Science.gov

Sample records for polycrystalline tungsten formed

  1. Chemically assisted ion beam etching of polycrystalline and (100)tungsten

    NASA Technical Reports Server (NTRS)

    Garner, Charles

    1987-01-01

    A chemically assisted ion-beam etching technique is described which employs an ion beam from an electron-bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 microns thick with good anisotropy and pattern definition over areas of 30 sq mm, and with a high degree of selectivity. (100) tungsten foils etched with this process exhibit preferred-orientation etching, while polycrystalline tungsten films exhibit high etch rates. This technique can be used to pattern the dispenser cathode surfaces serving as electron emitters in traveling-wave tubes to a controlled porosity.

  2. Controlled nanostructuration of polycrystalline tungsten thin films

    SciTech Connect

    Girault, B.; Eyidi, D.; Goudeau, P.; Guerin, P.; Bourhis, E. Le; Renault, P.-O.; Sauvage, T.

    2013-05-07

    Nanostructured tungsten thin films have been obtained by ion beam sputtering technique stopping periodically the growing. The total thickness was maintained constant while nanostructure control was obtained using different stopping periods in order to induce film stratification. The effect of tungsten sublayers' thicknesses on film composition, residual stresses, and crystalline texture evolution has been established. Our study reveals that tungsten crystallizes in both stable {alpha}- and metastable {beta}-phases and that volume proportions evolve with deposited sublayers' thicknesses. {alpha}-W phase shows original fiber texture development with two major preferential crystallographic orientations, namely, {alpha}-W<110> and unexpectedly {alpha}-W<111> texture components. The partial pressure of oxygen and presence of carbon have been identified as critical parameters for the growth of metastable {beta}-W phase. Moreover, the texture development of {alpha}-W phase with two texture components is shown to be the result of a competition between crystallographic planes energy minimization and crystallographic orientation channeling effect maximization. Controlled grain size can be achieved for the {alpha}-W phase structure over 3 nm stratification step. Below, the {beta}-W phase structure becomes predominant.

  3. Heated die facilitates tungsten forming

    NASA Technical Reports Server (NTRS)

    Chattin, J. H.; Haystrick, J. E.; Laughlin, J. C.; Leidy, R. A.

    1966-01-01

    Tungsten forming in a press brake employs a bottom die assembly with a heating manifold between two water-cooled die sections. The manifold has hydrogen-oxygen burners spaced along its length for even heat during forming.

  4. Scandium oxide coated polycrystalline tungsten studied using emission microscopy and photoelectron spectroscopy.

    PubMed

    Wan, Congshang; Vaughn, Joel M; Sadowski, Jerzy T; Kordesch, Martin E

    2012-08-01

    Thermionic electron emission from 200 to 500 nm thick coatings of scandium oxide on tungsten foil have been examined in thermionic emission microscopy, spectroscopic photoelectron microcopy, synchrotron radiation and ultraviolet photoelectron spectroscopy (UPS). A clear dependence of the scandium oxide-W electron yield on the grain orientation of the polycrystalline tungsten is observed in thermionic emission and photoelectron emission.

  5. Positron annihilation lifetime measurement and X-ray analysis on 120 MeV Au+7 irradiated polycrystalline tungsten

    NASA Astrophysics Data System (ADS)

    Dube, Charu Lata; Kulriya, Pawan Kumar; Dutta, Dhanadeep; Pujari, Pradeep K.; Patil, Yashashri; Mehta, Mayur; Patel, Priyanka; Khirwadkar, Samir S.

    2015-12-01

    In order to simulate radiation damages in tungsten, potential plasma facing materials in future fusion reactors, surrogate approach of heavy ion irradiation on polycrystalline tungsten is employed. Tungsten specimen is irradiated with gold heavy ions of energy 120 MeV at different fluences. Positron annihilation lifetime measurements are carried out on pristine and ion beam irradiated tungsten specimens. The variation in positron annihilation lifetime in ion irradiated specimens confirms evolution of vacancy clusters under heavy ion irradiation. The pristine and irradiated tungsten specimens have also been characterized for their microstructural, structural, electrical, thermal, and mechanical properties. X-ray diffractograms of irradiated tungsten specimens show structural integrity of polycrystalline tungsten even after irradiation. Nevertheless, the increase in microstrain, electrical resistivity and microhardness on irradiation indicates creation of lattice damages inside polycrystalline tungsten specimen. On the other hand, the thermal diffusivity has not change much on heavy ion irradiation. The induction of damages in metallic tungsten is mainly attributed to high electronic energy loss, which is 40 keV/nm in present case as obtained from SRIM program. Although, concomitant effect of nuclear losses on damage creation cannot be ignored. It is believed that the energy received by the electronic system is being transferred to the atomic system by electron-phonon coupling. Eventually, elastic nuclear collisions and the transfer of energy from electronic to atomic system via inelastic collision is leading to significant defect generation in tungsten lattice.

  6. Failure of semiclassical models to describe resistivity of nanometric, polycrystalline tungsten films

    SciTech Connect

    Choi, Dooho; Liu, Xuan; Schelling, Patrick K.; Coffey, Kevin R.; Barmak, Katayun

    2014-03-14

    The impact of electron scattering at surfaces and grain boundaries in nanometric polycrystalline tungsten (W) films was studied. A series of polycrystalline W films ranging in thickness from 10 to 310 nm and lateral grain size from 74 to 133 nm were prepared on thermally oxidized Si. The Fuchs-Sondheimer surface-scattering model and Mayadas-Shatzkes grain-boundary scattering model were employed for quantitative analyses. Predictions from the theoretical models were found to deviate systematically from the experimental data. Possible reasons for the failure of the theoretical models to describe the experimental data are explored. Finally, a discussion of the crucial features lacking from existing models is presented, along with possible avenues for improving the models to result in better agreement with experimental data.

  7. Measurement of thermophysical property of plasma forming tungsten nanofiber layer

    NASA Astrophysics Data System (ADS)

    Kajita, Shin; Yagi, Takashi; Kobayashi, Kenichi; Tokitani, Masayuki; Ohno, Noriyasu

    2016-05-01

    Thermophysical property of a nanostructured tungsten layer formed on a tungsten film was investigated. A 1-µm-thick tungsten film deposited on a quartz glass substrate was irradiated with a high density helium plasma at the surface temperature of 1500 K. The plasma irradiation led to the formation of highly porous fiberform-nanostructured tungsten layer with a thickness of 3.5 µm. Impulse heating was applied at the interface of the film/substrate, and transient heat diffusion was observed using a pulsed light heating thermoreflectance apparatus. The thermoreflectance signals clearly differed between the nanostructure existing and mechanically removed regions; the difference can be attributed to thermal effusivity of the nanostructured tungsten layer. The estimated thermal conductivity of the nanostructured tungsten decreases to ∼2% of that of bulk when the density of the nanostructure is assumed to be ∼6% of the bulk value.

  8. The relationship between structural evolution and electrical percolation of the initial stages of tungsten chemical vapor deposition on polycrystalline TiN

    SciTech Connect

    Rozenblat, A.; Haimson, S.; Shacham-Diamand, Y.; Horvitz, D.

    2012-01-16

    This paper presents experimental results and a geometric model of the evolution of sheet resistance and surface morphology during the transition from nucleation to percolation of tungsten chemical vapor deposition over ultrathin polycrystalline titanium nitride (TiN). We observed two mechanisms of reduction in sheet resistance. At deposition temperatures higher than 310 deg. C, percolation effect is formed at {approx}35% of surface coverage, {theta}, and characterized with a sharp drop in resistance. At temperature below 310 deg. C, a reduction in resistance occurs in two steps. The first step occurs when {theta} = 35% and the second step at {theta} = 85%. We suggest a geometric model in which the electrical percolation pass is modulated by the thickness threshold of the islands at the instant of collision.

  9. Tungsten

    SciTech Connect

    1996-08-01

    The name tungsten, derived from the Swedish words {open_quotes}tung{close_quotes} and {open_quotes}sten{close_quotes}, meaning heavy stone, was first applied to a tungsten-containing mineral in 1755. The mineral, itself, was subsequently identified by C.W. Scheele in 1781, and named scheelite. Metallic tungsten was first isolated from the mineral wolframite in 1783, and given the German name {open_quotes}wolfram,{close_quotes} which remains an alternative name for the element. Ultimately, the English word, tungsten, became the official name, while W remains the element`s chemical symbol. This article discusses the geology, exploitation, applications, and market overview of tungsten.

  10. Vacuum Plasma Spray Forming of Tungsten Lorentz Force Accelerator Components

    NASA Technical Reports Server (NTRS)

    Zimmerman, Frank R.

    2001-01-01

    The Vacuum Plasma Spray (VPS) Laboratory at NASA's Marshall Space Flight Center has developed and demonstrated a fabrication technique using the VPS process to form anode sections for a Lorentz force accelerator from tungsten. Lorentz force accelerators are an attractive form of electric propulsion that provides continuous, high-efficiency propulsion at useful power levels for such applications as orbit transfers or deep space missions. The VPS process is used to deposit refractory metals such as tungsten onto a graphite mandrel of the desired shape. Because tungsten is reactive at high temperatures, it is thermally sprayed in an inert environment where the plasma gun melts and accelerates the metal powder onto the mandrel. A three-axis robot inside the chamber controls the motion of the plasma spray torch. A graphite mandrel acts as a male mold, forming the required contour and dimensions of the inside surface of the anode. This paper describes the processing techniques, design considerations, and process development associated with the VPS forming of the Lorentz force accelerator.

  11. Vacuum Plasma Spray Forming of Tungsten Lorentz Force Accelerator Components

    NASA Technical Reports Server (NTRS)

    Zimmerman, Frank R.

    2004-01-01

    The Vacuum Plasma Spray (VPS) Laboratory at NASA's Marshall Space Flight Center, working with the Jet Propulsion Laboratory, has developed and demonstrated a fabrication technique using the VPS process to form anode and cathode sections for a Lorentz force accelerator made from tungsten. Lorentz force accelerators are an attractive form of electric propulsion that provides continuous, high-efficiency propulsion at useful power levels for such applications as orbit transfers or deep space missions. The VPS process is used to deposit refractory metals such as tungsten onto a graphite mandrel of the desired shape. Because tungsten is reactive at high temperatures, it is thermally sprayed in an inert environment where the plasma gun melts and deposits the molten metal powder onto a mandrel. A three-axis robot inside the chamber controls the motion of the plasma spray torch. A graphite mandrel acts as a male mold, forming the required contour and dimensions for the inside surface of the anode or cathode of the accelerator. This paper describes the processing techniques, design considerations, and process development associated with the VPS forming of Lorentz force accelerator components.

  12. Temperature dependence of helium-implantation-induced lattice swelling in polycrystalline tungsten: X-ray micro-diffraction and Eigenstrain modelling

    SciTech Connect

    de Broglie, I.; Beck, C. E.; Liu, W.; Hofmann, Felix

    2015-05-30

    Using synchrotron X-ray micro-diffraction and Eigenstrain analysis the distribution of lattice swelling near grain boundaries in helium-implanted polycrystalline tungsten is quantified. Samples heat-treated at up to 1473 K after implantation show less uniform lattice swelling that varies significantly from grain to grain compared to as-implanted samples. An increase in lattice swelling is found in the vicinity of some grain boundaries, even at depths beyond the implanted layer. As a result, these findings are discussed in terms of the evolution of helium-ion-implantation-induced defects.

  13. Ordered arrangement of irradiation-induced defects of polycrystalline tungsten irradiated with low-energy hydrogen ions

    NASA Astrophysics Data System (ADS)

    Ni, Weiyuan; Yang, Qi; Fan, Hongyu; Liu, Lu; Berthold, Tobias; Benstetter, Günther; Liu, Dongping

    2015-09-01

    Low-energy (20-520 eV) hydrogen ion irradiations were performed at W surface temperature of 373-1073 K and a fluence ranging from 5.0 × 1023 to 1.0 × 1025/m2. Conductive atomic force microscopy (CAFM) as a nondestructive analytical technique was successfully used to detect irradiation-induced defects in polycrystalline W. The size and density of these nanometer-sized defects were strongly dependent on the fluence of hydrogen ions. Both ion energy (E) and temperature (T) play a crucial role in determining the ordering of nanometer-sized defects. Ordered arrangements were formed at relatively high E and T. This can be attributed to the stress-driven ripple effect of defect growth at crystal grains, resulting in the movement of W lattice along one certain crystal planes.

  14. Deuterium and helium release and microstructure of tungsten deposition layers formed by RF plasma sputtering

    SciTech Connect

    Katayama, K.; Imaoka, K.; Tokitani, M.; Miyamoto, M.; Nishikawa, M.; Fukada, S.; Yoshida, N.

    2008-07-15

    It is important to evaluate tritium behavior in tungsten deposition layers considering a long-term plasma operation. In this study, tungsten deposition layers were formed by deuterium or helium RF plasma sputtering. The release behavior of deuterium or helium from the layers were observed by a thermal desorption method. When a tungsten deposition layer does not contain oxygen, the retained deuterium is mainly released as D{sub 2}. When oxygen exists in the layer, the majority of deuterium is released as water vapor. Tungsten deposition layers have an amorphous structure and consist offline grain with size of 2-3 nm. Numerous bubbles are observed in the layers. A formation of tungsten deposition layer in a fusion reactor may make tritium control more difficult. (authors)

  15. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts.

    PubMed

    Rizo, Hanika; Walker, Richard J; Carlson, Richard W; Horan, Mary F; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G

    2016-05-13

    How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth's primary accretionary period have survived to the present. PMID:27174983

  16. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts.

    PubMed

    Rizo, Hanika; Walker, Richard J; Carlson, Richard W; Horan, Mary F; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G

    2016-05-13

    How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth's primary accretionary period have survived to the present.

  17. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts

    NASA Astrophysics Data System (ADS)

    Rizo, Hanika; Walker, Richard J.; Carlson, Richard W.; Horan, Mary F.; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G.

    2016-05-01

    How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth’s primary accretionary period have survived to the present.

  18. Microstructural Characterization of a Polycrystalline Nickel-Based Superalloy Processed via Tungsten-Intert-Gas-Shaped Metal Deposition

    NASA Astrophysics Data System (ADS)

    Clark, Daniel; Bache, Martin R.; Whittaker, Mark T.

    2010-12-01

    Recent trials have produced tungsten-inert-gas (TIG)-welded structures of a suitable scale to allow an evaluation of the technique as an economic and commercial process for the manufacture of complex aeroengine components. The employment of TIG welding is shown to have specific advantages over alternative techniques based on metal inert gas (MIG) systems. Investigations using the nickel-based superalloy 718 have shown that TIG induces a smaller weld pool with less compositional segregation. In addition, because the TIG process involves a pulsed power source, a faster cooling rate is achieved, although this rate, in turn, compromises the deposition rate. The microstructures produced by the two techniques differ significantly, with TIG showing an absence of the detrimental delta and Laves phases typically produced by extended periods at a high temperature using MIG. Instead, an anisotropic dendritic microstructure was evident with a preferred orientation relative to the axis of epitaxy. Niobium was segregated to the interdendritic regions. A fine-scale porosity was evident within the microstructure with a maximum diameter of approximately 5 μm. This porosity often was found in clusters and usually was associated with the interdendritic regions. Subsequent postdeposition heat treatment was shown to have no effect on preexisting porosity and to have a minimal effect on the microstructure.

  19. Numerical Simulation on Sheet Metal Forming with Rate-independent Polycrystalline Plasticity FEM

    NASA Astrophysics Data System (ADS)

    Zhang, Shaorui; Li, Dayong; Peng, Yinghong

    2004-06-01

    It has long been found that, during deformation process, the crystal orientations would gradually rotate around some ideal orientations, and then would affect the later deformation properties of sheet metal. So it is very important to introduce texture model into metal forming processes. In this paper, a rate-independent polycrystalline plasticity model is developed and introduced into dynamic explicit element method. Metal flow is assumed to occur by crystallographic slip on given slip systems within each crystal. Every integration point represents a single crystal. Then cup drawing of sheet metal is studied using crystalline plasticity finite element analysis. For the rolled aluminum sheet, which contains strong {001}<110> texture, earing is formed at 45° direction after cup drawing. For the annealing aluminum sheet, due to the balance between two main textures, the flange earing tendency is not obvious. And for the soft steel sheet with a faintish orientation distribution, the flange earing tendency is not obvious, too.

  20. Measurement of ion species produced due to bombardment of 450 eV N2+ ions with hydrocarbons-covered surface of tungsten: Formation of tungsten nitride

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Bhatt, P.; Kumar, A.; Singh, B. K.; Singh, B.; Prajapati, S.; Shanker, R.

    2016-08-01

    A laboratory experiment has been performed to study the ions that are produced due to collisions of 450 eV N2+ ions with a hydrocarbons-covered surface of polycrystalline tungsten at room temperature. Using a TOF mass spectrometry technique, the product ions formed in these collisions have been detected, identified and analyzed. Different ion-surface reaction processes, namely, neutralization, reflection, surface induced dissociation, surface induced chemical reactions and desorption are observed and discussed. Apart from the presence of desorbed aliphatic hydrocarbon and other ions, the mass spectra obtained from the considered collisions show the formation and sputtering of tungsten nitride (WN). A layer of WN on tungsten surface is known to decrease the sputtering of bulk tungsten in fusion devices more effectively than when the tungsten is bombarded with other seeding gases (He, Ar). It is further noted that there is a negligible diffusion of N in the bulk tungsten at room temperature.

  1. Strongly linked current flow in polycrystalline forms of the superconductor MgB2.

    PubMed

    Larbalestier, D C; Cooley, L D; Rikel, M O; Polyanskii, A A; Jiang, J; Patnaik, S; Cai, X Y; Feldmann, D M; Gurevich, A; Squitieri, A A; Naus, M T; Eom, C B; Hellstrom, E E; Cava, R J; Regan, K A; Rogado, N; Hayward, M A; He, T; Slusky, J S; Khalifah, P; Inumaru, K; Haas, M

    2001-03-01

    The discovery of superconductivity at 39 K in magnesium diboride, MgB2, raises many issues, a critical one being whether this material resembles a high-temperature copper oxide superconductor or a low-temperature metallic superconductor in terms of its behaviour in strong magnetic fields. Although the copper oxides exhibit very high transition temperatures, their in-field performance is compromized by their large anisotropy, the result of which is to restrict high bulk current densities to a region much less than the full magnetic-field-temperature (H-T) space over which superconductivity is found. Moreover, the weak coupling across grain boundaries makes transport current densities in untextured polycrystalline samples low and strongly sensitive to magnetic field. Here we report that, despite the multiphase, untextured, microscale, subdivided nature of our MgB2 samples, supercurrents flow throughout the material without exhibiting strong sensitivity to weak magnetic fields. Our combined magnetization, magneto-optical, microscopy and X-ray investigations show that the supercurrent density is mostly determined by flux pinning, rather than by the grain boundary connectivity. Our results therefore suggest that this new superconductor class is not compromized by weak-link problems, a conclusion of significance for practical applications if higher temperature analogues of this compound can be discovered.

  2. Tungsten bronze-based nuclear waste form ceramics. Part 1. Conversion of microporous tungstates to leach resistant ceramics

    NASA Astrophysics Data System (ADS)

    Luca, Vittorio; Griffith, Christopher S.; Drabarek, Elizabeth; Chronis, Harriet

    2006-11-01

    The effective immobilization of Cs + and/or Sr 2+ sorbed on hexagonal tungsten oxide bronze (HTB) adsorbent materials has been achieved by heating in air at temperatures in the range 500-1000 °C. Crystalline powdered HTB materials formed by heating at 800 °C displayed leach characteristics comparable to Cs-containing hot-pressed hollandites in the pH range from 0 to 12. If the Cs-loaded HTB sorbents were pressed into pellets prior to calcination, ceramic monoliths could be prepared with negligible Cs volatilization losses. Heating to temperatures in excess of 1250 °C under dynamic air flow resulted in the melting of the sorbent to form phase assemblages consisting of millimetre-sized crystals of bronzoid phases. Up to 5 wt% mass loss was observed for small scale samples of melted materials under dynamic air flow. Both the calcined and melted bronzoid waste forms are multiphase ceramics in which Cs + remains bound within, and appears to stabilize, the hexagonal bronze phase, even after complete melting at 1300 °C. The leachability of Sr from the phases prepared by heating appears to be somewhat worse than that of Cs. Saturation of the HTB adsorbents with lanthanide elements (Nd, La, Ce) gave rise to cubic bronze phases in which we propose that the lanthanides substitute at the tungsten or molybdenum sites rather than the tunnel positions. The lanthanides were rather easily leached from the calcined phases in 0.1 M HNO 3 at 150 °C.

  3. Mineral resource of the month: tungsten

    USGS Publications Warehouse

    Shedd, Kim B.

    2012-01-01

    The article offers information on tungsten. It says that tungsten is a metal found in chemical compounds such as in the scheelite and ore minerals wolframite. It states that tungsten has the highest melting point and it forms a compound as hard as diamond when combined with carbon. It states that tungsten can be used as a substitute for lead in fishing weights, ammunition, and hunting shot. Moreover, China started to export tungsten materials and products instead of tungsten raw materials.

  4. Determination of carbide-forming metals, chromium and barium, by graphite furnace atomic absorption spectrometry using a tungsten coil platform

    NASA Astrophysics Data System (ADS)

    Moreno Camero, Rosa; Alvarado, José

    2000-07-01

    The use of a tungsten coil as a platform has been evaluated for the determination of carbide-forming metals, Cr and Ba. The methodology developed has been used for Cr and Ba determinations in HPS CRM, Trace Metals in Drinking Water, and NIST SRM 1643b, Trace Elements in Water. Good agreement was found between the results obtained and the certified values for Cr in both reference materials and for Ba in the NIST SRM. Barium results were approximately 14% lower than the certified results for the HPS CRM. This inaccuracy was ascribed to the presence of considerable amounts of Ca in this particular material. Precision of the measurements, 3σ relative standard deviation as percentage, were 2.5 and 5.8 for Cr and Ba, respectively. Characteristic masses, in picograms, were 1.70 for Cr and 19.0 for Ba. These results compare favorably with the literature values for Cr but not for Ba.

  5. Synthesis and electrochemical capacitance of long tungsten oxide nanorod arrays grown vertically on substrate

    SciTech Connect

    Park, Sun Hwa; Kim, Young Heon; Lee, Tae Geol; Shon, Hyun Kyong; Park, Hyun Min; Song, Jae Yong

    2012-11-15

    Highlights: ► Growth of long amorphous tungsten oxide nanorods on a substrate. ► Formation of single-crystalline tungsten oxide nanorods by a heat-treatment. ► High electrochemical pseudocapacitance of 2.8 mF cm{sup −2}. ► Excellent cyclability of psuedocapacitance up to 1000 cycles. -- Abstract: Long tungsten oxide nanorods are vertically grown on Al/W/Ti coated silicon substrates using a two-step anodization process. The first anodization of the Al film forms a mesh-like mask of anodic aluminum oxide, and the second anodization of the W film results in the formation of a buffer layer, a bottom nanorod, and a top nanorod of amorphous tungsten oxide. A pore-widening process prior to the second anodization leads to the enhancement of nanorod length above approximately 500 nm. After a heat-treatment, the tungsten oxide nanorods are crystallized to form a single crystalline structure while the buffer layer forms a polycrystalline structure. The crystalline tungsten oxide nanorods show a cyclic voltammogram retaining the quasi-rectangular shape of an electrochemically reversible faradaic redox reaction, i.e., a typical pseudocapacitive behavior. The maximum electrochemical capacitance per apparent surface area reaches approximately 2.8 mF cm{sup −2} at the voltage scan rate of 20 mV s{sup −1}, and the excellent cyclability of charge–discharge process is maintained up to 1000 cycles.

  6. Thermal Shock and Ablation Behavior of Tungsten Nozzle Produced by Plasma Spray Forming and Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Wang, Y. M.; Xiong, X.; Zhao, Z. W.; Xie, L.; Min, X. B.; Yan, J. H.; Xia, G. M.; Zheng, F.

    2015-08-01

    Tungsten nozzle was produced by plasma spray forming (PSF, relative density of 86 ± 2%) followed by hot isostatic pressing (HIPing, 97 ± 2%) at 2000 °C and 180 MPa for 180 min. Scanning electron microscope, x-ray diffractometer, Archimedes method, Vickers hardness, and tensile tests have been employed to study microstructure, phase composition, density, micro-hardness, and mechanical properties of the parts. Resistance of thermal shock and ablation behavior of W nozzle were investigated by hot-firing test on solid rocket motor (SRM). Comparing with PSF nozzle, less damage was observed for HIPed sample after SRM test. Linear ablation rate of nozzle made by PSF was (0.120 ± 0.048) mm/s, while that after HIPing reduced to (0.0075 ± 0.0025) mm/s. Three types of ablation mechanisms including mechanical erosion, thermophysical erosion, and thermochemical ablation took place during hot-firing test. The order of degree of ablation was nozzle throat > convergence > dilation inside W nozzle.

  7. Paste development and co-sintering test of zirconium carbide and tungsten in freeze-form extrusion fabrication

    NASA Astrophysics Data System (ADS)

    Li, Ang

    Ultra-high temperature ceramics are being investigated for future use in aerospace applications due to their superior thermo-mechanical properties, as well as oxidation resistance, at temperatures above 2000°C. However, their brittle properties make them susceptible to thermal shock failure. Components fabricated as functionally graded materials (FGMs) can combine the superior properties of ceramics with the toughness of an underlying refractory metal by fabricating graded composites. This paper discusses the grading of two materials through the use of a Freeze-form Extrusion Fabrication (FEF) system to build FGMs parts consisting of zirconium carbide (ZrC) and tungsten (W). Aqueous-based colloidal suspensions of ZrC and W were developed and utilized in the FEF process to fabricate test bars graded from 100%ZrC to 50%W-50%ZrC (volume percent). Following FEF processing the test bars were co-sintered at 2300°C and characterized to determine their resulting density and micro-structure. Four-point bending tests were performed to assess the strength of test bars made using the FEF process, compared to test bars prepared using conventional powder processing and isostatic pressing techniques, for five distinct ZrC-W compositions. Scanning electron microscopy (SEM) was used to verify the inner structure of composite parts built using the FEF process.

  8. Polycrystalline photovoltaic cell

    SciTech Connect

    Jordan, J.F.; Lampkin, C.M.

    1983-10-25

    A photovoltaic cell is disclosed, having an electrically conductive substrate, which may be glass having a film of conductive tin oxide; a first layer containing a suitable semiconductor, which layer has a first component film with an amorphous structure and a second component film with a polycrystalline structure; a second layer forming a heterojunction with the first layer; and suitable electrodes where the heterojunction is formed from a solution containing copper, the amorphous film component is superposed above an electrically conductive substrate to resist permeation of the copper-containing material to shorting electrical contact with the substrate. The penetration resistant amorphous layer permits a variety of processes to be used in forming the heterojunction with even very thin layers (1-6 /SUB u/ thick) of underlying polycrystalline semiconductor materials. In some embodiments, the amorphous-like structure may be formed by the addition of aluminum or zirconium compounds to a solution of cadmium salts sprayed over a heated substrate.

  9. Process Of Bonding Copper And Tungsten

    DOEpatents

    Slattery, Kevin T.; Driemeyer, Daniel E.; Davis, John W.

    2000-07-18

    Process for bonding a copper substrate to a tungsten substrate by providing a thin metallic adhesion promoting film bonded to a tungsten substrate and a functionally graded material (FGM) interlayer bonding the thin metallic adhesion promoting film to the copper substrate. The FGM interlayer is formed by sintering a stack of individual copper and tungsten powder blend layers having progressively higher copper content/tungsten content, by volume, ratio values in successive powder blend layers in a lineal direction extending from the tungsten substrate towards the copper substrate. The resulting copper to tungsten joint well accommodates the difference in the coefficient of thermal expansion of the materials.

  10. Evolution of Plasma-Exposed Tungsten Surfaces Due to Helium Diffusion and Bubble Growth

    NASA Astrophysics Data System (ADS)

    Hammond, Karl; Hu, Lin; Maroudas, Dimitrios; Wirth, Brian; PSI-SciDAC Team

    2013-10-01

    Helium from linear plasma devices and tokamak plasmas causes the formation of microscopic features, termed ``fuzz'' or ``coral,'' on the surface of plasma-exposed materials after only a few hours of plasma exposure. The details of such surface modifications are only beginning to be understood. This study examines the initial and intermediate stages of fuzz formation by large-length-scale molecular dynamics (MD) simulations of helium-implanted tungsten over time scales of up to microseconds using single-crystalline and polycrystalline supercell models of tungsten. The large-scale MD simulations employ state-of-the-art many-body interatomic potentials and implantation depth distributions for the insertion of helium atoms into the tungsten matrix constructed based on MD simulations of helium-atom impingement onto tungsten surfaces under prescribed thermal and implantation conditions. The large-scale MD simulations reveal surface features formed via the sequence of helium implantation, diffusion of helium atoms and their aggregation to form bubbles, growth of bubbles and consequent production of tungsten self-interstitial atoms, organization of those atoms into prismatic loops, glide of those loops to the surface, and bubble rupture.

  11. Surface morphologies of He-implanted tungsten

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.; Meyer, F. W.; Hijazi, H.; Unocic, K. A.; Garrison, L. M.; Parish, C. M.

    2016-09-01

    Surface morphologies of tungsten surfaces, both polycrystalline and single-crystal [1 1 0], were investigated using SEM and FIB/SEM techniques after implantations at elevated surfaces temperatures (1200-1300 K) using well-characterized, mono-energetic He ion beams with a wide range of ion energies (218 eV-250 keV). Nanofuzz was observed on polycrystalline tungsten (PCW) following implantation of 100-keV He ions at a flux threshold of 0.9 × 1016 cm-2 s-1, but not following 200-keV implantations with similar fluxes. No nanofuzz formation was observed on single-crystal [1 1 0] tungsten (SCW), despite fluxes exceeding those demonstrated previously to produce nanofuzz on polycrystalline tungsten. Pre-damaging the single-crystal tungsten with implanted C impurity interstitials did not significantly affect the surface morphologies resulting from the high-flux He ion implantations. The main factor leading to the different observed surface structures for the pristine and C-implanted single-crystal W samples appeared to be the peak He ion flux characterizing the different exposures. It was speculated that nanofuzz formation was not observed for any SCW target exposures because of increased incubation fluences required for such targets.

  12. High strength and density tungsten-uranium alloys

    DOEpatents

    Sheinberg, Haskell

    1993-01-01

    Alloys of tungsten and uranium and a method for making the alloys. The amount of tungsten present in the alloys is from about 55 vol % to about 85 vol %. A porous preform is made by sintering consolidated tungsten powder. The preform is impregnated with molten uranium such that (1) uranium fills the pores of the preform to form uranium in a tungsten matrix or (2) uranium dissolves portions of the preform to form a continuous uranium phase containing tungsten particles.

  13. Multiple Diamond Anvil (MDA) apparatus using nano-polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Irifune, T.; Kunimoto, T.; Tange, Y.; Shinmei, T.; Isobe, F.; Kurio, A.; Funakoshi, K.

    2011-12-01

    Thanks to the great efforts by Dave Mao, Bill Bassett, Taro Takahashi, and their colleagues at the University of Rochester through 1960s-70s, diamond anvil cell (DAC) became a major tool to investigate the deep Earth after its invention by scientists at NBS in 1958. DAC can now cover almost the entire pressure and temperature regimes of the Earth's interior, which seems to have solved the longstanding debate on the crystal structure of iron under the P-T conditions of the Earth's inner core. In contrast, various types of static large-volume presses (LVP) have been invented, where tungsten carbide has conventionally been used as anvils. Kawai-type multianvil apparatus (MA), which utilize 6 first-stage harden steel and 8 tungsten carbide anvils, is the most successful LVP, and has been used for accurate measurements of phase transitions, physical properties, element partitioning, etc. at high pressure and temperature. However, pressures using tungsten carbide as the second-stage anvils have been limited to about 30 GPa due to significant plastic deformation of the anvils. Efforts have been made to expand this pressure limit by replacing tungsten carbide anvils with harder sintered diamond (SD) anvils over the last two decades, but the pressures available in KMA with SD anvils have still been limited to below 100 GPa. We succeeded to produce nano-polycrystalline diamond (NPD or HIME-Diamond) in 2003, which is known to have ultrahigh hardness, very high toughness and elastic stiffness, high transmittance of light, relatively low thermal conductivity. These properties are feasible for its use as anvils, and some preliminary experiments of application of NPD anvils to laser heated DAC have successfully made in the last few years. We are now able to synthesize NPD rods with about 1cm in both diameter and length using a newly constructed 6000-ton KMA at Geodynamics Research Center, Ehime University, and have just started to apply this new polycrystalline diamond as anvils

  14. Electrical Behavior of SnO2 Polycrystalline Ceramic Pieces Formed by Slip Casting: Effect of Surrounding Atmosphere (Air and CO)

    NASA Astrophysics Data System (ADS)

    Aguilar-Paz, C. J.; Ochoa-Muñoz, Y.; Ponce, M. A.; Rodríguez-Páez, J. E.

    2016-01-01

    Pieces of porous polycrystalline SnO2 with and without cobalt have been formed by the slip-casting method, using ceramic powders synthesized by the controlled precipitation method. A suitable methodology was developed for forming and sintering the pieces to enable controlled modification of their microstructure, principally grain size, porosity, and type of intergranular contacts. Better control of the microstructure was obtained in the samples containing cobalt. In these, predominance of open necks and intergranular contacts was observed, which can represent Schottky barriers. Because of its good structural homogeneity, porosity, and small grain size (of the order of 1 μm), the sample with 2 mol.% Co sintered at 1250°C for 2 h was selected for electrical characterization by complex impedance spectroscopy, varying the operating temperature, concentration and nature of the surrounding gas (air or CO), and bias voltage. The resulting R p and C p curves were very sensitive to variation in these parameters, being most obvious for the C p curves, which showed a phenomenon of low-frequency dispersion when bias voltages other than zero were used, in the presence of O2, and at operating temperature of 280°C. The electrical behavior of the SnO2 with 2 mol.% Co sample sintered at 1250°C was consistent with the nature and microstructural characteristics of the active material and was justified based on the presence of shallow- and deep-type defects, and variations in barrier height and width, caused by adsorption of gas molecules.

  15. Process Of Bonding Copper And Tungsten

    DOEpatents

    Slattery, Kevin T.; Driemeyer, Daniel E.

    1999-11-23

    Process for bonding a copper substrate to a tungsten substrate by providing a thin metallic adhesion promoting film bonded to a tungsten substrate and a functionally graded material (FGM) interlayer bonding the thin metallic adhesion promoting film to the copper substrate. The FGM interlayer is formed by thermal plasma spraying mixtures of copper powder and tungsten powder in a varied blending ratio such that the blending ratio of the copper powder and the tungsten powder that is fed to a plasma torch is intermittently adjusted to provide progressively higher copper content/tungsten content, by volume, ratio values in the interlayer in a lineal direction extending from the tungsten substrate towards the copper substrate. The resulting copper to tungsten joint well accommodates the difference in the coefficient of thermal expansion of the materials.

  16. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, Andreas M.; Haggerty, John S.; Danforth, Stephen C.

    1983-01-01

    A process for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by imgingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step.

  17. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, A.M.; Haggerty, J.S.; Danforth, S.C.

    1983-04-05

    A process is described for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by impingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step. 10 figs.

  18. Gelcasting Polycrystalline Alumina

    SciTech Connect

    Janney, M.A.; Zuk, K.J.; Wei, G.C.

    2000-01-01

    OSRAM SYLVANIA INC. is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux TM line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency ({approximately}97% total transmittance in the visible), their refractoriness (inner wall temperature can reach l2OOC), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, up to 100 initial lumens per watt. (Compare incandescent lamps 10-20 lumens per watt, fluorescent lamps 25-90 lumens per watt.)

  19. Software optimization for electrical conductivity imaging in polycrystalline diamond cutters

    SciTech Connect

    Bogdanov, G.; Ludwig, R.; Wiggins, J.; Bertagnolli, K.

    2014-02-18

    We previously reported on an electrical conductivity imaging instrument developed for measurements on polycrystalline diamond cutters. These cylindrical cutters for oil and gas drilling feature a thick polycrystalline diamond layer on a tungsten carbide substrate. The instrument uses electrical impedance tomography to profile the conductivity in the diamond table. Conductivity images must be acquired quickly, on the order of 5 sec per cutter, to be useful in the manufacturing process. This paper reports on successful efforts to optimize the conductivity reconstruction routine, porting major portions of it to NVIDIA GPUs, including a custom CUDA kernel for Jacobian computation.

  20. A deep-submicron single gate CMOS technology using in-situ boron-doped polycrystalline silicon-germanium gates formed by rapid thermal chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Li, Vivian Zhi-Qi

    This thesis presents a comprehensive study of in-situ boron doped polycrystalline-Sisb{1-x}Gesb{x} films deposited in a rapid thermal chemical vapor deposition system and used as the gate electrode in the deep submicron bulk CMOS technology. This work includes an investigation of the nucleation behavior of poly-Sisb{1-x}Gesb{x} films on the oxide surface, development of a deposition process using Sisb2Hsb6,\\ GeHsb4 and Bsb2Hsb6 gases in addition to using common gas mixture of SiHsb4,\\ GeHsb4 and Bsb2Hsb6 in a RTCVD system, characterization of the deposited film structure and its properties, examination of the electrical properties, extraction of the workfunction as a function of the Ge content in the film, development of the NMOS, PMOS and CMOS processes for in-situ boron doped poly-Sisb{1-x}Gesb{x} gate technology, assessment of the impact of poly-Sisb{1-x}Gesb{x} gate on the device performance through computer simulations. The process integration issues such as boron penetration, poly-depletion and gate oxide reliability, and characterization of deep submicron CMOS devices are also studied. One critical concern with the use of poly-Sisb{1-x}Gesb{x} gate materials is its partially selective deposition process on the SiOsb2. In this work, we demonstrated non-selective deposition processes for poly-Sisb{1-x}Gesb{x} without conventional Si pre-deposition onto oxide. One approach is by using in-situ boron doping method and another is by using Sisb2Hsb6 as the Si source gas. Also, it was found that the density of the nucleation sites at the initial stage of deposition increases with the increase of the Bsb2Hsb6 gas flow rate. The resulting continuous poly-Sisb{1-x}Gesb{x} films were attributed to the preferential adsorption of boron atoms onto the oxide surface providing the necessary nucleation sites for the subsequent Sisb{1-x}Gesb{x} film growth. For undoped poly-Sisb{1-x}Gesb{x} films, continuous films can be formed on the oxide using Sisb2Hsb6 and GeHsb4 gases

  1. Raman scattering from rapid thermally annealed tungsten silicide

    NASA Technical Reports Server (NTRS)

    Kumar, Sandeep; Dasgupta, Samhita; Jackson, Howard E.; Boyd, Joseph T.

    1987-01-01

    Raman scattering as a technique for studying the formation of tungsten silicide is presented. The tungsten silicide films have been formed by rapid thermal annealing of thin tungsten films sputter deposited on silicon substrates. The Raman data are interpreted by using data from resistivity measurements, Auger and Rutherford backscattering measurements, and scanning electron microscopy.

  2. Photovoltaic Cell Having A P-Type Polycrystalline Layer With Large Crystals

    DOEpatents

    Albright, Scot P.; Chamberlin, Rhodes R.

    1996-03-26

    A photovoltaic cell has an n-type polycrystalline layer and a p-type polycrystalline layer adjoining the n-type polycrystalline layer to form a photovoltaic junction. The p-type polycrystalline layer comprises a substantially planar layer portion having relatively large crystals adjoining the n-type polycrystalline layer. The planar layer portion includes oxidized impurities which contribute to obtainment of p-type electrical properties in the planar layer portion.

  3. Synthesis of Nano-Polycrystalline Synroc-B Powders as a High Level Radioactive Wastes Ceramic Forms by a Solution Combustion Synthesis.

    PubMed

    Han, Young-Min; Lee, Sang-Jin; Kim, Yeon-Ku; Jung, Choong-Hwan

    2016-02-01

    Synroc (Synthetic Rock) consists of four main titanate phases: peroveskite (CaTiO3), zirconolite (CaZrTi2O7), hollandite (BaAl2Ti6O16) and rutile (TiO2). Nano-polycrystalline synroc powders were made by a synthesis combustion process. The combustion process, an externally initiated reaction is self-sustained owing to the exothermic reaction. A significant volume of gas is evolved during the combustion reaction and leads to loosely agglomerated powders. This exothermic reaction provides necessary heat to further carry the reaction in forward direction to produce nanocrystalline powders as the final product. Glycine is used as a fuel, being oxidized by nitrate ions. It is inexpensive, has high energy efficiency, fast heating rates, short reaction times and high compositional homogeneity. In this study, combustion synthesis of nano-sized synroc-B powder is introduced. The fabrication of synroc-B powder result of observation XRD were prepared for polycrystalline (perovskite, zirconolite, hollandite, rutile) structures. The characterization of the synthesized powders is conducted by using XRD, SEM/EDS and TEM.

  4. Synthesis of Nano-Polycrystalline Synroc-B Powders as a High Level Radioactive Wastes Ceramic Forms by a Solution Combustion Synthesis.

    PubMed

    Han, Young-Min; Lee, Sang-Jin; Kim, Yeon-Ku; Jung, Choong-Hwan

    2016-02-01

    Synroc (Synthetic Rock) consists of four main titanate phases: peroveskite (CaTiO3), zirconolite (CaZrTi2O7), hollandite (BaAl2Ti6O16) and rutile (TiO2). Nano-polycrystalline synroc powders were made by a synthesis combustion process. The combustion process, an externally initiated reaction is self-sustained owing to the exothermic reaction. A significant volume of gas is evolved during the combustion reaction and leads to loosely agglomerated powders. This exothermic reaction provides necessary heat to further carry the reaction in forward direction to produce nanocrystalline powders as the final product. Glycine is used as a fuel, being oxidized by nitrate ions. It is inexpensive, has high energy efficiency, fast heating rates, short reaction times and high compositional homogeneity. In this study, combustion synthesis of nano-sized synroc-B powder is introduced. The fabrication of synroc-B powder result of observation XRD were prepared for polycrystalline (perovskite, zirconolite, hollandite, rutile) structures. The characterization of the synthesized powders is conducted by using XRD, SEM/EDS and TEM. PMID:27433644

  5. Influence of tungsten substitution and oxygen deficiency on the thermoelectric properties of CaMnO{sub 3−δ}

    SciTech Connect

    Thiel, Philipp; Eilertsen, James; Populoh, Sascha Saucke, Gesine; Shkabko, Andrey; Sagarna, Leyre; Karvonen, Lassi; Döbeli, Max; Weidenkaff, Anke

    2013-12-28

    Polycrystalline tungsten-substituted CaMn{sub 1−x}W{sub x}O{sub 3−δ} (0.00 ≤ x ≤ 0.05) powders were synthesized from a polymeric precursor, pressed and sintered to high density. The impact of tungsten substitution on the crystal structure, thermal stability, phase transition, electronic and thermal transport properties is assessed. Tungsten acts as an electron donator and strongly affects high-temperature oxygen stoichiometry. Oxygen vacancies form in the high figure-of-merit (ZT)-region starting from about T = 1000 K and dominate the carrier concentration and electronic transport far more than the tungsten substitution. The analysis of the transport properties yields that in the investigated regime the band filling is sufficiently high to overcome barriers of polaron transport. Therefore, the Cutler-Mott approach describes the electrical transport more accurately than the Mott approach for small polaron transport. The lattice thermal conductivity near room temperature is strongly suppressed with increasing tungsten concentration due to mass-difference impurity scattering. A ZT of 0.25 was found for x = 0.04 at 1225 K.

  6. TUNGSTEN BASE ALLOYS

    DOEpatents

    Schell, D.H.; Sheinberg, H.

    1959-12-15

    A high-density quaternary tungsten-base alloy having high mechanical strength and good machinability composed of about 2 wt.% Ni, 3 wt.% Cu, 5 wt.% Pb, and 90wt.% W is described. This alloy can be formed by the powder metallurgy technique of hot pressing in a graphite die without causing a reaction between charge and the die and without formation of a carbide case on the final compact, thereby enabling re-use of the graphite die. The alloy is formable at hot- pressing temperatures of from about 1200 to about 1350 deg C. In addition, there is little component shrinkage, thereby eliminating the necessity of subsequent extensive surface machining.

  7. Tungsten bronze-based nuclear waste form ceramics. Part 2: Conversion of granular microporous tungstate polyacrylonitrile (PAN) composite adsorbents to leach resistant ceramics

    NASA Astrophysics Data System (ADS)

    Griffith, Christopher S.; Sebesta, Ferdinand; Hanna, John V.; Yee, Patrick; Drabarek, Elizabeth; Smith, Mark E.; Luca, Vittorio

    2006-11-01

    Conversion of a granular molybdenum-doped, hexagonal tungsten bronze (MoW-HTB)-polyacrylonitrile (PAN) composite adsorbent to a leach resistant ceramic waste form capable of immobilizing adsorbed Cs + and Sr 2+ has been achieved by heating in air at temperatures in the range 600-1200 °C. Thermal treatment of the Cs- and Sr-loaded composite material at 1000 °C was sufficient to invoke a 60% reduction in volume of the composite while still retaining its spherical morphology. Cs-133 MAS NMR studies of this sample suite at 9.4 T and 14.1 T showed that multiple Cs sites are present throughout the entire thermal treatment range. Scanning electron microscopy investigations of the phase assemblages resulting from thermal treatment demonstrated that the full complement of Cs, and the majority of Sr, partitions into HTB phases (A 0.16-0.3MO 3; A = Cs +, Sr 2+ and Na +; M = Mo, W). The potentially reducing conditions resulting from the removal of the PAN matrix or the presence of high concentrations of Na + relative to either Cs + or Sr 2+ does not retard the formation of the high temperature HTB phases. The fraction of Cs + and Sr 2+ leached from the tungstate phase assemblages was superior or comparable with cesium hollandite (Cs 0.8Ba 0.4Ti 8O 18; f = ≈8 × 10 -5; rate = <1.2 × 10 -4 g/m 2/day) and strontium titanate (SrTiO 3; f = 3.1 × 10 -3; rate = 2.63 × 10 -4 g/m 2/day), respectively, using a modified PCT test in Millipore water at 90 °C. Furthermore, where aggressive leaching conditions were employed (0.1 M HNO 3; 150 °C; 4 days), the tungstate phase assemblages displayed leach resistance almost two orders of magnitude greater than the reference phases.

  8. Strengthening mechanisms of tungsten powder reinforced uranium

    SciTech Connect

    Lewis, M.A.K.; Hill, M.A.; Rollett, A.D.; Dunn, P.S.; Mortensen, A.; Massachusetts Inst. of Tech., Cambridge, MA )

    1989-01-01

    Tungsten powder reinforced uranium exhibits a three-fold increase in yield strength due to precipitation hardening. The tungsten-rich interphase precipitates form at moving phase boundaries during slow cooling. Further increases in yield strength, attained with increasing tungsten content, are due to composite strengthening; this is verified by increasing elastic modulus with increasing tungsten content. Age hardening behavior is observed, with strengthening occurring at aging temperatures low in the alpha phase. Aging higher in alpha gives initial strengthening followed by rapid overaging. Beta phase aging results in a very soft structure with precipitates visible optically. Wrought material exhibits significant strain hardening as well as composite strengthening due to elongation of the tungsten particles. 7 refs., 15 figs., 4 tabs.

  9. Strengthening mechanisms of tungsten powder reinforced uranium

    SciTech Connect

    Krawizcki, M.A.

    1990-04-01

    Tungsten powder reinforced uranium composites exhibit a three-fold increase in yield strength due to precipitation hardening. The tungsten-rich interphase precipitates form at the moving beta to alpha phase boundary during slow cooling. Further increases in yield strength, attained with increasing tungsten content, are due to composite strengthening. The composite strengthening is verified by increasing elastic modulus with increasing tungsten content. Age hardening behavior is observed, with strengthening occurring at aging temperatures low, in the alpha phase. Temperatures higher in alpha give initial strengthening followed by rapid overaging. Beta phase aging temperatures result in a very soft structure with interphase precipitates observable optically. Wrought material exhibits significant strain hardening as well as composite strengthening due to elongation of the tungsten particles. 36 refs., 36 figs., 10 tabs.

  10. Gelcasting polycrystalline alumina

    SciTech Connect

    Janney, M.A.

    1997-04-01

    This work is being done as part of a CRADA with Osram-Sylvania, Inc. (OSI) OSI is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux{reg_sign} line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency (95% total transmittance in the visible region), their refractoriness (inner wall temperature can reach 1400{degrees}C), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, on the order of several hundred lumens / watt. (Compare - incandescent lamps -13 lumens/watt fluorescent lamps -30 lumens/watt.) Osram-Sylvania would like to explore using gelcasting to form PCA tubes for Lumalux{reg_sign} lamps, and eventually for metal halide lamps (known as quartz-halogen lamps). Osram-Sylvania, Inc. currently manufactures PCA tubes by isostatic pressing. This process works well for the shapes that they presently use. However, there are several types of tubes that are either difficult or impossible to make by isostatic pressing. It is the desire to make these new shapes and sizes of tubes that has prompted Osram-Sylvania`s interest in gelcasting. The purpose of the CRADA is to determine the feasibility of making PCA items having sufficient optical quality that they are useful in lighting applications using gelcasting.

  11. Highly Doped Polycrystalline Silicon Microelectrodes Reduce Noise in Neuronal Recordings In Vivo

    PubMed Central

    Saha, Rajarshi; Jackson, Nathan; Patel, Chetan; Muthuswamy, Jit

    2013-01-01

    The aims of this study are to 1) experimentally validate for the first time the nonlinear current-potential characteristics of bulk doped polycrystalline silicon in the small amplitude voltage regimes (0–200 μV) and 2) test if noise amplitudes (0–15 μV) from single neuronal electrical recordings get selectively attenuated in doped polycrystalline silicon microelectrodes due to the above property. In highly doped polycrystalline silicon, bulk resistances of several hundred kilo-ohms were experimentally measured for voltages typical of noise amplitudes and 9–10 kΩ for voltages typical of neural signal amplitudes (>150–200 μV). Acute multiunit measurements and noise measurements were made in n = 6 and n = 8 anesthetized adult rats, respectively, using polycrystalline silicon and tungsten microelectrodes. There was no significant difference in the peak-to-peak amplitudes of action potentials recorded from either microelectrode (p > 0.10). However, noise power in the recordings from tungsten microelectrodes (26.36 ± 10.13 pW) was significantly higher (p < 0.001) than the corresponding value in polycrystalline silicon microelectrodes (7.49 ± 2.66 pW). We conclude that polycrystalline silicon microelectrodes result in selective attenuation of noise power in electrical recordings compared to tungsten microelectrodes. This reduction in noise compared to tungsten microelectrodes is likely due to the exponentially higher bulk resistances offered by highly doped bulk polycrystalline silicon in the range of voltages corresponding to noise in multiunit measurements. PMID:20667815

  12. Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation.

    PubMed

    Yang, Qi; You, Yu-Wei; Liu, Lu; Fan, Hongyu; Ni, Weiyuan; Liu, Dongping; Liu, C S; Benstetter, Günther; Wang, Younian

    2015-01-01

    We report the formation of wave-like structures and nanostructured fuzzes in the polycrystalline tungsten (W) irradiated with high-flux and low-energy helium (He) ions. From conductive atomic force microscope measurements, we have simultaneously obtained the surface topography and current emission images of the irradiated W materials. Our measurements show that He-enriched and nanostructured strips are formed in W crystal grains when they are exposed to low-energy and high-flux He ions at a temperature of 1400 K. The experimental measurements are confirmed by theoretical calculations, where He atoms in W crystal grains are found to cluster in a close-packed arrangement between {101} planes and form He-enriched strips. The formations of wave-like structures and nanostructured fuzzes on the W surface can be attributed to the surface sputtering and swelling of He-enriched strips, respectively.

  13. Decomposition pathways of C2 oxygenates on Rh-modified tungsten carbide surfaces

    NASA Astrophysics Data System (ADS)

    Kelly, Thomas G.; Ren, Hui; Chen, Jingguang G.

    2015-10-01

    Ethanol decomposition on tungsten monocarbide (WC) and Rh-modified WC was investigated using ultrahigh vacuum (UHV) surface science experiments and density functional theory (DFT) calculations. DFT calculations indicated that the binding energies of ethanol and its decomposition intermediates on WC(0001) were modified by Rh, with Rh/WC(0001) showing similar values to those on Rh(111). Through temperature-programmed desorption (TPD) experiments on polycrystalline WC and Rh-modified WC, it was shown that the selectivity for ethanol decomposition was different on these surfaces. On WC, the C-O bond of ethanol was preferentially broken to produce ethylene; on Rh-modified WC, the C-C bond was broken to produce carbon monoxide and methane. Furthermore, high-resolution electron energy loss spectroscopy (HREELS) was used to determine likely surface intermediates. On Rh-modified WC, ethanol first formed ethoxy through O-H scission, then reacted through an aldehyde intermediate to form the C1 products.

  14. Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation

    PubMed Central

    Yang, Qi; You, Yu-Wei; Liu, Lu; Fan, Hongyu; Ni, Weiyuan; Liu, Dongping; Liu, C. S.; Benstetter, Günther; Wang, Younian

    2015-01-01

    We report the formation of wave-like structures and nanostructured fuzzes in the polycrystalline tungsten (W) irradiated with high-flux and low-energy helium (He) ions. From conductive atomic force microscope measurements, we have simultaneously obtained the surface topography and current emission images of the irradiated W materials. Our measurements show that He-enriched and nanostructured strips are formed in W crystal grains when they are exposed to low-energy and high-flux He ions at a temperature of 1400 K. The experimental measurements are confirmed by theoretical calculations, where He atoms in W crystal grains are found to cluster in a close-packed arrangement between {101} planes and form He-enriched strips. The formations of wave-like structures and nanostructured fuzzes on the W surface can be attributed to the surface sputtering and swelling of He-enriched strips, respectively. PMID:26077598

  15. Fabrication of tungsten wire needles

    SciTech Connect

    Roder, A.

    1983-02-01

    Fine point needles for field emissoin are conventionally produced by electrolytically or chemically etching tungsten wire. Points formed in this manner have a typical tip radius of about 0.5 microns and a cone angle of some 30 degrees. The construction of needle matrix detector chambers has created a need for tungsten needles whose specifications are: 20 mil tungsten wire, 1.5 inch total length, 3 mm-long taper (resulting in a cone angle of about 5 degrees), and 25 micron-radius point (similar to that found on sewing needles). In the process described here for producing such needles, tungsten wire, immersed in a NaOH solution and in the presence of an electrode, is connected first to an ac voltage and then to a dc supply, to form a taper and a point on the end of the wire immersed in the solution. The process parameters described here are for needles that will meet the above specifications. Possible variations will be discussed under each approprite heading.

  16. Recrystallization of polycrystalline silicon

    NASA Technical Reports Server (NTRS)

    Lall, C.; Kulkarni, S. B.; Graham, C. D., Jr.; Pope, D. P.

    1981-01-01

    Optical metallography is used to investigate the recrystallization properties of polycrystalline semiconductor-grade silicon. It is found that polycrystalline silicon recrystallizes at 1380 C in relatively short times, provided that the prior deformation is greater than 30%. For a prior deformation of about 40%, the recrystallization process is essentially complete in about 30 minutes. Silicon recrystallizes at a substantially slower rate than metals at equivalent homologous temperatures. The recrystallized grain size is insensitive to the amount of prestrain for strains in the range of 10-50%.

  17. Improvement of polycrystalline silicon wafer solar cell efficiency by forming nanoscale pyramids on wafer surface using a self-mask etching technique.

    PubMed

    Lin, Hsin-Han; Chen, Wen-Hwa; Hong, Franklin C-N

    2013-05-01

    The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6), and oxygen (O2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120-130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6-10 min to create surface nanostructures by varying the compositions of SF6, Cl2, and O2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H2O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm(2)) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching.

  18. Improvement of polycrystalline silicon wafer solar cell efficiency by forming nanoscale pyramids on wafer surface using a self-mask etching technique.

    PubMed

    Lin, Hsin-Han; Chen, Wen-Hwa; Hong, Franklin C-N

    2013-05-01

    The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6), and oxygen (O2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120-130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6-10 min to create surface nanostructures by varying the compositions of SF6, Cl2, and O2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H2O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm(2)) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching. PMID:23847751

  19. Improvement of polycrystalline silicon wafer solar cell efficiency by forming nanoscale pyramids on wafer surface using a self-mask etching technique

    PubMed Central

    Lin, Hsin-Han; Chen, Wen-Hwa; Hong, Franklin C.-N.

