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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Composition for fuel cell electrode

In some examples, a fuel cell including an anode; electrolyte; and cathode separated from the anode by the electrolyte, wherein the cathode includes a Pr-nickelate based material with (Pr.sub.1-xA x ) n+1 (Ni 1-y B y ) n O 3 n+1+.delta. as a general formula, where n is 1 as an integer, A is an A-site dopant including of a metal of a group formed by one or more lanthanides, and B is a B-site dopant including of a metal of a group formed by one or more transition metals, wherein the A and B-site dopants are provided such that there is an increase in phase-stability and reduction in degradation of the Pr-nickelate based material, and A is at least one metal cation of lanthanides, La, Nd, Sm, or Gd, B is at least one metal cation of transition metals, Cu, Co, Mn, Zn, or Cr, where: 0<x<1, and 0<y.ltoreq.0.4.

25 ENERGY STORAGE↗
DOE OSTI2020

Phase Formation in Nuclear Fallout

An understanding of the physical and chemical process occurring in a nuclear explosion enables predictions of the effects of nuclear weapons, including characteristics of radioactive fallout resulting from the explosion. Near-surface nuclear explosions are of particular interest due to the potential for significant amounts of environmental material to interact with and alter the physical and chemical behavior of the fireball. Such interactions have the potential to affect the distribution of radioactive species in the fireball and subsequently become incorporated into fallout through a process known as radiochemical fractionation. Studying variations in fallout formed in different historical testing environments allows us to understand the influence of local environments on fallout formation processes. In particular, constraining variations in thermal evolution and redox conditions during the evolution of the fireball can be useful to understanding how sensitive fallout radiochemical fractionation may be to the local explosion environment. However, untangling these conditions in complex, multicomponent fallout is a challenge. Here we present one method of constraining and interpreting fallout formation conditions by relating computationally derived phase stability predictions to observations in historic fallout. Development of such approaches will help improve physics-based models of fallout formation and radiochemical fractionation in complex, near surface nuclear detonations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High Entropy Alloys: Irradiation

High entropy alloys (HEAs) have been considered as structural materials for nuclear applications due to their promising mechanical properties and radiation resistance. For this purpose, irradiation-induced defect evolution and microstructure change have been characterized to evaluate the irradiation performance of different HEAs. This article reviews recent advances in understanding the irradiation response of HEAs, including the effect of disordered states on the defect energy landscape and defect evolution, irradiation-induced microstructure changes, void swelling, phase stability, mechanical properties under irradiation, as well as the He irradiation effects.

Zhao, Shijun↗
DOE OSTI2016

Dependencies of α' Embrittlement in Neutron-Irradiated Model Fe-Cr-Al Alloys

Fe-Cr-Al alloys are currently under consideration as accident tolerant fuel cladding materials due to their superior performance in high temperature steam environments when compared to Zr-based alloys. These alloys have also shown promise for other nuclear reactor and power production applications due to their excellent high-temperature oxidation and corrosion resistance. However, like other high-Cr ferritic Fe-based alloys, these alloys are prone to radiation-induced hardening and embrittlement due to the precipitation of a Cr-rich-α' phase under typical LWR operating conditions. Additionally, the kinetics of this phase separation have been shown to be accelerated by irradiation. Current research efforts are focused on developing an ideal candidate Fe-Cr-Al alloy composition and microstructure that retains its exceptional environmental compatibility while maintaining adequate mechanical performance over the duration of its operational lifetime. The current work investigates both the composition and dose dependencies of α' phase precipitation, as it can be the primary contributor to radiation-induced hardening and embrittlement in these alloys. The comprehensive analysis of phase stability in irradiated Fe-Cr-Al alloys provided by this work is a key step forward in assessing the radiation tolerance and overall viability of these materials for accident tolerant fuel cladding applications. Additional work is underway to assess radiation-induced dislocation loop formation in these specimens and correlate the morphologies of both the dislocation loop and α' precipitate morphologies to the results of mechanical testing campaigns in order to fully develop the structure-property relationships for this class of alloys. Completion of this work will allow for a comprehensive evaluation of the suitability of Fe-Cr-Al alloys for nuclear applications and result in the recommendation of an optimized candidate alloy ideally suited for LWR environments. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2025

