Jan 24 2003
Discovered in 1808 by L.J. Lussac and L.J. Thenard (in Paris) and Sir Humphrey Davy (in London).
Boron is a non-metallic element which occurs in several allotropes. It is rarely found in nature, normally occurring as borates or orthoboric acid (the abundance of boron in the earth’s crust is 10 ppm, the principal ore being borax, Na2B4O7.xH2O.
Amorphous Boron is the more common allotrope and exists as a dark powder which is unreactive towards water, oxygen, acids and alkalis.
Boron finds importance within nuclear reactors due to its neutron absorbing capabilities, Boron steel being used as control rod material.
Boron compounds are used for a number of applications including the manufacture of certain grades of glass and detergents.
Boron will react directly with most metals to produce metal borides which are hard, inert binary compounds of various formulae and arrangements of the boron atoms.
For example, as single atoms (M2B), pairs, (M3B2), single and double chains (MB, M3B4), sheets (MB2), B6 octahedra (MB6) and B12 clusters (MB12).
Boron also forms the binary compound, boron nitride, which is of interest as it is isoelectronic with carbon and occurs in two structural modifications; one is a layer structure similar to graphite which is soft and lubricating, whilst the other (formed under high pressure) has a very hard, stable, tetrahedral structure as found in diamond.
Key Properties
The key properties of Boron are tabulated below.
Table 1. Key properties
| Atomic Properties |
| Atomic number |
5 |
| Atomic radius – Goldschmidt |
0.097 nm |
| Atomic weight |
10.81 amu |
| Crystal structure |
Tetragonal |
| Electronic structure |
He 2s2 2 p1 |
| Photo-electric work function |
4.5 eV |
| Thermal neutron absorption cross-section |
672 Barns |
| Valences shown |
3 |
| Neutral Isotope Distribution |
Mass No. |
% |
| |
10 |
19.8 |
| |
11 |
80.2 |
| Ionisation Potential |
No. |
eV |
| |
1 |
8.30 |
| |
2 |
25.2 |
| |
3 |
37.9 |
| |
4 |
259 |
| |
5 |
340 |
| Physical Properties |
| Boiling point |
3700 °C |
| Density at 20 °C |
2.34-2.37 g.cm-3 |
| Melting point |
2180 °C |
| Electrical Properties |
| Electrical resistivity at 27 °C |
1.8x1012 ìOhm.cm |
| Thermal Properties |
| Latent heat of evaporation |
35000 J.g-1 |
| Latent heat of fusion |
2090 J.g-1 |
| Linear expansion co-efficient 0-100 °C |
8.3x10-6 K-1 |
| Specific heat at 25 °C |
1030 J.K-1.kg-1 |
| Mechanical Properties |
| Material condition |
Arc melted |
| Hardness – Mohs |
9.5 |
| Tensile modulus |
441 GPa |
| Tensile strength |
1580-2410 MPa |
About Goodfellow
Goodfellow supplies metals, ceramics and other materials to meet the research, development and specialist production requirements of science and industry worldwide.
.gif)
Source: Goodfellow
For more information on this source please visit Goodfellow.