We continue to review some of the most important materials in heat treatment and metallurgy.
Ruthenium (chemical symbol: Ru)
Ruthenium is a shiny, silvery-white metal (Fig. 1). It is typically found as a minor constituent of platinum ore and is highly inert. Ruthenium will tarnish at room temperature but will oxidize if subjected to high temperature. As the 74th most-plentiful element in Earth's crust, ruthenium is quite rare, existing at a concentration of about 100 parts per trillion. Only about 12 tons of ruthenium is mined annually and is obtained from the waste after the refining of nickel.
Ruthenium was the last of the six platinum-group metals (platinum, palladium, rhodium, osmium, iridium and ruthenium) to be discovered. In 1808, Polish chemist Jedrzej Sniadecki was studying platinum ores mined in South America when he thought he discovered a new metal, which he called vestium. When his discovery couldn’t be independently confirmed, he withdrew his claim.
Later, in 1825, Gottfried Osann of the University of Dorpat (now Tartu) on the Baltic was examining residues left over from dissolving unrefined platinum obtained from the Ural Mountains, and he described three new elements that he named pluranium, polinium and ruthenium. Although pluranium and polonium were never verified, ruthenium was determined to be real.
In 1840 at the University of Kazan, Russian pharmacist and chemist Karl Karlovich Klaus extracted a new metal from waste residues of the platinum refinery in St. Petersburg. After refining and confirming Osann’s discovery of the new element, he retained Osann’s name of ruthenium, which is derived from Ruthenia, the Latin word for Russia.
Due to its extremely high melting point of 2334°C (4233°F), pure ruthenium is difficult to cast. Even when heated, it is extremely hard and brittle, which makes it impractical for rolling, shaping or drawing into a wire. As a result, it is used primarily as an alloying agent for platinum and other metals of the platinum group. It is very effective as a hardener for platinum and palladium, and it is alloyed with these metals to make extreme-duty electrical contacts with severe wear resistance. Platinum-ruthenium alloys can also be found used in some jewelry.
An emerging-technological use for ruthenium is in dye-sensitized solar cells (DSCs), which are third-generation solar cells with the potential for high efficiency and low production costs (Fig. 2). While current DSCs provide light-to-electricity conversion of up to 11%, it is thought that significant additional improvement is possible.
Ruthenium-based DSC devices can be made semi-transparent to allow some of the light to pass through while converting the remainder to electricity. This characteristic gives them promise for use in photovoltaic windows in buildings or small devices.
Here are some important facts about ruthenium.
- Atomic number: 44
- Atomic weight: 101.07
- Melting point: 2607 K (2334°C or 4233°F)
- Boiling point: 4423 K (4150°C or 7502°F)
- Density: 12.1 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal
- Period number: 5
- Group number: 8
- Group name: none