Ash and slag waste (ASW) from coal-fired thermal power plants (TPPs), the amounts of which make several tens or even hundreds of millions of tons per annum, require allocation of large land areas for storing them. This waste is a source of pollution emitted into the atmosphere and it poisons the aqueous medium and soil. Ash and slag waste consists primarily of powderlike material containing a large quantity of unburned carbon (5–25%), magnetic materials (5–20%), and alumino-silicate components. All these components are a valuable raw material for industry, especially silicon and aluminum oxides, which can be used in the production of construction materials. For this purpose, ash must be preliminarily subjected to beneficiation using physical and physicochemical methods. The article presents an analysis of dry and wet ash beneficiation methods with a view to increase the volumes of using ASW produced from domestic power plants. For achieving higher strength of concretes, mechanical activation is carried out, which relates to dry ASW beneficiation methods. To obtain an alumino-silicate product containing 1.5–4.5% of carbon, such dry processing method as electrostatic separation is used. By subjecting dry ash to combined magnetic and electrostatic separation methods, it is possible to obtain an ash and a conducting product with a high concentration of carbon. For Russia, wet ASW beneficiation methods are of the greatest importance, because wet ash and slag removal is used at the majority of TPPs. Hydraulic classification of waste for obtaining products containing particles of different sizes is one of the wet beneficiation process stages. By using the froth flotation method, it is possible to obtain a concentrate containing 65–70% of carbon, a material that can serve as boiler fuel. The froth flotation is regarded as a necessary method for integrated utilization of ASW. Wet magnetic and electrostatic separation are the basic methods for producing magnetic concentrate containing 62–65% of iron. The article presents methods for separating hollow microspheres from AWS, which are a valuable product for aggregates used in the civil construction industry. The article also considers integrated ash beneficiation methods for obtaining four basic products (the figures in parentheses indicate the content of the relevant element): hollow microspheres, carbon product (64.5% of carbon), magnetic product (62% of iron), and alumino-silicate product (no more than 3% of carbon).

Structures of the massive MgB2 samples deformed in Bridgman anvils that were initially in different structural states, namely, as-synthesized and post-four-stage-treated (via deformation + annealing), have been studied by methods of the X-ray diffraction, scanning and transmission electron microscopy, and measurements of microhardness. The process of the deformation of brittle ceramic samples of MgB2 under high pressure has been discussed. An analysis of the obtained data has shown that the plastic deformation of the superconductor MgB2 preliminarily compacted by a four-stage treatment has been implemented in the main through the mutual rotation of crystallites (grains) and by grain-boundary sliding without a noticeable refinement of the grain structure.

The structure of the MgB2 superconductor subjected to high-temperature restoration annealing after cold deformation under high pressure in a Toroid chamber or Bridgman anvils has been investigated by transmission electron microscopy. It has been shown that after postdeformation annealing at 950°C the average size of crystallites in the matrix phase increases 5–10 times compared to the deformed state, reaching ~50–150 nm, as well as the critical current density increases by a factor of three (up to 6.7 × 104 A/cm2, 30 K) compared to the initial state. It has been found that the MgO phase and the higher magnesium borides are present in the form of dispersed precipitates 10–70 nm in size.

Методами рентгенографии, сканирующей электронной микроскопии и микроанализа исследованы сверхпроводники MgB2, подвергнутые деформации под давлением в наковальнях Бриджмена и последующим отжигам при 800 и 950oC. Показано, что при этих температурах кристаллы фазы MgB2 вместе с остаточным бором растворяются в остаточном жидком магнии с образованием как плотных, так и рыхлых областей фазы MgB2. Последние плохо влияют на критический ток. Вместе с тем после этих обработок образцы становятся более однородными по фазовому и химическому составу. Работа выполнена по теме "Кристалл" (N г.р. 01201463333) при поддержке проектом УрО РАН N 15-17-2-16. DOI: 10.21883/FTT.2017.09.44835.076

MgB2 superconductors subjected to deformation under pressure on Bridgeman anvils and subsequent annealings at 800 and 950°C were investigated by X-ray diffraction, scanning electron microscopy, and microanalysis. It was shown that at these temperatures crystals of MgB2 phase along the residual boron dissolute in the residual liquid magnesium with the formation of both dense and loose areas of MgB2 phase. The latter has a negative influence on critical current. At the same time, after these treatments, the samples become more uniform by the phase and chemical composition.

