Properties of zinc coatings electrochemically passivated in sodium molybdate

Abstract

Molybdenum compounds are considered to be promising, environmentally friendly substances for passivation of zinc coatings. Conversion coatings on electroplated zinc coatings obtained by cathodic polarization of a solution of molybdate of sodium with the addition of phosphoric acid are studied. These coatings had a pronounced needle-shaped structure and were homogeneous. X-ray photoelectronic spectroscopy analysis showed that zinc hydroxides and phosphates, Mo (VI), and Mo (V) compounds are present in the conversion coating. As part of this study, the influence of the current density and deposition time of the coating on the surface morphology and the chemical composition of conversion films was determined. Polarization measurements and electrochemical impedance spectroscopy have shown that the investigated coatings significantly increase the corrosion resistance of galvanized steel in chloridecontaining solution.

Enhancing the Stability of Passive Film on 304 SS by Chemical Modification in Alkaline Phosphate–Molybdate Solutions

“…Mo-or P-containing passive films are beneficial to passivity, leading to an increased corrosion potential [22][23][24]. Phosphate and molybdate have been considered to be beneficial passivators for carbon steel, aluminum alloy, and zinc [25,26]. However, passivation in molybdate-only solution has resulted in a film with cracks [27].…”