materialsand ceramics
TRANSCRIPT
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Materials Classificationand Properties
Metals, Ceramics, andSemiconductors
NANO 52Foothill 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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Metal Structure / Bonding
Metallic bonds
All metals are made up of avast collection of ions that areheld together by metallic bonds.
A metal atom has a positivenucleus with negative electronsoutside of it.
In a solid, each atom loses theoutermost electron, which takes
part in bonding. They form a lattice of regularly
spaced positive ions. Each ionhas no control over its bondingelectron.
http://www.chm.bris.ac.uk/pt/harvey/gcse/other.html
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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 theirconstituent 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 withionic bonding. Why?
Sliding atom planes over each other (deformation) veryunfavorable energetically in ionic solids!
metals are ductile & ceramics (ionic) are brittle
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Semiconductors
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Semiconductors
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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 excitedfrom the valence band to the conduction band depends on the bandgap between the bands, and it is the size of this energy bandgapthat serves as an arbitrary dividing line (roughly 4 eV) betweensemiconductors and insulators.
Electrons excited to the conduction band also leave behind electronholes, or unoccupied states in the valence band. Both theconduction band electrons and the valence band holes contribute toelectrical conductivity.
The holes themselves don't actually move, but a neighboringelectron 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 theholes behave as if they were actual positively charged particles.