Lecture #11Corrosion

Learning objective outcomes:

1-Corrosion in metals.2-Distinguish between oxidation and reductionelectrochemical reactions.3. Describe the following: galvanic couple, standardhalf-cell, and standard hydrogen electrode.4. Compute the cell potential and write the spontaneous electrochemical reaction direction for two pure metals that are electrically connected and also submerged in solutions of their respective ions.5-Corrosin in ceramics.6- Corrosion in polymers

CORROS ION OF METALS

Corrosion is defined as the destructive and unintentional attack of a metal; it iselectrochemical and ordinarily begins at the surface. The problem of metallic corrosion is one of significant proportions; in economic terms, it has been estimated that approximately 5% of an industrialized nation’s income is spent on corrosion prevention and the maintenance or replacement of products lost or contaminated as a result of corrosion reactions..ELECTROCHEMICAL CONSIDERATIONS:

An oxidation reaction:

Reduction reaction:A- In acidic medium:

B-In basic or neutral medium:

solution of H ions, saturated with hydrogen gas that is bubbled through the solution at a pressure of 1 atm and a temperature of 25C (77F). The platinum itself does not take part in the electrochemical reaction; it acts only as a surface on whichhydrogen atoms may be oxidized or hydrogen ions may be reduced.

Degradation of polymers:Polymeric materials deterioration by means of environmental interactions.

However an undesirable interaction is specified as degradation rather than corrosion.