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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Photodissociation dynamics of xylene isomers C 6 H 4 (CH 3 ) 2 at 157nm using an ultracompact velocity map imaging spectrometer – The C 7 H 7 channel

Here, we investigated the photodissociation dynamics of three xylene isomers C 6 H 4 (CH 3 ) 2 at 157nm. The center-of-mass translational energy distributions of C 7 H 7 radicals were found to peak at 26kJmol −1 . Although the ionization energy of the C 7 H 7 tolyl fragment exceeds the energy of a 157nm photon, C 7 H 7 + was observed as a result of the photoionization of vibrationally ‘hot’ tolyl (C 7 H 7 ) radicals and/or two-photon ionization. The formation of rovibrationally excited tolyl fragments was discussed. Our experiments suggest the presence of tolyl radicals in the interstellar medium as a precursor to methylated polycyclic aromatic hydrocarbons upon reaction with vinylacetylene (C 4 H 4 ).

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

CO 2 electroreduction favors carbon isotope 12 C over 13 C and facilitates isotope separation

We discovered that CO 2 electroreduction strongly favors the conversion of the dominant isotope of carbon ( 12 C) and discriminates against the less abundant, stable carbon 13 C isotope. Both absorption of CO 2 in the alkaline electrolyte and CO 2 electrochemical reduction favor the lighter isotopologue. As a result, the stream of unreacted CO 2 leaving the electrolyzer has an increased 13 C content, and the depletion of 13 C in the product is several times greater than that of photosynthesis. Using a natural abundance feed, we demonstrate enriching of the 13 C fraction to ~1.3% (i.e., +18%) in a single-pass reactor and propose a scalable and economically attractive process to yield isotopes of a commercial purity. Our finding opens pathways to both cheaper and less energy-intensive production of stable isotopes ( 13 C, 15 N) essential to the healthcare and chemistry research, and to an economically viable, disruptive application of electrolysis technologies developed in the context of sustainability transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Improved cycling behavior of ZEBRA battery operated at intermediate temperature of 175°C

Operation of sodium-nickel chloride battery at temperatures lower than 200°C reduces cell degradation and improves the cyclability. One of the main technical issues in terms of operating this battery at intermediate temperatures such as 175°C is the poor wettability of molten sodium on β”-alumina solid electrolyte (BASE) causing reduced active area and limited charging . In order to overcome the problem related to poor wettability of Na melt on BASE at 175°C, Pt grid was applied on the anode side of BASE using a screen printing technique. Deeper charging and improved cycling behavior was observed on the cells with metalized BASEs due to extended active area.

intermediate temperature↗
DOE OSTI2014

Small-angle neutron scattering analysis of Mn–C clusters in high-manganese 18Mn–0.6C steel

Nanometer-scale particles (Mn–C clusters) were analyzed quantitatively using small-angle neutron scattering in 18Mn–0.6C (wt.%) austenite high-manganese steel. The size, number, and volume fraction of the particles were determined as a function of strain (0, 5, 15, 30, 45, 50%) at different temperatures (25 and 100 °C). The diameter of the cluster ranges from 2 to 14 nm in the matrix. The total volume fraction of the cluster significantly increases from 2.7 × 10{sup −6} to 8.7 × 10{sup −6} as the strain increases. Such clustering phenomenon is correlated to the serration behavior under loading in high-manganese steels. - Highlights: • Show Mn-C clustering as function of strain in 18Mn-0.6C TWIP steel. • Determine the size, number, and volume fraction of clusters quantitatively. • Compare the clustering behavior at 25 and 100 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Trace level of atomic copper in N-doped graphene quantum dots switching the selectivity from C 1 to C 2 products in CO electroreduction

