Characterization of hot-dip galvanized (HDG) steel treated with bis-1,2-(triethoxysilyl)ethane and γ-aminopropyltriethoxysilane

The aim of this work was to study the suitability of silane treatments for hot-dip galvanized (HDG) steel. Silane coupling agents were used as adhesion promoters between paint and galvanized steel. The focus was on characterization of the silane-treated surfaces. The adhesion and corrosion performance of the selected silanes in painted galvanized steel systems will be reported separately. In this work, HDG steel was treated with bis-1,2-(triethoxysilyl) ethane (BTSE, Y-11710) and γ-aminopropyltriethoxysilane (γ-APS, A-1100), and the samples were characterized by using various surface analytical methods. The results indicate that if BTSE is deposited onto HDG steel from an ethanol-water solution, hydrolytically stable bonds can be formed between BTSE and HDG steel. Thermodynamically, the film is stable but it has a low total surface energy. FTIR analysis showed that the film contained unhydrolyzed ethoxy groups and unreacted silanol groups, but the surface energy results indicate that the outermost film has hardly any acid or base functionality. ESCA results of the γ-APS treatments indicate that the initial bonds between the deposited γ-APS silanols, and between the silanols and the HDG steel, are not very strong, but upon drying and curing the films the stability of the bonds increases. The FTIR results also show that the γ-APS film deposited at pH 8.5 has a higher degree of amine functionality than the film deposited at pH 10.5. It was also observed that the surface energy of the γ-APS films decreased due to a decrease in surface polarity. The results of a two-step treatment consisting of BTSE and γ-APS on HDG steel showed that the BTSE film affected the orientation of the γ-APS silanols deposited onto it.