struct ure
Jan 02, 2016
structure
structure
The world of materials The world of materials
The world of materialsThe world of materials
The world of materialsThe world of materials
The world of materialsThe world of materials
The importance of structure
We start with metals
The importance of structure
We start with metals
Metals come from?Metals come from?
Chemical reaction:ore + reducing agent –––> metal +
byproducts
Chemical reaction:ore + reducing agent –––> metal +
byproductsExample - steel:
Fe2O3 + C –––> Fe (as steel) + CO2
Example - steel:Fe2O3 + C –––> Fe (as steel) + CO2
What makes metals so useful to us?What makes metals so useful to us?
The importance of structure
We can change shape of metals by 'plastic deformation'
The importance of structure
We can change shape of metals by 'plastic deformation'Why?Why?
Because most metals have very simple structures!Because most metals have very simple structures!
arrangements of the atoms in a solid
arrangements of the atoms in a solid
Let us explore this 'structure' for metalsLet us explore this 'structure' for metals
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The importance of structure
Metals
cubic close-packed (ccp)
The importance of structure
Metals
cubic close-packed (ccp)
Al, Cu, Ni……..Al, Cu, Ni……..a few of atoms of a crystal arranged in unit cell (cube shaped)
a few of atoms of a crystal arranged in unit cell (cube shaped)rest of atoms in crystal found by stacking unit cells together
rest of atoms in crystal found by stacking unit cells together
The importance of structure
We start with metals
cubic close-packed (ccp)
close-packed plane of atoms
The importance of structure
We start with metals
cubic close-packed (ccp)
close-packed plane of atoms
The importance of structure
We start with metals
cubic close-packed (ccp)
ABCABC layer sequence close-packed plane of atoms
The importance of structure
We start with metals
cubic close-packed (ccp)
ABCABC layer sequence close-packed plane of atoms
AB
C
A
AB
C
The importance of structure
Metals
hexagonal close-packed (hcp)
The importance of structure
Metals
hexagonal close-packed (hcp)
Zn, Cd, Co, Ti, Zr……Zn, Cd, Co, Ti, Zr……
close-packed plane of atomsclose-packed plane of atoms
hexagonhexagon
The importance of structure
Metals
hexagonal close-packed (hcp)
ABAB layer sequence close-packed plane of atoms
The importance of structure
Metals
hexagonal close-packed (hcp)
ABAB layer sequence close-packed plane of atoms
AB
AB
AB
Fe, V, Cr, Mo, W, Ta……
The importance of structure
Metals
A2 structure - so-called "bcc" metal structure
almost close-packed atom planes
The importance of structure
Metals
A2 structure - so-called "bcc" metal structure
almost close-packed atom planes
some empty space
The importance of structure
Metals - summary
Most metals exhibit one of 3 simple crystal structures:
The importance of structure
Metals - summary
Most metals exhibit one of 3 simple crystal structures:
ccp - ductilehcp - probably ductileA2 - moderately ductile
ccp - ductilehcp - probably ductileA2 - moderately ductile
The importance of structure
Diamond
is it ductile?
The importance of structure
Diamond
is it ductile?
Diamond is extremely hard
Diamond 7000 (Knoop hardness)B4C (boron carbide) 2800 SiC (silicon carbide) 2500 WC (tungsten carbide) 2100 Al2O3 (corundum) 2100 SiO2 (Quartz) 800 SiO2 (Glass) 550
Hard materials tend to be very brittle, not ductile
Why is diamond not ductile?
The importance of structure
Diamond
is it ductile?
The importance of structure
Diamond
is it ductile? tetrahedron
The importance of structure
Si, Ge - semiconductors
The importance of structure
Si, Ge - semiconductors
ore + reducing agent –––> semi-metal + byproducts
SiO2 + C ––––––––––––> Si + CO2
1700-1900 C
The importance of structure
Si, Ge - semiconductors
ductile?
The importance of structure
Si, Ge - semiconductors
ductile?
Sb
As
P
SnIn
Ga
B N
Al
Ge
Si
C
The importance of structure
(Al,Ga,In) (N,P,As,Sb) - III-V semiconductors
ductile?
The importance of structure
(Al,Ga,In) (N,P,As,Sb) - III-V semiconductors
ductile?
Sb
As
P
SnIn
Ga
B N
Al
Ge
Si
C
Si structure GaAs structure
The importance of structure
SiC
Structure below (-SiC) one of many forms of SiC (3C, 2H, 4H, 6H, 15R, 21R, 33R,
105R…)
These forms called polytypes
The importance of structure
SiC
Structure below (-SiC) one of many forms of SiC (3C, 2H, 4H, 6H, 15R, 21R, 33R,
105R…)
These forms called polytypes
Polytypes have different layer stacking sequences
Polytypes have different layer stacking sequencesPolytypes have different properties
The importance of structure
TiO2
The importance of structure
TiO2
From where does it come?
rutile ore + C + Cl2 ––––> TiCl4 + CO2
TiCl4 + O2 ––––> TiO2 + Cl2
Not same as producing a metal
oxide ore ––––> oxide product
The importance of structure
TiO2
Exhibits 3 structures (polymorphs): rutile, anatase, brookite
The importance of structure
TiO2
Exhibits 3 structures (polymorphs): rutile, anatase, brookite
octahedron
The importance of structure
TiO2
Exhibits 3 structures (polymorphs): rutile, anatase, brookite
Is this important?
