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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Evaluation of the Component of Bias of X-Ray Microanalysis Related to Surface Relief of the Specimen

A semiempirical approach to the a priori evaluation of the effect of the surface relief on the results of X-ray spectral analysis of binary compounds is proposed. Dimensionless parameter k characterizing the effect of the relief on the intensity of intrinsic X-ray radiation is determined using the experimental data obtained for reference monocrystal specimens GaAs with known geometrical parameters of the relief.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Understanding the Electronic and Structural Effects in ORR Intermediate Binding on Anion‐Substituted Zirconia Surfaces

Abstract For oxygen reduction reaction (ORR), the surface adsorption energies of O and OH* intermediates are key descriptors for catalytic activity. In this work, we investigate anion‐substituted zirconia catalyst surfaces and determine that adsorption energies of O and OH* intermediates is governed by both structural and electronic effects. When the adsorption energies are not influenced by the structural effects of the catalyst surface, they exhibit a linear correlation with integrated crystal orbital Hamiltonian population (ICOHP) of the adsorbate‐surface bond. The influence of structural effects, due to the re‐optimisation slab geometry after adsorption of intermediate species, leads to stronger adsorption of intermediates. Our calculations show that there is a change in the bond order to accommodate the incoming adsorbate species which leads to stronger adsorption when both structural and electronic effects influence the adsorption phenomena. The insights into the catalyst‐adsorbate interactions can guide the design of future ORR catalysts.

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

Effect of the Molecular Structure of Surface Vanadia on Activity and Regenerability of VO $x$ /In 2 O 3 Catalysts for CO 2 -Assisted Oxidative Dehydrogenation of Propane

Our recent work has reported that higher propylene selectivity and improved stability can be achieved by combining redox-active VO $x$ and basic In 2 O 3 for CO 2 -assisted oxidative dehydrogenation of propane (CO 2 -ODHP). In the present work, we continued to explore the stability and regenerability of V/In catalysts. In particular, our interest lies in identifying the effect of mono- and polyvanadate on catalytic performance and regenerability. A V/In catalyst with an increased proportion of monovanadate was prepared using the Schlenk line under moisture-free conditions (V/In–S), while the fully polymerized vanadate catalyst was prepared through a regular impregnation (V/In) for comparison. The Schlenk-line-prepared catalyst, namely, V/In–S, not only exhibits a 17–30% enhanced propylene yield at high temperatures (500–540 °C) over V/In but also presents improved stability and regenerability with nearly 88% activity recovered after regeneration in O 2 . Detailed characterizations have been performed to reveal the catalyst structure–performance relationship, including chemisorption (NH 3 /CO 2 -temperature-programmed desorption, NH 3 /CO 2 -TPD), H 2 -temperature-programmed reduction (H 2 -TPR), and spectroscopic studies [Raman spectroscopy, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), and high-sensitivity low-energy ion scattering (HS-LEIS)]. Characterization results demonstrate that compared with polyvanadates, monovanadates lead to strengthened interaction with In 2 O 3 and a more stabilized V/In surface and subsurface, as well as improved redox properties of VO $x$ . These advantages give rise to the observed enhancement in activity, stability, and regenerability. In conclusion, these findings advance the understanding of the relationship between the activity/stability and the molecular structure of surface oxide species (vanadia) and the interplay between acid–base interactions and redox properties of mixed metal-oxide catalysts for efficient CO 2 -ODHP.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Atomic-Scale Understanding of Catalyst Activation: Carboxylic Acid Solutions, but Not the Acid Itself, Increase the Reactivity of Anatase (001) Faceted Nanocatalysts

