MAE 20 Homework_2_summer_2008

MAE 20 Homework_2_summer_2008 - MAE 20 Homework 2 Due on...

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MAE 20 July 9, 2008 Homework 2 Due on Wednesday (July 16), at the beginning of class Clearly show the detailed steps in your solutions. 1. Calculate the number of vacancies per cm 3 , expected in Copper at 1080 o C (just below the melting point). The energy for vacancy formation is 20,000 calories/mole. 2. A sample of Pb (face centered cubic structure with a lattice parameter of 0.4949 nm) contains one vacancy per 500 Pb atoms. Calculate, (a) the density, and (b) the number of vacancies per gram of Pb? 3. The density of Iron (bcc structure) is 7.882 g/cm 3 and the lattice parameter is 0.2866 nm when hydrogen atoms are introduced at the interstitial positions. Calculate (a) the atomic fraction of hydrogen atoms, (b) the number of unit cells, on the average, that contain hydrogen atoms. 4. An iron sheet is to be manufactured that will allow no more than 50g of hydrogen to be lost per year through each cm 2 of iron at 400 o C. If the concentration of hydrogen at one surface is 0.05 H atom per unit cell and is 0.001 H atom per unit cell at the second surface, determine the minimum thickness of the sheet.
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