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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Topotaxial growth of α-Fe{sub 2}O{sub 3} nanowires on iron substrate

α-Fe{sub 2}O{sub 3} (hematite) nanowires have been grown by simple thermal oxidation of iron foil at 700°C in a moist oxygen flow. It was observed that the growth of nanowires highly depends on the texture of the iron substrate, in particular the presence of [110] oriented iron grains. Cross-sectional Transmission Electron Microscopy (TEM) investigation of as-grown sample revealed that the growth of nanowires has definite orientation relation with the underlying oxide grains Fe{sub 3}O{sub 4} (magnetite) and FeO (wustite), which can be interpreted by the primary orientation relationships of topotaxial growth of iron oxides. The observation can pave the way for patterning of the nanowire growth by controlling the texture of original substrate. Samples were also characterized with Scanning Electron Microscope (SEM) and X-ray diffraction (XRD).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Corrosion evaluation of Ti–6Al–4V manufactured by electron beam melting in Ringer’s physiological solution: an in vitro study of the passive film

We report that electrochemical characteristics and semiconducting behavior of additively manufactured electron beam melted (EBM) and wrought (WR) Ti–6Al–4V (Ti-G5) are compared in Ringer’s physiological solution. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) confirmed the α+β structure of the tested materials, with two different microstructure types of “bimodal” and “basket-weave” for WR and EBM, respectively. Potentiodynamic polarization (PDP) revealed that the corrosion current density for EBM (i corr =0.27±0.06 μA cm -2 ) is less than the WR (i corr =0.70±0.05 μA cm -2 ). Moreover, potentiostatic polarization (PS) that was employed to form the passive layers at three different potentials of 300, 500, and 700 mV Ag/AgCl , showed that the passive films on the EBM sample are thinner. This finding was confirmed by electrochemical impedance spectroscopy (EIS). Furthermore, through Mott–Schottky (M–S) analysis, donor densities on WR passive films were found to be ~1.5 times larger than EBM. Although PS and EIS confirmed that the passive layer on EBM is thinner, it provides higher corrosion resistance than WR. The passive layer on both samples were found to have n-type characteristics with a duplex structure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of X80 and X100 Microalloyed Pipeline Steel Using Quantitative X-ray Diffraction

Quantitative X-ray diffraction characterization of four (4) X80 and three (3) X100 microalloyed steels was undertaken. The effect of through-thickness position, processing parameters, and composition on the measured crystallite size, microstrain, and J index (relative magnitude of crystallographic texture) was determined. Microstructure analysis using optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-backscattered diffraction was also undertaken. The measured value of microstrain increased with increasing alloy content and decreasing cooling interrupt temperature. Microstructural features corresponding to crystallite size in the X80 steels were both above and below the detection limit for quantitative X-ray diffraction. The X100 steels consistently exhibited microstructure features below the crystallite size detection limit. The yield stress of each steel increased with increasing microstrain. The increase in microstrain from X80 to X100 is also associated with a change in microstructure from predominantly polygonal ferrite to bainitic ferrite.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure Optimization and Cracking Control of Additive Manufactured Bainite Steel by Gas Metal Arc Welding Technology

In this work, bainite steel thin wall was prepared by additive manufacturing (AM) with an in situ isothermal transformation at 300 °C. The microstructures were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of the AM samples were measured by microhardness testing and tensile testing. The results show that the bainite steel thin wall is free from cracks and each layer has a good bond with preceding one. The bainite steel thin wall displays consistent mechanical properties. The formation of the bainite microstructure improves the toughness of the thin wall and reduces the embrittlement caused by dendritic segregation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure evolution and properties of graphene nanoplatelets reinforced aluminum matrix composites

