1. USNA Chemistry Department
CORROSION
LECTURE
OK to have attention grabbers at the beginning.

2. What is Corrosion? Why is it a problem?
Corrosion is the oxidation of a metal due to an ELECTROCHEMICAL reaction. The oxidizing agent is most often O2 (atmospheric corrosion) or H+ (chemical corrosion) or both.
But they can be distracting if used too much. Poor contrast here. I changed font sizes and size of picture
Why is it a problem?
Financial - $350 Billion Dollar Annual Problem in U.S. (4.25% of GNP) Department of Defense spends $6 – 8 Billion

3. Recipe for corrosion Electrolyte Metal Active metal Water Oxygen
(atmospheric corrosion)
Acid
(chemical corrosion)
Salt
High temperature
Corrosion
Triangle
Electrolyte
Metal
Oxidize

4. Chemical vs. Atmospheric Corrosion (H+ vs. O2)
Eo red (V)
Anodic Reaction:
Fe0(s) Fe2+(aq) + 2e- Deterioration of metal
Cathodic Reaction:
2H+(aq) + 2e H2 (g) Chemical
O2 (g) + 2H2O (l) + 4e OH-(aq) Atmospheric
O2 (g) + 4H+(aq) + 4e H2O (l) Combination
Which of these will oxidize copper? Silver? Gold?
Overall Reaction:
Fe0(s) + 2H+(aq) Fe2+(aq) + H2 (g) Chemical
2Fe0(s) + O2 (g) + 2H2O (l) Fe2+(aq) + 4OH-(aq) Atmospheric
2Fe0(s) + O2 (g) + 4H+(aq) Fe2+(aq) + 2H2O (l) Combination
Ag(s) Ag+(aq) + e-
Cu(s) Cu2+(aq) + 2e-
Au(s) Au3+(aq) + 3e-
+1.50
+0.34
-0.44
+0.80
0.00
+0.40
+1.23
Eocell (V)
+0.44
+0.84
+1.67

5. Why won’t iron corrode in pure (degassed) water?
Eo (V)
Anodic Reaction:
Fe0(s) Fe2+(aq) + 2e-
Cathodic Reaction:
-0.44
2H2O (l) + 2e H2 (g) + 2OH-(aq)
-0.83
Eocell (V)
Overall reaction:
Fe0(s) + 2H2O (l) Fe2+(aq) + H2 (g) + 2OH-(aq)
-0.39
What metals will corrode in pure (degassed) water?
Any sufficiently active metal Eored < V
(alkali metals, alkaline earth metals, aluminum, manganese)

6. Example of Atmospheric Corrosion
Corrosion on wing of Navy aircraft
F/A-18C Hornet
Contrast. What exactly is shown in the pictures? Too wordy.
Why does corrosion of an airplane occur primarily while the plane is on the ground?
How might this corrosion be minimized?

7. Example of Chemical Corrosion Nuclear Reactor Vessel Head Degradation
February 16, 2002, Davis-Besse Nuclear Power Station in Oak Harbor, Ohio
Boric Acid leak from control rod drive mechanism led to chemical corrosion of reactor vessel head
Serious potential for loss of reactor coolant access

8. Corrosion of a Ship’s Hull Anodic and Cathodic Regions
Hull of ship
O2 + 2H2O + 4e OH-
Cathodic Region
OH-
RUST
Fe2+ + 2OH Fe(OH)2
4Fe(OH)2 + O (Fe2O3·H2O) + 2H2O
RUST
Anodic Region e-
Fe2+
Fe Fe2+ + 2e-
Electrons Migrate from Anodic to Cathodic Region

9. STRESS CORROSION 2Fe0(s) + O2 (g) + 2H2O (l) → 2Fe2+(aq) + 4OH-(aq)
anode
Nail is embedded in a gel.
Gel contains phenolphthalein
and ferricyanide ion.
Phenolphthalein turns pink in
basic solution.
Ferricyanide reacts with Fe2+
to produce a blue color.
cathode
The gel has been prepared with a little phenolphthalein indicator and a little potassium ferricyanide mixed in. As corrosion occurs, the hydroxide ion produced in the cathodic region turns the phenolphthalein pink while the ferrous and ferric ions produced in the anodic region react with the ferricyanide to make Prussian blue (the deep blue color appears almost black on the photographs).

10. STRESS CORROSION

11. Example of Stress Corrosion Aloha Flight 243 (28 APR 1988)
Lesson:
Frequent inspections
to detect signs of stress!

12. Preventing Corrosion
Salt
Figure: 20-25
High pH (> 9)

13. Preventing the Corrosion of Iron
(cathodic protection/sacrificial anode)
Sacrificial anode

14. Applications of Cathodic Protection
Galvanized Steel
Zinc coating
Sacrificial Anodes
Ship Hulls
Subs (free flooding areas)
Los Angeles Class Sub
Arleigh-Burke Destroyer

15. Impressed Current Cathodic Protection
Paint
Layer
Shipboard Power
Shipboard Power
Controller
Reference
Electrode
Hull e- e-
Power Supply
Pt Anode
Insulation

16. (contact between unlike metals; opposite of cathodic protection)
Galvanic Corrosion
(contact between unlike metals;
opposite of cathodic protection)
H2O O2
Copper
Iron
Cathode:
O2 + 2H2O + 4e- → 4OH-
Anode:
Fe → Fe2+ + 2e-

17. GALVANIC CORROSION

18. There are some leaks in Sampson Hall
There are some leaks in Sampson Hall. Upon inspection it turns out that copper (Cu) was attached to lead (Pb) on the roof. I guess it turns out when they are mixed with water (H2O) or air (N2, O2, CO2, etc) there is some kind of reaction that breaks down the properties of the copper and lead.