Abstract
The passivity of titanium was studied in mixed sulfate-chloride solutions. Polarization results confirmed that Cl− ions can effectively facilitate the anodic passivity of Ti in sulfuric acids at 25°C. According to Mott-Schottky analysis, and with point defect model (PDM) analysis, this facilitating effect can be attributed to the lower density and higher diffusivity of point defects within the pasive films formed on titanium in H2SO4 solutions with Cl− additions. Electrochemical impediance spectroscopy (EIS) measurements also revealed that films formed in 0.5 M H2SO4 + 0.5 M NaCl have a two-layer structure and present higher corrosion resistance compared with films formed in 0.5 M H2SO4 which have a one-layer structure. All the results obtained at 75°C showed that the electrochemical responses of films formed in 0.5 M H2SO4 with and without 0.5 M NaCl addition are similar. Titanium is immune to Cl− ions in H2SO4 solutions at 75°C.
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