Have you seen rhodium plated coins recently and wondered what exactly rhodium was and where it fits in the scheme of more traditional metals like gold and silver? Keep reading to learn more!
Discovery of Rhodium
English chemist William Hyde Wollaston discovered rhodium in 1803. He made the discovery thanks to a tip from Hippolyte-Victor Collet-Descotils. Collet-Descotils surmised that the red color found in some platinum salts came from an unidentified metal. Wollaston removed the platinum and palladium ore through chemical reactions, resulting in a dark red powder. This substance was sodium rhodium chloride. Today, commercial rhodium is typically a nickel and copper byproduct.
Just 25 tons of rhodium are produced every year, just over 1% of the amount of gold produced. South Africa provides about 80% of that, with Russia accounting for another 8%. The metal is also found in river sands in the Americas and copper-nickel sulfide ores in Canada.
Chemical and Physical Properties of Rhodium
Chemically, rhodium falls into the category of noble metals, which do not react quickly to oxygen. It is among six platinum group metals, including platinum, palladium, osmium, iridium, and ruthenium. The metal is less dense than platinum and has a higher melting point. Rhodium shows no effects of water or air up to 600 degrees Celsius and has a melting point of 1,964 degrees Celsius. It has just one stable isotope that occurs naturally, Rh-103.
Rhodium is naturally a white metal, but black rhodium can be created by giving it an ink dye that binds to metal. Coins with black rhodium plating have become extremely popular among collectors in recent years. The plating gives the coins a sharp look and helps to protect them from corrosion.
Uses of Rhodium
Why is the price of rhodium so high, and what is its relationship to the economy writ large? To date, rhodium’s primary use has been in catalytic converters that clean emissions from motor vehicles. Sometimes used alone and other times with platinum and/or palladium, the metal reduces the amount of nitrogen oxide in the exhaust. This lesser amount of nitrogen oxide dramatically reduces air pollution, especially in cities. Therefore, the metal’s price collapsed in 2008, as the auto industry was hit hard by the crisis. The metal is also used to finish coins and jewelry, as well as searchlights and mirrors. Alloyed with platinum, it is also used in airplane turbine engines.
Recent studies have shown promising results for using rhodium in converting water and carbon dioxide into high energy fuels by using thermal energy from the sun. In this case, it is used as a catalyst in conjunction with cerium oxide. Scientists hope that this will create a new way of storing chemical energy.
Rhodium Plated Coins
The Royal Canadian Mint (RCM) has taken firmly to the rhodium plating trend. One of the most famous examples of this is with the 2020 Black Proof Incuse Silver Maple Leaf. This unique take on the popular series has a mintage of just 5,000 pieces, each of which was struck from 1 oz .9999 fine silver. The selective black plating brings out the maple leaf and Queen Elizabeth II designs by darkening the rest of the coin. The RCM also used selective black rhodium plating in its Nocturnal by Nature series. The plating created stunning contrasts against the silver moon while offering a look at four of the issuing country’s wild animals as they would be seen at night.
Due to the relatively high prices of the metal combined with the relative popularity of gold, silver, and other metals among collectors, rhodium coins tend to be low mintage and hard to find. Pieces plated in the unique metal, though, are much more readily available. These pieces are sure to stand out and draw the attention of collectors and non-collectors alike.
Sources
https://www.livescience.com/36988-rhodium.html
https://www.kitco.com/charts/rhodium.html
https://www.mining-technology.com/features/five-most-expensive-metals-and-where-they-are-mined/
