Structure. The world of materials The importance of structure We start with metals The importance of structure We start with metals Metals come

structure

structure

The world of materials The world of materials

The world of materialsThe world of materials



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?


We can change shape of metals by 'plastic deformation'


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

QuickTime™ and aVideo decompressor

are needed to see this picture.


Metals

cubic close-packed (ccp)


Metals


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




close-packed plane of atoms




close-packed plane of atoms




ABCABC layer sequence close-packed plane of atoms




ABCABC layer sequence close-packed plane of atoms

AB

C

A

AB

C


Metals

hexagonal close-packed (hcp)


Metals


Zn, Cd, Co, Ti, Zr……Zn, Cd, Co, Ti, Zr……

close-packed plane of atomsclose-packed plane of atoms

hexagonhexagon


Metals


ABAB layer sequence close-packed plane of atoms


Metals


ABAB layer sequence close-packed plane of atoms

AB

AB

AB

Fe, V, Cr, Mo, W, Ta……


Metals

A2 structure - so-called "bcc" metal structure

almost close-packed atom planes


Metals

A2 structure - so-called "bcc" metal structure

almost close-packed atom planes

some empty space


Metals - summary

Most metals exhibit one of 3 simple crystal structures:


Metals - summary

Most metals exhibit one of 3 simple crystal structures:

ccp - ductilehcp - probably ductileA2 - moderately ductile

ccp - ductilehcp - probably ductileA2 - moderately ductile


Diamond

is it ductile?


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?


Diamond

is it ductile?


Diamond

is it ductile? tetrahedron


Si, Ge - semiconductors



ore + reducing agent –––> semi-metal + byproducts

SiO2 + C ––––––––––––> Si + CO2

1700-1900 C



ductile?



ductile?

Sb

As

P

SnIn

Ga

B N

Al

Ge

Si

C


(Al,Ga,In) (N,P,As,Sb) - III-V semiconductors

ductile?


(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


SiC

Structure below (-SiC) one of many forms of SiC (3C, 2H, 4H, 6H, 15R, 21R, 33R,

105R…)

These forms called polytypes


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


TiO2


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


TiO2

Exhibits 3 structures (polymorphs): rutile, anatase, brookite


TiO2


octahedron


TiO2


Is this important?


TiO2


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


TiO2

Both rutile & anatase produced together

Must control production process to getalmost all rutile


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


TiO2


TiO2

anatase

rutile


BaTiO3 - more TiO6 octahedra



Several methods to prepare BaTiO3

Common high temperature (~ 1350° C) method:

BaCO3 + TiO2 ––––> BaTiO3 + CO2

(solid powders mixed together & reacted)


BaTiO3 - important dielectric material


BaTiO3 - important dielectric material





centric BaTiO3 ––––––> non-centric BaTiO3 centric BaTiO3 ––––––> non-centric BaTiO3 below 120° Cbelow 120° C

ferroelectricferroelectric


BaTiO3 - phase transition


BaTiO3 - phase transition

centric BaTiO3 ––––––> non-centric BaTiO3 centric BaTiO3 ––––––> non-centric BaTiO3 below 130° Cbelow 130° C

high temperature form

low temperature form


BaTiO3 - phase transition X-ray diffraction


BaTiO3 - phase transition X-ray diffraction


BaTiO3 structure (perovskite) - basis of atom arrangement for many electronic

materials


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


What do you think of this Na silicate structure?

(red tetrahedra are SiO4 atom groups)


What do you think of this Na silicate structure?

(red tetrahedra are SiO4 atom groups)

This is a "zeolite" there are 100s of zeolites


Ion exchange - ex: water softener - Na inside can interchange with Ca in water


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


Carbon nanotubes ( 纳米管 ) (CNTs)

can have different structures


Carbon nanotubes ( 纳米管 ) (CNTs)

can have different structures


Carbon nanotubes (CNTs)

can have different structures - depending onhow 'graphene' sheet is rolled


Carbon nanotubes (CNTs)

can have different structures - depending onhow 'graphene' sheet is rolled


Polymers - consist of very long, flexible atom chains- very different 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 )


Some polymers crystallize - but not completely



Get crystalline + amorphous regions






Some polymers form 'spherulites' ( 球粒 ) example: polyethylene

polarizing microscopeimage







Polymers - polyethylene

The crystalline regions in polyethylenehave their molecular chains arranged like this:



The crystalline regions in polyethylenehave their molecular chains arranged like this:



X-ray scattering from amorphous regions



X-ray scattering from amorphous regions

Documents

Structure. The world of materials The importance of structure We start with metals The importance of structure We start with metals Metals come