chromium

[From French chrome. See chrome.]

For more information on chromium, visit Britannica.com.

A chemical element, Cr, atomic number 24, and atomic weight 51.996, which is the weighted average for several isotopes weighing 50 (4.31%), 52 (83.76%), 53 (9.55%), and 54 (2.38%). The orbital arrangement of the electrons is 1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁵, 4s¹. The stability of the half-filled d shell doubtless accounts for this rather unusual arrangement. In the crust of the Earth, chromium is the twenty-first element in abundance, which ranks it along with vanadium, zinc, nickel, and copper. Traces of chromium are present in the human body; in fact, it is essential to life. See also Periodic table.

The element was discovered in 1797 and isolated the following year by the French chemist L. N. Vauquelin. It was named chromium because of the many colors of its compounds. It occurs in nature largely as the mineral chromite (FeO · Cr₂O₃), which is a spinel, but the ore is usually contaminated with Al³⁺, Fe³⁺, Mn²⁺, and Mg²⁺. Smaller quantities are found as the yellow mineral crocoite (PbCrO₄).

As a transition metal, chromium exists in all oxidation states from 2− to 6+. The chemistry of its aqueous solutions, at least in the 3+ (chromic) state, is complicated by the fact that the compounds exist in many isomeric forms, which have quite different chemical properties.

Pure chromium metal has a bluish-white color, reflects light well, and takes a high polish. When pure, it is ductile, but even small amounts of impurities render it brittle. The metal melts at about 1900°C (3452°F) and boils at 2642°C (4788°F). Chromium shows a wide range of oxidation states; the compounds in which the metal is in a low oxidation state are powerful reducing agents, whereas those in which it shows a high oxidation state are strong oxidizing agents.

The bright color and resistance to corrosion make chromium highly desirable for plating plumbing fixtures, automobile radiators and bumpers, and other decorative pieces. Unfortunately, chrome plating is difficult and expensive. It must be done by electrolytic reduction of dichromate in sulfuric acid solution. This requires the addition of six electrons per chromium ion. This reduction does not take place in one step, but through a series of steps, most of which are not clearly understood. The current efficiency is low (maybe 12%), and the chromium plate contains microscopic cracks and other flaws, and so it does not adequately protect the metal under it from corrosion. It is customary, therefore, to first plate the object with copper, then with nickel, and finally, with chromium.

In alloys with iron, nickel, and other metals, chromium has many desirable properties. Chrome steel is hard and strong and resists corrosion to a marked degree. Stainless steel contains roughly 18% chromium and 8% nickel. Some chrome steels can be hardened by heat treatment and find use in cutlery; still others are used in jet engines. Nichrome and chromel consist largely of nickel and chromium; they have low electrical conductivity and resist corrosion, even at red heat, so they are used for heating coils in space heaters, toasters, and similar devices. Other important alloys are Hastelloy C (Cr, Mo, W, Fe, Ni), used in chemical equipment which is in contact with HCl, oxidizing acids, and hypochlorite. Stellite [Co, Cr, Ni, C, W (or Mo)], noted for its hardness and abrasion resistance at high temperatures, is used for lathes and engine valves, and Inconel (Cr, Fe, Ni) is used in heat treating and in corrosion-resistant equipment in the chemical industry.

Several chromium compounds are used as paint pigments—chrome oxide green (Cr₂O₃), chrome yellow (PbCrO₄), chrome orange (PbCrO₄ · PbO), molybdate orange (a solution of PbSO₄, PbCrO₄, and PbMoO₄), chrome green (a mixture of PbCrO₄ and Prussian blue), and zinc yellow (potassium zinc chromate). Several of these, particularly zinc yellow, are used to inhibit corrosion. The gems ruby, emerald, and alexandrite owe their colors to traces of chromium compounds.See also Paint.

Dichromates are widely used as oxidizing agents, as rust inhibitors on steel, and as wood preservatives. In the last application, they kill fungi, termites, and boring insects. The wood can still be painted and glued, and retains its strength. Other chromium compounds find use as catalysts, as drilling muds, and in photochemical reactions. The last are important in the printing industry. A metal plate is coated with a colloidal material (for example, glue, shellac, or casein) containing a dichromate. On exposure to strong light under a negative image, the dichromate is reduced to Cr³⁺, which reacts with the colloid, hardening it and making it resistant to removal by washing. The unexposed material is washed off, and the metal plate is etched with acid to give a printing plate.

Chromium is essential to life. A deficiency (in rats and monkeys) has been shown to impair glucose tolerance, decrease glycogen reserve, and inhibit the utilization of amino acids. It has also been found that inclusion of chromium in the diet of humans sometimes, but not always, improves glucose tolerance. Certain chromium(III) compounds enhance the action of insulin.

On the other hand, chromates and dichromates are severe irritants to the skin and mucous membranes, so workers who handle large amounts of these materials must be protected against dusts and mists. Continued breathing of the dusts finally leads to ulceration and perforation of the nasal septum. Contact of cuts or abrasions with chromate may lead to serious ulceration. Even on normal skin, dermatitis frequently results. Cases of lung cancer have been observed in plants where chromates are manufactured.

A metallic element that is a dietary essential. It forms an organic complex with nicotinic acid, known as the glucose tolerance factor, which facilitates the interaction of insulin with receptors on cell surfaces. Deficiency results in impaired glucose tolerance.

There is little evidence on which to base estimates of requirements; deficiency has been observed at intakes below 6 μg (0.12 μmol)/day; the US/Canadian adequate intake is 35 μg for men and 25 μg for women. High intakes of inorganic chromium salts (in excess of 1-2 mg/day) are associated with kidney and liver damage.

A metallic element essential in the diet for efficient carbohydrate metabolism. It improves the ability of insulin to convert glucose to glycogen (the main energy store in muscles).

Some body-builders use a salt of chromium (chromium picolinate) as an anabolic agent. They claim it burns fat and increases lean body mass by accelerating protein metabolism. They also claim that it may reduce the risk of cardiovascular diseases by increasing the proportion of high density lipoproteins in the blood. Studies in the USA have recently disproved these claims. Obesity experts state that chromium supplements do not speed up metabolism or burn fat. Nutritionists generally advise that you should get enough chromium from a well-balanced diet. Good sources of chromium include liver, meat, cheese, wholegrains, brewer's yeast, and wine.

A hard, brittle, metallic element with an atomic number of 24 and an atomic weight of 51.996. Chromium strongly resists corrosion and is used extensively to plate other metals and as an alloy to harden steel. Stainless steels are more than 10% chromium.

Brand names: Chroma-Pak®CRM®

Chemical formula:

Drug Forms:
• Chromium tablets or capsules (below)
• Chromium injection
• Chromium Picolinate Oral capsule
• Chromium Picolinate Oral tablet

Español:
• Tabletas o cápsulas de cromo
• Inyección de cromo
• Picolinato de cromo, Cápsula oral
• Picolinato de cromo, Tableta oral

Chromium tablets or capsules

What is chromium?

CHROMIUM (Chroma-Burn®, Chromax®, Chroma Slim®, Chroma Trim®, chromium picolinate, chromium nicotinate) is an essential nutrient. People require very small amounts of chromium in our diet daily to help our bodies use and process dietary sugars properly. Chromium appears to help the body use and process fats and proteins. Very few people develop true chromium deficiency. Most people should obtain their needed amount of chromium by eating a balanced, healthy diet. There is some information available that chromium supplements, when used under a prescriber's advice and monitoring, may be useful to help regulate blood sugar in adults with Type 2 diabetes or diabetes due to the use of corticosteroids. Chromium supplements do not appear to increase athletic performance or muscle mass in athletes nor do they decrease body fat in dieters. Chromium supplements are not officially endorsed by the FDA for these uses. Generic chromium picolinate and chromium nicotinate are available.

