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15 Cards in this Set
- Front
- Back
Electronic materials are classified according to _________.
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conductivity
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Metals
Semiconductors Insulators |
properties controlled by energies and shapes of orbitals, particularly band gap
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band gap
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separation b/w valence band and conduction band
small amt of energy needed to move e- from VB to CB |
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semiconductor types:
intrinsic doping: n-type, p-type |
pure-silica (4 e-)
negative-replace some w/ phosphorus (5 e- makes excess) positive-replace some w/ aluminum (3 e- makes deficiency) |
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superconductors
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transmit electricity w/o resistance--materials become superconducting at low temperatures
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band gap energies for semiconductors, insulators
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~50-300 kJ/mol
< 350 kJ/mol |
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types of insulators
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ionic solids, complex network solids, organic cpds
ceramics--inorganic ionic solids |
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ceramics--types
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oxides (oxygen and metals)
carbides (carbon and metals) nitrides (nitrogen and metals) silicates (silica with metal oxides) aluminates |
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ceramics--properties
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hard, brittle
resistant to heat, corrosion, wear, do not deform under stress, less dense than metals |
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semiconductors--types
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silicon, germanium, carbon in graphite form
inorganic cpds with valence electron count of four bonding is covalent-network, ionic, or combination |
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plastics
thermoplastic termosetting plastic elastomer |
materials that can be formed into various shapes
can be reshaped shaped through irreversible chemical processes exhibits rubbery or elastic behavior |
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making polymers:
addition polymerization condensation |
coupling of monomers through their pi bonds
elimination of small molecule like water |
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crystallinity
cross-linking vulcanization |
degree of ordering in polymer
forming bonds b/w chains--stiffens adding sulfur to natural rubber cross-links chains together |
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making ceramics
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sol-gel process forms fine particles of uniform size
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materials for optics
liquid crystals intermediate liquid crystalline phase-classifications |
nematic-one dimensional ordering along long axis
smectic-two-dimensional ordering along long axes and in layers (ends line up) cholesteric-aligned along long axes but in flat planes rotated at different angles for a screwlike spiral (changes in temp and pressure change the order and hence the color) |