Electrochemical Noise Signals Research Articles

Data Mining Applied to the Electrochemical Noise Technique in the Time/Frequency Domain for Stress Corrosion Cracking Recognition

In this paper, time/frequency domain data processing was proposed to analyse the EN signal recorded during stress corrosion cracking on precipitation-hardening martensitic stainless steel in a chloride environment. Continuous Wavelet Transform, albeit with some limitations, showed a suitable support in the discriminatory capacity among transient signals related to the different stress corrosion cracking mechanisms. In particular, the aim is to propose the analysis of electrochemical noise signals under stress corrosion cracking conditions in the time–frequency domain by using the Hilbert–Huang approach. The Hilbert–Huang Transform (performed by the Empirical Mode Decomposition approach) was finally proposed to carry out an identification of the corrosion mechanisms in comparison to conventional data processing methods. By using this approach, a detailed simultaneous decomposition of the original electrochemical noise data in the time and frequency domain was carried out. The method gave useful information about transitions among different corrosion mechanisms, allowing us to (i) identify a specific characteristic response for each corrosion damaging phenomenon induced by stress corrosion cracking, (ii) time each corrosion of the damaging phenomenon, and (iii) provide a topological description of the advancing SCC damaging stages. This characteristic evidences that the Hilbert–Huang Transform is a very powerful technique to potentially recognize and distinguish the different corrosion mechanisms occurring during stress corrosion cracking.

Effect of loading conditions on corrosion fatigue process of FSW AA6061-T6 joint in 3.5% NaCl studied by electrochemical noise

Electrochemical noise (EN) signals generated during corrosion fatigue (CF) process of friction stir welded (FSW) AA6061-T6 joints in 3.5 wt% NaCl solution under different loading conditions were monitored. Wavelet analysis and cumulative probability calculations showed that the increase in peak stress, stress ratio and stress frequency all lead to a decrease in Rn and an increase in the incubation rate of local events. Under current experimental conditions, the influence of peak stress is the most significant, while the influence of frequency is the least. The combination of EN signal analysis and transmission electron microscopy (TEM) observations indicates that the coarsening of β′ phase and the extensive dissolution of β'' phase are the main reasons for preferential failure in the weakest heat affected zone. The main contribution of this study is preliminary investigating the CF behavior of FSW AA6061 joints under different low cycle fatigue conditions. Moreover, EN is an effective strategy for monitoring CF process and establishes a connection between an alternative EN technique and in-situ CF behavior research.

Comparative, real-time in situ monitoring of passivation phenomenon in the copper electrorefining process based on wavelet series

Electrochemical noise signals can be analyzed to predict the passivation tendency of anodes in electrorefining. An industrial case study began with the sampling of six different casting anodes. Potentiostat/Galvanostat analysis was used to record voltage-time changes through electrorefining at intensified current density (220 mA.cm−2). Wavelet series were used to analyze electrochemical noise signals. Those samples with a higher average contribution of low-frequency signals, with average values of 0.172, 0.173, and 0.173, had long passivation times of 3451, 3693, and 4640 s, respectively. Experimental measurements were carried out using the copper refinery's industrial current density (30 mA.cm−2) as a test bed, and excellent matching was obtained by registering the data.

Imidazoline behavior as corrosion inhibitor in the electrochemical characterization of SCC behavior of an API X70 steel exposed to brine solution

Abstract The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

Identifying the cavitation erosion stages of AA5083 by electrochemical noise analyses

PurposeThe purpose of this paper is to study the cavitation erosion stages of AA5083 by electrochemical noise (EN).Design/methodology/approachEN technology including noise resistance and fast Fourier transform were used to characterize the electrochemical process during the cavitation erosion process.FindingsAA5083 suffers from uniform corrosion during the cavitation erosion process. The whole cavitation erosion process can be divided into three stages: incubation stage, acceleration stage and steady-state stage. EN signals showed obvious differences in different stages of cavitation erosion.Originality/valueEN technique is a suitable method that can be used to study cavitation erosion mechanism and identify cavitation erosion stages.

