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The paper investigates commercially pure titanium VT1-0 (US analog Grade 2) in the ultrafine grain state after the aluminum ion implantation at a fluence of 1∙1017, 5∙1017 and 10∙1017 ion/cm2. The investigation techniques include X-ray diffraction analysis, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy. Auger electron spectrometer is used to analyze the chemical composition of the implanted layer. The grain size in the longitudinal and transverse directions and the phase composition of ultrafine titanium are studied depending on the irradiation exposure. It is found that the ion implantation leads to the formation of such intermetallic compounds as Al3Ti and AlTi3 phases, β-phase titanium and aluminum oxide (Al2O3). The increased irradiation exposure results in the formation of a thicker implanted layer without changing its phase composition.

Using the transmission electron microscopy of thin foils the paper studies the phase composition and fine structure of 0.18С–1Cr–3Ni–1Mo–Fe steel after plasma electrolytic carbonitriding carried out through the surface saturation with nitrogen and carbon. The steel specimens are studied before and after carbonitriding on the surface and at a ~40 μm distance from the surface. It is found that carbonitriding causes significant qualitative and quantitative changes in the steel structure. Thus, the layers of residual austenite appear along the boundaries of martensitic lamellas, and the particles of alloyed cementite and carbonitrides are observed inside the lamellas. The layers of residual austenite locate at a ~40 μm depth along the boundaries of all martensitic crystals, while inside the crystals there are only particles of alloyed cementite and carbonitride M23(C, N)6. The control parameter of changes in the structure and phase composition is the concentration of interstitial atoms of carbon and nitrogen. Changes in this concentration lead to the system deviation from thermodynamic equilibrium. The transition of system to equilibrium or quasi-equilibrium states is considered to be performed through the transition of crystal lattices, which form a gradient structural-unstable state of the matrix, intermetallics and carbonitride compounds, to a low-stability state.

The paper studies the structure and phase composition of steel 0.12C–1Cr–1Mo–1V–Fe (grade DIN 14MoV63) after a long-term operation using the transmission electron microscopyю Investigated are the nontreated specimen (not subjected to operation) and specimens after a long-term operation with and without fracture. The phase composition and morphology of the steel structure are determined for each specimen. It is found that the steel servicing leads to the destruction of lamellar perlite, intensive fragmentation of ferrite, redistribution of the carbide component and elastic distortion of the crystal lattice.

The extraction of valuable components from brackish waters, such as lithium ions, is of considerable practical interest. A promising approach is the separation of solutes by their physical properties, such as charge and diffusion coefficient. We propose a simple one-dimensional model of ion transport in an electro-baromembrane system with a track-etched membrane, which makes it possible to calculate the flux densities of the separated components across the membrane as functions of the applied voltage and pressure drop. The model takes into account the parameters of the membrane (pore radius, length, and volume fraction in the membrane), hydrodynamic, and other external conditions of the separation process (thickness of diffusion layers, composition of the feeding and receiving solutions). The calculation results are given for a mixed solution containing three sorts of ions (two cations, K+ and Li+, and one anion, Cl−) with different diffusion coefficients, but the same absolute value of the charge. The electric field and the pressure drop are superimposed in such a way that the electromigration and convective transport of ions in the pore are directed oppositely. Since the mobility of competing cations is different, only lithium chloride or only potassium chloride is removed from the mixture at certain values of the potential drop and pressure.

The principle of operation and the characteristics of the experimental equipment intended for the generation of boron ion plasma and beams are presented. The equipment comprises a vacuum arc source of boron ions with boron isotope separation in a magnetic field and a plasma generator for deposition of boron-containing coatings based on a planar magnetron sputter. Common to this equipment is the use of lanthanum hexaboride cathodes, but for planar magnetron, a pure boron cathode heated in the discharge is also used. It is shown that, when silicon wafer is implanted with beams of 10B+ and 11B+ boron isotope ions with doses of 1014–1016 ion/cm2, the isotopic effect of the diode properties of the implanted surface is observed. The results of studies of the properties of the obtained boron-containing coatings on model materials: stainless steel, crystal silicon, and E110 (Zr–1Nb) reactor alloy are presented.

Using transmission electron microscopy (TEM), phase composition and fine texture changes in the ferrite-pearlitic steels 0.18C–1Cr–3Ni–1Mo–Fe, 0.3C–1Cr–1Mn–1Si–Fe and 0.34C–1Cr–1Ni–1Mo–Fe due to electrolytic plasma nitrocarburizing has been studied in thin foils. The procedure of electrolytic-plasma enhanced nitrocarburizing has been performed by steel surface saturation with nitrogen and carbon in an aqueous solution at a temperature of 800–860°C for 5 min. All the steels under investigation have been studied before and after the nitrocarburizing procedure. In the initial state, the steels were discovered to be composed of a pearlitic and ferritic grain mixture. The nitrocarburizing procedure leads to the formation of modified layers. Thus, the greater is the amount of pearlite before nitrocarburizing, the thicker is the modified layer. Nitrocarburizing results in significant qualitative changes in the phase state and the steel structure. In the modified layer surface area alongside the matrix, the particles of other phases such as carbides, nitrides and carbonitrides occur. As the distance from the surface of a nitrocarburized sample increases, the phases of set and volume decrease, whereas the only carbide phase—cementite—occurs at the end of modified layer in the case of all the steels. After nitrocarburizing, the matrix of all the steels represents tempered lath and lamellar martensite. In the nitrocarburized layer surface zone, the volume fractions of lath and lamellar martensite depend on the initial steel state: the greater is the amount of pearlite in steel, the less is the amount of lath martensite; then a greater amount of lamellar martensite is formed. Such a dependence is not observed in the nitrocarburized layer central zone, whereas the volume fractions of lath and lamellar martensite at the end of the layer are close to each other.

