Silica flakes

In addition to popular mesoporous silica materials, mesoporous silica supports with various morphologies have also been used for protein immobilization. Tang and coworkers synthesized lotus-leaf-like silica flakes with a three-dimensionally connected nanoporous structure and controllable thickness, which were used for immobilization of ribonuclease A [126]. The synthesized silica flakes have a thickness of200 nm, and a diameter of 3 mm, showing a much higher initial adsorbing rate of... 

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... 

A sample of cerium metal (approximately 15 g.), previously cleaned and weighed, is placed in a V-shaped tungsten boat. The boat is positioned inside a 26-mm.-o.d., heavy-wall, silica reaction tube, and a curved shield of tungsten foil is placed over the boat to prevent the possibility of silica flakes (formed by reaction with cerium vapor) from falling into the melt. The silica reaction tube is transferred anaerobically from the glove box and installed on the vacuum and gas-handling system. 

Si02 can be coated not only with Ti02 but also with other metal oxides that are deposited from hydrolysable salts. Iron(III) oxide is deposited as hydrated iron oxide on the transparent silica flakes. Subsequent drying and calcining produces a-Fe203... 

Improved color strength and very high luster are produced by the combination of precise thickness silica flake substrate materials, selected for their interference chro-maticity, and by deposition of titania or iron oxide coating layers of the precise thickness required to generate the same interference color. These pearl luster pigments show stronger chromaticity L a b -values than can be produced with mica-based designs. 

The SEM micrograph in Figure 5.25 shows a cross section through a Ti02 silica flake pigment. It shows clearly that both the Si02 flake and the Ti02 layer thickness are precisely controlled. 

Fig. 5.24 Angle-dependent color travel of Fe203-coated silica flakes of different thickness.

Fig. 5.25 Cross-section through a silica flake coated with Ti02.

Figure 7-7 shows a cross-sectional diagram of metal oxide coated on mica and metal oxide deposited on silica flake pigments. The new properties available with silica flake pigments can be summarized as follows. 

The silica flakes are manufactured by a web coating process as shown in Figure 7-8. The web, moving at a controlled speed, is wet with an aqueous solution of a silica compound. The film on the web is dried to form a stable coating layer that can be selected between 50 nm and 1000 nm thick by adjustment of process parameters. The layer is then removed from the web and processed further to generate flakes... 

Figure 7-8 Manufacturing process of transparent silica flakes.

Figure 7-9 Coating of transparent silica flakes with various metal oxides.

Pearlescent Pigment on Mica Pearlescent Pigment on Silica Flakes... 

Figure 7.12 Properties of new pearl lustre pigments on silica flakes.

The first interferential pigments were created on the basis of natural muscovite mica as a substrate and coated with titanium or iron oxide. Other substrates have subsequently been used in this type of pigment, notably the silica flake and the alumina flake. The substrate provides the necessary platelet shape, while the interference colour is determined by the thickness of the metal oxide layer and its refractive index. 

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