Properties of niobium. Physical properties of niobium Nb at different temperatures
Physical properties niobium
Niobium is a shiny silver-gray metal.
Elemental niobium is an extremely refractory (2468°C) and high-boiling (4927°C) metal, very resistant to many aggressive environments. All acids, with the exception of hydrofluoric acid, have no effect on it. Oxidizing acids “passivate” niobium, covering it with a protective oxide film (No. 205). But at high temperatures, the chemical activity of niobium increases. If at 150...200°C only a small amount is oxidized surface layer metal, then at 900...1200°C the thickness of the oxide film increases significantly.
The crystal lattice of Niobium is body-centered cubic with parameter a = 3.294A.
Pure metal is ductile and can be rolled into thin sheets (up to a thickness of 0.01 mm) in a cold state without intermediate annealing.
One can note such properties of niobium as high melting and boiling points, lower electron work function compared to other refractory metals - tungsten and molybdenum. The last property characterizes the ability for electron emission (electron emission), which is used for the use of niobium in electric vacuum technology. Niobium also has a high transition temperature to the superconducting state.
Density 8.57 g/cm3 (20 °C); melting point 2500 °C; boiling point 4927 °C; vapor pressure (in mm Hg; 1 mm Hg = 133.3 n/m2) 1 10-5 (2194 °C), 1 10-4 (2355 °C), 6 10- 4 (at melting point), 1·10-3 (2539 °C).
At ordinary temperatures, niobium is stable in air. The onset of oxidation (discoloration film) is observed when the metal is heated to 200 - 300°C. Above 500°, rapid oxidation occurs with the formation of Nb2O5 oxide.
Thermal conductivity in W/(m·K) at 0°C and 600°C is 51.4 and 56.2, respectively, and the same in cal/(cm·sec·°C) is 0.125 and 0.156. Specific volumetric electrical resistance at 0°C is 15.22·10-8 ohm·m (15.22·10-6 ohm·cm). The transition temperature to the superconducting state is 9.25 K. Niobium is paramagnetic. Electron work function 4.01 eV.
Pure Niobium is easily processed by cold pressure and retains satisfactory mechanical properties at high temperatures. Its tensile strength at 20 and 800 °C is respectively 342 and 312 Mn/m2, the same in kgf/mm234.2 and 31.2; relative extension at 20 and 800 °C, 19.2 and 20.7%, respectively. The hardness of pure Niobium according to Brinell is 450, technical 750-1800 Mn/m2. Impurities of certain elements, especially hydrogen, nitrogen, carbon and oxygen, greatly impair the ductility and increase the hardness of Niobium.
Chemical properties niobium
Niobium is especially valued for its resistance to inorganic and organic substances.
There is a difference in the chemical behavior of powdered and lump metal. The latter is more stable. Metals have no effect on it, even if heated to high temperatures. Liquid alkali metals and their alloys, bismuth, lead, mercury, and tin can be in contact with niobium for a long time without changing its properties. Even such strong oxidizing agents as perchloric acid, aqua regia, not to mention nitric, sulfuric, hydrochloric and all the others, cannot do anything with it. Alkali solutions also have no effect on niobium.
There are, however, three reagents that can convert niobium metal into chemical compounds. One of them is a melt of hydroxide of an alkali metal:
4Nb+4NaOH+5O2 = 4NaNbO3+2H2O
The other two are hydrofluoric acid (HF) or its mixture with nitric acid (HF+HNO). In this case, fluoride complexes are formed, the composition of which largely depends on the reaction conditions. In any case, the element is part of an anion of type 2- or 2-.
If you take powdered niobium, it is somewhat more active. For example, in molten sodium nitrate it even ignites, turning into an oxide. Compact niobium begins to oxidize when heated above 200°C, and the powder becomes covered with an oxide film already at 150°C. At the same time, one of the wonderful properties of this metal manifests itself - it retains its ductility.
In the form of sawdust, when heated above 900°C, it completely burns to Nb2O5. Burns vigorously in a stream of chlorine:
2Nb + 5Cl2 = 2NbCl5
When heated, it reacts with sulfur. It is difficult to alloy with most metals. There are, perhaps, only two exceptions: iron, with which solid solutions of different ratios are formed, and aluminum, which has the compound Al2Nb with niobium.
What qualities of niobium help it resist the action of strong acids - oxidizing agents? It turns out that this does not refer to the properties of the metal, but to the characteristics of its oxides. Upon contact with oxidizing agents, a thin (therefore unnoticeable) but very dense layer of oxides appears on the metal surface. This layer becomes an insurmountable barrier on the way of the oxidizing agent to pure metal surface. Only certain chemical reagents, in particular fluorine anion, can penetrate through it. Consequently, the metal is essentially oxidized, but practically the results of oxidation are imperceptible due to the presence of a thin protective film. Passivity towards dilute sulfuric acid is used to create an AC rectifier. It is designed simply: platinum and niobium plates are immersed in a 0.05 m solution of sulfuric acid. Niobium in a passivated state can conduct current if it is a negative electrode - a cathode, that is, electrons can pass through the oxide layer only from the metal side. The path for electrons out of the solution is closed. Therefore, when they pass through such a device alternating current, then only one phase passes, for which platinum is the anode and niobium is the cathode.
niobium metal halogen
Niobium is an element of the side subgroup of the fifth group of the fifth period of the periodic table of chemical elements of D. I. Mendeleev, atomic number 41. Denoted by the symbol Nb (lat. Niobium).
History of the discovery of niobiumIt so happened that element #41 was opened twice. The first time was in 1801, the English scientist Charles Hatchet examined a sample of the true mineral sent to the British Museum from America. From this mineral he isolated the oxide of a previously unknown element. Hatchet named the new element columbium, thereby noting its overseas origin. And the black mineral was called columbite.
In a year Swedish chemist Ekeberg isolated the oxide of another new element, called tantalum, from columbite. The similarity between the compounds Columbia and tantalum was so great that for 40 years most chemists believed that tantalum and columbium were the same element.
In 1844, German chemist Heinrich Rose examined samples of columbite found in Bavaria. He again discovered oxides of two metals. One of them was the oxide of the already known tantalum. The oxides were similar, and, emphasizing their similarity, Rose named the element forming the second oxide niobium, after Niobe, the daughter of the mythological martyr Tantalus.
