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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Local atomic structure of Pd and Ag in the SiC containment layer of TRISO fuel particles fissioned to 20% burn-up

The structure and speciation of fission products within the SiC barrier layer of tristructural-isotropic (TRISO) fuel particles irradiated to 19.6% fissions per initial metal atom (FIMA) burnup in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) was investigated. As-irradiated fuel particles, as well as those subjected to simulated accident scenarios, were examined. The TRISO particles were characterized using synchrotron X-ray absorption fine-structure spectroscopy (XAFS) at the Materials Research Collaborative Access Team (MRCAT) beamline at the Advanced Photon Source. The TRISO particles were produced at Oak Ridge National Laboratory under the Advanced Gas Reactor Fuel Development and Qualification Program and sent to the ATR for irradiation. XAFS measurements on the palladium and silver K-edges were collected using the MRCAT undulator beamline. Analysis of the Pd edge indicated the formation of palladium silicides of the form Pd x Si (2 ≤ x ≤ 3). In contrast, Ag was found to be metallic within the SiC shell safety tested to 1700 °C. To the best of our knowledge, this is the first result demonstrating metallic bonding of silver from fissioned samples. Knowledge of these reaction pathways will allow for better simulations of radionuclide transport in the various coating layers of TRISO fuels for next generation nuclear reactors. In conclusion, they may also suggest different ways to modify TRISO particles to improve their fuel performance and to mitigate potential fission product release under both normal operation and accident conditions.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2019

Enhanced Catalyst Durability for Bio-Based Adipic Acid Production by Atomic Layer Deposition

Harsh reaction environments challenge the lifetime productivity of conventional catalysts and impede emerging biobased chemical processes. Condensed-phase processing of muconic acid, a biobased platform chemical, leads to problematic levels of catalyst leaching and fouling. Atomic layer deposition (ALD) can improve catalyst durability using protective metal oxide coatings; however, a targeted coating strategy and cost models thereof are needed for application-specific deactivation challenges that can surmount these challenges while accounting for process implications. Herein, we utilize thin (<5 wt% Al) Al2O3 ALD coatings to increase the lifetime productivity of Pd/TiO2 during muconic acid hydrogenation to adipic acid. The ALD coating decreases Pd leaching by >3x and markedly improves the thermal stability of Pd and TiO2. Economic analysis for an adipic acid biorefinery supports that increased material costs and reduced catalyst productivity can be justified through lifetime extension. Broadly, this work lays the foundation for reducing the cost of biobased chemical processes through catalyst stability.

Settle, Amy↗
DOE OSTI2023

Dual atom catalysts for rapid electrochemical reduction of CO to ethylene

Strong CO adsorption and facile CO dimerization are the key challenges in electrochemical CO2 reduction towards multi-carbon (C2+) products. We recently showed that CoPc immobilized on a single-walled carbon nanotube can selectively reduce CO2 to methanol. This is enabled through molecular strain, which dramatically improves the CO adsorption energy to CoPc, which in turn facilitates methanol formation. We now examine the extended Phthalocyanine (PcEx) dual atom catalyst (DAC), which is intrinsically strained and contains two catalyst centers, making it a candidate for reducing CO to C2+ products. Using Quantum Mechanics (QM), we screened 20 elements embedded in the PcEx, seeking catalysts with weak hydrogen binding, strong CO binding, and facile CO dimerization. We identi>ied Fe, Ru, Co, and Ir as the best performers and subsequently evaluated the entire CO to C2H4 mechanism (9 steps) using each of these elements as catalysts. In terms of limiting potential and overall exergonicity, we identi>ied CoPcEx as the best catalyst, followed by IrPcEx. We then examined the full CO to C2H4 mechanism on the bimetallic IrCoPcEx catalyst using grand canonical QM to obtain the reaction energetics as a function of applied potential. We conclude that the bimetallic IrCoPcEx is most promising for ef>iciently converting CO to ethylene.

Musgrave, Charles B.↗
DOE OSTI2015

Application of atomic layer deposited microchannel plates to imaging photodetectors with high time resolution

Novel microchannel plates have been constructed using borosilicate glass micro-capillary array substrates with 20 mu m and 10 mu m pores and coated with resistive, and secondary electron emissive, layers by atomic layer deposition. Microchannel plates in 33 mm, 50 mm and 20 cm square formats have been made and tested. Although their amplification, imaging, and timing properties are comparable to standard glass microchannel plates, the background rates and lifetime characteristics are considerably improved. Sealed tube detectors based on the Planacon tube, and a 25 mm cross delay line readout tube with a GaN(Mg) opaque photocathode deposited on borosilicate microchannel plates have been fabricated. Considerable progress has also been made with 20 cm microchannel plates for a 20 cm format sealed tube sensor with strip-line readout that is being developed for Cherenkov light detection.

