**Domna Merachtsaki, Panagiotis Xidas, Panagiotis Giannakoudakis, Konstantinos Triantafyllidis \* and Panagiotis Spathis \***

Department of Chemistry, Aristotle University of Thessaloniki, University Campus, Thessaloniki 54124, Greece; do7mera@gmail.com (D.M.); pxidas@chem.auth.gr (P.X.); panjian@chem.auth.gr (P.G.)

**\*** Correspondence: ktrianta@chem.auth.gr (K.T.); spathis@chem.auth.gr (P.S.);

Tel.: +3-23-1099-7730 (K.T.); +3-23-1099-7835 (P.S.)

Received: 16 March 2017; Accepted: 13 June 2017; Published: 22 June 2017

**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.

**Keywords:** steel; corrosion; protection; coatings; epoxy—clay nanocomposites
