O., E-mail: zacatem1@nku.edu [Northern Kentucky University, Department of Physics, Geology, and Engineering Technology (United States)

    2016-12-15

    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.

  4. Multielement preconcentration of trace heavy metals in seawater with an emulsion containing 8-quinolinol for graphite-furnace atomic absorption spectrometry

    Matsumiya, Hiroaki; Kageyama, Tomohiro; Hiraide, Masataka

    2004-01-01

    A water-in-oil type emulsion containing 8-quinolinol has been used for the concentration of traces of heavy metals from seawater prior to their determinations by graphite-furnace atomic absorption spectrometry. The emulsion used was prepared by dissolving 40 mg of 8-quinolinol and 60 mg of sorbitan monooleate (Span-80) in 3.0 ml of toluene and vigorously mixing with 0.70 ml of aqueous hydrochloric acid solution (1.5 mol l -1 ) by ultrasonic irradiation. The resulting emulsion was gradually injected into 100 ml of sample solution (pH 8.5) and dispersed by stirring as numerous tiny globules. Four heavy metals (Co, Ni, Cu, and Cd) in the sample solution were quantitatively transported through the organic layer into the acidic aqueous droplets encapsulated in the emulsion. After collecting the dispersed emulsion globules, they were demulsified by heating and the heavy metals in the segregated aqueous phase were determined by atomic absorption spectrometry. Owing to the highly efficient concentration (100-fold), these heavy metals at sub-ng ml -1 levels in seawater were determined with satisfactory accuracy and precision, being confirmed with certified reference samples

  5. Specific heat characteristics of Ce70Ga8.5Cu18.5Ni3 metallic glass at low temperatures

    Liu, Rentao; Zhong, Langxiang; Zhang, Bo

    2018-03-01

    Specific heat behaviors have been studied in Ce70Ga8.5Cu18.5Ni3 bulk metallic glass (BMG) from 2 K to 50 K. The low-temperature specific heat of the Ce-based metallic glass is a combined action of the Fermi liquids term, Debye oscillator term, and Einstein oscillator term as well as excess term. We also observed an intense boson peak around 15 K and attributed it to a harmonic localized Einstein mode influenced by the dense-packed atomic cluster structure. It is also demonstrated that Ce70Ga8.5Cu18.5Ni3 BMG belongs to the strongly correlated heavy-fermion system with a great electron specific heat coefficient and a high Wilson ratio. It exhibits a typical Fermi-Liquid feature when the temperature is above 10 K, while it exhibits a Non-Fermi-Liquid feature when the temperature is below 3.5 K.

  6. Multiplicity dependence of matrix-induced frequency shifts for atomic transitions of the group 12 metals in rare gas solids

    Laursen, S.L.; Cartland, H.E.

    1991-01-01

    Atomic resonances of the group 12 metal atoms, Hg, Cd, and Zn, undergo frequency shifts from the gas phase atomic line when trapped in rare gas matrices of Ar, Kr, and Xe at 12 K. As expected, the shifts are approximately linear in polarizability of the rare gas, but the slope of this line depends on whether the transition in question is 1 P 1 left-arrow 1 S 0 or 3 P 1 left-arrow 1 S 0 . Thus the matrix-induced frequency shift is dependent on the singlet or triplet nature of the excited state as well as on the matrix material. This dependence on multiplicity is discussed in terms of interactions between the excited-state atomic orbitals and the matrix. The results are compared to matrix studies of other metals and to related gas-phase work on diatomic van der Waals complexes of group 12 metals with rare gases

  7. The method of the atomic-absorption analysis in a graphite furnace with the metallic collector-ballast

    Katskov, D.A.; Vasil'eva, L.A.; Grinshtejn, I.L.; Savel'eva, G.O.

    1987-01-01

    New method of atomic-absorption analysis in a graphite furnace with the metallic collector-ballast (tungsten were) is suggested. It enables to widen the number of analyzed objects of liquid products wetting readily graphite and metals. It is shown that application of metallic collector-ballast enables to improve sensitivity and reproducibility of analysis, increase the volume of dosed samples as well as to suppress effectively the influence of excess of mineral and organic substrate on results of atomic-absorption analysis of several elements, including Cd, Sr, In, Te

  8. On the modification of metal/ceramic interfaces by low energy ion/atom bombardment during film growth

    Rigsbee, J.M.; Scott, P.A.; Knipe, R.K.; Hock, V.F.

    1986-01-01

    Elemental Cu and Ti films have been deposited onto ceramic substrates with a plasma-aided physical vapor deposition (ion-plating) process. This paper discusses how the structure and chemistry of the metallic film and the metal/ceramic interface are modified by low energy ion and neutral atom bombardment. Emphasis is placed on determining how low energy ion/neutral atom bombardment affects the strength of the metal/ceramic interface. Analyses of the film, interface and substrate regions have employed scanning Auger microprobe, secondary ion mass spectroscopy, SEM/STEM-energy dispersive X-ray and TEM/STEM imaging and microdiffraction techniques. (Auth.)

  9. Kinetical analysis of the heat treatment procedure in SmCo5 and other rare-earth transition-metal sintered magnets

    Campos, Marcos Flavio de; Rangel Rios, Paulo

    2004-01-01

    In the processing of all types of commercial sintered rare-earth transition-metal magnets (SmCo 5 , Sm(CoCuFeZr) z , NdFeB) a post-sintering heat treatment is included, which is responsible for large increase of the coercive field. During this post-sintering heat treatment, there are phase transformations with diffusion of the alloying elements, moving the system towards the thermodynamic equilibrium. Due to the larger size of the rare-earth atoms, the diffusion of the rare-earth atoms in the lattice of rare-earth transition-metal phases like SmCo 5 , Sm 2 (Co, Fe) 17 or Nd 2 Fe 14 B should be very slow, implying that the diffusion of the rare-earth atoms should be controlling the overall kinetics of the process. From the previous assumption, a parameter named 'diffusion length of rare-earth atoms' is introduced as a tool to study the kinetics of the heat treatment in rare-earth magnets. Detailed microstructural characterization of SmCo 5 and NdFeB magnets did not indicate significant microstructural changes between sintering and heat treatment temperatures and it was suggested that the increase of coercivity can be related to decrease of the content of lattice defects. The sintering temperature is high, close to melting temperature, and in this condition there are large amount of defects in the lattice, possibly rare-earth solute atoms. Phase diagram analysis has suggested that a possible process for the coercivity increase can be the elimination of excess rare-earth atoms, i.e. solute atoms from a supersatured matrix. The 'diffusion length of rare-earth atoms' estimated from diffusion kinetics is compatible with the diffusion length determined from microstructure. For the case of SmCo 5 , it was found that the time of heat treatment necessary is around 20 times lower if an isothermal treatment at 850 deg. C is substituted by a slow cooling from sintering temperature 1150 to 850 deg. C. These results give support for the thesis that the coercivity increase is

  10. Transient heat transfer phenomena of the liquid metal layer cooled by overlying R113 coolant

    Cho, J. S.; Seo, K. R.; Jung, C. H.; Park, R. J.; Kim, S. B.

    1999-01-01

    To understand the fundamental relationship of the natural convection heat transfer in the molten metal pool and the boiling mechanism of the overlying coolant, experiments were performed for the transient heat transfer of the liquid metal pool with overlying R113 coolant with boiling. The simulant molten pool material is tin (Sn) with the melting temperature of 232 deg C. The metal pool is heated from the bottom surface and the coolant is injected onto the molten metal pool. Tests were conducted by changing the bottom surface boundary condition. The bottom heating condition was varied from 8kW to 14kW. As a result the boiling mechanism of the R113 coolant is changed from the nuclear boiling to film boiling. The Nusselt number and the Rayleigh number in the molten metal pool region obtained as functions of time. Analysis was made for the relationship between the heat flux and the temperature difference of the metal layer surface temperature and the boiling coolant bulk temperature

  11. Tunable reactivity of supported single metal atoms by impurity engineering of the MgO(001) support.

    Pašti, Igor A; Johansson, Börje; Skorodumova, Natalia V

    2018-02-28

    Development of novel materials may often require a rational use of high price components, like noble metals, in combination with the possibility to tune their properties in a desirable way. Here we present a theoretical DFT study of Au and Pd single atoms supported by doped MgO(001). By introducing B, C and N impurities into the MgO(001) surface, the interaction between the surface and the supported metal adatoms can be adjusted. Impurity atoms act as strong binding sites for Au and Pd adatoms and can help to produce highly dispersed metal particles. The reactivity of metal atoms supported by doped MgO(001), as probed by CO, is altered compared to their counterparts on pristine MgO(001). We find that Pd atoms on doped MgO(001) are less reactive than on perfect MgO(001). In contrast, Au adatoms bind CO much more strongly when placed on doped MgO(001). In the case of Au on N-doped MgO(001) we find that charge redistribution between the metal atom and impurity takes place even when not in direct contact, which enhances the interaction of Au with CO. The presented results suggest possible ways for optimizing the reactivity of oxide supported metal catalysts through impurity engineering.

  12. Ultra thin metallic coatings to control near field radiative heat transfer

    Esquivel-Sirvent, R.

    2016-09-01

    We present a theoretical calculation of the changes in the near field radiative heat transfer between two surfaces due to the presence of ultra thin metallic coatings on semiconductors. Depending on the substrates, the radiative heat transfer is modulated by the thickness of the ultra thin film. In particular we consider gold thin films with thicknesses varying from 4 to 20 nm. The ultra-thin film has an insulator-conductor transition close to a critical thickness of dc = 6.4 nm and there is an increase in the near field spectral heat transfer just before the percolation transition. Depending on the substrates (Si or SiC) and the thickness of the metallic coatings we show how the near field heat transfer can be increased or decreased as a function of the metallic coating thickness. The calculations are based on available experimental data for the optical properties of ultrathin coatings.

  13. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2016-12-01

    Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by 1H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  14. Joule heating of Fe-B metallic glasses

    Miglierini, M.; Sitek, J.; Lipka, J. (Dept. of Nuclear Physics and Technology, Slovak Technical Univ., Bratislava, Slovak Republic (Czechoslovakia))

    1993-04-01

    Amorphous Fe[sub 80]B[sub 20] and Fe[sub 83]B[sub 17] ribbons were heated in air and in vacuum, respectively, by a dc electric current passing through the specimen. During the Joule heating, [sup 57]Fe transmission Moessbauer spectra were recorded. Ribbons of the same geometrical dimensions, cut from a natural iron foil, were treated in the same way as a reference. The influence of the current-induced magnetic field in addition to the Joule heating is supposed to cause fluctuations in a short-range order observed. Changes in the hyperfine magnetic fields are compared with those obtained by a conventional heating in a vacuum furnace. (orig.).

  15. Efficient atomization of cesium metal in solid helium by low energy (10 μJ) femtosecond pulses

    Melich, M.; Dupont-Roc, J.; Jacquier, Ph.

    2009-10-01

    Metal atoms in solid and liquid helium-4 have attracted some interest either as a way to keep the atoms in a weakly perturbing matrix, or using them as a probe for the helium host medium. Laser sputtering with nanosecond pulsed lasers is the most often used method for atom production, resulting however in a substantial perturbation of the matrix. We show that a much weaker perturbation can be obtained by using femtosecond laser pulses with energy as low as 10 μJ. As an unexpected benefit, the atomic density produced is much higher.

  16. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    Cho, Jae Seon; Suh, Kune Yull; Chung, Chang Hyun [Seoul National University, Seoul (Korea, Republic of); Paark, Rae Joon; Kim, Sang Baik [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1997-12-31

    This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. Ad a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 deg C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleigh number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer. 10 refs., 4 figs., 1 tab. (Author)

  17. Natural convection heat transfer characteristics of the molten metal pool with solidification by boiling coolant

    Cho, Jae Seon; Suh, Kune Yull; Chung, Chang Hyun [Seoul National University, Seoul (Korea, Republic of); Paark, Rae Joon; Kim, Sang Baik [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    1998-12-31

    This paper presents results of experimental studies on the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. The metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. Ad a result, the crust, which is a solidified layer, may form at the top of the molten metal pool. Heat transfer is accomplished by a conjugate mechanism, which consists of the natural convection of the molten metal pool, the conduction in the crust layer and the convective boiling heat transfer in the coolant. This work examines the crust formation and the heat transfer rate on the molten metal pool with boiling coolant. The simulant molten pool material is tin (Sn) with the melting temperature of 232 deg C. Demineralized water is used as the working coolant. The crust layer thickness was ostensibly varied by the heated bottom surface temperature of the test section, but not much affected by the coolant injection rate. The correlation between the Nusselt number and the Rayleigh number in the molten metal pool region of this study is compared against the crust formation experiment without coolant boiling and the literature correlations. The present experimental results are higher than those from the experiment without coolant boiling, but show general agreement with the Eckert correlation, with some deviations in the high and low ends of the Rayleigh number. This discrepancy is currently attributed to concurrent rapid boiling of the coolant on top of the metal layer. 10 refs., 4 figs., 1 tab. (Author)

  18. Three-Dimensional Heat Transfer Analysis of Metal Fasteners in Roofing Assemblies

    Manan Singh

    2016-11-01

    Full Text Available Heat transfer analysis was performed on typical roofing assemblies using HEAT3, a three-dimensional heat transfer analysis software. The difference in heat transferred through the roofing assemblies considered is compared between two cases—without any steel fasteners and with steel fasteners. In the latter case, the metal roofing fasteners were arranged as per Factor Mutual Global (FMG approvals, in the field, perimeter, and corner zones of the roof. The temperature conditions used for the analysis represented summer and winter conditions for three separate Climate Zones (CZ namely Climate Zone 2 or CZ2 represented by Orlando, FL; CZ3 represented by Atlanta, GA; and CZ6 zone represented by St. Paul, MN. In all the climatic conditions, higher energy transfer was observed with increase in the number of metal fasteners attributed to high thermal conductivity of metals as compared to the insulation and other materials used in the roofing assembly. This difference in heat loss was also quantified in the form of percentage change in the overall or effective insulation of the roofing assembly for better understanding of the practical aspects. Besides, a comparison of 2D heat transfer analysis (using THERM software and 3D analysis using HEAT3 is also discussed proving the relevance of 3D over 2D heat transfer analysis.

  19. Elastic fields, dipole tensors, and interaction between self-interstitial atom defects in bcc transition metals

    Dudarev, S. L.; Ma, Pui-Wai

    2018-03-01

    Density functional theory (DFT) calculations show that self-interstitial atom (SIA) defects in nonmagnetic body-centered-cubic (bcc) metals adopt strongly anisotropic configurations, elongated in the direction [S. Han et al., Phys. Rev. B 66, 220101 (2002), 10.1103/PhysRevB.66.220101; D. Nguyen-Manh et al., Phys. Rev. B 73, 020101 (2006), 10.1103/PhysRevB.73.020101; P. M. Derlet et al., Phys. Rev. B 76, 054107 (2007), 10.1103/PhysRevB.76.054107; S. L. Dudarev, Annu. Rev. Mater. Res. 43, 35 (2013), 10.1146/annurev-matsci-071312-121626]. Elastic distortions, associated with such anisotropic atomic structures, appear similar to distortions around small prismatic dislocation loops, although the extent of this similarity has never been quantified. We derive analytical formulas for the dipole tensors of SIA defects, which show that, in addition to the prismatic dislocation looplike character, the elastic field of a SIA defect also has a significant isotropic dilatation component. Using empirical potentials and DFT calculations, we parametrize dipole tensors of defects for all the nonmagnetic bcc transition metals. This enables a quantitative evaluation of the energy of elastic interaction between the defects, which also shows that in a periodic three-dimensional simple cubic arrangement of crowdions, long-range elastic interactions between a defect and all its images favor a orientation of the defect.

  20. Higher-order Cn dispersion coefficients for the alkali-metal atoms

    Mitroy, J.; Bromley, M.W.J.

    2005-01-01

    The van der Waals coefficients, from C 11 through to C 16 resulting from second-, third-, and fourth-order perturbation theory are estimated for the alkali-metal (Li, Na, K, and Rb) atoms. The dispersion coefficients are also computed for all possible combinations of the alkali-metal atoms and hydrogen. The parameters are determined from sum rules after diagonalizing a semiempirical fixed core Hamiltonian in a large basis. Comparisons of the radial dependence of the C n /r n potentials give guidance as to the radial regions in which the various higher-order terms can be neglected. It is seen that including terms up to C 10 /r 10 results in a dispersion interaction that is accurate to better than 1% whenever the inter-nuclear spacing is larger than 20a 0 . This level of accuracy is mainly achieved due to the fortuitous cancellation between the repulsive (C 11 ,C 13 ,C 15 ) and attractive (C 12 ,C 14 ,C 16 ) dispersion forces

  1. Chemical resistance of thin film materials based on metal oxides grown by atomic layer deposition

    Sammelselg, Väino; Netšipailo, Ivan; Aidla, Aleks; Tarre, Aivar; Aarik, Lauri; Asari, Jelena; Ritslaid, Peeter; Aarik, Jaan

    2013-01-01

    Etching rate of technologically important metal oxide thin films in hot sulphuric acid was investigated. The films of Al-, Ti-, Cr-, and Ta-oxides studied were grown by atomic layer deposition (ALD) method on silicon substrates from different precursors in large ranges of growth temperatures (80–900 °C) in order to reveal process parameters that allow deposition of coatings with higher chemical resistance. The results obtained demonstrate that application of processes that yield films with lower concentration of residual impurities as well as crystallization of films in thermal ALD processes leads to significant decrease of etching rate. Crystalline films of materials studied showed etching rates down to values of < 5 pm/s. - Highlights: • Etching of atomic layer deposited thin metal oxide films in hot H 2 SO 4 was studied. • Smallest etching rates of < 5 pm/s for TiO 2 , Al 2 O 3 , and Cr 2 O 3 were reached. • Highest etching rate of 2.8 nm/s for Al 2 O 3 was occurred. • Remarkable differences in etching of non- and crystalline films were observed

  2. Irradiation of tungsten with metallic diatomic molecular ions: atomic-resolution observations of depleted zones

    Pramanik, D.; Seidman, D.N.

    1982-08-01

    Direct evidence, on an atomic scale, is presented for the enhancement of damage production per projectile ion in diatomic metallic molecular ion (dimer) irradiations of tungsten as compared to monatomic metallic ion (monomer) irradiations. Irradiations were performed in situ at less than or equal to 10 K, in a field-ion microscope, employing 20 keV Ag + or W + monomer ions and the results are compared with 40 keV W 2 + or Ag 2 + dimer ion bombardments; the average energy per ion was 20 keV. First, in the near-surface region the depleted zones produced by the W 2 + dimer ions give rise to void-like contrast effects. The W + monomer ions do not produce this void-like damage. The existence of voids was explained employing a nucleation and diffusion-limited growth model which suggests that the growth can occur on a time scale -9 s, if the effective diffusivity of an atom in the fully-developed collision cascade is > 3 x 10 -4 cm 2 s -1 . Second, by counting the number of vacancies in individual depleted zones, produced by the different ions, it was demonstrated that the number of vacancies produced per incoming ion of the dimer is 1.55 times greater than the number of vacancies produced per monomer ion

  3. Atomic layer deposition of HfO{sub 2} for integration into three-dimensional metal-insulator-metal devices

    Assaud, Loic [Aix Marseille Univ, CNRS, CINAM, Marseille (France); ICMMO-ERIEE, Universite Paris-Sud / Universite Paris-Saclay, CNRS, Orsay (France); Pitzschel, Kristina; Barr, Maissa K.S.; Petit, Matthieu; Hanbuecken, Margrit; Santinacci, Lionel [Aix Marseille Univ, CNRS, CINAM, Marseille (France); Monier, Guillaume [Universite Clermont Auvergne, Universite Blaise Pascal, CNRS, Institut Pascal, Clermont-Ferrand (France)

    2017-12-15

    HfO{sub 2} nanotubes have been fabricated via a template-assisted deposition process for further use in three-dimensional metal-insulator-metal (MIM) devices. HfO{sub 2} thin layers were grown by Atomic Layer Deposition (ALD) in anodic alumina membranes (AAM). The ALD was carried out using tetrakis(ethylmethylamino)hafnium and water as Hf and O sources, respectively. Long exposure durations to the precursors have been used to maximize the penetration depth of the HfO{sub 2} layer within the AAM and the effect of the process temperature was investigated. The morphology, the chemical composition, and the crystal structure were studied as a function of the deposition parameters using transmission and scanning electron microscopies, X-ray photoelectron spectroscopy, and X-ray diffraction, respectively. As expected, the HfO{sub 2} layers grown at low-temperature (T = 150 C) were amorphous, while for a higher temperature (T = 250 C), polycrystalline films were observed. The electrical characterizations have shown better insulating properties for the layers grown at low temperature. Finally, TiN/HfO{sub 2}/TiN multilayers were grown in an AAM as proof-of-concept for three-dimensional MIM nanostructures. (orig.)

  4. Resonant charging and stopping power of slow channelling atoms in a crystalline metal

    Mason, D R; Race, C P; Foo, M H F; Horsfield, A P; Foulkes, W M C; Sutton, A P

    2012-01-01

    Fast moving ions travel great distances along channels between low-index crystallographic planes, slowing through collisions with electrons, until finally they hit a host atom initiating a cascade of atomic displacements. Statistical penetration ranges of incident particles are reliably used in ion-implantation technologies, but a full, necessarily quantum-mechanical, description of the stopping of slow, heavy ions is challenging and the results of experimental investigations are not fully understood. Using a self-consistent model of the electronic structure of a metal, and explicit treatment of atomic structure, we find by direct simulation a resonant accumulation of charge on a channelling ion analogous to the Okorokov effect but originating in electronic excitation between delocalized and localized valence states on the channelling ion and its transient host neighbours, stimulated by the time-periodic potential experienced by the channelling ion. The charge resonance reduces the electronic stopping power on the channelling ion. These are surprising and interesting new chemical aspects of channelling, which cannot be predicted within the standard framework of ions travelling through homogeneous electron gases or by considering either ion or target in isolation. (paper)

  5. Local atomic order of a metallic glass made visible by scanning tunneling microscopy

    Luo, Yuansu; Samwer, Konrad

    2018-06-01

    Exploring the atomic level structure in amorphous materials by STM becomes extremely difficult due to the localized electronic states. Here we carried out STM studies on a quasi-low-dimensional film of metallic glass Zr65Cu27.5Al7.5 which is ‘ultrathin’ compared with the localization length and/or the length scale of short range order. The local electronic structure must appear more inherent, having states at E f available for tip-sample tunneling current. To enhance imaging contrasts between long-range and short-range orders, the highly oriented pyrolytic graphite was chosen as substrate, so that the structural heterogeneity arising from competition between the glass former ability and the epitaxy can be ascertained. A chemical order predicted for this system was observed in atomic ordered regimes (1–2 monolayers), accompanied with a superstructure with the period Zr–Cu(Al)–Zr along three hexagonal axes. The result implies a chemical short range order in disordered regimes, where polyhedral clusters are dominant with the solute atom Cu(Al) in the center. An attempt for the structural modelling was made based on high resolution STM images, giving icosahedral order on the surface and different Voronoi clusters in 3D space.

