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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Comparison of chromium poisoning between lanthanum strontium manganite and lanthanum strontium ferrite composite cathodes in solid oxide fuel cells

Degradation mechanisms of chromium poisoning have been extensively investigated for last two decades on various cathode materials for solid oxide fuel cells. While most researchers used half-cell experiments to investigate the effects of chromium impurities, this paper compares the degradation phenomena of LSM-YSZ and LSF-GDC cathodes in full cells under different operating conditions, namely polarized current density and humidity over the cathode. Under cathodic load, performance degradation of LSF-GDC cathode is significantly less than that of LSM-YSZ cathode. Most interestingly, under humidified air condition, LSF-based cell hardly experiences performance degradation while LSM-based cell shows a catastrophic degradation. Cr deposition in LSM-based cells occurs mainly near the electrolyte under both dry and humidified air conditions. In contrast, Cr deposition in LSF-based cell concentrates at the cathode surface under dry air condition, but concentrates both at cathode surface and near electrolyte under humidified air condition. Microstructure analysis reveals Mn-associated Cr deposits in LSM-based cathode, and Sr- and Fe-associated Cr deposits in LSF-based cathode. With the help of distribution of relaxation time analysis, the different electrochemical behaviors of LSM- and LSF-based cells are carefully interpreted. The effects of electrochemical deposition, Sr surface segregation, and humidity on LSM- and LSF-based cathodes are discussed.

25 ENERGY STORAGE↗
DOE OSTI2012

Microstructural and compositional characterization of terbium-doped Nd-Fe-B sintered magnets

Anisotropic sintered magnets based on the Nd{sub 2}Fe{sub 14}B phase doped with Tb were prepared using a grain-boundary diffusion process (GBDP) in order to enhance their coercivity. A FEGSEM microstructural analysis revealed that these GBDP magnets had a core-shell structure, where thin, Tb-rich, (NdTb){sub 2}Fe{sub 14}B shells are formed on the original matrix Nd{sub 2}Fe{sub 14}B grains after diffusion of the Tb. This shell thickness varies from a few tens of nanometres in the middle of the magnet up to a few micrometers near the edge. The exact chemical composition of these shells was determined using EDS and WDS electron-probe microanalyses, which were modified and optimized for submicrometer scale analyses. When analyzing the common Nd-L{alpha}, Tb-L{alpha} and Fe-K{alpha} lines a mutual multiple overlap in the EDS spectra is present and, as a result, an accurate quantitative analysis was only feasible when using WDS. Using this technique we were able to achieve a lateral analytical resolution of 0.4 {mu}m. A further improvement in resolution, down to 0.15 {mu}m, was realized with a dedicated set-up using low-voltage EDS, analyzing the 'atypical' low-energy Nd-M{alpha}, Tb-M{alpha} and Fe-L{alpha} lines. Quantitative analyses confirmed that the reaction phase (Nd{sub x}Tb{sub 1} {sub -x}){sub 2}Fe{sub 14}B is formed after the diffusion of Tb with the equilibrium concentration of Tb being equal to x Almost-Equal-To 0.5, i.e., with the atomic ratio of Nd/Tb equal to 1/1. We also found that a relatively sharp Tb concentration gradient from the shell to the core occurs within a length of Almost-Equal-To 0.5 {mu}m, while the Fe concentration remains unchanged. In terms of magnetic properties, the Tb-doping significantly increased coercivity by Almost-Equal-To 30% while the remanence remained at the same value as in the undoped Nd-Fe-B. - Highlights: Black-Right-Pointing-Pointer Nd-Fe-B sintered magnets were doped with Tb using grain-boundary diffusion process. Black-Right-Pointing-Pointer A tiny core-shell reaction phase was formed around the Nd{sub 2}Fe{sub 14}B matrix grains. Black-Right-Pointing-Pointer EDS and WDS analyses confirmed (Nd{sub 0.5}Tb{sub 0.5}){sub 2}Fe{sub 14}B equilibrium shell composition. Black-Right-Pointing-Pointer Coercivity of Tb-doped Nd-Fe-B increases by 30% without a drop in remanence.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A complex approach to assessing porous structure of structured ceramics obtained by SPS technique

