| Identification | More | [Name]
Chromium | [CAS]
7440-47-3 | [Synonyms]
chrom
chrome
CHROMIUM
CR000060
CR004850
CR000170
CR000130
CR008010
CR000020
CR004200
CR000050
CR000110
CR000150
CR000180
CR004600
CR004700
CR000090
CR007920
CR000190
CR000160
CR004300
CR000191
CR000040
CR000120
CR000100
CR000140
CR000340
CR000030
CR000080
CR000360
CR007910
CR000070
CR007930
CR000025
CHROMERGE
Cr solution
N{2} <50ppM)
CHROME FLOUR
chromium atom
chromium fume
ChroMiuM sheet
19 MM AND DOWN
STANDARDCHROME
Chromium in B5
CHROMIUM METAL
nm 99 chromium
Chromium cubes
chrome(french)
CHROMIUM, LUMPS
Chromium in B20
ChroMiuM pieces
CHROMIUM POWDER
Chromium, flake
Chromium in B100
2-5% Nitric acid
elementalchromium
CHROMIUM STANDARD
Chromium granules
Chromium, 99.996%
chromium metallic
Chromium ICP Std.
ChroMiuM solution
Chromium, granular
CHROMIUMMETALDUSTS
ChromiumpelletsNmm
ChromiumpowderNmesh
Cr Target 99.95%
CHROMIUM CHIPS, 4N6
Chromiumpowder(99%)
CHROMIUMMETAL,CHIPS
CHROMIUM 99.5% LUMP
Chromium powder (Cr)
CHROMIUMMETAL,POWDER
MICRO-FISSUREDCHROME
CHROMIUM POWDER , 2N
CHROMIUM AA STANDARD
YEAST BOUND CHROMIUM
Chromium target (Cr)
CHROMIUM ICP STANDARD
ELECTROLYTIC CHROMIUM
Chromiumchips(99.99%)
ChroMiuM(VI) standard
LEAD 1,000PPM FOR ICP
ROSE BENGAL CHLORAMP.
LEAD 10,000PPM FOR ICP
Chromium chips (99.8%)
Chromium, Flake, 99.9%
Chromium power 22%-25%
Chromium flakes(99.3%)
Chromium pellets(99.7%)
Chromium chips, 99.995%
CHROMIUM 99.999% PIECES
Chromiumpellets(99.997%)
LITHIUM 1,000PPM FOR ICP
CHROMIUM POWDER 99+ 5 KG
Chromium chunks, 99.999%
ChromiumflakesNmmanddown
Chromiumlumpelectrolytic
CHROMIUM, PIECES, 99.99%
CHROMIUM, CHUNKS, 99.99+%
Chromium, pieces, 99.999%
Chromium powder, GR 99.9%
CHROMIUM POWDER 99+ 500 G
CHROMIUM POWDER -100 mesh
LANTHANUM 1,000PPM FOR ICP
CHROMIUM STANDARD SOLUTION
Chromium solution 1000 ppm
CHROMIUM (METAL) POWDER 99%
LANTHANUM 10,000PPM FOR ICP
Chromium, Chips 3-6mm Thick
CHROMIUM FLAKES: 99.3%, 2N3
Chromium solution 10 000 ppm
ChromiumchipsNmmthick 99,99%
electrolytic chromium powder
QUILON(R) L CHROMIUM COMPLEX
Chromium Rod/Φ2x100mm/99.95%
Chromium Rod/Φ3x100mm/99.95%
Chromium Rod/Φ5x100mm/99.95%
Chromium Rod/Φ8x100mm/99.95%
Chromium ISO 9001：2015 REACH
Chromium Rod/Φ10x100mm/99.95%
CHROMIUM, ANALYTICAL STANDARD
Chromium pieces, Electrolytic
Chromiumcrystallites(99.996%)
CHROMIUM PELLETS: 99.997%, 4N7
Chromium and compounds (as Cr)
Chromium crystallites (99.99%)
Chromium ion standard solution
Chromium powder, <40 μm, 99.9%
Chromium shots, 1-5 mm, 99.95%
Chromium pieces, 3-8 mm, 99.99%
CHROMIUM, AAS STANDARD SOLUTION
CHROMIUM AA STANDARD CONCENTRATE
ChroMiuM Metal, 100 Mesh, Powder
Chromium pellets, 1-3 mm, 99.95%
Chromium chunks, 1-10 mm, 99.95%
CHROMIUM, POWDER, -200 MESH, 99%
CHROMIUM SINGLE ELEMENT STANDARD
Chromium, irregular pieces, 99+%
Chromium+61000mg/L±2%inH20,250ml
CHROMIUM PLASMA EMISSION STANDARD
CHROMIUM METALLO-ORGANIC STANDARD
Chromium Sheet/1.0x50x50mm/99.95%
Chromium powder, -60 mesh, 99.99%
ChroMiuM piece,1-10MM(Low Oxygen)
COBALT:IRON SPUTTERTARGET (50:50)
Chromium powder, 99.5%, -100 mesh
Chromium, Chips 3-6mm Thick 99.99%
CHROMIUM CRYSTALLITES: 99.99%, 4N6
CHROMIUM, PLASMA STANDARD SOLUTION
Chromium powder, -200 mesh, 99.95%
Chromium powder, -10 mesh, 99.996%
Chromium Target/Φ25.4x3.2mm/99.99%
Chromium Target/Φ25.4x6.3mm/99.99%
Chromium Target/Φ50.8x3.2mm/99.99%
Chromium Target/Φ50.8x6.3mm/99.99%
Chromium Sheet/ 0.5x50x50mm/99.95%
CHROMIUM POWDER -100 MESH 99.5%
Chromium, lump, electrolytic, 99.5%
CHROMIUM ATOMIC ABSORPTION STANDARD
Chromium @500 μg/g in Biodiesel 100
3D printing spherical chrome powder
Chromium pieces, dia 1-3 mm, 99.99%
Chromium, pieces, 1 - 10 mm, 99.95%
