The effect of tantalum on the structure/properties of two polycrystalline nickel-base superalloys: B-1900 + Hf MAR-M247. M.S. Thesis, Final Report

NASA Technical Reports Server (NTRS)

Janowski, G. M.

1985-01-01

The microstructure, phase compositions, and phase fractions were studied in conventionally cast B-1900 + Hf and both conventionally cast and directionally solidified MAR-M247 as a function of tantalum concentration. The hot tensile and creep rupture properties of the solutionized and aged MAR-M247-type alloys were also determined as a function of tantalum level. The effects of tantalum on the microstructure and phase compositions of B-1900 + Hf and MAR-M247 (conventionally cast and directionally solidified) were found to be very similar. The addition of tantalum to the as cast and heat treated alloys was shown to cause the partial replacement of the Hf in the MC carbides by Ta, although the degree of replacement was decreased by the solutionizing and aging heat treatment. The gamma prime and minor phase fractions (primarily MC type carbides) both increased approximately linearly with tantalum concentration. The gamma prime phase compositions were relatively insensitive to tantalum variations with the exception of the tantalum and/or hafnium levels. Bulk tantalum additions increased the tantalum, chromium, and cobalt levels of the gamma phase in both alloy series. The increase in the concentrations of the latter two elements in the gamma phase was a result of the decrease in the gamma phase fraction with increasing bulk tantalum concentration and constant gamma/gamma prime partitioning ratio. Tantalum additions increased the yield stress and ultimate tensile strength of the directionally solidified MAR-M247 type alloys and had no significant effect on ductility.

Amorphous metal alloy

DOEpatents

Wang, R.; Merz, M.D.

1980-04-09

Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

Characteristics of laser produced plasmas of hafnium and tantalum in the 1-7 nm region

NASA Astrophysics Data System (ADS)

Li, Bowen; Otsuka, Takamitsu; Sokell, Emma; Dunne, Padraig; O'Sullivan, Gerry; Hara, Hiroyuki; Arai, Goki; Tamura, Toshiki; Ono, Yuichi; Dinh, Thanh-Hung; Higashiguchi, Takeshi

2017-11-01

Soft X-ray (SXR) spectra from hafnium and tantalum laser produced plasmas were recorded in the 1-7 nm region using two Nd:YAG lasers with pulse lengths of 170 ps and 10 ns, respectively, operating at a range of power densities. The maximum focused peak power density was 2. 3 × 1014 W cm-2 for 170 ps pulses and 1. 8 × 1012 W cm-2 for 10 ns pulses, respectively. Two intense quasicontinuous intensity bands resulting from n = 4 - n = 4 and n = 4 - n = 5 unresolved transition arrays (UTAs) dominate both sets of experimental spectra. Comparison with calculations performed with the Cowan suite of atomic structure codes as well as consideration of previous experimental and theoretical results aided identification of the most prominent features in the spectra. For the 10 ns spectrum, the highest ion stage that could be identified from the n = 4 - n = 5 arrays were lower than silver-like Hf25+ and Ta26+ (which has a 4 d 104 f ground configuration) indicating that the plasma temperature attained was too low to produce ions with an outermost 4 d subshell, while for the 170 ps plasmas the presence of significantly higher stages was deduced and lines due to 4 d-5 p transitions were clearly evident. Furthermore, we show an enhancement of emission from tantalum using dual laser irradiation, and the effect of pre-pulse durations and delay times between two pulses are demonstrated.

Amorphous metal alloy and composite

DOEpatents

Wang, Rong; Merz, Martin D.

1985-01-01

Amorphous metal alloys of the iron-chromium and nickel-chromium type have excellent corrosion resistance and high temperature stability and are suitable for use as a protective coating on less corrosion resistant substrates. The alloys are stabilized in the amorphous state by one or more elements of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The alloy is preferably prepared by sputter deposition.

ON THE GEOCHEMISTRY OF NIOBIUM AND TANTALUM IN CLAYS (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pachadzhanov, D.N.

1963-10-01

With the aid of the spectral method with a preliminary enrichment in tannin, the niobium and tantalum content was determined in some humid and arid clays of the Russian platform. The investigated samples were composed of 354 specimens. The average content of niobium in humid clays is 0.0020%, of tantalum 0.00024% (the Nb/Ta ratio is 8.4) and in arid clays is respectively the content of niobium 0.00133% and the content of tantalum 0.00009% (the Nb/Ta ratio is 14.8). The average value of the content of niobium content for all studied clays is 0.00183% and of the tantalum content 0.00020%, themore » Nb/Ta ratio being 9.1. In clays an interconnection of niobium with tantalum, as well as with aluminium, titanium, zirconium, and hafnium was observed. However, on the background of this connection some separation of the named elements is noted. A tendency for the Nb/Ta ratio shift from the region of matter removal towards the center of the marine basin was observed. The study of niobium and tantalum distribution over different clay fractions showed that one part of elements is connected with zircon and titanium minerals in aleuosand fraction (0.1-- 0.01 mm). Another, approximately similar part is contained in the proper clay fraction (<0. 01 mm), the tantalum somewhat more concentrating in the aleurosand fraction and niobium in the clay fraction. (P.C.H.)« less

CVD aluminiding process for producing a modified platinum aluminide bond coat for improved high temperature performance

NASA Technical Reports Server (NTRS)

Nagaraj, Bangalore A. (Inventor); Williams, Jeffrey L. (Inventor)

2003-01-01

A method of depositing by chemical vapor deposition a modified platinum aluminide diffusion coating onto a superalloy substrate comprising the steps of applying a layer of a platinum group metal to the superalloy substrate; passing an externally generated aluminum halide gas through an internal gas generator which is integral with a retort, the internal gas generator generating a modified halide gas; and co-depositing aluminum and modifier onto the superalloy substrate. In one form, the modified halide gas is hafnium chloride and the modifier is hafnium with the modified platinum aluminum bond coat comprising a single phase additive layer of platinum aluminide with at least about 0.5 percent hafnium by weight percent and about 1 to about 15 weight percent of hafnium in the boundary between a diffusion layer and the additive layer. The bond coat produced by this method is also claimed.

Creep and Fatigue Interaction Characteristics of PWA1484

DTIC Science & Technology

2009-03-01

Tungsten) , 5.6% Al (aluminum) , 9% Ta (tantalum) , 3% Re (rhenium) , .1% Hf (hafnium) , and 59.3% Ni (nickel) by weight [1]. The alloy was invented...Work by Hael Mughrabi sought to determine the effect that the rafting behavior of the gamma prime precipitates had on the creep performance of...inclusions and in-homogeneities in 1961 [6]. Mughrabi further states that there is a tensile stress present in the gamma prime phase and a compressive

Precipitation hardening austenitic superalloys

DOEpatents

Korenko, Michael K.

1985-01-01

Precipitation hardening, austenitic type superalloys are described. These alloys contain 0.5 to 1.5 weight percent silicon in combination with about 0.05 to 0.5 weight percent of a post irradiation ductility enhancing agent selected from the group of hafnium, yttrium, lanthanum and scandium, alone or in combination with each other. In addition, when hafnium or yttrium are selected, reductions in irradiation induced swelling have been noted.

A simple spectrophotometric method for determination of zirconium or hafnium in selected molybdenum-base alloys

NASA Technical Reports Server (NTRS)

Dupraw, W. A.

1972-01-01

A simple analytical procedure is described for accurately and precisely determining the zirconium or hafnium content of molybdenum-base alloys. The procedure is based on the reaction of the reagent Arsenazo III with zirconium or hafnium in strong hydrochloric acid solution. The colored complexes of zirconium or hafnium are formed in the presence of molybdenum. Titanium or rhenium in the alloy have no adverse effect on the zirconium or hafnium complex at the following levels in the selected aliquot: Mo, 10 mg; Re, 10 mg; Ti, 1 mg. The spectrophotometric measurement of the zirconium or hafnium complex is accomplished without prior separation with a relative standard deviation of 1.3 to 2.7 percent.

Metal alloy coatings and methods for applying

DOEpatents

Merz, Martin D.; Knoll, Robert W.

1991-01-01

A method of coating a substrate comprises plasma spraying a prealloyed feed powder onto a substrate, where the prealloyed feed powder comprises a significant amount of an alloy of stainless steel and at least one refractory element selected from the group consisting of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten. The plasma spraying of such a feed powder is conducted in an oxygen containing atmosphere and forms an adherent, corrosion resistant, and substantially homogenous metallic refractory alloy coating on the substrate.

Study of gas tungsten arc welding procedures for tantalum alloy T-111 (Ta-8 W-2Hf) plate

NASA Technical Reports Server (NTRS)

Gold, R. E.; Kesterson, R. L.

1973-01-01

Methods of eliminating or reducing underbread cracking in multipass GTA welds in thick T-111 plate were studied. Single V butt welds prepared using experimental filler metal compositions and standard weld procedures resulted in only moderate success in reducing underbread cracking. Subsequent procedural changes incorporating manual welding, slower weld speeds, and three or fewer fill passes resulted in crack-free single V welds only when the filler metal was free of hafnium. The double V joint design with successive fill passes on opposite sides of the joint produced excellent welds. The quality of each weld was determined metallographically since the cracking, when present, was very slight and undetectable using standard NDT techniques. Tensile and bend tests were performed on selected weldments. The inherent filler metal strength and the joint geometry determined the strength of the weldment. Hardness and electron beam microprobe traverses were made on selected specimens with the result that significant filler metal-base metal dilution as well as hafnium segregation was detected. A tentative explanation of T-111 plate underbread cracking is presented based on the intrinsic effects of hafnium in the weldment.

Observation of oxide particles below the apparent oxygen solubility limit in tantalum

NASA Technical Reports Server (NTRS)

Stecura, S.

1973-01-01

The apparent solubility of oxygen in polycrystalline tantalum as determined by the X-ray diffraction lattice parameter technique is about 1.63 atomic percent at 820 C. However, oxide particles were identified in samples containing as low as 0.5 atomic percent of oxygen. These oxide particles were present at the grain boundaries and within the grains. The number of oxide particles increased with increasing oxygen concentration in tantalum. The presence of oxide particles suggests that the true solubility of oxygen in the polycrystalline tantalum metal is probably significantly lower than that reported in the literature.

Development study of compositions for advanced wrought nickel-base superalloys

NASA Technical Reports Server (NTRS)

Kent, W. B.

1972-01-01

Using NASA IIb as a base composition, the effects of five key elements (carbon, tungsten, tantalum, aluminum, and hafnium) on resultant properties were investigated in an effort to optimize the composition and derive new wrought high temperature alloys with improved strength characteristics. A total of nineteen compositions were melted, extruded, and rolled to bar stock using thermomechanical processing. Both full and partial solution heat treatments were developed for the compositions. Tensile properties from room temperature to 1800 deg F, stress and creep rupture properties to 1800 deg F, and thermal stability characteristics were evaluated. NASA IIb-7 exhibited the best response to the partial solution heat treatment for optimum properties up to 1200 deg F. The alloy contained 0.13C, 9.0 Cr, 9.0 Co, 2.0 Mo, 7.5 W, 10.0 Ta, 3.5 Al, 0.75 Ti, 0.02 B, 0.10 Zr, 0.50 V, 1.0 Hf, and balance nickel.

All-alkoxide synthesis of strontium-containing metal oxides

DOEpatents

Boyle, Timothy J.

2001-01-01

A method for making strontium-containing metal-oxide ceramic thin films from a precursor liquid by mixing a strontium neo-pentoxide dissolved in an amine solvent and at least one metal alkoxide dissolved in a solvent, said at least one metal alkoxide selected from the group consisting of alkoxides of calcium, barium, bismuth, cadmium, lead, titanium, tantalum, hafnium, tungsten, niobium, zirconium, yttrium, lanthanum, antimony, chromium and thallium, depositing a thin film of the precursor liquid on a substrate, and heating the thin film in the presence of oxygen at between 550 and 700.degree. C.

Role of electron concentration in softening and hardening of ternary molybdenum alloys

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1975-01-01

Effects of various combinations of hafnium, tantalum, rhenium, osmium, iridium, and platinum in ternary molybdenum alloys on alloy softening and hardening were determined. Hardness tests were conducted at four test temperatures over the temperature range 77 to 411 K. Results showed that hardness data for ternary molybdenum alloys could be correlated with anticipated results from binary data based upon expressions involving the number of s and d electrons contributed by the solute elements. The correlation indicated that electron concentration plays a dominant role in controlling the hardness of ternary molybdenum alloys.

IER-297 CED-2: Final Design for Thermal/Epithermal eXperiments with Jemima Plates with Polyethylene and Hafnium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, A. J.; Percher, C. M.; Zywiec, W. J.

This report presents the final design (CED-2) for IER-297, and focuses on 15 critical configurations using highly enriched uranium (HEU) Jemima plates moderated by polyethylene with and without hafnium diluent. The goal of the U.S. Nuclear Criticality Safety Program’s Thermal/Epithermal eXperiments (TEX) is to design and conduct new critical experiments to address high priority nuclear data needs from the nuclear criticality safety and nuclear data communities, with special emphasis on intermediate energy (0.625 eV – 100 keV) assemblies that can be easily modified to include various high priority diluent materials. The TEX (IER 184) CED-1 Report [1], completed in 2012,more » demonstrated the feasibility of meeting the TEX goals with two existing NCSP fissile assets, plutonium Zero Power Physics Reactor (ZPPR) plates and highly enriched uranium (HEU) Jemima plates. The first set of TEX experiments will focus on using the plutonium ZPPR plates with polyethylene moderator and tantalum diluents.« less

Method for making hot-pressed fiber-reinforced carbide-graphite composite

DOEpatents

Riley, Robert E.; Wallace Sr., Terry C.

1979-01-01

A method for the chemical vapor deposition of a uniform coating of tantalum metal on fibers of a woven graphite cloth is described. Several layers of the coated cloth are hot pressed to produce a tantalum carbide-graphite composite having a uniformly dispersed, fine grained tantalum carbide in graphite with compositions in the range of 15 to 40 volume percent tantalum carbide.

Effects of anode material on arcjet performance

NASA Technical Reports Server (NTRS)

Sankovic, John M.; Curran, Frank M.; Larson, C. A.

1992-01-01

Anodes fabricated from four different materials were tested in a modular arcjet thruster at 1 kW power level on nitrogen/hydrogen mixtures. A two-percent thoriated tungsten anode served as the control. Graphite was chosen for its ease in fabrication, but experienced severe erosion in the constrictor and diverging side. Hafnium carbide and lanthanum hexaboride were chosen for their low work functions but failed due to thermal stress and reacted with the propellant. When compared to the thoriated tungsten nozzle, thruster performance was significantly lower for the lanthanum hexaboride insert and the graphite nozzle, but was slightly higher for the hafnium carbide nozzle. Both the lanthanum hexaboride and hafnium carbide nozzle operated at higher voltages. An attempt was made to duplicate higher performance hafnium carbide results, but repeated attempts at machining a second anode insert were unsuccessful. Graphite, hafnium carbide, and lanthanum hexaboride do not appear viable anode materials for low power arcjet thrusters.

Alloy hardening and softening in binary molybdenum alloys as related to electron concentration

NASA Technical Reports Server (NTRS)

Stephens, J. R.; Witzke, W. R.

1972-01-01

An investigation was conducted to determine the effects of alloy additions of hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum on hardness of molybdenum. Special emphasis was placed on alloy softening in these binary molybdenum alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to molybdenum, while those elements having an equal number or fewer s+d electrons that molybdenum failed to produce alloy softening. Alloy softening and alloy hardening can be correlated with the difference in number of s+d electrons of the solute element and molybdenum.

Mixed oxide solid solutions

DOEpatents

Magno, Scott; Wang, Ruiping; Derouane, Eric

2003-01-01

The present invention is a mixed oxide solid solution containing a tetravalent and a pentavalent cation that can be used as a support for a metal combustion catalyst. The invention is furthermore a combustion catalyst containing the mixed oxide solid solution and a method of making the mixed oxide solid solution. The tetravalent cation is zirconium(+4), hafnium(+4) or thorium(+4). In one embodiment, the pentavalent cation is tantalum(+5), niobium(+5) or bismuth(+5). Mixed oxide solid solutions of the present invention exhibit enhanced thermal stability, maintaining relatively high surface areas at high temperatures in the presence of water vapor.

Development of high temperature materials for solid propellant rocket nozzle applications. [tantalum carbides-tungsten fiber composites

NASA Technical Reports Server (NTRS)

Manning, C. R., Jr.; Honeycutt, L., III

1974-01-01

Evaluation of tantalum carbide-tungsten fiber composites has been completed as far as weight percent carbon additions and weight percent additions of tungsten fiber. Extensive studies were undertaken concerning Young's Modulus and fracture strength of this material. Also, in-depth analysis of the embrittling effects of the extra carbon additions on the tungsten fibers has been completed. The complete fabrication procedure for the tantalum carbide-tungsten fiber composites with extra carbon additions is given. Microprobe and metallographic studies showed the effect of extra carbon on the tungsten fibers, and evaluation of the thermal shock parameter fracture strength/Young's Modulus is included.

Carbide and carbonitride surface treatment method for refractory metals

DOEpatents

Meyer, Glenn A.; Schildbach, Marcus A.

1996-01-01

A carbide and carbonitride surface treatment method for refractory metals is provided, in steps including, heating a part formed of boron, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten or zirconium, or alloys thereof, in an evacuated chamber and then introducing reaction gases including nitrogen and hydrogen, either in elemental or water vapor form, which react with a source of elemental carbon to form carbon-containing gaseous reactants which then react with the metal part to form the desired surface layer. Apparatus for practicing the method is also provided, in the form of a carbide and carbonitride surface treatment system (10) including a reaction chamber (14), a source of elemental carbon (17), a heating subassembly (20) and a source of reaction gases (23). Alternative methods of providing the elemental carbon (17) and the reaction gases (23) are provided, as well as methods of supporting the metal part (12), evacuating the chamber (14) with a vacuum subassembly (18) and heating all of the components to the desired temperature.

Article having an improved platinum-aluminum-hafnium protective coating

NASA Technical Reports Server (NTRS)

Nagaraj, Bangalore Aswatha (Inventor); Williams, Jeffrey Lawrence (Inventor)

2005-01-01

An article protected by a protective coating has a substrate and a protective coating having an outer layer deposited upon the substrate surface and a diffusion zone formed by interdiffusion of the outer layer and the substrate. The protective coating includes platinum, aluminum, no more than about 2 weight percent hafnium, and substantially no silicon. The outer layer is substantially a single phase.

The Hot-Pressing of Hafnium Carbide (Melting Point, 7030 F)

NASA Technical Reports Server (NTRS)

Sanders, William A.; Grisaffe, Salvatore J.

1960-01-01

An investigation was undertaken to determine the effects of the hot-pressing variables (temperature, pressure, and time) on the density and grain size of hafnium carbide disks. The purpose was to provide information necessary for the production of high-density test shapes for the determination of physical and mechanical properties. Hot-pressing of -325 mesh hafnium carbide powder was accomplished with a hydraulic press and an inductively heated graphite die assembly. The ranges investigated for each variable were as follows: temperature, 3500 to 4870 F; pressure, 1000 to 6030 pounds per square inch; and time, 5 to 60 minutes. Hafnium carbide bodies of approximately 98 percent theoretical density can be produced under the following minimal conditions: 4230 F, 3500 pounds per square inch, and 15 minutes. Further increases in temperature and time resulted only in greater grain size.

Zirconium and hafnium in the southeastern Atlantic States

USGS Publications Warehouse

Mertie, J.B.

1958-01-01

The principal source of zirconium and hafnium is zircon, though a minor source is baddeleyite, mined only in Brazil. Zircon is an accessory mineral in igneous, metamorphic, and sedimentary rocks, but rarely occurs in hardrock in minable quantities. The principal sources of zircon are therefore alluvial deposits, which are mined in many countries of five continents. The principal commercial deposits in the United States are in Florida, though others exist elsewhere in the southeastern Coastal Plain. The evidence indicates that conditions for the accumulation of workable deposits of heavy minerals were more favorable during the interglacial stages of the Pleistocene epoch than during Recent time. Therefore detrital ores of large volume and high tenor are more likely to be found in the terrace deposits than along the present beaches. Other concentrations of heavy minerals, however, are possible at favored sites close to the Fall Line where the Tuscaloosa formation rests upon the crystalline rocks of the Piedmont province. A score of heavy and semiheavy minerals occur in the detrital deposits of Florida, but the principal salable minerals are ilmenite, leucoxene, rutile, and zircon, though monazite and staurolite are saved at some mining plants. Commercial deposits of heavy minerals are generally required to have a tenor of 4 percent, though ores with a lower tenor can be mined at a profit if the content of monazite is notably high. The percentages of zircon in the concentrates ranges from 10 to 16 percent, and in eastern Florida from 13 to 15 percent. Thus the tenor in zircon of the ore-bearing sands ranges from 0.4 to 0.6 percent. The content of hafnium in zircon is immaterial for many uses, but for some purposes very high or very low tenors in hafnium are required. Alluvial zircon cannot be separated into such varieties, which, if needed, must be obtained from sources in bedrock. It thus becomes necessary to determine the Hf : Zr ratios in zircon from many kinds of bedrock.Granitic rocks are the principal sources of zircon, though not the best sources of zircon with a high tenor in hafnium. A general study by the Geological Survey of the granitic rocks of the Southeastern Atlantic States has been in progress for 10 years, and hundreds of samples of granitic accessory minerals have been acquired. Thirty samples of zircon from these collections were selected for spectrographic and X-ray determinations of their tenors in hafnium. Nine other samples of alluvial zircon were included, of which three are from Florida and six from foreign countries. No domestic zircon was discovered with very high or very low tenors in hafnium.The volume of zircon in the southeastern Coastal Plain is enormous, but most of it is not recoverable. The minable reserves of heavy minerals, however, are very large, and from these it is estimated conservatively that 10 million short tons of zircon can be obtained. The corresponding amounts of zirconium and hafnium, using the mean Hf:Zr ratio of the deposits in Florida, are 4,868,000 and 112,000 tons, respectively. These reserves could be delivered, if needed, at the rate of 100,000 tons a year.

Refractory ceramic compositions and method for preparing same

DOEpatents

Holcombe, Jr., Cressie E.; Morrow, Margaret K.

1976-07-13

This invention relates to ceramic compositions of tungsten and tantalum oxides including 0 to 33 1/3 mole percent of a metal oxide such as hafnia. These ceramics are characterized by melting points greater than about 1400.degree.C and selectively controlled coefficients of thermal expansion of essentially zero to a negative value in the temperature range of 20.degree. to 1000.degree.C.

Hafnium isotope stratigraphy of ferromanganese crusts

PubMed

Lee; Halliday; Hein; Burton; Christensen; Gunther

1999-08-13

A Cenozoic record of hafnium isotopic compositions of central Pacific deep water has been obtained from two ferromanganese crusts. The crusts are separated by more than 3000 kilometers but display similar secular variations. Significant fluctuations in hafnium isotopic composition occurred in the Eocene and Oligocene, possibly related to direct advection from the Indian and Atlantic oceans. Hafnium isotopic compositions have remained approximately uniform for the past 20 million years, probably reflecting increased isolation of the central Pacific. The mechanisms responsible for the increase in (87)Sr/(86)Sr in seawater through the Cenozoic apparently had no effect on central Pacific deep-water hafnium.

Nickel aluminide alloy suitable for structural applications

DOEpatents

Liu, Chain T.

1998-01-01

Alloys for use in structural applications based upon NiAl to which are added selected elements to enhance room temperature ductility and high temperature strength. Specifically, small additions of molybdenum produce a beneficial alloy, while further additions of boron, carbon, iron, niobium, tantalum, zirconium and hafnium further improve performance of alloys at both room temperature and high temperatures. A preferred alloy system composition is Ni--(49.1.+-.0.8%)Al--(1.0.+-.0.8%)Mo--(0.7.+-.0.5%)Nb/Ta/Zr/Hf--(nearly zero to 0.03%)B/C, where the % is at. % in each of the concentrations. All alloys demonstrated good oxidation resistance at the elevated temperatures. The alloys can be fabricated into components using conventional techniques.

Processing, physical metallurgy and creep of NiAl + Ta and NiAl + Nb alloys. Ph.D. Thesis. Final Contractor Report

NASA Technical Reports Server (NTRS)

Pathare, Viren M.

1988-01-01

Powder processed NiAl + Ta alloys containing 1, 2, and 4.5 at percent tantalum and NiAl + Nb alloys containing 1 and 2 at percent niobium were developed for improved creep properties. In addition, a cast alloy with 5 at percent tantalum was also studied. Hot extrusion parameters for processing alloys with 1 and 2 at percent of tantalum or niobium were designed. The NiAl + 4.5 at percent Ta alloy could be vacuum hot pressed successfully, even though it could not be extruded. All the phases in the multiphase alloys were identified and the phase transformations studied. The Ni2AlTa in NiAl + 4.5 at percent Ta alloy transforms into a liquid phase above 1700 K. Solutionizing and annealing below this temperature gives rise to a uniform distribution of fine second phase precipitates. Compressive creep properties were evaluated at 1300 K using constant load and constant velocity tests. In the higher strain rate region single phase NiAl + 1 at percent Ta and NiAl + 1 at percent Nb alloys exhibit a stress exponent of 5 characteristic of climb controlled dislocation creep. In slower strain rate regime diffusional creep becomes important. The two phase alloys containing 2 to 5 at percent Ta and 2 at percent Nb show considerable improvement over binary NiAl and single phase alloys. Loose dislocation networks and tangles stabilized by the precipitates were found in the as crept microstructure. The cast alloy which has larger grains and a distribution of fine precipitates shows the maximum improvement over binary NiAl.

Niobium and tantalum

USGS Publications Warehouse

Schulz, Klaus J.; Piatak, Nadine M.; Papp, John F.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Niobium and tantalum are transition metals that are almost always found together in nature because they have very similar physical and chemical properties. Their properties of hardness, conductivity, and resistance to corrosion largely determine their primary uses today. The leading use of niobium (about 75 percent) is in the production of high-strength steel alloys used in pipelines, transportation infrastructure, and structural applications. Electronic capacitors are the leading use of tantalum for high-end applications, including cell phones, computer hard drives, and such implantable medical devices as pacemakers. Niobium and tantalum are considered critical and strategic metals based on the potential risks to their supply (because current production is restricted to only a few countries) and the significant effects that a restriction in supply would have on the defense, energy, high-tech industrial, and medical sectors.The average abundance of niobium and tantalum in bulk continental crust is relatively low—8.0 parts per million (ppm) niobium and 0.7 ppm tantalum. Their chemical characteristics, such as small ionic size and high electronic field strength, significantly reduce the potential for these elements to substitute for more common elements in rock-forming minerals and make niobium and tantalum essentially immobile in most aqueous solutions. Niobium and tantalum do not occur naturally as pure metals but are concentrated in a variety of relatively rare oxide and hydroxide minerals, as well as in a few rare silicate minerals. Niobium is primarily derived from the complex oxide minerals of the pyrochlore group ((Na,Ca,Ce)2(Nb,Ti,Ta)2(O,OH,F)7), which are found in some alkaline granite-syenite complexes (that is, igneous rocks containing sodium- or potassium-rich minerals and little or no quartz) and carbonatites (that is, igneous rocks that are more than 50 percent composed of primary carbonate minerals, by volume). Tantalum is derived mostly from the mineral tantalite ((Fe,Mn)(Ta,Nb)2O6), which is found as an accessory mineral in rare-metal granites and pegmatites that are also enriched in lithium and cesium (termed lithium-cesium-tantalum (LCT)-type pegmatites).Brazil and Canada are the leading nations that produce niobium mineral concentrates, but Brazil is by far the leading producer, accounting for about 90 percent of production, which comes mostly from weathered material derived from carbonatites. Brazil and Canada also have the largest identified niobium resources; additional resources, although they are less well reported, occur in Angola, Australia, China, Greenland, Malawi, Russia, and South Africa. Australia and Brazil have been the leading producers of tantalum mineral concentrates, although recently Ethiopia and Mozambique have also been significant suppliers of tantalum. Artisanal mining of columbite-tantalite (also called coltan) is practiced in many countries, particularly Burundi, the Democratic Republic of the Congo (Congo [Kinshasa]), Nigeria, Rwanda, and Uganda. Brazil has about 40 percent of the identified tantalum resources; other countries and regions with identified tantalum resources include, in decreasing order of resources, Australia, Asia, Russia and the Middle East, Africa, North America, and Europe. Identified niobium and tantalum resources in the United States are small, low grade, and difficult to recover and process, and are thus not commercially recoverable at current prices. Consequently, the United States meets its current and expected future needs for niobium and tantalum through imports of primary mineral concentrates and alloys and through recovery from foreign and domestic alloy scrap that contain the metals.Environmentally, the main issues related to niobium and tantalum mining are land disruptions, the volume of waste materials and their disposal, and the radioactivity of some tailings and waste materials that contain thorium and uranium. Because of the relative biological inertness of niobium and tantalum, human and ecological health concerns are generally minimal under most natural conditions.Demand for both niobium and tantalum is expected to increase as the world economy continues to recover from the downturn that began in 2008. Increased demand for niobium is linked to increased consumption of microalloyed steel, which is used in the manufacture of cars, buildings, ships, and refinery equipment. Demand for these steels will likely increase with continued economic development in such countries as Brazil, China, and India. In addition, increased global demand for cars, cell phones, computers, superconducting magnets, and other high-tech devices will likely spur increased demand for both niobium and tantalum. The estimated global reserves and resources of niobium and tantalum are large and appear more than sufficient to meet global demand for the foreseeable future, possibly the next 500 years. The sale of “conflict coltan” attributed to rebel forces waging a civil war in Congo (Kinshasa) has been of recent concern and has highlighted the need for a transparent and traceable global supply chain that can exclude illegal columbite-tantalite from the conventional market while discerning legitimate artisanal mine production in central Africa.

Nickel aluminide alloy suitable for structural applications

DOEpatents

Liu, C.T.

1998-03-10

Alloys are disclosed for use in structural applications based upon NiAl to which are added selected elements to enhance room temperature ductility and high temperature strength. Specifically, small additions of molybdenum produce a beneficial alloy, while further additions of boron, carbon, iron, niobium, tantalum, zirconium and hafnium further improve performance of alloys at both room temperature and high temperatures. A preferred alloy system composition is Ni--(49.1{+-}0.8%)Al--(1.0{+-}0.8%)Mo--(0.7 + 0.5%)Nb/Ta/Zr/Hf--(nearly zero to 0.03%)B/C, where the % is at. % in each of the concentrations. All alloys demonstrated good oxidation resistance at the elevated temperatures. The alloys can be fabricated into components using conventional techniques. 4 figs.

Deep-ocean ferromanganese crusts and nodules

USGS Publications Warehouse

Hein, James R.; Koschinsky, Andrea

2014-01-01

Ferromanganese crusts and nodules may provide a future resource for a large variety of metals, including many that are essential for emerging high- and green-technology applications. A brief review of nodules and crusts provides a setting for a discussion on the latest (past 10 years) research related to the geochemistry of sequestration of metals from seawater. Special attention is given to cobalt, nickel, titanium, rare earth elements and yttrium, bismuth, platinum, tungsten, tantalum, hafnium, tellurium, molybdenum, niobium, zirconium, and lithium. Sequestration from seawater by sorption, surface oxidation, substitution, and precipitation of discrete phases is discussed. Mechanisms of metal enrichment reflect modes of formation of the crusts and nodules, such as hydrogenetic (from seawater), diagenetic (from porewaters), and mixed diagenetic–hydrogenetic processes.

Process for production of a metal hydride

DOEpatents

Allen, Nathan Tait; Butterick, III, Robert; Chin, Arthur Achhing; Millar, Dean Michael; Molzahn, David Craig

2014-08-12

A process for production of a metal hydride compound MH.sub.x, wherein x is one or two and M is an alkali metal, Be or Mg. The process comprises combining a compound of formula (R.sup.1O).sub.xM with aluminum, hydrogen and at least one metal selected from among titanium, zirconium, hafnium, niobium, vanadium, tantalum and iron to produce a compound of formula MH.sub.x. R.sup.1 is phenyl or phenyl substituted by at least one alkyl or alkoxy group. A mole ratio of aluminum to (R.sup.1O).sub.xM is from 0.1:1 to 1:1. The catalyst is present at a level of at least 200 ppm based on weight of aluminum.

40 CFR 471.91 - Effluent limitations representing the degree of effluent reduction attainable by the application...

Code of Federal Regulations, 2010 CFR

2010-07-01

... million off-pounds) of zirconium-hafnium extruded Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0... million off-pounds) of zirconium-hafnium heat treated Chromium 0.151 0.062 Cyanide 0.100 0.041 Nickel 0...-hafnium surface treated Chromium 0.150 0.61 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20...

40 CFR 471.91 - Effluent limitations representing the degree of effluent reduction attainable by the application...

Code of Federal Regulations, 2011 CFR

2011-07-01

... million off-pounds) of zirconium-hafnium extruded Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0... million off-pounds) of zirconium-hafnium heat treated Chromium 0.151 0.062 Cyanide 0.100 0.041 Nickel 0...-hafnium surface treated Chromium 0.150 0.61 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20...

40 CFR 471.94 - Pretreatment standards for existing sources (PSES).

Code of Federal Regulations, 2011 CFR

2011-07-01

...-hafnium extruded Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0.301 Ammonia 31.6 13.9 Fluoride 14...-hafnium heat treated Chromium 0.015 0.006 Cyanide 0.010 0.004 Nickel 0.066 0.044 Ammonia 4.57 2.01...-hafnium surface treated Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20.0...

40 CFR 471.94 - Pretreatment standards for existing sources (PSES).

Code of Federal Regulations, 2010 CFR

2010-07-01

...-hafnium extruded Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0.301 Ammonia 31.6 13.9 Fluoride 14...-hafnium heat treated Chromium 0.015 0.006 Cyanide 0.010 0.004 Nickel 0.066 0.044 Ammonia 4.57 2.01...-hafnium surface treated Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20.0...

Draft critical mineral list—Summary of methodology and background information—U.S. Geological Survey technical input document in response to Secretarial Order No. 3359

USGS Publications Warehouse

Fortier, Steven M.; Nassar, Nedal T.; Lederer, Graham W.; Brainard, Jamie; Gambogi, Joseph; McCullough, Erin A.

2018-02-16

Pursuant to the Presidential Executive Order (EO) No. 13817, “A Federal Strategy to Ensure Secure and Reliable Supplies of Critical Minerals,” the Secretary of the Interior, in coordination with the Secretary of Defense, and in consultation with the heads of other relevant executive departments and agencies, was tasked with developing and submitting a draft list of minerals defined as “critical minerals” to the Federal Register within 60 days of the issue of the EO (December 20, 2017).Based on an analysis by the U.S. Geological Survey and other U.S. Government agencies, using multiple criteria, 35 minerals or mineral material groups have been identified that are currently (February 2018) considered critical. These include the following: aluminum (bauxite), antimony, arsenic, barite, beryllium, bismuth, cesium, chromium, cobalt, fluorspar, gallium, germanium, graphite (natural), hafnium, helium, indium, lithium, magnesium, manganese, niobium, platinum group metals, potash, rare earth elements group, rhenium, rubidium, scandium, strontium, tantalum, tellurium, tin, titanium, tungsten, uranium, vanadium, and zirconium. The categorization of minerals as critical may change during the course of the review process and is thus provisional.

Facility for assessing spectral normal emittance of solid materials at high temperature.

PubMed

Mercatelli, Luca; Meucci, Marco; Sani, Elisa

2015-10-10

Spectral emittance is a key topic in the study of new compositions, depositions, and mechanical machining of materials for solar absorption and for renewable energies in general. The present work reports on the realization and testing of a new experimental facility for the measurement of directional spectral emittance in the range of 2.5-20 μm. Our setup provides emittance spectral information in a completely controlled environment at medium-high temperatures up to 1200 K. We describe the layout and first tests on the device, comparing the results obtained for hafnium carbide and tantalum diboride ultrarefractory ceramic samples to previous quasi-monochromatic measurements carried out in the PROMES-CNRS (PROcedes, Materiaux et Energie Solaire- Centre National de la Recherche Scientifique, France) solar furnace, obtaining a good agreement. Finally, to assess the reliability of the widely used approach of estimating the spectral emittance from room-temperature reflectance spectrum, we compared the calculation in the 2.5-17 μm spectral range to the experimental high-temperature spectral emittance, obtaining that the spectral trend of calculated and measured curves is similar but the calculated emittance underestimates the measured value.

40 CFR 471.93 - New source performance standards (NSPS).

Code of Federal Regulations, 2010 CFR

2010-07-01

... monthly average mg/off-kg (pounds per million off-pounds) of zirconium-hafnium extruded Chromium 0.104 0... monthly average mg/off-kg (pounds per million off-pounds) of zirconium-hafnium heat treated Chromium 0.015... Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20.0 Fluoride 20.0 8.98 Oil and...

40 CFR 471.93 - New source performance standards (NSPS).

Code of Federal Regulations, 2011 CFR

2011-07-01

... monthly average mg/off-kg (pounds per million off-pounds) of zirconium-hafnium extruded Chromium 0.104 0... monthly average mg/off-kg (pounds per million off-pounds) of zirconium-hafnium heat treated Chromium 0.015... Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20.0 Fluoride 20.0 8.98 Oil and...

Development of tungsten-tantalum generator

NASA Technical Reports Server (NTRS)

Leblanc, A.; Babich, J.; Jhingran, S. G.

1985-01-01

The purpose of this project was to develop a useable tungsten (W)/tantalum (Ta) generator. Ta-178 is formed following the decay of its parent, W-178 (half-life: 21.7d) and has a half life of 9.3 minutes in turn yielding stable Hf-178. The decay of the parent isotope (W-178) occurs entirely by electron capture to the 9.3 minute Ta-178 state, without feeding the high spin Ta-178 isomer (half life 2.2 hours). In Ta-178 decay, 99.2% of the disintegrations proceed by electron capture and 0.18% by positron emission. Electron capture results in a 61.2% branch to the ground state of Hf-178 and 33.7% to the first excited state at 93 1KeV. The most prominent features of the radionuclide's energy spectrum are the hafnium characteristic radiation peaks with energies between 54.6 and 65.0 KeV. The radiation exposure dose of Ta-118 was calculated to be approximately one-twentieth that of Tc-99m on a per millicurie basis. A twenty-fold reduction in radiation exposure from Ta-178 compared with Tc-99m means that the usual administered dose can be increased three or four times, greatly increasing statistical accuracy while reducing radiation exposure by a factor of five.

Niobium (columbium) and tantalum resources of Brazil

USGS Publications Warehouse

White, Max Gregg

1975-01-01

Most of the niobium resources of Brazil occur as pyrochlore in carbonatites within syenitic intrusives of Late Cretaceous to early Tertiary age in western Minas Gerais and southeastern Goils. Minor amounts of it are produced together with tantalum from columbite-tantalite concentrates from pegmatites and placers adjacent to them, in the Sao Joao del Rei district in south-central Minas Gerais. All the niobium and tantalum produced in Brazil is exported. The only pyrochlore mined is from the Barreiro carbonatite deposit near Araxa in Minas Gerais where concentrates and ferroniobium are produced. Exploration work for pyrochlore and other mineral resources are being undertaken on other carbonatites, particularly at Catalao I in southeast Goias and at Tapira and Serra Negra in western Minas Gerais. Annual production and export from the Barreiro deposit are about 8,000 metric tons of pyrochlore concentrate containing about 60 percent Nb205 and about 2,700 metric tons of ferroniobium with 63 percent Nb2O5. The annual production capacity of the Barreiro plant is 18,000 tons of concentrate and 4,000 tons of ferroniobium. Ore reserves of the Barreiro deposit in all categories are 380 million tons with percent Nb2O5. Annual production of tantalite-columbite from the Sao Joao del Rei district, most of which is exported to the United States, is about 290 tons, of which about 79 percent is tantalite and about percent is columbite. Reserves of tantalite-columbite in the Sao Joao del Rei district are about 43,000 tons of proved and 73,000 tons of probable ore.

Electrodeposition of Tantalum and Tantalum-Chromium Alloys

DTIC Science & Technology

1980-05-01

Electrochem Soc, 112, 840 (1965). 7Ibid, 113,60 (1966). 8Ibid, 113.66 (1966). J. Wurm, "European Conference on the Development of Molten Salts Applica...Chem. 35, 161-3 (1887). 16. J. Wurm, "European Conference on the Development of Molten Salts Applica- tions," Extended Abstracts and Proceedings, pp...Metals Tantalum Tantalum-Chromium Alloys Chromium Coating Fused Salt Electrolyte Electrodeposition FLINAK 20. ABSTRACT (Continue on reverse

Hardness and Microstructure of Binary and Ternary Nitinol Compounds

NASA Technical Reports Server (NTRS)

Stanford, Malcolm K.

2016-01-01

The hardness and microstructure of twenty-six binary and ternary Nitinol (nickel titanium, nickel titanium hafnium, nickel titanium zirconium and nickel titanium tantalum) compounds were studied. A small (50g) ingot of each compound was produced by vacuum arc remelting. Each ingot was homogenized in vacuum for 48 hr followed by furnace cooling. Specimens from the ingots were then heat treated at 800, 900, 1000 or 1100 degree C for 2 hr followed by water quenching. The hardness and microstructure of each specimen was compared to the baseline material (55-Nitinol, 55 at.% nickel - 45 at.% titanium, after heat treatment at 900 degC). The results show that eleven of the studied compounds had higher hardness values than the baseline material. Moreover, twelve of the studied compounds had measured hardness values greater 600HV at heat treatments from 800 to 900 degree C.

Carbide and carbonitride surface treatment method for refractory metals

DOEpatents

Meyer, G.A.; Schildbach, M.A.

1996-12-03

A carbide and carbonitride surface treatment method for refractory metals is provided, in steps including, heating a part formed of boron, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten or zirconium, or alloys thereof, in an evacuated chamber and then introducing reaction gases including nitrogen and hydrogen, either in elemental or water vapor form, which react with a source of elemental carbon to form carbon-containing gaseous reactants which then react with the metal part to form the desired surface layer. Apparatus for practicing the method is also provided, in the form of a carbide and carbonitride surface treatment system including a reaction chamber, a source of elemental carbon, a heating subassembly and a source of reaction gases. Alternative methods of providing the elemental carbon and the reaction gases are provided, as well as methods of supporting the metal part, evacuating the chamber with a vacuum subassembly and heating all of the components to the desired temperature. 5 figs.

Comparative studies of Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors with HfSiON dielectric and TaN metal gate

NASA Astrophysics Data System (ADS)

Hu, Ai-Bin; Xu, Qiu-Xia

2010-05-01

Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with hafnium silicon oxynitride (HfSiON) gate dielectric and tantalum nitride (TaN) metal gate are fabricated. Self-isolated ring-type transistor structures with two masks are employed. W/TaN metal stacks are used as gate electrode and shadow masks of source/drain implantation separately. Capacitance-voltage curve hysteresis of Ge metal-oxide-semiconductor (MOS) capacitors may be caused by charge trapping centres in GeO2 (1 < x < 2). Effective hole mobilities of Ge and Si transistors are extracted by using a channel conductance method. The peak hole mobilities of Si and Ge transistors are 33.4 cm2/(V · s) and 81.0 cm2/(V · s), respectively. Ge transistor has a hole mobility 2.4 times higher than that of Si control sample.

Zirconium and hafnium

USGS Publications Warehouse

Jones, James V.; Piatak, Nadine M.; Bedinger, George M.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Zirconium and hafnium are corrosion-resistant metals that are widely used in the chemical and nuclear industries. Most zirconium is consumed in the form of the main ore mineral zircon (ZrSiO4, or as zirconium oxide or other zirconium chemicals. Zirconium and hafnium are both refractory lithophile elements that have nearly identical charge, ionic radii, and ionic potentials. As a result, their geochemical behavior is generally similar. Both elements are classified as incompatible because they have physical and crystallochemical properties that exclude them from the crystal lattices of most rock-forming minerals. Zircon and another, less common, ore mineral, baddeleyite (ZrO2), form primarily as accessory minerals in igneous rocks. The presence and abundance of these ore minerals in igneous rocks are largely controlled by the element concentrations in the magma source and by the processes of melt generation and evolution. The world’s largest primary deposits of zirconium and hafnium are associated with alkaline igneous rocks, and, in one locality on the Kola Peninsula of Murmanskaya Oblast, Russia, baddeleyite is recovered as a byproduct of apatite and magnetite mining. Otherwise, there are few primary igneous deposits of zirconium- and hafnium-bearing minerals with economic value at present. The main ore deposits worldwide are heavy-mineral sands produced by the weathering and erosion of preexisting rocks and the concentration of zircon and other economically important heavy minerals, such as ilmenite and rutile (for titanium), chromite (for chromium), and monazite (for rare-earth elements) in sedimentary systems, particularly in coastal environments. In coastal deposits, heavy-mineral enrichment occurs where sediment is repeatedly reworked by wind, waves, currents, and tidal processes. The resulting heavy-mineral-sand deposits, called placers or paleoplacers, preferentially form at relatively low latitudes on passive continental margins and supply 100 percent of the world’s zircon. Zircon makes up a relatively small percentage of the economic heavy minerals in most deposits and is produced primarily as a byproduct of heavy-mineral-sand mining for titanium minerals.From 2003 to 2012, world zirconium mineral concentrates production increased by more than 40 percent, and Australia and South Africa were the leading producers. Global consumption of zirconium mineral concentrates generally increased during the same time period, largely as a result of increased demand in developing economies in Asia and the Middle East. Global demand weakened in 2012, causing a decrease in world production of zirconium mineral concentrates and delaying the development of several new mining projects. Global consumption is expected to increase in the future, however, as demand from the ceramics, chemicals, and metals industries increases (driven by renewed growth in developing economies) and demand for zirconium and hafnium metal increases (driven by the construction and operation of new nuclear powerplants).The behaviors of zirconium and hafnium in the environment are very similar to one another in that most zirconium- and hafnium-bearing minerals have limited solubility and reactivity. Anthropogenic sources of zirconium, and likely hafnium, are from industrial zirconium-containing byproducts and emissions from the processing of sponge zirconium, and exposure to the general population from these sources is small. Zirconium and hafnium are likely not essential to human health and generally are considered to be of low toxicity to humans. The main exposure risks are associated with industrial inhalation and dermal exposure. Because of the low solubility of zirconium and hafnium, ecological health concerns in the aquatic environment and in soils are minimal. Heavy-mineral-sand mining may lead to increased erosion rates when the mining is managed improperly. In addition, surface mining requires removal of the overlying organic soil layer and produces waste material that includes tailings and slimes. The soil removal and mining activity disturbs the surrounding ecosystem and alters the character of the landscape. Dry mineral separation processes create high amounts of airborne dust, whereas wet mineral separation processes do not. In operations that restore the landscape to pre-mining conditions, the volume of waste and the impact on the landscape may be relatively temporary.

Corrosion Studies on Titanium and Zirconium Metals

DTIC Science & Technology

1950-12-01

respectively 1.08 percent tantalum and 3.70 percent oolumbium. These alloys were in the cold rolled condition. The tantalum metal used was in the annealed ... vo2 iI 1’os th-, n 6 dr s Tal’ V17. C v"-" ’’ 4 Tesi,: s,.li tix , r - :.il s jer ce tr C..C. 73I 5 S1SO) + 5 ]r 0 s U.31 1.36 2, . O Ŗsf4 + 10 H 0...CDCD64 L O 1- V4. .06 14 ct-o to 400 toE La- LOr~ La 10 Go t O 0 d dojtc dtI- d. 0 . W0W44 .OC J 4 . 4d430 to0 0~e-0O ca 1.10t0 bQ 0a002t 0 OK 4140 to

Feasibility study of oxygen-dispensing emitters for thermionic converters, phase 1

NASA Technical Reports Server (NTRS)

Desteese, J. G.

1972-01-01

A metal/ceramic Marchuk tube was used to measure work functions of oxygen-doped tantalum, to determine applicability of the material to plasma-mode thermionic converters. Oxygen-doped tantalum was shown to increase in work function monotonically with oxygen doping in the range 0.1 to 0.3 atomic percent. Oxygenated test emitters were run at an average temperature of 2165 K and a T/T sub Cs ratio -5.8 to observe the influence of oxygen depletion. Bare work function decreased with outgassing of oxygen. Projections were made based on outgassing kinetics and area/volume ratios to calculate the longevity of oxygen doping in a practical converter. Calculations indicated that the program goal of 10,000 hr could be achieved at 1800 K with an initial oxygen doping of 1 atomic percent and a practical emitter area/volume ratio.

Processing development of 4 tantalum carbide-hafnium carbide and related carbides and borides for extreme environments

NASA Astrophysics Data System (ADS)

Gaballa, Osama Gaballa Bahig

Carbides, nitrides, and borides ceramics are of interest for many applications because of their high melting temperatures and good mechanical properties. Wear-resistant coatings are among the most important applications for these materials. Materials with high wear resistance and high melting temperatures have the potential to produce coatings that resist degradation when subjected to high temperatures and high contact stresses. Among the carbides, Al4SiC4 is a low density (3.03 g/cm3), high melting temperature (>2000°C) compound, characterized by superior oxidation resistance, and high compressive strength. These desirable properties motivated this investigation to (1) obtain high-density Al4SiC4 at lower sintering temperatures by hot pressing, and (2) to enhance its mechanical properties by adding WC and TiC to the Al4SiC4. Also among the carbides, tantalum carbide and hafnium carbide have outstanding hardness; high melting points (3880°C and 3890°C respectively); good resistance to chemical attack, thermal shock, and oxidation; and excellent electronic conductivity. Tantalum hafnium carbide (Ta4HfC 5) is a 4-to-1 ratio of TaC to HfC with an extremely high melting point of 4215 K (3942°C), which is the highest melting point of all currently known compounds. Due to the properties of these carbides, they are considered candidates for extremely high-temperature applications such as rocket nozzles and scramjet components, where the operating temperatures can exceed 3000°C. Sintering bulk components comprised of these carbides is difficult, since sintering typically occurs above 50% of the melting point. Thus, Ta4 HfC5 is difficult to sinter in conventional furnaces or hot presses; furnaces designed for very high temperatures are expensive to purchase and operate. Our research attempted to sinter Ta4HfC5 in a hot press at relatively low temperature by reducing powder particle size and optimizing the powder-handling atmosphere, milling conditions, sintering temperature, and hot-pressing pressure. Also, WC additions to Ta4HfC5 were found to improve densification and increase microhardness. The ability to process these materials at relatively low temperature would save energy and reduce cost. Boron-based hard materials are used in numerous applications such as industrial machining, armor plating, and wear-resistant coatings. It was often thought that in addition to strong bonding, super-hard materials must also possess simple crystallographic unit cells with high symmetry and a minimum number of crystal defects (e.g., diamond and cubic boron nitride (cBN)). However, one ternary boride, AlMgB14, deviates from this paradigm; AlMgB 14 has a large, orthorhombic unit cell (oI64) with multiple icosahedral boron units. TiB2 has been shown to be an effective reinforcing phase in AlMgB 14, raising hardness, wear resistance, and corrosion resistance. Thus, it was thought that adding other, similar phases (i.e., ZrB2 and HfB2) to AlMgB14 could lead to useful improvements in properties vis-à-vis pure AlMgB14. Group IV metal diborides (XB2, where X = Ti, Zr, or Hf) are hard, ultra-high temperature ceramics. These compounds have a primitive hexagonal crystal structure (hP3) with planes of graphite-like boride rings above and below planes of metal atoms. Unlike graphite, there is strong bonding between the planes, resulting in high hardness. For this study two-phase composites of 60 vol. % metal diborides with 40 vol. % AlMgB14 were produced and characterized.

Low-voltage bendable pentacene thin-film transistor with stainless steel substrate and polystyrene-coated hafnium silicate dielectric.

PubMed

Yun, Dong-Jin; Lee, Seunghyup; Yong, Kijung; Rhee, Shi-Woo

2012-04-01

The hafnium silicate and aluminum oxide high-k dielectrics were deposited on stainless steel substrate using atomic layer deposition process and octadecyltrichlorosilane (OTS) and polystyrene (PS) were treated improve crystallinity of pentacene grown on them. Besides, the effects of the pentacene deposition condition on the morphologies, crystallinities and electrical properties of pentacene were characterized. Therefore, the surface treatment condition on dielectric and pentacene deposition conditions were optimized. The pentacene grown on polystyrene coated high-k dielectric at low deposition rate and temperature (0.2-0.3 Å/s and R.T.) showed the largest grain size (0.8-1.0 μm) and highest crystallinity among pentacenes deposited various deposition conditions, and the pentacene TFT with polystyrene coated high-k dielectric showed excellent device-performance. To decrease threshold voltage of pentacene TFT, the polystyrene-thickness on high-k dielectric was controlled using different concentration of polystyrene solution. As the polystyrene-thickness on hafnium silicate decreases, the dielectric constant of polystyrene/hafnium silicate increases, while the crystallinity of pentacene grown on polystyrene/hafnium silicate did not change. Using low-thickness polystyrene coated hafnium silicate dielectric, the high-performance and low voltage operating (<5 V) pentacene thin film transistor (μ: ~2 cm(2)/(V s), on/off ratio, >1 × 10(4)) and complementary inverter (DC gains, ~20) could be fabricated.

Composition effects on mechanical properties of tungsten-rhenium-hafnium-carbon alloys

NASA Technical Reports Server (NTRS)

Witzke, W. R.

1973-01-01

The mechanical properties of rod and sheet fabricated from arc melted W-4Re-Hf-C alloys containing up to about 0.8 mol percent hafnium carbide (HfC) were evaluated in the as-worked condition. The DBTT's of electropolished bend and tensile specimens were independent of HfC content in this range but dependent on excess Hf or C above that required for stoichiometric HfC. Low temperature ductility was a maximum at Hf contents slightly in excess of stoichiometric. Variations in high temperature strength were also dependent on excess Hf and C. Maximum creep strengthening also occurred at Hf contents in excess of stoichiometric. Analysis of extracted second phase particles indicated that creep strength was reduced by increasing WC content in the HfC particles.

RF sputtered silicon and hafnium nitrides as applied to 440C steel

NASA Technical Reports Server (NTRS)

Grill, A.; Aron, P. R.

1984-01-01

Silicon nitride and hafnium nitride coatings were deposited on oxidized and unoxidized 440C stainless steel substrates. Sputtering was done in mixtures of argon and nitrogen gases from pressed powder silicon nitride and from hafnium metal targets. The coatings and the interface between the coating and substrate were investigated by X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray analysis and Auger electron spectroscopy. Oxide was found at all interfaces with an interface width of at least 600 A for the oxidized substrates and at least 300 A for the unoxidized substrates. Scratch test results demonstrate that the adhesion of hafnium nitride to both oxidized and unoxidized 440C is superior to that of silicon nitride. Oxidized 440C is found to have increased adhesion, to both nitrides, over that of unoxidized 440C. Coatings of both nitrides deposited at 8 mtorr were found to have increased adhesion to both oxidized and unoxidized 440C over those deposited at 20 mtorr.

40 CFR 471.95 - Pretreatment standards for new sources (PSNS).

Code of Federal Regulations, 2011 CFR

2011-07-01

... extruded Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0.301 Ammonia 31.6 13.9 Fluoride 14.1 6.26...-hafnium heat treated Chromium 0.015 0.006 Cyanide 0.010 0.004 Nickel 0.066 0.044 Ammonia 4.57 2.01...-hafnium surface treated Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20...

40 CFR 471.95 - Pretreatment standards for new sources (PSNS).

Code of Federal Regulations, 2010 CFR

2010-07-01

... extruded Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0.301 Ammonia 31.6 13.9 Fluoride 14.1 6.26...-hafnium heat treated Chromium 0.015 0.006 Cyanide 0.010 0.004 Nickel 0.066 0.044 Ammonia 4.57 2.01...-hafnium surface treated Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20...

Synthesis of Coral-Like Tantalum Oxide Films via Anodization in Mixed Organic-Inorganic Electrolytes

PubMed Central

Yu, Hongbin; Zhu, Suiyi; Yang, Xia; Wang, Xinhong; Sun, Hongwei; Huo, Mingxin

2013-01-01

We report a simple method to fabricate nano-porous tantalum oxide films via anodization with Ta foils as the anode at room temperature. A mixture of ethylene glycol, phosphoric acid, NH4F and H2O was used as the electrolyte where the nano-porous tantalum oxide could be synthesized by anodizing a tantalum foil for 1 h at 20 V in a two–electrode configuration. The as-prepared porous film exhibited a continuous, uniform and coral-like morphology. The diameters of pores ranged from 30 nm to 50 nm. The pores interlaced each other and the depth was about 150 nm. After calcination, the as-synthesized amorphous tantalum oxide could be crystallized to the orthorhombic crystal system. As observed in photocatalytic experiments, the coral-like tantalum oxide exhibited a higher photocatalytic activity for the degradation of phenol than that with a compact surface morphology, and the elimination rate of phenol increased by 66.7%. PMID:23799106

40 CFR 421.282 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2010 CFR

2010-07-01

... pounds) of tantalum powder produced from leaching Copper 38.380 20.200 Lead 8.484 4.040 Nickel 38.780 25...) Leaching wet air pollution control. BPT Limitations for the Secondary Tantalum Subcategory Pollutant or...

40 CFR 421.282 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2013 CFR

2013-07-01

... pounds) of tantalum powder produced from leaching Copper 38.380 20.200 Lead 8.484 4.040 Nickel 38.780 25...) Leaching wet air pollution control. BPT Limitations for the Secondary Tantalum Subcategory Pollutant or...

40 CFR 421.282 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2011 CFR

2011-07-01

... pounds) of tantalum powder produced from leaching Copper 38.380 20.200 Lead 8.484 4.040 Nickel 38.780 25...) Leaching wet air pollution control. BPT Limitations for the Secondary Tantalum Subcategory Pollutant or...

40 CFR 421.282 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2012 CFR

2012-07-01

... pounds) of tantalum powder produced from leaching Copper 38.380 20.200 Lead 8.484 4.040 Nickel 38.780 25...) Leaching wet air pollution control. BPT Limitations for the Secondary Tantalum Subcategory Pollutant or...

40 CFR 421.282 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2014 CFR

2014-07-01

... pounds) of tantalum powder produced from leaching Copper 38.380 20.200 Lead 8.484 4.040 Nickel 38.780 25...) Leaching wet air pollution control. BPT Limitations for the Secondary Tantalum Subcategory Pollutant or...

Electrospinning of ceramic nanofibers

NASA Astrophysics Data System (ADS)

Eick, Benjamin M.

Silicon Carbide (SiC) nanofibers of diameters as low as 20 nm are fabricated. The fibers were produced through the electrostatic spinning of the preceramic poly(carbomethylsilane) with pyrolysis to ceramic. A new technique was used where the preceramic was blended with polystyrene (PS) and, subsequent to electrospinning, was exposed to UV to crosslink the PS and prevent fibers flowing during pyrolysis. Electrospun SiC fibers were characterized by FTIR, TGA-DTA, SEM, TEM, XRD, and SAED. Fibers were shown to be polycrystalline and nanograined with alpha-SiC 15R polytype being dominant, where commercial fiber production methods form beta-SiC 3C. Pyrolysis of the bulk polymer blend to SiC produced alpha-SiC 15R as the dominant polytype with larger grains showing that electrospinning nanofibers affects resultant crystallinity. Fibers produced were shown to have a core-shell structure of an oxide scale that was variable by pyrolysis conditions. Metal oxide powders (chromium oxide, cobalt oxide, iron oxide, silicon oxide, tantalum oxide, titanium oxide, tungsten oxide, vanadium oxide, and zirconium oxide), were converted to metal carbide powders and metal nitride powders by the process of carbothermal reduction (CTR). Synthetic pitch was explored as an alternative to graphite which is a common carbon source for CTR. It was shown via characterization with XRD that pitch performs as well and in some cases better than graphite and is therefore a viable alternative in CTR. Conversion of metal oxide powders with pitch led to conversion of sol-gel based metal oxide nanofibers produced by electrospinning. Pitch was soluble in the solutions xv that were electrospun allowing for intimate contact between the sol-gel and the carbon source for CTR. This method became a two step processing method to produce metal carbide and nitride nanofibers: first electrospin sol-gel based metal oxide nanofibers and subsequently pyrolize them in the manner of CTR to transform them. Results indicate that this method was capable of transforming hafnium, niobium, tantalum, titanium, vanadium, and zirconium sol-gel nanofibers to metal carbides and nitrides.

