Corrosion performance of TiO₂ coated type 304L stainless steel in nitric acid medium

Abstract

The corrosion resistance of sputter deposited TiO₂ on austenitic type 304L stainless steel has been evaluated in the oxidizing medium of 1 M and 8 M nitric acid by monitoring corrosion potential, polarization behaviour and electrochemical impedance. Glancing incidence X-ray diffraction study of the TiO₂ coated surface revealed anatase phase and surface morphological study using an atomic force microscope showed evenly spaced particles with nano pores in the matrix. The particle size measurement showed that particles are within the range of 20-50 nm and measured root mean square roughness of coated surface was around 10 nm. The open circuit potential-time results in 1 M and 8 M nitric acid showed an increase in corrosion potential in both the test solutions for TiO₂ coated specimens. Electrochemical impedance analysis revealed an increase in magnitude of total impedance as well as phase angle for TiO₂ coated specimens in both the concentrations as compared to uncoated specimens. Potentiodynamic polarization study of coated specimens revealed overall resistance to corrosion by increase in corrosion potential, decrease in passive current density and increase in transpassive potential. Morphological examination of the polarized specimens using an atomic force microscope revealed resistance to surface dissolution in 1 M nitric acid and uniform surface dissolution at higher concentrations of nitric acid (8 M).