Tungsten

• 1. Introduction

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  Tungsten melts at 3422 C and does not boil until 5930 C, and no other known element matches either figure. Tungsten is also called wolfram, which is why its chemical symbol is W, and it is element 74. Its weight is just as striking as its heat tolerance. It is about as dense as uranium and gold, and roughly 1.7 times denser than lead. Yet pure tungsten has never been found in nature. It turns up locked inside compounds, mostly in ores called scheelite and wolframite. This documentary follows that stubborn metal. Why does one element carry two names, and why does one of them trace back to a wolf? Who first coaxed the metal out of its ore, and where did they do it? Why did governments bargain and scramble over tungsten during two world wars? And how can a metal so much cheaper than gold end up in counterfeit gold bars?

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• 2. A Wolf's Name

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  In 1546, Georg Agricola used a Latin name for a certain mineral, and the name pointed to a wolf. The reason was tin. During tin extraction, this mineral swallowed large amounts of the metal, as though a wolf had devoured it. In 1747, Johan Gottschalk Wallerius gave the mineral the German name wolf rahm. The mineral later became known as wolframite, and that is where the symbol W comes from.

  The wolf was part of a habit among miners from the Ore Mountains, who gave colorful names to troublesome minerals. Some minerals looked as if they held valuable metals but, once extracted, proved somehow hexed. Cobalt takes its name from the same miners' idiom and echoes the German word Kobold. Nickel echoes Old Nick, and pitchblende draws on the German word blenden.

  Tungsten is the other name, and it comes from Sweden. It was the old Swedish name for scheelite and for other minerals of similar density. English, French and many other languages use it for the element. Most European languages, especially Germanic and Slavic ones, use wolfram instead.

  In 1949, the International Union of Pure and Applied Chemistry accepted wolfram as the official name. English-speaking scientists disputed the choice. The next year it was revised to reflect how widely tungsten was used in that region, though the symbol W stayed. Germany and several other European countries still prefer wolfram, while Britain and the United States say tungsten. That Swedish mineral name leads straight to the chemist who, in 1781, first pulled an acid out of scheelite.

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• 3. Basque Isolation

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  In 1781, the chemist Carl Wilhelm Scheele found that a new acid, tungstic acid, could be made from scheelite. At that time the mineral itself was called tungsten. Scheele and Torbern Bergman suspected that reducing this acid might yield a new metal.

  In 1783, the brothers José and Fausto Elhuyar found an acid made from wolframite that proved identical to tungstic acid. Later that year, at the Royal Basque Society in the town of Bergara, Spain, the brothers succeeded. They reduced the acid with charcoal and isolated the metal. Credit for discovering the element goes to them, and they called it wolfram, or volfram.

  Tungsten later became the subject of an unusual legal fight. No other element has been the subject of patent proceedings. A patent had been granted in 1913 to William D. Coolidge, and General Electric sought to hold it. In 1928, a United States court rejected the attempt and overturned the grant.

  There is also a hint that the metal was handled long before the Basque brothers. It has been suggested that remnants of wolfram were found in what may have been the garden of Tycho Brahe, the astronomer and alchemist.

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• 4. Stubborn Matter

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  Carbon stays solid at temperatures higher than tungsten can survive, yet carbon has no melting point at all. At atmospheric pressure it sublimes instead of melting. That technicality leaves tungsten holding the melting record among pure metals. It also has the lowest vapor pressure above 1650 C, the highest tensile strength, and the lowest thermal expansion of any pure metal. All of this comes from strong covalent bonds formed between tungsten atoms by their 5d electrons. Its most stable crystal phase shows no pressure-induced structural change up to at least 364 gigapascals.

  In raw form, tungsten is a steel-grey metal, hard and often brittle. Polycrystalline tungsten is difficult to work. Pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw. Forging, drawing and extruding are possible, but sintering is more common because of the extreme melting point. Casting ingots is not commercially feasible. Manufacturers mix powdered tungsten with a little powdered nickel or another metal and sinter it. The nickel diffuses into the tungsten and forms an alloy. Adding even small amounts of tungsten to steel greatly increases its toughness.

