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→13.5.2 Special Types of Corrosion
*Fatigue corrosion: <br />Fatigue fracture during repeated mechanical stresses in corrosive environments. This effect is often observed on brittle electroplated surface coatings that are exposed to repeated cycling between mechanical stresses and corrosive chemicals. Air access corrosion: Through differences in the amount of exposure to air or oxygen surface areas of a metal are becoming cathodes at the more exposed spots and therefore corrode less than those protected (for example: gap corrosion in screw or press connections).<br />
===13.5.3 Electrochemical Potentials===
Corrosion effects are mainly governed by the electrode potential of the respective metals. The electrochemical potential table provides a measure for corrosion resistance. Non-precious (corrosion prone) metals are characterized by a negative, precious (corrosion resistant) metals by a positive normal potential against hydrogen.
Table 13.3: Electrode Potential of Metals
===13.5.4 Corrosion Testing===
The following pages describe test methods and procedures which are mainly related to the effects of environmental exposure of electrical contacts which are used in contact components for the telecommunication and information technology.
Corrosion products on the surface of electrical contacts can reduce the reliability of contact making significantly by, for example, higher contact
resistance, which will negatively affect the transmission of current and data signals. This can cause major problems in electromechanical contact
components used in the information processing technology. Causes for the formation of tarnish film on electrical contacts include for example the presence of corrosive gases such as H<sub>2S</sub>, SO<sub>2</sub>, NO<sub>x</sub>, O<sub>3</sub>, Cl<sub>2</sub>, and NH<sub>3</sub> ''(Table 13.4)'' in industrial environments.
