Mercury porosimetry and its application to the analysis of coal pore structure

Mercury porosimetry, gas adsorption, helium and mercury densities and small angle X-ray scattering were the methods used for studying porosity characteristics of a number of Czechoslovak coals ranging from lignite to semi-anthracite. Total pore volumes were measured in the pore radii range 0.1 – 7500 nm and then divided into the following groups: micropores (smaller than 1.8 nm), mesopores (1.8 – 30 nm) and macropores (over 30 nm). Coal porosity values ranged from 1.3 up to 43%. With low and medium-rank coals (carbon content under 76%), porosity is mostly due to mesopores. Micropores and mesopores account for a substantial share of the porosity of bituminous coals (carbon content over 80.6%). The distribution of mesopores was determined for an identical pore radii interval on the basis of data obtained independently by means of mercury penetration, gas adsorption and small angle X-ray scattering. High-pressure mercury penetration is an effective method of obtaining the coal porosity spectrum within a broad interval of pore radii, provided that a correction is made for the coal compressibility when evaluating the measured data. The recommended value of the mercury—coal contact angle is 1352 for brown coal and 130° for bituminous coal.     

Mercury porosimetry in pharmaceutical technology

The literature on the use of mercury porosimetry in pharmaceutical technology is reviewed. The relation between the application and the preferable pore size distribution presentation is also discussed. In addition, pore size distributions of lactose tablets are presented and the calculated values for the porosity, pore diameter and specific surface area are compared with results from air permeability and nitrogen adsorption measurements. The agreement is acceptable taking into account the simplifications and the inaccuracy of the methods.     

Mercury porosimetry of ceramics

Mercury porosimetry has been used in ceramics for the characterization of products and for studies of processing. Specifications including PSD (pore size distribution by mercury porosimetry) are now applied to magnesia refractories used in basic oxygen furnaces and to building brick which may be exposed to frost. Other products cited as examples are the silica fiber tile used on the space shuttle, plasma sprayed coatings, carbon composites and filters.In ceramic processing research, PSD has proved valuable for evaluating the firing of basic refractories, brick and sanitary ware. Pore growth during the early stages of sintering several materials was first identified by PSD. The character of clay agglomerates and the presence of alumina aggregates in compacts have been measured, the latter showing bimodal PSD. The progressive change in PSD while compacting glass spheres outlines the stages of compaction. The most frequent pore diameter in plaster slip casting molds correlates directly with plaster consistency.In dense or vitrified ceramics, errors may occur due to closed pores or pores with narrow openings. However, in ceramic compacts and highly porous ceramics, pores have several openings so PSD is a realistic measure of structure.     

Mercury porosimetry studies I. Low melting alloy intrusion studies as an aid to the interpretation of mercury porosimetry data

Low melting alloy intrusion experiments offer a convenient and simple technique to aid in interpretation of mercury intrusion curves. By substituting a low melting alloy (Cerrolow^® 117, m.p. 47 °C) for mercury in an intrusion experiment, it is possible to ‘freeze’ the intrusion process at any given pressure merely by cooling the alloy below its melting point. The ‘frozen’ intrusion sample may then be sectioned and examined under the microscope to determine how the metal is entering the porous structure.Two samples of poly(vinyl chloride) resin were investigated by this technique. The inter-particle penetration process was found to be consistent with the notion of bed depacking rather than bed penetration. The intraparticle penetration process was observed to be different for the two samples investigated. In one case the limiting pores were located in the outer surface while in the other sample they were located in the interior of the particle.     

Mercury intrusion porosimetry in concrete technology: tips in measurement,pore structure parameter acquisition and application

Mercury intrusion porosimetry (MIP) has been widely used to investigate the pore structure of cement based materials for many years. The purpose of this paper is to present views of how to make MIP results of similar materials from different research institutes compatible and how to use MIP results in modeling. Factors that influence MIP results are analyzed comprehensively considering characteristics of cement based materials, and recommendations corresponding to these factors are illustrated. According to these recommendations, when specific tests are unavailable, mercury surface tension of 480 mM/m and mercury-solid contact angle of 130° may be used in theoretical calculations of pore size; sampling by either sawing or core-drilling, maximum value of the minimum sample dimension of 5 mm, and solvent drying are recommended for sample preparation; and staged operation mode which set appropriate equilibrium time is recommended for MIP measurements of cement based materials. From a MIP result, the methods which are necessary to be unified to determine pore structure parameters are discussed. Besides, it is shown that sometimes pore structure parameters should be used carefully in physical models by considering their physical or statistical meanings.     

Mercury intrusion porosimetry in pulp and paper technology

Mercury intrusion is frequently used for the characterization of porous materials, giving access to parameters such as porosity and pore size distribution as well as density (skeletal and bulk).The present work aims at studying the suitability of the mercury intrusion technique to evaluate the pore structure and related information of different kinds of woods used for pulp production, pulp handsheets and commercial paper sheets. Differences in wood structure, pulp composition and paper composition and structure could be easily detected by changes in the measured parameters, thus enabling a better understanding and/or prediction of the behaviour of these materials.     

