Influence Of Pore Size Distribution Research Articles

Structure-property relationships of polydisperse open-cell foams: Application to melamine foams

The melamine foam presents a unique microstructure characterized by an interconnected network of solid struts, which form the edges and faces of high porosity open cells. This study investigates the influence of pore size distribution on acoustic properties for three commercially available melamine foams. Based on the measured transport parameters, a top-down approach is employed to determine the equivalent Kelvin-cell size corresponding to each transport parameter. The differences found in these equivalent pore sizes indicate that the mono-size model is not suitable for these materials, a difference from which a quantitative estimate of the level of polydispersity can be deduced (using macro-scale information). The polydispersity was confirmed from experimental evidence at micro-scale from the analysis of SEM images. Moreover, the measurements collected at micro-scale (average pore size and its standard deviation) can be used as input data to determine the transport and sound absorbing behavior of melamine foam samples from structure-property relationships available for open cell microstructures. This work provides evidence that the polydispersity of melamine foams should be taken into account to obtain an accurate and consistent picture of microstructure and transport properties of such open cell high porosity foams.

Influence of pore size distribution and applied cross-flow on ion rejection and separation

To improve the understanding of the separation mechanism of ions through membrane filtration, ion transport through a membrane with non-uniform pore sizes is investigated theoretically by solving the coupled Poisson-Nernst-Planck and Navier-Stokes equations under various conditions. The model focuses on a membrane with pore sizes following a log-normal distribution and considers the flow interaction between pores. The rejection performance for different pore arrangements is addressed for a rational assessment of the best ion rejection and selectivity in membrane filtration processes. In addition to the dead-end setting, a cross-flow is applied on the feed side to alleviate the concentration polarization effect. In the presence of positively charged nanopore surfaces, both the cases of a single salt (NaCl) and mixed salts (NaCl, MgCl2) present in the liquid are considered. We show that the uniform pore system outperforms non-uniform ones in terms of the overall rejection and selectivity between salts. When pore size polydispersity is present, the arrangement among the larger and smaller pores impacts the local rejection and volumetric flux of pores. Moreover, the competitive transport between cationic co-ions makes Mg2+ demonstrate generally higher rejection in all the pore arrangements considered. As uniform pores show lower flow rates, the separation efficiency of ions may be improved by pore size polydispersity at the same concentration and pressure difference.

Influence of pore size distribution on pool boiling heat transfer in porous artery structure

To enhance the boiling heat transfer (BHT) performance is of great significance for high heat flux heat dissipation. Through effective liquid/vapor separation mechanism, porous artery structures are proved to significantly enhance the BHT performance. However, such structures are mainly focused on adjusting the liquid/vapor distribution on the macroscale, and the engineering of liquid/vapor distribution inside the porous structure is still missing. To facilitate the vapor escape and also the liquid replenishment inside the porous structure, porous artery structures with four types of pore size distribution, i.e., mono-porous, bi-porous, gradient-aperture, and gradient aperture and bi-porous distributions, were fabricated and experimentally investigated. Experimental results show that porous artery structures with both bi-porous and gradient-aperture distributions exhibit superior heat transfer performance compared to that with mono-porous distribution due to i) reduced liquid and vapor flow resistance; ii) increased liquid replenishment via capillary suction; and iii) efficient liquid/vapor phase separation. The maximum heat flux reached up to 554 W/cm2 for the optimized bi-porous distribution, which is increased by 269% compared to that on a smooth copper surface. In addition, the effects of particle size and the amount of additive PMMA on the BHT performance are investigated, and the underlying physical mechanisms are discussed.