    2013-01-01

    The creation of nanostructures on polycrystalline silicon wafer surface to reduce the solar reflection can enhance the solar absorption and thus increase the solar-electricity conversion efficiency of solar cells. The self-masking reactive ion etching (RIE) was studied to directly fabricate nanostructures on silicon surface without using a masking process for antireflection purpose. Reactive gases comprising chlorine (Cl2), sulfur hexafluoride (SF6), and oxygen (O2) were activated by radio-frequency plasma in an RIE system at a typical pressure of 120–130 mTorr to fabricate the nanoscale pyramids. Poly-Si wafers were etched directly without masking for 6–10 min to create surface nanostructures by varying the compositions of SF6, Cl2, and O2 gas mixtures in the etching process. The wafers were then treated with acid (KOH:H2O = 1:1) for 1 min to remove the damage layer (100 nm) induced by dry etching. The damage layer significantly reduced the solar cell efficiencies by affecting the electrical properties of the surface layer. The light reflectivity from the surface after acid treatment could be significantly reduced to <10% for the wavelengths between 500 and 900 nm. The effects of RIE and surface treatment conditions on the surface nanostructures and the optical performance as well as the efficiencies of solar cells will be presented and discussed. The authors have successfully fabricated large-area (156 × 156 mm2) subwavelength antireflection structure on poly-Si substrates, which could improve the solar cell efficiency reproducibly up to 16.27%, higher than 15.56% using wet etching. PMID:23847751

  20. Tungsten silicide formation from sequentially sputtered tungsten and silicon films

    NASA Astrophysics Data System (ADS)

    Molarius, J. M.; Franssila, S.; Drozdy, G.; Saarilahti, J.

    1991-11-01

    As-deposited tungsten silicide films have typically high resistivity and require annealing to lower the resistivity to practical values. Rapid thermal annealing (RTA) has emerged as the main method because impurity diffusion in silicides is extremely fast. In this study we have explored the possibility of reducing the required thermal budget for tungsten silicide annealing by sputtering multilayer W /Si films. In addition to direct technological relevance, multilayer structures offer new insights into silicide formation. We propose a hypothesis "oxygen supply to interface ratio" for explaining why multilayer W /Si structures are beneficial for silicide formation. We have prevented the possible oxygen barrier formation at the W /Si interface by diminishing the oxygen supply by several means: substrate heating during deposition, multiple thin layers, a silicon capping layer and argon purging during RTA. Tetragonal WSi 2 is formed at 700°C and no silicon-rich phases are observed. Low-resistivity WSi 2 is produced by RTA at 1000°C, 120 s. Sheet resistance values around 3 ω/□ amends the use of tungsten silicide in practical polycide structures. The ultimate resistivity of our WSi 2, 30 μω · cm, is among the lowest reported for tungsten silicide, and it is achieved in a very straightforward fashion, using typical production equipment.

  1. Tungsten-induced carcinogenesis in human bronchial epithelial cells.

    PubMed

    Laulicht, Freda; Brocato, Jason; Cartularo, Laura; Vaughan, Joshua; Wu, Feng; Kluz, Thomas; Sun, Hong; Oksuz, Betul Akgol; Shen, Steven; Peana, Massimiliano; Medici, Serenella; Zoroddu, Maria Antonietta; Costa, Max

    2015-10-01

    Metals such as arsenic, cadmium, beryllium, and nickel are known human carcinogens; however, other transition metals, such as tungsten (W), remain relatively uninvestigated with regard to their potential carcinogenic activity. Tungsten production for industrial and military applications has almost doubled over the past decade and continues to increase. Here, for the first time, we demonstrate tungsten's ability to induce carcinogenic related endpoints including cell transformation, increased migration, xenograft growth in nude mice, and the activation of multiple cancer-related pathways in transformed clones as determined by RNA sequencing. Human bronchial epithelial cell line (Beas-2B) exposed to tungsten developed carcinogenic properties. In a soft agar assay, tungsten-treated cells formed more colonies than controls and the tungsten-transformed clones formed tumors in nude mice. RNA-sequencing data revealed that the tungsten-transformed clones altered the expression of many cancer-associated genes when compared to control clones. Genes involved in lung cancer, leukemia, and general cancer genes were deregulated by tungsten. Taken together, our data show the carcinogenic potential of tungsten. Further tests are needed, including in vivo and human studies, in order to validate tungsten as a carcinogen to humans. PMID:26164860

  2. Tungsten-induced carcinogenesis in human bronchial epithelial cells.

    PubMed

    Laulicht, Freda; Brocato, Jason; Cartularo, Laura; Vaughan, Joshua; Wu, Feng; Kluz, Thomas; Sun, Hong; Oksuz, Betul Akgol; Shen, Steven; Peana, Massimiliano; Medici, Serenella; Zoroddu, Maria Antonietta; Costa, Max

    2015-10-01

    Metals such as arsenic, cadmium, beryllium, and nickel are known human carcinogens; however, other transition metals, such as tungsten (W), remain relatively uninvestigated with regard to their potential carcinogenic activity. Tungsten production for industrial and military applications has almost doubled over the past decade and continues to increase. Here, for the first time, we demonstrate tungsten's ability to induce carcinogenic related endpoints including cell transformation, increased migration, xenograft growth in nude mice, and the activation of multiple cancer-related pathways in transformed clones as determined by RNA sequencing. Human bronchial epithelial cell line (Beas-2B) exposed to tungsten developed carcinogenic properties. In a soft agar assay, tungsten-treated cells formed more colonies than controls and the tungsten-transformed clones formed tumors in nude mice. RNA-sequencing data revealed that the tungsten-transformed clones altered the expression of many cancer-associated genes when compared to control clones. Genes involved in lung cancer, leukemia, and general cancer genes were deregulated by tungsten. Taken together, our data show the carcinogenic potential of tungsten. Further tests are needed, including in vivo and human studies, in order to validate tungsten as a carcinogen to humans.

  3. Properties of tungsten oxide thin films formed by ion-plasma and laser deposition methods for MOSiC-based hydrogen sensors

    SciTech Connect

    Fominski, V. Y.; Grigoriev, S. N.; Romanov, R. I.; Zuev, V. V.; Grigoriev, V. V.

    2012-03-15

    Thin-film structures based on gas-sensitive tungsten oxide and catalytic platinum are fabricated by room-temperature deposition on a silicon carbide wafer using pulsed laser and ion-plasma methods. Oxide layer annealing in air to 600 Degree-Sign C caused the formation of microstructured and nanostructured crystalline states depending on the deposition conditions. Structural differences affect the electrical parameters and the stability of characteristics. The maximum response to hydrogen is detected in the structure fabricated by depositing a low-energy laser-induced flow of tungsten atoms in oxygen. The voltage shift of the currentvoltage curves for 2% H{sub 2} in air at 350 Degree-Sign C was 4.6 V at a current of {approx}10 {mu}A. The grown structures' metastability caused a significant decrease in the shift after long-term cyclic testing. The most stable shifts of {approx}2 V at positive bias on the Pt contact were detected for oxide films deposited by ion-plasma sputtering.

  4. Femtosecond laser-induced periodic surface structure formation on tungsten

    SciTech Connect

    Vorobyev, A. Y.; Guo Chunlei

    2008-09-15

    In this paper, we demonstrate the generation of periodic surface structures on a technologically important material, tungsten, at both 400 and 800 nm, despite that the table values of dielectric constants for tungsten at these two wavelengths suggest the absence of surface plasmons, a wave necessary for forming periodic structures on metals. Furthermore, we find that the structure periods formed on tungsten are significantly less than the laser wavelengths. We believe that the dielectric constants of tungsten change significantly due to intense laser pulse heating and surface structuring and roughening at nanometer scales, permitting surface plasmon excitation and periodic structure formation.

  5. Recrystallization of tungsten wire for fabrication of sharp and stable nanoprobe and field-emitter tips.

    PubMed

    Greiner, M; Kruse, P

    2007-02-01

    Atomically sharp tungsten tips made from single crystal tungsten wire are superior to those made from cold-drawn polycrystalline wire but are rarely used due to their high price. We have devised a method of obtaining highly crystalline tungsten wire by recrystallizing cold-drawn wire. The effect of various heat treatments on the wire microstructure was observed using scanning electron microscopy and x-ray diffraction. A dramatic difference in the shapes of tips etched from cold-drawn and recrystallized wires was observed using transmission electron microscopy. The described annealing process is an inexpensive alternative to using single crystal wires.

  6. Tungsten Filament Fire

    ERIC Educational Resources Information Center

    Ruiz, Michael J.; Perkins, James

    2016-01-01

    We safely remove the outer glass bulb from an incandescent lamp and burn up the tungsten filament after the glass is removed. This demonstration dramatically illustrates the necessity of a vacuum or inert gas for the environment surrounding the tungsten filament inside the bulb. Our approach has added historical importance since the incandescent…

  7. Tungsten filament fire

    NASA Astrophysics Data System (ADS)

    Ruiz, Michael J.; Perkins, James

    2016-05-01

    We safely remove the outer glass bulb from an incandescent lamp and burn up the tungsten filament after the glass is removed. This demonstration dramatically illustrates the necessity of a vacuum or inert gas for the environment surrounding the tungsten filament inside the bulb. Our approach has added historical importance since the incandescent light bulb is being replaced by compact fluorescent and LED lamps.

  8. Low flux and low energy helium ion implantation into tungsten using a dedicated plasma source

    NASA Astrophysics Data System (ADS)

    Pentecoste, Lucile; Thomann, Anne-Lise; Melhem, Amer; Caillard, Amael; Cuynet, Stéphane; Lecas, Thomas; Brault, Pascal; Desgardin, Pierre; Barthe, Marie-France

    2016-09-01

    The aim of this work is to investigate the first stages of defect formation in tungsten (W) due to the accumulation of helium (He) atoms inside the crystal lattice. To reach the required implantation conditions, i.e. low He ion fluxes (1011-1014 ions.cm2.s-1) and kinetic energies below the W atom displacement threshold (about 500 eV for He+), an ICP source has been designed and connected to a diffusion chamber. Implantation conditions have been characterized by means of complementary diagnostics modified for measurements in this very low density helium plasma. It was shown that lowest ion fluxes could only be reached for the discharge working in capacitive mode either in α or γ regime. Special attention was paid to control the energy gained by the ions by acceleration through the sheath at the direct current biased substrate. At very low helium pressure, in α regime, a broad ion energy distribution function was evidenced, whereas a peak centered on the potential difference between the plasma and the biased substrate was found at higher pressures in the γ mode. Polycrystalline tungsten samples were exposed to the helium plasma in both regimes of the discharge and characterized by positron annihilation spectroscopy in order to detect the formed vacancy defects. It was found that W vacancies are able to be formed just by helium accumulation and that the same final implanted state is reached, whatever the operating mode of the capacitive discharge.

  9. Deuterium retention and surface modifications of nanocrystalline tungsten films exposed to high-flux plasma

    NASA Astrophysics Data System (ADS)

    `t Hoen, M. H. J.; Dellasega, D.; Pezzoli, A.; Passoni, M.; Kleyn, A. W.; Zeijlmans van Emmichoven, P. A.

    2015-08-01

    Deuterium retention studies are presented for nanostructured tungsten films exposed to high-flux deuterium plasmas. Thin tungsten films of ∼1 μm thickness were deposited with pulsed laser deposition (PLD) on bulk tungsten. Surface modifications were studied with scanning electron microscopy and deuterium retention with thermal desorption spectroscopy. Three types of PLD films with different densities and crystallinity were studied after exposure to deuterium plasmas. The surface temperature ranged from about 460 K at the periphery to about 520 K in the centre of the targets. The films withstand the intense plasma exposure well and maintain their overall integrity. An increase of deuterium retention is observed with decreasing tungsten density and crystallite size. We found that the filling of these thin films with deuterium is significantly faster than for pre-damaged polycrystalline tungsten. We observed formation of micrometer-sized blisters as well as structures on the nanometer scale, both depending on the layer type.

  10. [Study on the micro-infrared spectra and origin of polycrystalline diamonds from Mengyin kimberlite pipes].

    PubMed

    Yang, Zhi-Jun; Liang, Rong; Zeng, Xiang-Qing; Ge, Tie-Yan; Ai, Qun; Zheng, Yun-Long; Peng, Ming-Sheng

    2012-06-01

    The natural polycrystalline diamonds from the Mengyin kimberlite pipes can be classified as the euhedral faceted polycrystalline diamonds and anhedral rounded polycrystalline diamonds. The results of micro-FTIR spectra characterization of the polycrystalline diamonds show that the concentration of nitrogen is low, varying from 16.69 to 72.81 microgram per gram and is different among different diamond grains or position in polycrystalline diamonds. The euhedral faceted polycrystalline diamonds are Ia AB type and have higher concentration of A-center defects than B-center defects. Most of the anhedral rounded polycrystalline diamonds are Ia AB type and have higher content of B-center defects. A minority of the anhedral rounded polycrystalline diamonds have C-center, A-center and B-center defects simultaneously. The polycrystalline diamonds probably originated from the relatively deeper mantle and were not formed in diamond nucleation stage, but in the diamond growth period or some special conditions after the diamond grains were formed already. Furthermore, the euhedral faceted polycrystalline diamonds were formed slightly later and the anhedral rounded polycrystalline diamonds were formed obviously earlier than the diamond single crystals from the Mengyin kimberlite pipes.

  11. [Study on the micro-infrared spectra and origin of polycrystalline diamonds from Mengyin kimberlite pipes].

    PubMed

    Yang, Zhi-Jun; Liang, Rong; Zeng, Xiang-Qing; Ge, Tie-Yan; Ai, Qun; Zheng, Yun-Long; Peng, Ming-Sheng

    2012-06-01

    The natural polycrystalline diamonds from the Mengyin kimberlite pipes can be classified as the euhedral faceted polycrystalline diamonds and anhedral rounded polycrystalline diamonds. The results of micro-FTIR spectra characterization of the polycrystalline diamonds show that the concentration of nitrogen is low, varying from 16.69 to 72.81 microgram per gram and is different among different diamond grains or position in polycrystalline diamonds. The euhedral faceted polycrystalline diamonds are Ia AB type and have higher concentration of A-center defects than B-center defects. Most of the anhedral rounded polycrystalline diamonds are Ia AB type and have higher content of B-center defects. A minority of the anhedral rounded polycrystalline diamonds have C-center, A-center and B-center defects simultaneously. The polycrystalline diamonds probably originated from the relatively deeper mantle and were not formed in diamond nucleation stage, but in the diamond growth period or some special conditions after the diamond grains were formed already. Furthermore, the euhedral faceted polycrystalline diamonds were formed slightly later and the anhedral rounded polycrystalline diamonds were formed obviously earlier than the diamond single crystals from the Mengyin kimberlite pipes. PMID:22870630

  12. Tungsten-induced carcinogenesis in human bronchial epithelial cells

    PubMed Central

    Laulicht, Freda; Brocato, Jason; Cartularo, Laura; Vaughan, Joshua; Wu, Feng; Kluz, Thomas; Sun, Hong; Oksuz, Betul Akgol; Shen, Steven; Paena, Massimilano; Medici, Serenella; Zoroddu, Maria Antonietta; Costa, Max

    2015-01-01

    Metals such as arsenic, cadmium, beryllium, and nickel are known human carcinogens; however, other transition metals, such as tungsten (W), remain relatively uninvestigated with regard to their potential carcinogenic activity. Tungsten production for industrial and military applications has almost doubled over the past decade and continues to increase. Here, for the first time, we demonstrate tungsten’s ability to induce carcinogenic related endpoints including cell transformation, increased migration, xenograft growth in nude mice, and the activation of multiple cancer related pathways in transformed clones as determined by RNA seq. Human bronchial epithelial cell line (Beas-2B) exposed to tungsten developed carcinogenic properties. In a soft agar assay, tungsten-treated cells formed more colonies than controls and the tungsten-transformed clones formed tumors in nude mice. RNA-sequencing data revealed that the tungsten-transformed clones altered the expression of many cancer-associated genes when compared to control clones. Genes involved in lung cancer, leukemia, and general cancer genes were deregulated by tungsten. Taken together, our data shows the carcinogenic potential of tungsten. Further tests are needed, including in vivo and human studies, in order to validate tungsten as a carcinogen to humans. PMID:26164860

  13. Fabrication and characterization of polycrystalline WO3 nanofibers and their application for ammonia sensing

    SciTech Connect

    Wang,G.; Ji, Y.; Huang, X.; Yang, X.; Gouma, P.; Dudley, M.

    2006-01-01

    We describe the fabrication and characterization of tungsten oxide nanofibers using the electrospinning technique and sol-gel chemistry. Tungsten isopropoxide sol-gel precursor was incorporated into poly(vinyl acetate)(PVAc)/DMF solutions and electrospun to form composite nanofibers. The as-spun composite nanofibers were subsequently calcinated to obtain pure tungsten oxide nanofibers with controllable diameters of around 100 nm. SEM and TEM were utilized to investigate the structure and morphology of tungsten oxide nanofibers before and after calcination. The relationship between solution concentration and ceramic nanofiber morphology has been studied. A synchrotron-based in situ XRD method was employed to study the dynamic structure evolution of the tungsten oxide nanofibers during the calcination process. It has been shown that the as-prepared tungsten oxide ceramic nanofibers have a quick response to ammonia with various concentrations, suggesting potential applications of the electrospun tungsten oxide nanofibers as a sensor material for gas detection.

  14. Fabrication and Characterization of Polycrystalline WO3 Nanofibers and Their Application for Ammonia Sensing

    SciTech Connect

    Wang,G.; Ji, Y.; Huang, X.; Yang, X.; Gouma, P.; Dudley, M.

    2006-01-01

    We describe the fabrication and characterization of tungsten oxide nanofibers using the electrospinning technique and sol-gel chemistry. Tungsten isopropoxide sol-gel precursor was incorporated into poly(vinyl acetate)(PVAc)/DMF solutions and electrospun to form composite nanofibers. The as-spun composite nanofibers were subsequently calcinated to obtain pure tungsten oxide nanofibers with controllable diameters of around 100 nm. SEM and TEM were utilized to investigate the structure and morphology of tungsten oxide nanofibers before and after calcination. The relationship between solution concentration and ceramic nanofiber morphology has been studied. A synchrotron-based in situ XRD method was employed to study the dynamic structure evolution of the tungsten oxide nanofibers during the calcination process. It has been shown that the as-prepared tungsten oxide ceramic nanofibers have a quick response to ammonia with various concentrations, suggesting potential applications of the electrospun tungsten oxide nanofibers as a sensor material for gas detection.

  15. Seed growth of tungsten diselenide nanotubes from tungsten oxides.

    PubMed

    Kim, Hyun; Yun, Seok Joon; Park, Jin Cheol; Park, Min Ho; Park, Ji-Hoon; Kim, Ki Kang; Lee, Young Hee

    2015-05-13

    We report growth of tungsten diselenide (WSe2) nanotubes by chemical vapor deposition with a two-zone furnace. WO3 nanowires were first grown by annealing tungsten thin films under argon ambient. WSe2 nanotubes were then grown at the tips of WO3 nanowires through selenization via two steps: (i) formation of tubular WSe2 structures on the outside of WO3 nanowires, resulting in core (WO3)-shell (WSe2) and (ii) growth of WSe2 nanotubes at the tips of WO3 nanowires. The observed seed growth is markedly different from existing substitutional growth of WSe2 nanotubes, where oxygen atoms are replaced by selenium atoms in WO3 nanowires to form WSe2 nanotubes. Another advantage of our growth is that WSe2 film was grown by simply supplying hydrogen gas, where the native oxides were reduced to thin film instead of forming oxide nanowires. Our findings will contribute to engineer other transition metal dichacogenide growth such as MoS2, WS2, and MoSe2. PMID:25581340

  16. Effective structural properties in polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Hossain, Zubaer

    This talk will discuss effective structural properties in polycrystalline graphene under the presence of atomic scale heterogeneity. Polycrystallinity is ubiquitous in solids, but theories describing their effective behavior remain limited, particularly when heterogeneity is present in the form of nonuniform deformation or composition. Over the decades, exploration of the effective transport and strength properties of heterogeneous systems has been carried out mostly with random distribution of grains or regular periodic structures under various approximations, in translating the underlying physics into a single representative volume element. Although heterogeneity can play a critical role in modulating the basic behavior of low-dimensional materials, it is difficult to capture the local characteristics accurately by these approximations. Taking polycrystalline graphene as an example material, we study the effective structural properties (such as Young's Modulus, Poisson's ratio and Toughness) by using a combination of density functional theory and molecular dynamic simulations. We identify the key mechanisms that govern their effective behavior and exploit the understanding to engineer the behavior by doping with a carefully selected choice of chemical elements.

  17. Reflection properties of hydrogen ions at helium irradiated tungsten surfaces

    NASA Astrophysics Data System (ADS)

    Doi, K.; Tawada, Y.; Lee, H. T.; Kato, S.; Tanaka, N.; Sasao, M.; Kisaki, M.; Nishiura, M.; Matsumoto, Y.; Kenmotsu, T.; Wada, M.; Ueda, Y.; Yamaoka, H.

    2016-02-01

    Nanostructured W surfaces prepared by He bombardment exhibit characteristic angular distributions of hydrogen ion reflection upon injection of 1 keV H+ beam. A magnetic momentum analyzer that can move in the vacuum chamber has measured the angular dependence of the intensity and the energy of reflected ions. Broader angular distributions were observed for He-irradiated tungsten samples compared with that of the intrinsic polycrystalline W. Both intensity and energy of reflected ions decreased in the following order: the polycrystalline W, the He-bubble containing W, and the fuzz W. Classical trajectory Monte Carlo simulations based on Atomic Collision in Amorphous Target code suggests that lower atom density near the surface can make the reflection coefficients lower due to increasing number of collisions.

  18. Tungsten diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Van Orman, J. A.

    2014-03-01

    Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 min to several weeks, at temperatures from 1050 to 1450 °C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for W diffusion in forsterite: D=1.0×10-8exp(-365±28 kJ mol/RT) m s Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity. The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

  19. High purity tungsten targets

    NASA Technical Reports Server (NTRS)

    1975-01-01

    High purity tungsten, which is used for targets in X-ray tubes was considered for space processing. The demand for X-ray tubes was calculated using the growth rates for dental and medical X-ray machines. It is concluded that the cost benefits are uncertain.

  20. Gas tungsten arc welder

    DOEpatents

    Christiansen, D.W.; Brown, W.F.

    A welder for automated closure of fuel pins by a gas tungsten arc process in which a rotating length of cladding is positioned adjacent a welding electrode in a sealed enclosure. An independently movable axial grinder is provided in the enclosure for refurbishing the used electrode between welds.

  1. Chemical downstream etching of tungsten

    SciTech Connect

    Blain, M.G.; Jarecki, R.L.; Simonson, R.J.

    1998-07-01

    The downstream etching of tungsten and tungsten oxide has been investigated. Etching of chemical vapor deposited tungsten and e-beam deposited tungsten oxide samples was performed using atomic fluorine generated by a microwave discharge of argon and NF{sub 3}. Etching was found to be highly activated with activation energies approximated to be 6.0{plus_minus}0.5thinspkcal/mol and 5.4{plus_minus}0.4thinspkcal/mol for W and WO{sub 3}, respectively. In the case of F etching of tungsten, the addition of undischarged nitric oxide (NO) directly into the reaction chamber results in the competing effects of catalytic etch rate enhancement and the formation of a nearly stoichiometric WO{sub 3} passivating tungsten oxide film, which ultimately stops the etching process. For F etching of tungsten oxide, the introduction of downstream NO reduces the etch rate. {copyright} {ital 1998 American Vacuum Society.}

  2. Joining of Tungsten Armor Using Functional Gradients

    SciTech Connect

    John Scott O'Dell

    2006-12-31

    The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

  3. Synthesis and mechanical properties of nano-polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Couvy, H.; Chen, J.

    2010-12-01

    The sample of nano-polycrystalline diamond (NPD) has been synthesized at the Center for the Study of Matter at Extreme Conditions using a 500t multi-anvil press equipped with a Walker module. A rod of polycrystalline graphite (99.9995%; Alfa Aesar) was used as starting material. The sample was directly inserted into the Re furnace of a 8mm octahedral edge length cell assembly. Tungsten carbide cubes with 3mm truncation edge length were used as anvils. The graphite sample converted directly into diamond at 19 GPa and 2400C. The temperature was maintained for 30 seconds. The recovered sample is transparent indicating that all graphite has been converted into cubic diamond. Raman spectroscopy and X-ray diffraction confirm the total conversion and purity of the sample. The latter has been mounted in epoxy and was finely polished for nano-indentation hardness test using metal-bonding diamond abrasive disks. In this study we do not measure the hardness of the material using the traditional method (impression hardness) which consist in measuring the dimension of the indent impression after indentation. We use depth-sensing nanoindentation. Our indenter used is equipped with piezo controller which monitor dynamically the depth of the indent during the hardness test. This method is considered to be more accurate and more adapted to elastic material. The hardness test has been performed using a Hysitron TriboIndenter. The probe is a diamond Berkovich tip (three sided pyramid) with 100 nm tip radius. NPD hardness and Young’s modulus has been compared with commercially available polycrystalline superhard material used in high-pressure devices as anvils: a cubic boron nitrite anvil (cBN) from Linatec (Ukraine) and a sintered polycrystalline diamond anvil (PCD) from Ringwood Superabrasives Pty Ltd (USA). The results show the superior hardness and elastic properties of NPD on cBN and PCD.

  4. Level-energy-dependent mean velocities of excited tungsten atoms sputtered by krypton-ion bombardment

    SciTech Connect

    Nogami, Keisuke; Sakai, Yasuhiro; Mineta, Shota; Kato, Daiji; Murakami, Izumi; Sakaue, Hiroyuki A.; Kenmotsu, Takahiro; Furuya, Kenji; Motohashi, Kenji

    2015-11-15

    Visible emission spectra were acquired from neutral atoms sputtered by 35–60 keV Kr{sup +} ions from a polycrystalline tungsten surface. Mean velocities of excited tungsten atoms in seven different 6p states were also obtained via the dependence of photon intensities on the distance from the surface. The average velocities parallel to the surface normal varied by factors of 2–4 for atoms in the different 6p energy levels. However, they were almost independent of the incident ion kinetic energy. The 6p-level energy dependence indicated that the velocities of the excited atoms were determined by inelastic processes that involve resonant charge exchange.

  5. Process for Polycrystalline film silicon growth

    DOEpatents

    Wang, Tihu; Ciszek, Theodore F.

    2001-01-01

    A process for depositing polycrystalline silicon on substrates, including foreign substrates, occurs in a chamber at about atmospheric pressure, wherein a temperature gradient is formed, and both the atmospheric pressure and the temperature gradient are maintained throughout the process. Formation of a vapor barrier within the chamber that precludes exit of the constituent chemicals, which include silicon, iodine, silicon diiodide, and silicon tetraiodide. The deposition occurs beneath the vapor barrier. One embodiment of the process also includes the use of a blanketing gas that precludes the entrance of oxygen or other impurities. The process is capable of repetition without the need to reset the deposition zone conditions.

  6. Tungsten bronze-based nuclear waste form ceramics. Part 3: The system Cs 0.3M xW 1- xO 3 for the immobilization of radio cesium

    NASA Astrophysics Data System (ADS)

    Luca, Vittorio; Drabarek, Elizabeth; Chronis, Harriet; McLeod, Terry

    2006-11-01

    Previous studies in this series have indicated that Cs- and Sr-loaded Mo-doped hexagonal tungsten bronze (MoW-HTB) oxides, either in the form of fine grained powders, or as composite granules, can be converted to leach resistant ceramics at modest temperatures in the range 600-1200 °C. In the present study it has been shown that such waste form ceramics can also be readily prepared through very simple conventional routes involving the blending of cesium nitrate with tungstic acid and other oxide components followed by heating in air. The phase chemistry resulting from the blending of these oxides has been explored. In the Cs 0.3M xW 1- xO 3 compositional system where x = Ti, Zr, Nb and Ta the solid solution limit has been found to be where x = 0.2. For all values of x between 0 and 0.2 mixed phase materials of HTB and WO 3 were obtained and Cs was found associated with HTB phases that are both rich and depleted in M element. At temperatures above about 1000 °C, phase pure HTB compounds in the space group P63/ mcm were obtained. Even when x greatly exceeds 0.2, the additional oxide content did not interfere with the formation of the HTB phase. Durability of the Cs 0.3M xW 1- xO 3 compositions as gauged by the fractional Cs loss in de-mineralized water was lowest when M = Ti and Nb, and greatest when M = Zr. From these results the durability appears intimately linked with the unit cell a-dimension which in turn varies with M cation radius.

  7. Abnormality in fracture strength of polycrystalline silicene

    NASA Astrophysics Data System (ADS)

    Liu, Ning; Hong, Jiawang; Pidaparti, Ramana; Wang, Xianqiao

    2016-09-01

    Silicene, a silicon-based homologue of graphene, arouses great interest in nano-electronic devices due to its outstanding electronic properties. However, its promising electronic applications are greatly hindered by lack of understanding in the mechanical strength of silicene. Therefore, in order to design mechanically reliable devices with silicene, it is necessary to thoroughly explore the mechanical properties of silicene. Due to current fabrication methods, graphene is commonly produced in a polycrystalline form; the same may hold for silicene. Here we perform molecular dynamics simulations to investigate the mechanical properties of polycrystalline silicene. First, an annealing process is employed to construct a more realistic modeling structure of polycrystalline silicene. Results indicate that a more stable structure is formed due to the breaking and reformation of bonds between atoms on the grain boundaries. Moreover, as the grain size decreases, the efficiency of the annealing process, which is quantified by the energy change, increases. Subsequently, biaxial tensile tests are performed on the annealed samples in order to explore the relation between grain size and mechanical properties, namely in-plane stiffness, fracture strength and fracture strain etc. Results indicate that as the grain size decreases, the fracture strain increases while the fracture strength shows an inverse trend. The decreasing fracture strength may be partly attributed to the weakening effect from the increasing area density of defects which acts as the reservoir of stress-concentrated sites on the grain boundary. The observed crack localization and propagation and fracture strength are well-explained by a defect-pileup model.

  8. Engineered Surface Properties of Porous Tungsten from Cryogenic Machining

    NASA Astrophysics Data System (ADS)

    Schoop, Julius Malte

    Porous tungsten is used to manufacture dispenser cathodes due to it refractory properties. Surface porosity is critical to functional performance of dispenser cathodes because it allows for an impregnated ceramic compound to migrate to the emitting surface, lowering its work function. Likewise, surface roughness is important because it is necessary to ensure uniform wetting of the molten impregnate during high temperature service. Current industry practice to achieve surface roughness and surface porosity requirements involves the use of a plastic infiltrant during machining. After machining, the infiltrant is baked and the cathode pellet is impregnated. In this context, cryogenic machining is investigated as a substitutionary process for the current plastic infiltration process. Along with significant reductions in cycle time and resource use, surface quality of cryogenically machined un-infiltrated (as-sintered) porous tungsten has been shown to significantly outperform dry machining. The present study is focused on examining the relationship between machining parameters and cooling condition on the as-machined surface integrity of porous tungsten. The effects of cryogenic pre-cooling, rake angle, cutting speed, depth of cut and feed are all taken into consideration with respect to machining-induced surface morphology. Cermet and Polycrystalline diamond (PCD) cutting tools are used to develop high performance cryogenic machining of porous tungsten. Dry and pre-heated machining were investigated as a means to allow for ductile mode machining, yet severe tool-wear and undesirable smearing limited the feasibility of these approaches. By using modified PCD cutting tools, high speed machining of porous tungsten at cutting speeds up to 400 m/min is achieved for the first time. Beyond a critical speed, brittle fracture and built-up edge are eliminated as the result of a brittle to ductile transition. A model of critical chip thickness ( hc ) effects based on cutting

  9. Combined single-crystalline and polycrystalline CVD diamond substrates for diamond electronics

    SciTech Connect

    Vikharev, A. L. Gorbachev, A. M.; Dukhnovsky, M. P.; Muchnikov, A. B.; Ratnikova, A. K.; Fedorov, Yu. Yu.

    2012-02-15

    The fabrication of diamond substrates in which single-crystalline and polycrystalline CVD diamond form a single wafer, and the epitaxial growth of diamond films on such combined substrates containing polycrystalline and (100) single-crystalline CVD diamond regions are studied.

  10. Tungsten Ditelluride: a layered semimetal

    NASA Astrophysics Data System (ADS)

    Lee, Chia-Hui; Silva, Eduardo Cruz; Calderin, Lazaro; Nguyen, Minh An T.; Hollander, Matthew J.; Bersch, Brian; Mallouk, Thomas E.; Robinson, Joshua A.

    2015-06-01

    Tungsten ditelluride (WTe2) is a transition metal dichalcogenide (TMD) with physical and electronic properties that make it attractive for a variety of electronic applications. Although WTe2 has been studied for decades, its structure and electronic properties have only recently been correctly described. We experimentally and theoretically investigate the structure, dynamics and electronic properties of WTe2, and verify that WTe2 has its minimum energy configuration in a distorted 1T structure (Td structure), which results in metallic-like transport. Our findings unambiguously confirm the metallic nature of WTe2, introduce new information about the Raman modes of Td-WTe2, and demonstrate that Td-WTe2 is readily oxidized via environmental exposure. Finally, these findings confirm that, in its thermodynamically favored Td form, the utilization of WTe2 in electronic device architectures such as field effect transistors may need to be reevaluated.

  11. Helium bubble bursting in tungsten

    SciTech Connect

    Sefta, Faiza; Juslin, Niklas; Wirth, Brian D.

    2013-12-28

    Molecular dynamics simulations have been used to systematically study the pressure evolution and bursting behavior of sub-surface helium bubbles and the resulting tungsten surface morphology. This study specifically investigates how bubble shape and size, temperature, tungsten surface orientation, and ligament thickness above the bubble influence bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom “islands,” craters, and pinholes. The present study provides insight into the mechanisms and conditions leading to various tungsten topology changes, which we believe are the initial stages of surface evolution leading to the formation of nanoscale fuzz.

  12. Systematic studies of the nucleation and growth of ultrananocrystalline diamond films on silicon substrates coated with a tungsten layer

    SciTech Connect

    Chu, Yueh-Chieh; Jiang, Gerald; Tu, Chia-Hao; Chang Chi; Liu, Chuan-pu; Ting, Jyh-Ming; Lee, Hsin-Li; Tzeng, Yonhua; Auciello, Orlando

    2012-06-15

    We report on effects of a tungsten layer deposited on silicon surface on the effectiveness for diamond nanoparticles to be seeded for the deposition of ultrananocrystalline diamond (UNCD). Rough tungsten surface and electrostatic forces between nanodiamond seeds and the tungsten surface layer help to improve the adhesion of nanodiamond seeds on the tungsten surface. The seeding density on tungsten coated silicon thus increases. Tungsten carbide is formed by reactions of the tungsten layer with carbon containing plasma species. It provides favorable (001) crystal planes for the nucleation of (111) crystal planes by Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD) in argon diluted methane plasma and further improves the density of diamond seeds/nuclei. UNCD films grown at different gas pressures on tungsten coated silicon which is pre-seeded by nanodiamond along with heteroepitaxially nucleated diamond nuclei were characterized by Raman scattering, field emission-scanning electron microscopy, and high resolution-transmission electron microscopy.

  13. Interaction of tungsten with tungsten carbide in a copper melt

    NASA Astrophysics Data System (ADS)

    Bodrova, L. E.; Goida, E. Yu.; Pastukhov, E. A.; Marshuk, L. A.; Popova, E. A.

    2013-07-01

    The chemical interaction between tungsten and tungsten carbide in a copper melt with the formation of W2C at 1300°C is studied. It is shown that the mechanical activation of a composition consisting of copper melt + W and WC powders by low-temperature vibrations initiates not only the chemical interaction of its solid components but also their refinement.

  14. Decomposition pathways of C2 oxygenates on Rh-modified tungsten carbide surfaces

    DOE PAGES

    Kelly, Thomas G.; Ren, Hui; Chen, Jingguang G.

    2015-03-27

    Ethanol decomposition on tungsten monocarbide (WC) and Rh-modified WC was investigated using ultrahigh vacuum (UHV) surface science experiments and density functional theory (DFT) calculations. DFT calculations indicated that the binding energies of ethanol and its decomposition intermediates on WC(0001) were modified by Rh, with Rh/WC(0001) showing similar values to those on Rh(111). Through temperature-programmed desorption (TPD) experiments on polycrystalline WC and Rh-modified WC, it was shown that the selectivity for ethanol decomposition was different on these surfaces. On WC, the C-O bond of ethanol was preferentially broken to produce ethylene; on Rh-modified WC, the C-C bond was broken to producemore » carbon monoxide and methane. In addition, high-resolution electron energy loss spectroscopy (HREELS) was used to determine likely surface intermediates. On Rh-modified WC, ethanol first formed ethoxy through O-H scission, then reacted through an aldehyde intermediate to form the C1 products.« less

  15. Decomposition pathways of C2 oxygenates on Rh-modified tungsten carbide surfaces

    SciTech Connect

    Kelly, Thomas G.; Ren, Hui; Chen, Jingguang G.

    2015-03-27

    Ethanol decomposition on tungsten monocarbide (WC) and Rh-modified WC was investigated using ultrahigh vacuum (UHV) surface science experiments and density functional theory (DFT) calculations. DFT calculations indicated that the binding energies of ethanol and its decomposition intermediates on WC(0001) were modified by Rh, with Rh/WC(0001) showing similar values to those on Rh(111). Through temperature-programmed desorption (TPD) experiments on polycrystalline WC and Rh-modified WC, it was shown that the selectivity for ethanol decomposition was different on these surfaces. On WC, the C-O bond of ethanol was preferentially broken to produce ethylene; on Rh-modified WC, the C-C bond was broken to produce carbon monoxide and methane. In addition, high-resolution electron energy loss spectroscopy (HREELS) was used to determine likely surface intermediates. On Rh-modified WC, ethanol first formed ethoxy through O-H scission, then reacted through an aldehyde intermediate to form the C1 products.

  16. Some observations on uranium carbide alloy/tungsten compatibility.

    NASA Technical Reports Server (NTRS)

    Phillips, W. M.

    1972-01-01

    Results of chemical compatibility tests between both pure tungsten and thoriated tungsten run at 1800 C for up to 3300 hours with uranium carbide alloys. Alloying with zirconium carbide appeared to widen the homogeneity range of uranium carbide, making additional carbon available for reaction with the tungsten. Reaction layers were formed both by vapor phase reaction and by physical contact, producing either or both UWC2 and W2C, depending upon the phases present in the starting fuel alloy. Formation of UWC2 results in slow growth of the reaction layer with time, while W2C reaction layers grow rapidly, allowing equilibrium to be reached in less than 2500 hours at 1800 C. Neither the presence of a thermal gradient nor the presence of thoria in the tungsten clad affect the reactions observed.

  17. Preparation of tungsten oxide

    DOEpatents

    Bulian, Christopher J.; Dye, Robert C.; Son, Steven F.; Jorgensen, Betty S.; Perry, W. Lee

    2009-09-22

    Tungsten trioxide hydrate (WO.sub.3.H.sub.2O) was prepared from a precursor solution of ammonium paratungstate in concentrated aqueous hydrochloric acid. The precursor solution was rapidly added to water, resulting in the crash precipitation of a yellow white powder identified as WO.sub.3.H.sub.2O nanosized platelets by x-ray diffraction and scanning electron microscopy. Annealing of the powder at 200.degree. C. provided cubic phase WO.sub.3 nanopowder, and at 400.degree. C. provided WO.sub.3 nanopowder as a mixture of monoclinic and orthorhombic phases.

  18. Acidic magnetorheological finishing of infrared polycrystalline materials

    DOE PAGES

    Salzman, S.; Romanofsky, H. J.; West, G.; Marshall, K. L.; Jacobs, S. D.; Lambropoulos, J. C.

    2016-10-12

    Here, chemical-vapor–deposited (CVD) ZnS is an example of a polycrystalline material that is difficult to polish smoothly via the magnetorheological–finishing (MRF) technique. When MRF-polished, the internal infrastructure of the material tends to manifest on the surface as millimeter-sized “pebbles,” and the surface roughness observed is considerably high. The fluid’s parameters important to developing a magnetorheological (MR) fluid that is capable of polishing CVD ZnS smoothly were previously discussed and presented. These parameters were acidic pH (~4.5) and low viscosity (~47 cP). MRF with such a unique MR fluid was shown to reduce surface artifacts in the form of pebbles; however,more » surface microroughness was still relatively high because of the absence of a polishing abrasive in the formulation. In this study, we examine the effect of two polishing abrasives—alumina and nanodiamond—on the surface finish of several CVD ZnS substrates, and on other important IR polycrystalline materials that were finished with acidic MR fluids containing these two polishing abrasives. Surface microroughness results obtained were as low as ~28 nm peak-to-valley and ~6-nm root mean square.« less

  19. Polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  20. Plastic flow of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Langer, James

    Leo Kadanoff had a long interest in fluid flows, especially fingering instabilities. This interest was one example of his insatiable curiosity about simple, fundamentally important, and often multidisciplinary phenomena. Here is an example of another class of such phenomena that I had hoped to show him this year. The experts in polycrystalline solid mechanics have insisted for decades that their central problem - dislocation-mediated strain hardening - is intrinsically unsolvable. I think they're wrong. My colleagues and I have made progress recently in theories of both amorphous and polycrystalline plasticity by introducing an effective disorder temperature as a dynamical variable in our equations of motion. In this way, we have been able to describe how the densities of flow defects or dislocations evolve in response to external forcing, and thus to develop theories that promise to become as predictive, and full of surprises, as the laws of fluid flow. For Kadanoff session.

  1. Polycrystalline thin film photovoltaic technology

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L.; Noufi, R.

    1991-03-01

    Low-cost, high-efficiency thin-film modules are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. In this paper we review the significant technical progress made in the following thin films: copper indium diselenide, cadmium telluride, and polycrystalline thin silicon films. Also, the recent US DOE/SERI initiative to commercialize these emerging technologies is discussed. 6 refs., 9 figs.

  2. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 2 2011-10-01 2011-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  3. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 2 2014-10-01 2014-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  4. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 2 2013-10-01 2013-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  5. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 2 2012-10-01 2012-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  6. 49 CFR 173.338 - Tungsten hexafluoride.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 2 2010-10-01 2010-10-01 false Tungsten hexafluoride. 173.338 Section 173.338... SHIPMENTS AND PACKAGINGS Gases; Preparation and Packaging § 173.338 Tungsten hexafluoride. (a) Tungsten... expansion test, must be condemned if removed from tungsten hexafluoride service....

  7. High strength uranium-tungsten alloy process

    DOEpatents

    Dunn, Paul S.; Sheinberg, Haskell; Hogan, Billy M.; Lewis, Homer D.; Dickinson, James M.

    1990-01-01

    Alloys of uranium and tungsten and a method for making the alloys. The amount of tungsten present in the alloys is from about 4 wt % to about 35 wt %. Tungsten particles are dispersed throughout the uranium and a small amount of tungsten is dissolved in the uranium.

  8. High strength uranium-tungsten alloys

    DOEpatents

    Dunn, Paul S.; Sheinberg, Haskell; Hogan, Billy M.; Lewis, Homer D.; Dickinson, James M.

    1991-01-01

    Alloys of uranium and tungsten and a method for making the alloys. The amount of tungsten present in the alloys is from about 4 wt % to about 35 wt %. Tungsten particles are dispersed throughout the uranium and a small amount of tungsten is dissolved in the uranium.

  9. METHOD OF MAKING TUNGSTEN FILAMENTS

    DOEpatents

    Frazer, J.W.

    1962-12-18

    A method of making tungsten filaments is described in which the tungsten is completely free of isotope impurities in the range of masses 234 to 245 for use in mass spectrometers. The filament comprises a tantalum core generally less than 1 mil in diameter having a coating of potassium-free tantalum-diffused tungsten molecularly bonded thereto. In the preferred process of manufacture a short, thin tantalum filament is first mounted between terminal posts mounted in insulated relation through a backing plate. The tungsten is most conveniently vapor plated onto the tantalum by a tungsten carbonyl vapor decomposition method having a critical step because of the tendency of the tantalum to volatilize at the temperature of operntion of the filament. The preferred recipe comprises volatilizing tantalum by resistance henting until the current drops by about 40%, cutting the voltage back to build up the tungsten, and then gradually building the temperature back up to balance the rate of tungsten deposition with the rate of tantalum volatilization. (AEC)

  10. Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions

    NASA Astrophysics Data System (ADS)

    Fan, Hongyu; Yang, Qi; Li, Xin; Ni, Weiyuan; Niu, Jinhai; Liu, Dongping

    2015-04-01

    Polycrystalline tungsten (W) and molybdenum (Mo) materials both non-annealed and annealed at temperatures of 800-1750°C have been irradiated with low-energy (220 eV), high-flux (∼1021 ions/m2 ·s) He+ at an irradiation temperature of 600°C and at a dose of 1.0×1025 ions/m2. This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials. A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He+ dose of 1.0×1025 ions/m2. Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W. Compared to W, Mo suffered much less surface damage after being irradiated at various He+ doses. supported by the National Magnetic Confinement Fusion Program of China (No. 2011GB108011), National Natural Science Foundation of China (No. 11405023) and the Scientific Research Fund of Liaoning Provincial Education Department (No. L2014539) and the Fundamental Research Funds for the Central Universities of China (No. DC201502080410)

  11. RECOVERY OF URANIUM FROM TUNGSTEN

    DOEpatents

    Newnam, K.

    1959-02-01

    A method is presented for the rccovery of uranium which has adhered to tungsten parts in electromagnetic isotope separation apparatus. Such a tungsten article is dissolved electrolytically in 20% NaOH by using the tungsten article as the anode. The resulting solution, containing soluble sodium lungstate and an insoluble slime, is then filtered. The slime residue is ignited successively with sodium nitrate and sodium pyrosulfate and leashed, and the resulting filtrates are combined with the original filtrate. Uranium is then recovered from the combined flltrates by diuranate precipitation.

  12. Tungsten Toxicity in Plants

    PubMed Central

    Adamakis, Ioannis-Dimosthenis S.; Panteris, Emmanuel; Eleftheriou, Eleftherios P.

    2012-01-01

    Tungsten (W) is a rare heavy metal, widely used in a range of industrial, military and household applications due to its unique physical properties. These activities inevitably have accounted for local W accumulation at high concentrations, raising concerns about its effects for living organisms. In plants, W has primarily been used as an inhibitor of the molybdoenzymes, since it antagonizes molybdenum (Mo) for the Mo-cofactor (MoCo) of these enzymes. However, recent advances indicate that, beyond Mo-enzyme inhibition, W has toxic attributes similar with those of other heavy metals. These include hindering of seedling growth, reduction of root and shoot biomass, ultrastructural malformations of cell components, aberration of cell cycle, disruption of the cytoskeleton and deregulation of gene expression related with programmed cell death (PCD). In this article, the recent available information on W toxicity in plants and plant cells is reviewed, and the knowledge gaps and the most pertinent research directions are outlined. PMID:27137642

  13. Tungsten resources of Brazil

    USGS Publications Warehouse

    White, Max Gregg

    1974-01-01

    Brazilian tungsten production, 85 percent of which is exported, comes almost entirely from scheelite-bearing tactites in northeast Brazil, and has reached an annual rate of about 2,000 metric tons (2,200 short tons) of scheelite concentrate with 70 percent WO3. Scheelite ore reserves, located principally in the State of Rio Grande do Norte, are estimated to be as high as 8,300,000 tons (9,100,000 short tons) containing 0.7 percent WO3. Minor deposits (or those about which only minimal information is available) of wolframite, with which some cassiterite is associated, are located in Sao Paulo, Santa Catarina, and Rio Grande do Sul. Both the scheelite and the wolframite deposits are considered . to be late Precambrian A (620 to 900 m.y.) or early Cambrian in age.

  14. Weldability of polycrystalline aluminides. Final report

    SciTech Connect

    Fasching, A.A.; Burt, R.P.; Edwards, G.R.; David, S.A.

    1996-07-01

    When gas-tungsten arc welded, iron aluminides form a coarse fusion zone microstructure which is susceptible to hydrogen cracking. Magnetic arc oscillation and weld pool inoculation were implemented to refine the fusion zone microstructure in iron aluminide alloy FA-129 weldments. Magnetic arc oscillation effectively refined the fusion zone microstructure, and slow strain rate tensile tests showed fine-grained microstructures to be less susceptible to hydrogen cracking. However, magnetic arc oscillation was found to be suitable only for well-controlled fabrication environments. Weld pool inoculation offers a potentially more robust refinement method. Titanium inoculation was also shown to effectively refined the fusion zone microstructure, but weldment properties were not improved using this refinement method. The effect of titanium on the size, shape and distribution of the second phase particles in the fusion zone appears to be the cause of the observed decrease in weldment properties.

  15. Polycrystalline Thin Film Device Degradation Studies

    SciTech Connect

    Albin, D. S.; McMahon, T. J.; Pankow, J. W.; Noufi, R.; Demtsu, S. H.; Davies, A.

    2005-11-01

    Oxygen during vapor CdCl2 (VCC) treatments significantly reduced resistive shunts observed in CdS/CdTe polycrystalline devices using thinner CdS layers during 100 deg C, open-circuit, 1-sun accelerated stress testing. Cu oxidation resulting from the reduction of various trace oxides present in as-grown and VCC treated films is the proposed mechanism by which Cu diffusion, and subsequent shunts are controlled. Graphite paste layers between metallization and CdTe behave like diffusion barriers and similarly benefit device stability. Ni-based contacts form a protective Ni2Te3 intermetallic layer that reduces metal diffusion but degrades performance through increased series resistance.

  16. Role of surface-reaction layer in HBr/fluorocarbon-based plasma with nitrogen addition formed by high-aspect-ratio etching of polycrystalline silicon and SiO2 stacks

    NASA Astrophysics Data System (ADS)

    Iwase, Taku; Matsui, Miyako; Yokogawa, Kenetsu; Arase, Takao; Mori, Masahito

    2016-06-01

    The etching of polycrystalline silicon (poly-Si)/SiO2 stacks by using VHF plasma was studied for three-dimensional NAND fabrication. One critical goal is achieving both a vertical profile and high throughput for multiple-stack etching. While the conventional process consists of multiple steps for each stacked layer, in this study, HBr/fluorocarbon-based gas chemistry was investigated to achieve a single-step etching process to reduce process time. By analyzing the dependence on wafer temperature, we improved both the etching profile and rate at a low temperature. The etching mechanism is examined considering the composition of the surface reaction layer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the adsorption of N–H and Br was enhanced at a low temperature, resulting in a reduced carbon-based-polymer thickness and enhanced Si etching. Finally, a vertical profile was obtained as a result of the formation of a thin and reactive surface-reaction layer at a low wafer temperature.

  17. Why Tungsten Instead of Wolfram?

    NASA Astrophysics Data System (ADS)

    Jensen, William B.

    2008-04-01

    In response to a reader query, the column traces the reason that American and British chemical literature use the name tungsten for element 74, while northern European literature uses the name wolfram.

  18. Process Research On Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wohlgemuth, J. H.

    1982-01-01

    Performance limiting mechanisms in polycrystalline silicon are investigated by fabricating a matrix of solar cells of various thicknesses from polycrystalline silicon wafers of several bulk resistivities. The analysis of the results for the entire matrix indicates that bulk recombination is the dominant factor limiting the short circuit current in large grain (greater than 1 to 2 mm diameter) polycrystalline silicon, the same mechanism that limits the short circuit current in single crystal silicon. An experiment to investigate the limiting mechanisms of open circuit voltage and fill factor for large grain polycrystalline silicon is designed. Two process sequences to fabricate small cells are investigated.

  19. DOE/SERI polycrystalline thin-film photovoltaic research

    SciTech Connect

    Hermann, A; Zweibel, K; Mitchell, R

    1984-05-01

    This paper presents recent results, status, and future prospects for the US Department of Energy's (DOE's) Polycrystalline Thin Film Photovoltaic program, managed by the Solar Energy Research Institute (SERI). The devices being studied most intensively are heterojunctions based on CuInSe/sub 2/ and on CdTe. Both materials have attained over 10% efficiency in polycrystalline form. The main emphasis is on CuInSe/sub 2/, for which Boeing has reported an 11%-efficient device (AMl ELH simulation). Important work is being done on studies of the composition/electronic properties of CuInSe/sub 2/ and its response to post-deposition annealing. In the CdTe research, ohmic, stable back-contacting and control of p-type doping are being investigated. New efforts to study polycrystalline two-junction stacked cells are underway with two-terminal cells (at IEC) and with four-terminal cells (at SMU). This preliminary work is expected to be expanded, with emphasis on CdTe and other top-cell (high-bandgap) materials. These efforts introduce a number of new research areas (e.g., transparent ohmic contacts to p-CdTe and sub-bandgap light-losses in polycrystalline materials). The aim of the program is to produce stable, high-efficiency (15%), thin-film cells that can be deposited inexpensively by techniques that are scalable to large areas.

  20. Low molybdenum state induced by tungsten as a model of molybdenum deficiency in rats.

    PubMed

    Yoshida, Munehiro; Nakagawa, Mikihito; Hosomi, Ryota; Nishiyama, Toshimasa; Fukunaga, Kenji

    2015-05-01

    Organ molybdenum (Mo) concentration and the activity of hepatic sulfite oxidase and xanthine oxidase were compared in tungsten-administered rats as well as rats fed with a low Mo diet to evaluate the use of tungsten-administered rats as a model of Mo deficiency. Twenty-four male 6-week-old Wistar rats were divided into four groups according to diet (AIN93G diet (control diet) or the control diet minus ammonium molybdate (low Mo diet)) and drinking water (deionized water or deionized water containing 200 μg/mL tungsten in the form of sodium tungstate). Mo content in the control and low Mo diets were 196 and 42 ng/g, respectively. Intake of the low Mo diet significantly reduced the Mo content of several organs and serum. Decrease in hepatic sulfite oxidase activity was also induced by the low Mo diet. The administration of tungsten induced marked decreases in organ Mo content and the activity of hepatic sulfite oxidase and xanthine oxidase. These decreases induced by tungsten administration were more pronounced than those induced by just a low Mo diet. Serum uric acid was also reduced by tungsten administration irrespective of Mo intake. Although a comparatively high accumulation of tungsten (3 to 9 μg/g) was observed in the kidneys and liver, adverse effects of tungsten accumulation on liver and kidney function were not observed in serum biochemical tests. These results indicate that tungsten-administered animals may be used as a model of Mo deficiency.

  1. Casting larger polycrystalline silicon ingots

    SciTech Connect

    Wohlgemuth, J.; Tomlinson, T.; Cliber, J.; Shea, S.; Narayanan, M.

    1995-08-01

    Solarex has developed and patented a directional solidification casting process specifically designed for photovoltaics. In this process, silicon feedstock is melted in a ceramic crucible and solidified into a large grained semicrystalline silicon ingot. In-house manufacture of low cost, high purity ceramics is a key to the low cost fabrication of Solarex polycrystalline wafers. The casting process is performed in Solarex designed casting stations. The casting operation is computer controlled. There are no moving parts (except for the loading and unloading) so the growth process proceeds with virtually no operator intervention Today Solarex casting stations are used to produce ingots from which 4 bricks, each 11.4 cm by 11.4 cm in cross section, are cut. The stations themselves are physically capable of holding larger ingots, that would yield either: 4 bricks, 15 cm by 15 an; or 9 bricks, 11.4 cm by 11.4 an in cross-section. One of the tasks in the Solarex Cast Polycrystalline Silicon PVMaT Program is to design and modify one of the castings stations to cast these larger ingots. If successful, this effort will increase the production capacity of Solarex`s casting stations by 73% and reduce the labor content for casting by an equivalent percentage.

  2. Mechanistic, kinetic, and processing aspects of tungsten chemical mechanical polishing

    NASA Astrophysics Data System (ADS)

    Stein, David

    . In this mechanism, the colloid reacts with the chemistry of the slurry to produce active sites. These active sites become inactive by removing tungsten from the film. The process repeats when then inactive sites are reconverted to active sites. It is shown that the empirical form of the heuristic mechanism fits all of the data obtained. The mechanism also agrees with the limiting cases that were investigated.

  3. VAPORIZATION OF TUNGSTEN-METAL IN STEAM AT HIGH TEMPERATURES.

    SciTech Connect

    GREENE,G.A.; FINFROCK,C.C.

    2000-10-01

    The vaporization of tungsten from the APT spallation target dominates the radiological source term for unmitigated target overheating accidents. Chemical reactions of tungsten with steam which persist to tungsten temperatures as low as 800 C result in the formation of a hydrated tungsten-oxide which has a high vapor pressure and is readily convected in a flowing atmosphere. This low-temperature vaporization reaction essentially removes the oxide film that forms on the tungsten-metal surface as soon as it forms, leaving behind a fresh metallic surface for continued oxidation and vaporization. Experiments were conducted to measure the oxidative vaporization rates of tungsten in steam as part of the effort to quantify the MT radiological source term for severe target accidents. Tests were conducted with tungsten rods (1/8 inch diameter, six inches long) heated to temperatures from approximately 700 C to 1350 C in flowing steam which was superheated to 140 C. A total of 19 experiments was conducted. Fifteen tests were conducted by RF induction heating of single tungsten rods held vertical in a quartz glass retort. Four tests were conducted in a vertically-mounted tube furnace for the low temperature range of the test series. The aerosol which was generated and transported downstream from the tungsten rods was collected by passing the discharged steam through a condenser. This procedure insured total collection of the steam along with the aerosol from the vaporization of the rods. The results of these experiments revealed a threshold temperature for tungsten vaporization in steam. For the two tests at the lowest temperatures which were tested, approximately 700 C, the tungsten rods were observed to oxidize without vaporization. The remainder of the tests was conducted over the temperature range of 800 C to 1350 C. In these tests, the rods were found to have lost weight due to vaporization of the tungsten and the missing weight was collected in the downstream condensate

  4. Drill with polycrystalline diamond drill blanks for soft, medium-hard and hard formations

    SciTech Connect

    Williamson, K.E.

