Impedance Diagrams Research Articles

An alN-based piezoelectric micromachined ultrasonic transducer with a double-beam suspended structure

ABSTRACT This paper presents an AlN-based piezoelectric micromachined ultrasonic transducer (PMUT) with a double-beam suspended structure. In order to obtain greater deflection displacement and output sound pressure compared to standard systems, a suspended structure is proposed, achieved by utilizing double-sided deep reactive ion etching of the silicon substrate. This structure is capable of greatly reducing the tensile stress caused by deflection on the membrane edge, thereby improving the piezoelectric micromachined ultrasound transducer performance. Simulations are performed using the finite element method and COMSOL software, with results demonstrating that the suspension structure exhibits a lower resonant frequency and a larger membrane deflection displacement than other methods, implying higher penetration and acoustic energy levels. Thus, the sound pressure is improved by changing the PMUT structure. Moreover, a PMUT with a double-beam is fabricated, and the impedance diagram is determined with an impedance analyzer. The resonant frequency of the transducer was 31.88 kHz, while the sound wave received by the standard lead zirconate titanate (PZT) ultrasonic transducer was converted to a voltage of 277.5 mV. In comparison, the proposed PMUT demonstrates an improved acoustic emission performance. In addition, the electromechanical coupling coefficient of the suspended PMUT is observed to be approximately 3.08%, which is significantly better than that of a fully clamped PMUT. This demonstrates the strong electromechanical conversion performance of the proposed PMUT. Results from the transmission and reception air experiments prove that the proposed double-beam PMUT can potentially be used for ranging and wireless energy transmission applications.

Epoxy coating as effective anti-corrosive polymeric material for aluminum alloys: Formulation, electrochemical and computational approaches

In this work, a formulation based on epoxy coating composed of DGEBA cured with polyaminoamide has been used as anti-corrosive material for aluminum alloys (2024-T3, 5086 and 7075-T6) substrates for accelerated corrosion assays. The epoxy coating on aluminum alloys samples was tested in 3.0 wt% NaCl solution using salt spray test chamber. The anticorrosive behavior of the aluminum alloys samples under these conditions was monitored by impedance diagrams Bode and Nyquist plots and theoretical studies by DFT, MC and MD. The results showed that the evolution of the impedance modulus plots |Z|0.01 Hz values of the epoxy coating applied on AA2024-T3, AA5086 and 7075-T6 samples began from 2.63, 1.46 and 0.43 MΩ.cm2 after 1 h of immersion and finally reached 0.27, 0.26 and 0.24 MΩ.cm2 after 4392 h of immersion, respectively. The lessening of impedance with submersion time means that the electrolyte scatters into the epoxy coating and diminishes the boundary properties of the film. DFT calculations were used to determine the coatings adsorption centers. Additionally, the Monte Carlo and Molecular Dynamics calculations support the coatings strong adsorption interaction with the metal surface, providing molecular evidence for the epoxy molecule's adsorption behavior (geometry) and adsorption energy on the aluminum surface. Theoretical results (DFT, MC, and MD) corroborate the experimental results.

Role of Alloying Elements in Passive and Transpassive Behavior of Ni–Cr-Based Alloys in Borate Buffer Solution

The role of the alloy composition of binary Ni–xCr alloys (x = 16, 20, 24, 28 wt.%) and ternary Ni–xCr–8Fe alloys (x = 14, 22, 30 wt.%) in borate buffer solution on the passive and transpassive behavior was investigated using successive electrochemical impedance measurements. These measurements supplement conventional polarization curves by enabling monitoring of the evolution of the electrochemical parameters extracted from impedance diagrams (thickness, resistivity at interfaces, etc) during the polarization. The polarization curves and evolution of the impedance parameters revealed that the Cr content and addition of Fe did not significantly affect the behavior of the alloys within the passive potential domain but directly affected the transpassivation process at higher potentials. For the Ni–xCr alloys, a higher Cr content resulted in a higher current-density peak for the transpassivation–second passivation processes. Conversely, the addition of Fe reduced or even prevented the appearance of this current-density peak. X-ray photoelectron spectroscopy analysis provided complementary information to help explain the role of alloying elements in the passivation (and secondary oxidation) mechanisms of Ni-based alloys in borate buffer solution.

