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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 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Investigation of the Effect of Foaming Agent on the Fabrication of NiTi Foams Using the Self-Propagating, High-Temperature Synthesis Process

Fabrication of NiTi intermetallic foams using the self-propagating, high-temperature synthesis (SHS) process was investigated. Weighed amounts of powders taken from an equimolar mixture of Ni and Ti powders along with 0.5, 1, and 1.5 wt pct of different foaming agents were cold pressed to form cylindrical compacts 10 mm in diameter, 20 mm in height, and 7 to 8 g in weight. A novel, induction-assisted ignition method was used for indirect heating and igniting the compressed mixtures at one end. As a result of intensive exothermic reaction between Ni and Ti and decomposition of foaming agents and liberation of gases, highly porous products were obtained. Characterization of the products was carried out using X-ray diffraction (XRD) and a scanning electron microscope equipped with an energy-dispersive spectroscope (SEM-EDS). The main phase in the products was detected to be B2(NiTi) with minor amounts of NiTi{sub 2} as the secondary phase. Other undesirable phases, such as Ni{sub 4}Ti{sub 3} and Ni{sub 3}Ti, were not detected. The effect of type and percentage of foaming agent on the formation and distribution of pores within the products was studied. Final products with porosities up to ~ 80 vol pct were obtained by adding foaming agent. Under the conditions of this study, CaH{sub 2} proved to be the most effective foaming agent considering its ability to generate a uniform distribution of pores, while TiH{sub 2} was not considered favorable due to its decomposition at relatively low temperatures. In general, the addition of foaming agents in amounts higher than 1wt pct is not recommended; due to the endothermic nature of thermal decomposition reactions of foaming agents, excessive use of these agents can result in suppression of the exothermic reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication of Silicon Nanowire Forests for Thermoelectric Applications by Metal-Assisted Chemical Etching

Silicon nanowires, whose thermal conductivity is strongly reduced with respect to that of the bulk silicon, are very promising for high-efficient thermoelectric conversion. This work focuses on the development of a technique for the fabrication of thermoelectric generators which are based on vertical silicon nanowire forests, achieved through a metal-assisted chemical etch. As heavily doped nanowires are essential in thermoelectric applications, this chemical process has been applied both on lightly and on highly doped (> 10{sup 19} cm{sup −3}) silicon substrates. A comparison of the results shows that the etch behaves in a completely distinct way when applied to the differently doped substrates. The results of this comparison and a preliminary insight into the diverse behavior occurred are reported. The different initial nucleation of silver, which determines the hole injection, essential to the etching of silicon, seems to be the key point of this different behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fabrication of Brushite Coating on AZ91D and AZ31 Alloys by Two-Step Chemical Treatment and Its Surface Protection in Simulated Body Fluid

A biocompatible dicalcium phosphate dihydrate (DCPD) brushite coating of flake-like crystals was developed on AZ91D and AZ31 magnesium (Mg) surfaces to control and slow down the rapid degradation rate of the substrates. The electrochemical behavior of the DCPD-coated substrates was examined in a simulated body fluid (SBF) with uncoated substrates as the control. Fabrication of the coating was achieved via chemical immersion technique by modifying the surfaces with Ca(NO{sub 3}){sub 2}·4H{sub 2}O and KH{sub 2}PO{sub 4} in addition to heat treatment. The morphology of the DCPD coating is uniform and dense with a flake-like crystal structure. After in vitro tests, the DCPD coating would have exhibited excellent corrosion resistance with more biomineralization of the active calcium phosphate (CaP). Moreover, the DCPD coating induced CaP formation after immersion in the SBF, indicating excellent bioactivity upon increasing the coating. Hence, the two-step chemical treatment enhances the bioactivity of DCPD coatings on Mg alloys, making them better implant materials.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Titanium Sheet Fabricated from Powder for Industrial Applications

