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排序方式: 共有49条查询结果,搜索用时 15 毫秒
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2.
D. Andreeva T. Tabakova I. Mitov A. Andreev 《Journal of Materials Science: Materials in Electronics》1991,2(4):199-203
The influence of the main reaction parameters (temperature, pH and concentration) in the oxidative hydrolysis of iron (II) sulphate in an acid medium on the properties of the obtained -Fe2O3 and its applicability in ferrite production has been studied. The addition of manganese(II) ions catalyses the process in the homogeneous phase, probably by activation of oxygen. The obtained results are discussed within the framework of the assumed reaction mechanism, which includes an homogeneous reaction and a heterogeneous one with the participation of the oxidative hydrolysis product -FeOOH. 相似文献
3.
Mario Mitov Rashko Rashkov Nikolay Atanassov Andreas Zielonka 《Journal of Materials Science》2007,42(10):3367-3372
In the present work, the catalytic activity of electrodeposited Co–Mn–B nanocomposites towards controllable hydrolysis of
sodium borohydride was studied. Deposition was performed on two types of Ni-foam (RECEMAT Int.) with different pore size,
specific surface area and thickness. Higher deposit loading, as well as bigger real surface area, was obtained with foam samples
possessing bigger pore size. The catalyst deposited on bigger pore foam promoted hydrogen generation with higher rates than
the other one when contacted with a base-stabilized NaBH4 solution. The same activation energy value, however, was determined for both supported catalysts. On the base of the obtained
results, it may be concluded that the geometric factor plays predominant role for the catalytic activity of studied catalysts. 相似文献
4.
The performance of electrodes, prepared from amorphous CoxByHz nanoparticles without additives, in 20% KOH solution was tested by means of cyclic voltammetry and chronopotentiometry. Peaks, assigned to hydrogen adsorption and desorption, are observed in the cyclic voltammograms. After charging, hydrogen atoms occupy different types of sites in the substrate, from which electrochemical desorption occurs. An increase in hydrogen content as a result of repeated cycling was established. Discharge capacity of the electrodes, estimated from the chronopotentiometric discharge curves obtained, is about 250mAhg–1. The observed changes in hydrogen and boron content, due to electrochemical treatment, indicate that the electrode material is an active participant in the whole electrochemical process. Hypotheses for the reaction mechanism are proposed. 相似文献
5.
Synthesis and characterization of yttrium-aluminum-iron and yttrium-cerium-iron citric complexes 总被引:1,自引:0,他引:1
Fe-, Y-Fe-Al- and Y-Ce-Fe- citrates were synthesized in ethylene glycol (EG) medium under conditions similar to those used in the polymerized complex method. Their elemental composition, IR,^ 13C and ^1H NMR, X-ray photoelectron and Mossbauer spectra were studied, and formulae describing their composition were proposed. The complexes contained EG bonded as adduct and ester with citric acid ligand and did not contain ligands with deprotonated alcoholic groups. The complexes consisted of agglomerated spheres, 0.7-3 μm in diameter. The local composition of the products was established by energy dispersive X-ray microanalysis. The comparison of the number of the ligands, their average electrical charge and the esterification degree of mono-, di- and trimetallic complexes proved the mixed-metal nature of the species studied. The thermal decomposition of the complexes was studied and a general scheme of the processes taking place was proposed. Highly crystalline, phase homogeneous YaFe4AlO12 was produced after heating the respective complex at 1000 ℃. Ce-doped yttrium-iron garnet, similarly prepared, contained traces of CeO2. 相似文献
6.
