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排序方式: 共有311条查询结果,搜索用时 31 毫秒
81.
Bumajdad A Zaki MI Eastoe J Pasupulety L 《Journal of colloid and interface science》2006,302(2):501-508
A surfactant-stabilized microemulsion method was used to prepare nano-sized particles (<10 nm) of cubic-CeO2 exposing surfaces of not only highest specific areas (142-201 m(2)/g) ever reported for polycrystalline ceria, but also high thermal stability at 800 degrees C. Three different surfactants, a non-ionic, an anionic and a cationic, were used to form the microemulsions. Then, N2 sorptiometry and pore volume distribution calculations, were used to reveal microporous and mesoporous structures of these cerias as a function of surfactant type. Transmission electron microscopy was used to visualize consequent particle behaviors. Suggestions have been made as to the textural attributes of the high surface area and thermal stability. Accordingly, cationic surfactants, in the presence or absence of added non-ionic surfactant, are seen to assist in producing cerias of promising surface textural properties for the chemical makeup of combustion catalysts. 相似文献
82.
Bradley DI Clubb DO Fisher SN Guénault AM Haley RP Matthews CJ Pickett GR Tsepelin V Zaki K 《Physical review letters》2006,96(3):035301
We describe measurements of the decay of pure superfluid turbulence in superfluid 3He-B, in the low temperature regime where the normal fluid density is negligible. We follow the decay of the turbulence generated by a vibrating grid as detected by vibrating wire resonators. Despite the absence of any classical normal fluid dissipation processes, the decay is consistent with turbulence having the classical Kolmogorov energy spectrum and is remarkably similar to that measured in superfluid 4He at relatively high temperatures. Further, our results strongly suggest that the decay is governed by the superfluid circulation quantum rather than kinematic viscosity. 相似文献
83.
Mercury(II) complexes of some pyrimidine derivatives were prepared and characterized by elemental analysis and spectral measurements. The 1H n.m.r and i.r. spectra show the ligands to be in the keto form. Thermal analysis and electrical conductivity measurements of the complexes were investigated in the temperature range 30–250°C. The results indicate slight semiconducting behaviour. The disparity in the activation energy values, ΔE as calculated from the slopes of the linear parts of the electrical conductivity curves is due to the difference in the concentration of the imperfections contained in the different types of the complexes. 相似文献
84.
Gemeay Ali H. Zaki Ahmed B. El-Sheikh Mohamed Y. El-Saied Hanan F. 《Transition Metal Chemistry》2003,28(6):625-631
Transition metal ion-imidazole complexes have been immobilized on silica, silica–alumina (25%Al2O3), and alumina supports by adsorption and functionalization methods. The catalytic activity of these supported complexes in the decomposition of H2O2 has been studied. The reaction exhibits first-order kinetics with respect to [H2O2] and the quantity of catalyst. The rate of reaction decreases as [H2O2]0 increases. The order of catalytic reactivity is strongly dependent on the type of metal ion, support, and the immobilization method. The complex anchored via adsorption exhibited a higher activity compared to the corresponding complex anchored via functionalization of the surface. The reaction proceed via formation of the peroxo-intermediate, which has an inhibiting effect on the reaction rate. The reaction is enthalpy-controlled as is concluded from the isokinetic relationship. A mechanism is proposed involving the generation of HO2
radicals from the peroxo-intermediate in the rate-determining step. 相似文献
85.
Magdi E.A. Zaki 《Tetrahedron》2007,63(18):3745-3753
1-Aryl-5-amino-4-cyanoformimidoyl imidazoles were reacted with acyl and sulfonyl acetonitriles, under mild experimental conditions, leading to imidazo[4,5-b]pyridines and imidazo[4,5-b]pyridine-5-ones. A reaction intermediate could be isolated in the reaction with methyl cyanoacetate, under carefully controlled experimental conditions. This intermediate cyclized to imidazo[4,5-b]pyridine-5-one, in the presence of DBU. Reaction between 5-amino-4-cyanoformimidoyl-1-(4-fluorophenyl)imidazole and acetylacetone, occurred by a different pathway to give a 6-carbamoylpurine. 相似文献
86.
Mohamed Y. El-Sheikh Abdel-Fatah M. Habib Fathy M. Ashmawy Ali H. Gemeay Ahmed B. Zaki 《Transition Metal Chemistry》1988,13(2):96-100
Summary Dowex 50 W resin in the form of an ethylamine-Cu11 complex ion was used as potentially active catalyst for the decomposition of H2O2 in aqueous medium. The stoichiometry of the amine-Cu11 complex on the resin, determined experimentally, was found to have the total [Cu2+]: [ethylamine]=14 concentration ratio. The kinetics of the decomposition was studied and the calculated rate constant (per g of dry resin) was found to decrease with increase the degree of resin crosslinking. The active species, formed as an intermediate at the beginning of the reaction, had an inhibiting effect on the reaction rate. The brown peroxo-copper complex formed as a result of H2O2 decomposition, was found to contain the catalytic active species. The order of the reaction increased with decreasing initial H2O2 concentration, a sign of a step-wise mechanism. A quantitative treatment of the decomposition of H2O2 was provided in terms of activation parameters. 相似文献
87.
