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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Fabrication and Characterization of A5083-WC-Al{sub 2}O{sub 3} Surface Composite by Friction Stir Processing

In this study, WC-Al{sub 2}O{sub 3} ceramic composite was incorporated into Al5083 to produce a surface composite by friction stir processing (FSP), and the microstructure, hardness and wear properties of Al5083-WC-Al{sub 2}O{sub 3} surface composite were evaluated. Optical microscopy of FSPed samples showed grain refinement in the stir zone. The addition of WC-Al{sub 2}O{sub 3} particles as well as increase in FSP pass number had a considerable effect on grain refinement, and the grain size of Al5083 base metal of 36 µm reduced to 11 µm for Al5083-WC-Al{sub 2}O{sub 3} surface composite after four passes. The SEM observation of the surface composite revealed that the WC-Al{sub 2}O{sub 3} particles distributed homogenously in the matrix and by increasing the FSP passes, the initial agglomerates of mechanochemically synthesized WC-Al{sub 2}O{sub 3} powders could be fractured. Microhardness evaluation showed a substantial improvement by adding WC-Al{sub 2}O{sub 3} particles and increase in FSP pass number. The maximum microhardness value of 101 HV belonged to surface composite after four passes, while the microhardness of the base metal was 65 HV. Wear test results revealed enhanced tribological behavior with a similar trend of microhardness values. Scanning electron microscopy tests revealed both adhesive and abrasive wear mechanisms on the surface of the wear test specimens.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Hydrothermal synthesis of a novel non-stoichiometric cubic bismuth phosphate (Bi{sub 12}(Bi{sub 4/5–5x}P{sub 5x})O{sub 19.2+5x}) crystal and the coexistence of multilevel Kink-Terrace-Step structures on Kossel (1 0 0) surface

- Highlights: • Pure cubic phase could be synthesized at high alkalinity. • The height of the lowest kinked [0 1 0] steps was about half of the unit cell. • Multilevel Kink-Terrace-Step structures coexisted on Kossel (1 0 0) surface. • Multilevel growth units are PO{sub 4}{sup −} incorporating into the channels of Bi–O frameworks. - Abstract: Nonstoichiometric cubic bismuth phosphate crystals were synthesized and grown by hydrothermal method. Under high alkalinity condition, three dimensional nuclei were generated and combined into cubic plates. The cubic bismuth phosphate crystals were combined by the corresponding cubic plates with various defects and rough surfaces. The cubic plates made (1 0 0) surface of the crystal cleavage face. Additionally, multilevel Kink-Terrace-Step structures on Kossel (1 0 0) surface were characterized through scanning electron microscopy and atomic force microscope techniques, respectively. It revealed that the lowest level Kink-Terrace-Step structure was in nano-scale, and the height of the elemental kinked [0 1 0] steps was about half of the unit cell. The elemental kinked [0 1 0] steps could bunch together and consequently constructed a higher level of Kink-Terrace-Step structures. As a result, multilevel Kink-Terrace-Step structures coexisted on the Kossel (1 0 0) surface of bismuth phosphate crystal, which were owing to the coexistence of multilevel growth units in crystal growth system.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Efficient SnO{sub 2}/CuO/porous silicon nanocomposites structure for NH{sub 3} gas sensing by incorporating CuO nanoparticles

In this paper, a porous silicon (Psi) surface modification process, including the incorporating of pure and CuO mixed SnO{sub 2} within a Psi layer, was investigated. A Psi layer with a pore-like structure prepared via laser-assisted etching process with a laser illumination intensity of (40) mW/cm{sup 2} was employed as a substrate for materialization SnO{sub 2}/CuO/Psi nanocomposites for gas sensing application. Pure SnO{sub 2} and SnO{sub 2}:CuO nanoparticles were synthesized via a chemical spray pyrolysis process on the Psi surface at 350 °C. The materialization of SnO{sub 2}:CuO/Psi nanocomposites were recognized through Field-Emission Scanning Electron Microscopy, X-ray Diffraction, Atomic Force Microscopy, and Energy-dispersive X-ray Analysis. The results displayed that the morphological properties of SnO{sub 2}:CuO nanoparticles were definitely controlled by varying the CuO contents. Different shapes (nearly cubic shape and spherical shape) with various sizes of SnO{sub 2} and SnO{sub 2}:CuO within the Psi surface were achieved by increasing the CuO content. SnO{sub 2}:CuO/Psi nanocomposites, plans, grain size, average surface roughness, homogeneity and specific surface area of SnO{sub 2}:CuO nanoparticles were considerably influenced by CuO content. The lower grain size and higher average surface roughness and specific surface area were attained when the percentage of CuO was about 30% within the structure of 70% SnO{sub 2}:30% CuO, and the performance of the NH{sub 3} gas sensor revealed a short response time with a high sensitivity of (88%).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Comparative dielectric studies of nanostructured BaTiO{sub 3}, CaCu{sub 3}Ti{sub 4}O{sub 12} and 0.5BaTiO{sub 3}⋅ 0.5CaCu{sub 3}Ti{sub 4}O{sub 12} nano-composites synthesized by modified sol–gel and solid state methods

