Multi-layer organic-inorganic hybrid anticorrosive coatings for protection of medium carbon steel

In the current study, sol-gel technology was used to produce organic-inorganic hybrid coatings onto AISI 1045 carbon steel as a means of corrosion protection. The organic-inorganic hybrid coatings were prepared using tetraethylorthosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate precursors. The coatings were thermally treated and the effect of temperature and time was studied. The results of scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that the coatings possess homogeneous morphologies and that their thickness decreases with increasing heat treatment temperatures. At the highest treatment the coating was 20% thinner and more than 25% more scratch resistant compared with the untreated coating. According to thermalgravimetric analysis the coating mass loss was approximately 15% up to 150 °C and 2.7% between 150 and 400 °C. The electrochemical measurements, in 3.5% NaCl aqueous solution, determined that the coatings treated at 100 °C have polarization resistance values on the order of 60 kΩ cm2 after 72 h of exposure time in saline solution. The phase angle at high frequency (close to −90° at 103-105 Hz) demonstrated that the coating presented capacitive behavior related to less aggressive corrosion in this electrolyte. Further increasing the temperature beyong 100 °C reduced the performance of the coatings as demonstrated by a decrease of the polarization resistance by about one order of magnitude and the shift of the corrosion potential to more negative values.