Search NASA⌕ Search

SEARCH · Search NASA

Results for “multivalent”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

High Tc superconductors: The scaling of Tc with the number of bound holes associated with charge transfer neutralizing the multivalence cations

It is observed that for the known high-T(sub c) Cu-, Tl-, and Bi-based superconductors, T(sub c) scales consistently with the number of bound holes per unit cell which arise from charge transfer excitations of frequency approximately = 3 x 10(exp 13) that neutralized the multivalence cations into diamagnetic states. The resulting holes are established on the oxygens. Extrapolation of this empirical fit in the up-temperature direction suggests a T(sub c) of about 220-230 K at a value of 25 holes/unit cell (approximately the maximum that can be materials-engineered into a high-T(sub c) K2MnF4 or triple Perovskite structure). In the down-temperature direction, the extrapolation gives a T(sub c) in the vicinity of 235 K for the Y-Ba-Cu-O system as well as the known maximum temperature of 23 K for low-T(sub c) materials shown by Nb3Ge. The approach is also consistent with the experimental findings that only multivalence ions which are diamagnetic in their atomic state (Cu, Tl, Bi, Pb, and Sb) associate with high-T(sub c) compounds.

Vezzoli, G. C.↗
NASA NTRS2021

Anion-Assisted Delivery of Multivalent Cations to Inert Electrodes

To understand and control key electrochemical processes - metal plating, corrosion, intercalation, etc. requires molecular-scale details of the active species at electrochemical interfaces and their mechanisms for de-solvation from the electrolyte. Using free energy sampling techniques we reveal the interfacial speciation of divalent cations in ether-based electrolytes and mechanisms for their delivery to an inert graphene electrode interface. Surprisingly, we find that anion solvophobicity drives a high population of anion-containing species to the interface that facilitate the delivery of divalent cations, even to negatively charged electrodes. Our simulations indicate that cation desolvation is greatly facilitated by cation-anion coupling. We propose anion solvophobicity as a molecular-level descriptor for rational design of electrolytes with increased efficiency for electrochemical processes limited by multivalent cation desolvation.

Electrochemical interfaces↗
NASA NTRS1967

Hydrated multivalent cations are new class of molten salt mixtures

Electrical conductance and activation energy measurements on mixtures of calcium and potassium nitrate show the hydrated form to be a new class of molten salt. The theoretical glass transition temperature of the hydrate varied in a manner opposite to that of the anhydrous system.

Angell, C. A.↗
NASA NTRS1977

Redox equilibria of multivalent ions in silicate glasses

Experimental studies were made on the compositional dependence of the redox equilibrium of Eu in synthetic silicate liquids, together with an empirical model describing the observed compositional dependence. Electron paramagnetic resonance (EPR) was used to measure the concentration ratio of Eu(2+) to Eu(3+) in various glasses formed by rapidly quenching silicate liquids. The compositional field studied comprised mixtures of SiO2, TiO2, Al2O3, CaO, MgO, and Na2O. The proposed model describes the Eu(2+)/Eu(3+) ratio over the entire compositional field in terms of parameters easily related to each glass composition. The general applicability and utility of the model is further demonstrated by its application to the Fe(2+)-Fe(3+), Ce(3+)-Ce(4+), and Cr(3+)-Cr(6+) redox reactions in binary alkali oxide silicate glasses of Li, Na, and K.

Lauer, H. V., Jr.↗
NASA NTRS2016

The Mineralogy, Geochemistry, and Redox State of Multivalent Cations During the Crystallization of Primitive Shergottitic Liquids at Various (f)O2. Insights into the (f)O2 Fugacity of the Martian Mantle and Crustal Influences on Redox Conditions of Martian Magmas.