PROCESS-STRUCTURE-PROPERTY RELATIONSHIPS IN LASER POWDER BED FUSION PRODUCED 17-4 PH STEEL

Laser powder bed fusion (LPBF) is a metal additive manufacturing method that produces non-traditional microstructures as a result of the rapid solidification and thermal cycling inherent to the process. When using LPBF-produced material in application, these unique microstructures challenge the applicability of well developed mechanical property databases achieved by conventional heat treatments. For wider adoption of this technology, a more holistic understanding is necessary on how process attributes develop material structure, which dictate mechanical properties. This dissertation explores the process– structure–property relationships in LPBF 17-4 PH steel through systematic evaluation of atmospheric processing and heat treatment effects on microstructure and mechanical performance. Specimens were fabricated under controlled build environments, subjected to a range of solutionizing, homogenizing, and aging treatments, and characterized using optical microscopy, electron back scatter diffraction (EBSD), and X-ray diffraction (XRD) to quantify phase evolution. Tensile testing was performed to directly link heat treatment pathway and nitrogen absorption to mechanical performance. This work demonstrates where conventional heat treatment standards are applicable to LPBF 17-4 PH steel and where modifications are required. By directly correlating phase stability, nitrogen effects, and tensile response, this work provides practical guidelines for tailoring post-processing strategies. These findings underscore that successful application of LPBF 17-4 PH steel requires explicit consideration of both build environment and post-processing. By linking processing conditions to microstructure and performance, this work advances understanding of critical variables that govern reliability of additively manufactured precipitation-hardened stainless steels in demanding applications.

Brown, Benjamin [Kansas City National Security Cam↗
DOE OSTI2025

Final report on assessment of molten salt corrosion testing of unirradiated and ion irradiated advanced manufactured high entropy alloys

Generation IV reactors and future fusion reactor designs have led to more demanding materials performance requirements due to their increased operating temperatures, corrosive coolants, and increased radiation doses compared to the current light-water reactor fleet. Among the innovative nuclear technologies under development, molten salt reactors stand out for their potential to offer superior fuel utilization, intrinsic safety characteristics, and economic viability. Of the proposed Generation IV designs, the gas fast reactor operates at 450 to 850°C and the molten salt reactor operates at 565 to 850°C, with the molten salt reactor design needing molten salt corrosion resistant materials [1, 2]. These increased temperatures and more extreme corrosion environments necessitate higher material performance, such as creep strength, radiation-tolerant microstructures, corrosion resistance, and high-temperature tensile properties. Hastelloy-N, a nickel-based alloy with additions of molybdenum and chromium, has been successfully employed to contain molten fluoride salt at temperatures up to 705°C. However, Hastelloy-N becomes embrittled upon neutron irradiation, primarily due to the accumulation of helium produced by (n,a) transmutation reactions. Furthermore, the corrosive nature of molten fluoride and chloride salts presents a formidable challenge, as these salts can react with and dissolve alloying elements such as Cr, Mo, and Fe, leading to selective leaching, loss of protective oxide layers, and accelerated degradation. High entropy alloys (HEAs) and refractory high entropy alloys (RHEAs) have emerged as a prominent area of interest, due to their ability to achieve tailored chemical compositions for specific applications. Unlike conventional alloys, HEAs are characterized by having multiple principal elements in equimolar or near equimolar ratios, leading to an unconventional alloying strategy [3]. This alloying strategy is believed to promote unique properties, such as single-phase stabilization of chemically compatible elements, lattice distortion effects due to atomic radius differences, and proposed sluggish diffusion effects. For extreme-environment applications, RHEAs have garnered much research interest because of the possibility of creating relatively ductile materials that can operate in extremely high-temperature environments, beyond the operating temperatures where other Ni-based superalloys begin to lose strength [4-6]. Idaho National Laboratory (INL) initiated a joint international effort with the Czech Republic to explore the feasibility of manufacturing HEAs for high-temperature nuclear applications using advanced manufacturing. This effort was funded at INL by the United States Department of Energy's Office of Nuclear Energy under the Advanced Reactor Technologies and Advanced Materials and Manufacturing Technologies (AMMT) Program. The HEAs were specifically designed for the corrosive and irradiation environments experienced in gas-cooled fast reactors, molten salt reactors, and fusion power. These alloys have been manufactured by multiple processes to determine the impact of manufacturing processes on the performance of the alloys in corrosive and irradiation environments. Preliminary molten salt corrosion testing showed that equimolar MoNbTiV and MoNbTi alloys exhibit exceptional performance, with arc-melted variants demonstrating only minimal degradation after 1000 hours of exposure to molten chloride salt at 700°C. Conversely, Nb2TiVZr2 showed significant molten salt corrosion susceptibility and microstructural instability during high-temperature molten salt exposures, and was, therefore deemed unfit for molten salt reactor applications. The MoNbTiV, MoNbTi, and Nb2TiVZr2 alloys were further evaluated through ion irradiation experiments conducted at the Michigan Ion Beam Laboratory at the University of Michigan. The microstructural stability and the evolution of irradiation-induced defects were characterized to assess the irradiation resistance of each of these alloys.

