Investigation of Cathodic Protection, Morphological, Rheological, and Mechanical Properties of Graphene/Iron Oxide Nanoparticle-Embedded Cold Galvanizing Compounds at Reduced Pigment Volume Concentration.

Abstract

The ultimate goal of this research was to produce a cold galvanizing compound (CGC) at reduced pigment volume concentration (PVC) to protect metallic structures from corrosion attacks. The influence of partial replacement of Zn by nanolayered graphene (NGr) and red iron oxide (Fe2O3) nanoparticles on the electrochemical, morphological, rheological, and mechanical properties of CGCs was investigated. Electrochemical impedance spectroscopy (EIS) was used to investigate the electrochemical nature of coatings. The EIS results revealed that the partial replacement of Zn by NGr and Fe2O3 nanoparticles enhanced the cathodic protection at reduced PVC (4:1) by improving the electrical contact between the Zn particles and the metal substrate. The Tafel scan was conducted to support the cathodic behavior of the coatings. It was found that the sample formulated solely with Zn at PVC 4:1 was dominated in physical barrier characteristics over cathodic protection. By increasing the concentration of NGr in the formulation, the corrosion potential shifted toward a more negative side, and the coating with 1.5% NGr showed the highest galvanic action at reduced PVC. Field-emission scanning electron microscopy confirmed the interconnected network of conducting particles. The coating without NGr and Fe2O3 at PVC 4:1 showed significant gaps between the Zn particles. The novelty was evidenced when micrographs showed the consistent distribution of NGr and Fe2O3 nanoparticles all over the surface, which acted as a bridge between spherical Zn particles and provided cathodic protection at a reduced PVC. The layered structure of graphene also improved the physical shielding effect of the coatings, which limited the diffusion of electrolytes and corrosion products (oxides/hydroxides) into the coatings, which was reflected by the salt spray test. The rheological properties of coatings were studied in continuous ramp, peak hold step, temperature ramp, and frequency sweep oscillation experiments. All the coatings showed good liquid/fluid properties. The coatings having less PVC displayed better flow behavior during the application due to the less frictional forces in the internal structure. All the coatings showed excellent adhesion but had different strength values. In NGr/Fe2O3-modified coatings, the strength increased from 7.14 to 14.12 Mpa at reduced PVC. The addition of NGr provided an additional chemical bonding (galvanic action) to steel, which supported the physical adhesion and increased the overall adhesion strength. A real-time scratch resistance assessment showed that all the coatings had good scratch resistance due to the solid interconnection between Zn, NGr, and Fe2O3 particles.