Abstract
Corrosion behaviour of steel in acid solutions was followed in presence of cationic micells of Cetyltrimethylammonium bromide (CTABr), n‐tetradecyl‐N,N,N‐trimethylammonium bromide (TDTABr), n‐dodecyltrimethylammonium bromide (DDTABr) and n‐decyltrimethylammonium bromide (DTABr) using gasometry and potentiodynamic techniques. Plots of adsorption isotherms produce S‐ shaped curves. Surfactants were found to act as corrosion inhibitors of mixed ‐ type, i.e., affecting the dissolution of the metal and the cathodic reaction of hydrogen evolution. Inhibitive effect of the surfactants has been shown to increase with the alkyl chain length and at concentrations above their critical micelle concentration (cmc). Corrosion kinetic empirical equation describing the relationship between the surfactants structure and their activity is introduced. The number of active sites on the metal occupied by the surfactant molecule, binding constant and change in free energy of adsorption are calculated following Temkin adsorption isotherms. All results obtained are compared to the kinetic‐thermodynamic model to certify its applicability. The mode of adsorption of the surfactant molecules according to their structure is also discussed.