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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Engineering microstructure to improve coercivity of bulk MnBi magnet

MnBi is a candidate material for high-temperature magnets because of its increasing coercivity with increasing temperatures up to 255 °C. However, most efforts in fabricating bulk MnBi magnets have run into the problem of preserving the coercivity (H cj) of its feedstock powders. About 70% of powder’s H cj would be lost during the densification process. Our micromagnetic modeling shows that the coercivity mechanism of the MnBi bulk magnet is controlled by nucleation of the reversal magnetization domains, and the large H cj loss that occurred during the powder consolidation process can be attributed to the inter-grain magnetic coupling. To attain a high H cj , the grains in the MnBi bulk magnet must be separated with a non-magnetic grain boundary phase (GBP). To validate this GBP hypothesis, we engineered MnBi bulk magnets with two different types of GBP. The first type of GBP was created in-situ by precipitating excessive Bi from the grains; the second type was created ex-situ by coating silicates on the feedstock powders before the consolidation. While both GBP work, the ex-situ approach resulted in a better H cj due to a more uniform GBP distribution. We report the H cj loss was reduced from 70% to 15%, and the (BH)max of a warm sintered bulk magnet reached 8.9 MGOe.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Bulk magnetic hardening in Sm(Fe,V) 12 alloys

Cast Sm-Fe-V magnets with the tetragonal crystal structure of the ThMn 12 type were prepared with high coercivity through a two-step annealing at 775°C and then at 825°C. The annealing processing used allowed us for the first time to successfully produce a large amount of non-magnetic Sm-rich grain-boundary phase in Sm-Fe-V cast ingots. As a result, the sample with composition Sm 11.1 Fe 75.8 V 13.1 showed the record-high coercivity (6.66 kOe) after annealing at 775°C for 72 h and then 825°C for 2 h. Furthermore, this coercivity, achieved without the use of powder metallurgy, has nearly doubled compared to the previously reported highest value of 3.70 kOe in a cast SmFe 10 V 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2017

On α' precipitate composition in thermally annealed and neutron-irradiated Fe- 9-18Cr alloys [On α' composition in thermally annealed and neutron-irradiated Fe- 9-18Cr alloys]

Ferritic-martensitic steels are a leading candidate for many nuclear energy applications. However, precipitation of nanoscale a’ precipitates during thermal aging at temperatures above 450 °C, or during neutron irradiation at lower temperatures, makes these Fe-Cr steels susceptible to embrittlement. To complement the existing literature, a series of Fe-9 to 18 Cr alloys were neutron-irradiated at temperatures between 320 and 455 °C up to fluences of 20 dpa. In addition, post-irradiation annealing treatments at 500 and 600 °C were performed on the neutron-irradiated Fe-18 Cr alloy to validate the a-a’ phase boundaries. The microstructures were characterized using atom probe tomography and the results were analyzed in light of the existing literature. In conclusion, under neutron irradiation and thermal annealing, the measured a’ concentrations ranged from ~81 to 96 at.% Cr, which were discussed in terms of temperature, precipitate size, technique artefacts, and, possibly, cascade ballistic mixing.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Corrosion behavior of ferritic FeCrAl alloys in simulated BWR normal water chemistry

Ferritic iron-chromium-aluminum (FeCrAl) alloys with varying Cr content were subjected to in-situ irradiation-corrosion with energetic protons or electron beams in pure water with various oxygen concentrations. Oxide microstructure and composition were characterized to compare the corrosion under irradiation with the thermal corrosion in the same water conditions. The dominant effect seems to be the production of H 2 O 2 at the surface by the intense proton and electron beams. The corrosion potential of FeCrAl under BWR-NWC condition is somewhat above the Cr 2 O 3 /CrO 4 2- phase boundary, oxidizing the Cr(III) to Cr(VI) in the outer part of the film, but with some Cr(III) remaining in the interior of the oxide. The beam increases the corrosion potential, significantly reducing Cr(III) content throughout the oxide. Finally, the crystallites on the surface, which form by re-precipitation from solution, do not contain Cr because at low potential Cr(III) is not soluble, and at high potential Cr(VI) is quite soluble.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Extended reaction zone of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 cathode for solid oxide fuel cell

