A study on localized corrosion behavior of 304 stainless steel in the presence of Allium Sativum extract inhibitor using electrochemical noise analysis

Highlights: • Allium Sativum extract inhibited 304 SS from localized corrosion in chloride medium. • N, S, O & C prevent the 304 SS surface from corrosion by forming a protective layer. • Garlic as green inhibitor decreased the radius of metastable pits on 304 SS surface. • Phosphate compounds hindered the pitting corrosion by filling the pit nuclei. The present work aimed to investigate the Allium Sativum (garlic) extract as a localized corrosion inhibitor for AISI 304 stainless steel in hydrochloric acid medium. The Allium Sativum extract was characterized by FTIR and UV–visible spectroscopy. The corrosion resistance of the 304 stainless steel was studied using electrochemical noise (EN), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). According to the EN analysis, it was demonstrated that the addition of the inhibitor up to the optimum amount (8 cc L⁻¹) increased the spectral noise resistance. The shot noise results illustrated that the distribution of the frequency of events shifts to a higher frequency region in the presence of Allium Sativum inhibitor, which is an indicator of less localized corrosion of stainless steel. Stochastic analysis for pit initiation and growth showed that although the pits initiation rate increased in the presence of the Allium Sativum extract because of its antioxidant nature, the formation of stable pits with a radius larger than 30 μm was significantly inhibited due to the filling of the metastable pits with phosphate compounds. Microscopic corrosion morphology confirmed the idea of the formation of phosphate compounds on the pits nuclei and re-passivation of the steel surface.