Vanadium hydride. Vanadium subgroup
Vanadium has a body-centered cubic lattice with a period a=3.0282A. Vanadium is malleable in its pure state and can be easily worked by pressure. Density 6.11 g/cm3; t pl 1900°С, t bp 3400°С; specific heat capacity (at 20-100°C) 0.120 cal/g deg; thermal coefficient of linear expansion (at 20-1000°C) 10.6 10-6 deg-1; electrical resistivity at 20°C 24.8 10-8 ohm m (24.8 10-6 ohm cm); below 4.5 K, vanadium passes into the state of superconductivity. Mechanical properties High purity vanadium after annealing: modulus of elasticity 135.25 n/m 2 (13520 kgf/mm 2), tensile strength 120 mn/m 2 (12 kgf/mm 2), relative elongation 17%, Brinell hardness 700 mn / m 2 (70 kgf / mm 2). Gas impurities sharply reduce the plasticity of vanadium and increase its hardness and brittleness.
Chemical properties Vanadium
Vanadium does not change in air, it is resistant to water, solutions of mineral salts and alkalis. Acids act on it only those that are also oxidizing agents. In the cold, it is not affected by dilute nitric and sulfuric acids. Apparently, the thinnest oxide film is formed on the metal surface, which prevents further oxidation of the metal. In order to make Vanadium react intensely, it must be heated. At 600-700°C, intensive oxidation of the compact metal occurs, and in a finely divided state, it enters into reactions at a lower temperature.
Sulfides, carbides, nitrides, arsenides, silicides can be obtained by direct interaction of elements during heating. For technology, yellow-bronze nitride VN (tmelt = 2050°C), resistant to water and acids, and also carbide VC with high hardness (tmelt = 2800°C) is important.
Vanadium is very sensitive to gas impurities (O 2 , N 2 , H 2 ), which dramatically change its properties, even if present in the smallest amounts. Therefore, even now it is possible to meet different melting points of Vanadium in different reference books. Contaminated vanadium, depending on the purity and method of obtaining the metal, can melt in the range from 1700 to 1900°C. With a purity of 99.8 - 99.9%, its density is 6.11 g / cm3 at 20 ° C, the melting point is 1919 ° C, and the boiling point is 3400 ° C.
The metal is extremely resistant both in organic and in most inorganic aggressive environments. In terms of resistance to HC1, HBr and cold sulfuric acid, it is significantly superior to titanium and stainless steel. It does not form compounds with halogens, except for the most aggressive of them - fluorine. With fluorine, however, it gives VF 5 crystals, colorless, sublime without turning into a liquid at 111 ° C. An atmosphere of carbon dioxide has a much weaker effect on metallic vanadium than on its counterparts, niobium and tantalum. It has a high resistance to molten metals, so it can be used in the design of nuclear reactors, where molten metals are used as coolants. Vanadium does not rust either in fresh or sea water, or in alkali solutions.
Of the acids, concentrated sulfuric and nitric acids, hydrofluoric and their mixtures act on it.
A feature of Vanadium is the high solubility of hydrogen in it. As a result of this interaction, solid solutions and hydrides are formed. The most probable form of the existence of hydrides is metal-like compounds with electronic conductivity. They can quite easily pass into the state of superconductivity. Vanadium hydrides can form solutions with some solid or liquid metals, in which the solubility of hydrogen increases.
Vanadium carbides are of independent interest, since their qualities provide a material with very valuable properties for modern technology. They are exceptionally hard, refractory and have good electrical conductivity. Vanadium is capable of even displacing other metals from their carbides to form its carbides:
3V + Fe3C \u003d V 3 C + 3Fe
A number of compounds of vanadium with carbon are known:
V 3 C; V2C; VC; V 3 C 2 ; V 4 C 3
With most members of the main subgroup, Vanadium gives compounds both binary (i.e., consisting of only two elements.), And more complex composition. Nitrides are formed by the interaction of a metal powder or its oxides with gaseous ammonia:
6V + 2NH 3 = 2V 3 N + 3H 2
V 2 O 2 + 2NH 3 \u003d 2VN + 2H 2 O + H 2
For semiconductor technology, phosphides V 3 P, V 2 P, VP, VP 2 and arsenides V 3 As, VAs are of interest.
The complexing properties of vanadium manifest themselves in the formation of complex compounds such as phosphoric vanadic acid H 7 PV 12 O 36 or H 7 [P(V 2 O 6) 6 ].
