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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Nitrification in a zeoponic substrate

Clinoptilolite is a zeolite mineral with high cation exchange capacity used in zeoponic substrates that have been proposed as a solid medium for growing plants or as a fertilizer material. The kinetics of nitrification has not been measured for NH4+ saturated zeoponic substrate. Experiments were conducted to evaluate the production of NO2- and NO3-, and nitrifier populations in zeoponic substrates. Small columns were filled with zeoponic substrate inoculated with a commercial inoculum or soil enrichment culture of nitrifying bacteria. In addition to column studies, a growth chamber study was conducted to evaluate the kinetics of nitrification in zeoponic substrates used to grow radishes (Raphanus sativus L.). The zeoponic substrate provided a readily available source of NH4+, and nitrifying bacteria were active in the substrate. Ammonium oxidation rates in column studies ranged from 5 to 10 micrograms N g-1 substrate h-1, and NO2- oxidation rates were 2 to 9.5 micrograms N g-1 substrate h-1. Rates determined from the growth chamber study were approximately 1.2 micrograms N g-1 substrate h-1. Quantities of NH4+ oxidized to NO2- and NO3- in inoculated zeoponic substrate were in excess of plant up-take. Acidification as a result of NH4+ oxidation resulted in a pH decline, and the zeoponic substrate showed limited buffering capacity.

NASA Discipline Life Support Systems↗
DOE OSTI2026

Corrosion of 316 SS in direct contact with Zircaloy-4 in repository relevant conditions

The effects of interfacial contact between 316 stainless steel (316 SS) waste canister and spent fuel cladding material (Zircaloy-4) in case of water intrusion into a deep geological repository are investigated. Hydrothermal corrosion experiments of 316 SS and Zircaloy-4 in direct contact were performed at elevated temperatures in MilliQ water and simulated Mont Terri groundwater. Hematite, magnetite, chromite, and baddeleyite form as secondary phases. pH of the Mont Terri solution increases with corrosion duration and magnetite forms preferentially instead of hematite. Thermodynamic modeling shows that iron oxidation in 316 SS controls the pH and redox potential of the aqueous environment and is in good agreement with experimental Mont Terri results, showing that experimental Mont Terri results trend to equilibrium. All oxides except hematite are predicted to exist at thermodynamic equilibrium based on calculations, implying that experimentally formed hematite will be reduced or transformed to magnetite at equilibrium. The thermodynamically predicted chromite was observed to form only at the interface where 316 SS was in contact with Zircaloy-4 at 250°C, showing that contact with Zircaloy-4 seems to accelerate the 316 SS corrosion to thermodynamic equilibrium. Finally, Mont Terri groundwater readily trends towards thermodynamic equilibrium, leading to a pH and redox buffered system that is dominated by iron in solution coming from the accelerated corrosion of 316 SS caused by Zircaloy-4 contact.

316 stainless steel↗
DOE OSTI2022

Oxide Two‐Dimensional Electron Gas with High Mobility at Room‐Temperature

Abstract The prospect of 2‐dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide‐bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high‐electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO 3 ‐based heterostructures. Here, 2DEG formation at the LaScO 3 /BaSnO 3 (LSO/BSO) interface with a room‐temperature mobility of 60 cm 2 V −1 s −1 at a carrier concentration of 1.7 × 10 13 cm –2 is reported. This is an order of magnitude higher mobility at room temperature than achieved in SrTiO 3 ‐based 2DEGs. This is achieved by combining a thick BSO buffer layer with an ex situ high‐temperature treatment, which not only reduces the dislocation density but also produces a SnO 2 ‐terminated atomically flat surface, followed by the growth of an overlying BSO/LSO interface. Using weak beam dark‐field transmission electron microscopy imaging and in‐line electron holography technique, a reduction of the threading dislocation density is revealed, and direct evidence for the spatial confinement of a 2DEG at the BSO/LSO interface is provided. This work opens a new pathway to explore the exciting physics of stannate‐based 2DEGs at application‐relevant temperatures for oxide nanoelectronics.

