|
|
lustrous, metallic and
silvery with a gold tinge
 |
|
General
|
| Name, symbol, number |
nickel, Ni, 28 |
| Element category |
transition metal |
| Group, period, block |
10, 4, d |
| Standard atomic weight |
58.6934(2) g·mol−1 |
| Electron configuration |
[Ar] 4s1 3d9 |
| Electrons per shell |
2, 8, 17, 1 (Image) |
|
Physical properties
|
| Phase |
solid |
| Density (near r.t.) |
8.908 g·cm−3 |
| Liquid density at m.p. |
7.81 g·cm−3 |
| Melting point |
1728 K
(1453 °C, 2651 °F) |
| Boiling point |
3186 K
(2732 °C, 5275 °F) |
| Heat of fusion |
17.48 kJ·mol−1 |
| Heat of vaporization |
377.5 kJ·mol−1 |
| Specific heat capacity |
(25 °C) 26.07 J·mol−1·K−1 |
Vapor pressure
| P/Pa |
1 |
10 |
100 |
1 k |
10 k |
100 k |
| at T/K |
1783 |
1950 |
2154 |
2410 |
2741 |
3184 |
|
|
Atomic properties
|
| Crystal structure |
face-centered cubic |
| Oxidation states |
4[1], 3, 2, 1 [2], -1
(mildly basic oxide) |
| Electronegativity |
1.91 (Pauling scale) |
Ionization energies
(more) |
1st: 737.1 kJ·mol−1 |
| 2nd: 1753.0 kJ·mol−1 |
| 3rd: 3395 kJ·mol−1 |
| Atomic radius |
124 pm |
| Covalent radius |
124±4 pm |
| Van der Waals radius |
163 pm |
|
Miscellaneous
|
| Magnetic ordering |
ferromagnetic |
| Electrical resistivity |
(20 °C) 69.3 nΩ·m |
| Thermal conductivity |
(300 K) 90.9 W·m−1·K−1 |
| Thermal expansion |
(25 °C) 13.4 µm·m−1·K−1 |
| Speed of sound (thin rod) |
(r.t.) 4900 m·s−1 |
| Young's modulus |
200 GPa |
| Shear modulus |
76 GPa |
| Bulk modulus |
180 GPa |
| Poisson ratio |
0.31 |
| Mohs hardness |
4.0 |
| Vickers hardness |
638 MPa |
| Brinell hardness |
700 MPa |
| CAS registry number |
7440-02-0 |
|
Most stable isotopes
|
|
|
|
References
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|
|
Nickel (pronounced /ˈnɪkəl/) is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature. Its use has been traced as far back as 3500 BC, but it was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially mistook its ore for a copper mineral. Its most important ore minerals are laterites, including limonite and garnierite, and pentlandite. Major production sites include Sudbury region in Canada, New Caledonia and Russia. The metal is corrosion-resistant, finding many uses in alloys, as a plating, in the manufacture of coins, magnets and common household utensils, as a catalyst for hydrogenation, and in a variety of other applications. Enzymes of certain life-forms contain nickel as an active center making the metal essential for them.
Characteristics
Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are magnetic at or near room temperature. It belongs to the transition metals and is hard and ductile. It occurs most often in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel galena.[3] Nickel is commonly found in iron meteorites as the alloys kamacite and taenite. Similar to the elements chromium, aluminium and titanium, nickel is a very reactive element, but is slow to react in air at normal temperatures and pressures due to the formation of a protective oxide surface. Due to its permanence in air and its slow rate of oxidation, it is used in coins, for plating metals such as iron and brass, for chemical apparatus, and in certain alloys such as German silver.
Nickel is chiefly valuable for the alloys it forms, especially many superalloys, and particularly stainless steel. Nickel is also a naturally magnetostrictive material, meaning that in the presence of a magnetic field, the material undergoes a small change in length.[4] In the case of nickel, this change in length is negative (contraction of the material), which is known as negative magnetostriction and is on the order of 50 ppm.
