Mercury porosimetry data

Fig. 2. Plot to calculate surface fractal dimension by mercury porosimetry data.

From the mercury porosimetry data, porosity can be calculated. A higher porosity means a more open pore structure, thus generally providing a higher permeability of the membrane. Porous inorganic membranes typically show a porosity of 20 to 60% in the separative layer. The porous support layers may have higher porosities. 

Fig. 2.1.14 Mercury porosimetry data for ordered silica packing structures.

Figures 11.1 and 11.2 illustrate mercury porosimetry data of a bimodal size distribution. However, other types of less typical curves are often encountered. For example, samples of controlled porous glass exhibit intrusion-extrusion curves illustrated by Fig. 11.3, in which all the pores are essentially of one radius.

Fio. 14. Integral and differential intrusion mercury porosimetry data for sample G1 (from Salejova et al., 2004). 

The pore size distribution (see Fig. 3) can be obtained from the mercury porosimetry data and the t-plot from N2 adsorption isotherms, using an active carbon with a very low surface area as a reference [13]. It was observed that the volumes of mercury intruded were very small. As a consequence, the volumes of meso (the largest ones) and macropores are low. Thus, the samples studied are mainly microporous, as already mentioned in the N2 and CO2 adsorption isotherm results. 

Table 1 summarizes the results. For Vycor, an average pore size 44 A is calculated, which is in an excellent agreement with that claimed by the manufacturer and also reported to several other studies [14, 20]. For CPG s the calculated pore sizes are in good agreement with their nominal ones. One may note that the polydispersity in CPG s is slightly overestimated. Further detailed analysis of the results and comparison with gas adsorption and mercury porosimetry data is under progress. 

Figure 4.10 shows the pore size distribution data of an alumina membrane by mercury porosimetry. This particular sample has a three-layered structure. The support has a relatively narrow pore size distribution but the membrane layer and the intermediate support layer do not show a clear distinction on the mercury porosimetry data. Typical mercury porosimetry analysis involves intrusion and extrusion of mercury. The intrusion data are normally used because the intrusion step precedes the extrusion step and complete extrusion of mercury out of the pores during the de-pressurization step may... 

The macropore size distributions of C8-C18 obtained from mercury porosimetry data had two peaks however, the peak observed at very high pressures of mercury is not considered because of the possible collapse of the structure at high pressures. The macropore diameter decreases in going from C8 to C16, with exception of C12 whose pore diameter is higher than that of C8. The pore diameter of C18 is also found to be higher than that all other samples except C12. 

Mercury porosimetry data can also be used to estimate grain size/particle size, assuming the shape of the particles to be spherical, using... 

Some materials, among the most porous, show a large volume variation due to mechanical compaction when submitted to mercury porosimetry. High dispersive precipitated silica shows, as low density xerogels and carbon black previously experimented, two successive volume variation mechanisms, compaction and intrusion. The position of the transition point between the two mechanisms allows to compute the buckling constant used to determine the pore size distribution in the compaction part of the experiment. The mercury porosimetry data of a high dispersive precipitated silica sample wrapped in a tight membrane are compared with the data obtained with the same sample without memlM ane. Both experiments interpreted by equations appropriate to the mechanisms lead to the same pore size distribution. 

Figure 3. Pore size distribution functions (mercury porosimetry data) for A) initial CPG (D = 30.5nm) (solid line) and the same material heated for 20 hrs at 650°C (dashed line) 20 hrs at 720°C (dotted line) 20 hrs at 805°C (dash-dotted line), B) initial silica gel (D = 32.8 nm) (solid line) and the same material heated for 20 hrs at 580°C.

Figure 5. Pore size distribution functions (mercury porosimetry data) for CPG (D = (solid line) and sihca gel (D 58.0 nm) (dashed line).

In order to quantify this pore-gradient structure, the corresponding mercury-porosimetry data have been shown in Fig. 4(a-c). From (a) to (c) in Fig. 4, a pore-gradient can be observed. This pore-gradient shows the largest pores with d 250 nm in the bottom layer and the smallest pores with d w 40 nm in the top layer. According to Kruyer [10] and Mason [11] (see 2.1), the particles which contribute to this pore size of d 40 nm, have a... 

Mercury-porosimetry data Tor sintered specimens at I000 C for 3 h... 

It is apparent that the bubble point is telling us that a 0.2 ju pore size membrane has at least one pore up to 0.8 ju in diameter. This is confirmed by mercury porosimetry data (see Figure 2.17). 

Z)(r) is obtained from the slopes of a plot of V versus AP. An example is shown in Figure 2.2. Mercury porosimetry data, in terms of the rate of penetration into the porous medium, can also be evaluated with the aid of the Washburn equation (Equation 3.31). 

A similar problem is encountered for the analysis of mercury porosimetry data. The approach based on Equation (6.13) neglects the surface area of the sample-mercury interphase at the beginning of the intrusion process So. If Equation (6.10) is applied to data over a range of mercury pressures, then the effect of neglecting So may be significant. Therefore, Equation (6.10) should be corrected by incorporating So, thus obtaining... 

---