According to Cahn's original treatment, the interdiffusion flux can be written in a particular coordinate system in 1 spatial dimension as: = ( ) where J is the interdiffusion flux, M is the mobility of the diffusing atoms and () is the chemical potential of A(B). 4. From your free energy plot illustrate the quantity . Then write an expression for the difference in chemical potential in terms of f and/or its derivative(s). 5. Write the diffusion equation using the flux given above and identify the diffusion coefficient and composition ranges, if any, in which the diffusion equation breaks down. Explain. An alternative expression for chemical potential difference is to add the expression: 2(²/ ²) to the chemical potential difference given above. 6. Based on the arguments made in part 5, what is the physical origin of this extra term and why is the extra term needed?

7. Write the diffusion equation for the case that includes the additional term in the chemical potential.