Barrier Properties of Some New Organic Coatings

The new organic coatings were realised from polyurethane resin and alkyd+melamine-formaldehyde resins. The electrochemical techniques of the electrochemical impedance spectroscopy (EIS), cyclic potentiodynamic polarisation and linear polarisation were applied and the tests were carried out in a normal aerated 3% NaCl solution at ambient temperature. Also, open circuit potentials in 3% NaCl solution were monitored for 300 immersion hours. Salt spray tests were carried out according to ASTM B117 Standard. An electric equivalent circuit with two time constants representing the barrier characteristics of the intact organic coating, and the corrosion process occurring at the substrate/paint interface was fitted. The both coatings revealed very good protective properties, assuring a very good resistance for about 8 years in the ambient environment.