126 | The History and Use of Our Earth’s Chemical Elements is a chemical “cousin” of tantalum and was originally purified by its separation through the
126 | The History and Use of Our Earth’s Chemical Elements is a chemical “cousin” of tantalum and was originally purified by its separation through the
process known as fractional crystallization (separation is accomplished as a result of the differ- ent rates at which some elements crystallize) or by being dissolved in special solvents. Today most of the niobium metal is obtained from columbite and pyrochlore through a complicated refining process that ends with the production of niobium metal by electrolysis of molten
niobium potassium fluoride (K 2 NbF 7 ).
History Niobium has a rather confusing history, starting in 1734 when the first governor of
Connecticut, John Winthrop the Younger (1681–1747), discovered a new mineral in the iron mines of the New England. He named this new mineral “columbite.” Although he did not know what elements the mineral contained, he believed it contained a new and as yet unidentified element. Hence, he sent a sample to the British Museum in London for analysis. It seems that the delivery was mislaid and forgotten for many years until Charles Hatchett (1765–1847) found the old sample and determined that, indeed, a new element was pres- ent. Hatchett was unable to isolate this new element that he named columbium, which was derived from the name of Winthrop’s mineral.
The story became more complicated when in 1809 the English scientist William Hyde Wollaston (1766–1828) analyzed the sample mineral and declared that columbium was really the same element as tantalum ( 73 Ta). This error is understandable given that the level of analytical equipment available to scientists in those days was fairly primitive. Also, tantalum and niobium are very similar metals that are usually found together and thus are difficult to separate for analysis.
However, the story does not end there. It was not until 1844 when Heinrich Rose (1795–1864) “rediscovered” the element by producing two similar acids from the mineral: niobic acid and pelopic acid. Rose did not realize he had discovered the old “columbium,” so
he gave this “new” element the name niobium. Twenty years later, Jean Charles Galissard de Marignac (1817–1894) proved that niobium and tantalum were two distinct elements. Later, the Swedish scientist Christian Wilhelm Blomstrand (1826–1899) isolated and identified the metal niobium from its similar “twin,” tantalum.
CommonUses Refined niobium metal is most useful as an alloy with other metals. It is used to produce
special stainless steel alloys, to make high-temperature magnets, as special metals for rockets and missiles, and for high- and low-temperature–resistant ceramics. Stainless steel that has been combined with niobium is less likely to break down under very high temperatures. This physical attribute is ideal for construction of both land- and sea-based nuclear reac- tors.
Niobium has special cryogenic properties. It can withstand very cold temperatures, which improves its ability to conduct electricity. This characteristic makes it an excellent metal for low-temperature electrical superconductors.
Niobium alloyed with germanium becomes a superconductor of electricity that does not lose its superconductivity at 23.2° Kelvin as large amounts of electrical current are passed through it, as do some other superconductive alloys. In the pure metallic state, niobium wires are also superconductors when the temperatures are reduced to near absolute zero (–273°C).
127 ExamplesofCompounds
Guide to the Elements |
Niobium in its +5 oxidation state forms both oxygen and halogen compounds (Niobium in oxidation states of +2, +3 and +4 also forms compounds—for example, niobium(II) dioxide and niobium(IV) tetraoxide):
Niobium (V) pentoxide: 2Nb + 5O 2 → 2Nb 2 O 5 . Niobium (V) pentachloride: Nb + 5Cl→ NbCl 5 .
Nibium (V) pentafluoride: Nb + 5F → NbF 5 .
Niobium carbide (NbC) is used to make hard-tipped tools and special steels and to coat graphite in nuclear reactors. Niobium silicide (NbSi 2 ) is used as a lining for high-temperature refractory furnaces. Niobium-uranium alloy has a high tensile strength, making it ideal in the manufacture of fuel rods for nuclear reactors that resist separation. Niobium alloys are components of experimental supermagnets that are being tested to “drive” super-fast forms of ground transportation.
Hazards Niobium is not considered reactive at normal room temperatures. However, it is toxic in its
physical forms as dust, powder, shavings, and vapors, and it is carcinogenic if inhaled or ingested. MOLYBDENUM SYMBOL:Mo PERIOD:5 GROUP:6(VIB) ATOMICNO: 42
ATOMICMASS:95.94amu VALENCE:6 OXIDATIONSTATE:+6(alsolowerstatesof +2,+3,+4,and+5) NATURALSTATE:Solid
ORIGINOFNAME:MolybdenumisderivedfromtheGreekwordmolybdos,meaninglead. Atonetime,themineralmolybdaena(latercalledmolybdenite)wasbelievedtobea varietyofleadore.
ISOTOPES:Thereare36isotopesofmolybdenum,ranginginatomicweightsfromMo-83 toMo-115.Ofthesevenisotopesconsideredstable,one(Mo-100)isradioactiveandis consideredstablebecauseithassuchalonghalf-life(0.95×10 +19 years).Thepropor- tionsofthesevenstableisotopescontributingtomolybdenum’snaturalexistenceon Earthareasfollows:Mo-92=14.84%,Mo-94=9.25%,Mo-95=15.92%,Mo-96= 16.68%,Mo-97=9.55%,Mo-98=24.13%,andMo-100=9.63%.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons