Chapter 6 - Corrosion Behavior Investigations of Titanium and its Alloys in the Media of Electrochemical Plants, Taking into Account the Attack by Anodic Leakage Currents

Abstract

This chapter discusses the corrosion behavior of titanium and its alloys in the media of electrochemical plants, taking into account the attack by anodic leakage currents. The corrosion stability of titanium is determined by its strong ability to passivate and by the high stability of the passive oxide film that is formed on its surface. Owing to the protective properties of this film, titanium possesses high corrosion resistance in many acidic, neutral, and alkaline media, including media containing activators such as chlor-ions. Titanium belongs to the group of valve metals. The oxide film that is formed on its surface functions as a diode: it allows a cathodic current to pass through and almost completely cuts off the metal surface for the passage of an anodic current. The presence of an oxidizer, which is most typical for the aggressive media of electrochemical plants, does not reduce the corrosion stability of titanium, and, in most cases, even increases it. For example, in hydrochloric acid solutions, in the presence of dissolved chlorine, the potential of titanium shifts from the active state to the passive field, as in the case of anodic protection. As a result, the corrosion process on titanium stops. Just by having the ability to maintain corrosion stability in media containing oxidizers and activators simultaneously, titanium found widespread application in electrochemical plants and, particularly, in chlor-alkali electrolysis plants, away from the zones of leakage currents attack. However, in the action zones of leakage currents, titanium can undergo intensive corrosion.