Chemical properties of niobium. Physical and chemical properties of Niobium Metal niobium original name

A chemical element named after the ancient Niobe, a woman who dared to laugh at the gods and paid for it with the death of her children. Niobium represents humanity's transition from industrial to digital production; from steam locomotives to rocket launchers; from coal-fired power plants to nuclear power. The global price of niobium per gram is quite high, as is the demand for it. Most of the latest scientific achievements are closely related to the use of this metal.

Niobium price per gram

Since the main uses of niobium are related to nuclear and space programs, it is classified as a strategic material. Recycling is much more financially profitable than the development and extraction of new ores, which makes niobium in demand in the secondary metal market.

The price for it is determined by several factors:

Metal purity. The more foreign impurities, the lower the price.
Delivery form.
Scope of delivery. Directly proportional to metal prices.
Location of the scrap collection point. Each region has a different need for niobium and, accordingly, its price.
Presence of rare metals. Alloys containing elements such as tantalum, tungsten, molybdenum are higher in price.
The meaning of quotes on world exchanges. These values are the basis for setting prices.

Indicative overview of prices in Moscow:

Niobium NB-2. The price varies between 420-450 rubles. per kg.
Niobium shavings. 500-510 rub. per kg.
Niobium stack NBSh00. Differs in increased prices due to the insignificant content of impurities. 490-500 rub. per kg.
Niobium rod NBSh-0. 450-460 rub. per kg.
Niobium NB-1 in the form of a rod. The price is 450-480 rubles. per kg.

Despite the high cost, the demand for niobium in the world continues to grow. This happens due to its enormous potential for use and the shortage of metal. There are only 18 grams of niobium per 10 tons of soil.

The scientific community continues to work to find and develop a substitute for such an expensive material. But so far I have not received a concrete result in this. This means that the price of niobium is not expected to fall in the near future.

To regulate prices and increase the speed of turnover, the following categories are provided for niobium products:

Niobium ingots. Their size and weight are standardized by GOST 16099-70. Depending on the purity of the metal, they are divided into 3 grades: niobium NB-1, niobium NB-2 and, accordingly, niobium NB-3.
Niobium staff. It has a higher percentage of foreign impurities.
Niobium foil. Manufactured in thicknesses up to 0.01 mm.
Niobium rod. According to TU 48-4-241-73 it is supplied in the grades NbP1 and NbP2.

Physical properties of niobium

The metal is gray with a white tint. Belongs to the group of refractory alloys. The melting point is 2500 ºС. Boiling point 4927 ºС. Differs in the increased value of heat resistance. Does not lose its properties at operating temperatures above 900 ºС.

Mechanical characteristics are also at a high level. The density is 8570 kg/m3, with the same indicator for steel being 7850 kg/m3. Resistant to operation under both dynamic and cyclic loads. Tensile strength - 34.2 kg/mm2. Has high plasticity. The relative elongation coefficient varies between 19-21%, which makes it possible to obtain rolled niobium sheets up to 0.1 mm thick from it.

Hardness is related to the purity of the metal from harmful impurities and increases with their composition. Pure niobium has a Brinell hardness rating of 450.

Niobium lends itself well to pressure treatment at temperatures below -30 ºС and is difficult to cut.

Thermal conductivity does not change significantly with large temperature fluctuations. For example, at 20 ºС it is 51.4 W/(m K), and at 620 ºС it increases by only 4 units. Niobium competes in electrical conductivity with elements such as copper and aluminum. Electrical resistance - 153.2 nOhm m. Belongs to the category of superconducting materials. The temperature at which the alloy enters the superconductor mode is 9.171 K.

Extremely resistant to acidic environments. Such common acids as sulfuric, hydrochloric, orthophosphoric, nitric do not affect its chemical structure in any way.

At temperatures above 250 ºС, niobium begins to be actively oxidized by oxygen, and also enter into chemical reactions with hydrogen and nitrogen molecules. These processes increase the fragility of the metal, thereby reducing its strength.

Does not apply to allergenic materials. Introduced into the human body, it does not cause a rejection reaction by the body.
It is a metal of the first group of weldability. The welds are tight and do not require preparatory operations. Resistant to cracking.

