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Tantalum

Tantalum

Tantalum is a sensible choice whenever high corrosion resistance is required. Even though tantalum is not one of the noble metals, it is comparable to them in terms of chemical resistance. In addition, tantalum is very easy to work at well below room temperature despite its body-centered cubic crystal structure. This makes it a valuable material in a large number of chemical applications. We use our "unyielding" material, for example, to produce heat exchangers for the equipment construction sector, riveted racks for furnace construction, implants for medical technology, and capacitor components for the electronics industry.

Atomic number 73
CAS number 7440-25-7
Atomic mass 180.95 [g/mol]
Melting point 2996 °C
Boiling point 5458 °C
Density at 20 °C 16.65 [g/cm3]
Crystal structure Body-centered cubic
Coefficient of linear thermal expansion at 20 °C
6.4 × 10-6 [m/(mK)]
Thermal conductivity at 20 °C
57.5 [W/(mK)]
Specific heat at 20 °C 0.14 [J/(gK)]
Electrical conductivity at 20 °C 8 × 106 [S/m]
Specific electrical resistance at 20 °C 0.125 [(Ωmm2)/m]
Range of materials

Pure tantalum or maybe an alloy?

You can rely on our quality. We produce our tantalum products entirely in-house from the metal powder to the finished product. We only use the purest tantalum powder as the source material. This is how we can guarantee you a very high material purity.

We guarantee a purity of 99.95% for our sintered quality tantalum (metallic purity without Nb). The remaining portion is made up of the following elements according to a chemical analysis:

Element Typical max. value
[μg/g]
Guaranteed max. value
[μg/g]
Fe
17
50
Mo
10
50
Nb
10
100
Ni
5 50
Si
10
50
Ti
1 10
W 20
50
C 11
50
H 2
15
N 5 50
O 81
150
Cd 5
10
Hg* -
1
Pb 5
10

*Erstwert

Die Anwesenheit von Cr (VI) und organischen Verunreinigungen kann durch den Produktionsprozess ausgeschlossen werden (mehrfache Wärmebehandlung bei Temperaturen über 1.000 °C im Hochvakuum).

We guarantee a purity of 99.95% for our melted quality tantalum (metallic purity without Nb). The remaining portion is made up of the following elements according to a chemical analysis:

Element Typical max. value
[μg/g]
Guaranteed max. value
[μg/g]
Fe
5
100
Mo
10
100
Nb
19
400
Ni
5 50
Si
10
50
Ti
1 50
W 20
100
C 10
30
H 4
15
N 5 50
O 13
100
Cd -
10
Hg* -
1
Pb -
10

*Erstwert

Die Anwesenheit von Cr (VI) und organischen Verunreinigungen kann durch den Produktionsprozess ausgeschlossen werden (mehrfache Wärmebehandlung bei Temperaturen über 1.000 °C im Hochvakuum).

Material designation Chemical composition
(percent by weight)
Sintered quality
S
Sintered quality tantalum (TaS)
Capacitor quality tantalum (TaK)
Grain stabilized tantalum (TaKS)
Ta2.5W
Ta10W
> 99.95
> 99.95
> 99.90
2.5% W
10% W
Melted quality M Melted quality tantalum > 99.95

We optimally prepare our tantalum for each application. We define the following properties due to various alloying additions:

  • Physical properties (e.g., melting point, vapor pressure, density, electrical conductivity, thermal conductivity, thermal expansion, heat capacity)
  • Mechanical properties (e.g., strength, fracture behavior, ductility)
  • Chemical properties (e.g., corrosion resistance, etching behavior)
  • Workability (e.g., machinability, formability, welding suitability)
  • Structure and recrystallization behavior (e.g., recrystallization temperature, proneness to embrittlement, aging effects, grain size)

And we don't stop there: we can also vary the tantalum properties in other areas due to tailor-made manufacturing processes. The result: tantalum alloys with different property profiles that are customized to the respective application.