The paper presents the transmission electron microscopy investigations of the structure and phase composition of ferritic-perlitic ST2 steel surface after electrolytic plasma quenching. The steel in the initial state represents the material after hardening at 890°С for 2 or 2.5 hours and quenching in warm (30–60°С) water with subsequent tempering at 580°C for 2.5 or 3 hours. Electrolytic plasma quenching is carried out at 850–900°С in an aqueous salt solution for 4 seconds, at 320 V voltage and 40 A current. In the initial state, the morphology of the steel matrix consists of lamellar perlite and nonfragmented and fragmented ferrite. Electrolytic plasma quenching of the steel surface results in the martensite transformation, steel self-tempering, and the formation of cementite particles in all martensite crystals. This treatment also leads to the diffusion transformation of γ → α phases, the release of residual austenite (γ -phase) along the low-temperature martensite laths and lamellas and in all crystals of lamellar martensite, the formation of М23С6 special carbides and, finally, to the enhancement of all parameters of the steel fine structure.

The paper presents the transmission electron microscopy investigations of the microstructure and phase composition of the nickel-based superalloy after high temperature annealing. All states of the superalloy are characterized by the single-crystal structure with [001] crystallographic orientation. The Ni–Al–Co alloy system also contains such elements as Mo, Cr, W, Ta, Re and Ru. The Ni–Al–Co system is studied in four states: initial (after directional crystallization) and after 1000°С annealing during 118, 372 and 1274 hours. The major phases forming the alloy system are γ- and γ′-phases. After annealing for 118 hours, the formation of Al6(Re, Ru) phase is observed. After longer high-temperature annealing new phases occur, such as σ-, δ- and Laves phase. The obtained alloy microstructure is classified into four types: 1) γ′-phase quasi-cuboids with γ-phase layers, 2) ribbon anisotropic microstructure of γ′+ γ-phase, 3) ribbon anisotropic microstructure with σ-phase particles in γ-phase layers, 4) γ-phase with δ-phase and Laves phase inclusions. The introduction of a large amount of various alloying elements and the annealing process modify the crystallographic texture of the superalloy.

The present study was conducted by transmission electron microscopy (TEM) in order to investigate the structure of multicomponent nickel-based alloy obtained by directional solidification and change in its phase composition at high-temperature annealing. All states of the alloy possessed monocrystalline structure with [001] orientation. The alloy under study contained other elements apart from Ni, such as: Al, Co, and also Mo, Cr, W, Ta, Re, and Ru. The alloy was investigated in three states after annealing for: 1) 118 h; 2) 372 h; 3) 1274 h at 1000°С. The basic phases that form the alloy were γ and γ′. In the state after annealing for 118 h Al6(Re,Ru) phase was observed in an insignificant amount. After longer high temperature annealing new phases occurred, such as σ-phase and δ-phase, Laves phase. The structures occurring during annealing can be classified into four types: 1) quasi-cuboids, 2) anisotropic stripe structures, 3) anisotropic structures of striped type with σ-phase separation, 4) structureless zones with large two-phase areas.

The present work summarizes and presents separate results obtained by the authors when investigating mesoscopic and microscopic internal stresses formed under the conditions of thermal and mechanical treatment of martensitic, pearlitic and austenitic steels. Internal stresses were investigated using the method based on the analysis of bend extinction contours. The results obtained on industrial steels were presented. The sources were described and examples of internal stresses induced by these sources were given. The nature of bending-torsion of the crystal lattice depending on the averaging volume was determined. It has been shown that in martensitic steels along with the increase in the averaging volume (carbide particle → separate martensitic lath → martensite packet→ martensitic plate → grain) the amplitude of bending-torsion of the crystal lattice decreases. The nature of distortions also changes. At large amplitudes and low volumes of averaging they are completely or partly elastic, at large volumes of averaging they are completely plastic. Thereby, distortions are fully driven by the excess dislocation density.

The paper presents the transmission electron microscopy (TEM) investigations of the thin film structure and phase composition of the heat-affected zone (HAZ) of a weld joint produced by manual metal arc welding (MMAW) of 0.12C–18Cr–10Ni–1Ti–Fe austenite steel exposed then to plastic deformation. The test machine INSTRON-1185 is used to perform quasi-static tensile tests at room temperature and a 1.7∙10–4 s–1 strain rate up to 5 and 37% deformations. TEM investigations are carried out within the HAZ, at a 1 mm distance to the weld line, in the direction of the parent metal and at 0.5 mm distance to the weld deposit. It is shown that MMAW results in the formation of e-martensite both in the parent metal and weld deposit regions. In the latter, γ → e phase transformation occurs faster. Plastic strain ranging between 0–5% throughout the HAZ leads to further γ → e phase transformation. In the weld deposit of the HAZ region, this phase transformation is also more intensive. Further increase in the degree of plastic strain from 5 to 37% results in γ → e → α phase transformation and an elastoplastic lattice distortion of the α-phase. The plastic flexure remains in the crystal lattice of the γ-phase. The bulk material in the HAZ region satisfies the following conditions: scalar dislocation density is higher than the excess, and internal shear stresses are higher than long-ranging.

