Mercury intrusion method

The mercury intrusion technique is a variation of the bubble-point method. In this technique, mercury is forced into a dr membrane with the volume of mercury being determined at each pressure. Again, the relationship pressure and pore size is given by the Laplace equation. Because mercury does not wet the membrane (since its contact angle is greater than 90° and consequently cos 0 has a negative value), eq. IV. 1 is modified to  

The contact angle of mercury with polymeric materials is often 141.3° and the surface tension at the mercuiy/air interface is 0.48 N/m. Hence eq. IV. 2 reduces to 

At the lowest pressures the largest pores will be filled with mercury. On increasing the pressure, progressively smaller pores will be filled according to eq. IV - 3. This will continue until ail the pores have been filled and a maximum intrusion value is reached. It is possible to deduce the pore size distribution from the curve given in figure IV - 10, because every pressure is related to one specific pore size (or entrance to the pore ). The pore sizes covered by this technique range from about 5 nm to 10 pm. This means that all microfiltration membranes can be characterised as well as a substantial proportion of the ultrafiltration membranes. 

In summary, both pore size and pore size distribution can be determined by the mercury intrusion technique. One disadvantage is that the apparatus is rather expensive and not widely used as a consequence. Another point is that small pore sizes require high pressures and damage of the membrane structure may occur. Furthermore, the method measures all the pores present in the structure, including dead-end pores. 

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FIGURE 5 Pore size distribution by the mercury intrusion method. 

Usually the plaques produced by either method are coined (compressed) in those areas where subsequent welded tabs are connected or where no active material is desired, eg, at the edges. The uncoined areas usually have a Brunauer-Emmet-Teller (BET) area in the range of 0.25—0.5 m2/g and a pore volume >80%. The pores of the sintered plaque must be of suitable size and interconnected. The mean pore diameter for good electrochemical efficiency is 6—12 Jim, determined by the mercury-intrusion method. 

These results confirm the suggestions of earlier workers (I, 2) that the mercury intrusion method can lead to structural deformation of solids during analysis. For silicas, there appears to be both an elastic deformation and an irreversible compression effect that contribute to the differences in... 

Precipitated silicas are typically macroporous materials where the mercury method is generally the best method available for the reliable determination of pore sizes above 30 nm. Washburn et al. [22] introduced the mercury intrusion method to measure the pore size of a porous silica. 

Pores are holes, cavities and/or channels communicating with the silica surface. Pores can be regarded as cylinders with a diameter, p, usually measured in nm, sometimes in A (=0.1 nm). Their total volume is the pore volume, Vp, measured in cmVg or mL/g of material. The pore size distribution is measured by the mercury intrusion method [1,4]. A good chromatographic silica packing should have a narrow pore size distribution. In such case, pore volume, pore diameter and specific surface area can be linked by the approximative relation ... 

In order to quantify microscopic damage, distribution of pore radii was also measured by the mercury intrusion method from concrete fragments at the three sites. After determining the pore distribution, the volume of pore radii over 0.5 pm was determined. This is because microvoids over 0.5 pm are dominantly responsible for deterioration of concrete. 

The pore radius assigned to each component of the network model is generated random numbers from 0 to 1 according to the probability density given from the pore-size measurement. The numerical assumption of the occurrence of the pore size is important in this model. The water saturation and hydraulic conductivity computed depend on the spatial distribution of the pore radius. The pore radii larger than 30 Ha, which can not be measured by the mercury intrusion method, are approximated to appear at the same probability as 3CTJm given by the PSD curve of Toyoura sand. 

A second peak in the mercury intrusion results represents the pore structure of the sponge-like structure, including the separation layer and walls between the fingerlike microchannels. For mercury intrusion method, mercury would fill larger pores. 

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