The oxygen reduction reaction at the cathode of solid oxide fuel cell (SOFC) is a complicated process which involves the interaction of oxygen molecules, electrons, and oxygen ions. Therefore, it can only proceed at locations where gas, electronic conductor, and an oxygen ion conductor meet. Although the extension of the reaction zone beyond the traditional so-called triple-phase-boundary (TPB) is widely accepted for a mixed ionically and electronically conductive cathode, work in this area has yet to reach a consensus on how far the reaction zone can be extended. In this study, anode-supported fuel cells with a variety of LSCF cathode thicknesses were fabricated and tested in two cathode environments, flowing oxygen and flowing air. In flowing oxygen, the cell performance increased with LSCF cathode thickness over the entire range investigated (from 5 to 33 μm). In flowing air, the cell performance also increased with the LSCF cathode thickness from 5 to 13 μm, but then remained almost constant with further increase in cathode thickness. In flowing oxygen, since there was no concentration polarization related to oxygen diffusion, the polarization resistance of oxygen reduction decreased with the LSCF cathode thickness because of the increased number of reaction sites. A linear relationship was established between the reciprocal of the polarization resistance and the cathode thickness, which was explained by a model developed for aqueous gas diffusion electrodes.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

A new composite cathode for intermediate temperature solid oxide fuel cells with zirconia-based electrolytes

Improving the electrocatalytic activity of electrode materials is vitally important to achieve practically meaningful performance for intermediate temperature solid oxide fuel cells (IT-SOFCs). Here the present work develops a composite cathode consisting of an electronic conductor Sr-doped LaMnO 3 (LSM) and an ionic conductor Y- and Ce- co-doped Bi 2 O 3 (BYC7). BYC7 is an excellent oxide-ion conductor, exhibiting a high and stable ionic conductivity of 0.008 S cm -1 at 500 °C. The polarization resistance of LSM-BYC7 cathode in a symmetrical cell with doped ZrO 2 as electrolyte varies from 5.76 at 500 °C to 0.25 Ω cm 2 at 650 °C. The surface diffusion and charge transfer at the triple phase boundaries are the rate determining steps based on the dependence of polarization resistance on partial pressure of oxygen. The maximum power density of a ZrO 2 -based anode-supported cell with LSM-BYC7 composite cathode is 56.4, 154.6, 327.9, and 451.0 mW cm-2 at 500, 550, 600, and 650 °C respectively. AC impedance analysis reveals that the performance of IT-SOFC prepared in this study is actually limited by the anode, not by LSM-BYC7 cathode.

25 ENERGY STORAGE↗
DOE OSTI2019

Electrochemical performance and stability of SrTi 0.3 Fe 0.6 Co 0.1 O 3-δ infiltrated La 0.8 Sr 0.2 MnO 3 Zr 0.92 Y 0.16 O 2-δ oxygen electrodes for intermediate-temperature solid oxide electrochemical cells

We report that the La 0.8 Sr 0.2 MnO 3 -Zr 0.92 Y 0.16 O 2-δ (LSM-YSZ) composite is the most widely used oxygen electrode for solid oxide electrochemical cells (SOCs). However, operating temperatures > 700 degrees C are required for good performance since oxygen reactions are limitied to three-phase boundaries (TPBs) because of poor ionic conductivity of LSM. Furthermore, LSM-YSZ electrodes typically delaminate during electrolysis operation leading to cell degradation. One strategy to improve SOCs with LSM-YSZ electrodes is to infiltrate a mixed ionically and electronically conducting (MIEC) material that promotes oxygen exchange. However, infiltrated materials have a nano-scale structure that may not be stable under SOC operating temperatures. Here, we report results on the infiltration of SrTi 0.3 Fe 0.6 Co 0.1 O 3-δ (STFC), a recently reported high performance MIEC, into LSM-YSZ to improve its electrochemical performance and stability at intermediate temperatures. The infiltrated STFC enhances LSM-YSZ and cell performance, typically yielding a decrease in electrode polarization resistance by a factor > 3 times, resulting in an increase in fuel cell maximum power density and electrolysis current density (at 1.3 V) by a factor > 2 times. Perhaps more significantly, the infiltrated electrodes show good performance stability, with suppression of electrode delamination during electrolysis and no evidence of coarsening or segregation induced degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A simple convertible electrolyzer in membraneless and membrane-based modes for understanding water splitting mechanism