Chromium foil, 1.5 mm thick, 99.95%
CHROMIUM AA SINGLE ELEMENT STANDARD
Chromium (IV) compounds - insoluble
CHROMIUM, CHIP, CA. 2MM THICK, 99.5%
CHROMIUM, OIL BASED STANDARD SOLUTION
Chromium granules, -4+7 mesh, 99.999%
Chromium Nanopowder, APS 70 nm, 99.9%
Chromium nanopowder, APS 50 nm, 99.5%
Chromium powder, -10+20 mesh, 99.996%
Chromium AA Standard,1000 ppm in HNO3
ChroMiuM Metal, 2 in. and Finer, Chips
CHROMIUM: 99.995%, POWDER, -300 MICRON
Chromium chips, thickness ~2 mm, 99.5%
CHROMIUM, CHIP, CA. 1MM THICK, 99.995%
CHROMIUM SINGLE ELEMENT PLASMA STANDARD
CHROMIUM, ORGANIC AAS STANDARD SOLUTION
Chromium@1000 μg/mL in 2-5% Nitric Acid
Chromium foil, thickness 0.5 mm, 99.99%
CHROMIUM STANDARD SOLUTION TRACEABLE TO
CHROMIUM ICP STANDARD TRACEABLE TO SRM F
QUILON? L chromium complex solution
CHROMIUM CRYSTALLITE 1 TO 15 MM 99.9&
QUILON(R) L chromium complex solution
Chromium (II) compounds (as Cr) inorganic
Chromium,99.996%,crystallites, 2 to 15 mm
Chromium (III) inorganic compounds (as Cr)
Chromium pieces, 1 to 25mm (0.04 to 1 in.)
Chromium chips, 99.995% trace metals basis
Chromium, crystallites, 2 to 15 mm, 99.996%
chromium coating quality balzers 0.7-3.5 mm
CHROMIUM COATING QUALITY UMICORE 0.7-3.5 MM
Chromium, irregular particles, <30 mm, 99.8%
Chromium chunks, 2 to 15mm (0.08 to 0.59 in.)
Chromium pieces, 3 to 12mm (0.12 to 0.47 in.)
CHROMIUM PLASMA EMISSION SPECTROSCOPY STANDARD
Chromium, plasma standard solution, Cr 10μg/mL
Chromium chunks, 2-15 mm (0.08-0.59in), 99.99%
CHROMIUM(III) AA/ICP CALIBRATION/CHECK STANDARD
Chromium plasma standard solution, Cr 1000μg/mL
Chromium pieces, 3-13mm, 99% trace metals basis
Chromium plasma standard solution, Cr 10000μg/mL
Chromiumpowder,-48mesh,99.95%(metalsbasis),99.8%
Chromiumpowder,APS<10micron,99.8%(metalsbasis)
Chromiumsinglecrystal;(100);nominal8-10mmdiax50mm
Chromium Oil based standard solution, Cr 1000μg/g
Chromium Wear Metal @5000 μg/g in 75 cSt Base oil
Chromium Wear Metal @1000 μg/g in 75 cSt Base oil
Chromium(III) atomic absorption standard solution
AChromium(III) atomic absorption standard solution
Chromium, Oil based standard solution, Cr 5000μg/g
Chromium, Reference Standard Solution, 1000ppm ±1%
Chromium cubes, Typically 6.35mm (0.25 in.) square
Chromium pieces, 2 to 3mm (0.08 to 0.12 in.) thick
CHROMIUM ATOMIC ABSORPTION SINGLE ELEMENT STANDARD
Chromium powder, -100 mesh, 99% trace metals basis
Chromium pieces, 1-25mm, 99.99% trace metals basis
Chromium pieces, irregular, 99% trace metals basis
Chromium chunks, 2-15mm, 99.995% trace metals basis
Chromium AA Standard@1000 μg/mL in 2-5% Nitric Acid
Standard solution for the determination of chromium
Chromium single element solution reference material
Chromium pieces, 2-3 mm (0.08-0.12in) thick, 99.995%
Chromium ICP Standard@1000 μg/mL in 2-5% Nitric Acid
Chromium powder, -60 mesh, 99.99% trace metals basis
Chromium powder, >=99% trace metals basis, -325 mesh
ChroMiuM powder, APS <10 Micron, 99.2% (Metals basis)
Chromium powder, -200 mesh, 99.95% trace metals basis
Standard solution for chromium impurity determination
Chromium ICP-MS Standard@100 μg/mL in 2-5% Nitric Acid | [EINECS(EC#)]
231-157-5 | [Molecular Formula]
Cr | [MDL Number]
MFCD00010944 | [Molecular Weight]
52 | [MOL File]
7440-47-3.mol |
| Chemical Properties | Back Directory | [Appearance]
Chromium may exist in one of three valence states in compounds, , , and . The most stable oxidation state is trivalent chromium; Hexavalent chromium is a less stable state. Chromium (element) blue-white to steel-gray, lustrous, brittle, hard, odorless solid. Elemental: | [Melting point ]
1857 °C (lit.) | [Boiling point ]
2672 °C (lit.) | [density ]
7.14 g/mL at 25 °C(lit.)
