Electrochemical Current Noise Signals Research Articles

Albumin Protein Impact on Early-Stage In Vitro Biodegradation of Magnesium Alloy (WE43).

Mg and its alloys are promising biodegradable materials for orthopedic implants and cardiovascular stents. The first interactions of protein molecules with Mg alloy surfaces have a substantial impact on their biocompatibility and biodegradation. We investigate the early-stage electrochemical, chemical, morphological, and electrical surface potential changes of alloy WE43 in either 154 mM NaCl or Hanks' simulated physiological solutions in the absence or presence of bovine serum albumin (BSA) protein. WE43 had the lowest electrochemical current noise (ECN) fluctuations, the highest noise resistance (Zn = 1774 Ω·cm2), and the highest total impedance (|Z| = 332 Ω·cm2) when immersed for 30 min in Hanks' solution. The highest ECN, lowest Zn (1430 Ω·cm2), and |Z| (49 Ω·cm2) were observed in the NaCl solution. In the solutions containing BSA, a unique dual-mode biodegradation was observed. Adding BSA to a NaCl solution increased |Z| from 49 to 97 Ω·cm2 and decreased the ECN signal of the alloy, i.e., the BSA inhibited corrosion. On the other hand, the presence of BSA in Hanks' solution increased the rate of biodegradation by decreasing both Zn and |Z| while increasing ECN. Finally, using scanning Kelvin probe force microscopy (SKPFM), we observed an adsorbed nanolayer of BSA with aggregated and fibrillar morphology only in Hanks' solution, where the electrical surface potential was 52 mV lower than that of the Mg oxide layer.

Using of asymmetric cell to monitor corrosion performance of 304 austenitic stainless steel by electrochemical noise method

In this study, corrosion of 304 Austenitic stainless steel (ASS) with varies oxide layers, developed at two temperatures, is investigated by an asymmetric (Asy) cells in 0.05 M FeCl3 solution with time. Therefore, the Asy electrodes system is introduced to perform valuable data. Electrochemical current noise (ECN) signals resulting from the Asy cells are elucidated using the standard deviation of partial signals (SDPS) plot, the recurrence plot (RP), and the statistical procedure which derived from wavelet transform (WT) along with electrochemical impedance spectroscopy (EIS). The Asy electrodes indicated a high advantage and improved the detection of intergranular corrosion (IGC) on the 304 ASS alloy compared with the symmetric (Sym) ones. The trend of signals is eliminated, and then the disintegration of every signal is also performed into 10 crystals. Afterward, the standard deviation of every crystal is shown with the SDPS plots. Besides, ECN signals related to dissimilar crystal numbers are distinguished by the RP, based on the signals population. According to EIS measurements, the thickness of passive oxide layer of sample heated at 0–700 °C is decreased from 57 to 33 nm with immersion time, while it is increased from 9 to 27 nm for sample heated at 1100-700 °C.

Electrochemical noise analysis of cathodically protected steel reinforcement in concrete using carbon fiber sheet as anode

This paper presents an efficiency and mechanism analysis of impressed current cathodic protection (ICCP) for corroded steel reinforcements in concrete by means of electrochemical noise (EN), which is an advanced technique that allows real-time monitoring without any disturbance. The considered variables include protection method (non-protection, ICCP) and current density of ICCP (30 mA/m2, 90 mA/m2). In the cases of ICCP, carbon fiber sheet is adopted as the anode thanks to its good electrochemical properties and durability. Electrochemical potential noise (EPN) and electrochemical current noise (ECN) of steel reinforcement in concrete are measured every 30 d during the 120-d exposure period and analyzed from the perspectives of time and frequency domains. The results show that ICCP treatment with a current density of 30 mA/m2 leads to slighter fluctuations in ECN signals, an improvement in noise resistance Rn, and decreases in the low frequency plateau WL in power density diagram (PSD) of ECN signals. It indicates that the corrosion of steel is alleviated. However, the results of the specimen protected with a current density of 90 mA/m2 are the opposite, which is overprotected and hydrogen corrosion may happen. Compared to the specimen with no protection, the specimen treated with 30 mA/m2 ICCP shows an evident increase in energy proportion of d1-d3 wavelet crystals. Additionally, with increasing the treatment duration, the energy proportion of d1-d3 wavelet crystals increases. This illustrates that ICCP is more effective in inhibiting general corrosion than pitting corrosion. Extra caution should be paid to EPN signals of specimens subjected to ICCP, namely polarization, because EPN signals may anomalously exhibit severer fluctuations as a result of insufficient depolarization. It is suggested to use ECN signals instead of EPN signals to analyze the corrosion behavior of specimens subjected to ICCP.

Use of electrochemical current noise method to monitor carbon steel corrosion under mineral wool insulation

Corrosion of carbon steel under mineral wool insulation was studied using the electrochemical current noise (ECN) method. Intensities of corrosion were validated using gravimetry, and the form of corrosion confirmed using optical microscopy. The standard deviation of the current noise signal agreed with weight loss results and was demonstrated as a reliable indicator of the degree of corrosion under mineral wool insulation. Recurrence quantification analysis was used to extract feature variables from ECN signals, which were later used to develop a random forest model to identify the type of corrosion, i.e., uniform or localised corrosion. The trained model was successfully applied to predict the extent of localised corrosion associated with mineral wool insulation.

Evaluation of the localized corrosion on Mg electrode surface by electrochemical noise technique

AbstractThe symmetrical and asymmetrical electrodes made of Mg were studied in 0.1‐M NaCl electrolyte adjusted at pH 12. The statistical and wavelet methods were employed for analyzing the electrochemical current noise (ECN) signals. The asymmetric configuration was used for electrochemical detection of filiform corrosion on Mg electrode. The real time scale of the dominant transients of the asymmetric electrodes was detected on the basis of the maximum peak in the SDPS plots. The SDPS values of the real time scale crystals of the ECN signals resulting from asymmetrical electrodes increased with the increase in immersion time due to the onset of filiform corrosion.

The Influence of H<sub>2</sub>SO<sub>4</sub>- NaCl Electrolyte Composition to the Electrochemical Noise Behaviour of a High-Alloy Cast Steel

In this study, the influence of varying sulphuric acid – sodium chloride electrolyte composition to the electrochemical noise behaviour of a high-alloy cast steel was analysed. The noise analysis was carried out in a bare 0.1 M sulphuric acid solution, in a pure 5 wt.% sodium chloride solution and three solutions with defined ratios of both. The electrochemical current noise signal was recorded with a sampling rate of 100 Hz for 1 hour in each test solution. For the identification of the frequency content of notified characteristic transients, the current-time records were analysed by the continuous wavelet transform (CWT). The characteristic transients were extracted from the noise signal for a further analysis of their frequency and amplitude characteristics. The results show high-frequency transients in the bare sulphuric acid and low-frequency transients in the pure sodium chloride solution. In the combined electrolyte solutions the portion of low-frequency components increases when the NaCl content increases and indicates the enhancing influence of localised damage evolution processes at the steel surface.

Electrochemical noise analysis of corrosion behaviour of asymmetric electrodes made of mild steel in NaHCO3 solutions at different NaCl concentrations

In this paper, the corrosion of asymmetrical electrodes made of mild steel was studied in 0.5 M NaHCO3 solutions with the addition of NaCl both before and after the immersion of electrodes. The statistical and wavelet methods were used for analysing the electrochemical current noise (ECN) signals. The ECN signals arising from asymmetric electrodes in 0.5 M NaHCO3 solution (pH 9) in the absence and presence of three different NaCl concentrations were unidirectional. This can pertain to the presence of the oxide layer. The thickness of the passive oxide layer and noise detection decreased on increasing the NaCl concentration from 0.3 to 0.7 M. The predominant transients of ECN signals and their SDPS values were lower in the case of 2 h delaying compared with simultaneous NaCl increase to 0.5 M NaHCO3 solution.

Discrete Wavelet Analysis of Electrochemical Current Noise of a High-Alloy Cast Steel in Sulfuric Acid and Sodium Chloride Solution

The electrochemical current noise signal of a high-alloy cast steel was investigated in a 0.1 M sulfuric acid solution and in a 5 wt.% sodium chloride solution. In the sulfuric acid solution, the current time signal reveals characteristic spikes of high amplitudes. In the chloride containing solution, spontaneous power drops with a subsequent recovery of comparatively low intensity characterize the noise signal. Both noise records were analyzed by the discrete wavelet transform. For the noise signal in the sulfuric acid solution, the received wavelet coefficients exhibit the highest values in the fine scale, which signal the dominance of short-time corrosion events that were attributed to the observed hydrogen bubble evolution. In the chloride containing medium, the signal decomposition by the wavelet analysis reveals the highest coefficients predominantly in the coarse scale, indicating a preferred initiation of corrosion processes of high duration. The subsequent observations by scanning electron microscopy, reveal an attack by micro pitting, which is associated with the noise events.