However, Rose, like Hatchet, was unable to obtain this element in a free state.
Metallic niobium was first obtained only in 1866 by the Swedish scientist Blomstrand during the reduction of niobium chloride with hydrogen. IN late XIX V. two more ways to obtain this element were found. First, Moissan obtained it in an electric furnace, reducing niobium oxide with carbon, and then Goldschmidt was able to reduce the same element with aluminum.
And call element No. 41 in different countries continued in different ways: in England and the USA - with Columbia, in other countries - with niobium. The International Union of Pure and Applied Chemistry (IUPAC) put an end to this controversy in 1950. It was decided to legitimize the name of the element “niobium” everywhere, and the name “columbite” was assigned to the main mineral of niobium. Its formula is (Fe, Mn) (Nb, Ta) 2 O 6.
Finding niobium in natureClark niobium 18 g/t. Niobium content increases from ultramafic (0.2 g/t Nb) to acidic rocks (24 g/t Nb). Niobium is always accompanied by tantalum. The similar chemical properties of niobium and tantalum determine their joint presence in the same minerals and participation in common geological processes. Niobium can replace titanium in a number of titanium-containing minerals (sphene, orthite, perovskite, biotite). The form of occurrence of niobium in nature can be different: dispersed (in rock-forming and accessory minerals of igneous rocks) and mineral. In total, more than 100 minerals containing niobium are known. Of these, only a few are of industrial importance: columbite-tantalite (Fe, Mn)(Nb, Ta) 2 O 6, pyrochlore (Na, Ca, TR, U) 2 (Nb, Ta, Ti) 2 O 6 (OH, F ) (Nb 2 O 5 0 - 63%), loparite (Na, Ca, Ce)(Ti, Nb)O 3 ((Nb, Ta) 2 O 5 8 - 10%), euxenite, torolite, ilmenorutile are sometimes used, as well as minerals containing niobium as impurities (ilmenite, cassiterite, wolframite). In alkaline - ultramafic rocks, niobium is dispersed in perovskite-type minerals and in eudialyte. In exogenous processes, niobium and tantalum minerals, being stable, can accumulate in colluvial-alluvial placers (columbite placers), sometimes in bauxites of the weathering crust.
Columbite (Fe, Mn) (Nb, Ta) 2 O 6 was the first niobium mineral known to mankind. And this same mineral is the richest in element No. 41. Oxides of niobium and tantalum account for up to 80% of the weight of columbite. There is much less niobium in pyrochlore (Ca, Na) 2 (Nb, Ta, Ti) 2 O 6 (O, OH, F) and loparite (Na, Ce, Ca) 2 (Nb, Ti) 2 O 6. In total, more than 100 minerals are known that contain niobium. There are significant deposits of such minerals in different countries: the USA, Canada, Norway, Finland, but the African state of Nigeria has become the largest supplier of niobium concentrates to the world market. Russia has large reserves of loparite, they were found on the Kola Peninsula.
Obtaining niobiumNiobium ores are usually complex and metal-poor. Ore concentrates contain Nb 2 O 5: pyrochlore - at least 37%, loparite - 8%, columbite - 30-60%. Most of them are processed by aluminum or silicothermal reduction into ferroniobium (40-60% Nb) and ferrotantaloniobium. Metallic niobium is obtained from ore concentrates using complex technology in three stages:
1) opening the concentrate, 2) separating niobium and tantalum and obtaining them pure chemical compounds, 3) reduction and refining of metallic niobium and its alloys.
Metallic niobium can be obtained by reducing its compounds, for example niobium chloride or potassium fluorine-niobate, with high temperature:
K 2 NbF 7 + 5Na → Nb + 2KF + 5NaF.
But before reaching this essentially final stage of production, niobium ore goes through many stages of processing. The first of them is ore beneficiation, obtaining concentrates. The concentrate is fused with various fluxes: caustic soda or soda. The resulting alloy is leached. But it does not completely dissolve. The insoluble precipitate is niobium. True, it is still in the composition of hydroxide, not separated from its analogue in the subgroup - tantalum - and has not been purified from some impurities.
Niobium crystals and metal niobium cube
Until 1866, no industrially suitable method for separating tantalum and niobium was known. The first method of separating these extremely similar elements was proposed by Jean Charles Galissard de Marignac. The method is based on the different solubility of complex compounds of these metals and is called fluoride. Complex tantalum fluoride is insoluble in water, but the analogous niobium compound is soluble.
The fluoride method is complex and does not allow complete separation of niobium and tantalum. Therefore, these days it is almost never used. It was replaced by methods of selective extraction, ion exchange, rectification of halides, etc. These methods are used to obtain pentavalent niobium oxide and chloride.
After the separation of niobium and tantalum, the main operation occurs - reduction. Niobium pentoxide Nb 2 O 5 is reduced with aluminum, sodium, soot or niobium carbide obtained by reacting Nb 2 O 5 with carbon; Niobium pentachloride is reduced with sodium metal or sodium amalgam. This is how powdered niobium is obtained, which must then be turned into a monolith, made plastic, compact, and suitable for processing. Like other refractory metals, niobium monolith is produced by powder metallurgy methods, the essence of which is as follows.
The resulting metal powder is pressed under high pressure (1 t/cm2) into so-called rectangular or square section. In a vacuum at 2300°C, these bars are sintered and combined into rods, which are melted in vacuum arc furnaces, and the rods in these furnaces act as an electrode. This process is called consumable electrode smelting.
Single-crystal plastic niobium is produced by crucible-free zone electron beam melting. Its essence is that a powerful beam of electrons is directed at powdered niobium (pressing and sintering operations are excluded!), which melts the powder. Drops of metal flow onto the niobium ingot, which gradually grows and is removed from the working chamber.
As you can see, the path of niobium from ore to metal is in any case quite long, and the production methods are complex.
Physical properties of niobiumNiobium is a shiny silver-gray metal.
Elemental niobium is an extremely refractory (2468°C) and high-boiling (4927°C) metal, very resistant to many aggressive environments. All acids, with the exception of hydrofluoric acid, have no effect on it. Oxidizing acids “passivate” niobium, covering it with a protective oxide film (No. 205). But at high temperatures, the chemical activity of niobium increases. If at 150...200°C only a small surface layer of metal is oxidized, then at 900...1200°C the thickness of the oxide film increases significantly.