Highlights: • A complex approach to microstructural analysis of nanostructured SPS ceramics was presented. • A bunch of gas, intrusion and microscopic methods were applied for open/closed porosity determination in nanoceramics. • Kinetic TPR analysis for structural changes in nanoceramic was carried out. • 3D pore visualization for nanoceramics was provided via SEM/FIB tomography • Porosity calculations were performed via BET, BJH, t-plot, Washburn equation, FEI Avizo 9.1 software results. - Abstract: Spark plasma sintering (SPS) is a highly prospective technology providing rapid consolidation of nano-disperse compositions into structured ceramics with complex structural organization. Characterizing pore structure of such systems remains a challenge due to different types, size and shape of the pores as well as structural defects occurring in the material, thus requiring special methods to quantify certain porosity type. The paper presents a complex approach to studying structure of SPS hematite-based structured ceramics. The method involves a number of gas, intrusion and electron microscopy probing techniques to characterize open and closed pores in the ceramics bulk. Low temperature nitrogen sorption has been implemented to estimate open micro- and mesoporosity in the size range 0.7–50 nm using BET, BJH and t-plot methods to process experimental data. Additionally, structural peculiarities of consolidated structured ceramics have been studied using temperature-programmed reduction (TPR) with the kinetic analysis of the results being carried out. Volume of macropores sized above 50 nm has been measured with mercury intrusion. Closed pores and structural defects have been quantified with SEM and FIB/SEM tomography. By comparing experimental and estimated results we have shown that addressing all porosity types provides a highly precise structural characterization of the material.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Surfactant selection as a strategy for tailoring the structure and properties of UCT manganese oxides

Mesoporous manganese oxides were synthesized using the UCT inverse micelle templating method with four different Pluronic surfactants to investigate the effects on the morphology, microstructure and desulfurization behavior of these materials. All of the as-synthesized samples exhibited similar hierarchical microstructures, but the size and shape of the primary nanoparticles for each sample was different. The primary nanoparticle sizes for these samples vary between 2.3 and 7.0 nm. Most of the samples are crystalline and are composed of a mixture of Mn 3 O 4 and Mn 5 O 8 phases. The adsorption behavior of these samples was tested using a fixed bed reactor at a temperature of 200 °C. Microstructural analysis of the samples after the desulfurization tests revealed a transformation of the mesoporous manganese oxide to a dense manganese sulfide phase; this involves a volumetric expansion of the crystal, leading to densification and a rapid decay in the sorption capacity after the breakthrough point. The variation in the structure and properties of these materials is related to ratio of the PEO and PPO chain segment lengths in the Pluronic surfactants used. This indicates that the ratio must dictate the volume, shape and assembly of the inverse micelles in the UCT synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2023

E-beam-enhanced solid-state mechanical amorphization of α-quartz: Reduced deformation barrier via localized excess electrons as network modifiers

Under hydrostatic pressure, α-quartz (α-SiO 2 ) undergoes solid-state mechanical amorphization wherein the interpenetration of [SiO 4 ] 2- tetrahedra occurs and the material loses crystallinity. This phase transformation requires a high hydrostatic pressure of 14GPa because the repulsive forces resulting from the ionic nature of the Si–O bonds prevent the severe distortion of the atomic configuration. Herein, we experimentally and computationally demonstrate that e-beam irradiation changes the nature of the interatomic bonds in α-quartz and enhances the solid-state mechanical amorphization at nanoscale. Specifically, during in situ uniaxial compression, a larger permanent deformation occurs in α-quartz submicron pillars compressed during e-beam irradiation than in those without e-beam irradiation. Microstructural analysis reveals that the large permanent deformation under e-beam irradiation originates from the enhanced mechanical amorphization of α-quartz and the subsequent viscoplastic deformation of the amorphized region. Further, atomic-scale simulations suggest that the delocalized excess electrons introduced by e-beam irradiation move to highly distorted atomic configurations and alleviate the repulsive force, thus reducing the barrier to the solid-state mechanical amorphization. In conclusion, these findings deepen our understanding of electron–matter interactions and can be extended to new glass forming and processing technologies at nano- and microscale.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The effects of microstructural stability on the compressive response of two cast aluminum alloys up to 300 °C