What should I tell my health care provider before I take this medicine?

It is important for you to tell your prescriber or health care professional or other health care professional that you are using chromium.

Talk to your health care provider BEFORE taking chromium supplements if you have any of the following conditions:
• dependent on intravenous nutrition (TPN) or liquid nutrition products for food
• diabetes mellitus or high blood sugar levels
• kidney disease
• an unusual or allergic reaction to chromium or other medicines, foods, dyes, or preservatives
• pregnant or trying to get pregnant
• breast-feeding

How should I use this medicine?

Chromium tablets and capsules should be taken orally (i.e., swallowed). It is recommended that these products be taken just prior to food or meals with a sip of water or other liquid. Follow the directions on the product label, or consult your health care professional for advice on how to take this supplement.

Contact your pediatrician or health care professional regarding the use of this medicine in children. Special care may be needed. Chromium should not be used in children without a prescription.

What if I miss a dose?

What drug(s) may interact with chromium?

• medications used to treat diabetes or to lower blood sugar

For many nutritional supplements, interactions with other medications are unknown. That is why you should always be careful when mixing chromium with traditional medications. If you take any other medications, consult with your health care professional prior to taking chromium.

Tell your prescriber or health care professional about all other medicines you are taking, including non-prescription medicines, nutritional supplements, or herbal products. Also tell your prescriber or health care professional if you are a frequent user of drinks with caffeine or alcohol, if you smoke, or if you use illegal drugs. These may affect the way your medicine works. Check with your health care professional before stopping or starting any of your medicines.

What should I watch for while taking chromium?

If you notice any changes in your physical or mental health while taking chromium, you should contact your health care provider.

Different brands of chromium might contain different amounts of active ingredient so be careful to use the same brand. It is recommended that you use a brand from a reliable manufacturer. Your health care professional or pharmacist can assist you in finding a chromium product.

Certain forms of chromium are not for human use. Do not take chromium products that are not labeled for use as nutritional supplements or medicine.

If you have diabetes and are taking chromium on the advice of your prescriber, visit your prescriber frequently for regular checks on your progress. Learn how to monitor blood sugar and urine ketones regularly. Check with your prescriber or health care professional if your blood sugar is high or low. Do not change your diabetic medicine doses without talking to your health care prescriber. Do not skip meals. If you are exercising much more than usual you may need extra snacks to avoid side effects caused by low blood sugar. If you have mild symptoms of low blood sugar, eat or drink something containing sugar at once and contact your prescriber or health care professional. It is wise to check your blood sugar to confirm that it is low. It is important to recognize your own symptoms of low blood sugar so that you can treat them quickly. Make sure family members know that you can choke if you eat or drink when you have serious symptoms of low blood sugar, such as seizures or unconsciousness. They must get medical help at once.

What side effects may I notice from using chromium?

Side effects that you should report to your prescriber or health care professional as soon as possible:
Symptoms of low blood sugar, for example:
• chills
• cold sweats
• confusion
• headache
• hunger
• irregular heartbeat or palpitations
• nausea or vomiting
• nervousness or anxious
• seizures (convulsions) or unusual movements
• shakiness
• unusual tiredness
• trembling
• vision changes

Other side effects that should be reported to your prescriber or health care professional as soon as possible:
• blurred vision
• drowsiness
• changes in emotions or mood
• change in urine amount, color, or frequency
• fever or chills
• muscle aches, cramps, or pains
• retaining fluid in your legs or abdomen
• skin rash or unusual skin reaction
• unusual weakness or muscle fatigue

Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
• mild stomach upset

Where can I keep my medicine?

Keep out of the reach of children.

Store at room temperature between 8 and 25 degrees C (46 and 77 degrees F); do not freeze. Throw away any unused medicine after the expiration date.

GENERAL INFORMATION REGARDING DIETARY SUPPLEMENTS:
Dietary supplements include amino acids, vitamins, minerals, herbs, and other plant-derived substances, and extracts of these substances. Products are easy to identify as they must state "Dietary Supplement" on the label. A "Supplement Facts" panel is provided on the label for most products. Supplements are not drugs and are not regulated like pharmaceuticals. You should note that rigid quality control standards are not required for dietary supplements. Differences in the potency and purity of these products can occur. Scientific data to support the use of a dietary supplement for a certain condition may not be available. This product is not intended to diagnose, treat, cure or prevent any disease.

The Food and Drug Administration suggests the following to help consumers protect themselves:
• Always read product labels and follow directions.
• Look for products containing ingredients with the "USP" notation. This indicates the manufacturer followed the standards of the US Pharmacopoeia.
• "Natural" doesn't mean a product is safe for humans to consume.
• Supplements produced or distributed by a nationally known food or drug company are more likely to be made under tight controls as these companies have standards in place for their other products. You can write to the company or manufacturer for more information about the conditions under which the products are made.

Last updated: 7/1/2002

Important Disclaimer: The drug information provided here is for educational purposes only. It is intended to supplement, not substitute for, the diagnosis, treatment and advice of a medical professional. This drug information does not cover all possible uses, precautions, side effects and interactions. It should not be construed to indicate that this or any drug is safe for you. Consult your medical professional for guidance before using any prescription or over the counter drugs.

Description

Chromium is a mineral that is essential to humans. It is found naturally in a variety of foods, and supplements are available in capsules or tablets. Supplements are prepared using a number of formulas, including chromium (III), chromium aspartate, chromium chloride, chromium citrate, chromium nicotinate, chromium picolinate, GTF chromium, and trivalent chromium.

General Use

Chromium supports the normal function of insulin, which is a hormone secreted by the pancreas. Insulin helps transport glucose from the bloodstream into liver, muscle, and fat cells. Once it is inside these cells, the sugar is metabolized into a source of energy. Insulin is also involved in regulating protein, fat, and catalytic enzyme processes. People with diabetes do not produce insulin (or produce very little) or their bodies cannot properly use the insulin that is produced. As a result, sugar builds up in the bloodstream, causing serious health effects. Numerous scientific studies have shown that chromium is useful in treating insulin resistance (metabolic syndrome) and diabetes. Diabetic peripheral neuropathy, a form of nerve damage that is a direct result of diabetes, is indirectly related to a lack of sufficient chromium.

Several studies have shown that chromium supplements may improve insulin sensitivity, and lower blood glucose and elevated body fat. In February 2004, the University of Pennsylvania School of Medicine began a comprehensive study of chromium as a therapy for insulin resistance. This condition occurs when the body fails to respond properly to the insulin it already produces. People who are insulin resistant may have the ability to overcome this problem by producing more insulin. However, if the body cannot produce sufficient amounts of insulin, glucose levels in the bloodstream rise, and type 2 diabetes ultimately occurs. It is estimated that up to 80 million Americans have insulin resistance.

A study conducted by Isala Clinics and University Hospital Groningen in the Netherlands, and released in 2003, showed that a daily dose of 1,000 micrograms of chromium significantly reduced blood sugar levels in people with poorly controlled type 2 diabetes who use insulin.

