Room temperature electrosynthesis of TinO2n-1 film and its bilayer with PNMPy on mild steel for corrosion protection in sulphuric acid
By Pekmez, Nuran Özçiçek; Uğur, Merve; Karaca, Erhan; Ertekin, Zeliha; Pekmez, Kadir
Published in Electrochimica Acta
2021
Abstract
The low-temperature electrosynthesis of titanium suboxide (TinO2n-1) is carried out cathodically on mild steel (MS) in acetonitrile solution containing TiO(ClO4)2•6H2O. A bilayer coating of TinO2n-1 and poly(N-methyl pyrrole) (PNMPy) is also performed to combine the protective and hydrophobic properties of metal oxide and conductive polymer, respectively. PNMPy top layer is deposited anodically on the TinO2n-1-coated MS electrode in an aqueous oxalic acid solution containing NMPy monomer. The parameters affecting the experimental conditions for the synthesis are optimized according to their resistances obtained from EIS. XRD, XPS, and SEM-EDX studies reveal that the homogeneously dispersed TinO2n-1 is obtained with phases containing different amounts of oxygen, such as Ti3O5, Ti4O7, and Ti5O9 simultaneously, together with Fe2O3 at room temperature. The co-deposition of some Fe2O3 on MS surface contributes to the protective property of the TinO2n-1 coating due to providing the rough surface. Besides, the formation of the Fe2TiO5 intermetallic phase on the surface could be an important factor for the quality of TinO2n-1 deposition. The corrosion performances of the coatings are evaluated by Tafel, long term OCP and EIS measurements. According to the EIS results, the TinO2n-1/PNMPy bilayer coating improves the corrosion resistance of the bare MS by about 50 times (702 ohm.cm2) in 0.5 M H2SO4 and enhances the protection efficiency up to about 98%. This is because hydrophobic PNMPy fills the pores of the TinO2n-1 undercoating layer; thus, not only conductive but also lower porosity and better protective properties are achieved.