The most common oxidation state of nickel is +2 with several Ni complexes known. It is also thought that a +6 oxidation state may exist, however, this has not been demonstrated conclusively. The unit cell of nickel is a face centered cube with a lattice parameter of 0.352 nm giving a radius of the atom of 0.125 nm.[5]
History
Because the ores of nickel are easily mistaken for ores of silver, understanding of this metal and its use dates to relatively recent times. However, the unintentional use of nickel is ancient, and can be traced back as far as 3500 BC. Bronzes from what is now Syria had contained up to 2% nickel.[6] Further, there are Chinese manuscripts suggesting that "white copper" (cupronickel, known as baitung) was used there between 1700 and 1400 BC. This Paktong white copper was exported to Britain as early as the 17th century, but the nickel content of this alloy was not discovered until 1822.[7]
In medieval Germany, a red mineral was found in the Erzgebirge (Ore Mountains) which resembled copper ore. However, when miners were unable to extract any copper from it they blamed a mischievous sprite of German mythology, Nickel (similar to Old Nick) for besetting the copper. They called this ore Kupfernickel from the German Kupfer for copper.[8][9][10][11] This ore is now known to be nickeline or niccolite, a nickel arsenide. In 1751, Baron Axel Fredrik Cronstedt was attempting to extract copper from kupfernickel and obtained instead a white metal that he named after the spirit which had given its name to the mineral, nickel.[12] In modern German, Kupfernickel or Kupfer-Nickel designates the alloy cupronickel.
In the United States, the term "nickel" or "nick" was originally applied to the copper-nickel Indian cent coin introduced in 1859. Later, the name designated the three-cent coin introduced in 1865, and the following year the five-cent shield nickel appropriated the designation, which has remained ever since. Coins of pure nickel were first used in 1881 in Switzerland.[9][13]
After its discovery the only source for nickel was the rare Kupfernickel, but from 1824 on the nickel was obtained as byproduct of cobalt blue production. The first large scale producer of nickel was Norway, which exploited nickel rich pyrrhotite from 1848 on. The introduction of nickel in steel production in 1889 increased the demand for nickel and the nickel deposits of New Caledonia, which were discovered in 1865, provided most of the world's supply between 1875 and 1915. The discovery of the large deposits in the Sudbury Basin, Canada in 1883, in Norilsk-Talnakh , Russia in 1920 and in the Merensky Reef, South Africa in 1924 made large-scale production of nickel possible.[7]
Occurrence
- See also: Ore genesis, Category:Nickel minerals
Widmanstätten pattern showing the two forms of Nickel-Iron, Kamacite and Taenite, in an octahedrite meteorite
The bulk of the nickel mined comes from two types of ore deposits. The first are laterites where the principal ore minerals are nickeliferous limonite: (Fe, Ni)O(OH) and garnierite (a hydrous nickel silicate): (Ni, Mg)3Si2O5(OH). The second are magmatic sulfide deposits where the principal ore mineral is pentlandite: (Ni, Fe)9S8.
In terms of supply, the Sudbury region of Ontario, Canada, produces about 30 percent of the world's supply of nickel. The Sudbury Basin deposit is theorized to have been created by a meteorite impact event early in the geologic history of Earth. Russia contains about 40% of the world's known resources at the Norilsk deposit in Siberia. The Russian mining company MMC Norilsk Nickel obtains the nickel and the associated palladium for world distribution. Other major deposits of nickel are found in New Caledonia, France, Australia, Cuba, and Indonesia. Deposits found in tropical areas typically consist of laterites which are produced by the intense weathering of ultramafic igneous rocks and the resulting secondary concentration of nickel bearing oxide and silicate minerals. Recently, a nickel deposit in western Turkey had been exploited, with this location being especially convenient for European smelters, steelmakers and factories. The one locality in the United States where nickel was commercially mined is Riddle, Oregon, where several square miles of nickel-bearing garnierite surface deposits are located. The mine closed in 1987.[14][15] In 2005, Russia was the largest producer of nickel with about one-fifth world share closely followed by Canada, Australia and Indonesia, as reported by the British Geological Survey.
Based on geophysical evidence, most of the nickel on Earth is postulated to be concentrated in the Earth's core. Kamacite and taenite are naturally occurring alloys of iron and nickel. For kamacite the alloy is usually in the proportion of 90:10 to 95:5 although impurities such as cobalt or carbon may be present, while for taenite the nickel content is between 20% and 65%. Kamacite and taenite occur in nickel-iron meteorites.
