|silvery white metallic
|Name, symbol, number||ruthenium, Ru, 44|
|Element category||transition metal|
|Group, period, block||8, 5, d|
|Standard atomic weight||101.07 g·mol−1|
|Electron configuration||[Kr] 4d7 5s1|
|Electrons per shell||2, 8, 18, 15, 1 (Image)|
|Density (near r.t.)||12.45 g·cm−3|
|Liquid density at m.p.||10.65 g·cm−3|
|Melting point||2607 K, 2334 °C, 4233 °F|
|Boiling point||4423 K, 4150 °C, 7502 °F|
|Heat of fusion||38.59 kJ·mol−1|
|Heat of vaporization||591.6 kJ·mol−1|
|Specific heat capacity||(25 °C) 24.06 J·mol−1·K−1|
|Oxidation states||8, 7, 6, 4, 3, 2, 1,, -2
(mildly acidic oxide)
|Electronegativity||2.3 (Pauling scale)|
|Ionization energies||1st: 710.2 kJ·mol−1|
|2nd: 1620 kJ·mol−1|
|3rd: 2747 kJ·mol−1|
|Atomic radius||134 pm|
|Covalent radius||146±7 pm|
|Electrical resistivity||(0 °C) 71 nΩ·m|
|Thermal conductivity||(300 K) 117 W·m−1·K−1|
|Thermal expansion||(25 °C) 6.4 µm·m−1·K−1|
|Speed of sound (thin rod)||(20 °C) 5970 m/s|
|Young's modulus||447 GPa|
|Shear modulus||173 GPa|
|Bulk modulus||220 GPa|
|Brinell hardness||2160 MPa|
|CAS registry number||7440-18-8|
|Most stable isotopes|
|Main article: Isotopes of ruthenium|
Ruthenium (pronounced /ruːˈθiːniəm/ roo-THEE-nee-əm) is a chemical element that has the symbol Ru and atomic number 44. A rare transition metal of the platinum group of the periodic table, ruthenium is found associated with platinum ores and used as a catalyst in some platinum alloys.
|Z||Element||No. of electrons/shell|
|26||iron||2, 8, 14, 2|
|44||ruthenium||2, 8, 18, 15, 1|
|76||osmium||2, 8, 18, 32, 14, 2|
|108||hassium||2, 8, 18, 32, 32, 14, 2|
but has an atypical configuration in its outermost electron shells compared to the rest of the members. (This can be observed in the neighborhood of niobium (41), ruthenium (44), rhodium (45), and palladium (46).)
Ruthenium has four crystal modifications and does not tarnish at normal temperatures, but does oxidize readily on exposure to air to form ruthenium tetroxide, RuO4, a strong oxidizing agent with properties analogous to those of osmium tetroxide. Ruthenium dissolves in fused alkalis, is not attacked by acids but is attacked by halogens at high temperatures. 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 oxidation states of ruthenium range from +1 to +8, and -2 is known, though oxidation states of +2, +3, and +4 are most common.
Ruthenium is a versatile metal that can easily form compounds with carbon-ruthenium bonds; these compounds tend to be darker in colour and react more quickly than the osmium compounds. The organometallic ruthenium compound that is easiest to make is RuHCl(CO)(PPh3)3. This compound has two forms (yellow and pink) that are identical once they are dissolved but different in the solid state.
An organometallic compound similar to ruthenocene, bis(2,4-dimethylpentadienyl)ruthenium, is readily synthesized in near quantitative yields and has applications in vapor-phase deposition of metallic ruthenium, as well as in catalysis, including Fischer-Tropsch synthesis of transportation fuels.
Ruthenium compounds are often similar in properties to those of osmium and exhibit at least eight oxidation states, but the +2, +3, and +4 states are the most common. Examples are ruthenium(IV) oxide (RuO2, oxidation state +4), dipotassium ruthenate (K2RuO4, +6), potassium perruthenate (KRuO4, +7) and ruthenium tetroxide (RuO4, +8). Compounds of ruthenium with chlorine are ruthenium(II) chloride (RuCl2) and ruthenium(III) chloride (RuCl3).
