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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Ultra-high wear resistance of ultra-nanocrystalline diamond film: Correlation with microstructure and morphology

Nanostructured diamond films are having numerous unique properties including superior tribological behavior which is promising for enhancing energy efficiency and life time of the sliding devices. High wear resistance is the principal criterion for the smooth functioning of any sliding device. Such properties are achievable by tailoring the grain size and grain boundary volume fraction in nanodiamond film. Ultra-nanocrystalline diamond (UNCD) film was attainable using optimized gas plasma condition in a microwave plasma enhanced chemical vapor deposition (MPECVD) system. Crystalline phase of ultra-nanodiamond grains with matrix phase of amorphous carbon and short range ordered graphite are encapsulated in nanowire shaped morphology. Film showed ultra-high wear resistance and frictional stability in micro-tribological contact conditions. The negligible wear of film at the beginning of the tribological contact was later transformed into the wearless regime for prolonged sliding cycles. Both surface roughness and high contact stress were the main reasons of wear at the beginning of sliding cycles. However, the interface gets smoothened due to continuous sliding, finally leaded to the wearless regime.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Epitaxial stabilization of thin films of the frustrated Ge-based spinels

Frustrated magnets can host numerous exotic many-body quantum and topological phenomena. GeNi 2 O 4 is a three-dimensional S=1 frustrated magnet with an unusual two-stage transition to the two-dimensional antiferromagnetic ground state, while GeCu 2 O 4 is a high-pressure phase with a strongly tetragonally elongated spinel structure and magnetic lattice formed by S=1/2 CuO 2 linear chains with frustrated interchain exchange interactions and exotic magnetic behavior. Here, we report on the thin-film epitaxial stabilization of these two compounds. The developed growth mode, surface morphology, crystal structure, and copper valence state were characterized by in situ reflection high-energy electron diffraction, atomic force microscopy, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and resonant x-ray absorption spectroscopy. Our results pave an alternative route to the comprehensive investigation of the puzzling magnetic properties of these compounds and the exploration of emergent features driven by strain.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Precision Synthesis of Conjugated Polymer Films by Surface-Confined Stepwise Sonogashira Cross-Coupling

Thin films of poly(arylene ethynylene)-conjugated polymers, including low-energy-gap donor–acceptor polymers, can be prepared via stepwise polymerization utilizing surface-confined Sonogashira cross-coupling. This robust and efficient polymerization protocol yields conjugated polymers with a precise molecular structure and with nanometer-level control of the organization and the uniform alignment of the macromolecular chains in the densely packed film. In addition to high stability and predictable and well-defined molecular organization and morphology, the surface-confined conjugated polymer chains experience significant interchain electronic interactions, resulting in dominating intermolecular π-electron delocalization which is primarily responsible for the electronic and spectroscopic properties of polymer films. The fluorescent films demonstrate remarkable performance in chemosensing applications, showing a turn-off fluorescent response on the sub-ppt (part per trillion) level of nitroaromatic explosives in water. This unique sensitivity is likely related to the enhanced exciton mobility in the uniformly aligned and structurally monodisperse polymer films.

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

Investigating the Influence of River Geomorphology on Human Presence Using Night Light Data: A Case Study in the Indus Basin

Human settlements have historically thrived near rivers due to enhanced navigation and trade, and the availability of water supply and resources. The use of night light data, representing economic activities, provides a novel approach to studying the interactions between human activity and rivers over time. Here, we use the Defense Meteorological Satellite Program (DMSP) stable night light data from 2000 to 2013 as a proxy for human presence and activities to quantify the statistical relationships between night light presence and intensity in the Indus Basin, Asia. We test how these data are affected by proximity to trunk channels and by channel type (single/multi-thread) in the study area. We find that night light presence is enhanced by 26% within a 0 to 5 km proximity range of the Indus River and its tributaries, relative to the basin as a whole. We interpret this to represent increased human presence and activity within this zone. However, the mean intensity is lower near the river and higher away from the river, signifying denser settlements, such as towns and cities, which are preferentially located away from the Indus and its tributaries. Moreover, the enhancement of lit pixels signifying human presence and activities is increased by 18% near single-thread sections of the Indus River, compared to segments of the Indus displaying multi-thread morphologies. We suggest that this is due to the enhanced stability of single-threaded channels, relative to mobile multi-threaded channel reaches. This study demonstrates how night lights are an important tool in studying the relationship between human presence and river dynamics in large catchments such as the Indus, and we suggest that these data will have an important role in assessing differential flood spatial and social vulnerability at a regional scale.

