Pore Structure Analysis Research Articles

Study on the Effect of Ultra-fine Limestone Powder on the Resistance of Cement-slag Powder System to Chloride Ion Permeability

The effect of different limestone powder fineness on the chloride ion migration coefficient of the cement paste was tested using the Rapid Chloride Migration (RCM) method. The changes in the phase composition and pore structure of the paste were studied using hydration kinetics analysis, XRD and pore structure analysis. The results showed that before the chloride ion erosion, the limestone powder mainly exhibited filling effect, microcrystalline nucleation effect, and chemical activity effect. It reacted with the hydration products of cement to form calcium aluminate carbonate, which improved the strength of the hardened paste. After chloride ion erosion, the diffraction peak of calcium aluminate carbonate weakened, and Friedel’s salt was formed. With the increase of the specific surface area of limestone powder, the chemical activity of the powder became more obvious, and the generation of Friedel’s salt increased, leading to stronger resistance to chloride ion penetration. Limestone powder can reduce the porosity of the hardened paste and optimize the pore structure. When the particle size of the powder increased from 800 to 5000 mesh, the total porosity of the hardened paste decreased from 20.7% to 14.7%, and the most probable pore size decreased from 450nm to 75nm. Limestone powder with a particle size larger than 1500 mesh can fully exert its activity and play a role in solidifying chloride ions, thus improving the resistance to chloride ion penetration of limestone powder cement-based materials.

Study on fire safety assessment of nuclear grade activated carbon

In order to further clarify the fire safety evaluation of nuclear grade activated carbon, thermal analysis combined with pore structure and phase analysis was adopted for coal-based activated carbon and coconut shell activated carbon used in nuclear power plants. On the basis of establishing the relative fire safety evaluation model by using four important parameters: activation energy (E), maximum mass loss rate (DTGp), maximum mass loss rate temperature (Tp) and rapid reaction percentage (A12), the O/C ratio and enthalpy (H) were further introduced into the evaluation model to calculate the relative fire safety factor (RFSF). The results show that O/C ratio and enthalpy have greater influence on the fire safety of activated carbon than porosity characteristics. The RFSF values of coal-based and coconut shell activated carbon are 1.33 and 1.08, indicating that fire safety is higher than that of impregnated coconut shell activated carbon.

Pore structure analysis via X-ray μCT: Enhancing soil macroaggregate models for water permeability and carbon sequestration

Soil macroaggregates are crucial for carbon sequestration, water retention, and soil fertility. Their ecological functions are influenced by their pore characteristics. Yet, the relationship between pore structure and the movement of water and carbon within macroaggregates is not fully understood. In this study, the porosity, connectivity, and morphology of macroaggregate pores in three typical soil types in China were characterized. Additionally, water permeability and carbon sequestration were modeled based on in-situ CT-scanning images. The results indicated that the macropores within the macroaggregates serve as the primary channels for water permeability, while pore morphology of mesopores significantly influences carbon sequestration. The water permeability increased with the presence of macropores and enhanced connectivity within the macroaggregates. Dissolved organic carbon (DOC) showed a pronounced correlation with oblate pores across all samples, and a more intricate structure offered more surface area space, trapping additional carbon particles. The established model not only elucidates how various pore structures influence the transport of carbon particles and carbon sequestration but also simulates the structural changes in macroaggregates throughout the process. This allows for an intuitive understanding of water and carbon distribution and migration. This research presents an innovative simulation of water and carbon distribution within macroaggregates using micron-scale CT data.

Utilization of municipal solid waste incinerator bottom ash (MSWIBA) in concrete as partial replacement of fine aggregate

Enhancing sustainable economic development while maintaining environmental integrity is of paramount importance. In this context, the effective utilization of municipal solid waste incinerator bottom ash (MSWIBA) presents a significant opportunity. This study investigated an approach for harnessing the potential of MSWIBA by incorporating it as a partial replacement for fine aggregate in concrete mixtures. Twelve concrete samples were prepared with varying proportions of MSWIBA. The mechanical and microstructural properties of the samples were comprehensively investigated. Moreover, the environmental and economic advantages of these concrete formulations were assessed. The results revealed that the water absorption of the concrete samples without MSWIBA was higher than that of the concrete samples with MSWIBA, suggesting that the added MSWIBA could fill the internal pores of concretes. The water absorption rate curve could be divided into three stages, i.e., rapid decline, slow decline, and stable. The optimal replacement ratio of fine aggregate with MSWIBA was between 24.8% and 57.8%. Notably, when the replacement ratio surpassed 24.8%, MSWIBA positively influenced the development of compressive strength, but it still lower than that of composite Portland cement-based concrete (OPC). Furthermore, pore structure analysis indicated that the efficacy of pore refinement was achieved within a certain replacement threshold. However, the efficacy of pore structure refinement diminished beyond that threshold. The substitution of fine aggregate with MSWIBA aligns with the technical specifications and building material standards, thereby complying with the principles of effective utilization, sustainability, and environmental consideration pertinent to MSWIBA management.