Naturally occurring ruthenium is composed of seven stable isotopes. Additionally, 34 radioactive isotopes have been discovered. Of these radioisotopes, the most stable are 106Ru with a half-life of 373.59 days, 103Ru with a half-life of 39.26 days and 97Ru with a half-life of 2.9 days.
Fifteen other radioisotopes have been characterized with atomic weights ranging from 89.93 u (90Ru) to 114.928 u (115Ru). Most of these have half-lives that are less than five minutes except 95Ru (half-life: 1.643 hours) and 105Ru (half-life: 4.44 hours).
The primary decay mode before the most abundant isotope, 102Ru, is electron capture and the primary mode after is beta emission. The primary decay product before 102Ru is technetium and the primary mode after is rhodium.
Though naturally occurring platinum, containing all six platinum group metals, was used for a long time by pre-Columbian Americans and known to European chemists from the mid-16th century, it took until the mid-17th century for platinum to be discovered. The discovery that natural platinum contained palladium, rhodium, osmium and iridium took place in the first decade of the 18th 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. Residues of platinum production for minting where available in the Russian Empire, and therefore most of the research on them was done in Eastern Europe.
It is possible that the Polish chemist Jędrzej Śniadecki isolated element 44 (which he called "vestium") from platinum ores in 1807. His work was never confirmed, however, and he later withdrew his claim of discovery. Jöns Berzelius and Gottfried Osann nearly discovered ruthenium in 1827. The men 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, pluranium, ruthenium and polinium. This discrepancy led to a long-standing controversy between Berzelius and Osann about the composition of the residues.
In 1844 the Russian scientist Karl Klaus showed that the compounds prepared by Gottfried Osann contained small amounts of ruthenium, which Klaus had discovered the same year. Klaus isolated ruthenium from the platinum residues of the rouble production while he was working in Kazan University, Kazan. Klaus showed that ruthenium oxide contained a new metal and obtained 6 grams of ruthenium from the part of crude platinum that is insoluble in aqua regia.
The name derives from Ruthenia, the Latin word for Rus', a historical area which includes present-day western Russia, Ukraine, Belarus, and parts of Slovakia and Poland. Karl Klaus named the element in honor of his birthland, as he was born in Tartu, Estonia, which was at the time a part of the Russian Empire.
This element 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 ruthenium is very rare mineral (Ir replaces part of Ru in its structure).
Roughly 12 tonnes of Ru is mined each year with world reserves estimated to be 5000 tonnes.
The composition of the mined platinum group metal (PGM) mixtures varies in a wide range depending on the geochemical formation, for example the PGMs mined in South Africa contain on average 11% ruthenium while the PGMs mined in the USSR contain only 2% based on research dating from 1992.
Ruthenium, like the other platinum group metals, is obtained commercially as a by-product from nickel and copper mining and processing or by direct processing of platinum group metal ores. During electrorefining of copper and nickel, noble metals such as silver, gold and the platinum group metals including selenium and tellurium settle to the bottom of the cell as anode mud, which forms the starting point for their extraction. In order to separate the metals, they must first be brought into solution. Several methods are available depending on the separation process and the composition of the mixture; two representative methods are fusion with sodium peroxide followed by dissolution in aqua regia, and dissolution in a mixture of chlorine with hydrochloric acid. Osmium, ruthenium, rhodium and iridium can be separated from platinum and gold and base metals by their insolubility in aqua regia, leaving a solid residue. Rhodium can be separated from the residue by treatment with molten sodium bisulfate. The insoluble residue, containing Ru, Os and Ir is treated with sodium oxide, in which Ir is insoluble, producing water-soluble Ru and Os salts. After oxidation to the volatile oxides, RuO4 is separated from OsO4 by precipitation of (NH4)3RuCl6 with ammonium chloride.
This metal is commercially isolated through a complex chemical process in which hydrogen is used to reduce ammonium ruthenium chloride yielding a powder. The powder is then consolidated by powder metallurgy techniques or by argon-arc welding.
After it is dissolved, osmium is separated from the other platinum group metals by distillation or extraction with organic solvents of the volatile osmium tetroxide. The first method is similar to the procedure Tennant and William Hyde Wollaston used for their separation. Both methods are suitable for industrial scale production. In either case, the product is reduced using hydrogen, yielding the metal as a powder or sponge that can be treated using powder metallurgy techniques.
It is also possible to extract ruthenium from used nuclear fuel. Each kilo of fission products of 235U will contain 63.44 grams of ruthenium isotopes with half-lifes longer than a day. Since a typical used nuclear fuel contains about 3% fission products, one ton of used fuel will contain about 1.9 kg of ruthenium. The 103Ru and 106Ru will render the fission ruthenium very radioactive. If the fission occurs in an instant then the ruthenium thus formed will have an activity due to 103Ru of 109 TBq g−1 and 106Ru of 1.52 TBq g−1. Ru 103 has a half life of about 39 days meaning that within 390 days it will have effectively decayed to ground state, well before any reprocessing is likely to occur. Ru 106 has a half life of about 373 days meaning that if the fuel is let to cool for 5 years before reprocessing only about 3% of the original quantity will remain, the rest will have decayed to ground state.
Because of its ability to harden platinum and palladium, ruthenium is used in platinum and palladium alloys to make wear-resistant electrical contacts. Because of its lower cost and similar properties compared to rhodium, the use as plating material for electric contacts is one of the major applications. The coatings are either put on by electroplating or sputtering.
Ruthenium dioxide, lead and bismuth ruthenates, the latter with perovskite crystal structure, are used in thick film chip resistors. The first two applications account for 50% of the ruthenium consumption.
Ruthenium is also used in some advanced high-temperature single-crystal superalloys, with applications including the turbine blades in jet engines. Several nickel based superalloy compositions described in the literature. Among them are EPM-102 (with 3 % Ru) and TMS-162 (with 6 % Ru), both contain 6 % rhenium, as well as TMS-138 and TMS-174.
Fountain pen nibs are frequently tipped with alloys containing ruthenium. From 1944 onward, the famous Parker 51 fountain pen was fitted with the "RU" nib, a 14K gold nib tipped with 96.2% ruthenium and 3.8% iridium.
Ruthenium is also a versatile catalyst. Hydrogen sulfide can be split by light by using an aqueous suspension of CdS particles loaded with ruthenium dioxide. This may be useful in the removal of H2S from oil refineries and from other industrial processes.
Ruthenium is a component of mixed-metal oxide (MMO) anodes used for cathodic protection of underground and submerged structures, and for electrolytic cells for chemical processes such as generating chlorine from saltwater.
Organometallic ruthenium carbene and allenylidene complexes have recently been found as highly efficient catalysts for olefin metathesis with important applications in organic and pharmaceutical chemistry.
Ruthenium-centered complexes are being researched for possible anticancer properties. Ruthenium, unlike traditional platinum complexes, shows greater resistance to hydrolysis and more selective action on tumors. NAMI-A and KP1019 are two drugs undergoing clinical evaluation against metastatic tumors and colon cancers.
Relatively recently, ruthenium has been suggested as a material that could beneficially replace other metals and silicides in microelectronics components. Ruthenium tetroxide (RuO4) is highly volatile, as is ruthenium trioxide (RuO3). By oxidizing ruthenium (for example with an oxygen plasma) into the volatile oxides, ruthenium can be easily patterned. The properties of the common ruthenium oxides make ruthenium a metal compatible with the semiconductor processing techniques needed to manufacture microelectronics.
In order to continue miniaturization of microelectronics, new materials are needed as dimensions change. There are three main applications for thin ruthenium films in microelectronics. The first is using thin films of ruthenium as electrodes on both sides of tantalum pentoxide (Ta2O5) or barium strontium titanate ((Ba, Sr)TiO3, also known as BST) in the next generation of three-dimensional dynamic random access memories (DRAMs). Ruthenium thin film electrodes could also be deposited on top of lead zirconate titanate (Pb(ZrxTi1-x)O3, also known as PZT) in another kind of RAM, ferroelectric random access memory (FRAM). Platinum has been used as the electrodes in RAMs in laboratory settings, but it is difficult to pattern. Ruthenium is chemically similar to platinum, preserving the function of the RAMs, but in contrast to Pt patterns easily. The second is using thin ruthenium films as metal gates in p-doped metal-oxide-semiconductor field effect transistors (p-MOSFETs). When replacing silicide gates with metal gates in MOSFETs, a key property of the metal is its work function. The work function needs to match the surrounding materials. For p-MOSFETs, the ruthenium work function is the best materials property match with surrounding materials such as HfO2, HfSiOx, HfNOx, and HfSiNOx, to achieve the desired electrical properties. The third large-scale application for ruthenium films is as a combination adhesion promoter and electroplating seed layer between TaN and Cu in the copper dual damascene process. Copper can be directly electroplated onto ruthenium, in contrast to tantalum nitride. Copper also adheres poorly to TaN, but well to Ru. By depositing a layer of ruthenium on the TaN barrier layer, copper adhesion would be improved and deposition of a copper seed layer would not be necessary.
