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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Surface and Structural Investigation of a MnO x Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Abstract Catalytically active MnO x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO x catalysts form without supports in situ under photocatalytic conditions. Our most active 4 MnO x catalyst (∼0.84 mmol O 2 mol Mn −1 s −1 ) forms from a Mn 4 O 4 bearing a metal–organic framework. 4 MnO x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m 2 g −1 ) and small regions of crystallinity and layer flexibility. In contrast, the S MnO x formed from Mn 2+ salt gives an amorphous species of lower surface area (80 m 2 g −1 ) and lower activity (∼0.15 mmol O 2 mol Mn −1 s −1 ). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p 3/2 core levels detects enriched Mn 3+ and Mn 2+ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.

Deibert, Benjamin J.↗
DOE OSTI2020

Self-accelerated corrosion of nuclear waste forms at material interfaces

The US plan for high-level nuclear waste includes the immobilization of long-lived radionuclides in glass or ceramic waste forms in stainless-steel canisters for disposal in deep geological repositories. Here we report that, under simulated repository conditions, corrosion could be significantly accelerated at the interfaces of different barrier materials, which has not been considered in the current safety and performance assessment models. Severe localized corrosion was found at the interfaces between stainless steel and a model nuclear waste glass and between stainless steel and a ceramic waste form. The accelerated corrosion can be attributed to changes of solution chemistry and local acidity/alkalinity within a confined space, which significantly alter the corrosion of both the waste-form materials and the metallic canisters. The corrosion that is accelerated by the interface interaction between dissimilar materials could profoundly impact the service life of the nuclear waste packages, which, therefore, should be carefully considered when evaluating the performance of waste forms and their packages. Moreover, compatible barriers should be selected to further optimize the performance of the geological repository system.

Guo, Xiaolei↗
DOE OSTI2013

THE FRAGMENTATION OF MAGNETIZED, MASSIVE STAR-FORMING CORES WITH RADIATIVE FEEDBACK

We present a set of three-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 M{sub Sun }), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single-star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single-star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for {approx}100 M{sub Sun} cores with many thermal Jeans masses of material. We also demonstrate that a {approx}40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Cyanobacteria from marine oxygen-deficient zones encode both form I and form II Rubiscos

Cyanobacteria are highly abundant in the marine photic zone and primary drivers of the conversion of inorganic carbon into biomass. To date, all studied cyanobacterial lineages encode carbon fixation machinery relying upon form I Rubiscos within a CO 2 -concentrating carboxysome. Here, we report that the uncultivated anoxic marine zone (AMZ) IB lineage ofProchlorococcusfrom pelagic oxygen-deficient zones (ODZs) harbors both form I and form II Rubiscos, the latter of which are typically noncarboxysomal and possess biochemical properties tuned toward low-oxygen environments. We demonstrate that these cyanobacterial form II enzymes are functional in vitro and were likely acquired from proteobacteria. Metagenomic analysis reveals that AMZ IB are essentially restricted to ODZs in the Eastern Pacific, suggesting that form II acquisition may confer an advantage under low-O 2 conditions. AMZ IB populations express both forms of Rubisco in situ, with the highest form II expression at depths where oxygen and light are low, possibly as a mechanism to increase the efficiency of photoautotrophy under energy limitation. Our findings expand the diversity of carbon fixation configurations in the microbial world and may have implications for carbon sequestration in natural and engineered systems.

Science & Technology - Other Topics↗
DOE OSTI2023

A Bacterial Form I’ Rubisco Has a Smaller Carbon Isotope Fractionation than Its Form I Counterpart

Form I rubiscos evolved in Cyanobacteria ≥ 2.5 billion years ago and are enzymatically unique due to the presence of small subunits (RbcS) capping both ends of an octameric large subunit (RbcL) rubisco assembly to form a hexadecameric (L 8 S 8 ) holoenzyme. Although RbcS was previously thought to be integral to Form I rubisco stability, the recent discovery of a closely related sister clade of octameric rubiscos (Form I’; L 8 ) demonstrates that the L 8 complex can assemble without small subunits (Banda et al. 2020). Rubisco also displays a kinetic isotope effect (KIE) where the 3PG product is depleted in 13 C relative to 12 C. In Cyanobacteria, only two Form I KIE measurements exist, making interpretation of bacterial carbon isotope data difficult. To aid comparison, we measured in vitro the KIEs of Form I’ (Candidatus Promineofilum breve) and Form I (Synechococcus elongatus PCC 6301) rubiscos and found the KIE to be smaller in the L 8 rubisco (16.25 ± 1.36‰ vs. 22.42 ± 2.37‰, respectively). Therefore, while small subunits may not be necessary for protein stability, they may affect the KIE. Our findings may provide insight into the function of RbcS and allow more refined interpretation of environmental carbon isotope data.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

The form factors of the nucleons

There has been much activity in the measurement of the elastic electromagnetic proton and neutron form factors in the last decade, and the quality of the data has been greatly improved by performing double-polarization experiments, in comparison with with previous unpolarized cross section data. Here we will review the experimental data base in view of the new results for the proton and the neutron, obtained at MIT-Bates, JLab and MAMI. The rapid evolution of phenomenological models triggered by these high-precision experiments will be discussed. In particular, the possibility that the proton is non-spherical in its ground state, and that the transverse charge density are model independently defined in the infinite momentum frame. Likewise, flavor decomposition of the nucleon form factors into dressed u and d quark form factors, may give information about the quark-diquark structure of the nucleon. The current proton radius “crisis” will also be discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Dehalogenation of electrochemical processing salt simulants with ammonium phosphates and immobilization of salt cations in an iron phosphate glass waste form

