|Name , symbol , atomic number||Wolfram, W, 74|
|Element category||Transition metals|
|Group , period , block||6 , 6 , d|
|Appearance||grayish white, shiny|
|Mass fraction of the earth's envelope||64 ppm|
|Atomic mass||183.84 (1) u|
|Atomic radius (calculated)||135 (193) pm|
|Covalent radius||162 pm|
|Electron configuration||[ Xe ] 4 f 14 5d 4 6 s 2|
|1. Ionization energy||7th.86403 (10) eV ≈ 758.76 kJ / mol|
|2. Ionization energy||16.37 (15) eV ≈ 1 580 kJ / mol|
|3. Ionization energy||26th.0 (4) eV ≈ 2 510 kJ / mol|
|4. Ionization energy||38.2 (4) eV ≈ 3 690 kJ / mol|
|5. Ionization energy||51.6 (3) eV ≈ 4 979 kJ / mol|
|Crystal structure||body-centered cubic|
|density||19.25 g / cm 3 (20 ° C )|
|magnetism||paramagnetic ( Χ m = 7.8 10 −5 )|
|Melting point||3695 K (3422 ° C)|
|boiling point||6203 K (5930 ° C)|
|Molar volume||9.47 10 −6 m 3 mol −1|
|Heat of evaporation||774 kJ / mol|
|Heat of fusion||35.2 kJ mol −1|
|Speed of sound||5174 m · s −1|
|Specific heat capacity||138 J kg −1 K −1|
|Work function||4.55 eV|
|Electric conductivity||18.52 · 10 6 A · V −1 · m −1|
|Thermal conductivity||170 W m −1 K −1|
|Oxidation states||6 , 5, 4, 3, 2|
|Normal potential||−0.119 V (WO 2 + 4H + + 4e -
→ W + 2H 2 O)
|Electronegativity||2.36 ( Pauling scale )|
|For other isotopes see list of isotopes|
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .
Tungsten [ ˈvɔlfram ] is a chemical element with the element symbol W and the ordinal number 74. It is one of the transition metals , in the periodic table it is in the 6th subgroup (group 6) or chromium group . Tungsten is a white, shiny heavy metal of high density that becomes brittle with very little contamination . It is the chemical element with the highest melting and boiling point . Its best-known use is therefore the filament in light bulbs .
As early as the 16th century, the Freiberg mineralogist Georgius Agricola described the occurrence of a mineral in Saxon tin ores that made tin extraction considerably more difficult due to the slagging of the tin. The part of the name “wolf” comes from this property, as the mineral “ate” the tin ore like a wolf. Whether it was wolframite is still controversial today, as he spoke of the “lightness” of the mineral. He named the mineral lupi spuma , which translated from Latin means "wolf (s) foam". Later it was called tungsten , from mhd. Rām “soot, cream, dirt”, as the black-gray mineral can be easily ground and then reminds of soot. Its chemical symbol W comes from tungsten.
The word tungsten , commonly used in English, Italian and French, is derived from tung sten ( Swedish for "heavy stone"). In Sweden at that time this was not used to refer to tungsten itself (Swedish volfram ), but calcium tungstate . In 1781, the German-Swedish chemist Carl Wilhelm Scheele recognized a previously unknown salt in it. Pure tungsten was first produced in 1783 by the Spanish brothers Fausto and Juan José Elhuyar by reducing tungsten trioxide , which is extracted from wolframite.
The tungsten content of the continental crust is around 1 ppm or 0.0001% by weight. The metal was not found in nature so far gediegen be detected (in pure form). The Doklady Akademii Nauk in Russia published a report on solid tungsten in 1995 without it being examined by the Commission on new Minerals, Nomenclature and Classification (CNMNC) belonging to the IMA . Some minerals , especially oxides and tungstates, are known. The most important tungsten ore minerals are wolframite (Mn, Fe) WO 4 and scheelite CaWO 4 . There are also other tungsten minerals such as Stolzite PbWO 4 and Tuneptite WO 3 · H 2 O.
