Manufacture of Magnetic Pigments

Manufacture of the iron-based magnetite pigments y-Fe203, FejOa and Fe from needle-shaped a-FeOOH or y-FeOOH 

Very complicated processes are currently necessary for the production of needle-shaped magnetic pigment particles. As regards needle-shaped pigments, chromium dioxide with a rutile structure is favored. It tends to crystallize as needles under hydrothermal production conditions (decomposition of Cr03 in an oxygen atmosphere or reaction of CrOOH with Cr03). 

In the synthesis of y-Fe203, careful oxidation of magnetite in a spinel lattice to a superstructure of crystallizing ferrimagnetic y-Fe203 (maghemite) under well-defined conditions is necessary  

Since the starting material is chemically and structurally changed several times, it is important that the initial needle shape be retained as completely as possible during the synthesis by, for example, using protective layers. 

The world production capacity for magnetic pigments in 1991 was ca. 40 10 t, magnetic iron oxide pigments accounting for over 90% of this. Metallic iron pigments are preferred for 8 mm camcorders tapes. 

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