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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Mesoporous Fe-doped MgO nanoparticles as a heterogeneous photo-Fenton-like catalyst for degradation of salicylic acid in wastewater

Mesoporous Fe-doped MgO nanoparticles were synthesized using a facile sol-gel method and utilized for photo-Fenton-like degradation of salicylic acid (SA). The MgO surface dissolution facilitated an increase in the pH under the reaction conditions that allowed the Fe-MgO catalyst to be active without detectable iron leaching. Under simulated solar radiation, SA was completely degraded with an initial rate constant of 0.048 min -1 at the optimal reaction conditions of 500 ppm loading of 5% Fe-MgO, 20 mM H 2 O 2 concentration, and 50 ppm SA concentration. The catalyst was stable over 5 reaction cycles. The Fe-MgO catalyst was shown to have a surface area up to 171 m 2 /g and contain hematite (Fe 2 O 3 ) nanoparticles with octahedrally coordinated iron catalytic centers, as inferred from diffuse reflectance UV–vis measurements. Post-reaction catalyst characterization showed that some Fe 2+ was present in the catalyst due to the redox cycle during the chain initiation and propagation steps of the reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Synthesis and properties of bulk cobalt-carbide permanent magnets

Nanocrystalline bulk Co-C permanent magnets were produced by rapid hot consolidation of ball milled powder precursors. Bulk magnets with an average grain size of 20 nm and densities up to 94 percent of the theoretical density were successfully processed at pressures exceeding 1 GPa for the first time. Their microstructural and magnetic properties along with their magnetocrystalline anisotropy values are reported. Presence of iron contamination that results from the use steel milling media in milling was confirmed by elemental mapping of the bulk magnets. It is concluded that iron bonds in the form of hematite and does not adversely affect coercivity values. Here, this study shows that the Co 3 C compound does possess a sizable magnetocrystalline anisotropy, making it a suitable candidate as a rare earth free permanent magnet.

Co3 C↗
DOE OSTI2020

The passivity of low-temperature carburized austenitic stainless steel AISI-316L in a simulated boiling-water-reactor environment

The passive film on low-temperature-carburized AISI-316L austenitic stainless steel was studied in an oxygenated, simulated boiling-water-reactor environment with normal water chemistry. The microstructure was studied using scanning electron microscopy, grazing-incidence X-ray diffractometry, Auger electron spectroscopy, X-ray energy-dispersive spectroscopy, and transmission electron microscopy. For non-surface engineered AISI-316L, three distinct layers were observed after exposure: an outer layer of larger nickel-oxide enriched particles with the spinel structure, an intermediate layer of small Cr-oxide-enriched hematite particles, and a compact inner layer of Cr-enriched oxide also having the spinel structure. Exposure of low-temperature-carburized AISI-316L, in contrast, resulted in only two distinct layers. These layers did not include a compact Cr-rich inner layer. Instead, the innermost layer consisted of an oxide with the spinel structure that was a mixture of Fe, Cr and Ni oxide. The outer layer on the low-temperature-carburized specimen consisted of large loosely stacked particles with the spinel structure of mixed composition. In addition to passive-film characterization, the corrosion rate was studied by monitoring mass loss. Finally, after 500 h of immersion, the mass changes measured were relatively low for all specimens indicating good adhesion and low oxidation rates.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multi-fidelity kinetic theory-based approach for the prediction of particle attrition: Application to jet cup attrition system

The timescale difference between the “fast” flow dynamics of fluidized bed reactors and the relatively “slow” rate of particle degradation makes the direct computational prediction of attrition challenging. An approach to this challenge is a multi-fidelity strategy where a high fidelity model for the flow dynamics is coupled with a lower fidelity model for the long-time resolution of the bulk attrition of the reactor inventory. We implement this approach using high-fidelity kinetic theory simulations to calculate the flow dynamics which are post-processed to calculate the frequency and intensity of the particle-particle and particle-wall collisions (e.g. collision energy spectra). This is combined with the particle breakage properties to construct the coefficients for a low-fidelity model [e.g. Monazam et al., 2018, Powder Technology 340, p. 528-536]. Simulations are performed of a jet cup attrition system containing Canadian hematite (Monazam et al. 2018). Furthermore, these are first analyzed using the collision energy spectra. Quantitative predictions of the mass loss are made using a low-fidelity model derived from the collision-spectra and a calibrated material breakage coefficient. The results are found to compare favorably with the experimental measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Aerosol iron speciation and seasonal variation of iron oxidation state over the western Antarctic Peninsula