Environmental Sciences & Ecology↗
NASA NTRS1994

Convective flow effects on protein crystal growth

The long-term stability of the interferometric setup for the monitoring of protein morphologies has been improved. Growth or dissolution of a crystal on a 100 A scale can now be clearly distinguished from dimensional changes occurring within the optical path of the interferometer. This capability of simultaneously monitoring the local interfacial displacement at several widely-spaced positions on the crystal surface with high local depth resolution, has already yielded novel results. We found with lysozyme that (1) the normal growth rate is oscillatory, and (2) the mean growth step density is greater at the periphery of a facet than in its center. The repartitioning of Na(+) and Cl(-) ions between lysozyme solutions and crystals was studied for a wide range of crystallization conditions. A nucleation-growth-repartitioning model was developed to interpret the large body of data in a unified way. The results strongly suggests that (1) the ion to lysozyme ratio in the crystal depends mostly on kinetic rather than crystallographic parameters, and (2) lysozyme crystals possess a salt-rich core with a diameter on the order of 10 microns. The computational model for diffusive-convective transport in protein crystallization (see the First Report) has been applied to a realistic growth cell geometry, taking into account the findings of the above repartitioning studies. These results show that some elements of a moving boundary problem must be incorporated into the model in order to obtain a more realistic description. Our experimental setup for light scattering investigations of aggregation and nucleation in protein solutions has been extensively tested. Scattering intensity measurements with a true Rayleigh scatterer produced systematically increased forward scattering, indicating problems with glare. These have been resolved. Preliminary measurements with supersaturated lysozyme solutions revealed that the scatterers grow with time. Work has begun on a computer program for the unified evaluation of simultaneously obtained, multi-angle static and dynamic light scattering data.

Rosenberger, Franz↗
DOE OSTI2020

Tortuosity Effects in Lithium-Metal Host Anodes

Lithium (Li) metal is the ultimate anode material for Li batteries because of its highest capacity among all candidates. Recent research has focused on stable interphase and host materials to address its low stability and reversibility. Here, we discover that tortuosity is a critical parameter affecting the morphology and electrochemical performances of hosted Li anodes. In three types of hosts—vertically aligned, horizontally aligned, and random reduced graphene oxide (rGO) electrodes with tortuosities of 1.25, 4.46, and 1.76, respectively—we show that high electrode tortuosity causes locally higher current density on the top surface of electrodes, resulting in thick Li deposition on the surface and degraded cycling performance. Low electrode tortuosity in the vertically aligned rGO host enables homogeneous Li transport and uniform Li deposition across the host, realizing greatly improved cycling stability. Furthermore, using this principle of low tortuosity, the designed electrode shows through-electrode uniform morphology with anodic Coulombic efficiency of ~99.1% under high current and capacity cycling conditions.

25 ENERGY STORAGE↗
DOE OSTI2015

Process depending morphology and resulting physical properties of TPU

Thermoplastic polyurethane (TPU) is a rubber like material with outstanding properties, e.g. for seal applications. TPU basically provides high strength, low frictional behavior and excellent wear resistance. Though, due to segmented structure of TPU, which is composed of hard segments (HSs) and soft segments (SSs), physical properties depend strongly on the morphological arrangement of the phase separated HSs at a certain ratio of HSs to SSs. It is obvious that the TPU deforms differently depending on its bulk morphology. Basically, the morphology can either consist of HSs segregated into small domains, which are well dispersed in the SS matrix or of few strongly phase separated large size HS domains embedded in the SS matrix. The morphology development is hardly ruled by the melt processing conditions of the TPU. Depending on the morphology, TPU provides quite different physical properties with respect to strength, deformation behavior, thermal stability, creep resistance and tribological performance. The paper deals with the influence of important melt processing parameters, such as temperature, pressure and shear conditions, on the resulting physical properties tested by tensile and relaxation experiments. Furthermore the morphology is studied employing differential scanning calorimeter (DSC), transmission light microscopy (TLM), scanning electron beam microscopy (SEM) and transmission electron beam microscopy (TEM) investigations. Correlations between processing conditions and resulting TPU material properties are elaborated. Flow and shear simulations contribute to the understanding of thermal and flow induced morphology development.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Temperature-dependent stability of θ'-Al 2 Cu precipitates investigated with phase field simulations and experiments

