Silica submicronic

As an example of composite core/shell submicron particles, we made colloidal spheres with a polystyrene core and a silica shell. The polar vapors preferentially affect the silica shell of the composite nanospheres by sorbing into the mesoscale pores of the shell surface. This vapor sorption follows two mechanisms physical adsorption and capillary condensation of condensable vapors17. Similar vapor adsorption mechanisms have been observed in porous silicon20 and colloidal crystal films fabricated from silica submicron particles32, however, with lack of selectivity in vapor response. The nonpolar vapors preferentially affect the properties of the polystyrene core. Sorption of vapors of good solvents for a glassy polymer leads to the increase in polymer free volume and polymer plasticization32. 

Fig. 4.2 TEM images of fabricated nanoparticles, (a) Isolated composite core/shell submicron particles, (b) Hollow silica submicron particles prepared by removing the polystyrene core to demonstrate the high quality of the formed sol gel shell of the composite nanospheres employed to prepare sensing colloidal crystal films...

Oostervink, R., Kraak, J.C., and Poppe, H., Hydrodynamic chromatography of soluble macromolecules of columns packed with submicron nonporous silica particles, Am. Lab., 30(6), 24C, 1998. 

Baral, S. and Schoen P. (1993) Silica-deposited phospholipids tubules as a precursor to hollow submicron-diameter silica cylinders. Chemistry of Materials, 5, 145-147. 

A new desiccant formulation was prepared from a mixture of submicron-sized silica gel and molecular sieves to achieve the best combination of large water capacity, rapid moisture adsorption and easy regenerability. The formulation also tolerates the presence of VOCs and smokes. Commercial NaX and silica gel were crushed and mixed in the proportion of 1 2 and wash coated on a monolith for testing. The same test cell shown in Fig. 12.7-2 was used. The airflow to the saturator was adjusted to obtain the desired humidity in the feed air. Humidity sensors located at the flow cell inlet and outlet, were used to... 

FIGURE 6.10 Experimentally measured diameter of submicron fused silica particles as a function of particles diameter determined from scanning electron microscopy measurements. Dashed line corresponds to 1 1 size relationship. (From Shcheslavskiy, V., Petrov, G. I., Faustov, A., Yakovlev, V. V., and Saltiel, 5. Optics Lett., 31(10) 1486-1488, 2006. Used with permission.)... 

We have combined these approaches of pore size engineering with another synthesis route where uniform spherical particles are obtained in the micron and submicron size range [7]. The latter procedure allows one to adjust the particle size and size distribution of the silica particles by the reaction conditions. 

W. Wang, X. Fu, J. Tang, L. Jiang, Preparation of submicron spherical particles of silica by the water-in-oil microemulsion method, Colloids Surf. A Physicochem. Eng. Aspects 81 (1993) 177-180. 

A direct application to chemical process technology of the principle of electric wind is in electrostatic precipitators (Leonard et al.,1983) and electrocyclones for size separation of particles in powder technology (Nenu et al., 2009). Electrostatic precipitators applied to exhaust gas cleaning have recently been reviewed 0aworek et al., 2007). A particularly interesting development is that of a small electrocyclone with a diameter of 75 mm (Shrimpton and Crane, 2001). With this device it was shown that the separation quality of the smallest size particles with a diameter below 38 pm doubled upon application of the electric wind. Later experiments performed with submicron silica particles demonstrated that classification of such particles is possible by use of an electrical hydrocyclone (Nenu et al., 2009). 

NIR-absorbing metal nanostructures are appealing for biomedical imaging applications for reasons discussed previously, and this includes biological applications of SERS. For example, NIR-active core-shell superparticles have been prepared by the electrostatic assembly of densely packed Au nanoparticles on submicron silica spheres.34 Such superparticle probes can be implanted into mammalian cells by cationic transfection,186 and have produced SERS signals from absorbed DNA.187 Biocompatible SERS nanoparticle tags can also be used as contrast agents for in vivo detection, as previously discussed.169... 

