Effect of Mean Diameter Size of Disperse Phase on Morphology and Corrosion Resistance of Phenol-Formaldehhyde Resin/Zn Coatings

Abstract

The present work has the purpose of obtaining composite coatings using phenol – formaldehyde (PF) resin electrodeposited with zinc. The phenol – formaldehyde resin/Zn coatings were electrodeposited from a suspension of PF resin particles with two dimensions for mean diameter size of particles (0.1 – 5.0 μm and 6 – 10 μm) in aqueous zinc sulphate electrolyte. Suspension was prepared by adding 10 g/L PF resin particles into solution. The thickness and morphology of the coatings were investigated by SEM method. By adding PF resin in zinc electrolyte for electrodepositing we obtained a very good distribution of PF resin particles on zinc surface. The electrochemical behavior of the layers in the corrosive solution was investigated by electrochemical methods. As electrochemical test solution 0.5M sodium chloride was used in a three electrode open cell. It was observed that by adding PF resin particles in zinc electrolyte for electrodeposition were obtained composite layers more resistant to corrosive attack of 0.5M NaCl than pure zinc obtained from electrodeposition at the same parameters for electrodeposition. Corrosion rate for pure zinc coatings was 72.05 μm/year versus 15.34 μm/year for coatings with mean diameter size of particles 0.1 – 5.0 μm, respectively 10.11μm/year for coatings with mean diameter size of particles 6 – 10μm. Values of polarization resistance obtained with both electrochemical methods (potentiodynamic polarization and electrochemical impedance spectroscopy) were in a very good agreement.