Chromium has also been used as an effective treatment for polycystic ovarian syndrome (PCOS), a hormonal condition affecting about two million American women. The condition can lead to infertility if untreated, and is associated with insulin resistance and type 2 diabetes. A study released in 2003 by the State University of New York at Stony Brook showed that insulin sensitivity increased an average of 35 percent after two months of daily treatment with 1,000 micrograms (μg) of chromium.

Through its involvement with insulin function, chromium plays an indirect role in lowering blood lipids. Studies suggest, but have not proven, that chromium supplementation can reduce the risk of cardiovascular (heart) disease in men, and may decrease total cholesterol and triglyceride levels. However, several studies contradict these claims. Studies in animals suggest chromium supplementation may reduce hypertension (high blood pressure). Lipid reduction is secondary to insulin regulation and control; therefore, persons whose insulin is well regulated and controlled may not achieve reduced heart disease risk by taking chromium supplements.

Chromium supplements in high doses—1,000 g or more a day—are sometimes used in weight loss and muscle development. However, a number of scientific studies have found that chromium supplements are not effective in these areas. In fact, precautions warn against chromium doses exceeding 1,000 g per day. Weight loss and muscle development are secondary to insulin regulation and control. Therefore, when insulin is well regulated and controlled, chromium may not impact weight loss or muscle development.

Preparations

A complete lack of chromium is rare, and the United States Food and Drug Administration (FDA) has not established recommended dietary allowances (RDA) for the mineral. However, national statistics on the prevalence of diabetes, heart disease, and obesity suggest that chromium deficiencies may be common. Chromium occurs naturally in meat, seafood, dairy products, eggs, whole grains, black pepper, and almonds. According to The PDR Family Guide to Natural Medicines and Healing Therapies, the usual chromium supplement dose for children ages seven and older and adults is 50–200 g a day in tablets or capsules. For persons with type 2 diabetes who are not taking insulin, doses from 200–1,000 g daily may be taken. However, persons should only take doses at these levels after consulting with a physician. Chromium should not be taken in doses exceeding 1,000 g a day. The cost of a bottle of 100 tablets or capsules (200 g) of chromium picolinate ranges from $5 to $10.

Precautions

Doses of 200–1,000 g of chromium should be taken only after consultation with a physician. Pregnant or breastfeeding women are advised to consult a physician before taking chromium supplements. Chromium should not be taken in doses exceeding 1,000 g a day. Increased dietary sugar may be associated with higher urinary excretion of chromium.

Side Effects

Several studies have noted occasional reports of irregular heartbeats with chromium use. Infrequently, chromium has been reported to cause such sleep pattern changes as insomnia and increased dream activity. Irritability has also been reported. In rare instances, persons may be allergic to a chromium formula. The symptoms of an allergic reaction include difficulty breathing, chest pain, hives, rash, and itchy or swollen skin. If this happens, the patient is advised to seek medical care immediately. High doses may also cause liver and kidney damage, or gastric irritation, although these side effects are rare.

Interactions

Persons who are taking antacids are advised to talk with a physician before taking chromium supplements. Studies in animals suggest that antacids, especially those containing calcium carbonate, may reduce the body's ability to absorb chromium. Studies have shown that chromium may enhance the effectiveness of drugs taken by people who have type 2 diabetes or insulin resistance. These drugs include glimepiride, glipizide, glyburide, insulin, and metformin. Individuals taking these drugs should discuss chromium supplementation with a physician because improved insulin function may necessitate medication dosage changes.

Resources

Books

Brown, Donald J. Herbal Prescriptions for Health and Healing: Your Everyday Guide to Using Herbs Safely and Effectively. Twin Lakes, WI: Lotus Press, 2003.

Evans, Gary. All About Chromium Picolinate: Frequently Asked Questions. Garden City Park, NY: Avery, 1999.

Icon Health Publications. Chromium Picolinate: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, CA: Icon Health Publications, 2003.

Kamen, Betty. The Chromium Connection: A lesson in Nutrition. Novato, CA: Nutrition Encounter Inc., 1995.

Passwater, Richard A. Chromium Picolinate. New York, NY: McGraw-Hill/Contemporary Books; Reprint Edition, 1995.

Periodicals

Biotech Week Editors and Staff. "Company Seeks FDA Approval of Health Claims for Chromium." Biotech Week (January 28, 2004): 308.

"Chromium." UC Berkeley Wellness Letter (July 2003): 3.

Drug Week Editors and Staff. "Chromium Picolinate May Benefit Patients with Insulin Resistance." Drug Week (December 26, 2003): 121.

Drug Week Editors and Staff. "Research: Lower Chromium Levels Linked to Increased Risk of Disease." Drug Week (April 2, 2004): 263.

Lamson, Davis W., and Steven M. Plaza. "The Safety and Efficacy of High-Dose Chromium. Alternative Medicine Review (June 2002): 218–236.

Lydic, Michael L., et al. "Effects of Chromium Supplementation on Insulin Sensitivity and Reproductive Function in Polycystic Ovarian Syndrome: A Pilot Study." Fertility and Sterility (Supplement 3) (September 2003): 45–46.

Volpe, Stella L., et al. "Effect of Chromium Supplementation and Exercise on Body Composition, Resting Metabolic Rate, and Selected Biochemical Parameters in Moderately Obese Women Following an Exercise Program." Journal of the American College of Nutrition (August 2001): 293–306.

Ward, Elizabeth M. "Top 10 Supplements for Men." Men's Health (December 2003): 106.

[Article by: Ken R. Wells]

A hard, brittle metal resistant to corrosion, workable when annealed, gray-white in color; used in alloys, esp. steel, and in plating.

A metallic element essential for efficient glucose metabolism. Chromium is readily available in a variety of foods, including liver, meat, cheese, wholegrains, brewer's yeast, and wine. Because chromium deficiency is rare, there is no Reference Nutrient Intake in the UK, but a safe daily intake is set at 25 μg.

A chemical element, atomic number 24, atomic weight 51.996, symbol Cr.

• c.-51 — a radioisotope of chromium having a half-life of 27.8 days; used to label red blood cells to determine red cell volume and red cell survival time. Symbol ⁵¹Cr. See also cr⁵¹ edta.
• c. nutritional deficiency — possibly causally related to the onset of diabetes mellitus in primates.
• c. trioxide — possibly carcinogenic in humans. See also chromate.

This article is about the element. For other uses, see Chromium (disambiguation).

vanadium ← chromium → manganese - ↑ Cr ↓ Mo 24Cr Periodic table
Appearance
silvery metallic
General properties
Name, symbol, number	chromium, Cr, 24
Element category	transition metal
Group, period, block	6, 4, d
Standard atomic weight	51.9961(6) g·mol−1
Electron configuration	[Ar] 3d5 4s1
Electrons per shell	2, 8, 13, 1 (Image)
Physical properties
Phase	solid
Density (near r.t.)	7.19 g·cm−3
Liquid density at m.p.	6.3 g·cm−3
Melting point	2180 K, 1907 °C, 3465 °F
Boiling point	2944 K, 2671 °C, 4840 °F
Heat of fusion	21.0 kJ·mol−1
Heat of vaporization	339.5 kJ·mol−1
Specific heat capacity	(25 °C) 23.35 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k at T/K 1656 1807 1991 2223 2530 2942
Atomic properties
Oxidation states	6, 5, 4, 3, 2, 1, -1, -2 (strongly acidic oxide)
Electronegativity	1.66 (Pauling scale)
Ionization energies (more)	1st: 652.9 kJ·mol−1
	2nd: 1590.6 kJ·mol−1
	3rd: 2987 kJ·mol−1
Atomic radius	128 pm
Covalent radius	139±5 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	AFM (rather: SDW[1])
Electrical resistivity	(20 °C) 125 nΩ·m
Thermal conductivity	(300 K) 93.9 W·m−1·K−1
Thermal expansion	(25 °C) 4.9 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 5940 m/s
Young's modulus	279 GPa
Shear modulus	115 GPa
Bulk modulus	160 GPa
Poisson ratio	0.21
Mohs hardness	8.5
Vickers hardness	1060 MPa
Brinell hardness	1120 MPa
CAS registry number	7440-47-3
Most stable isotopes
Main article: Isotopes of chromium
iso NA half-life DM DE (MeV) DP 50Cr 4.345% > 1.8×1017y εε - 50Ti 51Cr syn 27.7025 d ε - 51V γ 0.320 - 52Cr 83.789% 52Cr is stable with 28 neutrons 53Cr 9.501% 53Cr is stable with 29 neutrons 54Cr 2.365% 54Cr is stable with 30 neutrons
This box: view • talk • edit

