Characterization of the Silica Conversion Film Formed on Zinc-Electroplated Steel

Abstract

The chemical conversion of zinc-electroplated steel sheet using colloidal silica was investigated as an alternative to chromate conversion. The corrosion resistance of zinc-electroplated steel sheet with and without this treatment was estimated from electrochemical impedance spectroscopy, open circuit potential in 3 mass% NaCl solution and the salt spray test. The solution used for the colloidal silica coating consisted of colloidal silica, titanium sulfate, cobalt sulfate, and succinic acid. This solution produced an adhesive film and maintained good corrosion resistance. Adding cobalt ions to the colloidal silica solution enhanced the adhesion between the silica film and the zinc layer electroplated on the steel sheet. In the electrochemical impedance analysis, the corrosion protection conferred by the colloidal silica film was about five times greater than that of a normal zinc-electroplated steel sheet, but not as good as that of a chromate film. In the salt spray test, rust appeared more quickly on chromate-coated specimens than on colloidal silica film surfaces.

Use of Silicon-Based Coating for High Temperature Protection of Metallic Alloys

“…Silica coatings are potential candidates for improving the resistance against high temperature corrosion of metals [1][2][3]. Various techniques had been used to prepare silica coatings, such as vacuum deposition [4], sputtering, chemical vapour deposition (CVD) [5] or sol-gel [6,7] methods.…”

Effects of Anodizing Time on Anodizing of Mg-Al Alloy in Alkaline Solution

“…They are potentially toxic to humans and are difficult to recycle. Therefore, there is an urgent need for research on techniques that do not use chrome when anodizing Mg and Mg alloys [1][2][3][4][5][6]. This paper investigated the effects of anodizing time on the formation of anodic oxide films on a Mg-Al alloy in alkaline solution.…”

Effects of Current Density on the Formation of Anodic Oxide Films on AZ91

“…However, magnesium must be surface treated to prevent corrosion, since it is a very active metal electrochemically. On anodizing, a compact film several tens of micrometers thick forms on magnesium, which imparts good corrosion resistance [1][2][3][4]. This paper investigates the effects of current density on the formation of anodic oxide films for a Mg-Al alloy (AZ91) in alkaline solution.…”