| [Fp ]
50 °F
| [storage temp. ]
no restrictions. | [solubility ]
reacts with dilute acid solutions | [form ]
powder
| [color ]
Silver-gray | [Specific Gravity]
7.2 | [Odor]
Odorless | [PH]
<1 (H2O, 20°C) | [Stability:]
Stable. Incompatible with carbonates, strong bases, mineral acids, lithium, sulfur dioxide, strong acids. | [Resistivity]
12.7 μΩ-cm, 20°C | [Water Solubility ]
Insoluble in water. | [Merck ]
13,2252 | [Exposure limits]
TLV-TWA: chromium metal 0.5 mg/m3
(ACGIH and MSHA), 1 mg/m3 (OSHA);
Cr(II) and Cr(III) compounds 0.5 mg/m3
(ACGIH); Cr(VI) compounds, water soluble
and certain water insoluble, 0.05 mg/m3
(ACGIH). | [History]
Chromium was discovered in 1797 by Vauquelin, who prepared
the metal the next year, chromium is a steel-gray, lustrous,
hard metal that takes a high polish. The principal ore is chromite
(FeCr2O4), which is found in Zimbabwe, Russia, South
Africa, Turkey, Iran, Albania, Finland, Democratic Republic
of Madagascar, the Philippines, and elsewhere. The U.S. has
no appreciable chromite ore reserves. Chromium is usually
produced by reducing the oxide with aluminum. Chromium
is used to harden steel, to manufacture stainless steel, and to
form many useful alloys. Much is used in plating to produce
a hard, beautiful surface and to prevent corrosion. Chromium
is used to give glass an emerald green color. It finds wide
use as a catalyst. All compounds of chromium are colored;
the most important are the chromates of sodium and potassium
(K2CrO4) and the dichromates (K2Cr2O7) and the potassium
and ammonium chrome alums, as KCr(SO4)2·12H2O.
The dichromates are used as oxidizing agents in quantitative
analysis, also in tanning leather. Other compounds are of industrial
value; lead chromate is chrome yellow, a valued pigment.
Chromium compounds are used in the textile industry
as mordants, and by the aircraft and other industries for anodizing
aluminum. The refractory industry has found chromite
useful for forming bricks and shapes, as it has a high melting
point, moderate thermal expansion, and stability of crystalline
structure. Chromium is an essential trace element for human
health. Many chromium compounds, however, are acutely or
chronically toxic, and some are carcinogenic. They should be
handled with proper safeguards. Natural chromium contains
four isotopes. Twenty other isotopes are known. Chromium
metal (99.95%) costs about $1000/kg. Commercial grade
chromium (99%) costs about $75/kg. | [CAS DataBase Reference]
7440-47-3(CAS DataBase Reference) | [IARC]
3 (Vol. Sup 7, 49) 1990 | [NIST Chemistry Reference]
Chromium(7440-47-3) | [EPA Substance Registry System]
7440-47-3(EPA Substance) |
| Safety Data | Back Directory | [Hazard Codes ]
F,C,Xn | [Risk Statements ]
R11:Highly Flammable.
R20/21/22:Harmful by inhalation, in contact with skin and if swallowed .
R34:Causes burns.
R40:Limited evidence of a carcinogenic effect.
R23:Toxic by inhalation. | [Safety Statements ]
S16:Keep away from sources of ignition-No smoking .
S26:In case of contact with eyes, rinse immediately with plenty of water and seek medical advice .
S36/37/39:Wear suitable protective clothing, gloves and eye/face protection .
