This text explained the difference between equilibrium potential and corrosion potential, relation between the change in corrosion potential and the change in corrosion rate, and the features of corrosion potential for corrosion-resistant metals by formation of passive films, on the main basis of the corrosion of iron in the acidic aqueous solution.
Polarization curve is one of many important electrochemical measurements. The polarization curve is the indispensable measurement for evaluating or understanding the corrosion behavior. The purpose on writing is to understand the relationship between the current and potential. The corrosion rate is calculated by the data of polarization behavior. The technique of Tafel extrapolation method and polarization resistance method from the polarization curve is used to find the corrosion rate.
The electrochemical measurement called a cathodic reduction method is a type of galvanostatic electrolysis. The cathodic reduction method was applied to determine the film thickness of copper oxide and copper sulfide. Plateaus are appeared in the potential vs. time curves when the commercial reagent-grade purity powder of cuprous oxide （Cu2O）, cupric oxide （CuO）, and cuprous sulfide （Cu2S） were cathodically reduced at a constant current density of −1mA/cm2. The plateau potentials of cuprous oxide, cupric oxide and cuprous sulfide are −0.7, −0.8, −1.15V vs.Ag/AgCl, respectively. A film formed on copper plate immersed in 1000 ppm NaCl and 1000 ppm Na2S solutions has been assessed qualitatively and quantitatively using cathodic reduction method. Cathodic reduction curves revealed that the films formed in NaCl and Na2S solutions were mainly composed of cuprous oxide and cuprous sulfide, respectively. The film thickness calculated from the cathodic reduction curves shows good agreement with the film thickness obtained from cross-sectional inspection.
In order to establish a new repainting method for aged steel structures, we examined the paint corrosion prevention property when painted on the steel surface where rust remains due to insufficient surface preparation of the rusted steel. Relationship between the surface condition and corrosion protection property when coated with paints was studied by various surface preparation methods on the rusted steel prepared through outdoor exposure.
The corrosion protection mechanism could not be explained by residual salt content or remained rust thickness. It was revealed that the electrochemical characteristics derived from the cyclic voltammetry method and the unevenness information analyzed from the laser displacement meter greatly influence the paint corrosion prevention on the remaining rust surface.
This study examined the surface texture formed by laser irradiation in sulfuric acid solution. Laser irradiation accelerated the localized corrosion in the solution, but other than laser irradiation area corroded. By applying passive potential, corrosion depth by laser irradiation was deeper than natural potential, and other than laser irradiation area did not corrode. Corrosion depth increased with increasing laser power and increasing number of scanning of laser.
Copper is generally known as a metal which is excellent in workability and resistant to corrosion. Copper tube has been used in a wide range of heat transfer field.
However, when ant's-nest corrosion occurs on copper tube, the progression rate of corrosion is enough fast to penetrate the tube in the early. In recent years, phosphorus which is added to the copper has been found to have an influence on progression of ant's-nest corrosion.
Test of ant's-nest corrosion on various low-phosphorus content in the copper was clarified the influence of low-phosphorus content in copper for ant's-nest corrosion.
Recently, the authors reported the improved corrosion resistance of the electro-galvanized steel coated with epoxy resin organic layers by the simultaneous additions of flaky Al and particulate Ni powders for the use in fuel tanks. In order to understand the roles of Ni and Al powders in the coatings on the corrosion behavior of the coated electro-galvanized steel, the electro-galvanized steel was coated with epoxy resin layers containing either Ni or Al powders, and their corrosion behavior was examined by the corrosion immersion tests in aqueous solution containing formic acid, acetic acid and NaCl, potentiodynamic polarization measurements, electrochemical impedance spectroscopy （EIS）, and oxygen gas and water vapor permeation measurements. Both Ni and Al powders in the organic coatings accelerated the corrosion. The potentiodynamic polarization curves disclosed the increased anodic and cathodic currents and the EIS study showed the reduced coating resistance by the addition of Ni or Al powders. Findings in this study suggested that the improved corrosion resistance of the coatings containing both Al and Ni powders were not simply explained by the corrosion behavior of the coated steel containing only Ni or Al powders and a possible synergistic effect of Ni and Al powders in improving the corrosion resistance is discussed.