Question

(a) compare interstitial and vacancy atomic mechanisms for diffusion. (b) cite two reasons why interstitial diffusion is normally more rapid than vacancy diffusion.

Answer 1

Interstitial and vacancy are two different diffusion mechanisms, with the former being typically faster due to the lighter mass of the diffusing species and the greater availability of interstitial sites for movement.

Step-by-step explanation:

(a) When comparing interstitial and vacancy diffusion mechanisms, the primary difference is in how atoms or molecules move from one location to another within a material. Interstitial diffusion occurs when the diffusing atoms or molecules move through the empty interstices in the crystal lattice. Conversely, vacancy diffusion requires a vacant lattice site or 'hole' to be near an atom; the atom can then jump into this void, leaving behind a new vacancy.

(b) There are two main reasons why interstitial diffusion is normally more rapid than vacancy diffusion. First, the mass of the diffusing species in interstitial diffusion tend to be lighter, allowing them to move faster. Second, interstitial sites are typically more available and require less activation energy to move into, compared to the energy required for an atom to leave its place and form a vacancy.

Answer 2

Interstitial sites are the spaces between atoms and are far smaller than vacancies, which are essentially the absence of an atom form the structure. Interstitial diffusion occurs when molecules move through the interstitial spaces of the substance, while vacancy diffusion is when the molecules move into the vacancies.


Because the interstitial spaces are far more numerous than the vacant spaces, and the bonding to the surrounding atoms in interstitial spaces is weaker, interstitial diffusion is faster than vacancy diffusion.