Diffusion.

Consider the diffusion of nitrogen into a semi$-$infinite steel block. Assume that the nitrogen concentration

at the steel surface is constant during diffusion, and that the steel block did not contain any nitrogen

initially. Assume also that the nitrogen diffusion coefficient is independent of composition.

$($a$)$ Sketch the nitrogen profile into the semi$-$infinite steel at a short, intermediate, and long diffusion

times.

$($b$)$ For the intermediate diffusion time, sketch on a separate plot the flux of nitrogen as a function of

distance into the steel. Where is the flux maximum?