Ruthenium is a metallic chemical element with the symbol Ru, atomic number 44 and atomic weight 101.07. It is a hard, lustrous, silver-gray metal with a close-packed hexagonal crystalline structure. Ruthenium is usually alloyed with other metals; with palladium as a hardener and with titanium to improve its corrosion resistance. It is also used as a catalyst in hydrogenation, isomerisation, nitrogenation, oxidation and reforming reactions.
The Russian chemist Karl Karlovich Klaus (also called Carl Ernst Claus) discovered ruthenium in 1844 after experimenting on the insoluble metallic residue that remained after crude platinum was dissolved in aqua regia. Here is the method he employed in his isolation and discovery of ruthenium:
- The residue was first mixed with potassium nitrate and heated to incandescence in a ceramic crucible.
- It was then removed from the crucible with an iron spatula, cooled and then ground to a coarse powder.
- Distilled water was then added to the powder and a yellow solution was formed.
- The solution was then decanted and potassium nitrate was added to it which resulted in the formation of a black precipitate.
- The solution was then filtered to remove the black precipitate.
- This precipitate was then washed and dissolved in hydrochloric acid which led to the precipitation of silicon dioxide.
- This solution was then evaporated to a gel-like consistency, diluted with water and filtered to remove the silicon dioxide.
- The filtrate was a bitter orange-yellow solution to which potassium chloride was added which resulted in the precipitation of red-brown crystals.
- He then filtered the same solution and crystallised the filtrate, and by doing so, isolated ruthenium.
Here is a photograph of 99.95% pure ruthenium cubes: