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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Comparative profiling of well-defined copper reagents and precursors for the trifluoromethylation of aryl iodides

A number of copper reagents were compared for their effectiveness in trifluoromethylating 4-iodobiphenyl, 4-iodotoluene, and 2-iodotoluene. Yields over time were plotted in order to refine our understanding of each reagent performance, identify any bottlenecks, and provide more insight into the rates of the reactions. Interestingly, differences in reactivity were observed when a well-defined [LCuCF 3 ] complex was employed directly or generated in situ from precursors by published reports. Relative reactivities were also found to highly dependent on the nature of the iodoarenes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Elucidating the Ultrafast Dynamics of Photoinduced Charge Separation in Metalloporphyrin-Fullerene Dyads Across the Electromagnetic Spectrum

Metalloporphyrins are prominent building blocks in the synthetic toolbox of advanced photodriven molecular devices. When the central ion is paramagnetic, the relaxation pathways within the manifold of excited states are highly intricate so that unravelling the intramolecular energy and electron transfer processes is usually a very complex task. This fact is critically hampering the development of applications based on the enhanced coupling offered by the electronic exchange interaction. In this work, the dynamics of charge separation in a copper porphyrin-fullerene are studied with several complementary spectroscopic tools across the electromagnetic spectrum (from near infra-red to X-ray wavelengths), each of them providing specific diagnostics. Correlating the various rates clearly demonstrates that the lifetime of the photoinduced charge-separated state exceeds by about 10 fold that of the isolated photoexcited CuII porphyrin. As revealed by the spectral modifications in the XANES region, this stabilization is accompanied by a transient change in covalency around the CuII center, which is induced by an enhanced interaction with the C60 moiety. This experimental finding is further confirmed by state-of-the art calculations using DFT and TD-DFT including dispersion effects that explain the electrostatic and structural origins of this interaction, as the CuIIP cation becomes ruffled and approaches closer to the fullerene in the charge-separated state. From a methodological point of view, these results exemplify the potential of multielectron excitation features in transient X-ray spectra as future diagnostics of sub-femtosecond electronic dynamics. From a practical point of view, this work is paving the way for elucidating out-of-equilibrium electron transfer events coupled to magnetic interaction processes on their intrinsic time-scales.

Zhang, J.↗
NASA NTRSDate not supplied

Expanding the Capability of A Legacy Combustion Flametube to Test High Temperature Engine Materials in Relevant Environments

New materials and component designs are needed to advance gas turbine engine technology and provide the performance and efficiency needs for future applications. In order to advance these materials, testing in combustion environments is a critical step prior to engine testing. In this work, we detail the design and the fabrication of a materials test sector in a flametube combustor facility. The facility simulates a combustion environment similar to that experienced by components in gas turbine engines. The flow regime is characterized by a combination of high-temperature, high-velocity, high-heat flux, and high-velocity that components experience in gas turbine engines. Exposure of components in this facility allows for the study of combined environmental effects and the impact on both coating and substrate durability. The test facility may operate across a wide range of pressures from 275-400 psig (1,896-2,758 kPa) and an air flow rate of 5 lb/s (2.27 kg/s). While combustion gas temperature is expected in excess of 3,000°F (1,649°C), 900°F (482°C) cooling air may be supplied to the backside of components or test articles. The flametube combustor was previously used to evaluate fuel injectors and combustion products, and the new test configuration will also allow for materials exposure to complex, engine-like conditions. The interior of the Test Section was additively manufactured from GRCop-84 and cryogenically fit and brazed to a stainless steel 304 housing. The use of a copper liner minimizes welds and with active cooling, is expected to provide better durability over traditional hardware using stainless steel or Inconel with a ceramic liner. The Test Section has two opposing removable windows approximately 230 mm x 80 mm that can accommodate articles up to 85 mm tall. This modular design allows for custom platforms to hold coupons, panels, or airfoil shapes to be tested with minimal re-engineering or fabrication. The bolted joint and sealing remains consistent, so any new testing only needs to work within the existing design footprint. This paper will provide an overview of the facility capabilities, design considerations, as well as thermal and structural analysis of the hardware. Future testing of ceramic matrix composite (CMC) airfoils and advanced environmental barrier coatings (EBCs) will also be discussed.