The crystal lattice of Niobium is body-centered cubic with parameter a = 3.294 Å.
Pure metal is ductile and can be rolled into thin sheets (up to a thickness of 0.01 mm) in a cold state without intermediate annealing.
One can note such properties of niobium as high melting and boiling points, lower electron work function compared to other refractory metals - tungsten and molybdenum. The last property characterizes the ability for electron emission (electron emission), which is used for the use of niobium in electric vacuum technology. Niobium also has a high transition temperature to the superconducting state.
Density 8.57 g/cm 3 (20 °C); t pl 2500 °C; boiling point 4927 °C; vapor pressure (in mm Hg; 1 mm Hg = 133.3 n/m 2) 1 10 -5 (2194 °C), 1 10 -4 (2355 °C), 6 10 -4 (at melting temperature), 1·10 -3 (2539 °C).
At ordinary temperatures, niobium is stable in air. The onset of oxidation (discoloration film) is observed when the metal is heated to 200 - 300°C. Above 500°, rapid oxidation occurs with the formation of Nb 2 O 5 oxide.
Thermal conductivity in W/(m·K) at 0°C and 600°C is 51.4 and 56.2, respectively, and the same in cal/(cm·sec·°C) is 0.125 and 0.156. Specific volumetric electrical resistance at 0°C 15.22·10 -8 ohm·m (15.22·10 -6 ohm·cm). The transition temperature to the superconducting state is 9.25 K. Niobium is paramagnetic. Electron work function 4.01 eV.
Pure Niobium is easily processed by pressure in the cold and retains satisfactory mechanical properties at high temperatures. Its tensile strength at 20 and 800 °C is respectively 342 and 312 Mn/m2, the same in kgf/mm2 34.2 and 31.2; relative elongation at 20 and 800 °C is 19.2 and 20.7%, respectively. The Brinell hardness of pure Niobium is 450, technical 750-1800 Mn/m2. Impurities of certain elements, especially hydrogen, nitrogen, carbon and oxygen, greatly impair the ductility and increase the hardness of Niobium.
Chemical properties of niobiumChemically, niobium is quite stable. When calcined in air, it is oxidized to Nb 2 O 5 . About 10 crystal modifications have been described for this oxide. At normal pressure, the β-form of Nb 2 O 5 is stable.
When Nb 2 O 5 is alloyed with various oxides, niobates are obtained: Ti 2 Nb 10 O 29, FeNb 49 O 124. Niobates can be considered as salts of hypothetical niobic acids. They are divided into metaniobates MNbO 3 , orthoniobates M 3 NbO 4 , pyroniobates M 4 Nb 2 O 7 or polyniobates M 2 O·nNb 2 O 5 (M is a singly charged cation, n = 2-12). Niobates of doubly and triply charged cations are known.
Niobates react with HF, melts of alkali metal hydrofluorides (KHF 2) and ammonium. Some niobates with a high M 2 O/Nb 2 O 5 ratio are hydrolyzed:
6Na 3 NbO 4 + 5H 2 O = Na 8 Nb 6 O 19 + 10NaOH.
Niobium forms NbO 2, NbO, a series of oxides intermediate between NbO 2.42 and NbO 2.50 and close in structure to the β-form of Nb 2 O 5.
With halogens, niobium forms pentahalides NbHal 5, tetrahalides NbHal 4 and phases NbHal 2.67 - NbHal 3+x, in which there are Nb 3 or Nb 2 groups. Niobium pentahalides are easily hydrolyzed by water.
A characteristic property of niobium is the ability to absorb gases - hydrogen, nitrogen and oxygen. Small impurities of these elements greatly affect the mechanical and electrical properties of the metal. At low temperatures, hydrogen is absorbed slowly; at a temperature of approximately 360°C, hydrogen is absorbed with maximum speed, and not only adsorption occurs, but also the NbH hydride is formed. Absorbed hydrogen makes the metal brittle, but when heated in a vacuum above 600°C, almost all of the hydrogen is released and the previous mechanical properties are restored.
Niobium absorbs nitrogen already at 600°C; at a higher temperature, NbN nitride is formed, which melts at 2300°C.
Carbon and carbon-containing gases (CH 4, CO) at high temperatures (1200 - 1400 ° C) interact with the metal to form solid and refractory carbide NbC (melts at 3500 ° C).
With boron and silicon, niobium forms a refractory and solid boride and silicide NbB 2 (melts at 2900°C).
In the presence of water vapor and oxygen, NbCl 5 and NbBr 5 form oxyhalides NbOCl 3 and NbOBr 3 - loose cotton wool-like substances.
When niobium and graphite interact, carbides Nb 2 C and NbC, solid heat-resistant compounds, are formed. In the Nb - N system there are several phases of variable composition and nitrides Nb 2 N and NbN. Niobium behaves in a similar way in systems with phosphorus and arsenic. When niobium interacts with sulfur, the following sulfides are obtained: NbS, NbS 2 and NbS 3. Double fluorides Nb and potassium (sodium) - K 2 - have been synthesized.
Niobium is resistant to the action of hydrochloric, sulfuric, nitric, phosphoric and organic acids of any concentration in the cold and at 100 - 150°C. The metal dissolves in hydrofluoric acid and especially intensively in a mixture of hydrofluoric and nitric acids.
Niobium is less stable in alkalis. Hot solutions of caustic alkalis noticeably corrode the metal; in molten alkalis and soda it quickly oxidizes to form the sodium salt of niobic acid.
From aqueous solutions It has not yet been possible to isolate niobium electrochemically. It is possible to electrochemically produce alloys containing niobium. Metallic niobium can be isolated by electrolysis of anhydrous salt melts.