The iron (Fe) speciation and oxidation state have been considered critical factors affecting Fe solubility in the atmosphere and bioavailability in the surface ocean. In this study, elemental composition and Fe speciation in aerosol samples collected at the Palmer Station in the West Antarctic Peninsula were determined using synchrotron-based X-ray fluorescence (XRF) and X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The elemental composition of coarse-mode (>1 mu m) Fe-containing particles suggests that the region's crustal emission is the primary source of aerosol Fe. The Fe minerals in these aerosol particles were predominantly hematite and biotite, but minor fractions of pyrite and ilmenite were observed as well. The Fe oxidation state showed an evident seasonal variation. Further, the Fe(II) content accounted for 71% of the total Fe in the austral summer, while this fraction dropped to 60% in the austral winter. Multivariate linear models involving meteorological parameters suggested that the wind speed, relative humidity, and solar irradiance were the factors that significantly controlled the percentage of Fe(II) in the austral summer. On the contrary, no relationship was found between these factors and the Fe(II) percentage in the austral winter, suggesting that atmospheric photoreduction and regional dust emission were limited. Moreover, the snow depth was significantly (p < 0.05) correlated with the aerosol Fe concentration, confirming the limiting effect of snow/ice cover on the regional dust emission. Given that the Antarctic Peninsula has experienced rapid warming during recent decades, the ice-free areas in the Antarctic Peninsula may act as potential dust sources.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Optical properties enhancement of thermal energy media for consistently high solar absorptivity

This study aimed to evaluate the optical properties of particles intended for use as thermal energy absorbers in generation 3 concentrated solar power systems. Their characterization involved UV–Vis NIR measurements with an integrating sphere for solar absorptivity, while a reflectometer was employed to measure thermal emittance. By combining absorptivity and emittance data, the solar absorption efficiency was calculated. Laser flash analysis, differential scanning calorimetry, and thermogravimetric analysis were utilized to determine thermal conductivity and specific heat. The solar absorptivity of the particles was initially measured at 0.90. After exposure to air at 1000 °C, it decreased to 0.73. However, following a reduction process, the particle recovered absorptivity of 0.90. The thermal aging and recovery were repeated multiple times, consistently achieving an absorptivity of 0.90. The thermal conductivity of the particles ranged from 0.50 to 0.88 W/(m-K). Solar absorptivity was found to be influenced by the types of iron oxide present in the particles. Particles with a predominance of hematite exhibited decreased solar absorptivity, while those containing magnetite, wüstite, and iron showed increased absorptivity. The estimated cost of the developed particles was more than ten times lower than that of current products. Given that component costs significantly impact the levelized cost of electricity (LCOE), this price reduction corresponded to an 8 % decrease in LCOE compared to other products. The low-cost thermal energy media show great promise for contributing to a reduced LCOE in the third generation of concentrating solar power systems.

14 SOLAR ENERGY↗
DOE OSTI2021

In Situ Grain Growth of Nanograined Magnetite under Ion Irradiation at Room Temperature and 500 ℃

Grain growth studies of nanograined metals under both thermal and ion irradiation conditions has been studied extensively. Oxides, on the other hand, have not been studied as extensively, especially under irradiation. Some studies have focused on nanograined oxide grain growth on ZnO under thermal conditions only and on SnO 2 and CeO 2 using 250 keV Ar 2+ and 3 MeV Au + ions at 300 K, respectively. There does not appear to be any studies on grain growth of nanosized oxides which are commonly found to form under light water reactor conditions. Oxides such as magnetite (Fe 3 O 4 ), hematite (α-Fe 2 O 3 ), maghemite (γ-Fe 2 O 3 ), and wustite (FeO) are examples of common oxides which have not been studied. Here, this study focused on the grain growth of nanograined Fe 3 O 4 under both thermal and ion irradiation conditions in situ inside a Transmission Electron Microscope (TEM) to better understand the kinetics of grain growth of oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Controls on Iron Reduction and Biomineralization over Broad Environmental Conditions as Suggested by the Firmicutes Orenia metallireducens Strain Z6

