**3. Relevance of corrosion and tribocorrosion monitoring**

The importance of corrosion and/or tribocorrosion monitoring is that it allows people of interest to study the extent of damage due chemical and/or mechanochemical attacks and to become aware of the rate at which such damage is progressing so that the necessary measures can be taken to avoid trouble. Generally, the application of continuous and adequate on-line corrosion or tribocorrosion monitoring includes the following advantages: enhanced security, ensuring operational reliability on-time, minimizing process contamination and maximizing product quality, providing a sentinel for equipment integrity, and preventing any further risk related to material or production. The most convenient way to successfully combat corrosion or tribocorrosion impact on materials and structures is (i) to understand the main causes of corrosion and/or wear, (ii) to use all available means to prevent it, (iii) and to implement a continuous improvement approach to corrosion and wear protection.

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**3.2 Corrosion forms**

*Electrochemical Techniques for Corrosion and Tribocorrosion Monitoring: Fundamentals…*

There are several factors that can come into play in the process of corrosion or tribocorrosion [1–3, 8]. Among the common influential criteria on corrosion, the following main parameters can generally be selected, namely the pH of the medium, the presence of chlorides (and other alkyl halides), the oxidizing power, the pressure, and the temperature. Fundamentally, corrosion depends on the dominating deterioration mechanism of surfaces exposed to chemical environment. The corrosion resistance properties can be characterized directly by the limits of use of the materials, which can be expressed, for example, in terms of maximum temperature in-service or maximum concentration of use. Under normal service conditions, the understanding and control of corrosion are based on the electrochemical interpretation of corrosion phenomena and the consideration of the relative ranking scales of materials in order to select, by successive approaches, the

Conversely, a more obvious mechanism of tribocorrosion is the periodic exposure

There are many electrochemical and non-electrochemical techniques for the study

of corrosion or tribocorrosion and many factors must be taken into account when choosing a technical method. The corrosion rate can be determined by extrapolation of Tafel from a potentiodynamic polarization curve [12, 13]. It can also be determined using the Stern-Geary equation from the polarization resistance derived from a linear polarization experiment or from electrochemical impedance spectroscopy [12, 13]. Furthermore, among the recently developed techniques, those using electrochemical noise analysis as a method of determining the rate of corrosion and estimating the tribocorrosion rate of some passive materials has been shown to be beneficial, although scientists are struggling through the interpretation of some conflicting results [2, 12–15]. Sensitivity to localized corrosion is often evaluated by determining

a breakdown potential and a repassivation potential for passivating materials.

Obviously, the most typically known mode of corrosion is the rusting of iron, or iron oxide, and ordinary steel. Contemporary corrosion research has established several forms of corrosion, all which are important to understanding, as the best methods of preventing corrosion depend upon the form of corrosion, as shown in **Figure 2**.

• *Uniform corrosion*: the damage by general or uniform corrosion is fairly predictable; however, the damage caused by localized corrosion is rather unpredictable if no proper monitoring techniques are applied. When left uncontrolled, corrosion will not only cause costly equipment maintenance and replacement

of fresh bare surfaces when sliding friction between surfaces occurs in corrosive liquids or gases [3]. This results in reaction products mainly driven by chemical and electrochemical interactions. The surfaces of the materials are quickly covered by a scale of the reaction product, the oxide in the case of metals and metallic alloys, acting as a protective barrier layer. Often, the thinner the scale, the faster the reaction, and the weaker the protectiveness [3]. Though, tribocorrosion processes are complex, combining both wear and corrosion. Modern research has established a consensus on four main forms of wear, namely, chemical wear (i.e., corrosion and corrosive wear), adhesive wear, abrasive wear or surface fatigue wear [3, 11]. Each process obeys its own laws and, to confuse things, one of the modes of wear acts to affect the others, hence the complexity of corrosive wear [1–3]. As a general rule, there is a combination of competitive wear mechanisms in a dynamic mechanical-chemical contact.

*DOI: http://dx.doi.org/10.5772/intechopen.85392*

materials best suited to each application of interest [3].

**3.1 Choice of technique (instrumentation)**

#### *Electrochemical Techniques for Corrosion and Tribocorrosion Monitoring: Fundamentals… DOI: http://dx.doi.org/10.5772/intechopen.85392*

There are several factors that can come into play in the process of corrosion or tribocorrosion [1–3, 8]. Among the common influential criteria on corrosion, the following main parameters can generally be selected, namely the pH of the medium, the presence of chlorides (and other alkyl halides), the oxidizing power, the pressure, and the temperature. Fundamentally, corrosion depends on the dominating deterioration mechanism of surfaces exposed to chemical environment. The corrosion resistance properties can be characterized directly by the limits of use of the materials, which can be expressed, for example, in terms of maximum temperature in-service or maximum concentration of use. Under normal service conditions, the understanding and control of corrosion are based on the electrochemical interpretation of corrosion phenomena and the consideration of the relative ranking scales of materials in order to select, by successive approaches, the materials best suited to each application of interest [3].

Conversely, a more obvious mechanism of tribocorrosion is the periodic exposure of fresh bare surfaces when sliding friction between surfaces occurs in corrosive liquids or gases [3]. This results in reaction products mainly driven by chemical and electrochemical interactions. The surfaces of the materials are quickly covered by a scale of the reaction product, the oxide in the case of metals and metallic alloys, acting as a protective barrier layer. Often, the thinner the scale, the faster the reaction, and the weaker the protectiveness [3]. Though, tribocorrosion processes are complex, combining both wear and corrosion. Modern research has established a consensus on four main forms of wear, namely, chemical wear (i.e., corrosion and corrosive wear), adhesive wear, abrasive wear or surface fatigue wear [3, 11]. Each process obeys its own laws and, to confuse things, one of the modes of wear acts to affect the others, hence the complexity of corrosive wear [1–3]. As a general rule, there is a combination of competitive wear mechanisms in a dynamic mechanical-chemical contact.
