L27 - SUMMARY FROM LAST CLASS Corrosion Corrosion is the...

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Dr. P. Lucas U of A MSE 110 Corrosion Corrosion is the deterioration of metals by spontaneous redox reactions. Corrosion in the environment is induced by the combination of water and oxygen. Most metal have E o <1.23 hence the thermodynamically stable equilibrium state of most metals in nature is in the oxidized form. Corrosion can be naturally slowed down by the lack of H 2 O or by formation of a protective layer such as Zn 2 (OH) 2 CO 3 or Al 2 O 3 . Fe oxidizes in two steps, first forming Fe(OH) 2 followed by Fe(OH) 3 . This rust peals off and re-expose the metal to further oxidation. At the anodic site Fe is oxidized as Fe 2+/3+ and goes in solution. At the cathodic site H 2 O and O 2 are reduced to OH - and the rust is deposited. •A sacrificial anode is a metals with low redox potential connected to Fe which is oxidized in place of the Fe part. SUMMARY FROM LAST CLASS E o (O2/H2O) = 1.23 V O 2 + 4 H + + 4e - Æ 2 H 2 O E o (O2/OH-) = 0.40 V O 2 + 2 H 2 O + 4e - Æ 4 OH -
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Dr. P. Lucas U of A MSE 110 Batteries: ELECTROCHEMICAL DEVICES There is two general class of batteries: rechargeable and non- rechargeable. Primary batteries : • The redox reaction taking place in a primary battery is non-reversible, the reactant can not be regenerated by applying a potential to drive the reverse reaction. • Alkaline batteries are a typical example of primary battery. Zn + 2 MnO 2 Æ ZnO + Mn 2 O 3 • This reaction can not be reversed, hence the alkaline battery is non-rechargeable
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Dr. P. Lucas U of A MSE 110 Batteries: ELECTROCHEMICAL DEVICES Secondary batteries : • In a secondary battery, the redox reaction is fully reversible. Under application of a potential, the reduced and oxidized reactants can diffuse back to the electrodes to be regenerated. Secondary batteries are therefore rechargeable and are used as a way of storing energy. They are also known as storage cells or accumulators . • Like mercury, cadmium is toxic and poses a serious recycling problem.
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This note was uploaded on 11/19/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at University of Arizona- Tucson.

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L27 - SUMMARY FROM LAST CLASS Corrosion Corrosion is the...

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