Multimodal Pore Size Distribution Research Articles

3D mapping of water in oolithic limestone at atmospheric and vacuum saturation using X-ray micro-CT differential imaging

Determining the distribution of fluids in porous sedimentary rocks is of great importance in many geological fields. However, this is not straightforward, especially in the case of complex sedimentary rocks like limestone, where a multidisciplinary approach is often needed to capture its broad, multimodal pore size distribution and complex pore geometries. This paper focuses on the porosity and fluid distribution in two varieties of Massangis limestone, a widely used natural building stone from the southeast part of the Paris basin (France). The Massangis limestone shows locally varying post-depositional alterations, resulting in different types of pore networks and very different water distributions within the limestone. Traditional techniques for characterizing the porosity and pore size distribution are compared with state-of-the-art neutron radiography and X-ray computed microtomography to visualize the distribution of water inside the limestone at different imbibition conditions. X-ray computed microtomography images have the great advantage to non-destructively visualize and analyze the pore space inside of a rock, but are often limited to the larger macropores in the rock due to resolution limitations. In this paper, differential imaging is successfully applied to the X-ray computed microtomography images to obtain sub-resolution information about fluid occupancy and to map the fluid distribution in three dimensions inside the scanned limestone samples. The detailed study of the pore space with differential imaging allows understanding the difference in the water uptake behavior of the limestone, a primary factor that affects the weathering of the rock.

Sulfur-infiltrated porous carbon microspheres with controllable multi-modal pore size distribution for high energy lithium–sulfur batteries

Sulfur has received increasing attention as a cathode material for lithium-sulfur (Li-S) batteries due to its high theoretical specific capacity. However, the commercialization of Li-S batteries is limited by the challenges of poor electrical conductivity of sulfur, dissolution of the polysulfide intermediates into the electrolyte, and volume expansion of sulfur during cycling. Herein, we report the fabrication of novel-structured porous carbon microspheres with a controllable multi-modal pore size distribution, i.e., a combination of interconnected micropores, mesopores and macropores. Cathodes made of sulfur infiltrated in such a hierarchical carbon framework provide several advantages: (1) a continuous and high surface area carbon network for enhanced electrical conductivity and high sulfur loading; (2) macropores and large mesopores bridged by small mesopores to provide good electrolyte accessibility and fast Li ion transport and to accommodate volume expansion of sulfur; and (3) small mesopores and micropores to improve carbon/sulfur interaction and to help trap polysulfides. An initial discharge capacity at 1278 mA h g(-1) and capacity retention at 70.7% (904 mA h g(-1)) after 100 cycles at a high rate (1 C) were achieved. The material fabrication process is relatively simple and easily scalable.

A novel method for the preparation of porous zirconia ceramics with multimodal pore size distribution

Abstract This work presents a new route of processing porous ceramic materials by vacuum induction melting of metallic ternary alloys from the system Ni–Zr–Y. Following internal oxidation results in an interpenetrating network of nickel and oxide phase consisting of yttria and zirconia. After dissolution of the metallic nickel matrix the oxide phase remains as a stable porous ceramic material with a multimodal pore size distribution. The porosity, pore size distribution and specific surface area can be controlled by alloy composition, solidification conditions and oxidation parameters.

Glass formation and confined melting in sol–gel derived nano-ZnO aggregates

Sol–gel processing of ZnO nanocolloids has been revisited to prepare various alkaline metal acetate (MAc: K, Na, Li-acetates) containing ZnO nanopowders. Using differential scanning calorimetry and X-ray diffraction investigations, several new relationships between the morphology and the thermodynamic behavior in the aforementioned particulate ZnO/MAc nanocomposites were noticed: (1) large MAc melting depression shifts −ΔTm ~ 80 °C due to salt confinement within porous ZnO aggregates, (2) corresponding MAc crystallization and re-crystallization temperature depression shifts, (3) presence of multimodal pore size distributions within nanoaggregates and (4) glass formation at temperatures Tg between −40 and 130 °C. We also note that the Tg value drops with rising alkaline metal size, increasing water content and decreasing ZnO particle size. In contrast, Tg rises in the case of co-doped Fe–LiAc/ZnO compositions.

