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In this paper, a new speed control algorithm for a permanent magnet DC motor which does not require implementation of the angular speed sensor is presented. Three steps are performed to develop the control system: design of speed tracking control algorithm assuming the speed measurement; design of speed observer; design of sensorless speed control algorithm based on the principle of separation. Information about speed is taken from the speed observer using the motor current value. The stability of the composite system dynamics consisting of three subsystems (the speed regulation loop, current regulation loop, and speed observer) is analyzed. The feedback gains tuning procedure for decoupling of three subsystems is given. The simulation results show that the dynamic performance of the designed system is similar to the performance of the system with angular speed measurement. The resulting closed-loop system has structural robustness properties with respect to parametric and coordinate disturbances. References 12, figures 2.

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 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.

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 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.

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.

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.

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

It is known that some components of the bathing solution can enhance water splitting at depleted solution/ion-exchange membrane interface via protonation/deprotonation reactions with water. In this paper, we show that not only the presence of such components is important, but also a mechanism ensuring their sufficiently high concentration near the membrane surface. A comparative study of the electrochemical behavior of a Neosepta® homogeneous cation-exchange CMX and an anion-exchange AMX membranes (Astom, Japan) in 0.02 M KCl or 0.02 M NH4Cl solutions is carried out. The NH4+/NH3 couple is an effective catalyst of water splitting. The deprotonation reaction rate constant of the NH4+ ions, which limits the rate of water splitting, is about 10 s−1. It is almost 6 orders of magnitude greater than the rate constant for direct water dissociation in free solution. A comprehensive electrochemical characterization of the membrane systems is made: voltammetry, chronopotentiometry, electrochemical impedancemetry, and pH-metry (including color indication of the pH of the membrane internal solution). It is found that the water splitting rate at the interface of the AMX membrane in the NH4Cl solution is essentially higher than in the KCl solution. The difference in the rates of this reaction in KCl and NH4Cl solutions at the CMX membrane is insignificant. The reason for the weak effect of the NH4+/NH3 couple on the rate of water splitting at the CMX membrane is that the concentration of both NH4+ and NH3 species is very low near its surface if the current density is close to or higher than its limiting value. As for the AMX membrane, we show that the ammonia-containing species can be transported to its depleted surface from the enriched solution by back “facilitated” diffusion through the membrane and this transport plays a crucial role in the occurrence of the rapid water splitting.

Diffusion dialysis (DD) is an environmentally appropriate method for separating components, which are unstable under the external influences (high temperature, high pressure, presence of electric field). The roadblock to the wider application of the DD method for separation and purification of amino acids is relatively low rate and selectivity of diffusion transport of these substances through ion-exchange membranes. In this paper, mechanisms of amino acid selective transport and possibilities to increase its flux across a cation-exchange membrane are considered. In particular, the effect of replacement of a flat membrane with a profiled one, prepared by the method of hot pressing, when using the same material is examined. Experimental and theoretical study is carried out using solutions of phenylalanine amino acid and NaCl when applying a commercial flat MK-40 cation-exchange membrane and its modification MK-40pr with profiled surface. It is found that the relatively high selective transport of phenylalanine is due to its facilitated diffusion, while the NaCl diffusion is reduced by the Donnan effect. The MK-40pr membrane allows a 8-fold increase in phenylalanine flux in comparison with the MK-40 membrane. This increase in partly due to the increased surface available for mass transfer (in 2.3 times), but also to better hydrodynamics reducing the diffusion layer thickness and to a higher fraction of conductive surface and higher pore radius. The latter is caused by water evaporation within the membrane pores in the course of its profiling.

