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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Scanning transmission electron microscopy analysis of Ge(O)/(graphitic carbon nitride) nanocomposite powder

Analytical electron microscopy has revealed the structure of particles that were synthesized by chemical reaction of GeO{sub 2} with NaBH{sub 4} in the basic solution including graphitic carbon nitride (g-C{sub 3}N{sub 4}) powders. The g-C{sub 3}N{sub 4} was arranged by recrystallization of melamine at 600 °C under N{sub 2} gas atmosphere. The samples were dried at 60 °C or 180 °C for 4 h. The g-C{sub 3}N{sub 4} was observed as lamellae of several ten nm or less in size and had an amorphous-like structure with a distorted lattice in an area as small as a few hundred pm in size. The reaction product was Ge(O) particles as fine as several nm in size and composed of Ge and O atoms. Most of the particles must be of GeO{sub 2−x} with the amorphous-like structure that has also a distorted lattice in an area of a few hundred pm in size. In the sample dried at 60 °C, the particles were found to be dispersed in a wide area on the g-C{sub 3}N{sub 4} lamella. It is hard to recognize those particles in TEM images. The particles in the sample dried at 180 °C became larger and were easily observed as isolated lumps. Hence, these powders can be regarded as GeO{sub 2}/g-C{sub 3}N{sub 4} or Ge/GeO{sub 2}/g-C{sub 3}N{sub 4} nanocomposites, and expected to be applicable to anode materials for high energy Li-ion batteries due to Ge catalysis effect, accordingly. - Graphical abstract: STEM analysis of Ge(O)/(graphitic carbon nitride) nanocomposite powder. - Highlights: • Graphitic (g)-C{sub 3}N{sub 4} powder was prepared at 600 °C by recrystallization of melamine. • Ge(O) was prepared by chemical reaction in a solution including the g-C{sub 3}N{sub 4} powders. • The products can be regarded as GeO{sub 2}/g-C{sub 3}N{sub 4} or Ge/GeO{sub 2}/g-C{sub 3}N{sub 4} nanocomposites. • GeO{sub 2} was amorphous several-nm particles and g-C{sub 3}N{sub 4} was amorphous lamella of several 10 nm in size. • We expect them to be applicable for high energy Li-ion battery anode materials.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Development of mechanical properties in a CaO added AZ31 magnesium alloy processed by equal-channel angular pressing

Processing through the application of equal-channel angular pressing (ECAP) is recognized as one of the attractive severe plastic deformation techniques where the processed bulk metals generally achieve ultrafine-grained microstructure leading to improved physical characteristics and mechanical properties. Magnesium has received much attention to date for its lightweight, high strength and excellent elasticity. Mg alloys with addition of CaO is reported to provide the successful casting procedure without usage of greenhouse gas, SF{sub 6}, whereas it is generally used for preventing the oxidation of Mg during casting. In the present investigation, a CaO added AZ31 (AZ31-CaO) magnesium alloy was processed by ECAP at elevated temepratures with a few steps of reduction which result in significant grain refinement to ~ 1.5 μm after 6 passes. Compression testing at room temperature demonstrated the AZ31-CaO alloy after ECAP showed enhanced yield strength more than the as-processed commercial AZ31 alloy while both alloys maintained ductility in spite of significant reduction in grain size. The improved strength in the AZ31-CaO alloy was attributed to the formation of fine Al{sub 2}Ca precipitates which experience breaking-up through ECAP and accelerate the microstructural refinement. Moreover, the preservation of ductility was attributed to the enhancement of strain hardening capability in the AZ31 alloy at room temperature. This study discusses the feasibility of using ECAP to improve both strength and ductility on magnesium alloys by applying the diagram describing the paradox of strength and ductility. - Highlights: • AZ31 and AZ31-CaO magnesium alloys were processed by ECAP up to 6 passes. • AZ31-CaO alloy after ECAP showed improved yield strength without losing ductility. • CaO in AZ31 forms fine Al{sub 2}Ca accelerating microstructural refinement during ECAP. • Feasibility of using ECAP was shown to improve both strength and ductility in Mg.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Cooling thermal parameters and microstructure features of directionally solidified ternary Sn–Bi–(Cu,Ag) solder alloys

