Pore macropores

In the majority of cases nanoporous materials exist in a highly dispersed state (seldom - as films). It limits practical application of these materials and in many cases makes difficult for study of their properties. Samples of the nanoporous carbon (NPC) used in this work are produced as a body of cylinder shape with a sufficient mechanical strength. They synthesized by heat treatment of carbide silicon and carbide titanium in chlorine have been studied in the present work. The samples of materials are characterized by the advanced structure of pores, which contains two types of pores macropores (with the sizes in a few micron) and nanopores with sizes about 0.8 nm. Surface area and volume of pores NPC with... 

As our earlier investigations of coal suggested that the scattering was due to pores in the coal (7), we analyzed our scattering data under the assumption that the scattering was produced by three classes (15) of pores—macropores, with dimensions of 1 micron or more transitional pores, which have dimensions of a few hundred A, and micropores, which were not larger than about 20 or 30 A. 

According to the porosity data of Uchida et al. [102] the matrix of carbon grains (20-40 nm) forms an agglomerated structure with a bimodal psd. Primary pores (micropores, 5-40 nm) exist within agglomerates, between the carbon grains. Larger, secondary pores (macropores, 40-200 nm) form the pore spaces between agglomerates. The relation between the relative pore volume fractions of the two pore types depends on the contents of PFSI and PTFE. Due to their molecular size these components are not able to penetrate micropores. They affect only the macropore volume. The experimental study revealed that an increased PFSI content leads to a decrease of the macropore volume fraction. The opposite effect was found for PTFE. 

In the following analysis, the catalytic activity is assumed to be proportional to the surface area per gram, Sg, which varies inversely with the pore radius [Eq. (4.5)]. The surface area is also proportional to the pore volume Vg, but increasing Vg gives a weaker pellet, and so Vg and e are assumed constant. Although a broad distribution of pore sizes is better than a narrow distribution for fast reactions, analysis shows that a bimodal distribution is likely to be the optimum. If there are just two types of pores, macropores and micropores, the total surface area is... 

Micropores Gel pores Macropores Capillary pores Air pores... 

Since recently, monoliths of silica gel or organic pofymers became popular in HPLC of low-molecular substances. They exhibit reduced flow resistance and high mechanical strength. Their internal structure forms the sohd matrix and two kinds of pores. Macropores or charmels allow fast transport of mobile phase, while the separation processes take place in the smaller mesopores. So far, however, most commercially available monoliths possess too small effective volume of the mesopores to compete with particulate colurrm packings in polymer HPLC, especially in SEC. 

Before consolidation, more than 90% pores are small pores. While, after consolidation, the quantity of small pores increases and medium pores, macropores almost disappear in horizontal section the quantity of small pores in vertical section also increase but the tendency is not as obverse as the former. The change of pore quantity indicates that the relative position among particles adjusts constantly during the consolidation process. 

If the trends in the pore size and the micropore volume data are compared, it may be concluded that the acid first affects the walls of the wider pores (macropores and mesopores), as these are more accessible. 

Comparing aerogels with differmt pore macropore sizes (samples 2 and 3), however, a similar microporosity yidds diffiision coeffidents that differ by hbout a fiictor of 10, Le. the ratio of the respective m xopore sizes. Le. despite dm same microporosity and an even larger external surface the sur m transport component decreases with the pore size (see also ref. [10]). 

Maxwellian diffusion (bulk molecular diffusion) in moderately large pores (macropores) or Knudsen diffusion in pores (micropores) which have a diameter smaller than the mean free path of the adsorbate molecules ... 

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