  Chemically, tungsten is mostly unreactive. It does not react with water, resists most acids and bases, and ignores air at room temperature. When red-hot, it reacts with oxygen to form the yellow trioxide WO3. Fluorine is the exception that attacks it at room temperature, producing a colorless gas, tungsten(VI) fluoride. Finely divided tungsten is pyrophoric.

  Naturally occurring tungsten has four stable isotopes and one very long-lived radioisotope, 180W. Its half-life is 1.8e18 years, which works out to about two alpha decays per gram of natural tungsten each year. Another 34 artificial radioisotopes have been characterized, and the longest-lived of these, 181W, has a half-life of 121.2 days. In gaseous form, tungsten atoms pair up as W2 molecules joined by a sextuple bond, the highest bond order known among stable atoms.

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• 5. Workhorse Uses

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  Roughly half of all tungsten goes into hard materials, above all tungsten carbide. Carbide tooling shows up as knives, drills, circular saws, dies, and milling and turning tools. Metalworking, woodworking, mining, petroleum and construction all rely on it. The tools are actually a ceramic and metal composite, in which metallic cobalt holds the carbide particles in place. Most of the remainder goes into alloys and steels, and less than 10% is used in other compounds.

  High-speed steel can contain as much as 18% tungsten. Superalloys such as Hastelloy and Stellite carry it into turbine blades and wear-resistant coatings. Rocket nozzles use it too, including those on the UGM-27 Polaris submarine-launched ballistic missile. In 1886, John Hopkinson noted that quenched tungsten steel, with roughly 5.5% to 7.0% tungsten, makes hard permanent magnets. Tungsten stabilizes the martensite phase in such steel, which resists the movement of magnetic domain walls better than iron's ferrite phase.

  Tungsten filaments glowed inside incandescent light bulbs, cathode-ray tubes and vacuum tubes. Doping the metal with potassium keeps a filament from sagging. Arc welders know the metal through gas tungsten arc welding, also called TIG welding. In electronics, tungsten links the transistors of integrated circuits to the surrounding insulating layer. It forms emitter tips in electron microscopes, serves as a main source of X-ray targets, and shields against high-energy radiation. Even the vibration motors that buzz a phone use tungsten for its density and wear resistance.

  In nuclear fusion research, tungsten is a lead candidate for the most exposed parts of a reactor's inner wall. It will line the divertor in the ITER reactor, and it did the same job in the JET test reactor until that machine closed in December 2023.

  Some of its jobs are far humbler. Darts made with tungsten alloys can be thinner, which allows tighter groupings. Tungsten beads help artificial fishing flies sink fast. Race cars in NASCAR and Formula One carry tungsten ballast, as do yacht keels and the tails of commercial aircraft. A heavy tungsten bolt cut the rate of fire of the SWD M11/9 sub-machine gun from 1300 rounds per minute to 700. For the 2012 Mars Science Laboratory, seventy-five-kg tungsten blocks served as cruise balance masses on the entry vehicle. Aboard the two Voyager spacecraft, tungsten acts as an absorber in the electron telescope of the Cosmic Ray System.

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• 6. Gold's Double

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  Tungsten is only 0.36% less dense than gold, and its price is of the order of one-thousandth. That coincidence drives two very different trades. The honest one is jewelry. Metallic tungsten is hypoallergenic and harder than gold alloys, so rings made of it resist scratching, especially with a brushed finish.

  Tungsten carbide rings are more common. Makers use nickel rather than cobalt as the binder, because nickel takes a higher luster when polished. Sellers sometimes call tungsten carbide a metal, but it is a ceramic. Such rings are extremely abrasion resistant and hold a burnished finish longer than rings of metallic tungsten. They are brittle, though, and may crack under a sharp blow.

  The dishonest trade is counterfeiting. Since the 1980s, fraudsters have plated tungsten bars with gold. Another method is to take a real gold bar, drill holes in it, and replace the removed gold with tungsten rods. The densities are not exactly equal, and other properties of the two metals differ. Even so, gold-plated tungsten passes superficial tests. It is sold commercially from China, the main source of tungsten, both as jewelry and as bars.