Redox-Cycling – A Tool for Artificial Electrochemical Aging of Solid Oxide Cells

Solid Oxide Cells (SOC) have an important role and hold great promise with their diverse and versatile portfolio in the energy application sector, ensuring opportunities for integration of renewable energy sources into the overall energy system. However, the spectrum of applications still meets some general barriers, summarized as durability and costs. The initial performance degrades over their lifetime due to the effect of use (electrochemical ageing), of time (calendar ageing), of different permanent and/or accidental stress conditions - thermal, current load, mechanical, poisoning etc. Considering the expected useful commercial maintenance-free lifetime of up to 80 000 hours for stationary applications, the performance of durability tests looks quite unrealistic, which opens the niche for introduction of accelerated stress tests.In respect to the fuel electrode, the main degradation mechanism during operation in both fuel cell and electrolysis mode is the reduction of the triple phase boundary points and of the Ni/gas specific surface area caused by microstructural changes in the Ni network due to Ni migration and coarsening. The migration over long distances can bring to Ni depletion near the electrolyte interface. Similar processes of Ni coarsening and migration can occur faster during oxidation of Ni caused by incidental change in the operation conditions (leakage, fuel starvation). Thus, artificial redox cycling can be applied for accelerated degradation testing. However, the oxidation/reduction cycles should mimic the normal aging.The most common experimental approach for evaluation of the redox cycling effect on the degradation is the oxidation in a furnace at high temperature for at least one hour, followed by post mortem analysis. However, this approach introduces severe oxidation conditions, even full oxidation of the Ni network, which does not represent the most common electrochemical and calendar aging.The aim of this work is to develop a procedure for accelerated stress tests by artificial aging of the anode via redox cycling. It is performed before the operation of the cell thus eliminating the influence of the degradation mechanisms coming from other components. The proposed procedure ensures reproducible and fine-tuned level of oxidation based on in situ impedance monitoring of the Ni network reduction/oxidation. A two-step algorithm is developed and approbated. Step 1. Performance of redox cycling on anode sample with in situ impedance monitoring of the Ni network reduction/oxidation. The anode sample (pellet with thickness 250 µm and diameter 20 mm) is placed between two Pt meshes. In the initial state (YSZ/NiO) the impedance of the anode has capacitive behavior with resistance about 20 kΩ which after reduction transforms into inductive one with resistance about 40 mΩ corresponding to the electronic conductivity of the produced Ni network (Fig. 1). In the same way the oxidation can be registered. Its level may vary from small oxidation depth (for instance two times increase of the resistance, i.e. from 40 mΩ to about 70-80 mΩ as it is presented in Fig. 1) to big oxidation (above 10 kΩ).For the performance of Step 2 small level of oxidation was chosen, as shown in Fig. 1, which prevents from potential irreversible damages. Thus, the redox cycling of single anode serves for definition of the experimental redox cycling conditions. The deepness of degradation is regulated by the number of cycles. Step 2. Performance of redox cycling on full cell. In this configuration the oxidation of the anode Ni network cannot be monitored, but the conditions are already defined in Step 1 which guarantees reproducible identical redox cycles. The impedance measurements ensure monitoring of the total cell behavior during redox cycling. The procedure is applied for fuel cell mode, but it is also valid for electrolyzer mode. The results are shown in Fig. 2 where the impedance diagrams after the initial reduction and after the 8th redox cycle are compared. Although there is a decrease of the ohmic resistance which is usually observed during the first 1000 hours of standard operation mainly due to improved contacts, the polarization resistance after the 8th cycle is about 14% higher. This behavior is similar to that observed for standard testing for at least 600 hours. The 8 cycles are performed for 16 working hours which confirms the accelerated aging produced by the developed algorithm. Acknowledgements: The research leading to these results received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 825027. The experiments were performed with equipment supported by the Bulgarian Ministry of Education and Science under the National Roadmap for Research Infrastructure 2017-2023 “Energy storage and hydrogen energetics (ESHER)”, approved by DCM No 354/29.08.2017. Figure 1

Electrode kinetics of porous Ni-3YSZ cermet operated in fuel cell and electrolysis modes for solid oxide cell application

The electrochemical reactions of hydrogen oxidation and steam reduction have been investigated for a porous cermet electrode made of Ni and 3YSZ. The electrochemical characterizations have been performed over a large range of gas compositions at 700°C. It has been shown that the fuel electrode response is activated by the potential under anodic current while a limiting current density appears under cathodic polarization. Moreover, the impedance diagrams exhibit a shape representative of a kind of finite-length Gerischer element with a low-frequency contribution sensitive to the steam content. To interpret these experimental results, a continuous dynamic model has been developed by describing the mass and charge transfers within the electrode. The reaction has been divided into a sequence of elementary steps considering two scenarios of charge transfer based on the oxygen and hydrogen spillover mechanisms. Three-dimensional reconstructions obtained by synchrotron X-ray nano-holotomography have been used to provide the cermet structural properties for the simulations. The numerical computations have shown that the hydrogen spillover scenario is the most appropriate mechanism to reproduce correctly the experiments. Besides, the electrode response is controlled by the charge transfer at triple phase boundary lengths, the oxygen vacancies migration in the 3YSZ network and a pure chemical surface process depending on the polarization. In fuel cell mode, desorption of water molecules from 3YSZ would co-limit the electrode response, while in electrolysis mode, the steam adsorption on Ni would become one of the rate determining steps. Finally, a sensitivity analysis has shown that surface diffusion would also play a key role in the electrode response.

