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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

The Oxidation State of Tungsten in Iron Bearing and Iron Free Silicate Glasses: Results from W L-Edge Xanes Measurements

Tungsten is important in constraining core formation of the Earth because this element is a moderately siderophile element (depleted approx. 10 relative to chondrites) and, as a member of the Hf-W isotopic system, it is useful in constraining the timing of core formation. A number of previous experimental studies have been carried out to determine the silicate solubility and metal-silicate partitioning behavior of W, including its concomitant oxidation state. However, results of previous studies (figure 1) are inconsistent on whether W occurs as W(4+) or W(6+).

Danielson, Lisa R.↗
NASA NTRS1971

Relationship between siderophilic-element content and oxidation state of ordinary chondrites.

The concentrations of Ni and Ir have been determined by neutron activation in a suite of ordinary chondrites for which accurate ferromagnesian-mineral compositional data were available. Although hiatus between the individual groups exist, the trends within the groups are in keeping with the hypothesis that the ordinary chondrites form a continuous fractionation sequence. A significant negative correlation is observed between the abundance of Ni or Ir and the Fe content of the ferromagnesian minerals in the H and L groups, and for Ir in the LL group, as expected if the metal-silicate fractionation and the variation in oxidation states were produced by the same or related processes. The Ir/Ni ratio decreases by a factor of 1.2 between the H and LL groups. This fractionation must have occurred at an early stage in the condensation phase of the solar nebula.

Mueller, O.↗
DOE OSTI2024

Plutonium Speciation and Oxidation State Distributions in the Presence of Citrate

We explored the speciation and kinetics of the Pu(VI)-citrate and Pu(III)-citrate systems (pH m = 2.5–11.0, I = 0.1 M NaCl, T = 23 °C, O 2 (g) < 2 ppm) using ultraviolet–visible–near-infrared (UV–vis–NIR) spectrophotometry, solvent extraction, and PHREEQC modeling. Formation constants were determined for PuO 2 (HcitH)(aq) (log K° 1,1 = 1.09 ± 0.05) and PuO 2 (HcitH)(citH) 3– (log K° 1,2 = -0.20 ± 0.07), and evidence for (PuO 2 ) m (citH –k ) n (OH) x 2m(3+k)n–x was identified under alkaline conditions. Pu(VI) species were found to be less stable in the presence of citrate than in the absence of citrate (t ≤ 168 days); the rate of reduction increased with increasing pH. Further, the direct reduction of Pu(VI) to Pu(IV) was required to fit experimental data in the presence of citrate but did not improve the fit for Pu in the absence of citrate. We also observed increased Pu(III) stability in the presence of citrate (t ≤ 293 days), with higher concentrations of Pu(III) favored at lower pH. Finally, we provide evidence of a radiolysis-driven mechanism for the citrate-mediated reduction of plutonium that involves electron transfer from the oxidative breakdown of citrate. Our work highlights the need to investigate the redox effect of organic ligands on plutonium oxidation states under repository-relevant conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Mantle redox evolution and the oxidation state of the Archean atmosphere

Current models predict that the early atmosphere consisted mostly of CO2, N2, and H2O, along with traces of H2 and CO. Such models are based on the assumption that the redox state of the upper mantle has not changed, so that volcanic gas composition has remained approximately constant with time. We argue here that this assumption is probably incorrect: the upper mantle was originally more reduced than today, although not as reduced as the metal arrest level, and has become progressively more oxidized as a consequence of the release of reduced volcanic gases and the subduction of hydrated, oxidized seafloor. Data on the redox state of sulfide and chromite inclusions in diamonds imply that the process of mantle oxidation was slow, so that reduced conditions could have prevailed for as much as half of the earth's history. To be sure, other oxybarometers of ancient rocks give different results, so the question of when the mantle redox state has changed remains unresolved. Mantle redox evolution is intimately linked to the oxidation state of the primitive atmosphere: A reduced Archean atmosphere would have had a high hydrogen escape rate and should correspond to a changing mantle redox state; an oxidized Archean atmosphere should be associated with a constant mantle redox state. The converses of these statements are also true. Finally, our theory of mantle redox evolution may explain why the Archean atmosphere remained oxygen-deficient until approximately 2.0 billion years ago (Ga) despite a probable early origin for photosynthesis.

NASA Discipline Number 52-30↗
NASA NTRS1986

Reduction-oxidation state and protein degradation in skeletal muscle of fasted and refed rats

Redox state and protein degradation were measured in isolated muscles of fasted (up to 10 d) and refed (up to 4 d) 7- to 14-wk-old rats. Protein degradation in the extensor digitorum longus muscle, but not in the soleus muscle, was greater in the fasted rats than in weight-matched muscle from fed rats. The NAD couple was more oxidized in incubated and fresh extensor digitorum longus muscles and in some incubated soleus muscles of fasted rats than in weight-matched muscle from fed rats. In the extensor digitorum longus muscle of refed or prolonged fasted rats, protein degradation was slower and the NAD couple was more reduced than in the fed state. Therefore, oxidation of the NAD couple was associated with increased muscle breakdown during fasting, whereas reduction of the NAD couple was associated with muscle conservation and deposition.

