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Cobalt(II) oxide or cobalt monoxide is an inorganic compound that appears as olive-green to red crystals, or as a greyish or black powder.[3] It is used extensively in the ceramics industry as an additive to create blue colored glazes and enamels as well as in the chemical industry for producing cobalt(II) salts.

Cobalt(II) oxide
Cobalt(II) oxide
IUPAC name
Cobalt(II) oxide
Other names
Cobaltous oxide
Cobalt monoxide
3D model (JSmol)
ECHA InfoCard 100.013.777
EC Number
  • 215-154-6
RTECS number
  • GG2800000
UN number 3288
Molar mass 74.9326 g/mol
Appearance black powder
Odor odorless
Density 6.44 g/cm3 [1]
Melting point 1,933 °C (3,511 °F; 2,206 K)
insoluble in water[2]
+4900.0·10−6 cm3/mol
cubic, cF8
Fm3m, No. 225
Main hazards Toxic (T)

Harmful (Xn)
Dangerous for the environment (N)

Safety data sheet ICSC 1551
Toxic THarmful XnDangerous for the Environment (Nature) N
R-phrases (outdated) R22, R43, R50/53
S-phrases (outdated) (S2), S24, S37, S60, S61
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
202 mg/kg
Related compounds
Other anions
Cobalt(II) sulfide
Cobalt(II) hydroxide
Other cations
Iron(II) oxide
Nickel(II) oxide
Related compounds
Cobalt(II,III) oxide
Cobalt(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure and propertiesEdit

CoO crystals adopt the periclase (rock salt) structure with a lattice constant of 4.2615 Å.[4]

It is antiferromagnetic below 16 °C.[5]


Cobalt(II,III) oxide decomposes to cobalt(II) oxide at 950 °C:[6]

2 Co3O4 → 6 CoO + O2

Though commercially available, cobalt(II) oxide may be prepared in the laboratory by electrolyzing a solution of cobalt(II) chloride.[7]

CoCl2 + H2O → CoO + H2 + Cl2

It may also be prepared by precipitating the hydroxide, followed by thermal dehydration:

CoX + 2 KOH → Co(OH)2 + K2X
Co(OH)2 → CoO + H2O


As can be expected, cobalt(II) oxide reacts with mineral acids to form the corresponding cobalt salts:

CoO + 2 HX → CoX2 + H2O


Cobalt(II) oxide has for centuries used as a coloring agent on kiln fired pottery. The additive provides a deep shade of blue named cobalt blue. The band gap (CoO) is around 2.4 eV.[citation needed] It also is used in cobalt blue glass.

See alsoEdit


  1. ^ Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. ISBN 0-07-049439-8. Retrieved 2009-06-06.
  2. ^ Advanced Search – Alfa Aesar – A Johnson Matthey Company Archived 2011-07-19 at the Wayback Machine. Retrieved on 2011-11-19.
  3. ^ "Safety (MSDS) data for cobalt oxide". The Physical and Theoretical Chemistry Laboratory, Oxford University. Retrieved 2008-11-11.
  4. ^ Kannan, R.; Seehra, Mohindar S. (1987). "Percolation effects and magnetic properties of the randomly diluted fcc system CopMg1-pO". Physical Review B. 35 (13): 6847–6853. doi:10.1103/PhysRevB.35.6847.
  5. ^ Silinsky, P. S.; Seehra, Mohindar S. (1981). "Principal magnetic susceptibilities and uniaxial stress experiments in CoO". Physical Review B. 24: 419–423. doi:10.1103/PhysRevB.24.419.
  6. ^ US 4389339, James, Leonard E.; Crescentini, Lamberto & Fisher, William B., "Process for making a cobalt oxide catalyst" 
  7. ^ Kern, S. (1876). "Inorganic chemistry". J. Chem. Soc. 29: 880. doi:10.1039/JS8762900876.