Evaluation Of Pore Size Distribution Research Articles

A Grand Canonical Monte Carlo Simulation for the Evaluation of Pore Size Distribution of Nuclear-Grade Graphite from Kr Adsorption Isotherms

Characterizing materials with low surface areas or with very small sample sizes requires innovative approaches beyond traditional N2 and Ar adsorption measurements. The measurement of Kr adsorption isotherms is often employed to serve this purpose, yet its potential remains limited by the lack of models for the interpretation of the experimental results in terms of pore size distribution. In this work, simulated adsorption isotherms of Kr onto graphite in slit-shaped pores are generated with a Grand Canonical Monte Carlo method. The pore size distributions of nuclear-grade graphite samples and activated carbon are modelled by fitting simulated isotherms to the experimental data. The resulting distributions are favourably compared with those generated by commercially available modelling packages, based on the use of N2 adsorption isotherms using GCMC and BJH methods. The new GCMC-Kr kernel developed in this study offers an alternative method for the evaluation of the distribution of pore sizes in nuclear graphite and other low surface area materials, which can be employed when N2 and Ar adsorption measurements cannot be carried out.

Evaluation of pore size distribution and permeability reduction behavior in pervious concrete

Pervious concrete is an environmentally friendly material that improves water permeability, skid resistance, and sound absorption characteristics. However, due to a large number of pores and the absorption capacity, pervious concrete faces the problem of clogging caused by dust particles and solid contaminants entering the internal pores. In this study, both pore size distributions (PSD) of the pervious concrete and permeability reduction behavior are studied by laboratory tests. The extent of permeability reduction is addressed by designing the penetration test for 21 groups of pervious concrete mixes with varying aggregate gradations and specimen thickness. The PSD is determined by the two-dimensional (2D) sliced image scanned by the Computed Tomography (CT). An approach to represent the characteristic pore size of pervious concrete is proposed and verified. Results showed that: the effect of thickness on permeability is negligible while on clogging behavior is significant. The ratio between the clogging sand sizes and the characteristic pore size is an important parameter that affects the clogging behavior and can be used to predict the anti-clogging performance.

혼화재 혼입 특성별 강섬유 보강 모르타르의 공극분포 및 염분확산 평가

강섬유 보강제는 콘크리트의 균열저항성을 개선시키는 역할을 하며, 그 이용량이 증가되고 있는 추세이다. 그러나 이전 연구들에 의하면, 급속염분침투시험 이후 강섬유 보강 콘크리트는 내부 섬유 부식으로 인한 결함현상을 보였으며, 이는 섬유 표면과 시멘트 복합체의 계면공극과 관련이 있는 것으로 알려졌다. 본 연구에서는 고로슬래그(GGBS)와 플라이애시(PFA) 혼화재를 적용하여 혼합시멘트 배합별 강섬유 보강 모르타르를 제작하였으며, 이들의 공극구조와 염분침투 저항성을 평가하였다. MIP 시험결과, 강섬유 보강 모르타르의 공극 분포도를 얻었으며, 직경 10 ㎛ 이상 범위에서 첫 번째 피크를 나타내어 계면공극에 해당하는 공극률로 판단되었으며, 압축강도가 증가할수록 해당 피크의 크기는 감소하는 경향을 보였다. 또한, 염수 1.0 M에 100일간 침지시킨 강섬유 보강 모르타르에 대해 염분 프로파일을 측정하고 이를 이용하여 각 배합별 염분확산계수를 산정한 결과, 30 % GGBS를 사용한 강섬유 보강 모르타르는 OPC만을 사용한 배합과 비교 시 26 % 저감된 확산계수를 나타내었다.

How dense is the gas adsorbed in nanopores?

