Difference between revisions of "Palladium" - New World Encyclopedia

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{{Elementbox_header | number=46 | symbol=Pd | name=palladium | left=[[rhodium]] | right=[[silver]] | above=[[nickel|Ni]] | below=[[platinum|Pt]] | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_header | number=46 | symbol=Pd | name=palladium | left=[[rhodium]] | right=[[silver]] | above=[[nickel|Ni]] | below=[[platinum|Pt]] | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_series | [[transition metal]]s }}
 
{{Elementbox_series | [[transition metal]]s }}
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{{Elementbox_brinellhardness_mpa | 37.3 }}
 
{{Elementbox_brinellhardness_mpa | 37.3 }}
 
{{Elementbox_cas_number | 7440-05-3 }}
 
{{Elementbox_cas_number | 7440-05-3 }}
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{{Elementbox_isotopes_begin | color1=#ffc0c0 | color2=black }}
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{{Elementbox_isotopes_begin | isotopesof=palladium | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_isotopes_decay2 | mn=100 | sym=Pd
 
{{Elementbox_isotopes_decay2 | mn=100 | sym=Pd
 
  | na=[[synthetic radioisotope|syn]] | hl=[[1 E5 s|3.63 d]]
 
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{{Elementbox_footer | color1=#ffc0c0 | color2=black }}
 
{{Elementbox_footer | color1=#ffc0c0 | color2=black }}
  
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'''Palladium''' ([[International Phonetic Alphabet|IPA]]: {{IPA|/pəˈleɪdiəm/}}) is a [[chemical element]] with symbol '''Pd''' and [[atomic number]] 46. A rare silver-white [[transition metal]] of the platinum group, palladium  resembles [[platinum]] chemically and is extracted from some [[copper]] and [[nickel]] ores. It is primarily used as an industrial [[catalyst]] and in [[jewelry]].
+
'''Palladium''' (chemical symbol '''Pd''', [[atomic number]] 46) is a rare, silver-white [[metal]]. It is a member of the [[platinum]] group of elements and resembles platinum chemically. It is extracted from some [[copper]] and [[nickel]] ores. It has the unusual ability to absorb large quantities of [[hydrogen]] gas, expanding visibly as it does so.
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{{toc}}
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Palladium and its [[chemical compound|compounds]] are extremely valuable [[catalyst]]s for various chemical reactions, and palladium can be found in [[automobile]] catalytic converters. Palladium [[alloy]]s are used in [[jewelry]]. In addition, this element is useful in a number of other applications, including [[dentistry]], [[watch]]making, [[aircraft]] [[spark plug]]s, [[surgical instrument]]s, and [[electrical contact]]s. [[Hydrogen]] absorbed in palladium is highly reactive and is used in [[Redox|reduction]] reactions. Palladium dichloride may be used in detectors for [[carbon monoxide]] and tests for the [[corrosion]]-resistance of stainless steel.
 +
 
 +
== Occurrence ==
 +
 
 +
Palladium occurs in [[nature]] as a free metal and alloyed with [[gold]], [[platinum]], and other platinum group metals. It has been found in [[placer mining|placer]] deposits in the [[Ural Mountains]] of western [[Russia]], and in some parts of [[Australia]], [[Ethiopia]], and [[South America|South]] and [[North America]]. In addition, it is commercially produced from [[nickel]]-[[copper]] deposits in [[South Africa]], [[Ontario]], and [[Siberia]]. Although the proportion of palladium in the nickel-copper ores is low, the processing of large volumes of ore makes this extraction profitable.
 +
 
 +
== Discovery ==
 +
 
 +
Palladium was [[discovery of the chemical elements|discovered]] by [[William Hyde Wollaston]] in 1803 in [[England]]. Using a platinum ore that presumably came from [[South America]], he performed a series of chemical reactions and obtained the compound [[palladium cyanide]]. Finally, by heating palladium cyanide, he was able to isolate palladium metal. He named the element in 1804, deriving the word from ''Pallas'', the name of an asteroid discovered two years earlier.
  
