Lec 19 - ENGR ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 ENGR 4250 – Advanced Materials Engineering Lecture 19 CORROSION AND DEGRADATION Continued Instructor: Ghaus Rizvi
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CHAPTER 17: SUES TO ADDRESS CORROSION AND DEGRADATION 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?
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Electro-Chemistry • If a chemical reaction is driven by an external applied voltage , as in electrolysis , or if a voltage is created by a chemical reaction as in a battery , it is an electrochemical reaction.
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STANDARD HYDROGEN (EMF) TEST Two outcomes: -- Metal sample mass -- Metal sample mass e - e - e - H + 2e - e - H 2 ( gas ) e - e - e - M n+ ions ne latinum etal, M H + M n+ ions ne 2e + H + 25°C 1M M n+ sol’n 1M H + sol’n P m 25°C 1M M n+ sol’n 1M H + sol’n H 0 o metal < V (relative to Pt) --Metal is the cathode (+) 0 o metal > V (relative to Pt) --Metal is the anode (-) Standard Electrode Potential Adapted from Fig. 17.2, Callister 7e .
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Corrosion Penetration Rate PR CPR CPR, the thickness loss of material per unit of time is given by t KW CPR = W is weight loss after exposure time t ρ and A are density and exposed specimen area, respectively; and At ρ K is a unit dependant constant Units of CPR are mils per year ( m py), or mm /yr for m py; K = 534 ; W milligram, ρ gm/cc, A sq in , t hrs py; ;g , g, q , for mm /yr; K = 87.6 ; W milligram, ρ gm/cc, A sq cm , t hrs For most applications, acceptable CPR is up to 20 mpy (0.5 mm/yr) pp , p p py ( y )
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Electric Current Associated with orrosion Corrosion • There is an electric current associated with the electrochemical corrosion reactions
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This note was uploaded on 10/18/2010 for the course ENGR 3360 taught by Professor Ahmadbarari during the Fall '10 term at UOIT.

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Lec 19 - ENGR ENGR 4250 Advanced Materials Engineering...

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