In collaboration with Ametek and Commonwealth Scientific and Industrial Research Organization (CSIRO), Oak Ridge National Laboratory has evaluated three different methods for converting titanium hydride-dehydride (HDH) powder into thin gauge titanium sheet from a roll compacted preform. Methodologies include sintering, followed by cold rolling and annealing; direct hot rolling of the roll-compacted sheet; and hot rolling of multiple layers of roll compacted sheet that are encapsulated in a steel can. All three methods have demonstrated fully consolidated sheet, and each process route has the ability to produce sheet that meets ASTM B265 specifications. However, not every method currently provides sheet that can be highly formed without tearing. The degree of sintering between powder particles, post processing density, and the particle to particle boundary layer where compositional variations may exist, have a significant effect on the ability to form the sheet into useful components. Uniaxial tensile test results, compositional analysis, bend testing, and biaxial testing of the titanium sheet produced from hydride-dehydride powder will be discussed. Multiple methods of fabrication and the resulting properties can then be assessed to determine the most economical means of making components for industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fused filament fabrication of thermoplastic polyurethane composites with microencapsulated phase-change material

Here, the present study examines the thermal energy storage (TES) effectiveness and printability of microencapsulated phase-change material (MEPCM) combined with thermoplastic polyurethane (TPU) for fused filament fabrication (FFF). Two formulations were assessed: 24D MEPCM, which changes phase at 24 ° C, compounded with TPU pellets and 43D MEPCM, which changes phase at 43 ° C, integrated with TPU powder. These combinations are designed to evaluate the effectiveness of the form of the TPU (pellets versus powder) in the FFF process. The investigation includes a comprehensive analysis of thermal characteristics, encompassing phase-change temperature, latent heat of fusion, thermal conductivity, and thermal decomposition, which are assessed through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Additionally, mechanical properties, including stress-strain behavior, are examined to evaluate material suitability for TES applications, while microstructural visualization is used to provide deeper insights into material performance, structural integrity, and the quality of printed components. The 24D MEPCM and TPU pellets formulation experienced a significant loss of approximately 39.6% of PCM during filament extrusion and printing, resulting in a reduced effective latent heat. Therefore, further characterization of the pellet formulation was discontinued due to excessive leakage. In contrast, the 43D MEPCM and TPU powder formulation demonstrated minimal PCM loss, with the 60 wt.% composition achieving an effective latent heat of 132 J/g. This value represents the highest effective latent heat currently documented in the literature for PCM-polymer-composite materials produced using an FFF-based additive manufacturing process.

25 ENERGY STORAGE↗
DOE OSTI2018

Nozzle clogging factors during fused filament fabrication of spherical particle filled polymers

Fused filament fabrication with reinforced or filled polymers provides improved material properties compared to ordinary feedstock. A current limitation of these materials is the occurrence of nozzle clogging at higher filler contents. In this paper, an experiment is designed to identify the factors causing nozzle clogging. Glass sphere-filled polycarbonate is investigated by varying nozzle and filler diameters, the resin viscosity, the filler content, and the extrusion pressure. Equations identifying nozzle clogging and intermittent clogging conditions are provided. Based on these results, a model for the clogging of sphere-filled polymers is proposed. Last, a mathematical model is derived, which approximates the printability of filled polymers without the preparation of composites. Finally, this model is based on the nozzle geometry, the filler type and content, the resin viscosity, and the printer’s maximum extrusion force.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Printing polymer blends through in situ active mixing during fused filament fabrication