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.

Interpreting electrochemical noise signal arising from stress corrosion cracking of 304 stainless steel in simulated PWR primary water environment by coupling acoustic emission

Electrochemical noise (EN) signals arising from stress corrosion cracking (SCC) of 304 stainless steel (SS) in borated and lithiated high-temperature water were monitored. Acoustic emission (AE) signals were simultaneously measured to relate the EN signals with the SCC process. Through Weibull analysis of the EN signals, it was demonstrated that the EN technique can in-situ capture the SCC events in high-temperature water. With evolution of the SCC process, Hilbert time-frequency spectrum of the EN signals gradually migrated from high frequency to low frequency. The capacity of EN and AE techniques to monitor the SCC process in high-temperature water is compared.

Electrochemical noise analysis to evaluate the localized anti-corrosion properties of PP/graphene oxide nanocomposite coatings

• Electrochemical noise was used to evaluate the localized corrosion of PP-based NCCs. • PP|Graft|GO = 0.1 illustrated the best localized corrosion performance. • PP|Graft|GO = 0.1 was able to re-passive and prevent the growth of large & deep pits. • In the presence of GO, the transients shift to the higher frequencies at all times. Electrochemical noise analysis was applied to evaluate the localized anti-corrosion performance of polypropylene (PP)-based nanocomposite coatings (NCC). In this regard, the NCCs were developed on mild steel from a solution containing PP, MAH-grafted PP, and different percentages of graphene oxide (GO). The coated samples were subjected to thermal tests, salt spray, and electrochemical noise (EN) analysis. Electrochemical potential and current noise (EPN & ECN) signals were evaluated to find information about localized corrosion. First, the raw signals were analyzed based on the empirical mode decomposition (EMD), then the 3D diagrams (intensity, time, and frequency) were plotted using the Hilbert transform. The results showed in the presence of GO, the transients shift to the higher frequencies at all times, which confirms more tendency to uniform corrosion instead of localized. Introducing 3 wt% of GO NPs into the coating leads to the electrochemical noise resistance increasing by 5 times (>10 8 Ω.cm 2 ), pit initiation rate decreasing, and pit radius reduction (by ∼5 times). As a result, MAH-grafted PP and GO in these NCCs can act as effective barriers against corrosive agents, especially the agents that cause pitting corrosion.

A study on synergistic effect of chloride and sulfate ions on copper corrosion by using electrochemical noise in asymmetric cells

The current study includes a systematic examination of copper corrosion initially in each of NaCl and Na2SO4 solutions separately and then in the mixture solution of Cl− and SO42− ions as aggressive ions. Electrochemical current noise (ECN) signals resulting from asymmetric (Asy) as well as symmetric (Sym) cells have been interpreted using wavelet transform (WT) along with statistical procedures. The signals have been detrended and the decomposition of every signal has been carried out into 8 crystals. Then the standard deviation of every crystal has been illustrated with the standard deviation of partial signal (SDPS) plots. The Asy electrodes increased the pitting detection on copper compared with the Sym ones, indicating higher efficiency of the Asy electrodes. Asymmetric-copper electrodes have been studied using SDPS plots at different temperatures (40, 60, as well as 80 °C). Finally, in order to partly understand the effect of Cl− and SO42− ions on the corrosion of copper, the stabilization of Cu2+ cations by Cl− and SO42− ions in aqueous solutions have been modeled by DFT calculations. The derived results are in accordance with the experimental data.

