4 What factors affect the diffusion rate in solid metal crys

4. What factors affect the diffusion rate in solid metal crystals? (2 points)

Solution

The factors that affect the diffusion rate in solid metal crystals are:

1. The type of diffusion: Interstitial diffusion or substitutional diffusion affects the diffusion rate. Smaller atoms diffuse interstitially as against the bigger ones which diffuse substitutionally.

2. The temperature at which diffusion takes place: As the temperature increases, the diffusion increases because more thermal energy is available. Also more vacancies are present at higher temperatures.

3. The type of crystal structure: Depending on whether the crystal structure is FCC, BCC or simple cube, the diffusion rate varies. In BCC iron, carbon diffuses more rapidly than in FCC due to lower packing fraction in BCC (more space for diffusion).

4. The type of imperfections in the diffusion region: More open structures allow for more rapid diffusion. Also diffusion rate is more along the grain boundary than in the matrix. More are the defects, more is the diffusion rate.

5. The concentration of diffusing species: More is the concentration of diffusing atoms; more is the diffusion rate due to more participation of atoms in diffusing into vacancies.