Spectroscopic and Simulation Insights into the Corrosion Mechanism of Sulfite on Titanium

Ion adsorption and hydrogen bond (HB) network reconstruction in electric double layer (EDL) have a profound impact on the interface properties. The microstructure in the bulk phase of 1.00-21.30 wt.% Na₂SO₃ aqueous solutions are investigated by X-ray scattering, confocal Raman spectroscopy, and classical molecular dynamics. The electronic properties of SO₃^2- adsorption and the geometric structure of the HB network in the EDL at the titanium TiO₂(101) surface are studied by density functional theory (DFT) and classical molecular dynamics. The SO₃^2- strongly weakens the fully hydrogen-bonded water (FHW) and transforms it into partial hydrogen-bonded water (PHW). The HB transformation index (HBTI = PHW/FHW) shows a linear relationship with the mass fraction of Na₂SO₃. The TiO_b-parallel adsorption configuration of SO₃^2- enhances the ionicity of the O_b-Ti₆ bond, resulting in the formation of oxygen vacancies at the titanium passive film surface. Besides, SO₃^2- and Na⁺ are enriched and thermodynamic supersaturated in the inner Helmholtz layer (IHL), and the ions are diluted in the outer Helmholtz layer (OHL). The diffusion coefficient of SO₃^2- and water molecules in EDL decreases seriously, which is easy to causes salt scaling on the surface of titanium passive film. This work provides evidence for the destruction of titanium passive film by SO₃^2-.