The Mercury Porosimeter

The method to be described determines the pore size distribution in a porous material or compacted powder surface areas may be inferred from the results. 

A procedure that is more suitable for obtaining the actual distribution of pore sizes involves the use of a nonwetting liquid such as mercury—the contact angle on glass being about 140° (Table X-2) (but note Ref. 31). If all pores are equally accessible, only those will be filled for which 

The analysis of the direct data, namely, volume penetrated versus pressure, is as follows. Let d V be the volume of pores of radii between r and r - dr d V will be related to r by some distribution function Z)(r)  

For constant 6 and y (the contact angle was found not to be very dependent on pressure), one obtains from the Laplace equation. 

Thus D(r) is given by the slope of the V versus P plot. The same distribution function can be calculated from an analysis of vapor adsorption data showing hysteresis due to capillary condensation (see Section XVII-16). Joyner and co-woikers [38] found that the two methods gave very similar results in the case of charcoal, as illustrated in Fig. XVI-2. See Refs. 36 and 39 for more recent such comparisons. There can be some question as to what the local contact angle is [31,40] an error here would shift the distribution curve. 

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Here, P is the equilibrium pressure. Therefore, Dj of the anode electrode can be also calculated through the slope of a log-log plot of Eq. (4) by the data from the mercury porosimeter. 

Figure 1 shows the pore size distribution of the two catalysts as determined from the mercury porosimeter data. The most frequent pore radius of the Monolith catalyst is 80°A as compared to 33°A of the Nalcomo 474 catalyst. On the other hand, the surface area of the Monolith catalyst is 92.0 m2/gm as compared to 240 m2/gm of the Nalcomo 474 catalyst. The chemical compositions of the two catalysts also differ as shown in Table II. 

The mercury porosimeters can be used to measure the pore sizes in the range of 5 nm to 200 pm. 

The mercury porosimeter is simply an instrument designed to apply a controlled mercury pre.ssure to the adsorbent and record the volume of mercury penetrating the pore structure. Because of practical limitations on the maximum pressure, the minimum pore radius which can be measured by this... 

Prior to the measurement, the sample is introduced into a sample cell that allows for degassing under vacuum. Usually the same port also provides the coimections to the low pressure system of the mercury porosimeter, where air pressure is applied onto the pool of mercury to force it into the sample in contrast, the high pressure port uses a hydraulic system to provide pressure up to 400 or even 600 MPa. The amount of mercury vanishing from the mercury reservoir, AVmercury. is recorded together with the net applied pressure and converted into a pore size distribution. 

Whereas the nitrogen isotherm provides quite reliable data for PSD with a mean size of about 20 nm or less, it is much less reliable for jx>res larger than this. Mercury porosimetry is the alternate technique for characterizing the sizes of the larger mesoporosity and dates back to 1921 and developed later by Ritter and Drake in 1945. TTie physical phenomenon of the mercury porosimeter is that mercury essentially does not wet surfaces of solids, it has a contact angle (0) with solids of about 140° and hence an applied force (pressure (/>)) is needed to push mercury into tubes, or pores with size Tp, as shown below ... 

The mercury porosimeter results seen on the sample fronts were echoed by similar results done on side samples. Here again the range of pore sizes in the distribution was very similar and the broader peak may be more attractive for TE scaffold. 

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