Properties of sodium molybdate-based compound corrosion inhibitor for hot-dip galvanized steel in marine environment

Abstract Sodium molybdate (Na2MoO4) was selected as the corrosion inhibitor, compounded with benzimidazole, in order to prolong the service life of the hot-dip galvanized steel (HDGS) in the marine environment in this article. XRD, SEM/FESEM and EDS were used to characterize the micro-morphology and elemental composition of HDGS. Immersion corrosion test, Tafel polarization and EIS test were carried out to study the effect of compound inhibitor on the corrosion resistance of HDGS in the marine environment. The best proportion of compound inhibitor was added to the self-made waterborne polyurethane coating (WPUC), aiming to evaluate its influence on the coating performance in the marine environment by immersion corrosion test and EIS test. The results showed that Na2MoO4, as a passivation type corrosion inhibitor, bounded Zn at the active sites of HDGS coupons and created structural defects. Benzimidazole, as an adsorption type corrosion inhibitor, was attracted by electricity and adsorbed at the structural defects. Under the premise of 1 wt% total content, the optimal ratio of Na2MoO4 & benzimidazole was 9:1 and the corrosion inhibition efficiency was 99.62%. The corrosion current density of HDGS in the simulated seawater with compound inhibitor was 5.650 × 10−8 A/cm2, while that of HDGS in the simulated seawater without compound inhibitor was 1.483 × 10−5 A/cm2. The WPUC containing compound inhibitor had a small decrease in corrosion resistance due to defects created by doping at the beginning of immersion, then the compound inhibitor would play an active role in the corrosion process to make more than double the service life of WPUC.