Low temperature soldering technology encompasses Sn–Bi based alloys as reference materials for joints since such alloys may be molten at temperatures less than 180 °C. Despite the relatively high strength of these alloys, segregation problems and low ductility are recognized as potential disadvantages. Thus, for low-temperature applications, Bi–Sn eutectic or near-eutectic compositions with or without additions of alloying elements are considered interesting possibilities. In this context, additions of third elements such as Cu and Ag may be an alternative in order to reach sounder solder joints. The length scale of the phases and their proportions are known to be the most important factors affecting the final wear, mechanical and corrosions properties of ternary Sn–Bi–(Cu,Ag) alloys. In spite of this promising outlook, studies emphasizing interrelations of microstructure features and solidification thermal parameters regarding these multicomponent alloys are rare in the literature. In the present investigation Sn–Bi–(Cu,Ag) alloys were directionally solidified (DS) under transient heat flow conditions. A complete characterization is performed including experimental cooling thermal parameters, segregation (XRF), optical and scanning electron microscopies, X-ray diffraction (XRD) and length scale of the microstructural phases. Experimental growth laws relating dendritic spacings to solidification thermal parameters have been proposed with emphasis on the effects of Ag and Cu. The theoretical predictions of the Rappaz-Boettinger model are shown to be slightly above the experimental scatter of secondary dendritic arm spacings for both ternary Sn–Bi–Cu and Sn–Bi–Ag alloys examined. - Highlights: • Dendritic growth prevailed for the ternary Sn–Bi–Cu and Sn–Bi–Ag solder alloys. • Bi precipitates within Sn-rich dendrites were shown to be unevenly distributed. • Morphology and preferential region for the Ag{sub 3}Sn growth depend on Ag content and Ṫ{sub L}. • Rappaz-Boettinger model reasonably estimated the experimental scatter of λ{sub 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides

The metallic binder phase dictates the toughening behavior of WC-Co cemented carbides (hardmetals), even though it occupies a relative small fraction of the composite. Studies on deformation and phase transformation of the binder constituent are scarce. Grinding represents a key manufacturing step in machining of hardmetal tools, and is well-recognized to induce surface integrity alterations. In this work, metallurgical alterations of the binder phase in ground WC-Co cemented carbides have been assessed by a combination of electron back scattered diffraction and transmission electron microscopy techniques. The Co-base binder experiences a martensitic phase transformation from fcc to hcp crystal structure, predominantly in the first 5 μm below the surface. The hcp fraction decreases gradually along a depth of 10 μm. Surface Co displays severe plastic deformation under the highest strain, resulting in formation of nanocrystalline grains in the first micrometer below the surface. Microstructural refinement within the binder phase is observed even at greater depth. Stacking faults were detected in most of the refined grains. The metallurgical alterations of the binder phase modify the local stress distribution during grinding, which affects the discerned subsurface microcracking. The resulting residual stress profile is the sum of multiple subsurface changes, such as phase transformation, severe plastic deformation and grain refinement, where it is discerned that the depth profile of the transformed hcp-Co fraction coincides with the grinding-induced residual stress profile.

