First-Principles Study on the Adsorption Characteristics of Corrosive Species on Passive Film TiO 2 in a NaCl Solution Containing H 2 S and CO 2.

The adsorption characteristics of corrosive anions (Cl⁻, HS⁻, S²⁻, HCO₃⁻ and CO₃²⁻) on TiO₂ of TC4 titanium alloy in a NaCl solution containing H₂S and CO₂ were studied by density functional theory (DFT). The stable adsorption configuration of each corrosive species on the TiO₂ (110) surface was obtained by geometric optimization, and the electronic structure and interface binding energy were calculated and analyzed. The results showed that the optimal adsorption positions of Cl⁻, HS⁻, S²⁻, HCO₃⁻ and CO₃²⁻ on TiO₂ (110) were all bridge positions. There was a strong charge interaction between the negatively charged Cl, S and O atoms in Cl⁻, HS⁻, S²⁻, HCO₃⁻ and CO₃²⁻ and the positively charged Ti atoms of TiO₂. The interface bonding was mainly caused by charge movement from around Ti atoms to around Cl, O, S atoms. The energy levels were mainly caused by the electron orbital hybridization of Cl-3p⁵, S-3p⁴, O-2p⁴ and Ti-3d². All adsorption configurations were chemical adsorption. The order of influence of the five ions on the stability of TiO₂ was S²⁻ > CO₃²⁻ > Cl⁻ > HS⁻ > HCO₃⁻. Finally, a novel corrosion mechanism was proposed to illustrate the dynamic evolution processes of pits. [ABSTRACT FROM AUTHOR]