Chemical Properties
The main composition of cobalt blue is CoO, Al2O3, or known as cobalt aluminate [CoAl2O4], according to the theory of chemical formula, the content of Al2O3 is 57.63%, the content of CoO is 42.36%, or 33.31% of Co. However, the actual composition of cobalt blue pigment Al2O3 is between 65% and 70%, and the CoO is between 30% and 35%, and the cobalt oxide of some cobalt blue pigments is 10% or 15% lower. Some cobalt blue pigments contain cobalt oxide in the amount of 10% or 15% lower, because there may contain a small amount of other elements' oxides, such as Ti, Li, Cr, Fe, Sn, Mg, Zn and so on. For example, the analysis of a variety of cobalt blue pigment shows that its CoO is 34%, Al2O3 is 62%, ZnO is 2% and P2O5 is 2%. In addition to the main composition, cobalt blue may contain a small amount of alumina, cobalt green (CoO-ZnO) and cobalt violet [Co2(PO4)2], in order to change the hue of cobalt blue pigment. All these pigments belong to spinel class, which are cubic with spinel crystals. The relative density is 3.8~4.54, the covering power is very weak, only 75~80g/m2, the oil absorption is 31%~37%, and the apparent specific volume is 630~740g/L. The quality of the cobalt blue pigment produced in modern times and the early products is fundamentally different. Cobalt blue pigment has distinctive color, excellent weather resistance, alkali resistance, can withstand a variety of solvents, heat resistance up to 1200 ℃. Its main weakness is that the coloring power is not as good as phthalocyanine blue pigment, because it is calcined at high temperature, although it is ground fine, but the particles still have a certain hardness.
Uses
Cobalt blue [Co(AlO2)2], also known as cobalt ultramarine or azure blue, is a compound of
aluminum oxide and cobalt. It is used as a pigment that mixes well with both oil and water.
It also has cosmetic uses for eye shadow and in grease paint. Cobalt blue is one of the most
durable blue pigments in that it resists weathering in paints and holds up to other wear and
tear.
Definition
COBALT BLUE is an inorganic pigment that is the reaction product of high temperature calcination in which cobalt (II) oxide and aluminum oxide in varying amounts are homogeneously and ionically interdiffused to form a crystalline matrix of spinel. Its composition may include any one or a combination of the modifiers MgO, ZnO, Li2O, or TiO2.
