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# sampeexamquestions - Sample Exam Questions 1 A piece of...

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Sample Exam Questions 1. A piece of Steidlium (St) with a dimension 10cm × 10cm × 1cm containing 1.0 at % Deikium (De) is put into an oven for removing De. The density of St is 5g/cm 3 . The surface concentration of De is maintained at 0 at%. The diffusion coefficient of De in St is 10 -8 cm 2 /s. Assuming that there is no out-diffusion of De on the bottom and lateral sides of the St plate, i.e. there is out-diffusion only from the top surface (10cm × 10cm). (a) Derive the concentration profile of De in St after 10 4 s of annealing (b) Calculate the De flux per unit area at the surface at 10 4 s (c) Calculate the total amount of De per unit area which has diffused out of St at 10 4 s (d) How long will it take to reduce the average concentration of De in glass to 0.5 at %? 2. Consider a crystal at a temperature T with a coordination number of z and a nearest neighbor distance λ . The Debye frequency for this crystal is ν . The vacancy formation free energy and the migrational free energy for an atom through a vacancy mechanism are G v

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## This note was uploaded on 01/19/2010 for the course MAT SCI 503 taught by Professor Chen during the Spring '02 term at Penn State.

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sampeexamquestions - Sample Exam Questions 1 A piece of...

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