Abstract Unlike macroscopic objects, any system of nanometric size shows characteristics that strongly depend on its size and geometric form. It is mainly because the major part of atoms (or molecules) of nano-object is located at its surface, and their cohesive energy is smaller than for the atoms in the bulk. Here we show that when a fluid is confined in nano-volume, delimited by non-attractive pore walls, its density is heterogeneous, in particular close to the pore wall, and, on average, smaller than the density of bulk fluid. This effect progressively weakens when the pore size increases, and totally disappears for pores larger than 5 nm. The reported observation has non-trivial influence on evaluation of total and excess amount of fluid adsorbed in nanopores, as these quantities are traditionally calculated assuming the known – and homogeneous –density of the bulk fluid. Additionally, we propose a new method of the estimations of the accessible pore volume, based on the analysis of the density of confined fluid. The right estimation of both: pore volume and gas density is essential for quantitative interpretation of experimental adsorption isotherms: evaluation of pore size distribution and of the adsorbed amount. Although we analyze these problems taking an example of hydrogen at 77 K, our conclusions are general and apply to any fluid confined in nanopores.

A study on the kinetics and thermal properties of polystyrene/diatomite nanocomposites prepared via in situ ATRP

Pristine mesoporous diatomite was employed to prepare polystyrene/diatomite composites. Diatomite platelets were used for in situ polymerization of styrene by atom transfer radical polymerization to synthesize tailor-made polystyrene nanocomposites. X-Ray fluorescence spectrometer analysis and thermogravimetric analysis (TGA) were employed for evaluating some inherent properties of pristine diatomite platelets. Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the diatomite platelets. Evaluation of pore size distribution and morphological studies were also performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography, respectively. Linear increase of ln ( M0/M) with time for all the samples shows that polymerization proceeds in a living manner. Addition of 3 wt% pristine mesoporous diatomite leads to an increase of conversion from 72% to 89%. Molecular weight of polystyrene chains increases from 11,326 g mol−1to 14134 g mol−1with the addition of 3 wt% pristine mesoporous diatomite; however, polydispersity index values increases from 1.13 to 1.38. Increasing thermal stability of the nanocomposites is demonstrated by TGA. Differential scanning calorimetry shows an increase in glass transition temperature from 81.9°C to 87.1°C by adding 3 wt% of mesoporous diatomite platelets.

Use of Computed Tomography for the Evaluation of Autoclaved Aerated Concrete Structure

This paper deals with the use of computed tomography (CT) images and analytical software for the nondestructive evaluation of the texture of autoclaved aerated concrete (AAC) with 20% fluidized bed combustion fly ash as a substitute for quartz sand. The samples of AAC, made in the laboratory with the same composition but different ways of curing in the fresh stage (before autoclaving), were subjected to observation of the differences in the texture of the silicate matrix, such as inhomogenity, defects, and pore size distribution. The curing conditions with limited drying resulted in formation of larger, locally-connected pores and additional cracking after autoclaving, which led to a decrease in compressive strength up to 1.32 MPa, compared to samples cured in conditions that allowed complete drying reaching 1.95-1.96 MPa. Also there were problems identified related to imperfect laboratory preparation of the samples, such as agglomeration of individual mixture compounds and larger air void formation, due to the absence of vibrating, cracking and weak spots formation. CT provided sufficient contrasting images for consequent software evaluation of pore size distribution, however a higher resolution of the images is needed for determination of pores smaller than 0,125 mm.

Investigation of the effect of mesoporous diatomaceous earth particles on RATRP of styrene and butyl acrylate