Alkali-resistant low-temperature atomic-layer-deposited oxides for optical fiber sensor overlays

NASA Astrophysics Data System (ADS)

Kosiel, K.; Dominik, M.; Ściślewska, I.; Kalisz, M.; Guziewicz, M.; Gołaszewska, K.; Niedziółka-Jonsson, J.; Bock, W. J.; Śmietana, M.

2018-04-01

This paper presents an investigation of properties of selected metallic oxides deposited at a low temperature (100 °C) by atomic layer deposition (ALD) technique, relating to their applicability as thin overlays for optical fiber sensors resistant in alkaline environments. Hafnium oxide (Hf x O y with y/x approx. 2.70), tantalum oxide (Ta x O y with y/x approx. 2.75) and zirconium oxide (Zr x O y with y/x approx. 2.07), which deposition was based, respectively, on tetrakis(ethylmethyl)hafnium, tantalum pentachloride and tetrakis(ethylmethyl)zirconium with deionized water, were tested as thin layers on planar Si (100) and glass substrates. Growth per cycle (GPC) in the ALD processes was 0.133-0.150 nm/cycle. Run-to-run GPC reproducibility of the ALD processes was best for Hf x O y (0.145 ± 0.001 nm/cycle) and the poorest for Ta x O y (0.133 ± 0.003 nm/cycle). Refractive indices n of the layers were 2.00-2.10 (at the wavelength λ = 632 nm), with negligible k value (at λ for 240-930 nm). The oxides examined by x-ray diffractometry proved to be amorphous, with only small addition of crystalline phases for the Zr x O y . The surfaces of the oxides had grainy but smooth topographies with root-mean square roughness ˜0.5 nm (at 10 × 10 μm2 area) according to atomic force microscopy. Ellipsometric measurements, by contrast, suggest rougher surfaces for the Zr x O y layers. The surfaces were also slightly rougher on the glass-based samples than on the Si-based ones. Nanohardness and Young modules were 4.90-8.64 GPa and 83.7-104.4 GPa, respectively. The tests of scratch resistance revealed better tribological properties for the Hf x O y and the Ta x O y than for the Zr x O y . The surfaces were hydrophilic, with wetting angles of 52.5°-62.9°. The planar oxides on Si, being resistive even to concentrated alkali (pH 14), proved to be significantly more alkali-resistive than Al2O3. The Ta x O y overlay was deposited on long-period grating sensor induced in optical fiber. Thanks to such an overlay the sensor proved to be long-lasting resistant when exposed to alkaline environment with a pH 9. Thereby, it also proved that it has a potential to be repeatedly reused as a regenerable optical fiber biosensor.

Method for locating metallic nitride inclusions in metallic alloy ingots

DOEpatents

White, Jack C.; Traut, Davis E.; Oden, Laurance L.; Schmitt, Roman A.

1992-01-01

A method of determining the location and history of metallic nitride and/or oxynitride inclusions in metallic melts. The method includes the steps of labeling metallic nitride and/or oxynitride inclusions by making a coreduced metallic-hafnium sponge from a mixture of hafnium chloride and the chloride of a metal, reducing the mixed chlorides with magnesium, nitriding the hafnium-labeled metallic-hafnium sponge, and seeding the sponge to be melted with hafnium-labeled nitride inclusions. The ingots are neutron activated and the hafnium is located by radiometric means. Hafnium possesses exactly the proper metallurgical and radiochemical properties for this use.

Alkali metal hafnium oxide scintillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bourret-Courchesne, Edith; Derenzo, Stephen E.; Taylor, Scott Edward

The present invention provides for a composition comprising an inorganic scintillator comprising an alkali metal hafnate, optionally cerium-doped, having the formula A 2HfO 3:Ce; wherein A is an alkali metal having a valence of 1, such as Li or Na; and the molar percent of cerium is 0% to 100%. The alkali metal hafnate are scintillators and produce a bright luminescence upon irradiation by a suitable radiation.

Hafnium Oxide Film Etching Using Hydrogen Chloride Gas

NASA Astrophysics Data System (ADS)

Habuka, Hitoshi; Yamaji, Masahiko; Kobori, Yoshitsugu; Horii, Sadayoshi; Kunii, Yasuo

2009-12-01

Hydrogen chloride gas removes the hafnium oxide film formed by atomic layer deposition at the etch rate of about 1 nm/min. A 100 nm-thick hafnium oxide film was perfectly etched off at 1173 K for 60 min by 100% hydrogen chloride gas at 100 sccm. A weight decrease in the hafnium oxide film was observed at temperatures higher than ca. 600 K, which corresponds to the sublimation point of hafnium tetrachloride. The etching by-product is considered to be hafnium tetrachloride. The etching technique developed in this study is expected to be applicable to various processes, such as the cleaning of a hafnium oxide film deposition reactor.

Mineral-deposit model for lithium-cesium-tantalum pegmatites

USGS Publications Warehouse

Bradley, Dwight C.; McCauley, Andrew D.; Stillings, Lisa L.

2017-06-20

Lithium-cesium-tantalum (LCT) pegmatites comprise a compositionally defined subset of granitic pegmatites. The major minerals are quartz, potassium feldspar, albite, and muscovite; typical accessory minerals include biotite, garnet, tourmaline, and apatite. The principal lithium ore minerals are spodumene, petalite, and lepidolite; cesium mostly comes from pollucite; and tantalum mostly comes from columbite-tantalite. Tin ore as cassiterite and beryllium ore as beryl also occur in LCT pegmatites, as do a number of gemstones and high-value museum specimens of rare minerals. Individual crystals in LCT pegmatites can be enormous: the largest spodumene was 14 meters long, the largest beryl was 18 meters long, and the largest potassium feldspar was 49 meters long.Lithium-cesium-tantalum pegmatites account for about one-fourth of the world’s lithium production, most of the tantalum production, and all of the cesium production. Giant deposits include Tanco in Canada, Greenbushes in Australia, and Bikita in Zimbabwe. The largest lithium pegmatite in the United States, at King’s Mountain, North Carolina, is no longer being mined although large reserves of lithium remain. Depending on size and attitude of the pegmatite, a variety of mining techniques are used, including artisanal surface mining, open-pit surface mining, small underground workings, and large underground operations using room-and-pillar design. In favorable circumstances, what would otherwise be gangue minerals (quartz, potassium feldspar, albite, and muscovite) can be mined along with lithium and (or) tantalum as coproducts.Most LCT pegmatites are hosted in metamorphosed supracrustal rocks in the upper greenschist to lower amphibolite facies. Lithium-cesium-tantalum pegmatite intrusions generally are emplaced late during orogeny, with emplacement being controlled by pre-existing structures. Typically, they crop out near evolved, peraluminous granites and leucogranites from which they are inferred to be derived by fractional crystallization. In cases where a parental granite pluton is not exposed, one is inferred to lie at depth. Lithium-cesium-tantalum LCT pegmatite melts are enriched in fluxing components including H2O, F, P, and B, which depress the solidus temperature, lower the density, and increase rates of ionic diffusion. This, in turn, enables pegmatites to form thin dikes and massive crystals despite having a felsic composition and temperatures that are significantly lower than ordinary granitic melts. Lithium-cesium-tantalum pegmatites crystallized at remarkably low temperatures (about 350–550 °C) in a remarkably short time (days to years).Lithium-cesium-tantalum pegmatites form in orogenic hinterlands as products of plate convergence. Most formed during collisional orogeny (for example, Kings Mountain district, North Carolina). Specific causes of LCT pegmatite-related magmatism could include: ordinary arc processes; over thickening of continental crust during collision or subduction; slab breakoff during or after collision; slab delamination before, during, or after collision; and late collisional extensional collapse and consequent decompression melting. Lithium-cesium-tantalum pegmatite deposits are present in all continents including Antarctica and in rocks spanning 3 billion years of Earth history. The global age distribution of LCT pegmatites is similar to those of common pegmatites, orogenic granites, and detrital zircons. Peak times of LCT pegmatite genesis at about 2640, 1800, 960, 485, and 310 Ma (million years before present) correspond to times of collisional orogeny and supercontinent assembly. Between these pulses were long intervals when few or no LCT pegmatites formed. These minima overlap with supercontinent tenures at ca. 2450–2225, 1625–1000, 875–725, and 250–200 Ma.Exploration and assessment for LCT pegmatites are guided by a number of observations. In frontier areas where exploration has been minimal at best, the key first-order criteria are an orogenic hinterland setting, appropriate regional metamorphic grades, and the presence of evolved granites and common granitic pegmatites. New LCT pegmatites are most likely to be found near known deposits. Pegmatites tend to show a regional mineralogical and geochemical zoning pattern with respect to the inferred parental granite, with the greatest enrichment in the more distal pegmatites. Mineral-chemical trends in common pegmatites that can point toward an evolved LCT pegmatite include: increasing rubidium in potassium feldspar, increasing lithium in white mica, increasing manganese in garnet, and increasing tantalum and manganese in columbite-tantalite. Most LCT pegmatite bodies show a distinctive internal zonation featuring four zones: border, wall, intermediate (where lithium, cesium, and tantalum are generally concentrated), and core. This zonation is expressed both in cross section and map view; thus, what may appear to be a common pegmatite may instead be the edge of a mineralized body.Neither lithium-cesium-tantalum pegmatites nor their parental granites are likely to cause serious environmental concerns. Soils and country rock surrounding a LCT pegmatite, as well as waste from mining operations, may be enriched in characteristic elements relative to global average soil and bedrock values. These elements may include lithium, cesium, tantalum, beryllium, boron, fluorine, phosphorus, manganese, gallium, rubidium, niobium, tin, and hafnium. Among this suite of elements, however, the only ones that might present a concern for environmental health are beryllium and fluorine, which are included in the U.S. Environmental Protection Agency drinking-water regulations with maximum contaminant levels of 4 micrograms per liter and 4 milligrams per liter, respectively.

Topical Report Tantalum – 2.5% Tungsten Machinability Testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

L. J. Lazarus

2009-09-02

Protection Association (NFPA). NFPA 484, Standard for Combustible Metals, Chapter 9 Tantalum and Annex E, supplemental Information on Tantalum require cutting oil be used when machining tantalum because it burns at such a high temperature that it breaks down the water in a water-based metalworking fluid (MWF). The NFPA guide devotes approximately 20 pages to this material. The Kansas City Plant (KCP) uses Fuchs Lubricants Ecocut Base 44 LVC as a MWF. This is a highly chlorinated oil with a high flash point (above 200° F). The chlorine is very helpful in preventing BUE (Built Up Edge) that occurs frequentlymore » with this very gummy material. The Ecocut is really a MWF additive that Fuchs uses to add chlorinated fats to other non-chlorinated MWF.« less

Formulation and method for preparing gels comprising hydrous hafnium oxide

DOEpatents

Collins, Jack L; Hunt, Rodney D; Montgomery, Frederick C

2013-08-06

Formulations useful for preparing hydrous hafnium oxide gels contain a metal salt including hafnium, an acid, an organic base, and a complexing agent. Methods for preparing gels containing hydrous hafnium oxide include heating a formulation to a temperature sufficient to induce gel formation, where the formulation contains a metal salt including hafnium, an acid, an organic base, and a complexing agent.

40 CFR 421.283 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2010 CFR

2010-07-01

... produced from leaching Copper 25.860 12.320 Lead 5.656 2.626 Nickel 11.110 7.474 Zinc 20.600 8.484 Tantalum....214 Lead 0.098 0.046 Nickel 0.193 0.130 Zinc 0.357 0.147 Tantalum 0.158 (e) Leaching wet air pollution...

40 CFR 421.283 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2011 CFR

2011-07-01

... produced from leaching Copper 25.860 12.320 Lead 5.656 2.626 Nickel 11.110 7.474 Zinc 20.600 8.484 Tantalum....214 Lead 0.098 0.046 Nickel 0.193 0.130 Zinc 0.357 0.147 Tantalum 0.158 (e) Leaching wet air pollution...

40 CFR 421.283 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2012 CFR

2012-07-01

... produced from leaching Copper 25.860 12.320 Lead 5.656 2.626 Nickel 11.110 7.474 Zinc 20.600 8.484 Tantalum....214 Lead 0.098 0.046 Nickel 0.193 0.130 Zinc 0.357 0.147 Tantalum 0.158 (e) Leaching wet air pollution...

40 CFR 421.283 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2014 CFR

2014-07-01

... produced from leaching Copper 25.860 12.320 Lead 5.656 2.626 Nickel 11.110 7.474 Zinc 20.600 8.484 Tantalum....214 Lead 0.098 0.046 Nickel 0.193 0.130 Zinc 0.357 0.147 Tantalum 0.158 (e) Leaching wet air pollution...

40 CFR 421.283 - Effluent limitations guidelines representing the degree of effluent reduction attainable by the...

Code of Federal Regulations, 2013 CFR

2013-07-01

... produced from leaching Copper 25.860 12.320 Lead 5.656 2.626 Nickel 11.110 7.474 Zinc 20.600 8.484 Tantalum....214 Lead 0.098 0.046 Nickel 0.193 0.130 Zinc 0.357 0.147 Tantalum 0.158 (e) Leaching wet air pollution...

Tailoring properties of lossy-mode resonance optical fiber sensors with atomic layer deposition technique

NASA Astrophysics Data System (ADS)

Kosiel, Kamil; Koba, Marcin; Masiewicz, Marcin; Śmietana, Mateusz

2018-06-01

The paper shows application of atomic layer deposition (ALD) technique as a tool for tailoring sensorial properties of lossy-mode-resonance (LMR)-based optical fiber sensors. Hafnium dioxide (HfO2), zirconium dioxide (ZrO2), and tantalum oxide (TaxOy), as high-refractive-index dielectrics that are particularly convenient for LMR-sensor fabrication, were deposited by low-temperature (100 °C) ALD ensuring safe conditions for thermally vulnerable fibers. Applicability of HfO2 and ZrO2 overlays, deposited with ALD-related atomic level thickness accuracy for fabrication of LMR-sensors with controlled sensorial properties was presented. Additionally, for the first time according to our best knowledge, the double-layer overlay composed of two different materials - silicon nitride (SixNy) and TaxOy - is presented for the LMR fiber sensors. The thin films of such overlay were deposited by two different techniques - PECVD (the SixNy) and ALD (the TaxOy). Such approach ensures fast overlay fabrication and at the same time facility for resonant wavelength tuning, yielding devices with satisfactory sensorial properties.

Process for production of a borohydride compound

DOEpatents

Allen, Nathan Tait; Butterick, III, Robert; Chin, Arthur Achhing; Millar, Dean Michael; Molzahn, David Craig

2014-08-19

A process for production of a borohydride compound M(BH.sub.4).sub.y. The process has three steps. The first step combines a compound of formula (R.sup.1O).sub.yM with aluminum, hydrogen and a metallic catalyst containing at least one metal selected from the group consisting of titanium, zirconium, hafnium, niobium, vanadium, tantalum and iron to produce a compound of formula M(AlH.sub.3OR.sup.1).sub.y, wherein R.sup.1 is phenyl or phenyl substituted by at least one alkyl or alkoxy group; M is an alkali metal, Be or Mg; and y is one or two; wherein the catalyst is present at a level of at least 200 ppm based on weight of aluminum. The second step combines the compound of formula M(AlH.sub.3OR.sup.1).sub.y with a borate, boroxine or borazine compound to produce M(BH.sub.4).sub.y and a byproduct mixture containing alkali metal and aluminum aryloxides. The third step separates M(BH.sub.4).sub.y from the byproduct mixture.

International strategic minerals inventory summary report; zirconium

USGS Publications Warehouse

Towner, R.R.

1992-01-01

Zircon, a zirconium silicate, is currently the most important commercial zirconium-bearing mineral. Baddeleyite, a natural form of zirconia, is less important but has some specific end uses. Both zircon and baddeleyite occur in hard-rock and placer deposits, but at present all zircon production is from placer deposits. Most baddeleyite production is from hard-rock deposits, principally as a byproduct of copper and phosphate-rock mining. World zirconium resources in identified, economically exploitable deposits are about 46 times current production rates. Of these resources, some 71 percent are in South Africa, Australia, and the United States. The principal end uses of zirconium minerals are in ceramic applications and as refractories, abrasives, and mold linings in foundries. A minor amount, mainly of zircon, is used for the production of hafnium-free zirconium metal, which is used principally for sheathing fuel elements in nuclear reactors and in the chemical-processing industry, aerospace engineering, and electronics. Australia and South Africa are the largest zircon producers and account for more than 70 percent of world output; the United States and the Soviet Union account for another 20 percent. South Africa accounts for almost all the world's production of baddeleyite, which is about 2 percent of world production of contained zirconia. Australia and South Africa are the largest exporters of zircon. Unless major new deposits are developed in countries that have not traditionally produced zircon, the pattern of world production is unlikely to change by 2020. The proportions, however, of production that come from existing producing countries may change somewhat.

40 CFR 471.90 - Applicability; description of the zirconium-hafnium forming subcategory.

Code of Federal Regulations, 2010 CFR

2010-07-01

... zirconium-hafnium forming subcategory. 471.90 Section 471.90 Protection of Environment ENVIRONMENTAL... POINT SOURCE CATEGORY Zirconium-Hafnium Forming Subcategory § 471.90 Applicability; description of the zirconium-hafnium forming subcategory. This subpart applies to discharges of pollutants to waters of the...

40 CFR 421.330 - Applicability: Description of the primary zirconium and hafnium subcategory.

Code of Federal Regulations, 2010 CFR

2010-07-01

... primary zirconium and hafnium subcategory. 421.330 Section 421.330 Protection of Environment ENVIRONMENTAL... CATEGORY Primary Zirconium and Hafnium Subcategory § 421.330 Applicability: Description of the primary zirconium and hafnium subcategory. The provisions of this subpart are applicable to discharges resulting...

Ablation Resistant Zirconium and Hafnium Ceramics

NASA Technical Reports Server (NTRS)

Bull, Jeffrey (Inventor); White, Michael J. (Inventor); Kaufman, Larry (Inventor)

1998-01-01

High temperature ablation resistant ceramic composites have been made. These ceramics are composites of zirconium diboride and zirconium carbide with silicon carbide, hafnium diboride and hafnium carbide with silicon carbide and ceramic composites which contain mixed diborides and/or carbides of zirconium and hafnium. along with silicon carbide.

Quinary metallic glass alloys

DOEpatents

Lin, Xianghong; Johnson, William L.

1998-01-01

At least quinary alloys form metallic glass upon cooling below the glass transition temperature at a rate less than 10.sup.3 K/s. Such alloys comprise zirconium and/or hafnium in the range of 45 to 65 atomic percent, titanium and/or niobium in the range of 4 to 7.5 atomic percent, and aluminum and/or zinc in the range of 5 to 15 atomic percent. The balance of the alloy compositions comprise copper, iron, and cobalt and/or nickel. The composition is constrained such that the atomic percentage of iron is less than 10 percent. Further, the ratio of copper to nickel and/or cobalt is in the range of from 1:2 to 2:1. The alloy composition formula is: (Zr,Hf).sub.a (Al,Zn).sub.b (Ti,Nb).sub.c (Cu.sub.x Fe.sub.y (Ni,Co).sub.z).sub.d wherein the constraints upon the formula are: a ranges from 45 to 65 atomic percent, b ranges from 5 to 15 atomic percent, c ranges from 4 to 7.5 atomic percent, d comprises the balance, d.multidot.y is less than 10 atomic percent, and x/z ranges from 0.5 to 2.

Quinary metallic glass alloys

DOEpatents

Lin, X.; Johnson, W.L.

1998-04-07

At least quinary alloys form metallic glass upon cooling below the glass transition temperature at a rate less than 10{sup 3}K/s. Such alloys comprise zirconium and/or hafnium in the range of 45 to 65 atomic percent, titanium and/or niobium in the range of 4 to 7.5 atomic percent, and aluminum and/or zinc in the range of 5 to 15 atomic percent. The balance of the alloy compositions comprise copper, iron, and cobalt and/or nickel. The composition is constrained such that the atomic percentage of iron is less than 10 percent. Further, the ratio of copper to nickel and/or cobalt is in the range of from 1:2 to 2:1. The alloy composition formula is: (Zr,Hf){sub a}(Al,Zn){sub b}(Ti,Nb){sub c}(Cu{sub x}Fe{sub y}(Ni,Co){sub z}){sub d} wherein the constraints upon the formula are: a ranges from 45 to 65 atomic percent, b ranges from 5 to 15 atomic percent, c ranges from 4 to 7.5 atomic percent, d comprises the balance, d{hor_ellipsis}y is less than 10 atomic percent, and x/z ranges from 0.5 to 2.

Hafnium(IV) chloride complexes with chelating β-ketiminate ligands: Synthesis, spectroscopic characterization and volatility study

NASA Astrophysics Data System (ADS)

Patil, Siddappa A.; Medina, Phillip A.; Antic, Aleks; Ziller, Joseph W.; Vohs, Jason K.; Fahlman, Bradley D.

2015-09-01

The synthesis and characterization of four new β-ketiminate hafnium(IV) chloride complexes dichloro-bis[4-(phenylamido)pent-3-en-2-one]-hafnium (4a), dichloro-bis[4-(4-methylphenylamido)pent-3-en-2-one]-hafnium (4b), dichloro-bis[4-(4-methoxyphenylamido)pent-3-en-2-one]-hafnium (4c), and dichloro-bis[4-(4-chlorophenylamido)pent-3-en-2-one]-hafnium (4d) are reported. All the complexes (4a-d) were characterized by spectroscopic methods (1H NMR, 13C NMR, IR), and elemental analysis while the compound 4c was further examined by single-crystal X-ray diffraction, revealing that the complex is monomer with the hafnium center in octahedral coordination environment and oxygens of the chelating N-O ligands are trans to each other and the chloride ligands are in a cis arrangement. Volatile trends are established for four new β-ketiminate hafnium(IV) chloride complexes (4a-d). Sublimation enthalpies (ΔHsub) were calculated from thermogravimetric analysis (TGA) data, which show that, the dependence of ΔHsub on the molecular weight (4a-c) and inductive effects from chlorine (4d).

Structure and Microhardness of Cu-Ta Joints Produced by Explosive Welding

PubMed Central

Maliutina, Iu. N.; Mali, V. I.; Bataev, I. A.; Bataev, A. A.; Esikov, M. A.; Smirnov, A. I.; Skorokhod, K. A.

2013-01-01

The structure and microhardness of Cu-Ta joints produced by explosive welding were studied. It was found that, during explosive welding, an intermediate layer 20⋯40 μm thick with a finely dispersed heterophase structure, formed between the welded copper and tantalum plates. The structure of the layer was studied by scanning and transmission electron microscopy. Microvolumes with tantalum particles distributed in a copper matrix and microvolumes of copper particles in a tantalum matrix were detected. The tantalum particles in copper have a size of 5⋯500 nm, with a predominance of 5⋯50 nm particles. A mechanism for the formation of the finely dispersed heterophase structure in explosive welding is proposed. The microhardness of interlayers with the heterophase structure reaches 280 HV, which far exceeds the microhardness of copper (~130 HV) and tantalum (~160 HV). Many twins of deformation origin were found in the structure of the copper plate. The effect of heating temperature in the range from 100 to 900°C on the microhardness of copper, tantalum, and the Cu-Ta welded joint was studied. Upon heating to 900°C, the microhardness of the intermediate layer decreases from 280 to 150 HV. The reduction in the strength properties of the weld material is mainly due to structural transformations in copper. PMID:24453818

A novel tantalum-based sol-gel packed microextraction syringe for highly specific enrichment of phosphopeptides in MALDI-MS applications.

PubMed

Çelikbıçak, Ömür; Atakay, Mehmet; Güler, Ülkü; Salih, Bekir

2013-08-07

A new tantalum-based sol-gel material was synthesized using a unique sol-gel synthesis pathway by PEG incorporation into the sol-gel structure without performing a calcination step. This improved its chemical and physical properties for the high capacity and selective enrichment of phosphopeptides from protein digests in complex biological media. The specificity of the tantalum-based sol-gel material for phosphopeptides was evaluated and compared with tantalum(V) oxide (Ta2O5) in different phosphopeptide enrichment applications. The tantalum-based sol-gel and tantalum(V) oxide were characterized in detail using FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM), and also using a surface area and pore size analyzer. In the characterization studies, the surface morphology, pore volume, crystallinity of the materials and PEG incorporation into the sol-gel structure to produce a more hydrophilic material were successfully demonstrated. The X-ray diffractograms of the two different materials were compared and it was noted that the broad signals of the tantalum-based sol-gel clearly represented the amorphous structure of the sol-gel material, which was more likely to create enough surface area and to provide more accessible tantalum atoms for phosphopeptides to be easily adsorbed when compared with the neat and more crystalline structure of Ta2O5. Therefore, the phosphopeptide enrichment performance of the tantalum-based sol-gels was found to be remarkably higher than the more crystalline Ta2O5 in our studies. Phosphopeptides at femtomole levels could be selectively enriched using the tantalum-based sol-gel and detected with a higher signal-to-noise ratio by matrix-assisted laser desorption/ionization-mass spectrometer (MALDI-MS). Moreover, phosphopeptides in a tryptic digest of non-fat bovine milk as a complex real-world biological sample were retained with higher yield using a tantalum-based sol-gel. Additionally, the sol-gel material was packed into a standard syringe (0.5 mL) to enhance the ease of use of the sol-gel material and for the elimination of additional mixing and separation procedures during the adsorption, washing and elution steps of the enrichment procedure. It was found that up to 28 phosphopeptides in milk digest were easily detectable by MALDI-MS at femtomole levels (around 20 fmol) using the microextraction syringe within less than one minute.

Irradiation of three T-111 clad uranium nitride fuel pins for 8070 hours at 990 C (1815 F)

NASA Technical Reports Server (NTRS)

Slaby, J. G.; Siegel, B. L.; Gedeon, L.; Galbo, R. J.

1973-01-01

The design and successful operation of three tantalum alloy (Ta-8W-2Hf) clad uranium mononitride (UN) fuel pins irradiated for 8070 hr at 990 C (1815 F) is described. Two pin diameters having measured burnups of 0.47 and 0.90 uranium atom percent were tested. No clad failures or swelling was detected; however, postirradiation clad samples tested failed with 1 percent strain. The fuel density decrease was 2 percent, and the fission gas release was less than 0.05 percent. Isotropic fuel swelling, which averaged about 0.5 percent, was less than fuel pin assembly clearances. Thus the clad was not strained. Thermocouples with a modified hot zone operated at average temperatures to 1100 C (2012 F) without failure. Factors that influence the ability to maintain uniform clad temperature as well as the results of the heat transfer calculations are discussed.

CHARACTERISTICS OF ANODIC AND CORROSION FILMS ON ZIRCONIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Misch, R.D.

1960-05-01

Zirconium anodizes similarly to tungsten in respect to the change of interference colors with applied voltage. However, the oxide layer on tungsten cannot reach as great a thickness. Hafnium does not anodize in the same way as zirconium but is similar to tantalum. By measuring the interference color and capacitative thicknesses on zirconium (Grades I and III) and a 2.5 wt.% tin ailoy, the film was found to grow less rapidly in terms of capacitance than in terms of iaterference colors. This was interpreted to mean that cracks develop in the oxide as it thickens. The effect was most pronouncedmore » on Grade III zirconium and least pronounced on the tin alloy. The reduction in capacitative thickness was especially noticeable when white oxide appeared. Comparative measurements on Grade I zirconium and 2.5 wt.% tin alloy indicated that the thickness of the oxide film on the tin alloy (after 16 hours in water) increased more rapidly with temperature than the film on zirconium. Tin is believed to act in ways to counteract the tendency of the oxide to form cracks, and to produce vacancies which promote ionic diffusion. (auth)« less

Advanced materials for radiation-cooled rockets

NASA Technical Reports Server (NTRS)

Reed, Brian; Biaglow, James; Schneider, Steven

1993-01-01

The most common material system currently used for low thrust, radiation-cooled rockets is a niobium alloy (C-103) with a fused silica coating (R-512A or R-512E) for oxidation protection. However, significant amounts of fuel film cooling are usually required to keep the material below its maximum operating temperature of 1370 C, degrading engine performance. Also the R-512 coating is subject to cracking and eventual spalling after repeated thermal cycling. A new class of high-temperature, oxidation-resistant materials are being developed for radiation-cooled rockets, with the thermal margin to reduce or eliminate fuel film cooling, while still exceeding the life of silicide-coated niobium. Rhenium coated with iridium is the most developed of these high-temperature materials. Efforts are on-going to develop 22 N, 62 N, and 440 N engines composed of these materials for apogee insertion, attitude control, and other functions. There is also a complimentary NASA and industry effort to determine the life limiting mechanisms and characterize the thermomechanical properties of these materials. Other material systems are also being studied which may offer more thermal margin and/or oxidation resistance, such as hafnium carbide/tantalum carbide matrix composites and ceramic oxide-coated iridium/rhenium chambers.

Novel hierarchical tantalum oxide-PDMS hybrid coating for medical implants: One pot synthesis, characterization and modulation of fibroblast proliferation.

PubMed

Tran, Phong A; Fox, Kate; Tran, Nhiem

2017-01-01

Surface properties such as morphology, roughness and charge density have a strong influence on the interaction of biomaterials and cells. Hierarchical materials with a combination of micron/submicron and nanoscale features for coating of medical implants could therefore have significant potential to modulate cellular responses and eventually improve the performance of the implants. In this study, we report a simple, one pot wet chemistry preparation of a hybrid coating system with hierarchical surface structures consisting of polydimethylsiloxane (PDMS) and tantalum oxide. Medical grade, amine functional PDMS was mixed with tantalum ethoxide which subsequently formed Ta 2 O 5 in situ through hydrolysis and condensation during coating process. The coatings were characterized by SEM, EDS, XPS, confocal scanning microscopy, contact angle measurement and in vitro cell culture. Varying PDMS and tantalum ethoxide ratios resulted in coatings of different surface textures ranging from smooth to submicro- and nano-structured. Strikingly, hierarchical surfaces containing both microscale (1-1.5μm) and nanoscale (86-163nm) particles were found on coatings synthesized with 20% and 40% (v/v) tantalum ethoxide. The coatings were similar in term of hydrophobicity but showed different surface roughness and chemical composition. Importantly, higher cell proliferation was observed on hybrid surface with hierarchical structures compared to pure PDMS or pure tantalum oxide. The coating process is simple, versatile, carried out under ambient condition and requires no special equipment. Copyright © 2016 Elsevier Inc. All rights reserved.

High rate buffer layer for IBAD MgO coated conductors

DOEpatents

Foltyn, Stephen R [Los Alamos, NM; Jia, Quanxi [Los Alamos, NM; Arendt, Paul N [Los Alamos, NM

2007-08-21

Articles are provided including a base substrate having a layer of an oriented material thereon, and, a layer of hafnium oxide upon the layer of an oriented material. The layer of hafnium oxide can further include a secondary oxide such as cerium oxide, yttrium oxide, lanthanum oxide, scandium oxide, calcium oxide and magnesium oxide. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of hafnium oxide or layer of hafnium oxide and secondary oxide.

SEPARATION OF HAFNIUM FROM ZIRCONIUM

DOEpatents

Overholser, L.B.; Barton, C.J. Sr.; Ramsey, J.W.

1960-05-31

The separation of hafnium impurities from zirconium can be accomplished by means of organic solvent extraction. The hafnium-containing zirconium feed material is dissolved in an aqueous chloride solution and the resulting solution is contacted with an organic hexone phase, with at least one of the phases containing thiocyanate. The hafnium is extracted into the organic phase while zirconium remains in the aqueous phase. Further recovery of zirconium is effected by stripping the onganic phase with a hydrochloric acid solution and commingling the resulting strip solution with the aqueous feed solution. Hexone is recovered and recycled by means of scrubbing the onganic phase with a sulfuric acid solution to remove the hafnium, and thiocyanate is recovered and recycled by means of neutralizing the effluent streams to obtain ammonium thiocyanate.

Pyroelectric response in crystalline hafnium zirconium oxide (Hf 1- x Zr x O 2 ) thin films

DOE PAGES

Smith, S. W.; Kitahara, A. R.; Rodriguez, M. A.; ...

2017-02-13

Pyroelectric coefficients were measured for 20 nm thick crystalline hafnium zirconium oxide (Hf 1-xZr xO 2) thin films across a composition range of 0 ≤ x ≤ 1. Pyroelectric currents were collected near room temperature under zero applied bias and a sinusoidal oscillating temperature profile to separate the influence of non-pyroelectric currents. The pyroelectric coefficient was observed to correlate with zirconium content, increased orthorhombic/tetragonal phase content, and maximum polarization response. The largest measured absolute value was 48 μCm -2K -1 for a composition with x = 0.64, while no pyroelectric response was measured for compositions which displayed no remanent polarizationmore » (x = 0, 0.91, 1).« less

Packed bed carburization of tantalum and tantalum alloy

DOEpatents

Lopez, Peter C.; Rodriguez, Patrick J.; Pereyra, Ramiro A.

1999-01-01

Packed bed carburization of a tantalum or tantalum alloy object. A method for producing corrosion-resistant tantalum or tantalum alloy objects is described. The method includes the steps of placing the object in contact with a carburizing pack, heating the packed object in vacuum furnace to a temperature whereby carbon from the pack diffuses into the object forming grains with tantalum carbide along the grain boundaries, and etching the surface of the carburized object. This latter step removes tantalum carbides from the surface of the carburized tantalum object while leaving the tantalum carbide along the grain boundaries.

Packed bed carburization of tantalum and tantalum alloy

DOEpatents

Lopez, P.C.; Rodriguez, P.J.; Pereyra, R.A.

1999-06-29

Packed bed carburization of a tantalum or tantalum alloy object is disclosed. A method for producing corrosion-resistant tantalum or tantalum alloy objects is described. The method includes the steps of placing the object in contact with a carburizing pack, heating the packed object in vacuum furnace to a temperature whereby carbon from the pack diffuses into the object forming grains with tantalum carbide along the grain boundaries, and etching the surface of the carburized object. This latter step removes tantalum carbides from the surface of the carburized tantalum object while leaving the tantalum carbide along the grain boundaries. 4 figs.

Hafnium-Based Contrast Agents for X-ray Computed Tomography.

PubMed

Berger, Markus; Bauser, Marcus; Frenzel, Thomas; Hilger, Christoph Stephan; Jost, Gregor; Lauria, Silvia; Morgenstern, Bernd; Neis, Christian; Pietsch, Hubertus; Sülzle, Detlev; Hegetschweiler, Kaspar

2017-05-15

Heavy-metal-based contrast agents (CAs) offer enhanced X-ray absorption for X-ray computed tomography (CT) compared to the currently used iodinated CAs. We report the discovery of new lanthanide and hafnium azainositol complexes and their optimization with respect to high water solubility and stability. Our efforts culminated in the synthesis of BAY-576, an uncharged hafnium complex with 3:2 stoichiometry and broken complex symmetry. The superior properties of this asymmetrically substituted hafnium CA were demonstrated by a CT angiography study in rabbits that revealed excellent signal contrast enhancement.

Tantalum recycling in the United States in 1998

USGS Publications Warehouse

Cunningham, Larry D.

2001-01-01

This report describes the flow of tantalum in the United States in 1998 with emphasis on the extent to which tantalum was recycled/reused. Tantalum was mostly recycled from new scrap that was generated during the manufacture of tantalum-related electronic components and new and old scrap products of tantalum-containing cemented carbides and superalloys. In 1998, about 210 metric tons of tantalum was recycled/reused, with about 43% derived from old scrap. The tantalum recycling rate was calculated to be 21%, and tantalum scrap recycling efficiency, 35%.

Etude de la nitruration carbothermique du dioxyde de hafnium par diffraction X à haute température

NASA Astrophysics Data System (ADS)

Pialoux, A.

1993-03-01

The carbothermal reduction of hafnium dioxide under atmospheric level nitrogen pressure has been investigated using a graphite resistance high temperature X-ray diffractometer up to around 2300 K. A carbon transfer reaction through the gaseous phase (N 2, CO/CO 2) is shown to precede, then to compete the direct reduction of the hafnium oxide by the graphite in pure nitrogen. A complex mechanism has been found that accounts for the formation of hafnium dioxynitride and possibly of three other hafnium oxynitrides, then of hafnium mononitride and hafnium monocarbonitride, along two different steps between 1613 and 1923 K. An evaluation has been made concerning the composition of these γ 1- HfO 2-xN x/2□ x/2 (CaF 2-type structure), γ 2- Hf 7O 11N 2, γ 3- Hf 7O 8N 4 (rhombohedral), γ 4- Hf 2ON 2 (Mn 2O 3-type structure), HfN and HfN 1-zC z (NaCl-type structure) phases, considering the variations of their lattice parameters and the available data in the literature, especially on the isomorphous compounds of zirconium. It must be emphasized the new γ 1- HfO 2-xN x/2 phase, the dilatation of which is linear ( overlineα = 12×10 -6K -1), shows a constant composition from 2158 down to 1473 K (x ≈ 0,2). But under 1473 K, inevitably, the hafnium dioxynitride disappears, and poorly crystallized monoclinic αHfO 2 and rhombohedral γ 2- Hf 7O 11N 2 are formed.

Method for the melting of metals

DOEpatents

White, Jack C.; Traut, Davis E.

1992-01-01

A method of quantitatively determining the molten pool configuration in melting of metals. The method includes the steps of introducing hafnium metal seeds into a molten metal pool at intervals to form ingots, neutron activating the ingots and determining the hafnium location by radiometric means. Hafnium possesses exactly the proper metallurgical and radiochemical properties for this use.

Methods for Melting Temperature Calculation

NASA Astrophysics Data System (ADS)

Hong, Qi-Jun

Melting temperature calculation has important applications in the theoretical study of phase diagrams and computational materials screenings. In this thesis, we present two new methods, i.e., the improved Widom's particle insertion method and the small-cell coexistence method, which we developed in order to capture melting temperatures both accurately and quickly. We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments. We propose the small-cell coexistence method based on the statistical analysis of small-size coexistence MD simulations. It eliminates the risk of a metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Using empirical potentials, we validate the method and systematically study the finite-size effect on the calculated melting points. The method converges to the exact result in the limit of a large system size. An accuracy within 100 K in melting temperature is usually achieved when the simulation contains more than 100 atoms. DFT examples of Tantalum, high-pressure Sodium, and ionic material NaCl are shown to demonstrate the accuracy and flexibility of the method in its practical applications. The method serves as a promising approach for large-scale automated material screening in which the melting temperature is a design criterion. We present in detail two examples of refractory materials. First, we demonstrate how key material properties that provide guidance in the design of refractory materials can be accurately determined via ab initio thermodynamic calculations in conjunction with experimental techniques based on synchrotron X-ray diffraction and thermal analysis under laser-heated aerodynamic levitation. The properties considered include melting point, heat of fusion, heat capacity, thermal expansion coefficients, thermal stability, and sublattice disordering, as illustrated in a motivating example of lanthanum zirconate (La2Zr2O7). The close agreement with experiment in the known but structurally complex compound La2Zr 2O7 provides good indication that the computation methods described can be used within a computational screening framework to identify novel refractory materials. Second, we report an extensive investigation into the melting temperatures of the Hf-C and Hf-Ta-C systems using ab initio calculations. With melting points above 4000 K, hafnium carbide (HfC) and tantalum carbide (TaC) are among the most refractory binary compounds known to date. Their mixture, with a general formula TaxHf 1-xCy, is known to have a melting point of 4215 K at the composition Ta4HfC 5, which has long been considered as the highest melting temperature for any solid. Very few measurements of melting point in tantalum and hafnium carbides have been documented, because of the obvious experimental difficulties at extreme temperatures. The investigation lets us identify three major chemical factors that contribute to the high melting temperatures. Based on these three factors, we propose and explore a new class of materials, which, according to our ab initio calculations, may possess even higher melting temperatures than Ta-Hf-C. This example also demonstrates the feasibility of materials screening and discovery via ab initio calculations for the optimization of "higher-level" properties whose determination requires extensive sampling of atomic configuration space.

Atomization from a tantalum surface in graphite furnace atomic absorption spectrometry

NASA Astrophysics Data System (ADS)

Gregoire, D. C.; Chakrabarti, C. L.

The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic graphite and tantalum metal surfaces has been studied. The mechanism of atom formation for U from a graphite tube atomizer is reported for the first time. The peak absorbance for U and Cu is increased by factors of 59.7 and 2.0, respectively, whereas that of V, Mo and Ni is reduced by several orders of magnitude when they are atomized from a tantalum metal surface. The peak absorbance of Mn and Mg is not appreciably affected by the material of the atomization surface. Interaction of Mn and Mg with the graphite surface and formation of their refractory carbides was found to be negligible. Uranium forms a refractory carbide when heated from a graphite surface.

The tantalum-cased tantalum capacitor

NASA Technical Reports Server (NTRS)

Moynihan, J. D.

1977-01-01

Tantalum-cased tantalum capacitors were tested with regard to temperature stability, capacitance ratio, surge current capabilities, shock, vibration, and thermal shock. They were found to be superior to the conventional wet slug tantalum capacitor cased in silver, since they are more resistant to sulfuric acid. The tantalum-cased tantalum capacitors are widely accepted for use in critical electronic equipment because of their excellent performance and reliability.

Effect of hafnium doping on density of states in dual-target magnetron co-sputtering HfZnSnO thin film transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Chuan-Xin; Li, Jun, E-mail: SHUniverjunli@163.com; Fu, Yi-Zhou

2015-11-23

This study investigates the effect of hafnium doping on the density of states (DOSs) in HfZnSnO thin film transistors fabricated by dual-target magnetron co-sputtering system. The DOSs is extracted by temperature-dependent field-effect measurements, and they decrease from 1.1 × 10{sup 17} to 4.6 × 10{sup 16 }eV/cm{sup 3} with increasing the hafnium concentrations. The behavior of DOSs for the increasing hafnium concentration HfZnSnO thin film transistors can be confirmed by both the reduction of ΔV{sub T} under bias stress and the trapping charges calculated by capacitance voltage measurements. It suggests that the reduction in DOSs due to the hafnium doping is closely related with themore » bias stability and thermal stability.« less

Development of advanced high strength tantalum base alloys. Part 1: Screening investigation

NASA Technical Reports Server (NTRS)

Buckman, R. W., Jr.

1971-01-01

Five experimental tantalum alloy compositions containing 13-18% W+Re+Hf solid solution solute additions with dispersed phase strengthening achieved by carbon or nitrogen additions were prepared as 1.4 inch diameter ingot processed to 3/8 inch diameter rod and evaluated. Elevated temperature tensile and creep strength increased monotonically with increasing solute content. Room temperature elongation decreased for 20% to less than 2% as the solute content was increased above 16%. Phase identification indicated that the precipitating phase in the carbide containing alloys was Ta2C.

In vivo comparison of tantalum, tungsten, and bismuth enteric contrast agents to complement intravenous iodine for double-contrast dual-energy CT of the bowel

PubMed Central

Rathnayake, Samira; Mongan, John; Torres, Andrew S.; Colborn, Robert; Gao, Dong-Wei; Yeh, Benjamin M; Fu, Yanjun

2016-01-01

To assess the ability of dual-energy CT (DECT) to separate intravenous contrast of bowel wall from intraluminal contrast, we scanned 16 rabbits on a clinical DECT scanner: n=3 using only iodinated intravenous contrast; and n=13 double-contrast enhanced scans using iodinated intravenous contrast and experimental enteric non-iodinated contrast agents in the bowel lumen (5 bismuth-, 4 tungsten-, and 4 tantalum-based). Representative image pairs from conventional CT images and DECT iodine density maps of small bowel (116 pairs from 232 images) were viewed by four abdominal imaging attending radiologists to independently score each comparison pair on a visual analog scale (−100 to +100%) for: 1) preference in small bowel wall visualization; and 2) preference in completeness of intraluminal enteric contrast subtraction. Median small bowel wall visualization was scored 39 and 42 percentage points (95% CI: 30–44% and 36–45%, p<0.001 both) higher at double-contrast DECT than at conventional CT with enteric tungsten and tantalum contrast, respectively. Median small bowel wall visualization at double-contrast DECT was scored 29 and 35 percentage points (95% CI: 20–35% and 33–39%, p<0.001 both) higher with enteric tungsten and tantalum, respectively, than with bismuth contrast. Median completeness of intraluminal enteric contrast subtraction in double-contrast DECT iodine density maps was scored 28 and 29 percentage points (95% CI: 15–31% and 28–33%, p<0.001 both) higher with enteric tungsten and tantalum, respectively, than with bismuth contrast. Results suggest that in vivo double-contrast DECT with iodinated intravenous and either tantalum- or tungsten-based enteric contrast provide better visualization of small bowel than conventional CT. PMID:26892945

Directionally solidified iron-base eutectic alloys

NASA Technical Reports Server (NTRS)

Tewari, S. N.

1976-01-01

Pseudobinary eutectic alloys with nominal compositions of Fe-25Ta-22Ni-10Cr and Fe-15.5Nb-14.5Ni-6.0Cr were directionally solidified at 0.5 centimeter per hour. Their microstructure consisted of the fcc, iron solid-solution, matrix phase reinforced by about 41-volume-percent, hcp, faceted Fe2Ta fibers and 41-volume-percent, hcp, Fe2Nb lamellae for the tantalum- and niobium-containing alloys, respectively. The microstructural stability under thermal cycling and the temperature dependence of tensile properties were investigated. These alloys showed low elevated-temperature strength and were not considered suitable for application in aircraft-gas-turbine blades although they may have applicability as vane materials.

Method of improving fatigue life of cast nickel based superalloys and composition

DOEpatents

Denzine, Allen F.; Kolakowski, Thomas A.; Wallace, John F.

1978-03-14

The invention consists of a method of producing a fine equiaxed grain structure (ASTM 2-4) in cast nickel-base superalloys which increases low cycle fatigue lives without detrimental effects on stress rupture properties to temperatures as high as 1800.degree. F. These superalloys are variations of the basic nickel-chromium matrix, hardened by gamma prime [Ni.sub.3 (Al, Ti)] but with optional additions of cobalt, tungsten, molybdenum, vanadium, columbium, tantalum, boron, zirconium, carbon and hafnium. The invention grain refines these alloys to ASTM 2 to 4 increasing low cycle fatigue life by a factor of 2 to 5 (i.e. life of 700 hours would be increased to 1400 to 3500 hours for a given stress) as a result of the addition of 0.01% to 0.2% of a member of the group consisting of boron, zirconium and mixtures thereof to aid heterogeneous nucleation. The alloy is vacuum melted and heated to 250.degree.-400.degree. F. above the melting temperature, cooled to partial solidification, thus resulting in said heterogeneous nucleation and fine grains, then reheated and cast at about 50.degree.-100.degree. F. of superheat. Additions of 0.1% boron and 0.1% zirconium (optional) are the preferred nucleating agents.

Biological Response of Human Bone Marrow-Derived Mesenchymal Stem Cells to Commercial Tantalum Coatings with Microscale and Nanoscale Surface Topographies

NASA Astrophysics Data System (ADS)

Skoog, Shelby A.; Kumar, Girish; Goering, Peter L.; Williams, Brian; Stiglich, Jack; Narayan, Roger J.

2016-06-01

Tantalum is a promising orthopaedic implant coating material due to its robust mechanical properties, corrosion resistance, and excellent biocompatibility. Previous studies have demonstrated improved biocompatibility and tissue integration of surface-treated tantalum coatings compared to untreated tantalum. Surface modification of tantalum coatings with biologically inspired microscale and nanoscale features may be used to evoke optimal tissue responses. The goal of this study was to evaluate commercial tantalum coatings with nanoscale, sub-microscale, and microscale surface topographies for orthopaedic and dental applications using human bone marrow-derived mesenchymal stem cells (hBMSCs). Tantalum coatings with different microscale and nanoscale surface topographies were fabricated using a diffusion process or chemical vapor deposition. Biological evaluation of the tantalum coatings using hBMSCs showed that tantalum coatings promote cellular adhesion and growth. Furthermore, hBMSC adhesion to the tantalum coatings was dependent on surface feature characteristics, with enhanced cell adhesion on sub-micrometer- and micrometer-sized surface topographies compared to hybrid nano-/microstructures. Nanostructured and microstructured tantalum coatings should be further evaluated to optimize the surface coating features to promote osteogenesis and enhance osseointegration of tantalum-based orthopaedic implants.

Upgrading tantalum and niobium oxides content in Bangka tin slag with double leaching

NASA Astrophysics Data System (ADS)

Soedarsono, J. W.; Permana, S.; Hutauruk, J. K.; Adhyputra, R.; Rustandi, A.; Maksum, A.; Widana, K. S.; Trinopiawan, K.; Anggraini, M.

2018-03-01

Tantalum has become one of the 14 types of critical materials where the level of its availability is assumed as the midterm critical metal. Benefits of the element tantalum in the electronics field increased the deficit balance of supply / demand, as more variations of electronic products developed. The tantalum experts calculated the level of availability until 2020. Base on the previous studies, tin slag is a secondary source of tantalum and niobium. This study uses tin slag from Bangka, Indonesia, abbreviated, Bangka Tin Slag (BTS). BTS was roasted, water quenched and sieved, abbreviated BTS-RQS.BTS was roasted, water quenched and sieved, abbreviated BTS-RQS.BTS-RQS was roasted at a temperature 700□C given sample code BTS-R700QS, while roasted at 800°C given sample code BTS-R800QS.A variable leaching experiment on BTS-R700QS was solvent concentration variable and on BTS-R800QS was time variable. The entire residue was characterized by X-Ray Fluorescence (XRF), and the optimum results are on the BTS-R800QS leaching into 5 M NaOH for 20 min followed by 5M HCl for 50 min, with content of Ta2O5 and Nb2O51.56% and 1.11%, respectively. The result of XRF measurement showed was the increasing of TNO content due to the increasing solvent concentration and time of acid leaching. The discussion of thermodynamics this study used was HSC Chemistry 6 as a supporting data.

Dual-phase Cr-Ta alloys for structural applications

DOEpatents

Liu, Chain T.; Brady, Michael P.; Zhu, Jiahong; Tortorelli, Peter F.

2001-01-01

Dual phase alloys of chromium containing 2 to 11 atomic percent tantalum with minor amounts of Mo, Cr, Ti, Y, La, Cr, Si and Ge are disclosed. These alloys contain two phases including Laves phase and Cr-rich solid solution in either eutectic structures or dispersed Laves phase particles in the Cr-rich solid solution matrix. The alloys have superior mechanical properties at high temperature and good oxidation resistance when heated to above 1000.degree. C. in air.

METHOD OF FORMING TANTALUM SILICIDE ON TANTALUM SURFACES

DOEpatents

Bowman, M.G.; Krikorian, N.H.

1961-10-01

A method is described for forming a non-corrosive silicide coating on tantalum. The coating is made through the heating of trirhenium silicides in contact with the tantalum object to approximately 1400 deg C at which temperature trirhenium silicide decomposes into rhenium and gaseous silicons. The silicon vapor reacts with the tantalum surface to form a tantalum silicide layer approximately 10 microns thick. (AEC)

High P-T phase transitions and P-V-T equation of state of hafnium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hrubiak, Rostislav; Drozd, Vadym; Karbasi, Ali

2016-07-29

We measured the volume of hafnium at several pressures up to 67 GPa and at temperatures between 300 to 780 K using a resistively heated diamond anvil cell with synchrotron x-ray diffraction at the Advanced Photon Source. The measured data allows us to determine the P-V-T equation of state of hafnium. The previously described [Xia et al., Phys. Rev. B 42, 6736-6738 (1990)] phase transition from hcp ({alpha}) to simple hexagonal ({omega}) phase at 38 GPa at room temperature was not observed even up to 51 GPa. The {omega} phase was only observed at elevated temperatures. Our measurements have alsomore » improved the experimental constraint on the high P-T phase boundary between the {omega} phase and high pressure bcc ({beta}) phase of hafnium. Isothermal room temperature bulk modulus and its pressure derivative for the {alpha}-phase of hafnium were measured to be B{sub 0} = 112.9{+-}0.5 GPa and B{sub 0}'=3.29{+-}0.05, respectively. P-V-T data for the {alpha}-phase of hafnium was used to obtain a fit to a thermodynamic P-V-T equation of state based on model by Brosh et al. [CALPHAD 31, 173-185 (2007)].« less

Quality Control for Ordnance

DTIC Science & Technology

1957-01-01

Hafnium 181. . . . . . . . . . . . . . . . . . . . . . . . . Mercury 204.. Chromium 51...43 days I Mercury 197 . . . . . . . . . . . . . . . . . . . . . . . . . 64 hr R u t h i m 103...desfrzlclive T e s i i g , Vol. VI, No. 1, Sum" mer 1947, pp. 9-20. (72) K. Frerichs, "The Cadmium Sulphide X-ray Detector," J o w n d o/ Applied Pkys- its

Radiopharmaceutical composition containing tantalum-178 and process therefor

DOEpatents

Neirinckx, Rudi D.; Holman, B. Leonard; Davis, Michael A.; Harris, Gale I.

1989-05-16

A physiologically acceptable solution of tantalum-178 having an activity of 0.1 to 200 millicuries per milliliter of tantalum-178 solution is provided. The solution is obtained from tungsten-178 bound to a column of an anion exchange resin which forms tantalum-178 in situ by eluting the column with a hydrochloric acid solution containing hydrogen peroxide to form an acidic solution of tantalum-178. The acidic solution of tantalum-178 then is neutralized.

SEPARATING HAFNIUM FROM ZIRCONIUM

DOEpatents

Lister, B.A.J.; Duncan, J.F.

1956-08-21

A dilute aqueous solution of zirconyl chloride which is 1N to 2N in HCl is passed through a column of a cation exchange resin in acid form thereby absorbing both zirconium and associated hafnium impurity in the mesin. The cation exchange material with the absorbate is then eluted with aqueous sulfuric acid of a O.8N to 1.2N strength. The first portion of the eluate contains the zirconium substantially free of hafnium.

Testing of uranium nitride fuel in T-111 cladding at 1200 K cladding temperature

NASA Technical Reports Server (NTRS)

Rohal, R. G.; Tambling, T. N.; Smith, R. L.

1973-01-01

Two groups of six fuel pins each were assembled, encapsulated, and irradiated in the Plum Brook Reactor. The fuel pins employed uranium mononitride (UN) in a tantalum alloy clad. The first group of fuel pins was irradiated for 1500 hours to a maximum burnup of 0.7-atom-percent uranium. The second group of fuel pins was irradiated for about 3000 hours to a maximum burnup of 1.0-atom-percent uranium. The average clad surface temperature during irradiation of both groups of fuel pins was approximately 1200 K. The postirradiation examination revealed the following: no clad failures or fuel swelling occurred; less than 1 percent of the fission gases escaped from the fuel; and the clad of the first group of fuel pins experienced clad embrittlement whereas the second group, which had modified assembly and fabrication procedures to minimize contamination, had a ductile clad after irradiation.

STUDIES ON ANALYTICAL METHODS FOR TRACE ELEMENTS IN METALS BY USING RADIOACTIVE ISOTOPE. III. DETERMINATION OF TANTALUM BY MEANS OF ISOTOPE DILUTION METHOD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amano, H.

1959-10-01

The determination of tantalum by the isotope dilution method in the presence of niobium was investigated by the use of the radioisotope Ta/sup 185/. Tantalum was separated from niobium as tantalum-tannin precipitate under the optimum conditions of a pH of 1.9 to 2.5 and a tantalum/niobium ratio of up to 1/ 50. If niobium was present in amounts 100 times or more that of tantalum, reprecipitation was needed. The reciprocal of the specific activity of tanthlum pentoxide precipitate was in a linear relation to the change in the amount of tantalum added. The recommended method gave an accurate result inmore » the determination of tantalum in steal. (auth)« less

Flow studies for recycling metal commodities in the United States [Chapters A-M : gold, platinum, chromium, zinc, magnesium, lead, iron, manganese, columbium (niobium), tantalum, tin, molybdenum, and cobalt

USGS Publications Warehouse

Sibley, Scott F.

2004-01-01

USGS Circular 1196, 'Flow Studies for Recycling Metal Commodities in the United States,' presents the results of flow studies for recycling 26 metal commodities, from aluminum to zinc. These metals are a key component of the U.S. economy. Overall, recycling accounts for more than half of the U.S. metal supply by weight and roughly 40 percent by value.

Highly selective catalytic process for synthesizing 1-hexene from ethylene

DOEpatents

Sen, Ayusman; Murtuza, Shahid; Harkins, Seth B.; Andes, Cecily

2002-01-01

Ethylene is trimerized to form 1-hexene, at a selectivity of up to about 99 mole percent, by contacting ethylene, at an ethylene pressure of from about 200-1500 psig and at a reaction temperature of from about 0.degree. C. to about 100.degree. C., with a catalyst comprising a tantalum compound (e.g., TaCl.sub.5) and a alkylating component comprising a metal hydrocarbyl compound or a metal hydrocarbyl halide compound (e.g., Sn(CH.sub.3).sub.4).

Tantalum coating of porous carbon scaffold supplemented with autologous bone marrow stromal stem cells for bone regeneration in vitro and in vivo.

PubMed

Wei, Xiaowei; Zhao, Dewei; Wang, Benjie; Wang, Wei; Kang, Kai; Xie, Hui; Liu, Baoyi; Zhang, Xiuzhi; Zhang, Jinsong; Yang, Zhenming

2016-03-01

Porous tantalum metal with low elastic modulus is similar to cancellous bone. Reticulated vitreous carbon (RVC) can provide three-dimensional pore structure and serves as the ideal scaffold of tantalum coating. In this study, the biocompatibility of domestic porous tantalum was first successfully tested with bone marrow stromal stem cells (BMSCs) in vitro and for bone tissue repair in vivo. We evaluated cytotoxicity of RVC scaffold and tantalum coating using BMSCs. The morphology, adhesion, and proliferation of BMSCs were observed via laser scanning confocal microscope and scanning electron microscopy. In addition, porous tantalum rods with or without autologous BMSCs were implanted on hind legs in dogs, respectively. The osteogenic potential was observed by hard tissue slice examination. At three weeks and six weeks following implantation, new osteoblasts and new bone were observed at the tantalum-host bone interface and pores. At 12 weeks postporous tantalum with autologous BMSCs implantation, regenerated trabecular equivalent to mature bone was found in the pore of tantalum rods. Our results suggested that domestic porous tantalum had excellent biocompatibility and could promote new bone formation in vivo. Meanwhile, the osteogenesis of porous tantalum associated with autologous BMSCs was more excellent than only tantalum implantation. Future clinical studies are warranted to verify the clinical efficacy of combined implantation of this domestic porous tantalum associated with autologous BMSCs implantation and compare their efficacy with conventional autologous bone grafting carrying blood vessel in patients needing bone repairing. © 2016 by the Society for Experimental Biology and Medicine.

