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Penny Collector Member
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 Posted - 04/12/2009 : 18:32:12
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What silver is to gold palladium is to platinum, the second choice of metal in spite of its beauty and industrial use.
Here is some information concerning palladium that you might enjoy.
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Part 1 - Ancient Civilizations
The history of palladium naturally starts with the history of platinum and the platinum group metals of which palladium is a member. Whether platinum was recognized as a separate body by early civilizations is doubtful. Traces of it have been found among artifacts from ancient Egypt, the best known example being a small strip of native platinum set on the surface of a box among many hieroglyphic inscriptions, dated to the seventh century BC and from Thebes. It had been hammered out in the same fashion that Thebian craftsmen treated silver, and most likely had been mistaken by them for silver.
The most successful early exploitation of platinum occurred rather in the Americas – the New World – by the Esmeraldas people in the coastal region of Northern Ecuador many centuries before the arrival of the Spanish. Small pieces of jewelry, rings, pendants, etc., have been found made of platinum or of platinum and gold combined, which displayed significant and sophisticated metallurgical skill. William Farabee, distinguished anthropologist of the University of Pennsylvania (1865-1925) wrote about one find:
“The native Indian workers of Esmeraldas were metallurgists of marked ability; they were the only people who manufactured platinum jewelry. In our collection will be seen objects of pure platinum, objects with a platinum background set with tiny balls of gold used to form a border, and objects with one side platinum and the other side gold.”
The Indian’s metallurgic method aroused considerable curiosity, and further study by others pointed to the conclusion that they had used a quite sophisticated technique of powder metallurgy – sintering in the presence of a liquid phase. Radio carbon dating has placed the date of these artifacts to between the first and fourth centuries AD. Photomicrographs of some samples, both of objects identified as starting materials and of finished pieces, clearly showed the presence of sintering and the dispersion of platinum particles in a gold matrix. Few of platinum finds from Ecuador or Columbia have an archeological context, unfortunately, because they were found by treasure hunters. Jewelry appears to have continued to be made up until the time of the conquest. Many centuries passed before the Spanish rediscovered the source of the platinum and longer yet before the scientists of Europe could make it malleable and useful.
....Palladium was finally isolated from platinum and identified as a separate elemental metal in 1803 by William Hyde Wollaston, a brilliant researcher who made many contributions to science. Wollaston made important discoveries in astronomy (the dark lines in the solar spectrum, a crucial tool in stellar astronomy today), biochemistry (he discovered cystine, the first amino acid), physiology (he was the first to postulate that human hearing is limited to certain frequencies), and physics (in atomic theory and crystallography).
......Wollaston’s process began with with platina - a natively occuring platinum mix which came from South America. To refine it, the common practice was to dissolve it in aqua regia (a mixture of hydrochloric and nitric acids). Adding ammonium chloride would then cause the platinum to precipitate out of solution in the form of an insoluble complex salt. Wollaston went further, adding iron, and treating the precipitate again with aqua regia. Adding iron a second time, he obtained a new precipitate, different than the previous ones.
When he treated this new precipitate with nitric acid, he obtained a reddish solution. This readily combined with mercury into an amalgam that when decomposed by heat left a new white metal.
Wollaston initially named his discovery “ceresium,” after the newly-discovered asteroid Ceres. But he soon changed it to palladium, after a different new asteroid: Pallas, which in turn was named after the Greek Goddess of wisdom.
Wollaston didn’t announce his discovery; he apparently thought it would have commercial value, and didn’t want to tell others how to make it. In April 1803, he anonymously printed notices of palladium’s properties, and made it available for sale in a Soho shop.
Other scientists were skeptical, especially chemist Richard Chenevix. He believed that palladium was a fraud; he suspected it was only an alloy of platinum, and not a new metal at all. Chenevix even claimed to have created his own palladium by combining mercuric oxide, platinum, aqua regina, and ferrous sulfate.
Wollaston rebutted Chevenix’s claims, anonymously offering a reward of twenty pounds to anybody who could synthesize palladium. After many failures, chemists finally accepted palladium as a new metal.
......Wollaston continued to refine and market platinum group metals for various applications. He was most successful marketing platinum, but considerably less so with palladium, and without a market for it, his stocks of palladium continued to grow. It was a metal that was available before technology found uses for it. Wollaston did market the metal for use in analytical weights. Eventually he gave a considerable quantity of palladium to the Royal Society. Unfortunately, Wollaston’s supply of native platinum ended in 1820, when he ceased offering his products to industry.
......Percival Norton Johnson, son and former apprentice of assayer John Johnson who had a close relationship with Wollaston, in 1817, formed a gold refining company and began refining gold,
the beginnings of what became the Johnson Matthey Company.
Johnson took up refining platinum when Wollaston abandoned his work. Brazilian gold, which had high palladium content, became a specialty largely because his refinery was the only one capable of refining the ore and separating the palladium. Like Wollaston, he had trouble finding an outlet for the large stores of palladium he began to collect. He marketed the metal for use in chemical balances, for rust free surgical instruments, use as lighthouse reflectors, and as a substitute for steel in some circumstances, such as pen tips.
.....In 1820 Humphrey Davy first observed the process of catalytic oxidation, describing it as a “perfectly new principal in combustion.” It was German Johann Wolfgang Döbereiner though, who carried on the experimentation to fully understand the process, finding that platinum group metals in a fine powder, had the power to unite oxygen and hydrogen even at low temperatures.
