A plate of 1020 steel (0.2 wt%C) is placed in a carburizing furnace at 900 C. The atmosphere forms a surface layer that is approximately 1.2 wt%C. Ti diffusion coefficient for C in 1020 steel follows the Arrhenius relationship, D-D, exp() where the activation energy, Q-80, and the diffusion coefficier Do = 6.2-10-7 (a) Using the finite difference technique, plot the concentration profile after 30 minutes, 2 hours, and 5 hours. These three curves should be plotted together c the same plot. (b) How long does it take for the carbon content to reach 0.8 wt% at a depth of 1 mm? (c) Compare your answers to that obtained in problem 2.1 To make sure that your calculations remain stable, you must pick a At to meet the following: 9.54x2 At s D In this problem, you no longer have a defined surface on the right side, i.e. your sample is semi-infinite. You will need to fix this surface to the initie concentration of 0.2 wt% and keep checking the nodes on this side of your Excel sheet to make sure that you have a few nodes near this interface that remain a 0.2 wt%, You are trying to determine if you have used "enough" nodes for your solid to behave semi-infinite. If not, add more columns