Electroconvection is the principal mechanism that allows markedly increasing the rate of ion transfer through ion-exchange membranes in intensive current regimes. In this work, we investigated the possibility of intensifying electroconvection in solution near heterogeneous MA-41 anion-exchange membrane (Shchekinoazot production) by the modifying of its surface. The use of weakly crosslinked ion-exchange resin (MA-41P) in the course of the membrane manufacturing, with subsequent chemical modification of its surface (MA-41PM), is shown to make it possible to increase the limiting current density almost twice. The value of the reduced potential drop (after subtracting the ohmic contribution), at which significant generation of H+ and OH– ions begins, is shifted from 0.8 V in the case of MA-41 to 1.7 V in the case of MA-41PM. The current density related to the onset of water splitting is equal to 0.9$$i_{{{\text{lim}}}}^{{{\text{Lev}}}},$$ in the case of MA-41; 2$$i_{{{\text{lim}}}}^{{{\text{Lev}}}},$$ in the case of MA-41PM (where $$i_{{{\text{lim}}}}^{{{\text{Lev}}}}$$ is the theoretical value of the limiting current density). The special feature of the modified membrane behavior is the presence of a range of potential drop (between 50 and 80 mV in the reduced scale), in which the system with the MA-41PM has negative differential resistance: in this range, the potential drop decreases when the current density increases. This behavior occurs when measuring quasi-stationary I–V curves; correspondingly, in the chronopotentiogram there is a time interval, where the potential drop decreases with time. The electroconvection is intensified near a modified membrane due to a higher fraction of conductive areas on the surface of the modified membrane and the redistribution of these areas via formation of their agglomerates in the centers of the cells formed by the reinforcing mesh. Mathematical modeling shows the concentration polarization of the modified membrane being less than that of the pristine one. Meanwhile, the structure of electroconvective vortices is optimized: the vortices near the modified membrane are larger; they do not extinguish each other, unlike the case of MA-41.

This article presents the results of hybrid treatment (cold working, ESA) of 09G2S structural low alloyed steel aimed at improving operation reliability.

This paper presents scanning and transmission electron microscope investigations of the structure, phase composition, and morphology of a heat-resistant alloy modified by thermal treatment and additionally alloyed by rhenium. The rhenium alloy was obtained by using the directional crystallization technique. The structural investigations were carried out for two states of the alloy, i.e., (1) original (after the directional crystallization); (2) after the directional crystallization with 1150 °C annealing for 1 h and 1100 °C annealing for 480 h. It is shown that fcc-based γ- and γ′-phases are primary in all states of the alloy. The γ′-phase has an L12 structure, while γ-phase is a disordered phase. It was found that after directed crystallization, the volume fraction of the γ′ phase is ~85%, the fraction of the γ-phase is less than 10%. Annealing leads to an increase in the γ′- phase up to 90%, the proportion of the γ-phase practically does not change. Rhenium is a phase-formation element. The investigations show that high-temperature annealing modifies the structural and phase conditions of the heat-resistant alloy.

Synthetic ion exchange membranes (IEMs) are made from organic, inorganic, or mixed and composite materials [...]

Transmission electron microscopy investigations were carried out to study the structural-phase state of ultra-fine grain (UFG) titanium with the average grain size of ~0.2 μm, implanted with aluminum ions. Implantation was carried out on MEVVA-V.RU ion source at room temperature, exposure time of 5.25 h and ion implantation dosage of 1⋅1018 ion/cm2. UFG-titanium was obtained by a combined multiple uniaxial compaction with rolling in grooved rolls and further annealing at 573 К for 1h. The specimens were investigated before and after implantation at a distance of 70-100 nm from the specimen surface. Concentration profile of aluminum implanted with α-Ti was obtained. It was revealed that the thickness of implanted layer was 200 nm, while maximum aluminum concentration was 70 at.%. Implantation of aluminum into titanium has resulted in formation of the whole number of phases having various crystal lattices, like β-Ti, TiAl3, Ti3Al, TiC and TiO2. The areas of their localization, the sizes, distribution density and volume fractions were determined. Grain distribution functions by their sizes were built, and the average grain size was defined. The paper investigates the influence of implantation on the grain anisotropy factor. It was revealed that implantation leads to the decrease in the average transverse and longitudinal grain size of α-Ti and decrease in the anisotropy factor by three times. The yield stress and contributions of separate strengthening mechanisms before and after implantation were calculated. The implantation has resulted in increase in the yield stress by two times.

Using the transmission electron microscopy technique, we have studied the structural-phase state of UFG titanium with an average grain size ~0.2 μm implanted with aluminum ions. An MEVVA-V.RU source has been used to implant the specimen at room temperature, implantation time 5.25 h, and irradiation dose 1 · 1018 ion/cm2. To produce the UFG titanium samples, we have employed the combined multiple uniaxial pressing technique (abc-pressing) followed by grooved rolling and subsequent annealing at 573 K for 1 h. The samples have been studied in two states: 1) before implantation (initial state) and 2) after implantation at a distance 70–100 nm from the sample surface. We have obtained the aluminum concentration profile of implanted α-Ti. It has been established that the maximum concentration of aluminum is 70 at.% and the thickness of the implanted layer is 200 nm. We have determined the grain distribution functions over the grain size, calculated the grain anisotropy coefficient before and after implantation. It has been established that implantation decreases the average longitudinal and transversal sizes of α-Ti grains, and reduces the anisotropy coefficient by three times. It has been established that aluminum implantation into titanium brings about formation of a whole set of phases with different crystal lattices, namely, β-Ti, TiAl3, Ti3Al, TiC, and TiO2.

