Transition metal
Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chemicals. Karl Ernst Claus, a Russian scientist of Baltic-German ancestry, discovered the element in 1844 at Kazan State University and named it in honor of Russia, using the Latin name Ruthenia. Ruthenium is usually found as a minor component of platinum ores; the annual production has risen from about 19 tonnes in 2009 to 35.5 tonnes in 2017. Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors. A minor application for ruthenium is in platinum alloys and as a chemical catalyst. A new application of ruthenium is as the capping layer for extreme ultraviolet photomasks in semiconductor lithography. Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, and in pyroxenite deposits in South Africa.
Though naturally occurring platinum alloys containing all six platinum-group metals were used for a long time by pre-Columbian Americans and known as a material to European chemists from the mid-16th century, not until the mid-18th century was platinum identified as a pure element. That natural platinum contained palladium, rhodium, osmium and iridium was discovered in the first decade of the 19th century. Platinum in alluvial sands of Russian rivers gave access to raw material for use in plates and medals and for the minting of ruble coins, starting in 1828.
It is possible that the Polish chemist Jędrzej Śniadecki isolated element 44 (which he called "vestium" after the asteroid Vesta discovered shortly before) from South American platinum ores in 1807. He published an announcement of his discovery in 1808. His work was never confirmed, however, and he later withdrew his claim of discovery.
Jöns Berzelius and Gottfried Osann nearly discovered ruthenium in 1827. They examined residues that were left after dissolving crude platinum from the Ural Mountains in aqua regia. Berzelius did not find any unusual metals, but Osann thought he found three new metals, which he called pluranium, ruthenium, and polinium. This discrepancy led to a long-standing controversy between Berzelius and Osann about the composition of the residues. As Osann was not able to repeat his isolation of ruthenium, he eventually relinquished his claims. …
Ruthenium, a polyvalent hard white metal, is a member of the platinum group and is in group 8 of the periodic table:
While other group 8 elements have two electrons in the outermost shell, in ruthenium the outermost shell has only one electron (the final electron is in a lower shell). This anomaly, which has no effect on chemical properties, is also observed in all other elements (except technetium) in the range of Z = 41-45.
Ruthenium has four crystal modifications and does not tarnish at ambient conditions; it oxidizes upon heating to 800 °C (1,070 K). Ruthenium dissolves in fused alkalis to give ruthenates (RuO2−4). It is not attacked by acids (even aqua regia) but is attacked by sodium hypochlorite at room temperature, and halogens at high temperatures. Ruthenium is most readily attacked by oxidizing agents. Small amounts of ruthenium can increase the hardness of platinum and palladium. The corrosion resistance of titanium is increased markedly by the addition of a small amount of ruthenium. The metal can be plated by electroplating and by thermal decomposition. A ruthenium–molybdenum alloy is known to be superconductive at temperatures below 10.6 K. Ruthenium is the only 4d transition metal that can assume the oxidation state +8, and even then it is less stable there than the heavier congener osmium: this is the first group from the left of the table where the second and third-row transition metals display notable differences in chemical behavior. …
Ruthenium is found in about 100 parts per trillion in the Earth's crust, making it the 78th most abundant element. It is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, Canada, and in pyroxenite deposits in South Africa. The native form of ruthenium is a very rare mineral (Ir replaces part of Ru in its structure).
Approximately 30.9 tonnes of ruthenium were consumed in 2016, 13.8 of them in electrical applications, 7.7 in catalysis, and 4.6 in electrochemistry.
Because it hardens platinum and palladium alloys, ruthenium is used in electrical contacts, where a thin film is sufficient to achieve the desired durability. With its similar properties to and lower cost than rhodium, electric contacts are a major use of ruthenium. The ruthenium plate is applied to the electrical contact and electrode base metal by electroplating or sputtering.
Ruthenium dioxide with lead and bismuth ruthenates are used in thick-film chip resistors. These two electronic applications account for 50% of the ruthenium consumption.
Ruthenium is occasionally alloyed with metals outside the platinum group, where small quantities improve some properties. The added corrosion resistance in titanium alloys led to the development of a special alloy with 0.1% ruthenium. Ruthenium is also used in some advanced high-temperature single-crystal superalloys, with applications that include the turbines in jet engines. Several nickel based superalloy compositions are described, such as EPM-102 (with 3% Ru), TMS-162 (with 6% Ru), TMS-138, and TMS-174, the latter two containing 6% rhenium. Fountain pen nibs are frequently tipped with ruthenium alloy. From 1944 onward, the Parker 51 fountain pen was fitted with the "RU" nib, a 14K gold nib tipped with 96.2% ruthenium and 3.8% iridium. …
Naturally occurring ruthenium is composed of seven stable isotopes: 96, 98-102, 104. Additionally, 34 synthetic radioactive isotopes have been discovered. Of these radioisotopes, the most stable are 106Ru with a half-life of 371.8 days, 103Ru with a half-life of 39.245 days and 97Ru with a half-life of 2.837 days.
Fifteen other radioisotopes have been characterized ranging from 85Ru to 125Ru. Most of these have half-lives that are less than five minutes; the exceptions are 94Ru (51.8 minutes), 95Ru (1.607 hours), and 105Ru (4.44 hours).
The primary decay mode for isotopes lighter than the most abundant isotope, 102Ru, is electron capture to produce technetium while the primary mode for heavier isotopes is beta emission to rhodium.
106Ru is a fission product of uranium or plutonium. High concentrations of this isotope detected in the atmosphere over Europe were associated with an alleged undeclared nuclear accident in Russia in 2017.
Little is known about the health effects of ruthenium and it is relatively rare for people to encounter ruthenium compounds. Metallic ruthenium is inert (is not chemically reactive). Some compounds such as ruthenium tetroxide (RuO4) are highly toxic and volatile.