The importance of structure
TiO2
Exhibits 3 structures (polymorphs): rutile, anatase, brookite
Is this important?
In paints, want rutile, not anataseIn paints, want rutile, not anatase
Hardness Refractive index Organic absorption Tint strength
rutile 6-7 2.76 16-48 1650-1900
anatase 5-6 2.55 18-30 1200-1300
The importance of structure
TiO2
Both rutile & anatase produced together
Must control production process to getalmost all rutile
The importance of structure
TiO2
Both rutile & anatase produced together
Must control production process to getalmost all rutile
How do we know how much anatase in product?How do we know how much anatase in product?Industry uses an analytical technique known as
X-ray diffraction
Industry uses an analytical technique known as
X-ray diffractionRutile & anatase have different structures -so they scatter X-rays differentlyRutile & anatase have different structures -so they scatter X-rays differently
The importance of structure
TiO2
The importance of structure
TiO2
anatase
rutile
The importance of structure
BaTiO3 - more TiO6 octahedra
The importance of structure
BaTiO3 - more TiO6 octahedra
Several methods to prepare BaTiO3
Common high temperature (~ 1350° C) method:
BaCO3 + TiO2 ––––> BaTiO3 + CO2
(solid powders mixed together & reacted)
The importance of structure
BaTiO3 - important dielectric material
The importance of structure
BaTiO3 - important dielectric material
The importance of structure
BaTiO3 - more TiO6 octahedra
The importance of structure
BaTiO3 - more TiO6 octahedra
centric BaTiO3 ––––––> non-centric BaTiO3 centric BaTiO3 ––––––> non-centric BaTiO3 below 120° Cbelow 120° C
ferroelectricferroelectric
The importance of structure
BaTiO3 - phase transition
The importance of structure
BaTiO3 - phase transition
centric BaTiO3 ––––––> non-centric BaTiO3 centric BaTiO3 ––––––> non-centric BaTiO3 below 130° Cbelow 130° C
high temperature form
low temperature form
The importance of structure
BaTiO3 - phase transition X-ray diffraction
The importance of structure
BaTiO3 - phase transition X-ray diffraction
The importance of structure
BaTiO3 structure (perovskite) - basis of atom arrangement for many electronic
materials
The importance of structure
BaTiO3 structure (perovskite) - basis of atom arrangement for many electronic
materialsex: YBa2Cu3O7- - 1st high temp superconductor ex: YBa2Cu3O7- - 1st high temp superconductor
BaTiO3
The importance of structureThe importance of structure
YBa2Cu3O7- - 1st high temp superconductor YBa2Cu3O7- - 1st high temp superconductor
Y
BaCu
O
The importance of structure
What do you think of this Na silicate structure?
(red tetrahedra are SiO4 atom groups)
The importance of structure
What do you think of this Na silicate structure?
(red tetrahedra are SiO4 atom groups)
This is a "zeolite" there are 100s of zeolites
The importance of structure
Ion exchange - ex: water softener - Na inside can interchange with Ca in water
The importance of structure
Ion exchange - ex: water softener - Na inside can interchange with Ca in water
Molecular sieve - hydrocarbons with bulky side groups cannot get through
Catalyst substrate
The importance of structure
Carbon nanotubes ( 纳米管 ) (CNTs)
can have different structures
The importance of structure
Carbon nanotubes ( 纳米管 ) (CNTs)
can have different structures
The importance of structure
Carbon nanotubes (CNTs)
can have different structures - depending onhow 'graphene' sheet is rolled
The importance of structure
Carbon nanotubes (CNTs)
can have different structures - depending onhow 'graphene' sheet is rolled
The importance of structure
Polymers - consist of very long, flexible atom chains- very different structure
The importance of structure
Polymers - consist of very long, flexible atom chains- very different structure
Ex: polyethylene ( 聚乙烯 )
carbon atoms tetrahedrally bonded - like diamond
But polymers largely amorphous ( 非晶的 )
The importance of structure
Some polymers crystallize - but not completely
The importance of structure
Some polymers crystallize - but not completely
Get crystalline + amorphous regions
The importance of structure
Some polymers crystallize - but not completely
The importance of structure
Some polymers crystallize - but not completely
Get crystalline + amorphous regions
Some polymers form 'spherulites' ( 球粒 ) example: polyethylene
polarizing microscopeimage
The importance of structure
Some polymers crystallize - but not completely
The importance of structure
Some polymers crystallize - but not completely
Get crystalline + amorphous regions
The importance of structure
Polymers - polyethylene
The crystalline regions in polyethylenehave their molecular chains arranged like this:
The importance of structure
Polymers - polyethylene
The crystalline regions in polyethylenehave their molecular chains arranged like this:
The importance of structure
Polymers - polyethylene
X-ray scattering from amorphous regions
The importance of structure
Polymers - polyethylene
X-ray scattering from amorphous regions