The efficiency of separation processes using ion exchange membranes (IEMs), especially in the food industry, is significantly limited by the fouling phenomenon, which is the process of the attachment and growth of certain species on the surface and inside the membrane. Pulsed electric field (PEF) mode, which consists in the application of constant current density pulses during a fixed time (Ton) alternated with pause lapses (Toff), has a positive antifouling impact. The aim of this study was to investigate the combined effect of three different relatively high flow rates of feed solution (corresponding to Reynolds numbers of 187, 374 and 560) and various pulse–pause ratios of PEF current regime on protein fouling kinetics during electrodialysis with bipolar membranes (EDBM) of a model caseinate solution. Four different pulse/pause regimes (with Ton/Toff ratios equal to 10 s/10 s, 10 s/20 s, 10 s/33 s and 10 s/50 s) during electrodialysis (ED) treatment were evaluated at a current density of 5 mA/cm2. It was found that increasing the pause duration and caseinate solution flow rate had a positive impact on the minimization of protein fouling occurring on the cationic surface of the bipolar membrane (BPM) during the EDBM. Both a long pause and high flow rate contribute to a more effective decrease in the concentration of protons and caseinate anions at the BPM surface: a very good membrane performance was achieved with 50 s of pause duration of PEF and a flow rate corresponding to Re = 374. A further increase in PEF pause duration (above 50 s) or flow rate (above Re = 374) did not lead to a significant decrease in the amount of fouling.

Carbide–boride coatings applied on both sides of V96Ts aluminum alloy samples by electric spark alloying (ESA) are metallographically studied. The coated samples are processed by laser on one side. Laser treatment of the surface decreases the pronounced roughness, pores, and cracks visible after ESA. Laboratory tests suggest combined (electric-spark–laser) hardening of the surface of V96Ts aluminum alloy samples to extend the service life of tools and machine parts.

The current methods for determination of the membrane specific permselectivity between two competing counter-ions are dependent on various factors, which hinder the comparison of ion selectivity of ion selective membranes. In this work, a new characteristic, “ideal selectivity” is suggested to be used for the evaluation of the specific permselectivity of monovalent selective membranes. Ideal selectivity is determined in a single electrolyte solution containing only one of the competing counterions. We show that this characteristic exhibits a stable value, which is independent from the molar fraction of ions in a solution. Thus, it may be directly used to predict the purity of a salt produced in a dynamic selectrodialysis (SED) process with a monovalent selective membrane. To elaborate this, thin film composite (TFC) cation exchange membranes were prepared with piperazine and trimesoyl chloride by interfacial polymerization. These membranes were compared with a commercial monovalent selective cation exchange membrane CIMS (ASTOM, Japan) in view of their permselectivity (Na+/Mg2+) and the performance in SED. The results show that when the TFC membranes were applied in SED, the purity of Mg2+ in the product reached 75%, which was higher than in the case of CIMS. Furthermore, ideal selectivity of those TFC and CIMS membranes were calculated and fitted with the experimental Mg2+ purity. It was found that ideal selectivity linearly correlates with the product final purity. The extrapolation of the fitting line predicts that when ideal selectivity approaches to 2, SED process the purity could theoretically approach to 100% in the same experimental conditions. Therefore, ideal selectivity can be used to predict the separation efficiency and the final product purity of SED process.

The object of the research is oxidized nickel ores from the Kulikovskoye deposit (Southern Urals) – non-conforming nickel-containing raw materials. The work is devoted to the study of chemical and phase composition to substantiate the choice of the method of processing this material in order to obtain valuable inorganic substances in demand in the chemical and metallurgical industries: oxide and (or) magnesium nitrate, iron and nickel containing concentrates, silicon dioxide. The chemical composition of ore demonstrating the feasibility of developing a technology for its complex processing is presented. X-ray phase analysis showed the presence of silicates of the serpentine group (lizardite-1M and lizardite-1T) and the group of spinelids (magnesioferrite) in the oxidized nickel ores of the Kulikovskoye deposit. A literary analysis suggested the presence of other hydrosilicates (antigorite, chrysotile, nimite, talc, revdinskite, clinochlore, etc.). IR spectroscopic analysis was performed to confirm the phase composition. A thermogravimetric analysis was performed, which makes it possible to determine the conditions for the preliminary preparation of ground raw materials. To determine the mechanism of thermal decomposition of ore in air, intermediate products were obtained at temperatures of 600, 700 and 900 °C. According to X-ray diffraction, IR and Raman spectroscopic analyzes, at 600 °C, the removal of OH groups, water molecules and the destruction of the crystal lattices that make up the mineral ore with the formation of oxides (FeO, SiO2, MgO) begins. At 700 °C, island silicates are formed: forsterite Mg2SiO4, larnite Ca2SiO4. At 900 °C, the interaction between silicates continues with the complication of the composition of functional groups. Based on the described properties of minerals and previous work on the hydrometallurgical technology of processing oxidized nickel ores and metal-containing silicate raw materials in order to obtain inorganic substances, nitric acid is proposed as a leaching agent.

Many transport properties of ion-exchange membranes can be described in terms of the microheterogeneous model using a single set of parameters. However, the model is applicable in a limited concentration range of electrolyte solutions. In this paper a new modification of this model is proposed, taking into account the contribution of the electrical double layer (EDL) at the internal boundaries of the gel phase and the intergel solution of the membrane to describe the electrical conductivity of membranes in dilute electrolyte solutions. The model suggests that the EDL thickness in the internal solution phase increases with dilution of the external solution. Since EDL is more conductive than the electroneutral part of the solution, it is possible to describe the concentration dependence of the electrical conductivity of membrane more precisely as compared with the basic version of the microheterogeneous model. Comparison of the concentration dependences of the electrical conductivity of membranes shows a good agreement between the experimental and calculated data.