Fused filament fabrication (FFF) enables production of 3D objects over a range of material compositions at low-cost relative to traditional manufacturing approaches. To date, a limited but growing number of materials are able to be used with FFF, however many applications exist where specific mechanical, thermal, or chemical properties are needed that cannot currently be met with the available feedstock selection. Therefore, a need exists to tune these materials for specific chemical or mechanical properties. One common formulation strategy to address these demanding design parameters is to develop composites or polymer blend filaments. Typically, this is a time-consuming and costly optimization process. Here, we have developed hardware for reproducibly mixing two filaments of similar or dissimilar compositions at the time of printing within individual printed layers. This mixing occurs via software-controlled rotating hardware in the chamber of an extruder’s hot-end. The efficiency of mixing within the printed layers has been characterized in detail as a function of the rotational speed and geometry of the blending hardware. These parameters were exploited to program the ratio and distribution of thermoplastic-based filaments blended within printed extrudate. Example printed specimens were produced with thermoplastic polyurethane (TPU) elastomer blended with rigid polylactic acid (PLA) and Nylon blended with PLA. In addition, a conductive carbon nanotube (CNT)-PLA composite was blended as a function of mixer geometry and input feed ratios with non-conductive PLA and resistance values were measured across the resulting printed specimens.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Fused filament fabrication of novel phase-change material functional composites

Additively manufactured polymer heat exchangers are of recent interest in the thermal sciences due to their lightweight and intricate heat-transfer-enhancing geometrical features. The goal of the present research is to directly encapsulate phase-change material (PCM) into polymer filament for the purpose of 3D printing polymer heat exchangers capable of latent heat thermal energy storage and management. PCMs have the ability to absorb large amounts of latent heat while undergoing a solid-to-liquid phase change at a nearly constant temperature. Encapsulation or containment of PCMs is necessary to prevent leaking since the material continuously cycles between a liquid and a solid state. An organic-based PCM and high-density polyethylene (HDPE) were combined and extruded into a functional composite filament. For the first time, with the aid of a heated enclosure and HDPE build plates, it was demonstrated that these functional composite materials can be printed using fused filament fabrication (FFF). Printing HDPE is known to be difficult; however, based on what was observed in the current study, the PCM and HDPE composite was easier to print than pure HDPE. Thermal properties, such as latent heat of fusion, phase-change temperature, and thermal conductivity, of the composite filament and 3D printed samples were investigated and compared with compression-molded bulk material. Finally, the microstructures of the composite filament and 3D printed samples were visualized, and the basic structures of the HDPE and PCM within both the filament and 3D printed parts were clearly delineated.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fabrication of porous transport electrodes: Development of quantitative approach for quality control

This work focuses on porous transport electrodes (PTEs), which integrate the anodic catalyst with the adjacent Ti porous transport layer (PTL). Challenges in catalyst deposition on PTLs, particularly at low loadings, motivated this study to evaluate various fabrication methods and characterization approaches. This work investigated Pt-treated PTLs coated with Ir-based catalysts using several common methods, including airbrush coating, rod coating, ultrasonic spray coating, electrodeposition, and sputter deposition, with catalyst loadings ranging from 2.9 to 0.1 mg/cm 2 , providing the opportunity for comparisons across a large set of samples produced by different methods. Two widely accessible characterization techniques: X-ray computed tomography (XCT) and scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) were explored. Initial evaluation of selected samples with XCT provided qualitative insights into catalyst distribution, however comprehensive quantitative analysis was limited. SEM-EDS enabled detailed information on the catalyst distribution both qualitatively and quantitatively using two metrics. Atomic and surface area % ratios of Pt:Ir and Ti:Ir revealed trends in catalyst loading and losses into the PTL pores, as well as evaluating the homogeneity of catalyst coatings. The analysis demonstrated that ultrasonic spray coating, electrodeposition, and sputter coating produced the most homogeneous coatings, with minimal catalyst losses observed for electrodeposition and sputter coating. By adapting common techniques with novel, standardized methodologies, this work establishes a universally applicable framework for cross-study comparison of PTEs. The SEM-EDS approach provides a practical, accessible tool for PTE characterization and contributes a reference dataset supporting both research development and rapid quality control.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Meso-scale modeling and damage analysis of carbon/epoxy woven fabric composite under in-plane tension and compression loadings