Detection of SCC of 304 NG stainless steel in an acidic NaCl solution using electrochemical noise based on chaos and wavelet analysis

The stress corrosion crack (SCC) of 304 nuclear grade (NG) stainless steel (SS) in 0.5 mol/L NaCl+1.5 mol/L H2SO4 was monitored using electrochemical noise (EN) based on chaos theory, statistics and wavelet analysis. The results indicated that the SCC process was divided into three stages according to the transient features in the EN. In the beginning, compared with the sample without applied stress, the enhanced fluctuation amplitude in the electrochemical current noise (ECN) of the stressed samples was attributed to stress-enhanced pitting corrosion and uniform corrosion; then the fluctuations of ECN for all the samples decreased due to a coverage by the corrosion products; however, the ECN fluctuations of stressed sample were larger than the unstressed sample, suggesting that the stress enhanced the SCC initiation and propagation. Chaos analysis revealed that the correlation dimensions increase from 2.1 to 2.5 during the corrosion process, and the applied stress seems increase the complexity and uncertainty of the ECN signal.

Quantitative evaluation of pit sizes for high strength steel: Electrochemical noise, 3-D measurement, and image-recognition-based statistical analysis

In this study, pit depths, diameters, and locations of high strength X80 pipeline steel in aerated sodium chloride solutions are quantitatively investigated by electrochemical current noise (ECN) measurements as well as confocal laser scanning microscopy (CLSM). From the results obtained via ECN signals and SEM images, pits are believed to be initiated immediately, and current transients are strongly affected by the cathodic process. The computer simulation of ECN reveals that overlapping processes lead to both increase and decrease of transient amplitude depending on the time delay of original transients. Furthermore, the pit sizes estimated from the current transients are far lower than the actual pit sizes observed from SEM images. Hence, current transients obtained from ECN correspond to nucleation instead of the propagation process of pits. An image recognition technique is introduced for the purpose of recognizing corrosion pits from optical images, which significantly increases the efficiency of statistical analysis of pit diameters and pit locations. Results obtained from the statistical analysis of high strength pipeline steel in aerated NaCl solutions indicate that pit diameter follows lognormal distribution, and pit sites are completely spatial random.

Comparison of electrochemical current noise signals arising from symmetrical and asymmetrical electrodes made of Al alloys at different pH values using statistical and wavelet analysis. Part I: Neutral and acidic solutions

In this paper, the electrochemical current noise (ECN) signals were measured on large symmetrical (100–100 mm2), small symmetrical (1–1 mm2) and asymmetrical electrodes (1–100 mm2) made of AA6061 and AA2024 alloys in 1.0 M chloride solutions at different pH values (6, 2, 1 and 0.4). The results were analyzed by statistical and wavelet methods. In the near-neutral solution the asymmetrical electrodes made of Al alloys were more favorable for ECN measurements compared to both the large and the small symmetrical electrodes. The asymmetrical electrodes in near-neutral solutions allowed recognizing the true timescale of the predominant transients directly from the maximum peak of the SDPS plots, so that the comparison of the partial and original signals was not necessary. According to the statistical analysis, the asymmetrical electrodes in acidic solutions gradually lost their essential characteristic for recording the unidirectional ECN signals with decreasing pH. This can be attributed to both the dissolution of the passive oxide layer and the cathodic noise arising from the hydrogen bubble evolution. According to the wavelet analysis, for the asymmetrical electrodes made of AA6061 it is possible to detect the true timescale of the predominant transients on the basis of the maximum peak in the SDPS plots, even in highly acidic solutions, while for those made of AA2024 it is necessary to compare the partial and original signals, whether at pH 2 or lower.

