Depassivation current transients measured between identical twin microelectrodes in open circuit

Current transients between identical twin titanium microelectrodes have been measured in open circuit. The electrodes showed transient breakdown of passivity in 1.5 M HCl although the potential is far below the pitting potential. Measurement of the current between the twin microelectrodes in sodium sulphate solution containing no chloride showed no detectable breakdown transients above the background noise. The current transients represent the breakdown of passivity and associated nucleation of corrosion pits. Some of the open circuit breakdown events show evidence of brief metastable pit propagation in the titanium surface.