Niobium

• 1. Introduction

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  Niobium sits quietly in the periodic table at atomic number 41, carrying two names, a century of mistaken identity, and a reach that extends from the steel in modern cars to the magnets inside MRI scanners. Its symbol, Nb, is a compromise. Its older name, columbium, still appears in American metallurgy today. And the story of how scientists figured out what niobium actually was took more than sixty years of argument, false starts, and competing claims.

  At the heart of that confusion was a single awkward fact: niobium and tantalum are so chemically similar that for decades, some of the best chemists in the world could not tell them apart. That similarity is even written into the element's name. Niobe, in Greek mythology, was the daughter of Tantalus, the namesake of tantalum. The kinship runs from the myth all the way down to the atomic scale.

  How did a mineral sample sent from Connecticut in 1734 eventually lead to a metal used in Apollo rockets, particle accelerators, and commemorative coins? That question opens onto a wider story about ambition, scientific rivalry, and an element that turns out to be nearly everywhere once you know to look.

• 2. Two Names, One Element

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  English chemist Charles Hatchett first reported the element in 1801, working from a mineral sample that John Winthrop, grandson of John Winthrop the Younger, had sent to England from Connecticut in 1734. Hatchett named the mineral columbite and the element columbium, after Columbia, the poetic name then used for the United States.

  Almost immediately, the trouble began. In 1809, William Hyde Wollaston compared the oxides of columbite and tantalite and measured their densities: 5.918 g/cm for the columbite oxide, and over 8 g/cm for tantalite. Despite that significant difference, Wollaston concluded the two oxides were identical and kept the name tantalum. The scientific community largely followed him.

  The dissent came in 1846, when German chemist Heinrich Rose examined a sample of tantalite and argued that it contained two distinct elements. He named them niobium, after Niobe, and pelopium, after Pelops, another child of Tantalus. Rose's instinct was right about the two-element claim, but pelopium turned out to be neither a new element nor columbium. It was simply a mixture of niobium and tantalum.

  Full clarity arrived in stages. Christian Wilhelm Blomstrand and Henri Etienne Sainte-Claire Deville demonstrated the differences between tantalum and niobium unequivocally in 1864. Louis J. Troost determined the formulas of key compounds in 1865. Swiss chemist Jean Charles Galissard de Marignac confirmed the picture in 1866. Articles defending the phantom element ilmenium continued appearing until 1871, a full quarter-century after Rose's paper.

  Blomstrand also produced the metal for the first time in 1866, by heating niobium chloride in an atmosphere of hydrogen. De Marignac managed to produce tantalum-free niobium on a larger scale that same year, but the metal sat without a commercial purpose for decades to come.

• 3. The Naming Compromise

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  By the mid-twentieth century, columbium was the standard name in American journals while niobium dominated in Europe, and no resolution was in sight. The last paper published by the American Chemical Society with columbium in its title appeared as late as 1953.

  The decision came at the 15th Conference of the Union of Chemistry in Amsterdam in 1949, where the name niobium was chosen for element 41. The following year, the International Union of Pure and Applied Chemistry formally adopted it, ending more than a hundred years of controversy. The choice was a deliberate trade. The IUPAC accepted tungsten, the North American preference, over wolfram; in exchange, it accepted niobium over columbium, the European preference. Neither side got everything it wanted.

  The compromise did not fully settle the matter on the ground. Many US chemical societies and government organizations now use the IUPAC name, but some metallurgists and metal trade societies continue to use columbium. The symbol Nb, derived from niobium, is universal.

• 4. Physical and Chemical Character

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  Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table, but its electron configuration in the outermost shells is atypical for that group. Similar unusual configurations occur near ruthenium (element 44) and rhodium (element 45).

  At 9.2 K and atmospheric pressure, niobium becomes a superconductor with the highest critical temperature of any elemental superconductor. It also has the greatest magnetic penetration depth of any element and is one of only three elemental type II superconductors, alongside vanadium and technetium. Purity is critical: impurities harden the metal significantly, while a very pure sample is comparatively soft and ductile.

  The metal's melting point reaches 2468 degrees Celsius, yet niobium is less dense than other refractory metals. It begins to oxidize in air at 200 degrees Celsius and takes on a bluish tinge when exposed to air at room temperature over extended periods. Niobium resists attack from aqua regia, hydrochloric, sulfuric, nitric, and phosphoric acids, though hot concentrated sulfuric acid and hydrofluoric acid do attack it.

  Chemically, niobium's properties closely track those of tantalum, which sits directly below it in the periodic table. This is partly a consequence of the lanthanide contraction, which makes niobium and tantalum virtually identical in atomic size. Niobium's corrosion resistance is not as strong as tantalum's, but its lower price and greater availability make it attractive for applications where that tradeoff is acceptable, including vat linings in chemical plants.

  Almost all of the niobium in Earth's crust takes the form of a single stable isotope. The most stable radioisotope carries a half-life of 34.7 million years.

• 5. Where Niobium Comes From

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  Niobium is estimated to be the 33rd most abundant element in Earth's crust, at 20 parts per million, though some researchers believe the true abundance is considerably higher, with much of it concentrated in Earth's core because of the element's density. The free element does not appear in nature; it always occurs combined with other elements, and minerals containing niobium typically contain tantalum as well.

  The three largest mined deposits of pyrochlore, the principal ore, were all found in the 1950s: two in Brazil and one in Canada. The largest sits within a carbonatite intrusion in Araxá, in the state of Minas Gerais, and is owned by CBMM, the Companhia Brasileira de Metalurgia e Mineracao. The second active Brazilian deposit lies near Catalao, in the state of Goias, and is owned by China Molybdenum. Together, those two mines produce about 88% of the world's supply.