Evaluating coal pore structure and gas sorption-diffusion behavior alteration induced by ultrasound stimulation using sorbing tests and matrix diffusion modeling

Coalbed methane development has great significance to ensure the safe and efficient coal mining, clean energy supplementation and carbon emission reduction. Ultrasound stimulation can effectively modify the coal pore/fracture structure and change the gas ad/de-sorption process and diffusion kinetics characteristics, thus altering gas production for coal deformations. This study estimated the pore structure damage and gas sorption-diffusion of coal before and after ultrasound stimulation with gas sorption tests and gas sorption-diffusion modeling. The results show that the maximum nitrogen adsorption capacity increases by 181.2%–218.9% in coal after ultrasound stimulation, and the pore volume and specific surface area of the ultrasound stimulated coals are 1.5–2.0 times and 5.6–7.6 times of those of the raw coals, respectively. Ultrasound stimulation (20 kHz) has a significant modification effect on pores with size of 2∼50 nm. Fractal analysis of pore structure indicates that the pore surface roughness reduces after the ultrasound treatment, and the development of coal pores has become more complex, and the pore heterogeneity has increased with ultrasound stimulation. The sorption tests and gas sorption-diffusion modeling indicate that gas sorption and diffusive transportation increases after the ultrasound treatment, especially in the initial period. In the initial pressure boosting stage (0∼0.5 MPa), the cumulative methane adsorption amount increases by 20.94%, the diffusion coefficient K increases by 17.32%, and the gas adsorption constant b increases by 62.66%, which is attributed to the “pore-forming” and “pore-expanding” effect caused by ultrasound vibration and cavitation. Ultrasonic stimulation technology has a special improvement performance on coal seams with poor matrix gas deliverability, which is beneficial for the life cycle production enhancement of coalbed methane wells.

Estimation of pore structure and permeability in tight carbonate reservoir based on machine learning (ML) algorithm using SEM images of Jaisalmer sub-basin, India

Analyzing the pore structure in carbonate reservoirs plays a crucial role in predicting fluid flow characteristics within these formations. The goal of the study was to use machine learning techniques for pore structure analysis and estimation of permeability in carbonate reservoirs. We implemented these algorithms by examining 2D scanning electron microscope (SEM) images of carbonate samples from the Jaisalmer sub-basin captured at various magnifications. In the initial stage of the analysis, various binarization algorithms were applied to determine carbonate sample porosity. Among these algorithms, the MaxEntropy algorithm gave a porosity value closely aligned with those obtained through petrography analysis. We employed the watershed algorithm to find the pore network parameters of carbonate samples at various magnifications. We observed that changes in magnification affected pore network parameters, resulting in a reduction in pore size distribution, throat radius, and grain size. Subsequently, we employed the numerical lattice Boltzmann method (LBM) to estimate the permeability of carbonate samples and compared to values derived from well logs. We employed machine learning (ML) algorithms, specifically Artificial Neural Network (ANN) and Support Vector Machine (SVM), to predict the permeability of carbonate samples. The input features for these models were the pore network parameters, while the LBM permeability values served as the output. We examine the prediction performance of these methods against the measured LBM permeability by conducting the error analysis and the coefficient of determination (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}$$\\end{document}) calculation. Our findings revealed that the ANN models outperformed the SVM models. Specifically, the ANN model displayed an impressive R2 value of 0.892, along with root mean square error (RMSE), mean squared error (MSE) and, mean absolute error (MAE) values of 1.927, 3.716 and 1.580, respectively. In contrast, the SVM model yielded an R2 value of 0.849, with RMSE, MSE and, MAE values of 2.324, 5.401 and, 2.166 respectively, when assessed on testing data of measured permeability. This study found that ANN is more dependable, robust, and precise than SVM in forecasting carbonate sample permeability.