  6. Performance investigations of liquid-metal heat pipes for space and terrestrial applications

    Kemme, J.E.; Keddy, E.S.; Phillips, J.R.

    1978-01-01

    The high heat transfer capacity of liquid-metal heat pipes is demonstrated in performance tests with mercury, potassium, sodium, and lithium working fluids and wick structures which serve to minimize liquid pressure losses and vapor/liquid interactions. Appropriate wicks for horizontal and vertical operation are described. It is shown that heat-transfer with these wicks is limited by vapor flow effects. Examples are given of particular effects associated with a long adiabatic section between evaporator and condenser and with a heat source of uniform temperature as opposed to a source of uniform power

  7. Comparison of heat flux measurement techniques during the DIII-D metal ring campaign

    Barton, J. L.; Nygren, R. E.; Unterberg, E. A.; Watkins, J. G.; Makowski, M. A.; Moser, A.; Rudakov, D. L.; Buchenauer, D.

    2017-12-01

    The heat fluxes expected in the ITER divertor raise concerns about the damage tolerances of tungsten, especially due to thermal transients caused by edge localized modes (ELMs) as well as frequent temperature cycling from high to low extremes. Therefore we are motivated to understand the heat flux conditions that can cause not only enhanced erosion but also bulk thermo-mechanical damage to a tungsten divertor. For the metal ring campaign in DIII-D, tungsten-coated TZM tile inserts were installed making two toroidal arrays of metal tile inserts in the lower divertor. This study examines the deposited heat flux on these rings with embedded thermocouples (TCs) sampling at 10 kHz and compares them to Langmuir probe (LP) and infrared thermography (IRTV) heat flux measurements. We see agreement of the TC, LP, and IRTV data within 20% of the heat flux averaged over the entire discharge, and that all three diagnostics suggest parallel heat flux at the OSP location increases linearly with input heating power. The TC and LP heat flux time traces during the discharge trend together during large changes to the average heat flux. By subtracting the LP measured inter-ELM heat flux from TC data, using a rectangular ELM energy pulse shape, and taking the relative size and duration of each ELM from {{D}}α measurements, we extract the ELM heat fluxes from TC data. This over-estimates the IRTV measured ELM heat fluxes by a factor of 1.9, and could be due to the simplicity of the TC heat flux model and the assumed ELM energy pulse shape. ELM heat fluxes deposited on the inserts are used to model tungsten erosion in this campaign. These TC ELM heat flux estimates are used in addition to IRTV, especially in cases where the IRTV view to the metal ring is obstructed. We observe that some metal inserts were deformed due to exposed leading edges. The thermal conditions on these inserts are investigated with the thermal modeling code ABAQUS using our heat flux measurements when these edges

  8. X-ray photoelectron spectroscopy study of the functionalization of carbon metal-containing nanotubes with phosphorus atoms

    Shabanova, I.N.; Terebova, N.S.

    2013-01-01

    Highlights: •Carbon metal-containing nanotubes (Me–Cu, Ni, Fe) were functionalized with chemical groups containing different concentrations of phosphorous. •The C1s and Me3s spectra were measured by the X-ray photoelectron spectroscopy method. •The values of the atomic magnetic moment of the carbon metal-containing nanotubes were determined. -- Abstract: In the present paper, carbon metal-containing (Me: Cu, Ni, Fe) nanotubes functionalized with phosphorus atoms (ammonium polyphosphate) were studied by X-ray photoelectron spectroscopy (XPS) on an X-ray electron magnetic spectrometer. It is found that the functionalization leads to the change of the metal atomic magnetic moment, i.e. the value of the atomic magnetic moment in the functionalized carbon metal-containing (Cu, Ni, Fe) nanotubes increases and is higher than that in pristine nanotubes. It is shown that the covalent bond of Me and P atoms is formed. This leads to an increase in the activity of the nanostructure surface which is necessary for the modification of materials

  9. A numerical study of spin-dependent organization of alkali-metal atomic clusters using density-functional method

    Liu Xuan, E-mail: liu.x.ad@m.titech.ac.jp; Ito, Haruhiko [Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology (Japan); Torikai, Eiko [Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi (Japan)

    2012-08-15

    We calculate the different geometric isomers of spin clusters composed of a small number of alkali-metal atoms using the UB3LYP density-functional method. The electron density distribution of clusters changes according to the value of total spin. Steric structures as well as planar structures arise when the number of atoms increases. The lowest spin state is the most stable and Li{sub n}, Na{sub n}, K{sub n}, Rb{sub n}, and Cs{sub n} with n = 2-8 can be formed in higher spin states. In the highest spin state, the preparation of clusters depends on the kind and the number of constituent atoms. The interaction energy between alkali-metal atoms and rare-gas atoms is smaller than the binding energy of spin clusters. Consequently, it is possible to self-organize the alkali-metal-atom clusters on a non-wetting substrate coated with rare-gas atoms.

  10. Discharge on boiling in a channel: effect of channel geometry on the performance characteristics of determining metals in a liquid flow by atomic emission spectrometry

    Zuev, B.K.; Yagov, V.V.; Grachev, A.S.

    2006-01-01

    Discharge on boiling in a channel was studied as a new atomization and excitation source for spectrochemical analysis in a flow of electrolyte solutions. The discharge arises between the liquid walls of a vapor lock formed in the channel of a dielectric membrane because of the rapid Joule heating of the liquid in the channel. The effect of channel geometry on the reproducibility of the integrated light intensity was studied. The background radiation spectrum was measured over the range 220-900 nm, and the possibility of determining alkali and alkaline earth metals in a flow was studied. The parameters of linear calibration equations and the detection limits for these metals are given [ru

  11. Laboratory Exercise for Studying the Morphology of Heat-Denatured and Amyloid Aggregates of Lysozyme by Atomic Force Microscopy

    Gokalp, Sumeyra; Horton, William; Jónsdóttir-Lewis, Elfa B.; Foster, Michelle; Török, Marianna

    2018-01-01

    To facilitate learning advanced instrumental techniques, essential tools for visualizing biomaterials, a simple and versatile laboratory exercise demonstrating the use of Atomic Force Microscopy (AFM) in biomedical applications was developed. In this experiment, the morphology of heat-denatured and amyloid-type aggregates formed from a low-cost…

  12. Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2.

    DeRita, Leo; Dai, Sheng; Lopez-Zepeda, Kimberly; Pham, Nicholas; Graham, George W; Pan, Xiaoqing; Christopher, Phillip

    2017-10-11

    Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO 2 . In these structures, isolated Pt atoms, Pt iso , remain stable through various conditions, and spectroscopic evidence suggests Pt iso species exist in homogeneous local environments. Comparing Pt iso to ∼1 nm preoxidized (Pt ox ) and prereduced (Pt metal ) Pt clusters on TiO 2 , we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Pt iso ≪ Pt metal atoms bonded to TiO 2 and that Pt iso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO 2 . This approach should be generally useful for studying the behavior of supported precious metal atoms.

  13. Measuring the Specific Heat of Metals by Cooling

    Dittrich, William; Minkin, Leonid; Shapovalov, Alexander S.

    2010-01-01

    Three in one? Yes, three standard undergraduate thermodynamics experiments in one, not an oval can of lubricating oil. Previously it has been shown that the PASCO scientific apparatus for measuring coefficients of thermal expansion of metals can also be used to illustrate Newton's law of cooling in the same experiment. Now it will be shown that by…

  14. The design of a heat transfer liquid metal MHD experiment for ALEX [Argonne Liquid-Metal Experiment

    Picologlou, B.F.; Reed, C.B.; Hua, T.Q.; Lavine, A.S.

    1988-01-01

    An experiment to study heat transfer in liquid metal MHD flow, under conditions relevant to coolant channels for tokamak first wall and high heat flux devices, is described. The experimental configuration is a rectangular duct in a transverse magnetic field, heated on one wall parallel to the field. The specific objective of the experiment is to resolve important issues related to the presence and heat transfer characteristics of wall jets and flow instabilities in MHD flows in rectangular duct with electrically conducting walls. Available analytical tools for MHD thermal hydraulics have been used in the design of the test article and its instrumentation. Proposed tests will cover a wide range of Peclet and Hartmann numbers and interaction parameters. 14 refs., 3 figs., 1 tab

  15. On Some Aspects of Levitation Heating of Metal Bodies

    Mach, M.; Karban, P.; Doležel, Ivo

    2005-01-01

    Roč. 5, č. 2 (2005), s. 5-10 ISSN 1335-8243 R&D Projects: GA ČR(CZ) GA102/04/0095 Institutional research plan: CEZ:AV0Z20570509 Keywords : electrodynamic levitation * induction heating * magnetic field Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  16. Adsorption of metal atoms at a buckled graphene grain boundary using model potentials

    Helgee, Edit E.; Isacsson, Andreas

    2016-01-01

    Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable

  17. Implantable polymer/metal thin film structures for the localized treatment of cancer by Joule heating

    Kan-Dapaah, Kwabena; Rahbar, Nima; Theriault, Christian; Soboyejo, Wole

    2015-04-01

    This paper presents an implantable polymer/metal alloy thin film structure for localized post-operative treatment of breast cancer. A combination of experiments and models is used to study the temperature changes due to Joule heating by patterned metallic thin films embedded in poly-dimethylsiloxane. The heat conduction within the device and the surrounding normal/cancerous breast tissue is modeled with three-dimensional finite element method (FEM). The FEM simulations are used to explore the potential effects of device geometry and Joule heating on the temperature distribution and lesion (thermal dose). The FEM model is validated using a gel model that mimics biological media. The predictions are also compared to prior results from in vitro studies and relevant in vivo studies in the literature. The implications of the results are discussed for the potential application of polymer/metal thin film structures in hyperthermic treatment of cancer.

  18. Specific heat of superconducting metallic glasses at low temperatures; Spezifische Waerme von supraleitenden metallischen Glaesern bei tiefen Temperaturen

    Reifenberger, Andreas

    2017-11-15

    In the framework of this thesis we performed, for the first time, an in-depth investigation of the thermodynamic properties of superconducting bulk metallic glasses (BMGs) by means of specific heat measurements in the temperature range between 25 mK and 300 K. To determine the specific heat we used a setup based on the well-established relaxation method. Furthermore we developed a novel micro-fabricated platform to measure superconducting, mg-sized samples down to T=5 mK. The platform temperature is measured by a metallic paramagnetic Ag:Er sensor that is inductively coupled to the input coil of a dc-SQUID by means of a micro-structured gradiometric meander coil. Thereby, we reached a temperature resolution of less than 30 nK/√(Hz) and a very low addenda heat capacity below 200 pJ/K at 50 mK. Connecting the obtained results with thermal conductivity data we were able to consistently model the various degrees of freedom in these BMGs and their interaction mechanisms: For temperatures T>2 K, we find pronounced low temperature anomalies in the phononic specific heat, which are attributed to localized harmonic vibration modes. In the superconducting state close to T{sub C}, where interactions of atomic tunneling systems with quasi-particles need to be taken into account, both measurements agree well with BCS-theory predictions. Far below T{sub C} we find good agreement between the data and the standard tunneling model predictions.

  19. The photo-assisted heat current and its Peltier coefficient in a metal/dot/metal junction

    Crépieux, A

    2012-01-01

    The photo-assisted heat current through a metal/dot/metal junction and its associated Peltier coefficient are computed in the framework of the time-dependent out-of-equilibrium Keldysh formalism in the presence of a dot energy modulation. When the frequency of the modulation is much larger than the amplitude of the modulation, the heat current follows the sinusoidal time evolution of the dot energy. This is no longer the case when the modulation frequency becomes of the order of or smaller than the amplitude of the modulation. To characterize this non-sinusoidal behavior, we have calculated the harmonics of the photo-assisted heat current. The zero-order harmonic can be expressed as an infinite sum of dc heat currents associated with a dot with shifted energies. It exhibits a devil's staircase profile with non-horizontal steps, whereas it is established that the steps are horizontal for the zero-order harmonic of the photo-assisted electric current. This particularity is related to the fact that the dot heat is not a conserved quantity due to energy dissipation within the tunnel barriers.

  20. Investigations of reactions between pure refractory metals and light gases with the field ion microscope and atom probe

    Krautz, E.; Haiml, G.

    1989-01-01

    The initial stages of selected reactions of the refractory metals tungsten, niobium and tantalum with hydrogen, oxygen, nitrogen and methane have been studied with the field ion microscope in atomic resolution whereby the composition of single net planes converages and surface zones could absolutely be analyzed with the atom probe by using field desorption under defined conditions at low temperatures. 14 refs., 9 figs. (Author)

  1. Research Investigation Directed Toward Extending the Useful Range of the Electromagnetic Spectrum. [atomic spectra and electronic structure of alkali metals

    Hartmann, S. R.; Happer, W.

    1974-01-01

    The report discusses completed and proposed research in atomic and molecular physics conducted at the Columbia Radiation Laboratory from July 1972 to June 1973. Central topics described include the atomic spectra and electronic structure of alkali metals and helium, molecular microwave spectroscopy, the resonance physics of photon echoes in some solid state systems (including Raman echoes, superradiance, and two photon absorption), and liquid helium superfluidity.

  2. Effective embedded-atom potential for metallic adsorbates on crystalline surfaces

    Förster, G D; Magnin, Y; Rabilloud, F; Calvo, F

    2014-01-01

    Based on the embedded-atom method (EAM), an analytical effective potential is developed to model the interaction of a metallic adsorbate on a perfect crystalline substrate, which is also metallic. The many-body character of the original EAM potential is preserved in the adsorbate energy and in the alteration of the substrate energy due to the presence of the adsorbate. A mean-field-type version neglecting corrugation of the substrate is first derived based on rigorous integration of individual monolayers, followed by an approximate form for the perturbation of the substrate energy. Lateral corrugation is subsequently included by additional phenomenological terms respecting the symmetry of the substrate, again preserving the many-body nature of the original potential. The effective model contains four parameters to describe uncorrugated substrates and eight extra parameters to describe every order of the Fourier lateral expansion. These parameters were fitted to reproduce the adsorption energy of a sample of random configurations of realistic 2D and 3D clusters deposited on the (1 1 1) fcc surface, for metals for which popular EAM models have been parametrized. As a simple application, the local relaxation of pre-formed icosahedral or truncated octahedral clusters soft-landed and exposing (1 1 1) faces in epitaxy to the substrate has been simulated at 0 and 300 K. The deformation of small clusters to wet the substrate is correctly captured by the effective model. This agreement with the exact potential suggests that the present model should be useful for treating metallic environments in large-scale surface studies, notably in structural optimization or as a template for more general models parametrized from ab initio data. (paper)

  3. Aspherical-atom modeling of coordination compounds by single-crystal X-ray diffraction allows the correct metal atom to be identified.

    Dittrich, Birger; Wandtke, Claudia M; Meents, Alke; Pröpper, Kevin; Mondal, Kartik Chandra; Samuel, Prinson P; Amin Sk, Nurul; Singh, Amit Pratap; Roesky, Herbert W; Sidhu, Navdeep

    2015-02-02

    Single-crystal X-ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid-state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical-atom least-squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld-atom refinement (Acta Crystallogr. Sect. A- 2008, 64, 383-393; IUCrJ. 2014, 1,61-79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B- 2013, 69, 91-104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear-coordinate 3d metal complexes, for which the wrong element is found if standard independent-atom model scattering factors are relied upon, are studied, and it is shown that only aspherical-atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Heat dissipation due to ferromagnetic resonance in a ferromagnetic metal monitored by electrical resistance measurement

    Yamanoi, Kazuto; Yokotani, Yuki; Kimura, Takashi

    2015-01-01

    The heat dissipation due to the resonant precessional motion of the magnetization in a ferromagnetic metal has been investigated. We demonstrated that the temperature during the ferromagnetic resonance can be simply detected by the electrical resistance measurement of the Cu strip line in contact with the ferromagnetic metal. The temperature change of the Cu strip due to the ferromagnetic resonance was found to exceed 10 K, which significantly affects the spin-current transport. The influence of the thermal conductivity of the substrate on the heating was also investigated

  5. Development of natural convection heat transfer correlation for liquid metal with overlying boiling coolant

    Cho, Jae Seon; Suh, Kune Y.; Chung, Chang Hyun; Park, Rae Joon; Kim, Sang Baik

    1999-01-01

    Experimental study was performed to investigate the natural convection heat transfer characteristics and the crust formation of the molten metal pool concurrent with forced convective boiling of the overlying coolant. Tests were performed under the condition of the bottom surface heating in the test section and the forced convection of the coolant being injected onto the molten metal pool. The constant temperature and constant heater input power conditions were adopted for the bottom heating. Test results showed that the temperature distribution and crust layer thickness in the metal layer are appreciably affected by the heated bottom surface temperature of the test section, but not much by the coolant injection rate. The relationship between the Nu number and Ra number in the molten metal pool region is determined and compared with the correlations in the literature, and the experiment without coolant boiling. A new correlation on the relationship between the Nu number and Ra number in the molten metal pool with crust formation is developed from the experimental data

  6. Wireless Metal Detection and Surface Coverage Sensing for All-Surface Induction Heating

    Veli Tayfun Kilic

    2016-03-01

    Full Text Available All-surface induction heating systems, typically comprising small-area coils, face a major challenge in detecting the presence of a metallic vessel and identifying its partial surface coverage over the coils to determine which of the coils to power up. The difficulty arises due to the fact that the user can heat vessels made of a wide variety of metals (and their alloys. To address this problem, we propose and demonstrate a new wireless detection methodology that allows for detecting the presence of metallic vessels together with uniquely sensing their surface coverages while also identifying their effective material type in all-surface induction heating systems. The proposed method is based on telemetrically measuring simultaneously inductance and resistance of the induction coil coupled with the vessel in the heating system. Here, variations in the inductance and resistance values for an all-surface heating coil loaded by vessels (made of stainless steel and aluminum at different positions were systematically investigated at different frequencies. Results show that, independent of the metal material type, unique identification of the surface coverage is possible at all freqeuncies. Additionally, using the magnitude and phase information extracted from the coupled coil impedance, unique identification of the vessel effective material is also achievable, this time independent of its surface coverage.

  7. Study of thermosiphon and radiant panel passive heating systems for metal buildings

    Biehl, F.A.; Schnurr, N.M.; Wray, W.O.

    1983-01-01

    A study of passive-heating systems appropriate for use on metal buildings is being conducted at Los Alamos National Laboratory for the Naval Civil Engineering Laboratory, Port Hueneme, California. The systems selected for study were chosen on the basis of their appropriateness for retrofit applications, although they are also suitable for new construction: simple radiant panels that communicate directly with the building interior and a backflow thermosiphon that provides heat indirectly.

  8. Determination of heavy metals impurities in low and medium atomic weight matrices

    Paiano, Silvestre; Prado Souza, Rose M.G. do

    1997-01-01

    Heavy materials have a mass attenuation coefficient in the energy interval from 100 to 400 KeV substantially higher than those corresponding to light and medium atomic weight matrices. They also show, in the same energy range, a more pronounced energy variation of this parameter. In a few cases, this property can be used for the determination of the concentration of impurities constituted by heavy metals in a lighter matrix. An Ytterbium gamma-ray source, which has several energy peaks in the considered interval, is used to supply a number of energy pairs from which the density of impurities can be found without the use of reference materials. (author). 1 ref., 4 figs

  9. High frequency measurements of shot noise suppression in atomic-scale metal contacts

    Wheeler, Patrick J.; Evans, Kenneth; Russom, Jeffrey; King, Nicholas; Natelson, Douglas

    2009-03-01

    Shot noise provides a means of assessing the number and transmission coefficients of transmitting channels in atomic- and molecular-scale junctions. Previous experiments at low temperatures in metal and semiconductor point contacts have demonstrated the expected suppression of shot noise when junction conductance is near an integer multiple of the conductance quantum, G0≡2e^2/h. Using high frequency techniques, we demonstrate the high speed acquisition of such data at room temperature in mechanical break junctions. In clean Au contacts conductance histograms with clear peaks at G0, 2G0, and 3G0 are acquired within hours, and histograms of simultaneous measurements of the shot noise show clear suppression at those conductance values. We describe the dependence of the noise on bias voltage and analyze the noise vs. conductance histograms in terms of a model that averages over transmission coefficients.

  10. Atomic-layer-deposited WNxCy thin films as diffusion barrier for copper metallization

    Kim, Soo-Hyun; Oh, Su Suk; Kim, Ki-Bum; Kang, Dae-Hwan; Li, Wei-Min; Haukka, Suvi; Tuominen, Marko

    2003-06-01

    The properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethyl boron as source gases were characterized as a diffusion barrier for copper metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΩ cm with a film density of 15.37 g/cm3. The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of ˜48, 32, and 20 at. %, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1-x and β-W2N with an equiaxed microstructure. The barrier property of this ALD-WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700 °C for 30 min.

  11. Transition metal atoms absorbed on MoS2/h-BN heterostructure: stable geometries, band structures and magnetic properties.

    Wu, Yanbing; Huang, Zongyu; Liu, Huating; He, Chaoyu; Xue, Lin; Qi, Xiang; Zhong, Jianxin

    2018-06-15

    We have studied the stable geometries, band structures and magnetic properties of transition-metal (V, Cr, Mn, Fe, Co and Ni) atoms absorbed on MoS2/h-BN heterostructure systems by first-principles calculations. By comparing the adsorption energies, we find that the adsorbed transition metal (TM) atoms prefer to stay on the top of Mo atoms. The results of the band structure without spin-orbit coupling (SOC) interaction indicate that the Cr-absorbed systems behave in a similar manner to metals, and the Co-absorbed system exhibits a half-metallic state. We also deduce that the V-, Mn-, Fe-absorbed systems are semiconductors with 100% spin polarization at the HOMO level. The Ni-absorbed system is a nonmagnetic semiconductor. In contrast, the Co-absorbed system exhibits metallic state, and the bandgap of V-absorbed system decreases slightly according to the SOC calculations. In addition, the magnetic moments of all the six TM atoms absorbed on the MoS2/h-BN heterostructure systems decrease when compared with those of their free-standing states.

