EIS Tests Research Articles

Physical, mechanical and corrosion properties of Zn-15Al alloy coating deposited at different voltage using thermal spray process

Steel is the most widely used metal on earth, cheap and found everywhere. It has good properties such as machinability, strength, ductility, and compatibility with other materials. However, it has weakness such as high corrosion rate which need to improve to achieve satisfying properties. The coating is one of the enhanced methods to improve the quality of steel coating methods are dipping and thermal deposition processes. Both processes have their own advantages and disadvantages. However, the thermal deposition method can produce a coating with better characteristics and performance. Zinc and aluminium are common metals to be used in the thermal spray process; however, a few parameters need to be concerned in the thermal spraying process. They include spraying voltage, spraying distance, deposition rate and applied current. The basic concept is that it melts the material and burst it to the substrate with high velocity. The purpose of this research is to evaluate the physical and corrosion properties of thermal sprayed pure zinc, aluminum and Zn-15Al alloy coating on a mild steel plate. The experimental procedures include roughness, thickness, adhesion, SEM with EDX, and EIS tests. The results show that at 30V, the surface roughness becomes lower, zinc’s decreases from 7.30um to 6.55um, Zn-15Al’s is from 8.52um to 7.93um. For aluminium, its surface roughness increases at higher voltage, from 13.10um to 18.25um. For coating thickness, the value of zinc, aluminium and Zn-15Al of 20V and 30V spraying voltage decreased from 629um to 601um, 486um to 452um, 541um to 536um respectively. The reason for sprays the material at higher velocity to the substrate; these findings depicted smooth and dense coating. Based on SEM/EDX analysis on the cross-sectioned samples, there is no gap between the coating and substrate and demonstrates good coating adhesion. The Daimler-Benz adhesion test shows all coating samples demonstrate good adhesion as no failure at the indentation boundary. In the EIS corrosion test, the frequency range 0.1Hz to 100kHz in 3.5wt.% NaCl solution, the highest impedance shown by zinc, aluminium and Zn-15Al at 20V are 21, 2122 and 49ohms; at 30V, they possess 11, 1347 and 20ohms. It illustrates those coatings with lower spraying voltages demonstrate better corrosion resistance due to the higher coating thickness. Hence, the coating which owns the best properties in all aspects is pure aluminum coating.

Insight into structural and electrochemical properties of Mg‐doped LiMnPO 4 /C cathode materials with first‐principles calculation and experimental verification

The LiMnPO4 material has the advantages of abundant raw materials, safety and environmental protection, low price, high theoretical capacity, high stable working voltage platform and so on, showing great potential in lithium-ion batteries. Dissimilar metal ion doping can essentially improve the electronic conductivity of LiMnPO4 and the material's charge and discharge performance, which is an ideal method to improve the electrochemical performance of LiMnPO4. In this paper, the optimal doping concentration of Mg-doped solid solution material was calculated by first principles. At the same time, the corresponding content of LiMn1−xMgxPO4/C cathode material was synthesized by hydrothermal method for experimental verification, so as to prepare the cathode material with excellent electrochemical performance. The results show that the doping of Mg cations does not change the phase of the main phase, but significantly changes the crystal structure parameters. The regulation of the band width directly affects the electronic conductivity of the material, which is directly proportional to the electrochemical performance. EIS and CV test results show that a proper amount of magnesium doping can effectively reduce the impedance of the material, and can effectively alleviate the polarization phenomenon of LiMnPO4 electrode material, accelerate the diffusion rate of Li+, and it is easier to obtain high capacity battery. LiMn23/24Mg1/24PO4/C showed the best electrochemical performance, with an initial capacity of 153.8 mAh/g at 0.05C ratio and a capacity retention rate of 97.5% after 100 cycles at 0.05C ratio. The theoretical calculation is in good agreement with the experimental results, which indicates that the theoretical calculation based on first principles can effectively provide a more reliable theoretical basis for experimental design and subsequent improvement.

