RUTHENIUM

(Ru), chemical element, one of the platinum metals of Group VIII of the periodic table, used as an alloying agent to harden platinum and palladium. Silver-gray ruthenium metal looks like platinum but is rarer, harder, and more brittle. The Russian chemist Karl Karlovich Klaus established (1844) the existence of this rare metal and retained the name his countryman Gottfried Wilhelm Osann had suggested (1828) for a platinum-group element whose discovery had remained inconclusive. Elemental ruthenium occurs in native alloys of iridium and osmium: up to 14.1 percent in iridosmine and 18.3 percent in siserskite. It also occurs in sulfide and other ores (e.g., in pentlandite of the Sudbury, Ont., Can., nickel-mining region) in very small quantities that are commercially recovered. Because of its high melting point, ruthenium is not easily cast; its brittleness, even at white heat, makes it very difficult to roll or draw into wires. Thus, the industrial application of metallic ruthenium is restricted to use as an alloy for platinum and other metals of the platinum group. It serves the same function as iridium for the hardening of platinum and, in conjunction with rhodium, is used to harden palladium. Ruthenium-hardened alloys of platinum and palladium are superior to the pure metals in the manufacture of fine jewelry and of electrical contacts for wear resistance. Ruthenium is found among the fission products of uranium and plutonium in nuclear reactors. Radioactive ruthenium-106 (one-year half-life) and its short-lived daughter rhodium-106 contribute an important fraction of the residual radiation in reactor fuels a year following their use. Recovery of the unused fissionable material is made difficult because of the radiation hazard and the chemical similarity between ruthenium and plutonium. Natural ruthenium consists of a mixture of seven stable isotopes: ruthenium-96 (5.54 percent), ruthenium-98 (1.86 percent), ruthenium-99 (12.7 percent), ruthenium-100 (12.6 percent), ruthenium-101 (17.1 percent), ruthenium-102 (31.6 percent), and ruthenium-104 (18.6 percent). It has four allotropic forms. The metal does not tarnish in air at ordinary temperatures and resists attack by strong acids, even by aqua regia. Ruthenium is brought into soluble form by fusion with an alkaline oxidizing flux, such as sodium peroxide (Na 2O2). The green melt contains the perruthenate ion, RuO-4; on dissolving in water, an orange solution containing the stable ruthenate ion, RuO42-, usually results. Very volatile ruthenium tetroxide, RuO4, used in separating ruthenium from other heavy metals, contains the element in the +8 oxidation state. All states from zero through +8 are known, but +3, +4, +6, and +8 are most important. Numerous coordination complexes are known, including a unique series of nitrosyl (NO) complexes. atomic number 44 atomic weight 101.07 melting point 2,250 C (4,082 F) boiling point 3,900 C (7,052 F) specific gravity 12.30 (20 C) valence 1, 2, 3, 4, 5, 6, 7, 8 electronic config. 2-8-18-15-1 or (Kr)4d75s1