Open Circuit Potential Measurements Research Articles

Correlation between the microstructure and corrosion performance of the HIPIMS nitrided bio-grade CoCrMo alloy

Corrosion performance of CoCrMo alloy (F75) plasma nitrided with High-Power Impulse Magnetron Sputtering (HIPIMS) technique was thoroughly investigated. Open Circuit Potential (OCP) measurements and potentiodynamic polarisation tests exhibited a strong correlation between the transmuting microstructure (as a result of varying nitriding voltage from −700 V to −1100 V) and its corrosion performance. A significant improvement in the ECorr values was noticed (around −590 mV for untreated as compared to −158.17 mV for −1000 V) when analysed against 3.5% wt. NaCl solution. Similarly, results against Hank's solution also exhibited a significant increase in ECorr values (around −776 mV for untreated as compared to −259 mV for −1000 mV). Irrespective of the nitriding voltage, HIPIMS nitriding led to a significant improvement in the corrosion resistance of the alloy. For nitriding voltages −700 V and −900 V, a diffusion based S phase layer played a significant role in imparting corrosion resistance. On the contrary, precipitation of chromium-based nitrides (CrN and Cr2N), observed in samples nitrided at relatively higher voltages of −1000 V and −1100 V, resulted in its relative deterioration. A preferential dissolution of the ϵN grains and its grain boundaries, along with a sluggish dissolution of the γN grains and metal carbides appeared to be the dominant corrosion mechanism for the nitrided alloys. Specimens nitrided at −700 V and −900 V displayed the best corrosion resistance, which was deemed to be derived from the right combination of a thicker S phase layer and the compound layer consisting of M2–3N and M4N phases.

Multiple-scan voltammetry and OCP: Archaeometric tools for dating archaeological bronzes

The application of a multiple-scan strategy to nanosamples taken from 18 cross-sections of Bronze Age arms and armour, as well as two Roman coins using two solid-state electrochemical techniques, the voltammetry of immobilized microparticles (VIMP) and open circuit potential measurements (OCP) is described. The voltammetric responses in contact with aqueous acetate buffer can be attributed to the reduction of cuprite with variable degree of compaction and crystallinity revealing significant differences in the gradient of such properties with depth. Such differences are also revealed by “dry” OCP measurements connecting points in the cross section near and separated from the corrosion layer. The voltammetric study of the metallographic samples of the bronze objects shows correlation with the age of the objects, respectively the period of their deposition. We discuss also (potential) influence of different factors on the VIMP and OCP measurements, such as deposition context (soil, water), chemical composition of the copper alloys, and microstructural features (as-cast, annealed, work-hardened), and how to overcome these issues.

Stability improvement of layered Au,Pt-YSZ mixed-potential gas sensing electrodes by cathodic polarization: Studies by steady state and dynamic electrochemical methods

Electrochemical characteristics of a layered Au,Pt-YSZ mixed-potential (APE) gas sensing electrode were studied by open circuit potential (OCP) and electrochemical impedance measurements (EIS), especially in relation to effects of aging under ambient air conditions and cathodic polarization. Mixed-potential response of the APE to CO was found to be drastically reduced after 100 days of operation in ambient air, which is correlated with a clear change in the shape of the EIS characteristics and a considerably increased polarization resistance (Rp). By applying a cathodic polarization, the reduced sensitivity can be almost fully restored. Also the EIS characteristics tend to show a similar behavior as observed in the initial state. The influence of cathodic polarization treatment on the regeneration of the electrochemical (OCP and EIS) behaviors is found to be clearly enhanced at elevated temperatures (700 °C), while oxygen concentration seems to play no role on this regeneration effect. This polarization treatment will highly improve stability of the APE and is expected to enable applications like flue gas analysis.

