Structural-Phase Transformations and Short-Range Order Evolution in the Fe–Cr System during Mechanical Alloying

Physics of the Solid State - Using Mössbauer spectroscopy on 57Fe nuclei and X-ray diffraction, the mechanism of mechanical alloying in a planetary ball mill of the Fe–Cr nanocrystalline...     

Gas sensitivity of etioporphyrin metal complexes in thin films

It is shown that porphyrin metal complexes have the potential for the creation of various gas sensors; the gas sensing properties of the materials on their basis change upon the replacement of the central metal atom and substituents in the porphyrin core. Films of etioporphyrin-II were prepared by vacuum deposition onto a front shaft system of electrodes on a pyroceramic support. Calibration dependences of the analytical signal (conductivity) on the concentration of ammonia were obtained. It was found that UV irradiation on the sensor layer enhances the sensitivity of ammonia determination. Relative sensitivities of thin films based on Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and Pt(II) etioporphyrin complexes in the temperature range from 303 K to 423 K and ammonia concentrations from 1.5 to 75 mg/m³ were determined. The relative sensitivity attains a maximum (0.8) at an ammonia concentration of 7.5 mg/m³ for the Co(II) etioporphyrin at 333 K in a dark mode, or at 303 K and under UV irradiation (λ = 406 nm, P = 1 mW). An experimental setup was assembled that allowed measurements at the controlled temperature and humidity of the gas and its mixtures with inert gases or air. The conditions of ammonia detection were optimized.     

Quantum-chemical study on the mechanism of formation of geminal hydroxy thiols by reaction of 1,3-dihalopropan-2-ones with hydrogen sulfide

The reaction mechanism of 1,3-dihalopropan-2-ones with hydrogen sulfide in the presence of hydrogen chloride was studied in terms of the density functional theory. Unlike 1-halopropan-2-ones which give rise to 1-halo-2-sulfanylpropan-2-ols via preliminary enolization, 1,3-dihalopropan-2-ones preferentially undergo direct nucleophilic attack on the carbonyl group by hydrogen sulfide. The potential energy surface for rotational isomerism of 1,3-dihalopropane-2-thiones and 1,3-dihalo-2-sulfanylpropan-2-ols was analyzed, and their most stable rotamers were identified.     

Determination of nanoparticle sizes by X-ray diffraction

Different procedures for analysis of particle sizes by the X-ray diffraction method are compared by the example of nanoparticles of nickel and iron(3+) oxide (Fe₂O₃). A modified Warren-Averbach method is proposed for the analysis of the X-ray diffraction line profile based on the approximation by the Voigt function, which yields stable solutions, and the efficiency of the method is shown. The analysis within the frame-work of the Warren-Averbach method makes it possible to restore the distribution function of nanoparticles (crystallites) over true diameters, which satisfactorily correlates with electron microscopy data. The applicability of the Warren-Averbach method to the estimation of crystallite sizes by the analysis of a single diffraction line is substantiated. The range of the applicability of the Scherrer, Williamson-Hall, Warren-Averbach, and modified Warren-Averbach methods to the substructure analysis by the X-ray diffraction is determined as depending on the method of nanostructure formation.     

Synthesis of poly(2,2′,3,3′-indole)

New approaches to the synthesis of poly(2,2′,3,3′-indole) were developed based on the photochemical dehydropolycondensation of indole in the presence of iodine and the photochemical polycondensation of 1-(1H-indol-3-yl)-2-iodo-1-ethanone in the absence of catalyst and solvent. A suggested mechanism for the formation of the oligomeric chain in these reactions includes the intermediate formation of 3,3′-diindole with subsequent polycondensation via elimination of hydrogen atoms at position 2 of the dimer pyrrole fragment.     

Resonances in the ωω system

Results of a partial-wave analysis for the reaction π ^? → ωωn studied at the VES spectrometer (Institute for High Emergy Physics, Protvino) are presented. The behavior of the J ^PC = 2⁺⁺ amplitudes in the ωω system is described by the f ₂(1565) and f ₂(1910) resonances, whose parameters were fixed at M = 1.590 ± 0.010 GeV and Γ = 0.140 ± 0.011 GeV for the former and at M = 1.890 ± 0.010 GeV and Γ = 0.165 ± 0.019 GeV for the latter. The decay f ₄(2050) → ωω was observed at parameters values of M = 1.960 ± 0.015 GeV, Γ = 0.290 ± 0.020 GeV.     

Method of the quantum defect Green’s function for calculation of dynamic atomic polarizabilities

The quantum defect Green’s function enabling one to take into account exactly the contribution of highly excited and continuum states to the polarizability is found. The contribution of the ground and low-lying excited states is taken into account by using experimental values of the corresponding oscillator strengths. The good accuracy of the method proposed is demonstrated by calculation of the scalar dipole dynamic polarizabilities of noble gas atoms with consideration of the fine structure of the terms.     

Stereoselective electrochemical transformation of 4-substituted cyclohexanones into cis-5-substituted 2,2-dimethoxycyclohexanols

Electrolysis of 4-substituted cyclohexanones in methanol in the presence of sodium halides as mediators in an undivided cell results in the stereoselective formation of cis-5-substituted 2,2-dimethoxycyclohexanols in 70—80% yields.