The atomic number of the chemical element rhodium is 45 and its symbol is the letter Rh. It is a relatively rare transition metal that is hard, silvery white and corrosion resistant. It is a platinum group element and a noble metal. It naturally contains only the 103Rh isotope. Rhodium is a naturally occurring metal and is typically found as a free metal, in alloys with other metals, or very rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the most expensive and rarest precious metals.
Along with other platinum group metals, rhodium is also found in nickel or platinum ores. It was named after the rose color of one of the chlorine compounds and was discovered in one of these ore deposits by William Hyde Wollaston in 1803.
The primary use of the element, which makes up more than 80% of all rhodium produced globally, is as one of the catalysts in three-way catalytic converters used in automobiles. Rhodium is typically alloyed with platinum or palladium and is used in high temperature and corrosion resistant coatings because the metal is inert to corrosion and most aggressive chemicals and is rare. Rhodium plating is often used to improve the appearance of white gold and to prevent corrosion of sterling silver.
A two-part silicone is mixed, one component of which is silicon hydride and the other is vinyl-terminated silicon; one of these liquids contains a rhodium complex. Rhodium is occasionally used to harden silicones.
Rhodium detectors are used to measure the level of neutron radiation in nuclear reactors. Rhodium is also used in the production of acetic acid and in asymmetric hydrogenation techniques used to create medicinal precursors.
History of Rhodium
William Hyde Wollaston discovered rhodium (the Greek word for rhodium is "rose") in 1803, shortly after discovering palladium. He used crude platinum ore, most likely from South America. In his method, the ore was dissolved in aqua regia and neutralized with acid sodium hydroxide (NaOH).
He then added ammonium chloride and precipitated the platinum as ammonium chloroplatinate.
Zinc; It precipitated with most other metals, including copper, lead, palladium, and rhodium. All metals except palladium and rhodium were dissolved with diluted nitric acid. Rhodium, Na3[RhCl6]·nH2Unlike palladium, which is precipitated by the addition of sodium chloride as O, it is insoluble in aqua regia.
The rose-red precipitate was cleaned with ethanol before being treated with zinc, which pushed rhodium out of the ionic combination and released it as a free metal.
For many years this rare element was used only sparingly; For example, thermocouples made of rhodium could measure temperatures up to 1800 °C at the turn of the century. They are very stable in the temperature range of 1300 to 1800 °C.
As an ornamental and corrosion resistant coating, electroplating is the first important application. The three-way catalytic converter was first used by Volvo in 1976, which led to an increase in demand for rhodium. Rhodium was used in the three-way catalytic converter instead of the previously used platinum or palladium to reduce the amount of NOx in the exhaust.
The strong, silvery, long-lasting metal rhodium is highly reflective. Even when heated, rhodium metal typically does not produce an oxide. Rhodium only absorbs oxygen as it melts; When it solidifies, it releases oxygen. Compared to platinum, rhodium has less density and a higher melting point. Most acids do not affect it; but nitric acid makes it completely insoluble, while aqua regia dissolves it only slightly.
Molecular Composition of Rhodium
Rhodium is a member of group 9 of the periodic table, but the electron configuration in its outermost shells deviates from the norm for the group. The nearby elements niobium (41), ruthenium (44), and palladium (46) also exhibit this peculiarity.
Rhodium is typically found in the +3 oxidation state, but oxidation levels 0 to +7 have also been noted.
Rhodium, unlike ruthenium and osmium, does not produce any volatile oxygen compounds. Among the currently known stable oxides Rh2O3, RHO2, RHO2·xH2O, Na2RHO3, Sr3LiRhO6 ve Sr3NaRhO6 .
Almost every potential oxidation state for halogen compounds is well known. Some examples include rhodium (III) chloride, rhodium trifluoride, rhodium pentafluoride, and rhodium hexafluoride. Low oxidation states are stable only when ligands are present.
