Results 1 - 10 of 7206
Results 1 - 10 of 7206. Search took: 0.034 seconds
|Sort by: date | relevance|
[en] Highlights: • Magnetite particles, after separation from reaction mixture and drying, were irradiated using electron beam (EB). • After EB irradiation bare Fe3O4 nanoparticles aggregated in aqueous dispersion. • Surface of uncoated Fe3O4 particles was oxidized during EB irradiation. • EB irradiation caused disaggregation of citrate-coated Fe3O4 particles. - Abstract: Influence of electron beam (EB) irradiation on surface properties of magnetite was investigated using XRD, TEM, DLS, zeta-potential, FTIR and Raman spectroscopy. Fe3O4 particles were synthesized by alkaline hydrolysis of ferrous ions and stabilized with sodium citrate. Dry samples of bare and citrate- coated Fe3O4 particles were EB-irradiated with doses up to 300 kGy. The crystallite sizes of uncoated and citrate-coated magnetite were found to be in the range of 25–27 nm and 30–32 nm, respectively. EB- irradiation did not result in phase and size change of Fe3O4 nanoparticles. Using DLS and TEM analysis, it has been found, that EB-irradiated bare Fe3O4 nanoparticles have aggregated in aqueous dispersion. Traces of hematite and maghemite were identified on the surface of EB-irradiated bare particles by Raman spectroscopy. Radiation-induced oxidation of magnetite was probably involved to radiolysis of water molecules adsorbed onto particle surface and formation of hydroxyl radicals which are strong oxidize species. Disaggregation of citrate-coated particles in water dispersion after EB irradiation has been assigned to disruption of Fe-citrate bonds.
[en] Highlights: • Gamma irradiation induced graft of glycidyl methacrylate on surface of nanofillers. • Homogeneous dispersion of nanofillers in polymeric matrix due to grafting. • Improving bond between the nanofillers and matrix by glycidyl methacrylate grafting. • Increases of tensile strength and modulus of flexible films with nanofillers grafted. • High UV–vis light absorption with energy gap shifted to the visible region. - Abstract: Many studies report that nanocomposites obtained by dispersion of a small amount nanofiller into the polymer have remarkable improvements achieved in the mechanical and physical properties. However, in order to achieve this great improvement in properties, it is necessary that the nanofillers be dispersed homogeneously into the polymeric matrix. Often this dispersion is difficult to achieve due to the high interfacial energy of the nanoparticles present. This study reports the effect of gamma irradiation induced graft of glycidyl methacrylate (GMA) onto the surface of TiO2 and Clay nanofillers to improve their dispersion into the EVA matrix. The physical and mechanical properties of Ethylene-vinyl acetate copolymer (EVA) flexible films with these nanoparticles were studied. EVA nanocomposite with adding of the different amount of TiO2 and modified montmorillonite clay grafted and un-grafted with glycidyl methacrylate (GMA) using gamma irradiation have been prepared by melt extrusion. The nanocomposite flexible films were produced using a flat die extrusion process. The PGMA-grafted nanofillers were characterized by XRD and TEM analysis. The flexible films were characterized by Tensile tests, ATR–FTIR, UV–VIS, XRD, TG, and FE-SEM analysis to understand the nature of the interaction between the nanofillers and EVA matrix. The results showed that the addition of PGMA-grafted TiO2 and Clay nanofillers into EVA matrix improved the bonding between the nanofillers and matrix. It was also found that the PGMA-grafted nanofillers could be well dispersed into an EVA matrix in contrast to that of un-grafted. The tensile strength and modulus of the resulting EVA/TiO2-PGMA enhanced in comparison to that of un-grafted TiO2. The EVA/Clay-PGMA had slightly decreased tensile strength comparable to that of EVA/Clay but had considerably improved elastic modulus. In addition, the flexible films based on TiO2 exhibited high UV–Vis light absorption with energy gap shifted to the visible region. The results demonstrated that TiO2 and Clay nanofillers grafted with GMA by gamma radiation can be used to prepare EVA flexible films with improved bonding between the nanofillers and matrix and, consequently, enhanced properties for food and cosmetic packaging application.