.....The 1830s saw discoveries of a number of properties of this group of metals. Michael Faraday’s experiments in electrochemistry provided further scientific insight for the platinum group metals. Faraday often used platinum plates as electrodes because it was resistant to reaction with the other elements involved. He coined the terms we still use today: anode, cathode, electrolysis, and electrolyte. William Robert Grove, chemist and lawyer, added to the experimentation and quite notably, developed the first platinum based fuel cell. During 1832, English chemist and astronomer Sir John Herschel made a remarkable discovery with platinum concerning the effect of light on certain chemical reactions, a discovery that placed his name among the inventors of photography.
......One of palladium’s most important properties was discovered as a result of researches of Thomas Graham, London chemist. In 1854, he was investigating how red-hot platinum absorbed hydrogen and discovered it could do so for an indefinite period of time, and no other gases produced the remarkable effect. Turning to palladium, he found that it could absorb 5 or 6 hundred times its own volume in hydrogen. When exposed to coal gas, only the hydrogen penetrated the palladium. This decade also saw considerable improvements in the achievement of high temperatures for melting metals. In France, the use of coal gas and oxygen in blow pipes were investigated, and using crucibles of lime or magnesia, achieved some success with platinum. Using these principals, Frenchmen Deville and Debray devised a process to refine native platinum and filed patents in France and Britain in 1857. The British rights were immediately acquired by George Matthey.
......The growth of more available platinum metals fueled further search for applications. In 1867, an international metallurgical exhibition held in Paris was a huge success for the platinum products of Johnson Matthey, featuring over 15,000 ounces of platinum products including huge boilers.
....In 1888, rich copper nickel ore was discovered in Ontario, Canada containing some PGMs, but the successful extraction of these would wait years.
....For over a hundred years, palladium was fairly rare. It had been produced in limited quantities from various sources. The Ural Mountains of Russia provided the vast bulk of the ores from which palladium was produced. Then in 1924, the great stores of South Africa were found.
Still, palladium could only be obtained from platinum ore by methods similar to Wollaston’s, or else by electrolytic refining of copper. But in 1930, the International Nickel Company of Canada began producing palladium in significant quantities from its rich ores, and the metal became more widely available.
For the first time, industry had affordable palladium, and was able to put its unusual properties to work. In 1931, a German company named Heraeus developed and patented alloys of palladium with silver and gold. These alloys were excellent materials in dentistry, and today are still used in bridges and crowns.
In the 1970s, another important application emerged. Growing concerns about pollution and the environment triggered a surge in pollution-reduction technologies. Thanks to its unique physical characteristics, palladium soon became an important part of these systems.
Modern catalytic converters rely heavily on palladium and its sister metal, platinum. These devices convert up to 90% of harmful gases in auto exhausts (hydrocarbons, carbon monoxide, and nitrogen oxide) into less harmful substances (nitrogen, carbon dioxide, and water vapor). Today, each car or light truck sold in the USA must have a catalytic converter.
Since the 1970s, demand for palladium has skyrocketed in other industries as well. Modern electronic circuitry uses palladium in electrical switches and contacts, for its superior conductivity and resistance to oxidation. Palladium pastes are also used in electronic components such as capacitors.
.....Today, scientists are studying even more uses for palladium. The white metal is playing an especially key role in fuel cell research. The fuel cell is an exciting new technology: a device that combines hydrogen and oxygen, producing electricity, heat, and water, with virtually no pollution. The fuel cell promises to completely transform modern society, and palladium plays an important role in current research.
Truly, palladium is a metal for the 21st century!
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Autocatalysts
Softer than platinum, ductile and resistant to oxidation and high temperature corrosion, palladium is useful in eliminating harmful emissions produced by internal combustion engines. Autocatalysts are by far the largest user of palladium; autocatalysts convert over 90 percent of hydrocarbons, carbon monoxide and oxides of nitrogen produced in the exhaust from gasoline engines into carbon dioxide, nitrogen and water vapor.
Electronics
Palladium has a number of electronic applications. For example, palladium’s chemical stability and electrical conductivity make it an effective and durable alternative to gold for plating in electronic components.
Dentistry
Palladium-based alloys are used in dentistry for dental crowns and bridges. And palladium metal is also compatible with human tissue and is used, in a radioactive form, in the medical industry for the treatment of cancer.
Chemical
Palladium is an important part of the refining of nitric acid, and has important uses in developing raw materials for synthetic rubber and nylon.
Fuel Cells
Palladium-based alloys are actively being researched for applications in fuel cell technology, an area of future promise for the metal.
Oil Refining
Palladium and other PGM metals serve important functions in catalytic reactions that are used in various stages in the refining of petroleum.
Polyester
Palladium is a critical catalyst in the manufacture of polyester.
Photography
Palladium and platinum are both used in an historic photographic printing process that many consider superior to conventional silver in tonal quality and archival longevity.
Water Treatment
Palladium is a unique and important catalyst being studied for use in removing a number of toxic and carcinogenic substances from groundwater.
Hydrogen Purification
Palladium’s ability to absorb and desorb hydrogen depending on circumstances allows it to be an effective material to filter hydrogen from other gasses resulting in an ultra pure hydrogen gas.
Medicine
Palladium-103, a radioactive isotope of palladium, is seeing promissing applications in the treatement of prostate cancer. A newly emerging added area of research is potential use in the treatment of breast cancer.
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Palladium, history & uses
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