S45:In case of accident or if you feel unwell, seek medical advice immediately (show label where possible) .
S36/37:Wear suitable protective clothing and gloves .
S27:Take off immediately all contaminated clothing . | [RIDADR ]
UN 2924 3/PG 2
| [WGK Germany ]
3
| [RTECS ]
GB4200000
| [Autoignition Temperature]
580°C | [TSCA ]
Yes | [HS Code ]
8112 21 90 | [HazardClass ]
4.1 | [PackingGroup ]
III | [Hazardous Substances Data]
7440-47-3(Hazardous Substances Data) | [IDLA]
250 mg Cr/m3 |
| Hazard Information | Back Directory | [General Description]
Very hard gray solid with a metallic luster. | [Reactivity Profile]
CHROMIUM(7440-47-3) reacts violently with NH4NO3, N2O2, Li, NO, KClO3, SO2 . Metal dusts when suspended in atmospheres of carbon dioxide may ignite and explode. | [Air & Water Reactions]
May be pyrophoric, as dust. Insoluble in water. | [Hazard]
Hexavalent chromium compounds are
questionable carcinogens and corrosive on tissue,
resulting in ulcers and dermatitis on prolonged contact. | [Potential Exposure]
Chromium metal is used in stainless and other alloy steels to impart resistance to corrosion, oxidation, and for greatly increasing the durability of metals; for chrome plating of other metals. | [Fire Hazard]
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated. | [First aid]
Move victim to fresh air. Call 911 or emergency medical service. Give artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. Administer oxygen if breathing is difficult. Remove and isolate contaminated clothing and shoes. In case of contact with substance, immediately flush skin or eyes with running water for at least 20 minutes. For minor skin contact, avoid spreading material on unaffected skin. Keep victim warm and quiet. Effects of exposure (inhalation, ingestion, or skin contact) to substance may be delayed. Ensure that medical personnel are aware of the material(s) involved and take precautions to protect themselves. Medical observation is recommended for 24 to 48 hours after breathing overexposure, as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consider administering a drug or other inhalation therapy. | [Shipping]
UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid. UN1759 Corrosive solids, n.o.s., Hazard class: 8; Labels: 8-Corrosive material, Technical Name required | [Incompatibilities]
Dust may be pyrophoric in air. Chromium metal (especially in finely divided or powder form) and insoluble salts reacts violently with strong oxidants, such as hydrogen peroxide, causing fire and explosion hazard. Reacts with diluted hydrochloric and sulfuric acids. Incompatible with alkalis and alkali carbonates | [Description]
Chromium as a metallic element was first discovered over 200
years ago, in 1797. But the history of chromium really began
several decades before this. In 1761, in the Beresof Mines of the
Ural Mountains, Johann Gottlob Lehmann obtained samples
of an orange-red mineral, which he called ‘Siberian red lead.’
He analyzed this mineral in 1766 and discovered that it contained
lead “mineralized with a selenitic spar and iron particles.”
The mineral he found was crocoite, a lead chromate
(PbCrO4). | [Waste Disposal]
Recovery and recycling is a viable alternative to disposal for chromium in plating wastes; tannery wastes; cooling tower blowdown water and chemical plant wastes. | [Isotopes]
There are 26 isotopes of the element chromium; four are stable and foundin nature, and the rest are artificially produced with half-lives from a few microsecondsto a few days. The four stable isotopes and their percentage of contribution to thetotal amount of chromium on Earth are as follows: 50Cr = 4.345%, 52Cr = 83.789%,53Cr = 9.501%, and 54Cr = 2.365%. Cr-50 is radioactive but has such a long halflife—1.8×10+17 years—that it is considered to contribute about 4% to the total amount ofchromium found on Earth. | [Origin of Name]
From the Greek word chroma or chromos, meaning “color,” because of
the many colors of its minerals and compounds. | [Occurrence]
Chromium is the 21st most common element found in the Earth’s crust, and chromiumoxide (Cr2O3) is the 10th most abundant of the oxide compounds found on Earth. It is notfound in a free metallic state.The first source of chromium was found in the mineral crocoite. Today it is obtained fromthe mineral chromite (FeCr2O4), which is found in Cuba, Zimbabwe, South Africa, Turkey,Russia, and the Philippines. Chromite is an ordinary blackish substance that was ignored formany years. There are different grades and forms of chromium ores and compounds, based onthe classification of use of the element. Most oxides of chromium are found mixed with othermetals, such as iron, magnesium, or aluminum.Astronauts found that the moon’s basalt rocks contain several times more chromium thanis found in basalt rocks of Earth. | [Characteristics]
