Niobium
| Tin |
Tantalum | Lithium |
Cesium | Niobium | Rubidium |
Niobium like Tantalum has had to weather tough economic times over the past year due to economic downturn. The good news is that it has been showing signs of upward movement and is picking up rather well of late.
Niobium has a limited number of major producers worldwide. The leading producers are concentrated in Brazil and Canada dominating the market with a combined 85% share. Niobium is sourced from pyrochlore. Niobium is associated with igneous intrusive.
End uses of Niobium include the production of steels for gas pipelines, construction and the automotive industry, as well as high-specification alloys for aerospace, nuclear and turbine-blade applications. Niobium producers can look forward to an assured future, recent oversupply is likely to overshadow the tantalum market for some time to come. Consumers are increasingly looking to scrap and secondary sources, while running on inventories.
Characteristics
Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table (see table), although it has an atypical configuration in its outermost electron shells compared to the rest of the members. This can be observed in the neighborhood of niobium (41), ruthenium (44), rhodium (45), and palladium (46).)
Niobium becomes a superconductor at cryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.2 K. Niobium has the largest magnetic penetration depth of any element. In addition, it is one of the three elemental Type II superconductors, along with vanadium and technetium. The superconductive properties are strongly dependent on the purity of the niobium metal. When very pure, it is comparatively soft and ductile, but impurities make it harder. The metal has a low capture cross-section for thermal neutrons; thus, it is used in the nuclear industries.
Occurrence
Niobium is estimated to be 33rd on the list of the most common elements in the Earth’s crust with 20 ppm. The abundance on Earth should be much greater, but the “missing” niobium may be located in the Earth’s core due to the metal's high density. The free element is not found in nature, but it does occur in minerals. Minerals that contain niobium often also contain tantalum, such as columbite ((Fe,Mn)(Nb,Ta)2O6) and columbite-tantalite (or coltan, (Fe,Mn)(Ta,Nb)2O6). Columbite-tantalite minerals are most usually found as accessory minerals in pegmatite intrusions, and in alkaline intrusive rocks. Less common are the niobates of calcium, uranium, thorium and the rare earth elements such as pyrochlore ((Na,Ca)2Nb2O6(OH,F)) and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). These large deposits of niobium have been found associated with carbonatites (carbonate-silicate igneous rocks) and as a constituent of pyrochlore.
Applications
It is estimated that out of 44,500 metric tons of niobium mined in 2006, 90% was used in the production of high-grade structural steel, followed by its use in superalloys. The use of niobium alloys for superconductors and in electronic components account only for a small share of the production.
Steel production
Niobium is an effective microalloying element for steel. Adding niobium to the steel causes the formation of niobium carbide and niobium nitride within the structure of the steel. These compounds improve the grain refining, retardation of recrystallization, and precipitation hardening of the steel. These effects in turn increase the toughness, strength, formability, and weldability of the microalloyed steel. Microalloyed stainless steels have a niobium content of less than 0.1%. It is an important alloy addition to high strength low alloy steels which are widely used as structural components in modern automobiles. These niobium containing alloys are strong and are often used in pipeline construction.
Superalloys
Appreciable amounts of the element, either in its pure form or in the form of high-purity ferroniobium and nickel niobium, are used in nickel-, cobalt-, and iron-based superalloys for such applications as jet engine components, gas turbines, rocket subassemblies, and heat resisting and combustion equipment. Niobium precipitates a hardening γ''-phase within the grain structure of the superalloy. The alloys contain up to 6.5% niobium. One example of a nickel-based niobium-containing superalloy is Inconel 718, which consists of roughly 50% nickel, 18.6% chromium, 18.5% iron, 5% niobium, 3.1% molybdenum, 0.9% titanium, and 0.4% aluminium. These superalloys are used, for example, in advanced air frame systems such as those used in the Gemini program.
Other uses
Electroceramics
Lithium niobate, which is a ferroelectric, is used extensively in mobile telephones and optical modulators, and for the manufacture of surface acoustic wave devices. It belongs to the ABO3 structure ferroelectrics like lithium tantalate and barium titanate. Niobium was evaluated as a cheaper alternative to tantalum in capacitors, but tantalum capacitors are still predominant. Niobium is added to glass in order to attain a higher refractive index, a property of use to the optical industry in making thinner corrective glasses.
Hypoallergenic applications: medicine and jewelry
Niobium and some niobium alloys are physiologically inert and thus hypoallergenic. For this reason, niobium is found in many medical devices such as pacemakers. Niobium treated with sodium hydroxide forms a porous layer that aids osseointegration.
Along with titanium, tantalum, and aluminium, niobium can also be electrically heated and anodized, resulting in a wide array of colours using a process known as reactive metal anodizing which is useful in making jewelry. The fact that niobium is hypoallergenic also benefits its use in jewelry.
Numismatics
Niobium is used as a precious metal in commemorative coins, often with silver or gold. For example, Austria produced a series of silver niobium euro coins starting in 2003; the colour in these coins is created by diffraction of light by a thin oxide layer produced by anodising. In 2008, six coins are available showing a broad variety of colours in the centre of the coin: blue, green, brown, purple, violet, or yellow. Two more examples are the 2004 Austrian €25 150 Years Semmering Alpine Railway commemorative coin, and the 2006 Austrian €25 European Satellite Navigation commemorative coin. Latvia produced a similar series of coins starting in 2004, with one following in 2007.