1. (a) An FCC iron-carbon alloy initially containing 0.35 wt% C is exposed to an oxygen- rich and virtually carbon free atmosphere at 1400 K. Under these circumstances the carbon diffuses from the alloy and reacts at the surface with the oxygen in the atmosphere; that is, the carbon concentration at the surface position maintained at 0 wt % C. At what position will the carbon concentration be 0.15 wt.% C after a 10 h treatment? The value of D at 1400 K is 6.9 x 101m/s. orf(z) erf(z) 2 orf(z) 0 0 0.55 0.5633 13 0.9340 0.025 0.0282 0.60 0.6039 1.4 0.9523 0.05 0.0564 0.65 0.6420 15 0.9661 0.10 0.1125 0.70 0.6778 1.6 0.9763 0.15 0.1680 0.75 0.7112 1.7 0.9838 0.20 0.2227 0.80 0.7421 1.8 0.9891 0.25 0.2763 0.85 0.7707 1.9 0.9928 0.30 0.3286 0.90 0.7970 2.0 0.9953 0.35 0.3794 0.95 0.8209 2.2 0.9981 0.40 0.4284 1.0 0.8427 2.4 0.9993 0.45 0.4755 1.1 0.8802 2.6 0.9998 0.50 0.5205 1.2 0.9103 2.8 0.9999 (b) Explain diffusion mechanisms of interstitial and vacancy and also explain which one is more rapid? Why?