Does Platinum Crack

[Shu Manwill]

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]

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 a lustrous, ductile, and malleable, silver-white metal.[12] Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals, but it is less malleable than gold.[13][14]

Platinum has excellent resistance to corrosion. Bulk platinum does not oxidize in air at any temperature, but it forms a thin surface film of '"`UNIQ--templatestyles-00000034-QINU`"'PtO2 that can be easily removed by heating to about 400 C.[16][17]

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.[18] 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:[19][20]

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).[22]

Platinum is an extremely rare metal,[25] occurring at a concentration of only 0.005 ppm in Earth's crust.[26][27] 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 Choc 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.[20]

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.[36]

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.[37]

Treatment of hexachloroplatinic acid with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate,[19] 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.[38]

Platinum(IV) oxide, PtO2, also known as "Adams' catalyst", is a black powder that is soluble in potassium hydroxide (KOH) solutions and concentrated acids.[40] PtO2 and the less common PtO both decompose upon heating.[12] Platinum(II,IV) oxide, Pt3O4, is formed in the following reaction:

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.[21] The use of platinum(II) acetylacetonate has also been reported.[41]

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.[21]

Cisplatin, or cis-diamminedichloroplatinum(II) is the first of a series of square planar platinum(II)-containing chemotherapy drugs.[47] Others include carboplatin and oxaliplatin. These compounds are capable of crosslinking DNA, and kill cells by similar pathways to alkylating chemotherapeutic agents.[48] (Side effects of cisplatin include nausea and vomiting, hair loss, tinnitus, hearing loss, and nephrotoxicity.)[49][50]

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.[51] 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.[52][53]

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 Darin and Mexico, "which no fire nor any Spanish artifice has yet been able to liquefy".[58] 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.[57]

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.[58]

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.[60] Brownrigg also made note of platinum's extremely high melting point and refractoriness toward borax.[

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.[58]

In 1786, Charles III of Spain provided a library and laboratory to Pierre-Franois 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 Joaqun Cabezas producing platinum ingots and utensils. This started what is known as the "platinum age" in Spain.[58]

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.[64]

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.[65]

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