Nitrogen from a gaseous phase is to be diffused into pure iron at 700°c. if the surface concentration is maintained at 0.26 wt% n, what will be the concentration (in weight percent) 2.8 mm from the surface after 6.3 h? the diffusion coefficient for nitrogen in iron at 700°c is 2.2 × 10-10 m2/s.

Explanation:

Given details

concentration of surface is Cs 0.26 wt%

distance from surface is x 2.8 mm

time t = 3.6 h

original concentration is Co 0

we know that

FROM TABLE OF ERROR FUNCTION WE HAVE

Z           erf(z)

0.60        0.6039

0.65         0.6420

so by interpolation technique we have

for z = 0.626 we have value of erf(0.626) =   0.623

b is the correct answer

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1 is the answer to this problem