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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Continuous Flow Fabrication of Block Copolymer-Grafted Silica Micro-Particles in Environmentally Friendly Water/Ethanol Media

Polymer-grafted inorganic particles (PGIPs) are attractive building blocks for numerous chemical and material applications. Surface-initiated controlled radical polymerization (SI-CRP) is the most feasible method to fabricate PGIPs. However, a conventional in-batch reaction still suffers from several disadvantages, including time-consuming purification processes, low grafting efficiency, and possible gelation problems. Herein, a facile method is demonstrated to synthesize block copolymer–grafted inorganic particles, that is, poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMEMA)-b-poly(N-isopropylacrylamide) (PNIPAM)–grafted silica micro-particles using continuous flow chemistry in an environmentally friendly aqueous media. Immobilizing the chain transfer agent and subsequent SI-CRP can be accomplished sequentially in a continuous flow system, avoiding multi-step purification processes in between. The chain length (MW) of the grafted polymers is tunable by adjusting the flow time or monomer concentration, and the narrower molar mass dispersity (&ETH; < 1.4) of the grafted polymers reveals the uniform polymer chains on the particles. Moreover, compared with the in-batch reaction at the same condition, the continuous system also suppresses possible gelation problems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Ultra–high molecular weight polyethylene micro–ribbon fibers gel spun using orange terpenes

Toxic, hazardous petrochemical solvents are commonly used for industrial-scale ultra-high molecular weight polyethylene (UHMWPE) fiber production, but orange terpenes, a byproduct of orange fruit production, present a bio-derived, sustainable alternative. In this work, fine UHMWPE fibers were spun using orange terpenes as the spin solvent, hot-drawn at a draw ratio of 5:1, investigated for their morphology, microstructure, and thermal and mechanical properties. The resulting fibers exhibited a flat, micro-ribbon cross-section, which is highly desirable for achieving high fiber volume fractions in UHMWPE-fiber reinforced composites. After drawing, the fibers possessed 4× greater breaking tenacity than any previously published studies on UHMWPE fibers spun using orange terpenes with a tenacity of 8.6 cN/dtex and tensile modulus of 229.2 cN/dtex. Microstructural analysis via differential scanning calorimetry and X-ray diffraction revealed that the hot drawing process significantly increased molecular orientation, but crystallinity decreased due to crystallite melting during drawing. Therefore, the mechanical properties of these fibers may be significantly improved with optimization of the fiber drawing process. As a work, this work establishes the strong potential of orange terpenes as an environmentally-friendly alternative solvent for UHMWPE gel spinning and sets a foundation for future parametric optimization of the spinning and drawing of these fibers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Polymer etching by atmospheric-pressure plasma jet and surface micro-discharge sources: Activation energy analysis and etching directionality

Treatments of polymer films using either a MHz atmospheric pressure plasma jet (APPJ) or an atmospheric pressure surface micro-discharge (SMD) plasma are investigated. While the typical approach to determine relevant reactive species is to correlate surface effects with gas phase species measurement, this does not capture potential synergistic or other complex effects that may be occurring. Activation energy and directionality of the etching process can characterize what is occurring at the surface for these processes in more detail. The APPJ source shows an apparent activation energy of ~0.18 eV at 8 mm distance and up to ~0.34 eV at 16mmdistance for a temperature range of 20–80 °C tested with thin polymer films. The APPJ source shows directional etching at 8 mm distance with less anisotropy the more distance is increased. The SMD source has an apparent activation energy of ~0.8–0.9 eV at a distance of 3 mm. The SMD also only shows isotropic etching behavior. However the SMD surface chemistry changes significantly to less oxidation with increased temperature while the APPJ source induced modifications remain very similar with temperature change. The lower apparent activation energy of the APPJ induced etching reactions as compared with low pressure work (0.5 eV) and observation of line-of-sight contribution to etching suggests the involvement of a directional species at closer distances facilitating the etching which falls off with increasing distance. The high activation energy of the SMD suggests that species with less capability for etching is responsible compared to the APPJ and low pressure plasma. In conclusion, the high surface oxidation from low temperature SMD treatments shows that the surface is being oxidized but not sufficiently to reach the desorption step of the etching process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Quantification of Sheet Resistance in Boron-Diffused Silicon Using Micro-Photoluminescence Spectroscopy at Room Temperature

