Wire Beam Electrode Method Research Articles

The effect of pulse current cathodic protection on cathodic disbondment of epoxy coatings

For coated pipelines with cathodic protection, cathodic delamination has been judged as the main reason of coating delamination. This work aims to use the pulse current cathodic protection (PCCP) to mitigate the coating cathodic delamination. Cathodic delamination tests, electrochemical impedance spectroscopy and wire beam electrode method (WBE) were used to study the effect of PCCP on the mitigation of coating disbondment. The results show that PCCP could successfully retard the cathodic delamination rates of organic coatings. Under different cathodic protection potential, the delamination area of the coating protected using PCCP is much smaller than that using direct current cathodic protection. With the increasing pulse frequency and duty ratio, the mitigation effect decreases. Within the range of pulse frequency from 5 Hz to 500 Hz and duty ratio from 0.1 to 0.9, the results of cathodic delamination tests and WBE tests indicate that when the cathodic potential is −1.5 V, the mitigation effect reaches the maximum with the pulse frequency of 5 Hz and the duty ratio of 0.1. PCCP alleviates cathodic delamination of coating mainly by intermittently shifting the surface polarization potential to positive direction and reducing the consumption of cathodic reaction charge.

Investigating crevice corrosion of copper and copper alloys using wire beam electrode

ABSTRACT A wire beam electrode (WBE) method for investigating the crevice corrosion has been demonstrated by mapping non-uniform corrosion processes occurring on copper and copper alloys including the pure copper UNS No. C11000 (Cu), brass UNS No. C28000 (Cu–Zn alloy) and tin bronze UNS No. C51900 (Cu–Sn alloy) in mass 0.6% NaCl solution with the crevice spacings of d=103 μm and 206 μm. It was found that the sequence of three copper alloys in susceptibility for the crevice corrosion was that Cu–Zn alloy > Cu–Sn alloy > pure Cu. The average galvanic current of the Cu–Sn alloy in the covered region was changed from cathode to anode when the crevice spacing was increased to 206 μm. To sum up, it is feasible to study the behaviours of crevice corrosion within the different crevice spacings with the WBE method.

The coating delamination mitigation of epoxy coatings by inhibiting the hydrogen evolution reaction

The mitigation of coating delamination is one of the important challenges for epoxy coatings under the cathodic protection. Herein we report the possibility to mitigate the coating delamination of epoxy coatings by inhibiting the hydrogen evolution reaction in the presence of thioureas. The wire beam electrode method, electrochemical impedance spectroscopy and traditional delamination test were employed to evaluate the mitigation efficiency in this work. Results show that in the absence of thioureas, the delamination rate increases significantly once the cathodic protection potential is more negative than hydrogen evolution potential, suggesting that hydrogen evolution reaction plays an important role in the coating delamination. Fortunately, the coating delamination is remarkably mitigated by adding thioureas since the hydrogen evolution reaction is suppressed. WBE results show that when delamination commences, the electrodes at the defect region act as anodes, while the electrodes around the defect region act as cathodes. In the presence of thioureas the delamination area is much less than that in the absence of thioureas. Therefore, the coating delamination of epoxy coatings under the cathodic protection could be successfully suppressed through inhibiting the hydrogen evolution reaction. The finding of this work could offer a new insight to reduce the cathodic delamination rate in both theoretical research and practical application engineering applications.

The vertical Non-uniform corrosion of Reinforced concrete exposed to the marine environments

Reinforced concrete (RC) structures usually are exposed to a wide variety of combined actions, which may cause various damages to the structures. The main objective of this study is to investigate the vertical non-uniform corrosion of reinforcement bar in concrete that was exposed to the marine environments. The concrete embedding rebar electrodes array (CRA) was designed and made based on the wire beam electrode (WBE). To simulate the submerged, tidal and splash marine environments, the marine environment simulation equipment (MESE) was set up. Electrochemical behaviors of rebar electrodes were characterized using the WBE method, linear polarization (LP) technique and electrochemical impedance spectroscopy (EIS). To monitor the carbonation and chloride ion penetration of concrete, the pH and chloride ion profiles of the concretes were analyzed. The vertical non-uniform corrosion of rebars was caused by the difference of oxygen concentration, moisture content, free chloride content and pH value in vertical direction. The macroscopic galvanic corrosion between the splash zone rebars and the tidal zone rebars was inhibited and the galvanic corrosion between the adjacent rebars was promoted by the high resistivity of the splash concrete. The concrete carbonation was a metathesis reaction between the bicarbonate ion (HCO3−) of seawater and the alkaline hydration products of concrete in the marine environments.

