Electrochemical Current Noise Measurements Research Articles

Zn-Al layered double hydroxide as an inhibitive conversion coating developed on AA2024-T3 by one-step hydrothermal crystallization: Crystal structure evolution and corrosion protection performance

In the present work, a ZnAl layered double hydroxide (LDH) conversion coating was synthesized on 2024-T3 aluminum alloy by a one-step hydrothermal method. For this purpose, the effect of synthesis parameters, including the amount of Zn2+ cations and hexamethylenetetramine molecules, on the structural changes were evaluated by using the scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) analysis and X-ray diffraction (XRD) spectroscopy. Also, benzimidazole (BI), as corrosion inhibitor of the AA2024-T3, was intercalated into the LDH film structure by an anion-exchange process. The intercalation of BI molecules into the LHD structure was studied using the SEM-EDS and XRD analysis. Furthermore, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PD), and electrochemical current noise measurements were employed in 3.5 wt% NaCl solution to assess the protection performance of the LDH coating. The PD test results showed that the LDH conversion coating's polarization resistance increases from 24.05 to 131.1 kΩ/cm2 after the intercalation of the BI molecules into the structure of the ZnAl LDH layer. The induction of active protection performance for the LDH film modified with BI molecules was demonstrated through the EIS test results.

Persian Liquorice extract as a highly efficient sustainable corrosion inhibitor for mild steel in sodium chloride solution

The Persian Liquorice was introduced as a sustainable corrosion inhibitor with excellent inhibition action for mild steel in sodium chloride solution. Persian Liquorice is a root of Glycyrrhiza glabra including many active compounds like Glycyrrhizin (GL), 18β- Glycyrrhetinic acid (GA), Liquritigenin (LTG), Licochalcone A (LCA), Licochalcone E (LCE), and Glabridin (GLD). The Fourier transform infrared (FT-IR) spectroscopy was utilized to track various active components exist in the Persian Liquorice extract. Electrochemical impedance spectroscopy, potentiodynamic polarization and electrochemical current noise measurements were conducted to investigate the corrosion inhibition role of various concentrations of Persian Liquorice extract toward mild steel corrosion in sodium chloride solutions. Surface analysis, molecular dynamics and quantum mechanics simulation methods were combined to get insights of inhibitor molecules adsorption on the mild steel surface. The electrochemical investigations revealed that in the presence of 600 ppm Persian Liquorice extract the maximum inhibition efficiency of 98.8% was obtained, which is connected to the build-up of a protecting layer over the mild steel surface, blocking the pathway of harsh ions diffusion. There is no report on use of any sustainable corrosion inhibitor for mild steel in chloride solution with this high level of inhibition power even after long immersion time (72 h). The formation of protecting layer on the mild steel surface was proved by scanning electron microscope and atomic force microscope results. The results derived from MD simulations and QM calculations revealed the adsorption of Persian Liquorice components on the steel substrate via donor-acceptor interactions.

Monitoring of carbon steel corrosion by use of electrochemical noise and recurrence quantification analysis

The corrosion of carbon steel in aqueous media resulting in uniform corrosion, pitting corrosion and passivation was investigated on a laboratory scale. Recurrence quantification analysis was applied to short segments of electrochemical current noise measurements. These segments were converted to recurrence variables, which could be used as reliable predictors in a multilayer perceptron neural network model to identify the type of corrosion. In addition, an automated corrosion monitoring scheme is proposed, based on the principal component scores of the recurrence variables. This approach used the uniform corrosion measurements as reference data and could differentiate between uniform and non-uniform corrosion.

Environmental factors affecting pitting corrosion of type 304 stainless steel investigated by electrochemical noise measurements under potentiostatic control

Electrochemical noise measurements on anodically polarised type 304 stainless steel surfaces in contact with buffer solutions of neutral pH were performed to study the effect of chloride ions in the nucleation of pitting corrosion. Passive layer stability and susceptibility to pitting corrosion after pickling and passivation at different environmental conditions were also investigated by means of electrochemical current noise measurements under cathodic and anodic polarisation. According to the obtained experimental results pits nucleate independently on the presence of chloride ions. It has been also shown that protectiveness of stainless steel surfaces after pickling strongly depends on the relative humidity of the environment in which the surface is subsequently passivated.

Micro- and Nano-scale Tribo-Corrosion of Cast CoCrMo

Previous studies have established that some of the wear damage seen on cast CoCrMo joint surface is caused by entrained third-body hard particles. In this study, wet-cell micro-indentation and nano-scratch tests have been carried out with the direct aim of simulating wear damage induced by single abrasive particles entrained between the surfaces of cast CoCrMo hip implants. In situ electrochemical current noise measurements were uniquely performed to detect and study the wear-induced corrosion as well as the repassivation kinetics under the micro-/nano-scale tribological process. A mathematical model has been explored for the CoCrMo repassivation kinetics after surface oxide film rupture. Greater insights into the nature of the CoCrMo micro-/nano-scale wear-corrosion mechanisms and deformation processes are determined, including the identification of slip band formation, matrix/carbide deformation, nanocrystalline structure formation and strain-induced phase transformation. The electrochemical current noise provides evidence of instantaneous transient corrosion activity at the wearing surface resulting from partial oxide rupturing and stripping, concurrent with the indent/scratch.

