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Life Tests of Tungsten and Tantalum Filaments in Ion Gauges

Description: Results of an investigation carried on for the following purposes: (1) To determine the relative life of filaments when operated at low emission (low temperatures) as compared to those operated at high emission values. (2) To determine the nature of the dependence of life upon the initial diameter of the filament. (3) To determine the effect of varying concentrations of water vapor and air upon the life of the filaments. (4) To determine the relative life characteristics of tantalum as compared to tungsten.
Date: August 9, 1949
Creator: Bush, W. E.
Partner: UNT Libraries Government Documents Department

Adhesion of Diamond Films on Tungsten

Description: The U.S. Bureau of Mines has investigated the chemical vapor deposition of diamond films on tungsten substrates. The effects of deposition parameters on the adhesion of the films was determined. The films were produced using a hot filament chemical vapor deposition system. Parameters investigated were substrate temperature and methane concentration in the feed gas. Film quality, morphology, and composition were characterized by scanning electron microscopy and Raman spectroscopy. Adhesion testing was performed using an indentation technique, and the results were quantified by relating adhesion to interface fracture toughness. Diamond films with well-faceted crystalline morphology with grain size greater than 1 pm had poor adhesion properties regardless of substrate temperature or methane concentration. Diamond films with smooth morphologies consisting of rounded clusters of small (<0.2 pm) diamond crystallites and amorphous carbon phases displayed much higher adhesion, although the conditions that led to the growth of these films are not understood.
Date: 1995
Creator: Maggs, K. J.; Walkiewicz, J. W. & Clark, A. E.
Partner: UNT Libraries Government Documents Department

Molybdenum and Tungsten Structural Differences are Dependent on ndz2/(n + 1)ѕ Mixing: Comparisons of (silox)3MX/R (M = Mo, W; silox = tBu3SiO)

Description: Article discussing molybdenum and tungsten structural differences being dependent on ndz2/(n + 1)s mixing and a comparison of (silox)3MX/R (M = Mo, W; silox - tBu3SiO).
Date: July 15, 2008
Creator: Kuiper, David S.; Douthwalte, Richard E.; Mayoi, Ana-Rita; Wolczanski, Peter T.; Lobkovsky, Emil B.; Cundari, Thomas R., 1964- et al.
Partner: UNT College of Arts and Sciences

Development and Evaluation of High-Temperature Tungsten Alloys : Quarterly Report No. 2, January 1, 1960 - March 31, 1960

Description: Abstract: "Room-temperature properties were determined for W-Ni-Fe-Ru base alloys containing Cr, Mo, Pd, and Ta; highest strength levels were found in W-Ni-Fe-Ru-Mo compositions. Annealing for 250 hours at 1600 F produced a precipitate in the matrix phase and increased hardness in some of the tungsten-base alloys under study. Oxidation tests at temperatures up to 2000 F showed that additions of Al, Cr, Mo, Pd, and Ti improved the oxidation resistance of the W-Ni-Fe base. A fused coating of AMS 4775 protected a 90W-6Ni-4Fe alloy for 72 hours in air at 2100 F."
Date: June 24, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Quarterly Report No. 3, April 1, 1960 - June 30, 1960

Description: Abstract: "High-tungsten alloys were prepared by powder metallurgy techniques. Excellent strength and ductility at room temperature were found in the W-Ni-Mo-Ry system and in W-Ni-Fe alloys containing platinum and/or ruthenium. The effects of prolonged annealing at 1600 F on room-temperature properties were studied; W-Ni-Fe-Pt-Ru alloys were least affected by this treatment. Oxidation rates for most alloys at 2000 F were 2 to 4 times that of unalloyed tungsten; an exception was a W-Ni-Mo-Ru alloy which oxidized at 1/5 the rate of tungsten. Slip casting techniques and induction-sintering of loosely compacted powders were used to produce compacts of W-Ni-Fe materials having section thicknesses of 1 to 2 inches."
Date: August 10, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Summary Report

Description: Abstract: "Tungsten-rich alloys, developed for use at temperatures up to 2000F, exhibit ductility, fabricability and joinability not found in commercially-available materials. An envelope type of microstructure was produced in compositions containing at least 90 wt% tungsten by liquid-phase sintering of cold-pressed powders in hydrogen. At room temperature the alloys could be rolled extensively, and tensile elongations up to 25% were noted. Strength properties of a W-Ni-Fe base were improved by small quaternary additions. The ultimate tensile strength of a 90W-4.8Ni-3.2Fe-2Ru alloy was 46,700 psi at 2000F, compared to 30,000 - 35,000 psi for unalloyed tungsten or W-Ni-Fe; the 100-hour stress-rupture strength at 1600F was 15,000 psi. Excellent joints were produced by spot welding and localized induction heating. The oxidation resistance of unprotected 90 wt% tungsten compositions was not significantly affected by alloying."
Date: November 12, 1959
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Quarterly Report No. 1, October 1, 1959 - December 31, 1959

Description: Abstract: "High-tungsten alloys were prepared by powder metallurgy techniques. Room-temperature strength properties were determined for W-Ni-Fe compositions with quaternary additions of Cr, Pd, and Ru; tungsten levels ranged from 80 to 94 wt%. Small (1-3 wt%) ruthenium additions were the most effective in improving strength. The oxidation resistance of a number of tungsten-base alloys was measured at 2000F. Quaternary W-Ni-Fe base alloys containing Al, Ru, Ti, and Zr were the most oxidation resistant, having values similar to unalloyed tungsten. Oxidation protection of a 90W-6Ni-4Fe material was accomplished by a fused coating of AMS 4775; the composite was tested for 482 hours in air at 2000F without damage to the base alloy."
Date: January 20, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Development and Evaluation of High-Temperature Tungsten Alloys : Final Report, October 1, 1960 - September 30, 1960

Description: This report summarizes investigations taken between October 1, 1959, to September 30, 1960 with the objectives of developing high-tungsten alloys which are readily fabricable into massive and complex shapes and which possess adequate strength for operation at temperatures up to 2000 F. Within this report, studies are divided into two main categories: alloy development and material fabrication techniques
Date: December 14, 1960
Creator: Holtz, F. C. & Van Thyne, R. J.
Partner: UNT Libraries Government Documents Department

Tungsten Deposits in Utah

Description: Report issued by the U.S. Bureau of Mines discussing tungsten deposits and mining practices in Utah. As stated in the introduction, "this paper describes the tungsten-bearing areas of Utah, inferred reserves, production practices and problems, and many of the mines" (p. 2). This report includes maps, tables, and illustrations.
Date: 1961
Creator: Everett, Floyd D.
Partner: UNT Libraries Government Documents Department

Selectivity Failure in the Chemical Vapor Deposition of Tungsten

Description: Tungsten metal is used as an electrical conductor in many modern microelectronic devices. One of the primary motivations for its use is that it can be deposited in thin films by chemical vapor deposition (CVD). CVD is a process whereby a thin film is deposited on a solid substrate by the reaction of a gas-phase molecular precursor. In the case of tungsten chemical vapor deposition (W-CVD) this precursor is commonly tungsten hexafluoride (WF6) which reacts with an appropriate reductant to yield metallic tungsten. A useful characteristic of the W-CVD chemical reactions is that while they proceed rapidly on silicon or metal substrates, they are inhibited on insulating substrates, such as silicon dioxide (Si02). This selectivity may be exploited in the manufacture of microelectronic devices, resulting in the formation of horizontal contacts and vertical vias by a self-aligning process. However, reaction parameters must be rigorously controlled, and even then tungsten nuclei may form on neighboring oxide surfaces after a short incubation time. Such nuclei can easily cause a short circuit or other defect and thereby render the device inoperable. If this loss of selectivity could be controlled in the practical applications of W-CVD, thereby allowing the incorporation of this technique into production, the cost of manufacturing microchips could be lowered. This research was designed to investigate the loss of selectivity for W-CVD in an attempt to understand the processes which lead to its occurrence. The effects of passivating the oxide surface with methanol against the formation of tungsten nuclei were studied. It was found that the methanol dissociates at oxide surface defect sites and blocks such sites from becoming tungsten nucleation sites. The effect of reactant partial pressure ratio on selectivity was also studied. It was found that as the reactant partial pressures are varied there are significant changes in the ...
Date: August 1994
Creator: Cheek, Roger W. (Roger Warren)
Partner: UNT Libraries

Electrodeposition of adherent copper film on unmodified tungsten.

Description: Adherent Cu films were electrodeposited onto polycrystalline W foils from purged solutions of 0.05 M CuSO4 in H2SO4 supporting electrolyte and 0.025 M CuCO3∙Cu(OH)2 in 0.32 M H3BO3 and corresponding HBF4 supporting electrolyte, both at pH = 1. Films were deposited under constant potential conditions at voltages between -0.6 V and -0.2 V vs Ag/AgCl. All films produced by pulses of 10 s duration were visible to the eye, copper colored, and survived a crude test called "the Scotch tape test", which stick the scotch tape on the sample, then peel off the tape and see if the copper film peels off or not. Characterization by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray photon spectroscopy (XPS) confirmed the presence of metallic Cu, with apparent dendritic growth. No sulfur impurity was observable by XPS or EDX. Kinetics measurements indicate that the Cu nucleation process in the sulfuric bath is slower than in the borate bath. In both baths, nucleation kinetics do not correspond to either instantaneous or progressive nucleation. Films deposited from 0.05 M CuSO4/H2SO4 solution at pH > 1 at -0.2 V exhibited poor adhesion and decreased Cu reduction current. In both borate and sulfate baths, small Cu nuclei are observable by SEM upon deposition at higher negative overpotentials, while only large nuclei (~ 1 micron or larger) are observed upon deposition at less negative potentials.
Access: This item is restricted to the UNT Community Members at a UNT Libraries Location.
Date: May 2004
Creator: Wang, Chen
Partner: UNT Libraries

