The Effects Functionalized Graphene Nano-Particles Have on the Corrosion Inhibition of Iron and Galvanised Steel

The ever present need to replace chromate in anti-corrosive coatings has lead to a number of alternative chemistries. Graphene is one such proposed chemistry that has garnered a large amount of interest in recent years. Ongoing studies at Swansea University have demonstrated effective corrosion-inhibition, to both iron and galvanised steel surfaces, by utilising the anti-corrosive properties of graphene nano-pigments (GNPs) dispersed within a polyvinylbutryal (PVB) carrier. In-situ scanning Kelvin probe (SKP) techniques have shown GNPs’ ability to stall and resist underfilm delamination of organic PVB systems to both iron and galvanized surfaces. Current theories attribute graphene inhibition to an electrochemical and mass-transport blocking effect. 

Throughout Swansea University’s studies the GNPs have been supplied by Haydale Ltd, who produce these nano-pigments by means of graphite exfoliation. HDPlas™ GNPs, produced by Haydale, are particles of graphene that have been plasma processed to modify the surface of the nanomaterials for enhancements in application. The plasma process imparts chemical species onto the surface of the GNPs; this plasma surface modification does not penetrate into the bulk of the material, leaving the GNPs undamaged. Two of the available functionalities are carboxyl (COOH) and amines (NH_x). In this study the effect that these functionalities have on the GNPs’ corrosion inhibition is examined by use of the SKP technique. The functionalized GNPs (FGNPs) are thought to have greater adhesion properties to the surfaces of the metal substrates on account of their polar structures. In order to test this hypothesis, several pigment volume fractions were tested (ranging from 5% to 25% by weight and dispersed within a PVB system) using a standard SKP setup. Figures 1 and 2 are plots of both delamination time and delamination rate versus the respective FGNP loading, coated onto iron substrates. Both demonstrate that, at concentrations >15%, both functionalized groups show an increased delay to initiation and reduced delamination rates. Despite showing similar delamination rates, the NH₂ functionality shows far slower initiation times, thought to be attributed to greater adhesion and keying to the iron substrate. The benefits that functionalization of GNPs provide to overall corrosion inhibition is discussed.