Lecture 4

Question 1

what are the close packed planes in a HCP? how many are there?

Answer 1

the hexagonal layers of close-packed spheres (basal planes)

1

Question 2

what are the close packed planes in a CCP? how many are there?

Answer 2

the (111) planes (think about them being across the X/s of the tops and bottoms), which are perpendicular to a cube’s body diagonal

4

Question 3

how many close-packed directions are in one close-packed plane for hcp and ccp?

Answer 3

3 in both

Question 4

What is the difference in the images of HCP versus simple hexagonal

Answer 4

Question 5

HCP vs. SH

atoms/unit cell
a = ___
CN =
APF =

Answer 5

HCP
6 atoms
a = 2r
CN = 12
AFP = 0.74

SH
3 atoms
a = 2r
CN = 8
APF = 0.605

Question 6

In the calculation of the simple hexagonal, what do we use in atoms/unit cell?

Answer 6

we use 1 atom bc it’s a primitive unit cell

Question 7

what does layer construction look like for hexagonal versus square

Answer 7

Question 8

how do you form ccp or simple cublic structure with layering

Answer 8

lay a cubic layer of atoms

CCP: next layer on the square interstices
SC: next layer on top of the first

Question 9

is the simple cubic a common or uncommon crystal structure

Answer 9

uncommon

Question 10

what is the one element that crystalizes in the simple cubic structure?

Answer 10

𝛼-polonium

Question 11

SC

what is the closest packed direction?
CN?
a = ?
atoms/unit cell?
APF:

Answer 11

closest packed direction: (100) (along the cube’s edges)
CN = 6
a = 2r
atoms/unit cell = 1
APF = 0.52

Question 12

What does the APF > to be close-packed?

Answer 12

0.74

Question 13

What are 6 elements that commonly have the BCC structure?

Answer 13

Fe, Cr, W, V, Nb, Mo

Question 14

can the BCC be constructed from hexagonal close packed or square packed layers of atoms?

Answer 14

no

Question 15

what is the only direction in which atoms are in contact along in BCC?

Answer 15

the body-diagonal

4r = sqrt(3)*a

Question 16

how many atoms are in the unit cell of a BCC

Answer 16

2

Question 17

what is the plane in the BCC that atoms are the most (not fully) close-packed?

Answer 17

110 (the face diagonal plane)

Question 18

what is the atomic packing factor for BCC

Answer 18

PD = (vol occupied by atoms)/(total volume of unit cell) = 0.68 = 68%

Question 19

what are the different lattice constant formulas for SC, BCC, FCC, HCP

Answer 19

SC: a = 2r
BCC: a = 4/(sqrt(3))r
FCC: a = 2 sqrt(2)*r
HCP: a = 2r

Question 20

how do you calculate the planar density of a certain plane?

Answer 20

PD = (area of total atoms on the plane) / (area of the plane)

Question 21

what are the close packed planes and directions for CCP

Answer 21

{111} and <110>

Question 22

what are the close packed planes and directions for BBC

Answer 22

{110} and <111>

Question 23

what are the close packed planes and directions for SC

Answer 23

{100} and <100>

Question 24

what are the close packed planes and directions for HCP

Answer 24

{001} and <100>

Question 25

When doing calculations for planar density, when there’s only a portion of the atom in the plane, what do you do?

Answer 25

use the fraction of the actual atom in the plane

for example, it may be 1/8 of a whole atom in the cube, but 1/4 of a circle in a plane. use the 1/4

Question 26

where does deformation in metals occur

Answer 26

on the closest packed planes and in the closest-packed directions

Question 27

what is a slip system

Answer 27

the combo of slip plane and direction