Tungsten

Nomenclature, origins and discovery

Tungsten is derived from the Swedish tung sten, or ‘’heavy stone’’. It is represented by the symbol W, as it is known as Wolfram in many European countries. This comes from German for ‘’wolf’s foam’’, as early tin miners noticed that a mineral they called wolframite reduced tin yield when present in tin ore, thus it seemed to consume tin like a wolf devours sheep. [i]

In 1779, Peter Woulfe examined sheelite from Sweden and discovered that it contained a new metal. Two years later, Carl Wilhelm Scheele reduced tungstic acid from this mineral and isolated an acidic white oxide. Another two years later, Juan and Fausto Elhuyar in Vergara, Spain, isolated the same metal oxide from an identical acid reduced from wolframite. They heated the metal oxide with carbon, reducing it to tungsten metal.

Physical and chemical properties

Tungsten is a shiny, silvery-white metal and has the atomic number 74 on the periodic table of elements and a standard atomic weight (A_r) of 183.84.[ii]

It has the highest melting point of all elements, ultra-high density and is very hard and stable. It has the lowest vapour pressure, lowest coefficient of thermal expansion and highest tensile strength of all metals. These properties are due to the strong covalent bonds between tungsten atoms formed by 5d electrons. The atoms form a body-centred cubic crystal structure.

Tungsten is also conductive, relatively chemically inert, hypoallergenic and possesses radiation shielding properties. The purest form of tungsten is easily malleable and worked by forging, extruding, drawing and sintering. Extruding and drawing involve the pushing and pulling, respectively, of hot tungsten through a “die” (mold), while sintering is the mixing of tungsten powder with other powdered metals to produce an alloy.

Commercial uses

Tungsten alloys are extremely hard, such as tungsten carbide, which is combined with ceramics to form ‘’high speed steel’’ – this is used to make drills, knives and cutting, sawing and milling tools. These are used in metal-working, mining, woodworking, construction and petroleum industries and account for 60% of tungsten use commercially.

Tungsten is used in heating elements and high-temperature furnaces. It is also found in ballasts in aircraft tails, yacht keels and racing cars, as well as weights and ammunition.

Calcium and magnesium tungstates were once commonly used for filaments in incandescent light bulbs, but are considered energy inefficient. Tungsten alloy are, however, used in low-temperature superconducting circuits.

Crystal tungstates are used in nuclear physics and nuclear medicine, X-ray and cathode ray tubes, arc-welding electrodes and electron microscopes. Tungsten trioxide is used in catalysts, such as one used in power plants that run on coal. Other tungsten salts are used in the chemical and tanning industries.

Some alloys are used as jewellery, while one is known to form permanent magnets and some superalloys are used as wear-resistant coatings.

Tungsten is the heaviest metal to have biological role, but only in bacteria and archaea. It is used by an enzyme that reduces carboxylic acids to aldehydes. [iii]

Titanium

Nomenclature, origins and discovery

Titanium is derived from the word ‘’Titans’’, sons of the Earth goddess in Greek mythology. Reverend William Gregor, an amateur geologist, noticed that black sand by a stream in Cornwall, 1791, was attracted to a magnet. He analysed it and learned that the sand contained iron oxide (explaining the magnetism), as well as a mineral known as menachanite, which he deduced was made of an unknown white metal oxide. This he reported to the Royal Geological Society of Cornwall.

In 1795, Prussian scientist Martin Heinrich Klaproth from Boinik investigated a red ore known as Schörl from Hungary and named the element of the unknown oxide it contained, Titanium. He also confirmed the presence of titanium in menachanite.

The compound TiO₂ is a mineral known as rutile. Titanium also occurs in the minerals ilmenite and sphene, found mainly in igneous rocks and sediments derived from them, but are also distributed throughout the Earth’s lithosphere.

Pure titanium was first made by Matthew A. Hunter in 1910 at the Rensselaer Polytechnic Institute by heating titanium tetrachloride (produced by heating titanium dioxide with chlorine or sulphur) and sodium metal in what is now known as the Hunter process. William Justin Kroll then reduced titanium tetrachloride with calcium in 1932 and later refined the process using magnesium and sodium. This allowed titanium to be used outside the laboratory and what is now known as the Kroll process is still used commercially today.