36 MATERIALS SCIENCE↗
DOE OSTI2018

TEM investigations on lath martensite substructure in quenched Fe-0.2C alloys

Highlights: • Twin can be lath martensite substructure in low-carbon steels. • Detwinning behavior occurs in an auto-tempering process during quenching. • Detwinning may result in the formation of twinned laths. • Detwinning may result in the laths with dislocation-like contrast as substructure. - Abstract: Lath martensite in low-carbon steels is the main microstructural feature in the quenched state, and dislocations have been generally recognized as the substructure of lath martensite. However, the effects of quenching conditions on the quenched substructure have not yet been fully understood. In the present work, a Fe-0.2C (wt%) alloy was selected for detailed investigations on the microstructural evolution at various austenitizing temperatures. Microstructural characterization was carried out by using a conventional transmission electron microscope (TEM). The substructure of lath martensite was found to vary with austenitizing temperature. In the 1200 °C-water-quenched (WQ) samples, twinned laths (two specific variants having a {112}<111>-type twin relationship) and a twinned region (laths with the twin structure as their substructure) can be observed. Almost all lath martensite with a high density of fine twins as its substructure can be obtained in the 1300 °C-WQ samples. The twins gradually disappear or detwinning-occurs during TEM observations carried out with in situ heating. A further increase in temperature results in the formation of twinned laths and then lath with dislocation-like contrasts or lines appears as the substructure. These results suggested that a completely twin structure can be the initial substructure of lath martensite, and lath with dislocation-like contrasts or lines as its substructure is most likely the auto-tempering result of twinning.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The microstructure and property variations of metals induced by electric current treatment: A review

Heat treatment has been widely applied for manipulating the microstructure and properties of metals with thermal energy. The thermal energy triggers the atomic diffusion accompanied by dislocation movement and results in the subsequent property variations in metals. One of the attractive efforts in the past decades is the development of a direct treatment of metals with electric current stressing as an alternative method for conventional heat treatment. Electric current treatment provides thermal energy from Joule heat (thermal effect) and kinetic energy from electron momentum (athermal effect). This article reviewed the practices of electric current treatment, microstructure-property variations and the physical metallurgy involved in a variety of metals. Both thermal and athermal effects have been well recognized in the literatures. An appropriate manipulation of the electric current treatment enables the control of both effects and thus the microstructure and properties of metals.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Quantifying the inter- and intra-granular stresses and their effects on deformation behaviors for the polycrystalline hexagonal beryllium by neutron diffraction

Highlights: • The inter- and intra-granular stresses are quantified for the polycrystalline hexagonal metal beryllium. • Composite behavior of the internal stresses is revealed in the polycrystalline beryllium. • Those internal stresses show the obvious grain-orientation dependence. • Those stresses can be significantly tuned by the temperature and strain rate effects. • The dislocation slip and twinning are quantified together with the inter- and intra-granular stored energies. - Abstract: The internal stresses developing at different length scales play the important role in materials performance. This importance has been well recognized for the cubic metals, however, not for the hexagonal close-packed (hcp) ones. The present work investigates the intergranular and intragranular stresses in the polycrystalline hexagonal beryllium by neutron diffraction. The correlation between those internal stresses and the deformation mechanism is revealed, and the strain rate and temperature effects on those stresses are presented. A composite behavior of intergranular and intragranular stresses is observed, which can be significantly tuned by the temperature and strain rate effects. The intergranular stress and stored energy are large for the soft-oriented grains (SOGs), while the intragranular stress and stored energy are large for the hard-oriented ones (HOGs). Both of those stresses are significantly high for the dynamic strain rate while they are relatively low for the elevated temperature. The large internal stresses in the dynamically compressed specimen should be attributed to the large number of twins and high density of dislocations. Different HOGs-SOGs configurations are proposed on the light of those observations, which might facilitate the properties controlling and extend the application scope for the hcp metal beryllium.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Predicting phase behavior in high entropy and chemically complex alloys

The interest in high entropy alloys and other metallic compounds with four or more elements at near-equiatomic ratios has drawn attention to the ability to rapidly predict phase behavior of these complex materials, particularly where existing thermodynamic data are lacking. In this paper, we discuss aspects of this from the point of view of predicting without utilizing (or fitting) experimental data. Of particular interest are heuristic approaches that provide prediction of single-phase compositions, more rigorous approaches that tackle the thermodynamics from a more fundamental point of view, and simulation approaches that provide further insight into the behaviors. This paper covers cases of all three of these, in order to examine the strengths and weaknesses of each approach, and to indicate directions where these may be utilized and improved upon. Of particular interest is moving beyond “which composition may form a solid solution,” to recognizing the importance of underlying thermodynamic realities that affect the temperature- and composition-dependent transformations of these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Photocatalytic performances of BiFeO{sub 3} particles with the average size in nanometer, submicrometer, and micrometer

