Tungsten

Tungsten or tungsten, also known as wolfram or wolframium, is an element chemical with atomic number 74 found in group 6 of the periodic table of elements. Its symbol is W.

It is a rare metal in the earth's crust, but it is found in certain minerals in the form of oxides or salts. It is steely gray in color, very hard and dense, and has the highest melting and boiling points of all known elements. It is used in the manufacture of fishing tackle, in the filaments of incandescent lamps, in non-consumable electrodes for welding, in electrical resistances and, alloyed with steel, in the manufacture of special steels.

Its variety of sintered tungsten carbide is used to make cutting tools. This variety absorbs more than 60% of the world demand for tungsten.

Tungsten is a strategic material and has been on the list of most coveted commodities since World War II. For example, the United States government maintains a national reserve of six months along with other products considered essential for their survival.

History

In 1779 Peter Woulfe, while studying a sample of the mineral wolframite, (Mn, Fe) (WO₄), predicted that it must contain a new element. Two years later, in 1781, Carl Wilhelm Scheele and Torbern Bergman suggested that a new element could be found by reducing an acid (called "tungstic acid") obtained from the mineral scheelite (CaWO₄). In 1783, in Spain, the brothers Juan José Elhúyar and Fausto Elhúyar found an acid, from wolframite, identical to tungstic acid; the first brought the mineral with him from his journey through the European mines and universities. In Upsala (Sweden) he took classes with Bergman who told him about his intuitions regarding tungsten. Thus they managed to isolate the new element, by means of a reduction with charcoal, in the Royal Seminary of Vergara where the Royal Basque Society of Friends of the Country had its laboratory. They later published Chemical analysis of wolfram and examination of a new metal that enters into its composition describing this discovery.

In 1820 the Swedish chemist Berzelius obtained tungsten by reduction with hydrogen. The method, still used today, began to open up the possibilities of using this extraordinary metal, but its development was very slow. The constant need for new materials to fuel the wars of the XIX century prompted Austrian and English steelmakers to begin researching the properties of tungsten as an alloying element. At the University of Vienna experiments were carried out with tungsten-based alloys.

Description

The word "tungsten" comes from Swedish; tung translates as “heavy” and sten, “stone”, that is, “heavy stone”. The word is due to the Swedish mineralogist Axel Fredrik Cronstedt, discoverer of nickel, who included a description of this unknown mineral in his book Essays on Mineralogy of 1758. In the English version, of renowned academic prestige in the time, the word tungsten was maintained, which explains its popularity in the Anglo-Saxon world.

The word "wolfram" comes from the German words wolf and rahm, meaning "little value". It is also translated as "wolf slime" in reference to the superstitions of medieval Saxon miners who believed that the devil appeared in the form of a wolf and inhabited the depths of the mines, corroding the cassiterite with his drooling jaws. This metal appeared mixed with the acid of another unknown - tungsten - which acted corroding it.

Tungsten or tungsten

IUPAC names element 74, symbol W, as tungsten. The name wolfram was dropped in the latest edition of his Red Book (Inorganic Chemistry Nomenclature. 2005 IUPAC Recommendations). However, said elimination has not been accepted by the Spanish members of the IUPAC nor by Spanish language bodies, which continue to consider the original name wolfram («wolframio» or «volframio») as the correct name. In Latin America, element 74 is usually known as tungsten.

The name wolfram had already been officially adopted, instead of tungsten, by the IUPAC at its 15th conference, held in Amsterdam in 1949.

Features

Physical properties

Tungsten block.

Naturally, tungsten is a steel-gray metal that is often brittle and difficult to work, but if pure, it is easily workable. It is worked by forging, drawing, extrusion, and sintering. Of all metals in pure form, tungsten has the highest melting point (3,410 °C, 6,170 °F), lowest vapor pressure (at temperatures above 1,650 °C, 3,002 °F), and highest tensile strength.. In addition, it has the lowest coefficient of thermal expansion of any pure metal, and it is easily detected with Arnulphi's reagent in basic medium (KOH), turning it colorless. Thermal expansion is low, its melting point is high, and the strength is due to strong covalent bonds that form between tungsten atoms in the 5d orbital. It should be noted that alloying small amounts with steel increases its resistance. It has a very good combination of advantages, among which its great strength and heat resistance stand out, as well as acceptable chemical resistance, since it is not easily attacked by acids.

