Mercury penetration measurements

These parameters can be determined from gas adsorption-desorption measurements, usually nitrogen, and from mercury penetration measurements [78,79]. 

In mercury penetration measurements, mercury is forced under various pressures into the pores of the material. Due to the large contact angle (0) of mercury in contact with most materials, the pressure required to force mercury into the pores can be expressed as a function of the pore radius ... 

The specific pore volume can be determined from nitrogen adsorption measurements if the adsorbent is meso- or microporous. For macroporous adsorbents with pore diameters above 1000 A, the pore volume can be determined by mercury penetration measurements by integrating the pressure volume curve. The total pore volume of meso- and microporous adsorbents can be calculated by assuming that, in the range 0.95 < pjpo < 1, all pores in the adsorbent are filled with condensed gas. The total pore volume is then simply calculated as ... 

As for the pore volume, the pore sizes of meso- and microporous adsorbents are characterised using gas sorption measurements, whereas the pore sizes of macroporous adsorbents are best estimated using mercury penetration measurements or by electron microscopy. The function dvpjddp = f dp) can be calculated using various models. In gas sorption on sorbents with mesopores the function is obtained using the Kelvin equation describing capillary condensation. 

FIGURE 1.14. Macropore size distribution determined from mercury penetration measurements for (i3) carbon molecular sieve (b) Linde 5A (extrudales), and (c) H-Zeolon (H-mordenite). 

The technique of mercury porosimetry consists essentially in measuring the extent of mercury penetration into an evacuated solid as a function of the applied hydrostatic pressure. The full scope of the method first became apparent in 1945 when Ritter and Drake developed a technique for ... 

Important physical properties of catalysts include the particle size and shape, surface area, pore volume, pore size distribution, and strength to resist cmshing and abrasion. Measurements of catalyst physical properties (43) are routine and often automated. Pores with diameters <2.0 nm are called micropores those with diameters between 2.0 and 5.0 nm are called mesopores and those with diameters >5.0 nm are called macropores. Pore volumes and pore size distributions are measured by mercury penetration and by N2 adsorption. Mercury is forced into the pores under pressure entry into a pore is opposed by surface tension. For example, a pressure of about 71 MPa (700 atm) is required to fill a pore with a diameter of 10 nm. The amount of uptake as a function of pressure determines the pore size distribution of the larger pores (44). In complementary experiments, the sizes of the smallest pores (those 1 to 20 nm in diameter) are deterrnined by measurements characterizing desorption of N2 from the catalyst. The basis for the measurement is the capillary condensation that occurs in small pores at pressures less than the vapor pressure of the adsorbed nitrogen. The smaller the diameter of the pore, the greater the lowering of the vapor pressure of the Hquid in it. 

The mercury penetration approach is based on the fact that liquid mercury has a very high surface tension and the observation that mercury does not wet most catalyst surfaces. This situation holds true for oxide catalysts and supported metal catalysts that make up by far the overwhelming majority of the porous commercial materials of interest. Since mercury does not wet such surfaces, the pressure required to force mercury into the pores will depend on the pore radius. This provides a basis for measuring pore size distributions through measurements of the... 

H. M. Rootare, Advanced E experimental Techniques in Powder Metallurgy, Plenum Press, New York, 1970, pp. 225—252. A comprehensive review of the use of mercury penetration to measure porosity. 

Helium and mercury densities were determined on the 6-8 mesh fraction. The larger mesh size was used to avoid the possibility that mercury would not penetrate the space between particles in the mercury density measurements. The coal was placed in a calibrated density tube, evacuated at room temperature for one hour, and then heated at 100°C. in vacuo for 2 hours. The weight of the coal after this treatment was used to compute the densities. Helium densities were determined at 30°C. by the method of Rossman and Smith (11). Mercury densities were determined by admitting mercury at an absolute pressure of 1140 torr to the coal sample after evacuation, following the helium density measurement. 

The only proof of the above contention are the results in Figure 3 of the paper where reaction rate is approximately proportional to external area. Figure A here shows the pore size distribution (from mercury penetration (3)) of each particle size, confirming that little additional pore structure was opened up during coal grinding. This would rule out the possibility that the effect measured in Figure 3 was caused by opening up entrances to sealed pores. 

From mercury penetration the surface area is determined knowing the surface tension and contact angle of mercury and the total volume of penetrated mercury. Measurements agree with the BET measurements below surface areas of 100 m /g. 

The evaluation of the commercial potential of ceramic porous membranes requires improved characterization of the membrane microstructure and a better understanding of the relationship between the microstructural characteristics of the membranes and the mechanisms of separation. To this end, a combination of characterization techniques should be used to obtain the best possible assessment of the pore structure and provide an input for the development of reliable models predicting the optimum conditions for maximum permeability and selectivity. The most established methods of obtaining structural information are based on the interaction of the porous material with fluids, in the static mode (vapor sorption, mercury penetration) or the dynamic mode (fluid flow measurements through the porous membrane). 

