Electrochemical and sorption characteristics and thermal stability of epoxy coatings electrodeposited on steel modified by Zn-Co alloy

The corrosion behaviour, transport properties and thermal stability of epoxy coatings electrodeposited on steel and steel modified by Zn-Co alloys were investigated during exposure to 3% NaCl solution. The electrochemical impedance spectroscopy (EIS), gravimetric liquid sorption measurements and thermogravimetric analysis (TGA) were used. Zn-Co alloys were electrodeposited on steel from chloride and sulphate baths, by different current densities. From the time dependence of pore resistance and coating capacitance of epoxy coating, diffusion coefficient of water through epoxy coating and thermal stability it was shown that Zn-Co sublayer obtained from chloride solution significantly improves the corrosion stability of the protective system based on epoxy coating. Almost unchanged values of pore resistance were obtained over the long period of exposure time, indicating the great stability of this protective system, due to the existence of a passive layer consisting of basic salts. (C) 2002 Elsevier Science B.V. All rights reserved.