Chromium is a hard, brittle metal that, with difficulty, can be forged, rolled, and drawn,unless it is in a very pure form, in which case the chromium is easier to work with. It is anexcellent alloying metal with iron. Its bright, silvery property makes it an appropriate metal toprovide a reflective, non-corrosive attractive finish for electroplating.Various compounds of chromium exhibit vivid colors, such as red, chrome green, andchromate yellow, all used as pigments. | [Uses]
Chromium is used in the manufacture ofits alloys, such as chrome-steel or chromenickel-steel. It is also used for chromeplatingof other metals, for tanning leather,and in catalysts. It occurs in chromite ores(FeO·Cr2O3). | [Uses]
In manufacture of chrome-steel or chrome-nickel-steel alloys (stainless steel), nonferrous alloys, heat resistant bricks for refractory furnaces. To greatly increase strength, hardness and resistance of metals to abrasion, corrosion and oxidation. For chrome plating of other metals; leather tanning; as pigment and mordant; wood preservative. Use of 51Cr as diagnostic aid see sodium chromate(VI). | [Uses]
The best-known use of chromium is for the plating of metal and plastic parts to producea shiny, reflective finish on automobile trim, household appliances, and other items where abright finish is considered attractive. It also protects iron and steel from corrosion.It is used to make alloys, especially stainless steel for cookware, and items for whichstrength and protection from rusting and high heat are important.Its compounds are used for high-temperature electrical equipment, for tanning leather, asa mordant (fixes the dyes in textiles so that they will not run), and as an antichalking agentfor paints.Some research has shown that, even though most chromium compounds are toxic, a smalltrace of chromium is important for a healthy diet for humans. A deficiency produces diabeteslike symptoms, which can be treated with a diet of whole-grain cereal, liver, and brewer’s yeast.Chromium’s most important radioisotope is chromium-51, which has a half-life of about27 days. It is used as a radioisotope tracer to check the rate of blood flowing in constrictedarteries.Some chromium compounds (e.g., chromium chloride, chromic hydroxide, chromic phosphate) are used as catalysts for organic chemical reactions.In 1960 the first ruby laser was made from a ruby crystal of aluminum oxide (Al2O3). Thesecrystals contain only a small amount of chromium, which stores the energy and is responsiblefor the laser action. A small amount of chromium found in the mineral corundum is responsible for the bright red color of the ruby gemstone. | [Definition]
chromium: Symbol Cr. A hard silverytransition element; a.n. 24;r.a.m. 52.00; r.d. 7.19; m.p. 1857°C;b.p. 2672°C. The main ore ischromite (FeCr2O4). The metal has abody-centred-cubic structure. It is extractedby heating chromite withsodium chromate, from whichchromium can be obtained by electrolysis.Alternatively, chromite can be heated with carbon in an electricfurnace to give ferrochrome, whichis used in making alloy steels. Themetal is also used as a shiny decorativeelectroplated coating and in themanufacture of certain chromiumcompounds.
At normal temperatures the metalis corrosion-resistant. It reacts withdilute hydrochloric and sulphuricacids to give chromium(II) salts.These readily oxidize to the more stablechromium(III) salts. Chromiumalso forms compounds with the +6oxidation state, as in chromates,which contain the CrO42- ion. The elementwas discovered in 1797 byVauquelin. | [Production Methods]
Chromium metal is prepared by reducing the ore in a blast furnace with carbon (coke) or silicon to form an alloy of chromium and iron called ferrochrome, which is used as the starting material for the many iron-containing alloys that employ chromium. Chromium to be used in iron-free alloys is obtained by reduction or electrolysis of chromium compounds.Chromiumisdif?culttoworkinthepuremetalform; it is brittle at low temperatures, and its high melting point makes it dif?cult to cast. | [Health Hazard]
The toxicity of chromium alloys and compoundsvaries significantly. Chromium metaldoes not exhibit toxicity. Divalent and trivalentcompounds of chromium have a loworder of toxicity. Exposure to the dusts ofchromite or ferrochrome alloys may causelung diseases, including pneumoconiosis andpulmonary fibrosis.
Among all chromium compounds onlythe hexavalent salts are a prime health hazard.Cr6+ is more readily taken up bycells, than any other valence state of themetal. Occupational exposure to these compoundscan produce skin ulceration, dermatitis,perforation of the nasal septa, and kidneydamage. It can induce hypersensitivityreactions of the skin and renal tubular necrosis.Examples of hexavalent salts are thechromates and dichromates of sodium, potassium,and other metals. The water-solublehexavalent chromium salts are absorbed intothe bloodstream through inhalation. Manychromium(VI) compounds are carcinogenic,causing lung cancers in animals and humans.The carcinogenicity may be attributed tointracellular conversion of Cr6+ to Cr3+,which is biologically more active. The trivalentCr3+ ion can bind with nucleic acid andthus initiate carcinogenesis.