Microbial iron reduction is a ubiquitous biogeochemical process driven by diverse microorganisms in a variety of environments. However, it is often difficult to separate the biological from the geochemical controls on bioreduction of Fe(III) oxides. In this study, we investigated the primary driving factor(s) that mediate secondary iron mineral formation over a broad range of environmental conditions using a single dissimilatory iron reducer, Orenia metallireducens strain Z6. A total of 17 distinct geochemical conditions were tested with differing pH (6.5–8.5), temperature (22–50 °C), salinity (2–20% NaCl), anions (phosphate and sulfate), electron shuttle (anthraquinone-2,6-disulfonate), and Fe(III) oxide mineralogy (ferrihydrite, lepidocrocite, goethite, hematite, and magnetite). The observed rates and extent of iron reduction differed significantly with k int between 0.186 and 1.702 mmol L –1 day –1 and Fe(II) production ranging from 6.3% to 83.7% of the initial Fe(III). Using X-ray absorption and scattering techniques (EXAFS and XRD), we identified and assessed the relationship between secondary minerals and the specific environmental conditions. It was inferred that the observed bifurcation of the mineralization pathways may be mediated by differing extents of Fe(II) sorption on the remaining Fe(III) minerals. These results expand our understanding of the controls on biomineralization during microbial iron reduction and aid the development of practical applications.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Toward a Machine Learning Approach to Interpreting X-ray Spectra of Trace Impurities by Converting XANES to EXAFS

The fact that the photoabsorption spectrum of a material contains information about the atomic structure, commonly understood in terms of multiple scattering theory, is the basis of the popular extended X-ray absorption spectroscopy (EXAFS) technique. How much of the same structural information is present in other complementary spectroscopic signals is not obvious. Here we use a machine learning approach to demonstrate that within theoretical models that accurately predict the EXAFS signal, the extended near-edge region does indeed contain the EXAFS-accessible structural information. We do this by exhibiting deep operator neural networks (DeepONets) that have learned the relationship between the extended and near edge portions of the X-ray absorption spectrum to predict the former from the latter. We find that we can accurately predict the EXAFS spectrum between 6 and 14 Å –1 from the first 6 Å –1 (≈100 eV) of the absorption spectrum of Cu 2 + substitutional defects in the Fe 3+ mineral hematite (α-Fe 2 O 3 ). This surprising finding implies that theoretical analyses of X-ray absorption spectra could be implemented that extract the same conclusions as high-quality EXAFS studies from spectra collected over a much smaller range of photon energies. This relaxes a host of experimental limitations related to the X-ray source and measurement sample, including collection time, minimum dopant concentration, source brilliance, and energy range. We describe the theoretical data sets and DeepONet construction and show that the resulting DeepONets produce EXAFS that recovers linear combination fits to experimental data with accuracy approaching the original ab initio calculations. We discuss the implications of our findings for minor constituent characterization and for understanding the information content of spectroscopic data more broadly, including how this approach might be applied to measured experimental spectra. In conclusion, to encourage similar efforts, the simulated X-ray spectra, machine learning, and fitting code are publicly available.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Electronic Structure, Optical Properties, and Photoelectrochemical Activity of Sn-Doped Fe 2 O 3 Thin Films

Hematite (Fe 2 O 3 ) is a well-known oxide semiconductor suitable for photoelectrochemical (PEC) water splitting and industry gas sensing. It is widely known that Sn doping of Fe 2 O 3 can enhance the device performance, yet the underlying mechanism remains elusive. In this work, we determine the relationship between electronic structure, optical properties and PEC activity of Sn doped Fe 2 O 3 by studying highly crystalline, well-controlled thin films prepared by pulsed laser deposition (PLD). We show that Sn doping substantially increases the n-type conductivity of Fe 2 O 3 , and the conduction mechanism is better described by small-polaron hoping (SPH) model. Only 0.2% Sn doping significantly reduce the activation energy barrier for SPH conduction from at least 0.5 eV for undoped Fe 2 O 3 to 0.14 eV for doped ones. A combination of X-ray photoemission, X-ray absorption spectroscopy and DFT calculations reveals the Fermi level gradually shifts toward the conduction band minimum with Sn doping. A localized Fe 2+ like gap state is observed at the top of valence band, accounting for the SPH conduction. Interestingly, in contrast to the literature, we find that only 0.2% Sn doping in Fe 2 O 3 significantly improves the PEC activity, while more Sn decreases it. The improved PEC activity is partially attributed to an increased band bending potential which facilitates the charge separation at space charge region. The reduced activation energy barrier for SPH will facilitate the transport of photo-excited carriers for the enhanced PEC, which is of interest for further carrier dynamics study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Critical Assessment of the Thermodynamics of Vacancy Formation in Fe 2 O 3 Using Hybrid Density Functional Theory