  12. Heat transfer enhancement in energy storage in spherical capsules filled with paraffin wax and metal beads

    Ettouney, Hisham; Alatiqi, Imad; Al-Sahali, Mohammad; Al-Hajirie, Khalida

    2006-01-01

    Energy storage is an attractive option to conserve limited energy resources, where more than 50% of the generated industrial energy is discarded in cooling water and stack gases. This study focuses on the evaluation of heat transfer enhancement in phase change energy storage units. The experiments are performed using spherical capsules filled with paraffin wax and metal beads. The experiments are conducted by inserting a single spherical capsule filled with wax and metal beads in a stream of hot/cold air. Experimental measurements include the temperature field within the spherical capsule and in the air stream. To determine the enhancement effects of the metal beads, the measured data is correlated against those for a spherical capsule filled with pure wax. Data analysis shows a reduction of 15% in the melting and solidification times upon increasing the number and diameter of the metal beads. This reduction is caused by a similar decrease in the thermal load of the sphere due to replacement of the wax by metal beads. The small size of the spherical capsule limits the enhancement effects; this is evident upon comparison of the heat transfer in a larger size, double pipe energy storage unit, where 2% of the wax volume is replaced with metal inserts, result in a three fold reduction in the melting/solidification time and a similar enhancement in the heat transfer rate

  13. Flameless atomic absorption determination of noble metals after extraction by mixture of di-2-ethylhexyldithiophosphoric acid and n-octylaniline

    Yukhin, Yu.M.; Udalova, T.A.; Tsimbalist, V.G.; AN SSSR, Novosibirsk. Inst. Geologii i Geofiziki)

    1985-01-01

    A possibility of using the mixture of di-2-ethylhexyl dithiophosphoric acid (D2EHDTPA) and p-octylaniline (OA) (extractants of acid and basic character) for extraction atomic absorption determination of noble metals is studied. The mixture of D2EHDTPA with OA is shown to extract noble metals from hydrochloric acid solutions with distribution factors > 10 3 . An extraction atomic absorption method for determination of noble metals in copperbearing materials is suggested. The minimum determined contents of noble metals at the initial sample equal to 100 for gold, silver, platinum, palladium, rhodium and ruthenium make up (g/t) 0.0005, 0.0001, 0.015, 0.005, 0.002 and 0.015 respectively. Relative standard deviation constitutes Ssub(r)<0.2

  14. Heat transfer of liquid-metal magnetohydrodynamic flow with internal heat generation

    Kumamaru, Hiroshige; Kurita, Kazuhisa; Kodama, Satoshi

    2000-01-01

    Numerical calculations on heat transfer of a magnetohydrodynamic (MHD) flow with internal heat generation in a rectangular channel have been performed for the cases of very-large Hartmann numbers, finite wall conductivities and small aspect ratio (i.e. small length ratios of the channel side perpendicular to the applied magnetic field and the side parallel to the field), simulating typical conditions for a fusion-reactor blanket. The Nusselt numbers of the MHD flow in rectangular channels with aspect ratios of 1/10 to 1/40 for Hartmann numbers of ∼5 x 10 5 become ∼10 times higher than those for the corresponding flow under no magnetic field. The Nusselt number becomes higher as the internal heat generation rate increases as far as the heat generation rates in a fusion reactor blanket are considered. (author)

  15. Beneficial effects of microwave-assisted heating versus conventional heating in noble metal nanoparticle synthesis.

    Dahal, Naween; García, Stephany; Zhou, Jiping; Humphrey, Simon M

    2012-11-27

    An extensive comparative study of the effects of microwave versus conventional heating on the nucleation and growth of near-monodisperse Rh, Pd, and Pt nanoparticles has revealed distinct and preferential effects of the microwave heating method. A one-pot synthetic method has been investigated, which combines nucleation and growth in a single reaction via precise control over the precursor addition rate. Using this method, microwave-assisted heating enables the convenient preparation of polymer-capped nanoparticles with improved monodispersity, morphological control, and higher crystallinity, compared with samples heated conventionally under otherwise identical conditions. Extensive studies of Rh nanoparticle formation reveal fundamental differences during the nucleation phase that is directly dependent on the heating method; microwave irradiation was found to provide more uniform seeds for the subsequent growth of larger nanostructures of desired size and surface structure. Nanoparticle growth kinetics are also markedly different under microwave heating. While conventional heating generally yields particles with mixed morphologies, microwave synthesis consistently provides a majority of tetrahedral particles at intermediate sizes (5-7 nm) or larger cubes (8+ nm) upon further growth. High-resolution transmission electron microscopy indicates that Rh seeds and larger nanoparticles obtained from microwave-assisted synthesis are more highly crystalline and faceted versus their conventionally prepared counterparts. Microwave-prepared Rh nanoparticles also show approximately twice the catalytic activity of similar-sized conventionally prepared particles, as demonstrated in the vapor-phase hydrogenation of cyclohexene. Ligand exchange reactions to replace polymer capping agents with molecular stabilizing agents are also easily facilitated under microwave heating, due to the excitation of polar organic moieties; the ligand exchange proceeds with excellent retention of

  16. Efficient atomization of cesium metal in solid helium by low energy (10 $\\mu$J) femtosecond pulses

    Melich, Mathieu; Dupont-Roc, Jacques; Jacquier, Philippe

    2009-01-01

    International audience; Metal atoms in solid and liquid helium-4 have attracted some interest either as a way to keep the atoms in a weakly perturbing matrix, or using them as a probe for the helium host medium. Laser sputtering with nanosecond pulsed lasers is the most often used method for atom production, resulting however in a substantial perturbation of the matrix. We show that a much weaker perturbation can be obtained by using femtosecond laser pulses with energy as low as 10 µJ. As an...

  17. Analysis of trace metals in sodium by flameless atomic absorption spectrophotometry

    Mahalingam, T.R.; Geetha, R.; Thiruvengadasamy, A.; Mathews, C.K.

    1981-01-01

    The estimation of trace metallic impurities in sodium is normally carried out by distilling off the sodium in vacuuum and analysing the residue by atomic absorption spectrophotometry (AAS). This paper describes the direct determination of the following impurities (viz.) Fe, Co, Ni, Cr, Mn, Ca, and Cu in sodium without going through the distillation step. Here sodium is simply dissolved and the solution is subjected to analysis by AAS using flameless atomisation in a graphite furnace. The method of standard additions is employed. Preliminary experiments were carried out to study the matrix effect of sodium on the atomic absorption of cobalt. It has been found that if pyrolysis is done at 1250 0 C for 20 seconds prior to atomisation, the bulk of the sodium nitrate matrix could be successfully removed. The use of the optimum pyrolysis temperatures for the various elements listed above and the matrix interference on the absorbances of these analytes are discussed in this paper. The precision and accuracy of our analytical procedure is also presented. (orig.)

  18. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage.

    Cho, Eun Seon; Ruminski, Anne M; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  19. Trace moisture emissions from heated metal surfaces in hydrogen service

    Funke, Hans H.; Yao Jianlong; Raynor, Mark W.

    2004-01-01

    The formation of trace moisture by exposure of dry heated surfaces of 316 L stainless-steel, Restek Silcosteel registered , and nickel 1/8 in. outer diameter line segments to purified Ar and H 2 was studied using atmospheric pressure ionization mass spectrometry at flow rates of 2 slpm. Prior to H 2 exposure, adsorbed moisture was removed by heating incrementally to 500 deg. C in an argon matrix, where the Restek Silcosteel registered material released a maximum of 50 ppb moisture at 300 deg. C and moisture spikes from the Ni and stainless-steel surfaces reached several 100 ppb. Upon exposure to H 2 , persistent low ppb moisture emissions due to the reduction of surface oxide species were observed at temperatures as low as 100 deg. C. Spikes at 300-500 deg. C ranged from ∼100 ppb for the stainless-steel lines to 400 ppb for the Restek Silcosteel registered material. The observed moisture emissions have to be considered as a potential contamination source for high-purity processes utilizing H 2 purge at elevated temperatures

  20. The direct heat measurement of mechanical energy storage metal-organic frameworks.

    Rodriguez, Julien; Beurroies, Isabelle; Loiseau, Thierry; Denoyel, Renaud; Llewellyn, Philip L

    2015-04-07

    In any process, the heat exchanged is an essential property required in its development. Whilst the work related to structural transitions of some flexible metal-organic frameworks (MOFs) has been quantified and linked with potential applications such as molecular springs or shock absorbers, the heat related to such transitions has never been directly measured. This has now been carried out with MIL-53(Al) using specifically devised calorimetry experiments. We project the importance of these heats in devices such as molecular springs or dampers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Aging of iron (hydr)oxides by heat treatment and effects on heavy metal binding

    Sørensen, Mette Abildgaard; Starckpoole, M. M.; Frenkel, A. I.

    2000-01-01

    their transformations caused by heat treatment prior to disposal or aging at a proper disposal site. The transformations were investigated by XRD, SEM, XANES, EXAFS, surface area measurements, pH static leaching tests, and extractions with oxalate and weak hydrochloric acid. It was found that at 600 and 900 °C the iron...... oxides were transformed to hematite, which had a greater thermodynamic stability but less surface area than the initial products. Heat treatment also caused some volatilization of heavy metals (most notably, Hg). Leaching with water at pH 9 (L/S 10, 24 h) and weak acid extraction showed that heat...

  2. Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

    Herrero Latorre, C., E-mail: carlos.herrero@usc.es [Universidad de Santiago de Compostela, Dpto. Quimica Analitica, Nutricion y Bromatologia, Facultad de Ciencias, Alfonso X el Sabio s/n, 27002 Lugo (Spain); Alvarez Mendez, J.; Barciela Garcia, J.; Garcia Martin, S.; Pena Crecente, R.M. [Universidad de Santiago de Compostela, Dpto. Quimica Analitica, Nutricion y Bromatologia, Facultad de Ciencias, Alfonso X el Sabio s/n, 27002 Lugo (Spain)

    2012-10-24

    Highlights: Black-Right-Pointing-Pointer The use of CNTs as sorbent for metal species in solid phase extraction has been described. Black-Right-Pointing-Pointer Physical and chemical strategies for functionalization of carbon nanotubes have been discussed. Black-Right-Pointing-Pointer Published analytical methods concerning solid phase extraction and atomic spectrometric determination have been reviewed. - Abstract: New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes - due to their high adsorption and desorption capacities - have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.

  3. Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

    Herrero Latorre, C.; Álvarez Méndez, J.; Barciela García, J.; García Martín, S.; Peña Crecente, R.M.

    2012-01-01

    Highlights: ► The use of CNTs as sorbent for metal species in solid phase extraction has been described. ► Physical and chemical strategies for functionalization of carbon nanotubes have been discussed. ► Published analytical methods concerning solid phase extraction and atomic spectrometric determination have been reviewed. - Abstract: New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.

  4. Reversible mechano-electrochemical writing of metallic nanostructures with the tip of an atomic force microscope

    Christian Obermair

    2012-12-01

    Full Text Available We recently introduced a method that allows the controlled deposition of nanoscale metallic patterns at defined locations using the tip of an atomic force microscope (AFM as a “mechano-electrochemical pen”, locally activating a passivated substrate surface for site-selective electrochemical deposition. Here, we demonstrate the reversibility of this process and study the long-term stability of the resulting metallic structures. The remarkable stability for more than 1.5 years under ambient air without any observable changes can be attributed to self-passivation. After AFM-activated electrochemical deposition of copper nanostructures on a polycrystalline gold film and subsequent AFM imaging, the copper nanostructures could be dissolved by reversing the electrochemical potential. Subsequent AFM-tip-activated deposition of different copper nanostructures at the same location where the previous structures were deleted, shows that there is no observable memory effect, i.e., no effect of the previous writing process on the subsequent writing process. Thus, the four processes required for reversible information storage, “write”, “read”, “delete” and “re-write”, were successfully demonstrated on the nanometer scale.

  5. Toxic metals distribution in different components of Pakistani and imported cigarettes by electrothermal atomic absorption spectrometer

    Kazi, T.G.; Jalbani, N.; Arain, M.B.; Jamali, M.K.; Afridi, H.I.; Sarfraz, R.A.; Shah, A.Q.

    2009-01-01

    It was extensively investigated that a significant flux of toxic metals, along with other toxins, reaches the lungs through smoking. In present study toxic metals (TMs) (Al, Cd, Ni and Pb) were determined in different components of Pakistani local branded and imported cigarettes, including filler tobacco (FT), filter (before and after normal smoking by a single volunteer) and ash by electrothermal atomic absorption spectrometer (ETAAS). Microwave-assisted digestion method was employed. The validity and accuracy of methodology were checked by using certified sample of Virginia tobacco leaves (ICHTJ-cta-VTL-2). The percentages (%) of TMs in different components of cigarette were calculated with respect to their total contents in FT of all branded cigarettes before smoking, while smoke concentration has been calculated by subtracting the filter and ash contents from the filler tobacco content of each branded cigarette. The highest percentage (%) of Al was observed in ash of all cigarettes, with range 97.3-99.0%, while in the case of Cd, a reverse behaviour was observed, as a range of 15.0-31.3% of total contents were left in the ash of all branded cigarettes understudy

  6. Thermal stability of atomic layer deposited WCxNy electrodes for metal oxide semiconductor devices

    Zonensain, Oren; Fadida, Sivan; Fisher, Ilanit; Gao, Juwen; Danek, Michal; Eizenberg, Moshe

    2018-01-01

    This study is a thorough investigation of the chemical, structural, and electrical stability of W based organo-metallic films, grown by atomic layer deposition, for future use as gate electrodes in advanced metal oxide semiconductor structures. In an earlier work, we have shown that high effective work-function (4.7 eV) was produced by nitrogen enriched films (WCxNy) dominated by W-N chemical bonding, and low effective work-function (4.2 eV) was produced by hydrogen plasma resulting in WCx films dominated by W-C chemical bonding. In the current work, we observe, using x-ray diffraction analysis, phase transformation of the tungsten carbide and tungsten nitride phases after 900 °C annealing to the cubic tungsten phase. Nitrogen diffusion is also observed and is analyzed with time-of-flight secondary ion mass spectroscopy. After this 900 °C anneal, WCxNy effective work function tunability is lost and effective work-function values of 4.7-4.8 eV are measured, similar to stable effective work function values measured for PVD TiN up to 900 °C anneal. All the observed changes after annealing are discussed and correlated to the observed change in the effective work function.

  7. Reversible mechano-electrochemical writing of metallic nanostructures with the tip of an atomic force microscope.

    Obermair, Christian; Kress, Marina; Wagner, Andreas; Schimmel, Thomas

    2012-01-01

    We recently introduced a method that allows the controlled deposition of nanoscale metallic patterns at defined locations using the tip of an atomic force microscope (AFM) as a "mechano-electrochemical pen", locally activating a passivated substrate surface for site-selective electrochemical deposition. Here, we demonstrate the reversibility of this process and study the long-term stability of the resulting metallic structures. The remarkable stability for more than 1.5 years under ambient air without any observable changes can be attributed to self-passivation. After AFM-activated electrochemical deposition of copper nanostructures on a polycrystalline gold film and subsequent AFM imaging, the copper nanostructures could be dissolved by reversing the electrochemical potential. Subsequent AFM-tip-activated deposition of different copper nanostructures at the same location where the previous structures were deleted, shows that there is no observable memory effect, i.e., no effect of the previous writing process on the subsequent writing process. Thus, the four processes required for reversible information storage, "write", "read", "delete" and "re-write", were successfully demonstrated on the nanometer scale.

  8. Test results from a helium gas-cooled porous metal heat exchanger

    North, M.T.; Rosenfeld, J.H.; Youchison, D.L.

    1996-01-01

    A helium-cooled porous metal heat exchanger was built and tested, which successfully absorbed heat fluxes exceeding all previously tested gas-cooled designs. Helium-cooled plasma-facing components are being evaluated for fusion applications. Helium is a favorable coolant for fusion devices because it is not a plasma contaminant, it is not easily activated, and it is easily removed from the device in the event of a leak. The main drawback of gas coolants is their relatively poor thermal transport properties. This limitation can be removed through use of a highly efficient heat exchanger design. A low flow resistance porous metal heat exchanger design was developed, based on the requirements for the Faraday shield for the International Thermonuclear Experimental Reactor (ITER) device. High heat flux tests were conducted on two representative test articles at the Plasma Materials Test Facility (PMTF) at Sandia National Laboratories. Absorbed heat fluxes as high as 40 MW/m 2 were successfully removed during these tests without failure of the devices. Commercial applications for electronics cooling and other high heat flux applications are being identified

  9. Effects of halogens on interactions between a reduced TiO{sub 2} (110) surface and noble metal atoms: A DFT study

    Tada, Kohei, E-mail: k-tada@aist.go.jp [Department of Chemistry, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043 (Japan); Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka, 563-8577 (Japan); Koga, Hiroaki [Element Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, 1-30 Goryo Ohara, Nishikyo, Kyoto, 615-8245 (Japan); Hayashi, Akihide; Kondo, Yudai; Kawakami, Takashi; Yamanaka, Shusuke [Department of Chemistry, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043 (Japan); Okumura, Mitsutaka [Department of Chemistry, Graduate School of Science, Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka, 560-0043 (Japan); Element Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, 1-30 Goryo Ohara, Nishikyo, Kyoto, 615-8245 (Japan)

    2017-07-31

    Highlights: • We investigated the halogen effect on the interactions of noble metals with TiO{sub 2}. • Halogen atoms inhibit electron transfer from TiO{sub 2} to noble metals. • Iodine stabilizes the adsorption of noble metals especially for Ag and Cu. • Electron transfer from the TiO{sub 2} is effective in anchoring Au and Pt atoms. • Covalent interaction with the support is effective in anchoring Ag and Cu atoms. - Abstract: Using DFT calculation, we investigate the effects of halogens on the interactions between rutile TiO{sub 2} (110) and noble metal atoms (Au, Ag, Cu, Pt, and Pd). Fluorine, chlorine, and bromine atoms occupy the oxygen defect sites of TiO{sub 2}, decreasing the stability of noble metal atoms on the surface. This decrease occurs because the halogens inhibit electron transfer from TiO{sub 2} to the noble metal atoms; the electron transfer from reduced TiO{sub 2} to the noble metal atom stabilizes the noble metal atom adsorption. In contrast, iodine strengthens the interactions between TiO{sub 2} and some noble metal atoms, namely Ag and Cu. This stabilization occurs because of the covalent interaction between iodine-doped TiO{sub 2} and the noble metal atom. Therefore, the stabilization is explained well by chemical hardness. This result suggests that iodine-doping of a TiO{sub 2} surface would be an effective method for the preparation of highly stabilized noble metal clusters.

  10. T5 heat treatment of semi-solid metal processed aluminium alloy F357

    Moller, H

    2009-04-01

    Full Text Available The T5 heat treatment of semi-solid metal (SSM) processed alloy F357 was investigated by considering the effects of cooling rate and natural aging after casting, as well as artificial aging parameters on tensile properties. In addition, the tensile...

  11. Evaporation equipment with electron beam heating for the evaporation of metals and other conducting materials

    Mueller, P.

    1977-01-01

    Equipment for the evaporation of metals and other conducting materials by electron beam heating is to be improved by surrou nding the evaporation equipment with a grid, which has a negative voltage compared to the cathode. This achieves the state where the cathode is hit and damaged less by the ions formed, so that its life period is prolonged. (UWI) [de

  12. Simplified computational simulation of liquid metal behaviour in turbulent flow with heat transfer

    Costa, E.B. da.

    1992-09-01

    The present work selected the available bibliography equations and empirical relationships to the development of a computer code to obtain the turbulent velocity and temperature profiles in liquid metal tube flow with heat generation. The computer code is applied to a standard problem and the results are considered satisfactory, at least from the viewpoint of qualitative behaviour. (author). 50 refs, 21 figs, 3 tabs

  13. Significant enhancement of metal heat dissipation from mechanically exfoliated graphene nanosheets through thermal radiation effect

    Junxiong Hu

    2017-05-01

    Full Text Available We demonstrate a facile approach to significantly enhance the heat dissipation potential of conventional aluminum (Al heat sinks by mechanically coating graphene nanosheets. For Al and graphene-coated Al heat sinks, the change in temperature with change in coating coverage, coating thickness and heat flux are studied. It is found that with the increase in coating coverage from 0 to 100%, the steady-state temperature is decreased by 5 °C at a heat flux of 1.8 W cm-1. By increasing the average thickness of graphene coating from 480 nm to 1900 nm, a remarkable temperature reduction up to 7 °C can be observed. Moreover, with the increase in heat flux from 1.2 W cm-1 to 2.4 W cm-1, the temperature difference between uncoated and graphene-coated samples increases from 1 °C to 6 °C. The thermal analysis and finite element simulation reveal that the thermal radiation plays a key role in enhancing the heat dissipation performance. The effect of heat convection remains weak owing to the low air velocity at surface-air boundary. This work provides a technological innovation in improving metal heat dissipation using graphene nanosheets.

  14. Transient thermal and nonthermal electron and phonon relaxation after short-pulsed laser heating of metals

    Giri, Ashutosh; Hopkins, Patrick E.

    2015-01-01

    Several dynamic thermal and nonthermal scattering processes affect ultrafast heat transfer in metals after short-pulsed laser heating. Even with decades of measurements of electron-phonon relaxation, the role of thermal vs. nonthermal electron and phonon scattering on overall electron energy transfer to the phonons remains unclear. In this work, we derive an analytical expression for the electron-phonon coupling factor in a metal that includes contributions from equilibrium and nonequilibrium distributions of electrons. While the contribution from the nonthermal electrons to electron-phonon coupling is non-negligible, the increase in the electron relaxation rates with increasing laser fluence measured by thermoreflectance techniques cannot be accounted for by only considering electron-phonon relaxations. We conclude that electron-electron scattering along with electron-phonon scattering have to be considered simultaneously to correctly predict the transient nature of electron relaxation during and after short-pulsed heating of metals at elevated electron temperatures. Furthermore, for high electron temperature perturbations achieved at high absorbed laser fluences, we show good agreement between our model, which accounts for d-band excitations, and previous experimental data. Our model can be extended to other free electron metals with the knowledge of the density of states of electrons in the metals and considering electronic excitations from non-Fermi surface states

  15. Heat-driven liquid metal cooling device for the thermal management of a computer chip

    Ma Kunquan; Liu Jing [Cryogenic Laboratory, PO Box 2711, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080 (China)

    2007-08-07

    The tremendous heat generated in a computer chip or very large scale integrated circuit raises many challenging issues to be solved. Recently, liquid metal with a low melting point was established as the most conductive coolant for efficiently cooling the computer chip. Here, by making full use of the double merits of the liquid metal, i.e. superior heat transfer performance and electromagnetically drivable ability, we demonstrate for the first time the liquid-cooling concept for the thermal management of a computer chip using waste heat to power the thermoelectric generator (TEG) and thus the flow of the liquid metal. Such a device consumes no external net energy, which warrants it a self-supporting and completely silent liquid-cooling module. Experiments on devices driven by one or two stage TEGs indicate that a dramatic temperature drop on the simulating chip has been realized without the aid of any fans. The higher the heat load, the larger will be the temperature decrease caused by the cooling device. Further, the two TEGs will generate a larger current if a copper plate is sandwiched between them to enhance heat dissipation there. This new method is expected to be significant in future thermal management of a desk or notebook computer, where both efficient cooling and extremely low energy consumption are of major concern.