The (f)O2 [oxygen fugacity] of crystallization for martian basalts has been estimated in various studies to range from IW-1 to QFM+4 [1-3]. A striking geochemical feature of the shergottites is the large range in initial Sr isotopic ratios and initial epsilon(sup Nd) values. Studies by observed that within the shergottite group the (f)O2 [oxygen fugacity] of crystallization is highly correlated with these chemical and isotopic characteristics with depleted shergottites generally crystallizing at reduced conditions and enriched shergottites crystallizing under more oxidizing conditions. More recent work has shown that (f)O2 [oxygen fugacity] changed during the crystallization of these magmas from one order of magnitude in Y980459 (Y98) to several orders of magnitude in Larkman Nunatak 06319. These real or apparent variations within single shergottitic magmas have been attributed to mixing of a xenocrystic olivine component, volatile loss-water disassociation, auto-oxidation during crystallization of mafic phases, and assimilation of an oxidizing crustal component (e.g. sulfate). In contrast to the shergottites, augite basalts such as NWA 8159 are highly depleted yet appear to be highly oxidized (e.g. QFM+4). As a first step in attempting to unravel petrologic complexities that influence (f)O2 [oxygen fugacity] in martian magmas, this study explores the effect of (f)O2 [oxygen fugacity] on the liquid line of descent (LLD) for a primitive shergottite liquid composition (Y98). The results of this study will provide a fundamental basis for reconstructing the record of (f)O2 [oxygen fugacity] in shergottites and other martian basalts, its effect on both mineral chemistries and valence state partitioning, and a means for examining the role of crystallization (and other more complex processes) on the petrologic linkages between olivine-phyric and pyroxene-plagioclase shergottites.

Shearer, C. K.↗
NASA NTRS2000

Preparation and Analysis of RNA Crystals

The crystallization of RiboNucleic Acids (RNA) was studied from the standpoint of mechanisms of crystal growth in three tasks: (1) preparation of high-quality crystals of oligonuclotides for X-ray diffraction, (2) finding pathways to the growth of high-quality crystals for X-ray diffraction and (3) investigation of mechanisms of action of inertial acceleration on crystal growth. In these tasks: (1) RNA crystals were prepared and studied by X-ray diffraction; (2) a pathway to high-quality crystals was discovered and characterized; a combination of kinetic and equilibrium factors could be optimized as described below; and (3) an interplay between purity and gravity was found in a combination of space and ground experiments with nucleic acids and proteins. Most significantly, the rate of concentration of precipitant and RNA can be controlled by membrane-based methods of water removal or by diffusion of multivalent cations across an interface stabilized by a membrane. Oligonucleotide solutions are electrokinetically stabilized colloids, and crystals can form by the controlled addition of multivalent cations.

Todd, Paul↗
NASA NTRS1987

Mutual interactions of redox couples via electron exchange in silicate melts - Models for geochemical melt systems

The mutual interactions via electron exchange of redox couples in glass-forming melts were investigated both theoretically and experimentally. A thermodynamic approach for considering the mutual interactions leads to conclusion that the degree of mutual interaction in the melt should be proportional in part to the difference in relative reduction potentials of the interacting redox couples. Experimental studies verify this conclusion for numerous redox couples in several composition/temperature/oxygen fugacity regimes. Geochemical systems simultaneously possess many potentially multivalent elements; the stabilized redox states in the resulting magmas can be explained in part by mutual interactions and by redox buffering through the central Fe(III)- Fe(II) couples in the melts. The significance of these results for basaltic magmas of the earth, moon, and meteorites is addressed.

Schreiber, Henry D.↗
NASA NTRS1990

The mechanism of high-T(sub c) superconductivity due to bound hole mediators: Relationship to ferroelectricity

The mediation by bound holes creating Cooper pairing in high T(sub c) superconductors has its origin in charge transfer excitations on the multivalence cation (virtual excitions) and in bound excitions or polarizations associated with the oxygen 2p electrons. These phenomena are produced and/or enhanced by a high internal electric field which is itself created by virtue of the unique crystal structures and polyhedral building blocks of high T(sub c) materials. The polarizations which can create oxygen holes (in addition to excitions) may be due to simply the internal electric field or to polaronic and electron-deficient bond behavior. This gives rise to two energy-dependent oxygen bands near the Fermi level. The magnitude and direction of the internal electric fields were calculated for Y1Ba2Cu3O(7-delta) (1-2-3) and show strong z-direction fields at the Cu(2), O2, and O3 sites and an even stronger -z direction field at the O4 site. The field calculations also show why electrical conductivity in the 1-2-3 material is essentially in the base plane of the CuO5 pyramid (the CuO2 plane).