Numerical analysis of the porous structure of spherical activated carbons obtained from ion-exchange resins

This paper presents the results of an analysis of the porous structure of spherical activated carbons obtained from cation-exchange resin beads subjected to ion exchange prior to activation. The study investigated the effects of the type of cation exchange resin, the concentration of potassium cations in the resin beads and the temperature of the activation process on the adsorption properties of the resulting spherical activated carbons. The numerical clustering-based adsorption analysis method and the quenched solid density functional theory were used to analyse the porous structure of spherical activated carbons. Based on original calculations and unique analyses, complex relationships between preparation conditions and the porous structure properties of the obtained spherical activated carbons were demonstrated. The results of the study indicated the need for simultaneous analyses using advanced methods for the analysis of porous structures, i.e., the numerical clustering-based adsorption analysis method and the quenched solid density functional theory. This approach allows a reliable and precise determination of the adsorption properties of the materials analysed, including, among other things, surface heterogeneities, and thus an appropriate selection of production conditions to obtain materials with the expected adsorption properties required for a given industrial process.

Study on the synergistic effect of calcium carbide residue -fly ash enhanced desulphurisation gypsum under high temperature maintenance condition

The preparation of cementitious materials from bulk industrial solid waste is an effective way to replace cement. Based on the multi-component synergistic coupling effect, the influence law of different dosage of fly ash (FA) and calcium carbide residue (CCR) on the performance of flue-gas desulfurization gypsum (FGDG) slurry was investigated, and the hydration process of composite cementitious materials was discussed through the analysis of hydration products, micro morphology and pore structure by the characterisation methods such as XRD, FTIR, MIP and SEM-EDS. The results show that FA incorporation can improve the flow properties of the slurry, and under the action of CCR and FGDG, the alkalinity of the whole system rises, and the FA vitreous body undergoes dissolution corrosion, releasing reactive SiO2 and Al2O3, and forming C-S-H gel and AFt. In addition, some of the tiny FA particles fill up the pore spaces and microcracks, and the structure becomes denser, and all these effects together contribute to the development of the mechanical properties. This research is conducive to the application of new green cementitious materials and promotes the resourceful use of industrial solid waste.

Remediation of Cd(II) contamination in aqueous solution by modified sludge biochar with molten salt-assisted pyrolysis

In this work, modified sludge biochar was prepared using molten salt-assisted pyrolysis method to remove Cd(II) from aqueous solution. The biochar was characterized using XRD, FTIR, Raman, XPS and pore structure analysis techniques, and the effects of initial pH, adsorption temperature, adsorption time and initial Cd(II) concentration on the Cd(II) removal were investigated. Compared with the virgin sludge biochar (VSBC), the modified sludge biochar (MSBC) by molten salt-assisted pyrolysis method was rougher surface, more developed pore structure and higher graphitization. The initial pH had a greater effect on the Cd(II) removal, and the high adsorption temperature promoted the Cd(II) removal. The Cd(II) removal behavior was in accordance with the pseudo-second-order kinetic model and Langmuir model, which indicated that the adsorption reaction was a single and uniform chemisorption. Thermodynamics indicated that the Cd(II) removal by VSBC and MSBC was spontaneous and heat-absorbing reaction. Additionally, the maximum adsorption capacities of Cd(II) by VSBC and MSBC were 39.02 and 101.26 mg/g at pH 5.0 and 25 °C, respectively. The mechanisms of Cd(II) removal included complexation of O-containing groups, ion exchange, precipitation, and electrostatic interaction. After three adsorption-desorption experiments, the Cd(II) removal efficiency by VSBC was maintained at 33.26%, while the Cd(II) removal efficiency on MSBC was maintained at 90.18%. This finding suggested that the modified sludge biochar using molten salt-assisted pyrolysis could be effective in remediating Cd(II)-contaminated water body.

