Micaceous iron oxide

Micaceous iron oxide consists of pure or doped hematite (a-FcjOj). Its density is 4.6-4.S g/cm7 Micaceous iron oxide can also be obtained by hydrothermal synthesis in alkaline media. Howevei the dull dark color is as unappeaUng as that of the natural product. If substantial amounts of dopants are incorporated, the aspect ratio can be increased up to 100, resulting in a much increased luster. The color can be also shifted to a more attractive reddish brown so that the products can be used for decorative purposes [1,11]. 

The most important dopants are AI2O3, Si02, and MnjO,. These can enforce a spinel structure. Si02 yields thin small platelets, AljO, yields thin larger platelets, and MnjOj reduces the thickness. 

The starting material FejOH), or better FeOOH is heated in an alkaline suspension together with the dopants to temperatures above 170 °C, typically 250-300 °C. After several minutes to hours, platelets of doped iron oxide are obtained. In a second reaction phase, the pH is further increased so that platelets grow and form flat basal faces. 

In addition to providing a barrier against diffusion of aggressive species through the coating, MIO confers other advantages  

For the latter reason, MIO is sometimes used in topcoat formulations to improve weatherability [40,109]. 

The chemical inertness of MIO means that it can be used in a variety of binders alkyd, chlorinated rubber, styrene-acrylic and vinyl copolymers, epoxy, and polyurethane [40]. 

It is not clear from the literature whether or not combining MIO and aluminum pigments in a coating poses a problem. There are recommendations both for and against mixing MIO with these pigments. 

In full-scale trials of various paint systems on bridges in England, Bishop found that topcoats with both MIO and aluminum pigments form a white deposit over 

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A frequently cited example of protection from atmospheric corrosion is the Eiffel Tower. The narrow and, for that age, thin sections required a good priming of red lead for protection against corrosion. The top coat was linseed oil with white lead, and later coatings of ochre, iron oxide, and micaceous iron oxide were added. Since its constmction the coating has been renewed several times [29]. Modern atmospheric corrosion protection uses quick-drying nitrocellulose, synthetic resins, and reaction resins (two-component mixes). The chemist Leo Baekeland discovered the synthetic material named after him, Bakelite, in 1907. Three years later the first synthetic resin (phenol formaldehyde) proved itself in a protective paint. A new materials era had dawned. 

Most pigments can be used in any type of binder therefore, paints cannot be identified by pigment type alone. For example, micaceous iron oxide pigment is traditionally in an oil-based binder but is being increasingly used in epoxies, etc. In the paint coating film, the pigment content may vary from 15 to 60 per cent. In the special case of zinc rich primers, it is over 90 per cent. 

Modified pretreatment primer plus zinc chromate primer plus two coats of micaceous iron oxide/polyurethane. 

Pretreatment primer plus micaceous iron oxide/long oil tung phenolic. 

Pigments for finishes are selected on the basis of their colour, but special attention must be paid to inertness in the chosen binder and stability and light fastness under the conditions of application and exposure. Flake pigments such as aluminium and micaceous iron oxide give finishes of lower moisture-vapour permeability than conventional pigments, and consequently contribute to better protection. 

Micaceous iron oxides are produced in a process which involves heating FeCl3 and iron at 500-1000 °C to form molten Fe complexes which are then oxidized to micaceous hematite the diameter of the plates can be varied from 5 to 75 pm depending on whether the oxide is intended for use in a primer paint or a topcoat (Carter, 1988). 

Uchida, S Sato,T. Okuwaki, A. (1993) Synthesis of monodispersed micaceous iron oxide by the oxidation of iron with oxygen under hydrothermal conditions. J. Chem. Techn. Biotechn. 57 221-227 Ugwuegbu, B.J. Prasher, S.O. Ahmad, D. Dutilleul, P. (2001) Bioremediation of residual fertilizer nitrate II. Soil redox potential and soluble iron as indicators of soil health during treatment. J. Environ. Qual. 30 Ills... 

Hematite is found in large quantities in the vicinity of Malaga in Spain (Spanish red) and near the Persian Gulf (Persian red). The Spanish reds have a brown undertone. Their water-soluble salt content is very low and their Fe203 content often exceeds 90 %. The Persian reds have a pure hue, but their water-soluble salt content is disadvantageous for some applications. Other natural hematite deposits are of only local importance. A special variety occurs in the form of platelets and is extracted in large quantities in Karnten (Austria). This micaceous iron oxide, is mainly used in corrosion protection coatings. 

In a new process, micaceous iron oxide is obtained in high yield by reacting iron(III) chloride and iron at 500-1000 °C in an oxidizing atmosphere in a tubular reactor [3.11],... 

Pigments with a physical protective action are chemically inert and are termed inactive or passive. An example is micaceous iron oxide [5.54], [5.55]. These lamellar pigments are packed in layers they lengthen the pathways and obstruct the penetration of ions. They improve adhesion between the substrate and the coating, absorb UV radiation, and protect the underlying binder (Fig. 68), [5.56]—[5.60]. 

In principle, all lamellar minerals may be used as barrier pigments, e.g., micaceous iron oxide [5.167]-[5.169], layer silicates (mica), linear polymeric silicates (wollas-tonite), and talc [5.170], However, untreated mica and talc are not very suitable because they are highly permeable to water [5.57]. The surface can be modified with, for example, silanes or titanates, to reduce water permeability and improve adhesion... 

Micaceous iron oxide [1317-60-8] Fe203 (specular hematite) 4.6-48 dark gray... 

Pigments used in barrier coatings should also be hydrophobic in nature, and possess good adhesion across pigment-binder interfaces. Some typical pigments used are flat platey aluminum flakes, glass flakes, stailness steel flakes and micaceous iron oxide. 

Micaceous iron oxide epoxy primer High-build epoxy lining... 

Heubach GmbH, Heucorox - Natural micaceous iron oxides, company information, Langelsheim, Germany, 2003... 

ISO 10601, Micaceous iron oxide pigments for paints - Specifications and test methods. International Organisation... 

Uchida, S., Sato, T. and Okuwaki, A. (1993) Synthesis of monodispersed micaceous iron oxide by the oxidation of iron with oxygen under hydrothermal conditions. J. Chem.Techn. Biotechn. 57 221-227. 

Lamellar-shaped crystalline haematite (a-Fe203) can also be used as a filler. Due to its morphological relationship to micas, it is known as micaceous iron oxide. 

Micaceous iron oxide, a flake-shaped a-Fc203 with a metallic gray color, is mainly mined in Carinthia (Austria). It is used in the top coat of corrosion protection coatings. Application fields are steel superstructures (stations, Eifel tower), petrochemical plants and ship building. The annual capacity worldwide is 10- 10 t/a. 

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