  • Sintered quality tantalum (TaS)

    Pure sintered quality tantalum and pure melted quality tantalum share the following properties:

    • High melting point of 2996 °C
    • Good cold ductility
    • Recrystallization between 900 °C and 1450 °C (depending on the level of deformation and purity)
    • Outstanding resistance against aqueous solutions and metal melts
    • Superconductivity
    • High level of biocompatibility

    Our sintered quality tantalum is used for those tricky situations: due to our powder metallurgy production process, sintered quality tantalum (TaS) is particularly fine-grained and pure. As a result, the material is very easy to work and excels due to its excellent surface quality and robust mechanical properties.

  • Melted quality tantalum (TaM)

    The most expensive product is not always the best. Melted quality tantalum (TaM) is usually more economical to produce than sintered quality tantalum and provides sufficient quality for many applications. However, the material is neither as fine nor as homogeneous as sintered quality tantalum. Get in touch. We would be happy to advise you.

  • Grain-stabilized tantalum (TaKS)

    We dope our sintered, grain-stabilized tantalum with silicon to prevent grain growth even at high temperatures. This makes our tantalum suitable for use at even the highest operating temperatures. The fine-grained microstructure remains stable even after being annealed at temperatures of up to approximately 2000 °C. This process ensures that the material's excellent mechanical properties such as its ductility and strength remain intact. Grain-stabilized tantalum in the form of wire or sheets is ideal for sintering into tantalum anodes or for furnace construction applications.

  • Tantalum-tungsten (TaW)

    Tantalum-tungsten (TaW) excels due to its good mechanical properties and excellent corrosion resistance. We add between 2.5 and 10 percent by weight of tungsten to pure tantalum. Although the resulting alloy is up to 1.4 times stronger than pure tantalum, it remains easy to work at temperatures of up to 1600 °C. Our TaW is therefore especially well-suited for the heat exchangers and hot zones used in chemical equipment construction.

Properties

A good all-rounder: material properties of tantalum

Tantalum belongs to the group of metals with a high melting point (also called refractory metals). Refractory metals have a higher melting point than platinum (1772 °C). The binding energy between the individual atoms is particularly high. Refractory metals are also characterized by a high melting point coupled with a low vapor pressure. In addition, high density and a low coefficient of thermal expansion are also characteristic of refractory metals.

In the periodic table, tantalum is located in the same period as tungsten. Like tungsten, tantalum has a very high density of 16.6 g/cm³. However, unlike tungsten, tantalum becomes brittle during manufacturing processes involving hydrogen atmospheres. That's why the material is produced in a high vacuum.

Tantalum is without doubt the most resistant of the refractory metals and is resistant to all acids and bases.

  • Physical properties

    Refractory metals are typically characterized by a low coefficient of thermal expansion and relatively high density. The same is true for tantalum. While the thermal conductivity of tantalum is lower than that of tungsten and molybdenum, the material has a higher thermal coefficient of expansion than many other metals. The thermophysical properties of tantalum change with temperature. The diagrams below illustrate the curves for the most important variables:

    • Coefficient of linear thermal expansion of tantalum and niobium
    • Specific heat capacity of tantalum and niobium
    • Thermal conductivity of tantalum and niobium
  • Mechanical properties

    Even small quantities of interstitially dissolved elements such as oxygen, nitrogen, hydrogen, and carbon are able to modify the mechanical properties of tantalum. In addition, the purity of the metal powder, the production process (sintered or melted quality), the level of deformation, and the type of heat treatment used also influence its mechanical properties.

    Like both tungsten and molybdenum, tantalum has a body-center cubic crystal structure. At -200 °C, the brittle-to-ductile transition temperature is well below room temperature. As a result, the metal is very easy to work. While its tensile strength and hardness increase with increased forming, this simultaneously causes the material's breaking elongation to decrease. Although the material loses ductility, it does not become brittle.

    The material's high-temperature stability is lower than that of tungsten but similar to the values found for pure molybdenum. We alloy our tantalum with refractory metals such as tungsten to increase the high-temperature stability.

