Platinum

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Platinum, 78Pt
Platinum crystals.jpg
Platinum
Pronunciation /ˈplætənəm/ ​(PLAT-ən-əm)
Appearancesilvery white
Standard atomic weight Ar°(Pt)
Platinum in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Pd
↑
Pt
↓
Ds
iridium ← platinum → gold
Atomic number (Z)78
Group group 10
Period period 6
Block   d-block
Electron configuration [ Xe ] 4f14 5d9 6s1
Electrons per shell2, 8, 18, 32, 17, 1
Physical properties
Phase at  STP solid
Melting point 2041.4  K ​(1768.3 °C,​3214.9 °F)
Boiling point 4098 K​(3825 °C,​6917 °F)
Density (at 20° C)21.452 g/cm3  [3]
when liquid (at  m.p.)19.77 g/cm3
Heat of fusion 22.17  kJ/mol
Heat of vaporization 510 kJ/mol
Molar heat capacity 25.86 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)2330(2550)2815314335564094
Atomic properties
Oxidation states −3, −2, −1, 0, +1, +2, +3, +4, +5, +6 (a mildly basic oxide)
Electronegativity Pauling scale: 2.28
Ionization energies
  • 1st: 870 kJ/mol
  • 2nd: 1791 kJ/mol
Atomic radius empirical:139  pm
Covalent radius 136±5 pm
Van der Waals radius 175 pm
Platinum spectrum visible.png
Spectral lines of platinum
Other properties
Natural occurrence primordial
Crystal structure ​ face-centered cubic (fcc)(cF4)
Lattice constant
Cubic-face-centered.svg
a = 392.36 pm (at 20 °C) [3]
Thermal expansion 8.93×10−6/K (at 20 °C) [3]
Thermal conductivity 71.6 W/(m⋅K)
Electrical resistivity 105 nΩ⋅m(at 20 °C)
Magnetic ordering paramagnetic
Molar magnetic susceptibility +201.9 × 10−6 cm3/mol(290 K) [4]
Tensile strength 125–240 MPa
Young's modulus 168 GPa
Shear modulus 61 GPa
Bulk modulus 230 GPa
Speed of sound thin rod2800 m/s(at  r.t.)
Poisson ratio 0.38
Mohs hardness 3.5
Vickers hardness 400–550 MPa
Brinell hardness 300–500 MPa
CAS Number 7440-06-4
History
Discovery Antonio de Ulloa (1735)
Isotopes of platinum
Main isotopes [5] Decay
abun­dance half-life (t1/2) mode pro­duct
190Pt0.0120%4.83×1011 y α 186Os
192Pt0.782% stable
193Pt synth 50 y ε 193Ir
194Pt32.9%stable
195Pt33.8%stable
196Pt25.2%stable
198Pt7.36%stable
Symbol category class.svg  Category: Platinum
| references

Platinum is a chemical element; it has symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish platina, a diminutive of plata "silver". [6] [7]

Contents

Platinum is a member of the platinum group of elements and group 10 of the periodic table of elements. It has six naturally occurring isotopes. It is one of the rarer elements in Earth's crust, with an average abundance of approximately 5  μg/kg. It occurs in some nickel and copper ores along with some native deposits, mostly in South Africa, which accounts for ~80% of the world production. Because of its scarcity in Earth's crust, only a few hundred tonnes are produced annually, and given its important uses, it is highly valuable and is a major precious metal commodity. [8]

Platinum is one of the least reactive metals. It has remarkable resistance to corrosion, even at high temperatures, and is therefore considered a noble metal. Consequently, platinum is often found chemically uncombined as native platinum. Because it occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artifacts. It was referenced in European writings as early as the 16th century, but it was not until Antonio de Ulloa published a report on a new metal of Colombian origin in 1748 that it began to be investigated by scientists.

Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Platinum is used in the glass industry [9] to manipulate molten glass, which does not "wet" platinum. As a heavy metal, it leads to health problems upon exposure to its salts; but due to its corrosion resistance, metallic platinum has not been linked to adverse health effects. [10] Compounds containing platinum, such as cisplatin, oxaliplatin and carboplatin, are applied in chemotherapy against certain types of cancer. [11]

Pure platinum is currently less expensive than pure gold, having been so continuously since 2015, but has been twice as expensive or more, mostly prior to 2008. [12] In early 2021, the value of platinum ranged from US$1,055 to US$1,320 per troy ounce. [13]

Characteristics

Physical

Pure platinum is a lustrous, ductile, and malleable, silver-white metal. [14] Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals, but it is less malleable than gold. [15] [16]

Its physical characteristics and chemical stability make it useful for industrial applications. [17] Its resistance to wear and tarnish is well suited to use in fine jewellery.

Chemical

Platinum being dissolved in hot aqua regia Platin lost sich in heissem Konigswasser.jpg
Platinum being dissolved in hot aqua regia

Platinum has excellent resistance to corrosion. Bulk platinum does not oxidize in air at any temperature, but it forms a thin surface film of PtO2 that can be easily removed by heating to about 400 °C. [18] [19]

The most common oxidation states of platinum are +2 and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species. Tetracoordinate platinum(II) compounds tend to adopt 16-electron square planar geometries. Although elemental platinum is generally unreactive, it is attacked by chlorine, bromine, iodine, and sulfur. It reacts vigorously with fluorine at 500 °C (932 °F) to form platinum tetrafluoride. [20] Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia (a mixture of nitric and hydrochloric acids), to form aqueous chloroplatinic acid, H2PtCl6: [21] [22]

Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O

As a soft acid, the Pt2+ ion has a great affinity for sulfide and sulfur ligands. Numerous DMSO complexes have been reported and care is taken in the choosing of reaction solvents. [23]

In 2007, the German scientist Gerhard Ertl won the Nobel Prize in Chemistry for determining the detailed molecular mechanisms of the catalytic oxidation of carbon monoxide over platinum (catalytic converter). [24]

Isotopes

Platinum has six naturally occurring isotopes: 190
Pt, 192
Pt, 194
Pt, 195
Pt, 196
Pt, and 198
Pt. The most abundant of these is 195
Pt, comprising 33.83% of all platinum. It is the only stable isotope with a non-zero spin. The spin of 1/2 and other favourable magnetic properties of the nucleus are utilised in 195
Pt NMR. Due to its spin and large abundance, 195
Pt satellite peaks are also often observed in 1
H and 31
P NMR spectroscopy (e.g., for Pt-phosphine and Pt-alkyl complexes). 190
Pt is the least abundant at only 0.01%. Of the naturally occurring isotopes, only 190
Pt is unstable, though it decays with a half-life of 6.5×1011 years, causing an activity of 15 Bq/kg of natural platinum. Other isotopes can undergo alpha decay, but their decay has never been observed, therefore they are considered stable. [25] Platinum also has 38 synthetic isotopes ranging in atomic mass from 165 to 208, making the total number of known isotopes 44. The least stable of these are 165
Pt and 166
Pt, with half-lives of 260 µs, whereas the most stable is 193
Pt with a half-life of 50 years. Most platinum isotopes decay by some combination of beta decay and alpha decay. 188
Pt, 191
Pt, and 193
Pt decay primarily by electron capture. 190
Pt and 198
Pt are predicted to have energetically favorable double beta decay paths. [26]

Occurrence

A native platinum nugget, Kondyor mine, Khabarovsk Krai Platinum-nugget.jpg
A native platinum nugget, Kondyor mine, Khabarovsk Krai
Platinum-palladium ore, Stillwater mine, Beartooth Mountains, Montana, US Platinum-palladium ore, Stillwater mine MT.JPG
Platinum-palladium ore, Stillwater mine, Beartooth Mountains, Montana, US
Sulfidic serpentintite (platinum-palladium ore) from the same mine as above Sulfidic serpentintite (platinum-palladium ore) Johns-Manville Reef, Stillwater Complex.jpg
Sulfidic serpentintite (platinum-palladium ore) from the same mine as above

Platinum is an extremely rare metal, [27] occurring at a concentration of only 0.005 ppm in Earth's crust. [28] [29] Sometimes mistaken for silver, platinum is often found chemically uncombined as native platinum and as alloy with the other platinum-group metals and iron mostly. Most often the native platinum is found in secondary deposits in alluvial deposits. The alluvial deposits used by pre-Columbian people in the Chocó Department, Colombia are still a source for platinum-group metals. Another large alluvial deposit is in the Ural Mountains, Russia, and it is still mined. [22]