Applications
Nickel superalloy jet engine (
RB199) turbine blade
Nickel is used in many industrial and consumer products, including stainless steel, magnets, coinage, rechargeable batteries, electric guitar strings and special alloys. It is also used for plating and as a green tint in glass. Nickel is pre-eminently an alloy metal, and its chief use is in the nickel steels and nickel cast irons, of which there are many varieties. It is also widely used in many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminium, lead, cobalt, silver, and gold [16]
The amounts of nickel used for various applications are 60% used for making nickel steels, 14% used in nickel-copper alloys and nickel silver, 9% used to make malleable nickel, nickel clad, Inconel and other superalloys, 6% used in plating, 3% use for nickel cast irons, 3% in heat and electric resistance alloys, such as Nichrome, 2% used for nickel brasses and bronzes with the remaining 3% of the nickel consumption in all other applications combined.[17][18] In the laboratory, nickel is frequently used as a catalyst for hydrogenation, most often using Raney nickel, a finely divided form of the metal alloyed with aluminium which adsorbs hydrogen gas. Nickel is often used in coins, or occasionally as a substitute for decorative silver. The American 'nickel' five-cent coin is 75% copper and 25% nickel. The Canadian nickel minted at various periods between 1922-81 was 99.9% nickel, and was magnetic.[19] Various other nations have historically used and still use nickel in their coinage.
Nickel is also used in fire assay as a collector of platinum group elements, as it is capable of full collection of all 6 elements, in addition to partial collection of gold. This is seen through the nature of nickel as a metal, as high throughput nickel mines may run PGE recovery (primarily platinum and palladium), such as Norilsk in Russia and the Sudbury Basin in Canada.
Extraction and purification
Nickel is recovered through extractive metallurgy. Most sulfide ores have traditionally been processed using pyrometallurgical techniques to produce a matte for further refining. Recent advances in hydrometallurgy have resulted in recent nickel processing operations being developed using these processes. Most sulfide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction.
Nickel is extracted from its ores by conventional roasting and reduction processes which yield a metal of >75% purity. Final purification of nickel oxides is performed via the Mond process, which increases the nickel concentrate to >99.99% purity[20]. This process was patented by L. Mond and was used in South Wales in the 20th century. Nickel is reacted with carbon monoxide at around 50 °C to form volatile nickel carbonyl. Any impurities remain solid while the nickel carbonyl gas passes into a large chamber at high temperatures in which tens of thousands of nickel spheres, called pellets, are constantly stirred. The nickel carbonyl decomposes, depositing pure nickel onto the nickel spheres. Alternatively, the nickel carbonyl may be decomposed in a smaller chamber at 230 degrees Celsius to create fine nickel powder. The resultant carbon monoxide is re-circulated through the process. The highly pure nickel produced by this process is known as carbonyl nickel. A second common form of refining involves the leaching of the metal matte followed by the electro-winning of the nickel from solution by plating it onto a cathode. In many stainless steel applications, 75% pure nickel can be used without further purification depending on the composition of the impurities.
Nickel sulfide ores undergo flotation (differential flotation if Ni/Fe ratio is too low) and then are smelted. After producing the nickel matte, further processing is done via the Sherritt-Gordon process. First copper is removed by adding hydrogen sulfide, leaving a concentrate of only cobalt and nickel. Solvent extraction then efficiently separates the cobalt and nickel, with the final nickel concentration >99%.
Compounds
Nickel(II) sulfate is produced in large quantities by dissolving nickel metal or oxides in sulfuric acid. This compound is useful for electroplating nickel.
Four halides are known to form nickel compounds, these are nickel(II) fluoride, chloride, bromide, and iodide. Nickel(II) chloride is produced analogously by dissolving nickel residues in hydrochloric acid. Tetracarbonylnickel (Ni(CO)4), discovered by Ludwig Mond,[21] is a homoleptic complex of nickel with carbon monoxide. Having no net dipole moment, intermolecular forces are relatively weak, allowing this compound to be liquid at room temperature. Carbon monoxide reacts with nickel metal readily to give this compound; on heating, the complex decomposes back to nickel and carbon monoxide. This behavior is exploited in the Mond process for generating high-purity nickel.
