Brightly saturated coloration of Ti sheets in deep eutectic solvents by anodic oxidation: the role of H2O

Brightly saturated oxide films are successfully prepared on Ti sheets surface by anodic oxidation in ethaline deep eutectic solvent (DES) with the regulation of H 2 O content, to enhance the decorative and corrosion resistance. As H 2 O content increases from 0 wt .% to 100 wt .% in the DES, the colored surface of Ti sheets exhibits a highly reproducible and a variety of colors including yellow, brown, red, purple, and blue. The role of H 2 O during the coloring process is discussed to shed light on the deeper causes of the color changes of Ti sheets. There exists a critical H 2 O content, i.e. 20 wt. %, and below this value, it benefits to the increase of bath voltage and the formation of oxide films, reflecting in a regular change in the color of Ti sheets. Above 20 wt. %, some characteristics conferred by ethaline DES may be weakened, so that the color of Ti sheets basically remains unchanged in blue tone. Besides, systematically characterizations of colored Ti sheets demonstrate that non-stoichiometric titanium oxides are formed as a mixture of TiO 2 , Ti 2 O 3 and TiO. The variations in H 2 O content have significant impacts on the surface composition of colored Ti sheets, resulting in an increased O/Ti ratio of the surface oxides and altering the optical properties of the colored films. Furthermore, the EIS and dynamic potential polarization tests show a significant increase in impedance and a decrease in corrosion current density for the colored Ti sheets compared to the untreated, implying an enhancement in corrosion resistance.