This paper concerns the mechanisms of aging of ion-exchange membranes (IEMs) during their use in electrodialysis (ED) of food industry solutions containing polyphenols (PPs), as well as their cleaning. The study focuses on anion-exchange membranes (AEMs); their behavior is compared with that of cation-exchange membranes (CEMs). First, physicochemical static characteristics, structural, morphological and tensile strength parameters are determined for new AEMs and two batches of used AEMs at different duration of their use in industry, subjected to regular “Cleaning In Place”. Second, non-aggressive and economic ex-situ static cleaning methods involving the application of NaCl at 35 g L−1, a reconstituted seawater and a water-ethanol mixture acidified with H2SO4 were examined. During the cleaning process, the evolution of physicochemical parameters, such as ion-exchange capacity (IEC), electrical conductivity (κm) and contact angle (θ), were followed. It is shown that the application of NaCl solution has a negligible effect on IEC and κm; when soaking the membranes in the reconstituted seawater, κm even slightly decreases; however, there is a significant increase in these parameters when soaking the membranes in the acidified water-ethanol solution. As for the mechanism of fouling, PPs are the main responsible constituents. Apparently, they form dense colloidal nanoparticles not permeable for ions within membrane meso- and macropores, not penetrating into micropores. A modification of the microheterogeneous model under this assumption allows an adequate description of membrane conductivity and explains the fact that the membrane pore size increases with the duration of membrane utilization, while the apparent volume fraction of the inter-gel solution (f2app) decreases. CEMs are found less prone to fouling. The soaking of CEMs in the water-ethanol solution leads to an increase in IEC and f2app by 33% and 60%, respectively, as well as to doubling κm and decreasing θ by 23%, after a 120 h. treatment.

Novel continuous-flow cascade reactions are developed for producing 1,4-diaryl-disubstituted dipolar γ-carbolines 2 that contain a carboxylate group and their two pentacyclic precursors 6, 7 from hemiindigos 1. The nucleophilic and pro-electrophilic chemistry described is new to the hemiindigos 1, and it led to the discovery of antimycobacterial scaffold characteristic of rimino-type pentacycles 6, 7 and potent drug clofazimine. The new scaffold like clofazimine appears to be useful in developing lead agents active against drug-resistant/dormant TB.

Swelling is an important property of charged gels and membranes. The size of pores and, therefore, membrane properties such as conductivity, diffusion and hydraulic permeability, permselectivity depend on water content and degree of swelling. In this paper we propose a simple model for equilibrium swelling of an ion-exchange membrane, allowing calculation of water content and membrane thickness as functions of the concentration and pH of the bathing solution. The model parameters include the equivalent volume of dry polyelectrolyte gel, the volume fraction of macropores and others. Three types of ion-exchange functional groups, namely, the secondary, tertiary and quaternary amino groups in an anion-exchange membrane are taken into account. The osmotic pressure exerted by micro- and mesopores, appearing in the gel when swelling, is expressed using the Gregor equation, which employs the mole fractions of free and bound water. The equilibria between protonated and deprotonated amino groups are assumed as well as the Donnan and ion-exchange equilibria between the membrane and bathing solution. The results of calculations are compared with experimental data on the membrane thickness and effective exchange capacity obtained for two heterogeneous anion-exchange membranes MA-40 and MA-41 (Shchekinoazot) differed by the composition of functional groups. The procedure of determining membrane structural and thermodynamic parameters is described. A good quantitative agreement between the theory and experiment is found for both membranes using the same set of ion hydration numbers and chemical equilibrium constants for secondary and tertiary amino groups. In particular, it is shown that with increasing pH of the bathing solution, the membrane thickness (and, hence, water content) pass through a local maximum and a local minimum. The simplicity of the model, which does not reduce adequacy, would enable it to be included later in other models describing the transport of ions and water to account for the swelling and change in the membrane structure with a change in pH and concentration of the bathing solution.

