Feb 7 2003
Background
Germanium (Ge) is a silvery white brittle metalloid member of the carbon group of elements, its physical properties being similar to those of silicon, the element which precedes it in the group.
Discovered in 1886 by C.A. Winkler at Freiberg, Germany.
Occurrence and Abundance
Other elements within the carbon group are relatively common, but Germanium is found only in trace amounts in some coals and as a minor component in some ores, the principle one being argyrodite, a double sulphide of silver and Germanium (the mineral from which germanium was first isolated). It has an abundance within the Earth’s crust of 1.8 ppm.
Extraction
The element Germanium is produced by reduction of the oxide, ultra-high purity material being obtained by zone refining (a process in which the element is formed into a rod which is then heated at one end to produce a narrow molten zone. The heater is moved along the length of the rod so that the molten zone travels from one end of the rod to the other. Impurities are more soluble in the molten metal than in the solid and thus concentrate in the liquid zone as it moves to one end of the rod).
Applications
Germanium is stable in air and water and is unaffected by alkalis and acids, with the exception of nitric acid. It is a poor conductor of electricity but has exceptional properties as a semiconductor material and it is in this area where germanium is primarily used.
However, other applications for Germanium include its use as an alloying element in the production of specific alloys and as an addition to glass in the manufacture of infrared devices.
Key Properties
The key properties of Germanium are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
32 |
| Atomic radius - Goldschmidt ( nm ) |
0.139 |
| Atomic weight ( amu ) |
72.59 |
| Crystal structure |
Diamond |
| Electronic structure |
Ar 3d10 4s2 4p2 |
| Photo-electric work function ( eV ) |
4.8 |
| Thermal neutron absorption cross-section ( Barns ) |
2.3 |
| Valences shown |
2, 4 |
| Ionisation Potential |
No. |
eV |
| |
1 |
7.90 |
| |
2 |
15.93 |
| |
3 |
34.22 |
| |
4 |
45.7 |
| |
5 |
93.5 |
| Natural Isotope Distribution |
Mass No. |
% |
| |
70 |
20.5 |
| |
72 |
27.4 |
| |
73 |
7.8 |
| |
74 |
36.5 |
| |
76 |
7.8 |
| Electrical Properties |
| Electrical resistivity @ 22 °C ( µOhm.cm ) |
46x106 |
| Thermal emf against Pt (cold 0 °C - hot 100 °C) ( mV ) |
+33.9 |
| Mechanical Properties |
| Material condition |
Polycrystalline |
| Bulk modulus ( GPa ) |
73.9 |
| Hardness - Mohs |
6.25 |
| Poisson’s ratio |
0.32 |
0.32 |
| Tensile modulus ( GPa ) |
79.9 |
79.9 |
| Physical Properties |
| Boiling point ( °C ) |
2830 |
| Density @ 20 °C ( g.cm-3 ) |
5.32 |
| Melting point (°C ) |
937.4 |
| Thermal Properties |
| Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) |
5.75 |
| Latent heat of evaporation ( J.g-1 ) |
4516 |
| Latent heat of fusion ( J.g-1 ) |
465 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
322 |
| Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) |
60.2 |
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