Influence Of Painting On Rusty Steel On The Anti-corrosion Performance Of Epoxy Coatings

In order to ensure the protection of the anti-corrosion coating on the steel, usually need toblast-clean the substrate to Sa2.5above before coated. Unfortunately, sometimes because ofactual working conditions or construction conditions, the surface cleanliness can not reach therequirements, generally less than St2. Therefore, it is necessary to research the corrosionbehavior of a paint coated on the surface with the rust. The influence of the corrosionprotection of the coatings on the surface with the rust was studied by Water Absorption Test,DSC testing, Electrochemical Impedance Spectroscopy (EIS) and Pull-Off Adhesion Test. Theresults of this paper was:(1) The failure processes of the varnish coatings with polyamide651as a curing agentcoated on the white metal made by blast cleaning or by rust hand cleaning were similar.Because of the loose rust layer covered on the substrate, the adhesion of the coating with rustgreatly decreased with immersion time. The loose rust layer promotes the corrosion of themetal, greatly reduces the anti-corrosion performance of the coating.(2) As a corrosion inhibitor in the coating, phytic acid did not change the failure processesof the coating, however the addition of phytic acid significantly improve the wet and dryadhesion, enhance the shielding properties of the coating, decrease the interface corrosionbeneath coating. The best corrosion protection of the coating were obtained while the additionof3wt%of phytic acid in the coating.(3) As a corrosion inhibitor in the coating, tripolyphosphate aluminum improved theadhesion of the coating gently, enhance the shielding properties of the coating, decrease theinterface corrosion beneath coating. The best corrosion protection of the coating wereobtained while the addition of30wt%of tripolyphosphate aluminum in the coating.(4) As an epoxy curing agent, Cardolite2015significantly improved the wet and dryadhesion of the coating. Comparing with the coating cured by polyamide651, the corrosionresistance was significantly higher. During immersion1200h, there are only two RC timeconstants. The addition of2wt%of phytic acid in the epoxy coating with Cardolite2015curing agent reduced the shielding properties of the coating, improved the corrosionprotection of the interface beneath coating, had better anti-corrosion performance than thevarnish coating on the white metal.