Answer:
a) D = 4.88 * 10^(-14) m^2 / s
b) t = 1.1 hr
Solution:
a) Magnesium in Aluminum diffusion:
D = Do * exp(-Qd / RT)
= (1.2 * 10^(-4) m^2 / s) * exp ( - 130,000 / 8.31 * 723.15)
= 4.88 * 10^(-14) m^2 / s
D = 4.88 * 10^(-14) m^2 / s
b) The composition remains same at say the distance Xo:
(Cx - Co) / (Cs - Co) = Constant
Xo^2 / D_{550} * t = Xo^2 / D_{450} * 15
D_{550} * t = D_{450} * 15
(1.2 * 10^(-4) m^2 / s) * exp ( - 130,000 / 8.31 * 723.15) * t
(4.88 * 10^(-14) m^2 / s) * 15
by, solving for t we get:
t = 1.1 hr
So, the time required is 1.1 hr.