Metal is usually worked by sintering. The method consists of agglomerating it in the form of a powder of tiny grains in a metallic matrix. Although the best option is cobalt, you can also find nickel and even iron in these cases. All its alloys are distinguished by their enormous hardness and resistance. The metal behaves excellently even at high temperatures, which is not the case with rhenium, for example, despite the fact that both metals share a similar melting point.

Tungsten is the most abundant metal among the transition metals in group 6 of the periodic table. In case of shortage, molybdenum usually replaces it. One of its characteristics is that when exposed to ultraviolet light it has a very bright bluish glow.

Chemical Properties

Tungsten resists redox reactions, almost all common acids (including hydrofluoric) and alkalis, although only in its highest purity state, but it oxidizes rapidly when exposed to hydrogen peroxide (commonly known as hydrogen peroxide). Tungsten at room temperature withstands attack by nearly all major acids at any concentration although it can readily corrode in nitric acid and hydrogen peroxide. With hydrofluoric acid, the passivation phenomenon occurs, forming fluorides on its surface. However, the tungsten oxide layer is not stable above 400°C and the metal is exposed. The most commonly used tungsten compounds (eg tungsten carbide) improve somewhat on their already high corrosion resistance, and actually have a hard time dissolving in aqua regia; in these cases, the metal is suitable for use as jewelry, especially in state-of-the-art rings. Although it resists acids well, ironically it can oxidize even with common kitchen salt; in fact pure water oxidizes it (although the rust will not advance beyond the surface).

It is a difficult metal to alloy; it only does so with refractory metals, ferrous metals, and a few exceptions. It does not amalgamate with mercury at any temperature. Tungsten dissolves in molten aluminium, which is one of the few metals that, despite not resembling tungsten at all, perfectly alloys with it. The most common oxidation state of tungsten is +6, but it exhibits all oxidation states from –2 to +6. It normally combines with oxygen to form yellow tungsten oxide (WO₃) that dissolves in aqueous alkaline solutions to form tungsten ions (WO₄^2-).

Tungsten carbides (W₂C and WC) are produced by heating coal dust and are some of the hardest carbides, with a melting point of 2770 °C for WC and 2780 °C for W₂C, WC is an efficient electrical conductor, but W₂C is not, carbide behaves similarly to the same element without alloy, and is resistant to chemical attack, although it reacts strongly with chlorine to form tungsten hexachloride (WCl₆).

Aqueous solutions are characterized by the formation of heteropolyacid acid and polyoxometalate anions under neutral and acidic conditions, further acidifying the highly soluble metatungstate anion, after which equilibrium is reached. Many polyoxometalate anions exist in other metastable species, the inclusion of an atom of different characteristics, such as phosphorus, instead of two central hydrogens, in metatungstate produces a wide variety of heteropoly acids, such as phosphotungstic acid. Supported phosphotungstic acid can be used as a catalyst.

Applications

In its pure state it is used in the manufacture of filaments for electric lamps, resistors for electric ovens with reducing or neutral atmospheres, electrical contacts for automobile distributors, also in anti-tank projectiles (arrow) due to its high melting point and density, and anodes for X-ray and television tubes.

It has important uses in alloys for high-speed cutting tools, such as milling cutters for dental instruments (W2C), in the manufacture of spark plugs and in the preparation of varnishes (WO₃) and mordents in dry cleaning, in the tips of ballpoint pens and in the production of hard and resistant steel alloys.

Tungsten and its more popular alloy, tungsten carbide, are both excellent reflectors of neutrons. Tungsten crystals with the BCC structure are so compressed that they are effective shields against radiation of all kinds. Tungsten or tungsten carbide bars and plates can resist emissions including gamma particles or neutron rays. It is a powerful shield, superior to lead and also offers zero toxicity, which lead does not. It repels neutrons and nuclear energy due to its high density and atomic stability.

Calcium and magnesium tungstates are used in the manufacture of fluorescent tubes.

Tungsten carbide, stable at temperatures in the order of 500 °C, is also used as a dry lubricant.

Tungsten hexafluoride gas is used in the manufacture of integrated circuits.

TIG Welding Accessories.