A microstructural insight into compacted clayey soils and their hydraulic properties

A review of the literature is initially presented to bring into light the important microstructural effects on the hydraulic properties of different compacted clayey soils. Experimental data coming from microstructural and macroscopic studies on different compacted clayey soils with dominant multi-modal pore size distribution are analysed to provide a comprehensive picture of different phenomenological features of hydraulic soil behaviour. The data come from clayey soils compacted on the dry side (i.e., with an intrinsic and permanent aggregated structure) or alternatively with dominant coarse fraction (i.e., sand–bentonite mixture with shielding skeleton and well-developed inter-grain porosity), which undergo important microstructural changes on wetting and drying. A microstructural model, already developed to take into account microstructural aspects on water retention curves, is used to plot in the Proctor plane the microstructure set up by compaction and its evolution along hydraulic paths. The model is also used to explain the evolution of hydraulic properties (water and air permeability, water retention) along wetting and drying paths on an artificially prepared mixture of sand and bentonite with dominant granular fraction. The bentonite strongly reacts to changes in water content and allows studying the transition from a granular soil with large pores between sand grains to a low-permeability material on wetting. The key point of this simple model is the introduction of the dependence of the microvoid volume (admitting saturated aggregates) on water content, following an equivalent behavioural response to the macroscopic shrinkage curve.

Preparation and N2, CO2 and H2 adsorption of super activated carbon derived from biomass source hemp (Cannabis sativa L.) stem

A series of activated carbons (ACs) were prepared by chemical activation of hemp (Cannabis sativa L.) stem with KOH. The porous structure of the samples was characterized by N2, CO2 and H2 adsorption, and the surface property was analyzed by IR. All samples show type I isotherms with multimodal pore size distributions in the <10nm region, and a super AC with BET surface area of 3241m2/g and total pore volume of 1.98cm3/g is obtained. Hydrogen uptakes are linear function of specific surface area, total pore volume, and micropore volume, and the maximum hydrogen uptakes are 3.28wt.% at −196°C, 1.0bar. The hydrogen adsorption mainly takes place in micropores but not absolutely, and mesopores in the range 2–5nm also make important contribution. The gas adsorption amount is dominated by ultramicropores at lower pressure, and then lager micropores and mesopores make major contributions at higher pressure.

Preparation of ZnO/SiO2 gel composites and their performance of H2S removal at room temperature

ZnO/SiO2 gel composites with different active component loading were prepared by sol–gel method combined with ambient drying process, followed by thermal treatment. The gel composites were characterized by scanning electron microscopy (SEM), nitrogen adsorption, X-ray diffraction (XRD), FTIR and X-ray photoelectron spectroscopy (XPS), and their performances for H2S removal were evaluated by dynamic testing at room temperature. The as prepared materials exhibited high surface area with multimodal pore size distributions in micropore and mesopore region. The porous properties were significantly influenced both by the ZnO loading ratio and the treated temperature. The gel composites showed a high performance for H2S removal, with the highest H2S adsorption capacity of 96.4mg/g for the sample treated at 400°C with 30wt% ZnO. Both physisorption and the active phase reactivation governed the H2S removal process. It needs to optimize the composites’ porous structure and active component loading amount.