State-of-the-art membrane-based electrolyzers such as proton exchange membrane electrolyzer cells, are costly, susceptible to degradation, and time-consuming for electrode evaluation and triple-phase boundary electrochemical reaction studies. Here, a simple convertible electrolyzer in membraneless and membrane-based modes is proposed. For the first time, this enables comprehensive investigations of water splitting with pure water, acidic and alkaline electrolytes in one cell. With the simple electrolyzer and high-speed visualization system, the influences of flow rate, electrolytes, concentration, and Nafion membrane on the oxygen evolution reactions (OERs), hydrogen evolution reactions (HERs) and electrolyzer performance are comprehensively investigated. Visualization results reveal that water splitting only occurred at the edge between the electrode and the Nafion membrane in pure water. However, they occurred on the whole electrode surface in alkaline and acidic electrolytes, indicating easily tunable reaction sites with the convertible electrolyzer. This demonstrates the feasibility of using the simple convertible electrolyzer for understanding the water splitting mechanism. The relation between electrolyte thickness and resistances with different electrolytes is also quantified. This research provides an insight for optimizing electrochemical devices while delivering an inexpensive and fast way for electrode evaluations and electrochemical reaction studies.

25 ENERGY STORAGE↗
DOE OSTI2025

Microstructure-based modeling of inner oxygen pressure in solid oxide electrolysis cells: Analysis of electrode delamination and mitigation

One major degradation mechanism during long-term operation of solid oxide electrolysis cells (SOECs) is delamination of oxygen electrodes (OEs). The driving force for the electrode delamination could be the generated high inner oxygen pressure near the electrode-electrolyte interface during operation. However, the effects of transport properties and electrode thickness on the inner oxygen partial pressure are not well understood. Here a microstructure-based electrochemical model, which includes the conduction of electrons and oxygen ions coupled with Butler-Volmer-type chemical reactions at triple-phase-boundaries (TPBs), is employed to investigate the oxygen pressure in lanthanum strontium manganate (LSM)-based SOECs. The model is applied to both two-dimensional (2D) prototype microstructures and three-dimensional (3D) realistic microstructures, and the oxygen pressure is analyzed as a function of transport properties and electrode thickness under both potentiostatic and galvanostatic operations. The simulation results suggest strategies to suppress electrode delamination. The simulation results are compared to an analytical solution, and the discrepancies are attributed to the Butler-Volmer-type kinetics included in the microstructure-based model.

25 ENERGY STORAGE↗
DOE OSTI2011

Ternary rare-earth zinc arsenides REZn{sub 1-x}As{sub 2} (RE=La-Nd, Sm)

