Niobium. Properties of niobium. Application of niobium. Physical and chemical properties of tantalum and niobium

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 production to digital; 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

Metal 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:

  1. 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.
  2. 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.
  3. High strength alloys. Used at temperatures up to 1300 ºС. With short-term exposure up to 1500 ºС. Are different chemical composition 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 only give general idea about 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 - crystalline powder white. 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 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.

    • True, empirical, or gross formula: Nb

    Molecular weight: 92.906

    Niobium- element of a secondary subgroup of the fifth group of the fifth period periodic table 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 the chemical element was named columbium (Cb) after 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 Theoretical and applied chemistry(IUPAC), the element was finally given the name niobium.
    Pure niobium was first obtained in late XIX 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. Close Chemical properties 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 ( , )(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. Niobium concentration in sea ​​water 1·10−5 mg/l.

    Place of Birth

    Niobium deposits are located in the USA, Japan, Russia ( Kola Peninsula), Brazil, 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.
    The main industrial methods for the production of niobium and its 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 pentoxide 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 soot. Niobium is reduced by the sodium-thermal method with sodium from K 2 NbF 7 , and by the aluminothermic method with 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 niobium single crystals - crucibleless electron beam zone melting.

    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, hydrofluoride melts alkali metals(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. Electrochemical production of alloys containing niobium is possible. 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

    • Parts are made from pure niobium or its alloys aircraft; claddings for uranium and plutonium fuel elements; containers and pipes for liquid metals; details 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 of 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.
    Austria issues bimetallic collector's coins of 25 euros from silver and niobium

    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 structural materials for high-power thermionic generators.

    Biological role

    ABOUT biological role There is currently no information about 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. Causes irritation if ingested internal organs and subsequent paralysis of the limbs.

    Physical properties of 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 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 = 3.294A.

    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 elongation at 20 and 800 °C is 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 of 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 a clean 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 invisible 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 sulfuric acid solution. 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 alternating current is passed through such a device, only one phase passes through, 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 niobium

    It so happened that element No. 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 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 nature

    Clark 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 niobium

    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:

    1) opening of the concentrate, 2) separation of niobium and tantalum and obtaining their pure chemical compounds, 3) reduction and refining of metallic niobium and its alloys.

    Metallic niobium can be obtained by reducing its compounds, such as niobium chloride or potassium fluorine-niobate, 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.


    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 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 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 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

    Chemically, 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.

    It has not yet been possible to isolate niobium electrochemically from aqueous solutions. Electrochemical production of alloys containing niobium is possible. 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 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.

    Chemical composition of niobium in ingots and bars

    Impurities, %, no more

    Niobium ingots

    GOST 16099-70

    Niobium in sticks

    GOST 16100-70
    Applications of niobium

    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 Russia

    IN last years world production niobium 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 SVMM, 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 feature of the development of industry in 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 OJSC ChMP, 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.

    It’s worth starting with the fact that niobium is inextricably linked with a substance such as tantalum. This is even despite the fact that these materials were not discovered at the same time.

    What is niobium

    What is known today about such a substance as niobium? He is chemical element, which is located in group 5 of the periodic table, having an atomic number of 41, as well as an atomic mass of 92.9. Like many other metals, this substance is characterized by a steel-gray luster.

    One of the most important physical parameters This is its refractoriness. It is thanks to this characteristic that the use of niobium has become widespread in many industries. The melting point of this substance is 2468 degrees Celsius, and the boiling point is 4927 degrees Celsius.

    The chemical properties of this substance are also at a high level. It is characterized by a high level of resistance to negative temperatures, as well as to most aggressive environments.

    Production

    It is worth saying that the presence of ore that contains the element Nb (niobium) is much greater than that containing tantalum, but the problem lies in the scarcity of the element itself in this ore.

    Most often, in order to obtain this element, a thermal reduction process is carried out, in which aluminum or silicon is involved. As a result of this operation, ferroniobium and ferrotantaloniobium compounds are obtained. It is worth noting that the metallic version of this substance is obtained from the same ore, but more complex technology is used. Niobium crucibles and other resulting materials are characterized by very high performance characteristics.

    Methods for obtaining niobium

    Currently, some of the most developed directions for obtaining this material are aluminothermic, sodium-thermic and carbothermic. The difference between these types also lies in the precursors that are used to reduce niobium. Let's say K2NbF7 is used in the sodium thermal method. But, for example, in the aluminothermic method, niobium pentoxide is used.

    If we talk about the carbothermic method of production, then this technology involves mixing Nb with soot. This process must take place in a high temperature and hydrogen environment. As a result of this operation, niobium carbide will be obtained. The second stage is that the hydrogen environment is replaced by a vacuum, and the temperature is maintained. At this point, its oxide is added to the niobium carbide and the metal itself is obtained.

    It is important to note that among the forms of metal produced, niobium in ingots is quite common. This product is intended for the production of metal-based alloys, as well as various other semi-finished products.

