EMF Method Research Articles

TRANSPORT PROPERTIES OF La2(WO4)3-Al2O3 COMPOSITES

Composites (1-φ)La2(WO4)3 – φAl2O3 (φ is the volume fraction of nanodispersed aluminum oxide) were obtained by the solid-phase method, their thermal properties, morphology, electrical conductivity depending on temperature, oxygen pressure in the gas phase, and composition were studied. It was found that the conductivity of composites (1-φ)La2(WO4)3 – φAl2O3 passes through a maximum at φ ~ 0.1 and reaches a value of 7 10-3 S/cm at 1000°C, which is 7 times higher than the conductivity of La2(WO4)3 at given temperature. Using the EMF method and measuring the dependence of electrical conductivity on oxygen pressure in the gas phase, the ionic nature of the conductivity of (1-φ)La2(WO4)3 – φAl2O3 composites was established.

Thermodynamic Study of Ag8GeTe6 and Ag8GeTe6 – xSex Solid Solutions by the EMF Method with Solid Ag+-Conducting Electrolyte

Thermodynamic Study of Ag8GeTe6 and Ag8GeTe6 – xSex Solid Solutions by the EMF Method with Solid Ag+-Conducting Electrolyte

THERMODYNAMIC PROPERTIES OF SOME TERNARY COMPOUNDS OF THE ARGYRODITE FAMILY

Compounds of the argyrodite family are valuable environmentally friendly functional materials with mixed ion-electronic conductivity, thermoelectric, photovoltaic, optical, and other properties. This paper presents the results of a thermodynamic study of the Cu8GeS6 and Cu8GeSe6 compounds - representatives of this family using the EMF method with Cu4RbCl3I2 solid electrolyte in the 295-430 K temperature range. From the EMF measurement data, the partial molar functions of copper were calculated in both crystal modifications of the Cu8GeS6 and Cu8GeSe6 compounds, undergoing polymorphic transformations at 330 and 335 K, respectively. Based on solid-phase equilibria diagrams of the Cu-Ge-S(Se) systems, the potential-forming reactions responsible for the partial molar functions of copper in the alloys were determined and the thermodynamic functions of formation and standard entropies of both modifications of these compounds, as well as the thermodynamic functions of their polymorphic transitions, were calculated. The work also presents and analyzes the thermodynamic data for compounds of the argyrodite family available in the literature

Online Adaptive Gain for Passivity-Based Control for Sensorless BLDC Motor Coupled With DC Motor for EV Application

Passivity based control (PBC) is an energy based control inwhich total energy is an algebraic sum of stored and dissipated energy. The energy equations are analysed using Hamiltonian operator. Exact Tracking Error Dynamics Passive Output Feedback (ETEDPOF) method is used to drive a BLDC motor coupled with DC motor. The controller is a linear controller which adapts precise variation by means of sensing output current as well as position of motor for varying speed reference. The system is made sensorless by eliminating both position and speed sensors to reduce cost of implementation using back EMF method. The back EMF of each winding is sensed and using zero crossing detectors, the initial position is found for starting the motor. The speed is observed from back EMF and also the gate signals are sent to inverter. The inverter is powered from single phase AC supply through DC filter and boost converter. In order to verify features of proposed control scheme, PBC is compared with widely used PI controller and Sliding Mode Control (SMC) for boost converter and inverter, simulated in MATLAB and results are observed with constant load torque and speed conditions.

Determination of phase equilibria in the CuxZryCr1-ySe2 system by the EMF method

Layered materials ZrSe2, CuZrSe2 and CuCr0.8Zr0.2Se2 were synthesized, and the structure of the obtained compounds was determined. The phase states in CuxZrSe2 and CuxZr0.2Cr0.8Se2 systems were determined by coulometric titration and electromotive force methods. An increase in the potential difference in the electrochemical cells Cu|Cu+|CuxZryCr1-ySe2 upon substituting Zr4+ for Cr3+ (0 < x < 0.5) was also noted. The copper diffusion coefficients for CuZrSe2 and CuCr0.8Zr0.2Se2 were estimated to be 10─9 and 10─10 respectively.