Production Analysis of Tight-Gas and Shale-Gas Reservoirs Using the Dynamic-Slippage Concept

Summary Shales and some tight-gas reservoirs have complex, multimodal pore-size distributions, including pore sizes in the nanopore range, causing gas to be transported by multiple flow mechanisms through the pore structure. Ertekin et al. (1986) developed a method to account for dual-mechanism (pressure- and concentration-driven) flow for tight formations that incorporated an apparent Klinkenberg gas-slippage factor that is not a constant, which is commonly assumed for tight gas reservoirs. In this work, we extend the dynamic-slippage concept to shale-gas reservoirs, for which it is postulated that multimechanism flow can occur. Inspired by recent studies that have demonstrated the complex pore structure of shale-gas reservoirs, which may include nanoporosity in kerogen, we first develop a numerical model that accounts for multimechanism flow in the inorganic- and organic-matter framework using the dynamic-slippage concept. In this formulation, unsteady-state desorption of gas from the kerogen is accounted for. We then generate a series of production forecasts using the numerical model to demonstrate the consequences of not rigorously accounting for multimechanism flow in tight formations. Finally, we modify modern rate-transient-analysis methods by altering pseudovariables to include dynamic-slippage and desorption effects and demonstrate the utility of this approach with simulated and field cases. The primary contribution of this work is therefore the demonstration of the use of modern rate-transient-analysis methods for reservoirs exhibiting multimechanism (non-Darcy) flow. The approach is considered to be useful for analysis of production data from shale-gas and tight-gas formations because it captures the physics of flow in such formations realistically.

Hierarchical porous carbons: design, preparation, and performance in energy storage

Hierarchical porous carbons (HPCs) possess a multimodal pore size distribution of micro-, meso-, and/or macropores, and thus show high electrochemically accessible surface area, short diffusion distance, and high mass transfer rate when used as electrode materials in energy storage devices. Because of this, HPCs show excellent rate capabilities and have attracted considerable attention in recent years. Normally, HPCs are prepared by templating methods or combined templating/activation methods, in which carbons are inverse replicas of the template and the pore structure parameters of HPCs can be easily tuned. Recently, simpler template-free methods have been developed and show a promising future. In this review, we describe the recent advances in design, preparation, and electrochemical performance of HPCs, with particular attention to the main achievements using HPCs developed in our groups since 2008. Finally we give a brief outlook.

Porous stainless steel for biomedical applications

Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density of 0.50 and 0.30 using 15 and 30 wt. (%) respectively of ammonium carbonate and ammonium bicarbonate as foaming agents. The powders were mixed in a planetary ball mill at 60 rpm for 10 minutes. The samples were uniaxially pressed at 287 MPa and subsequently vacuum heat treated in two stages, the first one at 200 ºC for 5 hours to decompose the carbonate and the second one at 1150 ºC for 2 hours to sinter the steel. The sintered samples had a close porous structure and a multimodal pore size distribution that varied with the foaming agent and its concentration. The samples obtained by addition of 30 wt. (%) of foaming agents had a more homogeneous porous structure than that obtained with 15 wt. (%). The MTT cytotoxicity test (3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide) was used to evaluate the mitochondrial activity of L929 cells with samples for periods of 24, 48, and 72 hours. The cytotoxicity test showed that the steel foams were not toxic to fibroblast culture. The sample with the best cellular growth, therefore the most suitable for biomedical applications among those studied in this work, was produced with 30 wt. (%) ammonium carbonate. In this sample, cell development was observed after 48 hours of incubation, and there was adhesion and spreading on the material after 72 hours. Electrochemical experiments using a chloride-containing medium were performed on steel foams and compared to massive steel. The massive steel had a better corrosion performance than the foams as the porosity contributes to increase the surface area exposed to the corrosive medium.

Direct electrodeposition of nanoporous gold with controlled multimodal pore size distribution

The fast one-step preparation of high-surface area nanoporous gold with a multimodal pore size distribution is proposed. The possibility of electrodepositing nanoporous gold was predicted based on Winand's metal classification. The influence of the experimental parameters on the gold morphology is studied. The deposition of porous Au foams is only possible when a sufficient amount of ammonium chloride is added to the electrolyte as a hydrogen source. The meta-stability of the material's morphology is examined. The freshly prepared samples have a very high-surface area, which decreases with stabilization of the gold. The stabilized Au foams have a well-known structure on the nanoscale with ligaments, which are usually obtained after dealloying, and the microscale morphology remains unchanged.

