E4511ps9 - Engineering 45 The Structure and Properties of...

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Page 1 Engineering 45 The Structure and Properties of Materials Spring, 2011 Problem Set No. 9 Problem 1: (a) The free energy change for the reaction Fe + O = FeO decreases with temperature, but the rate of oxidation increases. Explain this result. (b) At high temperature the iron oxidizes at a roughly linear rate. Why? (c) The addition of more than 12% Cr to Fe decreases the rate of high-temperature oxidation significantly, and leads to an oxidation rate that is parabolic ( δ t , where δ is the oxide thickness). Explain this result, which is a key feature in the behavior of stainless steels. Problem 2: (a) Two materials, gold and aluminum, are often used in engineering systems for their excellent corrosion resistance. The two sit at opposite ends of the galvanic series. Explain how both can be highly resistant to corrosion. (b) Would it be a good idea to gold-plate aluminum for extra corrosion resistance? Problem 3:
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E4511ps9 - Engineering 45 The Structure and Properties of...

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