The configuration of the outer electrons of the Nb atom is 4d 4 5s l. The most stable compounds are pentavalent Niobium, but compounds with oxidation states + 4, +3, +2 and +1 are also known, to the formation of which Niobium is more prone than tantalum. For example, in the niobium-oxygen system the following phases are established: Nb 2 O 5 oxide (melt 1512 °C, white), non-stoicheometric NbO 2.47 and NbO 2.42, NbO 2 oxide (melt 2080 °C, black) , NbO oxide (mp 1935 °C, gray color) and solid solution of oxygen in Niobium. NbO 2 - semiconductor; NbO, fused into an ingot, has a metallic luster and electrical conductivity of the metallic type, noticeably evaporates at 1700 °C, intensively at 2300-2350 °C, which is used for vacuum purification of Niobium from oxygen; Nb 2 O 5 is acidic in nature; niobic acids have not been isolated in the form of specific chemical compounds, but their salts, niobates, are known.
With hydrogen, Nb forms an interstitial solid solution (up to 10 at.% H) and a hydride of composition from NbH 0.7 to NbH. Solubility of hydrogen in Nb (in g/cm3) at 20 °C 104, at 500 °C 74.4, at 900 °C 4.0. The absorption of hydrogen is reversible: when heated, especially in a vacuum, hydrogen is released; this is used to purify Nb from hydrogen (which makes the metal brittle) and to hydrogenate compact Nb: the brittle hydride is crushed and dehydrogenated in a vacuum, obtaining pure Niobium powder for electrolytic capacitors. The solubility of nitrogen in Niobium is (% by weight) 0.005, 0.04 and 0.07, respectively, at 300, 1000 and 1500 °C. Niobium is refined from nitrogen by heating in a high vacuum above 1900 °C or by vacuum melting. Higher nitride NbN is light gray with a yellowish tint; the transition temperature to the superconducting state is 15.6 K. With carbon at 1800-2000°C, Nb forms 3 phases: α-phase - solid solution of carbon intercalation in Niobium, containing up to 2 at.% C at 2335°C; β-phase - Nb 2 C, δ-phase - NbC.
Chemical composition of niobium in ingots and bars
|
Impurities, %, no more |
|||||||||
|
Niobium ingots |
|||||||||
|
GOST 16099-70 |
|||||||||
|
Niobium in sticks |
|||||||||
|
GOST 16100-70 |
|||||||||
Now the properties and capabilities of niobium are appreciated by aviation, mechanical engineering, radio engineering, the chemical industry, and nuclear energy. All of them became consumers of niobium.
The unique property - the absence of noticeable interaction of niobium with uranium at temperatures up to 1100°C and, in addition, good thermal conductivity, a small effective absorption cross section of thermal neutrons - made niobium a serious competitor to metals recognized in the nuclear industry - aluminum, beryllium and zirconium. In addition, the artificial (induced) radioactivity of niobium is low. Therefore, it can be used to make containers for storing radioactive waste or installations for their use.
Niobium production in RussiaIN last years world niobium production is at the level of 24-29 thousand tons. It should be noted that the world niobium market is significantly monopolized by the Brazilian company CBMM, which accounts for about 85% of the world niobium production.
The main consumer of niobium-containing products (primarily ferroniobium) is Japan. This country annually imports over 4 thousand tons of ferroniobium from Brazil. Therefore, Japanese import prices for niobium-containing products can be taken with great confidence as being close to the world average.
In recent years, there has been a tendency for prices for ferroniobium to rise. This is due to its growing use for the production of low-alloy steels intended mainly for oil and gas pipelines. In general, it should be noted that over the past 15 years, global consumption of niobium has increased by an average of 4-5% annually.
It is with regret that we must admit that Russia is on the sidelines of the niobium market. In the early 90s, according to Giredmet specialists, the former USSR produced
About 2 thousand tons of niobium were consumed (in terms of niobium oxide). Currently, the consumption of niobium products by the Russian industry does not exceed only 100 - 200 tons.
It should be noted that in the former USSR significant niobium production capacities were created, scattered across different republics - Russia, Estonia, Kazakhstan. This traditional trait The industrial development of the USSR has now put Russia in a very difficult situation regarding many types of raw materials and metals.
The niobium market begins with the production of niobium-containing raw materials. Its main type in Russia was and remains loparite concentrate produced at the Lovozersky Mining and Processing Plant (now Sevredmet JSC, Murmansk region). Before the collapse of the USSR, the enterprise produced about 23 thousand tons of loparite concentrate (the content of niobium oxide is about 8.5%). Subsequently, concentrate production steadily decreased, in 1996-1998. The company stopped several times due to lack of sales. Currently, it is estimated that the production of loparite concentrate at the enterprise is at the level of 700 - 800 tons per month.
It should be noted that the enterprise is quite strictly tied to its only consumer - the Solikamsk magnesium plant. The fact is that loparite concentrate is a rather specific product that is obtained only in Russia. Its processing technology is quite complex due to the complex of rare metals it contains (niobium, tantalum, titanium). In addition, the concentrate is radioactive, which is largely why all attempts to enter the world market with this product ended in vain. It should also be noted that it is impossible to obtain ferroniobium from loparite concentrate.
In 2000, at the Sevredmet plant, the Rosredmet company launched an experimental installation for processing loparite concentrate to produce, among other metals, marketable niobium-containing products (niobium oxide).
The main markets for SMZ's niobium products are non-CIS countries: deliveries are made to the USA, Japan and European countries. The share of exports in total production is over 90%.
Significant niobium production capacities in the USSR were concentrated in Estonia - at the Sillamae Chemical and Metallurgical Production Association (Sillamae). Now the Estonian company is called Silmet. In Soviet times, the enterprise processed loparite concentrate from the Lovoozersk mining and processing plant; since 1992, its shipment was stopped. Currently, Silmet processes only a small volume of niobium hydroxide from the Solikamsk magnesium plant. The company currently receives most of its niobium-containing raw materials from Brazil and Nigeria. The management of the enterprise does not exclude the supply of loparite concentrate, however, Sevredmet is trying to pursue a policy of processing it locally, since exporting raw materials is less profitable than finished products.
Production of niobium semiconductors in Russia
The only Russian production of superconductors based on niobium-tin and niobium-titanium, created in 2009 at JSC ChMZ, is a closed cycle, starting from the production of source materials and components (niobium, niobium-titanium alloys, high-tin bronze) to finished superconductors strands, equipped with areas for measuring electrical characteristics and monitoring parameters of the entire technological stage. The creation of large-scale production of superconducting materials is being carried out under the scientific leadership of JSC VNIINM im. A.A. Bochvara".
