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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Diffusion Behavior of Mn and Si Between Liquid Oxide Inclusions and Solid Iron-Based Alloy at 1473 K

In order to clarify the changes in the composition of oxide inclusions in steel, the effect of the metal and oxide composition on the reaction between solid Fe-based alloys and liquid multi-component oxides was investigated using the diffusion couple method at 1473 K. The measured concentration gradients of Mn and Si in the metal indicated that Mn diffused into the metal from the oxide, while the diffusion of Si occurred in the opposite direction. In addition, the MnO content in the oxide decreased with heat treatment time, while the SiO{sub 2} content increased. The compositional changes in both phases indicated that the Mn content in the metal near the interface increased with heat treatment with decreasing MnO content in the oxide. Assuming local equilibrium at the interface, the calculated [Mn]{sup 2}/[Si] ratio at the interface in equilibrium with the oxide increased with increases in the MnO/SiO{sub 2} ratio in the oxide. The difference in the [Mn]{sup 2}/[Si] ratios between the interface and the metal matrix increased, which caused the diffusion of Mn and Si between the multi-component oxide and metal. By measuring the diffusion lengths of Mn and Si in the metal, the chemical diffusion coefficients of Mn and Si were obtained to calculate the composition changes in Mn and Si in the metal. The calculated changes in Mn and Si in the metal agreed with the experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Laser powder bed fusion of oxide dispersion-strengthened IN718 alloys: A complementary study on microstructure and mechanical properties

In this study, two new grades of oxide dispersion strengthened (ODS) Inconel 718 (IN718) alloys were designed by the thermochemical CALPHAD method and produced by laser powder bed fusion (LPBF) technique. Alloys designated as IN718-YF and IN718-YFH, that consist Y 2 O 3 –FeO and Y 2 O 3 –FeO–Hf, respectively, were fabricated with >99.9 % densification using optimized process parameters. CALPHAD calculations were highly consistent with experimental findings, highlighting the formation of Al-containing Y–Ti–O and Y–Hf–O nano-oxides in both alloy types. Texture analyzes revealed no significant texture development in as-built (AB) or heat-treated (HT) alloys. Heat treatment was applied at 1050 °C for 1 h to enhance nano-oxide density. Further, the nano-oxide number density remained similar in IN718-YF while it decreased in IN718-YFH alloy as a result of carbide formation after the heat treatment. Besides, formation of secondary γ' particles was observed in the IN718-YFH/HT alloy. Even though the yield strengths of IN718-YF and IN718-YFH alloys in both AB and HT conditions were similar, the ductility of IN718-YFH was ~50 % less in almost all conditions compared to the ductility of IN718-YF. This has been shown to be as a result of irregular shaped micron-sized Y-Hf-O oxides, martensite formation in AB condition, increased amount of carbides and existence of secondary γ' particles in HT condition in IN718-YFH. High density of stacking faults (SF) forming at the interface of the nano-oxides have been detected in IN718-YF alloys. Besides dislocation/nanoparticle interactions, SFs which are responsible for the delocalization of the deformation improve the ductility of IN718-YF alloys. Overall, high temperature mechanical tests exhibit that both alloys have higher strength with improved ductility compared to the standard IN718 alloys, indicating the contribution of the nano-oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Manipulating the polar mismatch at the LaNi O 3 / SrTi O 3 (111) interface

Heteroepitaxial growth of transition-metal oxide films on the open (111) surface of SrTi O 3 results in significant restructuring due to the polar mismatch. Monitoring the structure and composition on an atomic scale of LaNi O 3 / SrTi O 3 (111) interface as a function of processing conditions has enabled the avoidance of the expected polar catastrophe. Using atomically resolved transmission electron microscopy and spectroscopy as well as low-energy electron diffraction, the structure of the thin film, from interface to the surface, has been studied. Here, we show that the proper processing can lead to a structure that is ordered, coherent with the substrate without intermediate structural phase. Using angle-resolved x-ray photoemission spectroscopy we show that the oxygen content of thin films increases with the film thickness, which indicates that the polar mismatch is avoided by the presence of oxygen vacancies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Misfit paradox on nucleation potency of MgO and MgAl{sub 2}O{sub 4} for Al