    1984-02-07

    A drill bit is disclosed for drilling boreholes in earth formations. The bit's cutting face is provided with cutter preforms composed of polycrystalline diamonds on a tungsten carbide substrate mounted in sets from the center of the bit's face to its periphery. The first set consists of one cutter preform at approximately the center of the cutting face. Each succeeding set has at least two preforms, all of which in a set are disposed at an equal radius from the bit's axis of rotation and are displaced from adjacent preforms in the same set by equal arcs around the axis, the cutting path of a set overlapping with that of the next set. The next to last set of preforms is mounted from a surface coinciding with a truncated cone having a relative angle to the bit's axis of rotation of about 33/sup 0/; the outermost preform set is disposed in or above the junk slots, with each preform mounted extending 90/sup 0/ relative to the axis of rotation and having its cutting portion extending above raised portions from the cutting face whereby they cut a circumference slightly larger than that of the bit's body. Four to six jets for drilling mud have outlets from the drilling face, each jet including a relatively narrow neck and flared mouth. Junk slots are defined by the raised portions, a first group of such portions in one embodiment being stepped inwardly to form off-sets adjacent the conical surface of the bit's face. A second group of portions in such embodiment which alternate with the first extend somewhat less outwardly than the bit's overall diameter and each has a length less than one-half of the length of those of the first group. The bit's overall diameter is approximately twice its length along the first group of raised portions.

  5. Polarographic determination of tungsten in rocks

    USGS Publications Warehouse

    Reichen, L.E.

    1954-01-01

    This work was undertaken to develop a simpler and faster method than the classical gravimetric procedure for the determination of tungsten in rocks and ores. A new polarographic wave of tungsten is obtained in a supporting electrolyte of dilute hydrochloric acid containing tartrate ion. This permits the determination of tungsten both rapidly and accurately. No precipitation of the tungsten is necessary, and only the iron need be separated from the tungsten. The accuracy is within the limits of a polarographic procedure; comparison of polarographic and gravimetric results is given. The method reduces appreciably the amount of time ordinarily consumed in determination of tungsten.

  6. Tungsten diffusion in silicon

    SciTech Connect

    De Luca, A.; Texier, M.; Burle, N.; Oison, V.; Pichaud, B.; Portavoce, A.; Grosjean, C.

    2014-01-07

    Two doses (10{sup 13} and 10{sup 15} cm{sup −2}) of tungsten (W) atoms were implanted in different Si(001) wafers in order to study W diffusion in Si. The samples were annealed or oxidized at temperatures between 776 and 960 °C. The diffusion profiles were measured by secondary ion mass spectrometry, and defect formation was studied by transmission electron microscopy and atom probe tomography. W is shown to reduce Si recrystallization after implantation and to exhibit, in the temperature range investigated, a solubility limit close to 0.15%–0.2%, which is higher than the solubility limit of usual metallic impurities in Si. W diffusion exhibits unusual linear diffusion profiles with a maximum concentration always located at the Si surface, slower kinetics than other metals in Si, and promotes vacancy accumulation close to the Si surface, with the formation of hollow cavities in the case of the higher W dose. In addition, Si self-interstitial injection during oxidation is shown to promote W-Si clustering. Taking into account these observations, a diffusion model based on the simultaneous diffusion of interstitial W atoms and W-Si atomic pairs is proposed since usual models used to model diffusion of metallic impurities and dopants in Si cannot reproduce experimental observations.

  7. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1985-01-01

    Results of hydrogen-passivated polycrysalline silicon solar cell research are summarized. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystalline silicon solar cells.

  8. Interface scattering in polycrystalline thermoelectrics

    SciTech Connect

    Popescu, Adrian; Haney, Paul M.

    2014-03-28

    We study the effect of electron and phonon interface scattering on the thermoelectric properties of disordered, polycrystalline materials (with grain sizes larger than electron and phonons' mean free path). Interface scattering of electrons is treated with a Landauer approach, while that of phonons is treated with the diffuse mismatch model. The interface scattering is embedded within a diffusive model of bulk transport, and we show that, for randomly arranged interfaces, the overall system is well described by effective medium theory. Using bulk parameters similar to those of PbTe and a square barrier potential for the interface electron scattering, we identify the interface scattering parameters for which the figure of merit ZT is increased. We find the electronic scattering is generally detrimental due to a reduction in electrical conductivity; however, for sufficiently weak electronic interface scattering, ZT is enhanced due to phonon interface scattering.

  9. Polycrystalline Silicon: a Biocompatibility Assay

    SciTech Connect

    Pecheva, E.; Fingarova, D.; Pramatarova, L.; Hikov, T.; Laquerriere, P.; Bouthors, Sylvie; Dimova-Malinovska, D.; Montgomery, P.

    2010-01-21

    Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HA and/or to the higher HA roughness.

  10. Accelerated Molecular Dynamics studies of He Bubble Growth in Tungsten

    NASA Astrophysics Data System (ADS)

    Uberuaga, Blas; Sandoval, Luis; Perez, Danny; Voter, Arthur

    2015-11-01

    Understanding how materials respond to extreme environments is critical for predicting and improving performance. In materials such as tungsten exposed to plasmas for nuclear fusion applications, novel nanoscale fuzzes, comprised of tendrils of tungsten, form as a consequence of the implantation of He into the near surface. However, the detailed mechanisms that link He bubble formation to the ultimate development of fuzz are unclear. Molecular dynamics simulations provide insight into the He implantation process, but are necessarily performed at implantation rates that are orders of magnitudes faster than experiment. Here, using accelerated molecular dynamics methods, we examine the role of He implantation rates on the physical evolution of He bubbles in tungsten. We find that, as the He rate is reduced, new types of events involving the response of the tungsten matrix to the pressure in the bubble become competitive and change the overall evolution of the bubble as well as the subsequent morphology of the tungsten surface. We have also examined how bubble growth differs at various microstructural features. These results highlight the importance of performing simulations at experimentally relevant conditions in order to correctly capture the contributions of the various significant kinetic processes and predict the overall response of the material.

  11. Some observations on uranium carbide alloy/tungsten compatibility

    NASA Technical Reports Server (NTRS)

    Phillips, W. M.

    1972-01-01

    Chemical compatibility between both pure and thoriated tungsten and uranium carbide alloys was studied at 1800 C for up to 3300 hours. Alloying with zirconium carbide appeared to widen the homogeneity range of uranium carbide, making additional carbon available for reaction with the tungsten. Reaction layers were formed both by vapor phase reaction and by physical contact, producing either or both UWC2 and W2C, dependent upon the phases present in the starting fuel alloy. Formation of UWC2 results in slow growth of the reaction layer with time, while W2C reaction layers grow rapidly, allowing equilibrium to be reached in less than 2500 hours at 1800 C. The presence of a thermal gradient had no effect on the reactions observed nor did the presence of thoria in the tungsten clad.

  12. Accurate pointing of tungsten welding electrodes

    NASA Technical Reports Server (NTRS)

    Ziegelmeier, P.

    1971-01-01

    Thoriated-tungsten is pointed accurately and quickly by using sodium nitrite. Point produced is smooth and no effort is necessary to hold the tungsten rod concentric. The chemically produced point can be used several times longer than ground points. This method reduces time and cost of preparing tungsten electrodes.

  13. Method of synthesizing tungsten nanoparticles

    DOEpatents

    Thoma, Steven G; Anderson, Travis M

    2013-02-12

    A method to synthesize tungsten nanoparticles has been developed that enables synthesis of nanometer-scale, monodisperse particles that can be stabilized only by tetrahydrofuran. The method can be used at room temperature, is scalable, and the product concentrated by standard means. Since no additives or stabilizing surfactants are required, this method is particularly well suited for producing tungsten nanoparticles for dispersion in polymers. If complete dispersion is achieved due to the size of the nanoparticles, then the optical properties of the polymer can be largely maintained.

  14. Density-functional studies of tungsten trioxide, tungsten bronzes, and related systems

    NASA Astrophysics Data System (ADS)

    Ingham, B.; Hendy, S. C.; Chong, S. V.; Tallon, J. L.

    2005-08-01

    Tungsten trioxide adopts a variety of structures which can be intercalated with charged species to alter the electronic properties, thus formingtungsten bronzes.” Similar effects are observed upon removing oxygen from WO3 . We present a computational study of cubic and hexagonal alkali bronzes and examine the effects on cell size and band structure as the size of the intercalated ion is increased. With the exception of hydrogen (which is predicted to be unstable as an intercalate), the behavior of the bronzes are relatively consistent. NaWO3 is the most stable of the cubic systems, although in the hexagonal system the larger ions are more stable. The band structures are identical, with the intercalated atom donating its single electron to the tungsten 5d valence band. A study of fractional doping in the NaxWO3 system (0⩽x⩽1) showed a linear variation in cell parameter and a systematic shift in the Fermi level into the conduction band. In the oxygen-deficient WO3-x system the Fermi level undergoes a sudden jump into the conduction band at around x=0.2 . Lastly, three compounds of a layered WO4•α,ω -diaminoalkane hybrid series were studied and found to be insulating, with features in the band structure similar to those of the parent WO3 compound that relate well to experimental UV-visible spectroscopy results.

  15. In vivo tungsten exposure alters B-cell development and increases DNA damage in murine bone marrow.

    PubMed

    Kelly, Alexander D R; Lemaire, Maryse; Young, Yoon Kow; Eustache, Jules H; Guilbert, Cynthia; Molina, Manuel Flores; Mann, Koren K

    2013-02-01

    High environmental tungsten levels were identified near the site of a childhood pre-B acute lymphoblastic leukemia cluster; however, a causal link between tungsten and leukemogenesis has not been established. The major site of tungsten deposition is bone, the site of B-cell development. In addition, our in vitro data suggest that developing B lymphocytes are susceptible to tungsten-induced DNA damage and growth inhibition. To extend these results, we assessed whether tungsten exposure altered B-cell development and induced DNA damage in vivo. Wild-type mice were exposed to tungsten in their drinking water for up to 16 weeks. Tungsten concentration in bone was analyzed by inductively coupled plasma mass spectrometry and correlated with B-cell development and DNA damage within the bone marrow. Tungsten exposure resulted in a rapid deposition within the bone following 1 week, and tungsten continued to accumulate thereafter albeit at a decreased rate. Flow cytometric analyses revealed a transient increase in mature IgD(+) B cells in the first 8 weeks of treatment, in animals of the highest and intermediate exposure groups. Following 16 weeks of exposure, all tungsten groups had a significantly greater percentage of cells in the late pro-/large pre-B developmental stages. DNA damage was increased in both whole marrow and isolated B cells, most notably at the lowest tungsten concentration tested. These findings confirm an immunological effect of tungsten exposure and suggest that tungsten could act as a tumor promoter, providing leukemic "hits" in multiple forms to developing B lymphocytes within the bone marrow.

  16. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1983-01-01

    The performance limiting mechanisms in large grain (greater than 1-2 mm in diameter) polycrystalline silicon was investigated by measuring the illuminated current voltage (I-V) characteristics of the minicell wafer set. The average short circuit current on different wafers is 3 to 14 percent lower than that of single crystal Czochralski silicon. The scatter was typically less than 3 percent. The average open circuit voltage is 20 to 60 mV less than that of single crystal silicon. The scatter in the open circuit voltage of most of the polycrystalline silicon wafers was 15 to 20 mV, although two wafers had significantly greater scatter than this value. The fill factor of both polycrystalline and single crystal silicon cells was typically in the range of 60 to 70 percent; however several polycrystalline silicon wafers have fill factor averages which are somewhat lower and have a significantly larger degree of scatter.

  17. Mineral of the month: tungsten

    USGS Publications Warehouse

    Shedd, Kim B.

    2006-01-01

    Tungsten has the highest melting point of all metals, one of the highest densities and, when combined with carbon, is almost as hard as diamond. These and other properties make it useful in a wide variety of important commercial, industrial and military applications.

  18. Vacuum Gas Tungsten Arc Welding

    NASA Technical Reports Server (NTRS)

    Weeks, J. L.; Todd, D. T.; Wooten, J. R.

    1997-01-01

    A two-year program investigated vacuum gas tungsten arc welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. After a vacuum chamber and GTAW power supply were modified, several difficult-to-weld materials were studied and key parameters developed. Finally, Incoloy 903 weld overlays were produced without microfissures.

  19. Composite polycrystalline semiconductor neutron detectors

    NASA Astrophysics Data System (ADS)

    Schieber, M.; Zuck, A.; Marom, G.; Khakhan, O.; Roth, M.; Alfassi, Z. B.

    2007-08-01

    Composite polycrystalline semiconductor detectors bound with different binders, both inorganic molten glasses, such as B 2O 3, PbO/B 2O 3, Bi 2O 3/PbO, and organic polymeric binders, such as isotactic polypropylene (iPP), polystyrene or nylon-6, and coated with different metal electrodes were tested at room temperature for α-particles and very weak thermal neutron sources. The detector materials tested were natural occurring hexagonal BN and cubic LiF, where both are not containing enriched isotopes of 10B or 6Li. The radiation sources were 5.5 MeV α's from 241Am, 5.3 MeV from 210Po and also 4.8 MeV from 226Ra. Some of these detectors were also tested with thermal neutrons from very weak 227Ac 9Be, 241Am- 10Be sources and also from a weak 238Pu+ 9Be and somewhat stronger 252Cf sources. The neutrons were thermalized with paraffin. Despite very low signal to noise ratio of only ˜2, the neutrons could be counted by subtracting the noise from the signal.

  20. Interactions of mobile helium clusters with surfaces and grain boundaries of plasma-exposed tungsten

    SciTech Connect

    Hu, Lin; Maroudas, Dimitrios; Hammond, Karl D.; Wirth, Brian D.

    2014-05-07

    We report results of atomistic computations for the interactions of small mobile helium clusters (He{sub n}) with free surfaces and grain boundaries (GBs) in tungsten toward development of continuum drift-diffusion-reaction models for the dynamics of mobile helium clusters in plasma-exposed tungsten. Molecular-statics (MS) simulations based on reliable many-body interatomic potentials are carried out for He{sub n} (1 ≤ n ≤ 7) clusters near sinks to obtain the potential energy profiles of the He{sub n} clusters as a function of the clusters' center-of-mass distance from a sink. Sinks investigated include surfaces, GBs, and regions in the vicinity of junctions where GBs intersect free surfaces. Elastic interaction potentials based on elastic inclusion theory provide an excellent description of the MS results for the cluster-sink interactions. The key parameter in the elastic models is the sink segregation strength, which is found to increase with increasing cluster size. Such cluster-sink interactions are responsible for the migration of small helium clusters by drift and for helium segregation on surfaces and grain boundaries in tungsten. Such helium segregation on sinks is observed in large-scale molecular-dynamics simulations of helium aggregation in model polycrystalline tungsten at 933 K upon helium implantation.

  1. Photoelectrochemical and physical properties of tungsten trioxide films obtained by aerosol pyrolysis

    SciTech Connect

    Sadale, S.B.; Chaqour, S.M.; Gorochov, O.; Neumann-Spallart, M.

    2008-06-03

    Aerosol pyrolysis (AP) was used for preparing semiconducting films of tungsten trioxide using peroxotungstic acid as a precursor. The films were characterized by SEM, XRD, and by their photoelectrochemical response. Porous, polycrystalline (monoclinic) films of thickness up to 3 {mu}m were prepared. An incident photon to current efficiency (IPCE) of 0.55 at 365 nm was obtained for films of 1 {mu}m thickness on conducting F:SnO{sub 2}/glass substrates under depletion conditions, in junctions with aqueous electrolytes. The spectral (photocurrent) response extended into the visible region (up to 470 nm) which is of importance for solar applications like photocatalysis.

  2. Process development for cladding APT tungsten targets

    SciTech Connect

    Horner, M H; Barber, R; Dalder, E

    2000-11-27

    This report describes development of processes for cladding APT Target tungsten components with a thin layer (0.127-mm) of Alloy 718, Alloy 600 or 316L stainless steel alloy. The application requires that the cladding be thermally bonded to the tungsten in order to transfer heat generated in the tungsten volume to a surrounding coolant. High temperature diffusion bonding using the hot isostatic processing (HIP) technique was selected as the method for creating a metallurgical bond between pure tungsten tubes and rods and the cladding materials. Bonding studies using a uniaxially loaded vacuum hot press were conducted in preliminary experiments to determine acceptable time-temperature conditions for diffusion bonding. The results were successfully applied in cladding tungsten rods and tubes with these alloys. Temperatures 800-810 C were suitable for cladding tungsten with Alloy 600 and 316L stainless steel alloy, whereas tungsten was clad with Alloy 718 at 1020 C.

  3. Solution-processed polycrystalline silicon on paper

    NASA Astrophysics Data System (ADS)

    Trifunovic, M.; Shimoda, T.; Ishihara, R.

    2015-04-01

    Printing electronics has led to application areas which were formerly impossible with conventional electronic processes. Solutions are used as inks on top of large areas at room temperatures, allowing the production of fully flexible circuitry. Commonly, research in these inks have focused on organic and metal-oxide ink materials due to their printability, while these materials lack in the electronic performance when compared to silicon electronics. Silicon electronics, on the other hand, has only recently found their way in solution processes. Printing of cyclopentasilane as the silicon ink has been conducted and devices with far superior electric performance have been made when compared to other ink materials. A thermal annealing step of this material, however, was necessary, which prevented its usage on inexpensive substrates with a limited thermal budget. In this work, we introduce a method that allows polycrystalline silicon (poly-Si) production directly from the same liquid silicon ink using excimer laser irradiation. In this way, poly-Si could be formed directly on top of paper even with a single laser pulse. Using this method, poly-Si transistors were created at a maximum temperature of only 150 °C. This method allows silicon device formation on inexpensive, temperature sensitive substrates such as polyethylene terephthalate, polyethylene naphthalate or paper, which leads to applications that require low-cost but high-speed electronics.

  4. Geometric considerations for diffusion in polycrystalline solids

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Schuh, Christopher A.

    2007-03-01

    Mass transport in polycrystals is usually enhanced by short-circuit diffusion along various defect paths, e.g., grain boundaries, dislocation cores, and triple junctions. In the "kinetic-A" regime, diffusion fields associated with the various diffusion paths overlap each other, forming a macroscopically homogeneous diffusion profile that can be described by an effective diffusion coefficient. Here, we develop a composite diffusion model for polycrystals based on realistic arrangements between various microstructural elements, which usually exhibit complex network morphologies. Asymmetric effective medium equations and power-law scaling relationships are used to evaluate the effective diffusivity of a general isotropic polycrystal, and are compared to predictions of the simple arithmetic rule of mixtures used frequently in the literature. We also examine the grain size and temperature dependence of polycrystalline diffusion in terms of the apparent grain size exponent and activation energy, which in turn provide the basis by which we assess dominant diffusion processes and construct generalized diffusion mechanism maps. Implications of geometry on experimental diffusivity measurements are also discussed.

  5. Solution-processed polycrystalline silicon on paper

    SciTech Connect

    Trifunovic, M.; Ishihara, R.; Shimoda, T.

    2015-04-20

    Printing electronics has led to application areas which were formerly impossible with conventional electronic processes. Solutions are used as inks on top of large areas at room temperatures, allowing the production of fully flexible circuitry. Commonly, research in these inks have focused on organic and metal-oxide ink materials due to their printability, while these materials lack in the electronic performance when compared to silicon electronics. Silicon electronics, on the other hand, has only recently found their way in solution processes. Printing of cyclopentasilane as the silicon ink has been conducted and devices with far superior electric performance have been made when compared to other ink materials. A thermal annealing step of this material, however, was necessary, which prevented its usage on inexpensive substrates with a limited thermal budget. In this work, we introduce a method that allows polycrystalline silicon (poly-Si) production directly from the same liquid silicon ink using excimer laser irradiation. In this way, poly-Si could be formed directly on top of paper even with a single laser pulse. Using this method, poly-Si transistors were created at a maximum temperature of only 150 °C. This method allows silicon device formation on inexpensive, temperature sensitive substrates such as polyethylene terephthalate, polyethylene naphthalate or paper, which leads to applications that require low-cost but high-speed electronics.

  6. Fuzzy tungsten in a magnetron sputtering device

    NASA Astrophysics Data System (ADS)

    Petty, T. J.; Khan, A.; Heil, T.; Bradley, J. W.

    2016-11-01

    Helium ion induced tungsten nanostructure (tungsten fuzz) has been studied in a magnetron sputtering device. Three parameters were varied, the fluence from 3.4 × 1023-3.0 × 1024 m-2, the He ion energy from 25 to 70 eV, and the surface temperature from 900 to 1200 K. For each sample, SEM images were captured, and measurements of the fuzz layer thickness, surface roughness, reflectivity, and average structure widths are provided. A cross-over point from pre-fuzz to fully formed fuzz is found at 2.4 ± 0.4 × 1024 m-2, and a temperature of 1080 ± 60 K. No significant change was observed in the energy sweep. The fuzz is compared to low fluence fuzz created in the PISCES-A linear plasma device. Magnetron fuzz is less uniform than fuzz created by PISCES-A and with generally larger structure widths. The thicknesses of the magnetron samples follow the original Φ1/2 relation as opposed to the incubation fluence fit.

  7. Physics of grain boundaries in polycrystalline photovoltaic semiconductors

    NASA Astrophysics Data System (ADS)

    Yan, Yanfa; Yin, Wan-Jian; Wu, Yelong; Shi, Tingting; Paudel, Naba R.; Li, Chen; Poplawsky, Jonathan; Wang, Zhiwei; Moseley, John; Guthrey, Harvey; Moutinho, Helio; Pennycook, Stephen J.; Al-Jassim, Mowafak M.

    2015-03-01

    Thin-film solar cells based on polycrystalline Cu(In,Ga)Se2 (CIGS) and CdTe photovoltaic semiconductors have reached remarkable laboratory efficiencies. It is surprising that these thin-film polycrystalline solar cells can reach such high efficiencies despite containing a high density of grain boundaries (GBs), which would seem likely to be nonradiative recombination centers for photo-generated carriers. In this paper, we review our atomistic theoretical understanding of the physics of grain boundaries in CIGS and CdTe absorbers. We show that intrinsic GBs with dislocation cores exhibit deep gap states in both CIGS and CdTe. However, in each solar cell device, the GBs can be chemically modified to improve their photovoltaic properties. In CIGS cells, GBs are found to be Cu-rich and contain O impurities. Density-functional theory calculations reveal that such chemical changes within GBs can remove most of the unwanted gap states. In CdTe cells, GBs are found to contain a high concentration of Cl atoms. Cl atoms donate electrons, creating n-type GBs between p-type CdTe grains, forming local p-n-p junctions along GBs. This leads to enhanced current collections. Therefore, chemical modification of GBs allows for high efficiency polycrystalline CIGS and CdTe thin-film solar cells.

  8. Fabrication of tungsten wire reinforced nickel-base alloy composites

    NASA Technical Reports Server (NTRS)

    Brentnall, W. D.; Toth, I. J.

    1974-01-01

    Fabrication methods for tungsten fiber reinforced nickel-base superalloy composites were investigated. Three matrix alloys in pre-alloyed powder or rolled sheet form were evaluated in terms of fabricability into composite monotape and multi-ply forms. The utility of monotapes for fabricating more complex shapes was demonstrated. Preliminary 1093C (2000F) stress rupture tests indicated that efficient utilization of fiber strength was achieved in composites fabricated by diffusion bonding processes. The fabrication of thermal fatigue specimens is also described.

  9. Hydrogen migration in polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Walker, J.

    1996-03-01

    Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2{endash}1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5{endash}1.7 eV below. The hydrogen chemical potential {mu}{sub H} decreases as the temperature increases. At lower concentrations, {mu}{sub H} was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. {copyright} {ital 1996 The American Physical Society.}

  10. Crystal-oriented tungsten-bronze type ceramics prepared by a rotating magnetic field

    NASA Astrophysics Data System (ADS)

    Tanaka, S.; Doshida, Y.; Shimizu, H.; Furushima, R.; Uematsu, K.

    2011-03-01

    Forming and sintering of c-axis-oriented Sr2NaNb5O15 (SNN) ceramics were examined. Particle-oriented SNN was fabricated by using a rotating high magnetic field and subsequent sintering without magnetic field. SNN ceramics are tungsten-bronze-type ferroelectric materials with a tetragonal crystal system. The diamagnetic susceptibilities of the c-axis are smaller than that of the a- and b-axis (χc < χa,b < 0). SNN powder was prepared by conventional solid-state reaction. The synthesized powder was mixed with distilled water and a dispersant by using ball milling to give a slurry with solid loading of 30 vol%. The slurry was poured into a plastic mold and this was placed in a 10Tesla magnetic field in a superconducting magnet. The mold was rotated at 30 rpm while the slurry dried at room temperature. The resulting powder compact with a columnar shape was heated at 5 K/min to 1473 K, held for 6 h, and then heated at 1525 K for 2 h to prevent exaggerated grain growth. XRD patterns showed that c-axis-oriented SNN polycrystalline ceramics were produced in the presence of the rotating magnetic field. In XRD patterns viewed from the top surface of the sintered specimens, peaks from the c-planes of the crystal, such as 001 and 002, were very strong. Diffraction peaks which were very strong in the ceramics, such as 320 and 410, were absent in the specimen. Oriented microstructure was developed well by sintering. Grain-growth along to c-axis was observed in the SNN ceramics heated at 1525 K.

  11. Defect behavior of polycrystalline solar cell silicon

    SciTech Connect

    Schroder, D.K.; Park, S.H.; Hwang, I.G.; Mohr, J.B.; Hanly, M.P.

    1993-05-01

    The major objective of this study, conducted from October 1988 to September 1991, was to gain an understanding of the behavior of impurities in polycrystalline silicon and the influence of these impurities on solar cell efficiency. The authors studied edge-defined film-fed growth (EFG) and cast poly-Si materials and solar cells. With EFG Si they concentrated on chromium-doped materials and cells to determine the role of Cr on solar cell performance. Cast poly-Si samples were not deliberately contaminated. Samples were characterized by cell efficiency, current-voltage, deep-level transient spectroscopy (DLTS), surface photovoltage (SPV), open-circuit voltage decay, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy measurements. They find that Cr forms Cr-B pairs with boron at room temperature and these pairs dissociate into Cr{sub i}{sup +} and B{sup {minus}} during anneals at 210{degrees}C for 10 min. Following the anneal, Cr-B pairs reform at room temperature with a time constant of 230 h. Chromium forms CrSi{sub 2} precipitates in heavily contaminated regions and they find evidence of CrSi{sub 2} gettering, but a lack of chromium segregation or precipitation to grain boundaries and dislocations. Cr-B pairs have well defined DLTS peaks. However, DLTS spectra of other defects are not well defined, giving broad peaks indicative of defects with a range of energy levels in the band gap. In some high-stress, low-efficiency cast poly-Si they detect SiC precipitates, but not in low-stress, high-efficiency samples. SPV measurements result in nonlinear SPV curves in some materials that are likely due to varying optical absorption coefficients due to locally varying stress in the material.

  12. The effect of phosphorus on the formation of tungsten dioxide: A novel morphology

    SciTech Connect

    Hegedus, E.; Neugebauer, J.

    1999-02-19

    The industrial production of tungsten is based on the hydrogen reduction of tungsten oxides, ammonium paratungstate (APT) or ammonium tungsten oxide bronze (ATOB). Hydrogen reduction is applied when high purity tungsten is required and when the addition of other elements or compounds (dopants) is desired for modification of the properties of the metal powder. The first stage of the reduction is finished when WO{sub 2} is formed and it seems that the efficient incorporation of the additives starts mainly at this reduction step. The study reported here was undertaken to investigate the effect of phosphorus dope on the morphology of the intermediate tungsten dioxide and analyze its influence on the grain size of the final tungsten metal powder. The authors observed star shaped morphology of WO{sub 2}, a structure which has not been describe in the literature. Contrary to the well-known cauliflower shaped tungsten dioxide, these starlets are not pseudomorphic to the initial ATOB particles; they grow separately and have a great influence on the grain size of the final metal powder.

  13. Ferromagnetism in exfoliated tungsten disulfide nanosheets

    PubMed Central

    2013-01-01

    Two-dimensional-layered transition metal dichalcogenides nanosheets have attracted tremendous attention for their promising applications in spintronics because the atomic-thick nanosheets can not only enhance the intrinsic properties of their bulk counterparts, but also give birth to new promising properties. In this paper, ultrathin tungsten disulfide (WS2) nanosheets were gotten by liquid exfoliation route from its bulk form using dimethylformamide (DMF). Compared to the antiferromagnetism bulk WS2, ultrathin WS2 nanosheets show intrinsic room-temperature ferromagnetism (FM) with the maximized saturation magnetization of 0.004 emu/g at 10 K, where the appearance of FM in the nanosheets is partly due to the presence of zigzag edges in the magnetic ground state at the grain boundaries. PMID:24134699

  14. Tungsten-doped thin film materials

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Gao, Chen; Takeuchi, Ichiro; Schultz, Peter G.

    2003-12-09

    A dielectric thin film material for high frequency use, including use as a capacitor, and having a low dielectric loss factor is provided, the film comprising a composition of tungsten-doped barium strontium titanate of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3, where X is between about 0.5 and about 1.0. Also provided is a method for making a dielectric thin film of the general formula (Ba.sub.x Sr.sub.1-x)TiO.sub.3 and doped with W, where X is between about 0.5 and about 1.0, a substrate is provided, TiO.sub.2, the W dopant, Ba, and optionally Sr are deposited on the substrate, and the substrate containing TiO.sub.2, the W dopant, Ba, and optionally Sr is heated to form a low loss dielectric thin film.

  15. Molybdenum-copper and tungsten-copper alloys and method of making

    DOEpatents

    Schmidt, F.A.; Verhoeven, J.D.; Gibson, E.D.

    1989-05-23

    Molybdenum-copper and tungsten-copper alloys are prepared by a consumable electrode method in which the electrode consists of a copper matrix with embedded strips of refractory molybdenum or tungsten. The electrode is progressively melted at its lower end with a superatmospheric inert gas pressure maintained around the liquefying electrode. The inert gas pressure is sufficiently above the vapor pressure of copper at the liquidus temperature of the alloy being formed to suppress boiling of liquid copper. 6 figs.

  16. Molybdenum-copper and tungsten-copper alloys and method of making

    DOEpatents

    Schmidt, Frederick A.; Verhoeven, John D.; Gibson, Edwin D.

    1989-05-23

    Molybdenum-copper and tungsten-copper alloys are prepared by a consumable electrode method in which the electrode consists of a copper matrix with embedded strips of refractory molybdenum or tungsten. The electrode is progressively melted at its lower end with a superatmospheric inert gas pressure maintained around the liquifying electrode. The inert gas pressure is sufficiently above the vapor pressure of copper at the liquidus temperature of the alloy being formed to suppress boiling of liquid copper.

  17. Tin-tungsten mineralizing processes in tungsten vein deposits: Panasqueira, Portugal

    NASA Astrophysics Data System (ADS)

    Lecumberri-Sanchez, P.; Pinto, F.; Vieira, R.; Wälle, M.; Heinrich, C. A.

    2015-12-01

    Tungsten has a high heat resistance, density and hardness, which makes it widely applied in industry (e.g. steel, tungsten carbides). Tungsten deposits are typically magmatic-hydrothermal systems. Despite the economic significance of tungsten, there are no modern quantitative analytical studies of the fluids responsible for the formation of its highest-grade deposit type (tungsten vein deposits). Panasqueira (Portugal) is a tungsten vein deposit, one of the leading tungsten producers in Europe and one of the best geologically characterized tungsten vein deposits. In this study, compositions of the mineralizing fluids at Panasqueira have been determined through combination of detailed petrography, microthermometric measurements and LA-ICPMS analyses, and geochemical modeling has been used to determine the processes that lead to tungsten mineralization. We characterized the fluids related to the various mineralizing stages in the system: the oxide stage (tin and tungsten mineralization), the sulfide stage (chalcopyrite and sphalerite mineralization) and the carbonate stage. Thus, our results provide information on the properties of fluids related with specific paragenetic stages. Furthermore we used those fluid compositions in combination with host rock mineralogy and chemistry to evaluate which are the controlling factors in the mineralizing process. This study provides the first quantitative analytical data on fluid composition for tungsten vein deposits and evaluates the controlling mineralization processes helping to determine the mechanisms of formation of the Panasqueira tin-tungsten deposit and providing additional geochemical constraints on the local distribution of mineralization.

  18. Grain boundaries and surfaces in polycrystalline photovoltaics

    NASA Astrophysics Data System (ADS)

    Haney, Paul; Yoon, Heayoung; Zhitenev, Nikolai

    Despite the fact that polycrystalline photovoltaics materials such as CdTe and CIGS are an established commercial technology, the precise role of grain boundaries in their performance remains poorly understood. The high defect density at grain boundaries is generally detrimental to carrier lifetime, however the electric fields surrounding charged grain boundaries may separate electrons and holes, effectively passivating the grain boundary. One difficulty in ascertaining the properties of grain boundaries is that high spatial resolution experimental techniques needed to probe individual grain boundaries are generally surface sensitive. For this reason, extracting quantitative grain boundary and other material properties from this data requires a quantitatively accurate model of the exposed surface. Motivated by these considerations, we present a theoretical analysis of the response of a polycrystalline semiconductor to a localized excitation near a grain boundary, and near the surface. We use our analytical results to interpret electron beam induced current (EBIC) data on polycrystalline CdTe solar cells.

  19. Process Research of Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1984-01-01

    A passivation process (hydrogenation) that will improve the power generation of solar cells fabricated from presently produced, large grain, cast polycrystalline silicon (Semix), a potentially low cost material are developed. The first objective is to verify the operation of a DC plasma hydrogenation system and to investigate the effect of hydrogen on the electrical performance of a variety of polycrystalline silicon solar cells. The second objective is to parameterize and optimize a hydrogenation process for cast polycrystalline silicon, and will include a process sensitivity analysis. The sample preparation for the first phase is outlined. The hydrogenation system is described, and some early results that were obtained using the hydrogenation system without a plasma are summarized. Light beam induced current (LBIC) measurements of minicell samples, and their correlation to dark current voltage characteristics, are discussed.

  20. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    PubMed

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere.

  1. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    PubMed

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere. PMID:10947983

  2. "CLASPing" tungsten's effects on microtubules with "PINs".

    PubMed

    Adamakis, Ioannis Dimosthenis S; Panteris, Emmanuel; Eleftheriou, Eleftherios P

    2015-01-01

    Tungsten, supplied as sodium tungstate, inhibits root elongation in Arabidopsis thaliana, which has been attributed to a diminishing of PIN2 and PIN3 auxin efflux carriers. In this work, we sought to analyze the effect of tungsten on cortical microtubules and CLASP (Cytoplasmic Linker Associated Protein), which are also involved in the anisotropic cell expansion of root cells. Seedlings grown in a tungsten-free substrate for 4 d and then transplanted into a tungsten-containing substrate exhibited randomly oriented microtubules in a time-dependent manner. While tungsten had no effect on roots treated for 3 h, microtubule alignment was obviously affected in the transition and elongation zones after a 6, 12, 24, 48 h tungsten treatment, at prolonged tungsten administrations and in seedlings grown directly in the presence of tungsten. This change in microtubule orientation may be associated with the reduction of CLASP protein expression induced by tungsten, as evidenced in experiments with plants expressing the CLASP-GFP protein. A possible mechanism, by which the coordinated functions of CLASP, PIN2 and microtubules are affected, as revealed by inhibited root growth, is discussed. PMID:26313814

  3. High temperature heterogeneous reaction kinetics and mechanisms of tungsten oxidation

    NASA Astrophysics Data System (ADS)

    Sabourin, Justin L.

    Tungsten, which is a material used in many high temperature applications, is limited by its susceptibility to oxidation at elevated temperatures. Although tungsten has the highest melting temperature of any metal, at much lower temperatures volatile oxides are formed during oxidation with oxygen containing species. This differs from many heterogeneous oxidation reactions involving metals since most reactions form very stable oxides that have higher melting or boiling points than the pure metal (e.g., aluminum, iron). Understanding heterogeneous oxidation and vaporization processes may allow for the expansion and improvement of high temperature tungsten applications. In order to increase understanding of the oxidation processes of tungsten, there is a need to develop reaction mechanisms and kinetics for oxidation processes involving oxidizers and environmental conditions of interest. Tungsten oxidation was thoroughly studied in the past, and today there is a good phenomenological understanding of these processes. However, as the design of large scale systems increasingly relies on computer modeling there becomes a need for improved descriptions of chemical reactions. With the increase in computing power over the last several decades, and the development of quantum chemistry and physics theories, heterogeneous systems can be modeled in detail at the molecular level. Thermochemical parameters that may not be measured experimentally may now be determined theoretically, a tool that was previously unavailable to scientists and engineers. Additionally, chemical kinetic modeling software is now available for both homogeneous and heterogeneous reactions. This study takes advantage of these new theoretical tools, as well as a thermogravimetric (TG) flow reactor developed as part of this study to learn about mechanisms and kinetics of tungsten oxidation. Oxidizers of interest are oxygen (O2), carbon dioxide (CO 2), water (H2O), and other oxidizers present in combustion and

  4. Tungsten coating for improved wear resistance and reliability of microelectromechanical devices

    DOEpatents

    Fleming, James G.; Mani, Seethambal S.; Sniegowski, Jeffry J.; Blewer, Robert S.

    2001-01-01

    A process is disclosed whereby a 5-50-nanometer-thick conformal tungsten coating can be formed over exposed semiconductor surfaces (e.g. silicon, germanium or silicon carbide) within a microelectromechanical (MEM) device for improved wear resistance and reliability. The tungsten coating is formed after cleaning the semiconductor surfaces to remove any organic material and oxide film from the surface. A final in situ cleaning step is performed by heating a substrate containing the MEM device to a temperature in the range of 200-600 .degree. C. in the presence of gaseous nitrogen trifluoride (NF.sub.3). The tungsten coating can then be formed by a chemical reaction between the semiconductor surfaces and tungsten hexafluoride (WF.sub.6) at an elevated temperature, preferably about 450.degree. C. The tungsten deposition process is self-limiting and covers all exposed semiconductor surfaces including surfaces in close contact. The present invention can be applied to many different types of MEM devices including microrelays, micromirrors and microengines. Additionally, the tungsten wear-resistant coating of the present invention can be used to enhance the hardness, wear resistance, electrical conductivity, optical reflectivity and chemical inertness of one or more semiconductor surfaces within a MEM device.

  5. Low molybdenum state induced by tungsten as a model of molybdenum deficiency in rats.

    PubMed

    Yoshida, Munehiro; Nakagawa, Mikihito; Hosomi, Ryota; Nishiyama, Toshimasa; Fukunaga, Kenji

    2015-05-01

    Organ molybdenum (Mo) concentration and the activity of hepatic sulfite oxidase and xanthine oxidase were compared in tungsten-administered rats as well as rats fed with a low Mo diet to evaluate the use of tungsten-administered rats as a model of Mo deficiency. Twenty-four male 6-week-old Wistar rats were divided into four groups according to diet (AIN93G diet (control diet) or the control diet minus ammonium molybdate (low Mo diet)) and drinking water (deionized water or deionized water containing 200 μg/mL tungsten in the form of sodium tungstate). Mo content in the control and low Mo diets were 196 and 42 ng/g, respectively. Intake of the low Mo diet significantly reduced the Mo content of several organs and serum. Decrease in hepatic sulfite oxidase activity was also induced by the low Mo diet. The administration of tungsten induced marked decreases in organ Mo content and the activity of hepatic sulfite oxidase and xanthine oxidase. These decreases induced by tungsten administration were more pronounced than those induced by just a low Mo diet. Serum uric acid was also reduced by tungsten administration irrespective of Mo intake. Although a comparatively high accumulation of tungsten (3 to 9 μg/g) was observed in the kidneys and liver, adverse effects of tungsten accumulation on liver and kidney function were not observed in serum biochemical tests. These results indicate that tungsten-administered animals may be used as a model of Mo deficiency. PMID:25627419

  6. Tungsten coatings electro-deposited on CFC substrates from oxide molten salt

    NASA Astrophysics Data System (ADS)

    Sun, Ningbo; Zhang, Yingchun; Lang, Shaoting; Jiang, Fan; Wang, Lili

    2014-12-01

    Tungsten is considered as plasma facing material in fusion devices because of its high melting point, its good thermal conductivity, its low erosion rate and its benign neutron activation properties. On the other hand, carbon based materials like C/C fiber composites (CFC) have been used for plasma facing materials (PFMs) due to their high thermal shock resistance, light weight and high strength. Tungsten coatings on CFC substrates are used in the JET divertor in the frame of the JET ITER-like wall project, and have been prepared by plasma spray (PS) and other techniques. In this study, tungsten coatings were electro-deposited on CFC from Na2WO4-WO3 molten salt under various deposition parameters at 900 °C in air. In order to obtain tungsten coatings with excellent performance, the effects of pulse duration ratio and pulse current density on microstructures and crystal structures of tungsten coatings were investigated by X-ray diffraction (XRD, Rigaku Industrial Co., Ltd., D/MAX-RB) and a scanning electron microscope (SEM, JSM 6480LV). It is found that the pulsed duration ratio and pulse current density had a significant influence on tungsten nucleation and electro-crystallization phenomena. SEM observation revealed that intact, uniform and dense tungsten coatings formed on the CFC substrates. Both the average grain size and thickness of the coating increased with the pulsed current density. The XRD results showed that the coatings consisted of a single phase of tungsten with the body centered cubic (BCC) structure. The oxygen content of electro-deposited tungsten coatings was lower than 0.05%, and the micro-hardness was about 400 HV.

  7. Tungsten Stable Isotope Compositions of Ferromanganese Crusts

    NASA Astrophysics Data System (ADS)

    Abraham, K.; Barling, J.; Hein, J. R.; Schauble, E. A.; Halliday, A. N.

    2014-12-01

    We report the first accurate and precise data for mass-dependent fractionation of tungsten (W) stable isotopes, using a double spike technique and MC-ICPMS. Results are expressed relative to the NIST 3136 W isotope standard as per mil deviations in 186W/184W (δ186W). Although heavy element mass-dependent fractionations are expected to be small, Tl and U both display significant low temperature isotopic fractionations. Theoretical calculations indicate that W nuclear volume isotopic effects should be smaller than mass-dependent fractionations at low temperatures. Hydrogenetic ferromanganese (Fe-Mn) crusts precipitate directly from seawater and have been used as paleoceanographic recorders of temporal changes in seawater chemistry. Crusts are strongly enriched in W and other metals, and are a promising medium for exploring W isotopic variability. Tungsten has a relatively long residence time in seawater of ~61,000 years, mainly as the tungstate ion (WO42-). Water depth profiles show conservative behaviour. During adsorption on Fe-Mn crusts, W species form inner-sphere complexes in the hexavalent (W6+) state. The major host phase is thought to be Mn oxides and the lighter W isotope is expected to be absorbed preferentially. Surface scrapings of 13 globally distributed hydrogenetic Fe-Mn crusts display δ186W from -0.08 to -0.22‰ (±0.03‰, 2sd). A trend toward lighter W isotope composition exists with increasing water depth (~1500 to ~5200m) and W concentration. One hydrothermal Mn-oxide sample is anomalously light and Mn nodules are both heavy and light relative to Fe-Mn crusts. Tungsten speciation depends on concentration, pH, and time in solution and is not well understood because of the extremely slow kinetics of the reactions. In addition, speciation of aqueous and/or adsorbed species might be sensitive to pressure, showing similar thermodynamic stability but different effective volumes. Thus, W stable isotopes might be used as a water-depth barometer in

  8. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  9. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  10. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  11. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  12. 40 CFR 421.100 - Applicability: Description of the primary tungsten subcategory.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... primary tungsten subcategory. 421.100 Section 421.100 Protection of Environment ENVIRONMENTAL PROTECTION... CATEGORY Primary Tungsten Subcategory § 421.100 Applicability: Description of the primary tungsten... tungsten at primary tungsten facilities....

  13. Tungsten bridge for the low energy ignition of explosive and energetic materials

    DOEpatents

    Benson, David A.; Bickes, Jr., Robert W.; Blewer, Robert S.

    1990-01-01

    A tungsten bridge device for the low energy ignition of explosive and energetic materials is disclosed. The device is fabricated on a silicon-on-sapphire substrate which has an insulating bridge element defined therein using standard integrated circuit fabrication techniques. Then, a thin layer of tungsten is selectively deposited on the silicon bridge layer using chemical vapor deposition techniques. Finally, conductive lands are deposited on each end of the tungsten bridge layer to form the device. It has been found that this device exhibits substantially shorter ignition times than standard metal bridges and foil igniting devices. In addition, substantially less energy is required to cause ignition of the tungsten bridge device of the present invention than is required for common metal bridges and foil devices used for the same purpose.

  14. Tungsten bridge for the low energy ignition of explosive and energetic materials

    DOEpatents

    Benson, D.A.; Bickes, R.W. Jr.; Blewer, R.S.

    1990-12-11

    A tungsten bridge device for the low energy ignition of explosive and energetic materials is disclosed. The device is fabricated on a silicon-on-sapphire substrate which has an insulating bridge element defined therein using standard integrated circuit fabrication techniques. Then, a thin layer of tungsten is selectively deposited on the silicon bridge layer using chemical vapor deposition techniques. Finally, conductive lands are deposited on each end of the tungsten bridge layer to form the device. It has been found that this device exhibits substantially shorter ignition times than standard metal bridges and foil igniting devices. In addition, substantially less energy is required to cause ignition of the tungsten bridge device of the present invention than is required for common metal bridges and foil devices used for the same purpose. 2 figs.

  15. Defects in tungsten responsible for molecular hydrogen isotope retention after exposure to low energy plasmas

    NASA Astrophysics Data System (ADS)

    Causey, R. A.; Doerner, R.; Fraser, H.; Kolasinski, R. D.; Smugeresky, J.; Umstadter, K.; Williams, R.

    2009-06-01

    Recent work on hydrogen isotope retention in tungsten has shown a substantial fraction of the retained hydrogen to be in the form of molecules. It can be expected that hydrogen permeating through a material such as tungsten, that has a very low solubility for hydrogen, would come out of solution and combine into molecules at voids located throughout the bulk. The purpose of this report is to determine the type of voids responsible for the molecular retention. High purity tungsten provided by Plansee Aktiengesellschaft was first polished, annealed at 1273 K in vacuum for one hour, and then exposed to high fluxes and high fluences of deuterium in the PISCES facility. High resolution Transmission Electron Microscopy was then used to examine the samples for voids. The results of these experiments were used to interpret the expected behavior of tungsten to be used as the divertor of the ITER fusion device.

  16. Stability and mobility of rhenium and osmium in tungsten: first principles study

    NASA Astrophysics Data System (ADS)

    Suzudo, T.; Yamaguchi, M.; Hasegawa, A.

    2014-10-01

    We report a series of ab initio studies based upon density functional theory for the behavior of rhenium and osmium atoms in body-centered-cubic tungsten crystal. Contrary to the fast one-dimensional migration of self-interstitial atoms, interstitials of these solute elements in tungsten have three-dimensional motion because they form a mixed dumbbell having a low rotation energy barrier. The migration of these solute elements strongly influences the effects of radiation upon the materials, and our results suggest that the low rotation energy barrier leading to three-dimensional migration is a property that is key to the explanation of the radiation effects experimentally observed in tungsten-rhenium and tungsten-osmium alloys.

  17. Process Research On Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J. H.; Culik, J. S.

    1982-01-01

    The mechanisms limiting performance in polycrystalline silicon was determined. The initial set of experiments in this task entails the fabrication of cells of various thicknesses for four different bulk resistivities between 0.1 and 10 omega-cm. The results for the first two lots are presented.

  18. In vivo corrosion, tumor outcome, and microarray gene expression for two types of muscle-implanted tungsten alloys.

    PubMed

    Schuster, B E; Roszell, L E; Murr, L E; Ramirez, D A; Demaree, J D; Klotz, B R; Rosencrance, A B; Dennis, W E; Bao, W; Perkins, E J; Dillman, J F; Bannon, D I

    2012-11-15

    Tungsten alloys are composed of tungsten microparticles embedded in a solid matrix of transition metals such as nickel, cobalt, or iron. To understand the toxicology of these alloys, male F344 rats were intramuscularly implanted with pellets of tungsten/nickel/cobalt, tungsten/nickel/iron, or pure tungsten, with tantalum pellets as a negative control. Between 6 and 12 months, aggressive rhabdomyosarcomas formed around tungsten/nickel/cobalt pellets, while those of tungsten/nickel/iron or pure tungsten did not cause cancers. Electron microscopy showed a progressive corrosion of the matrix phase of tungsten/nickel/cobalt pellets over 6 months, accompanied by high urinary concentrations of nickel and cobalt. In contrast, non-carcinogenic tungsten/nickel/iron pellets were minimally corroded and urinary metals were low; these pellets having developed a surface oxide layer in vivo that may have restricted the mobilization of carcinogenic nickel. Microarray analysis of tumors revealed large changes in gene expression compared with normal muscle, with biological processes involving the cell cycle significantly up-regulated and those involved with muscle development and differentiation significantly down-regulated. Top KEGG pathways disrupted were adherens junction, p53 signaling, and the cell cycle. Chromosomal enrichment analysis of genes showed a highly significant impact at cytoband 7q22 (chromosome 7) which included mouse double minute (MDM2) and cyclin-dependant kinase (CDK4) as well as other genes associated with human sarcomas. In conclusion, the tumorigenic potential of implanted tungsten alloys is related to mobilization of carcinogenic metals nickel and cobalt from corroding pellets, while gene expression changes in the consequent tumors are similar to radiation induced animal sarcomas as well as sporadic human sarcomas.

  19. Novel properties of Tungsten ditelluride

    NASA Astrophysics Data System (ADS)

    Liu, Huimei; National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Cent Collaboration

    Tungsten ditelluride has attracted intense research interest due to the recent discovery of its large unsaturated magnetoresistance up to 60 Tesla. By using density functional theory calculations, we qualitatively reproduced the observed spin texture. Since the spin texture would forbid back scatterings that are directly involved in the resistivity, we suggest that the SOC and the related spin and orbital angular momentum textures may play an important role in the anomalously large magnetoresistance of WTe2. Motivated by the presence of a small, sensitive Fermi surface of 5d electronic orbitals, we also boost the electronic properties by applying a high pressure, and introduce superconductivity successfully.

  20. Study on the oxidation and reduction of tungsten surface for sub-50 nm patterning process

    SciTech Connect

    Kim, Jong Kyu; Nam, Seok Woo; Cho, Sung Il; Jhon, Myung S.; Min, Kyung Suk; Kim, Chan Kyu; Jung, Ho Bum; Yeom, Geun Young

    2012-11-15

    The oxidation characteristics of tungsten line pattern during the carbon-based mask-layer removal process using oxygen plasmas have been investigated for sub-50 nm patterning processes, in addition to the reduction characteristics of the WO{sub x} layer formed on the tungsten line surface using hydrogen plasmas. The surface oxidation of tungsten lines during the mask layer removal process could be minimized by using low-temperature (300 K) plasma processing for the removal of the carbon-based material. Using this technique, the thickness of WO{sub x} on the tungsten line could be decreased to 25% compared to results from high-temperature processing. The WO{sub x} layer could also be completely removed at a low temperature of 300 K using a hydrogen plasma by supplying bias power to the tungsten substrate to provide a activation energy for the reduction. When this oxidation and reduction technique was applied to actual 40-nm-CD device processing, the complete removal of WO{sub x} formed on the sidewall of tungsten line could be observed.

  1. Stochastic multiscale modeling of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Wen, Bin

    Mechanical properties of engineering materials are sensitive to the underlying random microstructure. Quantification of mechanical property variability induced by microstructure variation is essential for the prediction of extreme properties and microstructure-sensitive design of materials. Recent advances in high throughput characterization of polycrystalline microstructures have resulted in huge data sets of microstructural descriptors and image snapshots. To utilize these large scale experimental data for computing the resulting variability of macroscopic properties, appropriate mathematical representation of microstructures is needed. By exploring the space containing all admissible microstructures that are statistically similar to the available data, one can estimate the distribution/envelope of possible properties by employing efficient stochastic simulation methodologies along with robust physics-based deterministic simulators. The focus of this thesis is on the construction of low-dimensional representations of random microstructures and the development of efficient physics-based simulators for polycrystalline materials. By adopting appropriate stochastic methods, such as Monte Carlo and Adaptive Sparse Grid Collocation methods, the variability of microstructure-sensitive properties of polycrystalline materials is investigated. The primary outcomes of this thesis include: (1) Development of data-driven reduced-order representations of microstructure variations to construct the admissible space of random polycrystalline microstructures. (2) Development of accurate and efficient physics-based simulators for the estimation of material properties based on mesoscale microstructures. (3) Investigating property variability of polycrystalline materials using efficient stochastic simulation methods in combination with the above two developments. The uncertainty quantification framework developed in this work integrates information science and materials science, and

  2. Mirrorlike pulsed laser deposited tungsten thin film

    SciTech Connect

    Mostako, A. T. T.; Khare, Alika; Rao, C. V. S.

    2011-01-15

    Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10{sup -5} Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness {approx}782 nm.

  3. Mirrorlike pulsed laser deposited tungsten thin film.

    PubMed

    Mostako, A T T; Rao, C V S; Khare, Alika

    2011-01-01

    Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ∼782 nm. PMID:21280810

  4. In vivo corrosion, tumor outcome, and microarray gene expression for two types of muscle-implanted tungsten alloys

    SciTech Connect

    Schuster, B.E.; Roszell, L.E.; Murr, L.E.; Ramirez, D.A.; Demaree, J.D.; Klotz, B.R.; Rosencrance, A.B.; Dennis, W.E.; Bao, W.; Perkins, E.J.; Dillman, J.F.; Bannon, D.I.

    2012-11-15

    Tungsten alloys are composed of tungsten microparticles embedded in a solid matrix of transition metals such as nickel, cobalt, or iron. To understand the toxicology of these alloys, male F344 rats were intramuscularly implanted with pellets of tungsten/nickel/cobalt, tungsten/nickel/iron, or pure tungsten, with tantalum pellets as a negative control. Between 6 and 12 months, aggressive rhabdomyosarcomas formed around tungsten/nickel/cobalt pellets, while those of tungsten/nickel/iron or pure tungsten did not cause cancers. Electron microscopy showed a progressive corrosion of the matrix phase of tungsten/nickel/cobalt pellets over 6 months, accompanied by high urinary concentrations of nickel and cobalt. In contrast, non-carcinogenic tungsten/nickel/iron pellets were minimally corroded and urinary metals were low; these pellets having developed a surface oxide layer in vivo that may have restricted the mobilization of carcinogenic nickel. Microarray analysis of tumors revealed large changes in gene expression compared with normal muscle, with biological processes involving the cell cycle significantly up‐regulated and those involved with muscle development and differentiation significantly down‐regulated. Top KEGG pathways disrupted were adherens junction, p53 signaling, and the cell cycle. Chromosomal enrichment analysis of genes showed a highly significant impact at cytoband 7q22 (chromosome 7) which included mouse double minute (MDM2) and cyclin‐dependant kinase (CDK4) as well as other genes associated with human sarcomas. In conclusion, the tumorigenic potential of implanted tungsten alloys is related to mobilization of carcinogenic metals nickel and cobalt from corroding pellets, while gene expression changes in the consequent tumors are similar to radiation induced animal sarcomas as well as sporadic human sarcomas. -- Highlights: ► Tungsten/nickel/cobalt, tungsten/nickel/iron, and pure tungsten were studied. ► Male Fischer rats implanted with

  5. The effects of tungsten's pre-irradiation surface condition on helium-irradiated morphology

    DOE PAGES

    Garrison, Lauren M.; Kulcinski, Gerald L.

    2015-07-17

    Erosion is a concern associated with the use of tungsten as a plasma-facing component in fusion reactors. To compare the damage progression, polycrystalline tungsten (PCW) and (110) single crystal tungsten (SCW) samples were prepared with (1) a mechanical polish (MP) with roughness values in the range of 0.018–0.020 μm and (2) an MP and electropolish (MPEP) resulting in roughness values of 0.010–0.020 μm for PCW and 0.003–0.005 μm for SCW samples. Samples were irradiated with 30 keV He+ at 1173 K to fluences between 3 × 1021 and 6 × 1022 He/m2. The morphologies that developed after low-fluence bombardment weremore » different for each type of sample—MP SCW, MPEP SCW, MP PCW, and MPEP PCW. At the highest fluence, the SCW MPEP sample lost significantly more mass and developed a different morphology than the MP SCW sample. The PCW samples developed a similar morphology and had similar mass loss at the highest fluence. Surface preparation can have a significant effect on post-irradiation morphology that should be considered for the design of future fusion reactors such as ITER and DEMO.« less

  6. The effects of tungsten's pre-irradiation surface condition on helium-irradiated morphology

    SciTech Connect

    Garrison, Lauren M.; Kulcinski, Gerald L.