Pore structure analysis of storage rocks during geological hydrogen storage: Investigation of geochemical interactions

Depleted oil and gas reservoirs have been widely studied for gas storage purposes such as carbon dioxide and methane, however, there are still some uncertainties when it comes to hydrogen operations. Understanding the geochemical interactions of hydrogen-rock-brine is a key factor for safe sub-surface hydrogen containment, due to the associated risks of altering the rock pore properties. Despite the recent interest in evaluating H2-rock interactions, there is limited knowledge on the reactivity of sandstone and carbonate rocks to hydrogen and the potential implications on pore structure. In this work, we experimentally treated sandstone and limestone samples with hydrogen at 75 °C and 1400 psi for an extended duration of 6 months. Analytical methods including optical microscope for thin sections, Nuclear magnetic resonance (NMR), and helium gas porosity analysis were conducted before and after the hydrogen treatment. The results confirm the occurrence of geochemical reactions between rock minerals and hydrogen, however, the level of mineral dissolution and precipitation is minimal, and only minor changes were observed on the surface morphology. Consequently, insignificant changes occurred in the pore properties of the samples; the weight of the samples did not exhibit significant changes (an average increase of 0.61 %), while the average reduction in porosity and pore volume of the samples did not exceed 6 %. NMR results show no notable changes in T2 distribution times curves, the average increase in porosity values for all the samples (sandstone and limestone) did not exceed 5 % after 6 months of H2 treatment, suggesting that no significant alterations occurred in the pore structure or rock geometry. We conclude that the geochemical reactions of the hydrogen-rock-brine system are very limited even after 6 months of hydrogen treatment, thus the suitability of sandstone and limestone rocks for hydrogen storage is promising.

Fe-N-C Oxygen Reduction Catalysts Via Chemical Vapor Deposition in Fluidized Bed Reactor

Metal nitrogen carbon catalysts (MNC) are an attractive substitute for platinum-based catalysts in the oxygen reduction reaction (ORR) in PEM fuel cells. However, state-of-the-art MNC catalysts still suffer from low activity and instability. Li et al. [1] demonstrated the use of zinc imidazolate frameworks (ZIF-8) in chemical vapor deposition (CVD) to form active sites without unwanted particle formation or additional treatment steps. In this method, gaseous iron chloride exchanges the zinc in the precatalyst to form active sites.In this work, we introduce a vertical fluidized bed reactor (FBR) for high-scale synthesis of FeNC via CVD, allowing for uniform dispersion of the precatalyst and better zinc-iron exchange. Furthermore, we investigated the influence of differently sized ZIF-8 on the CVD and the formation of the FeNC catalyst.The final catalysts were characterized for their electrochemical activity in a rotating ring disc setup, their site density via CO-chemisorption, and their respective turnover frequency. The physicochemical characterization includes the analysis of surface area and pore structure via nitrogen physisorption, SEM, and TEM, as well as surface structure and compositional analysis via elemental analysis, ICP-OES, and XPS.The exchange of Zn was in the range of 90%, resulting in an iron content of 3.8 wt% with only the formation of desired Fe-Nx active sites. STEM-EDX imaging shows an even distribution of iron and nitrogen in the catalyst, with mean particle sizes of 110 nm. In rotating disc electrode experiments with 0.5 M sulfuric acid, mass activities of 0.23 A/g at 0.9 V vs RHE were achieved.Commercially nano-scaled ZIF-8 with mean particle sizes of 500 nm, synthesized particles with mean sizes of 110 nm were tested, compared to the commercial ZIF-8 Basolite Z1200 with mean particle sizes of 4.9 µm. We could show improved activity in RRDE of the nano-scaled ZIF-8 materials compared to the macro-scaled Basolite.Applying this highly scalable synthesis method for MNC catalysts could be a viable way to achieve high-performance catalysts for ORR.[1] Li Jiao, Jingkun Li, Lynne Larochelle Richard, Qiang Sun, Thomas Stracensky, et al.. Chemical vapour deposition of Fe–N–C oxygen reduction catalysts with full utilization of dense Fe–N4 sites. Nature Materials, 2021, 20, pp.1385-1391.

