CHROMATE CONVERSION COATINGS FORMATION ON ZINC STUDIED BY ELECTROCHEMICAL AND ELECTROHYDRODYNAMICAL IMPEDANCES

摘要

The formation of chromate conversion coatings on zinc was studied by chronopotentiometric, electrochemical and electrohydrodynamic impedances, and interfacial pH measurements. The electrochemical experiments were performed with a rotating disk electrode of pure zinc, and the pH measurements were obtained with a zinc deposit on a gold grid electrode in a submerged impinging jet cell. The electrolyte was an industrial chromate bath. The experimental results were achieved for different immersion times, temperature, and rotation speeds. Kinetic reactions and physical model for the chromate layer formation on zinc were proposed, and the electrochemical and electrohydrodynamic impedances were well simulated. The goal of this survey is to get a better knowledge of the formation of chromate layers in order to facilitate the research of a non-toxic alternative conversion coating.