Rhenium price
rhenium is a chemical element with the element symbol Re and the atomic number 75. In the periodic table of the elements it is in the 7th subgroup (group 7) or manganese group. It is a very rare, silver-white, shiny, heavy transition metal. Alloys with rhenium components are used in aircraft engines, in the manufacture of unleaded gasoline and in thermocouples.
Biological functions of rhenium are not known, it does not normally occur in the human organism. The metal is also not known to have any toxic effects;
History
The existence of the later rhenium was first predicted in 1871 by Dmitri Ivanovich Mendeleev as Dwi-Mangan. From the principles of the periodic table he designed, he concluded that two as yet unknown elements, the later technetium and rhenium, must be below manganese.
Ida Noddack-TackeRhenium was only discovered in 1925 by Walter Noddack, Ida Tacke and Otto Berg. They examined columbite to find the elements they were looking for, Eka and Dwi manganese. Since the samples contained only a very small amount of the elements sought, they had to be enriched by separating the other components. Finally, the later rhenium could be detected by X-ray spectroscopy. Noddack and Tacke also claimed to have found very small amounts of the eka manganese (later technetium), but this could not be confirmed by representation of the element. They named the elements Rhenium (lat. Rhenus for Rhine) and masurium (from Masuria). However, the latter did not prevail after the discovery of technetium in 1937.
In 1928, Noddack and Tacke were able to extract one gram of rhenium from 660 kilograms of molybdenum ore for the first time. Because of the high costs, the production of significant quantities did not begin until 1950, when there was a greater need for newly developed tungsten-rhenium and molybdenum-rhenium alloys.
occurrence
With a proportion of only 0,7 ppb in the continental crust, rhenium is rarer than rhodium, ruthenium and iridium. It does not occur naturally, but is exclusively bound in some ores. Since rhenium has similar properties to molybdenum, it is mainly used in molybdenum ores such as molybdenum luster MoS2 found. These can contain up to 0,2% rhenium. Further minerals containing rhenium are columbite (Fe, Mn) [NbO3], Gadolinite Y2 Fe Be [O | SiO4]2 and Alvit ZrSiO4. The Mansfeld copper slate also contains small amounts of rhenium. The largest deposits of rhenium-containing ores are in the United States, Canada and Chile.
So far only one rhenium mineral, rheniite (rhenium (IV) sulfide, ReS2) discovered. It was found in a fumarole on the summit crater of the Kudrjawyj volcano (Russian: Кудрявый) on the island of Iturup, which belongs to the Kuril Islands (Russia).
Extraction and presentation
The basic material for the extraction of rhenium are molybdenum ores, especially molybdenum luster. If these are roasted in the course of molybdenum extraction, rhenium accumulates as volatile rhenium (VII) oxide in the fly ash. This can be converted into ammonium perrhenate (NH4ReO4) are implemented.
The ammonium perrhenate is then reduced to elemental rhenium using hydrogen at high temperatures.
The main producers in 2006 were Chile, Kazakhstan and the United States, the total amount of rhenium produced was around 45 tons.
Features
Physical Properties
Rhenium is a shiny white, hard heavy metal that looks similar to palladium and platinum. It crystallizes in a hexagonal close packing of spheres in the space group P63/mmc with the grid parameters a = 276,1 pm and c = 445,8 pm and two formula units per unit cell. The density of rhenium is 21,03 g / cm3 is only surpassed by the three platinum metals osmium, iridium and platinum.
At 3186 ° C, rhenium has one of the highest melting points of all elements. It is only surpassed by the highest melting metal tungsten (3422 ° C) and carbon. However, the boiling point of 5596 ° C is the highest of all metals and exceeds tungsten (boiling point 5555 ° C) by 41 K.
Below 1,7 K, rhenium becomes a superconductor.
Rhenium can be easily processed by forging and welding, as it is ductile and, unlike tungsten or molybdenum, remains this even after recrystallization. When welding rhenium, there is no embrittlement that would lead to greater brittleness and thus poorer material properties.
The activity of rhenium is 1,0 MBq / kg.
Chemical properties
Although rhenium with a negative standard potential is not a noble metal, it is unreactive at room temperature and stable to air. Only when heated does it react with oxygen above 400 ° C to form rhenium (VII) oxide. It also reacts with the non-metals fluorine, chlorine and sulfur when heated.
Rhenium is not soluble in non-oxidizing acids such as hydrochloric acid or hydrofluoric acid. In contrast, the oxidizing sulfuric and nitric acids dissolve rhenium easily. Colorless perrhenates (VII) of the form ReO are easily formed with oxidation melts4- or green rhenates (VI) of the ReO type42−.
isotope
A total of 34 isotopes and a further 20 core isomers of rhenium are known. Of these, two come, the isotopes 185Re and 187Re, of course, before. 185Re, which accounts for 37,40% of the natural isotope distribution, is the only stable isotope. The more frequent with a share of 62,60% 187Re is weakly radioactive. It disintegrates with beta decay with a half-life of 4,12 · 1010Years too 187Os, resulting in a specific activity of 1020 becquerels / gram. Along with indium, rhenium is one of the few elements that have a stable isotope, but are most frequently found in their radioactive form in nature. Both isotopes can be detected with the aid of nuclear magnetic resonance spectroscopy. Of the artificial isotopes are 186Re and 188Re used as a tracer. As the main beta emitter 186Re used in nuclear medicine for radiosynoviorthesis therapy. 188Re is used as a radioactive drug in tumor therapy.