2-dimensional electron gas↗
DOE OSTI2023

Gas-mediated trace element incorporation into rhyolite-hosted topaz: A synchrotron microbeam XAS study

Magmatic gas exsolving during late-stage cooling of shallow magmas has been considered an important facilitator of low-pressure alteration and metal transport. However, the chemical properties of such gas, particularly its metal transport mechanisms and capacity, remain elusive. Trace elements in minerals produced by gas-mediated surface reaction or precipitation from gas capture details of gas composition and reaction pathways. However, interpretation of mineral trace element contents is dependent on understanding crystallographic controls on gas/mineral partitioning. Here, this work investigates the structural accommodation of As, Mn, Ga, Ge, Fe, and Ti in vapor-deposited topaz of vesicular topaz rhyolite from the Thomas Range, Utah, through single-crystal synchrotron microbeam X-ray techniques on picogram quantities of those trace elements. X-ray absorption near edge structure (XANES) data indicates that these elements are incorporated into topaz as As 5+ , Fe 3+ , Mn 3+ , Ti 4+ , Ga 3+ , and Ge 4+ . Extended X-ray absorption fine structure (EXAFS) analysis for these trace elements, compared to EXAFS of structural Al and Si, reveals that As 5+ and Ge 4+ are incorporated directly into the tetrahedral site of the topaz structure, with the octahedral site accommodating Mn 3+ , Fe 3+ , Ga 3+ , and Ti 4+ . For As 5+ and Fe 3+ , the structural impact of substitution extends to at least second neighbors (other elements were only resolvable to first neighbors). Further interpretation of the EXAFS results suggests that the substitution of Ti 4+ results in increased distortion of the octahedral site, while the other trace elements induce more uniform expansion correlating in magnitude to their ionic radius. Comparison of quantified X-ray fluorescence (XRF) data for two topaz crystals from this rhyolite reveals variable trace element concentrations for As 5+ , Fe 3+ , Ga 3+ , and Ti 4+ , reflective of a source gas undersaturated in these trace elements changing in concentration over the period of topaz deposition. The identical Ge 4+ content of the two topaz crystals suggests that Ge 4+ in the gas was buffered by the growth of another Ge 4+ -bearing phase, such as quartz. The very low Mn 3+ content in the topaz crystals does not reflect the abundance of Mn 3+ in the gas (saturation of Mn is evidenced by coexisting bixbyite). Instead, it suggests a strong Jahn-Teller inhibitory effect to the substitution of Mn 3+ for Al 3+ in the distorted octahedral site of topaz. It is proposed that exsolution of an HF-enriched gas from cooling rhyolitic magma led to local scouring of Al, Si, and trace metals from the magma. Once topaz crystals nucleated, self-catalyzed reactions that recycle HF led to continued growth of topaz.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of Shear Strength Assumptions on BISON Debonding Simulations

Accurately predicting the thermomechanical response of buffer–IPyC debonding in TRISO fuel particles requires reliable mechanical property inputs for each coating layer, particularly the normal and shear strengths that influence interlayer delamination and stress concentrations. Micro tensile testing of AGR-2 fuel particles provided experimentally measured normal strengths for the buffer, IPyC, and buffer–IPyC interface; however, shear strength was not measured. As a result, BISON simulations of interface debonding must rely on assumed shear strength values, typically estimated as 20–40% of the measured ultimate tensile strength. This study evaluates how these assumed shear strength values influence cohesive zone model (CZM) predictions of buffer–IPyC separation in AGR 2 TRISO particles. Using micro tensile data from three AGR 2 compacts (2 1 3, 5 1 3, and 6 3 3), BISON simulations were performed with multiple shear strength assumptions to quantify their effect on radial and tangential stress evolution, debonding, and gap propagation. The results show that shear strength is a high sensitivity parameter: increasing the assumed shear strength significantly alters the stress distribution at the buffer–IPyC junction, shifts the predicted debonding location, and changes the extent of partial gap formation. While normal strength controls the initiation of interface separation, shear strength strongly influences the mode mixity of the failure process and the resulting stress concentrations transmitted to the IPyC and SiC layers. These findings highlight a critical gap in current TRISO mechanical characterization. Without experimentally measured shear strength, BISON simulations must rely on approximations that introduce uncertainty into predictions of coating layer integrity and fission product barrier performance. Future fuel qualification campaigns should therefore consider measurement of shear strength at the interlayer interfaces to reduce model uncertainty and improve the fidelity of TRISO fuel performance simulations.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Bifacial CdTe Solar Cells with Copper Chromium Oxide Back-Buffer Layer