For TIG (Tungsten Inert Gas) welding: it consists of using a non-fusible electrode (which does not melt), to make an electric arc between the piece and the machine, since it supports 3410 °C when it is pure (it is used to weld aluminum or magnesium, in alternating current). In this case, the electrode is marked with a green color. Likewise, if it is alloyed with thorium (2%), it supports 4000 °C and its use reaches the welding of stainless steels, copper and titanium, among others, in direct current, in which case the painted strip is red. There are also alloys with other chemical elements, such as zirconium, lanthanum, etc.

Since World War II it was used to armor the tip of anti-tank projectiles, such as AP ammunition, and in the armor of armored vehicles. The acquisition of tungsten became a vital and indispensable element for Germany Nazi, which acquired it through Franco's Spain and Salazar's Portugal. The supply of tungsten to the Nazis became so important that it caused a serious diplomatic crisis with the Allied Powers, since it was essential to the German war machine.

It is also used for the manufacture of darts, specifically in dart barrels, in an alloy with nickel, and in a proportion from 80% to 97%. In recent years it has been used for the manufacture of jewelry such as bracelets, rings and watches, and also for horseshoes as small studs to prevent them from slipping.^{[citation required]}

Research has been carried out on the use of tungsten mining waste for the production of new types of ceramic pastes, using them as tempering agents. During the extractive activity of the mineral, a large part of the rock from which it comes is discarded. These residues can be used to obtain manufactured ceramic products for possible applications in industry, architecture, conservation and restoration of heritage or fine arts.

The presence of tungsten improves the catalytic properties of mixed oxide catalysts for the oxidation of propylene to acrylic acid.

Biological paper

Tungsten is the heaviest known element used by living things; it has not been used by eukaryotes, but it is an essential nutrient for some bacteria. For example, enzymes called oxidoreductases use tungsten in a similar way to molybdenum by using it in a pterin-molybdopterin complex. Molybdopterin, despite its name, does not contain molybdenum, but can be complexed with molybdenum or tungsten for use in living things, and uses enzymes to reduce carboxylic acids to aldehydes. The first enzyme that requires discovery is also requires selenium, and in this case, selenium tungsten to function analogously to molybdenum binding enzymes. One of the enzymes in the oxidoreductase family that sometimes employs tungsten is known to use a version of molybdenum (molybdopterin selenium). Although a xanthine dehydrogenase-containing enzyme from bacteria has been found to contain tungsten molybdopterin and not selenium proteins, a tungsten molybdopterin-selenium complex has not been definitively described.

Biochemical Effects

In the soil it oxidizes, becoming a negative ion, forming the tungstate anion (WO2−
4). It is possible that molybdenum is substituted in some enzymes, and in such cases, the resulting enzyme in eukaryotes would presumably be inert. Soil chemistry determines the form of polymerization of tungsten; alkaline soils cause monomeric tungstates, while acidic soils cause polymeric tungstates.

Sodium tungstate and lead have been studied for their effects on earthworms. Lead is lethal at its lowest levels and sodium tungstate is much less toxic, but tungstate completely inhibited their reproductive ability.

Abundance and obtaining

To extract the element from its ore, it is melted with sodium carbonate, obtaining sodium tungstate, Na₂WO₄. The soluble sodium tungstate is then extracted with hot water and treated with hydrochloric acid to give tungstic acid, H₂WO₄. This last compound, once washed and dried, forms the oxide WO₃, which is reduced with hydrogen in an electric furnace. The fine powder obtained is reheated in molds in a hydrogen atmosphere, and pressed into bars that are rolled and hammered at a high temperature to make them compact and ductile.

Wolframita

There are tungsten ores mainly in China, Bolivia, Portugal, Russia, South Korea, Peru and the United States (in California and Colorado). In Spain, tungsten minerals are found in León (Bierzo Occidental), Salamanca (Barruecopardo and Los Santos), Galicia, especially in Puenteceso, Santa Comba and Carballo (La Coruña), in Extremadura, especially in some towns in Badajoz, in Tornavacas and Acebo. in Cáceres, or in the Conchita de Estepona Mine, in Málaga. During World War II, the tungsten mines in Spain and Portugal were very important as a source of supply for Nazi Germany, causing mineral prices to rise enormously, and that new mines were opened.

The main exporters are Russia (15.2%), Portugal (13.6%), Bolivia (11.9%), Spain (9.57%), North Korea (7.89%), United Kingdom Kingdom (7.37%) and Rwanda (3.91%).

This element ranks 57th in the classification of the most abundant elements in the earth's crust.

