636 Matching Results

Search Results

Advanced search parameters have been applied.

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

World Survey of Tantalum Ore

Description: Report issued by the U.S. Bureau of Mines discussing the occurrences of tantalum in different areas of the world. The tantalum deposits are described in reference to each individual country that it is found in. This report includes maps, tables, and illustrations.
Date: March 1945
Creator: Baker, James S.
Partner: UNT Libraries Government Documents Department

Vapor deposition of tantalum and tantalum compounds

Description: Tantalum, and many of its compounds, can be deposited as coatings with techniques ranging from pure, thermal chemical vapor deposition to pure physical vapor deposition. This review concentrates on chemical vapor deposition techniques. The paper takes a historical approach. The authors review classical, metal halide-based techniques and current techniques for tantalum chemical vapor deposition. The advantages and limitations of the techniques will be compared. The need for new lower temperature processes and hence new precursor chemicals will be examined and explained. In the last section, they add some speculation as to possible new, low-temperature precursors for tantalum chemical vapor deposition.
Date: April 1996
Creator: Trkula, M.
Partner: UNT Libraries Government Documents Department

Passivation effects of surface iodine layer on tantalum for the electroless copper deposition.

Description: The ability to passivate metallic surfaces under non-UHV conditions is not only of fundamental interests, but also of growing practical importance in catalysis and microelectronics. In this work, the passivation effect of a surface iodine layer on air-exposed Ta for the copper electroless deposition was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Although the passivation effect was seriously weakened by the prolonged air exposure, iodine passivates the Ta substrate under brief air exposure conditions so that enhanced copper wetting and adhesion are observed on I-passivated Ta relative to the untreated surface.
Access: This item is restricted to the UNT Community Members at a UNT Libraries Location.
Date: May 2004
Creator: Liu, Jian
Partner: UNT Libraries

Micromechanics of spall and damage in tantalum

Description: The authors conducted a series of plate impact experiments using an 80-mm launcher to study dynamic void initiation, linkup, and spall in tantalum. The tests ranged in peak shock pressures so that the effect of peak pressure on the transition from void initiation, incipient spall, and full spall could be studied. Wave profiles were measured using a velocity interferometry system (VISAR), and targets were recovered using {open_quotes}soft{close_quotes} recovery techniques. The authors utilized scanning electron microscopy, metallographic cross-sections, and plateau etching techniques to obtain quantitative information concerning damage evolution in tantalum under spall conditions. The data (wave profiles and micrographs) are analyzed in terms of a new theory and model of dynamic damage cluster growth.
Date: May 1, 1996
Creator: Zurek, A.K.; Thissell, W.R.; Johnson, J.N.; Tonks, D.L. & Hixson, R.
Partner: UNT Libraries Government Documents Department

LASNEX modeling of target expansion in the ETA-II experiment

Description: We have used the hydrodynamics code LASNEX to model the hydro-expansion of the tantalum target for the ETA-II experiment. The electron beam has kinetic energy of 6 MeV and has a total energy ranges from 720 to 1440 J. The electron beam profile resembles that of a Bennett pinch. The radius for the full-width-at-half-maximum ranges from 1 to 3 mm. For all these parameters, simulations show that the electron beam is able to ablate the central portion of the target. The expansion velocity of the target ranges from about 10� to 5 x 105 cm/s. The target is hot enough so that the surrounding low-density air is ionized and is expanding at a considerably higher velocity than the target itself. Therefore, care must be taken during the experiment to ensure that the measurement is for the tantalum and not for the ionized air.
Date: May 20, 1998
Creator: Ho, D D-M
Partner: UNT Libraries Government Documents Department

Evidence for Strong Tantalum-to-Boron Dative Interactions in (silox)3Ta(BH3) and (silox)3Ta(ɳ2-B,CI-BCI2Ph) (silox = tBu3SiO)1

Description: This article discusses strong tantalum-to-boron dative interactions in (silox)3Ta(BH3) and (silox)3Ta(ɳ2-B,CI-BCI2Ph) (silox = tBu3SiO)1.
Date: January 24, 2007
Creator: Bonanno, Jeffrey B.; Henry, Thomas P.; Wolczanski, Peter T.; Pierpont, Aaron W. & Cundari, Thomas R., 1964-
Partner: UNT College of Arts and Sciences