OXYGEN-ION COMPOSITES MWO4-SiO2 (M – Sr, Ba)

Composite materials (1-f)SrWO4–fSiO2 and (1–f)BaWO4–fSiO2, where f is the volume fraction of the dispersed SiO2 additive, were prepared by the solid-phase method. The resulting composites were studied by XPA, TG-DSC, SEM-EDA. The electrical conductivity of the composites was measured by the electrochemical impedance method as a function of temperature, oxygen partial pressure in the gas phase, and composition. To estimate the contribution of ionic conductivity, the sum of ionic transfer numbers was measured by the EMF method. It has been shown that the addition of 20–25 vol % nano-SiO2 to low-conductivity oxygen-ion conductors SrWO4 and BaWO4 leads to an increase in the ionic conductivity of composites based on them by two orders of magnitude and by 12 times, respectively. The increase in conductivity in the systems under study is explained by the additional contribution of interfacial boundaries formed between the MeWO4 matrix and dispersoid nanoparticles. The mixing rule [1] was used to calculate the electrical conductivity of (1-f)SrWO4–fSiO2 and (1-f)BaWO4–fSiO2 composites depending on the SiO2 content. The calculated concentration dependences of the conductivity obtained are in satisfactory agreement with the experimental results.

Mutual impedance computation using spherical harmonics between two closely spaced antennas

Mutual coupling between two identical radiators is computed using vector spherical harmonics and reaction theorem for small element spacing cases. For closely spaced antennas, the minimum spheres that enclose the antennas overlap, and the vector spherical harmonic expansions do not converge on the surface that separates the two antennas. The proposed method mainly uses addition theorems to translate the vector spherical harmonic expansions to a different center. These operations on spherical waves enable to redefine the minimum spheres and convergence regions. The proposed method has been validated by analyzing the coupling between two half-wave dipoles in a side-by-side configuration. The results clearly show excellent agreement with that obtained from induced EMF method. The theory is also tested experimentally. A printed dipole antenna is designed, and its spherical harmonic coefficients are obtained by spherical near field measurement. Mutual impedance between two such dipoles is computed using the proposed method. The computed results for different element spacings in a side-by-side configuration are compared to those obtained from s-parameter measurements.

Preparation, electrical and thermal properties of new anode material based on Ca-doped perovskite CeAlO3

Tetragonal perovskite phase Ce0.9Ca0.1AlO2.95 + x was obtained for the first time. Such phase, containing cerium in the oxidation state of 3+, can be promising anode materials for a solid oxide fuel cells (SOFCs). Ce0.9Ca0.1AlO2.95 + х (space group I4/mcm) was synthesized by the solid-phase method at 1400°С in a nitrogen flow with using ammonium oxalate (NH4)2C2O4 to create a reducing atmosphere. Thermogravimetry results showed that Ce0.9Ca0.1AlO2.95 + x was stable to oxidation up to 500°С in air and up to 700°С in argon (partial pressure of oxygen рО2 = 10−4 bar). The thermal expansion coefficient measured by dilatometry was equal to 11.16·10−6 К−1. The temperature dependences of the electrical conductivity (for undoped phase CeAlO3σ ≈ 1·10−3 S/cm and for doped Ce0.9Ca0.1AlO2.95 + xσ ≈ 3·10−2 S/cm at 500°С in air) were obtained by the electrochemical impedance spectroscopy measurements). The electrical conductivity of these samples at the temperatures range of 350–500°С was almost independent of the partial pressure of oxygen рО2 from 10−18 to 0.21 bar, however, there was a slight negative slope at T > 500 °C (рО2). The total ionic transport numbers measured by the EMF method were close to 1·10−3, which indicated the dominance of electronic conductivity. The measurement of the sign of the thermal-EMF showed that positive charge carriers (holes) were dominant charge carriers.

Synthesis and Electrical Properties of Nd2(WO4)3–SiO2 Composites

t—The (1 – x)Nd2(WO4)3–xSiO2 composites where the silicon oxide mole fraction is x ≤ 0.5 were manufactured by the solid-phase method. The phase compositions of the composites and their thermodynamic stability were verified by X-ray powder diffraction and thermogravimetry, respectively, in combination with differential scanning calorimetry (DSC). The morphology of the composites was studied by scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis. The electrical conductivity of the composites measured by electrochemical impedance was studied as functions of temperature, oxygen vapor pressure, and the amount of silicon oxide (the dispersed additive). The sums of ion transference numbers were studied as a function of temperature by the EMF method; the ionic character of conduction in the composites was found. The composite-conductivity effect was found to occur in the studied system: additions of 30 mol % nanosized silica to neodymium tungstate increased the ionic conductivity by more than two orders of magnitude.

Thermodynamic study of silver-silicon selenides (tellurides) by the EMF method with AG4RBI5 solid electrolyte

Thermodynamic study of silver-silicon selenides (tellurides) by the EMF method with AG4RBI5 solid electrolyte

PRODUCTION OF FUNCTIONALLY GRADIENT MATERIALS BASED ON SILICON CARBIDE AND HIGH-ALLOY STEEL USING SPARK PLASMA SINTERING TECHNOLOGY

An important scientific task of practical materials science is the production of metal-ceramic composites in the form of functional gradient materials (FGM) for special-purpose products. In this regard, a study was conducted on the application of spark plasma sintering (IPS) technology for the effective diffusion connection of SiC ceramics and high-alloy steel (grade X18R15) to obtain a combined FGM composite. In a comprehensive experimental study, the dynamics of consolidation and changes in the phase composition of dispersed SiC under conditions of different temperatures and heating rates, pressing pressure, and holding time were studied. As a result, the IPS conditions were optimized for obtaining SiC ceramics of high relative density (82%) and microhardness (500 HV) of stable phase composition. The physicochemical foundations of the formation of a strong compound of a two-component SiC-ceramic and steel system under IPS conditions without additives and using a mixture of additives in the form of a binder, a reaction binder and a damper (Ti–Ag, Ti–TiH2, Ti–Ag–TiH2 and Ti–Ag/Mo additive systems) have been studied. The structure, composition of ceramics and intermediate (binding and damping) layers, as well as the diffusion of elements at the boundary of the formed compounds in FGM composites, were studied using XRF, SEM and EMF methods. It was found that the Ti–Ag/Mo additive in the ratio of 30 wt. % Ti–70 wt. % Ag and a dense layer of Mo (thickness ~ 2 mm), acting as a damper to compensate for the temperature coefficient of linear expansion, ensure the formation of a connected FGM composite of an integral shape. The presented studies have been implemented for the first time, are promising and require further development in order to gain scientific knowledge of the manufacture of composite products for special purposes.

Interaction between Iron Fluoride and Molten FLiBe

The equilibrium potentials of iron in a LiF-BeF2-FeF2 melt were measured using the EMF method and were dependent upon the temperature and iron fluoride concentrations. The empirical equations for the isotherms and equilibrium polytherms of the iron fluoride concentration were obtained. The cathode polarization of iron fluoride in the molten mixture of lithium and beryllium fluoride was measured using the current switch off method from the stationary state. It was found that in the studied temperature and concentration ranges of iron fluoride in the LiF-BeF2 electrolyte, the valence state of iron in the melt is mainly +2. According to the experimental values of the equilibrium potentials of the iron electrode in the LiF-BeF2-FeF2 melt, the conditional standard potentials of iron were calculated relative to the fluoride reference electrode in the molten mixture of lithium and beryllium fluoride. The conditional standard values of the Gibbs energy change were calculated at the formation of iron difluoride from the element in the form of dilute solutions, as were the thermodynamic values (enthalpy and entropy) when iron difluoride was mixed with LiF-BeF2.

Ionic Equilibria in Polytungstate Melts

Polytungstate melts are used for the electrodeposition of oxide tungsten bronzes (OTBs). The scarce information on the ionic composition and properties of these electrolytes hinders effective control of the electrochemical synthesis of OTBs with desired electrical and optical properties. In this work, a comprehensive study of Na2WO4–WO3 melts that contained up to 55 mol% of tungsten trioxide was performed in the temperature range from 983 to 1073 K. Melt densities were measured using the Archimedes method. DFT calculations were carried out for various tungsten-containing compounds, including WxO3x−12+, WxO3x+12−, NaWxO3x+1−, and Na2WxO3x+1. The calculated values of the W–O bond energy indicate that the tested compounds are stable in the specified temperature range, and the WO22+ cation is the most stable. The experimental dependences of the redox potential on the mole fraction of tungsten trioxide in the Na2WO4–WO3 melt were obtained using the EMF method. A model that considers the processes of interaction between tungsten-containing ions and O2− ions was proposed for the quantitative interpretation of these dependences. The equilibrium constants were found through fitting according to the Levenberg–Marquardt algorithm. The effect of the WO3 mole fraction and temperature on the concentrations of WO42−, W2O72−, W3O102−, W4O132−, WO22+, and O2− ions was analyzed.

ТЕРМОДИНАМІЧНІ ВЛАСТИВОСТІ СПОЛУКИ AgGaGe3Se8 ЗА Т≤500 К, ВСТАНОВЛЕНІ МЕТОДОМ ЕРС

The division of the concentration space of the Ag–Ga–Ge–Se system in the GeSe–Se–Ga2Se3–AgGaGe3Se8–GeSe section was carried out by the EMF method. The concentration space of the Ag–Ga–Ge–Se system contains the four-phase regions GeSe2–Se–Ga2Se3–AgGaGe3Se8 (I) and GeSe–GeSe2–Ga2Se3–AgGaGe3Se8 (II). The spatial positions of these phase regions vs the point of silver were used to express equations of the overall cell reactions of synthesis of the AgGaGe3Se8 compound: 2Ag + 6GeSe2 + Ga2Se3 + Se = 2AgGaGe3Se8 and 2Ag + 7GeSe2 + Ga2Se3 = GeSe + 2AgGaGe3Se8. Reactions were performed in the positive electrodes of the following electrochemical cells (ECCs): (−) С | Ag | SЕ | R(Ag+) | PЕ | С (+), where C is graphite, Ag is the left (negative) electrode, SE is the purely Ag+ ion conducting solid electrolyte (Ag3GeS3Br-glass), PE is the right (positive) electrode, and R(Ag+) is the region of PE that contact with SE. Shifted from the left electrode to the R(Ag+) region for thermodynamic reasons Ag+ ions acted as the small nucleation centers for reconstruction of the metastable mixtures of compounds in the thermodynamically stable mixture of phases. Linear dependences of EMF vs temperature of ECCs were used to calculate the standard thermodynamic properties of the AgGaGe3Se8 equilibrium in the regions (I) and (II): ∆_f G_((I))^○= –(575,0 ± 8,9) kJ·mol −1, ∆_f H_((I))^○= –(574,7 ± 12,0) kJ·mol−1, S_((I))^○ = (515,9 ± 14,1) J·(mol·K)−1 and ∆_f G_((II))^○ = –(588,4 ± 9,4) kJ·mol−1, ∆_f H_((II))^○ = –(590,6 ± 12,9) kJ·mol−1, S_((II))^○ = (507,8 ± 13,2) J·(mol·K)−1, respectively. The relative difference between the calculated values ∆_f G_((I))^○ and ∆_f G_((II))^○ within ~2.3% and the overlap of the uncertainty intervals characterize the four-phase sections (I) and (II) by the combination of compounds of the formula composition. Moreover, values of the partial thermodynamic functions of the potential-determining component (Ag) of the AgGaGe3Se8 compound were calculated.

Analysis, Optimization, and Hardware Implementation of Dipole Antenna Array for Wireless Applications

The antenna pattern synthesis is one of the significant problems in the phased array antenna. Pattern synthesis refers to the optimized weight excitation of each antenna element in order to steer the beam electronically without mechanically rotating the antenna. It can be achieved by using a combination of phase shifters and attenuator circuits. In this paper, a 2 by 2 dipole antennas with an RF beamforming circuit has been designed to steer the main beam along the azimuth plane. The main beam coverage from 100° to 140° with a step size of 10° has been successfully optimized using a hybrid of the induced EMF method and a genetic algorithm. The optimization results were compared to the full-wave simulation technique implemented in Empire XCCel. The design is realistically implemented at 2.45 GHz, with both simulation and measurement results shown. The measured reflection coefficient of the phased array antenna is −48 dB at 2.56 GHz. The feasibility of the beam synthesis has been validated successfully with the main beam being steered at 110°. The possibility of a fabrication discrepancy resulting in minor radiation degradation is also discussed in this research. The dipole antenna system with RF beamformer circuit can be applied to indoor positioning systems such as Wi-Fi, wireless local area network (WLAN), and fifth-generation.

Activity measurements of Ga in liquid Ga–Tl alloys by EMF method with zirconia solid electrolyte

Abstract Electromotive force measurements (EMF) of an electrochemical cell with zirconia as solid electrolyte were performed to determine the Ga activity from 973 to 1273 K in the entire composition range of liquid Ga–Tl alloys. In the whole concentration range, the activity of Ga shows large positive deviations from ideality, and the activity of Tl which is derived by the Gibbs–Duhem equation shows also positive deviation from ideality. The parameters of the Redlich – Kister equation for excess Gibbs energies of mixing are determined from the results obtained in this study which were compared with Chou’s model calculation.

Thermodynamic properties of liquid Cu–In–Zn alloys

Abstract The partial Gibbs energies of zinc in the liquid Cu– In–Zn system as a function of temperature and concentration were measured in the temperature range between the melting points of the alloys and 1073 K using an EMF method with a liquid electrolyte. The thermodynamic properties were determined for 30 alloys at three different constant ratios of Cu : In of 1 : 2, 1 : 1, and 2 : 1 with zinc added in the concentration range between 5 and 90 at.%. The integral Gibbs free energy and the integral enthalpy of mixing of the ternary system were calculated with the Gibbs Duhem equation.

An optimized design modelling of PV integrated SEPIC-based four-switch inverter for sensorless PMBLDC motor control

The design of PV-based high gain SEPIC converter integrated with four-switch strategy, which has been used to achieve sensorless speed control of Permanent magnet Brushless DC motor (PMBLDC) is analysed in this work. Hence SEPIC converter coupled with Fuzzy Logic, MPPT Algorithm is employed to retain voltage. SEPIC converter is chosen as it has a continuous current operation with high gain; Fuzzy MPPT algorithm is used as it provides accurate results faster while the classical MPPT techniques provide the results with fluctuations in attaining the maximum power. Regarding the sensorless control of PMBLDC motor, the conventional six-switch strategy is replaced by four-switch strategy and the sensors are replaced by back EMF method. Four-switch strategy has the capability of reducing the losses, size, cost and complexity of control. For achieving the nominal speed, a closed-loop control is implemented with PI controller, which is tuned by GWO technique. The proposed methodology is more efficient as the motor speed remains unchanged even under the full load condition. The end result of traditional PI algorithm and PI algorithm, which have been tuned by GWO algorithm, is compared and simulated through MATLAB. This is also implemented and validated in hardware by FPGA Spartan 6E controller.

Thermodynamic study of the thallium-thulium tellurides by EMF method

In this study the phase equilibria in the Tl2Te–Tl2Te3–TlTmTe2compositions area of the Tl–Tm–Te ternary system were studied by powder X-ray diffraction (PXRD) analysis. Based on PXRD data, the solid-phase equi-libria diagram was plotted. The thermodynamic functions of the Tl9TmTe6and TlTmTe2ternary compounds were calculated by the electromotive forces method. The electrochemical cells of the following type (−) TmТе (s.) | glycerol + KCl + TmCl3 | (Tm in alloys of Tl–Tm–Te system) (s.) (+) were assembled and their EMF were measured in the 300-450 Ktemperature range. Based on obtained EMF data for the Tl2Te3–TlTe–TlTmTe2and TlTe–TlTmTe2–Tl9TmTe6three-phase regions, the relative partial thermodynamic functions of TmTe in alloys were calculated. The combination of these functions with the partial molar functions of thulium in TmTe allowed calculating the corresponding partial functions of thulium in the above phase regions. The potential-forming reactions responsible for the indicated partial molar values were obtained based on con-structed solid-phase equilibria diagram. Using indicated potential-forming reactions, for the first time, the standard thermodynamic functions of formation and standard entropies of the Tl9TmTe6and TlTmTe2 compounds were calculated.

Thermodynamic Study of the Ag–Sb–Se System by the EMF Method with Ag4RbI5 Solid Electrolyte

Thermodynamic Study of the Ag–Sb–Se System by the EMF Method with Ag4RbI5 Solid Electrolyte