Materialsand Ceramics

7/28/2019 Materialsand Ceramics

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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
http://en.wikipedia.org/wiki/Image:Materials_science_tetrahedron%3Bstructure%2C_processing%2C_performance%2C_and_proprerties.JPG


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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


8/16http

://www.corro

sionsource.com/


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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
http://www.chm.bris.ac.uk/pt/harvey/gcse/other.htmlhttp://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

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 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.

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