Nitrogen from a gaseous phase is to diffused into pure iron at 700 o C. If the s

Question

Nitrogen from a gaseous phase is to diffused into pure iron at 700 oC. If the surface concentration is maintained at 0.10 wt. % N, what will the concentration 1.0 mm from the surface be after 10 hours? The diffusion coefficient for nitrogen in iron at 700 oC is 2.5 X 10 -11 m2/s

What is the Co  if nitrogen                         

                            
           0.0%  wt % N                                         
           0.10 wt % N                                         
           80 % wt % N            

Explanation / Answer

This is a time-varying problem, so we need Fick's second law. Since the question involves diffusion into a semi-infinite slab, we can use the error function solution,




So Cx/Cs = 1 - 0.544 = 0.456

=0.1 wt%

So Cx = 0.1 = 0.1% by weight nitrogen.

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