Studies of (3-mercaptopropyl)trimethoxylsilane and bis(trimethoxysilyl)ethane sol–gel coating on copper and aluminum

Bis(trimethoxysilyl)ethane (BTMSE) and (3-mercaptopropyl)trimethoxysilane (MPTMS) have been used as precursors to prepare sol–gels and hybrid sol–gel under acidic condition. From the X-ray photoelectron spectroscopy data on MPTMS sol–gel coated aluminum and copper, it has been shown that the silane film is covalently bonded to Al surface through the interfacial condensation. There is no evidence of bonding interaction between the thiol group and the Cu. The recorded reflection adsorption IR (RAIR) spectrum has provided evidence that the coating BTMSE film covalently interacts with Al. Vibrational assignments have been suggested for pure BTMSE, BTMSE sol–gel, BTMSE xerogel, and BTMSE coated Al panel based on the group frequencies and the variation of frequencies with the sample treatment conditions. The progression of condensation reaction has been observed from the IR spectra of the BTMSE sol–gel and the sol–gel coated film after the treatments at different temperatures with different lengths of time. The corrosion protection of the sol–gel coated Al and Cu has been characterized in NaCl solutions by cyclic voltammetric, potentiodynamic polarization and impedance spectroscopy methods. All these electrochemical measurements indicate that the sol–gel coated metals have better corrosion protection than the corresponding uncoated metals.