Diameter of silica

Fig. 23 Confocal laser scanning microscopic image of rhodamine-labeled SiP coated with PMMA brush The diameter of silica particle core is 230 nm, and the Mn of the graft polymer is 256000...

Unfortunately, even this modified equation does not describe the true practical situation in LC, as it is complicated by the fact that all silica-based materials exhibit exclusion properties. The pore diameter of silica-based stationary phases can range from, perhaps, 2-3 Angstrom to as much as 1000-2000 Angstrom. Consequently, some, otherwise open pores, are accessible to the solute while others are not, depending on the size of the molecule. Therefore, only those pores that have a diameter equal to, or greater than, that of the solute molecules are accessible and only the stationary phase within those pores can effect retention. In addition, the static interstitial volume between the particles can also exhibit exclusion properties and some of the static interstitial volume may also be inaccessible to the larger solutes. As a consequence, equation (12) must be further modified to give,... 

Fig. I. Average particle diameter of silica gels as a function of the volume ratio of H2O to EtOH and the addition amount of NH3, a base

MCM-41 (Cl2) < MCM-41 (C16) < silica 40A. The mean pore diameter of silica 40A is about 40 A, according to the calculation using the BJH method It is very interesting that the peaks on these curves can be related to the pore structures of the samples. There should be an intrinsic relation between the pore size and the position of the peak on the / axis We now try to derive an empirical expression for this relation from known experimental data of Al-PILM and MCM-41 samples of various pore sizes. These samples have a well-defined pore structure and a narrow... 

Table 1 lists the surface area of prepared catalysts and the chemisorption results of CO2 and H2 on the catalysts. In case of supported Fe catalysts, the sxirface area is support-dependent. In contrast, Fe-K/Si02 shows much smaller surface area compared with silica or Fe/Si02. This indicates that with increased mass of active phase, iron and potassium blocks the micro-pore of silica support. This seems to be due to the smaller pore diameter of silica (see experimental). In addition, if Fe-K exists mainly as poorly dispersed masses, it would block easily the micro-pores of the support. From the chemisorption results, it is apparent that only y-alumina-supported catalysts, Fe/Al203 and Fe-K/Al203 give greatly... 

A column (5 cm in diameter) of silica gel (J. T. Baker, 233-400 mesh, 250 g, dry-packed) was equilibrated with 20% hexanes in dichloromethane. The crude material dissolved in a minimal amount of chloroform was loaded on the column and eluted with 20% hexanes in dichloromethane. Fractions were collected in 15 x 160 mm test tubes. 

The pore diameter limitation also was found for Pd-Cnd catalysts active in the C=C hydrogenation of ( )-2-phenylcinnamic acid. On a 5% Pd-silica catalyst the ee s increased with increasing average pore diameter of silica, and the conclusion was that Pd metal particles should be located in pores large enough to accommodate the bulky alkaloid-modifier molecules and the substrate forming intermediate complex modifier-reactant that have been identified on the surface of Pd-titania catalyst (Nitta et al. ). Palladium metal particles in smaller pores are difficult to modify and they behave therefore as non-selective centers. 

Effect of Sodium Silicate Concentration On Nuclei Diameter of Silica Made by Deionization with Ion Exchange Resins, Electrodialysis and Acidification... 

A. Braun, K. Franks, V. Kestens, G. Roebben, A. Lamberty, T. linsingta. Certification Report. Certification of Equivalent Spherical Diameters of Silica Nanoparticles in Water. Certified Reference Material ERM -FDI00 (Publications Office of the European Union, Luxembourg, 2011). ISSN 1018-5593, doi 10.2787/33725... 

Figure 43 (a) Measured mobility magnitudes for four silica sols as a function of frequency. The units on the y-axis are 10 m s. Diameter of silica particles (O) 1 micron,... 

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