Showing papers on "Tungsten published in 1976"

Valence Electron Spectra of Benzene and the Hexafluorides of Sulphur, Molybdenum, Tungsten and Uranium. An Application of Multichannel Detector Technique to UV-Valence Electron Spectroscopy

Abstract: HeI induced valence electron spectra of benzene and the hexafluorides of sulphur, molybdenum, tungsten and uranium are presented together with a HeII spectrum of sulphur hexafluoride. Vibrational band structure has been resolved in the spectra of all molecules and the energies of these bands are reported. A description is also given of the multichannel detector system which has facilitated the recordings of these spectra.

Studies of hydrogen spillover. Part 1.—Study of the rate, extent and products of hydrogen spillover from platinum to the trioxides of tungsten and molybdenum

Abstract: The rates and extents of hydrogen sorption by platinised tungsten trioxide and molybdenum trioxide have been measured between 273 and 363 K and between 3 and 101 kN m–2. Maximum diffusion coefficients for hydrogen spilling-over from platinum to the trioxide supports have been estimated. X-Ray diffraction, differential thermal analysis and thermogravimetric analysis, e.s.r. and i.r. spectroscopy indicate that the products of this spillover are hydrogen bronzes of tungsten and molybdenum. These may be represented as HxWO3, where x has a maximum value of 0.46, and HxMoO3, where x has a maximum value of 1.63. The latter violates the ranges of composition previously accepted for bronzes. The chemical and thermal stability of these bronzes is discussed in terms of their structures.

Enhanced low-temperature sintering of tungsten

Abstract: The effects of various transition metal additions on the sintering of a well-characterized, fine tungsten powder were analyzed using both isothermal and constant heating rate experiments in the temperature range 900 to 1400°C. Approximately four atomic mono-layers of palladium on the tungsten powder surface were found to be the optimal enhancer, followed by nickel, cobalt, platinum, and iron. The addition of Cu to the tungsten had no appreciable effect on the sintering kinetics. Sintering enhancement by these transition metals is related to their periodic chart position (i.e., electron structure). An overall non-Arrhenius shrinkage temperature dependence is attributed to grain growth in the activator-treated specimens. The activation energy for tungsten densification was determined to be 430 to 450 kJ/mol, which is in general agreement with a grain boundary diffusion process.

Surface alloying and heat treating processes

Abstract: A method is disclosed for increasing physical properties of a non-allotropic metal article along a beam affected zone. A preferred method comprises passing a high energy beam (of at least 10,000 watts/cm2 measured at the interface of the beam with the article across a predetermined surface area at a rate to cooperate with the proportioning of the total article mass with respect to the beam affected zone mass to produce a rapid self-quenching rate and thus assure a desired precipitate and/or intermetallic compound in the resolidification zone. The high energy beam is preferably a laser generated by a device having a power level of at least 500 watts. The method requires and facilitates alloying which may be varied in several respects: (a) alloying ingredients may be previously deposited over the beam affected zone so as to be turbulently mixed with melting of the base material in said zone, (b) alloying ingredients may be constituted as a wire and fed into the high energy beam to be contemporaneously melted with the base material, (c) the alloying ingredients are selected as those having an affinity to form intermetallic compounds with the non-alloptropic metal base, such as copper, manganese, chromium, zinc, cobalt, magnesium, molybdenum, titanium, vanadian, tungsten, zirconium, iron and nickel for an aluminum base and silicon as an independent wear resistance particle, and (d) the alloying ingredients are proportioned with respect to the thickness of the melted zone to render a desired alloy concentration after melting to facilitate greater hardness, greater corrosion resistance, or greater fatigue life of the affected surface region of the article.

Surface studies of barium and barium oxide on tungsten and its application to understanding the mechanism of operation of an impregnated tungsten cathode

Abstract: Surface studies have been made of multilayer and monolayer films of barium and barium oxide on a tungsten substrate. The purpose of the investigation was to synthesize the surface conditions that exist on an activated impregnated tungsten cathode and obtain a better understanding of the mechanism of operation of such cathodes. The techniques employed in these measurements were Auger spectroscopy and work-function measurements. The results of this study show that the surface of an impregnated cathode is identical to that observed for a synthesized monolayer or partial monolayer of barium on oxidized tungsten by evaluating Auger spectra and work-function measurements. Data obtained from desorption studies of barium monolayers on a tungsten substrate in conjunction with Auger and work-function results have been interpreted to show that throughout most of its life an impreganated cathode has a partial monolayer, rather than a monolayer, of barium on its surface.

