Revisiting inhibition stability of 2-mecaptobenzimidazole as corrosion inhibitor against saline corrosive media: A combined in-situ and ex-situ investigation

• The presence of 2-mercaptobenzoimidazole initiates effective surface film formation upon AA6061. • Inhibitor film evolution was revealed through both in-situ and ex-situ surface analytical approaches. • Time-dependent inhibition performance was correlated with the mechanical properties of developed inhibitor film. • Upon further inhibitor exposure a gradual softening effect was determined leading to reduced protection efficacy. Developing long-term corrosion protection through inhibitor molecules requires in-depth understanding of dynamic film formation processes under corrosive media. To this end, this study explores time-dependent film growth of inhibitor 2-mercaptobenzimidazole (2-MBI) upon Al alloy 6061 (AA6061) in saline solution through both in-situ and ex-situ surface analytical approaches. Electrochemical study reveals that the inhibition efficiency increases to the 94 % after treatment by 2-MBI for 90 min, associating with the growth of porosity-free elastic film formed over AA6061 as evidenced by high-resolution AFM imaging. The self-assembly film grew from 30 min with a Young’s modulus value of approx. 8000 MPa which has increased to nearly 30000 MPa after 90 min, indicating pronounced surface film cohesion. A subsequent film softening with extended treatment was observed in which nano-/micro-sized pores emerged significantly in the film structure from 12 to 24 h, resulting in reduced inhibition efficiency to 71 %. XPS results suggest that the presence of S and N heteroatoms promote active chemical adsorption. Further inhibitor exposure gives rise to physisorption process thickening the inhibitor layer with increased porosity. However, the defective nature of subsequent layer formation casts detrimental effects by channeling electrolyte and metal substrate for local film breakdown, leading to degraded inhibition performance.