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 interplay between the ion exchange capacity, water content and concentration dependences of conductivity, diffusion permeability, and counterion transport numbers (counterion permselectivity) of CJMA-3, CJMA-6 and CJMA-7 (Hefei Chemjoy Polymer Materials Co. Ltd., China) anion-exchange membranes (AEMs) is analyzed using the application of the microheterogeneous model to experimental data. The structure–properties relationship for these membranes is examined when they are bathed by NaCl and Na2SO4 solutions. These results are compared with the characteristics of the well-studied homogenous Neosepta AMX (ASTOM Corporation, Japan) and heterogeneous AMH-PES (Mega a.s., Czech Republic) anion-exchange membranes. It is found that the CJMA-6 membrane has the highest counterion permselectivity (chlorides, sulfates) among the CJMAED series membranes, very close to that of the AMX membrane. The CJMA-3 membrane has the transport characteristics close to the AMH-PES membrane. The CJMA-7 membrane has the lowest exchange capacity and the highest volume fraction of the intergel spaces filled with an equilibrium electroneutral solution. These properties predetermine the lowest counterion transport number in CJMA-7 among other investigated AEMs, which nevertheless does not fall below 0.87 even in 1.0 eq L−1 solutions of NaCl or Na2SO4. One of the reasons for the decrease in the permselectivity of CJMAED membranes is the extended macropores, which are localized at the ion-exchange material/reinforcing cloth boundaries. In relatively concentrated solutions, the electric current prefers to pass through these well-conductive but nonselective macropores rather than the highly selective but low-conductive elements of the gel phase. It is shown that the counterion permselectivity of the CJMA-7 membrane can be significantly improved by coating its surface with a dense homogeneous ion-exchange film.

Bipolar membranes (BPMs) are a special class of ion-exchange membranes constituted by a cation- and an anion-exchange layer, allowing the generation of protons and hydroxide ions via a water dissociation mechanism. Such unique feature makes bipolar membranes attractive for a variety of applications in many sectors, such as (bio)chemical industry, food processing, environmental protection, and energy conversion and storage, among others. Research and development on BPMs over the past two decades have created a growing market with commercial BPMs available today from multiple manufacturers. Moreover, BPMs are rapidly gaining attention for their technical, environmental, and economical advancements compared to conventional processes for the production of acid and base, or local pH control. This review article aims to provide an overall understanding of BPM technology by describing the current state of the art on membrane synthesis, properties, theoretical models, and applications, based on the last 70 years of scientific publications and patents in this field. Optimised BPM properties are discussed, together with a summary of the advances in BPM fabrication to attain the targeted optimised characteristics. Furthermore, novel BPM applications are presented, including a list of shortcomings of current membranes that need to be overcome to unlock new promising applications.

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.

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.

Recently developed and produced by Hefei Chemjoy Polymer Material Co. Ltd., homogeneous CJMC-3 and CJMC-5 cation-exchange membranes (CJMCED) are characterized. The membrane conductivity in NaCl, Na2SO4, and CaCl2 solutions, permeability in respect to the NaCl and CaCl2 diffusion, transport numbers, current&ndash, voltage curves (CVC), and the difference in the pH (DpH) of the NaCl solution at the desalination compartment output and input are examined for these membranes in comparison with a well-studied commercial Neosepta CMX cation-exchange membrane produced by Astom Corporation, Japan. It is found that the conductivity, CVC (at relatively low voltages), and water splitting rate (characterized by DpH) for both CJMCED membranes are rather close to these characteristics for the CMX membrane. However, the diffusion permeability of the CJMCED membranes is significantly higher than that of the CMX membrane. This is due to the essentially more porous structure of the CJMCED membranes, the latter reduces the counterion permselectivity of these membranes, while allowing much easier transport of large ions, such as anthocyanins present in natural dyes of fruit and berry juices. The new membranes are promising for use in electrodialysis demineralization of brackish water and natural food solutions.

This paper develops a novel algorithm for interior permanent magnet synchronous motors (IPMSM) parameters identification for a self-commissioning procedure. The proposed algorithm is based on adaptive current controllers with robustness properties to inverter nonlinearities. It guarantees the stator resistance and inductances asymptotic estimation with permanent magnets flux if the conditions of persistency of excitation are provided. The validity of the conclusions is confirmed by the coincidence of the simulation study results with the experimental data.

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.