    Tantalum's modulus of elasticity is lower than that of tungsten and molybdenum and resembles that of pure iron. The modulus of elasticity falls with increasing temperature.

    • Modulus of elasticity of tantalum compared to that of tungsten, molybdenum, and niobium.

    Thanks to its high level of ductility, tantalum is well suited for chipless forming processes such as bending, stamping, pressing, or deep drawing. It is very difficult to use machining processes with tantalum. The chips do not break cleanly. We therefore recommend the use of chip breakers. Tantalum offers excellent weldability compared to tungsten and molybdenum.

    Do you have any questions about the mechanical processing of refractory metals? We would be delighted to help you with our many years of experience.

  • Chemical behavior

    Because tantalum is resistant to all types of chemical substances, this material is often compared to noble metals. However, in thermodynamic terms, tantalum is a base metal which can nevertheless form stable compounds with a wide variety of elements. When exposed to air, tantalum forms a very dense oxide layer (Ta2O5) which protects the base material from chemical attack. This oxide layer therefore makes tantalum corrosion-resistant.

    At room temperature, the only inorganic substances that tantalum is not resistant to are: concentrated sulfuric acid, fluorine, hydrogen fluoride, hydrofluoric acid, and acid solutions containing fluoride ions. Alkaline solutions, molten sodium hydroxide, and potassium hydroxide also attack tantalum. In contrast, the material is resistant to aqueous ammonia solutions. If tantalum is exposed to chemical aggression, hydrogen enters its metal lattice and the material becomes brittle. The corrosion resistance of tantalum falls gradually with increasing temperature.

    Tantalum is inert in contact with many solutions. However, if tantalum is exposed to mixed solutions, its corrosion resistance may be impaired even if it is resistant to the individual components taken separately. Do you have any questions regarding complex corrosion-related topics? We would be delighted to help you with our experience and our in-house corrosion laboratory.

    MEDIUM RESISTANT (+), NON-RESISTANT (-) NOTE
    Water    
    Hot water < 150 °C +  
    Acids    
    Hydrofluoric acid, HF -  
    Hydrochloric acid, HCI + < 30%, < 190 °C
    Phosphoric acid, H3PO4 + < 85%, < 150 °C
    Sulfuric acid, H2SO4 + < 98%, < 190 °C
    Nitric acid, HNO3 + < 65%, < 190 °C
    Organic acids  
    Lyes    
    Ammonia solution, NH4OH + < 17%, < 50 °C
    Potassium hydroxide, KOH + < 5%, < 100 °C
    Sodium carbonate, Na₂CO₃ + < 20%, < 100 °C
    Sodium hydroxide, NaOH + < 5%, < 100 °C
    Halogens    
    Fluorine, F2 -  
    Chlorine, Cl2 + < 150 °C
    Bromine, Br2 + < 150 °C
    Iodine, I2 + < 150 °C
    Non-metals    
    Borine, B + < 1000 °C
    Phosphorous, P + < 150 °C
    Sulfur, S + < 150 °C
    Gases    
    Tantalum does not react with noble gases. As a result, high purity noble gases can be used as protective gases. However, with increasing temperature, tantalum reacts very strongly with oxygen or air and may absorb large quantities of hydrogen and nitrogen. This causes the material to become brittle. Annealing tantalum in a high vacuum gets rid of these impurities. Hydrogen is eliminated at 800 °C and nitrogen at 1700 °C.
    Ammonia, NH3 + < 700 °C
    Carbon monoxide, CO + < 1100 °C
    Carbon dioxide, CO2 + < 500 °C
    Hydrocarbons + < 800 °C
    Air and oxygen, O2 + < 300 °C
    Noble gases (He, Ar, N2) +  
    Hydrogen, H2 + < 340 °C
    Water vapor + < 200 °C
    Melts    
    Chemical reactions arise very quickly when base materials such as tantalum are brought into contact with noble materials such as platinum. You should therefore take careful account of the behavior of tantalum in contact with the other materials present in the system, especially at high operating temperatures.
    Aluminum, Al -  
    Beryllium, Be -  
    Lead, Pb + < 1000 °C
    Cesium, Cs + < 980 °C
    Copper, Cu + < 1300 °C
    Gallium, Ga + < 450 °C
    Iron, Fe -  
    Lithium, Li + < 1000 °C
    Magnesium, Mg + < 1150 °C
    Mercury, Hg + < 600 °C
    Nickel, Ni -  
    Potassium, K + < 1000 °C
    Silver, Ag + < 1200 °C
    Sodium, Na + < 1000 °C
    Tin, Sn + < 260 °C
    Zinc, Zn + < 500 °C
    Furnace construction materials    
    In high-temperature furnaces, tantalum may react with construction parts made of refractory oxides or graphite. Even very stable oxides such as aluminum, magnesium, or zirconium oxide may be reduced at high temperatures when in contact with tantalum. Contact with graphite may cause the formation of tantalum carbide and lead to the embrittlement of the tantalum. Although tantalum can usually be combined without problems with other refractory metals such as molybdenum or tungsten, it may react with hexagonal boron nitride and silicon nitride. The limit temperatures listed below apply in a vacuum. If a protective gas is used, these temperatures are approximately 100 to 200 °C lower.
    Alumina, Al2O3 + < 1900 °C
    Beryllium oxide, BeO + < 1600 °C
    Hex. boron nitride, BN + < 700 °C
    Graphite, C + < 1000 °C
    Magnesium oxide, MgO + < 1800 °C
    Molybdenum, Mo +  
    Silicon nitride, Si3N4 + < 700 °C
    Thorium oxide, ThO2 + < 1900 °C
    Tungsten, W +  
    Zirconium oxide, ZrO2 + < 1600 °C