Types of alloys

Based on the value of mechanical properties at elevated temperatures, niobium alloys are divided into:

Low strength. They operate within the range of 1100-1150 ºС. They have a simple set of alloying elements. This mainly includes zirconium, titanium, tantalum, vanadium, hafnium. Strength is 18-24 kg/mm2. After passing the critical temperature threshold, it drops sharply and becomes similar to pure niobium. The main advantage is high plastic properties at temperatures up to 30 ºС and good workability under pressure.
Medium strength. Their operating temperature is in the range of 1200-1250 ºС. In addition to the above alloying elements, they contain impurities of tungsten, molybdenum, and tantalum. The main purpose of these additives is to preserve mechanical properties with increasing temperature. They have moderate ductility and can be easily processed under pressure. A striking example of an alloy is niobium 5VMC.
High strength alloys. Used at temperatures up to 1300 ºС. With short-term exposure up to 1500 ºС. They differ in their chemical composition of higher complexity. 25% consist of additives, the main share of which is tungsten and molybdenum. Some types of these alloys are characterized by a high carbon content, which has a positive effect on their heat resistance. The main disadvantage of high-strength niobium is low ductility, which makes processing difficult. And, accordingly, obtaining industrial semi-finished products.

It should be noted that the categories listed above are of a conditional nature and give only a general idea of the method of using a particular alloy.

Also worth mentioning are compounds such as ferroniobium and niobium oxide.

Ferroniobium is a compound of niobium with iron, where the content of the latter is at the level of 50%. In addition to the main elements, it includes hundredths of titanium, sulfur, phosphorus, silicon, and carbon. The exact percentage of elements is standardized by GOST 16773-2003.

Niobium pentaxide is a white crystalline powder. Not susceptible to dissolution in acid and water. It is produced by burning niobium in an oxygen environment. Completely amorphous. Melting point 1500 ºС.

Applications of niobium

All of the above properties make the metal extremely popular in various industries. Among the many ways to use it, the following positions are distinguished:

Used in metallurgy as an alloying element. Moreover, both ferrous and non-ferrous alloys are alloyed with niobium. For example, adding just 0.02% of it to stainless steel 12Х18Н10Т increases its wear resistance by 50%. Aluminum improved with niobium (0.04%) becomes completely impervious to alkali. Niobium acts on copper as a hardening agent on steel, increasing its mechanical properties by an order of magnitude. Note that even uranium is doped with niobium.
Niobium pentoxide is the main component in the manufacture of highly refractory ceramics. It has also found application in the defense industry: armored glass of military equipment, optics with a large refractive angle, etc.
Ferroniobium is used to alloy steels. Its main task is to increase corrosion resistance.
In electrical engineering they are used for the manufacture of capacitors and current rectifiers. Such capacitors are characterized by increased capacitance and insulation resistance, and small sizes.
Compounds of silicon and germanium with niobium are widely used in the field of electronics. Superconducting solenoids and elements of current generators are made from them.

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. Swedish scientist Blomstrand during the reduction of niobium chloride with hydrogen. At the end of the 19th century. were; Two more ways to obtain this element have been found. Moissan first produced it in an electric furnace by reducing niobium oxide with carbon, and then Goldschmidt was able to reduce the same element with aluminum.

And they continued to call element No. 41 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 the controversy in 1950. It was decided to universally legalize the name of the element “niobium,” and the name “columbite” was assigned to the main mineral of niobium. Its formula is (Fe, Mn) (Nb,

Elemental niobium- 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 (Nb 2 O 5). 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 valency 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 3 → 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 -rnH 2 O). 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 5 - yellow, NbBr 5 - purple-red) easily dissolve 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 oxo compounds can also be formed, for example potassium oxofluoroniobate 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 of element number 41's compounds are its compounds with other metals.

Niobium and superconductivity

The amazing phenomenon of superconductivity, when when the temperature of a conductor decreases, an abrupt disappearance of electrical resistance occurs in it, was first observed by the Dutch physicist G. Kamerlingh-Onnes in 1911. The first superconductor turned out to be, 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).

More than 2000 superconducting metals, materials and compounds are now known, but the vast majority of them have not come into use and apparently will never come into use in technology, either due to the extremely low values of the critical parameters mentioned above, or due to unacceptable technological characteristics. Among superconductors of practical importance, niobium-titanium alloys are especially popular. Most of the superconducting magnets working today are made from them. They are plastic and can be used to make technical devices and conductors of complex shapes.

As a material for strip superconductors, the alloy of niobium with tin Nb 3 Sn, niobium stannide, discovered back in 1954, is valuable. The superconducting current-carrying element - a bus with 150,000 cores - is made from niobium stannide in our country. They intend to use similar multi-core superconducting conductors in the new Tokomak-15 thermonuclear installations.

Another intermetallic compound of niobium, Nb 3 Ge, is of practical interest. A thin film of this composition has a record high critical temperature - 24.3 K. However, cast Nb 3 Ge has a critical temperature of only 6 K, and the technology for preparing superconducting elements from this material is quite complex.

Ternary alloys have rather high critical temperature values: niobium - germanium - aluminum, as well as some intermetallic compounds of vanadium. And yet, it is with niobium and its compounds that the greatest hopes of superconductor specialists are pinned.

