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1.
The Ag diffusion in superconducting YBa2Cu3O7 (YBaCuO) ceramic has been studied over the duration of the diffusion range 5-24 h in the temperature range 700-850 °C by the energy-dispersive X-ray fluorescence (EDXRF) technique. For the excitation of silver atoms, an annular Am-241 radioisotope source (50 mCi) emitting 59.543 keV photons was used. The temperature dependences of silver diffusion coefficients in grains (D1) and over the grain boundaries in the range 700-850 °C (D2) are described by the relations D1=1.4×10−2 exp[−(1.18±0.10)/kT] and D2=3.1×10−4 exp[−(0.87±0.10)/kT].  相似文献   

2.
The adsorption of chloridazon (5-amino-4-chloro-2-phenylpyridazin-3(2H)-one) on natural and ammonium kerolite samples from aqueous solution at 10, 25 and 40 °C has been studied by using batch experiments. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacities (Xm) of the samples; two straight lines were obtained, which indicates that the adsorption process takes place in two different stages. Values for Xm1 (first stage) ranged from 1.1 × 10−2 mol kg−1 for natural kerolite at 40 °C up to 5.1 × 10−2 mol kg−1 for ammonium kerolite at 10 °C and the values for Xm2 (second stage) ranged from 9.1 × 10−2 mol kg−1 for natural kerolite at 40 °C up to 14 × 10−2 mol kg−1 for natural kerolite at 10 °C. The adsorption experiments showed on the one hand, that the ammonium kerolite is more effective than natural kerolite to adsorb chloridazon in the range of temperature studied and on the other hand, that the lower temperature, the more effective the adsorption of chloridazon on the adsorbents studied.  相似文献   

3.
Nucleation, as an important stage of freezing process, can be induced by the irradiation of power ultrasound. In this study, the effect of irradiation temperature (−2 °C, −3 °C, −4 °C and −5 °C), irradiation duration (0 s, 1 s, 3 s, 5 s, 10 s or 15 s) and ultrasound intensity (0.07 W cm−2, 0.14 W cm−2, 0.25 W cm−2, 0.35 W cm−2 and 0.42 W cm−2) on the dynamic nucleation of ice in agar gel samples was studied. The samples were frozen in an ethylene glycol-water mixture (−20 °C) in an ultrasonic bath system after putting them into tubing vials. Results indicated that ultrasound irradiation is able to initiate nucleation at different supercooled temperatures (from −5 °C to −2 °C) in agar gel if optimum intensity and duration of ultrasound were chosen. Evaluation of the effect of 0.25 W cm−2 ultrasound intensity and different durations of ultrasound application on agar gels showed that 1 s was not long enough to induce nucleation, 3 s induced the nucleation repeatedly but longer irradiation durations resulted in the generation of heat and therefore nucleation was postponed. Investigation of the effect of ultrasound intensity revealed that higher intensities of ultrasound were effective when a shorter period of irradiation was used, while lower intensities only resulted in nucleation when a longer irradiation time was applied. In addition to this, higher intensities were not effective at longer irradiation times due to the heat generated in the samples by the heating effect of ultrasound. In conclusion, the use of ultrasound as a means to control the crystallization process offers promising application in freezing of solid foods, however, optimum conditions should be selected.  相似文献   

4.
Sintered NdFeB-based scrap magnets were recovered and processed using the HD and HDDR routes. The effects of varying the HDDR processing temperature were investigated (over the range 835-930 °C). The disproportion was carried out with a pressure ramp to a maximum of 1000 mbar hydrogen pressure with a 1 h hold time at each step and the optimum recombination conditions were set at 100 mbar with a 20 min hold time. Anisotropic NdFeB powder was produced in all cases with the best magnetic properties achieved at a processing temperature of 880 °C, producing powder with a remanence of 1.10(±0.02) T and an intrinsic coercivity of 800 (±16) kA m−1 and giving a (BH)max of 129(±2.5) kJ m−3.  相似文献   

5.
Ag-N doped ZnO film was synthesized by ion beam assisted deposition and its electrical properties and annealing property were investigated. The films remained p-type even after annealing at 400 °C in air for 10 min. While the annealing temperature went up to 500 °C, the conduction type of these films shifted from p-type to n-type. The p-type ZnO film revealed low resistivity (0.0016 Ω cm), low Hall mobility (0.65 cm2 V−1 s−1) and high carrier concentration (5.8 × 1020 cm−3). ZnO p-n homojunction consisting of a p-type layer (Ag-N doped ZnO film) and an n-type layer (In-doped ZnO film) had been fabricated by ion beam assisted deposition. With electrical measurement, its current-voltage curve had a typical rectifying characteristic with current rectification ratio of 25 at bias ±5 V and a reverse current of 0.01 mA at −5 V. The depletion width was estimated 3.8 nm by using p-n junction equation.  相似文献   

