Titania and Titanates

Sol-gel routes for binary titanium dioxide, tertiary titanates, and other mbced metal oxide systems not only employ various Ti(lV) alkoxides and modified alk-oxides but also Ti(IV) chlorides, oxychlorides, oxynitrates, and so on. The microstructure of the resulting titania and titanates depends on the morphology and interactions between primary particles (clusters) forming upon hydrolysis-condensation of Ti(IV) precursors. An apparent lack of crystalline order and very small size of primary particles and clusters ( 1 nm) is observed in the early stages of reaction. At a more advanced stage, the morphology is determined by interparticle interactions and aggregation mechanisms. 

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Rutile. The most common form of TITANIUM OXIDE (q.v.) sp. gr. 4.26. It occurs in the beach sands of Australia, Florida and elsewhere used as an opacifying agent in enamels and glazes. Rutile is also used in the production of titania and titanate dielectrics pure rutile has a dielectric constant of 89 perpendicular to the principal axis and 173 parallel to this axis the value for a polycrystalline body is 85-95 at 20°C. 

Titanium Oxides. The common oxide is Ti02 m.p. approx. 1850 C. Used as an opacifier, particularly in vitreous enamels, and as a constituent of some ceramic colours. Titania and titanate electroceramics, for use in the radiofrequency field, are based on this oxide and its compounds. Titania occurs in three crystalline forms anatase, BROOKiTE and rutile (see under each mineral name). Ti20, TiO, Ti203 and Ti305 also exist. 

Figure 12 Variation of the tan 6 with temperature for steatite, titania and titanate ceramics and porcelain at 10 GHz. (Extracted from ref 2 by permission of the MIT Press).

Some elucidation of the mechanism of elastomer reinforcement is being obtained by precipitating chemically-generated fillers into network structures rather than blending badly agglomerated filler particles into elastomers prior to their cross-linking. This has been done for a variety of fillers, for example, silica by hydrolysis of organosilicates, titania from titanates, alumina from aluminates, etc. [85-87], A typical, and important, reaction is the acid- or base-catalyzed hydrolysis of tetraethylorthosilicate ... 

Characterization of the surface impurities on the catalyst is also essential, and photoreactivity data should be analyzed in terms of active and accessible surface area. The defect state of the surface and nanostructure are also important aspects to understand. Current advances in the synthesis allow preparing Titania or titanate nanorods with different diameter and aspect ratio, and different surface nanostructure as well. Limiting the discussion here to only preparations by hydrothermal treatment (for reasons of conciseness), various mechanisms of growing of the nanorods has been reported. The differences in the mechanism of formation would imply differences in the surface characteristics of the nanorods, but there is no literature available on this topic. 

Liao J.F., Senna M. Crystallization of titania and magnesium titanate from mechanically activated Mg(OH)2 and T1O2 gel mixture. Mater. Res. Bull. 1995 30 385-92. 

FIGURE 108 XPS Ti/Si 2p intensity ratios for silica-titania cogel and titanated silica, both containing 3.3 wt% Ti02, as a function of activation temperature. 

FIGURE 109 Melt indices of polymers made with Cr/silica-titania cogels and titanated Cr/silica catalysts, both activated at 760 and 870 °C. 

To increase the mixing effects and interaction with the hydroxyl groups, the PEG polymer may be replaced by its monomer, ethylene glycol (EG, 0H(CH2)0H). The EG method also has the advantage of the use of alcohol soluble source chemical such as titanium isopropoxide. Nano-sized titania, calcium titanate [17,18] and barium titanate [9] have been synthesized by the EG method at relatively low organic weight percentages. 

A properly chosen support may stabilize a catalyst against sintering. In the case of NijS2 catalysts such supports are commonly used. Supports of this type include refractory oxides which do not react appreciably with hydrogen sulfide, for example alumina, silica, thoria, zirconia, and titania, as well as certain silicates, aluminates, thorates, zirconates, and titanates. Active carbon can be used as a support for NiS or NiaS2 catalysts for reactions which do not involve oxygen. 

Katagiri, K., Kamiya, J., Koumoto, K., and Inumaru, K. (2012) Preparation of hollow titania and strontium titanate spheres using sol-gel derived silica gel particles as templates./. Sol-GelSci. Technol, 63, 366-372. 

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

Fig. 5. A 90° polished cross section of a production white titania enamel, with the microstructure showing the interface between steel and direct-on enamel as observed by reflected light micrography at 3500 x magnification using Nomarski Interface Contrast (oil immersion). A is a steel substrate B, complex interface phases including an iron—nickel alloy C, iron titanate crystals D, glassy matrix E, anatase, Ti02, crystals and F, quart2 particle.

The technology for the production of titania slag by direct reduction smelting in electric arc furnaces (particularly for smelting of iron titanates and ilmenites having lower amounts of titania) is very old and the process has been in vogue in Canada, Norway, South Africa,... 

Mao, Y. and Wong, S.S. (2006) Size-andshape-dependent transformation of nanosized titanate into analogous anatase titania nanostructures. Journal of the American Chemical Society, 128 (25), 8217-8226. 

At temperatures of 6OO°-65O°C, the waste form dehydrates and crystallizes to form a mixture of titanates (niobates, zirconates) and titania (niobia, zirconia) as illustrated for the case of U. 

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