Local electrochemical impedance spectroscopy (LEIS) technique is a novel method for the study of local corrosion, which is based on the assumption that the local impedance can be generated by measuring the AC-local-current density in the vicinity of the working electrode in a usual three-electrode cell configuration. From a practical point of view, this was achieved with the use of a dual microelectrode for sensing the local AC-potential gradient, the local current being obtained from the direct application of the Ohm's law. In this paper, the history and principles of this technique were reviewed, while the applications in the field of corrosion research and the characteristics of this method were also discussed.

Inhibition performance and synergistic effect of an imidazoline derivative, namely 1-[N,N-bis(hydroxylethylether)-aminoethyl]-2-stearicimidazoline (HASI) with tetraethylenepentamine (TEPA) on the corrosion inhibition of steel rebar in an artificial concrete pore solution containing 3.5%NaCl were investigated using linear polarization, potentialdynamic polarization and electroch-emical impedance spectroscopy (EIS) techniques, while molecular dynamics (MD) simulation was employed to explore the co-adsorption behavior of the composite inhibitors on the metallic iron surface. Results indicate that after the addition of inhibitors, the corrosion current density of steel rebar was reduced and the corrosion resistance of steel rebar was enhanced. With increasing content of HASI in the composite inhibitors, the inhibition efficiency gradually increased, the corrosion potential shifted significantly to negative, and therewith a more positive pitting potential and a wide passive region were observed in comparison with that in the blank solution, which reveal that the chloride-induced corrosion on steel rebar was effectively retarded by the composite inhibitor, in other words, HASI and TEPA exhibited a good synergistic effect on the corrosion inhibition of steel rebar in the artificial concrete pore solution. MD results show that molecules of HASI and TEPA could simultaneously be adsorbed on the metallic iron surface to form a more compact protective film and consequently became a barrier to hinder the access of aggressive species in the corrosive solution to the metal surface, thereby to effectively inhibit the corrosion of steel rebar.

The corrosion and corrosion inhibition of type 304 stainless steel (304SS) were studied by weight loss method and electrochemical methods in 6%FeCl₃ solution of pH=1 with or without inhibitor K₂Cr₂O₇ under quiescent and ultrasonic vibration. Then the surface morphology of the corroded steel was observed by scanning electron microscope (SEM). The results indicate that the general corrosion and pitting corrosion of 304SS can be suppressed by the application of ultrasound. The corrosion of 304SS is accelerated when concentration of K₂Cr₂O₇ is lower in the quiescence FeCl₃ solution, but different concentration of K₂Cr₂O₇ exhibits a good corrosion inhibition effect under ultrasonic vibration in the same FeCl₃ solution. The combination of ultrasound and inhibitor K₂Cr₂O₇ make the break potential for pitting corrosion and charge transfer resistance of 304SS increased greatly. Therefore, a good synergistic inhibition effect occurs between ultrasonic vibration and inhibitor K₂Cr₂O₇ for 304SS in the acidic medium.

The corrosion behavior of AA5052 Al-alloy in 4 mol/L NaOH solution was investigated by means of mass loss method, measurements of hydrogen gas evolution,polarization curve and electrochemical impedance spectroscopy. It was found that the inhibitor of 30 mmol/L L-Cysteine exhibited the optimal corrosion inhibition performance. Moreover, the adsorption of the L-Cysteine on the Al-alloy surface obeyed the amended Langmuir's adsorption isotherm. The polarization curves indicated that the L-Cysteine inhibited the cathodic reaction and acted as a cathodic inhibitor. The inhibition mechanism was dominated by the geometric covering effect.

The effect of phytic acid concentration, self-assembling time and concentration of sodium molybdate on the corrosion inhibition of the self-assembled monolayer of phytic acid for HAl77-2 brass was investigated by using potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and dezincification factor analysis etc. The results showed that with the increase of phytic acid concentration, the corrosion current density of HAl77-2 brass decreased first and then increased; with the increase of assembling time, the phytic acid layeron HAl77-2 brass became denser, however with further increase of time (for example upto 16 h), the self-assembled layer of phytic acid turned to be aged and spalled off, correspondingly, the corrosion current density increased and the impedance arc radius decreased for the brass electrode. The corrosion inhibition of the phytic acid on HAl77-2 brass was significantly increased with the addition of sodium molybdate. Besides, the synergistic action of phytic acid and sodium molybdate can weaken the dezincification of brass obviously. These results provide theoretical support for the application of the self-assembled monolayer of phytic acid in corrosion protection for brass.

The corrosion process of Q345 steel in a simulated acidic marine aerosol environment was performed by atomizing NaCl+HCl containing aerosols on the test steel surface with a home-made aerosols simulated device. The corrosion evolution of Q345 steel as a function of corrosion time was investigated by mass-loss method, X-ray diffraction (XRD), scanning electron microscopy microscopy (SEM), and electrochemical techniques. The influence of the formed rust layers on the corrosion of Q345 steel was also studied. The results show that the formed rust layers exhibit little protectiveness. The protective effect of the rust layers decreased first with corrosion time, and then enhanced slightly at last.

