Rhodium is a chemical element with symbols Rh and atomic number 45. It is a rare transition metal, silvery white, hard, corrosion-resistant and chemically inert. It is a precious metal and a platinum group member. It has only one natural isotope, 103 Rh. The naturally occurring rhodium is usually found as a free metal, mixed with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most precious metals.
Rhodium is found in platinum or nickel ore along with other members of platinum group metals. It was discovered in 1803 by William Hyde Wollaston in one ore, and was named for the color of a rose of one of its chlorine compounds, which is produced after reacting with a strong aqua regia acid mixture.
The main use of the element (about 80% of world rhodium production) is as one of the catalysts in the three-way catalytic converter in the car. Because rhodium metal is inert against corrosion and the most aggressive chemicals, and because of its rarity, rhodium is usually mixed with platinum or palladium and is applied in high temperatures and corrosion resistant layers. White gold is often coated with a thin rhodium layer to enhance its appearance while sterling silver is often coated rhodium to stain the resistance.
Rhodium detector is used in nuclear reactors to measure the level of neutron flux.
Video Rhodium
Histori
Rhodium (Greek rhodon meaning "rose") was discovered in 1803 by William Hyde Wollaston, soon after the discovery of palladium. He used the raw platinum ore that he allegedly obtained from South America. The procedure involves dissolving the ore in aqua regia and neutralizing the acid with sodium hydroxide (NaOH). He then deposited platinum as ammonium chloroplatinate by adding ammonium chloride ( NH
4 Cl ). Most other metals such as copper, lead, palladium and rhodium are deposited with zinc. The dilute nitric acid dissolves all except palladium and rhodium. Of this amount, palladium is dissolved in aqua regia but rhodium is not, and rhodium is precipitated by the addition of sodium chloride as Na
3 [RhCl
6 ] Ã, Â · n H
2 O . After washing with ethanol, the red rose deposit is reacted with zinc, which replaces rhodium in ionic compounds and thereby releases rhodium as the free metal.
Upon discovery, rare elements have only small applications; for example, at the turn of the century, rhodium-containing thermocouples are used to measure temperatures up to 1800 ° C. The first major application is electroplating for decorative use and as a corrosion resistant coating. The introduction of a three-way catalytic converter by Volvo in 1976 increased the demand for rhodium. Previous catalytic converters use platinum or palladium, while three-way catalytic converters use rhodium to reduce the amount of NO x in the exhaust.
Maps Rhodium
Characteristics
Rhodium is a hard, silver, and durable metal that has high reflectivity. Rhodium metal usually does not form oxides, even when heated. Oxygen is absorbed from the atmosphere only at the melting point of rhodium, but is released in freezing. Rhodium has a higher melting point and lower density of 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 the group of 9 from the periodic table, but the configuration of the electrons in the outer shell is not typical for the group. This anomaly is also observed in neighboring elements, niobium (41), ruthenium (44), and palladium (46).
The general state of oxidation of rhodium is 3, but oxidation states from 0 to 6 are also observed.
Tidak seperti ruthenium dan osmium, rhodium tidak membentuk senyawa oksigen volatil. Oksida stabil yang dikenal termasuk Rh
2 O < span>
3 , RhO
2 , RhO
2 Â · x H
2 O , Na
2 RhO
3 , Sr
3 LiRhO
6 dan Sr
3 NaRhO
6 . Senyawa-senyawa halogen dikenal hampir dalam berbagai keadaan oksidasi yang mungkin. Rhodium (III) klorida, rodium (IV) fluorida, rodium (V) fluorida dan rodium (VI) fluorida adalah contoh. Keadaan oksidasi yang lebih rendah stabil hanya di hadapan ligan.
The best known rhodium-halogen compound is the Wilkinson chlorotris (triphenylphosphine) rhodium (I) catalyst. This catalyst is used in hydroformylation or alkene hydrogenation.
Isotope
The natural rodium consists only of one isotope, 103 Rh. The most stable radioisotope is 101 Rh with a half-life of 3.3 years, 102 Rh with a half-life of 207 days, 102 m Rh with half-life 2 , 9 years, and 99 Rh with a half-life of 16.1 days. Twenty other radioisotopes have been characterized by atomic weights ranging from 92,926 u ( 93 Rh) to 116,925 u ( 117 Rh). Most have half-life shorter than one hour, except 100 Rh (20.8 hours) and 105 Rh (35.36 hours). It has many meta states, the most stable is 102m Rh (0.141Ã, MeV) with a half-life of about 2.9 years and 101m Rh (0.157Ã, MeV) with part-time 4.34 days (see rhodium isotope).
In isotopes weighing less than 103 (stable isotope), the main mode of decay is electron capture and the major decay product is ruthenium. In isotopes greater than 103, the main mode of decay is the emission of beta and the primary product is palladium.
Genesis
Rhodium is one of the rarest elements in the Earth's crust, which consists of about 0.0002 parts per million (2 ÃÆ'â € "10 -10 ). Its scarcity affects the price and its use in commercial applications.
Mining and price
Rhodium industrial extraction is complex because the ore is mixed with other metals such as palladium, silver, platinum, and gold and there are very few rhodium-bearing minerals. It is found in platinum ore and extracted as an inert metal that is difficult to converge. The main source is located in South Africa; in the river sands of the Ural Mountains; and in North America, including a copper-nickel sulphide mining area in the Sudbury, Ontario region. Although the quantity at Sudbury is very small, large quantities of processed nickel ore make cost-effective recovery rhodium.