(54,. (57) METHODS OF VANADIUM, include allic irradiated prn demetal o.t with the fact that, for the purpose of using 1 p. inventions and related (71) Institute of New Chemical Problems of the Academy of Sciences of the USSR (56) 1, Mikheeva V.I. Transition metal hydrides. Academy of Sciences of the USSR, I. 1946, p97-99.2, "1. Aveg, Spev. 1961, 83Р 17, pp. 3728-3729.3 Journal of inorganic vol. priming with hydrogen, semi"zhenin of hydrides of incompounds composition 1 General Order 10312/24 Circulation 471 Subscription VNIIPI of the State Committee of the USSR for Inventions and Discoveries 113035, Moscow, Zh, Raushskaya nab., d, 4/5 Projectnaya, 4 The invention relates to methods for producing vanadium dihydride, which can be used in powder metallurgy, as well as a source of hydrogen and a catalyst for the hydrogenation of organic substances. There is a method for producing vanadium hydrode by reducing vanadium pentoxide with calcium hydride 1.1. There is also a method for preparing vanadium dihydride by treating vanadium hydride with the composition CN O with hydrogen under a pressure of 70 atm at room temperature for 6 hours. maximum. The closest in technical essence and the achieved result to the proposed one is a method for obtaining vanadium dihydride by processing. metal vanadium hydrogen formed during the thermal decomposition of titanium hydride. Hydrogen treatment is carried out at first 30 at room temperature to the composition; corresponding to vanadium monohydride, after which hydrogen treatment is carried out at a temperature of -70 to -20 C. Hydrogen pressure is 1 atm. Process duration is 8-10 days. The resulting product corresponds to vanadium dihydride of the composition ChN, 2 3), ) temperature and reduction of its duration. The goal is achieved by the fact that the treatment of metallic vanadium is carried out at a pressure of 5-30 atm with hydrogen obtained by the decomposition of intermetallic compounds of the composition LaI 1 Hbz or T 1 Ren 2, When the hydrides of intermetallic compounds of the composition 50 LaB 1 Hb B or T 1 GeH hydrogen is released with a purity of 99.9999. Hydrogen of this purity is able to easily penetrate through the oxide film located on the surface of the metal into the depth of the sample and interact with the unoxidized metal. It has a large diffusion coefficient and high mobility. This allows the hydrogenation process to be carried out at a high rate and at a sufficient depth without the use of low temperatures necessary to reduce the dissociation pressure of the resulting vanadium dihydride. When the hydrogen pressure drops below 5 atm, the hydrogenation time increases. An increase in pressure above 30 atm does not affect the speed of the process, but leads to its complication. the sample is pumped out for 0.5 h at 250 C. After cooling to 20 C, the autoclave is filled with hydrogen from a canister with a hydride of the composition La 1 R 1 H n to a pressure of 10 atm. The reaction starts immediately and lasts 1 hour. The end of the reaction is set when the pressure drop in the autoclave ceases. As a result of hydrogenation, vanadium dihydride of the composition CNO is obtained, which is established on the basis of data from X-ray phase, gas volumetric and chemical analyzes, EXAMPLE 2. Similarly to example 1, from 4 g of vanadium powder at 20 ° C and under a hydrogen pressure of 5 atm for 1.5 h get vanadium hydride composition ChNdr. PRI me R 3. Similarly to example 1 from 8 g of vanadium in the form of a piece at 20 C and under a hydrogen pressure of 30 atm for 2 h receive vanadium hydride composition ChN. Thus, the invention makes it possible to simplify the process by eliminating the need to use low (minus) temperatures and reduce its duration from 8-10 days to 1-2 hours.
Request
3421538, 13.04.1982
INSTITUTE OF NEW CHEMICAL PROBLEMS AS USSR
SEMENENKO KIRILL NIKOLAEVICH, FOKINA EVELINA ERNESTOVNA, FOKIN VALENTIN NAZAROVICH, TROITSKAYA STELLA LEONIDOVNA, BURNASHEVA VENIANNA VENEDIKTOVICH, VERBETSKY VIKTOR NIKOLAEVICH, MITROKHIN SERGEY VLADILENOVICH
IPC / Tags
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Method for obtaining vanadium dihydride
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Chemical formula
Molar mass of VH, Vanadium(I) Hydride 51.94944 g/mol
Mass fractions of elements in the compound
Using the Molar Mass Calculator
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Molar mass calculator
mole
All substances are made up of atoms and molecules. In chemistry, it is important to accurately measure the mass of substances entering into a reaction and resulting from it. By definition, the mole is the SI unit for the amount of a substance. One mole contains exactly 6.02214076×10²³ elementary particles. This value is numerically equal to the Avogadro constant N A when expressed in units of moles⁻¹ and is called Avogadro's number. Amount of substance (symbol n) of a system is a measure of the number of structural elements. A structural element can be an atom, a molecule, an ion, an electron, or any particle or group of particles.
Avogadro's constant N A = 6.02214076×10²³ mol⁻¹. Avogadro's number is 6.02214076×10²³.
In other words, a mole is the amount of a substance equal in mass to the sum of the atomic masses of the atoms and molecules of the substance, multiplied by the Avogadro number. The mole is one of the seven basic units of the SI system and is denoted by the mole. Since the name of the unit and its symbol are the same, it should be noted that the symbol is not declined, unlike the name of the unit, which can be declined according to the usual rules of the Russian language. One mole of pure carbon-12 equals exactly 12 grams.