Tungsten Resources of Montana: Deposits of the Mount Torrey Batholith, Beaverhead County

Description: Report issued by the Bureau of Mines over the tungsten deposits on Beaverhead County, Montana. As stated in the introduction, "this report presents information obtained from July 1955 to September 1957 on tungsten deposits in and near the Mount Torrey batholith" (p. 1). This report includes tables, maps, illustrations, and photographs.
Date: 1960
Creator: Pattee, Eldon C.
Partner: UNT Libraries Government Documents Department

Domain and Surface Structures of Sodium Tungsten Bronzes, NaxWO₃ (0.4 [x [1)

Description: The domain and surface structures of metallic sodium tungsten bronzes, NaxWO₃, 0.4 < x < 1, were studied using optical microscopy, supplemented by chemical methods, photoelectron spectroscopy, electron microscopy, etc. The birefringent, multidomain structure of the bronze is exhibited by a sodium-deficient, epitaxial surface film and hence is not, as reported elsewhere, a bulk property. The film can be synthesized by anodic electrolysis in alkaline solution and can exist only epitaxially with the substrate. It is chemically inert, translucent, and often laminated to a multilayered film. The film domain is hypersensitive to lateral stress and to thermal change, and appears to be modulated by minute structural changes of the substrate. This epitaxial modulation of the film is strikingly large at the phase transitions of the substrate induced by slightly different tiltings of the oxygen octahedra. The domain-wall movement is often slow enough to be visible, and that by thermal effect is occasionally accompanied by an audible, high-pitched, snapping sound.
Date: September 1978
Creator: Atoji, Masao
Partner: UNT Libraries Government Documents Department

Dynamic compaction of tungsten carbide powder.

Description: 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.
Date: April 1, 2005
Creator: Gluth, Jeffrey Weston; Hall, Clint Allen; Vogler, Tracy John & Grady, Dennis Edward
Partner: UNT Libraries Government Documents Department

Process Evaluation and Characterization of Tungsten Nitride as a Diffusion Barrier for Copper Interconnect Technology

Description: The integration of copper (Cu) and dielectric materials has been outlined in the International Technology Roadmap for Semiconductors (ITRS) as a critical goal for future microelectronic devices. A necessity toward achieving this goal is the development of diffusion barriers that resolve the Cu and dielectric incompatibility. The focus of this research examines the potential use of tungsten nitride as a diffusion barrier by characterizing the interfacial properties with Cu and evaluating its process capability for industrial use. Tungsten nitride (β-W2N) development has been carried out using a plasma enhanced chemical vapor deposition (PECVD) technique that utilizes tungsten hexafluoride (WF6), nitrogen (N2), hydrogen (H2), and argon (Ar). Two design of experiments (DOE) were performed to optimize the process with respect to film stoichiometry, resistivity and uniformity across a 200 mm diameter Si wafer. Auger depth profiling showed a 2:1 W:N ratio. X-ray diffraction (XRD) showed a broad peak centered on the β-W2N phase. Film resistivity was 270 mohm-cm and film uniformity < 3 %. The step coverage (film thickness variance) across a structured etched dielectric (SiO2, 0.35 mm, 3:1 aspect ratio) was > 44 %. Secondary ion mass spectroscopy (SIMS) measurements showed good barrier performance for W2N between Cu and SiO2 with no intermixing of the Cu and silicon when annealed to 390o C for 3 hours. Cu nucleation behavior and thermal stability on clean and nitrided tungsten foil (WxN = δ-WN and β-W2N phases) have been characterized by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, the Auger intensity ratio vs. time plots demonstrates layer by layer Cu growth for the clean tungsten (W) surface and three-dimensional nucleation for the nitride overlayer. Auger intensity ratio vs. temperature measurements for the Cu/W system indicates a stable interface up to 1000 ...
Date: August 2005
Creator: Ekstrom, Bradley Mitsuharu
Partner: UNT Libraries

Welding Development W87 Baseline

Description: This report covers the development activities used to qualify the Gas Tungsten Arc (FTA) girth weld and the resistance stem attachments on the W87 Base Line (W87BL). Design of experiments was used throughout the development activities.
Date: November 1, 1998
Creator: Newman, A.; Gibbs, G. & Hicken, G. K.
Partner: UNT Libraries Government Documents Department