40 Fun Facts About Rhodium

Which former Beatle received a rhodium-plated disc from Guinness in 1979 as history's best-selling songwriter?

Paul McCartney was handed rhodium because ordinary record-industry award discs no longer matched his sales. The metal was picked as something rarer than platinum.

Rhodium takes its name from the Greek word for which flower, after the colour of its dissolved salts?

Rose is 'rhodon' in Greek, and the name suited the pinkish-red crystals the element's discoverer coaxed out of platinum ore. The pure metal has no such tint.

Thieves hunting rhodium most often saw the catalytic converters off which hybrid car, a pioneer of its kind?

Toyota Prius converters carry extra precious metal because a hybrid's engine runs less often and its exhaust stays cooler. More catalyst is needed to do the same cleaning job.

Which country mines about three-quarters of the world's rhodium, mostly from its vast Bushveld Complex?

South Africa holds about 90% of the world's known reserves of platinum-family metals, packed into two rock layers that miners call reefs.

Jewellers routinely coat which metal, popular for engagement rings, with a thin layer of rhodium that slowly wears away?

White gold is naturally rather dull, so the rhodium supplies the bright shine buyers expect, a match for platinum. Some higher-quality alloys keep their lustre without it.

Rhodium is among the rarest elements in Earth's crust, yet traces have been measured in which staple vegetable?

Potatoes tested for the metal held between 0.8 and 30 parts per trillion. The crust itself averages less than one part per billion.

Which Swedish company introduced the three-way catalytic converter in 1976, sending demand for rhodium soaring?

Volvo fitted the device first to its 240 model. Earlier converters, built on platinum or palladium, handled only two of the three main exhaust pollutants.

Rhodium catalysts helped industry turn methanol into acetic acid, the sour ingredient of which kitchen staple?

Vinegar has been made for thousands of years, which probably makes acetic acid the first acid ever produced in large amounts.

A rhodium catalyst, part of a process devised by Japan's Ryoji Noyori, makes which cooling flavour for chewing gum?

Menthol comes naturally from mint plants, but a single Japanese firm makes about 3,000 tonnes of it a year this synthetic way.

Cars whose catalytic converters contain rhodium must avoid fuel laced with which metal, which ruins the catalyst?

Lead was added to petrol for decades to stop engines knocking, so the spread of converters forced the switch to unleaded fuel.

Which symbol stands for rhodium on the periodic table, where it sits at atomic number 45, just before palladium?

Rh also labels a blood-group factor, but there is no link: that name is short for rhesus, after the monkeys used in the original research.

Rhodium sits directly below which metal, famous for its deep blue pigments, in group 9 of the periodic table?

Cobalt once did rhodium's job in making acetic acid, until a rhodium catalyst discovered in the late 1960s proved able to work at lower pressure with almost no waste.

Rhodium detectors inside nuclear reactors, including Arizona's Palo Verde plant, track the flow of which particles?

Neutrons are tracked at Palo Verde by 305 rhodium detectors in each reactor, stacked on five levels to give a 3D picture of how the fuel is burning.

Which metal, abundant in the clay left by the dinosaur-killing asteroid, sits directly below rhodium in group 9?

Iridium has largely taken over one of rhodium's old industrial jobs, turning methanol into acetic acid, because it does the same conversion more efficiently.

Rhodium was first isolated in a private laboratory in which capital city, where its discoverer had moved in 1797?

London was where the discoverer set up a laboratory behind his house in 1801 and guarded its privacy to the utmost. A secret platinum process worked out there made his fortune.

Rhodium's discoverer was also the first person to notice dark lines crossing the spectrum of which celestial body?

The Sun's spectrum showed him the gaps twelve years before Joseph von Fraunhofer, whose name they now carry. He took them for mere boundaries between the colours.

A rhodium coating protects which jewellery metal from the black tarnish caused by sulfur compounds in the air?

Silver slowly blackens as sulfur in the air turns its surface into a dark sulfide. Rhodium never reacts that way, so a thin skin of it keeps sterling pieces bright.

Inside a three-way catalytic converter, rhodium's main job is to break down which family of smog-forming gases?

Nitrogen oxides are split by the rhodium into harmless gases that already make up the air we breathe. Platinum and palladium deal with the other exhaust pollutants.

The first cars with rhodium-bearing three-way catalytic converters were 1977 models built for sale in which US state?

California got the system three years before the same cars sold in the other 49 states, because its own smog rules demanded it.

A rhodium catalyst let industry mass-produce L-DOPA, a drug for which illness, earning its inventor a 2001 Nobel?