Molar mass
Molar mass is a physical property of a substance, defined as the ratio of the mass of that substance to the amount of the substance in moles. In other words, it is the mass of one mole of a substance. In the SI system, the unit of molar mass is kilogram/mol (kg/mol). However, chemists are accustomed to using the more convenient unit g/mol.
molar mass = g/mol
Molar mass of elements and compounds
Compounds are substances made up of different atoms that are chemically bonded to each other. For example, the following substances, which can be found in the kitchen of any housewife, are chemical compounds:
- salt (sodium chloride) NaCl
- sugar (sucrose) C₁₂H₂₂O₁₁
- vinegar (acetic acid solution) CH₃COOH
The molar mass of chemical elements in grams per mole is numerically the same as the mass of the element's atoms expressed in atomic mass units (or daltons). The molar mass of compounds is equal to the sum of the molar masses of the elements that make up the compound, taking into account the number of atoms in the compound. For example, the molar mass of water (H₂O) is approximately 1 × 2 + 16 = 18 g/mol.
Molecular mass
Molecular weight (the old name is molecular weight) is the mass of a molecule, calculated as the sum of the masses of each atom that makes up the molecule, multiplied by the number of atoms in this molecule. The molecular weight is dimensionless a physical quantity numerically equal to the molar mass. That is, the molecular weight differs from the molar mass in dimension. Although the molecular mass is a dimensionless quantity, it still has a value called the atomic mass unit (amu) or dalton (Da), and is approximately equal to the mass of one proton or neutron. The atomic mass unit is also numerically equal to 1 g/mol.
Molar mass calculation
The molar mass is calculated as follows:
- determine the atomic masses of the elements according to the periodic table;
- determine the number of atoms of each element in the compound formula;
- determine the molar mass by adding the atomic masses of the elements included in the compound, multiplied by their number.
For example, let's calculate the molar mass of acetic acid
It consists of:
- two carbon atoms
- four hydrogen atoms
- two oxygen atoms
- carbon C = 2 × 12.0107 g/mol = 24.0214 g/mol
- hydrogen H = 4 × 1.00794 g/mol = 4.03176 g/mol
- oxygen O = 2 × 15.9994 g/mol = 31.9988 g/mol
- molar mass = 24.0214 + 4.03176 + 31.9988 = 60.05196 g/mol
Our calculator does just that. You can enter the formula of acetic acid into it and check what happens.
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INORGANIC MATERIALS, 2015, Volume 51, No. 8, p. 850-853
UDC 546.112+546.881+546.76
INTERACTION OF VANADIUM ALLOYS WITH HYDROGEN AT HIGH PRESSURE © V. N. Verbetsky, S. A. Lushnikov, and E. A. Movlaev
Moscow State University M.V. Lomonosov e-mail: [email protected] Received July 2, 2014
The interaction of V0.95Cu0 05, V0.94Co006, and V0.9W0.i alloys with hydrogen at a hydrogen pressure of up to 250 MPa has been studied. Hydrogen absorption and desorption isotherms are constructed at different temperatures, and the thermodynamic parameters of the systems are determined. XRD analysis of samples of hydride phases V0 94Co0 06Hi 4 and V0.9W0.1H1.2 formed at high pressure showed that they consist of a phase with a face-centered cubic lattice, similar to the y-phase of vanadium dihydride. In the case of an alloy with copper, the maximum composition of the hydride is V0.95Cu0 05H05.
DOI: 10.7868/S0002337X15080199
INTRODUCTION
Vanadium hydride with a high mass content of hydrogen (3.8%) is a promising material for hydrogen storage. However, the hydrogenation conditions of metallic vanadium and the values of the dissociation pressure of vanadium mono- and dihydride limit the possibility of its practical application. In order to improve these indicators, the interaction of hydrogen with vanadium alloys is intensively studied and the influence of various elements on the hydrogen sorption properties of vanadium is studied.
In one of the first works, in which the influence of doping of vanadium was studied, it was found that most elements increase the equilibrium pressure of dissociation of vanadium dihydride, with the strongest influence being exerted by 81, Ge, ^ Fe, Mo and N1. In the works, the interaction of hydrogen with vanadium alloys alloyed with other metals (T1, Cr, Mn, Fe, Co, N1, Cu) in an amount of 1, 3 and 6 at. %. For vanadium alloys containing 1% of another metal, hydrogen absorption and desorption isotherms were measured at a temperature of 313 K and a pressure of up to 4 MPa. For the U0.99Co001 alloy, as well as in the vanadium-hydrogen system, the formation of s- and y-hydride phases was established. The area of formation of the dihydride phase lies in the range from 0.8 N/M to 1.8 N/M, and the dissociation pressure increases compared to vanadium. When vanadium is doped with a large amount of cobalt (3 and 6 at.%), further destabilization of the β-hydride phase occurs, and the γ-phase is no longer formed under the conditions of this experiment. According to the work, compounds YCo and U3Co do not interact with hydrogen at pressures up to 10 MPa.
