28 resultados para ENERGY-ELECTRON DIFFRACTION
em Deakin Research Online - Australia
Resumo:
An austenitic Ni-30 wt pct Fe alloy, with a stacking-fault energy and deformation characteristics similar to those of austenitic low-carbon steel at elevated temperatures, has been used to examine the defect substructure within austenite deformed by single-pass strip rolling and to identify those features most likely to provide sites for intragranular nucleation of ultrafine ferrite in steels. Samples of this alloy and a 0.095 wt pct C-1.58Mn-0.22Si-0.27Mo steel have been hot rolled and cooled under similar conditions, and the resulting microstructures were compared using transmission electron microscopy (TEM), electron diffraction, and X-ray diffraction. Following a single rolling pass of ∼40 pct reduction of a 2mm strip at 800 °C, three microstructural zones were identified throughout its thickness. The surface zone (of 0.1 to 0.4 mm in depth) within the steel comprised a uniform microstructure of ultrafine ferrite, while the equivalent zone of a Ni-30Fe alloy contained a network of dislocation cells, with an average diameter of 0.5 to 1.0 µm. The scale and distribution and, thus, nucleation density of the ferrite grains formed in the steel were consistent with the formation of individual ferrite nuclei on cell boundaries within the austenite. In the transition zone, 0.3 to 0.5 mm below the surface of the steel strip, discrete polygonal ferrite grains were observed to form in parallel, and closely spaced “rafts” traversing individual grains of austenite. Based on observations of the equivalent zone of the rolled Ni-30Fe alloy, the ferrite distribution could be correlated with planar defects in the form of intragranular microshear bands formed within the deformed austenite during rolling. Within the central zone of the steel strip, a bainitic microstructure, typical of that observed after conventional hot rolling of this steel, was observed following air cooling. In this region of the rolled Ni-30Fe alloy, a network of microbands was observed, typical of material deformed under plane-strain conditions.
Resumo:
Long and straight β-SiC nanowires are synthesized via the direct current arc discharge method with a mixture of silicon, graphite and silicon dioxide as the precursor. Detailed investigations with x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, Raman scattering spectroscopy, transmission electron microscopy and selected area electron diffraction confirm that the β-SiC nanowires, which are about 100–200 nm in stem diameter and 10–20 µm in length, consist of a solid single-crystalline core along the (1 1 1) direction wrapped with an amorphous SiOx layer. A broad photoluminescence emission peak with a maximum at about 336 nm is observed at room temperature. A direct current arc plasma-assisted self-catalytic vapour–liquid–solid process is proposed as the growth mechanism of the β-SiC nanowires. This synthesis technique is capable of producing SiC nanowires free of metal contamination with a preferential growth direction and a high aspect ratio, without the designed addition of transition metals as catalysts.
Resumo:
Poly(triazine imide) with intercalation of lithium and chloride ions (PTI/Li+Cl−) was synthesized by temperature-induced condensation of dicyandiamide in a eutectic mixture of lithium chloride and potassium chloride as solvent. By using this ionothermal approach the well-known problem of insufficient crystallinity of carbon nitride (CN) condensation products could be overcome. The structural characterization of PTI/Li+Cl− resulted from a complementary approach using spectroscopic methods as well as different diffraction techniques. Due to the high crystallinity of PTI/Li+Cl− a structure solution from both powder X-ray and electron diffraction patterns using direct methods was possible; this yielded a triazine-based structure model, in contrast to the proposed fully condensed heptazine-based structure that has been reported recently. Further information from solid-state NMR and FTIR spectroscopy as well as high-resolution TEM investigations was used for Rietveld refinement with a goodness-of-fit (χ2) of 5.035 and wRp=0.05937. PTI/Li+Cl− (P63cm (no. 185); a=846.82(10), c=675.02(9) pm) is a 2D network composed of essentially planar layers made up from imide-bridged triazine units. Voids in these layers are stacked upon each other forming channels running parallel to [001], filled with Li+ and Cl− ions. The presence of salt ions in the nanocrystallites as well as the existence of sp2-hybridized carbon and nitrogen atoms typical of graphitic structures was confirmed by electron energy-loss spectroscopy (EELS) measurements. Solid-state NMR spectroscopy investigations using 15N-labeled PTI/Li+Cl− proved the absence of heptazine building blocks and NH2 groups and corroborated the highly condensed, triazine-based structure model.
Resumo:
A solid-state displacement reaction of Ga2O3 with Mg3N2 has been used to synthesize GaN nanocrystals by mechanochemical processing. X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) measurements indicated that the nanocrystals had a hexagonal structure and sizes ranging from 4 to 20thinspnm. Optical absorption and transmission measurement showed the bandgap of the nanocrystals was consistent with that of bulk GaN samples (3.43thinspeV). This study demonstrates that mechanochemical processing has significant potential for the synthesis of GaN nanocrystals in a simple and efficient way.
