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= Platinum =
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Introduction
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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, making platinum about 30
times rarer than gold. It occurs in some nickel and copper ores along
with some native deposits, with 90% of current production from
deposits across Russia's Ural Mountains, Colombia, the Sudbury basin
of Canada, and a large reserve in South Africa. 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 as well
as a major precious metal commodity.
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 to manipulate molten glass, which does not "wet" platinum.
Elemental platinum has not been linked to adverse health effects.
Compounds containing platinum, such as cisplatin, oxaliplatin and
carboplatin, are applied in chemotherapy against certain types of
cancer.
Physical
==========
Pure 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, but it is less malleable than
gold.
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
==========
Platinum has excellent resistance to corrosion. Bulk platinum does not
oxidize in air at any temperature, but it forms a thin surface film of
Platinum dioxide that can be easily removed by heating to about 400
°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 500 C 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. The spin of 1/2 and
other favourable magnetic properties of the nucleus are utilised 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). is the least abundant at only 0.012%. Of the
naturally occurring isotopes, only is unstable, though it decays with
a half-life of 4.83 years, causing an activity of 16.8 Bq/kg of
natural platinum. Other isotopes can undergo alpha decay, but their
decay has never been observed, 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 least
stable of these are and , with half-lives of 260 μs, whereas the most
stable is with a half-life of 50 years. Most platinum isotopes decay
by some combination of beta decay and alpha decay. , , and decay
primarily by electron capture. and are predicted to have
energetically favorable double beta decay paths.
Occurrence
============
Platinum is an extremely rare metal, 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.
In nickel and copper deposits, platinum-group metals occur as sulfides
(e.g., , tellurides (e.g., ), antimonides (PdSb), and arsenides (e.g.
), and as end alloys with nickel or copper. Platinum arsenide,
sperrylite (), is a major source of platinum associated with nickel
ores in the Sudbury Basin deposit in Ontario, Canada. At Platinum,
Alaska, about 17000 kg was mined between 1927 and 1975. The mine
ceased operations in 1990. 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. 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, 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 192,000 kg.
New approaches to finding platinum deposits by studing ground water
found some evidence of new deposits in the state of Tamil Nadu, India.
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.
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(II,IV) oxide, , is formed in the following reaction:
:
Other compounds
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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. The use of platinum(II)
acetylacetonate has also been reported.
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. Barium platinides include BaPt, ,
and . 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.
Cisplatin, or is the first of a series of square planar
platinum(II)-containing chemotherapy drugs. 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 antitumour agents, as well
as soluble inorganic platinum complexes, are routinely characterised
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
Early uses
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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
hieroglyphics. 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.
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.
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.
In 1741, Charles Wood, 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.
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.
Because the other platinum-family members were not discovered yet
(platinum was the first), 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 exceeds that of gold and
its malleability similar to gold's. 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" with
gold as the only solution at the time to obtain a pliable compound.
Presently, very pure platinum is readily available, and extremely long
wires can easily be drawn from pure platinum due to its crystalline
structure, which is similar to that of many soft metals.
"Platinum age" in Spain
=========================
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.
Production
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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.
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.
Applications
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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.
Platinum also strongly catalyzes the decomposition of hydrogen
peroxide into water and oxygen 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
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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 including: Rolex, Vacheron Constantin, Patek Philippe,
Breitling, and other companies which use platinum in select watches.
Watchmakers appreciate the unique properties of platinum, as it is
more durable than gold, but similar to gold, it 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.
In the 18th century, platinum's scarcity, traits, and intrinsic value
made King Louis XV of France declare it "the only metal fit for a
king".
File:One litre of Platinum.jpg|1,000 cubic centimeters of 99.9% pure
platinum, worth about US$696,000 at 29 Jun 2016 prices
File:Platinum price.webp|Platinum price 1970-2022
Other uses
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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. Platinum-based anodes are used in ships,
pipelines, and steel piers. 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.
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". For example, in the United States, a musical
album that has sold more than 1 million copies will be credited as
"platinum", though an album that has sold more than 10 million copies
will be certified as "diamond". 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.
Health risks
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Elemental platinum is not believed to cause significant health risks
and no adverse effects have been attributed to platinum exposure.
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.
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. Chemically unbonded
(metallic, colloidal, or amalgam) platinum has been identified by the
FDA as a "fake cancer 'cure'".
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.
See also
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* Chelated platinum
* Iron-platinum nanoparticle
* List of countries by platinum production
* Mixed metal oxide electrode
* Nox (unit)
* Platinum group
* Platinum in Africa
* Platinum nanoparticle
* Platinum print
* Skot (unit)
* 2000s commodities boom
External links
======================================================================
* [
http://www.periodicvideos.com/videos/078.htm Platinum] at 'The
Periodic Table of Videos' (University of Nottingham)
* [
https://www.cdc.gov/niosh/npg/npgd0519.html NIOSH Pocket Guide to
Chemical Hazards - Platinum] Centers for Disease Control and
Prevention
*
*
*
*
License
=========
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Original Article:
http://en.wikipedia.org/wiki/Platinum