Combustion↗
DOE OSTI2018

The activation of carbon dioxide by first row transition metals (Sc – Zn)

The activation of CO2 by chloride-tagged first-row transition metal anions [ClM]- (M=Sc–Zn), was examined by mass spectrometry, quantum chemical calculations, and statistical analysis. The direct formation of [ClM(CO2)]- complexes was demonstrated in the reaction between [ClM] - and neutral CO2. In addition, the reverse reaction was investigated by energy-variable collisionally induced dissociation (CID) of the corresponding [ClM(CO2)]- anions generated in-source. Five different mono- and bi-dentate binding motifs present in the ion/CO2 complexes were identified by quantum chemical calculations and the relative stability of the each of these isomers was established and analyzed for all first-row transition metals based on the experimental and theoretical ion/molecule binding energies. It was found that the early first row transition metals form strong covalent bonds with the neutral CO2 molecule, while the late in particular copper and zinc are weakly bonded. Using simple valence bond Lewis diagrams, the binding motifs and their relative stabilities across the first row were described in a quantitative manner based on the electronic structure of the individual metals. This analysis provides an explanation for the change of most favorite bonding motif of the transition metals with CO2 along the 1st transition metal row. The nature of the activated CO2 complex and the relationship between its stability and other structural and spectral properties was also analyzed by Principal Component Analysis (PCA) and Artificial Neural Networks.

Blaziak, Kacper↗
NASA NTRS1991

Creep behavior of copper at intermediate temperatures. II - Surface microstructural observations. III - A comparison with theory

Three different types of microstructural slip features are noted to occur during the creep of Cu at 0.46-0.72 of absolute melting point. While single slip is associated with higher temperatures and lower stresses, complex wavy slip features are observed at higher temperatures and higher stresses as well as with increasing strains: suggesting the importance of cross-slip mechanisms. At lower temperatures and higher stresses the multiple-slip morphologies observed indicate that cross-slip mechanisms may control the creep of polycrystalline Cu only over a limited stress and temperature range. A phenomenological model is proposed which assumes that (1) cell boundaries within subgrains act as both sources of, and obstacles to, gliding dislocations, and (2) dislocation annihilation occurs at the cell boundaries by climb and cross-slip.

Raj, S. V.↗
DOE OSTI2017

Nano-scale stoichiometry analysis of a high temperature superconductor by atom probe tomography

The functional properties of the high-temperature superconductor Y 1 Ba 2 Cu 3 O 7-δ (Y-123) are closely correlated to the exact stoichiometry and oxygen content. Exceeding the critical value of 1 oxygen vacancy for every five unit cells (δ>0.2, which translates to a 1.5 at% deviation from the nominal oxygen stoichiometry of Y 7.7 Ba 15.3 Cu 23 O 54-δ ) is sufficient to alter the superconducting properties. Stoichiometry at the nanometer scale, particularly of oxygen and other lighter elements, is extremely difficult to quantify in complex functional ceramics by most currently available analytical techniques. The present study is an analysis and optimization of the experimental conditions required to quantify the local nanoscale stoichiometry of single crystal yttrium barium copper oxide (YBCO) samples in three dimensions by atom probe tomography (APT). APT analysis required systematic exploration of a wide range of data acquisition and processing conditions to calibrate the measurements. Laser pulse energy, ion identification, and the choice of range widths were all found to influence composition measurements. The final composition obtained from melt-grown crystals with optimized superconducting properties was Y 7.9 Ba 10.4 Cu 24.4 O 57.2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Examining and Modeling Oxygen Uncoupling Kinetics of Cu-Based Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU) in a Drop Tube Fluidized Bed Reactor

Chemical looping combustion with oxygen uncoupling (CLOU) is a promising carbon capture and storage (CCS) technology for conversion of gaseous and solid hydrocarbon fuels where the release of gaseous O 2 from an oxygen carrier is favored at high temperature and low O 2 partial pressure. One promising CLOU material is the copper oxide redox system (CuO–Cu 2 O). The primary objective of this study was to examine the use of a drop tube fluidized bed reactor (DT-FBR) for evaluating the kinetics of oxygen uncoupling with Cu-based oxygen carriers. Appropriate rate expressions from redox experiments are needed to model and scale up CLOU systems. Additionally, the determined oxygen uncoupling kinetic parameters were validated using a computational fluid dynamic model. Two oxygen carriers consisting of 20 wt % CuO/Al 2 O 3 and 9 wt % CuO/Al 2 O 3 were prepared by physical mixing. A third oxygen carrier sample was prepared at 9 wt % CuO/Al 2 O 3 by incipient wetness impregnation. The reaction rates of the copper oxide redox system are strongly dependent on thermodynamic effects of the oxygen partial pressure relative to the equilibrium oxygen partial pressure. The results presented in this paper offer an alternative and simplified kinetic analysis compared to that traditionally presented in the literature for the thermal reduction of copper oxide or other CLOU oxygen carriers. The reactor system used in this study allows for operating parameters to be adjusted, minimizing thermodynamic and mass transfer limitations, which eliminates the need for more complex kinetic/thermodynamic reaction models. The reaction kinetics measured in this study is compared based on the preparation method and the CuO weight percent loading. These results may aid in the development of CLOU technologies during reactor design and process modeling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Large-Scale and Galvanic Replacement Free Synthesis of Cu@Ag Core–Shell Nanowires for Flexible Electronics