BaTiO{sub 3} (BTO), CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) and 0.5BaTiO{sub 3}·0.5CaCu{sub 3}Ti{sub 4}O{sub 12} (BTO–CCTO), as a new nano-composite ceramic, were successfully designed and fabricated by a semi-wet gel route and a modified solid state method. The dielectric properties of the BTO–CCTO ceramic were compared to those of the BTO and CCTO ceramics at lower sintering temperatures and durations. The X-ray diffraction analysis revealed that the BTO and CCTO ceramics form a single crystalline phase and the average crystalline sizes calculated from X-ray diffraction data were in the range of 40–65 nm. The particle sizes of the BTO, CCTO, and BTO–CCTO ceramics obtained from transmission electron microscopy images were in the ranges of 40–65 nm, 80–110 nm, and 70–95 nm, respectively. The phase composition and microstructure were studied by X-ray diffraction and scanning electron microscopy. The energy dispersive X-ray results demonstrated the purity and stoichiometry of the BTO–CCTO nano-composite. The grain sizes of the BTO, CCTO and BTO–CCTO ceramics were found to be in the ranges of 500 nm–1 μm, 4–24 μm, and 250 nm–4 μm, respectively. The AC conductivity as a function of frequency confirmed the semiconducting nature of all of the ceramics and obeyed the Jonscher's power law. The impedance spectrum measurement result showed that the CCTO ceramic possessed an exceptional grain boundary resistance, which supports the internal barrier layer capacitance (IBLC) mechanism present in this ceramic and is responsible for the high ε{sub r} values. - Highlights: • Nanostructured BaTiO{sub 3}, CaCu{sub 3}Ti{sub 4}O{sub 12}, and 0.5BaTiO{sub 3}⋅ 0.5CaCu{sub 3}Ti{sub 4}O{sub 12} have been synthesized. • XRD and TEM analysis confirmed the formation of nanoparticles, 40–65 and 50–90 nm. • Impedance analysis shows high grain-boundary resistance present in CCTO ceramic. • AC conductivity as a function of frequency confirms the semiconducting nature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermally initiated disproportionation of manganese(II) bis(1-hydroxyethylidene)diphosphonate. Formation and properties of the lepidoid structure of manganese(II) (1-hydroxyethylidene)diphosphonate-2-hydroxyethaneaminium whiskers. Agronomical efficiency of the manganese(II) complex with (1-hydroxyethylidene)diphosphonic acid

The reaction of poorly soluble manganese(II) bis(1-hydroxyethylidene)diphosphonate tetrahydrate (Mn(H{sub 3}L){sub 2}•4H{sub 2}O) with 2-aminoethanol (H{sub 2}NCH{sub 2}CH{sub 2}OH) in an aqueous medium on heating to 70—80 оС causes the initial formation of soluble manganese(II) bis(1-hydroxyethylidene)diphosphonate tris(1-hydroxyethaneaminium) (Mn(H{sub 3}L)2• •3H{sub 2}NCH{sub 2}CH{sub 2}OH•4H{sub 2}O), which then disproportionates to slightly soluble manganese(II) (1-hydroxyethylidene)diphosphonate-2-hydroxyethaneaminium (MnH{sub 2}L•H{sub 2}NCH{sub 2}CH{sub 2}OH) and coordination polymer of 1-hydroxyethylidenediphosphonic acid with 2-aminoethanol containing no metal cations. In the course of the reaction, MnH{sub 2}L•H{sub 2}NCH{sub 2}CH{sub 2}OH precipitates as whiskers that are grouped into a leaf (lepidoid) structure. The latter was examined by IR spectroscopy, X-ray phase analysis, scanning electron microscopy, atomic force microscopy, optical microscopy, and thermal desorption of nitrogen. The starting and resulting manganese compounds refer to poorly soluble crystalline complexes. The presence of a 2-aminoethanol molecule in the final product leads to an increase in the solubility from 0.40 to 0.54 g in 100 mL of the solution. Poorly soluble MnH{sub 2}L•H{sub 2}NCH{sub 2}CH{sub 2}OH is easily converted to a soluble form by the treatment with 2-aminoethanol or 2-amino-2-(hydroxy- methyl)propane-1,3-diol (H{sub 2}NC(CH{sub 2}OH)3). The agronomical efficiency of a solution of the Mn(H{sub 3}L){sub 2}•3H{sub 2}NCH{sub 2}CH{sub 2}OH•4H{sub 2}O complex was studied on the cultures of white lupine Degas, spring wheat Ester, spring rape, and pea Stabil.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Fission Products Distribution in TRISO Coated Fuel Particles Irradiated to 3.22 x 1021 n/cm2 Fast Fluence at 1092°C

