Tantalum

Tantalum is a heavy metal which in its chemical and physical properties is very similar to niobium. Up to ~250°C it is resistant to air and protects itself with a thin oxide layer. It is a metal which can be easily formed and which crystallizes in the body centered cubic structure. At temperatures over 250°C tantalum reacts with oxygen, nitrogen, hydrogen and carbon. This means that processing at higher temperatures has to take place in vacuum or under a protective gas atmosphere. Tantalum is resistant to all acids with the exception of hot, fuming sulfuric acid (oleum) and hydrofluoric acid. It is only attacked slowly by alkaline solutions. In its compounds it occurs with valencies of -3, -1, 0, +2, +3, +4 and +5, whereby the majority may be derived from the pentavalent form. At temperatures below 4.28 K tantalum is superconducting.

The most important deposits are found in Australia (~70 %), Brazil (~20 %), Canada and Africa. In its minerals tantalum generally appears as a mixed oxide (most important one: tantalite) and also in tin placer ores. It is always found together with niobium. For this reason the niobium must be separated out in the manufacture of tantalum. After dissolving the ore concentrate, separation is achieved by a complex liquid/liquid extraction using methyl-isobutyl-ketone or by distillation of the chlorides. The Ta₂O₅, which is won as a result, can then be reduced to Ta metal with Na (most important process) or Mg. Further purification of the metal is carried out by multiple melting under vacuum in an electron beam furnace.

Approximately 60 % of the worldwide annual production (2007 approx. 1100 t) is processed into condensers. Due to its high resistance to corrosion, tantalum has a further application in chemical process equipment and in laboratory equipment. Heraeus supplies a broad range of semi-finished products from very small disks, wires and foils for the lamp industry and ultrafine tubes for analysis technology. Pure Ta from Heraeus is used in semiconductor technology for sputtering targets and in medical technology for surgical implants and electrodes for X-ray tubes. Furthermore, it is used in nickel superalloys for turbines / high temperature applications and as Ta₂O₅ in optical glasses due to its high refractive index. Tantalum carbide, which has a hardness approaching that of diamond and a very high melting point (~3900°C), is used as a protective layer on high temperature alloys for jet engines and cutting tools. Ta is also used as a constituent of sintered tungsten carbide materials, especially in order to increase the hardness at higher temperatures.