Influence of the annealing temperature and metal salt precursor on the structural characteristics and anti-corrosion barrier effect of CeO2 sol–gel protective coatings of carbon steel

Abstract

Metal corrosion protection is one of the most important challenges in the world; moreover, the need for replacement of hazardous chromates in barrier coatings is of tremendous interest. Thus, we report the development of ceramic cerium oxide coatings by the sol–gel method on carbon steel substrates to improve their corrosion resistance and compare the influence of the use of ceric ammonium nitrate and cerium chloride as metal salt precursors. Different calcination temperatures (200, 300, 400 or 500°C) and heating rates (1 or 5°Cmin−1) of the deposited coatings were also used for synthesis of the coatings and their corrosion behavior was investigated through potentiostatic polarization and electrochemical impedance spectroscopy experiments. Electrochemical results indicated that the ceria coatings deposited using ceric ammonium nitrate at 200°C and 5°Cmin−1 are very efficient in the corrosion protection of carbon steel, thus diminishing the current density of corrosion by two orders of magnitude and shifting the corrosion potential by 380mV to more positive values when compared with bare carbon steel. The physical characterization of the sol–gel coatings carried out by atomic force microscopy and X-ray diffraction pointed out that the use of low calcination temperatures yielded homogeneous and non-cracked surfaces of ceramic cerium oxides with improved anticorrosive efficiency. By contrast, the use of high temperatures results in cracked surfaces of crystalline ceramic ceria with poor anticorrosion efficiency and also probably provokes the diffusion of components from the alloy to the coating–substrate interface. Furthermore, the use of ceric ammonium nitrate as cerium precursor resulted in the most resistive coatings for all the temperatures and heating rates studied here.