1 Basics of Corrosion Chemistry

Metallic materials in practical use are normally exposed to corrosion in the atmospheric and aqueous environments. Metallic corrosion is one of the problems we have often encountered in our industrialized society; hence it has been studied comprehensively since the industrial revolution in the late eighteenth century. Modern corrosion science was set off in the early twentieth century with the local cell model proposed by Evans [1] and the corrosion potential model proved by Wagner and Traud [2]. The twomodels have joined into themodern electrochemical theory of corrosion,which describesmetallic corrosion as a coupled electrochemical reaction consisting of anodic metal oxidation and cathodic oxidant reduction. The electrochemical theory is applicable not only to wet corrosion of metals at normal temperature but also to dry oxidation of metals at high temperature [3]. Metallic materials corrode in a variety of gaseous and aqueous environments. In this chapter, we restrict ourselves to the most common corrosion of metals in aqueous solution and in wet air in the atmosphere. In general, metallic corrosion produces in its initial stage solublemetal ions inwater, and then, themetal ions develop into solid corrosion precipitates such as metal oxide and hydroxide. We will discuss the whole process of metallic corrosion from the basic electrochemical standpoint.