Liquid porosimetry

The high pressures used in mercury porosimetry gives erroneous results with deformable material such as fabric. A more general version of liquid porosimetry, based on the same principles, uses a variety of liquids and can be carried out in the extrusion mode [79,80]. In this technique, a pre-saturated specimen is placed on a microporous membrane supported on a rigid porous plate in an enclosed chamber. The gas pressure within the chamber is increased in steps causing the liquid to flow out of the pores. The amount of liquid removed is monitored by a top-loading recording balance. One also has the 

Mean pore diameter in microns Fig. 4.29 Raw intrusion data for a polymer. 

1 Zweitering, P. (1958), The Structure and Properties of Porous Solids, Butterworths, 149 

40 Scholten, J.J.F. (1967), Porous Carbon Solids, ed. R.L. Bond, Academic Press, pp. 225-249, 157 

49 loannidis, M.A. and Chatzis, I., (1993), Hysteresis and Entrapment from Porosimetry, Academic Press, 159 

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The formation of microvoids (or micropores) in drawn /3-PP is a well-known feature, used successfully to produce breathable films and membranes. Macroscopically their occurrence is correlated with an opacification (i.e. whitening) of the specimen. Their amount can, for example, be measured at given strain rate/draw ratio by liquid porosimetry (e.g. mercury intrusion), gas absorption or by the determination of the density of the deformed sample [129,177,178]. 

Pore size. The bubble point method (BCI Test Method 3-015) [10] is used to measure the maximum pore diameter. The maximum pore size and the pore-size distribution can be determined by means of the liquid porosimetry method which uses, for example, a Coulter porosimeter (BCI Test Method 3-017) [10]. 

S. Jaganathan, H. V. Taff eshi, B. Pouideyhimi, Modeling liquid porosimetry in modeled and imaged 3-D fibrous microstructures , J. Colloid Interface Sci., 326,166 (2008)... 

Previous experimental works have attempted to make a connection between liquid porosimetry and gas adsorption by proposing transformations between the respective isotherms based upon macroscopic considerations [31-33], We have shown that the Hamiltonian symmetry contained in our model leads to an exact transformation between gas adsorption and liquid porosimetry curves [20], The integration of the Gibbs-Duhem equation expressed in terms of activity leads to... 

By using Eq. (10) and the hole-particle symmetry of the lattice model we can transform the liquid porosimetry isotherm into an adsorption/desorption isotherm of density versus relative pressure for the wetting fluid. This is shown in Fig. 3 together with the gas adsorption results and the agreranent is excellent. 

Fig. 6.2 Liquid-liquid porosimetry data for nanoporous carbon membrane formed after deposition of three carbon layers. The flux-pressure curves are shown for the fully intruded (solidcurve)...

Fig. 6.3 Pore size distribution for the nanoporous carbon determined from liquid-liquid porosimetry. (From [5])...

Although a number of methods are available to characterize the interstitial voids of a solid, the most useful of these is mercury intrusion porosimetry [52], This method is widely used to determine the pore-size distribution of a porous material, and the void size of tablets and compacts. The method is based on the capillary rise phenomenon, in which excess pressure is required to force a nonwetting liquid into a narrow volume. 

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... 

Fig. 3 Diagram of the contact angle used in porosimetry measurements (a) Wetting liquid, 0 < 90° (b) nonwetting liquid, 8 > 90°.

Inert polymer matrices, studied for use in possible controlled release applications, have used porosimetry to investigate a number of properties [54-56]. The kinetics of liquid capillary penetration into these matrices was explored using a modified Washburn equation [54]. It was shown that water... 

According to the Washburn equation (10.23) a capillary of sufficiently small radius will require more than one atmosphere of pressure differential in order for a nonwetting liquid to enter the capillary. In fact, a capillary with a radius of 18 A (18 x 10 ° m) would require nearly 60 000 pounds per square inch of pressure before mercury would enter-so great is the capillary depression. The method of mercury porosimetry requires evacuation of the sample and subsequent pressurization to force mercury into the pores. Since the pressure difference across the mercury interface is then the applied pressure, equation (10.23) reduces to... 