The paper presents research into the structure and phase composition of Ni–Al–Co alloy modified by rhenium (~3 аt.%) alloying. Observations are carried out using the transmission electron microscopy. The initial state of the alloy is the state after the directional crystallization. The alloy is further subjected to 900°С annealing during 1143 h. Creep tests are additionally carried out for this alloy at the same temperature and time and 400 MPa load. It is shown that FCC disordered γ- and ordered γ′-phases are major in all alloy states. Secondary phases are found to be σ-phase, χ-phase, Laves and AlRe2 phases. Experiments show that the high temperature annealing changes the phase composition of the alloy. Thus, the amount of the ordered γ′-phase increases, while that of disordered γ-phase decreases. During the creep process, the amount of the former reduces and the amount of the latter increases. The annealing process modifies the phase composition in secondary phases. It is found that the structural modification caused by the creep process differs from that caused by the annealing process. Thus, the creep-induced modification of the cuboid structure in γ′-phase is stronger than due to annealing. Dislocations are observed in γ- and γ′-phases in all states of the alloy. During the annealing process, the dislocation density in γ-phase is higher than in γ′-phase, and vice versa during the creep process. The experiments show that the behavior of the dislocation structures is different during the annealing and creep processes.

Chronopotentiometry is largely used for electrochemical characterization of ion-exchange membranes. Nevertheless, the theory is poorly developed in the range of overlimiting currents. This paper proposes a two dimensional convective-diffusion model of ion transport in electromembrane system in galvanostatic mode. We use direct numerical simulation taking into account electroconvection to develop a comprehensive analysis of mechanisms of reaching transition states, which depend on the parameters of electrically heterogeneous surface of ion exchange membrane. We find that the occurrence of two transition times is typical for the simulated electrodialysis systems with heterogeneous membranes. The value of the first transition time, τ1, is conditioned by the fact that the normal and tangential diffusion delivery of ions from the solution bulk to the conductive membrane areas reaches its limiting value. When τ1 is attained, electroconvective vortices appear at the conductive-nonconductive boundaries. They mix the near-surface solution in the vicinity of these boundaries and increase the delivery of the “fresh” solution to the conductive regions. The second transition time, τ2, is reached when electroconvection-diffusion ion delivery to the overall membrane surface attains its limiting value. At t = τ2, electroconvective vortices whose size is comparable with the diffusion layer thickness arise. Both τ1 and τ2 depend on the size and fraction of conductive regions. In the case of conventional commercial ion-exchange membranes τ1

Long-term (over 20 h) operation of the AMX-Sb membrane in the electrodialysis desalination of 0.02 M NaCl solution in overlimiting current regimes can lead to an increase in experimentally determined limiting current by more than 30% compared to the pristine membrane. This growth is caused by electrochemical degradation of the ion-exchange material at the AMX-Sb/solution interface, which leads to (1) a decrease in hydrophilicity of the membrane surface and (2) the formation of membrane cavities with linear dimensions of 2–3 μm. Both of these effects stimulate electroconvection, which develops in underlimiting current regimes via the mechanism of electroosmosis of the first kind. The resulting microvortex structures deliver a more concentrated solution to the AMX-Sb surface, shifting the limiting state and the onset of the intense generation of H+ and OH− ions to higher currents. The study has been carried out using the techniques of voltammetry and impedance spectroscopy, as well as contact angle measurements and optical visualization of the membrane surface.

Membranes are widely used in modern technology. The demand for different types of membranes and membrane processes is increasing every year. This review summarizes the current state of the art and prospects of membrane science developments including membrane materials for gas separation, pervaporation, and pressure-driven membrane processes; ion-exchange, hybrid, and track-etched membranes; membranes for electrochemical sensors; and mathematical modeling of membrane separation processes and ion and water transport in membrane systems. Studies aimed at improving the selectivity and performance of membranes and their stability are surveyed. New approaches to the synthesis and modification of membranes as well as their advanced applications are discussed.

It has been found that after 300 h of operation of AMX and AMX-Sb anion-exchange membranes (Astom, Japan) in overlimiting current regimes in the process of electrodialysis desalination of 0.02 M NaCl, NH4Cl, NaH2PO4, and KC4H5O6 (KHT) solutions, the limiting currents, $$i_{{\lim }}^{{\exp }}$$ , determined by graphic processing of current–voltage curves increase in the order NaCl < NaH2PO4 < KHT. Their increments relative to those for the “fresh” membrane are 33, 90, and 128%, respectively. The growth in $$i_{{\lim }}^{{\exp }}$$ is accompanied by an increase in the thickness of the samples occurring in the NaH2PO4 and KHT solutions. In the case of NH4Cl, the values of $$i_{{\lim }}^{{\exp }}$$ decrease. It has been shown that a small decrease in counterion transport numbers during membrane operation has almost no effect on the values of limiting currents. The main contribution to the increase in $$i_{{\lim }}^{{\exp }}$$ is apparently made by electroconvection, which develops according to the mechanism of electroosmosis of the first kind. Its development is facilitated by the growth in the number and size of free-standing micrometer-sized cavities on the surface of anion-exchange membranes, the area and linear dimensions of which increase in the order NaCl < NaH2PO4 < KHT. These cavities are formed as a result of enhancement of electrochemical degradation of the ion-exchange material and the inert filler polyvinyl chloride at the membrane/solution interface in ampholyte solutions.

