Carbon from a gaseous phase is to be diffused into pure iron (a- Fe) at 900C. If the surface concentration is maintained at 0.4 wt% C, what will be the concentration 2.1 mm from the surface after 8 hours? The diffusion coefficient for carbon in a- Fe at 900C is 1.7x 10^-10 m2/s. Use four decimal places. For z-0.45, erf(z)=0.4755; For 2-0.50. erf(z)-0.5205. Cx-Co/(Cs-Co) 1- erf [x/(2(Dt)^1/2)]