Electrochemical noise studies on the effect of nitrogen on the pitting corrosion of stainless steel using wavelet analysis

ABSTRACT The effect of nitrogen on the pitting process is investigated using the electrochemical noise (EN) approach in 0.01 M FeCl3 for 24 h at a sampling frequency of 1 Hz. The EN signals were investigated using wavelet analysis on four alloys of 316L SS containing varying quantities of nitrogen (0.07, 0.12, 0.14 and 0.22 wt-% nitrogen). Using an energy distribution (ED) and standard deviation of partial signal (SDPS) plot, the primary corrosion process in various nitrogen-containing 316L SS was found. The ED plot showed that as the nitrogen percentage in the alloy increased, the energy of the low-frequency signal decreased, indicating that long-time transients were suppressed. The SDPS figure revealed a drop in pit density as nitrogen levels increased. For specimens containing 0.07, 0.11, 0.14 and 0.22 wt-% nitrogen, the pit density was determined to be 439 ± 8, 383 ± 6, 212 ± 6 and 108 ± 4 pits mm−2, respectively.

Evaluation of the formation and protectiveness of a lithium-based conversion layer using electrochemical noise

The formation process of a lithium-based conversion layer on AA2024-T3 and its corrosion protective behavior are studied using electrochemical noise (EN). Wavelet transform, as well as noise resistance analysis, have been employed to interpret the EN data. The EN data confirmed five different stages during the conversion layer growth, accompanied by anodic dissolution, increasing corrosion protection of the conversion layer, and adsorption, growth and desorption of hydrogen bubbles simultaneously. The detachment of hydrogen bubbles, localized and uniform corrosion generate different features in the EN signals with energy maxima in high, intermediate and low frequency bands, respectively. In addition, EN results show that the lithium-based conversion layer still provides efficient protection after re-immersion in a corrosive environment, even though localized damage occurs. Moreover, the EN data corresponds well with the morphological layer formation and breakdown observed with microscopy techniques. The results demonstrate that EN is a powerful tool to provide continuous time- and frequency-resolved information about inhibition efficiency.

Failure mode diagnosis in proton exchange membrane fuel cells using local electrochemical noise

Early diagnosis of fuel cell failure modes is a very active research topic, as it improves robustness and durability of fuel cells used in commercial applications. The diagnosis method should be suited for being applied in real time, without interfering with the fuel cell operation, and it should be implemented using inexpensive hardware and light equipment. A novel method of failure diagnosis in PEM fuel cells, based on the analysis of local electrochemical noise, is proposed. Seven electrochemical noise signals are acquired in different parts of the cell, significantly increasing the information for an effective diagnosis, since previous studies have only analyzed a single signal from the electrochemical noise in the cell.Each electrochemical noise signal is frequency decomposed using wavelet transform to create a characteristic pattern. These patterns are used in a deep learning neural network to perform the cell state classification. The proposed method has been successfully applied to the classification of 26 different states achieved in experiments where the following factors have been varied: (1) average current density; (2) airflow; (3) drying; and (4) air pressure. The mean successful identification rate of the 26 states is above 85%. The proposed diagnosis method is well-suited for real-time diagnosis, and it can be implemented using lightweight and inexpensive hardware.

The Use of a Time-Frequency Transform for the Analysis of Electrochemical Noise for Corrosion Estimation

This work shows the results of evaluating the corrosion type and rate (CR) in the 6061-T6 aluminum alloy exposed to ethanol-gasoline blends (E0, E10, E20, E30, E40, E60, E80, and E100) by analyzing electrochemical noise (EN) signals using the Shannon energy (SSE) and the synchrosqueezing transform (SST). The obtained results are compared against the obtained with the statistical method (Location Index, LI). The results obtained with the SSE method showed that the corrosion type in the 6061-T6 aluminum alloy is classified better than using the statistical method. Moreover, the SST results showed that the corrosion rate increased with the increment of the ethanol content in the ethanol-gasoline blends from values in the order of10−4to10−3mm/year.

