Cobalt green is an ambiguous term for either of two families of green inorganic
pigments. Both are obtained by doping cobalt(II) oxide into colorless host oxides.
Spinel-based cobalt green
Doping Co(II) into Mg(II) and Zn(II) sites of Mg
2TiO
4 and Zn
2TiO
4, respectively gives one family of cobalt greens. These materials adopt the
spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals.
Properties
S ...
structure.
[Völz, Hans G. ''et al.'' "Pigments, Inorganic" in ''Ullmann's Encyclopedia of Industrial Chemistry'', 2006 Wiley-VCH, Weinheim. .]
Rinman's green
Rinman's green, also referred to as Rinmann's green, is obtained by doping cobalt(II) oxide into zinc oxide.
Sven Rinman, a Swedish chemist, discovered this compound in 1780.
Zinc oxide–derived pigments have been used in many industries and processes. It is rarely used because it is a weak chromophore and relatively expensive compared to
chromium(III) oxide.
The structure and color of compositions Zn
1−xCo
xO depends on the value of x. For x ≤ 0.3, the material adopts the
Wurzite
Zinc sulfide (or zinc sulphide) is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various i ...
structure (of ZnO) and is intensely green. For x ≥ 0.7, the material has the
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
structure (of CoO) and is pink. Intermediate values of x give a mixture of the two phases.
Cobalt green has been tested for use in "
spintronic" devices. Cobalt green is attractive in this application because it is magnetic at room temperature.
See also
*
Cobalt blue
Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter ...
*
List of inorganic pigments
References
External links
Pigments through the Ages
{{zinc compounds
Inorganic pigments
Cobalt compounds
Zinc compounds
Transition metal oxides