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Results for “morphological stability”

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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Urchin-like m-LaVO{sub 4} and m-LaVO{sub 4}/Ag microspheres: Synthesis and characterization

The semiconductor nanostructures decorated with noble metals have attracted increasing attention due to their interesting physical and chemical properties. In this work, urchin-like monoclinic (m-) LaVO{sub 4} microspheres were prepared by a hydrothermal method and used as a template to fabricate Ag nanoparticle-decorated m-LaVO{sub 4} composites. The morphology and structure were characterized by transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, and energy-dispersive X-ray. It was found that Ag nanoparticles with narrow size distribution were uniformly loaded on urchin-like m-LaVO{sub 4} microspheres, and the resulted composite microspheres showed distinct surface plasmon absorption band compared to pure m-LaVO{sub 4} microspheres. Photocatalytic activities of as-prepared samples were examined by studying the degradation of methyl orange solutions under visible-light irradiation (> 400 nm). Results clearly showed that urchin-like m-LaVO{sub 4}/Ag microspheres possess much higher photocatalytic activity than pure m-LaVO{sub 4} microspheres and P25. - Highlights: • m-LaVO{sub 4}/Ag composites microspheres were fabricated by a hydrothermal method. • m-LaVO{sub 4} microspheres show higher photocatalytic activity than m-LaVO{sub 4} microspheres. • m-LaVO{sub 4}/Ag microspheres exhibit a good stability.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Enhancement of stability of aqueous suspension of alumina nanoparticles by femtosecond laser irradiation

In this work, we report substantially enhanced colloidal stability of aqueous nanoparticle suspensions by ultrashort laser pulse irradiation. A Ti:Sapphire femtosecond laser (wavelength: 800 nm; pulse duration: 50 fs at full width at half maximum) was used to modify the electrochemical properties of nanoparticle suspensions at laser fluences below the particle ablation threshold. The colloidal stability of the suspension was evaluated by zeta potential and dynamic light scattering (DLS). The DLS results along with the images from transmission electron microscopy revealed that the laser irradiation caused no distinct morphological change to the individual alumina particles, but a substantial portion of the clustered particles was fragmented by the laser pulses, decreasing the apparent size of the suspended particles. Also, X-ray photoelectron spectroscopy analysis indicates that the laser irradiation modified the surface chemistry of the alumina particles. The stabilizing capability of the proposed technique was turned out to be better than that of conventional ultrasonic treatments. The stability of the laser-treated sample with no added surfactant was maintained for up to 30 days, without requiring an additional homogenizing process such as magnetic stirring.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

In situ X-ray nanotomography of metal surfaces during electropolishing

A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. We show that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. We discovered that the kinetics of shell growth at the triple line, where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Recent trends in binary and ternary rare-earth fluoride nanophosphors: How structural and physical properties influence optical behaviour

Rare-earth (RE) doped binary and ternary fluoride nanomaterials are currently receiving the highest attention as phosphor materials due to their potential for a wide range of photonic and biophotonic applications. This review article aims providing and introduction to the field and giving a critical overview about the latest developments in this fast evolving field. First, the underlying photoluminescence mechanisms like up- and downconversion (UC and DC), charge transfer (CT) and energy transfer (ET) between optically active trivalent RE ions are explained. Then, the influence of particle size and surface, shape and lattice strain, as well as the crystal phase of the host materials on the optical properties of rare earth based nanomaterias are illustrated. In addition, the effect of surface plasmon resonance (SPR) on the rare earth luminescence is discussed. In the following, different synthesis strategies which have been developed for tuning the crystal phase, shape, size, and morphology of the host nanomaterial are presented. The role of surface modification and functionalization for improving the luminescence intensity, stability, aqueous dispersity/dispersibility and biocompatibility of the materials is discussed. Lastly, photonic applications of RE-doped nanofluorides for energy efficient lighting, improved solar cells and biophotonic applications like photodynamic therapy, and biological detection techniques including in vivo and in vitro bioimaging are presented.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Precipitation behavior of ωo phase and texture evolution of a forged Ti-45Al-8.5Nb-(W, B, Y) alloy during creep