  16. Heat-driven liquid metal cooling device for the thermal management of a computer chip

    Ma Kunquan; Liu Jing

    2007-01-01

    The tremendous heat generated in a computer chip or very large scale integrated circuit raises many challenging issues to be solved. Recently, liquid metal with a low melting point was established as the most conductive coolant for efficiently cooling the computer chip. Here, by making full use of the double merits of the liquid metal, i.e. superior heat transfer performance and electromagnetically drivable ability, we demonstrate for the first time the liquid-cooling concept for the thermal management of a computer chip using waste heat to power the thermoelectric generator (TEG) and thus the flow of the liquid metal. Such a device consumes no external net energy, which warrants it a self-supporting and completely silent liquid-cooling module. Experiments on devices driven by one or two stage TEGs indicate that a dramatic temperature drop on the simulating chip has been realized without the aid of any fans. The higher the heat load, the larger will be the temperature decrease caused by the cooling device. Further, the two TEGs will generate a larger current if a copper plate is sandwiched between them to enhance heat dissipation there. This new method is expected to be significant in future thermal management of a desk or notebook computer, where both efficient cooling and extremely low energy consumption are of major concern

  17. Assembling three-dimensional nanostructures on metal surfaces with a reversible vertical single-atom manipulation: A theoretical modeling

    Yang Tianxing; Ye Xiang; Huang Lei; Xie Yiqun; Ke Sanhuang

    2012-01-01

    Highlights: ► We simulate the reversible vertical single-atom manipulations on several metal surfaces. ► We propose a method to predict whether a reversible vertical single-atom manipulation can be successful on several metal surfaces. ► A 3-dimensional Ni nanocluster is assembled on the Ni(1 1 1) surface using a Ni trimer-apex tip. - Abstract: We propose a theoretical model to show that pulling up an adatom from an atomic step requires a weaker force than from the flat surfaces of Al(0 0 1), Ni(1 1 1), Pt(1 1 0) and Au(1 1 0). Single adatom in the atomic step can be extracted vertically by a trimer-apex tip while can be released to the flat surface. This reversible vertical manipulation can then be used to fabricate a supported three-dimensional (3D) nanostructure on the Ni(1 1 1) surface. The present modeling can be used to predict whether the reversible vertical single-atom manipulation and thus the assembling of 3D nanostructures can be achieved on a metal surface.

  18. Reactivity of transition metal atoms supported or not on TiO2(110) toward CO and H adsorption

    Helali, Zeineb; Jedidi, Abdesslem; Markovits, Alexis; Minot, Christian; Abderrabba, Manef Ben

    2015-01-01

    Following our strategy to analyze the metal–support interaction, we present periodic DFT calculations for adsorption of metal atoms on a perfect rutile TiO2(110) surface (at low coverage, θ = 1/3) to investigate the interaction of an individual

  19. Influence of a transition metal atom on the geometry and electronic structure of Mg and Mg-H clusters

    Siretskiy, M.Yu.; Shelyapina, M.G.; Fruchart, D.; Miraglia, S.; Skryabina, N.E.

    2009-01-01

    We report on the study of (MgH 2 ) n + M complexes (M = Ti or Ni) carried out within the framework of the cluster density functional theory (DFT) method. The influence of such transition metal atoms on the cluster geometry and electronic structure is discussed considering the stability of MgH 2 hydride.

  20. Determination of heat transfer coefficient for an interaction of sub-cooled gas and metal

    Sidek, Mohd Zaidi; Kamarudin, Muhammad Syahidan

    2016-01-01

    Heat transfer coefficient (HTC) for a hot metal surface and their surrounding is one of the need be defined parameter in hot forming process. This study has been conducted to determine the HTC for an interaction between sub-cooled gas sprayed on a hot metal surface. Both experiments and finite element have been adopted in this work. Initially, the designated experiment was conducted to obtain temperature history of spray cooling process. Then, an inverse method was adopted to calculate the HTC value before we validate in a finite element simulation model. The result shows that the heat transfer coefficient for interaction of subcooled gas and hot metal surface is 1000 W/m 2 K. (paper)

  1. Investigation of the atom-atom and structural relaxation in liquid alkali metals by means of the memory function formalism

    Blagoveshchenskii, N. M.; Novikov, A. G.; Savostin, V. V.

    2011-01-01

    An attempt is made to systematize the data on the relaxation characteristics of liquid alkali metals (Li, Na, and K), which were investigated based on neutron-scattering data with the application of the two-time memory function formalism.

  2. Laminar natural convection heat transfer from a horizontal circular cylinder to liquid metals

    Sugiyama, K.; Ma, Y.; Ishiguro, R.

    1991-01-01

    The objective of the present study is to clarify the heat transfer characteristic of natural convection around a horizontal circular cylinder immersed in liquid metals. Experimental work concerning liquid metals sometimes involves such a degree of error that is impossible to understand the observed characteristics in measurement. Numerical analysis is a powerful means to overcome this experimental disadvantage. In the present paper the authors first show that the Boussinesq approximation is more applicable heat transfer rates, even for a cylinder with a relatively large temperature difference (>100K) between the heat transfer surface and fluid. It is found from a comparison of the present results with previous work that the correlation equations that have already been proposed predict values lower than the present ones

  3. Influence of Strain Rate on Heat Release under Quasi-Static Stretching of Metals. Experiment

    Zimin, B. A.; Sventitskaya, V. E.; Smirnov, I. V.; Sud'enkov, Yu. V.

    2018-04-01

    The paper presents the results of experimental studies of energy dissipation during a quasi-static stretching of metals and alloys at room temperature. The strain rates varied in the range of 10-3-10-2 s-1. Samples of M1 copper, AZ31B magnesium alloy, BT6 titanium, 12Cr18Ni10Ti steel, and D16AM aluminum alloy were analyzed. The experimental results demonstrated a significant dependence of the heat release on the strain rate in the absence of its influence on stress-strain diagrams for all the metals studied in this range of strain rates. The correlation of the changes in the character of heat release with the processes of structural transformations at various stages of plastic flow is shown on the qualitative level. A difference in the nature of the processes of heat release in materials with different ratios of the plasticity and strength is noted.

  4. Liquid metal MHD and heat transfer in a tokamak blanket slotted coolant channel

    Reed, C.B.; Hua, T.Q.; Black, D.B.; Kirillov, I.R.; Sidorenkov, S.I.; Shapiro, A.M.; Evtushenko, I.A.

    1993-01-01

    A liquid metal MHD (Magnetohydrodynamic)/heat transfer test was conducted at the ALEX (Argonne Liquid Metal Experiment) facility of ANL (Argonne National Laboratory), jointly between ANL and NIIEFA (Efremov Institute). The test section was a rectangular slotted channel geometry (meaning the channel has a high aspect ratio, in this case 10:1, and the long side is parallel to the applied magnetic field). Isothermal and heat transfer data were collected. A heat flux of ∼9 W/cm 2 was applied to the top horizontal surface (the long side) of the test section. Hartmann Numbers to 1050 (2 Tesla), interaction parameters to 9 x 10 3 , Peclet numbers of 10--200, based on the half-width of the small dimension (7mm), and velocities of 1--75 cm/sec. were achieved. The working fluid was NaK (sodium potassium eutectic). All four interior walls were bare, 300-series stainless steel, conducting walls

  5. Theoretical investigation of the use of nanocages with an adsorbed halogen atom as anode materials in metal-ion batteries.

    Razavi, Razieh; Abrishamifar, Seyyed Milad; Rajaei, Gholamreza Ebrahimzadeh; Kahkha, Mohammad Reza Rezaei; Najafi, Meysam

    2018-02-21

    The applicability of C 44 , B 22 N 22 , Ge 44 , and Al 22 P 22 nanocages, as well as variants of those nanocages with an adsorbed halogen atom, as high-performance anode materials in Li-ion, Na-ion, and K-ion batteries was investigated theoretically via density functional theory. The results obtained indicate that, among the nanocages with no adsorbed halogen atom, Al 22 P 22 would be the best candidate for a novel anode material for use in metal-ion batteries. Calculations also suggest that K-ion batteries which utilize these nanocages as anode materials would give better performance and would yield higher cell voltages than the corresponding Li-ion and Na-ion batteries with nanocage-based anodes. Also, the results for the nanocages with an adsorbed halogen atom imply that employing them as anode materials would lead to higher cell voltages and better metal-ion battery performance than if the nanocages with no adsorbed halogen atom were to be used as anode materials instead. Results further implied that nanocages with an adsorbed F atom would give higher cell voltages and better battery performance than nanocages with an adsorbed Cl or Br atom. We were ultimately able to conclude that a K-ion battery that utilized Al 21 P 22 with an adsorbed F atom as its anode material would afford the best metal-ion battery performance; we therefore propose this as a novel highly efficient metal-ion battery. Graphical abstract The results of a theoretical investigation indicated that Al 22 P 22 is a better candidate for a high-performance anode material in metal-ion batteries than Ge 44 is. Calculations also showed that K-ion batteries with nanocage-based anodes would produce higher cell voltages and perform better than the equivalent Li-ion and Na-ion batteries with nanocage-based anodes, and that anodes based on nanocages with an adsorbed F atom would perform better than anodes based on nanocages with an adsorbed Cl or Br atom.

  6. Heat energy from hydrogen-metal nuclear interactions

    Hadjichristos, John [Defkalion GT SA, 1140 Homer Street, Suite 250, Vancouver BC V682X6 (Canada); Gluck, Peter [Retired from INCDTIM Cluj-Napoca in 1999 (Romania)

    2013-11-13

    The discovery of the Fleischmann-Pons Effect in 1989, a promise of an abundant, cheap and clean energy source was premature in the sense that theoretical knowledge, relative technologies and the experimental tools necessary for understanding and for scale-up still were not available. Therefore the field, despite efforts and diversification remained quasi-stagnant, the effect (a scientific certainty) being of low intensity leading to mainstream science to reject the phenomenon and not supporting its study. Recently however, the situation has changed, a new paradigm is in statunascendi and the obstacles are systematically removed by innovative approaches. Defkalion, a Greek company (that recently moved in Canada for faster progress) has elaborated an original technology for the Ni-H system [1-3]. It is about the activation of hydrogen and creation of nuclear active nano-cavities in the metal through a multi-stage interaction, materializing some recent breakthrough announcements in nanotechnology, superconductivity, plasma physics, astrophysics and material science. A pre-industrial generator and a novel mass-spectrometry instrumentations were created. Simultaneously, a meta-theory of phenomena was sketched in collaboration with Prof. Y. Kim (Purdue U)

  7. Heat energy from hydrogen-metal nuclear interactions

    Hadjichristos, John; Gluck, Peter

    2013-01-01

    The discovery of the Fleischmann-Pons Effect in 1989, a promise of an abundant, cheap and clean energy source was premature in the sense that theoretical knowledge, relative technologies and the experimental tools necessary for understanding and for scale-up still were not available. Therefore the field, despite efforts and diversification remained quasi-stagnant, the effect (a scientific certainty) being of low intensity leading to mainstream science to reject the phenomenon and not supporting its study. Recently however, the situation has changed, a new paradigm is in statunascendi and the obstacles are systematically removed by innovative approaches. Defkalion, a Greek company (that recently moved in Canada for faster progress) has elaborated an original technology for the Ni-H system [1-3]. It is about the activation of hydrogen and creation of nuclear active nano-cavities in the metal through a multi-stage interaction, materializing some recent breakthrough announcements in nanotechnology, superconductivity, plasma physics, astrophysics and material science. A pre-industrial generator and a novel mass-spectrometry instrumentations were created. Simultaneously, a meta-theory of phenomena was sketched in collaboration with Prof. Y. Kim (Purdue U)

  8. Atomic reactor thermal engineering

    Kim, Gwang Ryong

    1983-02-01

    This book starts the introduction of atomic reactor thermal engineering including atomic reaction, chemical reaction, nuclear reaction neutron energy and soon. It explains heat transfer, heat production in the atomic reactor, heat transfer of fuel element in atomic reactor, heat transfer and flow of cooler, thermal design of atomic reactor, design of thermodynamics of atomic reactor and various. This deals with the basic knowledge of thermal engineering for atomic reactor.

  9. Atomic force microscopy and Raman scattering spectroscopy studies on heat-induced fibrous aggregates of β-lactoglobulin

    Ikeda, Shinya

    2003-01-01

    Nanometer-thick fibrous aggregates of β-lactoglobulin alone and its mixture with other globular proteins were formed by heating aqueous solutions at pH 2 with maintaining an effective level of electrostatic repulsion among denatured protein molecules. In atomic force microscopy (AFM) images, these fibrous aggregates appeared to be fairly uniform in width and height and composed of strings of globular elements. Fibrous aggregates formed in β-lactoglobulin individual systems were only slightly ...

  10. Three dimensional atom probe study of Ni-base alloy/low alloy steel dissimilar metal weld interfaces

    Choi, Kyoung Joon; Shin, Sang Hun; Kim, Jong Jin; Jung, Ju Ang; Kim, Ji Hyun

    2012-01-01

    Three dimensional atom probe tomography (3D APT) is applied to characterize the dissimilar metal joint which was welded between the Ni-based alloy, Alloy 690 and the low alloy steel, A533 Gr. B, with Alloy 152 filler metal. While there is some difficulty in preparing the specimen for the analysis, the 3D APT has a truly quantitative analytical capability to characterize nanometer scale particles in metallic materials, thus its application to the microstructural analysis in multicomponent metallic materials provides critical information on the mechanism of nanoscale microstructural evolution. In this study, the procedure for 3D APT specimen preparation was established, and those for dissimilar metal weld interface were prepared near the fusion boundary by a focused ion beam. The result of the analysis in this study showed the precipitation of chromium carbides near the fusion boundary between A533 Gr. B and Alloy 152.

  11. Three dimensional atom probe study of Ni-base alloy/low alloy steel dissimilar metal weld interfaces

    Choi, Kyoung Joon; Shin, Sang Hun; Kim, Jong Jin; Jung, Ju Ang; Kim, Ji Hyun [Interdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2012-08-15

    Three dimensional atom probe tomography (3D APT) is applied to characterize the dissimilar metal joint which was welded between the Ni-based alloy, Alloy 690 and the low alloy steel, A533 Gr. B, with Alloy 152 filler metal. While there is some difficulty in preparing the specimen for the analysis, the 3D APT has a truly quantitative analytical capability to characterize nanometer scale particles in metallic materials, thus its application to the microstructural analysis in multicomponent metallic materials provides critical information on the mechanism of nanoscale microstructural evolution. In this study, the procedure for 3D APT specimen preparation was established, and those for dissimilar metal weld interface were prepared near the fusion boundary by a focused ion beam. The result of the analysis in this study showed the precipitation of chromium carbides near the fusion boundary between A533 Gr. B and Alloy 152.

  12. Study of heavy metals in the grass-milk product chain by means of neutron activation and atomic absorption

    Bruant, C; Bruant, J P; Neuburger, M; Vassal, L; Disant, C; Bittel, R; Fourcy, A

    1974-12-31

    with the heavy metals Hg, Cu, Zn, Pb, and Cd is studied. The first three metals were determined by neutron activation and tae last two by atomic absorption spectrophotometry. The chemical rature of these metals and their biological effect leads to different results from those obtained for tae principal fission products. As a rule the heavy metal concentrations at harvest are much lower than taat of the foods ingested by lactating cows. The cow plays the role of filter. If the concentration of these elements is considered in mu g/g of fresh material there is a reconcentration of these heavy metals in cream and cheese, probably cornected with their physico-chemical affinity for proteins. (JSR)

  13. Inter-subchannel heat transfer modeling for a subchannel analysis of liquid metal-cooled reactors

    Hae-Yong, Jeong; Kwi-Seok, Ha; Young-Min, Kwon; Yong-Bum, Lee; Dohee, Hahn

    2007-01-01

    In a subchannel approach, the temperature, pressure and velocity in a subchannel are averaged, and one representative thermal-hydraulic condition specifies the state of a subchannel. To enhance the predictability of a subchannel analysis code, it is required to model the inter-subchannel heat transfer between the adjacent subchannels as accurately as possible. One of the critical parameters which determine the thermal-hydraulic behavior of the coolant in subchannels is the heat conduction between two neighboring sub-channels. This portion of a heat transfer becomes more important in the design of an LMR (Liquid Metal-cooled Reactor) because of the high heat capacity of the liquid metal coolant. The other important part of heat transfer is the mixing of flow as a form of cross flow. Especially, the turbulent mixing caused by the eddy motion of fluid across the gap between the subchannels enhances the exchange of the momentum and the energy through the gap with no net transport of the mass. Major results of recent efforts on these modeling have been implemented in a subchannel analysis code MATRA-LMR-FB. The analysis shows that the accuracy of a subchannel analysis code is improved by enhancing the models describing the conduction heat transfer and the cross-flow mixing, especially at low flow rate. (authors)

  14. Determination of concentration of heavy metals (Pb, Cd, Fe) in animal tissues using atomic absorption spectrometry

    RAZAFINTSALAMA, V.T.

    2009-01-01

    Heavy metals are classified among the inorganic compounds. The latter type of metal is found in rocks, fertilizers, urban mud but may also originate from the atmospheric pollution. A particular characteristic of heavy metals is their bioaccumulation in the food chain. Therefore, lead and cadmium, which are classified as heavy metals may be easily found in animal products and can lead to food poisoning if their concentrations are higher than the maximum permissible values as requested by international agencies such as the c odex alimentarius . The values are set down and differ according to types of food for human consuption and the trading companies take action accordingly. Therefore, it is necessary to set up a quality control system through analytical laboratory measurements and testings. This study underlies the method of determination of lead, cadmium and iron in animal tissues by atomic absorption spectrometry. The results showed that the method is sensitive and reliable. For each analyte, the Z-score lies between -2 and 2, indicating that the method is working properly. The analytical results showed that: (i) only beef and chicken meats and beef liver contain lead [0,09μg.g - 1; 0,29μg.g - 1]. The limit value of 0,1μg.g - 1 is almost reached in beef and chicken meats, (ii) as far as cadmium is concerned, the five studied samples contain this analyte [0,02μg.g - 1; 0,9μg.g - 1]. Except the chicken liver of which the concentration (0,15μg.g - 1) exceeds the maximum permissible value (0,1μg.g - 1), the others are in conformity with the standards and appropriate to be consumed,(iii) iron is higher in the liver and kidney samples: beef liver 282mg.g - 1, chicken liver 250 mg.g - 1, pork kidney 247mg.g - 1. The study also showed that the calcium concentration in animal tissues is low and they can be classified as poor-calcium food. [fr

  15. Metal hydride/chemical heat-pump development project. Phase I. Final report

    Argabright, T.A.

    1982-02-01

    The metal hydride/chemical heat pump (MHHP) is a chemical heat pump containing two hydrides for the storage and/or recovery of thermal energy. It utilizes the heat of reaction of hydrogen with specific metal alloys. The MHHP design can be tailored to provide heating and/or cooling or temperature upgrading over a wide range of input and ambient temperatures. The system can thus be used with a variety of heat sources including waste heat, solar energy or a fossil fuel. The conceptual design of the MHHP was developed. A national market survey including a study of applications and market sectors was conducted. The technical tasks including conceptual development, thermal and mechanical design, laboratory verification of design and material performance, cost analysis and the detailed design of the Engineering Development Test Unit (EDTU) were performed. As a result of the market study, the temperature upgrade cycle of the MHHP was chosen for development. Operating temperature ranges for the upgrader were selected to be from 70 to 110/sup 0/C (160 to 230/sup 0/F) for the source heat and 140 to 190/sup 0/C (280 to 375/sup 0/F) for the product heat. These ranges are applicable to many processes in industries such as food, textile, paper and pulp, and chemical. The hydride pair well suited for these temperatures is LaNi/sub 5//LaNi/sub 4/ /sub 5/Al/sub 0/ /sub 5/. The EDTU was designed for the upgrade cycle. It is a compact finned tube arrangement enclosed in a pressure vessel. This design incorporates high heat transfer and low thermal mass in a system which maximizes the coefficient of performance (COP). It will be constructed in Phase II. Continuation of this effort is recommended.

  16. Radio-frequency heating and neutral atom transport in a fluid-magnetohydrodynamic treatment of burning tokamak plasmas

    Conn, R.W.; Mau, T.K.; Prinja, A.K.

    1983-01-01

    A physical model for the space and time evolution of the primary parameters of ordinary and burning tokamak plasmas is described by employing a fluid plasma treatment coupled to a magnetohydrodynamic equilibrium description, the solution to the appropriate Maxwell equations, and the solution of the linear transport equation describing neutral atom transport in plasmas. The specific problems of plasma heating by ion cyclotron radiofrequency (ICRF) waves and neutral atom transport in the plasma edge and in complicated geometrical components such as divertor channels or pumped limiter structures are analyzed. A theoretical, onedimensional slab model of ICRF heating at ω = 2ω/SUB cD/ is developed and applied to determine the space-time response of tokamak plasmas. Generally, strong single-pass absorption is found for high-density, high (β) plasmas using a low k 11 spectrum (0.05 to 0.1 cm -1 ) although for (β > 1%, electron Landau damping becomes important. Deterministic and Monte Carlo methods to solve the neutral atom transport problem are described. Specific application to determine the spectrum of neutral atoms emerging from the duct of a pump limiter shows it to be hard (mean energy > 20 eV), indicating very incomplete energy thermalization. Uncertainties are identified in the overall problem of dynamic burning plasma analysis caused by the complexity of the problem itself and by uncertainties in fundamental areas such as plasma transport coefficients, stability, and plasma edge physics

  17. Effect of Liquid Ga on Metal Surfaces: Characterization of Morphology and Chemical Composition of Metals Heated in Liquid Ga

    Eun Je Lee

    2013-01-01

    Full Text Available This study investigates the effect of liquid gallium (Ga on metal foils made of titanium (Ti, niobium (Nb, and molybdenum (Mo. The Ti, Nb, and Mo foils were heated in liquid Ga at 120°C for a maximum of two weeks. After heating, the changes in the morphology and the chemical composition of the metal foils were analyzed by using a field emission scanning electron microscope, energy-dispersive X-ray spectrometer, X-ray diffractometer, and X-ray photoelectron spectrometer. The results of the analysis indicated that the Nb foil showed the minimum adhesion of liquid Ga to the surface while the maximum amount of liquid Ga was observed to adhere to the Ti foil. In addition, the Nb foil was oxidized and the Mo foil was reduced during the heating process. Considering these effects, we conclude that Mo may be used as an alternative encapsulation material for Ga in addition to Nb, which is used as the conventional encapsulation material, due to its chemical resistance against oxidation in hot liquid Ga.