Delineating the effects of pore structure and N-doping on CO2 adsorption using coco peat derived carbon

The CO2 adsorption capacity of carbon materials depends on their structural properties and chemical nature of the functionalization of carbon networks. In this work, amorphous carbon materials are derived from coco peat by activation using KOH and melamine. These are studied to determine the relative influence of pore size distribution and N-doping effect on CO2 adsorption capacity at 298 K and 1 bar. Melamine is used as a pore-directing template and N-doping agent in the preparation of ultra-microporous carbons. The surface areas and ultra-micropore volumes of carbon materials are estimated by NLDFT method based on CO2 adsorption-desorption isotherms at 273 K which vary from 753 m2 g−1 to 1702 m2 g−1 and from 0.13 cm3 g−1 to 0.33 cm3 g−1, respectively. Contrary to many theoretical and experimental studies where N-doping in carbon is reported to have a positive impact on CO2 adsorption, the present study does not indicate any beneficial effect of nitrogen content in biomass-derived carbon while the pore size distribution has a profound effect on CO2 adsorption. A direct correlation has been observed between ultra-micropore (< 0.7 nm) volume and the CO2 adsorption capacity. This study demonstrates that pore size distribution can be tuned in coco peat-derived carbons to achieve maximum CO2 adsorption capacity of 4.8 mmol g−1 at 298 K and 1 bar. It is, therefore, possible to utilize biomass materials to generate carbons with suitable pore size distribution and pore volume for CO2 capture effectively at room temperature.

Influence of pore size distribution on concrete cracking with different AEA content and curing age using acoustic emission and low-field NMR

Concrete pore sizes are in the range of a few nanometers to a few millimeters, and these pores directly affect the cracking characteristics of concrete. In this study, the influence of the pore size distribution on concrete cracking damage was evaluated. Low-field nuclear magnetic resonance (LF-NMR) was used to test the effects of curing age and air-entraining agent (AEA) content on the pore structure of concrete. Three sets of concrete samples with different AEA dosages (0%, 0.7%, and 1.4% of the cementitious material) were prepared, and standard curing was carried out for 3, 7, 28, and 90 days before the tests. During the uniaxial compression test, the cracking signal of the concrete specimen was collected with an acoustic emission (AE) system. The results show that as the curing age increased, the proportion of macropores decreased and the combined proportion of gel pores and transition pores increased. The proportions of macropores and capillary pores increased with AEA content. During the compression process, the relative ringing count at low strain levels was positively correlated with concrete cracking damage. Based on the AE and LF-NMR data, a mathematical model between concrete cracking and the pore size distribution was established, and the effect of the pore size distribution on concrete cracking was quantitatively described by multiple regression equations.

Effects of microstructure on compressive strength of silica sand-enhanced oil well cement at a wide temperature range.

The influence of microstructure of silica-enhanced cement on the mechanical performance of cement is difficult to describe. In this study, we used the scanning electron microscope and image processing method to investigate the relationship between the complicity of cement microstructure and compressive strength under various temperatures and curing times. Fractal dimension was applied to describe the complicity of silica-enhanced cement. The relationships among compressive strength, fractal dimension, temperature, curing time and pore structure of cement were identified. The results show that curing time directly controls the complicity of microstructure of silica-enhanced cement and compressive strength by altering the pore orientation and macropore ratio in silica-enhanced cement. The curing temperature affects the complicity of cement microstructure and compressive strength indirectly by changing the ratio of micropore and small pore. The fractal dimension of silica-enhanced cement shows good correlation with compressive strength. Pore size distribution is the most important factor that influences the complicity of cement matrix and compressive strength of silica-enhanced cement. When building up the macroscopic mechanical performance model of silica-enhanced cement, we should consider the influence of pore size distribution in cement under different curing temperatures and times on the complicity of cement microstructure.

The influence of pore size distribution on thermal conductivity, permeability, and phase change behavior of hierarchical porous materials

The influence of pore size distribution on thermal conductivity, permeability, and phase change behavior of hierarchical porous materials

Influence of Pore Size Distribution on the Electrokinetic Coupling Coefficient in Two-Phase Flow Conditions

