Inhibition of Pitting Corrosion by Surfactants as a Function of Temperature

Pitting corrosion in many important industrial materials such as stainless steels (SS) and aluminum alloys causes significant damage in terms of material loss or resulting accidents. Organic surfactants such as N-lauroylsarcosine sodium salt (NLS) and sodium dodecylsulfate (SDS) have been tested as possible pitting corrosion inhibitors for SS. Most of the pitting inhibition measurements have been performed at room temperature. However, since SS are frequently used at elevated temperatures, the inhibition of pitting corrosion of Type 304 (UNS S30400) SS by SDS and NLS in chloride solutions was investigated as a function of temperature in this study. NLS and SDS were found to prevent the initiation of pitting corrosion of SS in chloride solutions at all temperatures tested but were not effective for enhancing the repassivation of existing pits. Although the two surfactants have similar inhibition effects at room temperature, NLS was a much better inhibitor than SDS at elevated temperatures. NLS was also found to inhibit the general corrosion of SS but SDS prevented only pitting corrosion. Based on the above results, it was proposed that because of the structural differences, NLS may inhibit the corrosion of SS through partial chemical adsorption while SDS adsorbs only physically.