For an alloy of vanadium with copper U0.99Cu0.01, similar hydride phases were also determined, and it was shown that the dissociation pressure of the corresponding dihydride phase practically does not change compared to vanadium. The interaction of hydrogen with alloys with a high content of copper has not been studied. The authors of the work associate the magnitude of the pressure change with the atomic radius and electronegativity of the elements: elements with a small atomic radius or high electronegativity increase the pressure of hydrogen desorption from vanadium dihydride.
The study of the hydrogen sorption properties of vanadium alloys with chromium, molybdenum and tungsten was carried out in the works. It has been established that with an increase in the chromium content in the alloy, the pressure of hydrogen desorption from vanadium dihydride increases. In this work, the use of high hydrogen pressure made it possible to synthesize hydrides of Y1 _ xCrx alloys with x from 0.2 to 0.5, which do not form hydride phases at low pressure. The main phase of the products of hydrogenation of samples Y09Cr01 and Y08Cr02 at high hydrogen pressure is a phase with an fcc structure, similar to vanadium dihydride UN2. High-pressure hydrides of the approximate composition Y0.6Cr0.4H10 and Y05Cr05H09 have an hcp lattice similar to that of CrH chromium hydride.
Study in the work of the interaction of hydrogen with alloys Y1-xMox (0< х < 0.1) также показало, что с увеличением содержания молибдена повышается давление диссоциации гидридных фаз. Так, например, гидрид состава У09Мо01Н1.74 был синтезирован авторами только лишь при снижении температуры реакции до - 30°С.
Hydrogen absorption properties of alloys V0.94Co006 and V0.9W01
Alloy Lattice period of alloy, nm Lattice period of hydride phases, nm Maximum hydrogen content N/M at 20°C AN, kJ/molH2 AS, JDmol^K
V 0.303 VH0.9 (bct): a = 0.604, c = 0.672 VH21 (fcc): a = 0.424 2.1 (1 MPa) 41 142
V0.94Co0.06 0.3000(2) V0.94Co0.06Hx.4 (fcc): a = 0.4268(3) 1.4 (170 MPa) 34.23(2) 130.86(2)
V0.9W0.1 0.3055(1) V0.9W0.1H0.6 (bct): a = 0.6077(2) c = 0.6630(1) V0.9W0.1HL2 (fcc): a = 0.4282(3) 1.2 (160 MPa) 32.47(2) 150.15(2)
binary (V08Mo0.2 and V0.75Mo0.25) and ternary (Ti-V-Mo) alloys based on vanadium. Hydrogen absorption and desorption isotherms were constructed in the studied systems and, on their basis, the thermodynamic parameters of the decomposition of hydride phases were determined. The XPA results showed that stable hydride phases based on all the studied alloys have a bcc lattice, in contrast to the bct lattice of pure vanadium monohydride. The hydride phases of all compounds formed at high pressure have an fcc lattice similar to that of vanadium dihydride. With an increase in the molybdenum content in both the binary and ternary alloys, the maximum hydrogen content in the hydride phases decreases and the hydrogen desorption pressure increases. The influence of tungsten on the nature of the interaction of vanadium with hydrogen has not been practically studied. It was found in the work that for the V095W005 alloy, the hydrogen permeability decreases even with an increase in temperature. In the temperature range from 400 to 500°C, the maximum hydrogen content corresponded to the composition 0.5–0.6 H/V095W005.
The purpose of this work was to study the interaction of hydrogen with alloys of vanadium with cobalt, copper, and tungsten using high-pressure techniques. It should also be noted that vanadium alloys are a promising structural material for nuclear power reactors. In this regard, the results of studying phase transitions in such alloys under the influence of hydrogen are undoubtedly of great importance for the developers of new structural materials.
EXPERIMENTAL PART
Alloy samples were prepared from pure metals in an electric arc furnace in an inert atmosphere. After melting, the samples were annealed in evacuated quartz ampoules at a temperature
temperature of 800°C for 240 h. Before hydrogenation, the “beads” of the alloys were split into pieces in an anvil in order to place the samples in the hydrogenation reactor. The synthesis of hydrides and the study of the alloy-hydrogen equilibrium were carried out at a hydrogen pressure of up to 250 MPa using the setup described in the work. The van der Waals equation for real gases was used to determine the molar volumes of hydrogen during hydrogenation. The accuracy of the composition of the hydride phases formed at high hydrogen pressure was 0.1 N/IMS. Samples of hydrides synthesized at high pressure were preliminarily passivated in air for X-ray photography. To do this, the autoclave with the sample was cooled to the temperature of liquid nitrogen (77 K) at a high hydrogen pressure and then the pressure was reduced to atmospheric pressure. After that, the open autoclave with the sample was kept in air for an hour at liquid nitrogen temperature (77 K).
RESULTS AND DISCUSSION
According to X-ray diffraction data, the obtained samples are single-phase and have a bcc lattice. The lattice period of the initial U0 95Cu0 05 alloy, according to XRD data, was 0.3021(3) nm. Data on the hydrogen sorption properties of the alloys and XPA of the synthesized high and low pressure hydrides are presented in the table.
