Silver and Gold form a continuous series of solid solutions, and interdiffusion occurs by a vacancy mechanism. A diffusion couple was made by depositing a thick layer of Silver onto a gold substrate. At 1000 K the interdiffusion coefficient of silver into gold is 10^-10 cm2/s and the interdiffusion coefficient of gold into silver is 2 x 10^-11 cm2/s.

a) Why can the two diffusion coefficients be different?

b) Will the plane where the concentration if 50:50 (metallurgical interface) move

during diffusion? If so, which way.

c) Willtherebeanetfluxofvacanciesthroughtheinterfaceduringdiffusion?On

which side of the interface would you expect to find voids (pores)?

d) Sketch the concentration profile at the junction after annealing at for 3 days at

1000K