Other

Ruthenium

Ruthenium is a silver-grey metal, which resembles platinum. This metal is however rarer, harder and more brittle than platinum. Ruthenium has a very high melting point (2,250°C) and as a result it is not easily cast. Its brittle nature at even white heat makes it very difficult to work. Nevertheless, ruthenium is used in chemical catalysts, in electrochemical processes, as ruthenium paste used in resistors, in electronic circuitry and, in North America, in jewellery alloys. Platinum and palladium, when they are hardened by the introduction of ruthenium, are superior to pure platinum and palladium in the manufacture of fine jewellery and of electrical contacts.

Iridium

Iridium is a very dense and rare PGM used mainly in platinum alloys. A silver-white metal, iridium is hard and brittle but becomes ductile and can be worked at a white heat from 1,200°C to 1,500°C. The metal has applications in specialised autocatalysts, in chemical catalysts, in electrochemical applications, in jewellery, in biochemical alloys and in crucibles.

Osmium

Osmium is the densest naturally occurring platinum group element. It is a grey-white metal which is very hard, brittle, and difficult to work at even very high temperatures. Of the PGMs, it has the highest melting point (3,000°C) so fusing and casting of osmium is very difficult. The main use of osmium is as a hardener of the other PGMs. Osmium is more readily attacked by air than the other PGMs.