Study On Electrochemical Noise And Its Application In Corrosion Detecting

Electrochemical Noise (EN) refers to spontaneous fluctuations appearing in the interface between electrode and solution whether at a certain potential or fixed current. The unique features of EN measurement make it a leading role in the field of corrosion electrochemical study. In this paper pilot studies were made on the data analysis techniques of EN technology. EN technique was also used in some specific systems to study corrosion of metals. Some achievements have been made. Removing dc trends from the raw EN data using polynomial fit proved to be necessary and feasible. Standard deviation of current noise is qualified to compare corrosion rates of metals with the same corrosion type. R_n and R^o_sn(f) can be used to judge the corrosion resistance of different metals or detect the changes of corrosion resistance of the same material during different corrosion periods. Larger is the dc limit of current PSD, more severe does the metal corrode. And the slope of potential PSD can tell us the corrosion inclination of the metal, and when the slope is above -20dB/decade local corrosion probably happens while on the contrary uniform corrosion or passivation may appears. EN features of LC4,LY12 alloys in EXCO solution were studied. By studying the EN featuring parameters such conclusions were made that in the early stages of immersion, the corrosion was severer but the corrosion products brought out later hinder the development of the corrosion therefore the corrosion rate was high at the beginning but low later. And research shows that the corrosion resistance of LY12 is better than that of LC4 in EXCO solution. Comparisons of EN featuring parameters among various brass specimens were made and HAl77-2 blank specimen was verified to have the highest corrosion resistance. The corrosion resistances of filmed brass specimens are greatly better than that of blank specimens. The resistances of HAl77-2 and HSn70-1 specimens immersed in seawater for 8 years lowered for the presence of protective corrosion product films. But the corrosion resistance of HSn62-1 lowered down a lot after immersed for 8 years in seawater. By calculating the slopes of potential PSD of the specimens, conclusion that all the brass specimens are inclined to be under local corrosion.