Intergrowth tungsten bronzes

Abstract: A series of phases has been found in the tungsten bronze systems MxWO3 for x ≤ 0.10 when M = K,Rb, Cs, Tl. The crystal structure of one of these was derived from a high-resolution electron micrograph (lattice image) and confirmed by X-ray diffraction analysis. It can be considered as an (ordered) intergrowth of slices of hexagonal tungsten bronze type with slabs of WO3 structure type. Different members of the series characterized by different thicknesses of the WO3 slabs have been observed. Members have been obtained only intermixed with others, never as single phases. Disorder in the form of varying widths of the two structure elements has been observed quite frequently.

Carbide compositions for wear-resistant facings and method of fabrication

Abstract: Refractory, hard carbide alloys, intended primarily as replacement for the cast eutectic WC + W 2 C tungsten carbides currently used as hard components in wear-resistant facings, consist of fine-grained and hard two-phase mixtures of subcarbide, (Mo,W) 2 C, and hexagonal monocarbide (Mo,W)C, solid solutions, and are formed by solid state decomposition of the pseudocubic, η-(Mo,W) 3 C 2 , or cubic α-(Mo,W)C 1-x solid solutions. The carbide alloys of the invention can be combined with low-melting metal binders to form cemented carbide alloys of at least equivalent wear-resistance to alloys using the eutectic tungsten carbides.

Reduction of tungsten oxide to tungsten metal

Abstract: Tungsten oxide, WO2.96, was reduced toα-W in hydrogen for various time periods over the temperature range 500°C to 900°C. Intermediate oxides were determined using X-ray diffraction analysis of the semireduced powders. Several dopant conditions were used, to find the effect on oxide structures and reaction kinetics of the usual dopants K, Si and Al. The scanning electron microscope was employed to determine the morphology of the crystallites at intermediate and final stages of reduction.

X-ray target

Abstract: An X-ray target, preferably a rotating target is disclosed in which at least part of the target surface outside the focal area contains a coating layer of a mixture composed of molybdenum, tungsten, niobium or tantalum, and from 20-60 volume percent of a ceramic oxide.

Mechanism for negative‐ion production in the surface‐plasma negative‐hydrogen‐ion source

Abstract: The system parameters and surface adsorption conditions of the surface‐plasma negative‐hydrogen‐ion source are reviewed. A mechanism is developed for the production of negative ions by incident energetic hydrogen atoms backscattering from a cesiated tungsten surface. The active electronic level during the course of the collision is approximated as the sum of the negative electron affinity of the cesium hydride negative molecular ion and the image potential. The model predicts negative‐ion formation for atomic collisions with all alkali‐coated surfaces for alkalis from sodium through cesium. In the case of lithium, the model does not apply due to the breakdown of the image potential approximation close to the surface. Negative‐ion formation is also expected to occur for incident positive ions which backscatter from the substrate tungsten as neutrals. The energy thresholds for incident atoms are established.

Tungsten as a marker in thin‐film diffusion studies

Abstract: Vacuum‐deposited tungsten of about 30‐A thickness has been used as a diffusion marker in the reaction between a thin Co film and Si. In order to produce a discontinuous W film, it is necessary first to deposit a Sn film with island structure and then W, after which the Sn is dissolved. It was found by MeV He+ backscattering analysis that the W is located at the Co‐Co2Si interface, which means that Co is the dominant diffuser in Co2Si.

Method of forming metal tungsten carbide composites

Abstract: Composites consisting of sintered tungsten carbide particles in a local matrix of a steel alloy having a carbon, cobalt and tungsten content are prepared by placing particles of tungsten carbide with cobalt binder, at least some of which are larger in size than those desired in the final composite in a mold. Matrixing alloy having little or no tungsten content is heated above its melting temperature and then poured into the relatively cold mold. The carbon, tungsten and cobalt dissolve at the outer surfaces of the particles and diffuse into the alloy which is allowed to naturally cool and solidify.