    Korrosionsverhalten von Tantal gegenüber ausgewählten Stoffen

    Hydrogen embrittlement
    Sulfuric acid 98% at 250 °C Atomic hydrogen > 25 °C
    Hydrochloric acid 30% at 190 °C Hydrogen at 350 °C
    Hydrogen at 350 °C Cathodic polarization with less noble,
    dissolving materials

    Measures against hydrogen embrittlement are as follows:

    • Electrical insulation of the metals
    • Positive polarization of the metals (approx. + 15 V)
    • Addition of oxidants to the solutions
    • Use of formed metal surfaces
    • Electrical contact with a more noble metal (e.g., Pt, Au, Pd, Rh, Ru)

    Tantalum that has become brittle can be regenerated by means of high-vacuum annealing at 800°C.

Characteristics and applications

Quality characteristics

The variety of industrial applications in which our tantalum is used reflect the unique properties of the material. We briefly present two of these below:

  • Customized chemical and electrical properties

    Due its particularly fine microstructure, tantalum is the perfect material for drawing ultra-slender wires with a flawless, exceptionally pure surface for use in tantalum capacitors. We can determine the chemical, electrical, and mechanical properties of these wires to a high degree of precision. As a result, our products give our customers tailor-made, consistent component properties which we are continuously developing and refining.

  • Outstanding resistance and excellent cold ductility

    Its excellent resistance coupled with its excellent formability and weldability make tantalum the perfect material for heat exchangers. Our tantalum heat exchangers are exceptionally stable and resistant. With our many years of experience in the machining of tantalum, we are also able to manufacture complex dimensions to precisely meet your requirements.

Deposits

Natural occurrence and preparation

In 1802, the Swedish chemist Anders Gustav Ekeberg separated tantalum pentoxide  (Ta2O5) from columbite ore for the very first time. The oxide is named after Tantalos, a figure in Greek mythology: Tantalus (lat.) was never able to satisfy his thirst because the water around him always receded before he could reach it. In the same way, tantalum oxide cannot react with any acid. The chemical symbol Ta was proposed by Jöns Jakob Berzelius in 1814. Berzelius was also the first person to produce elementary tantalum. However, Heinrich Rose recognized that the tantalum produced in this way actually only consisted of 50% tantalum. In 1844, Rose succeeded in proving that tantalum and niobium were different and distinctive elements. And it was not until 100 years later that Werner von Bolton was able to produce pure tantalum by reducing potassium heptafluorotantalate with sodium.

