Search results for "engineering.material"

Neutron irradiation influence on magnesium aluminium spinel inversion

2002

Abstract Grown by the Verneuil method MgO · nAl2O3 single crystals and natural spinel crystal have been studied using X-ray diffraction and photoluminescence spectra. The fast neutron irradiation of magnesium aluminium spinel leads to the lattice parameter decrease. The bond lengths of Mg–O and Al–O vary with the u-parameter and the lattice parameter. On the other hand, the bond lengths are related with the inversion parameter. Using changes of the lattice parameter during irradiation we have calculated the inversion parameter, which is 15–20%. In the luminescence spectra, the fast neutron radiation (fluence 1016 cm−2) produces an increase in the intensity ratio of the N- to R-lines by 5–20…

In situ XRD analysis of the oxide layers formed by oxidation at 743 K on Zircaloy 4 and Zr–1NbO

2000

Abstract Two alloys, having different oxidation behaviour (Zy4 and Zr–1NbO), have been investigated during oxidation at high temperature (743 K) and low oxygen pressure (10 kPa) by in situ X-ray diffraction (XRD). Tetragonal phase content and ‘pseudo-stresses’ on the monoclinic phase have been measured as a function of the oxide layer thickness. The tetragonal phase contents are similar for both alloys and decreased with the oxide layer thickness. Pseudo-stresses were much more compressive on Zr–1NbO alloy, with limited changes at the corrosion kinetics transition. On cooling, the tetragonal fractions do not change, while ‘pseudo-stresses’ decreased in different ways for the two alloys. Wit…

Electroless synthesis of lepidocrocite (γ-FeOOH) nanotubes in ion track etched polycarbonate templates

2012

In this study, we describe the electroless synthesis of lepidocrocite (γ-FeOOH) nanotubes produced in ion track etched polycarbonate foils. The foils act as templates after they had been irradiated with heavy ions to produce latent tracks that were etched with a desired diameter. Templates are used to fabricate shape formed 1D nanostructures in general. The synthesis of lepidocrocite nanotubes was carried out in a simple two-step method: firstly, particles were formed by precipitation in aqueous solution; secondly, nanotubes were produced by the deposition of the particles inside the nanochannels of the polycarbonate template. Solvent effects were considered to achieve homogeneous growth re…

Modelling of point defects in α-AL2O3

1995

Abstract The semiempirical method of the Intermediate Neglect of Differential Overlap (INDO), in the program SYMSYM, has been used for calculations on perfect and imperfect corundum crystals. For the perfect crystal the periodical Large Unit Cell (LUC) model was used while the Molecular Cluster (MC) model was used in defect calculations. By means of the MC model, we have investigated the optical properties of electronic centers (F+, F, F−, FMg, F− Mg) in corundum. Calculated optical properties of these defects are compared with experimental values and new bands are predicted to exist in the absorption spectrum of Mg-doped corundum. The energy levels of F-type and Mg-impurity related centers…

Radiation-induced point defects in simple oxides

1998

We present a survey of recent theoretical studies of radiation-induced point defects in simple oxides with emphasis on highly ionic MgO, partly-covalent corundum (Al2O3) and ferroelectric KNbO3. The atomic and electronic structure of the electronic (F a and F centers) and hole centers, as well as interstitial atoms therein are discussed in light of the available experimental data. Results for defect diAusion and photo-stimulated F a fi F center conversion are also ana

Co2CrIn: A Further Magnetic Heusler Compound

2006

Summary and Outlook In summary, this work presents the synthesis andcharacterisation of the Heusler compound Co 2 CrIn.The compound is L2 1 ordered and shows no major an-tisite disorder. Co 2 CrIn turns out to be a ferrimagnetwith a magnetic moment of 1.18 µ B at 5 K. In addi-tion, the hysterisis curve reveals a soft magnetic be-haviour. A measurement of the site specific magneticmomentsis highlydesirableas it might leadto a deeperunderstanding of the magnetic properties of Co 2 CrIn.Furthermore, the measured magnetic moment is not aninteger number, as expected for a half-metallic ferro-magnet. Thus, Co 2 CrIn can not be a half-metallic fer-romagnet, as most of the other Co 2 YZ Heusler com-…

Positron Annihilation in Deformed and Hydrogenated Pd-23%atcu Alloy

1999

The structural properties of soda–silicate sols and of the lime–soda–silicate gel formation

1999

Abstract Alkaline silicate solutions were prepared with varying SiO 2 –Na 2 O ratios, Rm=[SiO 2 ]/[Na 2 O]=2 or 3, with a constant silica concentration equal to 1.5 M. The structure and the number fraction of different silicate molecular species present in the solutions were classically determined for molar ratio Rm=2 using 29 Si nuclear magnetic resonance ( 29 Si NMR). In the case of the sample with Rm=3, for which no NMR data was available, we used small-angle X-ray scattering (SAXS) experiments to get this information. The SAXS model was previously tested with Rm=2 silicate solution. When Ca ++ is added to alkaline silicate solutions, a gel is obtained under well-defined conditions. The …

Organic Fertilization in Traditional Mediterranean Grapevine Orchards Mediates Changes in Soil Microbial Community Structure and Enhances Soil Fertil…

2016

Soil microbial populations and their functions related to nutrient cycling contribute substantially to the regulation of soil fertility and the sustainability of agroecosystems. A field experiment was performed to assess the medium-term effect of a mineral fertilizer and two organic fertilization systems with different nitrogen sources on the soil microbial community biomass, structure, and composition (phospholipid fatty acids, pattern, and abundance), microbial activity (basal respiration, dehydrogenase, protease, urease, β-glucosidase, and total amount of phosphomonoesterase activities), and physical (aggregate stability) and chemical (total organic C, total N, available P and water-solu…

Unravelling textural heterogeneity in obsidian:shear-induced outgassing in the Rocche Rosse flow

2016

Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2. km long, 100. m thick, ~. 800. year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: 'glassy' obsidian (<. 15% vesicles), 'pumiceous' lava (>. 40% vesicles), high aspect ratio, 'shear banded' lava (20-40% vesicles) and lo…