Electrodeposition Obtaining and Corrosion Behaviour of Phenol Formaldehyde Resin/Zinc Composite Coatings

Abstract

The present work has the purpose of obtaining composite coatings in zinc matrix by using phenol - formaldehyde resin type NOVOLAC (RESITAL 6358/1) in the electrodeposition process of zinc. The PF resin/Zn composite coatings were electrodeposited from a suspension of PF resin particles (diameter < 56 μm) in aqueous zinc sulphate electrolyte. Suspension was prepared by adding 10 g/L and 25 g/L PF resin particles into solution. The pure zinc coating has a rather regular surface, whereas the composite coatings surface has fine surface structure. For layers obtained at 3 A/dm² the polarization resistance is higher for composite coatings with 10 g/L PF resin (R_p = 238.75 Ω cm²) than pure zinc (R_p = 34.54 Ω cm²). For layers obtained at 5 A/dm² the polarization resistance is higher for composite coatings with 25 g/L PF resin (Rp = 430.19 Ω cm²) than pure zinc (Rp = 127.34Ω cm²). As test solution 0.5 M sodium chloride was used, it was observed that by adding PF resin particles in zinc electrolyte for electrodeposition it was obtained a very good distribution of resin particles on zinc surface and PF resin/Zn composite coatings obtained are most resistant at corrosive attack than pure zinc obtained from electrodeposition under the same conditions.