Highlights: • Three different synthesis routes have been taken to successfully prepare the BiFeO{sub 3} particles with the different morphologies and average size in 50, 500 nm, and 15 μm. • For photodegradation of dyes under visible irradiation in the presence of BiFeO{sub 3}, the photocatalytic efficiency increases quickly with the decrease in size. • The enhanced photocatalytic efficiency of BiFeO{sub 3} nanoparticles may attribute to more surface active catalytic-sites and shorter distances carriers have to migrate to the surface reaction sites. - Abstract: Three different synthesis routes were taken to successfully prepare the BiFeO{sub 3} particles with the different morphologies and average size in 50, 500 nm, and 15 μm, respectively. The crystal structure was recognized to be a distorted rhombohedral one with the space group R3c. With the decrease in particle size, obvious decrease in peak intensity and redshift in peak position were observed for the Raman active bands. The narrow band gap was determined from the UV–vis absorption spectra, indicating the semiconducting nature of the BiFeO{sub 3}. For photodegradation of dyes under visible irradiation in the presence of BiFeO{sub 3}, the photocatalytic efficiency increased quickly with the decrease in size which may attribute to more surface active catalytic-sites and shorter distances carriers had to migrate to the surface reaction sites.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Geometric magnetic frustration in RE{sub 2}O{sub 2}S oxysulfides (RE = Sm, Eu and Gd)

Graphical abstract: Stacked planes in the <001> direction of an oxysulfide structure, showing the triangular nets formed by rare earth cations, which moments present geometric magnetic frustration. - Highlights: • We prepared monophasic RE{sub 2}O{sub 2}S Oxysulfides (RE = Sm, Eu and Gd). • RE{sub 2}O{sub 2}S compounds were characterized regarding structural and magnetic properties. • Mössbauer spectra were obtained for Eu{sub 2}O{sub 2}S and Gd{sub 2}O{sub 2}S at different temperatures. • Oxysulfides present geometric magnetic frustration of the rare-earth sublattice. - Abstract: RE{sub 2}O{sub 2}S oxysulfides (with RE = Sm, Eu and Gd) were prepared and characterized regarding their structural and magnetic properties. The compounds crystallized in the trigonal symmetry (space group P-3m/D{sub 3}{sup 3}d), with the lattice parameter varying linearly with the ionic radius of the RE cation. All these oxysulfides are magnetically frustrated and only the gadolinium sample showed magnetic order down to 3 K. The magnetic frustration is attributed to the spatial distribution of cations over the lattice, where the RE’s magnetic moments occupy the sites forming a triangular plane lattice, perpendicular to the direction. This geometric magnetic frustration was firstly recognized for these oxysulfides.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Oxygen deficiency induced nickel based oxides for UV & IR sensitive photo-conductive devices

Ni(NO{sub 3}){sub 3}.6H{sub 2}O has been thermally decomposed to synthesize NiO{sub x} (0 3-δ synthesis. These metal oxides have been characterized by XRD, SEM, TEM, XPS and UV–vis spectroscopy for the determination of their crystal structures, structural morphologies, oxidation states and optical band gaps. The devices, made of nanocrystalline-composites or nanocomposites, have been fabricated on gold coated soda lime glasses, where the device based on NiO{sub x} has been found applicable for UV photo-conducting and LaNiO{sub 3-δ} has been recognized as a potential IR photo-conducting sensors. Their respective current amplifications have been recorded 8 and 2.2 times more than the dark current at 2 V of DC bias. The UV sensor has been explained by direct band gap semiconducting nature of NiO{sub x} and IR sensitivity of LaNiO{sub 3-δ} was explained in terms oxygen deficiency induced band gap opening.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Machine learning for materials science: Barriers to broader adoption

We report machine learning is on a bit of a tear right now, with advances that are infiltrating nearly every aspect of our lives. In the domain of materials science, this wave seems to be growing into a tsunami. Yet, there are still real hurdles that we face to maximize its benefit. This Matter of Opinion, crafted as a result of a workshop hosted by researchers at Sandia National Laboratories and attended by a cadre of luminaries, briefly summarizes our perspective on these barriers. By recognizing these problems in a community forum, we can share the burden of their resolution together with a common purpose and coordinated effort.

