Synthetic Iron Oxide Pigments

19 октября, 2015 Pokraskin

Synthetic iron oxide pigments have become increasingly important due to their pure hue, consistent properties, and tinting strength. Single-component forms are mainly produced with red, yellow, orange, and black colors. Their composition corresponds to that of the minerals hematite, geothite, lepidocrocite, and magnetite. Brown pig­ments usually consist of mixtures of red and/or yellow and/or black; homogeneous brown phases are also produced, e. g., (Fe, Mn)2O3 and y-Fe2O3, but quantities are small in comparison to the mixed materials. Ferrimagnetic y-Fe2O3 is of importance for magnetic recording materials (see Section 5.1.).

Several processes are available (Table 3.2) for producing high-quality iron oxide pigments with controlled mean particle size, particle size distribution, particle shape, etc.

1. Solid-state reactions (red, black, brown)

2. Precipitation and hydrolysis of solutions of iron salts (yellow, red, orange, black)

3. Laux process involving reduction of nitrobenzene (black, yellow, red)

The raw materials are mainly byproducts from other industries: steel scrap ob­tained from deep drawing, grindings from cast iron, FeSO4 -7 H2O from TiO2 pro­duction or from steel pickling, and FeCl2 also from steel pickling.

Tab. 3.2: Reaction equations for the production of iron oxide pigments.

Color

Reaction

Process

Red

6 FeSO4 •x H2O + 11 O2

Fe2O3 + 2 Fe2(SO4)3 + 6 H2O

(3.1a)

copperas

process

2 Fe2(SO4)3

2 Fe2O3 + 6 SO3

(3.1b)

2 Fe3O4 + 1 O2

3 Fe2O3

(3.2)

calcination

2 FeOOH

Fe2O3 + H2O

(3.3)

calcination

2 FeCl2 + 2 H2O + 1 O2

Fe2O3 + 4 HCl

(3.4)

Ruthner

2 FeSO4+1 O2 + 4 NaOH

process

Fe2O3 + 2 Na2SO4 + 2 H2O

(3.5)

precipitation

Yellow

2 FeSO4 + 4 NaOH + § O2

2 а-FeOOH + 2 Na2SO4 + H2O

(3.6)

precipitation

2 Fe + 2 H2SO4 2 FeSO4+1 O2 + 3 H2O

2 FeSO4 + 2 H2 2 а-FeOOH + 2 H2SO4

(3.7a)

(3.7b)

1 Penniman process

2 Fe + 1 O2 + 3 H2O

2 а-FeOOH + 2 H2

(3.7c)

2 Fe + C6H5NO2 + 2 H2O

2 а-FeOOH + C6H5NH2

(3.8)

Laux process

Orange

2 FeSO4 + 4 NaOH +1 O2

2 у-FeOOH + 2 Na2SO4 + H2O

(3.9)

precipitation

Black

3 FeSO4 + 6 NaOH +1 O2

Fe3O4 + 3 Na2SO4 + 3 H2O

(3.10)

1-step precip-

itation

2 FeOOH + FeSO4 + 2 NaOH

Fe3O4 + Na2SO4 + 2 H2O

(3.11)

2-step precip-

itation

9 Fe + 4 C6H5NO2 + 4 H2O

3 Fe3O4 + 4 C6H5NH2

(3.12)

Laux process

3 Fe2O3 + H2

2 Fe3O4 + H2O

(3.13)

reduction

Brown

2 Fe3O4 + 1 O2

3 Y-Fe2O3

(3.14)

calcination

3 Fe3O4 + Fe2O3 + MnO2 + 1 O2

(Fen, Mn)O18

(3.15)

calcination

Iron oxides obtained after flame spraying of spent hydrochloric acid pickle liquor, red mud from bauxite processing, and the product of pyrites combustion are of minor importance. They yield pigments with inferior color properties that contain considerable amounts of water-soluble salts. They can therefore only be used in low-grade applications.

Опубликовано в рубрике Industrial Inorganic Pigments
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