Siegmund, O. H. W.↗
DOE OSTI2013

Atomic dynamics in molten AlCu alloys of different compositions and at different temperatures by cold neutron scattering

The atomic motions in molten Al1-xCux (x=0.10, 0.171 and 0.25) around the eutectic composition (x=0.171) were studied by cold neutron inelastic scattering at three different temperatures (973 K, 1173 K and 1373 K). An alloy of eutectic composition containing the 63Cu isotope was also studied. Self-diffusion coefficients for the Cu ions were determined from the width of quasielastic peaks and were found to decrease slightly with increasing Cu concentration. Longitudinal current correlation functions Jl(Q,E) exhibit at all temperatures and at all compositions a shoulder at energies below 10 meV and one main maximum at higher energies. These features can be interpreted in terms of excitations of acoustic and optic nature. The shape of Jl(Q,E) is sensitive to composition, being considerably more structured for larger Cu content. This can be coupled to the existence of a prepeak in the measured zeroth moment of dynamic scattering function indicating an increased chemical ordering with increasing Cu concentration for all temperatures. Indications for an existence of a liquid–liquid phase transition are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Atomic worlds: Current state and future of atom probe tomography in geoscience

Atom Probe Microscopy(APM)is rapidly finding new applications within the geosciences. Historically connectedwithmaterials science, and semiconductor device applications, recent years have seen an excitingtrend as APM hasproveda useful tool for nanoscale geochemistry, as itoffersunique capabilities when compared withthe suite of conventional geoanalytical techniques. The ability to characterize 3D nanoscale chemistry with isotopic sensitivityhas uncoveredintricate details of complex trace element distributions within a varietyof minerals and has opened the door to nanoscale isotope geochemistry. Already these advances are having an impact on long-standing questions within geochronology, planetary science and many other fields of research. As this trend gathers pace, we present here a brief summary of the current statusof APM geoscience applications and discuss the likely future directions in this developingresearch space.

58 GEOSCIENCES↗
DOE OSTI2016

Epitaxial Atomic Layer Deposition of Sn-Doped Indium Oxide

Coherently strained, epitaxial Sn-doped In2O3 (ITO) thin films were fabricated at temperatures as low as 250 degrees C using atomic layer deposition (ALD) on (001)-, (011)-, and (111)-oriented single-crystal Y-stabilized ZrO2 (YSZ) substrates. Resultant films possess cube-on-cube epitaxial relationships with the underlying YSZ substrates and are smooth, highly conductive, and optically transparent. This epitaxial ALD approach is favorable compared to many conventional growth techniques as it is a large-scale synthesis method that does not necessitate the use of high temperatures or ultrahigh vacuum. These films may prove valuable as a conductive growth template in areas where high-quality crystalline thin film substrates are important, such as solar energy materials, light-emitting diodes, or wide bandgap semiconductors. Furthermore, we discuss the applicability of this ALD system as an excellent model system for the study of ALD surface chemistry, nucleation, and film growth.

Emery, Jonathan D.↗
DOE OSTI2015

Low Temperature ABC-Type Ru Atomic Layer Deposition through Consecutive Dissociative Chemisorption, Combustion, and Reduction Steps

Thermal atomic layer deposition (ALD) of noble metals is frequently performed using molecular oxygen as the nonmetal precursor to effect a combustion-type chemistry at relatively high temperatures of 300 °C. Bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2) is one of the common used metal precursors for Ru ALD. Using Ru(EtCp)2 and oxygen as reactants, Ru ALD was acheived at near 300 °C. Here, we demonstrate that Ru ALD can proceed at as low as 150 °C by using successive exposures to oxygen and hydrogen as the co-reactants. In situ quartz crystal microbalance (QCM) and quadrupole mass spectroscopy (QMS) measurements both suggest that this ABC-type ALD occurs through dissociative chemisorption, combustion, and reduction for the Ru(EtCp)2, oxygen and hydrogen steps, respectively, in a similar manner to processes using ozone and hydrogen as co-reactants reported previously. Moreover, we believe this molecular O2 and H2 based ABC-type ALD could be exploited for the ALD of other noble metals to decrease the deposition temperature and reduce oxygen impurities.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Metal–Ligand Cooperativity Promoting Sulfur Atom Transfer in Ferrous Complexes and Isolation of a Sulfurmethylenephosphorane Adduct