The mechanical properties and damage behaviors of carbon/epoxy woven fabric composite under in-plane tension and compression are studied at the meso-scale level through experiment and simulation. An efficient representative volume element (RVE) modeling method with consistent mesh, high yarn volume fraction and realistic geometry is proposed. The material constitutive laws with plasticity, tension-compression asymmetry and damage evolution are established for the three components - yarn, matrix and interface, respectively. Significantly different mechanical properties and damage evolutions are observed depending on loading conditions and initial geometry characteristics. It shows a non-linear stress-strain curve with clear transition region and intensive damage in tension, while a quasi-linear behavior up to facture is observed in compression with little damage prior to final fracture. Furthermore, compared to the constant Poisson's ratio with straining in compression, a dramatic increase in Poisson's ratio appears in tension. Simulation shows damage mechanisms including transverse damage, matrix damage and delamination, which all play critical roles in the property evolution. In particular, the rapid damage accumulation after elastic deformation destroys the strong bonds and causes the easy deformation of transverse yarns which results in the transition region and large Poisson's ratio in tension. All the mechanical behaviors and damage evolutions are well captured and explained with the current RVE model.

42 ENGINEERING↗
DOE OSTI2014

From coin cells to 400 mAh pouch cells: Enhancing performance of high-capacity lithium-ion cells via modifications in electrode constitution and fabrication

In this article we describe efforts to improve performance and cycle life of cells containing Li1.2Ni0.15Mn0.55Co0.1O2-based positive and graphite-based negative electrodes. Initial work to identify high-performing materials, compositions, fabrication variables, and cycling conditions is conducted in coin cells. The resulting information is then used for the preparation of double-sided electrodes, assembly of pouch cells, and electrochemical testing. We report the cycling performance of cells with electrodes prepared under various conditions. Our data indicate that cells with positive electrodes containing 92 wt% Li1.2Ni0.15Mn0.55Co0.1O2, 4 wt% carbons (no graphite), and 4 wt% PVdF (92-4-4) show ~20% capacity fade after 1000 cycles in the 2.5-4.4V range, significantly better than our baseline cells that show the same fade after only 450 cycles. Our analyses indicate that the major contributors to cell energy fade are capacity loss and impedance rise. Therefore incorporating approaches that minimize capacity fade and impedance rise, such as electrode coatings and electrolyte additives, can significantly enhance calendar and cycle life of this promising cell chemistry.

Electrode fabrication↗
DOE OSTI2020

Fabrication of high-performance gas-diffusion-electrode based membrane-electrode assemblies

This paper demonstrates the fabrication and processing steps required to produce high performance fuel cell membrane electrode assemblies (MEAs) based on spray-coated gas-diffusion electrodes (GDEs). It is demonstrated that coating the catalyst layer with a thin layer of ionomer and then hot pressing the GDEs to the membrane is required to achieve comparable catalyst activity and air performance to catalyst-coated-membrane MEAs. We show that there is a critical amount of ionomer required to achieve maximized performance. Using electron microscopy, we show that the combination of the ionomer overlayer and hot-pressing bonds the catalyst layer to the membrane, increasing the interfacial contact area and quality of this interface. We also find that the ionomer overlayer smooths the surface of the GDE and provides increased contact area between the GDE and the membrane. Additionally, we demonstrate that much less ionomer is required for high-performance than has been previously reported. Through model fitting of electrochemical impedance spectroscopy, we show that this improvement in the catalyst layer - membrane interface reduces the effective catalyst layer resistance, which reduces Ohmic losses and increases catalyst utilization.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2014

Fabrication and temperature-dependent magnetic properties of one-dimensional multilayer Au–Ni–Au–Ni–Au nanowires

