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Chapter 15 Corrosion

Chapter 15 Corrosion. Gross National Product. EMF-electromotive force, 电动势. Example 1. One half of an electrochemical cell consists of a pure nickel electrode in a solution of Ni 2+ ions; the other is a cadmium electrode immersed in a Cd 2+ solution;

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Chapter 15 Corrosion

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  1. Chapter 15 Corrosion

  2. Gross National Product

  3. EMF-electromotive force, 电动势

  4. Example 1 One half of an electrochemical cell consists of a pure nickel electrode in a solution of Ni2+ ions; the other is a cadmium electrode immersed in a Cd2+ solution; (a) If the cell is a standard one, write the spontaneous overall reaction and calculate the voltage that is generated. (b) Compute the cell potential at 25C if the Cd2+ and Ni2+ concentrations are 0.5 and 10-3 M, respectively. Is the spontaneous reaction direction still the same as for the standard cell?

  5. -V10 +V20 The overall cell potential V0 = V20 – V10

  6. INFLUENCE OF CONCENTRATION AND TEMPERATURE ON CELL POTENTIAL Nernst equation T = 25C

  7. Schematic illustration of the mechanism of crevice corrosion between two riveted sheets.

  8. CORROSION OF CERAMIC MATERIALS • Ceramic materials, being compounds between metallic and nonmetallic elements, maybe thought of as having already been corroded. Thus, they are exceedingly immune to corrosion by almost all environments, especially at room temperature. • Corrosion of ceramic materials generally involves simple chemical dissolution, in contrast to the electrochemical processes found in metals, as described above. • Ceramic materials are frequently utilized because of their resistance to corrosion. Glass is often used to contain liquids for this reason. Refractory ceramics must not only withstand high temperatures and provide thermal insulation but, in many instances, must resist high-temperature attack by molten metals, salts, slags, and glasses.

  9. DEGRADATION OF POLYMERS • SWELLING AND DISSOLUTION • BOND RUPTURE RADIATION EFFECTS CHEMICAL REACTION EFFECTS THERMAL EFFECTS • WEATHERING

  10. Example 2 • An electrochemical cell is composed of pure copper and pure lead electrodes immersed in solutions of their respective divalent ions. For a 0.6 M concentration, of Cu2+ , the lead electrode is oxidized yielding a cell potential of 0.507V. Calculate the concentration of Pb2+ ions if the temperature is 25C.

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