Bifacial solar cells have the potential to maintain energy output higher than monofacial devices under unfavorable weather conditions. A transparent back-buffer layer which can passivate the interface and improve the minority carrier lifetime is critical in CdTe-based bifacial devices. Herein, solution-processed Cu x Cr y O z as a promising back-buffer for CdTe/CdS solar cells is demonstrated. The carrier lifetimes measured at the front and back of the device are 31.2 and 3.1 ns, respectively, which correspond to an increase of ≈38% and 138%, respectively, compared to the reference device. This dramatic improvement in lifetime results in a 100% increase in short-circuit current measured with backside illumination. The best bifacial device has efficiencies 7.6% and 12.5%, respectively, from back and front illumination, yielding a bifaciality factor of 0.60.

14 SOLAR ENERGY↗
DOE OSTI2024

Optical and microstructural studies of erbium-doped TiO 2 thin films on silicon, SrTiO 3 , and sapphire

Rare-earth ion doped oxide thin films integrated on silicon substrates provide a route toward scalable, chip-scale platforms for quantum coherent devices. Erbium-doped TiO 2 is an attractive candidate: the Er 3+ optical transition is compatible with C-band optical fiber communications, while TiO 2 is an insulating dielectric compatible with silicon process technology. Through structural and optical studies of Er-doped TiO 2 thin films grown via molecular beam deposition on silicon, SrTiO 3 , and sapphire substrates, we have explored the impact of polycrystallinity and microstructure on the optical properties of the Er emission. Comparing polycrystalline TiO 2 (rutile)/Si with single-crystalline TiO 2 (rutile)/r-sapphire and polycrystalline TiO 2 (anatase)/Si with single-crystalline TiO 2 (anatase)/SrTiO 3 , we observe that the inhomogeneous linewidth (Γ inh ) of the most prominent peak in the Er spectrum (the Y 1 –Z 1 transition, 1520 and 1533 nm in rutile and anatase TiO 2 ) is significantly narrower in the polycrystalline case. This implies a relative insensitivity to extended structural defects and grain boundaries in such films (as opposed to, e.g., point defects). We show that the growth of an undoped, underlying TiO 2 buffer on Si can reduce Γ inh by a factor of 4–5. Expectedly, Γ inh also reduces with decreasing Er concentrations: we observe a ∼2 order of magnitude reduction from ∼1000 ppm Er to ∼10 ppm Er. Γ inh then gets limited to a residual value of ∼5 GHz that is insensitive to further reduction in the Er concentration. Based upon the above results, we argue that the optical properties in these thin films are limited by the presence of high “grown-in” point defect concentrations.