Hierarchical zeolite-LTA@Mg-Al layered double hydroxide core@shell structure with enhanced corrosion protection of steel in saturated Ca(OH)2 solution

In this article, a novel type of core@shell Linde type A zeolite@Mg-Al layered double hydroxides (zeolite-LTA@ Mg-Al LDHs) was fabricated via in situ co-deposition method for efficient corrosion protection of carbon steel. The corrosion inhibition effect of fabricated zeolite-LTA@ Mg-Al LDH on steel was decided by a comparative experiment in saturated Ca(OH)2 solution. The batch experiment on the equilibrium isotherms of chloride binding in the solution clearly demonstrated that compared to pure Mg-Al LDHs, the zeolite-LTA@Mg-Al LDHs exhibited an higher chloride binding capacity due to the highly dispersed LDHs with large surface area on the zeolite-LTA support. In addition, a better corrosion inhibition capacity of zeolite-LTA@Mg-Al LDHs was proved by the measurements of open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP) and optical microscopy (OM). Some nitrate ions on the steel surface detected by X-ray photoelectron spectroscopy (XPS) confirmed the dual effects of aggressive chloride removal and simultaneously released NO3−, which were responsible for the ultimate inhibition effect of zeolite-LTA@Mg-Al LDHs.

A study on corrosion resistance of ISO 5832-1 austenitic stainless steel used as orthopedic implant

The ISO 5832-1 austenitic stainless steel used as biomaterial is largely applied in the area of orthopedics, especially in the manufacture of implants, such as temporary or permanent replacement of bone structures. The objective of this study was to evaluate the localized corrosion resistance of the ISO 5832-1 stainless steel used in orthopedic implants by electrochemical tests in two different solutions. The results of this study are of great interest to evaluate the corrosion of metallic implants that can result in the release of corrosion products into bodily fluids causing possible adverse biological reactions. The determination of the chemical elements in the composition of the ISO 5832-1 stainless steel was performed by neutron activation analysis (NAA). The samples for electrochemical tests were grinded with silicon carbide paper up to #4000 finishing, followed by mechanical polishing with diamond paste. The open circuit potential measurements and anodic polarization curves were obtained in solution of 0.90 wt. % of NaCl and of simulated body fluid (SBF). The results indicated that the ISO 5832-1 stainless steel presented a high resistance to crevice corrosion in simulated body fluid solution but high susceptibility to this form of corrosion in the chloride solution.

Assessing the Fly Ash Effect on the Durability of Reinforced Concrete of Water Treatment Tanks Exposed to Coagulating Ferric Chloride by an Electrochemical Process

This study aims to assess the corrosion behaviour of reinforcing steel of blended concretes using pozzolanic additives—fly ash—replacing 15% and 25% of cement weight in order to enhance the durability of potable water treatment tanks exposed to 3.5 wt% FeCl3. The test was evaluated in a very short time by the acceleration corrosion (impressed constant voltage 15 V). Specimens were analysed through open-circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) tests after placing them in a 3.5wt% FeCl3 and drinking water solution. The depth of chloride penetration was also measured to determine the extent of chloride permeability. Moreover, SEM/EDS techniques were carried out to identify corrosion products. The results have indicated that cement concretes mixed with fly ash exhibit a positive impact on compressive strength at 7 and 28 days. OCP and EIS measurements have shown that the addition of fly ash enhances the corrosion resistance of reinforced concrete exposed to ferric chloride and potable water. In addition, the results have also shown that the fly ash dosage with 25% is more effective in improving durability, while the one with 15% is less effective in reducing durability.

