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Metal Profile: Tantalum

What is tantalum?

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Metal Profile: Tantalum

Tantalum metal crucibles.

Strategic Metal Investments Ltd.

Tantalum is a hard, corrosion resistant refractory metal with electrical properties that make it a valued ingredient in capacitors, such as those found in mobile phones and laptop computers.

Properties:

  • Atomic Symbol: Ta
  • Atomic Number: 73
  • Element Category: Transition Metal
  • Density:  16.69g/cm3
  • Melting Point:  5463°F (3017°C)
  • Boiling Point:  5458°F (9856°C)
  • Mohs hardness: 6.5

Characteristics:
Pure tantalum metal is hard and heavy, as well as both ductile and malleable (it can be both stretched into wire and rolled as sheets).

Being a refractory metal, tantalum has one of the highest melting points of any pure metal, 5463°F (3017°C), which is only exceeded by rhenium and tungsten.

The blue-grey metal is non-toxic and forms a protective oxide layer that makes it resistant to both acid and alkali chemical corrosion. Tantalum is also inert to virtually all organic and inorganic compounds.

The metal's most unique property, however, may be its large capacitance (that is, its ability to store an electrical charge), which is the highest of all metals. In metal, powder and oxide form, element number 73 has a high dielectric constant, a measure of ability to store electrical charge, making it an ideal component for capacitors used in electronic devices.

History:
Tantalum was first identified by Anders Gustav Ekeberg in 1802, despite the fact that what he had actually found may have been niobium, a metal element with properties profoundly similar to tantalum.

It took another 60 years until the differences between niobium and tantalum were unequivocally proven, the first pure example of metallic tantalum not actually being extracted until 1864.

In 1902, Siemens and Halske Company developed the first tantalum filament lightbulbs. Tantalum was chosen because of its electrical conductivity, high melting temperature and ability to be drawn into wires. The bulbs were the commercial standard until 1909 when they were displaced by the more ductile and efficient tungsten filament bulbs.

Later, following the development of the first modern cemented carbides in the 1920s, scientists began experimenting with various metals to create stronger, more durable powders. The first tantalum carbide (TaC) was patented in 1936 and sold under the trade name Vascoloy-Remat. Its resistance to cavitation opened up new opportunities in the field of steel cutting and machining.

During the 1940s, research into sold state electronics led to the growth of consumer electronics. In an effort to make these electronic devices smaller and more efficient, Bell Laboratories developed solid electrolyte tantalum capacitors.

Tantalum allowed the capacitors to not only be smaller, but also provided a better electrical performance and made them more reliable than wet electrolytic capacitors. The Sprague Electric Company patented the first commercially viable process for manufacturing tantalum capacitors in 1960.

Demand from the electronics industry, particularly computer electronics, significantly increased consumption of tantalum in the 1990s. This trend has continued for much of the last ten years as a result of the popularity of mobile phones and electronic hand-held devices.

One result of this growth in consumption has been a volatile evolution of the production and supply market. In their search for lowest cost producers, electronics companies have sourced material produced in tantalum-rich, but unstable, regions of the world where artisanal mining of tantalum is often carried out in conflict zones, under hazardous conditions and with the use of forced labor.

Tantalum consequently has, in recent years, been at the center of a discussion regarding conflict minerals. In 2010, a provision on the Frank-Dodd financial reform act required public companies to disclose whether they use tantalum, or other raw materials, sourced from conflict-prone areas of Central Africa.

Production:
Tantalum is extracted as both a primary material from tantalite, microlite and wodginite ores, and as a by-product of cassiterite, which is mined as a source of tin.

In most cases, tantalum-containing ores are concentrated to greater than 30% tantalum content at, or near, the mine site. The concentrated ore is then sent to processors for refining into high purity materials.

Generally, extraction of tantalum concentrates first begins with treatment by a mixture of hydrofluoric and sulphuric acids at high temperatures, which dissolves both tantalum and niobium into complex fluorides.

