Multicomponent Organic Corrosion Inhibitors: I. Suggested Mechanism of Synergistic Action; II. Improvements of Inhibition in Acid Corrosion of Steel Coupons

Abstract

I. Application of surface chemical considerations to coadsorption of suitably chosen inhibitors suggests that on the heterogeneous metallic surfaces two types of mixed inhibitor films may exist: an ideal film represented by a close-packed monolayer of ad1ineated surfactants, or a less ordered, and thus less effective, multilayer coating. Three types of bonds are involved in the film formation: (I) adhesion bonds between the polar groups and the adsorption sites on the metal surface, (II) lateral bonds between the polar groups of adsorbed surfactants and (III) van der Waals bonds between the ad1ineated nonpolar portions of inhibitors. These 3 types of bonds have to be suitably co-ordinated in order to give a continuous, nonporous and firmly adhering corrosion barrier. The structure of the inhibitor molecules and the relative steric factors (sizes) playa decisive role in the development of an effective protection barrier against corrosion.II. Results of corrosion tests on mild steel coupons in HCl solution of pH 1, at temperatures 60° and 80°C. are presented. Inhibition obtained with aliphatic amines is compared with that obtained in mixed solutions of amines and alcohols, amines with alcohols and carboxylic acids, and finally in 4-component systems with dodecyl sulphate or phosphate. Weight data gave a decrease in corrosion from 0.45% loss in hexadecyl amine alone to 0.2% lose in the 4-component solution (for 6-hr tests at 60 °C, 1 × 10−4M total concentration these correspond to an increase from 88 to 94.6 % inhibition, for approximately 0.004 to 0.005% inhibitor solutions.