Paustenbach et al. (1996) reported a casestudy on the uptake and elimination ofCr(VI) in drinking water on a male volunteerwho ingested 2 L/day of water containing2 mg/L Cr(VI) for 17 consecutivedays. The total chromium was measured inurine, plasma and red blood cells. The eliminationhalf-life in plasma was 36 hoursand the bioavailability was estimated as 2%.The steady-state chromium concentrations inurine and blood were achieved after sevendays of Cr(VI) ingestion. This study furthermorerevealed that Cr(VI) in drinkingwater at concentrations below 10 mg/L couldbe completely reduced to Cr(III) prior tosystemic distribution. In a follow-up study,Kergen et al. (1997) examined the magnitudeof absorption, distribution and excretionof Cr(VI) in drinking water in human volunteersfollowing oral exposures to singleand repeated doses at 5 and 10 mg Cr(VI)/L.The data obtained from this study indicatedthat virtually all (> 99.7%) of the ingestedCr(VI) was reduced to Cr(III) before enteringthe blood stream. No toxicity was observed.The endogenous reducing agents within theupper GI tract and the blood were attributedto reduce hexavalent chromium into its trivalentstate and, thus, prevented any systemicuptake of Cr(VI). Such reduction appearedto be effective even under the fasting conditions.
Wise et al. (2002) investigated the cytotoxicityand clastogenicity of both water-insolubleand water-soluble Cr(VI) compounds in primaryhuman bronchial fibroblasts and foundthat they were overall cytotoxic and genotoxicto human lung cells. Although the genotoxicmechanisms of both may be mediated bysoluble Cr(VI) ions the water-insoluble saltsapparently are the potent carcinogens comparedto the water-soluble salts (Wise et al.2004). Exposure to Cr(VI) enhanced the bindingof polycyclic aromatic hydrocarbons toDNA in human lung cells (Feng et al. 2003).Hexavalent chromium has been found to besynergistic to benzo a pyrene diol epoxide onmutagenesis and cell transformation.
The catalytic effect of iron on enhancingthe rate of reduction of Cr(VI) byhuman microsomes has been reported earlier(Myers and Myers 1998). Various formsof exogenous iron markedly enhanced bothliver and lung microsomal rates of Cr(VI)reduction. Small increases in intracellulariron have shown to cause large increases inin the rate and extent of Cr(VI) reduction.Thus, individuals exposed simultaneously toCr(VI) and agents that may increase intracellulariron could, therefore, be at potentiallygreater risk for toxicity and carcinogenicityof Cr(VI). | [Industrial uses]
An elementary metal, chromium (symbol Cr)is used in stainless steels, heat-resistant alloys,high-strength alloy steels, electrical-resistancealloys, wear-resistant and decorative electroplating,and, in its compounds, for pigments,chemicals, and refractories. The specific gravityis 6.92, melting point 1510°C, and boiling point2200°C. The color is silvery white with a bluishtinge. It is an extremely hard metal; the electrodepositedplates have a hardness of 9 Mohs.It is resistant to oxidation, is inert to HNO3, butdissolves in HCl and slowly in H2SO4. At temperaturesabove 816°C, it is subject to intergranularcorrosion.
Chromium occurs in nature only in combination.Its chief ore is chromite, from which itis obtained by reduction and electrolysis. It ismarketed for use principally in the form of masteralloys with iron or copper.Most pure chromium is used for alloyingpurposes such as the production of Ni–Cr orother nonferrous alloys where the use of thecheaper ferrochrome grades of metal is not possible.In metallurgical operations such as theproduction of low-alloy and stainless steels, thechromium is added in the form of ferrochrome,an electric-arc furnace product that is the formin which most chromium is consumed.
Its bright color and resistance to corrosion makechromium highly desirable for plating plumbingfixtures, automobile radiators and bumpers,and other decorative pieces. Unfortunately,chrome plating is difficult and expensive. Itmust be done by electrolytic reduction ofdichromate in H2SO4 solution. It is customary,therefore, to first plate the object with copper,then with nickel, and finally, with chromium. | [Veterinary Drugs and Treatments]
Chromium supplementation may be useful in the adjunctive treatment
of diabetes mellitus or obesity, particularly in cats; there is
controversy whether this treatment is beneficial. It does not appear
to be useful in dogs with diabetes mellitus. | [Carcinogenicity]
Exposure to chromium compounds over a prolonged period has been observed in manyepidemiologicalstudiestoenhancetheriskofcancerof the respiratory organs among the exposed. The relationshipbetweenemploymentinindustriesproducingchromium compounds from chromite ore and enhanced risk of lungcancer iswell established.There isagreement inseveral studies that long-term exposure to some chromium-based pigments enhance the risk of lung cancer. An association has alsobeenobservedbetweenexposuretochromicacidinhard plating and lung cancer, but that association is not strong. Somestudieshaveweaklyindicatedexcessesofcancerofthe GItract,buttheresultsareinconsistentandarenotcon?rmed inwell-designedstudies.Thereisnoindicationthatchromite ore does have an associated enhanced risk of cancer. Although it has not yet been identi?ed which chromium compound (or compounds) is (are) responsible for enhanced risk of cancer in respiratory organs, there is general agreementthatitisthechromium(6+)speciesthatareresponsible for the elevated cancer risks and that the chromium species are not. | [Environmental Fate]
Chromium is distributed to the air, water, and soil from natural and anthropogenic sources. The environmental fate of chromium is dependent on the oxidation state and solubility of the compound and the environmental conditions affecting reduction or oxidation, such as pH. Oxidizing conditions favor the formation of Cr(VI) compounds, particularly at higher temperatures, while reducing conditions favor the formation of Cr(III) compounds. Chemical manufacturing and natural gas, oil, and gas combustion are the primary sources of chromium in the atmosphere.Most of the chromium in air eventually ends up in water or soil. Electroplating, textile manufacturing, cooling water, and leather tanning are major sources of chromium in wastewater discharges to surface waters.
