Extended sampling , equilibrium phase diagrams

The final case to be treated in this section is the reaction between two metals A and B whose phase diagram exhibits a miscibility gap and extended regions of solubility a and p as shown in Fig, 7-5. Once again, many practically important applications can be found. Examples are the systems Ag-Cu (800 °C), Au-Co (900 C), Zn-Cd (250 °C), or Co-Cu (1000 °C). Consider two sufficiently long samples A and B which are welded together at the point x = 0. Assume that local equilibrium is achieved everywhere and at all times. After a diffusion time t there will be a discontinuity in concentration at x = which can be calculated from the phase... 

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