Interaction with hydrogen of alloy V0.94Co0.06.
The addition of cobalt to vanadium reduced the amount of reversibly stored hydrogen and reduced its maximum content (Fig. 1). As can be seen from fig. 1, two segments are observed on the hydrogen desorption isotherms. The first section up to a composition of about 0.6 N/M at 20°С is the region of formation of a stable hydride phase, which does not noticeably release hydrogen at the given measurement temperatures. At higher hydrogen concentrations
VERBETSKY and others.
0.4 0.6 0.8 1.0 1.2 1. N/M
Rice. Fig. 1. Hydrogen desorption isotherms in the Y0.94Co0.06_H2 system at (1) 20, (2) 50, and (3) 70°С.
1 - -2 - 3 --4
Rice. Fig. 2. Hydrogen desorption isotherms in the V0.9W0.1-H2 system at (1) 0, (2) 20, (3) 40, and (4) 60°C.
a plateau is observed - the region of formation of a high-pressure hydride phase up to a composition of 1.3 N/M. At 170 MPa, the maximum hydrogen content in the high-pressure hydride phase corresponds to the composition V0.94Co0.06H14. The values of the enthalpy and entropy of the hydrogen desorption reaction calculated from the equilibrium pressures in the plateau region are given in the table.
Interaction with hydrogen of alloy V0.95Cu0.05.
During hydrogenation of the alloy sample, a stable hydride phase first formed with the highest hydrogen content of about 0.3 N/M. With a further increase in pressure to 200 MPa, an insignificant absorption of hydrogen was observed, and the maximum composition of the hydride corresponded to 0.5 H/M at 200 MPa and room temperature.
Interaction with hydrogen alloy V09W01.
The addition of tungsten to vanadium significantly reduces the amount of reversibly stored hydrogen (Fig. 2). On the constructed isotherms, two sections can be distinguished. The first ranges up to a composition of 0.6 N/IMS and corresponds to the formation of a stable hydride phase, which practically does not desorb hydrogen at room temperature. With an increase in the hydrogen pressure in the system, a second section appears on the isotherm with an inclined plateau in the composition range from about 0.8 to 1.0 N/M at room temperature. As the temperature increases, the region of the high-pressure hydride phase narrows, while the region of the stable hydride phase expands. The maximum hydrogen content in the hydride phase corresponds to 1.2 N/M at a pressure of 160 MPa and a temperature of 20°C. Based on the obtained experimental equilibrium pressures, the values of enthalpy and
Verbetsky V.N., Mitrokhin S.V. - 2005
I. I. Korobov, B. P. Tarasov, V. N. Fokina, and E. E. Fokina - 2013
Vanadium is more common in the earth's crust than Cu, Zr, Pb, but its compounds are rarely found in the form of large deposits. Vanadium is scattered in various silicate and sulfide ores. Its most important minerals patronite VS 2–2.5, sulvanite Cu 3 VS 4, alait V2O3×H2O, vanadinite Pb 5 (VO 4) 3 Cl. Niobium and tantalum are almost always found together, most often in the composition of niobate-tantalate minerals of the composition M + 2 E 2 O 6 (M = Fe, Mn). In the case of the predominance of tantalum, the mineral M + 2 (TaO 3) 2 is called tantalate, with the predominance of niobium columbite M (NbO 3) 2.
simple substances. In the form of simple substances V, Nb and Ta are gray refractory metals with a body-centered cubic lattice. Some of their constants are listed below:
The physicochemical properties of vanadium, niobium, and tantalum essentially depend on their purity. For example, pure forging metals, while impurities (especially O, H, N and C) greatly impair ductility and increase the hardness of metals.
Under normal conditions, V and especially Nb and Ta are distinguished by high chemical resistance. Vanadium in the cold dissolves only in aqua regia and concentrated HF, and when heated in HNO 3 and concentrated H 2 SO 4 . Niobium and tantalum dissolve only in hydrofluoric acid and a mixture of hydrofluoric and nitric acids with the formation of anionic fluorine complexes corresponding to their highest oxidation state:
3Ta 0 + 5HNO 3 + 2INF \u003d 3H 2 [Ta +5 F 7] + 5NO + 10H 2 O
Vanadium, niobium and tantalum also interact during fusion with alkalis in the presence of oxidizing agents, i.e. under conditions conducive to the formation of anionic oxo complexes corresponding to their highest oxidation state:
4E 0 + 5O 2 + 12KOH ===== 4K 3 [E +5 O 4] + 6H 2 O
c melting
When heated, metals are oxidized by oxygen to E 2 O 5, by fluorine to EF 5. At high temperatures, they also react with chlorine, nitrogen, carbon, etc.
To obtain vanadium, niobium and tantalum, their natural compounds are first converted into oxides or into simple or complex halides, which are then reduced by the metallothermic method.
E 2 O 5 + 5Ca = 5CaO + 2E
K 2 [EF 7] + 5Na \u003d 2KF + 5NaF + E
Tantalum is also obtained by electrolysis of Ta 2 O 5 in molten complex fluorides K 2 [TaF 7 ].