MgO and MgAl{sub 2}O{sub 4} are believed to be effective heterogeneous nuclei for Al based alloys due to their small lattice misfits with Al. However, there is a strong evidence to suggest that liquid Al reacts with MgO and MgAl{sub 2}O{sub 4} phases but the heterogeneous nucleation behavior of such phases is rarely discussed. In order to identify the nucleation mechanism of Al, under the interference of the chemical reaction, the heterogeneous nucleation process is systematically investigated through thermal analysis and high resolution transmission electron microscopy (HRTEM). The observed multi-nucleation interfaces (Al/MgO, Al/MgAl{sub 2}O{sub 4} and Al/Al{sub 2}O{sub 3}) and scattered experimental undercooling data indicate an independent multi-phase nucleation process in these systems. - Highlights: •Theoretical lattice misfit doesn’t always disclose nucleation potency. •The nucleation of liquid can be triggered by multi-nucleation interfaces. •An independent multi-agents nucleation was verified in the study.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multiphysics modeling of SOFC performance degradation caused by interface delamination and active layer cracking

In solid oxide device operation, delamination and cracking cause more catastrophic damage to cell life than other degradation mechanisms, leading to more rapid cell failure. The electrochemical performance degradation caused by electrode/electrolyte interface delamination and active layer cracking were investigated through in-house developed three-dimensional multiphysics simulations. Here the multiphysics simulations, fully calibrated against experimental datasets for button cells in a previous study, were extended to quantitatively investigate the effects of electrode/electrolyte interface delamination and active layer cracking. The simulated polarization curves and impedance behavior with various levels of delamination and cracking provided insights of the performance degradation. Furthermore, the local current distributions within the cell were analyzed for three different operating modes: constant voltage, constant current, and constant power. Finally, a practical strategy was proposed to mitigate the performance degradation in the realistic cell operations, extending overall cell lifetime.

08 HYDROGEN↗
DOE OSTI2021

New Insights into Secondary Organic Aerosol Formation at the Air–Liquid Interface

Air-liquid interfacial processing of volatile organic compound oxidation has been suggested as an important source of secondary organic aerosols. However, owing to the lack of techniques for in situ air-liquid interface analysis, the detailed interfacial mechanism remains speculative. To obviate this, the analysis of air-liquid interfacial reactions and the dynamics of glyoxal oxidation as a model volatile organic compound using in situ liquid synchrotron-based vacuum ultraviolet single photon ionization mass spectrometry enabled by the system for analysis at the liquid vacuum interface microreactor is reported. This approach allows for determination of reaction intermediates and oxidation products including polymers and oligomers at the air-liquid interface by mass spectral analysis and appearance energy measurements. Furthermore, an expanded reaction mechanism of photooxidation free radical induced reactions as a source of aqueous secondary organic aerosol formation is proposed based on these new results, suggesting that single photon ionization could be applied to provide unique insights into interfacial chemistry changing the earth atmospheric composition.

aqueous secondary organic aerosol, glyoxal, photoo↗
DOE OSTI2016

First Principle Estimation of Geochemically Important Transition Metal Oxide Properties: Structure and Dynamics of the Bulk, Surface and Mineral/Aqueous Fluid Interface

Reactions in the mineral surface/reservoir fluid interface control many geochemical processes such as the dissolution and growth of minerals (Yanina and Rosso 2008), heterogeneous oxidation/reduction (Hochella 1990, Brown 2001, Hochella, Lower et al. 2008, Navrotsky, Mazeina et al. 2008), and inorganic respiration (Newman 2010). Key minerals involved in these processes are the transition metal oxides and oxyhydroxides (e.g., hematite, Fe2O3, and goethite, FeOOH)(Brown, Henrich et al. 1999, Brown 2001, Hochella, Lower et al. 2008, Navrotsky, Mazeina et al. 2008). To interpret and predict these processes, it is necessary to have a high level of understanding of the interactions between the formations containing these minerals and their reservoir fluids. However, these are complicated chemical events occurring under a wide range of T, P, and X conditions and the interpretation is complicated by the highly heterogeneous nature of natural environments (Hochella 1990, Hochella, Lower et al. 2008, Navrotsky, Mazeina et al. 2008) and the electronic and structural complexity of the oxide materials involved(Cox 1992, Kotliar and Vollhardt 2004, Navrotsky, Mazeina et al. 2008). In addition, also because of the complexity of the minerals involved and the heterogeneous nature of natural systems, the direct observation of these reactions at the atomic level is experimentally extremely difficult. Theoretical simulations will provide important support for analysis of the geochemistry of the mineral surface/fluid region as well as provide essential tools to extrapolate laboratory measurements to the field environment.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Tuning giant anomalous Hall resistance ratio in perpendicular Hall balance

