How Tantalum is Used in Corrosive Environments

Tantalum

Tantalum (Ta) is a vital element for a number of sectors in the modern electronics industry. Tantalum is one of the rarest elements on earth and is utilized in huge quantities in both alloy and pure forms.

Due to their superior corrosion resistance and higher strength compared to pure tantalum, alloys like tantalum-3wt%tungsten (Ta3W) are important. Tantalum subsequently provides limitless material potential and tangible results in challenging markets.

Tantalum is a rare element that is valued for its applications in industry and emerging technologies. As a refractory metal, tantalum has a very high melting point (3017°C), a very high density (16.7 g/cm3 at room temperature) and good mechanical strength at high temperatures.

Tantalum is different from other refractory metals because of its extreme chemical inertness and electrical properties, making it ideal for a range of unique applications. Tantalum is also compatible with silicon dioxide and silicon, which makes it a highly valuable material for semiconductor processing.

Properties of Tantalum

Tantalum is an extremely rare transition metal that has a lustrous grey finish similar in tone to platinum. Its discovery in 1802 was challenged by contemporary chemists who claimed it was an allotrope of niobium, not a new element.

Even today, they are still difficult to distinguish from each other as the two are almost chemically identical. Tantalum is the most corrosion resistant metal available for a wide range of industrial acids and liquids, with corrosion resistance that is comparable to glass in many acids.

Tantalum is twice as dense as steel, with a density of 16.6 g/cm3 and a Mohs hardness of around 6. This is in spite of having high ductility at room and elevated temperatures and an exceedingly high melting point of 2996 °C (5425 °F) – the fourth highest of all known metals.

Tantalum’s Applications

Semiconductors

Silicon and other semiconductor materials have drastically reduced in size (and corresponding performance improvements) in electronics. Today, semiconductor technologies are the building blocks of almost all electronic devices, and the basis of a trillion-dollar industry.

Semiconductor manufacturers increasingly rely on materials science to solve problems that arise in nanoscale features as the critical dimensions of semiconductor devices continue to decrease.

By facilitating the utilization of copper interconnects in devices like logic chips and DRAMS, tantalum plays a key role in many semiconductor devices. Tantalum atoms do not diffuse into silicon at chip operating temperatures, unlike copper (and other comparable metals).

To stop electromigration of copper atoms, high-purity tantalum nitrides can be grown on top of copper chips. This is to ensure that the semiconductor devices remain reliable for longer.

Chemical Processing

Tantalum shows extreme chemical inertness, resisting corrosion from a large variety of acids and other corrosive chemicals.

Tantalum alloys, like ULTRA 76+ which exhibit significantly improved corrosion resistance compared to the more traditional Ta-2.5W alloy, are invaluable for creating chemical processing equipment exposed to high temperature chemical attack.

Tantalum alloys are employed to create equipment like tank cladding, heat exchangers, piping, feed lances, valve liners and rupture disks, allowing reliable and long-life service under extreme process conditions.

Electronics

Although tantalum is conductive, tantalum oxide (Ta2O5) has an extremely high electromagnetic permittivity, meaning that tantalum can be utilized to create small capacitors with very high capacitance.

Tantalum capacitors are usually manufactured by pressing and sintering pure tantalum into a porous pellet with a large effective surface area – a very small tantalum capacitor generally has a capacitance equal to that of a much larger conventional capacitor plate.2

The formation of a thin oxide surface layer via anodization adds to the high capacitance of the pellet. The capacitance of a tantalum capacitor can be much higher than that of equivalently sized ceramic or aluminum capacitors, which is why tantalum capacitors are in widespread use in compact electronic devices like computers and cellphones.

Medical Equipment

Tantalum oxide, which naturally forms on the surface of pure tantalum when exposed to air, is highly biocompatible as it is completely inert to bodily fluids. Therefore, tantalum is a highly desirable material for the construction of durable, strong surgical implants.

Surgical applications of tantalum include knee and hip replacement fixtures, clips for blood vessel ligation, monofilament and braided suture wires for skin closure (as well as tendon and nerve repair), plates for reconstructive surgeries and staples for abdominal surgery.

As tantalum capacitors can be made very small and are extremely durable, they are frequently utilized in implantable medical devices, especially implantable cardioverter defibrillators (ICDs).

Military and Aerospace

Tantalum additions to nickel-based superalloys can yield materials capable of withstanding mechanical stress and extremely high temperatures. These superalloys are extensively utilized in the production of gas turbine engines for military and commercial aircraft, in addition to land-based power generation.

Good dimensional stability and high temperature strength are both key qualities for such applications. Components made from alloys containing tantalum can handle higher internal combustion temperatures, which leads to lower fuel consumption and enhanced thrust efficiencies.

Furnace Applications

Furnace boats and trays are employed to hold finished or semi-finished products during high-temperature furnace processes like sintering and annealing. These containers need to be able to withstand fast and repeated temperature cycling to extremely high temperatures.

Tantalum provides strength and dimensional stability at high process temperatures and shows excellent resistance to creep deformation, so it excels in such applications.

Tantalum and Tantalum Alloys from H.C. Starck Solutions

H.C. Starck Solutions is one of the largest suppliers of pure tantalum and tantalum alloys for engineering applications in the world.

Manufactured using a combination of thermo-mechanical processes refined over decades, their signature NRC®76 (Ta2.5 %W) welded tubing provides a defect-free product with a tightly controlled composition and uniform wall thickness which is key for engineering calculations to secure safety for many years in operation.

Their ongoing research into tantalum alloys led to the development of ULTRA76+, a modified Ta2.5 %W alloy with superlative mechanical and anti-corrosion properties and a lower cost when compared with the previous generation ULTRA76 alloy.

Tantalum is often sputtered to produce thin tantalum layers for electronics and semiconductor applications. H.C. Starck is a major producer of high-purity tantalum sputtering target blanks, exhibiting highly controlled grain size with low defect rates.

This information has been sourced, reviewed and adapted from materials provided by H.C. Starck Solutions.

For more information on this source, please visit H.C. Starck Solutions.

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