Vol 8, No 5 (2017)

The review concerns some problems of hydrogen in the main reactor structural materials used in the core of nuclear reactors. Zirconium alloys, steels, and vanadium alloys, as well as the hydrogen and helium synergetic effect exerted on the radiation resistance, are considered. The main sources resulting in the accumulation of hydrogen isotopes in reactor materials are discussed. The causes and consequences of hydride embrittlement of zirconium alloys at relatively low temperatures are analyzed. It is shown that hydrogen can induce the embrittlement of vessel steels through the weakening interatomic bond forces and a stabilization of radiation-induced defects. It is demonstrated that hydrogen in the presence of helium behaves like a gas that enhances the irradiation effect on the microstructure and properties of materials in many cases. The irradiation with simultaneous introduction of hydrogen and helium causes, in particular, a catastrophic swelling of chromium steels and vanadium alloys, whereas in the case of austenitic steel the effect is less pronounced.

The kinetic parameters of curing of the binder VSK-14-2m are determined. The heat release power in the specified hardening regime in the temperature range from 100 up to 200°C is estimated on the basis of the obtained data. A mathematical model of heat transfer when forming the thick-walled fiberglass plate is proposed. Temperature differences of the outer and middle layers of the plate and temperature gradients over the plate thickness are revealed—significant temperature differences of the outer and middle layers of the plate (more than 30°C) and temperature gradients of layers (more than 7 K/mm) are observed, resulting in decrease in mechanical characteristics. Comparison of theoretical and experimental data on the temperature distribution over the plate thickness is performed. The level of correlation with each other is 99.5%.

The effect of the conditions of ammonolysis of mesoporous magnesiothermic tantalum powders with the specific surface area of 56–63 m² g^–1 on phase composition and specific surface area of the products is studied in the temperature range of 400–900°C. The ammonolysis products are shown to be X-ray amorphous at 400–600°C. At the heating rate of 20 K/min, the nitrogen content in these products is 5.4–7.3% and the specific surface area is 42–35 m² g^–1, while at heating rate of 8 K/min these parameters are 2.4–5.4% and 56–49 m² g^–1, respectively. The crystalline phase of tantalum oxynitride TaON is formed at a temperature of 700°C and above. The resulting materials exhibit a high photocatalytic activity in the reactions of ferroin and methylene blue degradation under irradiation with visible light (λ ≥ 420 nm).

In LiNbO₃:ZnО crystals grown from melts containing ~4.0–9.0 mol % ZnO, the evolution of structure was studied, the lattice periods were detected, and the models of atomic structure were analyzed. Raman spectroscopy and full-profile analysis of XRD patterns were used to obtain the results. The rise in ZnO concentration in the melt from 4.0 to ~6.99 mol % leads to the decrease in the unit cell volume of the crystals. The further rise in ZnO concentration in the melt to ~7.8 mol % results in the increase in the unit cell volume of the crystals. Refinement of the profile characteristics of XRD patterns and structural characteristics of the researched crystal samples was performed by the Rietveld method using the PDWin software package. All samples were considered single-phase, taking into consideration the absence of intense bands coinciding with the lithium niobate bands. Zn²⁺ cations were detected to occupy Li sites (which are vacant in the congruent LiNbO₃ crystal). In this case, Nb vacancies are absent. Zinc displaces all excess Nb atoms in Li sites. In the sample grown from melt with ~6.12 mol % ZnO. In this case, Li vacancies and electroneutrality stay the same in the sample. Thus, NbLi antistructure defects are absent in the LiNbO₃:ZnО crystal (~6.12 mol % ZnО in the melt). In LiNbO₃:ZnО crystals with higher ZnO concentration, NbLi antistructure defects appear again. In this case, the concentration of Zn in Li sites almost coincides with the one in the LiNbO₃:ZnО crystal. Unit cell parameters are equal in crystals grown from melts with ~7.8 and ~6.76 mol %. The biggest changes in the Raman spectra of these crystals are observed in the regions of vibrations of cations (200–300 cm^–1) located in oxygen octahedra ВО6 (В: Nb⁵⁺, Li⁺, Zn²⁺) and in the region of vibrations of oxygen atoms in oxygen octahedra (500–900 cm^–1). This indicates a change in order of alteration of intrinsic, doping cations and vacancies along the polar axis and deformation of oxygen octahedra during doping. This corresponds to anisotropic expansion of oxygen octahedra along the polar axis in LiNbO₃:ZnО crystals.