The largest deposits can be found in China , Peru , the USA , Korea , Bolivia , Kazakhstan , Russia , Austria and Portugal . Tungsten ores can also be found in the Ore Mountains . The safe and probable world deposits are currently 2.9 million tons of pure tungsten.
In 2017, tungsten production was 95,000 tons. By far the largest producer of tungsten is China. More than 80% of the tungsten produced in the world is extracted there. The states with the greatest extraction of tungsten are:
|(in tons )|
|People's Republic of China||79,000||77,000||68,000||68,000||73,000||72,000||79,000||1,800,000|
|Democratic Republic of Congo||830||800||not specified|
|North Korea||600||600||not specified|
Promotion in Austria
In Austria, Scheelite was first discovered in 1815/16 on the Schellgaden gold deposit in the municipality of Muhr ( State of Salzburg ). As a result, beautiful scheelite crystals, sometimes several centimeters in size, were found in many crevices of the Hohe Tauern. All of these finds were of no practical use. The large deposit in the Felbertal remained undiscovered for the time being.
In 1950 it became known that large amounts of scheelite appeared in the magnesite deposit on the Wanglalm near Lanersbach / Tux (Tyrol) in the rear of the Zillertal, which had been being mined since 1927 . It was coarse scheelite intergrown with magnesite and quartz . In the following years around 10,000 tons of ore with an average tungsten oxide content of 1.8% were extracted. Because of the low market price, tungsten extraction was stopped at the end of the 1960s, but resumed in 1971 and continued until the end of magnesite mining in 1976.
In 1967 the largest deposit of scheelite in Europe was discovered in the Felbertal. The pieces of ore in streams were traced with the help of UV light (Scheelite fluoresces). The difficult exploration work in the high alpine terrain (highest mining site on the Brentling at 2100 m above sea level) began in 1971, while the mining company Wolfram Bergbau und Hütten AG (WBH) began in the Felbertal in 1976. From 1979 ore was also extracted in civil engineering and open-cast mining was stopped in 1986 for environmental reasons. Since then, the tungsten ore from the Felbertal has been transported to Mittersill via an underground conveyor system and processed there by WBH. From here the scheelite concentrate reaches Sankt Martin im Sulmtal (Styria). The Wolframhütte, which has been producing tungsten oxide, tungsten metal and tungsten carbide powders from concentrates from Mittersill and other countries, was built on the site of the Pölfing-Bergla underground lignite mine, which was closed in 1976. From the beginning of 1993 to mid-1995, mining was temporarily suspended due to the low market price for tungsten. The most important processors in Germany are the HC Starck company , and in Austria the WBH and the Plansee Group .
Extraction and presentation
Tungsten cannot be obtained from oxidic ores by reduction with coal, as this results in tungsten carbide .
Ores containing tungsten are initially enriched to WO 3 concentrations of 10 to 75% by processes such as gravity separation or flotation . The concentrate is then calcined in an oxidizing atmosphere at 500-600 ° C. in order to remove impurities such as additives from the flotation process. Wolframite ores are then reacted with sodium hydroxide solution , Scheelite ores with a sodium carbonate solution, with sodium tungstate Na 2 WO 4 being formed, which is then purified by a series of reprecipitations . Tungsten (VI) oxide is precipitated as ammonium paratungstate from the purified solution obtained by liquid-liquid extraction with ammoniacal solutions or ion exchange with ammonium ions . Scrap containing tungsten, such as hard metal scrap, can also be converted into sodium tungstate after oxidation and then into ammonium tungstate. This complex is filtered off and then converted into relatively pure tungsten (VI) oxide at 600 ° C. Annealing gives anhydrous tungsten (VI) oxide (WO 3 ), which is reduced at 800 ° C in a hydrogen atmosphere:
This results in steel-gray tungsten powder, which is usually compacted in molds and electrically sintered into bars . At temperatures above 3400 ° C, a compact tungsten metal can be melted in special electric furnaces with a reducing hydrogen atmosphere ( zone melting process ).