Analysis on Electrochemical Property of Gold Electrode Modification for Water Quality Examination

Water plays an indispensable role in manufacturing industry. However, discharge of polluted water containing heavy metal ions often appears in streams and causes serious damage to creatures and environment. Therefore, water-quality monitoring is essential to ensure both developments and safeties. To address this need, different approaches of metal ion detection include spectrophotometry, conductivity test, membrane electrode method and atomic emission spectroscopy. Nevertheless, the accuracy and efficiency of these approaches could still be improved. For these reasons, this study aims to develop an innovative water quality examination technique by using electrochemical impedance spectroscopy (EIS) measurements. By improving the sensitivity and reproducibility of the developed approach, this technique could contribute to metal ion detection. In this work, the main approach to detect the target ion, Cu2+, is surface modification for electrochemical impedance analysis method. To accomplish the development, first, the relationship between ion concentration and the impedance of solution was analyzed. CuCl2 solutions with a concentration between 10-2 to 10-6 M were used as samples for measurement. The experiment, in the Faradaic Mode, was carried out at a starting voltage of 0.34 V. The amplitude was 200 mV, with frequencies varied from 1 MHz to 1 Hz. The effect of temperature variations between 40 to 140 degree Celsius was also discussed. Then, the electrodes were respectively immersed in solutions which are 11-MUA (24 hours), 3-MPA (6 hours) and 2-thiobarbituric acid molecules (24 hours) to construct different exterior structures. Finally, histidine is connected to the electrode for capturing and recognizing copper ions [1].With the modified electrode, the measured ion concentration was changed to 10-3 to 10-9 M. The same experimental parameters as mentioned above were used to measure Ca2+, Mg2+, Na+ and Cu2+, respectively. Also, the copper ion selectivity of each type of monolayers was evaluated. The diameter of the semicircle extrapolated in the Nyquist diagram represents the charge transfer resistance (Rct ) of the solution. In Faradaic mode, Rct should have a negative relationship with ion concentration [2]. By adopting the method proposed by Edward & Craig (2013), the copper ions can be identified by the Rct value obtained in this study.According to experimental results illustrated in Fig. 1, the diameter of the impedance diagram becomes smaller as the concentration increases, meaning a decrease of the Rct. Besides, as the temperature increases, Rct decreases gradually (Fig. 2). On the other hand, there is no significant difference between the trend of Rct when using electrodes with different modification materials (Fig. 3). The detection limit of the bare electrode or modified with planar structured thiolates falls on 10-6 M. However, the detection limit of the electrode with 11-MUA or 3-MPA is approximately reduced to 10-8 M (Fig. 4). Compared to other ions, Rct of Ca2+ and Mg2+ in specific concentration performs similarly when using 11-MUA modified electrode. The correlation coefficient of the calibration relationship between Na+ concentration and the resistance are lower than those in Cu2+ detection (Fig. 5). Based on the above results, it is illustrated that MUA modified electrode performs the best ion selectivity in Cu2+ detection. Finally, for the MPA electrode, the quadratic calibration function between ion concentration and Rct of Cu2+ can also be established as shown in Fig. 6. Based on this experimental result, MPA modified electrode also has high selectivity to Cu2+.In the study, it has been confirmed that the lower ion concentration results a higher impedance of the solution. Besides, the negative logarithm of the concentration (-log[Cu2+], pCu2+) is positively related to Rct in a quadratic form. Also, as the temperature increases, the ion migration rate becomes faster, and the Rct value gets lower; hence, the environmental temperature was controlled to be 25 degree Celsius during the experiments. By modifying 11-MUA and 3-MPA on the electrode, the measurement limit has been significantly reduced, verified by a smoother fitting trend. In conclusion, the proposed 11-MUA and 3-MPA modified approaches have a higher copper ion selectivity and concentration measurement accuracy. In other words, an efficient and sensitive ion detection approach becomes available for water quality examination by utilizing the method proposed in the study.[1] Perrin D. D. (1959). Histidine-Copper (II) Complexes. [2] Edward P, and Craig E (2013). Electrochemical impedance spectroscopy: an overview of bioanalytical applications, Analytical Methods, 2013(5), 1098–1115. Figure 1

An Elementary Kinetic Model for the LSCF and LSCF-CGO Electrodes of Solid Oxide Cells: Impact of Operating Conditions and Degradation on the Electrode Response

An elementary kinetic model was developed to predict the electrochemical response of porous LSCF and LSCF-CGO electrodes. The model was validated thanks to experiments performed on symmetrical cells using a three-electrode setup. After the model calibration on polarization curves, it has been shown that the model is able to simulate accurately the experimental impedance diagram at OCP and under polarization without additional fitting. Moreover, the evolution of the electrode polarization resistance with the oxygen partial pressure is well reproduced by the model. The electrodes reaction mechanism was thoroughly analyzed and it has been shown that the transition from the bulk path to the surface path depends on the temperature, the polarization and the oxygen partial pressure. The rate-determining steps for the LSCF electrode have been identified at OCP as function of the oxygen partial pressure. Finally, a sensitivity analysis has been performed to study the impact of LSCF demixing on the electrode performances. For a given decomposition, it has been highlighted that the surface passivation would be more impacting than the decrease of the ionic conductivity. Moreover, the impact of the LSCF decomposition would be more detrimental for the electrode performances evaluated in electrolysis mode. List of symbols Roman Symbols: Surface double layer capacitance(F m−2) Double layer capacitance at the LSCF/CGO interface(F m−2) Maximum concentration of neutral oxygen atoms in LSCF(mol m−3) Vacancies concentration in LSCF(mol m−3) Vacancies concentration in LSCF at equilibrium(mol m−3) Bulk oxygen chemical diffusion coefficient in LSCF(m2 s−1) Effective diffusion for the i-th species(m2 s−1) Oxygen vancancies self-diffusion coefficient(m2 s−1) Knudsen diffusion coefficient(m2 s−1) Molecular diffusion coefficient(m2 s−1) Diffusion coefficient of the oxygen ad-ions(m2 s−1) Diffusion coefficient of the oxygen ad-atoms(m2 s−1) Diffusion coefficient of the oxygen ad-molecules(m2 s−1) Local electrode potential(V) Activation energy for the i-th species(kJ mol−1) Faraday’s constant(C mol−1) Total inlet gas flow rate(mol s−1) Hole defect in LSCF(–) Ionic current density in CGO/Electronic current density in LSCF(A m−2) Thermodynamic equilibrium constant for the i-th species(–) Forward reaction kinetic constants for R1 for the LSCF(*) or LSCF-CGO(**) electrode (*) (mol m−1 s−1) or (**) (mol m−2 s−1) Forward reaction kinetic constants for R2(m3 mol−1 s−1) Forward reaction kinetic constants for R3 for the LSCF(*) or LSCF-CGO(**) electrode (*) (m s−1) or (**) (s−1) Forward reaction kinetic constants for R4(s−1) Forward reaction kinetic constants for R5(mol2 m−1 s−1) Forward reaction kinetic constants for R6(s−1) Electrode thickness(μm) CGO Electrolyte thickness(μm) Molar mass for the i-th species(g mol−1) m Reaction order(–) Molar flux of the i-th species(mol·m−2·s−1) Oxygen atom in the LSCF lattice(–) Oxygen atom in the CGO lattice(–) Oxygen ad-ion on LSCF surface(–) Oxygen ad-atom on LSCF surface(–) Oxygen ad-molecule on LSCF surface(–) O 2 Gaseous oxygen molecule(–) Oxygen partial pressure(atm) Total pressure(atm) Mean pore radius(m) universal gas constant(J mol−1 K−1) Serial resistanceΩ cm2 Polarization resistanceΩ cm2 Adsorption site on LSCF surface(–) Specific surface area between CGO and LSCF for the LSCF(*) or LSCF-CGO(**) electrode (*) (–) or (**) (m−1) Specific surface area between LSCF and gas phase(m−1) Electrode surface(cm2) Absolute temperature(K) Fuller’s volume for the i-th species(–) Oxygen vacancy in the LSCF lattice(–) Oxygen vacancy in the CGO lattice(–) Molar fraction of species i-th species(–)Greek Symbols: Charge transfer coefficient for oxidation or reduction for the reaction Ri(–) Surface density of available sites on LSCF(mol m−2) ε X Phase volume fraction for the phase X(–) η Overpotential(V) Coverage of oxygen ions on LSCF(–) Coverage of oxygen atoms on LSCF(–) Coverage of oxygen molecules on LSCF(–) Free sites on the LSCF surface(–) Coverage rate of oxygen ions on LSCF at equilibrium(–) Coverage rate of oxygen atoms on LSCF at equilibrium(–) Coverage rate of oxygen molecules on LSCF at equilibrium(–) Free site on LSCF at equilibrium(–) Kinetic rate of chemical/electrochemical reaction (i) in the electrode(*) or at the electrolyte interface(**) (*) (mol m−3 s−1) or (**) (mol m−2 s−1) Electrochemical potential(J mol−1) Density of triple phase boundary lengths for the LSCF(*) or LSCF-CGO(**) electrode (*) (m−1) or (**) (m−2) Electronic conductivity of LSCF(S m−1) Ionic conductivity of CGO(S m−1) Effective conductivity for th i-th species(S m−1) φ i Potential(V) χ Surface electrostatic potential(V) τ X Tortuosity factor for the phase X(–)