The main exporter of rhodium is South Africa (about 80% in 2010) followed by Russia. The annual production of the world is 30 tons. The price of rhodium varies greatly. In 2007, rhodium cost about eight times more than gold, 450 times more than silver, and 27,250 times more than copper by weight. In 2008, prices briefly rose above $ 10,000 an ounce ($ 350,000 per kilogram). The 3rd quarter economic slowdown of 2008 pushed the rhodium prices back sharply below $ 1,000 an ounce ($ 35,000 per kilogram); the price rebounded to $ 2,750 in early 2010 ($ 97,000 per kilogram) (more than twice the price of gold), but by the end of 2013, the price is less than $ 1000.
Political and financial problems caused the oil price to be very low and oversupply, causing most of the metal to fall in price. The economies of China, India and other developing countries are slowing down in 2014 and 2015. By 2014 alone, 23,722,890 vehicles are manufactured in China, excluding motorcycles. This produces a rhodium price of 740.00 US $ per troy ounce (31.1 grams) at the end of November 2015.
Used nuclear fuel
Rhodium is a fission product of uranium-235: every kilogram of fission products contains a large number of lighter platinum group metals. Therefore, the nuclear fuel used is a potential source of rhodium, but the extraction is complicated and expensive, and the presence of rhodium radioisotopes requires a cooling storage period for some of the longest life isotopes of life (about 10 years). These factors make the source unattractive and no large-scale extraction has been attempted.
Apps
The main use of this element is in the car as a catalytic converter, transforming unburned hazardous hydrocarbons, carbon monoxide, and nitrogen oxide emissions into less harmful gases. Of the 30,000 kg of rhodium consumed worldwide in 2012, 81% (24,300 kg) goes into this application, and 8060 kg is obtained from the old converter. Approximately 964 kg of rhodium is used in the glass industry, mostly for fiberglass production and flat panel glass, and 2,520 kg used in the chemical industry.
Catalyst
Rhodium is preferred over other platinum metals in the reduction of nitrogen oxides to nitrogen and oxygen:
- 2 NO
x -> x O
2 N
2
Rhodium catalysts are used in a number of industrial processes, particularly in the catalytic catalytic methanol to produce acetic acid by the Monsanto process. It is also used to catalyze the addition of hydrosilan to molecular double bonds, an important process in the manufacture of certain silicone rubbers. Rhodium catalysts are also used to reduce benzene to cyclohexane.
The ionic complex with BINAP is a chiral catalyst which is widely used for synthesis of chiral, as in the synthesis of bulbs.
Decorate using
Rhodium finds are used in jewelry and for decoration. It is coated in white and platinum gold to give it a reflective white surface at the time of sale, after which a thin layer is used up. This is known as rhodium flashing in the jewelry business. It can also be used in sterling silver coating to protect against stains (silver sulphide, Ag 2 S, produced from atmospheric hydrogen sulfide, H 2 S). Solid (solid) rhodium jewelry is very rare, more due to the difficulty of fabrication (high melting point and poor flexibility) than for high prices. The high cost ensures that rhodium is only used as an electroplating.
Rhodium has also been used for honor or to indicate elite status, when more commonly used metals such as silver, gold or platinum are considered insufficient. In 1979, the Guinness Book of World Records gave Paul McCartney a rhodium-plated disc to become the best-selling songwriter and recording artist in history.
Other uses
Rhodium is used as an alloying agent for hardening and increases the corrosion resistance of platinum and palladium. These alloys are used in rolls of bolsters, bushes for the production of glass fibers, thermocouple elements, electrodes for sparkplugs, and laboratory crucibles. Other uses include:
- Electrical contact, where it is valued for small electrical resistance, small and stable contact resistance, and great corrosion resistance.
- Rhodium plated by electroplating or evaporation is very hard and useful for optical instruments.
- Filters in the mammography system for the X-ray characteristics it produces.
- Rhodium neutron detector is used in a fired nuclear reactor reactor to measure the level of neutron flux - this method requires a digital filter to determine the current neutron flux rate, yielding three separate signals: immediate, a few seconds delay, and a one-minute delay, respectively with its own signal level; the 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, delivering accurate 3D "images" of reactivity and allowing fine tuning to consume the most economical nuclear fuel.
Precautions
Being a precious metal, pure rhodium is inert. However, the rhodium chemical complex can be reactive. Median lethal dose (LD 50 ) for mice is 198 mg rodium chloride ( RhCl
3 ) per kilogram of body weight. Like other precious metals, all of which are too inert to occur as chemical compounds in nature, rhodium has not yet been found to serve any biological function. In elemental form, the metal is harmless.
People may be exposed to rhodium at work if inhaled. Occupational Safety and Health Administration (OSHA) has set legal limits (Exposure limits are allowed) for rhodium exposure at workplace 0.1 m/m 3 for 8 hours of work, and the National Institute for Occupational Safety and Health Work (NIOSH) has set a recommended exposure limit (REL), at the same level. At a level of 100 mg/m 3 , rhodium is immediately harmful to life or health. For dissolved compounds, PEL and REL are both 0.001, mg/m 3 .
See also
- The rhodium compound
- commodity boom of the 2000s
References
External links
- Rhodium in Periodic Video Table (University of Nottingham)
- Rhodium Technical and Security Data
- CDC - NIOSH A Pocket Guide for Chemical Hazards
Source of the article : Wikipedia
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