 
== Notable characteristics ==
 
== Notable characteristics ==
 
[[Image:Palladium 1.jpg|left|thumb|75px|Palladium]]
 
[[Image:Palladium 1.jpg|left|thumb|75px|Palladium]]
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Palladium is a soft silver-white metal that resembles [[platinum]].  It is the least dense and has the lowest [[melting point]] of the [[platinum group]] metals. It is soft and ductile when [[Annealing (metallurgy)|annealed]] and greatly increases its strength and hardness when it is cold-worked. Palladium is chemically attacked by [[sulfuric acid|sulfuric]], [[nitric acid]] and [[hydrochloric acid]] in which it dissolves slowly. This metal also does not react with [[oxygen]] at normal temperatures (and thus does not tarnish in [[Earth's atmosphere|air]]). Palladium heated to 800°C will produce a layer of palladium(II) oxide (PdO).  It lightly tarnishes in moist atmosphere containing sulfur.
 
  
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This metal has the uncommon ability to [[absorption (chemistry)|absorb]] up to 900 times its own volume of [[hydrogen]] at room temperatures. It is thought that this possibly forms [[palladium hydride]] (PdH<sub>2</sub>)  but it is not yet clear if this is a true [[chemical compound]].
+
Palladium is classified as a [[transition metal]]. In the [[periodic table]], it lies in period five between [[rhodium]] and [[silver]] and is closely related to the latter two elements. In addition, it is situated in group ten (former group 8B), between [[nickel]] and [[platinum]].
 +
 
 +
This silver-white metal does not react with [[oxygen]] at normal temperatures, and thus does not tarnish in [[Earth's atmosphere|air]]. It does, however, acquire a light tarnish in moist air containing [[sulfur]].
  
−
When palladium has absorbed large amounts of hydrogen, it can swell up, like a sponge full of water, visible to the naked eye.
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This element resembles [[platinum]], but among the [[platinum group]] metals, it has the lowest density and [[melting point]]. It is soft and ductile when [[Annealing (metallurgy)|annealed]], but it greatly increases in strength and hardness when cold-worked. Palladium is chemically attacked by [[sulfuric acid]], [[nitric acid]], and [[hydrochloric acid]] in which it dissolves slowly. When it is heated to 800°C, a layer of palladium(II) oxide (PdO) is produced.
  
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Common [[oxidation state]]s of palladium are 0,+1, +2 and +4. Although originally +3 was thought of as one of the fundamental oxidation states of palladium, there is no evidence for palladium occurring in the +3 oxidation state; this has been investigated via [[X-ray diffraction]] for a number of compounds, indicating a [[dimer]] of palladium(II) and palladium(IV) instead. Recently, compounds with an oxidation state of +6 were synthesised.
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Palladium has the uncommon ability to [[absorption (chemistry)|absorb]] up to 900 times its own volume of [[hydrogen]] at room temperature. As it absorbs hydrogen, it expands visibly, like a sponge that swells when soaking up water. In so doing, it is thought to form [[palladium hydride]] (PdH<sub>2</sub>), but scientists are unsure if this is a true [[chemical compound]].
  
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== Applications ==
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Common [[oxidation state]]s of palladium are 0, +1, +2, and +4. Although it was once thought that +3 was one of the fundamental oxidation states of palladium, there is no evidence for that. When several palladium compounds were investigated by the technique of [[X-ray diffraction]], a [[dimer]] of palladium(II) and palladium(IV) was discovered instead. Recently, researchers synthesized compounds in which palladium has an oxidation state of +6.
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When it is finely divided, palladium forms a good [[catalyst]] and is used to speed up [[hydrogenation]] and [[dehydrogenation]] reactions, as well as in [[petroleum]] [[cracking (chemistry)|cracking]]. A large number of [[carbon-carbon bond]] forming reactions in [[organic chemistry]] (such as the [[Suzuki coupling]]) are facilitated by catalysis with palladium compounds. It is also [[alloy]]ed and used in [[jewelry]]. Other uses;
 
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*The largest use of palladium today is in [[catalytic converters]].  Much research is in progress to discover ways to replace the much more expensive [[platinum]] with palladium in this application.
 