Highlights: • Lamellar structure of GNPs fibers and Al matrix was obtained in the rolling direction. • Stacking faults were observed in Al grains due to greatly increased GNPs/Al interfaces. • Strength of Al-0.2 wt% GNPs increased 36.8% with negligible electrical conductivity loss. - Abstract: Aluminum matrix composites reinforced with graphene nanoplatelets (GNPs) were prepared by continuous casting and subsequent rolling. Al-GNPs master alloy, prepared by ball milling and cold pressing, was added into Al melts to fabricate the composites. Microstructure evolution of the composites were observed using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). GNPs distributed uniformly in the as-cast specimen and then transformed into fibers in the rolling direction after deformation and finally a lamellar structure formed in the composites. Raman spectra showed that the structural damage of GNPs mainly came from ball milling. The interface between GNPs and Al was well combined in general while a few microcracks were observed, which reduced the ductility of the composites and no adverse aluminum carbide (Al{sub 4}C{sub 3}) was detected at the interface. Stacking faults were observed interior of the aluminum grain, which may due to the existence of plentiful interface introduced by GNPs. Fracture observation revealed that the load transferred from Al matrix to GNPs. The ultimate tensile strength of Al-0.2 wt% GNPs composites was about 36.8% higher than that of pure Al with the same casting and rolling process, which should result from the lamellar structure and load transfer, while the conductivity of the composites decreased slightly, indicating that interface scattering between Al and GNPs is very limited. The investigation results show that Al-GNPs composite is potential for high strength and high conductivity application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Thermal performance of glass fiber reinforced intumescent fire retardant coating for structural applications

The results of influence of glass fiber addition into the basic intumescent coating formulation towards the enhancement of its thermal insulation properties are presented. The intumescent coatings were formulated from expandable graphite, ammonium polyphosphate, melamine, boric acid, bisphenol A epoxy resin BE-188, polyamide amine H-2310 hardener and fiberglass (FG) of length 3.0 mm. Eight intumescent formulations were developed and the samples were tested for their fire performance by burning them at 450°C, 650°C and 850°C in the furnace for two hours. The effects of each fire test at different temperatures; low and high temperature were evaluated. Scanning Electron Microscope, X-Ray Diffraction technique and Thermo Gravimetric Analysis were conducted on the samples to study the morphology, the chemical components of char and the residual weight of the coatings. The formulation, FG08 containing 7.0 wt% glass fiber provided better results with enhanced thermal insulation properties of the coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microwave-Hydrothermal Synthesis of Y{sub 3}Fe{sub 5}O{sub 12} Nanoparticles: Sintering Temperature Effect on Structural, Magnetic and Dielectric Properties

Herein, we report a facile microwave-assisted hydrothermal method for the preparation of yttrium iron garnet (YIG, Y{sub 3}Fe{sub 5}O{sub 12})nanocrystals and realized the synergy between its structural and magnetic properties. The as-prepared powder thermal stability was characterized in detail by using thermogravimetric-differential thermal analysis (TG-DTA). The synthesized powder was microwave sintered at six different temperatures ranging from 973 to 1373 K for 60 min and characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Magnetic properties were investigated by vibrating-sample magnetometer (VSM) and ferromagnetic resonance (FMR) studies. The frequency variation of dielectric and magnetic properties was measured in the frequency range of 100 kHz–1.8 GHz. The observed magnetic and dielectric parameters such as saturation magnetization, coercivity, permeability, linewidth, dielectric constant and magnetodielectric losses are strongly affected by sintering temperature. The saturation magnetization and coercivity of YIG were found in the range 14.4–28.0 emu/g and 35–87 Oe, respectively. Furthermore, the FMR linewidth decreases from 844 to 204 Oe. This analysis undoubtedly demonstrates that the synthesis method and sintering temperature have the prominent effect on the electrical and magnetic properties of YIG and would be very useful for the garnet-based microwave device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Facile synthesis and characterization of erythrocyte-like Y-doped PbWO{sub 4} mesocrystals and their photocatalytic activity

Novel erythrocyte-like Y-doped PbWO{sub 4} mesocrystals with average diameter and thickness of 1.5 and 0.7 μm are fabricated via a facile co-precipitation route at room temperature in the ethylene glycol (EG)-water mixed solvent. Time-dependent samples centrifuged at different times are carefully characterized by powder X-ray diffraction (pXRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectrum. The possible formation mechanism for the novel erythrocyte-like mesocrystals is proposed on the basis of these observations. The photocatalytic activity of the Y-doped PbWO{sub 4} mesocrystals is further investigated in terms of the degradation of the acid orange II under UV irradiation. This simple and environment-friendly strategy presented here offers promising route for the synthesis of other inorganic materials with unique morphologies and interesting properties. - Graphical abstract: Display Omitted - Highlights: • Novel erythrocyte-like Y-doped PbWO{sub 4} mesocrystals are firstly synthesized via a facile co-precipitation route. • The mesocrystals are assembled by small nanoparticles a common crystallographic fashion. • The erythrocyte-like mesocrystals exhibit well photocatalytic activity. • A recrystallization-growth-oriented attachment formation mechanism is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The effect of gallium substitution on the microstructure and magnetic properties of yttrium iron garnet