Examination of T-111 clad uranium nitride fuel pins irradiated up to 13,000 hours at a clad temperature of 990 C

NASA Technical Reports Server (NTRS)

Slaby, J. G.; Siegel, B. L.

1973-01-01

The examination of 27 fuel pins irradiated for up to 13,000 hours at 990 C is described. The fuel pin clad was a tantalum alloy with uranium nitride as the nuclear fuel. Two nominal fuel pin diameters were tested with a maximum burnup of 2.34 atom percent. Twenty-two fuel pins were tested for fission gas leaks; thirteen pins leaked. Clad ductility tests indicated clad embrittlement. The embrittlement is attributed to hydrogen from an n,p reaction in the fuel. Fuel swelling was burnup dependent, and the amount of fission gas release was low, generally less than 0.5 percent. No incompatibilities between fuel, liner, and clad were in evidence.

Tensile and stress-rupture behavior of hafnium carbide dispersed molybdenum and tungsten base alloy wires

NASA Technical Reports Server (NTRS)

Yun, Hee Mann; Titran, Robert H.

1993-01-01

The tensile strain rate sensitivity and the stress-rupture strength of Mo-base and W-base alloy wires, 380 microns in diameter, were determined over the temperature range from 1200 K to 1600 K. Three molybdenum alloy wires; Mo + 1.1w/o hafnium carbide (MoHfC), Mo + 25w/o W + 1.1w/o hafnium carbide (MoHfC+25W) and Mo + 45w/o W + 1.1w/o hafnium carbide (MoHfC+45W), and a W + 0.4w/o hafnium carbide (WHfC) tungsten alloy wire were evaluated. The tensile strength of all wires studied was found to have a positive strain rate sensitivity. The strain rate dependency increased with increasing temperature and is associated with grain broadening of the initial fibrous structures. The hafnium carbide dispersed W-base and Mo-base alloys have superior tensile and stress-rupture properties than those without HfC. On a density compensated basis the MoHfC wires exhibit superior tensile and stress-rupture strengths to the WHfC wires up to approximately 1400 K. Addition of tungsten in the Mo-alloy wires was found to increase the long-term stress rupture strength at temperatures above 1400 K. Theoretical calculations indicate that the strength and ductility advantage of the HfC dispersed alloy wires is due to the resistance to recrystallization imparted by the dispersoid.

Effect of cathode cooling efficiency and oxygen plasma gas pressure on the hafnium cathode wall temperature

NASA Astrophysics Data System (ADS)

Ashtekar, Koustubh; Diehl, Gregory; Hamer, John

2012-10-01

The hafnium cathode is widely used in DC plasma arc cutting (PAC) under an oxygen gas environment to cut iron and iron alloys. The hafnium erosion is always a concern which is controlled by the surface temperature. In this study, the effect of cathode cooling efficiency and oxygen gas pressure on the hafnium surface temperature are quantified. The two layer cathode sheath model is applied on the refractive hafnium surface while oxygen species (O2, O, O+, O++, e-) are considered within the thermal dis-equilibrium regime. The system of non-linear equations comprising of current density balance, heat flux balance at both the cathode surface and the sheath-ionization layer is coupled with the plasma gas composition solver. Using cooling heat flux, gas pressure and current density as inputs; the cathode wall temperature, electron temperature, and sheath voltage drop are calculated. Additionally, contribution of emitted electron current (Je) and ions current (Ji) to the total current flux are estimated. Higher gas pressure usually reduces Ji and increases Je that reduces the surface temperature by thermionic cooling.

40 CFR 471.92 - Effluent limitations representing the degree of effluent reduction attainable by the application...

Code of Federal Regulations, 2011 CFR

2011-07-01

... Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0.301 Ammonia 31.6 13.9 Fluoride 14.1 6.26 (e... monthly average mg/off-kg (pounds per million off-pounds) of zirconium-hafnium heat treated Chromium 0.015... Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20 Fluoride 20.3 8.98 (i) Surface...

40 CFR 471.92 - Effluent limitations representing the degree of effluent reduction attainable by the application...

Code of Federal Regulations, 2010 CFR

2010-07-01

... Chromium 0.104 0.043 Cyanide 0.069 0.029 Nickel 0.455 0.301 Ammonia 31.6 13.9 Fluoride 14.1 6.26 (e... monthly average mg/off-kg (pounds per million off-pounds) of zirconium-hafnium heat treated Chromium 0.015... Chromium 0.150 0.061 Cyanide 0.099 0.041 Nickel 0.653 0.432 Ammonia 45.3 20 Fluoride 20.3 8.98 (i) Surface...

Raman Spectra of High-κ Dielectric Layers Investigated with Micro-Raman Spectroscopy Comparison with Silicon Dioxide

PubMed Central

Borowicz, P.; Taube, A.; Rzodkiewicz, W.; Latek, M.; Gierałtowska, S.

2013-01-01

Three samples with dielectric layers from high-κ dielectrics, hafnium oxide, gadolinium-silicon oxide, and lanthanum-lutetium oxide on silicon substrate were studied by Raman spectroscopy. The results obtained for high-κ dielectrics were compared with spectra recorded for silicon dioxide. Raman spectra suggest the similarity of gadolinium-silicon oxide and lanthanum-lutetium oxide to the bulk nondensified silicon dioxide. The temperature treatment of hafnium oxide shows the evolution of the structure of this material. Raman spectra recorded for as-deposited hafnium oxide are similar to the results obtained for silicon dioxide layer. After thermal treatment especially at higher temperatures (600°C and above), the structure of hafnium oxide becomes similar to the bulk non-densified silicon dioxide. PMID:24072982

Nuclear-grade zirconium prepared by combining combustion synthesis with molten-salt electrorefining technique

NASA Astrophysics Data System (ADS)

Li, Hui; Nersisyan, Hayk H.; Park, Kyung-Tae; Park, Sung-Bin; Kim, Jeong-Guk; Lee, Jeong-Min; Lee, Jong-Hyeon

2011-06-01

Zirconium has a low absorption cross-section for neutrons, which makes it an ideal material for use in nuclear reactor applications. However, hafnium typically contained in zirconium causes it to be far less useful for nuclear reactor materials because of its high neutron-absorbing properties. In the present study, a novel effective method has been developed for the production of hafnium-free zirconium. The process includes two main stages: magnesio-thermic reduction of ZrSiO 4 under a combustion mode, to produce zirconium silicide (ZrSi), and recovery of hafnium-free zirconium by molten-salt electrorefining. It was found that, depending on the electrorefining procedure, it is possible to produce zirconium powder with a low hafnium content: 70 ppm, determined by ICP-AES analysis.

Superconducting characteristics in purified tantalum-foils

NASA Astrophysics Data System (ADS)

Hu, Qinghua; Wang, Zhihe

2018-07-01

We have conducted extensive investigations on the electrical transport and magnetization on a purified tantalum foil with extremely sharp resistive transition (transition width ΔTc < 0.02 K) at 0 T and residual resistivity ratio ρ290K/ρ5K= 16.75. Many effects, such as anisotropic field-induced resistive broadening and second peak of the magnetization-hysteresis loop, are observed in the sample. The maximum upper critical field determined by criteria of R/Rn = 0.9 is about 1.08 T rather weak compared to that in cuprate and/or iron-based superconductors. Although the value of upper critical field Hc2(0) and the field dependence of effective pinning energy U show that the flux pinning potential is weaker, the critical current density Jc(2 K, 0 T) = 1.145 × 105 A/cm2 and the effect of second peak indicate that there should be higher collective vortex pinning potential in the tantalum foil. The carriers are dominated by holes with the density n = 6.6 × 1022/cm3.

Performance comparison: Aluminum electrolytic and solid tantalum capacitor

NASA Technical Reports Server (NTRS)

Hawthornthwaite, B. G.; Piper, J.; Holland, H. W.

1981-01-01

Several key electrical and environmental parameters of latest technology aluminum electrolytic and solid tantalum capacitors were evaluated in terms of price fluctuations of tantalum metal. Performance differences between solid tantalums and aluminum electrolytics are examined.

Design of thermoelectrically highly efficient Heusler compounds using phase separations and nano-composites under an economic point of view

NASA Astrophysics Data System (ADS)

Balke, Benjamin

Half-Heusler (HH) compounds are one of the most promising candidates for thermoelectric materials for automotive and industrial waste heat recovery applications. In this talk, I will give an overview about our recent investigations of phase separations in HH thermoelectrics, focusing on the ternary system TiNiSn-ZrNiSn-HfNiSn. I will show how we adapted this knowledge to design a p-type HH compound which exhibits a ZT that is increased by 130% compared to the best published bulk p-type Heusler. I will also present how we used the phase separation to design thermoelectric highly efficient nano-composites of different single-phase materials. Since the price for Hafnium doubled within the last year, our research focused on the design of HH compounds without Hafnium. I will present a very recent calculation on ZT per Euro and efficiency per Euro for various materials followed by our latest very promising results for n-type Heusler compunds without Hafnium resulting in 20 times higher ZT/Euro values. These results strongly underline the importance of phase separations as a powerful tool for designing highly efficient materials for thermoelectric applications that fulfill the industrial demands for a thermoelectric converter. The author gratefully acknowledges financial support by the thermoHEUSLER2 Project (Project No. 19U15006F) of the German Federal Ministry of Economics and Technology (BMWi).

All-tantalum electrolytic capacitor

NASA Technical Reports Server (NTRS)

Green, G. E., Jr.

1977-01-01

Device uses single-compression tantalum-to-tantalum seal. Single-compression seal allows better utilization of volume within device. As result of all-tantalum case and lengthened cathode, electrical parameters, particularly equivalent series resistance and capacitance stability, improved over silver-cased capacitor.

Tantalum coating of porous carbon scaffold supplemented with autologous bone marrow stromal stem cells for bone regeneration in vitro and in vivo

PubMed Central

Wei, Xiaowei; Wang, Benjie; Wang, Wei; Kang, Kai; Xie, Hui; Liu, Baoyi; Zhang, Xiuzhi; Zhang, Jinsong; Yang, Zhenming

2016-01-01

Porous tantalum metal with low elastic modulus is similar to cancellous bone. Reticulated vitreous carbon (RVC) can provide three-dimensional pore structure and serves as the ideal scaffold of tantalum coating. In this study, the biocompatibility of domestic porous tantalum was first successfully tested with bone marrow stromal stem cells (BMSCs) in vitro and for bone tissue repair in vivo. We evaluated cytotoxicity of RVC scaffold and tantalum coating using BMSCs. The morphology, adhesion, and proliferation of BMSCs were observed via laser scanning confocal microscope and scanning electron microscopy. In addition, porous tantalum rods with or without autologous BMSCs were implanted on hind legs in dogs, respectively. The osteogenic potential was observed by hard tissue slice examination. At three weeks and six weeks following implantation, new osteoblasts and new bone were observed at the tantalum–host bone interface and pores. At 12 weeks postporous tantalum with autologous BMSCs implantation, regenerated trabecular equivalent to mature bone was found in the pore of tantalum rods. Our results suggested that domestic porous tantalum had excellent biocompatibility and could promote new bone formation in vivo. Meanwhile, the osteogenesis of porous tantalum associated with autologous BMSCs was more excellent than only tantalum implantation. Future clinical studies are warranted to verify the clinical efficacy of combined implantation of this domestic porous tantalum associated with autologous BMSCs implantation and compare their efficacy with conventional autologous bone grafting carrying blood vessel in patients needing bone repairing. PMID:26843518

Tungsten-reinforced tantalum

NASA Technical Reports Server (NTRS)

Bacigalupi, R. J.; Breitwieser, R.

1972-01-01

Method is described for producing tungsten-reinforced tantalum, a material possessing the high temperature strength of tungsten and room temperature ductility and weldability of tantalum. This material is produced by bonding together and overlaying structure of tungsten wires with chemical vapor deposited tantalum.

Semimicrodetermination of tantalum with selenous acid

USGS Publications Warehouse

Grimaldi, F.S.; Schnepfe, M.M.

1958-01-01

Tantalum is separated and determined gravimetrically by precipitation with selenous acid from a highly acidic solution containing oxalic and tartaric acids. The method is selective for the determination of up to 30 mg. of tantalum pentoxide, and tolerates relatively large amounts of scandium, yttrium, cerium, titanium, zirconium, thorium, vanadium, niobium, molybdenum, tungsten, uranium, iron, aluminum, gallium, tin, lead, antimony, and bismuth. The separation of tantalum from niobium and titanium is not strictly quantitative, and correction is made colorimetrically for the small amounts of niobium and titanium co-precipitating with the tantalum. The method was applied to the determination of tantalum in tantaloniobate ores.

Extraction chromatographic separations of tantalum and tungsten from hafnium and complex matrix constituents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snow, Mathew S.; Finck, Martha R.; Carney, Kevin P.

2017-02-01

Ta, Hf, and W analyses from complex matrices (including environmental samples) require high purification of these analytes from each other and major/trace matrix constituents, however, current state-of-the-art Ta/Hf/W separations rely on traditional anion exchange approaches that suffer from relatively similar distribution coefficient (Kd) values for these analytes. This work reports assessment of three commercially available extraction chromatographic resins (TEVA, TRU, and UTEVA) for Ta/Hf/W separations. Batch contact studies show differences in Ta/W,Hf Kd values of up to 106, representing an improvement of a factor of 100 and 300 in Ta/Hf and Ta/W Kd values (respectively) over AG1x4 resin. Variations inmore » the Kd values as a function of HCl concentration for TRU resin show that this resin is well suited for Ta/Hf/W separations, with Ta/Hf, Ta/W, and W/Hf Kd value improvements of 10, 200, and 30 (respectively) over AG1x4 resin. Finally, analyses of digested soil samples (NIST 2710a) using TRU resin and tandem TEVA-TRU columns demonstrate the ability to achieve extremely high purification (>99%) of Ta and W from each other and Hf, as well as enabling very high purification of Ta and W from the major and trace elemental constituents present in soils, using a single chromatographic step.« less

Extraction chromatographic separations of tantalum and tungsten from hafnium and complex matrix constituents

DOE PAGES

Snow, Mathew S.; Finck, Martha R.; Carney, Kevin P.; ...

2017-01-08

Ta, Hf, and W analyses from complex matrices (including environmental samples) require high purification of these analytes from each other and major/trace matrix constituents, but, current state-of-the-art Ta/Hf/W separations rely on traditional anion exchange approaches that suffer from relatively similar distribution coefficient (Kd) values for these analytes. Our work reports assessment of three commercially available extraction chromatographic resins (TEVA, TRU, and UTEVA) for Ta/Hf/W separations. Batch contact studies show differences in Ta/W,Hf Kd values of up to 10 6, representing an improvement of a factor of 100 and 300 in Ta/Hf and Ta/W Kd values (respectively) over AG1x4 resin. Furthermore,more » variations in the Kd values as a function of HCl concentration for TRU resin show that this resin is well suited for Ta/Hf/W separations, with Ta/Hf, Ta/W, and W/Hf Kd value improvements of 10, 200, and 30 (respectively) over AG1x4 resin. Finally, analyses of digested soil samples (NIST 2710a) using TRU resin and tandem TEVA-TRU columns demonstrate the ability to achieve extremely high purification (>99%) of Ta and W from each other and Hf, as well as enabling very high purification of Ta and W from the major and trace elemental constituents present in soils, using a single chromatographic step.« less

Characteristics and production of tantalum powders for solid-electrolyte capacitors

NASA Astrophysics Data System (ADS)

Yoon, Jae Sik; Kim, Byung Il

The effects of using K 2TaF 7 as the raw material and sodium as the reducing agent on the characteristics of tantalum powder are investigated. Batch-type metallothermic reduction (BTMR) is used to charge the reactor with the raw material and the reducing agent, and external continuous supply metallothermic reduction (ESMR) is used to supply the raw material and the reducing agent at a constant rate at the temperature of the reduction reaction. In the case of ESMR, the yield increases by several tens of percent because of the uniform reaction between the raw material and the reducing agent. It is possible to obtain a powder of over 99.5% purity. The powder particles obtained with BTMR are relatively large (4-6 μm) and have a coarse lamellar shape, while those prepared via ESMR are of uniform 1-2 μm size with a coral-like shape. Measurements of the electric properties show that the leakage current and the dielectric dissipation are low with higher reliability in ESMR than in BTMR, and the capacitance is 26,000 and 8400 CV for ESMR and in BTMR, respectively.

PROCESS OF RECOVERING ZIRCONIUM VALUES FROM HAFNIUM VALUES BY SOLVENT EXTRACTION WITH AN ALKYL PHOSPHATE

DOEpatents

Peppard, D.F.

1960-02-01

A process of separating hafnium nitrate from zirconium nitrate contained in a nitric acid solution by selectively. extracting the zirconium nitrate with a water-immiscible alkyl phosphate is reported.

Method for fabricating hafnia films

DOEpatents

Hu, Michael Z [Knoxville, TN

2007-08-21

The present invention comprises a method for fabricating hafnia film comprising the steps of providing a substrate having a surface that allows formation of a self-assembled monolayer thereon via covalent bonding; providing an aqueous solution that provides homogeneous hafnium ionic complexes and hafnium nanoclusters wherein the aqueous solution is capable of undergoing homogeneous precipitation under controlled conditions for a desired period of time at a controlled temperature and controlled solution acidity for desired nanocluster nucleation and growth kinetics, desired nanocluster size, desired growth rate of film thickness and desired film surface characteristics. The method further comprising forming the self-assembled monolayer on the surface of the substrate wherein the self-assembled monolayer comprises a plurality of hydrocarbon chains cross-linked together along the surface of the substrate, the hydrocarbon chains being uniformly spaced from one another and wherein each of the hydrocarbon chains having a functional anchoring group at a first end of the chain covalently bonded with the surface of the substrate and each of the hydrocarbon chains having a functional terminating group projected away from the surface wherein the functional terminating group provides a bonding site for the hafnium film to grow; and exposing the substrate to the aqueous solution for a desired period of time at a controlled temperature wherein the hafnium ionic complexes and the hafnium nanoclusters are deposited on the bonding site of the functional terminating group thereby forming the hafnia film wherein the hafnium bonded to the hydrocarbons and to one another provide a uniform ordered arrangement defined by the uniform arrangement of the hydrocarbons.

Hafnium silicate and hafnium silicon oxynitride gate dielectrics for strained Si_xGe_1-x: Interface stability

NASA Astrophysics Data System (ADS)

Addepalli, Swarna; Sivasubramani, Prasanna; El-Bouanani, Mohamed; Kim, Moon; Gnade, Bruce; Wallace, Robert

2003-03-01

Strained Si_xGe_1-x layers have gained considerable attention due to hole mobility enhancement, and ease of integration with Si-based CMOS technology. The deposition of stable high-κ dielectrics [1] such as hafnium silicate and hafnium silicon oxynitride in direct contact with SiGe would simultaneously improve the capacitance of the gate stack and lower the leakage current for high performance SiGe devices. However, the oxidation of the Si_xGe_1-x substrate either during dielectric deposition or post-deposition processing would degrade device performance due to the thermodynamic instability of germanium oxide [2,3]. Results from XPS, HR-TEM, and C-V, and I-V analyses after various annealing treatments will be presented for hafnium silicate and hafnium silicon oxynitride films deposited on strained Si_xGe_1-x(100), and correlated with dielectric-Si_xGe_1-x(100) interface stability. Implications to the introduction of these oxides as viable gate dielectric candidates for SiGe-based CMOS technology will be discussed. This work is supported by DARPA through SPAWAR Grant No. N66001-00-1-8928, and the Texas Advanced Technology Program. References: [1] G. D. Wilk, R. M. Wallace and J. M. Anthony, Journal of Applied Physics, 89, 5243 (2001) [2] W. S. Liu, J .S. Chen, M.-A. Nicolet, V. Arbet-Engels, K. L. Wang, Journal of Applied Physics, 72, 4444 (1992), and, Applied Physics Letters, 62, 3321 (1993) [3] W. S. Liu, M. -A. Nicolet, H. -H. Park, B. -H. Koak, J. -W. Lee, Journal of Applied Physics, 78, 2631 (1995)

Effects of a Tantalum Addition on the Morphological and Compositional Evolutions of a Model Ni-AL-Cr Superalloy

NASA Technical Reports Server (NTRS)

Booth-Morrison, Christopher; Seidman, David N.; Noebe, Ronald D.

2008-01-01

The effects of a 2.0 at.% addition of Ta to a model Ni-Al-Cr superalloy aged at 1073 K are assessed using scanning electron microscopy and atom-probe tomography. The addition of Ta results in appreciable strengthening, and the morphology is found to evolve from a bimodal distribution of spheroidal precipitates, to cuboidal precipitates aligned along the elastically soft <001>-type directions. Tantalum is observed to partition preferentially to the gamma -precipitate phase and decreases the mobility of Ni in the gamma- matrix sufficiently to cause an accumulation of Ni on the gamma-matrix side of the gamma -precipitate/gamma-matrix heterophase interface.

Method of making tantalum capacitors

DOEpatents

McMillan, April D.; Clausing, Robert E.; Vierow, William F.

1998-01-01

A method for manufacturing tantalum capacitors includes preparing a tantalum compact by cold pressing tantalum powder, placing the compact, along with loose refractory metal powder, in a microwave-transparent casket to form an assembly, and heating the assembly for a time sufficient to effect at least partial sintering of the compact and the product made by the method.

Copper-tantalum alloy

DOEpatents

Schmidt, Frederick A.; Verhoeven, John D.; Gibson, Edwin D.

1986-07-15

A tantalum-copper alloy can be made by preparing a consumable electrode consisting of an elongated copper billet containing at least two spaced apart tantalum rods extending longitudinally the length of the billet. The electrode is placed in a dc arc furnace and melted under conditions which co-melt the copper and tantalum to form the alloy.

Phase Transformation Synthesis of Strontium Tantalum Oxynitride-based Heterojunction for Improved Visible Light-Driven Hydrogen Evolution.

PubMed

Zeng, Weixuan; Bian, Yuan; Cao, Sheng; Ma, Yongjin; Liu, Yi; Zhu, Anquan; Tan, Pengfei; Pan, Jun

2018-06-07

Tantalum oxynitride-based materials, which possess narrow bandgaps and sufficient band energy potentials, have been of immense interest for water splitting. However, the efficiency of photocatalytic reactions is still low due to the fast electron-hole recombination. Here, a Sr2Ta2O7-xNx/SrTaO2N heterostructured photocatalyst with well-matched band structure was in situ constructed by nitridation of hydrothermal-prepared Sr2Ta2O7 nanosheets. Compared to Sr2Ta2O7-xNx and pure SrTaO2N, the Sr2Ta2O7-xNx/SrTaO2N heterostructured photocatalyst exhibited highest rate of hydrogen evolution, which is ca. 2.0 and 76.4 times of Sr2Ta2O7-xNx and pure SrTaO2N under the similar reaction condition, respectively. The enhanced performance arises from the formation of suitable band matched heterojunction accelerated charge separation. This work provides a promising strategy for the construction of tantalum oxynitride-based heterojunction photocatalysts.

Composition and method for brazing graphite to graphite

DOEpatents

Taylor, Albert J.; Dykes, Norman L.

1984-01-01

The present invention is directed to a brazing material for joining graphite structures that can be used at temperatures up to about 2800.degree. C. The brazing material formed of a paste-like composition of hafnium carbide and uranium oxide with a thermosetting resin. The uranium oxide is converted to uranium dicarbide during the brazing operation and then the hafnium carbide and uranium dicarbide form a liquid phase at a temperature about 2600.degree. C. with the uranium diffusing and vaporizing from the joint area as the temperature is increased to about 2800.degree. C. so as to provide a brazed joint consisting essentially of hafnium carbide. This brazing temperature for hafnium carbide is considerably less than the eutectic temperature of hafnium carbide of about 3150.degree. C. The brazing composition also incorporates the thermosetting resin so that during the brazing operation the graphite structures may be temporarily bonded together by thermosetting the resin so that machining of the structures to final dimensions may be completed prior to the completion of the brazing operation. The resulting brazed joint is chemically and thermally compatible with the graphite structures joined thereby and also provides a joint of sufficient integrity so as to at least correspond with the strength and other properties of the graphite.

Mineral resource of the month: tantalum

USGS Publications Warehouse

,

2011-01-01

The article offers information on a rare transition metal called tantalum. It says that the blue-gray mineral resource was discovered in 1801 or 1802 and was used for capacitors in 1940. It adds that the tantalite ore and other minerals in the ore should be separated in order to generate concentrates of tantalum. The use of tantalum are also cited.

Tantalum-copper alloy and method for making

DOEpatents

Schmidt, Frederick A.; Verhoeven, John D.; Gibson, Edwin D.

1984-11-06

A tantalum-copper alloy can be made by preparing a consumable electrode consisting of an elongated copper billet containing at least two spaced apart tantalum rods extending longitudinally the length of the billet. The electrode is placed in a dc arc furnace and melted under conditions which co-melt the copper and tantalum to form the alloy.

Tantalum-copper alloy and method for making

DOEpatents

Schmidt, F.A.; Verhoeven, J.D.; Gibson, E.D.

1983-06-01

A tantalum-copper alloy can be made by preparing a consumable electrode consisting of an elongated copper billet containing at least two spaced apart tantalum rods extending longitudinally the length of the billet. The electrode is placed in a dc arc furnace and melted under conditions which co-melt the copper and tantalum to form the alloy.

Fabrication of a Tantalum-Based Josephson Junction for an X-Ray Detector

NASA Astrophysics Data System (ADS)

Morohashi, Shin'ichi; Gotoh, Kohtaroh; Yokoyama, Naoki

2000-06-01

We have fabricated a tantalum-based Josephson junction for an X-ray detector. The tantalum layer was selected for the junction electrode because of its long quasiparticle lifetime, large X-ray absorption efficiency and stability against thermal cycling. We have developed a buffer layer to fabricate the tantalum layer with a body-centered cubic structure. Based on careful consideration of their superconductivity, we have selected a niobium thin layer as the buffer layer for fabricating the tantalum base electrode, and a tungsten thin layer for the tantalum counter electrode. Fabricated Nb/AlOx-Al/Ta/Nb and Nb/Ta/W/AlOx-Al/Ta/Nb Josephson junctions exhibited current-voltage characteristics with a low subgap leakage current.

Cathodoluminescence Study of Hafnium Oxide

NASA Astrophysics Data System (ADS)

Purcell, Emily; Hengehold, Robert; McClory, John

2011-10-01

Hafnium dioxide (HfO2) is increasingly being used in place of silicon oxide as a gate insulator in field effect transistors. This is primarily due to its high dielectric constant, κ, of 25. Samples of HfO2 were grown by either atomic layer deposition (ALD) or pulsed laser deposition (PLD), with the PLD samples having assorted substrate temperatures during deposition (300 C, 500 C, and 750 C). Cathodoluminescence (CL) was chosen as the technique used for studying these HfO2 samples. The CL system used was capable of beam energies ranging from 1 keV to 20 keV and beam currents ranging from 10 μA to 50 μA. A Monte Carlo calculation using CASINO software was performed in order to determine the beam energy for the desired depth of penetration. Measurements were taken at sample temperatures ranging from 7K (closed cycled cryostat) to 300K (room temperature), as well as at various beam energies and beam currents. Comparison will be made between the PLD and ALD spectra.

Protective interlayer for high temperature solid electrolyte electrochemical cells

DOEpatents

Singh, Prabhakar; Vasilow, Theodore R.; Richards, Von L.

1996-01-01

The invention comprises of an electrically conducting doped or admixed cerium oxide composition with niobium oxide and/or tantalum oxide for electrochemical devices, characterized by the general formula: Nb.sub.x Ta.sub.y Ce.sub.1-x-y O.sub.2 where x is about 0.0 to 0.05, y is about 0.0 to 0.05, and x+y is about 0.02 to 0.05, and where x is preferably about 0.02 to 0.05 and y is 0, and a method of making the same. This novel composition is particularly applicable in forming a protective interlayer of a high temperature, solid electrolyte electrochemical cell (10), characterized by a first electrode (12); an electrically conductive interlayer (14) of niobium and/or tantalum doped cerium oxide deposited over at least a first portion (R) of the first electrode; an interconnect (16) deposited over the interlayer; a solid electrolyte (18) deposited over a second portion of the first electrode, the first portion being discontinuous from the second portion; and, a second electrode (20) deposited over the solid electrolyte. The interlayer (14) is characterized as being porous and selected from the group consisting of niobium doped cerium oxide, tantalum doped cerium oxide, and niobium and tantalum doped cerium oxide or admixtures of the same. The first electrode (12), an air electrode, is a porous layer of doped lanthanum manganite, the solid electrolyte layer (18) is a dense yttria stabilized zirconium oxide, the interconnect layer (16) is a dense, doped lanthanum chromite, and the second electrode (20), a fuel electrode, is a porous layer of nickel-zirconium oxide cermet. The electrochemical cell (10) can take on a plurality of shapes such as annular, planar, etc. and can be connected to a plurality of electrochemical cells in series and/or in parallel to generate electrical energy.

Transition metal complexes supported on metal-organic frameworks for heterogeneous catalysts

DOEpatents

Farha, Omar K.; Hupp, Joseph T.; Delferro, Massimiliano; Klet, Rachel C.

2017-02-07

A robust mesoporous metal-organic framework comprising a hafnium-based metal-organic framework and a single-site zirconium-benzyl species is provided. The hafnium, zirconium-benzyl metal-organic framework is useful as a catalyst for the polymerization of an alkene.

PRODUCTION OF METALS AND THEIR COMPOUNDS

DOEpatents

Arden, T.V.; Burstall, F.H.; Davies, G.R.; Linstead, R.P.; Wells, R.A.

1958-11-18

Zirconium nitrate can be separated from hafnium nitrate by mixing the nitrates with ethyl cellulose pulp, eluting the mass with diethyl ether containing nitric acid, and passing the eluent through a column of cellulose pulp the outflow of which is substantially free of hafnium.

Thermochemistry of amorphous and crystalline zirconium and hafnium silicates.

NASA Astrophysics Data System (ADS)

Ushakov, S.; Brown, C. E.; Navrotsky, Alexandra; Boatner, L. A.; Demkov, A. A.; Wang, C.; Nguyen, B.-Y.

2003-03-01

Calorimetric investigation of amorphous and crystalline zirconium and hafnium silicates was performed as part of a research program on thermochemistry of alternative gate dielectrics. Amorphous hafnium and zirconium silicates with varying SiO2 content were synthesized by a sol-gel process. Crystalline zirconium and hafnium silicates (zircon and hafnon) were synthesized by solid state reaction at 1450 °C from amorphous gels and grown as single crystals from flux. High temperature oxide melt solution calorimetry in lead borate (2PbO.B2O3) solvent at 800 oC was used to measure drop solution enthalpies for amorphous and crystalline zirconium and hafnium silicates and corresponding oxides. Applying appropriate thermochemical cycles, formation enthalpy of crystalline ZrSiO4 (zircon) from binary oxides (baddeleite and quartz) at 298 K was calculated as -23 +/-2 kJ/mol and enthalpy difference between amorphous and crystalline zirconium silicate (vitrification enthalpy) was found to be 61 +/-3 kJ/mol. Crystallization onset temperatures of amorphous zirconium and hafnium silicates, as measured by differential scanning calorimetry (DSC), increased with silica content. The resulting crystalline phases, as characterized by X-ray diffraction (XRD), were tetragonal HfO2 and ZrO2. Critical crystallite size for tetragonal to monoclinic transformation of HfO2 in the gel was estimated as 6 +/-2 nm from XRD data Crystallization enthalpies per mole of hafnia and zirconia in gels decrease slightly together with crystallite size with increasing silica content, for example from -22 to -15 +/-1 kJ per mol of HfO2 crystallized at 740 and 1006 °C from silicates with 10 and 70 mol Applications of thermal analyses and solution calorimetry techniques together with first-principles density functional calculations to estimate interface and surface energies are discussed.

Purification of tantalum by plasma arc melting

DOEpatents

Dunn, Paul S.; Korzekwa, Deniece R.

1999-01-01

Purification of tantalum by plasma arc melting. The level of oxygen and carbon impurities in tantalum was reduced by plasma arc melting the tantalum using a flowing plasma gas generated from a gas mixture of helium and hydrogen. The flowing plasma gases of the present invention were found to be superior to other known flowing plasma gases used for this purpose.

Metastable tantalum oxide formation during the devitrification of amorphous tantalum thin films

DOE PAGES

Donaldson, Olivia K.; Hattar, Khalid; Trelewicz, Jason R.

2016-07-04

Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright-field imaging, and electron-diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO 2 phase. While the appearance of these phases indicated the films were evolving tomore » the stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. As a result, new insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide-based dielectric materials for novel memristor designs.« less

Hafnium, Tungsten, and the Differentiation of the Moon and Mars

NASA Astrophysics Data System (ADS)

Taylor, G. J.

2003-11-01

Measurements of the isotopic composition of tungsten (W) show that lunar samples and Martian meteorites have an excess of W-182. This was produced by the decay of hafnium-182 (Hf-182), an isotope with a half-life of only 9 million years. Because tungsten dissolves enthusiastically in metallic iron and hafnium does not, it is possible to use the abundance of W-182 in rocks formed by melting of the silicate mantle as an indicator of the timing of core formation. However, the concentrations of Hf and W in rocky material can be affected by melting and crystallization, so we also need to know how each element concentrates in common minerals in the mantles of the Moon and Mars. The behavior of Hf has been studied experimentally, but this is not true of W. Kevin Righter (Johnson Space Center) and Charles (Chip) Shearer (University of New Mexico) have filled this knowledge void by determining how W partitions between olivine, high- and low-calcium pyroxene, plagioclase feldspar, and garnet. The new data allowed Righter and Shearer to reexamine available measurements of the isotopic composition of W in lunar samples and Martian meteorites. Their analysis suggests that the lunar magma ocean, a huge magma system that surrounded the Moon when it formed, solidified in less than 30 million years. This is shorter than many theoretical calculations suggest. Pathfinder data and chemical data from Martian meteorites suggest that the core of Mars makes up about 20% of the planet. Core formation and subsequent melting of a region of the mantle containing garnet and high-calcium pyroxene took place less than 20-30 million years after the formation of the first solids in the solar system. This type of research shows the importance of measurements of isotopic compositions of radioactive elements or their decay products and laboratory experiments on the geochemical behavior of those elements.

METHOD OF MAKING TUNGSTEN FILAMENTS

DOEpatents

Frazer, J.W.

1962-12-18

A method of making tungsten filaments is described in which the tungsten is completely free of isotope impurities in the range of masses 234 to 245 for use in mass spectrometers. The filament comprises a tantalum core generally less than 1 mil in diameter having a coating of potassium-free tantalum-diffused tungsten molecularly bonded thereto. In the preferred process of manufacture a short, thin tantalum filament is first mounted between terminal posts mounted in insulated relation through a backing plate. The tungsten is most conveniently vapor plated onto the tantalum by a tungsten carbonyl vapor decomposition method having a critical step because of the tendency of the tantalum to volatilize at the temperature of operntion of the filament. The preferred recipe comprises volatilizing tantalum by resistance henting until the current drops by about 40%, cutting the voltage back to build up the tungsten, and then gradually building the temperature back up to balance the rate of tungsten deposition with the rate of tantalum volatilization. (AEC)

High strength forgeable tantalum base alloy

NASA Technical Reports Server (NTRS)

Buckman, R. W., Jr.

1975-01-01

Increasing tungsten content of tantalum base alloy to 12-15% level will improve high temperature creep properties of existing tantalum base alloys while retaining their excellent fabrication and welding characteristics.

Grindability of cast Ti-Hf alloys.

PubMed

Kikuchi, Masafumi; Takahashi, Masatoshi; Sato, Hideki; Okuno, Osamu; Nunn, Martha E; Okabe, Toru

2006-04-01

As part of our systematic studies characterizing the properties of titanium alloys, we investigated the grindability of a series of cast Ti-Hf alloys. Alloy buttons with hafnium concentrations up to 40 mass% were made using an argon-arc melting furnace. Each button was cast into a magnesia-based mold using a dental titanium casting machine; three specimens were made for each metal. Prior to testing, the hardened surface layer was removed. The specimens were ground at five different speeds for 1 min at 0.98 N using a carborundum wheel on an electric dental handpiece. Grindability was evaluated as the volume of metal removed per minute (grinding rate) and the volume ratio of metal removed compared to the wheel material lost (grinding ratio). The data were analyzed using ANOVA. A trend of increasing grindability was found with increasing amounts of hafnium, although there was no statistical difference in the grindability with increasing hafnium contents. We also found that hafnium may be used to harden or strengthen titanium without deteriorating the grindability.

Thermochemistry of tantalum-wall cooling system with lithium and sodium working fluids

NASA Technical Reports Server (NTRS)

Tower, L. K.

1972-01-01

Plots are presented which show the distribution of oxygen between liquid lithium and tantalum or niobium, and between liquid sodium and tantalum at elevated temperatures. Additional plots showing the composition of the gas phase above the solutions of oxygen and alkali metal are presented. The use of the plots is illustrated by an example tantalum heat pipe filled with lithium.

Hafnium transistor process design for neural interfacing.

PubMed

Parent, David W; Basham, Eric J

2009-01-01

A design methodology is presented that uses 1-D process simulations of Metal Insulator Semiconductor (MIS) structures to design the threshold voltage of hafnium oxide based transistors used for neural recording. The methodology is comprised of 1-D analytical equations for threshold voltage specification, and doping profiles, and 1-D MIS Technical Computer Aided Design (TCAD) to design a process to implement a specific threshold voltage, which minimized simulation time. The process was then verified with a 2-D process/electrical TCAD simulation. Hafnium oxide films (HfO) were grown and characterized for dielectric constant and fixed oxide charge for various annealing temperatures, two important design variables in threshold voltage design.

The effect of tantalum and carbon on the structure/properties of a single crystal nickel-base superalloy. M.S. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Nguyen, H. C.

1984-01-01

The microstructure, phase chemistry, and creep and hot tensile properties were studied as a function of tantalum and carbon levels in Mar-M247 type single crystal alloys. Microstructural studies showed that several types of carbides (MC, M23C6 and M5C) are present in the normal carbon (0.10 wt % C) alloys after heat treatment. In general, the composition of the MC carbides changes from titanium rich to tantalum rich as the tantalum level in the alloy increases. Small M23C6 carbides are present in all alloys. Tungsten rich M6C carbides are also observed in the alloy containing no tantalum. No carbides are present in the low carbon (0.01 wt % C) alloy series. The morphology of gamma prime is observed to be sensitive to heat treatment and tantalum level in the alloy. Cuboidal gamma prime is present in all the as cast structures. After heat treatment, the gamma prime precipitates tend to have a more spheroidal like morphology, and this tendency increases as the tantalum level decreases. On prolonged aging, the gamma prime reverts back to a cuboidal morphology or under stress at high temperatures, forms a rafted structure. The weight fraction and lattice parameter of the spheroidal gamma prime increases with increasing tantalum content. Changes in the phase chemistry of the gamma prime matrix and gamma prime have also been analyzed using phase extraction techniques. The partitioning ratio decreases for tungsten and aluminum and increases for tantalum as the tantalum content increases for both alloy series; no significant changes occur in the partitioning ratios of the other alloying elements. A reduction in secondary creep rate and an increase in rupture time result from increasing the tantalum content and decreasing the carbon level.

Study on the property of low friction complex graphite-like coating containing tantalum

NASA Astrophysics Data System (ADS)

Wang, Zuoping; Feng, Lajun; Shen, Wenning

2018-03-01

In order to enhance equipment lifetime under low oil or even dry conditions, tantalum was introduced into the graphite-like coating (GLC) by sputtering mosaic targets. The results showed that the introduction of Ta obviously reduced the friction coefficient and hardness of the GLC, while improved the wearability. When the atomic percentage of Ta was larger than 3%, the steady friction coefficient was lower than 0.01, suggesting the coating exhibited super lubricity. When the content of Ta was about 5.0%, the average friction coefficient was 0.02 by a sliding friction test under load of 20 N in unlubricated condition. Its average friction coefficient reduced by 75%, compared with that of control GLC (0.0825).

Quaternary and quinary modifications of eutectic superalloys strengthened by delta Ni3Cb lamellae and gamma prime Ni3Al precipitates

NASA Technical Reports Server (NTRS)

Lemkey, F. D.; Mccarthy, G. P.

1975-01-01

By means of a compositional and heat treatment optimization program based on the quaternary gamma/gamma prime-delta, a tantalum modified gamma/gamma prime-delta alloy with improved shear and creep strength combined with better cyclic oxidation resistance was identified. Quinary additions, quaternary adjustments, and heat treatment were investigated. The tantalum modified gamma/gamma prime-delta alloy possessed a slightly higher liquidus temperature and exhibited rupture strength exceeding NASA VIA by approximately three and one-half Larson-Miller parameters (C = 20) above 1000 C. Although improvements in longitudinal mechanical properties were achieved, the shear and transverse strength property goals of the program were not met and present a continuing challenge to the alloy metallurgist.

Structure refinement for tantalum nitrides nanocrystals with various morphologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lianyun; School of Science, Beijing Jiaotong University, 3 Shang Yuan Cun, Haidian District, Beijing 100044; Huang, Kai

2012-07-15

Graphical abstract: Tantalum nitrides nanocrystals with various phases and morphologies for the first time have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. Highlights: ► The spherical TaN, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. ► The crystal structures of different tantalum nitrides were determined by Rietveld refinement on the X-ray diffraction data and the examinations of electron microcopies. ► The specific surface area of the tantalum nitrides powders was around 10 m{supmore » 2} g{sup −1}. ► Tantalum nitrides powders could be suitable for capacitor with high specific capacitance. -- Abstract: Tantalum nitrides (TaN{sub x}) nanocrystals with different phase and morphology have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. The crystal structures of tantalum nitrides were determined by Rietveld refinement based on the X-ray diffraction data. The morphologies of various tantalum nitrides nanocrystals in high quality were analyzed through the electron microcopies examinations. The spherical TaN nanoparticles, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been selectively prepared at different annealing temperatures. In addition, the specific surface areas of the tantalum nitrides nanocrystals measured by BET method were around 9.87–11.64 m{sup 2} g{sup −1}, indicating that such nano-sized tantalum nitrides could be suitable for capacitor with high specific capacitance.« less

Tantalum-based semiconductors for solar water splitting.

PubMed

Zhang, Peng; Zhang, Jijie; Gong, Jinlong

2014-07-07

Solar energy utilization is one of the most promising solutions for the energy crises. Among all the possible means to make use of solar energy, solar water splitting is remarkable since it can accomplish the conversion of solar energy into chemical energy. The produced hydrogen is clean and sustainable which could be used in various areas. For the past decades, numerous efforts have been put into this research area with many important achievements. Improving the overall efficiency and stability of semiconductor photocatalysts are the research focuses for the solar water splitting. Tantalum-based semiconductors, including tantalum oxide, tantalate and tantalum (oxy)nitride, are among the most important photocatalysts. Tantalum oxide has the band gap energy that is suitable for the overall solar water splitting. The more negative conduction band minimum of tantalum oxide provides photogenerated electrons with higher potential for the hydrogen generation reaction. Tantalates, with tunable compositions, show high activities owning to their layered perovskite structure. (Oxy)nitrides, especially TaON and Ta3N5, have small band gaps to respond to visible-light, whereas they can still realize overall solar water splitting with the proper positions of conduction band minimum and valence band maximum. This review describes recent progress regarding the improvement of photocatalytic activities of tantalum-based semiconductors. Basic concepts and principles of solar water splitting will be discussed in the introduction section, followed by the three main categories regarding to the different types of tantalum-based semiconductors. In each category, synthetic methodologies, influencing factors on the photocatalytic activities, strategies to enhance the efficiencies of photocatalysts and morphology control of tantalum-based materials will be discussed in detail. Future directions to further explore the research area of tantalum-based semiconductors for solar water splitting are also discussed.

"Decarbonization" of an imino N-heterocyclic carbene via triple benzyl migration from hafnium

USDA-ARS?s Scientific Manuscript database

An imino N-heterocyclic carbene underwent three sequential benzyl migrations upon reaction with tetrabenzylhafnium, resulting in complete removal of the carbene carbon from the ligand. The resulting eneamido-amidinato hafnium complex showed alkene polymerization activity comparable to that of a prec...

Mineral resource of the month: zirconium and hafnium

USGS Publications Warehouse

Gambogi, Joseph

2007-01-01

Zirconium and hafnium are corrosion-resistant metals that are grouped in the same family as titanium on the periodic table. The two elements commonly occur in oxide and silicate minerals and have significant economic importance in everything from ink, ceramics and golf shoes to nuclear fuel rods.

40 CFR 421.110 - Applicability: Description of the primary columbium-tantalum subcategory.

Code of Federal Regulations, 2010 CFR

2010-07-01

... PROTECTION AGENCY (CONTINUED) EFFLUENT GUIDELINES AND STANDARDS NONFERROUS METALS MANUFACTURING POINT SOURCE... the production of columbium or tantalum by primary columbium-tantalum facilities. [49 FR 8817, Mar. 8...

The application of porous tantalum cylinder to the repair of comminuted bone defects: a study of rabbit firearm injuries

PubMed Central

Ren, Bo; Zhai, Zhenbo; Guo, Kai; Liu, Yanpu; Hou, Weihuan; Zhu, Qingsheng; Zhu, Jinyu

2015-01-01

The aim of this study is to investigate the effect of porous tantalum material in repair tibial defects caused by firearm injuries in a rabbit model. A multifunctional biological impact machine was used to establish a rabbit tibial defect model of firearm injury. Porous tantalum rods were processed into a hollow cylinder. Kirschner wires were used for intramedullary fixation. We compared the differences of the bone ingrowth of the porous tantalum material by gross observations, X-rays and histological evaluations. The radiographic observations revealed that fibrous tissue covered the material surface after 4 weeks, and periosteal reactions and new bone callus extending materials appeared after 8 weeks. After 16 weeks, the calluses of the firearm injury group were completely wrapped around a porous tantalum material. The group with the highest Lane-Sandhu X-rays cores was the firearm injury and tantalum implant group, and the blank control group exhibited the lowest scores. The histological evaluations revealed that the presence of new bone around the biomaterial had grown into the porous tantalum. By the 16th week, the areas of bone tissue of the firearm injury group was significant higher than that of non-firearm injury group (P<0.05). The comminuted fractures treated with tantalum cylinders exhibited greater bone ingrowth in the firearm injury group. In conditions of firearm injuries, the porous tantalum biomaterial exhibited bone ingrowth that was beneficial to the treatment of bone defects. PMID:26131078

Development and Applications of Porous Tantalum Trabecular Metal Enhanced Titanium Dental Implants

PubMed Central

Bencharit, Sompop; Byrd, Warren C.; Altarawneh, Sandra; Hosseini, Bashir; Leong, Austin; Reside, Glenn; Morelli, Thiago; Offenbacher, Steven

2013-01-01

Statement of Problem Porous tantalum trabecular metal has recently been incorporated in titanium dental implants as a new form of implant surface enhancement. However, there is little information on the applications of this material in implant dentistry. Methods We, therefore review the current literature on the basic science and clinical uses of this material. Results Porous tantalum metal is used to improve the contact between osseous structure and dental implants; and therefore presumably facilitate osseointegration. Success of porous tantalum metal in orthopedic implants led to the incorporation of porous tantalum metal in the design of root-from endosseous titanium implants. The porous tantalum three-dimensional enhancement of titanium dental implant surface allows for combining bone ongrowth together with bone ingrowth, or osseoincorporation. While little is known about the biological aspect of the porous tantalum in the oral cavity, there seems to be several possible advantages of this implant design. This article reviews the biological aspects of porous tantalum enhanced titanium dental implants, in particular the effects of anatomical consideration and oral environment to implant designs. Conclusions We propose here possible clinical situations and applications for this type of dental implant. Advantages and disadvantages of the implants as well as needed future clinical studies are discussed. PMID:23527899

Process for manufacturing tantalum capacitors

DOEpatents

Lauf, Robert J.; Holcombe, Cressie E.; Dykes, Norman L.

1993-01-01

A process for manufacturing tantalum capacitors in which microwave energy is used to sinter a tantalum powder compact in order to achieve higher surface area and improved dielectric strength. The process comprises cold pressing tantalum powder with organic binders and lubricants to form a porous compact. After removal of the organics, the tantalum compact is heated to 1300.degree. to 2000.degree. C. by applying microwave radiation. Said compact is then anodized to form a dielectric oxide layer and infiltrated with a conductive material such as MnO.sub.2. Wire leads are then attached to form a capacitor to said capacitor is hermetically packaged to form the finished product.

Process for manufacturing tantalum capacitors

DOEpatents

Lauf, R.J.; Holcombe, C.E.; Dykes, N.L.

1993-02-02

A process for manufacturing tantalum capacitors in which microwave energy is used to sinter a tantalum powder compact in order to achieve higher surface area and improved dielectric strength. The process comprises cold pressing tantalum powder with organic binders and lubricants to form a porous compact. After removal of the organics, the tantalum compact is heated to 1,300 to 2,000 C by applying microwave radiation. Said compact is then anodized to form a dielectric oxide layer and infiltrated with a conductive material such as MnO[sub 2]. Wire leads are then attached to form a capacitor to said capacitor is hermetically packaged to form the finished product.

Interfacial phenomena in high-kappa dielectrics

NASA Astrophysics Data System (ADS)

Mathew, Anoop

The introduction of novel high-kappa dielectric materials to replace the traditional SiO2 insulating layer in CMOS transistors is a watershed event in the history of transistor development. Further, replacement of the traditional highly-doped polycrystalline silicon gate electrode with a new set of materials for metal gates complicates the transition and introduces further integration challenges. A whole variety of new material surfaces and interfaces are thus introduced that merit close investigation to determine parameters for optimal device performance. Nitrogen is a key component that improves the performance of a variety of materials for the next generation of these CMOS transistors. Nitrogen is introduced into new gate dielectric materials such as hafnium silicates as well as in potential metal gate materials such as hafnium nitride. A photoemission study of the binding energies of the various atoms in these systems using photoemission reveals the nature of the atomic bonding. The current study compares hafnium silicates of various compositions which were thermally nitrided at different temperatures in ammonia, hafnium nitrides, and thin HfO2 films using photoelectron spectroscopy. A recurring theme that is explored is the competition between oxygen and nitrogen atoms in bonding with hafnium and other atoms. The N 1s photoemission peak is seen to have contributions from its bonding with hafnium, oxygen, and silicon atoms. The Hf 4f and O 1s spectra similarly exhibit signatures of their bonding environment with their neighboring atoms. Angle resolved photoemission and in-situ annealing/argon sputtering experiments are used to elucidate the nature of the bonding and its evolution with processing. A nondestructive profilitng of nitrogen distribution as a function of composition in nitrided hafnium silicates is also constructed using angle resolved photoemission as a function of the take-off angle. These results are corroborated with depth reconstruction obtained using medium energy ion scattering (MEIS). A comparison of samples nitrided at progressively increasing temperatures in an ammonia environment shows substitution of oxygen with nitrogen atoms and increasing penetration of nitrogen into the gate stack. Trends in the binding energy of the the as-prepared hafnium silicates suggest that they are non-phase separated, and the binding energy of the hafnium and silicon track the relative composition. Upon being subject to rapid thermal annealing, the samples are observed to show behavior consistent with phase separation. There is also the evidence of charges at the oxide/Si interface that modify the expected behavior of the shifts in binding energy. In another set of experiments, a one-cycle atomic layer deposition (ALD) growth reaction on the water terminated Si(100) -- (2x1) surface is shown to lead to successful nucleation, high metal oxide coverage, and an abrupt metal-oxide/silicon interface as confirmed by photoemission, reflection high energy electron diffraction (RHEED), and Rutherford back scattering (RBS) measurements. Photoemission results confirm the coordination states of the hafnium and oxygen atoms. A Hf 4f core level shift is observed and assigned to the presence of the Si-O-Hf bonding environment with the more electronegative Si atom inducing the binding energy shift. This Hf 4f shift is smaller than that reported previously for silicates because of the difference of the semiconductor bonding environment. The subspecies *(O)2HfCl2 and *OHfCl3 are seen to be the predominant intermediate species in these reactions and photoemission results provide corroborative evidence for their presence. Experiments indicate that the hydroxyl sites bound to Si(100) are active for adsorption. The abrupt interface could be useful for aggressive Effective Oxide Thickness (EOT) scaling.

Heating element support clip

DOEpatents

Sawyer, William C.

1995-01-01

An apparatus for supporting a heating element in a channel formed in a heater base is disclosed. A preferred embodiment includes a substantially U-shaped tantalum member. The U-shape is characterized by two substantially parallel portions of tantalum that each have an end connected to opposite ends of a base portion of tantalum. The parallel portions are each substantially perpendicular to the base portion and spaced apart a distance not larger than a width of the channel and not smaller than a width of a graphite heating element. The parallel portions each have a hole therein, and the centers of the holes define an axis that is substantially parallel to the base portion. An aluminum oxide ceramic retaining pin extends through the holes in the parallel portions and into a hole in a wall of the channel to retain the U-shaped member in the channel and to support the graphite heating element. The graphite heating element is confined by the parallel portions of tantalum, the base portion of tantalum, and the retaining pin. A tantalum tube surrounds the retaining pin between the parallel portions of tantalum.

Heating element support clip

DOEpatents

Sawyer, W.C.

1995-08-15

An apparatus for supporting a heating element in a channel formed in a heater base is disclosed. A preferred embodiment includes a substantially U-shaped tantalum member. The U-shape is characterized by two substantially parallel portions of tantalum that each have an end connected to opposite ends of a base portion of tantalum. The parallel portions are each substantially perpendicular to the base portion and spaced apart a distance not larger than a width of the channel and not smaller than a width of a graphite heating element. The parallel portions each have a hole therein, and the centers of the holes define an axis that is substantially parallel to the base portion. An aluminum oxide ceramic retaining pin extends through the holes in the parallel portions and into a hole in a wall of the channel to retain the U-shaped member in the channel and to support the graphite heating element. The graphite heating element is confined by the parallel portions of tantalum, the base portion of tantalum, and the retaining pin. A tantalum tube surrounds the retaining pin between the parallel portions of tantalum. 6 figs.

Efficacy of Tantalum Tungsten Alloys for Diffusion Barrier Applications

NASA Astrophysics Data System (ADS)

Smathers, D. B.; Aimone, P. R.

2017-12-01

Traditionally either Niobium, Tantalum or a combination of both have been used as diffusion barriers in Nb3Sn Multi-filament wire. Vanadium has also been used successfully but the ultimate RRR of the copper is limited unless an external shell of Niobium is included. Niobium is preferred over Tantalum when alternating current losses are not an issue as the Niobium will react to form Nb3Sn. Pure Tantalum tends to deform irregularly requiring extra starting thickness to ensure good barrier qualities. Our evaluations showed Tantalum lightly alloyed with 3 wt% Tungsten is compatible with the wire drawing process while deforming as well as or better than pure Niobium. Ta3wt%W has been processed as a single barrier and as a distributed barrier to fine dimensions. In addition, the higher modulus and strength of the Tantalum Tungsten alloy improves the overall tensile properties of the wire.

Composition and method for brazing graphite to graphite

DOEpatents

Taylor, A.J.; Dykes, N.L.

1982-08-10

A brazing material is described for joining graphite structures that can be used up to 2800/sup 0/C. The brazing material is formed of a paste-like composition of hafnium carbide and uranium oxide with a thermosetting resin. The uranium oxide is converted to uranium dicarbide during the brazing operation and then the hafnium carbide and uranium dicarbide form a liquid phase at a temperature about 2600/sup 0/C with the uranium diffusing and vaporizing from the joint area as the temperature is increased to about 2800/sup 0/C so as to provide a brazed joint consisting essentially of hafnium carbide. The resulting brazed joint is chemically and thermally compatible with the graphite structures.

METHOD OF PROTECTING TANTALUM CRUCIBLES AGAINST REACTION WITH MOLTEN URANIUM

DOEpatents

Feder, H.M.; Chellew, N.R.

1960-08-16

Tantalum crucibles against reaction with molten uranium by contacting the surfaces to be protected with metallic boron (as powder, vapor, or suspension in a liquid-volatilenonreacting medium, such as acetone and petroleum oil) at about 1800 deg C in vacuum, discontinuing contact with the boron, and heating the crucibles to a temperature of between 1800 aad 2000 deg C, whereby the tantalum boride formed in the first heating step is converted to tantalum monoboride.

Isoelectronic substitutions and aluminium alloying in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor

NASA Astrophysics Data System (ADS)

von Rohr, Fabian O.; Cava, Robert J.

2018-03-01

High-entropy alloys (HEAs) are a new class of materials constructed from multiple principal elements statistically arranged on simple crystallographic lattices. Due to the large amount of disorder present, they are excellent model systems for investigating the properties of materials intermediate between crystalline and amorphous states. Here we report the effects of systematic isoelectronic replacements, using Mo-Y, Mo-Sc, and Cr-Sc mixtures, for the valence electron count 4 and 5 elements in the body-centered cubic (BCC) Ta-Nb-Zr-Hf-Ti high-entropy alloy (HEA) superconductor. We find that the superconducting transition temperature Tc strongly depends on the elemental makeup of the alloy, and not exclusively its electron count. The replacement of niobium or tantalum by an isoelectronic mixture lowers the transition temperature by more than 60%, while the isoelectronic replacement of hafnium, zirconium, or titanium has a limited impact on Tc. We further explore the alloying of aluminium into the nearly optimal electron count [TaNb] 0.67(ZrHfTi) 0.33 HEA superconductor. The electron count dependence of the superconducting Tc for (HEA)Al x is found to be more crystallinelike than for the [TaNb] 1 -x(ZrHfTi) x HEA solid solution. For an aluminum content of x =0.4 the high-entropy stabilization of the simple BCC lattice breaks down. This material crystallizes in the tetragonal β -uranium structure type and superconductivity is not observed above 1.8 K.

Square lattice honeycomb tri-carbide fuels for 50 to 250 KN variable thrust NTP design

NASA Astrophysics Data System (ADS)

Anghaie, Samim; Knight, Travis; Gouw, Reza; Furman, Eric

2001-02-01

Ultrahigh temperature solid solution of tri-carbide fuels are used to design an ultracompact nuclear thermal rocket generating 950 seconds of specific impulse with scalable thrust level in range of 50 to 250 kilo Newtons. Solid solutions of tri-carbide nuclear fuels such as uranium-zirconium-niobium carbide. UZrNbC, are processed to contain certain mixing ratio between uranium carbide and two stabilizing carbides. Zirconium or niobium in the tri-carbide could be replaced by tantalum or hafnium to provide higher chemical stability in hot hydrogen environment or to provide different nuclear design characteristics. Recent studies have demonstrated the chemical compatibility of tri-carbide fuels with hydrogen propellant for a few to tens of hours of operation at temperatures ranging from 2800 K to 3300 K, respectively. Fuel elements are fabricated from thin tri-carbide wafers that are grooved and locked into a square-lattice honeycomb (SLHC) shape. The hockey puck shaped SLHC fuel elements are stacked up in a grooved graphite tube to form a SLHC fuel assembly. A total of 18 fuel assemblies are arranged circumferentially to form two concentric rings of fuel assemblies with zirconium hydride filling the space between assemblies. For 50 to 250 kilo Newtons thrust operations, the reactor diameter and length including reflectors are 57 cm and 60 cm, respectively. Results of the nuclear design and thermal fluid analyses of the SLHC nuclear thermal propulsion system are presented. .

The sensitivity of EGRET to gamma ray polarization

NASA Astrophysics Data System (ADS)

Mattox, John R.