Due to the close properties of niobium and tantalum, their separation from each other presents considerable difficulties. Highly pure metals are obtained by thermal decomposition of iodides. For technical purposes, usually smelted ferrovanadium, ferroniobium and ferrotantal.
The main consumer of vanadium is ferrous metallurgy. Valuable physical and chemical properties of V, Nb and Ta make it possible to use them in the creation of nuclear reactors. Niobium and, to an even greater extent, tantalum are of interest as structural materials for particularly aggressive media in the chemical industry.
Compounds of elements of the vanadium subgroup
Metallic and metal-like compounds. Powdered V, Nb, and Ta adsorb significant amounts of hydrogen, oxygen, and nitrogen, forming interstitial solid solutions. In this case, non-metals pass into the atomic state and their electrons participate in the construction d- zones of a metal crystal. When heated, the solubility of non-metals increases; at the same time, the nature of the chemical bond and the properties of the compounds formed change. Thus, during the formation of oxides, the gradual oxidation of niobium (as well as V and Ta) with oxygen proceeds through the following stages:
Nb + O ® Nb-O ® Nb 6 O ® Nb 2 O ® NbO ® NbO 2 ® Nb 2 O 5
solid solution
According to the properties of Nb 6 O and Nb 2 O, typical metal compounds; NbO (gray) - a compound of variable composition (NbO 0.94–1.04) with a metallic luster and metallic conductivity. Dioxide NbO 2 (black) is also of variable composition (NbO 0.19-2.09), but already a semiconductor. And, finally, Nb 2 O 5 has a more or less constant composition and does not possess electronic conductivity. Thus, as the oxygen content increases, the proportion of the metallic bond gradually decreases and the proportion of the covalent bond increases, which causes a change in the properties of oxides.
Hydrides of vanadium and its analogues EN- brittle metal-like powders of gray or black color, have a variable composition. Hydrides are chemically stable, do not interact with water and dilute acids.
They also have high corrosion resistance nitrides(EN, Nb 2 N, Ta 2 N), carbides(ES, E 2 C), borides(EV, EV 2, E 3 V 4), a number of other compounds of vanadium and its analogues with inactive non-metals.
Vanadium, niobium and tantalum among themselves and with metals close to them in the periodic system (subgroups of iron, titanium and chromium) form metallic solid solutions. As the differences in the electronic structure of the interacting metals increase, the possibility of forming solid solutions decreases and the possibility of forming intermetallic compounds increases, for example, of the type Co 3 V, Fe 3 V, Ni 3 V, Al 3 V, etc.
Intermetallic compounds of vanadium and its analogs impart valuable physical and chemical properties to alloys. Thus, vanadium sharply increases the strength, toughness and wear resistance of steel. Niobium gives steels increased corrosion resistance and heat resistance. In this regard, most of the extracted vanadium and niobium is used in metallurgy for the manufacture of tool and structural steel.
Of great interest are alloys based on carbides, nitrides, borides, and silicides of niobium and tantalum, which are distinguished by exceptional hardness, chemical inertness, and heat resistance.
Compounds V (II), Nb (II), Ta (II). Of the derivatives in which elements of the vanadium subgroup exhibit an oxidation state of +2, vanadium compounds are relatively more stable. The coordination number of vanadium (II) is 6, which corresponds to the octahedral structure of its complexes (structural units) in compounds.
Vanadium oxide (P) VO (UO 0.9 -VO 1.3) has a crystal lattice of the NaCl type. It is black in color, has a metallic luster and a relatively high electrical conductivity. Get VO reduction V 2 O 5 in a stream of hydrogen. VO does not interact with water, but as a basic compound it reacts quite easily with dilute acids:
VO + 2OH 3 + + 3H 2 O \u003d 2+
Ion 2+ purple. Crystalline hydrates have the same color, for example, M +1 2 SO 4 × VSO 4 × 6H 2 O, VSO 4 × 7H 2 O, VCl 2 × 6H 2 O.
Compounds V (II) are strong reducing agents. Violet solutions of 2+ derivatives are quite easily oxidized to 3+ and their color becomes green. In the absence of oxidizing agents (for example, atmospheric oxygen), solutions of V(II) compounds gradually decompose even water with evolution of hydrogen.
Derivatives of Nb(II) and Ta(II) belong to cluster-type compounds.
Compounds V (III), Nb (III), Ta(III). The coordination number of vanadium (III) is 6. In terms of structure, compounds V (III) are similar to the same type derivatives of Al (IP). Black oxide of vanadium (III) V 2 O 3 has a crystal lattice like corundum a-A1 2 O 3; its composition is variable VO 1.60-1.80. From alkaline solutions of compounds V (III), green hydroxide V (OH) 3 of variable composition V 2 O × nH 2 O is released. These compounds are amphoteric, but with a predominance of basic properties. So, V 2 O 3 and V 2 O 3 × nH 2 O dissolve in acids:
V 2 O 3 + 6OH 3 + + 3H 2 O \u003d 2 3+
The resulting 3+ aquo complexes and the crystalline hydrates VCl 3 ×6H 2 O, VI 3 ×6H 2 O produced from them are green in color. Vanadium alum M +1 × 12H 2 O have a violet color, which, when dissolved, give green solutions.