Tetracoordinate nickel(II) takes both tetrahedral and square planar geometries. This is in contrast with the other group 10 elements, which tend to exist as square planar complexes. Bis(cyclooctadiene)nickel(0) is a useful intermediate in organometallic chemistry due to the easily displaced cod ligands. Nickel(III) oxide is used as the cathode in many rechargeable batteries, including nickel-cadmium, nickel-iron, nickel hydrogen, and nickel-metal hydride, and used by certain manufacturers in Li-ion batteries.[22]
Isotopes
Naturally occurring nickel is composed of 5 stable isotopes; 58Ni, 60Ni, 61Ni, 62Ni and 64Ni with 58Ni being the most abundant (68.077% natural abundance). 62Ni is the most stable known nuclide of all the existing elements, even exceeding the stability of 56Fe. 18 radioisotopes have been characterised with the most stable being 59Ni with a half-life of 76,000 years, 63Ni with a half-life of 100.1 years, and 56Ni with a half-life of 6.077 days. All of the remaining radioactive isotopes have half-lives that are less than 60 hours and the majority of these have half-lives that are less than 30 seconds. This element also has 1 meta state.
Nickel-56 is produced in large quantities in type Ia supernovae and the shape of the light curve of these supernovae corresponds to the decay via beta radiation of nickel-56 to cobalt-56 and then to iron-56. Nickel-59 is a long-lived cosmogenic radionuclide with a half-life of 76,000 years. 59Ni has found many applications in isotope geology. 59Ni has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. Nickel-60 is the daughter product of the extinct radionuclide 60Fe (half-life = 1.5 Myr). Because the extinct radionuclide 60Fe had such a long half-life, its persistence in materials in the solar system at high enough concentrations may have generated observable variations in the isotopic composition of 60Ni. Therefore, the abundance of 60Ni present in extraterrestrial material may provide insight into the origin of the solar system and its early history. Nickel-62 has the highest binding energy per nucleon of any isotope for any element (8.7946 Mev/nucleon). [23] Isotopes heavier than 62Ni cannot be formed by nuclear fusion without losing energy. Nickel-48, discovered in 1999, is the most proton-rich heavy element isotope known. With 28 protons and 20 neutrons 48Ni is "double magic" (like 208Pb) and therefore unusually stable [24].
The isotopes of nickel range in atomic weight from 48 u (48-Ni) to 78 u (78-Ni). Nickel-78's half-life was recently measured to be 110 milliseconds and is believed to be an important isotope involved in supernova nucleosynthesis of elements heavier than iron.[25]
Biological role
Nickel plays numerous roles in the biology of microorganisms and plants, though they were not recognized until the 1970s.[26][27] In fact urease (an enzyme which assists in the hydrolysis of urea) contains nickel. The NiFe-hydrogenases contain nickel in addition to iron-sulfur clusters. Such [NiFe]-hydrogenases characteristically oxidise H2. A nickel-tetrapyrrole coenzyme, F430, is present in the methyl coenzyme M reductase which powers methanogenic archaea. One of the carbon monoxide dehydrogenase enzymes consists of an Fe-Ni-S cluster.[28] Other nickel-containing enzymes include a class of superoxide dismutase[29] and a glyoxalase.[30]
Toxicity
Exposure to nickel metal and soluble compounds should not exceed 0.05 mg/cm³ in nickel equivalents per 40-hour work week. Nickel sulfide fume and dust is believed to be carcinogenic, and various other nickel compounds may be as well.[31][32] Nickel carbonyl, [Ni(CO)4], is an extremely toxic gas. The toxicity of metal carbonyls is a function of both the toxicity of a metal as well as the carbonyl's ability to give off highly toxic carbon monoxide gas, and this one is no exception. It is explosive in air.[33]
Sensitized individuals may show an allergy to nickel affecting their skin, also known as dermatitis. Nickel is an important cause of contact allergy, partly due to its use in jewellery intended for pierced ears.[34] Nickel allergies affecting pierced ears are often marked by itchy, red skin. Many earrings are now made nickel-free due to this problem. The amount of nickel which is allowed in products which come into contact with human skin is regulated by the European Union. In 2002 researchers found amounts of nickel being emitted by 1 and 2 Euro coins far in excess of those standards. This is believed to be due to a galvanic reaction.[35]
It was voted Allergen of the Year in 2008 by the American Contact Dermatitis Society.[36]
Metal value
The market price of nickel surged throughout 2006 and the early months of 2007; as of April 5, 2007, the metal was trading at 52,300 USD/tonne or 1.47 USD/oz.[37] The price subsequently fell dramatically from these peaks, and as of 19 January 2009 the metal was trading at 10,880 USD/tonne.[37]
The US nickel coin contains 0.04 oz (1.25 g) of nickel, which at the April 2007 price was worth 6.5 cents, along with 3.75 grams of copper worth about 3 cents, making the metal value over 9 cents. Since the face value of a nickel is 5 cents, this made it an attractive target for melting by people wanting to sell the metals at a profit. However, the United States Mint, in anticipation of this practice, implemented new interim rules on December 14, 2006, subject to public comment for 30 days, which criminalize the melting and export of cents and nickels.[38] Violators can be punished with a fine of up to $10,000 and/or imprisoned for a maximum of five years.