In nickel and copper deposits, platinum-group metals occur as sulfides (e.g., (Pt,Pd)S), tellurides (e.g., PtBiTe), antimonides (PdSb), and arsenides (e.g. PtAs2), and as end alloys with nickel or copper. Platinum arsenide, sperrylite (PtAs2), is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. At Platinum, Alaska, about 17,000 kg (550,000 ozt) was mined between 1927 and 1975. The mine ceased operations in 1990. [30] The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Gauteng, South Africa. [31]

In 1865, chromites were identified in the Bushveld region of South Africa, followed by the discovery of platinum in 1906. [32] In 1924, the geologist Hans Merensky discovered a large supply of platinum in the Bushveld Igneous Complex in South Africa. The specific layer he found, named the Merensky Reef, contains around 75% of the world's known platinum. [33] [34] The large copper–nickel deposits near Norilsk in Russia, and the Sudbury Basin, Canada, are the two other large deposits. In the Sudbury Basin, the huge quantities of nickel ore processed make up for the fact platinum is present as only 0.5 ppm in the ore. Smaller reserves can be found in the United States, [34] for example in the Absaroka Range in Montana. [35] In 2010, South Africa was the top producer of platinum, with an almost 77% share, followed by Russia at 13%; world production in 2010 was 192,000 kg (423,000 lb). [36]

Large platinum deposits are present in the state of Tamil Nadu, India. [37]

Platinum exists in higher abundances on the Moon and in meteorites. Correspondingly, platinum is found in slightly higher abundances at sites of bolide impact on Earth that are associated with resulting post-impact volcanism, and can be mined economically; the Sudbury Basin is one such example. [38]

Compounds

Halides

Hexachloroplatinic acid mentioned above is probably the most important platinum compound, as it serves as the precursor for many other platinum compounds. By itself, it has various applications in photography, zinc etchings, indelible ink, plating, mirrors, porcelain coloring, and as a catalyst. [39]

Treatment of hexachloroplatinic acid with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate, [21] which is relatively insoluble in ammonium solutions. Heating this ammonium salt in the presence of hydrogen reduces it to elemental platinum.Potassium hexachloroplatinate is similarly insoluble, and hexachloroplatinic acid has been used in the determination of potassium ions by gravimetry. [40]

When hexachloroplatinic acid is heated, it decomposes through platinum(IV) chloride and platinum(II) chloride to elemental platinum, although the reactions do not occur stepwise: [41]

(H3O)2PtCl6·nH2O ⇌ PtCl4 + 2 HCl + (n + 2) H2O
PtCl4 ⇌ PtCl2 + Cl2
PtCl2 ⇌ Pt + Cl2

All three reactions are reversible. Platinum(II) and platinum(IV) bromides are known as well. Platinum hexafluoride is a strong oxidizer capable of oxidizing oxygen.

Oxides

Platinum(IV) oxide, PtO2, also known as "Adams' catalyst", is a black powder that is soluble in potassium hydroxide (KOH) solutions and concentrated acids. [42] PtO2 and the less common PtO both decompose upon heating. [14] Platinum(II,IV) oxide, Pt3O4, is formed in the following reaction:

2 Pt2+ + Pt4+ + 4 O2− → Pt3O4

Other compounds

Unlike palladium acetate, platinum(II) acetate is not commercially available. Where a base is desired, the halides have been used in conjunction with sodium acetate. [23] The use of platinum(II) acetylacetonate has also been reported. [43]

Several barium platinides have been synthesized in which platinum exhibits negative oxidation states ranging from −1 to −2. These include BaPt, Ba
3Pt
2, and Ba
2Pt. [44] Caesium platinide, Cs
2Pt, a dark-red transparent crystalline compound [45] has been shown to contain Pt2−
 anions. [46] Platinum also exhibits negative oxidation states at surfaces reduced electrochemically. [47] The negative oxidation states exhibited by platinum are unusual for metallic elements, and they are attributed to the relativistic stabilization of the 6s orbitals. [46]