Microstructural characterization and corrosion behavior of AlxCoCrFeNi high entropy alloys

In this study, AlxCoCrFeNi high entropy alloys (x = 0, 0.25, 0.75, 1.25 and 2) with multiprincipal elements were prepared by induction-melting in Ar atmosphere. The microstructural evaluation showed that with increasing aluminum content, the AlxCoCrFeNi alloys change from a single FCC phase to a single BCC phase with a transition duplex FCC/BCC region. Moreover, the increase of aluminum led to dendritic structure in associated with elemental segregation and alloy strengthening. The highest hardness (700 HV) was observed to be achieved for x = 0.75, in which the structure changed from FCC to FCC/BCC dual phase. The potentiodynamic polarization test of the AlxCoCrFeNi alloys showed that the corrosion current densities increased with increment of molar ratio of aluminum element. The FCC structure is a corrosion resistant phase regarding to promotion of polarization resistance values. Also, EIS test demonstrated that with increasing molar ratio of Al and presence of BCC phase, the value of corrosion resistance reduced due to passive layer properties and elemental segregation.

Characterization of Sn@TiO2 Anode Material for Li-Ion Battery Application

In this work, various phases of nanorod TiO2 were fabricated by hydrothermal process. Different crystalline phases of TiO2 nanowires will be analyzed by electrochemical analysis (CV, LSV, C-rate, charge and discharge, and EIS test) to investigate the influence of Li+ diffusion rate on specific capacitance. The in-situ XRD structure for charging and discharging will be carried out to explore the diffusion and structural behavior of Li+ in TiO2 was explored its fast charging, high capacitance and high safety characteristics, which will be a fundamental research of Sn modified on TiO2 nanowire. Transmission electron microscope image showed a range of 20 to 80 nm length TiO2 nanorods was success synthesized, and the XRD indicated the phase were rutile, anatase and rutile/anatase mixed by controlling the chelating agents (citric acid). The specific capacity of TiO2 nanorod was 120 mAh/g which the Columbic efficiency was ~ 99% under 0.1 C. A morphology of Sn@TiO2 was investigated as nano-capsule. The results are supposed to clarify the key factors of the fast charge, high specific capacitance and safety. It is expected that the Li+ ion influence on structure changes during the charge and discharge process by implementing this research. The fast charging, high specific capacity and high safety mechanism will be established as an index for material application and commercial products.Keywords: TiO2 anode materials, Sn@TiO2 anode materials, Li-ion battery, In-operando XRD

Molecular dynamic (MD) simulation and electrochemical assessments of the Satureja Hortensis extract for the construction of effective zinc-based protective film on carbon steel

In this work, for the first time, the Satureja Hortensis leaves was extracted by ultra-pure water solution and then, the synergistic inhibition effect of various mixtures of Satureja Hortensis extract (SHE) and zinc cations on carbon steel corrosion in 3.5% saline (NaCl) solution was investigated. The proposed compounds' effectiveness in carbon steel corrosion mitigation was surveyed by polarization and EIS tests. The inhibition efficiency of 99.34% was recorded for 700 ppm Zn + 300 ppm SHE. Surface characterizations were conducted employing scanning electron microscope (SEM) equipped with EDX, ultraviolet–visible (UV–Vis) analysis, Fourier transmission infrared (FTIR) spectroscopy, grazing incidence X-ray diffraction (GIXRD), and contact angle (CA) analysis which vividly proved the results of the electrochemical investigation. A mixed protection behavior was observed according to the polarization test results. Molecular dynamics (MD) simulation results complemented the experimental findings in affording insights into the adsorption mechanism at the atomic/molecular scale.

Study on the corrosion resistance of sulfonated graphene/aluminum phosphate composites in waterborne polyurethane coatings

Abstract Sulfonated graphene/aluminum phosphate (SG/AlPO4) composites were synthesized by precipitation method, and composites with different mass ratios were added to water-based polyurethane (WPU) resins to prepare coatings. According to tests, composites with the addition of 2 wt% composite coating has good anticorrosion performance, and its protection efficiency is increased by 79.6% compared with pure resin. In the early stage of the corrosion, the SG layer forms the barrier. During the corrosion process, the SG layer was destroyed, the phosphate ions decomposed by the exposed spherical AlPO4 in the corrosive medium and the divalent iron ions on the iron-based surface form a stable precipitation protective layer to achieve the anticorrosion effect. From the EIS test, the coating with 2 wt% composite material has a larger radius of curvature in the Nyquist diagram at different time periods. According to the fitted circuit, it is further confirmed that the precipitation protection layer has a larger resistance value. After soaking for 24 h the resistance value is the largest, which is 1.231 × 104 Ω cm2.