Combined cement matrixes are proposed for petrification of organic liquid radioactive liquid wastes (spent tributyl phosphate in hydrocarbon solvent, process oil) containing radionuclides ¹³⁷Cs and ⁹⁰Sr. The high level of filling of the matrixes with waste is achieved by premixing thermally expanded graphite with the latter. To confine cesium firmly, bentonite clay additions with a montmorillonite content not less than 65 vol % should be included in the compounds. It is demonstrated that the desired content of extracting agent in the compound is 25 vol % and that of oil is 20 vol %. The minimum time of aging of the compounds before transportation for long-term storage or burial should be not less than 42 days from the moment of cement mixing. The moisture-resistant enamel coating of the surface of compounds does not prevent substantial diffusion of ¹³⁷Cs. However, it slows down the water absorption by the cement, thus postponing the beginning of transition ¹³⁷Cs and other radionuclides to the liquid phase. The strength of the compounds obtained in the paper complies with the standardized values (GOST R 51883-2002). The average leaching rate of ¹³⁷Cs is not more than 1 mg/(cm² day) and that of ⁹⁰Sr + ⁹⁰Y is not more than 0.1 mg/(cm² day). The leaching kinetics of cesium radionuclides from the compound has a diffusive character. The leaching kinetics of strontium and yttrium radionuclides from the compound has a sorption-desorption character. The leaching rates of radionuclides of elements of groups I, II, and III form the following series: R(¹³⁷Cs) > R(⁹⁰Sr) ≫ R(⁹⁰Y).

Modification of the polyester fabric using the diluted suspension of nanosized titanium dioxide is shown to make the fabric capable of decomposing the adsorbed contaminants under irradiation. The effect of different types of preactivation of polyester material on the self-cleaning ability of the fabrics is investigated. Chemical preactivation and preactivation using surface barrier discharge plasma additionally enhances the photochemical activity of the modified fabrics. The resistance of the achieved effect to operational impacts, such as washing and dry friction, is estimated and is found to be satisfactory. Modification of polyester fabrics using nanosized titanium dioxide protects it against intense UV radiation.

The effect of low-temperature aging of ceramics Zr_0.97Y_0.03O₂ (Y-TZP) and Zr_0.98Y_0.02O₂ (Yb-TZP) by the methods of the high-grade diffraction analysis and atomic force microckopy is studied. Formation of the phase M-ZrO₂ in ceramic (Y-TZP) in a large quantity after hydrothermal impact in subsurface layers of ceramic samples is shown. A positive effect of the stabilizing cation Yb⁺³ on the phase composition stability and strength properties of ceramic based on T-ZrO₂ is registered. Adaptation of the structural ceramic based on T-ZrO₂ according to medical requirements is the aim of this study.

The method of obtaining highly porous ceramics by chemical transformation of ceramics based on α-tricalcium phosphate (TCP) to dicalcium phosphate dihydrate (DCPD) followed by hydrolysis to octacalcium (OCP) phosphate was explored. This method provides an opportunity to get monophase OCP as well as biphasic calcium phosphate with a different ratio of α-TCP/DCPD or DCPD/OCP. The microstructure and mechanical properties depending on the phase composition and processes in held conditions were studied. Using this method makes it possible to increase the compressive strength by up to 7 times because of morphological modifications inside the crystals.

The effect of water-soluble polymer—chitosan succinamide—on surface activity of such commonly used surfactants as anionic sodium dodecylsulfate and nonionic TWEEN-80 is investigated. It is shown that the combined use of sodium dodecylsulfate and TWEEN-80 with chitosan succinamide increases the surface activity of the investigated surfactants. It is found that the association of chitosan succinamide with sodium dodecylsulfate or TWEEN-80 begins at concentrations an order of magnitude lower than the critical micelle concentration of studied surfactants. The fact of reduction in the dynamic viscosity of the solution of chitosan succinamide in the presence of both ionic and nonionic surfactants, apparently owing to the formation of polymer-colloid complexes, is revealed. The obtained systems have a stabilizing effect on the membrane of red blood cells in stringent hypotonic conditions, which may indicate a decrease in the adverse effect of surfactants on the skin.