Streaming potential is a promising method for a variety of hydrogeophysical applications, including the characterisation of the critical zone, contaminant transport or saline intrusion. A simple bundle of capillary tubes model that accounts for realistic pore and pore throat size distribution of porous rocks is presented in this paper to simulate the electrokinetic coupling coefficient and compared with previously published models. In contrast to previous studies, the non-monotonic pore size distribution function used in our model relies on experimental data for Berea sandstone samples. In our approach, we combined this explicit capillary size distribution with the alternating radius of each capillary tube to mimic pores and pore throats of real rocks. The simulation results obtained with our model predicts water saturation dependence of the relative electrokinetic coupling coefficient more accurately compared with previous studies. Compared with previous studies, our simulation results demonstrate that the relative coupling coefficient remains stable at higher water saturations but vanishes to zero more rapidly as water saturation approaches the irreducible value. This prediction is consistent with the published experimental data. Moreover, our model was more accurate compared with previously published studies in computing the true irreducible water saturation relative to the value reported in an experimental study on a Berea sandstone sample saturated with tap water and liquid CO2. Further modifications, including explicit modelling of the capillary trapping of the non-wetting phase, are required to improve the accuracy of the model.

Preparation and characterization of K2CO3-doped powdered activated carbon for effective in-vitro adsorption of deoxynivalenol

In this work, the preparation and characterization of new steam-activated K2CO3-doped powdered activated carbons based on modified charcoal with different gasification levels are described and used to test the deoxynivalenol (DON) adsorption behavior. The influence of pore size distribution of the carbons, the adsorbent dose, the initial DON concentration and adsorption time were tested in batch mode. The extent of DON adsorption was measured by using kinetic fluorescence polarization spectroscopy. The experimental results indicated that the DON adsorption is very effective on 8 μm-sized carbon particles containing a pore volume of 0.56 cm3/g for pore sizes <2.6 nm and 0.65 cm3/g for pore sizes >20 nm, respectively. A high percentage of DON adsorption (95.4%) at 37 °C was obtained within a contact time of 1 h by using an adsorbent dosage of 0.2 mg/mL and a DON concentration of 4 μg/mL at pH = 7.

Pore size distribution and swelling behavior of compacted bentonite/claystone and bentonite/sand mixtures

The swelling behavior of clayey materials has been studied for many years, and the influence of pore size distribution and suction has been found to be significant. Swelling tests with suction control have been commonly and successfully performed on highly expansive clayey materials, but such work has not always included materials with small percentages of expansive clay minerals. In this study, compacted bentonite (Be), clayey material (C) from claystone, and mixtures of bentonite with clayey material (BeC) and sandy material (BeS) were subjected to swelling tests by the constant volume method in both conventional oedometers with water hydration (water wetting) and oedometers with suction control by relative humidity imposed by NaCl solutions (vapor wetting). The C samples at the optimal moisture content showed no swelling pressure by the vapor wetting method, even for an initial suction of 40,000 kPa. The BeC mixtures showed a lower swelling pressure with the vapor wetting method than with the water wetting method for samples with less than 70% bentonite, whereas the BeS mixtures showed similar swelling pressures in both methods. The BeC and BeS samples had a maximum swelling pressure that was directly proportional to the percentage of bentonite added when tested by the water wetting method. Mixtures with the same percentage of bentonite showed an increase in the swelling pressure that was directly proportional to the initial suction imposed before the tests. Pore size distribution (PSD) curves generated before the swelling tests showed that the greater the initial interaggregate porosity difference among the BeC and BeS mixtures, the greater the swelling pressure difference among the BeC mixtures tested by the water wetting method and the BeS mixtures tested by the vapor wetting method for the same percentages of bentonite. The PSD analysis also showed that the mixtures with higher volumes of entrapped air had higher swelling pressures, mainly during testing by the water wetting procedure. Therefore, the results of the swelling tests are highly dependent on the initial sample suction and the clay mineralogy, but the swelling tests with the vapor wetting method may lead to measurements lower than actual swelling pressures when clayed materials with reduced percentages of expansive clays are tested.

Influence of Pore-Size Distribution on the Resistance of Clay Brick to Freeze–Thaw Cycles

This study examines the influence of raw material characteristics, methods of shaping and of parameters of firing process of clay bricks, on pore-size distribution and on resistance to freeze–thaw cycles (with particular emphasis on the retention time of the specimens at the maximum achieved temperature). Pore-size distribution was measured by mercury-intrusion porosimetry, while the resistance to freeze–thaw cycles was assessed by exposing the bricks to freeze–thaw cycles (HRN B.D8.011 standard) monitoring the appearance of surface changes, decrease of compressive strength as well as the Maage factor. A correlation was set up between the Maage factor and the ratio of the compressive strength before and after freezing as a quantitative indicator of bricks resistance to frost. By using this correlation for all the examined bricks, regardless of their raw material and shaping procedure, a low coefficient of correlation (R2 = 0.26) was obtained. When processed separately, machine-made bricks had a significantly higher correlation coefficient value (R2 = 0.60) than the hand-made bricks (R2 = 0.28).

