Pore volume porosimetry

Since in practice the lower limit of mercury porosimetry is around 35 A, and the upper limit of the gas adsorption method is in the region 100-200 A (cf. p. 133) the two methods need to be used in conjunction if the complete curve of total pore volume against pore radius is to be obtained. 

Fig. 3J1 Comparison of pore volume size distributions for Clear Creek sandstone" (courtesy Dullien.) Curve (A), from mercury porosimetry curve (B), from photomicrography (sphere model).

Values of pore volume of samples of porous silica, determined by ethanol titration (v (EtOH)) and by mercury porosimetry (v (Hg, i) and v (Hg, ii)) ... 

Porosity and pore-size distribution usually are measured by mercury porosimetry, which also can provide a good estimate of the surface area (17). In this technique, the sample is placed under vacuum and mercury is forced into the pore stmcture by the appHcation of external pressure. By recording the extent of mercury intmsion as a function of the pressure appHed, it is possible to calculate the total pore volume and obtain the population of the various pore sizes in the range 2 nm to 10 nm. 

With these facts in mind, it seems reasonable to calculate the pore volume from the calibration curve that is accessible for a certain molar mass interval of the calibration polymer. A diagram of these differences in elution volume for constant M or AM intervals looks like a pore size distribution, but it is not [see the excellent review of Hagel et al. (5)]. Absolute measurements of pore volume (e.g., by mercury porosimetry) show that there is a difference on principle. Contrary to the absolute pore size distribution, the distribution calcu-... 

Porosimetry data can be graphed in a variety of ways and can be tailored to the purpose of the study. Plotting volume versus pore size will easily display the pore sizes observed in the sample. Pore size distributions can be calculated from the raw data and plotted to give the pore volume per unit radius interval. Other parameters can be calculated from porosimetry data, including average pore radius [40,48], surface area [7,39,40], pore surface area [6], particle size [40], and density [6,49]. 

The first task was to produce carriers from different recipes and in different shapes as shown schematically in Fig. 8. The raw materials diatomaceous earth, water and various binders are mixed to a paste, which is subsequently extruded through a shaped nozzle and cut off to wet pellets. The wet pellets are finally dried and heated in a furnace in an oxidising atmosphere (calcination). The nozzle geometry determines the cross section of the pellet (cf. Fig. 3) and the pellet length is controlled by adjusting the cut-off device. Important parameters in the extrusion process are the dry matter content and the viscosity of the paste. The pore volume distribution of the carriers is measured by Hg porosimetry, in which the penetration of Hg into the pores of the carrier is measured as a function of applied pressure, and the surface area is measured by the BET method, which is based on adsorption of nitrogen on the carrier surface [1]. 

Mercury porosimetry has somewhat the same constraints at the narrow pore end of its range, in that the same questions arise regarding the constancy of surface tension and wetting angle for mercury as exist for an adsorbate. Consequently, both methods have nearly the same lower limit which is about 18 A pore radius for mercury intrusion (e.g. bOOOOpsia). However, at the wide-pore end porosimetry does not have the limitation of the Kelvin equation and for example, at 1.0 psia pore volumes can be measured in pores of 107 micrometer radius or 1.07 x 10 A. 

Another factor which can lead to BET areas slightly higher than those from porosimetry is pore wall roughness. Slight surface roughness will not alter the porosimetry surface area since it is calculated from the pore volume while the same roughness will be measured by gas adsorption. 

Drakef has reported the accompanying data for the porosimetry analysis of a catalyst preparation the cumulative pore volume occupied by mercury is given for the applied pressures indicated ... 

Figure 2. Cumulative pore volume vs. pore radius for AC-ref, SC-100 and SC-155 Mercury intrusion porosimetry.

The amorphous aluminosilicate gel (AAA-alumina) used in this study contains about 80.4% Si02, 19.4% A1203 and 0.056ft Na20. Mercury porosimetry measurements have indicated a 479 nr/9 surface area and 1.67 cc/g pore volume the average pore diameter of the dried gel was 134 A. 

