Anticorrosive performance of AA6061 aluminium alloy treated with sol-gel coatings doped with mangrove bark tannins in 3.5 wt% NaCl

Two different tannin extracts (70% acetone and methanol) were isolated from mangrove bark. Isolated tannins were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, Folin-Ciocalteu method and antioxidant assay. The inhibitive effects of sol-gel coatings doped with mangrove bark tannin extracts (0, 10, 50 and 100 ppm) on the corrosion protection of aluminium alloy were evaluated via potentiodynamic polarization, electrochemical impedance spectroscopy, and electrochemical noise analyses. It was revealed that sol-gel coatings doped with tannin extracts yielded high percentage inhibition efficiencies (% IE) of more than 80% than that of in the absence of tannins where 70% acetone tannin extract doped sol-gel coated aluminium alloy offered % IE of 87.20%. Electrochemical noise analysis depicted that aluminium alloy coated with 70% acetone tannin extract doped sol-gel film experienced the least current noise fluctuation among all tested samples. SEM-EDX analyses verified that the developed sol-gel coatings were able to inhibit the local dissolution of aluminium alloy. The present study unveiled the potential of mangrove bark tannins in enhancing the anticorrosive performance of TEOS based sol-gel coatings over AA6061 Al alloy surface. (paper)