Linear carboxylates as corrosion inhibitors from plant chemistry. Towards biomimetic surface treatments

摘要

The research on surface treatments of metals is carried on with the need to develop "clean and sustainable" processes, fulfilling the REACH standards on chemical reagents. The use of linear saturated carboxylic acid with long carbon chain is an interesting alternative to much corrosion inhibiting formulations, because of their low cost and their easy and secure use. Moreover, this kind of carboxylates is extracted from vegetal oils (colza, sunflower, ricin...) and is not impacted by the REACH regulation. This paper proposes to review the use of long chain- carboxylate as corrosion inhibitors in several applications: 1 as anticorrosion additives in industrial waters, 2 in temporary surface treatments against atmospheric corrosion, 3 in multifunctional surface treatment on galvanized steel. In each application, the strategy of protection is to build insoluble and hydrophobic layer acting as a barrier. According to pH and concentration, this barrier can be very thin (around 100 nm) or thicker and crystallized (several micrometers) layer of metal carboxylates. Previous works have proved that the protection due to the metallic soap are due the cohesion of the crystallographic structure, assured by the electrostatic interactions in metallic plans, and the Van der Waals forces between the aliphatic chains hung on both sides of these plans. Now, this compact metallic-organic framework (MOF) with long carbon chain can be synthesized with "soft" processes on metal surface without use of organic solvent or high temperature (T<40 °C). These protective layers are similar to the extreme surface of some plants, which trap the air in the nanoporosity to increase the barrier effect against water ("lotus"effect).