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Last class - More corrosion - micro cells Welding HAZ Sensitization Ol' Harold's story

The purpose of scientific thought is to predict what will happen in given experimental circumstances. All the philosophical discussion is an evasion of the point. – Feynman. Last class - More corrosion - micro cells Welding HAZ Sensitization Ol' Harold's story. Today -

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Last class - More corrosion - micro cells Welding HAZ Sensitization Ol' Harold's story

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  1. The purpose of scientific thought is to predict what will happen in given experimental circumstances. All the philosophical discussion is an evasion of the point. – Feynman

  2. Last class - More corrosion - micro cells Welding HAZ Sensitization Ol' Harold's story Today - Suppressing corrosion Corrosion examples

  3. Suppressing corrosion Components of a cell: anode cathode electrolyte connection

  4. Suppressing corrosion Occlude electrolyte - coatings asphalt greases, oils paints polymers ceramic coatings "noble" metals

  5. Suppressing corrosion Occlude electrolyte - coatings "noble" metals: unless scratch heals, a galvanic cell is set up

  6. Suppressing corrosion Cathodic protection galvanizing: Zn coating applied by hot-dipping electroplating

  7. Suppressing corrosion Cathodic protection galvanizing: presence of scratch does not promote corrosion of protected metal but steel helps Zn corrode

  8. Suppressing corrosion Cathodic protection set up cell by adding metal which is more anodic than metal or alloy to be protected

  9. Suppressing corrosion Cathodic protection example: protecting ship plate

  10. Suppressing corrosion Cathodic protection example: protecting hot water heater tanks

  11. Suppressing corrosion Cathodic protection Problem: steel fermentation tank in brewery sacrificial anodes add metallic ions to electrolyte

  12. Suppressing corrosion Cathodic protection Different approach: Impose a voltage across cell formed by tank (cathode) and an inert anode choice of anode material: very inert material like Pt but oxygen gas produced at anode

  13. Suppressing corrosion Cathodic protection Different approach: Impose a voltage across cell formed by tank (cathode) and an inert anode choice of anode material: use carbon - inert C + O2  CO2

  14. Suppressing corrosion Cathodic protection "…..join in a planned discussion of whether it is best to use copper tubing coils or stainless steel tubing coils inside of a stainless steel beer fermenter, the coils being used as a chiller? There has been a discussion in another brewing forum about competing concerns between the two, i.e., copper conducts heat better and is easier to bend, versus copper will slowly dissolve in the acidic environment of beer"

  15. Suppressing corrosion Use passivated materials Ni - NiO Ti - TiO2 Al - Al2O3 COR-TEN: 0.19% C 0.30% Cu 0.40% Ni 0.50% Cr 0.05% V

  16. Suppressing corrosion Anodizing Al & other materials can be anodized very thick oxide coating formed (8-50 microns)

  17. Suppressing corrosion 2300x 540x Thinking again of noble metal coatings, what about Cr plating? Cr plating usually filled w/ microcracks due to stresses in plating

  18. Suppressing corrosion Cr plating frequently a series of layers

  19. Corrosion examples in shuttle mat'ls 60x 1x 235x 1180x

  20. Corrosion examples in shuttle mat'ls

  21. Corrosion examples in shuttle mat'ls

  22. Corrosion examples in shuttle mat'ls

  23. Corrosion examples in shuttle mat'ls

  24. Corrosion area effect Area effect: large cathode & small anode - corrosion accelerated electrochemical cell current density high try to keep potential anodic areas large relative to cathode

  25. Polymers - the nightmare begins I am inclined to think that the development of polymerization is, perhaps, the biggest thing that chemistry has done, where it has the biggest effect on everyday life LORD TODD President of the Royal Society of London

  26. What are polymers? Why important ? • Long chain molecules • Extraordinary range of • physical properties • Many (not all) are cheap • Low densities

  27. Assignment: Review today's classnotes a. coatings b. cathodic protection c. passivation d. anodizing e. Cr plating f. corrosion examples g. area effect h. what is a polymer? Read: pp 569-585, 589-591, chapter 14

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