[en] Highlights: • NEXAFS spectroscopy around C K-edge with compact LPP SXR source, • 2-D spectromicroscopy using an LPP SXR source of EUV etched polymer sample. • Single-shot (1 ns), time resolution NEXAFS spectroscopy with an LPP SXR source. - Abstract: The near edge X-ray absorption fine structure (NEXAFS) is an established method employed for a compositional analysis of the samples. The information about sample's elemental composition is obtained through the observation of the soft X-ray (SXR) spectra in the proximity of the high energy side of the X-ray absorption edge of a particular element of interest. This technique allows one to characterize the matter, obtaining useful and important information, such as the structure of intermolecular and atomic bonds in SXR spectral range. The NEXAFS requires, however, short wavelength sources, capable of delivering sufficiently high flux to obtain high quality spectral data. Typical sources for NEXAFS are synchrotrons, free electron lasers, but, more recently, also compact laser produced plasma (LPP) sources; among them, the laser-plasma source based on a double stream gas puff target. In this short review, the application of this source to the recently developed NEXAFS spectroscopy and spectromicroscopy systems will be presented and discussed in more details with the references to the original works.
[en] Highlights: • Extraction of the Fe3+/Fetot ratio from the pre-edge structure at the Fe K-edge. • Fitting of the pre-edge with 4 Gaussians representative of ferric and ferrous ion. • Calibration line combining the pre-edge analysis and Mössbauer spectroscopy data. • Method suitable to investigate Fe dynamics in complex systems such as amphiboles. - Abstract: A new approach to extract accurate information on the Fe oxidation state has been tested on three different Fe-rich amphiboles annealed at 194–520 °C. The method is based on the analysis of the pre-edge structure of the X-ray absorption spectra at the Fe-K edge. The pre-edge band is deconvolved into four Gaussian components where the integrated intensities of the pairs of lower- and higher-energy bands are related to the ferrous to ferric ion ratio. These Fe3+/Fetot ratios have been compared with those obtained with independent techniques (X-ray diffraction and Mossbauer spectroscopy) on the same samples. The experimental data allowed establishing a calibration curve that is in good agreement with a recent statistical analysis based on spectroscopic data for the same type of minerals. The method could be extended to the analysis of other complex systems containing both Fe3+ and Fe2+ in octahedral coordination or to study the dynamics of iron under non-ambient conditions.
[en] A simple method for non-empirical ligand field multiplet calculations for transition metal L-edge spectra is presented. Ligand field splittings and anisotropic scaling factors for Coulomb integrals are obtained from density functional theory. The method is applied to transition metal monoxide solids and nickel and cobalt phthalocyanines molecules and good agreement with experiment is obtained.
[en] The Radiation MONitoring (RadMON) system is widely employed at CERN to measure the radiation levels in the accelerators, as well as the degradation of electronics located in the Large Hadron Collider (LHC) tunnel and shielded areas. Radiation Field Effect Transistors (RadFETs) integrated in the RadMON specifically measure the Total Ionizing Dose (TID) in the accelerators complex and are affected in turn by the CERN radiation field. The CERN High energy AcceleRator Mixed-field test facility (CHARM) has been built with the intention of reproducing different mixed-fields (atmospheric, space, accelerators, ground,…), to test electronics when exposed to specific radiation environments. Among these fields, LHC-like environments are reproduced to test the RadMON's electronic components: the main goal is a full characterization of the RadMON response and the monitoring of its degradation, when it is exposed to the LHC radiation field. FLUKA Monte Carlo simulations are crucial at this stage as a powerful tool to reproduce and calibrate the RadMON response. Our present FLUKA Monte Carlo model of the RadFET is well representative of its experimental dose response to the CHARM mixed-field, in unshielded layout. However, the simulations-experiments agreement in lateral shielded positions is less accurate, probably due to the neutron component of the field. This paper focuses on the study of the RadFET dose response to neutrons, when the dosimeter is irradiated by mixed-fields. FLUKA Monte Carlo simulations and neutron test campaigns performed at ILL (Institut Laue Langevin) and LPSC (Laboratoire de Physique subatomique et de Cosmologie) in Grenoble, as well as at CERN are compared, to further investigate and fully characterize the RadFET response to neutrons. The simulations-measurements agreement is within the experimental uncertainties, while an overall agreement within a factor 2 is found in positions shielded by the movable walls, at CHARM. The test campaign showed the RadFET is insensitive to the thermal neutron component of the mixed-field at CHARM.
[en] The ultradivided matter is used for long in various applications, for example in colloids, inks and paints, cosmetics, stained glasses, catalysts, photographic emulsions, ... But the progressive need of nanoparticles for various miniaturized devices and the different approaches for the synthesis have suddenly increased. All of the bottom-up synthesis methods from a diluted precursor to metal nanoparticles imply several steps: a reduction reaction of ionic precursors by electron transfer, inducing the nucleation of atoms then the growth of the seeds into particles, more or less inhibited by stabilizers. The final size, shape, structure and dispersity of the particles strongly depend on the thermodynamics and the kinetics of these steps. The interaction of high energy radiation with the solvent provides, quantitatively and homogeneously distributed in the bulk, strong electron donors (solvated electrons, reducing radicals) which reduce metal ions as precursors into atoms. The radiation chemistry, on one hand in the steady state regime with an accurate knowledge of the yields of all the radiolytic products, and on the other hand in the pulse regime giving access to time-resolved data, constitutes a unique tool to elucidate the detailed mechanisms and to provide the keys of really controlling these processes in view of various applications.
