Corrosion (Rusting) The annual cost of corrosion to the U.S. economy is $350 billion!

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Presentation transcript:

Corrosion (Rusting) The annual cost of corrosion to the U.S. economy is $350 billion!

The Corrosion Process Cell Reaction: 2 Fe (s) + O 2 (g) + 2H 2 O (l)  2Fe 2+ (aq) + 4OH – (aq)

How Can Adjacent Pieces of Iron Be Chemically Different? 1. Defects (due to compression or chipping) 2. Impurities (e.g.- Sn) * 3. Differences in [O2] * Sn is less active than Fe and will therefore act as the cathode.

How Can Rusting Be Prevented? 1. Protective coatings paint * Sn will promote rusting if the coating is damaged. Fe galvanized with Zn or Sn *

2. Alloying Fe with Cr to form stainless steel.

3. Cathodic protection a) Attaching a more active metal (e.g.- Mg) to Fe. sacrificial anodes Anode half-reaction: Mg  Mg e - Cathode half-reaction: O 2 + H 2 O + 4 e -  4 OH -

b) Connecting the Fe object to the – terminal of a power source.

4. Electroplating