Here in this study, the high temperature compressive response of cast aluminum alloys 319 and RR350 is compared in light of their microstructures. The 319 alloy is widely used in thermally critical automotive applications and provides a baseline for comparison with the RR350 alloy, whose microstructural stability at high homologous temperatures was recently reported. Cylindrical compression samples from each alloy were tested at four temperatures up to 300 °C at a constant true strain rate that was varied over four orders of magnitude. Although both alloys are strengthened by metastable precipitates (nominally Al 2 Cu) in the as-aged condition, their mechanical response diverges at temperatures greater than 250 °C as the strengthening precipitates evolve in the 319 alloy and retain their as-aged morphology in the RR350 alloy. Deformation mechanisms of each alloy are examined using microstructural analysis and empirical activation energy calculations. The stability of the θ' phase in the RR350 alloy leads to effective precipitation hardening at homologous temperatures up to 0.6 and an extensive regime of grain boundary controlled deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Exceptional thermal stability of additively manufactured CoCrFeMnNi high-entropy alloy with cellular dislocation structures

CoCrFeMnNi high-entropy alloy (HEA) was additively manufactured (AM) by laser powder-bed fusion (L-PBF). The AM CoCrFeMnNi has prominent cellular dislocation structures with a small number of Mn-rich oxides. The thermal stability of the AM CoCrFeMnNi was investigated by isochronal annealing treatment at various temperatures from 400 to 1300°C for 1h. Microstructural analysis shows slow dislocation recovery, retarded recrystallization process, and precipitation of additional Cr-Mn based oxides during thermal annealing, resulting in exceptional thermal stability and retained high hardness at elevated temperatures. Further, by thermodynamic calculations, a low stored energy of 1.31 MJ/m 3 and a high activation energy of 353 kJ/mol for recrystallization were estimated for the AM CoCrFeMnNi. The exceptional thermal stability of the AM CoCrFeMnNi HEA is mechanistically attributed to the low crystallographic misorientations across the dislocation cell walls, sluggish atomic diffusion, and the pinning effects of the oxide nanoprecipitates.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Optimizing processing conditions for additively reinforced thermoforming (ART) in convergent manufacturing

This study utilized additively reinforced thermoforming (ART) to enhance the thermomechanical properties of polyethylene terephthalate glycol (PETG) sheet. ART materials were produced by overprinting PETG/carbon fiber filament (PETG/CF) on neat PETG sheets at varying conditions. The mechanical properties of the PETG sheet, PETG/CF, and ART materials were assessed, showing that ART exhibited superior tensile strength and modulus of elasticity. The tensile strength and modulus in the x-direction for ART at 265°C were 57.32 ± 2.9 MPa and 3.41 ± 0.4 GPa, respectively, compared to 49.1 ± 0.5 MPa and 1.92 ± 0.09 GPa for neat PETG. Microstructural analysis revealed strong interfacial adhesion between layers, while thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and heat deflection temperature analysis provided insights into the ART material's thermoforming behavior, aiding design optimization for enhanced stiffness, reduced necking, and improved customization. In conclusion, this information can be used to design for the thermoforming operation.

Additive reinforcement↗
DOE OSTI2026

Temperature dependent interfacial microstructure in HIP-bonded Al6061/Zr joints

Pressing (HIP) at 450 °C and 560 °C under 103 MPa for 90 minutes to evaluate interfacial diffusion and microstructural evolution. Sound metallurgical bonding was achieved at both temperatures, with Zr serving as an effective diffusion barrier. Microstructural analysis revealed the the formation of a (Al,Si)3Zr intermetallic layer at the Al/Zr interface, whose thickness increased from ~100 nm at 450 °C to ~2100 nm at 560 °C, consistent with temperature-driven diffusion kinetics. The thin and continuous reaction layer observed at 450 °C indicates controlled interdiffusion and minimal reaction zone growth, favorable for maintaining interface stability and ductility. At 560 °C, enhanced atomic mobility led to pronounced intermetallic development, confirming diffusion-controlled growth behavior. These results provide valuable insights for optimizing Al/Zr interface design and diffusion barrier performance in advanced structural and energy systems.