Anomalous Hall effect at room temperature in perpendicular Hall balance with a core structure of [Pt/Co]{sub 4}/NiO/[Co/Pt]{sub 4} has been tuned by functional CoO layers, where [Pt/Co]{sub 4} multilayers exhibit perpendicular magnetic anisotropy. A giant Hall resistance ratio up to 69 900% and saturation Hall resistance (R{sub S}{sup P}) up to 2590 mΩ were obtained in CoO/[Pt/Co]{sub 4}/NiO/[Co/Pt]{sub 4}/CoO system, which is 302% and 146% larger than that in the structure without CoO layers, respectively. Transmission electron microscopy shows highly textured [Co/Pt]{sub 4} multilayers and oxide layers with local epitaxial relations, indicating that the crystallographic structure has significant influence on spin dependent transport properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Thickness-dependent photoelectrochemical water splitting on ultrathin LaFeO 3 films grown on Nb:SrTiO 3

The performance of photoelectrodes can be modified by changing the material chemistry, geometry, and interface engineering. Specifically, nanoscale active layers can facilitate the collection of charge carriers. In heterostructure devices, the multiple material interfaces are particularly important, which at present are not well understood for oxides. Here, we report a detailed study of ultrathin (2-25 nm) LaFeO 3 films grown epitaxially on Nb-doped SrTiO 3 . The films exhibit thickness-dependence with sensitivity to less than 10 nm in both the through-plane charge transfer conductivity and in the potential-dependent photoresponse. Supplementing photoelectrochemical measurements with X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and electrochemical impedance spectroscopy, we construct a band model that accounts for this thickness dependence via a shifting valence-band offset at the film-substrate interface and the potential-dependent overlap of the depletion regions present at both the film-substrate and film-electrolyte interfaces. Lastly, these results illustrate the utility of using active layer thickness and film-substrate interactions to tune the performance of photoelectrodes, providing insight for the design of efficient heterostructure oxide photoelectrochemical devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

An efficient construction of nano-interfaces for excellent coking tolerance of cermet anodes

Solid oxide fuel cells (SOFCs) are promising energy conversion devices for the effective and convenient utilization of hydrocarbons (for example, methane) to electricity. However, the development of direct methane SOFCs is primarily hindered by the poor coking tolerance of the state-of-the-art Ni-based cermet anodes. Herein, we efficiently construct nano-interfaces in the anode by infiltrating a Ni 0.6 Y 0.064 Zr 0.336 O 2-δ (NYZ) catalyst onto the traditional Ni-based cermet anode to effectively enhance the coking tolerance. After being reduced in H 2 , Ni and Y 0.16 Zr 0.84 O 2-δ (YSZ) nanoparticles (NPs) are in situ formed on the surface of the Ni-YSZ substrate. The roughened anode demonstrates significantly improved fuel oxidation activity and coking tolerance, due likely to the formation of nano-interfaces. Specifically, when applied in the Ni-YSZ-based anode-supported SOFCs, a high peak power density of 1.785 W cm –2 and a stable operation of ~ 240 h with no observable degradation is achieved at 750 °C in nearly dry methane (3% H 2 O). Finally, a density functional theory study suggests that the excellent coking tolerance is attributed to the formation of OH species on Ni/YSZ nano-interfaces, which would further interact with intermediate carbon species to generate COH intermediates.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS2006

Oxidation Microstructure Studies of Reinforced Carbon/Carbon

Laboratory oxidation studies of reinforced carbon/carbon (RCC) are discussed with particular emphasis on the resulting microstructures. This study involves laboratory furnace (500-1500 C deg) and arc-jet exposures (1538 C deg) on various forms of RCC. RCC without oxidation protection oxidized at 800 and 1100 C deg exhibits pointed and reduced diameter fibers, due to preferential attack along the fiber edges. RCC with a SiC conversion coating exhibits limited attack of the carbon substrate at 500, 700 and 1500 C deg. However samples oxidized at 900, 1100, and 1300 C deg show small oxidation cavities at the SiC/carbon interface below through-thickness cracks in the SiC coating. These cavities have rough edges with denuded fibers and can be easily distinguished from cavities created in processing. Arc-jet tests at 1538 C deg show limited oxidation attack when the SiC coating and glass sealants are intact. When the SiC/sealant protection system is damaged, attack is extensive and proceeds through matrix cracks, creating denuded fibers on the edges of the cracks. Even at 1538 C deg, where diffusion control dominates, attack is non-uniform with fiber edges oxidizing in preference to the bulk fiber and matrix.

