|
|
|
|
|
|
|
| |
1. Silicon and silicone
Silicon and silicone appear to be similar
in English, but chemically they mean strictly
different things.
Silicon means the dark gray metal silicon
represented as the elementary symbol Si, and
it is a dark gray metal substance. And the
silicone, a high-capacity material, that is
essentially used in most industry areas these
days, is a unique chemical material having
both inorganism and organism, and it means
a polymer where such substances as organosilicone
and oxygene that have organic components are
connected through chemical bonding(Siloxane
bonding).
The origin of this name is follows. A.LADENBURG,
a silcon scientist saw a hydrolyzed and drained
substance as the form of a structure similar
to ketone((C2H5)1C=O),
that is (C2H5)2Si=O,
and named it Silico-Ketone. After that, in
1905, W.DILTHEY identified that the produced
drained substance is cyclic, but the name
Silico-Ketone was abbreviated as 『Silicone』and
was generalized to indicate silicone compounds
in general and is being widely used. |
| |
| 2. Silicon and carbon |
|
|
|
|
The molecule backbone is composed of silicon(Si)
and oxygen(O), and this makes it fundamentally
different from general compound macromolecules.
Carbon(C) and Silicon(Si) belong to group
4 in the periodic table, and as carbon(C)
in 2nd period is adjacent to silicon(Si) in
3rd period we can assume that they have similar
characteristics. Also, as you can see in the
above figure, the 4 bond points of both carbon
and silicon are in the shape of a regular
tetrahedron with an atom at the center.
However, the element in the 3rd period has
an orbital larger by one roll than the element
in the 2nd period, which makes the two elements
chemically different.
First, compared to carbon whose diameter of
covalent bonding is 0.77∈, the diameter of
covalent bonding of silicon is 1.17∈, which
is about 1.5 times. This diameter of covalent
bonding has an absolute influence on the characteristic
of the element.
Also, as seen in the table below, the difference
in electronegativity also shows the difference
in physical and chemical properties such as
bond energy. We can see that the electronegativity
of silicon is lower than that of carbon and
rather close to that of Ge or Sn, metals of
the same group, and is likely to receive electrostatic
charge in the molecule. Besides, the silicone
is different from carbon atom in that silicon
has little tendency to make double or triple
bondings and has more coordination bond property. |
|
| Electronegativity |
|
H2.1 |
|
|
|
|
|
|
|
Li
1.0 |
Be
1.5 |
B
2.0 |
C
2.5 |
N
3.0 |
O
3.5 |
F
4.0 |
|
Na
0.9 |
Mg
1.2 |
Al
1.5 |
Si
1.8 |
P
2.1 |
S
2.5 |
Cl
3.0 |
|
K
0.8 |
Ca
1.0 |
Sc
1.3 |
Ge
1.7 |
As
2.0 |
Se
2.4 |
Br
2.8 |
|
Rb
0.8 |
Sr
1.0 |
Y
1.3 |
Sn
1.7 |
Sb
1.8 |
Te
2.1 |
I 2.4 |
|
Cs
0.7 |
Ba
0.9 |
|
|
|
|
|
|
| |
| 3. Physical·chemical properties of silicone |
|
One of the most unique characteristic
of silicone is its strength to heat
and oxidation, which can be explained
as the intensity of chemical bonding.
As indicated on the right table, we
can see that the Si-O bonding, which
can be regarded as the backbone of silicone,
is larger than that of others, which
is partly because its energy level is
stabilized as the big difference in
the electronegativity of Si and O approximates
to ionic bonding.
|
|
|
|
Bonding
enery ( Kcal / mol ) |
| C
|
Si |
|
C |
83.2 |
58
~ 80 |
|
Si |
58
~ 80 |
45.0 |
|
H |
98.8 |
72.6 |
|
O |
83.2 |
101.0 |
|
|
| The fact that the silicone's heat-resistance
and oxidation-resistance is good, in other
words, the fact that it can be used in high
temperature, is one of its important characteristics
in practice. |
Liquid's surface
tension
(Temperature: 20∩) |
|
As
the Si-O bonding, unlike pure covalent
bonding such as C-C, is in the midway
between ionic bonding and covalent bonding,
the attraction between the molecules
are small, which is why the surface
tension of silicone oil is particularly
lower than that of other liquids. For
the same reason the silicone rubber
and silicone oil have excellent cold-resistance,
and the low dependence of these various
property values on temperature can be
regarded as one of the important characteristics
in practice. |
|
Liquid
type |
Surface
tension (dyn/cm) |
|
Dimethylsilicon
oil |
20
~ 21 |
|
Fluoride
oil |
18
~ 19 |
|
Tetradecan |
26.5 |
|
Liquid
paraffin |
29.7 |
|
Polyethylene |
34
~ 36 |
|
Toluene |
28.5 |
|
Glycerine |
63.1 |
|
Water |
72 |
|
|
|
|
