Anti-corrosion Properties of Functionalized Organo-silane Coupling Agents for Galvanized Steel

Silane precursor selection is an important criterion for achieving great anticorrosive performance on steel substrates using sol-gel technology. A density functional theory (DFT) study was performed on functional and nonfunctional organosilane precursors. The global reactivity parameters, such as the global hardness (ƞ), dipole moment (μ), and number of electrons transferred (∆N) to the metal substrate, were calculated to identify suitable silane coupling agents. DFT studies revealed that precursors containing functional groups such as epoxy, amine, and mercapto offer better protection against corrosion to galvanized steel by providing stronger interfacial adhesion than precursors without functional moieties. The DFT-calculated adsorption energy (Eads) is more than 40.0kcal/mol for the adsorption of functional organosilanes onto the (ZnO)12 cluster. Evidence of chemical bond formation at the interface for functional organosilanes is found in the electron density overlap in the MOs. Natural charge analyses revealed clear charge transfer from the organosilane moiety to the (ZnO)12 cluster. The theoretical predictions were validated via experiments. Electrochemical studies demonstrated a protective efficiency of 92.5% for Ie with an impedance of 92.9kΩ·cm2. The presence of the respective functional groups and surface morphology were evaluated by FTIR and SEM. The order of corrosion inhibition of organosilanes was found to be MPTMS≈APTES>GPTMS>TEOS.