General
Vanadium, also outdated vanadium, is a chemical element with the symbol V and the atomic number 23. It is a steel-gray, bluish shimmering transition metal that is very soft in its pure state. In the periodic table, the metal, together with the heavier niobium, tantalum and dubnium, forms the 5th group or vanadium group. Most of the vanadium is used as so-called ferrovanadium in steel production. The addition of vanadium in chrome-vanadium steels increases the toughness and thus increases the resistance of the steel.
The element has different biological meanings and is essential for many living things. It plays a role in the control of phosphorylation enzymes and is used by bacteria to fix nitrogen.
The best-known compound of vanadium is vanadium (V) oxide, which is used as a catalyst for the production of sulfuric acid.
The later vanadium was discovered for the first time in 1801 by the Spanish mineralogist Andrés Manuel del Río in a Mexican lead ore, later vanadinite. He initially named the new element because of the multicolored connections panchromium, later Erythronium, since the salts turned red when acidified. However, del Rio revoked the discovery a short time later when first Alexander von Humboldt and later the French chemist HV Collett-Desotils claimed that the new element was contaminated chromium due to its similarity to chromium compounds.
The rediscovery of the element succeeded in 1830 by the Swedish chemist Nils Gabriel Sefström. He examined iron from the Swedish iron ore mine Taberg by dissolving it in hydrochloric acid. Besides other known substances, he discovered an unknown element that resembled chromium in some properties and uranium in others, but was not one of these elements after further research. He named the new element after Vanadis, an epithet of the Nordic deity Freyja. A short time later, Friedrich Wöhler, who had already dealt with the task at Berzelius, provided evidence of the identity of vanadium with erythronium.
Metallic vanadium was first produced in 1867 by Henry Enfield Roscoe by reducing vanadium (II) chloride with hydrogen. 99,7% pure vanadium was first obtained in 1925 by John Wesley Marden and Malcolm Rich by reducing vanadium (V) oxide with calcium.
Vanadium was first used in 1903 when the first vanadium-containing steel was produced in England. The element's increased use in the steel industry began in 1905 when Henry Ford began using vanadium steels in the construction of automobiles.
occurrence
Vanadium is a common element on earth, its share in the continental crust is about 120 ppm. Zirconium, chlorine and chromium have a similar abundance of elements. The element does not occur naturally, but only bound in various minerals. Despite the abundance of vanadium, deposits with high concentrations of the element are rare, and many vanadium minerals are not common. Compared to the earth's crust, the content in seawater is significantly lower, it is around 1,3 μg / l.
The most important vanadium minerals include above all vanadates such as vanadinite [Pb5(VO4)3Cl], Descloizit Pb (Zn, Cu) [OH | VO4] and carnotite [K2(UO2)2(VO4)2· 3H2O], as well as the vanadium sulfide Patronit VS4. Most of the vanadium is found in traces in other minerals, especially iron ores such as magnetite. The vanadium content of titanium magnetite ores is usually between 0,3 and 0,8%, but can reach up to 1,7% in some South African ores.
Animals and plants contain vanadium, so humans contain about 0,3 mg / kg of the element. This is mostly located in cell nuclei or mitochondria. Some living things, especially some species of sea squirt and the fly agaric, are able to enrich vanadium. In sea squirts the vanadium content is up to 107 sometimes as big as in the surrounding seawater. Due to the vanadium content of living beings, coal and crude oil that arise from them also contain vanadium. The content is up to 0,1%. Particularly high levels of vanadium are found in petroleum from Venezuela and Canada.
Promotion of vanadium ore
In 2006 a total of 55.700 tons of vanadium ore were mined (calculated as vanadium metal). The most important producing countries are South Africa, China and Russia. Vanadium is not a scarce raw material, there are known reserves of 63 million tons.
Extraction and presentation
Vanadium is represented in several steps. First of all, vanadium (V) oxide must be obtained from various starting materials. This can then be reduced to elementary metal and cleaned if necessary.
