3.091 Fall Term 2004 Homework #10 November 9 (to be tested on Test 3 November 17) 1. A membrane is to be manufactured to the following specifications. At 700 ° C the leak rate of hydrogen is not to exceed 10 –3 mol cm –2 h –1 when the concentrations of hydrogen are maintained at 1.5 × 10 19 atoms cm –3 on one side of the membrane and effectively zero on the other side. What is the minimum thickness of iron foil that will meet these requirements? The 2 –1 diffusion coefficient of atomic hydrogen in iron at 700 ° C is 3.091 × 10 –4 cm s . 2. To increase its corrosion resistance, chromium is diffused into steel at 980 ° C. If during diffusion the surface concentration of chromium remains constant at 100%, how long will it take (in days) to achieve a Cr concentration of 1.8% at a depth of 0.002 cm below the steel surface? ( D o = 0.54 cm 2 /s; E a = 286 kJ/mol) 3. By planar diffusion of antimony (Sb) into p-type germanium, a p-n junction is obtained at a depth of 3 × 10 –3
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This note was uploaded on 11/02/2009 for the course CHEMISTRY 3.091 taught by Professor Donsadoway during the Fall '04 term at MIT.