The dependence of electrochemical migration (ECM) of tin on chloride was investigated using in situ electrochemical and optical techniques. An interesting phenomenon is first found that tin dendrite grows not only in the electrolyte layer with low chloride concentration but also in the electrolyte layer with high chloride concentration, although it is generally suggested that the growth of tin dendrite through ECM is not available in solution with high chloride concentration. Mechanisms have been proposed to explain the ECM of tin in the electrolyte layer with various chloride concentrations.Highlights► Electrochemical migration was first investigated under thin electrolyte layer. ► The dependence of ECM on chloride was clarified. ► Tin dendrite can be observed in electrolyte with high chloride concentration. ► More chloride in electrolyte layer, more OH− ions will be created on the cathode.

The effects of continuous cathodic and anodic polarisation on the corrosion of polypyrrole (PPy) films were investigated in neutral 0.1 M NaCl with various electrochemical methods and spectroscopic analyses. With continuous cathodic polarisation, the PPy film nearly maintains the conjugated structure of PPy chains, but loses its electroactivity slightly. With increases in anodic polarisation potential and polarisation time, the electroactivity loss of the polarised PPy film increases rapidly especially at a higher anodic potential; while the damage to the conjugated structure of PPy chains also becomes severer with increasing polarisation time. The mechanisms involved were discussed.Highlights► PPy films nearly keep the conjugated structure after cathodic polarisation. ► PPy films slightly lose their electroactivity after cathodic polarisation. ► PPy films lose more electroactivity with increases in anodic potential and time. ► Cl− attacks PPy to break the conjugated structure at an anodic potential.

In this study, the corrosion performance of magnesium-based rare-earth containing alloy Mg–10Gd–3Y–0.5Zr (GW103) was evaluated in an ethylene glycol solution with a group of selected aliphatic, aromatic carboxylates and inorganic salts as inhibitors. The dependence of inhibition efficiency on the concentration ratio of sodium phosphate to sodium dodecylbenzenesulfonate (SDBS) and the total inhibitor concentration was measured by means of electrochemical techniques. It was found that the corrosion rate of GW103 decreased by addition of inorganic–organic inhibitors at both ambient and elevated temperatures. The inhibitors were more effective at the ambient temperature than at the elevated temperature. The corrosion of GW103 in the ethylene glycol solution can be effectively inhibited by 1000 ppm of the inorganic–organic inhibitor mixture. It is believed that the added phosphate can interact with SDBS, resulting in a more compact surface film on the GW103 surface. Based on these results, as well as Environmental Scanning Electron Microscope (ESEM) observations, a synergistic mechanism was proposed to explain the inhibition behavior of the sodium phosphate + SDBS combination.Highlights► Sodium phosphate can inhibit the dissolution of GW103 Mg alloy in ethylene glycol. ► Sodium dodecylbenzenesulfonate can also inhibit the corrosion of GW103. ► These two inhibitors have different inhibition mechanisms on GW103. ► The two inhibitors have a synergistic inhibition effect on GW103 if used together.

In order to identify the different pitting states, some pattern recognition (PR) procedures, including principal component analysis (PCA), hierarchical agglomerative cluster analysis (HACA) and linear discriminant analysis (LDA), were applied for analyzing electrochemical noise (EN) statistical parameters from a typical pitting system of Q235 carbon steels in NaHCO3 + NaCl solutions. Firstly, according to the PCA results, the EN mean value (E¯ and I¯) and standard deviation (σE and σI) were determined as the descriptors for clustering. Then, using the selected four statistical parameters as variables, the cases from different pitting states were classified by the HACA to three clusters, which relates to the metastable state, intermediate state and stable state, respectively. It shows a good agreement with the classification obtained from k-means cluster with E and log|I| as variables. Based on the cluster results, the pitting states of the ungrouped data points from the similar pitting processes also can be distinguished according to the established discriminant function(s).

A new occluded corrosion cavity (OCC) simulation cell was designed to study the underscale corrosion behavior of carbon steel (N80) in 0.2 mol L−1 NaCl solution. The chemical components of the solution in the OCC were measured and the electrochemical behavior of the occluded anode and the bulk cathode were studied by electrochemical impedance spectroscopy (EIS). The newly designed OCC cell can easily simulate the auto-catalyzing acidification process and may be used to study the mechanism of underscale corrosion. The corrosion scale exacerbates the underscale corrosion and the area ratio of the bulk cathode to the occluded anode (R = Sc/Sa) determines the development of simulated localized corrosion in the OCC cell. When R was within a certain range, the corrosion rate in the OCC could be kept at a persistently high level. The pH of the solution in the OCC decreased and the chloride ions (Cl−) concentrated as the local corrosion developed. The anodic process on the occluded anode was controlled by irreversible charge transfer and the cathodic process on the bulk cathode was controlled mainly by oxygen diffusion.

The analysis of coulostatically induced transients (CITs) has been used as a tool to evaluate the corrosion rate of metallic materials, and a new algorithm has been developed to calculate the Tafel slopes (ba and bc). This new algorithm is based on the coulostatic strong polarization integration (CSPI) method. Experimental results for carbon steels exposed to 0.5 M H2SO and 1 M HCl show excellent agreement between the proposed method and the Tafel line extrapolation method with IR drop correction. Furthermore, the calculated average corrosion currents over 8 h tests are in good agreement with solution analysis data from atomic absorption spectroscopy. The improved CSPI algorithm shows superior performance over the differential algorithm and the conventional algorithm due to its simplicity and higher signal/noise ratio.

The corrosion inhibition effect of Capsella bursa-pastoris extracts (CBE) for Q235 carbon steels in 1 mol·L− 1 hydrochloric acid solution was studied using electrochemical methods, environmental scanning electron microscopy (SEM) and Raman microscopy analysis. The polarization plots indicate that CBE serves as an effective, mixed-type inhibitor. Linear polarization resistance shows that increasing CBE concentration and temperature results in increased inhibition efficiency. The highest inhibition efficiency can reach 97% when adding 60 mg·L− 1 CBE, which is better than some reported plant extracts under the similar environment. The adsorption of CBE molecules is found to obey the Langmuir adsorption isotherm. Some thermodynamic and kinetic parameters for the adsorption process, such as the adsorption equilibrium constant (K), free energy of adsorption (∆Gads), activation energy of corrosion reaction (Ea) and the heat of adsorption (Qads), are calculated and discussed. SEM and Raman microscopy analysis also demonstrate the formation of a CBE inhibition film on the metal surface.The corrosion inhibition effect of Capsella bursa-pastoris extracts (CBE) for Q235 carbon steels in 1 mol·L− 1 hydrochloric acid solution was studied using electrochemical methods, environmental scanning electron microscopy (SEM) and Raman microscopy analysis. The results indicate that CBE serves as an effective, mixed-type inhibitor and the highest inhibition efficiency can reach 97% when adding little amount of (60 × 10− 6) CBE. The inhibition effect due to the formation of a CBE inhibition film which were demonstrated by SEM and Raman microscopy analysis. And the adsorption of CBE molecules on the metal surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic and kinetic parameters for the adsorption process are also calculated and discussed.Download full-size image