Polarization Curve Measurements Research Articles

Study on corrosion mechanism of high-nitrogen steel laser-arc hybrid welded joints

In this paper, the electrochemical microcorrosion behavior of High-nitrogen steel hybrid weld joints with different wires addition were investigated. Polarization curves measurement was conducted to evaluate the corrosion feature in 3.5% NaCl solution. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to analyze the specific corrosion behavior and pitting deepening mechanism induced by precipitated ferrite-dendrites. The experimental results showed that the addition of nitrogen-containing welding wire improved the corrosion resistance of whole weld joint. As a transitional region, the HAZ exhibited relative weak pitting resistance and severe shedding behavior. The coherent dendrites and similar complex geometries led to the accumulation of continuous corrosion channels. The XPS spectra results indicated that the additional nitrogen in the welding wire optimized oxide composition of the surface passive film.

Hybrid Methodology for Efficient on the Fly (Re)Parametrization of Proton Exchange Membrane Fuel Cells Electrochemical Model for Diagnostics and Control Applications

Prevention and diminution in effects of degradation phenomena under highly dynamic operation of proton exchange membrane fuel cells (PEMFC), while retaining sufficiently high efficiency and performance of the system, are considered significant obstacles toward their wider use in transport applications. Overcoming these obstacles calls for precise on-line monitoring and control tools such as coupled observers, which enable combined performance and service life optimizations. Models used in these applications should feature low computational effort, good extrapolation capabilities and should be easy to parametrize. The first requirement, which is obvious for on-line applications, in frequently in contradiction to the last two, which are heavily intertwined. Good extrapolation capabilities of the model significantly reduce the size of experimental data sets needed for successful parametrization, thus enabling the parametrization on small data sets, while retaining higher accuracy outside of trained variation space. This rationale motivates the use of the computationally-fast reduced-dimensionality electrochemical models e.g. [1, 2], featuring a more profound mechanistic basis; thus, exhibiting better prediction capability of the model.To present significant progress in the aforementioned area, this contribution presents framework of computationally-fast electrochemical models that can be parametrized whether on experimental data from polarization curves or on data obtained by electrochemical impedance spectroscopy (EIS). This hybrid methodology consists of interchangeable thermodynamically consistent reduced-dimensionality electrochemical model for PEMFC [2] and newly developed analytical physical model for impedance spectra with the same set of calibration parameters. The latter is developed by applying electrochemical ansatzes for the cathode and anode reactions derived in [2] on the proposed modelling approach used for calculation of the cathode catalyst layer impedance in the inspiring work of Kulikovsky [3]. Profound modelling basis using the same set of calibration parameters enable enhanced identification of individual calibration parameters that are otherwise harder to be uniquely determined [4] on one hand, and enable parametrization of the model from either of the two separate measurements in time and frequency domains on the other.Enhanced identifiability of calibration parameters using proposed hybrid methodology is especially pronounced in the case of parameters describing anodic and cathodic reaction rates and their activation energies, which are extremely hard to be uniquely determined based on the experimental data consisting of polarization curves only, due to coupling of their information with other calibration parameters. Additionally, proposed hybrid methodology also enables a significant reduction in the measurement time in the case of experimental data obtained by EIS, allowing the low frequency regions, where the transport phenomena could be otherwise characterized, to be omitted due to already uniquely determined calibration parameters from polarization curve measurements. Furthermore, to reduce the necessary amount of experiments for successful parametrization of the model even further, the optimal design of experiments (DoE) is used, based on D-optimal criterion applied onto Fisher information matrix.To assess developed hybrid methodology calibration parameters, obtained by means of minimizing penalty function value with differential evolution algorithm on EIS data, are used for validation against polarization curves measured at the same RuL (remaining useful life). Furthermore, to confirm applicability of the methodology, the same procedure is also used for calibration on the measured polarization curves and validation on the EIS experimental data. Small discrepancy between the values of the root-mean-square errors show plausibility of the proposed hybrid methodology. On the other hand, Fisher information analysis is performed to assess increment in the information about individual calibration parameter when each experimental point from EIS data set is added to experimental space used for parametrization.Results of this joint analysis offer unique insight into the information that data set obtained with the EIS measurements possess about individual calibration parameter in the individual frequency interval and intuitively confirm the results obtained by application of the optimal DoE for a synthetic space of EIS measurements. The latter extremely reduces experimental workload needed for successful calibration of the model in comparison with the full factorial. Innovative hybrid methodology of the measurements in time and frequency domains can thus be used for achieving reduced costs and efforts in initial parametrization and during operation in re-parametrization procedures of the modelling framework for virtual observers.

