BCC -iron with a concentration of carbon initially being 0.1 wt.% throughout is packed in carbon black and then placed in a furnace at 900°C. This effectively makes the concentration of carbon 100 wt.% at the surface. How much time will it take (in seconds) for the concentration of carbon to reach 5 wt.% at 1 mm from the surface of the steel? The diffusion coefficient for carbon in BCC -iron at 900°C is 1.4 x 10-10 m²/s