Mercury intrusion experiments with

Mercury Intrusion Experiments with Silica Spheres. These silica spheres (S980 G1.7 from Shell) were not examined in the same detail as were the other silica samples, but the photographs are included because they illustrate the effect of mercury intrusion on the integrity of the solid. These particular spheres have a typical pore volume of 1 cm3/g and a pore diameter of 60 nm. The particles are also much larger than the Sorbsil materials (1.7 mm in diameter, compared to 40 to 60 pm for the Sorbsil materials). 

Mercury Intrusion Experiments with Silica Spheres... 

In this study, a mercury intrusion experiment was performed with a constant injection rate by regulating the intrusion pressure [58]. This is different from the conventional mercury intrusion experiment where the intrusion pressure is initially kept constant to record the mercury intrusion volume, then incremented to record the resultant incremental intrusion. In our experiment, the injection rate was kept extremely low so that the pressure loss due to flow was negligible compared with the capillary pressure. The data from this constant-rate mercury intrusion (CRMI) method, also called APEX [58], was collected through the pressure fluctuations as a function of intrusion volume, shown in Figure 3.7.4. 

Fig. 1.18A shows the pore size distribution for nonporous methacrylate based polymer beads with a mean particle size of about 250 pm [100]. The black hne indicates the vast range of mercury intrusion, starting at 40 pm because interparticle spaces are filled, and down to 0.003 pm at highest pressure. Apparent porosity is revealed below a pore size of 0.1 pm, although the dashed hne derived from nitrogen adsorption shows no porosity at aU. The presence or absence of meso- and micropores is definitely being indicated in the nitrogen sorption experiment. 

Table II provides another illustration of this effect. In these experiments analysis was done by mercury intrusion, which is sensitive to a broader range of pores. In this series of experiments, samples of hydrogel were washed in various alcohol-water mixtures to yield pore volumes ranging from high, for the sample washed in pure alcohol, to low, for the sample washed in pure water. This procedure does not affect the surface area, which remained constant at 375 m2/g The activity of the finished catalyst increases with the pore volume. Notice that all samples have about the same volume inside...

In Fig. 9 three orthogonal slices through the reconstruction of the XVUSY crystal are displayed. The x-z projection shows a cylindrical mesopore that connects the interior of the crystal with the outside world . For one and the same mesopore marked with a white arrow in all three projections it is clear that no connection to the external surface via the mesopore network exists. In other words, this mesopore is a cavity in the crystal and will hardly contribute to reduction of mass transfer resistance. From independent measurements based on physisorption and mercury intrusion [29] it has been found that 30% of the mesopore volume in this material is present in cavities that are connected to the external surface only via micropores. More recently elegant proof from thermoporometry experiments for the existence of these cavities has been published [31]. 

Curves c and d in Figure 9 show nitrogen desorption and mercury intrusion traces, respectively, for pore size distributions after the initial intrusion experiment and subsequent mercury removal. In a surprising result, no permanent modification to the structure was caused by the initial intrusion experiment. In view of the results obtained with the silicas of larger pore size (Sorbsil C200 and C500), the results can be rationalized only in terms of a completely elastic compression of the structure during the intrusion experiment. 

Figure 5 shows the mercury intrusion and retraction curves, analysed using Bqs. (4) and (S), respectively, for a sample of pellets from batch G2. It can be seer that at smaller pore sizes, widiin the error in eqs. (4) and (S), the intrusion and extrusion curves overlay each otoer, while the point of separation of the intrusion and retraction curves occurs at a fractional occupied volume of 0.67, and that die final level of mercury entrapment is 40 %. Table 1 shows the mmeuty entrapment levels for several samples taken from bmch G2. From Table 1, it can be seen that the experiments are rep tabl and toe value of entr ped mercury agre well with that predicted from toe models derived from MR images above. 

The CFP and Darcy air-permeability data discussed in Sect. 5.1 were correlated with mercury porosimetry (total PSD) and water porosimetry (hydrophobic PSD) before and after the consecutive aging/durability-testing experiments for cell M2. Mercury porosimetry can be effectively used to measure the total porosity and PSD of a GDL. This technique measures all porosity that exists (including constricted or dead-ended pores). The mercury intrusion volume also represents the hydrophobic plus hydrophilic surface domains because mercury is nonwetting for both types of pores. 

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. 

As was observed for the C500 silica, reanalysis of the pore structure by nitrogen sorption (Figure 8, curve c) following intrusion and removal of mercury indicates that the porosimetry experiment results in a permanent loss in pore volume and a shift to smaller pore sizes. In C200, however, this loss in pore volume no longer approximates that associated with the broad-diffuse area of the intrusion trace. Instead, the loss represents only... 

In order to calculate the true volume intrusion of mercury into the pores of a sample, a correction must be made to account for the compression of mercury, sample cell and sample [69]. The usual procedure is to carry out a blank experiment in the absence of a sample or with a non-porous sample [70]. During the course of calibration measurements on non-porous nylon it was found that a normal blank correction procedure led to erroneous mercury penetration volumes [71]. In particular it was found that the shape of the intrusion curve varied with the size of the sample. 

The contact angle 0 between the mercury and the sample surface has a great impact on the pore size distribution calculated from MIP experiments (Figure 9.4). Most MIP users adopt 0 = 140° but the Hg contact angle may vary with sample properties (e.g. chemical composition and intrusion or extrusion step). 

---