Preparation of c-Mercaptopropyltrimethoxysilanes films to protect steel against corrosion

Abstract

Traditionally, chromates and phosphates were used as pretreatments for metals to protect them from corrosion during a temporary period. Nowadays, due to their toxicity, replacements are being study. The most studied compounds are based on silanes and, among them, glicidoxypropyltrimethoxysilane, aminopropyltrimethoxysilane, and mercaptopropyltrimethoxysilane are the most important ones. The objective of this research work was to study the anticorrosive protection afforded by films of c-mercaptopropyltrimethoxysilane deposited on SAE 1010 steel in order to select the optimum preparation conditions. The films were applied on sandblasted steel after 24 or 48 h of hydrolysis of the silane in a water/methanol solution (1.5/1, by volume) and cured for 10 min at 80 C or for 1 h at 100 C. In order to evaluate the characteristics of the films, Fourier transformed infrared spectroscopy was done on the films and the coated surfaces were observed by scanning electron microscopy. The anticorrosive protection afforded by the films was studied by electrochemical tests employing polarization curves (Tafel mode) in 0.5 M NaCl solution and corrosion potential measurements in NaCl 0.05 M. The best results were obtained with silane hydrolyzed for 48 h cured at 80 C for 10 min.