A micro-photoluminescence-based technique is presented, to quantify and map sheet resistances of boron-diffused layers in silicon solar cell precursors with micron-scale spatial resolution at room temperature. The technique utilizes bandgap narrowing effects in the heavily-doped layers, yielding a broader photoluminescence spectrum at the long-wavelength side compared to the spectrum emitted from lightly doped silicon. By choosing an appropriate spectral range as a metric to assess the doping density, the impacts of photon reabsorption on the analysis can be avoided; thus, an accurate characterization of the sheet resistance can be made. This metric is demonstrated to be better representative of the sheet resistance than the surface doping density or the total dopant concentration of the diffused layer. The technique is applied to quantify sheet resistances of 12-um-wide diffused fingers in interdigitated back-contact solar cell precursors and large diffused areas. The results are confirmed by both 4-point probe and time-of-flight secondary-ion mass spectrometry measurements. Lastly, the practical limitations associated with extending the proposed technique into an imaging mode are presented and explained.

14 SOLAR ENERGY↗
DOE OSTI2020

Numerical investigation of micro-galvanic corrosion in Mg alloys: Role of the cathodic intermetallic phase size and spatial distributions

Magnesium alloys are of increasing interest in structural applications due to their low-density, moderate specific strength and stiffness, recyclability, and high damping among other properties. However, the wide-scale applicability of magnesium alloys in structural applications has been limited due to many factors including its poor corrosion resistance. In this work, a numerical investigation to simulate the micro-galvanic corrosion behavior was performed to examine the influence of size and distribution of cathodic intermetallic phase (ß-Mg17Al12) in a Mg matrix. The ratio of cathodic to anodic surface area was kept constant in each simulation condition to understand the effect of size and spacing distributions. In general, fragmentation of a larger intermetallic particle into smaller ones was found to enhance the localized current density. However, the uniform distribution of this small intermetallic phase throughout the matrix was found to reduce the overall dissolution current density and hence, pitting corrosion severity.

Beura, Vikrant↗
DOE OSTI2020

Toward Real-Time Analysis of Synchrotron Micro-Tomography Data: Accelerating Experimental Workflows with AI and HPC

ynchrotron light sources are routinely used to perform imaging experiments. In this paper, we review the relevant computational stages, identify bottlenecks, and highlight future opportunities to streamline data acquisition for experimental microscopy workflows. We demonstrate our preliminary exploration with an end-to-end scientific workflow on Summit based on micro-computed tomography data. Computational elements include: 1) reconstruction of volumetric image data; 2) denoising with deep neural networks; and 3) non-local means based segmentation and quantitative analysis.

Mcclure, James↗
DOE OSTI2022

Cross Inference of Throughput Profiles Using Micro Kernel Network Method

Dedicated network connections are being increasingly deployed in cloud, centralized and edge computing and data infrastructures, whose throughput profiles are critical indicators of the underlying data transfer performance. Due to the cost and disruptions to physical infrastructures, network emulators, such as Mininet, are often used to generate measurements needed to estimate throughput profiles, typically expressed as a function of the connection round trip time. The profiles estimated using measurements from such emulated networks are usually inaccurate for high bandwidth and high latency connections, since they do not accurately reflect the critical network transport dynamics mainly due to computing and memory constraints of the host. We present a machine learning (ML) method to estimate the throughput profiles using emulation measurements to closely match the testbed and production network profiles. In particular, we propose a micro Kernel Network (mKN) that provides baseline throughput measurements on the host running Mininet emulations, which are used to learn a regression map that converts them to the corresponding testbed measurement estimates. Once initially learned, this map is applied to measurements from subsequent network emulations on the same host. We present experimental measurements to illustrate this approach, and derive generalization equations for the proposed mKN-ML method. Using a four-site scenario emulation, we show the effectiveness of this method in providing accurate concave throughput profiles from inaccurate convex or non-smooth ones indicated by Mininet emulation.

