Anodic Polarization Behavior of Titanium and Titanium Alloys in Sulfuric Acids

Anodic polarization behavior of unalloyed titanium (Ti-75A) and four commercially-important titanium alloys was studied in hydrogen-saturated 1, 5 and 10 N sulfuric acid at 22 C (71.6 F) using a potentiostatic technique. Specimens exhibited an active-to-passive transition in all acid environments. A transpassive region was observed only for a specimen containing 11 w/o chromium. Transpassive behavior for this alloy (Ti-13V-11Cr-3Al) was associated with chromate formation. Corrosion potentials were not appreciably affected by acid concentration or alloy composition. Critical current densities varied with pH according to the expression: logicr=logicro-apH,where icro=0.05±0.008ma/cm2 and a = 0.77. Passivation potentials were linear functions of pH with a slope dependence dEp/dpH of −0.05 to −0.06. Values of Epo (pH=0) varied from −0.50 to −0.54 volt vs SCE. Passive current densities increased with decreasing pH according to the expression: logip=logipo-apH,where ip = 0.005 ± 0.002 ma/cm2 and a = 0.44. Critical current densities, passivation potentials and passive current densities were considered to be composition independent.