Copper nanowires (CuNWs) are considered a promising alternative to indium tin oxide (ITO) due to their high transparency, conductivity and low cost. However, the susceptibility to oxidation of copper in ambient conditions largely overshadows their practical applications. Here, a facile adsorption and subsequent heat-treatment method is developed to obtain uniform Cu@Ag core-shell nanowires. Ag-ammonia complex (Ag[(NH2R)2]+) as silver source adsorbs on the surface of CuNWs to form Cu@Ag-ammonia core-shell precursors and then decomposes to pure Ag shell through a simple thermal annealing process under air. The thickness of Ag shell can easily be controlled by adjusting the concentration of Ag-ammonia. The Ag shell perfectly prevents the oxidation of CuNWs, enabling the core-shell nanowires to maintain stability at high temperature (140 °C) and high humidity (85 °C, 85% RH) for at least 500 h. More importantly, transparent conductive films made from our Cu@Ag nanowires hold comparable optical and electrical properties to pure CuNWs. The large-scale and facile strategy demonstrated in this study offers huge potential to further explore the applications of CuNWs in flexible and stretchable electronic and optoelectronic devices.

Zhang, Bowen (ORCID:000000030432745X)↗
DOE OSTI2017

Identifying Cu( ii )–amyloid peptide binding intermediates in the early stages of aggregation by resonance Raman spectroscopy: a simulation study

The aggregation of amyloid beta (Aβ) peptides plays a crucial role in the pathology and etiology of Alzheimer's disease. Experimental evidence shows that copper ion is an aggregation-prone species with the ability to coordinately bind to Aβ and further induce the formation of neurotoxic Aβ oligomers. However, the detailed structures of Cu(II)–Aβ complexes have not been illustrated, and the kinetics and dynamics of the Cu(II) binding are not well understood. Two Cu(II)–Aβ complexes have been proposed to exist under physiological conditions, and another two might exist at higher pH values. By using ab initio simulations for the spontaneous resonance Raman and time domain stimulated resonance Raman spectroscopy signals, we obtained the characteristic Raman vibronic features of each complex. Finally, these signals contain rich structural information with high temporal resolution, enabling the characterization of transient states during the fast Cu–Aβ binding and interconversion processes.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1984

Potential energy surfaces of MH2 (M = Co, Fe, and Cu)

In many important catalytic processes, the dissociation of the hydrogen molecule is a fundamental step, and the chemisorption of dihydrogen by metal surfaces has been studied. However, quantitative results from theoretical treatments are not very encouraging. Blomberg and Siegbahn (1983) have found that the negative binding energy for NiH2 obtained with the aid of the commonly used Hartree-Fock approximation differs greatly from the result found on the basis of a more sophisticated calculation, including electron correlation. Another study showed the great importance of d orbitals in the dissociation process. A study, similar to the one on NH2, has been conducted for three other metals, including cobalt, iron, and copper. The present investigation is concerned with the results of this study. The potential surfaces of CoH2, FeH2, and CuH2 are discussed, taking into account the lowest atomic states, the bent low spin complex, the bent high spin saddle points, and the linear states.

Siegbahn, P. E. M.↗
NASA NTRS1995

Graphite fiber textile preform/copper matrix composites

Graphite fiber reinforced/copper matrix composites have sufficiently high thermal conduction to make them candidate materials for critical heat transmitting and rejection components. The term textile composites arises because the preform is braided from fiber tows, conferring three-dimensional reinforcement and near net shape. The principal issues investigated in the past two years have centered on developing methods to characterize the preform and fabricated composite and on braidability. It is necessary to have an analytic structural description for both processing and final property modeling. The structure of the true 3-D braids used is complex and has required considerable effort to model. A structural mapping has been developed as a foundation for analytic models for thermal conduction and mechanical properties. The conductivity has contributions both from the copper and the reinforcement. The latter is accomplished by graphitization of the fibers, the higher the amount of graphitization the greater the conduction. This is accompanied by an increase in the fiber modulus, which is desirable from a stiffness point of view but decreases the braidability; the highest conductivity fibers are simply too brittle to be braided. Considerable effort has been expended on determining the optimal braidability--conductivity region. While a number of preforms have been fabricated, one other complication intervenes; graphite and copper are immiscible, resulting in a poor mechanical bond and difficulties in infiltration by molten copper. The approach taken is to utilize a proprietary fiber coating process developed by TRA, of Salt Lake City, Utah, which forms an itermediary bond. A number of preforms have been fabricated from a variety of fiber types and two sets of these have been infiltrated with OFHC copper, one with the TRA coating and one without. Mechanical tests have been performed using a small-scale specimen method and show the coated specimens to have superior mechanical properties. Final batches of preforms, including a finned, near net shape tube, are being fabricated and will be infiltrated before summer.

