Rhodium Mini Forum, Tips, Tricks & Codes

Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant, and chemically inert transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isotope, ¹⁰³Rh. Naturally occurring rhodium is usually found as a free metal, as an alloy with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals.

Rhodium is found in platinum or nickel ores together with the other members of the platinum group metals. It was discovered in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds.

The element's major use (approximately 80% of globerhodium production) is as one of the catalysts in the three-methodcatalytic converters in automobiles. Because rhodium metal is inert versuscorrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its appearance while sterling silver is often rhodium-plated for tarnish resistance. Rhodium is sometimes utilize to cure silicones; a two-part silicone in which one part containing a silicon hydride and the other containing a vinyl-terminated silicone are mixed. One of these liquids include a rhodium complex.

Rhodium detectors are utilize in nuclear reactors to measure the neutron flux level. Other utilize of rhodium containasymmetric hydrogenation utilize to form drug precursors and the processes for the production of acetic acid.

History

Rhodium (Greek rhodon (ῥόδον) meaning "rose") was discovered in 1803 by William Hyde Wollaston, soon after his uncover of palladium. He utilize crude platinum ore presumably obtained from South America. His procedure involved dissolving the ore in aqua regia and neutralizing the acid with sodium hydroxide (NaOH). He then precipitated the platinum as ammonium chloroplatinate by adding ammonium chloride (NH
₄Cl). Most other metals like copper, lead, palladium and rhodium were precipitated with zinc. Diluted nitric acid dissolved all but palladium and rhodium. Of these, palladium dissolved in aqua regia but rhodium did not, and the rhodium was precipitated by the addition of sodium chloride as Na
₃[RhCl
₆]·nH
₂O. After being washed with ethanol, the rose-red precipitate was reacted with zinc, which displaced the rhodium in the ionic compound and thereby released the rhodium as free metal.

After the uncover, the rare element had only minor app; for example, by the turn of the century, rhodium-containing thermocouples were utilize to measure temperatures up to 1800 °C. They have exceptionally awesomestability in the temperature range of 1300 to 1800 °C.

The first major appwas electroplating for decorative utilize and as corrosion-resistant coating. The introduction of the three-way catalytic converter by Volvo in 1976 increased the demand for rhodium. The previous catalytic converters utilize platinum or palladium, while the three-methodcatalytic converter utilize rhodium to reduce the amount of NOx in the exhaust.

Characteristics

Rhodium is a hard, silvery, durable metal that has a high reflectance. Rhodium metal does not normally form an oxide, even when heated. Oxygen is absorbed from the atmosphere only at the melting point of rhodium, but is released on solidification. Rhodium has both a higher melting point and lower density than platinum. It is not attacked by most acids: it is completely insoluble in nitric acid and dissolves slightly in aqua regia.

Chemical properties

Rhodium belongs to group 9 of the periodic table, but the configuration of electrons in the outermost shells is atypical for the group. This anomaly is also observed in the neighboring elements, niobium (41), ruthenium (44), and palladium (46).

The common oxidation state of rhodium is +3, but oxidation states from 0 to +6 are also observed.

Unlike ruthenium and osmium, rhodium forms no volatile oxygen compounds. The known stable oxides include Rh2O3, RhO2, RhO
₂·xH
₂O, Na
₂RhO
₃, Sr
₃LiRhO
₆ and Sr
₃NaRhO
₆. Halogen compounds are known in nearly the full range of possible oxidation states. Rhodium(III) chloride, rhodium trifluoride, rhodium pentafluoride and rhodium hexafluoride are examples. The lower oxidation states are stable only in the presence of ligands.

The best-known rhodium-halogen compound is the Wilkinson's catalyst chlorotris(triphenylphosphine)rhodium(I). This catalyst is utilize in the hydroformylation or hydrogenation of alkenes.