Investigation on the Overlithiation Mechanism of LiCoO2 Cathode for Lithium Ion Batteries

Overlithiation of lithium ion batteries often causes a structural transformation of the electrode and capacity degradation and may even lead to severe safety problems. In this study, the electrode structure, surface morphology and compositions at the different overlithiation depths of LiCoO2 cathode material were investigated in detailed by examining the LCO/Li cells and anode-free cells, combined with post-mortem characterizations. When LiCoO2 is found in a slight overlithiation state, the cycle capacity fades slightly and minority of LiCoO2 reduces to CoO and Li2O. After LiCoO2 undergoes a deep overlithiation reaction, a long flat voltage plateau appears at 1.2 V and the cycle performance is greatly deteriorated. SEM and EIS tests show that the single-crystal particles are fractured into small particles with thick-layer formation at the surface and the shape of the EIS curve changes strongly with increasing overlithiation depth. Additionally, as shown by XPS Ar-ion etching and TEM characterization, the LiCoO2 surface is converted into greater amounts of Li2O, CoO and Co metal associated with the severe electrolyte decomposition, and LiF, Li2CO3 and LixPOyFz are the main electrolyte decomposition products. The detailed investigation of the overlithiation mechanism of LiCoO2 provides comprehensive and thorough guidance for understanding the overlithiation mechanism of cathode materials as well as important reference information for practical all-solid-state battery applications.

Improved Li6.5La3Zr1.5Nb0.5O12 electrolyte and effects of atmosphere exposure on conductivities

Cubic Li6.5La3Zr1.5Nb0.5O12 ceramic electrolyte is prepared by a simple modified sol-gel process. Quite fine mother powders are obtained through pressing, crushing and grinding for several times instead of ball milling. The Li6.5La3Zr1.5Nb0.5O12 electrolyte achieves a high relative density of ~97% and excellent properties with a high ionic conductivity of 7.00 × 10−4 S cm−1 and a low electronic conductivity of 9.94 × 10−8 S cm−1 at room temperature. When exposed to the atmosphere, the ionic conductivity of Li6.5La3Zr1.5Nb0.5O12 gradually decreases to 2.25 × 10−4 S cm−1 after 22 days. EIS test provides a direct evidence to demonstrate an increase trend of grain boundary impedances. Rietveld refinement reveals the lattice parameters increase with the exposure time and obvious changes in lithium occupancies at 24d and 96h sites occur before and after the atmosphere exposure. A linear increase of Li2CO3 impurity with exposure days is also found. Moreover, the electronic conductivity of Li6.5La3Zr1.5Nb0.5O12 is reduced as well after atmosphere exposure (from 9.94 × 10−8 S cm−1 to 7.60 × 10−8 S cm−1). This work reports a simple, effective method for the preparation of high-quality LLZO ceramics and may be helpful to further concern on the atmosphere stability of them.

Corrosion behavior of zirconium-pretreated/epoxy-coated mild steel: New approach for determination of cathodic disbondment resistance by electrochemical impedance spectroscopy

The protective performance of zirconium-pretreated epoxy films with and without zinc sulfate additive in 3.5 wt% NaCl solution was investigated. A new parameter with a reasonable relation based on EIS tests for the scratched samples was introduced to determine the amount of corrosive electrolyte diffusing into the coating/substrate interface, and it was attributed to cathodic disbondment resistance. It was revealed that coating segregation was reduced via surface pretreating by zirconium with additives.

A study on corrosion behavior of micro-arc oxidation coatings doped with 2-aminobenzimidazole loaded halloysite nanotubes on AZ31 magnesium alloys

Abstract Micro-Arc oxidation (MAO) coatings with actively protective functionality by incorporating 2-aminobenzimidazole (2-ABi) loaded halloysite nanotubes (HNTs) was presented. The coatings were characterized by SEM, EDX and XRD. Corrosion behavior was evaluated by EIS, PDP and salt spray test. With the SEM and EDX analysis, the existence of HNT or 2ABi-loaded HNT was confirmed. The OCP evolution, EIS complex spectra and the result of salt spray test showed the enhanced corrosion resistance of 2-ABi-HNT MAO coating owing to the self-healing effect, suggesting 2-ABi has good potential as corrosion inhibitor for Mg alloys.