In total, the Chepetsk Mechanical Plant will produce 170 tons of SPM for the ITER project based on niobium-titanium and niobium-tin by 2013.
Mankind has been familiar with the element that occupies the 41st cell in the periodic table for a long time. Its current name, niobium, is almost half a century younger. It so happened that element #41 was opened twice. The first time was in 1801, the English scientist Charles Hatchet examined a sample of the true mineral sent to the British Museum from America. From this mineral he isolated the oxide of a previously unknown element. Hatchet named the new element columbium, thereby noting its overseas origin. And the black mineral was called columbite.
A year later, the Swedish chemist Ekeberg isolated the oxide of another new element from columbite, called tantalum. The similarity between the compounds Columbia and tantalum was so great that for 40 years most chemists believed that tantalum and columbium were the same element.
In 1844, German chemist Heinrich Rose examined samples of columbite found in Bavaria. He again discovered oxides of two metals. One of them was the oxide of the already known tantalum. The oxides were similar, and, emphasizing their similarity, Rose named the element forming the second oxide niobium, after Niobe, the daughter of the mythological martyr Tantalus.
However, Rose, like Hatchet, was unable to obtain this element in a free state.
Metallic niobium was first obtained only in 1866 by the Swedish scientist Blomstrand during the reduction of niobium chloride with hydrogen. At the end of the 19th century. two more ways to obtain this element were found. First, Moissan obtained it in an electric furnace, reducing niobium oxide with carbon, and then Goldschmidt was able to reduce the same element with aluminum.
And element No. 41 continued to be called differently in different countries: in England and the USA - Columbia, in other countries - niobium. The International Union of Pure and Applied Chemistry (IUPAC) put an end to this controversy in 1950. It was decided to legitimize the name of the element “niobium” everywhere, and the name “columbite” was assigned to the main mineral of niobium. Its formula is (Fe, Mn) (Nb, Ta) 2 O 6.
Through the eyes of a chemist
Elemental niobium is an extremely refractory (2468°C) and high-boiling (4927°C) metal, very resistant to many aggressive environments. All acids, with the exception of hydrofluoric acid, have no effect on it. Oxidizing acids “passivate” niobium, covering it with a protective oxide film (No. 205). But at high temperatures, the chemical activity of niobium increases. If at 150...200°C only a small surface layer of metal is oxidized, then at 900...1200°C the thickness of the oxide film increases significantly.
Niobium reacts actively with many nonmetals. Halogens, nitrogen, hydrogen, carbon, and sulfur form compounds with it. In this case, niobium can exhibit different valences - from two to five. But the main valence of this element is 5+. Pentavalent niobium can be present in the salt both as a cation and as one of the anion elements, which indicates the amphoteric nature of element No. 41.
Salts of niobic acids are called niobates. They are obtained as a result of exchange reactions after fusing niobium pentoxide with soda:
Nb 2 O 5 + 3Na 2 CO 4 → 2Na 3 NbO 4 + 3CO 2.
The salts of several niobic acids have been studied quite well, primarily metaniobium HNbO 3 , as well as diniobates and pentaniobates (K 4 Nb 2 O 7 , K 7 Nb 5 O 16 · m H2O). And salts in which element No. 41 acts as a cation are usually obtained by direct interaction of simple substances, for example 2Nb + 5Cl 2 → 2NbCl 5.
Brightly colored needle-shaped crystals of niobium pentahalides (NbCl - yellow color, NbBr 5 - purple-red) are easily dissolved in organic solvents - chloroform, ether, alcohol. But when dissolved in water, these compounds completely decompose and hydrolyze to form niobates:
NbCl 5 + 4H 2 O → 5HCl + H 3 NbO 4.
Hydrolysis can be prevented by adding some strong acid to the aqueous solution. In such solutions, niobium pentahalides dissolve without hydrolyzing.
Niobium forms double salts and complex compounds, most easily fluoride. Fluoroniobates are the name of these double salts. They are obtained if fluoride of any metal is added to a solution of niobic and hydrofluoric acids.
The composition of the complex compound depends on the ratio of the components reacting in the solution. X-ray analysis of one of these compounds showed a structure corresponding to the formula K 2 NbF 7 . Niobium oxocompounds can also be formed, for example potassium oxofluorinepobate K 2 NbOF 5 H 2 O.
The chemical characteristics of the element are not exhausted, of course, by this information. Today, the most important compounds of element 41 are those with other metals.
Niobium and superconductivity
An amazing phenomenon of superconductivity, when when the temperature of a conductor decreases, an abrupt disappearance occurs in it. electrical resistance, was first observed by the Dutch physicist G. Kamerlingh-Onnes in 1911. The first superconductor was mercury, but not it, but niobium and some intermetallic compounds of niobium were destined to become the first technically important superconducting materials.
Two characteristics of superconductors are practically important: the value of the critical temperature at which the transition to the state of superconductivity occurs, and the critical magnetic field (Kamerlingh Onnes also observed the loss of superconductivity by a superconductor when exposed to a sufficiently strong magnetic field). As of January 1, 1975, the superconductor – the “record holder” for the critical temperature – was the intermetallic compound of niobium and germanium with the composition Nb 3 Ge. Its critical temperature is 23.2°K; This is higher than the boiling point of hydrogen. (Most known superconductors become superconductors only at the temperature of liquid helium).
The ability to transition to a state of superconductivity is also characteristic of niobium stannide Nb 3 Sn, alloys of niobium with aluminum and germanium or with titanium and zirconium. All these alloys and compounds are already used to make superconducting solenoids, as well as some other important technical devices.
Niobium – metal
Metallic niobium can be obtained by reducing its compounds, such as niobium chloride or potassium fluoroniobate, at high temperature:
K 2 NbF 7 + 5Na → Nb + 2KF + 5NaF.
But before reaching this essentially final stage of production, niobium ore goes through many stages of processing. The first of them is ore beneficiation, obtaining concentrates. The concentrate is fused with various fluxes: caustic soda or soda. The resulting alloy is leached. But it does not completely dissolve. The insoluble precipitate is niobium. True, it is still in the composition of hydroxide, not separated from its analogue in the subgroup - tantalum - and has not been purified from some impurities.