Al/Zr interface↗
DOE OSTI2021

Lattice misorientation evolution and grain refinement in Al-Si alloys under high-strain shear deformation

The starting microstructure of an alloy can be tailored to achieve varying degrees of microstructural refinement and enhance mechanical properties through severe plastic shear deformation during solid-phase processing. Crystal plasticity-based grain misorientation modeling, coupled with systematic pin-on-disk tribometry-based subsurface shear deformation experiments on as-cast Al-xSi alloys (x = 0, 1, 4 at %), was conducted. The post-deformation microstructural analysis, through a combined computational and experimental approach, conclusively shows that the initial volume fraction of the hard Si phase enhances the evolution of local lattice misorientation, leading to efficient grain refinement during severe plastic shear deformation. The shear–deformation-induced nanostructure resulted in more than double the nanoindentation hardness in the processed alloy.

Gwalani, Bharat↗
DOE OSTI2023

Integrating fiber optic sensors into metallic components for sensing in harsh environments

The integration of fiber optic sensors into high-temperature materials is critical for real-time monitoring and autonomous operation of engineering systems. This study demonstrated a spark plasma sintering (SPS)-assisted embedding process for integrating sapphire fiber optic sensors into stainless steel components during part fabrication. Optical fibers were encapsulated in stainless steel 316L powders which were sintered at different fabrication conditions using SPS to investigate the effects of sintering parameters on the embedment. Measurements of optical transmittance, combined with microstructural analysis (X-ray computed tomography and scanning electron microscopy) and mechanical testing (tensile and microhardness), were conducted to examine the fiber functionality, fiber–matrix bonding quality, and properties of the sintered materials. Here, the results show that under suitable fabrication conditions, intact optical fibers can be encapsulated in highly-densified (>98 % relative density) stainless steel components. These conditions also led to a good bond at the fiber–matrix interface with micron-sized material interdiffusion across the interface. The sintering parameters were observed to affect fiber optical attenuation, where high temperature, pressure, and hold time during SPS enhanced fiber–matrix bonding and adversely affected optical transmission. Tensile testing confirmed the superior tensile strength and ductility of the matrix fabricated by SPS. Furthermore, the materials exhibited limited strength reduction (~70 MPa) upon the integration of fibers. This study demonstrates the effectiveness of SPS for fiber-material integration for high-temperature applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Complexity of segregation behavior at localized deformation sites formed while in service in a 316 stainless steel baffle-former bolt

Here, post-irradiation evaluation was performed on a 316 stainless steel baffle former bolt harvested after 40 years of service in a pressurized water reactor. Microstructure analysis revealed the presence of defect-free dislocation channels and strain-induced twins, indicative of loading at a stress level close to yield stress at least once while in service. Primary radiation-induced Ni/Si precipitates were destroyed during channel and twin formation, and secondary, significantly coarser Ni/Si precipitates formed along newly formed Σ3 boundaries during the continued irradiation. Additionally, an elevated phosphorus level was observed inside the strain-induced twin. Complex chemistry inside the strain-induced feature may overlap with dislocation pileups and impact localized corrosion, material long-term performance, and safety.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Rapid surface hardening and enhanced tribological performance of 4140 steel by friction stir processing

