Mercury penetration method: pore

One problem is that if the silica gel is not very strong, the structure collapses by the external pressure of mercury before pores are penetrated. It is for this reason that the nitrogen adsorption isotherm method is preferred for research purposes. Nevertheless, for strong bodies like industrial catalyst gels, the mercury penetration method is far more rapid not only in execution, but also in converting results to pore size distribution curves. 

The specific surface area was determined by a Micromeritics Model 2200 high-speed, surface-area analyzer using nitrogen as the adsorbate. The pore volume was determined by the mercury penetration method on a Micromeritics Model 900/910 series porosimeter. 

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... 

Mercury-penetration Method By equating the force due to surface tension (which tends to keep mercury out of a pore) to the applied force, Ritter and Drake obtained... 

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

There is considerable evidence that the product (r./.)(l — ) appearing in equations (4c) and (4b) approximately equals 1.0 since average pore radii determined, say, by the mercury penetration method (5), agree quite well with the ratio 2Vp/Sp. This agreement is no doubt due to the fact that a roughness factor of 2.0 is reasonable for many surfaces and the valqe of 6, the porosity, is about 0.5 for most catalysts. 

Mercury Penetration Method. Mercury docs not wet the surface of silica and, higher pressure is required to force the liquid into a small pore. Washburn (187) developed the equation... 

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). 

Purcell Method. Name sometimes given to the MERCURY PENETRATION METHOD (q.v.) for determining pore-size distribution (W. R. Purcell, J. Petroleum Tech., 1, (2), 39,1949). 

Schenck Porosimeter. Apparatus for the determination of pore size DISTRIBUTION (q.V.) by the mercury PENETRATION METHOD (q.V.) it haS... 

The most common methods to determine pore size distributions are the A. mercury penetration method, B. nitrogen adsorption method, and C. molecular probe method. 

The mercury penetration method is based on the fact that mercury has a significant surface tension and does not wet most catalytic surfaces. For a cylindrical pore, the force acting against the entrance of mercury to the pores equals —Z trrcr cos 6. The external pressure applied to overcome this force is Trr P. At equilibrium, the two forces are equal and ... 

There are two well-established experimental techniques for determining the distribution of pore radii. They are the mercury penetration technique and the desorption isotherm method. 

The technique of mercury porosimetry consists essentially of measuring the extent of mercury penetration into an evaluated solid as a function of the applied hydrostatic pressure. The full scope of the method first became apparent in 1945 when Ritter and Drake39 developed a technique for making measurements at high pressures. The method has enjoyed increasing popularity with the passing of years, and automatic porosimeters are now in use for the routine examination of the pore structure of... 

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). 

The action of capillary pressure underlies the mercury porosimetry method, which is commonly used for the determination of pore size distribution in ceramics, adsorbents, catalysts and other porous materials [15]. Mercury is known to wet non-metallic surfaces poorly, and thus the capillary pressure, equal to 2o/r (where r is the pore radius, or the average radius of pores having complex shape), prevents its spontaneous penetration into the pores. The pore size distribution can be established by measuring the volume... 

A much more accurate method of determining the pore volnme of a catalyst sample is the helium-mercury method. One places a known weight of catalyst (W) in a chamber of known volume. After the chamber has been evacnated, a known quantity of helium is admitted. From the gas laws and measurements of the temperature and pressure, one may then proceed to determine the volume occupied by the helium (Vne)- This volume is equal to the sum of the volume exterior to the pellets proper and the void volume within the pellets (Vv,jj<,). The helium is then pumped out and the chamber is filled with mercury at atmospheric pressure. Since the mercury will not penetrate the pores of most catalysts at atmospheric pressure, the mercury will occupy only the volume exterior to the pellets proper (Eng)- Hence,... 

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. 

The total volume of mercury VHg(p) penetrating the pores of the material at pressure p leads via equation (1.2) to the integral volume Vp(r) of all pores with radii (p) larger than r < p < oo, i. e. Vp(r) = VHg(p). By differentiation to the pore radius r this yields the differential pore size distribution of the material. This method is valuable to investigate macro- and mesopores (lUPAC, cp. Sect. 3), but not for micropores, i. e. it is limited to pore radii r > 1 nm. 

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