The corrosion behavior of copper exposed in a simulated high H₂S containing atmosphere was investigated by weight change measurement, scanning electron microscope with energy dispersive spectrometry and X-ray diffraction, while an non-equal interval grey model GM(1, 1) was established, of which the precision and forecast dependability were evaluated. The results indicates that the weight gain of Cu increase slowly at the initial stage, whereas increase rapidly at the later stage. Surface observation shows that the corrosion products on Cu were layered with cracks. The corrosion products are made up of Cu₂S and Cu₂O. The model GM(1, 1) exhibits good accuracy of fitting and higher forecast reliability.

The electrochemical corrosion behavior of X80 pipeline steel in a simulated soil solution for coastal tidal flat wetland was studied by using the polarization curves, electrochemical impedance spectroscopy and corrosion morphology observation. The results indicated that immersion time and corrosion products had a significant impact on the corrosion behavior of X80 pipeline steel in the simulated soil solution. At the initial immersion, the impedance of X80 increased slowly. With the prolongation of immersion time and the formation of a black rust layer, the impedance of X80 increased sharply. And then, since the spallation of the rust layer, the impedance of X80 rapidly decreased. The electrochemical corrosion behavior of X80 pipeline steel can be divided into three phases. In the initial phase, the corrosion rate increases slowly before the formation of a corrosion product film. In the interim phase, the corrosion rate decreases rapidly due to the formation of a protective corrosion product film. In the later phase, the corrosion rate increases again due to the partial spallation of the protective film and other facts.

The corrosion behavior of copper in culture medium inoculated with dominant actinomycetes is studied by means of microbiological test, surface analysis and electrochemical measurement method. The dominant actinomycetes are separated from the soil of Beishan in Gansu province, where is one of the preselected areas for high-level radioactive waste repository. The results show that the sustain activity of actinomycetes in a certain period could be maintained by adding high concentration culture medium for 2, 9 and 30 d after corrosion. The biofilm caused by actinomycetes is completely formed on the surface of copper after corrosion for 9 d and the hydroxide products of copper serve as the main corrosion products. The active biofilm inhibits the corrosion process of copper in the early stage, however in the later stage, while the enhanced activity of actinomycetes changes the structure and character of the double electric layer on the copper surface, thereby increases the corrosion rate and promotes the formation of corrosion pits.

Hydrogen permeation behavior of X80 steel under applied cathodic polarization and stress in 3.5%NaCl+1 g/L Na₂S solution was studied by means of a modified D-S cell combined with slow strain rate tensile machine. The effect of polarization potential on hydrogen permeation behavior and the hydrogen evolution potential were acquired by hydrogen permeation test with changing polarization potential. Besides, potentiostatic polarization hydrogen permeation test under different stress levels was performed and then the hydrogen permeation parameters were calculated by the Laplace equation. Results show that under various stress levels, the steady-state hydrogen permeation current density increased as the cathodic polarization potential decreased, and the hydrogen evolution potential was lower than -1000 mV (vs SCE). In the stage of elastic strain, hydrogen trap density decreased and the apparent hydrogen diffusion coefficient increased. After entering the stage of plastic deformation, hydrogen trap density increased and the hydrogen diffusion coefficient gradually decreased due to the generation of dislocation. The concentration of adsorbed hydrogen shows a change tendency opposite to the hydrogen diffusivities.

Rebar with and without hot-rolled was prepassivated by immersion in a simulated concrete pore solution or saturated calcium hydroxide solution, as well as anodic polarization. The corrosion resistance of the pretreated rebar was examined by immersion in an artificial rain water for 24 h. The results show that the polished rebar and the rebar with hot-rolled could both be passivated in the two type alkali solutions mentioned above, but the hot-rolled could remarkably reduce the protective performance of the passive films formed on the rebar, and promote the corrosion of rebar in the artificial rain water. All the rebar prepassivated by immersion in the two solutions or anodic polarization in the present work are not able to stand against the corrosion attack of the simulated rainwater for 24 h.

Electrochemical corrosion behavior of steel 20G used in boiler-front system was studied by means of a series of electrochemical measurements in simulated high temperature waters, which reproduced the situation of chemical conversion film formation by both the oxygenated treatment (OT) and all volatile treatment (reduction) (AVT(R)). The surface of the test steel was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results show that, when the temperature is between 40 to 140 ℃, the corrosion current density of 20G rises in the OT waters, EIS has the Warburg impedance in low frequency region. While the corrosion current first rises and then decreases in the AVT(R) waters with the increase of temperature, while capacitive reactance impedance radius in the high frequency region of EIS spectra presents a minimum value at 120 ℃ with the increase of temperature. The analysis of XRD shows that the surface of the steel forms a passivation film consisted mainly of Fe₃O₄.

Passivation behavior of a deformed stainless steel in a simulated concrete pore solution was studied by means of open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and Mott-Schottky plots. The results show that with the increasing strain, the OCP and impedance of the steel decreased, whereas the concentration of oxygen vacancy in passive films increased. This result suggests that the passivation of the stainless steel is degraded by the increasing strain. In addition, the difference in passivation between the deformed samples would not be diminished with the increasing immersion time.