Effects of 4-bromoaniline and pentylamine compounds on the stress corrosion cracking of mild steel and brass in dilute electrolyte solutions

The inhibition effect of 4-bromoaniline (4BA), pentylamine (PTL) and their combined admixture on the stress corrosion behaviour of mild steel and brass in 0.5 M and 0.3 M H2SO4 and NH4OH solution was studied through open circuit potential measurement and visual observation. The experiment was performed at 90% stress level for optimal results. Results obtained showed that the inhibitor compounds generally influenced the thermodynamic tendency of the alloys to corrode, delayed the onset of crack formation and specimen failure in the electrolytes. The combined admixture of 4BA and PTL performed most effectively in the both acid solutions, increasing the corrosion potential to -0.391 V and -0.281 V compared to the corresponding values obtained in the control acid solutions at -0.446 V and -0.451 V. 4BA performed most effectively in NH4OH solutions with corrosion potential values of -0.743 at 504 h. Visual observation of the metallic alloys shows crack initiated on mild steel in both acids without inhibitor addition at 72 h of exposure and specimen failure occurred at 216 h. The corresponding observation for brass in 0.5 M NH4OH solution showed crack initiated at 144 h before failure at 360 h. In 0.3M NH4OH, crack initiation and failure occurred at 216 h and 504 h respectively. The admixture of 4BA and PTL delayed crack initiation on mild steel to 216 h and no specimen failure was observed at 504 h. 4BA delayed the onset of crack formation on brass in 0.5 M and 0.3 M NH4OH solution to 216 h and 288h. However, failure occurred at 432 h in 0.5 M NH4OH compared to no failure at 504 h of exposure in 0.3 M NH4OH solution.

Passivation behaviour and localized corrosion activities of non-toxic surfactant derivatives on Copper

In this paper surfactant extracted from Zea mays was experimented on as a corrosion inhibitor for Copper in 0.5 M HCl solution using electrochemical measurement at 298 K at several surfactant concentrations. Open circuit potential measurement, polarization analysis, adsorption, SEM/EDX analysis, were investigated to find out how effective the surfactant is as an inhibitor on Copper. Results gotten depicts that the surfactant extracted from Zea mays performed excellently on Copper as the peak efficiency of inhibition of 86.99% at 20ml. The electrochemical polarization data revealed the inhibitor behaves as an inhibitor of the anodic type. Temkin isotherm of adsorption explained the surfactant adsorption onto the copper layer. SEM/EDX studies indicated that the corrosive impact on copper surface reduced due to the addition of the surfactant. The polarization tests have shown strong concordance with the SEM images.

Oxygen-ion conductivity and mechanical properties of Lu2O3-doped ZrO2 as a solid electrolyte

The characteristics of Lu2O3-doped ZrO2 as a solid electrolyte material were investigated in terms of its oxygen ion conductivity and flexural strength to realize its electrolytic function at intermediate and high temperatures. The effect of doping Lu3+, which has a high nuclear charge electric field strength, was examined through impedance spectroscopy, open-circuit potential measurements, and bending tests. The results with Lu2O3 dopant were compared with those obtained with a widely used dopant, Y3+, having a similar ionic radius with Lu3+, as well as a dopant that provides high ionic conduction, Sc3+, having a smaller ionic radius with Zr4+. The results revealed that, at the same dopant concentration, both the ionic conductivity and the flexural strength of Lu2O3-doped ZrO2 are higher than those of the widely used Y2O3-doped ZrO2. The conductivity of 8 mol% Lu2O3-doped ZrO2 surpassed that of 8 mol% Sc2O3-doped ZrO2 in the range of 800–950 °C (0.153 S/cm vs. 0.121 S/cm at 900 °C). These results indicate the potential of Lu3+ as a dopant for enhancing the performance of ZrO2 solid electrolytes.

Half-Cell State of Charge Monitoring for Determination of Crossover in VRFB-Considerations and Results Concerning Crossover Direction and Amount.

Membranes play a crucial role in efficiency and longevity of flow batteries. Vanadium flow batteries suffer self-discharge and capacity fading due to crossover of electrolyte components through the membrane from one battery half-cell to the other. We consider the impact of vanadium species crossing ion exchange membranes on state of charge of the battery and we present a simple method to determine crossoverll open circuit potential measurements. State of s. State of charge for the negative and positive half-cell is simulated based on assumptions and simplifications for cation and anion exchange membranes and different crossover parameters. We introduce a crossover index “Ind” which enables the determination of crossover direction from state of charge data for the negative and positive half-cell and therewith identification of the half-cell in which predominant self-discharge occurs. Furthermore Ind allows statements on crossover amount in dependence on state of operation. Simulated case studies are compared to experimental state of charge values estimated from half-cell potential measurements. Our results reveal that half-cell potential monitoring respectively half-cell SOC estimation, is a simple and suitable tool for the identification of crossover direction and relative amount of crossover in VFB.