Mechanisms by which fission products (especially Ag) migrate across the intact coating layers of tristructural isotropic (TRISO) coated fuel particles designed for next generation nuclear reactors have been the subject of numerous studies but remain poorly understood. This paper presents results obtained from the electron microscopic examination of selected irradiated tristructural isotropic (TRISO) coated particles (CPs) taken from fuel Compact 3-1-1 irradiated in Advanced Gas Reactor (AGR) experiment AGR-1. Studying this particles are of specific interest as it was fabricated using a different carrier gas composition ratio for the SiC layer deposition compared with the baseline fuel coated particles reported previously. These fabrication parameters are expected to reduce defects in the SiC layers resulting from uranium dispersion and potentially reducing the SiC layer permeability for metallic fission products. Basic scanning electron microscopy (SEM) and SEM montage investigations of the particles indicate that the number density of fission products in the inner pyrolytic carbon (IPyC) layer is far higher than that in the SiC layer, and that the number density of fission products in the SiC layer is far lower than the corresponding value for compacts with baseline fuel. Preliminary comparative fission product distribution montages suggest that the SiC layers of particles in Compact 1-3-1 are less permeable to fission products than those in compacts with baseline fuel. Transmission electron microscopy (TEM) samples were sectioned by focused ion beam (FIB) technique from the IPyC layer, the SiC layer and the IPyC-SiC interlayer of the particle. Detailed TEM and scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectroscopy (EDS) or electron energy loss spectroscopy (EELS) were performed to identify fission products and characterize their distribution across the IPyC and the SiC layers. Based on the distribution of the fission products, transport mechanisms are discussed and proposed, with emphasis placed on Ag. Our study contributes to enhancing the understanding of fission product transport mechanisms in TRISO coated fuel particles with SiC layer possessing reduced concentration of processing defects.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Workflow Using a Cryogenic Coincident Fluorescence, Electron, and Ion Beam Microscope for Targeted Milling of Cells

This workflow enables lamella production targeting fluorescently labeled biological structures that are small (<1 μm in axial extent) and rare (1 copy per cell) using a cryogenic tri-coincident imaging platform. In conclusion, this platform integrates fluorescence microscopy, focused ion beam milling, and scanning electron microscopy at a single focal position and enables simultaneous fluorescence microscopy while milling.

Wang, Jue [California Institute of Technology (Cal↗
DOE OSTI2016

Electrical properties of films of zinc oxide nanoparticles and its hybrid with reduced graphene oxide

Free-standing films of ZnO nanoparticles (NPs) and reduced graphene oxide (rGO)-ZnO NPs hybrid are prepared at a liquid/liquid interface. The films are characterized by UV-visible spectroscopy, X-ray diffraction, scanning electron microscopy and atomic force microscopy. ZnO film consists of spherical aggregated NPs while the hybrid film contains folded sheets of rGO with embedded ZnO NPs. Electrical properties of the films and its photoresponse in presence of UV radiation are investigated using current sensing atomic force microscopy (CSAFM) at nanoscale and bulk measurements using two probe methods. Enhancement in photocurrent is observed in both cases and the current imaging reveals an inhomogeneous contribution by different ZnO grains in the film.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Study of the physical properties of CuS thin films grown by SILAR method