Gehinderte Ligandenbewegungen in Übergangsmetallkomplexen, VIII. Untersuchungen an Übergangsmetallkomplexen mit cyclischen Carbenliganden, II. Chrom‐, Molybdän‐ und Wolframkomplexe mit 1,3‐Dimethyl‐4‐imidazolin‐2‐yliden‐Liganden

Abstract: Pentacarbonyl(1,3-dimethyl-4-imidazolin-2-yliden)chrom(0) (1), -molybdan(0) (2) und -wolfram(0) (3 disproportionieren thermisch zu cis-Tetracarbonylbis(1,3-dimethyl-4-imidazolin-2-yliden)-chrom(0) (4), -molybdan (0) (5) und -wolfram (0) (6) und den entsprechenden Metallhexacarbonylen. 1 reagiert in Benzol mit P(C6H5)3 bzw. C6H11 NC zu cis- Cr(CO)4H8N2)[P(C6H5)3] (7) bzw cis-Cr(CO)4(C5H8N2)(CNC6H11) (8). Die 1H-NMR-Spektren von 4–6 sind temperaturabhangig als Folge einer Hinderung der Rotation der cyclischen Carbenliganden um die Carbenkohlenstoff-Metall-Bindung. Die Hinderung ist auf sterische Wechselwirkungen zwischen den N-Methyl-gruppen der C5H8N2-Liganden und den dazu cis-standigen Liganden zuruckzufuhren. Die Rotationsbarrieren liegen um 9kcal/mol und sind vom Zentralmetall abhangig. In 7 und 8 konnte dagegen das Einfrieren der Carbenligandrotation NMR-spektroskopisch nicht nachgewiesen werden. Hindered Ligand Motions in Transition Metal Complexes, VIII. Investigations in Transition Metal Complexes with Cyclic Carbene Ligands, II. Chromium, Molybdenum, and Tungsten Complexes with 1,3-Dimethyl-4-imidazolin–ylidene Ligands Pentacarbonyl(1,3-dimethyl-4-imidazolin-2-ylidene)chromium(0) (1), molybdenum(0) (2), and -tungsten(0) (3) disproportionate thermally to yield cis-tetracarbonylbis (1,3-dimethyl-4-imidazolin-2-ylidene)chromium(0) (4), -Molybdenum(0) (5) and -tungsten (0) (6) as well as the corresponding metal hexacarbonyls. 1 reacts in benzene with P(C6H5)3 and C6H11 NC to give cis-Cr(CO)4(C5H8N2) [P(C6H5)3] (7) and cis-Cr(CO)4 (C5H8N2) CNC6H11 (8), respectively. The 1H n. m. r. spectra of 4–6 are temperature-dependent resulting from a hindrance of the rotations of the cyclic carbene ligands around the carbene carbon-metal bonds. The hindrance is due to steric interactions between the N-methyl groups of the C5H8N2-ligands and the cis-standing ligands. The rotational barriers are about 9 kcal/mol and depend on the central metal. In contrast to this it was impossible to prove by n.m.r. spectroscopy a freezing of the rotations fo the carbene ligands in 7 and 8.

Direct observation of liquid-phase sintering in the system tungsten carbide-cobalt

Abstract: The hot-stage of a scanning electron microscope has been used to observe liquid-phase sintering in the system tungsten carbide-cobalt. Densification behaviour and the mechanism for the first, fast stage of sintering have been determined; the influence of particle size and the amount of liquid phase has been investigated. In all samples the densification kinetics is that of a rearrangement process; direct observation confirmed this result.

Metallic glasses having a combination of high permeability, low magnetostriction, low ac core loss and high thermal stability

Abstract: Metallic glasses having high permeability, low magnetostriction, low ac core loss and high thermal stability are disclosed. In contrast to the prior art in which one, or at most two, of these properties are attained in one metallic glass, all those outstanding properties are achieved in a single metallic glass selected from one of the compositions of the invention. The metallic glasses consist essentially of about 63 to 83 atom percent of at least one metal selected from the group consisting of iron and cobalt, from 0 to about 60% of which metal may be replaced with nickel, about 2 to 12 atom percent of at least one element selected from the group consisting of molybdenum, tungsten, niobium and titanium, and about 15 to 25 atom percent of at least one metalloid element selected from the group consisting of boron, phosphorus and carbon plus incidental impurities.

Lattice vibrations in tungsten at 22 °C studied by neutron scattering

Abstract: The phonon spectrum of tungsten at 22 °C has been reexamined along major symmetry directions using triple-axis neutron spectrometry. The purposes of the experiment were to search for a predicted Ko...