Influence of shockwave obliquity on deformation twin formation in Ta

Description: Energetic loading subjects a material to a 'Taylor wave' (triangular wave) loading profile that experiences an evolving balance of hydrostatic (spherical) and deviatoric stresses. While much has been learned over the past five decades concerning the propensity of deformation twinning in samples shockloaded using 'square-topped' profiles as a function of peak stress, achieved most commonly via flyer plate loading, less is known concerning twinning propensity during non-I-dimensional sweeping detonation wave loading. Systematic small-scale energetically-driven shock loading experiments were conducted on Ta samples shock loaded with PEFN that was edge detonated. Deformation twinning was quantified in post-mortem samples as a function of detonation geometry and radial position. In the edge detonated loading geometry examined in this paper, the average volume fraction of deformation twins was observed to drastically increase with increasing shock obliquity. The results of this study are discussed in light of the formation mechanisms of deformation twins, previous literature studies of twinning in shocked materials, and modeling of the effects of shock obliquity on the evolution of the stress tensor during shock loading.
Date: January 1, 2009
Creator: Gray Iii, George T; Livescu, V; Cerreta, E K; Mason, T A; Maudlin, P J & Bingert, J F
Partner: UNT Libraries Government Documents Department

Chemistry modification of high oxygen-carbon powder by plasma melting: Follow up to complete the story

Description: State of the art melting of tantalum and tantalum alloys has relied on electron beam (EB) or vacuum arc remelting (VAR) for commercial ingot production. Plasma arc melting (PAM) provides an alternative for melting tantalum that contains very high levels of interstitials where other melting techniques can not be applied. Previous work in this area centered on plasma arc melt quality and final interstitial content of tantalum feedstock containing excessive levels of interstitial impurities as a function of melt rate and plasma gas. This report is an expansion of this prior study and provides the findings from the analysis of second phase components observed in the microstructure of the PAM tantalum. In addition, results from subsequent EB melting trials of PAM tantalum are included.
Date: March 1, 1998
Creator: Dunn, P.S.; Korzekwa, D.R.; Garcia, F.G. & Michaluk, C.A.
Partner: UNT Libraries Government Documents Department

Mechanical behavior of tantalum and tantalum-tungsten alloys: texture gradients and macro/micro-response

Description: We have examined the mechanical response of unalloyed Ta and Ta-W alloy annealed plates over a wide range of loadings. It was observed in general that Ta exhibits nonuniform mechanical behavior, for example, hourglassing of compression samples and multiple instabilities during tensile deformation. In contrast, the Ta-W alloys do not exhibit any unusual nonuniform behavior. This work presents data revealing the spatial distribution of texture in Ta and Ta-W alloys. Significant variations in texture both through the thickness and from one area of the plate to another were found to be characteristic of Ta. The dominant feature of the texture variations was found to be enhanced <111> crystal direction fractions at the center of the plate, with a decreasing fraction near the surface. We find that the variation in texture in the Ta-W alloys is substantially less than that seen in Ta with primarily a <100> cube texture throughout. This study suggest that the texture gradients are responsible for the nonuniform mechanical response of Ta and that the uniform behavior of the Ta-W alloys is a consequence of the absence of texture gradients.
Date: November 30, 1996
Creator: Lassila, D.H.; Schwartz, A.J.; LeBlanc, M.M. & Wright, S.I.
Partner: UNT Libraries Government Documents Department

Diffusion Barriers/Adhesion Promoters. Surface and Interfacial Studies of Copper and Copper-Aluminum Alloys

Description: The focus of this research is to study the interaction between copper and the diffusion barrier/adhesion promoter. The behavior of copper sputter-deposited onto sputter-cleaned tantalum nitride is investigated. The data show that copper growth on tantalum nitride proceeds with the formation of 3-D islands, indicating poor adhesion characteristics between copper and Ta0.4N. Post-annealing experiments indicate that copper will diffuse into Ta0.4N at 800 K. Although the data suggests that Ta0.4N is effective in preventing copper diffusion, copper's inability to wet Ta0.4N will render this barrier ineffective. The interaction of copper with oxidized tantalum silicon nitride (O/TaSiN) is characterized. The data indicate that initial copper depositions result in the formation a conformal ionic layer followed by Cu(0) formation in subsequent depositions. Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 800 K, copper "de-wetting" occurs for temperatures above 500 K. These results indicate that in conditions where the substrate has been oxidized facile de-wetting of copper may occur. The behavior of a sputter-deposited Cu0.6Al0.4 film with SiO2 (Cu0.6Al0.4/SiO2) is investigated. The data indicate that aluminum segregates to the SiO2 interface and becomes oxidized. For copper coverages less than ~ 0.31 ML (based on a Cu/O atomic ratio), only Cu(I) formation is observed. At higher coverages, Cu(0) is observed. These data are in contrast with the observed behavior of copper metal deposited onto SiO2 (Cu/SiO2). The data for Cu/SiO2 show that copper does not wet SiO2 and forms 3-D nuclei. Furthermore, post-annealing experiments performed on Cu0.6Al0.4/SiO2 show that neither de-wetting nor diffusion of copper occurs for temperatures up to 800 K, while Cu diffusion into SiO2 occurs ~ 600 K. These data indicate that aluminum alloyed with copper at the SiO2 interface serves as an effective adhesion promoter and thermal diffusion barrier.
Date: August 2000
Creator: Shepherd, Krupanand Solomon
Partner: UNT Libraries