Chlorotris(triphenylphosphine)rhodium(I), the catalyst used by Wilkinson, is the most widely used rhodium-halogen compound. Alkenes are hydroformylated or hydrogenated using this catalyst.
Isotopes of Rhodium
Rhodium contains only the 103Rh isotope in its natural state. Radioactive elements with the longest half-lives are 3,3Rh, which decays after 101 years, 207Rh, which decays after 102 days, 2,9mRh, which decays after 102 years, and 16,1Rh, which decays after 99 days. Twenty more radioisotopes have been identified, with atomic weights ranging from 92.926 u (93Rh) to 116.925 u (117Rh). With the exception of 100Rh (20,8 hours) and 105Rh (35,36 hours), most have half-lives less than one hour. Rhodium has a number of meta states, the two most stable states being 102mRh (0,141 MeV) and 101mRh (0,157 MeV), both with half-lives of 4,34 days and about 2,9 years, respectively (see isotopes of rhodium).
Ruthenium is the main decay product and electron capture is the main decay method for isotopes less than 103 (stable isotope). Palladium is the main product, and for isotopes greater than 103, beta emission is the main decay mechanism.
Availability of Rhodium
Rhodium, one of the rarest elements in the earth's crust, is thought to be only 0,0002 parts per million (2 1010). Its pricing and commercial applications are affected by its scarcity. Rhodium is usually found in nickel meteorites at a concentration of 1 pb. According to tests, the amount of rhodium in some potatoes is between 0,8 and 30 ppt.
Rhodium is a difficult metal to extract industrially because there are very few rhodium-containing minerals, and ores are often combined with other metals such as palladium, silver, platinum, and gold. When found, platinum is mined from ores as a white inert metal that is difficult to dissolve. Its main sources are South Africa, the Ural Mountains in Russia, and the copper-nickel sulfide mining sector in North America, particularly the Sudbury, Ontario region. Despite Sudbury's very low rhodium richness, the high volume of nickel ore processed makes rhodium recovery economical.
Rhodium is mostly exported by South Africa (almost 2010% in 80), followed by Russia.
Every year, 30 tons are produced worldwide. Rhodium's pricing is incredibly volatile. Rhodium was almost eight times more expensive by weight than gold, 2007 times more expensive than silver, and 450 times more expensive than copper in 27.250. The cost momentarily exceeded $2008 per ounce ($10.000 per kilogram) in 350.000. In the third quarter of 2008, rhodium prices fell dramatically to less than $1.000 per ounce ($35.000 per kilogram). In early 2010, prices rose to $2.750 ($97.000 per kilogram), more than double the price of gold, but dropped below $2013 again by late 1.000.
Most metals suffered price declines as a result of oversupply and extremely low oil prices caused by political and financial problems. In 2014 and 2015, the economies of China, India and other developing countries stagnated. China produced a total of 2014 cars in 23.722.890, excluding motorcycles.[More information needed] As a result, the price of rhodium in late November 2015 was US$31,1 per troy ounce (740,00 grams).
Owners of rhodium, a metal with a highly volatile market price, are at times in a very advantageous position because mining more rhodium-containing ores also requires mining ores containing other more abundant precious metals, primarily platinum and palladium, which is over-priced in the market. It will create supply and lower the price of other metals.
The market is often completely constrained in terms of rhodium supply, which drives up prices. This is because it is not commercially viable to simply extract these other metals to obtain rhodium.
Recovery from this shortage of supply situation can be quite difficult in the future, for many reasons, including manufacturers not knowing how much rhodium (and other precious metals) is actually used in catalytic converters for many years of using emissions cheat software. Rhodium is mostly found in recycled catalytic converters from discarded old vehicles. At the beginning of November 2020, the spot price of rhodium was $14.700 per troy ounce. In Metals Daily, the price of rhodium rose to US$2021 per troy ounce in early March 29.400.
Source: Wikipedia
📩 17/05/2023 20:42