Pore parameters

The surface areas and pore parameters of AMM samples are listed in Table 1. It is found that, after post-synthesis alumination, the surface area of the resulting AMM material decreases. For PSM, the surface area is 1311 m2/g. With the increase of A1 content, the surface area of AMM samples drops gradually from 1211 to 997 m2/g. Meanwhile, the pore diameter and total pore volume decrease with increasing A1 content. Since the dioo spacing is not affected by post-synthesis alumination, the decrease of pore diameter indicates that the pore wall becomes thicker. The results... 

The Nj adsorption isotherms at 77 K were of Type I. The adsorption isotherms of Nj were analyzed by the SPE method using the high resolution a, -plots, as shown in Figure 1. The adsorption isotherm of N, on nonporous carbon black (Mitsubishi Chemical Co. 32B) was used as the standard isotherm. The features of the a -plots were similar to that published in the preceding paper." We can determine the micropore volume W , total surface area a , and the external surface area from the a -plots. The average pore width w can be evaluated from both the surface area and pore volume of slit-shaped micropores. Table 1 summarizes these pore parameters. 

Pore parameters of Carbosil E and their activation product (Carbosil E/A). (The data from the adsorption and desorption isotherms of benzene vapours measured at 25 C)... 

Table 2.1 lists some of the pore parameters obtained from a 3D image analysis of a fried product. Miri et al. (2006) studied the effect of frying time and temperature on crust formation and pore characteristics of French fries using the x-ray micro-CT technique, and conclnded that the method allowed not only a fundamental understanding of the frying process, but also a process design that would result in specific microstructnres. 

Resistance to the flow of liquids depends on the same pore parameters but is, by nature, much higher. Therefore, during typical processing speeds, it is impossible to remove liquids from the pore space. In addition, liquids are incompressible. Therefore, if the pores are completely filled with liquid from the outset or as soon as the diminishing pore volume becomes saturated, densification ceases and the applied force increases suddenly endangering the equipment if no safety features are provided. The characteristic of the pressure rise depends on the type of drive and whether it is mechanical or hydraulic. 

In Fig. 7, the power spectrum obtained from TEM images is shown together with the PSD detennined by gas adsorption for three ACFs with different BET surface areas. Here, it has to be mentioned that, since the power spectrum is expressed in the reciprocal space, the distance in the real space indicated on the abscissa increases to the left-hand side. Therefore, the PSDs are plotted in the same manner. By taking into account that the magnification of TEM observation for this analysis does not provide information on distances >5 nm, there is a relatively good correspondence between the power spectrum from TEM observation and the PSD from gas adsorption. The distribution estimated from the TEM image is a little broader than that from gas adsorption, which is supposed to be due to the fact that three-dimensional averaging is performed in the former, whereas the minimum value of pore parameters is detected in the latter. As shown in Fig. 7, the area under the power spectrum curve coiTesponds to the relative pore volume. 

Pore parameters measured by image analysis on high-density isotropic graphite blocks. Reprinted with permission from Ref. [58] with pennission from Carbon Society of Japan. 

The same procedure as for oxidation yield was applied to Sbet and to several porous textural parameters determined by the alpha method (total surface area, external surface area and micropore volume) on each sample oxidized in dry air. This led to the master curves at 673 K for the respective parameters shown on Fig. 21. All master curves for pore parameters were derived by using the same shift factors as for the oxidation yield (i.e., the same apparent activation energy). 

From this pore parameter analysis with air oxidation, it is deduced that pore development in glass-like carbon spheres proceeds principally through the progressive enlargement of ultramicropores to macropores through supermicropores and mesopores. 

Changes in pore parameters of the carbon aerogels with the heat treatment at high temperatures are listed in Table 13 [153]. With increasing heat treatment temperature, both total surface area and volume decrease, which is mainly due to the decrease in micropores. As a consequence, heat treatment of the carbon aerogel above 2273 K was found to give a carbon containing only mesopores. 

TABLE 12. The composition and pore parameters of some zeolites (Maxwell, 1982). 

Utilizing the low volume shrinkage process, a total of five samples of nanoencapsulated OPAA were prepared along with control samples. The control samples either lacked the pore-forming agent (template) or the enzyme. Note that data for the control samples are not presented. Table I summarized the physical pore parameters (pore size, surface area, and pore volume) and... 

Fig. 9.3 Complex plane plot of impedance of single pore parameters ...

Because the correct numerical solution for a porous electrode in the presence of a potential gradient in pores demands knowledge of the pore parameters and more complex mathematics, in practice, a simplified de Levie equation (9.7) is used in approximations, which means that the experimentally measured impedances are fitted to Eq. (9.7). As was shown earlier, for the same pore and kinetic parameters, de Levie s equation underestimates low-frequency impedances by up to 100%, which might not be that important for very porous electrodes characterized by a very large surface area. 

Fig. 9.26 Complex plane plots at porous electrode in presence of redox proeess at eonstant overpotential rjO = 0.2 V and different exehange current densities continues lines - simulatirais, Eq. (9.46), dashed line - according to de Levie s equation (9.7) Cji = 20 uF cm, other pore parameters as in Fig. 9.22 (From Ref. [72] with kind permission from Springer Seience and...

Fig. 9.33 Complex plane plots on porous electrode at various concentrations of oxidized species in absence of potential gradient in pores parameters E — ° = 0V, / = 0.05 cm, r = 10 cm, D = 10" cm s", k° = 10 cm s", o = 1.58 concentrations indicated in graph continuous line total impedance, dashed lines faradaic impedances...

Fig. 9.36 Tafel plots on porous electrode at different concentratirais of active species. Concentrations (

The simplest method of taking into account the distribution of pores of different sizes is to use the transmission line ladder network (Fig. 9.4,9.14,9.17, or 9.19) and use different values for the parameters ri, r, and Ci or interfacial impedances z-, and calculate the total admittance by the addition of the admittances of the small pore elements. Such a method was used, for example, by Macdonald et al. [446,447] and Pyun et al. [448]. Although such a model can be used to simulate impedance spectra assuming changes in parameters with the position in the pore, it is difficult to obtain the pore parameters from the experimental spectra. 

Another method is to assume a certain distribution of pore parameters. Song et al. [449 52], in a series of papers, considered the distribution of pore parameters for electrodes in the absence of electroactive species, i.e., for purely capacitive electrodes. De Levie s equation (9.7) is applicable to individual pores, but for different pores different values of the parameter A are obtained. The dimensionless penetrability parameter, a, was defined as... 

It indicates that the threshold value is a very important factor affecting the determined pore parameter, and significantly depends on the tested soil samples. However, it is suggested that a relative small threshold value (60-100) should be chosen when a SEM image is employed to quantify the pore parameters. In this study, a value of 80 is chosen as the reference in the next sections. 

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