7440-33-7Relevant articles and documents
(W6I8)Cl4– A Basic Model Compound for Photophysically Active [(W6I8)L6]2–Clusters?
Str?bele, Markus,Enseling, David,Jüstel, Thomas,Meyer, H.-Jürgen
, p. 1435 - 1438 (2016)
The heteroleptic cluster compound (W6I8)Cl4was prepared by thermal conversion of the homoleptic clusters W6I12and W6Cl12at 700 °C to yield a bright yellow powder. The presence of the smaller chlorido ligands in apical positions of [(W6I8)Cl6]2–creates nearly spherically clusters showing thermal and chemical inertness. Photoluminescence studies revealed a strong red phosphorescence from excited spin-triplet states.
Gruenert, W.,Shpiro, E. S.,Feldhaus, R.,Anders, K.,Antoshin, G. V.,Minachev, Kh. M.
, p. 522 - 534 (1987)
On the formation of defects and morphology during chemical vapor deposition of tungsten
Wang,Cao,Wang,Zhang
, p. 2192 - 2198 (1994)
Face-to-face wafers were used to observe anomalous tungsten deposition in the gap-edge between wafers. In the WF6-H2 atmosphere, three regions are identified: (i) an open-deposition region (region A), (ii) a half-sealed deposition region (region B), and (iii) an etching or tunnel region (region C). In the WF6-Ar atmosphere, there are only two regions: (i) an open deposition region (region A'), and (ii) a half-sealed deposition region (region B'). The third region disappears because HF does not form in the absence of H2. Different chemical reactions are expected in different regions, dictated by the local gas composition. A half-sealed structure model proposed here is supported by thermodynamic calculations, and applied to explain encroachment, wormholes, and other well-known effects during the chemical vapor deposition of tungsten from tungsten hexafluoride.
Preparation of tungsten and tungsten carbide submicron powders in a chlorine-hydrogen flame by the chemical vapor phase reaction
Zhao, G. Y.,Revankar, V. V. S.,Hlavacek, V.
, p. 269 - 280 (1990)
A hydrogen-chlorine flame chemical vapor deposition reactor has been developed to synthesize ultrafine powders of refractory compounds (e.g. carbides and nitrides). At the laboratory scale, synthesis of tungsten and tungsten carbides (both (WC)1-x and α - W2C) gave encouraging results. The collected refractory powders do not have internal porosity, they exhibit spherical shape and have a very narrow size distribution. The size of the particles and the crystalline structure depends on the flame temperature, flow rate of the reactants and residence time of particles. In short, they depend on the flame characteristics. Thermochemical calculations were carried out to obtain the optimum conditions for different carbide powder synthesis. The flame is completely characterized and the temperature distribution within the reactor is obtained.
Carbon nanotubes produced by tungsten-based catalyst using vapor phase deposition method
Lee, Cheol Jin,Lyu, Seung Chul,Kim, Hyoun-Woo,Park, Jong Wan,Jung, Hyun Min,Park, Jaiwook
, p. 469 - 472 (2002)
We have demonstrated that W-based catalysts can produce carbon nanotubes (CNTs) effectively. Well-aligned, high-purity CNTs were synthesized using the catalytic reaction of C2H2 and W(CO)6 mixtures. The CNTs had a multiwalled structure with a hollow inside. The graphite sheets of CNTs were highly crystalline but the outmost graphite sheets were defective.