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*Palladium is one of the two metals which can be alloyed with [[gold]] to produce [[White gold]]. ([[Nickel]] can also be used.)
 
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*Similar to gold, palladium can be beaten into a thin leaf form as thin as 100 nm (1/250,000 in).
 
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*Since 1939 palladium itself has occasionally been used as a precious metal in [[jewelry]], often as a replacement for [[platinum]]. ([http://www.stillwaterpalladium.com/jewelry.html]).
 
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*Hydrogen easily diffuses through heated palladium; thus, it provides a means of purifying the gas. Also, [[hydrogen]] dissolved in palladium is highly reactive, allowing it to be used in various chemical [[Redox|reductions]].
 
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*Palladium (and palladium-[[silver]] alloys) are used as electrodes in multi-layer ceramic [[Capacitor (component)|capacitors]]. [http://www.unctad.org/infocomm/anglais/palladium/uses.htm#electrics]
 
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*Palladium (sometimes alloyed with [[nickel]]) is used in connector platings in consumer electronics.
 
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*Palladium is also used in [[dentistry]][http://www.platinummetalsreview.com/dynamic/article/view/48-1-030-031], [[watch]] making, in aircraft [[spark plug]]s and in the production of [[surgical instrument]]s and [[electrical contact]]s.
 
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*Palladium is also used to make professional transverse flutes.
 
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*It is also used as [[Palladium-Hydrogen electrode]] in electrochemical studies.
 
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*[[Palladium dichloride]] can absorb large amounts of [[carbon monoxide]] gas, and is used in carbon monoxide detectors.
 
  
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== History ==
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=== Isotopes ===
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Palladium was [[discovery of the chemical elements|discovered]] by [[William Hyde Wollaston]] in [[1803]]. This element was named by Wollaston in 1804 after the asteroid [[2 Pallas|Pallas]], which was discovered two years earlier.
 
  
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Wollaston found element 46 in crude platinum ore from [[South America]]. He did this by dissolving the ore in [[aqua regia]], neutralizing the solution with [[sodium hydroxide]], [[sodium|Na]][[hydroxide|OH]], precipitating platinum as [[ammonium chloroplatinate]] through treatment with [[ammonium chloride]], [[nitrogen|N]][[hydrogen|H]]<sub>4</sub>[[chlorine|Cl]], and then adding [[mercuric cyanide]] to form the compound [[palladium cyanide]]. Finally, he heated the resulting compound in order to extract palladium metal.
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Naturally occurring palladium is composed of six stable [[isotope]]s: <sup>102</sup>Pd, <sup>104</sup>Pd, <sup>105</sup>Pd, <sup>106</sup>Pd, <sup>108</sup>Pd, and <sup>110</sup>Pd. In addition, numerous radioactive isotopes are known, with mass numbers ranging from 91 to 124. The longest-lived radioisotopes are <sup>107</sup>Pd, with a [[half-life]] of 6.5 million years; <sup>103</sup>Pd, with a half-life of 17 days; and <sup>100</sup>Pd, with a half-life of 3.63 days. Most of the other radioisotopes have half-lives that are less than a half hour.
  