Isotopes

Naturally occurring rhodium is composed of only one isotope, ¹⁰³Rh. The most stable radioisotopes are ¹⁰¹Rh with a half-life of 3.3 years, ¹⁰²Rh with a half-life of 207 days, ^102mRh with a half-life of 2.9 years, and ⁹⁹Rh with a half-life of 16.1 days. Twenty other radioisotopes have been characterized with atomic weights ranging from 92.926 u (⁹³Rh) to 116.925 u (¹¹⁷Rh). Most of these have half-lives shorter than an hour, except ¹⁰⁰Rh (20.8 hours) and ¹⁰⁵Rh (35.36 hours). Rhodium has numerous meta states, the most stable being ^102mRh (0.141 MeV) with a half-life of about 2.9 years and ^101mRh (0.157 MeV) with a half-life of 4.34 days (see isotopes of rhodium).

In isotopes weighing less than 103 (the stable isotope), the primary decay mode is electron capture and the primary decay product is ruthenium. In isotopes greater than 103, the basicdecay mode is beta emission and the basicproduct is palladium.

Occurrence

Rhodium is one of the rarest elements in the Earth's crust, comprising an estimated 0.0002 parts per million (2 × 10⁻¹⁰). Its rarity affects its price and its utilizein commercial app. The concentration of rhodium in nickel meteorites is typically 1 part per billion. Rhodium has been measured in some potatoes with concentrations between 0.8 and 30 ppt.

Mining and price

The industrial extraction of rhodium is complex because the ores are mixed with other metals such as palladium, silver, platinum, and gold and there are very few rhodium-bearing minerals. It is found in platinum ores and extracted as a white inert metal that is difficult to fuse. Principal sources are located in South Africa; in river sands of the Ural Mountains in Russia; and in North America, including the copper-nickel sulfide mining locationof the Sudbury, Ontario, region. Although the rhodium abundance at Sudbury is very small, the hugeamount of processed nickel ore makes rhodium recovery cost-effective.

The main exporter of rhodium is South Africa (approximately 80% in 2010) followed by Russia. The annual globeproduction is 30 tonnes. The price of rhodium is highly variable. In 2007, rhodium cost approximately eight times more than gold, 450 times more than silver, and 27,250 times more than copper by weight. In 2008, the price briefly rose above $10,000 per ounce ($350,000 per kilogram). The economic slowdown of the 3rd quarter of 2008 pushed rhodium prices sharply back below $1,000 per ounce ($35,000 per kilogram); the price rebounded to $2,750 by early 2010 ($97,000 per kilogram) (more than twice the gold price), but in late 2013, the prices were less than $1000. Political and financial issuessup class="noprint Inline-Template" style="margin-left:0.1em; white-zonenowrap;">[clarification needed] led to very low oil prices and over supply, causing most metals to drop in price. The economies of China, India and other emerging countries slowed in 2014 and 2015. In 2014 alone, 23,722,890 motor car were produced in China, excluding motorbikes.^{[clarification needed]} This resulted in a rhodium price of 740.00 US-$ per Troy ounce (31.1 grams) in late November 2015.

Registrant of rhodium—a metal with a highly volatile market price—are periodically put in an extremely advantageous market position: extracting more rhodium-containing ore from the ground will necessarily also extract other much more abundant precious metals—notably platinum and palladium—which would oversupply the market with those other metals, lowering their prices. Since it is economically infeasible to simply extract these other metals just to obtain rhodium, the market is often left hopelessly squeezed for rhodium supply, causing prices to spike. Recovery from this supply-deficit position may be quite problematic in the future for many reasons, notably because it is not known how much rhodium (and other precious metals) actually was territory in catalytic converters during the many years when manufacturers' emissions-cheating programwas in use. Much of the globesupply of rhodium is obtained from recycled catalytic converters obtained from scrapped car. As of early November 2020, the spot price of rhodium was US$14,700 per troy ounce. In early March 2021, rhodium reached a price of US$29,400 per troy ounce on Metals Daily (a precious metals commodity listing).

Utilize nuclear fuels

Rhodium is a fission product of uranium-235: each kilogram of fission product include a significant amount of the lighter platinum group metals. Utilize nuclear fuel is therefore a potential source of rhodium, but the extraction is complex and expensive, and the presence of rhodium radioisotopes requires a period of cooling storage for multiple half-lives of the longest-lived isotope (¹⁰¹Rh with a half-life of 3.3 years, and ^102mRh with a half-life of 2.9 years), or about 10 years. These factors make the source unattractive and no large-scale extraction has been attempted.

