Quiz One Practice

Question 1

What direction does the Burgers vector go in for an edge dislocation?

Answer 1

Perpendicular to the dislocation

Question 2

What direction does the Burgers vector go in for a screw dislocation?

Answer 2

Parallel to the dislocation

Question 3

In a HCP structure, what directions are identical?

Answer 3

[100], [010], [110]

Question 4

What are the coordination numbers of the following:

Simple cubic

BCC

FCC

HCP

Answer 4

6

8

12

12

Question 5

Which direction does the Burgers vector point in a mixed dislocation?

Answer 5

The Burgers vector of the dislocation varies along the dislocation line.

Question 6

What is the formula for calculating the atomic packing factor?

Answer 6

Question 7

What is the total unit cell volume for an FCC structure?

Answer 7

Question 8

What is the total unit cell volume for a BCC structure?

Answer 8

Question 9

What is the total unit cell volume for a HCP structure?

Answer 9

Question 10

How many atoms per unit cell in a FCC structure?

Answer 10

4

Question 11

How many atoms per unit cell in a HCP structure?

Answer 11

6

Question 12

How many atoms per unit cell in a BCC structure?

Answer 12

2

Question 13

How many atoms per unit cell in a SC structure?

Answer 13

1

Question 14

How do you calculate the total unit cell volume for a HCP structure?

Answer 14

Question 15

List the steps needed to determine the indices for vectors in a 3D plane.

Answer 15

1. Vector repositioned to pass through origin.
2. Read off projections in terms of unit cell dimensions a, b and c.
3. Reduce numbers to smallest integer values.
4. Enclose in square brackets with no commas.

Question 16

List the steps required to determine the Miller indices for a plane.

Answer 16

1. Read off intercepts of plane with axes in terms of a, b, c.
2. Take reciprocals of intercepts.
3. Reduce to smallest integer values.
4. Enclose in parentheses, no commas.

Question 17

The triclinic crystal system is the crystal system without any symmetry i.e. their lattice parameters are not equal (a,b,c,alpha,beta,gamma, do not equal 90 degrees). Based on the definition of the unit cell, explain why we do not choose a unit cell with a base-centered, body centered, or face centered triclinic lattice in the triclinic system.

Answer 17

There are seven possible combinations of a, b and c and alpha, beta and gamma, each of which represents a distinct crystal system.

FCC and BCC structures both belong to the cubic crystal system, whereas HCP falls within the hexagonal system.

The triclinic crystal system has no symmetry, and a unit cell is chosen based on two conditions, having the highest symmetry and the smallest repetitive volume.

Question 18

Briefly explain why 4-digit indexes are used in hexagonal structures.

Answer 18

If crystal planes in hexagonal systems are indexed using Miller indices, then crystallographically equivalent planes would have indices that appear dissimilar. To overcome this, the Miller-Bravais four index system is used.

Question 19

List the steps required in determining the 3-digit indices for a plane in a hexagonal unit cell.

Answer 19

1. Intercepts (a1,a2,z)
2. Reciprocals
3. Reduction
4. Parentheses

Question 20

How do you convert from a 3 digit representation to a 4 digit representation in a hexagonal unit cell?

Answer 20

i = -(h+k)

a3 = -(a1+a2)