Electrodeposition of tungsten from ZnCl2-NaCl-KCl-KF-WO3 melt and investigation on tungsten species in the melt
Nitta, Koji,Nohira, Toshiyuki,Hagiwara, Rika,Majima, Masatoshi,Inazawa, Shinji
, p. 1278 - 1281 (2010)
The electrodeposition of tungsten in ZnCl2-NaCl-KCl-KF-WO3 melt at 250 °C was further studied to obtain a thicker deposit. In the ordinary electrolysis at 0.08 V vs. Zn(II)/Zn, the current density decreased from 1.2 mA cm-2 to 0.3 mA cm-2 in 6 h. A thickness of the obtained tungsten layer was 2.1 μm and the estimated current efficiency was 93%. A supernatant salt and a bottom salt were sampled after 6 h from the melting and were analyzed by ICP-AES and XRD. It was found that the soluble tungsten species slowly changes to insoluble ones in the melt. The soluble species was suggested to be WO3F- anion. One of the insoluble species was confirmed to be ZnWO4 and the other one was suggested to be K2WO2F4. Electrodeposition was carried out under the same condition as above except for the intermittent addition of WO3 every 2 h. The current density was kept at the initial value and the thickness was 4.2 μm. The intermittent addition of WO3 was confirmed to be effective to obtain a thicker tungsten film.
Kinetic study of tungsten atoms (a 7S3 and a 5DJ) in the presence of C2H4 and NH3 at room temperature
Ishikawa, Yo-ichi,Matsumoto, Yoshitaka
, p. 1145 - 1153 (2003)
The gas-phase reactivity of W (a 7S3 and a 5DJ) with C2H4 and NH3 at room temperature was investigated using a time-resolved laser induced fluorescence (LIF) spectroscopy. Tungsten atoms were produced by a 266-nm multiphoton decomposition (MPD) of W(CO)6. The reactant pressure dependence of the pseudo-first-order depletion rates of W (a 7S3) could allow an estimation of the pseudo-second-order depletion rate constant of W (a 7S3), (4.5 ± 0.5) × 10-10 cm3 molecule-1 s-1 for C2H4 and (0.73 ± 0.10) × 10-10 for NH3 at 6.0-Torr total pressure with an Ar buffer. A simulation of the transient curves based on a modification of the observed apparent decay rate constants, involving nearby a 5DJ states in the presence of C2H4 and NH3, allowed us to separately estimate the contribution of the chemical quenching (W (a 7S3) + R → product(s)) and the physical quenching (W (a 7S3) + R → W (a 5D1) + R) processes. In the case of C2H4, chemical quenching appeared to dominate over the physical quenching, while the physical quenching was the main depletion process in the case of NH3. The large reactivity of the W (a 7S3) state not only for C2H4, but also for NH3, is discussed in terms of the relativistic effects.
Study of the preparation of bulk powder tungsten carbides by temperature programmed reaction with CH4 + H2 mixtures
Leclercq,Kamal,Giraudon,Devassine,Feigenbaum,Leclercq,Frennet,Bastin,Loefberg,Decker,Dufour
, p. 142 - 169 (1996)
The synthesis of bulk tungsten carbides by carburization of W metal or of WO3 with mixtures of CH4 in hydrogen at various pressures has been studied in temperature programmed experiments. The resulting solids have been characterized by elemental analysis, X-ray diffraction, XPS analysis, and specific surface area measurements. The carburization occurs in two distinct steps: W2C is formed in the first step taking place at about 650°C at atmospheric pressure with a 20% CH4-H2 mixture, while the formation of WC occurs only at higher temperatures. During carburization some free carbon is deposited, the importance of which is very much dependent on CH4 partial pressure and on the temperature of carburization. It has also been shown that direct carburization of WO3 by CH4-H2 does not take place, but that the carburization occurs via the reduction of WO3 to W metal. The rate of reduction of WO3 and that of carburization of W metal are very much dependent on, respectively, hydrogen partial pressure and CH4 partial pressure. The extent of reduction of WO3 into W metal required for carburization which takes place also depends on CH4 partial pressure, indicating a competition between carburization of W metal at the surface and diffusion of W metal into the bulk of the Solid.
Zhang, S.-L.,Palmas, R.,Keinonen, J.,Petersson, C. S.,Maex, K.