Niobium metal

Niobium metal can be prepared 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.

It is most logical to start the story about the use of niobium with metallurgy, since it is in metallurgy that it has found the widest 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 chromium-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.

NIOBIA 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. Niobium and tantalum oxides 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 doparite (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.

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” has made niobium monocarbide a valuable material for the manufacture of coatings. Layers of this substance with a thickness of only 0.5 mm reliably protect 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 STITCHED 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 successfully uses 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 stainless steel, the weld seam has much less strength than the steel itself. To improve the properties of the seam, various additives began to be introduced into the “stainless steel”. The best of them turned out to be niobium.

LOW 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 different reference publications the clarke (content in the earth’s crust) of niobium is different. This is mainly explained by the fact that in recent years new deposits of minerals containing niobium have been found in African countries. The Chemist's Handbook, vol. I (M., Chemistry, 1963) gives the following figures: 3.2-10 -5%, 1*10 -3% and 2.4*10 -3%. 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.

In ancient Greek mythology * a. niobium; n. Niob, Niobium; f. niobium; And. niobio), is a chemical element of group V of the periodic system of Mendeleev, atomic number 41, atomic mass 92.9064. It has one natural isotope 93 Nb.

Niobium oxide was first isolated by the English chemist C. Hatchet in 1801 from columbite. Metallic niobium was obtained in 1866 by the Swedish scientist K. V. Blomstrand.

Niobium properties

Niobium is a steel-colored metal, has a body-centered cubic lattice with a = 0.3294 nm; density 8570 kg/m3; melting temperature 2500°С, boiling temperature 4927°С; heat capacity (298 K) 24.6 J/(mol.K); thermal conductivity (273 K) 51.4 W/(m.K); temperature coefficient of linear expansion (63-1103 K) 7.9.10 -6 K -1 ; electrical resistivity (293 K) 16.10 -8 Ohm.m; thermal coefficient of electrical resistance (273 K) 3.95.10 -3 K -1. The transition temperature to the superconducting state is 9.46 K.

Oxidation state +5, less often from +1 to +4. Its chemical properties are close to tantalum, extremely resistant to cold and, with slight heating, to the action of many aggressive environments, incl. and acids. Niobium is dissolved only by hydrofluoric acid, its mixture with nitric acid and alkali. Amphoteric. When interacting with halogens, it forms niobium halides. When Nb 2 O 5 is fused with soda, salts of niobic acids are obtained - niobates, although the acids themselves do not exist in a free state. Niobium can form double salts and complex compounds. Non-toxic.

Receipt and use

To obtain niobium, niobium concentrate is fused with caustic soda or soda and the resulting alloy is leached. The Nb and Ta contained in the undissolved precipitate are separated, and niobium oxide is reduced separately from tantalum oxide. Compact niobium is produced by powder metallurgy, electric arc, vacuum and electron beam melting.

Niobium is one of the main components in alloying heat-resistant steels and alloys. Niobium and its alloys are used as structural materials for parts of jet engines, rockets, gas turbines, chemical equipment, electronic devices, electrical capacitors, and superconducting devices. Niobates are widely used as ferroelectrics, piezoelectrics, and laser materials.

Niobium(lat. Niobium), Nb, chemical element of group V of the periodic system of Mendeleev; atomic number 41, atomic mass 92.9064; metal gray-steel color. The element has one natural isotope, 93 Nb.

Niobium was discovered in 1801 by the English scientist C. Hatchet (1765-1847) in a mineral found in Columbia, and he named it “Columbium”. In 1844, the German chemist G. Roes (1795-1864) discovered a “new” element and named it “niobium” in honor of Tantalus’ daughter Niobe, which emphasized the similarities between Niobium and tantalum. Niobium was later found to be the same element as Columbia.

Distribution of Niobium in nature. The average content of niobium in the earth's crust (clarke) is 2·10 -3% by mass. Only in alkaline igneous rocks - nifeline syenites and others, the Niobium content is increased to 10 -2 - 10 -1%. In these rocks and associated pegmatites, carbonatites, as well as in granitic pegmatites, 23 Niobium minerals and about 130 other minerals containing increased amounts of Niobium were discovered. These are mainly complex and simple oxides. In minerals, Nb is associated with rare earth elements and with Ta, Ti, Ca, Na, Th, Fe, Ba (tantalum-niobates, titanates and others). Of the 6 industrial minerals, pyrochlore and columbite are the most important. Industrial deposits of Niobium are associated with massifs of alkaline rocks (for example, on the Kola Peninsula), their weathering crusts, as well as with granitic pegmatites. Placers of tantalonium bates are also important.