Titanium bipolar plates augmented by nanocrystalline TiZrHfMoW coatings for application in proton exchange membrane fuel cells

A TiZrHfMoW refractory high entropy alloy (RHEA) nanocrystalline coating was engineered onto a commercially pure Ti (CP-Ti) substrate to enhance its corrosion resistance for potential application as bipolar plates for use in proton exchange membrane fuel cells (PEMFCs). The as-prepared RHEA coating possesses a single-phase BCC structure with an average grain size of ∼12 nm. The electrochemical corrosion behavior of the RHEA coating in simulated PEMFC environment, with varying HF concentrations, was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), in conjunction with detection and analysis of electrochemical noise (EN). The potentiodynamic polarization and EIS measurements of the RHEA coating indicated that, at a given HF concentration, the RHEA coating exhibits a higher Ecorr, a lower icorr and a larger resistance value compared to uncoated CP-Ti. The analysis of the EN signals indicated that the RHEA coating has low correlation dimensions (below 1.4) and small instantaneous amplitudes in the Hilbert spectra, confirming that the RHEA coating was capable of maintaining a stable passive state, regardless of the HF concentrations. Furthermore, the electron work function of TiZrHfMoW RHEA was derived by first-principles calculations to unravel the physics origin of the corrosion resistance of the RHEA coating.

Effect of chloride ion concentration on corrosion process of selective laser melted AlSi10Mg with different heat treatments studied by electrochemical noise

The effect of chloride ion concentration on corrosion behavior of selective laser melted (SLMed) AlSi10Mg with different heat treatment (300 °C and 400 °C) was in-situ investigated by electrochemical noise (EN) technique and corrosion morphology observation. The EN signals were analyzed by noise resistance (Rn) analysis, wavelet analysis and recurrence quantification analysis (RQA). It was found that the corrosion rates of as-building and heat treated at 300 °C samples are close at the corrosion early stage when exposed to 0.1 M NaCl, while the corrosion resistance of the sample heat treated at 300 °C is lower than that of as-building sample during the whole test period when exposed to 1 M NaCl. Corrosion resistance of the sample heat treated at 400 °C is lowest in the two NaCl solutions. The relationship between the microstructures and the corrosion mechanisms is discussed. The main contribution of present study is to provide an alternative EN technique to in-situ study the corrosion behavior of SLMed AlSi10Mg and obtain some useful information, which is different from that obtained by traditional polarization curve and electrochemical impedance spectroscopy.

In-situ monitoring of pitting corrosion of AZ31 magnesium alloy by combining electrochemical noise and acoustic emission techniques

Pitting corrosion of AZ31 magnesium (Mg) alloy was in-situ monitored by combining electrochemical noise (EN) and acoustic emission (AE) techniques. The EN signals were analyzed by transient shape observation, Hilbert spectrum and recurrence quantification analysis (RQA) based on recurrence plot (RP). AE characteristic parameters including rise time, amplitude, absolute energy and peak count were adopted to classify the AE signals. According to the mutual information obtained by EN and AE measurements, three corrosion stages including film-forming process, pit initiation and pit propagation can be identified. The detailed relationship between the AE and EN parameters and different corrosion mechanisms is discussed. The main contribution of present study is to provide a feasible method to effectively monitor the self-corrosion process of Mg alloy.

An imidazole-based benzilic-dicationic ionic liquid performance in 1.0 M HCl solution to mitigate the mild steel degradation: Electrochemical noise/impedance investigation

The corrosion prevention capability of an imidazole-based benzilic-dicationic ionic liquid labeled 1,4 -di [1′ –methylene- 3′- methyl imidazolium bromide]- benzene (DMIBr2) over mild steel in hydrochloric acid was investigated through experimental and theoretical studies. The excellent corrosion inhibitor ability of DMIBr2 was demonstrated using a new concept in noise resistance and spectral noise resistance interrelation to adequately eliminate the trend of electrochemical noise (EN) signals, which is in line with electrochemical impedance spectroscopy findings. EN also revealed that DMIBr2 mitigated both localized and general mild steel corrosion, as evidenced by SEM analysis. Potentiodynamic polarization suggested DMIBr2 can be described as a mixed-type corrosion inhibitor with cathodic control predominance in 1.0 M HCl. Langmuir adsorption isotherm was considered to interpret the DMIBr2 adsorption behavior on mild steel. Furthermore, according to quantum chemical calculations, the probable protonation process in the acid can affect the functionalities of different DMIBr2 components.

