Showing papers on "Tungsten published in 1970"
TL;DR: In this paper, experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide-cobalt alloys are presented.
Abstract: The paper reviews experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide–cobalt alloys.
169 citations
IBM1
TL;DR: A limited portion of the liquidus field and the entire subsolidus stability region has been determined for tungsten bronze-type solid solutions in the K2O|Li 2O|Nb2O5 system.
115 citations
TL;DR: In this article, ultrahigh vacuum deposited Ni, Fe, W and Mo films were used to determine molecular oxygen adsorption efficiencies, and the results showed that Ni and Fe showed the best performance.
113 citations
TL;DR: In this paper, a correlation between the structure of cesium films on the tungsten (011) face and the work function of this system has been studied in a wide range of Cesium concentrations by the low-energy electron diffraction and contact potential difference methods.
110 citations
TL;DR: In this article, the energy distribution of field-emitted electrons from single-crystal faces of tungsten exhibits structure which is extremely sensitive to surface contaminants, and the structure for the (100) plane has the correct shape and energy expected for surface states resulting from spin-orbit split bands.
Abstract: The energy distribution of field-emitted electrons from single-crystal faces of tungsten exhibits structure which is extremely sensitive to surface contaminants. The structure for the (100) plane has the correct shape and energy expected for surface states resulting from spin-orbit---split bands. These results are in good agreement with recent theoretical predictions.
109 citations
TL;DR: The surface energies of solid molybdenum, niobium, tantalum, and tungsten at 1500 °C have been determined using the multi-phase equilibration technique.
Abstract: The surface energies of solid molybdenum, niobium, tantalum, and tungsten at 1500 °C have been determined using the multi-phase equilibration technique The values obtained were 2050, 2550, 2680 and 2830 erg/cm2, respectively The grain boundary energy/surface energy ratios for the four metals varied from 028 to 038 with an average of 032
108 citations
TL;DR: In this paper, the adsorption of Ar, Kr, and Xe on the (110), (120), (100), (211), and (111) planes of a tungsten field emitter was studied under conditions of immobile adsorptions and also under conditions under surface equilibrium.
Abstract: The adsorption of Ar, Kr, and Xe on the (110), (120), (100), (211), and (111) planes of a tungsten field emitter was studied under conditions of immobile adsorption and also under conditions of surface equilibrium. The relative dipole moments and heats of binding could be determined, and it was found that both these quantities were largest on the (110) plane. A discussion in terms of charge transfer bonding is presented to rationalize these results. It was found that chemisorption of oxygen prevented the relatively strong first layer adsorption observed on the clean surface, and also the dipole moment associated with it.
107 citations
TL;DR: In this article, the diffusivity of single atoms of Ta, Mo, W, Re, Ir, and Pt, adsorbed on clean tungsten surfaces, was studied by field ion microscopy.
Abstract: The diffusivity of single atoms of Ta, Mo, W, Re, Ir, and Pt, adsorbed on clean tungsten surfaces, was studied by field ion microscopy. Activation energies for diffusion of third transition series metals on (110), (211), and (321) surfaces increase with atomic number to Re, then decline, confirming the importance of 5d-electrons in the adatom bonding. Except for Re, adatom diffusion on (211) surfaces at low temperatures is characterized by low activation energies and very low values of D0 in the range 10−5-10−7 cm2 s−1. This is consistent with a facilitation of adatom displacement by correlated substrate motion. For all adsorbates, activation energies are larger for diffusion on (110) than on (211) surfaces, contrary to the predictions of pair-bond model calculations. This, and the restricted and directional bonding in Re, Ir, and Pt adatom clusters on (110) surfaces, are consistent with more localized bonding of adatoms on (110) than on (211) or (321) tungsten surfaces.
96 citations
TL;DR: A detailed study of the recovery of defects in tungsten after fast neutron (E m ⩾ 1 MeV ) irradiation at about 70° C over a fast neutron fluence range from 8.5 × 10 17 n/cm 2 to 1.5× 10 21 n/ cm 2 has been completed as discussed by the authors.
92 citations
TL;DR: In this article, the sticking coefficients and desorption kinetics of oxygen on a (110) tungsten crystal have been investigated by a step-desorption/reflection technique.
Abstract: The sticking coefficients and desorption kinetics of oxygen on a (110) tungsten crystal have been investigated by a step desorption/reflection technique. Sticking coefficients follow a generalized Kisliuk model, if allowance for reflection on first impact with the surface is made. Unlike CO on (110) W, reflection of O2 is appreciable and appears to have an activation energy of 0.6 kcal, with respect to substrate temperature. Desorption follows first‐order kinetics and has an activation energy of ∼ 92 kcal. The process is complex, however, as shown by the variation in pre‐exponential with surface treatment. A mechanism involving the formation and subsequent decomposition of two distinct surface oxide phases is postulated and shown to fit the experimental results. On the basis of this mechanism the observed activation energy corresponds to the process oxide→mobile adsorbed O, and it is shown that this implies an upper limit of 126 kcal for the heat of adsorption of O atoms on (110) W.