Tantalum and niobium are then separated out via either solvent extraction with methyl isobutyl ketone or liquid ion exchange using an amine extractant in kerosene.

By washing with dilute sulphuric acid, niobium can be extracted, leaving a solution with a high tantalum content. This is then treated with ammonia, precipitating tantalum hydroxide, which, in turn, can be calcined as tantalum pentoxide (Ta2O5) or, along with potassium fluoride to produce potassium tantalum fluoride.

The introduction of potassium is often preferable for refiners producing capacitor grade tantalum powder, as it can be reduced from the fluoride using sodium at high temperatures. Alternatively, the oxide can be reduced with carbon or aluminum.

Tantalum metal powder is sintered into rods at over 4532°F (2500°C) and finally purified by either a vacuum-arc or electron beam melting to produce pure tantalum ingots.

The tantalum industry is a relatively opaque owing to the high percentage of private ownership in both the mining and refining sectors. As a result, production figures are often based on estimates.

According to the US Geological Survey, global production of mined tantalum in 2011 was 790 metric tonnes. The largest tantalum ore producing countries were Brazil, Mozambique and Rwanda.

It is also worth noting that there are only a limited number of large-scale, mechanized operations currently producing tantalum. These mines also tend to be the most susceptible to price fluctuations in the tantalum market.

The world's largest tantalum mine, Australia's Wodgina Mine, which supplied roughly half of the world's tantalum ore between 1997 and 2003, has been put on 'care and maintenance' multiple times since 2005. Most recently, Global Advanced Metals, the mine's current owner, stopped production in February of 2012 as a result of competition from lower priced, smaller artisanal mines.

Most tantalum refining takes place in the USA, Germany, Japan and China. Cabot Corp., H.C. Starck and Ningxia Non Ferrous Metals are the largest refiners of tantalum.

Recycled tantalum alloys and electronic scrap account for an estimated 20% of annual supply.

Applications:
Approximately 60% of all tantalum produced ends-up in electronic capacitors. Tantalum capacitors are widely used in electronic devices because of their high reliability, high capacitance in a small volume and good stability throughout a range of temperatures.

Billions of tantalum capacitors are produced each year for use in numerous electronic devices and medical and automotive systems, including:

  • laptop computers
  • wireless phone devices
  • handheld electronics
  • ignition systems
  • engine emission systems
  • airbag deployment systems
  • antilock breaking systems
  • hearing aids
  • pacemakers
  • digital video cameras
  • still cameras
  • military electronics

Superalloys account for an estimated 15% of tantalum consumption. These metal alloys, which often contain 3-11% tantalum, are stable at high temperatures, offer resistance to corrosion by hot gases and, as such, are often found in turbine blades of jet engines as well as in land-based gas turbines.

Tantalum alloys are also found in computer hard drive disks and certain types of explosive projectiles and missiles.

Sputtering targets account for another 10% of tantalum demand. Tantalum targets are used to deposit a thin protective substrate coating of tantalum metal, oxide or nitride on semiconductors and glass.

Tantalum carbide is often used as a hardening and strengthening additive in carbide powders, which are used to produce cutting tools, drill bits and automotive parts. TaC is considered the most refractory metallic substance with a melting point of over 7232°F (4000°C).

Milled tantalum sheets, rods and tubes are valued for their corrosion resistance, particularly in chemical environments, and are found in the chemical processing industry, high temperature furnaces, heat exchanger installations as well as in orthopedic implants and defense applications.

Sources:
Tantalum-Niobium International Study Center
Source: http://tanb.org/tantalum
Serjak, William A. Tantalum. Mining Journal (2005).
Source: http://www.mmta.co.uk/uploaded_files/TantalumMJ.pdf
Vulcan, Tom. "Tantalum: A Modern Metal, Actually". 13 January 2009.
Source: http://www.mmta.co.uk/uploaded_files/Hard%20Assets,%20Tantalum.pdf
NEPP Task 1.21.5. Characterization of Tantalum Polymer Capacitors. Phase 1, FY05 Erik K. Reed Jet Propulsion Laboratory

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