Phenol - Formaldehyde Resin/Zn Composite Layers - A Way To Improve Corrosion Resistance Of Zinc Electrodeposition

摘要

Zinc is the most widely used material for protection of steel against corrosion. The major drawback of thick coatings is poor weldability and difficulty to achieve a specular finish after painting. This provides the need to develop composite layers with improved propertiessuchashardness,ductility,corrosionetc.Electrodeposition offers rigid control of film thickness, uniformity and deposition rate and is especially attractive owing to its low equipment cost and starting materials. The present work has the purpose of realization of composite layers obtained by using phenol -formaldehyde (PF) resin type NOVOLAC with commercial name RESITAL 6358/1 (for the first time) synthesised by HUTTENES - ALBERTUS Germany electrodeposited with zinc. It is necessary to note that by involving the particles of PF resin in a zinc matrix we can obtain materials with properties differing from those of the individual materials.The phenol - formaldehyde resin/Zn composite layers were electrodeposited from a suspension of PF resin particles (means diameter 0.1 urn - μm) in aqueous zinc sulphate electrolyte. Suspension was prepared by adding 25g/L PF resin particles into solution. The structure of the layers was investigated by SEM - EDX methods. The surface morphology of composite layers is different compared with pure zinc coated. The regular crystal structure characteristic of electroplated zinc layers was disturbed by PF resin particles that perturb the zinc growth during electrodeposition. 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 polarization potentiodynamic and electrochemical impedance spectroscopy methods. 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 layers (-1.44V for composite layers than - 1.51V for pure zinc layers). For composite layers the polarization resistance is 127.340. cm2 by using polarization potentiodynamic method and 127.37? cm~2 by using electrochemical impedance spectroscopy method, than polarization resistance of pure zinc layer by 430.19? cm~2 by using polarization potentiodynamic method and 428.69? cm~2 by using electrochemical impedance spectroscopy method. It was observed that by adding PF resin particles in zinc electrolyte for electrodeposition it was obtained composite layers most resistant at corrosive attack of 0.5M sodium chloride than pure zinc obtained from electrodeposition in same conditions (corrosion rate for composite layers is 6.33um/year than pure zinc with corrosion rate of 24.52?m/year).