Enhancement of physico-mechanical and electrochemical properties of zinc-rich epoxy coatings by optimised interfacial behaviour of reduced graphene oxide

High porosity and low utilization of zinc powder are two major challenges for conventional zinc-rich epoxy (ZRE) coatings. Although these two challenges can be overcome by the addition of graphene material, it also brings new challenges due to the addition of more fillers leading to degradation of mechanical properties and galvanic coupling corrosion. In this work, the effect of the interfacial behaviour of reduced graphene oxide (RGO) in coatings on the mechanical properties, shielding properties and cathodic protection properties of RGO/ZRE composite coatings has been comprehensively evaluated. In terms of mechanical properties, RGO additions of 0.3 wt%, 0.75 wt% and 1.2 wt% exhibited RGO enhancement stage, RGO interfacial compatibility influence stage and RGO agglomeration influence stage. In terms of cathodic protection performance, RGO additions of 0.3 wt%, 0.75 wt% and 1.2 wt% exhibited a zinc powder utilization enhancement stage, an accelerated zinc powder consumption stage by galvanic coupling corrosion, and a significantly reduced initial shielding stage, respectively. The RGO/ZRE composite coating has the best comprehensive performance at 0.3 wt% RGO addition, and the composite coating did not crack or peel off in impact and bending tests, the coefficient of friction was 0.64465, the width of abrasion mark was 1.18 mm, and the coating adhesion was 5.81 MPa. The 0.3 wt%-RGO/ ZRE composite coating has insignificant galvanic coupling corrosion and has a cathodic protection time of 720 h, and significantly higher low-frequency impedance modulus than the ZRE coatings. The shielding, mechanical, and cathodic protection properties of ZRE coatings can be significantly improved with appropriate RGO additions, and the galvanic coupling corrosion and agglomeration induced by the high RGO content are the key factors limiting the application of RGO in the coatings.