Collaborative modification based on Ti-ion effectively improves the electrochemical performance of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials

Through the wet coating method combined with high temperature calcining, samples based on Ti element coating and doping collaborative modification at different temperatures were obtained respectively (NCM811-Ti450, NCM811-Ti650, and NCM811-Ti850). Tests have shown that the TiO2 coating layer was successfully coated on the surface of the pure sample (NCM811). Additionally, with the increase of sintering temperature, Ti element in the part of the coating layer diffused into the crystal structure of LiNi0.8Co0.1Mn0.1O2 to form doping modification, which reduced the mixing degree of lithium nickel and expands the diffusion channel of lithium-ion. The electrochemical performance of co-modified samples displayed better cyclic stability and rate performance. Besides, the EIS test shows that the samples obtained from the collaborative modification have higher DLi+, which is improved from 9.14 × 10−16 cm2s−1 (NCM811) to 5.66 × 10−15 cm2s−1 (NCM811-Ti850).

Enhancement of the electrochemical performance of free-standing graphene electrodes with manganese dioxide and ruthenium nanocatalysts for lithium-oxygen batteries

Hybrid ternary Graphene/Ruthenium/α-MnO2 (rGO/Ru/α-MnO2) flexible nanocomposite cathodes were fabricated via controlling both reduction and vacuum filtration processes without using a binder and conductive carbon additives for flexible Li-air battery system. To compare the electrochemical performance of the Graphene/Ruthenium/α-MnO2 cathodes, bare rGO and rGO/Ru free-standing cathodes were also manufactured. rGO cathodes with well-dispersed α-MnO2 nanowires and ruthenium nanoparticles were successfully synthesized and shown to dramatically increase (decrease) oxygen reduction (evolution) reactions. The enhancement on the electrochemical performance of the synthesized cathodes was attributed not only to catalysis effect of ruthenium and α-MnO2 but also well-stacked morphology of the nanocomposite architecture which enables increased oxygen flow between the layers and, hence boosted reaction kinetics.Physical characterization of the cathodes was carried out using FESEM, EDS, TEM, XRD, XPS and Raman spectroscopy. The discharge product of the cathodes was also evaluated using TEM and XPS. Electrochemical performances of the cathodes were evaluated by means of CV, EIS, galvanostatic charge-discharge and electrochemical cycling tests. Thanks to the synergetic effect of Ruthenium and α-MnO2 catalysts, our ternary rGO/Ru/α-MnO2 cathodes were shown to serve full discharge capacity of 2225 mAh/g while rGO/Ru can deliver only 1670 mAh/g. Besides, the cycling stability of the ternary rGO/Ru/α-MnO2 cathodes was shown for 50 cycles at 650 mAh/g capacity limited tests in assembled Li–O2 batteries.

Folded graphene/copper oxide hybrid aerogels: folding, self-reinforcement, and electrochemical performance

In our previous work, the Origami and enhancement theory was introduced into the construction of graphene aerogels to achieve the self-enhancement effect of graphene aerogels through the folding process of graphene lamellae. Based on the above work, after the graphene lamination was folded by Cu ion, it was further converted to cupric oxide by in situ mode, thus participating in the enhancement of the electrochemical behavior of graphene aerogels, and the "folding—enhanced—electrochemical" multiple effects were obtained. The innovation of this article was to use copper ions to achieve the folding of graphene sheet, and convert copper ions into copper oxides to improve the electrochemical properties of graphene aerogels, thereby achieving self-enhancement and electrochemical applications of graphene aerogels.The molecular structure and elemental composition of fGA/CuO were studied by FTIR and XPS. The surface microstructure of fGA/CuO was studied by SEM and bet. The results showed that fGA/CuO was successfully prepared with small and round micropores on the surface.The mechanical and electrochemical properties of fGA/CuO were studied by mechanical properties test, CV, GCD, and EIS tests. The results show that fGA/CuO has good mechanical and electrochemical properties.