To unravel the relationship between trace Cu on the metal-free catalysts toward CO/CO 2 reduction reaction (CO/CO 2 RR), we investigated the effect of trace Cu loading in N-doped graphene quantum dots (NGQDs) on CO/CO 2 RR. A general trend is that increasing the Cu loading in NGQDs switches the selectivity from C 1 (CH 4 ) to C 2 products in CORR. When 2.5 μg/cm 2 Cu with the atomic size is loaded on NGQDs, the selectivity shifts from 62% Faradaic efficiency (FE) of CH 4 to 52% FE of C 2 products in CORR. Further increasing the atomic Cu loading to 3.8 μg/cm 2 promotes the FE of C 2 products to 78%. CO 2 RR requires one order of magnitude higher Cu loading than CORR to switch the selectivity from C 1 to C 2 products due to the low partial pressure of CO. Finally, this study clarifies the distinct impact of trace (ppm level) Cu on the activity/selectivity between CORR and CO 2 RR.

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

Organic amendments change soil organic C structure and microbial community but not total organic matter on sub-decadal scales

Organic C has many benefits for soil, but it is depleted by tillage and crop harvest, and especially so for biofuel crops. Accordingly, strategies such as partially retaining stover or planting a cover crop can help ameliorate the negative effect of C removal. We used a long-term field experiment to study the impacts of stover retention and planting cover crop on soil organic matter (SOM), its extractable components and the soil microbial community. SOM chemical composition characterization was determined by electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in sequential water, methanol (MeOH), and chloroform (CHCl3) extracts. The characteristics of the soil bacterial community were measured by phospholipid fatty acid (PLFA), real-time quantitative PCR, and 16S rRNA gene sequence. The variations in total SOM content, total microbial biomass, and bacterial population were slight among treatments, but SOM chemical compounds, arbuscular mycorrhizal fungi (AMF) biomass, and bacterial structure changed significantly, and especially so in the coupled application of stover retention and cover crop. Specifically, stover retention enriched more lignin-like compounds in soil, whereas cover crop enriched more condensed hydrocarbons, and had more compounds with an aromaticity index (AI) >0.5. The bacterial community was not altered by the cover crop, but the corn stover retention increased the relative abundances of Myxococcales (Deltaproteobacteria) and decreased that of Actinobacteria. Redundancy analysis (RDA) further unveiled that the bacterial community in the stover treatments had significantly positive association with CHCl3-extracted chemical classes, i.e. unsaturated hydrocarbon and lipid with the coupled application (stover and cover crop), and lignin and protein with the single corn stover treatment. Taken together, our study shows how different C addition practices influence the molecular composition of SOM and the structure of soil microbial communities.

Xu, Jiangbin↗
DOE OSTI2018

Microstructural evolution of an aluminide coating on alloy 625 during wet air exposure at 900 °C and 1000 °C

The microstructural changes of the aluminized alloy 625 during cyclic oxidation in air + 6% H 2 O at 900 °C and 1000 °C were analyzed using optical metallography (OM), scanning electron microscopy (SEM) with energy and wave length dispersive X-ray analysis (EDX/WDX) as well as electron backscatter diffraction (EBSD). An in-house developed thermodynamic-kinetic procedure was employed to predict the microstructural evolution of aluminized alloy 625 during high temperature exposure by considering simultaneously occurring surface oxidation and interdiffusion processes. Because of the lack of mobility data for the relevant alloying elements in the σ-phase, assumptions for the mobilities were made based on the value of the mobilities in α-Cr. Despite these assumptions, the calculated results were found to be in good agreement with experimental observations. The complete depletion of β-NiAl in the coating observed during exposure at 1000 °C was correctly predicted by the model. The model was also able to infer dissolution of the precipitate phases α-Cr and σ in the interdiffusion zone during exposures at 900 °C and 1000 °C. The model was yet unable to predict the formation of the μ-phase in the alloy after 1000 h of exposure at 1000 °C. The developed modelling method offers the potential to predict microstructural changes of aluminized nickel base alloys thus reducing cost and time consuming experimental efforts.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Light-Driven C(sp 3 )–C(sp 3 ) Bond Functionalizations Enabled by the PCET Activation of Alcohol O–H Bonds