Possible starting materials from which vanadium can be extracted are vanadium ores such as carnotite or patronite, vanadium-containing titanium-magnetite ores and petroleum. Vanadium ores were important for production in the past, but no longer play an important role and have mainly been replaced by titanium-magnetite ores.
If iron ores containing vanadium are reduced to iron in the blast furnace process, the vanadium initially remains in the pig iron. In order to further process the pig iron into steel, oxygen is blown in during the refining process. The vanadium goes into the slag. This contains up to 25% vanadium (V) oxide and is the most important source for the extraction of the metal. In order to obtain the pure vanadium (V) oxide, the finely ground slag is roasted in an oxidizing manner using sodium salts such as sodium chloride or sodium carbonate. In the process, water-soluble sodium metavanadate is formed, which is separated from the remaining slag by leaching. The resulting insoluble ammonium polyvanadate precipitates out of the solution by adding acid and ammonium salts. This can be converted to vanadium (V) oxide by roasting. The oxide can also be obtained from other vanadium-containing ores in an identical way. The vanadium can be extracted from petroleum by forming an emulsion with the addition of water and magnesium nitrate. The further processing takes place as with the extraction from iron ores.
The actual vanadium production takes place by reducing the vanadium (V) oxide with other metals. As the reducing agent, aluminum, calcium, ferro-silicon or carbon can be used; with the latter, however, carbides are formed in the reaction, which are difficult to separate from the metal.
Reduction with calcium
In order to obtain pure vanadium, expensive calcium or aluminum is used as a reducing agent, since a high degree of purity cannot be achieved with the cheaper ferrosilicon. Whereas pure vanadium is obtained directly with calcium, a vanadium-aluminum alloy is initially formed with aluminum, from which pure vanadium is obtained by sublimation in a vacuum.
However, much of the vanadium is not pure metal, but in the form of iron-vanadium alloy ferrovanadiumcontaining at least 50% vanadium is used. In order to produce this, it is not necessary to extract the pure vanadium beforehand. Instead, the vanadium and iron-containing slag is reduced to ferrovanadium with ferro-silicon and lime. This alloy is sufficient for most technical applications.
The purest vanadium can be produced either electrochemically or according to the Van-Arkel-de-Boer method. For this purpose, the pure vanadium is melted together with iodine in an empty glass ampoule. The vanadium (III) iodide formed in the heated ampoule decomposes on a hot tungsten wire to form highly pure vanadium and iodine.
Reaction in the Van Arkel-de-Boer process
Features
Physical Properties
Crystal structure of vanadium, a = 302,4 pm
Vanadium is a non-magnetic, tough, malleable and clearly steel-blue heavy metal with a density of 6,11 g / cm3. Pure vanadium is relatively soft, but becomes harder when other elements are added and then has high mechanical strength. In most of its properties it is similar to its neighbor in the periodic table, titanium. The melting point of pure vanadium is 1910 ° C, but this is significantly increased by impurities such as carbon. With a carbon content of 10% it is around 2700 ° C. Vanadium crystallizes like chromium or niobium in a body-centered cubic crystal structure with the space group 
and the lattice parameter a = 302,4 pm and two formula units per unit cell.
Vanadium becomes a superconductor below a transition temperature of 5,13 K. Just like pure vanadium, alloys of vanadium with gallium, niobium and zirconium are superconducting. At temperatures below 5,13 K, vanadium, like the vanadium group metals niobium and tantalum, shows a so far unexplained, spontaneous electrical polarization in tiny lumps of up to 200 atoms, which is otherwise only exhibited by non-metallic substances.
Chemical properties
Vanadium is a base metal and is able to react with many non-metals. In the air it remains shiny metallic for weeks. When viewed over longer periods of time, clearly visible green rust is perceived. If vanadium is to be preserved, it must be kept under argon. In the heat it is attacked by oxygen and oxidized to vanadium (V) oxide. While carbon and nitrogen only react with vanadium when it is incandescent, the reaction with fluorine and chlorine takes place in the cold.
Vanadium is mostly stable to acids and bases at room temperature due to a thin, passivating oxide layer; it is only attacked by hydrofluoric acid and strongly oxidizing acids such as hot nitric acid, concentrated sulfuric acid and aqua regia.
