Mercury intrusion porosimetry pore diameter

In this study mercury intrusion porosimetry (MIP) analyses were employed to determine the pore size distribution and pore volume over the range of approximately 100 pm down to 7.5 nm diameter, utilising CE Instruments Pascal 140/240 apparatus, on samples previously dried overnight at 150°C. The pressure/volume data were analysed by use of the Washburn Equation [14] assuming a cylindrical nonintersecting pore model and taking the mercury contact angle as 141° and surface tension as 484 mN m [10]. For the monolith... 

Therefore, it is anticipated that an increase in the granulometric size of the SDDP particles during scale up will probably not effect the SDDP particles dissolution rate of the powder as long as the texture of the SDDP is not modified Hence the critical parameters to be followed during scale up are the internal porosity and the intraparticular pore diameter as determined by Mercury Intrusion Porosimetry or by Scanning Electron Microscopy... 

Figure 2. Illustration of possible errors introduced by the characterization of mercury intrusion porosimetry data. 8 is the pore throat diameter and 8b is the pore body diameter.

Reaction conditions 20% w/v TRIM based on volume of H2O, 2,2"-azobisisobutyronitrile (AIBN, 2% w/v), 0.5% w/v poly(vinyl alcohol) (88% hydrolyzed, 88,000 g/mol), 60 C, 6h. Mean diameter calculated fiom >100 particles. Measured by mercury intrusion porosimetry over the pore size range 7 nm-20 pm. Measured by N2 adsorption desorption using the Brunauer-Emmett-Teller method. 

Individual primary particles could be dense, while agglomerates are most likely porous. Therefore, it is desirable to quantitatively characterize the porosity and pore size and distribution of the agglomerates. For accessible pores, i.e., those that are not completely isolated from the external surface, they can be characterized by using two methods (i) gas adsorption, also known as capillary condensation and (ii) mercury intrusion porosimetry, also called mercury porosimetry for simplicity. The pore size can be diameter, radius, or width. Three types of pores have been classified according to their sizes micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm). Generally, gas condensation is applicable to the measurement in mesopores, whereas mercury porosimetry is more suitable to macropores. 

Bulk porosity, hydrophobic/hydrophilic porosity, and pore size distribution are the most important parameters of the GDL microstructure. Bulk porosity and hydrophobic/hydrophilic porosity are always determined as follows [54, 58]. The sample is immersed in water and then in decane. The water fills only the hydrophilic pores while the decane can fill both hydrophilic and hydrophobic pores. By weighing the sample before and after measurement, total pore volume and hydrophilic pore volume can be calculated. The solid volume of the GDL is calculated using the principle of buoyancy. The bulk or hydrophilic porosity of the GDL is defined as its total pore volume or hydrophilic pore volume divided by the sum of its total pore volume and its solid volume. Hydrophobic porosity is determined by subtracting the hydrophilic porosity from the bulk porosity. Pore distribution is determined by mercury-intrusion porosimetry [54]. Measurement is made of the amount of mercury that penetrates the pores of the sample as a function of the applied pressure. The pressure required for mercury to penetrate a certain size of pore is a function of the pore diameter. The pore size distribution of the GDL is then collected and analysis yields the cumulative pore size distribution. 

In addition to determining the specific surface area, pores below 50 nm may also be characterized by gas adsorption. Distribution of larger pores, 0.003-0.004 pm, can be determined by mercury intrusion porosimetry technique, where the volume of mercury intruded under pressure represents the volume of pores whose entrant diameter can be calculated from the applied pressure (15). The main suppliers of equipment for surface and porosimetry include Quantachrome, Boynton, FL, USA, and Micromeritics, Norcross, GA, USA. 

Mercury intrusion porosimetry is used extensively for the characterization of various aspects of porous media, including porous membranes and powders, and is applicable to pores from 30 A to 900 A in diameter. It is well commercialized. 

In mercury intrusion porosimetry, the pressure at which intmsion takes place in a pore is related to the curvature of the mercury meniscus at the pore entrance. The knowledge of the contact angle between mercury and the sohd enables calculating the pore radius. The characteristic size defined here is the diameter of a reference cylindrical pore, in which the curvature of the mercury meniscus is the same as it is at the entrance of the true pore in which mercury penetrates. 

For the detailed information, pore structure porosimetry techniques are used. These methods enable measurement of pore diameter, pore shape, pore volume, and pore distribution in the electrode catalyst and gas diffusion layers. However, for PEMFC, these layers have hydrophobic and hydrophilic pores and there is no suitable technique available for characterization of such complex pore structures. Combination of multiple porosimetry techniques are employed to characterize layers with both hydrophobic and hydrophilic pores. The pore structure characterization techniques include capillary flow porosimetry, water intrusion porosimetry, and mercury intrusion porosimetry (Jena and Gupta, 2002). In water... 

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. 

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. 

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" ... 

Gas sorption (nitrogen at 77 K), mercury intrusion (mercury porosimetry) Specific surface area (BET), pore size distribution, average pore diameter, specific pore volume, particle porosity Retention of solutes, mass loadability, column regeneration, column performance, mass loadability, pore and surface accessibility for solutes of given molecular weight, mechanical stability, column pressure drop, pore connectivity... 

Fig. 4.5. Mercury porosimetry analysis of a commercial (SCT-US Filter) tubular aAhOa asymmetric membrane support (Micromeritics ASAP 2000). (a) Cumulative intrusion volume as a function of the applied pressure/pore diameter (b) differential intrusion volume as a function of the pore diameter.

Mercury porosimetry can also be used for the investigation of such large pores. One can observe penetration into pores ranging from 100,000 A down to about 60 A in diameter. In another series in which total pore volume was varied, such as that in Figure 49, catalysts were analyzed by mercury intrusion. Measured penetration was divided into six pore diameter ranges 60-100 A, 100-300 A, 300-1000 A, 1,000-10,000 A, and 10,000-100,000 A. Attempts were then made to correlate the activity with certain pore sizes. The largest pores, 100,000 A in diameter... 

Mercury porosimetry (or intrusion) Measurement of the specific porous volume and of the pore size distribution function by applying a continuous increasing pressure oti liquid mercury such that an immersed or submerged porous solid is penetrated by mercury. If the porous body can withstand the pressure without fracture the Washburn equation, relating capillary pressure to capiUaiy diameter allows converting the pressure penetration curves into a size distribution curve. If a sample is contracted without mercury intrusion, a specific mechanical model based on the buckling theory must be used... 

The results obtained from the indirect methods are often controversial, because actually it is not a pore system that is examined but rather the processes applied in these methods the results reflect only the pore size distribution response. Any established value of pore diameter has only conventional meaning and may be different than diameters obtained from other methods. The indirect methods more or less influence the object of observation and measurements because the interventions disrupt material structure. Determining of distribution of pore diameters in cement paste is performed by the mercury porosimetry method and the results are partly confirmed by observations and counting the pores by computer image analysis, but mercury intrusion may damage and alter the material microstructure. Furthermore, the intrusion of mercury into a pore is related to the orifice of the pore rather than to its real dimension (Diamond 2000). Other methods, like capillary condensation, give considerably different values. 

After drying at room temperature for 24 h, the clay membrane was sintered at 900 °C for 2h, after debonding at 250 °C for 1 h. Total porous volume and pore size distribution are measured by mercury porosimetry. This technique relies on the penetration of mercury into a membrane s pores under pressure. The intrusion volume is recorded as a function of the applied pressure and then the pore size was determined. The pore diameters measured were centered near 0.18 mm (Fig. 8). 

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