Synergistic Effect between Fragaria ananassa and Cucurbita pepo L Leaf Extracts on Mild Steel Corrosion in Hydrochloric Acid Solutions

The thermodynamic, inhibitive and synergistic properties of Fragaria ananassa (strawberry) and Cucurbita pepo L (zucchini) leaf extracts on the corrosion of mild steel in Hydrochloric acid solutions were examined by potentiodynamic polarization curves measurements and electrochemical impedance spectroscopy (EIS) technique as well as optical photographic study. Fourier transform infrared spectroscopy (FTIR) and UV-Spectroscopy were applied to predict the possible functional groups and constituents of both leaf extracts. Potentiodynamic polarization curves proved that Fragaria ananassa and Cucurbita pepo L leaf extracts act as mixed type inhibitors for mild steel in 0.5 M HCl solutions. Impedance plots indicated that the corrosion process occurred under activation control. Thermodynamic parameters proved that the formation of the activated complex is an endothermic association instead of a dissociation step. The inhibitive efficiency of these leaf extracts relies on their physical adsorption on the metal surface rather than the complexation with Fe2+ ions. Cucurbita pepo L leaf extract is more efficient than Fragaria ananassa as a corrosion inhibitor for mild steel in 0.5 M HCl. The synergistic effect between both extracts may be due to co-adsorption between their molecules, which could be either competitive or co-operative adsorptions. The synergistic parameter value S was higher than unity indicating a cooperative synergistic effect.

Corrosion performance of DLC coatings with laser-induced graphitized periodic surface structure

Two types of diamond-like carbon (DLC) thin films, hydrogenated amorphous carbon (a-C:H) and super-hard tetrahedral amorphous carbon (ta-C), were irradiated with femtosecond laser pulses, and the corrosion resistance of the DLC films with laser-induced periodic surface structure (LIPSS) and modified to nanocrystalline graphite (nc-G) was electrochemically evaluated from anodic polarization measurements. The polarization curve for a glassy carbon (GC) plate, which is a type of nc-G, was measured for comparison. The polarization curve for stainless steel with LIPSS was also measured, and it was confirmed that LIPSS increased the surface area of the irradiated part, which resulted in an increased apparent corrosion current density. Polarization curve measurements for irradiated DLC indicated that the corrosion current density was reduced, despite the effect of an increased surface area by the formation of LIPSS, and the polarization curves tended to approach those for GC plates. Therefore, the irradiated surface layer of DLC is modified to nc-G, which results in excellent corrosion resistance similar to that of GC.

Influence of Surface Ultrasonic Rolling on Microstructure and Corrosion Property of T4003 Ferritic Stainless Steel Welded Joint

In this paper, the effect of surface ultrasonic rolling treatment (SURT) on surface properties of T4003 cold metal transfer (CMT) welded joints was studied. Surface topography and microstructure changes of the welded joint surface before and after SURT were observed by optical microscope and scanning electron microscope. The hardness and residual stress distribution of welded joint were measured by a microhardness tester and X-ray diffractometer. The change of corrosion resistance of welded joints was studied by electrochemical polarization curve measurement. The results show that surface roughness (Ra) of the weld zone, heat affect zone (HAZ), and base metal after SURT was reduced to 0.320 μm, 0.156 μm, and 0.227 μm, respectively, and surface morphology became smooth. The plastic deformation layer and working hardening layer were formed at the welded joint. The degree of plastic deformation of the weld zone was more serious than that in the base metal, and grains in weld zone was obviously refined. The thickness of plastic deformation layer was about 100 μm. The surface hardness in the weld zone was highest, which is about 420 HV. The refinement of grains and the increase of surface hardness can improve the fatigue life of welded joint. After SURT, the residual stress in the welded joint changes from residual tensile stress to residual compressive stress, which can also improve fatigue life of the welded joint. Surface corrosion resistance of welded joints after SURT was improved due to smooth surface and the formation of fine grains layer.

