Abstract
The behaviors of colloidal silica in organic coating on galvanized steel were studied in viewpoints of corrosion resistance. The samples coated with polyolefin resin including colloidal silica showed better corrosion resistance than that coated with resin only. Anodic polarization resistance showed a good relationship with corrosion resistance, and this was improved as colloidal silica increased in quantity or decreased in size. On the other hand, cathodic current density showed not so good correlations. The corrosion potentials of samples coated with resin including colloidal silica dropped once and then rose. On the other hand, those of the samples with only resin coat continue to decline. Colloidal silica in organic coating dissolves in water, and solubility also increased in quantity, as their particles decreased in diameter or pH rose above 8. At the pH below 4, colloidal silica did not dissolve at all. Some evidences to suggest the dissolution of silica in cathodic region and deposit on anodic site on zinc surface could be obtained, and the improvement of corrosion resistance seems to cause the film fbrmation on anodic site.