Data on electrochemical deterioration of mild steel in rice husk agro-waste developed nano-coolant

Investigation of the electrochemical deterioration of mild steel in rice husk agro-waste developed nano-coolant is presented in this study. Corrosion rates of mild steel versus nano-coolant concentration are presented. Linear polarization test data was also covered. Mild steel coupons were immersed in different concentrations (ten concentrations and the control as a reference) of the developed nano-fluid for a period of 24, 48, 72, 96, 120, 144 and 168 h. Corrosion rate was calculated based on ASTM Standard G1–03 standard practice for preparing, cleaning and evaluation of corrosion test specimens. Open circuit potential measurements (OCP) were also carried out. The potential of the steel samples in the nano-fluid with respect to time was investigated. This dataset could be used in evaluating the performance of mild steel in rice husk based nano-coolant.

Microstructural and electrochemical studies of spark plasma sintered multiwall carbon nanotubes reinforced TiO2–MnO2 based composite

An electrochemical study was conducted to investigate the suitability of TiO2, TiO2-MWCNTs and (5,10 and 15 wt.%) of MnO2 in TiO2-MWCNTs composites as dimensional stable electrodes which were developed via conventional powder processing and spark plasma sintering. The following electrochemical tests were carried out including open circuit potential, galvanostatic chronoamperometry and cyclic voltammetry measurements. The results showed that an increase on MnO2 content in the composites did not only lower the potentials but enhanced the stability of the composites. The degradation which translates to corrosion susceptibility was favorable on composite samples with lower MnO2 content. Also, the presence of MWCNTs in the composites improved the electrocatalytic capacity of the material. Furthermore, the anodic layers formed on the composites during polarization was analyzed using SEM, XRD and cyclic voltammetry. The results showed that the formation of anodic layer during 24 h of polarization increased with the addition of MnO2 content and 15 MnO2–TiO2-MWCNT composite grade showed minimal pores after polarization which translates to higher protection.

Preparation of high performance coating films based on urethane acrylate oligomer and liquid silicone rubber for corrosion protection of mild steel using electron beam radiation

The aim of this article is to prepare high performance anti-corrosion formulations for mild steel panels, which are based on mixing solvent-free aliphatic urethane triacrylate oligomer (AUTA) and liquid silicone rubber (LSR) under electron beam irradiation (EB). Initially, different concentrations of LSR were added to the AUTA-based formulations to prepare 100 μm thin films on different substrates and then exposed to a dose of 10 kGy of EB radiation. The homogeneity and distribution of the previous components were confirmed by FT-IR spectroscopy, water contact angle, and scanning electron microscope. All EB-cured coated films for all formulations were evaluated in terms of gel content, degree of swelling, hardness, bending, glossiness, adhesion, scratching, abrasion, thermal gravimetric analysis, and acid/alkali tests to select the best formulation with high performance properties. The different LSR concentrations were then evaluated as an anti-corrosion agent for mild steel in 3.5 % sodium chloride. The various corrosion-resistant properties of all LSR-containing EB-coated films were evaluated through open-circuit potential measurements, degrees of rust, blistering, adhesion failure at the scribe, water uptake, and weight loss measurements. The results showed that all the formulations were homogeneous and compatible and their films had high performance properties. It was also found that the formula containing 10 % of LSR per 100 g of coating is considered one of the best formulations, where it gave the highest protection to the mild steel panels without having a negative effect on all the different properties of its films.