Methods that enable the selective functionalization of C–C bonds offer unique opportunities for the skeletal diversification of complex molecules and provide access to unique structures without the need for de novo synthesis. While considerable advances have been made in transition-metal-based approaches, much recent work has focused on alternative strategies for C–C bond cleavage enabled by transient free radicals. In particular, alkoxy radicals derived from simple alcohols are known to significantly destabilize adjacent C–C bonds, enabling spontaneous cleavage to eject a carbon-centered radical and afford carbonyl products via β-fragmentation. Here, while this reactivity has long been recognized, its applications in synthesis have been limited, in part, by the challenges associated with generating the key alkoxy radical intermediates.

Alcohols↗
DOE OSTI2018

Probing Cytochrome c Folding Transitions upon Phototriggered Environmental Perturbations Using Time-Resolved X-ray Scattering

Direct tracking of protein structural dynamics during folding–unfolding processes is important for understanding the roles of hierarchic structural factors in the formation of functional proteins. As such, using cytochrome c (cyt c) as a platform, we investigated its structural dynamics during folding processes triggered by local environmental changes (i.e., pH or heme iron center oxidation/spin/ligation states) with time-resolved X-ray solution scattering measurements. Starting from partially unfolded cyt c, a sudden pH drop initiated by light excitation of a photoacid caused a structural contraction in microseconds, followed by active site restructuring and unfolding in milliseconds. In contrast, the reduction of iron in the heme via photoinduced electron transfer did not affect conformational stability at short timescales (<1 ms), despite active site coordination geometry changes. These results demonstrate how different environmental perturbations can change the nature of interaction between the active site and protein conformation, even within the same metalloprotein, which will subsequently affect the folding structural dynamics.

Rimmerman, Dolev↗
DOE OSTI2014

Magnetic Properties and Electronic Structures of Ar 3 U IV –L Complexes with Ar = C 5 (CH 3 ) 4 H – or C 5 H 5 – and L = CH 3 , NO, and Cl

Electronic structures and magnetic properties of the U 4+ complexes (C 5 Me 4 H) 3 UNO, (C 5 Me 4 H) 3 UCl, (C 5 H 5 ) 3 UCH 3 , and (C 5 H 5 ) 3 UCl are investigated by quantum chemical calculations. On the basis of wave function calculations including spin–orbit (SO) interactions, all complexes have nondegenerate nonmagnetic ground states. However, for L = CH 3 and Cl magnetic doublet excited states are very low in energy, rendering the magnetic susceptibility strongly temperature dependent above ca. 50–100 K. In contrast, (C 5 Me 4 H) 3 UNO exhibits temperature-independent paramagnetism even at room temperature. The calculated susceptibilities agree well with available experimental data. An analysis of the ground states and the magnetic behavior is performed using crystal-field (CF) models with parameters extracted from the ab initio calculations, and with the help of natural orbitals contributing to the electron density, generated from scalar relativistic and SO wave functions for the ground states and selected excited states. Electronic g-factors calculated from the CF models agree well with ab initio data. The U–NO bond order in (C 5 Me 4 H) 3 UNO decreases somewhat due to SO coupling, because U–NO bonding π orbitals with strong U 5f π character mix with nonbonding 5f δ orbitals under the SO interaction. This complex also exhibits pronounced multireference character. All complexes afford U-ligand 5f covalent character.

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

C–C Bond Formation during Electrochemical CO 2 Reduction on Pristine Cu(100) Unlikely to Involve Adsorbed CO at Any Potential

