Search results for "Metallurgy"
showing 10 items of 1419 documents
Computer Simulations of I-Center Annealing in KCl and KBr Crystals. Theoretical Interpretation of Thermostimulated Experiments
1995
Results of computer simulations of the kinetics of correlated annealing of pairs of close α–I and F–I centers in KCI and KBr crystals, enhanced by I-center diffusion and Coulomb or elastic attractions, respectively, are presented. Special attention is paid to the conditions under which multi-stage annealing stages arise as it has been observed experimentally more than once. Our general conclusions are: (i) a weak elastic interaction affects the recombination kinetics and the survival probability even for relatively well-separated F–I pairs, the more so is true for the case of Coulomb attraction between charged α–I pairs; (ii) the multi-step (kink) structure arises only for close (typically,…
PHOTOINDUCED HARDENING AND REDUCTION OF DISLOCATION MOBILITY IN C60SINGLE CRYSTALS: THE WAVELENGTH DEPENDENCE
2002
An increase of the microhardness and decrease of the dislocation mobility in C60 single crystals after light-irradiation in the wavelength range of 150–900nm in air has been observed giving evidence for photo-induced change in bonding. Efficiency of C60 phototransformation was found to increase with decreasing the wavelength.
Electrochemical Characterization of Coinage Techniques the 17(th) Century: The maravedis Case
2017
[EN] The voltammetry of immobilized particles (VIMP) methodology was applied to the discrimination of Spanish maravedis produced in 10 different mints between 1661 and 1664 using characteristic signatures for the reduction of cuprite and tenorite in the patina of the coins and catalytic effects on the hydrogen evolution reaction (HER). The variation of the apparent tenorite/cuprite ratio with depth was fitted to potential laws differing from one mint to another for A Coruna, Burgos, Cordoba, Cuenca, Granada, Madrid, Trujillo, Segovia, Sevilla and Valladolid coins. Electrochemical data permitted to detect the changes in the composition (with lowering of the silver content) and manufacturing …
Microchemical surface analysis of historic copper-based coins by the combined use of FIB-FESEM-EDX, OM, FTIR spectroscopy and solid-state electrochem…
2019
[EN] A multi-technique strategy, including microscopy, spectroscopic and electrochemical techniques, is proposed to study thin corrosion layers that form on the surface of historic copper-based coins. An accurate characterisation of this external corrosion layer is important for selecting a suitable conservation and/or restoration treatment. For this purpose, a series of copper-based coins from different historical periods and provenances, which mainly exhibited atmospheric corrosion, was analysed. The morphology of the corrosion layer and the upper core of coins was studied in trenches done on coin surfaces with a focused ion beam gun, coupled to a field emission scanning electron microsco…
Raman spectroscopy characterization of 10-cash productions from the late Chinese emperors to the Republic
2017
[EN] The use of Raman spectroscopy for discriminating monetary emissions, a recurrent problem in much archaeological studies, is described. The method involves the record of Raman signatures of tenorite and crystalline and defective cuprite in the patina based on the idea that subtle, mint-characteristic variations in the composition and metallography of the base metal during the manufacturing process are reflected in the variation in depth of the composition and crystallinity of the corrosion patina. The technique was applied to a series of 10-cash copper coins produced around the transition between the Kuang Hsu and Hsuan Tung last Chinese emperors and the first Republic whose averaged co…
Archaeometric analysis of Roman bronze coins from the Magna Mater temple using solid-state voltammetry and electrochemical impedance spectroscopy
2017
Voltammetry of microparticles (VMP) and electrochemical impedance spectroscopy (EIS) techniques, complemented by SEM-EDX and Raman spectroscopy, were applied to a set of 15 Roman bronze coins and one Tessera from the temple of Magna Mater (Rome, Italy). The archaeological site, dated back between the second half and the end of the 4th century A.D., presented a complicated stratigraphic context. Characteristic voltammetric patterns for cuprite and tenorite for sub-microsamples of the corrosion layers of the coins deposited onto graphite electrodes in contact with 0.10 M HClO4 aqueous solution yielded a grouping of the coins into three main groups. This grouping was confirmed and refined usin…
Grain-size-induced relaxor properties in nanocrystalline perovskite films
2004
Thin films of ${\mathrm{Pb}}_{0.76}{\mathrm{Ca}}_{0.24}{\mathrm{TiO}}_{3}$ (PTC), which is a classical ferroelectric as a bulk material and of the relaxor material $\mathrm{Pb}({\mathrm{Sc}}_{0.5}{\mathrm{Nb}}_{0.5}){\mathrm{O}}_{3}$, have been produced to find out whether nanocrystalline ferroelectric films show a grain-size-induced relaxor behavior. Amorphous films were deposited onto a $\mathrm{Ti}∕\mathrm{Pt}$ coated silicon (100) wafer by reactive $\text{rf}$ sputtering. Different grain sizes were prepared by a controlled annealing process and they were determined by profile analysis of x-ray diffraction spectra. Temperature dependent Raman spectroscopy was used to look for phase trans…
Variational methods for the steady state response of elastic–plastic solids subjected to cyclic loads
2003
Abstract Solids (or structures) of elastic–plastic internal variable material models and subjected to cyclic loads are considered. A minimum net resistant power theorem, direct consequence of the classical maximum intrinsic dissipation theorem of plasticity theory, is envisioned which describes the material behavior by determining the plastic flow mechanism (if any) corresponding to a given stress/hardening state. A maximum principle is provided which characterizes the optimal initial stress/hardening state of a cyclically loaded structure as the one such that the plastic strain and kinematic internal variable increments produced over a cycle are kinematically admissible. A steady cycle min…
Fuel inventory and material migration of JET main chamber plasma facing components compared over three operational periods
2020
Fuel retention and material migration results from JET ITER-like wall beryllium limiter tiles are presented for three operating periods. Ion beam analysis results support the general picture of erosion during limiter configurations with local deposition on tile ends far into the scrape off layer. Similar trends of fuel concentrations are observed in all JET operating periods; (i) low on surfaces exposed to high heat flux and erosion and (ii) higher in deposits. The pattern of fuel retention and deposition correlates with heat flux and distribution of limiter plasmas touching inner and outer limiters. The D/Be ratio in the thickest deposit is similar to 0.01. Global fuel retention attributed…
Load-deflection characteristics of superelastic and thermal nickel-titanium wires
2011
SUMMARY The aim of this study was to investigate the mechanical properties of superelastic and thermal nickel–titanium (NiTi) archwires for correct selection of orthodontic wires. Seven different NiTi wires of two different sizes (0.014 and 0.016 inches), commonly used during the alignment phase, were tested. A three-point bending test was carried out to evaluate the load–deflection characteristics. The archwires were subjected to bending at a constant temperature of 37°C and deflections of 2 and 4 mm. Analysis of variance showed that thermal NiTi wires exerted significantly lower working forces than superelastic wires of the same size in all experimental tests (P < 0.05). Wire size had a s…