Niobium is a very important metal in both ferrous and nonferrous metallurgy. As an additive to alloys or when alloyed with other metals niobium imparts high mechanical strength, high electrical conductivity, and ductility to alloys. It enhances corrosion resistance of most alloys. The metal and several of its alloys exhibit superconductivity. Nobium is used as an additive in the manufacture of most high strength, low alloy carbon steels and microalloyed steels that are used in the construction of oil and gas pipelines, bridges, buildings, concrete bars, and automobiles.
Nobium also is added to nickel- and cobalt-based superalloys and is a component of zirconium, titanium and tungsten alloys.
Other applications of niobium are in electronic and propulsion devices, in electrodes; in catalysis; and in vacuum tubes and high-pressure sodium vapor lamps.
shiny grey metallic solid
The element was discovered in 1801 by British chemist Charles Hatchett during analysis of a black mineral sample from the British Museum, originally sent in 1753 from Connecticut. He named the element columbium, after the country of its origin, Columbia (United States). In 1844, Rose announced the discovery of a new element which he named as niobium, in honor of Niobe, the daughter of Tantalus, the mythological Goddess of Tears. Later, it was established that Hatchett’s columbium and Roses’ niobium were the same element. Both names remained in use for more than one hundred years. In 1949 at the Fifteenth International Union of Chemistry Congress held at Amsterdam, the name niobium was officially adopted as the international name.
Niobium was prepared in the metallic state for the first time by Blomstrand in 1866, later by Moissan, and still later, by Goldschmidt. While Blomstrand reduced niobium chloride with hydrogen to form niobium, Moissan and Goldschmidt reduced the oxide with carbon (in an electrical furnace) and aluminum powder, respectively.
Niobium occurs naturally in several minerals, mostly associated with tantalum and many rare earth elements. The metal is never found in free elemental form. It occurs mostly as hydroxide, silicate, or borate or as its oxy salt, niobate, which is mostly associated with isomorphous tantalate. The principal niobium minerals are pyrochlore, loparite, and koppite all of which contain titanium together with calcium and other metals, such as cerium. They are complex hydroxide minerals and their composition may vary with place. Another type of niobium mineral is the niobates-tantalates mixed ores of Nb2O6—Ta2O6 or of compositions (Nb,Ta)2O6. Such ores usually contain iron and sometimes manganese which partially replaces iron. A typical example is an isomorphous admixture of Fe(NbO3)2—Fe(TaO2)2. Many impurity metals, such as tungsten, titanium, and tin are also found in these ores.
The abundance of niobium in the earth’s crust is estimated to be in the range 20 mg/kg and its average concentration in sea water is 0.01 mg/L. The metal also is found in the solar system including the lunar surface. Radionucleides niobium-94 and -95 occur in the fission products of uranium- 235.
There are several processes for extracting and refining niobium from its ores. The process of choice depends on nature of the ore and end use intended for the metal. Some common steps in these recovery processes involve ore preconcentration, breaking or opening the ore, obtaining pure niobium compounds, reduction of niobium compounds to niobium metal, purification or refining metal and fabrication. If niobium is extracted from a niobium-tantalum ore, the most important step is separation of niobium from tantalum, both of which are chemically very similar.
Ferroniobium can be produced from the ore pyrochlore in batch process by thermal reduction in a refractory-lined steel or preferably an electric furnace reactor. Aluminum powder is used as a reducing agent.
Ore-opening is a key step in the recovery of niobium, and separation of niobium from tantalum and impurity metals is the most important step in its extraction from the ore. It may be achieved by several methods that include solvent extraction, ion exchange, fractional crystallization, fractional sublimation, and other techniques.
High purity grade metal may be produced by reduction of niobium pentaoxide, Nb2O5 or pentachloride, NbCl5 at elevated temperatures ranging from 1400 to 2000°C and often under vacuum using various reducing agents, such as carbon, hydrogen, sodium and other substances:
Nb2O5 + 7C → 2NbC + 5CO
Nb2O5 + 5NbC → 7Nb + 5CO
2NbCl5 + 5H2 → 2Nb + 10HCl
NbCl5 + 5Na → Nb + 5NaCl
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.