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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Recovery and separation of precious metals from space

During the past year a viable procedure centered around centrifugal partition chromatography (CPC), a multistage liquid-liquid partitioning technique for the separation of precious metals (Pt, Pd, Rh, Ir, Os, Ru), was developed. Stable and inexpensive ligands that can be readily recycled to achieve the separations of the precious metals were identified. The separation methods developed so far yield three separate fractions: Pt, Pd, and Rh-Ir. The Rh-Ir pair can be separated in a subsequent run. The total amount of precious metals separated in a single experiment varied from 1 to 50 mg. The factors affecting the efficiencies of these separations were studied. The kinetics of the decomposition of the complex and the ion pair have a major bearing on these efficiencies, with slow kinetics resulting in poor efficiencies. The methods for the improvement of the efficiencies were also investigated. For example, significant improvement in the efficiencies and separation times for Pt and Pd were achieved by the use of chloride gradient in the mobile phase. Two papers were published and talks were presented on our work at the FACSS meeting in Anaheim, Oct. 1991, and at the Pittsburgh Conference in New Orleans, Mar. 1992.

Freiser, H.↗
NASA NTRS1993

Ionization states of metallic absorption-line systems in continua of quasars

Ionization states of metallic absorption-line systems in continua of quasars (QSO's) are studied, assuming that the metallic lines arise in gaseous halos of high-redshift galaxies in photoionization equilibrium under the background UV radiation, and constraints on the intensity and spectral shape of the UV radiation are obtained. Then a structure of absorbers suitable for all of the metallic absorption line systems are discussed.

Denda, Kiyomi↗
NASA NTRS1993

Alkali metal carbon dioxide electrochemical system for energy storage and/or conversion of carbon dioxide to oxygen

An alkali metal, such as lithium, is the anodic reactant; carbon dioxide or a mixture of carbon dioxide and carbon monoxide is the cathodic reactant; and carbonate of the alkali metal is the electrolyte in an electrochemical cell for the storage and delivery of electrical energy. Additionally, alkali metal-carbon dioxide battery systems include a plurality of such electrochemical cells. Gold is a preferred catalyst for reducing the carbon dioxide at the cathode. The fuel cell of the invention produces electrochemical energy through the use of an anodic reactant which is extremely energetic and light, and a cathodic reactant which can be extracted from its environment and therefore exacts no transportation penalty. The invention is, therefore, especially useful in extraterrestrial environments.

Hagedorn, Norman H.↗
NASA NTRS1992

The Combustion Phase of Burning Metals

Glassman's hypothesis and burn ratio are examined for their suitability for predicting the phase of combustion of metals. Neither criterion is validated based on either published property values or experimental evidence. Inconsistencies in published property values and definitions are noted. Computer calculations provide a more appropriate descriptions of the compositions of the combustion products and the adiabatic flame temperature of a burning metal at equilibrium. Dissociation temperatures (and product compositions) for 11 metals are computed using a specified quantity of thermal energy and compared with adiabatic flame temperatures.

Steinberg, Theodore A.↗
NASA NTRS1992

A new analysis of beam waveguide antennas considering the presence of the metal enclosure

Large beam waveguide (BWG) type ground station antennas are generally designed using analysis which ignores the presence of the metallic tube enclosing the beam waveguide mirrors. The common analysis approaches are physical optics and Gaussian mode analyses. The weakness of these analyses is that they do not shed any light with regards to the effect of the metal tube. In this paper, the first known BWG analysis which considers the presence of the metal tube is presented. Numerical results of a two-mirror system using the new analysis are compared with experiments which have verified the new analysis.

Cha, Alan G.↗
NASA NTRS1993

Kinematics of metal-poor giants in an inner-halo field, with implications for disk formation

A sample of approximately 100 predominantly metal-weak giants, identified in a high-latitude field towards the galactic center using an automated objective-prism survey technique, is presented. Abundances and radial velocities have been measured for these giants, whose distances from the Sun range from 1 to 18 kpc. While the extremely metal-weak stars in the field have halo kinematics, the majority of the stars with intermediate abundance have thick disk kinematics, despite the fact that their average distance from the galactic plane is 3 kpc. The most satisfactory explanation for this effect is that the inner halo is moderately flattened, and the metal-weak stars of the thick disk have a scale height of about 2 kpc. It is suggested that the thick disk may have formed in a dissipational collapse, rather than in a separate event such as the accretion of a small satellite galaxy.

