Mercury intrusion porosimetry Washburn equation

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... 

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... 

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],... 

We now consider application of percolation theory to describing mercury intrusion into porous solids. First we briefly recall the main physical principles of mercury porosimetry (in particular, the Washburn equation). These principles are treated in detail in many textbooks [e.g., Lowell and Shields 49)]. The following discussions (Sections IV,B and IV,C) introduce general equations describing mercury penetration and demonstrate the effect of various factors characterizing the pore structure on this process. Mercury extrusion from porous solids is briefly discussed in Section IV,D. 

Mercury porosimetry is the most widely used technique for characterizing macroporosity in solids this technique covers a wide range of pore sizes, which also includes the majority of mesopores. Mercury porosimetry is based on the penetration of mercury, under pressure, into porosity. As mercury does not wet the carhon surface, pressui e is required to force the mercury into the structure. The relationship between pore radius, r, and mercury intrusion follows the so-called Washburn equation, already suggested in 1921 ... 

In mercury porosimetry the liquid is forced into the pores with the aid of high pressure. The volume of intruded liquid is plotted against the applied pressure as shown in Fig. 4. The large increase in volume at low pressure indicates the filling of the extra particle volume. The intrusion and extrusion curves do not coincide vdiich has been attributed to the shc of the pores (i.e. narrcw neck and wide-l30dy pores) and also to the entrapment of mercury in the porous network (66). The pressure at vdiich penetration occurs can )3e related to the dimension of the pore entrance by the Washburn equation... 

What immediately becomes apparent is a well-defined ring of void space within the pellet. These voids are observed in every pellet sectioned and studied and must be a result of the method of manufacture of the pellet. What also becomes apparent is a clear deviation from the mercury porosimetry intrusion curve in the pellet case. It ears that the pellet is constructed of large voids spaces, which, by the Washburn equation, should be filled with alloy at very low pressure, of the order of Ibara to 3bara. In fact, these voids are being... 

On initial inspection the results obtained from serial sectioning of LMPA intruded samples appear at odds with the principle theory behind intrusion and retraction as predicted by the Washburn equation. But further inspection shows it is not the Washburn equation, but mercury porosimetry that is at fault. Pore network models have often been used to characterise the behaviour of pore structure in relation to mercury porosimetry. But the model is only as good as the assumptions and the data that it is based iqron. Without artificially shielding the network, the model caimot propa ly detomine the correct psd and cannot derive a more spatially accurate structure that could be used for diffusion and reaction modelling. In order to characterise the pore structure more accurately, we need to introduce some of the elements usually revealed by LMPA intrusion tests. 

The structure-dependent constant ks can be calculated from the crossover of the mercury porosimetry data from compression to intrusion using the argument that at this transition point the Washburn equation (21.39) as well as (21.40) have to hold [79]. 

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... 

In spite of the growing popularity of mercury porosimetry and the ready availability of excellent automated equipment, the interpretation of the mercury intrusion-extrusion data is still far from clear. The values of surface tension and contact angle which must be inserted in the Washburn equation are still uncertain - as are the limits of applicability of the equation itself. Other problems include the reversible or irreversible deformation of the pore structure, which undoubtedly occurs with some corpuscular or weakly agglomerated systems. 

Mercury porosimetry is a method currently used to characterize the texture of porous materials. It enables determining pore volume, specific surface area and also distributions of pore volume and surface area versus pore size. It can be applied to powders, as weU as to monolithic porous materials. The basic hypothesis usually accepted is that mercury penetrates into narrower and narrower cavities or pores as pressure increases. Data analysis is performed using the intrusion equation proposed by Washburn (1921) ... 

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