Iron oxide pigment

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As the iron oxide pigments are called a group of pigments based on the element iron based. They are approved as food additives under the designation E  172 .

Iron oxide yellow is the name for FeO (OH), listed in the Color Index under CI Pigment Yellow 42. The pigment is inexpensive, has good hiding power and excellent weather resistance. In contrast, the color is cloudy. At high temperatures (permanently above 200 ° C), iron oxide yellow is dehydrated to Fe 2 O 3 .

Iron oxide red is the name for Fe 2 O 3 , listed in the Color Index under CI Pigment Red 101. Like iron oxide yellow, iron oxide red has good coverage, is inexpensive and highly weatherproof, but also shows the typical cloudy color. Depending on the particle size, iron oxide red pigments can be set to have a very yellowish cast (small particle size) to a very bluish cast (coarse particles).

Iron oxide black is listed in the Color Index under CI Pigment Black 11. Iron oxide black has a low color strength compared to carbon black and is ferromagnetic . The chemical formula is often given as Fe 3 O 4 , in reality there is a mixed crystal of Fe 2 O 3 and FeO with an inverse spinel structure . Additional black pigments are obtained by doping with chromium , copper or manganese . The pure iron oxide black pigments have good temperature resistance, but are oxidized by atmospheric oxygen at around 180 ° C, so that the color shifts from brown to red. Under certain circumstances, even longer storage at over 80 ° C can lead to color changes.

Transparent iron oxide pigments are obtained by very strong fine grinding of iron oxide yellow or iron oxide red. They are labeled with the same color indices as the raw materials.

Iron oxide brown usually does not refer to a defined pigment, but a mixture of iron oxide yellow, red and black.

Web links

Individual evidence

  1. Entry on E 172: Iron oxides and hydroxides in the European database on food additives, accessed on June 16, 2020.
  2. Iron oxides at supplements-online
  3. a b c d e G. Buxbaum, G. Pfaff; Industrial inorganic pigments; 3. Edition; Wiley-VCH; Weinheim; 2005; ISBN 3-527-30363-4
  4. a b c The Society of Dyers and Chemists; Color index; Third edition; Second revision; Charlesworth & Co .; Huddersfield; 1982
  5. Kittel, Textbook of Lacquers and Coatings, 2nd edition, Volume 5, S. Hirzel Verlag 2003
  6. Lanxess iron oxide pigments