The internal structure and orientation of thin (150–300 μm) flexible Al2O3 fibers used as substrates for third-generation high-temperature superconducting wires are studied by different methods. It is shown that using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction, one can reliably determine the position of the \((1\bar 102)\) plane, on which good YBa2Cu3O y films can be grown.

A composite superconductor SiO 2 /YSZ/CeO 2 /YBa 2 Cu 3 O y with a critical current density of 7 × 10 4 A/cm 2 has been prepared by laser ablation. Small hills enriched in copper and oxygen on the surface of the deposited films have been detected using scanning electron microscopy. A grain structure (sizes of 0.2–0.3 μm) and a system of twins ~400 Å in width have been detected in the superconducting film using transmission electron microscopy. Such a structure and high (001) texture of the film provide the noted critical current density.

A synthesized MgB2 superconductor has been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and by the measurements of the superconducting characteristics and microhardness after cold high-pressure deformation in a Toroid chamber and in Bridgman anvils and subsequent high-temperature annealing. A nanocrystalline structure is formed in the superconductor after high-pressure treatment, but internal cracks appear, and the critical current density decreases strongly. The annealing leads to a coarsening of the structure and to an increase in the critical current density up to 5.8–6.7 × 104 А/сm2, which is more than three times greater than that in the initial state.

The crystal structure of the high-temperature Y1–x Ca x Ba2Cu3O6.8 superconductor has been studied in a temperature range of 80–300 K using low-temperature X-ray diffraction analysis; its microstructure has been studied by scanning and transmission electron microscopy. Changes of the bond length in the structure of principal phase and precipitation topology of impurity phases and their compositions have been analyzed. An addition of calcium was shown to increase the environmental tolerance of the principal Y123 phase and its microhardness and ensures the low unchanged coefficient of thermal expansion. All of the facts indicate that the material can be used to manufacture composite superconducting articles.

The structure and properties of synthesized massive MgB2-based samples subjected to deformation with Bridgman anvils have been studied. Deformation results in the formation of fine-grained structure of the MgB2 phase, enhancement of interconnection of grains, complete disappearance of friable MgB2-phase areas, and abrupt increase in the microhardness.

The structure of MgB 2 samples synthesized from magnesium flakes and a boron powder at temperatures of 900–1000°C has been investigated. It has been found that the samples have “dendrite-like” and layered structures formed as a result of the dissolution of solid boron in liquid magnesium followed by crystallization. The obtained structures have been analyzed within the theoretical concepts of crystallization from melt.

Using different methods, it has been revealed that two MgB2 phases with the same hexagonal lattice, which differ in the contents of Mg and B (in the limits of the homogeneity range), as well as in the concentration of impurity oxygen and in the microstructure, are formed. The regions that correspond to these two phases of MgB2 have relatively large sizes (100–500 μm) and, alternatingly, fill the entire volume of the sample. It is assumed that the two-phase state of MgB2 is due to the specific features of the mechanism of its formation (when synthesizing at 800–1000°C), which includes the stage of the melting of magnesium, the dissolution of solid boron in the melt to a concentration that corresponds to the composition of the MgB2 compound, and the subsequent crystallization of the MgB2 compound in the melt with the formation of a dendrite-like structure, which is accompanied by an appropriate redistribution of the main components and impurities.

The Y3d, Ba3d 5/2, Cu2p 3/2, and O1s X-ray photoelectron spectra of thick (600 nm) superconducting YBa2Cu3O7 − δ films deposited on textured Ni-W substrates with Y2O3 + ZrO2 and CeO2 buffer layers have been studied. It has been established that, after the mechanical removal of surface layers with a diamond scraper (and as the analyzed region of the film approaches the interface), a decrease in the oxygen content leads to a decrease of the orthophase fraction and an increase of the tetraphase and Cu+ ion fractions. This is caused by the presence of elastic stresses in the superconducting film due to the lattice misfit between the phases making up a composite sample. These stresses prevent oxygen diffusion involved in oxidizing annealing. The spectra of the superconducting film have not revealed signals generated by elements of the substrate and buffer layers.