Question

Chromium is diffused into steel at 980o C to increase its corrosion resistance. If during the diffusion the surface concentration of chromium is maintained constant, how long will it take to achieve 1.8% of the surface concentration at a depth of 0.002 cm below the steel surface? Express your answer in seconds. The diffusivity has a pre-exponential term equal to 0.54 cm2/s and an activation energy of 286 kJ/mole.