Effect of conditions of preparation on the thermoelectric properties of solid solutions of Bi<Subscript>0.5</Subscript>Sb<Subscript>1.5</Subscript>Te<Subscript>3</Subscript>

The effect the conditions of preparing thermoelectric solid solutions of Bi_0.5Sb_1.5Te₃ + 0.06 wt % Pb by hardening from the liquid state with subsequent hot pressing have on their thermoelectric properties is studied. It is found that the optimum thermoelectric quality factors are achieved at a 2200–2800 rpm rate of copper disc rotation.     

Ferroelectric properties of SiO<Subscript>2</Subscript>-<Emphasis Type="Italic">TGS</Emphasis> nanocomposite

Dielectric and pyroelectric properties of a composite based on nanodisperse silica hydrosol and ferroelectric triglycinesulfate (TGS) were investigated. The performed studies allow us to assume that a ferroelectric state exists in this composite.     

Octane numbers (ONs) of hydrocarbons: a QSPR study using optimal topological indices for the topological equivalents of the ONs

A new method proposed for solving QSPR tasks is based on transition from numerical values to topological equivalents (TEs) of physicochemical properties of chemical compounds. The TEs are unambiguously related to corresponding properties; for n-alkanes, they are linear functions of the number, n, of carbon atoms. Since the TE depends only on the corresponding physicochemical parameter, it can be calculated for any hydrocarbon using the same relationships as those known for n-alkanes. The optimal topological index (OTI) constructed using the chemical structure matrix for TEs usually has a much smaller basis compared to the topological index obtained by analogous procedure for the physicochemical property. An algorithm for modeling of physicochemical properties using the TEs was developed and evaluated taking the octane numbers of alkanes and cycloalkanes as examples. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1619–1631, September, 2007.     

Influence of humidity and acidity of the titanium dioxide surface on the kinetics of photocatalytic oxidation of volatile organic compounds

The influence of the humidity and acidity of the TiO₂ surface on the kinetics of the photocatalytic processes of deep oxidation of volatile organic compounds was studied. At 20 °C the rates of acetone and benzene oxidation are maximum at the coverages of TiO₂ with water close to monolayer and are 3—5 times higher than that in the dry atmosphere. The activation energy of benzene oxidation (E _a = 6.3±0.4 and 43.0±3.2 kJ mol^–1 at relative humidities of 8 and 70%, respectively) at a humidity higher than 30% decreases according to the exponential law with an increase in the surface acidity when multilayer water films are formed on the surface. Under the real conditions of operation of photocatalytic air purifiers, a TiO₂ particle is covered by water nanofilms. As in aqueous solutions, photoprocesses on the TiO₂ surface depend substantially on the solvation of the participants of the reaction, the formation of the double electric layer, and the concentration of the electrolyte (due to the dissociation of the surface acid-base groups).     

Control over the hierarchical structure of titanate nanotube agglomerates

An alkaline hydrothermal treatment of several types of ordered macroporous TiO(2) structures, namely, microtubes, sea urchin shapes, and anodic nanotube arrays, has been investigated under stationary conditions. The effect of the size and geometry of these structures on the morphology of the forming hierarchical agglomerates of titanate nanotubes has been systematically studied. It has been revealed that, at sizes larger than the critical value (ca. 1 μm), the whole geometry of the initial ordered TiO(2) structure is maintained under reaction conditions leading to formation of hierarchical structures, in which bulk TiO(2) is replaced with titanate nanotube agglomerates. This principle provides a convenient route for the preparation of multiscale micro- and nanostructures of TiO(2) based materials. The analysis of critical size suggests that, under reaction conditions, due to the limited transport of dissolved Ti(IV) species, the growth of nanotubes occurs locally.     

Cetane numbers of hydrocarbons: calculations using optimal topological indices

The QSPR problem for cetane numbers of hydrocarbons, a key property of oil fuels, was considered for the first time. Based on the approach developed, calculations have been carried out and relations derived for prediction of the cetane numbers of alkanes and cycloalkanes. Results of cetane number calculations for 180 unknown and non studied hydrocarbons are presented. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–457, March, 2008.     

Magnetite nanorod thermotropic liquid crystal colloids: Synthesis, optics and theory

We have developed a facile method for preparing magnetic nanoparticles which couple strongly with a liquid crystal (LC) matrix, with the aim of preparing ferronematic liquid crystal colloids for use in magneto-optical devices. Magnetite nanoparticles were prepared by oxidising colloidal Fe(OH)(2) with air in aqueous media, and were then subject to alkaline hydrothermal treatment with 10moldm(-3) NaOH at 100°C, transforming them into a polydisperse set of domain magnetite nanorods with maximal length ～500nm and typical diameter ～20nm. The nanorods were coated with 4-n-octyloxybiphenyl-4-carboxylic acid (OBPh) and suspended in nematic liquid crystal E7. As compared to the conventional oleic acid coating, this coating stabilizes LC-magnetic nanorod suspensions. The suspension acts as a ferronematic system, using the colloidal particles as intermediaries to amplify magnetic field-LC director interactions. The effective Frederiks magnetic threshold field of the magnetite nanorod-liquid crystal composite is reduced by 20% as compared to the undoped liquid crystal. In contrast with some previous work in this field, the magneto-optical effects are reproducible on time scales of months. Prospects for magnetically switched liquid crystal devices using these materials are good, but a method is required to synthesize single magnetic domain nanorods.