Fagan, Julie M.↗
DOE OSTI2026

Li + /H + Exchange in Solid-State Oxide Li-Ion Conductors

Understanding the moisture stability of oxide Li-ion conductors is important for their practical applications in solid-state batteries. Unlike sulfide or halide conductors, oxide conductors generally better resist degradation when in contact with water but can still undergo topotactic Li + /H + exchange (LHX). Here, we combine density functional theory (DFT) calculations with a machine-learning interatomic potential model to investigate the thermodynamic driving force of the LHX reaction for two representative oxide Li-ion conductor families: garnets and NASICONs. Li-stuffed garnets exhibit a strong driving force for proton exchange due to their high Li chemical potential. In contrast, NASICONs demonstrate a higher resistance against proton exchange due to the lower Li chemical potential and the lower O–H bond covalency for polyanion-bonded oxygens. Our findings reveal a critical trade-off: Li stuffing enhances conductivity but increases moisture susceptibility. This study underscores the importance of designing Li-ion conductors that possess both high conductivity and high stability in practical environments.

Li, Zhuohan [Lawrence Berkeley National Laboratory↗
NASA NTRS1994

The oxidation state of the surface of Venus

We present experimental results showing that basalt is oxidized in CO-CO2 gas mixtures having CO number densities close to those (approximately 2 times higher) at the surface of Venus. The results suggest that the red color observed by Pieters et al at the Venera 9 and 10 landing sites is due to subaerial oxidation of Fe(2+)-bearing basalt on the surface of Venus, and that hematite, instead of magnetite, is present on the surface of Venus. Well-characterized basalt powder was iosthermally heated in 1000 ppm CO-CO2 gas mixtures at atmospheric pressure for several days. The starting material and reacted samples were analyzed by Mossbauer spectroscopy to determine the amount of Fe(2+) and Fe(3+) in the samples. X-ray diffraction and optical microscopy were also used to characterize samples. The basalt oxidation occurs because the CO and CO2 do not equilibrate in the gas mixture at the low temperatures used. Thus, the basalt reacts with the more abundant CO2 and is oxidized. We propose that the red color of the surface of Venus is due to failure of CO and CO2 to equilibrate with one another in the near-surface atmosphere of Venus, leading to subaerial oxidation of erupted Fe(2+)-bearing basalts. Our interpretation is supported by our studies of magnetite oxidation, which show that synthetic magnetite powders are oxidized to hematite in CO-CO2 gas mixtures inside the magnetite stability field, by our studies of pyrite decomposition, and by independent work on CO-CO2 equilibration in furnace gases.

Fegley, B., Jr.↗
NASA NTRS2001

Geochemical Constraints on the Oxidation States of the Europan Ocean and Mantle

We present observational, meteoritic, and physical-chemical arguments for an oxidized Fe-metal free mantle and an oxidized sulfate-carbonate rich ocean on Europa. The ocean should be out of equilibrium even with oxidized igneous rocks at the oceanic floor. Additional information is contained in the original extended abstract.

Zolotov, M. Yu.↗
NASA NTRS1992

The -SiH vibrational stretch as an indicator of the oxidation state of silicon in a cometary or asteroidal regolith

It has been experimentally shown that the position of the -SiH fundamental vibrational stretch is very sensitive to the chemical environment surrounding the Si atom. Si in an oxidizing environment will display an -SiH feature near 4.4 microns, whereas Si in a reducing grain could be responsible for a feature at 4.74 microns. It is further shown that, as an oxidized grain is reduced, the -SiH fundamental shifts to longer wavelengths through a series of intermediate bands.

