Showing papers on "Tungsten published in 1975"

Mechanism of electrochromism in WO3

Abstract: X‐ray photoelectron spectra of colored WO3 films, thermodynamic analysis of galvanic behavior of the tungstic oxide cathode, plus other new lines of evidence, clearly establish the previously uncertain mechanism of the electro‐optic effect in amorphous WO3, viz., a simultaneous injection of electrons and positive ions into a film via an electrochemical process, with the consequent development of a low‐x tungsten bronze. The positive ion, in both the films and in tungsten bronzes, remains fully ionized even in the presence of high densities of injected electrons.

A review of chromium, molybdenum, and tungsten alloys

Abstract: The mechanical properties of chromium, molybdenum, and tungsten alloys are reviewed with particular emphasis on high-temperature strength and low-temperature ductility. Precipitate strengthening is highly effective at 0.4 to 0.8 times the melting temperature in these metals, with HfC being most effective in tungsten and molybdenum, and Ta(B,C) most effective in chromium. Low-temperature ductility can be improved by alloying to promote rhenium ductilizing or solution softening. The low-temperature mechanical properties of these alloys appear related to electronic interactions rather than to the usual metallurgical considerations.

Field electron cathode stability studies: Zirconium/tungsten thermal‐field cathode

Abstract: The emission angular distribution, total energy distribution, noise spectrum, and emitter life have been measured for the W/Zr thermal‐field cathode The results give an emitter life in excess of 1000 h at T=1350 to 1450 K, P?2×10−8 Torr, and a total current of ∼100 μA A low‐noise highly confined beam long the (100) direction can be obtained A source brightness of 1010 A/cm2 sr at 3 kV and an energy spread of less than 09 eV were measured under operational conditions

Long-Range Migration of Self-Interstitial Atoms in Tungsten

Abstract: Resistivity annealing following irradiation with 3-MeV electrons at 4.5 K has been investigated on tungsten single crystals. High-purity samples showed a recovery stage between 24 and 30 K, which apparently shifts with increasing dose to lower temperatures. We conclude that it is associated with long-range migration of self-interstitial atoms with a migration energy of 54 \ifmmode\pm\else\textpm\fi{} 5 meV. The relationship to recent conclusions of other authors is discussed.

Formation of vacancy-type dislocation loops in tungsten bombarded by 60 keV Au ions

Abstract: The formation of vacancy-type dislocation loops in tungsten specimens as produced by irradiation with 60 keV Au ions is investigated by transmission electron microscopy. The majority of the loops is found to have Burgers vectors b=1/2〈111〉 and loop planes normal to n ≈ {110} (∢(b, n) ≈ 35°). The 12 different loop orientations of this type are observed with significantly different frequencies depending sensitively on the crystallographic orientation of the specimen surface. The observations are explained in terms of the elastic interaction of the growing loops with the adjacent specimen surface. The proposed interpretation of the results leads to a critical resolved shear stress τ0 of the order of magnitude of 10 N/mm2 for the onset of microslip in tungsten single crystals at room temperature, in agreement with data reported in the literature. The specific stacking fault energy on {110}-planes is estimated as γ110≈0.8 × 10−6 J/mm2.

The origin of internal stress in low−voltage sputtered tungsten films

Abstract: The internal stress can be of importance in the tungsten metallization process used for the fabrication of large−scale integrated circuits. The present work is an extension of an earlier study on the dependence of the stress in low−voltage triode sputtered tungsten films upon deposition conditions and substrate materials. As a function of film thickness, the stress was found to decrease with increasing thickness at various substrate temperatures. The effect of higher substrate temperatures is just to change from large compressive stress to smaller compressive stress and finally into tension. For example, the stress in a 5000−A film decreases from 1.6×1010 dyn/cm2 in compression to 5×109 dyn/cm2 in tension as substrate temperature increases from 370 to 850 °C. Generally, no gross difference was found for films deposited on SiO2, Al2O3, or Si3N4 at higher substrate temperatures. As a function of deposition rate, the stress can be described in three regions. The stress was found to be small and relatively co...

Process for fabricating articles of tungsten-nickel-iron alloy

Abstract: A high density W--Ni--Fe alloy of composition 85-96% by weight W and the remainder Ni and Fe in a wt. ratio of 5:5-8:2 having enhanced mechanical properties is prepared by compacting the mixed powders, sintering the compact in reducing atmosphere to near theoretical density followed by further sintering at a temperature where a liquid phase is present, vacuum annealing, and cold working to achieve high uniform hardness.