A remarkable increase in the adsorbed H2 amount: Influence of pore size distribution on the H2 adsorption capacity of Fe-BTC

Here we show the crucial role of ultramicropores on the adsorbed H2 amount. By synthesizing Fe-BTCs via a perturbation assisted nanofusion synthesis strategy and by the control of textural porosity via Fe:BTC ratio, BET surface area (1312 m2/g), total pore volume (1.41 cm3/g), and H2 adsorption capacity (1.10 wt% at 7.6 bar and 298 K) were enhanced by 1.6, 3.1, and 2.6 times, respectively. The reported BET surface area, and the total pore volume are the highest of those reported for Fe-BTC, to date. The enhanced H2 adsorption capacity of Fe-BTC-3 is attributed to the ultramicropores present in its pore structure. Presence of ultramicropores maximizes van der Waals potential, and the adsorbed H2 amount increases. By the perturbation assisted nanofusion synthesis strategy and the control over textural porosity, an Fe-BTC that possesses a H2 adsorption capacity higher than those of reported MOFs with higher BET surface areas has been reported.

Influence of Pore Size Variation on Thermal Conductivity of Open-Porous Foams.

This study addresses the influence of pore size variation on the effective thermal conductivity of open-cell foam structures. Numerical design procedure which renders it possible to control chosen structural parameters has been developed based on characterization of commercially available open-cell copper foams. Open-porous materials with various pore size distribution were numerically designed using the Laguerre–Voronoi Tessellations procedure. Heat transfer through an isolated structure was simulated with the finite element method. The results reveal that thermal conductivity is strongly related to porosity, which is in agreement with the literature. The influence of pore size distribution has also been observed and compared with analytical formulas proposed in the literature.

Effects of Enhanced Flexibility and Pore Size Distribution on Adsorption-Induced Deformation of Mesoporous Materials.

Here, we present a new model of adsorption-induced deformation of mesoporous solids. The model is based on a simplified version of local density functional theory in the framework of solvation free energy. Instead of density, which is treated as constant here, we used film thickness and pore radius as order parameters. This allows us to obtain a self-consistent system of equations describing simultaneously the processes of gas adsorption and adsorbent deformation, as well as conditions for capillary condensation and evaporation. In the limit of infinitely rigid pore walls, when the film becomes several monolayers thick, the model reduces to the well-known Derjaguin-Broekhoff-de Boer theory for pores with cylindrical geometry. We have investigated the effects of enhanced flexibility of the solid as well as the influence of pore size distribution on the adsorption/deformation process. The formulation of the theory allows to determine the average pore size and its width from the desorption branch of the strain isotherm only. The model reproduces the nonmonotonic behavior of the strain isotherm at low relative pressure. Furthermore, we discuss the effect of rigidity of the adsorbent on the pore size distribution, showing qualitatively different results of the adsorption isotherms for rigid and highly flexible materials, in particular, the shift of evaporation pressure to lower values and the absence of a limiting value of the loading at high relative pressure. We also discuss the results of the theory with respect to experimental data obtained from the literature.

Influence of pore size distribution on the adsorption of phenol on PET-based activated carbons

The role of pore size distribution in the adsorption of phenol in aqueous solutions on polyethylene terephthalate (PET)-based activated carbons (ACs) has been analyzed. The ACs were prepared from PET and mixtures of PET with coal-tar pitch (CTP) by means of carbonization and subsequent steam and carbon dioxide activation at 850 and 950°C, respectively. The resultant ACs were characterized on the basis of similarities in their surface chemical features and differences in their micropore size distributions. The adsorption of phenol was carried out in static conditions at ambient temperature. The pseudo-second order kinetic model and Langmuir model were found to fit the experimental data very well. The different adsorption capacities of the ACs towards phenol were attributed to differences in their micropore size distributions. Adsorption capacity was favoured by the volume of pores with a size smaller than 1.4nm; but restricted by pores smaller than 0.8nm.

