Homogeneity corrosion

The measurement of corrosion current has provided, as is well known, a quite useful electrochemical technique for determining corrosion rates. However, contrary to homogeneous corrosion, pitting corrosion is a typical heterogeneous reaction on a metal surface, so that it is difficult to estimate the actual corrosion state from the usual corrosion current data. 

Assume the homogeneous corrosion of iron in a deaerated acid solution at pH = 4 (i.e., the anodic and cathodic reactions are occurring uniformly over any unit area). Plot the anodic polarization curve for iron and the cathodic polarization curve for the hydrogen reaction. Estimate Ecorr, icorr, and the corrosion penetration rate in pm/year. Given ... 

It is of importance to predict the lifetime of a metallic component in a specific corrosive system. For uniform corrosion (also called homogeneous corrosion), the lifetime can be calculated if the kinetics of the reactions are known and if no localized attack or corrosion cracks could appear. In this chapter, the kinetic aspects of the homogenous corrosion process will be considered. Only electrochemical corrosion mechanisms are regarded, not chemical and physical ones. 

During homogenous corrosion, several nonreversihle reactions take place at one electrode at the same time, which leads to a uniform reduction of the component thickness. Homogenous corrosion is often found in solutions in which no corrosion products could be formed at the metal surface. Corrosion is composed of at least two partial reactions (see Fig. 1) ... 

I 2 Homogeneous Corrosion of Metallic Materials in Electrolytes Electrolyte... 

The most common method for the determination of the corrosion rate of homogeneous corrosion is the measurement of weight loss. The mass change is measured after exposure of the metal to the corrosive media for a defined time and conditions. The material consumption rate II is calculated by the weight loss Am per time t and area A... 

For the determination of weight loss, the corrosion products have to be removed. Inhibited acids are normally used for this purpose, but it is important to be sure that such acids remove only the corrosion products and do not attack the base metal. For example, the following acids could be used inhibited hydrochloric acid for iron, sulfuric acid for copper, and chromium trioxide solutions for zinc. The chemical cleaning procedures for the removal of corrosion products are further described in ISO 8407 (3). The removal of corrosion products is also necessary to confirm homogenous corrosion and exclude possible local corrosion attack. 

In the following section, examples for homogenous corrosion are given. It is impossible to discuss all possible corrosion systems, but the main principles of the corrosion process in acids or neutral and alkaline solutions will be demonstrated. 

The homogenous corrosion rate of copper in nonoxidizing deaerated acids is... 

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