Mesoporous diatomite nanoplatelets were employed to prepare various poly (styrene-co-butyl acrylate)/diatomite nanocomposites by in situ reverse atom transfer radical polymerization of styrene and butyl acrylate. Fourier-transform infrared spectroscopy, thermogravimetric analysis (TGA), and nitrogen adsorption/desorption isotherm were employed for evaluating some properties of the pristine diatomite nanoplatelets. Evaluation of pore size distribution and morphological studies were also performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography, respectively. Addition of 3 wt% pristine mesoporous diatomite nanoplatelets leads to an increase in conversion from 77% to 92%. Molecular weight of poly (styrene-co-butyl acrylate) chains increases from 17,348 g mol−1 to 21,346 g mol−1 with the addition of 3 wt% pristine mesoporous diatomite nanoplatelets; however, polydispersity index values increases from 1.38 to 1.65. Increasing thermal stability of the nanocomposites is demonstrated by TGA. Differential scanning calorimetry shows an increase in glass transition temperature from 35.5°C to 39.4°C with the addition of 3 wt% mesoporous diatomite nanoplatelets.

Effect of Mesoporous Diatomite Particles on the Kinetics of SR&NI ATRP of Styrene and Butyl Acrylate

Abstract Mesoporous diatomite particles were employed to prepare different poly(styrene-co-butyl acrylate)/diatomite nanocomposites. Diatomite nanoplatelets were used for in situ copolymerization of styrene and butyl acrylate by SR&NI ATRP to synthesize well-defined poly(styrene-co-butyl acrylate) nanocomposites. Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the diatomite nanoplatelets. Evaluation of pore size distribution and morphological studies were also performed by SEM and TEM. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography respectively. Addition of 3 wt% pristine mesoporous diatomite nanoplatelets leads to increase of conversion from 73 to 89%. Molecular weight of poly(styrene-co-butyl acrylate) chains increases from 17,115 to 20,343 g·mol−1 by addition of 3 wt% pristine mesoporous diatomite; however, polydispersity index values increases from 1.14 to 1.37. Increasing thermal stability of the nanocomposites is demonstrated by TGA. Differential scanning calorimetry shows an increase in glass transition temperature from 35.26 to 39.61°C by adding 3 wt% of mesoporous diatomite nanoplatelets.

Poly(styrene-co-butyl acrylate)/mesoporous diatomaceous earth mineral nanocomposites by in situ AGET ATRP

Mesoporous diatomite platelets were used for in situ copolymerization of styrene and butyl acrylate by activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) to synthesize tailor-made poly(styrene-co-butyl acrylate) nanocomposites. FTIR spectroscopy, nitrogen adsorption/desorption isotherm and thermo-gravimetric analysis (TGA) were employed for evaluating some inherent properties of the pristine diatomite platelets. Evaluation of pore size distribution and morphological studies were also performed by SEM and TEM. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography, respectively. Addition of 3 mass% pristine mesoporous diatomite leads to increase in conversion from 69 to 83%. Molecular weight of poly(styrene-co-butyl acrylate) chains increases from 7920 to 9940 g mol−1 by addition of 3 mass% pristine mesoporous diatomite; however, Đ values increase from 1.17 to 1.45. Appropriate agreement between theoretical and experimental molecular weight in combination with low Đ values can appropriately demonstrate the living nature of copolymerization. Copolymers composition was evaluated using 1H NMR spectroscopy. Increasing thermal stability of the nanocomposites is demonstrated by TGA. Differential scanning calorimetry shows an increase in glass transition temperature from 33 to 36 °C by adding 3 mass% of mesoporous diatomite platelets.

Synthesis and Characterization of Polystyrene/Mesoporous Diatomite Composites via Activators Generated by Electron Transfer for Atom Transfer Radical Polymerization

Abstract Diatomite platelets were employed to synthesize different polystyrene/diatomite composites. Mesoporous diatomite platelets were used for in situ polymerization of styrene by activators generated by electron transfer for atom transfer radical polymerization to synthesize tailor-made polystyrene nanocomposites. FTIR spectroscopy and thermogravimetric analysis were employed for evaluating some inherent properties of the pristine mesoporous diatomite platelets. Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the diatomite platelets. Evaluation of pore size distribution and morphological studies were also performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography, respectively. Addition of 3 wt% pristine mesoporous diatomite leads to increase of conversion from 78 to 95%. Molecular weight of polystyrene chains increases from 15800 to 20000 g·mol−1 by addition of 3 wt% pristine mesoporous diatomite; however, polydispersity index values increases from 1.14 to 1.38. Increasing thermal stability of the nanocomposites is demonstrated by thermogravimetric analysis. Differential scanning calorimetry shows an increase in glass transition temperature from 93.8 to 97.4°C by adding 3 wt% of mesoporous diatomite platelets.