Capacitive performance of mesoporous carbons derived from the citrates in ionic liquid

Mesoporous carbons with different pore structures are prepared via a simple pyrolysis process using citrate salts as precursors. BaC-T carbons derived from barium citrate possess large pore volume and typical multimodal pore size distribution (PSD), while MgC-T carbons derived from magnesium citrate possess high specific surface areas due to their dominant small mesopores and micropores. The capacitive performance of the prepared carbons is investigated in ionic liquid and high specific capacitances (maximum of 180.3Fg−1 for MgC-700) are achieved. Experimental data demonstrate that porosity and surface chemistry corporately determine the capacitive performance. BaC-700 and BaC-800 present good rate performance, and exhibit energy densities of about 50Whkg−1. The good capacitive performance of these carbons is attributed to their bimodal PSD with large pore size and appropriate surface properties. The MgC-800 and BaC-800 carbons present good durability of capacitance during three thousand of charge/discharge cycles.

The saturated hydraulic conductivity of soils with n-modal pore size distributions

A model for water retention in bi-modal soils (soils having structural and matrix porosity only) is further developed into a model for tri-modal soils so that the effects of macro-pores can also be included. This model is based on the exponential (Boltzmann) water retention function. It is suggested that this could be extended to include any number, n, of modes of porosity as may exist due to the hierarchical nature of soil structure. This is then used in combination with Marshall's pore model for hydraulic conductivity to produce a model for the saturated hydraulic conductivity, K sat, of n-modal soils that appears as a very simple and elegant equation. This simple expression for K sat allows for scaling of the porosity and also the characteristic pore size. The model is illustrated with a Polish data set (a sub-set of the POLHYDRO database). Measured values of water retention, bulk density and K sat are used to estimate the parameters of the macro-pore term that explains the contribution of the soil macro-pores to K sat. The mean values and distributions of these macro-pore parameters are presented for the 42 Polish arable soils. However, the existence of macro-pores does not necessarily imply that they are connected and that they contribute to the hydraulic conductivity. It is found that in normal agricultural fields at harvest time, they do not contribute to the hydraulic conductivity. Examination of measured and predicted values of K sat showed that in the normal field conditions that were studied, water movement occurs almost entirely through the structural pores. However, it is predicted that flow through the macro-pore spaces occurs in freshly-tilled soil. The effects of compaction on K sat are easily modelled using the new approach. Different scenarios may readily be compared. A simple one in which the characteristic size of the structural pores decreases as the soil becomes more dense is found not to be consistent with the observations. We are left with the conclusion that the number of structural pores and not their size decreases as soil becomes more dense. It is concluded that the multi-modal nature of soil pore size distributions has a big influence on water retention and on saturated hydraulic conductivity. Taking the multi-modal pore size distribution into account leads not only to physically-based predictions of soil hydraulic properties, but also to improved understanding of soil structure and function.

Synthesis and bioactive properties of macroporous nanoscale SiO 2–CaO–P 2O 5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO 2–CaO–P 2O 5 system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.

Preparation and photocatalytic activity of multi-modally macro/mesoporous titania

Hierarchically disorder sponge-like macro/mesoporous titania was prepared by adding distilled water dropwise to a coating of tetrabutyl titanate. The results reveal that the un-calcined samples show obvious photocatalytic activity and multi-modal pore-size distribution. With increasing calcination temperatures, the photocatalytic activity and crystallinity increase. At 400°C, the calcined sample shows the highest photocatalytic activity. Further increasing the calcination temperatures results in the decrease of photocatalytic activity due to the drastic decrease of specific surface areas. However, the 600°C-calcined sample exhibits the highest specific photocatalytic activity due to high anatase crystallinity.