Chromium(III) is the predominant oxidation state of chromium in many soils. Cr(III) binds to soil and has low mobility. A lower soil pH favors the reduction of Cr(VI) to Cr(III). Runoff from soil and industrial processes may transport chromium to surface water.Cr(VI) compounds may leach into groundwater. The pH of the soil and aquatic environment is an important factor in chromium mobility, bioavailability, and toxicity. The chromate form predominates in most natural surface waters that are basic or neutral. The hydrochromate concentration increases in more acidic conditions. | [storage]
Color Code—Green (metal, not powder): Generalstorage may be used. Prior to working with chromium youshould be trained on its proper handling and storage. A regulated, marked area should be established where this chemical is handled, used, or stored in compliance with OSHAStandard 1910.1045. Store in tightly closed containers in acool, well-ventilated area. Chromium must be stored toavoid contact with strong oxidizers (such as chlorine, bromine, and fluorine) since violent reactions occur. Sources ofignition, such as smoking and open flames, are prohibitedwhere chromium is used, handled, or stored in a mannerthat could create a potential fire or explosion hazard | [Structure and conformation]
Two types of chromium crystals, α and β, are obtained depending on the growth method. The β type is semi-stable. It changes to a type above 800℃. The space lattice of β-Cr belongs to the hexagonal system, and its closely-packed hexagonal lattice has lattice constants of a=0.272 nm and c=0.442 nm. The space lattice of α-Cr belongs to the cubic system, and its body-centered cubic lattice has a lattice constant of a=0.28796 nm (18℃).
| [Toxicity evaluation]
Chromium enters the air, water, and soil mostly in the chromium(
III) and chromium(VI) forms. In air, chromium
compounds are present mostly as fine dust particles, which
eventually settle over land and water. Chromium can strongly
attach to sediment and soil, and only a small amount is
expected to dissolve in water and leach though the soil to
groundwater. Fish do not accumulate much chromium in their
bodies.
Most chromium exposure in the general population is
through ingestion of the chemical in food containing chromium(
II), although exposure is also possible as a result of
drinking contaminated well water, or living near uncontrolled
hazardous waste sites containing chromium or industries that
use chromium. Inhalation of chromium dust and skin contact
during use in the workplace are the main routes of occupational
exposure. |
| Questions And Answer | Back Directory | [Introduction]
Chromium occurs in the minerals chromite, FeO•Cr2O3 and crocoite, PbCrO4. The element is never found free in nature. Its abundance in earth's crust is estimated in the range 0.01% and its concentration in sea water is 0.3 μg/L. The element was discovered by Vaquelin in 1797.
The most important application of chromium is in the production of steel. High-carbon and other grades of ferro-chomium alloys are added to steel to improve mechanical properties, increase hardening, and enhance corrosion resistance. Chromium also is added to cobalt and nickel-base alloys for the same purpose.
Refractory bricks composed of oxides of magnesium, chromium, aluminum and iron and trace amounts of silica and calcium oxide are used in roofs of open hearths, sidewalls of electric furnaces and vacuum apparatus and copper converters. Such refractories are made in an arc furnace by fusing mixtures of magnesite and chrome ore.
Chromium coatings are applied on the surface of other metals for decorative purposes, to enhance resistance, and to lower the coefficient of friction. Radioactive chromium–51 is used as a tracer in the diagnosis of blood volume.
| [Chemical Properties]
Chromium occurs in oxidation states from Cr-2 through Cr+6 but exists mainly in the Cr(III) and Cr(VI) states; Cr(III) is the most stable. Hexavalent chromium compounds have varying physical and chemical properties. Most Cr(VI) compounds are solids; chromyl chloride is a liquid. Their properties include corrosion-resistance, durability, and hardness. Sodium dichromate is the most common chromium chemical from which other Cr(VI) compounds are produced. Examples of other Cr(VI) compounds include sodium chromate, potassium dichromate, potassium chromate, ammonium dichromate, and chromic oxide.
