ADSORPTION EFFECT OF CATIONIC SURFACTANTS ON CORROSION INHIBITION OF STEEL

Corrosion behaviour of steel in acid solutions was followed in presenc e of cationic micelles of Cetyltrimethylammonium bromide (CTABr), n-te tradecyl-N,N,N-trimethylammonium bromide (TDTABr), n-dodecyltrimethyla mmonium bromide (DDTABr) and n-decyltrimethylammonium bromide (DTABr) using gasometry and potentiodynamic techniques. Plots of adsorption is otherms produce S-shaped curves. Surfactants were found to act as corr osion inhibitors of mixed - type, i.e., affecting the dissolution of t he metal and the cathodic reaction of hydrogen evolution. Inhibitive e ffect of the surfactants has been shown to increase with the alkyl cha in length and at concentrations above their critical micelle concentra tion (cmc). Corrosion kinetic empirical equation describing the relati onship between the surfactants structure and their activity is introdu ced. The number of active sites on the metal occupied by the surfactan t molecule, binding constant and change in free energy of adsorption a re calculated following Temkin adsorption isotherms. All results obtai ned are compared to the kinetic-thermodynamic model to certify its app licability. The mode of adsorption of the surfactant molecules accordi ng to their structure is also discussed.