Highlights: • The morphology of ω{sub o} and residual β{sub o} phases depends on creep temperature and stress. • Stress can increase the tendency of the α{sub 2} to ω{sub o} phase transformation. • The strength of the texture components depend on temperature and stress. • β{sub o}(ω{sub o}) precipitation retards the growth of recrystallized γ grains. • ω{sub o} precipitation resists and deflects the crack during the crack propagation. - Abstract: Creep rupture tests of the as-forged Ti-45Al-8.5Nb-(W,B,Y) alloy with a duplex microstructure were carried out at 750–850 °C and 130–300 MPa. An investigation was performed to study the effects of temperature and stress on the microstructure and texture evolution, as well as on the creep properties of the forged high Nb-containing TiAl alloy with a duplex microstructure. The results show that the stress exponent n = 2.8–3.3, and the creep activation energy values are in the range of 300–400 kJ/mol. After creep, a regular arrangement of ω{sub o} precipitations was observed in the β{sub o} region. The un-transformed β{sub o} phase, which remained in the ω{sub o} interval, was examined using high resolution transmission electron microscope (HRTEM). It is shown that the growth of ω{sub o} precipitations and the morphology of residual β{sub o} phases are related to the creep temperature and stress. Certain β{sub o} stabilizer elements, such as Nb, segregate into α{sub 2} plates and cause ω{sub o} precipitation during dissolution of α{sub 2} plates at high temperature. The interfacial structure between the ω{sub o} and α{sub 2} phases was studied in detail using HRTEM. Meanwhile, texture evolution and dynamic recrystallization of the γ phase were studied using electron backscatter diffraction (EBSD). Observations on the deformation structure also demonstrate that ω{sub o} precipitation acts as an obstacle inhibiting crack propagation and growth of the γ phase. The corresponding formation mechanism and possible effects on creep are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Two-Dimensional Holey Co 3 O 4 Nanosheets for High-Rate Alkali-Ion Batteries: From Rational Synthesis to in Situ Probing

A general template-directed strategy is developed for the controlled synthesis of two-dimensional (2D) assembly of Co 3 O 4 nanoparticles (ACN) with unique holey architecture and tunable hole sizes that enable greatly improved alkali-ion storage properties (demonstrated for both Li and Na ion storage). The as-synthesized holey ACN with 10 nm holes exhibit excellent reversible capacities of 1324 mAh/g at 0.4 A/g and 566 mAh/g at 0.1 A/g for Li and Na ion storage, respectively. The improved alkali-ion storage properties are attributed to the unique interconnected holey framework that enables efficient charge/mass transport as well as accommodates volume expansion. In situ TEM characterization is employed to depict the structural evolution and further understand the structural stability of 2D holey ACN during the sodiation process. The results show that 2D holey ACN maintained the holey morphology at different sodiation stages because Co 3 O 4 are converted to extremely small interconnected Co nanoparticles and these Co nanoparticles could be well dispersed in a Na 2 O matrix. These extremely small Co nanoparticles are interconnected to provide good electron pathway. In addition, 2D holey Co 3 O 4 exhibits small volume expansion (~6%) compared to the conventional Co 3 O 4 particles. The 2D holey nanoarchitecture represents a promising structural platform to address the restacking and accommodate the volume expansion of 2D nanosheets for superior alkali-ion storage.

