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Clathrates
Clathrates
Cage-like frameworks of metals
with other metals occupying the
cavities of the cages.
Clathrates
These can be synthesized by mixing
finely divided quantities of the metals in the
correct proportions and careful
heating and cooling.
5 membered rings
5 membered rings
5 + 6 membered rings
Clathrates of this type have useful
thermal and semiconductor
properties.
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.
Thermo-electric cooler
Thermo-electric cooler
Holes and electronscarry energy electrically.
Thermo-electric cooler
Holes and electronscarry energy electrically.
Electrical energy isconverted to heat.
Thermo-electric cooler
Holes and electronscarry energy electrically.
Electrical energy isconverted to heat.
Poor thermalconductivity ofsemiconductorkeeps heat fromreturning to cooling site.
Ceramics and glass
quartz
quartz
Each O bonds to2 Si
quartz
Each O bonds to2 Si
Each Si bonds to4 O
quartz
Each O bonds to2 Si
Each Si bonds to4 O
SiO2
GlassNa2O.CaO.(SiO2)6
GlassNa2O.CaO.(SiO2)6
Approximateformula
Quartz:crystalline,long-rangeorder
glass: short-rangeorder but notcrystalline
glass: short-rangeorder but notcrystalline
All Si bound to4 O
glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
Ratio of O/Si Is > 2.
glass: short-rangeorder but notcrystalline
All Si bound to4 O
Many O are‘terminal’
Ratio of O/Si Is > 2.
SixOy cluster is anionic
glass: short-rangeorder but notcrystalline
SixOy cluster is anionic
Na+ and Ca2+
balance chargeof anion
Properties of glass vs. quartz.
Properties of glass vs. quartz.
Glass has a lower melting point
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.
Special glasses:
Special glasses:
Borosilicate glass
Borosilicate glass
Replace some ofthe Si sites withB
Borosilicate glasses have lower
coefficients of expansion than
soda-lime glasses.
Borosilicate glasses have lower
coefficients of expansion than
soda-lime glasses.
Most materials expand when heated.
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.
Since glasses are quite brittle, they are
less likely to break when the temperature
changes if they have a relatively low
coefficient of expansion.
Borosilicate glasses have higher melting
points than soda-lime glasses.
Borosilicate glasses have higher melting
points than soda-lime glasses.
Soda-lime glasses can be melted using
a flame generated from methane and air.
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.
Cements:
Cements:
Portland cement is a specifically
formulated powder.
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.
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.
(CaO)3.Al2O3(s) + 3 (CaSO4
.2 H2O)(s) + 26 H2O
(CaO)3.Al2O3
.(CaSO4)3.32H2O(s)
(CaO)3.Al2O3(s) + 3 (CaSO4
.2 H2O)(s) + 26 H2O
(CaO)3.Al2O3
.(CaSO4)3.32H2O(s)
exothermic
(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.
6 (CaO)3.SiO2(s) + 18 H2O(l)
(CaO)5.(SiO2)6
.5H2O(s) + 13 Ca(OH)2(s)
6 (CaO)3.SiO2(s) + 18 H2O(l)
(CaO)5.(SiO2)6
.5H2O(s) + 13 Ca(OH)2(s)
crystals
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.