    A stack of this material can also be produced, which is divided into several categories depending on the purity of the substance. The least amount of impurities is contained in the beaker labeled NBS-00. The NBSh-0 class is characterized by a higher presence of elements such as iron, titanium and tantalum silicon. The category that has the highest impurity indicator is NBS-1. It can be added that niobium in ingots does not have such a classification.

    Alternative production methods

    TO alternative ways can be attributed to crucibleless electron beam zone melting. This process makes it possible to obtain Nb single crystals. Niobium crucibles are produced using this method. It belongs to powder metallurgy. It is used to first obtain an alloy of this material, and then its pure sample. The presence of this method is the reason why advertisements for the purchase of niobium are quite common. This method allows you to use not the ore itself, which is quite difficult to extract, or a concentrate from it, but secondary raw materials to obtain pure metal.

    To one more alternative method production can include rolled niobium. It is worth noting that most different companies prefer to purchase rods, wire or sheet metal.

    Rolled and foil

    Foil made from this material is a fairly common semi-finished product. He is the most thin sheet rental of this substance. Used for the production of certain products and parts. Niobium foil is obtained from pure raw materials by cold rolling of Nb ingots. The resulting products are characterized by such indicators as high resistance to corrosion, aggressive environments, and high temperatures. Rolled niobium and its ingots also provide such characteristics as wear resistance, high ductility, and good machinability.

    Products obtained in this way are most often used in such fields as aircraft manufacturing, rocket science, medicine (surgery), radio engineering, electrical engineering, nuclear energy, and nuclear energy. Niobium foil is packaged in coils and stored in a dry place, protected from moisture, as well as in a place protected from mechanical influence from outside.

    Applications in electrodes and alloys

    The use of niobium is very widespread. It can be used, like chromium and nickel, as a material that is part of the iron alloy used to make electrodes. Due to the fact that niobium, like tantalum, is capable of forming superhard carbide, it is often used to produce superhard alloys. It can be added that they are currently trying to use this material to improve the properties of alloys obtained on the basis

    Since niobium is a raw material capable of creating carbide elements, it, like tantalum, is used as an alloying mixture in the production of steel. It is worth noting that for a long time the use of niobium as an impurity in tantalum was considered a negative effect. However, today the opinion has changed. It was found that Nb can act as a substitute for tantalum, and with great success, since due to its lower atomic mass you can use a smaller amount of the substance, maintaining all the old capabilities and effects of the product.

    Applications in electrical engineering

    It is worth emphasizing that the use of niobium, like its brother tantalum, is possible in rectifiers due to the fact that they have the property of unipolar conductivity, that is, these substances pass electrical current in only one direction. It is possible to use this metal to create devices such as anodes, which are used in powerful generators and amplification tubes.

    It is very important to note that the use of niobium has reached nuclear power. In this industry, products made from this substance are used as structural materials. This became possible because the presence of Nb in the parts makes them resistant to heat and also gives them high quality chemical resistance.

    The excellent physical characteristics of this metal have led to its widespread use in rocketry, jet aircraft, and gas turbines.

    Niobium production in Russia

    If we talk about the reserves of this ore, there are about 16 million tons in total. The largest deposit, occupying approximately 70% of the total volume, is located in Brazil. About 25% of the reserves of this ore are located in Russia. This indicator is considered a significant part of all niobium reserves. The largest deposits of this substance are located in Eastern Siberia, as well as in Far East. Today, on the territory of the Russian Federation, the Lovozersky GOK company is engaged in the extraction and production of this substance. It can be noted that the Stalmag company was also involved in the production of niobium in Russia. It developed the Tatar deposit of this ore, but was closed in 2010.

    You can also add that it is engaged in the production of niobium oxide. They obtain it by processing loparite concentrate. This enterprise produces from 400 to 450 tons of this substance, most of from which it is exported to countries such as the USA and Germany. Part of the remaining oxide goes to the Chepetsk Mechanical Plant, which produces both pure niobium and its alloys. There are significant capacities there, allowing the production of up to 100 tons of material per year.

    Niobium metal and its cost

    Despite the fact that the scope of application of this substance is quite wide, its main purpose is the space and nuclear industries. For this reason, Nb is classified as a strategic material.

    The main parameters that affect the cost of niobium:

    Approximate list of prices for materials in Moscow:

    • niobium grade NB-2 costs between 420-450 rubles per kg;
    • niobium shavings cost from 500 to 510 rubles per kg;
    • a stick of the NBSh-00 brand costs from 490 to 500 rubles per kg.

    It is worth noting that, despite the enormous cost of this product, the demand for it is only increasing.



What else to read

Abstract: History of the development of hygiene 1. The development of hygiene in primitive and slave societies. The emergence and development of hygiene has a centuries-old history...
Formation of estimated liabilities and reserves for vacations As in 1s 8 Hello, dear blog readers. Lately, in my consulting work, I have quite often...
Puff khinkal in a pressure cooker Puff DAGESTAN KHINKAL Puff khinkal is often prepared in Dagestan. A very tasty, but high-calorie, masculine dish....