SYNTHESIS, CHARACTERISATION AND ANTI-CORROSION BEHAVIOUR OF NiO-CNTs-SnO2 NANOCOMPOSITES COATINGS ON AISI 1020 STEEL

Abstract

In this study, synthesised NiO-CNTs-SnO2 nanocomposites based coatings were applied on AISI 1020 steel samples to prevent corrosion. NiO-SnO2 based nanocomposites were obtained via combination of green-impregnation and sonochemical methods followed by incorporation of CNTs at different ratios. The influence of process parameters on the synthesis of NiO and SnO2 nanoparticles such as; solution pH, precursor concentration, and synthesis temperature on particle size were investigated via surface response methodology (RSM) using the Box-Behnken method. The synthesised nanocomposites were characterised with the aid of High resolution scanning electron microscopy (HRSEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), High Resolution Transmission Electron Microscope (HRTEM) and Selective Area Diffraction Spectroscopy (SAED) and X-ray Photoelectron Spectroscopy. Subsequently, NiO-SnO2, NiO-CNTs, SnO2-CNTs and NiO-CNTs-SnO2, were dip coated on the surface of AISI 1020 steel coupons. The corrosion performance of the (NiO-SnO2, NiO-CNTs, SnO2-CNTs) and NiO-CNTs-SnO2, coatings in soil environment as corrosive media were investigated by Gravimetry, Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy methods (EIS). HRSEM analysis showed that the obtained NiO-CNTS-SnO2 nanocomposites were aggregated, with combined spherical, tubular and cubic structures with an average crystalline size of 25 nm. Energy Dispersive Spectroscopy (EDS) analysis revealed the presence of Sn, Ni, C and O as major elements in the nanocomposites. The XRD analysis of as-synthesised nanocomposites revealed the formation of crystallinity bunsenite, graphite and cassiterite phases belonging to NiO, CNTs and SnO2 respectively. The X-ray Photoelectron Spectroscopy (XPS) analysis of the nanocomposites revealed the formation of Nickel Oxycarbide-Tin alloy responsible for the improved anti-corrosion properties of the developed nanomaterial. Gravimetry analysis showed its lowest corrosion rate at 8.76E-08 mpy for a coupon coated and buried with NiO-CNTs-SnO2 composite in the ratio (1:1:2) and a Protection Efficiency of 92.61% after 12 months of reweighing. The PDP showed that NiO-CNTs-SO2, in the ratio (1:1:2), had excellent corrosion resistance behavior with lowest corrosion current of 0.0064 µA/cm2 and Protection Efficiency of 93.30% while the charge transfer resistance, Rct of 6.244 KΩ·cm2 and Protection Efficiency of 93.90% were established with the same NiO-CNTs-SnO2 composite coating of the same ratio (1:1:2) for EIS measurement against the corrosion of AISI 1020 steel substrate. The corrosion rate was also found decreased from 0.0335 to 0.0022 mpy showing evidence of a slow rate of uniform corrosion and better Protection Efficiency of the steel substrate. HRSEM/Cross-Sectional analysis of steel coated with NiO-CNTs-SnO2 (1:1:2) buried in the soil revealed successful protection of the steel coupon. XRD analysis also showed non-destruction of the diffraction peaks of NiO, CNTs and SnO2, respectively. This study demonstrated NiO-CNTs-SnO2 based coatings in the mixing ratio 1:1:2, as the most effective material to protect the steel coupon.