  18. Vacancies and atomic processes in intermetallics - From crystals to quasicrystals and bulk metallic glasses

    Schaefer, Hans-Eckhardt [Institute of Theoretical and Applied Physics, Stuttgart University, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Baier, Falko [Voith Turbo Comp., Alexanderstr. 2, 89552 Heidenheim (Germany); Mueller, Markus A. [GFT Technologies A. G., Filderhauptstr. 142, 70599 Stuttgart (Germany); Reichle, Klaus J. [Philipp-Matthaeus-Hahn School, Jakob-Beutter-Str. 15, 72336 Balingen (Germany); Reimann, Klaus [NXP Semiconductors, Central Research and Development, High Tech Campus 4, 5656 AE Eindhoven (Netherlands); Rempel, Andrey A. [Institute of Solid State Chemistry, Russian Academy of Sciences, Ul. Pervomaiskaya 91, 620041 Ekaterinburg (Russian Federation); Sato, Kiminori [Tokyo Gakugei University, Nukuikita 4-1-1, Koganei, Tokyo 184-8501 (Japan); Ye, Feng [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, 30 Xue Yuan Road, Beijing 100083 (China); Zhang, Xiangyi [Yanshan University, Qinhuangdao 066004 (China); Sprengel, Wolfgang [Institute of Materials Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)

    2011-10-15

    A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1{sub 2}-Ni{sub 3}Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe{sub 61}Al{sub 39} and in MoSi{sub 2}. In the icosahedral quasicrystal Al{sub 70}Pd{sub 21}Mn{sub 9} the thermal vacancy concentration is low, whereas in the BMG Zr{sub 57}Cu{sub 15.4}Ni{sub 12.6}Nb{sub 3}Al{sub 10} thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Faehnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Electronic and magnetic properties of 1T-HfS{sub 2} by doping transition-metal atoms

    Zhao, Xu, E-mail: zhaoxu@htu.cn [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Wang, Tianxing; Wang, Guangtao [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Dai, Xianqi [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Department of Physics, Zhengzhou Normal University, Zhengzhou, Henan 450044 (China); Xia, Congxin [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Yang, Lin [School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang 453007 (China)

    2016-10-15

    Highlights: • Pristine 1T-HfS{sub 2} is a semiconductor with indirect gaps of 1.250 eV • Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. • Strong p–d hybridization was found between TM 3d orbitals and S 3p orbitals. • V-doped 1T-HfS{sub 2} is ideal for spin injection. - Abstract: We explored the electronic and magnetic properties of 1T-HfS{sub 2} doped by transition metal (TM) atom using the first-principles calculation. We doped the transition metal atoms from the IIIB to VIB groups in nonmagnetic 1T-HfS{sub 2}. Numerical results show that the pristine 1T-HfS{sub 2} is a semiconductor with indirect gaps of 1.250 eV. Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. The polarized charges mainly arise from the localized 3d electrons of the TM atom. The strong p–d hybridization was found between the 3d orbitals of TM and 3p orbitals of S. The substituted 1T-HfS{sub 2} can be a metal, semiconductor or half-metal. Analysis of the band structure and magnetic properties indicates that TM-doped HfS{sub 2} (TM = V, Fe, Cu) are promising systems to explore two-dimensional diluted magnetic semiconductors. The formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate transition metal atom into the HfS{sub 2} under S-rich experimental conditions. In contrast, V-doped HfS{sub 2} has relatively wide half-metallic gap and low formation energy. So V-doped 1T-HfS{sub 2} is ideal for spin injection, which is important for application in semiconductor spintronics.

  20. Self-healing properties of recycled asphalt mixtures containing metal waste: An approach through microwave radiation heating.

    González, A; Norambuena-Contreras, J; Storey, L; Schlangen, E

    2018-05-15

    The concept of self-healing asphalt mixtures by bitumen temperature increase has been used by researchers to create an asphalt mixture with crack-healing properties by microwave or induction heating. Metals, normally steel wool fibers (SWF), are added to asphalt mixtures prepared with virgin materials to absorb and conduct thermal energy. Metal shavings, a waste material from the metal industry, could be used to replace SWF. In addition, reclaimed asphalt pavement (RAP) could be added to these mixtures to make a more sustainable road material. This research aimed to evaluate the effect of adding metal shavings and RAP on the properties of asphalt mixtures with crack-healing capabilities by microwave heating. The research indicates that metal shavings have an irregular shape with widths larger than typical SWF used with asphalt self-healing purposes. The general effect of adding metal shavings was an improvement in the crack-healing of asphalt mixtures, while adding RAP to mixtures with metal shavings reduced the healing. The average surface temperature of the asphalt samples after microwave heating was higher than temperatures obtained by induction heating, indicating that shavings are more efficient when mixtures are heated by microwave radiation. CT scan analysis showed that shavings uniformly distribute in the mixture, and the addition of metal shavings increases the air voids. Overall, it is concluded that asphalt mixtures with RAP and waste metal shavings have the potential of being crack-healed by microwave heating. Copyright © 2018 Elsevier Ltd. All rights reserved.

  1. Coolant material effect on the heat transfer rates of the molten metal pool with solidification

    Cho, Jae Seon; Suh, Kune Y.; Chung, Chang Hyun; Park, Rae Joon; Kim, Sang Baik

    1998-01-01

    Experimental studies on heat transfer and solidification of the molten metal pool with overlying coolant with boiling were performed. The simulant molten pool material is tin (Sn) with the melting temperature of 232 degree C. Demineralized water and R113 are used as the working coolant. This work examines the crust formation and the heat transfer characteristics of the molten metal pool immersed in the boiling coolant. The Nusselt number and the Rayleigh number in the molten metal pool region of this study are compared between the water coolant case and the R113 coolant case. The experimental results for the water coolant are higher than those for R113. Also, the empirical relationship of the Nusselt number and the Rayleigh number is compared with the literature correlations measured from mercury. The present experimental results are higher than the literature correlations. It is believed that this discrepancy is caused by the effect of the heat loss to the environment on the natural convection heat transfer in the molten pool

  2. Study on the application of electrothermal atomization atomic absorption spectrometry for the determination of metallic Cu, Pb, Zn, Cd traces in sea water samples

    Nguyen Thi Kim Dung; Doan Thanh Son; Tran Thi Ngoc Diep

    2004-01-01

    The trace amount of some heavy metallic elements (Cu, Zn, Pb, Cd) in sea water samples were determined directly (without separation) and quantitatively by using Electro-Thermal Atomization Atomic Absorption Spectrometry (ETA-AAS). The effect of mainly major constituents such as Na, Mg, Ca, K, and the mutual effect of the trace elements, which were present in the matrix on the absorption intensity of each analyzed element was studied. The adding of a certain chemical modification for each trace element was also investigated in order to eliminate the overall effect of the background during the pyrolysis and atomization. The sea water sample after fitrating through a membrane with 0.45 μm-hole size was injected in to the graphite tube via an autosampler (MPE50). The absorption intensity of each element was then measured on the VARIO-6 under the optimum parameters for spectrometer such as: maximum wavelength, current of hollow cathode lamp, and that for graphite furnace such as dry temperature, pyrolysis temperature, atomization temperature, ect. The analytical procedures were set-up and applied for the determination of these above mentioned elements in the synthesized sea water sample and in the real sea water samples with high precision and accuracy. (author)

  3. Osteoinduction on acid and heat treated porous Ti metal samples in canine muscle.

    Toshiyuki Kawai

    Full Text Available Samples of porous Ti metal were subjected to different acid and heat treatments. Ectopic bone formation on specimens embedded in dog muscle was compared with the surface characteristics of the specimen. Treatment of the specimens by H2SO4/HCl and heating at 600 °C produced micrometer-scale roughness with surface layers composed of rutile phase of titanium dioxide. The acid- and heat-treated specimens induced ectopic bone formation within 6 months of implantation. A specimen treated using NaOH followed by HCl acid and then heat treatment produced nanometer-scale surface roughness with a surface layer composed of both rutile and anatase phases of titanium dioxide. These specimens also induced bone formation after 6 months of implantation. Both these specimens featured positive surface charge and good apatite-forming abilities in a simulated body fluid. The amount of the bone induced in the porous structure increased with apatite-forming ability and higher positive surface charge. Untreated porous Ti metal samples showed no bone formation even after 12 months. Specimens that were only heat treated featured a smooth surface composed of rutile. A mixed acid treatment produced specimens with micrometer-scale rough surfaces composed of titanium hydride. Both of them also showed no bone formation after 12 months. The specimens that showed no bone formation also featured almost zero surface charge and no apatite-forming ability. These results indicate that osteoinduction of these porous Ti metal samples is directly related to positive surface charge that facilitates formation of apatite on the metal surfaces in vitro.

  4. Microstructural features and heat flow analysis of atomized and spray-formed Al-Fe-V-Si alloy

    Srivastava, A.K.; Ranganathan, S.; Ojha, S.N.

    1998-01-01

    Microstructural features of rapidly solidified powders and preforms of Al 80 Fe 10 V 4 Si 6 alloy produced by spray forming process have been studied. The atomization and spray deposition were carried out using a confined gas atomization process and the microstructural features were characterized using scanning electron microscopy and transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The microstructure of a wide size range of atomized powders invariably revealed cellular and dendritic morphology. The extent of dendritic region and the dendritic arm spacing were observed to increase with power particle size. The TEM investigations indicated the presence of ultrafine second-phase particles in the intercellular or interdendritic regions. In contrast, the spray deposits of the alloy showed considerable variation in microstructure and size and dispersion of the second-phase particles at specific distances from the deposit-substrate interface and the exterior regions of the deposit. Nevertheless, considerable homogeneity was observed in the microstructure toward the center of the spray deposit. The formation and distribution of a cubic phase α-Al(Fe, V)Si has been characterized in both atomized powders and spray deposits. A one-dimensional heat flow model has been used to analyze the evolution of microstructure during atomization and also during spray deposition processing of this alloy. The results indicate that thermal history of droplets in the spray on deposition surface and their solidification behavior considerably influence the microstructural features of the spray deposits

  5. Quantum interference between two phonon paths and reduced heat transport in diamond lattice with atomic-scale planar defects

    Kosevich, Yu. A.; Strelnikov, I. A.

    2018-02-01

    Destructive quantum interference between the waves propagating through laterally inhomogeneous layer can result in their total reflection, which in turn reduces energy flux carried by these waves. We consider the systems of Ge atoms, which fully or partly, in the chequer-wise order, fill a crystal plane in diamond-like Si lattice. We have revealed that a single type of the atomic defects, which are placed in identical positions in different unit cells in the defect crystal plane, can result in double transmission antiresonances of phonon wave packets. This new effect we relate with the complex structure of the diamond-like unit cell, which comprises two atoms in different positions and results in two distinct vibration resonances in two interfering phonon paths. We also consider the propagation of phonon wave packets in the superlatticies made of the defect planes, half-filled in the chequer-wise order with Ge atoms. We have revealed relatively broad phonon stop bands with center frequencies at the transmission antiresonances. We elaborate the equivalent analytical quasi-1D lattice model of the two phonon paths through the complex planar defect in the diamond-like lattice and describe the reduction of phonon heat transfer through the atomic-scale planar defects.

  6. Effect of crust increase on natural convection heat transfer in the molten metal pool

    Park, Rae Joon; Kim, Sang Baik; Kim, Hee Dong; Choi, Sang Min

    1999-01-01

    An experimental study has been performed on natural convection heat transfer with a rapid crust formation in the molten metal pool of a low Prandtl number fluid. Two types of steady state tests, a low and high geometric aspect ratio cases in the molten metal pool, were performed. The crust thickness by solidification was measured as a function of boundary surface temperatures. The experimental results on the relationship between the Nusselt number and Rayleigh number in the molten metal pool with a crust formation were compared with existing correlations. The experimental study has shown that the bottom surface temperature of the molten metal layer, in all experiments, is the major influential parameter in the crust formation, due to the natural convection flow. The Nusselt number of the case without a crust formation in the molten metal pool is greater than that of the case with the crust formation at the same Rayleigh number. The present experimental results on the relationship between the Nusselt number and Rayleigh number in the molten metal pool match well with Globe and Dropkin's correlation. From the experimental results, a new correlation between the Nusselt number and Rayleigh number in the molten metal pool with the crust formation was developed as Nu=0.0923 (Ra) 0.0923 (2 X 10 4 7 ). (author)

  7. Elastic interactions between hydrogen atoms in metals. II. Elastic interaction energies

    Shirley, A.I.; Hall, C.K.

    1986-01-01

    The fully harmonic lattice approximation derived in a previous paper is used to calculate the elastic interaction energies in the niobium-hydrogen system. The permanent-direct, permanent-indirect, induced-direct, and induced-indirect forces calculated previously each give rise to a corresponding elastic interaction between hydrogen atoms. The latter three interactions have three- and four-body terms in addition to the usual two-body terms. These quantities are calculated and compared with the corresponding two-body permanent elastic interactions obtained in the harmonic-approximation treatment of Horner and Wagner. The results show that the total induced elastic energy is approximately (1/3) the size of the total permanent elastic energy and opposite to it in sign. The total elastic energy due to three-body interactions is approximately (1/4) the size of the total two-body elastic energy, while the total four-body elastic energy is approximately 5% of the total two-body energy. These additional elastic energies are expected to have a profound effect on the thermodynamic and phase-change behavior of a metal hydride

  8. Electronic and spectroscopic properties of early 3d metal atoms on a graphite surface

    Rakotomahevitra, A.; Garreau, G.; Demangeat, C.; Parlebas, J. C.

    1995-07-01

    High-sensitivity magneto-optic Kerr effect experiments failed to detect manifestations of magnetism in epitaxial films of V on Ag(100) substrates. More recently V 3s XPS of freshly evaporated V clusters on graphite exhibited the appearance of a satellite structure which has then been interpreted by the effect of surface magnetic moments on V. It is the absence of unambiguous results on the electronic properties of early 3d supported metals that prompts us to examine the problem. Our purpose is twofold. In a first part, after a total energy calculation within a tight-binding method which yields the equilibrium position of a given adatom, we use the Hartree-Fock approximation to find out a possible magnetic solution of V (or Cr) upon graphite for a reasonable value of the exchange integral Jdd. In a second part the informations given by the density of states of the graphite surface as well as the additional states of the adsorbed atom are taken into account through a generalised impurity Anderson Hamiltonian which incorporates the various Coulomb and exchange interactions necessary to analyse the 3s XPS results.

  9. A first-principles study of light non-metallic atom substituted blue phosphorene

    Sun, Minglei [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Tang, Wencheng, E-mail: 101000185@seu.edu.cn [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Ren, Qingqiang [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, Hunan (China); Wang, Sa-ke [Department of Physics, Southeast University, Nanjing 210096, Jiangsu (China); Yu, Jin [School of Materials Science and Engineering, Southeast University, Nanjing 211189, Jiangsu (China); Jiangsu Key Laboratory of Advanced Metallic Materials, Southeast University, Nanjing 211189, Jiangsu (China); Du, Yanhui [School of Mechanical Engineering, Southeast University, Nanjing 211189, Jiangsu (China)

    2015-11-30

    Graphical abstract: - Highlights: • All the impurities are covalently bonded to blue phosphorene (with a single vacancy). • All the substituted systems are semiconductors. • B-substituted system exhibits direct bandgap semiconductor behavior. • The band gaps with spin polarization are found in C and O-substituted systems. • Our works can paves a new route at nanoscale for novel functionalities of optical and spintronics devices. - Abstract: First-principles calculations are implemented to study the geometric, electronic and magnetic properties of light non-metallic atom (B, C, N, O and F) substituted blue phosphorene. All the substituted systems are highly stable. The B-substituted system is a direct bandgap semiconductor with a bandgap size about 1.5 eV. The C, O-substituted systems are promising systems to explore two-dimensional diluted magnetic semiconductors. Magnetism is observed for C and O substitution, while for the other impurities no magnetic moment is detected. Our works paves a new route at nanoscale for novel functionalities of optical and spintronics devices.

  10. Determination of some metal ions in various meat and baby food samples by atomic spectrometry.

    Daşbaşı, Teslima; Saçmacı, Şerife; Ülgen, Ahmet; Kartal, Şenol

    2016-04-15

    In this paper, we report a simple and rapid solid phase extraction system for the separation/preconcentration and determination of Cd(II), Co(II), Cu(II), Fe(III), Cr(III), Pb(II), and Zn(II) ions by flame atomic absorption spectrometry (FAAS). This method is based upon the retention of metal ions on a column packed with poly[N-(3-methyl-1H-indole-1-yl)]-2-methacrylamide-co-2-acrylamido-2-methyl-1-propane sulphonic acid-co divinylbenzene] (MMAD) resin as a solid-phase extraction (SPE) sorbent at pH 8. At the optimized conditions, the limits of detection (3 s/b) between 0.12 and 1.6 μg L(-1), preconcentration factor of 100, and the relative standard deviation of ⩽1.8% were achieved (n=10). The accuracy of the method was verified by analyzing certified reference materials (CRMs) and performing recovery experiments. The developed method was successfully applied to the various natural water, meat products and baby food samples. The recoveries of analyte ions were found in added real samples and CRMs from 95% to 102%. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Atomic-layer-deposited WNxCy thin films as diffusion barrier for copper metallization

    Kim, Soo-Hyun; Oh, Su Suk; Kim, Ki-Bum; Kang, Dae-Hwan; Li, Wei-Min; Haukka, Suvi; Tuominen, Marko

    2003-01-01

    The properties of WN x C y films deposited by atomic layer deposition (ALD) using WF 6 , NH 3 , and triethyl boron as source gases were characterized as a diffusion barrier for copper metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΩ cm with a film density of 15.37 g/cm 3 . The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of ∼48, 32, and 20 at. %, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC 1-x and β-W 2 N with an equiaxed microstructure. The barrier property of this ALD-WN x C y film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700 deg. C for 30 min

  12. Metal hydride hydrogen and heat storage systems as enabling technology for spacecraft applications

    Reissner, Alexander, E-mail: reissner@fotec.at [FOTEC Forschungs- und Technologietransfer GmbH, Viktor Kaplan Straße 2, 2700 Wiener Neustadt (Austria); University of Applied Sciences Wiener Neustadt, Johannes Gutenberg-Straße 3, 2700 Wiener Neustadt (Austria); Pawelke, Roland H.; Hummel, Stefan; Cabelka, Dusan [FOTEC Forschungs- und Technologietransfer GmbH, Viktor Kaplan Straße 2, 2700 Wiener Neustadt (Austria); Gerger, Joachim [University of Applied Sciences Wiener Neustadt, Johannes Gutenberg-Straße 3, 2700 Wiener Neustadt (Austria); Farnes, Jarle, E-mail: Jarle.farnes@prototech.no [CMR Prototech AS, Fantoftvegen 38, PO Box 6034, 5892 Bergen (Norway); Vik, Arild; Wernhus, Ivar; Svendsen, Tjalve [CMR Prototech AS, Fantoftvegen 38, PO Box 6034, 5892 Bergen (Norway); Schautz, Max, E-mail: max.schautz@esa.int [European Space Agency, ESTEC – Keplerlaan 1, 2201 AZ Noordwijk Zh (Netherlands); Geneste, Xavier, E-mail: xavier.geneste@esa.int [European Space Agency, ESTEC – Keplerlaan 1, 2201 AZ Noordwijk Zh (Netherlands)

    2015-10-05

    Highlights: • A metal hydride tank concept for heat and hydrogen storage is presented. • The tank is part of a closed-loop reversible fuel cell system for space application. • For several engineering issues specific to the spacecraft application, solutions have been developed. • The effect of water contamination has been approximated for Ti-doped NaAlH{sub 4}. • A novel heat exchanger design has been realized by Selective Laser Melting. - Abstract: The next generation of telecommunication satellites will demand a platform payload performance in the range of 30+ kW within the next 10 years. At this high power output, a Regenerative Fuel Cell Systems (RFCS) offers an efficiency advantage in specific energy density over lithium ion batteries. However, a RFCS creates a substantial amount of heat (60–70 kJ per mol H{sub 2}) during fuel cell operation. This requires a thermal hardware that accounts for up to 50% of RFCS mass budget. Thus the initial advantage in specific energy density is reduced. A metal hydride tank for combined storage of heat and hydrogen in a RFCS may overcome this constraint. Being part of a consortium in an ongoing European Space Agency project, FOTEC is building a technology demonstrator for such a combined hydrogen and heat storage system.

  13. Polymerization of a divalent/tetravalent metal-storing atom-mimicking dendrimer

    Albrecht, Ken; Hirabayashi, Yuki; Otake, Masaya; Mendori, Shin; Tobari, Yuta; Azuma, Yasuo; Majima, Yutaka; Yamamoto, Kimihisa

    2016-01-01

    The phenylazomethine dendrimer (DPA) has a layer-by-layer electron density gradient that is an analog of the Bohr atom (atom mimicry). In combination with electron pair mimicry, the polymerization of this atom-mimicking dendrimer was achieved. The valency of the mimicked atom was controlled by changing the chemical structure of the dendrimer. By mimicking a divalent atom, a one-dimensional (1D) polymer was obtained, and by using a planar tetravalent atom mimic, a 2D polymer was obtained. Thes...

  14. Artificial crystals with 3d metal and palladium particles subjected to high-temperature heat treatment

    Rinkevich, A. B.; Nemytova, O. V.; Perov, D. V.; Samoylovich, M. I.; Kuznetsov, E. A.

    2018-04-01

    High-temperature heat treatment has valuable impact on the structure and physical properties of artificial crystals with 3d metal and palladium particles. Artificial crystals are obtained by means of introduction of particles into the interspherical voids of opal matrices. The magnetic properties are studied at the temperatures ranging from 2 to 300 K and in fields up to 350 kOe. Microwave properties are investigated in the millimeter frequency range. The complex dielectric permittivity of several nanocomposites is measured. The influence of heat treatment up to 960 °C on the structure of artificial crystals is clarified.

  15. Required momentum, heat, and mass transport experiments for liquid-metal blankets

    Tillack, M.S.; Sze, D.K.; Abdou, M.A.

    1986-01-01

    Through the effects on fluid flow, many aspects of blanket behavior are affected by magnetohydrodynamic (MHD) effects, including pressure drop, heat transfer, mass transfer, and structural behavior. In this paper, a set of experiments is examined that could be performed in order to reduce the uncertainties in the highly related set of issues dealing with momentum, heat, and mass transport under the influence of a strong magnetic field (i.e., magnetic transport phenomena). By improving our basic understanding and by providing direct experimental data on blanket behavior, these experiments will lead to improved designs and an accurate assessment of the attractiveness of liquid-metal blankets

  16. A concentrated solar cavity absorber with direct heat transfer through recirculating metallic particles

    Sarker, M. R. I., E-mail: islamrabiul@yahoo.com; Saha, Manabendra, E-mail: manabendra.saha@adelaide.edu.au, E-mail: manab04me@gmail.com; Beg, R. A. [Department of Mechanical Engineering, Rajshahi University of Engineering and Technology, Rajshahi-6204 (Bangladesh)

    2016-07-12

    A recirculating flow solar particle cavity absorber (receiver) is modeled to investigate the flow behavior and heat transfer characteristics of a novel developing concept. It features a continuous recirculating flow of non-reacting metallic particles (black silicon carbide) with air which are used as a thermal enhancement medium. The aim of the present study is to numerically investigate the thermal behavior and flow characteristics of the proposed concept. The proposed solar particle receiver is modeled using two phase discrete particle model (DPM), RNG k-flow model and discrete ordinate (DO) radiation model. Numerical analysis is carried out considering a solar receiver with only air and the mixture of non-reacting particles and air as a heat transfer as well as heat carrying medium. The parametric investigation is conducted considering the incident solar flux on the receiver aperture and changing air flow rate and recirculation rate inside the receiver. A stand-alone feature of the recirculating flow solar particle receiver concept is that the particles are directly exposed to concentrated solar radiation monotonously through recirculating flow inside the receiver and results in efficient irradiation absorption and convective heat transfer to air that help to achieve high temperature air and consequently increase in thermal efficiency. This paper presents, results from the developed concept and highlights its flow behavior and potential to enhance the heat transfer from metallic particles to air by maximizing heat carrying capacity of the heat transfer medium. The imposed milestones for the present system will be helpful to understand the radiation absorption mechanism of the particles in a recirculating flow based receiver, the thermal transport between the particles, the air and the cavity, and the fluid dynamics of the air and particle in the cavity.