36 MATERIALS SCIENCE↗
DOE OSTI2017

High thermoelectric performance in (Bi 0.25 Sb 0.75 ) 2 Te 3 due to band convergence and improved by carrier concentration control

Bi 2 Te 3 has been recognized as an important cooling material for thermoelectric applications. Yet its thermoelectric performance could still be improved. Here we propose a band engineering strategy by optimizing the converging valence bands of Bi 2 Te 3 and Sb 2 Te 3 in the (Bi 1-x Sb x ) 2 Te 3 system when x = 0.75. Band convergence successfully explains the sharp increase in density-of-states effective mass yet relatively constant mobility and optical band gap measurement. This band convergence picture guides the carrier concentration tuning for optimum thermoelectric performance. To synthesize homogeneous textured and optimally doped (Bi 0.25 Sb 0.75 ) 2 Te 3 , excess Te was chosen as the dopant. Uniform control of the optimized thermoelectric composition was achieved by zone-melting which utilizes separate solidus and liquidus compositions to obtain zT = 1.05 (at 300 K) without nanostructuring.

36 MATERIALS SCIENCE↗
DOE OSTI2013

An investigation into positron emission tomography contouring methods across two treatment planning systems

Positron emission tomography (PET) imaging has been used to provide additional information regarding patient tumor location, size, and staging for radiotherapy treatment planning purposes. This additional information reduces interobserver variability and produces more consistent contouring. It is well recognized that different contouring methodology for PET data results in different contoured volumes. The goal of this study was to compare the difference in PET contouring methods for 2 different treatment planning systems using a phantom dataset and a series of patient datasets. Contouring methodology was compared on the ADAC Pinnacle Treatment Planning System and the CMS XiO Treatment Planning System. Contours were completed on the phantom and patient datasets using a number of PET contouring methods—the standardized uptake value 2.5 method, 30%, 40%, and 50% of the maximum uptake method and the signal to background ratio method. Differences of >15% were observed for PET-contoured volumes between the different treatment planning systems for the same data and the same PET contouring methodology. Contoured volume differences between treatment planning systems were caused by differences in data formatting and display and the different contouring tools available. Differences in treatment planning system as well as contouring methodology should be considered carefully in dose-volume contouring and reporting, especially between centers that may use different treatment planning systems or those that have several different treatment planning systems.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Accuracy evaluation of the optical surface monitoring system on EDGE linear accelerator in a phantom study

Frameless stereotactic radiosurgery (SRS) requires dedicated systems to monitor the patient position during the treatment to avoid target underdosage due to involuntary shift. The optical surface monitoring system (OSMS) is here evaluated in a phantom-based study. The new EDGE linear accelerator from Varian (Varian, Palo Alto, CA) integrates, for cranial lesions, the common cone beam computed tomography (CBCT) and kV-MV portal images to the optical surface monitoring system (OSMS), a device able to detect real-time patient's face movements in all 6 couch axes (vertical, longitudinal, lateral, rotation along the vertical axis, pitch, and roll). We have evaluated the OSMS imaging capability in checking the phantoms' position and monitoring its motion. With this aim, a home-made cranial phantom was developed to evaluate the OSMS accuracy in 4 different experiments: (1) comparison with CBCT in isocenter location, (2) capability to recognize predefined shifts up to 2° or 3 cm, (3) evaluation at different couch angles, (4) ability to properly reconstruct the surface when the linac gantry visually block one of the cameras. The OSMS system showed, with a phantom, to be accurate for positioning in respect to the CBCT imaging system with differences of 0.6 ± 0.3 mm for linear vector displacement, with a maximum rotational inaccuracy of 0.3°. OSMS presented an accuracy of 0.3 mm for displacement up to 1 cm and 1°, and 0.5 mm for larger displacements. Different couch angles (45° and 90°) induced a mean vector uncertainty < 0.4 mm. Coverage of 1 camera produced an uncertainty < 0.5 mm. Translations and rotations of a phantom can be accurately detect with the optical surface detector system.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2017

