An iron-carbon alloy initially containing 0.239 wt% C is exposed to an oxygen-rich and virtually carbon-free atmosphere at 1100°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 0.0 wt% C. At what position will the carbon concentration be 0.179 wt% after a 9 h treatment? The value of D at 1100°C is 4.4 × 10-10 m2/s.