Question

In: Chemistry

22) the diffusion coefficient of carbon FCC iron is lower than BCC iron because a) the...

22) the diffusion coefficient of carbon FCC iron is lower than BCC iron because

a) the temperature is higher for FCC

b) FCC has a higher packing factor

c) FCC is more cubic

d) Carbon is substitional in FCC

Solutions

Expert Solution

Answer is B.

Body centered cubic structure is more loosly pack than that of face centered cubic structure.beacuse the body-centered cubic unit cell has atoms at each of the eight corners of a cube and one atom in the center of the cube.It is said to have a coordination number of 8.The bcc unit cell consists of a net total of two atoms. one in the center and eight eighths from corners atoms.

The face centered cubic structure has atoms located at each of the corners and the centers of all the cubic faces.Each of the corner atoms is the corner of another cube so the corner atoms are shared among eight unit cells. Additionally, each of its six face centered atoms is shared with an adjacent atom. because 12 of its atoms are shared, it is said to have a coordination number 12.

so we can easily say when atoms are loosly pack in a structure diffusion is easy.

according to the structure of BCC and FCC we can also calculate packing factor.

packing factor=The volume of atoms in a cell/total volume of a cell.

packing factor of BCC=0.68

packing factor of FCC in iron=0.74

queen_honey_blossom answered 2 years ago
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