(02) Corrosion behavior of epoxy coating / carbon steel system under the wet-dry cycles

摘要

In view of occasion that the coating/metal system served in atmosphere inevitably occurs the local degradation and thus results the exposure of metal,an electrochemical cell to simulate such system was built up.By using this cell,the corrosion behavior of epoxy coating/carbon steel system covered by a thin layer of electrolyte of 3wt％ NaCl solution under the wet-dry cycles was investigated with using electrochemical impedance spectroscopy,scanning electronic microscopy and Fourier transformation infrared spectroscopy.The results show that the corrosion rate of exposed steel reaches the largest value at the 4th wet-dry cycle and then gradually decreases,however,the corrosion rate of coated steel reaches maximum at the 6th cycle and then decreases slowly to a steady-state with cycles.Furthermore,the ions diffusion and migration between the open electrolyte layer covering on the exposed metal and the confined layer under the coating cause the corrosion products onto the exposed steel to present the layered ladder morphology from the centre of exposed steel to its periphery,however,the corrosion product formed under the coating has radial ripple morphology.