There is, nevertheless, some evidence (35, 36), based in NiNaY and NiMo/ alumina/Y model catalyst systems, that the amount of coke formed is reduced with increasing intimacy of mixing of the two functions at the submicron level. This concept is further supported by the reported relatively high performance of NiW/ASA (amorphous silica-alumina) cogel HC catalysts which, it is claimed, exhibit an excellent distribution of the NiW hydrogenation function throughout the catalyst particles (37). 

Fumed silica appears as a fluffy white powder characterized by an extremly low bulk density down to the range of about 20-50 g f. In contrast, the submicron fumed silica particle consists of amorphous silicon dioxide and, hence, its true density is about 2200 g 1 ... 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

Commonly used enamels contain multiple ingredients. Typically silica, alumina and other metal oxides such as calcia arc the major ingredients. In addition, some organic additives such as dispersants and viscosity modifiers (e.g., polyvinyl alcohol) arc used to ensure that the starting slip consists of finely divided and dispersed particles in the submicron range in order to seal the pores on the end surfaces. The pores can be filled with very fine ceramic particles (Garcera and Gillot, 1986] or calcined colloidal silica... 

As previously explained, it can be advantageons to generate extraporosity at a larger scale in the separative layer. The main condition that has to be respected is that the additional porosity mnst not be directly interconnected in order to preserve the entoff fixed by the porosity of the continuous phase. Templating by polystyrene latex was nsed to prodnee individnal macropores inside the silica layer (Figure 25.25). This route can be applied to prepare membranes of other oxides with varions possible strategies in terms of the synthesis process (Figure 25.26). In addition, the presence of dispersed micron-size or submicron-size... 

The submicron-sized and nanosized light-sensitive polyelectrolyte containers have been proposed and laser-stimulated release of corrosion inhibitor from their inner volume was studied. It was shown that the release of corrosion inhibitors from containers embedded into the silica-zirconia based sol-gel matrix under UV or IR laser irradiation ensures effective suppression of corrosion at the damaged sites at the surface of the coating. The possibility of controlling the release properties of polyelectrolyte containers by tuning the illumination wavelength and intensity of the incident laser beam makes the proposed method to be a versatile tool for corrosion protection. 

Rational design, tailored synthesis and characterisation of ordered mesoporous silicas in the micron and submicron size range... 

A schematic flowsheet of the WCF is shown in Figure 3. Solidiflca-tion takes place in the 4-ft-diameter by 13-ft-high fluidized-bed calciner. Most of the plant equipment is devoted to cleaning up the entrained radioactive particles in the calciner off-gas. The off-gas passes into a cyclone to remove most of the solids, a quench tank to cool the gas, a venturi scrubber-separator-demister, a silica gel adsorber for the removal of voltaile ruthenium, another cyclone, and Anally a high-efficiency HEPA filter to remove submicron particles before discharging to the 250-ft plant stack. 

A long list of oxides was prepared sonochemically. Almost all the above-mentioned oxides were synthesized in organic solvents. The other oxides that will be discussed from here on were all prepared in aqueous solutions. Submicron size spheres of silica and alumina prepared by well-known methods were coated sonochemically by nanoparticles of oxides of europium and terbium using the same concentration of ions [81]. We have also used sonochemistry to prepare nanoparticles of silica and alumina doped with the same rare-earth ions for comparison. The highest luminescence intensities were observed for europium and terbium doped in nanoparticles of alumina of dimension 20-30 run. The intensities are comparable or higher than in commercial phosphors. 

Mesoporous silica fibers[289] were also directly drawn from a highly viscous triblock copolymer-silicate sol. These fibers have uniform exterior diameters of submicron to several hundred micron size and no apparent limit on aspect ratios. Figure 8.56 shows SEM and TEM images of nanofibers. 

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