Papers by Keyword: Electrochemical Noise

Abstract: 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.

Abstract: 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.

Abstract: An in situ characterization has been carried out for several active systems (sulfuric acid, ferric iron, 9k medium and bioleaching solutions) to investigate the bioleaching process of natural pyrite using electrochemical noise (ECN) technique. Spectral noise impedance spectra obtained from power spectral density (PSD) plots for the different systems were compared. It has been observed that the bioleaching system obtained the lowest noise resistance Rsn 0.101MΩ. The reaction mechanism was proposed based on experimental data analysis. The bioleaching process of natural pyrite has been identified as the main function of bio-battery reactions, which distinguishes from the chemical oxidation reaction for the ferric ion and 9k solutions.

Abstract: Corrosion is one of the most decisive factors determining the lifetime of materials, especially of the surface layers. Monitoring corrosion rate and mapping the overall corrosion on the surface of solar cells become very important step in preventing failures in long-term atmospheric exposure. Electrochemical noise technique in no contact to the substrate setup (ENA NOCS) as non-destructive technique was used to monitor potential and current and finally calculation of noise resistance ratio Rn was determined. The technique is already successfully executed on zinc and zinc alloy coatings [1] and organic coatings [2]. In this paper, the reliability of the corrosion monitoring system in adapting the technique to measure potential and current fluctuations on silicon based photovoltaic solar cells was verified. Tests were performed and finally compared on monocrystalline and polycrystalline silicon using different approaches (placement of sensor, intensity of light etc.) Graphical abstract: Non-destructive corrosion monitoring on solar cells

Abstract: Electrochemical Noise (EN) measurements for low carbon pipeline steel (X52) samples were carried out in 3.5% NaCl aqueous and NACE solutions. Both testing solutions were saturated with hydrogen sulphide (H₂S) at 20 and 60 ^oC, under static conditions. EN data was analysed in the time domain. Parameter such as Electrochemical Noise Resistance (R_n) and Localization Index (LI) were determined from the analysis in the time domain. Also, R_n results are compared with traditional Linear Polarization Resistance (LPR) data. A superficial analysis was carried out by a scanning electron microscopy (SEM) with Energy Dispersive X-Ray analyses (EDX). A good correlation was observed among the used techniques and relevant electrochemical data related to the corrosion phenomena was obtained. According to R_n, the corrosion rate (CR) values of the steel sample immersed in 3.5% NaCl are higher than the CR of the steel samples immersed in NACE solution. The morphology of the corrosion process obtained by SEM was a localized type and this behaviour was corroborated by the results obtained by LI where these LI values are 1 or close to 1.

Abstract: The electrochemical noise (EN) of N80 steel in NaCl solution has been studied by the wavelet and the equivalent circuit theory. Spectrum analysis showed that the corrosion data is no transient peaks, the variations of potential and current showed typical characteristics of uniform corrosion. Wavelet analysis results show that the different time energy fluctuations of different size ranges, low-level occur fluctuations repeatedly and high-level appear concave curve. Analysis shows that it is mainly due to uniform corrosion process, and the control step is diffusion process of corrosive ion. The applications of equivalent circuit analyze electrochemical noise data in theory, and describe the corrosion process by the components of potential noise and current noise power spectral density

Abstract: In this work, an overview of recent developments in materials characterization and performance assessment methods applied to corrosion is given. It is shown that 3D techniques represent a powerful tool to gain fundamental information on the relationship between alloy microstructure and corrosion initiation and propagation. Subsequently, taking as an example an aluminium alloy anodized at two different potentials, the use of image assisted electrochemical noise analysis for the assessment of the practical performance of protective treatments is illustrated.

Abstract: An investigation was carried out on the features of electrochemical noises of 304 nitrogen controlled stainless steel (304NGSS) in solution 4mol/LNaCl +0.01mol/LNa₂S₂O₃ under slow strain rate testing (SSRT) conditions. Electrochemical voltage and current noise were measured simultaneously in the Zero Resistance Ammeter (ZRA) mode. After experiment, there are several cracks on the edge of pit on the specimen. In order to characterize the stress corrosion cracking (SCC) processes of 304NGSS, time analysis of data alongwith the spectral estimation using FFT method, the results show SCC processes consisted of breakdown of the oxide film, the formation of pitting, crack initiation and crack propagation. According to the varieties of spectrums in time and frequency, the different state can be distinguished. The work in this paper will contribute to the research of indicator for real-time detection of SCC in plant.

Abstract: The electrochemical potential noise (EPN) of 304 stainless steel (SS) weld zone in boiling 50%NaOH solution were studied, in order to monitor stress corrosion cracking (SCC). Several EPN parameters were extracted from time domain, frequency domain and statistical analysis. The results showed its corrosion potential appears a downward trend during the experiment. When localized corrosion cracks initiation, amplitude was large and termination appeared. A high frequency plateau appeared using the Fast Fourier Transform (FFT) method in the power spectrum densities (PSD) s, and its standard deviation was larger, indicating the variation of corrosion state. Moreover, Visual records and frequency of events (fn) were discussed. Its fn can distinguish the different state of specimens. EPN shows considerable promise for detecting localized corrosion. Further development work is expected to lead to a useful, for real time detection of localized corrosion.

Abstract: This work presents the electrochemical corrosion results of the structural metals, aluminium (Al), brass and copper (Cu), immersed in coastal waters of Veracruz Port in Mexico at room temperature, atmospheric pressure and eight weeks of the exposition time. The electrochemical technique used was electrochemical noise (EN). A typical three-electrode electrochemical cell was used. Where the reference electrode was the silver/seawater (Ag/SW) and two nominally identical metallic samples were used as working electrodes (WE1 and WE2). The metallic samples of Al, brass and Cu were used as working electrode. The potential and current fluctuations were measured simultaneously between the two working electrodes (current measured) and the Ag/SW electrode (potential measured). The electrochemical noise measurements (ENM) were analysed by three different methods: Potential and current versus time (transients), Localization Index (LI) and Electrochemical Noise Resistance (R_n). The results shown a good correlation between the superficial analysis and the results obtained by the ENM. In addition, Cu presents the highest corrosion rate and, a corrosion attack was obtained by localization index; this behaviour was confirmed by superficial analysis.