Rao, Nageswara↗
DOE OSTI2017

Balloon-Assisted Chemoembolization Using a Micro-Balloon Catheter Alongside a Microcatheter for a Hepatocellular Carcinoma with a Prominent Arterioportal Shunt: A Case Report

Although transcatheter arterial chemoembolization is one of the established treatments for hepatocellular carcinoma (HCC), it is difficult to treat HCCs with prominent arterioportal (AP) shunts because anticancer drugs and embolic materials migrate into the non-tumorous liver through the AP shunts and may cause liver infarction. We developed a novel method of balloon-assisted chemoembolization using a micro-balloon catheter alongside a microcatheter simultaneously inserted through a single 4.5-Fr guiding sheath, comprising proximal chemoembolization with distal arterial balloon occlusion. We applied this method to treat an HCC with a prominent distal AP shunt induced by previous proton beam therapy and achieved successful chemoembolization without non-tumorous liver infarction under temporal balloon occlusion of a distal AP shunt.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

MVP™ Micro Vascular Plug Systems for the Treatment of Pulmonary Arteriovenous Malformations

Purpose: To describe our institutional experience with MVP™ micro vascular plug systems for the treatment of pulmonary arteriovenous malformations (PAVMs). Materials and Methods: We performed a retrospective medical record review of 52 patients with 119 PAVMs treated exclusively with MVP™ systems (69 procedures/153 MVP™ systems) between July 2014 and July 2018. All patients had PAVMs with feeding artery diameters ≥ 2 mm. MVP™ systems were deployed according to physician preference. We collected patient demographic information; procedural data (including size of feeding artery, size and number of embolics used per PAVM, fluoroscopy time, contrast administration), technical success rates, complications, and persistence. Persistence was assessed using computed tomography angiography (CTA) performed 1–3 months and 3–5 years after embolization per clinical protocol. Results: All procedures were technically successful without major complications. Mean feeding artery diameter was 3.3 ± 1.2 mm. Mean fluoroscopy time per procedure and contrast volume administered per procedure were 35 ± 16 min and 217 ± 101 mL, respectively. A mean of 1.3 ± 0.8 MVP™ systems was used per PAVM. There were no instances of persistence during a mean follow-up time of 328 ± 258 days (range 26 to 914 days). Conclusions: For PAVMs with feeding artery diameters of 2 to 7.9 mm (mean 3.3 ± 1.2 mm), MVP™ systems are safe and effective given their high technical success rates and lack of persistence. Further prospective work will be required to elucidate the advantages and disadvantages of these MVP™ systems for PAVM embolization. Level of Evidence: Level III.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Regimes of Micro-bubble Formation Using Gas Injection into Ladle Shroud

Gas injection into a ladle shroud is a practical approach to produce micro-bubbles in tundishes, to promote inclusion removal from liquid steel. A semi-empirical model was established to characterize the bubble formation considering the effect of shearing action combined with the non-fully bubble break-up by turbulence. The model shows a good accuracy in predicting the size of bubbles formed in complex flow within the ladle shroud.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evolutions of the Micro- and Macrostructure and Tensile Property of Cu-15Ni-8Sn Alloy During Electromagnetic Stirring-Assisted Horizontal Continuous Casting

The present study investigates the evolution of the micro- and macrostructure and tensile property of the Cu-15Ni-8Sn (weight percent) alloy prepared by horizontal continuous casting and electromagnetic stirring (EMS). The results show that the application of EMS is beneficial for grain refinement and for microstructure transformation from the dendrite to the rosette structure and that it leads to a significant improvement in the tensile property. The forced flow induced by EMS homogenizes the temperature field ahead of the solid-liquid interface, disturbing the heat flow direction and resulting in the columnar to equiaxed transition. The grain refinement under different electromagnetic stirring frequencies is mainly derived from the homogenization of the temperature and the remelting of dendritic arms. In addition, the evolution of the tensile property with and without EMS is discussed from the perspective of fracture mode and fine-grain strengthening.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Voltage on Microstructure and Corrosion Resistance of Micro-arc Oxidation Ceramic Coatings Formed on KBM10 Magnesium Alloy

