Chapter 3: Structure of Crystalline Solids

Question 1

2 Types of Packing

Answer 1

1. Non Dense, Random Packing

2. Dense, Ordered Packing

Question 2

This structure tends to have lower energies.

Answer 2

Dense, Ordered Packing

Question 3

Crystalling Materials

Answer 3

Packed in periodic, 3D arrays.

Metals, ceramics, Polymers…

Question 4

Noncrystalline / Amorphous Materials

Answer 4

No periodic packing.

Complex structures, rapid cooling.

Question 5

Metallic Crystal Structures

Answer 5

Densely Packed

Simplest Crystal Structures

Question 6

3 Metal Crystal Structures

Answer 6

Simple Cubic Structure (SC)

Body Centered Cubic Structure (BCC)

Face Centered Structure (FCC)

Question 7

Simple Cubic Structure

Answer 7

Rare due to low packing density.

Close-packed directions are cube edges

1 atom / unit cell

APF: 0.52

Question 8

Atomic Packing Factor (APF) Formula

Answer 8

Volume of atoms in unit cell / Volume of unit cell

Question 9

Body Centered Cubic Structure (BCC)

Answer 9

Atoms touch each other along cube diagonals

2 atoms / unit cell

APF: 0.68

Question 10

Face Centered Cubic Structure (FCC)

Answer 10

Atoms touch each other along face diagonals

4 atoms / unit cell

APF : 0.74

Question 11

FCC Stacking Sequence

Answer 11

ABC ABC

2D Projection

Question 12

Hexagonal Close-Packed Structure (HCP)

Answer 12

ABAB Stacking Sequence

6 atoms / unit cell

APF: 0.74

A Sites: Hexagon
B Sites: Triangle

Question 13

Theoretical Density (p)

Answer 13

Mass of Atoms in Unit Cell / Total Volume of Unit Cell

(n * A) / (V * N)

n: Number of atoms / unit cell
A: Atomic weight
V: Volume of Unit Cell
N: Avogadro’s Number

Question 14

Density of Material Classes

Answer 14

Metals > Ceramics > Polymers

Question 15

Density of Metals

Answer 15

Close-Packing (Metallic Bonding)

Large atomic masses

Question 16

Density of Ceramics

Answer 16

Less Dense Packing

Lighter elements

Question 17

Density of Polymers

Answer 17

Low-packing density (amorphous)

Lighter elements

Question 18

Density of Composites

Answer 18

Intermediate values

Question 19

Polycrystals

Answer 19

Most engineering materials fall into this category

Each “grain” is a single crystal

Grain size: 1 nm - 2 cm

Question 20

Single Vs Polycrystals

Answer 20

Single Crystals:

Properties vary with direction (ansiotropic)

Polycrystals:

Properties may or may not vary with direction

If grains randomly oriented : Isotropic

Else textured: Ansiotropic

Question 21

Poymorphism

Answer 21

Consists of two or more distinct crystal structures for the same material

Question 22

Unit Cell

Answer 22

Smallest repetitive volume which contains the complete lattice pattern of a crysta

Question 23

Linear Density (LD)

Answer 23

Number of Atoms / Unit length of directional vector

Question 24

X-Ray Diffraction

Answer 24

Used for crystal structure and interplanar spacing determinations