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Corrosion

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Engineering Chemistry Lecture by USNA

Engineering Chemistry Lecture by USNA

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  • OK to have attention grabbers at the beginning.
  • But they can be distracting if used too much. Poor contrast here. I changed font sizes and size of picture
  • Contrast. What exactly is shown in the pictures? Too wordy.
  • 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).
  • Figure: 20-25
  • Transcript

    • 1. USNA Chemistry Department CORROSIONCORROSION LECTURELECTURE
    • 2. What is Corrosion? 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. 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 Active metal Water Oxygen (atmospheric corrosion) Acid (chemical corrosion) Salt High temperature
    • 4. Chemical vs. Atmospheric Corrosion (H+ vs. O2) Anodic Reaction: Fe0 (s) Fe2+ (aq) + 2e- Deterioration of metal Cathodic Reaction: 2H+ (aq) + 2e- H2 (g) Chemical O2 (g) + 2H2O (l) + 4e- 4OH- (aq) Atmospheric O2 (g) + 4H+ (aq) + 4e- 2H2O (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) 2Fe2+ (aq) + 4OH- (aq) Atmospheric 2Fe0 (s) + O2 (g) + 4H+ (aq) 2Fe2+ (aq) + 2H2O (l) Combination Eo red (V) Eo cell (V) -0.44 0.00 +0.40 +1.23 +1.67 +0.84 +0.44 Cu(s) Cu2+ (aq) + 2e- +0.34Ag(s) Ag+ (aq) + e- +0.80Au(s) Au3+ (aq) + 3e- +1.50
    • 5. Why won’t iron corrode in pure (degassed) water? Anodic Reaction: Fe0 (s) Fe2+ (aq) + 2e- Cathodic Reaction: Eo (V) -0.44 -0.83 Fe0 (s) + 2H2O (l) Fe2+ (aq) + H2 (g) + 2OH- (aq) Eo cell (V) -0.39 What metals will corrode in pure (degassed) water? Any sufficiently active metal Eo red < -0.83 V (alkali metals, alkaline earth metals, aluminum, manganese) Overall reaction: 2H2O (l) + 2e- H2 (g) + 2OH- (aq)
    • 6. Example of Atmospheric Corrosion Corrosion on wing of Navy aircraft Why does corrosion of an airplane occur primarily while the plane is on the ground? How might this corrosion be minimized? F/A-18C Hornet
    • 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 O2 O2 + 2H2O + 4e- 4OH- OH- Fe2+ Fe2+ + 2OH- Fe(OH)2 4Fe(OH)2 + O2 2(Fe2O3·H2O) + 2H2O Fe Fe2+ + 2e- Hull of ship Cathodic Region RUST Anodic Region Electrons Migrate from Anodic to Cathodic Region e-
    • 9. STRESS CORROSION 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. 2Fe0 (s) + O2 (g) + 2H2O (l) → 2Fe2+ (aq) + 4OH- (aq) anode cathode
    • 10. STRESS CORROSION
    • 11. Example of Stress Corrosion Aloha Flight 243 (28 APR 1988) Lesson: Frequent inspections to detect signs of stress!
    • 12. High pH (> 9) Preventing Corrosion Salt
    • 13. Preventing the Corrosion of IronPreventing the Corrosion of Iron (cathodic protection/sacrificial anode)(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 Power Supply Shipboard Power Controller Shipboard Power Insulation Pt Anode Reference Electrode Paint Layer Hull e- e-
    • 16. Galvanic CorrosionGalvanic Corrosion (contact between unlike metals;(contact between unlike metals; opposite of cathodic protection)opposite of cathodic protection) Copper Iron H2O O2 Cathode: O2 + 2H2O + 4e- → 4OH- Anode: Fe → Fe2+ + 2e-
    • 17. GALVANIC CORROSION
    • 18. 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.

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