Influence of pore structure on steam disinfection heat and mass transfer in Yunnan red loam

The obstacles to the continuous cropping of Chinese herbs in Yunnan have become increasingly prominent. Many soil-borne diseases can infect the roots of crops, affect the growth of crops, and eventually lead to quality and yield reduction. Soil steam disinfection can still be used as one of the first methods to solve the problem of continuous cropping obstacles of Chinese herbs such as Panax notoginseng. However, the steam will condense into a large amount of liquid water when it is cold, which will cause soil pore blockage and seriously affect the steam diffusion efficiency. Therefore, it is necessary to study the influence mechanism of the pore structure of Yunnan red loam on heat and mass transfer of steam disinfection. The experimental research was conducted on steam disinfection's heat and mass transfer patterns under different soil pore structure conditions. Image processing technology was used to collect accurate soil profiles and to establish real soil pore structure analysis. Then, fluid simulation technology was used to simulate the heat and mass transfer process and trend of steam distribution within the soil profile under different soil pore structures. The results showed that the steam heat flow of <2 mm, 2–4 mm and 4–6 mm treatments were uniformly diffused in the form of matrix flow in a 1/4 ellipse, and the effective disinfection range was 18 cm horizontal distance and 20 cm vertical distance, in which the highest temperature could reach more than 90 °C. The steam heat flow of the 6–8 mm and >8 mm treatment groups diffused irregularly in large pore steam flow. Therefore, some devices for breaking soil and rotary tillage need to finely rotate the soil in the future. The end effector's disinfection pipe spacing can refer to the effective disinfection range.

Particle size effect of pre-wet zeolites on autogenous shrinkage and mechanical properties of LECC

The conservation effects can vary significantly when utilizing zeolite internal curing (IC) agents of different particle sizes in Lightweight Engineered Cementitious Composites (LECC). This paper addresses this issue by investigating the impact of zeolites with varying particle sizes (with average particle sizes of 90 μm, 240 μm, and 410 μm) on the mechanical and shrinkage properties of LECC. Furthermore, it delves into the intrinsic influencing mechanisms through pore characterization parameters and quantitative techniques for assessing the degree of hydration. The results demonstrate that the particle size of zeolite exerts a substantial influence on the conservation efficiency of LECC. Specifically, small-sized zeolite effectively eliminates pores larger than 200 μm within the LECC matrix, resulting in significant enhancements in its mechanical properties (a 16% increase in compressive strength) and shrinkage resistance (a 54% reduction in shrinkage). Conversely, large-sized zeolite diminishes the mechanical properties of LECC, albeit contributing to some extent to improved shrinkage properties (a 32% reduction in shrinkage). The improved conservation effect of small-sized zeolite stems from the refined pore structure and the filling effect of volcanic ash. Pore structure analysis reveals that small-sized zeolite yields a finer pore structure, primarily distributed within the 12 μm range. This enhances water absorption and release, consequently improving conservation efficiency. Additionally, hydration product analysis indicates that small-sized zeolite promotes cement hydration, resulting in a 9% increase in the degree of cement hydration.

Microstructure and Efflorescence Resistance of Metakaolin Geopolymer Modified by 5A Zeolite.

In order to reduce the degree of efflorescence in alkali-activated metakaolin geopolymers, a modified 5A zeolite with cation-exchange properties was used to reduce the content of free alkali metal cations in the geopolymer. This work aims to investigate the effect of different dosages of modified 5A zeolite on the microstructure and properties of geopolymer by using compressive strength testing, pore structure analysis (BET), and SEM-EDS. The cation content in the leachate was evaluated using inductively coupled plasma atomic emission spectrometry (ICP-OES). The efflorescence area of the geopolymer was calculated using Image Pro Plus (IPP) software to evaluate the effect of modified 5A zeolite on the degree of efflorescence of the geopolymer and to reveal the effect of modified 5A zeolite on the migration patterns of Na+ and Ca2+ in the geopolymer. The results showed that modified 5A zeolite with a 4 wt.% content could optimize the pore structure and enhance the mechanical properties of MK geopolymer through internal curing and micro-aggregate effects, which could also exchange cations with the pore solution to form (N, C)-A-S-H gels. The Na+ leaching was reduced by 19.4%, and the efflorescence area of the MK geopolymer was reduced by 57.3%.