The use of reactive electrochemical membranes (REM) in flow-through mode during the anodic oxidation of organic compounds makes it possible to overcome the limitations of plate anodes: in the case of REM, the area of the electrochemically active surface is several orders of magnitude larger, and the delivery of organic compounds to the reaction zone is controlled by convective flow rather than diffusion. The main problem with REM is the formation of fouling and gas bubbles in the pores, which leads to a decrease in the efficiency of the process because the hydraulic resistance increases and the electrochemically active surface is shielded. This work aims to study the processes underlying the reduction in the efficiency of anodic oxidation, and in particular the formation of gas bubbles and the recharge of the REM pore surface at a current density exceeding the limiting kinetic value. We propose a simple one-dimensional non-stationary model of the transport of diluted species during the anodic oxidation of paracetamol using REM to describe the above effects. The processing of the experimental data was carried out. It was found that the absolute value of the zeta potential of the pore surface decreases with time, which leads to a decrease in the permeate flux due to a reduction in the electroosmotic flow. It was shown that in the solution that does not contain organic components, gas bubbles form faster and occupy a larger pore fraction than in the case of the presence of paracetamol, with an increase in the paracetamol concentration, the gas fraction decreases. This behavior is due to a decrease in the generation of oxygen during the recombination reaction of the hydroxyl radicals, which are consumed in the oxidation reaction of the organic compounds. Because the presence of bubbles increases the hydraulic resistance, the residence time of paracetamol—and consequently its degradation degree—increases, but the productivity goes down. The model has predictive power and, after simple calibration, can be used to predict the performance of REM anodic oxidation systems.

The application of pulsed electric field (PEF) in electrodialysis has been proven to be efficient for a number of effects: increasing mass transfer rate, mitigation of scaling and fouling, reducing water splitting. Recently, the improvement of the membrane permselectivity for specific counterions was discovered experimentally by the group of Laurent Bazinet (N. Lemay et al. J. Memb. Sci. 604, 117878 (2020)). To better understanding the effect of PEF in electrodialysis, simulations were performed using a non-stationary mathematical model based on the Nernst–Planck and Poisson equations. For the first time, it was not only the condition used when the current density is specified but also the condition when the voltage is set. A membrane and two adjacent diffusion layers are considered. It is shown that when applying the regime used by Lemay et al. (the same current density in conventional continuous current (CC) mode and during the pulses in PEF mode), there is a significant gain in specific permselectivity. It is explained by a reduction in the membrane concentration polarization in PEF mode. In the CC mode of electrodialysis, increasing current density leads to a loss in specific permselectivity: concentration profiles in the diffusion layers and membrane are formed in such a way that ion diffusion reduces the migration flux of the preferentially transferred ion and increases that of the poorly transferred ion. In PEF mode, the concentration profiles are partially restored during the pauses when the current is zero. However, if a different condition is used than the condition applied by Lemay et al., that is, when the same average current density is applied in both the PEF and CC modes, there is no gain in specific permeability. It is shown that within the framework of the applied mathematical model, the specific selectivity depends only on the average current density and does not depend on the mode of its application (CC or PEF mode).

The broad possibilities of electrochemical impedance spectroscopy for assessing the capacitance of interphase boundaries, the resistance and thickness of the foulant layer were shown by the example of AMX-Sb membrane contacted with red wine from one side and 0.02 M sodium chloride solution from the other side. This enabled us to determine to what extent foulants affect the electrical resistance of ion-exchange membranes, the ohmic resistance and the thickness of diffusion layers, the intensity of water splitting, and the electroconvection in under- and over-limiting current modes. It was established that short-term (10 h) contact of the AMX-Sb membrane with wine reduces the water-splitting due to the screening of fixed groups on the membrane surface by wine components. On the contrary, biofouling, which develops upon a longer membrane operation, enhances water splitting, due to the formation of a bipolar structure on the AMX-Sb surface. This bipolar structure is composed of a positively charged surface of anion-exchange membrane and negatively charged outer membranes of microorganisms. Using optical microscopy and microbiological analysis, it was found that more intense biofouling is observed on the AMX-Sb surface, that has not been in contacted with wine.

We report the study of commercially pure titanium (VТ1-0 alloy under Russian classification) in the submicrocrystalline state obtained by the abc-pressing method with the surface modified by the ion implantation technique. Ion implantation was performed using aluminum ions at irradiation doses 1 × 1017, 5 × 1017, and 10 × 1017 ion/cm2 using a MEVVA5.RU source. The grain longitudinal and transverse dimensions were determined before and after ion implantation for varying irradiation doses. We studied the influence of ion implantation and the irradiation dose on the elemental and phase composition of the surface layers of VT1-0 alloy. It has been found that ion implantation results in restructuring of titanium surface layers and in a change of the grain size with the depth of the surface layers. For example, the grain longitudinal size decreases 5 times at the dose rate of 1·1017 ion/cm2. It has been found that aluminum ion implantation modifies the surface layers containing intermetallic phases of TiAl3, Ti3Al, and aluminum and titanium oxides (Al2O3, TiO2, TiO и Ti2O3). Increasing the irradiation dose does not qualitatively change the alloy phase composition, but affects the quantitative characteristics of the formed secondary phases.

