Silica compounds spherical particles

FIGURE 2.49 Pore size distributions for selected oxides calculated on the basis of nitrogen desorption and hexane adsorption with the model of voids between spherical particles. (Adapted from J. Colloid Interface ScL, 348, Gun ko, V.M., G.R. Yurchenko, Turov, V.V. et ak. Adsorption of polar and nonpolar compounds onto complex nanooxides with silica, alumina, and titania, 546-558, 2010d, Copyright 2010, with permission from Elsevier.)... 

Untreated silicas in PVC compounds show a decrease in yield stress with increasing particle content and size, which is higher when the filler particles are irregular in shape than when the compounds are filled with particles of spherical shape. To improve the adhesion at the particle/matrix interfaces, treatment with a silane coupling agent (y-aminopropyl methyldiethoxysilane) increases the yield stress generally, and more so with irregular shaped than spherical particles. 

Thus it appears that the colloidal behavior of Th02 slurries may be minimized through the use of spherical particles, larger particles, coating the particles with silica or some other compound, or by the use of some as-yet-unperfected additive. 

The most common support is highly pure, spherical, microporous particles of silica that are permeable to solvent and have a surface area of several hundred square meters per gram (Figure 25-5). Most silica should not be used above pH 8, because it dissolves in base. Special grades of silica are stable up to pH 9 or 10. For separation of basic compounds at pH 8-12, polymeric supports such as polystyrene (Figure 26-1) can be used. Stationary phase is covalently attached to the polymer. 

Ocana, M. and Gonzalez-Elipe, A.R., Preparation and characterization of uniform spherical silica particles coated with Ni and Co compounds. Colloids Surf. A, 157, 315, 1999. 

Hematite was selected as a model colloid in this study due to its well understood a egation behaviour, the monodisperse, spherical nature of the colloids and the fact that the synthesis of colloids of various primary particle sizes (40 to 500 nm) is possible. While silica and clays may be more abundant in surface waters, hematite appears to be a good compromise between real systems and a simple model compound. 

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