Ruthenium is a hard, white metal belonging to the platinum family of metals. It is a chemical element with the symbol Ru and atomic number 44 in the periodic table. Like the other metals of the platinum group, ruthenium is usually found in platinum ore. 

Ruthenium has the remarkable ability to harden platinum and palladium and is also extremely resistant to corrosion and cannot be attacked by acids. As such, the primary use of ruthenium is as a hardening agent in platinum and palladium alloys used to make, amongst other things, wear-resistant electrical contacts. A very small amount of ruthenium (0.1%) added to titanium can make it one hundred times more resistant to corrosion.

Ruthenium is also used in the manufacturing of hard disks. It is a key ingredient and plays a critical role in increasing data storage densities of modern hard drives.