Vezzoli, G. C.↗
NASA NTRS1992

A Backscatter Moessbauer Spectrometer (BaMS) for use on Mars

The use of Moessbauer spectroscopy for in situ analysis on the surface of Mars was proposed and the design and implementation of a backscatter Moessbauer spectrometer (BaMS) instrument suitable for planetary missions to the surfaces of Mars (MESUR), the Moon (Artemis and lunar outpost), asteroids, or other solid solar system objects is discussed. The BaMS instrument is designed to be capable of analysis of a sample for the mineralogy of its iron-bearing phases without any sample preparation. A requirement of lander missions to Mars is instrumentation for in situ mineralogical analyses. Such analyses provide data needed for primary characterization as to the type of surface materials present and by inference the processes that formed and subsequently modified them. For purposes of providing diagnostic information about naturally occurring materials, the element iron is particularly important because it is abundant and multivalent (primarily 0, +2, and +3 oxidation states). Knowledge of the oxidation state of iron and its distribution among iron-bearing mineralogies tightly constrains the types of materials present. The pivotal role of iron was already recognized in 1978 by COMPLEX, who recommended development of flight instruments that would identify mineralogy and the oxidation state of iron in planetary surface materials. The near-term U.S. strategy for the exploration of Mars is the MESUR (Mars Environmental SURvey) program, which entails emplacement of a network of small, long-lived surface landers. For the Moon, BaMS was recommended as part of a three-instrument landed payload for the Artemis missions, targeted for 1997. BaMS would prospect for ilmenite, an oxygen resource material, and provide data to assess the maturity of lunar soil. Because instrumental characteristics are low mass, low volume, and low power consumption, BaMS is suitable for implementation on even small landers and rovers, as are being envisioned in MESUR and Artemis concepts. In addition to providing highly diagnostic data, a BaMS analyzer is inherently simple and, as is highly desirable for remote operation, no sample preparation is required.

Agresti, D. G.↗
NASA NTRS1997

Moessbauer Mineralogy on the Moon: The Lunar Regolith

A first-order requirement for spacecraft missions that land on solid planetary objects is instrumentation for mineralogical analyses. For purposes of providing diagnostic information about naturally-occurring materials, the element iron is particularly important because it is abundant and multivalent. Knowledge of the oxidation state of iron and its distribution among iron-bearing mineralogies tightly constrains the types of materials present and provides information about formation and modification (weathering) processes. Because Moessbauer spectroscopy is sensitive to both the valence of iron and its local chemical environment, the technique is unique in providing information about both the relative abundance of iron-bearing phases and oxidation state of the iron. The Moessbauer mineralogy of lunar regolith samples (primarily soils from the Apollo 16 and 17 missions to the Moon) were measured in the laboratory to demonstrate the strength of the technique for in situ mineralogical exploration of the Moon. The regolith samples were modeled as mixtures of five iron-bearing phases: olivine, pyroxene, glass, ilmenite, and metal. Based on differences in relative proportions of iron associated with these phases, volcanic ash regolith can be distinguished from impact-derived regolith, impact-derived soils of different geologic affinity (e.g., highlands, maria) can be distinguished on the basis of their constituent minerals, and soil maturity can be estimated. The total resonant absorption area of the Moessbauer spectrum can be used to estimate total FeO concentrations.