It is predicted that even the cation PtO2+
4 in which platinum exists in the +10 oxidation state may be achievable. [48]

Zeise's salt, containing an ethylene ligand, was one of the first organometallic compounds discovered. Dichloro(cycloocta-1,5-diene)platinum(II) is a commercially available olefin complex, which contains easily displaceable cod ligands ("cod" being an abbreviation of 1,5-cyclooctadiene). The cod complex and the halides are convenient starting points to platinum chemistry. [23]

Cisplatin, or cis-diamminedichloroplatinum(II) is the first of a series of square planar platinum(II)-containing chemotherapy drugs. [49] Others include carboplatin and oxaliplatin. These compounds are capable of crosslinking DNA, and kill cells by similar pathways to alkylating chemotherapeutic agents. [50] (Side effects of cisplatin include nausea and vomiting, hair loss, tinnitus, hearing loss, and nephrotoxicity.) [51] [52]

Organoplatinum compounds such as the above antitumour agents, as well as soluble inorganic platinum complexes, are routinely characterised using 195
Pt nuclear magnetic resonance spectroscopy.

History

Early uses

Archaeologists have discovered traces of platinum in the gold used in ancient Egyptian burials as early as 1200 BCE. For example, a small box from burial of Shepenupet II was found to be decorated with gold-platinum hieroglyphics. [53] However, the extent of early Egyptians' knowledge of the metal is unclear. It is quite possible they did not recognize there was platinum in their gold. [54] [55]

The metal was used by Native Americans near modern-day Esmeraldas, Ecuador to produce artifacts of a white gold-platinum alloy. Archeologists usually associate the tradition of platinum-working in South America with the La Tolita Culture (c. 600 BCE – 200 CE), but precise dates and location are difficult, as most platinum artifacts from the area were bought secondhand through the antiquities trade rather than obtained by direct archeological excavation. [56] To work the metal, they would combine gold and platinum powders by sintering. The resulting gold–platinum alloy would then be soft enough to shape with tools. [57] [58] The platinum used in such objects was not the pure element, but rather a naturally occurring mixture of the platinum group metals, with small amounts of palladium, rhodium, and iridium. [59]

European discovery

The first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger as a description of an unknown noble metal found between Darién and Mexico, "which no fire nor any Spanish artifice has yet been able to liquefy". [60] From their first encounters with platinum, the Spanish generally saw the metal as a kind of impurity in gold, and it was treated as such. It was often simply thrown away, and there was an official decree forbidding the adulteration of gold with platinum impurities. [59]

This alchemical symbol for platinum was made by joining the symbols of silver (moon) and gold (sun). Platinum symbol.svg
This alchemical symbol for platinum was made by joining the symbols of silver (moon) and gold (sun).
Antonio de Ulloa is credited in European history with the discovery of platinum. Almirante Antonio de Ulloa.jpg
Antonio de Ulloa is credited in European history with the discovery of platinum.

In 1735, Antonio de Ulloa and Jorge Juan y Santacilia saw Native Americans mining platinum while the Spaniards were travelling through Colombia and Peru for eight years. Ulloa and Juan found mines with the whitish metal nuggets and took them home to Spain. Antonio de Ulloa returned to Spain and established the first mineralogy lab in Spain and was the first to systematically study platinum, which was in 1748. His historical account of the expedition included a description of platinum as being neither separable nor calcinable. Ulloa also anticipated the discovery of platinum mines. After publishing the report in 1748, Ulloa did not continue to investigate the new metal. In 1758, he was sent to superintend mercury mining operations in Huancavelica. [60]

In 1741, Charles Wood, [61] a British metallurgist, found various samples of Colombian platinum in Jamaica, which he sent to William Brownrigg for further investigation.