2D holey assembly of nanoparticles↗
DOE OSTI2017

Unrivaled combination of surface area and pore volume in micelle-templated carbon for supercapacitor energy storage

Here, we created Immense Surface Area Carbons (ISACs) by a novel heat treatment that stabilized the micelle structure in a biological based precursor prior to high temperature combined activation – pyrolysis. While displaying a morphology akin to that of commercial activated carbon, ISACs contain an unparalleled combination of electrochemically active surface area and pore volume (up to 4051 m 2 g –1 , total pore volume 2.60 cm 3 g –1 , 76% small mesopores). The carbons also possess the benefit of being quite pure (combined O and N: 2.6–4.1 at%), thus allowing for a capacitive response that is primarily EDLC. Tested at commercial mass loadings (~10 mg cm –2 ) ISACs demonstrate exceptional specific capacitance values throughout the entire relevant current density regime, with superior rate capability primarily due to the large fraction of mesopores. In the optimized ISAC, the specific capacitance ( C g ) is 540 F g –1 at 0.2 A g –1 , 409 F g –1 at 1 A g –1 and 226 F g –1 at a very high current density of 300 A g –1 (~0.15 second charge time). At intermediate and high currents, such capacitance values have not been previously reported for any carbon. Tested with a stable 1.8 V window in a 1 M Li 2 SO 4 electrolyte, a symmetric supercapacitor cell yields a flat energy–power profile that is fully competitive with those of organic electrolyte systems: 29 W h kg –1 at 442 W kg –1 and 17 W h kg –1 at 3940 W kg –1 . The cyclability of symmetric ISAC cells is also exceptional due to the minimization of faradaic reactions on the carbon surface, with 80% capacitance retention over 100 000 cycles in 1 M Li 2 SO 4 and 75 000 cycles in 6 M KOH.

25 ENERGY STORAGE↗
DOE OSTI2016

Preparation of atomically flat rutile TiO 2 (001) surfaces for oxide film growth

The availability of low-index rutile TiO 2 single crystal substrates with atomically flat surfaces is essential for enabling epitaxialgrowth of rutile transition metal oxide films. The high surface energy of the rutile (001) surface often leads to surface faceting, which precludes the sputter and annealing treatment commonly used for the preparation of clean and atomically flat TiO 2 (110) substrate surfaces. In this work, we reveal that stable and atomically flat rutile TiO 2 (001) surfaces can be prepared with an atomically ordered reconstructedsurface already during a furnace annealing treatment in air. We tentatively ascribe this result to the decrease in surface energy associated with the surface reconstruction, which removes the driving force for faceting. Despite the narrow temperature window where this morphology can initially be formed, we demonstrate that it persists in homoepitaxialgrowth of TiO 2 (001) thin films. The stabilization of surface reconstructions that prevent faceting of high-surface-energy crystal faces may offer a promising avenue towards the realization of a wider range of high quality epitaxial transition metal oxide heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2015

TU-AB-BRA-10: Prognostic Value of Intra-Radiation Treatment FDG-PET and CT Imaging Features in Locally Advanced Head and Neck Cancer

Purpose: To predict response to radiation treatment using computational FDG-PET and CT images in locally advanced head and neck cancer (HNC). Methods: 68 patients with State III-IVB HNC treated with chemoradiation were included in this retrospective study. For each patient, we analyzed primary tumor and lymph nodes on PET and CT scans acquired both prior to and during radiation treatment, which led to 8 combinations of image datasets. From each image set, we extracted high-throughput, radiomic features of the following types: statistical, morphological, textural, histogram, and wavelet, resulting in a total of 437 features. We then performed unsupervised redundancy removal and stability test on these features. To avoid over-fitting, we trained a logistic regression model with simultaneous feature selection based on least absolute shrinkage and selection operator (LASSO). To objectively evaluate the prediction ability, we performed 5-fold cross validation (CV) with 50 random repeats of stratified bootstrapping. Feature selection and model training was solely conducted on the training set and independently validated on the holdout test set. Receiver operating characteristic (ROC) curve of the pooled Result and the area under the ROC curve (AUC) was calculated as figure of merit. Results: For predicting local-regional recurrence, our model built on pre-treatment PET of lymph nodes achieved the best performance (AUC=0.762) on 5-fold CV, which compared favorably with node volume and SUVmax (AUC=0.704 and 0.449, p<0.001). Wavelet coefficients turned out to be the most predictive features. Prediction of distant recurrence showed a similar trend, in which pre-treatment PET features of lymph nodes had the highest AUC of 0.705. Conclusion: The radiomics approach identified novel imaging features that are predictive to radiation treatment response. If prospectively validated in larger cohorts, they could aid in risk-adaptive treatment of HNC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Experimental Investigation of Low Cost, Low Thermal Conductivity Thermal Barrier Coating on HCCI Combustion, Efficiency, and Emissions