  17. Heat Treatment of Gas-Atomized Powders for Cold Spray Deposition

    Story, William A.; Brewer, Luke N.

    2018-02-01

    This communication demonstrates the efficacy of heat treatment on the improved deposition characteristics of aluminum alloy powders. A novel furnace was constructed for solutionizing of feedstock powders in an inert atmosphere while avoiding sintering. This furnace design achieved sufficiently high cooling rates to limit re-precipitation during powder cooling. Microscopy showed homogenization of the powder particle microstructures after heat treatment. Cold spray deposition efficiency with heat-treated powders substantially increased for the alloys AA2024, AA6061, and AA7075.

  18. Removal of contaminated asphalt layers by using heat generating powder metallic systems

    Barinov, A.S.; Karlina, O.K.; Ojovan, M.I.

    1996-01-01

    Heat generating systems on the base of powder metallic fuel were used for the removal of contaminated asphalt layers. Decontamination of spots which had complex geometric form was performed. Asphalt layers with deep contamination were removed essentially all radionuclides being retained in asphalt residue. Only a small part (1 - 2 %) of radionuclides could pass to combustion slag. No radionuclides were detected in aerosol-gas phase during decontamination process

  19. Matter, energy, and heat transfer in a classical ballistic atom pump.

    Byrd, Tommy A; Das, Kunal K; Mitchell, Kevin A; Aubin, Seth; Delos, John B

    2014-11-01

    A ballistic atom pump is a system containing two reservoirs of neutral atoms or molecules and a junction connecting them containing a localized time-varying potential. Atoms move through the pump as independent particles. Under certain conditions, these pumps can create net transport of atoms from one reservoir to the other. While such systems are sometimes called "quantum pumps," they are also models of classical chaotic transport, and their quantum behavior cannot be understood without study of the corresponding classical behavior. Here we examine classically such a pump's effect on energy and temperature in the reservoirs, in addition to net particle transport. We show that the changes in particle number, of energy in each reservoir, and of temperature in each reservoir vary in unexpected ways as the incident particle energy is varied.

  20. Complexity of MRI induced heating on metallic leads: Experimental measurements of 374 configurations

    Mendoza Gonzalo

    2008-03-01

    Full Text Available Abstract Background MRI induced heating on PM leads is a very complex issue. The widely varying results described in literature suggest that there are many factors that influence the degree of heating and that not always are adequately addressed by existing testing methods. Methods We present a wide database of experimental measurements of the heating of metallic wires and PM leads in a 1.5 T RF coil. The aim of these measurements is to systematically quantify the contribution of some potential factors involved in the MRI induced heating: the length and the geometric structure of the lead; the implant location within the body and the lead path; the shape of the phantom used to simulate the human trunk and its relative position inside the RF coil. Results We found that the several factors are the primary influence on heating at the tip. Closer locations of the leads to the edge of the phantom and to the edge of the coil produce maximum heating. The lead length is the other crucial factor, whereas the implant area does not seem to have a major role in the induced temperature increase. Also the lead structure and the geometry of the phantom revealed to be elements that can significantly modify the amount of heating. Conclusion Our findings highlight the factors that have significant effects on MRI induced heating of implanted wires and leads. These factors must be taken into account by those who plan to study or model MRI heating of implants. Also our data should help those who wish to develop guidelines for defining safe medical implants for MRI patients. In addition, our database of the entire set of measurements can help those who wish to validate their numerical models of implants that may be exposed to MRI systems.

  1. Preparation and Heat-Treatment of DWPF Simulants With and Without Co-Precipitated Noble Metals

    Koopman, David C.:Eibling, Russel E

    2005-01-01

    simulants were visually very viscous compared to the traditional SB3 simulant. (4) Heat-treatment reduced the viscosity of the two new simulants with and without coprecipitated noble metals, though they were still more viscous than the traditional SB3. (5) The approach of using a 97 C heat-treatment step to qualitatively simulate tank farm aging may not be optimal. A significant change in the base equivalent molarities of both simulants was observed during heat-treatment. (6) Heat-treatment appeared to make phosphates insoluble in water. The following recommendations came out of the work: (1) Washed slurry should be checked for TIC and base equivalents before calculating the final trim chemical additions of sodium carbonate and sodium hydroxide. (2) Final insoluble trim chemicals should be added to the slurry in the cross-flow filtration unit mixing tank, since significant slurry is lost in the CUF equipment. Adding the chemicals here would keep them in the correct proportion relative to the precipitated insoluble solids. (3) A composite wash and decant sample should be prepared containing proportionally weighted masses of each aqueous stream removed during preparation of a co-precipitated noble metal simulant. This sample should then be checked for noble metal losses. This would reduce the sample load, while still confirming that there was no significant noble metal loss. (4) A study of the impact of heat-treatment on existing simulants should be undertaken. If there is a shift in base equivalents, then SRNL acid stoichiometries may be biased relative to real waste. The study should be extended to several real wastes as well

  2. Energy and exergy analyses of medium temperature latent heat thermal storage with high porosity metal matrix

    Kumar, Ashish; Saha, Sandip K.

    2016-01-01

    Graphical abstract: I. Metal matrix is used as the thermal conductivity enhancers (TCE) in PCM-based TES. II. Time evolution second law analysis is evaluated for different porosities and pore diameters. III. Reduction in fluctuation in HTF temperature is significantly affected by the change in porosity (ε) shown in figure. IV. Maximum energy and exergy efficiencies are obtained for porosity of 0.85. V. Effect of pore diameter on first law and second law efficiencies is found to be marginal. - Abstract: Thermal energy storage system in a concentrating solar plant (CSP) reduces the gap between energy demand and supply caused by the intermittent behaviour of solar radiation. In this paper, detailed exergy and energy analyses of shell and tube type latent heat thermal storage system (LHTES) for medium temperature solar thermal power plant (∼200 °C) are performed to estimate the net useful energy during the charging and discharging period in a cycle. A commercial-grade organic phase change material (PCM) is stored inside the annular space of the shell and the heat transfer fluid (HTF) flows through the tubes. Thermal conductivity enhancer (TCE) in the form of metal matrix is embedded in PCM to augment heat transfer. A numerical model is developed to investigate the fluid flow and heat transfer characteristics using the momentum equation and the two-temperature non-equilibrium energy equation coupled with the enthalpy method to account for phase change in PCM. The effects of storage material, porosity and pore-diameter on the net useful energy that can be stored and released during a cycle, are studied. It is found that the first law efficiency of sensible heat storage system is less compared to LHTES. With the decrease in porosity, the first law and second law efficiencies of LHTES increase for both the charging and discharging period. There is no significant variation in energy and exergy efficiencies with the change in pore-diameter of the metal matrix.

  3. Effects of Liquid Metal Fin on Critical Heat Flux under IVR-ERVC Condition

    Park, Seong Dae; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2014-05-15

    The molten fuel is relocated to bottom of reactor vessel after core is damaged and not cooled continuously. In-vessel retention through external reactor vessel cooling (IVR-ERVC) is presented to terminate the progression of accidents by removing the decay heat. IVR-ERVC is suitable for small size reactors like AR-600, AP-1000. There is uncertainty for high power reactor like APR-1400 and CAP-1400. This uncertainty originates from the thermal margin between the CHF value and real heat flux on the reactor vessel under severe accidents. The main mechanism of heat removal on IVR-ERVC strategy is boiling on the outer wall of reactor vessel. The boiling heat transfer is limited due to the CHF phenomenon. There should be an enough margin for preventing the CHF in boiling heat transfer systems. The CHF tests for IVR-ERVC system were conducted to confirm or increase the thermal margin. The design of thermal insulator was changed to vent the vapor smoothly. Forming the coating layer on the vessel surface was proposed to enhance the CHF margin. The liquid metal was designed to flood the space around the reactor vessel. The liquid metal has high boiling point and superb thermal conductivity in comparison with the coolant. In this work, experimental tests were conducted to validate the CFD results about the IVR-ERVC system with liquid metal. The behavior of vapor was observed to predict the tendency of CHF increase with small-scaled facility to simulate the IVR-ERVC system.

  4. Atomic-level structure and structure-property relationship in metallic glass

    Cheng, Yongqiang

    One of the key tasks in material science is to understand the structure and structure-property relationship. The recently emerging bulk metallic glasses (BMGs) have demonstrated unique properties, especially intriguing mechanical properties such as their high strength and high propensity to localize deformation in shear bands. However, a comprehensive understanding of the structure of BMGs has been hindered by the complexity of these amorphous materials. Even more challenging is the structure-property correlation, which has been well established in crystals but has been seriously lacking for BMGs. This thesis presents a systematic study of the atomic-level structures of two representative BMGs, Cu-Zr and Cu-Zr-Al. The interpenetrating Cu-centered icosahedral clusters have been identified to be the primary structural feature. The fraction of icosahedra increases with increasing Cu or Al contents, and with decreasing cooling rate. The effect of Al in improving the icosahedral order is two-fold: the geometric effect due to the atomic-size mismatch and the chemical effect originated from the Cu-Al bond shortening. The resolved structure is used to study the structure-property relationship. The full icosahedra are found to be responsible for the dynamical slowdown of the supercooled liquid, which underlies the non-Arrhenius behavior, and explains the composition dependence of glass transition temperature, glass forming ability, and the room temperature strength. By simulated deformation, the initiation of plasticity and tendency for strain localization are also investigated. The full icosahedra are found to be the most rigid and resistant cluster with solid-like character, while the unstable clusters with liquid-like character serve as the fertile sites for initiating shear transformations. In addition, the elastic moduli are calculated and analyzed, and the origins of the different configurational dependence of shear modulus (G) and bulk modulus ( B) are explained. The

  5. Diffusion induced nuclear reactions in metals: a possible source of heat in the core

    Hamza, V.M.; Iyer, S.S.S.

    1989-01-01

    It has recently been proposed that diffusion of light nuclei in metals can give rise to unusual electrical charge distributions in their lattice structures, inducing thereby certain nuclear reactions that are otherwise uncommon. In the light of these results we advance the hypothesis that such nuclear reactions take place in the metal rich core of the earth, based on following observations: 1 - The solubility of hydrogen in metals is relatively high compared to that in silicates. 2 - Studies of rare gas samples in intraplate volcanos and diamonds show that 3 He/ He ratio increases with depth in the mantle. 3 - There are indications that He is positively correlated with enrichment of metals in lavas. We propose that hydrogen incorporated into metallic phases at the time of planetary accretion was carried to the core by downward migration of metal rich melts during the early states of proto-earth. Preliminary estimates suggest that cold fusion reactions can give rise to an average rate of heat generation of 8.2x10 12 W and may thus serve as a supplementary source of energy for the geomagnetic dynamo. (author)

  6. Ground state of the polar alkali-metal-atom-strontium molecules: Potential energy curve and permanent dipole moment

    Guerout, R.; Aymar, M.; Dulieu, O.

    2010-01-01

    In this study, we investigate the structure of the polar alkali-metal-atom-strontium diatomic molecules as possible candidates for the realization of samples of ultracold polar molecular species not yet investigated experimentally. Using a quantum chemistry approach based on effective core potentials and core polarization potentials, we model these systems as effective three-valence-electron systems, allowing for calculation of electronic properties with full configuration interaction. The potential curve and the permanent dipole moment of the 2 Σ + ground state are determined as functions of the internuclear distance for LiSr, NaSr, KSr, RbSr, and CsSr molecules. These molecules are found to exhibit a significant permanent dipole moment, though smaller than those of the alkali-metal-atom-Rb molecules.

  7. From Single Atoms to Nanoparticles: Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO2 Nanopowder.

    Grillo, Fabio; Van Bui, Hao; La Zara, Damiano; Aarnink, Antonius A I; Kovalgin, Alexey Y; Kooyman, Patricia; Kreutzer, Michiel T; van Ommen, Jan Rudolf

    2018-05-10

    A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO 2 nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O 2 as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (P O2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke-Watzky two-step model. Even at relatively high oxygen exposures ( 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high P O2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high P O2 . © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Evaluation of Heat Losses Behind the Front of the Detonation Moving Along the Metallic Porous Surface

    S. V. Golovastov

    2016-01-01

    Full Text Available The paper considers a computational technique of the heat flow from the hot products of detonation combustion into the porous coating and estimates the efficiency of the coating layer that results in slowing the flame front down with disregard the transverse displacement of the combustion products weight of a hydrogen-air mixture.Initial thermodynamic parameters of combustion products on the porous coating surface have been estimated. A drag (stagnation temperature of flow was determined.The statement of task was to calculate the heat flow into the long cylindrical metal fiber with radius of 15 μm. The reference values of heat capacity and heat diffusivity were used to estimate a thermal diffusivity in a wide range of temperatures. An approximation of the parameters is given for a wide range of temperatures.The calculation algorithm using an explicit four-point scheme is presented. The convergence and accuracy of the results were confirmed. The theoretical estimation using cylindrical Bessel functions was made to prove the accuracy of the results.Total heat loss was estimated using the photos of moving detonation front and hot combustion gases.Comparison of the total heat loss and the amount of energy absorbed by a single fiber allowed us to find that the porous coating thickness, resulting in attenuation of detonation wave, is efficient.

  9. Trace metal characterization and speciation in geothermal effluent by multiple scanning anodic stripping voltammetry and atomic absorption analysis

    Kowalski, B.R.

    1979-05-25

    Recent studies have shown geothermal power plants to have a significant environmental impact on the ground water of the area. The heavy metals arsenic and mercury are special problems, as both are concentrated by flora and fauna exposed to the effluent waters. Because the toxicity of these and other metallic pollutants present in geothermal effluent depends on the chemical form, or speciation, of the particular metal, any serious study of the environmental impact of a geothermal development should include studies of trace metal speciation, in addition to trace metal concentration. This proposal details a method for determining metal speciation in dilute waters. The method is based on ion-exchange and backed by atomic absorption spectrometry and multiple scanning anodic stripping voltammetry. Special laboratory studies will be performed on mercury, arsenic and selenium speciation in synthetic geothermal water. The method will be applied to three known geothermal areas in Washington and Oregon, with emphasis on the speciation of mercury, arsenic and selenium in these waters. The computer controlled electrochemical instrumentation was built and tested. Using this instrumentation, a new experimental procedure was developed to determine the chemical form (speciation) of metal ions in very dilute solutions (ng/ml). This method was tested on model systems including Pb, Cd, and As with C1/sup -/, CO/sub 3//sup 2 -/ and glycine ligands. Finally, the speciation of lead in a geothermal water was examined and the PbC1/sup +/ complex was observed and quantified.

  10. Lotus-like effect for metal filings recovery and particle removal on heated metal surfaces using Leidenfrost water droplets.

    Tan, Cher Lin Clara; Sapiha, Kostantyn; Leong, Yoke Fun Hannah; Choi, Siwon; Anariba, Franklin; Thio, Beng Joo Reginald

    2015-07-21

    A "lotus-like" effect is applied to demonstrate the ability of the Leidenfrost water droplets to recover Cu particles on a heated Al substrate. Cu particles on the heated surface adhere to the rim of the Leidenfrost droplets and eventually coat the droplets' surface to form an aggregation. When Fe filings are added to the Cu particles, the aggregated mixture can then be collected using a strong rare earth magnet (NdFeB) upon evaporation of the water. We also show that the Leidenfrost effect can be effectively utilized to recover both hydrophobic (dust and activated carbon) and hydrophilic (SiO2 and MgO) particles from heated Al surfaces without any topographical modification or surfactant addition. Our results show that hydrophobic and hydrophilic materials can be collected with >92% and >96% effectiveness on grooved and smooth Al surfaces, respectively. Furthermore, we observed no significant differences in the amount of material collected above the Leidenfrost point within the tested temperature range (240 °C vs. 340 °C) as well as when the Al sheet was replaced with a Cu sheet as the substrate. However, we did observe that the Leidenfrost droplets were able to collect a greater amount of material when the working liquid was water than when it was ethanol. Our findings show promise in the development of an effective precious coinage metal filings recovery technology for application in the mint industry, as well as the self-cleaning of metallic and semiconductor surfaces where manual cleaning is not amenable.

  11. First-principles dynamics treatment of light emission in collisions between alkali-metal atom and noble-gas atom collisions at 10keV

    Pacheco, Alexander B.; Reyes, Andrés; Micha, David A.

    2006-12-01

    Collision-induced light emission during the interaction of an alkali-metal atom and a noble-gas atom is treated within a first-principles, or direct, dynamics approach that calculates a time-dependent electric dipole for the whole system, and spectral emission cross sections from its Fourier transform. These cross sections are very sensitive to excited diatomic potentials and a source of information on their shape. The coupling between electronic transitions and nuclear motions is treated with atomic pseudopotentials and an electronic density matrix coupled to trajectories for the nuclei. A recently implemented pseudopotential parametrization scheme is used here for the ground and excited states of the LiHe system, and to calculate state-to-state dipole moments. To verify the accuracy of our new parameters, we recalculate the integral cross sections for the LiHe system in the keV energy regime and obtain agreement with other results from theory and experiment. We further present results for the emission spectrum from 10keV Li(2s)+He collisions, and compare them to experimental values available in the region of light emitted at 300-900nm .

  12. Thermal Aging Effects on Heat Affected Zone of Alloy 600 in Dissimilar Metal Weld

    Ham, Jun Hyuk; Choi, Kyoung Joon; Yoo, Seung Chang; Kim, Ji Hyun [UNIST, Ulsan (Korea, Republic of)

    2016-05-15

    Dissimilar metal weld (DMW), consists of Alloy 600, Alloy 182, and A508 Gr.3, is now being widely used as the reactor pressure vessel penetration nozzle and the steam generator tubing material for pressurized water reactors (PWR) because of its mechanical property, thermal expansion coefficient, and corrosion resistance. The heat affected zone (HAZ) on Alloy 600 which is formed by welding process is critical to crack. According to G.A. Young et al. crack growth rates (CGR) in the Alloy 600 HAZ were about 30 times faster than those in the Alloy 600 base metal tested under the same conditions [3]. And according to Z.P. Lu et al. CGR in the Alloy 600 HAZ can be more than 20 times higher than that in its base metal. To predict the life time of components, there is a model which can calculate the effective degradation years (EDYs) of the material as a function of operating temperature. This study was conducted to investigate how thermal aging affects the hardness of dissimilar metal weld from the fusion boundary to Alloy 600 base metal and the residual strain at Alloy 600 heat affected zone. Following conclusions can be drawn from this study. The hardness, measured by Vickers hardness tester, peaked near the fusion boundary between Alloy 182 and Alloy 600, and it decreases as the picked point goes to Alloy 600 base metal. Even though the formation of precipitate such as Cr carbide, thermal aging doesn't affect the value and the tendency of hardness because of reduced residual stress. According to kernel average misorientation mapping, residual strain decreases when the material thermally aged. And finally, in 30 years simulated specimen, the high residual strain almost disappears. Therefore, the influence of residual strain on primary water stress corrosion cracking can be diminished when the material undergoes thermal aging.

  13. Transient performance of a thermal energy storage-based heat sink using a liquid metal as the phase change material

    Fan, Li-Wu; Wu, Yu-Yue; Xiao, Yu-Qi; Zeng, Yi; Zhang, Yi-Ling; Yu, Zi-Tao

    2016-01-01

    Highlights: • A liquid metal is adopted as the PCM in a thermal energy storage-based heat sink. • Transient performance of the heat sink is tested in comparison to an organic PCM. • The liquid metal has a similar volumetric latent heat of fusion to the organic PCM. • Outperformance of the liquid metal is found due to its higher thermal conductivity. • Liquid metals are preferred when the system weight is less important than volume. - Abstract: In this Technical Note, the use of a liquid metal, i.e., a low melting point Pb–Sn–In–Bi alloy, as the phase change material (PCM) in thermal energy storage-based heat sinks is tested in comparison to an organic PCM (1-octadecanol) having a similar melting point of ∼60 °C. The thermophysical properties of the two types of PCM are characterized, revealing that the liquid metal is much more conductive while both have nearly identical volumetric latent heat of fusion (∼215 MJ/m"3). By using at the same volume of 80 mL, i.e., the same energy storage capacity, the liquid metal is shown to outperform significantly over the organic PCM under the various heating powers up to 105.3 W/cm"2. During the heating period, the use of the liquid metal leads to a remarkable extension of the effective protection time to nearly twice longer as well as a reduction of the highest overheating temperature by up to 50 °C. The cool-down period can also be shortened significantly by taking advantage of the much higher thermal conductivity of the liquid metal. These findings suggest that liquid metals could serve as a promising PCM candidate for particular applications where the volume limit is very rigorous and the penalty in weight increment is acceptable.

  14. Coloration of metallic and/or ceramic surfaces obtained by atomic layer deposited nano-coatings

    Guzman, L.; Vettoruzzo, F.; Laidani, N.

    2016-01-01

    By depositing single layer coatings by means of physical vapor techniques, tailoring of their coloration is generally complex because a given color can be obtained only by very high composition control. Physical vapor deposition (PVD) processes are expensive and cannot be easily used for obtaining conformal coating on three-dimensional objects. Moreover PVD coatings exhibit intrinsic defects (columnar structures, pores) that affect their functional properties and applications such as barrier layers. Atomic layer deposition (ALD) technology delivers conformal coatings on different materials with very low defectiveness. A straightforward coloration can be obtained by a combination of two types of layers with different refraction index, deposited to high thickness precision. Computer simulation studies were performed to design the thickness and architecture of multilayer structures, to a total thickness of approximately 100 nm, suitable to modify the typical coloration of some materials, without altering their other physical and chemical properties. The most promising nano-layered structures were then deposited by ALD and tested with regard to their optical properties. Their total thicknesses were specified in such a way to be technically feasible and compatible with future industrial production. The materials employed in this study to build the optical coatings, are two oxides (Al_2O_3, TiO_2) deposited at 120 °C and two nitrides (AlN, TiN), which need a deposition temperature of 400 °C. The possibility of using such modern deposition technology for esthetic and decorative purposes, while maintaining the functional properties, opens perspectives of industrial applications. - Highlights: • Computer simulation is done to design multilayers made of Al_2O_3, TiO_2, AlN, and TiN. • Total thickness (< 120 nm) is specified to be compatible with industrial production. • The most promising nano-layered structures are then produced and optically tested. • An

  15. Collision cross sections and equilibrium fractions of ions and atoms in metal vapor targets. Project progress report, June 1, 1979-May 31, 1980

    Morgan, T.J.