36 - MATERIALS SCIENCE↗
DOE OSTI2017

Enhanced Hydrothermal Stability and Catalytic Activity of LaxZryOz Mixed Oxides for the Ketonization of Acetic Acid in the Aqueous Condensed Phase

Common ketonization catalysts such as ZrO2, CeO2, and TiO2-based catalysts have been reported to lose surface area, undergo phase transformation, and lose catalytic activity when utilized in the condensed aqueous phase. In this work, we synthesized a series of LaxZryOz mixed-metal oxides with different La:Zr atomic ratios with the goal of enhancing the catalytic activity and stability for the ketonization of acetic acid in condensed aqueous media at 568 K. We synthesized a hydrothermally stable LaxZryOz mixed-metal oxide catalyst with ketonization activity360 and 40 times more active than La2O3 and ZrO2, respectively. Catalyst characterization techniques suggest that the enhanced stability of the LaxZryOz catalysts is observed with the formation of a phase isomorphic with tetragonal ZrO2. DRIFT spectroscopy measurements indicated the enhanced catalytic activity of LaxZryOz catalysts correlated with greater acetic acid surface population in the presence of H2O versus pure ZrO2.

ketonization, deoxygenation, carboxylic acid, acet↗
DOE OSTI2016

Stabilization of metastable phases in hafnia owing to surface energy effects

The recent empirical observation of ferroelectricity in hafnia is rather surprising since all of its known ground-state phases are nonpolar. In this letter, we show that finite size effects, relevant under experimental conditions, may themselves lead to this unexpected phenomenon due to stabilization of metastable polar phase(s). Using surface energies computed from first principles, we determine the thermodynamic stability of a parallelepiped shaped particle constructed from various low energy nonpolar and polar phases of hafnia. We find that at small dimensions, surface effects may stabilize either one of the polar phases or the nonpolar tetragonal phase (the parent phase of the polar phases), suggesting a possible explanation of the ferroelectric behavior observed in pure hafnia films. These results also explain the stabilization of the metastable tetragonal phase in nanoparticles of zirconia, the twin oxide of hafnia. While a comprehensive understanding of the origins of ferroelectricity in hafnia will require inclusion of other relevant factors (such as strain and dopants), this work highlights the importance of finite size effects as a possible key factor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Large-Signal Stability of Phase-Balanced Equilibria in Single-Phase Grid-Forming Inverter Systems

This article explores the setup where large numbers of single-phase grid-forming inverters with droop control across distribution networks self-organize into a stable and balanced system with 120° phase offsets across aggregates in the absence of balanced three-phase generating resources or external communication. A suite of circuit- and system-theoretic notions are leveraged to derive a dynamical model for phase-angle differences across aggregates of inverters connected in the three phases. Focusing on this model, large-signal stability is established and the region of attraction of the phase-balanced equilibria is determined with the aid of a Lyapunov function. Experimental validation for a bench-top prototype network is included to support the analytical developments. Altogether, the effort supports the vision of facilitating balanced operation of distribution networks with grid-forming inverters during service disruptions at the bulk transmission network.

Droop control↗
NASA NTRS1991

Influence of mass diffusion on the stability of thermophoretic growth of a solid from the vapor phase

The stability of solid planar growth from a binary vapor phase with a condensing species dilute in a carrier gas is examined when the ratio of depositing to carrier species molecular mass is large and the main diffusive transport mechanism is thermal diffusion. It is shown that a deformation of the solid-gas interface induces a deformation of the gas phase isotherms that increases the thermal gradients and thereby the local mass deposition rate at the crests and reduces them at the valleys. The initial surface deformation is enhanced by the modified deposition rates in the absence of appreciable Fick/Brownian diffusion and interfacial energy effects.