In 1750, after studying the platinum sent to him by Wood, Brownrigg presented a detailed account of the metal to the Royal Society, stating that he had seen no mention of it in any previous accounts of known minerals. [62] Brownrigg also made note of platinum's extremely high melting point and refractoriness toward borax.[ clarification needed ] Other chemists across Europe soon began studying platinum, including Andreas Sigismund Marggraf, [63] Torbern Bergman, Jöns Jakob Berzelius,William Lewis, and Pierre Macquer. In 1752, Henrik Scheffer published a detailed scientific description of the metal, which he referred to as "white gold", including an account of how he succeeded in fusing platinum ore with the aid of arsenic. Scheffer described platinum as being less pliable than gold, but with similar resistance to corrosion. [60]

Means of malleability

Karl von Sickingen researched platinum extensively in 1772. He succeeded in making malleable platinum by alloying it with gold, dissolving the alloy in hot aqua regia , precipitating the platinum with ammonium chloride, igniting the ammonium chloroplatinate, and hammering the resulting finely divided platinum to make it cohere. Franz Karl Achard made the first platinum crucible in 1784. He worked with the platinum by fusing it with arsenic, then later volatilizing the arsenic. [60]

Because the other platinum-family members were not discovered yet (platinum was the first in the list), Scheffer and Sickingen made the false assumption that due to its hardness—which is slightly more than for pure iron—platinum would be a relatively non-pliable material, even brittle at times, when in fact its ductility and malleability are close to that of gold. Their assumptions could not be avoided because the platinum they experimented with was highly contaminated with minute amounts of platinum-family elements such as osmium and iridium, amongst others, which embrittled the platinum alloy. Alloying this impure platinum residue called "plyoxen"[ citation needed ] with gold was the only solution at the time to obtain a pliable compound, but nowadays, very pure platinum is available and extremely long wires can be drawn from pure platinum, very easily, due to its crystalline structure, which is similar to that of many soft metals. [64]

In 1786, Charles III of Spain provided a library and laboratory to Pierre-François Chabaneau to aid in his research of platinum. Chabaneau succeeded in removing various impurities from the ore, including gold, mercury, lead, copper, and iron. This led him to believe he was working with a single metal, but in truth the ore still contained the yet-undiscovered platinum-group metals. This led to inconsistent results in his experiments. At times, the platinum seemed malleable, but when it was alloyed with iridium, it would be much more brittle. Sometimes the metal was entirely incombustible, but when alloyed with osmium, it would volatilize. After several months, Chabaneau succeeded in producing 23 kilograms of pure, malleable platinum by hammering and compressing the sponge form while white-hot. Chabeneau realized the infusibility of platinum would lend value to objects made of it, and so started a business with Joaquín Cabezas producing platinum ingots and utensils. This started what is known as the "platinum age" in Spain. [60]

Production

An aerial photograph of a platinum mine in South Africa. South Africa accounts for ~80% of global platinum production and a majority of the world's known platinum deposits. Platinum Mining.jpg
An aerial photograph of a platinum mine in South Africa. South Africa accounts for ~80% of global platinum production and a majority of the world's known platinum deposits.
Time trend of platinum production Platinum world production.svg
Time trend of platinum production

Platinum, along with the rest of the platinum-group metals, is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copper, noble metals such as silver, gold and the platinum-group metals as well as selenium and tellurium settle to the bottom of the cell as "anode mud", which forms the starting point for the extraction of the platinum-group metals. [66]

If pure platinum is found in placer deposits or other ores, it is isolated from them by various methods of subtracting impurities. Because platinum is significantly denser than many of its impurities, the lighter impurities can be removed by simply floating them away in a liquid. Platinum is paramagnetic, whereas nickel and iron are both ferromagnetic. These two impurities are thus removed by running an electromagnet over the mixture. Because platinum has a higher melting point than most other substances, many impurities can be burned or melted away without melting the platinum. Finally, platinum is resistant to hydrochloric and sulfuric acids, whereas other substances are readily attacked by them. Metal impurities can be removed by stirring the mixture in either of the two acids and recovering the remaining platinum. [67]

One suitable method for purification for the raw platinum, which contains platinum, gold, and the other platinum-group metals, is to process it with aqua regia, in which palladium, gold and platinum are dissolved, whereas osmium, iridium, ruthenium and rhodium stay unreacted. The gold is precipitated by the addition of iron(II) chloride and after filtering off the gold, the platinum is precipitated as ammonium chloroplatinate by the addition of ammonium chloride. Ammonium chloroplatinate can be converted to platinum by heating. [68] Unprecipitated hexachloroplatinate(IV) may be reduced with elemental zinc, and a similar method is suitable for small scale recovery of platinum from laboratory residues. [69] Mining and refining platinum has environmental impacts. [70]