    1980-01-01

    The objective of this program is to measure atomic collision cross sections and equilibrium fractions of ions and atoms in metal vapor targets. The goal is to obtain experimental information on atomic collision processes relevant to the Magnetic Fusion Energy Program. In particular, in connection with the development of double charge exchange D - ion sources, we are measuring D - formation cross sections in alkaline-earth metal vapor targets. During the period covered in this report we have measured electron transfer cross sections for 3-40 keV D + ions and D 0 atoms in collision with calcium vapor

  16. Testing of Frank's hypothesis on a containerless packing of macroscopic soft spheres and comparison with mono-atomic metallic liquids

    Sahu, K.K.; Wessels, V.; Kelton, K.F.; Loeffler, J.F.

    2011-01-01

    Highlights: → Testing of Frank's hypothesis for Centripetal Packing (CP) has been proposed. → It is shown that CP is an idealized model for Monatomic Supercooled Liquid (MSL). → The CP is fit for comparing with studies on MSL in a containerless environment. → We measure local orders in CP by HA and BOO methods for the first time. → It is shown that icosahedral order is greater in CP than MSL and reasons explored. - Abstract: It is well-known that metallic liquids can exist below their equilibrium melting temperature for a considerable time. To explain this, Frank proposed that icosahedral ordering, incompatible with crystalline long-range order, is prevalent in the atomic structure of these liquids, stabilizing them and enabling them to be supercooled. Some studies of the atomic structures of metallic liquids using Beam-line Electrostatic Levitation (BESL; containerless melting), and other techniques, support this hypothesis . Here we examine Frank's hypothesis in a system of macroscopic, monodisperse deformable spheres obtained by containerless packing under the influence of centripetal force. The local structure of this packing is analyzed and compared with atomic ensembles of liquid transition metals obtained by containerless melting using the BESL method.

  17. Adsorption of 3d transition metal atoms on graphene-like gallium nitride monolayer: A first-principles study

    Chen, Guo-Xiang; Li, Han-Fei; Yang, Xu; Wen, Jun-Qing; Pang, Qing; Zhang, Jian-Min

    2018-03-01

    We study the structural, electronic and magnetic properties of 3d transition metal (TM) atoms (Cr, Mn, Fe, Co, Ni and Cu) adsorbed GaN monolayer (GaN-ML) using first-principles calculations. The results show that, for 6 different TM adatoms, the most stable adsorption sites are the same. The adsorption of TM atoms results in significant lattice distortions. A covalent chemical bonding character between TM adatom and GaN-ML is found in TM adsorbed systems. Except for Ni adsorbed system, all TM adsorbed systems show spin polarization implying that the adsorption of TM induces magnetization. The magnetic moments of the adsorbed systems are concentrated on the TM adatoms and the nearest-neighbor N atoms of the adsorption site contributed slightly. Our analysis shows that the GaN-ML properties can be effectively modulated by TM adsorption, and exhibit various electronic and magnetic properties, such as magnetic metals (Fe adsorption), half-metal (Co adsorption), and spin gapless semiconductor (Cu adsorption). These present properties of TM adsorbed GaN-ML may be of value in electronics and spintronics applications.

  18. Ab initio effective core potentials for molecular calculations. Potentials for the transition metal atoms Sc to Hg

    Hay, P.J.; Wadt, W.R.

    1985-01-01

    Ab initio effective core potentials (ECP's) have been generated to replace the Coulomb, exchange, and core-orthogonality effects of the chemically inert core electron in the transition metal atoms Sc to Hg. For the second and third transition series relative ECP's have been generated which also incorporate the mass--velocity and Darwin relativistic effects into the potential. The ab initio ECP's should facilitate valence electron calculations on molecules containing transition-metal atoms with accuracies approaching all-electron calculations at a fraction of the computational cost. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3d,4s,4p), (4d,5s,5p), and (5d,6s,6p) orbitals of the first, second, and third transition series atoms, respectively. All-electron and valence-electron atomic excitation energies are also compared for the low-lying states of Sc--Hg, and the valence-electron calculations are found to reproduce the all-electron excitation energies (typically within a few tenths of an eV)

  19. Heat treatment of large-sized welded rotors of steam turbines for atomic power stations

    Kutasov, R F; Mukhina, M P; Tustanovskii, A S

    1977-01-01

    The heat treatment of a welded rotor of grade 25Kh2NMFA steel for steam turbines of nuclear power plants was considered. A following heat treatment schedule was suggested: charging the rotor in to a furnace at 100-150 deg C, heating to 200-250 deg C and holding for 12 hrs; slow heating (10 deg C/h) to 400-450 deg C and holding for 12 hrs; slow heating to 630-640 deg C and holding for 50 hrs, cooling at a rate of 5 deg C/h down to 100 deg C, holding for 20 hrs and cooling with the furnace open. The proposed heat treatment schedule of a duration of 356 hrs ensures a temperature gradient throughout the cross section and the length of the rotor of not more than +-5 deg C, least deviations of geometric dimensions and makes possible machining finish to within 0-0.02 mm. Described are the particularities of the design of a roll-out hearth electric chamber furnace, measuring 13000x5500x5000 mm and built for the purpose of carrying out said heat treatment. The power rating of the furnace is 2850 kW.

  20. Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS2

    X. D. Li

    2015-05-01

    Full Text Available Single adsorption of different atoms on pristine two-dimensional monolayer MoS2 have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS2. Additionally, local or long-range magnetic moments of two-dimensional MoS2 sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS2 monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

  1. Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS{sub 2}

    Li, X. D.; Fang, Y. M.; Wu, S. Q., E-mail: zzhu@xmu.edu.cn, E-mail: wsq@xmu.edu.cn [Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005 (China); Zhu, Z. Z., E-mail: zzhu@xmu.edu.cn, E-mail: wsq@xmu.edu.cn [Department of Physics and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen 361005 (China); Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Xiamen 361005 (China)

    2015-05-15

    Single adsorption of different atoms on pristine two-dimensional monolayer MoS{sub 2} have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS{sub 2}. Additionally, local or long-range magnetic moments of two-dimensional MoS{sub 2} sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS{sub 2} monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

  2. High-resolution X-ray spectroscopy of hollow atoms created in plasma heated by subpicosecond laser radiation

    Faenov, A.Ya.; Magunov, A.I.; Pikuz, T.A.

    1997-01-01

    The investigations of ultrashort (0.4-0.6 ps) laser pulse radiation interaction with solid targets have been carried out. The Trident subpicosecond laser system was used for plasma creation. The X-ray plasma emission was investigated with the help of high-resolution spectrographs with spherically bent mica crystals. It is shown that when high contrast ultrashort laser pulses were used for plasma heating its emission spectra could not be explained in terms of commonly used theoretical models, and transitions in so called hollow atoms must be taken into account for adequate description of plasma radiation

  3. Understanding Atom Probe Tomography of Oxide-Supported Metal Nanoparticles by Correlation with Atomic-Resolution Electron Microscopy and Field Evaporation Simulation.

    Devaraj, Arun; Colby, Robert; Vurpillot, François; Thevuthasan, Suntharampillai

    2014-04-17

    Oxide-supported metal nanoparticles are widely used in heterogeneous catalysis. The increasingly detailed design of such catalysts necessitates three-dimensional characterization with high spatial resolution and elemental selectivity. Laser-assisted atom probe tomography (APT) is uniquely suited to the task but faces challenges with the evaporation of metal/insulator systems. Correlation of APT with aberration-corrected scanning transmission electron microscopy (STEM), for Au nanoparticles embedded in MgO, reveals preferential evaporation of the MgO and an inaccurate assessment of nanoparticle composition. Finite element field evaporation modeling is used to illustrate the evolution of the evaporation front. Nanoparticle composition is most accurately predicted when the MgO is treated as having a locally variable evaporation field, indicating the importance of considering laser-oxide interactions and the evaporation of various molecular oxide ions. These results demonstrate the viability of APT for analysis of oxide-supported metal nanoparticles, highlighting the need for developing a theoretical framework for the evaporation of heterogeneous materials.

  4. Charge transfer rates for xenon Rydberg atoms at metal and semiconductor surfaces

    Dunning, F.B. [Department of Physics and Astronomy, Rice University, MS 61, 6100 Main Street, Houston, TX 77005-1892 (United States)]. E-mail: fbd@rice.edu; Wethekam, S. [Institut fuer Physik der Humboldt-Universitaet zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Dunham, H.R. [Department of Physics and Astronomy, Rice University, MS 61, 6100 Main Street, Houston, TX 77005-1892 (United States); Lancaster, J.C. [Department of Physics and Astronomy, Rice University, MS 61, 6100 Main Street, Houston, TX 77005-1892 (United States)

    2007-05-15

    Recent progress in the study of charge exchange between xenon Rydberg atoms and surfaces is reviewed. Experiments using Au(1 1 1) surfaces show that under appropriate conditions each incident atom can be detected as an ion. The ionization dynamics, however, are strongly influenced by the perturbations in the energies and structure of the atomic states that occur as the ion collection field is applied and as the atom approaches the surface. These lead to avoided crossings between different atomic levels causing the atom to successively assume the character of a number of different states and lose much of its initial identity. The effects of this mixing are discussed. Efficient surface ionization is also observed at Si(1 0 0) surfaces although the ion signal is influenced by stray fields present at the surface.

  5. MD simulation of atomic displacements in metals and metallic bilayers under low energy ion bombardment at 300 K

    Kornich, G.V.; Betz, G.; Bazhin, A.I.

    1999-01-01

    MD simulations of 100 eV Ar ion bombardment of (1 0 0) Ni and Al as well as Al/Ni bilayer crystals at 300 K have been performed and compared to previous calculations at 0 K. The Al/Ni bilayer crystal consisted of one Al layer on a (1 0 0) Ni substrate. Sputtering yields for Ni and Al/Ni show no temperature dependence, while for Al a pronounced increase with temperature was observed. The contributions of different mechanisms to the production of surface and bulk defects are discussed. The mean square displacement (MSD) of atoms is in all cases larger at 300 K as compared to 0 K. The larger MSD at 300 K is mainly due to an increase in lateral (perpendicular to the ion beam) motion of displaced atoms. Similar the number of atomic jumps, in which an atom leaves its original Wigner-Seitz cell, increases in all cases with temperature. For the pure elements the production of bulk vacancies and interstitials decreases with temperature, but the number of surface vacancies and ad-atoms increases with temperature. For the bilayer system practically no temperature dependence for defects was observed

  6. Tuning the electronic structure and transport properties of graphene by noncovalent functionalization: effects of organic donor, acceptor and metal atoms

    Zhang Yonghui; Zhou Kaige; Xie Kefeng; Zeng Jing; Zhang Haoli; Peng Yong

    2010-01-01

    Using density functional theory and nonequilibrium Green's function (NEGF) formalism, we have theoretically investigated the binding of organic donor, acceptor and metal atoms on graphene sheets, and revealed the effects of the different noncovalent functionalizations on the electronic structure and transport properties of graphene. The adsorptions of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tetrathiafulvalene (TTF) induce hybridization between the molecular levels and the graphene valence bands, and transform the zero-gap semiconducting graphene into a metallic graphene. However, the current versus voltage (I-V) simulation indicates that the noncovalent modifications by organic molecules are not sufficient to significantly alter the transport property of the graphene for sensing applications. We found that the molecule/graphene interaction could be dramatically enhanced by introducing metal atoms to construct molecule/metal/graphene sandwich structures. A chemical sensor based on iron modified graphene shows a sensitivity two orders of magnitude higher than that of pristine graphene. The results of this work could help to design novel graphene-based sensing or switching devices.

  7. Atom-Probe Tomographic Investigation of Austenite Stability and Carbide Precipitation in a TRIP-Assisted 10 Wt Pct Ni Steel and Its Weld Heat-Affected Zones

    Jain, Divya; Seidman, David N.; Barrick, Erin J.; DuPont, John N.

    2018-04-01

    Newly developed low-carbon 10 wt pct Ni-Mo-Cr-V martensitic steels rely on the Ni-enriched, thermally stable austenite [formed via multistep intercritical Quench-Lamellarization-Tempering ( QLT)-treatment] for their superior mechanical properties, specifically ballistic resistance. Critical to the thermal stability of austenite is its composition, which can be severely affected in the weld heat-affected zones (HAZs) and thus needs investigations. This article represents the first study of the nanoscale redistributions of C, Ni, and Mn in single-pass HAZ microstructures of QLT-treated 10 wt pct Ni steels. Local compositions of Ni-rich regions (representative of austenite compositions) in the HAZs are determined using site-specific 3-D atom-probe tomography (APT). Martensite-start temperatures are then calculated for these compositions, employing the Ghosh-Olson thermodynamic and kinetics approach. These calculations predict that austenite (present at high temperatures) in the HAZs is susceptible to a martensitic transformation upon cooling to room temperature, unlike the austenite in the QLT-treated base-metal. While C in the QLT-treated base-metal is consumed primarily in MC and M2C-type carbide precipitates (M is Mo, Cr, V), its higher concentration in the Ni-rich regions in the HAZs indicates the dissolution of carbide precipitates, particularly M2C carbide precipitates. The role of M2C carbide precipitates and austenite stability is discussed in relation to the increase in microhardness values observed in the HAZs, relative to the QLT-treated base-metal. Insights gained from this research on austenite stability and carbide precipitation in the single-pass HAZ microstructures will assist in designing multiple weld cycles for these novel 10 wt pct Ni steels.

  8. Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

    Kaasbjerg, Kristen; Martiny, Johannes H. J.; Low, Tony

    2017-01-01

    protectionmechanism against intervalley scattering in monolayer TMDs. The predicteddefectdependent selection rules for intervalley scattering can be verified viaFourier transform scanning tunneling spectroscopy (FT-STS), and provide aunique identification of, e.g., atomic vacancy defects (M vs X). Our findingsare......Intervalley scattering by atomic defects in monolayer transition metaldichalcogenides (TDMs; MX2) presents a serious obstacle for applicationsexploiting their unique valley-contrasting properties. Here, we show that thesymmetry of the atomic defects can give rise to an unconventional...

  9. Heaters to simulate fuel pins for heat transfer tests in single-phase liquid-metal-flow

    Casal, V.; Graf, E.; Hartmann, W.

    1976-09-01

    The development of heaters for thermal simulation of the fuel elements of liquid metal cooled fast breeder reactors (SNR) is reported. Beginning with the experimental demands various heating methods are discussed for thermodynamic investigations of the heat transfer in liquid metals. Then a preferred heater rod is derived to simulate the fuel pins of a SNR. Finally it is reported on the fabrication and the operation practice. (orig.) [de

  10. Visible Light-Induced Metal Free Surface Initiated Atom Transfer Radical Polymerization of Methyl Methacrylate on SBA-15

    Liang Ma

    2017-02-01

    Full Text Available Surface-initiated atom transfer radical polymerization (SI-ATRP is one of the most versatile techniques to modify the surface properties of materials. Recent developed metal-free SI-ATRP makes such techniques more widely applicable. Herein photo-induced metal-free SI-ATRP of methacrylates, such as methyl methacrylate, N-isopropanyl acrylamide, and N,N-dimethylaminoethyl methacrylate, on the surface of SBA-15 was reported to fabricate organic-inorganic hybrid materials. A SBA-15-based polymeric composite with an adjustable graft ratio was obtained. The structure evolution during the SI-ATRP modification of SBA-15 was monitored and verified by FT-IR, XPS, TGA, BET, and TEM. The obtained polymeric composite showed enhanced adsorption ability for the model compound toluene in aqueous conditions. This procedure provides a low-cost, readily available, and easy modification method to synthesize polymeric composites without the contamination of metal.

  11. Effect of diameter of metal nanowires on pool boiling heat transfer with FC-72

    Kumar G., Udaya; S., Suresh; M. R., Thansekhar; Babu P., Dinesh

    2017-11-01

    Effect of varying diameter of metal nanowires on pool boiling heat transfer performance is presented in this study. Copper nanowires (CuNWs) of four different diameters (∼35 nm, ∼70 nm, ∼130 nm and ∼200 nm) were grown directly on copper specimen using template-based electrodeposition technique. Both critical heat flux (CHF) and boiling heat transfer coefficient (h) were found to be improved in surfaces with nanowires as compared to the bare copper surface. Moreover, both the parameters were found to increase with increasing diameter of the nanowires. The percentage increases observed in CHF for the samples with nanowires were 38.37%, 40.16%, 48.48% and 45.57% whereas the percentage increase in the heat transfer coefficient were 86.36%, 95.45%, 184.1% and 131.82% respectively as compared to the bare copper surface. Important reasons believed for this enhancement were improvement in micron scale cavity density and cavity size which arises as a result of the coagulation and grouping of nanowires during the drying process. In addition to this, superhydrophilic nature, capillary effect, and enhanced bubble dynamics parameters (bubble frequency, bubble departure diameter, and nucleation site density) were found to be the concurring mechanisms responsible for this enhancement in heat transfer performance. Qualitative bubble dynamics analysis was done for the surfaces involved and the visual observations are provided to support the results presented and discussed.

  12. Parametric investigation on transient boiling heat transfer of metal rod cooled rapidly in water pool

    Lee, Chi Young [Department of Fire Protection Engineering, Pukyong National University, 45, Yongso-ro, Nam-gu, Busan 48513 (Korea, Republic of); Kim, Sunwoo, E-mail: swkim@alaska.edu [Mechanical Engineering Department, University of Alaska Fairbanks, P. O. Box 755905, Fairbanks, AK 99775-5905 (United States)

    2017-03-15

    Highlights: • Effects of liquid subcooling, surface coating, material property, and surface oxidation are examined. • Liquid subcooling affects remarkably the quenching phenomena. • Cr-coated surfaces for ATF might extend the quenching duration. • Solids with low heat capacity shorten the quenching duration. • Surface oxidation can affect strongly the film boiling heat transfer and MFB point. - Abstract: In this work, the effects of liquid subcooling, surface coating, material property, and surface oxidation on transient pool boiling heat transfer were investigated experimentally using the vertical metal rod and quenching method. The change in rod temperature was measured with time during quenching, and the visualization of boiling around the test specimen was performed using the high-speed video camera. As the test materials, the zircaloy (Zry), stainless steel (SS), niobium (Nb), and copper (Cu) were tested. In addition, the chromium-coated niobium (Cr-Nb) and chromium-coated stainless steel (Cr-SS) were prepared for accident tolerant fuel (ATF) application. Low liquid subcooling and Cr-coating shifted the quenching curve to the right, which indicates a prolongation of quenching duration. On the other hand, the material with small heat capacity and surface oxidation caused the quenching curve to move to the left. To examine the influence of the material property and surface oxidation on the film boiling heat transfer performance and minimum film boiling (MFB) point in more detail, the wall temperature and heat flux were calculated from the present transient temperature profile using the inverse heat transfer analysis, and then the curves of wall temperature and heat flux in the film boiling regime were obtained. In the present experimental conditions, the effect of material property on the film boiling heat transfer performance and MFB point seemed to be minor. On the other hand, based on the experimental results of the Cu test specimen, the surface

  13. Magnetic properties of Mg12O12 nanocage doped with transition metal atoms (Mn, Fe, Co and Ni): DFT study

    Javan, Masoud Bezi

    2015-07-01

    Binding energy of the Mg12O12 nanocage doped with transition metals (TM=Mn, Fe, Co and Ni) in endohedrally, exohedrally and substitutionally forms were studied using density functional theory with the generalized gradient approximation exchange-correlation functional along 6 different paths inside and outside of the Mg12O12 nanocage. The most stable structures were determined with full geometry optimization near the minimum of the binding energy curves of all the examined paths inside and outside of the Mg12O12 nanocage. The results reveal that for all stable structures, the Ni atom has a larger binding energy than the other TM atoms. It is also found that for all complexes additional peaks contributed by TM-3d, 4s and 4p states appear in the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap of the host MgO cluster. The mid-gap states are mainly due to the hybridization between TM-3d, 4s and 4p orbitals and the cage π orbitals. The magnetic moment of the endohedrally doped TM atoms in the Mg12O12 are preserved to some extent due to the interaction between the TM and Mg12O12 nanocage, in contrast to the completely quenched magnetic moment of the Fe and Ni atoms in the Mg11(TM)O12 complexes. Furthermore, charge population analysis shows that charge transfer occurs from TM atom to the cage for endohedrally and substitutionally doping.

  14. Atomic structure of shear bands in Cu64Zr36 metallic glasses studied by molecular dynamics simulations

    Feng, Shidong; Qi, Li; Wang, Limin; Pan, Shaopeng; Ma, Mingzhen; Zhang, Xinyu; Li, Gong; Liu, Riping

    2015-01-01

    Graphical abstract: Figure shows that atoms in the shear band (SB) moved desultorily compared with those in the matrix. These atoms seriously interacted with each other similar to the grain boundary in crystalline materials. Figuratively, if these atoms wanted to “pass” the shear band, they should arrange their irritations. However, stress concentrations and high energy were observed in SB, which resulted in instability in the deformation process and finally led to a disastrously brittle fracture. - Abstract: Molecular dynamics simulations on the atomic structure of shear bands (SBs) in Cu 64 Zr 36 metallic glasses are presented. Results show that the atoms in the SB move desultorily, in contrast to those in the matrix. The saturated degree of bonded pairs considering the “liquid-like” character of SB quantitatively provides important details in extending earlier studies on SBs. Zr-centered 〈0, 2, 8, 5〉 clusters exhibit strong spatial correlations and tendency to connect with each other in short-range order. The 〈0, 2, 8, 5〉 cluster-type medium-range order is the main feature inside the SB relative to the matrix. The fractal results demonstrate the planar-like fashion of the 〈0, 2, 8, 5〉 network in SB, forming an interpenetrating solid-like backbone. Such heterogeneous structure provides a fundamental structural perspective of mechanical instability in SB

  15. Tungsten determination in heat resistant nickel-base-alloys by the method of atomic absorption

    Gregorczyk, S.; Wycislik, A.

    1980-01-01

    A method of atomic absorption was developed. It allows for the tungsten to be determined in heatresistant nickel-base-alloys within the range 0.01 to 7%. It consists in precipitating tungsten acid in the presence of alkaloids with its following decomposition by hydrofluoric acid in the teflon bomb. (author)

  16. Metals on graphene and carbon nanotube surfaces: From mobile atoms to atomtronics to bulk metals to clusters and catalysts

    Sarkar, Santanu C.; Moser, Matthew L.; Tian, Xiaojuan; Zhang, Xixiang; Al-Hadeethi, Yas Fadel; Haddon, Robert C.

