Cr - Chromium
|Chemical Element||Chromium||Melting Point °C||1860|
|Chemical Symbol||Cr||Boiling Point °C||2672|
|Atomic Number||24||Density g/cm3||7.2|
Chromium is a hard, silvery metal with a blue tinge and belongs to Group 6 of the Periodic Table; it is the 21st most abundant element in the Earth’s crust. Chromium can be polished to an extremely high shine but due to its reactivity with oxygen, an oxide layer forms and dulls the surface. The name chromium comes from the Greek word “chroma” meaning colour. This name was given as all chromium compounds are coloured. Chromium will dissolve in hydrochloric and sulphuric acids but not phosphoric acid, due to reaction and formation of a protective layer on the surface. Chromium is a beautiful looking metal when polished, and the only reason that it is not used in jewellery as an alternative to silver is that it is too cheap to be taken seriously.
Chromium was both discovered and isolated in 1798 by the French chemist Nicholas Louis Vauquelin in Paris. Vauquelin came across a bright red mineral that had been discovered in a Siberian gold mine in 1766. This mineral was referred to as Siberian red lead (now known as crocoite, a form of lead chromate). By concluding that lead was present, he proceeded to precipitate the lead out of the solution and concentrated the remains, although it was not until one year later that he isolated the chromium element.
The first commercially exploitable deposits were discovered in Maryland, USA, and fulfilled the demand of commercial chromium for around 30 years. In 1848, large deposits were established in Turkey and this became the next main source.
The first commercially exploitable deposits were discovered in Maryland, USA, and fulfilled the demand of commercial chromium for 30 years. In 1848 large deposits were established in Turkey, followed by South Africa, Zimbabwe, Finland, India, Brazil, Albania, Kazakhstan and the Philippines. 14 million tonnes of chromite ore is extracted, whereas chromium production itself is only around 20,000 tonnes, with somewhere in the order of 1 billion tonnes of chromite ore in reserves. South Africa and Russia produce half of the world’s chromium through chromite ore and ferro-chromium, with Zimbabwe producing 8%.
The USA is the largest end user of chromium, although it does not have any of its own resources. 20% of chromite mined is used in refractories, foundry mould sand and other non metallurgical uses. The other two major uses are in the form of alloys, such as stainless steel and for plating purposes to give steel a polished silvery coating. Pure chromium is also used to manufacture non-ferrous alloys and super alloys, which can be used in magnets, in metallurgy to impart corrosion resistance and shiny finish and as dyes and paints. Its salts are used to colour glass, due to the emerald green colour, and chromium is also used to produce synthetic rubies. Additionally, chromium is used as a catalyst in dying and in the tanning of leather, to make moulds for firing bricks and its oxide is used to manufacture magnetic tape.
- Emsley, John. Nature’s Building Blocks, An A-Z Guide to the Elements, New Edition, Oxford University Press, 2011
- Gray, Theodore. The Elements, A Visual Exploration of Every Known Atom in the Universe, Black Dog & Leventhal Publishers, Inc, NY, 2009
- Stwertka, Albert. A Guide to the Elements, 3rd Edition, Oxford University Press, 2012