Effect of Fine‐Grained AZ91D Coating with Graphene Oxide/Hydroxyapatite on Biocompatibility

AbstractA graphene oxide/hydroxyapatite(GO/HA) composite coating were prepared on the surface of fine‐grained AZ91D magnesium alloy. The morphologies and structures of the coatings were characterized by Scanning Electron Microscopy and X‐Ray Diffraction. The corrosion behaviors were studied by polarization curve measurement and alternating current impedance spectroscopy, respectively. Also, the changes of the Mg2+ concentration in rat plasma were detected. Besides, changes of muscle, liver, and kidney in rats and bone in rabbit were tested to prove whether it was toxic to the body after implantation. Results showed that GO/HA‐AZ91D had good corrosion resistance. Compared to AZ91D, the corrosion potential, the membrane capacitance and the transfer resistance increased, the current decreased, and the corrosion performance was greatly improved. There was no significant difference of magnesium concentration among different groups. The structural characterization showed that the surface compactness of the composite coating was better, and the composite coating could effectively improve the corrosion resistance of the magnesium alloy.

Phosphating passivation of vacuum evaporated Al/NdFeB magnets boosting high anti-corrosion performances

A phosphating passivation is conducted on the surface of Al coated NdFeB magnets by a gaseous process. The surface morphology, structure and elemental compositions of the samples are characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The anti-corrosion performances of the phosphating passivated Al/NdFeB magnets are analyzed by neutral salt spray test, potentiodynamic polarization curve and electrochemical impedance spectroscopy measurements. The corrosion process and corrosion mechanism of the samples are studied by analyzing the coating morphologies, potentiodynamic polarization curves and surface elemental compositions during the immersion test in 3.5 mass% NaCl solution for different time. The surface passivation of Al coated NdFeB magnets can be realized by gaseous phosphating technology, which can effectively improve the corrosion resistance of Al coating. The optimized sample obtained with phosphating temperature at 300 °C achieves the improvement of NSS time from 96 h to 288 h. Gaseous phosphating can effectively seal the pores in vacuum evaporated Al coatings, and form a phosphating passivation film on the coating surface, which contribute to the enhancement of anti-corrosion performances of Al coated NdFeB magnets.

Investigation of oxygen evolution reaction kinetic process and kinetic parameters on iridium electrode by electrochemistry impedance spectroscopy analysis

Though metallic iridium catalyst is broadly used as an efficient OER catalyst due to its high OER activity, however, there is a current dearth of researches on its OER mechanism and kinetic parameters. The present study aims to investigate the OER kinetic process and obtain kinetic parameters of the iridium catalyst. The OER rate determining step was investigated by EIS measurements. Meanwhile, OER kinetic parameters were obtained by both steady-state polarization curve measurement and microkinetic modelling. Results show that the rate determining step of OER is the adsorption of Ir-OHads species on active sites. Values of both Tafel slope and exchange current density are important kinetic parameters which are about 48.6 mV/dec and 1.88 × 10−11 A/cm2 according to the microkinetic modelling. The obtained parameters could be referred in the novel OER catalysts investigation. The approaches for OER kinetic process study and kinetic parameters evaluation are useful in the investigation of other catalysts.

Effect of Chloride Concentration on Stress Corrosion Behavior and Mechanism of SA516Gr70N Steel in Alkaline NaCl/Na2S Solution

The effects of chloride on the electrochemical process and susceptibility to stress corrosion cracking (SCC) of SA516Gr70N steel in alkaline NaCl/Na2S solution were investigated by using electrochemical techniques (impedance spectroscopy and polarization curve measurement) and slow strain rate tensile (SSRT) tests. SA516Gr70N steel exhibited SCC susceptibility to a certain extent in alkaline NaCl/Na2S solution. The susceptibility to SCC decreased with increasing chloride concentrations in solutions with pH values of 9 and 11, while susceptibility was not apparent in higher pH solutions. Electrochemical analysis showed that the corrosion potential became more negative, and the anodic corrosion rate decreased with increasing chloride concentration due to the competitive adsorption of HS− and Cl−. The mechanism of SCC is mainly controlled by anodic dissolution with the addition of chloride.

Analyzing Galvanic Corrosion Behavior of Metal Alloys Based on First-Principles Simulations

Galvanic corrosion behaviors of alloys have usually been investigated through experiments, where the measured polarization curves, the corrosion potential and current could differ a lot between different literature. Herein, we proposed a semi-empirical model based on the mixed potential theory and first principles calculation to analyze the galvanic corrosion of the metal alloys. Our model is further validated in the case of Mg-Ge alloys, which is composed of anode Mg matrix and cathode Mg2Ge second phase. The combination of the large anode equilibrium potential difference between Mg and Mg2Ge, and the Schottky barrier across the interface indicates that the Mg2Ge second phase can prevent the Mg grain from serving as the cathode and impede the electron transfer between the Mg grains. First principles calculations on the kinetics of hydrogen evolution reaction upon Mg2Ge reveal that the rate-determining step is the hydrogen adsorption, which is extremely energetically unfavored but an inevitable intermediate state. The estimated exchange current of the hydrogen evolution upon Mg2Ge is about 3 orders of magnitude smaller than that on pure Mg, indicating the depressed galvanic corrosion of the Mg-Ge alloys is also the result of the low hydrogen exchange current upon Mg2Ge. Moreover, some typical intermetallics, such as MgZn2 and MgSc, were selected to compare the corrosion properties of different Mg alloys, which is in close agreement with the experimental observations. Our model to predict the galvanic corrosion behavior provides a promising perspective for designing better corrosion-resistant metal alloys.

Rate Determining Factors in Multi-Step Electrocatalytic Processes

This paper offers a mechanistic perspective applicable to a range of technically significant electrocatalytic processes , based on measured polarization curves and impedance spectra. The diagnostics offered is based on a comprehensive rate equation which includes a potential dependent pre-exponential factor. A common pattern observed in mechanisms of electrocatalytic processes, involves a step preceding the RDS, that establishes the surface composition required for the onset of the RDS [1,2]. Such “pre-step” can involve activation of surface sites by removal of surface blocking species and/or formation of adsorbed intermediates which serve as reactants in the RDS. Electrically speaking, these “pre-steps” are overpotential-driven surface charging processes, i.e., the current associated with the pre-step is pseudocapacitive in nature. Consequently, the rate of the electrocatalytic process is determined by combined effects of the overpotential on: (i) the catalyst surface composition and, (ii) the activation energy of the RDS.Recognizing that active intermediate formation and/or surface site activation involve switching of a surface redox system, the comprehensive expression for the rate of a cathodic electrocatalytic process, is expected to have the following general form [1,2] : (1) J(Ecath) = Cr g Fk0 A ∗ × f(Ecath−E0 redox)×10ˆ{[− D H# act /2.3RT]−[(Ecath−E◦ cell)/b]} where, f (Ecath−E0 surf. redox) represents the fraction of surface sites in active form at Ecath For a 1e surface redox system obeying the Nernst equation, the fractional population of sites in active form is given by:(2) f(Ecath−E0 redox) = 10ˆ [(F/2.3RT) (Ecath− E0 surf. redox )+1]−1 and the explicit , full expression for J(Ecath), becomes:(3) J(Ecath) = Cr g Fk0 A ∗ × 10ˆ[(F/2.3RT)(Ecath−E0 redox )+1]−1 ×10ˆ{[− D H# act /2.3RT]−[(Ecath−E◦ cell)/b]} The last equation reveals that both types of over-potential driven surface transformation processes --site activation and active intermediate formation-- are expected to leave the same signature in the polarization curve. : a low Tafel slope of ~ 60 mV/decade at lower current densities, gradually transitioning to a slope of ~120mV/decade with increase of the current. We show in this contribution that these two different causes of a lower Tafel slope at low current density, can be distinguished from EIS measurements.In the case of the HOR, a sequence of two steps, taking place ,for example, according to the Heyrovsky-Volmer mechanism, results in two capacitive arcs in the Nyquist plot. In contrast, the EIS reported in the literature in the low current range of the ORR , typically exhibits only one capacitive arc in the frequency range 5kHz- 0.1Hz [ 3 ]. The low Tafel slope observed near the onset potential of the ORR has been ascribed to overpotential-driven removal of a surface blocking oxide formed by water discharge [ 4 ] , however, no spectral feature corresponding to this process could be detected in the EIS spectrum in the frequency range 5kHz- 0.1Hz [3]. This “miss” is resolved when EIS spectra for the ORR are recorded down to significantly lower frequencies [5]. At frequencies under 0.1Hz, the EIS spectrum for the ORR , exhibits an additional, inductive loop .The inductive loop in the EIS observed for the ORR, reflects the slow process of surface oxide reduction which enhances the rate of electron transfer to the dioxygen molecule by increasing the population of active, metal surface sites. Another example of an EIS exhibiting an inductive loop at low frequency , is that recorded for hydrogen oxidation at Pt in the presence of COads [6]. The similar patterns of the spectra for ORR and, for HOR in the presence of COads, provide further support for the assignment of the inductive loop in the EIS for the ORR to slow removal of a site blocking species.These different types of EIS spectra will be further discussed in this talk, with reference to the comprehensive dependence of the rate of multi-step electrocatalytic processes on overpotential .Acknowledgement: This is a contribution to the Electrocatalysis Symposium at the ECS meeting in Montreal , memorizing Andrzej Wieckowski.I remember vividly many technical discussions and very friendly interactions with Andrzej over many years of close acquaintance.

