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Rare earth cuprates as electrocatalysts for methanol oxidation   总被引:9,自引:0,他引:9  
A series of rare earth cuprates with overall composition Ln2−xMxCu1−yMy′O4−δ (where Ln=La and Nd; M=Sr, Ca and Ba; M′=Ru and Sb: 0.0≤x≤0.4 and y=0.1) have been tested as anode electrocatalysts for methanol oxidation. The evaluation of electrode kinetic parameters was made galvanostatically. The catalyst characterization was carried out by specific conductivity measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Iodometry. These materials exhibit significant activity for methanol oxidation at higher potentials. The linear correlation between Cu(3+) content and methanol oxidation activity suggests that the active sites for adsorption of methanol is Cu(3+). The methanol oxidation onset potential depends on the ease of Cu(2+)→Cu(3+) oxidation reaction. These materials show better tolerance towards the poisoning by the intermediates of methanol oxidation compared to that of conventional noble metal electrocatalysts (supported and bulk). The lattice oxygen in these oxides could be considered as active oxygen to remove CO intermediates of methanol oxidation reaction.  相似文献
2.
Features of the effect of ion bombardment and its influence on the composition of solid surfaces are considered. During ion bombardment, not only does cleaning (sputtering) of the surface take place, but the formation of carbides through the implantation of carbon from contamination also occurs. Such species were recognized clearly from their chemical shifts of XPS on intermetallic compounds, namely LaNi5, CaNi5, TiFe, MgaNi and Mg2Cu and on the hydride Mg2NiH4. These surface carbides, for example, can seriously restrict data analysis owing to their contribution to the core level alterations, and the rate of sputtering owing to their extreme hardness. However, ion bombardment would serve as an unusual method of preparation of some compounds which cannot be obtained by conventional means. Types of problems, methods and results of their investigation are described.  相似文献
3.
Polyethylene oxide (PEO) has been introduced into HNbWO6·1.5H2O using melt-intercalation technique and its effect on the structure and properties of the host material studied using powder X-ray diffraction, FT-IR, impedance spectroscopy and TGA/DTA measurements. The intercalation reaction leads to loss of stacking coherence along the c-axis of the host layered material, as evidenced by the XRD data. FT-IR spectra of the nanocomposite show changes, indicative of complexing of the guest polymer with the host layered structure. TGA/DTA isothermal profiles exhibit marked changes upon prolonged periods of intercalation. The conductivity of the nanocomposite is found to be about 2×10−6 S/cm.  相似文献
4.
181Ta time differential perturbed angular correlation (TDPAC) and positron lifetime measurements were carried out on homogeneously α-implanted CuHf samples. TDPAC measurements indicate the trapping of vacancy clusters and helium associated defect complexes by Hf atoms. The presence of helium-vacancy complexes and helium stabilised voids has been identified by positron lifetime measurements. Further the nucleation and growth stages of helium bubbles have been identified. TDPAC and positron lifetime measurements indicate that Hf atoms act as heterogeneous nucleating centers for helium bubbles. Hf atoms are found to suppress the bubble growth in CuHf as indicated by the results of positron lifetime measurements.  相似文献
5.
Positron lifetime has been measured as a function of temperature in Sidoped GaAs single crystals subjected to various heat treatments. Defects produced by these heat treatments trap positrons. In all the GaAs samples containing defects positron lifetime was found to decrease with temperature in the range from 375 K to 16 K. The decrease is explained as due to the decrease in the trapping rate. The trapping rate is mainly controlled by the diffusion of the positron to the trap. The diffusion constant is determined mainly by the scattering from charged Si impurities.  相似文献
6.
Hydrostatic pressure has negligible effect on the resistivity anomaly and thec H /a H ratio of Ti2O3. The results are consistent with the band-crossing mechanism wherein the a T and e T bands cross as thec H /a H ratio increases.  相似文献
7.
The influence of helium, introduced by the 10B(n, α)7Li reaction, on the evolution of defect structure in copper containing a few hundred ppm boron has been studied by detailed positron lifetime and two-photon angular correlation measurements, supplemented by TEM studies. In the as-irradiated state of Cu-B, two lifetime components have been resolved. The shorter lifetime, τ1, = 167 ps of 97% intensity, has been understood as due to positron trapping at small helium-vacancy complexes, while the longer lifetime τ2 = 450 ps of 3% intensity is explained as due to helium-free voids. Marked changes in the annihilation characteristics observed at 670 K are interpreted in terms of the nucleation of microbubbles, controlled by thermally activated helium migration to vacancy traps. Corroborative evidence for the onset of helium clustering is obtained from the change in the average size of positron traps as deduced from the smearing of the measured angular correlation spectra. Helium bubbles and helium-free voids coexisting in the system have been distinguished by a three-component analysis of the lifetime spectra. Bubbles are found to be stable beyond the temperature of dissociation of voids. The size and concentration of bubbles, determined independently by TEM measurements, are in accordance with the positron annihilation results in the growth stage. The observed positron lifetime at higher annealing temperatures has been analysed by relating the annihilation rate to helium atom density and helium pressures in bubbles evaluated. These pressures are in satisfactory agreement with the estimates of equilibrium pressures, leading to the conclusion that bubble relaxation occurs by the mechanism of thermal vacancy condensation.  相似文献
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