The tungsten, tungsten or tungsten is a heavy transition metal whose chemical symbol is W. It is located in period 6 with group 6 of the periodic table, and its atomic number is 74. Its name has two etymological meanings: hard stone and wolf foam ; of the second is because this metal is also known as tungsten.
It is a silvery-gray metal and, although it is brittle, it has great hardness, density, and high melting and boiling points. Therefore, it has been used in all those applications that involve high temperatures, pressures or mechanical forces, such as drills, projectiles, or radiation-emitting filaments..
The best known use for this metal, at a cultural and popular level, is in the filaments of electric bulbs. Whoever has manipulated them will realize how fragile they are; however, they are not made of pure tungsten, which is malleable and ductile. In addition, in metallic matrices such as alloys, it provides excellent resistance and hardness.
It is characterized and distinguished by being the metal with the highest melting point, and also being denser than lead itself, surpassed only by other metals such as osmium and iridium. Likewise, it is the heaviest metal known to play a biological role in the body..
The tungstate anion, WO4two-, which can polymerize to form clusters in an acid medium. On the other hand, tungsten can form intermetallic compounds, or be sintered with metals or inorganic salts so that its solids acquire different shapes or consistencies..
It is not very abundant in the earth's crust, with only 1.5 grams of this metal per ton. Furthermore, as it is a heavy element, its origin is intergalactic; specifically from supernova explosions, which must have thrown “jets” of tungsten atoms towards our planet during its formation.
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The history of tungsten or wolfram has two faces like their names: one Swiss, and the other German. In the 1600s, in regions currently occupied by Germany and Austria, miners worked in the extractions of copper and tin to produce bronzes.
By then the miners found themselves with a thorn in the process: there was an extremely difficult mineral to melt; mineral consisting of wolframite, (Fe, Mn, Mg) WO4, which retained or "devoured" the tin as if it were a wolf.
Hence the etymology for this element, 'wolf' for wolf in Spanish, a wolf that ate tin; and 'ram' of foam or cream, whose crystals resembled a long black fur. It was thus that the name 'wolfram' or 'wolfram' arose in honor of these first observations.
In 1758, on the Swiss side to a similar mineral, scheelite, CaWO4, it was named 'tung sten', which means 'hard stone'.
Both names, tungsten and tungsten, are widely used interchangeably, depending solely on culture. In Spain, for example, and in western Europe, this metal is best known as tungsten; while in the American continent the name tungsten predominates.
It was known then that between the seventeenth and eighteenth centuries there were two minerals: wolframite and scheelite. But who saw that there was a metal different from the others in them? They could only be characterized as minerals, and it was in 1779 that the Irish chemist Peter Woulfe carefully analyzed tungsten and deduced the existence of tungsten..
On the Swiss side, again, Carl Wilhelm Scheele in 1781 was able to isolate tungsten as WO3; and even more, he obtained tungstic (or tungstic) acid, HtwoWO4 and other compounds.
However, this was not enough to get to the pure metal, since it was necessary to reduce this acid; that is, subjecting it to a process such that it unlinked from oxygen and crystallized as metal. Carl Wilhelm Scheele did not have the appropriate furnaces or methodology for this chemical reduction reaction.
It is here where the Spanish brothers d'Elhuyar, Fausto and Juan José, came into action, who reduced both minerals (wolframite and scheelite) with coal, in the city of Bergara. Both of them are awarded the merit and honor of being the discoverers of metallic wolfram or tungsten (W).
Like other metals, its uses define its history. Among the most prominent at the end of the 19th century were steel-tungsten alloys, and tungsten filaments to replace carbon in electric light bulbs. It can be said that the first light bulbs, as we know them, were marketed in 1903-1904.
It is a lustrous silver-gray metal. Fragile but very hard (not to be confused with toughness). If the piece is of high purity it becomes malleable and hard, as much or more as several steels.
74.
183.85 g / mol.
3422ºC.
5930ºC.
19.3 g / mL.
52.31 kJ / mol.
774 kJ / mol.
24.27 kJ / mol.
7.5.
2.36 on the Pauling scale.
139 pm
52.8 nΩ · m at 20ºC.
It occurs predominantly in nature as five isotopes: 182W, 183W, 184W, 186W and 180W. According to the molar mass of 183 g / mol, which averages the atomic masses of these isotopes (and the other thirty radioisotopes), each tungsten or tungsten atom has about one hundred and ten neutrons (74 + 110 = 184).
It is a metal highly resistant to corrosion, as its thin layer of WO3 It protects it against the attack of oxygen, acid and alkalis. Once dissolved and precipitated with other reagents, its salts are obtained, which are called tungstates or wolframates; in them usually tungsten has an oxidation state of +6 (assuming there are cations W6+).
Chemically, tungsten is quite particular because its ions tend to clustering together to form heteropoly acids or polyoxometalates. What are they? They are groups or clusters of atoms that come together to define a three-dimensional body; mainly, one with a spherical cage-like structure, in which they “enclose” another atom.
