Effect of nature of templates on formation mechanism of aluminum oxide mesoporous structure

Mesoporous aluminum oxide is produced by the sol-gel method from aluminum isopropoxide using molecular structures of a cationic polyelectrolyte (polyethylenimine) and dodecylamine micelles as nanotemplates. The mechanism for the formation of mesophases of hybrid materials in colloidal systems upon template synthesis is discussed.     

Unravelling low lying phonons and vibrations of carbon nanostructures: The contribution of inelastic and quasi-elastic neutron scattering

We illustrate the contribution of inelastic neutron scattering to the understanding of the vibrations and lattice excitations of fullerenes and carbon nanotubes, through some significant experimental results. Particular emphasis is placed on the study of intra and inter-molecular modes of fullerene C₆₀, as well as on the order/disorder transition characteristic of these molecules. In addition, a significant part of this article is dedicated to various intercalation compounds of fullerenes and carbon nanotubes, such as the co-crystal ??fullerene-cubane?? consisting of an arrangement of molecules of spherical and cubic shapes, or the compound called ??peapods??, in which fullerene C₆₀ are inserted inside carbon nanotubes.     

X-pinch source of subnanosecond soft X-ray pulses based on small-sized low-inductance current generator

For the first time, the regime of a micrometer-size hot spot formation is impemented for an X-pinch in a plasma, which is fed from a current generator based on low-inductance capacitors and rapid current switches. The configurations of X-pinches, which can be used effectively as point sources of soft X-rays with this type of current generator, are determined. A prototype of a small-size radiation source for high-resolution point projection X-ray radiography has been constructed. The main parameters of X-pinch as a radiation source are analyzed and compared with X-pinch parameters in high-voltage setups with shaping lines. An analysis of the data on the operation of X-pinches in generators with different parameters has led to simple relations that can be used to select optimal initial X-pinch parameters.     

Soot formation in the pyrolysis of benzene,methylbenzene, and ethylbenzene in shock waves

Soot formation in the pyrolysis of benzene, methylbenzene, and ethylbenzene and in the oxidative pyrolysis of benzene in shock waves has been investigated using an absorption-emission technique. Even in the presence of small amounts of oxygen, soot formation in the pyrolysis of these hydrocarbons is accompanied by a decrease in the temperature of the reacting mixture. The soot yield has been measured as a function of temperature over wide initial reactant concentration ranges. A new, larger value was obtained for the coefficient of light absorption by soot particles at a wavelength of 632.8 nm. A revised, substantially modified kinetic model is suggested for soot formation. This model has been verified against experimental data available from the literature on the time profiles of the concentrations of some key components at the early stages of pyrolysis and oxidation of various hydrocarbons in a wide range of process conditions. The model reproduces fairly well the time dependences of the soot yield and soot particle temperature measured in this study for benzene, methylbenzene, and ethylbenzene pyrolysis.     

Prebreakdown phase in atmospheric discharges

Pulsed X-ray radiation with quanta energy higher than 5 keV is recorded during the prebreakdown phase under discharges in atmospheric-pressure air at a maximum voltage from the 0.8?C1.2 MV range. The UV and X-ray generation region has been localized using collimated and time-resolved diagnostics. In the near-UV range, the maximum radiation intensity corresponds to the instant of X-ray generation.     

Electrorheological behavior of the hybrid material prepared by cohydrolysis of titanium(IV) isopropoxide with minor additions of a liquid crystal

A new organic-inorganic hybrid material based on Ti(IV) dioxide and a liquid crystal of alkyloxybenzoic acid with variable-length alkyl chain was prepared by the sol-gel procedure. Physicochemical analysis of the resulting material was carried out, and the electrorheological activity and dielectric properties of the dispersions of the synthesized powders in polydimethylsiloxane (PMS-20) were examined in relation to the length of the alkyl chain of the liquid crystal.     

Cross section of inelastic polarized neutron scattering by superconducting rings

A general expression for the cross section of inelastic magnetic scattering of cold polarized neutrons by superconducting rings has been derived. In this scattering process, the metastable superconducting current changes via quantum jumps corresponding to a decrease in the number of fluxoids in the superconducting ring by one or several units and the change in the energy of the ring is transferred to the kinetic energy of the scattered neutron. For rings from type-II superconductors with a thickness smaller than the field penetration depth but larger than the electron mean free path, the cross sections of inelastic scattering with neutron spin flip have been obtained for the first time. The possibility of increasing the cross section of neutron scattering by a system of rings has been discussed.     

High-pressure alkylation of azomethines

Reaction of anils with alkyl halides under high pressure (10 kbar) was studied. Alkylation in polar media (dioxane or acetonitrile) followed by hydrolysis yields pureN-monoalkylamines in high yields. Optimum conditions for high-pressure alkylation were found.     

Sol–gel synthesis,characterization and catalytic activity of mesoporous γ-alumina prepared from boehmite sol by different methods

In this study, boehmite sols were used as alumina precursors for preparing mesoporous γ-aluminas by two different methods. In one case polyethylenimine was used as a structure-directing agent, and in another case ultrasound treatment was applied. Nitrogen physisorption showed that aluminas that had been prepared by these methods demonstrated different porous structures. The sample obtained without additional treatment had closely packed spherical particles and pores had ink-bottle neck morphology. Ultrasound treatment led to the transformation of ink-bottle pores into cylindrical form and to the increase in surface area and pore volume. Aluminas prepared using polyethylenimine as a template showed larger cylindrical wormhole-like mesopores with a broader pore size distribution, high surface area and pore volume. Catalytic tests showed that textural properties as well as crystallite size were very important parameters of synthesized samples which affected the catalytic activity in the methanol dehydration reaction. It was found that γ-Al₂O₃ prepared by ultrasound treatment had large crystallite size and demonstrated high catalytic activity.     

Electron microscopic studies of single crystal inclusions in pyroboroncarbon

A study of the composition and structure of large single crystal inclusions formed inside cavities in pyroboroncarbon by means of energy dispersive X-ray microanalysis and electron diffraction analysis shows that they correspond to one phase of rhombohedral boron carbide. Bright-field images obtained by transmission electron microscopy show that their growth continues throughout the technological cycle of material growth due to the diffusion of boron atoms from the pyrocarbon phase of pyroboroncarbon adjacent to the cavities.