91 citations
TL;DR: In this paper, the slow stages of the catalytic reduction of WO3 to hydrogen tungsten bronzes HxWO3 were studied by NMR spectroscopy between −50 and −195 °C.
TL;DR: In this article, two tungsten surfaces have been bombarded with helium ions of selected energies between 5 and 2000eV, and the helium thermal desorption spectra obtained when the targets were subsegmented.
Abstract: Two (100) and two (110) tungsten surfaces have been bombarded with helium ions of selected energies between 5 and 2000 eV. The helium thermal desorption spectra obtained when the targets were subse...
01 May 1970-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the authors studied the deformation of tungsten single crystals as a function of strain, temperature, and alloying, and found that the dislocation substructures in single-crystal tengsten are similar to those in other refractory metals when compared on a homologous temperature basis.
Abstract: Deformation of tungsten single crystals as a function of strain, temperature, and alloying was studied by transmission electron microscopy. Single crystals oriented for (−101)[lll] slip were grown by electron beam zone refining. Compression specimens of tungsten, W-l and 3 pct Re and W-l and 3 pct Ta were deformed to 2 pct strain at 150°, 300°, and 590°K (0.04, 0.08, and 0.16T
m). Specimens were also strained to 0.5 and 5.0 pct strain at 300°K. Transmission microscopy revealed that the dislocation substructures in single-crystal tungsten are similar to substructures in other refractory metals when compared on a homologous temperature basis. At temperatures greater than 0.1T
m, the substructure is characterized primarily by edge dipoles. At temperatures less than 0.1T
m, long screw dislocations lying parallel to the primary [111] slip direction characterize the substructure. Rhenium additions to tungsten promote formation of edge dipoles at temperatures of 300° and 150°K and increase dislocation density at all three temperatures. In addition, dislocations consistent with (1−12)[−111] slip were observed in the W-Re single crystals after deformation at 150°K. Tantalum additions had a lesser effect on the dislocation substructure compared to rhenium additions. The W-l and 3 pct Ta alloys exhibited higher dislocation densities than unalloyed tungsten after similar strains and, at 150°K, W-3 pct Ta contained a few dislocations consistent with (1−12)[−111] slip. It is concluded that the reduction in ductile-brittle transition temperature of poly crystalline tungsten containing dilute rhenium additions, 1 to 5 pct, can be attributed to an increase in dislocation mobility at temperatures less than 0.1 Tm.
01 Jan 1970
TL;DR: In this article, the migration energies and binding energies for adatoms on tungsten surfaces were calculated by means of a pairwise interaction model, and the inclusion of significant relaxation effects in these calculations has eliminated previous qualitative discrepancies between the calculated and the measured orientation dependence of migration energies.
TL;DR: In this article, the authors used lock-in detection to determine both the mean speed and density patterns of the scattered gas in a tungsten surface, and compared the theoretical predictions of the hard-cube and soft-cube models.
Abstract: The scattering of He, Ne, Ar, and Kr from a (110) tungsten surface has been investigated for surface temperatures, Ts, in the range 300°–2100°K and for angles of incidence, θi, of 40, 50, and 60 deg. The apparatus consists of a nozzle‐type molecular beam modulated at 2650 Hz so that lock‐in detection may be used to determine both the mean speed and density patterns of the scattered gas. The majority of the data are for Ts = 2100°K since thermal desorption of contaminants should be sufficiently rapid at this temperature to insure that the surface is essentially clean. (For Ts < 1000°K, the surface became contaminated by residual gases (primarily CO) before measurements could be obtained.) At Ts = 2100°K, the maxima of the density patterns for θi = 40, 50, and 60 deg are at the specular angles for He, whereas they are increasingly subspecular for Ne, Ar, and Kr. Both the mean speed and density patterns are compared with the theoretical predictions of the hard‐cube and soft‐cube models.
TL;DR: In this article, anodic oxide films were prepared from pure aluminium, titanium, niobium, tantatlum and tungsten, and examined by direct transmission electron microscopy.
TL;DR: In this paper, it was shown that the reduction of the evaporation field by the imaging gas is to a considerable extent due to the field induced adsorption of the gas.
Abstract: : Essential parameters of the theory of field evaporation are the higher ionization potentials of the metal, the surface atom's distance from the effective electronic surface plane of the metal, the polarizability of the surface atom in its site, the energy difference between the atomic and the ionic states of the surface atom, the rate and temperature dependent activation energy, and the pre-exponential factor of the Arrhenius equation. It is shown how these data can be obtained from field evaporation rate measurements. Experiments with the (110) plane of tungsten were carried out in a range from 0.01 layer/sec to 10,000,000 layers/sec using both DC and pulsed field evaporation techniques. Results are discussed. It is also shown that the well known reduction of the evaporation field by the imaging gas is to a considerable extent due to the field induced adsorption of the gas. (Author)
TL;DR: Tungsten carbide is the only compound to have shown catalytic activity and sufficient resistance against corrosion in acid media under anodic polarization to act as an anode catalyst in low temperature fuel cells containing an acid electrolyte.