This study demonstrates the conversion of simulated pyroprocessing salt wastes [i.e., ER(SF) and ERV2] into chemically durable iron phosphate glass waste forms through reactions with ammonium hydrogen phosphate precursors [i.e., NH4H2PO4 and (NH4)2HPO4] and added Fe2O3. The reaction of the salt simulants with the phosphate precursors resulted in dehalogenation of the salt through the production of NH4Cl and NH4I (along with water), of which the NH4Cl can be used to produce UCl3 oxidant for use in the electrorefiner during pyroprocessing. These iron phosphate glasses contain a notably higher waste loading than the baseline glass-bonded sodalite ceramic waste form, which requires about 70 vol% sodalite to accommodate Cl from the salt, because they are dehalogenated prior to vitrification. The high waste loadings coupled with higher bulk densities (~3×103 kg/m3) than glass-bonded sodalite (~2.3×103 kg/m3) mean that these glasses have a higher storage volume, i.e., the volume required to immobilize a given mass of waste. The iron phosphate glass waste forms were characterized using a variety of techniques including physical property measurements and chemical durability testing. Following initial testing, a proof-of-concept demonstration was conducted to show that the NH4Cl generated from this process could be used to produce UCl3 using depleted uranium dendrites as a feedstock.

phosphate glass, pyroprocessing, waste forms, salt↗
DOE OSTI2016

Application of micro X-ray diffraction to investigate the reaction products formed by the alkali–silica reaction in concrete structures

Alkali–silica reaction (ASR) is one of the most important deterioration mechanisms in concrete leading to substantial damages of structures worldwide. Synchrotron-based micro-X-ray diffraction (micro-XRD) was employed to characterize the mineral phases formed in micro-cracks of concrete aggregates as a consequence of ASR. This high spatial resolution technique enables to directly gain structural information on ASR products formed in a 40-year old motorway bridge damaged due to ASR. Micro-X-ray-fluorescence was applied on thin sections to locate the reaction products formed in veins within concrete aggregates. Micro-XRD pattern were collected at selected points of interest along a vein by rotating the sample. Rietveld refinement determined the structure of the ASR product consisting of a new layered framework similar to mountainite and rhodesite. It is conceivable that understanding the structure of the ASR product may help developing new technical treatments inhibiting ASR.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Aqueous Synthesis of Technetium-Doped Titanium Dioxide by Direct Oxidation of Titanium Powder, a Precursor for Ceramic Nuclear Waste Forms

Technetium-99 (Tc) is a problematic fission product that complicates the long-term disposal of nuclear waste due to its long half-life, high fission yield, and the environmental mobility of pertechnetate, its stable form in aerobic environments. One approach to preventing Tc contamination is through incorporation into durable waste forms based on weathering-resistant minerals such as rutile (titanium dioxide). Here, the incorporation of technetium into titanium dioxide by means of simple, aqueous chemistry - direct oxidation of titanium powder in the presence of ammonium fluoride - is achieved. X-ray absorption fine structure spectroscopy and diffuse reflectance spectroscopy indicate that Tc(IV) replaces Ti(IV) within the structure. Rather than being incorporated as isolated Tc(IV) ions, Tc is present as pairs of edge-sharing Tc(IV) octahedra similar to molecular Tc(IV) complexes such as [(H 2 EDTA)TcIV](μ-O) 2 . Technetium-doped TiO 2 was suspended in deionized water under aerobic conditions, and the Tc leached under these conditions was followed for 8 months. The normalized release rate of Tc (LR Tc ) from the TiO 2 particles is low (3 × 10 -6 g m -2 d -1 ), which illustrates the potential utility of TiO 2 as waste form. However, the small size of the as-prepared TiO 2 nanoparticles results in an estimated retention of Tc of 10 4 years, which is only a fraction of the half-life of Tc (2.1 × 10 5 years).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Microscopic insight into the origin of enhanced glass-forming ability of metallic melts on micro-alloying

Extensive efforts have been made to develop metallic-glasses with large casting diameter. Such efforts were hindered by the poor understanding of glass formation mechanisms and the origin of the glass-forming ability (GFA) in metallic glass-forming systems. In this work, we have investigated relaxation dynamics of a model bulk glass-forming alloy system that shows the enhanced at first and then diminished GFA on increasing the percentage of micro-alloying. The micro-alloying did not have any significant impact on the thermodynamic properties. The GFA increasing on micro-alloying in this system cannot be explained by the present theoretical knowledge. Our results indicate that atomic caging is the primary factor that influences the GFA. The composition dependence of the atomic caging time or residence time is found to be well correlated with GFA of the system.

36 MATERIALS SCIENCE↗
DOE OSTI2012

CHARACTERIZING COSMIC-RAY PROPAGATION IN MASSIVE STAR-FORMING REGIONS: THE CASE OF 30 DORADUS AND THE LARGE MAGELLANIC CLOUD

Using infrared, radio, and {gamma}-ray data, we investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using a phenomenological model based on the radio-far-infrared correlation within galaxies. Employing a correlation analysis, we derive an average propagation length of {approx}100-140 pc for {approx}3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed {gamma}-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and {gamma}-ray data, we estimate a {approx}20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for {approx}3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is {approx}4 times higher, scaling as (R/GV){sup {delta}} with {delta} Almost-Equal-To 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include {approx}70 GeV CR nuclei traced by the 3-10 GeV {gamma}-ray data ({delta} Almost-Equal-To 0.66 {+-} 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D{sub R} Almost-Equal-To (0.9-1.0) Multiplication-Sign 10{sup 27}(R/GV){sup 0.7} cm{sup 2} s{sup -1}. We compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor.

79 ASTRONOMY AND ASTROPHYSICS↗