Electrochemical characteristics of corrosion behavior of organic/Dacromet composite systems pretreated with gamma-aminopropyltriethoxysilane

The corrosion behavior of four organic/Dacromet composite systems, namely three solvent-borne coatings, polyurethane, alkyd and fluorinated polymer as well as a water-borne coating, styrene-acrylate emulsion, was studied after pretreatment with gamma-aminopropyltriethoxysilane (γ-APTS). Electrochemical experiment in 3.5% NaCl solution and scanning electron microscopy (SEM) were performed. The results showed that: (1) γ-APTS treatment increased the polarization resistance but decreased the total impedance of the corrosion reaction contrast to the untreated Dacromet after immersion for a period. (2) The silane pretreatment significantly influenced the corrosion behavior of the organic/Dacromet composite systems mainly through restraining the corrosion of the substrate (Dacromet) by the reduction of the active surface (due to the barrier effect of surface film), which was confirmed by EIS experiments under anodic polarization. (3) Pretreatment with γ-APTS improved the protective performance of the polyurethane and alkyd/Dacromet composite systems. However, a conversion evolution between the untreated and the pretreated water-borne styrene-acrylate emulsion composite system appeared due to the particular interfacial effect. (4) Parameter Z|0.1 Hz and fb in the studied systems manifested a mathematical correlation and the constant K = log (Z|0.1Hz/fb) could be used in protective performance evaluation for various coatings on substrates.