Calcinations composite particles

Fig. 4 a, b. TEM micrographs of hollow silica spheres produced by calcining PS particles coated with (a) one and (b) three Si02 nanoparticle/PDADMAC layer pairs at 450°C. The wall thickness of the hollow capsules is approximately three times greater for those shown in (b) compared with those shown in (a), c, d Cross-sections of the hollow silica spheres of the same composition as those shown in (b). The hollow silica spheres retain the spherical shape of the original PS particle templates (see Fig. 3). (Adapted from [22,62] by permission of the American Association for the Advancement of Science and the American Chemical Society)...

In case of the specimens calcined at 1300 and 1400 °C composite particles were observed with a transmission electron microscope. However, no composite particles were found in the specimens prepared at 1200 °C. The maximum deposit weight was 115.2 mg/cm (1200 "C), followed by 70.0 mg/cm (1300 °C), and 66.6 mg/cm (1400 °C). The deposit weight tended to decrease as the calcination temperature increased and the particle size became larger. 

TEM pictures of samples deposited by EPD revealed that some particles started necking in the sample prepared at a calcination temperature of 1200 C, but no composite particles were found (Figure 1). 

However, the powders prepared as calcination temperatures at 1300°C and at 1400°C were composite particles with black particles incorporated into the white particles (Figs 2 and 3). EDX revealed that the white particles were alumina and the black particles were zirconia. This demonstrated that when the powders were calcinated at 1300X or 1400 C, the zirconia became incorporated with the alumina to form composite particles. 

Figure 2.TEM micrograph of Ce-TZP/Al203 mixture calcined at 1300 °C. A TEM micrograph showed composite particles with black particles (zireonia) incorporated into the white alumina particles.

Figure 3. TEM micrograph of Ce-TZP/AUOs mixture calcined at 1400 °C. Composite particles were also observed and the size of the particles was greater than that observed in the specimens calcined at 1300 °C.

Preparation of mixed metal oxide precursors for SOFCs represents a very complex chemical process in which a metal may form oxides, hydroxides, and various complex basic salts as intermediates. Understanding of the relationship between the calcination process, the final composition, particle sizes, sinterability, and SOFC performance for nickel, copper and cobalt-based anode materials is a necessity [26]. 

Several steps of preparation, including the support composition, metal salt, method of metal addition, pH, metal loading, calcination, etc., affect the ultimate particle size in the reduced catalyst. The... 

Homogeneous, nanosized, copper-loaded anatase titania was synthesized by an improved sol-gel method [197], These titania composite photocatalysts were applied to the photoreduction of carbon dioxide to evaluate their photocatalytic performance. Methanol was found to be the primary hydrocarbon product [198], Under calcination conditions, small copper particles are well dispersed on the surface of anatase titania. According to XAS and XPS analysis, the oxidation state of Cu(I) was suggested to be the active species for C02 photoreduction [199], Higher copper dispersion and smaller copper particles on the titania surface are responsible for a great improvement in the performance of C02 photoreduction. 

The nebulization was also employed to generate composite powders for specific applications, such as in ceramics, by hydrolyzing with water vapor droplets containing Al(5ec-OBu) and silicon methoxide in the atomic ratio Al/Si = 3. This ratio of alkoxides was chosen in order to produce mullite, which was achieved by calcination of the resulting amorphous particles at rather high temperatures (up to I400 C) (52). In another approach a mixed Al-Mg-Si ethoxide was first synthesized, and then nebulized and hydrolyzed as usual (77). Depending on the experimental conditions, the powders calcined at 500 C exhibited structures of pure cordierite, or mixed with forsterite. In all of these described cases the nebulization yielded spherical but polydisperse particles. 

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