CuS thin films were obtained using the SILAR method on an amorphous glass substrate. All experiments were performed at room temperature. CuS thin films were deposited at 30, 40, 50 and 60 cycles, respectively. Structural, morphological and optical properties of the structures that increase the thickness of nanostructured CuS thin films were investigated. X-ray diffraction, scanning electron microscopy, atomic force microscopy, RAMAN and optical absorption measurements were carried out in order to examine the physical properties of CuS thin films. As a result of the analysis, we can say that the thickness increase positively affects the crystal structure of CuS thin films. In addition, the energy bandgap range of CuS thin films ranged from 2.22 to 1.78 eV. Analysis results of CuS thin films using SILAR method show that thickness is an important factor for thin film studies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Structural evolution and strain induced mixing in Cu–Co composites studied by transmission electron microscopy and atom probe tomography

A Cu–Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu–26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain. - Highlights: • Structural evolution in a deformed Cu–Co composite is studied on all length scales. • Amount of intermixing is examined by atom-probe tomography. • Supersaturated solid solutions up to 26 at.% Co in Cu are observed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ru nucleation and thin film smoothness improvement with ammonia during chemical vapor deposition

This study reports the use of ammonia to inhibit the growth of previously nucleated ruthenium islands and force the nucleation of additional islands such that thinner films form as the islands coalesce with continued growth. Ruthenium films are grown at 448 K in a chemical vapor deposition process on SiO{sub 2}/Si(001) using triruthenium dodecacarbonyl, Ru{sub 3}(CO){sub 12}, with and without a constant partial pressure of ammonia. Film growth was performed at a Ru{sub 3}(CO){sub 12}/Ar pressure of 47.2 mTorr. The ammonia partial pressure varied from 0 to 27.8 mTorr. X-ray photoelectron spectroscopy was used to analyze the samples in situ. Ex situ characterization included scanning electron microscopy, atomic force microscopy, and x-ray diffraction and x-ray reflectivity. Nucleation studies limited to the first 10 min of growth revealed the maximum nanoparticle (island) density of 8.1 × 10{sup 11 }cm{sup −2} occurred at an intermediate ammonia pressure (5.25 mTorr) compared to a density of 3.1 × 10{sup 11 }cm{sup −2} for no ammonia addition. Extending film growth to 120 min and varying the ammonia partial pressure during the first 10 min followed by 5.25 mTorr ammonia pressure for the final 110 min reveals the importance of nucleation on film smoothness. A model describing the inhibition effects of ammonia during nucleation and growth is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Corrosion Behavior of Annealed Steels with Different Carbon Contents (0.002, 0.17, 0.43 and 0.7% C) in Freely Aerated 3.5% NaCl Solution

Four annealed carbon steels with different carbon contents (0.002, 0.17, 0.43, and 0.7% C), consisting of ferrite, ferrite-pearlite and fully pearlite microstructures, were selected to understand the corrosion behavior of carbon steel as a function of carbon content in freely aerated 3.5% NaCl solution. Dynamic polarization, electrochemical impedance and linear polarization methods were used. The corrosion rate obtained from the different carbon steels was found to increase greatly from ultra-low carbon steel (0.002%) to low carbon steel (0.17%) due to the presence of pearlite in the low carbon steel. However, the increase in corrosion rate was marginal with the increase in carbon content from low carbon (0.17%) to medium (0.43% C) and high carbon steels (0.7% C). The mirostrucural evolution of the steels before and after polarization test without etching as observed by scanning electron microscopy could show that the corrosion behavior of the steels with the presence of pearlite was due to the combined effect from % pearlite, interlamellar spacing and cementite/ferrite area ratio in pearlite. Pearlite morphology also led to the differential corrosion within the pearlite colony in all the steels except the steel with 0.002% C. Catalytic activity of cementite on enhancing oxygen reduction reaction attributes to the higher corrosion rates in case of the steels with the presence of pearlite.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Control of wetting and uniformity via ZrSi x formation in ceramic-to-metal joints fabricated using Ag-Zr brazes

