1. Electrochemical Cells:
* Galvanic Corrosion: When two dissimilar metals with different electronegativities are in contact in the presence of an electrolyte (like water), an electrochemical cell is formed.
* Anode: The metal with lower electronegativity becomes the anode. It loses electrons and undergoes oxidation, forming metal ions.
* Cathode: The metal with higher electronegativity becomes the cathode. It gains electrons and undergoes reduction, typically of oxygen or hydrogen ions.
* Corrosion: The anode corrodes as it loses metal ions.
2. Standard Electrode Potential:
* Electronegativity is directly related to the standard electrode potential of a metal.
* Metals with lower electronegativity have more negative standard electrode potentials, indicating a greater tendency to lose electrons and undergo oxidation.
* Metals with higher electronegativity have more positive standard electrode potentials, indicating a lesser tendency to lose electrons and undergo oxidation.
3. Example:
* Consider a steel pipe (iron) in contact with a copper fitting.
* Iron has a lower electronegativity than copper, making it the anode and more prone to corrosion.
* Copper becomes the cathode and is less susceptible to corrosion.
* This is why galvanic corrosion is a concern when dissimilar metals are in contact, especially in the presence of moisture.
4. Other Factors Affecting Corrosion:
* Environment: Temperature, humidity, pH, and presence of aggressive chemicals can all influence corrosion rates.
* Metal Surface: Surface imperfections, stress concentrations, and coatings can affect the initiation and propagation of corrosion.
In summary:
* Electronegativity is a fundamental property that directly influences the tendency of a metal to corrode.
* Metals with lower electronegativity are more likely to be anodes and undergo oxidation, leading to corrosion.
* The difference in electronegativity between two metals in contact is a key factor in determining the severity of galvanic corrosion.
