Effects of Filler Type in Bismaleimide Matrix on Corrosion Resistance of Steel in Sea Salt

Abstract

Bismaleimide (BMI) coating with and without aluminum oxide (Al2O3), silica oxide (SiO2), hexagonal boron nitride (h-BN), or organophilic montmorillonite clay 30B (OMMT) fillers on 1018 steel substrates was studied. Bilayer coatings consisting of BMI with one of the fillers at 5 wt.% for the first layer and pure BMI for the second layer were applied on 1018 steel substrates. The corrosion resistance of all coated samples was investigated through potentiodynamic polarization by using Tafel method in 4.2 wt.% sea salt solution. The results of the test showed that pure BMI coating improved the corrosion resistance by reducing the corrosion rate by 88%. Addition of 5 wt.% of OMMT or SiO2 fillers increased the efficiency of the coating in reducing corrosion rate by 99 and 97%, respectively. Adding 5 wt.% h-BN showed marginal improvements in the reduction in corrosion rates (89%). Addition of 5 wt.% Al2O3 as a filler dropped the efficiency of BMI coating to 64%. Adhesion of the coated steel was also affected depending on the filler type. Micro-hardness measurements using Vickers scale were taken to assess coating hardness, and scanning electron microscopy was used to investigate the dispersion of filler particles in the matrix.