Results 1 - 10 of 2423
Results 1 - 10 of 2423. Search took: 0.018 seconds
|Sort by: date | relevance|
[en] A ceramic sample of uranium dioxide is probed by Raman imaging followed by a combined Lorentzian fitting - Principal Component Analysis process. This allows to evidence structural or chemical inhomogeneities of the material, which affect Raman line intensities but also line positions, evidencing local symmetry lowering. The inhomogeneities were observed not only between grain cores and boundaries, but also inside grain cores themselves. Only a part of these intensity inhomogeneities is as expected due to different orientations of the ceramic grains. Besides, a zone noticeably differing from others has been distinguished, presumably due to local strains or to chemical nature (oxygen stoichiometry), showing the sensitivity of the analysis. This underlines the importance to perform Raman analysis in such ceramic materials at least on several points and better, in imaging mode. (authors)
[en] We report monodisperse, chain-like particles (nanochains) consisted of silica-coated maghemite (γ-Fe2O3) nanoparticle clusters prepared by colloidal chemistry and magnetic field-induced self-assembly of nanoparticle clusters. In order to quantify the shapes of chain-like particles, we have used the measure for shape convexity which is also called solidity. We functionalize the surface of the nanochains with amino (–NH2) and carboxyl groups (–COOH) in order to modify surface charge. These surfaces of nanochains provide better colloidal stability and their potential for practical applications in biomedicine. The enhanced colloidal stability of the surface modified nanochains is confirmed by Zeta potential (ζ-potential) analysis. Magnetic properties of the nanochains show superparamagnetic state at room temperature since the nanochains are composed of tiny nanoparticles as their building blocks. The measured M(H) data at room temperature have been successfully fitted by the Langevin function and magnetic moment μp = 20,526 μB for sphere-like nanoparticle clusters and μp = 20,767 μB for nanochains are determined. The determined magnetic parameters have revealed that the nanochains show a magnetic moment of the nanoparticles higher than the one of individual nanoparticle clusters. These differences can be attributed to the collective magnetic properties of superparamagnetic iron oxide nanoparticles (SPION) assembled in different morphologies (isotropic and anisotropic morphology). © 2018
[en] Anomalous small-angle X-ray scattering (ASAXS) is a technique developed in the 1980's giving access to chemical information of nano-objects besides characteristic features like size and volume fraction given by classical SAXS. ASAXS is an element-selective technique based on the anomalous variation of the scattering factor near the absorption edge of one chosen element. A simple approach is proposed to extract chemical information from anomalous SAXS data. To illustrate the procedure, data treatment is applied to discriminate between different possible phases that may form nano-oxides in oxide-dispersion-strengthened (ODS) steels. (authors)
[en] The network of sub-boundaries formed in a sintered UO2 pellet after dislocational creep was examined. Very low angle boundaries, down to 0.1 degree were reliably detected by Electron Backscattered Diffraction (EBSD). This angular resolution was achieved by optimizing EBSD data collection and processing. Moreover, Accurate-Electron Channeling Contrast Imaging (Accurate-ECCI) was able to image the dislocations produced by creep, directly on the bulk sample. The dislocations were mostly organized in sub-boundaries with low energy configurations. Only a limited number of isolated dislocations were observed. Finally, the deformation substructure obtained after 8% creep deformation (at 1500 C under a 50 MPa uniaxial state) was quantified. The original grains with a mean size of 20 μm were in average fragmented in sub-grains of about 5 μm. The geometrically necessary dislocations density (GND) was evaluated from the filtered EBSD data to 7.9 x 1012 m-2. This value was 10 times higher than that measured on the as-sintered sample. This confirms that the GND density calculation is sensitive to the dislocation increase after 8% deformation by creep. (authors)
[en] Optical microscopy, scanning electron microscopy, and transmission electron microscopy were employed to examine the interfacial microstructural effects of impurities in alumina substrates used to fabricate alumina-niobium interfaces via liquid-film-assisted joining. Three types of alumina were used: undoped high-purity single-crystal sapphire; a high-purity, high-strength polycrystalline alumina; and a lower-purity, lower-strength polycrystalline alumina. Interfaces formed between niobium and both the sapphire and high-purity polycrystalline alumina were free of detectable levels of impurities. In the lower-purity alumina, niobium silicides were observed at the alumina-niobium interface and on alumina grain boundaries near the interface. These silicides formed in small-grained regions of the alumina and were found to grow from the interface into the alumina along grain boundaries. Smaller silicide precipitates found on grain boundaries are believed to form upon cooling from the bonding temperature
[en] The Idaho National Laboratory (INL) is investigating U-Pu-Zr alloys with low concentrations of minor actinides (Np and Am) and rare-earth elements (La, Ce, Pr, and Nd) as possible nuclear fuels to be used to transmute minor actinides. Alloys with compositions 60U-20Pu- 3Am-2Np-15Zr, 42U-30Pu-5Am-3Np-20Zr, 59U-20Pu-3Am-2Np-1RE-15Zr, 58.5U-20Pu- 3Am-2Np-1.5RE-15Zr, 41U-30Pu-5Am-3Np-1RE-20Zr, and 40.5U-30Pu-5Am-3Np-1.5RE- 20Zr (where numbers represent weight percents of each element and RE is a rare-earth alloy consisting of 6% La, 16% Pr, 25% Ce, and 53% Nd by weight) were arc-melted and vacuum cast as fuel pins approximately 4 mmin diameter. The as-cast pins were sectioned, polished, and examined by scanning electron microscopy. Each alloy contains high-Zr inclusions surrounded by a high-actinide matrix. Alloys with rare-earth elements also contain inclusions that are high in these elements. Within the matrix, concentrations of U and Zr vary inversely, while concentrations of Np and Pu appear approximately constant. Am occurs in the matrix and with some high-rare-earth inclusions, and occasionally as high-Am inclusions in samples without rare-earth elements.