Chemical elements↗
DOE OSTI2024

Development of “GaSb-on-silicon” metamorphic substrates for optoelectronic device growth

The epitaxial development and characterization of metamorphic “GaSb-on-silicon” buffers as substrates for antimonide devices is presented. The approach involves the growth of a spontaneously and fully relaxed GaSb metamorphic buffer in a primary epitaxial reactor, and use of the resulting “GaSb-on-silicon” wafer to grow subsequent layers in a secondary epitaxial reactor. The buffer growth involves four steps—silicon substrate preparation for oxide removal, nucleation of AlSb on silicon, growth of the GaSb buffer, and finally capping of the buffer to prevent oxidation. This approach on miscut silicon substrates leads to a buffer with negligible antiphase domain density. The growth of this buffer is based on inducing interfacial misfit dislocations between an AlSb nucleation layer and the underlying silicon substrate, which results in a fully relaxed GaSb buffer. A 1 μm thick GaSb layer buffer grown on silicon has ~9.2 × 10 7 dislocations/cm 2 . The complete lack of strain in the epitaxial structure allows subsequent growths to be accurately lattice matched, thus making the approach ideal for use as a substrate. Here we characterize the GaSb-on-silicon wafer using high-resolution x-ray diffraction and transmission electron microscopy. The concept’s feasibility is demonstrated by growing interband cascade light emitting devices on the GaSb-on-silicon wafer. The performance of the resulting LEDs on silicon approaches that of counterparts grown lattice matched on GaSb.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electrogenerated Chemiluminescence of Near-Infrared-Emitting CdSe@CdSe Nanorods in Aqueous Solution

Electrogenerated chemiluminescence (ECL) was observed from TOPO-capped CdSe@CdSe nanorods (NRs) depositing on a metal electrode in phosphate buffer solution (PBS). Two ECL peaks at -1.05 and -1.33 V in pH 9.2, 0.1 M PBS were found under cyclic voltammetric conditions. Cyclic voltammetry of this solution displayed no distinctive features, on the other hand, light emission was observed during cyclic potential scans. Additionally, the photoluminescence (PL) spectrum showed an emission maximum at 692 nm. The spectrum of ECL possesses one peak which coincides very well with the PL spectrum of the nanorods film. The mechanism for ECL peaks was proposed. Electron transfer reactions between charged nanorods and molecular redox-active coreactants such as dissolved oxygen and H2O2 or between positively and negatively charged nanorods occurred that led to electron and hole annihilation, producing light.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanostructured ZnO-Based Electrochemical Sensor with Anionic Surfactant for the Electroanalysis of Trimethoprim

In this research, detection of trimethoprim (TMP) was carried out using a nanostructured zinc oxide nanoparticle-modified carbon paste electrode (ZnO/CPE) with an anionic surfactant and sodium dodecyl sulphate (SDS) with the help of voltametric techniques. The electrochemical nature of TMP was studied in 0.2 M pH 3.0 phosphate-buffer solution (PBS). The developed electrode displayed the highest peak current compared to nascent CPE. Effects of variation in different parameters, such as pH, immersion time, scan rate, and concentration, were investigated. The electrode process of TMP was irreversible and diffusion controlled with two electrons transferred. The effective concentration range (8.0 × 10 -7 M–1.0 × 10 -5 M) of TMP was obtained by varying the concentration with a lower limit of detection obtained to be 2.58 × 10 -8 M. In addition, this approach was effectively employed in the detection of TMP in pharmaceutical dosages and samples of urine with the excellent recovery data, suggesting the potency of the developed electrode in clinical and pharmaceutical sample analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Integration of a new Cryogenic Liquefier into the IB-1 Cryogenic Test Facility

aThe increase over the last years of the testing activities related to superconducting quantum materials, SRF cavities for the PIP-II and the LCLS-II projects, as well as superconducting magnets for the HL-LHC project and Fusion research activities, has required the addition of a new Helium cryogenic plant into the existing IB-1 Industrial Cryogenic Test Facility. The new cryogenic plant is composed of a cryogenic liquefier (Cold Box) able to provide up to 340 L/h, a 4kL Dewar and two Mycom compressors providing up to 120 g/s. AL-AT (Air Liquide Advanced Technologies) has taken part of this project by designing and manufacturing the cryogenic liquefier. This new cryogenic plant is connected through a cryogenic distribution system to a 10 kL Dewar, which is part of the existing cryogenic test facility, itself composed of another Cold Box and a Sullair compressor. The new cryogenic plant has two main operating modes: one allows to transfer liquid helium at 1.7 bar between the two Dewars, the other allows to transfer supercritical Helium at 2 bar or more between the new Cold Box and the 10 kL Dewar. The entire industrial cryogenic facility is handled by a common Inventory Control System, composed of three regulatory valves, and 9 tanks giving a total buffer volume of more than 1000 m3. This paper presents the technical features of the new Helium cryogenic plant, as well as the main results of the liquefier commissioning phase and details of the helium transfer between the two dewars, making the connection between the cryogenic plants at the IB-1 Industrial Cryogenic Test Facility.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2007