6.
Silver nanorods with average diameters of 120-230 nm and aspect ratio of 1.7-5.0 were deposited on the surface of TiO2 films by photoelectrochemical reduction of Ag+ to Ag under UV light. The composite films prepared on soda-lime glass substrates were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the TiO2 film after UV irradiation in AgNO3 solution is composed of anatase phase TiO2 and metallic silver with face centered cubic structure. Other compounds cannot be found in the final films. The maximum deposition content of silver particles on the surface of TiO2 film was obtained with the AgNO3 concentration of 0.1 M. The kinetic growth rates of silver particles can be controlled by photocatalytic activity of TiO2 films. The studies suggest that the growth rates of silver particles increase with the enhancement of photocatalytic activity of TiO2 films. The maximum growth rate of silver particles loaded on TiO2 films can be up to 0.353 nm min−1 among samples 1#, 2# and 3#, while the corresponding apparent rate constant of TiO2 is 1.751 × 10−3 min−1.  相似文献   

7.
d-limonene in water nanoemulsion was prepared by ultrasonic emulsification using mixed surfactants of sorbitane trioleate and polyoxyethylene (20) oleyl ether. Investigation using response surface methodology revealed that 10% d-limonene nanoemulsions formed at S0 ratio (d-limonene concentration to mixed surfactant concentration) 0.6-0.7 and applied power 18 W for 120 s had droplet size below 100 nm. The zeta potential of the nanoemulsion was approximately −20 mV at original pH 6.4, closed to zero around pH 4.0, and around −30 mV at pH 12.0. The main destabilization mechanism of the systems is Ostwald ripening. The ripening rate at 25 °C (0.39 m3 s−1 × 1029) was lower than that at 4 °C (1.44 m3 s−1 × 1029), which was in agreement with the Lifshitz-Slezov-Wagner (LSW) theory. Despite of Ostwald ripening, the droplet size of d-limonene nanoemulsion remained stable after 8 weeks of storage.  相似文献   

8.
Using ascorbic acid as the reducing agent, AgNO3 as the source of Ag, the ultrafine silver powder was prepared by liquid-phase reduction method. The optimal conditions to prepare the ultrafine silver powder were obtained by studying the effects of following factors, such as the selection of dispersant, the doses of dispersant and pH, on the dispersibility of silver powder under other constant conditions. The pure ultrafine silver powder with quasi-spherical shape and mean size of 1.15 μm was synthesized under the optimal conditions of polyvinyl alcohol (PVA) as disperser, PVA/AgNO3 mass ratio of 4:100 and pH 7 while maintaining other conditions exactly in the same circumstances, such as AgNO3 concentration of 0.20 mol L−1, ascorbic acid concentration of 0.15 mol L−1 and reaction temperature of 40 °C. The ultrafine silver powder was characterized by SEM and XRD. And a PVA dispersive mechanism for preparing highly dispersive ultrafine silver powder, proved by the ultraviolet spectra, is that PVA absorbed on the surface of silver particles by coordination bond preventing the silver particles from diffusion and aggregation. In addition, the steric effect may help to reduce aggregation.  相似文献   

9.
In this work, 650 nm polycrystalline SnS thin films were grown by thermal evaporation of high purity tin sulfide powder at 250 °C substrate temperature, followed by post deposition annealing at 200 °C and 300 °C for 2, 4 and 6 h, and at 400 °C for 2 and 4 h in argon ambient. The XRD pattern of the as-deposited and annealed SnS films led to the conclusion that the as-deposited films were polycrystalline in nature with preferentially oriented along (1 1 1) direction. The direct bandgap of all the films was found to be observed between 1.33 and 1.53 eV. Except for annealing at 400 °C all the films were nearly stoichiometric in nature, suggesting lower rate of desulfurization at that ambient. However, higher annealing temperature has resulted in the segregation of tin phase. All the films showed good absorption in the visible range. The as-deposited and annealed films showed p-type conductivity. Hall measurement revealed the carrier concentration and mobility ranging from 1015 to 1016 cm−3 and 0.8 to 31.6 cm2 V−1 s−1 respectively. The photoconductivity measurements of all the SnS films were carried out by recording the lowering of resistance of the respective films with time under illumination.  相似文献   

10.
Long period gratings (LPGs) were written into a D-shaped optical fibre that has an elliptical core with a W-shaped refractive index profile and the first detailed investigation of such LPGs is presented. The LPGs’ attenuation bands were found to be sensitive to the polarisation of the interrogating light with a spectral separation of about 15 nm between the two orthogonal polarisation states. A finite element method was successfully used to model many of the behavioural features of the LPGs. In addition, two spectrally overlapping attenuation bands corresponding to orthogonal polarisation states were observed; modelling successfully reproduced this spectral feature. The spectral sensitivity of both orthogonal states was experimentally measured with respect to temperature and bending. These LPG devices produced blue and red wavelength shifts depending upon the orientation of the bend with measured maximum sensitivities of −3.56 and +6.51 nm m, suggesting that this type of fibre LPG may be useful as a shape/bend orientation sensor with reduced errors associated with polarisation dependence. The use of neighbouring bands to discriminate between temperature and bending was also demonstrated, leading to an overall curvature error of ±0.14 m−1 and an overall temperature error of ±0.3 °C with a maximum polarisation dependence error of ±8 × 10−2 m−1 for curvature and ±5 × 10−2 °C for temperature.  相似文献   

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