    2014-01-01

    , and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight some

  17. Heating treatment schemes for enhancing chelant-assisted phytoextraction of heavy metals from contaminated soils.

    Chen, Yahua; Wang, Chunchun; Wang, Guiping; Luo, Chunling; Mao, Ying; Shen, Zhenguo; Li, Xiangdong

    2008-04-01

    Recent research has shown that chelant-assisted phytoextraction approaches often require a high dosage of chelant applied to soil. The present study focused on optimization of phytoremediation processes to increase the phytoextraction efficiency of metals at reduced chelant applications. Pot experiments were carried out to investigate the effects of increased soil temperature on shoot uptake of heavy metals by corn (Zea mays L.) and mung bean (Vigna radiat L. Wilczek) from heavy metal-contaminated soils. After the application of S,S-ethylenediaminedisuccinic acid or ethylenediaminetetra-acetic acid, soils were exposed to high temperatures (50 or 80 degrees C) for 3 h, which significantly increased the concentration of heavy metals in shoots. The heating treatment 2 d after the chelant addition resulted in higher concentrations of metals compared with those treatments 2 d before or simultaneously with the chelant application. Irrigation with 100 degrees C water 2 d after the chelant addition, or irrigation with 100 degrees C chelant solutions directly, also resulted in significantly higher phytoextraction of metals in the two crops compared with 25 degrees C chelant solutions. In addition, a novel application method to increase soil temperature using underground polyvinyl chloride tubes would increase the chelant-assisted extraction efficiency of Cu approximately 10- to 14-fold in corn and fivefold in mung bean compared with those nonheating treatments. In a field experiment, increasing soil temperature 2 d after chelant addition also increased the shoot Cu uptake approximately fivefold compared with those nonheating treatments. This new technique may represent a potential, engineering-oriented approach for phytoremediation of metal-polluted soils.

  18. Controlling magnetism of MoS2 sheets by embedding transition-metal atoms and applying strain.

    Zhou, Yungang; Su, Qiulei; Wang, Zhiguo; Deng, Huiqiu; Zu, Xiaotao

    2013-11-14

    Prompted by recent experimental achievement of transition metal (TM) atoms substituted in MoS2 nanostructures during growth or saturating existing vacancies (Sun et al., ACS Nano, 2013, 7, 3506; Deepak et al., J. Am. Chem. Soc., 2007, 129, 12549), we explored, via density functional theory, the magnetic properties of a series of 3d TM atoms substituted in a MoS2 sheet, and found that Mn, Fe, Co, Ni, Cu and Zn substitutions can induce magnetism in the MoS2 sheet. The localizing unpaired 3d electrons of TM atoms respond to the introduction of a magnetic moment. Depending on the species of TM atoms, the substituted MoS2 sheet can be a metal, semiconductor or half-metal. Remarkably, the applied elastic strain can be used to control the strength of the spin-splitting of TM-3d orbitals, leading to an effective manipulation of the magnetism of the TM-substituted MoS2 sheet. We found that the magnetic moment of the Mn- and Fe-substituted MoS2 sheets can monotonously increase with the increase of tensile strain, while the magnetic moment of Co-, Ni-, Cu- and Zn-substituted MoS2 sheets initially increases and then decreases with the increase of tensile strain. An instructive mechanism was proposed to qualitatively explain the variation of magnetism with elastic strain. The finding of the magnetoelastic effect here is technologically important for the fabrication of strain-driven spin devices on MoS2 nanostructures, which allows us to go beyond the current scope limited to the spin devices within graphene and BN-based nanostructures.

  19. Studying nearest neighbor correlations by atom probe tomography (APT) in metallic glasses as exemplified for Fe40Ni40B20 glassy ribbons

    Shariq, Ahmed; Al-Kassab, Talaat; Kirchheim, Reiner

    2012-01-01

    resolution of the analytical technique. However, fitting Gaussian distributions to the distribution of atomic distances yields average distances with statistical uncertainties of 2 to 3 hundredth of an Angstrom. Fe 40Ni40B20 metallic glass ribbons

  20. Liquid metal targets for high-power applications : pulsed heating and shock hydrodynamics

    Hassanein, A.

    2000-01-01

    Significant interest has recently focused on the use of liquid-metal targets flowing with high velocities for various high-power nuclear and high-energy physics applications such as fusion reactor first-walls, the Spallation Neutron Source, Isotope Separation On Line, and Muon Collider projects. This is because the heat generated in solid targets due to beam or plasma bombardment cannot be removed easily and the resulting thermal shock damage could be a serious lifetime problem for long-term operation. More recently, the use of free or open flying-liquid jets has been proposed for higher-power-density applications. The behavior of a free-moving liquid mercury or gallium jet subjected to proton beam deposition in a strong magnetic field has been modeled and analyzed for the Muon Collider project. Free-liquid-metal jets can offer significant advantages over conventional solid targets, particularly for the more demanding and challenging high-power applications. However, the use of free-moving liquid-metal targets raises a number of new and challenging problems such as instabilities of the jet in a strong magnetic field, induced eddy-current effects on jet shape, thermal-shock formation, and possible jet fragmentation. Problems associated with shock heating of liquid jets in a strong magnetic field are analyzed in this study

  1. Ceramic or metallic? - material aspects of compact heat regenerator energy efficiency

    Wnek, M

    2012-01-01

    The metal industry cannot afford the financial mismanagement in the era of rising energy prices and thus, the high efficiency devices should be used. In the metallurgical thermal processes the combustion air temperature increasing is one of the methods for obtaining the heat transfer intensification and the furnaces efficiency rising. Therefore the new and effective heating technologies in thermal processes are demanded all the time. The regenerative systems are most effective in terms of the heated air level. The individual regenerators for burners are the newest solutions where the temperature of 1100 °C is reachable for the exhaust temperature of 1200 °C. Based on research results, performed for the assumed exhaust temperature of 1100 °C, the paper presents possibilities of changeable different materials using as a regenerator filling in the aspect of its operation efficiency. Such materials as high-temperature steel, Al 2 O 3 and SiC have been considered. The paper presents the selected data research, dealing with the air combustion temperature obtained for the same type of regenerator filling of considered materials. The fuel consumption reduction and reduction of CO 2 emission, for metal regenerator filling, have been presented finally as an economic and environmental aspect accordingly to the air preheated.

  2. Ceramic or metallic? - material aspects of compact heat regenerator energy efficiency

    Wnek, M.

    2012-05-01

    The metal industry cannot afford the financial mismanagement in the era of rising energy prices and thus, the high efficiency devices should be used. In the metallurgical thermal processes the combustion air temperature increasing is one of the methods for obtaining the heat transfer intensification and the furnaces efficiency rising. Therefore the new and effective heating technologies in thermal processes are demanded all the time. The regenerative systems are most effective in terms of the heated air level. The individual regenerators for burners are the newest solutions where the temperature of 1100 °C is reachable for the exhaust temperature of 1200 °C. Based on research results, performed for the assumed exhaust temperature of 1100 °C, the paper presents possibilities of changeable different materials using as a regenerator filling in the aspect of its operation efficiency. Such materials as high-temperature steel, Al2O3 and SiC have been considered. The paper presents the selected data research, dealing with the air combustion temperature obtained for the same type of regenerator filling of considered materials. The fuel consumption reduction and reduction of CO2 emission, for metal regenerator filling, have been presented finally as an economic and environmental aspect accordingly to the air preheated.

  3. Prediction of heat generation in rubber or rubber-metal springs

    Banić Milan S.

    2012-01-01

    Full Text Available The temperature of rubber or rubber-metal springs increases under cyclic loading, due to hysteresis losses and low rubber thermal conductivity. Hysteresis losses correspond to energy dissipation from the rubber, which is primarily converted into heat. This well-known phenomenon, called heat build-up, is the primary reason for rubber aging. Increase in temperature within the rubber compound leads to degradation of its physical and chemical properties, increase in stiffness and loss of damping capability. This paper presents a novel procedure of heat generation prediction in rubber or rubber-metal springs. The procedure encompasses the prediction of hysteresis loss, i. e. dissipated energy within the rubber, by finite element analysis and application of a modern visco-plastic rubber constitutive model. The obtained dissipated energy was used as an input for transient thermal analysis. Verification of the proposed procedure was performed by comparison of simulation results with experimentally obtained data during the dynamic loading of the rubber specimen. The proposed procedure is highly computationally efficient and it enables time integration, which can be problematic in coupled mechanical thermal analysis. [Projekat Ministarstva nauke Republike Srbije, br. TR35005: Research and Development of New Generation of Wind Turbines of High Energy Efficiency

  4. Investigation on Minimum Film Boiling Point of Highly Heated Vertical Metal Rod in Aqueous Surfactant Solution

    Lee, Chi Young; Kim, Jae Han [Pukyong Nat’l Univ., Busan (Korea, Republic of)

    2017-09-15

    In this study, experiments were conducted on the MFB(minimum film boiling) point of highly heated vertical metal rod quenched in aqueous surfactant solution at various temperature conditions. The aqueous Triton X-100 solution(100 wppm) and pure water were used as the liquid pool. Their temperatures ranged from 77 °C to 100 °C. A stainless steel vertical rod of initial center temperature of 500 °C was used as a test specimen. In both liquid pools, as the liquid temperature decreased, the time to reach the MFB point decreased with a parallel increase in the temperature and heat flux of the MFB point. However, over the whole present temperature range, in the aqueous Triton X-100 solution, the time to reach the MFB point was longer, while the temperature and heat flux of the MFB point were reduced when compared with pure water. Based on the present experimental data, this study proposed the empirical correlations to predict the MFB temperature of a high temperature vertical metal rod in pure water and in aqueous Triton X-100 solution.

  5. Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy

    Fardi Ilkhchy, A.; Jabbari, Masoud; Davami, P.

    2012-01-01

    The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat...... conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula...... was presented for correlation between external pressure and heat transfer coefficient. Acceptable agreement with data in literature shows the accuracy of the proposed formula....

  6. Use of electrothermal atomization for determining metallic impurities in nuclearly pure uranium compounds

    Franco, M.B.

    1986-01-01

    Atomic absorption spectrometry with electrothermal atomization was used for the determination of Al, Cd, Cr, Fe, Mn, Mo and Ni as impurities in uranium oxide samples. The determinations were performed in solubilized samples both with and without uranium separation as well as in solid samples. (Author) [pt

  7. Use of electrothermal atomization for determining metallic impurities in nuclearly pure uranium compounds

    Franco, M.B.

    1985-01-01

    Atomic absorption spectrometry with electrothermal atomization was used for the determination of Al, Cd, Cr, Fe, Mn, Mo and Ni as impurities in uranium oxide samples. The determinations were performed in solubilized samples both with and without uranium separation as well as in solid samples. (Author) [pt

  8. Thermophysical data for various transition metals at high temperatures obtained by a submicrosecond-pulse-heating method

    Seydel, U.; Bauhof, H.; Fucke, W.; Wadle, H.

    1979-01-01

    Thermophysical data for several transition metals are reported including enthalpies, electric resistivities, and specific volumes at the melting transition, and volume expansion coefficients and heat capacities in the liquid phase. Values for the critical temperatures, pressures, and volumes are given for molybdenum and tungsten. All data have been obtained by a submicrosecond-pulse-heating method. (author)

  9. Atomic fusion, Gerrard atomic fusion

    Gerrard, T.H.

    1980-01-01

    In the approach to atomic fusion described here the heat produced in a fusion reaction, which is induced in a chamber by the interaction of laser beams and U.H.F. electromagnetic beams with atom streams, is transferred to a heat exchanger for electricity generation by a coolant flowing through a jacket surrounding the chamber. (U.K.)

  10. Silica gel modified with N-(3-propyl)-O-phenylenediamine: functionalization, metal sorption equilibrium studies and application to metal enrichment prior to determination by flame atomic absorption spectrometry.

    Akl, Magda Ali Abd-elAziz; Kenawy, Ibraheim Mohamed; Lasheen, Rabab Ramadan

    2005-08-01

    The use of the chemically modified silica gel N-(3-propyl)-O-phenylenediamine (SiG-NPPDA) adsorbent, for the preconcentration and separation of trace heavy metals, was described. SiG-NPPDA sorbs quantitatively (90-100% recovery) trace amounts of nine heavy metals, viz., Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) at pH 7-8. The sorption capacity varies from 350 to 450 micromol g(-1). Desorption was found to be quantitative with 1-2 M HNO3 or 0.05 M Na2EDTA. The distribution coefficient, Kd and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C(M,eqm)% (Recovery, R%), were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, log Kd, ranges between 4.0 and 6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS). The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance), potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the SiG-NPPDA adsorbent and the investigated metal ions is proposed to be due to the reaction of the investigated metal ions with the two nitrogen atoms of the SiG-NPPDA adsorbent. The present adsorbent coupled with flame AAS has been used to enrich and determine the nine metal ions in natural aqueous systems and in certified reference materials (RSD < or = 5%). The copper, iron, manganese and zinc present in some pharmaceutical vitamin samples were also preconcentrated on SiG-NPPDA adsorbent and determined by flame AAS (RSD < or = 4.2%). Nanogram concentrations (0.07-0.14 ng ml(-1)) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.

  11. Coloration of metallic and/or ceramic surfaces obtained by atomic layer deposited nano-coatings

    Guzman, L., E-mail: luisg47@gmail.com [Fondazione Bruno Kessler (FBK), Centro Materiali e Microsistemi, Functional Materials & Photonic Structures Unit, via Sommarive 18, 38123 Trento (Italy); Vettoruzzo, F. [Ronda High Tech, via Vegri 83, 36010 Zane’, Vicenza (Italy); Laidani, N. [Fondazione Bruno Kessler (FBK), Centro Materiali e Microsistemi, Functional Materials & Photonic Structures Unit, via Sommarive 18, 38123 Trento (Italy)

    2016-02-29

    By depositing single layer coatings by means of physical vapor techniques, tailoring of their coloration is generally complex because a given color can be obtained only by very high composition control. Physical vapor deposition (PVD) processes are expensive and cannot be easily used for obtaining conformal coating on three-dimensional objects. Moreover PVD coatings exhibit intrinsic defects (columnar structures, pores) that affect their functional properties and applications such as barrier layers. Atomic layer deposition (ALD) technology delivers conformal coatings on different materials with very low defectiveness. A straightforward coloration can be obtained by a combination of two types of layers with different refraction index, deposited to high thickness precision. Computer simulation studies were performed to design the thickness and architecture of multilayer structures, to a total thickness of approximately 100 nm, suitable to modify the typical coloration of some materials, without altering their other physical and chemical properties. The most promising nano-layered structures were then deposited by ALD and tested with regard to their optical properties. Their total thicknesses were specified in such a way to be technically feasible and compatible with future industrial production. The materials employed in this study to build the optical coatings, are two oxides (Al{sub 2}O{sub 3}, TiO{sub 2}) deposited at 120 °C and two nitrides (AlN, TiN), which need a deposition temperature of 400 °C. The possibility of using such modern deposition technology for esthetic and decorative purposes, while maintaining the functional properties, opens perspectives of industrial applications. - Highlights: • Computer simulation is done to design multilayers made of Al{sub 2}O{sub 3}, TiO{sub 2}, AlN, and TiN. • Total thickness (< 120 nm) is specified to be compatible with industrial production. • The most promising nano-layered structures are then produced and

  12. INDUCTION HEATING OF NON-MAGNETIC SHEET METALS IN THE FIELD OF A FLAT CIRCULAR MULTITURN SOLENOID

    Y. Batygin

    2016-06-01

    Full Text Available The theoretical analysis of electromagnetic processes in the system for induction heating presented by a flat circular multiturn solenoid positioned above a plane of thin sheet non-magnetic metal has been conducted. The calculated dependences for the current induced in a metal sheet blank and ratio of transformation determined have been obtained. The maximal value of the transformation ratio with regard to spreading the eddy-currents over the whole area of the sheet metal has been determined.

  13. Joule-Heated Molten Regolith Electrolysis Reactor Concepts for Oxygen and Metals Production on the Moon and Mars

    Sibille, Laurent; Dominques, Jesus A.

    2012-01-01

    The maturation of Molten Regolith Electrolysis (MRE) as a viable technology for oxygen and metals production on explored planets relies on the realization of the self-heating mode for the reactor. Joule heat generated during regolith electrolysis creates thermal energy that should be able to maintain the molten phase (similar to electrolytic Hall-Heroult process for aluminum production). Self-heating via Joule heating offers many advantages: (1) The regolith itself is the crucible material, it protects the vessel walls (2) Simplifies the engineering of the reactor (3) Reduces power consumption (no external heating) (4) Extends the longevity of the reactor. Predictive modeling is a tool chosen to perform dimensional analysis of a self-heating reactor: (1) Multiphysics modeling (COMSOL) was selected for Joule heat generation and heat transfer (2) Objective is to identify critical dimensions for first reactor prototype.

  14. Can heavy metal pollution defend seed germination against heat stress? Effect of heavy metals (Cu(2+), Cd(2+) and Hg(2+)) on maize seed germination under high temperature.

    Deng, Benliang; Yang, Kejun; Zhang, Yifei; Li, Zuotong

    2016-09-01

    Heavy metal pollution, as well as greenhouse effect, has become a serious threat today. Both heavy metal and heat stresses can arrest seed germination. What response can be expected for seed germination under both stress conditions? Here, the effects of heavy metals (Cu(2+), Cd(2+) and Hg(2+)) on maize seed germination were investigated at 20 °C and 40 °C. Compared with 20 °C, heat stress induced thermodormancy. However, this thermodormancy could be significantly alleviated by the addition of a low concentration of heavy metals. Heavy metals, as well as heat stress induced H2O2 accumulation in germinating seeds. Interestingly, this low concentration of heavy metal that promoted seed germination could be partly blocked by DMTU (a specific ROS scavenger), irrespective of temperature. Accordingly, H2O2 addition reinforced this promoting effect on seed germination, which was induced by a low concentration of heavy metal. Furthermore, we found that the NADPH oxidase derived ROS was required for seed germination promoted by the heavy metals. Subsequently, treatment of seeds with fluridone (a specific inhibitor of ABA) or ABA significantly alleviated or aggravated thermodormancy, respectively. However, this alleviation or aggravation could be partly attenuated by a low concentration of heavy metals. In addition, germination that was inhibited by high concentrations of heavy metals was also partly reversed by fluridone. The obtained results support the idea that heavy metal-mediated ROS and hormone interaction can finally affect the thermodormancy release or not. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100- x Al x Metallic Glasses

    Tahiri, M.; Hasnaoui, A.; Sbiaai, K.

    2018-06-01

    In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to model the atomic interaction with different compositions. The results showed evidence of the metallic glass formation induced by the split occurring in the second peak of the radial distribution function (RDF) curves implying both Ti and Al atoms. The common neighbor analysis (CNA) method confirmed the presence of the icosahedral clusters with a maximum amount observed for an alloy with 75 pct of Al. Analysis of coordination numbers (CNs) indicated that the total CNs are nearly unchanged in these systems. Finally, Voronoi tessellation analyses (VTA) showed a higher value of the number of icosahedral units at Ti25Al75 composition. This specific composition represents a nearby peritectic point localized at a low melting point in the Ti-Al binary phase diagram. The glass forming ability (GFA) becomes important when the fraction of Al increases by forming and connecting "icosahedral-like" clusters (12-coordinated and 13-coordinated ) and by playing a main role in the structure stability of the Ti-Al MGs.

  16. Atomic Scale Investigation of Structural Properties and Glass Forming Ability of Ti100-x Al x Metallic Glasses

    Tahiri, M.; Hasnaoui, A.; Sbiaai, K.

    2018-03-01

    In this work, we employed molecular dynamics (MD) simulations to study Ti-Al metallic glasses (MGs) using the embedded atom method (EAM) potential to model the atomic interaction with different compositions. The results showed evidence of the metallic glass formation induced by the split occurring in the second peak of the radial distribution function (RDF) curves implying both Ti and Al atoms. The common neighbor analysis (CNA) method confirmed the presence of the icosahedral clusters with a maximum amount observed for an alloy with 75 pct of Al. Analysis of coordination numbers (CNs) indicated that the total CNs are nearly unchanged in these systems. Finally, Voronoi tessellation analyses (VTA) showed a higher value of the number of icosahedral units at Ti25Al75 composition. This specific composition represents a nearby peritectic point localized at a low melting point in the Ti-Al binary phase diagram. The glass forming ability (GFA) becomes important when the fraction of Al increases by forming and connecting "icosahedral-like" clusters (12-coordinated and 13-coordinated ) and by playing a main role in the structure stability of the Ti-Al MGs.

  17. Bed geometries, fueling strategies and optimization of heat exchanger designs in metal hydride storage systems for automotive applications: A review

    Mazzucco, Andrea; Dornheim, Martin; Sloth, Michael

    2014-01-01

    This review presents recent developments for effective heat management systems to be integrated in metal hydride storage tanks, and investigates the performance improvements and limitations of each particular solution. High pressures and high temperatures metal hydrides can lead to different design...... given to metal hydride storage tanks for light duty vehicles, since this application is the most promising one for such storage materials and has been widely studied in the literature. Enhancing cooling/heating during hydrogen uptake and discharge has found to be essential to improve storage systems...

  18. MHD and heat transfer benchmark problems for liquid metal flow in rectangular ducts

    Sidorenkov, S.I.; Hua, T.Q.; Araseki, H.

    1994-01-01

    Liquid metal cooling systems of a self-cooled blanket in a tokamak reactor will likely include channels of rectangular cross section where liquid metal is circulated in the presence of strong magnetic fields. MHD pressure drop, velocity distribution and heat transfer characteristics are important issues in the engineering design considerations. Computer codes for the reliable solution of three-dimensional MHD flow problems are needed for fusion relevant conditions. Argonne National Laboratory and The Efremov Institute have jointly defined several benchmark problems for code validation. The problems, described in this paper, are based on two series of rectangular duct experiments conducted at ANL; one of the series is a joint ANL/Efremov experiment. The geometries consist of variation of aspect ratio and wall thickness (thus wall conductance ratio). The transverse magnetic fields are uniform and nonuniform in the axial direction

  19. A Difference in Using Atomic Layer Deposition or Physical Vapour Deposition TiN as Electrode Material in Metal-Insulator-Metal and Metal-Insulator-Silicon Capacitors

    Groenland, A.W.; Wolters, Robertus A.M.; Kovalgin, Alexeij Y.; Schmitz, Jurriaan

    2011-01-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the

  20. Enhanced apatite formation on Ti metal heated in PO2-controlled nitrogen atmosphere.

    Hashimoto, Masami; Hayashi, Kazumi; Kitaoka, Satoshi

    2013-10-01

    The oxynitridation of biomedical titanium metal under a precisely regulated oxygen partial pressure (PO2) of 10(-14)Pa in nitrogen atmosphere at 973 K for 1 h strongly enhanced apatite formation compared with that on Ti heated in air. The factors governing the high apatite-forming ability are discussed from the viewpoint of the surface properties of Ti heated under a PO2 of 10(-14)Pa in nitrogen atmosphere determined from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. Nitrogen (N)-doped TiO2 (interstitial N) was formed on pure Ti heated under a PO2 of 10(-14)Pa in nitrogen atmosphere at 973 K. The XPS O1s main peak shifted toward a lower binding energy upon heating under a PO2 of 10(-14)Pa. This shift may be due to the formation of oxygen vacancies. This Ti surface had a positive zeta potential of approximately 20 mV. According to time-of-flight secondary ion mass spectroscopy results, PO4(3-) ions were predominantly adsorbed on Ti soaked in simulated body fluid (SBF) after heat treatment, followed by calcium ions. It was concluded that the apatite formation kinetics can be described using the Avrami-Erofeev equation with an Avrami index of n=2, which implies the instantaneous nucleation of apatite on the surface of Ti soaked in SBF after heat treatment at 973 K under a PO2 of 10(-14)Pa. Copyright © 2013 Elsevier B.V. All rights reserved.