The Grand Challenges in Electrochemical Corrosion Research

Abstract

Corrosion is the process of degradation orfailure of a material resulting from a chem-ical reaction between the material and itssurrounding environment. It is an indis-pensible research area in material scienceand engineering, because corrosion resis-tance characterizes the stability or dura-bility of a material, which is one of themost important material performances inapplication.Compared with other materials, met-als are relatively active, and likely to besusceptible to corrosion attack. Corrosionresearch thus mainly deals with the dam-aging mechanism and behavior of var-ious metals, including ferrous or non-ferrous, single crystal or nano-crystalline,cast or wrought, and structural or func-tional alloys. It has naturally grown intodifferent branches based on alloy (Shreiret al., 1994), such as steel corrosion, Alalloy corrosion,Ni alloy corrosion,etc. Thecompositionandmicrostructurearealwaysthe most decisive factors in determiningthe corrosion resistance of an alloy. Onthis aspect, a critical issue to address ishow corrosion process is affected by matrixphasecomposition,segregatedalloyingele-ment, lattice structure, crystalline defect,crystal orientation, grain size, secondaryphase constituent, inter-metallic particledistribution,porosity,micro-crack density,impurity level, and surface state.Another important aspect of corrosionresearch is the complicated influence ofenvironmental factors on corrosion. Thesensitivity of corrosion behavior to envi-ronmental factors has led to varied degreesand forms of damage of metals underdifferent service conditions (Cramer andCovino, 2006). According to the mediumthat metals are exposed to, corrosion canbe easily classified into different types,such as aqueous or non-aqueous corro-sion, ambient or high temperature cor-rosion, acidic or alkaline corrosion, etc.In the natural environment, atmosphericcorrosion, seawater corrosion, and under-ground corrosion usually attack metals dif-ferently. A variety of corrosion problemsassociated with service environments havealso been frequently reported in chemi-cal, oil/gas, pipeline, civil, auto, aerospace,military, nuclear, and medical industries.As most environmental factors, like tem-perature, pressure, chemical composition,constituent concentration, pH value, elec-trical or thermal conductivity, viscosity,etc., can directly or indirectly interact, andcontinuously or inconstantly influence acorrosion process, the prediction of long-term corrosion behavior is quite difficult.Identifying a key influencing factor andunderstandingitseffectoncorrosionkinet-ics would be a research focus on thisaspect.The core of corrosion research focuseson the material–environment reactionmechanism. It is the fundamental under-standing of the detailed reaction processes,procedures, and steps, as well as theirinfluencing factors that underpins corro-sionscience.Mostambientcorrosionprob-lems can be ascribed to electrochemicalreactions (Kaesche, 2003), because mois-ture and aqueous liquid are widely presentin the natural environment, and an elec-trochemical reaction is generally fasterthan oxidation–reduction reactions underambient conditions. Stress-induced corro-sion failure under many circumstances is aresult of complicated interactions betweenstress and electrochemical reactions; thestress dramatically facilitates the electro-chemical process and the latter strikinglyamplifies the former’s damaging effect.Even at high temperatures, the molten saltcorrosion may also be described as an elec-trochemical process. Therefore, electro-chemistry is one of the most pertinent sub-jects in corrosion research (Mansfeld andBertocci, 2005). To gain an insight into thecoreareaof corrosionscience,investigationof detailed electrochemical mechanismsand establishment of metal–electrolyteinterface models should be prioritized.Having gone through the basic aspectsand the core of corrosion science, oneshould never forget that the ultimategoal of corrosion research is to mini-mize corrosion damage. In this regard,all the methods that can interfere withthe metal–environment reaction and effec-tively slow down the corrosion processare of great interest. In fact, cathodicprotection (Baeckmann et al., 1997),coating (Swaraj, 1996), surface treat-ment/modification (Biestek and Weber,1976), and inhibitor (Braford, 1993) tech-niques that retard the corrosion throughdifferentmechanismshavealonghistoryofsuccessfully mitigating corrosion damagein practice. They have built up an impor-tant extension of corrosion science, whichmore or less overlaps surface and coat-ing science, technology, and engineering.Although technological innovation is thecentral theme in this area, scientific break-throughs are highly desired. Innovations incorrosion prevention often emerge whennew ideas, techniques, and results fromother disciplines are introduced into thisapplied field of corrosion research.From the above brief introduction, thebasic characteristics that virtually differ-entiate corrosion research from the otherdisciplines in materials science and engi-neering can be outlined as follows:(1) Corrosion occurs in a complicatedsystem simultaneously influenced byenvironmental factors and metallurgi-cal parameters. These interactive fac-tors tremendously complicate the cor-rosion system. Thus, the key influenc-ing factor and the rate-determiningstep that govern the fundamentalkinetics of a corrosion process can-notbeclearlyidentified.Consequently,many corrosion phenomena cannotbe interpreted theoretically. Corrosion