Effect of pore penetration on transport through supported membranes studied by electron microscopy and pervaporation

It has long been recognized that the performance of supported membranes comprising a thin, selective layer and a microporous support layer, is affected by penetration of the selective layer into the porous support. We have attempted to shed light on this phenomenon using a combination of pervaporation experiments and hard angle dark-field scanning transmission electron microscopy (HAADF-STEM). We use a nanophase-separated polystyrene-b-polydimethylsiloxane-b-polystyrene (SDS) as the selective layer and microporous polytetrafluoroethylene (PTFE) as the support layer. Effective permeabilities of butanol and water were measured as a function of selective layer thickness using a dilute butanol/water mixture as the feed in pervaporation. We were able to estimate the pore penetration layer thickness by comparing experiments with model calculations. We were also able to directly observe the pore penetration by HAADF-STEM. The choice in using a nanophase-separated block copolymer as the selective layer enabled identification of the regions of pore penetration. In conclusion, the pore penetration layer thickness obtained from the HAADF-STEM micrographs corresponded well with estimates based on pervaporation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Maximizing selectivity: An analysis of isoporous membranes

Membranes are compelling candidates for many separation-based industrial processes. However, all synthetic membranes are subject to well-recognized permeability-selectivity trade-offs that hinder their use in advanced applications. Having uniform nanoscale pore size, isoporous nanofiltration and ultrafiltration membranes have attracted wide research interest. However, quantitative analysis of isoporous membrane performance is lacking - particularly at module and system-level scales. In this study, an analytical model is built to investigate how membrane pore-size distribution affects the solute separation efficiency (i.e., rejection and selectivity). The model accounts for convective hindrance as well as concentration polarization and explores effects on separation from the solute-to-pore-size ratio and percent recovery (i.e., fraction of feed flow that passes through the membrane). At the module level, our analysis suggests that a notably sharper rejection vs. solute size curve can be obtained as the pore-size distribution becomes narrower. Additionally, as the recovery increases, the rejection of a solute is maintained at a high level using isoporous membranes while the rejection drops rapidly for membranes that possess a disperse pore-size distribution. Furthermore, in the separation of mixed solutes, isoporous membranes achieve a large selectivity with a modest loss of permeability. Overall, this study elaborates the unique role that isoporous membranes play within the permeability-selectivity trade-off relations and identifies the most exciting opportunities for their future applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A critical review and commentary on recent progress of additive manufacturing and its impact on membrane technology

Membrane separations has been increasingly recognized as a key technology platform for improving the energy efficiency of many separations processes. Likewise, additive manufacturing (AM), or 3-dimensional (3D) printing as it is often called, is a rapidly emergent technology platform for manufacturing in many industrial sectors. It has become increasingly common to marry these two platforms to take advantage of the additive nature of 3D printing with the increasing need for membrane technology that is adaptable to separations needs. Conventional membrane manufacturing approaches, such as casting, typically result in thick membranes that limit productivity and potentially waste material in a non-performing support layer. Interfacial polymerization (IP) offered a new vision for thin-film composite desalination membranes, yet it was limited to certain chemistries while exhibiting other drawbacks. Additive manufacturing offers certain benefits over these techniques to membranes, including the ability to expand the library of materials that can be processed while also offering a degree of customization that is impossible in conventional manufacturing. This review article evaluates an increasing body of literature on using printing to make membranes and considers the limitations and opportunities for printing to enhance existing membrane technology and expand the reach of membranes into other industries. Furthermore, we also provide a perspective from leading experts in membrane technology to see where there are opportunities to use printing in different membrane science disciplines.

36 MATERIALS SCIENCE↗