Influence of pH values on the electrochemical performance of low carbon steel coated by plasma thin SiOxCy films

Chromium (VI) coatings are highly toxic and carcinogenic; therefore, thea should be replaced by a new eco-friendly material that retains its effectiveness in terms of corrosion. Herein, thin silicon oxycarbide films as an eco-friendly anticorrosive coating were deposited on a low carbon steel substrate by a radio frequency capacitively coupled plasma technique using tetraethyl orthosilicate (TEOS) as a precursor. The corrosion performance of the coatings were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in dependence on the gap distance between the plasma electrodes and the pH values at room temperature. The chemical bonding and morphological features of the deposited films were investigated by Fourier Transformer Infrared Spectroscopy in Attenuated Total Reflectance (ATR-FTIR) mode, X-Ray Diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX) coupled with scanning electron microscopy (SEM). The Icorr values were significantly decreased by reducing the gap distance and reached a minimum at 1 cm gap distance. It was reduced from 12 µA/cm2 for the blank sample to 0.714 µA/cm2 in treated sample at gap distance 1 cm and protective efficiency reached ~ 94% in the neutral solution. Nevertheless, the best protective efficiency achieved more than 99% of the total protection in alkaline medium as measured at room temperature for treated sample at gap distance 1 cm.