Refractive index, of titanium dioxide

Zinc sulfide has the next highest refractive index to titanium dioxide and zirconium oxide making it a very efficient pigment. The spectrum of absorption of zinc sulfide resembles more closely anatase than rutile. Because it does not absorb certain UV wavelength, zinc sulfide is useful as a pigment for UV curable materials. 

In the chloride process, dried ore reacts with chlorine gas to produce titanium tetrachloride. The titanium tetrachloride is purified chemically and by distillation and then reacted with oxygen to form titanium dioxide and chlorine. The chlorine is recycled. Prior to the oxidation, a minor amount of aluminum chloride is added to promote rutile formation [22]. The rutile is preferred because it is more durable and has a higher refractive index. Untreated titanium dioxide is used, but more commonly a surface treatment is done to improve specific end-use property requirements such as ability to disperse or weather resistance. 

Antireflection coatings are used over the silicon surface which, without the coating, reflects ca 35% of incident sunlight. A typical coating consists of a single layer of a transparent dielectric material with a refractive index of ca 2, which is between the index of siUcon and ait or cover material. Materials such as titanium dioxide, tantalum pentoxide, Ta20, or siUcon nitride, Si N, ca 0.08-p.m thick are common. The coating and a physically textured... 

Measuring the index of refraction of a material is generally done using an instrument known as a refractometer. Typical values of the index of refraction of gemstones and other materials are listed in Table 19. The relatively high index of refraction of diamond, for example, accounts for its distinct brilliance and multicolor display the index of refraction of rutile, a gemstone composed of titanium dioxide, is even higher than that of diamond, and rutile is indeed more brilliant than diamond. 

The refractive index of these pigments is about 1.5, which means that they give a transparent blue when used in paints and clear plastics. Opacity can be increased by adding small amounts of titanium dioxide. The principal failing of ultramarine is its lack of resistance to acid, which can even decompose the pigment if there is sufficient available. Coated grades are made with substantially improved acid resistance. 

The refractive index of a pigment at each wavelength is determined by its crystal structure. Titanium dioxide pigments (rutile and anatase) differ from each other and from other white pigments or crystalline substances, like silicon dioxide, in the proportion of radiant energy that is transmitted, absorbed, or re-... 

Refractive index influences light scattering in fillers and pigments. A correct choice in the refractive index of the particulate material and binder permits a formulation of transparent materials containing fillers (for further information on light scattering see Chapter 2, especially section on titanium dioxide and Section 5.3). Table 5.16 gives an overview of refractive indices of various fillers. 

Plasticizers which have been used successfully include polyethylene tetrasulfide, polyethylene diacetate tetrasulfide, dimercaptobutane diallyl tetrasulfide, and the (mercaptoethyl) cyclohexanethiols (6, 50, 51,52), The development of yellow and other colors for highway marking paints was accomplished easily. However, a white paint which meets color and reflectance specifications is difficult to prepare. The absorption characteristics and high refractive index of elemental sulfur present formidable problems. The simple addition of titanium dioxide and other white pigments does not produce a white paint, and masking agents or other additives usually must be incorporated. 

Another GRIN system is the binary titania-silicate system of Konishi and coworkers [62,63]. Small 2 mm diameter lens of low A-n have been produced with good index profiles [62, 63]. The low solubility of titanium dioxide in silica limits the maximum refractive index gradient in this binary system. 

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