Until 1866, no industrially suitable method for separating tantalum and niobium was known. The first method of separating these extremely similar elements was proposed by Jean Charles Galissard de Marignac. The method is based on the different solubility of complex compounds of these metals and is called fluoride. Complex tantalum fluoride is insoluble in water, but the analogous niobium compound is soluble.
The fluoride method is complex and does not allow complete separation of niobium and tantalum. Therefore, these days it is almost never used. It was replaced by methods of selective extraction, ion exchange, rectification of halides, etc. These methods are used to obtain pentavalent niobium oxide and chloride.
After the separation of niobium and tantalum, the main operation occurs - reduction. Niobium pentoxide Nb 2 O 5 is reduced with aluminum, sodium, soot or niobium carbide obtained by reacting Nb 2 O 5 with carbon; Niobium pentachloride is reduced with sodium metal or sodium amalgam. This is how powdered niobium is obtained, which must then be turned into a monolith, made plastic, compact, and suitable for processing. Like other refractory metals, niobium monolith is produced by powder metallurgy methods, the essence of which is as follows.
The resulting metal powder is pressed under high pressure (1 t/cm2) into so-called bars of rectangular or square cross-section. In a vacuum at 2300°C, these bars are sintered and combined into rods, which are melted in vacuum arc furnaces, and the rods in these furnaces act as an electrode. This process is called consumable electrode smelting.
Single-crystal plastic niobium is produced by crucible-free zone electron beam melting. Its essence is that a powerful beam of electrons is directed at powdered niobium (pressing and sintering operations are excluded!), which melts the powder. Drops of metal flow onto the niobium ingot, which gradually grows and is removed from the working chamber.
As you can see, the path of niobium from ore to metal is in any case quite long, and the production methods are complex.
Niobium and metals
It is most logical to start the story about the use of niobium with metallurgy, since it was in metallurgy that he found the most wide application. Both in non-ferrous metallurgy and in ferrous metallurgy.
Niobium alloyed steel has good corrosion resistance. "So what? – another experienced reader will say. “Chrome also increases the corrosion resistance of steel, and it is much cheaper than niobium.” This reader is right and wrong at the same time. Wrong because I forgot about one thing.
Chromium-nickel steel, like any other, always contains carbon. But carbon combines with chromium to form carbide, which makes the steel more brittle. Niobium has a greater affinity for carbon than chromium. Therefore, when niobium is added to steel, niobium carbide is necessarily formed. Steel alloyed with niobium acquires high anti-corrosion properties and does not lose its ductility. The desired effect is achieved when only 200 g of niobium metal is added to a ton of steel. And niobium imparts high wear resistance to chrome-manganese steel.
Many non-ferrous metals are also alloyed with niobium. Thus, aluminum, which easily dissolves in alkalis, does not react with them if only 0.05% niobium is added to it. And copper, known for its softness, and many of its alloys seem to be hardened by niobium. It increases the strength of metals such as titanium, molybdenum, zirconium, and at the same time increases their heat resistance and heat resistance.
Now the properties and capabilities of niobium are appreciated by aviation, mechanical engineering, radio engineering, the chemical industry, and nuclear energy. All of them became consumers of niobium.
The unique property - the absence of noticeable interaction of niobium with uranium at temperatures up to 1100°C and, in addition, good thermal conductivity, a small effective absorption cross section of thermal neutrons - made niobium a serious competitor to metals recognized in the nuclear industry - aluminum, beryllium and zirconium. In addition, the artificial (induced) radioactivity of niobium is low. Therefore, it can be used to make containers for storing radioactive waste or installations for their use.
The chemical industry consumes relatively little niobium, but this can only be explained by its scarcity. Equipment for the production of high-purity acids is sometimes made from niobium-containing alloys and, less commonly, from sheet niobium. Niobium's ability to influence the rate of certain chemical reactions is used, for example, in the synthesis of alcohol from butadiene.
Rocket and space technology also became consumers of element No. 41. It is no secret that some quantities of this element are already rotating in near-Earth orbits. Some parts of rockets and on-board equipment of artificial Earth satellites are made from niobium-containing alloys and pure niobium.
Niobium Minerals
Columbite (Fe, Mn) (Nb, Ta) 2 O 6 was the first niobium mineral known to mankind. And this same mineral is the richest in element No. 41. Oxides of niobium and tantalum account for up to 80% of the weight of columbite. There is much less niobium in pyrochlore (Ca, Na) 2 (Nb, Ta, Ti) 2 O 6 (O, OH, F) and loparite (Na, Ce, Ca) 2 (Nb, Ti) 2 O 6. In total, more than 100 minerals are known that contain niobium. There are significant deposits of such minerals in different countries: the USA, Canada, Norway, Finland, but the African state of Nigeria has become the largest supplier of niobium concentrates to the world market. The USSR has large reserves of loparite; they were found on the Kola Peninsula.
Pink carbide
Niobium monocarbide NbC is a plastic substance with a characteristic pinkish luster. This important compound is formed quite easily when metallic niobium reacts with hydrocarbons. The combination of good malleability and high heat resistance with pleasant “external properties” made niobium monocarbide valuable material for the manufacture of coatings. A layer of this substance with a thickness of only 0.5 mm reliably protects many materials from corrosion at high temperatures, in particular graphite, which is virtually unprotected by other coatings. NbC is also used as a structural material in rocket science and turbine production.
Nerves cross-linked with niobium
The high corrosion resistance of niobium has made it possible to use it in medicine. Niobium threads do not cause irritation to living tissue and adhere well to it. Reconstructive surgery has successfully used such threads to stitch together torn tendons, blood vessels and even nerves.
Appearances are not deceiving
Niobium not only has a set of properties necessary for technology, but also looks quite beautiful. Jewelers tried to use this white shiny metal to make watch cases. Alloys of niobium with tungsten or rhenium sometimes replace noble metals: gold, platinum, iridium. The latter is especially important, since the niobium-rhenium alloy not only looks similar to the metallic iridium, but is almost as wear-resistant. This allowed some countries to do without expensive iridium in the production of soldering tips for fountain pen nibs.