As of June 24, 2009 the melt value of a U.S. nickel is $0.0363145 which is less than the face value.[39]
References
- ^ M. Carnes et al. (2009). "A Stable Tetraalkyl Complex of Nickel(IV)". Angewandte Chemie International Edition 48: 3384. doi:10.1002/anie.200804435.
- ^ S. Pfirrmann et al. (2009). "A Dinuclear Nickel(I) Dinitrogen Complex and its Reduction in Single-Electron Steps". Angewandte Chemie International Edition 48: 3357. doi:10.1002/anie.200805862.
- ^ National Pollutant Inventory - Nickel and compounds Fact Sheet
- ^ UCLA - Magnetostrictive Materials Overview
- ^ Callister, William D. (2007). Materials Science and Engineering: An Introduction (7th ed.). John Wiley & Sons. ISBN 978-0-471-73696-7.
- ^ Rosenberg, Samuel J. (1968). Nickel and Its Alloys. National Bureau of Standards. http://handle.dtic.mil/100.2/ADA381960.
- ^ a b McNeil, Ian (1990). "The Emergence of Nickel". An Encyclopaedia of the History of Technology. Taylor & Francis. pp. 96–100. ISBN 9780415013062.
- ^ Chambers Twentieth Century Dictionary, p888, W&R Chambers Ltd, 1977.
- ^ a b Baldwin, W. H. (1931). "The story of Nickel. I. How "Old Nick's" gnomes were outwitted.". Journal of Chemical Education 8: 1749.
- ^ Baldwin, W. H. (1931). "The story of Nickel. II. Nickel comes of age.". Journal of Chemical Education 8: 1954.
- ^ Baldwin, W. H. (1931). "The story of Nickel. III. Ore, matte, and metal.". Journal of Chemical Education 8: 2325.
- ^ Weeks, Mary Elvira (1932). "The discovery of the elements: III. Some eighteenth-century metals". Journal of Chemical Education 9: 22.
- ^ Molloy, Bill (2001-11-08). "Trends of Nickel in Coins - Past, Present and Future". The Nickel Institute. http://www.nidi.org/index.cfm/ci_id/160.htm. Retrieved on 2008-11-19.
- ^ "The Nickel Mountain Project". Ore Bin 15 (10): 59–66. 1953. http://www.oregongeology.com/sub/publications/OG/OBv15n10.pdf.
- ^ "Environment Writer: Nickel". National Safety Council. 2006. http://www.environmentwriter.org/resources/backissues/chemicals/nickel.htm. Retrieved on 2009-01-10.
- ^ Davis, Joseph R. (2000). "Uses of Nickel". ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys. ASM International. pp. 7–13. ISBN 9780871706850. http://books.google.de/books?id=IePhmnbmRWkC.
- ^ Kuck, Peter H.. "Mineral Commodity Summaries 2006: Nickel". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/nickel/mcs-2008-nicke.pdf. Retrieved on 2008-11-19.
- ^ Kuck, Peter H.. "Mineral Yearbook 2006: Nickel". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/nickel/myb1-2006-nicke.pdf. Retrieved on 2008-11-19.
- ^ "Industrious, enduring–the 5-cent coin". Royal Canadian Mint. 2008. http://www.mint.ca/store/mint/learn/circulation-currency-1100028. Retrieved on 2009-01-10.
