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  • Methods of synthesis, properties and application of silica-zols for obtaining composite materials Part I

    The article considers examples of obtaining silica sols by ion-exchange methods. An analysis was made of the factors of this method that affect the properties of the resulting sols. The principal technological scheme of an industrial plant for the production of silica-sol by an ion-exchange method were considered. The results of studies of the sol-gel transition in silica-sol obtained by the ion exchange method were presented. The growth kinetics of colloidal silica-sol particles, which were obtained from solutions of polysilicic acid, was investigated. The dependence of the growth kinetics of colloidal particles from solutions of polysilicic acid on the temperature and on the initial pH of the sol was shown. The dependence of the gel time on the dimensions of the colloidal particles in the ash, on temperature, concentration and pH, was shown. The effect of the composition of the liquid phase on the stability of silica sols was established. Influence of the charcoal characteristics on the properties of the xerogels obtained. The effect of silica powder on the properties of the xerogels obtained was analyzed. An analysis of the possibilities of the practical application of silica powder as a binder in the preparation of heat-resistant heat-shielding composite materials was carried out.

    Keywords: silica-sol, ion exchange, sol-gel technology, stability of sols, xerogels, composite materials

  • Methods of synthesis, properties and application of silica-zols for obtaining composite materials Part I

    The article considers examples of obtaining silica sols by ion-exchange methods. An analysis was made of the factors of this method that affect the properties of the resulting sols. The principal technological scheme of an industrial plant for the production of silica-sol by an ion-exchange method were considered. The results of studies of the sol-gel transition in silica-sol obtained by the ion exchange method were presented. The growth kinetics of colloidal silica-sol particles, which were obtained from solutions of polysilicic acid, was investigated. The dependence of the growth kinetics of colloidal particles from solutions of polysilicic acid on the temperature and on the initial pH of the sol was shown. The dependence of the gel time on the dimensions of the colloidal particles in the ash, on temperature, concentration and pH, was shown. The effect of the composition of the liquid phase on the stability of silica sols was established. Influence of the charcoal characteristics on the properties of the xerogels obtained. The effect of silica powder on the properties of the xerogels obtained was analyzed. An analysis of the possibilities of the practical application of silica powder as a binder in the preparation of heat-resistant heat-shielding composite materials was carried out.

    Keywords: silica-sol, ion exchange, sol-gel technology, stability of sols, xerogels, composite materials

  • Self-consistent model of the sol-gel process of film formation on substrates with homogeneous precipitation of particles of hydrated oxides

    This article analyzes the regularities of precipitation of solid colloidal particles of hydrated metal oxides on the surface of various substrates. Two models of this process are proposed. The proposed α-model is a process of continuous nucleation of interaction centers, at random points of a free surface throughout the process. The proposed β-model provides for the instantaneous nucleation of these centers when they are randomly distributed over the entire surface of the substrate. Based on the proposed models, the average values of the following values are calculated: the thickness of the gel film; its roughness and specific surface area. The calculations carried out in the article showed that these parameters are universal functions of the degree of filling of the surface and do not depend on the specific model of the mechanism of the process.

    Keywords: modeling, homogeneous precipitation, formation of thin films, sorbents, catalysts, heat-resistant composites

  • Purification of wastewaters using matrix-isolated nanocomposite flocculant-coagulants

    This work relates to the technology of inorganic substances. It can be used in the production of aluminum-silicon and iron-silicon flocculants-coagulants. With their help, methods for treating wastewater from industrial enterprises, as well as storm water containing oil products. In this paper, concrete examples of the research results on the purification of natural, industrial and oily wastewater. With the use of new nanocomposite silica-alumina and iron-silicon flocculants-coagulants ASFC and ISFC, obtained by the new technology. The authors have developed and patented the technology of obtaining flocculants-coagulants of this type in solid form. Method of matrix isolation of active components has been used to prepare such composite materials. Performance evaluation was given to the action of coagulants, flocculants and ASFC ISFC. A comparison was made with the new composite materials commonly used for these purposes the conventional art, coagulants - aluminum sulphate and iron sulphate. With their help, the methods of treating wastewater from industrial enterprises, as well as storm water containing oil products. An assessment was made of the effectiveness of the action of coagulant flocculants ASFC and ISFC on real industrial wastewater.

    Keywords: reagent purification of water, Natural water, Wastewater, Flocculants-coagulants, Matrix isolation, Nanocomposites; ASFC, ISFC

  • Homogeneous precipitation of aluminum hydrous oxide and its application for obtaining composite materials

    The paper presents the results of studies of the process of hydrated alumina homogeneous precipitation. The variants of this process are considered. As the most convenient embodiment of this process, precipitation of hydrated alumina from its salts using auxiliary substances. As such auxiliary substances, it is proposed to use urea. Urea hydrolysis proceeds slowly even with heating, which allows a homogeneous precipitation process under the most mild conditions. It is shown that the process of hydrolytic precipitation in the aluminum salt-urea system proceeds according to the dissociative mechanism SN1. For SN1, a two-step mechanism is characteristic, in which the first step is slow monomolecular hydrolytic dissociation, followed by a rapid coordination reaction with the second reagent. To determine the nature of the interaction of the aluminum salt with alkaline agents, experiments were conducted on potentiometric titration of the aluminum salt with solutions of ammonia and sodium hydroxide in the presence of various amounts of ammonium chloride and urea. When titrating with sodium hydroxide solution, the process proceeds to the formation of sodium aluminate, titration with a solution of ammonia produces a precipitate of hydrated alumina. Addition of ammonium salts shifts the equilibrium of the hydrolysis reaction towards the formation of aluminum hydroxide. The presence of urea virtually does not affect the course of the deposition process. To determine the uniformity of the formed sediment, the laser radiation scattering method. For these purposes, a special installation has been created that allows the capillary to be scanned through a focused laser beam. The homogeneity of the hydrated alumina precipitate formed was shown. Studies have been carried out on the use of homogeneously precipitated aluminum hydroxide as a binder in lightweight fibrous refractory materials. The process of precipitation of aluminum hydroxide particles proceeds primarily on the filler fibers, covering them with a thin film. The resulting film acts as a gluing agent. After drying and calcination, the gel deposited by the thin film becomes a solid that binds the fibers into a single monolith. The resulting materials have a developed specific surface area and porosity.

    Keywords: homogeneous precipitation, hydrated alumina, composite materials, urea