Corrosion of Metals

Corrosion Process of metals being oxidized by moist air. Causes metals to lose structural integrity or lose aenesthetics. Why do metals oxidize easily?? Metals develop thin layer of oxidized metal to protect deeper layers of atoms from oxidizing (oxide coating)

Corrosion of Iron Used in bridges, automobiles, etc. Mimics a galvanic cell Steel—not uniform substance Has weak anodic area—metal ions migrate from these areas Cathodic areas—metal ions accumulate to form “hills” Fe(s)  Fe2+ + 2e- Electrons provided by oxidation are used to reduce O2 O2 + 2H+ +4e-  2H2O

Practice Write the overall reaction for the rusting of iron. Calculate the cell potential for the reaction.

Factors that contribute to rusting Moisture must be present—water is a reactant and ions must be free to flow from anodic to cathodic regions. Additional electrolytes—enhances current flow (why cars rust quickly in colder climates) Presence of acid—lower pH enhances cathodic region because it reduces oxygen better.

Protection of Metal Surfaces Coatings Hydrophobic regions that repel water Galvanizing Sacrificial electrode