1990-05-01

A Monte Carlo simulation shows that EGRET (Energetic Gamma-Ray Experimental Telescope) does not even have sufficient sensitivity to detect 100 percent polarized gamma-rays. This is confirmed by analysis of calibration data. A Monte Carlo study shows that the sensitivity of EGRET to polarization peaks around 100 MeV. However, more than 10 5 gamma-ray events with 100 percent polarization would be required for a 3 sigma significance detection - more than available from calibration, and probably more than will result from a single score source during flight. A drift chamber gamma ray telescope under development (Hunter and Cuddapah 1989) will offer better sensitivity to polarization. The lateral position uncertainty will be improved by an order of magnitude. Also, if pair production occurs in the drift chamber gas (xenon at 2 bar) instead of tantalum foils, the effects of multiple Coulomb scattering will be reduced.

Cell and method for electrolysis of water and anode

NASA Technical Reports Server (NTRS)

Aylward, J. R. (Inventor)

1981-01-01

An electrolytic cell for converting water vapor to oxygen and hydrogen include an anode comprising a foraminous conductive metal substrate with a 65-85 weight percent iridium oxide coating and 15-35 weight percent of a high temperature resin binder. A matrix member contains an electrolyte to which a cathode substantially inert. The foraminous metal member is most desirably expanded tantalum mesh, and the cell desirably includes reservoir elements of porous sintered metal in contact with the anode to receive and discharge electrolyte to the matrix member as required. Upon entry of a water vapor containing airstream into contact with the outer surface of the anode and thence into contact with iridium oxide coating, the water vapor is electrolytically converted to hydrogen ions and oxygen with the hydrogen ions migrating through the matrix to the cathode and the oxygen gas produced at the anode to enrich the air stream passing by the anode.

MOLTEN PLUTONIUM FUELED FAST BREEDER REACTOR

DOEpatents

Kiehn, R.M.; King, L.D.P.; Peterson, R.E.; Swickard, E.O. Jr.

1962-06-26

A description is given of a nuclear fast reactor fueled with molten plutonium containing about 20 kg of plutonium in a tantalum container, cooled by circulating liquid sodium at about 600 to 650 deg C, having a large negative temperature coefficient of reactivity, and control rods and movable reflector for criticality control. (AEC)

Reusable crucible for containing corrosive liquids

DOEpatents

de Pruneda, Jean A. H.

1995-01-01

A reusable, non-wetting, corrosion-resistant material suitable for containment of corrosive liquids is formed of a tantalum or tantalum alloy substrate that is permeated with carbon atoms. The substrate is carburized to form surface layers of TaC and Ta.sub.2 C, and then is heated at high temperature under vacuum until the carbon atoms in the carbide layers diffuse throughout the substrate to form a solid solution of carbon atoms randomly interspersed in the tantalum or tantalum alloy lattice.

Reusable crucible for containing corrosive liquids

DOEpatents

Pruneda, J.A.H. de.

1995-01-24

A reusable, non-wetting, corrosion-resistant material suitable for containment of corrosive liquids is formed of a tantalum or tantalum alloy substrate that is permeated with carbon atoms. The substrate is carburized to form surface layers of TaC and Ta[sub 2]C, and then is heated at high temperature under vacuum until the carbon atoms in the carbide layers diffuse throughout the substrate to form a solid solution of carbon atoms randomly interspersed in the tantalum or tantalum alloy lattice. 10 figures.

World War II, tantalum, and the evolution of modern cranioplasty technique.

PubMed

Flanigan, Patrick; Kshettry, Varun R; Benzel, Edward C

2014-04-01

Cranioplasty is a unique procedure with a rich history. Since ancient times, a diverse array of materials from coconut shells to gold plates has been used for the repair of cranial defects. More recently, World War II greatly increased the demand for cranioplasty procedures and renewed interest in the search for a suitable synthetic material for cranioprostheses. Experimental evidence revealed that tantalum was biologically inert to acid and oxidative stresses. In fact, the observation that tantalum did not absorb acid resulted in the metal being named after Tantalus, the Greek mythological figure who was condemned to a pool of water in the Underworld that would recede when he tried to take a drink. In clinical use, malleability facilitated a single-stage cosmetic repair of cranial defects. Tantalum became the preferred cranioplasty material for more than 1000 procedures performed during World War II. In fact, its use was rapidly adopted in the civilian population. During World War II and the heyday of tantalum cranioplasty, there was a rapid evolution in prosthesis implantation and fixation techniques significantly shaping how cranioplasties are performed today. Several years after the war, acrylic emerged as the cranioplasty material of choice. It had several clear advantages over its metallic counterparts. Titanium, which was less radiopaque and had a more optimal thermal conductivity profile (less thermally conductive), eventually supplanted tantalum as the most common metallic cranioplasty material. While tantalum cranioplasty was popular for only a decade, it represented a significant breakthrough in synthetic cranioplasty. The experiences of wartime neurosurgeons with tantalum cranioplasty played a pivotal role in the evolution of modern cranioplasty techniques and ultimately led to a heightened understanding of the necessary attributes of an ideal synthetic cranioplasty material. Indeed, the history of tantalum cranioplasty serves as a model for innovative thinking and adaptive technology development.

21 CFR 886.3100 - Ophthalmic tantalum clip.

Code of Federal Regulations, 2010 CFR

2010-04-01

... blood vessels in the eye. (b) Classification. Class II (special controls). The device is exempt from the...) MEDICAL DEVICES OPHTHALMIC DEVICES Prosthetic Devices § 886.3100 Ophthalmic tantalum clip. (a) Identification. An ophthalmic tantalum clip is a malleable metallic device intended to be implanted permanently...

Ultraviolet spectrophotometric determination of tantalum with pyrogallol

USGS Publications Warehouse

Dinnin, J.I.

1953-01-01

In a search for a more rapid method for the determination of tantalum in rocks and minerals, an intensive study was made of the tantalum-pyrogallol reaction recommended by Platanov and Krivoshlikov, and a better modified spectrophotometric procedure is given. The improved method consists in measuring the absorbancy of the tantalum-pyrogallol complex at 325 m?? in 4N hydrochloric acid and a fixed concentration (0.0175M) of ammonium oxalate. Beer's law is followed for the concentration range up to 40 ?? per ml. Sensitivity in terms of molar absorbancy index is 4775. Most interferences are additive in character and readily correctable. Separations or major corrections are required in the presence of significant amounts of molybdenum, tungsten, antimony, and uranium. The method has been successfully applied to three ores previously analyzed by gravimetric techniques. The method affords greater speed, sensitivity, and reproducibility in the determination of tantalum in rocks and minerals. A more reliable technique for preparing standard solutions of tantalum has been developed.

Tribological performance of polycrystalline tantalum-carbide-incorporated diamond films on silicon substrates

NASA Astrophysics Data System (ADS)

Ullah, Mahtab; Rana, Anwar Manzoor; Ahmed, E.; Malik, Abdul Sattar; Shah, Z. A.; Ahmad, Naseeb; Mehtab, Ujala; Raza, Rizwan

2018-05-01

Polycrystalline tantalum-carbide-incorporated diamond coatings have been made on unpolished side of Si (100) wafer by hot filament chemical vapor deposition process. Morphology of the coatings has been found to vary from (111) triangular-facetted to predominantly (111) square-faceted by increasing the concentration of tantalum carbide. The results have been compared to those of a diamond reference coating with no tantalum content. An increase in roughness has been observed with the increase of tantalum carbide (TaC) due to change in morphology of the diamond films. It is noticed that roughness of the coatings increases as grains become more square-faceted. It is found that diamond coatings involving tantalum carbide are not as resistant as diamond films with no TaC content and the coefficient of friction for such coatings with microcrystalline grains can be manipulated to 0·33 under high vacuum of 10-7 Torr. Such a low friction coefficient value enhances tribological behavior of unpolished Si substrates and can possibly be used in sliding applications.

Pyroelectricity of silicon-doped hafnium oxide thin films

NASA Astrophysics Data System (ADS)

Jachalke, Sven; Schenk, Tony; Park, Min Hyuk; Schroeder, Uwe; Mikolajick, Thomas; Stöcker, Hartmut; Mehner, Erik; Meyer, Dirk C.

2018-04-01

Ferroelectricity in hafnium oxide thin films is known to be induced by various doping elements and in solid-solution with zirconia. While a wealth of studies is focused on their basic ferroelectric properties and memory applications, thorough studies of the related pyroelectric properties and their application potential are only rarely found. This work investigates the impact of Si doping on the phase composition and ferro- as well as pyroelectric properties of thin film capacitors. Dynamic hysteresis measurements and the field-free Sharp-Garn method were used to correlate the reported orthorhombic phase fractions with the remanent polarization and pyroelectric coefficient. Maximum values of 8.21 µC cm-2 and -46.2 µC K-1 m-2 for remanent polarization and pyroelectric coefficient were found for a Si content of 2.0 at%, respectively. Moreover, temperature-dependent measurements reveal nearly constant values for the pyroelectric coefficient and remanent polarization over the temperature range of 0 ° C to 170 ° C , which make the material a promising candidate for IR sensor and energy conversion applications beyond the commonly discussed use in memory applications.

Arcjet Cathode Phenomena

NASA Technical Reports Server (NTRS)

Curran, Francis M.; Haag, Thomas W.; Raquet, John F.

1989-01-01

Cathode tips made from a number of different materials were tested in a modular arcjet thruster in order to examine cathode phenomena. Periodic disassembly and examination, along with the data collected during testing, indicated that all of the tungsten-based materials behaved similarly despite the fact that in one of these samples the percentage of thorium oxide was doubled and another was 25 percent rhenium. The mass loss rate from a 2 percent thoriated rhenium cathode was found to be an order of magnitude greater than that observed using 2 percent thoriated tungsten. Detailed analysis of one of these cathode tips showed that the molten crater contained pure tungsten to a depth of about 150 microns. Problems with thermal stress cracking were encountered in the testing of a hafnium carbide tip. Post test analysis showed that the active area of the tip had chemically reacted with the propellant. A 100 hour continuous test was run at about 1 kW. Post test analysis revealed no dendrite formation, such as observed in a 30 kW arcjet lifetest, near the cathode crater. The cathodes from both this test and a previously run 1000 hour cycled test displayed nearly identical arc craters. Data and calculations indicate that the mass losses observed in testing can be explained by evaporation.

Arcjet cathode phenomena

NASA Technical Reports Server (NTRS)

Curran, Francis M.; Haag, Thomas W.; Raquet, John F.

1989-01-01

Cathode tips made from a number of different materials were tested in a modular arcjet thruster in order to examine cathode phenomena. Periodic disassembly and examination, along with the data collected during testing, indicated that all of the tungsten-based materials behaved similarly despite the fact that in one of these samples the percentage of thorium oxide was doubled and another was 25 percent rhenium. The mass loss rate from a 2 percent thoriated rhenium cathode was found to be an order of magnitude greater than that observed using 2 percent thoriated tungsten. Detailed analysis of one of these cathode tips showed that the molten crater contained pure tungsten to a depth of about 150 microns. Problems with thermal stress cracking were encountered in the testing of a hafnium carbide tip. Post test analysis showed that the active area of the tip had chemically reacted with the propellant. A 100 hour continuous test was run at about 1 kW. Post test analysis revealed no dendrite formation, such as observed in a 30 kW arcjet lifetest, near the cathode crater. The cathodes from both this test and a previously run 1000 hour cycled test displayed nearly identical arc craters. Data and calculations indicate that the mass losses observed in testing can be explained by evaporation.

NON-CORROSIVE REACTOR FUEL SYSTEM

DOEpatents

Herrick, C.C.

1962-08-14

A non-corrosive nuclear reactor fuel system was developed utilizing a molten plutonium-- iron alloy fuel having about 2 at.% carbon and contained in a tantalum vessel. This carbon reacts with the interior surface of the tantalum vessel to form a plutonium resistant self-healing tantalum carbide film. (AEC)

40 CFR 421.286 - Pretreatment standards for new sources.

Code of Federal Regulations, 2011 CFR

2011-07-01

... wastewater pollutants in secondary tantalum process wastewater introduced into a POTW shall not exceed the... per million pounds) of tantalum powder produced from leaching Copper 25.860 12.320 Lead 5.656 2.626...) Leaching wet air pollution control. PSNS for the Secondary Tantalum Subcategory Pollutant or pollutant...

2017 NEPP Tasks Update for Ceramic and Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander A.

2017-01-01

This presentation gives an overview of current NEPP tasks on ceramic and tantalum capacitors and plans for the future. It includes tasks on leakage currents, gas generation and case deformation in wet tantalum capacitors; ESR degradation and acceleration factors in MnO2 and polymer cathode capacitors. Preliminary results on the effect of moisture on degradation of reverse currents in MnO2 tantalum capacitors are discussed. Latest results on mechanical characteristics of MLCCs and modeling of degradation of leakage currents in BME capacitors with defects are also presented.

Electronic structure and charge transport in nonstoichiometric tantalum oxide

NASA Astrophysics Data System (ADS)

Perevalov, T. V.; Gritsenko, V. A.; Gismatulin, A. A.; Voronkovskii, V. A.; Gerasimova, A. K.; Aliev, V. Sh; Prosvirin, I. A.

2018-06-01

The atomic and electronic structure of nonstoichiometric oxygen-deficient tantalum oxide TaO x<2.5 grown by ion beam sputtering deposition was studied. The TaO x film content was analyzed by x-ray photoelectron spectroscopy and by quantum-chemistry simulation. TaO x is composed of Ta2O5, metallic tantalum clusters and tantalum suboxides. A method for evaluating the stoichiometry parameter of TaO x from the comparison of experimental and theoretical photoelectron valence band spectra is proposed. The charge transport properties of TaO x were experimentally studied and the transport mechanism was quantitatively analyzed with four theoretical dielectric conductivity models. It was found that the charge transport in almost stoichiometric and nonstoichiometric tantalum oxide can be consistently described by the phonon-assisted tunneling between traps.

Additively manufactured porous tantalum implants.

PubMed

Wauthle, Ruben; van der Stok, Johan; Amin Yavari, Saber; Van Humbeeck, Jan; Kruth, Jean-Pierre; Zadpoor, Amir Abbas; Weinans, Harrie; Mulier, Michiel; Schrooten, Jan

2015-03-01

The medical device industry's interest in open porous, metallic biomaterials has increased in response to additive manufacturing techniques enabling the production of complex shapes that cannot be produced with conventional techniques. Tantalum is an important metal for medical devices because of its good biocompatibility. In this study selective laser melting technology was used for the first time to manufacture highly porous pure tantalum implants with fully interconnected open pores. The architecture of the porous structure in combination with the material properties of tantalum result in mechanical properties close to those of human bone and allow for bone ingrowth. The bone regeneration performance of the porous tantalum was evaluated in vivo using an orthotopic load-bearing bone defect model in the rat femur. After 12 weeks, substantial bone ingrowth, good quality of the regenerated bone and a strong, functional implant-bone interface connection were observed. Compared to identical porous Ti-6Al-4V structures, laser-melted tantalum shows excellent osteoconductive properties, has a higher normalized fatigue strength and allows for more plastic deformation due to its high ductility. It is therefore concluded that this is a first step towards a new generation of open porous tantalum implants manufactured using selective laser melting. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Micro/Nano Structural Tantalum Coating for Enhanced Osteogenic Differentiation of Human Bone Marrow Stem Cells

PubMed Central

Ding, Ding; Xie, Youtao; Li, Kai; Huang, Liping; Zheng, Xuebin

2018-01-01

Recently, tantalum has been attracting much attention for its anticorrosion resistance and biocompatibility, and it has been widely used in surface modification for implant applications. To improve its osteogenic differentiation of human bone marrow stem cells (hBMSCs), a micro/nano structure has been fabricated on the tantalum coating surface through the combination of anodic oxidation and plasma spraying method. The morphology, composition, and microstructure of the modified coating were comprehensively studied by employing scanning electron microscopy (SEM), X-ray diffraction (XRD) as well as transmission electron microscopy (TEM). The effects of hierarchical structures as well as micro-porous structure of tantalum coating on the behavior for human bone marrow stem cells (hBMSCs) were evaluated and compared at both cellular and molecular levels in vitro. The experimental results show that a hierarchical micro/nano structure with Ta2O5 nanotubes spread onto a micro-scale tantalum coating has been fabricated successfully, which is confirmed to promote cell adhesion and spreading. Besides, the hierarchical micro/nano tantalum coating can provide 1.5~2.1 times improvement in gene expression, compared with the micro-porous tantalum coating. It demonstrates that it can effectively enhance the proliferation and differentiation of hBMSCs in vitro. PMID:29614022

Micro/Nano Structural Tantalum Coating for Enhanced Osteogenic Differentiation of Human Bone Marrow Stem Cells.

PubMed

Ding, Ding; Xie, Youtao; Li, Kai; Huang, Liping; Zheng, Xuebin

2018-04-03

Recently, tantalum has been attracting much attention for its anticorrosion resistance and biocompatibility, and it has been widely used in surface modification for implant applications. To improve its osteogenic differentiation of human bone marrow stem cells (hBMSCs), a micro/nano structure has been fabricated on the tantalum coating surface through the combination of anodic oxidation and plasma spraying method. The morphology, composition, and microstructure of the modified coating were comprehensively studied by employing scanning electron microscopy (SEM), X-ray diffraction (XRD) as well as transmission electron microscopy (TEM). The effects of hierarchical structures as well as micro-porous structure of tantalum coating on the behavior for human bone marrow stem cells (hBMSCs) were evaluated and compared at both cellular and molecular levels in vitro. The experimental results show that a hierarchical micro/nano structure with Ta₂O₅ nanotubes spread onto a micro-scale tantalum coating has been fabricated successfully, which is confirmed to promote cell adhesion and spreading. Besides, the hierarchical micro/nano tantalum coating can provide 1.5~2.1 times improvement in gene expression, compared with the micro-porous tantalum coating. It demonstrates that it can effectively enhance the proliferation and differentiation of hBMSCs in vitro.

The Evaluation of Hydroxyapatite (HA) Coated and Uncoated Porous Tantalum for Biomedical Material Applications

NASA Astrophysics Data System (ADS)

Safuan, Nadia; Sukmana, Irza; Kadir, Mohammed Rafiq Abdul; Noviana, Deni

2014-04-01

Porous tantalum has been used as an orthopedic implant for bone defects as it has a good corrosion resistance and fatigue behaviour properties. However, there are some reports on the rejection of porous Ta after the implantation. Those clinical cases refer to the less bioactivity of metallic-based materials. This study aims to evaluate hydroxyapatite coated and uncoated porous Tantalum in order to improve the biocompatibility of porous tantalum implant and osseointegration. Porous tantalum was used as metallic-base substrate and hydroxyapatite coating has been done using plasma-spraying technique. Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM) techniques were utilizes to investigate the coating characteristics while Confocal Raman Microscopy to investigate the interface and image. The effect of coating to the corrosion behaviour was assessed by employing potentiodynamic polarization tests in simulated body fluid at 37±1 °C. Based on SEM and FESEM results, the morphologies as well the weight element consists in the uncoated and hydroxyapatite coated porous tantalum were revealed. The results indicated that the decrease in corrosion current density for HA coated porous Ta compared to the uncoated porous Ta. This study concluded that by coating porous tantalum with HA supports to decrease the corrosion rate of pure porous.

A program continuation to develop processing procedures for advanced silicon solar cells

NASA Technical Reports Server (NTRS)

Avery, J. E.; Scott-Monck, J. A.

1976-01-01

Shallow junctions, aluminum back surface fields and tantalum pentoxide (Ta205) antireflection coatings coupled with the development of a chromium-palladium-silver contact system, were used to produce a 2 x 4 cm wraparound contact silicon solar cell. One thousand cells were successfully fabricated using batch processing techniques. These cells were 0.020 mm thick, with the majority (800) made from nominal ten ohm-cm silicon and the remainder from nominal 30 ohm-cm material. Unfiltered, these cells delivered a minimum AMO efficiency at 25 C of 11.5 percent and successfully passed all the normal in-process and acceptance tests required for space flight cells.

High Temperature Evaluation of Tantalum Capacitors - Test 1

DOE Data Explorer

Cieslewski, Grzegorz

2014-09-28

Tantalum capacitors can provide much higher capacitance at high-temperatures than the ceramic capacitors. This study evaluates selected tantalum capacitors at high temperatures to determine their suitability for you in geothermal field. This data set contains results of the first test where three different types of capacitors were evaluated at 260C.

Electrical characterization of glass, teflon, and tantalum capacitors at high temperatures

NASA Technical Reports Server (NTRS)

Hammoud, A. N.; Baumann, E. D.; Myers, I. T.; Overton, E.

1991-01-01

Dielectric materials and electrical components and devices employed in radiation fields and the space environment are often exposed to elevated temperatures among other things. Therefore, these systems must withstand the high temperature exposure while still providing good electrical and other functional properties. Experiments were carried out to evaluate glass, teflon, and tantalum capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature up to 200 C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. The DC leakage current measurements were also performed in a temperature range from 20 to 200 C. The obtained results are discussed and conclusions are made concerning the suitability of the capacitors investigated for high temperature applications.

Evidence for oxygen vacancies movement during wake-up in ferroelectric hafnium oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Starschich, S.; Böttger, U.; Menzel, S.

The wake-up effect which is observed in ferroelectric hafnium oxide is investigated in yttrium doped hafnium oxide prepared by chemical solution deposition. It can be shown that not the amount of cycles but the duration of the applied electrical field is essential for the wake-up. Temperature dependent wake-up cycling in a range of −160 °C to 100 °C reveals a strong temperature activation of the wake-up, which can be attributed to ion rearrangement during cycling. By using asymmetrical electrodes, resistive valence change mechanism switching can be observed coincident with ferroelectric switching. From the given results, it can be concluded that redistribution ofmore » oxygen vacancies is the origin of the wake-up effect.« less

The performance of hafnium and gadolinium self powered neutron detectors in the TREAT reactor

NASA Astrophysics Data System (ADS)

Imel, G. R.; Hart, P. R.

1996-05-01

The use of gadolinium and hafnium self powered neutron detectors in a transient reactor is described in this paper. The detectors were calibrated to the fission rate of U-235 using calibrated fission chambers; the calibration factors were tested in two reactors in steady state and found to be consistent. Calibration of the detectors in transient reactor conditions was done by using uranium wires that were analyzed by radiochemistry techniques to determine total fissions during the transient. This was correlated to the time-integrated current of the detectors during the transient. A temperature correction factor was derived to account for self-shielding effects in the hafnium and gadolinium detectors. The dynamic response of the detectors under transient conditions was studied, and found to be excellent.

Fabrication of Nano-Crossbar Resistive Switching Memory Based on the Copper-Tantalum Pentoxide-Platinum Device Structure

NASA Astrophysics Data System (ADS)

Olga Gneri, Paula; Jardim, Marcos

Resistive switching memory has been of interest lately not only for its simple metal-insulator-metal (MIM) structure but also for its promising ease of scalability an integration into current CMOS technologies like the Field Programmable Gate Arrays and other non-volatile memory applications. There are several resistive switching MIM combinations but under this scope of research, attention will be paid to the bipolar resistive switching characteristics and fabrication of Tantalum Pentaoxide sandwiched between platinum and copper. By changing the polarity of the voltage bias, this metal-insulator-metal (MIM) device can be switched between a high resistive state (OFF) and low resistive state (ON). The change in states is induced by an electrochemical metallization process, which causes a formation or dissolution of Cu metal filamentary paths in the Tantalum Pentaoxide insulator. There is very little thorough experimental information about the Cu-Ta 2O5-Pt switching characteristics when scaled to nanometer dimensions. In this light, the MIM structure was fabricated in a two-dimensional crossbar format. Also, with the limited available resources, a multi-spacer technique was formulated to localize the active device area in this MIM configuration to less than 20nm. This step is important in understanding the switching characteristics and reliability of this structure when scaled to nanometer dimensions.

Lowering the environmental impact of high-kappa/ metal gate stack surface preparation processes

NASA Astrophysics Data System (ADS)

Zamani, Davoud

ABSTRACT Hafnium based oxides and silicates are promising high-κ dielectrics to replace SiO2 as gate material for state-of-the-art semiconductor devices. However, integrating these new high-κ materials into the existing complementary metal-oxide semiconductor (CMOS) process remains a challenge. One particular area of concern is the use of large amounts of HF during wet etching of hafnium based oxides and silicates. The patterning of thin films of these materials is accomplished by wet etching in HF solutions. The use of HF allows dissolution of hafnium as an anionic fluoride complex. Etch selectivity with respect to SiO2 is achieved by appropriately diluting the solutions and using slightly elevated temperatures. From an ESH point of view, it would be beneficial to develop methods which would lower the use of HF. The first objective of this study is to find new chemistries and developments of new wet etch methods to reduce fluoride consumption during wet etching of hafnium based high-κ materials. Another related issue with major environmental impact is the usage of large amounts of rinsing water for removal of HF in post-etch cleaning step. Both of these require a better understanding of the HF interaction with the high-κ surface during the etching, cleaning, and rinsing processes. During the rinse, the cleaning chemical is removed from the wafers. Ensuring optimal resource usage and cycle time during the rinse requires a sound understanding and quantitative description of the transport effects that dominate the removal rate of the cleaning chemicals from the surfaces. Multiple processes, such as desorption and re-adsorption, diffusion, migration and convection, all factor into the removal rate of the cleaning chemical during the rinse. Any of these processes can be the removal rate limiting process, the bottleneck of the rinse. In fact, the process limiting the removal rate generally changes as the rinse progresses, offering the opportunity to save resources. The second objective of this study is to develop new rinse methods to reduce water and energy usage during rinsing and cleaning of hafnium based high-κ materials in single wafer-cleaning tools. It is necessary to have a metrology method which can study the effect of all process parameters that affect the rinsing by knowing surface concentration of contaminants in patterned hafnium based oxides and silicate wafers. This has been achieved by the introduction of a metrology method at The University of Arizona which monitors the transport of contaminant concentrations inside micro- and nano- structures. This is the only metrology which will be able to provide surface concentration of contaminants inside hafnium based oxides and silicate micro-structures while the rinsing process is taking place. The goal of this research is to study the effect of various process parameters on rinsing of patterned hafnium based oxides and silicate wafers, and modify a metrology method for end point detection.

Thermal hydraulic design and decay heat removal of a solid target for a spallation neutron source

NASA Astrophysics Data System (ADS)

Takenaka, N.; Nio, D.; Kiyanagi, Y.; Mishima, K.; Kawai, M.; Furusaka, M.

2005-08-01

Thermal hydraulic design and thermal stress calculations were conducted for a water-cooled solid target irradiated by a MW-class proton beam for a spallation neutron source. Plate type and rod bundle type targets were examined. The thickness of the plate and the diameter of the rod were determined based on the maximum and the wall surface temperature. The thermal stress distributions were calculated by a finite element method (FEM). The neutronics performance of the target is roughly proportional to its average density. The averaged densities of the designed targets were calculated for tungsten plates, tantalum clad tungsten plates, tungsten rods sheathed by tantalum and Zircaloy and they were compared with mercury density. It was shown that the averaged density was highest for the tungsten plates and was high for the tantalum cladding tungsten plates, the tungsten rods sheathed by tantalum and Zircaloy in order. They were higher than or equal to that of mercury for the 1 2 MW proton beams. Tungsten target without the cladding or the sheath is not practical due to corrosion by water under irradiation condition. Therefore, the tantalum cladding tungsten plate already made successfully by HIP and the sheathed tungsten rod are the candidate of high performance solid targets. The decay heat of each target was calculated. It was low enough low compared to that of ISIS for the target without tantalum but was about four times as high as that of ISIS when the thickness of the tantalum cladding was 0.5 mm. Heat removal methods of the decay heat with tantalum were examined. It was shown that a special cooling system was required for the target exchange when tantalum was used for the target. It was concluded that the tungsten rod target sheathed with stainless steel or Zircaloy was the most reliable from the safety considerations and had similar neutronics performance to that of mercury.

SU-E-J-201: Position Verification in Breast Cancer Radiotherapy Using Tantalum Clips in the Lumpectomy Cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santvoort, J van; Van der Drift, M; Kuipers, J

2014-06-01

Purpose: To find out whether tantalum surgical clips can be used for online position verification in treatment of the lumpectomy cavity (LC) in breast cancer patients. Tantalum is a high density metal that could be visible on Electronic Portal Images (EPIs) and be an affordable alternative to gold markers. Clips are considered more representative for the LC position than nearby bony structures. Methods: In twelve patients the surgeon had placed 2 to 5 tantalum clips in the LC. The AP and lateral fields used for portal imaging, were adapted. In doing so, both bony structures and tantalum clips were visiblemore » on EPIs. The following analyses were performed:1. Image degradation, with respect to delineating the CTV, of the axial CT slices by artefacts because of the tantalum clips was evaluated by a radiation oncologist;2. The visibility of the tantalum clips on the EPIs was evaluated by four radiation therapists (RTTs);3. Bony anatomy and tantalum clip matches were performed on the same images independently by two observers. Results: 1. Delineation of the CTV by the radiation oncologist was not hampered by CT image artefacts because of the clips.2. The mean score for visibility of the clips on the EPIs, analysed by the four RTTs, was 5.6 on a scale of 10 (range 3.9 – 8.0).3. In total 12 patients with 16 fractions each were analysed. The differences between clip match and bone match are significant with a mean vector length of 5.2 mm (SD 1.9 mm) for the difference. Conclusion: Results of matches on tantalum clips as compared to matches on bony structures differ substantially. Therefore clip matches can result in smaller CTV to PTV margins than bone matches. Visibility of the clips on EPIs is sufficient, so they can be an alternative to gold markers.« less

Effect of the oxygen content in a salt solution on the characteristics of sodium-reduced tantalum powders

NASA Astrophysics Data System (ADS)

Kolosov, V. N.; Orlov, V. M.; Miroshnichenko, M. N.; Prokhorova, T. Yu.; Masloboeva, S. M.; Belyaevskii, A. T.

2009-02-01

The characteristics of the tantalum powders produced by sodium thermal reduction from salt melts based on K2TaF7 and NaCl with various amounts of added oxycompounds K3TaOF6 and K2Ta2O3F6 are studied. At a molar ratio of oxygen to tantalum of 1.25 in the initial melt, capacitor tantalum powders with a specific surface area more than 3 m2/g are produced. The specific capacitance of the anodes made from these powders reaches 58 mC/g.

Guidelines for the selection and application of tantalum electrolytic capacitors in highly reliable equipment

NASA Technical Reports Server (NTRS)

Holladay, A. M.

1978-01-01

Guidelines are given for the selection and application of three types of tantalum electrolytic capacitors in current use in the design of electrical and electronic circuits for space flight missions. In addition, the guidelines supplement requirements of existing military specifications used in the procurement of capacitors. A need exists for these guidelines to assist designers in preventing some of the recurring, serious problems experienced with tantalum electrolytic capacitors in the recent past. The three types of capacitors covered by these guidelines are; solid, wet foil, and tantalum cased wet slug.

Ion beam and dual ion beam sputter deposition of tantalum oxide films

NASA Astrophysics Data System (ADS)

Cevro, Mirza; Carter, George

1994-11-01

Ion beam sputter deposition (IBS) and dual ion beam sputter deposition (DIBS) of tantalum oxide films was investigated at room temperature and compared with similar films prepared by e-gun deposition. Optical properties ie refractive index and extinction coefficient of IBS films were determined in the 250 - 1100 nm range by transmission spectrophotometry and at (lambda) equals 632.8 nm by ellipsometry. They were found to be mainly sensitive to the partial pressure of oxygen used as a reactive gas in the deposition process. The maximum value of the refractive index of IBS deposited tantalum oxide films was n equals 2.15 at (lambda) equals 550 nm and the extinction coefficient of order k equals 2 X 10-4. Films deposited by e-gun deposition had refractive index n equals 2.06 at (lambda) equals 550 nm. Films deposited using DIBS ie deposition assisted by low energy Ar and O2 ions (Ea equals 0 - 300 eV) and low current density (Ji equals 0 - 40 (mu) A/cm2) showed no improvement in the optical properties of the films. Preferential sputtering occurred at Ea(Ar) equals 300 eV and Ji equals 20 (mu) A/cm2 and slightly oxygen deficient films were formed. Different bonding states in the tantalum-oxide films were determined by x-ray spectroscopy while composition of the film and contaminants were determined by Rutherford scattering spectroscopy. Tantalum oxide films formed by IBS contained relatively high Ar content (approximately equals 2.5%) originating from the reflected argon neutrals from the sputtering target while assisted deposition slightly increased the Ar content. Stress in the IBS deposited films was measured by the bending technique. IBS deposited films showed compressive stress with a typical value of s equals 3.2 X 109 dyn/cm2. Films deposited by concurrent ion bombardment showed an increase in the stress as a function of applied current density. The maximum was s approximately equals 5.6 X 109 dyn/cm2 for Ea equals 300 eV and Ji equals 35 (mu) A/cm2. All deposited films were amorphous as measured by the x-ray diffraction method.

Ion-beam and dual-ion-beam sputter deposition of tantalum oxide films

NASA Astrophysics Data System (ADS)

Cevro, Mirza; Carter, George

1995-02-01

Ion-beam sputter deposition (IBS) and dual-ion-beam sputter deposition (DIBS) of tantalum oxide films was investigated at room temperature and compared with similar films prepared by e-gun deposition. The optical properties, i.e., refractive index and extinction coefficient, of IBS films were determined in the 250- to 1100-nm range by transmission spectrophotometry and at (lambda) equals 632.8 nm by ellipsometry. They were found to be mainly sensitive to the partial pressure of oxygen used as a reactive gas in the deposition process. The maximum value of the refractive index of IBS deposited tantalum oxide films was n equals 2.15 at (lambda) equals 550 nm and the extinction coefficient of order k equals 2 X 10-4. Films deposited by e-gun deposition had refractive index n 2.06 at (lambda) equals 550 nm. Films deposited using DIBS, i.e., deposition assisted by low energy Ar and O2 ions (Ea equals 0 to 300 eV) and low current density (Ji equals 0 to 40 (mu) A/cm2), showed no improvement in the optical properties of the films. Preferential sputtering occurred at Ea(Ar) equals 300 eV and Ji equals 20 (mu) A/cm2 and slightly oxygen deficient films were formed. Different bonding states in the tantalum-oxide films were determined by x-ray spectroscopy, whereas composition of the film and contaminants were determined by Rutherford backscattering spectroscopy (RBS). Tantalum oxide films formed by IBS contained relatively high Ar content (approximately equals 2.5%) originating from the reflected argon neutrals from the sputtering target whereas assisted deposition slightly increased the Ar content. Stress in the IBS-deposited films was measured by the bending technique. IBS-deposited films showed compressive stress with a typical value of s equals 3.2 X 109 dyn/cm2. Films deposited by concurrent ion bombardment showed an increase in the stress as a function of applied current density. The maximum was s approximately equals 5.6 X 109 dyn/cm2 for Ea equals 300 eV and Ji equals 35 (mu) A/cm2. All deposited films were amorphous as measured by the x-ray diffraction (XRD) method.

Hafnium-Based Bulk Metallic Glasses for Kinetic Energy Penetrators

DTIC Science & Technology

2004-12-01

uranium -based (DU) and tungsten- nickel -iron (W-Ni-Fe) composite kinetic energy (KE) munitions is primarily ascribed to their high densities (U: ρ...based on an invariant point identified in the hafnium- copper- nickel ternary system. They are denser than zirconium-based glass-forming compositions...depleted- uranium penetrators. 1. INTRODUCTION 1.1 Criterion for Effective Kinetic Energy Penetrator Performance The lethality of depleted

Time-Series Radiocarbon Measurements Indicate Carbon Turnover Across Soil Fractions is Correlated With Productivity in a Long-Term Agricultural Experiment

NASA Astrophysics Data System (ADS)

Sanderman, J.; Baisden, W. T.; Creamer, C.; Farrell, M.; Fallon, S.

2016-12-01

Carbonatites and alkaline intrusions are important sources of REEs. Environmental risks related to these deposit types have been assessed through literature review and evaluation of the geochemical properties of representative samples of mill tailings and their leachates. The main ore mineral in carbonatite deposits is bastnasite [(Ce,La)(CO3)F], which is found with dolomite and calcite ( 65 %), barite (20 - 25 %), plus a number of minor accessory minerals including sulfides such as galena and pyrite. Generally, alkaline intrusion-related REE deposits either occur in layered complexes or with dikes and veins cutting alkaline intrusions. Such intrusions have a more diverse group of REE ore minerals that include fluorcarbonates, oxides, silicates, and phosphates. Ore also can include minor calcite and iron (Fe), lead (Pb), and zinc (Zn) sulfides. The acid-generating potential of both deposit types is low because of a predominance of carbonate minerals in the carbonatite deposits, the presence of feldspars and minor calcite in alkaline intrusion-related deposits, and to only minor to trace occurrence of potentially acid-generating sulfide minerals. Both deposit types, however, are produced by igneous and hydrothermal processes that enrich high-field strength, incompatible elements, which typically are excluded from common rock-forming minerals. Elements such as yttrium (Y), niobium Nb), zirconium (Zr), hafnium (Hf), tungsten (W), titanium (Ti), tantalum (Ta), scandium (Sc), thorium (Th), and uranium (U) can be characteristic of these deposits and may be of environmental concern. Most of these elements, including the REEs, but with the exception of U, have low solubilities in water at the near-neutral pH values expected around these deposits. Mill tailings from carbonatite deposits can exceed residential soil and sediment criteria for Pb, and leachates from mill tailings can exceed drinking water guidelines for Pb. The greatest environmental challenges, however, are linked to the presence of Th and U, although mineral hosts for these elements are moderately unreactive in the environment. Both deposit types can have mill tailings that exceed residential soil criteria for U. Uranium can be recovered as a byproduct to mitigate its environmental effects, but Th remains a waste product that requires management.

Environmental Characteristics of Carbonatite and Alkaline Intrusion-related Rare Earth Element (REE) Deposits

NASA Astrophysics Data System (ADS)

Seal, R. R., II; Piatak, N. M.

2017-12-01

Carbonatites and alkaline intrusions are important sources of REEs. Environmental risks related to these deposit types have been assessed through literature review and evaluation of the geochemical properties of representative samples of mill tailings and their leachates. The main ore mineral in carbonatite deposits is bastnasite [(Ce,La)(CO3)F], which is found with dolomite and calcite ( 65 %), barite (20 - 25 %), plus a number of minor accessory minerals including sulfides such as galena and pyrite. Generally, alkaline intrusion-related REE deposits either occur in layered complexes or with dikes and veins cutting alkaline intrusions. Such intrusions have a more diverse group of REE ore minerals that include fluorcarbonates, oxides, silicates, and phosphates. Ore also can include minor calcite and iron (Fe), lead (Pb), and zinc (Zn) sulfides. The acid-generating potential of both deposit types is low because of a predominance of carbonate minerals in the carbonatite deposits, the presence of feldspars and minor calcite in alkaline intrusion-related deposits, and to only minor to trace occurrence of potentially acid-generating sulfide minerals. Both deposit types, however, are produced by igneous and hydrothermal processes that enrich high-field strength, incompatible elements, which typically are excluded from common rock-forming minerals. Elements such as yttrium (Y), niobium Nb), zirconium (Zr), hafnium (Hf), tungsten (W), titanium (Ti), tantalum (Ta), scandium (Sc), thorium (Th), and uranium (U) can be characteristic of these deposits and may be of environmental concern. Most of these elements, including the REEs, but with the exception of U, have low solubilities in water at the near-neutral pH values expected around these deposits. Mill tailings from carbonatite deposits can exceed residential soil and sediment criteria for Pb, and leachates from mill tailings can exceed drinking water guidelines for Pb. The greatest environmental challenges, however, are linked to the presence of Th and U, although mineral hosts for these elements are moderately unreactive in the environment. Both deposit types can have mill tailings that exceed residential soil criteria for U. Uranium can be recovered as a byproduct to mitigate its environmental effects, but Th remains a waste product that requires management.

Nuclear design analysis of square-lattice honeycomb space nuclear rocket engine

NASA Astrophysics Data System (ADS)

Widargo, Reza; Anghaie, Samim

1999-01-01

The square-lattice honeycomb reactor is designed based on a cylindrical core that is determined to have critical diameter and length of 0.50 m and 0.50 c, respectively. A 0.10-cm thick radial graphite reflector, in addition to a 0.20-m thick axial graphite reflector are used to reduce neutron leakage from the reactor. The core is fueled with solid solution of 93% enriched (U, Zr, Nb)C, which is one of several ternary uranium carbides that are considered for this concept. The fuel is to be fabricated as 2 mm grooved (U, Zr, Nb)C wafers. The fuel wafers are used to form square-lattice honeycomb fuel assemblies, 0.10 m in length with 30% cross-sectional flow area. Five fuel assemblies are stacked up axially to form the reactor core. Based on the 30% void fraction, the width of the square flow channel is about 1.3 mm. The hydrogen propellant is passed through these flow channels and removes the heat from the reactor core. To perform nuclear design analysis, a series of neutron transport and diffusion codes are used. The preliminary results are obtained using a simple four-group cross-section model. To optimize the nuclear design, the fuel densities are varied for each assembly. Tantalum, hafnium and tungsten are considered and used as a replacement for niobium in fuel material to provide water submersion sub-criticality for the reactor. Axial and radial neutron flux and power density distributions are calculated for the core. Results of the neutronic analysis indicate that the core has a relatively fast spectrum. From the results of the thermal hydraulic analyses, eight axial temperature zones are chosen for the calculation of group average cross-sections. An iterative process is conducted to couple the neutronic calculations with the thermal hydraulics calculations. Results of the nuclear design analysis indicate that a compact core can be designed based on ternary uranium carbide square-lattice honeycomb fuel. This design provides a relatively high thrust to weight ratio.

Evaluation of the 3D Finite Element Method Using a Tantalum Rod for Osteonecrosis of the Femoral Head

PubMed Central

Shi, Jingsheng; Chen, Jie; Wu, Jianguo; Chen, Feiyan; Huang, Gangyong; Wang, Zhan; Zhao, Guanglei; Wei, Yibing; Wang, Siqun

2014-01-01

Background The aim of this study was to contrast the collapse values of the postoperative weight-bearing areas of different tantalum rod implant positions, fibula implantation, and core decompression model and to investigate the advantages and disadvantages of tantalum rod implantation in different ranges of osteonecrosis in comparison with other methods. Material/Methods The 3D finite element method was used to establish the 3D finite element model of normal upper femur, 3D finite element model after tantalum rod implantation into different positions of the upper femur in different osteonecrosis ranges, and other 3D finite element models for simulating fibula implant and core decompression. Results The collapse values in the weight-bearing area of the femoral head of the tantalum rod implant model inside the osteonecrosis area, implant model in the middle of the osteonecrosis area, fibula implant model, and shortening implant model exhibited no statistically significant differences (p>0.05) when the osteonecrosis range was small (60°). The stress values on the artificial bone surface for the tantalum rod implant model inside the osteonecrosis area and the shortening implant model exhibited statistical significance (p<0.01). Conclusions Tantalum rod implantation into the osteonecrosis area can reduce the collapse values in the weight-bearing area when osteonecrosis of the femoral head (ONFH) was in a certain range, thereby obtaining better clinical effects. When ONFH was in a large range (120°), the tantalum rod implantation inside the osteonecrosis area, shortening implant or fibula implant can reduce the collapse values of the femoral head, as assessed by other methods. PMID:25479830

Study of constitution diagram aluminum-tantalum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glazov, V.M.; Mal'tsev, M.V.; Chistyakov, Y.D.

1988-10-20

Alloys of aluminum with tantalum were for the first time obtained by aluminothermic method in 1868 by Moriniak. Later these alloys were studied in the works of Schirmeister (1915) and Brouwer (1938), moreover Brouwer established that tantalum with aluminum forms the chemical compound TaA1, which has tetragonal crystal lattice with parameters a=5.422 angstroms and c=8.536 angstroms (1). However despite the fact that alloys of aluminum with tantalum long ago are obtained already, constitution diagram of this system is not studied until recently. In connection with the application of tantalum as the modifying additive in aluminum alloys an emergency in themore » construction of this diagram, without the knowledge by which it is not possible to give the correct explanation of the mechanism of the very process of the modification of primary grain. For this purpose was undertaken this work. Russian translations.« less

Hafnium germanosilicate thin films for gate and capacitor dielectric applications: thermal stability studies

NASA Astrophysics Data System (ADS)

Addepalli, Swarna; Sivasubramani, Prasanna; El-Bouanani, Mohamed; Kim, Moon; Gnade, Bruce; Wallace, Robert

2003-03-01

The use of SiO_2-GeO2 mixtures in gate and capacitor dielectric applications is hampered by the inherent thermodynamic instability of germanium oxide. Studies to date have confirmed that germanium oxide is readily converted to elemental germanium [1,2]. In sharp contrast, germanium oxide is known to form stable compounds with transition metal oxides such as hafnium oxide (hafnium germanate, HfGeO_4) [3]. Thus, the incorporation of hafnium in SiO_2-GeO2 may be expected to enhance the thermal stability of germanium oxide via Hf-O-Ge bond formation. In addition, the introduction of a transition metal would simultaneously enhance the capacitance of the dielectric thereby permitting a thicker dielectric which reduces leakage current [4]. In this study, the thermal stability of PVD-grown hafnium germanosilicate (HfGeSiO) films was investigated. XPS, HR-TEM, C-V and I-V results of films after deposition and subsequent annealing treatments will be presented. The results indicate that the presence or formation of elemental germanium drastically affects the stability of the HfGeSiO films. This work is supported by DARPA through SPAWAR Grant No. N66001-00-1-8928, and the Texas Advanced Technology Program. References: [1] W. S. Liu, J .S. Chen, M.-A. Nicolet, V. Arbet-Engels, K. L. Wang, Journal of Applied Physics, 72, 4444 (1992), and, Applied Physics Letters, 62, 3321 (1993) [2] W. S. Liu, M. -A. Nicolet, H. -H. Park, B. -H. Koak, J. -W. Lee, Journal of Applied Physics, 78, 2631 (1995) [3] P. M. Lambert, Inorganic Chemistry, 37, 1352 (1998) [4] G. D. Wilk, R. M. Wallace and J. M. Anthony, Journal of Applied Physics, 89, 5243 (2001)

Inter-diffusion of copper and hafnium as studied by x-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Pearson, Justin; Chourasia, A. R.

The Cu/Hf interface has been characterized by x-ray photoelectron spectroscopy. Thin films (thicknesses ranging from 100 nm to 150 nm) of hafnium were deposited on a silicon substrate. About 80 nm of copper was then deposited on such samples. The e-beam method was used for the deposition. The samples were annealed for 30 min at temperatures of 100, 200, 300, 400, and 500°C. The inter-diffusion of copper and hafnium was investigated by sequential sputter depth profiling and x-ray photoelectron spectroscopy. The interdiffusion in each case was analyzed by the Matano-Boltzmann's procedure using the Fick's second law. The interdiffusion coefficients and the width of the interface as determined from the data have been correlated with the annealing temperature. Supported by Organized Research, TAMU-Commerce.

Synthesis of transparent nanocomposite monoliths for gamma scintillation

NASA Astrophysics Data System (ADS)

Liu, Chao; Hajagos, Tibor J.; Kishpaugh, David; Jin, Yunxia; Hu, Wei; Chen, Qi; Pei, Qibing

2015-08-01

During the past decade, inorganic nanoparticles/polymer nanocomposites have been intensively studied to provide a low cost, high performance alternative for gamma scintillation. However, the aggregation of nanoparticles often occurs even at low nanoparticle concentrations and thus deteriorates the transparency and performance of these nanocomposite scintillators. Here we report an efficient fabrication protocol of transparent nanocomposite monoliths based on surface modified hafnium oxide nanoparticles. Using hafnium oxide nanoparticles with surface-grafted methacrylate groups, highly transparent bulk-size nanocomposite monoliths (2 mm thick, transmittance at 550 nm >75%) are fabricated with nanoparticle loadings up to 40 wt% (net hafnium wt% up to 28.5%). These nanocomposite monoliths of 1 cm diameter and 2 mm thickness are capable of producing a full energy photopeak for 662 keV gamma rays, with the best deconvoluted photopeak energy resolution reaching 8%.

Catalytic Hydroamination of Alkynes and Norbornene with Neutral and Cationic Tantalum Imido Complexes

PubMed Central

Anderson, Laura L.; Arnold, John; Bergman, Robert G.

2005-01-01

Several tantalum imido complexes have been synthesized and shown to efficiently catalyze the hydroamination of internal and terminal alkynes. An unusual hydroamination/hydroarylation reaction of norbornene catalyzed by a highly electrophilic cationic tantalum imido complex is also reported. Factors affecting catalyst activity and selectivity are discussed along with mechanistic insights gained from stoichiometric reactions. PMID:15255680

Intense photoluminescence from amorphous tantalum oxide films

NASA Astrophysics Data System (ADS)

Zhu, Minmin; Zhang, Zhengjun; Miao, Wei

2006-07-01

Tantalum oxide films were deposited on silicon substrates at a temperature of ˜450°C by heating a pure tantalum foil in a rough vacuum. The films were amorphous in structure and consisted of fully oxidized Ta2O5 and (TaOx, x <2.5) suboxides. This feature resulted in strong visible light emission from the films further oxidized in the air at temperatures of 200-300°C. The mechanism for this photoluminescence behavior of the amorphous tantalum oxide films was also investigated and discussed. This study suggests that wide-band-gap materials could act as effective visible light emitters and provides a simple route to synthesize such materials.

Thermal shock and erosion resistant tantalum carbide ceramic material

NASA Technical Reports Server (NTRS)

Honeycutt, L., III; Manning, C. R. (Inventor)

1978-01-01

Ceramic tantalum carbide artifacts with high thermal shock and mechanical erosion resistance are provided by incorporating tungsten-rhenium and carbon particles in a tantalum carbide matrix. The mix is sintered by hot pressing to form the ceramic article which has a high fracture strength relative to its elastic modulus and thus has an improved thermal shock and mechanical erosion resistance. The tantalum carbide is preferable less than minus 100 mesh, the carbon particles are preferable less than minus 100 mesh, and the tungsten-rhenium particles are preferable elongate, having a length to thickness ratio of at least 2/1. Tungsten-rhenium wire pieces are suitable as well as graphite particles.

Investigating the oxidation mechanism of tantalum nanoparticles at high heating rates

NASA Astrophysics Data System (ADS)

DeLisio, Jeffery B.; Wang, Xizheng; Wu, Tao; Egan, Garth C.; Jacob, Rohit J.; Zachariah, Michael R.

2017-12-01

Reduced diffusion length scales and increased specific surface areas of nanosized metal fuels have recently demonstrated increased reaction rates for these systems, increasing their relevance in a wide variety of applications. The most commonly employed metal fuel, aluminum, tends to oxidize rapidly near its melting point (660 °C) in addition to undergoing a phase change of the nascent oxide shell. To further expand on the understanding of nanosized metal fuel oxidation, tantalum nanoparticles were studied due to their high melting point (3017 °C) in comparison to aluminum. Both traditional slow heating rate and in-situ high heating rate techniques were used to probe the oxidation of tantalum nanoparticles in oxygen containing environments in addition to nanothermite mixtures. When oxidized by gas phase oxygen, the oxide shell of the tantalum nanoparticles rapidly crystallized creating cracks that may attribute to enhanced oxygen diffusion into the particle. In the case of tantalum based nanothermites, oxide shell crystallization was shown to induce reactive sintering with the metal oxide resulting in a narrow range of ignition temperatures independent of the metal oxide used. The oxidation mechanism was modeled using the Deal-Grove model to extract rate parameters, and theoretical burn times for tantalum based nanocomposites were calculated.

Effects of the [OC6F5] moiety upon structural geometry: crystal structures of half-sandwich tantalum(V) aryloxide complexes from reaction of Cp*Ta(N(t)Bu)(CH2R)2 with pentafluorophenol.

PubMed

Cole, Jacqueline M; Chan, Michael C W; Gibson, Vernon C; Howard, Judith A K

2011-10-01

The synthesis, chemical and structural characterization of a series of pentamethylcyclopentadienyl (Cp*) tantalum imido complexes and aryloxide derivatives are presented. Specifically, the imido complexes Cp*Ta(N(t)Bu)(CH(2)R)(2), where R = Ph [dibenzyl(tert-butylamido) (η(5)-pentamethylcyclopentadienyl)tantalum(IV) (1)], Me(2)Ph [tert-butylamido)bis(2-methyl-2-phenylpropyl) (η(5)-pentamethylcyclopentadienyl)tantalum(IV) (2)], CMe(3) [(tert-butylamido)bis(2,2-dimethylpropyl) (η(5)-pentamethylcyclopentadienyl)tantalum(IV) (3)], are reported. The crystal structure of (3) reveals α-agostic interactions with the Ta atom. The resulting increase in the tantalum core coordination improves electronic stability. As such it does not react with pentafluorophenol, in contrast to the other two reported imido complexes [(1) and (2)]. Addition of C(6)F(5)OH to (1) yields a dimeric aryl-oxide derivative, [Cp*Ta(CH(2)Ph)(OC(6)H(5))(μ-O)](2) [di-μ-oxido-bis[benzyl(pentafluorophenolato) (η(5)-pentamethylcyclopentadienyl)tantalum(V)] (4)]. Its crystal structure reveals long Ta-O(C(6)H(5)) bonds but short oxo-bridging Ta-O bonds. This is explained by accounting for the fierce electronic competition for the vacant d(π) orbitals of the electrophilic Ta(V) centre. Steric congestion around each metal is alleviated by a large twist angle (77.1°) between the benzyl and pentafluorophenyl ligands and the ordering of each of these groups into stacked pairs. The imido complex (2) reacts with C(6)F(5)OH to produce a mixture of Cp*Ta(OC(6)F(5))(4) [tetrakis(pentafluorophenolato)(η(5)-pentamethylcyclopentadienyl)tantalum(V) (5)] and [Cp*Ta(OC(6)F(5))(2)(μ-O)](2) [di-μ-oxido-bis[bis(pentafluorophenolato)(η(5)-pentamethylcyclopentadienyl)tantalum(V)] (6)]. Steric congestion is offset in both cases by the twisting of its pentafluorophenyl ligands. Particularly strong electronic competition for the empty d(π) metal orbitals in (6) is reflected in its bond geometry, and owes itself to the more numerous electron-withdrawing pentafluorophenyl ligands. The balance of steric and electronic factors affecting the reactivity of Cp* tantalum imido based complexes with pentafluorophenol is therefore addressed.

Ternary boride product and process

NASA Technical Reports Server (NTRS)

Clougherty, Edward V. (Inventor)

1976-01-01

A hard, tough, strong ceramic body is formed by hot pressing a mixture of a powdered metal and a powdered metal diboride. The metal employed is zirconium, titanium or hafnium and the diboride is the diboride of a different member of the same group of zirconium, titanium or hafnium to form a ternary composition. During hot pressing at temperatures above about 2,000.degree.F., a substantial proportion of acicular ternary monoboride is formed.

Investigation of gamma radiation induced changes in local structure of borosilicate glass by TDPAC and EXAFS

NASA Astrophysics Data System (ADS)

Kumar, Ashwani; Nayak, C.; Rajput, P.; Mishra, R. K.; Bhattacharyya, D.; Kaushik, C. P.; Tomar, B. S.

2016-12-01

Gamma radiation induced changes in local structure around the probe atom (Hafnium) were investigated in sodium barium borosilicate (NBS) glass, used for immobilization of high level liquid waste generated from the reprocessing plant at Trombay, Mumbai. The (NBS) glass was doped with 181Hf as a probe for time differential perturbed angular correlation (TDPAC) spectroscopy studies, while for studies using extended X-ray absorption fine structure (EXAFS) spectroscopy, the same was doped with 0.5 and 2 % (mole %) hafnium oxide. The irradiated as well as un-irradiated glass samples were studied by TDPAC and EXAFS techniques to obtain information about the changes (if any) around the probe atom due to gamma irradiation. TDPAC spectra of unirradiated and irradiated glasses were similar and reminescent of amorphous materials, indicating negligible effect of gamma radiation on the microstructure around Hafnium probe atom, though the quaqdrupole interaction frequency ( ω Q) and asymmetry parameter ( η) did show a marginal decrease in the irradiated glass compared to that in the unirradiated glass. EXAFS measurements showed a slight decrease in the Hf-O bond distance upon gamma irradiation of Hf doped NBS glass indicating densification of the glass matrix, while the cordination number around hafnium remains unchanged.

Atomic layer deposition and characterization of hafnium oxide grown on silicon from tetrakis(diethylamino)hafnium and water vapor

NASA Astrophysics Data System (ADS)

Deshpande, Anand; Inman, Ronald; Jursich, Gregory; Takoudis, Christos

2004-09-01

In this work thin films of hafnium oxide are deposited on Si(100) substrates by means of atomic layer deposition (ALD) using tetrakis(diethylamino)hafnium and water vapor at substrate temperatures of 250-350ºC. Our system capabilities include fast transient delivery of reactive fluids, real-time vapor phase detection (in situ tunable diode laser hygrometer), precursor thermochemical capabilities, and ppt level elemental analysis by inductive coupling plasma mass spectrometry. The composition, purity, and other properties of the films and resulting interfaces are determined using x-ray and Fourier transform infrared spectroscopies, Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope with A˚ scale resolution, and spectroscopic ellipsometry. The observed ALD rate is ~1.4 A˚ per cycle. The nonuniformity across the film is less than 4%. Negligible carbon contamination is found in the resulting stoichiometric films under all conditions studied. The pulse sequence was optimized to prevent disastrous particulate problems while still minimizing purge times. The film deposition is investigated as a function of substrate temperature and reagent pulsing characteristics. A mild inverse temperature dependence of the ALD rate is observed. The initial stage of the HfO2 growth is investigated in detail.

Effects of substrate temperature on properties of pulsed dc reactively sputtered tantalum oxide films

NASA Astrophysics Data System (ADS)

Jain, Pushkar; Juneja, Jasbir S.; Bhagwat, Vinay; Rymaszewski, Eugene J.; Lu, Toh-Ming; Cale, Timothy S.

2005-05-01

The effects of substrate heating on the stoichiometry and the electrical properties of pulsed dc reactively sputtered tantalum oxide films over a range of film thickness (0.14 to 5.4 μm) are discussed. The film stoichiometry, and hence the electrical properties, of tantalum oxide films; e.g., breakdown field, leakage current density, dielectric constant, and dielectric loss are compared for two different cases: (a) when no intentional substrate/film cooling is provided, and (b) when the substrate is water cooled during deposition. All other operating conditions are the same, and the film thickness is directly related to deposition time. The tantalum oxide films deposited on the water-cooled substrates are stoichiometric, and exhibit excellent electrical properties over the entire range of film thickness. ``Noncooled'' tantalum oxide films are stoichiometric up to ~1 μm film thickness, beyond that the deposited oxide is increasingly nonstoichiometric. The presence of partially oxidized Ta in thicker (>~1 μm) noncooled tantalum oxide films causes a lower breakdown field, higher leakage current density, higher apparent dielectric constant, and dielectric loss. The growth of nonstoichiometric tantalum oxide in thicker noncooled films is attributed to decreased surface oxygen concentration due to oxygen recombination and desorption at higher film temperatures (>~100 °C). The quantitative results presented reflect experience with a specific piece of equipment; however, the procedures presented can be used to characterize deposition processes in which film stoichiometry can change.

Electrical characteristics of thin Ta2O5 films deposited by reactive pulsed direct-current magnetron sputtering

NASA Astrophysics Data System (ADS)

Kim, J.-Y.; Nielsen, M. C.; Rymaszewski, E. J.; Lu, T.-M.

