Titanium dioxides

Titanium dioxide [13463-67-7], Ti02, Mr 79.90, occurs in nature in the modifications rutile, anatase, and brookite. Rutile and anatase are produced industrially in large quantities and are used as pigments and catalysts, and in the production of ceramic and electronic materials. 

Titanium dioxide is of outstanding importance as a white pigment because of its scattering properties (which are superior to those of all other white pigments), its chemical stability, and lack of toxicity. Titanium dioxide is the most important inorganic pigment in terms of quantity, 3.2 x 106 t were produced in 1995. World production of titanium dioxide pigment is shown in Table 9 [2.1], [2.2], [2.3]. 

Physical Properties. Of the three modifications of TiOz, rutile is the most thermodynamically stable. Nevertheless, the lattice energies of the other phases are similar and hence are stable over long periods. Above 700 °C, the monotropic conversion of anatase to rutile takes place rapidly. Brookite is difficult to produce, and therefore has no value in the TiOz pigment industry. 

In all three TiOz modifications one titanium atom in the lattice is surrounded octahedrally by six oxygen atoms, and each oxygen atom is surrounded by three titanium atoms in a trigonal arrangement. The three modifications correspond to different ways of linking the octahedra at their corners and edges. Crystal lattice constants and densities are given in Table 10. 

Rutile and anatase crystallize in the tetragonal system, brookite in the rhombic system. The melting point of TiOz is ca. 1800 °C. Above 1000 °C, the oxygen partial 

Titanium dioxide is a large industrial commodity with world production over 4,000,000 tons but only a very small proportion is used as a food colorant. Commercial Ti02 is produced from the mineral ilmanite, which occurs in three crystalline forms, but the only one approved for food use is synthetic anatase. Anatase occurs in nature but only the synthetic version is approved because it contains fewer impurities.41 

Titanium dioxide is a very stable compound with excellent stability towards light, oxidation, pH changes, and microbiological attack. It is virtually insoluble in all common solvents. It is available in oil-dispersible and water-dispersible forms with a wide variety of carriers. Titanium dioxide is a very effective whitener for confectionery, baked goods, cheeses, icings, toppings, and numerous pharmaceuticals and cosmetics. 

Titanium dioxide is well established and will probably remain that way. 

Titanium dioxide is a large industrial commodity with world production over 

Titanium Dioxide. - The extensive literature on the surface properties of Ti02 (rutile, anatase) was reviewed in 1976 by Parfitt. Since then, papers on the subject using conventional spectroscopies have been published mainly by Rochester and co-workers (rutile), Munuera, and our group (anatase). 

Sheppard has recently studied the reaction of acetylene on thoroughly outgassed rutile by Raman-laser spectroscopy, and found that polymerization to fraws-polyacetylene occurs. A resonance effect is observed. 

Morterra, A. Chiorino, A. Zecchina, and E. Fisicaro, Gazz. Chim. Ital., 1979, 109, 683. 

Titanium dioxide (Ti02) is probably best known, and most widely used, as a brilliant white pigment and component of sunscreens. Recently, it has attracted increasing attention in the electronics industry due to its high dielectric and semi onducting properties, photocatalytic activity, and good biocompatibility. 

Crystal Structure and Properties of Single-Crystal Ti02 

Titanium oxide forms three polymorphs rutile, brooldte, and anatase [133]  

Anatase and brookite are metastable phases, and their exothermic and irreversible 

Titanium dioxide is extremely stable at high temperatures (melting point 1800 °C). Titanium oxide pigments are chemically very stable. They are insoluble in all liquids with the exception of concentrated sulfuric acid and hydrofluoric acid (and only at 1000 °C). They are also resistant to hydrogen sulfide and other gases generally found in industrial atmospheres. 

Despite having the highest hiding power and reducing power, one of the primary concerns with titanium dioxide pigments is their photochemical reactivity upon exterior exposure. Titanium dioxide 

Titanium dioxide is manufactured by two processes, the sulfate process and the chloride process. In the sulfate process, ilmenite ore (FeTiOg) is dissolved in concentrated sulfuric acid and insoluble impurities are removed by clarification, flocculation, sedimentation and filtration. The resulting solution is further purified by crystallization to remove ferrous sulfate from titanyl sulfate solution. The titanyl sulfate solution is then hydrolyzed to give hydrated titanium dioxide, which is calcined at about 900 to 1100 °C to give the titanium dioxide pigment. Both anatase and rutile-type titanium dioxide pigments are produced using this method. 

Titanium dioxide possesses many of the ideal properties required by a pigment for a coating, including excellent hiding power, very 

Titanium dioxide (Ti02) exists in two morphological crystalline forms, which exhibit different photoactivities when incorporated into a polymer matrix  

Anatase (Ti02), which is photochemically active and sensitizes (or catalyses) polymer photodegradation. 