Fe 2 O 3 hematite is a technologically important material with applications in energy storage as well as being the key phase formed in the rust of iron-based materials. Despite this central importance, there is much that is still unknown regarding the properties of defects in Fe 2 O 3 and consequently oxide growth. In this work, using screened hybrid density functional theory (HSE06), we consider the thermodynamics of vacancies in Fe 2 O 3 , considering the effects of ionic and electronic chemical potentials on both iron and oxygen vacancy formation. We find that, in the oxygen-rich limit, iron vacancies are easier to form, though the difference in formation energy between the two vacancies is only about 1 eV. In contrast, in the Fe-rich limit, oxygen vacancies have an extremely low formation energy, only 0.07 eV at mid-gap, and would spontaneously form as the Fermi level is reduced, while Fe vacancies require over 5 eV to form. Consistent with experiment, this indicates that Fe 2 O 3 is relatively easily reduced but not oxidized. However, the theoretical picture is very different when considering other exchange–correlation functionals (GGA + U or SCAN), emphasizing the critical role of the exchange–correlation functional in describing this system accurately.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Second Harmonic Generation Electric Field Triplet Interferometry for Absolute Phasing

We report second harmonic generation (SHG) electric field triplet interferometry performed using three mutually coherent ultrafast pulses in a common path with controllable relative phases, namely, the light fields of a sample signal (SI), a reference oscillator (RO), and a local oscillator (LO). The ROLO phase determined from the interference of the light fields produced by two quartz wafers is subtracted from the phase determined from the SIROLO interferogram to yield the signal phase, ϕ SI . The new method also calibrates the measured SHG intensity from a given sample internally by sending the fundamental light field reflected from the sample into one of the quartz wafers in the ROLO element. The approach avoids having to exchange the sample against a reference material with a known χ(2) value or known phase and accounts on-the-fly for situations where the reflected fundamental light field intensity changes with experimental conditions. The new method is successfully benchmarked against z-cut α-quartz, fused silica held at its point of zero charge, and hematite nanolayers in air, across three different interferometers. Furthermore, the approach should be applicable for other second-order nonlinear spectroscopies, such as vibrational or electronic sum-frequency generation.

Interfaces↗
DOE OSTI2022

Vanadate Retention by Iron and Manganese Oxides

Anthropogenic emissions of vanadium (V) into terrestrial and aquatic surface systems now match those of geogenic processes, and yet, the geochemistry of vanadium is poorly described in comparison to other comparable contaminants like arsenic. In oxic systems, V is present as an oxyanion with a +5 formal charge on the V center, typically described as H x VO 4 (3–x)– , but also here as V(V). Iron (Fe) and manganese (Mn) (oxy)hydroxides represent key mineral phases in the cycling of V(V) at the solid–solution interface, and yet, fundamental descriptions of these surface-processes are not available. Here, we utilize extended X-ray absorption fine structure (EXAFS) and thermodynamic calculations to compare the surface complexation of V(V) by the common Fe and Mn mineral phases ferrihydrite, hematite, goethite, birnessite, and pyrolusite at pH 7. Inner-sphere V(V) complexes were detected on all phases, with mononuclear V(V) species dominating the adsorbed species distribution. Our results demonstrate that V(V) adsorption is exergonic for a variety of surfaces with differing amounts of terminal –OH groups and metal–O bond saturations, implicating the conjunctive role of varied mineral surfaces in controlling the mobility and fate of V(V) in terrestrial and aquatic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Inhibition of Chromium(III) Oxidation through Manganese(IV) Oxide Passivation and Iron(II) Abiotic Reduction