Rectifying characteristics of semiconductor minerals: A model on seismo-electromagnetic radiation mechanism from ore bodies

Radiations of low to medium frequency (LF-MF) waves from ore deposits with semiconductor properties by rock burst have been reported. However, the radiation mechanism has not been fully understood yet due to the lack of knowledge of the semiconductor properties of ore minerals. So, we clarified the semiconductor properties of natural pyrite (FeS2) by electroetching and indentation-type probe method. Due to the presence of impurities (particularly Pb), the pyrite possesses the quasi-diode junctions with rectifying properties. The current-applied voltage characteristic of the junctions can be represented by an equivalent circuit of the sample, and its forward breakdown voltage is estimated to be 0.3 V. Calculating the surface charge density and separation distance based on the contact electrification, the electric discharge could occur under Paschen's law during the process of contact or separating between ore deposits. Then, the electromagnetic radiation from ore deposits depends on dielectric characteristics, and the skin depth of pyrite for LF-MF waves is estimated to be in the range of 0.1–1 m, indicating the radiation only from the surface deposit excited by seismic wave. Furthermore, the current-voltage characteristics of semiconductor minerals can be changed by the variation of the capacitance and the parallel resistance of the equivalent circuit of semiconductor minerals associated with contact pressure changes. With respect to the dielectric characteristics of ore deposits, the resistivity presents the diameter of circular arc on the complex-plane impedance diagram. Therefore, the continuous monitoring of complex resistivity, such as induced-polarization (IP) method, would detect electromagnetic phenomena associated with earthquakes in dry ore deposits.

Effect of Environmental Media on the Electrochemical Behavior of API X70 Pipeline Steel

This work investigates the corrosion behavior of X70 steel in different environments: sea sand, desert sand, mud and sea water. The principle of extracting solutions from these media consisted of mixing a soil material with distilled water, the mixture was agitated using an automatic agitator, which resulted in the extraction of solution. Potentiodynamic polarization and electrochemical impedance tests are used to characterize the samples in both media. The results show that the pipeline steel X70 has an excellent corrosion resistance in the sea sand solution, resulting in a low corrosion current density compared to other media. The impedance diagrams for both media are characterized by two capacitive loops, the first loop is attributed to charge transfer processes and the second loop is related to diffusion phenomena. The observation of corroded surfaces shows that the corrosion mechanism in different media is by pitting.

Impedance spectroscopy analysis of an FeNbO4 matrix with different additions of TiO2 and the effects of temperature variation

In this work, investigations of the FeNbO4 ceramic matrix (FNO) and TiO2 additions were carried out in 0, 20, 40, 60, and 80% wt. proportions. The material was synthesized using the solid-state reaction method in an energy mill, and the phases were confirmed by X-ray diffraction and Rietveld refinement. The study of complex electrical impedance was carried out using real and imaginary impedance, with measurements such as permittivity, conductivity, activation energy, and complex impedance diagrams in the range from 1 Hz to 1 MHz and with temperature variation from 100 to 300 oC using a Solartron 1260 impedance analyzer. Furthermore, the temperature coefficients of capacitance for the FNO matrix and its additions were also studied. The complex impedance diagrams showed a non-Debye type relaxation, where the adjustments made showed a good relationship between the experimental and simulated results, and the conduction process was thermally activated, following the Arrhenius relation, where the activation energies calculated were 0.46 and 0.53 eV for the FNO sample, calculated by the displacement of the maximum impedance peak and by the conductivity with temperature variation at 1 Hz. The results showed a greater understanding of the conduction processes of the FNO-TiO2 composite.

Relationship between the Resistivity Profiles Obtained from the Power Law Model and the Physico-Chemical Properties of Passive Films

The constant-phase-element behavior measured for passive films was analysed using the power law model. It allows to obtain the variation of the resistivity through the passive film thickness. To avoid many unknown parameters required for the model, a methodology to analyze the impedance diagrams has been described. It is illustrated with several examples. First, the resistivity profiles were obtained for a Ni-20Cr alloy immersed in solutions with different pH values to validate the proposed methodology. The dielectric properties of the passive films were discussed from the duplex character of these passive layers. It was shown that the shape of the resistivity profile could be attributed to the contribution and the thickness of the inner dense oxide and the outer hydroxide layers, respectively. Then, the second example provided information on the evolution of the behavior of the passive film formed on 316L stainless steel under irradiation.

