Research Concerning the Correlation between the Phenomena of Coating Degradation in Steel Coated with Various Paints and Impedance Value

Abstract

In order to make a quantitative evaluation of degradation in coatings by the electrochemical impedance spectroscopy method, it is necessary to be able to understand the relationship between each coating method and coatings' degradation phenomena and the behavior of the impedance. In this research, using test pieces for different coating methods, salt slay test, sunshine weather meter test and combined cyclic corrosion test were performed, and evaluations were made by means of the electrochemical impedance spectroscopy method and surface observations. As a result, though it was difficult to determine the corrosion resistance from the impedance prior to the test, from impedance measurements performed over time, it was found that it was possible to detect the presence of cracks and blistering. As a simple method of determining the degradation, investigations were performed observing the time rate of change of the impedance. From variations in the time rate of change of impedance, it was found that it would be possible unambiguously to detect degradation regardless of the coating method employed.

Surface Characteristics and Corrosion Behavior of Carbon Steel Treated by Abrasive Blasting

“…The impedance modulus value decreased to the range of 5-8 Ω cm 2 in the case of CAL but decreased to 3-5 Ω cm 2 in the case of CST. In particular, |Z| f = 0.1 Hz represents the coating film degradation index [29], which was smaller for CST than that for CAL, regardless of the exposure time, and it decreased when the exposure time was increased to 24 h. The larger the corroded area, the smaller the |Z| f = 0.1 Hz . The result exhibited that the larger the corroded area on the steel surface was characterized by lower the adhesion of the coating film, and more easily the coating film deteriorates.…”

“…17 The effects of corrosion and the residual grinding materials remaining on the exposed surface of CST and CAL on the coating durability were evaluated through EIS experiments. According to reference [29][30][31], it represents the values |Z| f = 0.1 Hz and f b can be used as significant parameters to evaluate the coating film degradation quantitatively.…”