, p. 2998 - 3000 (1995)
Mechanism for selectivity loss during tungsten CVD
Creighton
, p. 271 - 276 (1989)
We have investigated possible mechanisms for the loss of selectivity (i.e., deposition on silicon dioxide) during tungsten CVD by reduction of tungsten hexafluoride and found strong evidence that selectivity loss is initiated by desorption of tungsten sub
LOW PRESSURE CHEMICAL VAPOR DEPOSITION OF TUNGSTEN ON POLYCRYSTALLINE AND SINGLE-CRYSTAL SILICON VIA THE SILICON REDUCTION.
Tsao,Busta
, p. 2702 - 2708 (1984)
High purity metallic tungsten films are deposited on phosphorus-doped and undoped polycrystalline and single-crystal silicon by the silicon reduction of WF//6. Depositions are performed in a commercial LPCVD hot wall reactor at temperatures ranging from 310 degree -540 degree C. Film formation is self-limiting, meaning that after a given film thickness any further reaction between WF//6 and the underlying silicon is inhibited. Obtainable film thickness depends strongly on the doping condition of silicon and on surface preparation prior to LPCVD. Conventional wet chemical cleaning limits the maximum obtainable film thickness to approximately 400A, whereas with a low power argon plasma treatment approximately 900A thick films can be obtained reproducibly. The resistivity of these films is 18. 3 plus or minus 4. 5 mu OMEGA cm.
Oxidation resistance of hafnium diboride ceramics with additions of silicon carbide and tungsten boride or tungsten carbide
Carney, Carmen M.,Parthasarathy, Triplicane A.,Cinibulk, Michael K.
, p. 2600 - 2607 (2011)
Dense samples of HfB2-SiC, HfB2-SiC-WC, and HfB 2-SiC-WB were prepared by field-assisted sintering. The WB and WC additives were incorporated by solid solution into the HfB2 and the HfC that formed during sintering. Oxidation of the samples was studied using isothermal furnace oxidation between 1600° and 2000°C. Sample microstructure and chemistry before and after oxidation were analyzed by scanning electron microscopy and X-ray diffraction. The addition of WC and WB did not alter oxidation kinetics of the baseline HfB2-SiC composition below 1800°C; however, at 2000°C, HfB2-SiC-WC and HfB 2-SiC-WB had oxide scales that were 30% thinner than the oxide scale of HfB2-SiC. It is believed that WC and WB promoted liquid-phase densification of the HfO2 scale, thereby reducing the path of oxygen ingress, during oxidation.
Temperature-programmed and X-ray diffractometry studies of hydrogen-reduction course and products of WO3 powder: Influence of reduction parameters
Zaki,Fouad,Mansour,Muftah
, p. 90 - 96 (2011)
The hydrogen-reduction course and products of synthetic tungsten(VI) oxide (WO3) were examined by means of temperature-programmed reduction (TPR) and X-ray powder diffractometry (XRD) studies. A set of model tungsten compounds was procured and examined similarly for reference purposes. Results obtained could help resolving two subsequent reduction stages: (i) a low-temperature stage (3 is reduced to the tetravalent state (WO2) via formation and subsequent reduction of intermediate WO2.96, WO2.9, WO2.72 oxides; and (ii) a high-temperature stage (>1050 K) through which WO2 thus produced is reduced to the metallic state (Wo) via two intermediate oxide species (tentatively, WO and W2O-W3O). Reduction events involved in the high-temperature stage were found to be relatively more sensitive to the reduction parameters; namely, the starting oxide mass, heating temperature and rate, and gas flow rate and composition. They were also found to require lower activation energies than those required by events occurring throughout the low-temperature stage, a fact that may suspect compliance of the high-temperature reduction events to autocatalytic effects.
Diffusion barrier properties of tungsten nitride films grown by atomic layer deposition from bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia
Becker, Jill S.,Gordon, Roy G.
