The use of chromium(III) oxide as a pigment for toys, cosmetics, and in plastics and paints that come into contact with food is permitted in national and international regulations [3.72-3.79]. Maximum limits for heavy metals or their soluble fractions are usually a prerequisite. Because pure starting materials are used, these limits are satisfied by most types of chromium oxide.
Chromium oxide is equally important as a colorant and in its other industrial applications. As a pigment, it is used predominantly in the paint and coatings industry for high-quality green paints with special requirements, especially for steel constructions (coil coating), facade coatings (emulsion paints), and automotive coatings.
A series of RAL (Reichs-Ausschuss fur Lieferbedingungen) tints (e. g., Nos. 6003, 6006, 6011, 6014, and 6015) can be formulated based on chromium oxide. As mentioned previously, chromium oxide is also an important pigment for the formulation of green camouflage coatings (e. g., RAL 6031-F 9, Natogreen 285, Stanag 2338, and Forestgreen MIL-C-46168 C).
Except for the expensive cobalt green, chromium oxide is the only green pigment that meets the high color stability requirements for building materials based on lime and cement [3.80]. In plastics, however, chromium oxide green is only of minor importance because of its dull tint, but is widely used in coloring beer crates.
The industrial significance of chromium oxide is due to its chemical and physical properties. Its high purity makes it suitable as a starting material for the aluminother — mic production of very pure chromium metal.
Since the late 1970s chromium oxide has gained significance as a raw material in the refractory industry. The addition of chromium oxide to bricks and refractory concrete based on alumina significantly improves their stability against slag in the production and processing of pig iron. Chromium oxide bricks containing ca. 95 wt.% Cr2O3 have become important in the production of E-glass reinforcement fibers for lining melting tanks. These linings have substantially improved furnace stability (i. e., prolonged furnace life).
The high hardness of chromium oxide resulting from its crystal structure is exploited in polishing agents for metals and in brake linings. Addition of a small amount of chromium oxide to magnetic materials of audio and videotapes imparts a self-cleaning effect to the sound heads.
3.1.2.6