Gilatovs, G. J.↗
DOE OSTI2023

Resolving metal binding properties within subunits of a multimeric enzyme Mnx by surface induced dissociation and native ion mobility mass spectrometry

Multi-subunit enzymes function as coordinated assemblies. Yet most enzymatic assays measure the summed output of all populations in solution and cannot easily differentiate contributions of individual subunits. Native mass spectrometry detects intact protein complexes in the gas phase. Surface induced dissociation further releases subunits from protein complexes while retaining compact conformations and bound ligands. Combined with ion mobility, the released subunits can then be carefully monitored for more in-depth structural analysis. Mnx is a unique bacterial multicopper oxidase complex that oxidizes Mn(II) to form MnO 2 minerals, and is composed of three subunits: MnxG, a multicopper oxidase containing the active site, and two accessory proteins, MnxE and MnxF which also bind copper ions. Other known multicopper oxidases do not require accessory proteins, therefore the functions of MnxE and MnxF are not well understood. Here, we use native mass spectrometry with surface induced dissociation and ion mobility to characterize the metal binding properties of Mnx with two metals, catalytic Cu(II) and Mn(II) substrate. We demonstrate our assay can detect subtle structural changes within each subunit, which are presumably related to the allosteric mechanism. We also noticed that ionic strength and solution composition can impact metal binding and must be carefully investigated for such experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Water-induced surface ordering facilitating the microcutting of ductile metals

Metal cutting is a crucial process in modern manufacturing. Enhancing the machinability of metals can significantly improve their production efficiency and surface integrity. Coating surface-active media (SAM) on the free surface of the metals before cutting is an easy method to improve machinability, which usually pertains to the category of the renowned Rehbinder effect. However, the existing SAM is usually hazardous and complex materials. Besides, the effect of SAM on the local structure of the metal surface remains unclear. In this study, water is employed as a simple yet often overlooked SAM in the microcutting of copper. Using water as SAM also allows the employment of X-ray absorption fine structure spectroscopy (XAFS) to study the local structure of copper with and without water coating. Results show that water coating on the free surface of copper can significantly reduce the cutting force and chip thickness, and improve the surface finish. Interestingly, removing the water coating enables the recovery of the cutting force, demonstrating a reversible effect. Based on the XAFS results and molecular dynamics simulation, a water-induced surface ordering mechanism is proposed to explain the findings from the microcutting experiments. This mechanism suggests that water molecules can induce surface ordering in copper, resulting in reduced surface energy and fracture toughness of copper, thus enhancing machinability. In conclusion, this work provides valuable insights into the comprehension of the Rehbinder effect and shows that picometer-scale modifications of the surface atom arrangement can considerably alter the deformation mode of metals, paving the way for the development of new manufacturing processes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight.

X-ray absorption near edge structure (XANES) spectroscopy is widely used for operando catalyst characterization. We show that, for highly fluxional supported nanoclusters, the customary extraction of the oxidation state of the metal from the XANES data by fitting to the bulk standards is highly questionable. The XANES signatures as well as the apparent oxidation state for such clusters arise from a complex combination of many factors, and not only from the chemical composition in reaction conditions (e.g., oxygen content in oxidizing atmosphere). The thermally accessible isomerization and population of several structurally distinct cluster forms, cluster-support interaction, and intrinsic size effects all impact the metal oxidation state and XANES signal. We demonstrate this on copper oxide clusters with different compositions, Cu4Ox(x = 2-5) and Cu5Oy (y = 3, 5), deposited on amorphous alumina and ultrananocrystalline diamond, for which we computed the XANES spectra and compare the results to the experiment. We show in addition that fitting the experimental spectrum to calculated spectra of supported clusters can, in contrast, provide good agreement and insight into the spectrum-composition-structure relation. Experimental XANES interpreted using the proposed fitting scheme shows the partial reduction of Cu oxide clusters at rising temperatures, and pinpoints the specific stoichiometries that dominate in the ensemble of cluster states as the temperature changes.

