Clathrates. Cage-like frameworks of metals with other metals occupying the cavities of the cages

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


Holes and electronscarry energy electrically.



Electrical energy isconverted to heat.



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


All Si bound to4 O


All Si bound to4 O

Many O are‘terminal’


All Si bound to4 O



All Si bound to4 O


Ratio of O/Si Is > 2.


All Si bound to4 O


Ratio of O/Si Is > 2.

SixOy cluster is anionic


SixOy cluster is anionic

Na+ and Ca2+

balance chargeof anion

Properties of glass vs. quartz.


Glass has a lower melting point


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.



Soda-lime glasses can be melted using

a flame generated from methane and air.



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)


.2 H2O)(s) + 26 H2O

(CaO)3.Al2O3

.(CaSO4)3.32H2O(s)

exothermic


.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.

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Clathrates. Cage-like frameworks of metals with other metals occupying the cavities of the cages