Synthetically Modified Tara and Oak Gall Nut Tannin-Based Corrosion Inhibitors for Combating the Corrosive Influence of Acidithiobacillus thiooxidans on Mild Steel

Natural tara and oak gall nut tannins, which lack corrosion inhibitive properties, were modified using gum arabic and tested against microbial corrosion induced by Acidithiobacillus thiooxidans under isothermal condition (28°C). Mild steel coated with the modified tannins was exposed to the causative under aerobic and anaerobic conditions. Based on the results, corrosion inhibition efficiencies of 75% (aerobic)/59.41% (anaerobic) and 77% (aerobic)/60.87% (anaerobic) were observed for 20 mL : 30 mL and 20 mL : 5 mL oak gall nut tannin-gum arabic combinations, which gave reduced corrosion rates of 519.46 and 488 mm/yr, respectively, under aerobic condition against the value (1630.74 mm/yr) recorded for the metal coated with 25 mL oak gall nut tannin only, whereas the best tara sample (i.e., the 20 mL : 25 mL tara tannin-gum arabic combination) gave corrosion inhibition efficiencies of 71.44% (aerobic)/54.16% (anaerobic), thus giving a reduction in corrosion rate from 1678.29 mm/yr for the metal coated with 25 mL tara tannin only to 556.19 mm/yr for the metal coated with 20 mL : 25 mL tara tannin-gum arabic in aerobic condition. Hence, the modified tannins are essential in boosting the corrosion inhibitive properties of ordinary oak gall nut and tara tannins by a maximum of 67.3% in aerobic condition.