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91.
P. A. Volkov E. V. Todorova N. D. Bakhteeva A. G. Ivanova A. L. Vasil’ev 《Crystallography Reports》2011,56(3):463-469
An aluminum amorphous alloy doped with transition (Fe and Ni) and rare earth (La) metals has been used as an object of systematic
study of the structural transformations that are characteristic of different methods of sample preparation for transmission
electron microscopy (the mechanical tearing of ribbons, electrochemical thinning, and Ar+-ion etching under different conditions). The results of X-ray diffraction analysis and a calorimetric study of the structure
in comparison with electron microscopy data made it possible to determine the optimal method of sample preparation, which
ensures minimum distortions in the structure of metastable amorphous alloys with a low crystallization temperature. 相似文献
92.
V. Balek N. Todorova C. Trapalis V. Štengl E. Večerníková J. Šubrt Z. Malek G. Kordas 《Journal of Thermal Analysis and Calorimetry》2005,80(2):503-509
Summary Titania-based photocatalytic materials were prepared by sol-gel method using Fe3+ and polyethyleneglycol (PEG600) as additives. Thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA) with MS detection were used to elucidate processes that take place during heating of Fe3+ containing titania gels. The microstructure development of the Fe2O3/TiO2 gel samples with and without PEG600 admixtures was characterized by emanation thermal analysis (ETA) under in situ heating in air. A mathematical model was used for the evaluation of ETA results. Surface area and porosity measurements of the samples dried at 120°C and the samples preheated for 1 h to 300 and 500°C were compared. From the XRD measurements it was confirmed that the crystallization of anatase took place after thermal heating up to 600°C. 相似文献
93.
E. Ivanova O. Todorova M. Stoimenova 《Fresenius' Journal of Analytical Chemistry》1992,344(7-8):316-318
Summary The sorption of milligram amounts of gold, palladium and silver on a chelating sorbent of pyrazolone type is studied. A fourfold increase in sorbent capacity towards the precious metals is recorded at 65°C, compared to room temperature. The developed procedure permits to separate milligram amounts of gold, palladium or silver from both microgram or milligram amounts of non-precious metals.Part I: see [6] 相似文献
94.
Lundgren E Gustafson J Mikkelsen A Andersen JN Stierle A Dosch H Todorova M Rogal J Reuter K Scheffler M 《Physical review letters》2004,92(4):046101
The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K. 相似文献
95.
J.-L. Lu S. Kaya T.K. Todorova J. Sauer S. Shaikhutdinov H.-J. Freund 《Surface science》2006,600(13):L164
We have observed formation of one-dimensional silica structures of 0.5 nm in width on Mo(1 1 2) single crystal surface. Combination of high-resolution scanning tunneling microscopy, photoelectron and infrared spectroscopy, and density functional theory provides strong evidence for formation of paired rows of corner sharing [SiO4] tetrahedra chemisorbed on a metal substrate. 相似文献
96.
Z. Cherkezova-Zheleva D. Paneva S. Todorova H. Kolev M. Shopska I. Yordanova I. Mitov 《Hyperfine Interactions》2014,226(1-3):529-543
Iron and iron-platinum catalysts supported on activated carbon have been successfully synthesized by wet impregnation method and low-temperature treatment in inert atmosphere. The content of the supported phases corresponds to 10 wt % Fe and 0.5 wt % Pt. Four catalytic samples were synthesized: Sample A—activated carbon impregnated with Fe nitrate; Sample B—activated carbon impregnated with Pt salt; Sample C—activated carbon impregnated consequently with Fe and Pt salts; Sample D—activated carbon impregnated simultaneously with Fe and Pt salts. The as-prepared materials were characterized by Mössbauer spectroscopy, X-ray diffraction, infrared and X-ray photoelectron spectroscopy. The spectra show that the activated carbon support and the preparation procedure give rise to the synthesis of isolated metal Pt ions and ultradispersed Fe and Pt oxide species. Probably the presence of different functional groups of activated carbon gives rise to registered very high dispersion of loaded species on support. The catalytic tests were carried out in PROX reaction. A lower activity of bimetallic Pt-Fe samples was explained with the increase in surface oxygen species as a result of predomination of iron oxide on the support leading to the increase in selectivity to the H2 oxidation. Partial agglomeration of supported iron oxide phase was registered after catalytic tests. 相似文献
97.
Trendafilova A Todorova M Nikolova M Gavrilova A Vitkova A 《Natural product communications》2011,6(12):1851-1854
Antioxidant capacity of the methanolic extract of Alchemilla mollis was measured by its ability to scavenge the DPPH radical. The EtOAc fraction obtained after partition of the total extract was found to be the most active radical scavenger (IC50 9.8 +/- 1.8 microg/mL) and was subjected to fractionation by Sephadex LH-20 CC. Further purification by RP-18 CC led to the isolation of eight flavonoid glycosides: cis- and trans-tiliroside (1 and 2), rhodiolgin (3), hyperoside (4), isoquercitrin (5), miquelianin (6), sinocrassoside D2 (7), and gossypetin-3-O-beta-D-galactopyranosyl-7-O-alpha-L-rhamnopyranoside (8). It was found that 8 is a new compound and its antioxidant activity is also reported. Identification of the isolated compounds was carried out by spectroscopic and spectrometric analysis (1D and 2D NMR, UV and MS). 相似文献
98.
In order to obtain highly active catalytic materials for oxidation of carbon monoxide and volatile organic compounds (VOCs), monometallic platinum, copper, and palladium catalysts were prepared by using of two types of ZSM-5 zeolite as supports—parent ZSM-5 and the same one treated by HF and NH4F buffer solution. The catalyst samples, obtained by loading of platinum, palladium, and copper on ZSM-5 zeolite treated using HF and NH4F buffer solution, were more active in the reaction of CO and benzene oxidation compared with catalyst samples containing untreated zeolite. The presence of secondary mesoporosity played a positive role in increasing the catalytic activity due to improved reactant diffusion. The only exception was the copper catalysts in the reaction of CO oxidation, in which case the catalyst, based on untreated ZSM-5 zeolite, was more active. In this specific case, the key role is played by the oxidative state of copper species loaded on the ZSM-5 zeolites. 相似文献
99.
Ginka Todorova Ernesto Pérez Mónica M. Marugán Manya Kresteva 《Macromolecular Symposia》2004,212(1):497-502
The main-chain thermotropic liquid-crystalline poly(heptane-1,7-diyl biphenyl-4,4′-dicarboxylate) (P7MB) was investigated by time-resolved small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and differential scanning calorimerty (DSC). Nonisothermal crystallisation with different rates of cooling and heating was used. On cooling, two phase transitions are observed, isotropic melt - smectic (I-Sm) and Sm- three-dimensional crystalline structure (Sm-Cr), whereas on heating only one transition is observed, Cr-I transition. The transition enthalpies were calculated. Temperature dependences of d-spacings of all crystalline peaks and of the peak observed at high values of scattering vector in the SAXS region were derived. The temperature dependence of the degree of crystallinity was established, based on the integrated intensities of the crystalline peaks and amorphous halo in WAXS. 相似文献