In the biosphere, the geochemistry of niobium is poorly studied. It has been established that in areas of alkaline rocks enriched in Niobium, it migrates in the form of compounds with organic and other complexes. Niobium minerals are known, formed during the weathering of alkaline rocks (murmanite, gerasimovskite and others). Seawater contains only about 1·10 -9% Niobium by mass.

Physical properties of Niobium. The crystal lattice of Niobium is body-centered cubic with parameter a = 3.294 Å. 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). 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 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/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 Niobium. In terms of chemical properties, Niobium is close to tantalum. Both of them are extremely resistant (tantalum more than niobium) in the cold and with slight heating to the action of many aggressive environments. Compact Niobium oxidizes noticeably in air only above 200 °C. Niobium is affected by: chlorine above 200 °C, hydrogen at 250 °C (intensively at 360 °C), nitrogen at 400 °C. Liquid Na, K and their alloys, Li, Bi, Pb, Hg, Sn, which are used as liquid metal coolants in nuclear reactors, have practically no effect on Niobium, purified from oxygen impurities.

Niobium is resistant to many acids and salt solutions. It is not affected by aqua regia, hydrochloric and sulfuric acids at 20 °C, nitric, phosphoric, perchloric acids, and aqueous solutions of ammonia. Hydrofluoric acid, its mixture with nitric acid and alkali dissolve niobium. In acidic electrolytes, an anodic oxide film with high dielectric characteristics is formed on Niobium, which makes it possible to use Niobium and its alloys with Ta instead of scarce pure Ta for the manufacture of miniature high-capacity electrolytic capacitors with low leakage currents.

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 deep 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. With halogens, Niobium produces halides, oxyhalides and complex salts. Of these, the most important are pentafluoride NbF 5, pentachloride NbCl 5, oxytrichloride NbOCl 3, potassium fluoroniobate K 2 NbF 7 and potassium oxyfluoroniobate K 2 NbOF 7 H 2 O. A small difference in the vapor pressure of NbCl 5 and TaCl 5 is used for their very complete separation and purification by rectification method.

Obtaining Niobium. Nb ores are usually complex and low in Nb, although their reserves far exceed those of Ta ores. Ore concentrates contain Nb 2 O 5: pyrochlore - at least 37%, loparite - 8%, columbite - 30-60%. Most of them are processed by alumino- or silicothermal reduction into ferroniobium (40-60% Nb) and ferrotantaloniobium. Metallic Nb is obtained from ore concentrates using complex technology in three stages: 1) opening of the concentrate, 2) separation of Nb and Ta and obtaining their pure chemical compounds, 3) reduction and refining of metallic Niobium and its alloys. The main industrial methods for the production of Nb and alloys are aluminothermic, sodium-thermal, carbothermic: from a mixture of Nb 2 O 5 and soot, carbide is first obtained at 1800 ° C in a hydrogen atmosphere, then from a mixture of carbide and oxide (V) at 1800-1900 ° C in a vacuum - metal; to obtain Niobium alloys, oxides of alloying metals are added to this mixture; according to another option, niobium is reduced at high temperature in a vacuum directly from Nb 2 O 5 with soot. Niobium is reduced by the sodium thermal method from K 2 NbF 7 with sodium, and by the aluminothermic method by aluminum from Nb 2 O 5 . Compact metal (alloy) is produced using powder metallurgy methods, sintering rods pressed from powders in a vacuum at 2300 °C, or electron beam and vacuum arc melting; high purity Nb single crystals - crucibleless electron beam zone melting.

Application of Niobium. The use and production of Niobium are rapidly increasing, which is due to a combination of such properties as refractoriness, small cross section for thermal neutron capture (1.15 b), the ability to form heat-resistant, superconducting and other alloys, corrosion resistance, getter properties, low electron work function, good cold workability and weldability. The main areas of application of Niobium are: rocketry, aviation and space technology, radio engineering, electronics, chemical engineering, nuclear energy. 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 electrical capacitors; "hot" fittings for electronic (for radar installations) and powerful generator lamps (anodes, cathodes, grids and others); corrosion-resistant equipment in the chemical industry. Other non-ferrous metals, including uranium, are alloyed with niobium. Niobium is used in cryotrons - superconducting elements of computers, and Nb 3 Sn stannide and Nb alloys with Ti and Zr - for the manufacture of superconducting solenoids. Nb and alloys with Ta in many cases replace Ta, which gives a great economic effect (Nb is cheaper and almost twice as light as Ta). Ferroniobium is introduced into stainless chromium-nickel steels to prevent their intergranular corrosion and destruction and into other types of steels to improve their properties. Niobium compounds are also used: Nb 2 O 5 (catalyst in the chemical industry; in the production of refractories, cermets, special glasses), nitride, carbide, niobates.