Due to the high material value, the recycling of tungsten is of considerable economic importance. Technologically, a distinction is made between soft scrap and hard scrap. Tungsten soft scrap is grinding sludge, powder and chips from the processing of workpieces containing tungsten. Tungsten hard scraps, on the other hand, are pieces of hard metal, tungsten metal and tungsten alloys.
Soft tungsten scrap is roasted in deck or rotary kilns . The resulting tungsten oxide is reacted under pressure with sodium hydroxide solution to form sodium tungstate. Tungsten hard scrap requires oxidizing fusion with sodium nitrate. A raw sodium tungstate solution is obtained from the resulting melt cake. For pure, clean hard metal scrap, there is a process with which hard metal powder can be recovered without going through oxidation. In a zinc melt, the hard metal pieces are heated to 900 to 1,000 ° C under protective gas . Zinc penetrates the binding metal and breaks the bond with the tungsten carbide powder. The zinc is then evaporated and the powder made from tungsten carbide and binder metal is processed into new hard metal products.
In addition to the main product tungsten, the recovery of cobalt, nickel, copper, silver and tantalum is technically possible and practiced in all processes. Around 30% of the tungsten contained in end-of-life scrap is recovered worldwide. The recycling of hard metal tools works better than the recycling of tungsten-containing alloys, chemicals and catalysts. In consumer goods such as B. lamps, pens and smartphones contains tungsten, but its concentration is too low for recycling.
Together with the new scrap that occurs during production and further processing, this results in a scrap usage rate of approx. 35% in tungsten production.
Tungsten is a shiny white, in its pure state malleable metal of medium hardness , as well as high density and strength . The density is almost the same as that of gold , the Brinell hardness is 250 HB , the tensile strength 550–620 N / mm 2 to 1920 N / mm 2 . The metal exists in a stable body-centered cubic α- modification with a lattice plane spacing (= lattice constant ) of 316 pm at room temperature. This type of crystal structure is often called the tungsten type. In contrast, a substance known as metastable β-modification of tungsten (distorted body-centered cubic) is the tungsten-rich oxide W 3 O.
With 3422 ° C of tungsten has the highest melting point of all chemical elements ( carbon does not melt but proceeds at 3642 ° C directly into the gaseous state) and 5930 ° C also has the highest boiling point .
Tungsten is a chemically very resistant metal that is hardly attacked even by hydrofluoric acid and aqua regia (at least at room temperature). However, it dissolves in mixtures of hydrofluoric and nitric acid and molten mixtures of alkali nitrates and carbonates.
33 isotopes and five core isomers are known of tungsten . In nature there are five isotopes before 180 W, 182 W, 183 W, 184 W and 186 W. The tungsten isotope 184 W has the greatest frequency. All five natural isotopes could theoretically be unstable, but it was not until 2004 that the CRESST experiment at the Laboratori nazionali del Gran Sasso, as a secondary result of the search for dark matter, was able to prove that the 180 W isotope is subject to alpha decay . The half-life is an extremely long 1.8 trillion years, so this decay cannot be detected in a normal laboratory environment. The radioactivity of this natural isotope is so low that it can be ignored for all practical purposes. According to current knowledge, the possible half-lives of the other four natural isotopes should be longer than at least eight trillion years. The artificial radioactive isotopes of tungsten, on the other hand, have short half-lives between 0.9 ms at 185 W and 121.2 days at 181 W.
Science, technology and medicine
Approx. 65 percent of the quantities of tungsten produced worldwide are processed into tungsten carbide , which is used to manufacture hard metal tools. In addition, tungsten is primarily used as an alloying element.
Because of its high melting point, the most important application of pure tungsten is in the lighting industry as a filament in incandescent lamps and fluorescent tubes , and also as an electrode in gas discharge lamps and in electron tubes . In incandescent lamps, a higher specific resistance of tungsten is more of an advantage, as it allows a sufficiently high resistance to be generated with a wire that is not too thin - often as a double helix. Thin wire is sensitive to vibrations. A particularly compact luminous surface is achieved by an upright, flat, square filament of comparatively thick tungsten wire, which has to be operated with low voltage in slide projectors because of the low resistance. The melting point of a tungsten filament limits the operating temperature and thus the light color of an incandescent lamp without a color filter. At a high operating temperature, the longer the operating time, the tungsten recrystallizes and typically shortens and stiffens the filament, and when switching on and off, changes in length due to the temperature change occur. Incandescent filaments are therefore resiliently suspended with some scope for shortening.
