Porosity of aluminium oxide-based binary systems obtained by sol-gel method

A comparative study of binary oxide systems Al₂O₃-SnO₂; Al₂O₃-GeO₂ and Al₂O₃-B₂O₃ obtained by the sol-gel method has been made. Particular attention was paid to changes in the texture as a function of the type of the second component and its concentration in the binary system. Additionally, we describe changes in the porosity of the above systems after annealing in hydrogen atmosphere. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface modification of finely dispersed NaCl

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Recovery of finely dispersed gold from ores by biofloccular flotation

The possibility of selective heterocoagulation of Bacillus cereus B5039 cells and ultradispersed gold particles in the presence of other minerals is shown. It is established that the cell is the base element determining the charge of forming biomineral flocs and the composition of bound mineral components. The high efficiency of bioflotation in the processes of gold extraction from the dilute suspensions of gold-containing ores is revealed.     

Preparation and characterization of finely dispersed pigment particles

Dispersions of uniform colloidal pigments were produced by precipitating solutions of disodium salts of 2-amino, 5-methyl benzosulfonic acid (4B-dye), and 2-amino, 4-chloro, 5-methyl benzosulfonic acid (2B-dye) with Ca(NO₃)₂, SrCl₂, or Ca(NO₃)₂/SrCl₂ solutions in the absence and in the presence of additives (surfactants and alcohols). The latter affected the morphology of the particles, but had a negligible effect on their crystal structures. However, drying the Ca-4B pigment resulted in the change of the crystal phase and morphology. As a rule, the Sr-4B pigment was spheroidal, while Ca-4B, Ca-2B, and Ca/Sr-4B consisted of elongated particles.     

Environmental problems of finely dispersed titanium dioxide production

Finely dispersed titanium dioxide is widely used in modern technologies. Proved reserves of titanium ores in Russia are expected to meet industrial needs. However, the available facilities for the manufacture of titanium dioxide from ores are clearly insufficient, which naturally requires new plants to be put into operation. The technologies used for the production of titanium dioxide were developed as early as 1940s, when ecological aspects of the production process were almost not taken into account. The present survey analyzes environmental problems related to the titanium dioxide production according to the sulfate and chloride technologies in comparison with the fluoride process proposed for industrial implementation. The fluoride process has been examined as applied to ilmenite from the Turan deposit in Tomsk oblast, and some actions directed toward improvement of ecological parameters of this process have been proposed.     

A silica-silver nanocomposite obtained by sol-gel method in the presence of silver nanoparticles

Silver nanoparticles (AgNPs) were obtained by a redox reaction, using a glucose-containing cyclosiloxane as a reduction agent and stabilizer. Then the AgNPs aqueous solution was used as the reaction medium for the sol-gel process, starting from tetraethylorthosilicate (TEOS) as silica precursor. The nanocomposite material resulted (SilAg) after solvent removal, aging and calcination and was investigated by infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy coupled with energy dispersive X-ray system (SEM/EDX), transmission electron microscopy (TEM), energy-dispersive X-ray fluorescence spectroscopy (EDXRF), X-ray diffraction (XRD) and dynamic vapor sorption (DVS). The results were compared to model silicas obtained without silver. A higher condensation degree in SilAg was obtained due to the basic medium used in the first step and was confirmed by a sorption capacity lower than for the model silicas. The solid surface area calculated with GAB analysis using DVS data for the water vapors is 210 m² g^?1. The nanocomposite showed good catalytic activity for hydrogen peroxide decomposition.      

Structural analysis of mixed tin oxides produced by the sol-gel method

Mixed oxides SiO₂/SnO₂ with 80/20 nominal weight composition have been obtained by the sol-gel method with different precursors. X-ray diffraction and low temperature transmission Mössbauer spectroscopy have been used to follow the structural evolution of the samples after treatments in the temperature range RT-1050 °C. The main results are that changes in the precursor nature and gel preparation affect the Sn(IV) homogeneity in the SiO₂ matrix and that the use of Sn-alkoxides increases the content of residual carbon which promotes reduction of Sn(IV) at intermediate temperatures.     