Triple and Quadruple Junctions Thermophotovoltaic Devices Lattice Matched to InP

Thermophotovoltaic (TPV) conversion of IR radiation emanating from a radioisotope heat source is under consideration for deep space exploration. Ideally, for radiator temperatures of interest, the TPV cell must convert efficiently photons in the 0.4-0.7 eV spectral range. Best experimental data for single junction cells are obtained for lattice-mismatched 0.55 eV InGaAs based devices. It was suggested, that a tandem InGaAs based TPV cell made by monolithically combining two or more lattice mismatched InGaAs subcells on InP would result in a sizeable efficiency improvement. However, from a practical standpoint the implementation of more than two subcells with lattice mismatch systems will require extremely thick graded layers (defect filtering systems) to accommodate the lattice mismatch between the sub-cells and could detrimentally affect the recycling of the unused IR energy to the emitter. A buffer structure, consisting of various InPAs layers, is incorporated to accommodate the lattice mismatch between the high and low bandgap subcells. There are evidences that the presence of the buffer structure may generate defects, which could extend down to the underlying InGaAs layer. The unusual large band gap lowering observed in GaAs(1-x)N(x) with low nitrogen fraction [1] has sparked a new interest in the development of dilute nitrogen containing III-V semiconductors for long-wavelength optoelectronic devices (e.g. IR lasers, detector, solar cells) [2-7]. Lattice matched Ga1-yInyNxAs1-x on InP has recently been investigated for the potential use in the mid-infrared device applications [8], and it could be a strong candidate for the applications in TPV devices. This novel quaternary alloy allows the tuning of the band gap from 1.42 eV to below 1 eV on GaAs and band gap as low as 0.6eV when strained to InP, but it has its own limitations. To achieve such a low band gap using the quaternary Ga1-yInyNxAs1-x, either it needs to be strained on InP, which creates further complications due to the creation of defects and short life of the device or to introduce high content of indium, which again is found problematic due to the difficulties in diluting nitrogen in the presence of high indium [9]. An availability of material of proper band gap and lattice matching on InP are important issues for the development of TPV devices to perform better. To address those issues, recently we have shown that by adjusting the thickness of individual sublayers and the nitrogen composition, strain balanced GaAs(1-x)N(x)/InAs(1-y)N(y) superlattice can be designed to be both lattice matched to InP and have an effective bandgap in the desirable 0.4- 0.7eV range [10,11]. Theoretically the already reduced band gap of GaAs(1-x)N(x), due to the nitrogen effects, can be further reduced by subjecting it to a biaxial tensile strain, for example, by fabricating pseudomorphically strained layers on commonly available InP substrates. While such an approach in principle could allow access to smaller band gap (longer wavelength), only a few atomic monolayers of the material can be grown due to the large lattice mismatch between GaAs(1-x)N(x) and InP (approx.3.8-4.8 % for x<0.05, 300K). This limitation can be avoided using the principle of strain balancing [12], by introducing the alternating layers of InAs(1-y)N(y) with opposite strain (approx.2.4-3.1% for x<0.05, 300K) in combination with GaAs(1-x)N(x). Therefore, even an infinite pseudomorphically strained superlattice thickness can be realized from a sequence of GaAs(1-x)N(x) and InAs(1-y)N(y) layers if the thickness of each layer is kept below the threshold for its lattice relaxation