The porous structure and physicochemical properties of aerogel type composites on the basis of polyvinyl alcohol/carbon black obtained by gas cryotreatment of a foamed composite are studied. The materials consist of more than 50 wt % carbon and have a real density of no less than 0.79 g/cm³ (the bulk density is less than 0.27 g/cm³). It is found that the molecular weight of polyvinyl alcohol and the presence of sodium tetraborate affect the size of the macropores of aerogel type composites, while carbon black does not affect this parameter. The dependence of the specific surface area of carbon black and average size of the macropores of aerogel type composites on their specific surface area is found. The thermal stability of the materials does not depend on their composition and synthesis conditions and falls within the range of 260–280°C. The thermal conductivity of the aerogel type composites on the basis of polyvinyl alcohol/carbon black is in the range of 33–59 mW/(m K). These materials are recommended for application as heat insulators.

This article discusses the microstructure and mechanical properties under compression and resistance against oxidation of Mo–9Si–8B (at %) alloy fabricated by casting. Despite generation of coarse dendritic structure, the as-cast alloy demonstrates excellent high-temperature strength: the alloy yield strength at 1200°C is 700 MPa, and the maximum compression strength is 750 MPa, which is significantly higher than the strength properties at this temperature of the top quality heat-resistant alloys on the basis of nickel. The article considers possible improvements of the alloy resistance against oxidation by disintegrating the dendritic structure and obtaining a fine-grained structure, which promotes a more uniform distribution in the bulk of the matrix phase and disperse intermetallic phases.

Two compounds with a layered structure of FeSe_0.88 superconductor and MoS₂ semiconductor are intercalated with molecular hydrogen (H₂) and ionized hydrogen (H⁺) formed in a special ion source. In the case of FeSe_0.88, intercalation with hydrogen ions causes a slight increase in the superconducting transition temperature of the compound. It is noteworthy that the temperature of the middle of superconducting transition Т_cm of this system can be a little higher on account of magnetization of the FeSe ferromagnetic phase (in a field up to 0.1 T) being in the contact with it. Hydrogen intercalation of MoS₂ is accompanied by an increase in the weight of the compound, and the lattice parameter c associated with the interlayer distance increases from 12.241(6) to 12.297(5) Å. At the same time, along with the existing van der Waals forces, one observes the emergence of Н bonds, which leads to the formation of MoS₂H_0.38 hydride and to an abrupt change in specific resistance (by an order of magnitude) relative to its value before hydrogen intercalation.

The aluminides with compositions Al₁₃Co₄, Al₁₃Fe₄, Al₁₃Co₂Fe₂, and Al₃Ti are synthesized in air after mechanical activation of the precursor metals followed by thermosynthesis. The phase compositions of the synthesized aluminides as well as Al₁₃Co₄/SiO₂, Al₁₃Fe₄/SiO₂, and Al₃Ti/SiO₂ composites are analyzed before and after partial oxidation of methane (POM). According to the X-ray powder diffraction data, Al₁₃Co₄ crystallizes as the Y phase. During POM, the Z phase with low content of aluminum is formed along with the Y phase. The Al₁₃Fe₄ sample is the eutectic mixture of the Al_13–xFe₄ monoclinic M phase and aluminum, but the Al₁₃Co₂Fe₂ solid solution crystallizes as the homogeneous M phase. The formation of Al₃Ti in air is accompanied by oxidation. With SiO₂ as a substrate, intermetallics Al₁₃Co₄ and Al₁₃Fe₄, albeit corrosion-resistant to atmospheric oxygen up to 600°C, decompose to form corundum Al₂O₃, mullite Al₆Si₂O₁₃, and silicides CoSi₂, CoSi, Co₂Si, FeSi₂, and Fe₃Si. The phase transformations occurring during the coannealing of Al₁₃Co₄ and Al₁₃Fe₄ with SiO₂ are described by irreversible reactions. The aluminide Al₃Ti does not form silicides during the contact with SiO₂, and the phase composition of the 3Al–Ti–1.5SiO₂ composite does not change during POM.

