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Chemistry: WebElements Periodic Table: Professional Edition: Chromium: key information
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Chroom chrome Chrom cromo Crômo cromo Krom
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Atomic number: 24
Atomic weight: 51.9961 (6)
CAS Registry ID: 7440-47-3
Group number: 6
Group name: (none)
Period number: 4
Here is a brief description of chromium.
Standard state: solid at 298 K
Colour: silvery metallic
This sample is from The Elements Collection
, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.
Chromium is steel-gray, lustrous, hard, metallic, and takes a high polish. Its compounds are toxic. It is found as chromite ore. Siberian red lead (crocoite, PrCrO4) is a chromium ore prized as a red pigment for oil paints.
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The picture above shows the result of burning ammonium dichromate, (NH4)2Cr2O7, containing pellets of mercuric thiocyanate (HgCNS). This is a large scale version of the indoor firework "Serpents in te grass". Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment. Improperly done, this reaction is dangerous! Select a movie icon to see the volcano and serpents (lighting not great - sorry).
cartoon included by kind permission of Nick Kim. Emerald is a form of beryl (a beryllium aluminium silicate) which is green because of the inclusion of a little chromium into the beryl crytal lattice in place of some of the aluminium ions. Similarly, traces of chromium incorporated into the crystal lattice of corundum (crystalline aluminium oxide, Al2O3) as a replacement for some of the Al3+ ions results in another highly coloured gem stone, in this case the red ruby.
Here is a brief summary of the isolation of chromium.
It is not normally necessary to make chromium in the laboratory as it is so readily available commercially. The most useful source of chromium commercially is the ore chromite, FeCr2O4. Oxidation of this ore by air in molten alkali gives sodium chromate, Na2CrO4 in which the chromium is in the +6 oxidation state. This is converted to the Cr(III) oxide Cr2O3 by extraction into water, precipitation, and reduction with carbon. The oxide is then further reduced with aluminium or silicon to form chromium metal.
Cr2O3 + 2Al 2Cr + Al2O3
2Cr2O3 + 3Si 4Cr + 3SiO2
Another kind of isolation is by electroplating processes. This involves the dissolution of Cr2O3 in sulphuric acid to give an electrolyte used for chromium electroplating.
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Chromium (Cr) has a wide range of uses in metals, chemicals, and refractories. It is one of the Nation's most important strategic and critical materials. Chromium use in iron, steel, and nonferrous alloys enhances hardenability and resistance to corrosion and oxidation. The use of chromium to produce stainless steel and nonferrous alloys are two of its more important applications. Other applications are in alloy steel, plating of metals, pigments, leather processing, catalysts, surface treatments, and refractories.
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Other Sources of Information
Boyle, E. H., Jr, Shields, D.J., and Wagner, L.A., 1993, Chromium availability in market economy countries and network flow model analysis of world chromium supply: U.S. Bureau of Mines Information Circular 9337, 131 p.
DeYoung, J.H., Jr., Lee, M.P., and Lipin, B.R., 1984, International strategic minerals inventory summary report -- Chromium: U.S. Geological Survey Circular 930-B, 41 p.
Papp, J.F., 1988, Superalloy recycling 1976-1986, in Reichman, D.N., Duhl, G.M., Antolovich, S., and Lund, C., Proceedings of 6th International Symposium on Superalloys, Champion, PA, September 18-22, 1988, Metall. Soc., AIME, Warrendale, PA, 1988, pp. 367-376.
Papp, J.F., 1991, Chromium, nickel, and other alloying elements in U.S.-produced stainless and heat-resisting steel: U.S. Bureau of Mines Information Circular 9275, 41 p.
Papp, J.F., 1993, Chromium, in Staff, Division of Mineral Commodities, Recycled metals in the United States: U.S. Bureau of Mines Special Publication, pp 9-11.
Papp, J.F., 1993, Chromium, in Staff, Branch of Industrial Minerals and Branch of Metals, Chemical industry applications of industrial minerals and metals: U.S. Bureau of Mines Special Publication, pp 35-40.
Papp, J.F., 1993, Chromium, in Staff, Branch of Metals and Branch of Industrial Minerals, Metal prices in the United States through 1991: U.S. Bureau of Mines Special Publication, pp 29-31.
Papp, J.F., 1994, Chromium life cycle study: U.S. Bureau of Mines Information Circular 9411, 41 p.
Papp, J.F., 1994, Chromite in Carr, D.D., Industrial Minerals and Rocks, 6th Edition, AIME, Society for Mining, Metallurgy, and Exploration, Littleton, CO, p. 209-228.
Papp, J.F., 1995, Chromium metal: U.S. Bureau of Mines Information Circular 9430, 64 p.
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- 延德Lv 61 decade ago
鉻的產地: Chromium is mined as chromite (FeCr2O4) ore. Chromium is obtained commercially by heating the ore in the presence of aluminium or silicon. Roughly half the chromite ore in the world is produced in South Africa. Kazakhstan, India and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa. Approximately 15 million tons of marketable chromite ore were produced in 2000, and converted into approximately 4 million tons of ferro-chrome with an approximate market value of 2.5 billion US dollars.Though native chromium deposits are rare, some native chromium metal has been discovered. The Udachnaya Mine in Russia produces samples of the native metal. This mine is a kimberlite pipe rich in diamonds, and the reducing environment so provided helped produce both elemental chromium and diamond.鉻的用途: Uses of chromium:In metallurgy, to impart corrosion resistance and a shiny finish: as an alloy constituent, e.g. in stainless steel, in chrome plating, in anodized aluminium (literally turning the surface of aluminium into ruby). As dyes and paints. Chromium(III) Oxide is a metal polish known as Green rouge. Chromium salts color glass an emerald green. Chromium is what makes a ruby red, and therefore is used in producing synthetic rubies. As a catalyst. Chromite is used to make molds for the firing of bricks. Chromium salts are used in the tanning of leather. Potassium dichromate is a chemical reagent, used in cleaning laboratory glassware and as a titrating agent. It is also used as a mordant (i.e. a fixing agent) for dyes in fabric. Chromium(IV) oxide (CrO2) is used to manufacture magnetic tape, where its higher coercivity than iron oxide tapes gives better performance. In well drilling muds as an anti-corrosive.Source(s): http://en.wikipedia.org/wiki/Chromium