Tungsten – facts and properties

Position in the periodic table

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Occurrence and extraction

Pure tungsten is not found in nature. The main ores are wolframite, a dark iron-manganese tungstate, and scheelite, a calcium tungstate that glows blue under ultraviolet light. China mines by far the largest share. Tungsten from crisis regions can also count as a conflict mineral.

The story of its discovery runs through two names. The Swedish chemist Carl Wilhelm Scheele showed in 1781 that a strikingly heavy mineral from Sweden contains an unknown acid. The Swedes called the mineral tung sten, meaning heavy stone, and that is the origin of the English name. Two years later, in 1783, the Spanish brothers Juan José and Fausto Elhuyar obtained the metal from wolframite in Bergara in the Basque Country by reducing the oxide with charcoal. The name wolfram is older. According to a common explanation, miners coined it because the mineral spoiled tin smelting, as if a wolf were devouring the tin.

The concentrated ore is broken down chemically, and ammonium tungstate leads to tungsten trioxide, which hydrogen reduces to fine powder. Melting and casting are hardly possible at these temperatures, so the powder is pressed, sintered just below the melting point and forged into rods and wire.

Properties and reactions

Tungsten is in period 6 and group 6, below molybdenum, which belongs to period 5. Its electron configuration is [Xe] 4f¹⁴ 5d⁴ 6s² and its electronegativity is 2.36. The metal has a density of 19.3 g/cm³, melts at 3422 °C and boils at 5555 °C. No other metal melts so high, and among all the elements only carbon goes beyond it, a substance that does not melt at normal pressure but turns straight into vapour.

The reason lies in the metallic bond. An unusually large number of d electrons take part in it, so the atoms hold on to each other very firmly. Pure tungsten is brittle at room temperature, but once it has been drawn into wire it becomes tough and flexible.

In compounds the oxidation numbers range from minus two to plus six, and plus six is the most common. The yellow trioxide WO₃ is the most important oxide. In air the metal only tarnishes at red heat and then burns to this oxide. Acids hardly attack it at room temperature, and it is dissolved by mixtures of hydrofluoric and nitric acid and by salt melts containing oxidising agents. Tungsten carbide, WC, is a compound with carbon that is almost as hard as diamond. The metal itself is considered of low toxicity.

Uses in everyday life and technology

Most tungsten is turned into hard metal. Tungsten carbide powder is mixed with cobalt, which holds the grains together like a glue, and sintered into plates and tips. Hard metal cuts steel, bores into rock and resists wear. It is found in drills, cutting inserts, tunnel boring machines and ballpoint pen balls.

Best known is the light bulb. A thin, coiled tungsten wire is heated by an electric current to about twenty-five hundred degrees Celsius and radiates bright light. The American engineer William Coolidge made a ductile tungsten wire around 1910, and tungsten finally displaced the older filaments of carbon, osmium and tantalum. Tungsten wire is still found in halogen and special lamps, in the heaters of vacuum furnaces and in the cathodes of electron tubes.

Because tungsten withstands so much heat, it serves as the electrode in TIG welding, as the anode in X-ray tubes and in rocket nozzles. Its high density suits balancing weights, vibration alarms in phones and darts, where it often replaces toxic lead.

Quick question

Why is argon (Ar) often used in light bulbs?

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