Resumo:
It is confirmed that a layer of vacuum-evaporated carbon on the surface of a preoriented ultrathin polymer film can lead to an oriented recrystallization of the polymer film. This has been attributed to a strong fixing effect of vacuum-evaporated carbon layer on the film surface of the polymer. To study the origin of the strong fixing effect of vacuum-evaporated carbon layer on the polymer films, the melting and recrystallization behaviors of the preoriented ultrathin PE film with a vacuum-evaporated carbon layer were studied by using atomic force microscopy, electron diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. We found that there exists some extent of chain orientation of carbon-coated polyethylene (PE) preoriented ultrathin film above its melting temperature. These oriented PE chain sequences act as nucleation sites and induce the oriented recrystallization of preoriented PE film from melt. Raman spectroscopy results suggest that new carbon-carbon bonds between the carbon layer and the oriented PE film are created during the process of vacuum carbon evaporation. As a result, some of the PE chain stems are fixed to the coated carbon substrate via covalent bond. Such a bonding has retarded the relaxation of the PE chains at the spot and, therefore, preserves the original orientation of the PE stems at high temperature, which in turn derives the recrystallization of the PE chains in an oriented structure.
Resumo:
This dataset includes orientation from xray diffraction, electron diffraction, and microstructural characterisation. Some transmission electronmicroscopy is also included.
Resumo:
V2O5·nH2O nanosheets are fabricated hydrothermally with the acidified peroxovanadate solution at 200 °C for 12 h. The X-ray diffraction suggests that V2O5·nH2O nanosheets display lamellar ordering along c-axis direction. Transmission electron microscopy, field-emission scanning electron microscopy, and selected area electron diffraction indicate that V2O5·nH2O nanosheets are very thin in thickness and micron-sized in lateral dimension, and they are two-dimensional crystallites. X-ray photoelectron spectroscopy and thermogravimetric analysis are utilized to confirm the elemental composition of nanosheets. The formation process of nanosheets is also discussed in terms of time- and temperature-controlled experiments.
Resumo:
Hexagonal V0.13Mo0.87O2.935 nanowires were hydrothermally synthesized at 220 °C for the first time. X-ray diffraction and field-emission scanning electron microscopy were utilized to characterize the phase and morphology of the nanowires, respectively. Transmission electron microscopy and selected area electron diffraction indicate that the nanowires are single crystalline, growing along the [001] direction. Interestingly, the nanowires easily become amorphous under the electron irradiation. The comparative hydrothermal experiments show that the molar ratio between the starting reagents of Mo and NH4VO3 plays a vital role in the anisotropic growth of nanowires. The photoluminescence measurement demonstrates that these nanowires exhibit two strong emission peaks at 420 and 438 nm, which are probably related to the intrinsic oxygen vacancies.
Resumo:
Semiconducting GaN and Gax In1-x N nanoparticles (4-10 nm in diameter, depending on the metal ratio) with tunable indium content are prepared through a chemical synthesis (the urea-glass route). The bandgap of the ternary system depends on its composition, and therefore, the color of the final material can be turned from bright yellow (the color of pure GaN) to blue (the color of pure InN). Transmission electron microscopy (TEM and HRTEM) and scanning electron microscopy (SEM) images confirm the nanoparticle character and homogeneity of the as-prepared samples. X-ray diffraction (XRD), electron diffraction (EDX), elemental mapping, and UV/Vis, IR, and Raman spectroscopy investigations are used to confirm the incorporation of indium into the crystal structure of GaN. These nanoparticles, possessing adjusted optical properties, are expected to have potential applications in the fabrication of novel optoelectronic devices.
Resumo:
Low temperature plasma carburising (LTPC) has been increasingly accepted as a hardening process for austenitic stainless steels because it produces a good combination of tribological and corrosion properties. The hardening mechanism is based on the supersaturation of the austenitic structure with carbon, which greatly hardens the material, significantly expands the fcc unit cell, produces high levels of compressive residual stresses and, ultimately, leads to the occurrence of deformation bands and rotation of the crystal lattice. The microstructural changes introduced during plasma carburising have a significant impact on the mechanical, tribological and corrosion performance and, for this reason, the microstructure of expanded austenite or S-phase has been extensively studied. However, modern surface characterisation techniques could provide new insights into the formation mechanism of S-phase layers. In this work, backscattered electron diffraction and atomic force microscopy were used to characterise the surface layers of expanded austenite produced by LTPC in an active screen furnace. Based on the experimental results, the plastic deformation, its dependence on crystallographic orientation, the evolution of grain boundaries, and their effects on mechanical, tribological and corrosion properties are discussed. © 2011 Elsevier B.V. All rights reserved.
Resumo:
An improved method for mass production of good-quality graphene nanosheets (GNs) via ball milling pristine graphite with dry ice is presented. We also report the enhanced performance of these GNs as working electrode in lithium-ion batteries (LIBs). In this improved method, the decrease of necessary ball milling time from 48 to 24 h and the increase of Brunauer–Emmett–Teller surface area from 389.4 to 490 m2/g might be resulted from the proper mixing of stainless steel balls with different diameters and the optimization of agitation speed. The as-prepared GNs are investigated in detail using a number of techniques, such as scanning electron microscope, atomic force microscope, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray diffractometer, and Fourier transform infrared spectroscopic. To demonstrate the potential applications of these GNs, the performances of the LIBs with pure Fe3O4 electrode and Fe3O4/graphene (Fe3O4/G) composite electrode were carefully evaluated. Compared to Fe3O4-LIBs, Fe3O4/G-LIBs exhibited prominently enhanced performance and a reversible specific capacity of 900 mAh g−1 after 5 cycles at 100 and 490 mAh g−1 after 5 cycles at 800 mA g−1. The improved cyclic stability and enhanced rate capability were also obtained.