(588g) Synergistic Effect of Chlorella sorokiniana and Neem Leaves on Corrosion Inhibition of Steel in Alkaline Medium

Corrosion of steel in alkaline environments, particularly in reinforced concrete, remains a critical challenge due to its economic, safety, and environmental repercussions. While conventional corrosion inhibitors offer mitigation, their ecological footprint necessitates sustainable alternatives. This study explores the synergistic potential of Chlorella sorokiniana (microalgae) and neem leaf extract (Azadirachta indica) as a green, biodegradable corrosion inhibitor for steel in alkaline media (pH 12.5). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization revealed a remarkable inhibition efficiency of 92% when combining 200 ppm neem extract with C. sorokiniana biofilm, outperforming individual components (75% for neem alone, 68% for microalgae alone). Weight loss measurements corroborated these findings, showing a corrosion rate reduction from 0.148 mm/year (unprotected steel) to 0.012 mm/year with the dual inhibitor system. Surface characterization via SEM confirmed the formation of a dense, adherent protective layer, while XPS analysis identified synergistic interactions between neem-derived phytochemicals (e.g., azadirachtin, nimbin) and algal extracellular polymeric substances (EPS), which facilitated passivation through chelation with Fe²⁺/Fe³⁺ ions. The hybrid inhibitor also demonstrated stability over 30 days, with minimal efficiency loss (<5%), highlighting its durability. This work establishes a paradigm for eco-friendly corrosion mitigation, combining renewable biological resources to enhance material longevity in infrastructure applications while aligning with global sustainability goals.