2. A diffusion couple is made from nickel and iron. After 30 hours of heat treatment at 1400 K, the concentration of nickel is 3.2 wt % at a distance of 1.5 mm from interface. If an identical diffusion couple is heated at 1200 K for 30 hours, at what depth from the interface will the concentration of nickel be 3.2 wt %? The pre-exponential factor (D.) and activation energy for diffusion is 1.8 x 10$ m²/s and 152 kJ/mol respectively, and the surface concentration of nickel is 100 wt%. (Note that this is a non-steady state diffusion process).

2. A diffusion couple is made from nickel and iron. After 30 hours of heat treatment at 1400 K, the concentration of nickel is 3.2 wt % at a distance of 1.5 mm from interface. If an identical diffusion couple is heated at 1200 K for 30 hours, at what depth from the interface will the concentration of nickel be 3.2 wt %? The pre-exponential factor (D.) and activation energy for diffusion is 1.8 x 10$ m²/s and 152 kJ/mol respectively, and the surface concentration of nickel is 100 wt%. (Note that this is a non-steady state diffusion process).