Titanium is protected against corrosion by a thin surface oxide film which may be only a few nanometers thick, and the chemical and physical durability of this film must be maintained if this metal and its alloys are to be used in industrial applications. Previous studies suggest that a temporary loss of passivity under high temperature aqueous conditions occurs at the grain boundaries in the material. The frequent breakdown and repair of the film yields electrochemical signals in the form of potential transients in the corrosion potential. The analysis of these potential signals provides very valuable information concerning the electrochemical behaviour of the alloy under these conditions. In this study, the electrochemical signals generated on Titanium (grade 7) were measured in aqueous chloride and sulphate solutions as a function of temperature (up to 150 deg C). In one experiment, the Ti-7 sample was allowed to form an air oxide film prior to exposure to the solution. Electrochemical impedance spectroscopy (EIS) was used to characterize the electrical properties of the film in each of the scenarios described above. By fitting EIS results to equivalent electrical circuits the consequences of film breakdown and repair on the overall film resistance were determined.
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