Technologies for Materials

1
Technologies for Materials

• Clothing, shelter, plastics, transistors,
  computer chips, cars, trains, etc

2
Types of Materials

• Metals and alloys
• Ceramics and glasses
• Polymers and plastic materials
• Composite materials
• Semi-conductors
• Superconductors

3
Metals

• Due to reactions with atmospheric O2, most metals
  occur as cations in ionic substances Fe2O3
  CaCO3, Al2O3
• A pure metal is obtained by its cation gaining
  electrons (called reduction)
• Iron occurs as oxide and is reduced by carbon to
  produce iron or structural steel (iron with
  carbon dissolved in it)

4
Production Of Iron and Steel in a Blast Furnace
Garland, Chemistry of Our World, MacMillan, NY,
1975, 352
5
Production of Steel
Garland, Chemistry of Our World, MacMillan, NY,
1975, 357
6
Electrolytic Production of Al by Hall Process
2 Al2O3 gt 4 Al 3 O2
Garland, Chemistry of Our World, MacMillan, NY,
1975, 351
7
Venugopalan, Chemistry and our World, Harper and
Row, NY, 1975, 177
8
Alloys

• Solid solutions of elements (usually metals)
  dissolved in a metal
• Alter the properties of the original metal in
  some desired manner

9
Venugopalan, Chemistry and our World, Harper and
Row, NY, 1975, 182
10
Corrosion

• Corrosion is oxidation (loss of electrons) of a
  metal - 20 of iron must be replaced annually due
  to rusting
• Corrosion of iron requires water and O2
• 2 Fe O2 2 H2O gt 2 Fe(OH)2
  4 Fe(OH)2 O2 gt 2 Fe2O3 4 H2O
• Prevented by coating iron with paint or Zn
  (galvanizing) - ZnO more dense

11
Ceramics and Glasses

• Ceramics are substances formed by heating
  mixtures of ionic substances to high temperatures
• Frequently involves oxides that are able to
  resist further oxidation
• Most common involve clay Al2O3.2SiO2.2H2O

12

Glasses are amorphous (do not have a repeating
structure) while ceramics are crystalline (have a
repeating structure).
Venugopalan, Chemistry and our World, Harper and
Row, NY, 1975, 188
13
Si red, O gray, Na yellow
Fine/Beal, Chemistry for Engineers and
Scientists, Saunders, NY, 1990, 694
14
Plastics

• Long chain-like structures (polymers) composed of
  individual repeating units (monomers)

15
Tro, 377
16
Polyethylene

• Thermoplastic - softens when heated
• Addition polymer - monomer units combine without
  eliminating any atoms
• High density (HDPE) has straight chains while low
  density (LDPE) has branches
• Substitution of one or more H atoms produces
  derivatives with different properties

17

Tro, 379
18
Tro, 379
19
Copolymers

• Two types of monomers are combined- chains
  composed of alternating units
• Condensation polymer - monomer units combine by
  expelling a small molecule such as water

20
Nylon
Tro, 382
21
Tro, 382
22
Tro, 382
23
Elastomer

• Polymer that stretches easily and returns to its
  original shape (rubber)
• Natural rubber is polyisoprene
• Vulcanization involves heating rubber with S
  which cross links chains

24
Natural Rubber
Tro, 383
25
Vulcanization - C. Goodyear, 1839
Tro, 383
26
Synthetic Rubber
Venugopalan, Chemistry and our World, Harper and
Row, NY, 1975, 244
27
Composites

• Combination of high strength fibers (of glass,
  graphite, or ceramics) held together by a polymer
• Fiber provides support and polymer protects
  fibers from breaking
• Fiber-glass is glass fiber in polyester - used in
  car panels, tennis rackets, molded chairs, boat
  hulls, etc

28
Sports Car with a Composite Body
Hill/Kolb, Chemistry for Changing Times, 9th,
Prentice Hall, NJ, 2001, 283
29
Semi-conductors

• A semiconductor is a substance that conducts
  electricity to a very limited extent when pure
  and its conductivity increases with increasing
  temperature
• Si forms covalent bonds with 4 Si atoms around
  itself and has no electrons free to move and
  conduct electricity - insulator

30
Si as a Semi-conductor
http//electronics.howstuffworks.com/diode1.htm
31
Doping Silicon

• Doping (mixing a small amount of an impurity
  into the silicon crystal) increases its
  electrical conductivity
• Elements from 3A and 5A families can be used as
  dopants for 4A semiconductors

32
3,5 - Dopants
http//electronics.howstuffworks.com/diode2.htm
33
Electron Donor and Acceptor Doped Si-Crystals
Donor Crystal N-type semi-conductor
Acceptor Crystal P-type semi- conductor
Hill/Kolb, Chemistry for Changing Times, 8th,
Prentice Hall, NJ, 1998, 375
34
A diode is the simplest possible semiconductor
device. A diode allows current to flow in one
direction but not the other.
http//electronics.howstuffworks.com/diode3.htm
35
Transistor

• A transistor is created by using three doped
  layers (PNP or NPN) rather than the two layers
  used in a diode
• A transistor can act as a switch or an amplifier
  - applying a small current to the center layer of
  the sandwich, causes a much larger current to
  flow through the sandwich as a whole

36
Silicon Chip

• A piece of silicon that can hold thous-ands of
  transistors
• With transistors acting as switches, you can
  create Boolean gates, and with Boolean gates you
  can create microprocessor chips and hence
  computers

http//electronics.howstuffworks.com/diode4.htm
37
Superconductors

• An element, inter-metallic alloy, or compound
  that will conduct electricity without resistance
  below a certain temperature, Tc
• Require low temperatures to slow down molecular
  vibrations sufficiently to facilitate unimpeded
  electron flow

http//superconductors.org/Type1.htmv
38
http//superconductors.org/Uses.htm
39
http//superconductors.org/Uses.htm
40
Meissner Effect

• When a substance becomes a superconductor, it is
  repelled by an external magnetic field
• If a small magnet is placed on top of a
  superconductor, the magnet levitates, i.e., it
  is repelled upward (floats) but is held within
  the space of the magnetic field (magnetic pinning)

41
The Yamanashi MLX01 MagLev Train
A 5-car MLX01 MagLev Train achieved a sustained
velocity of 343 miles/hr on 4/14/99
http//superconductors.org/Uses.htm