App

The basicutilizeof this element is in automobiles as a catalytic converter, changing harmful unburned hydrocarbons, carbon monoxide, and nitrogen oxide exhaust emissions into less noxious gases. Of 30,000 kg of rhodium consumed worldwide in 2012, 81% (24,300 kg) went into this application, and 8,060 kg was recovered from old converters. About 964 kg of rhodium was utilize in the glass industry, mostly for production of fiberglass and flat-panel glass, and 2,520 kg was utilize in the chemical industry.

Catalyst

Rhodium is preferable to the other platinum metals in the reduction of nitrogen oxides to nitrogen and oxygen:

Rhodium catalysts are utilize in a number of industrial processes, notably in catalytic carbonylation of methanol to produce acetic acid by the Monsanto process. It is also utilize to catalyze addition of hydrosilanes to molecular double bonds, a process necessaryin manufacture of certain silicone rubbers. Rhodium catalysts are also utilize to reduce benzene to cyclohexane.

The complex of a rhodium ion with BINAP is a widely utilize chiral catalyst for chiral synthesis, as in the synthesis of menthol.

Ornamental utilize

Rhodium search utilizein jewelry and for decorations. It is electroplated on white gold and platinum to give it a reflective white surface at time of sale, after which the thin layer wears away with use. This is known as rhodium flashing in the jewelry business. It may also be utilize in coating sterling silver to protect versustarnish (silver sulfide, Ag₂S, produced from atmospheric hydrogen sulfide, H₂S). Solid (pure) rhodium jewelry is very rare, more because of the difficulty of fabrication (high melting point and badmalleability) than because of the high price. The high cost ensures that rhodium is applied only as an electroplate. Rhodium has also been utilize for honors or to signify elite status, when more commonly utilize metals such as silver, gold or platinum were deemed insufficient. In 1979 the Guinness Book of GlobeRecords gave Paul McCartney a rhodium-plated disc for being history's all-time best-selling songwriter and recording artist.

Other utilize

Rhodium is utilize as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium. These alloys are utilize in furnace windings, bushings for glass fiber production, thermocouple elements, electrodes for aircraft spark plugs, and laboratory crucibles. Other utilize include:

• Electrical contacts, where it is valued for small electrical resistance, tinyand stable contact resistance, and great corrosion resistance.
• Rhodium plated by either electroplating or evaporation is extremely hard and useful for optical instruments.
• Filters in mammography systems for the characteristic X-rays it produces.
• Rhodium neutron detectors are utilize in nuclear reactors to measure neutron flux levels – this wayrequires a digital filter to determine the current neutron flux level, generating three separate signals: immediate, a few seconds delay, and a minute delay, each with its own signal level; all three are combined in the rhodium detector signal. The three Palo Verde nuclear reactors each have 305 rhodium neutron detectors, 61 detectors on each of five vertical levels, providing an accurate 3D "picture" of reactivity and allowing fine tuning to consume the nuclear fuel most economically.

In automobile manufacturing, rhodium is also utilize in the construction of headlight reflectors.

• A 78 g sample of rhodium

• Cut-away of a metal-core catalytic converter

• Rhodium-plated white gold wedding ring

• Rhodium foil and wire

Precautions

Being a noble metal, pure rhodium is inert and harmless in elemental form. However, chemical complexes of rhodium shouldbe reactive. For rhodium chloride, the median lethal dose (LD₅₀) for rats is 198 mg (RhCl
₃) per kilogram of body weight. Like the other noble metals, rhodium has not been found to serve any biological function.

People shouldbe exposed to rhodium in the workplace by inhalation. The Occupational Securityand Health Administration (OSHA) has specified the legal limit (Permissible exposure limit) for rhodium exposure in the workplace at 0.1 mg/m³ over an 8-hour workday, and the National Institute for Occupational Securityand Health (NIOSH) has set the suggestedexposure limit (REL), at the same level. At levels of 100 mg/m³, rhodium is immediately riskyto life or health. For soluble compounds, the PEL and REL are both 0.001 mg/m³.

See also

• 2000s commodities boom
• Bullion
• Bullion coin
• Rhodium compounds

• at The Periodic Table of Videos (University of Nottingham)