structure

The world of materials

The world of materials

The world of materials

The world of materials

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?

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

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

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 A B C C A A B

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

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

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

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

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? Sb As P Sn In Ga B N Al Ge Si C

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

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

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

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? 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 In paints, want rutile, not anatase

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

The importance of structure TiO2 rutile anatase

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 - more TiO6 octahedra centric BaTiO3 ––––––> non-centric BaTiO3 below 120° C

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

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

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

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

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 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 (CNTs) can have different structures - depending on how 'graphene' sheet is rolled

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 Get crystalline + amorphous regions

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

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

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

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