Analysis of the effect of drying conditions on the structural and surface heterogeneity of silica aerogels and xerogel by using cryogenic nitrogen adsorption characterization

Monolithic silica aerogels were prepared by means of sol–gel method followed by carbon dioxide (CO 2) supercritical drying (SCD). By changing the pressure of liquid CO 2 used to replace ethanol in the autoclave before CO 2-SCD from 8.5 MPa to 4.5 MPa in steps of 1 MPa, a series of silica aerogels with different ratio of micropore, mesopore and macropore volume, having a BET surface area of 678–949 m 2 g −1, a pore volume of 1.63–5.16 cm 3 g −1 and a average pore width of 9.61–21.76 nm were obtained. Silica aerogel and xerogel were also prepared by ethanol-SCD and ambient pressure drying respectively for comparison. N 2 adsorption isotherm was used to characterize the porous texture of the silica aerogels as prepared. Surface energy distributions were calculated by Density Functional Theory (DFT) method deduced from N 2 adsorption data. Infrared spectroscopy (IR) was used to determine the surface groups of these samples. All samples exhibited a multimodal pore size distribution with maxima in the micropore and meso-/macropore regions. The pore size distribution of CO 2-SCD silica aerogels was narrowed by increasing the pressure of liquid CO 2, and the position of maximum also shifted from large pore width region to small pore width region. Maximum in pore volume was attained at 6.5 MPa for mesopores with little decrease of surface area. Surface energy distribution depended not only on the pore size but also on the pore size distributions and surface properties. Different surface groups lead to significant change of surface energy distribution between ethanol supercritical drying and CO 2 supercritical drying silica aerogels. The relationship between surface energy distribution and pore size was introduced.

Biomorphous porous hydroxyapatite-ceramics from rattan (Calamus Rotang)

The three-dimensional, highly oriented pore channel anatomy of native rattan (Calamus rotang) was used as a template to fabricate biomorphous hydroxyapatite (Ca(5)(PO(4))(3)OH) ceramics designed for bone regeneration scaffolds. A low viscous hydroxyapatite-sol was prepared from triethyl phosphite and calcium nitrate tetrahydrate and repeatedly vacuum infiltrated into the native template. The template was subsequently pyrolysed at 800 degrees C to form a biocarbon replica of the native tissue. Heat treatment at 1,300 degrees C in air atmosphere caused oxidation of the carbon skeleton and sintering of the hydroxyapatite. SEM analysis confirmed detailed replication of rattan anatomy. Porosity of the samples measured by mercury porosimetry showed a multimodal pore size distribution in the range of 300 nm to 300 microm. Phase composition was determined by XRD and FT-IR revealing hydroxyapatite as the dominant phase with minimum fractions of CaO and Ca(3)(PO(4))(2). The biomorphous scaffolds with a total porosity of 70-80% obtained a compressive strength of 3-5 MPa in axial direction and 1-2 MPa in radial direction of the pore channel orientation. Bending strength was determined in a coaxial double ring test resulting in a maximum bending strength of approximately 2 MPa.

A Universal Model for Nanoporous Carbon Supercapacitors Applicable to Diverse Pore Regimes, Carbon Materials, and Electrolytes