Transmission electron microscopy (TEM) investigations were carried out to study the structural-phase state of ultra-fine grained (UFG) titanium with the average grain size of ∼0.2 and 0.3 µm, implanted with aluminium ions. MEVVA-V.RU ion source was used for ion implantation under room temperature, exposure time of 5.25 h, at ion implantation dosage of 1×1018 ion/cm2. UFG-titanium was obtained by means of multiple uniaxial compacting with multipass rolling in grooved rolls and further annealing at 573 K during 1 hour to reach the average grain size of ∼0.2 µm, and annealing at 623 K during 1 hour to reach the size of ∼0.3 µm. The study revealed that in alloy with the average grain size of ∼0.2 µm implantation results in a decrease in longitudinal grain size of α-Ti (from 1.9 to 0.7 µm), however lateral size in its turn changed insignificantly (from 0.15 to 0.12 µm). Grain anisotropy factor decreased by 3 times. In the alloy with the average grain size of ∼0.3 µm both longitudinal and lateral grain sizes decreased (from 0.33 to 0.19 µm and from 2.1 to 0.8 µm correspondingly). The studies also showed that implantation of titanium with aluminium has led to the formation of a number of phases, such as: β-Ti, TiAl3, Ti3Al, TiC and TiO2. Their places of concentration, sizes, distribution density and volume ratios were determined. TiAl3 and Ti3Al phases were established to be ordered ones, formed within the conditions of ion exposure along the boundaries of α-Ti grains. Conducted calculations demonstrated that implantation contributed to the alloy strengthening, i.e. in alloy with the average grain size of ∼0.2 µm the value of yield stress increased by 2 times, and in the alloy with the average grain size of ∼0.3 µm—by 4 times.

Fouling is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect of five different solution flow rates (corresponding to Reynolds numbers of 162, 242, 323, 404 and 485) combined with the use of pulsed electric field (PEF) current mode on protein fouling of bipolar membrane (BPM) during electrodialysis with bipolar membranes (EDBM) of skim milk. The application of PEF prevented the fouling formation by proteins on the cationic interface of the BPM almost completely, regardless of the flow rate or Reynolds number. Indeed, under PEF mode of current the weight of protein fouling was negligible in comparison with CC current mode (0.07 &plusmn, 0.08 mg/cm2 versus 5.56 &plusmn, 2.40 mg/cm2). When a continuous current (CC) mode was applied, Reynolds number equals or higher than 323 corresponded to a minimal value of protein fouling of BPM. This positive effect of both increasing the flow rate and using PEF is due to the facts that during pauses, the solution flow flushes the accumulated protein from the membrane while in the same time there is a decrease in concentration polarization (CP) and consequently decrease in H+ generation at the cationic interface of the BPM, minimizing fouling formation and accumulation.

Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.

Water splitting (WS) and electroconvection (EC) are the main phenomena affecting ion transfer through ion-exchange membranes in intensive current regimes of electrodialysis. While EC enhances ion transport, WS, in most cases, is an undesirable effect reducing current efficiency and causing precipitation of sparingly soluble compounds. A mathematical description of the transfer of salt ions and H+ (OH&minus, ) ions generated in WS is presented. The model is based on the Nernst&ndash, Planck and Poisson equations, it takes into account deviation from local electroneutrality in the depleted diffusion boundary layer (DBL). The current transported by water ions is given as a parameter. Numerical and semi-analytical solutions are developed. The analytical solution is found by dividing the depleted DBL into three zones: the electroneutral region, the extended space charge region (SCR), and the quasi-equilibrium zone near the membrane surface. There is an excellent agreement between two solutions when calculating the concentration of all four ions, electric field, and potential drop across the depleted DBL. The treatment of experimental partial current&ndash, voltage curves shows that under the same current density, the surface space charge density at the anion-exchange membrane is lower than that at the cation-exchange membrane. This explains the negative effect of WS, which partially suppresses EC and reduces salt ion transfer. The restrictions of the analytical solution, namely, the local chemical equilibrium assumption, are discussed.

Today the common view of the Neosepta membranes is that their material is electrically homogeneous, i.e. it does not include heterogeneities (except reinforcing fabric). However, there are a few publications, according to which their surface is not homogeneous geometrically and this fact has an important impact on the mass transfer rate. In this paper, we thoroughly study geometric heterogeneity of four commercial homogeneous Neosepta cation-exchange (CMX and CMX-Sb) and anion-exchange (AMX and AMX-Sb) membranes by applying optical microscopy, scanning electron microscopy, scanning electrochemical microscopy (SECM) and digital micrometer. It is found that the surface of all membranes is undulated: there are repeating hills and valleys due to the waved reinforcing fabric. The amplitude of undulation increases when swelling: in the case of dry samples, it varies from 10 (AMX-Sb) to 30 (CMX-Sb) microns, while for swollen samples, from 20 (AMX-Sb) to 55 (CMX) microns. These values are comparable to the diffusion layer thickness in industrial electrodialyzers, hence might make an essential impact in enhancement of mass transfer. The period of undulation is several hundreds of microns. Despite common use of micrometer, it gives overestimated membrane thickness since its measuring faces are applied only to the tops of the hills.

Pulsed electric fields (PEF) have been used to advantage in electroplating for more than half a century. Recently, interest has increased in the application of these electric modes in the membrane processes. In this work, the effect of parameters (potential, frequency of current, and duty cycle) of pulsed current mode on the average current density in the electrodialysis cell is studied. For this purpose, the plots of current vs. time were measured in the mode of pulsed potential drop on a Nafion 438 (NafionTM N438) cation-exchange membrane. It is shown that the largest gain in the current density of 33% can be attained by varying parameters of PEF.

