Chapter 2 - Structure of Crystalline Solids Flashcards
What is the structure of the atoms in a crystalline material?
Atoms self organize in a periodic way
What is the structure of the atoms in a single crystal
Atoms are in a repeating or periodic array over the entire material
What’s the Polycrystalline Material composed of
many small crystals or grains.
What’s the shape of an Amorphous Material
Disordered due to a lack of a systematic atomic arrangement
Crystalline solids characteristics
- 3D periodic array
- Strength of all the bonds (ions, molecules & atoms) are equal
- Sharp Melting point due to equal bonds breaking at the same time
- Not isotropic
- Most stable solids
Non-Crystalline/Amorphous Structures characteristics
- Bond strengths are all different
- No regularity in the external structure
- Don’t have a sharp melting point due to bond strengths being different
- They are isotropic in nature
What is the melting point of crystalline solids?
Sharp, as all the bonds are equal and break at the same time.
What does Isotropic mean?
In all directions the physical properties of that structure will remain the same
What is an Amorphous polymer?
Structure of disordered polymeric chains (as in liquid) but behaves like a solid
What are the regions of a Semicrystalline Polymer?
Has Amorphous regions (disordered chains) and crystalline regions (ordered chains)
Main Metallic structures
- Body Centered Cubic (BCC)
- Face Centered Cubic (FCC)
- Hexagonal Close Packed (HCP)
Face Centered Cubic Structure
- Atoms are located at each of the corners and on the centers of all the faces of a cubic unit cell
- 4 atoms per cell
- 74% atomic packing factor
Body Centered Cubic Structure
- There is an atom at each corner and the center of each cubic unit cell
- 2 atoms per cell
- 68% atomic packing factor
Hexagonal Closed Packing Structure
- 6 atoms per cell
- common structure of metallic crystals
- 74% atomic packing factor
Density of the unit cell equation
((Atoms in the unit cell)*(Mass of the atom))/(Volume of the cell)
