Thallium alloys

When freshly exposed to air, thallium exhibits a metallic luster, but soon develops a bluish-gray tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydride is formed. The metal is very soft and malleable. It can be cut with a knife. Twenty five isotopic forms of thallium, with atomic masses ranging from 184 to 210 are recognized. Natural thallium is a mixture of two isotopes. A mercury-thallium alloy, which forms a eutectic at 8.5% thallium, is reported to freeze at -60C, some 20 degrees below the freezing point of mercury. 

T.R. Finlayson and H.G. Smith, Neutron scattering studies of premartensitic indium-thallium alloys. Met. Trans A 19A 193 (1988). 

Gold-thallium, alloy (Au5T15), calculation of thermodynamic quantities, 136... 

According to our interpretation the lead-thallium alloys in the range 0-75 atomic percent thallium have the structure Pb(Pb, Tl)3, and between 75 and 87-5 atomic percent thallium they have the structure Pb(Pb, TlJTlg. The values of a0 shown in Fig. 2 indicate that at 75 atomic percent thallium there is nearly complete order, corresponding to the compound PbTl3. 

We have found it possible to formulate a simple treatment of the lead-thallium alloys that accounts satisfactorily for the existence of a maximum in melting-point displaced from the composition PbTls of the ordered structure, and that also accounts in a reasonably satisfactory way for the shapes of the liquidus and solidus curves throughout the range 0—75 atomic percent thallium (Fig. 1). The maximum in these curves occurs at a composition near that for a compound Pb2Tl3 or a compound PbTl2. If either of these compounds existed, it would have to be considered as forming solid solutions with lead and with thallium. The data, however, give no evidence for the existence of such compounds. 

Uses. The unalloyed metal cannot be directly used owing to its bad mechanical properties and its high oxidability. Several thallium alloys are used as semiconductors or ceramic compounds it may be used as additive to gold, silver or copper contacts in the electronic industries. Thallium is dangerously toxic. 

For a number of years, thallium sulfate had been used in rodenticides. Some use of thallium has been made in connection with alloys for low-temperature applications, particularly for switches, seals, and thermometers. The ternary eutectic mercury-thallium-indium alloy has a freezing point of —63.3 JCt while the binary eutectic mercury-thallium alloy has a freezing point of — 60°C. These freezing points are considerably lower than that of mercury usually used for similar applications at higher temperatures. Mercury freezes at —38.87JC. 

Abowitz, G., and if. B. Gordon Internal Friction in Liquid Metals. Mercury and Mercury-Thallium-Alloys. Acta Met. 10, 671—680 (1962). 

Haider, N. C., R. J. Metzger, and C. N. J. Wagner Atomic Distribution and Electrical Properties of Liquid Mercury-Thallium Alloys. J. Chem. Phys. 45, 1259 (1966). 

Smallman, R. and B. R. T. Frost An X-Ray Investigation of the Structure of Liquid Mercury and Liquid Mercury-Thallium Alloys. Acta Met. 4, 611 (1956). 

Ward, R. G., and J. R. Wilson Ordering in Liquid Mercury-Thallium Alloys Containing 25—35 At.-% Thallium. Nature 182, 334 (1958). 

Thallium alloys readily with many metals, especially sodium, potassium, mercury, magnesium, calcium, gold, silver, cadmium, copper, and zinc. 

Lead/thallium alloys which show good resistance against acids multicomponent alloys such as Pb/Sb/Sn/Tl may be used as carrier materials. 

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