Influence of particles size on the morphology and corrosion behaviour of phenol-formaldehyde/Zn composite coatings obtained by electrodeposition
Résumé
The present work has the purpose of studying the structure and corrosion behaviour of composite coatings having zinc as matrix, and phenol - formaldehyde resin type Novolac (RESITAL 6358/1) as dispersed phase obtained during electrodeposition process of zinc. The phenol - formaldehyde resin/Zn composite coatings were electrodeposited from a suspension of phenol - formaldehyde resin particles in aqueous zinc sulphate electrolyte by adding 10g/L of phenol formaldehyde resin particles in the electrolyte solution. Two dimensions of dispersed particles were used: 0.1 - 5 mu m and 6 - 10 mu m respectively. The surface morphologies of the coatings were investigated by scanning electron microscopy (SEM - EDS) and atomic force microscopy (AFM) methods. The pure zinc coating has a rather regular surface, whereas the composite coating surfaces have finer grains and different morphologies. The electrochemical behaviour of the coatings in the corrosive solutions was investigated by electrochemical impedance spectroscopy (EIS) method. As electrochemical test solution 0.5M sodium chloride was used in a three electrode open cell. The corrosion potential is shifted to more negative values for composite coatings than that of pure zinc coating. The polarization resistances of phenol - formaldehyde resin/Zn composite coatings are bigger than that of pure zinc coating obtained in the same condition for electrodeposition.