Platinum

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 , a diminutive of "silver".

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. Because of its scarcity in Earth's crust, barely a few hundred metric tonnes are produced annually, and given its critical and important uses, it is highly valuable as well as a major precious metal commodity.

Platinum does not corrode, 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 understood by scientists.

Platinum is a key component in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Platinum is also used in the glass industry to manipulate molten glass, which does not "wet" platinum. Compounds containing platinum, such as cisplatin, oxaliplatin and carboplatin, are applied in chemotherapy as treatment for certain types of cancer.

Characteristics

Physical

Platinum is a lustrous, ductile, and malleable, silver-white metal. Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals.

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

Chemical

thumb| upright=1.3|left|Platinum being dissolved in hot [[aqua regia]]

Platinum does not corrode, and bulk platinum does not oxidize in air at any temperature, but heated metal wires lose weight faster in air or oxygen than it does in a vacuum. The suggestion is that Pt forms a thin surface film of Platinum dioxide| that decomposes when heated above 500 °C.

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 to form platinum tetrafluoride. 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, :

As a soft acid, the 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.

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).

Isotopes

Platinum has six naturally occurring isotopes: , , , , , and . The most abundant of these is , comprising 33.83% of all platinum; it is the only stable isotope with a non-zero spin, of 1/2, and it is favorable for use in NMR. Due to its spin and large abundance, satellite peaks are also often observed in and NMR spectroscopy (e.g., for Pt-phosphine and Pt-alkyl complexes). The radioactive is the least abundant of these at only 0.012%; it undergoes alpha decay with a half-life of 4.83 years, causing the very low activity of 16.8 Bq/kg of natural platinum.

The other natural isotopes are theoretically capable of alpha decay also, but this has never been observed, and therefore they are considered stable. Platinum also has 38 synthetic isotopes ranging in atomic mass from 165 to 208, making the total number of known isotopes 44. The most stable of these radioisotopes is , with a half-life of 50 years. Most platinum isotopes decay by some combination of beta decay and (on the proton-rich side) alpha decay. , , and decay only by electron capture (besides the very small alpha branch of the first). and are predicted to have energetically favorable double beta decay paths.

Occurrence

thumb|left|A native platinum nugget, [[Kondyor Massif|Kondyor mine, Khabarovsk Krai]]

thumb|left|Platinum-palladium ore, Stillwater mine, Beartooth Mountains, Montana, US

thumb|left|Sulfidic serpentinite (platinum-palladium ore) from Stillwater Mine, Beartooth Mountains, Montana, USA

Platinum is an extremely rare metal on Earth, occurring at a concentration of only 0.005 ppm in Earth's crust. Platinum is often found chemically uncombined as native platinum and as alloy with the other platinum-group metals mostly. Most often native platinum is found in secondary deposits among 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. The rare sulfide mineral cooperite, , contains platinum along with palladium and nickel. Cooperite occurs in the Merensky Reef within the Bushveld complex, Gauteng, South Africa.

In 1865, chromites were identified in the Bushveld region of South Africa, followed by the discovery of platinum in 1906. 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. for example in the Absaroka Range in Montana. 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 .

Advanced techniques to finding platinum deposits by studying ground water found some evidence of new deposits in the state of Tamil Nadu, India.

Platinum exists in somewhat higher quantity 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.

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.

Treatment of hexachloroplatinic acid with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate, 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.

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:

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, , also known as "Adams' catalyst", is a black powder that is soluble in potassium hydroxide (KOH) solutions and concentrated acids. and the less common both decompose upon heating.

Platinum exhibits negative oxidation states at surfaces reduced electrochemically, and several "platinides" have been synthesized in which platinum exhibits oxidation states ranging from −1 to −2. The negative oxidation states exhibited by platinum are unusual for metallic elements, and they are attributed to the relativistic stabilization of the 6s orbitals. Caesium platinide, , a dark-red transparent crystalline compound has been shown to contain Pt anions. The "platinum Grignard" Pt(MgCl)2·THF conjecturally contains Pt2− as well.

It is predicted that even the cation in which platinum exists in the +10 oxidation state may be achievable.

Zeise's salt, containing an ethylene ligand, was one of the first organometallic compounds discovered. 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. Others include carboplatin and oxaliplatin. These compounds are capable of crosslinking DNA, and kill cells by similar pathways to alkylating chemotherapeutic agents. (Side effects of cisplatin include nausea and vomiting, hair loss, tinnitus, hearing loss, and nephrotoxicity.)