‘Dry’ electrochemistry: A non-invasive approach to the characterization of archaeological iron objects

A methodology for monitoring the corrosion state of archaeological iron objects using ‘dry’ open circuit potential (OCP) measurements is described. Application of this technique to a set of objects from La Bastida de les Alcusses archaeological site (Moixent, València, Spain), dating back to the 4th century BCE, reveals significant differences depending on the conservation state. The transient OCP responses (which last between a few seconds and 10–15 min) were superimposed with much shorter (less than one second) intense features.

Electrochemical Stability of n-Si Photoanodes Protected by TiO2 Thin Layers Grown by Atomic Layer Deposition

This work investigates the n-Si photoanodes corrosion protection by Atomic Layer Deposition (ALD) of a TiO2 film. A specific electrochemical experimental sequence (including successive rest potential measurements and voltammetries under illumination or not) has been established to study the stability of the electrodes in KOH. Depending on the deposition conditions (precursor composition and temperature), the electrochemical properties of the layers are different. The photoanodes coated using titanium tetraisopropoxide (TTIP) at low temperature exhibit a low photocurrent (j ph) that is progressively enhanced during the electrochemical sequence and their stability decreases. When using tetrakis(dimethylamido)titanium (TDMAT), the j ph is almost constant and the film prevents from corrosion. The characterizations show that the ALD parameters drive the microstructure of the layer that is found critical for the electrochemical response. A hydrogen doping occurring during the open circuit potential measurements under illumination is evidenced by IR spectroscopy. It is mainly localized at the grain boundaries and pores of the layers as well as in the n-Si and it modifies the charge transfer at the electrode/solution junction and the hydrogen diffusion weakens the film causing the Si corrosion. The different charge transfer mechanisms are finally proposed depending on the ALD conditions and the film thickness.

Protection performance of orange oil distillates on low carbon steel in dilute acid electrolytes

Orange essential oil distillate (OOE) was studied for its inhibition performance on low carbon steel in 0.5 M H2SO4 and HCl aqueous electrolyte by electrochemical method and open circuit potential measurement. OOE performance was significantly proportional to it concentration with highest protection efficiency of 76.93% and 94.90% at optimal OOE concentration (10% OOE) in H2SO4 and HCl electrolyte. The performance of OOE at low concentration in H2SO4 was quite poor with inhibition efficiency values below 40%. OOE exhibited greater inhibition action in HCl solution with effective performance beginning at 4% OOE concentration compared to 6% concentration in H2SO4 electrolyte. Corrosion potential deviated basically in the anodic direction signifying the dominant inhibition effect to be through surface coverage of the steel surface. OOE exhibited mixed type corrosion inhibition. Open circuit potential graphs show OOE increases the thermodynamic fluctuation of the carbon steel in H2SO4 solution relative to the plots at 0% OOE, despite effective protection. In HCl, the open circuit potential plots were more electropositive relative to the plots at 0% OOE signifying decreased tendency to corrosion. Optical images of the carbon steel after evaluation with and without OOE significantly contrast each other.

Mechanism of corrosion inhibition of intermetallic Al2Cu in acidic solution

The objective of this work was to study the kinetics of phosphomolybdenum blue formation onto the surface of intermetallic Al2Cu in orthophosphoric acid solution. This was performed using UV–Vis spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical methods. The latter included measurement of open circuit potential, cyclic voltammograms, polarisation, and chronoamperometric curves as well as impedance spectra. It was shown that a stable form of phosphomolybdenum blue is formed via decomposition of an intermediate in the solution. However, neither phosphomolybdenum blue nor heteropolyoxomolybdate species behave as a corrosion inhibitor. A protective layer of molybdenum oxides formed immediately upon immersion of intermetallic in the corrosive environment, is responsible for corrosion inhibition.

