Question $2$

$1$ pts

Nitrogen from a gaseous phase is to be diffused into pure iron at $675C.$ If the surface concentration is maintained at $0\mathrm{.}2wt\%N,$ what will be the concentration $2mm$ from the surface after $25$ h$?$ The diffusion coefficient for nitrogen in iron at $675C$ is $1\mathrm{.}9{10}^{-11}\frac{m^2}{s}.$

Give your answer in wt$\%$ of $N$ in Fe$.$

Hint: remember to use linear extrapolation on the erf table $($Table $5\mathrm{.}1).$

Hint $2$: There is no concentration of nitrogen in pure iron $($i$.$e$.C_0=0).$