Materials and Applications for Sensors and Transducers III

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Authors: Pavel Alekseev, Eugene Grishanin, Alexander Shimkevich
Abstract: A precise monitoring of reductionoxidation (RedOx) potential is necessary for using molten salts as fuel compositions and coolants in molten-salt reactors as well as for pyrochemical processing of a spent fuel. So, low over-potentials (~10 mV) are required for rigorously selective extraction of impurities out of the molten salt due to a permanent diffusive cathode polarization in galvanic cell. At the same time, a weak identification of cationic disproportionation (Mk+ Ml+) of metal impurities in liquid salts reflects the common defect of all known internal monitoring tools using salt as a sensor: realizing high over-potential and thereby strong polarization of the cathode. It leads to appreciable energy deformation of allowed electron states in the molten salt near the electrodes so that metal components of the basic salt are extracted out of the salt solution together with the selected impurity. Obviously, such the kinetic monitoring of RedOx potential cannot be a precise method since there is impossible eliminating the uncertain polarizing cathode effects in the galvanic cell with the molten salt as an electrolyte. Therefore a monitoring of the RedOx potential of liquid salts by means of an external potentiometer is necessary. This method is based upon the using of a gauge with Na+βAl2O3 electrolyte as a solid membrane with unipolar sodium conductivity assigned for monitoring a thermodynamic activity, , of neutral sodium atoms (Na0) in the molten salt. The principle of operation of such the gauge is based on the e.m.f. method. A measuring electrode, Pb [N (a thin layer of liquid lead on the solid electrolyte), directly contacts with the molten salt, easily exchanges by dissolved sodium atoms, and corrosive protects the solid electrolyte. The e.m.f., E, of this electrode is defined relatively a reference electrode (liquid sodium) located on the other side of solid electrolyte, Na+βAl2O3, in the four-layer galvanic cell: NaNa+βAl2O3Pb [Nsalt [], by equation, E = (RT/F) ln, where R is the universal gas constant, T is Kelvin temperature, F is Faraday constant.
Authors: M. El-Hofy, M. Dawoud, M. Elkhatib, A. Abdel Aziz
Abstract: Clay consists of about 50% SiO2 + 25% Al2O3 plus some other oxides with low abundance ratio like CaO, TiO2, Fe2O3, MgO and Mn2O3. Burning the clay at 700°C removes out the organic compounds and the mentioned oxides only remain. Our aim is to dope ZnO by the remaining oxides for varistors fabrication. Six types of clay were collected from Egyptian Red Sea Coast mines, after burning for 2 hrs the remaining oxides were mixed and ball milled with ZnO for 10 hrs according to the formula (100-Xn) ZnO +Xn, where n is the clay type and X is the ratio of the clay in grams, X takes the values 0.525 in 15 steps. Samples were pressed and sintered at three different temperatures (Tsin) 1200°C, 1300°C and 1400°C for 1 hr, and then studied via XRD, SEM, EDAX, J-E and C-V measurements. The obtained results were discussed in terms of the microstructure of the samples and the formation of Schottky barriers. Barrier height Ф, width W, interface state density Ns and donor state density Nd were calculated for the samples with highest nonlinearity α. It was found that the breakdown electric field Eo is related exponentially with the ratio of Zinc silicate phase whereas α scales with ratio of ZnO phase and the later increases linearly with Tsin. The electrical characteristics of the most promising sample were compared with those of ZnO samples doped pure SiO2 and Al2O3 obtained at the same preparation condition. This sample is comparable with the Japanese commercial varistor 5N220k Dc JVR.
Authors: Ming Wei Wu, Yan Chi Chen, Chung Ya Tsao, Chien Chi Lin
Abstract: Transparent conductive oxide (TCO) films have been widely used in various optoelectronic devices as the transparent conductive electrode. Niobium-doped titania (TNO) films were recently found to be highly transparent and conductive and thus could be a potential substitute for tin-doped indium oxide (ITO) films. For the preparation of TCO films, magnetron sputtering is a versatile method due to its high deposition rate, feasibility for large-area deposition, and other advantages. The quality of the sputtering target has been found to obviously affect the performances of the films. However, the fabrication and the properties of sputtering targets have rarely been examined. Thus, the purpose of this study was to prepare and characterize TNO ceramic for application as a TNO sputtering target. Sub-micrometer TiO2 and Nb2O5 powders were used to formulate the ceramic slurry with a dispersant and a binder. The ceramic slurry was then spray-dried to form spray-dried granules. TNO green compact was produced by uniaxial compacting of the spray-dried granules. After 1200°C sintering in air, the sintered density of the TNO ceramic was 100%. The grain size was only 2.8μm. Moreover, after 1200°C sintering, the TNO ceramic was fully rutile phase, as verified by XRD. Nb2O5 diffused and dissolved into the titania. Furthermore, the dopant of Nb greatly decreased the resistivity of titania from 108Ωcm to 90Ωcm, though the resistivities of the TNO ceramics were higher than those of TNO films reported in the literature.
