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Survivors learn to adapt – Zufa Cenva

Survivors learn to adapt – Zufa Cenva. Corrosion. Galvanic cell is necessary. electrical connection. anode. cathode. electrolyte. Most corrosion is electrochemical. No corrosion if one of these is missing: anode cathode electrolyte electrical connection.

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Survivors learn to adapt – Zufa Cenva

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  1. Survivors learn to adapt –Zufa Cenva

  2. Corrosion Galvanic cell is necessary electrical connection anode cathode electrolyte Most corrosion is electrochemical No corrosion if one of these is missing: anode cathode electrolyte electrical connection

  3. Corrosion Galvanic cell is necessary electrical connection anode cathode electrolyte Most corrosion is electrochemical Corrosion at anode Me = Me+n + ne– (metal dissolves) No dissolution at cathode

  4. Corrosion electrical connection Zn Cu electrolyte What constitutes an anode/cathode pair? Dissimilar metals Ex: Cu & Zn (Zn corrodes) How do we know? Many combos tried experimentally

  5. Corrosion more cathodic electrical connection electrical connection Zn anode Cu cathode electrolyte electrolyte more anodic Result: the galvanic series

  6. Corrosion Ex: 1 contains little dissolved oxygen 2 contains much dissolved oxygen 1 2 What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes

  7. Corrosion Practical example: crevice corrosion 1 2 What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes

  8. Corrosion Deformation ––> non-homogeneous residual stress 1 2 What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes

  9. Corrosion Deformation ––> non-homogeneous residual stress 1 2 What constitutes an anode/cathode pair? Dissimilar metals Different electrolytes Non-passivated vs. passivated metal or alloy

  10. Corrosion What constitutes an anode/cathode pair? In summary– Anything that makes two half-cells different gives anode & cathode ––> corrosion We can call these types macro cells

  11. Corrosion Then what about micro cells? anode & cathode within single material operating on a micro scale Grain boundary - high energy region…anodic wrt bulk of grain Differently oriented grains - some planes of atoms dissolve faster than others Segregation (coring)

  12. Corrosion Then what about micro cells? anode & cathode within single material operating on a micro scale Segregation (coring)

  13. Assignment: Review today's classnotes a. The Galvanic cell b. Types of macro cells c. Types of microcells Read: pp 569-585

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