Tribological performance of steel materials can be substantially enhanced by various thermal surface hardening processes. For relatively low-carbon steel alloys, case carburization is often used to improve surface performance and durability. If the carbon content of steel is high enough (>0.4%), thermal treatments such as induction, flame, laser, etc. can produce adequate surface hardening without the need for surface compositional change. This paper presents an experimental study of the use of friction stir processing (FSP) as a means to hardened surface layer in AISI 4140 steel. The impacts of this surface hardening process on the friction and wear performance were evaluated under both dry and lubricated contact conditions in reciprocating sliding. FSP produced the same level of hardening and superior tribological performance when compared to conventional thermal treatment, using only 10% of the energy and without the need for quenching treatments. With FSP surface hardness of about 7.8 GPa (62 Rc) was achieved while water quenching conventional heat treatment produced about 7.5 GPa (61 Rc) hardness. Microstructural analysis showed that both FSP and conventional heat treatment produced martensite. Although the friction behavior for FSP treated surfaces and the conventional heat treatment were about the same, the wear in FSP processed surfaces was reduced by almost 2× that of conventional heat treated surfaces. Furthermore, the superior performance is attributed to the observed grain refinement accompanying the FSP treatment in addition to the formation of martensite. As it relates to tribological performance, this study shows FSP to be an effective, highly energy efficient, and environmental friendly (green) alternative to conventional heat treatment for steel.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Salt-Mediated Coarsening in Conversion-Reaction-Synthesized Nanoporous Metals and Nanocomposites Resolved through In Situ Synchrotron Diffraction Studies

High-energy synchrotron X-rays were used to probe the structural and microstructural evolution in Fe, Co, and Cu nanoporous metals (NPMs) and metal/salt nanocomposites (NCs) produced by recently developed conversion reaction synthesis (CRS) methods. Microstructure analysis of as-synthesized samples via whole pattern fitting showed that the NPMs exhibit domain sizes that increase as Co < Fe < Cu, with both Fe and Co having crystallite sizes below 3.0 nm. The as-synthesized metal/salt NCs had similar metal sizes, and additionally, the salt in the composite had unusually large lattice microstrain whose origin is attributed to chemical substitution of metal ions into the salt (e.g., Li $1–3x$ Fe $x$ Cl for Fe 3+ ). When thermal annealing is used to modify crystallite size, pore collapse often occurs in NPMs but NCs can be effectively tuned without this problem. While the NC coarsening occurs slowly at low temperatures, it was found that there is a drastic acceleration of the reaction rate at a specific onset temperature that results in the crystallite size increasing by an order of magnitude in about a minute. Curiously, there was no evidence in the diffraction data for salt melting at this onset temperature. However, there was a sharp reduction in the salt chemical lattice strain at the onset temperature, indicating that rapid metal coarsening is facilitated by the salt. Importantly, this behavior indicates an unexpectedly coupled reaction mechanism by which the metal ions needed for grain growth are supplied by the salt in a rate-limiting fashion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Eu 3+ -doped wide band gap Zn 2 SnO 4 semiconductor nanoparticles: Structure and luminescence

Nanocrystalline Zn 2 SnO 4 powders doped with Eu 3+ ions were synthesized via a mechanochemical solid-state reaction method followed by postannealing in air at 1200 °C. X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and Raman and photoluminescence (PL) spectroscopies provide convincing evidence for the incorporation of Eu 3+ ions into the host matrix on noncentrosymmetric sites of the cubic inverse spinel lattice. Microstructural analysis shows that the crystalline grain size decreases with the addition of Eu 3+ . Formation of a nanocrystalline Eu 2 Sn 2 O 7 secondary phase is also observed. Luminescence spectra of Eu 3+ -doped samples show several emissions, including narrow-band magnetic dipole emission at 595 nm and electric dipole emission at 615 nm of the Eu 3+ ions. Excitation spectra and lifetime measurements suggest that Eu 3+ ions are incorporated at only one symmetry site. According to the crystal field theory, it is assumed that Eu 3+ ions participate at octahedral sites of Zn 2+ or Sn 4+ under a weak crystal field, rather than at the tetrahedral sites of Zn2+, because of the high octahedral stabilization energy for Eu 3+ . Activation of symmetry forbidden (IR-active and silent) modes is observed in the Raman scattering spectra of both pure and doped samples, indicating a disorder of the cation sublattice of Zn 2 SnO 4 nanocrystallites. These results were further supported by the first principle lattice dynamics calculations. The spinel-type Zn 2 SnO 4 shows effectiveness in hosting Eu 3+ ions, which could be used as a prospective green/red emitter. As a result, this work also illustrates how sustainable and simple preparation methods could be used for effective engineering of material properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Integration of CeO 2 -Based Memristor with Vertically Aligned Nanocomposite Thin Film: Enabling Selective Conductive Filament Formation for High-Performance Electronic Synapses