Distribution of elements in the terrestrial crust

It is never found free in nature, but in the form of salts combined with other elements, such as mainly scheelite (CaWO₄) and wolframite ((Fe, Mn)WO ₄), which are its most important minerals. Natural tungsten is a mixture of five stable isotopes. In addition, 21 unstable isotopes are known.

Tungsten is extracted from various tungsten minerals, such as tungsten ((Fe, Mn)WO₄), scheelite (CaWO₄), cuproscheelite (CuWO₄), ferrerite (FeWO₄), hübnerite (MnWO₄) and stolzite (PbWO₄ sub>). These ores are mined and used to produce about 37,400 tons of tungsten concentrates per year. China produced over 75% of this total, with most of the remaining production coming from Austria, Bolivia, Portugal and Russia.

Tungsten is extracted from its mines in several stages. The ore is further converted to tungsten trioxide (WO₃), which is heated with hydrogen or carbon to produce powdered tungsten. It can be used in that state or pressed into solid bars.

Tungsten can also be extracted by hydrogen reduction of WF₆:

WF₆ + 3 H₂ → W + 6 HF

or by pyrolytic decomposition:

WF₆ → W + 3 F₂ (Δ)H_r = +)

Tungsten prices are recorded on the London Metal Exchange. The price of pure metal is around USD 20,075 per ton.

World production in 2019, in tons per year

1.	ChinaChina	69,000
2.	VietnamVietnam	4,500
3.	Russia Russia	2.200
4.	Mongolia	1,900
5.	North KoreaNorth Korea	1.130
6.	BoliviaBolivia	1.060
7.	RwandaRwanda	900
8.	AustriaAustria	892
9.	SpainSpain	603
10.	Portugal	518

Source: USGS. NOTE: No data has been published for the United States.

Compounds

It can present oxidation states from –II to +VI, but the most common are the elevated ones. The flexibility in the oxidation state gives rise to a series of mixed valence compounds. Its most characteristic compounds are:

• Oxides of wolframium, and from them is obtained:
  • Mixed oxides with alkaline or alkainotere metals
  • Blue oxides, mixed valence, prepared by soft reduction
  • Volfram, mixed and non-stereometric valence, with a certain proportion of sodium
• Simple Volframatoes
• Iso and heteropoly acids and their salts, polyoxometalates of a great wealth and structural variety
• Sulfuros and halogenuros

Isotopes

Tungsten naturally consists of four stable isotopes and one unstable, ¹⁸⁰W. Tungsten isotopes are only unstable in theory, and since this is an assumption it cannot be considered feasible. In theory, all five isotopes can be broken down into hafnium isotopes by the emission of alpha radiation, but only ¹⁸⁰W has been observed with a half-life of (1.8 ± 0.2)×10 ¹⁸ years, on average, is the yield of about two ¹⁸⁰W alpha decays in one gram of natural tungsten per year. The other natural isotopes that have not been directly observed have limited their half-life to:

¹⁸²W, T_1/2  8,3×10¹⁸ years

¹⁸³W, T_1/2 ▪ 29×10¹⁸ years

¹⁸⁴W, T_1/2 ▪ 13×10¹⁸ years

¹⁸⁶W, T_1/2 ▪ 27×10¹⁸ years

A further 30 man-made radioisotopes of tungsten have been characterized as having a stable half-life, of which¹⁸¹W have a half-life of 121.2 days, ¹⁸⁵W with a half-life of 75.1 days, ¹⁸⁸W with a half-life of 69.4 days, ¹⁷⁸W with a half-life of 21.6 days, and ¹⁸⁷W with a half-life of 23.72 h. All other isotopes have half-lives of less than three hours, and most of these have half-lives of less than 8 minutes. Tungsten also has 4 nuclear isomers, the most stable being ^179mW (T_½ 6.4 minutes).

Precautions

Although data regarding the toxicity of tungsten are limited, cases of intoxication are known where the lethal dose for humans is estimated to be between 500 mg/kg and 5 g/kg. Tungsten is known to generates seizures and renal failure with acute tubular necrosis.

The effects of tungsten on the environment are virtually unknown; One concern that has been raised is the increasingly widespread use of the material in fishing sinkers, some of which are inevitably lost in the water. The unknown variable applies when tungsten may be deposited into the environment, either knowingly or unknowingly.