Feb 13 2003
Silicon (Si) was discovered in 1824 by J.J. Berzelius in Stockholm, Sweden.
Abundance and Occurrence
After carbon, Silicon is the most abundant element on earth, the abundance being 277,000 ppm. Silicon is generally present as a silicate, these being found in many rocks, clays and soils.
Extraction
Silicon is obtained by reducing silica (sand, SiO2), with carbon. Further purification of the element for applications requiring high purity material (e.g. semi conductor devices) is achieved by zone refining, the resulting purity being better than 1:109. Silicon exists in two allotropic forms; brown Silicon is a powder, whereas crystalline (metallic) Silicon is grey and it is the latter which is more widely used. Bulk Silicon is unreactive towards oxygen, water, acids (excluding HF), but is soluble in hot alkalis.
Applications
Silicon has many applications in various industries; for example, ultra high purity Silicon is used in the semiconductor industry as a result of its semiconducting properties. Silicon is also used as an alloying element in the manufacture of certain alloys (e.g. ferrosilicon, an alloy of iron and silicon which is used to introduce Silicon into steel and cast iron). It is also used in the manufacture of glass.
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Silicon can also be used in the manufacture of glass – Image Credit – Havoc/Shutterstock
Key Properties
The key properties of Silicon are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
14 |
| Atomic radius - Goldschmidt ( nm ) |
0.117 |
| Atomic weight ( amu ) |
28.0855 |
| Crystal structure |
Diamond |
| Electronic structure |
Ne 3s2 3p2 |
| Photo-electric work function ( eV ) |
4.2 |
| Thermal neutron absorption cross-section ( Barns ) |
0.16 |
| Valences shown |
4 |
| Ionisation Potential |
No. |
eV |
| |
1 |
8.15 |
| |
2 |
16.3 |
| |
3 |
33.5 |
| |
4 |
45.1 |
| |
5 |
167 |
| |
6 |
205 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
28 |
92.23 |
| |
29 |
4.67 |
| |
30 |
3.10 |
| Electrical Properties |
| Electrical resistivity @ 20 °C ( µOhm.cm ) |
23 x 1010 |
| Thermal emf against Pt (cold 0 °C - hot 100 °C) ( mV ) |
-41.56 |
| Mechanical Properties |
| Material condition |
Polycrystalline |
| Bulk modulus ( GPa ) |
100 |
| Hardness - Mohs |
7.0 |
| Poisson’s ratio |
0.42 |
| Tensile modulus ( GPa ) |
113 |
| Physical Properties |
| Boiling point (°C ) |
2355 |
| Density @ 20 °C ( g.cm-3 ) |
2.34 |
| Melting point (°C ) |
1410 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
4.7-7.6 |
| Latent heat of evaporation ( J.g-1 ) |
13700 |
| Latent heat of fusion ( J.g-1 ) |
1650 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
703 |
| Thermal conductivity @ 0-100 °C ( W m-1 K-1 ) |
80-150 |
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