In-cylinder surface temperature is of heightened importance for Homogeneous Charge Compression Ignition (HCCI) combustion since the combustion mechanism is thermo-kinetically driven. Thermal Barrier Coatings (TBCs) selectively manipulate the in-cylinder surface temperature, providing an avenue for improving thermal and combustion efficiency. A surface temperature swing during combustion/expansion reduces heat transfer losses, leading to more complete combustion and reduced emissions. At the same time, achieving a highly dynamic response sidesteps preheating of charge during intake and eliminates the volumetric efficiency penalty. The magnitude and temporal profile of the dynamic surface temperature swing is affected by the TBC material properties, thickness, morphology, engine speed, and heat flux from the combustion process. This study follows prior work of authors with Yttria Stabilized Zirconia, which systematically engineered coatings for HCCI combustion. Herein, a modeling study was used to assess the impacts of various TBC material properties, e.g. density, thickness, and thermal conductivity on the temperature swing effect. Reducing conductivity emerged as a most promising avenue, rather than reducing both the density and effective conductivity by increasing porosity, the current work emphasizes a material with natively low conductivity. A novel TBC formulation was developed, leverages a class of materials that, to the author’s best knowledge, have not been used as a thermal barrier coating previously. Here, a systematic experimental investigation was carried out using single-cylinder research engine. Experimental engine studies utilizing the novel ‘glassy’ low-K coating exhibit advanced ignition phasing and reduced combustion duration relative to the baseline engine. Heat transfer measurements indicate a net reduction in heat flux over the entire cycle, although main effect is felt during expansion, and the reduced heat transfer losses manifest in higher gross indicated thermal efficiency by approximately 5-6% on a relative basis.

42 ENGINEERING↗
NASA NTRS2005

Polymer Crosslinked 3-D Assemblies of Nanoparticles: Mechanically Strong Lightweight Porous Materials

In analogy to supramolecular assemblies, which are pursued because of properties above and beyond those of the individual molecules, self-standing monolithic three-dimensional assemblies of nanoparticles also have unique properties attributed to their structure. For example, ultra low-density 3-D assemblies of silica nanoparticles, known as silica aerogels, are characterized by large internal void space, high surface area and very low thermal conductivity. Aerogels, however, are also extremely fragile materials, limiting their application to a few specialized environments, e.g., in nuclear reactors as Cerenkov radiation detectors, in space (refer to NASA's Stardust Program) and aboard certain planetary vehicles (thermal insulators on Mars Rovers in 1997 and 2004). The fragility problem is traced to well-defined weak points in the aerogel skeletal framework, the interparticle necks. Using the surface functionality of the nanoparticle building blocks as a focal point, we have directed attachment of a conformal polymer coating over the entire framework, rendering all necks wider. Thus, although the bulk density may increase only by 3x, the mesoporosity (pores in the range 2-50 nm) remains unchanged, while the strength of the material increases by up to 300... Having addressed the fragility problem, aerogels are now robust materials, and a variety of applications, ranging from thermal/acoustic insulators to catalyst supports, to platform for sensors, and dielectrics are all within reach. Our approach employs molecular science to manipulate nanoscopic matter for achieving useful macroscopic properties, and in our view it resides at the core of what defines nanotechnology. In that spirit, this technology is expandable in three directions. Thus, we have already crosslinked successfully amine-modified silica, and we anticipate that more rich chemistry will be realized by been creative with the nanoparticle surface modifiers. On the other hand, although we do not expect orders-of-magnitude increase in strength, nevertheless, by varying the polymer we expect to impart other properties such as hydrophobicity, thermal stability and perhaps electrical conductivity. Besides polymers, crosslinkers will include metals and ceramics (e.g., through POSS precursors). Finally, network morphology directs load dissipation, and of approximately 30 different crosslinked oxide aerogels, vanadia, whose structure is fibrous rather than particulate, yields a much stronger (by 4..) material than silica of the same density. It seems imperative to implement control of network morphology, even through templating.