There are also other suggested uses. In 1990, IBM scientists discovered that a thin layer of ruthenium atoms created a strong anti-parallel coupling between adjacent ferromagnetic layers, stronger than any other nonmagnetic spacer-layer element. Such a ruthenium layer was used in the first giant magnetoresistive read element for hard disk drives. In 2001, IBM announced a three-atom-thick layer of the element ruthenium, informally referred to as "pixie dust", which would allow a quadrupling of the data density of current hard disk drive media.
A unique challenge arises in trying to grow impurity-free films of a catalyst in Chemical vapor deposition (CVD). Ruthenium metal activates C-H and C-C bonds, that aids C-H and C-C bond scission. This creates a potential catalytic decomposition path for all metal-organic CVD precursors that is likely to lead to significant carbon incorporation. Platinum, a chemically similar catalyst, catalyzes dehydrogenation of five- and six-member cyclic hydrocarbons into benzene. The d-bands of ruthenium lie higher than those in platinum, generally predicting stronger ruthenium-adsorbate bonds than on platinum. Therefore, it is likely that ruthenium also catalyzes dehydrogenation of five- and six-member hydrocarbon rings to benzene. Benzene dehydrogenates further on ruthenium surfaces into hydrocarbon fragments similar to those formed by acetylene and ethene on ruthenium surfaces. In addition to benzene, acetylene and ethene, pyridine also decomposes on ruthenium surfaces, leaving bound fragments on the surface. Ruthenium is unusually well studied in the surface science and catalysis literature due to its industrial importance as a catalyst. There are many studies of individual molecular behavior on ruthenium in surface science. However, understanding the behavior of each ligand on its own is not equivalent to understanding their behavior when co-adsorbed with each other and with the precursor. While there is no significant pressure difference between surface science studies and CVD, there is often a temperature gap between temperatures reported in surface science studies and CVD growth temperatures. Despite these complications, ruthenium is a promising candidate for understanding chemical vapor deposition and precursor design of catalytic films.
Ligands that are stable compounds in their own right, short ligand-ruthenium contact times and moderate substrate temperatures help minimize unwanted ligand decomposition on the surface. The C-H and C-C bond activation is temperature-dependent. Product desorption is also temperature-dependent, if the products are not bound to the ruthenium surface. This suggests that there is some optimum temperature, at which most independently stable ligands have just enough thermal energy to desorb from the ruthenium film surface before C-H activation can occur. For example, benzene starts decomposing on ruthenium at 87°C. However, the dehydrogenation reaction does not go to fragments until 277°C, and compete fragmentation is not seen at low surface coverage. This suggests that provided adsorbed benzene molecules are not close to one another on the surface and temperatures are below 277°C, the vast majority of benzene molecules may not contribute to carbon incorporation in films. Therefore, a key consideration in growing CVD films of catalytic metals such as ruthenium is combining molecule design and the kinetic aspects of growth in a favorable way.
Before metal-organic precursors were explored, triruthenium dodecacarbonyl (Ru3(CO)12) was tested as a CVD precursor. While this precursor gives good-quality films, the vapor pressure is poor, complicating its practical use in a CVD process. Ruthenocene and bis(ethylcyclopentadienyl)ruthenium(II) and beta-diketonate ruthenium(II) compounds have been fairly extensively explored. Although these precursors also can give pure films of low resistivity when reacted with oxygen, the growth rates are very low or not reported. One high-growth precursor, cyclopentadienyl-propylcyclopentadienylruthenium(II) (RuCp(i-PrCp)), has been identified. (RuCp(i-PrCp) has achieved growth rates of 7.5 nm/min to 20 nm/min as well as low resistivities. However, it does not nucleate on oxides, ruling out its use in all applications but copper interconnect layers.