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The compound [[palladium chloride]] was at one time prescribed as a [[tuberculosis]] treatment at the rate of 0.065g per day (approximately one milligram per kilogram of body weight). This treatment did not have many negative [[Adverse effect (medicine)|side effects]], but was later replaced by more effective drugs.
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== Compounds ==
  
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The element played an essential role in the [[Fleischmann-Pons experiment]], also known as [[cold fusion]].
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* ''Palladium(II) chloride'', or ''palladium dichloride'' (PdCl<sub>2</sub>): This compound, prepared by the [[chlorination]] of palladium, is a common starting material for the synthesis of other palladium compounds. Palladium-based materials are valuable catalysts for the synthesis of organic chemicals. Moreover, palladium(II) chloride can rapidly stain stainless [[steel]]. Thus, solutions of this compound are sometimes used to test for the [[corrosion]]-resistance of stainless steel. Also, palladium(II) chloride is sometimes used in [[carbon monoxide]] detectors, as it can absorb large quantities of carbon monoxide gas.
  
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In [[2000]], [[Ford Motor Company]] created a [[Economic bubble|price bubble]] in palladium by stockpiling large amounts of the metal, fearing interrupted supplies from [[Russia]]. As prices fell in early [[2001]], Ford lost nearly $1 billion [[United States dollar|U.S. dollars]].
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* ''Palladium hydride'': This material consists of metallic palladium with a substantial quantity of [[hydrogen]] in its [[crystal]] lattice. At [[room temperature]] and [[Earth's atmosphere|atmospheric]] [[pressure]], palladium can [[adsorb]] up to 900 times its own volume of hydrogen. Thus, palladium can store substantial quantities of hydrogen safely, and it is also useful for performing unusual chemical reactions. Details of how this adsorption process works are poorly understood.
  
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== Occurrence ==
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== Applications ==
−
Palladium is found as a free metal and alloyed with platinum and gold with platinum group metals in [[placer mining|placer]] deposits of the [[Ural Mountains]], [[Australia]], [[Ethiopia]], [[South America|South]] and [[North America]]. It is commercially produced from [[nickel]]-[[copper]] deposits found in [[South Africa]], [[Ontario]] and [[Siberia]]; the huge volume of ore processed makes this extraction profitable in spite of the low proportion of palladium in these ores.  The world's largest single producer of Palladium is [[MMC Norilsk Nickel]], headquartered in [[Moscow]].
 
  
−
About the possibility of producing palladium in reactors or extracting it from spent nuclear fuel, see [[Synthesis of noble metals]].
+
* Finely divided palladium forms a good [[catalyst]] for various chemical reactions, such as [[hydrogenation]] (addition of hydrogen atoms), [[dehydrogenation]] (removal of hydrogen atoms), and [[petroleum]] [[cracking (chemistry)|cracking]] (breaking of large, complex [[hydrocarbon]]s to smaller, simpler ones). Also, palladium compounds are used as catalysts for reactions in which [[carbon-carbon bond]]s are formed.
 +
* The largest use of palladium today is in [[catalytic converter]]s for automobiles. Much research is in progress to discover ways of replacing the much more expensive [[platinum]] with palladium in this application.
 +
* Palladium [[alloy]]s are used in [[jewelry]].
 +
* Palladium is one of two metals that can be alloyed with [[gold]] to produce "[[white gold]]." ([[Nickel]] can also be used.)
 +
* Like gold, palladium can be beaten into a thin leaf form, as thin as 100 nanometers (nm) (1/250,000 inch).
 +
* Since 1939, palladium itself has occasionally been used as a precious metal in [[jewelry]], often as a replacement for [[platinum]].<ref>[http://www.stillwaterpalladium.com/jewelry.html Palladium Jewelry] Retrieved December 9, 2007.</ref>
 +
* Hydrogen readily diffuses through heated palladium. It thus provides a means of purifying the gas. Also, [[hydrogen]] dissolved in palladium is highly reactive, allowing it to be used in various chemical [[Redox|reductions]].
 +
* Palladium and its alloys with [[silver]] are used as electrodes in multilayer ceramic [[Capacitor (component)|capacitors]].<ref>[http://www.unctad.org/infocomm/anglais/palladium/uses.htm#electrics Palladium] Retrieved December 9, 2007.</ref>
 +
* Palladium (sometimes alloyed with [[nickel]]) is used in connector platings in consumer electronics.
 +
* Palladium is also used in [[dentistry]],<ref>[http://www.platinummetalsreview.com/dynamic/article/view/48-1-030-031 Palladium in Dentistry] Retrieved December 9, 2007.</ref> [[watch]] making, [[aircraft]] [[spark plug]]s, and the production of [[surgical instrument]]s and [[electrical contact]]s.
 +
* This element is also used to make professional transverse flutes.
 +
* It is also used for [[palladium-hydrogen electrode]]s in electrochemical studies.
 +
* Palladium dichloride is sometimes used in carbon monoxide detectors and in tests for the [[corrosion]]-resistance of stainless steel, as noted above.
  
