Ruthenium

Ruthenium is a hard (HV 250–500), brittle metal with the highest-density crystal structure—hexagonal. It cannot be shaped by standard metal refining processes even at high temperatures. It does not tarnish at room temperature, but forms oxides at temperatures over 800°C, some of which are volatile. Ruthenium is resistant to all mineral acids including aqua regia, but alkali melts—particularly in combination with strong oxidizing agents such as sodium peroxide or sodium chlorate—can corrode it. Ruthenium occurs with valences of +8, +7, +6, +4, +3, +2, 0 and -2 in compounds, but the oxidation states +3 and +4 are the most common. Ruthenium tetroxide, RuO₄, is a strong oxidizing agent used in chemical processes, but it can also react explosively with organic materials.

The largest ruthenium deposits with the greatest economic significance are found in nickel/copper sulfide ores containing precious metals in South Africa’s Bushveld Complex. The precious metals present in the ore as chalcogenides or alloys can be concentrated in an involved process using gravity separation, flotation, scorification in a smelter, and then bessemerization of the matte. Leaching the matte with sulfuric acid leaves a precious metal concentrate behind. Before separating the individual precious metals, this concentrate is dissolved in oxidized hydrochloric acid, from which volatile ruthenium tetroxide can be distilled with oxidation and absorbed as hexachlororuthenic acid in hydrochloric acid. After separating overdistilled traces of osmium, the metal can then be produced from the scarcely soluble ammonium ruthenium chloride solution using calcination and hydrogen reduction. Ruthenium recycled from the sputtering target business is a significant secondary source, as are ruthenium containing residues from industrial applications such as catalysts and DSA electrodes.

Ruthenium’s key application is in magnetic storage media (hard drives). The introduction of perpendicular magnetic recording (PMR) has dramatically increased storage capacity. Heraeus produces high-purity Ru sputtering targets for creating nanometer-thin films on a hard drive’s complex layer structure. Thick film pastes from Heraeus are used to manufacture thick film resistors for the electronics industry, taking advantage of the impressive electrical conductivity of RuO2. A further application for ruthenium is in pastes for conductor structures in plasma displays. Heraeus also produces ruthenium to coat titanium electrodes used in the chloralkali process. Ruthenium catalysts are utilized for synthesizing ammonia or acetic acid, and ruthenium alloys are used to produce fountain pen points, to strengthen platinum jewelry alloys and to improve titanium’s resistance to corrosion.