The present paper provides an understanding of an equivalent circuit for an electrochemical impedance spectroscopy （EIS）. First, an interpretation of the equivalent circuit composed of solution resistance, charge transfer resistance and electric double layer capacitance is explained, and an electrochemical impedance simulation is performed by using the equivalent circuit in order to understand the relationship between the impedance spectrum and these parameters. In addition, an application of EIS to corrosion monitoring of steel rebar in concrete is described based on the results of the impedance measurement by using probe electrodes embedded in concrete.
An introductory review on the techniques for measurement and analysis in electrochemical noise is presented. An outline of the electrode system as well as the requirements for the instruments to be used are delivered on the five representative measuring methods. A training experiment for estimating the polarization resistance of a carbon-steel electrode in acid solution is described as a walk-through of the methods of measurement and the analysis.
The principles and theories of a channel flow double electrode （CFDE） and a rotating ring disk electrode （RRDE） were explained as examples of hydrodynamic electrochemical method. In addition, some applications of CFDE to corrosion mechanism analysis were introduced. The contents of this article are presented as follows.
Principle of channel flow double electrode （CFDE）
Principle of rotating ring-disk electrode （RRDE）
Measurement of diffusion limiting current in reversible electrochemical system
Anodic dissolution of copper electrode
Real-Time Surface Observation CFDE cell
In order to establish a repainting system when rust is hardly removed completely, the corrosion resistance of paints on the surface where rust remaining surface was studied. In order to change the properties of paints, we changed the kind of resin, antirust pigment and solvent for used undercoat, and confirmed the degree of influence on corrosion protection. Corrosion resistance of solvent type paint was less influenced by the type of resin and antirust pigment. On the other hand, antirust pigment greatly affected the anticorrosive property of aqueous epoxy resin paint. The results were focused on the effect of water solvent and antirust pigment on the remaining rust surface.
In this study, we focused on the combination of blast furnace slag mixed cement that imparts alkalinity, and nitrite that has proven in rust prevention treatment method of reinforced concrete. Also influence of these compositions on rust prevention of iron and verified the mechanism was dissassed.
In order to observe the influence of alkaline powder and nitrite on iron, iron plates were immersed in aqueous solutions in which these additives were added as model samples. XPS analyses of the surface of iron plate immersed for 14 days, revealed that a large amount of adsorbed oxygen considered to nitrite ion was existed on the iron surface of the sample treated in containing nitrite.
As for the energy state of iron, only the test piece containing nitrite ion showed lower peak, suggesting the adsorption of nitrite ion to the iron surface.
In the actual steel sheet sample, an intermediate layer was composed of mainly iron and oxygen was confirmed at the interface between under coat containing nitrite and steel plate.
The purpose of this study is to establish an electrochemical technique to monitor corrosion of rebar in concrete. Electrochemical impedance spectra of probe electrodes installed in uncarbonated concrete specimens and carbonated concrete specimens were measured. As a result, charge transfer resistance of electrode/concrete interface, Rct, was about 1400 kΩ in the uncarbonated concrete, indicating that passive film was formed on probe electrode. The Rct in the carbonated concrete was about 80 kΩ and this value was 20 times smaller than that measured in the uncarbonated concrete. From these results, it was found that carbonation of concrete can be judged by the impedance measurement with probe electrodes. Electrochemical impedance spectroscopy with the probe electrodes was employed to evaluate the carbonation of a reinforced concrete structure on an expressway at 35 years after construction. The order of Rct was consistent with that in the uncarbonated concrete. In addition, the core was extracted from concrete near the probe electrodes and a carbonation test with a phenolphthalein solution was performed. As a result, the concrete at the same depth as the rebar was not carbonated. The results of electrochemical impedance spectra and phenolphthalein test were consistent. It was found that the corrosion environment of the rebar in the concrete can be evaluated by the impedance measurement with probe electrodes.