Y{sub 3}Fe{sub (5-y)}Ga{sub y}O{sub 12} (y = 0, 0.4, 1.4 and 2,4) thin films were prepared by sol-gel method and annealed for 2h in oxygen. The thin film’s characteristic were studied by an X-ray diffraction (XRD), a field emission scanning electron microscope (FESEM) and a vibration sample magnetometer (VSM). The XRD show that all films have the garnet phase structure. The grain size particles measured using FESEM were between 45.08 nm to 51.58 nm, and the thickness were between 42 nm to 90 nm. The magnetic properties measured using VSM showed that result was shown with hysteresis loop. The magnetization saturation decreased from 144.26 to 2.76 emu/cm{sup 3} with the increasing substitution gallium. The substitution for y = 2.4 was shown the saturation magnetization was very low. The coercivity increased 35 to 75 Oe due the the increasing grain size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The role of tungsten phases formation during tungsten metal powder consolidation by FAST: Implications for high-temperature applications

Highlights: • Lowering the sintering temperature of W to 2173 K by using FAST. • Application of electron microscopy for microstructure characterisation. • W{sub 2}C shell formation due to C difussion from graphite tooling. • Identification of co-formed secondary phase, WO{sub 2}. • Influence of WO{sub 2} on high-thermal applications. - Abstract: Tungsten is a candidate material for the demonstration fusion power plant DEMO. To ensure high density and structural stability, Field-Assisted Sintering Technique (FAST) is proposed as a consolidation method. This study discusses the formation of phases during sintering of tungsten by the FAST. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were used to evaluate the microstructure in tungsten-based materials. The results of microscopic examinations revealed the in-situ formation of tungsten oxide and a formation of tungsten carbide shell around tungsten core. Tungsten carbide-rich shell is formed due to the carbon diffusion from the graphite die used in the FAST into tungsten at high temperatures. In contrast to easy removal of tungsten carbide shell by mechanical grinding, the formation of tungsten oxide in the W-matrix can influence the performance of such material when used as plasma-facing material in the fusion reactor. High-temperature experiments at 1873 K showed that tungsten-oxide phase starts to decompose, which results in material degradation and formation of voids and surface blisters.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Nano-Y{sub 2}O{sub 3} on Microstructure and Crack Formation in Laser Direct-Deposited In Situ Particle-Reinforced Fe-Based Coatings

In situ hard-particle-reinforced Fe-based composite coatings were prepared on Q235 steel substrates by direct laser deposition using Fe-based alloy powders containing 2 wt.% B, 3 wt.% Si and 1-3 wt.% nano-Y{sub 2}O{sub 3}. The microstructures, phase compositions, hardnesses and wear resistances of the deposited coatings with different nano-Y{sub 2}O{sub 3} contents were studied using metallographic microscopy, scanning electron microscopy, x-ray diffraction, transmission electron microscopy, microhardness tests and pin-on-disk abrasion tests (MMW-1A), respectively. The results showed that the appropriate addition of Y{sub 2}O{sub 3} played a role in grain refinement and in decreasing the number of brittle phases and impurity elements in the grain boundaries. Consequently, the number of cracks in the laser-deposited coating also decreased. The Fe-based composite coatings were mainly composed of α-Fe, γ-Fe and in situ-produced reinforced particle phases, such as Cr{sub 23}C{sub 6}, Cr{sub 7}C{sub 3}, (Cr, Fe){sub 7}C{sub 3}, Fe{sub 2}B, and CrFeB. When the content of nano-Y{sub 2}O{sub 3} was 2 wt.%, a Fe-based composite coating with a thickness of 4 mm that was free of cracks was obtained, and its surface hardness reached 650HV. Moreover, the wear resistance of the coating with 2 wt.% nano-Y{sub 2}O{sub 3} was the best among the samples studied. The presence of nano-Y{sub 2}O{sub 3} increased the solubility of Cr and Si in the solid solution, which eliminated the residual austenite region, and as a result, the phase transformation from γ-Fe to α-Fe was restrained and the transformation stress was also limited, thereby decreasing the probability of cracks in the coatings.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Process dependent thermoelectric properties of EDTA assisted bismuth telluride