Micro-arc oxidation (MAO) coatings on KBM10 magnesium alloy were prepared in an electrolyte system with sodium silicate, potassium hydroxide, sodium tungstate, and citric acid. The effects of voltage on the microstructure and corrosion resistance of MAO coatings were studied using stereoscopic microscopy, scanning electron microscopy, x-ray diffraction, scratch tests, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results showed that the roughness of the MAO coatings, diameter, and number of pores increase with the increase in voltage. The coating formed at the voltage of 350 V exhibited the best adhesive strength when evaluated by the automatic scratch tester. The coatings were mainly composed of MgO, MgWO{sub 4}, and Mg{sub 2}SiO{sub 4}, and the content of Mg{sub 2}SiO{sub 4} increased with the increase in voltage. The corrosion resistance of MAO coatings could be improved by changing the applied voltage, and the best corrosion resistance of MAO coating was observed at the voltage of 350 V.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of Micro-arc Oxidation Coatings on 6N01 Aluminum Alloy Under Different Electrolyte Temperature Control Modes

The micro-arc oxidation coatings of 6N01 aluminum alloy produced under different control modes of the electrolyte temperature are discussed in detail. Compared to those coated by a thermostatically controlled treatment, the coatings had different surface characterizations when they were coated without controlling the electrolyte temperature, particularly after treatment involving boiling electrolytes. Scanning electron microscopy and confocal laser scanning microscopy were used to observe the morphology of the coatings. Energy-dispersive spectrometry and x-ray diffractometer were used to characterize their elemental and crystalline phase compositions. The results indicate that the treatment without a controlled electrolyte temperature ultimately led to a thicker and rougher film with a respectably thick inner barrier film, a lower content of γ-Al{sub 2}O{sub 3} and better corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Micro-crack Pinning and Interfacial Fracture in Mixed Metal Oxide Reinforced Epoxy Nanocomposite

The effects of mixed metal oxides (Ce{sub x}Zr{sub 1−x}O{sub 2}) nanoparticle dispersion on the mechanical properties and fracture mechanisms of epoxy polymer matrix and its composite with glass fiber system are reported in this paper. Ce{sub x}Zr{sub 1−x}O{sub 2} nanoparticles are synthesized using sol–gel method, and its crystallinity is optimized. Epoxy nanocomposites are synthesized by a dispersion technique, and the compressive properties are optimized. The glass transition temperature has been improved. Epoxy with 5 wt.% of Ce{sub 0.75}Zr{sub 0.25}O{sub 2} shows optimal results with an increase of 17.4% in compressive modulus, and an increase of 23.4% in compressive strength with respect to those of neat epoxy. This improvement attributes to higher strength of shearing of polymer during the fracture of the nanoparticle interface. Micro-crack kinks at the interfaces can further delay fracture under compression. E-glass fabric-reinforced 5 wt.% Ce{sub 0.75}Zr{sub 0.25}O{sub 2}–epoxy nanocomposite also shows improvement in the mechanical properties via nanoscale interface with fibers. This type of ceramic nanocomposites has useful applications in thermal/electrical insulations besides improving the compressive/buckling properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Microstructure and Work Hardening Behavior of Micro-plasma Arc Welded AISI 316L Sheet Joint

The aim of this research is to investigate the microstructural changes and work hardening behavior of AISI 316L 0.5-mm-thick sheet due to micro-plasma arc welding. AISI 316L similar sheets were welded in single-pass square butt joint configuration. The microstructure in the fusion zone typically contains a variety of complex δ-ferrite-austenitic structure, which significantly increased hardness value compared to the base material because of rapid solidification of the weld pool. Systematic tensile test was performed to investigate strain rate sensitivity of the welded joint under quasi-static loading conditions. The multistage work hardening behavior was determined by Kocks–Mecking (K–M) model and differential Crussard–Jaoul analysis. In both the cases, stage III work hardening behavior and stage IV work hardening behavior were observed. The stress–strain curves of welded specimen at different strain rates were analyzed in terms of Hollomon, Ludwik and Swift equations to determine work hardening exponent values. The welded joints were ruptured in the transition zone of heat affected and fusion zones. The fractographic observation exhibited variation in dimple and void density over strain rate from 0.0001 to 0.0015 s{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Micro-Arc Oxidation on Friction–Wear Behavior of Cold-Sprayed Al Coating in 3.5 wt.% NaCl Solution

