PASSIVE BEHAVIOR OF TITANIUM IN ALKALINE-SOLUTION

The passive behavior of titanium in alkaline acetate, borate and carbonate solutions of pH 7-13 has been studied by quasi-stationary (20 h stabilization) transient polarization measurements and by dc capacitance determinations over potentials from minus 0. 75 to plus 2. 5 V(sce), all at 25 degree C. Titanium exhibits approach to active/passive transition at low potentials, regular passive behavior with nearly pH independent passive current over an intermediate potential range, and electron extraction from solution species at higher potentials. In the regular passive region, potentiostatic transients accord with the Cabrera-Mott equation. Capacitance data largely obey expectations from an 'insulator' model, revealing the main charge distribution at the passive titanium electrode.