$($Problem $3)$

$5\mathrm{.}10$ A sheet of BCC iron $1$ mm thick was exposed to a carburizing gas atmosphere on one side and a

decarburizing atmosphere on the other side at $725C.$ After having reached steady state, the iron was quickly

cooled to room temperature. The carbon concentrations at the two sunfaces of the sheet were determined to be

$0\mathrm{.}012$ and $0\mathrm{.}0075wt\%.$ Compute the diffusion coefficient if the diffision flux is $1\mathrm{.}4{10}^{-8}k\frac{g}{m^2}-s.$ Hint: Use

Equation $4\mathrm{.}9$ to convert the concentrations from weight percent to kilograms of carbon per cubic meter of iron.