Derived from the Greek word for colour, Chroma, Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first of the elements in Group 6 of the Periodic Table, which contains transition metals. Chromium has a long history and was used by the Chinese in the Qin Dynasty over 2000 years ago to coat the weapons that can be found with the Terracotta Army.
Chromium is a steely-grey, hard and brittle metal. It can be polished to a high standard and resists tarnishing so it is often plated to other metals to form a protective and aesthetically pleasing covering. It also has an extremely high melting point at 1860°C and is often added to steel to harden it and form stainless steel – an alloy containing at least 10% chromium. Other chromium-steel alloys can be used to make armour plate, safes, ball bearings and cutting tools.
Perhaps it is not a surprise given the origins of its name, but Chromium can also be used to form several colourful compounds with industrial uses. Lead chromate can be used as a yellow pigment in paints whilst chromic oxide is used as a green pigment. Chromium compounds are also responsible for the colour in rubies and emeralds. Chromium salts, in particular chrome alum and chromium (III) sulfate, are used in the tanning of leather and chromium tanned leather can contain between 4-5% chromium.
Approximately 28.8 million metric tons of marketable chromium ore were produced in 2013. The largest producers have been South Africa, Kazakhstan, Turkey and India, although other countries are also involved in the production of chromium ore.
William Rowland is the UK distributor for DCX Chrome (formerly Delachaux), who produce aluminothermic grades 99.4% min for air melting and 99.6% Cr min. for vacuum melt applications. DCX Chrome also produces a unique double degassed briquette (DDB) 99.8% Cr min. which is equivalent to the highest quality electrolytic grades.