Titania, rutile

Titania most often appears in the form of one of two predominant crystallographic polymorphs, rutile and anatase. At least seven other distinct phases have been characterized by x-ray diffraction [3], but none are sufficiently commonplace to play a role in pigmentation using titanias. Rutile possesses a higher refractive index than anatase. It is also inherently considerably less photoactive than anatase. For these reasons, rutile has become the predominant polymorph of titania for pigmentary uses in polymers. 

Calcination of powders in the presence of different gases may induce solid phase transformation, which in turn affects the PZC/IEP. Hydrogen-treated and untreated zirconia were studied in [160], but no substantial shift in CIP was detected. Two titanias were heated in O2 or in H2 at 530 or 6OO C, but no substantial change in lEP or CIP was observed in one sample [161], Dehydration of titania (rutile) as a function of temperature was studied in [162]. The Og of silica was depressed by a factor of 10 by heating at 800°C for 3 hours, further heating (up to 36 hours) did not affect CTq. Rehydration of heated powders for 3-56 days brought about a gradual increase in Og [163], A few examples of different phase transformations induced in the same initial material by calcination at various temperatures are presented in Chapter 3. 

FIGURE 8.28 The electrophoretic mobility of titania (rutile) particles in aqueous solutions of 0.33.10 mol/dm nitrate solutions of different mono- and divalent cations as a function of pH. (From Fuerstenau, D.W. et ah, in Adsorption from Aqueous Solutions, Vol. 3, P.W. Tewari, Ed., Plenum Press, New York, 1981, 112. With permission.)... 

Both ciystal forms of titania, rutile and anatase, have a high Mohs hardness rating and are abrasive. For example, the pigment particles can etch glass fibers and greatly reduce the tensile strength of glass fiber reinforced thermoplastic blends and alloys. 

Fig. 4.38 Averaged normalised interaction energy versus normalised centre distance for randomly arranged DLCA aggregates of varying aggregation number N (x = 2Q nm) error bars for N = 200 represent variation due to changing orientation and aggregate configuration left result for silica right result for titania (rutile) (cf. Table B.l)...

The experimental material was a sample of rutile on which a layer of tnicrocrystalline titania had been deposited. Isotherms of nitrogen were determined on the original material outgassed at 1S0°C and on samples that had been outgassed at 25°, 150° or 250°C respectively after being charged with n-nonane. 

Titanium Dioxide (Titania, Titanium White, Rutile, Anatase, Brookite, Titanic Anhydride, Titanic Acid Anhydride, Titanic Oxide). Ti02, mw 79.90, Selected Parameters of the Allotropic Forms of Ti02... 

The present study revealed effects of various rutile/anatase ratios in titania on the reduction behaviors of titania-supported cobalt catalysts. It was found that the presence of rutile phase in titania could facilitate the reduction process of the orbalt catalyst. As a matter of fact, the number of reduced cobalt metal surface atoms, which is related to the overall activity during CO hydrogenation increased. 

The various ratios of rutileranatase in titania support were obtained by calcination of pure anatase titania (obtained fi om Ishihara Sangyo, Japan) in air at temperatures between 800-1000°C for 4 h. The high space velocity of air flow (16,000 h" ) insured the gradual phase transformation to avoid rapid sintering of samples. The ratios of rutile anatase were determined by XRD according to the method described by Jung et al. [5] as follows ... 

Co/Rn titania support containing n% of rutile phase (R)-supported cobalt... 

In this present study, we basically showed dependence of the number of reduced cobalt metal surface atoms on dispersion of cobalt oxides along with the presence of rutile phase in titania. Both XRD and SEM/EDX results (not shown) revealed good distribution of cobalt oxides over the titania support. However, it can not differentiate all samples containing various ratios of rutile/anatase phase. Thus, in order to determine the dispersion of cobalt oxide species on titania, a more powerful technique such as TEM was applied with all samples. The TEM micrographs for all samples are shown in Figure 1. The dark spots represented cobalt oxides species present after calcination of samples dispersing on titania consisting various... 

Figure 1 TEM micrographs of samples on various rutile/anatase ratios in titania...

The present research showed a dependence of various ratios of rutile anatase in titania as a catalyst support for Co/Ti02 on characteristics, especially the reduction behaviors of this catalyst. The study revealed that the presence of 19% rutile phase in titania for CoATi02 (C0/RI9) exhibited the highest number of reduced Co metal surface atoms which is related the number of active sites present. It appeared that the increase in the number of active sites was due to two reasons i) the presence of ratile phase in titania can fadlitrate the reduction process of cobalt oxide species into reduced cobalt metal, and ii) the presence of rutile phase resulted in a larger number of reduced cobalt metal surface atoms. No phase transformation of the supports further occurred during calcination of catalyst samples. However, if the ratios of rutile anatase were over 19%, the number of active sites dramatically decreased. 

Titania photocatalyst is used for air and water purification, photo-splitting of water to produce hydrogen, odor control and disinfectant. Crystal structure and crystallite size of titania particles are one of the most important factors that affect on the photoactivity. Photoactivity of anatase is higher than that of rutile, and increases with crystallite size [1]. Therefore, to increase photoactivity, it is desirable to find a route for the synthrais of the pure anatase titania with large crystallite size. 

In general, the increase of preparation or calcination temperature helps to increase the crystallite size of anatase titania. However, anatase phase is thennally unstable and is easily converted to rutile phase. Moreover, reactive surface area decreases with increasing the... 

The properties of titania particles were investigated using X-ray diffraction (XRD, Model D/MAX-RB, Rigaku Ltd.), scanning electron microscopy (SEM, Model 535M, Philips Ltd.), transmission electron microscopy (TEM, Model 2000EX, JEOL Ltd.). The crystallite sizes were estimated by Scherrer s equation and the composition of rutile phase in titania were estimated from the respective integrated XRD peak intensities. 

The reason for the formation of anatase phase at such a high temperature might be explained as following. The as-prqiared ultrafine titania particles are liquefied at sufficimtly high temperature because melting point of nanoparticlra are lower than that of bulk titania (1850 C). The liquid titania particles are supercooled and became metastable states. The residence time in the flame is only in the order of miU-second so that the metastable phase has no time to become thermodynamically stable phase, rutile. 

The commonly used catalyst today is a vanadia on a titania support, which is resistant to the high SO2 content. Usually the titania is in the anatase form since it is easier to produce with large surface areas than the rutile form. Several poisons for the catalyst exist, e.g. arsenic and potassium. The latter is a major problem with biomass fuel. In particular, straw, a byproduct from grain production, seems to be an attractive biomass but contains potassium, which is very mobile at reaction tern-... 

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