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''See also [[:category:Palladium minerals|palladium minerals]].''
+
== "Cold fusion" ==
  
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== Isotopes ==
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In March 1989, researchers Stanley Pons and Martin Fleischmann announced that they had found a way to carry out a safe nuclear reaction at low temperatures in a tabletop experiment. The reaction, which was thought to involve the fusion of hydrogen nuclei, was dubbed "cold fusion." Palladium electrodes played an important role in this experiment. It was postulated that hydrogen atoms could be "squeezed" between the palladium atoms to help them fuse at lower temperatures than usually required for fusion to proceed. Since then, many other experiments have been conducted to test the possibility of cold fusion, but scientists remain divided on the issue of whether the observations are based on genuine cases of nuclear fusion.
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Naturally-occurring palladium is composed of six [[isotope]]s. The most stable [[radioisotope]]s are <sup>107</sup>Pd with a [[half-life]] of 6.5 million years, [[Pd-103|<sup>103</sup>Pd]] with a half-life of 17 days, and <sup>100</sup>Pd with a half-life of 3.63 days. Eighteen other radioisotopes have been characterized with [[atomic weight]]s ranging from 92.936 [[atomic mass unit|u]] (<sup>93</sup>Pd) to 119.924 u (<sup>120</sup>Pd). Most of these have half-lifes that are less than a half an hour except <sup>101</sup>Pd (half-life: 8.47 hours), <sup>109</sup>Pd (half-life: 13.7 hours), and <sup>112</sup>Pd (half-life: 21 hours).
 
  
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The primary [[decay mode]] before the most abundant stable isotope, <sup>106</sup>Pd, is [[electron capture]] and the primary mode after is [[beta decay]]. The primary [[decay product]] before <sup>106</sup>Pd is [[rhodium]] and the primary product after is [[silver]].
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==See also==
  
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[[Radiogenic]] <sup>107</sup>Ag is a decay product of <sup>107</sup>Pd and was first discovered in the [[Santa Clara, California]] meteorite of [[1978]]. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a [[nucleosynthetic]] event. <sup>107</sup>Pd versus Ag correlations observed in bodies, which have clearly been melted since accretion of the [[solar system]], must reflect the presence of short-lived nuclides in the early solar system.
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* [[Adsorption]]
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* [[Catalyst]]
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* [[Chemical element]]
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* [[Metal]]
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* [[Periodic table]]
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* [[Platinum]]
 +
* [[Transition metal]]
 +
 
 +
==Notes==
 +
<references/>
  
 
==References==
 
==References==
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*[http://periodic.lanl.gov/elements/46.html Los Alamos National Laboratory &ndash; Palladium]
 
  
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==See also==
+
* Chang, Raymond. 2006. ''Chemistry'', ninth ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
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* [[Palladium coin]]
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* Cotton, F. Albert, and Wilkinson, Geoffrey. 1980. ''Advanced Inorganic Chemistry'', 4th ed. New York: Wiley.
−
* [[Precious metal]]
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* Greenwood, N.N. and Earnshaw, A. 1998. ''Chemistry of the Elements''. 2nd Edition. Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
−
* [[:Category:Palladium compounds|Palladium compounds]]
+
* [http://periodic.lanl.gov/elements/46.html Palladium] Los Alamos National Laboratory. Retrieved December 9, 2007.
  