Leventis, Nicholas↗
NASA NTRS2012

Advanced Lithium-ion Batteries with High Specific Energy and Improved Safety for Nasa's Missions

High Energy Materials ( Cathodes, anodes and high voltage and safe electrolyte are required to meet the needs of the future space missions. A. Cathodes: The layered layered composites of of Li2MnO3 and LiMO2 are promising Power capability of the materials, however requires further improvement. Suitable morphology is critical for good performance and high tap (packing) density. Surface coatings help in the interfacial kinetics and stability. B. Electrolytes: Small additions of Flame Retardant Additives improves flammability without affecting performance (Rate and cycle life). 1.0 M in EC+EMC+TPP was shown to have good performance against the high voltage cathode; Performance demonstrated in large capacity prototype MCMB- LiNiCoO2 Cells. Formulations with higher proportions are looking promising. Still requires further validation through abuse tests (e.g., on 18650 cells).

NASA Missions↗
DOE OSTI2024

Virtual Substrates for Wide Bandgap AlyX1-yN Growth

Lattice-matched substrates are critical for growth of high quality, compositionally-targeted ternary AlyX1-yN compounds with properties suitable for a wide variety of next-generation opto- and power electronic applications. [DOI:10.1149/2.0111702jss] We have identified the (111) plane of transition metal carbides and nitrides as lattice matched "virtual" substrate layers that have additional benefits of electrical conductivity and appropriate coefficients of thermal expansion for nitride layer at both growth and operating temperatures. [arXiv:2208.11769 2022] In this work, (111)-oriented TaC and ZrN are grown by RF sputtering and optimized as substrate layers for AlyGa1-yN and AlyGd1-yN, respectively. TaC is demonstrated as a full proof of concept. (111)-stabilized TaC layers with a rock-salt crystal structure are annealed to improve surface crystal quality and surface morphology and then used as a template for growth of an Al0.7Ga0.3N layer by molecular beam epitaxy. X-ray diffraction (XRD) demonstrates epitaxial registry of the grown layer to the substrate. High resolution transmission electron microscopy (TEM) is used to investigate interface behavior, showing regions of abrupt interface transitions and nitrogen polar termination of the Al0.7Ga0.3N. We also grew (111)-oriented ZrN on Ti-Zr-N graded buffer layers as a lattice-matched virtual substrate for AlyGd1-yN. Structure, morphology, and strain are analyzed using XRD and atomic force microscopy. Structure and quality of initial Al0.8Gd0.2N thin films are investigated for both in-situ and ex-situ growths.

AlyX1-yN↗
NASA NTRS1993

Alloys for hydrogen storage in nickel/hydrogen and nickel/metal hydride batteries

Since 1990, there has been an ongoing collaboration among the authors in the three laboratories to (1) prepare alloys of the AB(sub 5) and AB(sub 2) types, using arc-melting/annealing and mechanical alloying/annealing techniques; (2) examine their physico-chemical characteristics (morphology, composition); (3) determine the hydrogen absorption/desorption behavior (pressure-composition isotherms as a function of temperature); and (4) evaluate their performance characteristics as hydride electrodes (charge/discharge, capacity retention, cycle life, high rate capability). The work carried out on representative AB(sub 5) and AB(sub 2) type modified alloys (by partial substitution or with small additives of other elements) is presented. The purpose of the modification was to optimize the thermodynamics and kinetics of the hydriding/dehydriding reactions and enhance the stabilities of the alloys for the desired battery applications. The results of our collaboration, to date, demonstrate that (1) alloys prepared by arc melting/annealing and mechanical alloying/annealing techniques exhibit similar morphology, composition and hydriding/dehydriding characteristics; (2) alloys with the appropriate small amounts of substituent or additive elements: (1) retain the single phase structure, (2) improve the hydriding/dehydriding reactions for the battery applications, and (3) enhance the stability in the battery environment; and (3) the AB(sub 2) type alloys exhibit higher energy densities than the AB(sub 5) type alloys but the state-of-the-art, commercialized batteries are predominantly manufactured using Ab(sub 5) type alloys.

