Intrusion pressures

The increase in pore volume brought about by high intrusion pressures may be caused by fracture of the pore walls that gives access to pores... 

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. 

Mercury porosimetry is based on the fact that mercury behaves as a nonwetting liquid toward most substances and will not penetrate the solid unless pressure is applied. To measure the porosity, the sample is sealed in a sample holder that is tapered to a calibrated stem. The sample holder and stem are then filled with mercury and subjected to increasing pressures to force the mercury into the pores of the material. The amount of mercury in the calibrated stem decreases during this step, and the change in volume is recorded. A curve of volume versus pressure represents the volume penetrated into the sample at a given pressure. The intrusion pressure is then related to the pore size using the Washburn equation... 

Hofer, H. and East, M.L. (1993b) The commuting system of Serengeti spotted hyaenas how a predator copes with migratory prey. II. Intrusion pressure and commuters space use. Anim. Behav. 46, 559-574. 

Calculated from the intrusion pressure, assuming Q = 140° For a sample weighing 1.0782 g. 

The poly-[HIPE] sample intrusion mercury porosimetry study reported in Figure 4.67 was carried out in a Micromeritics, Atlanta, GA, USA, AutoPore IV-9500 automatic mercury porosimeter.1 The sample holder chamber was evacuated up to 5 x 10-5 Torr the contact angle and surface tension of mercury applied by the AutoPore software in the Washburn equation to obtain the pore size distribution was 130° and 485mN/m, respectively. Besides, the equilibration time was 10 s, and the mercury intrusion pressure range was from 0.0037 to 414 MPa, that is, the pores size range was from 335.7 to 0.003 pm. The poly-(HIPE) sample was prepared by polymerizing styrene (90%) and divinylbenzene (10%) [157],... 

As far as mechanical applications are concerned, the use of grafted MCM-41 materials represents a real improvement first, high pressure extrusions allow cyclic use without complete discharge of the operational device. Secondly, low intrusion pressure... 

This method is commonly used to determine Ds of the inner surface of porous matrices. In this method, mercury will fill smaller pores as the intrusion pressure increases. The surface fractal dimension, Ds, can then be determined using Eq. (11) ... 

When Ds is obtained using Eq. (11), it is assumed that cumulative surface of inner pores is zero at the lowest intrusion pressure. However, in a real system, this assumption might not be true because large pores will be filled even at low intrusion pressure. This will lead to underestimation of the surface area and hence Ds. 

SEM measurements were performed using a field emission electron microscope (Hitachi S4200). Samples were coated ( 2nm) with sputtered platinum. Mercury porosimetry measurements (Micromeritics, ASAP, Autopore II 9220) were made on outgassed samples of small fragments ( 100 mg) with intrusion pressures correspondmg to pore diameters (pm) in the range 10 to 5x10" ... 

For instance, the Blaine Fisher (which does not take into account porosity) and the BET (which takes into account intraparticular porosity) values are of the same order of magnitude, thereby indicating that the micronized DS particles do not exhibit intraparticular porosity (figure 5). This is confirmed by MIP since no intraparticular volume at high intrusion pressure is observed. 

Mercury Intrusion Analysis. Mercury intrusion measurements were carried out with a porosimeter (Micromeritics 9220) capable of intruding mercury with intrusion pressures (p) up to 414 MPa (60,000 psi). Pore size distributions were calculated from the intrusion curve by using the Washburn (7) equation ... 

Mercury is a non-wetting fluid for most materials. Because the contact angle (0) is 180°, cos = -1, and pressure is required to force mercury into the pores-see equation (1). We speak of mercury "intrusion pressures" these are quite high due to the high surface tension of mercury (476 dynes/cm). Thus, for a given pore size, the pressure required to force mercury into the pores is almost seven times greater than the pressure required to expel water from the pores. 