Evaluation of Pore Size Distribution for Controlled Permeability Formwork Liner

Controlled permeability formwork liner (CPFL) is the functional material similar to nonwoven fabrics and its filtration and drainage performance is dominated by the pore size distribution (PSD) of matrix. In this paper, suction table method, generally used to measure soil pore diameter, is improved for testing PSD of CPFL and experimental data was compared to the results from four other normal experimental methods, i.e., wet sieving method, bubble point method, mercury intrusion porosimetry (MIP) method and image analysis. The comparison indicates that PSD of CPFL obtained from suction table show good accuracy and repeatability. Furthermore, a modified mathematical model derived from Rawal model and Fature model is proved to be suitable for determinating PSD of the matrix of CPFLwith bilayer structure, and have a good agreement with the experimental data from suction table.

Estimating Pore-Size Distributions of Moderately Hydrophobic Mesoporous Solids

In this paper, standard reduced data for adsorption of nitrogen on moderately hydrophobic surface are reported. This surface was obtained by chemical modification of macroporous silica with 3-mercaptopropyltrimethoxysilane. In addition, the statistical film thickness, t curve, is derived using these data and nitrogen adsorption isotherms measured on two large-pore ordered mesoporous silica MCM-41 samples modified with the same organosilane. The application of these reference adsorption data is shown in the evaluation of pore-size distribution and in the related characterization of mesoporous materials with moderate surface hydrophobicity.

A proposed 2D framework for estimation of pore size distribution by double pulsed field gradient NMR

Reconstructing a pore size distribution of porous materials is valuable for applications in materials sciences, oil well logging, biology, and medicine. The major drawback of NMR based methods is an intrinsic limitation in the reconstruction which arises from the ill-conditioned nature of the pore size distribution problem. Consequently, while estimation of the average pore size was already demonstrated experimentally, reliable evaluation of pore size distribution remains a challenging task. In this paper we address this problem by analyzing the mathematical characteristics that create the difficulty and by proposing an NMR methodology and a numerical analysis. We demonstrate analytically that an accurate reconstruction of pore size distribution is problematic with the current known strategies for conducting a single or a double pulsed field gradient (s-PFG, d-PFG) experiment. We then present a method for choosing the experimental parameters that would significantly improve the estimation of the size distribution. We show that experimental variation of both q (the amplitude of the diffusion gradient) and ϕ (the relative angle between the gradient pairs) is significantly favorable over single and double-PFG applied with variation of only one parameter. Finally, we suggest a unified methodology (termed Concentric d-PFG) that defines a multidimensional approach where each data point in the experiment is characterized by ϕ and q. The addition of the angle parameter makes the experiment sensitive to small compartment sizes without the need to use strong gradients, thus making it feasible for in-vivo biological applications.

Pore structure analysis of PFSA/SiO2 composite catalysts from nitrogen adsorption isotherms