A new zero-valent, single-source precursor design paradigm was launched with (1,5-cyclooctadiene)(toluene)Ru(0) ((1,5-COD)(toluene)Ru) and (1,3-cyclohexadiene)(benzene)Ru(0) ((1,3-CHD)(benzene)Ru), also independently tested Using (1,5-COD)(toluene)Ru; it was found that C-H bonds were readily activated in 1,5-COD. Although carbon incorporation levels were low (1-3%), the growth rates were only around 0.28 nm/min at best. Using (1,3-CHD)(benzene)Ru, the 1,3-CHD was dehydrogenated to benzene as expected, but the large variety of possible surface reactions involving the two ligands resulted in a narrow process window in which carbon concentrations were low.
The compound ruthenium tetroxide, RuO4, similar to osmium tetroxide, is volatile, highly toxic and may cause explosions if allowed to come into contact with combustible materials. Ruthenium plays no biological role but does strongly stain human skin, may be carcinogenic and bio-accumulates in bone.
RUTHENIUM [[[symbol]] Ru, atomic weight To' 7 (O = 0)1, in chemistry, a metallic element, found associated with platinum, in platinum ore and in osmiridium. The metal may be obtained from the residues obtained in the separation of osmium from osmiridium. These are washed with ammonium chloride until the filtrate is colourless, ignited, fused with caustic potash and nitre, the melt dissolved in water and nitric acid added to the solution until the colour of potassium ruthenate disappears. A precipitate of ruthenium oxide gradually separates; this is collected and ignited in a graphite crucible and finally fused in the oxyhydrogen furnace (H. Sainte-Claire Deville and H. J. Debray, Ann. chim. phys., 18 59, (3), 56, p. 406). For other methods see C. E. Claus, Pogg. Ann., 1845, 65, p. 200; E. Fremy, Comptes rendus, 1854, 38, p. Io08; T. Wilm, Bey., 1883, 16, p. 1524. A purer ruthenium is obtained by A. Gutbier and L. Trenkner (Zeit. anorg. Chem., 1905, 45, p. 166) by heating the crude metal (obtained by other processes) in a current of oxygen until all the osmium is volatilized as tetroxide. The residue is then fused with caustic potash and nitre, dissolved in water, saturated with chlorine and distilled on the water-bath in a current of chlorine. Pure ruthenium tetroxide distils over. This is then dissolved in water, reduced by alcohol and ignited in oxygen. Ruthenium in bulk resembles platinum in its general appearance, and has been obtained crystalline by heating an alloy of ruthenium and tin in a current of hydrochloric acid gas. Its specific gravity (after fusion) is 12.063 (A. Joly, Comptes rendus, 1893, 116, p. 430). It fuses easily in the electric arc. It oxidizes superficially when heated, but fairly rapidly when ignited in an oxidizing blowpipe flame, forming a black smoke of the oxide. It is also oxidized when fused with caustic potash and nitre, forming a ruthenate. Acids have practically no action on the metal, but it is soluble in solutions of the alkaline hypochlorites. Like most of the other metals of the group, it absorbs gases. A colloidal form has been obtained by A. Gutbier and G. Hofmeier (Jour. prakt. Chem., 1905, (2), 71, p. 452) by reducing ruthenium salts with hydrazine hydrate in the presence of gum-arabic.
