Effect of structural analogy between ZSM-5 and silicalite catalysts on the oxidative methylation of toluene with methane

Summary With ZSM-5 and silicalite (both initial and BaO modified) the yield of styrene, the most desirable reaction product, was highly represented when BaO modified silicalite was used as catalyst for the reaction. The catalytic results fitted the basicity, surface area and structural crystallinity.     

Kinetics of copper slag oxidation under nonisothermal conditions

The kinetics of air copper slag oxidation under nonisothermal conditions is studied using simultaneous TG–DTA at a varying heating rate of slag and flow rate of the oxidizing gas flux. The values of the kinetic parameters, activation energy and pre-exponential factor, have been determined based on: data from DTA by the methods of Kissinger and Ozawa; data from TG using an isoconversion method and the computation procedures of Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose. No relationship between the kinetic parameters and the oxidation gas flow rate has been established. The changes of the phase composition with temperature are investigated by X-ray powder diffraction analysis on the basis of data obtained for the products formed at the different stages of the oxidation process. The morphology of the oxidized slag as well as the elements distribution is studied by electron microscopy and EDS analysis.     

Quantitative analysis of resorcinol,quinol and cathechol by IRT-method

In the present paper the determination of resorcinol(I), quinol(II) and catechol(III) in mixture is demonstrated by IRT method using nonsophisticated IR spectrophotometer. The sample dissolved in acetone is poured in the sample cell. The absorbances at 963 cm^?1 (I), 829 cm^?1 (II) and 745 cm^?1 (III) are consecutively compensated by titration of pure acetone in the reference cell with solutions of I,II,III respectively. The accuracy obtained is 1,5 %, 4,7 % and 10 % rel. The method is applied for quatitative investigation of reactionary mixtures containing resorcinol and quinol.     

Mechanochemical effects in U3O8

The effect of the mechanical treatment of U₃O₈ in a planetary ball mill in air or as a suspension in benzene solution of thyolilthreefluoroacetone (TTA) on the nature of the oxide and on the leaching of U and ²³⁴Th into diluted aqueous solutions of HCl, Na₂EDTA and NaCl has been studied. Transformation of U₃O₈ to UO₂, is much stronger expressed when the mechanoactivation is performed in air is established. The leaching behavior of U and Th depends significantly on the activation mode and on the leaching reagent nature. The role of mechanochemically enhanced UO₂-ThO₂ solid solution formation for the observed effects is discussed.     

Characterizations of self-combustion reactions (SCR) for the production of nanomaterials used as advanced cathodes in Li-ion batteries

In this work, self-combustion reactions (SCR) for the preparation of important cathode materials for rechargeable Li-ion batteries were investigated by thermal analytical tools (DSC, ARC, TGA), electron microscopy, XRD, various spectroscopies (MS, Raman, FTIR) and elemental analysis by ICP. The systems studied include solutions containing metal nitrates at the right stoichiometry and sucrose as a fuel, for the preparation of LiMn_0.5Ni_0.5O₂ (layered), LiMn_1.5Ni_0.5O₄ (spinel), LiMn_0.33Ni_0.33Co_0.33O₂ (layered), and LiMn_0.4Ni_0.4Co_0.2O₂ (layered). Similar products, which do not depend on the atmosphere of the processes (air or inert) were obtained by spontaneous SCR and the gradual heating of the same solutions by DSC, ARC, and TGA. The reactions involve the partial caramelization of sucrose, complicated by red-ox reactions with the nitrates that form solid products, whose organic part is finally decomposed around 400 °C. The presence of cobalt ions has a stabilizing effect, which is expressed by the low dissolution rates of Li ions from the solid products thus formed, into aqueous solutions. The reaction mechanisms are discussed herein.     

Combined laser and magnetic field treatment of YFeO<Subscript>3</Subscript>—containing films grown by spray-pyrolysis

Thin films (50–1200 nm) of YFeO₃ were deposited on fused silica substrates by spray-pyrolysis using ethylene glycol solution of Y-Fe(III) citric complexes. The films were post deposition annealed at 750°C in static air for 2 h. Films obtained in this way were afterwards irradiated by a burst mode operated Nd-YAG laser (pulse energy 650 mJ, pulse duration 700 μs, energy density 110 mJ/cm²). The laser’s onset was synchronized with that of a magnetic field pulse of nearly square shape (magnetic induction 0.5 T, pulse duration 900 μs). The samples were placed normally to the direction of the magnetic field. The treatment does not affect the phase composition of the film but significantly increases the crystallite sizes of the phases presenting in the sample. The saturation magnetization of the films decreases as a result of the laser and magnetic field treatment and the coercive force increases by 50%.     

Rational functions of best L p- approximation and analytic continuability

Sufficient conditions for the analytic (resp. meromorphic) continuability of a function f ∈ L _p([?1, l]), p > 0, in terms of rational functions of best weighted L _p- approximation with an unbounded number of finite poles are established.     

Auto-combustion synthesis,Mössbauer study and catalytic properties of copper-manganese ferrites

Spinel ferrites with nominal composition Cu _0.5Mn _0.5Fe ₂ O ₄ and different distribution of the ions are obtained by auto-combustion method. Mössbauer spectroscopy, X-ray Diffraction, Thermogravimetry-Differential Scanning Calorimetry, Scanning Electron Microscopy and catalytic test in the reaction of methanol decomposition is used for characterization of synthesized materials. The spectral results evidence that the phase composition, microstructure of the synthesized materials and the cation distribution depend on the preparation conditions. Varying the pH of the initial solution microstructure, ferrite crystallite size, cation oxidation state and distribution of ions in the in the spinel structure could be controlled. The catalytic behaviour of ferrites in the reaction of methanol decomposition also depends on the pH of the initial solution. Reduction transformations of mixed ferrites accompanied with the formation of Hägg carbide χ-Fe ₅ C ₂ were observed by the influence of the reaction medium.     

Mechanochemistry of the 5f-element compounds

The effect of the mechanical treatment of UO₂(NO₃)₂·6H₂O in a planetary ball mill in air and as a suspension in toluene has been studied. The X-ray diffractometry results strongly suggest that part of the mechanoactivated material is transformed in nitrosyl uranyl nitrate.     

Sign changes in rational L w 1 -approximation

Let f ∈ L _w ¹ [−1, 1], let r _n,m(f) be the best rational L _w ¹ -approximation for f with respect to real rational functions of degree at most n in the numerator and of degree at most m in the denominator, let m = m(n), and let lim _{n → ∞} (n-m(n)) = ∞. In this case, we show that the counting measures of certain subsets of sign changes of f-r _n,m (f) converge weakly to the equilibrium measure on [−1, 1] as n → ∞. Moreover, we prove estimates for discrepancy between these counting measures and the equilibrium measure. Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 2, pp. 283–287, February, 2006.