Our ability to predict nanocatalyst reactivity has been hindered by our lack of atomic-scale understanding of nanocatalyst surface structure. Do nanocatalyst surfaces adopt a bulk-terminated structure or do they reconstruct to minimize their free energy, thereby lowering their reactivity as often observed in vacuum? Similarly, do nanocatalysts processed at high temperatures maintain their low reactivity, reconstructed surfaces when used at low temperatures? Using a new technique for the preparation of anatase nanocatalysts suitable for atomic-scale imaging and surface spectroscopy, we show that solution-prepared anatase is terminated by a monolayer of fluorine, which acts as an atomic-scale oleophobic coating, preventing the accumulation of adventitious carbon. We further show that the most common TiO 2 functionalization chemistry, a carboxylic acid solution, causes the spontaneous reorganization of a reconstructed anatase nanocatalyst, leading to a five-fold increase in reactive sites. This reorganization is not observed when carboxylic acids are deposited from the gas phase, suggesting that model experiments in vacuum environments can lead to a nonequilibrium, kinetically trapped state that may not be catalytically relevant. Aqueous carboxylic acid solutions produce densely packed carboxylate monolayers with richer adsorption geometries than previously predicted. Ab initio simulations show that although the carboxylate termination is somewhat less effective at removing surface stress than the reconstruction, it is more effective in lowering the surface energy. This observation suggests that bulk-terminated metal-oxide nanocrystals may be common in reactive environments, even if high temperatures are used to process the nanocatalyst or if the reactant is later rinsed off. As such, the assumption of a bulk-terminated surface may be a reasonable starting point for “materials-by-design” approaches to computationally engineered nanocatalysts.

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

Surface albedo and reflectance: Review of definitions, angular and spectral effects, and intercomparison of major data sources in support of advanced solar irradiance modeling over the Americas

This study defines albedo and reflectance in the context of solar applications. It examines the main sources of surface albedo data that can be used to help solar irradiance modeling efforts, such as undertaken by the National Renewable Energy Laboratory (NREL) over the Americas, for instance, per the National Solar Radiation Database (NSRDB). The MODIS-based albedo database, as used as input to derive historical time series of solar irradiance in the current version of the NSRDB, is compared to other sources of global gridded data over the Americas in general and some specific areas in particular. The particular role of snow cover is analyzed. It is found that, in the current MODIS-based NSRDB implementation, snow-impacted areas have been assigned a too high albedo in general because of the lack of consideration for the antagonistic effect of surface roughness, among other factors. Other albedo databases, such as CMSAF, MINES-ParisTech or the ERA5 reanalysis, do not display such high albedos at latitudes above ~40 degrees N. The gap-free and snow-free MODIS MCD43GF product is found affected by a long-term downward trend over some areas and out-of-phase seasonal effects over other areas, in comparison with MERRA-2 reanalysis data in particular. Comparisons with actual albedo measurements at the arid Desert Rock site in Nevada also show that albedo data derived from land surface models are affected by systematic bias. Five albedo databases are intercompared for the area around Ivanpah Playa, California, which has great importance in both remote sensing and solar applications. Various aspects of the proper usage of albedo data in solar radiation modeling are discussed, regarding calculations of both the backscattering process and reflections on a tilted surface: spatial resolution, temporal resolution, angular effects, and spectral effects. An important distinction is made between the use of albedo data at ~4 km resolution for backscattering calculations and at ~10 m resolution for transposition calculations to tilted planes, which might additionally require spectral information for monofacial or bifacial PV applications. It is shown that the tilted calculations usually performed in solar resource assessments are far from realistic in the case of most large-scale PV applications, for which a more suitable methodological approach is described. For such needs, the limitations of the current sources of high-resolution reflectance data are discussed. The impact of surface albedo estimation errors on the estimation of backscattered irradiance over snowy areas is evaluated. It is found non-negligible, and even large under cloudy conditions.

14 SOLAR ENERGY↗
DOE OSTI2020

Sulfurization as a promising surface passivation approach for both n- and p-type Si

Sulfur is shown to be an effective and promising surface passivation element for both n- and p-type Si wafers after reacting in dilute hydrogen sulfide gas (2 - 6% in argon) at 550°C. Effective minority carrier lifetimes of > 2 ms and > 0.25 ms are achieved for n- and p-type Si wafers, respectively, comparable to the industry standard thermal oxide and atomic layer deposited aluminum oxide passivation level. Surface characterization by x-ray photoelectron and emission spectroscopy reveals that sulfur is primarily bonded in a sulfide environment.