A series of anion-exchange membranes based on a Neosepta AMX-Sb homogeneous membrane (Japan) have been studied by applying parallel nonconducting strips of a 100 to 600 μm width with the interstrip distance ranging from 400 to 1900 μm. The current–voltage characteristics of the membranes and the pH of a NaCl solution (of 0.02 mol/L concentration) have been measured in the course of passing the solution through the desalination compartment of a flow-through electrodialysis cell. Two sets of membranes with a nonconducting surface fraction snc of 5 to 60%, in which the pattern steps on the surface are 1000 and 2000 μm, have been considered. It has been shown that the limiting current density, ilim, depends on the nonconducting surface fraction: ilim exceeds the corresponding value for the initial membrane in the case when snc is in the range from 5 to 20%, reaching a maximum approximately at snc = 10% followed by a decrease with the further increase in snc. At snc = 10%, the value of ilim is greater when the inhomogeneity step is 2000 μm. It has been assumed that the growth in both the limiting current density and the rate of mass transfer through the modified membranes is due to electroconvection. The obtained experimental results correlate well with known mathematical models describing ion transport in membrane systems with allowance for electroconvection in the case of homogeneous and heterogeneous membranes.

Using the methods of electron diffraction microscopy and X-ray diffraction analysis, the influence of alloying of the austenitic steel, Grade 110H13, with chromium and vanadium, as well as high-melting, ultrafine-grained TiO2, ZrO2 powders and Na3AlF6 cryolite on its structural-phase state and microstructure is investigated. It is shown that the matrix of non-modified steel is completely austenitic and consists of an iron-based solid solution and the interstitial (C, N, O and other) and substitutional (Cr, V and other) atoms simultaneously. Alloying with chromium and vanadium changes neither its phase composition nor defect structure, while alloy modification results in qualitatively new structural features: γ → e-transformation, high-intensity microtwinning, defect structure changes, and a sharp increase in the scalar dislocation density. The features of the deformation-induced microtwinning and e-martensite plates identified in the modified steel promote revealing additional microtwin systems in the matrix γ-phase, which result in structural changes making it possible to classify it as a γ′-phase. It is found out that an introduction of modifying additions gives rise to the following sequence of structural-phase transformations: γ→γ′→(γ′ +e). The experimental data obtained demonstrate that as a result of modification the crystal lattice transits into a low-stability state. This transition is accompanied by marked structural-phase changes consisting in the formation of several microtwin systems and γ → e-transformation. These structural-phase changes in the modified steel are due to the crystal-lattice transition into the low-stability state, followed by new structural-phase alterations.

Chronopotentiograms and current-voltage curves were measured to characterize the transport of sodium, calcium, and magnesium ions through cation-exchange membranes MK-40 and MK-40MOD. A microfluidic electrodialysis cell was used to visualize electroconvective vortices. The MK-40MOD membrane was obtained by covering the heterogeneous surface of a commercial MK-40 membrane with a thin (about 15 μm) homogeneous film of the MF-4SK sulfonated fluoropolymer. It has been shown that the combination of relatively high hydrophobicity of the MK-40MOD membrane surface with a certain electrical and geometrical (surface undulation) heterogeneity facilitate the generation of electroconvective vortices. The effect of vortices is manifested in reduction of the potential drop under a fixed current density and potential oscillations on the chronopotentiogram. It was found that in all studied systems potential drop in stationary state decreases in the order Na+>Ca2+>Mg2+. This correlates with the amplitude of potential drop oscillations (which increases in the range Na+

Changes in the structural and phase state of low-carbon steel with a mixed structure of tempered martensite and ferrite, and deformed by equal channel angular pressing (ECAP), are analyzed by means of transmission electronic microscopy and X-ray diffraction. The impact ECAP has on the phase composition and morphology of the alloy is determined. The behavior of the carbide phase is studied. Grain misorientations are measured. Special attention is given to the problem of fine grain formation upon ECAP.

A batch of new cation-exchange membranes (CEM(n)) and three batches of used cation-exchange membranes (CEM(u)) at various use durations, from different electrodialysis (ED) units used in food industry, were characterized to evaluate the effects of prolonged use and organic fouling on their microstructure. Different characterization methods were experimented: ion-exchange capacity (IEC), thickness (Tm), conductivity (km), contact angle (θ), water content (WC), volume fraction of the inter-gel solution (f2), tensile strength tests, FTIR, structural and elementary SEM analysis and morphological analysis by optical microscopy. Non-aggressive, easy and economic cleaning strategy was tested in the ex-situ static mode. Three solutions (35 g L−1 NaCl, reconstituted seawater and a water-ethanol mixture) were used as regenerative solutions, where the membranes were soaked from 2 to 120 h. The efficiency of the cleaning procedures were evaluated, for each sample of treated membrane, by following km, IEC, θ, and f2 as functions of the cleaning time in order to judge the recovery of their physicochemical properties. The water-ethanol cleaning method was found to be the most efficient for these membranes. This method leads, first, to significant increases in km, IEC and f2 (at least 47%, 26% and 63%, respectively after 120 h) which indicates the effectiveness of internal cleaning, and second, to a decrease of about 15% in θ (after 120 h), that confirms the stripping of a part of the external fouling layer. We have used the microheterogeneous model to demonstrate the progressive increase of f2 as a function of the cleaning duration with the water-ethanol mixture.