- ^ Mond L, Langer K, Quincke F (1890). "Action of carbon monoxide on nickel". Journal of the Chemical Society 57: 749–753. doi:10.1039/CT8905700749.
- ^ Mond L, Langer K, Quincke F (1890). "Action of carbon monoxide on nickel". Journal of the Chemical Society 57: 749–753. doi:10.1039/CT8905700749.
- ^ http://www.greencarcongress.com/2008/12/imara-corporati.html
- ^ "The Most Tightly Bound Nuclei". http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin2.html#c1. Retrieved on 2008-11-19.
- ^ W., P. (October 23, 1999). "Twice-magic metal makes its debut - isotope of nickel". Science News. http://www.findarticles.com/p/articles/mi_m1200/is_17_156/ai_57799535. Retrieved on 2006-09-29.
- ^ Castelvecchi, Davide (2005-04-22). "Atom Smashers Shed Light on Supernovae, Big Bang". http://skyandtelescope.com/news/article_1502_1.asp. Retrieved on 2008-11-19.
- ^ Astrid Sigel, Helmut Sigel and Roland K.O. Sigel, ed (2008). Nickel and Its Surprising Impact in Nature. Metal Ions in Life Sciences. 2. Wiley. ISBN 978-0-470-01671-8.
- ^ Hausinger, R. P. (1987). "Nickel utilization by microorganisms". Microbiol Review 51 (1): 22–42. http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=373090&blobtype=pdf.
- ^ Jaouen, G. (2006). Bioorganometallics: Biomolecules, Labeling, Medicine. Wiley-VCH: Weinheim.
- ^ Szilagyi, R. K.; Bryngelson, P. A.; Maroney, M. J.; Hedman, B.; Hodgson, K. O.; Solomon, E. I. (2004). "S K-Edge X-ray Absorption Spectroscopic Investigation of the Ni-Containing Superoxide Dismutase Active Site: New Structural Insight into the Mechanism". Journal of the American Chemical Society 126 (10): 3018–3019. doi:10.1021/ja039106v.
- ^ Thornalley, P. J. (2003). "Glyoxalase I--structure, function and a critical role in the enzymatic defence against glycation". Biochemical Society Transactions 31: 1343–1348. doi:10.1042/BST0311343. http://www.biochemsoctrans.org/bst/031/bst0311343.htm.
- ^ KS Kasprzak, FW Sunderman Jr, K Salnikow. Nickel carcinogenesis. Mutation Research. 2003 December 10;533(1-2):67-97. PubMed
- ^ JK Dunnick, MR Elwell, AE Radovsky, JM Benson, FF Hahn, KJ Nikula, EB Barr, CH Hobbs. Comparative Carcinogenic Effects of Nickel Subsulfide, Nickel Oxide, or Nickel Sulfate Hexahydrate Chronic Exposures in the Lung. Cancer Research. 1995 November 15;55(22):5251-6. PubMed
- ^ http://msds.chem.ox.ac.uk/NI/nickel_carbonyl.html
- ^ Thyssen JP, Linneberg A, Menné T, Johansen JD (2007). "The epidemiology of contact allergy in the general population—prevalence and main findings". Contact Dermatitis 57 (5): 287–99. doi:10.1111/j.1600-0536.2007.01220.x. PMID 17937743. http://www.blackwell-synergy.com/doi/full/10.1111/j.1600-0536.2007.01220.x.
- ^ Nestle, O.; Speidel, H.; Speidel, M. O. (2002). "free abstract High nickel release from 1- and 2-euro coins". Nature 419: 132. doi:10.1038/419132a. http://www.nature.com/nature/journal/v419/n6903/abs/419132a.html free abstract.
- ^ "Nickel Named 2008 Contact Allergen of the Year". http://www.nickelallergyinformation.com/2008/06/nickel-named-2008-contact-alle.htm. Retrieved on 2009-06-06.
- ^ a b "LME nickel price graphs". London Metal Exchange. http://www.lme.co.uk/nickel_graphs.asp. Retrieved on 2009-06-06.
- ^ United States Mint Moves to Limit Exportation & Melting of Coins, The United States Mint, press release, December 14, 2006
- ^ "United States Circulating Coinage Intrinsic Value Table". Coininflation.com. http://www.coinflation.com/. Retrieved on 2009-06-06.
External links
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