Niobium and welding
At the end of the 20s of our century, electric and gas welding began to replace riveting and other methods of connecting components and parts. Welding has improved the quality of products, speeding up and reducing the cost of their assembly processes. Welding seemed especially promising for the installation of large installations operating in corrosive environments or under high pressure. But then it turned out that when welding of stainless steel the weld has much less strength than the steel itself. To improve the properties of the weld, various additives began to be introduced into the “stainless steel”. The best of them turned out to be niobium.
Underestimated figures
It is no coincidence that niobium is considered a rare element: it is indeed found infrequently and in small quantities, always in the form of minerals and never in the native state. An interesting detail: in various reference books Clarke (contents in earth's crust) niobium is different. This is mainly explained by the fact that in recent years new deposits of minerals containing niobium have been discovered in African countries. The Chemist's Handbook, vol. 1 (M., Chemistry, 1963) gives the following figures: 3.2 10 –5% (1939), 1 10 –3% (1949) and 2, 4·10 –3% (1954). But the latest figures are also underestimated: African deposits discovered in recent years are not included here. Nevertheless, it is estimated that approximately 1.5 million tons of metallic niobium can be smelted from minerals of already known deposits.
True, empirical, or gross formula: Nb
Molecular weight: 92.906
Niobium- an element of the secondary subgroup of the fifth group of the fifth period of the periodic system of chemical elements of D.I. Mendeleev, atomic number - 41. Denoted by the symbol Nb (lat. Niobium). The simple substance niobium (CAS number: 7440-03-1) is a shiny metal of silver-gray color with a cubic body-centered crystal lattice of the α-Fe type, a = 0.3294. For niobium, isotopes with mass numbers from 81 to 113 are known.
Story
Niobium was discovered in 1801 by the English scientist Charles Hatchet in a mineral sent back in 1734 to the British Museum from Massachusetts by John Winthrop (grandson of John Winthrop Jr.). The mineral was named columbite, and chemical element was named "Colombium" (Cb) in honor of the country from which the sample was obtained - Colombia (at that time a synonym for the United States).
In 1802, A. G. Ekeberg discovered tantalum, which coincided in almost all chemical properties with niobium, and therefore for a long time it was believed that they were the same element. It was only in 1844 that the German chemist Heinrich Rose established that it was a different element from tantalum and renamed it “niobium” in honor of Tantalus’ daughter Niobe, thereby emphasizing the similarities between the elements. However, in some countries (USA, England) the original name of the element, columbium, was retained for a long time, and only in 1950, by a decision of the International Union of Pure and Applied Chemistry (IUPAC), the element was finally given the name niobium.
Pure niobium was first obtained at the end of the 19th century by the French chemist Henri Moissan by electrothermal means, reducing niobium oxide with carbon in an electric furnace.
Being in nature
Clarke niobium - 18 g/t. Niobium content increases from ultramafic (0.2 g/t Nb) to felsic rocks (24 g/t Nb). Niobium is always accompanied by tantalum. The similar chemical properties of niobium and tantalum determine their joint occurrence in the same minerals and participation in common geological processes. Niobium can replace titanium in a number of titanium-containing minerals (sphene, orthite, perovskite, biotite). The form of occurrence of niobium in nature can be different: dispersed (in rock-forming and accessory minerals of igneous rocks) and mineral. In total, more than 100 minerals containing niobium are known. Of these, only a few are of industrial importance: columbite-tantalite ( , )(Nb, Ta) 2 O 6 , pyrochlore ( , Ca, TR, U) 2 (Nb, Ta, Ti) 2 O 6 (OH, F) (Nb 2 O 5 0 - 63%), loparite (, Ca, Ce)(Ti, Nb)O 3 ((Nb, Ta) 2 O 5 8 - 10%), euxenite, torolite, ilmenorutile, as well as minerals are sometimes used, containing niobium as impurities (ilmenite, cassiterite, wolframite). In alkaline - ultramafic rocks, niobium is dispersed in perovskite-type minerals and in eudialyte. In exogenous processes, niobium and tantalum minerals, being stable, can accumulate in deluvial-alluvial placers (columbite placers), sometimes in bauxites of the weathering crust. The concentration of niobium in sea water is 1·10−5 mg/l.
Place of Birth
Niobium deposits are located in the USA, Japan, Russia (Kola Peninsula), Brazil, and Canada.
| A country | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Australia | 160 | 230 | 290 | 230 | 200 | 200 | 200 | - | - | - | - | - |
| Brazil | 30 000 | 22 000 | 26 000 | 29 000 | 29 900 | 35 000 | 40 000 | 57 300 | 58 000 | 58 000 | 58 000 | 58 000 |
| Canada | 2290 | 3200 | 3410 | 3280 | 3400 | 3310 | 4167 | 3020 | 4380 | 4330 | 4420 | 4400 |
| Democratic Republic of the Congo | - | 50 | 50 | 13 | 52 | 25 | - | - | - | - | - | - |
| Mozambique | - | - | 5 | 34 | 130 | 34 | 29 | - | - | - | - | - |
| Nigeria | 35 | 30 | 30 | 190 | 170 | 40 | 35 | - | - | - | - | - |
| Rwanda | 28 | 120 | 76 | 22 | 63 | 63 | 80 | - | - | - | - | - |
| Total in the world | 32 600 | 25 600 | 29 900 | 32 800 | 34 000 | 38 700 | 44 500 | 60 400 | 62 900 | 62 900 | 62 900 | 63 000 |
Receipt
Niobium ores are usually complex and metal-poor. Ore concentrates contain Nb 2 O 5: pyrochlore - at least 37%, loparite - 8%, columbite - 30-60%. Most of them are processed by aluminum or silicothermal reduction into ferroniobium (40-60% Nb) and ferrotantaloniobium. Metallic niobium is obtained from ore concentrates using complex technology in three stages:
- opening the concentrate,
- separation of niobium and tantalum and obtaining their pure chemical compounds,
- recovery and refining of metallic niobium and its alloys.
Isotopes
Natural niobium consists of a single stable isotope - 93 Nb. All other artificially obtained isotopes of niobium with mass numbers from 81 to 113 are radioactive (a total of 32 of them are known). The longest-lived isotope is 92 Nb with a half-life of 34.7 million years. There are also 25 known metastable states of the nuclei of its different isotopes.
