FORMATION MECHANISM AND ANTICORROSIVE PROPERTIES OF THIN SILOXANE FILMS ON METAL-SURFACES

The adsorption of different ethoxysilanes on Al was studied. It was es tablished that during polymolecular adsorption of ethoxysilanes from t he vapor phase on aluminum the first monolayer is adsorbed irreversibl y with adsorption van der Waals bonds between silane molecules and the aluminum surface. The covalent bonding of silanes with the surface (A l-O-Si bonds) occurs in the presence of adsorbed water on the aluminum surface. The presence of a silane monolayer on Al decreases water ads orption on the surface, and inhibits hydration of the oxide metal film . The formation of a negatively charged siloxane film on the aluminum surface inhibits local metal corrosion, and a positively charged layer activates it in chloride containing media. The formation of the surfa ce siloxane polymer by the modification of metals inhibits the metal d issolution under polymer coatings. It is caused by silane chemisorptio n and negative charging of the metal surface. The presence of negative ly charged groups causes difficulties of an electrostatic character fo r the migration of aggressive ions to the metal surface.