The diffusion couple shown below is made from two A-B alloys. The initial compositions of the two alloys are indicated in the diagram. The centreline is at x = 0. The couple is held at an elevated temperature for 40 hours. Diffusivity; D = 3 × 10-11 m-2 s-1. Assume the diffusion couple to be infinitely long. Which of the parameters give the composition profile in the following form? C ( x,t ) + c_1 + c_2\,erf ( 12 Dt )

The diffusion couple shown below is made from two A-B alloys. The initial compositions of the two alloys are indicated in the diagram. The centreline is at x = 0. The couple is held at an elevated temperature for 40 hours. Diffusivity; D = 3 × 10^-11 m^-2 s^-1. Assume the diffusion couple to be infinitely long.

Which of the parameters give the composition profile in the following form?
$$C\left(x,t\right)+c_1+c_{2}erf\left(\frac{1}{2\sqrt{Dt}}\right)$$

Answer: Option A