Bhusal, L.↗
NASA NTRS2015

Jarosite in Gale Crater, Mars: The Importance of Temporal and Spatial Variability and Implications for Habitiability

The Curiosity rover has recently found evidence for small amounts of jarosite, a ferric sulfate, in the Pahrump Hills region at the base of Aeolis Mons (Mount Sharp), Gale crater. While jarosite has been described previously at other locations on Mars, including several sites at Meridiani Planum (explored by the Opportunity rover; and Mawrth Vallis (by remote MRO-CRISM observations; this is the first identification in Gale. Jarosite is interpreted to be a mineral indicator of acidic conditions (pH less than 4; on Earth, it is most commonly found in acid rock-drainage or acid sulfate soil environments. However, jarosite has also been described from a number of terrestrial environments where widespread acidic conditions are not prevalent. As a case study, we describe here an occurrence of sedimentary pyrite nodules that have been variably oxidized in situ to gypsum, schwertmannite, K-/Na-jarosite and iron oxides in a polar desert environment on Devon Island, Nunavut, Canada. Remarkably, these nodules occur in loosely consolidated carbonate sediments, which would have required a higher pH environment at their time of formation and deposition. Thus, acidic conditions may only exist at a small (sub-cm) scale or in a restricted temporal window in an otherwise well-buffered environment. On Devon Island, the jarosite occurs in the most oxidized nodules and is never associated directly with pyrite. Schwertmannite, a metastable iron oxyhydroxysulfate that can form at pH higher than that required for jarosite, occurs in association with partially oxidized pyrite. The paragenetic sequence observed here suggests initial formation of schwertmannite and late-stage precipitation of jarosite in restricted micro-environments, possibly forming via transformation of an amorphous schwertmannite-like phase. While the carbonate environment on Devon Island differs significantly from that of Gale crater, i.e., where we find predominantly basaltic sedimentary rocks, this terrestrial analog provides insight into the significance of jarosite with respect to habitability. For example, the variable abundance of jarosite on Mars and possibly in Gale crater points to potentially localized conditions favorable for jarosite formation. Interestingly, small amounts of sulfide minerals have also been detected by Curiosity at Yellowknife Bay; oxidation of sulfide minerals at Pahrump could explain the presence of small amounts of jarosite. The iron-rich rocks at Pahrump may also represent relatively altered basaltic sediments, or they could be sediments that were altered further by a fluid with a distinct, possibly more acidic, composition. In addition, the abundance of iron-rich amorphous material in Gale rocks allows for the possibility that pre-cursor, iron-bearing phases transform to jarosite post-depositionally. Thus, the occurrence of jarosite at Pahrump could reflect changing paleoenvironmental conditions, though continuing study of its context and textural relationships should provide a fuller understanding of the significance of this mineral to past fluid compositions and past habitability at Gale crater.

Leveille, R. J.↗
NASA NTRS2017

The Role of Carbon in Core Formation Under Highly Reducing Conditions With Implications for the Planet Mercury

