41-Which of the following is defined as "a mechanism that involves the interchange of an atom from a normal lattice position to an adjacent vacant lattice site"?
self-diffusion
Interstitial diffusion
Inter-diffusion
Vacancy diffusion
Answer: Option 4) Vacancy diffusion
Substitutional diffusion occurs only if a vacancy is present. A vacancy is a “missing atom” in the lattice. If a vacancy is present, one of the adjacent atoms can move into the vacancy, creating a vacancy on the site that the atom has just left. This vacancy is filled by another adjacent atom creating a vacancy in it's own place, and so on.. Therefore diffusion of an atom is dependent on the presenceof an adjacent vacancy.
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