[Au197]

I have a problem that, Id like to seek clarification on,

6.12 An FCC iron-carbon alloy initially containing 0.35 wt% C is exposed to an oxygen-rich and virtually carbonfree
atmosphere at 1400 K (1127C). Under these circumstances the carbon diffuses from the alloy and reacts at
the surface with the oxygen in the atmosphere; that is, the carbon concentration at the surface position is
maintained essentially at 0 wt% C. (This process of carbon depletion is termed decarburization.) At what position
will the carbon concentration be 0.15 wt% after a 10-h treatment? The value of D at 1400 K is 6.9  10-11 m2/s.

I have calculated

cx = .15
c0 = .35
cs =
D = 6.9*10^-11
t = 10
x =

(cx-c0)/(cs-c0) to be 0.5714, but during our lecture, they didn't explain how to get to the next part, they just gave an answer to the 3 problems they had. For this problem I know the answer is 0.4286. the problem is defined as erf(2/2sqrtDt). Ive used all the examples during our lecture, ive punched them into the calculator 100 different ways and can't get any of the results that they got. This is the only part of the question holding me back, as I can do the rest.

Any help would be great.

[Au197]

I finally worked it out, all is good.