  The third-largest producer is the Niobec mine, a carbonatite-hosted deposit in Saint-Honore, Quebec, operated by Magris Resources, which accounts for between 7% and 10% of global output. Brazil also holds a large but still unexploited deposit near Sao Gabriel da Cachoeira, in the state of Amazonas.

  In 2006, global production reached 44,500 tonnes, a rise from 38,700 tonnes the year before. Over the decade between 1995 and 2005, production more than doubled, climbing from 17,800 tonnes. By the period spanning 2009 to 2011, output had stabilized at 63,000 tonnes per year. As of the data available, CBMM alone controlled 85% of world niobium production.

• 6. The Steel That Holds Everything

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  Out of the 44,500 tonnes of niobium mined in 2006, an estimated 90% went into high-grade structural steel. That single application dominates the element's commercial existence.

  The discovery that niobium strengthens steel dates to the 1920s. Within steel, niobium forms niobium carbide and niobium nitride. These compounds improve grain refining, retard recrystallization, and contribute to precipitation hardening. The practical effects are meaningful: increased toughness, strength, formability, and weldability, all from a niobium content of less than 0.1% in the final alloy.

  Those gains appear in structures people rely on daily. Niobium-containing high-strength low-alloy steels are widely used in modern automobiles. The same alloys go into gas pipelines. For more demanding applications requiring wear resistance, some steels contain as much as 3% niobium: Crucible CPM S110V stainless steel reaches that concentration for use in machine components and knives.

  Niobium's role in superalloys extends the reach further. Nickel-, cobalt-, and iron-based superalloys can contain as much as 6.5% niobium, used in jet engine components, gas turbines, rocket subassemblies, and turbocharger systems. Inconel 718, one well-known example, contains roughly 50% nickel, 18.6% chromium, 18.5% iron, and 5% niobium. This superalloy served in advanced airframe systems for the Gemini program; a different niobium alloy was used for the nozzle of the Apollo Service Module.

• 7. Rockets, Accelerators, MRI

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  C-103, a niobium alloy composed of 89% niobium, 10% hafnium, and 1% titanium, came out of a joint development effort between Wah Chang Corporation and Boeing in the early 1960s. DuPont, Union Carbide, General Electric, and several other companies were pursuing their own niobium alloys in parallel, driven largely by the demands of the Cold War and the Space Race.

  The project that produced C-103 began in 1959 with as many as 256 experimental compositions in the C-series. Wah Chang held a stock of hafnium refined from nuclear-grade zirconium alloys and needed a commercial use for it. The 103rd experimental composition, designated Nb-10Hf-1Ti, showed the best combination of formability and high-temperature properties. Wah Chang produced the first 500 pounds of C-103 in 1961. The alloy became the material for the descent engine nozzle of the Apollo Lunar Modules. Decades later, SpaceX adopted C-103 for the nozzle of the Merlin Vacuum engines on the upper stage of the Falcon 9 rocket.

  On the superconductor side, the year 1961 brought a different breakthrough. American physicist Eugene Kunzler and colleagues at Bell Labs showed that niobium-tin maintains superconductivity even in the presence of strong electric currents and magnetic fields. That made it the first material capable of supporting the high currents and fields needed for powerful magnets. Two decades on, this finding made possible long multi-strand cables wound into coils for particle accelerators and rotating machinery.

  In 1992 alone, more than one billion US dollars' worth of clinical MRI systems were built using niobium-titanium wire. The Large Hadron Collider uses 600 short tonnes of superconducting strands; the International Thermonuclear Experimental Reactor uses an estimated 600 long tonnes plus 250 long tonnes of NbTi strands. Pure niobium forms the superconducting radio frequency cavities at the FLASH and XFEL free-electron laser facilities, and the same technology is planned for the 30-kilometre International Linear Collider.

• 8. Coins, Lenses, and Pacemakers

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  Austria began producing a series of silver niobium euro coins in 2003. The distinctive colour in each coin comes from the diffraction of light through a thin anodized oxide layer. By 2012, ten different coins were available, with centres ranging from blue and green to brown, purple, violet, and yellow. Two of the series mark specific occasions: a 2004 coin valued at 25 euros commemorated the 150th anniversary of the Semmering Alpine Railway, and a 2006 coin at the same denomination marked European satellite navigation. The Austrian mint also produced a parallel series for Latvia starting in 2004. In 2011, the Royal Canadian Mint introduced a five-dollar sterling silver and niobium coin called Hunter's Moon, in which the niobium was selectively oxidized to create surface finishes that made no two coins identical.

  Beyond currency, niobium's low toxicity and its capacity to produce iridescent colours through anodization make it attractive for jewelry. The same physiological inertness that suits it for jewelry applies in medicine: niobium appears in prosthetics and pacemakers. When treated with sodium hydroxide, it forms a porous layer that aids osseointegration, meaning the surrounding bone grows into and bonds with the implant surface.

  Niobium also enters corrective lenses. Added to glass, it raises the refractive index, which allows lens manufacturers to produce thinner and lighter prescription lenses. Lithium niobate, a ferroelectric compound, is used extensively in mobile telephones and optical modulators. Niobium is also used to make the high-voltage wire for the solar corona particles receptor module of the Parker Solar Probe, carrying the element from earthbound steel mills all the way to the outer edge of the solar atmosphere.