The CeO 2 -based memristor has attracted significant attention due to its intrinsic resistive switching (RS) properties, large on/off ratio, and great plasticity, making it a promising candidate for artificial synapses. However, significant challenges such as high power consumption and poor device reliability hinder its broad application in neuromorphic microchips. To tackle these issues, in this work, we design a novel bilayer (BL) memristor by integrating a CeO 2 -based memristor with a Co-CeO 2 vertically aligned nanocomposite (VAN) layer and compare it with the single layer (SL) memristor. Preliminary electrical testing reveals that the BL memristor offers a reduced set/reset voltage (~67% lower), a higher on/off ratio (~5 × 10 2 ), enhanced device reliability, and improved device-to-device variation compared to the SL memristor. Insight from COMSOL simulation, coupled with microstructural analysis, provides a comprehensive elucidation on how the VAN layer facilitates the selective conductive filament (CF) formation. Subsequently, the plasticity of the BL memristor is evaluated through long-term potentiation/depression (LTP/LTD), paired-pulse facilitation (PPF), and spike-time-dependent plasticity (STDP). The spiking neural network (SNN) built upon the BL memristor achieves remarkable accuracy (~94%) after only 12 iterations, underscoring its potential for high-performance neural networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Dynamics of Radiation Damage Buildup in Ultrathin Hexagonal Boron Nitride Films under Ion Bombardment

Two-dimensional hexagonal boron nitride (hBN) is attractive for several emerging applications. Ion bombardment can be used to modify the hBN properties. However, the understanding of radiation damage buildup in hBN remains limited. Here, we investigate the effects of the dose rate and ion mass on radiation damage buildup by studying 40 nm-thick hBN films bombarded at room temperature with 500 keV 4 He, 15 N, 40 Ar, and 129 Xe ions and comparing with results for ion bombardment of polycrystalline hBN ceramics. Raman spectroscopy is used to quantify damage buildup, and transmission electron microscopy is used for microstructural analysis. Experiments are complemented by molecular dynamics simulations of the formation and evolution of point defects. Lighter ions are found to be more efficient at disordering hBN than heavier ions. This observation points to a critical role of intracascade defect processes. In contrast, a negligible dose rate effect observed suggests limited intercascade defect dynamic annealing processes for these irradiation conditions. These findings provide a fundamental basis for hBN defect engineering.

2D materials↗
DOE OSTI2023

Lithiation Gradients and Tortuosity Factors in Thick NMC111-Argyrodite Solid-State Cathodes

Achieving high energy density in all-solid-state lithium batteries will require the design of thick cathodes, and these will need to operate reversibly under normal use conditions. We use high-energy depth-profiling X-ray diffraction to measure the localized lithium content of Li 1-x Ni 1/3 Mn 1/3 Co 1/3 O 2 (NMC111) through the thickness of 110 μm thick composite cathodes. The composite cathodes consisted of NMC111 of varying mass loadings mixed with argyrodite solid electrolyte Li 6 PS 5 Cl (LPSC). During cycling at C/10, substantial lithiation gradients developed, and varying the NMC111 loading altered the nature of these gradients. Microstructural analysis and cathode modeling showed this was due to high tortuosities in the cathodes. This was particularly true in the solid electrolyte phase, which experienced a marked increase in tortuosity factor during the initial charge. Our results demonstrate that current distributions are observed in sulfide-based composites and that these will be an important consideration for practical design of all-solid-state batteries.

25 ENERGY STORAGE↗