    2015-07-17

    Erosion is a concern associated with the use of tungsten as a plasma-facing component in fusion reactors. To compare the damage progression, polycrystalline tungsten (PCW) and (110) single crystal tungsten (SCW) samples were prepared with (1) a mechanical polish (MP) with roughness values in the range of 0.018–0.020 μm and (2) an MP and electropolish (MPEP) resulting in roughness values of 0.010–0.020 μm for PCW and 0.003–0.005 μm for SCW samples. Samples were irradiated with 30 keV He+ at 1173 K to fluences between 3 × 1021 and 6 × 1022 He/m2. The morphologies that developed after low-fluence bombardment were different for each type of sample—MP SCW, MPEP SCW, MP PCW, and MPEP PCW. At the highest fluence, the SCW MPEP sample lost significantly more mass and developed a different morphology than the MP SCW sample. The PCW samples developed a similar morphology and had similar mass loss at the highest fluence. Surface preparation can have a significant effect on post-irradiation morphology that should be considered for the design of future fusion reactors such as ITER and DEMO.

  7. Polycrystalline nanowires of gadolinium-doped ceria via random alignment mediated by supercritical carbon dioxide

    PubMed Central

    Kim, Sang Woo; Ahn, Jae-Pyoung

    2013-01-01

    This study proposes a seed/template-free method that affords high-purity semiconducting nanowires from nanoclusters, which act as basic building blocks for nanomaterials, under supercritical CO2 fluid. Polycrystalline nanowires of Gd-doped ceria (Gd-CeO2) were formed by CO2-mediated non-oriented attachment of the nanoclusters resulting from the dissociation of single-crystalline aggregates. The unique formation mechanism underlying this morphological transition may be exploited for the facile growth of high-purity polycrystalline nanowires. PMID:23572061

  8. Gas-tungsten arc welding of aluminum alloys

    DOEpatents

    Frye, L.D.

    1982-03-25

    The present invention is directed to a gas-tungsten arc welding method for joining together structures formed of aluminum alloy with these structures disposed contiguously to a heat-damagable substrate of a metal dissimilar to the aluminum alloy. The method of the present invention is practiced by diamond machining the fay surfaces of the aluminum alloy structures to profice a mirror finish thereon having a surface roughness in the order of about one microinch. The fay surface are aligned and heated sufficiently by the tungsten electrode to fuse the aluminum alloy continguous to the fay surfaces to effect the weld joint. The heat input used to provide an oxide-free weld is significantly less than that required if the fay surfaces were prepared by using conventional chemical and mechanical practices.

  9. Gas-tungsten arc welding of aluminum alloys

    DOEpatents

    Frye, Lowell D.

    1984-01-01

    A gas-tungsten arc welding method for joining together structures formed of aluminum alloy with these structures disposed contiguously to a heat-damagable substrate of a metal dissimilar to the aluminum alloy. The method of the present invention is practiced by diamond machining the fay surfaces of the aluminum alloy structures to provide a mirror finish thereon having a surface roughness in the order of about one microinch. The fay surfaces are aligned and heated sufficiently by the tungsten electrode to fuse the aluminum alloy contiguous to the fay surfaces to effect the weld joint. The heat input used to provide an oxide-free weld is significantly less than that required if the fay surfaces were prepared by using conventional chemical and mechanical practices.

  10. Synthesis, Crystal Structure, and Elastic Properties of Novel Tungsten Nitrides

    SciTech Connect

    Wang, Shanmin; Yu, Xiaohui; Lin, Zhijun; Zhang, Ruifeng; He, Duanwei; Qin, Jiaqian; Zhu, Jinlong; Han, Jiantao; Wang, Lin; Mao, Ho-kwang; Zhang, Jianzhong; Zhao, Yusheng

    2012-12-13

    Among transition metal nitrides, tungsten nitrides possess unique and/or superior chemical, mechanical, and thermal properties. Preparation of these nitrides, however, is challenging because the incorporation of nitrogen into tungsten lattice is thermodynamically unfavorable at atmospheric pressure. To date, most materials in the W-N system are in the form of thin films produced by nonequilibrium processes and are often poorly crystallized, which severely limits their use in diverse technological applications. Here we report synthesis of tungsten nitrides through new approaches involving solid-state ion exchange and nitrogen degassing under pressure. We unveil a number of novel nitrides including hexagonal and rhombohedral W{sub 2}N{sub 3}. The final products are phase-pure and well-crystallized in bulk forms. For hexagonal W{sub 2}N{sub 3}, hexagonal WN, and cubic W3N4, they exhibit elastic properties rivaling or even exceeding cubic-BN. All four nitrides are prepared at a moderate pressure of 5 GPa, the lowest among high-pressure synthesis of transition metal nitrides, making it practically feasible for massive and industrial-scale production.

  11. Development of tungsten fibre-reinforced tungsten composites towards their use in DEMO—potassium doped tungsten wire

    NASA Astrophysics Data System (ADS)

    Riesch, J.; Han, Y.; Almanstötter, J.; Coenen, J. W.; Höschen, T.; Jasper, B.; Zhao, P.; Linsmeier, Ch; Neu, R.

    2016-02-01

    For the next step fusion reactor the use of tungsten is inevitable to suppress erosion and allow operation at elevated temperature and high heat loads. Tungsten fibre-reinforced composites overcome the intrinsic brittleness of tungsten and its susceptibility to operation embrittlement and thus allow its use as a structural as well as an armour material. That this concept works in principle has been shown in recent years. In this contribution we present a development approach towards its use in a future fusion reactor. A multilayer approach is needed addressing all composite constituents and manufacturing steps. A huge potential lies in the optimization of the tungsten wire used as fibre. We discuss this aspect and present studies on potassium doped tungsten wire in detail. This wire, utilized in the illumination industry, could be a replacement for the so far used pure tungsten wire due to its superior high temperature properties. In tensile tests the wire showed high strength and ductility up to an annealing temperature of 2200 K. The results show that the use of doped tungsten wire could increase the allowed fabrication temperature and the overall working temperature of the composite itself.

  12. 11% efficient single-crystal solar cells and 10% efficient polycrystalline cells made from refined metallurgical silicon

    NASA Astrophysics Data System (ADS)

    Hanoka, J. I.; Strock, H. B.; Kotval, P. S.

    1981-09-01

    The performances of single-crystal and polycrystalline solar cells fabricated from a refined form of low-cost metallurgical silicon are presented. Czochralski-pulled single crystal and cast polycrystalline silicon solar cells with an n on p structure were made from metallurgical silicon processed by Al dissolution followed by Al removal through slagging and directional solidification to obtain material purities in the fractional ppm by weight range. For the single-crystal cells, measurements reveal AM1 efficiencies up to 11.1%, open circuit voltages up to 596 mV and fill factors up to 81%. The cast polycrystalline substrates have yielded cells with efficiencies up to 10.1%, fill factors of 79% and open circuit voltages of 585 mV. The low short circuit current densities are attributed to impurities in the base region in the single-crystal cell, and to grain boundary segregation of impurities and grain boundary recombination in the polycrystalline cells.

  13. The electrical conductivity of polycrystalline metallic films

    NASA Astrophysics Data System (ADS)

    Moraga, Luis; Arenas, Claudio; Henriquez, Ricardo; Bravo, Sergio; Solis, Basilio

    2016-10-01

    We calculate the electrical conductivity of polycrystalline metallic films by means of a semi-numerical procedure that provides solutions of the Boltzmann transport equation, that are essentially exact, by summing over classical trajectories according to Chambers' method. Following Mayadas and Shatzkes (MS), grain boundaries are modeled as an array of parallel plane barriers situated perpendicularly to the direction of the current. Alternatively, according to Szczyrbowski and Schmalzbauer (SS), the model consists in a triple array of these barriers in mutual perpendicular directions. The effects of surface roughness are described by means of Fuchs' specularity parameters. Following SS, the scattering properties of grain boundaries are taken into account by means of another specularity parameter and a probability of coherent passage. The difference between the sum of these and one is the probability of diffuse scattering. When this formalism is compared with the approximate formula of Mayadas and Shatzkes (Phys. Rev. B 1, 103 (1986)) it is shown that the latter greatly overestimates the film resistivity over most values of the reflectivity of the grain boundaries. The dependence of the conductivity of thin films on the probability of coherent passage and grain diameters is examined. In accordance with MS we find that the effects of disorder in the distribution of grain diameters is quite small. Moreover, we find that it is not safe to neglect the effects of the scattering by the additional interfaces created by stacked grains. However, when compared with recent resitivity-thickness data, it is shown that all three formalisms can provide accurate fits to experiment. In addition, it is shown that, depending on the respective reflectivities and distance from a surface, some of these interfaces may increase or diminish considerably the conductivity of the sample. As an illustration of this effect, we show a tentative fit of resistivity data of gold films measured by

  14. Direct laser deposition of nanostructured tungsten oxide for sensing applications

    NASA Astrophysics Data System (ADS)

    Palla-Papavlu, Alexandra; Filipescu, Mihaela; Schneider, Christof W.; Antohe, Stefan; Ossi, Paolo M.; Radnóczi, György; Dinescu, Maria; Wokaun, Alexander; Lippert, Thomas

    2016-05-01

    Nanostructured tungsten trioxide (WO3) thin films are deposited by pulsed laser deposition (PLD) and radio-frequency (RF) assisted PLD onto interdigitated sensor structures. Structural characterization by x-ray diffraction and Raman spectroscopy shows the WO3 films are polycrystalline, with a pure monoclinic phase for the PLD grown films. The as-fabricated WO3 sensors are tested for ammonia (NH3) detection, by measuring the electrical response to NH3 at different temperatures. Sensors based on WO3 deposited by RF-PLD do not show any response to NH3. In contrast, sensors fabricated by PLD operating at 100 °C and 200 °C show a slow recovery time whilst at 300 °C, these sensors are highly sensitive in the low ppm range with a recovery time in the range of a few seconds. The microstructure of the films is suggested to explain their excellent electrical response. Columnar WO3 thin films are obtained by both deposition methods. However, the WO3 films grown by PLD are porous, (which may allow NH3 molecules to diffuse through the film) whereas RF-PLD films are dense. Our results highlight that WO3 thin films deposited by PLD can be applied for the fabrication of gas sensors with a performance level required for industrial applications.

  15. Environmental fate of tungsten from military use.

    PubMed

    Clausen, Jay L; Korte, Nic

    2009-04-01

    This manuscript describes the distribution, fate and transport of tungsten used in training rounds at three small arms ranges at Camp Edwards on the Massachusetts Military Reservation (MMR), USA. Practice with tungsten/nylon rounds began in 2000 subsequent to a 1997 US Environmental Protection Agency ban on training with lead. Training with the tungsten rounds was halted in 2005 because of concerns regarding tungsten's environmental mobility and potential toxicity. This study, therefore, examines how tungsten partitions in the environment when fired on a small arms training range. Soil sampling revealed surface soil concentrations, highest at the berm face, up to 2080 mg/kg. Concentrations decreased rapidly with depth--at least by an order of magnitude by 25 cm. Nonetheless, tungsten concentrations remained above background to at least 150 cm. Pore-water samples from lysimeters installed in berm areas revealed a range of concentrations (<1-400 mg/L) elevated with respect to background although there was no discernable trend with depth. Groundwater monitoring well samples collected approximately 30 m below ground surface showed tungsten (0.001-0.56 mg/L) attributable to range use.

  16. Environmental fate of tungsten from military use.

    PubMed

    Clausen, Jay L; Korte, Nic

    2009-04-01

    This manuscript describes the distribution, fate and transport of tungsten used in training rounds at three small arms ranges at Camp Edwards on the Massachusetts Military Reservation (MMR), USA. Practice with tungsten/nylon rounds began in 2000 subsequent to a 1997 US Environmental Protection Agency ban on training with lead. Training with the tungsten rounds was halted in 2005 because of concerns regarding tungsten's environmental mobility and potential toxicity. This study, therefore, examines how tungsten partitions in the environment when fired on a small arms training range. Soil sampling revealed surface soil concentrations, highest at the berm face, up to 2080 mg/kg. Concentrations decreased rapidly with depth--at least by an order of magnitude by 25 cm. Nonetheless, tungsten concentrations remained above background to at least 150 cm. Pore-water samples from lysimeters installed in berm areas revealed a range of concentrations (<1-400 mg/L) elevated with respect to background although there was no discernable trend with depth. Groundwater monitoring well samples collected approximately 30 m below ground surface showed tungsten (0.001-0.56 mg/L) attributable to range use. PMID:19217645

  17. Single crystal tungsten kinetic energy penetrators

    SciTech Connect

    Cline, C.F.; Gogolewski, R.P.

    1992-05-01

    We have explored the terminal ballistic performance of single crystal tungsten as a kinetic energy penetrator. Scientific speculation as to the anticipated penetration performance and nature of the interaction between such a kinetic energy penetrator and semi-infinite and spaced metallic targets has led us to perform laboratory scale experiments and metallographic examinations of post-impact penetrator materials. The single tungsten crystals were ground into kinetic energy penetrators with the [l angle]111[r angle] and [l angle]100[r angle] crystal direction being coincident with the axis of symmetry of the penetrators. The crystals were electro-polished to their final diameter. We, compared the terminal performance at current ordnance speeds of [l angle]111[r angle] single crystal tungsten to 90W-10 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against a spaced steel (triple) target at sixty-five degrees obliquity. We also compared the terminal performance of [l angle]100[r angle] and [l angle]111[r angle] single crystal tungsten with 90W-10 and 98W02 (NiFe) cemented tungsten and textured pure tungsten in laboratory scale ballistic experiments against monolithic 4340 alloy steel (HRC = 36) at normal impact. We radiographed the penetrators during the interactions with the targets, we recovered portions of the penetrators after the ballistic experiments, and we conducted metallographic examinations of penetrator remnants. From the radiographic records and the metallographic examinations, we drew conclusions pertaining to insights into the terminal interactions of the penetrators with the targets and suggestions as to improved compositions of the cemented tungsten penetrators.

  18. Correlating grain size to radiation damage tolerance of tungsten materials exposed to relevant fusion conditions

    NASA Astrophysics Data System (ADS)

    Gonderman, Sean

    Tungsten remains a leading candidate for plasma facing component (PFC) in future fusion devices. This is in large part due to its strong thermal and mechanical properties. The ITER project has already chosen to use an all tungsten divertor. Despite having a high melting temperature and low erosion rate, tungsten faces a large variety of issues when subject to fusion like conditions. These include embrittlement, melting, and extreme morphology change (growth of fuzz nanostructure). The work presented here investigates mechanisms that drive surface morphology change in tungsten materials exposed to fusion relevant plasmas. Specifically, tungsten materials of different grain sizes are studied to elucidate the impact of grain boundaries on irradiation damage. Exposure of ultrafine (< 500 nm) and nanocrystalline (< 100 nm) grain materials are exposed to high flux helium plasmas at the Dutch Institute for Fundamental Energy Research (DIFFER) in the Netherlands. These samples are then compared to large grain (1-5 microns) tungsten materials exposed to similar conditions at DIFFER or tungsten samples from other published studies. After exposing the ultrafine grain materials to a variety of helium plasmas to different fluences between 1 x 1023 - 1 x 1027 ions-m-2, temperatures between 600-1500 °C, and ion energies between 25-70 eV, it is observed that ultrafine grained tungsten samples develop fuzz at an order of magnitude larger fluence when compared to large grained tungsten. These observations suggest that grain boundaries play a role in dictating damage accumulation and damage rate caused by ion bombardment of tungsten surfaces. These experiments are complemented by In-situ TEM analysis during 8 keV Helium irradiation of ultrafine tungsten samples to see damage propagation in different sized grains in real time. The in-situ TEM work was completed in a JEOL JEM-2000FX TEM at the Microscope and Ion Accelerator for Materials Investigation (MIAMI) facility at the

  19. Fabrication of transparent spinel polycrystalline materials

    SciTech Connect

    Shimada, M.; Endo, T.; Saito, T.

    1996-12-31

    The novel polycrystalline material of spinel-alumina solid solution, MgO{center_dot}nAl{sub 2}O{sub 3} (1 {le} n < 3):(Mg{sub x}Al{sub (2{minus}2x)/3})Al{sub 2}O{sub 4}(0.4 < x {le} 1.0), was fabricated by reaction sintering using commercial spinel, magnesia and alumina powders as starting material. The mixed powders of (magnesia + alumina) or (spinel + alumina) with above chemical composition were sintered at 1,450--1,550 C in air, followed by post-HIPing at 1,600--1,800 C and 150 MPa in Ar gas atmosphere. The resulting polycrystalline materials showed superior properties such as about 90% in-line optical transmittance at 300--5,000 nm, 250 MPa in fracture strength and 2.8 MPam{sup 1/2} in fracture toughness.

  20. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting ``next-generation`` options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called ``government/industry partnerships``) that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  1. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting next-generation'' options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called government/industry partnerships'') that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  2. Modeling of polycrystalline thin film solar cells

    NASA Astrophysics Data System (ADS)

    Fahrenbruch, Alan L.

    1999-03-01

    This paper describes modeling polycrystalline thin-film solar cells using the program AMPS-1D1 to visualize the relationships between the many variables involved. These simulations are steps toward two dimensional modeling the effects of grain boundaries in polycrystalline cells. Although this paper describes results for the CdS/CdTe cell, the ideas presented here are applicable to copper-indium-gallium selenide (CIGS) cells as well as other types of cells. Results of these one-dimensional simulations are presented: (a) the duplication of experimentally observed cell parameters, (b) the effects of back-contact potential barrier height and its relation to stressing the cell, (c) the effects of the depletion layer width in the CdTe layer on cell parameters, and (d) the effects of CdS layer thickness on the cell parameters. Experience using the software is also described.

  3. Equilibrium shapes of polycrystalline silicon nanodots

    SciTech Connect

    Korzec, M. D. Wagner, B.; Roczen, M.; Schade, M.; Rech, B.

    2014-02-21

    This study is concerned with the topography of nanostructures consisting of arrays of polycrystalline nanodots. Guided by transmission electron microscopy (TEM) measurements of crystalline Si (c-Si) nanodots that evolved from a “dewetting” process of an amorphous Si (a-Si) layer from a SiO{sub 2} coated substrate, we investigate appropriate formulations for the surface energy density and transitions of energy density states at grain boundaries. We introduce a new numerical minimization formulation that allows to account for adhesion energy from an underlying substrate. We demonstrate our approach first for the free standing case, where the solutions can be compared to well-known Wulff constructions, before we treat the general case for interfacial energy settings that support “partial wetting” and grain boundaries for the polycrystalline case. We then use our method to predict the morphologies of silicon nanodots.

  4. Dynamic Failure of a Transparent Polycrystalline Ceramic

    NASA Astrophysics Data System (ADS)

    Bless, Stephan; Manoj Simha, C. Hari; Hartnett, Thomas

    1999-06-01

    We have performed some bar impact experiments on the transparent polycrystalline ceramic aluminum oxynitride (AlON). The experiments use embedded manganin gauges that measure the peak stress that propagates down the bar, and also high speed single frame photography. The peak stress measured in the AlON bars is 4 GPA, about 10% higher than that measured in AD-99.5 bars. The results of our work suggest that the behavior of AlON is similar to that of opaque polycrystalline alumina AD-99.5. The high speed photography has revealed some interesting insights into the behavior of the opaque alumina AD-99.5 which we have been investigating.

  5. Fabrication and properties of tungsten heavy metal alloys containing 30% to 90% tungsten

    SciTech Connect

    Gurwell, W.E.; Nelson, R.G.; Dudder, G.B.; Davis, N.C.

    1984-09-01

    In 1983, Pacific Northwest Laboratory conducted a survey of tungsten heavy metal alloys having lower-than-normal (<90%) tungsten content. The purpose of the work was to develop tougher, more impact-resistant high-density alloys for applications benefitting from improved mechanical properties. Tungsten heavy metal alloys of 30 to 90% tungsten content were fabricated and their mechanical properties measured. Although ultimate strength was essentially independent of tungsten content, lower tungsten-content alloys had lower yield stress, hardness, and density, and decidedly higher elongations and impact energies. Cold work was effective in raising strength and hardness but detrimental to elongation and impact energies. Precipitation hardening and strain aging raised hardness effectively but had less influence on other mechanical properties. 34 figures, 7 tables.

  6. Fluidized bed for production of polycrystalline silicon

    SciTech Connect

    Flagella, R.N.

    1992-08-18

    This patent describes a method for removing silicon powder particles from a reactor that produces polycrystalline silicon by the pyrolysis of a silane containing gas in a fluidized bed reaction zone of silicon seed particles. It comprises introducing the silane containing gas stream into the reaction zone of fluidized silicon seed particles; heterogeneously decomposing the silane containing gas under conditions; collecting the silicon product particles from the collection zone; and removing silicon powder particles from the reactor.

  7. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  8. Tungsten wire for incandescent lamps

    SciTech Connect

    Walter, J.L.; Briant, C.L. )

    1990-09-01

    Tungsten wire for incandescent lamp filaments must operate at high temperatures and for long times. To meet these requirements, the grain morphology of the wire must be controlled to reduce the propensity for grain boundary sliding. The morphology is a function of the distribution of very small pockets of potassium in the wire and the mechanical processing from ingot to wire. The behavior of the filament is directly related to the grain morphology. This paper describes the mechanism by which the potassium is incorporated into and distributed in the ingot. The elongation and spheroidization of the bubbles during hot rolling and swaging is also examined and related to the grain morphology of wire. Some indications of the relationship between grain morphology and filament behavior are also given.

  9. Dielectronic recombination of tungsten ions

    NASA Astrophysics Data System (ADS)

    Li, Bowen; O'Sullivan, Gerry; Dong, Chenzhong; Chen, Ximeng

    2016-08-01

    Ab initio calculations of dielectronic recombination rate coefficients of Ne-, Pd- and Ag-like tungsten have been performed. Energy levels, radiative transition probabilities and autoionization rates were calculated using the Flexible Atomic Code. The contributions from different channels to the total rate coefficients are discussed. The present calculated rate coefficients are compared with other calculations where available. Excellent agreement has been found for Ne-like W while a large discrepancy was found for Pd-like W, which implies that more ab initio calculations and experimental measurements are badly needed. Further calculations demonstrated that the influence of configuration interaction is small while nonresonant radiative stabilizing (NRS) contribution to doubly excited non-autoionizing states are vital. The data obtained are expected to be useful for modeling plasmas for fusion applications, especially for the ITER community, which makes experimental verification even more essential.

  10. Characterization of electrochemically modified polycrystalline platinum surfaces

    SciTech Connect

    Krebs, L.C.; Ishida, Takanobu.

    1991-12-01

    The characterization of electrochemically modified polycrystalline platinum surfaces has been accomplished through the use of four major electrochemical techniques. These were chronoamperometry, chronopotentiommetry, cyclic voltammetry, and linear sweep voltammetry. A systematic study on the under-potential deposition of several transition metals has been performed. The most interesting of these were: Ag, Cu, Cd, and Pb. It was determined, by subjecting the platinum electrode surface to a single potential scan between {minus}0.24 and +1.25 V{sub SCE} while stirring the solution, that the electrocatalytic activity would be regenerated. As a consequence of this study, a much simpler method for producing ultra high purity water from acidic permanganate has been developed. This method results in water that surpasses the water produced by pyrocatalytic distillation. It has also been seen that the wettability of polycrystalline platinum surfaces is greatly dependent on the quantity of oxide present. Oxide-free platinum is hydrophobic and gives a contact angle in the range of 55 to 62 degrees. We have also modified polycrystalline platinum surface with the electrically conducting polymer poly-{rho}-phenylene. This polymer is very stable in dilute sulfuric acid solutions, even under applied oxidative potentials. It is also highly resistant to electrochemical hydrogenation. The wettability of the polymer modified platinum surface is severely dependent on the choice of supporting electrolyte chosen for the electrochemical polymerization. Tetraethylammonium tetrafluoroborate produces a film that is as hydrophobic as Teflon, whereas tetraethylammonium perchlorate produces a film that is more hydrophilic than oxide-free platinum.

  11. Phase-Field Crystal Modeling of Polycrystalline Materials

    NASA Astrophysics Data System (ADS)

    Adland, Ari Joel

    promote GB sliding and strain localization underlying hot tearing. The second class of polycrystalline materials investigated are nanocrystalline materials with a grain size less than a few hundred nanometers. Those materials exhibit desirable properties that include high strength and corrosion resistance. In order to understand basic mechanisms that control the thermal and mechanical stability of nanocrystalline materials, we investigate the stress-driven motion of GBs over a complete range of GB bicrystallography, which includes asymmetrical tilt boundaries with non-vanishing misorientation and inclination angles. We show that asymmetrical GBs exhibit coupled motion to a shear stress parallel to the GB plane and identify a wealth of different dislocation mechanisms mediated by glide, climb, and dislocation reactions, which underlie this coupled motion. We also show that asymmetrical GBs exhibit sliding due to the existence of discontinuous transitions between different coupling modes. Importantly, unlike sliding of symmetrical GBs promoted by GB premelting, sliding of asymmetrical GBs can exist at low temperature, thereby providing an important mechanism for the stress-driven evolution of nanocrystalline structures. In addition to the above studies of polycrystalline materials, we also use the PFC method as a theoretical framework for investigating the grain coarsening dynamics of polycrystalline structures in a broad class of systems that form crystal lattices through self-organization or self-assembly, including driven non-equilibrium systems, modulated phases of macromolecular systems such as diblock copolymers, and colloidal crystals. Our studies reveal that grain growth in those systems is governed by an entirely different dissipation mechanism than in polycrystalline materials. While the rate of curvature-driven grain growth in polycrystalline materials is well-known to be limited by interface dissipation, we find that bulk dissipation associated with lattice

  12. Growth of Ordered Ultrathin Tungsten Oxide Films on Pt(111)

    SciTech Connect

    Li, Zhenjun; Zhang, Zhenrong; Kim, Yu Kwon; Smith, R. Scott; Netzer, Falko; Kay, Bruce D.; Rousseau, Roger J.; Dohnalek, Zdenek

    2011-04-07

    Ordered tungsten oxide ultra-thin films were prepared on a Pt(111) substrate at 700 K via direct sublimation of monodispersed cyclic (WO3)3 trimers. The surface composition, structure and morphology were determined using a combination of atomically resolved imaging, ensemble-averaged surface-sensitive spectroscopies, and density functional theory (DFT). We find that half of the (WO3)3 tungsten atoms get partially reduced to the (5+) oxidation state in the first layer at the Pt(111) interface. The opening of the (WO3)3 ring leads to the formation of a tungsten oxide layer with a zig-zag chain structure with a c(4×2) periodicity. In the second layer, the (WO3)3 clusters remain intact and form an ordered (3×3) array of molecularly-bound (WO3)3. DFT calculations provide a detailed understanding of the structure, oxidation states, and the vibrational frequencies for both the c(4×2) and (3×3) overlayers.

  13. Tungsten fiber reinforced copper matrix composites: A review

    NASA Technical Reports Server (NTRS)

    Mcdanels, David L.

    1989-01-01

    Tungsten fiber reinforced copper matrix (W/Cu) composites have served as an ideal model system with which to analyze the properties of metal matrix composites. A series of research programs were conducted to investigate the stress-strain behavior of W/Cu composites; the effect of fiber content on the strength, modulus, and conductivity of W/Cu composites; and the effect of alloying elements on the behavior of tungsten wire and of W/Cu composites. Later programs investigated the stress-rupture, creep, and impact behavior of these composites at elevated temperatures. Analysis of the results of these programs as allows prediction of the effects of fiber properties, matrix properties, and fiber content on the properties of W/Cu composites. These analyses form the basis for the rule-of-mixtures prediction of composite properties which was universally adopted as the criteria for measuring composite efficiency. In addition, the analyses allows extrapolation of potential properties of other metal matrix composites and are used to select candidate fibers and matrices for development of tungsten fiber reinforced superalloy composite materials for high temperature aircraft and rocket engine turbine applications. The W/Cu composite efforts are summarized, some of the results obtained are described, and an update is provided on more recent work using W/Cu composites as high strength, high thermal conductivity composite materials for high heat flux, elevated temperature applications.

  14. International strategic mineral issues summary report: tungsten

    USGS Publications Warehouse

    Werner, Antony B.T.; Sinclair, W. David; Amey, Earle B.

    1998-01-01

    In 1995, China and the former Soviet Union accounted for over three-fourths of the world's mine production of tungsten. China alone produced about two-thirds of world output. Given its vast resources, China will likely maintain its prominent role in world tungsten supply. By the year 2020, changes in supply patterns are likely to result from declining output from individual deposits in Australia, Austria, and Portugal and the opening of new mines in Canada, China, and the United Kingdom.

  15. Dioxo-Fluoroalkoxide Tungsten(VI) Complexes for Growth of WOx Thin Films by Aerosol-Assisted Chemical Vapor Deposition.

    PubMed

    Bonsu, Richard O; Kim, Hankook; O'Donohue, Christopher; Korotkov, Roman Y; Abboud, Khalil A; Anderson, Timothy J; McElwee-White, Lisa

    2015-08-01

    The soluble bis(fluoroalkoxide) dioxo tungsten(VI) complexes WO2(OR)2(DME) [1, R = C(CF3)2CH3; 2, R = C(CF3)3] have been synthesized by alkoxide-chloride metathesis and evaluated as precursors for aerosol-assisted chemical vapor deposition (AACVD) of WOx. The (1)H NMR and (19)F NMR spectra of 1 and 2 are consistent with an equilibrium between the dimethoxyethane (DME) complexes 1 and 2 and the solvato complexes WO2(OR)2(CD3CN)2 [1b, R = C(CF3)2CH3; 2b, R = C(CF3)3] in acetonitrile-d3 solution. Studies of the fragmentation of 1 and 2 by mass spectrometry and thermolysis resulted in observation of DME and the corresponding alcohols, with hexafluoroisobutylene also generated from 1. DFT calculations on possible decomposition mechanisms for 1 located pathways for hydrogen abstraction by a terminal oxo to form hexafluoroisobutylene, followed by dimerization of the resulting terminal hydroxide complex and dissociation of the alcohol. AACVD using 1 occurred between 100 and 550 °C and produced both substoichiometric amorphous WOx and a polycrystalline W18O49 monoclinic phase, which exhibits 1-D preferred growth in the [010] direction. The work function (4.9-5.6 eV), mean optical transmittance (39.1-91.1%), conductivity (0.4-2.3 S/cm), and surface roughness (3.4-7.9 nm) of the WOx films are suitable for charge injection layers in organic electronics. PMID:26172992

  16. Development and evaluation of polycrystalline cadmium telluride dosimeters for accurate quality assurance in radiation therapy

    NASA Astrophysics Data System (ADS)

    Oh, K.; Han, M.; Kim, K.; Heo, Y.; Moon, C.; Park, S.; Nam, S.

    2016-02-01

    For quality assurance in radiation therapy, several types of dosimeters are used such as ionization chambers, radiographic films, thermo-luminescent dosimeter (TLD), and semiconductor dosimeters. Among them, semiconductor dosimeters are particularly useful for in vivo dosimeters or high dose gradient area such as the penumbra region because they are more sensitive and smaller in size compared to typical dosimeters. In this study, we developed and evaluated Cadmium Telluride (CdTe) dosimeters, one of the most promising semiconductor dosimeters due to their high quantum efficiency and charge collection efficiency. Such CdTe dosimeters include single crystal form and polycrystalline form depending upon the fabrication process. Both types of CdTe dosimeters are commercially available, but only the polycrystalline form is suitable for radiation dosimeters, since it is less affected by volumetric effect and energy dependence. To develop and evaluate polycrystalline CdTe dosimeters, polycrystalline CdTe films were prepared by thermal evaporation. After that, CdTeO3 layer, thin oxide layer, was deposited on top of the CdTe film by RF sputtering to improve charge carrier transport properties and to reduce leakage current. Also, the CdTeO3 layer which acts as a passivation layer help the dosimeter to reduce their sensitivity changes with repeated use due to radiation damage. Finally, the top and bottom electrodes, In/Ti and Pt, were used to have Schottky contact. Subsequently, the electrical properties under high energy photon beams from linear accelerator (LINAC), such as response coincidence, dose linearity, dose rate dependence, reproducibility, and percentage depth dose, were measured to evaluate polycrystalline CdTe dosimeters. In addition, we compared the experimental data of the dosimeter fabricated in this study with those of the silicon diode dosimeter and Thimble ionization chamber which widely used in routine dosimetry system and dose measurements for radiation

  17. Development of tungsten-tantalum generator

    NASA Astrophysics Data System (ADS)

    Leblanc, A.; Babich, J.; Jhingran, S. G.

    The purpose of this project was to develop a useable tungsten (W)/tantalum (Ta) generator. Ta-178 is formed following the decay of its parent, W-178 (half-life: 21.7d) and has a half life of 9.3 minutes in turn yielding stable Hf-178. The decay of the parent isotope (W-178) occurs entirely by electron capture to the 9.3 minute Ta-178 state, without feeding the high spin Ta-178 isomer (half life 2.2 hours). In Ta-178 decay, 99.2% of the disintegrations proceed by electron capture and 0.18% by positron emission. Electron capture results in a 61.2% branch to the ground state of Hf-178 and 33.7% to the first excited state at 93 1KeV. The most prominent features of the radionuclide's energy spectrum are the hafnium characteristic radiation peaks with energies between 54.6 and 65.0 KeV. The radiation exposure dose of Ta-118 was calculated to be approximately one-twentieth that of Tc-99m on a per millicurie basis. A twenty-fold reduction in radiation exposure from Ta-178 compared with Tc-99m means that the usual administered dose can be increased three or four times, greatly increasing statistical accuracy while reducing radiation exposure by a factor of five.

  18. Development of tungsten-tantalum generator

    NASA Technical Reports Server (NTRS)

    Leblanc, A.; Babich, J.; Jhingran, S. G.

    1985-01-01

    The purpose of this project was to develop a useable tungsten (W)/tantalum (Ta) generator. Ta-178 is formed following the decay of its parent, W-178 (half-life: 21.7d) and has a half life of 9.3 minutes in turn yielding stable Hf-178. The decay of the parent isotope (W-178) occurs entirely by electron capture to the 9.3 minute Ta-178 state, without feeding the high spin Ta-178 isomer (half life 2.2 hours). In Ta-178 decay, 99.2% of the disintegrations proceed by electron capture and 0.18% by positron emission. Electron capture results in a 61.2% branch to the ground state of Hf-178 and 33.7% to the first excited state at 93 1KeV. The most prominent features of the radionuclide's energy spectrum are the hafnium characteristic radiation peaks with energies between 54.6 and 65.0 KeV. The radiation exposure dose of Ta-118 was calculated to be approximately one-twentieth that of Tc-99m on a per millicurie basis. A twenty-fold reduction in radiation exposure from Ta-178 compared with Tc-99m means that the usual administered dose can be increased three or four times, greatly increasing statistical accuracy while reducing radiation exposure by a factor of five.

  19. Tungsten targets the tumor microenvironment to enhance breast cancer metastasis.

    PubMed

    Bolt, Alicia M; Sabourin, Valérie; Molina, Manuel Flores; Police, Alice M; Negro Silva, Luis Fernando; Plourde, Dany; Lemaire, Maryse; Ursini-Siegel, Josie; Mann, Koren K

    2015-01-01

    The number of individuals exposed to high levels of tungsten is increasing, yet there is limited knowledge of the potential human health risks. Recently, a cohort of breast cancer patients was left with tungsten in their breasts following testing of a tungsten-based shield during intraoperative radiotherapy. While monitoring tungsten levels in the blood and urine of these patients, we utilized the 66Cl4 cell model, in vitro and in mice to study the effects of tungsten exposure on mammary tumor growth and metastasis. We still detect tungsten in the urine of patients' years after surgery (mean urinary tungsten concentration at least 20 months post-surgery = 1.76 ng/ml), even in those who have opted for mastectomy, indicating that tungsten does not remain in the breast. In addition, standard chelation therapy was ineffective at mobilizing tungsten. In the mouse model, tungsten slightly delayed primary tumor growth, but significantly enhanced lung metastasis. In vitro, tungsten did not enhance 66Cl4 proliferation or invasion, suggesting that tungsten was not directly acting on 66Cl4 primary tumor cells to enhance invasion. In contrast, tungsten changed the tumor microenvironment, enhancing parameters known to be important for cell invasion and metastasis including activated fibroblasts, matrix metalloproteinases, and myeloid-derived suppressor cells. We show, for the first time, that tungsten enhances metastasis in an animal model of breast cancer by targeting the microenvironment. Importantly, all these tumor microenvironmental changes are associated with a poor prognosis in humans. PMID:25324207

  20. Tungsten Targets the Tumor Microenvironment to Enhance Breast Cancer Metastasis

    PubMed Central

    Bolt, Alicia M.; Sabourin, Valérie; Molina, Manuel Flores; Police, Alice M.; Negro Silva, Luis Fernando; Plourde, Dany; Lemaire, Maryse; Ursini-Siegel, Josie; Mann, Koren K.

    2015-01-01

    The number of individuals exposed to high levels of tungsten is increasing, yet there is limited knowledge of the potential human health risks. Recently, a cohort of breast cancer patients was left with tungsten in their breasts following testing of a tungsten-based shield during intraoperative radiotherapy. While monitoring tungsten levels in the blood and urine of these patients, we utilized the 66Cl4 cell model, in vitro and in mice to study the effects of tungsten exposure on mammary tumor growth and metastasis. We still detect tungsten in the urine of patients’ years after surgery (mean urinary tungsten concentration at least 20 months post-surgery = 1.76 ng/ml), even in those who have opted for mastectomy, indicating that tungsten does not remain in the breast. In addition, standard chelation therapy was ineffective at mobilizing tungsten. In the mouse model, tungsten slightly delayed primary tumor growth, but significantly enhanced lung metastasis. In vitro, tungsten did not enhance 66Cl4 proliferation or invasion, suggesting that tungsten was not directly acting on 66Cl4 primary tumor cells to enhance invasion. In contrast, tungsten changed the tumor microenvironment, enhancing parameters known to be important for cell invasion and metastasis including activated fibroblasts, matrix metalloproteinases, and myeloid-derived suppressor cells. We show, for the first time, that tungsten enhances metastasis in an animal model of breast cancer by targeting the microenvironment. Importantly, all these tumor microenvironmental changes are associated with a poor prognosis in humans. PMID:25324207

  1. Tungsten targets the tumor microenvironment to enhance breast cancer metastasis.

    PubMed

    Bolt, Alicia M; Sabourin, Valérie; Molina, Manuel Flores; Police, Alice M; Negro Silva, Luis Fernando; Plourde, Dany; Lemaire, Maryse; Ursini-Siegel, Josie; Mann, Koren K

    2015-01-01

    The number of individuals exposed to high levels of tungsten is increasing, yet there is limited knowledge of the potential human health risks. Recently, a cohort of breast cancer patients was left with tungsten in their breasts following testing of a tungsten-based shield during intraoperative radiotherapy. While monitoring tungsten levels in the blood and urine of these patients, we utilized the 66Cl4 cell model, in vitro and in mice to study the effects of tungsten exposure on mammary tumor growth and metastasis. We still detect tungsten in the urine of patients' years after surgery (mean urinary tungsten concentration at least 20 months post-surgery = 1.76 ng/ml), even in those who have opted for mastectomy, indicating that tungsten does not remain in the breast. In addition, standard chelation therapy was ineffective at mobilizing tungsten. In the mouse model, tungsten slightly delayed primary tumor growth, but significantly enhanced lung metastasis. In vitro, tungsten did not enhance 66Cl4 proliferation or invasion, suggesting that tungsten was not directly acting on 66Cl4 primary tumor cells to enhance invasion. In contrast, tungsten changed the tumor microenvironment, enhancing parameters known to be important for cell invasion and metastasis including activated fibroblasts, matrix metalloproteinases, and myeloid-derived suppressor cells. We show, for the first time, that tungsten enhances metastasis in an animal model of breast cancer by targeting the microenvironment. Importantly, all these tumor microenvironmental changes are associated with a poor prognosis in humans.

  2. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  3. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Dragica, Vasileska; Ringhofer, Christian

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  4. Effect of negative bias on the composition and structure of the tungsten oxide thin films deposited by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Meihan; Lei, Hao; Wen, Jiaxing; Long, Haibo; Sawada, Yutaka; Hoshi, Yoichi; Uchida, Takayuki; Hou, Zhaoxia

    2015-12-01

    Tungsten oxide thin films were deposited at room temperature under different negative bias voltages (Vb, 0 to -500 V) by DC reactive magnetron sputtering, and then the as-deposited films were annealed at 500 °C in air atmosphere. The crystal structure, surface morphology, chemical composition and transmittance of the tungsten oxide thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrophotometer. The XRD analysis reveals that the tungsten oxide films deposited at different negative bias voltages present a partly crystallized amorphous structure. All the films transfer from amorphous to crystalline (monoclinic + hexagonal) after annealing 3 h at 500 °C. Furthermore, the crystallized tungsten oxide films show different preferred orientation. The morphology of the tungsten oxide films deposited at different negative bias voltages is consisted of fine nanoscale grains. The grains grow up and conjunct with each other after annealing. The tungsten oxide films deposited at higher negative bias voltages after annealing show non-uniform special morphology. Substoichiometric tungsten oxide films were formed as evidenced by XPS spectra of W4f and O1s. As a result, semi-transparent films were obtained in the visible range for all films deposited at different negative bias voltages.

  5. Generation and characterization of nano tungsten oxide particles by wire explosion process

    SciTech Connect

    Aravinth, S.; Sankar, Binu; Chakravarthi, S.R.; Sarathi, R.

    2011-02-15

    Nano tungsten oxide particles are produced by wire explosion process. It is realized that by exploding tungsten conductor in lower pressure of oxygen, unreacted phase of tungsten was present and it could be reduced by increasing the operating pressure and increasing the amount of energy deposited to the exploding conductor. It is realized that the nucleation rate of the particle could be high only at the point of maximum saturation ratio, irrespective of the pressure of the oxygen. The size of the critical nucleus formed is low when the saturation ratio and the nucleation rate are at maximum. The nano metal oxide particle formation by wire explosion process allows one to conclude that the second stage annealing process has a major impact on the final grain size formed. The high speed camera photographs of wire explosion process were used to understand the dynamics of particle formation by wire explosion process. The Transmission Electron Microscopy (TEM) analysis indicates that the nano tungsten oxide (WO{sub 3}) particles are of spherical shape and the analysis of particle size indicates that it follows log normal distribution. - Graphical Abstract: Nano tungsten oxide (WO{sub 3}) particles are produced by wire explosion process. Theoretical analysis indicates that the size of the critical nucleus formed is low when the saturation ratio and the nucleation rate are at maximum. High speed camera photographs of wire explosion process were used to understand the dynamics of particles formed. Research Highlights: {yields}Lower particle size is possible with lower pressure. {yields}Particle size is increased with reduced energy ratio. {yields}Unreacted tungsten content reduces when oxygen pressure increases.

  6. Polycrystalline gamma plutonium's elastic moduli versus temperature

    SciTech Connect

    Migliori, Albert; Betts, J; Trugman, A; Mielke, C H; Mitchell, J N; Ramos, M; Stroe, I

    2009-01-01

    Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline {sup 239}Pu in the {gamma} phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease of all elastic moduli with increasing temperature was observed. They calculated the Poisson ratio and found that it increases from 0.242 at 519 K to 0.252 at 571 K. These measurements on extremely well characterized pure Pu are in agreement with other reported results where overlap occurs.

  7. Dynamic failure of a transparent polycrystalline ceramic

    NASA Astrophysics Data System (ADS)

    Cazamias, J. U.; Bless, S. J.; Simha, C. Hari Manoj; Hartnett, T. M.

    2000-04-01

    We have performed bar impact experiments on aluminum oxynitride (AlON), a transparent polycrystalline ceramic, measuring the peak stress and taking high-speed photographs. The peak stress measured in the AlON bars is 4 GPa, about 10% higher than that measured in AD-99.5 bars. Failure was observed propagating up the center of the bar, leaving the outer part intact at relatively late times. There was anomalous damage to the witness bar, similar to what happens with glass bars, indicating either retained strength in the center column or explosive fracture of the AlON bar.

  8. The production of oxygenated polycrystalline graphene by one-step ethanol-chemical vapor deposition

    PubMed Central

    Paul, Rajat K.; Badhulika, Sushmee; Niyogi, Sandip; Haddon, Robert C.; Boddu, Veera M.; Costales-Nieves, Carmen; Bozhilov, Krassimir N.; Mulchandani, Ashok

    2012-01-01

    Large-area mono- and bilayer graphene films were synthesized on Cu foil (~ 1 inch2) in about 1 min by a simple ethanol-chemical vapor deposition (CVD) technique. Raman spectroscopy and high resolution transmission electron microscopy revealed the synthesized graphene films to have polycrystalline structures with 2–5 nm individual crystallite size which is a function of temperature up to 1000°C. X-ray photoelectron spectroscopy investigations showed about 3 atomic% carboxylic (COOH) functional groups were formed during growth. The field-effect transistor devices fabricated using polycrystalline graphene as conducting channel (Lc=10 μm; Wc=50 μm) demonstrated a p-type semiconducting behavior with high drive current and Dirac point at ~35 V. This simple one-step method of growing large area polycrystalline graphene films with semiconductor properties and easily functionalizable groups should assist in the realization of potential of polycrystalline graphene for nanoelectronics, sensors and energy storage devices. PMID:22408276

  9. Electrical properties of polycrystalline methane hydrate

    USGS Publications Warehouse

    Du Frane, W. L.; Stern, L.A.; Weitemeyer, K.A.; Constable, S.; Pinkston, J.C.; Roberts, J.J.

    2011-01-01

    Electromagnetic (EM) remote-sensing techniques are demonstrated to be sensitive to gas hydrate concentration and distribution and complement other resource assessment techniques, particularly seismic methods. To fully utilize EM results requires knowledge of the electrical properties of individual phases and mixing relations, yet little is known about the electrical properties of gas hydrates. We developed a pressure cell to synthesize gas hydrate while simultaneously measuring in situ frequency-dependent electrical conductivity (σ). Synthesis of methane (CH4) hydrate was verified by thermal monitoring and by post run cryogenic scanning electron microscope imaging. Impedance spectra (20 Hz to 2 MHz) were collected before and after synthesis of polycrystalline CH4 hydrate from polycrystalline ice and used to calculate σ. We determined the σ of CH4 hydrate to be 5 × 10−5 S/m at 0°C with activation energy (Ea) of 30.6 kJ/mol (−15 to 15°C). After dissociation back into ice, σ measurements of samples increased by a factor of ~4 and Ea increased by ~50%, similar to the starting ice samples.

  10. US polycrystalline thin film solar cells program

    SciTech Connect

    Ullal, H S; Zweibel, K; Mitchell, R L

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R D on copper indium diselenide and cadmium telluride thin films. The objective of the Program is to support research to develop cells and modules that meet the US Department of Energy's long-term goals by achieving high efficiencies (15%-20%), low-cost ($50/m{sup 2}), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The US Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe{sub 2} and CdTe with subcontracts to start in Spring 1990. 23 refs., 5 figs.

  11. Reversible piezomagnetoelectric switching in bulk polycrystalline ceramics

    SciTech Connect

    Stevenson, T. Bennett, J.; Brown, A. P.; Wines, T.; Bell, A. J.; Comyn, T. P.; Smith, R. I.

    2014-08-01

    Magnetoelectric (ME) coupling in materials offer tremendous advantages in device functionality enabling technologies including advanced electronic memory, combining electronic speed, and efficiency with magnetic robustness. However, low cost polycrystalline ME materials are excluded from most commercial applications, operating only at cryogenic temperatures, impractically large electric/magnetic fields, or with low ME coefficients (1-100 mV/cm Oe). Despite this, the technological potential of single compound ME coupling has continued to drive research into multiferroics over the last two decades. Here we show that by manipulating the large induced atomic strain within the polycrystalline, room temperature multiferroic compound 0.7BiFeO{sub 3}–0.3PbTiO{sub 3}, we can induce a reversible, piezoelectric strain controlled ME effect. Employing an in situ neutron diffraction experiment, we have demonstrated that this piezomagnetoelectric effect manifests with an applied electric field >8 kV/mm at the onset of piezoelectric strain, engineered in to the compound by crystallographic phase mixing. This produces a remarkable intrinsic ME coefficient of 1276 mV/cm Oe, due to a strain driven modification to the oxygen sub-lattice, inducing an increase in magnetic moment per Fe{sup 3+} ion of +0.142 μ{sub B}. This work provides a framework for investigations into strain engineered nanostructures to realize low-cost ME devices designed from the atoms up, as well as contributing to the deeper understanding of single phase ME coupling mechanisms.

  12. Pyranopterin conformation defines the function of molybdenum and tungsten enzymes.

    PubMed

    Rothery, Richard A; Stein, Benjamin; Solomonson, Matthew; Kirk, Martin L; Weiner, Joel H

    2012-09-11

    We have analyzed the conformations of 319 pyranopterins in 102 protein structures of mononuclear molybdenum and tungsten enzymes. These span a continuum between geometries anticipated for quinonoid dihydro, tetrahydro, and dihydro oxidation states. We demonstrate that pyranopterin conformation is correlated with the protein folds defining the three major mononuclear molybdenum and tungsten enzyme families, and that binding-site micro-tuning controls pyranopterin oxidation state. Enzymes belonging to the bacterial dimethyl sulfoxide reductase (DMSOR) family contain a metal-bis-pyranopterin cofactor, the two pyranopterins of which have distinct conformations, with one similar to the predicted tetrahydro form, and the other similar to the predicted dihydro form. Enzymes containing a single pyranopterin belong to either the xanthine dehydrogenase (XDH) or sulfite oxidase (SUOX) families, and these have pyranopterin conformations similar to those predicted for tetrahydro and dihydro forms, respectively. This work provides keen insight into the roles of pyranopterin conformation and oxidation state in catalysis, redox potential modulation of the metal site, and catalytic function.

  13. Evaporites and strata-bound tungsten mineralization

    SciTech Connect

    Ririe, G.T. )

    1989-02-01

    Discoidal gypsum crystal cavities occur in quartzites that host varying amounts of strata-bound scheelite mineralization near Halls Creek in Western Australia. The host quartzites have been regionally metamorphosed to greenschist facies and are contained within a Middle Proterozoic sequence that includes pelites, mafic and felsic volcanics, and volcaniclastic rocks. Textural, fluid inclusion, and oxygen isotope data indicate that scheelite was present in the host quartzites prior to regional metamorphism. The presence of crystal cavities after gypsum in the quartzites implies an evaporitic origin for this sequence. The continental-sabkha playa basins of the Mojave Desert, California, are suggested to be possible modern analogs-e.g., Searles Lake, where the tungsten content is up to 70 ppm WO{sub 3} in brines and 118 ppm in muds, and exceeds the amount of tungsten in all known deposits in the United States. Metamorphism of a continental evaporitic sequence containing tungsten could produce an assemblage of rocks very similar to those reported from several stratabound tungsten deposits. Some of these, such as at Halls Creek, may be related to original accumulations of tungsten in nonmarine evaporitic environments.

  14. Modeling Plasma Surface Interactions in Tungsten through High-Performance Computing

    NASA Astrophysics Data System (ADS)

    Wirth, Brian D.

    2013-10-01

    The plasma facing components of future tokamak-based fusion power plants arguably represent the single greatest materials engineering challenge of all time. Fortunately, recent innovations in computational modeling, increasingly powerful high performance computing platforms and improved experimental characterization tools provide the opportunity to develop self-consistent, experimentally validated models of materials performance in the fusion energy environment. This presentation will describe the challenges of modeling plasma facing components in a fusion materials environment, opportunities to utilize high performance computing and then focus on recent progress to investigate the surface evolution of tungsten exposed to low-energy He/H plasmas. These results identify the mechanisms of tungsten surface morphology changes during 100 eV He plasma exposure as a function of temperature and initial tungsten microstructure. The results demonstrate that He clusters create self-interstitial defect clusters in W by a trap mutation process, followed by the migration of these defects to the surface that forms adatom layers on the tungsten surface. As the helium clusters grow into nanometer bubbles, their proximity to the surface and extremely high gas pressures leads to rupture the surface. Helium bubble bursting induces additional surface damage and tungsten mass loss. on behalf of the SciDAC-PSI team.

  15. Electroanalytical determination of tungsten and molybdenum in proteins.

    PubMed

    Hagedoorn, P L; van't Slot, P; van Leeuwen, H P; Hagen, W R

    2001-10-01

    Recent crystal structure determinations accelerated the progress in the biochemistry of tungsten-containing enzymes. In order to characterize these enzymes, a sensitive determination of this metal in protein-containing samples is necessary. An electroanalytical tungsten determination has successfully been adapted to determine the tungsten and molybdenum content in enzymes. The tungsten and molybdenum content can be measured simultaneously from 1 to 10 microg of purified protein with little or no sample handling. More crude protein samples require precipitation of interfering surface active material with 10% perchloric acid. This method affords the isolation of novel molybdenum- and tungsten-containing proteins via molybdenum and tungsten monitoring of column fractions, without using radioactive isotopes. A screening of soluble proteins from Pyrococcus furiosus for tungsten, using anion-exchange column chromatography to separate the proteins, has been performed. The three known tungsten-containing enzymes from P. furiosus were recovered with this screening.

  16. Some Tungsten Oxidation-Reduction Chemistry: A Paint Pot Titration.

    ERIC Educational Resources Information Center

    Pickering, Miles; Monts, David L.

    1982-01-01

    Reports an oxidation-reduction experiment using tungsten, somewhat analogous to the classical student experiment involving oxidation-reduction of vanadium. Includes experimental procedures, results, and toxicity/cost of tungsten compounds. (Author/JN)

  17. Growth of tungsten oxide on carbon nanowalls templates

    SciTech Connect

    Wang, Hua; Su, Yan; Chen, Shuo; Quan, Xie

    2013-03-15

    Highlights: ► Tungsten oxide deposited on carbon nanowalls by hot filament chemical vapor deposition technique. ► This composite has two-dimensional uniform morphology with a crystalline structure of monoclinic tungsten trioxide. ► Surface photoelectric voltage measurements show that this product has photoresponse properties. - Abstract: In the present work we present a simple approach for coupling tungsten oxide with carbon nanowalls. The two-dimensional carbon nanowalls with open boundaries were grown using plasma enhanced hot filament chemical vapor deposition, and the subsequent tungsten oxide growth was performed in the same equipment by direct heating of a tungsten filament. The tungsten oxide coating is found to have uniform morphology with a crystalline structure of monoclinic tungsten trioxide. Surface photoelectric voltage measurements show that this product has photoresponse properties. The method of synthesis described here provides an operable route to the production of two-dimensional tungsten oxide nanocomposites.

  18. Molybdenum and tungsten oxygen transferases--and functional diversity within a common active site motif.

    PubMed

    Pushie, M Jake; Cotelesage, Julien J; George, Graham N

    2014-01-01

    Molybdenum and tungsten are the only second and third-row transition elements with a known function in living organisms. The molybdenum and tungsten enzymes show common structural features, with the metal being bound by a pyranopterin-dithiolene cofactor called molybdopterin. They catalyze a variety of oxygen transferase reactions coupled with two-electron redox chemistry in which the metal cycles between the +6 and +4 oxidation states usually with water, either product or substrate, providing the oxygen. The functional roles filled by the molybdenum and tungsten enzymes are diverse; for example, they play essential roles in microbial respiration, in the uptake of nitrogen in green plants, and in human health. Together, the enzymes form a superfamily which is among the most prevalent known, being found in all kingdoms of life. This review discusses what is known of the active site structures and the mechanisms, together with some recent insights into the evolution of these important enzyme systems.

  19. An alternative isolation of tungsten tips for a scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Abelev, E.; Sezin, N.; Ein-Eli, Y.

    2005-10-01

    Experimental results obtained from electrochemical preparation of tungsten followed by a novel insulating technique are reported. An additional effective method for insulation of the electrochemically etched W tips based on cathophoretic paint deposition is described. The cathophoretic paint deposition isolation method was found to be highly reproducible, forming an isolated stable film in both aqueous and nonaqueous organic solvents.

  20. Progress in polycrystalline thin-film solar cells

    SciTech Connect

    Zweibel, K; Hermann, A; Mitchell, R

    1983-07-01

    Photovoltaic devices based on several polycrystalline thin-film materials have reached near and above 10% sunlight-to-electricity conversion efficiencies. This paper examines the various polycrystalline thin-film PV materials including CuInSe/sub 2/ and CdTe in terms of their material properties, fabrication techniques, problems, and potentials.

  1. Stable powders made from photosensitive polycrystalline complexes of heterocyclic monomers and their polymers

    NASA Technical Reports Server (NTRS)

    Hodko, Dalibor (Inventor); Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor)

    1999-01-01

    The present invention relates to a low electronic conductivity polymer composition having well dispersed metal granules, a stable powder made from photosensitive polycrystalline complexes of pyrrole, or its substituted derivatives and silver cations for making the polymer composition, and methods of forming the stable powder and polymer composition, respectively. A polycrystalline complex of silver and a monomer, such as pyrrole, its substituted derivatives or combinations thereof, is precipitated in the form of a stable photosensitive powder upon addition of the monomer to a solvent solution, such as toluene containing an electron acceptor. The photosensitive powder can be stored in the dark until needed. The powder may be dissolved in a solvent, cast onto a substrate and photopolymerized.

  2. Element 74, the Wolfram Versus Tungsten Controversy

    SciTech Connect

    Holden,N.E.

    2008-08-11

    Two and a quarter centuries ago, a heavy mineral ore was found which was thought to contain a new chemical element called heavy stone (or tungsten in Swedish). A few years later, the metal was separated from its oxide and the new element (Z=74) was called wolfram. Over the years since that time, both the names wolfram and tungsten were attached to this element in various countries. Sixty years ago, IUPAC chose wolfram as the official name for the element. A few years later, under pressure from the press in the USA, the alternative name tungsten was also allowed by IUPAC. Now the original, official name 'wolfram' has been deleted by IUPAC as one of the two alternate names for the element. The history of this controversy is described here.