[en] Highlights: • Multilayer TiN/ZrN films were deposited using sequential vacuum-arc deposition of Ti and Zr targets in nitrogen atmosphere; • Several samples were annealed in air at the temperature 700 °C; • First-principles calculations of TiN(111), ZrN(111) structures and TiN(111)/ZrN(111) multilayer were carried out; • All deposited samples were highly polycrystalline with quite large 20–25 nm crystals; • The nanohardness and elastic modulus of non-annealed coatings reached 42 GPa and 348 GPa, respectively; • Deposited coatings demonstrate good wear and oxidation resistance; - Abstract: Nanoscale multilayered TiN/ZrN films were deposited using sequential vacuum-arc deposition of Ti and Zr targets in a nitrogen atmosphere. Studies of film's properties were carried out using various modern methods of analysis, such as XRD, STEM, HRTEM, SIMS combined with results of nanoindentation and tribological tests. To interpret the mechanical properties of the deposited multilayer films first-principles calculations of TiN(111), ZrN(111) structures and TiN(111)/ZrN(111) multilayer were carried out. To study the influence of thermal annealing, several samples were annealed in air at the temperature 700 °C. All deposited samples were highly polycrystalline with quite large 20–25 nm crystals. The crystalline planes were very ordinated and demonstrated an excellent coordinated growth. The nanohardness and elastic modulus of non-annealed coatings reached 42 GPa and 348 GPa, respectively. Annealing in air at the temperature 700 °C led to partial oxidation of the multilayered coatings, however hardness of the non-oxidized part of the coatings remained as high, as for initial coatings. All deposited coatings demonstrate good wear resistance.
[en] Highlights: • The depth-dependence of radiation-induced cavities was characterized in self-ion irradiated HT9 co-implanted with He. • The injected interstitial effect was revealed to suppress cavity swelling in the vicinity of the damage peak. • ChemiSTEM elemental maps revealed the segregation of Ni at cavity surfaces and its possible synergistic influence on swelling was discussed. - Abstract: Ferritic/Martensitic HT9 steel was irradiated at 432 °C to 16.6 displacements per atom (dpa) (at the depth of 600 nm) using a defocused beam of 5 MeV Fe++ ions, while co-implanted with 3.22 appm He at the same depth. The helium concentration profile was designed so to follow the damage curve with a 0.22 appm He/dpa ratio at the depth from 300 to 1000 nm in the material. The depth-dependence of the cavity size and number density were characterized by both transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) imaging methods. A comparison between the two techniques was done showing good agreement. Cavity number density and the resulting swelling were found to be suppressed by the injected interstitial effect in the vicinity of the ion induced damage peak. The region between 300 and 750 nm depth which excludes the injected interstitial effect was thus proposed for improved cavity swelling analysis. The swelling ratio in this region was found to be ~(0.86–1.02) × 10− 2%/dpa. In addition, ChemiSTEM characterization revealed radiation-induced segregation occurring throughout the irradiated region and precipitation of G-phase particles. Segregation of Ni to cavity surfaces was also observed and its possible synergistic influence on swelling was discussed.
[en] Highlights: • Intragranular thin-platelet LPSO phases strongly restrict the DRX. • The low extrusion ratio fails to widely break the intragranular LPSO. • The large extrusion ratio results in the full DRX via the CDRX mechanism. • Finer DRX-ed grains and LPSO induce the higher yield strength and elongation. • The larger grain size causes an increase in the strain hardening rate. - Abstract: A comparison has been made on the dynamic recrystallization (DRX), texture, and mechanical properties of the Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr (wt%) alloys extruded with different ratios (ER, 36 and 7.1). Intragranular long-period stacking ordered (LPSO) phases strongly restrict the DRX by restraining the lattice rotation of α-Mg grains and hindering the migration of the boundaries of DRX-ed grains. Extrusion with ER of 36 can widely break the intragranular LPSO phases and create a fully DRX-ed microstructure with a relatively random texture, while the lower ER of 7.1 fails to break the LPSO and leads to a bimodal microstructure with a strong basal fiber texture. Finer DRX-ed grains and smaller LPSO phases account for the superior tensile yield strength and elongation of the ER36 alloy. However, the ultimate tensile strength of the ER7.1 alloy catches up because its larger grain size causes an increase in the strain hardening rate.