Question

(15%) An unknown amount of radioactive gold is deposited as a thin layer on one end each of two rods of gold. The two rods are then joined to form a specimen having the planar source of gold (Au*) atoms at the center of the joined rods. After diffusion for 100 hours at 920ºC (with the origin x = 0 taken at the planar source, where the relative concentration of radioactive gold, CAu* is defined as unity) at x = 0.3 mm, CAu* is 0.78 on this relative scale, and at x = 0.6 mm, it is 0.28. a) (5%) Sketch the concentration profile along the length of the bar specimen at 100 hours into the experiment. b) (10%) Calculate the self-diffusion coefficient of gold from this data.

Answer 1

Using the below equation for part b annd putting Ca1 = 0.78, Ca2= 0.28

Putting, X1=0.6mm = 6*10^-4

X2=0.3*10^-4

t=100 hour = 3.6*10⁵ sec