Study On The Invalidation Mechanism And EIS Of Several Coating Systems In UV/SALT Bringe Dipping Condition

Failure analyses of heavy-duty anticorrosive single coating layer and composite coatings under the influence of ultraviolet ray (UV)/salt brine dipping were studied in this dissertation. Electrochemical impendence spectroscopy (EIS) and physical methods (FTIR,SEM,XRD) were used to characterize the invalidation mechanism of the coating systems. Water uptake, desquamation rate and the corrosion resistance of coatings were also studied by using electrochemical parameters.Top coating chlorinated rubber invalidated in a short time. UV was the more important factor than salt brine dipping in the degradation of the coating. Fourier transform infrared spectroscopy (FTIR) analysis showed that breakdown occurs in the C-H of the coating after aging, some hydrophilic group-OH was formed simultaneously. Scanning electron microscope (SEM) was employed to analyze the morphology of coating and the results show that chlorinated rubber was blooming in a short time, and the blooming made the coating form many pores and holes. So electrolytes could go though the coating easily and conduced the coating invalidation. Study on corrosion occurring in zinc-rich epoxy coating process suggested that ultraviolet radiation make the epoxy degradation, but the zinc powder continue protecting the coating by sacrificial anode. The corrosion products also block the gap, in the later exposure stage, zinc powder had been oxidized completely and could not provide the protection anymore. Zinc-rich epoxy coating was invalidation.Analysis on water uptake of heavy-duty anticorrosive single coating layer and composite coatings was studied. The results showed that water uptake curves could compare the protection of difference single coating layer and the curves also present two stage absorptions obviously for single coating layer, but three stages absorption for three layers composite coating. And the water uptake curves of composite coatings had a close connection with kinds of each layer.Some studies on invalidation of two epoxy coatings were carried out by using electrochemical parameters. Theta at 10 kHz, the relative permittivity (e_r), break-point frequency (f_b) could be easily extracted with no error in calculation and they have a very good agreement in evaluating the protection capability of epoxy coating. These studies provided rapid methods to evaluate protective property of coatings.