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排序方式: 共有93条查询结果,搜索用时 15 毫秒
1.
The effects of lithium oxide dopants (0.5–0.8 at. % Li) on the electrophysical and sorption properties of ZnO were studied in the temperature range from 150 °C to 410 °C. The introduction of lithium increases the activation energy of the conductivity of ZnO, decreases its conductivity, and increases the amount of S02 sorbed. Two forms of chemisorbed SO2 (donor and acceptor) are observed on the surface.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1096–1100, May, 1996. 相似文献
2.
Different ratios of phosphomolybdic acid PMA supported on silica gel (1–30 wt%) and promoted with alkali metal hydroxide have been prepared by an impregnation method and calcinated at 350 °C for 4 h. The catalysts were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N2 adsorption measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of 2-propanol. The gas-phase esterification of acetic acid by ethanol was carried out in a conventional flow bed reactor. The results clearly revealed that among the PMA loading, the use of 10 wt% catalyst showed maximum yield of ethyl acetate. This catalyst also improved on addition of Na or K-hydroxide. These results were correlated with the structure and the acid–base properties of the prepared catalysts. 相似文献
3.
Uwe Emmerling Jurgen Lindau Siegmar Diele Johannes Werner Horst Kresse 《Liquid crystals》2013,40(8):1069-1073
A tin-containing liquid crystalline side group polymer was synthesized and characterized. Two glass transitions were detected by calorimetric investigations. The X-ray pattern corresponds to a smectic C order of the side groups and a disordered isotropic main chain. Dielectric measurements show two relaxation ranges which are influenced by the glass transitions and a fast local process. The low frequency mechanism can be related to the reorientation of the side groups and the higher glass transition temperature. The second is connected with the α-relaxation of the main chain and freezes in at lower temperatures. 相似文献
4.
Koki Ikemoto Shotaro Harada Seungmin Yang Taisuke Matsuno Hiroyuki Isobe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202114305
A 3-nm molecule comprising a cylindrical core and cross-shaped rims was designed and synthesized by developing a modular synthetic route. By using a cyclic precursor from previous studies as a starting material, multiple carbazole units were installed at the rims of the defective cylinder. The defective cylinder was synthetically doped with two types of nitrogen atoms, that is, pyridinic and pyrrolic nitrogen atoms, which resulted in solvatochromic shifts in fluorescence by charge-transfer interactions. The structure of the large, C552H496N24 molecule was fully disclosed by crystallographic analyses, and the unique helical arrangement of nitrogen-doped cylinders in the crystal was revealed. 相似文献
5.
In this article, an assessment of surface structural heterogeneity in porous metal organic framework (MOF) structure has been demonstrated by employing the methane and carbon-dioxide adsorption isotherms data. The virgin MIL-101-(Cr) MOF was synthesized by the hydrothermal method and defects were induced in the MOF structure by doping with various alkali (K, Na, Li) cations. The synthesized MOFs were characterized by XRD, SEM, EDX and BET measurement techniques. In order to understand the defect induced surface heterogeneity by alkali cation dopants, the surface energy distributions for CH4 and CO2 adsorptions on MOFs were measured by Dubinin – Astakhov model equation. The surface heterogeneity is mainly controlled by the limiting uptakes of adsorbates, the polarizability of adsorbates and the adsorbate-adsorbent interaction energy. 相似文献
6.
R. Anbarasan V. Sangeeth M. Saravanan R. Rajkumar M. Anandhaalaguraja V. Dhanalakshmi 《Journal of Macromolecular Science: Physics》2013,52(4):704-719
Effects of substituents and dopants on the structure–property relationships of poly(aniline) (PANI)-type homopolymers are analyzed. The gravimetric method was used for the estimation of rate of polymerization (Rp). FTIR spectroscopy was used for the calculation of relative intensities (RI) of benzenoid (RI[B/CH]), quinonoid (RI[Q/CH]), and their internal conversion (RI[B/Q]). Thermogravimetric analysis (TGA) characterized the thermal stability of PANIs. A standard four probe method was employed for the conductivity measurements. The results are analyzed and critically compared. 相似文献
7.