Mercury porosimetry studies II. The application of mercury porosimetry to porous polymer powders

Two experimental methods are outlined for the separation of the inter- and intraparticle intrusion volumes of porous powders. The first of these relies upon the control of interparticle bed packing by mounting the particles upon a transparent adhesive substrate. The pressure at which interparticle penetration occurs (critical pressure) is measured by observing the penetration process directly in a microscope pressure cell. A mercury intrusion experiment is then run on a similarly mounted sample and the value of the critical pressure obtained previously used to define the interparticle volume.In the second method, the critical pressure is determined by running a mercury intrusion experiment on a powder sample whose intraparticle volume has been filled with a wetting liquid—dioctyl phthalate (DOP). This technique depends upon the observation made previously in Part I of this series that bed depacking rather than bed penetration is the initial step of the penetration process.Total intraparticle volumes determined by both of these methods were compared with those obtained by the uptake of a wetting oil (DOP). Although an excellent degree of correlation was observed between the two methods, the DOP uptake values were found to be high by a constant amount. This was demonstrated to be due to oil retained in the interparticle volume. The values of critical pressure determined in this study indicate that the filling of the interparticle voids in a mercury intrusion experiment may not correspond to any feature observed in the penetration curve. Thus it is necessary to determine this quantity separately.     

Mercury penetration porosimetry in analysis of exhaust catalysts and catalyst supports

The application of mercury penetration porosimetry is reported, in which data of samples from several manufacturers are presented. The technique has been used to investigate the loss of catalyst activity by high-temperature aging as correlated with pore structure alterations. It has been possible to determine the difference between catalyst deterioration due to poisons deposited on the catalyst and deterioration due to loss of surface area resulting from extremely high temperatures. Some data are also presented which indicate that, by choosing the proper conditions in the honeycomb fabrication process, the porosity of the resulting product can be controlled.     

Mercury porosimetry curves of sandstones. Mechanisms of mercury penetration and withdrawal

A simple and accurate mercury porosimeter has been built and used to determine the primary drainage, imbibition, and secondary drainage curves of sandstone samples in the pressure range of 0 to 1000 cm Hg column. The results, which include electrical indication of the breakthrough capillary pressures, are practically free of the usual boundary effects. The microscopic displacement mechanisms have been studied in transparent, 2-D capillary networks. It has been concluded that mercury withdrawal takes place by the ‘frontal drive’ mechanism. The primary drainage, imbibition, and secondary drainage in a square 2-D network have been simulated by computer. The results have confirmed the experimental finding that the breakthrough capillary pressure is lower in secondary drainage than in primary drainage.     

Mercury porosimetry of hardened cement paste: the influence of particle size

Mercury Porosimetry tests have been made on four different particle sizes of the same mature hardened cement paste, w/c = 0.40. The pore volume penetrated by mercury appears to be independent of particle size. The pore size distribution functions show an increasing concentration of large pores for decreasing particle sizes.     

Evaluation of the pore size distribution in mercury porosimetry using computer simulations of porous media

The pore size distribution calculated using the Washburn equation was evaluated. The pore-sphere network was selected as a model for porous media since this model could qualitatively describe hysteresis and retention phenomena. 3-Dimensional lattices of square configuration were considered with normal, skewed and bimodal pore size distributions. The calculated pore size distribution was accurate up to the average size pores, but significantly different for larger pores. The fraction of average size pores was always exaggerated. Pore connectivity had larger influence on the pore size distribution than the lattice structures.     

Microstructural evolution of cemented paste backfill: Mercury intrusion porosimetry test results

The microstructural evolution of different cemented paste backfill (CPB) samples made with ground silica was evaluated using mercury intrusion porosimetry (MIP). The influence of three binders (OPC, OPC with fly ash, and OPC with blast furnace slag) and of three types of water (one deionised and two sulphated) on the microstructure was studied over the curing time. Uniaxial compressive strength (UCS) tests were also performed to relate MIP results to the backfill mechanical strength. Among other findings, the MIP analyses indicate that the slag based binder combined with a mixing water having a high sulphate content (of 7549 ppm) showed the highest percentage of fine pores and the highest strength. This behaviour is related to the potential precipitation of sulphate phases in pores, which may contribute to strength enhancement. Based on MIP pore size distributions and UCS results, the authors propose a general relationship applicable for CPB.     

A study of the inter- and intra-fibre pore characteristics of some nylon fabrics by mercury porosimetry

The effective pore size distributions of twelve non-woven nylon materials have been measured using the mercury injection technique. All show intrusions at pressures up to 20 psi due to inter-fibre voids; five materials show significant intrusions between 50 and 30,000 psi corresponding to intra-fibre voids the presence of which is confirmed by scanning electron microscopy. It appears, on applying a rigorous correction to the data for the compressibilities of the glass sample cell and contents, that the nylon remains compressed on releasing the pressure from 30,000 psi, and the mercury has a lower compressibility above 10,000 psi than it has below this pressure; the glass sample cell shows a delayed elastic effect when the pressure is reduced. The maxima of the effective pore size distributions of the intra-fibre voids are in the range 80 – 600 Å radius.     

