ABSTRACT
Since Iverson's seminal publication “Transient Voltage Changes Produced in Corroding Metals and Alloys” in 1968, the assessment of electrochemical noise signals has been successfully used, as an electrochemical technique, to study localized corrosion on passive materials. This paper reviews the work done by many research groups worldwide using electrochemical noise to elucidate the mechanisms of pitting corrosion, which occur in several electrochemical systems. This short review concentrates on passive layer stability and breakdown, metastable pitting and stable pit growth in stainless steels. In addition, the benefits and challenges of using electrochemical noise for studying localized corrosion of stainless steels are discussed in the context of the milestones accomplished with this electrochemical technique in the last 50 years.
ELECTROCHEMICAL NOISE – FROM THE PHENOMENON TO THE METHOD
Electrochemical noise (EN) is, in principle, a physicochemical phenomenon related to the dynamic equilibrium state of electrochemical processes. EN consists of fluctuations detectable in current and in the electrochemical potential produced by the difference between the kinetics of the concerned anodic and cathodic partial reactions involved in an electrochemical reaction. Because corrosion in metallic materials is an electrochemical process, EN also occurs during corrosion. Iverson, however, did not employ the term EN in his publication “Transient Voltage Changes Produced in Corroding Metals and Alloys”1, which was preceded by one publication in Nature.2 Iverson reported in 1968 on voltage fluctuations produced on AISI 1010 mild steel partly immersed in a NaCl-solution, and how those fluctuations disappeared once the sample was transferred to a Cl-bearing solution containing NaNO2 as an inhibitor. He rationalized these fluctuations as “minute transient changes in the electrical charge” of the corroding material due to an “imbalance of charge” as a result of cathodic and anodic reactions during the corrosion process. The term transient deserves at that point some explanation, because it is commonly used in literature related to EN. A transient, as introduced by Iverson in 19681, is a shortterm electrochemical event that can be measured as a change in potential, or in current, or in both.