Comparison between the structure and thermoelectric properties of EDTA (Ethylene-diamine-tetra-acetic acid) assisted bismuth telluride prepared by electrochemical deposition and hydrothermal route is reported in the present work. The prepared samples have been structurally characterized by high resolution X-ray diffraction spectra (HRXRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopic images (HRTEM). Crystallite size and strain have been determined from Williamson-Hall plot of XRD which is in conformity with TEM images. Measurement of transport properties show sample in the pellet form (S{sub 1}) prepared via hydrothermal route has higher value of thermoelectric power (S) than the electrodeposited film (S{sub 2}). But due to a substantial increase in the electrical conductivity (σ) of the film (S{sub 2}) over the pellet (S{sub 1}), the power factor and the figure of merit is higher for sample S{sub 2} than the sample S{sub 1} at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Facile synthesis of one dimensional ZnO nanostructures for DSSC applications

Development of zinc oxide (ZnO) nanostructure based third generation dye sensitized solar cell is interesting compared to conventional silicon solar cells. ZnO nanostructured thin films were electrochemically deposited onto fluorine doped tin oxide (FTO) glass substrate. The effect of ethylene-diamine-tetra-acetic acid (EDTA) on structural, morphological and optical properties is investigated using X-ray diffraction (XRD) meter, field emission scanning electron microscope (FE-SEM) and micro Raman spectroscopy. XRD patterns reveal that the prepared nanostructures are hexagonal wutrzite structures with (101) plane orientation, the nanostructure prepared using EDTA exhibits better crystallinity. FE-SEM images illustrate that the morphological changes are observed from nanorod structure to cauliflower like structure as EDTA is added. Micro Raman spectra predict that cauliflower like structure possesses a higher crystalline nature with less atomic defects compared to nanorod structures. Dye sensitized solar cell (DSSC) is constructed for the optimized cauliflower structure, and open circuit voltage, short circuit density, fill factor and efficiency are estimated from the J-V curve.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Characterization of high-temperature mechanical properties of plasma-cladded coatings with thermo-mechanical coupling

High temperature mechanical properties was detected here to study the failure and strengthening mechanism of the coating-substrate (cobalt-based coatings were fabricated on FV520B substrate) integral structure with thermo-mechanical coupling effects. Microstructure, phase composition, element distribution of the coatings was characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscope (TEM), electron back scattering diffraction (EBSD), X-ray diffraction (XRD), electron probe microanalysis (EPMA) and energy dispersive X-ray analysis (EDS). Results elucidate that fracture occurs in the coating for Co50 coating-substrate structure from 300 °C to 700 °C, but failure position transfer to substrate from coating at elevated temperatures with the addition of niobium and cerium oxide. Throughout, there is no crack originated from the interface. Fracture mechanism: the dislocation pile-up causes great stress concentration in the grain boundary, which results in the nucleation of the crack, and then the crack extends along the hard brittle Fe-Cr phase until the material fails. HRTEM shows the high density dislocation and the severe lattice distortion was formed during tensile deformation. On the macro level, the fracture tends to occur in the coarse dendrites region.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Analysis of compositional uniformity in Al{sub x}Ga{sub 1−x}N thin films using atom probe tomography and electron microscopy

Calculated frequency distributions of atom probe tomography reconstructions (∼80 nm field of view) of very thin Al{sub x}Ga{sub 1−x}N (0.18 ≤ x ≤ 0.51) films grown via metalorganic vapor phase epitaxy on both (0001) GaN/AlN/SiC and (0001) GaN/sapphire heterostructures revealed homogeneous concentrations of Al and chemically abrupt Al{sub x}Ga{sub 1−x}N/GaN interfaces. The results of scanning transmission electron microscopy and selected area diffraction corroborated these results and revealed that neither superlattice ordering nor phase separation was present at nanometer length scales.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth and characterization of epitaxially stabilized ceria(001) nanostructures on Ru(0001)

