Q4. The following data refer to the steady-state diffusion of carbon through the thickness of a sheet of steel, which is 0.2mm thick and has length of 2m and width of 1.5m. One of the surfaces is maintained at a constant concentration of carbon given by its equilibrium solubility with respect to the environment (provided in the table), and the other surface is at zero concentration. (a) What is the mechanism by which carbon diffuses in iron? Illustrate your answer with a sketch of the mechanism. (2 marks) (b) Using the data provided in the table above, calculate how long it would take for 100g of carbon to diffuse through the plate at 1240K. (3 marks) (c) The forms of Fick's 1st Law and Fick's 2nd Law are as follows: Fick's 1st Law: J=DxC Fick's 2nd Law: tC=Dx22C By using the appropriate Law, and the data in the table above, calculate the diffusivity values of carbon at 1350K and 1240K. (5 marks) (d) Using your answers to part (c), find the activation energy for diffusion of carbon through the plate. The gas constant R=8.31Jmol1K1. (6 marks) (e) The plate used is formed from polycrystalline iron that has been cold worked. Discuss whether your calculated activation energy is likely to be higher or lower than that for carbon diffusion in a single crystal of iron. Justify your answer. (4 marks)