In applications in the lamp industry, tungsten is characterized by its low thermal expansion, which means that it can be melted directly into special borosilicate glasses , for example as a contact bushing . Such glass-metal connections are extremely tight .
Because of its high resistance to corrosion, tungsten can also be used as a material for equipment in chemical plants. However, because of the poor machinability of tungsten (tungsten can only be welded using laser or electron beams), this form of application is rarely used. The same applies to a conceivable application in medical technology. In addition, electrodes for welding processes are made from tungsten, for example for resistance welding, especially when materials such as copper, bronze or brass are to be welded. Even with universal TIG welding ( tungsten inert gas welding ), an electrode consists of tungsten or an alloy thereof. These electrodes are not melted off in the welding process. The arc burns as a plasma in a protective gas between the electrode and the component. The filling material is supplied separately in the form of rods.
Due to its high density, it is used for balance weights and for shielding against radiation. Although its density and thus the shielding effect are much higher than that of lead , it is used less often than lead for this purpose because it is more expensive and difficult to process.
The and lines of the characteristic X-ray radiation are around 59 keV and 67 keV, respectively. In scanning tunneling microscopy , tungsten is often used as the material for the probe tip. In physiology , especially neurophysiology , tungsten microelectrodes are used for extracellular recordings .
Tungsten is also used in the generation of X-rays as a target material in X-ray tubes or in linear accelerators . When accelerated electrons hit the cooled tungsten target, the X-rays are generated as bremsstrahlung . The X-rays generated in this way are used, among other things, in medicine for X-ray diagnostics .
Because of the high density of tungsten, armor-piercing ammunition with a projectile core made of tungsten carbide is used in some armies instead of the depleted uranium , which is technically and collaterally deadly, and which is more deadly, from the uranium enrichment . During the Second World War , tungsten projectiles were first used by the German Wehrmacht and are still used today in the Bundeswehr. The Nazi regime went to great lengths to obtain large quantities of tungsten, which was considered essential for the war effort. Portugal exported tungsten to both the Allies and the German Empire during this period. In Norway, the Knabengrube produced MO concentrate for Germany. The mine was owned by IG Farben and Friedrich Krupp AG . The OKW reported in 1944 that it covered 25% of its needs from Finland and 40% from Norway.
In sport, tungsten is used for high-quality dart barrels and for the tips of special arrows in archery . In hammer throwing , hammer heads were also made of tungsten to reduce air resistance and the radius of rotation. In addition, tungsten plates are used as additional weights in Formula 1 in order to achieve the prescribed minimum weight for Formula 1 cars. In sailing, too, it has been used in the keel bombs of large racers for some time . The water resistance is greatly reduced due to the greater density compared to conventional materials such as lead or cast iron. There are also rackets in tennis that have tungsten fibers incorporated into their carbon frame mesh. In this way, specific areas of the racket frame can be additionally stabilized in order to increase the playing precision. In golf , tungsten is sometimes used as a counterweight for smaller, more precise club heads.
In fly fishing , fishing lures are weighted down with pierced tungsten beads that are pushed onto the shank of the hook so that they dive faster and deeper. In fishing , especially spin fishing, tungsten is used as an environmentally friendly and even better sinking substitute for lead.
Since the beginning of the 21st century, tungsten carbide, incorrectly referred to as tungsten, has also been used in jewelry (tungsten jewelry), e.g. B. rings processed. This is very easy to determine from the hardness and density. WC has a Mohs hardness of 9.5, tungsten only 7.5. So far, all jewelry parts on the market have been made from tungsten carbide.