Very high purity titanium was produced in small quantities by Anton Eduard van Arkel and Jan Hendrik de Boer in the iodide or crystal bar process in 1925 by reacting titanium with iodine and separating the vapors formed over a hot filament.[iv]

Physical & chemical properties

Titanium is a hard, shiny, silvery-white metal represented by the symbol Ti on the periodic table. It has the atomic number 22 and a standard atomic weight (A_r) of 47.867. The atoms form a hexagonal close-packed crystal structure which results in the metal being as strong as steel, but much less dense. In fact, Titanium has the highest strength-to-density ratio of all the metals.

Titanium is ductile in an oxygen-free environment and can withstand extreme temperatures due to its relatively high melting point. It is non-magnetic and has low electrical and thermal conductivities.

The metal is resistant to corrosion in seawater, acidic water and chlorine, as well as a good reflector of infrared radiation. As a photocatalyst, it releases electrons in the presence of light, which react with molecules to form free radicals that kill bacteria. [v]

Titanium connects well with bone and is non-toxic, although fine titanium dioxide is a suspected carcinogen. Zirconium, the most common titanium isotope, has many different chemical and physical properties.

Commercial uses

Titanium is most commonly used in the form of titanium dioxide, which is a main component of a bright white pigment found in paints, plastics, enamels, paper, toothpaste and the food additive E171 which whitens confectionary, cheeses and icings. Titanium compounds are a component of sunscreens and smokescreens, are used in pyrotechnics and improve visibility in solar observatories. [vi]

Titanium is also used in the chemical and petrochemical industries and the development of lithium batteries. Certain titanium compounds form catalyst components, for example that used in the production of polypropylene.

Titanium is known for its use in sporting gear such as tennis rackets, golf clubs and bicycle frames and electronic equipment like mobile phones and laptops. Its surgical applications include use in orthopaedic implants and medical prostheses.

When alloyed with aluminium, molybdenum, iron or vanadium, titanium is used to coat cutting tools and protective coatings or even in jewellery or as a decorative finish. TiO₂ coatings onto glass or tile surfaces may reduce infections in hospitals, prevent fogging of side-view mirrors in motor vehicles and reduce dirt build-up on buildings, pavements and roads.

Titanium forms an important part of structures exposed to seawater, such as desalination plants, ship and submarine hulls and propeller shafts, as well as power plant condenser pipes. Other uses include making components for the aerospace and transport industries and the military, such as aircraft, spacecraft, missiles, armour plating, engines and hydraulic systems. Research is being conducted to determine titanium’s suitability as a nuclear waste storage container material. iv

Key differences between tungsten and titanium

• Tungsten originates from the minerals scheelite and wolframite. Titanium is found in the minerals ilmenite, rutile and sphene.
• Tungsten is produced by reducing tungstic acid from the mineral, isolating the metal oxide and reducing it to metal by heating with carbon. Titanium is produced by forming titanium tetrachloride via chloride or sulphate processes and heating it with magnesium and sodium.
• Tungsten is number 74 on the periodic table, with relative atomic weight 84. Titanium is number 22, with relative atomic weight 47.867.
• Tungsten atoms form a body-centred cubic crystal structure. Titanium atoms form a hexagonal close-packed crystal structure.
• Tungsten is extremely strong, hard and dense. Titanium is very strong and hard and has much lower density.
• Tungsten is slightly magnetic and slightly electrically conductive. Titanium is non-magnetic and less electrically conductive.
• Tungsten is not as corrosion-resistant in saltwater as titanium and is not a photocatalyst like titanium.
• Tungsten has a biological role, but titanium does not.
• Tungsten is malleable in its purest form. Titanium is ductile in an oxygen-free environment.

Tungsten is used in heating elements, weights, low-temperature superconducting circuits and have applications in nuclear physics and electron-emitting devices. Titanium is used in white pigments, sports equipment, surgical implants and marine structures.

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