2000-02-01

Room temperature deposition of tantalum oxide films on metallized silicon substrates was investigated by reactive pulsed magnetron sputtering of Ta in an Ar/O2 ambient. The dielectric constant of the tantalum oxide ranged from 19 to 31 depending on the oxygen percentage [P(%)=PO2/(PO2+PAr)] used during sputtering. The leakage current density was less than 10 nA/cm2 at 0.5 MV/cm electric field and the dielectric breakdown field was greater than 3.8 MV/cm for P=60%. A charge storage as high as 3.3 μF/cm2 was achieved for 70-Å-thick film. Pulse frequency variation (from 20 to 200 kHz) did not give a significant effect in the electrical properties (dielectric constant or leakage current density) of the Ta2O5 films.

Two-dimensional tantalum disulfide: controlling structure and properties via synthesis

NASA Astrophysics Data System (ADS)

Zhao, Rui; Grisafe, Benjamin; Krishna Ghosh, Ram; Holoviak, Stephen; Wang, Baoming; Wang, Ke; Briggs, Natalie; Haque, Aman; Datta, Suman; Robinson, Joshua

2018-04-01

Tantalum disulfide (TaS2) is a transition metal dichalcogenide (TMD) that exhibits phase transition induced electronic property modulation at low temperature. However, the appropriate phase must be grown to enable the semiconductor/metal transition that is of interest for next generation electronic applications. In this work, we demonstrate direct and controllable synthesis of ultra-thin 1T-TaS2 and 2H-TaS2 on a variety of substrates (sapphire, SiO2/Si, and graphene) via powder vapor deposition. The synthesis process leads to single crystal domains ranging from 20 to 200 nm thick and 1-10 µm on a side. The TaS2 phase (1T or 2H) is controlled by synthesis temperature, which subsequently is shown to control the electronic properties. Furthermore, this work constitutes the first demonstration of a metal-insulator phase transition in directly synthesized 1T-TaS2 films and domains by electronic means.

Performance of Surface-Mount Ceramic and Solid Tantalum Capacitors for Cryogenic Applications

NASA Technical Reports Server (NTRS)

Patterson, Richard L.; MacDonald, Thomas L.; Hammoud, Ahmad; Gerber, Scott

1998-01-01

Low temperature electronics are of great interest for space exploration programs. These include missions to the outer planets, earth-orbiting and deep-space probes, remote-sensing and communication satellites. Terrestrial applications would also benefit from the availability of low temperature electronics. Power components capable of low temperature operation would, thus, enhance the technologies needed for the development of advanced power systems suitable for use in harsh environments. In this work, ceramic and solid tantalum capacitors were evaluated in terms of their dielectric properties as a function of temperature and at various frequencies. The surface-mount devices were characterized in terms of their capacitance stability and dissipation factor in the frequency range of 50 Hz to 100 kHz at temperatures ranging from room temperature (20 deg. C) to about liquid nitrogen temperature (-190 deg. C). The results are discussed and conclusions made concerning the suitability of the capacitors investigated for low temperature applications.

Effect of Osteonecrosis Intervention Rod Versus Core Decompression Using Multiple Small Drill Holes on Early Stages of Necrosis of the Femoral Head: A Prospective Study on a Series of 60 Patients with a Minimum 1-Year-Follow-Up.

PubMed

Miao, Haixiong; Ye, Dongping; Liang, Weiguo; Yao, Yicun

2015-01-01

The conventional CD used 10 mm drill holes associated with a lack of structural support. Thus, alternative methods such as a tantalum implant, small drill holes, and biological treatment were developed to prevent deterioration of the joint. The treatment of CD by multiple 3.2 mm drill holes could reduce the femoral neck fracture and partial weight bearing was allowed. This study was aimed to evaluate the effect of osteonecrosis intervention rod versus core decompression using multiple small drill holes on early stages of necrosis of the femoral head. From January 2011 to January 2012, 60 patients undergoing surgery for osteonecrosis with core decompression were randomly assigned into 2 groups based on the type of core decompression used: (1) a total of 30 osteonecrosis patients (with 16 hips on Steinburg stageⅠ,20 hips on Steinburg stageⅡ) were treated with a porous tantalum rod insertion. The diameter of the drill hole for the intervention rod was 10mm.(2) a total of 30 osteonecrosis patients (with 14 hips on Steinburg stageⅠ,20 hips on Steinburg stageⅡ) were treated with core decompression using five drill holes on the lateral femur, the diameter of the hole was 3.2 mm. The average age of the patient was 32.6 years (20-45 years) and the average time of follow-up was 25.6 months (12- 28 months) in the rod implanted group. The average age of the patient was 35.2 years (22- 43 years) and the average time of follow-up was 26.3 months (12-28 months) in the small drill holes group. The average of surgical time was 40 min, and the mean volume of blood loss was 30 ml in both surgical groups. The average of Harris score was improved from 56.2 ± 7.1 preoperative to 80.2 ± 11.4 at the last follow-up in the rod implanted group (p < 0.05). The mean Harris score was improved from 53.8 ± 6.6 preoperative to 79.7 ± 13.2 at the last follow-up in the small drill holes group (p<0. 05). No significant difference was observed in Harris score between the two groups. At the last follow-up, 28 of 36 hips were at the same radiographic stages as pre-operation, and 8 deteriorated in the rod implanted group. 26 of 34 hips were at the same radiographic stage as pre-operation, and 8 deteriorated in the small drill holes group. No significant difference was observed in radiographic stage between the two groups. There was no favourable result on the outcome of a tantalum intervention implant compared to multiple small drill holes. CD via multiple small drill holes would allow similar postoperative load-bearing and seems to result in similar or even better clinical outcome without the prolonged implantation of an expensive tantalum implant. A tantalum rod intervention and core decompression using multiple small drill holes were effective on the stage I hips rather than stage II hips.

Use of a Tantalum Liner to Reduce Bore Erosion and Increase Muzzle Velocity in Two-Stage Light Gas Guns

NASA Technical Reports Server (NTRS)

Bogdanoff, David W.

2015-01-01

Muzzle velocities and gun erosion predicted by earlier numerical simulations of two stage light gas guns with steel gun tubes were in good agreement with experimental values. In a subsequent study, simulations of high performance shots were repeated with rhenium (Re) gun tubes. Large increases in muzzle velocity (2 - 4 km/sec) were predicted for Re tubes. In addition, the hydrogen-produced gun tube erosion was, in general, predicted to be zero with Re tubes. Tantalum (Ta) has some mechanical properties superior to those of Re. Tantalum has a lower modulus of elasticity than Re for better force transmission from the refractory metal liner to an underlying thick wall steel tube. Tantalum also has greater ductility than Re for better survivability during severe stress/strain cycles. Also, tantalum has been used as a coating or liner in military powder guns with encouraging results. Tantalum has, however, somewhat inferior thermal properties to those of rhenium, with a lower melting point and lower density and thermal conductivity. The present study was undertaken to see to what degree the muzzle velocity gains of rhenium gun tubes (over steel tubes) could be achieved with tantalum gun tubes. Nine high performance shots were modeled with a new version of our CFD gun code for steel, rhenium and tantalum gun tubes. For all except the highest velocity shot, the results with Ta tubes were nearly identical with those for Re tubes. Even for the highest velocity shot, the muzzle velocity gain over a steel tube using Ta was 82% of the gain obtained using Re. Thus, the somewhat inferior thermal properties of Ta (when compared to those of Re) translate into only very slightly poorer overall muzzle velocity performance. When this fact is combined with the superior mechanical properties of Ta and the encouraging performance of Ta liners/coatings in military powder guns, tantalum is to be preferred over Re as a liner/coating material for two stage light gas guns to increase muzzle velocity and reduce bore erosion.

Development of a high efficiency thin silicon solar cell. [fabrication and stability tests

NASA Technical Reports Server (NTRS)

Lindmayer, J.

1976-01-01

One hundred thin (120 microns to 260 microns) silicon-aluminum solar cells were fabricated and tested. Silicon slices were prepared, into which an aluminum alloy was evaporated over a range of temperatures and times. Antireflection coatings of tantalum oxide were applied to the cells. Reflectance of the silicon-aluminum interfaces was correlated to alloy temperature (graphs are shown). Optical measurements of the rear surface-internal reflectance of the cells were performed using a Beckman spectrophotometer. An improved gridline pattern was evaluated and stability tests (thermal cycling tests) were performed. Results show that: (1) a high-index, high-transmittance antireflection coating was obtained; (2) the improved metallization of the cells gave a 60 percent rear surface-internal reflectance, and the cells displayed excellent fill factors and blue response of the spectrum; (3) an improved gridline pattern (5 micron linewidths compared to 13 micron linewidths) resulted in a 1.3 percent improvement in short circuit currents; and (4) the stability tests showed no change in cell properties.

Anomalous softening of yield strength in tantalum at high pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jing, Qiumin, E-mail: j-qm@163.com; Wu, Qiang; Xu, Ji-an

2015-02-07

The pressure dependence of the yield strength of tantalum was investigated experimentally up to 101 GPa at room temperature using a diamond anvil cell. A yield strength softening is observed between 52 and 84 GPa, whereas a normal trend is observed below 52 GPa and above 84 GPa. The onset pressure of the softening is in agreement with previous results obtained by the pressure gradient method and shock wave experiments. This unusual strength softening in tantalum is not related with structural transformation, preferred orientation, or material damage. Our measurements indicate that microscopic deviatoric strain is the major reason for the observed strength softening inmore » tantalum.« less

Tantalum coatings for inertial confinement fusion dry wall designs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, L.H.; Green, L.

1996-12-31

The coating on a dry first wall inertial confinement fusion reactor must survive the target explosion and be ductile, inexpensive, and compatible with the materials in the target, i.e. have a high atomic number Z. Calculations indicate that tantalum is the best choice for the coating material. As a test of this design 1 mm tantalum coatings were plasma sprayed onto ferrite steel tubes. They were then subjected to 100 heating-cooling cycles which simulated the stressful thermal cycling which would be encountered during five years of plant startups and shutdowns. The coatings were undamaged and continued to bond well tomore » the steel. Furthermore, chemical reactions should not degrade tantalum coatings.« less

Hafnium nitride buffer layers for growth of GaN on silicon

DOEpatents

Armitage, Robert D.; Weber, Eicke R.

2005-08-16

Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

Studies of Ultra High Temperature Ceramic Composite Components: Synthesis and Characterization of HfOxCy and Si Oxidation in Atomic Oxygen Containing Environments

DTIC Science & Technology

2008-08-01

Andrea Hafeman and Dr Scott Guelcher for the use of the SDT analysis software. I would like to thank my committee members: Dr Clare McCabe, Dr Sharon...76 4.2: Thermogravimetric curves obtained during oxidation of hafnium...77 4.3: The thermogravimetric curves for hafnia and hafnium oxycarbide (28 mTorr) oxidized at 600°C

Review of anhydrous zirconium-hafnium separation techniques. Information circular/1984

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skaggs, R.L.; Rogers, D.T.; Hunter, D.B.

1983-12-01

Sixteen nonaqueous techniques conceived to replace the current aqueous scheme for separating hafnium and zirconium tetrachlorides were reviewed and evaluated by the Bureau of Mines. The methods are divided into two classes: separation by fractional volatilization of the tetrachlorides, which takes advantage of the higher volatility of hafnium tetrachloride; and separation by chemical techniques, based on differences in chemical behavior of the two tetrachlorides. The criteria used to evaluate separation methods were temperature, pressure, separation factor per equilibrium stage, complexity, compatibility with existing technology, and potential for continuous operation. Three processes were selected as being most promising: (1) high-pressure distillation,more » (2) extractive distillation from a molten salt, and (3) preferential reduction of gaseous ZrCl4. Any of the proposed nonaqueous Hf-Zr separation schemes must be supplemented with additional purification to remove trace impurities.« less

X-ray analyses of thermally grown and reactively sputtered tantalum oxide films on NiTi alloy

NASA Astrophysics Data System (ADS)

McNamara, Karrina; Tofail, Syed A. M.; Conroy, Derek; Butler, James; Gandhi, Abbasi A.; Redington, Wynette

2012-08-01

Sputter deposition of tantalum (Ta) on the surface of NiTi alloy is expected to improve the alloy's corrosion resistance and biocompatibility. Tantalum is a well-known biomaterial which is not affected by body fluids and is not irritating to human tissue. Here we compare the oxidation chemistry crystal structure evolution of tantalum oxide films grown on NiTi by reactive O2 sputtering and by thermal oxidation of sputter deposited Ta films. The effect of sputtering parameters and post-sputtering treatments on the morphology, oxidation state and crystal structure of the tantalum oxide layer have been investigated by field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The study has found that it may be better to avoid oxidation at and above 600 °C. The study establishes that reactive sputtering in presence of low oxygen mixture yields thicker film with better control of the film quality except that the surface oxidation state of Ta is slightly lower.

Synthesis and characterization of polystyrene embolization particles doped with tantalum oxide nanoparticles for X-ray contrast.

PubMed

Morrison, Rachel; Thompson, James; Bird, Luke; Hill, Mark A; Townley, Helen

2015-08-01

Radiopaque and fluorescent embolic particles have been synthesized and characterised to match the size of vasculature found in tumours to ensure effective occlusion of the vessels. A literature search showed that the majority of vessels surrounding a tumour were less than 50 µm and therefore polydispersed polystyrene particles with a peak size of 50 µm have been synthesised. The embolic particles contain 5-8 nm amorphous tantalum oxide nanoparticles which provide X-ray contrast. Embolic particles containing up to 9.4 wt% tantalum oxide were prepared and showed significant contrast compared to the undoped polystyrene particles. The X-ray contrast of the embolic particles was shown to be linear (R(2) = 0.9) with respect to the concentration of incorporated tantalum nanoparticles. A model was developed which showed that seventy-five 50 µm embolic particles containing 10% tantalum oxide could provide the same contrast as 5 cm of bone. Therefore, the synthesized particles would provide sufficient X-ray contrast to enable visualisation within a tumour.

Physically-based strength model of tantalum incorporating effects of temperature, strain rate and pressure

DOE PAGES

Lim, Hojun; Battaile, Corbett C.; Brown, Justin L.; ...

2016-06-14

In this work, we develop a tantalum strength model that incorporates e ects of temperature, strain rate and pressure. Dislocation kink-pair theory is used to incorporate temperature and strain rate e ects while the pressure dependent yield is obtained through the pressure dependent shear modulus. Material constants used in the model are parameterized from tantalum single crystal tests and polycrystalline ramp compression experiments. It is shown that the proposed strength model agrees well with the temperature and strain rate dependent yield obtained from polycrystalline tantalum experiments. Furthermore, the model accurately reproduces the pressure dependent yield stresses up to 250 GPa.more » The proposed strength model is then used to conduct simulations of a Taylor cylinder impact test and validated with experiments. This approach provides a physically-based multi-scale strength model that is able to predict the plastic deformation of polycrystalline tantalum through a wide range of temperature, strain and pressure regimes.« less

Vacuum pyrolysis characteristics and parameter optimization of recycling organic materials from waste tantalum capacitors.

PubMed

Chen, Zhenyang; Niu, Bo; Zhang, Lingen; Xu, Zhenming

2018-01-15

Recycling rare metal tantalum from waste tantalum capacitors (WTCs) is significant to alleviate the shortage of tantalum resource. However, environmental problems will be caused if the organic materials from WTCs are improperly disposed. This study presented a promising vacuum pyrolysis technology to recycle the organic materials from WTCs. The organics removal rate could reach 94.32wt% according to TG results. The optimal parameters were determined as 425°C, 50Pa and 30min on the basis of response surface methodology (RSM). The oil yield and residual rate was 18.09wt% and 74.94wt%, respectively. All pyrolysis products can be recycled through a reasonable route. Besides, to deeply understand the pyrolysis process, the pyrolysis mechanism was also proposed based on the product and free radical theory. This paper provides an efficient process for recycling the organic material from WTCs, which can facilitate the following tantalum recovery. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of Post-HALT Annealing on Leakage Currents in Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2010-01-01

Degradation of leakage currents is often observed during life testing of tantalum capacitors and is sometimes attributed to the field-induced crystallization in amorphous anodic tantalum pentoxide dielectrics. However, degradation of leakage currents and the possibility of annealing of degraded capacitors have not been investigated yet. In this work the effect of annealing after highly accelerated life testing (HALT) on leakage currents in various types of solid tantalum capacitors was analyzed. Variations of leakage currents with time during annealing at temperatures from 125 oC to 180 oC, thermally stimulated depolarization (TSD) currents, and I-V characteristics were measured to understand the conduction mechanism and the reason for current degradation. Annealing resulted in a gradual decrease of leakage currents and restored their initial values. Repeat HALT after annealing resulted in reproducible degradation of leakage currents. The observed results are explained based on ionic charge instability (drift/diffusion of oxygen vacancies) in the tantalum pentoxide dielectrics using a modified Schottky conduction mechanism.

Elastic Deformation Properties of Implanted Endobronchial Wire Stents in Benign and Malignant Bronchial Disease: A Radiographic In Vivo Evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hautmann, Hubert; Rieger, Johannes; Huber, Rudolf M.

1999-03-15

Purpose: To evaluate the long-term mechanical behavior in vivo of expandable endobronchial wire stents, we imaged three different prostheses in the treatment of tracheobronchial disease. Methods: Six patients with bronchial stenoses (three benign, three malignant) underwent insertion of metallic stents. Two self-expandable Wallstents, two balloon-expandable tantalum Strecker stents and two self-expandable nitinol Accuflex stents were used. Measurements of deformation properties were performed during voluntary cough by means of fluoroscopy, at 1 month and 7-10 months after implantation. The procedures were videotaped, their images digitized and the narrowing of stent diameters calculated at intervals of 20 msec. Results: After stent implantationmore » all patients improved with respect to ventilatory function. Radial stent narrowing during cough reached 53% (Wallstent), 59% (tantalum Strecker stent), and 52% (nitinol Accuflex stent) of the relaxed post-implantation diameter. Stent compression was more marked in benign compared with malignant stenoses. In the long term permanent deformation occurred with the tantalum Strecker stents; the other stents were unchanged. Conclusion: Endobronchial wire stents can be helpful in the treatment of major airway collapse and obstructing bronchial lesions. However, evidence of material fatigue as a possible effect of exposure to recurrent mechanical stress on the flexible mesh tube may limit their long-term use. This seems to be predominantly important in benign bronchial collapse.« less

Modified porous tantalum rod technique for the treatment of femoral head osteonecrosis

PubMed Central

Pakos, Emilios E; Megas, Panayiotis; Paschos, Nikolaos K; Syggelos, Spyridon A; Kouzelis, Antonios; Georgiadis, Georgios; Xenakis, Theodoros A

2015-01-01

AIM: To study a modified porous tantalum technique for the treatment of osteonecrosis of the femoral head. METHODS: The porous tantalum rod was combined with endoscopy, curettage, autologous bone grafting and use of bone marrow aspirates from iliac crest aspiration in 49 patients (58 hips) with a mean age of 38 years. The majority of the patients had idiopathic osteonecrosis, followed by corticosteroid-induced osteonecrosis. Thirty-eight hips were of Steinberg stage II disease and 20 hips were of stage III disease. Patients were followed for 5 years and were evaluated clinically with the Merle D’Aubigne and Postel score and radiologically. The primary outcome of the study was survival based on the conversion to total hip arthroplasty (THA). Secondary outcomes included deterioration of the osteonecrosis to a higher disease stage at 5 years compared to the preoperative period and identification of factors that were associated with survival. The Kaplan-Meier survival analysis was performed to evaluate the survivorship of the prosthesis, and the Fisher exact test was performed to test associations between various parameters with survival. RESULTS: No patient developed any serious intraoperative or postoperative complication including implant loosening or migration and donor site morbidity. During the 5-year follow up, 1 patient died, 7 patients had disease progression and 4 hips were converted to THA. The 5-year survival based on conversion to THA was 93.1% and the respective rate based on disease progression was 87.9%. Stage II disease was associated with statistically significant better survival rates compared to stage III disease (P = 0.04). The comparison between idiopathic and non-idiopathic osteonecrosis and between steroid-induced and non-steroid-induced osteonecrosis did not showed any statistically significant difference in survival rates. The clinical evaluation revealed statistically significantly improved Merle d’Aubigne scores at 12 mo postoperatively compared to the preoperative period (P < 0.001). The mean preoperative Merle d’Aubigne score was 13.0 (SD: 1.8). The respective score at 12 mo improved to 17.0 (SD: 2.0). The 12-mo mean score was retained at 5 years. CONCLUSION: The modified porous tantalum rod technique presented here showed encouraging outcomes. The survival rates based on conversion to THA are the lowest reported in the published literature. PMID:26601065

Modified porous tantalum rod technique for the treatment of femoral head osteonecrosis.

PubMed

Pakos, Emilios E; Megas, Panayiotis; Paschos, Nikolaos K; Syggelos, Spyridon A; Kouzelis, Antonios; Georgiadis, Georgios; Xenakis, Theodoros A

2015-11-18

To study a modified porous tantalum technique for the treatment of osteonecrosis of the femoral head. The porous tantalum rod was combined with endoscopy, curettage, autologous bone grafting and use of bone marrow aspirates from iliac crest aspiration in 49 patients (58 hips) with a mean age of 38 years. The majority of the patients had idiopathic osteonecrosis, followed by corticosteroid-induced osteonecrosis. Thirty-eight hips were of Steinberg stage II disease and 20 hips were of stage III disease. Patients were followed for 5 years and were evaluated clinically with the Merle D'Aubigne and Postel score and radiologically. The primary outcome of the study was survival based on the conversion to total hip arthroplasty (THA). Secondary outcomes included deterioration of the osteonecrosis to a higher disease stage at 5 years compared to the preoperative period and identification of factors that were associated with survival. The Kaplan-Meier survival analysis was performed to evaluate the survivorship of the prosthesis, and the Fisher exact test was performed to test associations between various parameters with survival. No patient developed any serious intraoperative or postoperative complication including implant loosening or migration and donor site morbidity. During the 5-year follow up, 1 patient died, 7 patients had disease progression and 4 hips were converted to THA. The 5-year survival based on conversion to THA was 93.1% and the respective rate based on disease progression was 87.9%. Stage II disease was associated with statistically significant better survival rates compared to stage III disease (P = 0.04). The comparison between idiopathic and non-idiopathic osteonecrosis and between steroid-induced and non-steroid-induced osteonecrosis did not showed any statistically significant difference in survival rates. The clinical evaluation revealed statistically significantly improved Merle d'Aubigne scores at 12 mo postoperatively compared to the preoperative period (P < 0.001). The mean preoperative Merle d'Aubigne score was 13.0 (SD: 1.8). The respective score at 12 mo improved to 17.0 (SD: 2.0). The 12-mo mean score was retained at 5 years. The modified porous tantalum rod technique presented here showed encouraging outcomes. The survival rates based on conversion to THA are the lowest reported in the published literature.

Fabrication of a tantalum-clad tungsten target for LANSCE

NASA Astrophysics Data System (ADS)

Nelson, A. T.; O'Toole, J. A.; Valicenti, R. A.; Maloy, S. A.

2012-12-01

Development of a solid state bonding technique suitable to clad tungsten targets with tantalum was completed to improve operation of the Los Alamos Neutron Science Centers spallation target. Significant deterioration of conventional bare tungsten targets has historically resulted in transfer of tungsten into the cooling system through corrosion resulting in increased radioactivity outside the target and reduction of delivered neutron flux. The fabrication method chosen to join the tantalum cladding to the tungsten was hot isostatic pressing (HIP) given the geometry constraints of a cylindrical assembly and previous success demonstrated at KENS. Nominal HIP parameters of 1500 °C, 200 MPa, and 3 h were selected based upon previous work. Development of the process included significant surface engineering controls and characterization given tantalums propensity for oxide and carbide formation at high temperatures. In addition to rigorous acid cleaning implemented at each step of the fabrication process, a three layer tantalum foil gettering system was devised such that any free oxygen and carbon impurities contained in the argon gas within the HIP vessel was mitigated to the extent possible before coming into contact with the tantalum cladding. The result of the numerous controls and refined techniques was negligible coarsening of the native Ta2O5 surface oxide, no measureable oxygen diffusion into the tantalum bulk, and no detectable carburization despite use of argon containing up to 5 ppm oxygen and up to 40 ppm total CO, CO2, or organic contaminants. Post bond characterization of the interface revealed continuous bonding with a few microns of species interdiffusion.

Intraoperative Localization of Tantalum Markers for Proton Beam Radiation of Choroidal Melanoma by an Opto-Electronic Navigation System: A Novel Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amstutz, Christoph A., E-mail: christoph.amstutz@usz.ch; Bechrakis, Nikolaos E.; Foerster, Michael H.

2012-03-15

Purpose: External beam proton radiation therapy has been used since 1975 to treat choroidal melanoma. For tumor location determination during proton radiation treatment, surgical tantalum clips are registered with image data. This report introduces the intraoperative application of an opto-electronic navigation system to determine with high precision the position of the tantalum markers and their spatial relationship to the tumor and anatomical landmarks. The application of the technique in the first 4 patients is described. Methods and Materials: A navigated reference base was attached noninvasively to the eye, and a navigated pointer device was used to record the spatial positionmore » of the tantalum markers, the tumor, and anatomical landmarks. Measurement accuracy was assessed on ex vivo porcine eye specimen by repetitive recording of the tantalum marker positions. The method was applied intraoperatively on 4 patients undergoing routine tantalum clip surgery. The spatial position information delivered by the navigation system was compared to the geometric data generated by the EYEPLAN software. Results: In the ex vivo experiments, the maximum repetition error was 0.34 mm. For the intraoperative application, the root mean square error of paired-points matching of the marker positions from the navigation system and from the EYEPLAN software was 0.701-1.25 mm. Conclusions: Navigation systems are a feasible tool for accurate localization of tantalum markers and anatomic landmarks. They can provide additional geometric information, and therefore have the potential to increase the reliability and accuracy of external beam proton radiation therapy for choroidal melanoma.« less

International strategic minerals inventory summary report; niobium (columbium) and tantalum

USGS Publications Warehouse

Crockett, R.N.; Sutphin, D.M.

1993-01-01

Major world resources of niobium and tantalum are described in this summary report of information in the International Strategic Minerals Inventory (ISMI). ISMI is a cooperative data-collection effort of earth-science and mineral-resource agencies in Australia, Canada, the Federal Republic of Germany, the Republic of South Africa, the United Kingdom, and the United States of America. Part I of this report presents an overview of the resources and potential supply of niobium and tantalum based on inventory information; Part II contains tables of both geologic and mineral-resource information and includes production data collected by ISMI participants. Niobium is used principally as an alloying element in special steels and superalloys, and tantalum is used mainly in electronics. Minerals in the columbite-tantalite series are principal ore minerals of niobium and tantalum. Pyrochlore is a principal source of niobium. These minerals are found in carbonatite, certain rocks in alkaline igneous complexes, pegmatite, and placer deposits. ISMI estimates show that there are over 7 million metric tons of niobium and almost 0.5 million metric tons of tantalum in known deposits, outside of China and the former Soviet Union, for which reliable estimates have been made. Brazilian deposits, followed by Canadian deposits, contain by far the largest source of niobium. Tantalum production is spread widely among several countries, and Brazil and Canada are the most significant of these producers. Brazil's position is further strengthened by potential byproduct columbite from tin mining. Present economically exploitable resources of niobium appear to be sufficient for the near future, but Brazil will continue to be the predominant world supplier of ferrocolumbium. Tantalum, a byproduct of tin production, has been captive to the fluctuations of that market, but resources in pegmatite in Canada and Australia make it likely that future increases in the present modest demand will be met.

Evaluation of a recycling process for printed circuit board by physical separation and heat treatment.

PubMed

Fujita, Toyohisa; Ono, Hiroyuki; Dodbiba, Gjergj; Yamaguchi, Kunihiko

2014-07-01

Printed circuit boards (PCBs) from discarded personal computer (PC) and hard disk drive were crushed by explosion in water or mechanical comminution in order to disintegrate the attached parts. More parts were stripped from PCB of PC, composed of epoxy resin; than from PCB of household appliance, composed of phenol resin. In an attempt to raise the copper grade of PCB by removing other components, a carbonization treatment was investigated. The crushed PCB without surface-mounted parts was carbonized under a nitrogen atmosphere at 873-1073 K. After screening, the char was classified by size into oversized pieces, undersized pieces and powder. The copper foil and glass fiber pieces were liberated and collected in undersized fraction. The copper foil was liberated easily from glass fiber by stamping treatment. As one of the mounted parts, the multi-layered ceramic capacitors (MLCCs), which contain nickel, were carbonized at 873 K. The magnetic separation is carried out at a lower magnetic field strength of 0.1T and then at 0.8 T. In the +0.5mm size fraction the nickel grade in magnetic product was increased from 0.16% to 6.7% and the nickel recovery is 74%. The other useful mounted parts are tantalum capacitors. The tantalum capacitors were collected from mounted parts. The tantalum-sintered bodies were separated from molded resins by heat treatment at 723-773 K in air atmosphere and screening of 0.5mm. Silica was removed and 70% of tantalum grade was obtained after more than 823K heating and separation. Next, the evaluation of Cu recycling in PCB is estimated. Energy consumption of new process increased and the treatment cost becomes 3 times higher comparing the conventional process, while the environmental burden of new process decreased comparing conventional process. The nickel recovery process in fine ground particles increased energy and energy cost comparing those of the conventional process. However, the environmental burden decreased than the conventional one. The process for recovering tantalum used more heat for the treatment and therefore the energy consumption increased by 50%, when comparing with conventional process. However, the market price for tantalum is very large; the profit for tantalum recovery is added. Also the environmental burden decreased by the recycling of tantalum recovery. Therefore, the tantalum recovery is very important step in the PCB recycling. If there is no tantalum, the consumed energy and treatment cost increase in the new process, though the environmental burden decreases. Copyright © 2014 Elsevier Ltd. All rights reserved.

Development and characterization of ultrathin hafnium titanates as high permittivity gate insulators

NASA Astrophysics Data System (ADS)

Li, Min

High permittivity or high-kappa materials are being developed for use as gate insulators for future ultrascaled metal oxide semiconductor field effect transistors (MOSFETs). Hafnium containing compounds are the leading candidates. Due to its moderate permittivity, however, it is difficult to achieve HfO2 gate structures with an EOT well below 1.0 nm. One approach to increase HfO2 permittivity is combining it with a very high-kappa material, such as TiO2. In this thesis, we systematically studied the electrical and physical characteristics of high-kappa hafnium titanates films as gate insulators. A series of HfxTi1-xO2 films with well-controlled composition were deposited using an MOCVD system. The physical properties of the films were analyzed using a variety of characterization techniques. X-ray micro diffraction indicates that the Ti-rich thin film is more immune to crystallization. TEM analysis showed that the thick stoichiometric HfTiO 4 film has an orthorhombic structure and large anisotropic grains. The C-V curves from the devices with the hafnium titanates films displayed relatively low hysteresis. In a certain composition range, the interfacial layer (IL) EOT and permittivity of HfxTi1-x O2 increases linearly with increasing Ti. The charge is negative for HfxTi1-xO2/IL and positive for Si/IL interface, and the magnitude increases as Hf increases. For ultra-thin films (less than 2 nm EOT), the leakage current increases with increasing HE Moreover, the Hf-rich sample has weaker temperature dependence of the current. In the MOSFET devices with the hafnium titanates films, normal transistor characteristics were observed, also electron mobility degradation. Next, we investigated the effects that different pre-deposition surface treatments, including HF dipping, NH3 surface nitridation, and HfO2 deposition, have on the electrical properties of hafnium titanates. Surface nitridation shows stronger effect than the thin HfO2 layer. The nitrided samples displayed a negative flat band voltage shift and larger hysteresis relative to the HF-dipped samples. The IL EOT reduction by mtridation increases with increasing HE Surface nitridation also induces extra charge, more considerable at the Si/IL interface. The leakage current is reduced in the Hf-rich samples with a nitride layer. Electron mobility degradation by surface nitridation was also observed.

Corrosion resistance of porous binary tantalum and titanium carbides of various composition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Artyunina, N.P.; Komratov, G.N.; Bolonova, E.A.

1993-12-20

Resistance of porous binary tantalum and titanium carbides in solutions of mineral acids and their mixtures, of several organic acids, and of ammonium and potassium hydroxide was studied. It has been shown that as the content of tantalum in a material increases its resistance in solutions of oxidizing acids is improved, but it is reduced in solutions of sulfuric and hydrofluoric acids and also in solutions of potassium hydroxide.

CONTRIBUTION TO THE GEOCHEMISTRY OF TANTALUM AND NIOBIUM IN THE HYDROTHERMAL-PNEUMATHOLYTIC PROCESS (in Russian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beus, A.A.; Sitnin, A.A.

1961-01-01

S>Data obtained as a result of geochemical investigations show that tantalum and niobium are typical elements of high-temperature postmagmatic processes (early albitization, greysening) connected with granites. The separation of tantalum and niobium in the hydrothermal-pneumatholytic process (greysening stage), which leads to the concentration of tantalum in albitized and greysenized granites (40 to 100 times compared to the average content in granites) is connected with the different mobility and stability of their acido- complex compounds (in particular fluor- and oxyfluorcomplexes), the existence of which in greysening solutions is suggested. A natural analogy in the behavior of both elements in the processesmore » of postmagmatic metasomatose in granites and granitic pegmatites is suggested. (tr-auth)« less

Separation of Zirconium and Hafnium: A Review

NASA Astrophysics Data System (ADS)

Xu, L.; Xiao, Y.; van Sandwijk, A.; Xu, Q.; Yang, Y.

Zirconium is an ideal material for nuclear reactors due to its low absorption cross-section for thermal neutrons, whereas the typically contained hafnium with strong neutron-absorption is very harmful for zirconium. This paper provides an overview of the processes for separating hafnium from zirconium. The separation processes are roughly classified into hydro- and pyrometallurgical routes. The current dominant zirconium production route involves pyrometallurgical ore cracking, multi-step hydrometallurgical liquid-liquid extraction for hafnium removal and the reduction of zirconium tetrachloride to the pure metal by the Kroll process. The lengthy hydrometallurgical Zr-Hf separation operations leads to high production cost, intensive labour and heavy environmental burden. Using a compact pyrometallurgical separation method can simplify the whole production flowsheet with a higher process efficiency. The known separation methods are discussed based on the following reaction features: redox characteristics, volatility, electrochemical properties and molten salt extraction. The commercially operating extractive distillation process is a significant advance in Zr-Hf separation technology but it suffers from high process maintenance cost. The recently developed new process based on molten salt-metal equilibrium for Zr-Hf separation shows a great potential for industrial application, which is compact for nuclear grade zirconium production starting from crude ore. In the present paper, the available separation technologies are compared. The advantages and disadvantages as well as future directions of research and development for nuclear grade zirconium production are discussed.

Aminopyridinate-FI hybrids, their hafnium and titanium complexes, and their application in the living polymerization of 1-hexene.

PubMed

Haas, Isabelle; Dietel, Thomas; Press, Konstantin; Kol, Moshe; Kempe, Rhett

2013-10-11

Based on two well-established ligand systems, the aminopyridinato (Ap) and the phenoxyimine (FI) ligand systems, new Ap-FI hybrid ligands were developed. Four different Ap-FI hybrid ligands were synthesized through a simple condensation reaction and fully characterized. The reaction of hafnium tetrabenzyl with all four Ap-FI hybrid ligands exclusively led to mono(Ap-FI) complexes of the type [(Ap-FI)HfBn2 ]. The ligands acted as tetradentate dianionic chelates. Upon activation with tris(pentafluorophenyl)borane, the hafnium-dibenzyl complexes led to highly active catalysts for the polymerization of 1-hexene. Ultrahigh molecular weights and extremely narrow polydispersities support the living nature of this polymerization process. A possible deactivation product of the hafnium catalysts was characterized by single-crystal X-ray analysis and is discussed. The coordination modes of these new ligands were studied with the help of model titanium complexes. The reaction of titanium(IV) isopropoxide with ligand 1 led to a mono(Ap-FI) complex, which showed the desired fac-mer coordination mode. Titanium (IV) isopropoxide reacted with ligand 4 to give a complex of the type [(ApH-FI)2 Ti(OiPr)2 ], which featured the ligand in its monoanionic form. The two titanium complexes were characterized by X-ray crystal-structure analysis. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The role of electronegativity on the extent of nitridation of group 5 metals as revealed by reactions of tantalum cluster cations with ammonia molecules.

PubMed

Arakawa, Masashi; Ando, Kota; Fujimoto, Shuhei; Mishra, Saurabh; Patwari, G Naresh; Terasaki, Akira

2018-05-10

Reactions of the free tantalum cation, Ta+, and tantalum cluster cations, Tan+ (n = 2-10), with ammonia are presented. The reaction of the monomer cation, Ta+, with two molecules of NH3 leads to the formation of TaN2H2+ along with release of two H2 molecules. The dehydrogenation occurs until the formal oxidation number of the tantalum atom reaches +5. On the other hand, all the tantalum cluster cations, Tan+, react with two molecules of NH3 and form TanN2+ with the release of three H2 molecules. Further exposure to ammonia showed that TanNmH+ and TanNm+ are produced through successive reactions; a pure nitride and three H2 molecules are formed for every other NH3 molecule. The nitridation occurred until the formal oxidation number of the tantalum atoms reaches +5 as in the case of TaN2H2+ in contrast to other group 5 elements, i.e., vanadium and niobium, which have been reported to produce nitrides with lower oxidation states. The present results on small gas-phase metal-nitride clusters show correlation with their bulk properties: tantalum is known to form bulk nitrides in the oxidation states of either +5 (Ta3N5) or +3 (TaN), whereas vanadium and niobium form nitrides in the oxidation state of +3 (VN and NbN). Along with DFT calculations, these findings reveal that nitridation is driven by the electron-donating ability of group 5 elements, i.e., electronegativity of the metal plays a key role in determining the composition of the metal nitrides.

High Atomic Number Contrast Media Offer Potential for Radiation Dose Reduction in Contrast-Enhanced Computed Tomography.

PubMed

Roessler, Ann-Christin; Hupfer, Martin; Kolditz, Daniel; Jost, Gregor; Pietsch, Hubertus; Kalender, Willi A

2016-04-01

Spectral optimization of x-ray computed tomography (CT) has led to substantial radiation dose reduction in contrast-enhanced CT studies using standard iodinated contrast media. The purpose of this study was to analyze the potential for further dose reduction using high-atomic-number elements such as hafnium and tungsten. As in previous studies, spectra were determined for which the patient dose necessary to provide a given contrast-to-noise ratio (CNR) is minimized. We used 2 different quasi-anthropomorphic phantoms representing the liver cross-section of a normal adult and an obese adult patient with the lateral widths of 360 and 460 mm and anterior-posterior heights of 200 and 300 mm, respectively. We simulated and measured on 2 different scanners with x-ray spectra from 80 to 140 kV and from 70 to 150 kV, respectively. We determined the contrast for iodine-, hafnium-, and tungsten-based contrast media, the noise, and 3-dimensional dose distributions at all available tube voltages by measurements and by simulations. The dose-weighted CNR was determined as optimization parameter. Simulations and measurements were in good agreement regarding their dependence on energy for all parameters investigated. Hafnium provided the best performance for normal and for obese patient phantoms, indicating a dose reduction potential of 30% for normal and 50% for obese patients at 120 kV compared with iodine; this advantage increased further with higher kV values. Dose-weighted CNR values for tungsten were always slightly below the hafnium results. Iodine proved to be the superior choice at voltage values of 80 kV and below. Hafnium and tungsten both seem to be candidates for contrast-medium-enhanced CT of normal and obese adult patients with strongly reduced radiation dose at unimpaired image quality. Computed tomography examinations of obese patients will decrease in dose for higher kV values.

Hafnium isotope evidence for a transition in the dynamics of continental growth 3.2 Gyr ago.

PubMed

Næraa, T; Scherstén, A; Rosing, M T; Kemp, A I S; Hoffmann, J E; Kokfelt, T F; Whitehouse, M J

2012-05-30

Earth's lithosphere probably experienced an evolution towards the modern plate tectonic regime, owing to secular changes in mantle temperature. Radiogenic isotope variations are interpreted as evidence for the declining rates of continental crustal growth over time, with some estimates suggesting that over 70% of the present continental crustal reservoir was extracted by the end of the Archaean eon. Patterns of crustal growth and reworking in rocks younger than three billion years (Gyr) are thought to reflect the assembly and break-up of supercontinents by Wilson cycle processes and mark an important change in lithosphere dynamics. In southern West Greenland numerous studies have, however, argued for subduction settings and crust growth by arc accretion back to 3.8 Gyr ago, suggesting that modern-day tectonic regimes operated during the formation of the earliest crustal rock record. Here we report in situ uranium-lead, hafnium and oxygen isotope data from zircons of basement rocks in southern West Greenland across the critical time period during which modern-like tectonic regimes could have initiated. Our data show pronounced differences in the hafnium isotope-time patterns across this interval, requiring changes in the characteristics of the magmatic protolith. The observations suggest that 3.9-3.5-Gyr-old rocks differentiated from a >3.9-Gyr-old source reservoir with a chondritic to slightly depleted hafnium isotope composition. In contrast, rocks formed after 3.2 Gyr ago register the first additions of juvenile depleted material (that is, new mantle-derived crust) since 3.9 Gyr ago, and are characterized by striking shifts in hafnium isotope ratios similar to those shown by Phanerozoic subduction-related orogens. These data suggest a transitional period 3.5-3.2 Gyr ago from an ancient (3.9-3.5 Gyr old) crustal evolutionary regime unlike that of modern plate tectonics to a geodynamic setting after 3.2 Gyr ago that involved juvenile crust generation by plate tectonic processes.

NON-CORROSIVE PLUTONIUM FUEL SYSTEMS

DOEpatents

Coffinberry, A.S.; Waber, J.T.

1962-10-23

An improved plutonium reactor liquid fuel is described for utilization in a nuclear reactor having a tantalum fuel containment vessel. The fuel consists of plutonium and a diluent such as iron, cobalt, nickel, cerium, cerium-- iron, cerium--cobalt, cerium--nickel, and cerium--copper, and an additive of carbon and silicon. The carbon and silicon react with the tantalum container surface to form a coating that is self-healing and prevents the corrosive action of liquid plutonium on the said tantalum container. (AEC)

Scintillation Breakdowns in Chip Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2008-01-01

Scintillations in solid tantalum capacitors are momentarily local breakdowns terminated by a self-healing or conversion to a high-resistive state of the manganese oxide cathode. This conversion effectively caps the defective area of the tantalum pentoxide dielectric and prevents short-circuit failures. Typically, this type of breakdown has no immediate catastrophic consequences and is often considered as nuisance rather than a failure. Scintillation breakdowns likely do not affect failures of parts under surge current conditions, and so-called "proofing" of tantalum chip capacitors, which is a controllable exposure of the part after soldering to voltages slightly higher than the operating voltage to verify that possible scintillations are self-healed, has been shown to improve the quality of the parts. However, no in-depth studies of the effect of scintillations on reliability of tantalum capacitors have been performed so far. KEMET is using scintillation breakdown testing as a tool for assessing process improvements and to compare quality of different manufacturing lots. Nevertheless, the relationship between failures and scintillation breakdowns is not clear, and this test is not considered as suitable for lot acceptance testing. In this work, scintillation breakdowns in different military-graded and commercial tantalum capacitors were characterized and related to the rated voltages and to life test failures. A model for assessment of times to failure, based on distributions of breakdown voltages, and accelerating factors of life testing are discussed.

Deformation of Cases in High Capacitance Value Wet Tantalum Capacitors under Environmental Stresses

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2016-01-01

Internal gas pressure in hermetic wet tantalum capacitors is created by air, electrolyte vapor, and gas generated by electrochemical reactions at the electrodes. This pressure increases substantially with temperature and time of operation due to excessive leakage currents. Deformation of the case occurs when the internal pressure exceeds pressure of the environments and can raise significantly when a part operates in space. Contrary to the cylinder case wet tantalum capacitors that have external sealing by welding and internal sealing provided by the Teflon bushing and crimping of the case, no reliable internal sealing exists in the button case capacitors. Single seal design capacitors are used for high capacitance value wet tantalum capacitors manufactured per DLA L&M drawings #04003, 04005, and 10011, and require additional analysis to assure their reliable application in space systems. In this work, leakage currents and case deformation of button case capacitors were measured during different environmental test conditions. Recommendations for derating, screening and qualification testing are given. This work is a continuation of a series of NEPP reports related to quality and reliability of wet tantalum capacitors.

Effect of Compressive Stresses on Leakage Currents in Microchip Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2012-01-01

Microchip tantalum capacitors are manufactured using new technologies that allow for production of small size capacitors (down to EIA case size 0402) with volumetric efficiency much greater than for regular chip capacitors. Due to a small size of the parts and leadless design they might be more sensitive to mechanical stresses that develop after soldering onto printed wiring boards (PWB) compared to standard chip capacitors. In this work, the effect of compressive stresses on leakage currents in capacitors has been investigated in the range of stresses up to 200 MPa. Significant, up to three orders of magnitude, variations of currents were observed after the stress exceeds a certain critical level that varied from 10 MPa to 180 MPa for capacitors used in this study. A stress-induced generation of electron traps in tantalum pentoxide dielectric is suggested to explain reversible variations of leakage currents in tantalum capacitors. Thermo-mechanical characteristics of microchip capacitors have been studied to estimate the level of stresses caused by assembly onto PWB and assess the risk of stress-related degradation and failures. Keywords: tantalum capacitors, leakage current, soldering, reliability, mechanical stress.

Niobium and tantalum: indispensable twins

USGS Publications Warehouse

Schulz, Klaus; Papp, John

2014-01-01

Niobium and tantalum are transition metals almost always paired together in nature. These “twins” are difficult to separate because of their shared physical and chemical properties. In 1801, English chemist Charles Hatchett uncovered an unknown element in a mineral sample of columbite; John Winthrop found the sample in a Massachusetts mine and sent it to the British Museum in London in 1734. The name columbium, which Hatchet named the new element, came from the poetic name for North America—Columbia—and was used interchangeably for niobium until 1949, when the name niobium became official. Swedish scientist Anders Ekberg discovered tantalum in 1802, but it was confused with niobium, because of their twinned properties, until 1864, when it was recognized as a separate element. Niobium is a lustrous, gray, ductile metal with a high melting point, relatively low density, and superconductor properties. Tantalum is a dark blue-gray, dense, ductile, very hard, and easily fabricated metal. It is highly conductive to heat and electricity and renowned for its resistance to acidic corrosion. These special properties determine their primary uses and make niobium and tantalum indispensable.

Effect of Temperature Cycling and Exposure to Extreme Temperatures on Reliability of Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2007-01-01

In this work, results of multiple temperature cycling (TC) (up to 1,000 cycles) of different types of solid tantalum capacitors are analyzed and reported. Deformation of chip tantalum during temperature variations simulating reflow soldering conditions was measured to evaluate the possibility of the pop-corning effect in the parts. To simulate the effect of short-time exposures to solder reflow temperatures on the reliability of tantalum capacitors, several part types were subjected to multiple cycles (up to 100) between room temperature and 240 C with periodical measurements of electrical characteristics of the parts. Mechanisms of degradation caused by temperature cycling and exposure to high temperatures, and the requirements of MIL-PRF-55365 for assessment of the resistance of the parts to soldering heat are discussed.

Thermocouples of tantalum and rhenium alloys for more stable vacuum-high temperature performance

NASA Technical Reports Server (NTRS)

Morris, J. F. (Inventor)

1977-01-01

Thermocouples of the present invention provide stability and performance reliability in systems involving high temperatures and vacuums by employing a bimetallic thermocouple sensor wherein each metal of the sensor is selected from a group of metals comprising tantalum and rhenium and alloys containing only those two metals. The tantalum, rhenium thermocouple sensor alloys provide bare metal thermocouple sensors having advantageous vapor pressure compatibilities and performance characteristics. The compatibility and physical characteristics of the thermocouple sensor alloys of the present invention result in improved emf, temperature properties and thermocouple hot junction performance. The thermocouples formed of the tantalum, rhenium alloys exhibit reliability and performance stability in systems involving high temperatures and vacuums and are adaptable to space propulsion and power systems and nuclear environments.

Dosimetric measurements of an n-butyl cyanoacrylate embolization material for arteriovenous malformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Labby, Zacariah E., E-mail: zelabby@humonc.wisc.edu; Chaudhary, Neeraj; Gemmete, Joseph J.

2015-04-15

Purpose: The therapeutic regimen for cranial arteriovenous malformations often involves both stereotactic radiosurgery and endovascular embolization. Embolization agents may contain tantalum or other contrast agents to assist the neurointerventionalists, leading to concerns regarding the dosimetric effects of these agents. This study investigated dosimetric properties of n-butyl cyanoacrylate (n-BCA) plus lipiodol with and without tantalum powder. Methods: The embolization agents were provided cured from the manufacturer with and without added tantalum. Attenuation measurements were made for the samples and compared to the attenuation of a solid water substitute using a 6 MV photon beam. Effective linear attenuation coefficients (ELAC) were derivedmore » from attenuation measurements made using a portal imager and derived sample thickness maps projected in an identical geometry. Probable dosimetric errors for calculations in which the embolized regions are overridden with the properties of water were calculated using the ELAC values. Interface effects were investigated using a parallel plate ion chamber placed at set distances below fixed samples. Finally, Hounsfield units (HU) were measured using a stereotactic radiosurgery CT protocol, and more appropriate HU values were derived from the ELAC results and the CT scanner’s HU calibration curve. Results: The ELAC was 0.0516 ± 0.0063 cm{sup −1} and 0.0580 ± 0.0091 cm{sup −1} for n-BCA without and with tantalum, respectively, compared to 0.0487 ± 0.0009 cm{sup −1} for the water substitute. Dose calculations with the embolized region set to be water equivalent in the treatment planning system would result in errors of −0.29% and −0.93% per cm thickness of n-BCA without and with tantalum, respectively. Interface effects compared to water were small in magnitude and limited in distance for both embolization materials. CT values at 120 kVp were 2082 and 2358 HU for n-BCA without and with tantalum, respectively; dosimetrically appropriate HU values were estimated to be 79 and 199 HU, respectively. Conclusions: The dosimetric properties of the embolization agents are very close to those of water for a 6 MV beam. Therefore, treating the entire intracranial space as uniform in composition will result in less than 1% dosimetric error for n-BCA emboli smaller than 3.4 cm without added tantalum and n-BCA emboli smaller than 1.1 cm with added tantalum. Furthermore, when effective embolization can be achieved by the neurointerventionalist using n-BCA without tantalum, the dosimetric impact of overriding material properties will be lessened. However, due to the high attenuation of embolization agents with and without added tantalum for diagnostic energies, artifacts may occur that necessitate additional imaging to accurately identify the spatial extent of the region to be treated.« less

Extreme Response in Tension and Compression of Tantalum

NASA Astrophysics Data System (ADS)

Remington, Tane Perry

This research on a model bcc metal, tantalum, has three components: the study of tensile failure; defects generated under a nanoindenter; and dislocation velocities in an extreme regime generated by pulsed lasers. The processes of dynamic failure by spalling were established in nano, poly, and mono crystalline tantalum in recovery experiments following laser compression and release. The process of spall was characterized by different techniques: optical microscopy, scanning electron microscopy, microcomputerized tomography and electron backscatter diffraction. Additionally, the pull back signal was measured by VISAR and the pressure decay was compared with HYADES simulations. There are clear differences in the microscopic fracture mechanisms, dictated by the grain sizes. In the nano and poly crystals, spalling occurred by ductile fracture favoring grain boundaries. In the monocrystals, grain boundaries are absent, and the process was of ductile failure by void initiation, growth and coalescence. The spall strength of single crystalline tantalum was higher than the poly and nano crystals. It was experimentally confirmed that spall strength in tantalum increases with strain rate. In order to generate dislocations close to the surface, single crystalline tantalum with orientations (100), (110) and (111) was nanoindented with a Berkovich tip. Atomic force microscopy showed pile-ups of dislocations around the perimeter of the nanoindentations. Sections of nanoindentations were focused ion beam cut into transmission electron microscope foils. The mechanisms of deformation under a nanoindentation in tantalum were identified and quantified. Molecular dynamics simulations were conducted and the simulated plastic deformation proceeds by the formation of nanotwins, which rapidly evolve into shear dislocation loops. Dislocation densities under the indenter were estimated experimentally (~1.2 x 1015 m-2), by MD (~7 x1015 m-2) and through an analytical calculation (2.6--19 x10 15 m-2). Considering the assumptions and simplifications, this agreement is considered satisfactory. These indented crystals were subjected to shock compression and the results are being analyzed with the objective of establishing the velocities of dislocations. A novel technique to establish dislocation velocities is being tested. It consists of subjecting tantalum containing a matrix of nanoindentations to shock compression for post shock characterization enabling the determination of mean dislocation displacements.

Hybrid nuclear reactor grey rod to obtain required reactivity worth

DOEpatents

Miller, John V.; Carlson, William R.; Yarbrough, Michael B.

1991-01-01

Hybrid nuclear reactor grey rods are described, wherein geometric combinations of relatively weak neutron absorber materials such as stainless steel, zirconium or INCONEL, and relatively strong neutron absorber materials, such as hafnium, silver-indium cadmium and boron carbide, are used to obtain the reactivity worths required to reach zero boron change load follow. One embodiment includes a grey rod which has combinations of weak and strong neutron absorber pellets in a stainless steel cladding. The respective pellets can be of differing heights. A second embodiment includes a grey rod with a relatively thick stainless steel cladding receiving relatively strong neutron absorber pellets only. A third embodiment includes annular relatively weak netron absorber pellets with a smaller diameter pellet of relatively strong absorber material contained within the aperture of each relatively weak absorber pellet. The fourth embodiment includes pellets made of a homogeneous alloy of hafnium and a relatively weak absorber material, with the percentage of hafnium chosen to obtain the desired reactivity worth.

Evaluation of T-111 forced-convection loop tested with lithium at 1370 C. [free convection

NASA Technical Reports Server (NTRS)

Devan, J. H.; Long, E. L., Jr.

1975-01-01

A T-111 alloy (Ta-8% W-2% Hf) forced-convection loop containing molten lithium was operated 3000 hr at a maximum temperature of 1370 C. Flow velocities up to 6.3 m/sec were used, and the results of this forced-convection loop are very similar to those observed in lower velocity thermal-convection loops of T-111 containing lithium. Weight changes were determined at 93 positions around the loop. The maximum dissolution rate occurred at the maximum wall temperature of the loop and was less than 1.3 microns/year. Mass transfer of hafnium, nitrogen, and, to a lesser extent, carbon occurred from the hotter to cooler regions. Exposed surfaces in the highest temperature region were found to be depleted in hafnium to a depth of 60 microns with no detectable change in tungsten content. There was some loss in room-temperature tensile strength for specimens exposed to lithium at 1370 C, attributable to depletion of hafnium and nitrogen and to attendant grain growth.

Self-cleaning and surface chemical reactions during hafnium dioxide atomic layer deposition on indium arsenide.

PubMed

Timm, Rainer; Head, Ashley R; Yngman, Sofie; Knutsson, Johan V; Hjort, Martin; McKibbin, Sarah R; Troian, Andrea; Persson, Olof; Urpelainen, Samuli; Knudsen, Jan; Schnadt, Joachim; Mikkelsen, Anders

2018-04-12

Atomic layer deposition (ALD) enables the ultrathin high-quality oxide layers that are central to all modern metal-oxide-semiconductor circuits. Crucial to achieving superior device performance are the chemical reactions during the first deposition cycle, which could ultimately result in atomic-scale perfection of the semiconductor-oxide interface. Here, we directly observe the chemical reactions at the surface during the first cycle of hafnium dioxide deposition on indium arsenide under realistic synthesis conditions using photoelectron spectroscopy. We find that the widely used ligand exchange model of the ALD process for the removal of native oxide on the semiconductor and the simultaneous formation of the first hafnium dioxide layer must be significantly revised. Our study provides substantial evidence that the efficiency of the self-cleaning process and the quality of the resulting semiconductor-oxide interface can be controlled by the molecular adsorption process of the ALD precursors, rather than the subsequent oxide formation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodenbücher, C.; Hildebrandt, E.; Sharath, S. U.

On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO{sub 2−x}) contaminated with adsorbates of carbon oxides, the formation of hafnium carbide (HfC{sub x}) at the surface during vacuum annealing at temperatures as low as 600 °C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfC{sub x} surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO{sub 2} thin films prepared and measured under identical conditions, the formation of HfC{sub x} was not detectable suggesting that the enhanced adsorption of carbon oxides on oxygen deficient films providesmore » a carbon source for the carbide formation. This shows that a high concentration of oxygen vacancies in carbon contaminated hafnia lowers considerably the formation energy of hafnium carbide. Thus, the presence of a sufficient amount of residual carbon in resistive random access memory devices might lead to a similar carbide formation within the conducting filaments due to Joule heating.« less

Effect of Reverse Bias Stress on Leakage Currents and Breakdown Voltages of Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander A.

2011-01-01

The majority of solid tantalum capacitors are produced by high-temperature sintering of a fine tantalum powder around a tantalum wire followed by electrolytic anodization that forms a thin amorphous Ta2O5 dielectric layer and pyrolysis of manganese nitrite on the oxide to create a conductive manganese dioxide electrode. A contact to tantalum wire is used as anode terminal and to the manganese layer as a cathode terminal of the device. This process results in formation of an asymmetric Ta -- Ta2O5 -- MnO2 capacitor that has different characteristics at forward (positive bias applied to tantalum) and reverse (positive bias applied to manganese cathode) voltages. Reverse bias currents might be several orders of magnitude larger than forward leakage currents so I-V characteristics of tantalum capacitors resemble characteristics of semiconductor rectifiers. Asymmetric I-V characteristics of Ta -- anodic Ta2O5 systems have been observed at different top electrode materials including metals, electrolytes, conductive polymers, and manganese oxide thus indicating that this phenomenon is likely related to the specifics of the Ta -- Ta2O5 interface. There have been multiple attempts to explain rectifying characteristics of capacitors employing anodic tantalum pentoxide dielectrics. A brief review of works related to reverse bias (RB) behavior of tantalum capacitors shows that the mechanism of conduction in Ta -- Ta2O5 systems is still not clear and more testing and analysis is necessary to understand the processes involved. If tantalum capacitors behave just as rectifiers, then the assessment of the safe reverse bias operating conditions would be a relatively simple task. Unfortunately, these parts can degrade with time under reverse bias significantly, and this further complicates analysis of the I-V characteristics and establishing safe operating areas of the parts. On other hand, time dependence of reverse currents might provide additional information for investigation of the processes under reverse bias conditions. In practice, there were instances when, due to unforeseen events, the system operated at conditions when capacitors experience periodically a relatively small reverse bias for some time followed by normal, forward bias conditions. In such a case an assessment should be made on the degree to which these capacitors are degraded by application of low-voltage reverse bias, and whether this degradation can be reversed by normal operating conditions. In this study, reverse currents in different types of tantalum capacitors were monitored at different reverse voltages below 15%VR and temperatures in the range from room to 145 C for up to 150 hours to get better understanding of the degradation process and determine conditions favorable to the unstable mode of operation. The reversibility of RB degradation has been evaluated after operation of the capacitors at forward bias conditions. The effect of reverse bias stress (RBS) on reliability at normal operating conditions was evaluated using highly accelerated life testing at voltages of 1.5VR and 2 VR and by analysis of changes in distributions of breakdown voltages. Possible mechanisms of RB degradation are discussed.

