EIS Study On The Invalidation Mechanism Of Sevearal Heavy-Duty Corrosion Protection Coating

In this paper, the effect of the failure of commonly used heavy-duty coating process in the ultraviolet radiation and 3.5% NaCl was researched by electrochemical impedance spectroscopy, combined with scanning electron microscopy and infrared spectroscopy of the coating failure mechanism, and the corrosion resistance of the coating and the absorption changes under different matching system by electrochemical parameters was comparesd, the main results are as follows:Firstly, the failure process of inorganic zinc-rich/micaceous iron oxide epoxy/aliphatic polyurethane composite coating in 3.5%NaCl solution under ultraviolet irradiation (UV) was studied by Electrochemical Impedance Spectroscopy (EIS) and Fourier Transform Infrared Spectroscopy (FT-IR). UV irradiation significantly accelerated the failure process of the composite coating in NaCl solution. The effect of UV on failure process of the coating system in 3.5% NaCl solution may be divided into two stages:In the early stage, the thermal effect generated by the ultraviolet irradiation is the main reason leading to the increase in coating porosity, but this effect is not serious and the coating remains high impedance and good protection ability. In the latter stage, the fracture of polymer chains in the coating by UV irradiation is the main factor resulting in quick decrease of coating performance. C-N and C-O bonds in polyurethane coating are broken by UV irradiation, leading to quick increase of coating porosity and quick decrease of coating resistance. Under the condition of immersion plus UV irradiation the failure process is divided into three phases:rapid infiltration of electrolyte solution, increase of coating porosity because of heat irradiation and breakage of polymer bondes in coating by UV irradiation.Secondly, the failure process of inorganic zinc-rich/micaceous iron oxide epoxy/aliphatic polyurethane composite coatings in 3.5%NaCl solution under ultraviolet radiation (UV) was studied with Electrochemical Impedance Spectroscopy (EIS). The result shows that the protective property of the coating increased with the total coating thickness, but the change got gradually smaller as the coating thickness increased. The shielding effect of the micaceous iron oxide epoxy was mainly reflected in the initial period of the service process, while in later period the coating performance largely depended on the zinc-rich primer. The change of the water uptake in the composite coating presented a 'three stage' characteristic. The thinner the coating, the quicker the water absorption to get saturation, and the faster the protective property of the coating decreased. Thirdly, phase angle with the medium frequency band were used to evaluate protection performance under different supporting systems. The results show that the protective effect of the inorganic zinc-rich and organic zinc-rich is roughly the same under the same corrosion condition, while the acrylic polyurethane is better than the aliphatic polyurethane; while the evaluation parameters (IF zone frequencies 10Hz) does not change evaluated by phase angle of the medium frequency.Finally, the reliability of the rapid evaluation system was verified by analysis the failure process of several other coating systems.