Arranged by name alphabetically, ruthenium is the last of six metallic elements in the platinum group. This precious metal is characterized as being both polyvalent and versatile. In fact, it is known to be more versatile than any of the other five precious metals in the platinum group.
A hard, white metal, ruthenium is known to have four crystal
modifications. While it does not tarnish under normal temperature, it
does oxidize readily when exposed to air.
It can be plated by means of
two methods: thermal decomposition and electrodeposition. Following is a list of some of the properties of ruthenium:
• Chemical Symbol: Ru
• Atomic Number: 44
• Category (as an element): Transition Metal
• Group/ Period/ Block (in the Periodic Table): 8/ 5/ d
• Atomic Weight: 101.07 g.mol-1
• Electron Configuration: [Kr] 4d7 5s1
• Density (near room temperature): 12.45 g.cm-3
• Liquid Density (at melting point): 10.65 g.cm-3
• Melting Point: 2334°C, 4233°F, 2607.4°K
• Boiling Point: 4150°C, 7502°F, 4423°K
• Heat of Fusion: 38.59 kJ.mol-1
• Heat of Vaporization: 591.6 kJ.mol-1
• Oxidation States: 8, 7, 6, 4, 3, 2, 1, -2
• Electronegativity: 2.3 (Pauling scale)
• Atomic Radius: 134 picometre
• Covalent Radius: 146±7 picometre
• Ionization Energies: 710.2 kJ.mol-1 (first), 1620 kJ.mol-1 (second), 2747 kJ.mol-1 (third)
Ruthenium-palladium and ruthenium-platinum alloys are used in making electrical contacts for wear resistance. As a matter of fact, ruthenium is a very effective hardener for both palladium and platinum. When a small amount of ruthenium is added to titanium, the latter's corrosion resistance is improved significantly.
As to its other applications, ruthenium is used in:
1. film chip resistors;
2. jewelry (when alloyed with gold);
3. high-temperature superalloys (used in making the turbine blades in jet engines);
4. fountain pen nibs;
5. removing hydrogen sulfide from various industrial processes;
6. electrolytic cells for various chemical processes (as a component of mixed-metal oxide anodes);
7. optical sensor device;
8. radiotherapy (particularly of eye tumors).
Along with the five other precious metals in the platinum group, ruthenium is generally found in ores in North America, South America, and the Ural Mountains in Russia. Small quantities of this element also occur in pentlandite (an iron-nickel sulfide) obtained from Sudbury in Ontario, Canada, and in South Africa's pyroxenite (an ultrabasic igneous rock) deposits.
Commercially, ruthenium is obtained as a by-product from copper and nickel processing (as how all the other platinum group metals are obtained), although it is likewise obtainable through direct processing of platinoid ores. It is isolated by means of a complex chemical process. The process involves reduction of ammonium ruthenium chloride with the use of hydrogen. This yields a powder which, in turn, is consolidated by means of a technique called argon-arc welding.
In terms of abundance in the Earth's crust, ruthenium ranks 74th among all the different known elements or metals and is, therefore, one of the rarest. Estimates place world reserves at 5,000 tonnes, and annual mining output about 12 tonnes. Ruthenium's price is estimated to be approximately 1,000 U.S. dollars per troy ounce.