Correlation of temperature with galvanic corrosion behaviour of copper alloys based on wire beam electrode

ABSTRACTGalvanic corrosion behaviour of copper and copper alloys in chloride solution (0.6 M NaCl) under different temperature conditions (35°C, 55°C and 80°C) was investigated by the wire beam electrode (WBE) method. It was found that the average galvanic current of the Cu and Cu–Sn alloy, which shifted from the cathode at 35°C to the anode at 80°C, increased as temperature increased during the immersion time. In contrast, the average galvanic current of Cu–Zn alloy can be ranked as 35°C > 55°C > 80°C. A sudden conversion was that the anode average current of Cu–Zn alloy at 35, 55°C changed into the cathode when the immersion time lasted untill 3 h at 80°C. The results indicate that it is feasible to study the corrosion behaviour under the different temperature environment with the WBE method.

Effects of metabolic activity of sulphate‐reducing bacteria on heterogeneous corrosion behaviors of copper in seawater

In this paper, wire beam electrode method combined with other analysis methods, that is, electrochemical impedance spectroscopy, scanning electron microscope, and X‐ray photoelectron spectroscopy, was used to investigate effects of metabolic activity of sulphate‐reducing bacteria (SRB) on heterogeneous corrosion behaviors of copper in seawater. Results show that heterogeneous corrosion behaviors of copper are associated with metabolic activity of SRB, that is, the higher metabolic activity of SRB is, the more heterogeneously current of copper distributes. In particularly, on the 5th day of exposure, SRB cells on cathodic and anodic areas display distinct micromorphologies. SRB attach onto corrosion products film surface in anodic area, while they implant in corrosion products film with self‐produced organic nanowires in cathodic area. These organic nanowires may be conductive, and help SRB to obtain electrons from cathodic area directly. The XPS results show that the relative content of corrosion products components on cathodic area is obviously different with that on anodic area when SRB with the high metabolic activity are present.

The study of the varying characteristics of cathodic regions for defective coating in 3.5% sodium chloride solution by EIS and WBE

The current distributions over carbon steel under iron red alkyd primer exposed to 3.5% sodium chloride solution were mapped using the wire beam electrode (WBE). The electrochemical impedance spectroscopy (EIS) of the WBE was carried out to analyze the performance of coating delamination and corrosion behavior of carbon steel beneath defective coating. The EIS data revealed that protective capability of coating decreased with immersion time and the degree of cathodic delamination showed a rapid rise. The current density distribution of WBE indicated that cathodic sites was located at the defect at the beginning of immersion and gradually spread into the intact coating. The cathodic regions were distinguished from the anodic area and distributed over the WBE. The changes of cathodic sites could reflect the deterioration process of defective coating. The cathodic area ratio was a more useful parameter than the cathodic delamination degree to evaluate the coating cathodic delamination. The polarity reversals of electrodes at the defect and beneath coating were observed. A simple discussion of relationship between the blister and the polarity reversal was made from a standpoint of electrochemical distribution. WBE method was able to map and record the changes of local cathodic sites beneath defective coating in real time, which could provide more detailed information about the local degradation of coating.

Study of corrosion behavior of carbon steel under seawater film using the wire beam electrode method

Corrosion behavior of carbon steel under seawater film with various thickness was investigated by the wire beam electrode (WBE) method. It was found that the corrosion rate of carbon steel increased significantly under thin seawater film than it was immersed in seawater. The current variation under seawater film indicated that the thickness of diffusion layer of oxygen was about 500μm, and the maximal current appeared around 40μm, at which corrosion rate transited from cathodic control to anodic control. The results suggest that WBE method is helpful to study the corrosion process under thin electrolyte film.

Electrochemical evaluation of under-deposit corrosion and its inhibition using the wire beam electrode method

A new experimental method has been applied to evaluate under-deposit corrosion and its inhibition by means of an electrochemically integrated multi-electrode array, namely the wire beam electrode (WBE). Maps showing galvanic current and corrosion potential distributions were measured from a WBE surface that was partially covered by sand. Under-deposit corrosion did not occur during the exposure of the WBE to carbon dioxide saturated brine under ambient temperature. The introduction of corrosion inhibitor imidazoline and oxygen into the brine was found to significantly affect the patterns and rates of corrosion, leading to the initiation of under-deposit corrosion over the WBE.