Strings for musical instruments are sometimes wound with tungsten in order to increase their weight and thereby reduce the pitch.
Due to the similar density of tungsten and gold, there are repeated reports that tungsten (Tungsten) is used to counterfeit gold bars (tungsten core with gold coating).
Tungsten is used as a positive bio-element by bacteria and archaea . Various enzymes that have tungsten as part of the cofactor from the hypertermophilic and strictly anaerobic archaeon Pyrococcus furiosus have been particularly well studied . Such tungsten enzymes could also be examined from anaerobic bacteria such as Eubacterium acidaminophilum . E. acidaminophilum is an amino acid fermenting bacterium that uses tungsten in the enzymes formate dehydrogenase and aldehyde oxidoreductase . In these organisms, tungsten replaces molybdenum because it is much more common in their natural environment (volcanic vents on the sea floor). But mesophilic facultative anaerobic microorganisms also have tungsten enzymes and have already been investigated.
According to the current state of knowledge, tungsten and its compounds are considered physiologically harmless. Lung cancer among workers in hard metal producing or processing plants is attributed to the cobalt that is also present .
In the animal model it was found that the largest amount of orally ingested tungsten compounds is quickly excreted in the urine . A small part of the tungsten goes into the blood plasma and from there into the erythrocytes . It is then deposited in the kidneys and the bone system. Three months after administration, most of the very small amounts of tungsten absorbed by the body are found in the bones.
In 2003 in Fallon / Nevada with 16 children suffering from leukemia since 1997 and in Sierra Vista / Arizona with nine children also suffering from blood cancer, two so-called cancer clusters - these are local areas with an above-average rate of cancer cases - were identified. In both places the drinking water has exceptionally high concentrations of tungsten. In the urine of the population significantly increased tungsten concentrations were detected. Both places are known for their tungsten ore deposits. In the following investigations by the Center for Disease Control (CDC), which lasted about a year , no direct connection between tungsten and leukemia could be established. Tungsten did not show any carcinogenic effects in any test method , and no cancer clusters were found in other places in Nevada with similarly high tungsten values in the urine of the population.
As a powder or dust it is highly flammable, in compact form it is non-combustible.
Tungsten forms several oxides. Between the initial link:
- Tungsten (VI) oxide WO 3 - lemon yellow
and the end link:
- Tungsten (IV) oxide WO 2 - brown
there are also the following intermediate oxides:
- W 10 O 29 blue-violet, homogeneity range WO 2.92 -WO 2.88
- W 4 O 11 red-violet, homogeneity range WO 2.76 -WO 2.73
- W 18 O 49 , WO 2.72 , red-violet crystal powder. Semiconductor. Density 7.72 g / cm 3 , crystal structure: deformed DO 6 type, monoclinic , space group P 2 / m (space group No. 10) , lattice parameters: a = 1832 pm, b = 379 pm, c = 1404 pm, β = 115.2 °.
- W 20 O 50 , WO 2.50
- Sodium tungstate Na 2 WO 4
- Zirconium tungstate ZrW 2 O 8 shows an anomaly when heated .
- Tungsten oxide hydroxides of a certain composition and with oxidation numbers between 5 and 6 are blue in color. They are called tungsten blue and correspond in many ways to molybdenum blue . Tungsten blue serves as evidence of tungstates , from which it is formed by reduction.
- Tungsten bronzes M x WO 3 ; M = alkali metal, alkaline earth metal, lanthanoid, approx. 0.3 <x <0.9 have electrical conductivity and are intense and differently colored depending on the metal content .
- Calcium tungstate CaWO 4 is known as a mineral under the name Scheelite .
- Tungsten Carbide WC is an extremely hard metal-like compound. There is also diwtungsten carbide W 2 C.
- Tungsten hexafluoride WF 6
- Lead tungstate PbWO 4
- Tungsten disulfide WS 2 Use as a dry lubricant (similar to MoS 2 )
Use of the connections
Tungstates are used to impregnate fabrics to make them flame-retardant.
Tungsten-containing paints are used in painting as well as in the ceramic and porcelain industries.
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