Pore structure analysis

A microscopic description characterizes the structure of the pores. The objective of a pore-structure analysis is to provide a description that relates to the macroscopic or bulk flow properties. The major bulk properties that need to be correlated with pore description or characterization are the four basic parameters porosity, permeability, tortuosity and connectivity. In studying different samples of the same medium, it becomes apparent that the number of pore sizes, shapes, orientations and interconnections are enormous. Due to this complexity, pore-structure description is most often a statistical distribution of apparent pore sizes. This distribution is apparent because to convert measurements to pore sizes one must resort to models that provide average or model pore sizes. A common approach to defining a characteristic pore size distribution is to model the porous medium as a bundle of straight cylindrical or rectangular capillaries (refer to Figure 2). The diameters of the model capillaries are defined on the basis of a convenient distribution function. 

A. Jena and K. Gupta. An innovative technique for pore structure analysis of fuel cell and battery components using flow porometry. Journal of Power Sources 96 (2001) 214-219. 

Another possible solution to the problem of analyzing multiple-layered membrane composites is a newly developed method using NMR spin-lattice relaxation measurements (Glaves 1989). In this method, which allows a wide range of pore sizes to be studied (from less than 1 nm to greater than 10 microns), the moisture content of the composite membrane is controlled so that the fine pores in the membrane film of a two-layered composite are saturated with water, but only a small quantity of adsorbed water is present in the large pores of the support. It has been found that the spin-lattice relaxation decay time of a fluid (such as water) in a pore is shorter than that for the same fluid in the bulk. From the relaxation data the pore volume distribution can be calculated. Thus, the NMR spin-lattice relaxation data of a properly prepared membrane composite sample can be used to derive the pore size distribution that conventional pore structure analysis techniques... 

A second approach to pore—structure analysis, small-angle scattering (SAS), probes the heteroge-... 

Mikhail, R. S., S. Brunauer, and E. E. Broder, Investigations of a complete pore structure analysis. II. Analysis of four silica gels , J. Colloid Int. Sci., 26, 54-61 (1968b). 

Thermoporometry. Thermoporometry is the calorimetric study of the liquid-solid transformation of a capillary condensate that saturates a porous material such as a membrane. The basic principle involved is the freezing (or melting) point depression as a result of the strong curvature of the liquid-solid interface present in small pores. The thermodynamic basis of this phenomenon has been described by Brun et al. [1973] who introduced thermoporometry as a new pore structure analysis technique. It is capable of characterizing the pore size and shape. Unlike many other methods, this technique gives the actual size of the cavities instead of the size of the openings [Eyraud. 1984]. 

The nitrogen isotherms discussed in this paper were determined on two representative porous carbons with the aid of commercial automated equipment and the manufacturer s software was used for the pore structure analysis. This approach has provided a basis for a critical appraisal of a number of readily available data processing procedures. 

S. Brunauer, R.Sh. Mikhail and E.E. Bodor, Pore structure analysis without a pore shape model. /. Colloid Interface Sci., 24 (1967) 451. 

C. L. Glaves and D.M. Smith, Membrane pore structure analysis via NMR-spin-lattice relaxation experiments. /. Membr. Sci., 46 (1989)167. 

D.W. Hua, J.V. D Souza, P.W. Schmidt and D.M. Smith, Pore structure analysis via small angle X-ray scattering, in J. Rouquerol, F. Rodriguez-Reinoso, K.S.W. Sing and... 

For scientific investigations the principal experimental methods are based on the measurement of physical adsorption. Results provide data on surface and pore size distribution. A recent publication showed that for a complete pore structure analysis complex calculations are necessary which demand the application of computers. Extensive software is available that includes presentation of the results as graphics that can be easily interpreted. However, it must be emphasized that all results are obtained indirectly through the use of models therefore, they can only be seen within the context of the applicable preconditions. If this is not considered, the conclusions may not be physically valid. 

