1. structure

2. The world of materials

3. The world of materials

4. The world of materials

5. The world of materials

6. The importance of structure
We start with metals
Metals come from?
Chemical reaction:
ore + reducing agent –––> metal + byproducts
Example - steel:
Fe2O3 + C –––> Fe (as steel) + CO2
What makes metals so useful to us?

7. The importance of structure
We can change shape of metals by 'plastic deformation'
Why?
Because most metals have very simple structures!
arrangements of the atoms in a solid
Let us explore this 'structure' for metals

8. The importance of structure
Metals
cubic close-packed (ccp)
Al, Cu, Ni……..
a few of atoms of a crystal arranged in unit cell (cube shaped)
rest of atoms in crystal found by stacking unit cells together

9. The importance of structure
We start with metals
cubic close-packed (ccp)
close-packed plane of atoms

10. The importance of structure We start with metals
cubic close-packed (ccp)
ABCABC layer sequence close-packed plane of atoms A B C C A A B

11. The importance of structure
Metals
hexagonal close-packed (hcp)
Zn, Cd, Co, Ti, Zr……
hexagon
close-packed plane of atoms

12. The importance of structure Metals hexagonal close-packed (hcp)
ABAB layer sequence close-packed plane of atoms B A B B A A

13. The importance of structure
Metals
A2 structure - so-called "bcc" metal structure
almost close-packed atom planes
Fe, V, Cr, Mo, W, Ta……
some empty space

14. The importance of structure
Metals - summary
Most metals exhibit one of 3
simple crystal structures:
ccp - ductile
hcp - probably ductile
A2 - moderately ductile

15. The importance of structure
Diamond
is it ductile?
Diamond is extremely hard
Diamond (Knoop hardness)
B4C (boron carbide) 2800
SiC (silicon carbide) 2500
WC (tungsten carbide) 2100
Al2O3 (corundum) 2100
SiO2 (Quartz)
SiO2 (Glass)
Hard materials tend to be very brittle, not ductile
Why is diamond not ductile?

16. The importance of structure
Diamond
is it ductile?
tetrahedron

17. The importance of structure Si, Ge - semiconductors
ore + reducing agent –––> semi-metal + byproducts
SiO2 + C ––––––––––––> Si + CO2 C

18. The importance of structure Si, Ge - semiconductors ductile?Sb As P Sn In Ga B N Al Ge Si C

19. The importance of structure
(Al,Ga,In) (N,P,As,Sb) - III-V semiconductors
ductile? Sb As P Sn In Ga B N Al Ge Si C
Si structure
GaAs structure

20. 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 properties

21. The importance of structure
TiO2
From where does it come?
Not same as producing a metal
oxide ore ––––> oxide product
rutile ore + C + Cl2 ––––> TiCl4 + CO2
TiCl4 + O2 ––––> TiO2 + Cl2

22. The importance of structure TiO2 Exhibits 3 structures (polymorphs):
rutile, anatase, brookite
octahedron

23. The importance of structure TiO2 Exhibits 3 structures (polymorphs):
rutile, anatase, brookite
Is this important?
Hardness Refractive index Organic absorption Tint strength
rutile
anatase
In paints, want rutile, not anatase

24. The importance of structure
TiO2
Both rutile & anatase produced together
Must control production process to get
almost all rutile
How do we know how much anatase in product?
Industry uses an analytical technique known as
X-ray diffraction
Rutile & anatase have different structures -
so they scatter X-rays differently

25. The importance of structure TiO2
rutile
anatase

26. 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)

27. The importance of structure
BaTiO3 - important dielectric material

28. The importance of structure
BaTiO3 - more TiO6 octahedra
centric BaTiO3 ––––––> non-centric BaTiO3
below 120° C

29. The importance of structure
BaTiO3 - phase transition
centric BaTiO3 ––––––> non-centric BaTiO3
below 130° C
ferroelectric

30. The importance of structure
BaTiO3 - phase transition X-ray diffraction
high temperature form
low temperature form

31. The importance of structure BaTiO3 structure (perovskite) - basis of
atom arrangement for many electronic materials
ex: YBa2Cu3O7-  - 1st high temp superconductor
BaTiO3

32. The importance of structure
YBa2Cu3O7-  - 1st high temp superconductor Y Ba Cu O

33. 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

34. 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

35. The importance of structure
Carbon nanotubes (纳米管) (CNTs)
can have different structures

36. The importance of structure
Carbon nanotubes (CNTs)
can have different structures - depending on
how 'graphene' sheet is rolled

37. 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)

38. The importance of structure
Some polymers crystallize - but not completely
Get crystalline + amorphous regions

39. The importance of structure
Some polymers crystallize - but not completely
Get crystalline + amorphous regions
Some polymers form 'spherulites' (球粒)
example: polyethylene
polarizing
microscope
image

40. The importance of structure
Some polymers crystallize - but not completely
Get crystalline + amorphous regions

41. The importance of structure
Polymers - polyethylene
The crystalline regions in polyethylene
have their molecular chains arranged like this:

42. The importance of structure
Polymers - polyethylene
X-ray scattering from amorphous regions