A cold-sprayed Al coating on S355 steel was processed using micro-arc oxidation (MAO). The friction–wear behavior of the obtained coating in 3.5 wt.% NaCl solution was investigated using a wear test, and the effects of wear loads and speeds on the friction–wear performances of the MAO coating were analyzed. The results show that the MAO coating is primarily composed of Al{sub 2}O{sub 3}, with no other phases. The average coefficients of friction (COFs) of the MAO coating under the wear loads of 0.5, 1.0 and 1.5 N are 0.48, 0.62, and 0.76, respectively, and the corresponding wear rates are 4.20 × 10{sup −5}, 4.21 × 10{sup −5} and 4.27 × 10{sup −5} mm{sup 3} m{sup −1} N{sup −1}, exhibiting the higher wear resistance. Under the wear load of 1.0 N, the average COFs of the MAO coating at the wear speeds of 5.0, 6.7 and 8.3 Hz are 0.32, 0.45 and 0.62, respectively; and the corresponding wear rates are 3.21 × 10{sup −5}, 3.49 × 10{sup −5} and 4.21 × 10{sup −5} mm{sup 3} m N{sup −1}, respectively, which increase with the increase in wear speeds. The wear mechanism of the MAO coating is fatigue wear and abrasive wear, and its wear resistance was better than the cold-sprayed Al coating.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Micro-cold Spray Deposition of YSZ Films from Ultrafine Powders Using a Pressure Relief Channel Nozzle

Abstract The use of ultrafine powders in the micro-cold spray (MCS) process, also referred to as the aerosol deposition method, typically results in porous and/or poorly adhering films because the particles do not impact at a high enough velocity for sufficient plastic deformation and interparticle bonding to occur. Under typical operating conditions, particles < 100 nm accelerate to high velocities but then are slowed by the stagnant gas in the bow shock that forms just upstream of the substrate. Using larger particles reduces particle slowing, but large particles can cause erosion of the film at high impact velocity, decreasing deposition efficiency. In this study, a pressure relief channel nozzle using helium as a carrier gas is proposed such that high-velocity deposition of yttria-stabilized zirconia particles as small as 10 nm in diameter is possible. This is well below the size range of powders previously used for MCS. The proposed nozzle design increases impact velocities for 10, 20, and 50 nm particles by ~ 880, 560, and 160 m/s, respectively, when compared to a conventional nozzle. Experimental deposition of ultrafine 8YSZ powder shows that the pressure relief channel nozzle results in lower porosity and more uniform deposits, with a ∼ 186% increase in deposition efficiency.

Materials Science↗
DOE OSTI2024

Laboratory-Based Micro-X-ray Computed Tomography of Energy Materials at Idaho National Laboratory

Abstract The Idaho National Laboratory (INL) has implemented laboratory-based micro-X-ray computed tomography in a laboratory equipped for the examination of highly radioactive samples. This capability provides nondestructive three-dimensional volumetric information on samples to inform subsequent traditional destructive examinations as well as real-world inputs for high-fidelity scientific modeling. Samples can be imaged with spatial resolutions ranging from several hundred nm/voxel up to ~ 100 µm/voxel. The best usable spatial resolution achieved to date is 384 nm/voxel with this instrument, while the highest radiological dose rate of a sample imaged is ~ 60 R/h β/γ on contact. Advanced data analysis, including custom tomographic reconstruction and segmentation methods, have also been developed to support this capability. In addition to traditional digital X-ray radiography and tomography, this instrument is also able to visualize in situ tensile and compression testing as well as perform diffraction contrast tomography. This work describes the X-ray computed tomography post-irradiation examination capabilities at INL, as well as detailing a variety of applications this instrument has examined.

36 MATERIALS SCIENCE↗