Comparison of electrochemical current noise signals arising from symmetrical and asymmetrical electrodes made of Al alloys at different pH values using statistical and wavelet analysis. Part II: Alkaline solutions

In this paper, the electrochemical current noise (ECN) signals arising from the symmetrical (both small and large) and asymmetrical electrodes made of AA6061 and AA2024 in 1.0M NaCl electrolyte adjusted to pH 9 and 12 were analyzed by statistical and wavelet methods. The asymmetrical electrodes (1–100mm2) retained their essential advantages in weak alkaline solutions as well as in the near-neutral solutions. However, their advantages were partly lost in the strong alkaline solutions. The use of statistical data made it possible to differentiate between the two symmetrical configurations. The statistical analysis of ECN signals arising from the symmetrical electrodes revealed that the small symmetrical electrodes (1–1mm2) were preferable for measuring ECN in near-neutral solutions, while the large symmetrical electrodes (100–100mm2) were preferable for measuring ECN in weak alkaline solutions. However, in strong alkaline solutions the large symmetrical electrodes were preferable for measuring ECN on AA6061, but the small symmetrical electrodes were preferable for measuring ECN on AA2024. The electrochemical behavior of intermetallic particles as a function of pH along with an earlier modeling of ECN transients were employed to interpret the ECN data of AA2024 asymmetrical electrodes at pH 9 in comparison with near-neutral pH. The SDPS values of the true timescale crystals of the ECN signals arising from asymmetrical electrodes increased with increasing pH value from 9 to 12 due to the enhanced corrosion severity. A recently presented model describing the process of EN generation has been employed to interpret all results obtained in near-neutral, acidic and alkaline solutions.

Detection of microbiologically influenced corrosion by electrochemical noise transients

This work investigates the electrochemical processes involved in pitting corrosion induced by microbiologically influenced corrosion by using time-resolved instantaneous frequency information of electrochemical current noise (ECN) transients obtained from Hilbert spectra. In addition to the time-frequency analyses, also the open corrosion potential is investigated and microscopic examinations of the specimens are performed after the tests. Hilbert spectra of the ECN signals indicated the development of transients in one of the two electrochemical cells containing sulphate-reducing bacteria with a different instantaneous frequency decomposition as compared to the background ECN signal, which resulted from the anaerobic general corrosion process. After day 13, the transients in the ECN signals developed towards consistent instantaneous frequency decompositions in the Hilbert spectra that are typical for relatively fast pitting corrosion processes. Post-exposure microscopic observations confirmed the existence of pits underneath the attached biofilms at the working electrodes.

Cover Picture: Materials and Corrosion. 5/2014

Cover: The determination of critical pitting temperatures (CPTs) in specific test media is a common testing method for the pit‐ting corrosion resistance of high alloyed materials. Com‐monly used test solutions for high alloyed steels like the ferric chloride test (ASTM G48) or the “Green Death” test have limitations using them for the highest alloyed Ni‐Cr‐Mo alloys. Furthermore the iterative test procedures limit their accuracy and effectiveness. To overcome these problems CPTs were determined by the examination of electrochemical current noise signals in a continuously heated 4.5 M calcium chloride solution under potentiostatic control, taking into account the limitation of pitting in the anodic range on alloys with a very high content of molybdenum. The new testing procedure also enables a significant better accuracy allowing an effective screening of cladding parameter and surface pre‐treatments on the resulting corrosion protection performance.More detailed information can be found in: S. Schmigalla, A. Heyn; Determination of critical pitting temperatures for Ni‐Cr‐Mo alloys using electrochemical noise measurements; Materials and Corrosion 2013, 64, 700.

Application of transient analysis using Hilbert spectra of electrochemical noise to the identification of corrosion inhibition

This study validates the ability of Hilbert spectra to investigate transients in an electrochemical noise signal for an aqueous corrosion inhibition process. The proposed analysis procedure involves the identification and analysis of transients in the electrochemical current noise signal. Their decomposition into instantaneous frequencies in a Hilbert spectrum allows detection of changes in corrosion characteristics, i.e. the evolution of corrosion inhibition with time. The effectiveness of the proposed analysis procedure is investigated for AA2024-T3 exposed to aqueous 10-1 M NaCl solutions with or without the addition of Ce ions at various concentrations. Examination of specific features in the electrochemical noise signals shows the presence of three characteristic regions, which represent surface activity regimes ranging from active (localized) corrosion to the inhibited state. Hilbert spectra of the electrochemical current noise signals allow identification of transients occurring in these successive regions.The analysis procedure introduced in this work yields improved applicability of electrochemical noise measurements for the identification of an inhibition effect in corrosion processes.

