The Grand Challenges in Electrochemical Corrosion Research

Corrosion is the process of degradation or failure of a material resulting from a chemical reaction between the material and its surrounding environment. It is an indispensible research area in material science and engineering, because corrosion resistance characterizes the stability or durability of a material, which is one of the most important material performances in application. Compared with other materials, metals are relatively active, and likely to be susceptible to corrosion attack. Corrosion research thus mainly deals with the damaging mechanism and behavior of various metals, including ferrous or nonferrous, single crystal or nano-crystalline, cast or wrought, and structural or functional alloys. It has naturally grown into different branches based on alloy (Shreir et al., 1994), such as steel corrosion, Al alloy corrosion, Ni alloy corrosion, etc. The composition and microstructure are always the most decisive factors in determining the corrosion resistance of an alloy. On this aspect, a critical issue to address is how corrosion process is affected by matrix phase composition, segregated alloying element, lattice structure, crystalline defect, crystal orientation, grain size, secondary phase constituent, inter-metallic particle distribution, porosity, micro-crack density, impurity level, and surface state. Another important aspect of corrosion research is the complicated influence of environmental factors on corrosion. The sensitivity of corrosion behavior to environmental factors has led to varied degrees and forms of damage of metals under different service conditions (Cramer and Covino, 2006). According to the medium that metals are exposed to, corrosion can be easily classified into different types, such as aqueous or non-aqueous corrosion, ambient or high temperature corrosion, acidic or alkaline corrosion, etc. In the natural environment, atmospheric corrosion, seawater corrosion, and underground corrosion usually attack metals differently. A variety of corrosion problems associated with service environments have also been frequently reported in chemical, oil/gas, pipeline, civil, auto, aerospace, military, nuclear, and medical industries. As most environmental factors, like temperature, pressure, chemical composition, constituent concentration, pH value, electrical or thermal conductivity, viscosity, etc., can directly or indirectly interact, and continuously or inconstantly influence a corrosion process, the prediction of longterm corrosion behavior is quite difficult. Identifying a key influencing factor and understanding its effect on corrosion kinetics would be a research focus on this aspect. The core of corrosion research focuses on the material–environment reaction mechanism. It is the fundamental understanding of the detailed reaction processes, procedures, and steps, as well as their influencing factors that underpins corrosion science. Most ambient corrosion problems can be ascribed to electrochemical reactions (Kaesche, 2003), because moisture and aqueous liquid are widely present in the natural environment, and an electrochemical reaction is generally faster than oxidation–reduction reactions under ambient conditions. Stress-induced corrosion failure under many circumstances is a result of complicated interactions between stress and electrochemical reactions; the stress dramatically facilitates the electrochemical process and the latter strikingly amplifies the former’s damaging effect. Even at high temperatures, the molten salt corrosion may also be described as an electrochemical process. Therefore, electrochemistry is one of the most pertinent subjects in corrosion research (Mansfeld and Bertocci, 2005). To gain an insight into the core area of corrosion science, investigation of detailed electrochemical mechanisms and establishment of metal–electrolyte interface models should be prioritized. Having gone through the basic aspects and the core of corrosion science, one should never forget that the ultimate goal of corrosion research is to minimize corrosion damage. In this regard, all the methods that can interfere with the metal–environment reaction and effectively slow down the corrosion process are of great interest. In fact, cathodic protection (Baeckmann et al., 1997), coating (Swaraj, 1996), surface treatment/modification (Biestek and Weber, 1976), and inhibitor (Braford, 1993) techniques that retard the corrosion through different mechanisms have a long history of successfully mitigating corrosion damage in practice. They have built up an important extension of corrosion science, which more or less overlaps surface and coating science, technology, and engineering. Although technological innovation is the central theme in this area, scientific breakthroughs are highly desired. Innovations in corrosion prevention often emerge when new ideas, techniques, and results from other disciplines are introduced into this applied field of corrosion research. From the above brief introduction, the basic characteristics that virtually differentiate corrosion research from the other disciplines in materials science and engineering can be outlined as follows: