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Unformatted text preview: 5/1/2008 1 Chapter 17 - 1 ISSUES TO ADDRESS... Why does corrosion occur? What metals are most likely to corrode? How do temperature and environment affect corrosion rate? How do we suppress corrosion? CHAPTER 17: CORROSION AND DEGRADATION Chapter 17 - 2 Corrosion :-- the destructive electrochemical attack of a material.-- Al Capone's ship, Sapona, off the coast of Bimini. Cost:-- 4 to 5% of the Gross National Product (GNP)*-- this amounts to just over $400 billion/yr** * H.H. Uhlig and W.R. Revie, Corrosion and Corrosion Control: An Introduction to Corrosion Science and Engineering , 3rd ed., John Wiley and Sons, Inc., 1985. **Economic Report of the President (1998). Photos courtesy L.M. Maestas, Sandia National Labs. Used with perm ission. THE COST OF CORROSION Chapter 17 - 3 Two reactions are necessary:-- oxidation reaction:-- reduction reaction: Zn Zn 2 2 e 2H 2 e H 2 (gas) Other reduction reactions:-- in an acid solution-- in a neutral or base solution O 2 4H 4 e 2H 2 O O 2 2H 2 O 4 e 4(OH ) Adapted from Fig. 17.1, Cal ister 7e . (Fig. 17.1 is from M.G. Fontana, Corrosion Engineering , 3rd ed., McGraw-Hil Book Com pany, 1986.) CORROSION OF ZINC IN ACID Zinc Oxidation reaction Zn Zn 2+ 2e- Acid solution reduction reaction H + H + H 2 (gas) H + H + H + H + H + flow of e- in the metal Chapter 17 - 4 STANDARD HYDROGEN (EMF) TEST Two outcomes: o metal V...
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- Spring '08