Cobalt(II) oxide

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Cobalt(II) oxide (CoO) is a grayish green cobalt compound used extensively in the ceramics industry as an additive to create blue colored glazes and enamels as well as in the chemical production industry for producing cobalt(II) salts.

Cobalt(II) oxide is a product of Cobalt(II,III) oxide decomposing at 895 °C through the reaction:

2 Co3O4(s) → 6 CoO(s) + O2(g)

Cobalt(II) oxide is also a product of Cobalt(II) carbonate decomposing when heated through the reaction:

CoCO3(s) → CoO(s) + CO2(g)

Recent research also indicates that Cobalt(II) oxide can be formed by allowing gaseous metallic cobalt to condense in an environment containing nitrogen and oxygen gases. The metallic cobalt is vaporized by a laser; the process is called Laser Vaporization Controlled Condensation (LVCC). The proportion of nitrogen to oxygen gas determines the resulting products, for example, a 1:1 mixture will yield products consisting mostly of cobalt(II) nitrate. [1].

Ceramics and Other Uses

Cobalt(II) oxide has been used for centuries as a coloring agent in glazes for kiln-fired ceramics. Instances of use have been found on pottery dating to 1400 BC.[2] When used as a glaze, it will retain its coloration indefinitely. It is one of the most powerful coloring agents commonly used in glazes, requiring only 1:100,000 parts oxide to glazing compound to produce the deep blue shade commonly referred to as cobalt blue. By varying the temperature of the kiln, the potter can adjust the coloring of the oxide ranging anywhere from the familiar blue, to a darker shade nearing black. [3] Cobalt(II) oxide is also used in dryers used with oil based paints to expedite their curing. These substances can be found at most art stores.

Industrial Uses

As stated earlier, cobalt(II) oxide is used in the production of cobalt(II) salts such as CoCl2 and Co(NO3)2. Cobalt(II) oxide is also found in animal feed and fertilizer as a supplement to aid in the production of Vitamin B12, or cobalamin.

Health Concerns

This oxide is also found in cobalt dryers, additives to paints that can be found at most art stores. These dryers are considered highly toxic and a "possible human carcinogen" by the International Agency for Research on Cancer. Symptoms of acute exposure include coughing, wheezing and difficulty breathing. The small particles also pose the risk of ocular inflammation. The use of NFPA/NIOSH approved respiratory equipment is recommended when handling this substance.[4] OSHA's established exposure limit is 0.1 milligrams per cubic foot of air per 8 hour period. [5]


LD50/LC50 tests indicate that in rats a dose of 202mg per kilogram given orally is fatal. In 1992 the State of California added Cobalt(II) oxide to its list of carcinogenic agents however RTECS does not officially list the oxide as a carcinogen.[6]

Reactivity Concerns

Cobalt(II) oxide rapidly decomposes hydrogen peroxide and oxidizes the drying of unsaturated oils in an exothermic reaction that can be potentially explosive. [7]


  1. Garry P. Glaspell, Paul W. Jagodzinski and A. Manivannan: "Formation of Cobalt Nitrate Hydrate, Cobalt Oxide, and Cobalt Nanoparticles Using Laser Vaporization Controlled Condensation" April 13th 2004 <>
  2. A. J. Shortland, C. A. Hope & M. S. Tite: "Cobalt blue painted pottery from 18th Dynasty Egypt" 2006 <> (describes use as far back as 1400 BC -- doesn't address when the "earliest known examples" are.)
  3. Zamek, Jeff: "A Problem With Cobalt?" Ceramics Today <>
  4. American Chemical Society: "Journal of Chemical Education" Vol.28 No. 10 October 2001 "Hazardous Characteristics" <>
  5. Occupational Safety and Health Administration: "Cobalt Metal, Dust, and Fume" <> 22 April 1999
  6. Fisher Scientific UK MSDS "Cobalt(II) oxide" § 11 'Toxicological Information'
  7. American Chemical Society: "Journal of Chemical Education" Vol.28 No. 10 October 2001 "Hazardous Characteristics" <>