Supercapacitors, commonly called electric double-layer capacitors (EDLCs), are emerging as a novel type of energy-storage device with the potential to substitute batteries in applications that require high power densities. In response to the latest experimental breakthrough in nanoporous carbon supercapacitors, we propose a heuristic theoretical model that takes pore curvature into account as a replacement for the EDLC model, which is based on a traditional parallel-plate capacitor. When the pore size is in the mesopore regime (2-50 nm), counterions enter mesoporous carbon materials and approach the pore wall to form an electric double-cylinder capacitor (EDCC); in the micropore regime (<2 nm), solvated/desolvated counterions line up along the pore axis to form an electric wire-in-cylinder capacitor (EWCC). In the macropore regime (>50 nm) at which pores are large enough so that pore curvature is no longer significant, the EDCC model can be reduced naturally to the EDLC model. We present density functional theory calculations and detailed analyses of available experimental data in various pore regimes, which show the significant effects of pore curvature on the supercapacitor properties of nanoporous carbon materials. It is shown that the EDCC/EWCC model is universal for carbon supercapacitors with diverse carbon materials, including activated carbon materials, template carbon materials, and novel carbide-derived carbon materials, and with diverse electrolytes, including organic electrolytes, such as tetraethylammonium tetrafluoroborate (TEABF(4)) and tetraethylammonium methylsulfonate (TEAMS) in acetonitrile, aqueous H(2)SO(4) and KOH electrolytes, and even an ionic liquid electrolyte, such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI). The EDCC/EWCC model allows the supercapacitor properties to be correlated with pore size, specific surface area, Debye length, electrolyte concentration and dielectric constant, and solute ion size It may lend support for the systematic optimization of the properties of carbon supercapacitors through experiments. On the basis of the insight obtained from the new model, we also discuss the effects of the kinetic solvation/desolvation process, multimodal (versus unimodal) pore size distribution, and exohedral (versus endohedral) capacitors on the electrochemical properties of supercapacitors.

Frontal Polymerization Synthesis of Monolithic Macroporous Polymers

AbstractA frontal polymerization method is used to produce highly porous polymer monoliths. The method is an approach to polymer synthesis that exploits the heat produced by the reaction itself. This heat triggers polymerization of neighboring monomer molecules, leading to a self‐sustaining hot front, which propagates along the reacting vessel. Dissolved or microencapsulated foaming agents are decomposed only at the fronts, synchronizing the polymerization and the foaming. The ultimate pore structures appear to depend on the polymerization‐front velocity and temperature. The resultant materials are porous, exhibiting tunable pore volume and a multimodal pore size distribution. No organic solvents or high‐pressure equipment are used in the process, and no solvent residues are left in the resulting materials. Specifically, this route allows for the synthesis of large‐scale samples with the additional advantages of high velocity, low energy cost, and the avoidance of multiple process steps. Substitution of hydrophilic acrylamide, N‐isopropylacrylamide, with hydrophobic styrene and methyl methacrylate also leads to porous monolithic materials, suggesting that frontal polymerization represents a powerful and facile method for an exothermic polymerization reaction and the creation of porous polymers.

Exploring Thermal Spray Gray Alumina Coating Pore Network Architecture by Combining Stereological Protocols and Impedance Electrochemical Spectroscopy

Complex multiscale pore network architecture characterized by multimodal pore size distribution and connectivity develops during the manufacture of ceramic thermal spray coatings from intra- and interlamellar cracks generated when each lamella spreads and solidifies to globular pores resulting from lamella stacking defects. This network significantly affects the coating properties and their in-service behaviors. De Hoff stereological analysis permits quantification of the three-dimensional (3D) distribution of spheroids (i.e., pores) from the determination of their two-dimensional (2D) distribution estimated by image analysis when analyzing the coating structure from a polished plane. Electrochemical impedance spectroscopy electrochemically examines a material surface by frequency variable current and potential and analyzes the complex impedance. When a coating covers the material surface, the electrolyte percolates through the more or less connected pore network to locally passivate the substrate. The resistive and capacitive characteristics of the equivalent electrical circuit will depend upon the connected pore network architecture. Both protocols were implemented to quantify thermal spray coating structures. Al2O3-13TiO2 coatings were atmospherically plasma sprayed using several sets of power parameters, are current intensity, plasma gas total flow rate, and plasma gas composition in order to determine their effects on pore network architecture. Particle characteristics upon impact, especially their related dimensionless numbers, such as Reynolds, Weber, and Sommerfeld criteria, were also determined. Analyses permitted identification of (a) the major effects of power parameters upon pore architecture and (b) the related formation mechanisms.