Nuth, Joseph A., III↗
NASA NTRS2010

Oxidation States of Grim Glasses in EET79001 Based on Vanadium Valence

Gas-rich impact-melt (GRIM) glasses in SNC meteorites are very rich in Martian atmospheric noble gases and sulfur suggesting a possible occurrence of regolith-derived secondary mineral assemblages in these samples. Previously, we have studied two GRIM glasses, 506 and 507, from EET79001 Lith A and Lith B, respectively, for elemental abundances and spatial distribution of sulfur using EMPA (WDS) and FE-SEM (EDS) techniques and for sulfur-speciation using K-edge XANES techniques. These elemental and FE-SEM micro-graph data at several locations in the GRIM glasses from Shergotty (DBS), Zagami 994 and EET79001, Lith B showed that FeO and SO3 are positively correlated (SO3 represents a mixture of sulfide and sulfate). FE-SEM (EDS) study revealed that the sulfur-rich pockets in these glasses contain numerous micron-sized iron-sulfide (Fe-S) globules sequestered throughout the volume. However, in some areas (though less frequently), we detected significant Fe-S-O signals suggesting the occurrence of iron sulfate. These GRIM glasses were studied by K-edge microXANES techniques for sulfur speciation in association with iron in sulfur-rich areas. In both samples, we found the sulfur speciation dominated by sulfide with minor oxidized sulfur mixed in with various proportions. The abundance of oxidized sulfur was greater in 506 than in 507. Based on these results, we hypothesize that sulfur initially existed as sulfate in the glass precursor materials and, on shock-impact melting of the precursor materials producing these glasses, the oxidized sulfur was reduced to predominately sulfide. In order to further test this hypothesis, we have used microXANES to measure the valence states of vanadium in GRIM glasses from Lith A and Lith B to complement and compare with previous analogous measurements on Lith C (note: 506 and 507 contain the largest amounts of martian atmospheric gases but the gas-contents in Lith C measured by are unknown). Vanadium is ideal for addressing this re-dox issue because it has multiple valence states and is a well-studied element. Ferrous-dominated iron valences determined by microXANES on the Lith A and Lith B glasses provide little redox sensitivity. Vanadium valence measurements for impact glass in Lith C at three different locations yielded valence values of 3.1, 3.2 and 3.4 with inferred fO2 values of IW-0.7, IW-0.1 and IW+0.7, respectively. This range of oxygen-fugacity values is understandable because the glasses are shock-molten impact glasses which are heterogeneous in nature. Oxygen fugacity values obtained from the analysis of Fe-Ti oxides and Eu partitioning in pyroxenes from EET79001 Lith A and Lith B (host lithologies) were in the range of IW+0.3 to IW+1.9 suggesting that V in the Lith C impact glass was reduced in the impact process. Here, we examine whether the 506 from Lith A and 507 from Lith B GRIM glasses yield similar or different fO2 values from those of Lith C using the vanadium K-edge microXANES technique.

Sutton, S. R.↗
DOE OSTI2024

Reductive Elimination From Tetra‐Alkyl Cuprates [Me n Cu(CF 3 ) 4− n ] − ( n =0–4): Beyond Simple Oxidation States

Abstract In recent years, the electronic structures of organocuprates in general and the complex [Cu(CF 3 ) 4 ] − in particular have attracted significant interest. A possible key indicator in this context is the reactivity of these species. Nonetheless, this aspect has received only limited attention. Here, we systematically study the series of tetra‐alkyl cuprates [Me n Cu(CF 3 ) 4− n ] − and their unimolecular reactivity in the gas phase, which includes concerted formal reductive eliminations as well as radical losses. Through computational studies, we characterize the electronic structures of the complexes and show how these are connected to their reactivity. We find that all [Me n Cu(CF 3 ) 4− n ] − ions feature inverted ligand fields and that the distinct reactivity patterns of the individual complexes arise from the interplay of different effects.

Zimmer, Bastian↗
DOE OSTI2025

Organophosphorus Binding Thermodynamics in Metal–Organic Frameworks: Interplay between Oxidation State, Lewis Acidity, and Node Structure

Organophosphorus compounds, including nerve agents and pesticides, represent a class of toxic chemicals causing harm to troops, civilians, and the environment. Metal–organic frameworks (MOFs) have emerged as a class of highly porous, crystalline, tunable materials adept at both capturing and catalytically neutralizing these harmful toxins. In particular, MOFs whose nodes display strong Lewis acidic character can hydrolyze such chemicals nearly instantaneously. However, without the help of a basic buffer to regenerate the active site, the benign organophosphorus product strongly binds to the node and prevents catalyst turnover. Here, we investigate a series of MOFs whose nodes contain metals of varying Lewis acidities and employ isothermal titration calorimetry (ITC) to directly measure the heat from the binding of an organophosphorus probe molecule, allowing the construction of a full thermodynamic binding profile (ΔH, ΔS, ΔG, K a ). We couple this with potentiometric titrations and solid state 31 P magic angle spinning (MAS) NMR to gain a clearer picture of how node identity, structure, and Lewis acidity interplay to impact binding strength and favorability. Furthermore, this study is the first to integrate these three complementary techniques to investigate binding interactions in MOFs, further showcasing the viability of ITC for probing MOF systems, which is still relatively underexplored.

Lewis acidity↗
DOE OSTI2025

Evaluate opportunities for monitoring the oxidation states of technetium in both organic and aqueous phases using Raman spectroscopy

An important isotope in the nuclear fuel cycle, 99 Tc is characterized by its long half-life of 2.1 × 10 5 years and its beta emission. It is generated through the fission of 235 U. As the burnup levels of nuclear waste continue to rise, the concentration of technetium in spent fuel increases, leading to a heightened interest in its quantification during the reprocessing of spent nuclear fuel. In HNO3 environments, technetium predominantly exists as TcO 4 − ; however, it tends to interfere with reducing agents, decreasing the separation efficiency for actinides. Therefore, accurate quantitative determination of technetium is critical to controlling its distribution and mitigating its negative effect on the reprocessing of spent fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