Authors: Abdelaziz Abbas, Ahcene Bouabdallah
Abstract: The aim of paper is to develop analytical mathematical models that describe the thermo dynamical equilibrium of resistive chemical sensor arrays /mixture of vapors multi-system. By using the Gibbs Duhem formalism, state equations in differential form, that the variations of intensive quantities (e.g. sensors partial sensitivity) as function of the gas mixture components concentrations and sensor array parameters describe, have been developed. Moreover, the responses of the sensor arrays as function of gas mixture components concentrations were modeled.
Authors: Hae Jo Kim
Abstract: Two novel fluorescent chemodosimeters will be presented for the selective detection of cysteine over homocysteine and glutathione in aqueous solvent. First, a rhodamine-based fluorescent probe (1) will be reported. Masked with a para-hydroxybenzyl alcohol (HBA) unit, probe 1 initially showed a weak fluorescence but displayed a strong fluorescence through a series of reactions of Michael addition and intramolecular cyclization of cysteine, followed by deprotection of HBA. The caged probe (1) exhibited a selective and sensitive response toward cysteine over homocysteine and glutathione in HEPES buffer. Secondly, a fluorescein-based fluorescent probe will be discussed. A bromoacetyl functionalized fluorescein chemodosimeter (2) was utilized as a fluorescent probe for cysteine. The probe showed a selective and sensitive response to cysteine over homocysteine and glutathione in aqueous buffer through a rapid cyclization reaction. When cysteine was added, a fast fluorescence turn-on change of 2 was observed and applied to the in-vivo imaging of cysteine.
Authors: Girolamo Costanza, Stefano Paoloni, Maria Elisa Tata
Abstract: The shape recovery efficiency of Ni-Ti shape memory springs has been investigated upon the application up to 6 X 105 thermo-activation cycles. The hysteretic behaviour of the Martensitic-Austenitic phase transition has been characterized by resistivity measurements and infrared thermography. A loss in the recovery efficiency of the original shape has been observed and has been ascribed to functional fatigue leading to the formation of the R phase upon sample heating. Nevertheless, one way shape memory effect was found to exhibit an asymptotic stable behaviour which makes possible the realization of Ni-Ti actuators able to operate for a relative large number of activation cycles.
Authors: Girolamo Costanza, Roberto Montanari, Stefano Paoloni, Maria Elisa Tata
Abstract: AISI 316 steel samples have been investigated by infrared thermography (IRT) after introducing controlled degrees of plastic deformation by means of tensile tests. Microstructural examinations of the same samples showed that the progressive decrease of thermal diffusivity observed for successive steps of plastic deformation is due to the increase of dislocation density. Dislocations affect thermal diffusivity in two ways, by acting as centres of scattering and by inducing elastic stress fields. To evaluate the two contributions, IRT measurements have been also carried out in-situ, during tensile tests at progressively increasing strain. For relevant plastic deformation, the dislocations mainly affect the thermal diffusivity by scattering mechanism. On the basis of these results, it can be concluded that thermal diffusivity is significantly affected by the increase of dislocations density therefore locally resolved IRT measurements seem promising to detect states of local plasticization in mechanical components.
Authors: Girolamo Costanza, R. Donnini, Saulius Kaciulis, Giorgio Maddaluno, Roberto Montanari
Abstract: W is a promising material to use as protection for thermal shields in future nuclear fusion reactors, however the joining to other metals is really challenging. For realizing such joints plasma spraying (PS) has been used for its simplicity, the possibility to cover complex and extended surfaces and the relatively low cost. An appropriate interlayer must be optimized to increase the adhesion of W on the substrates and to provide a soft interface for better thermo-mechanical compatibility.The present work demonstrates that high-temperature X-ray diffraction (HT-XRD) permits to quickly assess the reliability and quality of the coating-interlayer-substrate system by measuring the strain of coating. This is very useful to orientate the work for optimizing the structure and composition of the interlayer and the parameters of deposition process.
Authors: Eirini Varouti
Abstract: The aim of the present work was the preparation and characterization of FeSiB amorphous magnetic ribbons with the following chemical composition: Fe80SixB20-x, x=5,6,8 and Fe75Si15B10. Differential Scanning Calorimetry was employed in order to study the thermal stability and structural changes during the transformations that took place. Much emphasis is placed on the analysis of the crystallization kinetics.

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