The temperature dependence of passivity breakdown on a titanium alloy determined by cyclic noise thermammetry

A new sensitive electrochemical technique is presented which is designed to measure the temperature dependence of the breakdown of passivity of metal surfaces. The method, termed “cyclic noise thermammetry”, consists of scanning the temperature of an electrochemical cell linearly and cyclically between two predefined limits, whilst simultaneously measuring the current flowing from a potentiostatically maintained microelectrode. An example of the new technique is presented, which describes the effect of temperature on the nucleation of corrosion pits on the titanium-based alloy, Ti-6Al-4V, in acidic chloride solution far below the pitting potential. Results are presented over the temperature range 20-50 °C. Events due to breakdown of passivity were detected throughout the entire temperature range. These events are the nucleation of corrosion pits, although they do not propagate into stable pits under the applied experimental conditions. Results show that passivity breaks down over the entire range of temperature, at a frequency that increases with increase in temperature.