Improvement of the anticorrosion ability of an inhibitor pigmented epoxy coating with hierarchical porous ZnO microspheres loaded with mimosa tannin

Purpose This paper aims to assess the positive impact on anticorrosion performance of a corrosion inhibitive pigment-based epoxy coating, when smart inhibitor carriers (SICs) consisting of Mimosa tenuiflora (MT) tannin-loaded ZnO nanosheet-assembled microspheres with a shell of tannic acid (TA)-Fe (III) complex are incorporated at a concentration of 0.5 wt.%. Design/methodology/approach Steel coupons were coated with a commercial epoxy resin pigmented with silicate-based inhibitor, in the absence and in the presence of the SICs. Samples with an artificial defect were exposed to a 3.5 wt.% NaCl solution and polarized at −0.7 V vs Ag/AgCl to simulate conditions where cathodic protection (CP) is switched off temporarily. Evaluation of the corrosion protection performance was carried out with electrochemical impedance measurements during 28 days of exposure to the corrosive solution. Scanning vibrating electrode measurements were also carried out for selected samples. Findings The SICs produced a positive impact on the anticorrosion performance of the coating only during the first 21 days of exposure to the chloride solution. The progress of corrosion for the sample with added SICs was significantly slower in that period, as compared to that observed for steel coated with inhibitive pigment-based epoxy resin. Originality/value The outcomes demonstrated that the ZnO/[MT]@TA-Fe (III) SICs can provide enhanced corrosion protection relative to inhibitor pigment-based epoxy coating. Such additional protection can be extremely useful for systems where organic coating is used in combination with a CP system, and cathodic protection is temporary turned off.