This set of Materials Science Multiple Choice Questions & Answers (MCQs) focuses on “Diffusion Mechanisms – 2″.
1. For steady-state diffusion, diffusion flux is proportional to the concentration gradient. Concentration gradient is:
a) Rate of change of concentration with respect to space
b) Rate of change of concentration with respect to time
c) Difference in concentrations at the source and sink
d) Ratio of concentrations at source and sink
2. Which of the following is not true for steady-state diffusion?
a) The concentration profile is linear
b) The concentration gradient is constant
c) There is no net transfer of mass
d) The diffusion flux is constant
3. In steady state diffusion, which of the following remain unchanged with time?
a) Concentration at source
b) Concentration at sink
c) Concentration profile
d) All of mentioned
4. Concentration of hydrogen gas across a 2mm thick palladium sheet differs by 4 kg/m3. Considering steady-state diffusion with diffusion constant 10-10 m2/s, diffusion flux is ______ kg/m2.s:
a) 2 x 1010
b) 2 x 10-10
c) 5 x 10-11
d) 5 x 109
5. If C is the concentration of the diffusing species at distance x from the source and time t, then according to Fick’s second law (assuming diffusion coefficient, D is constant):
a) ∂C/∂x = D.(∂C/∂t)
b) ∂C/∂t = D.(∂2C/∂x2)
c) ∂C/∂x = D.(∂2C/∂t2)
d) ∂C/∂t = D.(∂C/∂x)
6. Predeposition and drive-in diffusion are two heat treatments used in the manufacture of integrated circuits.
Assertion: Predepostion is carried at a higher temperature than drive-in diffusion.
7. The expression J = M/(A.t), where J, M, A, & t are diffusion flux, mass of diffusing species, cross sectional area, and time respectively is:
b) valid for steady-state diffusion only
c) valid for non steady state diffusion only
d) valid for both steady and non steady state diffusion
8. The relation between temperature and diffusion coefficient is:
d) Diffusion coefficient is not related to temperature
What is the correct relationship between the two?
a) T1 > T2
b) T2 > T1
c) Insufficient data
d) Same process can’t have two concentration profiles
10. Diffusion through grain boundaries is very fast and is called short-circuit diffusion.
Assertion: Their contribution to overall diffusion is negligible.