Morris, Richard V.↗
NASA NTRS2001

A Survey of Complex Object Technologies for Digital Libraries

Many early web-based digital libraries (DLs) had implicit assumptions reflected in their architecture that the unit of focus in the DL (frequently "reports" or "e-prints") would only be manifested in a single, or at most a few, common file formats such as PDF or PostScript. DLs have now matured to the point where their contents are commonly no longer simple files. Complex objects in DLs have emerged from in response to various requirements, including: simple aggregation of formats and supporting files, bundling additional information to aid digital preservation, creating opaque digital objects for e-commerce applications, and the incorporation of dynamic services with the traditional data files. We examine a representative (but not necessarily exhaustive) number of current and recent historical web-based complex object technologies and projects that are applicable to DLs: Aurora, Buckets, ComMentor, Cryptolopes, Digibox, Document Management Alliance, FEDORA, Kahn-Wilensky Framework Digital Objects, Metadata Encoding & Transmission Standard, Multivalent Documents, Open eBooks, VERS Encapsulated Objects, and the Warwick Framework.

Nelson, Michael L.↗
NASA NTRS2004

The Relationship Between Clinopyroxene Fe3+ Content and Oxygen Fugacity

The intrinsic oxygen fugacity (fO2) imposed on a magma has the ability to influence the crystallization sequence of the melt, as well as the composition of the resulting minerals. fO2 is an easily controlled parameter in the lab, either through gas-mixing equilibria or with a solid-state buffer assemblage. In nature, the fO2 of a closed system is imposed on the system internally through multivalent equilibria involving the phenocryst-melt assemblage. This results in a characteristic oxidation state. The physical parameter used to quantify oxidation state is oxygen fugacity. Iron is the only major rock forming element in basaltic melts to exist in multiple valence states and, therefore, it is commonly used to assess fO2. Traditional methods to quantify fO2 utilize the ferric content of glasses or coexisting Fe-Ti oxides. However, many rocks, such as the Martian meteorites, do not contain the necessary phases or have oxides which have suffered reequilibration, thereby rendering them unmeasureable by current techniques. For these rocks, new methods, utilizing other phases are needed. Mafic minerals have Fe(3+)/SigmaFe ratios that are a function of two factors: 1) crystal chemistry and 2) their intrinsic fO2 during crystallization. Olivine and orthopyroxene, for example, have steric constraints on the extent to which Fe(3+) can be incorporated in their structures, and may not record changes in magmatic fO2 in a way that can easily be measured. The chemistry of clinopyroxene, however, allows for extensive incorporation of Fe(3+) in its crystal structure, making it a potentially useful oxybarometer. To date, there have been few, if any, systematic experimental studies of the variation of the Fe(3+)/SigmaFe ratio as a function of fO2 in clinopyroxene. This study seeks to address this lack of data.

McCanta, M. C.↗
NASA NTRS1982

Coating for gasifiable carbon-graphite fibers

A thin, uniform, firmly adherent coating of metal gasification catalyst is applied to a carbon-graphite fiber by first coating the fiber with a film-forming polymer containing functional moieties capable of reaction with the catalytic metal ions. Multivalent metal cations such as calcium cross-link the polymer such as a polyacrylic acid to insolubilize the film by forming catalytic metal macro-salt links between adjacent polymer chains. The coated fibers are used as reinforcement for resin composites and will gasify upon combustion without evolving conductive airborne fragments.

Harper-Tervet, Jan↗
NASA NTRS2010

Molybdenum Valence in Basaltic Silicate Melts

The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (~IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

Danielson, L. R.↗
NASA NTRS2013

A New Spinel-Olivine Oxybarometer: Near-Liquidus Partitioning of V between Olivine-Melt, Spinel-Melt, and Spinel-Olivine in Martian Basalt Composition Y980459 as a Function of Oxygen Fugacity

