Anatase phase

Figure C2.17.8. Powder x-ray diffraction (PXRD) from amoriDhous and nanocry stalline Ti02 nanocrystals. Powder x-ray diffraction is an important test for nanocrystal quality. In the top panel, nanoparticles of titania provide no crystalline reflections. These samples, while showing some evidence of crystallinity in TEM, have a major amoriDhous component. A similar reaction, perfonned with a crystallizing agent at high temperature, provides well defined reflections which allow the anatase phase to be clearly identified.

Taking titanium dioxide as an example, we may mention that PMC transients decay rapidly in the rutile phase (10"6 s) and much slower in the (catalytically more active) anatase phase (10"2-1 s).35 When a Ti02... 

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... 

After gas-phase oxidation reaction finished, the reactor wall surfece was coated with a thick rough scale layer. The thickness of scale layer along axial direction was varied. The scale layer at front reactor was much thicker than that at rear. The SEM pictures were shown in Fig. 1 were scale layers stripped from the reactor wall surface. Fig. 1(a) was a cross sectional profile of scale layer collected from major scaling zone. Seen from right side of scale layer, particles-packed was loose and this side was attached to the wall surface. Its positive face was shown in Fig. 1(b). Seen from left side of scale layer, compact particles-sintered was tight and this side was faced to the reacting gases. Its local amplified top face was shown in Fig. 1(c). The XRD patterns were shown in Fig. 2(a) were the two sides of scale layer. Almost entire particles on sintered layer were characterized to be rutile phase. While, the particle packed layer was anatase phase. 

Nanocrystals titania was prepared by sol-gel method. X-ray diffraction result is shown in Figure 1, all samples were anatase phase. Based on Sherrer s equation, these samples had crystallite sizes about 7 nm. From XRD results, it indicated that titania samples showed the similar of crystallinity because the same ordering in the structure of titania particles make the same intensity of XRD peaks. 

Preparation of titania nanopartidei of anatase phase by using flame spray pyrolysis... 

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 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. 

Compared with the conventional spray pyrolysis, flame spray pyrolysis produces titania particles that are strikingly different in crystd phase and surfece arra. The fraction of anatase phase increases with the increase of flame tempCTature while it decreases with the increase of preparation temperature in the conventional spray pyrolysis. The sur e area and... 

The extra-framework Ti was identified as belonging to a segregated Ti02 anatase phase. Higher level of incorporation of as much as ca. 6 and 8 % were claimed, using either silicon... 

This facilitates the flow of degradable species through these tunnels onto the surface of the TiC>2 where electron could be donated to the holes of the anatase phase and the photocatalytic action in combination with the cavitational effect of the ultrasound can accelerate the fragmentations of pollutants. The details of this mechanism are however discussed at the end of chapter. Ultrasound also breaks TiC>2 particles to still smaller size and increases the active surface area manifold. 

Moziaa S, Morawskia AW, Toyodab M et al (2009) Application of anatase-phase Ti02 for decomposition of azo dye in a photocatalytic membrane reactor. Desalination 24 97-105... 

Fig. 3 Suggested scheme for the transformation of layered titanate to anatase Ti02 nanoroad. The structure models presented are the projection along the nanotube axis, i.e., the [010] of the titanate. The final TiOz nanorod product shown is the (010) face of the anatase phase. Elaborated from the picture reported by Nian and Teng.165...

Figure 1.2 XRD patterns for three Ti02 samples obtained by hydrothermal treatments at 80°C (a) and 180°C (b) and after calcination at 450°C (c) [21 ]. From the six XRD peaks identified with the anatase phase, the broadening of the (101) peak at 25.4° was chosen to estimate the average grain size of these samples. Generally, the sharper the peaks, the larger the particle size. The differences in grain size identified in these experiments were correlated with photocatalytic activity. (Reproduced with permission from The American Chemical Society.)...

Pilling-Bedworth ratio of 1 96, anatase phase films can show cracks and fissures with, consequendy, a loss of mechanical stability, however a hydrogen reduction treatment above 600°C leads to phase transition from anatase (101) to rutile (110) [43] with XRD detecting TiH2 upon prolonged hydrogen treatment of titania. As shown in Fig. 4.4, introduction of vanadium increases the intensity of the anatase Ti02 peak above 700°C disappearance of the vanadium (001) peak and the simultaneous appearance of the rutile (110) peak are observed, but anatase continues to dominate even after heat treatment at 800° C. A sharp vanadium (001) peak is observed for heat treatments carried out in air, while no vanadium peak has been seen in the case of heat treatment at 600°C in presence of Ar/H2. 

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