Vanadium is able to absorb hydrogen up to a temperature of 500 ° C. The metal becomes brittle and can be easily powdered. The hydrogen can be removed at 700 ° C in a vacuum.
Isotope
A total of 25 isotopes and a further 6 core isomers are known of vanadium. Of these, two occur naturally. These are the isotopes 50V with a natural frequency of 0,25% and 51V with a frequency of 99,75%. 50V is weakly radioactive, it decays with a half-life of 1,5 x 1017 Years to 83% under electron capture 50Ti, 17% below β-Decay too 50Cr. Both cores can be used for investigations with NMR spectroscopy.
The most stable artificial isotopes are 48V with a half-life of 16 days and 49V with a half-life of 330 days. These are used as tracers. All other isotopes and core isomers are very unstable and disintegrate in minutes or seconds.
Usage
Only a small percentage of pure vanadium is used as a cladding material for nuclear fuels due to its small neutron capture cross-section.[23] However, more resistant vanadium alloys can also be used. Over 90% of production is used in a variety of alloys, mostly with the metals iron, titanium, nickel, chromium, aluminum or manganese. Only a small part is used in compounds, mostly as vanadium (V) oxide.
With 85% of the vanadium produced, by far the largest part is consumed in the steel industry. Since this does not require high purities, ferrovanadium is used as a raw material. Even in small quantities, vanadium increases the strength and toughness and thus the wear resistance in steels significantly. This is caused by the formation of hard vanadium carbide. Depending on the application, different amounts of vanadium are added. Structural steels and tool steels contain only small amounts (0,2 to 0,5%) of vanadium, high-speed steel up to 5%. Vanadium-containing steels are mainly used for tools and springs that are subject to mechanical stress. Steels that contain cobalt in addition to iron and vanadium are magnetic.
Titanium alloys, which contain vanadium and mostly aluminum, are particularly stable and heat-resistant and are used in aircraft construction for load-bearing parts and turbine blades of aircraft engines.
Vanadium is used as the main electrolyte in one type of so-called redox flow cell; an example of such an application is the vanadium redox accumulator.
Proof
A preliminary sample is provided by the phosphorus salt bead, in which vanadium appears characteristic green in the reduction flame. The oxidation flame is pale yellow and therefore too unspecific.
Qualitative evidence for vanadium is based on the formation of peroxovanadium ions. To do this, an acidic solution containing vanadium in the +5 oxidation state is mixed with a little hydrogen peroxide. The reddish-brown [V (O2)]3+-cation. This reacts with larger amounts of hydrogen peroxide to form the pale yellow peroxovanadic acid H.3[VO2(O2)2].
Vanadium can be quantitatively determined by titration. For this purpose, a vanadium-containing sulfuric acid solution is oxidized with potassium permanganate to pentavalent vanadium and then back-titrated with an iron (II) sulfate solution and diphenylamine as an indicator. A reduction of existing pentavalent vanadium with iron (II) sulfate to the tetravalent oxidation state and subsequent potentiometric titration with potassium permanganate solution is also possible.
In modern analytics, vanadium can be detected using several methods. These are, for example, atomic absorption spectrometry at 318,5 nm and spectrophotometry with N-benzoyl-N-phenylhydroxylamine as the color reagent at 546 nm.
Biological significance
Vanadium compounds have different biological meanings. Characteristic of vanadium is that it is both anionic as vanadate, and cationic as VO2+, VO2+ or V3+ occurs. Vanadates are very similar to phosphates and accordingly have similar effects. Since vanadate binds more strongly to suitable enzymes than phosphate, it is able to block and thus control enzymes of phosphorylation. This concerns, for example, the sodium-potassium-ATPase, which controls the transport of sodium and potassium into cells. This blockage can be quickly removed with desferrioxamine B, which forms a stable complex with vanadate. Furthermore, vanadium affects glucose uptake. It is able to stimulate glycolysis in the liver and inhibit the competitive process of gluconeogenesis. This leads to a lowering of the glucose level in the blood. It is therefore being investigated whether vanadium compounds are suitable for the treatment of type 2 diabetes mellitus. However, no clear results have yet been found. In addition, vanadium also stimulates the oxidation of phospholipids and suppresses the synthesis of cholesterol by inhibiting squalene synthase, a microsomal enzyme system in the liver. Consequently, a deficiency causes increased levels of cholesterol and triglycerides in the blood plasma.