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• 7. War And Mines

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  In 1912, British authorities acted to free the Carrock mine from the German-owned Cumbrian Mining Company. During World War I they also restricted German access to tungsten elsewhere. The strategic value of the metal had become obvious. In World War II the maneuvering grew more intense. Portugal, Europe's main source, held wolframite deposits at Panasqueira, and both sides pressured it. Tungsten's heat resistance, hardness, density and strengthening effect on alloys made it vital to arms makers, both in weapons and in carbide tools that machined steel.

  Germany used tungsten in shells for anti-tank guns built on the Gerlich squeeze bore principle. These guns achieved very high muzzle velocity and strong armor penetration from a small caliber and a light weight. The weapons were highly effective, but a tungsten shortage, caused in part by the Wolfram Crisis, limited their use. Today, tungsten heavy alloys with nickel, iron or cobalt serve as kinetic energy penetrators. They are an alternative to depleted uranium where its radioactivity is a problem. Alloys of tungsten have also been used in shells, grenades and missiles, creating supersonic shrapnel.

  The world's tungsten reserves stand at 3,200,000 tonnes. China holds 1,800,000 tonnes, Canada 290,000, Russia 160,000 and Vietnam 95,000, with Bolivia also on the list. In 2017, China mined 79,000 tonnes, Vietnam 7,200 and Russia 3,100. Canada stopped producing in late 2015 when its only tungsten mine closed. Vietnam had expanded output during the 2010s by optimizing its domestic refining. The Chinese government strictly regulates supply and fights illegal mining and pollution.

  Some mines have changed hands repeatedly. The Hemerdon Mine on the edge of Dartmoor in the United Kingdom was exploited in both world wars. Rising prices led to its reactivation in 2014, but it ceased activity in 2018. South Korea's Sangdong mine was closed in 1994 due to low profitability, and it was scheduled to resume in 2024. Austria's Felbertal scheelite deposit is one of the few producing mines in the European Union. From 1910 to 2020, Portugal produced 121 kt of contained tungsten, roughly 3.3% of global production. Tungsten is also considered a conflict mineral because of unethical mining practices in the Democratic Republic of the Congo.

  Pricing is unusual too. Tungsten is not traded as a futures contract and cannot be tracked on exchanges like the London Metal Exchange. Contracts instead lean on independent references such as Argus Media or Metal Bulletin.

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• 8. Life And Harm

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  At atomic number 74, tungsten is the heaviest element known to be biologically functional. Some bacteria and archaea use it, though eukaryotes do not. Enzymes called oxidoreductases pair it with molybdopterin, much as others use molybdenum. These enzymes typically reduce carboxylic acids to aldehydes. The first tungsten-requiring enzyme discovered also needs selenium.

  In archaea, the list of tungsten-using enzymes includes aldehyde ferredoxin oxidoreductase in Thermococcus strain ES-1. Formaldehyde ferredoxin oxidoreductase appears in Thermococcus litoralis, and glyceraldehyde-3-phosphate ferredoxin oxidoreductase in Pyrococcus furiosus. A transport system called wtp selectively carries tungsten into archaea. Acetylene hydratase is an unusual metalloenzyme, because it catalyzes a hydration reaction. In one proposed mechanism, the tungsten atom interacts directly with the carbon triple bond.

  For most animals, however, tungsten is somewhat toxic, because it interferes with molybdenum and copper metabolism. In an earthworm study, lead proved lethal at low levels, while sodium tungstate was much less toxic. Yet the tungstate completely inhibited the worms' ability to reproduce. Tungsten is rare, with a crustal abundance of about 1.5 parts per million, making it the 58th most abundant element on Earth.

  It was first thought to be relatively inert and only slightly toxic. Beginning in the year 2000, experiments in vitro and in vivo highlighted a risk that tungsten alloys, dusts and particulates can cause cancer and other adverse effects in animals and humans. The median lethal dose varies strongly with species and method of administration. It runs from 59 mg/kg for intravenous doses in rabbits to 5000 mg/kg for tungsten metal powder given intraperitoneally to rats. For workers, the National Institute for Occupational Safety and Health recommends an exposure limit of 5 mg/m3 over an 8-hour workday, with a short-term limit of 10 mg/m3.

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