Improving the interpretation of mercury porosimetry data using computerised X-ray tomography and mean-field DFT

Despite widespread use of the technique for a long time, the proper interpretation of mercury porosimetry data, particularly retraction curves, remains uncertain. In this work, the usefulness of two complementary techniques, mean-field density functional theory (MF-DFT) and micro-computerized X-ray tomography (micro-CXT), for aiding interpretation of ambiguous mercury porosimetry data has been explored. MF-DFT has been used to show that a specific, idiosyncratic form for the top of the mercury intrusion and extrusion curves is probably associated with a particular network structure where the smallest pores only form through connections between larger pores. CXT has been used to study the pore potential theory of hysteresis and entrapment directly using a model porous material with spatially varying pore wetting properties. CXT has also been used to directly study the percolation properties, and entrapment of mercury, within a macroporous pellet. Particular percolation pathways across the heart of the pellet have been directly mapped. The forms of entrapped mercury ganglia have been directly observed and related to retraction mechanisms. A combination of CXT and mercury porosimetry can be used to map spatial variation in pore neck sizes below the spatial resolution of imaging.     

Mercury porosimetry of hardened cement paste cured or stored at 97°C

Mercury Porosimetry tests have shown that steam cured cement pastes have a coarser pore structure than cement pastes cured at room temperature. Heating of mature, room temperature cured pastes also makes the pore structure coarser. It was found that specimen size has an important influence on the mercury porosimetry results.     

Pore geometry of 3D-Cf/SiC composites by mercury intrusion porosimetry

The 3D-C_f/SiC composites fabricated via precursor infiltration and pyrolysis (PIP) are porous inside due to their specific processing. To evaluate the porosity of 3D-C_f/SiC, a novel procedure of mercury intrusion porosimetry (MIP) was adopted to extract information from the hysteresis and entrapment. This method is able to eliminate the temporarily retained Hg at atmospheric pressure from the real entrapment due to topological reasons. From the interpretation of the MIP primary and secondary intrusion–extrusion data, accompanied by scanning electron microscopy (SEM) analysis and bubble point measurement, the pore geometry of 3D-C_f/SiC is supposed to be a 3D network originating from the architecture of braided carbon fabrics. This network is composed of hundreds of micron-sized large chambers between bundles, micro-cracks below 0.1 μm and medium-sized channels about 20–4 μm that bridge the former two and provide passages for fluids permeating the material.     

Recovery of heavy organics from gas-bearing sedimentary rocks

The characteristics of recovery of high-molecular-mass compounds in various model systems reflecting the reservoir structure were studied with the use of the technique of cyclic solvent (toluene and diesel fuel) flooding and dissolving these compounds over a given period of time at temperatures of 30 and 70°C. The dynamics of recovery of the macromolecular compounds showed that the major portion of soluble compounds was extracted in the first 3–5 cycles, and the rock permeability substantially increased.     

Characterization of pore structure in cement-based materials using pressurization-depressurization cycling mercury intrusion porosimetry (PDC-MIP)

Numerous mercury intrusion porosimetry (MIP) studies have been carried out to investigate the pore structure in cement-based materials. However, the standard MIP often results in an underestimation of large pores and an overestimation of small pores because of its intrinsic limitation. In this paper, an innovative MIP method is developed in order to provide a more accurate estimation of pore size distribution. The new MIP measurements are conducted following a unique mercury intrusion procedure, in which the applied pressure is increased from the minimum to the maximum by repeating pressurization-depressurization cycles instead of a continuous pressurization followed by a continuous depressurization. Accordingly, this method is called pressurization-depressurization cycling MIP (PDC-MIP). By following the PDC-MIP testing sequence, the volumes of the throat pores and the corresponding ink-bottle pores can be determined at every pore size. These values are used to calculate pore size distribution by using the newly developed analysis method. This paper presents an application of PDC-MIP on the investigation of the pore size distribution in cement-based materials. The experimental results of PDC-MIP are compared with those measured by standard MIP. The PDC-MIP is further validated with the other experimental methods and numerical tool, including nitrogen sorption, backscanning electron (BSE) image analysis, Wood's metal intrusion porosimetry (WMIP) and the numerical simulation by the cement hydration model HYMOSTRUC3D.     

Effects of wettability and pore geometry on mobilization of oil and gas in physical models and application to water-alternating-gas (WAG) injections

Experiments in capillary tubes show that the mobilization of discontinuous oil and/or gas in a hydrophobic (oil-wet) system requires a pressure gradient of about 6 to 7 times larger than for a comparable water-wet system. The mobilization pressure is directly proportional to the contact angle hysteresis and interfacial tension and inversely proportional to tube radius. For experiments in glass micromodels, where pores were ～ 3 times as large as connecting throats, mobilization pressures for oil-wet systems were only ～ 1.7 times as large as for equivalent water-wet systems and pore geometry had more effect on mobilization pressure than did differences in wettability. These pore-level events are thought to affect mobility within WAG banks used to stabilize gas drives.