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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:
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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?
arrangements of the atoms in a solid The importance of structure We can change shape of metals by 'plastic deformation' Why? Because most metals have very simple structures! Let us explore this 'structure' for metals
Al, Cu, Ni…….. The importance of structure Metals cubic close-packed (ccp) 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
C B The importance of structure We start with metals cubic close-packed (ccp) ABCABC layer sequence close-packed plane of atoms A C A A B
close-packed plane of atoms hexagon The importance of structure Metals hexagonal close-packed (hcp) Zn, Cd, Co, Ti, Zr……
B The importance of structure Metals hexagonal close-packed (hcp) ABAB layer sequence close-packed plane of atoms B A B A A
Fe, V, Cr, Mo, W, Ta…… some empty space The importance of structure Metals A2 structure - so-called "bcc" metal structure almost close-packed atom planes
The importance of structure Metals - summary Most metals exhibit one of 3 simple crystal structures: ccp - ductile hcp - probably ductile A2 - moderately ductile
Hard materials tend to be very brittle, not 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 Why is diamond not ductile?
tetrahedron The importance of structure Diamond is it ductile?
ore + reducing agent –––> semi-metal + byproducts SiO2 + C ––––––––––––> Si + CO2 1700-1900 C The importance of structure Si, Ge - semiconductors
C N B Al Si P As Ga Ge Sn In Sb The importance of structure Si, Ge - semiconductors ductile?
C N B Si structure GaAs structure Al Si P As Ga Ge Sn In Sb The importance of structure (Al,Ga,In) (N,P,As,Sb) - III-V semiconductors ductile?
Polytypes have different layer stacking sequences 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 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
octahedron The importance of structure TiO2 Exhibits 3 structures (polymorphs): rutile, anatase, brookite
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 Exhibits 3 structures (polymorphs): rutile, anatase, brookite Is this important? 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
rutile anatase The importance of structure TiO2
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
below 120° C centric BaTiO3 ––––––> non-centric BaTiO3 The importance of structure BaTiO3 - more TiO6 octahedra
below 130° C centric BaTiO3 ––––––> non-centric BaTiO3 ferroelectric The importance of structure BaTiO3 - phase transition
high temperature form low temperature form The importance of structure BaTiO3 - phase transition X-ray diffraction
BaTiO3 The importance of structure BaTiO3 structure (perovskite) - basis of atom arrangement for many electronic materials ex: YBa2Cu3O7- - 1st high temp superconductor
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
Ex: polyethylene (聚乙烯) carbon atoms tetrahedrally bonded - like diamond The importance of structure Polymers - consist of very long, flexible atom chains - very different structure But polymers largely amorphous (非晶的)
The importance of structure Some polymers crystallize - but not completely Get crystalline + amorphous regions
polarizing microscope image The importance of structure Some polymers crystallize - but not completely Get crystalline + amorphous regions Some polymers form 'spherulites' (球粒) example: polyethylene
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