The effect of pH and concentration of the NaCl solution on the exchange capacity and transport properties of the MA-40 and MA-41 anion-exchange heterogeneous membranes with different nature of fixed groups has been studied: MA-40 has weakly basic groups, and MA-41 has strongly basic groups with a small proportion of weakly basic ones. The exchange capacity, thickness, water content, and electrical conductivity of the membranes equilibrated with NaCl solutions of various concentrations and pH were measured; for the same solutions, the diffusion permeability coefficients were found. The capacity was measured in the pH range from 1.5 to 12; the remaining properties, in the pH range from 3 to 9. Using the values of electrical conductivity and diffusion permeability, the ion transport numbers in the membranes were calculated. It was shown that at the external solution pH 9 the thickness of the membranes and their electric conductivity are minimal, and the transport numbers of co-ions are maximum. This is explained by the fact that in basic solutions weakly basic functional groups are largely deprotonated, and the effective capacity of the membrane is significantly reduced. The maximum effective capacity is achieved at pH $$ \leqslant $$ 3; in this case, transport numbers of co-ions in the MA-40 membrane are 5-fold, and in the MA-41 membrane, two-fold lower than corresponding values at pH 6 and 9. The changes in the transport properties of the membranes with increasing pH are due to a decrease in the degree of protonation of weakly basic functional groups, these changes are more pronounced for the MA-40 membrane than for MA-41.

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.

Current-voltage characteristics (CVCs) of a Neosepta AMX membrane are studied in NaH2PO4 (pH = 4.7, C = 0.02 mol/L) and KC4H5O6 (pH = 3.6, C = 0.02 mol/L) solutions. It is shown that in the case of NaH2PO4 there are two plateaus in the CVC, which correspond to achievement of the first, i lim I , and second, i lim I I , limiting currents. i lim I occurs when the NaH2PO4 salt diffusion to the membrane surface is saturated, i lim I I refers to the saturation of the proton flux when the membrane is almost completely converted into the HPO42− form. In the case of potassium hydrotartrate, there is no state corresponding to i lim I . The difference in CVC for two ampholytes is due to the difference in the ratio between the dissociation constants related to the first (Ka1) and second (Ka2) steps of ampholyte dissociation. In the case of NaH2PO4, where pKa1 and pKa2 differ greatly, a solution of this salt contains nearly exclusively the singly charged phosphate form. However, a KC4H5O6 solution contains, together with the C4H5O6− anion, about 15% of the doubly charged tartrates, which take part in charge transfer. Approximate analytical expressions are obtained for i lim I and i lim I I in the case of monosodium hydrophospate solution. Their application gives the i lim I and i lim I I values, which are in good agreement with the experiment and with numerical calculations using a mathematical model based on the Nernst-Planck equation, the electroneutrality condition, and the local chemical equilibrium condition in the membrane and two adjacent diffusion boundary layers.

A simple non-steady state mathematical model is proposed for the process of purification of an amino acid solution from mineral salts by the method of neutralization dialysis (ND), carried out in a circulating hydrodynamic mode. The model takes into account the characteristics of membranes (thickness, exchange capacity and electric conductivity) and solution (concentration and components nature) as well as the solution flow rate in dialyzer compartments. In contrast to the known models, the new model considers a local change in the ion concentration in membranes and the adjacent diffusion layers. In addition, the model takes into consideration the ability of the amino acid to enter the protonation/deprotonation reactions. A comparison of the results of simulations with experimental data allows us to conclude that the model adequately describes the ND of a strong electrolyte (NaCl) and amino acid (phenylalanine) mixture solutions in the case where the diffusion ability of amino acids in membranes is much less, than mineral salts. An example shows the application of the model to predict the fluxes of salt ions through ion exchange membranes as well as pH of the desalination solution at a higher than in experiments flow rate of solutions in ND dialyzer compartments.

