Electrochemical monitoring of atmospheric corrosion phenomena

An atmospheric corrosion monitor (ACM) which consists of CuZn or Cu/steel couples, has been used to study various aspects of atmospheric corrosion. Calibration of ACM's is carried out under 1 ml of distilled water. Measurements under 10−510−1N KCl show that the conductivity of the electrolyte is not an important parameter in determining the amount of current flow. A detailed study was related to the effect of salt particles on atmospheric corrosion. While no current flow and no corrosion occurred on clean surfaces up to r.h. ≈ 95%, large increases of the galvanic current were observed when salt particles were placed on the ACM surface provided that the relative humidity in the test cell was higher than the r.h. value of a saturated solution of the salt particle applied. The ACM has also been used to monitor changes in the composition of gaseous atmospheres (air, N2, N2 plus SO2). Outdoor exposure of the CuZn and Cu/steel ACM suggests that this instrument can be used not only to monitor time-of-wetness, but also the corrosivity of a test environment.