Results from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft have shown elevated abundances of carbon on the surface of Mercury. Furthermore, the X-Ray Spectrometer on board MESSENGER measured elevated abundances of sulfur and low abundances of iron, suggesting the planet's oxygen fugacity (fO2) is several log10 units below the Iron-Wüstite (IW) buffer. Similar to the role of other volatiles (e.g. sulfur) on highly reducing planetary bodies, carbon is expected to behave differently than it would under higher fO2. As discussed by Nittler et al. and Hauck et al., under such highly reducing conditions, the majority of the iron partitions into the core. On Mercury, this resulted in a relatively large core and a thin mantle. Using a composition similar to the largest volcanic field on the planet (the northern volcanic plains), Vander Kaaden and McCubbin conducted sink-float experiments to determine the density of melts and minerals on Mercury. They showed that graphite would be the only buoyant mineral in a mercurian magma ocean. Therefore, Vander Kaaden and McCubbin proposed a possible primary flotation crust on the planet composed of graphite. Concurrently, Peplowski et al. used GRS data from MESSENGER to show an average northern hemisphere abundance of C on the planet of 1.4 +/- 0.9 wt%. However, as this result was only at the one-sigma detection limit, possible carbon abundances at the three-sigma detection limit for Mercury range from 0 to 4.1 wt% carbon. Additionally, Murchie et al. investigated the possible darkening agent on Mercury and concluded that coarse-grained graphite could darken high reflectance plains to the low reflectance material. To further test the possibility of elevated abundances of carbon in Mercury's crust, Peplowski et al. used the low-altitude MESSENGER data to show that carbon is the only material consistent with both the visible to near-infrared spectra and the neutron measurements of low reflectance material on Mercury, confirming that C is the primary darkening agent on Mercury. Confirmation of carbon on the planet prompts many questions regarding the role of carbon during the differentiation and evolution of Mercury. Given the elevated abundances of both S and C on Mercury's surface, it begs the question, what is the core composition of the planet? This study seeks to understand the impact of C as a light element on potential core compositions on Mercury.

Vander Kaaden, Kathleen E..↗
DOE OSTI2023

Controlling the Magneto-Optical Response in Ultrathin Films of EuO 1– x via Interface Engineering with Ferroelectric BaTi 2 O 5

Utilizing pulsed laser deposition, a film of EuO 1–x was deposited onto a Si(001) substrate with MgO buffer and compared to the same heterostructure with an additional BaTi 2 O 5 thin film on top of the EuO 1–x surface. X-ray diffraction (XRD) indicates the films crystallize into a preferred EuO(111) orientation; it also reveals the clear presence of EuSi 2 , which suggests Si or Eu diffuses across the MgO buffer layer. EuO 1–x films exhibit a ferromagnetic (FM) signature and temperature-dependent exchange bias, indicated by MOKE measurements, suggesting the presence of a magnetic order well above the EuO Curie temperature with possible origins in charge carrier density near the interface. In comparison, an antiferromagnetic character persists well above the EuO Curie temperature of 69 K and the enhanced Curie temperature of 150 K for BaTi 2 O 5 films grown on the EuO 1–x films. Furthermore, the antiferromagnetic behavior is not seen in thicker EuO 1–x thin films when integrated with other ferroelectric (FE) phases of the BaO–TiO 2 system, suggesting an origin in the perturbed charge population at the BaTi 2 O 5 /EuO 1–x interface.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Enhanced NO, CO and C 3 H 6 conversion on Pt/Pd catalysts: Impact of oxygen storage material and catalyst architecture

Simultaneous conversion of NO, CO and C 3 H 6 under stoichiometric conditions was carried out on washcoated monoliths containing oxygen storage material (OSM)-promoted mixed Platinum group metals (PGM: Pt(95 %)/Pd(5 %)), to evaluate OSM promotion and to identify the best architecture. The studied OSMs include ceria-zirconia (Ce 0.3 Zr 0.7 O 2 ; CZO) and mixed metal oxide spinel (Mn 0.5 Fe 2.5 O 4 ; MFO). PGM supported directly on the OSM was found to be the best design for CZO, leading to a ~70 °C simultaneous decrease in the light-off temperature (T 80 ; feed temperature giving 80 % conversion) for NO, CO and C 3 H 6 conversion compared to the alumina-supported PGM. Close coupling between the PGM and CZO is responsible for the activity promotion. In contrast, a dual-layer architecture (top PGM layer, bottom MFO layer) outperformed the MFO-supported PGM catalyst. The dual-layer PGM-MFO catalyst decreased the T 80 by ~50 °C for NO, CO and C 3 H 6 conversion compared to the PGM-only catalyst. Enhancement obtained with the dual-layer PGM-MFO architecture relies on a direct catalytic contribution from the spinel. During lean/rich modulation the addition of CZO or spinel helps to mitigate the detrimental impact of modulation on NO, CO and C 3 H 6 conversion above 400 °C. The data suggest that both CZO and MFO can buffer lean/rich modulation but exhibit preference to different reductants; CZO-supported PGM and dual-layer PGM-MFO show no conversion decrease during modulation for CO or C 3 H 6 modulation, respectively. Dynamic oxygen storage capacity (DOSC) measurements show that the spinel exhibits ~10 times higher DOSC than CZO for both CO and C 3 H 6 reductants. Both CO and C 3 H 6 are equally effective reductants for the MFO but CO is better for CZO and PGM-deposited CZO. The study provides useful insight into benefits of OSM and provides guidance for optimization of the multi-component PGM + OSM catalyst composition and architecture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