Vanadium trihalides VHal 3 are crystalline substances. Trichloride VCl 3 has a layered structure. With the corresponding basic halides, VHal 3 form halide vanadates - derivatives of ions 3- and 3-:
3KF + VF 3 \u003d K 3; EXl + 2VCl 3 = K 3
Derivatives of vanadium (III) are strong reducing agents, in solutions they are quite easily oxidized by atmospheric oxygen to derivatives V (IV). Trihalides disproportionate when heated:
2VCl 3 (t) \u003d VCl 2 (t) + VCl 4 (g)
This reaction is endothermic, and its occurrence is due to the entropy factor (due to the formation of volatile VCl 4).
Derivatives of Nb (PI) and Ta (III) are mainly cluster-type compounds.
Compounds V (IV), Nb (IV), Ta (IV). Under normal conditions, the oxidation state +4 for vanadium is most characteristic. Compounds V (III) are rather easily oxidized to derivatives V (IV) by molecular oxygen, and compounds V (V) are reduced to derivatives V (IV). The most stable coordination number of vanadium (IV) is 6, and the coordination numbers 4 and 5 are also stable.
Of the derivatives of V (IV), blue VO 2 (VO 1.8-2.17), brown VF 4 and red-brown liquid VCl 4, as well as oxohalides of the VOHal 2 type are known. VO dioxide is formed by careful reduction of V 2 O 5 with hydrogen, and VCl 4 by oxidation of vanadium (or ferrovanadium) with chlorine or by the interaction of hot V 2 O 5 with CCl 4 .
The dioxide has a rutile TiO 2 type crystal lattice. The VCl 4 molecule, like TiCl 4 , has a tetrahedral shape.
Compared with similar derivatives V (II) and V (IP), binary compounds V (IV) show acidic properties more clearly. Thus, water-insoluble VO 2 interacts relatively easily with alkalis when heated. In this case, brown oxovanadates (IV) are formed, most often of the composition M 2:
4VO 2 + 2KOH \u003d K 2 + H 2 O
VO 2 is even easier to dissolve in acids. In this case, not simple aquocomplexes V 4+ are formed, but aqua derivatives oxovanadil VO 2+, characterized by a light blue color: VO 2 + 2H + + 4H 2 O \u003d 2+
The oxovanadyl group VO 2+ is highly stable, since the VO bond is close to double:
The interatomic distance d VO in the vanadyl group is 0.167 ni, while the distance d V - OH 2 = 0.23 im.
The grouping of VO 2+ remains unchanged during various reactions; depending on the nature of the ligands, it can be part of both cationic or anionic complexes and neutral molecules.
The interaction of VHal 4 with basic halides is not typical, but derivatives of anionic oxovanadyl complexes of the K 2, (NH 4) 3 type are very typical for V (IV).
Vanadium tetrahalides are easily hydrolyzed. So, in water, VCl 4 instantly turns into VOCl 2 (vanadyl dichloride):
VCl 4 + H 2 O \u003d VOCl 2 + 2HCl
For niobium and tantalum, EO 2 dioxides, ENal4 tetrahalides, and EONal 2 oxodihalides are known. It is believed that in these compounds a metal-metal bond is manifested, i.e. they belong to clusters.
The characteristic tendency for niobium and tantalum to use all of its valence electrons in the formation of a chemical bond is usually carried out due to their transition to the highest oxidation state +5. At low degrees of oxidation, this tendency is carried out due to the formation of M-M bonds.
Compounds V (V), Nb (V), Ta (V). In the series V (V) - Nb (V) - Ta (V), the stability of the compounds increases. This, in particular, is evidenced by a comparison of the Gibbs energies of the formation of compounds of the same type, for example:
For vanadium (V), only V 2 O 5 oxide and VF 5 fluoride are known, while for niobium (V) and tantalum (V) all other ENal 5 halides are known, for E (V), in addition, oxohalides of the EONal type are characteristic 3 . All of these compounds are typically acidic. Some corresponding anionic complexes are listed below:
For V (V), the most typical coordination numbers are 4 and 6, and for Nb (V) and Ta (V) 6 and 7. In addition, there are compounds in which the coordination numbers of Nb (V) and Ta (V) reach 8.
oxides red V 2 O 5 (T pl. 670 ° C), white Nb 2 O 5 (T pl. 1490 ° C) and Ta 2 O 5 (T pl. 1870 ° C) are refractory crystalline substances. The structural unit of E 2 O 5 is the EO 6 octahedron. (In the case of V 2 O 5, the VO 6 octahedron is very strongly distorted - almost a trigonal bipyramid with one additional oxygen atom removed.) Oxides have high heats and Gibbs energies of formation. In this case, due to lanthanide compression, the values of DH 0 f and DG o f for Nb 2 O 5 and Ta 2 O 5 are close and noticeably differ from those for V 2 O 5 .
