THEORETICAL AND EXPERIMENTAL STUDY OF ICE IN THE PRESENCE OF A SPACE CHARGE

Une étude théorique et expérimentale de la glace par la méthode des électrodes bloquantes est proposée dans ce travail. L'analyse effectuée permet de comprendre les processus physiques provoquant une dispersion de charge d'espace (SC-dispersion) à basse fréquence et de déterminer la mobilité et la concentration des porteurs de charge dans la glace. La valeur de la mobilité de H3O+ a été obtenue à partir des résultats expérimentaux.Ice, with ideally-blocking electrodes, has been described theoretically and studied experimentally. The analysis performed makes it possible both to understand the physical processes causing the low-frequency space charge dispersion (SC-dispersion) and to develop a method for determining mobility and concentration of proton charge carriers in ice. The value of the H3O+ -defect mobility has been obtained from the experimental data

THEORETICAL AND EXPERIMENTAL STUDY OF PURE AND DOPED ICE Ih BY THE METHOD OF THERMALLY STIMULATED DEPOLARIZATION

Les théories concernant les courants de polarisation et de dépolarisation stimulé thermiquement ont été appliquées au cas de la glace étudiée à l'aide d'une cellule à électrodes ohmiques. Les résultats obtenus diffèrent de ceux obtenus de manière usuelle. De nouvelles données expérimentales pour la glace dopée avec HCl et NH4OH sont présentées.TSDC and TSPC theories have been proposed for ice with ohmic electrodes. The results obtained differ from those derived by a traditional approach. New experimental data for HCl and NH4OH doped ice are presented

Development of tungsten doped Ni-Zn nano-ferrites with fast response and recovery time for hydrogen gas sensing application

This paper reports on the study of series of tungsten doped Ni0.5Zn0.5WxFe2−xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites synthesized by a co-precipitation scheme. The crystallite size varies from 62 to 49 nm and the scanning electron microscope (SEM) images show the spinel cubic structure of the powder sample. Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF) confirms the presence of Ni, Zn, W and Fe elements in the prepared samples. The specific surface areas of the Ni0.5Zn0.5W0.2Fe1.8O4, Ni0.5Zn0.5W0.4Fe1.6O4 and Ni0.5Zn0.5W0.6Fe1.4O4 samples calculated from Brunauer-Emmett-Teller (BET) method are 18.9 m2/g, 21.5 m2/g and 24.6 m2/g, respectively. The metal oxide pellet type resistive sensor was made for gas sensor application. These sensors are selective for hydrogen (H2) gas. The performance of these sensors for sensing hydrogen gas at a concentration of 1000 ppm in the temperature range 80–300 °C has been investigated. Platinum electrodes were deposited on all the pellets by RF sputtering technique. The subsequent decomposition of platinum oxides on the metal oxide pellet surface results in an increase in surface roughness and electrical resistivity. The sensor shows a change in resistance from 1.21 × 105 Ω to 7.83 × 104 Ω in the presence of H2 gas even at alow temperature. The composition with x = 0.2 at an optimum temperature of 180 °C showed a fast response (14 s) and recovery time (20 s). High sensitivity, low cost, long term stability, high selectivity and fast response at low temperature makes this sensor useful for industrial applications. © 201

Manganese/Yttrium Codoped Strontium Nanohexaferrites: Evaluation of Magnetic Susceptibility and Mossbauer Spectra

Manganese (Mn)- and yttrium (Y)-substituted Sr-nanohexaferrites (MYSNHFs) of composition Sr1−xMnxFe12−xYxO19 (with 0.0 ≤ x ≤ 0.5) were prepared by citrate sol-gel autocombustion method. As-prepared MYSNHFs were characterized via diverse analytical techniques to determine the influence of Mn and Y cosubstitution on their microstructures and magnetic properties. 57Fe Mössbauer spectra of the MYSNHFs were used to evaluate the variation in the line width, isomer shift, quadrupole splitting, and hyperfine magnetic field values. It was shown that the dopant ions could preferentially occupy the 12k, 4f2, and 2b sites. Furthermore, the observed shift in the blocking temperatures of the studied MYSNHFs towards lower values with rising Mn2+ and Y3+ contents was attributed to the overall particles size reduction. Meanwhile, the AC susceptibility of the proposed MYSNHFs revealed that the magnetic interactions were weakened with the increase in dopant contents which was ascribed to the replacement of both Sr2+ and Fe3+ ions by the Mn2+ and Y3+ dopants

Development of tungsten doped Ni-Zn nano-ferrites with fast response and recovery time for hydrogen gas sensing application

International audienceThis paper reports on the study of series of tungsten doped Ni0.5Zn0.5WxFe2−xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrites synthesized by a co-precipitation scheme. The crystallite size varies from 62 to 49 nm and the scanning electron microscope (SEM) images show the spinel cubic structure of the powder sample. Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF) confirms the presence of Ni, Zn, W and Fe elements in the prepared samples. The specific surface areas of the Ni0.5Zn0.5W0.2Fe1.8O4, Ni0.5Zn0.5W0.4Fe1.6O4 and Ni0.5Zn0.5W0.6Fe1.4O4 samples calculated from Brunauer-Emmett-Teller (BET) method are 18.9 m2/g, 21.5 m2/g and 24.6 m2/g, respectively. The metal oxide pellet type resistive sensor was made for gas sensor application. These sensors are selective for hydrogen (H2) gas. The performance of these sensors for sensing hydrogen gas at a concentration of 1000 ppm in the temperature range 80–300 °C has been investigated. Platinum electrodes were deposited on all the pellets by RF sputtering technique. The subsequent decomposition of platinum oxides on the metal oxide pellet surface results in an increase in surface roughness and electrical resistivity. The sensor shows a change in resistance from 1.21 × 105 Ω to 7.83 × 104 Ω in the presence of H2 gas even at alow temperature. The composition with x = 0.2 at an optimum temperature of 180 °C showed a fast response (14 s) and recovery time (20 s). High sensitivity, low cost, long term stability, high selectivity and fast response at low temperature makes this sensor useful for industrial applications. © 201