Evaluation of a recycling process for printed circuit board by physical separation and heat treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujita, Toyohisa, E-mail: tfujita@sys.t.u-tokyo.ac.jp; Ono, Hiroyuki; Dodbiba, Gjergj

Highlights: • The parts mounted on printed circuit board (PCB) were liberated by underwater explosion and mechanical crushing. • The crushed PCB without surface-mounted parts was carbonized under inert atmosphere at 873 K to recover copper. • The multi-layered ceramic capacitors including nickel was carbonized at 873 K to recover nickel by the magnetic separation. • The tantalum powders were recovered from the molded resins by heat treatment at 723 and 823 K in air atmosphere and screening. • Energy and treatment cost of new process increased, however, the environmental burden decreased comparing conventional one. - Abstract: Printed circuit boardsmore » (PCBs) from discarded personal computer (PC) and hard disk drive were crushed by explosion in water or mechanical comminution in order to disintegrate the attached parts. More parts were stripped from PCB of PC, composed of epoxy resin; than from PCB of household appliance, composed of phenol resin. In an attempt to raise the copper grade of PCB by removing other components, a carbonization treatment was investigated. The crushed PCB without surface-mounted parts was carbonized under a nitrogen atmosphere at 873–1073 K. After screening, the char was classified by size into oversized pieces, undersized pieces and powder. The copper foil and glass fiber pieces were liberated and collected in undersized fraction. The copper foil was liberated easily from glass fiber by stamping treatment. As one of the mounted parts, the multi-layered ceramic capacitors (MLCCs), which contain nickel, were carbonized at 873 K. The magnetic separation is carried out at a lower magnetic field strength of 0.1 T and then at 0.8 T. In the +0.5 mm size fraction the nickel grade in magnetic product was increased from 0.16% to 6.7% and the nickel recovery is 74%. The other useful mounted parts are tantalum capacitors. The tantalum capacitors were collected from mounted parts. The tantalum-sintered bodies were separated from molded resins by heat treatment at 723–773 K in air atmosphere and screening of 0.5 mm. Silica was removed and 70% of tantalum grade was obtained after more than 823 K heating and separation. Next, the evaluation of Cu recycling in PCB is estimated. Energy consumption of new process increased and the treatment cost becomes 3 times higher comparing the conventional process, while the environmental burden of new process decreased comparing conventional process. The nickel recovery process in fine ground particles increased energy and energy cost comparing those of the conventional process. However, the environmental burden decreased than the conventional one. The process for recovering tantalum used more heat for the treatment and therefore the energy consumption increased by 50%, when comparing with conventional process. However, the market price for tantalum is very large; the profit for tantalum recovery is added. Also the environmental burden decreased by the recycling of tantalum recovery. Therefore, the tantalum recovery is very important step in the PCB recycling. If there is no tantalum, the consumed energy and treatment cost increase in the new process, though the environmental burden decreases.« less

Experimental Observations of Nuclear Activity in Deuterated Materials Subjected to a Low-Energy Photon Beam

NASA Technical Reports Server (NTRS)

Steinetz, Bruce M.; Benyo, Theresa L.; Pines, Vladimir; Pines, Marianna; Forsley, Lawrence P.; Westmeyer, Paul A.; Chait, Arnon; Becks, Michael D.; Martin, Richard E.; Hendricks, Robert C.;

Metallic glass alloys of Zr, Ti, Cu and Ni

DOEpatents

Lin, X.; Peker, A.; Johnson, W.L.

1997-04-08

At least quaternary alloys form metallic glass upon cooling below the glass transition temperature at a rate less than 10{sup 3} K/s. Such alloys comprise titanium from 19 to 41 atomic percent, an early transition metal (ETM) from 4 to 21 atomic percent and copper plus a late transition metal (LTM) from 49 to 64 atomic percent. The ETM comprises zirconium and/or hafnium. The LTM comprises cobalt and/or nickel. The composition is further constrained such that the product of the copper plus LTM times the atomic proportion of LTM relative to the copper is from 2 to 14. The atomic percentage of ETM is less than 10 when the atomic percentage of titanium is as high as 41, and may be as large as 21 when the atomic percentage of titanium is as low as 24. Furthermore, when the total of copper and LTM are low, the amount of LTM present must be further limited. Another group of glass forming alloys has the formula (ETM{sub 1{minus}x}Ti{sub x}){sub a} Cu{sub b} (Ni{sub 1{minus}y}Co{sub y}){sub c} wherein x is from 0.1 to 0.3, y{center_dot}c is from 0 to 18, a is from 47 to 67, b is from 8 to 42, and c is from 4 to 37. This definition of the alloys has additional constraints on the range of copper content, b. 2 figs.

Metallic glass alloys of Zr, Ti, Cu and Ni

DOEpatents

Lin, Xianghong; Peker, Atakan; Johnson, William L.

1997-01-01

At least quaternary alloys form metallic glass upon cooling below the glass transition temperature at a rate less than 10.sup.3 K/s. Such alloys comprise titanium from 19 to 41 atomic percent, an early transition metal (ETM) from 4 to 21 atomic percent and copper plus a late transition metal (LTM) from 49 to 64 atomic percent. The ETM comprises zirconium and/or hafnium. The LTM comprises cobalt and/or nickel. The composition is further constrained such that the product of the copper plus LTM times the atomic proportion of LTM relative to the copper is from 2 to 14. The atomic percentage of ETM is less than 10 when the atomic percentage of titanium is as high as 41, and may be as large as 21 when the atomic percentage of titanium is as low as 24. Furthermore, when the total of copper and LTM are low, the amount of LTM present must be further limited. Another group of glass forming alloys has the formula (ETM.sub.1-x Ti.sub.x).sub.a Cu.sub.b (Ni.sub.1-y Co.sub.y).sub.c wherein x is from 0.1 to 0.3, y.cndot.c is from 0 to 18, a is from 47 to 67, b is from 8 to 42, and c is from 4 to 37. This definition of the alloys has additional constraints on the range of copper content, b.

40 CFR 421.284 - Standards of performance for new sources.

Code of Federal Regulations, 2010 CFR

2010-07-01

... for monthly average mg/kg (pounds per million pounds) of tantalum powder produced from leaching Copper... all times. (e) Leaching wet air pollution control. NSPS for the Secondary Tantalum Subcategory...

40 CFR 421.284 - Standards of performance for new sources.

Code of Federal Regulations, 2013 CFR

2013-07-01

... for monthly average mg/kg (pounds per million pounds) of tantalum powder produced from leaching Copper... all times. (e) Leaching wet air pollution control. NSPS for the Secondary Tantalum Subcategory...

40 CFR 421.284 - Standards of performance for new sources.

Code of Federal Regulations, 2014 CFR

2014-07-01

... for monthly average mg/kg (pounds per million pounds) of tantalum powder produced from leaching Copper... all times. (e) Leaching wet air pollution control. NSPS for the Secondary Tantalum Subcategory...

40 CFR 421.284 - Standards of performance for new sources.

Code of Federal Regulations, 2012 CFR

2012-07-01

... for monthly average mg/kg (pounds per million pounds) of tantalum powder produced from leaching Copper... all times. (e) Leaching wet air pollution control. NSPS for the Secondary Tantalum Subcategory...

40 CFR 421.284 - Standards of performance for new sources.

Code of Federal Regulations, 2011 CFR

2011-07-01

... for monthly average mg/kg (pounds per million pounds) of tantalum powder produced from leaching Copper... all times. (e) Leaching wet air pollution control. NSPS for the Secondary Tantalum Subcategory...

Clustering of transmutation elements tantalum, rhenium and osmium in tungsten in a fusion environment

NASA Astrophysics Data System (ADS)

You, Yu-Wei; Kong, Xiang-Shan; Wu, Xuebang; Liu, C. S.; Fang, Q. F.; Chen, J. L.; Luo, G.-N.

2017-08-01

The formation of transmutation solute-rich precipitates has been reported to seriously degrade the mechanical properties of tungsten in a fusion environment. However, the underlying mechanisms controlling the formation of the precipitates are still unknown. In this study, first-principles calculations are therefore performed to systemically determine the stable structures and binding energies of solute clusters in tungsten consisting of tantalum, rhenium and osmium atoms as well as irradiation-induced vacancies. These clusters are known to act as precursors for the formation of precipitates. We find that osmium can easily segregate to form clusters even in defect-free tungsten alloys, whereas extremely high tantalum and rhenium concentrations are required for the formation of clusters. Vacancies greatly facilitate the clustering of rhenium and osmium, while tantalum is an exception. The binding energies of vacancy-osmium clusters are found to be much higher than those of vacancy-tantalum and vacancy-rhenium clusters. Osmium is observed to strongly promote the formation of vacancy-rhenium clusters, while tantalum can suppress the formation of vacancy-rhenium and vacancy-osmium clusters. The local strain and electronic structure are analyzed to reveal the underlying mechanisms governing the cluster formation. Employing the law of mass action, we predict the evolution of the relative concentration of vacancy-rhenium clusters. This work presents a microscopic picture describing the nucleation and growth of solute clusters in tungsten alloys in a fusion reactor environment, and thereby explains recent experimental phenomena.

Small rocket research and technology

NASA Technical Reports Server (NTRS)

Schneider, Steven; Biaglow, James

1993-01-01

Small chemical rockets are used on nearly all space missions. The small rocket program provides propulsion technology for civil and government space systems. Small rocket concepts are developed for systems which encompass reaction control for launch and orbit transfer systems, as well as on-board propulsion for large space systems and earth orbit and planetary spacecraft. Major roles for on-board propulsion include apogee kick, delta-V, de-orbit, drag makeup, final insertions, north-south stationkeeping, orbit change/trim, perigee kick, and reboost. The program encompasses efforts on earth-storable, space storable, and cryogenic propellants. The earth-storable propellants include nitrogen tetroxide (NTO) as an oxidizer with monomethylhydrazine (MMH) or anhydrous hydrazine (AH) as fuels. The space storable propellants include liquid oxygen (LOX) as an oxidizer with hydrazine or hydrocarbons such as liquid methane, ethane, and ethanol as fuels. Cryogenic propellants are LOX or gaseous oxygen (GOX) as oxidizers and liquid or gaseous hydrogen as fuels. Improved performance and lifetime for small chemical rockets are sought through the development of new predictive tools to understand the combustion and flow physics, the introduction of high temperature materials to eliminate fuel film cooling and its associated combustion inefficiency, and improved component designs to optimize performance. Improved predictive technology is sought through the comparison of both local and global predictions with experimental data. Results indicate that modeling of the injector and combustion process in small rockets needs improvement. High temperature materials require the development of fabrication processes, a durability data base in both laboratory and rocket environments, and basic engineering property data such as strength, creep, fatigue, and work hardening properties at both room and elevated temperature. Promising materials under development include iridium-coated rhenium and a ceramic composite of mixed hafnium carbide and tantalum carbide reinforced with graphite fibers.

Solid state consolidation nanocrystalline copper-tungsten using cold spray

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hall, Aaron Christopher; Sarobol, Pylin; Argibay, Nicolas

It is well known that nanostructured metals can exhibit significantly improved properties compared to metals with conventional grain size. Unfortunately, nanocrystalline metals typically are not thermodynamically stable and exhibit rapid grain growth at moderate temperatures. This severely limits their processing and use, making them impractical for most engineering applications. Recent work has shown that a number of thermodynamically stable nanocrystalline metal alloys exist. These alloys have been prepared as powders using severe plastic deformation (e.g. ball milling) processes. Consolidation of these powders without compromise of their nanocrystalline microstructure is a critical step to enabling their use as engineering materials. Wemore » demonstrate solid-state consolidation of ball milled copper-tantalum nanocrystalline metal powder using cold spray. Unfortunately, the nanocrystalline copper-tantalum powder that was consolidated did not contain the thermodynamically stable copper-tantalum nanostructure. Nevertheless, this does this demonstrates a pathway to preparation of bulk thermodynamically stable nanocrystalline copper-tantalum. Furthermore, it demonstrates a pathway to additive manufacturing (3D printing) of nanocrystalline copper-tantalum. Additive manufacturing of thermodynamically stable nanocrystalline metals is attractive because it enables maximum flexibility and efficiency in the use of these unique materials.« less

A niobium oxide-tantalum oxide selector-memristor self-aligned nanostack

NASA Astrophysics Data System (ADS)

Diaz Leon, Juan J.; Norris, Kate J.; Yang, J. Joshua; Sevic, John F.; Kobayashi, Nobuhiko P.

2017-03-01

The integration of nonlinear current-voltage selectors and bi-stable memristors is a paramount step for reliable operation of crossbar arrays. In this paper, the self-aligned assembly of a single nanometer-scale device that contains both a selector and a memristor is presented. The two components (i.e., selector and memristor) are vertically assembled via a self-aligned fabrication process combined with electroforming. In designing the device, niobium oxide and tantalum oxide are chosen as materials for selector and memristor, respectively. The formation of niobium oxide is visualized by exploiting the self-limiting reaction between niobium and tantalum oxide; crystalline niobium (di)oxide forms at the interface between metallic niobium and tantalum oxide via electrothermal heating, resulting in a niobium oxide selector self-aligned to a tantalum oxide memristor. A steady-state finite element analysis is used to assess the electrothermal heating expected to occur in the device. Current-voltage measurements and structural/chemical analyses conducted for the virgin device, the electroforming process, and the functional selector-memristor device are presented. The demonstration of a self-aligned, monolithically integrated selector-memristor device would pave a practical pathway to various circuits based on memristors attainable at manufacturing scales.

The preparation of tantalum powder using a MR-EMR combination process

NASA Astrophysics Data System (ADS)

Yoon, Jae Sik; Kim, Byung Il

2007-04-01

In the conventional metallothermic reduction (MR) process used to obtain tantalum powder in batch-type operation, it is difficult to control the morphology and location of the tantalum deposits. In contrast, an electronically mediated reaction (EMR) process is capable of overcoming this difficulty. It has the advantage of being a continuous process, but has the disadvantage of a poor reduction yield. A process known as the MR-EMR combination process is able to overcome the shortcomings of the MR and EMR processes. In this study, an MR-EMR combination process is applied to the production of tantalum powder via sodium reduction of K2TaF7. In the MR-EMR combination process, the total charge passed through an external circuit and the average particle size (FSSS) increase as the reduction temperature increases. In addition, the proportion of fine particles (-325 mesh) decreases as the reduction temperature increasess. The tantalum yield improved from 65 to 74% as the reduction temperature increased. Taking into account the charge, impurities, morphology, particle size and yield, a reduction temperature of 1123 K was found to be optimum for the MR-EMR combination process.

Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

NASA Astrophysics Data System (ADS)

Jakubowicz, J.; Adamek, G.; Sopata, M.; Koper, J. K.; Siwak, P.

2017-12-01

The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.

The structure, bond strength and apatite-inducing ability of micro-arc oxidized tantalum and their response to annealing

NASA Astrophysics Data System (ADS)

Wang, Cuicui; Wang, Feng; Han, Yong

2016-01-01

In this study, the tantalum oxide coatings were formed on pure tantalum (Ta) by micro-arc oxidation (MAO) in electrolytic solutions of calcium acetate and β-glycerophosphate disodium, and the effect of the applied voltage on the microstructure and bond strength of the MAO coatings was systematically investigated. The effect of annealing treatment on the microstructure, bond strength and apatite-inducing ability of the MAO coatings formed at 350 and 450 V was also studied. The study revealed that during the preparation of tantalum oxide coatings on Ta substrate by MAO, the applied voltage considerably affected the phase components, morphologies and bond strength of the coatings, but had little effect on surface chemical species. After annealing treatment, newly formed CaTa4O11 phase mainly contributed to the much more stronger apatite-inducing ability of the annealed tantalum oxide coatings than those that were not annealed. The better apatite-inducing ability of the MAO coatings formed at 450 V compared to those formed at 350 V was attributed to the less amorphous phase and more crystalline phase as well as more Ca and P contained in the MAO coatings with increasing the applied voltage.

40 CFR 421.286 - Pretreatment standards for new sources.

Code of Federal Regulations, 2010 CFR

2010-07-01

... per million pounds) of tantalum powder produced from leaching Copper 25.860 12.320 Lead 5.656 2.626...) Leaching wet air pollution control. PSNS for the Secondary Tantalum Subcategory Pollutant or pollutant...

40 CFR 421.286 - Pretreatment standards for new sources.

Code of Federal Regulations, 2014 CFR

2014-07-01

... per million pounds) of tantalum powder produced from leaching Copper 25.860 12.320 Lead 5.656 2.626...) Leaching wet air pollution control. PSNS for the Secondary Tantalum Subcategory Pollutant or pollutant...

40 CFR 421.286 - Pretreatment standards for new sources.

Code of Federal Regulations, 2012 CFR

2012-07-01

... per million pounds) of tantalum powder produced from leaching Copper 25.860 12.320 Lead 5.656 2.626...) Leaching wet air pollution control. PSNS for the Secondary Tantalum Subcategory Pollutant or pollutant...

40 CFR 421.286 - Pretreatment standards for new sources.

Code of Federal Regulations, 2013 CFR

2013-07-01

... per million pounds) of tantalum powder produced from leaching Copper 25.860 12.320 Lead 5.656 2.626...) Leaching wet air pollution control. PSNS for the Secondary Tantalum Subcategory Pollutant or pollutant...

Effects of severe stressing on tantalum capacitors

NASA Technical Reports Server (NTRS)

Shakar, J. F.; Fairfield, E. H.

1981-01-01

The ultimate capabilities of an all tantalum capacitor were determined and evaluated. The evaluation included: 175 C life; 100 cycle thermal shock; 70 g random vibration; 3000 g shock; and 90 C ase ripple current.

Tantalum capacitor behavior under fast transient overvoltages. [circuit protection against lightning

NASA Technical Reports Server (NTRS)

Zill, J. A.; Castle, K. D.

1974-01-01

Tantalum capacitors were tested to determine failure time when subjected to short-duration, high-voltage surges caused by lightning strikes. Lightning is of concern to NASA because of possible damage to critical spacecraft circuits. The test was designed to determine the minimum time for tantalum capacitor failure and the amount of overvoltage a capacitor could survive, without permanent damage, in 100 microseconds. All tested exhibited good recovery from the transient one-shot pulses with no failure at any voltage, forward or reverse, in less than 25 microseconds.

A preliminary deposit model for lithium-cesium-tantalum (LCT) pegmatites

USGS Publications Warehouse

Bradley, Dwight; McCauley, Andrew

2013-01-01

This report is part of an effort by the U.S. Geological Survey to update existing mineral deposit models and to develop new ones. We emphasize practical aspects of pegmatite geology that might directly or indirectly help in exploration for lithium-cesium-tantalum (LCT) pegmatites, or for assessing regions for pegmatite-related mineral resource potential. These deposits are an important link in the world’s supply chain of rare and strategic elements, accounting for about one-third of world lithium production, most of the tantalum, and all of the cesium.

Sol-gel-derived double-layered nanocrystal memory

NASA Astrophysics Data System (ADS)

Ko, Fu-Hsiang; You, Hsin-Chiang; Lei, Tan-Fu

2006-12-01

The authors have used the sol-gel spin-coating method to fabricate a coexisting hafnium silicate and zirconium silicate double-layered nanocrystal (NC) memories. From transmission electron microscopic and x-ray photoelectron spectroscopic analyses, the authors determined that the hafnium silicate and zirconium silicate NCs formed after annealing at 900°C for 1min. When using channel hot electron injection for charging and band-to-band tunneling-induced hot hole injection for discharging, the NC memories exhibited superior Vth shifting because of the higher probability for trapping the charge carrier.

Multimode resistive switching in nanoscale hafnium oxide stack as studied by atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hou, Y., E-mail: houyi@pku.edu.cn, E-mail: lfliu@pku.edu.cn; IMEC, Kapeldreef 75, B-3001 Heverlee; Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Heverlee

2016-07-11

The nanoscale resistive switching in hafnium oxide stack is investigated by the conductive atomic force microscopy (C-AFM). The initial oxide stack is insulating and electrical stress from the C-AFM tip induces nanometric conductive filaments. Multimode resistive switching can be observed in consecutive operation cycles at one spot. The different modes are interpreted in the framework of a low defect quantum point contact theory. The model implies that the optimization of the conductive filament active region is crucial for the future application of nanoscale resistive switching devices.

Reliability Effects of Surge Current Testing of Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2007-01-01

Solid tantalum capacitors are widely used in space applications to filter low-frequency ripple currents in power supply circuits and stabilize DC voltages in the system. Tantalum capacitors manufactured per military specifications (MIL-PRF-55365) are established reliability components and have less than 0.001% of failures per 1000 hours (the failure rate is less than 10 FIT) for grades D or S, thus positioning these parts among electronic components with the highest reliability characteristics. Still, failures of tantalum capacitors do happen and when it occurs it might have catastrophic consequences for the system. This is due to a short-circuit failure mode, which might be damaging to a power supply, and also to the capability of tantalum capacitors with manganese cathodes to self-ignite when a failure occurs in low-impedance applications. During such a failure, a substantial amount of energy is released by exothermic reaction of the tantalum pellet with oxygen generated by the overheated manganese oxide cathode, resulting not only in destruction of the part, but also in damage of the board and surrounding components. A specific feature of tantalum capacitors, compared to ceramic parts, is a relatively large value of capacitance, which in contemporary low-size chip capacitors reaches dozens and hundreds of microfarads. This might result in so-called surge current or turn-on failures in the parts when the board is first powered up. Such a failure, which is considered as the most prevalent type of failures in tantalum capacitors [I], is due to fast changes of the voltage in the circuit, dV/dt, producing high surge current spikes, I(sub sp) = Cx(dV/dt), when current in the circuit is unrestricted. These spikes can reach hundreds of amperes and cause catastrophic failures in the system. The mechanism of surge current failures has not been understood completely yet, and different hypotheses were discussed in relevant literature. These include a sustained scintillation breakdown model [1-3]; electrical oscillations in circuits with a relatively high inductance [4-6]; local overheating of the cathode [5,7, 8]; mechanical damage to tantalum pentoxide dielectric caused by the impact of MnO2 crystals [2,9, 10]; or stress-induced-generation of electron traps caused by electromagnetic forces developed during current spikes [11]. A commonly accepted explanation of the surge current failures is that at unlimited current supply during surge current conditions, the self-healing mechanism in tantalum capacitors does not work, and what would be a minor scintillation spike if the current were limited, becomes a catastrophic failure of the part [l, 12]. However, our data show that the scintillation breakdown voltages are significantly greater that the surge current breakdown voltages, so it is still not clear why the part, which has no scintillations, would fail at the same voltage during surge current testing (SCT).

Tantalum-containing catalyst useful for producing alcohols from synthesis gas

DOEpatents

Kinkade, Nancy E.

1991-01-01

A catalyst useful for selectively converting a mixture of carbon monoxide and hydrogen to a mixture of lower alkanols consisting essentially of a mixture of molybdenum sulfide, an alkali metal compound and a tantalum compound.

Tantalum-containing catalyst useful for producing alcohols from synthesis gas

DOEpatents

Kinkade, Nancy E.

1992-01-01

A catalyst useful for selectively converting a mixture of carbon monoxide and hydrogen to a mixture of lower alkanols consisting essentially of a mixture of molybdenum sulfide, an alkali metal compound and a tantalum compound.

An exploration in mineral supply chain mapping using tantalum as an example

USGS Publications Warehouse

Soto-Viruet, Yadira; Menzie, W. David; Papp, John F.; Yager, Thomas R.

2013-01-01

This report uses the supply chain of tantalum (Ta) to investigate the complexity of mineral and metal supply chains in general and show how they can be mapped. A supply chain is made up of all the manufacturers, suppliers, information networks, and so forth, that provide the materials and parts that go into making up a final product. The mineral portion of the supply chain begins with mineral material in the ground (the ore deposit); extends through a series of processes that include mining, beneficiation, processing (smelting and refining), semimanufacture, and manufacture; and continues through transformation of the mineral ore into concentrates, refined mineral commodities, intermediate forms (such as metals and alloys), component parts, and, finally, complex products. This study analyses the supply chain of tantalum beginning with minerals in the ground to many of the final goods that contain tantalum.

Advanced Wet Tantalum Capacitors: Design, Specifications and Performance

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2016-01-01

Insertion of new types of commercial, high volumetric efficiency wet tantalum capacitors in space systems requires reassessment of the existing quality assurance approaches that have been developed for capacitors manufactured to MIL-PRF-39006 requirements. The specifics of wet electrolytic capacitors is that leakage currents flowing through electrolyte can cause gas generation resulting in building up of internal gas pressure and rupture of the case. The risk associated with excessive leakage currents and increased pressure is greater for high value advanced wet tantalum capacitors, but it has not been properly evaluated yet. This presentation gives a review of specifics of the design, performance, and potential reliability risks associated with advanced wet tantalum capacitors. Problems related to setting adequate requirements for DPA, leakage currents, hermeticity, stability at low and high temperatures, ripple currents for parts operating in vacuum, and random vibration testing are discussed. Recommendations for screening and qualification to reduce risks of failures have been suggested.

Advanced Wet Tantalum Capacitors: Design, Specifications and Performance

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2017-01-01

Insertion of new types of commercial, high volumetric efficiency wet tantalum capacitors in space systems requires reassessment of the existing quality assurance approaches that have been developed for capacitors manufactured to MIL-PRF-39006 requirements. The specifics of wet electrolytic capacitors is that leakage currents flowing through electrolyte can cause gas generation resulting in building up of internal gas pressure and rupture of the case. The risk associated with excessive leakage currents and increased pressure is greater for high value advanced wet tantalum capacitors, but it has not been properly evaluated yet. This presentation gives a review of specifics of the design, performance, and potential reliability risks associated with advanced wet tantalum capacitors. Problems related to setting adequate requirements for DPA, leakage currents, hermeticity, stability at low and high temperatures, ripple currents for parts operating in vacuum, and random vibration testing are discussed. Recommendations for screening and qualification to reduce risks of failures have been suggested.

Analysis of Weibull Grading Test for Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2010-01-01

Weibull grading test is a powerful technique that allows selection and reliability rating of solid tantalum capacitors for military and space applications. However, inaccuracies in the existing method and non-adequate acceleration factors can result in significant, up to three orders of magnitude, errors in the calculated failure rate of capacitors. This paper analyzes deficiencies of the existing technique and recommends more accurate method of calculations. A physical model presenting failures of tantalum capacitors as time-dependent-dielectric-breakdown is used to determine voltage and temperature acceleration factors and select adequate Weibull grading test conditions. This, model is verified by highly accelerated life testing (HALT) at different temperature and voltage conditions for three types of solid chip tantalum capacitors. It is shown that parameters of the model and acceleration factors can be calculated using a general log-linear relationship for the characteristic life with two stress levels.

Evaluation of Ferrite Chip Beads as Surge Current Limiters in Circuits with Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2014-01-01

Limiting resistors are currently required to be connected in series with tantalum capacitors to reduce the risk of surge current failures. However, application of limiting resistors decreases substantially the efficiency of the power supply systems. An ideal surge current limiting device should have a negligible resistance for DC currents and high resistance at frequencies corresponding to transients in tantalum capacitors. This work evaluates the possibility of using chip ferrite beads (FB) as such devices. Twelve types of small size FBs from three manufacturers were used to evaluate their robustness under soldering stresses and at high surge current spikes associated with transients in tantalum capacitors. Results show that FBs are capable to withstand current pulses that are substantially greater than the specified current limits. However, due to a sharp decrease of impedance with current, FBs do not reduce surge currents to the required level that can be achieved with regular resistors.

Reliability of High-Voltage Tantalum Capacitors. Parts 3 and 4)

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2010-01-01

Weibull grading test is a powerful technique that allows selection and reliability rating of solid tantalum capacitors for military and space applications. However, inaccuracies in the existing method and non-adequate acceleration factors can result in significant, up to three orders of magnitude, errors in the calculated failure rate of capacitors. This paper analyzes deficiencies of the existing technique and recommends more accurate method of calculations. A physical model presenting failures of tantalum capacitors as time-dependent-dielectric-breakdown is used to determine voltage and temperature acceleration factors and select adequate Weibull grading test conditions. This model is verified by highly accelerated life testing (HALT) at different temperature and voltage conditions for three types of solid chip tantalum capacitors. It is shown that parameters of the model and acceleration factors can be calculated using a general log-linear relationship for the characteristic life with two stress levels.

As-Received, Ozone Cleaned and Ar+ Sputtered Surfaces of Hafnium Oxide Grown by Atomic Layer Deposition and Studied by XPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Engelhard, Mark H.; Herman, Jacob A.; Wallace, Robert

2012-06-27

In this study, X-ray photoelectron spectroscopy (XPS) characterization was performed on 47 nm thick hafnium oxide (HfO{sub 2}) films grown by atomic layer deposition using TEMA-Hf/H{sub 2}O at 250 C substrate temperature. HfO{sub 2} is currently being studied as a possible replacement for Silicon Oxide (SiO{sub 2}) as a gate dielectric in electronics transistors. XPS spectra were collected on a Physical Electronics Quantum 2000 Scanning ESCA Microprobe using a monochromatic Al K{sub a} X-ray (1486.7 eV) excitation source. The sample was analyzed under the following conditions: as received, after UV irradiation for five minutes, and after sputter cleaning with 2more » kV Ar{sup +} ions for 180 seconds. Survey scans showed carbon, oxygen, and hafnium as the major species in the film, while the only minor species of argon and carbide was detected after sputtering. Adventitious carbon initially composed approximately 18.6 AT% of the surface, but after UV cleaning it was reduced to 2.4 AT%. This demonstrated that that the majority of carbon was due to adventitious carbon. However, after 2 kV Ar{sup +} sputtering there was still only trace amounts of carbon at {approx}1 AT%, Some of this trace carbon is now in the form of a carbide due to the interaction with Ar{sup +} used for sputter cleaning. Furthermore, the stoiciometric ratio of oxygen and hafnium is consistent with a high quality HfO{sub 2} film.« less

NUCLEAR REACTOR ELEMENT

DOEpatents

Sanz, M.C.; Scully, C.N.

1961-06-27

The patented fuel element is a hexagonal graphite body having an axial channel therethrough. The graphite is impregnated with uranium which is concentrated near the axial channel. Layers of tantalum nitride and tantalum carbide are disposed on the surface of the body confronting the channel.

Tantalum modified ferritic iron base alloys

NASA Technical Reports Server (NTRS)

Oldrieve, R. E.; Blankenship, C. P. (Inventor)

1977-01-01

Strong ferritic alloys of the Fe-CR-Al type containing 0.4% to 2% tantalum were developed. These alloys have improved fabricability without sacrificing high temperature strength and oxidation resistance in the 800 C (1475 F) to 1040 C (1900 F) range.

Hafnium transistor design for neural interfacing.

PubMed

Parent, David W; Basham, Eric J

2008-01-01

A design methodology is presented that uses the EKV model and the g(m)/I(D) biasing technique to design hafnium oxide field effect transistors that are suitable for neural recording circuitry. The DC gain of a common source amplifier is correlated to the structural properties of a Field Effect Transistor (FET) and a Metal Insulator Semiconductor (MIS) capacitor. This approach allows a transistor designer to use a design flow that starts with simple and intuitive 1-D equations for gain that can be verified in 1-D MIS capacitor TCAD simulations, before final TCAD process verification of transistor properties. The DC gain of a common source amplifier is optimized by using fast 1-D simulations and using slower, complex 2-D simulations only for verification. The 1-D equations are used to show that the increased dielectric constant of hafnium oxide allows a higher DC gain for a given oxide thickness. An additional benefit is that the MIS capacitor can be employed to test additional performance parameters important to an open gate transistor such as dielectric stability and ionic penetration.

Metal-Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal-Organic Framework.

PubMed

Cliffe, Matthew J; Castillo-Martínez, Elizabeth; Wu, Yue; Lee, Jeongjae; Forse, Alexander C; Firth, Francesca C N; Moghadam, Peyman Z; Fairen-Jimenez, David; Gaultois, Michael W; Hill, Joshua A; Magdysyuk, Oxana V; Slater, Ben; Goodwin, Andrew L; Grey, Clare P

2017-04-19

We report a hafnium-containing MOF, hcp UiO-67(Hf), which is a ligand-deficient layered analogue of the face-centered cubic fcu UiO-67(Hf). hcp UiO-67 accommodates its lower ligand:metal ratio compared to fcu UiO-67 through a new structural mechanism: the formation of a condensed "double cluster" (Hf 12 O 8 (OH) 14 ), analogous to the condensation of coordination polyhedra in oxide frameworks. In oxide frameworks, variable stoichiometry can lead to more complex defect structures, e.g., crystallographic shear planes or modules with differing compositions, which can be the source of further chemical reactivity; likewise, the layered hcp UiO-67 can react further to reversibly form a two-dimensional metal-organic framework, hxl UiO-67. Both three-dimensional hcp UiO-67 and two-dimensional hxl UiO-67 can be delaminated to form metal-organic nanosheets. Delamination of hcp UiO-67 occurs through the cleavage of strong hafnium-carboxylate bonds and is effected under mild conditions, suggesting that defect-ordered MOFs could be a productive route to porous two-dimensional materials.

Early/Late Heterobimetallic Tantalum/Rhodium Species Assembled Through a Novel Bifunctional NHC-OH Ligand.

PubMed

Srivastava, Ravi; Moneuse, Raphaël; Petit, Julien; Pavard, Paul-Alexis; Dardun, Vincent; Rivat, Madleen; Schiltz, Pauline; Solari, Marius; Jeanneau, Erwann; Veyre, Laurent; Thieuleux, Chloé; Quadrelli, Elsje Alessandra; Camp, Clément

2018-03-20

The straightforward synthesis of a new unsymmetrical hydroxy-tethered N-heterocyclic carbene (NHC) ligand, HL, is presented. The free ligand exhibits an unusual OH-carbene hydrogen-bonding interaction. This OH-carbene motif was used to yield 1) the first tantalum complex displaying both a Fischer- and Schrock-type carbene ligand and 2) a unique NHC-based early/late heterobimetallic complex. More specifically, the protonolysis chemistry between the ligand's hydroxy group and imido-alkyl or alkylidene-alkyl tantalum precursor complexes yielded the rare monometallic tantalum-NHC complexes [Ta(XtBu)(L)(CH 2 tBu) 2 ] (X=N, CH), in which the alkoxy-carbene ligand acts as a chelate. In contrast, HL only binds to rhodium through the NHC unit in [Rh(HL)(cod)Cl] (cod=cycloocta-1,5-diene), the hydroxy pendant arm remaining unbound. This bifunctional ligand scaffold successfully promoted the assembly of rhodium/tantalum heterobimetallic complexes upon either 1) the insertion of [Rh(cod)Cl] 2 into the Ta-NHC bond in [Ta(NtBu)(L)(CH 2 tBu) 2 ] or 2) protonolysis between the free hydroxy group in [Rh(HL)(cod)Cl] and one alkyl group in [Ta(NtBu)(CH 2 tBu) 3 ]. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effects of argon ion bombardment on the corrosion resistance of tantalum

NASA Astrophysics Data System (ADS)

Ramezani, A. H.; Sari, A. H.; Shokouhy, A.

2017-02-01

Application of ion beam has been widely used as a surface modification method to improve surface properties. This paper investigates the effect of argon ion implantation on surface structure as well as resistance against tantalum corrosion. In this experiment, argon ions with energy of 30 keV and in doses of 1 × 1017-10 × 1017 ions/cm2 were used. The surface bombardment with inert gases mainly produces modified topography and morphology of the surface. Atomic Force Microscopy was also used to patterned the roughness variations prior to and after the implantation phase. Additionally, the corrosion investigation apparatus wear was applied to compare resistance against tantalum corrosion both before and after ion implantation. The results show that argon ion implantation has a substantial impact on increasing resistance against tantalum corrosion. After the corrosion test, scanning electron microscopy (SEM) analyzed the samples' surface morphologies. In addition, the elemental composition is characterized by energy-dispersive X-ray (EDX) analysis. The purpose of this paper was to obtain the perfect condition for the formation of tantalum corrosion resistance. In order to evaluate the effect of the ion implantation on the corrosion behavior, potentiodynamic tests were performed. The results show that the corrosion resistance of the samples strongly depends on the implantation doses.

Towards sustainable processing of columbite group minerals: elucidating the relation between dielectric properties and physico-chemical transformations in the mineral phase.

PubMed

Sanchez-Segado, Sergio; Monti, Tamara; Katrib, Juliano; Kingman, Samuel; Dodds, Chris; Jha, Animesh

2017-12-21

Current methodologies for the extraction of tantalum and niobium pose a serious threat to human beings and the environment due to the use of hydrofluoric acid (HF). Niobium and tantalum metal powders and pentoxides are widely used for energy efficient devices and components. However, the current processing methods for niobium and tantalum metals and oxides are energy inefficient. This dichotomy between materials use for energy applications and their inefficient processing is the main motivation for exploring a new methodology for the extraction of these two oxides, investigating the microwave absorption properties of the reaction products formed during the alkali roasting of niobium-tantalum bearing minerals with sodium bicarbonate. The experimental findings from dielectric measurement at elevated temperatures demonstrate an exponential increase in the values of the dielectric properties as a result of the formation of NaNbO 3 -NaTaO 3 solid solutions at temperatures above 700 °C. The investigation of the evolution of the dielectric properties during the roasting reaction is a key feature in underpinning the mechanism for designing a new microwave assisted high-temperature process for the selective separation of niobium and tantalum oxides from the remainder mineral crystalline lattice.

Design and Fabrication of Ta filled microcavites in the delay paths of SAW devices for improved power transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richardson, Mandek; Sankaranarayanan, S. K. R. S.; Bhethanabotla, V. R.

2015-03-01

The authors report the design and fabrication of a surface acoustic wave (SAW) device with improved power transfer due to modification of its delay path. Typically, SAW delay-line devices suffer from relatively high insertion loss (IL) (similar to 10-30 dB). Our approach is to incorporate an array of microcavities, having square cross-sectional area (lambda/2 x lambda/2) and filled with tantalum, within the delay path to maximize acoustic confinement to the surface and reduce IL. To determine the effectiveness of the cavities without expending too many resources and to explain trends found in actual devices, a finite element model of amore » SAW device with tantalum filled cavities having various depths was utilized. For each depth simulated, IL was decreased compared to a standard SAW device. Microcavities 2.5 mu m deep filled with tantalum showed the best performance (Delta IL = 17.93 dB). To validate simulated results, the authors fabricated a SAW device on ST 90 degrees-X quartz with microcavities etched into its delay path using deep reactive ion etching and filled with tantalum. Measurement of fabricated devices showed inclusion of tantalum filled microcavities increased power transfer compared to a device without cavities. (C) 2015 American Vacuum Society.« less

Shock Propagation In Crustal Rock

DTIC Science & Technology

1991-04-29

liquid produced above the melting point during unloading. Figure 5 displays calculations of release adiabats in the mixed phase regime based on the...muscovite [Bridgman, 1949]. The zero-pressure densities at points 1, 2 and 3 correspond to mixtures of orthoclase + A1203+H20, of wadeite + kyanite ...shocked tantalum and the high pressure melting point , in Shock Waves in Condensed Matter-1983, edited by J. R. Asay, R. A. Graham and G. K. Straub, pp. 91

Tantalum-containing catalyst useful for producing alcohols from synthesis gas

DOEpatents

Kinkade, N.E.

1992-04-07

A catalyst is described which is useful for selectively converting a mixture of carbon monoxide and hydrogen to a mixture of lower alkanols. The catalyst consists essentially of a mixture of molybdenum sulfide, an alkali metal compound and a tantalum compound.

SEPARATING HAFNIUM FROM ZIRCONIUM

DOEpatents

Lister, B.A.J.; Duncan, J.F.; Hutcheon, J.M.

1956-08-21

Substantially complete separation of zirconium from hafnium may be obtained by elution of ion exchange material, on which compounds of the elements are adsorbed, with an approximately normal solution of sulfuric acid. Preferably the acid concentration is between 0.8 N amd 1.2 N, amd should not exceed 1.5 N;. Increasing the concentration of sulfate ion in the eluting solution by addition of a soluble sulfate, such as sodium sulfate, has been found to be advantageous. The preferred ion exchange materials are sulfonated polystyrene resins such as Dowex 50,'' and are preferably arranged in a column through which the solutions are passed.

[Short-term curative effects of Tantalum rod treatment in early avascular necrosis].

PubMed

Ye, Fu-Sheng; Ni, Zhe-Ji; Chu, Xiao-Bing; He, Bang-Jian; Li, Ju; Tong, Pei-Jian

2013-08-01

To explore the recent clinical curative effect of Tantalum rod in treating the early avascular necrosis. From January 2008 to November 2008, the 25 patients (39 hips) with early avascular necrosis accepted tantalum rod placement and included 9 males (11 hips) and 16 females (28 hips) with an average age of 37 years old ranging from 18 to 74 years old. Four patients (6 hips) caused by Alcoholic, 6 patients (8 hips) by hormone, 2 cases (2 hips) by traumatic, 13 cases (23 hips) by idiopathic. Steinberg preoperative stage involved 7 hips in period I, 24 hips in period II, 8 hips in period III. Curative effect analysis included preoperative and postoperative Harris score, radiographic changes and hip replacement for follow-up to accept the end of the femoral head survival rate. All patients were followed up for 6 to 47 months (averaged 37.4 months). All 12 hips imaging appeard progress,including tantalum rod exit in 1 hip, hip hemiarthroplasty collapse in 3 hips, the area increased to avascular necrosis in 8 hips. Six hips accepted total hip replacement, including imaging progress in 5 hips (41.7%, 5/12), no imaging progress in 1 hip (3.7%,1/27). All hips' Kaplan-Meier survival curves showed 6-month survival rate was (97.4 +/- 2.5)% after tantalum stick insertion, 1-year survival rate was (94.7 +/- 3.6), and 2-year survival rate was (88.6 +/- 5.4)%, 3-year survival rate was (72.5 +/- 11.2). It is effective for treatment of avascular necrosis of femoral head in Steinberg I and II by Tantalum rod, and it can effectively relieve femoral head replacement time.

Machine Gun Liner Bond Strength

DTIC Science & Technology

2007-08-01

explosive bonding of pure tantalum, several tantalum alloys, and Stellite 25 (an alloy of cobalt, chrome , nickel, and tungsten) in a liner...smoothly as elastic stresses increase in the plug and liner. At a certain level of displacement, the load reaches a peak and then drops sharply. The

Semimicrodetermination of combined tantalum and niobium with selenous acid

USGS Publications Warehouse

Grimaldi, F.S.; Schnepfe, M.

1959-01-01

Tantalum and niobium are separated and determined gravimetrically by precipitation with selenous acid from highly acidic solutions in the absence of complexing agents. Hydrogen peroxide is used in the preparation of the solution and later catalytically destroyed during digestion of the precipitate. From 0.2 to 30 mg., separately or in mixtures, of niobium or tantalum pentoxide can be separated from mixtures containing 100 mg. each of the oxides of scandium, yttrium, cerium, vanadium, molybdenum, iron, aluminum, tin, lead, and bismuth with a single precipitation; and from 30 mg. of titanium dioxide, and 50 mg. each of the oxides of antimony and thorium, when present separately, with three precipitations. At least 50 mg. of uranium(VI) oxide can be separated with a single precipitation when present alone; otherwise, three precipitations may be needed. Zirconium does not interfere when the tantalum and niobium contents of the sample are small, but in general, zirconium as well as tungsten interfere. The method is applied to the determination of the earth acids in tantaloniobate ores.

High efficiency tantalum-based ceramic composite structures

NASA Technical Reports Server (NTRS)

Stewart, David A. (Inventor); Leiser, Daniel B. (Inventor); DiFiore, Robert R. (Inventor); Katvala, Victor W. (Inventor)

2010-01-01

Tantalum-based ceramics are suitable for use in thermal protection systems. These composite structures have high efficiency surfaces (low catalytic efficiency and high emittance), thereby reducing heat flux to a spacecraft during planetary re-entry. These ceramics contain tantalum disilicide, molybdenum disilicide and borosilicate glass. The components are milled, along with a processing aid, then applied to a surface of a porous substrate, such as a fibrous silica or carbon substrate. Following application, the coating is then sintered on the substrate. The composite structure is substantially impervious to hot gas penetration and capable of surviving high heat fluxes at temperatures approaching 3000.degree. F. and above.

Design, Development, manufacture and qualification of wet-slug all-tantalum capacitors

NASA Technical Reports Server (NTRS)

Maher, R. H.

1977-01-01

Specifications and qualification tests data are presented for over eleven hundred T3 case all-tantalum capacitors encompassing four ratings. The finalized product has all the advantages of the silver cased wet and is capable of withstanding some reverse potential ac ripple current.

Metal/ceramic composites with high hydrogen permeability

DOEpatents

Dorris, Stephen E.; Lee, Tae H.; Balachandran, Uthamalingam

2003-05-27

A membrane for separating hydrogen from fluids is provided comprising a sintered homogenous mixture of a ceramic composition and a metal. The metal may be palladium, niobium, tantalum, vanadium, or zirconium or a binary mixture of palladium with another metal such as niobium, silver, tantalum, vanadium, or zirconium.

Effects of Tantalum on the Temporal Evolution of a Model Ni-Al-Cr Superalloy During Phase Decomposition

NASA Technical Reports Server (NTRS)

Booth, Morrison, Christopher; Seidman, David N.; Noebe, Ronald D.

2009-01-01

The effects of a 2.0 at.% addition of Ta to a model Ni-10.0Al-8.5Cr (at.%) superalloy aged at 1073 K are assessed using scanning electron microscopy and atom-probe tomography. The gamma'(Ll2)-precipitate morphology that develops as a result of gamma-(fcc)matrix phase decomposition is found to evolve from a bimodal distribution of spheroidal precipitates, to {001}-faceted cuboids and parallelepipeds aligned along the elastically soft {001}-type directions. The phase compositions and the widths of the gamma'-precipitate/gamma-matrix heterophase interfaces evolve temporally as the Ni-Al-Cr-Ta alloy undergoes quasi-stationary state coarsening after 1 h of aging. Tantalum is observed to partition preferentially to the gamma'-precipitate phase, and suppresses the mobility of Ni in the gamma-matrix sufficiently to cause an accumulation of Ni on the gamma-matrix side of the gamma'/gamma interface. Additionally, computational modeling, employing Thermo-Calc, Dictra and PrecipiCalc, is employed to elucidate the kinetic pathways that lead to phase decomposition in this concentrated Ni-Al-Cr-Ta alloy.

Low temperature synthesis of monolithic transparent Ta2O5 gels from hydrolysis of metal alkoxide

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

1993-01-01

Tantalum oxide gels in the form of transparent monoliths and powder were prepared from hydrolysis of tantalum pentaethoxide under controlled conditions using different mole ratios of Ta(OC2H5)5:C2H50H:H20:HCl. Alcohol acts as the mutual solvent and HCl as the deflocculating agent. For a fixed alkoxide:water:HCl ratio, time of gel formation increased with the alcohol to alkoxide mole ratio. Thermal evolution of the physical and structural changes in the gel was monitored by differential thermal analysis, thermogravimetric analysis, x-ray diffraction, and infrared spectroscopy. On heating to approximately 400 C, the amorphous gel crystallized into the low temperature orthorhombic phase Beta-Ta2O5, which transformed into the high temperature tetragonal phase Alpha-Ta2O5 when further heated to approximately 1450 C. The volume fraction of the crystalline phase increased with the firing temperature. The Alpha-Ta205 converted back into the low temperature phase, Beta-Ta2O5, on slow cooling through the transformation temperature of 1360 C indicating a slow but reversible transformation.

Tensile behavior of tungsten and tungsten-alloy wires from 1300 to 1600 K

NASA Technical Reports Server (NTRS)

Hee, Man Yun

1988-01-01

The tensile behavior of a 200-micrometer-diameter tungsten lamp (218CS-W), tungsten + 1.0 atomic percent (a/o) thoria (ST300-W), and tungsten + 0.4 a/o hafnium carbide (WHfC) wires was determined over the temperature range 1300 t0 1600 K at strain rates of 3.3 X 10 to the -2 to 3.3 X 10 to the -5/sec. Although most tests were conducted on as-drawn materials, one series of tests was undertaken on ST300-W wires in four different conditions: as-drawn and vacuum-annealed at 1535 K for 1 hr, with and without electroplating. Whereas heat treatment had no effect on tensile properties, electropolishing significantly increased both the proportional limit and ductility, but not the ultimate tensile strength. Comparison of the behavior of the three alloys indicates that the HfC-dispersed material possesses superior tensile properties. Theoretical calculations indicate that the strength/ductility advantage of WHfC is due to the resistance to recrystallization imparted by the dispersoid.

Low temperature mobility in hafnium-oxide gated germanium p-channel metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Beer, Chris; Whall, Terry; Parker, Evan; Leadley, David; De Jaeger, Brice; Nicholas, Gareth; Zimmerman, Paul; Meuris, Marc; Szostak, Slawomir; Gluszko, Grzegorz; Lukasiak, Lidia

2007-12-01

Effective mobility measurements have been made at 4.2K on high performance high-k gated germanium p-type metal-oxide-semiconductor field effect transistors with a range of Ge/gate dielectric interface state densities. The mobility is successfully modelled by assuming surface roughness and interface charge scattering at the SiO2 interlayer/Ge interface. The deduced interface charge density is approximately equal to the values obtained from the threshold voltage and subthreshold slope measurements on each device. A hydrogen anneal reduces both the interface state density and the surface root mean square roughness by 20%.

Use of steel and tantalum apparatus for molten Cd-Mg-Zn alloys

NASA Technical Reports Server (NTRS)

Bennett, G. A.; Burris, L., Jr.; Kyle, M. L.; Nelson, P. A.

1966-01-01

Steel and tantalum apparatus contains various ternary alloys of cadmium, zinc, and magnesium used in pyrochemical processes for the recovery of uranium-base reactor fuels. These materials exhibit good corrosion resistance at the high temperatures necessary for fuel separation in liquid metal-molten salt solvents.

PHYSICAL VAPOR DEPOSITION OF TANTALUM ON GUN BARREL STEEL (SYSTEMS ANLAYSIS BRANCH, SUSTAINABLE TECHNOLOGY DIVISION, NRMRL)

EPA Science Inventory

This project entails the development of an alternative technology for plating gun barrel steel to replace the process electroplating of chrome (Cr-electroplate) with physical vapor deposition of tantalum (Ta-PVD). Developed by Benet Laboratory at Watervliet Arsenal, this project'...

Synthesis of Monodispersed Tantalum(V) oxide Nanospheres by an Ethylene Glycol Mediated Route

EPA Science Inventory

Tantalum(V) oxide (Ta2O5) nanospheres have been synthesized by a very simple ethylene glycol mediated route. The two-step process involves the formation of glycolate nanoparticles and their subsequent hydrolysis and calcination to generate the final Ta2O5 nanospheres. The synthes...

Slow DNA Transport through Nanopores in Hafnium Oxide Membranes

PubMed Central

Bell, David C.; Cohen-Karni, Tzahi; Rosenstein, Jacob K.; Wanunu, Meni

2016-01-01

We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2–7 nm thick) free-standing hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore. PMID:24083444

Metal–Organic Nanosheets Formed via Defect-Mediated Transformation of a Hafnium Metal–Organic Framework

PubMed Central

2017-01-01

We report a hafnium-containing MOF, hcp UiO-67(Hf), which is a ligand-deficient layered analogue of the face-centered cubic fcu UiO-67(Hf). hcp UiO-67 accommodates its lower ligand:metal ratio compared to fcu UiO-67 through a new structural mechanism: the formation of a condensed “double cluster” (Hf12O8(OH)14), analogous to the condensation of coordination polyhedra in oxide frameworks. In oxide frameworks, variable stoichiometry can lead to more complex defect structures, e.g., crystallographic shear planes or modules with differing compositions, which can be the source of further chemical reactivity; likewise, the layered hcp UiO-67 can react further to reversibly form a two-dimensional metal–organic framework, hxl UiO-67. Both three-dimensional hcp UiO-67 and two-dimensional hxl UiO-67 can be delaminated to form metal–organic nanosheets. Delamination of hcp UiO-67 occurs through the cleavage of strong hafnium-carboxylate bonds and is effected under mild conditions, suggesting that defect-ordered MOFs could be a productive route to porous two-dimensional materials. PMID:28343394

Ferroelectric memory based on molybdenum disulfide and ferroelectric hafnium oxide

NASA Astrophysics Data System (ADS)

Yap, Wui Chung; Jiang, Hao; Xia, Qiangfei; Zhu, Wenjuan

Recently, ferroelectric hafnium oxide (HfO2) was discovered as a new type of ferroelectric material with the advantages of high coercive field, excellent scalability (down to 2.5 nm), and good compatibility with CMOS processing. In this work, we demonstrate, for the first time, 2D ferroelectric memories with molybdenum disulfide (MoS2) as the channel material and aluminum doped HfO2 as the ferroelectric gate dielectric. A 16 nm thick layer of HfO2, doped with 5.26% aluminum, was deposited via atomic layer deposition (ALD), then subjected to rapid thermal annealing (RTA) at 1000 °C, and the polarization-voltage characteristics of the resulting metal-ferroelectric-metal (MFM) capacitors were measured, showing a remnant polarization of 0.6 μC/cm2. Ferroelectric memories with embedded ferroelectric hafnium oxide stacks and monolayer MoS2 were fabricated. The transfer characteristics after program and erase pulses revealed a clear ferroelectric memory window. In addition, endurance (up to 10,000 cycles) of the devices were tested and effects associated with ferroelectric materials, such as the wake-up effect and polarization fatigue, were observed. This research can potentially lead to advances of 2D materials in low-power logic and memory applications.

Evaluation of wet tantalum capacitors after exposure to extended periods of ripple current, volume 1

NASA Technical Reports Server (NTRS)

Watson, G. W.; Lasharr, J. C.; Shumaker, M. J.

1974-01-01

The application of tantalum capacitors in the Viking Lander includes both dc voltage and ripple current electrical stress, high temperature during nonoperating times (sterilization), and high vibration and shock loads. The capacitors must survive these severe environments without any degradation if reliable performance is to be achieved. A test program was established to evaluate both wet-slug tantalum and wet-foil capacitors under conditions accurately duplicating actual Viking applications. Test results of the electrical performance characteristics during extended periods of ripple current, the characteristics of the internal silver migration as a function for extended periods of ripple current, and the existence of any memory characteristics are presented.

Evaluation of wet tantalum capacitors after exposure to extended periods of ripple current, volume 2

NASA Technical Reports Server (NTRS)

Ward, C. M.

1975-01-01

The application of tantalum capacitors in the Viking Lander includes dc voltage and ripple current electrical stress, high temperature during nonoperating times (sterilization), and high vibration and shock loads. The capacitors must survive these severe environments without any degradation if reliable performance is to be achieved. A test program was established to evaluate both wet-slug tantalum and wet-foil capacitors under conditions accurately duplicating actual Viking applications. Test results of the electrical performance characteristics during extended periods of ripple current, the characteristics of the internal silver migration as a function of extended periods of ripple current, and the existence of any memory characteristics are presented.

Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta₂O₅)

DOE PAGES

Bassiri, Riccardo; Liou, Franklin; Abernathy, Matthew R.; ...

2015-03-01

Amorphous tantala (a-Ta₂O₅) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta₂O₅ coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta₂O₅ and other a-T₂O₅ studies.

Environmental dosimeter of the thermoluminescent type

DOEpatents

Eichner, F.N.; Kocher, L.F.

1974-01-29

A dosimeter for accurately monitoring normally low-energy radiation including a thermoluminescent CaF phosphor enclosed within a tantalum capsule is described. The tantalum acts as a filter to weaken the measured dose due to photons having energies below about 0.2 MeV. Tantalum end caps are maintained on the capsule body by a polyolefin sheath formed from heat-contractable tubing. After exposing the dosimeter to environmental radiation, it is placed in a shielded chamber for about 24 h and subsequently annealed at about 80 deg C to release radiation energy accumulated in low-temperature traps. The dosimeter is then disassembled and the phosphors photometrically read at temperatures about 50 deg C to determine the absorbed radiation dose. (Official Gazette)

High-acoustic-impedance tantalum oxide layers for insulating acoustic reflectors.

PubMed

Capilla, Jose; Olivares, Jimena; Clement, Marta; Sangrador, Jesús; Iborra, Enrique; Devos, Arnaud

2012-03-01

This work describes the assessment of the acoustic properties of sputtered tantalum oxide films intended for use as high-impedance films of acoustic reflectors for solidly mounted resonators operating in the gigahertz frequency range. The films are grown by sputtering a metallic tantalum target under different oxygen and argon gas mixtures, total pressures, pulsed dc powers, and substrate biases. The structural properties of the films are assessed through infrared absorption spectroscopy and X-ray diffraction measurements. Their acoustic impedance is assessed by deriving the mass density from X-ray reflectometry measurements and the acoustic velocity from picosecond acoustic spectroscopy and the analysis of the frequency response of the test resonators.

Silicon Materials Task of the Low Cost Solar Array Project, Phase 3. Effect of Impurities and Processing on Silicon Solar Cells

NASA Technical Reports Server (NTRS)

Hopkins, R. H.; Davis, J. R.; Blais, P. D.; Rohatgi, A.; Campbell, R. B.; Rai-Choudhury, P.; Stapleton, R. E.; Mollenkopf, H. C.; Mccormick, J. R.

1979-01-01

The effects of impurities, various thermochemical processes, and any impurity process interactions on the performance of terrestrial silicon solar cells are defined. Determinations of the segregation coefficients of tungsten, tantalum, and cobalt for the Czochralski pulling of silicon single crystals are reported. Sensitive neutron activation analysis was used to determine the metal impurity content of the silicon while atomic absorption was used to measure the metal content of the residual liquid from which the doped crystals were grown. Gettering of Ti doped silicon wafers improved cell performance by one to two percent for the highest temperatures and longest times. The HCl is more effective than POCl3 treatments for deactivating Ti but POCl3 and HCl produced essentially identical results for Mo or Fe.

Conflict minerals from the Democratic Republic of the Congo: global tantalum processing plants, a critical part of the tantalum supply chain

USGS Publications Warehouse

Papp, John F.

2014-01-01

Post-beneficiation processing plants (generally called smelters and refineries) for 3TG mineral ores and concentrates were identified by company and industry association representatives as being the link in the 3TG mineral supply chain through which these minerals can be traced to their source of origin (mine). The determination of the source of origin is critical to the development of a complete and transparent conflict-free mineral supply chain. Tungsten processing plants were the subject of the first fact sheet in this series published by USGS NMIC in August 2014. Background information about historical conditions and multinational stakeholders’ voluntary due diligence guidance for minerals from conflict-affected and high-risk areas is presented in the tungsten fact sheet. This fact sheet, the second in a series about 3TG minerals, focuses on the tantalum supply chain by listing selected processors that produced tantalum materials commercially worldwide during 2013–14. It does not provide any information regarding the sources of material processed in these facilities.