Vanadium (V) oxide is obtained by thermal decomposition of NH 4 VO 3:
NH 4 VO 3 \u003d V 2 O 5 + 2H 3 N + H 2 O
It is very poorly soluble in water (~0.007 g/l at 25°C), forms an acidic light yellow solution; quite easily soluble in alkalis, and in acids - only with prolonged heating. Oxides Nb (V) and Ta (V) are chemically inactive, practically do not dissolve in water and acids, and react with alkalis only when fused:
E 2 O 5 + 2KOH \u003d 2KEO 5 + H 2 O
Oxovanadates (V), oxoniobates (V) and oxotantalates (V) are crystalline with a complex composition and structure. Their diversity and complexity of composition can be judged from the nature of the corresponding fusibility diagrams (for example, Fig. 2). The simplest compounds of the type M +1 EO 3 and M +1 3 EO 4 in composition. For the most part, oxovanadates (V) and, in particular, oxoniobates (V) and oxotantalate (V) are polymeric compounds.
Acids, acting on solutions of oxovanadates, cause the polymerization of vanadate ions up to the formation of a precipitate of hydrated oxide V 2 O 5 × nH 2 O. A change in the composition of vanadate ions is accompanied by a color change from almost colorless VO 4 3- to orange V 2 O 5 × nH 2 O.
Enal 5 pentagalides have an island structure, so they are fusible, volatile, soluble in organic solvents, and chemically active. Fluorides are colorless, the rest of the halides are colored.
Crystals of NbF 5 (T pl. 80 ° C, T bp. 235 ° C) and TaF 5 (T pl. 95 ° C, T b. 229 ° C) consist of tetrameric molecules (EF 5) 4, and ESl 5 and EVr 5 (T pl. and T boil. about 200-300 ° C) - from dimer molecules (ENal 5) 2:
VF 5 is a viscous liquid (T pl. 19.5 ° C), similar in structure to SbF 5 . Being acidic compounds, pentahalides are easily hydrolyzed, forming amorphous precipitates of hydrated oxides:
2ENal 5 + 5H 2 O \u003d E 2 O 5 + 10HHal
Pentafluorides, as well as Nb and Ta pentachlorides, in addition, react with the corresponding basic halides to form anionic complexes [EF 6 ] - , and in the case of Nb (V) and Ta (V), in addition, [EF 7 ] 2-, [EF 8] 3- and [ESl 6] -, for example:
KF + VF 5 = K
2KF + TaF 5 \u003d K 2 [TaF 7]
Oxohalides EONal 3 are usually solids, mostly volatile, and VOCl 3 is a liquid (T pl. - 77 o C, T bp. 127 o C).
The VOCl 3 molecule has the shape of a distorted tetrahedron with a vanadium atom in the center:
In the NbOCl 3 lattice, the Nb 2 Cl 6 dimer groups are connected via Nb-O-Nb bridges, forming endless chains of NbO 2 Cl 4 octahedra.
Oxohalides are easily hydrolyzed with the formation of hydrated oxides E 2 O 5 ×nH 2 O and HHal
2EONal 3 + 3H 2 O \u003d E 2 O 5 + 6HNal
and interact with basic halides to form anionic complexes of composition 2-, and for NB (V) and Ta (V), in addition, [EOCl 4] -, [EONal 5 I 2-, [EOF 6] 3- ( Нal = F, Сl), for example:
2KF + VOF 3 = K 2
3KF + NbOF 3 \u003d K 3
When interacting with aqueous solutions containing KF and HF, Nb 2 O 5 gives K 2, and Ta 2 O 5 forms K 2 [TaF 7]:
Nb 2 O 5 + 4KF + 6HF = 2K 2 + 3H 2 O
Ta 2 O 5 + 4KF + 10HF \u003d 2K 2 [TaF 7] + 5H 2 O
One of the methods for separating niobium and tantalum is based on the difference in the solubility of K 2 [TaF 7 ] and K 2 .
For vanadium (V) and its analogues, peroxo complexes of the yellow 3-, blue-violet 3- and colorless 3- and [Ta(O 2) 4 ] 3- types are very characteristic. According to the structure [E (O 2) 4] 3- are a dodecahedron.
Peroxovanadates, peroxoniobates, and peroxotantalates are formed by the action of hydrogen peroxide and the corresponding E(M) compounds in an alkaline medium. For example:
In the solid state, these compounds are stable. Under the action of acids, peroxovanadates decompose, and peroxoniobates and peroxotantalates are converted into the corresponding peroxo acids of the HEO 4 composition.
Derivatives of vanadium (V) in an acidic environment exhibit oxidizing properties, for example, they oxidize concentrated hydrochloric acid:
To transfer niobium (V) and especially tantalum (V) to lower oxidation states, vigorous reducing agents and heating are required.
Vanadium compounds are used in the chemical industry as catalysts (production of sulfuric acid), and are also used in glass and other industries.