The reduction of Cr(VI) to Cr(III) and the oxidation of Cr(III) to Cr(VI) are important sampling considerations when determining Cr(VI) levels in workplace air (Ashley et al., 2003). Factors that affect the reduction of Cr(VI) or oxidation of Cr(III) include the presence of other compounds in the sample (e.g., iron), the ratio of Cr(VI) to Cr(III) concentrations in the sample, and solution pH. The reduction of Cr(VI) is favored in acidic conditions while Cr(VI) is stabilized in basic conditions.
| [Physical Properties]
Hard blue-white metal; body-centered cubic crystal; density 7.19 g/cm3; melts at 1,875°C; vaporizes at 2,199°C; electrical resistivity at 20°C, 12.9 microhm–cm; magnetic susceptibility at 20°C, 3.6x10–6 emu; standard electrode potential 0.71 V (oxidation state 0 to +3).
| [Reactions]
Chromium is oxidized readily in air forming a thin, adherent, transparent coating of Cr2O3.
Chromium forms both the chromous (Cr2+) and chromic (Cr3+) compounds that are highly colored.
Chromium metal reacts readily with dilute acids forming a blue Cr2+ (aq) solution with the evolution of hydrogen:
Cr + 2HCl → CrCl2 + H2
Chromium in metallic form and as Cr2+ ion are reducing agents. The Cr2+ reduces oxygen within minutes, forming violet Cr3+ ion:
4Cr2+(aq) + O2(g) + 4H+ (aq) → 4Cr3+ + 2H2O (l)
The standard redox potential for the overall reaction is 1.64V.
Cr3+ ion forms many stable complex ions. In the aqueous medium, it forms the violet Cr(H2O)63+ ion which is slightly basic. Chromium(III) ion is amphoteric, exhibiting both base and acid behavior.
Chromium reaction in an aqueous solution with a base produces a pale blue-violet precipitate having composition: Cr(H2O)3(OH)3.
Cr(H2O)63+ (aq) + 3OH– (aq) → Cr(H2O)3(OH)3 (s) + H2O
The above precipitate redissolves in excess base:
Cr(H2O)3(OH)3 (s) + H+ (aq) → Cr(H2O)4(OH)2+ (aq) + H2O
Chromium forms chromium(VI) oxide in which the metal is in +6 oxidation state. In acid medium it yields yellow chromate ion, CrO42–, and the redorange dichromate ion, Cr2O72–.
Chromium is oxidized in nitric, phosphoric or perchloric acid forming a thin oxide layer on its surface, thus making the metal even more unreactive to dilute acids.
Elemental chromium reacts with anhydrous halogens, hydrogen fluoride, and hydrogen chloride forming the corresponding chromium halides. At elevated temperatures in the range 600 to 700°C, chromium reacts with hydrogen sulfide or sulfur vapor, forming chromium sulfides.
Chromium metal reacts at 600 to 700°C with sulfur dioxide and caustic alkalis. It combines with phosphorus at 800°C. Reaction with ammonia at 850°C produces chromium nitride, CrN. Reaction with nitric oxide forms chromium nitride and chromium oxide.
5Cr + 3NO → 3CrN + Cr2O3
| [Production]
Chromium metal is produced by thermal reduction of chromium(III) oxide, Cr2O3 by aluminum, silicon or carbon. The starting material in all these thermal reduction processes are Cr2O3 which is obtained from the natural ore chromite after the removal of iron oxide and other impurities. In the aluminum reduction process, the oxide is mixed with Al powder and ignited in a refractory-lined vessel. The heat of reaction is sufficient to sustain the reaction at the required high temperature. Chromium obtained is about 98% pure, containing traces of carbon, sulfur and nitrogen.
Cr2O3 + 2Al→ 2Cr + Al2O3
The carbon reduction process is carried out at 1,300 to 1,400°C at low pressure in a refractory reactor:
Cr2O3 + 3C→ 2Cr + 3CO
The silicon reduction process is not thermally self-sustaining and, therefore, is done in an electric arc furnace:
2Cr2O3 + 3Si → 4Cr + 3 SiO2
Chromium may be produced from high-carbon ferrochrome by electrolytic process. Alternatively, the metal may be obtained by electrolysis of chromic acid, H2CrO4.
High-carbon ferrochromium alloys are made by the reduction of chromite ore with carbon in an arc furnace. On the other hand, low-carbon ferrochromium is obtained by silicon reduction of the ore. The carbon content of ferrochromium can be reduced further by heating high-carbon alloys with ground quartzite or by oxidation in vacuum and removal of carbon monoxide formed. Ferrochromium alloys are used in the manufacture of stainless steel.
| [Toxicity]
While chromium metal or trivalent chromium is not very toxic, hexavalent chromium (Cr6+) is carcinogenic and moderately toxic. Cr6+ is corrosive to skin and causes denaturation and precipitation of tissue proteins. Inhalation of Cr6+ dust or mist can cause perforation of the nasal septum, lung irritation, and congestion of the respiratory passsages. Chronic exposure may produce cancer of the respiratory tract.
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