Metal complexes were prepared on the basis of polymer ligands with carboxylic and nitrogen-containing functionalities by complexation
with iron ions in aqueous solutions of FeCl3·6H2O and FeSO4·2H2O. The degree of introduction of iron ions into the polymer matrices depended on the relative content of the functional groups
in the polymers studied such as polyacrylic acid, poly-4-vinylpyridine, and poly(2-N,N-dimethylaminoethyl) methacrylate. The metal content in the polymer complexes was found to vary between 9.0 and 30.0 (for
acrylic acid-based copolymers); 0.1 and 5.3 (for copolymers of 4-vinylpyridine), and 19.7 and 34.4 (for poly(2-N,N-dimethylaminoethyl) methacrylate) mg metal ions per gram of polymer carrier, respectively. An attempt was made to evaluate
the structure of the Fe-containing polymeric materials by Moessbauer spectroscopy. The parameters of the Moessbauer spectra
such as the isomer shift, quadrupole splitting, effective internal magnetic field, and relative weight of the partial components
were consequently determined for the complexes studied at different temperatures. The results obtained proved the existence
of high-spin Fe3+ ions in oxygen- or nitrogen-containing ligand environment. 相似文献
7.
E. Manova T. Tsoncheva Cl. Estourns D. Paneva K. Tenchev I. Mitov L. Petrov 《Applied Catalysis A: General》2006,300(2):170-180
Nanosized iron and mixed iron–cobalt oxides supported on activated carbon materials and their bulk analogues prepared by thermal synthesis are studied by X-rays diffraction, Mössbauer spectroscopy, magnetic measurements and temperature programmed reduction. Their catalytic behavior in methanol decomposition to H2, CO and methane is tested. Phase transformations in the metal oxides affected by the reaction medium are also investigated. Changes in the reaction mechanism of the methanol decomposition after the metal oxides deposition on the support as compared to the bulk phases are discussed. 相似文献
8.
Nikolay Velinov Dimitar Dimitrov Kremena Koleva Krassimir Ivanov Ivan Mitov 《金属学报(英文版)》2015,(3):367-372
Nanocrystalline copper-cobalt ferrites with composition Cu_(1-x)Co_xFe_2O_4,where x = 0.2 and 0.8,were synthesized by mechanochemical treatment of co-precipitated precursors.The ferrite powders were characterized by XRD and Mossbauer spectroscopy.Results proved obtaining of spinel ferrites with crystallite size smaller than 10 nm.Increasing of crystallite size of samples with increasing of mechanochemical treatment duration was established,too.Catalytic properties of obtained ferrites were tested in reactions of oxidation of CO,methanol and dimethyl ether.High catalytic activity of nanocrystalline copper-cobalt ferrites toward CO and CH_3OH(about 100% conversions of CO and CH_3OH at 160 ℃)and moderate activity toward(CH_3)_2O oxidation were established.The results obtained revealed that the Co/Cu atomic ratio is an important factor determinant the behavior of catalysts toward methanol and DME oxidation. 相似文献
9.
The wide adoption of path‐tracing algorithms in high‐end realistic rendering has stimulated many diverse research initiatives. In this paper we present a coherent survey of methods that utilize Monte Carlo integration for estimating light transport in scenes containing participating media. Our work complements the volume‐rendering state‐of‐the‐art report by Cerezo et al. [ CPP*05 ]; we review publications accumulated since its publication over a decade ago, and include earlier methods that are key for building light transport paths in a stochastic manner. We begin by describing analog and non‐analog procedures for free‐path sampling and discuss various expected‐value, collision, and track‐length estimators for computing transmittance. We then review the various rendering algorithms that employ these as building blocks for path sampling. Special attention is devoted to null‐collision methods that utilize fictitious matter to handle spatially varying densities; we import two “next‐flight” estimators originally developed in nuclear sciences. Whenever possible, we draw connections between image‐synthesis techniques and methods from particle physics and neutron transport to provide the reader with a broader context. 相似文献
10.
Ibón Guillén Carlos Ureña Alan King Marcos Fajardo Iliyan Georgiev Jorge López‐Moreno Adrian Jarabo 《Computer Graphics Forum》2017,36(4):179-187
We present new methods for uniformly sampling the solid angle subtended by a disk. To achieve this, we devise two novel area‐preserving mappings from the unit square [0,1]2 to a spherical ellipse (i.e. the projection of the disk onto the unit sphere). These mappings allow for low‐variance stratified sampling of direct illumination from disk‐shaped light sources. We discuss how to efficiently incorporate our methods into a production renderer and demonstrate the quality of our maps, showing significantly lower variance than previous work. 相似文献