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Supplier Data - Thallium (Tl) (Goodfellow)

Background

Thallium (T1) was discovered in 1861 by W. Crookes in London, and isolated by C.A. Lamy the following year in Paris.

Occurrence

Thallium is a soft, silvery-grey, reactive metal which is only found as a minor constituent of various minerals (it has an abundance of 0.6 ppm in the earth’s crust), from which the metal is obtained by electrolytic reduction in aqueous solution.

Reactivity

Thallium tarnishes readily in moist air and reacts with steam to form TlOH. It is readily soluble in acids, particularly HNO3, and is highly toxic.

Applications

As a result of its toxicity, Thallium is rarely used, with the exception of the manufacture of special grades of glass.

In the past, Thallium compounds found applications as diverse as rat poisons and hair restorers!

Key Properties

The key properties of Thallium are tabulated below.

Table 1. Key properties

Atomic Properties
Atomic number 81
Atomic radius - Goldschmidt ( nm ) 0.171
Atomic weight ( amu ) 204.383
Crystal structure Hexagonal close packed
Electronic structure Xe 4f14 5d10 6s2 6p1
Photo-electric work function ( eV ) 3.8
Thermal neutron absorption cross-section ( Barns ) 3.4
Valences shown 1, 3
Ionisation Potential No. eV
1 6.11
2 20.4
3 29.8
4 50.7
Natural Isotope Distribution Mass No. %
203 29.5
205 70.5
Electrical Properties
Electrical resistivity @ 20 °C ( µOhm.cm ) 16.6
Temperature coefficient @ 0-100 °C ( K-1 ) 0.0052
Superconductivity critical temperature ( K ) 2.38
Thermal emf against Pt (cold 0 °C - hot 100 °C) ( mV ) +0.58
Mechanical Properties
Material condition Polycrystalline
Bulk modulus ( GPa ) 28.5
Hardness – Brinell 2.0
Poisson’s ratio 0.45
Tensile modulus ( GPa ) 7.9
Tensile strength ( MPa ) 8.96
Physical Properties
Boiling point ( °C ) 1457
Density @ 20 C ( g.cm-3 ) 11.85
Melting point ( °C ) 303.5
Thermal Properties
Coefficient of thermal expansion @ 0-100 °C ( x10-6 K-1 ) 30.0
Latent heat of evaporation ( J.g-1 ) 813
Latent heat of fusion ( J.g-1 ) 21.0
Specific heat @ 25 °C ( J.K-1.kg-1 ) 128
Thermal conductivity @ 0-100 °C ( W.m-1.K-1 ) 46.1

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