The concentration dependencies of diffusion permeability of homogeneous (AMX-Sb and AX) and heterogeneous (MA-41 and FTAM-EDI) anion-exchange membranes (AEMs) is obtained in solutions of ampholytes (sodium bicarbonate, NaHCO3, monosodium phosphate, NaH2PO4, and potassium hydrogen tartrate, KHT) and a strong electrolyte (sodium chloride, NaCl). It is established that the diffusion permeability of AEMs increases with dilution of the ampholyte solutions, while it decreases in the case of the strong electrolyte solution. The factors causing the unusual form of concentration dependencies of AEMs in the ampholyte solutions are considered: (1) the enrichment of the internal AEM solution with multiply charged counterions and (2) the increase in the pore size of AEMs with dilution of the external solution. The enrichment of the internal solution of AEMs with multiply charged counterions is caused by the Donnan exclusion of protons, which are the products of protolysis reactions. The increase in the pore size is conditioned by the stretching of the elastic polymer matrix due to the penetration of strongly hydrated anions of carbonic, phosphoric, and tartaric acids into the AEMs.

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.

Electrodialysis finds broader use in reagent-free pH correction and tartrate stabilization of wines. The efficiency of these processes strongly depends on longevity of employed anion-exchange membranes. We report a comprehensive study of bulk and surface properties of a homogeneous Neosepta AMX-Sb and a heterogeneous MA-41P anion-exchange membranes after its contact with a red wine for 3, 10 and 72 h. The ion-exchange capacity, conductivity, thickness, as well as surface roughness (AFM and optical microscopy), local surface and bulk pH (by color indicator), surface chemical structure (ATR FTIR), contact angle and surface charge are measured. In addition, the AMX-Sb membrane is characterized by voltammetry and pH-metry. It is found that polyphenols act an important role in membrane fouling. Initially, it is relatively small and mobile anthocyanins, which penetrate inside the membrane; then they are followed by larger and slower tannins and/or anthocyanin-tannin complexes. Polyphenols together with polysaccharides and other wine constituents form colloidal aggregates, which fill the membrane pores and are deposited by islets on the surface as a foulant layer. The appearance of this layer increases hydrophilicity of the surface while reducing its charge. The membrane conductivity decreases with increasing the duration of membrane contact with wine. However, the effect of this contact on the limiting current density, ilim, overlimiting transfer and water splitting is unexpected. In early stages of fouling, ilim of the AMX-Sb membrane increases and water splitting is found suppressed, electroconvection is essentially enhanced. The latter should be due to the isle-type structure of the foulant layer: surface electrical heterogeneity promotes electroconvection. However, the contact of the membrane with wine for several tens of hours results in formation of all-over foulant layer stimulating water splitting and reducing electroconvection.

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.

The preparation of inorganic brown pigment from red mud is investigated. The results of the phase and chemical analyses of raw material and the product are given. A flow diagram is proposed and the parameters of the pigment production are recommended. This approach has provided a pigment of pure color with the opacity of 8 to 10 g m–2 from red mud (up to 80%) without additives and the reduction of Fe(III) into Fe(II) using sulfide sulfur.

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.

Transition time in chronopotentiometry is an important parameter, which is widely used for electrochemical characterization of various systems. Occurrence of multiple transition times is typical for multicomponent or multilayer electrode and membrane systems. In this paper we show that there may be another cause of multiple transition times. It is electrical heterogeneity of ion exchange membrane surface. It is found that there are two transition times on the chronopotentiograms of a commercial anion-exchange MA-41 (Shchekinoazot) and two specially prepared cation-exchange heterogeneous membranes in dilute electrolyte solutions (0.02 M NaCl in the experiment). It is found that both transition times are determined by diffusion limitations of ion delivery to the membrane surface in the depleted diffusion layer. The value of the first transition time depends on the dimensions of the conductive regions and their surface fraction; this transition time is determined as the time necessary for the depletion of electrolyte concentration near the conductive regions of the surface. The rate of concentration depletion depends on the electromigration through the conductive regions, on the one hand, and on the normal the tangential ion diffusion to the conductive surface regions, which mitigate the concentration decrease, on the other hand. The experimental value of the first transition time for the laboratory-made membranes is in a good agreement with simulation using a 3D electrodiffusion model. The value of the second transition time is in a good agreement with the Sand theory, hence it is conditioned by the normal diffusion delivery of electrolyte from the solution bulk to the entire membrane surface. The tangential diffusion plays a secondary role in this stage of concentration polarization since current-induced convection levels off the concentrations along the heterogeneous membrane surface.

