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Keywords:

  • coating;
  • corrosion;
  • titania;
  • liquid-phase deposition;
  • electrochemical impedance spectroscopy;
  • Tafel curves;
  • cyclic voltammetry;
  • AISI304 stainless steel

Abstract

Fouling deposition and localized corrosion on the heat-transfer surfaces of the stainless steel equipments often simultaneously exist, which can introduce additional thermal resistance to heat-transfer and damage heat-transfer surfaces. It is a good anticorrosion way to coat a barrier layer of certain materials on the metal surface. In this article, the TiO2 coatings with nanoscale thicknesses were obtained by liquid-phase deposition method on the substrates of AISI304 stainless steel (ASS). The coating thickness, surface roughness, surface morphology, crystal phase, and chemical element were characterized with the film thickness measuring instrument, roughmeter, atomic force microscopy, field emission scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy analyzer, respectively. Corrosion behavior of the TiO2 coatings was evaluated by potentiodynamic polarization, cyclic voltammograms scanning, and electrochemical impedance spectroscopy tests with the mixed corrosion solution composed of 3.5 wt. % NaCl and 0.05 M NaOH. It is shown that the TiO2 coating is composed of the nanoparticles with smooth, crack-free, dense, and uniform surface topography; the roughness of coating surface increases slightly compared with that of the polished ASS substrate. The anatase-phase TiO2 coatings are obtained when sintering temperature being varied from 573.15 to 923.15 K and exhibit better anticorrosion behavior compared with ASS surfaces. The corrosion current density decreases and the polarization resistance increases with the increase of the coating thickness. The corrosion resistance of the TiO2 coatings deteriorates with the increase of the corrosion time. The capacitance and the resistance of the corrosion product layer between the interface of the ASS substrate and the TiO2 coating are found after the corrosion time of 240 h. A corrosion model was introduced, and a possible new explanation on the anticorrosion mechanisms of the TiO2 coating was also analyzed. The corrosion mechanism of the TiO2 coating might comply with the multistage corrosion process. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1907–1920, 2012