Effect of UV aging on electrochemical behavior of an anticorrosion paint

The effect of the photochemical artificial ageing (UVA) on the electrochemical behavior of an anticorrosion paint has been studied by electrochemical impedance spectroscopy (EIS). Two types of coatings have been tested: a formulated tri coat system (FS) formed by a primer (epoxy), an intermediate coat (epoxy) and a topcoat (alkyd) which presents a total film thickness of 240 μm and, on the other hand, a non-formulated varnish (NFV) which presents a total film thickness of 70 μm. Panels have been aged in a QUV chamber and the maximal exposure's time was about 1000 h. EIS testing were carried out with a naturally aerated 3% NaCl solution.Results present Nyquist diagrams for formulated system (FS) and corresponding varnish (NFV) versus UV exposure time after immersion. Evolutions of water uptake for the FS system and the NFV varnish are also presented. In the two cases, we can observe that UV treatment generates a decrease of up taken volume water due to a post-reticulation process. The post-reticulation process concerns both the varnish and the formulated system but its effects are different in the two cases because of the thickness and formulation influences.In order to precise that result, water uptake evolutions according to UV exposure time have been studied for formulated system and NFV varnish, looking at saturation stage. A post reticulation stage followed by a degradation stage is observed. The evolution of the coefficient of diffusion to half sorption according to UV exposure time completes the previous interpretation.