The influence of pore size distribution on the oxygen reduction reaction performance in nitrogen doped carbon microspheres

High-performance nitrogen-doped carbon electrocatalysts for the oxygen reduction reaction have been synthesized by the rational design of their pore structure.

Combined influence of pore size distribution and surface hydrophilicity on the water adsorption characteristics of micro- and mesoporous silica

Adsorption processes are ubiquitous in nature as well as of great technological importance for gas separation, purification, storage and thermally driven heat pumps. This has led to a strong interest in the fundamental mechanisms governing adsorption phenomena and their exploitation to tailor adsorption systems for specific applications. In particular, the adsorption of water on porous silica exhibits remarkable properties due to the strong polarity of the adsorbate and moderate hydrophilicity of the adsorbent. It is generally accepted that the adsorption of water vapor on porous silica depends upon the concentration of surface silanols and the pore size. In fact, materials with ordered mesopores and a well-defined pore size have been used as model systems to demonstrate that water adsorption occurs predominantly through capillary condensation. While the pore surface chemistry is modified to become more hydrophilic after filling of the pores in these materials, the overall shape of the water adsorption isotherm (Type V) is not significantly affected in subsequent adsorption measurements. The present contribution shows that conservation of the isotherm shape is a unique phenomenon related to ordered mesopores but doesn't apply to materials with a more complex pore structure. For materials with wider pore size distributions including micropores, a synergistic effect of surface hydroxylation and pore size leads to a dramatic change in the water adsorption isotherm after the first adsorption/desorption cycle. In fact, we demonstrate that the water cycling capacity at relative pressures below the onset of capillary condensation increases significantly in these systems. These results contribute to a fundamental understanding of water adsorption in complex systems and have important implications in applications such as adsorption heat pumps where a large water cycling capacity in a specific relative pressure window is required.

Numerical simulation of chloride penetration in concrete in rapid chloride migration tests

This paper presents a new transport model for describing the penetration of chlorides in cement-based materials. The model uses the concept of double porosity to reflect the influence of pore size distribution on the transport of ionic species in porous materials. In addition to the use of two porosities, the model also considers the effects of ionic exchange between the pores of different sizes, ionic binding between liquid and solid phases, and the boundary-layer effect of the exposed surface on chloride transport. The model is validated using experimental data obtained from rapid chloride migration tests. Good agreement between calculated and measured chloride concentration profiles is demonstrated.

Adsorption kinetics and diffusion of Saxitoxins on granular-activated carbon: influence of pore size distribution

Saxitoxin (STX) is the most toxic non-protein substance known. STX-producing cyanobacteria have been identified in most continents and are being detected more widely because of global warming, threatening human drinking water supplies worldwide. Removal of these components can be accomplished by adsorption on granular-activated carbon (GAC) but little is yet known about the kinetics of the process. This research investigated adsorption kinetics and diffusion behaviour of a decarbomoyl saxitoxin (dc-STX) and a carbamate toxin (STX) on four coconut shell-based GAC samples with different pore size distribution. It was observed that equilibrium concentration was reached within 24 h and that a pseudo-second-order model best represented experimental data. Of the four GAC samples tested, the example with the largest volume of mesopores adsorbed more STX and with a faster upload rate, while dc-STX was adsorbed equally in all four GAC samples.

Case studies on the influence of microstructure voids on thermal conductivity in fractal porous media

Several studies have shown that fractal geometry is a tool that can replicate and investigate the nature of the materials and their physical properties. The Sierpinski carpet is often utilized to simulate porous microstructures. By using this geometric figure it is possible to study the influence of pore size distribution on deterministic fractal porous media. The determination of the thermal conductivity can be carried out using the electrical analogy. So, microstructure models have been converted in electrical fractal patterns. This fractal procedure is characterized by a close relationship with the actual microstructure and prevent papers has been validate it with experimental data in a series of former papers. In this work it is possible to show how thermal conductivity changes in relation to pore size distribution and geometric microstructure parameters.