The upper limit of service temperature for many Al-Cu alloys is determined by the thermal stability of strengthening θ' (Al 2 Cu) precipitates. Above a certain temperature, θ' precipitates will undergo morphological evolution and transform into the detrimental, equilibrium θ phase, leading to a rapid drop in strength. Certain alloying elements have recently been reported to increase the thermal stability of θ' precipitates, by mechanisms that are yet unclear. Herein, we investigate the effect of modified interfacial energy and solute chemical mobility on the thermal stability of θ' via high-throughput phase field study. We identify a critical θ' aspect ratio to predict the onset of θ formation. Using this criterion, we predict the time required for θ' to θ phase transformation as a function of temperature, Cu diffusivity, and the interfacial energy of θ' precipitates. The predicted times compare favorably with reported times for θ formation under similar experimental conditions. Furthermore, these phase field simulations predict that a moderate reduction in Cu mobilityis adequate to stabilize the as-aged microstructure up to 300 °C, while substantial reductions to both interfacial energy and Cu mobility are needed to achieve similar stability at 400 °C. Experimental microstructural evolution results in commercial (319) and thermally stabilized (RR350) cast aluminum alloys are presented to complement the simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Endocytosis of the non-catalytic ADAM23: Recycling and long half-life properties

A Disintegrin And Metalloprotease 23 (ADAM23) is a member of the ADAMs family of transmembrane proteins, mostly expressed in nervous system, and involved in traffic and stabilization of Kv1-potassium channels, synaptic transmission, neurite outgrowth, neuronal morphology and cell adhesion. Also, ADAM23 has been linked to human pathological conditions, such as epilepsy, cancer metastasis and cardiomyopathy. ADAM23 functionality depends on the molecule presence at the cell surface and along the secretory pathway, as expected for a cell surface receptor. Because endocytosis is an important functional regulatory mechanism of plasma membrane receptors and no information is available about the traffic or turnover of non-catalytic ADAMs, we investigated ADAM23 internalization, recycling and half-life properties. Here, we show that ADAM23 undergoes constitutive internalization from the plasma membrane, a process that depends on lipid raft integrity, and is redistributed to intracellular vesicles, especially early and recycling endosomes. Furthermore, we observed that ADAM23 is recycled from intracellular compartments back to the plasma membrane and thus has longer half-life and higher cell surface stability compared with other ADAMs. Our findings suggest that regulation of ADAM23 endocytosis/stability could be exploited therapeutically in diseases in which ADAM23 is directly involved, such as epilepsy, cancer progression and cardiac hypertrophy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Support-induced morphology and content tailored NiCo 2 O 4 nanostructures on temperature-dependent carbon nanofibers with enhanced pseudocapacitive performance

Direct anchorage of metal oxides on carbon nanofibers is challenging, and simultaneous modulation of morphology, content and thus pseudocapacitance of anchored metal oxides has never been achieved. In this paper, we report direct anchorage of NiCo 2 O 4 nanostructures with tailored morphology, content and pseudocapacitance, on temperature-dependent carbon nanofibers (CNEs), which are derived from zinctrimesic acid fibers at a temperature no more than 600 degrees C. The temperature-dependent CNEs, including CNF-390, CNF-450 and CNF-600, were first investigated by SEM, TG, FT-IR, XPS and Boehm titration studies. It is found that their textural property, thermal stability and surface functionality vary depending on pyrolysis temperature. As a result, the morphology, content and thus the pseudocapacitance of anchored NiCo 2 O 4 nanostructures are also temperature-dependent. It is revealed that as increasing the pyrolysis temperature, the shape of NiCo 2 O 4 is transformed from embedded nanoparticles to exposed nanosheets while its content decreases from 95 to 55 wt%. The resultant NiCo 2 O 4 /CNF-450, bearing highly dispersed nanosheets and optimized NiCo 2 O 4 content (72.6%), exhibits the best capacitive performance with a large specific capacitance of 870 F g -1 at a scan rate of 1 mV s -1 , and a high energy density of 39.3 Wh kg -1 in the case of power density of 300 W kg -1 . The elaborately fabricated NiCo 2 O 4 /CNF-450 also shows excellent charge-discharge stability (with the capacity retention ratio of 85.7% after 5000 cycles). The improved accessibility for more pseudocapacitive NiCo 2 O 4 nanosheets, as well as the strong interaction between NiCo2O4 and carbon nanofiber, should be responsible for the enhanced capacitive performance of NiCo 2 O 4 /CNF-450. Lastly, this research also provides the concept of support-induced modulation of property and pseudocapacitive performance of anchored metal oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Study of phase transformation and microstructure of alcohol washed titania nanoparticles for thermal stability