The perfluorosulfonic acid (PFSA)/SiO2 composite catalysts were prepared by sol-gel method. Differences concerning pore structure analysis of PFSA/SiO2 catalysts were discussed on the basis of nitrogen adsorption. Their surface area and pore size distributions were evaluated by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. The nitrogen adsorption-desorption isotherms associated with adsorption hysteresis of PFSA/SiO2 catalysts were analyzed in detail. The adsorption isotherms of PFSA/SiO2 catalysts belonged to Type IV isotherms accompanied by hysteresis loops of Type H1 for PFSA/SiO2 catalysts with content of 5%, 13% and 20% PFSA (PFSA-5, PFSA-13 and PFSA-20), and the hysteresis loop of Type H2 for PFSA/SiO2 catalyst with 40% PFSA content (PFSA-40). It indicated that PFSA-5, PFSA-13 and PFSA-20 catalysts had narrow pore size distributions and the well-defined cylindrical pores, while PFSA-40 catalyst had wide pore size distribution and inkbottle-like pores. The pore structure of PFSA-40 catalyst from the analysis of the hysteresis loop was not in agreement with that from BJH method. As an emendation for evaluation of pore size distributions of PFSA/SiO2 catalysts, the comparison plots method was introduced, which was helpful to evaluate the pore structure of PFSA/SiO2 catalysts more factually.

Evaluation of local pore sizes and transport properties in porous catalysts

A methodology for the analysis of local pore size in an arbitrary porous medium, based on the maximum sphere inscription method, has been developed. The method has been validated for regular cylindrical pores and used for the evaluation of pore size distribution on several random media, both computer-generated and scanned using X-ray microtomography. The local pore radii have then been used for the calculation of effective diffusion across the porous medium, whereby local Knudsen diffusion coefficients were employed depending on the local pore radius. This continuum-based approach was then compared with the results of Knudsen diffusion through the same porous media simulated by the molecular dynamics method. A difference of maximum 40% was obtained, which is deemed acceptable given the significantly faster computing speed and higher versatility of the continuum-based models.

A comparison of liquid–liquid porosimetry equations for evaluation of pore size distribution

This paper reviews and numerically tests many of the methods for the determination of pore size distribution of liquid membranes by liquid–liquid porosimetry. The flux through membranes was defined for flow of two immiscible liquids when drops or a liquid jet is formed, as well as the case when the interface is forced out by sufficient pressure. Several methods from literature for the determination of pore size distribution, some variations of these, and one new method are presented with a consistent theoretical basis. Using numerical tests it was found that all methods were very sensitive to measurement noise as low as ±0.1%, and that some form of data smoothing, such as a smoothing spline, was required to obtain a satisfactory distribution. The effects of elastic and permanent membrane compression were tested and a method was proposed to reduce the resulting error. A method based on the ratio of flux liquids with and without a liquid–liquid interface was recommended as it was less sensitive to the effects of compression in some cases and it provides a check when compression is not repeatable.

Characterisation of porous media by the virtual capillary condensation method

A computational methodology for the calculation of pore size distribution from three-dimensional digitally represented porous media of any pore morphology is described in this work. The methodology consists of two steps: simulation of capillary condensation for a given porous medium by the Volume of Fluid (VOF) method, and then evaluating the equivalent pore size distribution from the calculated dependence of the fraction of filled pore volume on the liquid–vapour interface curvature radius. The methodology is first demonstrated on the example of capillary condensation in a single ink-bottle pore and then used for the evaluation of pore size distribution in three classes of porous media with qualitatively different microstructure: model Vycor glass represented by Gaussian porous media; model nanoparticle assemblies; and model open-cell solid foams created by colloidal templating. The relationship between the shape of the pore-size distribution and the morphological features of the porous medium is discussed, and the mean pore radius evaluated by the virtual capillary condensation method is compared with the equivalent hydraulic radius in each case. The two radii are shown to be correlated, but the correlation coefficient is different, and therefore characteristic, for each class of porous media.