There are two established methods for measuring the distribution of pore volumes. The mercury-penetration method depends on the fact that mercury has a significant surface tension and does not wet most catalytic surfaces. This means that the pressure required to force mercury into the pores depends on the pore radius. The pressure varies inversely with a 100 psi (approximately) is required to fill pores for which a = 10,000 A, and 10,000 psi is needed for a — 100 A. Simple techniques and equipment are satisfactory for evaluating the porervolume distribution down to 100 to 200 A, but special high-pressure apparatus is necessary to go below a = 100 A, where much of the surface resides. In the second method, the nitrogen-adsorption experiment (described in Sec. 8-5 for surface area measurement) is continued until the nitrogen pressure approaches the... 

For a chosen value of plpo, Eqs. (8-22) and (8-23) give the pore radius above which all pores will be empty of capillary condensate. Hence, if the amount of desorption is measured for various plpo, the pore volume corresponding to various radii can be evaluated. Differentiation of the curve for cuniulative pore volume ys radius gives the distribution of volume as described in Example 8-6. Descriptions of the method of computation are given by several investigators. As in the mercury-penetration method, errors will result unless each pore is connected to at least one larger pore. 

Mercury porosimetry can also be used for the investigation of such large pores. One can observe penetration into pores ranging from 100,000 A down to about 60 A in diameter. In another series in which total pore volume was varied, such as that in Figure 49, catalysts were analyzed by mercury intrusion. Measured penetration was divided into six pore diameter ranges 60-100 A, 100-300 A, 300-1000 A, 1,000-10,000 A, and 10,000-100,000 A. Attempts were then made to correlate the activity with certain pore sizes. The largest pores, 100,000 A in diameter... 

Mercury penetration method was used to measure pore volume of the catalyst samples ( Micromeritics Pore Sizer 9320 ). 

The whole set of measurements carried out has shown that using a mercury penetration curve to get information on the porous structure of a support gives an idea of the probable effective diffusivity, but specifies neither its absolute value nor the direction of its variation. Moreover, our experiments have demonstrated the necessity of taking the measurements of effective diffusivity in a device with a flowing external fluid so as to determine the influence of the internal convection flux on the value of the effective diffusivity. 

Pore size distributions are routinely measured using the mercury penetration test. Liquid mercury, which does not wet most solids, is forced into the pores under successively higher pressures. The pressure required to fill a cylindrical pore of radius r is [6]... 

From such measurements, surface areas (normalized cumulative and relative), pore radii (choice of three measuring units), pore volumes (raw, normalized, cumulative and relative) and pore-size distribution functions of samples can calculated. Figure 8 presents the graphs of mercury-penetrated volume versus pressure in pores of Na- and La-montmorillonite samples. Figure 9 shows pore-size distribution functions from porosimetry data. 

FIGURE 2.13. Comparison of pore size distribution for Cr203-Fe203 catalyst measured by mercury penetration and from the nitrogen desorption isotherm, (j Pore size distribution from N2 desorption isotherm. Pore size distribution from mercury penetration. (From ref. 33, reprinted with permission.)... 

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... 

Because of its low evaporation rate, silicone oil remains entrapped in the pores of these materials. This imbibing quality was utilized to obtain a rough estimate of the void volume fraction of hard elastic HIPS and polypropylene as a function of strain. These values are only estimates since the oil may not penetrate the smaller pores in the materials. The method, however, does offer a simple alternative to other techniques such as mercury porosimetry. As shown in Fig. 11, the results for hard elastic polypropylene are, in fact, reasonably close to void volume fraction measurements determined by mercury penetration [4]. Note that a linear relationship exists between the void volume fraction and strain for hard elastic polypropylene the slope of the line is about one. On the other hand, void volume estimates for hard elastic HIPS are much lower overall (slope is about one-half). Furthermore, the crazed HIPS has a small initial void content at zero strain, whereas no measurable voids were detected for the unstrained hard elastic polypropylene film. 

Mercury Penetration. The pressure, p, required to force mercury into a pore is inversely related to its diameter, and the volume of mercury, v, which penetrates at that pressure measures the volume and thus the length of the pore. From this the internal area of the pore can be calculated. However, in practice, the pores are widely different in size and the surface area is determined by an integral ... 

Mercury penetration whereby the volume of mercury forced into pores is measured as a function of pressure. The pores must be completely nonwetted by the penetrating liquid and mercury is the only suitable liquid available at ordinary temperature. 

Merch Bricks. Term sometimes used in USA for building bricks that come from the kiln discoloured, warped or off-sized. Mercury Penetration Method. A procedure for the determination of the range of pore sizes in a ceramic material. It depends on the fact that the volume of mercury that will enter a porous body at a pressure of P dynes /cm2 is a measure of the volume of pores larger than a radius r cm where r = -2a cos8/P, a being the surface tension of mercury in dynes/cm and 6 being the contact angle between mercury and the ceramic. A development of the method has been described by R. D. Hill (Trans. Brit. Ceram. Soc., 59, 198,1960). 

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