[en] Highlights: • Distorted octahedral Ni complexes have been studied using EXAFS as well as XANES. • Simulated XANES spectra show different features depending on metal p- and s-DOS. • s-DOS contribution to rising part of edge has been found to vary among complexes. • Constant p-DOS over 0–10 eV give rise to weak and split while line in complex 1. - Abstract: Distortion in mononuclear Schiff base nickel (II) complexes having pyridine and related N-containing heterocyclic derivatives has been studied using X-ray absorption spectroscopy. Extended X-ray absorption fine structure (EXAFS) analysis has been used to confirm the octahedral nature of Ni center and obtain a simple cluster of atoms around this metal ion. Ab-initio X-ray absorption near edge structure (XANES) simulations have been performed using FEFF9 for almost similar coordination around nickel metal in these complexes. The study supports variation in the order of distorted octahedral nature of Ni complexes with O and N atoms around the metal ions, with respect to changing nature of ligand. Theoretical XANES spectra generated for clusters of atoms around the metal ion have been correlated to corresponding p-DOS and s-DOS of the metal.
[en] Highlights: • The single scattering term of the spin-orbit interaction at scattering sites has a negligible contribution to magnetic EXAFS. • This result substantially differs from the case of x-ray magnetic circular dichroism. • This small contribution comes from the narrow effective range of the spin-orbit interaction. - Abstract: We present an effect of the spin-orbit interaction (SOI) at surrounding atoms on K-edge magnetic extended x-ray absorption fine structure (MEXAFS). A contribution of the SOI to a K-edge MEXAFS spectrum is described by a perturbative way within a multiple scattering (MS) theory. A numerical calculation shows that a photoelectron single scattering by the SOI at surrounding atomic sites has a negligibly small contribution to MEXAFS. Although a negligible contribution of the SOI at surrounding atoms has been attributed to a cancellation of various MS contributions, this small contribution can be understood by the small number of its effective partial wave components, at least within the single scattering approximation. For further detailed analyses of MS with a path expansion method, only the small number of the partial wave components for the SOI is necessary. This leads to faster computations for MEXAFS including the photoelectron scattering by the SOI.
[en] Highlights: • Radiation synthesis of metallic and polymeric nanoparticles has been reviewed. • Applications of nanoparticles in biomedicine, electronics, engineering, and bioengineering. • Advantages of radiolytic synthesis of nanoparticles over chemical routes are presented. • Properties of nanoparticles can be modified by dose, dose rate, among others. - Abstract: Controlled synthesis of nanostructured materials allows the development of new materials with fine-tuned mechanical, optical, magnetic, electronic, conductive, and catalytic properties that are used in numerous applications for example in medical area as vehicles for drug delivery, in diagnostics or combinations thereof. Advantages of using radiation chemistry for this purpose are many, minimal use of potentially harmful chemicals and simple production schemes in aqueous systems, which minimizes the use of organic solvents and the need for separation and purification of the final product. High energies particularly gamma-rays (1.17 and 1.33 MeV from 60Co) can be used to initiate free radical based reactions in solids, liquids or gases and because of non-selectivity of absorption of gamma-rays in matter free radicals and electrons that are dependent on the factor G. These radiolitycal species in aqua solution are extensively used in the synthesis of metallic nanoparticles (NPs) from its corresponding salts. However, in the case of organic NPs, the gamma-rays are used mainly to stabilize by cross-linking preformed NPs from natural or synthetic polymers and proteins, or in any case, start polymerisation reactions from monomers that become to form the NPs. Therefore, the unique properties of ionizing radiation make it a very useful tool in the synthesis of a broad variety of metallic NPs with several compositions by a combination of different metal ions, polymers, monomers, and even proteins, giving core-shell and alloyed NPs. This method of synthesis represents a clean alternative to chemical methods and it has shown huge potential in morphological control and particle size by means of parameters that include absorbed dose, dose rate, stabilizing agents, and concentration of metal ion, polymer/monomer, and protein precursors. In this work, we reviewed the synthesis of metallic and organic NPs through gamma-rays with prospects for a future outlook.