Materials Classification and Properties Metals, Ceramics, and Semiconductors

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Materials Classification and PropertiesMetals,
Ceramics, and Semiconductors

• NANO 52
• Foothill College

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Properties of Materials

• Physical
• Mechanical
• Chemical
• Thermal
• Electrical
• Optical

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Physical Properties

• Strength
• Ductility
• Melting point
• Glass transition
• Density

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Mechanical Properties

• Stress strain behavior
• Strength
• Tensile properties
• Compression, shear, torsion
• Deformation
• Hardness

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Chemical Properties

• Acid - base
• Reactivity
• Corrosion
• Oxidation
• Passivation

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Thermal Properties

• Heat conductance
• Heat capacity
• Thermal expansion
• Annealing temperature
• (Melting point, softening point)

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Electrical Properties

• Electrical conductivity
• Electrical resistance/impedance

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http//www.corrosionsource.com/
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Metal Structure / Bonding

• Metallic bonds
• All metals are made up of a vast collection of
  ions that are held together by metallic bonds.
• A metal atom has a positive nucleus with negative
  electrons outside of it.
• In a solid, each atom loses the outermost
  electron, which takes part in bonding.
• They form a lattice of regularly spaced positive
  ions. Each ion has no control over its bonding
  electron.

http//www.chm.bris.ac.uk/pt/harvey/gcse/other.htm
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Examples of Ceramics

• Clay, Minerals, Salts and Oxides
• Technical Ceramics can also be classified into
  three distinct material categories
• Oxides Alumina, zirconia
• Non-oxides Carbides, borides, nitrides
• Composites Particulate reinforced, combinations
  of oxides and non-oxides.

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Ionic Bonding in Ceramics

• Ceramic materials are formed from ionic bonds
  within their constituent atoms, oxides and salts.
• Ionic bonds are not nearly as ductile as
  metals, causing ceramics to be brittle.

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Metallic vs. Ionic Bonding

• Much easier to deform materials with metallic
  than with ionic bonding. Why?

• Sliding atom planes over each other (deformation)
  very unfavorable energetically in ionic solids!
• ? metals are ductile ceramics (ionic) are
  brittle

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Semiconductors
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Semiconductors
http//worldwatts.com/silicon_semiconductor.html
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Semiconductors

• In solid state physics and related applied
  fields, the band gap is the energy difference
  between the top of the valence band and the
  bottom of the conduction band in insulators and
  semiconductors.

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Semiconductors

• The ease with which electrons in a semiconductor
  can be excited from the valence band to the
  conduction band depends on the band gap between
  the bands, and it is the size of this energy
  bandgap that serves as an arbitrary dividing line
  (roughly 4 eV) between semiconductors and
  insulators.
• Electrons excited to the conduction band also
  leave behind electron holes, or unoccupied states
  in the valence band. Both the conduction band
  electrons and the valence band holes contribute
  to electrical conductivity.
• The holes themselves don't actually move, but a
  neighboring electron can move to fill the hole,
  leaving a hole at the place it has just come
  from, and in this way the holes appear to move,
  and the holes behave as if they were actual
  positively charged particles.