Organoplatinum compounds such as the above anti-tumor agents, as well as soluble inorganic platinum complexes, are routinely characterized using nuclear magnetic resonance spectroscopy.

File:Hexachloridoplatinat-Ion.svg|The hexachloroplatinate ion

File:Zeise's-salt-anion-3D-balls.png|The anion of Zeise's salt

File:Dichloro(cycloocta-1,5-diene)platinum(II)-from-xtal-3D-balls-E.png|

File:Cisplatin-3D-balls.png|Cisplatin</gallery>

Non-reactivity with animal life

Platinum exposure has shown no adverse effects with animal life as it is one of the least reactive metals.

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 been studied. The Food and Drug Administration and other institutions have reviewed the issue and found no evidence to suggest toxicity in vivo.

Platinum salts

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.

History

Early uses

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

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 ( 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. 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. 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.

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". 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. 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. Brownrigg also made note of platinum's extremely high melting point and refractoriness toward borax. Other chemists across Europe soon began studying platinum, including Andreas Sigismund Marggraf, 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.

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.

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. Unprecipitated hexachloroplatinate(IV) may be reduced with elemental zinc, and a similar method is suitable for small scale recovery of platinum from laboratory residues. Mining and refining platinum has environmental impacts.

thumb|An aerial photograph of a platinum mine in South Africa.

thumb|Time trend of platinum production

{| class="wikitable sortable static-row-numbers col1left" style="text-align:right;"

|+Platinum production by country

! Country !! Production (kg)

!Year

|World||170,000

|2024

| ||120,000

|2024

| ||19,000

|2024

| ||18,000

|2024

| ||5,200

|2024

|2,800

|2022

|||2,000

|2024

|||1,243

|2022

|||501

|2022

|||100

|2022

|||30

|2022

|||10

|2022

|||5

|2022

Applications

thumb|Cutaway view of a [[Catalytic converter|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.

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. In an automobile catalytic converter, it completes the 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. , also known as Adams' catalyst, is used as a hydrogenation catalyst, specifically for vegetable oils. and it is used in fuel cells as a catalyst for the reduction of oxygen.

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 membrane (PEM) technologies required in green hydrogen production as well as fuel cell electric vehicle adoption (FCEV).

Standard

thumb|upright=1.2|right|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.

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). 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.

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 jewelry, commonly sold as .999 or .9995 fine. It is used for this purpose for its prestige and inherent bullion value.

In watchmaking, Rolex, Vacheron Constantin, Patek Philippe, Breitling, and other master watchmakers use platinum in select watches. Watchmakers appreciate the unique properties of platinum, as it is more durable than gold, but similarly does not tarnish.

During periods of sustained economic stability and growth, the price of platinum can exceed that of the price of gold. As an investment, platinum is similar to gold in being a relatively low risk investment, or "safe-haven", in times of economic crisis. When the price of gold has exceeded that of platinum, many buyers in major markets, including the famous Dubai "gold souk" have turned to buying platinum instead for investment and for jewelry.

In the 18th century King Louis XV of France said of platinum that it is "the only metal fit for a king", owing to platinum's scarcity, traits, and intrinsic value.

As of 2024, the American multinational warehouse club chain, Costco, sells platinum bars on its website.

File:One litre of Platinum.jpg|1,000 cubic centimeters of 99.9% pure platinum, worth about US$696,000 as of 29 Jun 2016 ($ adjusted for inflation)

File:Platinum price.webp|Platinum price 1970–2022

</gallery>

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.

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. "Platinum awards" are frequently the highest, or near highest possible, often ranking above "gold", "silver" and "bronze". In the United States, a musical album that has sold more than 1 million copies will be credited as "platinum". Some products, such as blenders and vehicles, with a silvery-white color are identified as "platinum". 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.

References

External links

Platinum at The Periodic Table of Videos (University of Nottingham)
NIOSH Pocket Guide to Chemical Hazards – Platinum Centers for Disease Control and Prevention

Characteristics

Physical

Chemical

Isotopes

Occurrence

Compounds

Halides

Oxides

Non-reactivity with animal life

Platinum salts

History

Early uses

European discovery

Applications

Catalyst

Green energy transition

Standard

As an investment

Other uses

Symbol of prestige in marketing

See also

References

Further reading

External links