The properties of high-temperature nickel alloys for manufacturing depend on the thermal stability of the structure, the particle size, the shape, the quantity of strengthening γ' phase, and the strength of the γ solid solution. Such alloys are strengthened by the addition of rhenium and lanthanum. In the present work, the structure and phase composition of high-temperature nickel alloy with added rhenium (0.4 at %) and lanthanum (0.006 at %) are qualitatively and quantitatively investigated. The methods employed are transmission diffraction electron microscopy and scanning electron microscopy. The alloy structure is considered in three states: after directed crystallization (the initial state, sample 1); after directed crystallization, annealing at 1150°C for 1 h, and annealing at 1100°C for 480 h (sample 2); and after directed crystallization, annealing at 1150°C for 1 h, and annealing at 1100°C for 1430 h (sample 3). Primary and secondary phases are observed in the superalloy. The primary phases are γ' and γ. They form the structure of the alloy and are present in the form of γ' quasi-cuboids separated by γ layers. The secondary phases due to the presence of rhenium and lanthanum are β NiAl, AlRe, NiAl2Re, σ, χ, and Ni3La2. The secondary phases seriously disrupt the structure of the γ + γ' quasi-cuboids. The rhenium and lanthanum do not uniformly fill the whole alloy volume, but only appear in local sections. Therefore, in all three states of the alloy, only some volume of γ + γ' quasicuboids is disrupted. Analysis of the secondary phases’ morphology shows that the σ particles are thin needles, whereas the Ni3La2 particles have internal structure with characteristic contrast and are relatively thick. Interestingly, the σ phase and Ni3La2 are deposited at the same locations. The introduction of rhenium and lanthanum changes the phase composition of the alloy, suppressing the formation of γ phase. The particles of secondary phase are localized in individual sections of the alloy with specific periodicity. The secondary phases are refractory: the melting point is about 1600°C for β phase, 2600°C for σ phase; and 2800° for χ phase. Thanks to the formation of refractory secondary phases and their periodic distribution in the structure, the strength of the superalloy with added rhenium and lanthanum is increased.

The phase composition, the structure and the morphology of the surface of the VT1-0 titanium modified by copper ions with an energy of ∼0.5 … 2.5 keV and an ion current density of ∼2 … 20 mA/cm2 have been investigated by X-ray, SEM and TEM. It has been established that there are the intermetallic phases of the Cu-Ti equilibrium diagram in the surface layer during the treatment of the VT-10 titanium by copper ions. The modified surface layer in the cross section is divided into two layers up to 1 μm and from 1 μm up to 4.5–5.0 μm in thickness depending on the treatment time. Two-level micro and nanoporous nanocrystalline structure is formed in modified layer. It has been found that the phase structure and the morphology of the surface layers of the VT1-0 alloys depend on the treatment time.

At current densities exceeding the limiting current density, H+ and OH− ions are generated at the interface of the ion-exchange membrane with a depleted solution as a result of the dissociation of water molecules. At present, it is generally accepted that water splitting occurs in a thin (a few nanometers) layer inside the membrane, this reaction being catalytic in nature. The mathematical model of ion transport in the diffusion layer near the membrane surface has been constructed and numerically studied under conditions when dissociation and recombination processes involving water molecules and H+ and OH− ions occur simultaneously. It has been shown that in overlimiting current regimes under very high voltages, intense noncatalytic dissociation of water molecules in the extended space charge region of the depleted solution can occur irrespective of the catalytic splitting of water. Since this region has macroscopic dimensions, the rate of noncatalytic water dissociation is comparable with the rate of the corresponding catalytic process. The obtained results significantly supplement modern concepts of the mechanism of generation of H+ and OH− ions in membrane systems, showing that this process can proceed not only in accordance with the conventional mechanism with the catalytic participation of functional groups and/or other compounds, but also via the noncatalytic mechanism that has not been taken into account to the present.