Large area graphene ion sensitive field effect transistors with tantalum pentoxide sensing layers for pH measurement at the Nernstian limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fakih, Ibrahim, E-mail: ibrahim.fakih@mail.mcgill.ca; Sabri, Shadi; Szkopek, Thomas, E-mail: thomas.szkopek@mcgill.ca

2014-08-25

We have fabricated and characterized large area graphene ion sensitive field effect transistors (ISFETs) with tantalum pentoxide sensing layers and demonstrated pH sensitivities approaching the Nernstian limit. Low temperature atomic layer deposition was used to deposit tantalum pentoxide atop large area graphene ISFETs. The charge neutrality point of graphene, inferred from quantum capacitance or channel conductance, was used to monitor surface potential in the presence of an electrolyte with varying pH. Bare graphene ISFETs exhibit negligible response, while graphene ISFETs with tantalum pentoxide sensing layers show increased sensitivity reaching up to 55 mV/pH over pH 3 through pH 8. Applying themore » Bergveld model, which accounts for site binding and a Guoy-Chapman-Stern picture of the surface-electrolyte interface, the increased pH sensitivity can be attributed to an increased buffer capacity reaching up to 10{sup 14} sites/cm{sup 2}. ISFET response was found to be stable to better than 0.05 pH units over the course of two weeks.« less

Surface nanotexturing of tantalum by laser ablation in water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barmina, E V; Simakin, Aleksandr V; Shafeev, Georgii A

2009-01-31

Surface nanotexturing of tantalum by ablation with short laser pulses in water has been studied experimentally using three ablation sources: a neodymium laser with a pulse duration of 350 ps, an excimer laser (248 nm) with a pulse duration of 5 ps and a Ti:sapphire laser with a pulse duration of 180 fs. The morphology of the nanotextured surfaces has been examined using a nanoprofilometer and field emission scanning electron microscope. The results demonstrate that the average size of the hillocks produced on the target surface depends on the laser energy density and is {approx}200 nm at an energy densitymore » approaching the laser-melting threshold of tantalum and a pulse duration of 350 ps. Their surface density reaches 10{sup 6} cm{sup -2}. At a pulse duration of 5 ps, the average hillock size is 60-70 nm. Nanotexturing is accompanied by changes in the absorption spectrum of the tantalum surface in the UV and visible spectral regions. The possible mechanisms of surface nanotexturing and potential applications of this effect are discussed. (nanostructures)« less

Large area graphene ion sensitive field effect transistors with tantalum pentoxide sensing layers for pH measurement at the Nernstian limit

NASA Astrophysics Data System (ADS)

Fakih, Ibrahim; Sabri, Shadi; Mahvash, Farzaneh; Nannini, Matthieu; Siaj, Mohamed; Szkopek, Thomas

2014-08-01

We have fabricated and characterized large area graphene ion sensitive field effect transistors (ISFETs) with tantalum pentoxide sensing layers and demonstrated pH sensitivities approaching the Nernstian limit. Low temperature atomic layer deposition was used to deposit tantalum pentoxide atop large area graphene ISFETs. The charge neutrality point of graphene, inferred from quantum capacitance or channel conductance, was used to monitor surface potential in the presence of an electrolyte with varying pH. Bare graphene ISFETs exhibit negligible response, while graphene ISFETs with tantalum pentoxide sensing layers show increased sensitivity reaching up to 55 mV/pH over pH 3 through pH 8. Applying the Bergveld model, which accounts for site binding and a Guoy-Chapman-Stern picture of the surface-electrolyte interface, the increased pH sensitivity can be attributed to an increased buffer capacity reaching up to 1014 sites/cm2. ISFET response was found to be stable to better than 0.05 pH units over the course of two weeks.

Probing topological Fermi-Arcs and bulk boundary correspondence in the Weyl semimetal TaAs

NASA Astrophysics Data System (ADS)

Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

The relation between surface Fermi-arcs and bulk Weyl cones in a Weyl semimetal, uniquely allows to study the notion of bulk to surface correspondence. We visualize these topological Fermi arc states on the surface of the Weyl semi-metal tantalum arsenide using scanning tunneling spectroscopy. Its surface hosts 12 Fermi arcs amongst several other surface bands of non-topological origin. We detect the possible scattering processes of surface bands in which Fermi arcs are involved including intra- and inter arc scatterings and arc-trivial scatterings. Each of the measured scattering processes entails additional information on the unique nature of Fermi arcs in tantalum arsenide: their contour, their energy-momentum dispersion and its relation with the bulk Weyl nodes. We further identify a sharp distinction between the wave function's spatial distribution of topological versus trivial bands. The non-topological surface bands, which are derived from the arsenic dangling bonds, are tightly bound to the arsenic termination layer. In contrast, the Fermi-arc bands reside on the deeper tantalum layer, penetrating into the bulk, which is predominantly derived from tantalum orbitals.

An experimental study of the solubility and speciation of tantalum in fluoride-bearing aqueous solutions at elevated temperature

DOE PAGES

Timofeev, Alexander; Migdisov, Art. A.; Williams-Jones, A. E.

2016-10-27

Here, the solubility of Ta 2O 5 (solid) and the speciation of tantalum in HF-bearing aqueous solutions have been determined at temperatures of 100-250 °C and vapour-saturated water pressure. Tantalum is transported as the species Ta(OH) 5 0 at low HF concentration and pH ~1-3. At higher HF concentration, tantalum mobility is controlled by the species TaF 3(OH) 3- and TaF 5; the presence of TaF 5 0 is only evident at ≤150 °C. Equilibrium constants range from -17.4 ± 0.45 to -16.4 ± 0.12 for the formation of Ta(OH) 5 from crystalline Ta 2O 5 and from -8.24 ±more » 0.64 to -8.55 ± 0.68 for the formation of TaF 3(OH) 3- at 100 and 250 °C, respectively. For TaF 5 0, they were determined to be 0.13 at 100 °C and -0.35 at 150 °C.« less

Achieving surface chemical and morphologic alterations on tantalum by plasma electrolytic oxidation.

PubMed

Goularte, Marcelo Augusto Pinto Cardoso; Barbosa, Gustavo Frainer; da Cruz, Nilson Cristino; Hirakata, Luciana Mayumi

2016-12-01

Search for materials that may either replace titanium dental implants or constitute an alternative as a new dental implant material has been widely studied. As well, the search for optimum biocompatible metal surfaces remains crucial. So, the aim of this work is to develop an oxidized surface layer on tantalum using plasma electrolytic oxidation (PEO) similar to those existing on oral implants been marketed today. Cleaned tantalum samples were divided into group 1 (control) and groups 2, 3, and 4 (treated by PEO for 1, 3, and 5 min, respectively). An electrolytic solution diluted in 1-L deionized water was used for the anodizing process. Then, samples were washed with anhydrous ethyl alcohol and dried in the open air. For complete anodic treatment disposal, the samples were immersed in acetone altogether, taken to the ultrasonic tank for 10 min, washed again in distilled water, and finally air-dried. For the scanning electron microscopy (SEM) analysis, all samples were previously coated with gold; the salt deposition analysis was conducted with an energy-dispersive X-ray spectroscopy (EDS) system integrated with the SEM unit. SEM images confirmed the changes on tantalum strips surface according to different exposure times while EDS analysis confirmed increased salt deposition as exposure time to the anodizing process also increased. PEO was able to produce both surface alteration and salt deposition on tantalum strips similar to those existing on oral implants been marketed today.

Performance and Reliability of Solid Tantalum Capacitors at Cryogenic Conditions

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2006-01-01

Performance of different types of solid tantalum capacitors was evaluated at room and low temperatures, down to 15 K. The effect of temperature on frequency dependencies of capacitance, effective series resistances (ESR), leakage currents, and breakdown voltages has been investigated and analyzed. To assess thermo-mechanical robustness of the parts, several groups of loose capacitors and those soldered on FR4 boards were subjected to multiple (up to 500) temperature cycles between room temperature and 77 K. Experiments and mathematical modeling have shown that degradation in tantalum capacitors at low temperatures is mostly due to increasing resistance of the manganese cathode layer, resulting in substantial decrease of the roll-off frequency. Absorption currents follow a power law, I approximately t(sup -m), with the exponent m varying from 0.8 to 1.1. These currents do not change significantly at cryogenic conditions and the value of the exponent remains the same down to 15 K. Variations of leakage currents with voltage can be described by Pool-Frenkel and Schottky mechanisms of conductivity, with the Schottky mechanism prevailing at cryogenic conditions. Breakdown voltages of tantalum capacitors increase and the probability of scintillations decreases at cryogenic temperatures. However, breakdown voltages measured during surge current testing decrease at liquid nitrogen (LN) compared to room-temperature conditions. Results of temperature cycling suggest that tantalum capacitors are capable of withstanding multiple exposures to cryogenic conditions, but the probability of failures varies for different part types.

Effect of oxygen deficiency on electronic properties and local structure of amorphous tantalum oxide thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denny, Yus Rama; Firmansyah, Teguh; Oh, Suhk Kun

2016-10-15

Highlights: • The effect of oxygen flow rate on electronic properties and local structure of tantalum oxide thin films was studied. • The oxygen deficiency induced the nonstoichiometric state a-TaOx. • A small peak at 1.97 eV above the valence band side appeared on nonstoichiometric Ta{sub 2}O{sub 5} thin films. • The oxygen flow rate can change the local electronic structure of tantalum oxide thin films. - Abstract: The dependence of electronic properties and local structure of tantalum oxide thin film on oxygen deficiency have been investigated by means of X-ray photoelectron spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS),more » and X-ray absorption spectroscopy (XAS). The XPS results showed that the oxygen flow rate change results in the appearance of features in the Ta 4f at the binding energies of 23.2 eV, 24.4 eV, 25.8, and 27.3 eV whose peaks are attributed to Ta{sup 1+}, Ta{sup 2+}, Ta{sup 3+}/Ta{sup 4+}, and Ta{sup 5+}, respectively. The presence of nonstoichiometric state from tantalum oxide (TaOx) thin films could be generated by the oxygen vacancies. In addition, XAS spectra manifested both the increase of coordination number of the first Ta-O shell and a considerable reduction of the Ta-O bond distance with the decrease of oxygen deficiency.« less

Multi-scale Modeling of Plasticity in Tantalum.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Hojun; Battaile, Corbett Chandler.; Carroll, Jay

In this report, we present a multi-scale computational model to simulate plastic deformation of tantalum and validating experiments. In atomistic/ dislocation level, dislocation kink- pair theory is used to formulate temperature and strain rate dependent constitutive equations. The kink-pair theory is calibrated to available data from single crystal experiments to produce accurate and convenient constitutive laws. The model is then implemented into a BCC crystal plasticity finite element method (CP-FEM) model to predict temperature and strain rate dependent yield stresses of single and polycrystalline tantalum and compared with existing experimental data from the literature. Furthermore, classical continuum constitutive models describingmore » temperature and strain rate dependent flow behaviors are fit to the yield stresses obtained from the CP-FEM polycrystal predictions. The model is then used to conduct hydro- dynamic simulations of Taylor cylinder impact test and compared with experiments. In order to validate the proposed tantalum CP-FEM model with experiments, we introduce a method for quantitative comparison of CP-FEM models with various experimental techniques. To mitigate the effects of unknown subsurface microstructure, tantalum tensile specimens with a pseudo-two-dimensional grain structure and grain sizes on the order of millimeters are used. A technique combining an electron back scatter diffraction (EBSD) and high resolution digital image correlation (HR-DIC) is used to measure the texture and sub-grain strain fields upon uniaxial tensile loading at various applied strains. Deformed specimens are also analyzed with optical profilometry measurements to obtain out-of- plane strain fields. These high resolution measurements are directly compared with large-scale CP-FEM predictions. This computational method directly links fundamental dislocation physics to plastic deformations in the grain-scale and to the engineering-scale applications. Furthermore, direct and quantitative comparisons between experimental measurements and simulation show that the proposed model accurately captures plasticity in deformation of polycrystalline tantalum.« less

Alkyl group effects on CO insertion into coordinatively unsaturated early-transition-metal alkyls. Preparations and the first structural characterizations of tantalum enolate-O and tantalum. eta. sup 2 -acyl complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyer, T.Y.; Garner, L.R.; Baenziger, N.C.

1990-10-03

Low-pressure carbonylation of the mono(peralkylcyclopentadienyl)tantalum(V) alkyls ({eta}-C{sub 5}Me{sub 4}R)TaR{prime}Cl{sub 3} (R = Me, Et; R{prime} = CH{sub 2}C{sub 6}H{sub 4}-p-Me, CH{sub 2}CMe{sub 3}) yields either the O-bound enolate or the {eta}{sup 2}-acyl as shown by ir/NMR spectroscopy and x-ray diffractometry. The p-tolyl enolate ({eta}-C{sub 5}Me{sub 5})Ta(OCH{double bond}CHC{sub 6}H{sub 4}-p-Me)Cl{sub 3}, derived directly from carbonylation of the tantalum 4-methylbenzyl precursor, is shown to possess a cis configuration in solution and in the solid state. Key structural features from a single-crystal x-ray diffraction study of the tetrahydrofuran-ligated enolate complex are reported. The mechanism of formation of the enolate from carbonylation of themore » 4-methylbenzyl complex is discussed. The previously reported acyl ({eta}-C{sub 5}Me{sub 4}R)Ta(C(O)CH{sub 2}CMe{sub 3})Cl{sub 3} has been reexamined and found to possess a symmetric, strongly distorted {eta}{sup 2}-acyl coordination by solution {sup 1}H NMR spectroscopy and solid-state x-ray diffractometry. The molecular structures of ({eta}-C{sub 5}Me{sub 5})Ta(OCH{double bond}CHC{sub 6}H{sub 4}-p-Me)Cl{sub 3} and ({eta}-C{sub 5}Me{sub 5})Ta(C(O)CH{sub 2}CMe{sub 3})Cl{sub 3}, which are reported here, are the first structural determinations of a tantalum enolate and of a tantalum {eta}{sup 2}-acyl. 41 refs., 2 figs., 8 tabs.« less

2014 NEPP Tasks Update for Ceramic and Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander A.

2014-01-01

Presentation describes recent development in research on MnO2, wet, and polymer tantalum capacitors. Low-voltage failures in multilayer ceramic capacitors and techniques to reveal precious metal electrode (PME) and base metal electrode (BME) capacitors with cracks are discussed. A voltage breakdown technique is suggested to select high quality low-voltage BME ceramic capacitors.

Gettering capsule for removing oxygen from liquid lithium systems

NASA Technical Reports Server (NTRS)

Tower, L. K.; Breitwieser, R.

1973-01-01

Capsule consisting of tantalum shell lined with tantalum screen and partially filled with lithium and pieces of yttrium is immersed in hot lithium stream. Oxygen is removed from stream by being absorbed by gettering capsule. Oxygen passes through capsule wall and into lithium inside capsule where it reacts with yttrium to form Y2O3.

Study of surge current effects on solid tantalum capacitors

NASA Technical Reports Server (NTRS)

1980-01-01

Results are presented of a 2,000 hour cycled life test program conducted to determine the effect of short term surge current screening on approximately 47 micron f/volt solid tantalum capacitors. The format provides average values and standard deviations of the parameters, capacitance, dissipation factor, and equivalent series resistance at 120 Hz, 1KHz, abd 40 KHz.

Antimicrobial activity of tantalum oxide coatings decorated with Ag nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Huiliang, E-mail: hlc@mail.sic.ac.cn; Meng, Fanhao; Liu, Xuanyong, E-mail: xyliu@mail.sic.ac.cn

Silver plasma immersion ion implantation was used to decorate silver nanoparticles (Ag NPs) on tantalum oxide (TO) coatings. The coatings acted against bacterial cells (Staphylococcus epidermidis) in the dark by disrupting their integrity. The action was independent of silver release and likely driven by the electron storage capability of the Schottky barriers established at the interfaces between Ag NPs and the TO support. Moreover, no apparent side effect on the adhesion and differentiation of rat bone mesenchymal stem cells was detected when using Ag NPs-modified TO coatings. These results demonstrate that decoration of tantalum oxide using Ag NPs could bemore » a promising procedure for improving the antibacterial properties for orthopedic and dental implants.« less

Direct electroplating of copper on tantalum from ionic liquids in high vacuum: origin of the tantalum oxide layer.

PubMed

Schaltin, Stijn; D'Urzo, Lucia; Zhao, Qiang; Vantomme, André; Plank, Harald; Kothleitner, Gerald; Gspan, Christian; Binnemans, Koen; Fransaer, Jan

2012-10-21

In this paper, it is shown that high vacuum conditions are not sufficient to completely remove water and oxygen from the ionic liquid 1-ethyl-3-methylimidazolium chloride. Complete removal of water demands heating above 150 °C under reduced pressure, as proven by Nuclear Reaction Analysis (NRA). Dissolved oxygen gas can only be removed by the use of an oxygen scavenger such as hydroquinone, despite the fact that calculations show that oxygen should be removed completely by the applied vacuum conditions. After applying a strict drying procedure and scavenging of molecular oxygen, it was possible to deposit copper directly on tantalum without the presence of an intervening oxide layer.

Reduction of Carbon Monoxide. Past Research Summary

DOE R&D Accomplishments Database

Schrock, R. R.

1982-01-01

Research programs for the year on the preparation, characterization, and reactions of binuclear tantalum complexes are described. All evidence to date suggest the following of these dimeric molecules: (1) the dimer does not break into monomers under mild conditions; (2) intermolecular hydride exchange is not negligible, but it is slow; (3) intermolecular non-ionic halide exchange is fast; (4) the ends of the dimers can rotate partially with respect to one another. The binuclear tantalum hydride complexes were found to react with carbon monoxide to give a molecule which is the only example of reduction of CO by a transition metal hydride to give a complex containing a CHO ligand. Isonitrides also reacted in a similar manner with dimeric tantalum hydride. (ATT)

Stress-rupture strength and microstructural stability of tungsten-hafnium-carbon-wire reinforced superalloy composites

NASA Technical Reports Server (NTRS)

Petrasek, D. W.; Signorelli, R. A.

1974-01-01

Tungsten-hafnium-carbon - superalloy composites were found to be potentially useful for turbine blade applications on the basis of stress-rupture strength. The 100- and 1000-hr rupture strengths calculated for 70 vol. % fiber composites based on test data at 1090C (2000F) were 420 and 280 MN/m2 (61,000 and 41,000 psi, respectively). The investigation indicated that, with better quality fibers, composites having 100- and 1000-hr rupture strengths of 570 and 370 MN/m2 (82,000 and 54,000 psi, respectively), may be obtained. Metallographic studies indicated sufficient fiber-matrix compatibility for 1000 hr or more at 1090C (2000F).

Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts.

PubMed

Rizo, Hanika; Walker, Richard J; Carlson, Richard W; Horan, Mary F; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G

2016-05-13

How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth's primary accretionary period have survived to the present. Copyright © 2016, American Association for the Advancement of Science.

Primary human osteoblasts grow into porous tantalum and maintain an osteoblastic phenotype.

PubMed

Welldon, Katie J; Atkins, Gerald J; Howie, Donald W; Findlay, David M

2008-03-01

Porous tantalum (Ta) has found application in orthopedics, although the interaction of human osteoblasts (HOB) with this material has not been reported. The aim of this study was to investigate the interaction of primary HOB with porous tantalum, using 5-mm thick discs of porous tantalum. Comparison was made with discs of solid tantalum and tissue culture plastic. Confocal microscopy was used to investigate the attachment and growth of cells on porous Ta, and showed that HOB attached successfully to the metal "trabeculae," underwent extensive cell division, and penetrated into the Ta pores. The maturation of HOB on porous Ta was determined in terms of cell expression of the osteoblast phenotypic markers, STRO-1, and alkaline phosphatase. Despite some donor-dependent variation in STRO-1/AlkPhos expression, growth of cells grown on porous Ta either promoted, or did not impede, the maturation of HOB. In addition, the expression of key osteoblastic genes was investigated after 14 days of culture. The relative levels of mRNA encoding osteocalcin, osteopontin and receptor activator of NFkappaB ligand (RANKL) was not different between porous or solid Ta or plastic, although these genes were expressed differently by cells of different donors. However, bone sialoprotein and type I collagen mRNA species showed a decreased expression on porous Ta compared with expression on plastic. No substrate-dependent differences were seen in the extent of in vitro mineralization by HOB. These results indicate that porous Ta is a good substrate for the attachment, growth, and differentiated function of HOB. (c) 2007 Wiley Periodicals, Inc.

Efficient UV-emitting X-ray phosphors: octahedral Zr(PO 4) 6 luminescence centers in potassium hafnium-zirconium phosphates K 2Hf 1- xZr x(PO 4) 2 and KHf 2(1- x) Zr 2 x(PO 4) 3

NASA Astrophysics Data System (ADS)

Torardi, C. C.; Miao, C. R.; Li, J.

2003-02-01

Potassium hafnium-zirconium phosphates, K 2Hf 1- xZr x(PO 4) 2 and KHf 2(1- x) Zr 2 x(PO 4) 3, are broad-band UV-emitting phosphors. At room temperature, they have emission peak maxima at approximately 322 and 305 nm, respectively, under 30 kV peak molybdenum X-ray excitation. Both phosphors demonstrate luminescence efficiencies that make them up to ˜60% as bright as commercially available CaWO 4 Hi-Plus. The solid-state and flux synthesis conditions, and X-ray excited UV luminescence of these two phosphors are discussed. Even though the two compounds have different atomic structures, they contain zirconium in the same active luminescence environment as that found in highly efficient UV-emitting BaHf 1- xZr x(PO 4) 2. All the three materials have hafnium and zirconium in octahedral coordination via oxygen-atom corner sharing with six separate PO 4 tetrahedra. This octahedral Zr(PO 4) 6 moiety appears to be an important structural element for efficient X-ray excited luminescence, as are the edge-sharing octahedral TaO 6 chains for tantalate emission.

Mineral resource of the month: tantalum

USGS Publications Warehouse

Cunningham, Larry D.

2004-01-01

Tantalum is a metal that is critical to the United States because of its defense-related applications in aircraft, missiles and radio communications. It is ductile, easily fabricated, highly resistant to corrosion by acids, a good conductor of heat and electricity, and has a high melting point. Tantalum’s first commercial usage was as filament material in incandescent electric lamps in the early 1900s.

Transition of dislocation glide to shear transformation in shocked tantalum

DOE PAGES

Hsiung, Luke L.; Campbell, Geoffrey H.

2017-02-28

A TEM study of pure tantalum and tantalum-tungsten alloys explosively shocked at a peak pressure of 30 GPa (strain rate: ~1 x 10 4 sec -1) is presented. While no ω (hexagonal) phase was found in shock-recovered pure Ta and Ta-5W that contain mainly a low-energy cellular dislocation structure, shock-induced ω phase was found to form in Ta-10W that contains evenly distributed dislocations with a stored dislocation density higher than 1 x 10 12 cm -2. The TEM results clearly reveal that shock-induced α (bcc) → ω (hexagonal) shear transformation occurs when dynamic recovery reactions which lead the formation low-energymore » cellular dislocation structure become largely suppressed in Ta-10W shocked under dynamic (i.e., high strain-rate and high-pressure) conditions. A novel dislocation-based mechanism is proposed to rationalize the transition of dislocation glide to twinning and/or shear transformation in shock-deformed tantalum. Lastly, twinning and/or shear transformation take place as an alternative deformation mechanism to accommodate high-strain-rate straining when the shear stress required for dislocation multiplication exceeds the threshold shear stresses for twinning and/or shear transformation.« less

STEM and APT characterization of scale formation on a La,Hf,Ti-doped NiCrAl model alloy.

PubMed

Unocic, Kinga A; Chen, Yimeng; Shin, Dongwon; Pint, Bruce A; Marquis, Emmanuelle A

2018-06-01

A thermally grown scale formed on a cast NiCrAl model alloy doped with lanthanum, hafnium, and titanium was examined after isothermal exposure at 1100 °C for 100 h in dry flowing O 2 to understand the dopant segregation along scale grain boundaries. The complex scale formed on the alloy surface was composed of two types of substrates: phase-dependent, thin (<250 nm) outer layers and a columnar-grained ∼3.5 μm inner alumina layer. Two types of oxides formed between the inner and outer scale layers: small (3-15 nm) La 2 O 3 and larger (≤50 nm) HfO 2 oxide precipitates. Nonuniform distributions of the hafnium, lanthanum, and titanium dopants were observed along the inner scale grain boundaries, with hafnium dominating in most of the grain boundaries of α-Al 2 O 3. The concentration of reactive elements (RE) seemed to strongly depend on the grain boundary structure. The level of titanium grain boundary segregation in the inner scale decreased toward the model alloy (substrate), confirming the fast outward diffusion of titanium. Hafnium was also observed at the metal-scale interface and in the γ' (Ni 3 Al) phase of the alloy. High-resolution scanning transmission electron microscopy (STEM) confirmed the substitution of REs for aluminum atoms at the scale grain boundaries, consistent with both the semiconducting band structure and the site-blocking models. Both STEM and atom probe tomography allowed quantification of REs along the scale grain boundaries across the scale thickness. Analysis of the scale morphology after isothermal exposure in flowing oxygen revealed a myriad of new precipitate phases, RE segregation dependence on grain boundary type, and atomic arrangement along scale grain boundaries, which is expected to influence the scale growth rate, stability, and mechanical properties. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effect of Mechanical Stresses on Characteristics of Chip Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander A.

2007-01-01

The effect of compressive mechanical stresses on chip solid tantalum capacitors is investigated by monitoring characteristics of different part types under axial and hydrostatic stresses. Depending on part types, an exponential increase of leakage currents was observed when stresses exceeded 10 MPa to 40 MPa. For the first time, reversible variations of leakage currents (up to two orders of magnitude) with stress have been demonstrated. Mechanical stresses did not cause significant changes of AC characteristics of the capacitors, whereas breakdown voltages measured during the surge current testing decreased substantially indicating an increased probability of failures of stressed capacitors in low impedance applications. Variations of leakage currents are explained by a combination of two mechanisms: stress-induced scintillations and stress-induced generation of electron traps in the tantalum pentoxide dielectric.

A highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film with the solvent bath treatment by dimethyl sulfoxide as cathode for polymer tantalum capacitor

NASA Astrophysics Data System (ADS)

Ma, Xiaopin; Wang, Xiuyu; Li, Mingxiu; Chen, Tongning; Zhang, Hao; Chen, Qiang; Ding, Bonan; Liu, Yanpeng

2016-06-01

The highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films were prepared on porous tantalum pentoxide surface as cathode for polymer tantalum capacitors (PTC). The electrical performances of PTC with PEDOT:PSS films as cathode were optimized by dimethyl sulfoxide (DMSO) bath treatment. With the DMSO-bath treatment of PTC, the equivalent series resistance (ESR) of PTC decreased from 25 mΩ to 9 mΩ. The ultralow ESR led to better capacitance-frequency performance. The device reliability investigation revealed the enhanced environmental stability of PTC. The enhanced performances were attributed to the conductivity improvement of PEDOT:PSS cathode films and the removal of excess PSS from PEDOT:PSS films.

Tantalum protective coatings for fusion reactor applications

NASA Astrophysics Data System (ADS)

Brossa, Francesco; Piatti, Giovanni; Bardy, Michel

Tantalum has a very low sputtering yield, high melting point, low vapour pressure and good mechanical properties at low and high temperatures, so it is a very interesting candidate for the first wall and blanket structural components. Tantalum coatings overcome the problems of fabrication and joining bulk Ta, thus reducing also dead weight and cost. Ta coatings were produced by chemical vapour deposition and plasma spraying on four conventional structural materials: Al, Cu, AISI 316 L and Inconel 600. The conditions which improve adherence have been studied. The composition of the films was determined by chemical means and by X-ray analysis. Metallographie examination was employed to define the morphological structure of the deposits. The adherence of the coatings was determined by subjecting the samples to bend tests and to thermal shocks.

The Electrochemical Behavior of Mo-Ta Alloy in Phosphoric Acid Solution for TFT-LCD Application.

PubMed

Lee, Sang-Hyuk; Kim, Byoung O; Seo, Jong Hyun

2015-10-01

Molybdenum-tantalum alloy thin film is a suitable material for the higher corrosion resistance and low resistivity for gate and data metal lines. In this study, Mo-Ta alloy thin films were prepared by using a DC magnetron co-sputtering system on a glass substrate. An abrupt increase in the etching rates of low Mo-Ta alloys was observed. From the observed impedance analysis, the defect densities in the MoTa oxide films increased from 5.4 x 10(21) (cm(-3)) to 8.02 x 10(21) (cm(-3)) up to the 6 at% of tantalum level; and above the 6 at% of tantalum level, the defect densities decreased. This electrochemical behavior is explained by the mechanical instability of the MoTa oxide film.

Chemical precursors to non-oxide ceramics: Macro to nanoscale materials

NASA Astrophysics Data System (ADS)

Forsthoefel, Kersten M.

Non-oxide ceramics exhibit a number of important properties that make them ideal for technologically important applications (thermal and chemical stability, high strength and hardness, wear-resistance, light weight, and a range of electronic and optical properties). Unfortunately, traditional methodologies to these types of materials are limited to fairly simple shapes and complex processed forms cannot be attained through these methods. The establishment of the polymeric precursor approach has allowed for the generation of advanced materials, such as refractory non-oxide ceramics, with controlled compositions, under moderate conditions, and in processed forms. The goal of the work described in this dissertation was both to develop new processible precursors to technologically important ceramics and to achieve the formation of advanced materials in processed forms. One aspect of this research exploited previously developed preceramic precursors to boron carbide, boron nitride and silicon carbide for the generation of a wide variety of advanced materials: (1) ultra-high temperature ceramic (UHTC) structural materials composed of hafnium boride and related composite materials, (2) the quaternary borocarbide superconductors, and (3) on the nanoscale, non-oxide ceramic nanotubules. The generation of the UHTC and the quaternary borocarbide materials was achieved through a method that employs a processible polymer/metal(s) dispersion followed by subsequent pyrolyses. In the case of the UHTC, hafnium oxide, hafnium, or hafnium boride powders were dispersed in a suitable precursor to afford hafnium borides or related composite materials (HfB2/HfC, HfB2/HfN, HfB2/SiC) in high yields and purities. The quaternary borocarbide superconducting materials were produced from pyrolyses of dispersions containing appropriate stoichiometric amounts of transition metal, lanthanide metal, and the polyhexenyldecaborane polymer. Both chemical vapor deposition (CVD) based routes employing a molecular precursor and porous alumina templating routes paired with solution-based methodologies are shown to generate non-oxide ceramic nanotubules of boron carbide, boron nitride and silicon carbide compositions. In the final phase of this work, a new metal-catalyzed route to poly(1-alkenyl- o-carborane) homopolymers and related copolymers was developed. Both homopolymers of 1-alkenyl-o-carboranes (1-vinyl-, 1-butenyl-, 1-hexenyl-) and copolymers of 1-hexenyl-o-carborane and allyltrimethylsilane or 1-hexenyl-o-carborane and 6-hexenyldecaborane were synthesized via the Cp2ZrMe2/B(C6F5) 3 catalyst system. A copolymer containing 1-hexenyl-o-carborane and the cross-linking agent, 6-hexenyldecaborane, was synthetically designed which exhibits initial cross-linking at ˜250°C and then converts in 75% yields to boron carbide at 1250°C.

NASA's activities in the conservation of strategic aerospace materials

NASA Technical Reports Server (NTRS)

Stephens, J. R.

1980-01-01

The United States imports 50-100 percent of certain metals critical to the aerospace industry, namely, cobalt, columbium, chromium, and tantalum. In an effort to reduce this dependence on foreign sources, NASA is planning a program called Conservation of Strategic Aerospace Materials (COSAM), which will provide technology minimizing strategic metal content in the components of aerospace structures such as aircraft engines. With a proposed starting date of October 1981, the program will consist of strategic element substitution, process technology development, and alternate materials research. NASA's two-fold pre-COSAM studies center on, first, substitution research involving nickel-base and cobalt-base superalloys (Waspaloy, Udimet-700, MAE-M247, Rene 150, HA-188) used in turbine disks, low-pressure blades, turbine blades, and combustors; and, second, alternate materials research devoted initially to investigating possible structural applications of the intermetallic alloys nickel aluminide and iron aluminide.

An evaluation of 10 percent and 20 percent benzocaine gels in patients with acute toothaches: efficacy, tolerability and compliance with label dose administration directions.

PubMed

Hersh, Elliot V; Ciancio, Sebastian G; Kuperstein, Arthur S; Stoopler, Eric T; Moore, Paul A; Boynes, Sean G; Levine, Steven C; Casamassimo, Paul; Leyva, Rina; Mathew, Tanya; Shibly, Othman; Creighton, Paul; Jeffers, Gary E; Corby, Patricia M A; Turetzky, Stanley N; Papas, Athena; Wallen, Jillian; Idzik-Starr, Cynthia; Gordon, Sharon M

2013-05-01

The authors evaluated the efficacy and tolerability of 10 percent and 20 percent benzocaine gels compared with those of a vehicle (placebo) gel for the temporary relief of toothache pain. They also assessed the compliance with the label dose administration directions on the part of participants with toothache pain. Under double-masked conditions, 576 participants self-applied study gel to an open tooth cavity and surrounding oral tissues. Participants evaluated their pain intensity and pain relief for 120 minutes. The authors determined the amount of gel the participants applied. The responders' rates (the primary efficacy parameter), defined as the percentage of participants who had an improvement in pain intensity as exhibited by a pain score reduction of at least one unit on the dental pain scale from baseline for two consecutive assessments any time between the five- and 20-minute points, were 87.3 percent, 80.7 percent and 70.4 percent, respectively, for 20 percent benzocaine gel, 10 percent benzocaine gel and vehicle gel. Both benzocaine gels were significantly (P ≤ .05) better than vehicle gel; the 20 percent benzocaine gel also was significantly (P ≤ .05) better than the 10 percent benzocaine gel. The mean amount of gel applied was 235.6 milligrams, with 88.2 percent of participants applying 400 mg or less. Both 10 percent and 20 percent benzocaine gels were more efficacious than the vehicle gel, and the 20 percent benzocaine gel was more efficacious than the 10 percent benzocaine gel. All treatments were well tolerated by participants. Practical Implications. Patients can use 10 percent and 20 percent benzocaine gels to temporarily treat toothache pain safely.

An evaluation of 10 percent and 20 percent benzocaine gels in patients with acute toothaches

PubMed Central

Hersh, Elliot V.; Ciancio, Sebastian G.; Kuperstein, Arthur S.; Stoopler, Eric T.; Moore, Paul A.; Boynes, Sean G.; Levine, Steven C.; Casamassimo, Paul; Leyva, Rina; Mathew, Tanya; Shibly, Othman; Creighton, Paul; Jeffers, Gary E.; Corby, Patricia M.A.; Turetzky, Stanley N.; Papas, Athena; Wallen, Jillian; Idzik-Starr, Cynthia; Gordon, Sharon M.

2013-01-01

Background The authors evaluated the efficacy and tolerability of 10 percent and 20 percent benzocaine gels compared with those of a vehicle (placebo) gel for the temporary relief of toothache pain. They also assessed the compliance with the label dose administration directions on the part of participants with toothache pain. Methods Under double-masked conditions, 576 participants self-applied study gel to an open tooth cavity and surrounding oral tissues. Participants evaluated their pain intensity and pain relief for 120 minutes. The authors determined the amount of gel the participants applied. Results The responders’ rates (the primary efficacy parameter), defined as the percentage of participants who had an improvement in pain intensity as exhibited by a pain score reduction of at least one unit on the dental pain scale from baseline for two consecutive assessments any time between the five- and 20-minute points, were 87.3 percent, 80.7 percent and 70.4 percent, respectively, for 20 percent benzocaine gel, 10 percent benzocaine gel and vehicle gel. Both benzocaine gels were significantly (P ≤ .05) better than vehicle gel; the 20 percent benzocaine gel also was significantly (P ≤ .05) better than the 10 percent benzocaine gel. The mean amount of gel applied was 235.6 milligrams, with 88.2 percent of participants applying 400 mg or less. Conclusions Both 10 percent and 20 percent benzocaine gels were more efficacious than the vehicle gel, and the 20 percent benzocaine gel was more efficacious than the 10 percent benzocaine gel. All treatments were well tolerated by participants. Practical Implications Patients can use 10 percent and 20 percent benzocaine gels to temporarily treat toothache pain safely. PMID:23633700

Characterization of Tantalum Polymer Capacitors

NASA Technical Reports Server (NTRS)

Spence, Penelope

2012-01-01

Overview Reviewed data Caution must be taken when accelerating test conditions Data not useful to establish an acceleration model Introduction of new failure mechanism skewing results Evidence of Anti-Wear-Out De-doping of polymer Decreased capacitance Increased ESR Not dielectric breakdown Needs further investigation Further investigation into tantalum polymer capacitor technology Promising acceleration model for Manufacturer A Possibility for use in high-reliability space applications with suitable voltage derating.

Super miniaturization of film capacitor dielectrics

NASA Technical Reports Server (NTRS)

Lavene, B.

1981-01-01

The alignment of the stable electrical characteristics of film capacitors in the physical dimensions of ceramic and tantalum capacitors are discussed. The reliability of polycarbonate and mylar capacitors are described with respect to their compatibility with military specifications. Graphic illustrations are presented which show electrical and physical comparisons of film, ceramic, and tantalum capacitors. The major focus is on volumetric efficiency, weight reduction, and electrical stability.

New PVD Technologies for New Ordnance Coatings

DTIC Science & Technology

2012-04-01

characteristics using a Tantalum and a Chrome target; 4) Deposition of Ta coatings and reactive deposition of CrN; 5) Deposition parameters affecting film...Vapor Deposition (PVD); High Power Impulse Magnetron Sputtering (HIPIMS); Modulated Pulsed Power (MPP); Tantalum; Chrome ; Ta coatings; CrN; coating...The pre-production chemicals and acids are hazardous and hexavalent Cr is a known carcinogen. Significant annual expenditures are necessary to

A COMPARISON OF EXPERIMENTS AND THREE-DIMENSIONAL ANALYSIS TECHNIQUES. PART I. UNPOISONED UNIFORM SLAB CORE WITH A PARTIALLY INSERTED HAFNIUM ROD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Renzi, N.E.; Roseberry, R.J.

>The experimental measurements and nuclear analysis of a uniformly loaded, unpoisoned slab core with a partially insented hafnium rod are described. Comparisons of experimental data with calculated results of the UFO code and flux synthesis techniques are given. It was concluded that one of the flux synthesis techniques and the UFO code are able to predict flux distributions to within approximately 5% of experiment for most cases. An error of approximately 10% was found in the synthesis technique for a channel near the partially inserted rod. The various calculations were able to predict neutron pulsed shutdowns to only approximately 30%.more » (auth)« less

Atomic layer deposition of hafnium oxide: A detailed reaction mechanism from first principles

NASA Astrophysics Data System (ADS)

Widjaja, Yuniarto; Musgrave, Charles B.

2002-08-01

Atomic layer deposition (ALD) of hafnium oxide (HfO2) using HfCl4 and H2O as precursors is studied using density functional theory. The mechanism consists of two deposition half-reactions: (1) HfCl4 with Hf-OH sites, and (2) H2O with Hf-Cl sites. Both half-reactions exhibit stable intermediates with energies lower than those of the final products. We show that increasing the temperature reduces the stability of the complex. However, increasing temperature also increases the dissociation free-energy barrier, which in turn results in increased desorption of adsorbed precursors. Both half-reactions are qualitatively similar to the corresponding reactions of ZrO2 ALD using ZrCl4 and H2O.

A change in the geodynamics of continental growth 3 billion years ago.

PubMed

Dhuime, Bruno; Hawkesworth, Chris J; Cawood, Peter A; Storey, Craig D

2012-03-16

Models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout Earth's history. The oxygen isotopic composition of zircons, for which uranium-lead and hafnium isotopic data provide age constraints, is a key archive of crustal reworking. We identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time. Growth of continental crust appears to have been a continuous process, albeit at variable rates. A marked decrease in the rate of crustal growth at ~3 billion years ago may be linked to the onset of subduction-driven plate tectonics.

[Immobilization of pectawamorine G10x on silichromes].

PubMed

Bogatskiĭ, A V; Davidenko, T I; Gren', T A

1980-01-01

Immobilization of pectawamorine G10x on silochromes, using cyanuric chloride, 2,4-toluylene diisocyanate, glutaric dialdehyde, thionyl chloride, phosphorus tribromide, titanium tetrachloride, zirconium oxychloride and hafnium oxychloride was studied. The use of glutaric dialdehyde assured the strongest binding and the preatest stability of activity. Properties of the native pectawamorine G10x and immobilized preparations were studied on a comparative basis. Pectawamorine G10x immobilized by means of hafnium oxychloride showed increased stability when stored at 5 degrees C and used repeatedly. In every case, except for cyanuric chloride and glutaric dialdehyde, maximum activity was at a temperature 10 degrees C higher than for the native enzyme, and optimum pH varied for the preparations with different binding reagents.

Investigation to develop a method to apply diffusion barrier to high strength fibers

NASA Technical Reports Server (NTRS)

Veltri, R. D.; Paradis, R. D.; Douglas, F. C.

1975-01-01

A radio frequency powered ion plating process was used to apply the diffusion barriers of aluminum oxide, yttrium oxide, hafnium oxide and titanium carbide to a substrate tungsten fiber. Each of the coatings was examined as to its effect on both room temperature strength and tensile strength of the base tungsten fiber. The coated fibers were then overcoated with a nickel alloy to become single cell diffusion couples. These diffusion couples were exposed to 1093 C for 24 hours, cycled between room temperature and 1093 C, and given a thermal anneal for 100 hours at 1200 C. Tensile testing and metallographic examinations determined that the hafnium oxide coating produced the best high temperature diffusion barrier for tungsten of the four coatings.

Tantalum-based thin film coatings for wear resistant arthroprostheses.

PubMed

Balagna, C; Faga, M G; Spriano, S

2011-10-01

Cobalt-chromium-molybdenum alloys with high carbon content (HC-CoCrMo) are widely used as materials for arthroprosthesis, in particular in metal-on-metal (MoM) hip joints. In spite of their good wear and corrosion resistance, production of metallic wear particles and metal ion release will occur on a large time-scale. An enhancement of the metal ion level in the patient's blood and urine is often reported in clinical data. Hypersensitivity, inflammatory response and cell necrosis can occur as consequence. So implants on young patients and women on childbearing age are not so widespread. The aim of this research is the realization of a thin film coating in order to improve the biocompatibility of Co-based alloys and to reduce debris production, ion release and citotoxicity. The innovative process consists of a thermal treatment in molten salts, in order to obtain a tantalum enriched thin film coating. Tantalum is chosen because it is considered a biocompatible metal with high corrosion resistance and low ion release. Three HC-CoCrMo alloys, produced by different manufacturing processes, are tested as substrates. The coating is a thin film of TaC or it can be composed by a multilayer of two tantalum carbides and metallic tantalum, depending on the temperature of the treatment and on the carbon content of the substrate. The thin films as well the substrates are characterized from the structural, chemical and morphological point of view. Moreover mechanical behaviour of treated and untreated materials is analyzed by means of nanohardness, scratch and ball-on-disc wear tests. The coating increases the mechanical and tribological properties of HC-CoCrMo.

Response and representation of ductile damage under varying shock loading conditions in tantalum

DOE PAGES

Bronkhorst, C. A.; Gray, III, G. T.; Addessio, F. L.; ...

2016-02-25

The response of polycrystalline metals, which possess adequate mechanisms for plastic deformation under extreme loading conditions, is often accompanied by the formation of pores within the structure of the material. This large deformation process is broadly identified as progressive with nucleation, growth, coalescence, and failure the physical path taken over very short periods of time. These are well known to be complex processes strongly influenced by microstructure, loading path, and the loading profile, which remains a significant challenge to represent and predict numerically. In the current study, the influence of loading path on the damage evolution in high-purity tantalum ismore » presented. Tantalum samples were shock loaded to three different peak shock stresses using both symmetric impact, and two different composite flyer plate configurations such that upon unloading the three samples displayed nearly identical “pull-back” signals as measured via rear-surface velocimetry. While the “pull-back” signals observed were found to be similar in magnitude, the sample loaded to the highest peak stress nucleated a connected field of ductile fracture which resulted in complete separation, while the two lower peak stresses resulted in incipient damage. The damage evolution in the “soft” recovered tantalum samples was quantified using optical metallography, electron-back-scatter diffraction, and tomography. These experiments are examined numerically through the use of a model for shock-induced porosity evolution during damage. The model is shown to describe the response of the tantalum reasonably well under strongly loaded conditions but less well in the nucleation dominated regime. As a result, numerical results are also presented as a function of computational mesh density and discussed in the context of improved representation of the influence of material structure upon macro-scale models of ductile damage.« less

Variation of Nb-Ta, Zr-Hf, Th-U and K-Cs in two diabase-granophyre suites

USGS Publications Warehouse

Gottfried, D.; Greenland, L.P.; Campbell, E.Y.

1968-01-01

Concentrations of Nb, Ta, Zr, Hf, Th, U and Cs have been determined in samples of igneous rocks representing the diabase-granophyre suites from Dillsburg, Pennsylvania, and Great Lake, Tasmania. Niobium and tantalum have a three to fourfold increase with differentiation in each of the suites. The chilled margin of the Great Lake intrusion contains half the niobium and tantalum content (5.3 ppm and 0.4 ppm, respectively) of the chilled basalt from Dillsburg (10 ppm and 0.9 ppm, respectively). The twofold difference between the suites is correlated with differences in their titanium content. The average Nb Ta ratios for each suite are similar: 13.5 for the Great Lake suite, and 14.4 for the Dillsburg suite. The zirconium content of the two suites is essentially the same and increases from 50 to 60 ppm in the chilled margins to 240-300 ppm in the granophyres. Hafnium is low in the early formed rocks (0.5 -1.5 ppm and achieves a maximum in the granophyres (5-8 ppm). The Zr Hfratio decreases from 68 to 33 with progressive differentiation. In the Dillsburg suite thorium and uranium increase from 2.6 ppm and 0.6 ppm, respectively, in the chilled samples to 11.8 ppm and 3.1 ppm in the granophyres. The chilled margin of the Great Lake suite contains 3.2 ppm thorium and 9.8 ppm uranium; the granophyre contains 11.2 ppm thorium and 2.8 ppm uranium. The average Th U ratios of the Dillsburg and Great Lake suites are nearly the same-4.1 and 4.4, respectively. Within each suite the Th U ratio remains quite constant. Cesium and the K Cs ratio do not vary systematically in the Dillsburg suite possibly because of redistribution or loss of cesium by complex geologic processes. Except for the chilled margin of the Great Lake suite, the variation of Cs and the K Cs ratio are in accord with theoretical considerations. Cesium increases from about 0.6 ppm in the lower zone to 3.5 ppm in the granophyre; the K Cs ratio varies from 10 ?? 103 in the lower zone to 6 ?? 103 in the granophyre. A comparison of the abundance of some of these elements is made with those reported on oceanic tholeiites from the Atlantic and Pacific oceans. Trace elements with large ionic radii (Th, U, Cs) are present in significantly greater concentrations in the two continental tholeiitic series than in the oceanic tholeiites. However, this does not seem to be true for lithophilic elements of smaller ionic radii (Zr and Nb). These trace element distribution patterns, when considered with other minor element and isotopic studies, indicate that 1. (1) crustal contamination does not entirely account for differences between continental and oceanic tholeiites, and 2. (2) the oceanic tholeiites do not necessarily delimit the geochemical characteristics of the mantle. ?? 1968.

The Tri-lab Tantalum Strength Consortium

NASA Astrophysics Data System (ADS)

Flicker, Dawn G.; Arsenlis, Thomas A.; Austin, Ryan; Barton, Nathan R.; Benage, John F.; Bronkhorst, Curt A.; Brown, Justin L.; Brown, Staci L.; Buttler, William T.; Shen, Shuh-Rong; Dattelbaum, Dana M.; Fensin, Sayu J.; Gray, George T., III; Lane, J. Matthew D.; Lim, Hojun; Luscher, D. J.; Mattsson, Thomas R.; McNabb, Dennis P.; Remington, Bruce A.; Park, Hye-Sook; Prisbrey, Shon T.; Prime, Michael B.; Scharff, Robert J.; Schraad, Mark W.; Sun, Amy C.

2017-06-01

A Tri-lab consortium of experimentalists and theorists at SNL, LLNL, and LANL is joining forces to better understand tantalum strength across an unprecedented range of loading conditions. The team is collecting and comparing tantalum strength data from Hopkinson bar, Taylor cylinder, guns, Z, Omega and the NIF. These experiments, all using Ta from a single lot, span pressures from tenths to hundreds of GPa and strain rates from 103 to 107. New experiments are underway to provide more overlap between the platforms. The experiments are being simulated with a variety of models in order to determine which processes are important under which conditions. The presentation will show results to date. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.

Synthesis, Consolidation and Characterization of Sol-gel Derived Tantalum-Tungsten Oxide Thermite Composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cervantes, O

2010-06-01

Energetic composite powders consisting of sol-gel (SG) derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition-tested and results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High Pressure Spark Plasma Sintering (HPSPS) technique, on the SG derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The SG derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta - WO3) energetic composite was consolidated to a density of 9.17 g·cm-3more » or 93% relative density. In addition, those samples were consolidated without significant pre-reaction of the constituents, thus retaining their stored chemical energy.« less

Physics of Shock Compression and Release: NEMD Simulations of Tantalum and Silicon

NASA Astrophysics Data System (ADS)

Hahn, Eric; Meyers, Marc; Zhao, Shiteng; Remington, Bruce; Bringa, Eduardo; Germann, Tim; Ravelo, Ramon; Hammerberg, James

2015-06-01

Shock compression and release allow us to evaluate physical deformation and damage mechanisms occurring in extreme environments. SPaSM and LAMMPS molecular dynamics codes were employed to simulate single and polycrystalline tantalum and silicon at strain rates above 108 s-1. Visualization and analysis was accomplished using OVITO, Crystal Analysis Tool, and a redesigned orientation imaging function implemented into SPaSM. A comparison between interatomic potentials for both Si and Ta (as pertaining to shock conditions) is conducted and the influence on phase transformation and plastic relaxation is discussed. Partial dislocations, shear induced disordering, and metastable phase changes are observed in compressed silicon. For tantalum, the role of grain boundary and twin intersections are evaluated for their role in ductile spallation. Finally, the temperature dependent response of both Ta and Si is investigated.

Climax-Type Porphyry Molybdenum Deposits

USGS Publications Warehouse

Ludington, Steve; Plumlee, Geoffrey S.

2009-01-01

Climax-type porphyry molybdenum deposits, as defined here, are extremely rare; thirteen deposits are known, all in western North America and ranging in age from Late Cretaceous to mainly Tertiary. They are consistently found in a postsubduction, extensional tectonic setting and are invariably associated with A-type granites that formed after peak activity of a magmatic cycle. The deposits consist of ore shells of quartz-molybdenite stockwork veins that lie above and surrounding the apices of cupola-like, highly evolved, calc-alkaline granite and subvolcanic rhyolite-porphyry bodies. These plutons are invariably enriched in fluorine (commonly >1 percent), rubidium (commonly >500 parts per million), and niobium-tantalum (Nb commonly >50 parts per million). The deposits are relatively high grade (typically 0.1-0.3 percent Mo) and may be very large (typically 100-1,000 million tons). Molybdenum, as MoS2, is the primary commodity in all known deposits. The effect on surface-water quality owing to natural influx of water or sediment from a Climax-type mineralized area can extend many kilometers downstream from the mineralized area. Waste piles composed of quartz-silica-pyrite altered rocks will likely produce acidic drainage waters. The potential exists for concentrations of fluorine or rare metals in surface water and groundwater to exceed recommended limits for human consumption near both mined and unmined Climax-type deposits.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neiman, Aleksei A., E-mail: nasa@ispms.tsc.ru; Lotkov, Aleksandr I.; Gudimova, Ekaterina Y.

The paper reports on a study of regularities of formation gradient nano-, submicron and microstructural conditions in the surface layers of the samples after pulsed electron-beam melting of tantalum coating on the substrate NiTi alloy. Experimentally revealed the presence of submicron columnar structure in the upper layers of the tantalum coating. After irradiation modified NiTi surface takes on a layered structure in which each layer differs in phase composition and structural phase state.

Direct observation of localized radial oxygen migration in functioning tantalum oxide memristors

DOE PAGES

Kumar, Suhas; Graves, Catherine E.; Strachan, John Paul; ...

2016-02-02

Oxygen migration in tantalum oxide, a promising next-generation storage material, is studied using in operando x-ray absorption spectromicroscopy and is used to microphysically describe accelerated evolution of conduction channel and device failure. Furthermore, the resulting ring-like patterns of oxygen concentration are modeled using thermophoretic forces and Fick diffusion, establishing the critical role of temperature-activated oxygen migration that has been under question lately.

Capacitor electrode stimulates nerve or muscle without oxidation-reduction reactions.

PubMed

Guyton, D L; Hambrecht, F T

1973-07-06

Porous tantalum disks, available as "slugs" from the capacitor industry, have large available surface area and a thin insulating coating of tantalum pentoxide. When implanted, they fill with extracellular fluid and operate as capacitor-stimulating electrodes having high capacitance per unit volume. Capable of stimulating excitable tissute without generating electrochemical by-products, these electrodes should provide a safer interface between neural prosthetic devices and human tissue.

Electron-ion temperature equilibration in warm dense tantalum

DOE PAGES

Doppner, T; LePape, S.; Ma, T.; ...

2014-11-05

We present measurements of electron-ion temperature equilibration in proton-heated tantalum, under warm dense matter conditions. Our results agree with theoretical predictions for metals calculated using input data from ab initio simulations. Furthermore, the fast relaxation observed in the experiment contrasts with much longer equilibration times found in proton heated carbon, indicating that the energy flow pathways in warm dense matter are far from being fully understood.

Application of pyrolysis to recycling organics from waste tantalum capacitors.

PubMed

Niu, Bo; Chen, Zhenyang; Xu, Zhenming

2017-08-05

Tantalum capacitors (TCs) are widely used in electronic appliances. The rapid replacement of electronic products results in generating large amounts of waste TCs (WTCs). WTCs, rich in valuable tantalum, are considered as high quality tantalum resources for recycling. However, environmental pollution will be caused if the organics of WTCs were not properly disposed. Therefore, effectively recycling the organics of WTCs is significant for recovering the valuable parts. This study proposed an argon (Ar) pyrolysis process to recycle the organics from WTCs. The organic decomposition kinetic was first analyzed by thermogravimetry. The results showed that the organics were decomposed in two major steps and the average activation energy was calculated to 234kJ/mol. Then, the suitable pyrolysis parameters were determined as 550°C, 30min and 100ml/min. The organics were effectively decomposed and converted to oils (mainly contained phenol homologs and benzene homologs) and gases (some hydrocarbon). These pyrolysis products could be reutilized as energy sources. Moreover, based on the products and bond energy theory, the pyrolysis mechanisms of the organics were also discussed. Finally, a reasonable technological process for products utilization was presented. This study contributes to the efficient recycling the organics before valuable material recovery from WTCs. Copyright © 2017 Elsevier B.V. All rights reserved.

Leakage Currents and Gas Generation in Advanced Wet Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2015-01-01

Currently, military grade, established reliability wet tantalum capacitors are among the most reliable parts used for space applications. This has been achieved over the years by extensive testing and improvements in design and materials. However, a rapid insertion of new types of advanced, high volumetric efficiency capacitors in space systems without proper testing and analysis of degradation mechanisms might increase risks of failures. The specifics of leakage currents in wet electrolytic capacitors is that the conduction process is associated with electrolysis of electrolyte and gas generation resulting in building up of internal gas pressure in the parts. The risk associated with excessive leakage currents and increased pressure is greater for high value advanced wet tantalum capacitors, but it has not been properly evaluated yet. In this work, in Part I, leakages currents in various types of tantalum capacitors have been analyzed in a wide range of voltages, temperatures, and time under bias. Gas generation and the level of internal pressure have been calculated in Part II for different case sizes and different hermeticity leak rates to assess maximal allowable leakage currents. Effects related to electrolyte penetration to the glass seal area have been studied and the possibility of failures analyzed in Part III. Recommendations for screening and qualification to reduce risks of failures have been suggested.

Analysis of shockless dynamic compression data on solids to multi-megabar pressures: Application to tantalum

DOE PAGES

Davis, Jean -Paul; Brown, Justin L.; Knudson, Marcus D.; ...

2014-11-26

In this research, magnetically-driven, planar shockless-compression experiments to multi-megabar pressures were performed on tantalum samples using a stripline target geometry. Free-surface velocity waveforms were measured in 15 cases; nine of these in a dual-sample configuration with two samples of different thicknesses on opposing electrodes, and six in a single-sample configuration with a bare electrode opposite the sample. Details are given on the application of inverse Lagrangian analysis (ILA) to these data, including potential sources of error. The most significant source of systematic error, particularly for single-sample experiments, was found to arise from the pulse-shape dependent free-surface reflected wave interactions withmore » the deviatoric-stress response of tantalum. This could cause local, possibly temporary, unloading of material from a ramp compressed state, and thus multi-value response in wave speed that invalidates the free-surface to in-material velocity mapping step of ILA. By averaging all 15 data sets, a final result for the principal quasi-isentrope of tantalum in stress-strain was obtained to a peak longitudinal stress of 330 GPa with conservative uncertainty bounds of ±4.5% in stress. The result agrees well with a tabular equation of state developed at Los Alamos National Laboratory.« less

Random Vibration Testing of Advanced Wet Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2015-01-01

Advanced wet tantalum capacitors allow for improved performance of power supply systems along with substantial reduction of size and weight of the systems that is especially beneficial for space electronics. Due to launch-related stresses, acceptance testing of all space systems includes random vibration test (RVT). However, many types of advanced wet tantalum capacitors cannot pass consistently RVT at conditions specified in MIL-PRF-39006, which impedes their use in space projects. This requires a closer look at the existing requirements, modes and mechanisms of failures, specifics of test conditions, and acceptance criteria. In this work, different lots of advanced wet tantalum capacitors from four manufacturers have been tested at step stress random vibration conditions while their currents were monitored before, during, and after the testing. It has been shown that the robustness of the parts and their reliability are mostly due to effective self-healing processes and limited current spiking or minor scintillations caused by RVT do not increase the risk of failures during operation. A simple model for scintillations events has been used to simulate current spiking during RVT and optimize test conditions. The significance of scintillations and possible effects of gas generation have been discussed and test acceptance criteria for limited current spiking have been suggested.

High reliability sheathed, beryllia insulated, tungsten-rhenium alloy thermocouple assemblies; their fabrication and EMF stability

NASA Technical Reports Server (NTRS)

Burns, G. W.; Hurst, W. S.; Scroger, M. G.

1974-01-01

Tantalum sheathed, BeO insulated, W-3% Re/W-25% Re thermocouple assemblies were fabricated and their emf drift determined during 2059 hours of exposure at 2073 K in a gaseous helium environment. The sheathed thermocouple assemblies were constructed from aged thermoelements, specially heat-treated BeO insulators, and specially cleaned and etched tantalum sheaths. Their thermal emf drifts ranged from the equivalent of only -0.3 to -0.8 K drift per 1000 hours of exposure at 2073 K. No evidence of any gross chemical attack or degradation of the component materials was found. The emf drift and material behavior of some unsheathed, BeO insulated, W-3% Re/W-25% Re thermocouples at 2250 and 2400 K were also determined. Unsheathed thermocouples tested in an argon environment at 2250 K for 1100 hours and at 2400 K for 307 hours exhibited changes in thermal emf that typically ranged from the equivalent of a few degrees K to as much as +11 K. Post-test examinations of these thermocouples revealed some undesirable material degradation and interaction which included erosion of the BeO insulators and contamination of the thermoelements by tantalum from the tantalum blackbody enclosure in which the thermocouples were contained.

Studies on Optical and Electrical Properties of Hafnium Oxide Nanoparticles

NASA Astrophysics Data System (ADS)

Jayaraman, Venkatachalam; Sagadevan, Suresh; Sudhakar, Rajesh

2017-07-01

In this paper, the synthesis and physico-chemical properties of hafnium oxide nanoparticles (HfO2 NPs) are analyzed and reported. The synthesis was carried out by the precipitation route by using hafnium tetrachloride (HfCl4) as precursor material with potassium hydroxide (KOH) dissolved in Millipore water. In the precipitation technique, the chemical reaction is comparatively simple, low-cost and non-toxic compared to other synthetic methods. The synthesized HfO2 NPs were characterized by using powder x-ray diffraction (PXRD), ultraviolet-visible (UV-Vis) spectroscopy, Raman analysis, and high-resolution transmission electron microscopy (HRTEM). The monoclinic structure of the HfO2 NPs was resolved utilizing x-ray diffraction (XRD). The optical properties were studied from the UV-Vis absorption spectrum. The optical band gap of the HfO2NPs was observed to be 5.1 eV. The Raman spectrum shows the presence of HfO2 NPs. The HRTEM image showed that the HfO2 NPs were of spherical shape with an average particle size of around 28 nm. The energy-dispersive x-ray spectroscopy (EDS) spectrum obviously demonstrated the presence of HfO2 NPs. Analysis and studies on the dielectric properties of the HfO2 NPs such as the dielectric constant, the dielectric loss, and alternating current (AC) conductivity were carried out at varying frequencies and temperatures.

