Characteristic Studies On Local Corrosion Of Coatings By Electrochemical Noise

The electrochemical noise (EN) technology as a new means of corrosion detection has obtained the good and rapid development. It is a detection method of in situ, non-destructive and no interference and can be sensitive to reflect the change of electrode surface corrosion especially local corrosion process. Its test method and equipment are simple, which will play a huge role in monitoring corrosion behavior under the condition of long-distance, on-line continuous detection and bad environment.The EN technology is studied in this paper. The corrosion process of the electrode is researched in depth by analyzing time-domain and frequency-domain characteristics of electrochemical noise together with morphology features. Firstly, one-to-one relationship between the electrochemical signals of coating system and reaction process of electrode surface was found. Based above study, use EN technology to evaluate protective performance of Al-based hydrotalcite coating and intelligent coating with self-healing function.The corrosion behavior of Al-based coatings with different pores in3.5%NaCl solution is characterized by electrochemical noise analysis technique. The results show that the time-domain spectroscopy of the electrochemical noise can be used to predict the occurrence of local corrosion and qualitatively distinguish the type of the corrosion. It was found that the current standard deviation σI, noise resistance Rn and current white noise levels W can reflect the corrosion intensity. When the corrosion occur,σI and W tend to increase, but Rn tends to decrease.The corrosion behavior of Al-based hydrotalcite coatings in3.5%NaCl solution was characterized by electrochemical noise analysis technique. The result showed that the pitting corrosion process of coatings could be divided into four different stages. At passivited stage, the EN fluctuated slightly, and the parameters were relatively stable. At metastable pitting nucleation stage, the EN began to fluctuate obviously, σV,σI, W and fc increased, Rn decreased. At stable pitting corrosion stage, the potential declined rapidly and rised slowly, meanwhile various parameters tended to extremum and Li was close to1. At later pitting corrosion stage, the EN fluctuated slightly and various parameters tended to be weakened.The corrosion behavior of self-healing coatings in3.5%NaCl solution was characterized by analysing of electrochemical noise technique. It was found that electrochemical noise fluctuation of time domain spectrum corresponds to the release of corrosion inhibitor of self-healing coatings. The release of the corrosion inhibitor can inhibit generation of pitting corrosion nuclear, which would result in an increase of noise resistance but a decrease of potential and current standard deviation in time domain statistical, meanwhile the white noise level is reduced, linear slope of sloping part is down in frequency domain statistical, leading to enhance the corrosion resistance of coating.