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About Chromium

Chromium Bohr

When French chemist Louis Nicolas Vauquelin first received a sample of Siberian red lead in 1797, the mineral--known today as crocoite--had been in use as a pigment for over three decades, but its chemical composition had remained a subject of dispute. Vauquelin resolved the debate when he was able to isolate a new metallic element, chromium, from the sample, a discovery he reported in the scientific literature the following year. The process he used to isolate the metal had produced a variety of vibrantly colored solutions and compounds, and it was due to this that Vauquelin’s colleagues had suggested the element be named from chroma, Greek for “color”. Vauquelin went on to detect traces of chromium in precious gems such as rubies and emeralds, and to hypothesize correctly that chromium gave these gems their brilliant colors.

The earliest uses of chromium exploited its compounds. Lead chromate, the main compound in crocoite, was used to produce a pigment called “chrome yellow”, a color well known due to its widespread use for school busses in the United States and postal vehicles in some European countries. Use of actual lead chromate has declined significantly due to toxicity concerns, but the color is still used, replicated using less toxic alternatives. Viridian, a green pigment produced from chromium (III) oxide, is not toxic and is still used widely in ceramics and glassware. Other chromium (III) compounds have been used in tanning since the early 19th century, as a reaction between chromium and the collagen fibers stabilizes leather.

Chromium compounds continue to find applications in industry. A number of chemical processes use chromium-containing catalysts, including the production of polyethylene, the most common form of plastic. Chromium salts are used in wood preservatives, and chromium provides color to synthetic rubies and emeralds. The first laser was built using a synthetic ruby. Both chromite and chromium (III) oxide can withstand high temperatures, and are frequently used as refractory materials such as brick molds and foundry sands. Chromium (IV) oxide is magnetic, and is used to manufacture the magnetic tape used in audio cassettes.

The vast majority of chromium is used in metalworking, either as a component of alloys or in various types of surface treatments. Chromium strengthens and imparts corrosion resistance to alloys. High-speed tool steels include small percentages of chromium for added strength, while higher percentages of chromium produce stainless steel. Additionally, nickel-based superalloys derive increased strength from the inclusion of chromium; these alloys are frequently found in devices such as jet engines that require materials to be stable and strong at very high temperatures. Chromium can be applied to metal surfaces via electroplating, and such surface treatments can provide wear resistance and, because chromium can be polished to an appealing silvery sheen, decoration. Additionally, chromic acid is used in chromate conversion coating, which produces a distinctive yellow finish on metal surfaces that may be used for corrosion inhibition or as a primer for further coatings. Anodization of aluminum is yet another finishing process that utilizes chromic acid, though it does not produce a chromium-containing coating.

Unfortunately, chromium (VI), known commonly as hexavalent chromium, is now known to be a potent carcinogen. Hexavalent chromium ions wreak havoc in the body because they are strong oxidizing agents that are easily transported into cells, where they cause significant damage to DNA and proteins. Many industrial processes using chromium, including chrome plating and chromium conversion coating, usually use hexavalent forms of chromium, and therefore the contamination of groundwater with hexavalent chromium from industrial waste is a major environmental problem. Alternative processes using trivalent chromium, which does not present the same toxicity concerns, are under investigation, as use and disposal of hexavalent chromium is now highly regulated.

Chromium is mined as chromite, an iron chromium oxide mineral. This ore can be processed either to pure chromium metal or to ferrochrome, an iron-chrome alloy used primarily in the production of stainless steel. Chromium can also be recovered from scrap, and recycled metal accounts for almost a third of chromium used annually.

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Sputtering Targets

High Purity (99.999%) Chromium Oxide (Cr2O3) PowderSummary. Chromium's hardness and high resistance to corrosion make it ideal for alloying and steel producing applications. Steel can be made highly resistant to corrosion and discoloration by the addition of chromium, forming stainless steel. High Purity (99.99%) Chromium (Cr) Sputtering TargetWhen chromium is added to glass or ceramic glazes, it produces a brilliant green color. Chromium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity). Elemental or metallic forms include pellets, rod, wire and granules for evaporation source material purposes. Chromium nanoparticles and nanopowders are also available. Chromium oxides are available in powder and dense pellet form for such uses as optical coating and thin film applications. Oxides tend to be insoluble. Chromium fluoride is another insoluble form for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Chromium is also available in soluble forms including chlorides, nitrates and acetates. These compounds can be manufactured as solutions at specified stoichiometries.

Chromium Properties

Chromium(Cr) atomic and molecular weight, atomic number and elemental symbolChromium is a Block D, Group 6, Period 4 element. Chromium Bohr ModelThe number of electrons in each of Chromium's shells is 2, 8, 13, 1 and its electron configuration is [Ar] 3d5 4s1. The chromium atom has a radius of 128.pm and its Van der Waals radius is 200.pm. In its elemental form, CAS 7440-47-3, Elemental Chromiumchromium has a lustrous steel-gray appearance. Chromium is the hardest metal element in the periodic table. The most common source of chromium is chromite ore (FeCr2O4). Chromium was first discovered by Louis Nicolas Vauquelin in 1797. Due to its various colorful compounds, chromium was named after the Greek word 'chroma' meaning color.

Symbol: Cr
Atomic Number: 24
Atomic Weight: 51.9961
Element Category: transition metal
Group, Period, Block: 6, 4, d
Color: silvery metallic/ silver-gray
Other Names: Chrom, Cromo, Krom, Crômio
Melting Point: 1907 °C, 3465 °F, 2180 K
Boiling Point: 2671 °C, 4840 °F, 2944 K
Density: 7.19 g/cm3; @ 20 °C
Liquid Density @ Melting Point: 6.3 g/cm3
Density @ 20°C: 7.19 g/cm3
Density of Solid: 7140 kg·m3
Specific Heat: 0.46 kJ/kg/K
Superconductivity Temperature: N/A
Triple Point: N/A
Critical Point: N/A
Heat of Fusion (kJ·mol-1): 15.3
Heat of Vaporization (kJ·mol-1): 341.8
Heat of Atomization (kJ·mol-1): 394.51
Thermal Conductivity: 93.9 W·m-1·K-1
Thermal Expansion: (25 °C) 4.9 µm·m-1·K-1
Electrical Resistivity: (20 °C) 125 nΩ·m
Tensile Strength: 282 MPa
Molar Heat Capacity: 23.35 J·mol-1·K-1
Young's Modulus: 279 GPa
Shear Modulus: 115 GPa
Bulk Modulus: 160 GPa
Poisson Ratio: 0.21
Mohs Hardness: 8.5
Vickers Hardness: 1060 MN m-2
Brinell Hardness: 1120 MN m-2
Speed of Sound: (20 °C) 5940 m·s-1
Pauling Electronegativity: 1.66
Sanderson Electronegativity: 1.66
Allred Rochow Electronegativity: 1.56
Mulliken-Jaffe Electronegativity: N/A
Allen Electronegativity: N/A
Pauling Electropositivity: 2.34
Reflectivity (%): N/A
Refractive Index: N/A
Electrons: 24
Protons: 24
Neutrons: 28
Electron Configuration: [Ar] 3d5 4s1
Atomic Radius: 128 pm
Atomic Radius,
non-bonded (Å):
2.06
Covalent Radius: 139±5 pm
Covalent Radius (Å): 1.3
Van der Waals Radius: 200 pm
Oxidation States: 6, 5, 4, 3, 2, 1, -1, -2 (strongly acidic oxide)
Phase: Solid
Crystal Structure: body-centered cubic
Magnetic Ordering: AFM
Electron Affinity (kJ·mol-1) 64.237
1st Ionization Energy: 652.87 kJ·mol-1
2nd Ionization Energy: 1590.64 kJ·mol-1
3rd Ionization Energy: 2987.21 kJ·mol-1
CAS Number: 7440-47-3
EC Number: 231-157-5
MDL Number: MFCD00010944
Beilstein Number: N/A
SMILES Identifier: [Cr]
InChI Identifier: InChI=1S/Cr
InChI Key: VYZAMTAEIAYCRO-UHFFFAOYSA-N
PubChem CID: 23976
ChemSpider ID: 22412
Earth - Total: 4120 ppm
Mercury - Total: 7180 ppm
Venus - Total: 4060 ppm 
Earth - Seawater (Oceans), ppb by weight: 0.6
Earth - Seawater (Oceans), ppb by atoms: 0.071
Earth -  Crust (Crustal Rocks), ppb by weight: 140000
Earth -  Crust (Crustal Rocks), ppb by atoms: 55000
Sun - Total, ppb by weight: 20000
Sun - Total, ppb by atoms: 400
Stream, ppb by weight: 1
Stream, ppb by atoms: 0.02
Meterorite (Carbonaceous), ppb by weight: 3100000
Meterorite (Carbonaceous), ppb by atoms: 1200000
Typical Human Body, ppb by weight: 30
Typical Human Body, ppb by atom: 4
Universe, ppb by weight: 15000
Universe, ppb by atom: 400
Discovered By: Louis Nicolas Vauquelin
Discovery Date: 1797
First Isolation: Louis Nicolas Vauquelin (1798)

