The term ‘precious metal’ probably feels synonymous with gold, or maybe silver to most people, but in reality, a different shiny metallic element takes the spot of most precious, and that’s rhodium.
Stable and Solid
One of six metals belonging to the platinum group, rhodium also serves as a noble metal, meaning that it doesn’t react easily with oxygen, serves as a strong catalyst, and resists corrosion aggressively. These traits are in addition to those shared by all platinum metals, like being non-toxic and having a high melting point.
The rarest of all platinum group metals, rhodium occurs at an abundance of about one part per 200 million on Earth, making it incredibly hard to come by. Still, rhodium is used as part of one of the most common machines on the planet.
William Hyde Wollaston discovered rhodium in 1803, not long after he discovered another platinum group element: palladium. Wollaston isolated rhodium by removing platinum and palladium from platinum ore, leaving him with sodium rhodium chloride.
Cleaning Up After Cars
The majority of commercial rhodium is used to make cars’ catalytic converters. The rhodium, along with other members of the platinum group, cleans up a great deal of nitrogen oxide emissions from exhausts and is therefore responsible for keeping air pollution down to a minimum.
This metal can also be used in the chemical industry as a catalyst in a number of reactions, or to coat mirrors. Because it is so rare, rhodium can get quite costly, so it is substituted whenever possible.
Being that it serves such an important function in minimizing pollution, it’s a shame that rhodium isn’t more abundant on Earth, but it is a gift that this rare metal exists at all.