Silicon doped hafnium oxide (HSO) and hafnium zirconium oxide (HZO) based FeFET: A material relation to device physics

NASA Astrophysics Data System (ADS)

Ali, T.; Polakowski, P.; Riedel, S.; Büttner, T.; Kämpfe, T.; Rudolph, M.; Pätzold, B.; Seidel, K.; Löhr, D.; Hoffmann, R.; Czernohorsky, M.; Kühnel, K.; Thrun, X.; Hanisch, N.; Steinke, P.; Calvo, J.; Müller, J.

2018-05-01

The recent discovery of ferroelectricity in thin film HfO2 materials renewed the interest in ferroelectric FET (FeFET) as an emerging nonvolatile memory providing a potential high speed and low power Flash alternative. Here, we report more insight into FeFET performance by integrating two types of ferroelectric (FE) materials and varying their properties. By varying the material type [HfO2 (HSO) versus hafnium zirconium oxide (HZO)], optimum content (Si doping/mixture ratio), and film thickness, a material relation to FeFET device physics is concluded. As for the material type, an improved FeFET performance is observed for HZO integration with memory window (MW) comparable to theoretical values. For different Si contents, the HSO based FeFET exhibited a MW trend with different stabilized phases. Similarly, the HZO FeFET shows MW dependence on the Hf:Zr mixture ratio. A maximized MW is obtained with cycle ratios of 16:1 (HfO2:Si) and 1:1 (Hf:Zr) as measured on HSO and HZO based FeFETs, respectively. The thickness variation shows a trend of increasing MW with the increased FE layer thickness confirming early theoretical predictions. The FeFET material aspects and stack physics are discussed with insight into the interplay factors, while optimum FE material parameters are outlined in relation to performance.

Tracing the history of submarine hydrothermal inputs and the significance of hydrothermal hafnium for the seawater budget - A combined Pb-Hf-Nd isotope approach

USGS Publications Warehouse

van de Flierdt, T.; Frank, M.; Halliday, A.N.; Hein, J.R.; Hattendorf, B.; Gunther, D.; Kubik, P.W.

2004-01-01

Secular variations in the Pb isotopic composition of a mixed hydrogenous-hydrothermal ferromanganese crust from the Bauer Basin in the eastern Equatorial Pacific provide clear evidence for changes in hydrothermal contributions during the past 7 Myr. The nearby Galapagos Rise spreading center provided a strong hydrothermal flux prior to 6.5 Ma. After 6.5 Ma, the Pb became stepwise more radiogenic and more similar to Equatorial Pacific seawater, reflecting the westward shift of spreading to the presently active East Pacific Rise (EPR). A second, previously unrecognized enhanced hydrothermal period occurred between 4.4 and 2.9 Ma, which reflects either off-axis hydrothermal activity in the Bauer Basin or a late-stage pulse of hydrothermal Pb from the then active, but waning Galapagos Rise spreading center. Hafnium isotope time-series of the same mixed hydrogenous-hydrothermal crust show invariant values over the past 7 Myr. Hafnium isotope ratios, as well as Nd isotope ratios obtained for this crust, are identical to that of hydrogenous Equatorial Pacific deep water crusts and clearly indicate that hydrothermal Hf, similar to Nd, does not travel far from submarine vents. Therefore, we suggest that hydrothermal Hf fluxes do not contribute significantly to the global marine Hf budget. ?? 2004 Elsevier B.V. All rights reserved.

77 FR 5017 - Agency Information Collection Activities; Proposed Collection; Comment Request

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-01

... 30 percent for computer programming, 20 percent for attorney services, 30 percent for skilled... workers, 25 percent for computer programming, and 20 percent for management time. (d) Dispute resolution...), or a total cost of $421,200. \\12\\ The blended rate is 40 percent for computer programming, 10 percent...

Passivation of InP heterojunction bipolar transistors by strain controlled plasma assisted electron beam evaporated hafnium oxide

NASA Astrophysics Data System (ADS)

Driad, R.; Sah, R. E.; Schmidt, R.; Kirste, L.

2012-01-01

We present structural, stress, and electrical properties of plasma assisted e-beam evaporated hafnium dioxide (HfO2) layers on n-type InP substrates. These layers have subsequently been used for surface passivation of InGaAs/InP heterostructure bipolar transistors either alone or in combination with plasma enhanced chemical vapor deposited SiO2 layers. The use of stacked HfO2/SiO2 results in better interface quality with InGaAs/InP heterostructures, as illustrated by smaller leakage current and improved breakdown voltage. These improvements can be attributed to the reduced defect density and charge trapping at the dielectric-semiconductor interface. The deposition at room temperature makes these films suitable for sensitive devices.

Study of bulk Hafnium oxide (HfO2) under compression

NASA Astrophysics Data System (ADS)

Pathak, Santanu; Mandal, Guruprasad; Das, Parnika

2018-04-01

Hafnium oxide (HfO2) is a technologically important material. This material has K-value of 25 and band gap 5.8 eV. A k value of 25-30 is preferred for a gate dielectric [1]. As it shows good insulating and capacitive properties, HfO2 is being considered as a replacement to SiO2 in microelectronic devices as gate dielectrics. On the other hand because of toughening mechanism due to phase transformation induced by stress field observed in these oxides, HFO2 has been a material of investigations in various configurations for a very long time. However the controversies about phase transition of HfO2 under pressure still exists. High quality synchrotron radiation has been used to study the structural phase transition of HfO2 under pressure.

Mineral resource of the month: niobium (columbium)

USGS Publications Warehouse

Papp, John F.

2007-01-01

It’s not just diamonds associated with conflict in Africa. Coltan, short for columbite-tantalite (a blend of niobium — also called columbium — and tantalum minerals), is linked with the recent conflicts in the Congo that involved several African countries. The metallic ore, which is processed to separate out niobium and the very valuable tantalum (see Geotimes, August 2004), is believed to be smuggled out and sold to help finance the armed conflicts.

Tantalum—A bioactive metal for implants

NASA Astrophysics Data System (ADS)

Balla, Vamsi Krishna; Bose, Susmita; Davies, Neal M.; Bandyopadhyay, Amit

2010-07-01

Metallic biomaterials currently in use for load-bearing orthopedic applications are mostly bioinert and therefore lack sufficient osseointegration. Although bioactive ceramics such as hydroxyapatite (HA) can spontaneously bond to living bone tissue, low fracture toughness of HA limits their use as a bone substitute for load-bearing applications. Surface modification techniques such as HA coating on metals are current options to improve osseointegration in load-bearing metal implants. Over the last few decades researchers have attempted to find a bioactive metal with high mechanical strength and excellent fatigue resistance that can bond chemically with surrounding bone for orthopedic applications. Recent in vitro, in vivo, and clinical studies demonstrated that tantalum is a promising metal that is bioactive. However, tantalum applications in biomedical devices have been limited by processing challenges rather than biological performances. In this article, we provide an overview of processing aspects and biological properties of tantalum for load-bearing orthopedic applications.

High-temperature corrosion of metals in the salt and metallic melts containing rare earths

NASA Astrophysics Data System (ADS)

Karpov, V. V.; Abramov, A. V.; Zhilyakov, A. Yu.; Belikov, S. V.; Volkovich, V. A.; Polovov, I. B.; Rebrin, O. I.

2016-09-01

A complex of independent methods was employed to study the corrosion resistance of molybdenum, zirconium, tantalum and tungsten in chloride, chloride-fluoride and fluoride-oxide melts based on LiCl, CaCl2, NaCl- KCl, LiF, and containing rare earths. Tests were conducted for 30 h at 750-1050 °C. The metals showed excellent corrosion resistance in fused chlorides (the corrosion rates were below 0.0005 g/(m2 h). Despite the presence of chemically active fluoride ions in the chloride-fluoride melts, the metals studied also showed very low corrosion rates, except molybdenum, for which the rate of corrosion was 0,8 g/(m2 h). The corrosion resistance of tantalum was considerably reduced in the fluoride-oxide melts; the corrosion rate was over 1 g/(m2 h) corresponding to the 8-th grade of stability and placing tantalum to the group of "low stability" materials.

Titanium modified with layer-by-layer sol-gel tantalum oxide and an organodiphosphonic acid: a coating for hydroxyapatite growth.

PubMed

Arnould, C; Volcke, C; Lamarque, C; Thiry, P A; Delhalle, J; Mekhalif, Z

2009-08-15

Titanium and its alloys are widely used in surgical implants due to their appropriate properties like corrosion resistance, biocompatibility, and load bearing. Unfortunately when metals are used for orthopedic and dental implants there is the possibility of loosening over a long period of time. Surface modification is a good way to counter this problem. A thin tantalum oxide layer obtained by layer-by-layer (LBL) sol-gel deposition on top of a titanium surface is expected to improve biocorrosion resistance in the body fluid, biocompatibility, and radio-opacity. This elaboration step is followed by a modification of the tantalum oxide surface with an organodiphosphonic acid self-assembled monolayer, capable of chemically binding to the oxide surface, and also improving hydroxyapatite growth. The different steps of this proposed process are characterized by surfaces techniques like contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM).

Shear-horizontal surface acoustic wave phononic device with high density filling material for ultra-low power sensing applications

NASA Astrophysics Data System (ADS)

Richardson, M.; Sankaranarayanan, S. K. R. S.; Bhethanabotla, V. R.

2014-06-01

Finite element simulations of a phononic shear-horizontal surface acoustic wave (SAW) sensor based on ST 90°-X Quartz reveal a dramatic reduction in power consumption. The phononic sensor is realized by artificially structuring the delay path to form an acoustic meta-material comprised of a periodic microcavity array incorporating high-density materials such as tantalum or tungsten. Constructive interference of the scattered and secondary reflected waves at every microcavity interface leads to acoustic energy confinement in the high-density regions translating into reduced power loss. Tantalum filled cavities show the best performance while tungsten inclusions create a phononic bandgap. Based on our simulation results, SAW devices with tantalum filled microcavities were fabricated and shown to significantly decrease insertion loss. Our findings offer encouraging prospects for designing low power, highly sensitive portable biosensors.

Influence of laser cladding regimes on structural features and mechanical properties of coatings on titanium substrates

NASA Astrophysics Data System (ADS)

Malyutina, Yulia N.; Lazurenko, Daria V.; Bataev, Ivan A.; Movtchan, Igor A.

2015-10-01

In this paper an influence of the tantalum content on the structure and properties of surface layers of the titanium alloy doped using a laser treatment technology was investigated. It was found that an increase of a quantity of filler powder per one millimeter of a track length contributed to a rise of the content of undissolved particles in coatings. The maximum thickness of a cladded layer was reached at the mass of powder per the length unit equaled to 5.5 g/cm. Coatings were characterized by the formation of a dendrite structure with attributes of segregation. The width of a quenched fusion zone grew with an increase in the rate of powder feed to the treated area. Significant strengthening of the titanium surface layer alloyed with tantalum was not observed; however, the presence of undissolved tantalum particles can decrease the hardness of titanium surface layers.

Tantalum-tungsten oxide thermite composites prepared by sol-gel synthesis and spark plasma sintering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuntz, Joshua D.; Gash, Alexander E.; Cervantes, Octavio G.

2010-08-15

Energetic composite powders consisting of sol-gel derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition-tested and the results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High-Pressure Spark Plasma Sintering (HPSPS) technique, on the sol-gel derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The sol-gel derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta-WO{sub 3}) energetic composite was consolidated to a density of 9.17 g cm{sup -3}more » or 93% relative density. In addition, those samples were consolidated without significant pre-reaction of the constituents, thus retaining their stored chemical energy. (author)« less

Tantalum-Tungsten Oxide Thermite Composite Prepared by Sol-Gel Synthesis and Spark Plasma Sintering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cervantes, O; Kuntz, J; Gash, A

2009-02-13

Energetic composite powders consisting of sol-gel derived nanostructured tungsten oxide were produced with various amounts of micrometer-scale tantalum fuel metal. Such energetic composite powders were ignition tested and results show that the powders are not sensitive to friction, spark and/or impact ignition. Initial consolidation experiments, using the High Pressure Spark Plasma Sintering (HPSPS) technique, on the sol-gel derived nanostructured tungsten oxide produced samples with higher relative density than can be achieved with commercially available tungsten oxide. The sol-gel derived nanostructured tungsten oxide with immobilized tantalum fuel metal (Ta - WO{sub 3}) energetic composite was consolidated to a density of 9.17more » g.cm{sup -3} or 93% relative density. In addition those parts were consolidated without significant pre-reaction of the constituents, thus the sample retained its stored chemical energy.« less

Micro- and nanostructure of a titanium surface electric-spark-doped with tantalum and modified by high-frequency currents

NASA Astrophysics Data System (ADS)

Fomin, A. A.; Fomina, M. A.; Koshuro, V. A.; Rodionov, I. V.; Voiko, A. V.; Zakharevich, A. M.; Aman, A.; Oseev, A.; Hirsch, S.; Majcherek, S.

2016-09-01

We have studied the characteristics of the porous microstructure of tantalum coatings obtained by means of electric spark spraying on the surface of commercial grade titanium. It is established that, at an electric spark current within 0.8-2.2 A, a mechanically strong tantalum coating microstructure is formed with an average protrusion size of 5.1-5.4 µm and pore sizes from 3.5 to 9.2 µm. On the nanoscale, a structurally heterogeneous state of coatings has been achieved by subsequent thermal modification at 800-830°C with the aid of high-frequency currents. A metal oxide nanostructure with grain sizes from 40 to 120 nm is formed by short-time (~30 s) thermal modification. The coating hardness reaches 9.5-10.5 GPa at an elastic modulus of 400-550 GPa.

Frequency spectrum of tantalum at temperatures of 293-2300 K

NASA Astrophysics Data System (ADS)

Semenov, V. A.; Kozlov, Zh. A.; Krachun, L.; Mateescu, G.; Morozov, V. M.; Oprea, A. I.; Oprea, K.; Puchkov, A. V.

2010-05-01

The temperature dependence of the frequency spectrum of tantalum in the temperature range from room temperature to 2300 K has been studied for the first time using inelastic slow-neutron scattering. The inelastic slow-neutron scattering spectra have been measured at different temperatures on a DIN-2PI time-of-flight spectrometer installed at the IBR-2 nuclear reactor (Joint Institute for Nuclear Research, Dubna, Russia) with the use of a TS3000K high-temperature thermostat. From the measured spectra, the frequency spectra of the tantalum crystal lattice have been determined at temperatures of 293, 1584, and 2300 K by the iteration method. As the temperature increases, the frequency spectrum, on the whole, is softened and the specific features manifested themselves at room temperature are smoothed. The variations observed have been explained by the increase in the role of the effects of vibration anharmonism at high temperatures.

30 CFR 57.22240 - Actions at 2.0 percent methane (V-A mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 2.0 percent methane (V-A mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22240 Actions at 2.0 percent methane (V-A mines). If methane reaches 2.0 percent in the mine atmosphere, all persons other than...

30 CFR 57.22239 - Actions at 2.0 percent methane (IV mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 2.0 percent methane (IV mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22239 Actions at 2.0 percent methane (IV mines). If methane reaches 2.0 percent in the mine atmosphere, all persons other than...

30 CFR 57.22239 - Actions at 2.0 percent methane (IV mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 2.0 percent methane (IV mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22239 Actions at 2.0 percent methane (IV mines). If methane reaches 2.0 percent in the mine atmosphere, all persons other than...

30 CFR 57.22240 - Actions at 2.0 percent methane (V-A mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 2.0 percent methane (V-A mines). 57... MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22240 Actions at 2.0 percent methane (V-A mines). If methane reaches 2.0 percent in the mine atmosphere, all persons other than...

Scenarios for Demand Growth of Metals in Electricity Generation Technologies, Cars, and Electronic Appliances

PubMed Central

2018-01-01

This study provides scenarios toward 2050 for the demand of five metals in electricity production, cars, and electronic appliances. The metals considered are copper, tantalum, neodymium, cobalt, and lithium. The study shows how highly technology-specific data on products and material flows can be used in integrated assessment models to assess global resource and metal demand. We use the Shared Socio-economic Pathways as implemented by the IMAGE integrated assessment model as a starting point. This allows us to translate information on the use of electronic appliances, cars, and renewable energy technologies into quantitative data on metal flows, through application of metal content estimates in combination with a dynamic stock model. Results show that total demand for copper, neodymium, and tantalum might increase by a factor of roughly 2 to 3.2, mostly as a result of population and GDP growth. The demand for lithium and cobalt is expected to increase much more, by a factor 10 to more than 20, as a result of future (hybrid) electric car purchases. This means that not just demographics, but also climate policies can strongly increase metal demand. This shows the importance of studying the issues of climate change and resource depletion together, in one modeling framework. PMID:29533657

Scenarios for Demand Growth of Metals in Electricity Generation Technologies, Cars, and Electronic Appliances.

PubMed

Deetman, Sebastiaan; Pauliuk, Stefan; van Vuuren, Detlef P; van der Voet, Ester; Tukker, Arnold

2018-04-17

This study provides scenarios toward 2050 for the demand of five metals in electricity production, cars, and electronic appliances. The metals considered are copper, tantalum, neodymium, cobalt, and lithium. The study shows how highly technology-specific data on products and material flows can be used in integrated assessment models to assess global resource and metal demand. We use the Shared Socio-economic Pathways as implemented by the IMAGE integrated assessment model as a starting point. This allows us to translate information on the use of electronic appliances, cars, and renewable energy technologies into quantitative data on metal flows, through application of metal content estimates in combination with a dynamic stock model. Results show that total demand for copper, neodymium, and tantalum might increase by a factor of roughly 2 to 3.2, mostly as a result of population and GDP growth. The demand for lithium and cobalt is expected to increase much more, by a factor 10 to more than 20, as a result of future (hybrid) electric car purchases. This means that not just demographics, but also climate policies can strongly increase metal demand. This shows the importance of studying the issues of climate change and resource depletion together, in one modeling framework.

Gradient Nanostructured Tantalum by Thermal-Mechanical Ultrasonic Impact Energy.

PubMed

Chae, Jong-Min; Lee, Keun-Oh; Amanov, Auezhan

2018-03-20

Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S²PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta.

Gradient Nanostructured Tantalum by Thermal-Mechanical Ultrasonic Impact Energy

PubMed Central

Chae, Jong-Min; Lee, Keun-Oh; Amanov, Auezhan

2018-01-01

Microstructural evolution and wear performance of Tantalum (Ta) treated by ultrasonic nanocrystalline surface modification (UNSM) at 25 and 1000 °C were reported. The UNSM treatment modified a surface along with subsurface layer with a thickness in the range of 20 to 150 µm, which depends on the UNSM treatment temperature, via the surface severe plastic deformation (S2PD) method. The cross-sectional microstructure of the specimens was observed by electron backscattered diffraction (EBSD) in order to confirm the microstructural alteration in terms of effective depth and refined grain size. The surface hardness measurement results, including depth profile, revealed that the hardness of the UNSM-treated specimens at both temperatures was increased in comparison with those of the untreated ones. The increase in UNSM treatment temperature led to a further increase in hardness. Moreover, both the UNSM-treated specimens with an increased hardness resulted in a higher resistance to wear in comparison with those of the untreated ones under dry conditions. The increase in hardness and induced compressive residual stress that depend on the formation of severe plastically deformed layer with the refined nano-grains are responsible for the enhancement in wear resistance. The findings of this study may be implemented in response to various industries that are related to strength improvement and wear enhancement issues of Ta. PMID:29558402

Colloidal metal oxide nanoparticle systems: the new promising way to prevent antibiotic resistance during treatment of local infectious processes

NASA Astrophysics Data System (ADS)

Karasenkov, Y.; Frolov, G.; Pogorelsky, I.; Latuta, N.; Gusev, A.; Kuznetsov, D.; Leont'ev, V.

2015-11-01

New bactericidal containing nanoparticles colloids for application in dentistry, maxillofacial surgery, urology, obstetrics, gynaecology, ENT, proctology have been developed. The various water colloidal nanodispersive systems of metals and oxides have been obtained by means of electric impulse - condensation (electroerosion) method. These systems are based pure elements and alloys of argentum (Ag), titanium dioxide (TiO2), iron oxide (Fe2O3), tantalum oxide (TaO), vanadium oxide (VO2), cobalt oxide (CoO), tantalum dioxide TaO2, zinc oxide (ZnO), copper oxide (CuO) and mixed suspensions of titanium, aluminium and molybdenum oxides. The research has been made on culture of dentobacterial plaque and mixed culture issued from gingival spaces. The composition of culture was identified with S.aureus, S.epidermidis and nonfermentable kinds of E.coli. The observation period lasted more than nineteen days. All solutions showed highly prolonged bactericidal activity in dilutions from the whole solution 1-20 mg/L. The bactericidal activity of powder specimen of silica containing Ag and Fe2O3 nanoparticles used as dental filling material and disintegrates of composite materials (produced by “StomaDent” CJSC) have been studied. Tested materials have long (up to 19 days and more) bactericidal activity.

NIOBIUM-TANTALUM SEPARATION

DOEpatents

Wilhelm, H.A.; Foos, R.A.

1959-01-27

The usual method for the separation of tantalum and niobium consists of a selective solvent extraction from an aqueous hydrofluoric acid solution of the metals. A difficulty encountered in this process is the fact that the corrosion problems associated with hydrofluoric acid are serious. It has been found that the corrosion caused by the hydrofluoric acid may be substantially reduced by adding to the acidic solution an amine, such as phenyl diethanolamine or aniline, and adjusting pH value to between 4 and 6.

FAST TRACK COMMUNICATION High rate straining of tantalum and copper

NASA Astrophysics Data System (ADS)

Armstrong, R. W.; Zerilli, F. J.

2010-12-01

High strain rate measurements reported recently for several tantalum and copper crystal/polycrystal materials are shown to follow dislocation mechanics-based constitutive relations, first at lower strain rates, for dislocation velocity control of the imposed plastic deformations and, then at higher rates, transitioning to nano-scale dislocation generation control by twinning or slip. For copper, there is the possibility of added-on slip dislocation displacements to be accounted for from the newly generated dislocations.

Electrical Conductivity of Dense Al, Ti, Fe, Ni, Cu, Mo, Ta, and W Plasmas

DTIC Science & Technology

2011-06-01

for all but tantalum and titanium shows a minimum at approximately 0.01 times solid density, followed by an increase as the density decreases further...internal energy and specific volume. Conductivity is observed to fall as the plasma expands for fixed internal energy, and for all but tantalum and...plasmas formed from elemental metal wires heated rapidly in a water bath by the electric current from discharge of a charged capacitor . Electrical

Four-Channel Threshold Detector With Optical Isolation

DTIC Science & Technology

2009-02-01

1uF tantalum 35 V Capacitor 6 75ohm 1l4 W Carbon or Metal Film Resistor I .1 uF tantalum 35V Capacitor 37 HCC / HCF 40688 CMOS 8 input NAND / AND 1...100uF aluminum 35 V Capacitor 3 1M340T15 1 5 V, 1 A TO –220 Regulator 1 MC7915ACT neg15 V, 1 A TO –220 Regulator 1 35952503 50 Kohm, 10-turn

Influence of Wall Material on VUV Emission from Hydrogen Plasma in H- Source

NASA Astrophysics Data System (ADS)

Bacal, M.; Glass-Maujean, M.; Ivanov, A. A., Jr; Nishiura, M.; Sasao, M.; Wada, M.

2002-11-01

The study of VUV emission from a hydrogen plasma produced in a filament discharge in a magnetic multicusp device showed that the use of tantalum and tungsten filaments leads to significant differences in the spectra. The effect of the filament material is interpreted in terms of the fresh film of this material, deposited on the wall. The synthetic spectrum convoluted with our apparatus function for the conditions of this experiment (gas temperature 500 K, electron energy 100 eV) agrees roughly well with the spectrum obtained with tungsten covered walls, but not with the spectrum obtained with tantalum covered walls. We show that in the case of tungsten covered walls the E-V singlet excitation is indeed a two-step Franck-Condon transition, going through either B or C state from an initial H2 molecule with v"=0, added to a Franck-Condon transition to highly excited states cascading to the B or C states. The excitation process to high v" states in the case of tantalum covered walls is a three step process, in which the first step is the formation by recombinative desorption on the wall of a vibrationally excited molecule with v"=1 or 2, which serves as the initial molecule in the subsequent E-V excitation through the B state. The results indicate a larger recombination coefficient of atoms on the tantalum covered wall.

30 CFR 57.22237 - Actions at 2.0 to 2.5 percent methane in bleeder systems (I-A and III mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

....22237 Actions at 2.0 to 2.5 percent methane in bleeder systems (I-A and III mines). If methane reaches 2... reduced to less than 2.0 percent within 30 minutes, or if methane levels reach 2.5 percent, all persons...

Atomic Layer Deposition of HfO2 and Si Nitride on Ge Substrates

NASA Astrophysics Data System (ADS)

Zhu, Shiyang; Nakajima, Anri

2007-12-01

Hafnium oxide (HfO2) thin films were deposited on Ge substrates at 300 °C using atomic layer deposition (ALD) with tetrakis(diethylamino)hafnium (termed as TDEAH) as a precursor and water as an oxidant. The deposition rate was estimated to be 0.09 nm/cycle and the deposited HfO2 films have a smooth surface and an almost stoichiometric composition, indicating that the growth follows a layer-by-layer kinetics, similarly to that on Si substrates. Si nitride thin films were also deposited on Ge by ALD using SiCl4 as a precursor and NH3 as an oxidant. Si nitride has a smaller deposition rate of about 0.055 nm/cycle and a larger gate leakage current than HfO2 deposited on Ge by ALD.

Tribo-electrochemical characterization of hafnium multilayer systems deposited on nitride/vanadium nitride AISI 4140 steel

NASA Astrophysics Data System (ADS)

Mora, M.; Vera, E.; Aperador, W.

2016-02-01

In this work is presented the synergistic behaviour among corrosion/wear (tribocorrosion) of the multilayer coatings hafnium nitride/vanadium nitride [HfN/VN]n. The multilayers were deposited on AISI 4140 steel using the technique of physical vapor deposition PVD magnetron sputtering, the tests were performed using a pin-on-disk tribometer, which has an adapted potentiostat galvanostat with three-electrode electrochemical cell. Tribocorrosive parameters such as: Friction coefficient between the coating and the counter body (100 Cr6 steel ball); Polarization resistance by means of electrochemical impedance spectroscopy technique and corrosion rate by polarization curves were determined. It was observed an increase in the polarization resistance, a decrease in the corrosion rate and a low coefficient of friction in comparison with the substrate, due to an increase on the number of bilayers.

Low-voltage high-performance organic thin film transistors with a thermally annealed polystyrene/hafnium oxide dielectric

NASA Astrophysics Data System (ADS)

Wang, Ying; Acton, Orb; Ting, Guy; Weidner, Tobias; Ma, Hong; Castner, David G.; Jen, Alex K.-Y.

2009-12-01

Low-voltage pentacene-based organic thin film transistors (OTFTs) are demonstrated with polystyrene (PS)/hafnium oxide (HfOx) hybrid dielectrics. Thermal annealing of PS films on HfOx at 120 °C (PS-120) induces a flatter orientation of the phenyl groups (tilt angle 65°) at the surface compared to PS films without annealing (PS-RT) (tilt angle 31°). The flatter phenyl group orientation leads to better matching of surface energy between pentacene and PS. Pentacene deposited on PS-120 display higher quality thin films with larger grain sizes and higher crystallinity. Pentacene OTFTs with PS-120/HfOx hybrid dielectrics can operate at low-voltage (<3 V) with high field-effect mobilities (1 cm2/V s), high on/off current ratios (106), and low subthreshold slopes (100 mV/dec).

Physical Therapy, AFSC 4J0X2

DTIC Science & Technology

1998-05-01

TABLE 19 HYDROTHERAPY EQUIPMENT USED OR OPERATED BY 20 PERCENT OR MORE OF 4J0X2 FIRST-JOB OR FIRST-ENLISTMENT PERSONNEL 37 TABLE 20 MEASUREMENT...which had responses of greater than 20 percent) (see Table 18) 9 types of hydrotherapy equipment (7 of which had responses greater than 20 percent...75 89 84 64 60 33 33 72 65 36 TABLE 19 HYDROTHERAPY EQUIPMENT USED OR OPERATED BY 20 PERCENT OR MORE OF 4J0X2 FIRST-JOB OR FIRST-ENLISTMENT

Fundamental Understanding of the Intrinsic Ductility in Nickel-Base L12 Type Alloys.

DTIC Science & Technology

1987-05-12

COSATI CO0ES I L SUBJE CT TIE RMS (Conue an eo e eee it necessary and identify by blb .un bPe) . ". Eo GROUP SUB. G. Nickel Aluminide , Single...Ni3Al alloys, three series of alloys were formulated and produced as singl’e--crtals. The alloying additions selected include tantalum, tin and titanium ...been completed-for a tantalum and a titanium -containing alloy. Relative .. to the binary alloy, the alloying additions were found to significantly

Thermophysical Properties of Matter - The TPRC Data Series. Volume 4. Specific Heat - Metallic Elements and Alloys

DTIC Science & Technology

1971-01-01

alloys— sodium — sodium alloya— solder—carbon ateels—chromium steels—silicon steels—tantalum—tantalum alloys—terbium—thallium—thallium alloys—thorium...Praseodymium 45 Rhenium 46 Rhodium 47 Rubidium 48 Ruthenium 4» Samarium 50 Scandium 51 Selenium 52 Silicon 5:i Silver 54 Sodium 55 Strontium 56...Potassium ♦ Sodium 111 Sodium * Potassium 112 Tantalum ♦ Tungsten 113 Thallium + Lead, PbTl| 114 Tin ♦ Bismuth 115 Tin ♦ Indium 116 Tin+ Lead 117

Flash melting of tantalum in a diamond cell to 85 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karandikar, Amol; Boehler, Reinhard

2016-02-09

Here, we demonstrate a new level of precision in measuring melting temperatures at high pressure using laser flash-heating followed by Scanning Electron Microscopy and Focused Ion Beam Milling. Furthermore, the new measurements on tantalum put unprecedented constraints on its highly debated melting slope, calling for a reevaluation of theoretical, shock compression and diamond cell approaches to determine melting at high pressure. X-ray analysis of the recovered samples confirmed the absence of chemical reactions, which likely played a significant role in previous experiments.

Metallic transfer between metals in sliding contact examined by auger emission spectroscopy

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1972-01-01

Metallic transfer between polycrystalline metals in sliding contact was examined. Hemispherical riders of iron, nickel, and cobalt were slid on tungsten, tantalum, niobium, and molybdenum disks in ultrahigh vacuum. Auger emission spectroscopy was used to monitor the elemental composition of the disk surfaces. Iron, nickel, and cobalt transferred to tungsten, whereas only cobalt transferred to tantalum, niobium, and molybdenum. The results of this investigation are discussed in terms of the cohesive energy and strain hardening characteristics of the specimen materials.

Microstructural Formations and Phase Transformation Pathways in Hot Isostatically Pressed Tantalum Carbides

DTIC Science & Technology

2012-01-01

and wear-resistant brake liners. The phase diagram for the tantalum–carbon system [5] is shown in Fig. 1a with corresponding crystal structures shown... structure ), with carbon atoms occupying the octahe- dral interstitial sites in a tantalum face-centered cubic (fcc) lattice [2,7]. The carbon-deficient...carbon sublattice. The allotropic phase trans- formation temperature between a-Ta2C (CdI2 antitype structure ) and b (L’3 structure ) is 2300 K [1,7]. In

Diffusion-Cooled Tantalum Hot-Electron Bolometer Mixers

NASA Technical Reports Server (NTRS)

Skalare, Anders; McGrath, William; Bumble, Bruce; LeDuc, Henry

2004-01-01

A batch of experimental diffusion-cooled hot-electron bolometers (HEBs), suitable for use as mixers having input frequencies in the terahertz range and output frequencies up to about a gigahertz, exploit the superconducting/normal-conducting transition in a thin strip of tantalum. The design and operation of these HEB mixers are based on mostly the same principles as those of a prior HEB mixer that exploited the superconducting/normal- conducting transition in a thin strip of niobium and that was described elsewhere.

Embedded Weapons-Grade Tungsten Alloy Shrapnel Rapidly Induces Metastatic High-Grade Rhabdomyosarcomas in F344 Rats

PubMed Central

Kalinich, John F.; Emond, Christy A.; Dalton, Thomas K.; Mog, Steven R.; Coleman, Gary D.; Kordell, Jessica E.; Miller, Alexandra C.; McClain, David E.

2005-01-01

Continuing concern regarding the potential health and environmental effects of depleted uranium and lead has resulted in many countries adding tungsten alloy (WA)-based munitions to their battlefield arsenals as replacements for these metals. Because the alloys used in many munitions are relatively recent additions to the list of militarily relevant metals, very little is known about the health effects of these metals after internalization as embedded shrapnel. Previous work in this laboratory developed a rodent model system that mimicked shrapnel loads seen in wounded personnel from the 1991 Persian Gulf War. In the present study, we used that system and male F344 rats, implanted intramuscularly with pellets (1 mm × 2 mm cylinders) of weapons-grade WA, to simulate shrapnel wounds. Rats were implanted with 4 (low dose) or 20 pellets (high dose) of WA. Tantalum (20 pellets) and nickel (20 pellets) served as negative and positive controls, respectively. The high-dose WA-implanted rats (n = 46) developed extremely aggressive tumors surrounding the pellets within 4–5 months after implantation. The low-dose WA-implanted rats (n = 46) and nickel-implanted rats (n = 36) also developed tumors surrounding the pellets but at a slower rate. Rats implanted with tantalum (n = 46), an inert control metal, did not develop tumors. Tumor yield was 100% in both the low- and high-dose WA groups. The tumors, characterized as high-grade pleomorphic rhabdomyosarcomas by histopathology and immunohistochemical examination, rapidly metastasized to the lung and necessitated euthanasia of the animal. Significant hematologic changes, indicative of polycythemia, were also observed in the high-dose WA-implanted rats. These changes were apparent as early as 1 month postimplantation in the high-dose WA rats, well before any overt signs of tumor development. These results point out the need for further studies investigating the health effects of tungsten and tungsten-based alloys. PMID:15929896

30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B... AND NONMETAL MINES Safety Standards for Methane in Metal and Nonmetal Mines Ventilation § 57.22238 Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). If methane reaches 2.0 percent in the mine...

30 CFR 57.22238 - Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). 57.22238 Section 57.22238 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION... Actions at 2.0 percent methane (I-B, II-B, V-B, and VI mines). If methane reaches 2.0 percent in the mine...

Processing of Ni30Pt20Ti50 High-Temperature Shape-Memory Alloy Into Thin Rod Demonstrated

NASA Technical Reports Server (NTRS)

Noebe, Ronald D.; Draper, Susan L.; Biles, Tiffany A.; Leonhardt, Todd

2005-01-01

High-temperature shape-memory alloys (HTSMAs) based on nickel-titanium (NiTi) with significant ternary additions of palladium (Pd), platinum (Pt), gold (Au), or hafnium (Hf) have been identified as potential high-temperature actuator materials for use up to 500 C. These materials provide an enabling technology for the development of "smart structures" used to control the noise, emissions, or efficiency of gas turbine engines. The demand for these high-temperature versions of conventional shape-memory alloys also has been growing in the automotive, process control, and energy industries. However these materials, including the NiPtTi alloys being developed at the NASA Glenn Research Center, will never find widespread acceptance unless they can be readily processed into useable forms.

16 CFR 306.10 - Automotive fuel rating posting.

Code of Federal Regulations, 2013 CFR

2013-01-01

...-20 Biodiesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (8) “20% Biomass-Based Diesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (9) “B-100 Biodiesel/contains 100 percent biodiesel” (10) “100% Biomass...

16 CFR 306.10 - Automotive fuel rating posting.

Code of Federal Regulations, 2011 CFR

2011-01-01

...-20 Biodiesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (8) “20% Biomass-Based Diesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (9) “B-100 Biodiesel/contains 100 percent biodiesel” (10) “100% Biomass...

16 CFR 306.10 - Automotive fuel rating posting.

Code of Federal Regulations, 2012 CFR

2012-01-01

...-20 Biodiesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (8) “20% Biomass-Based Diesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (9) “B-100 Biodiesel/contains 100 percent biodiesel” (10) “100% Biomass...

16 CFR 306.10 - Automotive fuel rating posting.

Code of Federal Regulations, 2014 CFR

2014-01-01

...-20 Biodiesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (8) “20% Biomass-Based Diesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (9) “B-100 Biodiesel/contains 100 percent biodiesel” (10) “100% Biomass...

16 CFR 306.10 - Automotive fuel rating posting.

Code of Federal Regulations, 2010 CFR

2010-01-01

...-20 Biodiesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (8) “20% Biomass-Based Diesel Blend/contains biomass-based diesel or biodiesel in quantities between 5 percent and 20 percent” (9) “B-100 Biodiesel/contains 100 percent biodiesel” (10) “100% Biomass...

40 CFR 471.95 - Pretreatment standards for new sources (PSNS).

Code of Federal Regulations, 2013 CFR

2013-07-01

... I—PSNS. There shall be no discharge of process wastewater pollutants. (p) Molten salt rinse. Subpart... (pounds per million off-pounds) of zirconium-hafnium rinsed following molten salt treatment Chromium 0.333...

40 CFR 471.95 - Pretreatment standards for new sources (PSNS).

Code of Federal Regulations, 2014 CFR

2014-07-01

... I—PSNS. There shall be no discharge of process wastewater pollutants. (p) Molten salt rinse. Subpart... (pounds per million off-pounds) of zirconium-hafnium rinsed following molten salt treatment Chromium 0.333...

40 CFR 471.95 - Pretreatment standards for new sources (PSNS).

Code of Federal Regulations, 2012 CFR

2012-07-01

... I—PSNS. There shall be no discharge of process wastewater pollutants. (p) Molten salt rinse. Subpart... (pounds per million off-pounds) of zirconium-hafnium rinsed following molten salt treatment Chromium 0.333...

Size-dependent disproportionation (in 2-20 nm regime) and hybrid Bond Valence derived interatomic potentials for BaTaO2N

NASA Astrophysics Data System (ADS)

Anbalagan, Kousika; Thomas, Tiju

2018-05-01

Interatomic potentials for complex materials (like ceramic systems) are important for realistic molecular dynamics (MD) simulations. Such simulations are relevant for understanding equilibrium, transport and dynamical properties of materials, especially in the nanoregime. Here we derive a hybrid interatomic potential (based on bond valence (BV) derived Morse and Coulomb terms), for modeling a complex ceramic, barium tantalum oxynitride (BaTaO2N). This material has been chosen due to its relevance for capacitive and photoactive applications. However, the material presents processing challenges such as the emergence of non-stoichiometric phases during processing, demonstrating complex processing-property correlations. This makes MD investigations of this material both scientifically and technologically relevant. The BV based hybrid potential presented here has been used for simulating sintering of BaTaO2N nanoparticles ( 2-20 nm) under different conditions (using the relevant canonical ensemble). Notably, we show that sintering of particles of diameter < 10 nm requires no external sintering aids such as the addition of barium sources (since stoichiometry is preserved during heat treatment in this size regime). Also, we observe that sintering of particles > 10 nm in size results in the formation of a cluster of tantalum and oxygen atoms at the interface of the BaTaO2N particles. This is in agreement with the experimental reports. The results presented here suggest that the potential proposed can be used to explore dynamical properties of BaTaO2N and related systems. This work will also open avenues for development of nanoscience-enabled aid-free sintering approaches to this and related materials.

Antibacterial properties and cytocompatibility of tantalum oxide coatings with different silver content

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Heng-Li; Chang, Yin-Yu, E-mail: yinyu@mail2000.com.tw; Chen, Hung-Jui

Tantalum (Ta) oxides and their coatings have been proved to increase their applications in the biomedical fields by improving osseointegration and wear resistance. In this study, Ta oxide coatings containing different proportions of Ag are deposited on SS304 materials. A twin-gun magnetron sputtering system is used to deposit the tantalum oxide-Ag coating. In this study, Staphylococcus aureus, which exhibits physiological commensalism on the human skin, nares, and mucosal and oral areas, is chosen as the model for in vitro antibacterial analyses via a fluorescence staining method using Syto9. The cytocompatibility and adhesive morphology of human skin fibroblast cells (CCD-966SK) onmore » the coatings are also determined by using the microculture tetrazolium assay. This study shows that Ta{sub 2}O{sub 5} and Ta{sub 2}O{sub 5}-Ag coatings with 12.5 at. % of Ag exhibit improved antibacterial effects against S. aureus and have good skin fibroblast cell cellular biocompatibility.« less

Effect of Surge Current Testing on Reliability of Solid Tantalum Capacitors

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander

2008-01-01

Tantalum capacitors manufactured per military specifications are established reliability components and have less than 0.001% of failures per 1000 hours for grades D or S, thus positioning these parts among electronic components with the highest reliability characteristics. Still, failures of tantalum capacitors do happen and when it occurs it might have catastrophic consequences for the system. To reduce this risk, further development of a screening and qualification system with special attention to the possible deficiencies in the existing procedures is necessary. The purpose of this work is evaluation of the effect of surge current stress testing on reliability of the parts at both steady-state and multiple surge current stress conditions. In order to reveal possible degradation and precipitate more failures, various part types were tested and stressed in the range of voltage and temperature conditions exceeding the specified limits. A model to estimate the probability of post-surge current testing-screening failures and measures to improve the effectiveness of the screening process has been suggested.

Degradation of Leakage Currents in Solid Tantalum Capacitors Under Steady-State Bias Conditions

NASA Technical Reports Server (NTRS)

Teverovsky, Alexander A.

2010-01-01

Degradation of leakage currents in various types of solid tantalum capacitors under steady-state bias conditions was investigated at temperatures from 105 oC to 170 oC and voltages up to two times the rated voltage. Variations of leakage currents with time under highly accelerated life testing (HALT) and annealing, thermally stimulated depolarization currents, and I-V characteristics were measured to understand the conduction mechanism and the reason for current degradation. During HALT the currents increase gradually up to three orders of magnitude in some cases, and then stabilize with time. This degradation is reversible and annealing can restore the initial levels of leakage currents. The results are attributed to migration of positively charged oxygen vacancies in tantalum pentoxide films that diminish the Schottky barrier at the MnO2/Ta2O5 interface and increase electron injection. A simple model allows for estimation of concentration and mobility of oxygen vacancies based on the level of current degradation.

Tensile properties of candidate structural materials for high power spallation sources at high helium contents

NASA Astrophysics Data System (ADS)

Jung, P.; Henry, J.; Chen, J.

2005-08-01

Low activation 9%Cr martensitic steels EUROFER97, pure tantalum, and low carbon austenitic stainless steel 316L were homogeneously implanted with helium to concentrations up to 5000 appm at temperatures from 70 °C to 400 °C. The specimens were tensile tested at room temperature and at the respective implantation temperatures. In all materials the helium caused an increased in strength and reduction in ductility, with both changes being generally larger at lower implantation and testing temperatures. After implantation some work hardening was retained in 316L and in tantalum, while it almost completely disappeared in EUROFER97. After tensile testing, fracture surfaces were analysed by scanning electron microscopy (SEM). Implantation caused reduction of necking, but up to concentrations of 2500 appm He fracture surface still showed transgranular ductile appearance. Completely brittle intergranular fracture was observed in tantalum at 9000 appm He and is also expected for EUROFER97 at this concentration, according to previous results on similar 9%Cr steels.

Perovskite phase thin films and method of making

DOEpatents

Boyle, Timothy J.; Rodriguez, Mark A.

2000-01-01

The present invention comprises perovskite-phase thin films, of the general formula A.sub.x B.sub.y O.sub.3 on a substrate, wherein A is selected from beryllium, magnesium, calcium, strontium, and barium or a combination thereof; B is selected from niobium and tantalum or a combination thereof; and x and y are mole fractions between approximately 0.8 and 1.2. More particularly, A is strontium or barium or a combination thereof and B is niobium or tantalum or a combination thereof. Also provided is a method of making a perovskite-phase thin film, comprising combining at least one element-A-containing compound, wherein A is selected from beryllium, magnesium, calcium, strontium or barium, with at least one element-B-containing compound, wherein B niobium or tantalum, to form a solution; adding a solvent to said solution to form another solution; spin-coating the solution onto a substrate to form a thin film; and heating the film to form the perovskite-phase thin film.

Influence of laser cladding regimes on structural features and mechanical properties of coatings on titanium substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malyutina, Yulia N., E-mail: iuliiamaliutina@gmail.ru; Lazurenko, Daria V., E-mail: pavlyukova-87@mail.ru; Bataev, Ivan A., E-mail: ivanbataev@ngs.ru

2015-10-27

In this paper an influence of the tantalum content on the structure and properties of surface layers of the titanium alloy doped using a laser treatment technology was investigated. It was found that an increase of a quantity of filler powder per one millimeter of a track length contributed to a rise of the content of undissolved particles in coatings. The maximum thickness of a cladded layer was reached at the mass of powder per the length unit equaled to 5.5 g/cm. Coatings were characterized by the formation of a dendrite structure with attributes of segregation. The width of a quenchedmore » fusion zone grew with an increase in the rate of powder feed to the treated area. Significant strengthening of the titanium surface layer alloyed with tantalum was not observed; however, the presence of undissolved tantalum particles can decrease the hardness of titanium surface layers.« less

Conflict minerals in the compute sector: estimating extent of tin, tantalum, tungsten, and gold use in ICT products.

PubMed

Fitzpatrick, Colin; Olivetti, Elsa; Miller, Reed; Roth, Richard; Kirchain, Randolph

2015-01-20

Recent legislation has focused attention on the supply chains of tin, tungsten, tantalum, and gold (3TG), specifically those originating from the eastern part of the Democratic Republic of Congo. The unique properties of these so-called “conflict minerals” lead to their use in many products, ranging from medical devices to industrial cutting tools. This paper calculates per product use of 3TG in several information, communication, and technology (ICT) products such as desktops, servers, laptops, smart phones, and tablets. By scaling up individual product estimates to global shipment figures, this work estimates the influence of the ICT sector on 3TG mining in covered countries. The model estimates the upper bound of tin, tungsten, tantalum, and gold use within ICT products to be 2%, 0.1%, 15%, and 3% of the 2013 market share, respectively. This result is projected into the future (2018) based on the anticipated increase in ICT device production.

Inferring Strength of Tantalum from Hydrodynamic Instability Recovery Experiments

NASA Astrophysics Data System (ADS)

Sternberger, Z.; Maddox, B.; Opachich, Y.; Wehrenberg, C.; Kraus, R.; Remington, B.; Randall, G.; Farrell, M.; Ravichandran, G.

2018-05-01

Hydrodynamic instability experiments allow access to material properties at extreme conditions, where strain rates exceed 105 s-1 and pressures reach 100 GPa. Current hydrodynamic instability experimental methods require in-flight radiography to image the instability growth at high pressure and high strain rate, limiting the facilities where these experiments can be performed. An alternate approach, recovering the sample after loading, allows measurement of the instability growth with profilometry. Tantalum samples were manufactured with different 2D and 3D initial perturbation patterns and dynamically compressed by a blast wave generated by laser ablation. The samples were recovered from peak pressures between 30 and 120 GPa and strain rates on the order of 107 s-1, providing a record of the growth of the perturbations due to hydrodynamic instability. These records are useful validation points for hydrocode simulations using models of material strength at high strain rate. Recovered tantalum samples were analyzed, providing an estimate of the strength of the material at high pressure and strain rate.

Constitutive behavior of tantalum and tantalum-tungsten alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, S.R.; Gray, G.T. III

1996-10-01

The effects of strain rate, temperature, and tungsten alloying on the yield stress and the strain-hardening behavior of tantalum were investigated. The yield and flow stresses of unalloyed Ta and tantalum-tungsten alloys were found to exhibit very high rate sensitivities, while the hardening rates in Ta and Ta-W alloys were found to be insensitive to strain rate and temperature at lower temperatures or at higher strain rates. This behavior is consistent with the observation that overcoming the intrinsic Peierls stress is shown to be the rate-controlling mechanism in these materials at low temperatures. The dependence of yield stress on temperaturemore » and strain rate was found to decrease, while the strain-hardening rate increased with tungsten alloying content. The mechanical threshold stress (MTS) model was adopted to model the stress-strain behavior of unalloyed Ta and the Ta-W alloys. Parameters for the constitutive relations for Ta and the Ta-W alloys were derived for the MTS model, the Johnson-Cook (JC), and the Zerilli-Armstrong (ZA) models. The results of this study substantiate the applicability of these models for describing the high strain-rate deformation of Ta and Ta-W alloys. The JC and ZA models, however, due to their use of a power strain-hardening law, were found to yield constitutive relations for Ta and Ta-W alloys that are strongly dependent on the range of strains for which the models were optimized.« less

Heat of combustion of tantalum-tungsten oxide thermite composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cervantes, Octavio G.; Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616; Kuntz, Joshua D.

2010-12-15

The heat of combustion of two distinctly synthesized stoichiometric tantalum-tungsten oxide energetic composites was investigated by bomb calorimetry. One composite was synthesized using a sol-gel (SG) derived method in which micrometric-scale tantalum is immobilized in a tungsten oxide three-dimensional nanostructured network structure. The second energetic composite was made from the mixing of micrometric-scale tantalum and commercially available (CA) nanometric tungsten oxide powders. The energetic composites were consolidated using the spark plasma sintering (SPS) technique under a 300 MPa pressure and at temperatures of 25, 400, and 500 C. For samples consolidated at 25 C, the density of the CA compositemore » is 61.65 {+-} 1.07% in comparison to 56.41 {+-} 1.19% for the SG derived composite. In contrast, the resulting densities of the SG composite are higher than the CA composite for samples consolidated at 400 and 500 C. The theoretical maximum density for the SG composite consolidated to 400 and 500 C are 81.30 {+-} 0.58% and 84.42 {+-} 0.62%, respectively. The theoretical maximum density of the CA composite consolidated to 400 and 500 C are 74.54 {+-} 0.80% and 77.90 {+-} 0.79%, respectively. X-ray diffraction analyses showed an increase of pre-reaction of the constituents with an increase in the consolidation temperature. The increase in pre-reaction results in lower stored energy content for samples consolidated to 400 and 500 C in comparison to samples consolidated at 25 C. (author)« less

Nickel aluminides and nickel-iron aluminides for use in oxidizing environments

DOEpatents

Liu, Chain T.

1988-03-15

Nickel aluminides and nickel-iron aluminides treated with hafnium or zirconium, boron and cerium to which have been added chromium to significantly improve high temperature ductility, creep resistance and oxidation properties in oxidizing environments.

40 CFR 471.94 - Pretreatment standards for existing sources (PSES).

Code of Federal Regulations, 2013 CFR

2013-07-01

... I—PSES. There shall be no discharge of process wastewater pollutants. (p) Molten salt rinse. Subpart... (pounds per million off-pounds) of zirconium-hafnium treated with molten salt Chromium 0.333 0.136 Cyanide...

40 CFR 471.93 - New source performance standards (NSPS).

Code of Federal Regulations, 2014 CFR

2014-07-01

... of process wastewater pollutants (p) Molten salt rinse. Subpart I—NSPS Pollutant or pollutant... zirconium-hafnium treated with molten salt Chromium 0.333 0.136 Cyanide 0.220 0.091 Nickel 1.45 0.960...

40 CFR 471.94 - Pretreatment standards for existing sources (PSES).

Code of Federal Regulations, 2014 CFR

2014-07-01

... I—PSES. There shall be no discharge of process wastewater pollutants. (p) Molten salt rinse. Subpart... (pounds per million off-pounds) of zirconium-hafnium treated with molten salt Chromium 0.333 0.136 Cyanide...

40 CFR 471.93 - New source performance standards (NSPS).

Code of Federal Regulations, 2012 CFR

2012-07-01

... of process wastewater pollutants (p) Molten salt rinse. Subpart I—NSPS Pollutant or pollutant... zirconium-hafnium treated with molten salt Chromium 0.333 0.136 Cyanide 0.220 0.091 Nickel 1.45 0.960...

40 CFR 471.94 - Pretreatment standards for existing sources (PSES).

Code of Federal Regulations, 2012 CFR

2012-07-01

... I—PSES. There shall be no discharge of process wastewater pollutants. (p) Molten salt rinse. Subpart... (pounds per million off-pounds) of zirconium-hafnium treated with molten salt Chromium 0.333 0.136 Cyanide...

40 CFR 471.93 - New source performance standards (NSPS).

Code of Federal Regulations, 2013 CFR

2013-07-01

... of process wastewater pollutants (p) Molten salt rinse. Subpart I—NSPS Pollutant or pollutant... zirconium-hafnium treated with molten salt Chromium 0.333 0.136 Cyanide 0.220 0.091 Nickel 1.45 0.960...

High-energy X-ray detection by hafnium-doped organic-inorganic hybrid scintillators prepared by sol-gel method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yan; Koshimizu, Masanori, E-mail: koshi@qpc.che.tohoku.ac.jp; Yahaba, Natsuna

2014-04-28

With the aim of enhancing the efficiency with which plastic scintillators detect high-energy X-rays, hafnium-doped organic-inorganic hybrid scintillators were fabricated via a sol-gel method. Transmission electron microscopy of sampled material reveals the presence of Hf{sub x}Si{sub 1−x}O{sub 2} nanoparticles, dispersed in a polymer matrix that constitutes the active material of the X-ray detector. With Hf{sub x}Si{sub 1−x}O{sub 2} nanoparticles incorporated in the polymer matrix, the absorption edge and the luminescence wavelength is shifted, which we attribute to Mie scattering. The detection efficiency for 67.4-keV X-rays in a 0.6-mm-thick piece of this material is two times better than the same thicknessmore » of a commercial plastic scintillator-NE142.« less

Hafnium—an optical hydrogen sensor spanning six orders in pressure

PubMed Central

Boelsma, C.; Bannenberg, L. J.; van Setten, M. J.; Steinke, N.-J.; van Well, A. A.; Dam, B.

2017-01-01

Hydrogen detection is essential for its implementation as an energy vector. So far, palladium is considered to be the most effective hydrogen sensing material. Here we show that palladium-capped hafnium thin films show a highly reproducible change in optical transmission in response to a hydrogen exposure ranging over six orders of magnitude in pressure. The optical signal is hysteresis-free within this range, which includes a transition between two structural phases. A temperature change results in a uniform shift of the optical signal. This, to our knowledge unique, feature facilitates the sensor calibration and suggests a constant hydrogenation enthalpy. In addition, it suggests an anomalously steep increase of the entropy with the hydrogen/metal ratio that cannot be explained on the basis of a classical solid solution model. The optical behaviour as a function of its hydrogen content makes hafnium well-suited for use as a hydrogen detection material. PMID:28580959

Zirconium and hafnium fractionation in differentiation of alkali carbonatite magmatic systems

NASA Astrophysics Data System (ADS)

Kogarko, L. N.

2016-05-01

Zirconium and hafnium are valuable strategic metals which are in high demand in industry. The Zr and Hf contents are elevated in the final products of magmatic differentiation of alkali carbonatite rocks in the Polar Siberia region (Guli Complex) and Ukraine (Chernigov Massif). Early pyroxene fractionation led to an increase in the Zr/Hf ratio in the evolution of the ultramafic-alkali magmatic system due to a higher distribution coefficient of Hf in pyroxene with respect to Zr. The Rayleigh equation was used to calculate a quantitative model of variation in the Zr/Hf ratio in the development of the Guli magmatic system. Alkali carbonatite rocks originated from rare element-rich mantle reservoirs, in particular, the metasomatized mantle. Carbonated mantle xenoliths are characterized by a high Zr/Hf ratio due to clinopyroxene development during metasomatic replacement of orthopyroxene by carbonate fluid melt.

Cesium hafnium chloride: A high light yield, non-hygroscopic cubic crystal scintillator for gamma spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burger, Arnold, E-mail: aburger@fisk.edu; Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235; Rowe, Emmanuel

We report on the scintillation properties of Cs{sub 2}HfCl{sub 6} (cesium hafnium chloride or CHC) as an example of a little-known class of non-hygroscopic compounds having the generic cubic crystal structure of K{sub 2}PtCl{sub 6}. The crystals are easily growable from the melt using the Bridgman method with minimal precursor treatments or purification. CHC scintillation is centered at 400 nm, with a principal decay time of 4.37 μs and a light yield of up to 54 000 photons/MeV when measured using a silicon CCD photodetector. The light yield is the highest ever reported for an undoped crystal, and CHC also exhibits excellent lightmore » yield nonproportionality. These desirable properties allowed us to build and test CHC gamma-ray spectrometers providing energy resolution of 3.3% at 662 keV.« less

Development of Advanced Environmental Barrier Coatings for SiC/SiC Ceramic Matrix Composites: Path Toward 2700 F Temperature Capability and Beyond

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Harder, Bryan; Hurst, Janet B.; Good, Brian; Costa, Gustavo; Bhatt, Ramakrishna T.; Fox, Dennis S.

2017-01-01

Advanced environmental barrier coating systems for SiC-SiC Ceramic Matrix Composite (CMC) turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant coating development challenges is to achieve prime-reliant environmental barrier coating systems to meet the future 2700F EBC-CMC temperature stability and environmental durability requirements. This presentation will emphasize recent NASA environmental barrier coating system testing and down-selects, particularly the development path and properties towards 2700-3000F durability goals by using NASA hafnium-hafnia-rare earth-silicon-silicate composition EBC systems for the SiC-SiC CMC turbine component applications. Advanced hafnium-based compositions for enabling next generation EBC and CMCs capabilities towards ultra-high temperature ceramic coating systems will also be briefly mentioned.

Fabrication of cermet bearings for the control system of a high temperature lithium cooled nuclear reactor

NASA Technical Reports Server (NTRS)

Yacobucci, H. G.; Heestand, R. L.; Kizer, D. E.

1973-01-01

The techniques used to fabricate cermet bearings for the fueled control drums of a liquid metal cooled reference-design reactor concept are presented. The bearings were designed for operation in lithium for as long as 5 years at temperatures to 1205 C. Two sets of bearings were fabricated from a hafnium carbide - 8-wt. % molybdenum - 2-wt. % niobium carbide cermet, and two sets were fabricated from a hafnium nitride - 10-wt. % tungsten cermet. Procedures were developed for synthesizing the material in high purity inert-atmosphere glove boxes to minimize oxygen content in order to enhance corrosion resistance. Techniques were developed for pressing cylindrical billets to conserve materials and to reduce machining requirements. Finishing was accomplished by a combination of diamond grinding, electrodischarge machining, and diamond lapping. Samples were characterized in respect to composition, impurity level, lattice parameter, microstructure and density.

Guidance on Compatibility of UST Systems with Ethanol Blends Greater Than 10 Percent and Biodiesel Blends Greater Than 20 Percent

EPA Pesticide Factsheets

EPA guidance on complying with the federal compatibility requirement for underground storage tank (UST) systems storing gasoline containing greater than 10 percent ethanol or diesel containing greater than 20 percent biodiesel.