Nanostructured titania have been successfully synthesized by hydrolysis of alkoxide at calcination temperatures 500 °C, 600 °C and 700 °C. As the calcination temperature increases, alcohol washed samples show lesser rutile content as compared to water washed samples. Morphology and Particle sizes was determined by field emission scanning electron microscopy (FESEM), while thermogravimetric-differential scanning calorimetry (TG-DSC) was used to determine thermal stability. Alcohol washed samples undergo 30% weight loss whereas 16% in water washed samples was observed. The mean particle sizes were found to be increase from 37 nm to 100.9 nm and 35.3 nm to 55.2 nm for water and alcohol washed samples respectively. Hydrolysis of alkoxide was shown to be an effective means to prepare thermally stable titania by using alcohol washed samples as a precursor.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Molten-Salt Synthesis of O 3 -Type Layered Oxide Single Crystal Cathodes with Controlled Morphology towards Long-Life Sodium-Ion Batteries

Sodium layered oxides show great promise as affordable alternatives to lithium layered oxides, but their poor cycle life and air stability limit their practical potential. Micron-scale single crystals with greater packing density and lower surface area can overcome these challenges and improve performance compared to the traditional polycrystalline morphology. Herein, the authors present the synthesis of layered O 3 -type Na(Ni 0.3 Fe 0.4 Mn 0.3 )O 2 single-crystals with greatly improved cycle life and air stability. A molten-salt synthesis technique is adopted with excess sodium hydroxide to obtain platelet-like single crystals. Because the main mechanisms of both capacity fade and air degradation occur as a result of surface reactions at the opening of the sodium diffusion channels, particle morphology is found to be a critical metric for materials performance. More important than particle size or total surface area, the smaller proportion of exposed edge planes in the platelet morphology greatly reduces the amount of harmful surface reactions. Furthermore, the molten-salt method is found to eliminate the need for coprecipitated precursors and even form better morphology, starting from metal oxides instead of coprecipitated hydroxides.

25 ENERGY STORAGE↗
DOE OSTI2018

Morphological instability of aqueous dissolution of silicate glasses and minerals [Nonlinear dynamics of aqueous dissolution of silicate glasses and minerals: Morphological instability]

Understanding of aqueous dissolution of silicate glasses and minerals is of great importance to both Earth science and materials science. Silicate dissolution exhibits complex temporal evolution and spatial pattern formations. Recently, we showed how observed complexity could emerge from a simple self-organizational mechanism: dissolution of the silica framework in a material could be catalyzed by the cations released from the reaction itself. This mechanism enables us to systematically predict many key features of a silicate dissolution process including the occurrence of a sharp corrosion front (vs. a leached surface layer), oscillatory dissolution and multiple stages of the alteration process (e.g., an alteration rate resumption at a late stage of glass dissolution). Here, through a linear stability analysis, we show that this same mechanism can also lead to morphological instability of an alteration front, which, in combination with oscillatory dissolution, can potentially lead to a whole suite of patterning phenomena, as observed on archaeological glass samples, including wavy dissolution fronts, growth rings, incoherent bandings of alteration products, and corrosion pitting. Here, the result thus further demonstrates the importance of the proposed self-accelerating mechanism in silicate material degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A novel blue-greenish emitting phosphor Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} with high thermal stability