Single-pulse and double-pulse chronopotentiograms of a homogeneous anion-exchange membrane AX in 0.02 M solutions of NaCl (system 1) or NaH2PO4 (system 2) have been recorded in underlimiting and overlimiting current modes. It has been found that in the case of exceeding the limiting current (i > i lim Lev ) calculated using the convection–diffusion model, the time required to establish a steady state in system 2 increases by more than an order of magnitude compared to system 1. The slow growth of the potential drop is due to a gradual transition of the membrane from the form in which the main counterion is H2PO 4 – to the HPO 4 2– form. This transition is due to the deprotonation of a part of H2PO 4 – ions forming HPO 4 2– and protons as they enter the membrane. The participation of H+ in charge transfer in the depleted diffusion layer at a given current density causes a lower value of the potential drop than in system 1 for the same i/i lim Lev ratio. In intense current regimes, chronopotentiograms of system 2 exhibit two inflection points. The first point corresponds to the classical Sand transition time and is due to reaching the limiting current of H2PO 4 – ions (the main charge carrier for i < i lim Lev ) in the depleted diffusion layer. The second point is associated with a critical current that can be called the second limiting current in the system with NaH2PO4 and has no analogue in the system with NaCl. This current, which is approximately 2i lim Lev , corresponds to the state when the membrane is completely transformed into the HPO 4 2– form. Meanwhile, the source of protons due to the transformation of H2PO 4 – into HPO 4 2– ions as they enter the membrane is exhausted. After reaching this critical value of the potential drop, either the HPO 4 2– deprotonation reaction to give triply charged PO 4 3– ions in the membrane or the water splitting on fixed groups located at the membrane/solution interface may occur.

Peptide fouling occurring on anion- (AEMs) and cation-exchange membranes (CEMs) is one of the most serious issues of conventional electrodialysis (ED) process for hydrolysate demineralization. Nonetheless, recent studies discussed the advantages of non-conventional ED phenomena such as water splitting and electroconvection on decreasing scaling and fouling. Thereby, peptide fouling was characterized using four different ED regimes: no current applied, underlimiting (conventional), limiting (water splitting) and overlimiting (electroconvection and water splitting) conditions. Results demonstrated that fouling-related interactions were mainly electrostatic with AEMs whereas they were both electrostatic and hydrophobic with CEMs. After 60 min, the demineralization rate was six times higher in overlimiting than underlimiting conditions. In addition, peptide fouling was 62% and 36% lower in overlimiting condition for AEMs and CEMs, respectively. It was hypothesized that (1) water splitting would have repealed the peptide charges through its "barrier effect" and (2) electroconvective vortices generated at the membranes interfaces would have washed-out their surfaces and hampered the attachment of peptides. Interestingly, ED under overlimiting conditions is a promising way to avoid peptide fouling. Consequently, membranes lifetime would be longer and new ED applications would be possible.

The membrane fouling formation during electrodialysis of complex solutions is one of the main issues affecting the process performance and costs. This work was focused on the investigation of electrochemical behavior of membrane systems containing a cation-exchange membrane whose surface was affected by mineral fouling of different composition. Together with the scaled membranes, the pristine membrane was studied for comparison. For membrane without scaling on its surface, it was found that the limiting current value exceeded the one theoretically calculated by the convection-diffusion model. It is most likely related to equilibrium electroconvection developed at the membrane surface. The presence of magnesium and calcium hydroxides on the membrane surface leads to an intensification of water splitting at the depleted membrane surface, resulting in suppression of electroconvection and reduction of the overlimiting current. The presence of calcium carbonate on top of magnesium and calcium hydroxides prevents their contact with water molecules. The current-voltage characteristic of such membrane system was almost identical to the characteristics of the membrane system containing the pristine membrane. To our knowledge, it was the first time that the impact of scaling nature on the electrochemical behavior of membrane system was revealed and the relative mechanisms identified and explained.