Applications

Cutaway view of a metal-core catalytic converter Aufgeschnittener Metall Katalysator fur ein Auto.jpg
Cutaway view of a metal-core catalytic converter

Of the 218 tonnes of platinum sold in 2014, 98 tonnes were used for vehicle emissions control devices (45%), 74.7 tonnes for jewelry (34%), 20.0 tonnes for chemical production and petroleum refining (9.2%), and 5.85 tonnes for electrical applications such as hard disk drives (2.7%). The remaining 28.9 tonnes went to various other minor applications, such as medicine and biomedicine, glassmaking equipment, investment, electrodes, anticancer drugs, oxygen sensors, spark plugs and turbine engines. [71]

Catalyst

The most common use of platinum is as a catalyst in chemical reactions, often as platinum black. It has been employed as a catalyst since the early 19th century, when platinum powder was used to catalyze the ignition of hydrogen. Its most important application is in automobiles as a catalytic converter, which allows the complete combustion of low concentrations of unburned hydrocarbons from the exhaust into carbon dioxide and water vapor. Platinum is also used in the petroleum industry as a catalyst in a number of separate processes, but especially in catalytic reforming of straight-run naphthas into higher-octane gasoline that becomes rich in aromatic compounds. PtO2, also known as Adams' catalyst, is used as a hydrogenation catalyst, specifically for vegetable oils. [39] Platinum also strongly catalyzes the decomposition of hydrogen peroxide into water and oxygen [72] and it is used in fuel cells [73] as a catalyst for the reduction of oxygen. [74]

Green energy transition

As a fuel cell catalyst, platinum enables hydrogen and oxygen reactions to take place at an optimum rate. It is used in platinum-based proton exchange memebrane (PEM) technologies required in green hydrogen production as well as fuel cell electric vehicle adoption (FCEV). [75] [76]

Standard

Prototype International Meter bar made by Johnson Matthey Platinum-Iridium meter bar.jpg
Prototype International Meter bar made by Johnson Matthey

From 1889 to 1960, the meter was defined as the length of a platinum-iridium (90:10) alloy bar, known as the international prototype meter. The previous bar was made of platinum in 1799. Until May 2019, the kilogram was defined as the mass of the international prototype of the kilogram, a cylinder of the same platinum-iridium alloy made in 1879. [77]

The Standard Platinum Resistance Thermometer (SPRT) is one of the four types of thermometers used to define the International Temperature Scale of 1990 (ITS-90), the international calibration standard for temperature measurements. The resistance wire in the thermometer is made of pure platinum (NIST manufactured the wires from platinum bar stock with a chemical purity of 99.999% by weight). [78] [79] In addition to laboratory uses, Platinum Resistance Thermometry (PRT) also has many industrial applications, industrial standards include ASTM E1137 and IEC 60751.

The standard hydrogen electrode also uses a platinized platinum electrode due to its corrosion resistance, and other attributes. [80]

As an investment

Platinum is a precious metal commodity; its bullion has the ISO currency code of XPT. Coins, bars, and ingots are traded or collected. Platinum finds use in jewellery, usually as a 90–95% alloy, due to its inertness. It is used for this purpose for its prestige and inherent bullion value. Jewellery trade publications advise jewellers to present minute surface scratches (which they term patina) as a desirable feature in an attempt to enhance value of platinum products. [81] [82]

In watchmaking, Vacheron Constantin, Patek Philippe, Rolex, Breitling, and other companies use platinum for producing their limited edition watch series. Watchmakers appreciate the unique properties of platinum, as it neither tarnishes nor wears out (the latter quality relative to gold). [83]

During periods of sustained economic stability and growth, the price of platinum tends to be as much as twice the price of gold, whereas during periods of economic uncertainty, [84] the price of platinum tends to decrease due to reduced industrial demand, falling below the price of gold. Gold prices are more stable in slow economic times, as gold is considered a safe haven. [85] Although gold is also used in industrial applications, especially in electronics due to its use as a conductor, its demand is not so driven by industrial uses. [86] In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king. [87]