Effect of nitriding pre‐treatment on the tribocorrosion behavior of physical vapor deposition‐coated tool steel

AbstractCr‐Al‐Ti‐B‐N hard coating is deposited onto the AISI D2 cold‐worked tool steel by means of a hybrid physical vapor deposition (PVD) technique. The effect of plasma nitriding pre‐treatment on the tribocorrosion behavior of the hard‐coated tool steel is investigated using a ball‐on‐disc sliding wear tribometer equipped with an electrochemical testing set up. Tribocorrosive characteristics are analyzed by optical and scanning electron microscopy, 3D surface profilometry, and open circuit potential (OCP) measurement. The coefficient of friction and OCP varies depending on the degree of damage to the hard coating, such that the point at which the substrate is first exposed can be identified by these measurements. The plasma nitriding pretreatment increases the surface hardness significantly and, therefore, the adhesion of the PVD hard coating to the substrate material. As a consequence, the material's wear resistance is enhanced and its durability against tribocorrosion is improved.

Fundamental insight into electrochemical oxidation of methane towards methanol on transition metal oxides

Electrochemical oxidation of CH4 is known to be inefficient in aqueous electrolytes. The lower activity of methane oxidation reaction (MOR) is primarily attributed to the dominant oxygen evolution reaction (OER) and the higher barrier for CH4 activation on transition metal oxides (TMOs). However, a satisfactory explanation for the origins of such lower activity of MOR on TMOs, along with the enabling strategies to partially oxidize CH4 to CH3OH, have not been developed yet. We report here the activation of CH4 is governed by a previously unrecognized consequence of electrostatic (or Madelung) potential of metal atom in TMOs. The measured binding energies of CH4 on 12 different TMOs scale linearly with the Madelung potentials of the metal in the TMOs. The MOR active TMOs are the ones with higher CH4 binding energy and lower Madelung potential. Out of 12 TMOs studied here, only TiO2, IrO2, PbO2, and PtO2 are active for MOR, where the stable active site is the O on top of the metal in TMOs. The reaction pathway for MOR proceeds primarily through *CH x intermediates at lower potentials and through *CH3OH intermediates at higher potentials. The key MOR intermediate *CH3OH is identified on TiO2 under operando conditions at higher potential using transient open-circuit potential measurement. To minimize the overoxidation of *CH3OH, a bimetallic Cu2O3 on TiO2 catalysts is developed, in which Cu reduces the barrier for the reaction of *CH3 and *OH and facilitates the desorption of *CH3OH. The highest faradaic efficiency of 6% is obtained using Cu-Ti bimetallic TMO.

Effect of annealing temperature on the microstructure and corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy in hydrochloric acid solution

The corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy annealed at 800 °C, 900 °C, 960 °C and 1040 °C was investigated in 5 wt. % hydrochloric acid (HCl) solution using open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. It was found that the Ti-6Al-3Nb-2Zr-1Mo alloy annealed at 1040 °C exhibited the best corrosion resistance. While the Ti-6Al-3Nb-2Zr-1Mo alloy annealed at 960 °C exhibited the least corrosion resistance. The difference in corrosion rate of Ti-6Al-3Nb-2Zr-1Mo alloy annealed at different temperatures was obtained by weight loss experiments in 20 wt. % HCl solution. The results showed that the corrosion rate of the Ti-6Al-3Nb-2Zr-1Mo alloy annealed at 960 °C was the highest, followed by the alloys annealed at 900 °C and 800 °C, while the corrosion rate of the Ti-6Al-3Nb-2Zr-1Mo alloy annealed at 1040 °C was the lowest, which was consistent with the results of the electrochemical experiments. The initial corrosion morphology of the Ti-6Al-3Nb-2Zr-1Mo alloy in 20 wt. % HCl solution was observed by scanning electron microscopy (SEM). The SEM images revealed that α/β phase boundaries were preferential sites for corrosion attack, and the α phase exhibited preferential dissolution in comparison to the β phase. First principle calculations proved the existence of microgalvanic cells, which accelerated the corrosion of the α phase. The results indicate that Ti-6Al-3Nb-2Zr-1Mo alloy corrosion behavior in HCl solution is predominantly affected by the fraction and grain size of α and β phase.