Effect of Zn2+ on Cathodic Reaction of Carbon Steel in Aqueous MgCl2 Solutions

We have shown that zinc dissolution is accelerated in relatively high concentrations of MgCl2 during the galvanic corrosion process consisting of zinc and carbon steel. In this study, in order to understand further the galvanic corrosion process of zinc and carbon steel in MgCl2, the cathode reaction on carbon steel was investigated in MgCl2 aqueous solution with and without Zn2+ which is generated during the galvanic corrosion process.The sample used for the experiment was carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined to a shape of 1.5 × 1.5 × 0.3 cm3. One side of this sample was ground up to #2000 grit with SiC abrasive papers and then degreased and washed in acetone before use in the following experiments. The test solutions were mixtures of 0.25 M MgCl2 and x mM ZnCl2 (x = 2.5, 5 mM, Mg / Zn molar ratio: 100, 50) and they were used at room temperature under a naturally aerated condition. As reference solutions, the mixtures of 0.5 M NaCl and y mM ZnCl2 (x = 5, 10 mM, Na / Zn molar ratio: 100, 50) with the same Cl- concentration were used. The cathodic polarization curve measurements were done by a conventional three-electrode method with a platinum wire as a counter electrode and an Ag / AgCl electrode (saturated KCl, SSE) as a reference electrode. The potential sweep rate was 0.5 mV/sOn the cathodic polarization curves for carbon steel measured in an aqueous MgCl2 solution containing Zn2+, the diffusion-limiting current region due to the cathodic reduction reaction of dissolved oxygen (ORR) was observed from -0.6 V to -0.8 V, and the magnitude of the limiting currents were almost the same regardless of the Zn2+ concentration. Furthermore, the cathodic polarization curves showed that an increase in the current due to the hydrogen evolution reaction (HER) occurred in the MgCl2 solution without Zn2+. By comparison with the cathodic polarization curve measured in the NaCl solution without Zn2+ showed a diffusion-limiting current of ORR was comparable to that in the MgCl2 solution, but the overvoltage of HER was increased by about 0.1 V. These results indicated that in the MgCl2 solution, HER on carbon steel was enhanced more than that in NaCl aqueous solution.On the other hand, in the MgCl2 solutions containing Zn2+, a shoulder was observed in the cathode polarization curve at around -0.95 V, and the the current due to HER was decreased with increasing the Zn2+ concentration. It was shown that HER was suppressed in MgCl2 solutions by the presence of Zn2+. This may be attributed to the precipitation of zinc corrosion products formed during cathodic polarization.

Corrosion Behavior of Plasma Transferred Arc Fe-based Coating Reinforced by Spherical Tungsten Carbide in Hydrochloric Acid Solutions

Fe-based coatings reinforced by spherical tungsten carbide were deposited on 304 stainless steel using plasma transferred arc (PTA) technology. The composition and phase microstructure of the coatings were evaluated using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The corrosion behaviors of the coatings in 0.5 mol/L HCl solution were studied using polarization curve and electrochemical impedance spectroscopy (EIS) measurements. The experimental results shows that the tungsten carbide improves the corrosion resistance of the Fe-based alloy coating, but increase in the mass fraction of tungsten carbide leads to increasing amount of defects of holes and cracks, which results in an adverse effect on the corrosion resistance. The defects are mainly present on the tungsten carbide but also extend to the Fe-based matrix. The tungsten carbide, acting as a cathode, and binding material of Fe-based alloy, acting as an anode, create a galvanic corrosion cell. The binding material is preferentially corroded and causes the degradation of the coating.

