T. V. Khamova

Kinetics of structuring in the sol-gel systems based on tetraethoxysilane with organic additives: I. Sols

This paper reports on the results of rheological investigations into the kinetics of gelation of the sol-gel systems based on a water-alcohol solution of tetraethoxysilane (TEOS) modified by a number of metal salts and organic polyhydroxyl compounds, such as glycerol, poly(ethylene glycol) (PEG-300), and hyperbranched aliphatic complex polyol polyethers (HBP-49, HBP-64). It is demonstrated that, at a dispersed phase concentration of approximately 10 wt %, water-ethanol sol-gel systems containing 2–4 g/l of high-molecular additives possess a shear strength and are characterized by anomalous properties in their flow. The gelation time of sols in the presence of organic additives is affected by the ratio between the numbers of OH− hydrophilic and CH3 hydrophobic groups in the polymer molecule, the concentration of the introduced additive, and the electrolyte multivalence. The presence of metal salts enhances the structuring effect of polymers.

Investigation of the structuring in the Sol-Gel systems based on tetraethoxysilane

The kinetics of change in the dynamic and structural viscosity of a number of silica sols based on tetraethoxysilane, including sols doped with aluminum and cobalt nitrates, is investigated. The results obtained are analyzed in the framework of the Derjaguin-Landau-Verwey-Overbeek theory. It is revealed that structural forces make a considerable contribution to the stability and structuring processes in these systems. The structuring in a rapidly gelating homogeneous heterophase dispersion formed by finely dispersed α-Al2O3 particles in the silica sol doped with aluminum and cobalt nitrates is examined, and the assumptions regarding the mechanism of the structuring processes occurring in this system are made.

Sol-gel synthesis and fluorescence properties of hybrid nanocomposite materials doped with the Nile Red dye

The hybrid organic-inorganic materials with optical properties are synthesized in the form of gels and thin-layer coatings by the sol-gel method. The fluorescence of the materials synthesized is investigated as a function of the Nile Red concentration and the composition of the precursors forming the hybrid sol-gel matrices. It is demonstrated that the materials synthesized hold much promise for use in the fabrication of optical gas sensors.

Influence of the composition and structure of epoxy siloxane matrix on the spectral behavior of the nile red dye: I. Sol-gel system based on tetraethoxysilane and a mixture of epoxy resins

The hybrid organic-inorganic materials with fluorescence properties are synthesized in the form of gels and xerogels from tetraethoxysilane and a mixture of epoxy resins by the sol-gel method. The concentration of the introduced Nile Red dye is 1.6 × 10−6M. The fluorescence spectra of the prepared materials are measured and analyzed as a function of the ratio between the initial components forming the sol-gel epoxy siloxane matrices. The assumption regarding the structure of the synthesized hybrids is made invoking the data obtained by Fourier-transform IR spectroscopy and atomic-force microscopy.

Sol-gel synthesis and the study of the surface of epoxide-siloxane and epoxide-titanate coatings

Three compositions based on epoxide-siloxane, epoxide-titanate, modified epoxide-titanate sols have been synthesized by the sol-gel method, and the morphology of surface and the hydrophobicity of coatings obtained on their basis has been studied. According to the results of the studies, the compositions of the coatings have been chosen for the conduction of tests on a rotor of high-rpm miniturbogenerator, with the aim to determine the effect of aerodynamic losses.

Synthesis and study of mesoporous xerogels and nanopowders of a metastable solid solution 97ZrO2–3Y2O3 for the fabrication of catalyst substrates

The—technology of the liquid-phase synthesis of metastable phases in the ZrO2–Y2O3 system has been developed. Mesoporous xerogels with the specific surface area of ~350 m2/g and monophase nanopowders (5–10 nm) of the tetragonal solid solution (ZrO2)0.97(Y2O3)0.03 have been obtained and their structural peculiarities have been revealed. The efficiency of the suggested technology and good prospects of the synthesized ZrO2-based precursors in creating catalysts’ substrates have been demonstrated.

Improvement of dielectric characteristics of cyanoethyl ether of polyvinyl alcohol-BaTiO3 composites by modifying filler surface

The effect of modifying the surface of submicron barium titanate by pure silica sol and silica sol mixed with Al(NO3)3 on the dielectric characteristics of composites produced by introducing modified BaTiO3 to cyanoethyl ether of polyvinyl alcohol is studied. An increase in the dielectric permittivity and a decrease in the dielectric loss of the composites are achieved through modifying the surface of BaTiO3 by applying a SiO2 layer. On the contrary, the simple hydration of BaTiO3 and the application of a SiO2-Al2O3 mixed layer lead to a sharp drop of the dielectric characteristics of the composite.

Investigation of the surface of silica films doped with Fe and Co

The silica films prepared from tetraethoxysilane sols and doped with iron and/or cobalt nitrates are investigated using atomic-force microscopy and Auger electron spectroscopy. The influence of the metal nature on the surface morphology of the films and the specific features of the distribution of doping elements over the film thickness are demonstrated.

Influence of a high-frequency field on the formation of photosensitive thin-film materials synthesized by the sol-gel method

This paper reports on the results of investigations of the possibility of applying a high-frequency field for the formation of thin-film coatings from sols based on an aqueous-alcoholic solution of tetraethoxysilane, lead nitrate Pb(NO3)2, and selenious acid H2SeO3 with the use of the centrifugation method. A comparison is made of the data obtained from differential thermal analysis, X-ray powder diffraction analysis, optical microscopy, and atomic-force microscopy of the composites and thin-film coatings formed under thermal and microwave treatment. It is demonstrated that the application of high-frequency fields makes it possible to activate the physicochemical processes and to expand the range of use of the sol-gel technology for the formation of thin-film coatings on dielectric materials under the conditions which exclude a strong thermal effect.

Porous ceramics based on the ZrO2(Y2O3)–Al2O3 system for filtration membranes

The results of the studies of the process of fabricating ceramic filtration membranes in the system ZrO2(Y2O3)–Al2O3 are presented. The phase compositions of the precursor powders and sintered ceramics have been investigated and their porous structures have been determined. Two stages of the implementation of the technology were demonstrated: fabrication of substrates with an open porosity ranging from 20 to 47% and pore sizes in the 100–300 nm range, as well as the deposition of nanocrystalline aluminum oxide layers on them. It has been established that the pore size distribution in the membrane layer of α-Al2O3 is unimodal (from 30 to 100 nm).