Supramolecular benzene structure and its changes under the action of dissolved fullerenes

A model of the supramolecular benzene structure and its changes induced by the introduction of fullerenes into benzene is proposed based on the complex consideration of previously calculated and experimental data.     

Consolidation mechanism of materials obtained from sodium silicate solution and silica-based aggregates

A study based on the use of sodium silicate gels as binder for cold consolidation of silica-based aggregates has been investigated. The gels used as precursor of binder were synthesized by adding hydrochloric acid to a concentrated sodium silicate solution. Consolidated materials were obtained by mixing the previous solution before gelation with granular materials (fine silica powder and sand). The study of the gel-silica-sand ternary system shows that the existence domain of materials depends on the sand size distribution. The microstructure of gel-silica-sand ternary samples reveals the presence of the three components with a partial attack of grain surface. This was confirmed by FTIR experiments during the monitoring of the synthesis. Actually, the ν_asSiOSi broad band resulting from the average of the contribution of the set of Q⁴, Q³ and Q² units with a sharp peak located around 1078 cm^− 1, firstly shifts to lower wavenumber until 21 days and then to higher wavenumber characteristic of dissolution/precipitation reactions. On the other hand, the consolidation of the material is strong when the amount of fine silica in the material is high leading to efficient mechanical properties. Therefore, consolidation could be explained by the dissolution of small particles of silica and their precipitation into the grain boundary of sand.     

Structure and Properties of Nanostructured SZO Films Obtained by Electron-Beam Evaporation

Crystallography Reports - The composition, structure and properties, as well as the current–voltage characteristics (CVCs) of nanostructured SZO films were studied. These films were...     

Novel carbon materials obtained by reactions of C60 fullerene with phosphorus at high temperature

C₆₀ fullerene reacted with phosphorus at high temperatures to graphitic materials with strongly differing properties. Several spectroscopic investigations as Raman, ESR, XPS and ³¹P-NMR as well as TEM and ESEM have shown that the structural order of the mostly micro-crystalline materials increased with increasing reaction temperatures and decreasing phosphorus content. At suitable preparation conditions carbon nanotubes are formed, which are disordered in most cases, but partly exhibit high structural order (single-wall nanotubes), too. The prepared materials are very hard, e.g. harder than silica, intensely coloured and electrically conductive. Their hardness decreased with rising phosphorus content, and their conductivity increased with decreasing phosphorus content.     

The properties of hydrogen forms of zeolite T obtained by the treatment with hydrochloric acid at 22°C

Hydrogen forms of zeolite T obtained by the treatment of synthetic zeolite of erionite-offretite type with hydrochloric acid at 22°C were tested with the methods of chemical analysis, sorption and X-ray diffraction. The influence of the variations in the number of treatments with acid, the concentration of acid and the calcination at 500°C on the properties of the samples was observed. It was found that the modification runs in two steps. The existence of the threshold of stability of the zeolite T structure under the treatment with 0.1 N HCl was indicated at the degree of decationization of 45–48% and the degree of dealumination of 25–28%. It was also found that about 30–33% of alkali cations in zeolite T are at the more accessible positions.     

Influence of various conditions of convective mixing of melt on the structure and magnetoresistance of eutectic InSb-NiSb alloys obtained by directional crystallization

The microstructures are analyzed of the eutectic alloys solidified in the quasi-binary InSb-NiSb system under different conditions of convective mixing of melts grown in an ampoule by the Czochralski and directional crystallization methods under earth and microgravity conditions. It is established that growth of the phases in directional solidification of the InSb-NiSb eutectics is determined not only by the diffusion mechanism of the component redistribution at the crystallization front but also by the diffusion-convection mechanism. The comparative analysis of the influence of the crystal microstructure on the value of the magnetoresistance, R _M , is performed for the first time. It is shown that the R _M value of directionally crystallized InSb-NiSb eutectics depends on the density of the NiSb needles, disorder of the eutectic structure, and electrophysical parameters of the matrix.     

Growth and removing of tungsten whiskers under controlled conditions

The growth kinetic and size decreasing process of tungsten rod-like crystals by heating in the iodine vapour are studied. Effects of tungsten filament temperature (2400 – 3500 K), iodine concentration (to 6 mg/cm³) and water contents (0.01 – 0.05 mg/cm³) are shown. Maximal growth rate of tungsten whiskers to 30 μm/min. Stopping of the growth and following removing by iodine reactions take place after heating to 3500 K.     

