Effect of EtOH/H₂O Ratio and pH on Bis-Sulfur Silane Solutions for Electrogalvanized Steel Joints Based on Anaerobic Adhesives

A minimum hydrolysis time is required to get an adequate crosslinking between a silane film and a metallic substrate and that depends on the contents of silane, ethanol, and water in the silane solution. The objectives for this work are: 1) to study the effect of different ratios of ethanol/water on the hydrolysis time for a 1% bis-sulfur silane solution at pH 6, by attenuated total reflectance infrared spectroscopy. The different solutions studied correspond to different ratios of silane/ethanol/water by volume. The study was done following appearance of the siloxane and silanol groups and the disappearance of the ethoxysilane groups. 2) Also studied was the adhesion and corrosion behaviour of bis-sulfur silane (bis[3-(bis[3-(triethoxysilyl)propyl]disulfide, DS) in solutions of ethanol/water at pH 4 and 6 and γ-methacryloxypropyltrimethoxysilane (MPS) coatings obtained by a two-step process on galvanized steel samples. This coated surface was analysed by reflection absorption infrared spectroscopy (FTIR-RA), scanning electron miscroscopy (SEM), and polarization curves. Results obtained at pH 6 were compared with the ones for pH 4. Single lap shear tests were used to contrast the behaviour of anaerobic adhesives on electrogalvanized steel silanized samples. It was observed that higher hydrolysis time was necessary to get good adhesion behaviour if the solution was prepared at pH 4, while at pH 6 the best behaviour was observed for short hydrolysis times.