The substitution of zinc particles with graphene nanoplatelets in zinc-rich epoxy coatings

Abstract

Conventional zinc-rich epoxy (ZRE) coatings require >70 wt% zinc to ensure effective sacrificial cathodic protection. However, high zinc content leads to porous microstructures, reduced adhesion, and environmental concerns such as zinc leaching and elevated carbon emissions. This study explores a more sustainable alternative: reducing zinc content to 60 wt% while incorporating minimal graphene additions (≤0.2 wt%). Coatings were evaluated using electrochemical impedance spectroscopy (EIS), salt spray testing, microscopy, and adhesion tests. At 0.05 wt% graphene, the 60 wt% ZRE coating exhibited enhanced cathodic protection beyond 600 h, outperforming traditional 80 wt% systems. This was attributed to improved interparticle connectivity and reduced porosity, as shown in microstructural and adhesion results. Conversely, increasing graphene to 0.2 wt% reduced the sacrificial effect, likely due to excessive polarization of zinc particles, which hindered anodic dissolution. While barrier properties improved (|Z|₀.₀₁Hz ∼3 × 10⁴ Ω·cm² after 556 h), cathodic protection diminished. This highlights the need to avoid excessive graphene loading, which may shift the protection mechanism toward passivation. Environmentally, the approach cuts zinc usage by 25%, reducing metal runoff and carbon impact. Overall, the study demonstrates the importance of optimizing graphene-to- zinc ratios to develop durable, eco-friendly, and high-performance anticorrosive coatings.