Influence of Long Time Polarization on Anodic Breakdown of Titanium in Concentrated NaCl Solutions

The breakdown resistance of titanium when anodically polarized in hot concentrated NaCl solutions is reported, and the influence of the applied voltage and of the testing method has been determined. Breakdown measurements during short-time tests (minutes) show breakdown is resisted until 9 V is applied. Measurements made during 24-hour constant voltage tests show breakdown is resisted only until 6 V is reached. In short term tests breakdown occurs generally over the entire electrode independently of any geometrical factor while under sustained tests, breakdown occurs inside crevices or underneath a salt crust which grows at the solution-air interface. A mechanism is proposed involving the intervention of transfer phenomena, hydrolysis processes and complex ions, which can account for the lower voltage at which breakdown occurs in crevices.