Supplier Data - Boron (B) (Goodfellow)

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
Melting point 2180 °C
Electrical Properties
Electrical resistivity at 27 °C 1.8x1012 ì
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
Mechanical Properties
Material condition Arc melted
Hardness – Mohs 9.5
Tensile modulus 441 GPa
Tensile strength 1580-2410 MPa

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