INDEX iron oxide

The disadvantage of this procedure is that the minerals maybe physically or chemically altered during burning. Eor example, the refractive index of clay minerals is changed the color, birefringence, and pleochroism of micas is altered carbonates are destroyed and the iron sulfides are oxidized to iron oxides. 

The color of pure diatomite is white, or near white, but impurities such as carbonaceous matter, clay, iron oxide, volcanic ash, etc, may darken it. The refractive index ranges from 1.41 to 1.48, almost that of opaline siUca. Diatomite is optically isotropic. 

As a pigment, each iron oxide has an optimum particle size which is that with the maximum scattering cross section. This optimum particle size is lower, the higher the refractive index of the mineral. For hematite, the size corresponding to the maximum in scattering/absorption cross section is ca. 1 pm. As the particle size decreases, the relative scattering cross section drops to zero and the relative absorption cross section levels out. As a result, very small particles of hematite are transparent. 

The lowest curve applies to pigments with a small absorption index k and high relative refractive index n, as is usually the case with inorganic pigments (e.g., red iron oxide). Here, there is a distinct maximum [1.11], [1.16]. 

Iron Oxide-Mica. Iron(III) oxide is suitable, like titanium dioxide, for coating of mica platelets. It combines a high refractive index (metallic luster) with good hiding power and weather resistance. 

In the cable industry, plasticization of CPVC by phthalates and phosphates improves the flexibility and processability of CPVC. However, the addition of plasticizer lowers the limiting oxygen index and increases smoke production. The schematic diagram below illnstrates the mechanism of degradation in the absence (A) and the presence (B) of the smoke-suppressing componnd - basic iron oxide, FeOOH. " ... 

The newest form of pearlescent pigment is a coated mica. The mica provides a transparent platelet shape with its two parallel faces. These faces are coated with a high-refractive-index layer of titanium dioxide or iron oxide. An absorption color layer can be overlaid on the oxide layer, giving additional reflective surfaces. These coated micas have high operating temperatures and are nontoxic. They are supplied in a range of particle sizes, usually from 10 to 50 xm. Loadings of coated mica pearlescents usually run about 1.5-3 percent. 

A filler such as titanium dioxide, having a refractive index much higher than that of the polymer, will therefore exhibit considerable scattering and will give white products, unless its absorption coefficient is high in which case dark, opaque composites will be produced (carbon black or black iron oxide are the ultimate in this instance). 

SiOj can be coated not only with TiOj but also with other metal oxides that are deposited from hydrolyzable salts. Iron(III) oxide is deposited as hydrated iron oxide on the transparent silica flakes. Subsequent drying and calcining produces a-Fe203 (hematite) layers on the flakes. The high refractive index of iron oxide generates strong interference effects and, in conjunction with the mass tone, brilliant red pigments. 

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