Effect of Surfactants on the Protection Efficiency of Zn-Phosphate Coat on Steel

摘要

Potentiodynamic polarization, electrochemical impedance spectroscopy, SEM study and EDX analysis have been used to investigate effect of Tween-80, Cetyl trimethyl ammonium bromide (Cetrimide), and Sodium Louryl Sulphate (SLS) surfactants on the corrosion resistance, porosity, structure and composition of Zn-phosphate coat on steel. Electrochemical results indicated that the presence of 0.01M surfactants in the coating solution caused a decrease in the porosity and an increase of the protection efficiency of the coat up to about 90%. The results proved that the coating process was controlled by adsorption of the surfactant molecules on the steel surface. Application of the adsorption isotherms and Kinetic-Thermodynamic model to fit the experimental data indicated that Langmuir isotherm is not applicable, however, Flory-Huggins isotherm and Kinetic-Thermodynamic model are applicable, and the three surfactants are chemisorbed on the steel surface. SEM study and EDX analysis gave very good support to the electrochemical data.