Iron Oxide

Iron oxide is a compound that usually comes out of rocks in mountainous regions. This compound can not be touched with bare hands because the oxidizing gas in the compound comes into contact with air and becomes a flammable substance. This compound east of Eastern Anatolia in Turkey are in abundance in the province of Van.

 Iron oxides are chemical compounds composed of iron and oxygen. There are sixteen known iron oxides and oxyhydroxides, the best known of which is rust, a form of iron(III) oxide. Iron oxides and oxyhydroxides are widespread in nature and play an important role in many geological and biological processes.

Iron oxide materials yield pigments that are nontoxic, nonbleeding, weather resistant, and lightfast.   Natural iron oxides include a combination of one or more ferrous or ferric oxides, and impurities, such as manganese, clay, or organics.   Synthetic iron oxides can be produced in various ways, including thermal decomposition of iron salts, such as ferrous sulfate, to produce reds; precipitation to produce yellows, reds, browns, and blacks (e.g., the Penniman-Zoph process); and reduction of organic compounds by iron (e.g., nitrobenzene reduced to aniline in the presence of particular chemicals) to produce yellows and blacks.   Reds can be produced by calcining either yellow or blacks.


The most important reaction is its cFe2O3 + 3 CO → 2 Fe + 3 CO2

Another redox reaction is the extremely 

2 Al + Fe2O3 → 2 Fe + Al2O3

This process is used to weld thick metals such as rails of train tracks by using a ceramic container to funnel the molten iron in between two sections of rail. Thermite is also used in weapons and making small-scale cast-iron sculptures and tools.

Partial reduction with hydrogen at about 400 °C produces magnetite, a black magnetic material that contains both Fe(III) and Fe(II):

3 Fe2O3 + H2 → 2 Fe3O4 + H2O

Iron(III) oxide is insoluble in water but dissolves readily in strong acid, e.g. hydrochloric and It also dissolves well in solutions of chelating agents such as 

Heating iron(III) oxides with other metal oxides or carbonates yields materials known as 

ZnO + Fe2O3 → Zn(FeO2)2


Kazuyuki Hayashi, in 

2.1 Improved Dispersibility of Nanosized Iron Oxide Red Particles

Iron oxide has been used in many kinds of industrial applications because it is a rich element on the Earth and a multifunctional material. α-Fe2O3 (hematite) is the most popular material and it is often called “Bengara” or iron oxide red. Bengara has a long history from ancient wall painting [2]. α-Fe2O3 particles are manufactured by various procedures today. An example of manufacturing process is shown in Fig. 38.1. One of the most popular methods is wet synthesis, where iron and sodium  are added to neutral reaction and oxidized to get iron oxide precursors such as Fe3O4 and α-FeOOH. Then the precursors are heated to derive α-Fe2O3 particles. Final particle size and distribution are almost decided by precursor's characteristics. Nanosized α-Fe2O3 particles have lower hiding power and can be applied for colorant particles as trans-iron oxide red, which have higher light  in coated films. Especially, a suitable trans-iron oxide red particle could be derived from nanosized α-FeOOH precursors.

Figure 38.1. Schematic illustration of iron oxide–manufacturing process.

Particularly, UV light is absorbed by iron oxide red–coated film. The relationship between wavelength and light transparency in trans-iron oxide red–coated film is shown in Fig. 38.2. The light transparency of UV light is lower; however, IR light easily passes through the coated film. The relationship between particle size of iron oxide red particles and light transparency at λ = 700 nm is shown in Fig. 38.3. When the particle size is finer than 100 nm, light transparency becomes larger. Then, iron oxide pigment can be applied as transpigment for transparency film with a function of UV 

Figure 38.3. The relationship between particle size and light transparency (λ = 700 nm).

The preparation procedure of trans-iron oxide red particles is mentioned as follows: iron sulfate solution and lution are mixed and aged in the reactor with N2-gas bubbling; then, the oxidation reaction occurs with aeration and nanosized α-FeOOH particles are synthesized in the reactor. α-FeOOH particles are washed and dried to derive α-FeOOH powder withf 80 nm as precursor particles of iron oxide red pigment. α-FeOOH particles are heated at 250–400°C in the oven and dehydrated to α-Fe2O3 particles, and then nanosized iron oxide red particles are derived as shown in Fig. 38.4. Nanosized iron oxide red particles are hard to disperse because particle size is so small. It seems that they tend to coagulate together as shown in TEM photograph. It is necessary to introduce a surface treatment onto particles for easy dispersion. We recommend silicone coating onto iron oxide red particles to reduce their orce between particles. Silicone is coated on nanosized iron oxide red particles in amounts such as 1, 1/2, 1/4, 1/8, 1/16, and 1/32-layer equivalent. If coagulation force between particles was reduced, particles would be dispersed well in the and light transparency becomes higher in coloring film. Silicone-coated iron oxide red particles with 1/4-layer equivalent coating are shown in Fig. 38.5. It is found that particles are dispersed well and pulverized to almost primary particles. The results concerning lacquer dispersibility and transparent film are described in Table 38.1. The small amount of silicone surface treatment is effective for the dispersibility improvement of nanosized iron oxide red particles. Then, the lacquer viscosity is reduced and light transparency becomes higher. It is found that 1/8-layer equivalent silicone coating is enough for the practical use of nanosized iron oxide red particles. The appropriate surface treatment such as silicone coating is very effective for the practical use of nanosized iron oxide red particles.



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