Morrison, Heather L.↗
NASA NTRS1992

Theoretical study of the alkaline-earth metal superoxides BeO2 through SrO2

Three competing bonding mechanisms have been identified for the alkaline-earth metal superoxides: these result in a change in the optimal structure and ground state as the alkaline-earth metal becomes heavier. For example, BeO2 has a linear 3Sigma(-)g ground-state structure, whereas both CaO2 and SrO2 have C(2v)1A1 structures. For MgO2, the theoretical calculations are less definitive, as the 3A2 C(2v) structure is computed to lie only about 3 kcal/mol above the 3Sigma(-)g linear structure. The bond dissociation energies for the alkaline-earth metal superoxides have been computed using extensive Gaussian basis sets and treating electron correlation at the modified coupled-pair functional or coupled-cluster singles and doubles level with a perturbational estimate of the triple excitations.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1946

Quantitative treatment of the creep of metals by dislocation and rate-process theories

An equation for the steady-state rate of creep has been derived by applying the theory of dislocations to the creep of pure metals. The form of this equation is in agreement with empirical equations describing creep rates. The theory was also used to predict the dependence of steady-state rate of creep on physical constants of the material and good agreement was obtained with data in the literature for pure annealed metals. The rate of creep was found to decrease with increasing modulus of rigidity. This relation suggest that one of the requirements for a heat-resisting alloy is that its matrix be a metal that has a high modulus of rigidity and therefore a high modulus of elasticity.

Nowick, A S↗
NASA NTRS1994

Fatigue-Resistant Metal Hook-And-Loop Fastener

Proposed metal hook-and-loop fastener engaged and disengaged many hundreds of times without breaking. Fastener opens by mechanical action. Translation moves hooks out of loops or pushes loops away from hooks. Hooks not required to flex and, therefore, do not fail by fatigue. Lifetime much greater than that of other metal hook-and-loop fasteners, depending on flexure for disengagement such as article, "Hook-and-Loop Metal Fastener" (MSC-21586).

Sawaf, Bernard↗
NASA NTRS1994

Plasma-Spray Metal Coating On Foam

Molds, forms, and other substrates made of foams coated with metals by plasma spraying. Foam might be ceramic, carbon, metallic, organic, or inorganic. After coat applied by plasma spraying, foam left intact or removed by acid leaching, conventional machining, water-jet cutting, or another suitable technique. Cores or vessels made of various foam materials plasma-coated with metals according to method useful as thermally insulating containers for foods, liquids, or gases, or as mandrels for making composite-material (matrix/fiber) parts, or making thermally insulating firewalls in automobiles.

Cranston, J.↗
NASA NTRS1993

Olivine-rich asteroids, pallasitic olivine and olivine-metal mixtures: Comparisons of reflectance spectra

The recent acquisition of high resolution 0.3 - 2.6 micron reflectance spectra for a number of olivine-rich asteroids permits the analysis of their surface compositions to be made on the basis of new and existing laboratory spectral data for pallasitic olivines and olivine-metal mixtures. Analysis of the spectral data for the latter has revealed a number of spectral parameters which can be used to constrain olivine and metal abundances, grain sizes, and olivine compositions. The following topics are discussed in greater detail: pallasite olivine spectra, olivine-metal mixture spectra, and olivine-rich asteroid spectra.

Cloutis, E. A.↗
NASA NTRS1993

The unusual metallic particles in Krymka LL3.0 chondrite

The composition, structure peculiarities, and possible scenario of formation of unusual metallic particles in Krymka LL3.0 are shown. In metal released from gentle crushed after removal of chondrules of Krymka LL3.0 chondrite matter, two types of unusual metallic particles were detected. The first type of particle mainly consists of coarse-grained (greater than or equal to 50 microns) kamacite and fine-grained (less than or equal to 10 microns) Ni-high (approximately 53 wt. percent) taenite. These particles have well-defined zonal structure: kamacite is in central part of particles whereas taenite is in outside and the grains of taenite form the mantle around kamacite. In the second type of particle Fe,Ni-phase contains only fine-grained Ni-rich taenite. In both particle types there are also fine-grained phosphate, troilite, and silicate. Both particle types have mostly rounded to subrounded form.

Fisenko, A. V.↗
NASA NTRS1993

Siderophile element fractionation in meteor crater impact glasses and metallic spherules

Meteor Crater, Arizona provides an opportunity to study, in detail, elemental fractionation processes occurring during impacts through the study of target rocks, meteorite projectile and several types of impact products. We have performed EMPA and INAA on target rocks, two types of impact glass and metallic spherules from Meteor Crater. Using literature data for the well studied Canyon Diablo iron we can show that different siderophite element fractionations affected the impact glasses than affected the metallic spherules. The impact glasses primarily lost Au, while the metallic spherules lost Fe relative to other siderophile elements.