High-Performance SiC/SiC Ceramic Composite Systems Developed for 1315 C (2400 F) Engine Components

As structural materials for hot-section components in advanced aerospace and land-based gas turbine engines, silicon carbide (SiC) ceramic matrix composites reinforced by high performance SiC fibers offer a variety of performance advantages over current bill-of-materials, such as nickel-based superalloys. These advantages are based on the SiC/SiC composites displaying higher temperature capability for a given structural load, lower density (approximately 30- to 50-percent metal density), and lower thermal expansion. These properties should, in turn, result in many important engine benefits, such as reduced component cooling air requirements, simpler component design, reduced support structure weight, improved fuel efficiency, reduced emissions, higher blade frequencies, reduced blade clearances, and higher thrust. Under the NASA Ultra-Efficient Engine Technology (UEET) Project, much progress has been made at the NASA Glenn Research Center in identifying and optimizing two highperformance SiC/SiC composite systems. The table compares typical properties of oxide/oxide panels and SiC/SiC panels formed by the random stacking of balanced 0 degrees/90 degrees fabric pieces reinforced by the indicated fiber types. The Glenn SiC/SiC systems A and B (shaded area of the table) were reinforced by the Sylramic-iBN SiC fiber, which was produced at Glenn by thermal treatment of the commercial Sylramic SiC fiber (Dow Corning, Midland, MI; ref. 2). The treatment process (1) removes boron from the Sylramic fiber, thereby improving fiber creep, rupture, and oxidation resistance and (2) allows the boron to react with nitrogen to form a thin in situ grown BN coating on the fiber surface, thereby providing an oxidation-resistant buffer layer between contacting fibers in the fabric and the final composite. The fabric stacks for all SiC/SiC panels were provided to GE Power Systems Composites for chemical vapor infiltration of Glenn designed BN fiber coatings and conventional SiC matrices. Composite panels with system B were heat treated at Glenn, and the pores that remained open were filled by silicon melt infiltration (MI). Panels with system A and the other SiC/SiC systems were not heat treated, and remaining open pores in these systems were filled with SiC slurry and silicon MI.

DiCarlo, James A.↗
DOE OSTI2025

Microstructural Characterization of AGR-2 TRISO-coated Particle Buffer, IPyC, and Buffer-IPyC Interfaces

Investigating the microstructural, mechanical, and chemical behaviors of Tristructural Isotropic (TRISO) fuel particles is vital for its qualification and use in advanced reactors. Central to the study of TRISO particles is understanding the silicon carbide (SiC) layer's ability to confine fission products, with failure mechanisms linked to chemical degradation following mechanical degradation of the buffer and IPyC layers. Research has been done to quantify the micro-tensile properties of the buffer, inner pyrolytic carbon (IPyC), and buffer-IPyC interlayer regions and their interactions within both irradiated and un-irradiated TRISO particles. Techniques such as atom probe tomography (APT) and transmission electron microscopy (TEM) have also been deployed to examine microstructural defects and fission product distribution in detail. The goal is to understand layer delamination, establish connections between microstructure and mechanical attributes, and inform computational predictions of fuel performance. This work may help refine predictive models of TRISO fuel behavior and facilitating its certification for use in advanced reactors.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