Abstract
The purpose of the present work was to study the corrosion behavior of steel coated with epoxy-(organo) clay nanocomposite films. The investigation was carried out using salt spray exposures, optical and scanning electron microscopy examination, open circuit potential, and electrochemical impedance measurements. The mechanical, thermomechanical, and barrier properties of pristine glassy epoxy polymer and epoxy-clay nanocomposites were examined. The degree of intercalation/exfoliation of clay nanoplatelets within the epoxy polymer also was determined. The mechanical, thermomechanical, and barrier properties of all the epoxy-clay nanocomposites were improved compared to those of the pristine epoxy polymer. In addition, both the pristine epoxy and the epoxy nanocomposite coatings protected the steel from corrosion. Furthermore, the protective properties of the nanocomposite coatings were superior compared to those of the pristine epoxy polymer. The protective properties of the nanocomposite coatings varied with the modified clay used. The epoxy-montmorillonite clay modified with primary octadecylammonium ions, Nanomer I.30E, had a better behavior than that modified with quaternary octadecylammonium ions, Nanomer I.28E.
Highlights
Organic coatings are widely used to prevent corrosion of metallic structures. These polymeric coatings are usually permeable to small gaseous molecules such as water vapor and oxygen, which can result in gradual corrosion of the surface
The pristine epoxy resins exhibit measureable adsorption and permeability of water vapor, which diffuses to the epoxy/steel interface and initiates corrosion of the metal substrate in intensely wet conditions
The protective properties of the nanocomposite coatings were superior compared to those of the pristine epoxy polymer, as it was revealed from the weight loss results, the optical and microscopy examination of the specimens after the exposure in the corrosive environment, the open circuit potential measurements, and the electrochemical impedance spectroscopy measurements
Summary
Organic coatings are widely used to prevent corrosion of metallic structures. These polymeric coatings are usually permeable to small gaseous molecules such as water vapor and oxygen, which can result in gradual corrosion of the surface. It is generally accepted that the coating efficiency is dependent on the barrier and mechanical (resistance to cracking) properties of the organic film, on the adherence of the polymeric coating to the metal substrate, and on the degree of environmental aggressiveness. Epoxy resins are commonly used as organic coatings, due to their strong adhesion capability to metallic substrates, their excellent resistance to chemicals, and their relatively high mechanical and impact strength. Effort has been devoted in recent years to develop epoxy-based protective coatings with good barrier properties, at least with regard to water vapor and oxygen [1,2,3]
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