Effects of SEM image resolution on organic pore structure estimation of shale reservoirs

SEM images on ion-polished shale samples can visualize organic pores and can be used to analyze the organic pore structures quantitatively. Compared to the routine fluid intrusion methods (e.g., helium porosity, N2 adsorption, mercury intrusion, etc.), the SEM image-based organic pore structure analysis has many unique benefits. However, image resolution can significantly influence the analysis results. This should be investigated carefully. The image resolution effects on the analysis of organic pore structures was confirmed and estimated through (1) imaging organic matters and their organic pores at different resolutions (0.7–29.2 nm/pixel), and (2) comparing the differences of 2D organic porosity, pore size distribution (PSD), and organic pore geometry calculated at different image resolutions. The two ways of image resolution effect on organic pore analysis was revealed. First, organic pores with a wall close to the sample surface were more challenging to recognize at low image resolution. Any incorrect recognition of these organic pores can significantly affect the calculated 2D organic porosity and the sectional area-based PSD. Second, the small size organic pores were also difficult to recognize at low image resolution, considerably affecting the estimation of pore amount-based PSD but only slightly affecting the calculated organic porosity and sectional area-based PSD due to their small pore size. When SEM image resolution is less than 10nm/pixel, organic porosity will be significantly underestimated, and the estimated PSD and geometry usually have high uncertainty. Therefore, SEM images with 5nm/pixel or higher resolution are recommended to assess organic pore structures.

Triazine-based sulphur-containing polymers for Hg2+ adsorption: Efficiency and mechanism

Recently the research on the materials for removal of heave metals is surging rapidly. Here we have studied four triazine-based sulfur-containing polymers with different linkers, namely PDT1, PDT2, EDT1, and EDT2. They have been successfully synthesized by the nucleophilic substitution reaction of cyanuric chloride with propane-1,3-dithiol (PDT1 and PDT2) and ethane-1,2-dithiol (EDT1 and EDT2) in different ratios. The physical and chemical properties of these polymers were characterized by scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, porous structure analysis and X-ray photoelectron spectroscopy. The optimized adsorption condition was established by examining dosing, co-existing substances, contact time, concentration, temperature and pH values. The adsorbing properties, which was mainly described by the pseudo-second-order kinetic and Langmuir isothermal model, indicated that the sorption of Hg2+ was the chemical adsorption. The maximum Hg2+ sorption capacities of PDT1, PDT2, EDT1 and EDT2 were 1440.97 mg g−1, 715.99 mg g−1, 237.87 mg g−1 and 181.48 mg g−1, respectively. Thermodynamically, the adsorption of Hg2+ by the adsorbent is a spontaneous process. Cyclic experiments demonstrated that all the adsorbents could be reused in five successive adsorption cycles without significant losses in performance. Our density functional theory calculations in combination with relevant experimental results revealed the coordination geometry of Hg and hence mercury-adsorbent chelation mechanism. These results suggested that triazine-based sulfur-containing polymers could be utilized as effective adsorbents for the removal of Hg2+ from polluted water.

Characterization of multiphase flow in shaly caprock for geologic CO2 storage

Geologic carbon dioxide (CO2) storage is a promising strategy for reducing its atmospheric levels, but concerns regarding potential leakage through faults or high-permeability inclusions in caprock highlight the importance of understanding its multiphase flow mechanism. In this study, a comprehensive experimental approach is introduced to characterize the pore structure of heterogeneous and fractured caprock and its relationship to water/CO2 relative permeability. It is observed that intact caprock with higher clay content exhibits a higher decrease in water relative permeability in the drainage: the exponent values in the Brooks-Corey model are 3.89 for sandy Eau Claire Shale, 5.04 for the clayey shale, and 6.77 for intact Opalinus Clay - consistent with observations for porous and tight rock. CO2 relative permeability also exhibits an exponential increase with CO2 saturation, which is more pronounced for sandy and fractured caprock due to the higher endpoint CO2 relative permeability and CO2 saturation. Moreover, a method to estimate relative permeability based on the water-CO2 capillary pressure response derived from the pore structure analysis is adopted and its results are compared to the direct measurements. This approach provides a better fit for intact clay-rich caprock but tends to underestimate the relative permeability as a function of fluid saturation for heterogeneous and fractured caprock. The pore structure-based estimation allows for pre-assessing the multiphase flow through caprock, although the direct measurements are highly recommended, especially for fractured materials.

