Effects of pH Value of the Electrolyte and Glycine Additive on Formation and Properties of Electrodeposited Zn-Fe Coatings

İsmail Hakki Karahan

doi:10.1155/2013/273953

Abstract

Environmentally friendly and cyanide-free sulfate bath under continuous current and the corrosion behavior of electrodeposits of zinc-iron alloys were studied by means of electrochemical tests in a solution of 3.5% NaCl in presence and absence of glycine. The effects of pH on the quality of Zn-Fe coatings were investigated in order to improve uniformity and corrosion protection performance of the coating films. The deposit morphology was analyzed using scanning electron microscopy (SEM), and X-ray diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. It was found that the uniformity and corrosion resistance of Zn-Fe coating films were strongly associated with pH of the coating electrolyte. To obtain the effect of pH on the film quality and corrosion performances of the films, the corrosion test was performed with potentiodynamic anodic polarization method. It was also observed that uniformity and corrosion resistivity of the coating films were decreased towards pH = 5 and then improved with increasing pH value of the electrolyte. The presence of glycine in the plating bath decreases the corrosion resistance of Zn-Fe coatings.

Highlights

The electrodeposited Zn-Fe coatings possess many superior properties, such as excellent paintability, good welding properties, and good corrosion resistance, and have been considered to be an alternative for pure zinc coating of iron and steel products
In another previous study investigating the relation of corrosion properties and gelatin as additive in Zn-Fe alloys [21], the results indicated strong evidence of an increase in corrosion potential with adding gelatin in the electrolyte
The shifting of onset potential for reduction at various pH values is influenced by protons in the case of low pH values and by hydroxide ions in the case of higher pH values

Summary

Introduction

The electrodeposited Zn-Fe coatings possess many superior properties, such as excellent paintability, good welding properties, and good corrosion resistance, and have been considered to be an alternative for pure zinc coating of iron and steel products. Depending on the electrolyte composition, temperature, current density, and pH of the solution, different properties can be obtained This fact makes Zn-Fe alloys important to explore the effect of pH on the structure of these alloys. Additive molecules adsorbed on the cathode surface can affect the activation energy [18] and the rate of charge transfer in the electrochemical reaction and may influence the mechanism of electrocrystallization [19, 20] In another previous study investigating the relation of corrosion properties and gelatin as additive in Zn-Fe alloys [21], the results indicated strong evidence of an increase in corrosion potential with adding gelatin in the electrolyte. We report on structural and corrosion properties of electrodeposited Zn-Fe films investigated as a function of electrolyte pH and glycine as additive to provide more insight to the Zn-Fe alloying system and to better understand how glycine acts as an additive to electrodeposition solutions

Experimental Details

Results and Discussion

Conclusions