Mass spectrometric investigation of the thermodynamic properties of glass melts in the Cs2O-B2O3-SiO2 system at high temperatures

The composition of the vapor and the activities of cesium metaborate CsBO₂ in glass melts of the Cs₂O-B₂O₃-SiO₂ system at a temperature of 1020 K are determined using high-temperature mass spectrometry. The activities of the individual oxides Cs₂O, B₂O₃, and SiO₂ in glass melts of the Cs₂O-B₂O₃-SiO₂ system at a temperature of 1020 K are calculated by the Wagner method from the obtained values of the activities of CsBO₂. The integral and excess Gibbs energies are determined.     

Synthesis of nanozirconooligocarbosilanes

We describe the first chlorine-free synthesis of nanozirconooligocarbosilanes through thermal cocondensation of low-molecular oligocarbosilanes and zirconium tetrakis(diethylamide). The starting reagents, reaction intermediates, and final products have been characterized by ¹H, ¹³C, and ²⁹Si nuclear magnetic resonance, UV and IR spectroscopy, gel-permeation chromatography, thermogravimetry, transmission electron microscopy (TEM), and elemental analysis. The synthesized nanozirconooligocarbosilanes have been used to fabricate ceramic fibers and matrices through thermal and chemical processing. TEM results demonstrate that the particles of zirconium and products of its reactions with silicon, carbon, and nitrogen range in size from 10 to 20 nm in the oligomers and from 20 to 30 nm in the ceramics.     

The complex express evaluation of tribotechnical properties of antifriction aluminum alloys by sclerometric tests

The results of an investigation of experimental aluminum alloys proposed for replacing the highcost bronzes in friction units have been presented. The alloys were preliminarily selected using sclerometric tests based on the criterion of relative shear strength τ/σ_mc as being more informative compared with contact microcutting stress smc. Tribotechnical tests of selected alloys have been performed according to the three pins-on-disc scheme, which imitates the operation of the plane journal bearing. The results of tests confirmed the possibility of using these alloys as bronze substitutes. The structure and chemical composition of the surface of both initial samples and tested samples have been investigated. The influence of the chemical composition of the alloy on the tribotechnical properties of alloys under study has been shown.     

Mechanisms of friction of bicomponent coatings of thermodynamically incompatible metals produced using vapor condensation on cryogenic surfaces

Comparative tribotests of bicomponent Al–Pb and Al–Sn coatings produced using the codeposition of the metals from the vapor phase on glass substrates having room temperature and cooled to–100°С have been carried out. It has been found that changes in the mechanisms of the friction of the cryogenic coatings are related to conditions of their condensation. If the dimensions of the structure units of the coatings are similar, the tribological characteristics of these coatings are inversely proportional to the strength and the adhesion of their components. The most fusible metals are recommended for use as the solid-lubricating component of the coatings, since they have lower strength and surface energy.     

Glass transition and liquidus temperatures of low-alkali rubidium and cesium borosilicate glasses from the small-angle X-ray scattering data

Glasses and melts that contain 5 and 20 mol % Rb₂O in the rubidium borosilicate system and 6 mol % Cs₂O in the cesium borosilicate system are studied by the small-angle X-ray scattering (SAXS) technique. The glass transition and liquidus temperatures are determined from the temperature dependences of the SAXS intensity.     

Research of photocatalytic activity of the Ag/TiO2 catalysts in the reduction reaction of nitrate-ions in aqueous media

We have conducted a research of photocatalytic denitrification of water using modified titanium dioxide obtained by the sol-gel method. We demonstrated the possibility of photoprecipitation of silver particles under the effect of visual light. The use of formic acid as a donor of electrons makes it possible to substantially intensify the process and reduce the yield of a by-product—NH₄ ⁺. It was shown that in the presence of catalysts Ag/TiO₂ and irradiation time for 30 min is achieved a 96% conversion of nitrate ions.     

On the structure of glasses in the BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The structure of single-phase glasses in the BaO-B₂O₃-SiO₂ system has been studied by the large- and small-angle X-ray scattering techniques. The glasses containing 40 mol % BaO upon equimolar replacement of B₂O₃ by SiO₂ have been investigated. It has been demonstrated that the incorporation of barium ions into structural groupings fixes their position and provides ordering in the distribution of barium ions at interatomic distances up to at least 5 Å. The glasses under investigation are homogeneous, and their inhomogeneity is determined by thermal density fluctuations and fluctuations of the concentration of a part of barium ions distributed in a statistically random manner in the volume of the glass. The observed ordering in the distribution of barium ions is not reduced to the formation of local clusters with an increased concentration of barium ions but is most likely a characteristic feature of the bulk glass structure. The glass structure is consistent with the model of ideal associated solutions.     

Mass spectrometric investigation of the vaporization and thermodynamic properties of components in the BaO-SiO2 system

The vapor composition and thermodynamic properties of components in the BaO-SiO₂ system at a temperature of 1970 K are determined using high-temperature mass spectrometry. The thermodynamic properties of melts in the BaO-SiO₂ system are calculated within the framework of the vacancy variant of the generalized lattice theory of associated solutions. This made it possible to establish the relation between the thermodynamic properties and the structural features of melts in the BaO-SiO₂ system.     

Temperature dependences of the viscosity for some glasses in the Cs2O-B2O3-SiO2 system

The viscosities of glasses in the Cs₂O-B₂O₃-SiO₂ system are measured by the bending method on a quartz viscosimeter in the temperature range 300–670°C. The temperature dependences of the viscosity of the glasses under investigation are determined, and the temperatures corresponding to the viscosities equal to 10¹¹, 10¹², and 10¹³ P are calculated.