Heterogeneous electrochemical characteristics of biofilm/metal interface and local electrochemical techniques used for this purpose

AbstractBiofilms on metal surface in an aqueous environment is a complex electrochemical system. The heterogeneous electrochemical characteristics of biofilm/metal interface and local electrochemical techniques used for this purpose are discussed in this work. The techniques presented in this work include microelectrode, scanning vibrating electrode, the wire beam electrode method, and scanning electrochemical microscopy. Two potentially useful techniques, localized electrochemical impedance spectroscopy and scanning Kelvin probe force microscopy, are also discussed. The advantages and limitations of these techniques are summarized. A new approach: numerical simulation of micro‐electrochemical heterogeneity of biofilm covered metals is introduced.

The heterogeneous electrochemical characteristics of mild steel in the presence of local glucose oxidase—A study by the wire beam electrode method

The influence of glucose oxidase (GOD) activity on the heterogeneous electrochemistry at artificial biofilm/mild steel interface was first characterized by the wire beam electrode (WBE) method. Potential/current distribution maps show that a cathodic zone can be formed at the GOD capsule site. The cathodic zone is gradually weakened due to the gluconic acid production in seawater. When GOD capsule is confined on rusted WBE surfaces, the formerly formed anodic zone is gradually changed into cathodic zone, in the presence of glucose. The novel device developed in our laboratory demonstrates powerful applications in heterogeneous electrochemistry measurements at the biofilm/mild steel interfaces.

The influence of local glucose oxidase activity on the potential/current distribution on stainless steel: A study by the wire beam electrode method

The wire beam electrode (WBE) method was first used to study the activity of local glucose oxidase (GOD) on stainless steel surface in seawater. Glucose oxidase was immobilized in calcium alginate gel capsules, which were embedded in a layer of artificial biofilm (calcium alginate gel) on the WBE surface. The potential/current distributions on the WBE surface were mapped using a newly developed device for the WBE method in our lab. The results demonstrated that the catalysis of H 2O 2 formation by GOD can produce local noble potential peaks and cathodic current zones on the stainless steel surface. An interesting fluctuant current distribution around cathodic zones was observed the first time. The potential and current maps showed that the enzyme heterogeneity of the artificial biofilm caused a corresponding electrochemical heterogeneity at the biofilm/metal interface. The application of the WBE method to ennoblement study enables us to observe the heterogeneous electrochemistry at biofilm/stainless steel interface directly, providing us with a powerful tool to investigate other biofilm-related processes such as microbially influenced corrosion (MIC).

A novel device for the wire beam electrode method and its application in the ennoblement study

A novel device used in the wire beam electrode (WBE) method was developed in our lab. The system consists of standard modules, and is controlled by a LabVIEW software (National Instruments Co., NI). Since all the components in this WBE test device are commercially available, and the detailed information of the modules can be readily accessed by researchers, the system is easy to be built and modified, depending on experimental designs. The device can perform desired measurements, which is controlled by programs written in LabVIEW, for which the researchers can easily design and modify to create user-defined tests and control applications. This device has a faster measurement rate than that in published literature. In our study, we have used this device for the first time to investigate the relationship between local potential/current patterns and H 2O 2 distribution in an artificial biofilm/stainless steel interface. The results showed that the electrochemical distribution of the biofilm-related system is closely correlated with the biofilm heterogeneity. The device improves the WBE measurement techniques and is expected to be widely used in academic and industrial fields.

