Corrosion Inhibition of Aluminium in Acidic Medium by Different Extracts of Ocimum gratissimum

Aims: This study is aimed at using plant extracts to prevent corrosion of aluminium in acidic medium. The inhibition efficiency of different extracts of 1M HCl, ethanol and distilled water were determined.
Study Design: Gravimetric method was used for the analysis.
Place and Duration of Study: Department of Chemistry, Federal University of Technology, Owerri, Nigeria, between March and November, 2011.
Methodology: Aluminium sheets of AA1060 and purity 98.98% was used. Each sheet was mechanically press-cut into coupons of dimension 3 cm x 3 cm. The solvents used for extraction of ocimum gratissimum leaf were 1M HCl, ethanol and distilled water, respectively. A hole with diameter 0.5 cm was drilled in each aluminium coupon and suspended in beakers containing test solution using glass hook. The weight loss was determined by retrieving coupons from test solutions at intervals. The coupons were weighed after retrieving. The different in weight was taken as weight loss of aluminium.
Results: The percentage of inhibition efficiency (% I.E) was calculated at 303 K and 333 K, respectively. The result indicates that % I.E increases as concentration of inhibitor increases. The trend of inhibition efficiency was in order: Distilled H2O > C2H5OH > 1M HCl. The result indicates that increase in temperature decreases inhibition efficiency and degree of surface coverage. The result shows that apparent activation energy Ea increases as inhibitor concentration increases. The activation energy of distilled water extract range between 45.02 to 79.90 kJ/mol. While the activation energies of ethanol and 1 M HCl extracts of the inhibitor ranges between 35.12 to 72.93 kJ/mol and 26.60 to 65.25 kJ/mol, respectively. The experimental data obtained corroborated with Langmuir and Flory Huggins adsorption isotherms.
Conclusion: This study indicates that different extracts of Ocimum gratissimum inhibits aluminium surface in presence of 1M HCl. The result of the analysis shows that inhibition efficiency and degree of surface coverage decreases as temperature increases. The activation energy of different extracts increases as concentration of inhibitor increases. The negative values of ∆Gads shows that adsorption of inhibitor on surface of aluminium is spontaneous.