Multilayer Au–Ni–Au–Ni–Au nanowires with a controlled diameter of ∼100 nm were synthesized by electrochemical deposition in porous alumina templates. The length of each Ni-segment was controlled up to ∼230 nm, while the length of the Au segment sandwiched between two Ni segments was ∼180 nm. X-ray diffraction patterns and energy-dispersive X-ray spectra confirmed the formation of purely crystalline nanowires. The magnetic properties of the multilayer Au–Ni–Au–Ni–Au nanowires were investigated in the temperature range 2–300 K. Room-temperature magnetic hysteresis confirmed the ferromagnetic nature of the nanowires. The plot of coercivity as a function of temperature (from 2 to 300 K) followed law applicable for ferromagnetic nanostructures. The magnetization tended to increase as the temperature decreased, following the modified Bloch's law similar to ferromagnetic nanoparticles. - Graphical abstract: (a) SEM image of Au–Ni–Au–Ni–Au nanowire with 230 nm Ni segment length and 180 nm Au sandwiched between Ni segments (b) Kneller's law (c) Bloch's law Display Omitted - Highlights: • Electrochemical fabrication of Au–Ni–Au–Ni–Au nanowires in alumina templates. • Formation of beadlike structure of Ni segments. • Coercivity versus T follows Kneller's law for ferromagnetic materials. • Magnetization as a function of temperature follows the modified Bloch's law.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Fabrication of p-type porous silicon nanowire with oxidized silicon substrate through one-step MACE

In this paper, the simple pre-oxidization process is firstly used to treat the starting silicon wafer, and then MPSiNWs are successfully fabricated from the moderately doped wafer by one-step MACE technology in HF/AgNO{sub 3} system. The PL spectrum of MPSiNWs obtained from the oxidized silicon wafers show a large blue-shift, which can be attributed to the deep Q. C. effect induced by numerous mesoporous structures. The effects of HF and AgNO{sub 3} concentration on formation of SiNWs were carefully investigated. The results indicate that the higher HF concentration is favorable to the growth of SiNWs, and the density of SiNWs is significantly reduced when Ag{sup +} ions concentrations are too high. The deposition behaviors of Ag{sup +} ions on oxidized and unoxidized silicon surface were studied. According to the experimental results, a model was proposed to explain the formation mechanism of porous SiNWs by etching the oxidized starting silicon. - Graphical abstract: Schematic cross-sectional views of PSiNWs array formation by etching oxidized silicon wafer in HF/AgNO{sub 3} solution. (A) At the starting point; (B) during the etching process; and (C) after Ag dendrites remove. - Highlights: • Prior to etching, a simple pre-oxidation is firstly used to treat silicon substrate. • The medially doped p-type MPSiNWs are prepared by one-step MACE. • Deposition behaviors of Ag{sup +} ions on oxidized and unoxidized silicon are studied. • A model is finally proposed to explain the formation mechanism of PSiNWs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Fabrication and applications of copper sulfide (CuS) nanostructures

This review article presents different fabrication procedures (under the headlines of solvothermal routes, aerosol methods, solution methods and thermolysis), and applications (photocatalytic degradation, ablation of cancer cells, electrode material in lithium ion batteries and in gas sensing, organic solar cells, field emission properties, super capacitor applications, photoelectrochemical performance of QDSCs, photocatalytic reduction of organic pollutants, electrochemical bio sensing, enhanced PEC characteristics of pre-annealed CuS film electrodes) of copper sulfide (Covellite). - Highlights: • This review article presents the synthesis and applications of copper sulfide. • CuS has been used over the years for different applications in nanoscience. • Different synthetic protocols are followed for their preparation which help in the possible modifications in the morphology of CuS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Fabrication and photocatalytic properties of free-standing TiO{sub 2} nanotube membranes with through-hole morphology