Formation of hydrocarbons containing two or more carbon atoms (C 2+ ) during heterogeneous electrochemical CO and CO 2 reduction (ECOR and ECO 2 R) only occurs, among pure metals, on Cu electrodes. Moreover, the activity and selectivity is facet dependent, with Cu(100) generally preferentially forming ethylene over methane. Previously, we found via quantum-mechanics-based modeling that, unlike standard density functional theory, more accurate correlated wavefunction methods predict that non-electroactive coupling pathways involving two adsorbed COs (*CO) or a *CO and a *COH to form C–C bonds on Cu(100) are kinetically inhibited, with the former also thermodynamically unfavorable. Here, we extend that embedded complete active space second order perturbation theory (ECASPT2) study, further showing that electrochemical coupling of two *COs to form an anionic dimer [OC*–*CO] (1+δ)– , followed by protonation to form [OC*–*COH] δ− , is not kinetically competitive with the reduction of *CO to *COH at relevant ECO/CO 2 R potentials. Our simulations therefore suggest that the ability of Cu(100) to electrochemically synthesize C 2+ molecules from CO and CO 2 is unlikely to be via *CO, at least on pristine Cu(100). Instead, hydrogenated CO species (*COH, *CH x OH, or *CH x ) are most likely to be the key intermediates in C–C bond formation.

Martirez, John Mark P. [Princeton Plasma Physics L↗
DOE OSTI2018

Theoretical Study of C-H Bond Cleavage via Concerted Proton-Coupled Electron Transfer in Fluorenyl-Benzoates

Developing new strategies to activate and cleave C-H bonds is important for a broad range of applications. Recently a new approach for C-H bond activation using multi-site concerted proton-coupled electron transfer (PCET) involving intermolecular electron transfer to an oxidant coupled to intramolecular proton transfer was reported. For a series of oxidants reacting with 2-(9H-fluoren-9-yl)benzoate, experimental studies revealed an atypical Brønsted a, defined as the slope of the logarithm of the PCET rate constant versus the logarithm of the equilibrium constant or the scaled driving force. Herein this reaction is modeled with a vibronically nonadiabatic PCET theory. Hydrogen tunneling, thermal sampling of the proton donor-acceptor mode, solute and solvent reorganization, and contributions from excited vibronic states are found to play important roles. The calculations qualitatively reproduce the experimental observation of a Brønsted a significantly less than 0.5 and explain this shallow slope in terms of exoergic processes between pairs of electron-proton vibronic states. These fundamental mechanistic insights may guide the design of more effective strategies for C-H bond activation and cleavage.

Sayfutyarova, Elvira R.↗
DOE OSTI2016

Spectromicroscopy of C 60 and azafullerene C 59 N: Identifying surface adsorbed water

C 60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C 60 and (C 59 N) 2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations. We compare the oxygen 1s spectra from oxygen impurities in C 60 and C 59 N, and calculate a range of possible oxidized and hydroxylated structures and associated formation barriers. These results allow us to propose a model for the oxygen present in these samples, notably the importance of water surface adsorption and possible ice formation. Water adsorption on C 60 crystal surfaces may prove important for astrobiological studies of interstellar amino acid formation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Direct observation of C 60 - nano-ion gas phase ozonation via ion mobility-mass spectrometry

Improved methods to probe the reactivity of nano-ions, such as C 60 -, would find utility in nanochemistry, combustion chemistry, and in generally understanding the behavior of matter at the nanometer scale. Here, we demonstrate that ion mobility-mass spectrometry (IM-MS) with a low-field differential mobility analyzer can be used to probe nano-ion reaction kinetics. We used the developed IM-MS approach to examine the gas phase reactivity of C 60 - ions with ozone at atmospheric pressure. Experimental results show that ozonation of C 60 - mainly leads to the formation of C 60 O n -. The controlled reaction time within the ion mobility instrument enables calculation of ozonation reaction rates and assuming oxygen atoms are added sequentially, we find that the reaction rate between C 60 - and O 3 is near the collision controlled limit. We propose an exponentially decaying reaction rate coefficient expression to describe ozonation leading to the addition of >20 oxygen atoms. At high ozone concentrations, CO or CO 2 loss from C 60 O n - is additionally observed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Direct measurements for the kinetics of C–C bond fission in the high temperature decomposition of isopropanol

