Evaluation of Corrosion Inhibition Efficiency of Local Plant Extracts on Mild Steel in Simulated Industrial Cooling Water Systems in Kaduna State

Industrial cooling water systems in Nigeria are susceptible to metal corrosion, leading to equipment failures and costly maintenance, with conventional phosphate-based chemical inhibitors raising environmental concerns. This study evaluates the corrosion inhibition efficiency of extracts from three locally abundant plants, specifically Azadirachta indica, Carica papaya, and Tithonia diversifolia, on mild steel coupons immersed in simulated industrial cooling water prepared to mimic the water chemistry of a textile factory cooling loop in Kaduna State. Corrosion experiments were conducted by the weight loss method over immersion periods of 24, 72, 168, and 336 hours at temperatures of 25 and 60 degrees Celsius. Inhibition efficiency, corrosion rate, and surface coverage were calculated. Electrochemical impedance spectroscopy and potentiodynamic polarisation measurements were performed to elucidate inhibition mechanisms. The adsorption behaviour of inhibitor constituents was modelled using Langmuir and Temkin isotherms. Results show that the methanol extract of Azadirachta indica leaves achieved the highest inhibition efficiency of 88.4 percent at an optimum concentration of 500 milligrams per litre, acting as a mixed-type inhibitor according to Tafel slope analysis. Inhibition efficiency was temperature-dependent, decreasing with increasing temperature. FTIR analysis of treated coupon surfaces confirmed the formation of a protective organic film. The findings demonstrate the viability of these plant extracts as eco-friendly corrosion inhibitors for industrial cooling water applications in the textile manufacturing context. Keywords: corrosion inhibition, plant extracts, mild steel, cooling water, Kaduna State