The paper considers possible use of aluminum production waste (recycled cryolite Na₃AlF₆) and quartz sand (SiO₂) as the main reagents in the synthesis of mica-crystalline materials based on fluorphlogopite under ambient conditions. The combustion process is shown to depend on the energy additive in the initial mixture and occurs at a rate of 2–5 mm/s in the temperature range of ~700 to 1600°C. The identity of the SHS-fluorphlogopite and pyrogenic fluorphlogopite structures is established. The conditions that allow synthesizing fluorphlogopites with the final product melting in the combustion wave or without it are determined. It appears to be possible to synthesize items by a direct method from dense (2.57 g/cm³) and porous materials based on SHS fluorphlogopites. The possibility of synthesizing materials with the open porosity of up to 35% is demonstrated. A material based on monoclinic sodium fluorphlogopites of NaMg₃AlSi₃O₁₀F₂ and Na₄Mg₆Al₄Si₄O₂₀F₄ compositions is obtained. The results of investigations can be used to develop the SHS technology of item production from mica-crystalline materials.

It is shown that one of the promising directions for the production of thermal insulation materials are waste coal (waste of the fuel and energy complex). Insulation materials (ceramic lightweight bricks) with the density not higher than 1250 kg/m³ were derived from waste coal without using the traditional natural raw materials. The innovative proposals for the use of waste coal in the manufacture of insulation materials were developed and their novelty was confirmed by four RF Patents. The investigated coal waste is characterized by high calorific value (1800–2800 kcal/kg); thus, such waste should be used not only as nonplastic materials but also as combustible additives so as to exclude the use of anthracite, coke breeze, etc., in the compositions of ceramic masses. Combustible additives containing increased amounts of organic compounds (the loss of ignition of >15%) and iron oxide (Fe₂O₃ of more than 3%) not only increase the porosity of ceramic products but also facilitate the uniform sintering of a ceramic crock. It was shown that there are three types of pores that mainly occur in samples of insulation materials: slitlike ones, isothermal ones, and bizarre pores. In addition, the samples contain relatively large oval pores and “channel” isometric pores. These pores determine the water absorption of ceramic materials. The presence of pores and, consequently, the heterogeneity of the material adversely affect the properties of ceramic products, and the harmful effect on the mechanical strength of the elongated (slitlike) pores is estimated at about 5 times higher than that for round ones. In addition, the presence of slit-shaped pores indicates the incompleteness of the sintering processes. The use of waste from the fuel and energy complex in the production of ceramic materials makes it possible to efficiently utilize industrial waste, to save scarce traditional natural materials, to expand the range of raw materials for construction materials, and to make a significant contribution to environmental protection.

The critical task for the manufacturing process management of metal-metal oxide catalysts (as exemplified by Co–Mo/Al₂O₃–MgO) for the synthesis of carbon nanotubes (CNT) was solved with application of a new technology. The following main characteristic groups of the catalytic systems determining their quality were identified and discussed: physical and mechanical (bulk density and tapped density; repose, tapped, and collapse angles), the degree of feedstock conversion (shares of the mass loss during heating and calcination), the catalyst activity (the CNT specific yield by the catalyst and their specific surface), and indirect indicators (pH of the aqueous suspension and the true density). Methods and modes of the study selected parameters of the catalyst were experimentally proved and analytical equipment was recommended. A new control factor of the thermal decomposition stage of the catalyst was identified. It is the specific consumption of dehydrated air. Its impact on the catalyst performance was shown. Necessary and sufficient specific consumption for the catalyst Co–Mo/Al₂O₃–MgO making it possible to stabilize the quality indicators was determined, which is equal to 55 kg_air/kg_catalyst. Metrological approaches to the certification of the produced catalysts, Co–Mo/Al2O3–MgO, under the conditions of an actual carbon nanotechnology enterprise (NanoTechCenter Ltd., Tambov, Russia) were considered, which allowed increasing the catalyst quality. The relative divergence of the mass loss during calcination was reduced from 110.0% to 24%; the specific yield, from 64.9% to 8.5%; and the specific surface area of nanotubes, from 45.6% to 15.4%.

Results of the application of a theory concerning elasticity of composite materials to calculate the elastic modulus of anodic aluminum oxide (AAO) are presented. The basis of the proposed AAO elasticity model is the assumption that the space of the anodic aluminum oxide may be represented as a composite material in the form of a matrix—bulk amorphous oxide filling the space between the pores reinforced by a hollow fiber with zero wall thickness. The maximum error of this simplification in the range of the actually used porosity values is 5% for the Young’s modulus and 0.7% for the shear modulus. The results are in proper agreement with the experimental data of other authors. Proper agreement of the results holds out a hope that this approach may be applied when the AAO pores are filled with some material (adsorbent, liquid, etc.), as is possible, for example, in cases of AAO application as a material for cantilever sensors.