The thermal decomposition of isopropanol was studied experimentally and theoretically with a view to isolate and directly measure rate coefficients for the dominant radical channel in this multi-channel process. Two complementary shock tube methods, laser schlieren densitomtery and H-atom atomic resonance absorption spectroscopy, were used to obtain rate coefficents for the C–C bond fission channel. The experimental ranges span temperatures from 1200–2100 K and pressures between 30–690 torr. These are the most direct measurements of this rate coefficent in the fall-off regime of relevance to high-temperature reacting systems. Theoretical studies also performed in this work confirm that the title reaction and a molecular elimination involving dehydration were the sole unimolecular processes at high temperatures. A master equation analysis yielded k ( T, P ) for the C–C fission and these are shown to be in good agreement with the present experimental measurements. Comparisons with prior experimental and theoretical studies in the literature indicate branching ratios as well as absolute k ( T, P ) for C–C bond-fission have been under-predicted for this decomposition reaction. Consequently, results from the present studies place an increased emphasis on radical-driven secondary processes in high-temperature pyrolysis of this simplest secondary alcohol.

Kim, John H. [Univ. of Michigan, Ann Arbor, MI (Un↗
DOE OSTI2014

GL(3,C) invariance of type B 3-fold supersymmetric systems

Type B 3-fold supersymmetry is a necessary and sufficient condition for a quantum Hamiltonian to admit three linearly independent local solutions in closed form. We show that any such a system is invariant under GL(3,C) homogeneous linear transformations. In particular, we prove explicitly that the parameter space is transformed as an adjoint representation of it and that every coefficient of the characteristic polynomial appeared in 3-fold superalgebra is algebraic invariants. In the type A case, it includes as a subgroup the GL(2,C) projective transformation studied in the literature. We argue that any N-fold supersymmetric system has a GL(N,C) invariance for an arbitrary integral N.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

C-H surface diamond field effect transistors for high temperature (400 °C) and high voltage (500 V) operation

By forming a highly stable Al{sub 2}O{sub 3} gate oxide on a C-H bonded channel of diamond, high-temperature, and high-voltage metal-oxide-semiconductor field-effect transistor (MOSFET) has been realized. From room temperature to 400 °C (673 K), the variation of maximum drain-current is within 30% at a given gate bias. The maximum breakdown voltage (V{sub B}) of the MOSFET without a field plate is 600 V at a gate-drain distance (L{sub GD}) of 7 μm. We fabricated some MOSFETs for which V{sub B}/L{sub GD} > 100 V/μm. These values are comparable to those of lateral SiC or GaN FETs. The Al{sub 2}O{sub 3} was deposited on the C-H surface by atomic layer deposition (ALD) at 450 °C using H{sub 2}O as an oxidant. The ALD at relatively high temperature results in stable p-type conduction and FET operation at 400 °C in vacuum. The drain current density and transconductance normalized by the gate width are almost constant from room temperature to 400 °C in vacuum and are about 10 times higher than those of boron-doped diamond FETs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

DFT study of small fullerene dimer complexes C{sub 20}-N{sub m}@C{sub n} (m = 1-6 and n = 24, 28, 32, 36 and 40)

First principle calculations based on density functional theory were performed to calculate the structural and electronic properties of C{sub 20}-N{sub m}@C{sub n} dimer complexes. The calculated binding energies of the complexes formed are comparable to C{sub 60} dimer which ensures their stability. The bond lengths of these dimer complexes were found to be nearly same as pure complexes C{sub 20}-C{sub n}. Further, nitrogen (N) atoms were encapsulated inside the secondary cage (C{sub n}) of dimer complexes and the number of N atoms depends on diameter of the cage. The HOMO-LUMO gaps of new proposed complexes indicate the increase in gap as compared to pure complexes. Mulliken charge analysis of these complexes has been studied which shows the significant charge transfer from the N atoms to the secondary cage of these complexes. The study propose the formation of the new dimer complexes which are stable and are able to encapsulate atoms which are otherwise reactive in free space.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