Protection of materials against corrosive attack has accompanied humankind since the Iron Age. It is difficult to imagine how we would be able to exist as a species without metals. It is estimated corrosion is generating a whooping cost of 3.4% of global GDP. Since steel is the most important structural material known to humanity, its share in the cost is the most substantial. Coatings present one of the most straightforward methods of corrosion prevention. Nowadays, it is sought after that the so-called “smart coatings” can dynamically respond to external stimuli and provide extra protection when necessary. Sol-gel technology provides ample means to prepare such coatings as they can be widely modified with the proper synthesis strategy and composition of precursors that give rise to diversified products. Sol-gel coatings can be made relatively thin and are easy to modify with fillers (like cerium compounds) that can bestow superior corrosion resistance in the event of mechanical damage.

In this study, 16Mo3 carbon steel and 316L stainless steel were coated with different sol-gel coating systems based on purely inorganic (silicate) material and/or the ones modified with organic moieties. Some of the coatings were also loaded with ceria and zirconia fillers. The substrates were selected to showcase the behavior of the coating systems with dramatically different corrosion behavior of the base steel. Steel coupons were then subjected to various electrochemical (OCP, PDP, EIS) and long-term immersion tests coupled with microscopic (SEM/EDX) investigations and analysis of the corrosion media composition (ICP-OES). It was found that both the presence of organic moieties and ceria contributed to the superior corrosion behavior of the coatings. It is also noteworthy that the type of substrate had a substantial effect on the behavior of the coating – as the interaction between the corrosion products and the sol-gel coating was different between carbon and stainless steels.