Adsorption and corrosion inhibitive properties of some organic molecules on iron electrode in sulfuric acid

Abstract

Adsorption and corrosion inhibitive properties of three different organic molecules: 2-naphthalenesulfonic acid, 2,7-naphthalenedisulfonic acid and 2-naphthol-3,6-disulfonic acid are investigated on Armco-iron electrode cathodically polarized, in 0.5 mol dm -3 H 2 SO 4 solution. The examinations show that the three organic molecules behave as a cathodic corrosion inhibitors. The inhibitive efficiency, changes with the number of functional groups substituted on benzene ring and increases with concentration. The experimentally obtained adsorption isoterms follow the Frumkin equation [0/n(1-0) n ] exp(-2aθ) = Bc and the best fit is obtained for n = 2 (for 2-NSA) and n = 3 (for 2,7-NDSA and 2N-3,6-DSA). The calculated values for the parameter a are 2.1-2.9 and Gibbs energies are 17-21 kJ mol -1 . The adsorption rate constants are very small, proving that iron surface permanently changes due to the corrosion processes.