clathrates. cage-like frameworks of metals with other metals occupying the cavities of the cages
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Clathrates
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Clathrates
Cage-like frameworks of metals
with other metals occupying the
cavities of the cages.
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Clathrates
These can be synthesized by mixing
finely divided quantities of the metals in the
correct proportions and careful
heating and cooling.
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5 membered rings
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5 membered rings
5 + 6 membered rings
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Clathrates of this type have useful
thermal and semiconductor
properties.
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Clathrates of this type have useful
thermal and semiconductor
properties.
A good semiconductor that has poor
thermal conductivity is useful for
making a thermo-electric device.
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Thermo-electric cooler
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Thermo-electric cooler
Holes and electronscarry energy electrically.
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Thermo-electric cooler
Holes and electronscarry energy electrically.
Electrical energy isconverted to heat.
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Thermo-electric cooler
Holes and electronscarry energy electrically.
Electrical energy isconverted to heat.
Poor thermalconductivity ofsemiconductorkeeps heat fromreturning to cooling site.
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Ceramics and glass
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quartz
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quartz
Each O bonds to2 Si
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quartz
Each O bonds to2 Si
Each Si bonds to4 O
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quartz
Each O bonds to2 Si
Each Si bonds to4 O
SiO2
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GlassNa2O.CaO.(SiO2)6
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GlassNa2O.CaO.(SiO2)6
Approximateformula
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Quartz:crystalline,long-rangeorder
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glass: short-rangeorder but notcrystalline
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glass: short-rangeorder but notcrystalline
All Si bound to4 O
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glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
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glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
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glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
Ratio of O/Si Is > 2.
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glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
Ratio of O/Si Is > 2.
SixOy cluster is anionic
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glass: short-rangeorder but notcrystalline
SixOy cluster is anionic
Na+ and Ca2+
balance chargeof anion
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Properties of glass vs. quartz.
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Properties of glass vs. quartz.
Glass has a lower melting point
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Properties of glass vs. quartz.
Glass has a lower melting point
Glass is softer
Glass does not crystallize – this
makes it easier to shape it as it
cools to a solid form.
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Special glasses:
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Special glasses:
Borosilicate glass
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Borosilicate glass
Replace some ofthe Si sites withB
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Borosilicate glasses have lower
coefficients of expansion than
soda-lime glasses.
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Borosilicate glasses have lower
coefficients of expansion than
soda-lime glasses.
Most materials expand when heated.
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Most materials expand when heated.
The coefficient of expansion is a
factor, which when multiplied by the
temperature change, gives the amount a
material will expand or contract.
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Since glasses are quite brittle, they are
less likely to break when the temperature
changes if they have a relatively low
coefficient of expansion.
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Borosilicate glasses have higher melting
points than soda-lime glasses.
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Borosilicate glasses have higher melting
points than soda-lime glasses.
Soda-lime glasses can be melted using
a flame generated from methane and air.
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Borosilicate glasses have higher melting
points than soda-lime glasses.
Soda-lime glasses can be melted using
a flame generated from methane and air.
It is necessary to use a methane/oxygen
flame to work borosilicate glass.
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Cements:
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Cements:
Portland cement is a specifically
formulated powder.
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Cements:
Portland cement is a specifically
formulated powder.
When mixed with the proper amount
of water it first forms a slurry which
flows and can be formed.
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When mixed with the proper amount
of water it first forms a slurry which
flows and can be formed.
The slurry hardens and gains strength
by the growth of a network of silicate
crystals.
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(CaO)3.Al2O3(s) + 3 (CaSO4
.2 H2O)(s) + 26 H2O
(CaO)3.Al2O3
.(CaSO4)3.32H2O(s)
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(CaO)3.Al2O3(s) + 3 (CaSO4
.2 H2O)(s) + 26 H2O
(CaO)3.Al2O3
.(CaSO4)3.32H2O(s)
exothermic
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(CaO)3.Al2O3(s) + 3 (CaSO4
.2 H2O)(s) + 26 H2O
(CaO)3.Al2O3
.(CaSO4)3.32H2O(s)
exothermic
Cooling should favor the formation of
products.
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6 (CaO)3.SiO2(s) + 18 H2O(l)
(CaO)5.(SiO2)6
.5H2O(s) + 13 Ca(OH)2(s)
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6 (CaO)3.SiO2(s) + 18 H2O(l)
(CaO)5.(SiO2)6
.5H2O(s) + 13 Ca(OH)2(s)
crystals
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6 (CaO)3.SiO2(s) + 18 H2O(l)
(CaO)5.(SiO2)6
.5H2O(s) + 13 Ca(OH)2(s)
crystalsIf the mixture is allowed to dry too
rapidly, sufficient water and time
will not be available for crystal growth.