Mittlefehldt, David W.↗
NASA NTRS1993

Size distributions and aerodynamic equivalence of metal chondrules and silicate chondrules in Acfer 059

The CR2 chondrite Acfer 059 is unusual in that the original droplet shapes of metal chondrules are well preserved. We determined separate size distributions for metal chondrules and silicate chondrules; the two types are well sorted and have similar size distributions about their respective mean diameters of 0.74 mm and 1.44 mm. These mean values are aerodynamically equivalent for the contrasting densities, as shown by calculated terminal settling velocities in a model solar nebula. Aerodynamic equivalence and similarity of size distributions suggest that metal and silicate fractions experienced the same sorting process before they were accreted onto the parent body. These characteristics, together with depletion of iron in Acfer 059 and essentially all other chondrites relative to primitive CI compositions, strongly suggest that sorting in the solar nebula involved a radial aerodynamic component and that sorting and siderophile depletion in chondrites are closely related.

Skinner, William R.↗
NASA NTRS1993

Lewis Cliff 87057: A new metal-rich E3 chondrite with similarities to Mt. Egerton, Shallowater and Happy Canyon

The Antarctic meteorites LEW87057, LEW87220, LEW87223, LEW87234, LEW87237, and LEW87285 were described as paired E3 chondrites by Brian Mason (Antarctic Meteorite Newsletters, 12(1) and 15(1,2)). LEW87223 is texturally unusual, containing abundant chondrules and jagged troilite grains which are enclosed in metal. Our INAA data show that the siderophile element abundance in two splits of LEW87223 are higher than the EH range, while chalcophile elements (Cr excepted) are highly depleted. Mineral compositions are unlike those normally found in EH or EL chondrites or aubites, and in some respects resemble those of several anomalous enstatite meteorites such as Shallowater, Mt. Egerton, and Happy Canyon. The bulk and mineral compositions are consistent with the addition of EL chondrite metal to an EL3 chondrite with the removal of sulfides other than troilite which is now Cr-rich. We suggest that this meteorite is an EL3 chondrite into which metal was introduced and sulfides redistributed during an event involving impact melting and brecciation.

Zhang, Y.↗
NASA NTRS1994

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

Epitaxial heterojunctions formed between high temperature superconductors and metallic or semiconducting oxide barrier layers are provided. Metallic perovskites such as LaTiO3, CaVO3, and SrVO3 are grown on electron-type high temperature superconductors such as Nd(1.85)Ce(0.15)CuO(4-x). Alternatively, transition metal bronzes of the form A(x)MO(3) are epitaxially grown on electron-type high temperature superconductors. Also, semiconducting oxides of perovskite-related crystal structures such as WO3 are grown on either hole-type or electron-type high temperature superconductors.

Vasquez, Richard P.↗
NASA NTRS1994

Formation of iron metal and grain coagulation in the solar nebula

The interstellar grain population in the giant molecular cloud from which the sun formed contained little or no iron metal. However, thermal processing of individual interstellar silicates in the solar nebula is likely to result in the formation of a population of very small iron metal grains. If such grains are exposed to even transient magnetic fields, each will become a tiny dipole magnet capable of interacting with other such dipoles over spatial scale orders of magnitude larger than the radii of individual grains. Such interactions will greatly increase the coagulation cross-section for this grain population. Furthermore, the magnetic attraction between two iron dipoles will significantly increase both the collisional sticking coefficient and the strength of the interparticle binding energy for iron aggregates. Formation of iron metal may therefore be a key step in the aggregation of planetesimals in a protoplanetary nebula. Such aggregates may have already been observed in protoplanetary systems. The enhancement in the effective interaction distance between two magnetic dipoles is directly proportional to the strength of the magnetic dipoles and inversely proportional to the relative velocity. It is less sensitive to the reduced mass of the interacting particles (alpha M(exp -1/2)) and almost insensitive to the initial number density of magnetic dipoles (alpha n(sub o)(exp 1/6)). We are in the process of measuring the degree of coagulation in our condensation flow apparatus as a function of applied magnetic field and correlating these results by means of magnetic remanance acquisition measurements on our iron grains with the strength of the magnetic field to which the grains are exposed. Results of our magnetic remanance acquisition measurements and the magnetic-induced coagulation study will be presented as well as an estimate of the importance of such processes near the nebular midplane.

Nuth, Joseph A., III↗