Lecture 3: The Structure of Crystalline Solids in Materials Science and Engineering, Summaries of Materials science

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Lecture 3 Lecture 3

Materials Science and Materials Science and

Engineering Engineering

Syllabus Syllabus

International University

National University – HCMC

Dr. Nguyen Dinh Uyen

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Chapter 3

The Structure of Crystalline Solids

Dr. Uyen Nguyen

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Chapter Outline

 Crystal Structure

 (^) A crystalline material is one in which the atoms are situated in a repeating or

periodic array over large atomic distances;

 (^) Crystallographic Points, Directions, and Planes

 (^) A specific points, direction, and planes of the crystal.

 (^) Crystalline and Non-crystalline Material

 (^) Explore different type of crystalline and non-crystalline materials

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• atoms pack in periodic, 3D arrays

Crystalline materials... -metals -many ceramics -some polymers

• atoms have no periodic packing

Noncrystalline materials... -complex structures -rapid cooling crystalline SiO 2 "Amorphous" = Noncrystalline noncrystalline SiO^2 Adapted from Fig. 3.22(b), Callister 7e. Adapted from Fig. 3.22(a), Callister 7e. Materials and Packing Si Oxygen

• typical of:
  • occurs for:

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Section 3.4 – Metallic Crystal

Structures



How can we stack metal atoms to minimize

empty space? 2-dimensions

vs. Now stack these 2-D layers to make 3-D structures https://www.youtube.com/watch?v=F4Du4zI4GJ

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• Tend to be densely packed.
• Reasons for dense packing:
  • Typically, only one element is present, so all atomic

radii are the same.

• Metallic bonding is not directional.
• Nearest neighbor distances tend to be small in

order to lower bond energy.

• Electron cloud shields cores from each other
• Have the simplest crystal structures.

We will examine three such structures...

Metallic Crystal Structures

FCC – Face Centered Cubic BCC – Body Centered Cubic HCP – Hexagonal Closed Packet https:// www.youtube.com/watch?v=HC WwRh5CXYU

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• APF for a face-centered cubic structure = 0.

Atomic Packing Factor: FCC

maximum achievable APF

APF =

4 3

( 2 a /4)

atoms unit cell atom volume a

unit cell volume Close-packed directions: length = 4 R = 2 a Unit cell contains: 6 x 1/2 + 8 x 1/ = 4 atoms/unit cell a 2 a Adapted from Fig. 3.1(a), Callister 7e.

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Use Matlab to

calculate the Unit Cell

Volume for the

followings:

1- Gold

2- Iron

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Atomic Packing Factor: BCC

a

APF =

4 3

 (^) ( 3 a /4)

atoms unit cell atom volume a

unit cell volume length = 4 R = Close-packed directions: 3 a

• APF for a body-centered cubic structure = 0.

a

R

Adapted from Fig. 3.2(a), Callister 7e. 2 a 3^ a

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Calculate the

Atomic Packing

Factor for BCC

structure