Micro Structure and Corrosion Resistance of Zn Composites Films Produced by Pulse Electrolysis from a Insoluble Particle-free Solution Containing Zr Ions

Abstract

Electrodeposition of Zn–Zr compound composite was performed under pulsed and double pulsed current conditions at 313 K on unagitated pH 2 sulfate solutions containing Zn²⁺, ZrO²⁺ ions and a polyethylene glycol (PEG). At constant current density of 5000 A∙m⁻², the coarse granular deposits containing Zr compound existed partially. Meanwhile, in pulse electrolysis, the coarse deposits were rarely seen and the both areas of deposited films containing Zr compound and its films being exfoliated were observed. On the contrary, in double pulse electrolysis of high current density (5000 A∙m⁻²) and low current density (500 A∙m⁻²), the coarse deposits were not observed and the fine particle deposits containing Zr compound were present. In double pulse electrolysis, since at low current density, the rate of hydrogen evolution decreases and Zn deposits without co-deposition of Zr compound, the continuous hydrogen evolution is suspended in some areas and the area of hydrogen evolution seems to become random. Although Zr compound concentrated at upper area of deposited films regardless of electrolytic method, it codeposited even at inner part with double pulse electrolysis. The corrosion current density in 3 mass% NaCl solution was the smallest for the films produced by double pulse electrolysis, comparing with films obtained by pulse electrolysis and constant current electrolysis. This is attributed to reduction reaction of dissolved oxygen being suppressed.