Jacobson, Nathan S.↗
DOE OSTI2024

Material exploration towards high quality factor microwave resonators

Niobium and aluminum have been widely used to realize superconducting resonators and qubits. However, the native oxide at the metal air interface limits the devices results. This layer is highly disordered, and it induces losses limiting the performances of the resonators or qubits. Recently, tantalum led to great improvement in qubit relaxation time. This improvement has been attributed to a thinner and less disordered oxide layer compared to Nb and Al. This study is aimed to limit the formation of the oxide layer, by the introduction of novel superconducting materials such as rhenium or by encapsulating the Nb surface with other superconducting materials such as Ta, Al, Re or other non-superconducting materials such as Au. To better understand the results, we are realizing these studies on coplanar waveguide resonators where the relation between surface losses and quality factor is clear. We are also analyzing different fabrication techniques to completely characterize our devices, linking material properties to the performances. In this work we are also varying the participation ratio of the devices in order to extract with higher fidelity and precision the losses introduced by the involved interfaces.

Crisa, F.↗
DOE OSTI2023

Surface termination control of charge transfer and band alignment across a semiconductor–crystalline-oxide heterojunction

Charge redistribution across heterojunctions has long been utilized to induce functional response in materials systems. Here we examine how the composition of the terminating surface affects charge transfer across a heterojunction consisting of Si and the crystalline complex oxide SrTiO 3 . Itinerant electrons in Si migrate across the interface toward the surface of SrTiO 3 due to surface depletion. The electron transfer in turn creates an electric field across the interface that modifies the interfacial dipole associated with bonding between SrTiO 3 and Si. The modification in the dipole leads to a change in band alignment, in which the conduction band of SrTiO 3 moves from being above the valence band of Si in energy, to below it. By capping the SrTiO 3 surface with ultrathin (≤ 1 nm) layers of BaO, SrO or TiO 2 , charge transfer across the interface can be weakened or inhibited. Ab initio modeling implicates the adsorption of oxygen associated with exposure to ambient conditions as driving the surface depletion in SrTiO 3 . In conclusion, the electronic coupling between the surface and buried interface expands the functionality of semiconductor-crystalline oxide heterojunctions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Investigation of Oxidation Mechanisms in HfS 2 and ZrS 2 via In Situ Electron Microscopy

Transition metal dichalcogenides (TMD) combine semiconducting properties with stability and are therefore widely studied for future microelectronic devices. However, applications require integration with a suitable dielectric at a planar, defect-free interface. For Hf- and Zr-based TMDs, the good dielectric properties of hafnia and zirconia imply that direct oxidation is a promising strategy, provided that a high-quality interface and suitable oxide morphology can be formed. Here, in this study, we investigate HfS 2 and ZrS 2 oxidation, aiming to understand pathways toward planar oxide layer formation and the mechanisms that determine the characteristics of the semiconductor/dielectric interface. We use conventional and environmental transmission electron microscopy to reveal changes in morphology and composition of the TMDs under different gaseous environments. We show that oxidation at ambient conditions causes compositional heterogeneities, with local replacement of S by O in both materials. Thermal oxidation causes desulfurization and formation of a smooth but defective oxide layer. In contrast, plasma oxidation appears the best-suited to forming a controlled TMD/dielectric interface with a smooth oxide layer and without major defects. These results provide insight into the opportunities available from HfS 2 and ZrS 2 through oxidation and suggest a materials processing strategy for electronic device fabrication.

HfS2↗
DOE OSTI2016

Fast Interconversion of Hydrogen Bonding at the Hematite (001)–Liquid Water Interface

The interface between transition-metal oxides and aqueous solutions plays an important role in biogeochemistry and photoelectrochemistry, but the atomistic structure is often elusive. Here we report on the surface geometry, solvation structure, and thermal fluctuations of the hydrogen bonding network at the hematite (001)–water interface as obtained from hybrid density functional theory-based molecular dynamics. We find that the protons terminating the surface form binary patterns by either pointing in-plane or out-of-plane. The patterns exist for about 1 ps and spontaneously interconvert in an ultrafast, solvent-driven process within 50 fs. This results in only about half of the terminating protons pointing toward the solvent and being acidic. The lifetimes of all hydrogen bonds formed at the interface are shorter than those in pure liquid water. The solvation structure reported herein forms the basis for a better fundamental understanding of electron transfer coupled to proton transfer reactions at this important interface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Dual-function lignin monomers enable high-performance graphene electrodes via interface confinement and proton transfer enhancement