Highlights: • The Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} phosphors exhibit a broad excitation band. • The Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} emission color adjust from blue to green. • The Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} show superior thermal stability. - Abstract: Ba{sub 3}La{sub 1−m}K(PO{sub 4}){sub 3}F:mTb{sup 3+}(m = 0.01–0.50) phosphors have been prepared by a traditional high temperature solid-state reaction. XRD analysis verified the apatite-type phase structure of the as-prepared samples, and the morphology has been checked by the Scanning electron microscope (SEM). The emission spectrum of Ba{sub 3}LaK(PO{sub 4}){sub 3}F:Tb{sup 3+} phosphor consists of two regions, blue emission band from 380 to 470 nm and green emission band from 470 to 650 nm. With increasing Tb{sup 3+} ions doped concentration (m), the color hue of Ba{sub 3}La{sub 1−m}K(PO{sub 4}){sub 3}F:mTb{sup 3+}adjusts from blue to green. On the basis of concentration quenching method, the critical distance between Tb{sup 3+} ions is calculated to be 7.98 Å, suggesting that multipolar interaction predominate in quenching process. In addition, the temperature-dependence PL spectra of Ba{sub 3}LaK(PO{sub 4}){sub 3}F:0.01Tb{sup 3+} and Ba{sub 3}LaK(PO{sub 4}){sub 3}F:0.40Tb{sup 3+} phosphor are given,which exhibit superior thermal stability.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Effect of structure and morphology on thermal and electrical properties of polycarbonate film capacitors

Research is reported to identify polycarbonate (PC) film characteristics and fabrication procedures which extend the reliable performance range of PC capacitors to 125 C without derating, and establish quality control techniques and transfer technology to US PC film manufacturers. The approach chosen to solve these problems was to develop techniques for fabricating biaxially oriented (BX) 2 microns or thinner PC film with a low dissipation factor up to 140 C; isotropic dimensional stability; high crystallinity; and high voltage breakdown strength. The PC film structure and morphology was then correlated to thermal and electrical capacitor behavior. Analytical techniques were developed to monitor film quality during capacitor fabrication, and as a result, excellent performance was demonstrated during initial capacitor testing.

Yen, S. P. S.↗
DOE OSTI2020

Electrochemical Synthesis and Investigation of Stoichiometric, Phase-Pure CoSb 2 O 6 and MnSb 2 O 6 Electrodes for the Oxygen Evolution Reaction in Acidic Media

The electrochemical oxidation of water to oxygen gas is the primary counter reaction to the formation of hydrogen gas via water splitting. In acidic media, the only well-established and active oxygen evolution catalysts are expensive noble metal oxides such as IrO x and RuO x , necessitating the development of practical oxygen evolution catalysts that are stable in acidic media. In this study, we prepared stoichiometric, phase-pure CoSb 2 O 6 and MnSb 2 O 6 electrodes using electrochemical synthesis and investigated their ability to oxidize water in 0.5 M H 2 SO 4 (pH 0.3). In addition, their stabilities during the oxygen evolution reaction (OER) were carefully examined by comparing their morphologies, crystallinities, compositions, and surface compositions before and after the OER. The chlorine evolution reaction on CoSb 2 O 6 and MnSb 2 O 6 in acidic media was also examined so that their performances can be compared with previously reported non-stoichiometric CoSb 2 O 6 and MnSb 2 O 6 electrodes. The electrochemical properties and stabilities of stoichiometric, phase-pure CoSb 2 O 6 and MnSb 2 O 6 reported in this study can provide useful insights into the development and understanding of acid-stable, non-noble metal oxide-based OER catalysts.

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

Current-Induced Skyrmion Generation through Morphological Thermal Transitions in Chiral Ferromagnetic Heterostructures

Magnetic skyrmions promise breakthroughs in future memory and computing devices due to their inherent stability and small size. Their creation and current driven motion have been recently observed at room temperature, but the key mechanisms of their formation are not yet well-understood. Here it is shown that in heavy metal/ferromagnet heterostructures, pulsed currents can drive morphological transitions between labyrinth-like, stripe-like, and skyrmionic states. Using high-resolution X-ray microscopy, the spin texture evolution with temperature and magnetic field is imaged and it is demonstrated that with transient Joule heating, topological charges can be injected into the system, driving it across the stripe-skyrmion boundary. The observations are explained through atomistic spin dynamic and micromagnetic simulations that reveal a crossover to a global skyrmionic ground state above a threshold magnetic field, which is found to decrease with increasing temperature. It is demonstrated how by tuning the phase stability, one can reliably generate skyrmions by short current pulses and stabilize them at zero field, providing new means to create and manipulate spin textures in engineered chiral ferromagnets.

36 MATERIALS SCIENCE↗