Health, Safety & Transportation Information for Chromium

Although chromium metal is an essential trace element, hexavalent chromium (Cr(VI)) is especially toxic and carcinogenic to humans. Safety data for Chromium and its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental (metallic) Chromium.

Safety Data
Material Safety Data Sheet MSDS
Signal Word Warning
Hazard Statements H400
Hazard Codes N/A
Risk Codes N/A
Safety Precautions N/A
RTECS Number GB4200000
Transport Information N/A
WGK Germany N/A
Globally Harmonized System of
Classification and Labelling (GHS)
Environment-Hazardous to the aquatic environment

Chromium Isotopes

Naturally occurring chromium (Cr) has four stable isotopes; 50Cr, 52Cr, 53Cr, and 54Cr. 52Cr is the most abundant (83.79%). 50Cr decays by β+β+ to 50Ti with a half-life of (more than) 1.8x1017 years.

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
42Cr 42.00643(32)# 14(3) ms [13(+4-2) ms] β+ to 42V; β+ + 2p to 40Ti (3/2+) N/A 306.79 -
43Cr 42.99771(24)# 21.6(7) ms β+ to 43V; β+ + p to 42Ti; β+ + 2p to 41Sc; β+ + α to 39Sc 0+ N/A 323.25 -
44Cr 43.98555(5)# 54(4) ms [53(+4-3) ms] β+ to 44V; β+ + p to 43Ti 7/2-# N/A 342.51 -
45Cr 44.97964(54) 50(6) ms β+ to 45V; β+ + p to 44Ti 0+ N/A 356.18 -
46Cr 45.968359(21) 0.26(6) s β+ to 46V 3/2- N/A 374.5 -
47Cr 46.962900(15) 500(15) ms β+ to 47V 0+ N/A 388.17 -
48Cr 47.954032(8) 21.56(3) h EC to 48V 5/2- N/A 403.7 -
49Cr 48.9513357(26) 42.3(1) min EC to 49V 0+ 0.476 414.58 -
50Cr 49.9460442(11) Observationally Stable - 7/2- N/A 403.7 4.345
51Cr 50.9447674(11) 27.7025(24) d EC to 51V 0+ -0.934 414.58 -
52Cr 51.9405075(8) STABLE - 3/2- N/A 427.31 83.789
53Cr 52.9406494(8) STABLE - 0+ -0.47454 437.26 9.501
54Cr 53.9388804(8) STABLE - 3/2- N/A 449.06 2.365
55Cr 54.9408397(8) 3.497(3) min β- to 55Mn 0+ N/A 457.14 -
56Cr 55.9406531(20) 5.94(10) min β- to 56Mn (3/2-) N/A 467.08 -
57Cr 56.943613(2) 21.1(10) s β- to 57Mn 0+ N/A 486.66 -
58Cr 57.94435(22) 7.0(3) s β- to 58Mn 5/2-# N/A 493.81 -
59Cr 58.94859(26) 460(50) ms β- to 59Mn 0+ N/A 498.16 -
60Cr 59.95008(23) 560(60) ms β- to 60Mn 5/2-# N/A 504.37 -
61Cr 60.95472(27) 261(15) ms β- to 61Mn; β- + n to 60Mn 0+ N/A 508.73 -
62Cr 61.95661(36) 199(9) ms β- to 62Mn; β- + n to 61Mn (1/2-)# N/A 514.94 -
63Cr 62.96186(32)# 129(2) ms β- to 63Mn; β- + n to 62Mn 0+ N/A 518.36 -
64Cr 63.96441(43)# 43(1) ms β- to 64Mn (1/2-)# N/A 523.65 -
65Cr 64.97016(54)# 27(3) ms β- to 65Mn 0+ N/A 526.14 -
66Cr 65.97338(64)# 10(6) ms β- to 66Mn 1/2-# N/A 531.42 -
67Cr 66.97955(75)# 10# ms [>300 ns] β- to 67Mn 1/2 N/A 533.91 -
Chromium Elemental Symbol