Vanadium plays a role in photosynthesis in plants. It is able to catalyze the reaction to form 5-aminolevulinic acid without enzyme. This is an important precursor to the formation of chlorophyll.
In some organisms there are vanadium-containing enzymes, so some types of bacteria have vanadium-containing nitrogenases for nitrogen fixation. These are, for example, species of the genus Azotobacter as well as the cyanobacterium Anabaenavariabilis. However, these nitrogenases are not as efficient as the more common molybdenum nitrogenases and are therefore only activated when there is a molybdenum deficiency. Other vanadium-containing enzymes can be found in brown algae and lichens. These have vanadium-containing haloperoxidases with which they build up organochlorine, bromine or iodine-organic compounds.
The function of vanadium, which is present in large quantities in sea squirts as the metalloprotein vanabine, is not yet known. It was originally assumed that vanadium, similar to hemoglobin, serves as an oxygen transporter; however, this has been found to be wrong.
hazards
Like other metal dusts, vanadium dust is flammable. Vanadium and its inorganic compounds have been shown to be carcinogenic in animal experiments. They are therefore classified in carcinogen category 2. If vanadium dust is inhaled by workers in metal smelting for a long time, so-called vanadism can occur. This recognized occupational disease can manifest itself in irritation of the mucous membranes, green-black discoloration of the tongue, as well as chronic bronchial, lung and intestinal diseases.
Connections
Vanadium can be present in compounds in various oxidation states. Often levels are +5, +4, +3 and +2, more rarely are +1, 0, −1 and −3. The most important and most stable oxidation states are +5 and +4.
Aqueous solution
In aqueous solution, vanadium can be easily converted into different oxidation states. As the various vanadium ions have characteristic colors, color changes occur.
In acidic solution, pentavalent vanadium forms colorless VO2+Ions, which at first reduce to blue tetravalent VO2+Ions. The trivalent level with V3+Ion is green in color, the deepest step achievable in aqueous solution, the bivalent V2+-Ion is gray-violet.
oxygen compounds
The most important and most stable vanadium-oxygen compound is vanadium (V) oxide V2O5. This orange-colored compound is used in large quantities as a catalyst for the production of sulfuric acid. There it acts as an oxygen carrier and during the reaction becomes another vanadium oxide, vanadium (IV) oxide VO2 reduced. Further known vanadium oxides are vanadium (III) oxide V2O3 and vanadium (II) oxide VO.
In an alkaline solution, vanadium (V) oxide forms vanadates, salts with the anion VO43−. In contrast to the analogous phosphates, however, the vanadate ion is the most stable form; Hydrogen and dihydrogen vanadates as well as free vanadium acid are unstable and only known in dilute aqueous solutions. If basic vanadate solutions are acidified, polyvanadates are formed instead of hydrogen vanadates, in which up to ten vanadate units accumulate. Vanadates can be found in various minerals, examples are vanadinite, descloicite and carnotite.
halogen compounds
Vanadium forms a multitude of compounds with the halogens fluorine, chlorine, bromine and iodine. Only one compound, vanadium (V) fluoride, is known to be in the +5 oxidation state. In the oxidation states +4, +3 and +2 there are compounds with all halogens, only with iodine only compounds in the states +2 and +3 are known. Of these halides, however, only the chlorides vanadium (IV) chloride and vanadium (III) chloride are technically relevant. Among other things, they serve as a catalyst for the production of ethylene-propylene-diene rubber.
