Tungsten

Dr Daniel J Bell et al.

Tungsten (chemical symbol, W) is a hard refractory metallic element with remarkable resilience which forms the basis for its industrial uses. It is the metal of choice in the filaments and targets of x-ray tubes. There is no evidence that tungsten is required by the human body, although some micro-organisms do use it.

Tungsten has the atomic number 74 and a relative atomic weight of 183.84 1. It is located in group VIb of the periodic table beneath chromium and molybdenum. At room temperature it is a solid steel-gray to white transition metal that is hard and brittle. It has the highest melting point of any metal at 3422°C, the lowest vapor pressure and the highest tensile strength at high temperatures (>1650°C). Its density is 19.3 g/cm3, only very slightly less than gold (19.32 g/cm3) 1,4.

There are four stable isotopes of tungsten, the commonest on earth being W-134 which accounts for 30.6% of the tungsten found terrestrially. Isotopes W-186, W-182 and W-183 account for 28.4%, 26.5% and 14.3% respectively 2. A fifth isotope, W-180, is technically unstable but has a half-life ~1.5 × 1018 years. It accounts for a mere 0.1% terrestrial tungsten 2.

At least 38 unstable isotopes have been characterized 2.

Tungsten has important niche roles in x-ray tubes and in radiation shielding.

  • tungsten is used as the metal in the filament in x-ray tubes due to its very high melting point 4
  • a tungsten-rhenium alloy (90%:10% mix) forms the basis for the target in modern x-ray tubes, rhenium improves the durability of the target 4
  • tungsten is used as a shielding material for FDG by the radiopharmaceutical industry, although it has a lower atomic number than lead it mitigates this with a higher density 5
  • tungsten is used for some embolization coils
  • tungsten carbide, an extremely hard-wearing material, is used for neurosurgical and dental burrs and drills

Elemental tungsten is relatively inert and toxicology studies have struggled to identify any significant toxicity from it 3,4.

There is contentious evidence that chronic occupational exposure to tungsten compounds (e.g. tungsten carbide) may have deleterious biological effects in people. Some metal workers have presented with symptoms following long-term cutaneous and/or respiratory exposure to mineral dusts. However, it is very difficult, if not impossible, to separate this out from coexisting dusts of other metals, e.g. cobalt, which are more likely the main culprit in these scenarios 3,4.

Acute tungsten poisoning has been reported but is very rare 4.

In 1758, the Swedish chemist Axel Fredrik Cronstedt found an especially weighty mineral, which he called “tung sten”, literally ‘heavy stone’, and he thought contained a novel element 4. Another Swedish chemist, Carl Wilhelm Scheele (1742-1786), isolated tungsten trioxide (WO3) from an acid derivative of the scheelite (the modern term for the tungsten mineral) in 1781 7,8. It was only two years later in 1783 that two Spanish brothers, Juan and Fausto Elhuyar, fully purified the element from wolframite, an ore, by reducing tungsten trioxide with charcoal, and they are recognized as the true ‘discoverers’ of the element 4,8.

So, they named their new element wolfram, but the name tungsten had already become well-known in the English-speaking chemistry world. In the past, IUPAC had recognized both names, but in 2005 it decided that tungsten would be the official international name for the element 1.

Biochemistry

Article information

rID: 84538
Synonyms or Alternate Spellings:
  • Tungsten carbide (WC)
  • Wolfram
  • Tungsten (W)

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Cases and figures

  • Figure 1: tungsten (photo)
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  • Figure 2: periodic table
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