Corrosion - Corrosion and Degradation Prof SH Teoh...

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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? Corrosion and Degradation Prof SH Teoh Department of Mechanical Engineering National University of Singapore [email protected] EA 05-30 2 Video “Spot Light on Corrosion” NACE Foundation (www.nace.org)
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3 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 permission. THE COST OF CORROSION 4 Corrosion Metallic Implant Materials Unintentional implantation of mixed metals. (Left) Broken and corroded screws and a broken drill bit from a patient. (Right) Radiograph of fracture fixation device showing screws and drill. From C.O.Bechtol, A.B. Ferguson, Jr. and P.G. Laing, Metals and Engineering in Bone and Joint Surgery, Williams and Wilkins, Baltimore, 1959
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5 • Two reactions are necessary: -- oxidation reaction: -- reduction reaction: Zn g Zn 2 G G 2 e ± 2H G G 2 e ± g H 2 (gas) • Other reduction reactions: -- in an acid solution -- in a neutral or base solution O 2 G 4H G G 4 e ± g 2H 2 O O 2 G 2H 2 O G 4 e ± g 4(OH) ± Adapted from Fig. 17.1, Callister 7e . (Fig. 17.1 is from M.G. Fontana, Corrosion Engineering , 3rd ed., McGraw-Hill Book Company, 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 6 Anodic and Cathodic Reaction • Two outcomes: 0 o metal ² V (relative to Pt) Standard Electrode Potential -- Metal sample mass --Metal is the cathode (+) M n+ ions ne - e - e - 25°C 1M M n+ sol’n 1M H + sol’n Platinum metal, M H + H + 2e - Adapted from Fig. 17.2, Callister 7e . 0 o metal ³ V (relative to Pt) -- Metal sample mass --Metal is the anode (-) M n+ ions ne - H 2 (gas) 25°C 1M M n+ sol’n 1M H + sol’n 2e - e - e - H + H + CORROSION when metal becomes Anodic
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7 STANDARD EMF SERIES EMF series Au Cu Pb Sn Ni Co Cd Fe Cr Zn Al Mg Na K +1.420 V
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This note was uploaded on 03/29/2008 for the course MLE 1101 taught by Professor Zhang during the Spring '08 term at National University of Singapore.

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Corrosion - Corrosion and Degradation Prof SH Teoh...

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