Why is Tantalum So Valuable?

Properties of tantalum

Tantalum has a series of excellent characteristics such as a high melting point, low vapor pressure, good cold processing performance, high chemical stability, strong resistance to liquid metal and acid and alkali corrosion, and large dielectric constant of the surface oxide film, which makes it an important modern functional material.

tantalum wire

Tantalum rapidly generates a surface oxide film that closely covers its metallic substrate in almost any environment, which is extremely thin and dense, impervious to almost all media, and self-healing once damaged. Thanks to this excellent protective film, tantalum has extremely good corrosion resistance. Except for fluorine, hydrofluoric acid, acidic solutions containing fluorine ions, fuming nitric acid, and strong alkalis, tantalum is impervious to corrosion in most media.

The main uses of tantalum

In the electronics industry, tantalum is mainly used as tantalum capacitors, which are usually applied in the form of capacitor-grade tantalum powder, tantalum wire, and tantalum foil. Tantalum capacitors are indispensable electronic components for radar, spacecraft, and missiles, and are widely used in civil applications such as mobile communication, electronic equipment, and instruments.

Tantalum powder can be made into small and large capacity capacitors because of its large specific surface area and large dielectric constant of the dielectric film, and therefore large capacity.

Electrolytic capacitors made of tantalum have the advantages of small size, lightweight, good reliability, large operating temperature range, shock resistance, and long service life. Tantalum electrolytic capacitors can be divided into solid electrolyte capacitors and liquid electrolyte capacitors according to their electrolytic degree.

Tantalum electrolytic capacitor

Capacitors can be distinguished by the form of their anodes, there are mainly two kinds of tantalum foil anodes and tantalum powder sintered anodes. Tantalum wire is used as the anode lead for these two types of capacitors. The development of the electronics industry is demanding more and more miniaturization and high reliability of tantalum capacitors. In the miniaturization of tantalum capacitors and chip types, efforts are made to increase the specific capacity of tantalum powder.

Tantalum is also used as a material for electronic tubes. Due to its high melting point, low vapor pressure, good processing properties, low coefficient of thermal expansion, and excellent gas absorption, tantalum is a good material for emitter tubes and high-power electron tube parts. Due to its high chemical stability, tantalum target is an important material for the magneto-space sputtering coating of electronic chips.

Tantalum carbide is a refractory metal, which occupies an extremely important position in cemented carbide industrial applications. Like the ceramic carbides of WC, TiC, and metallic cobalt, TaC has excellent wear resistance, toughness, hardness, and stability.

There are two types of tantalum carbide use: one is to add tantalum carbide directly to WC-Co or WC-TiC-Co alloy in small amounts, which plays a role in controlling grain growth, etc.; the other is to form a solid solution with niobium carbide or other carbides, which can improve the high-temperature hardness, high-temperature strength and oxidation resistance of the alloy, greatly improving cutting speed and extending tool life.

Ceramic carbide has excellent cutting performance, generally composed of α, γ, β three phases. α phase is tungsten carbide; β phase is the metal phase binder, metal cobalt is the most commonly used binder for ceramic carbide; γ phase is the solid solution formed by TaC, NbC, and TiC, γ phase is dissolved in tungsten carbide, its role is as a crystal generation inhibitor.

The deep processing of tantalum and its application

Tantalum has very good plasticity and is extremely easy to be processed plastic. Various industrial profiles (tantalum tube, tantalum rod, tantalum wire, tantalum strip) can be produced by using conventional processing processes (extrusion, forging, rolling, and drawing). Tantalum and tantalum alloy molten ingots have a coarse grain organization and must first be extruded or hot-forged to open the billet and break the grains before they can be further processed into the material.

Pure tantalum can be forged at room temperature to open the billet, tantalum alloy open billet temperature is generally 1100- l200 ℃. During processing, the oxidation of the tantalum alloy surface generates loose oxides and can penetrate into the alloy matrix, forming a hard permeable layer that cracks during processing. Therefore, it is important to try to protect the metal surface from oxidation during the entire machining process.

