Fabrication and Corrosion Resistance of Hot-Dip Galvanized Steel Plates Coated with Silica-Sol Prepared from Tetraethoxysilane
Tetsuya KOMEDA, Koshi TAKADA, Yoshihiko TAKANO, Kazuki SAKAI, Shigekazu TANAKA, Atsushi KAWADA, Ken HIROTA and Osamu YAMAGUCHI
Abstract:Silica-sol solution was prepared using tetraethoxysilane as a starting material. A silica-gel film was formed on both silica glass substrates and hot-dip galvanized steel plates by single-step dip coating and drying at room temperature. X-ray diffraction (XRD) analysis was performed on the films formed on the silica glasses and the steel plates; it revealed that the film formed on the former consisted of H2Si2O5 and both Zn2SiO4 and ZnNO3(OH) EH2O were detected in the film on the latter. From these results, it was cleared that the as-prepared silica-sol itself was H2Si2O5, however the silica-sol was changed to Zn2SiO4 when coated on the hot-dip galvanized steel plates resulting from a reaction with Zn on the surface of plates. The thickness of tripe-layered film formed by three-times dipping was estimated to be about 1.3 ƒÊm by direct SEM observation. Using a salt spray test and a stack test, corrosion resistance of the hot-dip galvanized steel plates coated with the silica-sol was examined, in comparison with a chromate-coated and a naked hot-dip galvanized steel plates. The silica-sol coated plates exhibited superior corrosion resistance to both former and latter samples in each test. This might be explained in terms of the formation of Zn2SiO4 and ZnNO3(OH)EH2O. The coating materials, insoluble in water, can protect the steel plates from corrosive oxygen and electrolyte ions etc. Key Words:Chromate free, Silicate, Sol-gel method, Hot-dip galvanized steel, Corrosion resistance