Chromium (pronounced /ˈkroʊmiəm/, KROH-mee-əm) is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρωμα), meaning color, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead chromate) in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well.

Chromium was regarded with great interest because of its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium and nickel to form stainless steel. This application, along with chrome plating (electroplating with chromium) are currently the highest-volume uses of the metal. Chromium and ferrochromium are produced from the single commercially viable ore, chromite, by silicothermic or aluminothermic reaction or by roasting and leaching processes. Although trivalent chromium (Cr(III)) is required in trace amounts for sugar and lipid metabolism in humans and its deficiency may cause a disease called chromium deficiency, hexavalent chromium (Cr(VI)) is toxic and carcinogenic, so that abandoned chromium production sites need environmental cleanup.

Contents 1 Characteristics 1.1 Occurrence 1.2 Isotopes 2 Chemistry 2.1 Chromium(III) 2.2 Chromium(VI) 2.3 Other oxidation states 2.4 Passivation 2.5 Quintuple bond 3 Physical properties 4 History 5 Production 6 Applications 6.1 Metallurgy 6.2 Dye and pigment 6.3 Tanning 6.4 Refractory material 6.5 Other use 7 Biological role 8 Precautions 8.1 Environmental issues 9 See also 10 Notes 11 References 12 External links

Characteristics

Occurrence

Chromium is the 21st most abundant element in Earth's crust with an average concentration of 100 ppm.^[2] Chromium compounds are found in the environment, due to erosion of chromium-containing rocks and can be distributed by volcanic eruptions. The concentrations range in soil is between 1 and 3000 mg/kg, in sea water 5 to 800 µg/liter, and in rivers and lakes 26 µg/liter to 5.2 mg/liter.^[3] The relation between Cr(III) and Cr(VI) strongly depends on pH and oxidative properties of the location, but in most cases, the Cr(III) is the dominating species,^[3] although in some areas the ground water can contain up to 39 µg of total chromium of which 30 µg is present as Cr(VI).^[4]

Chromite ore

Chromium is mined as chromite (FeCr₂O₄) ore.^[5] About two-fifths of the chromite ores and concentrates in the world are produced in South Africa, while Kazakhstan, India, Russia, and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.^[6]

Though native chromium deposits are rare, some native chromium metal has been discovered.^[7][8] The Udachnaya Pipe in Russia produces samples of the native metal. This mine is a kimberlite pipe rich in diamonds, and the reducing environment helped produce both elemental chromium and diamond.^[9]

Isotopes

Main article: Isotopes of chromium

Naturally occurring chromium is composed of three stable isotopes; ⁵²Cr, ⁵³Cr and ⁵⁴Cr with ⁵²Cr being the most abundant (83.789% natural abundance). Nineteen radioisotopes have been characterized with the most stable being ⁵⁰Cr with a half-life of (more than) 1.8x10¹⁷ years, and ⁵¹Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 meta states.^[10]

⁵³Cr is the radiogenic decay product of ⁵³Mn. Chromium isotopic contents are typically combined with manganese isotopic contents and have found application in isotope geology. Mn-Cr isotope ratios reinforce the evidence from ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. Hence ⁵³Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system.^[11]

The isotopes of chromium range in atomic mass from 43 u (⁴³Cr) to 67 u (⁶⁷Cr). The primary decay mode before the most abundant stable isotope, ⁵²Cr, is electron capture and the primary mode after is beta decay.^[10] 53Cr has been posited as a proxy for atmospheric oxygen concentration.^[12]

Chemistry

Oxidation states of chromium[note 1][13]
−2	Na2[Cr(CO)5]
−1	Na2[Cr2(CO)10]
0	Cr(C6H6)2
+1	K3[Cr(CN)5NO]
+2	CrCl2
+3	CrCl3
+4	K2CrF6
+5	K3CrO8
+6	K2CrO4

Chromium is a member of the transition metals, in group 6. Chromium(0) has an electronic configuration of 4s¹3d⁵, due to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. The +1, +4 and +5 states are rare.

The following is the Pourbaix diagram for chromium in pure water, perchloric acid or sodium hydroxide:^[3][14]

Chromium(III)

The oxidation state +3 is the most stable, and a large number of chromium(III) compounds are known. Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid. The Cr³⁺ ion has a similar radius (0.63 Å) to the Al³⁺ ion (radius 0.50 Å), so they can replace each other in some compounds, such as in chrome alum and alum. When a trace amount of Cr³⁺ replaces Al³⁺ in corundum (aluminium oxide, Al₂O₃), the red-colored ruby is formed.

Chromium(III) chloride hexahydrate ([CrCl₂(H₂O)₄]Cl·2H₂O)

Chromium ions tend to form complexes; chromium ions in water are usually octahedrally coordinated with water molecules to form hydrates. The commercially available chromium(III) chloride hydrate is the dark green complex [CrCl₂(H₂O)₄]Cl, but two other forms are known: pale green [CrCl(H₂O)₅]Cl₂, and the violet [Cr(H₂O)₆]Cl₃. If water-free green chromium(III) chloride is dissolved in water then the green solution turns violet after some time, due to the substitution of water for chloride in the inner coordination sphere. This kind of reaction is also observed in chrome alum solutions and other water-soluble chromium(III) salts. The reverse reaction may be induced by heating the solution.

Chromium(III) hydroxide (Cr(OH)₃) is amphoteric, dissolving in acidic solutions to form [Cr(H₂O)₆]³⁺, and in basic solutions to form [Cr(OH)₆]³⁻. It is dehydrated by heating to form the green chromium(III) oxide (Cr₂O₃), which is the stable oxide with a crystal structure identical to that of corundum.^[15]

Chromium(III) chloride (CrCl₃)

Chromium(VI)

Chromium(VI) compounds are powerful oxidants, and, except the hexafluoride, contain oxygen as a ligand, such as the chromate anion (CrO₄²⁻) and chromyl chloride (CrO₂Cl₂).^[15]

Chromium(VI) is most commonly encountered in the chromate (CrO2−4) and dichromate (Cr₂O2−7) anions. Chromate is produced industrially by the oxidative roasting of chromite ore with calcium or sodium carbonate. The chromate and dichromate anions are in equilibrium:

2 CrO₄²⁻ + 2 H₃O⁺ → Cr₂O₇²⁻ + 3 H₂O

The dominant species is therefore, by the law of mass action, determined by the pH of the solution. The change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of potassium chromate. At yet lower pH values, further condensation to more complex oxyanions of chromium is possible.

