Chemical element Niobium

Niobium or columbium is the chemical element with the symbol Nb and the atomic number 4. Physical and chemical properties Niobium. Niobium is in many ways similar to its predecessors in group 5. Application of the given chemical element in the industry.
Краткое сожержание материала:

Размещено на

General Information

niobium chemical element

Niobium (pronounced |nо'фbз?m|) (Greek mythology: Niobe, daughter of Tantalus), or columbium (|k?'l?mbз?m|), is the chemical element with the symbol Nb and the atomic number 4. A rare, soft, grey, ductile transition metal, niobium is found in the minerals pyrochlore, the main commercial source for niobium, and columbite.

Niobium has physical and chemical properties similar to those of the element tantalum, and the two are therefore difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801, and named it columbium. In 1809, the English chemist William Hyde Wollaston wrongly concluded that tantalum and columbium were identical. The German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element (as distinguished from tantalum), and for a century both names were used interchangeably. The name of the element was officially adopted as niobium in 1949.

It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines. Although alloys contain only a maximum of 0.1%, that small percentage of Niobium improves the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet engines and rocket engines. Niobium is used in various superconducting materials. These superconducting alloys, also containing titanium and tin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include its use in welding, nuclear industries, electronics, optics, numismatics and jewellery. In the last two applications, niobium's low toxicity and ability to be colored by anodisation are particular advantages.

History

Niobium was discovered by the English chemist Charles Hatchett in 1801. He found a new element in a mineral sample that had been sent to England from Massachusetts in 1734 by a John Winthrop, and named the mineral columbite and the new element columbium after Columbia, the poetical name for America. The columbium discovered by Hatchett was probably a mixture of the new element with tantalum.

Subsequently, there was considerable confusion over the difference between columbium (niobium) and the closely related tantalum. In 1809, the English chemist William Hyde Wollaston compared the oxides derived from both columbium--columbite, with a density 5.918 g/cmі, and tantalum--tantalite, with a density 7.935 g/cmі, and concluded that the two oxides, despite the significant difference in density, were identical; thus he kept the name tantalum. This conclusion was disputed in 1846 by the German chemist Heinrich Rose, who argued that there were two different elements in the tantalite sample, and named them after children of Tantalus: niobium (from Niobe, the goddess of tears), and pelopium (from Pelops). This confusion arose from the minimal observed differences between tantalum and niobium. Both tantalum and niobium react with chlorine and traces of oxygen, including atmospheric concentrations, with niobium forming two compounds: the white volatile niobium pentachloride (NbCl5) and the non-volatile niobium oxychloride (NbOCl3). The claimed new elements pelopium, ilmenium and dianium were in fact identical to niobium or mixtures of niobium and tantalum.

The differences between tantalum and niobium were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand, and Henri Etienne Sainte-Claire Deville, as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865 and finally by the Swiss chemist Jean Charles Galissard de Marignac in 1866, who all proved that there were only two elements. These discoveries did not stop scientists from publishing articles about ilmenium until 1871. De Marignac was the first to prepare the metal in 1864, when he reduced niobium chloride by heating it in an atmosphere of hydrogen.

Although de Marignac was able to produce tantalum-free niobium on an increased scale by 1866, it was not until the early 20th century that niobium was first used commercially, in incandescent lamp filaments. This use quickly became obsolete through the replacement of niobium with tungsten, which has a higher melting point and thus is preferable for use in incandescent lamps. The discovery that niobium improves the strength of steel was made in the 1920s, and this remains its predominant use. In 1961 the American physicist Eugene Kunzler and coworkers at Bell Labs discovered that niobium-tin continues to exhibit superconductivity in the presence of strong electric currents and magnetic fields, making it the first material known to support the high currents and fields necessary for making useful high-power magnets and electrically powered machinery. This discovery would allow--two decades later--the production of long multi-strand cables that could be wound into coils to create large, powerful electromagnets for rotating machinery, particle accelerators, or particle detectors.

Columbium (symbol Cb) was the name originally given to this element by Hatchett, and this name remained in use in American journals--the last paper published by American Chemical Society with columbium in its title dates from 1953--while niobium was used in Europe. To end this confusion, the name niobium was chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam in 1949. A year later this name was officially adopted by the International Union of Pure and Applied Chemistry (IUPAC) after 100 years of controversy, despite the chronological precedence of the name Columbium. The latter name is still sometimes used in US industry. This was a compromise of sorts; the IUPAC accepted tungsten instead of wolfram, in deference to North American usage; and niobium instead of columbium, in deference to European usage. Not everyone agreed, and while many leading chemical societies and government organizations refer to it by the official IUPAC name, many leading metallurgists, metal societies, and the United States Geological Survey still refer to the metal by the original "columbium".

Characteristics

Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table (see table to right), 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).)

The metal takes on a bluish tinge when exposed to air at room temperature for extended periods. Despite presenting a high melting point in elemental form (2,468 °C), it has a low density in comparison to other refractory metals. Furthermore, it is corrosion resistant, exhibits superconductivity properties, and forms dielectric oxide layers. These properties-- especially the superconductivity --are strongly dependent on the purity of the niobium metal. When very pure, it is comparatively soft and ductile, but impurities make it harder.

Niobium is slightly less electropositive and smaller than its predecessor in the periodic table, zirconium, while it is virtually identical in size to the heavier tantalum as a consequence of the lanthanide contraction. As a result, niobium's chemical properties are very similar to the chemical properties of tantalum, which appears directly below niobium in the periodic table. Although its corrosion resistance is not as outstanding as that of tantalum, its lower price and greater availability make niobium attractive for less exact uses such as linings in chemical plants.

Isotopes of niobium

Naturally occurring niobium (Nb) is composed of one stable isotope (Nb-93). The most stable radioisotopes are Nb-92 with a half-life of 34.7 million years, Nb-94 (half life: 20300 years), and Nb-91 with a half life of 680 years. There is also a meta state at 31 keV whose half-life is 16.13 years. Twenty three other radioisotopes have been characterized. Most of these have half lives that are less than two hours except Nb-95 (35 days), Nb-96 (23.4 hours) and Nb-90 (14.6 hours). The primary decay mode before the stable Nb-93 is electron capture and the primary mode after is beta emission with some neutron emission occurring in the first mode of the two mode decay of Nb-104, 109 and 110.

Only Nb-95 (35 days) and Nb-97 (72 minutes) and heavier isotopes (halflives in seconds) are fission products in significant quantity, as the other isotopes are shadowed by stable or very long-lived (Zr-93) isotopes of the preceding element zirconium from production via beta decay of neutron-rich fission fragments. Nb-95 is the decay product of Zr-95 (64 days), so disappearance of Nb-95 in used nuclear fuel is slower than would be expected from its own 35 day halflife alone. Tiny amounts of the other isotopes may be produced as direct fission products.

Standard atomic mass: 92.90638(2) u.

Chemistry

Niobium is in many ways similar to its predecessors in group 5. It reacts with most nonmetals at high temperatures: niobium reacts with fluorine at room temp...