42 ENGINEERING↗
DOE OSTI2025

Faceted NiO(111) nanosheets: morphological and catalytic evolution for the oxygen evolution reaction

The renaissance of the energy system through the use of green hydrogen by water electrolysis lies behind the development of abundant, active, and scalable catalysts for the oxygen evolution reaction (OER). A fundumental understanding of the surface properties for these materials is of vital importance in producing viable heterogenous catalysts. In this feature article, we summarize several years of collaborative work on a uniquely faceted NiO(111) nanosheet possessing hexagonal holes with a focus on understanding how the evolution of the catalyst surface and bulk composition effects OER performance. The importance of surface faceting, morphological evolution, and metal combination by different doping strategies are all analyzed and summarized to further improve the material's performance. Furthermore, microwave and supercritical synthesis processes are utilized to understand how varying wet-chemical techniques effect the formation of the NiO(111) nanosheet and activity of the material. We discuss our chosen strategies and the difficulties encountered with optimizing a catalyst surface for the OER.

08 HYDROGEN↗
DOE OSTI2021

Study of the niobium oxide structure and microscopic effect of plasma processing on the Nb surface

A study of the niobium oxide structure is presented here, focusing on the niobium suboxides. Multiple steps of argon sputtering and XPS measurements were carried out until the metal surface was exposed. Subsequently, the sample was exposed to air for different time intervals and the oxide regrowth was studied. In addition, three Nb samples prepared with different surface treatments were studied before and after being subjected to plasma processing. The scope is investigating the microscopic effect that the reactive oxygen contained in the glow discharge may have on the niobium surface. This study suggests that the Nb 2 O 5 thickness may increase. Nevertheless, since the Nb 2 O 5 is dielectric, its thickening would not negatively affect the cavity performance.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Study of the Niobium Oxide Structure and Microscopic Effect of Plasma Processing on the Nb Surface

A study of the niobium oxide structure is presented here, focusing on the niobium suboxides. Multiple steps of argon sputtering and XPS measurements were carried out until the metal surface was exposed. Subsequently, the sample was exposed to air for different time intervals and the oxide regrowth was studied. In addition, three Nb samples prepared with different surface treatments were studied before and after being subjected to plasma processing. The scope is investigating the microscopic effect that the reactive oxygen contained in the glow discharge may have on the niobium surface. This study suggests that the Nb 2 O 5 thickness may increase. Nevertheless, since the Nb 2 O 5 is dielectric, its thickening would not negatively affect the cavity performance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sensitivity study on the fin effect of thermocouple mounted on the heated surface under film boiling condition

In the reactivity-initiated accident (RIA) scenario, right after the power burst with the occurrence of departure from nucleate boiling (DNB), the cladding temperature quickly reaches its maximum and is maintained in a steady film boiling regime. Then, under limited heat transfer performance of film boiling, the local cooling effect by the thermocouple wire may not be neglected. A computational model is developed to estimate the local cooling effect of the thermocouple wire mounted on the cladding surface under film boiling condition. The model predicts the temperature profile along the cladding surface as physically expected and is verified against the benchmark problem. Sensitivity studies reveal the significant effects of the thickness of vapor film layer and the diameter of thermocouple on the temperature drop near the thermocouple, for they increase the heat transfer area to the liquid water region. The impact of film boiling heat transfer coefficient, however, is not significant, as the primary heat transfer mechanism near the thermocouple is the heat conduction to the wire. Future study will include the contribution of radiative heat transfer between the cladding surface and the vapor film layer, as well as a transient power history which represents an actual RIA scenario.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Obtaining bulk-like correlated oxide surfaces with protective caps

