Crystal structures

Question 1

Which of the following are close packed structures?

bcc

ccp

hcp

fcc

Answer 1

ccp

hcp

fcc

Question 2

The stacking sequence in fcc is ABABAB

Answer 2

FALSE

Question 3

What is the packing fraction in hcp?

Answer 3

0.74
The answer is the same as for fcc as they are both close packed structures.

Question 4

How many different crystal systems are there?

Answer 4

7

Question 5

What is the crystal structure of alpha iron?

ccp

hcp

fcc

bcc

Answer 5

bbc

Question 6

Answer 6

Question 7

Answer 7

Question 8

A metal atom has a radius of 0.310 nm. If the metal has an fcc crystal structure calculate the volume of the unit cell in nm3.

Answer 8

0.674 +/- 1%

Question 9

A metal atom has a radius of 0.229 nm. If the metal has a bcc crystal structure calculate the volume of the unit cell in nm3.

Answer 9

0.148 +/- 1%

Question 10

Iron has an atomic mass of 56 amu. Given that 1 amu = 1.661 × 10–27 kg, the metallic radius of an iron atom is 126 pm and that alpha iron has a bcc structure calculate the density of alpha iron in kg m–3.

Answer 10

7,550
Remember there are 2 atoms in a bcc unit cell

Question 11

What structure does FFC (face centred cubic) or CCP (cubic close packed) have?

Answer 11

ABCABC`

Question 12

What structure does HCP (hexagonal Close Packed) have?

Answer 12

ABABAB…

Question 13

How many atoms are in fcc unit cell?

Answer 13

a given cell has 8 corners but only 1/8 of each corner atom is in the cell, the other 7/8 belong to adjacent cells
a given cell has 6 faces, 1/2 of each atom at the centre of a face is in the cell, the other 1/2 belongs to an adjacent cell
Hence total = 8 x 1/8 + 6 x 1/2 = 4