Both the chromate and dichromate anions are strong oxidizing reagents at low pH:^[15]

Cr₂O₇²⁻ + 14 H₃O⁺ + 6 e⁻ → 2 Cr³⁺ + 21 H₂O (ε₀ = 1.33V)

However, they are only moderately oxidizing at high pH:^[15]

CrO₄²⁻ + 4 H₂O + 3 e⁻ → Cr(OH)³⁺ + 5 OH⁻ (ε₀ = −0.13V)

Chromium(VI) oxide

Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO₅) is formed, which can be stabilized as an ether adduct CrO₅·OR₂.^[15]

Chromic acid has the hypothetical structure H₂CrO₄. Neither chromic nor dichromic acid can be isolated, but their anions are found in a variety of compounds, the chromates and dichromates. The dark red chromium(VI) oxide CrO₃, the acid anhydride of chromic acid, is sold industrially as "chromic acid".^[15] It can be produced by mixing sulfuric acid with dichromate, and is an extremely strong oxidizing agent.

Sodium chromate

Other oxidation states

The oxidation state +5 is only realized in few compounds. The only binary compound is the highly volatile chromium(V) fluoride (CrF₅). This red solid has a melting point of 30°C and a boiling point of 117°C, and can be synthesized by reacting fluorine with chromium at 400°C and 200 bar pressure. The peroxochromate(V) is another example of the +5 oxidation state. Potassium peroxochromate (K₃[Cr(O₂)₄]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures. This red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.^[16]

Chromium(IV) compounds (in the +4 oxidation state) are slightly more stable than the chromium(V) compounds. The tetrahalides, CrF₄, CrCl₄, and CrBr₄, can be produced by reacting the trihalides (CrX₃) with excess amounts of the corresponding halogen at elevated temperatures. Most of the compounds are susceptible to disproportionation reactions and are not stable in water.

An example of a stable chromium(II) compound is the water-stable chromium(II) chloride, CrCl₂, which can be made by reduction of chromium(III) chloride with zinc. The resulting bright blue solution is only stable at neutral pH when the solution is very pure.^[15]

Passivation

Chromium metal left standing in air is passivated by oxygen, forming a thin protective oxide surface layer. This layer is a spinel structure only a few atoms thick. It is very dense, and prevents the diffusion of oxygen into the underlying material. This is in contrast to iron or plain carbon steels, where the oxygen migrates into the underlying material and causes rusting.^[17] The passivation can be increased by short contact with oxidizing acids like nitric acid. Passivated chromium is stable against acids. The opposite effect can be achieved by treatment with a strong reducing reactant that destroys the protective oxide layer on the metal. Chromium metal treated in this way readily dissolves in weak acids.^[15]

Chromium, unlike metals such as iron and nickel, does not suffer from hydrogen embrittlement. However, it does suffer from nitrogen embrittlement, reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.^[18]

Quintuple bond

Chromium compound determined experimentally to contain a Cr-Cr quintuple bond

Chromium is notable for its ability to form quintuple covalent bonds. The product of a reaction between chromium(I) and a hydrocarbon radical was shown via X-ray diffraction to contain a quintuple bond of length 183.51(4) pm (1.835 Å) joining the two central chromium atoms.^[19] Extremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.

Physical properties

Chromium is remarkable for its magnetic properties: it is the only elemental solid which shows antiferromagnetic ordering at room temperature (and below). Above 38 °C, it transforms into a paramagnetic state.^[1]

History

Crocoite (PbCrO₄)

Weapons found in burial pits dating from the late 3rd century BC Qin Dynasty of the Terracotta Army near Xi'an, China have been analyzed by archaeologists. Although buried more than 2,000 years ago, the ancient bronze tips of crossbow bolts and swords found at the site showed no sign of corrosion, because the bronze was coated with chromium.^[20]

Chromium came to the attention of westerners in the 18th century. On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the mineral was Crocoite (lead chromate) with a formula of PbCrO₄.^[21]

In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red lead mineral that had useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow pigment made from crocoite also became fashionable.^[21]

Ruby is colored by a small amount of chromium

In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He produced chromium oxide (CrO₃) by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven.^[22] He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald.^[21][23]

During the 1800s, chromium was primarily used as a component of paints and in tanning salts. At first, crocoite from Russia was the main source, but in 1827, a larger chromite deposit was discovered near Baltimore, United States. This made the United states the largest producer of chromium products till 1848 when large deposits of chromite where found near Bursa, Turkey.^[5]

Chromium is also known for its luster when polished. It is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by electroplating. Chromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.^[24]

Metal alloys now account for 85% of the use of chromium. The remainder is used in the chemical industry and refractory and foundry industries.

Production

World production trend of chromium

Approximately 4.4 million metric tons of marketable chromite ore were produced in 2000, and converted into ~3.3 million tons of ferro-chrome with an approximate market value of 2.5 billion United States dollars.^[25] The largest producers of chromium ore have been South Africa (44%) India (18%), Kazakhstan (16%) Zimbabwe (5%), Finland (4%) Iran (4%) and Brazil (2%) with several other countries producing the rest of less than 10% of the world production.^[25]

The two main products of chromium ore refining are ferrochromium and metallic chromium. For those products the ore smelter process differs considerably. For the production of ferrochromium, the chromite ore (FeCr₂O₄) is reduced in large scale in electric arc furnace or in smaller smelters with either aluminium or silicon in an aluminothermic reaction.^[26]

Chromium ore output in 2002^[25]

For the production of pure chromium, the iron has to be separated from the chromium in a two step roasting and leaching process. The chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms the stable Fe₂O₃. The subsequent leaching at higher elevated temperatures dissolves the chromates and leaves the insoluble iron oxide. The chromate is converted by sulfuric acid into the dichromate.^[26]

4 FeCr₂O₄ + 8 Na₂CO₃ + 7 O₂ → 8 Na₂CrO₄ + 2 Fe₂O₃ + 8 CO₂

2 Na₂CrO₄ + H₂SO₄ → Na₂Cr₂O₇ + Na₂SO₄ + H₂O

The dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.^[26]

Na₂Cr₂O₇ + 2 C → Cr₂O₃ + Na₂CO₃ + CO

Cr₂O₃ + 2 Al → Al₂O₃ + 2 Cr

Applications

Metallurgy

Decorative chrome plating on a motorcycle.

The strengthening effect of forming stable metal carbides at the grain boundaries and the strong increase in corrosion resistance made chromium an important alloying material for steel. The high speed tool steels contain between 3 and 5% chromium. An important stainless steel is 18/10 stainless, made from iron with 10% nickel and 18% chromium, is widely used for cookware and cutlery. For these applications, ferrochromium is added to the molten iron. Also nickel-based alloys increase in strength due to the formation of discrete, stable metal carbide particles at the grain boundaries. For example, Inconel 718 contains 18.6% chromium. Because of the excellent high temperature properties of these nickel superalloys, they are used in jet engines and gas turbines in lieu of common structural materials.^[27]

The relative high hardness and corrosion resistance of unalloyed chromium makes it a good surface coating. A thin layer of chromium is deposited on pretreated metallic surfaces by electroplating techniques. There are two deposition methods: Thin, below 1 µm thickness, layers are deposited by chrome plating, and are used for decorative surfaces. If wear-resistant surfaces are needed then thicker chromium layers of up to mm thickness are deposited. Both methods normally use acidic chromate or dichromate solutions. To prevent the energy consuming change in oxidation state, the use of Chromium(III) sulfate is under development, but for most applications, the established process is used.^[24]