  3. Modelling heat conduction in polycrystalline hexagonal boron-nitride films.

    PubMed

    Mortazavi, Bohayra; Pereira, Luiz Felipe C; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  4. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    PubMed Central

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  5. Multiscale modeling of thermal conductivity of polycrystalline graphene sheets.

    PubMed

    Mortazavi, Bohayra; Pötschke, Markus; Cuniberti, Gianaurelio

    2014-03-21

    We developed a multiscale approach to explore the effective thermal conductivity of polycrystalline graphene sheets. By performing equilibrium molecular dynamics (EMD) simulations, the grain size effect on the thermal conductivity of ultra-fine grained polycrystalline graphene sheets is investigated. Our results reveal that the ultra-fine grained graphene structures have thermal conductivity one order of magnitude smaller than that of pristine graphene. Based on the information provided by the EMD simulations, we constructed finite element models of polycrystalline graphene sheets to probe the thermal conductivity of samples with larger grain sizes. Using the developed multiscale approach, we also investigated the effects of grain size distribution and thermal conductivity of grains on the effective thermal conductivity of polycrystalline graphene. The proposed multiscale approach on the basis of molecular dynamics and finite element methods could be used to evaluate the effective thermal conductivity of polycrystalline graphene and other 2D structures.

  6. Higher-order elastic constants and megabar pressure effects of bcc tungsten: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Vekilov, Yu. Kh.; Krasilnikov, O. M.; Lugovskoy, A. V.; Lozovik, Yu. E.

    2016-09-01

    The general method for the calculation of n th (n ≥2 ) order elastic constants of the loaded crystal is given in the framework of the nonlinear elasticity theory. For the crystals of cubic symmetry under hydrostatic compression, the two schemes of calculation of the elastic constants of second, third, and fourth order from energy-finite strain relations and stress-finite strain relations are implemented. Both techniques are applied for the calculation of elastic constants of orders from second to fourth to the bcc phase of tungsten at a 0-600 GPa pressure range. The energy and stress at the various pressures and deformations are obtained ab initio in the framework of projector augmented wave+generalized gradient approximation (PAW+GGA) method, as implemented in Vienna Ab initio Simulation Package (VASP) code. Using the obtained results, we found the pressure dependence of Grüneisen parameters for long-wave acoustic modes in this interval. The Lamé constants of second and third order were estimated for polycrystalline tungsten. The proposed method is applicable for crystals with arbitrary symmetry.

  7. Review and statistical analysis of the ultrasonic velocity method for estimating the porosity fraction in polycrystalline materials

    NASA Technical Reports Server (NTRS)

    Roth, D. J.; Swickard, S. M.; Stang, D. B.; Deguire, M. R.

    1990-01-01

    A review and statistical analysis of the ultrasonic velocity method for estimating the porosity fraction in polycrystalline materials is presented. Initially, a semi-empirical model is developed showing the origin of the linear relationship between ultrasonic velocity and porosity fraction. Then, from a compilation of data produced by many researchers, scatter plots of velocity versus percent porosity data are shown for Al2O3, MgO, porcelain-based ceramics, PZT, SiC, Si3N4, steel, tungsten, UO2,(U0.30Pu0.70)C, and YBa2Cu3O(7-x). Linear regression analysis produced predicted slope, intercept, correlation coefficient, level of significance, and confidence interval statistics for the data. Velocity values predicted from regression analysis for fully-dense materials are in good agreement with those calculated from elastic properties.

  8. Review and statistical analysis of the use of ultrasonic velocity for estimating the porosity fraction in polycrystalline materials

    NASA Technical Reports Server (NTRS)

    Roth, D. J.; Swickard, S. M.; Stang, D. B.; Deguire, M. R.

    1991-01-01

    A review and statistical analysis of the ultrasonic velocity method for estimating the porosity fraction in polycrystalline materials is presented. Initially, a semiempirical model is developed showing the origin of the linear relationship between ultrasonic velocity and porosity fraction. Then, from a compilation of data produced by many researchers, scatter plots of velocity versus percent porosity data are shown for Al2O3, MgO, porcelain-based ceramics, PZT, SiC, Si3N4, steel, tungsten, UO2,(U0.30Pu0.70)C, and YBa2Cu3O(7-x). Linear regression analysis produces predicted slope, intercept, correlation coefficient, level of significance, and confidence interval statistics for the data. Velocity values predicted from regression analysis of fully-dense materials are in good agreement with those calculated from elastic properties.

  9. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  10. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  11. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  12. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  13. 40 CFR 721.10168 - Cesium tungsten oxide.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Cesium tungsten oxide. 721.10168... Substances § 721.10168 Cesium tungsten oxide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as cesium tungsten oxide (PMN P-08-275; CAS No....

  14. Ultra-broad band absorber made by tungsten and aluminium

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhao, Ding; Li, Qiang; Qiu, Min

    2016-01-01

    A broadband absorber comprising tungsten cubic arrays, a alumina layer and a tungsten film, is numerically and experimentally investigated, which exhibits near-unity absorption of visible and near-infrared light from 400 nm to 1150 nm. Benefiting from high melting points of tungsten and alumina, this device has great application potential in solar cells and thermal emission.

  15. Equipment simulation of selective tungsten deposition

    SciTech Connect

    Werner, C.; Ulacia, J.I.; Hopfmann, C.; Flynn, P. )

    1992-02-01

    This paper presents the numerical modeling of a cold wall reactor for selective tungsten chemical vapor deposition. In a two dimensional simulation the mass and heat transfer equations were solved considering the five chemical species H{sub 2}, WF{sub 6}, HF, WF{sub x}, and SiF{sub y}. Detailed models for multicomponent diffusion and for the autocatalytic tungsten nucleation process were implemented. Model results are in good agreement with experimental findings. The simulations are used to study the impact of reactor design on selectivity.

  16. Material ejection and surface morphology changes during transient heat loading of tungsten as plasma-facing component in fusion devices

    NASA Astrophysics Data System (ADS)

    Suslova, A.; El-Atwani, O.; Harilal, S. S.; Hassanein, A.

    2015-03-01

    We investigated the effect of edge-localized mode like transient heat events on pristine samples for two different grades of deformed tungsten with ultrafine and nanocrystalline grains as potential candidates for plasma-facing components. Pulses from a laser beam with durations ∼1 ms and operating in the near infrared wavelength were used for simulating transient heat loading in fusion devices. We specifically focused on investigating and analysis of different mechanisms for material removal from the sample surface under repetitive transient heat loads. Several techniques were applied for analysing different mechanisms leading to material removal from the W surface under repetitive transient heat loads which include witness plates for collected ejected material, and subsequent analysis using x-ray photoelectron spectroscopy and scanning electron microscopy, visible imaging using fast-gated camera, and evaluating thermal emission from the particles using optical emission spectroscopy. Our results show a significantly improved performance of polycrystalline cold-rolled tungsten compared to tungsten produced using an orthogonal machining process under repetitive transient loads for a wide range of the power densities.

  17. Microscopic Deformation of Tungsten Surfaces by High Energy and High Flux Helium/Hydrogen Particle Bombardment with Short Pulses

    NASA Astrophysics Data System (ADS)

    Tokitani, Masayuki; Yoshida, Naoaki; Tokunaga, Kazutoshi; Sakakita, Hajime; Kiyama, Satoru; Koguchi, Haruhisa; Hirano, Yoichi; Masuzaki, Suguru

    The neutral beam injection facility in the National Institute of Advanced Industrial Science and Technology was used to irradiate a polycrystalline tungsten specimen with high energy and high flux helium and hydrogen particles. The incidence energy and flux of the beam shot were 25 keV and 8.8 × 1022 particles/m2 s, respectively. The duration of each shot was approximately 30 ms, with 6 min intervals between each shot. Surface temperatures over 1800 K were attained. In the two cases of helium irradiation, total fluence of either 1.5 × 1022 He/m2 or 4.0 × 1022 He/m2 was selected. In the former case, large sized blisters with diameter of 500 nm were densely observed. While, the latter case, the blisters were disappeared and fine nanobranch structures appeared instead. Cross-sectional observations using a transmission electron microscope (TEM) with the focused ion beam (FIB) technique were performed. According to the TEM image, after irradiation with a beam shot of total fluence 4.0 × 1022 He/m2 , there were very dense fine helium bubbles in the tungsten of sizes 1-50 nm. As the helium bubbles grew the density of the tungsten matrix drastically decreased as a result of void swelling. These effects were not seen in hydrogen irradiation case.

  18. Nuclear thermionic converter. [tungsten-thorium oxide rods

    NASA Technical Reports Server (NTRS)

    Phillips, W. M.; Mondt, J. F. (Inventor)

    1977-01-01

    Efficient nuclear reactor thermionic converter units are described which can be constructed at low cost and assembled in a reactor which requires a minimum of fuel. Each converter unit utilizes an emitter rod with a fluted exterior, several fuel passages located in the bulges that are formed in the rod between the flutes, and a collector receiving passage formed through the center of the rod. An array of rods is closely packed in an interfitting arrangement, with the bulges of the rods received in the recesses formed between the bulges of other rods, thereby closely packing the nuclear fuel. The rods are constructed of a mixture of tungsten and thorium oxide to provide high power output, high efficiency, high strength, and good machinability.

  19. Residual Stress Predictions in Polycrystalline Alumina

    SciTech Connect

    VEDULA,VENKATA R.; GLASS,S. JILL; SAYLOR,DAVID M.; ROHRER,GREGORY S.; CARTER,W. CRAIG; LANGER,STEPHEN A.

    1999-12-13

    Microstructure-level residual stresses arise in polycrystalline ceramics during processing as a result of thermal expansion anisotropy and crystallographic disorientation across the grain boundaries. Depending upon the grain size, the magnitude of these stresses can be sufficiently high to cause spontaneous microcracking during the processing of these materials. They are also likely to affect where cracks initiate and propagate under macroscopic loading. The magnitudes of residual stresses in untextured and textured alumina samples were predicted using object oriented finite (OOF) element analysis and experimentally determined grain orientations. The crystallographic orientations were obtained by electron-backscattered diffraction (EBSD). The residual stresses were lower and the stress distributions were narrower in the textured samples compared to those in the untextured samples. Crack initiation and propagation were also simulated using the Griffith fracture criterion. The grain boundary to surface energy ratios required for computations were estimated using AFM groove measurements.

  20. Modeling of Irradiation Hardening of Polycrystalline Materials

    SciTech Connect

    Li, Dongsheng; Zbib, Hussein M.; Garmestani, Hamid; Sun, Xin; Khaleel, Mohammad A.

    2011-09-14

    High energy particle irradiation of structural polycrystalline materials usually produces irradiation hardening and embrittlement. The development of predict capability for the influence of irradiation on mechanical behavior is very important in materials design for next generation reactors. In this work a multiscale approach was implemented to predict irradiation hardening of body centered cubic (bcc) alpha-iron. The effect of defect density, texture and grain boundary was investigated. In the microscale, dislocation dynamics models were used to predict the critical resolved shear stress from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent model was applied to predict the irradiation hardening in samples with changes in texture and grain boundary. This multiscale modeling can guide performance evaluation of structural materials used in next generation nuclear reactors.

  1. Polycrystalline-thin-film thermophotovoltaic cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    1996-02-01

    Thermophotovoltaic (TPV) cells convert thermal energy to electricity. Modularity, portability, silent operation, absence of moving parts, reduced air pollution, rapid start-up, high power densities, potentially high conversion efficiencies, choice of a wide range of heat sources employing fossil fuels, biomass, and even solar radiation are key advantages of TPV cells in comparison with fuel cells, thermionic and thermoelectric convertors, and heat engines. The potential applications of TPV systems include: remote electricity supplies, transportation, co-generation, electric-grid independent appliances, and space, aerospace, and military power applications. The range of bandgaps for achieving high conversion efficiencies using low temperature (1000-2000 K) black-body or selective radiators is in the 0.5-0.75 eV range. Present high efficiency convertors are based on single crystalline materials such as In1-xGaxAs, GaSb, and Ga1-xInxSb. Several polycrystalline thin films such as Hg1-xCdxTe, Sn1-xCd2xTe2, and Pb1-xCdxTe, etc., have great potential for economic large-scale applications. A small fraction of the high concentration of charge carriers generated at high fluences effectively saturates the large density of defects in polycrystalline thin films. Photovoltaic conversion efficiencies of polycrystalline thin films and PV solar cells are comparable to single crystalline Si solar cells, e.g., 17.1% for CuIn1-xGaxSe2 and 15.8% for CdTe. The best recombination-state density Nt is in the range of 10-15-10-16 cm-3 acceptable for TPV applications. Higher efficiencies may be achieved because of the higher fluences, possibility of bandgap tailoring, and use of selective emitters such as rare earth oxides (erbia, holmia, yttria) and rare earth-yttrium aluminium garnets. As compared to higher bandgap semiconductors such as CdTe, it is easier to dope the lower bandgap semiconductors. TPV cell development can benefit from the more mature PV solar cell and opto

  2. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  3. Polycrystalline silicon ion sensitive field effect transistors

    NASA Astrophysics Data System (ADS)

    Yan, F.; Estrela, P.; Mo, Y.; Migliorato, P.; Maeda, H.; Inoue, S.; Shimoda, T.

    2005-01-01

    We report the operation of polycrystalline silicon ion sensitive field effect transistors. These devices can be fabricated on inexpensive disposable substrates such as glass or plastics and are, therefore, promising candidates for low cost single-use intelligent multisensors. In this work we have developed an extended gate structure with a Si3N4 sensing layer. Nearly ideal pH sensitivity (54mV /pH) and stable operation have been achieved. Temperature effects have been characterized. A penicillin sensor has been fabricated by functionalizing the sensing area with penicillinase. The sensitivity to penicillin G is about 10mV/mM, in solutions with concentration lower than the saturation value, which is about 7 mM.

  4. Polycrystalline Silicon ISFETs on Glass Substrate

    PubMed Central

    Yan, Feng; Estrela, Pedro; Mo, Yang; Migliorato, Piero; Maeda, Hiroshi

    2005-01-01

    The Ion Sensitive Field Effect Transistor (ISFET) operation based on polycrystalline silicon thin film transistors is reported. These devices can be fabricated on inexpensive disposable substrates such as glass or plastics and are, therefore, promising candidates for low cost single-use intelligent multisensors. In this work we have developed an extended gate structure with PE-CVD Si3N4 deposited on top of a conductor, which also provides the electrical connection to the remote TFT gate. Nearly ideal pH sensitivity (54 mV/pH) and stable operation have been achieved. Temperature effects have also been characterized. A penicillin sensor has been fabricated by functionalizing the sensing area with penicillinase. The shift increases almost linearly upon the increase of penicillin concentration until saturation is reached for ∼ 7 mM. Poly-Si TFT structures with a gold sensing area have been also successfully applied to field-effect detection of DNA.

  5. Dynamical electrophotoconductivity in polycrystalline thin films

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.

    1982-01-01

    Polycrystalline cadmium sulfide (CdS) films were deposited on lithium niobate (LiNbO3) substrates by vacuum evaporation and annealed to obtain high photosensitivity. The change in photoconductivity of these films due to the penetration of electric fields associated with elastic waves propagating on their substrates was demonstrated and studied. The relationship between the acoustic electric field and the induced change in film conductivity was found to be a nonlinear one. The fractional change in conductivity is strongly dependent on the light intensity and the film temperature, showing a prominent maximum as a function of these quantities. The largest recorded fractional change in conductivity was about 25% at electric fields of the order of 1,000 volts per centimeter. A phenomological model was developed based on the interaction between the space charge created by the electric field and the electron trapping states in the photoconductor.

  6. Investigation of polycrystalline ferroelectric tunnel junction

    NASA Astrophysics Data System (ADS)

    Hou, Pengfei; Wang, Jinbin; Zhong, Xiangli

    2016-07-01

    Ferroelectric tunnel junction (FTJ) is a breakthrough for addressing the nondestructive read in the ferroelectric random access memories. However, FTJs with nearly ideal characteristics have only been demonstrated on perovskite heterostructures that are deposited on closely lattice-matched and non-silicon substrates, or silicon substrates with epitaxial multilayer. In order to promote the application of FTJs, we develop a polycrystalline FTJ with ultrathin bottom electrode, in which the resistance variations exceed two orders of magnitude. And we achieve two stable logic states written and read easily using voltage pulses. Especially the device integrates with the silicon technology in modern microelectronics. Our results suggest new opportunities for ferroelectrics as nonvolatile resistive switching memory.

  7. Plastic deformation of polycrystalline zirconium carbide

    NASA Technical Reports Server (NTRS)

    Darolia, R.; Archbold, T. F.

    1976-01-01

    The compressive yield strength of arc-melted polycrystalline zirconium carbide has been found to vary from 77 kg per sq mm at 1200 C to 19 kg per sq mm at 1800 C. Yield drops were observed with plastic strain-rates greater than 0.003/sec but not with slower strain rates. Strain-rate change experiments yielded values for the strain-rate sensitivity parameter m which range from 6.5 at 1500 C to 3.8 at 1800 C, and the product dislocation velocity stress exponent times T was found to decrease linearly with increasing temperature. The deformation rate results are consistent with the Kelly-Rowcliffe model in which the diffusion of carbon assists the motion of dislocations.

  8. Helium Migration Mechanisms in Polycrystalline Uranium Dioxide

    SciTech Connect

    Martin, Guillaume; Desgardin, Pierre; Sauvage, Thierry; Barthe, Marie-France; Garcia, Philippe; Carlot, Gaelle

    2007-07-01

    This study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO{sub 2} sintered samples presenting different microstructures were implanted with {sup 3}He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the {sup 3}He(d,{alpha}){sup 1}H reaction. {sup 3}He release is measured in-situ during sample annealing at temperatures ranging between 700 deg. C and 1000 deg. C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900 deg. C in the vicinity of grain boundaries possibly as a result of the presence of defects. (authors)

  9. Direct growth of transparent conducting Nb-doped anatase TiO{sub 2} polycrystalline films on glass

    SciTech Connect

    Yamada, Naoomi; Kasai, Junpei; Hitosugi, Taro; Hoang, Ngoc Lam Huong; Nakao, Shoichiro; Hirose, Yasushi; Shimada, Toshihiro; Hasegawa, Tetsuya

    2009-06-15

    This paper proposes a novel sputter-based method for the direct growth of transparent conducting Ti{sub 1-x}Nb{sub x}O{sub 2} (TNO) polycrystalline films on glass, without the need for any postdeposition treatments, by the use of an initial seed-layer. Anatase TNO epitaxial films grown on LaAlO{sub 3} (100) substrates under a reducing atmosphere exhibited a low resistivity (rho) of (3-6)x10{sup -4} OMEGA cm. On glass, however, highly resistive rutile phase polycrystalline films (rhoapprox100 OMEGA cm) formed preferentially under the same conditions. These results suggest that epitaxial stabilization of the oxygen-deficient anatase phase occurs on lattice-matched substrates. To produce a similar effect on a glass surface, we deposited a seed-layer of anatase TNO with excellent crystallinity under an increased oxygen atmosphere. As a result, anatase phase TNO polycrystalline films could be grown even under heavily reducing atmospheres. An optimized film exhibited rho=1.1x10{sup -3} OMEGA cm and optical absorption lower than 10% in the visible region. This rho value is more than one order of magnitude lower than values reported for directly deposited TNO polycrystalline films. This indicates that the seed-layer method has considerable potential for producing transparent conducting TNO polycrystalline films on glass.

  10. 1000 to 1200 K time-dependent compressive deformation of single-crystalline and polycrystalline B2 Ni-40Al

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Noebe, R. D.; Kumar, K. S.; Mannan, S. K.; Cullers, C. L.

    1991-01-01

    The 1000-K and 1200-K time-dependent deformation of 100-line-oriented and non-100-line-oriented single crystals of Ni-40Al (made by a modified Bridgman technique) was examined over a large range of strain rates (from 0.1 to 10 to the -7th per sec). The results were compared with those for polycrystalline Ni-40Al made by hot pressing XD synthesized powder. The results from measurements of slow-plastic-strain-rate properties of the two materials show that single crystals offer no strength advantage over polycrystalline material. Both forms were found to deform via a dislocation climb mechanism.

  11. Redox potentials of tungsten and its alloying partners-fundamentals of tungsten determination by redox titration.

    PubMed

    Wünsch, G

    1980-08-01

    The fundamentals of tungsten determination by redox titration in hydrochloric acid medium are describe. Conditional redox potentials are given for W, Cr, V, Fe, Ti, Mo, Cu and Sn as a function of HCl concentration. The basic experimental conditions and the difference in conditional potentials required for consecutive titrations are discussed. Any mixture of tungsten with other metals can be analysed without separation if it does not contain both Cr and Ti or both Mo and V.

  12. Thermal cycling and high power density hydrogen ion beam irradiation of tungsten layers on tungsten substrate

    NASA Astrophysics Data System (ADS)

    Airapetov, A. A.; Begrambekov, L. B.; Gretskaya, I. Yu; Grunin, A. V.; Dyachenko, M. Yu; Puntakov, N. A.; Sadovskiy, Ya A.

    2016-09-01

    Tungsten layers with iron impurity were deposited on tungsten substrates modeling re-deposited layers in a fusion device. The samples were tested by thermocycling and hydrogen ion beam tests. Thermocycling revealed globule formation on the surface. The size of the globules depended on iron impurity content in the coating deposited. Pore formation was observed which in some cases lead to exfoliation of the coatings. Hydrogen ion irradiation lead to formation of blisters on the coating and finally its exfoliation.

  13. Spinarc gas tungsten arc torch holder

    NASA Technical Reports Server (NTRS)

    Brace, D. F.; Crockett, J. L.

    1970-01-01

    Semiautomatic welding torch enables operator to control arc length, torch angle, and spring tension when welding small diameter aluminum tubing. Tungsten is preset for the weld to make arc initiation easier and to eliminate searching for the joint through a dark welding lens.

  14. Gas tungsten arc welder with electrode grinder

    DOEpatents

    Christiansen, David W.; Brown, William F.

    1984-01-01

    A welder for automated closure of fuel pins by a gas tungsten arc process in which a rotating length of cladding is positioned adjacent a welding electrode in a sealed enclosure. An independently movable axial grinder is provided in the enclosure for refurbishing the used electrode between welds.

  15. Aminobisphenolate supported tungsten disulphido and dithiolene complexes.

    PubMed

    Salojärvi, E; Peuronen, A; Sillanpää, R; Damlin, P; Kivelä, H; Lehtonen, A

    2015-05-28

    Dioxotungsten(vi) complexes with tetradentate amino bisphenolates were converted into the corresponding Cs-symmetric amino bisphenolate disulphido complexes by a reaction with either Lawesson's reagent or P2S5. Further reaction with diethyl acetylenedicarboxylate leads to the formation of diamagnetic tungsten(iv) dithiolene compounds. The syntheses, crystal structures, spectroscopic and electrochemical characterization of such disulphido and dithiolene complexes are presented.

  16. Detonation in tungsten-loaded HMX

    SciTech Connect

    Goldstein, S.; Mader, C.L.

    1985-01-01

    The detonation behavior of X-0233, a heavily tungsten-loaded HMX explosive, has been studied using failure diameter measurements, plate dents, and aquarium tests. A model with features resembling those of a weak detonation describe the experimental results. 7 refs., 10 figs.

  17. Gas-driven permeation of deuterium through tungsten and tungsten alloys

    DOE PAGES

    Buchenauer, Dean A.; Karnesky, Richard A.; Fang, Zhigang Zak; Ren, Chai; Oya, Yasuhisa; Otsuka, Teppei; Yamauchi, Yuji; Whaley, Josh A.

    2016-03-25

    Here, to address the transport and trapping of hydrogen isotopes, several permeation experiments are being pursued at both Sandia National Laboratories (deuterium gas-driven permeation) and Idaho National Laboratories (tritium gas- and plasma-driven tritium permeation). These experiments are in part a collaboration between the US and Japan to study the performance of tungsten at divertor relevant temperatures (PHENIX). Here we report on the development of a high temperature (≤1150 °C) gas-driven permeation cell and initial measurements of deuterium permeation in several types of tungsten: high purity tungsten foil, ITER-grade tungsten (grains oriented through the membrane), and dispersoid-strengthened ultra-fine grain (UFG) tungstenmore » being developed in the US. Experiments were performed at 500–1000 °C and 0.1–1.0 atm D2 pressure. Permeation through ITER-grade tungsten was similar to earlier W experiments by Frauenfelder (1968–69) and Zaharakov (1973). Data from the UFG alloy indicates marginally higher permeability (< 10×) at lower temperatures, but the permeability converges to that of the ITER tungsten at 1000 °C. The permeation cell uses only ceramic and graphite materials in the hot zone to reduce the possibility for oxidation of the sample membrane. Sealing pressure is applied externally, thereby allowing for elevation of the temperature for brittle membranes above the ductile-to-brittle transition temperature.« less

  18. Method of making a cathode from tungsten and iridium powders using a strontium peroxide containing material as the impregnant

    SciTech Connect

    Branovich, L.E.; Freeman, G.L.; Smith, B.

    1988-11-25

    This invention relates in general to a method of making a long-life high-current-density cathode and in particular, to a method of making such a cathode from a mixture of tungsten and iridium powders using a strontium peroxide containing material as the impregnant. The general object of this invention is to provide an improved method of making a long life high current density cathode. A more specific object of the invention is to provide such a method in which lower temperatures can be used than were used in S.N. 204,327 for the impregnation of the tungsten-iridium billet. It has now been found that the aforementioned objects can be attained by a method that uses a strontium peroxide-containing material as the impregnant. More particularly, according to the invention, a suitable porous billet of tungsten, or tungsten-iridium, or tungsten-osmium or tungsten-rhodium is impregnated with a strontium peroxide containing material in a hydrogen atmosphere and slowly heated to above 215 C to decompose the strontium peroxide, SrO/sub 2/ to form strontium oxide, SrO, and oxygen, O/sub 2/.

  19. Ablation study of tungsten-based nuclear thermal rocket fuel

    NASA Astrophysics Data System (ADS)

    Smith, Tabitha Elizabeth Rose

    The research described in this thesis has been performed in order to support the materials research and development efforts of NASA Marshall Space Flight Center (MSFC), of Tungsten-based Nuclear Thermal Rocket (NTR) fuel. The NTR was developed to a point of flight readiness nearly six decades ago and has been undergoing gradual modification and upgrading since then. Due to the simplicity in design of the NTR, and also in the modernization of the materials fabrication processes of nuclear fuel since the 1960's, the fuel of the NTR has been upgraded continuously. Tungsten-based fuel is of great interest to the NTR community, seeking to determine its advantages over the Carbide-based fuel of the previous NTR programs. The materials development and fabrication process contains failure testing, which is currently being conducted at MSFC in the form of heating the material externally and internally to replicate operation within the nuclear reactor of the NTR, such as with hot gas and RF coils. In order to expand on these efforts, experiments and computational studies of Tungsten and a Tungsten Zirconium Oxide sample provided by NASA have been conducted for this dissertation within a plasma arc-jet, meant to induce ablation on the material. Mathematical analysis was also conducted, for purposes of verifying experiments and making predictions. The computational method utilizes Anisimov's kinetic method of plasma ablation, including a thermal conduction parameter from the Chapman Enskog expansion of the Maxwell Boltzmann equations, and has been modified to include a tangential velocity component. Experimental data matches that of the computational data, in which plasma ablation at an angle shows nearly half the ablation of plasma ablation at no angle. Fuel failure analysis of two NASA samples post-testing was conducted, and suggestions have been made for future materials fabrication processes. These studies, including the computational kinetic model at an angle and the

  20. Microscopic and spectroscopic analysis of tungsten trioxide and titanium-doped tungsten trioxide thin films

    NASA Astrophysics Data System (ADS)

    Yun, Young Taek

    Tungsten oxide (WO3) has been a subject of high interest for its unique properties, and recently for its importance in different types of industrial applications which ranges from non-emissive displays, optical, microelectronic, catalytic/photocatalytic, humidity, temperature, gas, and biosensor devices. In this study, WO3 and Ti doped thin films were prepared using radio frequency magnetron reactive sputtering at different substrate temperatures ranging from room temperature to 500 °C in increments of 100 °C. After forming a hypothesis based on knowledge of established WO3 properties, we attempt in this work to investigate how the doping influences the roughness and the mean grain size of the nanoparticles on the surface layer of the thin films, its structure, and crystallinity. Therefore we pursued analysis by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy, using a comparative approach. The outcomes of these analyses demonstrate that higher temperatures are necessary for growing crystalline material if doping is used. Also, smaller nanoparticles are obtained when a small amount of dopant, e.g. 5% Ti, is incorporated. Both XRD and Raman measurement indicate morphological changes of the doped material. Finally, annealing of the amorphous doped samples at temperatures of 600 °C and 900 °C did not contribute significantly to material properties improvement.

  1. Electrokinetic treatment of firing ranges containing tungsten-contaminated soils.

    PubMed

    Braida, Washington; Christodoulatos, Christos; Ogundipe, Adebayo; Dermatas, Dimitris; O'Connor, Gregory

    2007-11-19

    Tungsten-based alloys and composites are being used and new formulations are being considered for use in the manufacturing of different types of ammunition. The use of tungsten heavy alloys (WHA) in new munitions systems and tungsten composites in small caliber ammunition could potentially release substantial amounts of this element into the environment. Although tungsten is widely used in industrial and military applications, tungsten's potential environmental and health impacts have not been thoroughly addressed. This necessitates the research and development of remedial technologies to contain and/or remove tungsten from soils that may serve as a source for water contamination. The current work investigates the feasibility of using electrokinetics for the remediation of tungsten-contaminated soils in the presence of other heavy metals of concern such as Cu and Pb with aim to removing W from the soil while stabilizing in situ, Pb and Cu. PMID:17686582

  2. Nucleation and growth of damage in polycrystalline aluminum under dynamic tensile loading

    SciTech Connect

    Qi, M. L.; Yao, Y.; Ran, X. X.; Ye, W.; Bie, B. X.; Fan, D.; Li, P.

    2015-03-15

    Plate-impact experiments were conducted to study the features and mechanisms of void nucleation and growth in the polycrystalline of pure aluminum under dynamic loading. Soft-recovered samples have been analyzed by metallographic microscopy, electron back scattering diffraction (EBSD), and synchrotron radiation x-ray tomography technology. It was found that most of the void nucleation in grains neared the boundaries of “weak-orientation” grains and grew toward the grain boundaries with fractured small grains around the boundaries. This was mainly caused by the accumulation and interaction of slip systems in the “weak-orientation” grains. In addition, the micro voids were nearly octahedron because the octahedral slip systems were formed by 8 slip planes in the polycrystalline of pure aluminum. The EBSD results are consistent with the three-dimensional structure observed by synchrotron radiation x-ray.

  3. Low-chromium reduced-activation chromium-tungsten steels

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.; Maziasz, P.J.

    1996-10-01

    Bainitic microstructures formed during continuous cooling can differ from classical upper and lower bainite formed during isothermal transformation. Two types of non-classical bainite were observed depending on the cooling rate: carbide-free acicular bainite at rapid cooling rates and granular bainite at slower cooling rates. The Charpy impact toughness of the acicular ferrite was found to be considerably better than for the granular bainite. It was postulated that alloying to improve the hardenability of the steel would promote the formation of acicular bainite, just as increasing the cooling rate does. To test this, chromium and tungsten were added to the 2 1/4Cr-2W and 2 1/4Cr-2WV steel compositions to increase their hardenability, and the microstructures and mechanical properties were examined.

  4. Characterization of tungsten films and their hydrogen permeability

    SciTech Connect

    Nemanič, Vincenc Kovač, Janez; Lungu, Cristian; Porosnicu, Corneliu; Zajec, Bojan

    2014-11-01

    Prediction of tritium migration and its retention within fusion reactors is uncertain due to a significant role of the structural disorder that is formed on the surface layer after plasma exposure. Tungsten films deposited by any of the suitable methods are always disordered and contain a high density of hydrogen traps. Experiments on such films with hydrogen isotopes present a suitable complementary method, which improves the picture of the hydrogen interaction with fusion relevant materials. The authors report on the morphology, composition, and structure of tungsten films deposited by the thermionic vacuum arc method on highly permeable Eurofer substrates. Subsequently, hydrogen permeation studies through these films were carried out in a wide pressure range from 20 to 1000 mbars at 400 °C. The final value of the permeation coefficient for four samples after 24 h at 400 °C was between P = 3.2 × 10{sup −14} mol H{sub 2}/(m s Pa{sup 0.5}) and P = 1.1 × 10{sup −15} mol H{sub 2}/(m s Pa{sup 0.5}). From the time evolution of the permeation flux, it was shown that diffusivity was responsible for the difference in the steady fluxes, as solubility was roughly the same. This is confirmed by XRD data taken on these samples.

  5. Failure mechanisms of polycrystalline diamond compact drill bits in geothermal environments

    SciTech Connect

    Hoover, E.R.; Pope, L.E.

    1981-09-01

    Over the past few years the interest in polycrystalline diamond compact (PDC) drill bits has grown proportionately with their successful use in drilling oil and gas wells in the North Sea and the United States. This keen interest led to a research program at Sandia to develop PDC drill bits suitable for the severe drilling conditions encountered in geothermal fields. Recently, three different PDC drill bits were tested using either air or mud drilling fluids: one in the laboratory with hot air, one in the Geysers field with air, and one in the Geysers field with mud. All three tests were unsuccessful due to failure of the braze joint used to attach the PDC drill blanks to the tungsten carbide studs. A post-mortem failure analysis of the defective cutters identified three major failure mechanisms: peripheral nonbonding caused by braze oxidation during the brazing step, nonbonding between PDC drill blanks and the braze due to contamination prior to brazing, and hot shortness. No evidence was found to suggest that the braze failures in the Geysers field tests were caused by frictional heating. In addition, inspection of the PDC/stud cutter assemblies using ultrasonic techniques was found to be ineffective for detecting the presence of hot shortness in the braze joint.

  6. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2013-06-01

    This National Center for Photovoltaics sheet describes the capabilities of its polycrystalline thin-film research in the area of cadmium telluride. The scope and core competencies and capabilities are discussed.

  7. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet that includes scope, core competencies and capabilities, and contact/web information for Polycrystalline Thin-Film Research: Cadmium Telluride at the National Center for Photovoltaics.

  8. Polycrystalline silicon semiconducting material by nuclear transmutation doping

    DOEpatents

    Cleland, John W.; Westbrook, Russell D.; Wood, Richard F.; Young, Rosa T.

    1978-01-01

    A NTD semiconductor material comprising polycrystalline silicon having a mean grain size less than 1000 microns and containing phosphorus dispersed uniformly throughout the silicon rather than at the grain boundaries.

  9. Polishing of dental porcelain by polycrystalline diamond.

    PubMed

    Nakamura, Yoshiharu; Sato, Hideaki; Ohtsuka, Masaki; Hojo, Satoru

    2010-01-01

    Polycrystalline diamond (PCD) exhibits excellent abrasive characteristics and is commonly used as loose grains for precision machining of hard ceramics and other materials that are difficult to grind and polish. In the present study, we investigated using bonded PCD for polishing dental porcelain, for which a lustrous surface is difficult to obtain by polishing. We compared the surface texture and characteristics of dental porcelain after polishing with bonded PCD with that obtained using bonded monocrystalline diamond (MCD), which is commonly used for this purpose. Polishing was performed at various pressures and rotational speeds on a custom-built polishing apparatus using bonded PCD or MCD with grain sizes of 3.92 μm on specimens consisting of VITA Omega 900 dentin porcelain after firing and then glazing to a specified surface roughness. The surface roughness of the polished porcelain and the abrasion quantity in terms of its polishing depth were measured, and its surface texture and characteristics were investigated. At low polishing pressures, PCD yielded a finer polished surface than MCD. The polishing depth after polishing for 20-30 min was approximately 2-3 μm with PCD and 1-2 μm with MCD. The polished surface was more uniform and smooth with PCD than with MCD.

  10. Nonlinear alternating current conduction in polycrystalline manganites

    NASA Astrophysics Data System (ADS)

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-01

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1-x -yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1-xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc˜Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent xf.

  11. Relaxation Mechanisms in Hyperpolarized Polycrystalline ^129Xe

    NASA Astrophysics Data System (ADS)

    Samuelson, G.; Su, T.; Saam, B.

    2002-10-01

    Through spin exchange with optically polarized Rb vapor, it is possible to achieve upwards of 30% nuclear spin polarization in ^129Xe and a corresponding NMR signal some 5 orders of magnitude stronger than typical thermally polarized ^129Xe. Due to such a strong signal, hyperpolarized ^129Xe is being used for several leading-edge technologies (eg. biochemical spectroscopy, MRI, and polarization transfer). We have measured the nuclear spin relaxation rate of polycrystalline hyperpolarized ^129Xe at 77K (well below the freezing point of 160K) in a magnetic field of only a few Gauss and have observed that the hyperpolarization completely survives the freezing process. Furthermore, in this regime we have observed non-exponential spin relaxation that depends strongly on magnetic field, isotopic concentration (between ^129Xe and ^131Xe) and differences in crystallite formation. We present a simple spin-diffusion model that fits and explains the features of the data. Our results agree with the hypothesis that at low fields and temperatures the dominant spin relaxation mechanism is cross-relaxation with ^131Xe on the surface of the crystallites (Gatzke, et al., PRL b70, 690 (1993)).

  12. Texture and Anisotropy of Polycrystalline Piezoelectics

    SciTech Connect

    Jones,J.; Iverson, B.; Bowman, K.

    2007-01-01

    Piezoelectricity is manifested in ferroelectric ceramics by inducing a preferred volume fraction of one ferroelectric domain variant orientation at the expense of degenerate orientations. The piezoelectric effect is therefore largely controlled by the effectiveness of the electrical poling in producing a bias in ferroelectric (180{sup o}) and ferroelastic (non-180{sup o}) domain orientations. Further enhancement of the piezoelectric effect in bulk ceramics can be accomplished by inducing preferred orientation through grain-orientation processes such as hot forging or tape casting that precede the electrical-poling process. Coupled crystal orientation and domain orientation processing yields ceramics with an even greater piezoelectric response. In this paper, preferred orientations of domains and grains in polycrystalline piezoelectric ceramics generated through both domain- and grain-orientation processing are characterized through pole figures and orientation distribution functions obtained using data from a variety of diffraction techniques. The processing methods used to produce these materials and the methods used to evaluate preferred orientation and texture are described and discussed in the context of prior research. Different sample and crystal symmetries are explored across a range of commercial and laboratory-prepared materials. Some of the variables presented in this work include the effects of in situ thermal depoling and the detailed processing parameters used in tape casting of materials with preferred crystallite orientations. Preferred orientation is also correlated with anisotropic properties, demonstrating a clear influence of both grain and domain orientations on piezoelectricity.

  13. Amorphous silicon/polycrystalline thin film solar cells

    SciTech Connect

    Ullal, H.S.

    1991-03-13

    An improved photovoltaic solar cell is described including a p-type amorphous silicon layer, intrinsic amorphous silicon, and an n-type polycrystalline semiconductor such as cadmium sulfide, cadmium zinc sulfide, zinc selenide, gallium phosphide, and gallium nitride. The polycrystalline semiconductor has an energy bandgap greater than that of the amorphous silicon. The solar cell can be provided as a single-junction device or a multijunction device.

  14. Thermophotovoltaic Cells on Zinc Diffused Polycrystalline GaSb

    SciTech Connect

    Sulima, O.V.; Bett, A.W.; Dutta, P.S.; Ehsani, H.; Gutmann, R.J.

    2000-05-01

    For the first time, it has been demonstrated that thermophotovoltaic cells made of polycrystalline GaSb with small grain sizes (down to 100 x 100 {micro}m) have similar characteristics to the best Zinc diffused single crystal GaSb cells with identified device parameters. The grain boundaries in polycrystalline GaSb do not degrade TPV cell parameters, indicating that such material can be used for high-efficiency thermophotovoltaic cells.

  15. Physical properties optimization of polycrystalline LiFeAs

    NASA Astrophysics Data System (ADS)

    Singh, Shiv J.; Gräfe, Uwe; Beck, Robert; Wolter, Anja U. B.; Grafe, Hans-Joachim; Hess, Christian; Wurmehl, Sabine; Büchner, Bernd

    2016-10-01

    We present a study of parameter optimization for synthesizing truly stoichiometric polycrystalline LiFeAs. Stoichiometric LiFeAs has been prepared in a very broad range of synthesis temperature (200-900 °C) under otherwise exactly the same conditions, and has been characterized by structural, magnetic, transport, nuclear quadrupole resonance (NQR), and specific heat measurements. Our study showed that the LiFeAs phase is formed at 200 °C with a large amount of impurity phases. The amount of these impurity phases reduces with increasing synthesis temperature and the clean LiFeAs phase is obtained at a synthesis temperature of 600 °C. Magnetic susceptibility and resistivity measurements confirmed that the superconducting properties such as the critical temperature Tc, and the upper critical field Hc2 do not depend on the synthesis temperature (≤ 700 °C), remaining at almost the same value of ∼19 K and ∼40 T, respectively. However, the width ΔTc of the transition and the NQR line width decrease with increasing the synthesis temperature and reached to minimum value for the synthesis temperature of 600 °C. Our careful analysis suggests that the best sample obtained at 600 °C is optimal concerning the low resistivity, high residual resistivity ratio (RRR), low ΔTc, high Tc and Hc2, and a small NQR line width with values which are comparable to that reported for LiFeAs single crystals. Specific heat measurements confirmed the bulk superconducting nature of the samples. The Hc2 value estimated from the specific heat is consistent with that of the resistivity measurements. Concisely, 600 °C synthesis temperature yields optimal high quality polycrystalline LiFeAs bulk samples. Further improvement of the quality of the sample prepared at 600 °C could be obtained by a controlled slow cooling process. Microstructural analysis reveals that the abundance of micro-cracks becomes strongly reduced by the slow cooling process, resulting in an increase in clean and

  16. Platinum-induced structural collapse in layered oxide polycrystalline films

    SciTech Connect

    Wang, Jianlin; Liu, Changhui; Huang, Haoliang; Fu, Zhengping; Peng, Ranran E-mail: yllu@ustc.edu.cn; Zhai, Xiaofang; Lu, Yalin E-mail: yllu@ustc.edu.cn

    2015-03-30

    Effect of a platinum bottom electrode on the SrBi{sub 5}Fe{sub 1−x}Co{sub x}Ti{sub 4}O{sub 18} layered oxide polycrystalline films was systematically studied. The doped cobalt ions react with the platinum to form a secondary phase of PtCoO{sub 2}, which has a typical Delafossite structure with a weak antiferromagnetism and an exceptionally high in-plane electrical conductivity. Formation of PtCoO{sub 2} at the interface partially consumes the cobalt dopant and leads to the structural collapsing from 5 to 4 layers, which was confirmed by X-ray diffraction and high resolution transmission electron microscopy measurements. Considering the weak magnetic contribution from PtCoO{sub 2}, the observed ferromagnetism should be intrinsic of the Aurivillius compounds. Ferroelectric properties were also indicated by the piezoresponse force microscopy. In this work, the platinum induced secondary phase at the interface was observed, which has a strong impact on Aurivillius structural configuration and thus the ferromagnetic and ferroelectric properties.

  17. On failure in polycrystalline and amorphous brittle materials

    NASA Astrophysics Data System (ADS)

    Bourne, Neil

    2009-06-01

    The response of brittle materials to uniaxial compressive shock loading is still not well understood. Describing the physical mechanisms resulting from the more complex triaxial states that result from impact and penetration is thus empirical. The physical interpretation of the yield point of brittle materials in one-dimensional strain (the Hugoniot elastic limit (HEL)), the rate dependence of this threshold, the form of stress histories and the effect of polycrystalline microstructure still remain to be comprehensively explained. However, evidence of failure occurring in glasses and ceramics behind a travelling front that follows a shock front has been accumulated and verified in several laboratories. Such a boundary has been called a failure front. The variations in properties across this front include complete loss of tensile strength, partial loss of shear strength, reduction in acoustic impedance, lowered sound speed and opacity to light. It is the object of this work to collect observations of these phenomena and their relation to failure and the HEL in brittle materials. Further, to relate these uniaxial strain measurements of their failed states to the depth of penetration (DoP) in the widely conducted test. British Crown Copyright MoD/2009.

  18. A new series of bis(ene-1,2-dithiolato)tungsten(IV), -(V), -(VI) complexes as reaction centre models of tungsten enzymes: preparation, crystal structures and spectroscopic properties.

    PubMed

    Sugimoto, Hideki; Hatakeda, Kohei; Toyota, Kazuo; Tatemoto, Susumu; Kubo, Minoru; Ogura, Takashi; Itoh, Shinobu

    2013-03-01

    The carbomethoxy substituted dithiolene ligand (L(COOMe)) enabled us to develop a series of new bis(ene-1,2-dithiolato)tungsten complexes including W(IV)O, W(IV)(OSiBuPh(2)), W(VI)O(2), W(VI)O(OSiBuPh(2)) and W(VI)O(S) core structures. By using these tungsten complexes, a systematic study of the terminal monodentate ligand effects has been performed on the structural, spectroscopic properties and reactivity. The structure and spectroscopic properties of the tungsten complexes have also been compared to those of the molybdenum complexes coordinated by the same ligand to investigate the effects of the metal ion (W vs. Mo). X-ray crystallographic analyses of the tungsten(IV) complexes have revealed that the tungsten centres adopt a distorted square pyramidal geometry with a dithiolene ligand having an ene-1,2-dithiolate form. On the other hand, the dioxotungsten(VI) complex exhibits an octahedral structure consisting of the bidentate L(COOMe) and two oxo groups, in which π-delocalization was observed between the W(VI)O(2) and ene-1,2-dithiolate units. The tungsten(IV) and dioxotungsten(VI) complexes are isostructural with the molybdenum counter parts. DFT calculation study of the W(VI)O(S) complex has indicated that the W=S bond of 2.2 Å is close to the bond length between the tungsten centre and ambiguously assigned terminal monodentate atom in aldehyde oxidoreductase of the tungsten enzyme. Resonance Raman (rR) spectrum of the W(VI)O(S) complex has shown the two inequivalent L(COOMe) ligands with respect to their bonding interactions with the tungsten centre, reproducing the appearance of two ν(C=C) stretches in the rR spectrum of aldehyde oxidoreductase. Sulfur atom transfer reaction from the W(VI)O(S) complex to triphenylphosphines has also been studied kinetically to demonstrate that the tungsten complex has a lower reactivity by about one-order of magnitude, when compared with its molybdenum counterpart.

  19. Atomistically derived cohesive zone model of intergranular fracture in polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Guin, Laurent; Raphanel, Jean L.; Kysar, Jeffrey W.

    2016-06-01

    Pristine single crystal graphene is the strongest known two-dimensional material, and its nonlinear anisotropic mechanical properties are well understood from the atomic length scale up to a continuum description. However, experiments indicate that grain boundaries in the polycrystalline form reduce the mechanical behavior of polycrystalline graphene. Herein, we perform atomistic-scale molecular dynamics simulations of the deformation and fracture of graphene grain boundaries and express the results as continuum cohesive zone models (CZMs) that embed notions of the grain boundary ultimate strength and fracture toughness. To facilitate energy balance, we employ a new methodology that simulates a quasi-static controlled crack propagation which renders the kinetic energy contribution to the total energy negligible. We verify good agreement between Griffith's critical energy release rate and the work of separation of the CZM, and we note that the energy of crack edges and fracture toughness differs by about 35%, which is attributed to the phenomenon of bond trapping. This justifies the implementation of the CZM within the context of the finite element method (FEM). To enhance computational efficiency in the FEM implementation, we discuss the use of scaled traction-separation laws (TSLs) for larger element sizes. As a final result, we have established that the failure characteristics of pristine graphene and high tilt angle bicrystals differ by less than 10%. This result suggests that one could use a unique or a few typical TSLs as a good approximation for the CZMs associated with the mechanical simulations of the polycrystalline graphene.

  20. Deformation and fracture of single-crystal and sintered polycrystalline silicon carbide produced by cavitation

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Hattori, Shuji; Okada, Tsunenori; Buckley, Donald H.

    1989-01-01

    An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 microns. The results of the investigation indicate that the SiC (0001) surface could be deformed in a plastic manner during cavitation. Dislocation etch pits were formed when the surface was chemically etched. The number of defects, including dislocations in SiC (0001) surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC.

  1. Deformation and fracture of single-crystal and sintered polycrystalline silicon carbide produced by cavitation

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Hattori, Shuji; Okada, Tsunenori; Buckley, Donald H.

    1987-01-01

    An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 microns. The results of the investigation indicate that the SiC (0001) surface could be deformed in a plastic manner during cavitation. Dislocation etch pits were formed when the surface was chemically etched. The number of defects, including dislocations in the SiC (0001) surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC.

  2. Bend ductility of tungsten heavy alloys

    SciTech Connect

    Gurwell, W.E.; Garnich, M.R.; Dudder, G.B.; Lavender, C.A.

    1992-11-01

    A bend ductility test is used to indicate the formability of tungsten heavy alloys sheet. The primary test bends a notchless Charpy impact specimen to a bend angle of approximately 100C. This can be augmented by a bend-completion test. Finite element modeling as well as strain-gaged bend specimens elucidate the strain distribution in the specimen as a function of material thickness and bend angle. The bend ductilities of 70%W, 807.W and 90%W alloys are characterized. As expected, decreasing thickness or tungsten content enhances bend ductility. Oxidation is not detrimental; therefore, controlled atmosphere is not required for cooling. The potentially detrimental effects of mechanical working (e.g., rolling, roller-leveling, grit blasting, and peening) and machining (e.g., cutting and sanding) are illustrated.

  3. Femtosecond fiber laser additive manufacturing of tungsten

    NASA Astrophysics Data System (ADS)

    Bai, Shuang; Liu, Jian; Yang, Pei; Zhai, Meiyu; Huang, Huan; Yang, Lih-Mei

    2016-04-01

    Additive manufacturing (AM) is promising to produce complex shaped components, including metals and alloys, to meet requirements from different industries such as aerospace, defense and biomedicines. Current laser AM uses CW lasers and very few publications have been reported for using pulsed lasers (esp. ultrafast lasers). In this paper, additive manufacturing of Tungsten materials is investigated by using femtosecond (fs) fiber lasers. Various processing conditions are studied, which leads to desired characteristics in terms of morphology, porosity, hardness, microstructural and mechanical properties of the processed components. Fully dense Tungsten part with refined grain and increased hardness was obtained and compared with parts made with different pulse widths and CW laser. The results are evidenced that the fs laser based AM provides more dimensions to modify mechanical properties with controlled heating, rapid melting and cooling rates compared with a CW or long pulsed laser. This can greatly benefit to the make of complicated structures and materials that could not be achieved before.

  4. Ultrasonic ranking of toughness of tungsten carbide

    NASA Technical Reports Server (NTRS)

    Vary, A.; Hull, D. R.

    1983-01-01

    The feasibility of using ultrasonic attenuation measurements to rank tungsten carbide alloys according to their fracture toughness was demonstrated. Six samples of cobalt-cemented tungsten carbide (WC-Co) were examined. These varied in cobalt content from approximately 2 to 16 weight percent. The toughness generally increased with increasing cobalt content. Toughness was first determined by the Palmqvist and short rod fracture toughness tests. Subsequently, ultrasonic attenuation measurements were correlated with both these mechanical test methods. It is shown that there is a strong increase in ultrasonic attenuation corresponding to increased toughness of the WC-Co alloys. A correlation between attenuation and toughness exists for a wide range of ultrasonic frequencies. However, the best correlation for the WC-Co alloys occurs when the attenuation coefficient measured in the vicinity of 100 megahertz is compared with toughness as determined by the Palmqvist technique.

  5. Computational studies of tungsten-catalyzed endo-selective cycloisomerization of 4-pentyn-1-ol.

    PubMed

    Sheng, Yinghong; Musaev, Djamaladdin G; Reddy, K Subba; McDonald, Frank E; Morokuma, Keiji

    2002-04-17

    Endo- and exo-cycloisomerizations of 4-pentyn-1-ol have been studied computationally with density functional theory, in conjunction with double-zeta and triple-zeta basis sets, both in the absence and in the presence of tungsten carbonyl catalyst. In the absence of the catalyst, both endo- and exo-cycloisomerizations have been calculated to have a very high activation barrier of approximately 50-55 kcal/mol and cannot take place. With tungsten pentacarbonyl catalyst, endo-cycloisomerization becomes a complex multiple-step reaction and proceeds with a rate-determining barrier of 26 kcal/mol at the C(alpha) --> C(beta) hydride migration step to form a vinylidene intermediate. The primary role of the tungsten catalyst is to stabilize the vinylidene intermediate, thus lowering the rate-determining barrier. The second important role of the tungsten catalyst in endo-cycloisomerization is to assist the OH hydride migration to C(alpha) by making it a multistep process with small activation barriers. The exo-cycloisomerization with the catalyst still has a high rate-determining barrier of 47 kcal/mol. These findings clearly explain the experimentally observed endo-selectivity in the cycloisomerization of 4-pentyn-1-ol derivatives and support the experimentally proposed mechanism.

  6. Sputtering and Reflection Data for Mixed Tungsten/Beryllium Layers Under Typical FIRE Divertor Fluxes

    NASA Astrophysics Data System (ADS)

    Ruzic, D. N.; Nieto, M.; Alman, D. A.; Brooks, J. N.

    2001-10-01

    Computer modeling has been done as part of the Fusion Ignition Research Experiment (FIRE) design study. The current focus is on beryllium/tungsten mixed-material erosion. The FIRE design calls for a beryllium first wall and tungsten divertors. Beryllium can be sputtered from the first wall and transported to the divertor, forming a Be/W mixture on the divertor. The beryllium sputtering from the first wall is obtained from fluxes calculated by the DEGAS2 neutral transport code. Subsequent transport to the divertor is calculated by the REDEP code. VFTRIM-3D, a variant of the TRIM-SP binary-collision code, is used to investigate the sputtering properties of the Be/W divertor. Finally, WBC can compute beryllium and tungsten erosion and core plasma contamination using the sputtering and reflection coefficients obtained with VFTRIM-3D. In the present work, the VFTRIM-3D code was run on a W/Be surface with the Be content varied from 0 to 100 atomic percent. Deuterium and tritium (ions and neutrals), oxygen, beryllium from the first wall, and tungsten being redeposited are all incident on this mixed W/Be layer. Data on reflection and sputtering coefficients as a function of beryllium content in the bombarded surface will be presented.

  7. The tungsten divertor experiment at ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Neu, R.; Asmussen, K.; Krieger, K.; Thoma, A.; Bosch, H.-S.; Deschka, S.; Dux, R.; Engelhardt, W.; García-Rosales, C.; Gruber, O.; Herrmann, A.; Kallenbach, A.; Kaufmann, M.; Mertens, V.; Ryter, F.; Rohde, V.; Roth, J.; Sokoll, M.; Stäbler, A.; Suttrop, W.; Weinlich, M.; Zohm, H.; Alexander, M.; Becker, G.; Behler, K.; Behringer, K.; Behrisch, R.; Bergmann, A.; Bessenrodt-Weberpals, M.; Brambilla, M.; Brinkschulte, H.; Büchl, K.; Carlson, A.; Chodura, R.; Coster, D.; Cupido, L.; de Blank, H. J.; de Peña Hempel, S.; Drube, R.; Fahrbach, H.-U.; Feist, J.-H.; Feneberg, W.; Fiedler, S.; Franzen, P.; Fuchs, J. C.; Fußmann, G.; Gafert, J.; Gehre, O.; Gernhardt, J.; Haas, G.; Herppich, G.; Herrmann, W.; Hirsch, S.; Hoek, M.; Hoenen, F.; Hofmeister, F.; Hohenöcker, H.; Jacobi, D.; Junker, W.; Kardaun, O.; Kass, T.; Kollotzek, H.; Köppendörfer, W.; Kurzan, B.; Lackner, K.; Lang, P. T.; Lang, R. S.; Laux, M.; Lengyel, L. L.; Leuterer, F.; Manso, M. E.; Maraschek, M.; Mast, K.-F.; McCarthy, P.; Meisel, D.; Merkel, R.; Müller, H. W.; Münich, M.; Murmann, H.; Napiontek, B.; Neu, G.; Neuhauser, J.; Niethammer, M.; Noterdaeme, J.-M.; Pasch, E.; Pautasso, G.; Peeters, A. G.; Pereverzev, G.; Pitcher, C. S.; Poschenrieder, W.; Raupp, G.; Reinmüller, K.; Riedl, R.; Röhr, H.; Salzmann, H.; Sandmann, W.; Schilling, H.-B.; Schlögl, D.; Schneider, H.; Schneider, R.; Schneider, W.; Schramm, G.; Schweinzer, J.; Scott, B. D.; Seidel, U.; Serra, F.; Speth, E.; Silva, A.; Steuer, K.-H.; Stober, J.; Streibl, B.; Treutterer, W.; Troppmann, M.; Tsois, N.; Ulrich, M.; Varela, P.; Verbeek, H.; Verplancke, Ph; Vollmer, O.; Wedler, H.; Wenzel, U.; Wesner, F.; Wolf, R.; Wunderlich, R.; Zasche, D.; Zehetbauer, T.; Zehrfeld, H.-P.

