The inhibition effect of tannic acid on mild steel corrosion in seawater wet/dry cyclic conditions

The inhibition effect of tannic acid on mild steel corrosion in seawater wet/dry cyclic conditions was studied by weight loss and electrochemical methods. Result of the polarisation curves shows that corrosion current density decreases from 47.85 μA cm−2 to 6.67 μA cm−2 after tannic acid is added; charge transfer resistance remains stable in the electrochemical impedance spectra. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared reflection are performed to study the corrosion inhibition. The inhibition effect of the compound is attributed to ferric tannate film formation on the steel surface, which is relatively stable during wet/dry cycles.

► Tannic acid has good inhibition effect for mild steel in wet/dry conditions.
► Significant difference in rust appearance is observed by means of SEM.
► Tannic acid acts as a cathodic-type inhibitor.
► The XRD and FT-IR analyses support the weight loss, EIS, and polarisation data.