Investigation of different permeability properties of self‐healing cementitious composites under colloidal nano silica curing conditions

AbstractIn this study, the self‐healing behavior of engineered cemetitious composites (ECC) containing different types and quantities of fly ash (FA) under colloidal nano silica (CNS) curing conditions was investigated through the examination of their different permeability properties. FA in two different characters, Class F and Class C, were used in the preparation of the mixtures in high volumes (FA/portland cement = 1.2 and 2.2). Self‐healing capacities developed under CNS curing conditions were evaluated by changes in different permeability properties such as rapid chloride permeability test (RCPT) and electrical impedance measurement methods. In addition to these, the self‐healing effects of the cracked composites were supported by microstructure analysis with the help of SEM–EDX and XRD tests on the sections taken from the crack interface of the sample. The results have showed that the CNS curing condition helps improve the permeability properties of composites by quickly and effectively covering their micro pores and cracks. In addition, the results of the experiment have revealed the effects of the use of different types and quantities of FA on the self‐healing behavior of the ECC material. Finally, correlation analysis of ECC samples was applied according to the results obtained from EI and RCPT test methods and it was revealed that there was a negative significant relationship between test methods.

A novel redox capacitor with a natural rubber-based solid polymer electrolyte for energy applications

The development of high-performance power sources such as super capacitors (EDLCs and redox capacitors) has become an urgent requirement in recent years due to the unprecedented growth of portable technology. The present study was carried out to fabricate a redox capacitor using a natural rubber-based solid polymer electrolyte (SPE). Zinc trifluoromethanesulfonate (ZnTf), propylene carbonate (PC), and pyrrole were used as electrode materials whereas ZnTf and methyl-grafted natural rubber (MGNR) were used to prepare the SPE. Warburg type diffusion as well as capacitive behavior was observed from the EIS test. Single electrode specific capacitance (Csc) from cyclic voltammetry (CV) was 27.5 Fg−1 at the scan rate of 10 mVs−1. Retention of the Csc value was 92% over 500 cycles. Single electrode specific discharge capacitance (Csd) found from galvanostatic charge discharge test was 6 Fg−1.

Preparation and properties of self-healing anticorrosive coating on methyl cellulose core-shell fibers

This work reports a core–shell fiber coating with self-healing and anticorrosive properties, which combined fibers with a silicone coating (PDMS) material for the corrosion protection of carbon steels. We innovatively encapsulated oleic acid (OA) into the methyl cellulose (MC) shell material by using electrostatic spinning. EIS, SKP and FTIR mapping test indicate that the MC-PDMS coating shows an excellent self-healing performance in 3.5 wt% NaCl solution (pH = 11.7). OA protective film was successfully formed in the damaged area. It has an important reference value for the development of new self-healing materials in the field of marine corrosion protection.

The role of ethanolic extract of Stachys byzantina's leaves for effective decreasing the mild-steel (MS) degradation in the acidic solution; coupled theoretical/experimental assessments

In the current research, the anti-corrosion performance of MS in the HCl solution was investigated when potentially corrosion inhibitive green molecules, extracted from the Stachys byzantina (SB) leaves, were added to the solution. Potentiodynamic polarization (PP) along with the EIS tests were carried out. Also, surface characterization was examined using FE-SEM, contact angle measurements, AFM, and EDS. The film composition formed on the MS surface was explored by Ultraviolet-visible spectroscopy (UV–Vis), GIXRD, FT-IR, and Raman spectroscopy. EIS test demonstrated that the MS surface exposed to the 1 M HCl solution into which 1200 ppm SB extract was incorporated yielded the highest resistance against corrosion after 4 h resulting in the inhibition efficiency of 96%; the optimum concentration was also substantiated with PP test. SB extract showed a mixed-inhibition performance, and the best-fitted adsorption isotherm was calculated to be Langmuir; furthermore, the inhibitor adsorption was a combination of physisorption and chemisorption. Surface studies showed that the inhibited surface exhibited a smoother texture with lower roughness because of the inhibitor adsorption. The presence of several SB extract's functional groups such as OH, CH, C=C, and C=O on the surface was confirmed through FT-IR spectroscopy and UV–Vis analysis. Via Raman spectroscopy, a graphene-like layer was observed on the surface. The results, as a whole, proved the presence of a protective layer, which adsorbed on the surface and subsequently prevented further corrosion attack. Finally, the interactions taking place between metal surface and corrosion inhibitor were examined from the theoretical point of view using molecular dynamics (MD), Monte Carlo (MC), and density functional theory (DFT). The results were suggestive of the formed complex affinity toward the surface resulting in corrosion prevention.