Currently, tantalum blanks are protected by salt bath heating, coating, jacketing, inert gas protection, etc. The extrusion method can produce metal tubes, bars, and profiles of different sizes; tantalum ingots can be directly forged into rolled slabs. Glass coating can be used as a lubricant; rolling of tantalum alloy plates, usually using two-roll or four-roll mills, with deformation of 10% and 15%, and total deformation of 70% and 80% when rolling 2.5mm thin plates. When rolling a 2.5mm thin plate, kerosene or palm oil is used as a lubricant.

How is Tantalum Carbide Applied?

Tantalum Carbide (TaC) is an extremely hard refractory ceramic material. It has a metallic luster but may also be found as a dark to light brown powder, and it burns in air with a bright flash and is slightly soluble in acids.

tantalum carbide

Tantalum carbide has excellent physical and chemical properties, such as high hardness, high melting point, good electrical conductivity, thermal shock resistance, good resistance to chemical corrosion, high resistance to oxidation and catalytic properties, etc. which make tantalum carbide widely used in industrial and military fields.

The main uses of tantalum carbide are cemented carbide, capacitors, electronic components, high-temperature components, chemical equipment, and armor-piercing projectiles.

Cemented carbide

Tantalum carbide plays an important role in cemented carbides. It improves the properties of the alloy by improving the fiber structure and phases transformation kinetics, giving the alloy higher strength, phase stability, and processability.

Tantalum is particularly effective in promoting nucleation and preventing precipitation of carbon in the core crystalline brittle film formed during the late solidification. Its main functions are: (1) preventing the growth of cemented carbide grains; (2) forming a third dispersed phase other than tungsten carbide (WC) and Co together with titanium carbide (TiC), thereby significantly increasing the thermal shock resistance and crater wear resistance of cemented carbide and improves its red hardness.

Electronics industry

In recent years, transition metal carbides have attracted much attention due to their chemical stability, high hardness, strong resistance to oxidation and corrosion, and low electrical resistivity. Carbide nanomaterials have shown great potential in metal coatings, tools, machine parts, and composites. Of all the carbide nanowire materials, silver carbide is one of the most popular materials and one of the most promising materials.

Tantalum carbide not only inherits many advantages of carbide nanomaterials but also has its own unique side, such as high hardness (Mohs hardness of 9-10 at normal temperature, high melting point (about 3880 ° C), high Young’s modulus (283-550 GPa), strong conductivity (32.7-117.4 μΩ•cm at 25 °C conductivity) ), high-temperature superconductivity (10.5K), chemical corrosion resistant candle and thermal shock capacity, high catalytic activity for ammonia decomposition and hydrogen separation.

At present, tantalum carbide powder and tantalum carbide whiskers have been prepared by carbothermal reduction, thermal plasma, solvothermal, sol-gel, microwave heating, alkali reduction, and self-propagating high-temperature synthesis, and high-frequency induction heating sintering.

Superalloy

Among the carbides, the most refractory resistance is tantalum carbide (TaC) (melting point 3890 ℃) and niobium carbide (HfC) (melting point 3880 ℃), followed by zirconium carbide (ZrC) (melting point 3500 ℃). At high temperatures, these materials have excellent mechanical properties, far exceeding the best polycrystalline graphite, especially tantalum carbide, which is the only material that maintains certain mechanical properties in the temperature range of 2900 ℃ to 3200 ℃. However, its shortcoming is that it is extremely sensitive to thermal shock, and the low thermal conductivity and high thermal expansion coefficient of carbides have become the biggest obstacles in the application of aerospace materials. The addition of tantalum carbide to the carbon/carbon composite material will result in higher thermal conductivity and lower thermal expansion conditions and will exert the oxidation resistance and ablation resistance of the refractory metal.

Stanford Advanced Materials supplies high-quality tantalum products to meet our customers’ R&D and production needs. Please visit https://www.samaterials.com/ for more information.


Reference

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