    1996-12-01

    Tungsten-coated tiles, manufactured by plasma spray on graphite, were mounted in the divertor of the ASDEX Upgrade tokamak and cover almost 90% of the surface facing the plasma in the strike zone. Over 600 plasma discharges have been performed to date, around 300 of which were auxiliary heated with heating powers up to 10 MW. The production of tungsten in the divertor was monitored by a W I line at 400.8 nm. In the plasma centre an array of spectral lines at 5 nm emitted by ionization states around W XXX was measured. From the intensity of these lines the W content was derived. Under normal discharge conditions W-concentrations around 0741-3335/38/12A/013/img12 or even lower were found. The influence on the main plasma parameters was found to be negligible. The maximum concentrations observed decrease with increasing heating power. In several low power discharges accumulation of tungsten occurred and the temperature profile was flattened. The concentrations of the intrinsic impurities carbon and oxygen were comparable to the discharges with the graphite divertor. Furthermore, the density and the 0741-3335/38/12A/013/img13 limits remained unchanged and no negative influence on the energy confinement or on the H-mode threshold was found. Discharges with neon radiative cooling showed the same behaviour as in the graphite divertor case.

  8. Tungsten-uranium penetrator target interaction

    SciTech Connect

    Dunn, P S; Damkroger, B K

    1994-10-01

    Several studies performed in recent years have been directed at determining the penetration mechanism of long rod kinetic energy penetrators into Rolled Homogeneous Armor (RHA). Much of the work has centered on comparing U-0.75Ti and Tungsten Heavy Alloys (WHA), with the goal being to relate the superior ballistic performance of the uranium materials to a fundamental difference in penetration mechanisms. This has been found to be true, with the dominant mechanisms being adiabatic shear in U-0.75Ti and bulk deformation in WHA. Recent work has sought to achieve improvements in the ballistic performance of the tungsten materials via both mechanical property improvements and alloy modifications designed to bring about adiabatic shear. As an alternative, the authors propose the consideration of materials which utilize mechanisms other than bulk deformation and adiabatic shear to optimize ballistic performance. This paper will present the postmortem analysis of a uranium-20 vol% tungsten composite penetrator fired into RHA at 0{degrees} obliquity. The analysis shows that the penetration mechanism in this material is bulk heating and extensive co-melting of the target and penetrator at the penetration interface. The results of the analysis will then be compared to a similar analysis made of targets into which U-0.75Ti penetrators had been fired.

  9. Surface response of tungsten to helium and hydrogen plasma flux as a function of temperature and incident kinetic energy

    NASA Astrophysics Data System (ADS)

    Sukumar, Harikrishnan

    Tungsten is a leading candidate material for the diverter in future nuclear fusion reactors. Previous experiments have demonstrated that surface defects and bubbles form in tungsten when ex- posed to helium and hydrogen plasmas, even at modest ion energies. In some regimes, between 1000K and 2000K, and for He energies below 100eV, "fuzz" like features form. The mechanisms leading to these surfaces comprised of nanometer sized tungsten tendrils which include visible helium bubbles are not currently known. The role of helium bubble formation in tendril morphology could very likely be the starting point of these mechanisms. Using Molecular dynamics (MD) simulations, the role of helium and hydrogen exposure in the initial formation mechanisms of tungsten "fuzz" are investigated. Molecular dynamics simulations are well suited to describe the time and length scales associated with initial formation of helium clusters that eventually grow to nano-meter sized helium bubbles. MD simulations also easily enable the modeling of a variety of surfaces such as single crystals, grain boundaries or "tendrils". While the sputtering yield of tungsten is generally low, previous observations of surface modification due to plasma exposure raise questions about the effects of surface morphology and sub-surface helium bubble populations on the sputtering behavior. Results of computational molecular dynamics are reported that investigate the influence of sub-surface helium bubble distributions on the sputtering yield of tungsten (100) and (110) surfaces induced by helium ion exposure in the range of 300 eV to 1 keV. The calculated sputtering yields are in reasonable agreement with a wide range of experimental data; but do not show any significant variation as a result of the pre-existing helium bubbles. Molecular dynamics simulations reveal a number of sub-surface mechanisms leading to nanometer- sized "fuzz" in tungsten exposed to low-energy helium plasmas. We find that during the bubble

  10. Nonlinear alternating current conduction in polycrystalline manganites

    SciTech Connect

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-28

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La{sub 1−x−y}Y{sub y}Ca{sub x}MnO{sub 3} with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn{sub 1−x}Fe{sub x}O{sub 3} with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ{sub 0} by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ{sub 0} up to a certain frequency, known as the onset frequency f{sub c} and increases from Σ{sub 0} as frequency is increased from f{sub c}. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. f{sub c} scales with Σ{sub 0} as f{sub c}∼Σ{sub 0}{sup x{sub f}}, where x{sub f} is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that x{sub f} is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent x{sub f}.

  11. Reactive sintering of tungsten-doped high strength ZrB{sub 2}–SiC porous ceramics using metastable precursors

    SciTech Connect

    Zhao, Bin; Jiang, Yanshan; Yang, Biyun; Wang, Tingyu; Hu, Yongzhen; Sun, Dongfeng; Li, Ruixing; Yin, Shu; Li, Junping; Feng, Zhihai; Sato, Tsugio

    2014-03-01

    Graphical abstract: - Highlights: • Tungsten-doped porous ZrB{sub 2}–SiC specimens were fabricated by reactive sintering. • Both sintering and mechanical properties were improved by doping with tungsten. • Optimum concentration to obtain high mechanical properties was W/Zr (mol) = 0.05. • Sintering might be promoted by self-accelerated diffusion. • Mechanical properties might be improved by solid solution strengthening. - Abstract: Tungsten-doped porous ZrB{sub 2}-20 vol.% SiC specimens with a high strength skeleton were fabricated by reactive sintering using metastable reactants, i.e., as-synthesized amorphous hydrous ZrO{sub 2}–WO{sub 3}/ZrO{sub 2}, amorphous boron, nanocarbon, and β-SiC. Doping with tungsten clearly promoted sintering and improved mechanical properties; the optimum tungsten concentration to obtain high mechanical properties was investigated. A single-phase solid solution (Zr,W)B{sub 2} was formed in the specimens with tungsten. We suggest that sintering was promoted by self-accelerated diffusion owing to the formation of point defects caused by doping with tungsten. The improvement of mechanical properties could be attributed to solid solution strengthening.

  12. Dynamic SEM wear studies of tungsten carbide cermets

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Buckley, D. H.

    1975-01-01

    Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined. Etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the WC and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation. The wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

  13. Study for identification of beneficial Uses of Space (BUS). Volume 2: Technical report. Book 3: Development and business analysis of space processed tungsten fox X-ray targets

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The development plans, analysis of required R and D and production resources, the costs of such resources, and finally, the potential profitability of a commercial space processing opportunity for containerless melting and resolidification of tungsten are discussed. The aim is to obtain a form of tungsten which, when fabricated into targets for X-ray tubes, provides at least, a 50 percent increase in service life.

  14. Toxicologic evaluation of tungsten: 28-day inhalation study of tungsten blue oxide in rats.

    PubMed

    Rajendran, Narayanan; Hu, Shu-Chieh; Sullivan, Dennis; Muzzio, Miguel; Detrisac, Carol J; Venezia, Carmen

    2012-12-01

    The toxicity and toxicokinetics of tungsten blue oxide (TBO) were examined. TBO is an intermediate in the production of tungsten powder, and has shown the potential to cause cellular damage in in vitro studies. However, in vivo evidence seems to indicate a lack of adverse effects. The present study was undertaken to address the dearth of longer-term inhalation toxicity studies of tungsten oxides by investigating the biological responses induced by TBO when administered via nose-only inhalation to rats at levels of 0.08, 0.325, and 0.65 mg TBO/L of air for 6 h/day for 28 consecutive days, followed by a 14-day recovery period. Inhaled TBO was absorbed systemically and blood levels of tungsten increased as inhaled concentration increased. Among the tissues analyzed for tungsten levels, lung, femur and kidney showed increased levels, with lung at least an order of magnitude greater than kidney or femur. By exposure day 14, tungsten concentration in tissues had reached steady-state. Increased lung weight was noted for both terminal and recovery animals and was attributed to deposition of TBO in the lungs, inducing a macrophage influx. Microscopic evaluation of tissues revealed a dose-related increase in alveolar pigmented macrophages, alveolar foreign material and individual alveolar foamy macrophages in lung. After a recovery period there was a slight reduction in the incidence and severity of histopathological findings. Based on the absence of other adverse effects, the increased lung weights and the microscopic findings were interpreted as nonadverse response to exposure and were not considered a specific reaction to TBO.

  15. 40 CFR 421.310 - Applicability: Description of the secondary tungsten and cobalt subcategory.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... or tungsten carbide scrap raw materials. ... secondary tungsten and cobalt subcategory. 421.310 Section 421.310 Protection of Environment ENVIRONMENTAL... CATEGORY Secondary Tungsten and Cobalt Subcategory § 421.310 Applicability: Description of the...

  16. 40 CFR 421.310 - Applicability: Description of the secondary tungsten and cobalt subcategory.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... or tungsten carbide scrap raw materials. ... secondary tungsten and cobalt subcategory. 421.310 Section 421.310 Protection of Environment ENVIRONMENTAL... CATEGORY Secondary Tungsten and Cobalt Subcategory § 421.310 Applicability: Description of the...

  17. Boron carbide coating deposition on tungsten and testing of tungsten layers and coating under intense plasma load

    SciTech Connect

    Airapetov, A. A.; Begrambekov, L. B.; Buzhinskiy, O. I.; Grunin, A. V.; Gordeev, A. A.; Zakharov, A. M.; Kalachev, A. M.; Sadovskiy, Ya. A.; Shigin, P. A.

    2015-12-15

    A device intended for boron carbide coating deposition and material testing under high heat loads is presented. A boron carbide coating 5 μm thick was deposited on the tungsten substrate. These samples were subjected to thermocycling loads in the temperature range of 400–1500°C. Tungsten layers deposited on tungsten substrates were tested in similar conditions. Results of the surface analysis are presented.

  18. Boron carbide coating deposition on tungsten and testing of tungsten layers and coating under intense plasma load

    NASA Astrophysics Data System (ADS)

    Airapetov, A. A.; Begrambekov, L. B.; Buzhinskiy, O. I.; Grunin, A. V.; Gordeev, A. A.; Zakharov, A. M.; Kalachev, A. M.; Sadovskiy, Ya. A.; Shigin, P. A.

    2015-12-01

    A device intended for boron carbide coating deposition and material testing under high heat loads is presented. A boron carbide coating 5 μm thick was deposited on the tungsten substrate. These samples were subjected to thermocycling loads in the temperature range of 400-1500°C. Tungsten layers deposited on tungsten substrates were tested in similar conditions. Results of the surface analysis are presented.

  19. Laser-assisted oxidation of multi-layer tungsten diselenide nanosheets

    NASA Astrophysics Data System (ADS)

    Tan, C.; Liu, Y.; Chou, H.; Kim, J.-S.; Wu, D.; Akinwande, D.; Lai, K.

    2016-02-01

    We report the structural and electrical characterization of tungsten oxides formed by illuminating multi-layer tungsten diselenide (WSe2) nanosheets with an intense laser beam in the ambient environment. A noninvasive microwave impedance microscope (MIM) was used to perform electrical imaging of the samples. The local conductivity ˜102 S/m of the oxidized product, measured by the MIM and conventional transport experiments, is much higher than that of the pristine WSe2, suggesting the formation of sub-stoichiometric WO3-x polycrystals with n-type carriers. With further efforts to improve the conductivity of the oxides, the laser-assisted oxidation process may be useful for patterning conductive features on WSe2 or forming electrical contacts to various transition metal dichalcogenides.

  20. Influence of process parameters on properties of reactively sputtered tungsten nitride thin films

    SciTech Connect

    Addonizio, Maria L.; Castaldo, Anna; Antonaia, Alessandro; Gambale, Emilia; Iemmo, Laura

    2012-05-15

    Tungsten nitride (WN{sub x}) thin films were produced by reactive dc magnetron sputtering of tungsten in an Ar-N{sub 2} gas mixture. The influence of the deposition power on the properties of tungsten nitride has been analyzed and compared with that induced by nitrogen content variation in the sputtering gas. A combined analysis of structural, electrical and optical properties on thin WN{sub x} films obtained at different deposition conditions has been performed. It was found that at an N{sub 2} content of 14% a single phase structure of W{sub 2}N films was formed with the highest crystalline content. This sputtering gas composition was subsequently used for fabricating films at different deposition powers. Optical analysis showed that increasing the deposition power created tungsten nitride films with a more metallic character, which is confirmed with resistivity measurements. At low sputtering powers the resulting films were crystalline whereas, with an increase of power, an amorphous phase was also present. The incorporation of an excess of nitrogen atoms resulted in an expansion of the W{sub 2}N lattice and this effect was more pronounced at low deposition powers. Infrared analysis revealed that in WN{sub x} films deposited at low power, chemisorbed N{sub 2} molecules did not behave as ligands whereas at high deposition power they clearly appeared as ligands around metallic tungsten. In this study, the influence of the most meaningful deposition parameters on the phase transformation reaction path was established and deposition conditions suitable for producing thermally stable and highly crystalline W{sub 2}N films were found.

  1. Polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, B. N.; Birkmire, R. W.; Phillips, J. E.; Shafarman, W. N.; Hegedus, S. S.; McCandless, B. E.

    1991-11-01

    Results and conclusions of Phase 1 of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe2 and CdTe solar cells. The kinetics of the formation of CuInSe2 by selenization with hydrogen selenide was investigated and a CuInSe2/Cds solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe2 films and a cell efficiency of 7 percent. Detailed investigations of the open circuit voltage of CuInSe2 solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe2 thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe2 is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10 percent can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm(exp 2) are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  2. Polycrystalline Garnet Porphyroblasts, an EBSD Study

    NASA Astrophysics Data System (ADS)

    Seaton, N. C.; Whitney, D. L.; Anderson, C.; Alpert, A.

    2008-12-01

    Polycrystalline garnet porphyroblasts (PGP's) are significant because their formation provides information about metamorphic crystalline mechanisms, in particular during early stages of crystal growth, which may differ from those governing later stages; and because their existence may affect the chemical and structural evolution of metamorphic rocks. For example, the extent of element exchange between the garnet interior and the matrix may be affected by the presence of grain boundaries within PGP's. There have been several previous studies of PGP's but important questions about them remain; e.g. whether early coalescence is a common method by which garnets crystallize, whether grains rotate during growth to attain an energetically favorable grain-grain contact, and whether deformation and/or precursor minerals or other chemical or mechanical heterogeneities influence the formation of PGP's. PGP's have been detected by us in several different localities including; micaschist from SE Vermont (USA), including locality S35j of Rosenfeld (1968); the Solitude Range (British Columbia, Canada); the Southern Menderes Massif (Turkey); and three zones (garnet, staurolite, kyanite) from the Dutchess County Barrovian sequence in NY (USA). We have identified two types of PGP: cryptic and morphologically distinct. Cryptic PGP have no obvious morphological expression of the high angle boundaries within them and appear to be a single crystal. Morphologically distinct PGP have an obvious depression in the outer grain boundary where it is intersected by the internal grain boundary. Most PGP's contain inclusion trails and the high angle grain boundaries crosscut the trend of these as well as the inclusions themselves. PGP also show major element growth zoning that is not influenced by the internal grain boundaries except in rare cases. PGP's comprise ~ 5-35% of the garnet populations analyzed. More than 95% of the PGP's we have analyzed are comprised of 2-3 domains; the rest contain

  3. Investigation of M1 transitions of the ground-state configuration of In-like tungsten

    NASA Astrophysics Data System (ADS)

    Li, W.; Xiao, J.; Shi, Z.; Fei, Z.; Zhao, R.; Brage, T.; Huldt, S.; Hutton, R.; Zou, Y.

    2016-05-01

    Three visible lines of M1 transitions from In-like tungsten were recorded using the Shanghai Permanent Magnet Electron Beam Ion Trap. The experimental wavelengths were measured as 493.84 ± 0.15, 226.97 ± 0.13 and 587.63 ± 0.23 nm (vacuum wavelengths). These results are in good agreement with theoretical predictions obtained using the large-scale relativistic many-body perturbation theory, in the form of the flexible atomic code.

  4. Equation of state for tungsten over a wide range of densities and internal energies

    NASA Astrophysics Data System (ADS)

    Khishchenko, K. V.

    2015-11-01

    A caloric model, which describes the pressure-density-internal-energy relationship in a broad region of condensed-phase states, is applied for tungsten. As distinct from previously known caloric equations of state for this material, a new form of the cold-compression curve at T = 0 K is used. Thermodynamic characteristics along the cold curve and shock Hugoniots are calculated for the metal and compared with some theoretical results and experimental data available at high energy densities.

  5. Systematic study of polycrystalline flow during tension test of sheet 304 austenitic stainless steel at room temperature

    NASA Astrophysics Data System (ADS)

    Muñoz-Andrade, Juan D.

    2013-12-01

    By systematic study the mapping of polycrystalline flow of sheet 304 austenitic stainless steel (ASS) during tension test at constant crosshead velocity at room temperature was obtained. The main results establish that the trajectory of crystals in the polycrystalline spatially extended system (PCSES), during irreversible deformation process obey a hyperbolic motion. Where, the ratio between the expansion velocity of the field and the velocity of the field source is not constant and the field lines of such trajectory of crystals become curved, this accelerated motion is called a hyperbolic motion. Such behavior is assisted by dislocations dynamics and self-accommodation process between crystals in the PCSES. Furthermore, by applying the quantum mechanics and relativistic model proposed by Muñoz-Andrade, the activation energy for polycrystalline flow during the tension test of 304 ASS was calculated for each instant in a global form. In conclusion was established that the mapping of the polycrystalline flow is fundamental to describe in an integral way the phenomenology and mechanics of irreversible deformation processes.

  6. Systematic study of polycrystalline flow during tension test of sheet 304 austenitic stainless steel at room temperature

    SciTech Connect

    Muñoz-Andrade, Juan D.

    2013-12-16

    By systematic study the mapping of polycrystalline flow of sheet 304 austenitic stainless steel (ASS) during tension test at constant crosshead velocity at room temperature was obtained. The main results establish that the trajectory of crystals in the polycrystalline spatially extended system (PCSES), during irreversible deformation process obey a hyperbolic motion. Where, the ratio between the expansion velocity of the field and the velocity of the field source is not constant and the field lines of such trajectory of crystals become curved, this accelerated motion is called a hyperbolic motion. Such behavior is assisted by dislocations dynamics and self-accommodation process between crystals in the PCSES. Furthermore, by applying the quantum mechanics and relativistic model proposed by Muñoz-Andrade, the activation energy for polycrystalline flow during the tension test of 304 ASS was calculated for each instant in a global form. In conclusion was established that the mapping of the polycrystalline flow is fundamental to describe in an integral way the phenomenology and mechanics of irreversible deformation processes.

  7. Conflict minerals from the Democratic Republic of the Congo: global tungsten processing plants, a critical part of the tungsten supply chain

    USGS Publications Warehouse

    Bermúdez-Lugo, Omayra

    2014-01-01

    The U.S. Geological Survey (USGS) analyzes supply chains to identify and define major components of mineral and material flows from ore extraction, through intermediate forms, to a final product. Two major reasons necessitate these analyses: (1) to identify risks associated with the supply of critical and strategic minerals to the United States and (2) to provide greater supply chain transparency so that policymakers have the information necessary to ensure domestic legislation compliance. This fact sheet focuses on the latter. The USGS National Minerals Information Center has been asked by governmental and non-governmental organizations to provide information on tin, tantalum, tungsten, and gold (collectively known as “3TG minerals”) processing facilities worldwide in response to U.S. legislation aimed at removing the link between the trade in these minerals and civil unrest in the Democratic Republic of the Congo. Post beneficiation processing plants (smelters and refineries) of 3TG mineral ores and concentrates were identified by company and industry association representatives as being the link in the 3TG mineral supply chain through which these minerals can be traced to their source of origin (mine); determining the point of origin is critical to establishing a transparent conflict mineral supply chain. This fact sheet, the first in a series of 3TG mineral fact sheets, focuses on the tungsten supply chain by listing plants that consume tungsten concentrates to produce ammonium paratungstate and ferrotungsten worldwide.

  8. Solid-state chemistry route for supported tungsten and tungsten carbide nanoparticles

    SciTech Connect

    Hugot, N.; Desforges, A.; Fontana, S.; Mareche, J.F.; Herold, C.; Albiniak, A.

    2012-10-15

    Nanoparticles of tungsten and tungsten carbide have been prepared using solid-state chemistry methods. After the vapor phase impregnation of a tungsten hexachloride precursor on a carbon support, a temperature-programmed reduction/carburization was performed. Several parameters were investigated and the evolution of obtained samples was followed by XRD and TEM. The optimization of the reaction parameters led to the preparation of W, W{sub 2}C and WC particles well dispersed on the support. WC phase however could not be obtained alone with less than 10 nm mean size. This could be explained by the carburization mechanism and the carbon diffusion on the support. - Graphical abstract: Bright field picture of carbon-supported WC nanoparticles dispersed on the surface of the sample 1223 K in 10% CH{sub 4}/90% H{sub 2}. Highlights: Black-Right-Pointing-Pointer We aimed at the preparation of supported nanoparticulate tungsten derivatives. Black-Right-Pointing-Pointer Several parameters were investigated. Black-Right-Pointing-Pointer The evolution of obtained samples was followed by XRD and TEM. Black-Right-Pointing-Pointer The optimal preparation led to W, W{sub 2}C and WC particles dispersed on the support.

  9. Effect of tungsten crystallographic orientation on He-ion-induced surface morphology changes

    SciTech Connect

    Parish, Chad M; Hijazi, Hussein Dib; Meyer III, Harry M; Meyer, Fred W

    2014-01-01

    In order to study the early stages of nanofuzz growth in fusion-plasma-facing tungsten, mirror-polished high-purity tungsten was exposed to 80 eV helium at 1130 C to a fluence of 4 1024 He/m2. The previously smooth surface shows morphology changes, and grains form one of four qualitatively different morphologies: smooth, wavy, pyramidal, or terraced/wide waves. Combining high-resolution scanning electron microscopy (SEM) observations to determine the morphology of each grain with quantitative measurement of the grain's orientation via electron backscatter diffraction (EBSD) in SEM shows that the normal-direction crystallographic orientation of the underlying grain controls the growth morphology. Specifically, near-<001> || normal direction (ND) grains formed pyramids, near-<114> to <112> || ND grains formed wavy and stepped structures, and near-<103> || ND grains remained smooth. Comparisons to control specimens indicate no changes to underlying bulk crystallographic texture, and the effects are attributed to surface energy anisotropy, although, surprisingly, the expected {101} low-energy planes were not the most stable. Future developments to control tungsten texture via thermomechanical processing, ideally obtaining a sharp near- <103> || ND processing texture, may delay the formation of nanofuzz.

  10. Thin Film Optical Coatings of Vanadium Oxide and Mixed Tungsten/Vanadium Oxide Deposited by APCVD Employing Precursors of Vanadyl Acetylacetonate and a Mixture with Tungsten Hexacarbonyl

    NASA Astrophysics Data System (ADS)

    Bodurov, Georgi; Ivanova, Tatyana; Abrashev, Miroslav; Nenova, Zoya; Gesheva, Kostadinka

    Thin films of transition metals oxides are studied and comparison is made for two types of mixed precursors, first containing only hexacarbonyls, and second containing tungsten hexacarbonyl and vanadyl acetylacetonate (Vanadium (III) acetylacetonate). The best electrochromic material is WO3, although when deposited by Atmospheric Pressure Chemical Vapour Deposition (APCVD) films of WO3 grow very slowly. In production stage, the growth-rate is very important factor for assuring a flow-through process. Our previous investigations showed that addition of a small fraction of lower temperature precursor such as Mo(CO)6, or V(CO)6, to the basic precursor of W(CO)6 result in higher growth rate of films. Our recent studies on mixed WxV1-xO3 showed excellent substrate coverage and high growth-rate. V(CO)6 is a lower thermally stable precursor that allows the first nuclei-islands to be formed on the hot substrates which further facilitate the tungsten oxide film deposition. However V(CO)6 is much too expensive for large-scale production, thus we adopted another compound as precursor - vanadium acetylacetonate, expecting eventual growth-rate increase. The paper describes optical properties of films of vanadium oxide grown in result of utilizing the acetylacetonate. Besides, the paper describes our attempt to deposit mixed films of tungsten/vanadium using a mixed precursor of vanadyl acetylacetonate and tungsten hexacarbonyl. To our knowledge this is a new mixed precursor based on largely used single precursors namely W(CO)6 and Vanadium acetylacetonate. Efforts were needed to adjust the mixed precursor ratio, keeping in mind the vapour pressures of the two chemicals at the deposition temperatures used. The paper presents the results for the visible transmittance and the film material modulation properties, studied by FTIR and Raman spectra. The dependence of the films optical behavior on APCVD process parameters, substrate temperatures, vapour source temperature

  11. Effect of copper impurity on polycrystalline silicon solar cells

    NASA Technical Reports Server (NTRS)

    Daud, T.; Koliwad, K. M.

    1978-01-01

    The presence of copper impurity, up to 10 to the 15th atoms/cc, in single crystal silicon has been shown to have no deleterious effect on the p-n junction solar cell performance. However, in polycrystalline silicon, copper atoms tend to migrate to the defect sites because of the structural sensitive properties of copper. This study was undertaken to investigate the influence of this behavior of copper impurity on the performance of p-n junction solar cells fabricated from structurally imperfect silicon. Two sets of polycrystalline silicon substrates containing copper were examined. In one set of samples, copper was incorporated during growth, whereas in the other, copper was diffused. Solar cells were fabricated on both the sets of substrates by a standard process. Dark and light I-V and spectral response characteristics of the cells were measured and compared with copper-free polycrystalline silicon solar cells. The results and the model are discussed.

  12. Concepts for interrelating ultrasnic attenuation, microstrucutre and fracture toughness in polycrystalline solids

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1986-01-01

    Conceptual models are advanced for explaining and predicting empirical correlations found between ultrasonic measurements and fracture toughness of polycrystalline solids. The models lead to insights concerning microstructural factors governing fracture processes and associated stress wave interactions. Analysis of the empirical correlations suggested by the models indicate that, in addition to grain size and shape, grain boundary reflections, elastic anisotropy, and dislocation damping are factors that underly both fracture toughness and ultrasonic attenuation. One outcome is that ultrasonic attenuation can predict the size of crack blunting or process zones that develop in the vicinity active cracks in metals. This forms a basis for ultrasonic ranking according to variations in fracture toughness.

  13. Changes in a surface of polycrystalline aluminum upon bombardment with argon ions

    NASA Astrophysics Data System (ADS)

    Ashkhotov, O. G.; Ashkhotova, I. B.; Bliev, A. P.; Magkoev, T. T.; Krymshokalova, D. A.

    2014-10-01

    The interaction between argon ions and a natural oxide layer of polycrystalline aluminum is studied via Auger electron (AE) and electron energy loss (EEL) spectroscopy. It is found that bombardment with argon ions whose energy is lower than the Al2O3 sputtering threshold results in the accumulation of bombarding ions in interstitial surface voids, thus forming a supersaturated solid solution of target atoms and bombarding ions of argon and nitrogen entrapped by the ion beam from the residual gas of the working chamber of the spectrometer.

  14. Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO

    NASA Technical Reports Server (NTRS)

    Drawdy, Jean E.; Hoflund, Gar B.; Davidson, Mark R.; Schryer, David R.

    1990-01-01

    Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.

  15. [60]Fullerene Displacement from (Dihapto-Buckminster-Fullerene) Pentacarbonyl Tungsten(0): An Experiment for the Inorganic Chemistry Laboratory, Part II

    ERIC Educational Resources Information Center

    Cortes-Figueroa, Jose E.; Moore-Russo, Deborah A.

    2006-01-01

    The kinetics experiments on the ligand-C[subscript 60] exchange reactions on (dihapto-[60]fullerene) pentacarbonyl tungsten(0), ([eta][superscript 2]-C[subscript 60])W(CO)[subscript 5], form an educational activity for the inorganic chemistry laboratory that promotes graphical thinking as well as the understanding of kinetics, mechanisms, and the…

  16. Xenon-Ion Drilling of Tungsten Films

    NASA Technical Reports Server (NTRS)

    Garner, C. E.

    1986-01-01

    High-velocity xenon ions used to drill holes of controlled size and distribution through tungsten layer that sheaths surface of controlled-porosity dispenser cathode of traveling wave-tube electron emitter. Controlled-porosity dispenser cathode employs barium/calcium/ aluminum oxide mixture that migrates through pores in cathode surface, thus coating it and reducing its work function. Rapid, precise drilling technique applied to films of other metals and used in other applications where micron-scale holes required. Method requires only few hours, as opposed to tens of hours by prior methods.

  17. Low temperature photoresponse of monolayer tungsten disulphide

    SciTech Connect

    Cao, Bingchen; Shen, Xiaonan; Shang, Jingzhi; Cong, Chunxiao; Yang, Weihuang; Eginligil, Mustafa E-mail: meginligil@ntu.edu.sg; Yu, Ting E-mail: meginligil@ntu.edu.sg

    2014-11-01

    High photoresponse can be achieved in monolayers of transition metal dichalcogenides. However, the response times are inconveniently limited by defects. Here, we report low temperature photoresponse of monolayer tungsten disulphide prepared by exfoliation and chemical vapour deposition (CVD) method. The exfoliated device exhibits n-type behaviour; while the CVD device exhibits intrinsic behaviour. In off state, the CVD device has four times larger ratio of photoresponse for laser on/off and photoresponse decay–rise times are 0.1 s (limited by our setup), while the exfoliated device has few seconds. These findings are discussed in terms of charge trapping and localization.

  18. Tungsten fiber reinforced superalloys: A status review

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Signorelli, R. A.

    1981-01-01

    Improved performance of heat engines is largely dependent upon maximum cycle temperatures. Tungsten fiber reinforced superalloys (TFRS) are the first of a family of high temperature composites that offer the potential for significantly raising hot component operating temperatures and thus leading to improved heat engine performance. This status review of TFRS research emphasizes the promising property data developed to date, the status of TFRS composite airfoil fabrication technology, and the areas requiring more attention to assure their applicability to hot section components of aircraft gas turbine engines.

  19. Tungsten imido catalysts for selective ethylene dimerisation.

    PubMed

    Wright, Christopher M R; Turner, Zoë R; Buffet, Jean-Charles; O'Hare, Dermot

    2016-02-14

    A tungsten imido complex W(NDipp)Me3Cl (Dipp = 2,6-(i)Pr-C6H3) is active for the selective dimerisation of ethylene to yield 1-butene under mild conditions. Immobilisation and activation of W(NDipp)Cl4(THF) on layered double hydroxides, silica or polymethylaluminoxane yields active solid state catalysts for the selective dimerisation of ethylene. The polymethylaluminoxane-based catalyst displays a turnover frequency (4.0 molC2H4 molW(-1) h(-1)) almost 7 times that of the homogeneous catalyst.

  20. Microstructure and tensile properties of tungsten at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Shen, Tielong; Dai, Yong; Lee, Yongjoong

    2016-01-01

    In order to support the development of the 5 MW spallation target for the European Spallation Source, the effect of fabrication process on microstructure, ductile-to-brittle transition temperature (DBTT), tensile and fracture behaviour of powder-metallurgy pure tungsten materials has been investigated. A hot-rolled (HR) tungsten piece of 12 mm thickness and a hot-forged (HF) piece of about 80 mm thickness were used to simulate the thin and thick blocks in the target. The two tungsten pieces were characterized with metallography analysis, hardness measurement and tensile testing. The HR piece exhibits an anisotropic grain structure with an average size of about 330 × 140 × 40 μm in rolling, long transverse and short transverse (thickness) directions. The HF piece possesses a bimodal grain structure with about 310 × 170 × 70 μm grain size in deformed part and about 25 μm sized grains remained from sintering process. Hardness (HV0.2) of the HR piece is slightly greater than that of the HF one. The ductility of the HR tungsten specimens is greater than that of the HF tungsten. For the HF tungsten piece, specimens with small grains in gauge section manifest lower ductility but higher strength. The DBTT evaluated from the tensile results is 250-300 °C for the HR tungsten and about 350 °C for the HF tungsten.

  1. Calibration and Temperature Profile of a Tungsten Filament Lamp

    ERIC Educational Resources Information Center

    de Izarra, Charles; Gitton, Jean-Michel

    2010-01-01

    The goal of this work proposed for undergraduate students and teachers is the calibration of a tungsten filament lamp from electric measurements that are both simple and precise, allowing to determine the temperature of tungsten filament as a function of the current intensity. This calibration procedure was first applied to a conventional filament…

  2. Gas Tungsten Arc Welding. Welding Module 6. Instructor's Guide.

    ERIC Educational Resources Information Center

    Missouri Univ., Columbia. Instructional Materials Lab.

    This guide is intended to assist vocational educators in teaching a three-unit module in gas tungsten arc welding. The module has been designed to be totally integrated with Missouri's Vocational Instruction Management System. The basic principles involved in gas tungsten arc welding, supplies, and applications are covered. The materials included…

  3. Measurement of the Properties of Tungsten at High Temperatures

    NASA Technical Reports Server (NTRS)

    Margrave, J. L.

    1985-01-01

    The thermophysical properties of tungsten and other materials were measured using containerless techniques. Levitation of liquid silver, gallium and tungsten were studied. The studies of liquid aluminum are almost complete and are expected to derive new, reliable properties for liquid aluminum.

  4. Mechanical wafer engineering for semitransparent polycrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Willeke, G.; Fath, P.

    1994-03-01

    A concept for the realization of semitransparent bifacially active highly efficient and light weight crystalline silicon solar cells is presented. The concept is based on the preparation of perpendicular V-grooves in silicon blanks by mechanical abrasion using a dicing saw and beveled blades. Holes of variable diameter are formed automatically in the processing step, which provide a connection between the passivated phosphorus doped front and back side emitters. A maximum bulk-emitter distance of ˜30 μm has been realized in 200 μm thick structures which should result in highly efficient solar cell devices even in small grain low quality polycrystalline material. The partial transparency of the presented solar cell structure opens the way for new applications (crystalline Si photovoltaic windows, etc.). The feasibility of the mechanical grooving process has been demonstrated on Wacker SILSO cast silicon. Double-side V-grooved structures (distance between grooves 90 and 140 μm, bevel angle 35°) with hole diameters in the range 10-70 μm, corresponding to a transmittance of up to 30% in the visible, have been prepared with excellent uniformity and mechanical stability over a large area (5×5 cm2). An average total reflectance in the range 500-1000 nm of Rav=0.9% has been measured on a structure with a geometrical hole fraction of 1.7% after growth of a 1170 Å thick layer of thermal oxide. This SILSO structure had an effective silicon thickness of 120 μm, whereas the absorptance spectrum near the band edge was similar to a 5.5 mm thick nongrooved silicon wafer, indicating the excellent light trapping obtained.

  5. MIS and SIS solar cells on polycrystalline silicon

    SciTech Connect

    Cheek, G.; Mertens, R.

    1980-02-01

    MIS and SIS structured solar cells are receiving much attention in the photovoltaic community. Seemingly, these cells could be a viable alternative to thermally diffused p-n junctions for use on thin-film polycrystalline silicon substrates. This review describes MIS/SIS structured solar cells and the possible advantages of these structures for use with thin-film polycrystalline silicon. The results of efficiency calculations are presented. Also addressed are lifetime stability and fabrication techniques amenable to large scale production. Finally, the relative advantages and disadvantages of these cells and the results obtained are presented.

  6. Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christian

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  7. Development of sensors on the basis of polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Obermeier, E.; Vonkienlin, F.; Hwang, H. J.

    1985-07-01

    Properties of polycrystalline silicon layers that are important for sensor applications were investigated. Layers were deposited from the gaseous phase through atmospheric pressure and low pressure chemical vaccuum deposition onto thermally oxidized single crystalline silicon wasfers; doping was carried out by ion implantation. Electrical properties, temperature behavior, and strain sensitivity were investigated. It is found that the temperature coefficients of polysilicon resistors can be determined within broad limits (negative, positive, zero) through selection of the doping. The layers are characterized by a relatively high piezoresistive effect. Based on experimental results, polysilicon thin film sensors (temperature, pressure, flow) were developed. These sensors clearly demonstrate the advantages of polycrystalline silicon layers as a sensor material.

  8. Effect of shear strength on Hugoniot-compression curve and the equation of state of tungsten (W)

    NASA Astrophysics Data System (ADS)

    Mashimo, Tsutomu; Liu, Xun; Kodama, Masao; Zaretsky, Eugene; Katayama, Masahide; Nagayama, Kunihiko

    2016-01-01

    The Hugoniot data for highly dense polycrystalline tungsten were obtained for pressures above 200 GPa, and the equation of state (EOS) was determined taking into account shear strength effects. For this study, we have made some improvements in measurement system and analyses of the shock wave data. Symmetric-impact Hugoniot measurements were performed using the high-time resolution streak camera system equipped on a one-stage powder gun and two-stage light gas gun, where the effects of tilting and bowing of flyer plate on the Hugoniot data were carefully considered. The shock velocity-particle velocity (US-UP) Hugoniot relation in the plastic regime was determined to be US = 4.137 + 1.242UP km/s (UP < 2 km/s). Ultrasonic and Velocity Interferometer System for Any Reflector measurements were also performed in this study. The zero-intercept value of the US-UP Hugoniot relation was found to be slightly larger than the ultrasonic bulk sound velocity (4.023 km/s). The hypothetical hydrostatic isothermal Us-Up Hugoniot curve, which corresponds to the hydrostatic isothermal compression curve derived from the Hugoniot data using the strength data, converged to the bulk sound velocity, clearly showing shear strength dependence in the Hugoniot data. The EOS for tungsten is derived from the hydrostatic isothermal compression curve using the strength data.

  9. Tungsten recycling in the United States in 2000

    USGS Publications Warehouse

    Shedd, Kim B.

    2011-01-01

    This report, which is one of a series of reports on metals recycling, defines and quantifies the flow of tungsten-bearing materials in the United States from imports and stock releases through consumption and disposition in 2000, with particular emphasis on the recycling of industrial scrap (new scrap) and used products (old scrap). Because of tungsten's many diverse uses, numerous types of scrap were available for recycling by a wide variety of processes. In 2000, an estimated 46 percent of U.S. tungsten supply was derived from scrap. The ratio of tungsten consumed from new scrap to that consumed from old scrap was estimated to be 20:80. Of all the tungsten in old scrap available for recycling, an estimated 66 percent was either consumed in the United States or exported to be recycled.

  10. Fluids Speciation in Deep Subduction Channels: Evidence From Polycrystalline Diamonds From UHPM Terranes

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, L.; Wirth, R.; Green, H. W.

    2011-12-01

    Geochemical characteristic of fluids circulating in deep subduction zones is of a great interest for many directions of geosciences. One of the intriguing processes is a fluid-rock interaction during subduction of the continental slab because the latter is characterized by contrast chemistry in comparison with the rocks of surrounding mantle and its fluids. Diamond due to its chemical inertness is the only mineral which contains "unchanged" fluid trapped during its crystallization at the peak of UHP metamorphism. Polycrystalline diamonds, that we have recently found within both the Kokchetav and the Earzgebirge UHPM terranes, represent an outstanding material to study geochemical diversity of the fluids circulating in deep subduction zones. Earlier studies of diamond monocrystals included in garnet, zircon, pyroxene and mica of the Kokchetav massif showed that the fluid responsible for diamond crystallization contains traces of both crustal and mantle components: Al, K, Ca, Mg, Fe, Si, Ti, V, Zn, Co, Fe F, Cl, S. The finding of polycrystalline diamonds in UHPM rocks of the Kokchetav and the Erzgebirge areas extends our knowledge related to UHP fluid composition. The polycrystalline diamonds consist of 5-15 single crystals of 0.3-5 micron size with a typical "zig-zag" grain boundaries and triangle voids filled with a C-O-H fluid with traces of Al, Co, F, V, Zn, Si, Cl, S, Ca, Mg, Fe, K in different combinations. Occurrences of "spider-like" dislocations, "zig-zag" boundaries, stacking faults and associated fluid pockets indicate presence of an internal stress accompanied diamond nucleation and growth from a fluid media. Observations of the carbonate (CaCO3) suggest an oxidizing environment of the fluids, close to the CCO buffer. Carbon isotopes speciation (delta 13C = -10 to -27 %) indicates organic carbon reservoir. Furthermore, studies by Sumino et al. (2011) showed that the Kokchetav diamonds, which are formed from organic carbon, are characterized by very high 3

  11. Corrosion and wear resistance of tungsten carbide-cobalt and tungsten carbide-cobalt-chromium thermal spray coatings

    SciTech Connect

    Quets, J.; Alford, J.R.

    1999-07-01

    Tungsten carbide thermal spray coatings provide wear surfaces to new and overhauled components for various industries. Their wear resistance is obtained by incorporating small tungsten carbide particles into a metal matrix. This presentation will show what parameters influence their corrosion resistance in the ASTM B-117 Salt Spray Corrosion Test,

  12. Clustering of H and He, and their effects on vacancy evolution in tungsten in a fusion environment

    NASA Astrophysics Data System (ADS)

    You, Yu-Wei; Li, Dongdong; Kong, Xiang-Shan; Wu, Xuebang; Liu, C. S.; Fang, Q. F.; Pan, B. C.; Chen, J. L.; Luo, G.-N.

    2014-10-01

    The behaviours of hydrogen and helium in tungsten are vitally important in fusion research because they can result in the degradation of the material. In the present work, we carry out density-functional theory calculations to investigate the clustering of hydrogen and helium atoms at interstitial sites, vacancy and small vacancy clusters (Vacm, m = 2, 3), and the influence of hydrogen and helium on vacancy evolution in tungsten. We find that hydrogen atoms are extremely difficult to aggregate at interstitial sites to form a stable cluster in tungsten. However, helium atoms are energetically favourable to cluster together in a close-packed arrangement between (1 1 0) planes forming helium monolayer structure, where the helium atoms are not perfectly in one plane. Both hydrogen and helium prefer to aggregate stably in vacancy and small vacancy cluster forming VacmXn (X = H, He). The concentrations of VacmHn (m = 1) clusters relative to temperature are evaluated through the law of mass action. The present calculations also show that the emission of a <1 1 1> dumbbell self-interstitial atom (SIA) from Hen to form VacHen and from VacHen to form Vac2Hen may take place for n > 5 and n > 9, respectively. According to the present results, we predict that a helium monolayer structure could nucleate for He atom platelet lying on (1 1 0) plane in tungsten, and the helium platelet formation on (1 1 0) plane in molybdenum observed by the experiment may be due to the initial monolayer arrangement of He atoms at interstitial sites. Meanwhile, our results contribute to the understanding for nucleation and the development of the voids and blisters in tungsten that are observed in the experiments.

  13. Tungsten tetraboride, an inexpensive superhard material

    PubMed Central

    Mohammadi, Reza; Lech, Andrew T.; Xie, Miao; Weaver, Beth E.; Yeung, Michael T.; Tolbert, Sarah H.; Kaner, Richard B.

    2011-01-01

    Tungsten tetraboride (WB4) is an interesting candidate as a less expensive member of the growing group of superhard transition metal borides. WB4 was successfully synthesized by arc melting from the elements. Characterization using powder X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) indicates that the as-synthesized material is phase pure. The zero-pressure bulk modulus, as measured by high-pressure X-ray diffraction for WB4, is 339 GPa. Mechanical testing using microindentation gives a Vickers hardness of 43.3 ± 2.9 GPa under an applied load of 0.49 N. Various ratios of rhenium were added to WB4 in an attempt to increase hardness. With the addition of 1 at.% Re, the Vickers hardness increased to approximately 50 GPa at 0.49 N. Powders of tungsten tetraboride with and without 1 at.% Re addition are thermally stable up to approximately 400 °C in air as measured by thermal gravimetric analysis. PMID:21690363

  14. Concentration dependent hydrogen diffusion in tungsten

    NASA Astrophysics Data System (ADS)

    Ahlgren, T.; Bukonte, L.

    2016-10-01

    The diffusion of hydrogen in tungsten is studied as a function of temperature, hydrogen concentration and pressure using Molecular Dynamics technique. A new analysis method to determine diffusion coefficients that accounts for the random oscillation of atoms around the equilibrium position is presented. The results indicate that the hydrogen migration barrier of 0.25 eV should be used instead of the presently recommended value of 0.39 eV. This conclusion is supported by both experiments and density functional theory calculations. Moreover, the migration volume at the saddle point for H in W is found to be positive: ΔVm ≈ 0.488 Å3, leading to a decrease in the diffusivity at high pressures. At high H concentrations, a dramatic reduction in the diffusion coefficient is observed, due to site blocking and the repulsive H-H interaction. The results of this study indicates that high flux hydrogen irradiation leads to much higher H concentrations in tungsten than expected.

  15. Dynamic compaction of tungsten carbide powder.

    SciTech Connect

    Gluth, Jeffrey Weston; Hall, Clint Allen; Vogler, Tracy John; Grady, Dennis Edward

    2005-04-01

    The shock compaction behavior of a tungsten carbide powder was investigated using a new experimental design for gas-gun experiments. This design allows the Hugoniot properties to be measured with reasonably good accuracy despite the inherent difficulties involved with distended powders. The experiments also provide the first reshock state for the compacted powder. Experiments were conducted at impact velocities of 245, 500, and 711 m/s. A steady shock wave was observed for some of the sample thicknesses, but the remainder were attenuated due to release from the back of the impactor or the edge of the sample. The shock velocity for the powder was found to be quite low, and the propagating shock waves were seen to be very dispersive. The Hugoniot density for the 711 m/s experiment was close to ambient crystal density for tungsten carbide, indicating nearly complete compaction. When compared with quasi-static compaction results for the same material, the dynamic compaction data is seen to be significantly stiffer for the regime over which they overlap. Based on these initial results, recommendations are made for improving the experimental technique and for future work to improve our understanding of powder compaction.

  16. Vaccum Gas Tungsten Arc Welding, phase 1

    NASA Technical Reports Server (NTRS)

    Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

    1995-01-01

    This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

  17. High temperature annealing of ion irradiated tungsten

    SciTech Connect

    Ferroni, Francesco; Yi, Xiaoou; Fitzgerald, Steven P.; Edmondson, Philip D.; Roberts, Steve G.

    2015-03-21

    In this study, transmission electron microscopy of high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications (500–1200°C). Bulk isochronal and isothermal annealing of ion irradiated pure tungsten (2 MeV W+ ions, 500°C, 1014 W+/cm2) with temperatures of 800, 950, 1100 and 1400°C, from 0.5 to 8 h, was followed by ex situ characterization of defect size, number density, Burgers vector and nature. Loops with diameters larger than 2–3 nm were considered for detailed analysis, among which all loops had View the MathML source and were predominantly of interstitial nature. In situ annealing experiments from 300 up to 1200°C were also carried out, including dynamic temperature ramp-ups. These confirmed an acceleration of loop loss above 900°C. At different temperatures within this range, dislocations exhibited behaviour such as initial isolated loop hopping followed by large-scale rearrangements into loop chains, coalescence and finally line–loop interactions and widespread absorption by free-surfaces at increasing temperatures. An activation energy for the annealing of dislocation length was obtained, finding Ea=1.34±0.2 eV for the 700–1100°C range.

  18. High temperature annealing of ion irradiated tungsten

    DOE PAGES

    Ferroni, Francesco; Yi, Xiaoou; Arakawa, Kazuto; Fitzgerald, Steven P.; Edmondson, Philip D.; Roberts, Steve G.

    2015-03-21

    In this study, transmission electron microscopy of high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications (500–1200°C). Bulk isochronal and isothermal annealing of ion irradiated pure tungsten (2 MeV W+ ions, 500°C, 1014 W+/cm2) with temperatures of 800, 950, 1100 and 1400°C, from 0.5 to 8 h, was followed by ex situ characterization of defect size, number density, Burgers vector and nature. Loops with diameters larger than 2–3 nm were considered for detailed analysis, among which all loops had View the MathML source andmore » were predominantly of interstitial nature. In situ annealing experiments from 300 up to 1200°C were also carried out, including dynamic temperature ramp-ups. These confirmed an acceleration of loop loss above 900°C. At different temperatures within this range, dislocations exhibited behaviour such as initial isolated loop hopping followed by large-scale rearrangements into loop chains, coalescence and finally line–loop interactions and widespread absorption by free-surfaces at increasing temperatures. An activation energy for the annealing of dislocation length was obtained, finding Ea=1.34±0.2 eV for the 700–1100°C range.« less

  19. Tungsten - Yttrium Based Nuclear Structural Materials

    NASA Astrophysics Data System (ADS)

    Ramana, Chintalapalle; Chessa, Jack; Martinenz, Gustavo

    2013-04-01

    The challenging problem currently facing the nuclear science community in this 21st century is design and development of novel structural materials, which will have an impact on the next-generation nuclear reactors. The materials available at present include reduced activation ferritic/martensitic steels, dispersion strengthened reduced activation ferritic steels, and vanadium- or tungsten-based alloys. These materials exhibit one or more specific problems, which are either intrinsic or caused by reactors. This work is focussed towards tungsten-yttrium (W-Y) based alloys and oxide ceramics, which can be utilized in nuclear applications. The goal is to derive a fundamental scientific understanding of W-Y-based materials. In collaboration with University of Califonia -- Davis, the project is designated to demonstrate the W-Y based alloys, ceramics and composites with enhanced physical, mechanical, thermo-chemical properties and higher radiation resistance. Efforts are focussed on understanding the microstructure, manipulating materials behavior under charged-particle and neutron irradiation, and create a knowledge database of defects, elemental diffusion/segregation, and defect trapping along grain boundaries and interfaces. Preliminary results will be discussed.

  20. A novel large-volume Kawai-type apparatus and its application to the synthesis of sintered bodies of nano-polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Irifune, Tetsuo; Isobe, Futoshi; Shinmei, Toru

    2014-03-01

    A Kawai-type multianvil apparatus operated in a 60 MN press has been constructed for materials synthesis at high pressure and temperature. After having tested various tungsten carbide anvils and optimization of the cell assembly for this novel apparatus, we are now able to perform synthesis experiments of high-pressure phases at temperatures to ∼2500 °C with relatively large sample volumes of about 2 cm3 in a pressure range up to about 16 GPa. Using this apparatus, synthesis of high-quality rods of sintered nano-polycrystalline diamond with dimensions to 1 cm in both diameter and length has been routinely made, which should be important as new anvil material for high-pressure mineral physics studies, as well as for some industrial applications.

  1. Encapsulation of carbides of chromium, molybdenum and tungsten in carbon nanocapsules by arc discharge

    NASA Astrophysics Data System (ADS)

    Saito, Yahachi; Matsumoto, Takehisa; Nishikubo, Keishi

    1997-02-01

    Encapsulation of Cr, Mo and W in multilayered graphitic cages by arc evaporation of metal/carbon composites under different pressures of helium gas (100, 600 and 1500 Torr) has been studied. Electron microscopy and X-ray diffraction of carbonaceous products revealed that encapsulated crystallites were carbides, i.e. Cr 7C 3 and Cr 3C 2 for Cr; Mo 2C, δ-MoC 1- x (NaCl type) and γ'-MoC (AsTi type) for Mo; W 2C and β-WC 1- x (NaCl type) for W. Effect of the pressure of helium gas on the formation of filled nanocapsules was markedly found for tungsten: Encapsulated tungsten carbides were formed at the highest pressure, but not in the lower pressures.

  2. Tungsten injector for scrape-off layer impurity transport experiments in the Tore Supra tokamak

    SciTech Connect

    Kočan, M.; Lunt, T.; Gunn, J. P.; Meyer, O.; Pascal, J.-Y.

    2013-07-15

    This paper describes the design and operation of a new tungsten (W) injection system for impurity transport experiments in the Tore Supra tokamak. The system is mounted on a reciprocating manipulator and injects a controlled amount of gaseous tungsten hexacarbonyl, W(CO){sub 6} at arbitrary depth in the scrape-off layer, using an inertially activated valve. Injected W(CO){sub 6} is dissociated in the plasma, forming a radially localized plume of W atoms. The injector does not require an external gas feed and can perform a large number of injections from an on-board reservoir of W(CO){sub 6}. Some examples of W injections in Tore Supra are included, demonstrating successful operation and discussing some technical issues of the injector prototype.

  3. Studies on growth and characterization of heterogeneous tungsten oxide nanostructures for photoelectrochemical and gas sensing applications

    NASA Astrophysics Data System (ADS)

    Senthilkumar, R.; Mahalingam, T.; Ravi, G.

    2016-01-01

    Tungsten oxide nanostructures were developed on indium tin oxide coated glass substrates by modified thermal evaporation process without using catalyst and vacuum. Depending on the substrate temperature and vapor concentration, different nanostructures like rod, sheet and pyramid were formed. Morphology, phase structure and crystallinity of the nanostructure films were characterized by Scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and HR-TEM. The samples were investigated under dark current and photocurrent and in H2SO4 aqueous solution as a function of applied potential. The saturated photocurrent density of tungsten oxide was found to be ≈14.4 μA cm-2. The films were also investigated as resistive gas sensor for ethanol gases (10-50 ppm) at room temperature. The response and recovery time were also determined.

  4. Preparation of silicate tungsten bronzes on aluminum by plasma electrolytic oxidation process in 12-tungstosilicic acid

    NASA Astrophysics Data System (ADS)

    Petković, M.; Stojadinović, S.; Vasilić, R.; Belča, I.; Nedić, Z.; Kasalica, B.; Mioč, U. B.

    2011-09-01

    The growth of silicate tungsten bronzes on aluminum by plasma electrolytic oxidation in 12-tungstosilicic acid is experimentally investigated and discussed. Real time imaging and optical emission spectroscopy characterization of plasma electrolytic oxidation show that spatial density of microdischarges is the highest in the early stage of the process, while the percentage of oxide coating area covered by active discharge sites decreases slowly with time. Emission spectrum of microdischarges has several intensive band peaks originating either from aluminum electrode or from the electrolyte. Surface roughness of obtained oxide coatings increases with prolonged time of plasma electrolytic oxidation, as their microhardness decreases. Raman spectroscopy and energy dispersive X-ray spectroscopy are employed to confirm that the outer layer of oxide coatings formed during the plasma electrolytic oxidation process is silicate tungsten bronze

  5. Dynamic SEM wear studies of tungsten carbide cermets. [friction and wear experiments

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Buckley, D. H.

    1975-01-01

    Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined, and etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the tungsten carbide (WC) and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation, and the wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation, and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

  6. Dynamic deuterium recycling on tungsten under carbon-deuterium implantation circumstance

    NASA Astrophysics Data System (ADS)

    Taguchi, Tomohisa; Kobayashi, Makoto; Kawasaki, Kiyotaka; Miyahara, Yuto; Ashikawa, Naoko; Sagara, Akio; Yoshida, Naoaki; Miyamoto, Mitsutaka; Ono, Kotaro; Hatano, Yuji; Oya, Yasuhisa; Okuno, Kenji

    2013-07-01

    Dynamics of deuterium recycling, including retention and sputtering behaviors was studied for C+ implanted tungsten. The amount of deuterium trapped by irradiation damages was clearly increased in the C+ implantation sample because the irradiation damages in the C+ implanted sample were formed more than those in the only D2+ implanted one. In addition, the deuterium diffusion toward the bulk would be refrained by the formation of W-C mixed layer, which would work as the deuterium diffusion barrier. The in situ sputtered particle measurement system has been established and revealed that the formation of hydrocarbons such as CD4 was directly observed during D2+ implantation into the C+ implanted tungsten. In the lower deuterium fluence, the CD4 sputtering rate was enhanced with increasing the deuterium fluence. It was considered that the sputtering rate of CD4 would be controlled by the concentration of deuterium on the top surface of the W-C mixed layer.

  7. Selective hydrodeoxygenation of cyclic vicinal diols to cyclic alcohols over tungsten oxide-palladium catalysts.

    PubMed

    Amada, Yasushi; Ota, Nobuhiko; Tamura, Masazumi; Nakagawa, Yoshinao; Tomishige, Keiichi

    2014-08-01

    Hydrodeoxygenation of cyclic vicinal diols such as 1,4-anhydroerythritol was conducted over catalysts containing both a noble metal and a group 5-7 transition-metal oxide. The combination of Pd and WOx allowed the removal of one of the two OH groups selectively. 3-Hydroxytetrahydrofuran was obtained from 1,4-anhydroerythritol in 72 and 74% yield over WOx -Pd/C and WOx -Pd/ZrO2 , respectively. The WOx -Pd/ZrO2 catalyst was reusable without significant loss of activity if the catalyst was calcined as a method of regeneration. Characterization of WOx -Pd/C with temperature-programmed reduction, X-ray diffraction, and transmission electron microscopy/energy-dispersive X-ray spectroscopy suggested that Pd metal particles approximately 9 nm in size were formed on amorphous tungsten oxide particles. A reaction mechanism was proposed on the basis of kinetics, reaction results with tungsten oxides under an atmosphere of Ar, and density functional theory calculations. A tetravalent tungsten center (W(IV) ) was formed by reduction of WO3 with the Pd catalyst and H2 , and this center served as the reductant for partial hydrodeoxygenation.