Dynamic material properties of refractory materials: Tantalum and tantalum/tungsten alloys

Description: We have made a careful set of impact wave-profile measurements (16 profiles) on tantalum and tantalum-tungsten alloys at relatively low stresses (to 15 GPa). Alloys used were Ta{sub 97.5}W{sub 2.5} and Ta{sub 90}W{sub 10} (wt. %) with oxygen contents of 30--70 ppM. Information available from these experiments includes Hugoniot, elastic limits, loading fates, spall strength, unloading paths, reshock structure and specimen thickness effects. Hugoniot and spall properties are illustrated, and are consistent with expectations from earlier work. Modeling the tests with the Steinberg-Lund rate-dependent material model provides for an excellent match of the shape of the plastic wave, although the release wave is not well modeled. There is also a discrepancy between experiments and calculations regarding the relative timing of the elastic and plastic waves that may be due to texture effects.
Date: August 1, 1995
Creator: Furnish, M.D.; Chhabildas, L.C.; Lassila, D.H. & Steinberg, D.J.
Partner: UNT Libraries Government Documents Department

Synthetic, Mechanistic, and Structural Studies of Polynuclear Metal Clusters and Hydrazido-Substituted Tantalum(V) Compounds

Description: A combined experimental and computational study on the reversible ortho-metalation exhibited by the triosmium cluster Os3(CO)10(dppm) (dppm = 1,1-bis(diphenylphosphino)methane is reported. The conversion of nonacarbonyl cluster HOs3(CO)9[&#61549;-PhP(C6H4)CH2PPh2] to Os3(CO)10(dppm) is independent of added CO and exhibits a significant inverse equilibrium isotope effect (EIE). Reductive coupling of the C-H bond in HOs3(CO)9[&#61549;-PhP(C6H4)CH2PPh2] leads to the formation of agostic C-H and two distinct aryl-&#960; species prior to the rate-limiting formation of the unsaturated cluster Os3(CO)9(dppm). Heating the unsaturated dimer H2Re2(CO)8 with Cp*Rh(CO)2 (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene) at elevated temperature affords the new trimetallic clusters H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6, and the spiked-triangular cluster HRhRe3Cp*(CO)14. H2Re2(CO)8 reacts with Cp*2Rh2(CO)2 under identical conditions to furnish H2RhRe2Cp*(CO)9 and HRh2ReCp*2(CO)6 as the principal products, in addition to the tetrahedral cluster H2Rh2Re2Cp*2(CO)8. H2RhRe2Cp*(CO)9 undergoes facile fragmentation in the presence of halogenated solvents and the thiols RSH (where R = H, C6H4Me-p) to afford the structurally characterized products Cp*Rh(&#61549;-Cl)3Re(CO)3, S2Rh3Cp*(CO)4, Cp*Rh(&#61549;-Cl)(&#61549;-SC6H4Me-p)2Re(CO)3, and Cp*Rh(&#61549;-SC6H4Me-p)3Re(CO)3. The new hydrazido-substituted compounds TaCl(NMe2)3[N(TMS)NMe2] (TMS = tetramethylsilyl) and Ta(NMe2)4[N(TMS)NMe2] have been synthesized and their structures established by X-ray crystallography. The latter product represents the first structurally characterized octahedral tantalum(V) complex containing a single hydrazido(I) ligand in an all-nitrogen coordinated environment about the metal center. The fluxional properties of the amido and hydrazido ligands in these new compounds have been established by VT 1H NMR spectroscopy (VT = variable temperature). Preliminary data using Ta(NMe2)4[N(TMS)NMe2] as an ALD (ALD = atomic layer deposition) precursor for the preparation of tantalum nitride and tantalum oxide thin films are presented.
Date: December 2010
Creator: Huang, Shih-huang
Partner: UNT Libraries

Tantalum- and ruthenium-based diffusion barriers/adhesion promoters for copper/silicon dioxide and copper/low κ integration.

