**1. Introduction**

396 Corrosion Resistance

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One of the main causes of degradation of metallic products during their operation time is their corrosion. The destruction by corrosion arises from spontaneous adverse chemical reactions in metallic materials with the surrounding environment. Irreversible corrosive processes damage any metallic products both, during their operation, and their storage. Economic losses due to destructive corrosive actions are very important and still growing due to increasing environmental pollution. The annual cost of corrosion and corrosion protection in the world is estimated to be in excess of hundred billion dollars. Reducing the continuing degradation of metallic materials by corrosion is one of the fundamental objectives of modern technological solutions and is still the subject of intensive research in many research centers in the world (Yang, 2008).

Metallic products in operational conditions are primarily exposed to electrochemical corrosion. Corrosion processes, which include oxidation and reduction reactions, mainly occur at the interface between the metal and the environment. Both, the structure and the properties of the metal as well as the characteristics of the environment affect the corrosive processes. The rate of corrosion processes depends on the electrochemical susceptibility of a given metal, its chemical composition, homogeneity and surface topography, on the type and chemical composition of the environment, the concentration of aggressive agents, temperature, as well as the type of corrosion products themselves. Electrochemical corrosion processes are accompanied by mass transport and flow of electric charge through the metal corrosive environment boundary. To characterize the susceptibility of metallic materials to electrochemical degradation modern research techniques increasingly use the relationship between voltage and current intensity occurring in corrosive systems. Such studies rely on computerized measuring system, in which suitable electrical stimulation is generated numerically while the system analyzes simultaneously the response. The results are presented in the form of graphs showing the current - voltage relationships (Trzaska, 2010).

In this chapter we present the results of investigations of corrosion properties of metallic materials with different chemical susceptibilities and different crystalline structures. The main focuses are materials playing important roles in current technologies.

Studies of Resistance to Corrosion

electrode system (Fig. 1).

**a)** 

2 and 3).

of Selected Metallic Materials Using Electrochemical Methods 399

steady state corrosion by applying the sinusoidal alternating potential signal of small amplitude, but in a wide range of frequencies and the automatic recording of current intensity responses of the system. Investigations of corrosion by those methods, based on a change in the relationship between potential and current were implemented in the three-

**b)** 

Fig. 1. Three-electrode system for corrosion studies: a) measuring system, b) circuit diagram.

Counter electrode (Pt)

Research of metallic materials corrosion was carried out by means of computerized measuring systems, which generated in a digital form an electrical signal of a certain shape to stimulate the system and simultaneously analyze the response of the corrosion test (Figs.

 **Generator Potentiostat Signal** 

**Corrosion cell**

In the three-electrode system, used in the current study, the examined metal takes the role of the active electrode. A calomel electrode, Hg/Hg2Cl2/KCl characterized by the potential +244 mV, was used as the reference electrode. Auxiliary electrode was made of platinum (Pt). The tests were carried out in the corrosive environment of 0.5M NaCl solution at pH =

Fig. 2. Block diagram of the electrochemical corrosion tests.

7 and a temperature of 293K (Trzaska Trzaska, 2010).

**traitement**

Calomel reference electrode

Working electrode (examined material)

Solution

Two electrochemical methods were used to characterize the corrosion properties of the materials under investigation: potentiodynamic polarization and impedance spectroscopy.