In the chromate conversion coating process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc and cadmium. This passivation and the self healing properties by the chromate stored in the chromate conversion coating, which is capable to migrate to local defects, are the benefits of this coating method.^[28] Because of environmental and health regulations on chromates, alternative coating method are under development.^[29]

Anodizing of aluminium is another electrochemical process, which does not lead to the deposition of chromium, but uses chromic acid as electrolyte in the solution. During anodization, an oxide layer is formed on the aluminium. The use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.^[30] The high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium or at least a change to less toxic chromium(III) compounds.^[24]

Dye and pigment

School bus painted in Chrome yellow^[31]

The mineral crocoite (lead chromate PbCrO₄) was used as a yellow pigment shortly after its discovery. After a synthesis method became available starting from the more abundant chromite, Chrome yellow was, together with cadmium yellow, one of the most used yellow pigments. The pigment does not degrade in the light and has a strong color. The signaling effect of yellow was used for school buses in the United States and for Postal Service (for example Deutsche Post) in Europe. The use of chrome yellow declined due to environmental and safety concerns and was substituted by organic pigments or other lead-free alternatives.^[32] Other pigments based on chromium are, for example, the bright red pigment Chrome red, which is a basic lead chromate (PbCrO₄•Pb(OH)₂).^[32] Chrome green is a mixture of Prussian blue and chrome yellow, while the Chrome oxide green is Chromium(III) oxide.^[32]

Glass is colored green by the addition of chromium(III) oxide. This is similar to emerald, which is also colored by chromium.^[33] A red color is achieved by doping chromium(III) into the crystals of corundum, which are then called ruby. Therefore, chromium is used in producing synthetic rubies.^[34]

The toxicity of chromium(VI) salts is used in the preservation of wood. For example, chromated copper arsenate (CCA) is used in timber treatment to prevent wood from decay fungi, wood attacking insects, including termites, and marine borers.^[35] The formulations contain chromium based on the oxide CrO₃ between 35.3% and 65.5%. In the United States, 65,300 metric tons of CCA solution have been used in 1996.^[35]

Tanning

Chromium(III) salts, especially chrome alum and chromium(III) sulfate, are used in the tanning of leather. The chromium(III) stabilizes the leather by cross linking the collagen fibers within the leather.^[36] Chromium tanned leather can contain between 4 and 5% of chromium, which is tightly bound to the proteins.^[5]

Refractory material

The high heat resistivity and high melting point makes chromite and chromium(III) oxide a material for high temperature refractory applications, like blast furnaces, cement kilns, molds for the firing of bricks and as foundry sands for the casting of metals. In these applications, the refractory materials are made from mixtures of chromite and magnesite. The use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).^[26]

Other use

Several chromium compounds are used as catalyst. For example the Phillips catalysts for the production polyethylene are mixtures of chromium and silicon dioxide or mixtures of chromium and titanium and aluminium oxide.^[37] Chromium(IV) oxide (CrO₂) is a magnetic compound. Its ideal shape anisotropy, which imparted high coercivity and remanent magnetization, made it a compound superior to the γ-Fe₂O₃. Chromium(IV) oxide is used to manufacture magnetic tape used in high performance audio tape and standard audio cassette.^[38] Chromates can prevent corrosion of steel under wet conditions, and therefore chromates are added to the drilling muds.^[39] The long known influence of chromium uptake on diabetes conditions suggested the positive influence of dietary supplement containing chromium(III) also on healthy persons. For this reason, dietary supplement or slimming aid usually contain chromium(III) chloride, chromium(III) picolinate, chromium(III) polynicotinate or amino acid chelate, such as chromium(III) D-phenylalanine. The benefit of those supplements is still under investigation and is questioned by some studies.^[40][41]

• Chromium hexacarbonyl Cr(CO)₆ is used as a gasoline additive.^[42]
• Chromium(III) oxide is a metal polish known as green rouge.
• Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds. It is prepared in situ by dissolving potassium dichromate in concentrated sulfuric acid, which is then used to wash the apparatus. Sodium dichromate is sometimes used because of its higher solubility (5 g/100 ml vs. 20 g/100 ml respectively). 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.

Biological role

Trivalent chromium (Cr(III) or Cr³⁺) in trace amounts influences sugar and lipid metabolism in humans, and its deficiency is suspected to cause a disease called chromium deficiency.^[43] In contrast, hexavalent chromium (Cr(VI) or Cr⁶⁺) is very toxic and mutagenic when inhaled. Cr(VI) has not been established as a carcinogen when in solution, though it may cause allergic contact dermatitis (ACD).^[44]

The use of chromium-containing dietary supplements is controversial due to the complex effects of the used supplements.^[45] The popular dietary supplement chromium picolinate complex generates chromosome damage in hamster cells.^[46] In the United States the dietary guidelines for daily chromium uptake were lowered from 50-200 µg for an adult to 35 µg (adult male) and to 25 µg (adult female).^[47]

Precautions

Water insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.^[48] An actual investigation into hexavalent chromium release into drinking water was used as the plot-basis of the motion picture Erin Brockovich.

Because of the specific transport mechanisms, only limited amounts of chromium(III) enter the cells. Several in vitro studies indicated that high concentrations of chromium(III) in the cell can lead to DNA damage.^[49] Acute oral toxicity ranges between 1500 and 3300 µg/kg.^[50] The proposed beneficial effects of chromium(III) and the use as dietary supplements yielded some controversial results, but recent reviews suggest that moderate uptake of chromium(III) through dietary supplements poses no risk.^[49]

World Health Organization recommended maximum allowable concentration in drinking water for chromium (VI) is 0.05 milligrams per liter. Hexavalent chromium is also one of the substances whose use is restricted by the European Restriction of Hazardous Substances Directive.

The acute oral toxicity for chromium(VI) ranges between 50 and 150 µg/kg.^[50] In the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells. The chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also sulfate and phosphate ions enter the cell. The acute toxicity of chromium(VI) is due to its strong oxidational properties. After it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions. Hemolysis, renal and liver failure are the results of these damages. Aggressive dialysis can improve the situation.^[51]

The carcinogenity of chromate dust is known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.^[52][53] Three mechanisms have been proposed to describe the genotoxicity of chromium(VI). The first mechanism includes highly reactive hydroxyl radicals and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III). The second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the DNA. The last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.^[54]

Chromium salts (chromates) are also the cause of allergic reactions in some people. Chromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives. Contact with products containing chromates can lead to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as "chrome ulcers". This condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.^[55][56][56]

In some parts of Russia, pentavalent chromium was reported as one of the causes of premature dementia.^[57]

Environmental issues

As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial sites, now needing environmental cleanup and remediation per the treatment of brownfield land. Primer paint containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications.

See also

• Chromium compounds
• Chromium minerals
• Chromium(III) picolinate
• Chromium VI

Notes

1. ^ Common oxidation states are in bold.

References

1. ^ ^{a b} Fawcett, Eric (1988). "Spin-density-wave antiferromagnetism in chromium". Reviews of Modern Physics 60: 209. doi:10.1103/RevModPhys.60.209. 
2. ^ Emsley, John (2001). "Chromium". Nature's Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 495–498. ISBN 0198503407. 
3. ^ ^{a b c} Kotaś, J.; Stasicka, Z (2000). "Chromium occurrence in the environment and methods of its speciation". Environmental Pollution 107 (3): 263–283. doi:10.1016/S0269-7491(99)00168-2. PMID 15092973. 
4. ^ Gonzalez, A. R.; Ndung'u, K; Flegal, AR (2005). "Natural Occurrence of Hexavalent Chromium in the Aromas Red Sands Aquifer, California". Environmental Science and Technology 39 (15): 5505–5511. doi:10.1021/es048835n. PMID 16124280. 
5. ^ ^{a b c} National Research Council (U.S.). Committee on Biologic Effects of Atmospheric Pollutants (1974). Chromium. National Academy of Sciences. pp. 155. ISBN 9780309022170. http://books.google.de/books?id=ZZsrAAAAYAAJ. 
6. ^ Papp, John F. "Commodity Summary 2009: Chromium". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/chromium/mcs-2009-chrom.pdf. Retrieved 2009-03-17. 
7. ^ Fleischer, Michael (l982). "New Mineral Names". American Mineralogist 67: 854–860. http://www.minsocam.org/ammin/AM67/AM67_854.pdf. 
8. ^ http://www.mindat.org/min-1037.html Mindat with location data
9. ^ http://www.mindat.org/locentry-27628.html Mindat
10. ^ ^{a b} Georges, Audi (2003). "The NUBASE Evaluation of Nuclear and Decay Properties". Nuclear Physics A (Atomic Mass Data Center) 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001. 
11. ^ Birck, J. L.; Rotaru, M; Allegre, C (1999). "⁵³Mn-⁵³Cr evolution of the early solar system". Geochimica et Cosmochimica Acta 63 (23–24): 4111–4117. doi:10.1016/S0016-7037(99)00312-9. 
12. ^ Frei, R.; Gaucher; Poulton; Canfield, D. (2009). "Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes". Nature 461 (7261): 250. doi:10.1038/nature08266. PMID 19741707. Lay summary.  edit
13. ^ Schmidt, Max (1968). "VI. Nebengruppe" (in German). Anorganische Chemie II.. Wissenschaftsverlag. pp. 119–127. 
14. ^ Ignasi Puigdomenech, Hydra/Medusa Chemical Equilibrium Database and Plotting Software (2004) KTH Royal Institute of Technology, freely downloadable software at [1]
15. ^ ^{a b c d e f g h} Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils; (1985). "Chromium" (in German). Lehrbuch der Anorganischen Chemie (91–100 ed.). Walter de Gruyter. pp. 1081–1095. ISBN 3110075113. 
16. ^ Haxhillazi, Gentiana. "Preparation, Structure and Vibrational Spectroscopy of Tetraperoxo Complexes of Cr^V+, V^V+, Nb^V+ and Ta^V+ (PhD thesis, University of Siegen, 2003)". http://deposit.ddb.de/cgi-bin/dokserv?idn=969592612&dok_var=d1&dok_ext=pdf&fi.... 
17. ^ Wallwork, G. R. (1976). "The oxidation of alloys". Reports on the Progress Physics 39: 401–485. doi:10.1088/0034-4885/39/5/001. http://www.iop.org/EJ/article/0034-4885/39/5/001/rpv39i5p401.pdf. 
18. ^ National Research Council (U.S.). Committee on Coatings (1970). High-temperature oxidation-resistant coatings: coatings for protection from oxidation of superalloys, refractory metals, and graphite. National Academy of Sciences. ISBN 0309017696. http://books.google.co.jp/books?id=CGMrAAAAYAAJ&hl=en. 
19. ^ T. Nguyen, A. D. Sutton, M. Brynda, J. C. Fettinger, G. J. Long and P. P. Power (2005). "Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers". Science 310 (5749): 844–847. doi:10.1126/science.1116789. PMID 16179432. 
20. ^ Cotterell, Maurice. (2004). The Terracotta Warriors: The Secret Codes of the Emperor's Army. Rochester: Bear and Company. ISBN 159143033X. Page 102.
21. ^ ^{a b c} Jacques Guertin, James Alan Jacobs, Cynthia P. Avakian, (2005). Chromium (VI) Handbook. CRC Press. pp. 7–11. ISBN 9781566706087. 
22. ^ Vauquelin, Louis Nicolas (1798). "Memoir on a New Metallic Acid which exists in the Red Lead of Sibiria". Journal of Natural Philosophy, Chemistry, and the Art 3: 146. http://books.google.com/books?id=6dgPAAAAQAAJ. 
23. ^ van der Krogt, Peter. "Chromium". http://elements.vanderkrogt.net/elem/cr.html. Retrieved 2008-08-24. 
24. ^ ^{a b c} Dennis, J. K.; Such, T. E. (1993). "History of Chromium Plating". Nickel and Chromium Plating. Woodhead Publishing. pp. 9–12. ISBN 9781855730816. 
25. ^ ^{a b c} Papp, John F. "Mineral Yearbook 2002: Chromium". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/chromium/chrommyb02.pdf. Retrieved 2009-02-16. 
26. ^ ^{a b c d} Papp, John F; Lipin Bruce R. (2006). "Chromite". Industrial Minerals & Rocks: Commodities, Markets, and Uses (7th ed.). SME. ISBN 9780873352338. http://books.google.de/books?id=zNicdkuulE4C&pg=PA309. 
27. ^ Bhadeshia, H. K. D. H.. "Nickel-Based Superalloys". University of Cambridge. http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html. Retrieved 2009-02-17. 
28. ^ Edwards, Joseph (1997). Coating and Surface Treatment Systems for Metals. Finishing Publications Ltd. and ASM International. pp. 66–71. ISBN 0-904477-16-9. 
29. ^ Zhao, J. (2001). "Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3". Surface and Coatings Technology 140 (1): 51–57. doi:10.1016/S0257-8972(01)01003-9. http://www.chemistry.ohio-state.edu/~rmccreer/group/mccreery157.pdf. 
30. ^ Sprague, J. A.; Smidt, F. A. (1994). ASM Handbook: Surface Engineering. ASM International. ISBN 9780871703842. http://books.google.com/books?id=RGtsPjqUwy0C&pg=PA484. Retrieved 2009-02-17. 
31. ^ Worobec, Mary Devine; Hogue, Cheryl (1992). Toxic Substances Controls Guide: Federal Regulation of Chemicals in the Environment. Washington, D.C.: Bureau of National Affairs. p. 13. ISBN 9780871797520. http://books.google.de/books?id=CjWQ6_7AnI4C&pg=PA13. 
32. ^ ^{a b c} Gettens, Rutherford John (1966). Painting Materials: A Short Encyclopaedia. Courier Dover Publications. pp. 105-–106. ISBN 9780486215976. http://books.google.de/books?id=bdQVgKWl3f4C&pg=PA106. 
33. ^ Carstens, Harald (1973). "The red-green change in chromium-bearing garnets". Contributions to Mineralogy and Petrology 41 (3): 273–276. doi:10.1007/BF00371036. 
34. ^ Moss, S. C. (1964). "The chromium position in ruby". Zeitschrift fur Kristallographie 120: 359–363. http://rruff.geo.arizona.edu/doclib/zk/vol120/ZK120_359.pdf. 
35. ^ ^{a b} "Leaching of chromated copper arsenate wood preservatives: a review". Environmental Pollution 111 (1): 53–66. 2001. doi:10.1016/S0269-7491(00)00030-0. PMID 11202715. 
36. ^ Brown, E. M. (1997). "A Conformational Study of Collagen as Affected by Tanning Procedures". Journal of the American Leather Chemists Association 92: 225–233. 
37. ^ Weckhuysen, Bert M. (1999). "Olefin polymerization over supported chromium oxide catalysts". Catalysis Today 51 (2): 215–221. doi:10.1016/S0920-5861(99)00046-2. 
38. ^ Mallinson, John C. (1993). "Chromium Dioxide". The foundations of magnetic recording. Academic Press. ISBN 9780124666269. http://books.google.de/books?id=rNifWsBxnWkC&pg=PA32. 
39. ^ Garverick, Linda (1994). Corrosion in the Petrochemical Industry. ASM International. ISBN 9780871705051. http://books.google.de/books?id=qTfNZZRO758C&pg=PA278. 
40. ^ Heimbach, J.T. (2005). "Chromium: Recent Studies Regarding Nutritional Roles and Safety". Nutrition Today 40 (4): 189–-195. http://journals.lww.com/nutritiontodayonline/Abstract/2005/07000/Chromium__Recent_Studies_Regarding_Nutritional.13.aspx. 
41. ^ Vincent,, John B . (2003). "The Potential Value and Toxicity of Chromium Picolinate as a Nutritional Supplement, Weight Loss Agent and Muscle Development Agent". Sports Medicine:Volume 33 (3): 213–230. doi:10.2165/00007256-200333030-00004. 
42. ^ Patnaik, Pradyot (2003). "Chromium hexacarbonyl". Handbook of Inorganic Chemicals. McGraw-Hill Professional. pp. 222–223. ISBN 9780070494398. http://books.google.de/books?id=Xqj-TTzkvTEC&pg=PA222. 
43. ^ Mertz, Walter (1 April 1993). "Chromium in Human Nutrition: A Review". Journal of Nutrition 123 (4): 626–636. PMID 8463863. http://jn.nutrition.org/cgi/content/abstract/123/4/626. 
44. ^ "ToxFAQs: Chromium". Agency for Toxic Substances & Disease Registry, Centers for Disease Control and Prevention. February 2001. http://www.atsdr.cdc.gov/tfacts7.html. Retrieved 2007-10-02. 
45. ^ Cronin, Joseph R. (2004). "The Chromium Controversy". Alternative and Complementary Therapies 10 (1): 39–42. doi:10.1089/107628004772830393. 
46. ^ Stearns, D. M.; W; P; W (1 December 1995). "Chromium(III) picolinate produces chromosome damage in Chinese hamster ovary cells". Federation of American Societies for Experimental Biology 9 (15): 1643–1648. PMID 8529845. http://www.fasebj.org/cgi/content/abstract/9/15/1643. 
47. ^ Vincent, J. B. (2007). "Recent advances in the nutritional biochemistry of trivalent chromium". Proceedings of the Nutrition Society 63 (01): 41–47. doi:10.1079/PNS2003315. 
48. ^ Barceloux, Donald G.; Barceloux, Donald (1999). "Chromium". Clinical Toxicology 37 (2): 173–194. doi:10.1081/CLT-100102418. PMID 10382554. 
49. ^ ^{a b} Eastmond, David A.; MacGregor, JT; Slesinski, RS (2008). "Trivalent Chromium: Assessing the Genotoxic Risk of an Essential Trace Element and Widely Used Human and Animal Nutritional Supplement". Critical Reviews in Toxicology 38 (3): 173–190. doi:10.1080/10408440701845401. PMID 18324515. 
50. ^ ^{a b} Katz, Sidney A.; Salem, H (1992). "The toxicology of chromium with respect to its chemical speciation: A review". Journal of Applied Toxicology 13 (3): 217–224. doi:10.1002/jat.2550130314. PMID 8326093. 
51. ^ Dayan, A. D.; Paine, AJ (2001). "Mechanisms of chromium toxicity, carcinogenicity and allergenicity: Review of the literature from 1985 to 2000". Human & Experimental Toxicology 20 (9): 439–451. doi:10.1191/096032701682693062. PMID 11776406. 
52. ^ Newman, D. (1890). "A case of adeno-carcinoma of the left inferior turbinated body, and perforation of the nasal septum, in the person of a worker in chrome pigments". Glasgow Med J 33: 469–470. 
53. ^ Langard, Sverre (1990). "One Hundred Years of Chromium and Cancer: A Review of Epidemiological Evidence and Selected Case Reports". American Journal of Industrial Medicine 17 (2): 189–215. doi:10.1002/ajim.4700170205. PMID 2405656. 
54. ^ M. D., Cohen; Kargacin, B; Klein, CB; Costa, M (1993). "Mechanisms of chromium carcinogenicity and toxicity". Critical reviews in toxicology 23 (3): 255–81. doi:10.3109/10408449309105012. PMID 8260068. 
55. ^ "Chrome Contact Allergy". DermNet NZ. http://dermnetnz.org/dermatitis/chrome-allergy.html. 
56. ^ ^{a b} Basketter, David; Horev, L; Slodovnik, D; Merimes, S; Trattner, A; Ingber, A (2000). "Investigation of the threshold for allergic reactivity to chromium". Contact Dermatitis 44 (2): 70–74. doi:10.1034/j.1600-0536.2001.440202.x. PMID 11205406. 
57. ^ Chromium Toxicity on the Corrosion Doctors Web site maintained by Canadian Physical Chemist, Pierre R. Roberge, PhD, P.Eng. (access date 27 april 2009)