Impedance analysis of the barrier effect of coil-coated materials: Water uptake and glass transition variations

In the present work, an industrial polyester coil-coated steel sample was characterized by electrochemical impedance spectroscopy. The diagrams were obtained for various immersion times in a 0.5 M NaCl solution for three different initial states of the same coil coating (as received, dried and dried after the impedance measurements). The aim of the study was to have a better knowledge of how the water uptake influences the coil coating physical properties and to extract relevant parameters of the ageing processes. From the high-frequency part of the impedance diagrams, the water uptake was calculated using a linear rule of mixtures. Two sorption regions were observed for the dried samples suggesting the presence of porosities already filled with ambient moisture for the as-received sample. It was shown that the water uptake was a slow process and, independently of the initial state of the sample, a saturation plateau was never reached, even after 456 h of immersion. A time constant, clearly visible on the phase angle of the impedance diagrams, was analysed through the dielectric permittivity formalism and attributed to the signature of the dielectric manifestation of the glass transition. This time constant was shifted to higher frequencies with increasing water fraction (increasing immersion time), consistent with a plasticization effect. This result was supported by differential scanning calorimetry measurements. Finally, the data obtained for the different initial states of the coating highlighted that, even if the water uptake was reversible, the sorption kinetics was different for the sample dried after the impedance measurements. This could be of importance in the degradation process of the coil coated steel.

COMPARATIVE FAULT LOCATION ESTIMATION BY USING IMAGE PROCESSING IN MIXED TRANSMISSION LINES

Overhead lines are generally used for electrical energy transmission. Also, XLPE underground cable lines are generally used in the city center and the crowded areas to provide electrical safety, so high voltage underground cable lines are used together with overhead line in the transmission lines, and these lines are called as the mixed lines. The distance protection relays are used to determine the impedance based fault location according to the current and voltage magnitudes in the transmission lines. However, the fault location cannot be correctly detected in mixed transmission lines due to different characteristic impedance per unit length because the characteristic impedance of high voltage cable line is significantly different from overhead line. Thus, determinations of the fault section and location with the distance protection relays are difficult in the mixed transmission lines. In this study, 154 kV overhead transmission line and underground cable line are examined as the mixed transmission line for the distance protection relays. Phase to ground faults are created in the mixed transmission line. overhead line section and underground cable section are simulated by using PSCAD/ EMTDC ™. The short circuit fault images are generated in the distance protection relay for the overhead transmission line and underground cable transmission line faults. The images include the R-X impedance diagram of the fault, and the R-X impedance diagram have been detected by applying image processing steps. Artificial neural network (ANN) and the regression methods are used for prediction of the fault location, and the results of image processing are used as the input parameters for the training process of ANN and the regression methods. The results of ANN and regression methods are compared to select the most suitable method at the end of this study for forecasting of the fault location in transmission lines.

(Invited) Relationship between the Resistivity Profiles Obtained from the Power Law Model and the Physico-Chemical Properties of Passive Films

Passive film (PF) could be considered a particular nanomaterial with its growth, chemical composition, microstructure, performance and evolution of its performance. The understanding of the film construction, its maintenance and its resistance is the result of a total complementarity between characterization from enhanced physico-chemical analysis techniques, especially those developed by P. Marcus and his group[1], and electrochemical measurements, mainly the electrochemical impedance spectroscopy (EIS).EIS gives access to the capacitive and resistive properties of the passive film. The first, complemented by the Mott-Schottky theory, allows a quantitative approach of electronic properties (semi-conductivity) and the maintenance process of passive films. The second involves the corrosion resistance of the film. Nevertheless, it is important to make a rigorous adjustment of the parameters resulting from the impedance diagrams. An adjustment that takes into account the physical meaning of parameters, especially for the analysis of the constant phase elements (CPE) used in the treatment of the diagrams that present one depressed semicircle [2]. The knowledge of the oxi-hydroxide character of the PF, evidenced from physicochemical characterizations, allows considerations of the spatial distribution of the heterogeneities (3D) within the thickness of the PF from the variation of its resistivity obtained from the Power Law Model (PLM)[3,4]. In fine, the resistivity profiles give information about interface reactivity and distribution of species along the thickness of the passive layer.The use of the PLM requires the assessment of several parameters, especially a and Q defining the CPE or the thickness of the PF, which is generally assessed by physicochemical measurements. Most of them can be determined by advanced graphical analysis of impedance diagrams[5,6]. It can then be used to guide the adjustment of the diagrams by inputting known parameters into the model.To exemplify the interdependency between physicochemical analysis and electrochemical impedance measurements, two studies illustrate the contribution of in-depth analyses of the resistivity profiles for two passive materials. That will be the opportunity to highlight which information can be drawn and finally, to propose reaction mechanism.First of all, the passivity of the Ni-20Cr alloy has been studied in different solutions[7]. In this work, the electrochemical impedance diagrams have been successively performed under applied potential in passive region. From PLM analysis, it was observed that the evolution of the resistivity at the Ni-20Cr/PF interface explains the evolution of the current density during polarization. The resistivity profiles obtained for increasing applied potentials on the passive plateau showed a decrease of the resistivity plateau at the substrate/PF interface and an increase of the resistivity at the PF/electrolyte interface, highlighting the modification of the passive film according to the anodic polarization.The second example concerns 316L stainless steel immersed in a 0.02M sodium sulphate solution and under proton irradiation[8]. It was shown that the impedance diagrams obtained before and after irradiation were almost superimposed, suggesting that the system was reversible. However, the resistivity profiles showed that under irradiation, the resistivity at the PF/electrolyte interface decreased and reached its initial value after irradiation. On the other hand, the length of the plateau at 316L/PF interface disappeared during irradiation and was reduced after irradiation by comparison with before irradiation.The case studies presented show that the advances proposed in the analysis of impedance diagrams, combined with physicochemical analyses, provide a global knowledge of passivation mechanisms. Maurice, P. Marcus, Current opinion in solid state & material science, 22 (2018) 156-167.Tribollet, V. Vivier, M.E. Orazem, in Encyclopedia of Interfacial Chemistry (2018), Ed. Elsevier, 93-107.B Hirschorn, M. E. Orazem, B. Tribollet, V. Vivier, I. Frateur, M. Musiani, Journal of the Electrochemical Society 157 (2010) C452-C457.B Hirschorn, M. E. Orazem, B. Tribollet, V. Vivier, I. Frateur, M. Musiani, Journal of the Electrochemical Society 157 (2010) C458-C463.E. Orazem, N. Pébère, B. Tribollet, Journal of the Electrochemical Society 153 (2006) B129-B136.Benoit, C. Bataillon, B. Gwinner, F. Miserque, M. E. Orazem, C. M. Sánchez-Sánchez, B. Tribollet, V. Vivier, Electrochimica Acta 201 (2016) 340-347.Zhang, B. Ter-Ovanessian, S. Marcelin, B. Normand, submitted to Electrochimica Acta.Normand, N. Bererd, P. Martinet, S. Marcelin, M. Moine, J. Ferreira, D. Baux, T. Sauvage, N. Moncoffre, submitted to Corrosion Science.

Karma İletim Hatlarında Makine Öğrenmesi Yöntemleri Kullanarak Hata Yeri Tahmini

Overhead lines are generally used for electrical energy transmission. Also, XLPE underground cable lines are generally used in the city center and the crowded areas to provide electrical safety, so high voltage underground cable lines are used together with overhead line in the transmission lines, and these lines are called as the mixed lines. The distance protection relays are used to determine the impedance based fault location according to the current and voltage magnitudes in the transmission lines. However, the fault location cannot be correctly detected in mixed transmission lines due to different characteristic impedance per unit length because the characteristic impedance of high voltage cable line is significantly different from overhead line. Thus, determinations of the fault section and location with the distance protection relays are difficult in the mixed transmission lines. In this study, 154 kV overhead transmission line and underground cable line are examined as the mixed transmission line for the distance protection relays. Phase to ground faults are created in the mixed transmission line, and overhead line section and underground cable section are simulated by using PSCAD/ EMTDC ™. The short circuit fault images are generated in the distance protection relay for the overhead transmission line and underground cable transmission line faults. The images include the R-X impedance diagram of the fault, and the R-X impedance diagram have been detected by applying image processing steps. The regression methods are used for prediction of the fault location, and the results of image processing are used as the input parameters for the training process of the regression methods. The results of regression methods are compared to select the most suitable method at the end of this study for forecasting of the fault location in transmission lines. When looking at the method and performance criteria used in the overhead transmission line fault location study, it is the Linear Regression (Robust Linear) method that gives the most accurate results with RMSE 0.017652. When looking at the method and performance criteria used in the underground cable transmission line fault location study, it is the Linear Regression (Stepwise Linear) method, which gives the most accurate results with RMSE 0.0060709. When the accuracy of the method was examined, it was seen that it was higher than other methods.

Investigation of the passive behavior of a Ni–Cr binary alloy using successive electrochemical impedance measurements

The passive behavior of a Ni–20Cr binary alloy was studied using an original methodology, based on successive electrochemical impedance spectroscopy (SEIS), over a wide potential range. The proposed method was first validated by comparing the resulting potentiostatic polarization curves with more conventional potentiodynamic polarization curves and determining the effect of the dwell time (30, 120, and 600 s) and potential step size (25 and 50 mV). Using the optimized parameters from this preliminary work, the passive behavior of the Ni–Cr alloy was then studied in solutions of varying pH: 10 g/L Na2SO4 with H2SO4 (pH = 2), 0.01 M Na2SO4 (pH = 5.8), and 0.05 M H3BO3 + 0.075 M Na2B4O7 10H2O (pH = 9.2). The obtained impedance diagrams were interpreted using enhanced graphical representation and fitted using the power-law model to determine the resistivity distribution throughout the passive film during polarizations. The results demonstrated that SEIS provides complementary information to conventional potentiodynamic curves. The evolution of the passive film properties was monitored in situ within the potential range corresponding to stable passivity. With the help of this original method, complementary to the evolution of the current density (measured at each potential step), the thickness, chemical composition, and reactivity changes were also highlighted.