Thermostability of glucose oxidase in silica gel obtained by sol-gel method and in solution studied by fluorimetric method

The thermostability of glucose oxidase entrapped in silica gel obtained by sol-gel method was studied by thermostimulated fluorescence of FAD at pH 5 and 7 and compared with that of the native enzyme in the solution and at the presence of ethanol. The unfolding temperatures were found to be lower for the enzyme immobilised in gel as compared with the native enzyme but higher as for the enzyme at the presence of ethanol. In gel, the thermal denaturation of glucose oxidase is independent on pH while in solution the enzyme is more stable at pH 5. The investigation the enzyme in different environment by steady-state fluorescence of FAD and tryptophan, synchronous fluorescence and time-resolved fluorescence of tryptophan indicates that the state of the molecule (tertiary structure and molecular dynamics) is different in gel and in solution. The ethanol produced during gel precursor hydrolysis is not the main factor influencing the thermostability of the enzyme but more important are interactions of the protein with the gel lattice.     

Preparation,structure and properties of silicate-phosphate glasses obtained by means of sol-gel method

Gels, densified amorphous materials and thin layers in SiO₂-P₂O₅, SiO₂-P₂O₅-Al₂O₃ and SiO₂-P₂O₅-Na₂O systems were obtained from alcohol solutions. Detailed DTA, XRD and FTIR investigations were carried out for dried gels and heat-treated samples. It has been found, among others, that the addition of aluminium to the silicate-phosphate glasses eliminates the doubly bonded oxygen (P=O) and leads to the formation of a continuous framework connected with [SiO₄], [PO₄] and [AlO₄] tetrahedra.There were measured the chemical and electrical properties of glasses covered with silicatephosphate gel layers. It has been found that the chemical resistance of the covered glasses is higher than that of the basic, sodium-calcium-silicate glass. Moreover, the silicate-phosphate layers modify the surface electrical conduction of the basic glasses. The layers of systems SiO₂-P₂O₅ and SiO₂-P₂O₅-Al₂O₃ show the electrical conduction considerable higher than the basic glass. The layers containing sodium, depending on its concentration, behave similarly to the basic glass or show lower electrical conductivity.     

Preparation of finely dispersed drugs. III. Cyclosporine

Two different precipitation processes are described, which produced dispersions of spherical particles of cyclosporine ranging in diameter from approximately 10 nm to several micrometers. This drug is of interest for its immunosuppressive activity in the antirejection of transplanted organs. The effects of several experimental parameters on the average particles size and uniformity have been investigated. Aging of spherical particles resulted in large crystalline-type aggregates.     

Effect of pseudoboehmite peptization by organic acids on texture characteristics of obtained aluminum oxides

The texture characteristics of aluminum hydroxides peptized by organic acids and then calcined were studied. A decrease in the pore volume and pore diameter for aluminum hydroxide was studied as a function of the amount of a peptizer. The calcination causes basic aluminum salts obtained by peptization to decompose at different temperatures, depending on the strength of a peptizing acid. The observed regularities were explained in terms of the thermal decomposition of organic aluminum salts of varied composition.     

Quantitative analysis of the fractionation of finely dispersed particles in a centrifugal separator

The kinetic characteristics of solid microparticles moving in the interdisk flow of a liquid separator with conical inserts were analyzed. On this basis, a technique was substantiated and calculation was performed for the process of isolation of particles with desired size from a finely dispersed powder in a liquid suspension.     

Surface structure of finely dispersed iron powders 4. Structure of a methylvinyldichlorosilane-modified coating

The surface structure of finely dispersed iron powders treated with methylvinyldichlorosilane vapors under vacuum has been examined by X-ray photoelectron spectroscopy, including chemical derivatization of functional groups. It is shown that the hydrolysis and condensation of modifier molecules lead to the formation of multilayer coatings (40–50 Å thick) consisting of methylvinyldichlorosilane oligomers. The modifier molecules are grafted onto the surface mainly owing to the formation of oxane Si---O---Fe bonds. A high degree of ordering is characteristic of the modifier molecules in the grafted layer, whereas a thin layer adjacent to the stabilizing coating surface exhibits a high extent of oligomerization of methylvinyldichlorosilane vinyl groups. Illumination (wavelength λ 35O nm) initiates the polymerization of vinyl groups in the grafted layer bulk. In this case the degree of oligomerization amounts to 80%.     

Photoelectrochemical properties of thin films on titanium obtained by thermal,electrochemical, or sol-gel method

Journal of Solid State Electrochemistry - The photosensitivity of the titanium dioxide films on titanium substrate formed by the electrochemical, thermal, or sol-gel method was compared under the...     

