Tantalum – History, Properties, Specification
Tantalum was first discovered in 1802 by Swedish naturalist Anders Gustaf Ekeberg, in a Finnish columbite sample. He separated a highly resistant oxide (Tantalum pentoxide), which would not dissolve in any acid. It was named after “Tantalus”, a figure in Greek mythology. Ekeberg gave the element this name because the highly resistant oxide “is forced to yearn, and is unable to quench its thirst, just like Tantalus in the underworld.” It wasn’t until 1903 that Werner von Bolton was able to successfully produce pure, ductile Tantalum. This was achieved by the reduction of the glowing oxide in a vacuum, and melting impure Tantalum metal in an electrical flame arc in a vacuum.
Tantalum, a grey metal with a high melting point, crystallises in a body-centred cubic structure. With a melting point of approx. 3000 °C, Tantalum has the highest melting point of all elements after Tungsten and Carbon. While pure Tantalum is ductile and highly malleable, even small amounts of Tungsten improve its mechanical strength dramatically.
In the periodic system, Tantalum (chemical symbol: Ta) is in the 5th group of elements with the atomic number 73.
A thin, but very stable film of Tantalum pentoxide provides the passivation that makes tantalum’s resistance to corrosion of comparable quality to that of noble metals.
As a result of the passivation, Tantalum is resistant to most acids, and not even aqua regia will dissolve the metal. Tantalum is susceptible to corrosion only by hydrofluoric acid, acidic fluoride solutions and oleum (a mixture of sulphuric acid and sulphur trioxide).
Due to the properties outlined above, Tantalum is an ideal substance for use in the construction of a broad spectrum of components used in the chemical and pharmaceutical industries. Furthermore, Tantalum is also used for the manufacture of medical instruments and implants, as it does not react with body tissue or bodily fluids. The electronics industry is another significant area of application.
The specifications for Tantalum and Tantalum alloys are determined by the ASTM as follows:
ASTM B365 – 98(2004) Standard Specification for Tantalum and Tantalum Alloys – Rod and Wire
ASTM B521 – 98(2004) Standard Specification for Tantalum and Tantalum Alloys – Seamless and Welded Tubes
ASTM B708 – 05 Standard Specification for Tantalum and Tantalum Alloys – Plate, Sheet and Strip
In addition, specifications are also provided for Tantalum in the materials datasheets of the VdTUEV.
VdTUEV 382 – 9.96 Unalloyed Tantalum
VdTUEV 507 – 9.96 Tantalum 2.5% Tungsten
In the chemical and pharmaceutical industries today, however, the alloy with 2.5 % Tungsten is used most widely, as it allows tensile strength of up to 240 Mpa at 20 °C to be achieved. The material specification for this alloy is defined by the ATSM under the grade R05252, and in the material datasheet VdTUEV 507.