Functional oxides exhibit a diverse range of correlated electron phenomena, some of which are highly attractive for novel electronic, magnetic, and optical devices. Despite decades of advancement of our fundamental understanding of these materials, they consistently fall short of realizing their promise in functional devices. We identify a significant bottleneck toward device realization to be surface overoxidation. Protective caps can effectively prevent overoxidation, but their interfaces with functional oxides are not well understood. These interfaces are critical for effectively using functional oxides in field-effect devices, where “the interface is the device.” This work addresses the chemistry and physics of the interface between protective caps and the correlated metal SrVO3, a model functional oxide. Our comparison of five different cap materials reveals effective protection and similar SrVO3 surface chemistry in all cases. Systematic comparisons of surface and bulk-sensitive photoelectron spectra reveal that negligible interface redox takes place, elucidating the cap-SrVO3 interface chemistry. This work demonstrates a robust and simple solution to the surface overoxidation problem in vanadates, paving the way toward effectively using these materials in field-effect devices. Our conclusions are general and can be applied to numerous other systems, thus moving oxide electronics closer to the realization of functional devices.

Cohen, Amit (ORCID:0009000276477510)↗
DOE OSTI2017

Corrosion and Fatigue Behavior of High-Strength Steel Treated with a Zn-Alloy Thermo-diffusion Coating

High and low cycle fatigue tests were conducted on high-strength steel using four-point bending. The materials tested were ASTM A723 steel in the as-machined condition, grit-blasted condition, MIL-DTL-16232 heavy manganese phosphate-coated condition, and ASTM A1059 Zn-alloy thermo-diffusion coated (Zn-TDC). The ASTM A723 steel base material exhibits a yield strength of ~1000 MPa. The effects of the surface treatments versus uncoated steel were examined. The fatigue life of the Zn-TDC specimens was generally reduced on as-coated specimens versus uncoated or phosphate-coated specimens. Several mechanisms are examined including the role of compressive residual stress relief with the Zn-TDC process as well as fatigue crack initiation from the hardened Zn-Fe alloy surface layer produced in the gas-metal reaction. Additionally, the effects of corrosion pitting on the fatigue life of coated specimens are explored as the Zn-TDC specimens exhibit significantly improved corrosion resistance over phosphate-coated and oiled specimens.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Revisiting Interior Water Mass Responses to Surface Forcing Changes and the Subsequent Effects on Overturning in the Southern Ocean

Abstract Two coupled climate models, differing primarily in horizontal resolution and treatment of mesoscale eddies, were used to assess the impact of perturbations in wind stress and Antarctic ice sheet (AIS) melting on the Southern Ocean meridional overturning circulation (SO MOC), which plays an important role in global climate regulation. The largest impact is found in the SO MOC lower limb, associated with the formation of Antarctic Bottom Water (AABW), which in both models is enhanced by wind and weakened by AIS meltwater perturbations. Even though both models under the AIS melting perturbation show similar AABW transport reductions of 4–5 Sv (50%–60%), the volume deflation of AABW south of 30°S is four times greater in the higher resolution simulation (−20 vs. −5 Sv). Water mass transformation (WMT) analysis reveals that surface‐forced dense water formation on the Antarctic shelf is absent in the higher resolution and reduced by half in the lower resolution model in response to the increased AIS melting. However, the decline of the AABW volume (and its inter‐model difference) far exceeds the surface‐forced WMT changes alone, which indicates that the divergent model responses arise from interactions between changes in surface forcing and interior mixing processes. This model divergence demonstrates an important source of uncertainty in climate modeling, and indicates that accurate shelf processes together with scenarios accounting for AIS melting are necessary for robust projections of the deep ocean's response to anthropogenic forcing.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Magnetically Recoverable and Reusable Titanium Dioxide Nanocomposite for Water Disinfection