Zandkarimi, Borna↗
DOE OSTI2019

Insights into an unusual Auxiliary Activity 9 family member lacking the histidine brace motif of lytic polysaccharide monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) are redox-enzymes involved in biomass degradation. All characterized LPMOs possess an active site of two highly conserved histidine residues coordinating a copper ion (the histidine brace), which are essential for LPMO activity. However, some protein sequences that belong to the AA9 LPMO family display a natural N-terminal His to Arg substitution (Arg-AA9). These are found almost entirely in the phylogenetic fungal class Agaricomycetes, associated with wood decay, but no function has been demonstrated for any Arg-AA9. Through bioinformatics, transcriptomic, and proteomic analyses we present data, which suggest that Arg-AA9 proteins could have a hitherto unidentified role in fungal degradation of lignocellulosic biomass in conjunction with other secreted fungal enzymes. We present the first structure of an Arg-AA9, LsAA9B, a naturally occurring protein from Lentinus similis The LsAA9B structure reveals gross changes in the region equivalent to the canonical LPMO copper-binding site, whereas features implicated in carbohydrate binding in AA9 LPMOs have been maintained. We obtained a structure of LsAA9B with xylotetraose bound on the surface of the protein although with a considerably different binding mode compared with other AA9 complex structures. In addition, we have found indications of protein phosphorylation near the N-terminal Arg and the carbohydrate-binding site, for which the potential function is currently unknown. Finally, our results are strong evidence that Arg-AA9s function markedly different from canonical AA9 LPMO, but nonetheless, may play a role in fungal conversion of lignocellulosic biomass.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Surface Preparation Techniques for Adhesive Bonding of Aluminum and Copper

Adhesive bonding is a commonly used technique to join different parts or structures. The bonding is attributed surface adhesion. Adhesion is defined by the ASTM as “the state in which two surfaces are held together by interfacial forces which consist of valence force or interlocking action or both.” Both of these are highly dependent on the surface conditions, which makes the surface preparation very critical to the performance of adhesive bonding. Obtaining a strong adhesive bond requires various considerations. Wegman and Levi describe several key steps of adhesive bonding that are summarized here: receiving materials, knowledge of the fabrication process for the parts, mating the parts to be bonded, and surface preparation. Among all these steps, surface preparation is usually the most critical, complex, and frequently neglected step in the bonding sequence. Surface preparation can remove the intermediate surface, paint, rust or oxide layer. Different materials including adherents, adhesives, and chemicals require different surface preparation techniques but in general, the surface preparation needs to consider the cleanliness, roughness, and functionality of the surface. Adhesive bonding techniques specific to Aluminum and Copper are highlighted.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Plasma-assisted chemical-looping combustion: Mechanistic insights into low temperature methane oxidation with CuO

The low-temperature oxidation of CH 4 by CuO in a coaxial, fixed bed, double dielectric barrier discharge (DBD) reactor was investigated with time-dependent species measurements by an electron-ionization molecular beam mass spectrometer (EI-MBMS). In the experiment, 10% methane carried by noble gasses was flown at 50 sccm through 1 g CuO dispersed in quartz wool both under plasma and non-plasma conditions, while time-dependent gas-phase species profiles were collected. Plasma conditions were explored from 300 to 600 °C while the non-plasma conditions were set from 300 to 900 °C. Mechanistic insights into the oxidation of CH 4 by CuO with plasma discharge at lower temperatures (≤ 600 °C) were obtained by quantifying the fuel oxidation, intermediate species, and CO 2 production in comparison to the non-plasma conditions. Here, we observed significant enhancement of fuel oxidation from the plasma discharge between 400 and 500 °C. The CO 2 production at 500 °C with plasma was greater than that at 700 °C without plasma, reducing fuel oxidation temperature by 200+ °C. During tests, three distinct reaction stages were observed: a gas-phase transport limited stage, a surface reaction limited kinetic stage, and an oxygen ion diffusion limited stage. It was observed that plasma greatly improved the reactivity of the second stage at low temperature. In addition, no carbon deposits were observed on the resultant particles, even under the presence of plasma. M. species such as C 4 H 2 and C 6 H 6 not previously observed or predicted in CuO/CH 4 chemical looping were observed, with some species such as CH 3 OH only becoming detectable as total flowrate was increased from 50 to 1500sccm. A non-plasma reaction pathway for CH 4 based the observed species from the MBMS spectrum and previous predictions from reactive molecular dynamics simulations was created, providing a framework from which more complex plasma CuO mechanisms can be crafted from.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