sampleMT2solutions

sampleMT2solutions - Sample Midterm MASC 310 Midterm II...

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Sample Midterm MASC 310 Midterm II Prof. Nutt CLOSED BOOK, CLOSED NOTES CALCULATORS ALLOWED SOLUTIONS
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Equations ( 29 ( 29 2 2 eff 1 erf 2 exp 8.31 J/mol 1 ln 1 x o s o d o T i T dC J D dx C C D x x C C x C C Dt x Dt Q D D RT R K F A σ ε = - = - = - - = - = = ° = = + = + ( 29 ( 29 ( 29 CRSS max 1 2 C cos cos %CW= 100% r o y y o y o d o Ic t E t k d A A A K Y a τ φ λ π - = = = + - × = % RA = A o - A f A o × 100 Tf = ln 100 100 - RA HYPERLINK "http://www.wiley.com/college/callister/0470125373/img_galleries/ch06/pages/c06tf02.htm" INCLUDEPICTURE "http://www.wiley.com/college/callister/0470125373/img_galleries/ch06/images/c06tf01.jpg" \* MERGEFORMATINET
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1. Diffusion The strength of many oxide glasses can be improved tremendously by exchanging larger ions for smaller ions in the surface of the glass, a process called ion stuffing. For example, immersion of a lithia-alumina-silicate glass plate in molten potassium nitrate (KNO 3 ) at ~500°C for four hours allows the potassium ions to replace the smaller lithium ions in the glass near the surface, putting the surface in compression. Composition profiles show that the concentration of potassium at a depth of 20 μ m increases from 0 to about 10 weight percent. During immersion in the salt, the concentration of potassium is ~16 weight percent. Estimate the diffusion coefficient. This is a Fick’s Second Law problem, with solution 1 erf 2 x o s o C C x C C Dt - = - - The initial concentration of potassium in the glass is 0 weight percent (wt%) so that C o = 0. The surface concentration is
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This note was uploaded on 12/22/2008 for the course MASC 310 taught by Professor Nutt during the Fall '08 term at USC.

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sampleMT2solutions - Sample Midterm MASC 310 Midterm II...

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