The ternary rare-earth zinc arsenides REZn{sub 1-x}As{sub 2} (RE=La-Nd, Sm) were prepared by reaction of the elements at 800 deg. C. Single-crystal and powder X-ray diffraction analysis revealed a defect SrZnBi{sub 2}-type average structure for the La member (Pearson symbol tI16, space group I4/mmm, Z=4; a=4.0770(9) A, c=20.533(5) A), in contrast to defect HfCuSi{sub 2}-type average structures for the remaining RE members (Pearson symbol tP8, space group P4/nmm, Z=2; a=4.0298(5)-3.9520(4) A, c=10.222(1)-10.099(1) A in the progression from Ce to Sm). The homogeneity range is not appreciable (estimated to be narrower than 0.6<1-x<0.7 in SmZn{sub 1-x}As{sub 2}) and the formula REZn{sub 0.67}As{sub 2} likely represents the Zn-rich phase boundary. The Ce-Nd members are Curie-Weiss paramagnets. LaZn{sub 0.67}As{sub 2} shows activated behavior in its electrical resistivity, whereas SmZn{sub 0.67}As{sub 2} exhibits anomalies in its temperature dependence of the electrical resistivity. - Graphical abstract: LaZn{sub 1-x}As{sub 2} adopts a SrZnBi{sub 2}-type structure whereas the remaining members of the REZn{sub 1-x}As{sub 2} series (RE=Ce-Nd, Sm) adopt a HfCuSi{sub 2}-type structure. Highlights: > REZn{sub 1-x}As{sub 2} adopts SrZnBi{sub 2}-type (RE=La) or HfCuSi{sub 2}-type (RE=Ce-Nd, Sm) structures. > Trends in RE substitution and local distortion around Zn-centered tetrahedra can be rationalized by geometrical factors. > Zn vacancies occur to reduce Zn-As and As-As antibonding interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

High temperature behavior of zirconium germanates

The high temperature behavior of zirconium germanates ZrGeO₄ and Zr₃GeO₈ up to 2300 °C has been studied using the original photoemission thermal analysis technique with the comprehensive physicochemical study of solid and gaseous intermediate and final products. The two-stage process of incongruent sublimation of GeO₂ was established and the phase boundary of the homogeneity range for ZrGeO₄ and Zr₃GeO₈ were deduced from the thermal analysis, X-ray diffraction and Raman spectroscopy studies. A high tendency to sintering of the final ZrO₂ product is discussed. - Graphical abstract: The decomposition of zirconium germanates leads to the formation of gaseous GeO₂ and solid sintered ZrO₂ and occurs via two stages with the formation of intermediate ZrO₂-rich solid solution. Highlights: •Thermal behavior of ZrGeO₄ and Zr₃GeO₈ was studied using the original thermal analysis technique in wide temperature range. •The decomposition occurs via two stages with the formation of intermediate ZrO₂-rich solid solution. •The decomposition of zirconium germanates leads to the formation of gaseous GeO₂ and solid sintered ZrO₂. •The temperature of decomposition is strongly depended on the total gas pressure.

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

Precipitation behavior of stainless steel weld overlay cladding exposed to a long-term thermal aging

Highlights: • Silicide phase formation with G-phase was first time to be observed. • Precipitation behavior discrepancy existed at different locations of ferrite phase. • G-phase and silicide phase formed along dislocations and within ferrite matrix. • Heterogeneous distribution of elements induced silicide phase formation. - Abstract: Thermal aging behavior of stainless steel weld overlay cladding aged at 400 °C for 10,000 h was investigated. The results showed that the precipitates along the dislocation and within ferrite matrix contained the face-centered cubic structural G-phase and silicide phase. Silicide phase, supposed to be (Fe, Mn){sub 3}Si phase, preferred to form with G-phase along the dislocations and within ferrite matrix. Silicide phase showed a cube-on-cube relationship with ferrite phase and G-phase. Heterogeneous distribution of elements within Ni-Mn-Si clusters was responsible for silicide phase formation during thermal aging process, and the corresponding precipitation behavior discrepancy at different forming sites (dislocations, ferrite matrix and phase boundary) was discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Temperature dependence of deformation mechanisms and tensile strength of a new Ni-Fe-base superalloy