It all starts from the tungstate anion, WO4two-, which in acid medium rapidly protonates (HWO4-) and binds with a neighboring anion to form [WtwoOR7(OH)two]two-; and this in turn joins another [WtwoOR7(OH)two]two- to originate the [W4OR12(OH)4]4-. So on until there are several politungstats in solution.
Paratungstates A and B, [W7OR24]6- and HtwoW12OR4210-, respectively, they are one of the most outstanding of these polyanions.
It can be challenging to come up with your outline and Lewis structures; but it is enough in principle to visualize them as sets of WO octahedra6 (top image).
Note that these grayish octahedra end up defining the decatungstate, a politungstat; If it contained a heteroatom (for example, phosphorus) inside, then it would be a polyoxometalate.
Tungsten atoms define a crystal with a body-centered cubic structure (bcc, for body-centered cubic). This crystalline form is known as the α phase; while the β phase is also cubic, but a little more dense. Both phases or crystalline forms, α and β, can coexist in equilibrium under normal conditions.
The crystalline grains of the α phase are isometric, while those of the β phase resemble columns. Regardless of how the crystal is, it is governed by the metallic bonds that hold the W atoms tightly together. Otherwise, the high melting and boiling points, or the high hardness and density of tungsten could not be explained..
Tungsten atoms have to be tightly bound somehow. To make a conjecture, the electronic configuration of this metal must first be observed:
[Xe] 4f145 d46stwo
The 5d orbitals are very large and fuzzy, which would imply that between two nearby W atoms there are effective orbital overlaps. Likewise, the 6s orbitals contribute to the resulting bands, but to a lesser degree. While the 4f orbitals are "deep in the background" and therefore their contribution to the metallic bond is less.
This, the size of the atoms, and the crystalline grains, are the variables that determine the hardness of tungsten and its density..
In tungsten or metallic wolfram the W atoms have zero oxidation state (W0). Returning to the electronic configuration, the 5d and 6s orbitals can be "emptied" of electrons depending on whether W is in the company of highly electronegative atoms, such as oxygen or fluorine..
When the two 6s electrons are lost, tungsten has oxidation state +2 (Wtwo+), which causes its atom to contract.
If it also loses all the electrons in its 5d orbitals, its oxidation state will become +6 (W6+); from here it cannot become more positive (in theory), since the 4f orbitals, because they are internal, would require great energies to remove their electrons. In other words, the most positive oxidation state is +6, where the tungsten is even smaller.
This tungsten (VI) is very stable in acidic conditions or in many oxygenated or halogenated compounds. Other possible and positive oxidation states are: +1, +2, +3, +4, +5 and +6.
Tungsten can also gain electrons if it combines with atoms less electronegative than itself. In this case, its atoms get bigger. It can gain a maximum of four electrons; that is, have an oxidation state of -4 (W4-).
It was mentioned earlier that tungsten is found in the minerals wolframite and scheelite. Depending on the process, two compounds are obtained from them: tungsten oxide, WO3, or ammonium paratungstate, (NH4)10(HtwoW12OR42) · 4HtwoO (or ATP). Either of them can be reduced to metallic W with carbon above 1050ºC.
It is not economically profitable to produce tungsten ingots, as they would need a lot of heat (and money) to melt them. That is why it is preferred to produce it in powder form to treat it at once with other metals to obtain alloys..
It is worth mentioning that China is the country with the largest tungsten production worldwide. And in the American continent, Canada, Bolivia and Brazil, they also occupy the list of the largest producers of this metal.
Here are some of the known uses for this metal:
-Its salts were used to color cottons of old theatrical attire.
-Combined with steel, it hardens it even more, being able to resist mechanical cuts at high speeds..
-Sintered tungsten filaments have been used for over a hundred years in electric bulbs and halogen lamps. Also, due to its high melting point, it has served as a material for cathode ray tubes, and for the nozzles of rocket engines..
-Replaces lead in the manufacture of projectiles and radioactive shields.
-Tungsten nanowires can be used in pH and gas sensitive nanodevices.
-Tungsten catalysts were used to deal with sulfur production in the oil industry.
-Tungsten carbide is the most widely used of all its compounds. From the strengthening of cutting and drilling tools, or the manufacture of pieces of military armaments, to machining wood, plastics and ceramics.
Being a relatively rare metal in the earth's crust, its negative effects are scarce. In acidic soils, polyungstates may not affect the enzymes that use molybdate anions; but in basic soils, the WO4two- does intervene (positively or negatively) in the metabolic processes of MoO4two- and copper.
Plants, for example, can absorb soluble tungsten compounds, and when an animal eats them and then after consuming its meat, W atoms enter our bodies. Most are expelled in urine and feces, and little is known what happens to the rest of them..
Studies in animals have shown that when they inhale high concentrations of powdered tungsten they develop symptoms similar to those of lung cancer.
By ingestion, an adult human would need to drink thousands of gallons of water enriched with tungsten salts to show appreciable inhibition of the enzymes cholinesterase and phosphatase..
In general terms, tungsten is a low toxic element, and therefore there are few environmental risks to health damage..
Regarding metallic tungsten, avoid breathing its dust; and if the sample is solid, it should be borne in mind that it is very dense and that it can cause physical damage if it falls or hits other surfaces.
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