Eucalyptus leaf extract as a eco-friendly corrosion inhibitor for mild steel in sulfuric and phosphoric acid solutions

The adsorption mechanism and inhibitive action of the Eucalyptus plant leaf extract (Eu) on the corrosion of mild steel in 0.5 M H2SO4 and 0.5 M H3PO4 solutions were investigated by potentiodynamic polarization curves measurements and electrochemical impedance spectroscopy technique. Potentiodynamic polarization curves revealed that the Eucalyptus leaf extract acts as a mixed type inhibitor in both acidic solutions. The impedance responses indicated that the corrosion process occurs under activation control. Fourier transform infrared spectroscopy has been used to predict the possible major chemical constituent of the leaf extract. Four adsorption isotherms including Langmuir, kinetic–thermodynamic, Flory–Huggins and Temkin model were used to investigate the mode of inhibition of Eucalyptus leaf extract. The free energy of adsorption showed that the corrosion inhibition takes place by spontaneous physical adsorption of Eucalyptus leaf extract molecules on the mild steel surface. The obtained data indicated that Eucalyptus leaf extract is a more efficient inhibitor of mild steel corrosion in 0.5 M H2SO4 than in 0.5 M H3PO4 solutions. Thermodynamics activation parameters were also calculated and discussed.

Anti-corrosion Properties of 2-Phenyl-4(3H)-quinazolinone-Substituted Compounds: Electrochemical, Quantum Chemical, Monte Carlo, and Molecular Dynamic Simulation Investigation

In this investigation, attempts have been made to study the corrosion inhibition properties of three new 2-phenyl-4(3H)-quinazolinone-substituted compounds for mild steel in 1.0 M hydrochloric acid medium. The evaluation was carried out using mass loss, electrochemical impedance spectroscopy, and polarization curves measurement. It is shown that 2-phenyl-4(3H)-quinazolinone-substituted compounds are very good inhibitor’s for mild steel corrosion in 1.0 M hydrochloric acid medium, which acts as mixed-type inhibitors. So, the inhibition efficiency was increased with inhibitor concentration in the order Q-p-Cl > Q-m-Cl > Q-H, which depends on their molecular structures and the chloride para/metapositions. Electrochemical impedance spectroscopy has shown that all compounds act by the formation of a protective film at the metal surface. The correspondence between inhibition property and molecular structure of the 2-phenyl-4(3H)-quinazolinone-substituted compounds is investigated, using density functional theory (DFT) . The effect of molecular structure on the inhibition efficiency has been explored by quantum chemical computations and obvious correlations were observed. The binding energies of tested compounds on Fe(110) surfaces were calculated using molecular dynamics simulation. Experimental and DFT study was further supported by molecular dynamic (MD) simulations study.

The influence of half-cycle rectified sinusoidal alternating current (AC) on corrosion of X80 pipeline steel in an acid bicarbonate solution

PurposeThis paper aims to investigate the effect of alternating current (AC) on corrosion, it is not yet clear about the exact mechanism of the corrosion induced by AC. Previous reports indicated that AC corrosion was similar to the effect of continuous cathodic and anodic polarization on the corrosion process of the metals. Wan et al. studied the effect of negative half-wave AC on stress corrosion cracking behavior and mechanism of X80 pipeline steel in near-neutral solution.Design/methodology/approachThis study attempted to understand the AC-induced corrosion by imposing the half-cycle AC on the X80 pipeline steel in an acid bicarbonate solution. The AC corrosion mechanism was determined by weight loss and potentiodynamic polarization curve measurements, as well as surface characterization.FindingsThe results show that the positive half-cycle AC accelerated the uniform corrosion in the NaHCO3 solution, the negative half-cycle AC would decrease the uniform corrosion and local corrosion was increased and some Ca and Mg deposited on the surface of X80 steel, so the corrosion rate decreased by negative half-cycle AC. The corrosion product was composed of α-FeOOH under the application of positive half-cycle AC. The oxygen reduction led to a local increase of pH near the electrode surface and led to the formation of α-FeOOH, which enhanced the protectability of corrosion products.Originality/valueResearchers studied the effect of negative half-wave AC on stress corrosion cracking behavior and mechanism of X80 pipeline steel in near-neutral solution. However, the AC behavior and corrosion mechanism in acid solution are unknown. So to make clear about the corrosion behavior of metals in different polarization states and the mechanism involved, diode technology was used to research the AC corrosion, half-wave AC was applied on the metals after the full-wave rectified.

