21 сентября, 2015 
Pokraskin Like titanium dioxide, iron(III) oxide is suitable for coating mica platelets. It combines a high refractive index (metallic luster) with good hiding power and excellent weather resistance. Commercial Fe2O3-mica pigments are produced by precipitation of iron(II) or iron(III) ions in aqueous mica suspensions and calcination of the resulting coated particles at 700-900 °C:
2 FeCl3 + mica + 3 H2O ^ Fe2O3-mica + 6 HCl
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Figure 7.5 TiO2-mica pigments: The dependence of interference color according to titanium dioxide layer thickness. |
Figure 7.6 SEM photo of a cross-section through an anatase/mica pigment particle.
It is also possible to produce iron oxide-mica pigments by a direct CVD fluidized bed process in which iron pentacarbonyl is oxidized and Fe2O3 is deposited on the mica surface.
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Table 7.3 Properties and applications of pearlescent pigments.
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Table 7.4 Technical data on pearlescent pigments.
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Independent of the synthesis route, iron(III) oxide crystallizes in the a-modifi — cation (hematite) after calcination. Brilliant, intense colors are obtained with 50-150 nm layers of Fe2O3 (hematite) on muscovite (see Figure 7.4c). Absorption and interference colors are produced simultaneously and vary with layer thickness. The red shades are especially intense because interference and absorption enhance each other. An intense green-red flop with different viewing angles is possible at a Fe2O3 layer thickness producing green interference.
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