PREPARATION OF CORROSION PROTECTIVE COATINGS ON GALVANIZED STEEL FROM AMINE-CURED EPOXY HYBRIDS PREPARED BY SOL-GEL METHOD

摘要

New inorganic-organic hybrid precursors for corrosion protective coatings on galvanized steel were prepared by sol-gel methods using an acetic acid-catalyzed hydrolysis and condensation with TEOS and GPTMS. Different hydrolysis times of TEOS-GPTMS, such as 24, 48 and 72 hours, were evaluated in order to get nanoparticles with epoxy-functionality. Mono-functional amino-silane (3-aminopropyltrimethoxysilane (γ-APS)) and diethylenetriamine (DETA) have been used as crosslinking agents. The effect induced by the curing agents on the corrosion performance of the coated samples were investigated. TEOS-GPTMS/γ-APS or DETAhybrids were deposited on ultrasonically cleaned and degreased galvanized steel plates by using dip coating technique at room temperature. All the coatings were cured at 150 °C for 1h in an oven, and their anticorrosion behavior was studied by electrochemical techniques like open-circuit potential (Eoc), electrochemical impedance spectroscopy (EIS) and polarization curves at room temperature in 0.1 M NaCl. The coatings formed with the hybrid TEOS-GPTMS/γ-APS presented higher impedance values for increasing time of hydrolysis, and also exhibited lower anodic currents and more positive and stable corrosion potentials, indicating the formation of a well-adhered and ordered coating with good barrier properties on galvanized steel. The worse performance of DETA croslinking agent was attributed to its involvement in the formation of a stable zinc complex. The role of the aminosilane, γ-APS, in the coating formation is twofolded, it is involved in the conventional chemistry of bonding epoxy groups, and it also undergoes sol-gel hydrolysis and condensation reactions, acting simultaneously as coupling agent and interacting with the surface of galvanized steel, thus improving the protective properties of the coating.