In the case of air-vents, even if the filter has been sized adequately to handle the passage of air commensurate with liquid filing and withdrawal rates, the use of hydrophilic filters has caused the implosion or collapse of more than one storage tank. A hydrophobic filter passes air preferentially indeed, a water intrusion pressure is required to force water into the pores. 

In Table 1 the results obtained from the textural characterization of the supports and catalysts by nitrogen adsorption and mercury intrusion porosimetry are presented. In the table the values of surface area obtained from the gas adsorption results, using the BET method for which the linear portion was usually located in the relative pressure range of 0.05 to 0.3 Sbet [9], and those from the intrusion curve of the porosimetry analysis, using a nonintersecting cylindrical pore model Sng [10], are shown. The pore volume Vp is that recorded at the liighest intrusion pressure reached during the porosimetry analysis, and as such represents the pore volume of pores between ca. SOpm to 3mn pore radius. The pore radii were taken from the maxima of the curves of pore size distribution. 

Total pore volume and pore size distribution were determined using mercury porosimeter (Mod. 225 Carlo Erba Strumentazione, Italy), with intrusion pressures ranging from 0 to 2000 atm. 

In mercury intrusion porosimetry, mercury surroimds the sample and application of differential pressure on mercury forces it into the pores. Mercury does not wet hydrophilic and hydrophobic pores and cannot enter these pores spontaneously owing to a small contact angle. Application of pressure on mercury can force it into the pores. The measured intrusion volume is equal to the pore volume and the differential intrusion pressure is related to pore diameter as given in Equation 8.43, where o and 0 are the surface tension and contact angle of mercury, respectively. Mercury porosimetry is valuable in determining the pore structure of the catalyst layer, especially for gas diffusion electrodes, where the distribution of gas and liquid phase pores is essential for the optimization of performance. 

Relationship between pore radii and intrusion pressure... 

The mercury intrusion porosimetry method (Fig. 8.4) is a well-known technique that has been widely used to measure pore structure. Mercury is not wetted by nonwovens because the mercury—nonwoven interfacial free energy is greater than the gas—nonwoven interface. Mercury does not enter the pores spontaneously but can be forced into pores. Pressure required to intrude mercury into a pore is determined by the diameter of the pore. The measure of intrusion pressure and the intrusion volume yields the diameter and volume of passed and blinded pores. 

The porosimeter was programmed to carry out four consecutive intrusion/extrusion cycles. In order to generate partial intrusion/extrusion loops, intrusion pressures up to the desired level were programmed, followed by extrusion to 200 kN/m, then reintrusion to the original intrusion level. 

In a previous work (12), we pointed to the possibility of obtaining additional information on the textural features of the solids by the study of the shape of the pi/pe curves (intrusion pressure/extrusion pressure at a constant volume) vs. the fraction of total pore volume Intruded by mercury (phi). Notwithstanding the validity of the obtained results the application of such a device to... 

A pore radius of 25 nm (corresponding to an intrusion pressure of 7 x 10 psia), in accordance with lUPAC recommendations (20) has been considered as the lower end of macroporosity. The total pore volume has been mentioned in the Table 1 and is the sum of the meso- and microporosity values resulting from Nj adsorption isotherms at a relative pressure of 0.98 and macroporosity from mercury intrusion up to 25 nm pore radius, as previously mentioned. 

Ink-bottle effect The main criticism of the MIP technique is the fact that MIP does not measure pore size but pore entry size. This phenomenon, known as the ink-bottle effect, leads to an overestimation of small pores and an underestimation of big pores (Diamond 2000 Moro and Bohni 2002). More simply said, if the only path towards a big pore is a smaller one, the volume of the big cavity will be evaluated at the small pore intrusion pressure. The main evidence of this phenomenon is that not all the mercury intruded in the sample can exit when the pressure is subsequently decreased and at the end of MIP experiments, some mercury remains entrapped in the sample (Van Brakel et al. 1981). Figure 9.11 shows an example of intrusion and extrusion curves when measuring mature cement samples. In the... 

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