New selective and sensitive Spectrophotometric methods for quinone determination are described. Quinone samples are treated with either methanolic solution of rhodanine, fluorene in ammoniacal media or aqueous semicarbazide hydrochloride solution. Semicarbazide is the most sensitive reagent for the determination of 1,4-benzoquinone, 1,4-naphthoquinone and 2-methyl-1,4-naphthoquinone. Quinones substituted with electron withdrawing groups are better determined using rhodanine. The average recovery is 99.1%, 98.7% and 99.2% using rhodanine, fluorene and semicarbazide as reagents, respectively. 相似文献
88.
A. M. Habib M. Y. El-Sheikh F. M. Ashmawy H. A. El-Daly A. B. Zaki 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(6):675-682
The kinetics of the induced decomposition ofp-NO2- andp-CH3-dibenzoyl peroxide in the presence of 4,4-diamino-trans-stilbene (DTS) were studied in ethanol under both homogenous and heterogeneous conditions. The heterogeneous reaction was carried out in the presence of the DTS/montmorillonite complex. The decomposition reaction was found to be second order and three-halves order for the peroxide concentration in homogeneous and heterogeneous systems, respectively. The reaction was first order for the amine concentration in the homogeneous system. The activation energies for the decomposition reaction were obtained as 54.7±2 and 59.5±3 kJ mol–1 forp-NO2- andp-CH3-dibenzoyl peroxides, respectively, in the homogeneous systems and are higher than the corresponding values of 41±1.5 and 47.6±1 kJ mol–1 for thep-NO2 andp-CH3 derivatives in heterogeneous media. 相似文献
89.
Zusammenfassung Das polarographische Verhalten der Solochrom-Violett RS-Komplexe des Zirkoniums und Thoriums wurde untersucht und Proportionalität zwischen der Höhe der Reduktionswellen der Farbstoffkomplexe und der Konzentration der Metallionen im pH- Gebiet zwischen 2 und 3 festgestellt. Nach eingehender Überprüfung der pH-Abhängigkeit von Form und Lage der Reduktionswelle konnte eine Arbeitsvorschrift ausgearbeitet werden, die die gemeinsame Bestimmung des Zirkoniums und Thoriums erlaubt und darüber hinaus durch Maskierung des Thoriums mit Acetationen die Möglichkeit zur selektiven Bestimmung des Zirkoniums neben Thorium bietet. Störungen durch Anionen und andere Kationen wurden untersucht und eingehend diskutiert.
Summary The polarographic behavior of the Solochrom-Violet RS-complexes of zirconium and thorium was studied, and a proportionality was found between the height of the reduction waves of the dyestuff complex and the concentration of the metal ions in the pH region between 2 and 3. After intensive checking of the pH-dependence of the form and position of the reduction waves, a working procedure could be worked out, which permits the simultaneous determination of zirconium and thorium, and which furthermore by masking the thorium with acetate ions, creates the possibility of the selective determination of zirconium in the presence of thorium. Interferences by anions and other cations were investigated and discussed at length.
Rèsumè Etude du comportement polarographique du complexe du violet solochrome RS et du zirconium et du thorium; il a été établi qu'il existait une relation de proportionalité entre les hauteurs des vagues de réduction du complexe coloré et la concentration des ions métalliques dans un domaine de pH compris entre 2 et 3. Après un contrôle précis de la variation en fonction du pH des vagues de réduction, en forme et en position, il a été possible d'établir un mode opératoire permettant le dosage global du zirconium et du thorium ainsi que le dosage sélectif du zirconium en présence du thorium lorsqu'on masque ce dernier par des ions acétates. Les perturbations apportées par les anions et d'autres cations ont été étudiées et discutées en détail.相似文献
90.
E. E. Zaki 《Journal of Radioanalytical and Nuclear Chemistry》2002,252(1):21-30
The transport of ionic species through ion exchange membranes found several applications for water effluents purification and metal ion separation. To enhance the transport performance, the effect of electric fields was suggested in this work. The transport of U(VI) species in nitric acid solutions across cation exchange membranes was investigated. Different parameters affecting the transport of U(VI) were studied. These parameters include: nitric acid concentration in the feed solution, stripping solution concentration and applied electric field. From the results obtained, the cationic flux of U(VI) was 6.5.10–8 geq.cm–2.s–1 at the optimal conditions of 10–3M HNO3 in the feed solution, 0.5M Na2CO3 in the stripping solution and 30 V. The modeling of the electrodialysis process was also made. The model correlates the mass transfer as a function of current density and voltage as variables and takes into account the electro-osmotic effect. The model is applied to the experimental data. 相似文献