Both Ti02 forms, anatase and rutile, show 6 3 coordination, i.e. each titanium atom is surrounded by six oxygen atoms and each oxygen atom is surrounded by three titanium atoms. The two morphological forms differ in the way in which the groups are linked together [179, 1565]  

A summary of the crystallographic properties of these two forms is given in Table 5.1. 

Titanium dioxide is used in rubber compounds to impart a white appearance. It is sometimes the preferred pigment because it possesses a great deal of hiding power because it has a higher refractive index than any other rubber filler available. 

In 2010, about 12 billion pounds of titanium dioxide was produced in the world however, only about 1% of this output was used in rubber. In the 1970s about 3% of tbe titanium dioxide produced was used in rubber when white sidewall tires were popular. However, while raised white letter tires are still popular, white sidewalls have dropped in popularity. Titanium dioxide is also the premium white colorant for many nontire rubber products as well. 

ASTM D4677 gives a standard classification for titanium dioxide used in rubber. There are two crystalline forms of titanium dioxide used in rubber anatase and rutile. 

Anatase is the softer form and will chalk in the compound, which can be good for self-cleaning the surface of a tire s white sidewall. 

Rutile does not chalk as much as anatase, but rutile has a slightly higher refractive index, which imparts more hiding power than anatase. Rutile is commonly used in nontire rubber applications. 

Titanium dioxide (TiOj) is an important pigment that produces white colors. It has a high refractive index (n 2.6), which leads to significant light scattering. It is added to synthetic fibers in the manufacturing process to make them seem white rather than translucent or transparent. It is also used with photographic paper and white tire sidewalls. 

The crystal structure of titanium dioxide has been studied [66,67]. Titanium dioxide exists in different crystalline forms. These are known as anatas and rutile forms, which have a tetragonal crystal structure with unit cell dimensions  

Titanium dioxide is commercially produced by two different processes. In the sulphate process, titanium dioxide is prepared by reacting titanium ores with sulphuric acid. In the chloride process, titanium dioxide is produced by reacting titanium ores with chlorine gas. Compounds with anatas Ti02 show an outstanding bluish white color. Rutile types exhibit a creamy white [26]. 

BP Titanium dioxide JP Titanium oxide PhEur Titanii dioxidum USP Titanium dioxide 

Anatase titanium dioxide brookite titanium dioxide color index number 77891 E171 Kronos 1171 pigment white 6 rutile titanium dioxide Tioxide TiPure titanic anhydride Tronox. 

Titanium dioxide is widely used in confectionery, cosmetics, and foods, in the plastics industry, and in topical and oral pharmaceutical formulations as a white pigment. 

In pharmaceutical formulations, titanium dioxide is used as a white pigment in film-coating suspensions, sugar-coated tablets, and gelatin capsules. Titanium dioxide may also be admixed with other pigments. 

Titanium dioxide is also used in dermatological preparations and cosmetics, such as sunscreens. 

Materials/characteristics Titanium dioxide zinc sulphide blanc fixe white calcites 

Disadvantages Possible problems of handling in powder form, needing extra ventilation titanium dioxide can act as photocatalyst, unless suitably treated 

New developments Improvement of presentation and dispersability high-performance masterbatches with other additives 

Anatase is used mainly in paper and elastomers in thermosetting resins systems, it retards gel time and may prevent cure altogether. 

The pigment is extracted from crude ore, removing impurities such as iron oxide. There are two manufacturing processes  

Semiconductor-Electrolyte Systems.—Titanium Dioxide. Interest continues in the cell devised by Fujishima and Honda30 for the electrochemical photolysis of water  

In this cell, irradiation of the semiconducting 2 with light of wavelength 413 nm results in the anodic evolution of oxygen at this electrode, coupled 

reaches the height of the equilibrium potential of H+-H2 then hydrogen is evolved at the Pt electrode. However, irradiation cannot cause , , to rise above the flat-band potential, which is at -0.5 V vs. SCE at pH = 4.7.31 (This value is in reasonable agreement with the value of —0.55 V vs. SCE interpolated from Honda s data.32) When this potential is reached, the equilibrium potential of the H+-H2 couple is only just reached and there is no space charge layer remaining to separate the hole-electron pairs. Consequently, the efficiencies shown in Table 3 are very low. The energy conversion efficiency, rj9 in Table 3, 

Wrighton et a/.86 also worked with single-crystal 2, irradiated by the 351 and 364 nm emission of an argon ion laser (1.3 x 10-7 E s-1). By mass spectro-metric methods and by the use of very small Ti02 crystals, they established that oxygen is evolved entirely from the aqueous phase, and does not come from the decomposition of the TiOa itself. Using a two-compartment chemically biased 

The use of polycrystalline 2, produced either by chemical vapour deposition (CVD)37 or by sheet titanium anodization,37 38 results in a somewhat 

Presently there are two main processes for manufacturing this important white pigment. The main one involves reaction of rutile ore (about 95% Ti02) with chlorine to give titanium tetrachloride. For this reason we have chosen to group this key chemical under chlorine and sodium chloride. The titanium tetrachloride is a liquid and can be purified by distillation, bp 136°C. It is then oxidized to pure titanium dioxide and the chlorine is regenerated. Approximately 94% of all titanium dioxide is made by this process. 

The other 6% of the product is made by taking ilmenite ore (45-60% Ti02) and treating it with sulfuric acid for digestion and filtration. Hydrolysis of the sulfate and final heating gives pure titanium dioxide. 

The iron sulfate crystallizes out from the TiOS04 solution and can be recycled to make more sulfuric acid. 

The use profile of titanium dioxide is given in Table 6.5. Titanium dioxide has been the best selling white pigment since 1939. We will discuss why this is so later when we study coatings as a unit. 

By electron microscopy, Churg et al. (1998) found TiOj particles in the epithelial cells of rat tracheal explants cultured in Dulbecco s modified Eagle s medium. The volume proportion of both fine (120 nm) and ultrafine (21 nm) particles in the epithelium increased from 3 to 7 days it was greater for ultrafine particles at 3 days but was greater for fine particles at 7 days. Ultrafine particles appeared to enter the epithelium faster, and once in the epithelium, a greater proportion of them was translocated to the subepithelial space compared with fine particles. However, if it was assumed that the volume proportion was representative of particle number, the number of particles reaching the interstitial space was directly proportional to the number applied, i.e., overall, there was no preferential transport from lumen to interstitium by size. 

For the preparation of large, spherical Ti02 particles, Bauer and Tomandl [166] first prepared a colloidal titania sol from TiCl4 (particle diameter 2.3 nm). 

Hardy et al. [177] dispersed Ti-2-ethylhexoxide and Ti-n-butoxide in propylene carbonate, form amide or acetonitrile by sonication the source of titanium was hydrolyzed to obtain particles several microns in size. A variety of non-ionic surfactants (Span, Tween and Brij families, HLB values varying in the range 3.7-16.9) were used to obtain emulsions. The uncalcined product was amorphous, but crystallized to anatase up to 600°C and rutile at 1000°C. 

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The reaction uses a fixed-bed vanadium pentoxide-titanium dioxide catalyst which gives good selectivity for phthalic anhydride, providing temperature is controlled within relatively narrow limits. The reaction is carried out in the vapor phase with reactor temperatures typically in the range 380 to 400°C. 

Acid refractory materials include fireclays, flint clays, china clays (kaolins), silica, flint, chalcedony, ganister and titanium dioxide. 

Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). 

If the normal carbonate is used, the basic carbonate or white lead, Pb(OH),. 2PbCO,. is precipitated. The basic carbonate was used extensively as a base in paints but is now less common, having been largely replaced by either titanium dioxide or zinc oxide. Paints made with white lead are not only poisonous but blacken in urban atmospheres due to the formation of lead sulphide and it is hardly surprising that their use is declining. 

Titanium tetrachloride is hydrolysed by water, to give a mixture of anions, for example [Ti(OH)Cl5]" and [TiClg] , together with some hydrated titanium dioxide (Ti02.4H2O is one possible hydrate, being equivalent to [Ti(0H)4(H20)2]). This suggests that titanium dioxide is amphoteric (see below). 

This occurs naturally as a white solid in various crystalline forms, in all of which six oxygen atoms surround each titanium atom. Titanium dioxide is important as a white pigment, because it is nontoxic. chemically inert and highly opaque, and can be finely ground for paint purposes it is often prepared pure by dissolving the natural form in sulphuric acid, hydrolysing to the hydrated dioxide and heating the latter to make the anhydrous form. 

Anhydrous titanium dioxide is only soluble with difficulty in hot concentrated sulphuric acid dilution allows the crystallisation of a sulphate of formula T10S04.H20, but it is doubtful if the titanyl cation TiO actually exists, either in solution or the solid. Certainly [TifHjOIn] does not exist, and solutions of titanyl salts may best be considered to contain ions [Ti(0H)2(H204)] . Titanium... 

Titanium metal is considered to be physiologically inert. When pure, titanium dioxide is relatively clear and has an extremely high index of refraction with an optical dispersion higher than diamond. 

Titanium dioxide is extensively used for both house paint and artist s paint, because it is permanent and has good covering power. Titanium oxide pigment accounts for the largest use of the element. Titanium paint is an excellent reflector of infrared, and is extensively used in solar observatories where heat causes poor seeing conditions. 

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