Silica particle pore diameter

Wikberg et al. (2011) studied porous silicas (average pore diameter 6, 20, and 30 nm [Purospher STAR] with 5 m particles, and silica 10 nm [Merck] with 3 xm particles used as hydrophilic stationary phases in liquid chromatography) using the NMR spectra of bound water... 

The main driving force for the electrochemical deposition of sol—gel films is the electrolysis of H2O, which not only generates OH ions but also induces H2 evolution on the cathode. The latter causes the deposited films to be porous. This structure may deteriorate the corrosion resistance of the films as reported by Hu et al. [18,42], but on the other hand it is beneficial for the application of the films in electroanalysis, as it does not completely block electron transfer on the electrode [20,28]. The pores induced by H2 are large, and the obtained films are macroporous consisting of silica particles with diameter of a few himdred nanometers. In order to better tune the morphology of the films, templates are desired for electrodeposition. 

Information on the morphology of the nanohybrid sorbents also was revealed with SEM analysis. Dispersed spherical polymer-silica particles with a diameter of 0.3-5 pm were observed. Every particle, in one s turn, is a porous material with size of pores to 200 nm and spherical particles from 100 nm to 500 nm. Therefore, the obtained samples were demonstrated to form a nanometer - scale porous structure. 

SynChropak GPC supports were introduced in 1978 as the first commercial columns for high-performance liquid chromatography of proteins. SynChropak GPC columns were based on research developed by Fred Regnier and coworkers in 1976 (1,2). The first columns were only available in 10-yu,m particles with a 100-A pore diameter, but as silica technology advanced, the range of available pore diameters increased and 5-yu,m particle diameters became available. SynChropak GPC and CATSEC occasionally were prepared on larger particles on a custom basis, but generally these products have been intended for analytical applications. 

SynChropak size exclusion supports are composed of spherical uniformly porous silica that has been derivatized with a suitable layer. SynChropak GPC supports are available in six pore diameters ranging from 50 to 4000 A and particle diameters from 5 to 10 /zm. SynChropak CATSEC supports are available in four pore diameters. Table 10.1 details the physical characteristics of the product lines. 

Microporous insulation materials consist mainly of highly dispersed silica with a particle size of only 5-30 nm. The highly dispersed silica powder is pressed to plates, which receive heat treatment up to 800 °C, after which the plates are self-supporting and possess a micropore structure with pore diameter of 0.1pm. The addition of opacifiers to the highly dispersed silica starting material reduces the loss of heat by radiation. The dates for such insulation boards are shown in Table 18. 

The number 10 refers to the diameter of the silica particles in micron and not the pore size. The five solutes (1-5) were largely hydrocarbon in nature having mean molecular diameters of 11,000, 240, 49.5, 27.1 and 7.4 A respectively. The mobile phase employed was tetrahydrofuran (THF). This solvent is adsorbed as a layer on the surface of the silica (a phenomenon that will be discussed in more detail... 

The column used in the separation depicted in figure 1 was 25 cm long and 6.2 mm in diameter packed with silica gel having a mean pore diameter of 100 A and a particle diameter of 5 jum. Thus, the column would have an HETP of approximately 0.001 cm (twice the particle diameter). Consequently, a column 25 cm long would have an 25... 

The mechanical incorporation of active nanoparticles into the silica pore structure is very promising for the general synthesis of supported catalysts, although particles larger than the support s pore diameter cannot be incorporated into the mesopore structure. To overcome this limitation, pre-defined Pt particles were mixed with silica precursors, and the mesoporous silica structures were grown by a hydrothermal method. This process is referred to as nanoparticle encapsulation (NE) (Scheme 2) [16] because the resulting silica encapsulates metal nanoparticles inside the pore structure. 

The first phase in the process is the formation of the sol . A sol is a colloidal suspension of solid particles in a liquid. Colloids are solid particles with diameters of 1-100 nm. After a certain period, the colloidal particles and condensed silica species link to form a gel - an interconnected, rigid network with pores of submicrometer dimensions and polymeric chains whose average length is greater than one micrometer. After the sol-gel transition, the solvent phase is removed from the interconnected pore network. If removed by conventional drying such as evaporation, so-called xerogels are obtained, if removed via supercritical evacuation, the product is an aerogel . 

Zirconia particles have been promoted recently as support replacing silica with the proposed advantage of better chemical, thermal, and mechanical stability. Such zirconia-supported chiral phases have been prepared by Park and coworkers [77] through coating, for example, of 0-9-[3-(triethoxysilyl)propylcarbamoyl]quinine onto 5 p.m zirconia particles (30-nm pore diameter) or carbon-cladded zirconia particles as support [78]. In comparative tests with corresponding silica materials. 

BET measurements (Table 1.2) prove the increase in mesopores, as decreasing the total polymerization time from 24 h to 45 min causes to raise by a factor of 3, resulting in 5p 80mVg, which is comparable to silica particles with a mean pore diameter of 300 A [112,113]. 

The physical properties of silica are determined by its specific surface area, pore volume, average pore diameter, porosity, and the particle diameter and shape [8]. The latter two are responsible for the efficiency, the physical stability and the pressure drop of the packed columns and do not contribute to retention and selectivity. 

In section 6.3.1 it was described, that macroporous silica particles are veiy effective carriers for lipase inunobilization, provided that the pore diameter is larger than about 500A. For industrial use the particle size catmot be less than 200-300 m. 

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,... 

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