Platinum

• 1. Introduction

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  Platinum sits at atomic number 78 on the periodic table, but its story stretches back to pre-Columbian South America, where native peoples worked it into artifacts before European science had even named it. Its very name comes from the Spanish platina, a diminutive of plata, meaning silver, because Spanish colonizers who first encountered it largely dismissed it as a kind of impurity in gold. There was even an official decree forbidding the adulteration of gold with platinum impurities. So how did a metal once thrown away become the symbol of the highest achievable rank in music, credit cards, and crowns? And how does an element so chemically stubborn that it resists most acids end up being a key reason cancer patients survive chemotherapy? The answers run from the alluvial sands of the Choco Department in Colombia to the Merensky Reef in South Africa, and from 18th-century Spanish laboratories to the catalytic converters in nearly every modern car.

• 2. The Metal Itself

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  Platinum is more ductile than gold, silver, or copper, making it the most ductile of all pure metals. That physical fact alone sets it apart from most of the elements around it on the periodic table. It is dense, malleable, and silverish-white, and its resistance to wear and tarnish makes it particularly well suited for fine jewelry and precision instruments.

  Chemically, platinum's defining trait is its unwillingness to react. Bulk platinum does not oxidize in air at any temperature. It is insoluble in hydrochloric and nitric acid. Only hot aqua regia, a mixture of both acids, can dissolve it. Even then, it forms aqueous chloroplatinic acid rather than simply breaking down. Platinum can be attacked by chlorine, bromine, iodine, and sulfur, and it reacts vigorously with fluorine at 500 degrees Celsius to form platinum tetrafluoride. But under ordinary conditions it stays largely inert.

  The most common oxidation states are plus two and plus four, with tetracoordinate platinum(II) compounds tending to adopt 16-electron square planar geometries. Platinum also exhibits unusual negative oxidation states, ranging from minus one to minus two, a property attributed to the relativistic stabilization of its 6s orbitals. It is even predicted that platinum could theoretically exist in a plus-10 oxidation state.

• 3. From the Americas to Europe

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  The Italian humanist Julius Caesar Scaliger provided the first European written reference to platinum in 1557, describing an unknown noble metal found between Darien and Mexico that no fire nor any Spanish artifice had yet been able to liquefy. The Spanish found the metal baffling and treated it as a nuisance.

  In 1735, Antonio de Ulloa and Jorge Juan y Santacilia encountered Native Americans mining platinum while travelling through Colombia and Peru over the course of eight years. Ulloa brought samples back to Spain, established the first mineralogy lab there, and published a report in 1748 that gave scientists their first systematic study of the metal. His account described platinum as being neither separable nor calcinable, and he anticipated the existence of platinum mines. After publishing, Ulloa did not continue investigating. In 1758 he was sent to superintend mercury mining operations in Huancavelica.

  In 1741, the British metallurgist Charles Wood had independently found samples of Colombian platinum in Jamaica and sent them to William Brownrigg. By 1750, Brownrigg presented a detailed account to the Royal Society, noting platinum's extremely high melting point and refractoriness toward borax. Other European chemists quickly joined the investigation, including Andreas Sigismund Marggraf, Torbern Bergman, Jons Jakob Berzelius, William Lewis, and Pierre Macquer. In 1752, Henrik Scheffer published a detailed scientific description, calling it white gold and recording how he succeeded in fusing platinum ore with the aid of arsenic.

• 4. Making It Workable

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  Karl von Sickingen researched platinum extensively in 1772 and found a path to malleability by alloying it with gold, dissolving the alloy in hot aqua regia, precipitating the platinum with ammonium chloride, igniting the resulting salt, and then hammering the finely divided platinum until it cohered. Franz Karl Achard took the next step in 1784 by making the first platinum crucible, working the metal by fusing it with arsenic and then volatilizing the arsenic away.

  In 1786, Charles III of Spain gave Pierre-Francois Chabaneau a library and laboratory to pursue platinum research. Chabaneau found himself wrestling with a confusing element: sometimes the platinum was malleable, but when it was alloyed with iridium, it turned brittle. Sometimes it was entirely incombustible, but when alloyed with osmium, it would volatilize. The inconsistency came from the fact that what he was working with still contained undiscovered platinum-group metals. After several months, Chabaneau succeeded in producing 23 kilograms of pure, malleable platinum by hammering and compressing the sponge form while white-hot. He then partnered with Joaquin Cabezas to produce platinum ingots and utensils, launching what became known as the platinum age in Spain.

