Microstructure and Corrosion Behaviour of Carbon Steel and Ferritic and Austenitic Stainless Steels in NaCl Solutions and the Effect of p-Nitrophenyl Phosphate Disodium Salt

摘要

The microstructure and corrosion behavior of carbon steel (CSA516) and ferritic (SS410) andaustenitic (SS304L) stainless steels were studied and compared. Corrosion tests were carried out in 0.5M NaCl solutions. Rates of corrosion were monitored based on weight loss, Tafel extrapolation andlinear polarization resistance (LPR) methods. Rates of corrosion were ranked following the order:CSA516 SS410 > SS304L. The impact of p-Nitrophenyl phosphate disodium salt (NPP) on thecorrosion rate of CSA516 was also studied using Tafel polarization and LPR measurements. Opticalmicroscopy (OM), scanning electron microscopy (SEM/EDX), and X-ray photoelectron spectroscopy(XPS) were employed to assess the chemical compositions and morphologies of the corroded andinhibited surfaces. FT-IR analyses were also performed to assess the functional groups of the inhibitedsample in a comparison with NPP itself. XPS and FT-IR studies revealed the presence of phosphategroups originating from tested inhibitor, thus proving formation of the protective layer on the steelsurface. The microstructural and defect investigations of as-polished, corroded, and inhibited CSA516samples were also carried out using positron annihilation lifetime (PAL) and positron annihilationDoppler broadening (PADB) techniques. Experimental findings revealed that NPP acted as an efficientInt. J. Electrochem. Sci., Vol. 11, 2016 10030mixed-type inhibitor with anodic predominance. It reached about 97% inhibition efficiency at a lowconcentration of 0.02M.