  8. Anomalous photoelectric effect of a polycrystalline topological insulator film.

    PubMed

    Zhang, Hongbin; Yao, Jiandong; Shao, Jianmei; Li, Hai; Li, Shuwei; Bao, Dinghua; Wang, Chengxin; Yang, Guowei

    2014-07-29

    A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi2Te3, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators.

  9. Raman Microscopic Characterization of Proton-Irradiated Polycrystalline Diamond Films

    NASA Technical Reports Server (NTRS)

    Newton, R. L.; Davidson, J. L.; Lance, M. J.

    2004-01-01

    The microstructural effects of irradiating polycrystalline diamond films with proton dosages ranging from 10(exp 15) to 10(exp 17) H(+) per square centimeter was examined. Scanning Electron Microscopy and Raman microscopy were used to examine the changes in the diamond crystalline lattice as a function of depth. Results indicate that the diamond lattice is retained, even at maximum irradiation levels.

  10. Research on polycrystalline thin-film materials, cells, and modules

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1990-11-01

    The US Department of Energy (DOE) supports research activities in polycrystalline thin films through the Polycrystalline Thin-Film Program at the Solar Energy Research Institute (SERI). This program includes research and development (R D) in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective of this program is to support R D of photovoltaic cells and modules that meet the DOE long-term goals of high efficiency (15%--20%), low cost ($50/m{sup 2}), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules. These have become the leading thin-film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe{sub 2} and CdTe modules. This paper focuses on the recent progress and future directions of the Polycrystalline Thin-Film Program and the status of the subcontracted research on these promising photovoltaic materials. 26 refs., 12 figs, 1 tab.

  11. Contents, seasonal variations, and forms of migration of major and minor elements in surface waters in the area of the Tyrnyauz Tungsten-Molybdenum Combine (TTMC) and adjacent areas (Kabardino-Balkarian Republic, Russian Federation) and actions for recovery of the ecological environment

    NASA Astrophysics Data System (ADS)

    Vinokurov, S. F.; Gurbanov, A. G.; Bogatikov, O. A.; Karamurzov, B. S.; Gazeev, V. M.; Lexin, A. B.; Shevchenko, A. V.; Dolov, S. M.; Dudarov, Z. I.

    2016-04-01

    Anomalous concentrations of numerous major and minor elements significantly exceeding the threshold limit values (TLV) for drinking water were registered in the area of the Tyrnyauz Tungsten-Molybdenum Combine (TTMC). The maximal excess of the TLV (by one or two orders of magnitude) were obtained for Mo (up to 11 mg/L), W (4.4 mg/L), As (1.5 mg/L), Mn (8.4 mg/L), and Tl (up to 3.3 μg/L) in water of the Bolshoi Mukulan Brook flowing through the mines and three brooks flowing out from the base of the embankment of the tailing store no. 1. They are the major pollutants for water of the Baksan River. Upon flowing out to the plain, water of the Baksan River shows significant excess of the TLVs (in summer) for Al, Fe, Mn, Be, Si, Ti, Tl, and Hg.

  12. 40 CFR 440.60 - Applicability; description of the tungsten ore subcategory.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... tungsten ore subcategory. 440.60 Section 440.60 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Tungsten Ore Subcategory § 440.60 Applicability; description of the tungsten ore subcategory. The provisions of this subpart F are applicable to discharges from (a) mines that produce tungsten ore and...

  13. 40 CFR 440.60 - Applicability; description of the tungsten ore subcategory.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... tungsten ore subcategory. 440.60 Section 440.60 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Tungsten Ore Subcategory § 440.60 Applicability; description of the tungsten ore subcategory. The provisions of this subpart F are applicable to discharges from (a) mines that produce tungsten ore and...

  14. 40 CFR 440.60 - Applicability; description of the tungsten ore subcategory.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... tungsten ore subcategory. 440.60 Section 440.60 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Tungsten Ore Subcategory § 440.60 Applicability; description of the tungsten ore subcategory. The provisions of this subpart F are applicable to discharges from (a) mines that produce tungsten ore and...

  15. Amorphous and polycrystalline water ices in space environments

    NASA Astrophysics Data System (ADS)

    Andrade, Diana; Pilling, Sergio; Da Silveira, Enio; Barros, Ana

    2016-07-01

    Ices are an important reservoir of more complex molecular species in several space environments, containing information about the composition and formation of these regions. Water ice is the dominant constituent of interstellar ices in most lines of sight and is about 70 % of the composition in comets, being a key molecule in astrochemical models. It is believed that one of the reactive species possibly evaporated from the water ices is the hydronium ion, H_{3}O^{+}, which plays an important role in the oxygen chemistry network. This ion has been detected in the lunar surface of Enceladus and Titan, and toward the Sagittarius B2 molecular Clouds, where H_{2}O and OH were also identified. In this work, the ion desorption due to radiolysis in ices constituted by water at three different temperatures (40, 70 and 125 K) is studied, to investigate the different allotropic water ices. A discussion on the rate of H_{3}O^{+} and water delivered to gas phase, as well as the half-life of water ice grains, inside dense molecular clouds considering a constants cosmic ray flux is given. The ions desorbed from water ice have been mass/charge analyzed by a time-of-flight spectrometer. Among the results, it is seen that in the positive ion spectrum of high density amorphous water ice at 40 K the highest desorption yields (ejected ions/impact) correspond to H^{+}, H_{3}O^{+} and clusters formed by (H_{2}O)_{n}R^{+}, where R^{+} is H_{3}O^{+} and 1 ≤ n ≤ 25. At T = 125 K, the ice is in its low density polycrystalline form and new clusters are present, such as (H_{2}O)_{n}R^{+}, where R^{+} is H_{2}^{+} and H_{3}^{+} (for low n), beyond H_{3}O^{+}. Therefore, it is seen that (H_{2}O)_{n}H_{3}O^{+} series (with n between 1 and 25) is dominant in all cases. The H_{3}O^{+} desorption yield at 40 K is about 5times10^{-3} ions/impact. This value is 4-5 times higher than the one obtained at T > 125 K. This behavior is also seen to all series member and consequently to the sum (Yn).

  16. Electron-bombarded ⟨110⟩-oriented tungsten tips for stable tunneling electron emission.

    PubMed

    Yamada, T K; Abe, T; Nazriq, N M K; Irisawa, T

    2016-03-01

    A clean tungsten (W) tip apex with a robust atomic plane is required for producing a stable tunneling electron emission under strong electric fields. Because a tip apex fabricated from a wire by aqueous chemical etching is covered by impurity layers, heating treatment in ultra-high vacuum is experimentally known to be necessary. However, strong heating frequently melts the tip apex and causes unstable electron emissions. We investigated quantitatively the tip apex and found a useful method to prepare a tip with stable tunneling electron emissions by controlling electron-bombardment heating power. Careful characterizations of the tip structures were performed with combinations of using field emission I-V curves, scanning electron microscopy, X-ray diffraction (transmitted Debye-Scherrer and Laue) with micro-parabola capillary, field ion microscopy, and field emission microscopy. Tips were chemically etched from (1) polycrystalline W wires (grain size ∼1000 nm) and (2) long-time heated W wires (grain size larger than 1 mm). Heating by 10-40 W (10 s) was found to be good enough to remove oxide layers and produced stable electron emission; however, around 60 W (10 s) heating was threshold power to increase the tip radius, typically +10 ± 5 nm (onset of melting). Further, the grain size of ∼1000 nm was necessary to obtain a conical shape tip apex. PMID:27036780

  17. Energy and tangential momentum accommodation coefficients of Ne and He on different vacuum flashed tungsten surfaces

    NASA Astrophysics Data System (ADS)

    Shields, F. Douglas

    1982-04-01

    The acoustical method has been used to determine energy and tangential momentum accomodation coefficients on three different polycrystalline tungsten surfaces. To obtain the second surface, the first was highly oxidized and then cleaned by vacuum flashing at 2150 K. The third surface, manufactured by the same chemical deposition process as the first, was specified as having half the microscopic roughness of the first. Photographs made with the scanning electron microscope indicate that though the oxidation dramatically increased the roughness of the surface, this roughness was removed in the flashing process. The electron micrographs also showed that flashing dramatically increased the grain size in the third surface. This third surface, though supposedly smoother, was found to have larger AC values than the first. This has been attributed to a shorter accumulated flashing time at the time the measurements were made and, therefore, smaller grain size. The microscopic roughness does not appear to be an important factor in determining AC values after the surface is flashed. The problem of simultaneously determining energy and tangential momentum accomodation coefficients is discussed.

  18. Thermal shock behaviour of H and H/He-exposed tungsten at high temperature

    NASA Astrophysics Data System (ADS)

    Lemahieu, N.; Greuner, H.; Linke, J.; Maier, H.; Pintsuk, G.; Wirtz, M.; Van Oost, G.; Noterdaeme, J.-M.

    2016-02-01

    Polycrystalline tungsten samples were characterized and exposed to a pure H beam or mixed H/He beam containing 6% He in GLADIS at a surface temperature of 600 °C, 1000 °C, or 1500 °C. After 5400 s of exposure time with a heat flux of 10.5 MW m-2, the total accumulated fluence of 2 × 1025 m-2 was reached. Thereafter, edge localized mode (ELM)-like thermal shocks with a duration of 1 ms and an absorbed power density of 190 MW m-2 and 380 MW m-2 were applied on the samples in JUDITH 1. During the thermal shocks, the base temperature was kept at 1000 °C. The ELM-experiments with the lowest transient power density did not result in any detected damage. The other tests showed the beginning of crack formation for every sample, except the sample pre-exposed with the pure H-beam at 1500 °C in GLADIS. This sample was roughened, but did not show any crack initiation. With exception to the roughened sample, the category of ELM-induced damage for the pre-exposed samples is identical to the reference tests without pre-exposure to a particle flux.

  19. Tungsten and tungsten-copper for coal-fired MHD power generation

    SciTech Connect

    Farrar, L.C. ); Shields, J.A. Jr. )

    1992-08-01

    This paper reports that magnetohydrodynamics (MHD) can improve the thermal efficiency and reduce levels of SO{sub x} and NO emissions of existing coal-fired power generation plants. Although the thermal and electrochemical environments for a coal-fired MHD channel challenge the materials used, platinum, tungsten, and tungsten-copper have been found to be suitable choices. Evaluations indicate these materials perform adequately as electrodes and other gas-side surfaces in the coal-fired MHD channel. Analysis of test elements has resulted in the identification of wear mechanisms. Testing of a prototypical coal-fired MHD channel incorporating these materials is under way and will be completed in 1993.

  20. Measurement of uptake and release of tritium by tungsten

    SciTech Connect

    Nakayama, M.; Torikai, Y.; Saito, M.; Penzhorn, R.D.; Isobe, K.; Yamanishi, T.; Kurishita, H.

    2015-03-15

    Tungsten is currently contemplated as plasma facing material for the divertor of future fusion machines. In this paper the uptake of tritium by tungsten and its release behavior have been investigated. Tungsten samples have been annealed at various temperatures and loaded at also different temperatures with deuterium containing 7.2 % tritium at a pressure of 1.2 kPa. A specific system was designed to assess the release of tritiated water and molecular tritium by the samples. Due to the rather low solubility of hydrogen isotopes in tungsten it is particularly important to be aware of the presence of hydrogen traps or thin oxide films. As shown in this work, traps or oxide films may affect the retention capability of tungsten and lead to significantly modified release properties. It became clear that there were capture sites that had different thermal stability and different capture intensity in tungsten after polishing, or oxide films that were grown on the surface of tungsten and had barrier effects.

  1. Amplitude equations for polycrystalline materials with interaction between composition and stress

    NASA Astrophysics Data System (ADS)

    Spatschek, Robert; Karma, Alain

    2010-06-01

    We investigate the ability of frame-invariant amplitude equations [G. H. Gunaratne, Q. Ouyang, and H. Swinney, Phys. Rev. E 50, 2802 (1994)] to describe quantitatively the evolution of polycrystalline microstructures and we extend this approach to include the interaction between composition and stress. Validations for elemental materials include studies of the Asaro-Tiller-Grinfeld morphological instability of a stressed crystal surface, polycrystalline growth from the melt, grain-boundary energies over a wide range of misorientation, and grain-boundary motion coupled to shear deformation. Amplitude equations with accelerated strain relaxation in the solid are shown to model accurately the Asaro-Tiller-Grinfeld instability. Polycrystalline growth is also well described. However, the survey of grain-boundary energies shows that the approach is only valid for a restricted range of misorientations as a direct consequence of an amplitude expansion. This range covers approximately half the complete range allowed by crystal symmetry for some fixed reference set of density waves used in the expansion. Over this range, coupled motion to shear is well described by known geometrical rules and a transition from coupling to sliding motion is also reproduced. Amplitude equations for alloys are derived phenomenologically in a Ginzburg-Landau spirit. Vegard’s law is shown to be naturally described by seeking a gauge-invariant form of those equations under a transformation that corresponds to a lattice expansion and deviations from Vegard’s law can be easily incorporated. Those equations realistically describe the dilute alloy limit and have the same flexibility as conventional phase-field models for incorporating arbitrary free-energy/composition curves. As a test of this approach, we recover known analytical expressions for open-system elastic constants [F. C. Larché and J. W. Cahn, Acta Metall. 33, 331 (1985)].

  2. Neutron irradiation effects on the microstructural development of tungsten and tungsten alloys

    NASA Astrophysics Data System (ADS)

    Hasegawa, Akira; Fukuda, Makoto; Yabuuchi, Kiyohiro; Nogami, Shuhei

    2016-04-01

    Data on the microstructural development of tungsten (W) and tungsten rhenium (Re) alloys were obtained after neutron irradiation at 400-800 °C in the Japan Materials Testing Reactor (JMTR), the experimental fast test reactor Joyo, and the High Flux Isotope Reactor (HFIR) for irradiation damage levels in the range of 0.09-1.54 displacement per atom (dpa). Microstructural observations showed that a small amount of Re (3-5%) in W-Re alloys is effective in suppressing void formation. In W-Re alloys with Re concentrations greater than 10%, acicular precipitates are the primary structural defects. In the HFIR-irradiated specimen, in which a large amount of Re was expected to be produced by the nuclear transmutation of W to Re because of the reactor's high thermal neutron flux, voids were not observed even in pure W. The synergistic effects of displacement damage and solid transmutation elements on microstructural development are discussed, and the microstructural development of tungsten materials utilized in fusion reactors is predicted.

  3. Tensile behavior of tungsten and tungsten-alloy wires from 1300 to 1600 K

    NASA Technical Reports Server (NTRS)

    Hee, Man Yun

    1988-01-01

    The tensile behavior of a 200-micrometer-diameter tungsten lamp (218CS-W), tungsten + 1.0 atomic percent (a/o) thoria (ST300-W), and tungsten + 0.4 a/o hafnium carbide (WHfC) wires was determined over the temperature range 1300 t0 1600 K at strain rates of 3.3 X 10 to the -2 to 3.3 X 10 to the -5/sec. Although most tests were conducted on as-drawn materials, one series of tests was undertaken on ST300-W wires in four different conditions: as-drawn and vacuum-annealed at 1535 K for 1 hr, with and without electroplating. Whereas heat treatment had no effect on tensile properties, electropolishing significantly increased both the proportional limit and ductility, but not the ultimate tensile strength. Comparison of the behavior of the three alloys indicates that the HfC-dispersed material possesses superior tensile properties. Theoretical calculations indicate that the strength/ductility advantage of WHfC is due to the resistance to recrystallization imparted by the dispersoid.

  4. Molecular Statics Simulation of Hydrogen Defect Interaction in Tungsten

    NASA Astrophysics Data System (ADS)

    Li, Xiaochun; Liu, Yinan; Yu, Yi; Niu, Guojian; Luo, Guangnan; Shu, Xiaolin

    2015-06-01

    Hydrogen (H) defect interactions have been investigated by molecular statics simulations in tungsten (W), including H-H interactions and interactions between H and W self-interstitial atoms. The interactions between H and small H-vacancy clusters are also demonstrated; the binding energies of an H, a vacancy and a self-interstitial W to an H-vacancy cluster depend on the H-to-vacancy ratio. We conclude that H bubble formation needs a high concentration of H in W for the H bubble nucleation and growth, which are also governed by the H-to-vacancy ratio of the cluster. The vacancy first combines with H atoms and a cluster forms, then the H-vacancy cluster goes through the whole process of vacancy capture, H capture, and vacancy capture again, and as a result the H-vacancy cluster grows larger and larger. Finally, the H bubble forms. supported by National Natural Science Foundation of China (Nos. 51171008 and 11405201) and the National Magnetic Confinement Fusion Science Program of China (No. 2013GB1090)

  5. Electrode potentials of tungsten in fused alkali chlorides

    NASA Astrophysics Data System (ADS)

    Ivanov, A. B.; Volkovich, V. A.; Poskryakov, D. A.; Vasin, B. D.; Griffiths, T. R.

    2016-09-01

    Anodic dissolution of tungsten was studied at 823-1173 K in the melts based on NaCl-CsCl, NaCl-KCl-CsCl and LiCl-KCl-CsCl eutectic mixtures. The process results in the formation of W(IV) ions. Prolonged contact with silica results in oxidation W(IV) ions and decreasing tungsten concentration in the electrolyte due to formation of volatile higher oxidation state chloro- and oxychloro-species. Tungsten electrode potentials were measured in NaCl-CsCl and NaCl-KCl-CsCl based melts using potentiometry.

  6. Thermal expansion method for lining tantalum alloy tubing with tungsten

    NASA Technical Reports Server (NTRS)

    Watson, G. K.; Whittenberger, J. D.; Mattson, W. F.

    1973-01-01

    A differential-thermal expansion method was developed to line T-111 (tantalum - 8 percent tungsten - 2 percent hafnium) tubing with a tungsten diffusion barrier as part of a fuel element fabrication study for a space power nuclear reactor concept. This method uses a steel mandrel, which has a larger thermal expansion than T-111, to force the tungsten against the inside of the T-111 tube. Variables investigated include lining temperature, initial assembly gas size, and tube length. Linear integrity increased with increasing lining temperature and decreasing gap size. The method should have more general applicability where cylinders must be lined with a thin layer of a second material.

  7. Reproductive effects and duckling survivability following chronic dosing with tungsten-iron and tungsten-polymer shot in adult game-farm mallards.

    PubMed

    Mitchell, R R; Fitzgerald, S D; Aulerich, R J; Balander, R J; Powell, D C; Tempelmen, R J; Stevens, W; Bursia, S J

    2001-07-01

    Tungsten-iron and tungsten-polymer shot were given conditional approval for waterfowl hunting by the U.S. Fish and Wildlife Service based partly on the results of a 30-day acute toxicity trial utilizing mallards (Anas platyrhynchos). Final approval of the two tungsten-containing shot was contingent on the results of a 150-day study that assessed the health and reproductive effects of tungsten-iron and tungsten-polymer shot in adult mallards. Reproductive data are presented in this paper. Sixteen male and 16 female adult mallards were dosed orally with eight #4 steel shot (control), eight #4 tungsten-iron shot, or eight #4 tungsten-polymer shot on days 0, 30, 60, 90, and 120 of a 150-day trial (26 January 1998 to 25 June 1998). Reproductive performance was assessed during the last 90 days (day 61 to day 150) of the trial. There were no significant differences in egg production and fertility and hatchability of eggs from tungsten-iron- and tungsten-polymer-dosed ducks compared to control ducks. There was no evidence of differences in percent survivability and body weight of ducklings from tungsten-iron and tungsten-polymer mallards compared to ducklings from control ducks. Tungsten-iron or tungsten-polymer shot repeatedly administered to adult mallards during the 150 day trial did not adversely affect reproduction or their offspring.

  8. A Study of Tungsten-Technetium Alloys

    NASA Technical Reports Server (NTRS)

    Maltz, J. W.

    1965-01-01

    Technetium is a sister element to rhenium and has many properties that are similar to rhenium. It is predicted that technetium will have about the same effects on tungsten as rhenium in regard to increase in workability, lowered ductile to brittle transition temperature, and improved ductility. The objectives of the current work are to recover technetium from fission product wastes at Hanford Atomic Products Operation and reduce to purified metal; prepare W-Tc alloys containing up to 50 atomic% Tc; fabricate the alloy ingots to sheet stock, assessing the effect of technetium on workability; and perform metallurgical and mechanical properties evaluation of the fabricated alloys. Previous reports have described the separation and purification of 800 g of technetium metal powder, melting of technetium and W-Tc alloys, and some initial observation of the alloy material.

  9. Thermomechanical processing of tungsten-copper composites

    SciTech Connect

    Ohriner, E.K.; Bryskin, B.

    1996-05-01

    A tungsten-40 wt% Cu composite was consolidated by liquid-phase sintering and further processed to full density by a number of deformation methods. Fully dense materials were obtained by hot extrusion or cold rolling of the W-Cu composite. Subsequent processing by cold rolling, cold swaging, or hot swaging did not produce large changes in the aspect ratio of the W particles. The materials develop high hardness with small grain sizes of 5 {mu}m or less. The work-hardening, recrystallization, and grain growth of the material are characterized, and the hardness and tensile properties are related to processing parameters. Wire with tensile strengths up to 1120 MPa were produced. Further improvements in properties are anticipated with optimized processing parameters.

  10. Numerical simulation and experiment on split tungsten carbide cylinder of high pressure apparatus

    SciTech Connect

    Yang, Yunfei; Li, Mingzhe Wang, Bolong; Liu, Zhiwei

    2015-12-15

    A new high pressure device with a split cylinder was investigated on the basis of the belt-type apparatus. The belt-type die is subjected to excessive tangential tensile stress and the tungsten carbide cylinder is easily damaged in the running process. Taking into account the operating conditions and material properties of the tungsten carbide cylinder, it is divided into 6 blocks to eliminate the tangential tensile stress. We studied two forms of the split type: radial split and tangential split. Simulation results indicate that the split cylinder has more uniform stress distribution and smaller equivalent stress compared with the belt-type cylinder. The inner wall of the tangential split cylinder is in the situation that compressive stress is distributed in the axial, radial, and tangential directions. It is similar to the condition of hydrostatic pressure, and it is the best condition for tungsten carbide materials. The experimental results also verify that the tangential split die can bear the highest chamber pressure. Therefore, the tangential split structure can increase the pressure bearing capacity significantly.

  11. Numerical simulation and experiment on split tungsten carbide cylinder of high pressure apparatus.

    PubMed

    Yang, Yunfei; Li, Mingzhe; Liu, Zhiwei; Wang, Bolong

    2015-12-01

    A new high pressure device with a split cylinder was investigated on the basis of the belt-type apparatus. The belt-type die is subjected to excessive tangential tensile stress and the tungsten carbide cylinder is easily damaged in the running process. Taking into account the operating conditions and material properties of the tungsten carbide cylinder, it is divided into 6 blocks to eliminate the tangential tensile stress. We studied two forms of the split type: radial split and tangential split. Simulation results indicate that the split cylinder has more uniform stress distribution and smaller equivalent stress compared with the belt-type cylinder. The inner wall of the tangential split cylinder is in the situation that compressive stress is distributed in the axial, radial, and tangential directions. It is similar to the condition of hydrostatic pressure, and it is the best condition for tungsten carbide materials. The experimental results also verify that the tangential split die can bear the highest chamber pressure. Therefore, the tangential split structure can increase the pressure bearing capacity significantly.

  12. Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV

    SciTech Connect

    Colgan, James; Fontes, Christopher; Zhang, Honglin; Abdallah, Jr., Joseph

    2015-04-30

    We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.

  13. Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV

    DOE PAGES

    Colgan, James; Fontes, Christopher; Zhang, Honglin; Abdallah, Jr., Joseph

    2015-04-30

    We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that weremore » submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.« less

  14. Covalent attachment of diamondoid phosphonic acid dichlorides to tungsten oxide surfaces.

    PubMed

    Li, Fei Hua; Fabbri, Jason D; Yurchenko, Raisa I; Mileshkin, Alexander N; Hohman, J Nathan; Yan, Hao; Yuan, Hongyuan; Tran, Ich C; Willey, Trevor M; Bagge-Hansen, Michael; Dahl, Jeremy E P; Carlson, Robert M K; Fokin, Andrey A; Schreiner, Peter R; Shen, Zhi-Xun; Melosh, Nicolas A

    2013-08-01

    Diamondoids (nanometer-sized diamond-like hydrocarbons) are a novel class of carbon nanomaterials that exhibit negative electron affinity (NEA) and strong electron-phonon scattering. Surface-bound diamondoid monolayers exhibit monochromatic photoemission, a unique property that makes them ideal electron sources for electron-beam lithography and high-resolution electron microscopy. However, these applications are limited by the stability of the chemical bonding of diamondoids on surfaces. Here we demonstrate the stable covalent attachment of diamantane phosphonic dichloride on tungsten/tungsten oxide surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy revealed that diamondoid-functionalized tungsten oxide films were stable up to 300-350 °C, a substantial improvement over conventional diamondoid thiolate monolayers on gold, which dissociate at 100-200 °C. Extreme ultraviolet (EUV) light stimulated photoemission from these diamondoid phosphonate monolayers exhibited a characteristic monochromatic NEA peak with 0.2 eV full width at half-maximum (fwhm) at room temperature, showing that the unique monochromatization property of diamondoids remained intact after attachment. Our results demonstrate that phosphonic dichloride functionality is a promising approach for forming stable diamondoid monolayers for elevated temperature and high-current applications such as electron emission and coatings in micro/nano electromechanical systems (MEMS/NEMS).

  15. Helium bubble formation in ultrafine and nanocrystalline tungsten under different extreme conditions

    SciTech Connect

    El-atwani, O.; Hattar, Khalid Mikhiel; Hinks, J. A.; Greaves, G.; Harilal, S. S.; Hassanein, A.

    2014-12-25

    We investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. Moreover, at energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. Finally, we discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formation.

  16. Helium bubble formation in ultrafine and nanocrystalline tungsten under different extreme conditions

    DOE PAGES

    El-atwani, O.; Hattar, Khalid Mikhiel; Hinks, J. A.; Greaves, G.; Harilal, S. S.; Hassanein, A.

    2014-12-25

    We investigated the effects of helium ion irradiation energy and sample temperature on the performance of grain boundaries as helium sinks in ultrafine grained and nanocrystalline tungsten. Irradiations were performed at displacement and non-displacement energies and at temperatures above and below that required for vacancy migration. Microstructural investigations were performed using Transmission Electron Microscopy (TEM) combined with either in-situ or ex-situ ion irradiation. Under helium irradiation at an energy which does not cause atomic displacements in tungsten (70 eV), regardless of temperature and thus vacancy migration conditions, bubbles were uniformly distributed with no preferential bubble formation on grain boundaries. Moreover,more » at energies that can cause displacements, bubbles were observed to be preferentially formed on the grain boundaries only at high temperatures where vacancy migration occurs. Under these conditions, the decoration of grain boundaries with large facetted bubbles occurred on nanocrystalline grains with dimensions less than 60 nm. Finally, we discuss the importance of vacancy supply and the formation and migration of radiation-induced defects on the performance of grain boundaries as helium sinks and the resulting irradiation tolerance of ultrafine grained and nanocrystalline tungsten to bubble formation.« less

  17. Polycrystalline Diamonds from the Erzgebirge Ultrahigh-Pressure Metamorphic Terrane, Germany

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, L.; Wirth, R.; Green, H. W.

    2010-12-01

    Previous studies showed that microdiamonds from Erzgebirge terrane of Germany are crystallized from a C-O-H fluid (Stoeckhert et al., 2001, 2009; Dobrzhinetskaya et al., 2003, 2007) due to course of the UHPM. Usually metamorphic diamonds are presented by single crystals of 5 to 80 micron size, which are caracterized by a complicated morphology suggesting that their crystallization took place in a media rich in impurities. Within the microdiamonds population ocurred in the Erzgebirge quartz-feldspathic gneisses, we have recently found polycrystalline diamonds which extend our knowledge related to mechanisms of their formation. These polycrystalline diamonds occur as inclusions in zircons. Several focused ion beam foils were prepared from polished slide containing zircon with diamond inclusions, and studied with transmission electron microscopy. Bright Field images revealed that single diamond inclusions in zircon consist of 5 to 15 microcrystals which are characterized by ’zig-zag’ boundaries. The series of triangle fluid-pockets are situated at the interface diamond-zircon, and ’glue’ together microcrystals. The octahedral voids accountered by (111) crystal faces are observed within polycrystalline sectors of diamond. The octahedral voids are characterized by low density contrast what suggests that the void is a negative nanocrystal of diamond filled by fluid/gas. In many cases the fluid was evaporated during the foil preparation by high energy Ga-ions beam. The fluid consisted of Ti, Cl, S, K, Cr, Ba, Pb, Mo, Co, Al. The presence of the negative crystals of diamonds filled with a fluid, suggest that such a fluid was in equilibrium with the diamond, and represents the diamond-forming media. Triangle pockets of the former fluid situated at the zircon-diamond interface are also penetrated by FIB, the residual fluid composition is characterized by presence of Al, Ti, Ca, F, V, Zn, Si, Cl, and S, or Ca, Al, K, Cl, Fe and Mg, or Al, Co, F, V, Zn, Si, Cl, or

  18. Tungsten carbide production from ore concentrates by molten salt-natural gas sparging treatment

    SciTech Connect

    Carnahan, T.G.; Kazonich, G.; Raddatz, A.E.

    1988-01-01

    The U.S. Bureau of Mines conducted a bench-scale study to delineate the important parameters in a three-step process to produce commercial-quality tungsten carbide (WC) directly from tungsten minerals. In the process, tungsten concentrates of wolframite or wolframite and scheelite are decomposed at 1,050{sup 0}C in a molten mixture of NcCl and Na{sub 2}SiO{sub 3} that forms two immiscible phases. Tungsten, as sodium tungstate, reports to the halide phase and is separated from the gangue constituents, which report to the silicate phase. After decanting to separate the two phases, natural gas is sparged into the molten halide phase a 1,070{sup 0}C. Submicrometer crystals of WC are initially produced. These crystals grow into thin triangular-shaped plates up to 100 {mu}m on a side or into popcorn-shaped conglomerates. Sparged WC was examined for its suitability for use in sintered carbide products. In physical evaluations, sparged WC ground to an average particle size of 1.52 {mu}m and compacted with 10 pct Co binder into standard 6-by 22-mm test bars had a density of 14.35 and a Rockwell A hardness of 89.6. This compared favorably with 14.39 and 89.7 respectively, for test bars made from a standard commercial 1.52-{mu}m WC powder. Test bars made from Bureau of Mines WC had no C'' porosity or eta phase.

  19. In-situ observation of sputtered particles for carbon implanted tungsten during energetic isotope ion implantation

    SciTech Connect

    Oya, Y.; Sato, M.; Uchimura, H.; Okuno, K.; Ashikawa, N.; Sagara, A.; Yoshida, N.; Hatano, Y.

    2015-03-15

    Tungsten is a candidate for plasma facing materials in future fusion reactors. During DT plasma operations, carbon as an impurity will bombard tungsten, leading to the formation of tungsten-carbon (WC) layer and affecting tritium recycling behavior. The effect of carbon implantation for the dynamic recycling of deuterium, which demonstrates tritium recycling, including retention and sputtering, has been investigated using in-situ sputtered particle measurements. The C{sup +} implanted W, WC and HOPG were prepared and dynamic sputtered particles were measured during H{sub 2}{sup +} irradiation. It has been found that the major hydrocarbon species for C{sup +} implanted tungsten is CH{sub 3}, while for WC and HOPG (Highly Oriented Pyrolytic Graphite) it is CH{sub 4}. The chemical state of hydrocarbon is controlled by the H concentration in a W-C mixed layer. The amount of C-H bond and the retention of H trapped by carbon atom should control the chemical form of hydrocarbon sputtered by H{sub 2}{sup +} irradiation and the desorption of CH{sub 3} and CH{sub 2} are due to chemical sputtering, although that for CH is physical sputtering. The activation energy for CH{sub 3} desorption has been estimated to be 0.4 eV, corresponding to the trapping process of hydrogen by carbon through the diffusion in W. It is concluded that the chemical states of hydrocarbon sputtered by H{sub 2}{sup +} irradiation for W is determined by the amount of C-H bond on the W surface. (authors)

  20. Synthesis, structure and theoretical investigation into a homoleptic tris(dithiolene) tungsten.

    PubMed

    Arifin, Khuzaimah; Minggu, Lorna Jeffery; Daud, Wan Ramli Wan; Yamin, Bohari M; Daik, Rusli; Kassim, Mohammad B

    2014-01-01

    A new homoleptic dithiolene tungsten complex, tris-{1,2-bis(3,5-dimethoxyphenyl)-1,2-ethylenodithiolene-S,S'}tungsten, was successfully synthesized via a reaction of the thiophosphate ester and sodium tungstate. The thiophosphate ester was prepared from 3,5-dimethoxybenzaldehyde via benzoin condensation to produce the intermediate 1,2-bis-(3,5-dimethoxyphenyl)-2-hydroxy-ethanone compound, followed by a reaction of the intermediate with phosphorus pentasulfide. FTIR, UV-Vis spectroscopy, 1H NMR and 13C NMR and elemental analysis confirmed the product as tris{1,2-bis-(3,5-dimethoxyphenyl)-1,2-ethylenodithiolene-S,S'}tungsten with the molecular formula of C54H54O12S6W. Crystals of the product adopted a monoclinic system with space group of P2(1)/n, where a=12.756(2) Å, b=21.560(3) Å, c=24.980(4) Å and β=103.998(3)°. Three thioester ligands were attached to the tungsten as bidentate chelates to form a distorted octahedral geometry. Density functional theory calculations were performed to investigate the molecular properties in a generalized-gradient approximation framework system using Perdew-Burke-Ernzerhof functions and a double numeric plus polarization basis set. The HOMO was concentrated on the phenyl ligands, while the LUMO was found along the W(S2C2)3 rings. The theoretical optical properties showed a slight blue shift in several low dielectric solvents. The solvatochromism effect was insignificant for high polar solvents.

  1. Surface damage and structure evolution of recrystallized tungsten exposed to ELM-like transient loads

    NASA Astrophysics Data System (ADS)

    Yuan, Y.; Du, J.; Wirtz, M.; Luo, G.-N.; Lu, G.-H.; Liu, W.

    2016-03-01

    Surface damage and structure evolution of the full tungsten ITER divertor under transient heat loads is a key concern for component lifetime and plasma operations. Recrystallization caused by transients and steady-state heat loads can lead to degradation of the material properties and is therefore one of the most serious issues for tungsten armor. In order to investigate the thermal response of the recrystallized tungsten under edge localized mode-like transient thermal loads, fully recrystallized tungsten samples with different average grain sizes are exposed to cyclic thermal shocks in the electron beam facility JUDITH 1. The results indicate that not only does the microstructure change due to recrystallization, but that the surface residual stress induced by mechanical polishing strongly influences the surface cracking behavior. The stress-free surface prepared by electro-polishing is shown to be more resistant to cracking than the mechanically polished one. The resulting surface roughness depends largely on the loading conditions instead of the recrystallized-grain size. As the base temperature increases from room temperature to 400 °C, surface roughening mainly due to the shear bands in each grain becomes more pronounced, and sub-grains (up to 3 μm) are simultaneously formed in the sub-surface. The directions of the shear bands exhibit strong grain-orientation dependence, and they are generally aligned with the traces of {1 1 2} twin habit planes. The results suggest that twinning deformation and dynamic recrystallization represent the predominant mechanism for surface roughening and related microstructure evolution.

  2. Enhanced toughness and stable crack propagation in a novel tungsten fibre-reinforced tungsten composite produced by chemical vapour infiltration

    NASA Astrophysics Data System (ADS)

    Riesch, J.; Höschen, T.; Linsmeier, Ch; Wurster, S.; You, J.-H.

    2014-04-01

    Tungsten is a promising candidate for the plasma-facing components of a future fusion reactor, but its use is strongly restricted by its inherent brittleness. An innovative concept to overcome this problem is tungsten fibre-reinforced tungsten composite. In this paper we present the first mechanical test of such a composite material using a sample containing multiple fibres. The in situ fracture experiment was performed in a scanning electron microscope for close observation of the propagating crack. Stable crack propagation accompanied with rising load bearing capacity is observed. The fracture toughness is estimated using the test results and the surface observation.

  3. Polarographic determination of tungsten and molybdenum in sedimentary rocks

    SciTech Connect

    Vakhobova, R.U.; Lykova, F.P.; Milyavskii, Yu. S.; Rachinskaya, G.F.

    1985-12-01

    In order to determine microamounts of tungsten and molybdenum, one the most sensitive versions of polarography is used in this paper, called catalytic currents. In the development of a procedure for the determination of tungsten and molybdenum in geochemical items, the reduction of hydroxylamine (HA) is used, catalyzed by tungsten and molybdenum compounds in the presence of pyrocatechol, as on a background of dicarboxylic acids and hydroxy acids the HA reduction half-wave potentials, catalyzed by these elements, coincide. The investigations were conducted on a PPT-1 polarograph in the classical regime in a thermostatically controlled cell with a mercury dripping electrode and a saturated calomel comparison electrode. The authors develop a procedure for the simultaneous determination of n.10/sup -5/-n.10/sup -4/% of tungsten and molybdenum in sedimentary rocks.

  4. Tungsten-nickel-cobalt alloy and method of producing same

    DOEpatents

    Dickinson, James M.; Riley, Robert E.

    1977-03-15

    An improved tungsten alloy having a tungsten content of approximately 95 weight percent, a nickel content of about 3 weight percent, and the balance being cobalt of about 2 weight percent is described. A method for producing said tungsten-nickel-cobalt alloy is further described and comprises (a) coating the tungsten particles with a nickel-cobalt alloy, (b) pressing the coated particles into a compact shape, (c) heating said compact in hydrogen to a temperature in the range of 1400.degree. C and holding at this elevated temperature for a period of about 2 hours, (d) increasing this elevated temperature to about 1500.degree. C and holding for 1 hour at this temperature, (e) cooling to about 1200.degree. C and replacing the hydrogen atmosphere with an inert argon atmosphere while maintaining this elevated temperature for a period of about 1/2 hour, and (f) cooling the resulting alloy to room temperature in this argon atmosphere.

  5. Surface binding energies of beryllium/tungsten alloys

    NASA Astrophysics Data System (ADS)

    Gyoeroek, Michael; Kaiser, Alexander; Sukuba, Ivan; Urban, Jan; Hermansson, Kersti; Probst, Michael

    2016-04-01

    Binding energies of beryllium and tungsten atoms on surfaces of the alloys Be2W and Be12W were obtained from density functional theory calculations. Values of 4.08-5.63 eV for beryllium and 6.81-10.04 eV for tungsten were obtained. An analytical force field agrees for beryllium, but its tungsten surface atoms are too strongly bound. The surface binding energies of Be and W on Be12W surfaces is slightly smaller than on the pure Be and W surfaces, respectively. For higher tungsten content, i.e. for Be2W, the situation is more complicated. For some surfaces of this alloy the surface binding energies are enhanced while for others they are diminished, compared to the pure metal surfaces. The dependency of the cohesive energy on the mole fraction follows a linear relationship.

  6. Growth of tungsten oxide nanorods with carbon caps.

    PubMed

    Kichambare, Padmakar; Hii, King-Fu; Vallance, R Ryan; Sadanadan, B; Rao, Apparao M; Javed, Kazi; Menguc, M Pinar

    2006-02-01

    Hybrid nanostructures consisting of tungsten oxide nanorods with mushroom-shaped carbon caps were grown on electrochemically etched tungsten tips by thermal chemical vapor deposition with methane and argon. These nanorods grow along the radial direction and are very straight and smooth. Electron microscopy revealed a dominant diameter and length of approximately 50 nm and approximately 0.6 microm, respectively. High-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) revealed the presence of crystalline monoclinic W18O49 in the nanorods, and the cap was entirely amorphous carbon. A plausible growth mechanism involves the reduction of tungsten oxide WO3, present on the tungsten surface, by methane at 900 degrees C. PMID:16573057

  7. Characterization of the impurities in tungsten/silicon-germanium contacts

    SciTech Connect

    Gregg, H.A. Sr.

    1986-03-26

    Secondary ion mass spectrometry and Auger electron spectrometry depth profiling were used to determine impurity distributions in sputter deposited tungsten films over N-type and P-type 80/20 silicon-germanium elements of thermoelectric devices. These analyses showed that silicon, oxygen, sodium, boron, and phosphorous were present as impurities in the tungsten film. All these impurities except oxygen and sodium came from the substrate. Oxygen was gettered by the tungsten films, while sodium was possibly the result of sample handling. Further, the results from this study indicate that an oxide build-up, primarily at the tungsten/silicon-germanium interface of the N-type materials, is the major contributor to contact resistance in thermoelectric devices.

  8. OBJECT KINETIC MONTE CARLO SIMULATIONS OF CASCADE ANNEALING IN TUNGSTEN

    SciTech Connect

    Nandipati, Giridhar; Setyawan, Wahyu; Heinisch, Howard L.; Roche, Kenneth J.; Kurtz, Richard J.; Wirth, Brian D.

    2014-03-31

    The objective of this work is to study the annealing of primary cascade damage created by primary knock-on atoms (PKAs) of various energies, at various temperatures in bulk tungsten using the object kinetic Monte Carlo (OKMC) method.

  9. Tungsten Mobility During Alteration Processes: An Experimental Approach

    NASA Astrophysics Data System (ADS)

    Yin, N. H.; Fabre, S.; Quitté, G.

    2016-08-01

    Most chondrites show evidence of relatively low temperature alteration. Mass-dependent fractionation of non-traditional stable isotopes such as tungsten (W) are well suited to trace metal-silicate differentiation and alteration processes.

  10. A Compact Gas/Tungsten-Arc Welding Torch

    NASA Technical Reports Server (NTRS)

    Morgen, Gene E.

    1991-01-01

    Compact gas/tungsten-arc welding torch delivers 100-A current, yet used in confined spaces inaccessible to even smallest commercially available torch. Despite its extremely small size, torch contains all usual components and delivers high current.

  11. Refractory metals welded or brazed with tungsten inert gas equipment

    NASA Technical Reports Server (NTRS)

    Wisner, J. P.

    1965-01-01

    Appropriate brazing metals and temperatures facilitate the welding or brazing of base metals with tungsten inert gas equipment. The highest quality bond is obtained when TIG welding is performed in an inert atmosphere.

  12. Tungsten isotope ratio determinations by negative thermal ionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Völkening, Joachim; Köppe, Manfred; Heumann, Klaus G.

    1991-07-01

    A precise determination of the isotopic abundances of tungsten with natural isotopic composition is presented. WO-3 ions are generated by negative thermal ionization (NTI) in a double-filament ion source. La2O3 is used as a chemical substance to reduce the electron work function of the rhenium filament material. An ionization efficiency of 1% is obtained for sample loadings of 100 ng. The isotopic abundances are measured with relative standard deviations of 0.2% for the least abundant 180W isotope and 0.02-0.004% for the other tungsten isotopes. These improved isotopic data are used to recalculate the atomic weight of tungsten as 183.8417 ± 0.0001. The new NTI technique is an ideal tool for the application of isotope dilution mass spectrometry to analyse tungsten traces and for the measurement of isotopic shifts of this element in meteorites produced by the decay of 182Hf.

  13. Natural occurrence of pure nano-polycrystalline diamond from impact crater.

    PubMed

    Ohfuji, Hiroaki; Irifune, Tetsuo; Litasov, Konstantin D; Yamashita, Tomoharu; Isobe, Futoshi; Afanasiev, Valentin P; Pokhilenko, Nikolai P

    2015-01-01

    Consolidated bodies of polycrystalline diamond with grain sizes less than 100 nm, nano-polycrystalline diamond (NPD), has been experimentally produced by direct conversion of graphite at high pressure and high temperature. NPD has superior hardness, toughness and wear resistance to single-crystalline diamonds because of its peculiar nano-textures, and has been successfully used for industrial and scientific applications. Such sintered nanodiamonds have, however, not been found in natural mantle diamonds. Here we identified natural pure NPD, which was produced by a large meteoritic impact about 35 Ma ago in Russia. The impact diamonds consist of well-sintered equigranular nanocrystals (5-50 nm), similar to synthetic NPD, but with distinct [111] preferred orientation. They formed through the martensitic transformation from single-crystal graphite. Stress-induced local fragmentation of the source graphite and subsequent rapid transformation to diamond in the limited time scale result in multiple diamond nucleation and suppression of the overall grain growth, producing the unique nanocrystalline texture of natural NPD. A huge amount of natural NPD is expected to be present in the Popigai crater, which is potentially important for applications as novel ultra-hard material. PMID:26424384

  14. Nucleation, growth, and control of ferroelectric-ferroelastic domains in thin polycrystalline films

    NASA Astrophysics Data System (ADS)

    Ivry, Yachin; Scott, James F.; Salje, Ekhard K. H.; Durkan, Colm

    2012-11-01

    The unique response of ferroic materials to external excitations facilitates them for diverse technologies, such as nonvolatile memory devices. The primary driving force behind this response is encoded in domain switching. In bulk ferroics, domains switch in a two-step process: nucleation and growth. For ferroelectrics, this can be explained by the Kolmogorov-Avrami-Ishibashi (KAI) model. Nevertheless, it is unclear whether domains remain correlated in finite geometries, as required by the KAI model. Moreover, although ferroelastic domains exist in many ferroelectrics, experimental limitations have hindered the study of their switching mechanisms. This uncertainty limits our understanding of domain switching and controllability, preventing thin-film and polycrystalline ferroelectrics from reaching their full technological potential. Here we used piezoresponse force microscopy to study the switching mechanisms of ferroelectric-ferroelastic domains in thin polycrystalline Pb0.7Zr0.3TiO3 films at the nanometer scale. We have found that switched biferroic domains can nucleate at multiple sites with a coherence length that may span several grains, and that nucleators merge to form mesoscale domains, in a manner consistent with that expected from the KAI model.

  15. Natural occurrence of pure nano-polycrystalline diamond from impact crater

    PubMed Central

    Ohfuji, Hiroaki; Irifune, Tetsuo; Litasov, Konstantin D.; Yamashita, Tomoharu; Isobe, Futoshi; Afanasiev, Valentin P.; Pokhilenko, Nikolai P.

    2015-01-01

    Consolidated bodies of polycrystalline diamond with grain sizes less than 100 nm, nano-polycrystalline diamond (NPD), has been experimentally produced by direct conversion of graphite at high pressure and high temperature. NPD has superior hardness, toughness and wear resistance to single-crystalline diamonds because of its peculiar nano-textures, and has been successfully used for industrial and scientific applications. Such sintered nanodiamonds have, however, not been found in natural mantle diamonds. Here we identified natural pure NPD, which was produced by a large meteoritic impact about 35 Ma ago in Russia. The impact diamonds consist of well-sintered equigranular nanocrystals (5–50 nm), similar to synthetic NPD, but with distinct [111] preferred orientation. They formed through the martensitic transformation from single-crystal graphite. Stress-induced local fragmentation of the source graphite and subsequent rapid transformation to diamond in the limited time scale result in multiple diamond nucleation and suppression of the overall grain growth, producing the unique nanocrystalline texture of natural NPD. A huge amount of natural NPD is expected to be present in the Popigai crater, which is potentially important for applications as novel ultra-hard material. PMID:26424384

  16. Natural occurrence of pure nano-polycrystalline diamond from impact crater.

    PubMed

    Ohfuji, Hiroaki; Irifune, Tetsuo; Litasov, Konstantin D; Yamashita, Tomoharu; Isobe, Futoshi; Afanasiev, Valentin P; Pokhilenko, Nikolai P

    2015-10-01

    Consolidated bodies of polycrystalline diamond with grain sizes less than 100 nm, nano-polycrystalline diamond (NPD), has been experimentally produced by direct conversion of graphite at high pressure and high temperature. NPD has superior hardness, toughness and wear resistance to single-crystalline diamonds because of its peculiar nano-textures, and has been successfully used for industrial and scientific applications. Such sintered nanodiamonds have, however, not been found in natural mantle diamonds. Here we identified natural pure NPD, which was produced by a large meteoritic impact about 35 Ma ago in Russia. The impact diamonds consist of well-sintered equigranular nanocrystals (5-50 nm), similar to synthetic NPD, but with distinct [111] preferred orientation. They formed through the martensitic transformation from single-crystal graphite. Stress-induced local fragmentation of the source graphite and subsequent rapid transformation to diamond in the limited time scale result in multiple diamond nucleation and suppression of the overall grain growth, producing the unique nanocrystalline texture of natural NPD. A huge amount of natural NPD is expected to be present in the Popigai crater, which is potentially important for applications as novel ultra-hard material.

  17. Cratering behavior in single- and poly-crystalline copper irradiated by an intense pulsed ion beam

    SciTech Connect

    Wood, B.P.; Bitteker, L.J.; Waganaar, W.J.; Perry, A.J.

    1998-12-31

    When treated with intense pulsed ion beams (IPIB), many materials exhibit increased wear resistance, fatigue life, and hardness. However, this treatment often results in cratering and roughening of the surface. In this work, high purity single crystal and polycrystalline copper samples were irradiated with pulses from an IPIB to gain insight into the causes of this cratering behavior. Samples were treated with 1,2,5, and 10 shots at 2 J/cm{sup 2} and 5 J/cm{sup 2} average energy fluence per shot. Shots were about 400 ns in duration and consisted of a mixture of carbon, hydrogen, and oxygen ions at 300 keV. It was found that the single crystal copper cratered far less than the polycrystalline copper at the lower energy fluence. At the higher energy fluence, cratering was replaced by other forms of surface damage, and the single crystal copper sustained less damage at all but the largest number of shots. Molten debris from the Lucite anode (the ion source) was removed and redeposited on the samples with each shot.

  18. Polycrystalline thin film materials and devices. Annual subcontract report, 16 January 1991--15 January 1992

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  19. The double effect of grain size on the work hardening behavior of polycrystalline copper

    SciTech Connect

    Gracio, J.J. . Dept. de Engenharia Mecanica)

    1994-08-15

    Following the approach by Ashby, one can consider that strain compatibility between adjacent grains of a polycrystal generates geometrical dislocations. These dislocations participated in the strengthening mechanism in conjunction with statistically stored dislocations which are related to the single-crystal behavior. The dislocations of either species are indistinguishable and, as a whole, they may contribute to cell formation. The dislocation structure formed in a polycrystal is then a function of the major or minor intergranular accommodation complexity. At intermediate strain values the accommodation is distributed over the cells leading to a linear relationship between the tensile stress and the inverse of the cell size, whatever the grain size of the tested samples. The aim of the present work is to check that the presence of statistical and geometrical dislocations in the grains, as well as the fact that at the very early stage of plastic deformation the mean free path of dislocations is of the order of the grain size, leads to a double effect of the grain size on the work hardening behavior of polycrystalline copper. Moreover, careful analysis of the mechanical behavior of polycrystalline copper, including the microstructural aspects of plastic deformation, is performed, allowing the understanding of the relationship between the work hardening ratio and the grain size.

  20. Ductile tungsten-nickel-alloy and method for manufacturing same

    DOEpatents

    Ludwig, Robert L.

    1978-01-01

    The tensile elongation of a tungsten-nickel-iron alloy containing essentially 95 weight percent reprocessed tungsten, 3.5 weight percent nickel, and 1.5 weight percent iron is increased from a value of less than about 1 percent up to about 23 percent by the addition of less than 0.5 weight percent of a reactive metal consisting of niobium and zirconium.

  1. Processing effects on the mechanical properties of tungsten heavy alloys

    NASA Technical Reports Server (NTRS)

    Kishi, Toshihito; German, R. M.

    1990-01-01

    Tungsten heavy alloys exhibit significant mechanical property sensitivities to the fabrication variables. These sensitivities are illustrated in this examination of vacuum sintering and the effects of composition, sintering temperature, and sintering time on the mechanical properties of tungsten heavy alloys. Measurements were conducted to assess the density, strength, hardness, and elongation dependencies. A detrimental aspect of vacuum sintering is matrix phase evaporation, although vacuum sintering does eliminate the need for postsintering heat treatments.

  2. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG&E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  3. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-01-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  4. Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

    SciTech Connect

    Jung, Min-Cherl; Zhang, Dongrong; Nikiforov, Gueorgui O.; Lee, Michael V.; Qi, Yabing; Joo Shin, Tae; Ahn, Docheon; Lee, Han-Koo; Baik, Jaeyoon; Shin, Hyun-Joon

    2015-03-15

    Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

  5. VLSI readout for imaging with polycrystalline mercuric iodide detectors

    NASA Astrophysics Data System (ADS)

    Turchetta, Renato; Dulinski, Wojtek; Husson, D.; Klein, N.; Riester, J. L.; Schieber, Michael M.; Zuck, A.; Braiman, M.; Melekhov, L.; Nissenbaum, J.; Sanguinetti, S.

    1998-11-01

    Recently polycrystalline mercuric iodide have become available, for room temperature radiation detectors over large areas at low cost. Though the quality of this material is still under improvement, ceramic detectors have been already been successfully tested with dedicated low-noise, low-power mixed signal VLSI electronics which can be used for compact, imaging solutions. The detectors used are of different kinds: microstrips and pixels; of different sizes, up to about 1 square inch; and of different thickness, up to 600 microns. The properties of this first-generation detectors are quite uniform from one detector to another. Also for each single detector the response is quite uniform and no charge loss in the inter-electrode space have been detected. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology equipment, which is an attractive feature where low cost and large area applications are needed.

  6. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  7. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Astrophysics Data System (ADS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-05-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  8. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy

    PubMed Central

    Schmid, T.; Schäfer, N.; Levcenko, S.; Rissom, T.; Abou-Ras, D.

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  9. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    PubMed Central

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  10. Mechanical instability of monocrystalline and polycrystalline methane hydrates.

    PubMed

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T; Kjelstrup, Signe; Vlugt, Thijs J H; He, Jianying; Skallerud, Bjørn H; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  11. Compton profile study of polycrystalline ZnBr{sub 2}

    SciTech Connect

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Kothari, R. K.; Sharma, B. K.

    2010-12-01

    The first ever Compton profile study of polycrystalline ZnBr{sub 2} is presented in this paper. The measurement of polycrystalline sample of ZnBr{sub 2} is performed using 59.54 keV gamma-rays emanating from an {sup 241}Am radioisotope. Theoretical calculations are performed following the Ionic model calculations for a number of configurations Zn{sup +x}Br{sub 2}{sup -x/2}(0.0{<=}x{<=}2.0 in step of 0.5) utilizing free atom profiles. The ionic model suggest transfer of 2.0 electrons from 4 s state of Zn to 4 p state of two Br atoms. The autocorrelation function B(z) is also derived from experiment and the most favoured ionic valence Compton profiles.

  12. Polycrystalline diamond photoconductive device with high UV-visible discrimination

    NASA Astrophysics Data System (ADS)

    McKeag, Robert D.; Chan, Simon S. M.; Jackman, Richard B.

    1995-10-01

    Planar metal-diamond-metal photoconductive devices have been fabricated from free standing large grain (20-30 μm) polycrystalline thin film diamond. An interdigitated electrode design with spacings of 20 μm was used to produce effective UV photodetecting devices at bias values in the range 0.1-10 V. A methane-air treatment has been used to modify the structures such that unprecedented performance characteristics have been recorded (106 higher response to 200 nm than visible wavelengths, <0.1 nA dark currents); spectral features similar to those observed in natural diamond crystals have been observed indicating that the treatment used led to near ideal electronic characteristics from polycrystalline material.

  13. Ultraprecision Machining Characteristics of Poly-Crystalline Germanium

    NASA Astrophysics Data System (ADS)

    Yan, Jiwang; Takahashi, Yasunori; Tamaki, Jun'Ichi; Kubo, Akihiko; Kuriyagawa, Tsunemoto; Sato, Yutaka

    Germanium is an excellent infrared optical material. On most occasions, single-crystalline germanium is used as optical lens substrate because its homogeneous structure is beneficial for fabricating uniform optical surfaces. In this work, we attempt to use poly crystals as lens substrates instead of single crystals, which may lead to a significant reduction in production cost. We conducted ultraprecision cutting experiments on poly-crystalline germanium to examine the microscopic machinability. The crystal orientations of specific crystal grains were characterized, and the machining characteristics of these crystal grains including surface textures, cutting forces, and grain boundary steps were investigated under various machining conditions. It was possible to produce uniformly ductile-cut surfaces cross all crystal grains by using an extremely small undeformed chip thickness (˜ 80nm) under negative tool rake angles (˜ -45°). This work indicates the possibility of fabricating high-quality infrared optical components from poly-crystalline germanium.

  14. Further development and application of polycrystalline metal whiskers

    NASA Technical Reports Server (NTRS)

    Schladitz, H. J.

    1979-01-01

    High strength metal whiskers have a larger versatile field of application than monocrystalline whiskers. Although polycrystalline metal whiskers can be used for composites, preferably by extrusion in thermoplastics or by infiltration of resins or metals into whisker networks, the chief application at present may be the production and various use of whisker networks. Such networks can be produced up to high degrees of porosity and besides high mechanical strength, they have high inside surfaces and high electric conductivity. There are for instance, applications concerning construction of electrodes for batteries and fuel cells, catalysts and also new heat-exchanger material, capable of preparing fuel oil and gasoline in order to assist a high-efficiency combustion. The technical application of polycrystalline metal whiskers require their modification as well as the construction of a pilot production unit.