The deposition of a 2.0 µm SiO 2 film on the alumina surface in Kovar TM /94% alumina joints enables the formation of a silicide reaction layer on the alumina during brazing with 97Ag2Zr1Cu. Additionally, the average and standard deviation of joint thickness decrease from 50 to 15 and 29 to 4 µm, respectively compared to joints without added SiO 2 . Finally, the average failure stress of these braze joints was 45 MPa, while that of similar joints without added SiO 2 was 90 MPa. Sessile drop experiments of 98Ag2Zr on SiO 2 and 99.6% Al 2 O 3 substrates show that the braze wets and spreads to 3x its original area on SiO 2 with a wetting angle near 0°, but remains the same area on 99.6% Al 2 O 3 with a wetting angle of 106.6°. Focused-ion-beam scanning electron microscopy analysis of a cross-section of the 98Ag2Zr sessile drop on the SiO 2 substrate has shown that Zr reacts with SiO 2 to form Zr oxide and silicide layers. Scanning transmission electron microscopy diffraction and energy dispersive X-ray spectroscopy analysis indicate this silicide layer contains tetragonal Zr 5 Si 4 . In conclusion, analysis shows the silicide layer enhances wetting and joint uniformity while unreacted SiO 2 embrittles the joint and degrades strength.

alumina↗
DOE OSTI2014

Synthesis, characterization and electrochemical studies of nanostructured CaWO{sub 4} as platinum support for oxygen reduction reaction

Highlights: • Nanostructured CaWO{sub 4} was fabricated by co-precipitation method. • Platinum was electrodeposited onto the surface prepared nanostructured CaWO{sub 4}. • Pt/CaWO{sub 4}-graphite demonstrate good oxygen reduction reaction activity. - Abstract: In the present work, we employed nanostructured calcium tungstate as a supporting material for platinum, a well-known electrocatalyst for oxygen reduction. The co-precipitation method has been utilized to synthesize nanostructured calcium tungstate from aqueous solution. The structure and morphology of the obtained CaWO{sub 4} were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Preparation of the Pt/CaWO{sub 4}-graphite catalyst was carried out by electrodeposition of Pt onto the surface of CaWO{sub 4}/graphite electrode. The physical properties of the catalyst were determined by scanning electron microscopy analysis and energy dispersive X-ray (SEM/EDX). The electrochemical activity of the Pt/CaWO{sub 4}-graphite for the oxygen reduction reaction (ORR) was investigated in acid solution by cyclic voltammetry measurements, linear sweep voltammetry, and electrochemical impedance spectroscopy. The results revealed that the Pt/CaWO{sub 4}-graphite has higher electrocatalytic activity for oxygen reduction in comparison with Pt/graphite catalyst.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermal Conductivity of β-Phase Ga 2 O 3 and (Al x Ga 1– x ) 2 O 3 Heteroepitaxial Thin Films

Heteroepitaxy of β-phase gallium oxide (β-Ga 2 O 3 ) thin films on foreign substrates shows promise for the development of next-generation deep ultraviolet solar blind photodetectors and power electronic devices. In this work, the influences of the film thickness and crystallinity on the thermal conductivity of ($\bar{2}01$)-oriented β-Ga 2 O 3 heteroepitaxial thin films were investigated. Unintentionally doped β-Ga 2 O 3 thin films were grown on c-plane sapphire substrates with off-axis angles of 0° and 6° toward $\langle$$11\bar{2}0$$\rangle$ via metal–organic vapor phase epitaxy (MOVPE) and low-pressure chemical vapor deposition. The surface morphology and crystal quality of the β-Ga 2 O 3 thin films were characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The thermal conductivities of the β-Ga 2 O 3 films were measured via time-domain thermoreflectance. The interface quality was studied using scanning transmission electron microscopy. The measured thermal conductivities of the submicron-thick β-Ga 2 O 3 thin films were relatively low as compared to the intrinsic bulk value. The measured thin film thermal conductivities were compared with the Debye–Callaway model incorporating phononic parameters derived from first-principles calculations. The comparison suggests that the reduction in the thin film thermal conductivity can be partially attributed to the enhanced phonon-boundary scattering when the film thickness decreases. They were found to be a strong function of not only the layer thickness but also the film quality, resulting from growth on substrates with different offcut angles. Growth of β-Ga 2 O 3 films on 6° offcut sapphire substrates was found to result in higher crystallinity and thermal conductivity than films grown on on-axis c-plane sapphire. However, the β-Ga 2 O 3 films grown on 6° offcut sapphire exhibit a lower thermal boundary conductance at the β-Ga 2 O 3 /sapphire heterointerface. In addition, the thermal conductivity of MOVPE-grown ($\bar{2}01$)-oriented β-(Al x Ga 1–x ) 2 O 3 thin films with Al compositions ranging from 2% to 43% was characterized. Because of phonon-alloy disorder scattering, the β-(Al x Ga 1–x ) 2 O 3 films exhibit lower thermal conductivities (2.8–4.7 W/m∙K) than the β-Ga 2 O 3 thin films. The dominance of the alloy disorder scattering in β-(Al x Ga 1–x ) 2 O 3 is further evidenced by the weak temperature dependence of the thermal conductivity. This work provides fundamental insight into the physical interactions that govern phonon transport within heteroepitaxially grown β-phase Ga 2 O 3 and (Al x Ga 1–x ) 2 O 3 thin films and lays the groundwork for the thermal modeling and design of β-Ga 2 O 3 electronic and optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Corrosion-induced microstructural developments in 316 stainless steel during exposure to molten Li 2 BeF 4 (FLiBe) salt

