• February 3, 2023
About Rhodium


What is Rhodium Metal?

Rhodium is a silver-white metallic element that is highly reflective and resistant to corrosion. It is considered the rarest and most valuable precious metal in the world — well above gold or silver. The name rhodium comes from the Greek word “rhodon,” meaning rose, named for the rose-red color of its salts.

Rhodium metal was discovered in 1803 by English chemist William Hyde Wollaston shortly after the palladium discovery. It often occurs with deposits of platinum and is commonly obtained from the mining and refining of platinum.

Pictures, stories, and facts about the element Rhodium in the Periodic TableProperties of Rhodium Metal

Rhodium is one of the 6 platinum group metals: platinum, palladium, rhodium, osmium, iridium, and ruthenium.

Some common characteristics of the platinum group metals include high melting points, general non-toxicity, and resistance to wear, oxidation, and corrosion, according to Chemistry Libretexts.

  • It is also classified as a noble metal, meaning that it does not react to oxygen easily, acts as a fantastic catalyst, and is resistant to corrosion and oxidation.
  • Rhodium is the rarest of the platinum group, occurring up to 1/200 million in the Earth’s crust
  • Has a lower density and a higher melting point than platinum.
  • Has low electrical resistance, low and stable contact resistance, and is highly resistant to corrosion.
  • Unaffected by air and water up to 1,112 degrees Fahrenheit
  • Very hard and has a high reflectance.
  • Rhodium has no known biological use and no known use for life processes.
  • Although it is generally considered non-toxic, some of its compounds are toxic and carcinogenic. Naturally occurring rhodium consists of just one stable isotope: Rh-103.

Sources: Rhodium occurs with other platinum metals in river sands in the Urals and in North and South America. It is found in the copper-nickel sulfide ores of the Sudbury, Ontario region.

Facts & Physical Data about Rhodium Metal

  • Atomic number: 45, Atomic symbol: Rh
  • Atomic weight: 102.90550, Atomic Radius (pm): 134, Atomic Volume (cc/mol): 8.3, Density: 12.41 grams per cubic cm
  • Phase at room temperature: Solid
  • Melting point: 3,567 degrees F (1,964 degrees C), Boiling point: 6,683 degrees F (3,695 degrees C)
  • Period number: 5, Group number: 9
  • Electron configuration: [Kr] 4d85s1
  • Number of isotopes (atoms of the same element with a different number of neutrons): 24 whose half-lives are known; one stable; Most common isotopes: One stable isotope Rh-103
  • Covalent Radius (pm): 125, Ionic Radius: 68 (+3e)
  • Oxidation States: 5, 4, 3, 2, 1, 0
  • Lattice Structure: Face-Centered Cubic

Did you Know?rhodium facts

  • An alloy of rhodium-platinum is used in heart pacemakers.
  • South African PGM producers extract a mix of metals comprising approximately: 60% platinum, 30% palladium, and 10% rhodium.
  • Resistant to most acids.
  • Rarely used by itself and almost always as an alloy.
  • Out of 3 precious metals (rhodium, platinum, and palladium) used in vehicle catalytic converters, rhodium has by far the highest activity for the removal of nitrogen oxides (NOx) from the exhaust.
  • Has very high activity for the oxidation of hydrocarbons (HC) and carbon monoxide (CO)
  • Has very good resistance to the poisons present in the exhaust stream
  • Its primary drawback, however, is its high cost.
  • All rhodium compounds are easily reduced or decomposed through heating to create powdered (or sponge) metal.

Rhodium Usage

  • Due to its low electrical resistance and its high corrosion resistance, it is used as an electrical contact material as well, according to RSC.
  • Since rhodium is quite brilliant and resistant to tarnishing, it is used as a finish for jewelry, searchlights, and mirrors.
  •  Plated rhodium is very hard and has a high reflectance, which makes it useful for optical instruments and jewelry.
  • Rhodium is also used as a catalyst in certain reactions.
  • Other uses for rhodium are coating optic fibers, crucibles, thermocouple elements, and headlight reflectors.

Rhodium Alloys

Rhodium Facts, Symbol, Discovery, Properties, UsesRhodium is often alloyed with platinum and iridium to make an oxidation-resistant metal that can stand against high temperatures. One major use of rhodium is as an alloying agent to harden platinum and palladium.

It is also alloyed with platinum for aircraft turbine engines.

These alloys are used in furnace windings, pen nibs, phonograph needles, high-temperature thermocouple and resistance wires, electrodes for aircraft spark plugs, bearings, and electrical contacts.

Rhodium as Catalytic converters

The main use for rhodium is in catalytic converters designed to clean vehicle emissions. Rhodium — often together with palladium and/or platinum — accomplishes this by reducing nitrogen oxide in the exhaust gas.

Without rhodium catalysts, the air in our cities would be much worse due to vehicle exhausts.

In the chemical industry, rhodium is used as a catalyst in the making of nitric acid, acetic acid, and hydrogenation reactions, according to the Royal Society of Chemistry (RSC).

To know more about the properties, features, and uses of precious metals like Rhodium, Palladium, Iridium, Ruthenium, etc., please follow and subscribe to Mintly Blog.

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