Description: The TaSiO6 films, ~8Å thick, were formed by sputter deposition of Ta onto ultrathin SiO2 substrates at 300 K, followed by annealing to 600 K in 2 torr O2. X-ray photoelectron spectroscopy (XPS) measurements of the films yielded a Si(2p) binding energy at 102.1 eV and Ta(4f7/2) binding energy at 26.2 eV, indicative of Ta silicate formation. O(1s) spectra indicate that the film is substantially hydroxylated. Annealing the film to > 900 K in UHV resulted in silicate decomposition to SiO2 and Ta2O5. The Ta silicate film is stable in air at 300K. XPS data show that sputter-deposited Cu (300 K) displays conformal growth on Ta silicate surface (TaSiO6) but 3-D growth on the annealed and decomposed silicate surface. Initial Cu/silicate interaction involves Cu charge donation to Ta surface sites, with Cu(I) formation and Ta reduction. The results are similar to those previously reported for air-exposed TaSiN, and indicate that Si-modified Ta barriers should maintain Cu wettability under oxidizing conditions for Cu interconnect applications. XPS has been used to study the reaction of tert-butylimino tris(diethylamino) tantalum (TBTDET) with atomic hydrogen on SiO2 and organosilicate glass (OSG) substrates. The results on both substrates indicate that at 300K, TBTDET partially dissociates, forming Ta-O bonds with some precursor still attached. Subsequent bombardment with atomic hydrogen at 500K results in stoichiometric TaN formation, with a Ta(4f7/2) feature at binding energy 23.2 eV and N(1s) at 396.6 eV, leading to a TaN phase bonded to the substrate by Ta-O interactions. Subsequent depositions of the precursor on the reacted layer on SiO2 and OSG, followed by atomic hydrogen bombardment, result in increased TaN formation. These results indicate that TBTDET and atomic hydrogen may form the basis for a low temperature atomic layer deposition (ALD) process for the formation of ultraconformal TaNx or Ru/TaNx barriers. The interactions ...
Date: December 2004
Creator: Zhao, Xiaopeng
Partner: UNT Libraries

Orientation imaging microscopy investigation of the compression deformation of a [011] ta single crystal

Description: High-purity tantalum single crystal cylinders oriented with [110] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The samples were subsequently sectioned for characterization using Orientation Imaging Microscopy (O&I) along two orthogonal sectioning planes: one in the plane containing [001] and [110] (longitudinal) and the other in the plane containing [1{anti 1}0] and[110] (transverse). To examine local lattice rotations, the Euler angles relative to a reference angle at the section center were decomposed to their in-plane and out-of-plane components. The in-plane and out-of-plane misorientation maps for all compression tests reveal inhomogeneous deformation everywhere and particularly large lattice rotations in the comers of the longitudinal section. Of particular interest are the observed alternating orientation changes. This suggests the existence of networks of dislocations with net alternating sign that are required to accommodate the observed rotations. Rotation maps from the transverse section are distinctly different in appearance from those in the longitudinal plane. However, the rotation maps confirm that the rotations observed above were about the [1{anti 1}0] axis. Alternating orientation changes are also observed on this section. Results will be directly compared with crystal rotations predicted using finite element methods and reviewed in light of the LLNL Multiscale Materials Modeling Program.
Date: January 8, 1999
Creator: Adams, B L; Campbell, G H; King, W E; Lassila, D H; Stolken, J S; Sun, S et al.
Partner: UNT Libraries Government Documents Department

Extraction of niobium and tantalum isotopes using organophosphorus compounds -- Part II -- Extraction of 'carrier-free' concentrations from HCl/LiCl solutions

Description: We have studied the extraction of niobium and tantalum from mixed hydrochloric acid/lithium chloride media by bis(2-ethylhexyl) hydrogen phosphate (HDEHP) and bis(2-ethylhexyl) hydrogen phosphite (BEHP) as a function of hydrogen ion (H+) concentration. The amount of niobium extracted by both HDEHP and BEHP decreased with increasing hydrogen ion concentration. Equilibrium with niobium occurred within 10 s at all hydrogen ion concentrations for both systems. For tantalum, the amount extracted increased until 6 - 9 M H+, before decreasing at higher H+ concentrations when extracted by both HDEHP and BEHP. Equilibrium occurred within 10 s at two H+ concentrations when extracted by HDEHP. The data obtained are used as the basis to discuss the speciation of Nb and Ta under the conditions studied and to evaluate possible extraction mechanisms.
Date: December 1, 2008
Creator: Gates, J. M.; Stavsetra, L.; Sudowe, R.; Ali, M. N.; Calvert, M. G.; Dragojevic, I. et al.
Partner: UNT Libraries Government Documents Department

Critical and Strategic Minerals in Alaska: Tin, Tantalum, and Columbium

Description: Report issued by the U.S. Bureau of Mines discussing critical and strategic Alaskan minerals. As stated in the introduction, "this report presents findings from the second phase of the Bureau's critical and strategic minerals program in Alaska; it summarizes information on tin, tantalum, and columbium production, reserves, and occurrences" (p. 2). This report includes tables and a map.
Date: 1985
Creator: Warner, J. Dean
Partner: UNT Libraries Government Documents Department