Our research on valence state partitioning began in 2005 with a review of Cr, Fe, Ti, and V partitioning among crystallographic sites in olivine, pyroxene, and spinel [1]. That paper was followed by several on QUE94201 melt composition and specifically on Cr, V, and Eu partitioning between pyroxene and melt [2-5]. This paper represents the continuation of our examination of the partitioning of multivalent V between olivine, spinel, and melt in martian olivine-phyric basalts of Y980459 composition [6, 7]. Here we introduce a new, potentially powerful oxybarometer, V partitioning between spinel and olivine, which can be used when no melt is preserved in the meteorite. The bulk composition of QUE94201 was ideal for our study of martian pyroxene-phyric basalts and specifically the partitioning between pyroxene-melt for Cr, V, and Eu. Likewise, bulk composition Y980459 is ideal for the study of martian olivine-phyric basalts and specifically for olivine-melt, spinel-melt, and spinel-olivine partitioning of V as a function of oxygen fugacity.

Papike, J. J.↗
NASA NTRS2013

The W-W02 Oxygen Fugacity Buffer at High Pressures and Temperatures: Implications for f02 Buffering and Metal-silicate Partitioning

Oxygen fugacity (fO2) controls multivalent phase equilibria and partitioning of redox-sensitive elements, and it is important to understand this thermodynamic parameter in experimental and natural systems. The coexistence of a metal and its oxide at equilibrium constitutes an oxygen buffer which can be used to control or calculate fO2 in high pressure experiments. Application of 1-bar buffers to high pressure conditions can lead to inaccuracies in fO2 calculations because of unconstrained pressure dependencies. Extending fO2 buffers to pressures and temperatures corresponding to the Earth's deep interior requires precise determinations of the difference in volume (Delta) V) between the buffer phases. Synchrotron x-ray diffraction data were obtained using diamond anvil cells (DAC) and a multi anvil press (MAP) to measure unit cell volumes of W and WO2 at pressures and temperatures up to 70 GPa and 2300 K. These data were fitted to Birch-Murnaghan 3rd-order thermal equations of state using a thermal pressure approach; parameters for W are KT = 306 GPa, KT' = 4.06, and αKT = 0.00417 GPa K-1. Two structural phase transitions were observed for WO2 at 4 and 32 GPa with structures in P21/c, Pnma and C2/c space groups. Equations of state were fitted for these phases over their respective pressure ranges yielding the parameters KT = 190, 213, 300 GPa, KT' = 4.24, 5.17, 4 (fixed), and αKT = 0.00506, 0.00419, 0.00467 GPa K-1 for the P21/c, Pnma and C2/c phases, respectively. The W-WO2 buffer (WWO) was extended to high pressure by inverting the W and WO2 equations of state to obtain phase volumes at discrete pressures (1-bar to 100 GPa, 1 GPa increments) along isotherms (300 to 3000K, 100 K increments). The slope of the absolute fO2 of the WWO buffer is positive with increasing temperature up to approximately 70 GPa and is negative above this pressure. The slope is positive along isotherms from 1000 to 3000K with increasing pressure up to at least 100 GPa. The WWO buffer is at a higher fO2 than the IW buffer at pressures lower than 40 GPa, and the magnitude of this difference decreases at higher pressures. This qualitatively indicates an increasingly lithophile character for W at higher pressures. The WWO buffer was quantitatively applied to W metal-silicate partitioning by using the WWO-IW buffer difference in combination with literature data on W metal-silicate partitioning to model the exchange coefficient (KD) for the Fe-W exchange reaction. This approach captures the pressure dependence of W metal-silicate partitioning using the WWO-IW buffer difference and models the activities of the components in the silicate and metallic phases using an expression of the Gibbs excess energy of mixing. Calculation of KD along a peridotite liquidus predicts a decrease in W siderophility at higher pressures that supports the qualitative behavior predicted by the WWO-IW buffer difference, and agrees with findings of others. Comparing the competing effects of temperature and pressure on W metal-silicate partitioning, our results indicate that pressure exerts a greater effect.

Shofner, G. A.↗