External links

Wikimedia Commons has media related to: Chromium

Look up chromium in Wiktionary, the free dictionary.

• ATSDR Case Studies in Environmental Medicine: Chromium Toxicity U.S. Department of Health and Human Services
• Los Alamos National Laboratory - Chromium
• WebElements.com – Chromium
• IARC Monograph "Chromium and Chromium compounds"
• International Chromium Development Association
• It's Elemental – The Element Chromium
• National Pollutant Inventory - Chromium (III) compounds fact sheet
• The Merck Manual – Mineral Deficiency and Toxicity
• National Institute for Occupational Safety and Health - Chromium Page

v • d • e Periodic table
H																															He
Li	Be																									B	C	N	O	F	Ne
Na	Mg																									Al	Si	P	S	Cl	Ar
K	Ca	Sc															Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr	Y															Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Uub	Uut	Uuq	Uup	Uuh	Uus	Uuo
Alkali metals Alkaline earth metals Lanthanoids Actinoids Transition metals Other metals Metalloids Other nonmetals Halogens Noble gases

v • d • e   Chromium compounds Cr(CO)6 · CrCl2 · CrCl3 · CrCl4 · CrF3 · CrN · Cr(NO3)3 · CrO · CrO2 · CrO3 · Cr2O3 · Cr2S3 · Cr2(SO4)3 · Cr3C2

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - krom

Nederlands (Dutch)
chromium

Français (French)
n. - chrome

Deutsch (German)
n. - Chrom

Ελληνική (Greek)
n. - (χημ.) χρώμιο

Italiano (Italian)
cromo

Português (Portuguese)
n. - cromo (m) (Quím.)

Русский (Russian)
хром

Español (Spanish)
n. - cromo

Svenska (Swedish)
n. - krom

中文（简体）(Chinese (Simplified))
铬

中文（繁體）(Chinese (Traditional))
n. - 鉻

한국어 (Korean)
n. - 원소기호 크로뮴

日本語 (Japanese)
n. - クロミウム

العربيه (Arabic)
‏(الاسم) معدن الكروميوم‏

עברית (Hebrew)
n. - ‮כרום‬

If you are unable to view some languages clearly, click here.

To select your translation preferences click here.