15 января, 2016 
Pokraskin Transparent cobalt blue (Color Index: Pigment Blue 28:77346) consists of minute, very thin, more or less hexagonal flakes. It is an ideal spinel with the composition MeIIMeIII2O4. The spinel structure is shown in Section 3.1.3.
The primary particles have a diameter of ca. 20 to 100 nm and a thickness of ca. 5 nm. The specific surface area as determined by the BET method is ca. 100 m2 g-1. Transparent cobalt blue has excellent light and weather fastness and very good chemical resistance. With regard to these fastness properties it easily outperforms organic blue pigments of comparably transparency. However, the pigment’s low color strength means it has never achieved any real market success. Transparent cobalt blue is manufactured by precipitating the hydroxides from very dilute solutions of cobalt and aluminum salts according to the following reaction:
2 Al(OH)3 + Co(OH)2 ^ CoAl2O4 + 4 H2O
The hydroxides are filtered, washed, dried, calcined at ca. 1000 °C and finally dry-ground [5.193].
5.4.3
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