Analysis of Electrochemical Current Noise From Metastable Pitting of SS304L in NaCl Solutions

Electrochemical noise emanating from a corrosion situation gives indication about the nature and form of corrosion. An attempt has been made to analyse electrochemical current noise signal generated under potentiostatic condition (for metastable pitting) for SS304L–NaCl system. To begin with polarisation plots of SS304L were obtained in various test solutions to precisely know pitting potential of SS304L. It is found that Epit and ipass increase on increasing chloride content. The electrochemical current noise was measured at potentials 20–30 mV below the pitting potentials. The current time record shows two types of current transients; (i) slow rise and rapid decay and (ii) rapid rise and slow decay. Power spectral density analysis of current noise shows that the power (A2/Hz) of the signal measured at metastable pitting range increases with increasing chloride. Sampling frequency has to be properly selected otherwise some of the spikes are not recorded and as a result, size and shape of few current transients is altered.

Comparison of Symmetrical and Asymmetrical Cells by Statistical and Wavelet Analysis of Electrochemical Noise Data

The most common cell configuration for electrochemical current noise (ECN) measurements consists of two identical working electrodes (WE) known as symmetrical cell, connected by a zero-resistance ammeter (ZRA). The analysis of ECN data is complicated by its reflection of the behavior of two identical WE, but it would be facilitated greatly if the behavior of one of two WE were measured separately. According to an earlier theoretical model, an asymmetrical cell with a large difference in size between two WE, which are otherwise identical, allows the measurement of ECN on the small electrode while allowing free corrosion to proceed. In this paper, the ECN signals obtained on the symmetrical cells are compared with those carried out on the asymmetrical cells by statistical and wavelet analysis methods. Three advantages of the asymmetrical cells for measurement of ECN data are clearly seen: the time scale preserving of current transients, the increase of amplitude of current transients, and the detection of a higher number of events.

Analysis of the dynamics of Intergranular corrosion process of sensitised 304 stainless steel using recurrence plots

This study presents the assessment of the dynamics of intergranular corrosion of austenitic stainless steel with different degrees of sensitization through the analysis of electrochemical current noise signals. Samples of S30400 stainless steel were aged at 923 K for 50, 250 and 1,000 min before being quenched in water. The double Loop Electrochemical Potentiokinetic Reactivation test was applied to assess the degree of sensitization. The electrochemical noise data were analysed using a novel mathematical tool named Recurrence Plots (RP). This method allowed us to assess the dynamics of the intergranular corrosion process of the steel in a H2SO4 + KSCN solution at room temperature. The study was conducted using a recurrence quantification analysis (RQA) from which it was possible to determine the percent of recurrence (%R), the percent of determinism (%D) and the information Entropy of the corrosion process. It was found that these parameters increased with the sensitisation intensity, which indicates that sensitisation induced a more deterministic dynamics on the electrochemical process.

Estudio por impedancia y ruido electroquímico de la pasivación anódica del paladio en medio alcalino

Anodic passivation of palladium in alkaline medium is studied by. means of different electrochemical techniques like potentiodynamic polarization curves, electrochemical impedance spectroscopy and electrochemical noise. A chaotic analysis of electrochemical current noise signals (current oscillations) corresponding to different palladium oxides formed anodically seem to give information about the different potentials characteristics of palladium oxides formation.

Use of electrochemical current noise to detect initiation of pitting conditions on copper tubes

Many failures in copper pipes used for cold water transportation result from type 1 pitting. This occurs when tubes containing a deleterious film from the manufacturing process are exposed in an aggressive water. Present tests to detect the presence of deleterious films are unsatisfactory and a possible alternative rapid test method has been studied. The technique involves collection and analysis of the electrochemical current noise signals emitted by the copper tube during corrosion. Tubes with different amounts of carbon contamination, produced at BNF and deliberately engineered by industry, have been studied using an electrochemical current noise technique. After only 20 h on test, the standard deviation and coefficient of variation of electrochemical noise signals clearly distinguished between grit blasted tube and contaminated tube. A longer, 30 h, test was needed to separate those that were borderline but satisfactory from those that were bordeline/unsatisfactory.