  15. Method of forming buried oxide layers in silicon

    DOEpatents

    Sadana, Devendra Kumar; Holland, Orin Wayne

    2000-01-01

    A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.

  16. A characterization study of a hydroxylated polycrystalline tin oxide surface

    NASA Technical Reports Server (NTRS)

    Hoflund, Gar B.; Grogan, Austin L., Jr.; Asbury, Douglas A.; Schryer, David R.

    1989-01-01

    In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

  17. Polycrystalline thin-film technology: Recent progress in photovoltaics

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe{sub 2}), cadmium telluride (CdTe), and thin-film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin-film CuInSe{sub 2}, has made some rapid advances in terms of high efficiency and long-term reliability. For CuInSe{sub 2} power modules, a world record has been reported on a 0.4-m{sup 2} module with an aperture-area efficiency of 10.4% and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe{sub 2} modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 cm{sup 2}. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10%; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  18. Paths for current flow in polycrystalline high temperature superconductors

    SciTech Connect

    Kroeger, D.M.; Goyal, A.; Specht, E.D.

    1995-12-01

    Determinations from x-ray and electron microdiffraction studies of the populations and geometrical arrangements of small angle grain boundaries in Bi-2223 and Bi-2212 conductors and Tl-1223 deposits suggest that current flow in these polycrystalline materials is percolative in character. Comparison of measured misorientation angle distributions to calculated distributions suggest that not only texture but also grain boundary energy is important in increasing the number of small angle grain boundaries.

  19. Irradiation effects in tungsten-copper laminate composite

    DOE PAGES

    Garrison, L. M.; Katoh, Yutai; Snead, Lance L.; Byun, Thak Sang; Reiser, Jens; Rieth, Michael

    2016-09-19

    Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410–780 °C and fast neutron fluences of 0.02–9.0 × 1025 n/m2, E > 0.1 MeV, 0.0039–1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa thismore » was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. In conclusion, tor elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.« less

  20. Alternative processing methods for tungsten-base composite materials

    SciTech Connect

    Ohriner, E.K.; Sikka, V.K.

    1995-12-31

    Tungsten composite materials contain large amounts of tungsten distributed in a continuous matrix phase. Current commercial materials include the tungsten-nickel-iron with cobalt replacing some or all of the iron, and also tungsten-copper materials. Typically, these are fabricated by liquid-phase sintering of blended powders. Liquid-phase sintering offers the advantages of low processing costs, established technology, and generally attractive mechanical properties. However, liquid-phase sintering is restricted to a very limited number of matrix alloying elements and a limited range of tungsten and alloying compositions. In the past few years, there has been interest in a wider range of matrix materials that offer the potential for superior composite properties. These must be processed by solid-state processes and at sufficiently low temperatures to avoid undesired reactions between the tungsten and the matrix phase. These processes, in order of decreasing process temperature requirements, include hot-isostatic pressing (HIPing), hot extrusion, and dynamic compaction. The HIPing and hot extrusion processes have also been used to improve mechanical properties of conventional liquid-phase-sintered materials. Results of laboratory-scale investigations of solid-state consolidation of a variety of matrix materials, including titanium, hafnium, nickel aluminide, and steels are reviewed. The potential advantages and disadvantages of each of the possible alternative consolidation processes are identified. Postconsolidation processing to control microstructure and macrostructure is discussed, including novel methods of controlling microstructure alignment.

  1. Alternative processing methods for tungsten-base composite materials

    SciTech Connect

    Ohriner, E.K.; Sikka, V.K.

    1996-06-01

    Tungsten composite materials contain large amounts of tungsten distributed in a continuous matrix phase. Current commercial materials include the tungsten-nickel-iron with cobalt replacing some or all of the iron, and also tungsten-copper materials. Typically, these are fabricated by liquid-phase sintering of blended powders. Liquid-phase sintering offers the advantages of low processing costs, established technology, and generally attractive mechanical properties. However, liquid-phase sintering is restricted to a very limited number of matrix alloying elements and a limited range of tungsten and alloying compositions. In the past few years, there has been interest in a wider range of matrix materials that offer the potential for superior composite properties. These must be processed by solid-state processes and at sufficiently low temperatures to avoid undesired reactions between the tungsten and the matrix phase. These processes, in order of decreasing process temperature requirements, include hot isostatic pressing (HEPing), hot extrusion, and dynamic compaction. The HIPing and hot extrusion processes have also been used to improve mechanical properties of conventional liquid-phase-sintered materials. The results of laboratory-scale investigations of solid-state consolidation of a variety of matrix materials, including titanium, hafnium, nickel aluminide, and steels are reviewed. The potential advantages and disadvantages of each of the possible alternative consolidation processes are identified. Post consolidation processing to control microstructure and macrostructure is discussed, including novel methods of controlling microstructure alignment.

  2. Ductile-Phase-Toughened Tungsten for Plasma-Facing Materials

    NASA Astrophysics Data System (ADS)

    Cunningham, Kevin Hawkins

    A variety of processing approaches were employed to fabricate ductile-phase-toughened (DPT) tungsten (W) composites. Mechanical testing and analytical modeling were used to guide composite development. This work provides a basis for further development of W composites to be used in structural divertor components of future fusion reactors. W wire was tested in tension, showing significant ductility and strength. Coatings of copper (Cu) or tungsten carbide (WC) were applied to the W wire via electrodeposition and carburization, respectively. Composites were fabricated using spark plasma sintering (SPS) to consolidate W powders together with each type of coated W wire. DPT behavior, e.g. crack arrest and crack bridging, was not observed in three-point bend testing of the sintered composites. A laminate was fabricated by hot pressing W and Cu foils together with W wires, and subsequently tested in tension. This laminate was bonded via hot pressing to thick W plate as a reinforcing layer, and the composite was tested in three-point bending. Crack arrest was observed along with some fiber pullout, but significant transverse cracking in the W plate confounded further fracture toughness analysis. The fracture toughness of thin W plate was measured in three-point bending. W plates were brazed with Cu foils to form a laminate. Crack arrest and crack bridging were observed in three-point bend tests of the laminate, and fracture resistance curves were successfully calculated for this DPT composite. An analytical model of crack bridging was developed using the basis described by Chao in previous work by the group. The model uses the specimen geometry, matrix properties, and the stress-displacement function of a ductile reinforcement ("bridging law") to calculate the fracture resistance curve (R-curve) and load-displacement curve (P-D curve) for any test specimen geometry. The code was also implemented to estimate the bridging law of an arbitrary composite using R-curve data

  3. In Situ Graphene Growth Dynamics on Polycrystalline Catalyst Foils

    PubMed Central

    2016-01-01

    The dynamics of graphene growth on polycrystalline Pt foils during chemical vapor deposition (CVD) are investigated using in situ scanning electron microscopy and complementary structural characterization of the catalyst with electron backscatter diffraction. A general growth model is outlined that considers precursor dissociation, mass transport, and attachment to the edge of a growing domain. We thereby analyze graphene growth dynamics at different length scales and reveal that the rate-limiting step varies throughout the process and across different regions of the catalyst surface, including different facets of an individual graphene domain. The facets that define the domain shapes lie normal to slow growth directions, which are determined by the interfacial mobility when attachment to domain edges is rate-limiting, as well as anisotropy in surface diffusion as diffusion becomes rate-limiting. Our observations and analysis thus reveal that the structure of CVD graphene films is intimately linked to that of the underlying polycrystalline catalyst, with both interfacial mobility and diffusional anisotropy depending on the presence of step edges and grain boundaries. The growth model developed serves as a general framework for understanding and optimizing the growth of 2D materials on polycrystalline catalysts. PMID:27576749

  4. Optical Properties of Anisotropic Polycrystalline Ce+3 activated LSO

    PubMed Central

    Roy, Sudesna; Lingertat, Helmut; Brecher, Charles; Sarin, Vinod

    2012-01-01

    Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission. PMID:23505329

  5. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials. PMID:26936563

  6. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials.

  7. Mechanical properties of irradiated multi-phase polycrystalline BCC materials

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Structure materials under severe irradiations in nuclear environments are known to degrade because of irradiation hardening and loss of ductility, resulting from irradiation-induced defects such as vacancies, interstitials and dislocation loops, etc. In this paper, we develop an elastic-viscoplastic model for irradiated multi-phase polycrystalline BCC materials in which the mechanical behaviors of individual grains and polycrystalline aggregates are both explored. At the microscopic grain scale, we use the internal variable model and propose a new tensorial damage descriptor to represent the geometry character of the defect loop, which facilitates the analysis of the defect loop evolutions and dislocation-defect interactions. At the macroscopic polycrystal scale, the self-consistent scheme is extended to consider the multiphase problem and used to bridge the individual grain behavior to polycrystal properties. Based on the proposed model, we found that the work-hardening coefficient decreases with the increase of irradiation-induced defect loops, and the orientation/loading dependence of mechanical properties is mainly attributed to the different Schmid factors. At the polycrystalline scale, numerical results for pure Fe match well with the irradiation experiment data. The model is further extended to predict the hardening effect of dispersoids in oxide-dispersed strengthened steels by the considering the Orowan bowing. The influences of grain size and irradiation are found to compete to dominate the strengthening behaviors of materials.

  8. Thin tungsten telluride layer preparation by thermal annealing.

    PubMed

    Lu, Wei; Zhang, Yudao; Zhu, Zusong; Lai, Jiawei; Zhao, Chuan; Liu, Xuefeng; Liu, Jing; Sun, Dong

    2016-10-14

    We report a simple method to prepare a thin Tungsten Telluride (WTe2) flake with accurate thickness control, which allows preparing and studying this two dimensional material conveniently. First, the WTe2 flake, which is relatively thick due to its strong interlayer van der Waals forces, is obtained by a conventional mechanical exfoliation method. Then, the exfoliated flake is annealed at 600 °C under a constant Ar protecting flow. Raman and atomic force spectroscopy characterizations demonstrate that thermal annealing can effectively thin down the WTe2 flake and retain its original lattice structure, though its surface smoothness is slightly deteriorated. Additionally, systematical study indicates that the thinning process strongly depends on the initial thickness of the WTe2 flake before annealing: the thinning rate increases from 0.12 nm min(-1) to 0.36 nm min(-1) as the initial thickness increases from 10 nm to 45 nm, while the roughness of the final product also increases with the increase of its initial thickness. However, the method fails when it is applied to WTe2 flakes thicker than 100 nm, resulting in uneven or burnt surface, which is possibly caused by big cavities formed by a large amount of defects gathered at the top surface.

  9. Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization

    NASA Astrophysics Data System (ADS)

    Neustetter, M.; Jabbour Al Maalouf, E.; Limão-Vieira, P.; Denifl, S.

    2016-08-01

    Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n+ (0 ≤ n ≤ 6) and W2(CO)n+ (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n+ (0 ≤ n ≤ 3) and W2C(CO)n+ (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.

  10. Thin tungsten telluride layer preparation by thermal annealing.

    PubMed

    Lu, Wei; Zhang, Yudao; Zhu, Zusong; Lai, Jiawei; Zhao, Chuan; Liu, Xuefeng; Liu, Jing; Sun, Dong

    2016-10-14

    We report a simple method to prepare a thin Tungsten Telluride (WTe2) flake with accurate thickness control, which allows preparing and studying this two dimensional material conveniently. First, the WTe2 flake, which is relatively thick due to its strong interlayer van der Waals forces, is obtained by a conventional mechanical exfoliation method. Then, the exfoliated flake is annealed at 600 °C under a constant Ar protecting flow. Raman and atomic force spectroscopy characterizations demonstrate that thermal annealing can effectively thin down the WTe2 flake and retain its original lattice structure, though its surface smoothness is slightly deteriorated. Additionally, systematical study indicates that the thinning process strongly depends on the initial thickness of the WTe2 flake before annealing: the thinning rate increases from 0.12 nm min(-1) to 0.36 nm min(-1) as the initial thickness increases from 10 nm to 45 nm, while the roughness of the final product also increases with the increase of its initial thickness. However, the method fails when it is applied to WTe2 flakes thicker than 100 nm, resulting in uneven or burnt surface, which is possibly caused by big cavities formed by a large amount of defects gathered at the top surface. PMID:27608057

  11. Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization.

    PubMed

    Neustetter, M; Jabbour Al Maalouf, E; Limão-Vieira, P; Denifl, S

    2016-08-01

    Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n (+) (0 ≤ n ≤ 6) and W2(CO)n (+) (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n (+) (0 ≤ n ≤ 3) and W2C(CO)n (+) (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves. PMID:27497555

  12. Thin tungsten telluride layer preparation by thermal annealing

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Zhang, Yudao; Zhu, Zusong; Lai, Jiawei; Zhao, Chuan; Liu, Xuefeng; Liu, Jing; Sun, Dong

    2016-10-01

    We report a simple method to prepare a thin Tungsten Telluride (WTe2) flake with accurate thickness control, which allows preparing and studying this two dimensional material conveniently. First, the WTe2 flake, which is relatively thick due to its strong interlayer van der Waals forces, is obtained by a conventional mechanical exfoliation method. Then, the exfoliated flake is annealed at 600 °C under a constant Ar protecting flow. Raman and atomic force spectroscopy characterizations demonstrate that thermal annealing can effectively thin down the WTe2 flake and retain its original lattice structure, though its surface smoothness is slightly deteriorated. Additionally, systematical study indicates that the thinning process strongly depends on the initial thickness of the WTe2 flake before annealing: the thinning rate increases from 0.12 nm min-1 to 0.36 nm min-1 as the initial thickness increases from 10 nm to 45 nm, while the roughness of the final product also increases with the increase of its initial thickness. However, the method fails when it is applied to WTe2 flakes thicker than 100 nm, resulting in uneven or burnt surface, which is possibly caused by big cavities formed by a large amount of defects gathered at the top surface.

  13. Deuterium thermal desorption from vacancy clusters in tungsten

    NASA Astrophysics Data System (ADS)

    Ryabtsev, S.; Gasparyan, Yu.; Zibrov, M.; Shubina, A.; Pisarev, A.

    2016-09-01

    Deuterium interaction with vacancy clusters in tungsten was studied by means of thermal desorption spectroscopy (TDS). A recrystallized W foil was used as a sample, and the vacancy clusters were formed in the bulk by irradiation with 10 keV/D ions to the fluence of 3 × 1019 D/m2 and subsequent annealing at the temperature of 800 K. Then the sample was loaded with deuterium (0.67 keV/D ions with a fluence of 1 × 1019 D/m2), and TDS measurements with varying heating rates β in the range of 0.25-4 K/s were performed. The high temperature peak with the maximum at around 700 K was attributed to deuterium desorption from vacancy clusters and the detrapping energy for this type of defects was determined from the slope of the Arrhenius-like plot ln (β / Tm2) versus 1 /Tm , where Tm is the peak position. The detrapping energy calculated this way is 2.10 ± 0.02 eV.

  14. T-1018 UCLA Spacordion Tungsten Powder Calorimeter

    SciTech Connect

    Trentalange, Stephen; Tsai, Oleg; Igo, George; Huang, Huan; Pan, Yu Xi; Dunkelberger, Jay; Xu, Wen Qin; Soha, Aria; Heppelmann, Steven; Gagliardi, Carl; /Texas A-M

    2011-11-16

    The present experiments at the BNL-RHIC facility are evolving towards physics goals which require the detection of medium energy electromagnetic particles (photons, electrons, neutral pions, eta mesons, etc.), especially at forward angles. New detectors will place increasing demands on energy resolution, hadron rejection and two-photon resolution and will require large area, high performance electromagnetic calorimeters in a variety of geometries. In the immediate future, either RHIC or JLAB will propose a facility upgrade (Electron-Ion Collider, or EIC) with physics goals such as electron-heavy ion collisions (or p-A collisions) with a wide range of calorimeter requirements. An R and D program based at Brookhaven National Laboratory has awarded the group funding of approximately $110,000 to develop new types of calorimeters for EIC experiments. The UCLA group is developing a method to manufacture very flexible and cost-effective, yet high quality calorimeters based on scintillating fibers and tungsten powder. The design and features of the calorimeter can be briefly stated as follows: an arbitrarily large number of small diameter fibers (< 0.5 mm) are assembled as a matrix and held rigidly in place by a set of precision screens inside an empty container. The container is then back-filled with tungsten powder, compacted on a vibrating table and infused with epoxy under vacuum. The container is then removed. The resulting sub-modules are extremely uniform and achieve roughly the density of pure Lead. The sub-modules are stacked together to achieve a final detector of the desired shape. There is no dead space between sub-modules and the fibers can be in an accordion geometry bent to prevent 'channeling' of the particles due to accidental alignment of their track with the module axis. This technology has the advantage of being modular and inexpensive to the point where the construction work may be divided among groups the size of typical university physics departments

  15. Tungsten-molybdenum fractionation in estuarine environments

    NASA Astrophysics Data System (ADS)

    Mohajerin, T. Jade; Helz, George R.; Johannesson, Karen H.

    2016-03-01

    Dissolved tungsten (W) and molybdenum (Mo) concentrations were measured in surface waters and sediment pore waters of Terrebonne Bay, a shallow estuary in the Mississippi River delta, to investigate the biogeochemical processes that fractionate these Group 6 elements relative to one another during transit from weathering to sedimentary environments. Although many of the chemical properties of W and Mo are similar, the two elements behave autonomously, and the fractionation mechanisms are only partly understood. In sulfidic pore waters, dissolved Mo is depleted relative to river water-seawater mixtures, whereas dissolved W is >10-fold enriched. Reductive dissolution of poorly crystalline phases like ferrihydrite, which is a preferential host of W relative to Mo in grain coatings on river-borne particles, can explain the dissolved W enrichment. Dissolved W becomes increasingly enriched as H2S(aq) rises above about 60 μM due to transformation of WO42- to thiotungstates as well as to additional reductive dissolution of phases that host W. In contrast, as rising sulfide transforms MoO42- to thiomolybdates in pore waters, dissolved Mo is suppressed, probably owing to equilibration with an Fe-Mo-S phase. This putative phase appears to control the aqueous ion product, Q = [Fe2+][MoS42-]0.6 [H2S0]0.4/[H+]0.8, at a value of 10-7.78. Concentrations of dissolved W and Mo in pore waters bear no relation to concentrations in surface waters of the same salinity. In surface waters, dissolved Mo is nearly conserved in the estuarine mixing zone. Dissolved W appears also to be conserved except for several cases where W may have been enhanced by exchange with underlying, W-rich pore waters. With increasing salinity, the molar Mo/W ratio rises from about 10 to about 1000 in surface waters whereas it is mostly <10 in underlying pore waters and in highly sulfidic pore waters is mostly near 1. Differences in two chemical properties may account for this fractionation of Mo with respect to

  16. Creep behavior of tungsten/niobium and tungsten/niobium-1 percent zirconium composites

    NASA Technical Reports Server (NTRS)

    Petrasek, D. W.; Titran, R. H.

    1988-01-01

    A study was conducted to determine the feasibility of using tungsten fiber reinforced niobium or niobium-1 percent zirconium matrix composites to meet the anticipated increased temperature and creep resistance requirements imposed by advanced space power systems. The results obtained on the short time tensile properties indicated that W/Nb composites showed significant improvements in high temperature strength and offer significant mass reductions for high temperature space power systems. The prime material requirement for space power systems applications is long time creep resistance. A study was conducted to determine the effect of high temperature exposure on the properties of these composites, with emphasis upon their creep behavior at elevated temperatures.

  17. The formation of tungsten doped Al2O3/ZnO coatings on aluminum by plasma electrolytic oxidation and their application in photocatalysis

    NASA Astrophysics Data System (ADS)

    Stojadinović, Stevan; Vasilić, Rastko; Radić, Nenad; Tadić, Nenad; Stefanov, Plamen; Grbić, Boško

    2016-07-01

    Tungsten doped Al2O3/ZnO coatings are formed by plasma electrolytic oxidation of aluminum substrate in supporting electrolyte (0.1 M boric acid + 0.05 M borax + 2 g/L ZnO) with addition of different concentrations of Na2WO4·2H2O. The morphology, crystal structure, chemical composition, and light absorption characteristics of formed surface coatings are investigated. The X-ray diffraction and X-ray photoelectron spectroscopy results indicate that formed surface coatings consist of alpha and gamma phase of Al2O3, ZnO, metallic tungsten and WO3. Obtained results showed that incorporated tungsten does not have any influence on the absorption spectra of Al2O3/ZnO coatings, which showed invariable band edge at about 385 nm. The photocatalytic activity of undoped and tungsten doped Al2O3/ZnO coatings is estimated by the photodegradation of methyl orange. The photocatalytic activity of tungsten doped Al2O3/ZnO coatings is higher thanof undoped Al2O3/ZnO coatings; the best photocatalytic activity is ascribed to coatings formed in supporting electrolyte with addition of 0.3 g/L Na2WO4·2H2O. Tungsten in Al2O3/ZnO coatings acts as a charge trap, thus reducing the recombination rate of photogenerated electron-hole pairs. The results of PL measurements are in agreement with photocatalytic activity. Declining PL intensity corresponds to increasing photocatalytic activity of the coatings, indicating slower recombination of electron-hole pairs.

  18. Polycrystalline silicon study: Low-cost silicon refining technology prospects and semiconductor-grade polycrystalline silicon availability through 1988

    NASA Technical Reports Server (NTRS)

    Costogue, E. N.; Ferber, R.; Lutwack, R.; Lorenz, J. H.; Pellin, R.

    1984-01-01

    Photovoltaic arrays that convert solar energy into electrical energy can become a cost effective bulk energy generation alternative, provided that an adequate supply of low cost materials is available. One of the key requirements for economic photovoltaic cells is reasonably priced silicon. At present, the photovoltaic industry is dependent upon polycrystalline silicon refined by the Siemens process primarily for integrated circuits, power devices, and discrete semiconductor devices. This dependency is expected to continue until the DOE sponsored low cost silicon refining technology developments have matured to the point where they are in commercial use. The photovoltaic industry can then develop its own source of supply. Silicon material availability and market pricing projections through 1988 are updated based on data collected early in 1984. The silicon refining industry plans to meet the increasing demands of the semiconductor device and photovoltaic product industries are overviewed. In addition, the DOE sponsored technology research for producing low cost polycrystalline silicon, probabilistic cost analysis for the two most promising production processes for achieving the DOE cost goals, and the impacts of the DOE photovoltaics program silicon refining research upon the commercial polycrystalline silicon refining industry are addressed.

  19. Effect of reinforcement phase on the mechanical property of tungsten nanocomposite synthesized by spark plasma sintering

    SciTech Connect

    Lee, Jin -Kyu; Kim, Song -Yi; Ott, Ryan T.; Kim, Jin -Young; Eckert, Jürgen; Lee, Min -Ha

    2015-07-15

    Nanostructured tungsten composites were fabricated by spark plasma sintering of nanostructured composite powders. The composite powders, which were synthesized by mechanical milling of tungsten and Ni-based alloy powders, are comprised of alternating layers of tungsten and metallic glass several hundred nanometers in size. The mechanical behavior of the nanostructured W composite is similar to pure tungsten, however, in contrast to monolithic pure tungsten, some macroscopic compressive plasticity accompanies the enhanced maximum strength up to 2.4 GPa by introducing reinforcement. As a result, we have found that the mechanical properties of the composites strongly depend on the uniformity of the nano-grained tungsten matrix and reinforcement phase distribution.

  20. Tungsten Oxides for Photocatalysis, Electrochemistry, and Phototherapy.

    PubMed

    Huang, Zhen-Feng; Song, Jiajia; Pan, Lun; Zhang, Xiangwen; Wang, Li; Zou, Ji-Jun

    2015-09-23

    The conversion, storage, and utilization of renewable energy have all become more important than ever before as a response to ever-growing energy and environment concerns. The performance of energy-related technologies strongly relies on the structure and property of the material used. The earth-abundant family of tungsten oxides (WOx ≤3 ) receives considerable attention in photocatalysis, electrochemistry, and phototherapy due to their highly tunable structures and unique physicochemical properties. Great breakthroughs have been made in enhancing the optical absorption, charge separation, redox capability, and electrical conductivity of WOx ≤3 through control of the composition, crystal structure, morphology, and construction of composite structures with other materials, which significantly promotes the efficiency of processes and devices based on this material. Herein, the properties and synthesis of WOx ≤3 family are reviewed, and then their energy-related applications are highlighted, including solar-light-driven water splitting, CO2 reduction, and pollutant removal, electrochromism, supercapacitors, lithium batteries, solar and fuel cells, non-volatile memory devices, gas sensors, and cancer therapy, from the aspect of function-oriented structure design and control.

  1. The DAMPE silicon-tungsten tracker

    NASA Astrophysics Data System (ADS)

    Azzarello, P.; Ambrosi, G.; Asfandiyarov, R.; Bernardini, P.; Bertucci, B.; Bolognini, A.; Cadoux, F.; Caprai, M.; De Mitri, I.; Domenjoz, M.; Dong, Y.; Duranti, M.; Fan, R.; Fusco, P.; Gallo, V.; Gargano, F.; Gong, K.; Guo, D.; Husi, C.; Ionica, M.; La Marra, D.; Loparco, F.; Marsella, G.; Mazziotta, M. N.; Mesa, J.; Nardinocchi, A.; Nicola, L.; Pelleriti, G.; Peng, W.; Pohl, M.; Postolache, V.; Qiao, R.; Surdo, A.; Tykhonov, A.; Vitillo, S.; Wang, H.; Weber, M.; Wu, D.; Wu, X.; Zhang, F.

    2016-09-01

    The DArk Matter Particle Explorer (DAMPE) is a spaceborne astroparticle physics experiment, launched on 17 December 2015. DAMPE will identify possible dark matter signatures by detecting electrons and photons in the 5 GeV-10 TeV energy range. It will also measure the flux of nuclei up to 100 TeV, for the study of the high energy cosmic ray origin and propagation mechanisms. DAMPE is composed of four sub-detectors: a plastic strip scintillator, a silicon-tungsten tracker-converter (STK), a BGO imaging calorimeter and a neutron detector. The STK is composed of six tracking planes of 2 orthogonal layers of single-sided micro-strip detectors, for a total detector surface of ca. 7 m2. The STK has been extensively tested for space qualification. Also, numerous beam tests at CERN have been done to study particle detection at silicon module level, and at full detector level. After description of the DAMPE payload and its scientific mission, we will describe the STK characteristics and assembly. We will then focus on some results of single ladder performance tests done with particle beams at CERN.

  2. Anthocyanins facilitate tungsten accumulation in Brassica

    SciTech Connect

    Hale, K.L.

    2002-11-01

    Accumulation of molybdenum in Brassica was recently found to be correlated with anthocyanin content, involving the formation of a blue complex. Here the role of anthocyanins in tungsten sequestration was investigated using three species of Brassica: B. rapa (cv. Fast plants), B. juncea (Indian mustard) and B. oleracea (red cabbage). Seedlings of B. rapa and B. juncea turned blue when supplied with colourless tungstate. The blue compound co-localized with anthocyanins in the peripheral cell layers, and the degree of blueness was correlated with anthocyanin content. The direct involvement of anthocyanins in the blue coloration was evident when purified anthocyanins showed a colour change from pink to blue in vitro upon addition of tungstate, over a wide pH range. Anthocyanin production was upregulated 3-fold by W in B. juncea, possibly reflecting a function for anthocyanins in W tolerance or sequestration. The presence of anthocyanins facilitated W accumulation in B. rapa: anthocyanin-containing seedlings accumulated 3-fold more W than an anthocyaninless mutant. There was no correlation between anthocyanin content and W tolerance under these conditions. The nature of the interaction between anthocyanins and tungstate was investigated. X-ray absorption spectroscopy showed no change in the local chemical environment of Wupon uptake of tungstate by the plant; HPLC analysis of purified anthocyanin with or without tungstate showed no peak shift after metal treatment.

  3. Rarefied gas flow through nanoscale tungsten channels.

    PubMed

    Ozhgibesov, M S; Leu, T S; Cheng, C H

    2013-05-01

    The aim of this work is to investigate argon flow behaviors through the channels with three types of boundary conditions. Current work deals with numerical simulations of rarefied gas flow through nano-channels using the Molecular Dynamics method. Taking into account that this method is very time consuming, we implemented all the simulations using CUDA capable graphic cards. We found that the well-known and relatively simple Maxwell model of boundary conditions is able to reproduce gas flow through a tungsten channel with irregularities and roughness, while it results in a significant error in the case of a smooth metal surface. We further found that the flow rate through a relatively short channel correlates nonlinearly with the channel's length. This finding is in contrast with the results available in extant literature. Our results are important for both numerical and theoretical analyses of rarefied gas flow in micro- and nano-systems where the choice of boundary conditions significantly influences flow. PMID:23528809

  4. Signal Analysis of Gas Tungsten Arc Welds

    NASA Technical Reports Server (NTRS)

    Eagar, T. W.

    1985-01-01

    Gas tungsten arc welding is a process in which the input parameters such as current, voltage and travel speed, can be easily controlled and/or monitored. However, weld quality is not solely a function of these parameters. An adaptive method of observing weld quality is desired to improve weld quality assurance. The use of dynamic electrical properties of the welding arc as a weld quality monitor was studied. The electrical properties of the arc are characterized by the current voltage transfer function. The hardware and software necessary to collect the data at a maximum rate of 45 kHz and to allow the off-line processing of this data are tested. The optimum input current waveform is determined. Bead-on-plate welds to observe such characteristics of the weld as the fundamental frequency of the puddle are studied. Future work is planned to observe changes of the arc response with changes in joint geometry, base metal chemistry, and shielding gas composition are discussed.

  5. Understanding the Oxygen Vacancy in Tungsten Trioxide

    NASA Astrophysics Data System (ADS)

    Wang, Wennie; Janotti, Anderson; van de Walle, Chris G.

    2015-03-01

    Tungsten trioxide (WO3) has a variety of applications in gas sensors, photocatalysis, and smart windows. As an electrochromic BO3 perovskite, WO3 turns from transparent to blue upon doping. This color change is correlated with a drop in transmittance of near-IR radiation, and is used in smart windows for energy efficiency. In addition to monovalent species doping that modulates optical properties, oxygen deficiencies have been found to have a similar electrochromic effect. The influence of oxygen vacancies on electronic structure and how it corresponds to electrochromic behavior remains a topic of debate. In this work, we examine the oxygen vacancy in monoclinic WO3 and its influence on electronic structure using density functional theory with a hybrid functional. We investigate the relative stability of different charge states and its implications for electrical properties, such as conductivity and electrochromism. We find oxygen vacancies to be shallow donors, and explore similarities and differences with monovalent species doping. Finally, we compare our theoretical findings with experiment to elucidate how vacancies may contribute to electrochromic behavior. This work is supported by DOE and NSF.

  6. Abnormal thermal conductivity in tetragonal tungsten bronze Ba{sub 6−x}Sr{sub x}Nb{sub 10}O{sub 30}

    SciTech Connect

    Kolodiazhnyi, T. Sakurai, H.; Vasylkiv, O.; Borodianska, H.; Mozharivskyj, Y.

    2014-03-17

    Ba{sub 6−x}Sr{sub x}Nb{sub 10}O{sub 30} solid solution with 0 ≤ x ≤ 6 crystallizes in centrosymmetric tetragonal “tungsten bronze” structure (space group P4/mbm). We report on the x dependence of thermal conductivity of polycrystalline samples measured in the 2–400 K temperature interval. Substitution of Sr for Ba brings about a significant decrease in thermal conductivity at x ≥ 3 accompanied by development of a low-temperature (T ≈ 10–30 K) “plateau” region reminiscent of a glass-like compounds. We explain this behaviour based on a size-driven site occupancy and atomic displacement parameters associated with an alkaline earth atomic positions in the title compounds.

  7. Growth and tribological properties of diamond films on silicon and tungsten carbide substrates

    NASA Astrophysics Data System (ADS)

    Radhika, R.; Ramachandra Rao, M. S.

    2016-11-01

    Hot filament chemical vapor deposition technique was used to deposit microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films on silicon (Si) and tungsten carbide (WC-6Co) substrates. Friction coefficient of larger diamond grains deposited on WC-6Co substrate shows less value approximately 0.2 while this differs marginally on films grown on Si substrate. The study claims that for a less friction coefficient, the grain size is not necessarily smaller. However, the less friction coefficient (less than 0.1 saturated value) in MCD and NCD deposited on Si is explained by the formation of graphitized tribolayer. This layer easily forms when diamond phase is thermodynamically unstable.

  8. Deposition studies of lithium and bismuth at tungsten microelectrodes in LiCl:KCl eutectic

    NASA Astrophysics Data System (ADS)

    Carlin, Richard T.; Osteryoung, Robert A.

    1989-05-01

    Tungsten microelectrodes (diam = 25 microns) have been used to study the deposition and stripping behavior of Li/Li(+) and Bi/Bi(3+) in the LiCl:KCl eutectic at 400 C. The Li deposition current can be simulated assuming the growth of a single hemisphere of liquid metal on the microelectrode. High stripping current densities were observed and quantitated using standard electrochemical equipment. An inverted microscope assembly was employed for in situ observation of the Li/Li(+) deposition and stripping processes at the microelectrode. A precipitate appears to form in the melt surrounding the electrode during Li deposition.

  9. Tungsten Contact and Line Resistance Reduction with Advanced Pulsed Nucleation Layer and Low Resistivity Tungsten Treatment

    NASA Astrophysics Data System (ADS)

    Chandrashekar, Anand; Chen, Feng; Lin, Jasmine; Humayun, Raashina; Wongsenakhum, Panya; Chang, Sean; Danek, Michal; Itou, Takamasa; Nakayama, Tomoo; Kariya, Atsushi; Kawaguchi, Masazumi; Hizume, Shunichi

    2010-09-01

    This paper describes electrical testing results of new tungsten chemical vapor deposition (CVD-W) process concepts that were developed to address the W contact and bitline scaling issues on 55 nm node devices. Contact resistance (Rc) measurements in complementary metal oxide semiconductor (CMOS) devices indicate that the new CVD-W process for sub-32 nm and beyond - consisting of an advanced pulsed nucleation layer (PNL) combined with low resistivity tungsten (LRW) initiation - produces a 20-30% drop in Rc for diffused NiSi contacts. From cross-sectional bright field and dark field transmission electron microscopy (TEM) analysis, such Rc improvement can be attributed to improved plugfill and larger in-feature W grain size with the advanced PNL+LRW process. More experiments that measured contact resistance for different feature sizes point to favorable Rc scaling with the advanced PNL+LRW process. Finally, 40% improvement in line resistance was observed with this process as tested on 55 nm embedded dynamic random access memory (DRAM) devices, confirming that the advanced PNL+LRW process can be an effective metallization solution for sub-32 nm devices.

  10. Kinetics of scheelite dissolution in groundwater: defining the release rate of tungsten contamination from a natural source

    NASA Astrophysics Data System (ADS)

    Montgomery, S. D.; Mckibben, M. A.

    2011-12-01

    Tungsten, an emerging contaminant, has no EPA standard for its permissible levels in drinking water. At sites in California, Nevada, and Arizona there may be a correlation between elevated levels of tungsten in drinking water and clusters of childhood acute lymphocytic leukemia (ALL). Developing a better understanding of how tungsten is released from rocks into surface and groundwaters is therefore of growing environmental interest. Knowledge of tungstate ore mineral weathering processes, particularly the rates of dissolution of scheelite (CaWO4) in groundwater, could improve models of how tungsten is released and transported in natural waters. Our research is focusing on experimental determination of the rates and products of tungstate mineral dissolution in synthetic groundwater, as a function of temperature, pH and mineral surface area. The initial rate method is being used to develop rate laws. Batch reactor experiments are conducted within constant temperature circulation baths over a pH range of 2-9. Cleaned scheelite powder with grain diameters of 106-150um is placed between two screens in a sample platform and then placed inside a two liter Teflon vessel filled with synthetic groundwater. Ports on the vessel allow sample extraction, temperature and pH measurement, gas inflow, and water circulation. Aliquots of solution are taken periodically for product analysis by ICP -MS. Changes in mineral surface characteristics are monitored using SEM and EDS methods. Results so far reveal that the dissolution of scheelite is incongruent at both neutral and low pH. Solid tungstic acid forms on scheelite mineral surfaces under acidic conditions, implying that this phase controls the dissolution rate in acidic environments. The influence of dissolved CO2 and resultant calcium carbonate precipitation on the dissolution of scheelite at higher pH is also being investigated. The rate law being developed for scheelite dissolution will be useful in reactive-transport computer

  11. Ultralow thermal conductivity in polycrystalline CdSe thin films with controlled grain size.

    PubMed

    Feser, Joseph P; Chan, Emory M; Majumdar, Arun; Segalman, Rachel A; Urban, Jeffrey J

    2013-05-01

    Polycrystallinity leads to increased phonon scattering at grain boundaries and is known to be an effective method to reduce thermal conductivity in thermoelectric materials. However, the fundamental limits of this approach are not fully understood, as it is difficult to form uniform sub-20 nm grain structures. We use colloidal nanocrystals treated with functional inorganic ligands to obtain nanograined films of CdSe with controlled characteristic grain size between 3 and 6 nm. Experimental measurements demonstrate that thermal conductivity in these composites can fall beneath the prediction of the so-called minimum thermal conductivity for disordered crystals. The measurements are consistent, however, with diffuse boundary scattering of acoustic phonons. This apparent paradox can be explained by an overattribution of transport to high-energy phonons in the minimum thermal conductivity model where, in compound semiconductors, optical and zone edge phonons have low group velocity and high scattering rates.

  12. Observing Graphene Grow: Catalyst–Graphene Interactions during Scalable Graphene Growth on Polycrystalline Copper

    PubMed Central

    2013-01-01

    Complementary in situ X-ray photoelectron spectroscopy (XPS), X-ray diffractometry, and environmental scanning electron microscopy are used to fingerprint the entire graphene chemical vapor deposition process on technologically important polycrystalline Cu catalysts to address the current lack of understanding of the underlying fundamental growth mechanisms and catalyst interactions. Graphene forms directly on metallic Cu during the high-temperature hydrocarbon exposure, whereby an upshift in the binding energies of the corresponding C1s XPS core level signatures is indicative of coupling between the Cu catalyst and the growing graphene. Minor carbon uptake into Cu can under certain conditions manifest itself as carbon precipitation upon cooling. Postgrowth, ambient air exposure even at room temperature decouples the graphene from Cu by (reversible) oxygen intercalation. The importance of these dynamic interactions is discussed for graphene growth, processing, and device integration. PMID:24041311

  13. Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

    NASA Astrophysics Data System (ADS)

    Machida, Emi; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ikenoue, Hiroshi

    2012-12-01

    We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 μm, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

  14. Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

    SciTech Connect

    Machida, Emi; Horita, Masahiro; Ishikawa, Yasuaki; Uraoka, Yukiharu; Ikenoue, Hiroshi

    2012-12-17

    We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 {mu}m, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

  15. Observing graphene grow: catalyst-graphene interactions during scalable graphene growth on polycrystalline copper.

    PubMed

    Kidambi, Piran R; Bayer, Bernhard C; Blume, Raoul; Wang, Zhu-Jun; Baehtz, Carsten; Weatherup, Robert S; Willinger, Marc-Georg; Schloegl, Robert; Hofmann, Stephan

    2013-10-01

    Complementary in situ X-ray photoelectron spectroscopy (XPS), X-ray diffractometry, and environmental scanning electron microscopy are used to fingerprint the entire graphene chemical vapor deposition process on technologically important polycrystalline Cu catalysts to address the current lack of understanding of the underlying fundamental growth mechanisms and catalyst interactions. Graphene forms directly on metallic Cu during the high-temperature hydrocarbon exposure, whereby an upshift in the binding energies of the corresponding C1s XPS core level signatures is indicative of coupling between the Cu catalyst and the growing graphene. Minor carbon uptake into Cu can under certain conditions manifest itself as carbon precipitation upon cooling. Postgrowth, ambient air exposure even at room temperature decouples the graphene from Cu by (reversible) oxygen intercalation. The importance of these dynamic interactions is discussed for graphene growth, processing, and device integration. PMID:24041311

  16. The sensitivity of mechanical properties of TFRS composites to variations in reaction zone size and properties. [Tungsten Fiber Reinforced Superalloys

    NASA Technical Reports Server (NTRS)

    Craddock, James N.; Hopkins, Dale A.; Petrasek, Donald W.; Brindley, Pamela K.

    1987-01-01

    The properties of tungsten fiber reinforced superalloys (TFRS) composites are calculated using a 3-component micromechanical model. The properties and size of the reaction zone are varied and the effect of these variations on the composite properties are studied. Results are presented in graphical and tabular form. Post-matrix yield behavior is examined in terms of the tangent modulus of the composite and measures of the effective strength of the lamina.

  17. Tungsten dust impact on ITER-like plasma edge

    DOE PAGES

    Smirnov, R. D.; Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2015-01-12

    The impact of tungsten dust originating from divertor plates on the performance of edge plasma in ITER-like discharge is evaluated using computer modeling with the coupled dust-plasma transport code DUSTT-UEDGE. Different dust injection parameters, including dust size and mass injection rates, are surveyed. It is found that tungsten dust injection with rates as low as a few mg/s can lead to dangerously high tungsten impurity concentrations in the plasma core. Dust injections with rates of a few tens of mg/s are shown to have a significant effect on edge plasma parameters and dynamics in ITER scale tokamaks. The large impactmore » of certain phenomena, such as dust shielding by an ablation cloud and the thermal force on tungsten ions, on dust/impurity transport in edge plasma and consequently on core tungsten contamination level is demonstrated. Lastly, it is also found that high-Z impurities provided by dust can induce macroscopic self-sustained plasma oscillations in plasma edge leading to large temporal variations of edge plasma parameters and heat load to divertor target plates.« less

  18. Tungsten dust impact on ITER-like plasma edge

    SciTech Connect

    Smirnov, R. D. Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2015-01-15

    The impact of tungsten dust originating from divertor plates on the performance of edge plasma in ITER-like discharge is evaluated using computer modeling with the coupled dust-plasma transport code DUSTT-UEDGE. Different dust injection parameters, including dust size and mass injection rates, are surveyed. It is found that tungsten dust injection with rates as low as a few mg/s can lead to dangerously high tungsten impurity concentrations in the plasma core. Dust injections with rates of a few tens of mg/s are shown to have a significant effect on edge plasma parameters and dynamics in ITER scale tokamaks. The large impact of certain phenomena, such as dust shielding by an ablation cloud and the thermal force on tungsten ions, on dust/impurity transport in edge plasma and consequently on core tungsten contamination level is demonstrated. It is also found that high-Z impurities provided by dust can induce macroscopic self-sustained plasma oscillations in plasma edge leading to large temporal variations of edge plasma parameters and heat load to divertor target plates.

  19. Tungsten dust impact on ITER-like plasma edge

    SciTech Connect

    Smirnov, R. D.; Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2015-01-12

    The impact of tungsten dust originating from divertor plates on the performance of edge plasma in ITER-like discharge is evaluated using computer modeling with the coupled dust-plasma transport code DUSTT-UEDGE. Different dust injection parameters, including dust size and mass injection rates, are surveyed. It is found that tungsten dust injection with rates as low as a few mg/s can lead to dangerously high tungsten impurity concentrations in the plasma core. Dust injections with rates of a few tens of mg/s are shown to have a significant effect on edge plasma parameters and dynamics in ITER scale tokamaks. The large impact of certain phenomena, such as dust shielding by an ablation cloud and the thermal force on tungsten ions, on dust/impurity transport in edge plasma and consequently on core tungsten contamination level is demonstrated. Lastly, it is also found that high-Z impurities provided by dust can induce macroscopic self-sustained plasma oscillations in plasma edge leading to large temporal variations of edge plasma parameters and heat load to divertor target plates.

  20. Stable Lewis acid chelate of a bis(imido) tungsten compound and implications for alpha-olefin dimerisation catalysis: a DFT study.

    PubMed

    Tobisch, Sven

    2008-04-28

    Dimerisation of alpha-olefins by a catalyst system comprising of a bis(imido) tungsten compound and a Lewis acid component has been investigated by density functional theory employing a catalyst model that closely mimics the real system together with ethylene chosen as a prototypical substrate. This study disclosed that the Lewis acid preferably forms four-membered chelates by bridging across tungsten-imido linkages. Complexation at one imido group is predicted as the favourable, stable mode of Lewis acid association onto a bis(imido) tungsten(VI) compound. The computational analysis revealed that the cocatalyst affects the energetics of the several steps to a different extent. Formation of the five-membered tungstanacycle and the further growth is moderately influenced, this is in contrast to its profound influence on metallacycle degradation. AlClMe2 chelation of both tungsten-imido groups is seen as being most effective in smoothing the energetics of the dimer-generating route. The predicted energy profile of the most accessible pathway, however, is at odds with observed catalytic abilities. This study indicates that the removal of one imido ligand by the Lewis acid is a viable process, thereby suggesting that mono(imido) tungsten compounds are effective in dimerisation catalysis of the reported catalyst system.

  1. Advances in polycrystalline thin-film photovoltaics for space applications

    SciTech Connect

    Lanning, B.R.; Armstrong, J.H.; Misra, M.S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 eV and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not `reactor-specific` and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a `substrate configuration` by physical vapor deposition techniques and CdTe cells/modules are fabricated in a `superstrate configuration` by wet chemical methods.

  2. Microstructure and texture analyses of polycrystalline ice during hot torsion

    NASA Astrophysics Data System (ADS)

    Journaux, B.; Montagnat, M.; Gest, L.; Barou, F.; Chauve, T.

    2015-12-01

    Water ice Ih is a material with very high plastic anisotropy where deformation is mainly accommodated by dislocation glide on the (0001) plane. This anisotropy gives rise to strong strain incompatibilities between grains during deformation, and therefore impacts texture and microstructure evolution. Accurate understanding of ice mechanical properties is significant for several areas of research such as glaciology, planetary sciences, but also in geosciences and metallurgy as ice can be seen as a model material with easier experimental handling at near melting temperatures. In the present study, we used torsion experiments to study non-coaxial shear strain (γ), very common in natural environments, up to very high values of γ. Numerous studies determined microstructure and texture evolution in polycrystalline assemblage submitted to torsion (metallic alloys and geological materials) but a very limited number focused on polycrystalline ice. Full cylinders of randomly oriented polycrystalline ice (grain size ~ 1 mm) were placed in a torsion apparatus and deformed under ductile regime under constant imposed torque at 266K (0.97 Tf). Macroscopic shear was monitored using a LVDT device or a rotary encoder. Several torsion tests with maximal shear strain up to γmax = 1 were performed. Tangent and axial sections were analyzed ex-situ using Automatic Ice Texture Analyzer (AITA) and Electron BackScatter Diffraction (EBSD). We were able to confirm the previously observed bimodal preferred orientation of the basal slip plane. Macroscopic strain evolution γ(t) displays a weakening after γmax = 0.04 (ɛmax ≃ 2 %), due to the beginning of dynamic recrystallization (DRX) processes. EBSD data provide novel informations on the microstructure that suggest very efficient grain boundary migration processes. In particular, we were able to measure differences of intra-granular misorientations density between the two ODF maxima populations that can highlight the role of DRX

  3. Polycrystalline lead selenide: the resurgence of an old infrared detector

    NASA Astrophysics Data System (ADS)

    Vergara, G.; Montojo, M. T.; Torquemada, M. C.; Rodrigo, M. T.; Sánchez, F. J.; Gómez, L. J.; Almazán, R. M.; Verdú, M.; Rodríguez, P.; Villamayor, V.; Álvarez, M.; Diezhandino, J.; Plaza, J.; Catalán, I.

    2007-06-01

    The existing technology for uncooled MWIR photon detectors based on polycrystalline lead salts is stigmatized for being a 50-year-old technology. It has been traditionally relegated to single-element detectors and relatively small linear arrays due to the limitations imposed by its standard manufacture process based on a chemical bath deposition technique (CBD) developed more than 40 years ago. Recently, an innovative method for processing detectors, based on a vapour phase deposition (VPD) technique, has allowed manufacturing the first 2D array of polycrystalline PbSe with good electro optical characteristics. The new method of processing PbSe is an all silicon technology and it is compatible with standard CMOS circuitry. In addition to its affordability, VPD PbSe constitutes a perfect candidate to fill the existing gap in the photonic and uncooled IR imaging detectors sensitive to the MWIR photons. The perspectives opened are numerous and very important, converting the old PbSe detector in a serious alternative to others uncooled technologies in the low cost IR detection market. The number of potential applications is huge, some of them with high commercial impact such as personal IR imagers, enhanced vision systems for automotive applications and other not less important in the security/defence domain such as sensors for active protection systems (APS) or low cost seekers. Despite the fact, unanimously accepted, that uncooled will dominate the majority of the future IR detection applications, today, thermal detectors are the unique plausible alternative. There is plenty of room for photonic uncooled and complementary alternatives are needed. This work allocates polycrystalline PbSe in the current panorama of the uncooled IR detectors, underlining its potentiality in two areas of interest, i.e., very low cost imaging IR detectors and MWIR fast uncooled detectors for security and defence applications. The new method of processing again converts PbSe into an

  4. Ion beam nitriding of single and polycrystalline austenitic stainless steel

    SciTech Connect

    Abrasonis, G.; Riviere, J.P.; Templier, C.; Declemy, A.; Pranevicius, L.; Milhet, X.

    2005-04-15

    Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 deg. C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm{sup -2}. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the <001> being more preferential for nitrogen diffusion than <011>. In both type of samples, XRD analysis shows the presence of the phase usually called 'expanded' austenite or {gamma}{sub N} phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress.

  5. Interaction of atomic and low-energy deuterium with tungsten pre-irradiated with self-ions

    NASA Astrophysics Data System (ADS)

    Ogorodnikova, O. V.; Markelj, S.; von Toussaint, U.

    2016-02-01

    Polycrystalline tungsten (W) specimens were pre-irradiated with self-ions to create identical samples with high density of defects up to ˜2.5 μm near the surface. Then, W specimens were exposed to either thermal atomic deuterium (D) beam with an incident energy of ˜0.2 eV or low energy D plasma with the incident energy varied between 5 and 200 eV at different sample temperatures. Each sample was exposed once at certain temperature and fluence. The D migration and accumulation in W were studied post-mortem by nuclear reaction method. It was shown that the rate of the D to occupy radiation-induced defects increases with increasing the incident energy, ion flux, and temperature. Experimental investigation was accompanied by modelling using the rate-equation model. Moreover, the analytical model was developed and benchmarked against numerical model. The calculations of the deuterium diffusion with trapping at radiation-induced defects in tungsten by analytical model are consistent with numerical calculations using rate-equation model. The data of reflection and penetration of atomic and low-energy D were taking from calculations using molecular dynamics (MD) with Juslin interatomic potentials and a binary collision code TRIM. MD calculations show an agreement with a binary collision code TRIM only in a very narrow range of deuterium energies between 1 and 20 eV. Incorporation of the data of reflection and penetration of deuterium in the macroscopic modelling has been done to verify the range of validity of calculations using MD and binary collision code TRIM by comparison of modelling results with experimental data. Modelling results are consistent with experiments using reflection and penetration data of D obtained from TRIM code for incident ion energy above 1 eV. Otherwise, the parameters obtained from MD should be incorporated in the rate-equation model to have a good agreement with the experiments.

  6. Progress and issues in polycrystalline thin-film PV technologies

    SciTech Connect

    Zweibel, K.; Ullal, H.S.; Roedern, B. von

    1996-05-01

    Substantial progress has occurred in polycrystalline thin-film photovoltaic technologies in the past 18 months. However, the transition to first-time manufacturing is still under way, and technical problems continue. This paper focuses on the promise and the problems of the copper indium diselenide and cadmium telluride technologies, with an emphasis on continued R&D needs for the near-term transition to manufacturing and for next-generation improvements. In addition, it highlights the joint R&D efforts being performed in the U.S. Department of Energy/National Renewable Energy Laboratory Thin-Film Photovoltaic Partnership Program.

  7. Polycrystalline diamond based detector for Z-pinch plasma diagnosis

    SciTech Connect

    Liu Linyue; Zhao Jizhen; Chen Liang; Ouyang Xiaoping; Wang Lan

    2010-08-15

    A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/{mu}m), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.

  8. Advances in polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Lanning, Bruce R.; Armstrong, Joseph H.; Misra, Mohan S.

    1994-01-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical

  9. Low temperature production of large-grain polycrystalline semiconductors

    DOEpatents

    Naseem, Hameed A.; Albarghouti, Marwan

    2007-04-10

    An oxide or nitride layer is provided on an amorphous semiconductor layer prior to performing metal-induced crystallization of the semiconductor layer. The oxide or nitride layer facilitates conversion of the amorphous material into large grain polycrystalline material. Hence, a native silicon dioxide layer provided on hydrogenated amorphous silicon (a-Si:H), followed by deposited Al permits induced crystallization at temperatures far below the solid phase crystallization temperature of a-Si. Solar cells and thin film transistors can be prepared using this method.

  10. Statistical thermodynamics of strain hardening in polycrystalline solids

    DOE PAGES

    Langer, James S.

    2015-09-18

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  11. Statistical thermodynamics of strain hardening in polycrystalline solids.

    PubMed

    Langer, J S

    2015-09-01

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman [Acta Mat. 58, 3718 (2010)ACMAFD1359-645410.1016/j.actamat.2010.03.009]. It then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  12. Advances in polycrystalline thin-film photovoltaics for space applications

    NASA Astrophysics Data System (ADS)

    Lanning, Bruce R.; Armstrong, Joseph H.; Misra, Mohan S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical

  13. Allylamine-mediated DNA attachment to polycrystalline diamond surface

    NASA Astrophysics Data System (ADS)

    Zhuang, H.; Srikanth, Vadali. V. S. S.; Jiang, X.; Luo, J.; Ihmels, H.; Aronov, I.; Wenclawiak, B. W.; Adlung, M.; Wickleder, C.

    2009-10-01

    Allylamine, an unsaturated short carbon chain amine was used to mediate ss-DNA attachment to an H-terminated polycrystalline diamond thin film surface for biosensoric applications. At first, allylamine was photochemically tethered onto the diamond film surface; ss-DNA was then attached via the allylamine linkage. The DNA molecules are then hybridized with the complementary DNA molecules containing fluorescence labels followed by denaturing. Time-of-fight secondary ion mass spectrometry and fluorescence spectroscopy are used to confirm the allylamine bonding and the covalent DNA bonding to the diamond film surface, respectively.

  14. Statistical thermodynamics of strain hardening in polycrystalline solids

    SciTech Connect

    Langer, James S.

    2015-01-01

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  15. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, Fred; Truher, Joel B.; Kaschmitter, James L.; Colella, Nicholas J.

    1998-02-03

    A method for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells.

  16. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, F.; Truher, J.B.; Kaschmitter, J.L.; Colella, N.J.

    1998-02-03

    A method is disclosed for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells. 1 fig.

  17. Ultrafast carrier dynamics in polycrystalline bismuth telluride nanofilm

    SciTech Connect

    Jia, Lin; Ma, Weigang; Zhang, Xing

    2014-06-16

    In this study, the dynamics of energy carriers in polycrystalline bismuth telluride nanofilm are investigated by the ultrafast pump-probe method. The energy relaxation processes are quantitatively analyzed by using the numerical fitting models. The extracted hot carrier relaxation times of photon excitation, thermalization, and diffusion are around sub-picosecond. The initial reflectivity recovery is found to be dominantly determined by the carrier diffusion, electron-phonon coupling, and photo-generated carriers trapping processes. High-frequency and low-frequency oscillations are both observed and attributed to coherent optical phonons and coherent acoustic phonons, respectively.

  18. An acoustic emission study of plastic deformation in polycrystalline aluminium

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Frederick, J. R.; Felbeck, D. K.

    1979-01-01

    Acoustic emission experiments were performed on polycrystalline and single crystal 99.99% aluminum while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single dislocation slip events. The rate of decline in acoustic emission activity as grain size is increased beyond the peak value suggests that grain boundary associated dislocation sources are giving rise to the bulk of the detected acoustic emissions.

  19. Penetration and lateral diffusion characteristics of polycrystalline graphene barriers.

    PubMed

    Yoon, Taeshik; Mun, Jeong Hun; Cho, Byung Jin; Kim, Taek-Soo

    2014-01-01

    We report penetration and lateral diffusion behavior of environmental molecules on synthesized polycrystalline graphene. Penetration occurs through graphene grain boundaries resulting in local oxidation. However, when the penetrated molecules diffuse laterally, the oxidation region will expand. Therefore, we measured the lateral diffusion rate along the graphene-copper interface for the first time by the environment-assisted crack growth test. It is clearly shown that the lateral diffusion is suppressed due to the high van der Waals interaction. Finally, we employed bilayer graphene for a perfect diffusion barrier facilitated by decreased defect density and increased lateral diffusion path.

  20. Machining graphite composites with polycrystalline diamond end mills

    NASA Astrophysics Data System (ADS)

    Kohkonen, Kent E.; Anderson, Scott; Strong, A. B.

    One area of focus in developing light-strong materials has been the development of graphite/epoxy composites. The graphite/epoxy materials have created challenges in the area of fabrication and machining. The research objective was to determine if cutting tool material and style of cutting edge showed any significant differences in tool life. The cutting tool materials and cutter styles included helical carbide-end mills and straight and helical polycrystalline diamond-end mill cutters. The experimental design was developed using a fractional factorial design running twelve tests. Results were taken from cutting tool flank edge wear, composite part surface finish, and visual delamination of the part.