Graphene oxide (GO)-based energy storage faces dual bottlenecks: unsustainable reduction methods and sluggish proton transfer kinetics. Here, we introduce a groundbreaking green strategy using lignin-derived vanillyl alcohol (VA) as a dual-function monomer to simultaneously address these challenges. By thermally annealing GO/VA films at mild temperatures (<100 °C), VA triggers an interface-confined reduction of GO while self-polymerizing into redox-active oligomers (P-VA) that intercalate between graphene layers. This dual role-reducing agent and proton highway enables a 3D conductive network with minimized graphene restacking, abundant redox sites, and rapid H + transport pathways. Density Functional Theory (DFT) reveals how P-VA optimizes proton dynamics, while the resulting rGO-P-VA4-T90 electrode achieves a record volumetric capacitance of 311.1F/cm 3 (777.8F/cm 2 ) and retains 87.8 % capacity after 10,000 cycles. Flexible solid-state supercapacitors deliver 94.2 μWh/cm 2 energy density at 63.8 μW/cm 2 , rivaling state-of-the-art devices. Furthermore, this work redefines sustainable graphene engineering, merging biomass valorization with high-performance energy storage in a scalable, eco-friendly paradigm.

Graphene oxide reduction↗
DOE OSTI2020

Microstructure Experiments-Enabled MARMOT Simulations of SiC/SiC-based Accident Tolerant Nuclear Fuel System

We have undertaken an experimental-computational project that addresses a few key technology gaps associated with the use of SiC/SiC composites for light water reactor fuel cladding. Two principal endeavors in this project are to assess the irradiation-induced microstructural changes and swelling in SiC/SiC composites, and to characterize and model the porous oxide surface layer (when exposed to steam) along SiC recession that is detrimental to the clad integrity under accident conditions. The project tasks are: (i) ion irradiation and characterization (University of Tennessee, Knoxville), (ii) mechanical tests and analysis (University of South Carolina), (iii) steam exposure tests (Oak Ridge National Laboratory), (iv) electron microscopy and spectroscopic characterization (NC State University), (v) x-ray microscopy and reconstruction (University of South Carolina and NC State University), (vi) phase field modeling and simulations (NC State University and Idaho National Laboratory). The effects of 10 MeV Au ion irradiation at 350°C on the microstructure evolution in SiC/SiC composites are investigated at doses up to 400 displacements per atom (dpa) at the University of Tennessee, Knoxville. Atomic force microscopy and optical profilometry reveal irradiation induced axial and radial shrinkage of the fibers for doses greater than 10 dpa. Based on detailed electron microscopy characterization, the primary cause of the fiber shrinkage is attributed to irradiation-induced loss of carbon packets. Additionally, the multilayer PyC interface is observed to portray high resistance to irradiation damage. The mechanical response and failure mechanisms of un-irradiated samples is also assessed through loading tests and X-ray imaging at the University of South Carolina. Steam exposure tests are performed at the Oak Ridge National Laboratory in a facility that represents a reactor pressure vessel under a loss-of-coolant-accident scenario. The samples that are analyzed methodically in this report are tested for 32/31 hours at 1200°C with a velocity of 0.25 cm/s for the pressures: 0.1 MPa, 0.45 MPa, 0.92 MPa and 1.38 MPa. Scanning/transmission electron microscopy analysis conducted at the NC State University (NCSU) shows that the oxide layer thickness increases with the steam pressure. While the oxide layer is crystalline (α- cristobalite) for the pressures 0.45 MPa, 0.92 MPa and 1.38 MPa, the layer is amorphous at 0.1 MPa. Results from Raman spectroscopy have also confirmed the formation of α-cristobalite phase of SiO₂. The abrupt increase in the integrated Raman intensity ratio between steam pressures 0.1 and 0.45 MPa suggests the onset of accelerated crystallization. Non-destructive three dimensional X-ray microscopy/tomography (XCT) and computational image processing techniques are employed by the University of South Carolina to probe the porous oxidation features on SiC samples at varying pressures. Interestingly, most pores are observed to be located away from the surface as well as the oxide-SiC interface. The average oxide layer thickness assessed from the XCT analysis is seen to be in excellent agreement with the values determined through scanning electron microscopy analysis for the highest pressures where the oxide layer is relatively more uniform. A phase-field model developed by the NC State University and Idaho National Laboratory for simulating oxidation of SiC by steam captures the paralinear kinetics of SiC oxidation with a high degree of fidelity. Results from quasi-one-dimensional and two dimensional simulations show that the pores with oxidizing species lead to a higher volatilization rate. These simulations indicate that the enhanced apparent volatilization rates at higher pressures observed in experiments can be rationalized by the increased volatilization from the pores. The project team has also successfully developed the capability to import images from experiments for realistic evolution of the oxidizing microstructure.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