Several oxides of ruthenium have been described, the definite existence of some of which appears to be doubtful. The dioxide, Ru02, is formed by heating sulphate, or by heating the metal in a current of oxygen. It crystallizes in octahedra isomorphous with stannic oxide. It is insoluble in acids and decomposes when heated to a sufficiently high temperature. Fusion with caustic potash converts it into a mixture of potassium ruthenate and ruthenium sesquioxide, Ru 2 0 3, which is a black, almost insoluble powder. An oxide of composition Ru 4 0 9 is obtained as a black hydrated powder when the peroxide is heated with water for some time. It becomes anhydrous at about 360° C., and is unattacked by acids and alkalis. The peroxide, Ru04, is formed when a solution of potassium ruthenate is decomposed by chlorine, or by oxidizing ruthenium compounds with potassium chlorate and hydrochloric acid, or with potassium permanganate and sulphuric acid. It forms a golden yellow crystalline mass, which sublimes slowly in vacuo, and melts at 25.5° C. It blackens on exposure to moisture, and decomposes when exposed to light. It is insoluble in water, but gradually decomposes, forming a hydrated oxide, Ru 2 0 5 H 2 O. It is readily reduced. Its vapour possesses a characteristic smell, somewhat resembling that of ozone. Ruthenium dichloride, RuC1 2, is obtained (in solution) by reducing the sesquichloride by sulphuretted hydrogen or zinc. It is stable in the cold. The sesquichloride, Ru 2 C1 6, is formed when a mixture of chlorine and carbon monoxide is passed over finely divided ruthenium heated to 350° C. (Joly, Comptes rendus, 1892, 114, p. 291). It is a brown powder which is readily decomposed by boiling water. It absorbs ammonia readily, forming Ru2C16.7NH,. Numerous double chlorides are known, e.g. Ru2C16.4KC1; Ru 2 C1 6.4NH 4 C1, &c. The pure tetrachloride, RuC1 4, has not been isolated, but is chiefly known in the form of its double salts, such as potassium ruthenium chloride, K 2 RuC1 6, which is obtained when finely divided ruthenium is fused with caustic potash and potassium chloride is gradually added to the fused mass (U. Antony and A. Luchesi, Gazz, 1899, 29, II. p. 82). It is a red-brown crystalline powder, which is soluble in water. A similar ammonium salt has been obtained. Ruthenium sulphides are obtained when the metal is warmed with pyrites and some borax, and the fused mass treated with hydrochloric acid first in the cold and then hot. The insoluble residue contains a mixture of two sulphides, one of which is converted into the sulphate by nitric acid, whilst the other (a crystalline solid) is insoluble in acids. Ruthenium sulphate, Ru(S04)2, as obtained by oxidizing the sulphide, is an orange-yellow mass which is deliquescent and dissolves in water, the solution possessing a strongly acid reaction. Rouge de Ruthene, Ru 2 (OH) 2 C1 4 (NH 4) 7, is obtained from ammonia and ruthenium sesquichloride at 40° C., the product being purified by crystallization from ammonia. It forms small brown lamellae which dissolve slowly in water to give a fuchsine-red solution possessing a violet reflex. The solution possesses a considerable tinctorial power, dyeing silk in the cold. Potassium ruthenium cyanide, K4Ru(CN) 6.3H 2 O, formed when potassium ruthenate is boiled with a solution of potassium cyanide, crystallizes in colourless plates which are soluble in water. A ruthenium silicide, RuSi, has been prepared by H. Moissan (Comptes rendus, 1903, 1 37, p. 229) by the direct combination of the two elements in the electric furnace. It forms very hard metallic-looking crystals, burns in oxygen and is not attacked by acids. Potassium ruthenate, K2Ru04 H20, obtained by fusion of the metal with caustic potash and nitre, crystallizes in prisms which become covered with a black deposit on exposure to moist air. It is soluble in water, giving an orangered solution which becomes green on standing, and gradually deposits the hydrated pentoxide, Ru 2 O 5 H 2 O (H. Debray and A. Joly, Comptes rendus, 1888, 106, p. 1494). The per-ruthenate, KRuO 4, formed by the action of chlorine on the ruthenate, or of alkalis on the peroxide at 50° C., is a black crystalline solid which is stable in dry air but decomposes when heated strongly. On the nitroso, nitroso-ammonium and nitroso-diammonium compounds see C. E. Claus, Ann., 1856, 98, p. 317; A. Joly, Comptes rendus, 1888, 107, p. 994; 1889, 108, pp. 8 54, 1300; 1890, III, p. 969; L. Brizard, ibid., 1896, 122, p. 730; 1896, 123, p. 182. The atomic weight of ruthenium was determined by A. Joly (Comptes rendus, 1889, 188, p. 946), who obtained the values 101.5 and 101 3.
Ruthenium is a chemical element. It has the chemical symbol Ru. It has the atomic number 44. It is a rare metal. It is silver white. In chemistry it is placed in a group of metal elements named the transition metals. It is also part of the platinum group. Ruthenium is found in platinum ores.