Corrosion Behavior of Mg–Zn–Ca–Mn Alloy Coated with Nano-hydroxyapatite by Cyclic Voltammetry Method

Coating and alloying are the two possible solutions for enhancing the corrosion resistance of magnesium. Nanostructured hydroxyapatite (n-HA) was coated on Mg–1% Zn–0.5% Ca–0.2% Mn by cyclic voltammetry method to increase its biocompatibility and bioactivity alongside corrosion resistance. XRD and EDS analyses approved the formation of hydroxyapatite. A central composite design (CCD) coupled with response surface methodology (RSM) was employed to optimize the four selected variables. Corrosion current density obtained from polarization tests in the simulated body fluid (SBF) was considered as the main response for optimization. The experimental values were fitted well by the derived model (R2 = 96.8%). The proposed optimum condition was − 1.4 V, 75 °C, 7 cycles, and 0.05 M for the start potential, temperature, cycle number and concentration of NaNO3, respectively. The corrosion current density of the sample made at the optimum condition was decreased around 90% compared with the bare one (1423 µA/cm2 to 136 µA/cm2). The FESEM images confirmed the formation of n-HA coating on magnesium alloy. The best coating adhesion among all samples was determined to be 4.52 MPa. Finally, the EIS test confirmed the results of previous corrosion experiments. The corrosion resistance of the optimized sample was measured to be about 2000 Ω cm2.

Coulostatic Perturbation Measurements and the Corresponding Time-to-Frequency Transform Data Analysis for Micro-Electrochemical Study

Traditional micro-electrochemical impedance spectroscopy measurement using a capillary cell presents problems such as high ohmic resistance, long test duration and the subsequent possible tip blocking by corrosion products. In comparison, coulostatic perturbation measurements can avoid these issues due to its unique test principle and much shorter test duration. In this work, the coulostatic perturbation tests were performed on microregions of duplex stainless steel (DSS) 2205 immersed in 3.5 wt.% NaCl solution. The micro-electrochemical parameters were estimated by linear fitting the time-domain curve (LFTC), and subsequently by fitting the frequency-domain curve (FFC) obtained through Fast Fourier Transform (FFC-FFT) for comparison. It is shown that FFC-FFT method minimizes the problem of manual error in slope and intercept evaluation during LFTC. In comparison to the traditional EIS tests, FFC-FFT method causes less perturbation to the tested system, less interference of ohmic resistance with shorter test duration, thus can obtain valid low frequency data more efficiently, which is particularly favorable in studying high polarization resistance system or unstable systems. The micro-electrochemical experimental tests of DSS 2205 show that the polarization resistance of the microregion gradually increases with the increase of austenite phase, while the double-layer capacitance shows a decreasing trend.

MIL-88A (Fe) filler with duplicate corrosion inhibitive/barrier effect for epoxy coatings: Electrochemical, molecular simulation, and cathodic delamination studies

The MIL-88A (Fe) as a MOF based on Fe+3 cations and fumaric acid was fabricated as a corrosion inhibitive filler to achieve a protective coating with duplicate active/passive inhibition properties. The polarization test indicated that the MIL-88A (Fe) saline-based extract had an inhibition effect. The formation of an inhibitive layer was seen in the EIS results for the sample immersed in the MIL-88A (Fe) extract. The slight solubility of MIL-88A (Fe) in the water (122.4ppm total organic carbon and 2ppm Fe+3) caused the inhibitive ions' release. The adsorption of release species from MIL-88A (Fe) scaffold on the substrate was confirmed by the theoretical (QM, MC/MD) computations. The EIS and salt spray test results obtained from scratched epoxy coated samples showed the Epoxy-MIL-88A (Fe) coating's active inhibition effect. The pull-off adhesion strength and cathodic delamination resistance were also improved in the presence of MIL-88A (Fe). The adhesion loss of epoxy coatings after 7 days of exposure to the salt spray decreased from 31.4% to 9.4%, respectively. The unscratched samples filled with MIL-88A (Fe) particles showed excellent barrier properties. The breakpoint frequency value declined from 2.4 to 0.8, and the reduction of low-frequency impedance magnitude decreased from 33% to 20%.