A significant aspect of the equivalency of mercury porosimetry and gas adsorption is the implication that mercury can fill pores by either liquid or vapor transport. 

Explain the basic principle behind porosimetry. How would you use a porosimetry experiment to measure the contact angle of a liquid with a powdered solid What are the limitations of this approach ... 

The method of standard porosimetry (MSP)41-43 was one of the first approaches used to obtain air-water capillary pressure curves for GDMs.16 In this test, a GDM sample is initially saturated with water and contacted with a water-saturated porous disc, which is a standard with known Pc(Sw) behavior. The capillary pressure of the sample-standard system is varied by allowing the liquid to evaporate from the standard and sample while in contact. If the two media can be assumed to be in capillary equilibrium, their capillary pressures are equal. Saturation is determined by measuring the weights of the sample and standard periodically. The capillary pressure of the system is found by reference to the known capillary pressure curve of the standard. This method is limited to scanning... 

Pore size distributions are often determined by the technique of mercury intrusion porosimetry. The volume of mercury (contact angle c. 140° with most solids) which can be forced into the pores of the solid is measured as a function of pressure. The pore size distribution is calculated in accordance with the equation for the pressure difference across a curved liquid interface,... 

Another method of estimating the pore size distribution of meso- and macropores is by mercury porosimetry. Here one measures the volume of mercury, a nonwetting liquid, which is forced under pressure into the pores ofa catalyst sample immersed in mercury. The pressure required to intrude mercury into the sample s pores is inversely proportional to the pore size [86]. For cylindrical pores of radius r, this... 

Kamran, M., Nemati, Paulo, J.M. and Monteiro (1997) A New Method to Observe Three-Dimensional Fractures in Concrete Using Liquid Metal Porosimetry Technique. Cement and Concrete Research 27, 1333-1341... 

In prepared catalysts the pore sizes may be quite uniform. However, in most naturally occurring materials there is a wide range of pore sizes. The actual pore size distribution can be obtained from methods such as porosimetry, in which a nonwetting liquid (usually mercury) is pumped into a solid sample [12,13,15,26,30,55]. The solid is considered to be composed of a bundle of capillaries. For each capillary, the Laplace equation (see Section 3.2.2) gives the pressure drop across a curved liquid surface ... 

Aerogels A special form of xerogel, from which the liquid has been removed in such a way as to prevent any collapse or change in the structure as liquid is removed (Iler). A gel with water-collapsible macropores as judged by direct porosimetry (Barby). 

Figure 3. Permeability and pore number distributions versus pore size. Liquid-liquid displacement porosimetry measurements...

The chemical composition can be measured by traditional wet and instrumental methods of analysis. Physical surface area is measured using the N2 adsorption method at liquid nitrogen temperature (BET method). Pore size is measured by Hg porosimetry for pores with diameters larger than about 3.0 nm (30 A) or for smaller pores by N2 adsorp-tion/desorption. Active catalytic surface area is measured by selective chemisorption techniques or by x-ray diffraction (XRD) line broadening. The morphology of the carrier is viewed by electron microscopy or its crystal structure by XRD. The active component can also be measured by XRD but there are certain limitations once its particle size is smaller than about 3.5 nm (35 A). For small crystallites transmission electron microscopy (TEM) is most often used. The location of active components or poisons within the catalyst is determined by electron microprobe. Surface contamination is observed directly by x-ray photoelectron spectroscopy (XPS). 

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. 

Mercury Porosimetry Method Mercury is a nonwetting liquid that must be forced to enter a pore by application of external pressure. Consequently it is an extremely useful and convenient liquid for measuring the density of powders and/or particles. This method can measure the apparent and true density of one sample by... 

Two methods are used to measure the pore size distribution in a powder mercury porosimetry and adsorption-desorption hysteresis. Both methods utilize the same principle capillary rise. A nonwetting liquid requires an excess pressure to rise in a narrow capillary. The pressure difference across the interface is given by the Young and Laplace equation [15]. 

The physical principle is in fact close to porosimetry experiments based on mercury injection. However, because of evident environmental disadvantages of mercury manipulation, it appeared convenient to find other (solid-liquid) systems. This difficulty was overcome by using hydrophobic solids and water [4]. 

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