We have studied (001) surface terminated cerium oxide nanoparticles grown on a ruthenium substrate using physical vapor deposition. Their morphology, shape, crystal structure, and chemical state are determined by low-energy electron microscopy and micro-diffraction, scanning probe microscopy, and synchrotron-based X-ray absorption spectroscopy. Square islands are identified as CeO 2 nanocrystals exhibiting a (001) oriented top facet of varying size; they have a height of about 7 to 10 nm and a side length between about 50 and 500 nm, and are terminated with a p(2 × 2) surface reconstruction. Micro-illumination electron diffraction reveals the existence of a coincidence lattice at the interface to the ruthenium substrate. The orientation of the side facets of the rod-like particles is identified as (111); the square particles are most likely of cuboidal shape, exhibiting (100) oriented side facets. Lastly, the square and needle-like islands are predominantly found at step bunches and may be grown exclusively at temperatures exceeding 1000 °C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Enhanced catalytic activity of mesoporous graphitic carbon nitride on thermal decomposition of ammonium perchlorate via copper oxide modification

Highlights: • Novel mpg-C{sub 3}N{sub 4}/rod-like CuO nanocomposites were synthesized via a facile precipitation method for the first time. • The BET surface area of as-synthesized mpg-C{sub 3}N{sub 4}/CuO is 111.33 m{sup 2} g{sup −1}, which is beneficial for catalyzing the thermal decomposition process of ammonium perchlorate (AP). • The synergistic effect between mpg-C{sub 3}N{sub 4} and CuO was the origin of the high catalytic activity. • The mpg-C{sub 3}N{sub 4}/CuO nanocomposites were applied in catalyzing the thermal decomposition of AP and the proposed catalytic mechanism was also proposed. - Abstract: Aiming at enhancing the catalytic activity of mpg-C{sub 3}N{sub 4} on thermal decomposition of ammonium perchlorate, mpg-C{sub 3}N{sub 4} was successfully modified by CuO nanorods, via a facile precipitation method. The structure, morphology and composition of mpg-C{sub 3}N{sub 4} and mpg-C{sub 3}N{sub 4}/CuO nanocomposites were characterized by nitrogen adsorption-desorption measurements, transmission electron microscopy, scanning electron microscope, X-ray power diffraction, fourier transform infrared spectroscopy, as well as X-ray photoelectron spectroscopy. The results demonstrated that CuO nanorods (length of 200–300 nm, diameter of 10–15 nm) were uniformly dispersed throughout mpg-C{sub 3}N{sub 4}, efficiently avoiding the agglomeration. Finally, it was demonstrated that the high weight-loss decomposition temperature of AP was decreased up to 118.5 °C in the presence of 2 wt% mpg-C{sub 3}N{sub 4}/CuO nanocomposites, which was higher than that of pure mpg-C{sub 3}N{sub 4} and CuO, respectively, demonstrating the catalytic performances of the nanocomposites was enhanced via the synergistic catalysis between mpg-C{sub 3}N{sub 4} and CuO.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure Analysis of Bismuth Absorbers for Transition-Edge Sensor X-ray Microcalorimeters

Given its large X-ray stopping power and low specific heat capacity, bismuth (Bi) is a promising absorber material for X-ray microcalorimeters and has been used with transition-edge sensors (TESs) in the past. However, distinct X-ray spectral features have been observed in TESs with Bi absorbers deposited with different techniques. Evaporated Bi absorbers are widely reported to have non-Gaussian low-energy tails, while electroplated ones do not show this feature. In this study, we fabricated Bi absorbers with these two methods and performed microstructure analysis using scanning electron microscopy and X-ray diffraction microscopy. The two types of material showed the same crystallographic structure, but the grain size of the electroplated Bi was about 40 times larger than that of the evaporated Bi. This distinction in grain size is likely to be the cause of their different spectral responses.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