 
== External links ==
 
== External links ==
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{{Commons|Palladium}}
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All links retrieved November 18, 2022.
−
{{wiktionary|palladium}}
 
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*[http://encyclopedia.jrank.org/PAI_PAS/PALLADIUM_symbol_Pd_atomic_weig.html Palladium in depth] - Online Encyclopedia
 
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*[http://investinmetal.com/?page_id=5 Current Palladium Price]
 
 
*[http://www.webelements.com/webelements/elements/text/Pd/index.html WebElements.com &ndash; Palladium]
 
*[http://www.webelements.com/webelements/elements/text/Pd/index.html WebElements.com &ndash; Palladium]
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*[http://www.stillwaterpalladium.com/ Palladium Discovery History Uses & Investments]
+
*[https://www.technology.matthey.com/article/47/4/175-183 Rhodium and Palladium: Events Surrounding Their Discoveries]
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*[http://www.platinummetalsreview.com/dynamic/article/view/47-4-175-183 Palladium Events Surrounding Its Discovery]
 
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*[http://www.platinummetalsreview.com/ Platinum Metals Review E-Journal]
 
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*[http://www.platinummetalsreview.com/jmpgm/index.jsp The Platinum Group Metals Database]
 
 
*[http://www.rene-frank.com/English/palladiumtabeng.html Palladium Coins]
 
*[http://www.rene-frank.com/English/palladiumtabeng.html Palladium Coins]
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*[http://www.stillwatermining.com/ Stillwater Palladium]
 
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* [http://www.nornik.ru/en/ MMC Norilsk Nickel, world's largest Pd producer]
 
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{{ChemicalSources}}
 
  
 
[[Category:Physical sciences]]
 
[[Category:Physical sciences]]
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[[Category:Earth sciences]]
 
[[Category:Earth sciences]]
  
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Latest revision as of 06:25, 18 November 2022


46 rhodium ← palladium → silver
Ni
↑
Pd
↓
Pt
Pd-TableImage.png
periodic table
General
Name, Symbol, Number palladium, Pd, 46
Chemical series transition metals
Group, Period, Block 10, 5, d
Appearance silvery white metallic
Pd,46.jpg
Atomic mass 106.42(1) g/mol
Electron configuration [Kr] 4d10
Electrons per shell 2, 8, 18, 18, 0
Physical properties
Phase solid
Density (near r.t.) 12.023 g/cm³
Liquid density at m.p. 10.38 g/cm³
Melting point 1828.05 K
(1554.9 °C, 2830.82 °F)
Boiling point 3236 K
(2963 °C, 5365 °F)
Heat of fusion 16.74 kJ/mol
Heat of vaporization 362 kJ/mol
Heat capacity (25 °C) 25.98 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1721 1897 2117 2395 2753 3234
Atomic properties
Crystal structure cubic face centered
Oxidation states ±1
(mildly basic oxide)
Electronegativity 2.20 (Pauling scale)
Ionization energies 1st: 804.4 kJ/mol
2nd: 1870 kJ/mol
3rd: 3177 kJ/mol
Atomic radius 140 pm
Atomic radius (calc.) 169 pm
Covalent radius 131 pm
Van der Waals radius 163 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 105.4 nΩ·m
Thermal conductivity (300 K) 71.8 W/(m·K)
Thermal expansion (25 °C) 11.8 µm/(m·K)
Speed of sound (thin rod) (20 °C) 3070 m/s
Speed of sound (thin rod) (r.t.) 121 m/s
Shear modulus 44 GPa
Bulk modulus 180 GPa
Poisson ratio 0.39
Mohs hardness 4.75
Vickers hardness 461 MPa
Brinell hardness 37.3 MPa
CAS registry number 7440-05-3
Notable isotopes
Main article: Isotopes of palladium
iso NA half-life DM DE (MeV) DP
100Pd syn 3.63 d ε - 107Rh
γ 0.084, 0.074,
0.126 		-
102Pd 1.02% Pd is stable with 56 neutrons
103Pd syn 16.991 d ε - 103Rh
104Pd 11.14% Pd is stable with 58 neutrons
105Pd 22.33% Pd is stable with 59 neutrons
106Pd 27.33% Pd is stable with 60 neutrons
107Pd syn 6.5×106 y β- 0.033 107Ag
108Pd 26.46% Pd is stable with 62 neutrons
110Pd 11.72% Pd is stable with 64 neutrons