Monitoring localised corrosion in inhibited solutions using wire beam electrode–noise signatures method

The objective of this work is to determine the nature of localised corrosion in inhibited solutions by establishing possible relationships between characteristic features in electrochemical noise and corrosion processes using an electrochemically integrated multielectrode system, namely the wire beam electrode (WBE) in combination with noise signatures method. Experiments have been carried out to simultaneously measure electrode potential noise and WBE current distribution maps from stainless steel (SS316L) WBE exposed to inhibited solutions containing 6%FeCl3 solution with inorganic inhibitors including 2 wt-% sodium chromate (Na2CrO4), cerium chloride (CeCl3) and lanthanum chloride (LaCl3). Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps that show corrosion rates distributions and the degree of localised corrosion. A new concept namely localisation parameter (LP) has been proposed to identify the degree of inhibition. Na2CrO4 effectively inhibited the pitting corrosion process and the LP successively decreased through out the corrosion process. With the presence of CeCl3 and LaCl3, pits on stainless steel in 6%FeCl3 solution were not repassivated and an increase in the LP was observed for both inhibitors. The results suggest that the WBE method could be used in combination with the noise signatures as a sensitive technique for monitoring inhibiting effect on localised corrosion.

Studying and evaluating anti‐corrosion coatings and inhibitors using the wire beam electrode method in conjunction with electrochemical noise analysis

PurposeTo provide a summary of research work carried out mainly in the authors' group for evaluating various protective coatings including rustproofing oils, and also for studying corrosion inhibitors using the wire beam electrode (WBE) method.Design/methodology/approachA range of published papers published during the past 15 years was summarised and reviewed. Recent research work in the authors' group was also included, which involved the combined use of the WBE with electrochemical noise analysis and the scanning reference electrode technique.FindingsThe WBE method has been developed into a very useful tool of evaluating the performance of coatings and inhibitors. In particular, The WBE is uniquely applicable for determining the performance of coatings and inhibitors to control localised corrosion.Research limitations/implicationsFocusing mainly on recent research.Practical implicationsA useful source of information for researchers and graduate students working in the areas of organic coating and inhibitor research.Originality/valueThe first summary or review on this research topic.

Understanding electrodeposition of polyaniline coatings for corrosion prevention applications using the wire beam electrode method

Polyaniline (PANI) films have been successfully electrodeposited on aluminium AA1100 electrode surfaces in acidic electrolytes as anti-corrosion coatings. The wire beam electrode (WBE) has been applied for the first time as a novel tool to monitor the electrodeposition processes; and also to understand the anti-corrosion performance and mechanism of the PANI coatings. During PANI electrodeposition, the WBE was polarised anodically, and anodic polarisation currents were measured from various locations over the WBE surface to produce anodic polarisation current maps (APC maps). Preliminary experiments have revealed that if an AA1100 electrode was not pre-treated, APC maps would show a localised anodic current distribution, resulting in a nonuniform PANI deposit. If the AA1100 electrode was pre-treated by a cathodic polarisation process, APC maps would show a random anodic current distribution, leading to a PANI coating covering the whole electrode surface. When exposed to a corrosive environment, PANI coatings were found to prevent localised corrosion of AA1100, primarily by enhancing its passive film rather than by a barrier mechanism. However, a nonuniform PANI coating has been found to accelerate general corrosion of AA1100. These results suggest that the WBE is a practical tool for monitoring, characterising and optimising PANI electrodeposition processes and for evaluating the anti-corrosion performance of PANI coatings.

Novel corrosion experiments using the wire beam electrode. (IV) Studying localised anodic dissolution of aluminium

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) has been applied in novel experiments to study the anodic dissolution behaviour of aluminium (AA1100), which was exposed to corrosive media with and without the presence of corrosion inhibitor potassium dichromate. The objective of this work is to demonstrate the applicability of the WBE for investigating corrosion processes under anodic polarisation. Anodic current measurements and mapping have been made, for the first time, with the WBE surface being anodically polarised. Pitting potential as well as anodic dissolution profile has been successfully determined by mapping anodic dissolution currents over the anodically polarised WBE surface. The pitting potential determined using the WBE method was found to correlate well with that determined using the conventional pitting scan method; and the anodic dissolution profile determined using the WBE method was found to correlate with maps obtained using the scanning reference electrode technique (SRET). Potassium dichromate was found to significantly affect the pitting potential, anodic dissolution profile and pitting initiation characteristics of aluminium. Two mechanisms of localised corrosion initiation have been identified. For WBE surface under free corrosion or low anodic polarisation conditions, the initiation of localised corrosion was found to be due to the disappearance of minor anodes, which lead to accelerated dissolution of a few major anodes. For WBE surface under large anodic polarisation, the initiation of localised corrosion was found to be due to the formation of active new anodic sites. This work suggests that the WBE method is useful for understanding the electrochemical behaviour of localised anodic processes, and their dependence on externally controllable variables.

