E. K. Papynov

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.

Production of porous ceramic materials using nanodisperse SiC powder

Porous ceramic materials were produced by hot pressing of a nanocrystalline (19 nm) silicon carbide powder synthesized by a hybrid method that combined the sol–gel processing of a finely divided and chemically reactive SiO2–C system and the carbothermic synthesis at moderate (1400°C) temperature in a vacuum. It was studied how such characteristics as density, porosity, sizes of crystallites and aggregates of SiC particles, specific surface area, and compressive strength depend on pressing temperature (1400, 1500, 1600, and 1700°C).

Uranium sorption on reduced porous iron oxides

The sorption properties of materials based on iron oxides and their reduced forms with respect to uranium were studied. A description was made of a method for consolidation of porous iron oxides and its effect on such characteristics as porosity, magnetism, morphology, phase composition, and sorption properties. The mechanism of uranium sorption on the obtained materials was determined. The interaction of the studied sorbents with uranium was shown to change, depending on the phase composition and the structure of the solid matrix.

Spark Plasma Sintering as a high-tech approach in a new generation of synthesis of nanostructured functional ceramics

The results of Spark Plasma Sintering (SPS) synthesis of different types of ceramic materials for various industrial applications are presented. A high quality of ceramics is achieved through the originality of the developed approach based on combining SPS technology with other methods of inorganic synthesis, for instance, with sol–gel technology. The suggested approach enables one to synthesize, at the first stage, nanostructured powders of inorganic materials, whose subsequent consolidation by the SPS method ensures the formation of nanostructured ceramics with unique physicochemical characteristics and properties.

Wollastonite ceramics with bimodal porous structures prepared by sol–gel and SPS techniques

In this work, we suggest a novel synthetic route combining sol–gel and SPS for the fabrication of porous ceramics based on wollastonite with bimodal pore size distributions (100–500 nm and 1–500 μm) and high mechanical strength (Youngs modulus from 72.5 to 172 MPa). We studied peculiarities in the formation of the biporous silicate framework using two types of pore forming additives (templates) of various natures, shapes and sizes, introduced during different stages of sol–gel and SPS synthesis: organo-nonorganic (polymer latex of “core–shell” type) and nonorganic (carbonaceous filler). The influence of carbonaceous template content (5% or 25%) on the structural and mechanical properties of ceramics synthesized by spark plasma current was described. The original approach presented here provides formation of wollastonite ceramics with high mechanical strength and a biporous structure that is similar to the texture of bone tissue and is capable of executing its main functions. The obtained ceramics meet all the requirements of the bioceramics class demanded by modern medicine.

Study of the Thermal Behavior of Wedge-Shaped Samples of HfB 2 –45 vol % SiC Ultra-High-Temperature Composite in a High-Enthalpy Air Flow

By spark plasma sintering, HfB2–45 vol % SiC ultra-high-temperature ceramic was prepared, from which wedge-shaped samples were cut. The behavior of the samples was examined in a flow of dissociated air produced by an induction plasmatron, where the surface temperature of the leading edges of the samples reached ~2700°C. The dependence of the temperature distribution gradient on the distance from the leading edges of the samples was experimentally investigated. For the samples after the experiments, the elemental and phase compositions were determined, and features of the surface microstructure in various regions of the sample and on its polished surface were studied.

Chemical modification of natural clays

Natural clay samples and calcined clay varieties treated with hydrochloric acid of various strengths were characterized by X-ray diffraction, positron annihilation spectroscopy, and IR spectroscopy. The specific surfaces and pore sizes were determined by nitrogen adsorption. The constituent phases of the clay were found to be nontronite, muscovite, quartz, and hematite; after calcination, quartz, muscovite, hematite, and an amorphous phase remained in the samples. The Brilliant Green adsorption properties and tribotechnical properties of the modified clays were studied. The natural clay was surface-modified chemically by means of consecutive exposure to 36.5% hydrochloric acid and an alkaline hydrolyzate of rice hulls. Calcination at 700°С destroyed the amorphous phase to a greater extent; exposure to acid provided a greater recovery of aluminum and iron ions from the surface of calcined samples. Native clay composites with an alkaline hydrolyzate of rice hulls were shown to have enhanced tribotechnical characteristics.

Processes for treatment of liquid radioactive waste containing seawater

The main sources of formation of liquid radioactive waste (LRW) containing seawater are determined, and the main problems arising in management of such waste are analyzed. Sorption methods for removing long-lived Cs and Sr radionuclides from highly mineralized (>1 g L–1) LRW are determined. The main physicochemical and sorption characteristics, advantages, and drawbacks of candidate sorbents for removing Cs and Sr radionuclides are described. Examples of using SRM and VS-5 chemical reaction sorption materials developed for removing Sr from LRW with the mineralization of up to 60 g L–1 are given. The results of studying composite materials based on BaSiO3 and resorcinol–formaldehyde resins, intended for removing Cs and Sr radionuclides from seawater, are analyzed. Composite sorbents of such type efficiently remove Cs and Sr radionuclides from seawater. Processes developed by the authors and brought into practice at various plants of the Far East for treatment of multicomponent LRW formed in the course of operation, repair, and decommissioning of nuclear-powered surface ships and submarines are described.

Quantum chemistry and experimental studies of hydrothermal destruction of Co-EDTA complexes

Hydrothermal oxidation, a promising method for removal of cobalt radionuclides from EDTA-containing liquid radioactive waste streams, is in the focus of the present study. It has been demonstrated that Co(III)-EDTA complexes, which are very stable under normal conditions, undergo oxidation as a result of the electron transfer from the EDTA carboxyl group to Co(III) ions under elevated temperature. The electron transfer reaction follows the first-order rate law with an activation energy of 91.8 kJ/mol at рH 12 and time of Co(III) ions half-conversion of 0.2 s at 200 °C. The rate of EDTA oxidation is proportional to the concentration of Co(III) ions and solution pH. Based on quantum chemistry simulations, possible intermediate structures formed upon the electron transfer from EDTA to Co(III) ions have been suggested. It has been shown that the introduction of hydrogen peroxide provides a continuous generation of Co(III) ions and a sequential decarboxylation of the EDTA until complete degradation of the chelate structure. The pathways of cobalt immobilization have been clarified.

Sorption of phosphates on macroporous synthetic calcium silicates

The sorption of phosphate ions on macroporous synthetic calcium silicates has been studied and it has been evaluated whether the latter are suitable to serve as sorbents of geochemical barriers preventing phosphorus losses from agricultural soils.