Ruthenium Dioxide, RuO₂

Ruthenium Dioxide, RuO₂, is obtained as a sublimate by heating ruthenium in a current of oxygen. The metal may thus be extracted, along with osmium in the form of its more volatile tetroxide, OsO₄, from osmiridium by heating the last named in oxygen (or air) to about 1080° С. If the mixed vapours are passed through a heated porcelain tube ruthenium dioxide condenses first.

If the ruthenium is finely powdered, the oxidation begins at 600° C. and increases rapidly with the temperature, being 4000 times as rapid at 1200° C. as at 700° C. Crystals of the dioxide may be detected in the sublimate. Previous ignition in hydrogen to a high temperature reduces the velocity of oxidation of the metal.

The dioxide may also be obtained by heating the sulphate or disulphide in the presence of air. It crystallises in the form of hard, tetragonal pyramids, of density 7.2, and isomorphous with cassiterite and rutile. The crystals exhibit a green iridescent metallic lustre. They are not acted upon by acids, but yield potassium ruthenate when fused with potassium hydroxide.

The dioxide undergoes partial dissociation at temperatures above 1000° C., and when heated in vacuo the oxygen tension amounts to 15 to 17 mm. at 1000° C., and a little metallic ruthenium remains behind on cooling beneath the layer of dioxide.

Ruthenium dioxide is obtained in the hydrated condition, RuO₂.xH₂O, as a dark red precipitate by heating the sulphate with potassium hydroxide solution. On heating to 300° C. it loses water, and at higher temperatures deflagrates with incandescence. It dissolves in acids and alkalies to yellow-coloured solutions. Claus gave the formula Ru(OH)₄.3H₂O to the precipitate, but Gutbier and Ransohoff show that the composition is variable.

Ruthenium dioxide unites with metallic oxides to yield ruthenites of general formula M''RuO₃. The best-known salt is barium ruthenite, BaRuO₃, which is obtained by heating barium ruthenate to 440° C. in vacuo, when oxygen is evolved and a bluish black residue of ruthenite remains, which is insoluble in water. Treatment with hydrochloric acid converts it into the trichloride.