Niobium Chemische Eigenschaften,Einsatz,Produktion Methoden
R-Sätze Betriebsanweisung:
R17:Selbstentzündlich an der Luft. Spontaneously flammable in air.
R36/37/38:Reizt die Augen, die Atmungsorgane und die Haut.
S-Sätze Betriebsanweisung:
S17:Von brennbaren Stoffen fernhalten.
S36:DE: Bei der Arbeit geeignete Schutzkleidung tragen.
S26:Bei Berührung mit den Augen sofort gründlich mit Wasser abspülen und Arzt konsultieren.
Chemische Eigenschaften
Niobium was discovered by Charles Hatchett in 1801 and isolated by Christian Blomstrand of Sweden in 1964. Its name was given after the Greek mythological ?gure Niobe, the daughter of Tantalos; tantalum always was associated with niobium. For many years, the terms “niobium” and “columbium”wereusedinterchangeably;however,thename “niobium” was of?cially adopted by International Union of Pure and Applied Chemistry (IUPAC) in 1950. Niobium is not a very rare element; its crustal abundance is 24ppm, which is similar or greater than those of many common elements, such as lead or cobalt.
Niobium is a shiny white, soft, and malleable metal. The element is inert to HCl, HNO3, or aqua regia at room temperature, slightly soluble in HF, but is attacked by alkali hydroxides or oxidizing agents at all temperatures. In pure
form, niobium is ductile, unless it is allowed to associate at elevated temperatures with common gases such as N2,H 2, or O2. Thus, when processed, it must be placed in a protective environment
No data were found in the literature; however, it might be assumed that niobium and most of their compounds are odorless. Niobium pentachloride (NbCl5) has pungent odor, because it decomposes slowly when heated, with Cl2 formation. Niobium in the form of dust is moderately explosive when exposed to ?ame or by chemical reaction.
Physikalische Eigenschaften
Niobium is a soft grayish-silvery metal that resembles fresh-cut steel. It is usually found inminerals with other related metals. It neither tarnishes nor oxidizes in air at room temperaturebecause of a thin coating of niobium oxide. It does readily oxidize at high temperatures(above 200°C), particularly with oxygen and halogens (group 17). When alloyed with tin andaluminum, niobium has the property of superconductivity at 9.25 Kelvin degrees.
Its melting point is 2,468°C, its boiling point is 4,742°C, and its density is 8.57 g/cm
3.
Isotopes
There are 49 isotopes of niobium, ranging from Nb-81 to Nb-113. All are radioactiveand made artificially except niobium-93, which is stable and makes up all of theelement’s natural existence in the Earth’s crust.
Origin of Name
Niobium is named after the Greek mythological figure Niobe who was
the daughter of Tantalus. Tantalus was a Greek god whose name is the source of the
word “tantalize,” which implies torture: he cut up his son to make soup for other gods.
Occurrence
Niobium is the 33rd most abundant element in the Earth’s crust and is considered rare.It does not exist as a free elemental metal in nature. Rather, it is found primarily in severalmineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca,Na)
2Nb
2O
6 (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum[(Fe, Mn)(Ta, Nb)
2O
6] are also products from tin mines in Malaysia and Nigeria. Niobium is a chemical “cousin” of tantalum and was originally purified by its separation through theprocess known as fractional crystallization (separation is accomplished as a result of the differentrates at which some elements crystallize) or by being dissolved in special solvents. Todaymost of the niobium metal is obtained from columbite and pyrochlore through a complicatedrefining process that ends with the production of niobium metal by electrolysis of moltenniobium potassium fluoride (K
2NbF
7).
Charakteristisch
Some of niobium’s characteristics and properties resemble several other neighboring elementson the periodic table, making them, as well as niobium, difficult to identify. This isparticularly true for tantalum, which is located just below niobium on the periodic table.
Niobium is not attacked by cold acids but is very reactive with several hot acids such ashydrochloric, sulfuric, nitric, and phosphoric acids. It is ductile (can be drawn into wiresthrough a die) and malleable, which means it can be worked into different forms.
History
Niobium was discovered in 1801 by Hatchett in an ore sent to England
more that a century before by John Winthrop the Younger,
first governor of Connecticut. The metal was first prepared
in 1864 by Blomstrand, who reduced the chloride by heating
it in a hydrogen atmosphere. The name niobium was adopted
by the International Union of Pure and Applied Chemistry in
1950 after 100 years of controversy. Most leading chemical societies
and government organizations refer to it by this name.
Some metallurgists and commercial producers, however, still
refer to the metal as “Niobium.” Niobium is found in
niobite (or columbite), niobite-tantalite, pyrochlore, and euxenite.
Large deposits of niobium have been found associated
with carbonatites (carbon-silicate rocks), as a constituent of
pyrochlore. Extensive ore reserves are found in Canada, Brazil,
Congo-Kinshasa, Rwanda, and Australia. The metal can be
isolated from tantalum, and prepared in several ways. It is a
shiny, white, soft, and ductile metal, and takes on a bluish cast
when exposed to air at room temperatures for a long time. The
metal starts to oxidize in air at 200°C, and when processed at
even moderate temperatures must be placed in a protective
atmosphere. It is used in arc-welding rods for stabilized grades
of stainless steel. Thousands of pounds of niobium have been
used in advanced air frame systems such as were used in the
Gemini space program. It has also found use in super-alloys
for applications such as jet engine components, rocket subassemblies,
and heat-resisting equipment. The element has
superconductive properties; superconductive magnets have
been made with Nb-Zr wire, which retains its superconductivity
in strong magnetic fields. Natural niobium is composed
of only one isotope, 93Nb. Forty-seven other isotopes and isomers
of niobium are now recognized. Niobium metal (99.9%
pure) is priced at about 50￠/g.
Verwenden
In ferrous metallurgy: Ferroniobium (produced by silicon reduction of columbite) is used to alloy stainless steels and metals for welding rods. In niobium base alloys for high temperatures and nuclear reactions. Niobium has some use as a getter in electronic vacuum tubes.
Definition
The name niobium is officially approved by chemical authorities, but columbium is still used chiefly
by metallurgists. Metallic element, atomic number
41, group VB of the periodic table, aw 92.9064,
valences of 2, 3, 4, 5; no stable isotopes
Vorbereitung Methode
Theextractingandre?ningprocessesforniobiumfromore are extremely complex and consist of a series of operations,
starting from upgrading the ores by concentration. Disruption of the niobium-containing matrix is then performed by an ore-opening procedure with hot HF or fusion with alkali ?uxes. The next steps include pure niobium compound preparation and reduction to metallic niobium, followed by re?ning, consolidation, and fabrication of the metal. Niobium is so closely associated with tantalum that they must be separated by fractional crystallization or by solvent extraction before puri?cation.
Hazard
Niobium is not considered reactive at normal room temperatures. However, it is toxic in itsphysical forms as dust, powder, shavings, and vapors, and it is carcinogenic if inhaled or ingested.
Carcinogenicity
No evidence was found that niobiumiscarcinogenic.Indeed,therearesomestudiessuggesting its antitumor activity. In the mouse study of Schroeder et al., occurrence of 23.6% of tumors in the niobiumtreated group (5–6.62ppm niobium in drinking water and diet for a lifetime) versus 34.8% for the controls was documented.
Niobium Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