Correlation between the physical structure of a commercially formulated epoxy paint and its electrochemical impedance response

In the present work, a commercial high solids epoxy-based paint used for the corrosion protection of steel was characterized by electrochemical impedance spectroscopy (EIS). The aim was to analyze the influence of water absorption on the physical structure of the paint, through the impedance data analysis. First, the water uptake was followed by gravimetric measurements on free-standing films as a function of the exposure time to a 0.5 M NaCl solution. Gravimetric measurements indicated a mass loss, linked to a release of a plasticizer from the formulation. This compound was dosed in the NaCl solution. The water volume fraction was also determined from the high-frequency part of the impedance diagrams, employing a linear rule of mixtures. The water fraction values obtained from the two methods were in acceptable agreement. The glass transition temperature (Tg) was determined by differential scanning calorimetry for the dry coating as well as for the coating after different immersion times in the NaCl solution. The use of the dielectric permittivity formalism allowed the mean relaxation times to be obtained from the impedance data analysis. The real part of the electrical conductivity was also considered. The variation of these parameters values as a function of the exposure time to the NaCl solution, was correlated with the Tg variation. They accounted for plasticization at the beginning of immersion (water uptake) and antiplasticization for longer exposure times (plasticizer release). For the studied system, it was possible to extract parameters representative of the molecular mobility from the impedance spectra analysis and to link them to the modification of the coating’s physical structure.

Corrosion behavior of aluminum oxide coatings created by electrolytic plasma method under different potential regimes

The electrolytic plasma coating is affected by various factors such as electrolyte conductivity, voltage, and current. However, there has not been much attention to the effect of the current regime. The main objective of the present study is to investigate the potential of Al2O3 coatings deposited by the electrolytic plasma method. Aluminum Series 2 was used in this study and the electrolyte was composed of sodium silicate, sodium tetraphosphate, sodium aluminate and potassium hydroxide. The results showed that, in general, according to the impedance diagrams, the corrosion resistance of the coated specimens greatly increases with the immersion time. Therefore, the unit of resistance increased on average to about 10 MHz after 72 hours. In the case of pulsed potential application regime, the corrosion behavior of the samples in the working cycle of 30% was better than that of 70%, which can be related to the thickness of the formed coatings and their porosity. This allows the coating to degrade the coating faster by increasing the thickness and decreasing the porosity of the aggressive chloride ion.

One-step spray of Cu2NiSnS4 thin films as absorber materials for photovoltaic applications

A simple one-step «Spray Pyrolysis» technique was developed for preparing Cu2NiSnS4 (CNTS) thin film followed by an annealing treatment process. Originally, the spray technique was successfully used to deposit the thin film onto glass substrate at 250 °C for 60 min spray duration. Again, the deposited thin film was annealed in a sulfur atmosphere at a temperature of 500 °C during 30 min. The sulfured thin film exhibits (111), (220) and (311) orientations correspond well to the cubic CNTS structure and other impurity compounds. The SEM data exhibit a uniform, rough and compact topography of CNTS thin films with an average-thickness of 1.36 µm. The absorption coefficient is found to be higher than 104 cm−1 in the visible region while the direct band energy of 1.62 eV, which is eminently suitable for use as an absorber in the solar cell. The complex impedance diagrams indicate the decrease of resistance by increasing temperature, which attributes to a semiconductor behavior. The close values of activation energies 0.63 and 0.54 eV determined from both angular frequency and DC conductivity indicate that the carrier transport mechanism is thermally activated.

The corrosion protection afforded by a commercial rust converter doped with graphene oxide

The present work is devoted to study the effect of the Graphene Oxide (GO) addition in the corrosion protection capacity of a commercial Rust Converter (RC). These substances are designed to be applied over corroded surfaces. It is supposed that they react with rust generating a stable layer, which protects to the metallic substrate. The RC used here is a commercial product that contains gallic acid as reactive compound, which reduces the GO added to reduced-GO (r-GO).Electrochemical Impedance Spectroscopy (EIS) was used to characterize the barrier properties of RC and RC + r-GO treatments, both as in free-standing films and in supported coatings on rusted steel. The results suggest that the RC + r-GO treatment generates more stable and protective films. For the interpretation of the impedance diagrams, the semiconducting character of the film obtained from the RC + r-GO treatment was considered. The initial lower impedance values observed in these samples are related to the presence of electronic paths in parallel with the ionic paths. The impedance values remain stable during long-term immersion. On the contrary, samples coated with the RC treatment undergo a continuous impedance decrease indicating a loss of the barrier properties of the coating.