Chemical properties
Chemically, niobium is quite stable, but is inferior in this regard to tantalum. It is practically unaffected by hydrochloric, orthophosphoric, diluted sulfuric, and nitrogen. The metal dissolves in hydrofluoric acid HF, a mixture of HF and HNO 3, concentrated solutions of caustic acid, and also in concentrated sulfuric acid when heated above 150 °C. When calcined in air, it is oxidized to Nb 2 O 5 . About 10 crystal modifications have been described for this oxide. At normal pressure, the β-form of Nb 2 O 5 is stable.
- When Nb 2 O 5 is alloyed with various oxides, niobates are obtained: Ti 2 Nb 10 O 29, FeNb 49 O 124. Niobates can be considered as salts of hypothetical niobic acids. They are divided into metaniobates MNbO 3 , orthoniobates M 3 NbO 4 , pyroniobates M 4 Nb 2 O 7 or polyniobates M 2 O·nNb 2 O 5 (M is a singly charged cation, n = 2-12). Niobates of doubly and triply charged cations are known.
- Niobates react with HF, melts of alkali metal hydrofluorides (KHF 2) and ammonium. Some niobates with a high M 2 O/Nb 2 O 5 ratio are hydrolyzed: 6Na 3 NbO 4 + 5H 2 O = Na 8 Nb 6 O 19 + 10NaOH.
- Niobium forms NbO 2 , NbO, a series of oxides intermediate between NbO 2 , 42 and NbO 2 , 50 and similar in structure to the β-form of Nb 2 O 5 .
- With halogens, niobium forms pentahalides NbHa 15, tetrahalides NbHa 14 and phases NbHa 12, 67 - NbHa 13 +x, in which there are Nb 3 or Nb 2 groups. Niobium pentahalides are easily hydrolyzed by water.
- In the presence of water vapor and oxygen, NbC 15 and NbBr 5 form oxyhalides NbOC 13 and NbOBr 3 - loose cotton wool-like substances.
- When niobium and graphite interact, carbides Nb 2 C and NbC, solid heat-resistant compounds, are formed. In the Nb - N system there are several phases of variable composition and nitrides Nb 2 N and NbN. Niobium behaves in a similar way in systems with phosphorus and arsenic. When niobium interacts with sulfur, the following sulfides are obtained: NbS, NbS 2 and NbS 3. Double fluorides Nb and potassium (sodium) - K 2 - have been synthesized.
- It has not yet been possible to isolate niobium electrochemically from aqueous solutions. It is possible to electrochemically produce alloys containing niobium. Metallic niobium can be isolated by electrolysis of anhydrous salt melts.
Application
The use and production of niobium are rapidly increasing, which is due to a combination of such properties as refractoriness, a small cross section for thermal neutron capture, the ability to form heat-resistant, superconducting and other alloys, corrosion resistance, getter properties, low electron work function, good workability under cold pressure and weldability. The main areas of application of niobium are: rocketry, aviation and space technology, radio engineering, electronics, chemical engineering, nuclear energy.
Applications of metallic niobium
- Aircraft parts are made from pure niobium or its alloys; claddings for uranium and plutonium fuel elements; containers and pipes for liquid metals; parts of electrolytic capacitors; “hot” fittings for electronic (for radar installations) and powerful generator lamps (anodes, cathodes, grids, etc.); corrosion-resistant equipment in the chemical industry.
- Other non-ferrous metals, including uranium, are alloyed with niobium. For example, aluminum, if only 0.05% niobium is added to it, does not react at all with alkalis, although under normal conditions it dissolves in them. An alloy of niobium with 20% copper has high electrical conductivity and is twice as hard and durable as pure copper.
- Niobium is used in cryotrons - superconducting elements computers. Niobium is also known for its use in the accelerating structures of the Large Hadron Collider.
- Niobium and tantalum are used to produce electrolytic capacitors with high specific capacitance. Tantalum allows the production of higher quality capacitors than the metal niobium. However, capacitors based on niobium oxide are the most reliable and resistant to fire.
Intermetallic compounds and alloys of niobium
- Nb 3 Sn stannide (triniobium stannide, also known as niobium-tin alloy), Nb 3 Ge germanide (germanium triniobium), NbN nitride and niobium alloys with titanium (niobium-titanium) and zirconium are used to make superconducting solenoids. Thus, the windings of the superconducting magnets of the Large Hadron Collider are made of 1200 tons of niobium-titanium alloy cable.
- Niobium and alloys with tantalum in many cases replace tantalum, which gives a great economic effect (niobium is cheaper and almost twice as light as tantalum).
- Ferroniobium is introduced (up to 0.6% niobium) into stainless chromium-nickel steels to prevent their intergranular corrosion (including that which would otherwise begin after welding the stainless steel) and destruction, and in other types of steel to improve their properties.
- Niobium is used in the minting of collectible coins. Thus, the Bank of Latvia claims that niobium is used along with silver in 1 lat collection coins.
Application of niobium compounds
- Nb 2 O 5 - catalyst in the chemical industry;
- in the production of refractories, cermets, special glasses, nitride, carbide, niobates.
- Niobium carbide (mp 3480 °C) alloyed with zirconium carbide and uranium-235 carbide is the most important structural material for fuel rods of solid-phase nuclear jet engines.
- Niobium nitride NbN is used to produce thin and ultrathin superconducting films with a critical temperature of 5 to 10 K with a narrow transition of the order of 0.1 K.
First generation superconducting materials
- One of the actively used superconductors (superconducting transition temperature 9.25 K). Niobium compounds have a superconducting transition temperature of up to 23.2 K (Nb 3 Ge).
- The most commonly used industrial superconductors are NbTi and Nb 3 Sn.
- Niobium is also used in magnetic alloys.
- Used as an alloying additive.
- Niobium nitride is used to produce superconducting bolometers.
- The exceptional resistance of niobium and its alloys with tantalum in superheated cesium-133 vapor makes it one of the most preferred and cheapest construction materials for high power thermionic generators.
Biological role
There is currently no information about the biological role of niobium.
Physiological action
Niobium metal dust is flammable and irritates the eyes and skin. Some niobium compounds are very toxic. MPC of niobium in water is 0.01 mg/l. When ingested, it causes irritation of internal organs and subsequent paralysis of the limbs.