, p. 2239 - 2241 (2003)
The synthesis of the highly uniform, smooth and conformal coatings of tungsten nitride (WN) using atomic layer deposition (ALD) from vapors of bis(tert-butylimido)bis(dimethylamido)tungsten and ammonia was discussed. The diffusion barrier properties of th
Size control of tungsten powder synthesized by self-propagating high temperature synthesis process
Won, Chang-Whan,Jung, Joong-Chai,Ko, Seog-Gueon,Lee, Jong-Hyeon
, p. 2239 - 2245 (1999)
Tungsten powder was prepared by self-propagating high temperature synthesis (SHS) from a mixture of WO3 and Mg. The MgO in the product was leached with an HCl solution. The complete reduction of WO3 required a 33% excess of magnesium over the stoichiometric molar ratio Mg/WO3 of 3. The tungsten product had a purity of 99.98%, which was higher than that of the reactants. The high purity resulted because the impurities in the reactants were volatilized during the highly exothermic reaction and dissolved during leaching of the product. Size distribution and the shape of the tungsten particles produced was affected by compaction pressure on the green pellet.
Bryant, W. A.
, p. 37 - 44 (1976)
ENTHALPY OF FORMATION OF PENTACARBONYL(TRIPHENYLPHOSPHINE) TUNGSTEN AND OF PENTACARBONYL(METHOXY(PHENYL)METHYLENE)TUNGSTEN
Al-Takhin, Ghassan,Connor, Joseph A.,Pilcher, Geoffrey,Skinner, Henry A.
, p. 263 - 270 (1984)
Microcalorimetric studies on the sublimation, thermal decomposition and bromination of W(CO)6, and of the complexes and > have provided standard enthalpies of formation (in kJ mol-1) of the crystalline and vapour
Characterization of selective tungsten films prepared by photo-chemical vapor deposition
Fang,Hwang,Sun
, p. 1720 - 1723 (1991)
Selective photo-chemical vapor deposition (CVD) of tungsten films decomposed by direct photoexcitation of WF6 have been studied. Film deposition rate increased with increasing temperature but was only slightly dependent on WF6 gas concentration. The selectivity deteriorated with increasing deposition temperature, WF6 concentration, and deposition time. Typically, in order to achieve selectivity, the flow rate of WF6 must be lower than 35 sccm and the deposition temperature must be lower than 230°C. No encroachment and self-limited thickness problems were found as in the low-pressure chemical vapor deposition method. In general, tungsten films prepared by photo-CVD were amorphous as observed by x-ray diffraction analysis. After annealing, the tungsten had a polycrystalline structure with a resistivity of 18 μΩ-cm.
Vacuum annealing of nanocrystalline WC powders
Kurlov,Gusev
, p. 680 - 690 (2012)
The effect of vacuum annealing temperature on the chemical and phase compositions, particle size, and lattice strain of nanocrystalline tungsten carbide (WC) powders with a particle size from 20 to 60 nm has been studied by X-ray diffraction and electron microscopy. The results demonstrate that vacuum annealing of WC nanopowders at tann ≤ 1400°C is accompanied by a marked decrease in carbon content and changes in phase composition due to carbon desorption from the surface of the powder as a result of the interaction of carbon with oxygen impurities. In addition, annealing leads to an increase in particle size due to coalescence of aggregated nanoparticles and reduces the lattice strain of the powder. Pleiades Publishing, Ltd., 2012.
Nucleation on SiO2 during the selective chemical vapor deposition of tungsten by the hydrogen reduction of tungsten hexafluoride
Desatnik,Thompson
, p. 3532 - 3539 (1994)
A horizontal hot-wall chemical vapor deposition (CVD) quartz reactor with rectangular cross section was used to study the effect of different process conditions on the nucleation of tungsten on SiO2 during selective WCVD by the H2 reduction of WF6. The experimental procedure included placing a metallic surface at the center of the reactor, and small samples of SiO2 at different positions both upstream and downstream with respect to the metallic surface. Digitized scanning electron microscopy micrographs were used to determine the particle size distributions of nuclei on the SiO2 surfaces. We found that the amount of nucleation on SiO2 decreases when smaller metallic surfaces are present and for lower temperatures and shorter process times. Although nucleation was always greatest on SiO2 samples closest to the metal sample, the effect of flow rate depended on the position of the SiO2. A statistical nearest neighbor analysis indicated a clustering of W nuclei on the SiO2. A simplified mathematical model was developed to predict concentration profiles of a gaseous intermediate generated at the metal surface during the thermal decomposition of the source gas. This intermediate has been proposed as being the reactive species that causes nucleation on SiO2 surface. Qualitative agreement between experimental and theoretical results reinforce the proposed role of the intermediate with this species being characterized by a short lifetime.
Electrolytes for tungsten refining
Pavlovskii
, p. 372 - 375 (2004)
Chloride-fluoride and phosphate-fluoride salts of alkali metals with additions of sodium tungstate and tungstic anhydride are studied as electrolyte systems for tungsten refining. The results demonstrate that the melts of these systems are suitable for el
Nanoscale electron-beam-stimulated processing
Rack,Randolph,Deng,Fowlkes,Choi,Joy
, p. 2326 - 2328 (2003)
Electron beam stimulated deposition and etching were investigated. These processes find application in nanoscale selective processing. During etching of silicon and silicon dioxide, inelastic scattering of the electron beam with the gas was found to take
Reactivity of hexanes (2MP, MCP and CH) on W, W2C and WC powders. Part II. Approach to the reaction mechanisms using concepts of organometallic chemistry
Hemming,Wehrer,Katrib,Maire
, p. 39 - 56 (1997)
The reactivity of 2-methylpentane (2MP), methyleyelopentante (MCP) and cyclohexane (CH) on reproducible and well-characterized surfaces of W, W2C and WC has been studied. A great deal of effort was put on the characterizations by physisorption, chemisorption and photoemission spectroscopy. The results obtained with these reference materials can be used for comparison with those appearing in the literature and sometimes debated because of the inconstancy of the active states due to non-stoichiometric compositions (excess of carbon, decarburization, oxidation by oxygen impurities). In agreement with the work of Boudart et al. [F.H. Ribeiro, R.A. Dalla Betta, M. Boudart, J. Baumbgartner, E. Iglesia, J. Catal. 130 (1991) 86; F.H. Ribeiro, M. Boudart, R.A. Dalla Betta, E. Iglesia, J. Catal. 130 (1991) 498; E. Iglesia, J.E. Baumgartner, E.H. Ribeiro, M. Boudart, J. Catal. 131 (1991) 523; E. Iglesia, F.H. Ribeiro, M. Boudart, J.E. Baumgartner, Catal, Today 15 (1992) 307.] we confirmed that reforming reactions do not take place in the temperature range 80-400°C and four experimental conditions. They dehydrogenation of cyclohexane appeared only when a strong position by carbonaceous residues occurred. For 2-methylpentane and methylcyclopentane the extensive hydrogenolysis character of WC is higher than for W2C and WC surfaces are interpreted by different possible reaction intermediates deduced from concepts of organometallic chemistry.
A reflectometric study of the reaction between Si and WF6 during W-LPCVD on Si and of the renucleation during the H2 reduction of WF6
Holleman,Hasper,Middelhoek
, p. 783 - 788 (1991)
The formation of W through the reduction of WF6 by Si is monitored in situ using a wavelength adjustable reflectometer. The reflectance-time relation can be understood and modeled by assuming island growth and a statistical distribution of the island thickness. The model is supported by SEM and Auger observations. The effect of surface layers like native oxides or a plasma treatment on the inhomogeneous Si consumption by the reaction between Si and WF6 (gouging) and its effect on the reflectance-time relation are understood. The model is also applicable in the case of renucleation during the H2 reduction of WF6. A renucleation step consists of the deposition of SiH4 followed by the Si consumption by WF6. A renucleation step reduces the surface roughing which occurs during the H2 reduction process.
