Chemical Properties
Cobalt blue is primarily composed of CoO and Al2O3, also known as cobalt aluminate [CoAl2O4]. According to the theoretical chemical formula, the Al2O3 content is 57.63%, the CoO content is 42.36%, or 33.31% Co. However, the actual composition of cobalt blue pigments ranges from 65% to 70% Al2O3 and 30% to 35% CoO. Some cobalt blue pigments contain even less than 10% or 15% cobalt oxide, as they may also contain small amounts of oxides of other elements, such as Ti, Li, Cr, Fe, Sn, Mg, and Zn. For example, analysis of one cobalt blue pigment revealed 34% CoO, 62% Al2O3, 2% ZnO, and 2% P2O5. In addition to the main components, cobalt blue may also contain small amounts of aluminum oxide, cobalt green (CoO·ZnO), and cobalt violet [Co2(PO4)2] to alter the pigment's hue. These pigments all belong to the spinel family and are cubic structures with spinel crystals. With a relative density of 3.8 to 4.54, its hiding power is very weak, at only 75 to 80 g/m??, its oil absorption is 31% to 37%, and its apparent specific volume is 630 to 740 g/L. Modern cobalt blue differs fundamentally from earlier products in quality. Cobalt blue pigment has a vibrant color and excellent weather and alkali resistance, is resistant to various solvents, and can withstand heat up to 1200°C. Its primary weakness is its tinting strength, which is inferior to that of phthalocyanine blue. Because it is calcined at high temperatures, the particles, despite being finely ground, 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.
