Chapter 2 Flashcards
(20 cards)
What are crystalline material?
Atoms formed in periodic 3D arrays (usually metals, ceramics and some polymers)
How does packing affect energy?
Dense packing reduces interatomic bond lengths and makes them harder to break
What is crystallinity?
A solid material in which atoms are situated in repeating periodic array over large atomic distances
Crystal structure
The way that atoms and ions are spacially arranged
What is a unit cell?
A unit that can be repeated over space to form the crystalline lattice
What are lattice parameters?
3 edge lengths (a, b, c)
3 interaxial angles (alpha, beta, gamma)
Coordination #
of neighboring atoms touching particular unit cell in a crystal
What is the atomic packaging factor? (APF)
Volume of atoms in a unit cell
______________________________
Volume of a unit cell
Simple cubic crystal structure (SC)
rare because of low density
.52% full
Body center cubic (BCC)
1 sphere with 8 corners
Coordination number is 8
.68%fill
Face centered cubic (FCC)
6 faces 8 cube corners
Coordination number is 12
74% fill
Hexagon closed packed( HCP)
Coordination number is 12
74% fill
Point coordinates
XYZ axis mapped onto parameters ABC
How to find Crystallographic directions
1) determine point coords of vector head and tail
2) head - tail coord
3) normalize differences (divide by A, B or C)
4) reduce to smallest whole numbers
5) enclose indicies in square brackets w/no comma
How to find crystallographic planes
1) Find find intercepts of plane through axes(A,B,C)
2) take reciprocal
3) clear fractions
4) reduce to lowest whole numbers
What is linear density?
Number of atoms per unit length
LD= #atoms on direction vector
__________________________
Length of direction vector
What is linear density?
Number of atoms per unit length
LD= #atoms on direction vector
__________________________
Length of direction vector
What is planar density?
PD= #atoms centered on a plane
___________________________
Area of plane
Polycrystalline
Composed of many small single crystals or grains
- properties vary with direction
- if grains are random isotropic properties
- if grains are textured anisotrophic
What is a grain boundary?
Atomic missmatch where 2 grains meet
