Cobalt green is an ambiguous term for either of two families of green inorganic
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...
s. 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
...
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
Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
–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
Chromium(III) oxide (or chromia) is an inorganic compound with the formula . It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.
Structure and properties
has the corundum ...
.
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 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 ...
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 lighte ...
*
List of inorganic pigments
The following list includes commercially or artistically important inorganic pigments of natural and synthetic origin..
Purple pigments
Aluminum pigments
* Ultramarine violet: (PV15) - a synthetic or naturally occurring sulfur containing silicat ...
References
External links
Pigments through the Ages
{{zinc compounds
Inorganic pigments
Cobalt compounds
Zinc compounds
Transition metal oxides