Recent Research & Development for Chromium

  • Guangye Wei, Jingkui Qu, Zhihui Yu, Yongli Li, Qiang Guo, Tao Qi, Mineralizer effects on the synthesis of amorphous chromium hydroxide and chromium oxide green pigment using hydrothermal reduction method, Dyes and Pigments, Volume 113, February 2015
  • Fei Liu, Yehua Jiang, Han Xiao, Jun Tan, Study on fragmentation and dissolution behavior of carbide in a hot-rolled hypereutectic high chromium cast iron, Journal of Alloys and Compounds, Volume 618, 5 January 2015
  • Zhiwei Zhao, Hongjuan Zheng, Shaojing Liu, Jianhong Shen, Weiqiang Song, Jinshen Chen, Low temperature synthesis of chromium carbide (Cr3C2) nanopowders by a novel precursor method, International Journal of Refractory Metals and Hard Materials, Volume 48, January 2015
  • Meike V.F. Schlupp, Ji Woo Kim, Aude Brevet, Cyril Rado, Karine Couturier, Ulrich F. Vogt, Florence Lefebvre-Joud, Andreas Züttel, Avoiding chromium transport from stainless steel interconnects into contact layers and oxygen electrodes in intermediate temperature solid oxide electrolysis stacks, Journal of Power Sources, Volume 270, 15 December 2014
  • T.J. Pan, B. Zhang, J. Li, Y.X. He, F. Lin, An investigation on corrosion protection of chromium nitride coated Fe–Cr alloy as a bipolar plate material for proton exchange membrane fuel cells, Journal of Power Sources, Volume 269, 10 December 2014
  • Chun Wu, Jiao Gao, Qinglan Zhao, Youwei Zhang, Yansong Bai, Xingyan Wang, Xianyou Wang, Preparation and supercapacitive behaviors of the ordered mesoporous/microporous chromium carbide-derived carbons, Journal of Power Sources, Volume 269, 10 December 2014
  • W. Węglewski, M. Basista, A. Manescu, M. Chmielewski, K. Pietrzak, Th. Schubert, Effect of grain size on thermal residual stresses and damage in sintered chromium–alumina composites: Measurement and modeling, Composites Part B: Engineering, Volume 67, December 2014
  • Tapas Debnath, Ahamed Ullah, Claus H. Rüscher, Altaf Hussain, Chromium substitution in mullite type bismuth aluminate: Bi2CrxAl4−xO9 with 0≤x≤2.0, Journal of Solid State Chemistry, Volume 220, December 2014
  • Konstantinos Kapnisis, Georgios Constantinides, Harry Georgiou, Daniel Cristea, Camelia Gabor, Daniel Munteanu, Brigitta Brott, Peter Anderson, Jack Lemons, Andreas Anayiotos, Multi-scale mechanical investigation of stainless steel and cobalt–chromium stents, Journal of the Mechanical Behavior of Biomedical Materials, Volume 40, December 2014
  • Hui Zhang, Yong Zou, Zengda Zou, Chuanwei Shi, Effects of chromium addition on microstructure and properties of TiC–VC reinforced Fe-based laser cladding coatings, Journal of Alloys and Compounds, Volume 614, 25 November 2014