• 5. Where It Comes From

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  Platinum occurs in Earth's crust at a concentration of only 0.005 parts per million, making it among the rarer elements on the planet. Because it is so unreactive, it is often found chemically uncombined, and alluvial deposits in river sands have historically been major sources. The alluvial deposits in the Choco Department of Colombia that pre-Columbian peoples used are still active today.

  Chromites were identified in the Bushveld region of South Africa in 1865, and platinum was found there in 1906. Then in 1924, the geologist Hans Merensky discovered a large platinum supply in the Bushveld Igneous Complex. The specific layer he found, named the Merensky Reef, contains around 75% of the world's known platinum. Cooperite, a rare sulfide mineral found in the Merensky Reef within the Bushveld complex in Gauteng, South Africa, contains platinum along with palladium and nickel.

  At Platinum, Alaska, about 17,000 kilograms were mined between 1927 and 1975 before the mine ceased operations in 1990. Large copper-nickel deposits near Norilsk in Russia and in the Sudbury Basin in Ontario, Canada are also major sources; the Sudbury Basin's platinum is present at only 0.5 ppm in the ore, but the sheer volume of nickel ore processed makes the operation viable. In 2010, South Africa held an almost 77% share of global production, followed by Russia at 13%, with world production that year at 192,000 kilograms.

• 6. Catalyst for Modern Life

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  Of the 218 tonnes of platinum sold in 2014-98 tonnes went into vehicle emissions control devices, representing 45% of total sales. The catalytic converter is the primary reason platinum enters so many lives without most people ever realizing it. Inside the converter, platinum completes the combustion of unburned hydrocarbons from exhaust, turning them into carbon dioxide and water vapor.

  In 2007, the German scientist Gerhard Ertl won the Nobel Prize in Chemistry specifically for determining the detailed molecular mechanisms behind platinum's catalytic oxidation of carbon monoxide. Platinum's catalytic role extends beyond vehicles. It is used in petroleum refining, particularly in catalytic reforming of straight-run naphthas into higher-octane gasoline. Platinum(IV) oxide, known as Adams' catalyst, serves as a hydrogenation catalyst for vegetable oils. Platinum also catalyzes the decomposition of hydrogen peroxide into water and oxygen and functions as a catalyst in fuel cells.

  The metal's future role in energy is considerable. As a fuel cell catalyst, platinum enables hydrogen and oxygen reactions to proceed at an optimum rate. It is used in platinum-based proton exchange membrane technologies required for green hydrogen production and in fuel cell electric vehicles.

• 7. Medicine, Standards, and Prestige

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  Cisplatin was the first of a series of square planar platinum(II)-containing chemotherapy drugs. It was followed by carboplatin and oxaliplatin. These compounds work by crosslinking DNA, killing cancer cells by pathways similar to alkylating agents. Platinum drugs are used to treat a wide range of cancers, including testicular and ovarian carcinomas, melanoma, small-cell and non-small-cell lung cancer, myelomas, and lymphomas.

  From 1889 to 1960, the meter was defined as the length of a platinum-iridium alloy bar, specifically a 90:10 ratio, known as the international prototype meter. A previous bar made of pure platinum in 1799 had served the same function. Until May 2019, the kilogram was defined as the mass of a cylinder of the same platinum-iridium alloy made in 1879. The standard platinum resistance thermometer is one of four thermometer types used to define the International Temperature Scale of 1990.

  In the 18th century, King Louis XV of France declared platinum the only metal fit for a king. That assessment has persisted in cultural form. In the United States, any musical album selling more than one million copies earns the platinum certification. The frame of the Crown of Queen Elizabeth the Queen Mother, made for her coronation as consort of King George VI, is platinum, making it the first British crown ever made from that particular metal. Watchmakers including Rolex, Vacheron Constantin, Patek Philippe, and Breitling use platinum in select watches, valued for being more durable than gold without tarnishing.