The particle size and surface area distributions of pharmaceutical powders can be obtained by microcomputerized mercury porosimetry. Mercury porosimetry gives the volume of the pores of a powder, which is penetrated by mercury at each successive pressure the pore volume is converted into a pore size distribution. Two other methods, adsorption and air permeability, are also available that permit direct calculation of surface area. In the adsorption method, the amount of a gas or liquid solute that is adsorbed onto the sample of powder to form a monolayer is a direct function of the surface area of the sample. The air permeability method depends on the fact that the rate at which a gas or liquid permeates a bed of powder is related, among other factors, to the surface area exposed to the permeant. The determination of surface area is well described by the BET (Brunauer, Emmett, and Teller) equation. 

Table III shows XRD and porosimetry data for calcined USY and AFS zeolites. All samples show shrinkage of the unit cell to comparable values following calcination. As a result, calcined samples are compared at similar silica-alumina framework ratios. All calcined samples have well developed microporous structures and comparable total pore volumes. These porosimetry data confirm that the hydrothermally dealuminated materials contain a significant fraction of mesopores relative to chemically dealuminated materials. The extensive washing given to AFS-1 results in higher micropore surface area and volume compared to AFS-2 and suggest that AFS-2 contains occluded fluoroaluminate and fluorosilicate compounds within the microporous structure.

Chemical and Physical Analysis. Carbon on the aged catalysts was determined by combustion, and metals were determined by wet chemical analysis and atomic absorption. Surface areas and pore volumes were measured by the standard BET method using nitrogen and the mercury porosimetry, respectively. All analyses were given on a fresh catalyst basis. 

Physico-chemical techniques are widely used for characterization of catalysts and porous materials in general. Well-known methods based on physical adsorption of inert gases (N2 and CO2) and penetration of mercury at elevated pressures provide information on the total surface area, pore volume, and pore size distribution (PSD) of the sample [1,2]. Gas adsorption and mercury porosimetry are often compared since they generate data of similar nature in the pore size range 4 - 100 nm. 

Transmission electron microscopy (TEM) observations, nitrogen adsorption-desorption and mercury porosimetry measurements indicated that increasing EDAS/TEOS ratio results in (a) a decrease of the building block particle size, (b) an increase of the specific surface area (S ), (c) an increase of mesopore volume determined at saturation pressure of N (Vp) and a decrease of the total pore volume (V,) (d) a general shift of the pore size distribution towards smaller pores, (e) an increase of the pressure of transition (P,), above which mercury can intrude the sample without destroying the pore structure [1-3]. To explain this behaviour... 

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... 

DVB were valid in this system as well. These concern the dependence of surface area and pore volume on the amount of diluent and cross-linker. The surface area increases with the amount of EDMA and goes through a maximum with increasing amount of diluent. Using cyclohexanol-dodecanol as a solvent-non-solvent pair, the factors of importance for the structure and morphology of the polymers were studied by experimental design [34]. In these experiments the concentration of the diluent mixture was varied between 20 and 77% (volume/total volume), the concentration of EDMA between 25 and 100% (volume/monomer volume), the concentration of initiator (AIBN) between 0.2 and 4% (w/w), the concentration of non-solvent (dodecanol), between 0 and 15% (v/v) and the polymerisation temperature between 70° and 90°C. The surface area (determined by nitrogen sorption), pore volume (determined by mercury porosimetry) (see Section 2.11.6.) and the mechanical properties were chosen as responses. 

The surface area, total pore volume, and microporc volume (in pores <7..S nm) were determined by CO adsorption and Hg porosimetry. 

In addition to surface fractal dimension ( Mercury Intrusion Porosimetry, under Boundary and Surface Fractal Dimensions ), this method can also be employed to determine mass fractal dimension of porous particles. Once the relative density of the particle at different pore volume, p, is obtained, then Dm can be deduced according to Eq. (20) ... 

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