Polyelectrolyte multilayer nanofiltration membranes (PEMMs) achieve tailor-made rejection and selectivity of ions for water treatment applications through a layer-by-layer coating procedure, in which a charged support membrane surface is sequentially contacted with positively and negatively charged polyelectrolytes. This results in the adsorption and formation of such selective multilayer membrane skins with defined molecular compositions. The selective properties of the PEMM depend on the intrinsic properties of the respective layers. Today’s research efforts aim to correlate the membrane’s selective characteristics, its structural parameters, and the operating conditions to a model representation of the membrane’s properties. We use our previously published pE n PE n model, which solves the pressure (p) driven transport of ions through n electrolyte layers (E n ) and n polyelectrolyte layers (PE n ). Here, we expand the model to predict the multi-ionic pressure-induced transport through PEMMs solving one-dimensional Nernst–Planck–Poisson equations. The simulations quantify the influence of asymmetric charge distributions and individual PE layers on the ion selectivity for multi-ion solutions. These asymmetric layer properties represent the nanometer-scale membrane properties emerging from the ionic crosslinking, fixed charge compensation, and overcompensation. The model gives insight into each ion’s concentration profile for n layers of electrolyte and n layers of polyelectrolytes. Now, multi-ion compositions inside and outside of the membrane are simulated, and it is shown that the membrane charge distribution even influences the onset of scaling at the fluid membrane interface. As pE n PE n provides a detailed understanding of the rejection and selectivity characteristics as a function of membrane flux and feed concentration including feed side concentration polarization, it can now predict flux-scaling boundaries for the different membrane charge distributions, making it a powerful tool for choosing process parameters and even for designing tailored PEMMs for specific separation tasks.

Combination of pressure and electrically driven membrane processes in one device is an intriguing but scarcely investigated option. We report here such a hybrid electro-baromembrane process applied to separate monovalent cations. In this process, an electric field and a pressure field are simultaneously applied to a track-etched membrane with an effective pore diameter of 28 nm in a way that the electric force and pressure force act on competing ions in opposite directions. The cases of separation of K+ and rhodamine cation and K+ and Li+ are studied experimentally. The permselectivity coefficient for separation of K+/Rh6G+ and K+/Li+ was found equal to 220 and 36, respectively; the K+ flux density in the first and second cases was 7.2 and 4.0 mol/(m2h), respectively. These results were obtained with rather low driving forces, the voltage and pressure drop across the membrane were 1 V and 0.12 bar, and 0.5 V and 0.28 bar in the first and second cases, respectively. The method allows the separation of ions with the same charge when consuming low energy, which is almost impossible using other membrane methods. A simplified mathematical model, which roughly describes the experimental data, is developed.

A novel and robust field oriented vector control method for standalone induction generators (IG) is presented. The proposed controller exploits the concept of direct field orientation and provides asymptotic rotor flux modulus and DC-link voltage regulations when a DC-load is constant or slowly varying. Flux subsystem, designed using Lyapunov’s second method, has, in contrast to standard structures, closed loop properties and therefore is robust with respect to rotor resistance variations. A decomposition approach on the base of the two-time scale separation of the voltage and torque current dynamics is used for design of the voltage subsystem. The feedback linearizing voltage controller is designed using a steady state IG power balance equation. The resulting quasi-linear dynamics of the voltage control loop allows use of simple controllers tuning procedure and provides an improved dynamic performance for variable speed and flux operation. Results of a comparative experimental study with standard indirect field oriented control are presented. In contrast to existing solutions, the designed controller provides system performances stabilization when speed and flux are varying. It is experimentally shown that a robust field oriented controller ensures robust flux regulation and robust stabilization of the torque current dynamics leading to improved energy efficiency of the electromechanical conversion process. The proposed controller is suitable for energy generation systems with variable speed operation. References 18, figures 8.