Durability tests on lime-based mortars from the historic built heritage of Catania (Eastern Sicily, Italy): An experimental study

Mortars, like any other natural and artificial stone materials, are subject to atmospheric weathering agents which affect their durability according to the intrinsic characteristics of the material, such as mineralogical composition, texture and pore structure.This paper aims to investigate the physical-chemical durability of lime-based mortars made with two different volcanic aggregates, locally known as azolo and ghiara, peculiar of the historic built heritage of Catania (Eastern Sicily, Italy). An experimental approach has been used, based on the reproduction in laboratory of historic mortars by using ancient recipes. The experimental samples have been characterized from a physical point of view and then subject to accelerated aging tests. Specifically, the samples have undergone: i) mineralogical investigations through X-ray diffraction (XRD); ii) thin section analysis by polarized optical microscopy; iii) pore structure analysis through mercury intrusion porosimetry (MIP); iii) water absorption by capillarity; iii) water vapor permeability test; iv) accelerated aging test by salt crystallization; v) decay by sulfur dioxide.Results obtained highlight that the higher microporosity which characterizes the ghiara mortars is certainly responsible for their greater water absorption by capillarity as well as for their lower resistance to salt crystallization and exposure to sulfur dioxide, with respect to azolo-based ones.

Easily Pyrolyzable Biomass Components Significantly Affect the Physicochemical Properties and Water-Holding Capacity of the Pyrolyzed Biochar

The influences of feedstocks on biochar properties are widely reported. However, the influence of the transformation of biomass components (mainly cellulose, hemicellulose, and lignin) during feedstock pyrolysis on the obtained biochar has not been clearly stated. Here, biochar was pyrolyzed from four biomass types with different fractions of the three main components, of which surface area, pore structure, functional group, and thermogravimetric analyses were conducted. Further, we investigated the links among the physicochemical properties and water-holding capacity (WHC) of the biochar by measuring the WHC of a biochar–silica-sand (SS) mixture. Cellulose and hemicellulose were considered the easily pyrolyzable components of the feedstock owing to their low thermal stabilities. Additionally, the thermal decomposition of the easily pyrolyzable components caused the disappearance of most functional groups from the biochar that was synthesized at &gt;350 °C. Moreover, the WHC of the biochar–SS mixture correlated significantly with the surface area and pore volumes of the biochar. Notably, the thermal residual mass and the WHC of the biochar–SS mixture exhibited the strongest correlation. Poplar wood sawdust (PT), which accounted for the highest mesopore volume of the biochar sample, contained the highest amount (86.09%) of the easily pyrolyzable components. The PT-derived biochar exhibited superior WHC than other biochar types, indicating that the dehydration, deoxygenation, and condensation of the easily pyrolyzable components of biomasses promoted gradual pore formation, further contributing to the increased WHC of the mixture. Rather than high-temperature-pyrolyzed biochar, PT350 demonstrated the highest WHC (599 mg/g), revealing that attention should be drawn to the contribution of low-temperature-pyrolyzed biochar to soil water retention in future research.

Automatic pore structure analysis in organic-rich shale using FIB-SEM and attention U-Net

The pore structure is an important factor in determining the productivity of shale, which can help us make better operational decisions. Shale formations have an extremely complex pore structure with a wide range of pore sizes, shapes, orientations, and connectivity. Advanced imaging techniques, such as focused ion beam scanning electron microscopes (FIB-SEM), contribute significantly to the analysis and understanding of complex pore networks in shale, but they are time-consuming. Developing new methods and techniques to capture the spatial distribution and connectivity of pores at various scales is essential to understanding pore structure and its impact on fluid flow. This study aims to analyze the pore characteristics of shale reservoirs by using artificial intelligence (AI) and FIB-SEM. We applied a novel attention gate (AG) model to FIB-SEM images that automatically learns to focus on target structures of varying pores’ shape and size. AG can be fully incorporated into the U-Net model with minimal computational impact. The AG improved prediction accuracy by making the U-Net model more sensitive to essential features in the input images and achieved a precision of 97%, recall of 71%, and F1 score of 81% at a confidence threshold of 1. Experimental results show that Attention U-Net outperformed in predicting the pore structures in shale samples from Longmaxi Formation, Qingshankou Formation, Cambrian Niutitang Formation, Yanchang shale oil, and Bakken shale while obtaining optimal performance without requiring multiple convolutional neural network (CNN) models. Additionally, Attention U-Net addresses some of the limitations of the Edge-Threshold Automatic Processing (ETAP) method, including the limited ability to obtain a complete description of the pore space as well as the low segmentation accuracy and sensitivity. The proposed workflow offers a promising solution for optimizing the automatic processing of microscopic images for pores and microfractures identification. Researchers and industry professionals can improve their understanding of shale properties and applications in various fields by maximizing the benefits of our workflow.