The decay of 187Re too 187Os is called Rhenium-osmium method used in geology for isotopic age determination of rocks or minerals. The isochronous method is used to correct the previously existing osmium
Usage
Rhenium is usually not used as an element, but is used as an admixture in a large number of alloys. About 70% of the rhenium is used as an additive in nickel superalloys. An addition of 4 to 6% rhenium improves the creep and fatigue behavior at high temperatures. These alloys are used as turbine blades for aircraft engines.
Another 20% of the rhenium produced is used for platinum-rhenium catalysts. These play a major role in increasing the octane number of unleaded gasoline through reforming ("rheniforming"). The advantage of rhenium is that, compared to pure platinum, it is not deactivated as quickly by carbon deposits on the surface of the catalyst (“coking”). This makes it possible to carry out production at lower temperatures and pressures and thus to produce more economically. Other hydrocarbons such as benzene, toluene and xylene can also be produced with platinum-rhenium catalysts.
Thermocouples for temperature measurement at high temperatures (up to 2200 ° C) are made of platinum-rhenium alloys. As an alloy with other metals such as iron, cobalt, tungsten, molybdenum or precious metals, rhenium improves resistance to heat and chemical influences. However, its use is limited by the rarity and high price of rhenium.
Rhenium is also used in some special applications, for example for hot cathodes in mass spectrometers or contacts in electrical switches.
proof
There are several ways to detect rhenium. Spectroscopic methods are one possibility. Rhenium has a pale green flame color with characteristic spectral lines at 346 and 488,9 nm. Rhenium can be detected gravimetrically via the characteristic crystallizing perrhenic acid or various perrhenate salts such as tetraphenylarsonium perrhenate. Modern analytical methods such as mass spectrometry or nuclear magnetic resonance spectroscopy are also suitable for detecting the element.
safety instructions
Like many metals, rhenium in powder form is highly flammable and combustible. No water may be used for extinguishing because of the hydrogen produced. Instead, extinguishing agents or metal fire extinguishers should be used. Compact rhenium, on the other hand, is not flammable and harmless. Rhenium has no known biological significance for the human organism. Although nothing more is known about the toxicity of rhenium and no toxicity values exist, rhenium is considered safe in terms of occupational hygiene.
Connections
Rhenium forms a large number of compounds; As with manganese and technetium, compounds in the oxidation states from −III to + VII are known. In contrast to manganese, however, compounds in the high oxidation states are more stable than in the lower ones.
Oxide
A total of five oxides of rhenium are known, the yellow Re2O7, red ReO3, Re2O5, brown-black ReO2 and Re2O3. Rhenium (VII) oxide Re2O7 is the most stable rhenium oxide. It is an intermediate product in the production of rhenium and can be used as a starting compound for the synthesis of other rhenium compounds such as methyltrioxorhenium. It dissolves in water to form the stable perrhenic acid HReO4. Rhenium (VI) oxide ReO3 has a characteristic crystal structure that serves as a crystal structure type (rhenium trioxide type).
halides
A total of 13 compounds of rhenium with the halogens fluorine, chlorine, bromine and iodine are known. Rhenium reacts preferentially to form hexahalides of the ReX type6. This creates pale yellow rhenium (VI) fluoride ReF6and green rhenium (VI) chloride ReCl6 directly from the elements at 125 ° C or 600 ° C. Reaction of rhenium with fluorine under slight pressure at 400 ° C leads to light yellow rhenium (VII) fluoride, besides osmium (VII) fluoride and iodine (VII) fluoride the only known halide in the + VII oxidation state. Red-brown rhenium (V) chloride (ReCl5)2 has a dimeric, octahedral structure. Chlorination of ReO2 with thionyl chloride gives a black, polymeric chloride Re2Cl9, which consists of chains of dimeric Re-Cl clusters that are bridged by chlorine atoms. If higher rhenium chlorides are thermally decomposed at over 550 ° C, dark red, trimeric rhenium (III) chloride Re is formed3Cl9. Structurally, its molecules consist of triangular metal clusters, the Re-Re distances of 248 pm proving the double bond character of the metal-metal bonds. The halides are sensitive to water and react with water to form halogen oxides or oxides.
Further rhenium compounds
The black rhenium (VII) sulfide Re2S7 produced from perrhenate solutions by introducing hydrogen sulfide. Thermal decomposition also gives black rhenium (IV) sulfide ReS2which is also accessible directly from the elements.
Rhenium forms a variety of complexes. Both classical complexes with individual metal centers and metal clusters are known. In these, rhenium-rhenium multiple bonds are sometimes also in the form of triple or quadruple bonds. A quadruple bond exists in the Re2X82−-Complex ion (X is a halogen atom or a methyl group).
Organometallic compounds of rhenium are also known. An important organic rhenium compound is methylrhenium trioxide (MTO), which can be used as a catalyst for metathesis reactions, for the epoxidation of olefins and for the olefination of aldehydes. MTO and other rhenium catalysts for metathesis are particularly resistant to catalyst poisons.
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