Highlights: • A new Ni-Fe-base superalloy with low cost has been developed. • The new alloy has excellent creep-rupture and tensile properties. • Its yield strength is insensitive to temperature below 700 °C. • The main tensile deformation mechanism of the alloy is APB shearing below 700 °C. - Abstract: After a standard heat treatment, the influence of temperature on the tensile strength and corresponding deformation mechanisms of a new Ni-Fe-base superalloy with a low γ' volume fraction are investigated in the temperature region between room temperature and 800 °C. Experimental results show that the yield strength of the experimental alloy is temperature independent below 700 °C, whereas, above the temperature, its yield strength decreases dramatically with temperature. Analyses of micromechanisms controlling the deformation behavior reveal that plastic deformation is accomplished mainly by anti-phase boundary (APB)-coupled dislocations shearing through γ' precipitates below 700 °C, while, above the temperature, the primary deformation mechanism changes from APB shearing to stacking fault shearing and then to precipitate bypassing via Orowan looping together with cross-slip and local climb of dislocations. Based on the experimental results, it is deemed that the transition in the operative strengthening mechanism with temperature accounts for the variation of the yield strength of the experimental alloy with temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of fabrication on microstructure and heat affected zone width in weldments of nuclear reactor pressure vessel steel

Advanced manufacturing routes such as electron beam welding and powder metallurgy with hot isostatic pressing are increasingly used across energy and aerospace industries, where the reliable prediction of weld behavior and heat affected zone (HAZ) evolution is critical. This study examines how fabrication routes and post-weld heat treatments influence phase distribution, crystallite size, microstrain, and dislocation density in nuclear reactor pressure vessel steels using synchrotron X-ray diffraction (SXRD). Retained austenite occurs only in samples that did not undergo austenitization, whereas an austenitizing heat treatment fully eliminates retained austenite and produces a more uniform microstructure across the weldment in terms of phase fraction, dislocation density, and microstrain. The Rosenthal solution underestimates the HAZ width for powder metallurgy samples. A newly proposed modified Rosenthal solution, reducing density by accounting for porosity, matches the SXRD-measured HAZ width with a 0.65% error. Structure–property correlations reveal that dislocation density correlates strongly with nanohardness in homogenous microstructures, while in heterogenous weldments nanohardness is further influenced by the presence of dissimilar phase boundaries. These findings provide new insight into the thermal and microstructural response of powder metallurgy fabricated steels and offer a framework for optimizing welding procedures and heat treatments in advanced manufacturing applications.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Both electric field and temperature independent behavior of piezoelectric property of Pb(Ni 1/3 Nb 2/3 )O 3 –PbTiO 3

The temperature stability of electromechanical properties is an important issue of major concern for the design of actuators. In this paper, temperature dependence of ferroelectric properties have been investigated in the (1 - x)Pb(Ni 1/3 Nb 2/3 )O 3– xPbTiO 3 (x = 0.30–0.38) solid solutions. Interestingly, the unipolar strain in the composition of x = 0.38 shows a good linear relationship with increasing electric field, and the large-signal d 33 is independent with increasing temperature from room temperature to 100 °C. Furthermore, it also exhibits a very high piezoelectric coefficient d 33 = 450 pC/N near the morphotropic phase boundary. All above indicates the present system of (1 - x)Pb(Ni 1/3 Nb 2/3 )O 3– xPbTiO 3 may be a kind of potential application for precisely controlling actuators.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Nanometric modulations of the magnetic structure of the element Nd

The rare earth neodymium arguably exhibits the most complex magnetic ordering and series of magnetic phase transitions of the elements. Here we report the results of small-angle neutron scattering (SANS) measurements as a function of temperature and applied magnetic field to study magnetic correlations on nanometer length scales in Nd. We support these results with additional neutron diffraction, thermodynamic and synchrotron x-ray measurements. The SANS measurements reveal the presence of modulation vectors characterizing the ordered spin configuration which exhibit changes in magnitude and direction that are phase dependent. Between 5.9 and 7.6 K an additional modulation vector is observed with magnitude Q = 0.12 Å -1 . This scattering appears to originate from order of the Nd layers which contain a center of inversion. Tracking this modulation vector as a function of magnetic field indicates a phase boundary at ≈1 T. The modulation vectors observed in this study establish the presence of nanometer length scale spin textures which are likely stabilized by frustrated Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions.

36 MATERIALS SCIENCE↗