The Secondary Hardening of Tungsten Steels

Abstract: The tempering characteristics of a steel with 2 at.−%W 1.1 at.−%C in the range 500–700°C have been studied and structural changes related to the secondary-hardening phenomenon. The sequence of carbides found both at grain boundaries and in the matrix has been established,and detailed structural observations have been made on the nucleation of W2C and M6C. The ageing behaviour is contrasted with that of a comparable molybdenum steel in which the carbide reactions occur more rapidly. Trace additions of Nb Ti and Ta improve the basic strengthening reaction by providing a fine secondary carbide dispersion which also inhibits the coarsening of the dislocation network. The main carbide dispersion is also refined.

The thermodynamic properties of chromium, molybdenum and tungsten hexacarbonyls in the gaseous state

Abstract: The thermodynamic properties, C o p , S o , - (G o −H o 0 ) T , H o −H o f , ΔH o f , ΔG o f and log K p are reported for the hexacarbonyls of chromium, molybdenum and tungsten in the gaseous state from 100 to 600 K.

Tungsten-nickel-iron-molybdenum alloys

Abstract: This invention is directed to the use of tungsten base alloys containing about 1 to 12 weight percent nickel, about 0.5 to 8 weight percent iron and about 0.5 to about 25 percent molybdenum and at least one additional additive selected from cobalt, chromium, manganese, vanadium, tantalum, zirconium, titanium, yttrium, rhenium, boron, and silicon. Chromium may substitute for molybdenum up to 15%. In addition to being useful for high density applications, structural applications, and high temperature applications, the alloys may be used for die casting dies, molds, cores and other metal shaping members.

Recombination dynamics of hydrogen on a tungsten surface

Abstract: The results of a series of classical trajectory calculations designed to simulate the recombination of two hydrogen atoms adsorbed on tungsten to form a gas phase H2 molecule are reported. (AIP)

A comparison of X-ray spectra and outputs from molybdenum and tungsten targets

Abstract: The relative merits of tungsten and molybdenum targets for mammography have been the subject of much discussion. Therefore the spectra and outputs (at constant potential) from molybdenum and tungsten targets, interchangeable in the same tube, have been measured with a Ge(Li) detector and ion chamber respectively. All conditions apart from the target material were unaltered. The spectra have been corrected for the distortions produced by the detector. The effects of filtration on spectra and exposure rates have been calculated and are in agreement with measured values. The spectra and outputs from molybdenum and tungsten targets filtered by aluminium and molybdenum have been investigated and the results are discussed with reference to mammography and the radiography of specimens.

Process for the production of tungsten carbide or mixed metal carbides

Abstract: A process for the production of tungsten carbide or mixed metal carbides, which comprises mixing tungsten oxide powder of mixed high melting point metal oxide powders with carbon powder in an amount sufficient to form the corresponding carbide, heating the mixture at a temperature of higher than 1000° C in an inert atmosphere or in vacuum to reduce the oxygen content and then heating at a temperature of higher than 1400° C in hydrogen atmosphere, thereby to form tungsten carbide or mixed metal carbides directly from the corresponding oxide.

Chemical specificity in the surface diffusion of clusters: Ir on W(211)

Abstract: Although the diffusion of tungsten and rhenium clusters over the (211) plane of tungsten has recently been found to be quite similar, a significant chemical specificity should be expected for cluster migration. Such specificity has now been established in quantitative measurements on iridium doublets diffusing on W(211). With tungsten and rhenium, dimers have a lower activation energy for diffusion than do single atoms. For iridium dimers, the situation is reversed: single atoms diffuse over a barrier of 51 ± 5 kJ mol−1, compared to a barrier of 65 ± 6 kJ mol−1 for dimers. This, and differences in the diffusion dynamics, are shown to be a consequence of interactions specific to iridium adatoms.

Cemented carbides containing hexagonal molybdenum

Abstract: A composition of material is disclosed which comprises sintered carbide-binder metal alloys. The carbide is a solid solution of hexagonal tungsten monocarbide and molybdenum monocarbide of stoichiometric composition containing between 10 and 100 mole percent molybdenum monocarbide. The binder is selected from the metals of the iron group, and comprises between 3 and 50 weight percent of the composition. A method for making the hexagonal carbide is also disclosed.