Abstract: NOBLE metals have been found to be the most suitable materials as anode catalysts for hydrogen oxidation in low temperature fuel cells containing an acid electrolyte. The one exception is tungsten carbide1, which is the only compound to have shown catalytic activity and sufficient resistance against corrosion in acid media under anodic polarization to act as an anode catalyst. In addition, tungsten carbide (WC) possesses a good electrical conductivity.
TL;DR: In this article, low energy electron diffraction intensities have been computed for muffin-tin models representing atomically clean crystal surfaces and surfaces formed by the adsorption of foreign atoms.
TL;DR: In this paper, the initial phases of high temperature ( T >2000°K) carburization of oriented tungsten single crystals by hydrocarbons at low pressures (10 −8 −10 −2 torr) are examined with LEED, X-ray diffraction and optical microscopy.
TL;DR: The decomposition of ammonium tetrathiotungstate, (NH4)2WS4, and the nature of the resulting tungsten sulfides have been studied by X-ray diffraction, differential thermal analysis, optical microscopy and electron spin resonance as mentioned in this paper.
Abstract: The decomposition of ammonium tetrathiotungstate, (NH4)2WS4, and the nature of the resulting tungsten sulfides have been studied, mainly by X-ray diffraction, differential thermal analysis, optical microscopy and electron spin resonance.
Non-stoichiometric tungsten trisulfide may be obtained by decomposition of (NH4)2WS4 at about 200°C. At 330°C crystallization of tungsten disulfide starts. Characteristic electron spin resonance spectra have been obtained for both sulfides.
Es wurde die thermische Zersetzung von NH4-Tetrathiowolframat, (NH4)2WS4, und die Natur der entstehenden Wolframsulfide rontgenographisch, differential-thermoanalytisch, lichtmikroskopisch und durch ESR-Messungen untersucht. Bei 200°C kann nicht-stochiometrisches Wolframtrisulfid erhalten werden. Beide Sulfide ergeben charakteristische ESR-Spektren.
TL;DR: In this paper, the thermochemical data for the condensed oxide phases and volatile oxide species for the refractory metals has made possible an analysis of the several types of high temperature oxidation processes.
Abstract: Recent developments in the thermochemical data for the condensed oxide phases and volatile oxide species for the refractory metals has made possible an analysis of the several types of high temperature oxidation processes. The analyses show the following factors to be important: (1) the presence or absence of oxide films or scales on the metals, (2) the melting points of the one or more oxide phases, (3) the equilibrium pressures of the several volatile oxides, and (4) the flow rate of reactant gases. The thermochemical predictions are compared to experimental observations for molybdenum and tungsten.
TL;DR: In this article, a simple dipole model was proposed to explain the variation in magnitude of the dipole and its reversal between different crystal planes for the same adsorbate for atomic adsorption.
TL;DR: In this paper, superconductivity and lattice parameters have been measured on annealed alloys of ZrMo 2, ZrW 2, HfMo 2 and HfW 2.
Abstract: Superconductivity and lattice parameters have been measured on annealed alloys of ZrMo 2 , ZrW 2 , HfMo 2 and HfW 2 Polymorphism for HfMo 2 was reconfirmed and the compound was found to be superconducting at 007 °K in the C 15 structure and normal down to 005 °K in the C 36 modification The C15 compounds ZrMo 2 , ZrW 2 and HfW 2 were normal down to at least 12 °K The bcc phase was investigated by rapid quenching from the melt It was possible to obtain single phase bcc alloys in the range 3–41 at% Mo in ZrMo alloys and about 9 to at least 67 at% Mo in HfMo alloys The lattice parameters at room temperature for these alloys could be accurately determined and extrapolated to room temperature bcc values for Zr and Hf It was possible to obtain HfMo 2 alloys in three different crystal structures The superconducting transition temperature is about 1 °K for the bcc modification and decreases with decreasing lattice symmetry The rapid quenching technique was less successful in the tungsten alloys, but superconductivity in the bcc phase could be observed in all four alloy systems A maximum in the transition temperature was found in all systems at an electron/ atom ratio between 4 and 5 In the ZrW system, a dip in the transition temperature versus concentration was observed at the composition of the compound ZrW 2 Some aspects of the superconductivity in the bcc phase are discussed It is found that the rigid band model is a good approximation in the dilute Zr region An extrapolation to bcc Zr gives 15 °K as the estimate for the transition temperature
TL;DR: In this paper, hydrogen adsorption and co-adsorption with oxygen on a single crystal surface measured by mass spectroscopy and low energy electron diffraction method was investigated.