Passivity of Titanium in Hydrochloric Acid Solutions'

Electrode potential measurements and weight loss corrosion tests indicate that air or low concentrations of certain dissolved metals passivate titanium in hydrochloric acid solutions and that passivity is accompanied by more noble electrode potentials. Air passivates titanium in acid up to 3N. Two hundred mg/l Cu ++ is effective in 10N hydro-chloric acid and 2 mg Cu ++ passivate titanium in 5N acid. The more noble electrode po-tentials indicate that a reaction involving oxygen, meted ions, or ions containing oxygen takes place at the passive surface but there is no visible deposit on, or change in, the ap-pearance of the surface except for an occasional slight tarnish. Titanium in contact with small volumes of stagnant 10N hydrochloric acid containing 200 mg/1 Cu ++ loses its passivity after a period of time. This time int rval seems to be directly proportional to the ratio of solution volume to specimen area and the loss of passivity is attributed to the presence of atomic hydrogen