In the figure below, the experiment carried out by Darken, (L.S. Darken, 1949, Trans. AIME, 180:430-438) shows the concentration of Carbon throughout a diffusion couple of Fe-C-Si and Fe-C, held for 13 days at 1323K. The initial diffusion couple had a constant C composition throughout the entire sample and the Si was present in the left part of the initial diffusion couple and there was no Si in the right hand side. 1. What is the effect of the Si on the chemical potential of the Carbon in the Iron? Explain how you know this. (Assume that the Si does not diffuse over this time period.) 2. Does the observation contradict Ficks first law? Explain.

2.6 Si 7.0 2.4 6.0 5.0 2.2 4.0 . 2.0 atom percent carbon atom percent silicon - 3.0 1 1.8 2.0 1.6 1.0 Si 1.4 0 - 2 +2 -1 0 +1 distance in cm