Other uses

In the laboratory, platinum wire is used for electrodes; platinum pans and supports are used in thermogravimetric analysis because of the stringent requirements of chemical inertness upon heating to high temperatures (~1000 °C). Platinum is used as an alloying agent for various metal products, including fine wires, noncorrosive laboratory containers, medical instruments, dental prostheses, electrical contacts, and thermocouples. Platinum-cobalt, an alloy of roughly three parts platinum and one part cobalt, is used to make relatively strong permanent magnets. [39] Platinum-based anodes are used in ships, pipelines, and steel piers. [22] Platinum drugs are used to treat a wide variety of cancers, including testicular and ovarian carcinomas, melanoma, small-cell and non-small-cell lung cancer, myelomas and lymphomas. [89]

Symbol of prestige in marketing

Platinum's rarity as a metal has caused advertisers to associate it with exclusivity and wealth. "Platinum" debit and credit cards have greater privileges than "gold" cards. [90] "Platinum awards" are the second highest possible, ranking above "gold", "silver" and "bronze", but below diamond. For example, in the United States, a musical album that has sold more than 1 million copies will be credited as "platinum", whereas an album that has sold more than 10 million copies will be certified as "diamond". [91] Some products, such as blenders and vehicles, with a silvery-white color are identified as "platinum". Platinum is considered a precious metal, although its use is not as common as the use of gold or silver. The frame of the Crown of Queen Elizabeth The Queen Mother, manufactured for her coronation as Consort of King George VI, is made of platinum. It was the first British crown to be made of this particular metal. [92]

Health problems

According to the Centers for Disease Control and Prevention, short-term exposure to platinum salts may cause irritation of the eyes, nose, and throat, and long-term exposure may cause both respiratory and skin allergies. The current OSHA standard is 2 micrograms per cubic meter of air averaged over an 8-hour work shift. [93] The National Institute for Occupational Safety and Health has set a recommended exposure limit (REL) for platinum as 1 mg/m3 over an 8-hour workday. [94]

As platinum is a catalyst in the manufacture of the silicone rubber and gel components of several types of medical implants (breast implants, joint replacement prosthetics, artificial lumbar discs, vascular access ports, etc.), the possibility that platinum could enter the body and cause adverse effects has merited study. The Food and Drug Administration and other institutions have reviewed the issue and found no evidence to suggest toxicity in vivo. [95] [96] Chemically unbounded platinum has been identified by the FDA as a "fake cancer 'cure'". [97] The misunderstanding is created by healthcare workers who are using inappropriately the name of the metal as a slang term for platinum-based chemotherapy medications like cisplatin.[ citation needed ] They are platinum compounds, not the metal itself.

See also

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Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.

<span class="mw-page-title-main">Iridium</span> Chemical element, symbol Ir and atomic number 77

Iridium is a chemical element; it has symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal with a density of 22.56 g/cm3 (0.815 lb/cu in) as defined by experimental X-ray crystallography. 191Ir and 193Ir are the only two naturally occurring isotopes of iridium, as well as the only stable isotopes; the latter is the more abundant. It is one of the most corrosion-resistant metals, even at temperatures as high as 2,000 °C (3,630 °F).

<span class="mw-page-title-main">Molybdenum</span> Chemical element, symbol Mo and atomic number 42

Molybdenum is a chemical element; it has symbol Mo and atomic number 42. The name derived from Ancient Greek Μόλυβδος molybdos, meaning lead, since its ores were confused with lead ores. Molybdenum minerals have been known throughout history, but the element was discovered in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.

<span class="mw-page-title-main">Osmium</span> Chemical element, symbol Os and atomic number 76

Osmium is a chemical element; it has symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element. When experimentally measured using X-ray crystallography, it has a density of 22.59 g/cm3. Manufacturers use its alloys with platinum, iridium, and other platinum-group metals to make fountain pen nib tipping, electrical contacts, and in other applications that require extreme durability and hardness.

<span class="mw-page-title-main">Palladium</span> Chemical element, symbol Pd and atomic number 46

Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the platinum group metals (PGMs). They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.

