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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

An Electrochemical Electrode to Detect Theophylline Based on Copper Oxide Nanoparticles Composited with Graphene Oxide

The electrochemical analysis of theophylline (THP) was investigated by fabricating a carbon paste electrode (CPE) modified with graphene oxide (GO) along with copper oxide (CuO) nanoparticles (CuO-GO/CPE). The impact of electro-kinetic parameters such as the heterogeneous rate constant, the scan rate, the accumulation time, the pH, the transfer coefficient, and the number of electrons and protons transferred into the electro-oxidation mechanism of THP has been studied utilizing electrochemical methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The differential pulse voltammetry technique was employed to investigate THP in pharmaceutical and biological samples, confirming the limit of detection (LOD) and quantification (LOQ) of the THP. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were performed to characterize the CuO nanoparticles. The CuO-GO/CPE was more sensitive in THP detection because its electrocatalytic characteristics displayed an enhanced peak current in the 0.2 M supporting electrolyte of pH 6.0, proving the excellent sensing functioning of the modified electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Crossover from disordered to core-shell structures of nano-oxide Y 2 O 3 dispersed particles in Fe

Here, molecular dynamic simulations of Y 2 O 3 in bcc Fe and transmission electron microscopy (TEM) observations were used to understand the structure of Y 2 O 3 nano-clusters in an oxide dispersion strengthened steel matrix. The study showed that Y 2 O 3 nano-clusters below 2 nm were completely disordered. Y 2 O 3 nano-clusters above 2 nm, however, form a core-shell structure, with a shell thickness of 0.5–0.7 nm that is independent of nano-cluster size. Y 2 O 3 nano-clusters were surrounded by off-lattice Fe atoms, further increasing the stability of these nano-clusters. TEM was used to corroborate our simulation results and showed a crossover from a disordered nano-cluster to a core-shell structure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Production of monodisperse cerium oxide microspheres with diameters near 100 µm by internal-gelation sol–gel methods

Cerium dioxide microspheres with uniform diameters between 65 – 211 µm were fabricated using internal gelation sol-gel methods. Although uniform microspheres are produced for nuclear fuel applications with diameters above 300 µm, sol-gel microspheres with diameters of 50 - 200 µm have historically been made by emulsion techniques and had poor size uniformity [1, 2]. An internal gelation, sol-gel apparatus was designed and constructed to accommodate the production of small, uniform microspheres whereby cerium-containing solutions were dispersed into flowing silicone oil and heated in a gelation column to initiate solidification [3, 4]. Problems with premature feed gelation and microsphere coalescence were overcome by equipment modifications unique among known internal gelation setups. Microspheres were fabricated and sized in batches as a function of dispersing needle diameter and silicone oil flow rate in the two-fluid nozzle in order to determine the range of sizes possible and corresponding degree of monodispersity. Initial experiments with poor size uniformity were linked to microsphere coalescence in the gelation column prior to solidification as well as excessive flow rates for the cerium feed solution. Average diameter standard deviations as low as 2.23% were observed after optimization of flow rates and minimization of coalescence reactions.

cerium oxide↗
DOE OSTI2026

Metal oxide-promoted calcium cuprate catalysts for diol oxidative dehydrocyclization to lactones

Here, this work investigates structure-function relationships in electronically tunable, redox-active, basic Cu-Ca mixed metal oxide catalysts for oxidative dehydrocyclization of liquid diols to lactones. Compositional screening identified Ni 2+ and Zn 2+ as effective promoters that increase the surface Cu 2+ population by ∼1.7× and Cu-normalized activity for liquid 1,4-butanediol conversion to γ-butyrolactone by ∼3–4×. In situ Raman spectroscopy, in situ X-ray absorption spectroscopy (XAS), in situ diffuse-reflectance Fourier transform infrared spectroscopy (DRIFTS), ex situ X-ray diffraction (XRD), and H 2 -temperature-programmed reduction (H 2 -TPR) show that Ni 2+ or Zn 2+ incorporation promotes the formation of Ca 0.82 Cu 1.00 O 2 nanoparticles under mild calcination conditions. This cuprate phase features stronger and shorter Cu–O bonds (1.90 Å) than inactive bulk CuO (1.95 Å) and square-planar Cu 2+ O 4 sites with enhanced d z2 electrophilicity, strengthening alkoxy adsorption. Pyridine-DRIFTS confirms the purely basic nature of the catalyst surface, while methanol-DRIFTS indicates Cu 2+ surface enrichment with Ni or Zn promotion, where Cu–O(Ca)–Cu sites can exist as amorphous domains or a truncation layer on crystalline nanoparticles.

09 BIOMASS FUELS↗
DOE OSTI2015

Crystalline ZrTiO{sub 4} gated p-metal–oxide–semiconductor field effect transistors with sub-nm equivalent oxide thickness featuring good electrical characteristics and reliability