Manganese (Mn) oxides are strong oxidants that are ubiquitous in soils and can oxidize redox-active metals, including chromium (Cr). In soil environments, trivalent chromium (Cr(III)) is a benign, immobile micronutrient, whereas the hexavalent Cr(VI) form is present as a highly mobile, toxic chromate oxyanion. Although many studies have characterized the capacity of Mn(III/IV) oxides to oxidize Cr(III) to toxic Cr(VI), the oxidative capacity of Mn oxides in the presence of potentially passivating soil constituents, specifically reduced soluble iron (Fe(II) aq ), remains unresolved. We hypothesized that chemical processes at redox interfaces, such as diffusion-limited environments within soil aggregates, can lead to decreased Cr(VI) production from Mn oxide-driven oxidation due to passivation by Fe(II) aq . A multichamber diffusion-limited reactor was used to simulate transport at soil redox interfaces and investigate the capacity of poorly crystalline and crystalline Mn oxides to oxidize solid Cr(III) minerals to Cr(VI) in the presence of Fe(II) aq . As predicted, Cr(VI) was produced through the Mn oxide-catalyzed oxidation of Cr(III) at a rate controlled by the solubility of Cr(OH) 3 . However, in the presence of Fe(II) aq , the concentration of aqueous Cr(VI) decreased as a function of the Fe(II) aq concentration, where high concentrations of Fe(II) aq completely inhibited Cr(VI) production, likely through both the passivation of the Mn oxide and the direct reduction of Cr(VI) by Fe(II). At both low (14 μM) and high (100 μM) Fe(II) aq concentrations, the iron oxide minerals hematite (Fe 2 O 3 ) and goethite (α-FeOOH) were associated with the Mn oxides, which can cause surface passivation, a likely role that decreases Cr(III) oxidation. Additionally, the Cr(III) oxidation rate decreased with increasing crystallinity of the Mn oxides whether or not Fe(II) was present.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Engineering Escherichia coli for Urease-Driven Synthesis of Metal Oxide Nanomaterials

The development of functional nanomaterials with controlled morphologies is essential for advancements in medicine, electronics and computing, energy, catalysis, and environmental applications. However, conventional synthesis methods often demand high energy input and pose significant environmental challenges. Urease-based biomineralization presents an efficient, eco-friendly alternative for nanomaterial production under mild conditions. In this study, we engineered Escherichia coli ( E. coli ) to express a urease gene cluster from Sporosarcina pasteurii using CRAGE-Duet technology. The engineered strain successfully synthesized calcium carbonate and calcium phosphate crystals. Expanding the approach, we synthesized metal oxide nanoparticles, including hematite (Fe 2 O 3 ), and nanocrystalline anatase titanium dioxide (TiO 2 ). These nanomaterials were characterized by electron microscopy, demonstrating the potential of E. coli as a sustainable and versatile platform for green nanomaterial synthesis.

bacteria↗
DOE OSTI2020

Synergistic ground and orbital observations of iron oxides on Mt. Sharp and Vera Rubin ridge

Visible/short-wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR, and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover’s traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also have the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported, (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late-stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity’s experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections, and the caveats in using these data for geologic interpretations and strategic path planning tools.

58 GEOSCIENCES↗
DOE OSTI2023

Crystal dissolution by particle detachment

Crystal dissolution, which is a fundamental process in both natural and technological settings, has been predominately viewed as a process of ion-by-ion detachment into a surrounding solvent. Here we report a mechanism of dissolution by particle detachment (DPD) that dominates in mesocrystals formed via crystallization by particle attachment (CPA). Using liquid phase electron microscopy to directly observe dissolution of hematite crystals — both compact rhombohedra and mesocrystals of coaligned nanoparticles — we find that the mesocrystals evolve into branched structures, which disintegrate as individual sub-particles detach. The resulting dissolution rates far exceed those for equivalent masses of compact single crystals. Applying a numerical generalization of the Gibbs-Thomson effect, we show that the physical drivers of DPD are curvature and strain inherently tied to the original CPA process. Based on the generality of the model, we anticipate that DPD is widespread for both natural minerals and synthetic crystals formed via CPA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