Here, the reaction of elemental sulfur with the cis-divacant octahedral complex [(pyrr 2 py)Fe(OEt 2 )] (1; pyrr 2 py 2– = 3,5- t Bu 2 -bis(pyrrolyl)pyridine) yields the iron dimer [(pyrr-1-S-pyrrpy)Fe] 2 (2; pyrr-1-S-pyrrpy 2– = 3,5-( t Bu2-pyrrolyl)(1-S-3,5-tBu2-pyrrolyl)pyridine) resulting from a pyrr 2 py 2– ligand based S-oxidation of one pyrrole arm. Addition of the phosphorus ylide H 2 CPPh 3 to 1 forms the ylide adduct [(pyrr 2 py)Fe(CH 2 PPh 3 )] (3), which upon reaction with elemental sulfur produces a rare example of a sulfurmethylenephosphorane adduct, [(pyrr 2 py)Fe(SCH 2 PPh 3 )] (4). The sulfur-oxidized pyrrole group of the ligand pyrr-1-S-pyrrpy 2– can be reversed, since complex 2 exhibits S atom transferability via the addition of 2 equiv of H 2 CPPh 3 to yield a mixture of compounds 3 and 4. For all complexes reported, the ferrous ion remains S = 2. Complexes 2–4 were characterized by single-crystal X-ray diffraction as well as 1 H NMR spectroscopy, solid and solution magnetic studies, and 57 Fe Mössbauer spectroscopic measurements.

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

Extension of structure-reactivity correlations for the hydrogen abstraction reaction by bromine atom and comparison to chlorine atom and hydroxyl radical

Recently we presented structure-reactivity correlations for the gas-phase ambient-temperature rate constants for hydrogen abstraction from sp 3 -hybridized carbon by chlorine atom and hydroxyl radical (Cl•/HO• + HCR 3 → HCl/HOH + •CR 3 ); the reaction enthalpy effect was represented by the independent variable Δ r H and the polar effect by the independent variables F and R, the Hammett constants for field/inductive and resonance effects. Both these reactions are predominantly exothermic and have early transition states. Here we present a parallel treatment for Br• whose reaction is significantly endothermic with a correspondingly late transition state. In spite of lower expectations because the available data base is less extensive and much more scattered and because long temperature extrapolations are often required, the resulting least-squares fit (log k 298,Br = –0.147 Δ r H –4.32 ΣF –4.28 ΣR –12.38 with r 2 = 0.92) was modestly successful and useful for initial predictions. The coefficient of Δ r H was ~4-fold greater, indicative of the change from an early to a late transition state; meanwhile the sizable coefficients of ΣF and ΣR indicate the persistence of the polar effect. Although the mean unsigned deviation of 0.79 log k 298 units is rather large, it must be considered in the context of a total span of over 15 log units in the data set. Lastly, the major outliers are briefly discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Submonolayer Is Enough: Switching Reaction Channels on Pt/SiO 2 by Atomic Layer Deposition

The reaction mechanism of CO 2 with H 2 is studied on platinum nanoparticles supported on fumed silica. It is found that platinum nanoparticle size, reaction temperature, and metal oxide promoters play important roles in determining the reaction rate and the mechanism of forming surface carbonyl species. Metal oxide promoters consist of sub-monolayer titanium oxide or aluminum oxide overcoated onto the catalysts by atomic layer deposition (ALD). Furthermore, these alter the CO formation rate, influence the adsorption and desorption behavior, and switch the surface reaction channel from Eley-Rideal to Langmuir-Hinshelwood mechanism due to an enhancement of CO 2 affinity to the metal-metal oxide interface. At the temperatures relevant for catalytic turnover, ALD overcoating significantly increases catalytic activity in CO 2 hydrogenation to CH 4 and CO, while the identity of the oxide overcoat helps control product selectivity.

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

Atomic Number Dependent “Structural Transitions” in Ordered Lanthanide Monolayers: Role of the Hydration Shell

When lanthanide ions are present in the aqueous subphase of a floating monolayer (Langmuir film), the ions attracted to the interface will in many cases form commensurate and/or incommensurate two-dimensional structures. These lattices depend not only on the molecules forming the monolayer, but also on the atomic number of the lanthanide, with a sudden change between the lattice formed by lighter ions and that formed by heavier ions under a given monolayer. Since there are few other relevant differences between the lanthanides, we attribute the Z-dependent “transition” to the number of water molecules associated with each ion. Finally, the first hydration shell is thought to vary continuously from ~9 in lighter lanthanides to ~8 in heavier lanthanides.

Miller, Mitchell↗