Surface morphology and quality of potassium bichromate crystals obtained from aqueous solutions in relation to growth conditions

The characteristics of macrospiral layers on growth surfaces of potassium bichromate crystals and their quality are examined in relation to growth conditions. It was observed that the layers become thick and rounded, more inclusions are trapped and the crystal quality deteriorates with an increase in supersaturation, while an opposite effect is noted with an increase in growth temperature. The observations are discussed from the standpoint of crystal growth theories.     

Fabrication and characterization of photocurable inorganic-organic hybrid materials using organically modified colloidal-silica nanoparticles and acryl resin

Photocurable inorganic-organic hybrid materials were prepared from colloidal-silica nanoparticles synthesized through the sol-gel process and using acryl resin. The synthesized colloidal-silica nanoparticles had uniform diameters of around 20 nm and were organically modified, using methyl and methacryl functional silanes, for efficient hybridization with acryl resin. The organically modified and stabilized colloidal-silica nanoparticles could be homogeneously hybridized with acryl resin without phase separation. The successfully fabricated hybrid materials exhibit efficient photocurability and simple film formation due to the photopolymerization of the organically modified colloidal-silica nanoparticles and acryl resin upon UV exposure as well as an excellent optical transmission of above 90% in the visible region and an enhanced surface smoothness of around 1 nm RMS roughness. They likewise exhibit improved thermal and mechanical characteristics, much better than those of acryl resin. Lastly and most importantly, these photocurable hybrid materials fabricated through the synergistic combination of colloidal-silica nanoparticles with acryl resin are candidates for optical and electrical applications.     

Facile synthesis and characterization of hierarchical CuO nanoarchitectures by a simple solution route

The controlled synthesis of hierarchical CuO nanomaterials in a solution phase has been realized with high yield at low temperature using copper acetate hydrate and NaOH as starting materials with the assistance of surfactant under hydrothermal conditions. X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet‐visible spectroscopy (UV‐Vis) were used to characterize the products. It was shown that the hierarchical CuO nanoarchitectures were formed through aggregation of tiny single‐crystal CuO nanorods. Experiments demonstrated that the morphology of CuO products was significantly influenced by hydrothermal temperature and reaction time. A rational growth mechanism based on oriented attachment was proposed for the selective formation of the hierarchical CuO nanoarchitectures. Our work demonstrated the growth of hierarchical CuO nanoarchitectures built from one‐dimentional nanorods through a one‐step solution‐phase chemical route under controlled conditions. In addition, The UV‐Vis spectrum of the hierarchical CuO nanoarchitectures showed large blue shift because of the quantum size effect. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Highly efficient photocatalytic degradation of methyl orange and Rhodamine B by hierarchical BiOBr microspheres

Hierarchical BiOBr microspheres were successfully synthesized via a solvothermal method by using the diethylene glycol(DEG) as the solvent and soft‐template. The as‐obtained products were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM), N₂ adsorption–desorption and UV–Vis diffuse reflectance spectroscopy(DRS) techniques. The formation mechanism for the growth of hierarchical BiOBr microspheres has been studied. The possible mechanism of photocatalysis has been discussed. Remarkably, the as‐prepared BiOBr microspheres has a large specific surface area, which can reach a maximum surface area of 55.9307 m²/g. In addition, the superior enhanced photocatalytic activities of BiOBr microspheres were evaluated by the photodegradation of methyl orange (MO) and Rhodamine B (RhB) under visible‐light illumination, which presented the efficiency up to 98.10% just within 50 min and 98.64% within 30 min, respectively. BiOBr microspheres can be a promising candidate as highly efficient photocatalyst for decompositing of organic contaminants for environmental remediation.     

The comparison of the properties of hydrogen forms of zeolite T obtained by the treatment with hydrochloric acid af 100 °C or through the ammonium form and its decompostion

The modification of zeolite T through the ammonium form and its decomposition is in comparison with the treatment with hydrochloric acid, more effective and more selective for the obtainment of hydrogen forms with high decationization degree at low dealumination. The calcination at 500 °C introduced between the treatments of zeolite with acid allows for the stabilization of the structure and enlargement of the H⁺/K⁺ exchange.     

Behavior of LiOH·H2O crystals obtained by evaporation and by drowning out

In the present work, the behavior of crystals derived from two different crystallization methods applied in a concentrated aqueous lithium salt solution was studied. The LiOH·H₂O crystals obtained by a simple evaporation (Crystal I) differed in terms of morphology and solubility from those precipitated from lithium hydroxide solutions by addition of ethanol as a co‐solvent (Crystal II). Solubility of Crystal II at different temperatures (15 to 35°C) and mass ratios of ethanol to water (0 to 0.1) was determined. Polymorphic like behavior of these crystals was evidenced from X‐ray diffraction patterns. Measurement of density, refractive index, absolute viscosity and electrical conductivity of saturated solutions are reported. A thermodynamic analysis in terms of the Chen model for the calculation of activity coefficients, indicate that the polymorphic system in water and in water + ethanol (ethanol/water ratio 0.1) is enantiotropic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chiral SmC* liquid crystals obtained by mixing of SmC and cholesteric phase