Parkinson's disease is treated with L-DOPA because the body turns the drug into dopamine. The catalyst was designed to make only the useful mirror-image form of the molecule.

Which chemist discovered both rhodium and palladium while secretly refining platinum for profit in the early 1800s?

William Wollaston hid the palladium discovery at first, selling the metal anonymously through a shop, and only owned up after he had found rhodium too.

Rhodium's discoverer gave up which profession in 1800, a few years before isolating the metal, to pursue chemistry?

Physician was a role that tormented him: worry over one patient reduced him to tears, and he wrote that losing thousands of pounds would hurt less than the anxiety.

Rhodium's discoverer began by dissolving crude platinum ore in which fuming acid mixture, long prized by alchemists?

Aqua regia, a blend of nitric and hydrochloric acids, barely touches solid rhodium itself, a stubbornness later used to separate the metal from platinum.

Rhodium's discoverer patented which optical drawing aid in 1806, letting artists trace a scene onto paper?

Camera lucida was his own coinage, Latin for a well-lit room, chosen as the opposite of the older camera obscura, or dark room.

Rhodium is among the most valuable precious metals; in 2021 one troy ounce peaked at close to how many US dollars?

$30,000 an ounce was more than forty times what the same metal had fetched five years earlier, when it sold for under $700.

Natural rhodium is one of just 26 elements with only a single stable what, giving every atom the same mass?

Isotope number 103 is the only form of rhodium found in nature. Dozens of radioactive versions have been made in laboratories, most of them lasting less than an hour.

Rhodium forms inside nuclear reactors as a fission product when atoms of which fuel element split apart?

Uranium fission leaves rhodium in spent fuel, but nobody extracts it on a large scale: the radioactive waste would first have to cool for about ten years.

Rhodium's discoverer and his partner bought the smuggled platinum ore that yielded it on which festive date in 1800?

Christmas Eve 1800 brought a purchase that yielded four new elements: the two partners divided the work, and each found a pair of them in the same batch of ore.

Which American company, later famous for Roundup weedkiller, built the first plant using rhodium to make acetic acid?

Monsanto opened the plant in 1970, and its rhodium method went on to become the dominant way of making the acid worldwide.

At Sudbury in Canada, rhodium is a by-product of mining which metal, a key ingredient of stainless steel?

Nickel ore at Sudbury holds only a trace of rhodium, but so much rock is processed there that recovering the precious metal still pays.

The platinum ore in which rhodium was discovered had been smuggled into Britain from which present-day country?

Colombia was Europe's chief early source of platinum, though the Spanish there generally treated the unfamiliar metal as an unwanted impurity in gold.

Molten rhodium soaks up which gas from the air, only to release it again as the metal sets solid?

Oxygen is taken up only once the rhodium melts, at nearly 2,000 °C. Solid rhodium at room temperature is so unreactive that it never tarnishes in air.

Which British Nobel laureate is honoured in the name of a rhodium compound that became a classic hydrogenation catalyst?

Geoffrey Wilkinson shared the 1973 Nobel Prize in Chemistry for work on compounds that bond metals to carbon, and also worked out the structure of ferrocene.

Wires of platinum alloyed with rhodium have been used for over a century in which devices for gauging furnace heat?

Thermocouples made with rhodium can read up to about 1,800 °C and stay exceptionally stable across the top 500 degrees of that range.

Rhodium filters and anodes lower the radiation dose in the X-ray machines used for which kind of medical screening?

Mammography machines with rhodium parts give a lower dose than comparable ones built with molybdenum.

Rhodium-platinum nozzle plates called bushings spin which material, used in boat hulls and loft insulation?

Fibreglass makers alloy their platinum with rhodium for durability, because the plates sit under a constant flow of molten material and pure platinum tends to wear.

Besides exhaust systems, rhodium has been used on cars as the reflective coating inside which other part?

Headlights have used rhodium reflectors because the metal is very hard, bounces back a high share of the light that hits it and resists corrosion.

Gauze woven from platinum and rhodium is the catalyst that burns which gas to make nitric acid for fertilisers?

Ammonia burns on the gauze at about 900 °C, and the punishing conditions soon degrade the metal into a knobbly state that engineers call cauliflowering.

Which platinum-group metal, named after the Latin word for Russia, sits just before rhodium at atomic number 44?

Ruthenium is what the lighter radioactive forms of rhodium decay into, usually by swallowing one of their own electrons.

Which French engineer patented the catalytic converter in the 1950s, two decades before rhodium was added to it?

Eugene Houdry had already invented the catalytic cracking process that modern oil refining is built on, then turned to exhaust after reading early studies of Los Angeles smog.