Chapter 3 Structure of Crystalline Solid

Question 1

Define Anistropy

Answer 1

Anisotropy is the property of substances to exhibit variations in physical properties with respect to different molecular or atomic direction

Question 2

Differentiate Crystalline, Noncrystalline and Amorphous materials

Answer 2

Crystalline - atomic packing ordered and periodic

Non-crystalline and amorphous - non-ordered

Question 3

Define Unit Cell

Answer 3

Unit cell is the smallest repetitive volume which

contains the complete lattice pattern of a crystal.

Question 4

Give the 7 Crystal System and 14 Crystal Structure

Answer 4

1. Cubic (FCC, BCC)
2. Orthorombic (Base Centered, BCC, FCC)
3. Tetragonal (BCC)
4. Hexagonal
5. Trigonal
6. Monoclinic (Base Centered)
7. Triclinic

Question 5

What is AFP?

Answer 5

AFP or Atomic Packing Factor tells how densely packed is a unit cell. The maximum AFP is for FCC and HCP which is 0.74. Full packing equals to 1.00.

Question 6

What is Theoretical Density

Answer 6

Theoretical density is equals to number of atoms * atomic weight divided by avogadros number * volume of the sphere

Question 7

Arrange the density of materials (qualitatively)

Answer 7

metal > ceramic > polymer

mainly due to the packing density and atomic weight

Question 8

What is polymorphism

Answer 8

It is the property of a material to have multiple crystal structure. E.g, Austenite (FCC) sigma-Fe and Ferrite (BCC) alpha-Fe

Question 9

What is the difference between crystal structure and crystal system?

Answer 9

Crystal structure is more detailed, it needs information about the geometry and arrangement of atoms in a unit cell.

Crystal system is simplier, it only tells the geometical arrangement of the unit cell.

For example FCC and BCC are Crystal Structure that belongs to Cubic Crystal System

Question 10

What is LD and PD?

Answer 10

Linear Density is the number of atoms per unit cell length (direction)

Planar Density is the number of atoms per unit cell area (plane)

Question 11

Impact of LD and PD?

Answer 11

Planar density (PD) is an important consideration
for slip, by which metals plastically deform.

Slip occurs on planes with the largest PD in
direction of highest linear density LD.

Question 12

Relationship of interplanar spacing (d) to planar indices hkl

Answer 12

As h+k+l increases, d decreases

Question 13

Give the basic assumption for the existence of hkl indices for FCC and BCC structure

Answer 13

FCC h,k,l should be either ALL even or ALL odd

BCC h+k+l should be even

Question 14

Give metals with FCC structure

Answer 14

Al, Ni, Ag, Au, Pt

Question 15

Give metals with BCC structure

Answer 15

Cr, W, Fe, Ta, Mo

Question 16

Give metals with HCP structure

Answer 16

C, Zn, Ti, Be, Mg