<span class="mw-page-title-main">Ruthenium</span> Chemical element, symbol Ru and atomic number 44

Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemicals. Karl Ernst Claus, a Russian-born scientist of Baltic-German ancestry, discovered the element in 1844 at Kazan State University and named ruthenium in honor of Russia. Ruthenium is usually found as a minor component of platinum ores; the annual production has risen from about 19 tonnes in 2009 to some 35.5 tonnes in 2017. Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors. A minor application for ruthenium is in platinum alloys and as a chemistry catalyst. A new application of ruthenium is as the capping layer for extreme ultraviolet photomasks. Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, and in pyroxenite deposits in South Africa.

<span class="mw-page-title-main">Rhodium</span> Chemical element, symbol Rh and atomic number 45

Rhodium is a chemical element; it has symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isotope, which is 103Rh. Naturally occurring rhodium is usually found as a free metal or 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.

<span class="mw-page-title-main">Rhenium</span> Chemical element, symbol Re and atomic number 75

Rhenium is a chemical element; it has symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. It has the third-highest melting point and second-highest boiling point of any element at 5869 K. It resembles manganese and technetium chemically and is mainly obtained as a by-product of the extraction and refinement of molybdenum and copper ores. It shows in its compounds a wide variety of oxidation states ranging from −1 to +7.

<span class="mw-page-title-main">Titanium</span> Chemical element, symbol Ti and atomic number 22

Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.

<span class="mw-page-title-main">Tungsten</span> Chemical element, symbol W and atomic number 74

Tungsten is a chemical element; it has symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite and wolframite, the latter lending the element its alternative name.

Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.

A period 5 element is one of the chemical elements in the fifth row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.

<span class="mw-page-title-main">Noble metal</span> Metallic elements that are nearly chemically inert

A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals are most often so classified. Silver, copper, and mercury are sometimes included as noble metals, but each of these usually occurs in nature combined with sulfur.

A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the chemical elements, including the lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, 209Bi, has a half-life of more than 1019 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.

The platinum-group metals (PGMs), also known as the platinoids, platinides, platidises, platinum group, platinum metals, platinum family or platinum-group elements (PGEs), are six noble, precious metallic elements clustered together in the periodic table. These elements are all transition metals in the d-block.

<span class="mw-page-title-main">Group 9 element</span> Group of chemical elements

Group 9, by modern IUPAC numbering, is a group (column) of chemical elements in the d-block of the periodic table. Members of Group 9 include cobalt (Co), rhodium (Rh), iridium (Ir) and meitnerium (Mt). These elements are among the rarest of the transition metals.

<span class="mw-page-title-main">Group 10 element</span> Group of chemical elements

Group 10, numbered by current IUPAC style, is the group of chemical elements in the periodic table that consists of nickel (Ni), palladium (Pd), platinum (Pt), and darmstadtium (Ds). All are d-block transition metals. All known isotopes of darmstadtium are radioactive with short half-lives, and are not known to occur in nature; only minute quantities have been synthesized in laboratories.

<span class="mw-page-title-main">Flux (metallurgy)</span> Chemical used in metallurgy for cleaning or purifying molten metal

In metallurgy, a flux is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time. They are used in both extractive metallurgy and metal joining.

Adams' catalyst, also known as platinum dioxide, is usually represented as platinum(IV) oxide hydrate, PtO2•H2O. It is a catalyst for hydrogenation and hydrogenolysis in organic synthesis. This dark brown powder is commercially available. The oxide itself is not an active catalyst, but it becomes active after exposure to hydrogen whereupon it converts to platinum black, which is responsible for reactions.

<span class="mw-page-title-main">Native metal</span> Form of metal

A native metal is any metal that is found pure in its metallic form in nature. Metals that can be found as native deposits singly or in alloys include aluminium, antimony, arsenic, bismuth, cadmium, chromium, cobalt, indium, iron, manganese, molybdenum, nickel, niobium, rhenium, selenium, tantalum, tellurium, tin, titanium, tungsten, vanadium, and zinc, as well as the gold group and the platinum group. Among the alloys found in native state have been brass, bronze, pewter, German silver, osmiridium, electrum, white gold, silver-mercury amalgam, and gold-mercury amalgam.

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