Evaluation of corrosion protective behaviour of alumina film deposited by oxime-modified aluminium(III) alkoxide precursor

Abstract

Oxime-modified aluminium(III) isopropoxide, [Al(OiPr){ONC(CH3)2}2] was used as a sol-gel precursor to deposit alumina film on steel substrate by dip coating method. The thermogravimetric analysis (TGA) of the above compound indicates its clean one step decomposition to alumina at low temperature, making it a suitable spray pyrolysis deposition (SPD) precursor for deposition of alumina film over steel at 400°C. The formed alumina films (dip and spray coated) were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopic (EDX) techniques. The XRD patterns of the films suggest deposition of amorphous alumina films while the FTIR and EDX analyses indicate the presence of alumina film on steel substrate. SEM images of coated samples indicate deposition of crack-free alumina films. The thickness of alumina films (dip and spray coated) were found to be in the range of ~1.4±0.2μm as indicated by their cross sectional views. The corrosion protection of the deposited alumina films has been checked by the electrochemical studies; open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The electrochemical studies suggest corrosion resistive nature of the alumina film in 3.5% (w/v) NaCl solution.