Anodic growth of TiO{sub 2} nanotubes has recently attracted intensive interests. However, the insulating, closed barrier layer has restricted their feasibility for the applications such as flow-through photocatalytic reactions, biofiltration, and diffusion controlling. In the present work, we fabricated free-standing TiO{sub 2} membranes with through-hole morphology by elevating the anodizing voltage at the end of anodization process. Characterization of the samples was carried out by means of scanning electron microscope, X-ray diffraction and thermogravimetry-differential scanning calorimetry. The experimental results show that the TiO{sub 2} membranes start to transform from amorphous phase to anatase at 300 Degree-Sign C, and the phase transformation from anatase to rutile starts at 650 Degree-Sign C. In addition, photocatalytic degradation of rhodamine B by the TiO{sub 2} membranes with closed bottoms and opened bottoms has also been systematically investigated. As compared to TiO{sub 2} membranes with closed bottoms, TiO{sub 2} membranes with opened bottoms exhibited superior photocatalytic activity due to its better access for rhodamine B molecules as well as the enhanced light harvesting and electron collection efficiencies. Highlights: Black-Right-Pointing-Pointer The closed bottoms were opened by elevating the anodizing voltage. Black-Right-Pointing-Pointer Phase transformation from anatase to rutile starts at 650 Degree-Sign C. Black-Right-Pointing-Pointer TiO{sub 2} membranes in the anatase form have a better catalytic performance. Black-Right-Pointing-Pointer Opened-bottom TiO{sub 2} membranes with exhibited superior photocatalytic activity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Fabrication and microstructural characterization of Al/Zn-enriched layers on pure magnesium

Al/Zn-enriched surface layers were fabricated by heating Mg specimens in contact with Al–Zn powder mixtures in a vacuum furnace at 445 °C. The layer formation process took place through partial melting at the Mg-substrate/powder-mixture interface. Heating times ranged from 20 to 80 min. The layer microstructure and composition were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The layers were 100–900 μm in thickness, depending on the treatment time. The examination results revealed that the layers consisted of Mg{sub 17}(Al,Zn){sub 12} and Mg{sub 5}Al{sub 2}Zn{sub 2} intermetallic phases and a solid solution of Al and Zn in Mg. Between the Al/Zn-enriched layer and the Mg substrate, there was a transition zone of a solid solution of Al and Zn in Mg with a thickness of 20–30 μm. The layers had much higher microhardness than the Mg substrate. - Highlights: ► The layers were produced by heating Mg in contact with an Al–Zn powder mixture. ► The layer formation process at 445 °C proceeded with the liquid phase contribution. ► The Al/Zn-enriched layers were thick, dense, uniform and continuous. ► The layers contained Mg–Al–Zn intermetallic phases. ► The hardness of the layers was much higher than that of the Mg substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Fabrication of superhydrophilic and antireflective silica coatings on poly(methyl methacrylate) substrates

Graphical abstract: Self-cleaning and antireflection properties were successfully achieved by assembling (PDDA/S-20){sub n} coatings on PMMA substrates followed by oxygen plasma treatment. Highlights: ► Porous silica coatings were created by layer-by-layer assembly on PMMA substrates. ► Silica coatings were treated by oxygen plasma. ► Porous silica coatings were highly antireflective and superhydrophilic on PMMA substrates. -- Abstract: Silica nanoparticles of ca. 20 nm in size were synthesized, from which hierarchically porous silica coatings were fabricated on poly(methyl methacrylate) (PMMA) substrates via layer-by-layer (LbL) assembly followed by oxygen plasma treatment. These porous silica coatings were highly transparent and superhydrophilic. The maximum transmittance reached as high as 99%, whereas that of the PMMA substrate is only 92%. After oxygen plasma treatment, the time for a water droplet to spread to a contact angle of lower than 5° decreased to as short as 0.5 s. Scanning and transmission electron microscopy were used to observe the morphology and structure of nanoparticles and coating surfaces. Transmission and reflection spectra were recorded on UV–vis spectrophotometer. Surface wettability was studied by a contact angle/interface system. The influence of mesopores on the transmittance and wetting properties of coatings was discussed on the basis of experimental observations.

36 MATERIALS SCIENCE↗