Palladium (chemical symbol Pd, atomic number 46) is a rare, silver-white metal. It is a member of the platinum group of elements and resembles platinum chemically. It is extracted from some copper and nickel ores. It has the unusual ability to absorb large quantities of hydrogen gas, expanding visibly as it does so.

Palladium and its compounds are extremely valuable catalysts for various chemical reactions, and palladium can be found in automobile catalytic converters. Palladium alloys are used in jewelry. In addition, this element is useful in a number of other applications, including dentistry, watchmaking, aircraft spark plugs, surgical instruments, and electrical contacts. Hydrogen absorbed in palladium is highly reactive and is used in reduction reactions. Palladium dichloride may be used in detectors for carbon monoxide and tests for the corrosion-resistance of stainless steel.

Occurrence

Palladium occurs in nature as a free metal and alloyed with gold, platinum, and other platinum group metals. It has been found in placer deposits in the Ural Mountains of western Russia, and in some parts of Australia, Ethiopia, and South and North America. In addition, it is commercially produced from nickel-copper deposits in South Africa, Ontario, and Siberia. Although the proportion of palladium in the nickel-copper ores is low, the processing of large volumes of ore makes this extraction profitable.

Discovery

Palladium was discovered by William Hyde Wollaston in 1803 in England. Using a platinum ore that presumably came from South America, he performed a series of chemical reactions and obtained the compound palladium cyanide. Finally, by heating palladium cyanide, he was able to isolate palladium metal. He named the element in 1804, deriving the word from Pallas, the name of an asteroid discovered two years earlier.

Notable characteristics

Palladium

Palladium is classified as a transition metal. In the periodic table, it lies in period five between rhodium and silver and is closely related to the latter two elements. In addition, it is situated in group ten (former group 8B), between nickel and platinum.

This silver-white metal does not react with oxygen at normal temperatures, and thus does not tarnish in air. It does, however, acquire a light tarnish in moist air containing sulfur.

This element resembles platinum, but among the platinum group metals, it has the lowest density and melting point. It is soft and ductile when annealed, but it greatly increases in strength and hardness when cold-worked. Palladium is chemically attacked by sulfuric acid, nitric acid, and hydrochloric acid in which it dissolves slowly. When it is heated to 800°C, a layer of palladium(II) oxide (PdO) is produced.

Palladium has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperature. As it absorbs hydrogen, it expands visibly, like a sponge that swells when soaking up water. In so doing, it is thought to form palladium hydride (PdH2), but scientists are unsure if this is a true chemical compound.

Common oxidation states of palladium are 0, +1, +2, and +4. Although it was once thought that +3 was one of the fundamental oxidation states of palladium, there is no evidence for that. When several palladium compounds were investigated by the technique of X-ray diffraction, a dimer of palladium(II) and palladium(IV) was discovered instead. Recently, researchers synthesized compounds in which palladium has an oxidation state of +6.

Isotopes

Naturally occurring palladium is composed of six stable isotopes: 102Pd, 104Pd, 105Pd, 106Pd, 108Pd, and 110Pd. In addition, numerous radioactive isotopes are known, with mass numbers ranging from 91 to 124. The longest-lived radioisotopes are 107Pd, with a half-life of 6.5 million years; 103Pd, with a half-life of 17 days; and 100Pd, with a half-life of 3.63 days. Most of the other radioisotopes have half-lives that are less than a half hour.