ZrTiO{sub 4} crystallized in orthorhombic (o-) phase was stacked with an amorphous Yb{sub 2}O{sub 3} interfacial layer as the gate dielectric for Si-based p-MOSFETs. With thermal annealing after gate electrode, the gate stack with equivalent oxide thickness (EOT) of 0.82 nm achieves high dielectric quality by showing a low interface trap density (D{sub it}) of 2.75 × 10{sup 11 }cm{sup −2}eV{sup −1} near the midgap and low oxide traps. Crystallization of ZrTiO{sub 4} and post metal annealing are also proven to introduce very limited amount of metal induced gap states or interfacial dipole. The p-MOSFETs exhibit good sub-threshold swing of 75 mV/dec which is ascribed to the low D{sub it} value and small EOT. Owing to the Y{sub 2}O{sub 3} interfacial layer and smooth interface with Si substrate that, respectively, suppress phonon and surface roughness scattering, the p-MOSFETs also display high hole mobility of 49 cm{sup 2}/V-s at 1 MV/cm. In addition, I{sub on}/I{sub off} ratio larger than 10{sup 6} is also observed. From the reliability evaluation by negative bias temperature instability test, after stressing with an electric field of −10 MV/cm at 85 °C for 1000 s, satisfactory threshold voltage shift of 12 mV and sub-threshold swing degradation of 3% were obtained. With these promising characteristics, the Yb{sub 2}O{sub 3}/o-ZrTiO{sub 4} gate stack holds the great potential for next-generation electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Entrapped Molecule‐Like Europium‐Oxide Clusters in Zinc Oxide with Nearly Unaffected Host Structure

Abstract Nanocrystalline ZnO sponges doped with 5 mol% EuO 1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X‐ray diffraction, transmission electron microscopy, and extended X‐ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c ‐Eu 2 O 3 takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu‐doping and an average Eu 3+ ion coordination number of ≈5.2. Comparisons of 23 density functional theory‐generated structures having differently sized Eu‐oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu 3+ excitation, while c ‐Eu 2 O 3 phase separation results in loss of the characteristic Eu 3+ photoluminescence. The formation of molecule‐like Eu‐oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of Pressure and Thermal Cycling on Long-Term Oxidation in CO 2 and Supercritical CO 2

Concentrating solar power plant designers are interested in supercritical CO 2 (sCO 2 ) for the power block to achieve > 50% electrical efficiency at > 700 °C. The goal of this project was to develop a long-term (> 100 kh) lifetime model for sCO 2 compatibility using 10–15 kh laboratory exposures. Three Ni-based alloys (625, 282 and 740H) and an advanced austenitic stainless steel were evaluated here in long-term exposures at 700–800 °C using 500-h cycles in laboratory air, 0.1 MPa industrial grade (IG) CO 2 and 30 MPa supercritical IG CO 2 and using 10-h cycles in 0.1 MPa IG CO 2 and O 2 . Mass change data and quantification of the oxide scale thickness and depth of internal attack after 1000–10,000 h exposures at 750 °C indicate that these materials are compatible with the sCO 2 environments with modeling used to predict long-term behavior. Comparison of the 0.1 and 30 MPa 500-h cycle results did not show a significant effect of pressure on the reaction, and no significant internal carburization was observed under these conditions, even for the stainless steel, suggesting that chromia scales may be better C diffusion barriers than expected. For the Ni-based alloys, thermal cycling to simulate the solar duty cycle did not result in scale spallation after 15 kh in 10-h cycles or 4 kh in 1-h cycles at 750 °C. However, the stainless steel specimens formed an Fe-rich oxide after ~ 1500-h cumulative exposure time in both 1- and 10-h cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Dissociative Chemisorption and Oxidation of H 2 on the Stoichiometric IrO 2 (110) Surface

In this work, we investigated the dissociative chemisorption and oxidation of H 2 and D 2 on the stoichiometric IrO 2 (110) surface (“s-IrO 2 (110)”) using temperature programmed reaction spectroscopy (TPRS) and density functional theory (DFT) calculations. We find that the dissociative chemisorption of hydrogen occurs efficiently on s-IrO 2 (110) during adsorption at 90 K, with ~90% of the dissociated H 2 oxidizing to H 2 O during TPRS and evolving in a broad feature between 400 and 800 K. We also observe small quantities of H 2 desorbing in TPRS peaks at 200 K and 530 K, and show that these peaks arise from the desorption of molecularly-adsorbed H 2 and the recombination of atomic hydrogen, respectively. Our results demonstrate that H 2 dissociation on s-IrO 2 (110) occurs by a precursor-mediated mechanism wherein H 2 molecules adsorb strongly on coordinatively-unsaturated Ir atoms (Ircus) and the resulting σ-complexes then serve as precursors for H 2 bond cleavage. Our DFT calculations predict that H 2 adsorbs strongly on an atop-Ircus site, and that the H 2 complex can dissociate by a facile pathway involving H-transfer to a neighboring bridging O atom (Obr) to produce an H-Ircus/HObr pair. For this pathway, we predict that the energy barrier for dissociation is ~65 kJ/mol lower than the binding energy of the adsorbed H 2 complex. We also find that the total hydrogen uptake on s-IrO 2 (110) saturates at an H 2 coverage of ~0.65 ML during adsorption at 90 K, and present evidence that this limited uptake results from a strong influence of HObr groups on H 2 sigma-complex formation. Finally, we used DFT to examine pathways for H 2 O formation on s-IrO 2 (110) and find that steps leading directly to H 2 O formation are energetically demanding and likely determine the overall rate of H 2 oxidation on s-IrO 2 (110).

Dissociative Chemisorption↗
DOE OSTI2020

High Temperature Oxidation Behavior of Aluminized Haynes 230

The effect of reactive air aluminizing (RAA) on the high-temperature oxidation behavior of the H230 superalloy is studied at 850 °C for 600 hours. Mass gain values are measured and microstructure is studied by XRD, SEM, and EDX. Post oxidation mass gain for the aluminized alloy is reduced compared to wrought alloy. A three-zone microstructure of diffusion coating is observed in RAA H230. Formation and growth of alumina scale during RAA process and oxidation is attributed to the complementary roles of ß-NiAl + ?'-Ni3Al phases in the composite coating.

Rashidi, S↗