Novel corrosion experiments using the wire beam electrode: (III) Measuring electrochemical corrosion parameters from both the metallic and electrolytic phases

The wire beam electrode (WBE) and the scanning reference electrode technique (SRET) have been applied in a novel combination to measure, for the first time, electrochemical parameters simultaneously from both the metallic and electrolytic phases of a corroding metal surface. The objective of this work is to demonstrate the application of this combined WBE–SRET method in obtaining unique information on localised corrosion mechanism, by investigating typical corrosion processes occurring over a mild steel WBE surface exposed to the classic Evans solution. The WBE method was used to map current and potential distributions in the metallic phase, and the SRET was used to map current or potential distribution in the electrolytic phase. It has been found that the combined WBE–SRET method is able to gain useful information on macro-cell electrochemical corrosion processes that involve macro-scale separation of anodes and cathodes. In such macro-cell corrosion systems, maps measured using WBE and SRET were found to correlate with each other and both methods were able to detect the locations of anodic sites. However the movement of the scanning probe during SRET measurements was found to affect the SRET detection of cathodic sites. In micro-cell corrosion systems where the separation of anodic and cathodic sites were less distinct, SRET measurement was found to be insensitive in detecting anodic and cathodic sites, while the WBE method was still able to produce results that correlated well with observed corrosion behaviour. Results obtained from this work suggest that the WBE–SRET method is applicable for understanding the initiation, propagation and electrochemical behaviour of localised corrosion anodes and cathodes, and also their dependence on externally controllable variables, such as solution pH changes and the existence of surface coatings.

Novel corrosion experiments using the wire beam electrode: (II) Monitoring the effects of ions transportation on electrochemical corrosion processes

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied for the first time to study the effects of the transportation of electrochemically active species on the process, rate and pattern of electrochemical corrosion. The objective of this work is to demonstrate the applicability of the WBE method for investigating ion transportation related corrosion processes. A series of experiments have been carried out using WBEs made from mild steel and stainless steel wires. The WBE working surfaces were exposed to simulated diffusion-controlled corrosion environments where there were diffusion induced ions concentration gradients (termed diffusion–corrosion environment). Corrosion potential and current distribution maps (CPCD maps) were measured from WBE surfaces in continuous bases. Typical patterns have been identified from CPCD maps and the characteristics of these patterns have been found to depend heavily upon the type of electrode material and the type of corrosive ion. For mild steel WBE surface exposed to a diffusion–corrosion environment containing NiSO 4 or FeCl 3, the characteristic pattern in CPCD maps was found to emulate NiSO 4 or FeCl 3 concentration gradients, suggesting an ion-concentration controlled corrosion behaviour. However, when the mild steel WBE surface was exposed to a diffusion–corrosion environment containing NaCl, the characteristic pattern was found to show higher cathodic currents along the WBE edges with the magnitude decreasing in a contour-like manner towards the centre of the WBE surface, suggesting an oxygen concentration-controlled corrosion behaviour. When a stainless steel (SS316L) WBE surface was exposed to a diffusion–corrosion environment containing NiSO 4 or NaCl, the corrosion pattern appeared to be mainly determined by the random distribution of weak sites in passive film. When the SS316L WBE was exposed to a diffusion–corrosion environment containing FeCl 3, the CPCD map revealed a characteristic pattern that shows localised damage to passive film. This work demonstrates that the recognition and analysis of characteristic maps from WBE measurements can be used as a means of studying diffusion, migration and other forms of mass transportation related electrochemical corrosion processes.

Characterising nonuniform electrodeposition and electrodissolution using the novel wire beam electrode method

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied as a new method of characterising nonuniform electrodeposition and electrodissolution, by measuring and identifying characteristic patterns in electrodeposition and electrodissolution current distribution maps. Various patterns of electrodeposition current distribution have been obtained from Watts nickel plating and bright acid copper plating baths with the effects of several affecting factors such as bath concentration, temperature, agitation and electrolyte flow. Typical patterns of electrodissolution current distribution have also been detected over a WBE surface under anodic dissolution. This work suggests that the WBE method can be used as a new tool for monitoring, characterising and optimising electrodeposition and electrodissolution processes in the laboratory, and can also be applied as an experimental method to verify the accuracy and completeness of mathematical models for electrodeposition and electrodissolution.