Electrochemically Accelerated Evaluation Of The Protectiveness Of Organic Coating

High corrosion resistant organic coatings are widely used in various industrial applications.These coatings normally have service life as long as tens of years.It is of great scientific interest and engineering significance to rapidly evaluate and compare the corrosion resistance of different long-life organic coatings.At present,the AC/DC/AC(alternating current/direct current/alternating current)technique,which combines traditional Electrochemical Impedance Spectroscopy(EIS)and negative DC voltage polarization,has been used in the lab as a convenient method in evaluating the corrosion performance of organic coating systems.However,the AC/DC/AC technique only destroys the binding force between the organic coating and the base metal and has a cathodic protection effect on the base metal during the cathodic polarization,which is inconsistent with the actual destruction of many organic coating systems.Unfortunately,published AC/DC/AC cyclic methods only study the influence of cathodic polarization on the degradation of organic coating systems,but ignore the effect of anodic polarization.Some researchers even believe that anodic polarization cannot accelerate the damage of an organic coating system.The purpose of this paper is to develop a more reasonable method for rapidly evaluating the protectiveness of organic coating systems.The paper includes two parts:(1)Different from the negative DC voltage used in the published AC/DC/AC cyclic method to cathodically polarize an organic coating system before AC EIS in each cycle,a positive voltage was employed as well in addition to a negative voltage for DC polarization in AC/DC/AC cycling.The modified AC/DC/AC technique proved to be able to accelerate the damage of an alkyd varnish coating on Q215 steel and thus quickly evaluate the coating corrosion resistance.Based on the measured impedance spectra and the recorded surface morphologic changes,the acceleration processes involved in the coating corrosion damage were analyzed,and a physical model for the accelerated failure of the coating/metal system was proposed.(2)Various corrosion acceleration tests were performed on acrylic varnish/Q215 steel systems.Their electrochemical behaviors and surface morphologies under different test conditions were compared and analyzed.The topographic features of corroded surface area of the coated metal were measured by means of non-contact optical surface profiler(OSP)technique.The back scattered electron images of the cross-sections around the corrosion area were also obtained.Based on the results,the effect of anodic polarization and temperature on accelerated corrosion damage of acrylic varnish/Q215 steel system was studied.The results show that the degradation process of the acrylic varnish/Q215 steel system accelerated by AC/cathodic DC/anodic DC/AC cycling,the anodic polarization can also facilitate the corrosion damage of the acrylic varnish/Q215 steel system.Thus,the AC/cathodic DC/anodic DC/AC cycling can accelerated the degradation of the acrylic varnish/Q215 steel system and shorten the test period without changing the corrosion mechanism.Meanwhile,temperature can be an additional influencing factor in simulating the service environment of organic coating/metal systems in the lab.By changing the temperature,the protectiveness of organic coating can be much more rapidly evaluated.