Oxide-coated metal platelets

Table 51 shows an overview of pigments with luster effects. Effect pigments can be classified as metal platelets, oxide-coated metal platelets, oxide-coated mica platelets, platelet-like mono-crystals and comminuted PVD-films (Physical Vapor Deposition). Aims of new developments are new effects, colors, improvement of hiding power, increase of the interference color, increase of light and weather stability and improved dispersibility characteristics. Of special interest are pigments which are toxicologically safe and which can be produced by ecologically acceptable processes. 

Metallic platelets Oxide coated metallic platelets... 

Oxide-coated metallic platelets Surface oxidized Cu-, Zn/Cu-platelets, Fe20j-coated Al-platelets... 

The dominant class of lustre pigments is based upon oxide coatings of mica platelets, but newer materials have appeared e.g. silica and alumina flakes from Merck, with better performance characteristics than traditional mica." " There has also been developments in the technology for the coating of reflective metal platelets, e.g. aluminium, with oxides using chemical vapour deposition that has led to exciting new products. ... 

Iron(III)oxide is also suitable for coating mica platelets. It combines a high refractive index (metallic luster) with good hiding power and weather resistance. Fe203-mica pigments are produced by precipitation of iron(II)- or iron(III)-ions in aqueous mica suspensions and then calcined at 700-900°C [5, 6, 8, 9] ... 

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... 

In practice, platelet crystals are synthesized with a layer thickness d calculated to produce the desired interference colors (iridescence) [5.206], [5.207], Most nacreous pigments now consist of at least three layers of two materials with different refractive indices (Fig. 73). Thin flakes (thickness ca. 500 nm) of a material with a low refractive index (mica) are coated with a highly refractive metal oxide (e.g., Ti02, layer thickness ca. 50-150 nm). This results in particles with four interfaces that constitute a more complicated but still predictable thin film system. The behavior of more... 

The dominant class of nacreous pigments is based on platelets of natural mica coated with thin films of transparent metal oxides (see Fig. 73). Mica minerals are sheet silicates (laminar). Nacreous pigments are usually based on transparent muscovite [9941-63-5] but some are based on natural or synthetic phlogopite [110710-26-4]. Although muscovite occurs worldwide, few deposits are suitable for pigments it is biologically inert and approved for use as a filler and colorant [5.220], [5.221],... 

Mica particles coated with a metal oxide film have three layers with different refractive indices (layer 1 and 3 are identical, layer 2 is mica) and four interfaces (see chapter 16.2). Interference of light is generated by reflections of all six possible combinations of the four interfaces. Some of them lead to equal effects. The thickness of the mica platelets varies according to a statistical distribution. As a con-... 

The graphite platelet deposit is formed indirectly, at the expense of the other two deposit forms and also requires the participation of a metal catalyst. It has been found that if the temperature of a metal foil, coated with carbon deposit, is raised to about 1000°C, a significant fraction of the carbon is taken into solution by the metal. On subsequent cooling this carbon is precipitated as highly crystalline graphite, underlaying excess amorphous and filamentous material remaining on the surface. This platelet deposit is the most oxidation resistant of the three... 

Chem. Descrip. Mica platelets coated with transparent layers of high refractive metal oxides... 

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