Castillo, J. L.↗
DOE OSTI2015

Phase formation, thermal stability and magnetic moment of cobalt nitride thin films

Cobalt nitride (Co-N) thin films prepared using a reactive magnetron sputtering process are studied in this work. During the thin film deposition process, the relative nitrogen gas flow (R{sub N{sub 2}}) was varied. As R{sub N{sub 2}} increases, Co(N), Co{sub 4}N, Co{sub 3}N and CoN phases are formed. An incremental increase in R{sub N{sub 2}}, after emergence of Co{sub 4}N phase at R{sub N{sub 2}} = 10%, results in a linear increase of the lattice constant (a) of Co{sub 4}N. For R{sub N{sub 2}} = 30%, a maximizes and becomes comparable to its theoretical value. An expansion in a of Co{sub 4}N, results in an enhancement of the magnetic moment, to the extent that it becomes even larger than pure Co. Such larger than pure metal magnetic moment for tetra-metal nitrides (M{sub 4}N) have been theoretically predicted. Incorporation of N atoms in M{sub 4}N configuration results in an expansion of a (relative to pure metal) and enhances the itinerary of conduction band electrons leading to larger than pure metal magnetic moment for M{sub 4}N compounds. Though a higher (than pure Fe) magnetic moment for Fe{sub 4}N thin films has been evidenced experimentally, higher (than pure Co) magnetic moment is evidenced in this work.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Predicting the stability of surface phases of molybdenum selenides

The selenization of molybdenum might become an important step in the production of nanostructures based on the layered compound MoSe{sub 2}. It is already technologically relevant for the production of thin film chalcopyrite solar cells. However, the control of the process is still very poor, due to the lack of basic knowledge of the surface thermodynamics of the system. Here, we present a theoretical study on the stability of surface adlayers of Se on the Mo(110) surface, predicting surface patterns and their stability range in terms of temperature and selenium partial pressure. Our results, based on density functional theory, show that the attainable Se coverages range from 1/4 to 3/4 of a monolayer for systems in equilibrium with a gas formed of Se molecules. We provide simulated scanning tunneling microscopy images to help the experimental characterization of adsorbed surface patterns.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Impact of CuInP 2 S 6 –metal interfaces on the stabilization of polar phases and polarization switching

The multifunctionality of two-dimensional ferroelectric CuInP 2 S 6 (CIPS) arises from the existence of multiple polar phases combined with a high ionic conductivity that facilitates polarization switching in unusual ways. The van der Waals (vdW) layered structure provides ultrathin flakes and ideal interfaces to integrate with other materials for microelectronics and neuromorphic elements. However, device integration necessitates metal contacts to read, write, or transmit signals. In this work, we find that different types of metal–CIPS interfaces strongly impact the stabilization of specific polar phases and the field-induced transitions between the polarization states. Cu electrodes initially suppress the piezoresponse, whereas, at CIPS–Ag interfaces, the electromechanical signal is increased. Under electric fields, the Cu electrodes, Ag electrodes and surrounding CIPS surfaces can show distinct switching behavior as different phases and polarization orientations are stabilized. These findings highlight that metal–CIPS interfaces provide the opportunity to optimize functional material properties.

Ferroelectrics and multiferroics↗
DOE OSTI2025

Strain Effects in SrHfO 3 Films Grown by Hybrid Molecular Beam Epitaxy

Perovskite oxide heterostructures host a large number of interesting phenomena such as ferroelectricity, which are often driven by octahedral distortions in the crystal that may induce polarization. SrHfO 3 (SHO) is a perovskite oxide with a pseudocubic lattice parameter of 4.08 Å that previous density functional theory (DFT) calculations suggest can be stabilized in a ferroelectric P4mm phase when stabilized with sufficient compressive strain. Additionally, it is insulating and possesses a large band gap and a high dielectric constant, making it an ideal candidate for oxide electronic devices. Here, to test the viability of epitaxial strain as a driver of ferroic phase transitions, SHO films were grown by hybrid molecular beam epitaxy (hMBE) with a tetrakis(ethylmethylamino)hafnium(IV) source on GdScO 3 and TbScO 3 substrates. Strained SHO phases were characterized using X-ray diffraction, X-ray absorption spectroscopy, and scanning transmission electron microscopy to determine the space group of the strained films, with the results compared to those of DFT-optimized models of phase stability versus strain. Contrary to past reports, we find that compressively strained SrHfO 3 undergoes octahedral tilt distortions without associated ferroelectric polarization and most likely takes on the I4/mcm phase with the a 0 a 0 c – tilt pattern.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