A New Approach in Modifying Polymeric Coatings to Increase Corrosion Resistance Properties

In this study, carbon steel sheets were coated with a modified epoxy coating. The urea-modified montmorillonite clay nanoparticles were added to a DGEBA epoxy resin in different contents and then applied to the surfaces. The corrosion resistance of the coated samples was determined by electrochemical techniques (open circuit potential and linear polarization) in 3.5 wt% NaCl solutions at room temperature and 80°C. Electrochemical impedance spectroscopy (EIS) evaluated the properties of polymer-coated metals and their changes during the exposure to corrosive environments. Scanning electron microscopy (SEM) was used to characterize the coatings. An improvement of protective properties of epoxy coatings with an optimal percentage of the modified clay in comparison with pure epoxy was achieved. 1. Introduction Organic coatings represent one of the most effective methods to control metallic corrosion; however, less researches concerning the corrosion performance of coatings modified by clay nanoparticles have been reported so far, but during the last years, polymer-clay nanocomposites have attracted a lot of attention. Incorporation of a small amount (1–5？wt%) of clay into organic polymers leads to significant improvements in mechanical performance [1–5], thermal stability [6–11], barrier properties, and properties such as dimensional stability, reduced gas permeability, optical clarity, and flame retardancy of organic coatings [12–15]. According to the mentioned studies, these improvements are related to the morphology of the layered silicates. The most widely used layered silicate is montmorillonite (MMT). The crystallographic structure of MMT consists of two sheets of tetrahedral silica fused to an edge-shared octahedral-based sheet of either magnesium or aluminium hydroxide. In order to improve dispersibility and protection properties of clay in the polymeric network, the surface of clay needs to be modified [11]. Using the inhibitors is one of the ways to modify the surface of clay (MMT). Even though there are many nontoxic organic compounds which are effective corrosion inhibitors in solutions, for example, carboxylic acids or heterocyclic compounds, these inhibitors have not yet found wide usage in protective organic coatings. The reason for their lack of usage is that the active part of the compounds (e.g., –COOH) which is responsible for the formation of strong bonds with the metal surface, can also react with the polymer resins used to produce the coating [16]. Thus, the inhibitor is trapped by the polymer chain and cannot diffuse through the