The microstructural evaluation and characterization of 316 stainless steel samples that were tested in molten Li 2 BeF 4 (FLiBe) salt were investigated in this study for evaluating its performance in high-temperature molten fluoride salts. Recently, 316 stainless steel and FLiBe salt are being actively considered as the main structural alloy and primary coolant of fluoride salt-cooled high-temperature reactor (FHR), a leading nuclear reactor concept for the next generation nuclear plants (NGNP). In support of the materials development for the FHR, high-temperature corrosion tests of 316 stainless steel in molten FLiBe salt at 700°C have been conducted in both bare graphite crucibles and 316 stainless steel-lined crucibles in an inert atmosphere for up to 3000 hours. The microstructure of the tested samples was comprehensively characterized using scanning electron microscopy (SEM) in conjunction with energy dispersive x-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM) with EDS. In addition to the noticeable intergranular corrosion attack on surface, the corrosion in terms of the Cr depletion along high angle grain boundaries (15-180º) extended to 22µm in depth after 3000-hour exposure to molten FLiBe salt in graphite crucible. The coherent Σ3 grain boundary appeared high resistance to the Cr depletion. The substantial Cr depletion from the near-to-surface layer induced phase transformation from γ-martensite to α-ferrite phase (FeNi x ) during corrosion at 700ºC. Furthermore, the presence of graphite in the molten salt doubled the corrosion attack depth and led to the formation of round Mo2C, hexagonal Cr 7 C 3 and needle-like Al 4 C 3 phase within the alloy as deep as 50 µm after 3000-hour corrosion testing. Based on the microstructural analysis, the corrosion mechanisms of 316 stainless steel in molten FLiBe salt in different corrosion crucibles were illuminated through schematic diagrams. Additionally, a thermal diffusion controlled corrosion model was developed and validated by experimental data for predicting the long-term corrosion attack depth.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis and characterization of brownmillerite SrFeO{sub 2.5} in nanostructured form

Synthesis of bulk polycrystalline and nanocrystalline oxygen-deficient SrFeO{sub 2.5} compounds, with potential applications as oxygen membranes, has been explored by chemical route to optimize an easy and reproducible method for high yield. The structure of the samples was investigated by X-ray powder diffraction followed by structural refinement. Both bulk and nanocrystalline SrFeO{sub 2.5} crystallize in Imma space group. X-ray powder diffraction pattern corresponds to the brownmillerite structure in which the Fe cations exist in an octahedral or tetrahedral configuration in alternate layers along the b axis. Brunauer−Emmett−Teller (BET) surface area is found to be 0.40m{sup 2}/g and 14 m{sup 2}/g for bulk and nanocrystalline SrFeO{sub 2.5} respectively. The morphology of these materials was also investigated by scanning electron microscopy and transmission electron microscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Tailoring oxidation of aluminum nanoparticles reinforced with carbon nanotubes

In this report, the oxidation temperature and reaction enthalpy of Aluminum (Al) nanoparticles has been controlled by reinforcing with carbon nanotubes. The physical mixing method with ultrasonication was employed to synthesize CNT/Al nanocomposite powders. The micro-morphology of nanoconmposite powders has been analysed by scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy and X-ray diffraction techniques. The oxidation behavior of nanocomposite powders analyzed by thermogravimetry/differential scanning calorimertry showed improvement in the exothermic enthalpy. Largest exothermic enthalpy of-1251J/g was observed for CNT (4 wt%)/Al nanocomposite.

77 NANOSCIENCE AND NANOTECHNOLOGY↗