Electrochemical and XPS study of polyethyleneimines of different molecular sizes as corrosion inhibitors for AISI 430 stainless steel in near-neutral chloride media

Polyethyleneimines (PEI) with different mean molar mass (from 1300 to 750,000 g mol−1) were studied as potential corrosion inhibitors for AISI 430 stainless steel in a 3% NaCl solution. Linear polarization measurements and immersion tests showed that all of the selected polymers protect this stainless steel against uniform corrosion. PEI with a mean molar mass of 2000 g mol−1 provides the best protection against localized corrosion, as demonstrated by cyclic polarization measurements. A closer insight into the polymer adsorption was obtained by XPS technique. PEI molecules most probably physisorb on the metal surface since no peak shift was observed that would indicate C–N–metal connection. PEI probably acts as a diffusion barrier by preventing an attack by the chloride of the salt solution.