Comparison of liquid–liquid displacement porosimetry and scanning electron microscopy image analysis to characterise ultrafiltration track-etched membranes

Liquid–liquid displacement porosimetry (LLDP) has been used to analyse very regular track-etched polymeric membranes in the ultrafiltration (UF) range, with a nominal pore diameter of 50 nm. A fully automated porosimeter has been used in the evaluation of pore size distributions and results have been compared with image analysis performed on scanning electron micrographs (SEM–CIA) of the membranes. Comparison gives a nice agreement between both results (mean pore radius of 23.6 nm for LLDP results and 24.0 nm for SEM–CIA performed on the same samples used for LLDP). A not so satisfactory agreement is obtained for other indirectly evaluated parameters as porosity (means of 1.4 and 2.1%) or the mean total number of pores (19.6×10 12 pores/m 2, from LLDP and 11.1×10 12 pores/m 2 for SEM–CIA). These results show that LLDP measurements have good accuracy and reproducibility and that the analysing fluid mixtures used do not significantly modify neither the chemical nature nor the structure of the membrane material used. Of course, ulterior research should be made in order to elucidate the influence of solvents and other parameters of the LLDP analysis. Membranes so regular as track-etched UF ones could be used as appropriate standards to refine the technical parameters for LLDP.

Evaluation of pore size distribution in boundary region of micropore and mesopore using gas adsorption method

This paper discusses an accurate method of pore size distribution evaluation in boundary regions of micropores and mesopores using the gas adsorption process on the basis of the capillary condensation theory, which is liable to be underestimated with the existing BJH and DH methods. A typical nitrogen adsorption isotherm for highly ordered mesoporous silica, which has cylindrical pores with diameter smaller than 4 nm, is considered to be type IV and it is well known for the steep increase of the amount adsorbed through capillary condensation in the region of the relative pressure P/ P 0 smaller than 0.4. In calculating the distribution of the pore size from the change of the amount adsorbed due to capillary condensation, it is important to accurately predict both the multilayer thickness t of the adsorbed nitrogen molecules and the critical radius r c where capillary condensation occurs. It is necessary to consider the curvature of the adsorption layer–gas phase interface when predicting the multilayer thickness t of nitrogen adsorbed within the pore of highly ordered mesoporous silica. Revision of the Kelvin equation is also required when r c is to be predicted. While the predicted value of t based on the Broekhoff and de Boer theory is matched well with the value of t which is actually measured using highly ordered mesoporous silica, and the predicted value of r c based on the GTKB–Kelvin–cylindrical equation that has been revised considering the effect of the interfacial curvature on the interfacial tension of the adsorption layer–gas phase interface is matched with the value of r c which is actually measured using highly ordered mesoporous silica. A combination method of the Broekhoff and de Boer equation and the GTKB–Kelvin–cylindrical equation is proposed as a means of accurately evaluating, from the nitrogen adsorption isotherm, the pore size distribution in the highly ordered mesoporous silica in boundary region of micropore and mesopore. The proposed new method of pore size evaluation features high accuracy and offers the convenience of obtaining the pore size distribution without repeated calculations by employing the same algorithm as DH method. The pore size predicted by the Halsey equation and the Kelvin equation of the conventional DH method is about 20% smaller than the pore size predicted by the newly proposed evaluation method.

Density functional theory model for calculating pore size distributions: pore structure of nanoporous catalysts

Using the example of nanoporous catalysts, we discuss the non-local density functional theory (NLDFT) model applied to physical adsorption of nitrogen and argon. The model has been used for predicting adsorption/desorption isotherms in nanopores of different geometries over a wide range of pore sizes (0.5–100 nm), and for calculating pore size distributions from adsorption isotherms based on given intermolecular fluid–fluid and fluid–solid potentials. The development of new nanoporous catalysts requires reliable characterization methods. We critically analyze different methods which are currently used for pore structure characterization in the range of nanometers. Calculations of the pore size distributions from nitrogen and argon adsorption isotherms are presented. Our primary method is based on the NLDFT model of adsorption on MCM-41, developed earlier. The results obtained with the NLDFT model are compared with other methods. It is shown, that the pore structure of nanoprous catalysts can be quite complex, and that Ar and N 2 isotherms contain complimentary information. The NLDFT model is recommended for evaluation of pore size distributions in nanoporous catalysts and other MCM-41 based materials.