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.
Recently, in Japan, an increasing number of community structures that have been built more than 50 years ago have required appropriate management to maintain their functionality. The painted steel structures are regularly repainted to maintain their corrosion resistance. Excellent corrosion resistance can be achieved by thoroughly removing the rust and residual coating film on the steel surface during surface preparation using either blasting or wire brush treatment. The wire brush treatment is very workable even when there is a problem with corrosion resistance after coating. This research examined surface preparations using three different types of wire brush treatments. Furthermore, the organic zinc-rich paint was applied to steel plates that had undergone different surface preparations, and the corrosion resistance of each painted steel plate was investigated by accelerated corrosion testing. The results demonstrated that the paint sample that was subjected to surface preparation using either a nickel-or zinc-plated steel wire wheel brush exhibited better corrosion resistance than that exhibited by the one subjected to surface preparation using a steel wire wheel brush without plating. This was caused by the difference between the corrosion barrier properties of the zinc-based corrosion product layers that were formed in the painted samples.
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