Blue-emitting ZnO sol and film obtained by sol-gel process

In this paper, bright blue-emitting ZnO sol and film were prepared by sol-gel process and the luminescent properties were investigated. The absorption spectrum of the sol consists of a wide band with two steps in the long wavelength region. The sol and film show a single wide blue-emission band under excitation of UV light, while the excitation spectra are composed by multiple bands. The quantum yield of the ZnO sol is 0.52 when the excitation wavelength is 348 nm. The particle size of the film is smaller than 10 nm, which results in the fine structure of the absorption and excitation spectra.     

Highly chemoselective hydrogenation method using novel finely dispersed palladium catalyst on silk-fibroin: its preparation and activity

A palladium-fibroin complex (Pd/Fib) was prepared by soaking silk-fibroin in MeOH solution of Pd(OAc)₂ for 2 days (under Ar atmosphere)—4 days (under air). Pd(OAc)₂ was gradually absorbed by fibroin and the rapid reduction of fibroin conjugated Pd(OAc)₂ proceeded with MeOH as a reductant at room temperature to be the Pd(0) complex. Pd/Fib catalyzed chemoselective hydrogenation of acetylenes, olefins and azides in the presence of aromatic ketones and aldehydes, halides, N-Cbz protective groups and benzyl esters which are readily hydrogenated using Pd/C or Pd/C(en) as a catalyst.     

Structural and dielectric characterization of LiNbO3 nano-size powders obtained by Pechini method

Lithium niobate is an artificially synthesized material with wide technological applications, due to its numerous physical properties, such as: ferroelectricity, birefringence and large pyroelectric, piezoelectric, non-linear, acousto-optic, electro-optic and photo-elastic coefficients. It also exhibits very strong bulk photovoltaic and photo refractive effects. In the present work, LiNbO₃ powders were prepared by the Pechini (sol?Cgel) method. The heat-treatment of the base amorphous powders, at 450?°C promotes the formation of LiNbO₃ crystalline phase. The electrical characterization, in function of the heat-treatment time, shows that the dc conductivity depends on the quantity of crystalline phase, which increases with the increase of heat-treatment time. The sample treated for 96?h shows a dielectric constant value of ~35, at low frequencies. A dielectric relaxation phenomenon independent of the temperature of measurement was detected in the samples treated at 48 and 96?h, shifting to higher frequencies with the increase of the heat-treatment time.     

Preparation and coating of finely dispersed drugs 4. Loratadine and danazol

The preparation of colloidal particles of different morphologies, including spheres, of two drugs, loratadine and danazol, is described. In principle these particles were obtained by precipitation when nonsolvents (water or aqueous surfactant solutions) were added to ethanol solutions of the drug. In addition, procedures were developed that made it possible to use the drug particles thus obtained as cores to be then coated with either silica or aluminum (hydrous) oxide layers. The presence of these inorganic shells was confirmed by electron microscopy, energy dispersive spectroscopy, and electrophoresis.     

Electron spin echo as a tool for investigation of surface structure of finely dispersed fractal solids

The ESE method was successfully used for investigating the texture of the adsorbents and catalysts. Equations were obtained for the kinetics of ESE signal decay due to dipole-dipole interaction between motionless paramagnetic centers distributed uniformly on the fractal surface of solid.

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Flexible free-standing films morphology characterization: PVA/silica polymer network dispersed cholesteric liquid crystals films by sol-gel method

A novel flexible free-standing films of polyvinyl alcohol (PVA)/silica polymer network dispersed cholesteric liquid crystals (CLC) have been prepared by the sol-gel process. In the hydrolysis of silicon alkoxides tetraethoxysilane (TEOS) processes, the silica having -OH with the -OH groups on PVA formed polymer networks with Si-O-C bonds by dehydration. The cholesteric liquid crystals were incorporated into the networks. The free-standing films were obtained by the spin-coating method. In order to improve the compatibility and microstructure of the cholesteric liquid crystals with PVA/silica polymer networks, the amphiphilic compound of hexadecyl trimethyl ammonium bromide (HDTMA) was introduced into the forming film solutions. Effects of the different ratios of raw materials on the structure of films were investigated. The microscopic morphology of free-standing films and the uniform dispersion of CLCs in the films have been characterized by polarizing optical microscopy (POM), the field emission scanning electron microscope (FESEM), Fourier transform infrared (FT-IR) spectrometer and atomic force microscope (AFM). The free-standing films exhibiting excellent CLC droplets dispersion, mechanical stability, and good flexibility could be useful for flexible displays, switchable optical elements and smart windows.