Electrochemical noise analysis of cavitation erosion corrosion resistance of NbC nanocrystalline coating in a 3.5 wt% NaCl solution

To combat cavitation erosion-corrosion damage inflicted upon mechanical components in marine applications, NbC nanocrystalline coatings were synthesized by a double cathode glow discharge assisted reactive sputtering method. The coating comprised equiaxed B1-NaCl-type NbC grains with an average grain size of ~10 nm and a strong NbC (200)-oriented texture by TEM observation. The electrochemical response of the coating exposed to a 3.5 wt% NaCl solution with and without the influence of cavitation was monitored by electrochemical noise (EN) measurements, in addition to open circuit potential and cyclic polarization. To differentiate the cavitation erosion-corrosion resistance between the NbC coating and a reference Ti-6Al-4V alloy substrate, the EN data were further evaluated, based on a series of analyses, including frequency domain, time-domain, shot noise and wavelet transform. For the Ti-6Al-4V alloy, with increasing output power, the noise resistance (Rn) and slope (k values) of potential and current power spectral density (PSD) decreased, and the average charge in each corrosion event (q) and the total energy of d series crystals increased markedly at the output power levels above 400 W, indicative of a high propensity of pitting corrosion for this alloy. Conversely, the Rn and k values for the NbC coating were found to be almost independent of the output power, and the charge of the corrosion event and the total energy of the d series crystals were much lower than that of the Ti-6Al-4V alloy. The findings garnered from analyzing the EN signals is in accord with what were uncovered from examining the eroded surface morphologies, suggesting that the EN method might offer a reliable and effective tool to probe the cavitation erosion-corrosion behavior in developing durable material.

Monitoring the heterogeneity in single cell responses to drugs using electrochemical impedance and electrochemical noise.

Impedance spectroscopy is a widely used technique for monitoring cell–surface interactions and morphological changes, typically based on averaged signals from thousands of cells. However, acquiring impedance data at the single cell level, can potentially reveal cell-to-cell heterogeneity for example in response to chemotherapeutic agents such as doxorubicin. Here, we present a generic platform where light is used to define and localize the electroactive area, thus enabling the impedance measurements for selected single cells. We firstly tested the platform to assess phenotypic changes in breast cancer cells, at the single cell level, using the change in the cell impedance. We next show that changes in electrochemical noise reflects instantaneous responses of the cells to drugs, prior to any phenotypical changes. We used doxorubicin and monensin as model drugs and found that both drug influx and efflux events affect the impedance noise signals. Finally, we show how the electrochemical noise signal can be combined with fluorescence microscopy, to show that the noise provides information on cell susceptibility and resistance to drugs at the single cell level. Together the combination of electrochemical impedance and electrochemical noise with fluorescence microscopy provides a unique approach to understanding the heterogeneity in the response of single cells to stimuli where there is not phenotypic change.

In-situ monitoring of pitting corrosion of Q235 carbon steel by electrochemical noise: Wavelet and recurrence quantification analysis

Abstract Pitting corrosion of Q235 carbon steel in 0.25 M NaHCO3 with different concentrations of chloride ions was in-situ monitored by electrochemical noise (EN) technique, and the EN signals were analyzed by transient shape analysis, wavelet analysis and recurrence quantification analysis (RQA). Four typical electrochemical current noise (ECN) transients corresponding to different pitting stages including passivation, random metastable pitting, transition stage and stable pitting stage were observed. It was found that the RQA parameters, recurrence rate (R) and determinism (D), show the ability to separate the four ECN transients, while wavelet parameter show poor ability to distinguish the ECN transients arising from random metastable pitting and transition stage. Furthermore, the ratio of D and R (η) was proposed to monitor the pitting corrosion. The average value of η for the passivation and random metastable pitting is 1.88 and 1.63, and it gradually increases to around 6 during the transition stage and early stable pitting stage, the value slightly decreased to 4.16 at the late stable pitting stage. The detailed relationship between the EN characteristic parameters and dynamic process of pitting corrosion is discussed.