Concentration Dependent Effects of Green Inhibitors on Gravimetric Indices of Corrosion Linked Metal Integrity

The use of plant phytochemicals as anti-corrosion agents is gaining widespread acceptance. This study was designed to evaluate the concentration dependent effects of green inhibitors from Pennisetum purpureum (elephant grass) Mangifera indica (mango leaves) and Heveabrasiliensis (rubber leaves) on some gravimetric indicators of corrosion linked metal stability. The material strength, weight loss, corrosion rate of the metal coupons and the inhibition efficiency of the green inhibitors were determined after 3 days. Our findings revealed a slight increase (p=0.05) in material strength (MS) of Pennisetum purpureum inhibitor treated - iron and steel at 100% inhibitor relative to their controls (minus Pennisetum purpureum -iron and steel coupons) and also relative to the (+Mangifera indica inhibitor and + Heveabrasiliensis -treated iron and steel coupons at 50% concentration. The material strength for P. purpureum-treated aluminium was slightly increased (p>0.05). There was also a slight decrease (p>0.05) in the weight loss of P. purpureum exposed iron coupon at a 100% inhibitor when compared to the controls, 50% P. purpureum exposed iron coupon and at 50 and 100% H. brasiliensis and M. indica-treated iron coupon in 15% acid medium. Pre-treatment of test metals with the combined green inhibitors at 50 and 100% concentration caused a significant (p≤0.05) decreases in weight loss and increases in material strength of all three test metals when compared to their respective inhibitor-free controls, and when treatment was done with a single green inhibitor. There was a slight decrease in the corrosion rate of iron, aluminium and steel coupons in acid medium treated with 50% P. purpureum inhibitor when compared to the same parameter of other green inhibitors evaluated in this study, albeit, the reduction was not significant (p>0.05). There was a further decreases (p≤0.05) in the corrosion rate of iron and steel when the combined green inhibitors at 100% concentration(+All green inhibitors (PAGI) at 100%) were used relative to when treatment was done using individual green inhibitors separately. The inhibition efficiency of the combined green inhibitors at 50% concentration on aluminium, iron and steel was 86% 57% and 60% respectively. While the treatment of the same coupons with combined inhibitors (+PAGI at100% concentration) increased the inhibition efficiency to 88% 75% and 74% for aluminium, iron and steel respectively. Overall, the study revealed the possible anti-corrosion effects of the extracts of H. brasiliensis, P. purpureum and M. indica on aluminium, iron and steel coupons and the synergism in anti-corrosion characteristics of these green inhibitors when combined. This study establishes the anticorrosion effects of H. brasiliensis, P. purpureum and M. indica extracts.