Vanadiumoxidchloride
Vanadium also forms mixed salts with oxygen and chlorine, the so-called Vanadiumoxidchloride. Vanadium (III) oxychloride, VOCl, is a yellow-brown, water-soluble powder. Vanadium (IV) oxychloride, VOCl, used in photography and as a textile stain2 consists of green, hygroscopic crystal tablets that dissolve in water with a blue color. Vanadium (V) oxychloride, VOCl3 after all, is a yellow liquid that is very easily hydrolyzed by water. VOCl3 serves as a catalyst component in low pressure polymerization.
Further vanadium compounds
In organic vanadium compounds, vanadium reaches its lowest oxidation states 0, −I and −III. The metallocenes, the so-called vanadocenes, are particularly important here. These are used as catalysts for the polymerization of alkynes.
Vanadium carbide VC is used in powder form for plasma spraying or plasma powder build-up welding, among other things. Furthermore, vanadium carbide is added to hard metals in order to reduce grain growth. The result is so-called cermets, which are particularly hard and wear-resistant.
| General | ||||||||||||||||||||||||||||||||||
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| Name, symbol, atomic number | Vanadium, V, 23 | |||||||||||||||||||||||||||||||||
| Series | Transition metals | |||||||||||||||||||||||||||||||||
| Group, period, block | 5, 4, d | |||||||||||||||||||||||||||||||||
| Appearance | steel gray metallic, bluish shimmering | |||||||||||||||||||||||||||||||||
| CAS number | 7440-62-2 | |||||||||||||||||||||||||||||||||
| Mass fraction of the earth shell | 0,041% | |||||||||||||||||||||||||||||||||
| Atomic | ||||||||||||||||||||||||||||||||||
| atomic mass | 50,9415 u | |||||||||||||||||||||||||||||||||
| Atomic radius (calculated) | 135 (171) pm | |||||||||||||||||||||||||||||||||
| Covalent radius | 153 pm | |||||||||||||||||||||||||||||||||
| electron configuration | [Ar] 3d3 4s2 | |||||||||||||||||||||||||||||||||
| 1. ionization | 650,9 kJ / mol | |||||||||||||||||||||||||||||||||
| 2. ionization | 1414 kJ / mol | |||||||||||||||||||||||||||||||||
| 3. ionization | 2830 kJ / mol | |||||||||||||||||||||||||||||||||
| 4. ionization | 4507 kJ / mol | |||||||||||||||||||||||||||||||||
| 5. ionization | 6298,7 kJ / mol | |||||||||||||||||||||||||||||||||
| Physically | ||||||||||||||||||||||||||||||||||
| Physical state | fest | |||||||||||||||||||||||||||||||||
| crystal structure | cubic body-centered | |||||||||||||||||||||||||||||||||
| density | 6,11 g / cm3 (20 ° C) | |||||||||||||||||||||||||||||||||
| Mohs hardness | 7,0 | |||||||||||||||||||||||||||||||||
| magnetism | paramagnetic ( = 3,8 10−4) |
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| melting point | 2183 K (1910 ° C) | |||||||||||||||||||||||||||||||||
| boiling point | 3680 K (3407 ° C) | |||||||||||||||||||||||||||||||||
| Molar volume | 8,32 · 10−6 m3/ mol | |||||||||||||||||||||||||||||||||
| Heat of vaporization | 453 kJ / mol | |||||||||||||||||||||||||||||||||
| heat of fusion | 21,5[5] kJ / mol | |||||||||||||||||||||||||||||||||
| speed of sound | 4560 m / s at 293,15 K | |||||||||||||||||||||||||||||||||
| Specific heat capacity | 489 J / (kg K) | |||||||||||||||||||||||||||||||||
| Electric conductivity | 5 · 106 A / (V · m) | |||||||||||||||||||||||||||||||||
| thermal conductivity | 31 W / (m K) | |||||||||||||||||||||||||||||||||
| Chemical | ||||||||||||||||||||||||||||||||||
| oxidation states | +5, + 4, + 3, + 2 | |||||||||||||||||||||||||||||||||
| electronegativity | 1,63 (Pauling scale) | |||||||||||||||||||||||||||||||||
| Isotope | ||||||||||||||||||||||||||||||||||
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