Tungsten fluorides: Syntheses and electrochemical characterization in the FLINAK molten salt eutectic
Eklund,Chambers,Mamantov,Diminnie,Barnes
, p. 715 - 722 (2001)
The following tungsten fluorides have been synthesized by simple addition reactions or by reduction with tungsten metal at elevated temperature: KWFT7, K2WF8, MWF6 (M = K, Na, Rb, Cs), K2WF7, M3WF8 (M = K, Na, Rb), and K3WF6. The compounds were characterized by their Raman spectra and by cyclic voltammetry in the molten FLINAK eutectic melt (46.5, 11.5, and 42.0 mol % of LiF, NaF, and KF, respectively) at 475-800 °C. X-ray crystal structures are reported for two new compounds K2WF7 and K3WF6. The crystals of K2WF7 were orthorhombic, space group Pnma (No. 62) with a = 9.800(2) A, b = 5.7360(11) A, c = 11.723(2) A, and Z = 4. Crystals of K3WF6 were cubic, space group Fm3 (No. 225) with a = b = c = 8.9160(10) A, Z = 4. Electrodeposition of tungsten metal on Pt from FLINAK, prepared by the addition of WF6 gas and metallic tungsten to the melt, is suggested to result from reduction of an equilibrium mixture of WF83- and WF63-.
Structural Transformations of [CuEn 3]WO4 Complex Salt in the Range 100–390 K and Its Degradation to [CuEn 2](WO4)·2H2O
Khranenko,Sukhikh,Komarov, V. Yu.,Gromilov
, p. 1790 - 1798 (2019/12/24)
The crystal structure of [CuEn3]WO4 (En is ethylenediamine) is studied in the temperature range 100–390 K. Crystallographic data at 100 K are: a = 27.6903(8) ?, c = 9.9405(3) ?, space group P3?, V = 6600.8(4) ?3, Z = 18. Copper atomic coordination is a distorted square bipyramid. Four short Cu–N distances are within 2.038(5)–2.110(6) ?; two long distances are within 2.374(8)–2.514(7) ?. The lengths of N–H…O interionic contacts lie within 1.96–2.17 ?. A temperature elevation makes the Cu–N distances equal: at 298 K they are within 2.066(2)–2.256(3) ?(a = 16.0391(8) ?, c = 9.9608(6) ?, space group P3?c1, V = 2219.1(3) ?3, Z = 6), and at 390 K they are 2.151(6) ?(a = 9.2986(10) ?, c = 10.0520(14) ?, P3?1c, V = 752.7(2) ?3, Z = 2). In the range from 100 K to 390 K the average W–O distances decrease from 1.776 ? to 1.734 ?. Hirshfeld surfaces of complex cations are analyzed. It is shown that with increasing temperature the number of interionic N–H…O contacts decreases. The [CuEn3]WO4 phase is found to be unstable and on storing in air it transforms into [CuEn2](WO4)·2H2O.
Novel aluminum-graphene and aluminum-graphite metallic composite materials: Synthesis and properties
Yolshina,Muradymov,Korsun,Yakovlev,Smirnov
, p. 449 - 459 (2016/01/09)
A novel method of creating new lightweight, aluminum-metallic, composite materials under halides melt at temperatures 973-1073 K under air atmosphere is proposed. The method for synthesizing aluminum-based metallic composite materials, containing up to 2 wt. % graphene sheets uniformly distributed in a metal matrix, is entirely new, having no analogies in current science and practice. The synthesis of graphene nanosheets in a metal matrix is one-step, simultaneous process, taking place directly in molten aluminum under alkali halides melt without the necessity of a separate stage of synthesis and introduction of graphene. This has the potential to facilitate the inexpensive synthesis of aluminum-graphene composites with a high concentration of graphene. The aluminum-graphene composites formed according to this method are characterized by a high uniformity of graphene films with linear dimensions from 100 nm to 50 μm and a thickness from one to three nm in the metal bulk. No aluminum carbide forms under synthesis; the aluminum-graphene and aluminum-graphite composites are resistant to corrosion in NaCl solution. The hardness, strength and ductility of aluminum-graphene composites are at least 2-3 times higher than the initial aluminum material, proportional to the concentration of graphene.