The binary mixtures of the substance providing cholesteric phase exhibit a chiral SmC* phase for certain concentration and temperature range. This phase was verified to be ferroelectric. The temperature dependences of the spontaneous polarization and the coercive field were determined for three concentrations. The pitch of the helical structure is approximately indirectly proportional to the molar concentration of the cholesteric substance and varies from 3 μm to about 25 μm in the concentration range from 20 mol% to 5 mol% of the cholesteric substance. For the lower concentrations the sample is unwound in planar samples due to the surface anchoring. Two possible unwound planar configurations can be switched by electric field.     

Magnetic and structural characterization of silver-iron oxide nanoparticles obtained by the microemulsion technique

In the present paper we report the magnetic characterization of silver-iron oxide nanocomposite obtained by the chemical microemulsion method. TEM images and X-ray diffractograms show that the nanocomposite consists of Ag nanoparticles of ～ 7 nm surrounded by a quasiamorphous matrix. The ZFC–FC curves and Mössbauer spectra obtained at different temperatures show a typical evolution of a system composed of weakly interacting nanoparticles with a blocking temperature (T_b) of ～50 K. The analysis of the magnetic data reveals that the matrix is formed by γ-Fe₂O₃ phase with a structural range order of ～2 nm.     

Dielectric and pyroelectric response of PVDF loaded with BaTiO3 obtained by mechanosynthesis

Electroactive composites based on ferroelectric ceramic and polymer components are still of interest since their properties can be easily tailored to the requirements of smart structures, sensors and actuators. We studied the dielectric and pyroelectric response of poly(vinylidene fluoride) loaded with BaTiO₃ nanograins obtained by mechanically activated synthesis from BaO and TiO₂. The BaTiO₃ nanopowder was characterized by X-ray diffraction, transmission electron microscopy and NIR Raman scattering. The relaxation processes in the polymer matrix were found to determine the dielectric response of the composites but with higher permittivity values due to the presence of BaTiO₃. The activation energy of the segmental motion of the polymer matrix was found to increase with increasing contents of the filler. The dielectric response of the composites with volumetric fraction of BaTiO₃ equal to and greater than 0.24 was found to be dominated by a broad maximum at ∼320 K, which we relate to the Curie point of the ferroelectric nanograins.     

Study of nanostructured materials by optical and photoelectron spectroscopy

The results of investigations of the electronic energy structure and physicochemical properties of nanostructured systems by optical and photoelectron spectroscopy using synchrotron radiation are briefly reviewed. The quantum-size effect in thin metal films and surface lateral superlattices are analyzed. The effect of structural defects on the chemical state of metal clusters on the surface of oxides in catalytically active systems is discussed. The results of the study of the specific features of chemical bonding in solid-state nanostructures within the quasi-molecular approach are presented. The possibility of using biological structures (proteins) as matrices for the formation of ensembles of nanoclusters is considered.     

Neutron diffraction studies of the orthorhombic lattice distortions and magnetic properties of lanthanum manganite obtained under different technological regimes

Neutron diffraction studies have been carried out on two series of lanthanum manganite compositions obtained under different technological regimes. Based on the plot of angle dependence β° characterizing the degree of monoclinic distortions on “tolerance factor” t Mn³⁺ concentration is determined in the compositions obtained by us. With partial oxygen pressure increasing in annealing atmosphere the crystalline transition (orthorhomb-cube) temperature lowers from 583 ± 10°K to 508 ± 10°K. The correlation between magnetic properties of the compositions obtained and the degree of orthorhombic distortions γ′ = \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm b}\sqrt {{\rm 2/c}} $\end{document}\end{document} is established. Neutron diffraction studies of magnetic properties of LaMnO₃ compositions show that with decrease of orthorhombic distortion degree the decrease of antiferromagnetic component and lowering of the Néel point occur, while the ferromagnetic contribution increases and the Curie point rises.     

Method of X-ray spectral microanalysis of PbTe and SnTe obtained by the iodide method

This an examination of the characteristics of the X-ray spectral microanalysis of the tellurides of lead and thin, obtained by the iodide method. It was demonstrated that applying the method of calculating the composition in relation to the relative intensity of the characteristic X-ray radiations of the analytical lines TeL_α and IL_α secures the possibility of analyzing relief surfaces. Besides that, the method makes it possible to make calculations without using numerous traditional semi-empirical expressions under conditions of changes in the values of the accelerating voltage.     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.