Effect of ageing temperature on microstructure, mechanical property and corrosion behavior of aluminum alloy 7085

The influence of ageing temperatures on mechanical properties, corrosion behavior and precipitation features of aluminum alloy 7085 have been investigated by using tensile testing, intergranular corrosion tests, polarization curve measurements and transmission electron microscopy (TEM) observations. The results show that the precipitate sequence of aluminum alloy 7085 is different at different ageing temperatures. GP II is the main strengthening precipitate in the alloy peak aged at 90 °C, while η′ contributes most to the strength of the alloy peak aged at 150 °C. Similar ultimate yield strength can be obtained under either peak ageing conditions, but the work-hardenability at 90 °C is much better than that at 150 °C due to the predominance of GP II zones. Alloy 7085 peak aged at 150 °C shows better corrosion resistance than at 90 °C.

New triazepine carboxylate derivatives: correlation between corrosion inhibition property and chemical structure

In this investigation, attempts have been made to study the corrosion inhibition properties of three new triazepine carboxylate compounds for mild steel in 1.0 M hydrochloric acid medium. The evaluation was carried out using mass loss, electrochemical impedance spectroscopy and polarization curves measurement. Impedance diagrams and Bode plots for uninhibited and inhibited systems were analyzed using Zview program. The fitted data observed trails in nearly the same pattern as the experimental results. It is showed that triazepine carboxylate compounds are very good inhibitors for mild steel corrosion in 1.0 M hydrochloric acid medium which act as mixed-type inhibitors. So, the inhibition efficiency was increased with inhibitor concentration in the order Cl–Me–CN > Me–CN > Cl–Me–CO2Et which depended on their molecular structures. Electrochemical impedance spectroscopy showed that all compounds act by the formation of a protective film at the metal surface. Surface analyses via SEM and Optical 3D profilometry were used to investigate the morphology of the steels before and after immersion in 1.0 M HCl solution containing inhibitors. The correspondence between inhibition property and molecular structure of the triazepine carboxylate compounds was investigated, using density functional theory (DFT). Experimental and DFT study was further supported by molecular dynamic simulations study.

Compact and planar type rapid response ppb-level SO2 sensor based on stabilized zirconia and SrMoO4 sensing electrode

The planar yttria-stabilized zirconia (YSZ) solid electrolyte based mixed potential type gas sensing devices attached with molybdate MMoO4 (M: Ni, Co, Zn, Mn and Sr) sensing electrodes (SEs) were designed and fabricated, attempting to sensitively and rapidly monitor ppb-level SO2. The sensor using SrMoO4-SE possessed the highest potential response signal of -37.5 mV to 500 ppb SO2 at 550 °C. More importantly, the low detection limit of 20 ppb SO2 and fast response time of 37 s to 200 ppb SO2 were presented for the device utilizing SrMoO4-SE at 550 °C. The linear dependence between response value and the SO2 concentration logarithm in the range of 0.02–1 ppm was observed, which the sensitivity (slop) was −29 mV/decade. Furthermore, the sensor also showed excellent selectivity, reproducibility and high temperature stability of 7 days to SO2 at 550 °C. The mixed potential sensing mechanism was discussed and further verified based on the measurement of polarization curves.

Power quality estimation of water electrolyzers based on current and voltage measurements

The ripple of the supplied direct current has a significant effect on the energy efficiency of the water electrolyzer cell. Hydrogen production is defined by the current mean value, but current harmonics generate additional losses in the electrolyzer cell. However, the direct measurement of the DC current in the kiloampere range may be a challenging task compared with the voltage, which is practically in the range of a few hundreds volts in the electrolyzer stack. The effect of current harmonics on the energy efficiency and the voltage mean and root-mean-square (RMS) values is analyzed analytically based on the measured polarization curve of the PEM electrolyzer cell. The results show that both in the case of a theoretical sinusoidal current ripple and a practical thyristor bridge supply, the voltage mean or RMS values do not give a reliable estimate of the power quality. Instead, the voltage waveform as a function of time or the difference between the current mean and RMS values should be monitored.