Mica color effects

Figure 80. Combination pigment consisting of Ti02-mica coated with an additional layer of an absorption colorant Under regular conditions (A), a brilliant color effect dominated by thin film reflection is visible. All other viewing angles (B) show the color of the transparent absorption colorant (Section 4.4, Transparent Pigments )...

The Ti02-coated and Fe203-coated micas are used to provide metallic, two-tone, and two-color effects in industrial and automotive coatings. They are widely used in the latter with surfaee treatments designed to improve dispersability and weatherability. 

Nacreous Pigments. Mica is used as a substrate for coatings (qv) of various metal oxides to obtain a peadescent effect. Mica coated in this fashion is used as filler and as a coloring agent in certain types of plastics. 

Colorants have been developed for special effects. Pearlescent or iridescent give an attractive appearance. They are often used for coating paper (e.g., cosmetic packaging). The pigment consists of thin platelets, less than 1 pm thickness, which have a high refractive index, e.g., mica coated with Ti02. 

Pearlescent pigments contain small flakes or platelets of the mineral mica that are additionally coated with a very thin layer of titanium dioxide. The simultaneous reflection of light from many layers of small platelets creates an impression of luster and sheen. By varying the thickness of the coating on the surface of the mica particles, pigment manufacturers can achieve a range of colors for the pearlescent effect. 

The presence of mica in pearlescent pigments only partly accounts for the appearance of the pigment. A very thin layer of the inorganic oxide titanium dioxide (TiC>2) or iron oxide (Fe2C>3) or both is coated on the mica platelets. The various colors and pearlescent effects are created as light is both refracted and reflected from the titanium dioxide layers. The very thin platelets are highly reflective and transparent. With their plate-like shape, the platelets are easily oriented into parallel layers as the paint medium is applied. Some of the incident light is reflected... 

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. 

On the other hand, new pigments based on transparent silica flakes show extremely strong optical effects, which are different to mica pigments [5.244]. Angle dependent colors and other effects, achieved by the combination of these Si02-flakes with... 

Nacreous and interference pigments are used as colorants or part of color formulations for all applications where traditional pigments are used, but where additional color depth, brilliance, iridescence, color shift (flop), and other spectacular effects are desired [5.253]. Mica-based pigments dominate their combination of pearl and interference effects, brilliance, stability, and weather resistance is unsurpassed. Furthermore, they are non-toxic [5.221],... 

Table VII shows that for cesium sorption, both KC1 and N H4 are significant for the two geologic solids studied. The negative values indicate that the presence of either KC1 or lowers sorption. Both appear to be competing with Cs+ ion for sorption sites. Competition between K+ and Cs+ ions for sorption sites on mica-like minerals is well known. However, displacement of Cs+ by hydrazine was surprising since N H, should exist mainly as a neutral species at pH 9-10. A small amount (0.0005M to 0.005M) will be protonated and apparently competes with Cs+. Ammonium ion is known to effectively compete with Cs+ for mineral sorption sites. Hydrazinium ion with a similar molecular structure should also displace Cs+. Since hydrazine will not reduce or complex Cs+, the only possible effects on cesium sorption is to compete for sorption sites or to alter the surface of the solid minerals. No evidence of surface alteration (change in color or texture) was observed. Therefore, it appears that an Eh buffer is not required for Cs+ sorption studies and hydrazine only interferes with the sorption reaction.

Interference pigments the optical effect of colored luster pigments is caused wholly or mainly by the phenomenon of interference (example iron oxide on mica)... 

Mica-Lyte, Dekorflake, Microfibers, Specular - selected natural, colored, and shaped materials designed as special-effect colorants to impart granite-hke, sparkling, and textured appearances to transparent and translucent polymers... 

Mica-Tek has an interesting approach to exploiting the variety of forms and colors of mica. A range of mica-based products have been developed which differ in the color and the shape of particle as well as in their glittering and sparkling effects. These decorative pigments are used in housewares, bathwares, toys, interior decorating, etc. 

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