Mercury-intrusion data

Fig. 15. Mesopore surface area as a function of pore diameter obtained from mercury intrusion data for PAN derived carbon fiber porous monoliths [28].

Mercury intrusion data for larger pores of 6.5 x 10 3 to 10 pm are shown in Figs 5.16 and 5.17 at various hydration times and at equal hydration, respectively [22]. It can be seen that the total intrusion at the limit of the instrument (6.5 x 10 3 pm) is less for chloride containing pastes at all ages, but when considered at equal degrees of hydration a higher proportion of coarse pores is formed. 

The surface area of all pores and voids filled up to pressure P can be obtained from mercury intrusion data. 

The most definitive surface area measurements are probably those made by nitrogen adsorption using the BET theory. Neither the Brunauer, Emmett and Teller (BET) theory nor equation (11.5), used to calculate surface area from mercury intrusion data makes any assumptions regarding pore shape for surface area determinations. When these two methods are compared there is often surprisingly good agreement. When... 

Figure 4 Treatment of the mercury intrusion data (1 intrusion) from Fig. 3.

The case of mN2 is once again interesting. It would seem that an overlap is obtained for the smaller pore size whereas adsorption manometry is not able to probe the larger pores. However, the smaller pores are at the limit at which the BJH method is valid. That is to say that from the adsorption data alone, one would discard the peak obtained at around 4 nm as an artefact. From the mercury intrusion data though, a peak is observed which would seem to confirm the presence of a meaningful porosity. 

Equation (6.13) requires only the measurement of the dependence of the volume of the intruded mercury on the applied pressure, and can be used to investigate irregularities of the solids within the range of scales provided by mercury intrusion data. Application of the mercury porosimetry technique has been reported in several papers studying soils [14, 17, 33, 37 5]. 

However, the porosimetric method does not directly measure the initial area So. To evaluate So, Kozak et al. [40] modified Neimark s approach based on the application of Equation (6.14). In addition to Neimark s approach, other alternative approaches have been developed that are aimed at evaluating the fractal dimension from mercury intrusion data [47],... 

Mercury intrusion data also may be misleading for porous materials having many inkbottle type pores, cp. middle portion of Fig. 1.1. In such situations high pressures are needed to overcome resistance of mercury to pass the narrow neck of the pore, i. e. the wider portion of the inkbottle pores will not be adequately reflected in the experimentally taken Vhj = Vng (p) curve. However, despite these disadvantages, mercury intrusion experiments often gives valuable information concerning the macro- and mesopores of a sorbent and hence very well may be used for comparative measurements and quality tests of sorbent samples. 

The distribution of interstitial pore sizes obtained by this technique, however, refers exclusively to that of the throat of the pores (rather than to the average size of lumen). This might be the pertinent value in characterizing liquid filter media or studying the amenability of scaffolding to cell movements within it. By contrast, the full range of pore diameters encountered within a pore contributes to the mercury intrusion data. 

The volume of a pore within a particle seen by a two dimensional image can be represented in various ways. For irregularly shaped pores one of the more acceptable ways would be to assume unit thickness and express the volume in terms of area. Comparison of the nitrogen adsorption and mercury intrusion data and calculation of pore sizes is based, however, on cylindrical models. The pore area, obtained from the electron microscope photographs, was taken as a means of describing the pore size distribution in materials 5A and 820 (Figures 1-6). 

Figure 7 The pore structure of some porous bodies, those similar in structure as a mathematical system known as an Apollonian gasket, should be describable by fractal dimensions deduced from mercury intrusion data...

Rootare and Penslow [66] obtained surface areas from mercury intrusion data using no assumption of any specific pore geometry. The problem was approached from the point of view that work is required to force mercury into the pores, the work, dW, required to immerse an area S5 of powder being ... 

Table 4.4 Mercury intrusion data for magnesium hydroxide...

Table 4.4 (continued) mercury intrusion data for magnesium... 

The paper by Pis et al provides a good example of the application of optical microscopy. In this case, image-analysis has been used to provide a quantitative evaluation of the number, size and shape of pores in cokes produced by progressive oxidation. The results are compared with the mercury intrusion data and the two techniques shown to be complementary. 

In summary, similar values are obtained for surface area and pore size distribution when nitrogen adsorption and mercury intrusion data are compared. 

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