Structure of Crystalline Solid Chpt 3 Flashcards
What is the structure of Crystalline materials
atoms pack in periodic arrays
What type of materials are typical to have crystalline structures?
metals, many ceramics, some polymers
What’s the structure of a noncrystalline material
atoms have no periodic packing
Where do you find noncrystalline materials?
complex structures, rapid cooling
Whats another word for noncrystalline?
Amorphous
What’s the correlation between density packing and energy?
dense, regular packed (compact) structures tend to have lower bonding energy
What’s a unit cell
basic repeating unit of crystalline materials
Repeating unit cells to form entire crystal
What’s lattice
atomic arrangements in crystalline solids that can be described with respect to a network of lines
What are lattice sites
the intersections of lines of unit cells in crystalline solids
What are the three characteristics of a lattice cell
lattice parameters: how many sides
axial length: length of each axix
interaxial angle: angle between each axis
describe the relationship between unit cells and atoms
an atom can share multiple unit cells
Why do Metallic Crystal Structures have dense packing?
metallic bonding is not directional, the nearest neighbor distance tends to be small in order to lower bond energy, and typically since only one element is present, all atomic radii are the same
They have simple structures
Do metallic crystal structures have dense or non-dense packing?
Dense
What are the four structures of metallic crystals
simple cubic (SC), Body-Centered Cubic (BCC), Face-Centered Cubic (FCC), Hexagonal Closed-Packed (HCP)
What is SC and describe it
Simple Cubic, arrangement of hard spheres in each (8) corner.
each corner of the unit cell is defined by a lattice point at which an atom can be found in the crystal
each of the 8 corners of the unit cell contain an identical particle
What is APF
Atomic packing factor
APF= Vol. of atoms in unit cell / vol. of unit cell
Whats the volume of a sphere
4/3pi(r)^3
What is the APF of a SC structure
(1*4/3pi(0.5d)^3) / d^3
d = length of a side
closed-packed directions contains:
8*1/8 = 1 atom/unit cell
0.52
What is BCC?
Body-Centered Cubic
contains 9 atoms, all identical, 8 in each corner of the unit cell (they say this is the atomic centers in the unit cell), and one in the center
What’s the APF of a BCC structure?
radius is 4r because you have 1/8 circles in corners and an atom in center with radius of that circle, so diameter of 2. from one corner to the other, it’s 4r. r = (sqrt(3)/4) * a
https://www.youtube.com/watch?v=ceOOxa1A6-A
of atoms: (one atom with all 8 components in each corner and another in the center)
APF = 2 * 4/3 pi (sqrt(3)a/4)^3 / a^3
0.68
What is FCC?
Faced-Centered Cubic structure
1/8 sphere in each corner, half a sphere on each face of the cube cell
How many lattice points in a FCC structure?
14 identical points.
What elements have the FCC structure?
Cu, Al, Ag, Au
Whats the APF of FCC structure?
on one face, its diagonal = sqrt(2)a = 4r
r = sqrt(2) / 4
https://www.youtube.com/watch?v=ceOOxa1A6-A
4 atoms per unit cell
APF = 4 * 4/3 pi (sqrt(2)a / 4)^3 / a^3
0.74