A bifunctional magnetic Fe3O4@SiO2@TiO2 or MS-TiO2 antimicrobial nanocomposite was prepared based on simple sol-gel methods with common equipment and chemicals. Reaction pH was found to influence the TiO2 upload in the nanocomposite. The alkaline condition produced the greatest TiO2 upload, while the acidic condition the least. Annealing at 300 °C turned the as-synthesized amorphous TiO2 into one with high content of anatase, the most photoactive form of TiO2. Irradiated by 365 nm UV light, a sample of 30 mg/mL of annealed nanocomposite containing 12.6 wt.% Ti was shown to be able to completely eradicate 104 CFU/mL of the laboratory-grown E. coli within 25 min, 25 min faster than the control when the 365 nm UV light was employed alone. The nanocomposite demonstrated consistent antimicrobial performance over repeated uses and was easily recoverable magnetically due to its high magnetization value (33 emu/g). Additionally, it was shown to reduce the bacterial count in a real surface water sample containing 500–5000 CFU/mL of different microbes by 62 ± 3% within 30 min. The irradiating 365 nm UV light alone was found to have generated little biocidal effect on this surface water sample. The nanocomposite is promising to serve as an effective, safe, and eco-friendly antimicrobial agent, especially for surface water disinfection.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

First-Principles Modeling of the Repassivation of Corrosion Resistant Alloys: Part II. Surface Adsorption Isotherms for Alloys and the Chloride Susceptibility Index

Quantitatively predicting the corrosion resistance of alloys is vital to the design and application of the next generation of superior corrosion resistant alloys (CRAs). Here, the Chloride Susceptibility Index (CSI), a scientifically based quantitative descriptor for repassivation tendency of CRAs, is proposed as a metric constructed through combining atomistically resolved information regarding adsorption and alloy surface composition with environmental conditions such as applied potential, temperature, pH, and Cl – concentration. Using this method, the response of CRAs to relevant environments can be predicted. CSI is determined by: (1) estimation of thermoequilibrium surface coverages of O and Cl by a Langmuir isotherm model using adsorption energies of different species (O, Cl, OH, H 2 O) obtained from DFT. (2) determination of CSI by integrating Cl surface coverage over a realistic window of applied potentials, thereby incorporating the effect of Cl surface coverage and electrochemical environment simultaneously. A series of Ni-Cr-X alloys was used as an example to develop and validate the method through studying the effect of different alloy solutes X on chloride resistance. Here, the trends and relations predicted by CSI are in qualitative agreements with experimental observations. Moreover, a quantitative correlation is found between CSI and the repassivation potential.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Remote surface optical phonon scattering in ferroelectric Ba 0.6 Sr 0.4 TiO 3 gated graphene

We report the effect of remote surface optical (RSO) phonon scattering on carrier mobility in monolayer graphene gated by ferroelectric oxide. We fabricate monolayer graphene transistors back-gated by epitaxial (001) Ba 0.6 Sr 0.4 TiO 3 films, with field effect mobility up to 23 000 cm 2 V –1 s –1 achieved. Switching ferroelectric polarization induces nonvolatile modulation of resistance and quantum Hall effect in graphene at low temperatures. Ellipsometry spectroscopy studies reveal four pairs of optical phonon modes in Ba 0.6 Sr 0.4 TiO 3 , from which we extract RSO phonon frequencies. The temperature dependence of resistivity in graphene can be well accounted for by considering the scattering from the intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter dominated by the mode at 35.8 meV. Furthermore, our study reveals the room temperature mobility limit of ferroelectric-gated graphene transistors imposed by RSO phonon scattering.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Room-Temperature Ferromagnetism Observed in SiO{sub 2}-Coated CuO Nanostructures

In this paper, the magnetic properties of pure CuO and SiO{sub 2}-coated CuO nanocrystals were reported. Strongly enhanced room-temperature ferromagnetism was observed in SiO{sub 2}-coated CuO nanocrystals, whose saturation magnetization is two orders of magnitude enhanced compared to that of the uncoated CuO nanocrystals. The mechanism of this enhancement was investigated. It points out the main origin of ferromagnetism in these CuO nanocrystals is the uncompensated surface state, so that the coating of SiO{sub 2} can effectively protect the surface state to improve the ferromagnetism in these CuO nanocrystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