Rhodium – The mystery of the most expensive material in cars

Gold is a rare and expensive metal, but there is another metal that surpasses both in price and rarity: rhodium. The prices of metals vary, depending on demand and accessibility. Due to its versatility, conductivity, durability, and beautiful appearance, gold is among the most expensive metals in the world.

Gold price is currently about 1,850 USD/ounce, but still very cheap compared to rhodium. Currently the most expensive precious metal and one of the rarest, the price per ounce of rhodium is around $10,300.

Rhodium is a silvery white metal that belongs to the platinum family. It has high reflective qualities (up to 80% of light) and does not tarnish. Rhodium is hypoallergenic, harder than gold, and extremely durable. Its name comes from the Greek word "rhodon", meaning rose-colored.

Possessing a silvery white appearance, it looks like silver but rhodium is very hard, has a high melting temperature and corrosion resistance. Rhodium does not react easily with oxygen, making it a noble metal and an ideal catalyst, resistant to both corrosion and oxidation. With an overall hardness and high melting point of 1,964 degrees Celsius, rhodium belongs to the platinum group along with the metals platinum, palladium, osmium, iridium, and ruthenium. The ability to withstand water and air temperatures up to 600 degrees Celsius, while being insoluble in most acids, makes rhodium very useful for cars, airplanes, electrical switches, resistance wires and high-temperature thermocouples.

Rhodium is hypoallergenic, harder than gold, and extremely durable. As a precious metal, rhodium resources on earth are relatively small compared to other metals. Rhodium is present at a density of about 0.000037 ppm (1 ppm = 1 milligram/kg) in the Earth's crust, while gold is much more abundant, about 0.0013 ppm, according to the Royal Society of Chemistry (RSC). Rhodium is produced mainly in Canada, South Africa and Russia, possibly as a by-product of refining nickel and copper ores, containing about 0.1% of the precious metal. About 16 tons of rhodium are produced annually, with estimated reserves of 3,000 tons.

Rhodium (also known as Rhodium) was discovered in 1803 by William Hyde Wollaston, shortly after he discovered the compound Palladium. At that time, he partnered with Smithson Tennat in a commercial venture, aimed at producing pure platinum for sale. Rhodium usually does not occur pure, but is found in compounds with other substances in platinum or nickel ores.

After its discovery, Rhodium only had small applications at that time, mainly used to measure temperatures up to 1,800 degrees Celsius because Rhodium has good stability in the temperature range of 1,300-1,800 degrees Celsius.

Car exhaust gas neutralizer. (Photo: Bellingham Herald)

The first application of Rhodium was electroplating for decoration and anti-corrosion coatings. Then, the introduction of three-way catalytic converters (also called exhaust gas neutralizers) by Volvo in 1976 increased demand for Rhodium. Previously, catalytic converters used only platinum or palladium, while three-way catalytic converters used Rhodium to reduce emissions, changing harmful unburned hydrocarbons, carbon monoxide and nitrogen oxide emissions. into less toxic gases. More specifically, to remove nitrate in exhaust gas, only Rhodium helps remove it and there is no substitute.

More and more, Rhodi's main uses are in exhaust gas neutralizers. It is estimated that in 2012, Rhodium consumption was about 30,000 kg, of which 81% (24,300 kg) was used in exhaust gas neutralizers. The remainder are mainly used in the glass industry and chemical industry.

Unlike other materials used on supercars and high-end vehicles. Automakers often use Rhodium even on low-end models. Since 1993, any gasoline-powered car has Rhodium in its exhaust gas neutralizer.

Structure of the car exhaust system with exhaust gas neutralizer. (Photo: YourMechanic)

However, because Rhodium is so rare and the mining process is so complicated, it is considered one of the 10 most expensive materials in the world. This means that the value increases rapidly over time. From 2016 onwards, Rhodium's price increased 5 times, similar to palladium. Currently, the price of Rhodium is about 29,400 USD/ounce (28.3 g), equivalent to more than 1 million USD/1 kg. Meanwhile, the price of gold is only 1,700 USD/ounce.

The high price has led to an increase in theft of car exhaust neutralizers in recent years. And this part is very easy to steal, groups of thieves act in just a few dozen seconds with a car jack, wrench or piston saw.

Victims of theft are often cars parked in one place for long periods of time. High-riding vehicles such as SUVs, pickup trucks, and vans are also targets because their height makes it easy to get under the chassis for theft. Especially later Toyotas because the chassis is higher and the bolts connecting the converter are easier to remove.

On the other hand, not all exhaust gas neutralizers are built the same. As a rule, older cars tend to use more metal, for example the Toyota Prius or Nissan Frontier are more sought after because they use less of the engine, which means more catalysts are discarded. more Rhodium.

To replace the exhaust gas neutralizer when stolen, the price the owner has to spend is up to 4,100 USD, and in some places can be fined 1,300 USD due to higher emissions than allowed. When the exhaust gas neutralizer is lost, the sound of the exhaust pipe will be louder than usual and the car owner will easily recognize the loss.

Steel wire catalytic converter locking cage. (Photo: Heycar).

However, there is no way to completely prevent catalytic converter theft. The simplest solution is to park the car in the garage at home (if available) or in a parking lot with lighting, a monitoring system, a caretaker, and engraved identification symbols or license plates. In some places, mechanics recommend welding the ends on the catalytic converter bolts, or using locking steel wire cages to completely protect the part.

Metal is so expensive that few people dare to use it

This expensive metal has also been used as a coating for jewelry and silverware since the 1930s. However, rhodium has never before been used to make jewelry even if it seems The outside is shiny and very beautiful. The simple reason is because rhodium bracelets and rings are too expensive and the materials are too difficult to find. So even though it looks like silver, rhodium is only used for external plating and is not chosen as a jewelry making material because of its lack of practicality.

As the most expensive precious metal in the world, people who dare to use it to plate jewelry are very rare. The most familiar example is the British monarchy's crown, which was coated with rhodium in 1858 to represent the luxury and power of the dynasty.

In addition, the conductive properties and stability of rhodium are also used in the field of electronics manufacturing. Components such as resistors, circuit boards, and hard drives are indispensable for rhodium metal.

Rhodium also appears in the chemical industry. The world's most expensive metal is needed in the synthesis of alkyl compounds, epoxy compounds and aldehyde compounds.