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Solution8 - EGN3365-Structure and Properties of Materials...

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EGN3365-Structure and Properties of Materials TTR 8:30-9:45 Instructor: Dr. S. Seal TA: Mr. Himesh Bhatt Solutions: Home-Work 8 Problem 1: We are asked to determine the position at which the nitrogen concentration is 2 kg/m 3 . This problem is solved by using Equation in the form J = - D If we take C A to be the point at which the concentration of nitrogen is 4 kg/m 3 , then it becomes necessary to solve for x B , as x B = x A + D Assume x A is zero at the surface, in which case x B = 0 + (6 x 10 -11 m 2 /s) = 1 x 10 -3 m = 1 mm Problem 2: Using Equation , we set up two simultaneous equations with Q d and D o as unknowns. Solving for Q d in terms of temperatures T 1 and T 2 (1273 K and 1473 K) and D 1 and D 2 (9.4x10 -16 and 2.4 x 10 -14 m 2 /s), we get Q d = - R = -
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= 252,400 J/mol Now, solving for D o from Equation D o = D 1 exp = (9.4 x 10 -16 m 2 /s) exp = 2.2 x 10 -5 m 2 /s (b) Using these values of D o and Q d , D at 1373 K is just D = (2.2 x 10 -5 m 2 /s) exp = 5.4 x 10 -15 m 2 /s Problem 3: This problem asks us to determine the values of Q d and D o for the diffusion of Fe in Cr from the plot of log D
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