Pore structure analysis methods based upon realistic disordered microstructures may be classified into two types. In one approach, the experimental procedures used to fabricate the material are reproduced, to the greatest extent possible, via molecular simulation, and the resulting amorphous material structure is then statistically analyzed to obtain the desired structural information. In the other approach, adsorbent structural data (e.g., smaU-angle neutron scattering) is used to construct a model disordered porous structure that is statistically consistent with the experimental measurements. As in the first approach, molecular simulations can then be carried out using the derived model structure to obtain the structural characteristics of the original adsorbent. 

Brunauer, Mikhail and Bodor (13) developed a method of pore structure analysis which employs a hydraulic radius, rj, as a measure of pore size. This radius is defined as r[ = V/S where V is the volume of a group of pore "cores" with the wall surface area S. The "core" refers to the empty... 

Table 11.1 Physiochemical methods for pore structure analysis.

Yu, Z. (2008). Pore Structure Analysis on Activated Carbon Fibers By Cluster and Watershed Transform Method, Applied Surface Science. 

Jagiello J, Olivier J P (2009) A Simple Two-Dimensional NLDFT Model of Gas Adsorption in Finite Carbon Pores. Application to Pore Structure Analysis. Journal of Physical Chemistry C 113 19382-19385 Ravikovitch P I, Neimark A V (2001) Characterization of micro- and mesoporosity in SBA-15 materials from adsorption data by the NLDIT method. Journal of Physical Chemistry B 105 6817-6823 Harkins W D, Jura G (1944) Surfaces of Solids. XII. An Absolute Method for the Determination of the Area of a Finely Divided Crystalline Solid. J. Am. Chem. Soc. 66 1362-1366... 

Pore structure analysis of five silica gels by Hagymassey and Brunauer (169) is typical of many similar evaluations of the method. In this paper, water vapor and nitrogen were compared as adsorbents and results were reasonably in agreement, with peak diameters of 4.1 and 4.6 A, respectively. However, for adsorbents that have any hydrophobic surface, nitrogen should be used. 

S. Bukowiecki, B. Straube, and K.K. Unger Pore structure analysis of close-packed silica spheres by means of nitrogen sorption and mercury porosimetry, in Principles and Applications of Pore Structural Characterization (Haynes J.M. Rossi-Doria P., eds) Arrowsmith,... 

D.M. Smith, T.E. Holt, D.P. Gallegos, and D.L. Stermer Pore structure analysis via NMR, mercury porosimetry, and dynamic methods, in Advances in Ceramics, Vol. 21, Ceramic Powder Sdence(Messing G.L., (Joe) Mazdiyasni K.S., McCauley J.W. Haber R.A., eds) The American Ceramic Sodety, Columbus, OH (1987) 779-791... 

Mikhail R.S, Bmnauer S., Bodor E.E. Investigations of a complete pore structure analysis. I. Analysis of micropores. J. Colloid Interface Sci. 1968 26(1) 45-53 Mulder M. Basic Principles of Membrane Technology. Dordrecht Kluwer Academic Publishers, 1991... 

Radjy and SeUevold [54] developed a phenomenological theoretical theory for the f-method of pore structure analysis for slit-shaped and cylindrical pores. A comparison [55] of adsoiption and desoiption methods for pore size distribution, with transmission electron microscopy using closely graded cylindrical pores in alumina, closed at one end, confirmed the superiority of the Broeckhoff-de Boer equations over the Kelvin equation. Lamond [56] found Lippen s t silica values unsuitable for carbon black and proposed a new set based on adsorption data for fluffy carbon blacks. 

Kim, S., Chu, C.C. Pore structure analysis of swollen dextran-methacrylate hydrogels by SEM and mercury intrusion porosimetry. J. Biomed. Mater. Res. 2000(53), 258... 

FTIR is especially useful for the characterization of surface species and the state of adsorbed molecules. A study of supported oxide catalysts involving FTIR and adsorption measurements is reported by Rives and his co-workers and the use of FTIR as an ancillary technique is referred to in several other papers. NMR measurements have been carried out in the context of image analysis (NMRI) of pore structures (Ewing et al), determination of dlffusivities of adsorbed species (Bahceli et al) and the pore structural analysis of wet materials (Smith and Davis). 

For pore structure analysis, the pore size distribution (PSD) may be obtained from... 

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