ABSTRACT
In recent years, a novel metal pretreatment based on the formation of silane films has been developed to improve the corrosion resistance of metal substrate and the adhesion between painted organic coatings and metals [1-3]. The silane agents used have a general structure (RO)3Si(CH2)nY, where RO is a hydrolysable alkoxy group, such as methoxy (OCH3), ethoxy (OC2H5) or acetoxy (OCOCH3) and Y is an organofunctional group. The formation of silane films is based on the condensation reactions between silanols (Si-OH, hydrolysis product of alkoxy groups) and the metal hydroxyls (M-OH). The organofunctional silane films deposited on the metal mainly act as a physical barrier against the permeation of water and corrosive ions in the initial period [4-7]. But once saturated with the electrolyte, the
silane films will lose the barrier effect and then the interfacial layer underneath plays a critical role in the subsequent corrosion inhibition process [3, 8]. A rapid upsurge of interest in silane films has been found in the field of corrosion control of metals in recent years and investigations are being directed at developing this approach as an alternative to the currently-used carcinogenic chromating and polluting phosphating processes [3-6]. However, single silane films cannot effectively protect metals against corrosion due to their low thickness (only tens or a few hundreds of nanometers as reported in the literatures [9-12]). Therefore, in practice silane films are usually applied in conjunction with organic coatings.
