Effect of anionic surfactants as pitting corrosion inhibitors for stainless steels

Abstract

Although anionic surfactants have been widely introduced as inhibitors against uniform corrosion, their efficiency as pitting inhibitors remains unclear. Herein, fatty alcohol ether sulfate (FAES), linear alkylbenzene sulfonate (LAS), and palm kernel oil (PKO) were tested for a Ti-stabilized (1.4510) and a nonstabilized grade (1.4016) of ferritic stainless steel in alkaline chloride solutions containing H2O2. Electrochemical impedance spectroscopy (EIS) measurements were performed to elucidate the adsorption of surfactants at OCP, followed by potentiodynamic polarization. For 1.4510, LAS and FAES did not significantly affect the EIS results but inhibited pitting initiation with identical efficiencies. In the case of 1.4016, Cr-rich carbides acted as adsorption sites, where LAS showed higher efficiency than FAES. While LAS and FAES interact preferentially with pitting initiation sites, PKO appears to adsorb randomly on the passive film. Consequently, inhibition can reach a maximum due to the electrical neutralization of the surface. Finally, LAS can be effective as an inhibitor for stainless steel containing carbides that can lead to pitting initiation.