S. P. Meenakshisundaram S. Parthiban G. Madhurambal S.C. Mojumdar 《Journal of Thermal Analysis and Calorimetry》2008,94(1):21-25
The influence of a new organic additive, chelating agent 1,10-phenanthroline (Phen) (∼5.0·10−3 M L−1) on potassium hydrogen phthalate (KHP) single crystals at 30° is investigated. The crystals were grown from the aqueous solutions
of pH ∼4.5 at constant temperature by solvent evaporation technique. The chelating agent leads to an increase in metastable
zone width and assists the bulk growth process. The growth rate of crystals in the presence of Phen decreases considerably
with an increase in impurity concentration. Not much variation is observed in FTIR and cell parameter values, determined by
XRD analysis. It appears that the growth promoting effect (GPE) of Phen is caused by the adsorption of the organic additive
on the prism of KHP crystals. Differential scanning calorimetry (DSC) and TG-DTA studies reveal the purity of the sample and
no decomposition is observed up to the melting point. Scanning electron microscope (SEM) photographs exhibit the effectiveness
of the impurity in changing the surface morphology of KHP crystals. Contrary to expectations, Phen depresses the NLO efficiency
of KHP, suggesting that the molecular alignments in the presence of Phen results in cancellation effects disturbing the non-linearity. 相似文献
8.
The effect of heat treatment on the Fe2+/Fe3+ ratio in some alkali phosphate glasses containing antimony and iron oxides has been investigated. Differential thermal analysis, Mossbauer spectroscopy, magnetic susceptibility and density measurements as well as the molar volume calculations were used in this study. The obtained data indicate that all glasses show approximately unchangeable stability. It is found, from the area under the Mossbauer absorption spectra that ferrous transformed gradually to ferric ions and the transformation rate constant was found to be 48 min−1. The elapsed time was found to be 160 min. This transformation represents a first-order solid state reaction. The molar magnetic susceptibility measurements confirm the above results. 相似文献
9.
C.V. Thompson 《Interface Science》1998,6(1-2):85-93
Grain growth in thin films is usually abnormal, leading not only to an increase in the average grain size, but also to an evolution in the shape of the grain size distribution and to an evolution in the distribution of grain orientations. The latter can be driven by surface, interface or strain energy minimization, depending on film and substrate properties and on deposition conditions, and can lead to different final textures depending on which energy dominates.In semiconductor films, as in other materials, grain growth stagnation coupled with texture-selective driving forces leads to secondary grain growth, the rate of which is higher in thinner films. Self ion-bombardment enhances the rate of pre-stagnation grain growth, and doping of Si with electron donor leads to enhanced pre-stagnation grain growth as well as surface-energy-driven secondary grain growth. The effects of ion-bombardment and dopants on grain growth in Si can be understood in terms of associated increases in point defect concentrations and the effects of point defects on grain boundary mobilities. 相似文献
10.
R. Klett D. Fink M. Mü ller H. Omichi F. Hosoi V. Hnatowicz J. Vacik G. Sanchez 《Radiation measurements》1997,28(1-6):51-53
Usually ion tracks are studies ex-situ, i.e. after removal of the ion-irradiated sample from the evacuated irradiation vessel. The exposure to ambient air leads to degradation effects which are frequently neglected and consequently have been studied rarely. They have never been explained consistently. In this work we compile and discuss them in the frame of today's general understanding of ion tracks in polymers. It appears that some pristine polymers such as polyethylene are covered by a surface layer which is badly permeable for gaseous contaminants. Ion irradiation leads to destruction of this protective layer so that oxygen and moisture from the ambient air can easily penetrate through the ion tracks, and eventually even into the surrounding pristine material. Moisture absorption along the tracks gives rise to some faint conductivity. Oxygen uptake adds new trapping centers to the existing ones along the tracks, so that on one hand an increased dopant uptake capability is recorded, and on the other hand oxygen-sensitive mobile dopants are immobilized along the ion tracks. Photooxidation processes contribute to the fading of the optical blackening of irradiated polymers. 相似文献