Material Science (Diffusion in Solids)

1. The unit of diffusion coefficient is
(1) m2 s1 
(2) m2 s-1 
(3) m2 s-2 
(4) m2 s2 
2. Substitutional diffusion becomes possible if
(1) the temperature of solid solution is sufficiently high.
(2) the activation energy for vacancy formation is low.
(3) atoms are significantly different in size.
(4) vacancies are present in a substitutional solid solution. 
3. The unit of flux J is
(1) moles m-2 s-1 or atoms m-2 s-1 
(2) atoms m2 s-1
(3) moles m-3 s-1 
(4) moles m-1 s-1 
4. For metal atoms, the most probable mechanism of diffusion is
(1) Vacancy mechanism 
(2) Interstitial mechanism
(3) Direct interchange mechanism 
(4) None of the above 
5. The dependence of diffusion coefficient on temperature in a certain temperature range is described by
(1) D = D0 exp (Q/T) 
(2) D = D0 exp (–Q/RT)
(3) D = D0 exp (–Q2/RT) 
(4) D = D0 exp (Q4/RT) 
6. The fastest diffusion coefficient in Fe is
(1) C 
(2) W 
(3) Ni 
(4) H 
7. Fick’s first law of diffusion is applicable under
(1) steady state conditions of mass flow
(2) non-steady state conditions
(3) steady as well as non-steady state conditions
(4) none of the above 
8. In the presence of impurities and deviations from stoichiometry, the diffusion rate of ions in ionic crystals
(1) enhances 
(2) decreases
(3) remains unaffected 
(4) first decreases and then enhances 
9. In comparison to lattice diffusion, the activation energy for diffusion along surfaces and grain boundaries is
(1) higher 
(2) lower
(3) almost negligible 
(4) infinite



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