Evaluation of Cassia fistula fruit extract as a sustainable corrosion inhibitor for mild steel in 5% HCl

This study investigates the corrosion inhibition performance of Cassia fistula fruit extract (CFFE) derived from the family of Fabaceae plant, for mild steel (MS) in 5% HCl solution that has been utilized as industrial scale cleaning medium. The phytochemicals profile of CFFE played the major role of adsorption on the MS surface for its inhibitive character against corrosion and has been characterized by Gas chromatography-Mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FT-IR). The corrosion studies such as gravimetric (weight loss), electrochemical (EIS and PDP) and surface studies such as FTIR, UV-Vis, SEM/EDS, XPS, AFM and Contact angle were undertaken to evaluate the performance of CFFE. CFFE showed optimum inhibition efficacy of 94% for 500 ppm concentration at 323 K in weight loss analysis, underscoring its performance at lower dosage and better stability at elevated temperatures. The EIS analysis indicates an upsurge in charge transfer resistance Rct (79.776 to 525.799 Ω.cm2) and a drop in double-layer capacitance Cdl (1.991 × 10−4 to 1.817 × 10−5 Fcm−2), so confirming the establishment of a resistant thin layer. PDP indicates mixed-type behavior of CFFE by impacting anodic and cathodic processes. The surface inspection revealed that robust adsorption of components of CFFE occurred on MS via physical and chemical mode of adsorption assisted by hetero atoms and π complexes. Adsorption by CFFE on MS has been proven by Langmuir adsorption isotherm model. CFFE derived from biological source showed strong adherence to MS and found as promising biodegradable/non-hazardous inhibitor and genuine replacement for synthetic corrosion inhibitors in industrial units.