Compounds

  • Palladium(II) chloride, or palladium dichloride (PdCl2): This compound, prepared by the chlorination of palladium, is a common starting material for the synthesis of other palladium compounds. Palladium-based materials are valuable catalysts for the synthesis of organic chemicals. Moreover, palladium(II) chloride can rapidly stain stainless steel. Thus, solutions of this compound are sometimes used to test for the corrosion-resistance of stainless steel. Also, palladium(II) chloride is sometimes used in carbon monoxide detectors, as it can absorb large quantities of carbon monoxide gas.
  • Palladium hydride: This material consists of metallic palladium with a substantial quantity of hydrogen in its crystal lattice. At room temperature and atmospheric pressure, palladium can adsorb up to 900 times its own volume of hydrogen. Thus, palladium can store substantial quantities of hydrogen safely, and it is also useful for performing unusual chemical reactions. Details of how this adsorption process works are poorly understood.

Applications

  • Finely divided palladium forms a good catalyst for various chemical reactions, such as hydrogenation (addition of hydrogen atoms), dehydrogenation (removal of hydrogen atoms), and petroleum cracking (breaking of large, complex hydrocarbons to smaller, simpler ones). Also, palladium compounds are used as catalysts for reactions in which carbon-carbon bonds are formed.
  • The largest use of palladium today is in catalytic converters for automobiles. Much research is in progress to discover ways of replacing the much more expensive platinum with palladium in this application.
  • Palladium alloys are used in jewelry.
  • Palladium is one of two metals that can be alloyed with gold to produce "white gold." (Nickel can also be used.)
  • Like gold, palladium can be beaten into a thin leaf form, as thin as 100 nanometers (nm) (1/250,000 inch).
  • Since 1939, palladium itself has occasionally been used as a precious metal in jewelry, often as a replacement for platinum.[1]
  • Hydrogen readily diffuses through heated palladium. It thus provides a means of purifying the gas. Also, hydrogen dissolved in palladium is highly reactive, allowing it to be used in various chemical reductions.
  • Palladium and its alloys with silver are used as electrodes in multilayer ceramic capacitors.[2]
  • Palladium (sometimes alloyed with nickel) is used in connector platings in consumer electronics.
  • Palladium is also used in dentistry,[3] watch making, aircraft spark plugs, and the production of surgical instruments and electrical contacts.
  • This element is also used to make professional transverse flutes.
  • It is also used for palladium-hydrogen electrodes in electrochemical studies.
  • Palladium dichloride is sometimes used in carbon monoxide detectors and in tests for the corrosion-resistance of stainless steel, as noted above.

"Cold fusion"

In March 1989, researchers Stanley Pons and Martin Fleischmann announced that they had found a way to carry out a safe nuclear reaction at low temperatures in a tabletop experiment. The reaction, which was thought to involve the fusion of hydrogen nuclei, was dubbed "cold fusion." Palladium electrodes played an important role in this experiment. It was postulated that hydrogen atoms could be "squeezed" between the palladium atoms to help them fuse at lower temperatures than usually required for fusion to proceed. Since then, many other experiments have been conducted to test the possibility of cold fusion, but scientists remain divided on the issue of whether the observations are based on genuine cases of nuclear fusion.

See also

Notes

  1. ↑ Palladium Jewelry Retrieved December 9, 2007.
  2. ↑ Palladium Retrieved December 9, 2007.
  3. ↑ Palladium in Dentistry Retrieved December 9, 2007.

References
ISBN links support NWE through referral fees

  • Chang, Raymond. 2006. Chemistry, ninth ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
  • Cotton, F. Albert, and Wilkinson, Geoffrey. 1980. Advanced Inorganic Chemistry, 4th ed. New York: Wiley.
  • Greenwood, N.N. and Earnshaw, A. 1998. Chemistry of the Elements. 2nd Edition. Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
  • Palladium Los Alamos National Laboratory. Retrieved December 9, 2007.

External links

All links retrieved November 18, 2022.

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