Investigation of micro-scale abrasion–corrosion of WC-based sintered hardmetal and sprayed coating using in situ electrochemical current-noise measurements

The micro-scale wear–corrosion interactions of WC-based sintered hardmetals and sprayed coatings are typically investigated by comparing the wear-rates in corrosive environments with neutral (pH 7) conditions and inferring electrochemical activity. However, for a greater understanding of the wear–corrosion interactions, there is a need to examine the repassivation kinetics during micro-abrasion tests under different pH conditions. This paper details in situ electrochemical current-noise measurements performed using a modified micro-abrasion tester to elucidate these wear–corrosion interactions for pH 7–13 conditions for sintered WC–5.7Co–0.3Cr and sprayed WC–10Co–4Cr specimens. Electrochemical measurements and SEM micrographs of worn surfaces are used to detail the degradation process. Discussion will focus on the wear–corrosion interactions present under neutral and alkaline conditions for sintered and sprayed specimens and the influence of microstructure on the electrochemical activity will be detailed.

Electrochemical noise from oxygen reduction on stainless steel surfaces

Oxygen reduction occurring at the passive layer is probably the most important cathodic reaction involved in corrosion processes on stainless steel. Furthermore, the influence of the surface state on the oxygen reduction reaction is a key point for the understanding of the mechanism of localized corrosion on stainless steel. In this study, electrochemical noise measurements under cathodic polarization were carried out to obtain new information about this influence. It has been confirmed that the surface state of stainless steel plays a very important role in the kinetic of this cathodic reaction. Oxygen reduction kinetics was significantly reduced on passivated surfaces and improved on pre-reduced and ground surfaces. In addition, electrochemical current noise measurements allowed to differentiate between the electrochemical activity produced by the oxygen reduction reaction and that due to the reduction of the passive layer, in direct dependence on the characteristics of the different surface states investigated.

Effects of proteins and pH on tribocorrosion performance of cast CoCrMo – a combined electrochemical and tribological study

Cast CoCrMo (F-75) based metal-on-metal (MOM) hip resurfacing implants are an increasing option for younger and more active patients as they are less invasive to the human body. However, symptoms such as inflammation, tissue necrosis and metal sensitivity have been reported for some patients with MOM joints, which may be associated with the liberated metal debris and the elevated metal ion levels from such joints. Therefore, there is a requirement to assess the tribocorrosion performance of the CoCrMo alloy in physiological environments. In this study, the wear corrosion of cast CoCrMo, more specifically, sliding wear corrosion and abrasive wear corrosion (using ∼4 μm SiC abrasive particles) have been investigated using a modified ball cratering rig with a three-electrode electrochemical cell. The concentration effects of proteinaceous material (25 and 50% bovine serum) and pH levels, i.e. pH 4·0 (the pH for an infected joint area) and pH 7·4 (the normal pH for a healthy joint) on the tribo-corrosion performance of the alloy are explored. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy have been deployed to study the protein adsorption/corrosion of the alloy under static, non-abrasive conditions, whereas in situ electrochemical current noise measurements were employed to quantify the mechanoelectrochemical mechanisms present in the tribocorrosion of the alloy under dynamic conditions. In general, protein adsorption was found to be dependent on pH and protein concentration. Protein adsorption in turn influenced the overall tribocorrosion performance of the CoCrMo alloy, including the in situ electrochemical current noise, the specific wear rates, as well as the wear scar morphologies. The presence of bovine serum enhanced the separation of the bearing surfaces and for the sliding wear corrosion the wear rate was markedly reduced. However, the bovine serum appeared to increase the abrasive particle entrainment and lead to accelerated wear in the presence of abrasive particles (abrasive wear). For the more acidic physiological environment, in comparison to pH 7·4, higher corrosion rates occurred under wear corrosion conditions leading to increased metal ion release. Consequently, the proteins and the pH level of hip joint environments play a significant role in the tribocorrosion performance of the cast CoCrMo and a discussion of the combined wear and corrosion mechanisms will be presented.

Electrochemical impedance and current fluctuations analysis during slow strain rate test of a UNS S30400 stainless steel in low pH media

This paper is aimed at investigating the electrochemical behavior of austenitic stainless steel UNS S30400 under stress corrosion cracking conditions in acidic solutions at room temperature. Electrochemical impedance spectroscopy and electrochemical current noise measurements were performed at different stress levels during slow strain rate tests at pH 0.00 and 1.00 in order to evaluate the influence of mechanical deformation on the evolution of the electrochemical responses of the interface. Results have shown that, differently to what happens at pH 1.00, the corrosive attack at pH 0.00 is characterized by intensive cracking concomitantly to the progressive spreading out of uniform corrosion on the metallic surface. The coupling of both electrochemical impedance and current noise techniques provided complementary information about the interplay between dissolution and cracking of the stainless steel exposed to electrolytes of different aggressiveness.

Characterising the quality of chemical tin coatings on copper by electrochemical current noise method

The electrochemical current noise method is widely applied for characterising the surface phenomena of bulk metals or polymer-coated metals. No studies, however, have been available on its use for the characterisation of metallic coatings. This study explores the potential of electrochemical current noise measurements to characterise the quality of chemical tin coatings on the inner surface of copper tubes. The study is carried out by using scanning electron microscopy (SEM), open circuit potential surveys and actual electrochemical current noise measurements. The results obtained by electrochemical current noise measurements were consistent with the microstructural examination and thermodynamical corrosion studies of chemical tin coatings on copper. The statistical analysis of electrochemical current noise data presented either in time or in frequency mode is capable of characterising the chemical tin coatings in terms of uniformity, surface morphology and porosity. The peak shapes of current noise transients reflect the electrochemical phenomena taking place in the tin coating–copper system exposed to drinking water.