Tantalum occurs naturally most frequently in the form of tantalite ore, which has the formula (Fe, Mn) [(Nb,Ta)O3]2. When the tantalum content predominates, the ore is referred to as tantalite. When more niobium than tantalum is present, it is known as columbite or niobite. The world's largest tantalum deposits can be found in Australia, Brazil, and a number of African countries.

The ore is refined using a variety of methods to obtain concentrates of approximately 70% (Ta, Nb)2O5 . This concentrate is then dissolved in a mixture of hydrofluoric and sulfuric acid. The resulting fluoride complex (TaF7) is then converted to an organic phase by means of a liquid extraction process. The organic phase is separated from the aqueous phase. The tantalum is then separated from the organic phase using potassium hydrogen fluoride. This process produces potassium heptafluorotantalate (K2TaF7). The tantalum compound obtained in this way is then reduced with sodium to produce pure metallic tantalum.

Production process

How do we do it? With powder metallurgy!

So what is powder metallurgy? It is well known that nowadays most industrial metals and alloys, such as steels, aluminum, and copper, are produced by melting and casting in a mold. In contrast, powder metallurgy does away with the melting process and the products are manufactured by compacting metal powders which are then subjected to a heat treatment (sintering) below the melting temperature of the material. The three most important factors in the field of powder metallurgy are the metal powder itself as well as the compacting and sintering processes. We are able to control and optimize these factors in-house.

Why do we use powder metallurgy? Powder metallurgy allows us to produce materials with melting points of well over 2000 °C. The procedure is particularly economical even when only small quantities are produced. In addition, by using tailor-made powder mixes, we can produce a range of extremely homogeneous materials endowed with specific properties.

The tantalum powder is mixed with alloying elements and then filled into molds. The mixture is then compacted at a pressure of up to 2000 bar. The resulting pressed blank (also known as a "green compact") is then sintered in special furnaces at temperatures of over 2000 °C. During this process, it acquires its density and its microstructure forms. The very special properties of our materials – such as their excellent high-temperature stability and hardness or their flow characteristics – are due to the use of the appropriate forming methods, for example, forging, rolling, or drawing. Only when all these steps dovetail perfectly can we achieve our exacting quality requirements and manufacture products of outstanding purity and quality.

    Oxide
    Reduction
    Mixing alloys
    Pressing
    Sintering
    Forming
    Heat treatment
    Mech. processing
    Quality assurance
    Recycling
OxideMolymet (Chile) is the world's largest processor of molybdenum ore concentrates and our main supplier of molybdenum trioxide. The Plansee Group holds a 21.15% share in Molymet. Global Tungsten & Powders (USA) is a division of the Plansee Group and our main supplier of tungsten metal powder.
Product range

Overview of semifinished products made of tantalum and tantalum alloys:

 

Material Sheets
[thickness]
Ribbons
[thickness]
Rods
[diameter]
Tubes
        OD
[diameter]
Wall thickness
TaS 0.025 – 2 mm Upon request Upon request 2 – 52 mm 0.25 – 4 mm
TaK     Upon request    
TaKS     Upon request    
TaM 0.10 – 40 mm 0.050 – 0.400 mm 3.0 – 120 mm 2 – 52 mm 0.25 – 4 mm

 

Other dimensions as well as formed and machined parts or finished parts according to customer specification are available upon demand.

Online shop

You can order sheets, rods, ribbons, and wires as well as other products in configurable dimensions quickly and easily in our online shop.

Take a look at our products in the Plansee online shop

Downloads

Would you like to learn more about tantalum and its alloys? Then take a look at our safety data sheet.

Safety data sheet: Tantalum
Other materials
4295.94
Mo
Molybdenum
74183.84
W
Tungsten
W-MMC
Metal Matrix Composites