Niobium and tantalum-the twin brothers in the metals


Rare metals – tantalum and niobium belong to the congener in the periodic table of elements. As they have very similar physical and chemical property and also grow together in the same ore body, they are called “twin brothers” in the metals.

Tantalum and niobium were successively found by the English chemist Charles Hatchett and Sweden chemist Ekeberg in 1801 and 1802. Columbite-tantalite is the main ore of tantalum and niobium. Also there is a small quantity of tantalum and niobium existing in the tungsten ores and some rare earth ores. While tantalum appears to be silver-white, the surface of niobium looks very much like the steel. Tantalum and niobium are both the high melting point metals of which the melting point is respectively as 2996 degrees celsius and 2468 degrees celsius. The chemical properties of tantalum and niobium are extremely stable. They are not only not afraid of nitric acid, hydrochloric acid, but also not afraid of aqua regia. Tantalum has rich ductility, which can be pulled into the tantalum wire finer than a human hair or crushed into the tantalum foil thinner than the paper. Tantalum and niobium both have the speciality of pressure resistance and wear resistance. They are also the excellent superconducting materials.

The tantalum surface can form the armorphous oxide film which is dense and stable and has high dielectric strength. It is easy to accurately and conveniently control the anodic oxidation process of the condensers and at the same time the tantalum powder sintering block can acquire prodigious superficial area in the pimping volume. Therefore the tantalum capacitor is the most excellent capacitor which has small volume, big capacity, low leak current, long service life and outstanding combination property. It not only has less volume, higher capacity and more stable function compared with ceramics, aluminum, thin film and other capacitors under normal condition, but also can work regularly in the severe conditions that many other capacitors cannot handle. As the tantalum capacitors have the excellent properties that many other capacitors cannot match, there is almost no equivalent substitution of capacitors that can compete with them in the field of microelectronics and surface mounting technology. As a result, the 60 percents to 65 percents tantalum is used in making the capacitors in the forms of capacitor grade tantalum powder and tantalum wire. Tantalum capacitors have already been more and more widely used in the areas of communication (program control units, interchangers, mobile phones, pagers, fax machines and cordless telephones), computers, cars, household and office appliances, instruments, aerospace, national defense and so on. As tantalum and niobium are the associated metals which belong to the same group, they have many similarities in the performance. The performance of capacitors made by metal niobium powder is only second to tantalum, it has the advantages of higher specific volume, lower equivalent series resistance and easier chip compared with the aluminum capacitors and may replace 10 percents of the aluminum capacitors with its development; compared with tantalum, the major defect of niobium in making capacitors is its bigger leak current (usually is 5-10 times of tantalum), lower breakdown voltage (<10V), lower operating temperature (< 105 degrees celsius). Therefore, it is not suitable for making the capacitors with high reliability requirements and high rated voltage. But in the range of low voltage (<10V) and high capacity (>100 μ f), the niobium capacitors may partially substitute the tantalum capacitors in this grades. The development and utilization of niobium capacitor is a good thing for the tantalum-niobium industry, which can gain new development opportunity.

As tantalum and niobium has all of the above excellent performance, they can be widely used in every field.

In the metallurgical industry, niobium is mainly used in the manufacture of heat-resistant alloy and increase the intensity of steel. When the carbon steel is smelting, the intensity of steel will be increased to more than one-third by just adding a few percents of niobium. The superalloys compounded by tantalum and niobium together with tungsten, aluminium, nickel, cobalt, vanadium and other series of metals are the good structural material for the superjets, rockets and guided missiles.

In the machinery industry, the tools made by niobium carbide, tantalum carbide and other cemented carbides are able to withstand the high temperature of 3000 degrees celsius. Its hardness can compare with diamond – the hardest material in the world.

In medicine, tantalum is an ideal biological fitness material. When tantalum is directly contacting with the skeletons, muscle tissue and liquid of human body, it can be compatible with biological cells, has wonderful affinity and almost has no stimulation and side effects to human bodies. Tantalum can not only be used in the bone fracture plates, bolts and clamping bars for the treatment of fractures, but also can directly use tantalum plate and tantalum sheet to renew the bones and use tantalum rod to replace the broken bones caused by trauma. Tantalum wire and tantalum foil can suture nerves, muscle and blood vessels with more than 1.5mm, of which the very fine tantalum wire can replace muscle and even the nerve fibre. The tantalum yarn and tantalum slug woven by tantalum wire can be used to repair the muscle tissue.