Anani, Anaba↗
DOE OSTI2019

A Simple Approach for the Synthesis of Cellulose Nanofiber Reinforced Chitosan/PVP Bio Nanocomposite Film for Packaging

The development of chitosan-based food packaging film has been increasing due to its wider availability, biodegradability, low-cost, and renewability. The purpose of this study was to develop cellulose nanofibers (CNFs) reinforced Chitosan/PVP(CHP) green bio nanocomposite film by solvent casting method with enhanced barrier and mechanical property. CNFs of dimension 9–11 nm and 100–200 nm were extracted from jute fibers by directly treating it with HNO{sub 3}–NaNO{sub 2} mixture. Bio nanocomposite films were synthesized with various concentrations of CNFs and evaluated using SEM, TGA/DTG and XRD to analyze the morphology, thermal behavior and crystallinity of bio nanocomposite films. SEM analysis revealed the uniform dispersion of CNFs in CHP matrix. Thermal stability of prepared bio nanocomposite films was improved with the loading of 5 wt% of cellulose nanofibers. ATR(FT-IR) spectra shows physical interaction between all the components of bio nanocomposite film. The bio nanocomposite films were also characterized for physical property like thickness, mechanical testing and barrier properties. The addition of CNFs significantly enhanced the mechanical property of bio nanocomposite films. Furthermore, water and oxygen transmission rate of bio nanocomposite film decreased with the increase in CNFs concentration. Overall the performed studies confirmed, the use of CNFs in polymer matrix makes it possible to produce a flexible, transparent, thermally stable bio nanocomposite film with enhanced mechanical and barrier properties for food packaging applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thermal aging modeling and validation on the Mo-containing Fe-Cr-Ni alloys

Thermodynamics of intermetallic phases in Fe-rich Fe-Cr-Ni-Mo alloys is critical knowledge to understand thermal aging effect on the phase stability of Mo-containing austenitic steels, which subsequently facilitates alloy design/improvement and degradation mitigation of these materials for reactor applications. Among the intermetallic phases, Chi (χ), Laves, and Sigma (σ) are often of concern because of their tendency to cause embrittlement of the materials. The focus of this study is thermal stability of the Chi and Laves phases as they were less studied compared to the Sigma phase. Coupled with thermodynamic modeling, thermal stability of intermetallic phases in Mo containing Fe-Cr-Ni alloys was investigated at 1000, 850 and 700°C for different annealing times. The morphologies, compositions and crystal structures of the precipitates of the intermetallic phases were carefully examined by scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and transmission electron microscopy. Three key findings resulted from this study. First, the Chi phase is stable at high temperature, and with decreasing temperature it transforms into the Laves phase that is stable at low temperature. Secondly, Cr, Mo, Ni are soluble in both the Chi and Laves phases, with the solubility of Mo playing a major role in the relative stability of the intermetallic phases. Thirdly, in situ transformation from Chi phase to Laves phase was directly observed, which increased the local strain field, generated dislocations in the intermetallic phases, and altered the precipitate phase orientation relationship with the austenitic matrix. The thermodynamic models that were developed and validated were then applied to evaluating the effect of Mo on the thermal stability of intermetallic phases in type 316 and NF709 stainless steels.

36 MATERIALS SCIENCE↗